| 1. |
- Frietsch, Rudyard, et al.
(författare)
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Early Proterozoic Cu-(Au) and Fe ore deposits associated with regional Na-Cl metasomatism in northern Fennoscandia
- 1997
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Ingår i: Ore Geology Reviews. - 0169-1368 .- 1872-7360. ; 12:1, s. 1-34
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Tidskriftsartikel (refereegranskat)abstract
- Scapolite is widely distributed in 1.9-2.5 Ga volcano-sedimentary rocks and 1.77-2.2 Ga igneous rocks over several hundred square kilometres in northern Fennoscandia, comprising northern Sweden, northern Finland and adjacent parts of Norway and Russia. This region is one of the largest scapolite-bearing Precambrian terranes in the world. Albitization, and to a lesser extent carbonatization, phyllic and tourmaline alteration, are spatially associated with scapolite. A number of epigenetic Cu-(Au) sulphide and Fe oxide deposits in northern Fennoscandia show a spatial and genetic relationship to this type of alteration, mainly scapolitization and albitization. The main metal occurrences are in 2.0-2.5 Ga mafic volcanics and sediments of the Lapponian Greenstone group and in 1.9 Ga intermediate-composition volcanic and volcaniclastic rocks of the Svecofennian Porphyry group. The scapolite is mainly a dipyre-mizzonite with Cl and CO3 and small amounts of SO4 and F, indicating high Na and Cl activity at the time of crystallization. Fluid inclusion data of the Lapponian Pahtohavare and similar Cu-Au deposits indicate formation temperatures of about 300°C and ore deposition from highly saline aqueous solutions. The deposition of copper and gold was in places regulated by a redox barrier; graphite in associated schists controlled the reduction reactions of the ore fluids and metals were precipitated. The Lapponian and Svecofennian sulphide deposits contain tourmaline of the schorl-dravite series. Aitik-Nautanen Cu-(Au) style deposits and in particular some deposits with vein-style iron ore, contain dravite-schorl deficient in Al and enriched in Fe3+, which is due to Fe-Al substitution in an oxidizing, relatively iron-rich environment. Scapolite and, probably also tourmaline, formed by a complex, multistage process. The source of the components in scapolite may have been evaporitic sequences or high salinity brines in Lapponian rift basins that contain 2.0-2.5 Ga mafic volcanics. During low to medium-grade (low P) regional metamorphism, the components that formed scapolite and tourmaline were mobilized and transported to their present positions in several metasomatic phases. Fault zones with fractures and breccias channeled the fluids, resulting in locally developed intense alteration. Gold and copper was transported by saline, high fO2, high temperature solutions as metal-chloride complexes. The ultimate source of fluids and heat sources is uncertain, but deep-seated crustal magmatic processes seem prerequisite. The alteration occurred mainly around 1.9 Ga at the peak of the main regional metamorphism and the intrusion of granitoids through to around 1.8 Ga. Cu-(Au) sulphide and Fe oxide ore deposits associated with large-scale scapolite-forming metasomatic processes are found elsewhere in the world (e.g., Australia, Kazakhstan, Russia) and show similarities with the Cu-(Au) deposits in northern Fennoscandia. However, the close genetic connection between scapolite-albite and ore formation of Fennoscandian deposits is not a common feature in other belts.
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| 2. |
- Frietsch, Rudyard, et al.
(författare)
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Rare earth elements in apatite and magnetite in Kiruna-type iron ores and some other iron ore types
- 1995
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Ingår i: Ore Geology Reviews. - 0169-1368 .- 1872-7360. ; 9:6, s. 489-510
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Tidskriftsartikel (refereegranskat)abstract
- An investigation has been conducted to determine the content and distribution of REE in apatite and magnetite in the iron ores of Kiruna type and some other iron ores. The purpose of this article is to discuss the results obtained from the investigation. In particular, it will be shown that REE in apatite and magnetite in different ore types exhibit characteristic patterns related to different modes of formation of the ores
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| 3. |
- Aiglsperger, Thomas, et al.
(författare)
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Critical metals (REE, Sc, PGE) in Ni laterites from Cuba and the Dominican Republic
- 2016
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Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 73, s. 127-147
-
Tidskriftsartikel (refereegranskat)abstract
- Ni laterites are considered worthy targets for critical metals (CM) exploration as Rare Earth Elements (REE), Sc and platinum group elements (PGE) can be concentrated during weathering as a result of residual and secondary enrichment. In this contribution geochemical and mineralogical data of CM from two different nickel laterite types (i) from the Moa Bay mining area in Cuba (oxide type) and (ii) from the Falcondo mining area in the Dominican Republic (hydrous Mg silicate type) are presented. Emphasis is given on examining their potential to accumulate CM and on processes involved. Results show that CM are concentrated towards the surface in specific zones: (i) REE in clay minerals rich horizons and within zones composed of secondary Mn oxide(s), (ii) Sc within zones rich in secondary Fe and Mn bearing oxide(s) and (iii) PGE in zones with high concentrations of residual chromian spinel and secondary Fe and Mn bearing oxide(s) at upper levels of the Ni laterite profiles. Concentration factors involve (i) residual enrichment by intense weathering, (ii) mobilization of CM during changing Eh and pH conditions with subsequent reprecipitation at favourable geochemical barriers and (iii) interactions between biosphere and limonitic soils at highest levels of the profile (critical zone) with involved neoformation processes. Total contents of CM in both Ni laterite types are low when compared with conventional CM ore deposits but are of economic significance as CM have to be seen as cost inexpensive by-products during the Ni (+ Co) production. Innovative extraction methods currently under development are believed to boost the significance of Ni laterites as future unconventional CM ore deposits.
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| 4. |
- Andersson, Stefan S., et al.
(författare)
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Mineral paragenesis and sulphide trace element distribution in the metamorphosed Lovisa Zn-Pb deposit, Bergslagen (Sweden), as revealed by 3D X-ray tomography, ore petrography and LA-ICP-MS analysis
- 2022
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 140
-
Tidskriftsartikel (refereegranskat)abstract
- This study encompasses the ore mineralogy, textures and sulphide trace element chemistry of the Palaeoproterozoic Lovisa stratiform Zn-Pb deposit and the stratigraphically underlying Lovisa Fe Formation in the Bergslagen ore province (Sweden). We investigate the relative timing of formation and subsequent modifications of its ores in relation to the c. 1.87-1.80 Ga Svecokarelian orogeny. The Lovisa Zn-Pb deposit consists of several different ore types. The massive sphalerite-galena ore is distinctly deformed, exhibiting a multiple-scale "ball ore" texture with rounded silicate clasts within a deformed, fine-grained sulphide matrix. Underlying the massive ore is a locally folded, sphalerite-rich laminated ore, interpreted to represent a metamorphosed relict primary lamination. Several generations of sphalerite-galena fracture fillings and veins occur adjacent to the main ore zones and they cross-cut early ductile structures and metamorphic features. The trace element signatures of the sphalerite-galena infillings generally mimic those of the two main ore zones, thus supporting an origin by localised remobilisation of the primary sulphide ore and demonstrating limited trace element redistribution during this process. In contrast, discrete sulphosalt-rich fracture fillings cross-cutting earlier galena-chalcopyriterich fracture fillings and veinlets in the Lovisa Fe Formation suggest a significant but still relatively localised redistribution of metals. Trace element mapping of sulphides from the Lovisa Zn-Pb deposit reveals that inclusion-free overgrowths on pyrite crystals are locally Co-enriched compared to the cores, which resulted from the redistribution of Co during late metamorphic processes. Combined textural and geochemical evidence suggest that the originally syngenetic exhalative sulphide ore at Lovisa was locally strongly affected by polyphase deformation and remobilisation. This was initiated during the first stage of amphibolite facies grade regional metamorphism and deformation (D1, c. 1.87-1.85 Ga) but is mostly evident from the later stages (D2) and the evolution to retrograde and brittle conditions (c. 1.83-1.80 Ga and later).
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| 5. |
- Andersson, Stefan S., et al.
(författare)
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Origin of the high-temperature Olserum-Djupedal REE-phosphate mineralisation, SE Sweden : A unique contact metamorphic-hydrothermal system
- 2018
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 101, s. 740-764
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish part of the Fennoscandian Shield hosts a variety of rare earth element (REE) deposits, including magmatic to magmatic-hydrothermal types. This paper focuses on the origin of the Olserum-Djupedal REEphosphate mineralisation located in the sparsely studied Vastervik region, SE Sweden. Here, mineralisation occurs in three main areas, Olserum, Djupedal and Bersummen. Primary hydrothermal REE mineralisation formed at high temperatures (about 600 degrees C), leading to precipitation of monazite-(Ce), xenotime-(Y), fluor apatite and minor (Y,REE,U,Fe)-(Nb,Ta)-oxides in veins and vein zones dominated by biotite, amphibole, magnetite and quartz. The veins are hosted primarily by metasedimentary rocks present close to, or within, the contact aureole of a local 1.8 Ga ferroan alkali feldspar granite pluton, but also occur within in the chemically most primitive granite in the outermost part of that pluton. In the Djupedal area, REE-mineralised metasedimentary bodies are extensively migmatised, with migmatisation post-dating the main stage of mineralisation. In the Olserum and Bersummen areas, the REE-bearing veins are cross-cut by abundant pegmatitic to granitic dykes. The field-relationships demonstrate a-protracted magmatic evolution of the granitic,pluton and a clear spatial and temporal relationship of the REE mineralisation to the granite. The major and trace element chemistry of ore-associated biotite and magnetite support genetic links between all mineralised areas. Biotite mineral chemistry data further demonstrate a distinct chemical trend from meta sediment-hosted ore-associated biotite distal to the major contact of the granite to the biotite in the granite hosted veins. This trend is characterised by a systematic decrease in Mg and Na and a coupled increase in Fe and Ti with proximity to the granite-hosted veins. The halogen compositions of ore-associated biotite indicate elevated contents of HCl and HF in the primary REE mineralising fluid. Calculated log(f(HF)/f(HCL)) values in the Olserum area suggest a constant ratio of about -1 at temperatures of 650-550 degrees C during the evolution of the primary hydrothermal system. In the Djupedal and Bersummen areas, the fluid locally equilibrated at lower log (f(HF)/f(HCl)) values down to -2. High Na contents in ore-associated biotite and amphibole, and the abundance of primary ore-associated biotite indicate a K- and Na-rich character of the primary REE mineralising fluid and suggest initial high-temperature K-Na metasomatism. With subsequent cooling of the system, the fluid evolved locally to more Ca-rich compositions as indicated by the presence of the Ca-rich minerals allanite-(Ce) and uvitic tourmaline and by the significant calcic alteration of monazite-(Ce). The later Ca-rich stages were probably coeval with low to medium-high temperature (200-500 degrees C) Na-Ca metasomatism variably affecting the granite and the wall rocks, producing distinct white quartz-plagioclase rocks. All observations and data lead us to discard the prevailing model that the REE mineralisation in the Olserum-Djupedal district represents assimilated and remobilised former heavy mineral-rich beds. Instead, we propose that the primary REE mineralisation formed by granite-derived fluids enriched in REE and P that were expelled early during the evolution of a local granitic pluton. The REE mineralisation developed primarily in the contact aureole of this granite and represents the product of a high temperature contact metamorphic-hydrothermal mineralising system. The REE mineralisation probably formed synchronously with K-Na and subsequent Na-Ca metasomatism affecting the granite and the wall rocks. The later Na-Ca metasomatic stage is probably related to a regional Na +/- Ca metasomatic and associated U +/- REE mineralising system operating concurrently with granitic magmatism at c. 1.8 Ga in the Vastervik region. This highlights the potential for discovering hitherto unknown REE deposits and for the reappraisal of already known deposits in this part of the Fennoscandian Shield.
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| 6. |
- Bark, Glenn, et al.
(författare)
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Geodynamic settings for Paleoproterozoic gold mineralization in the Svecofennian domain : a tectonic model for the Fäboliden orogenic gold deposit, northern Sweden
- 2012
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 48, s. 403-412
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Tidskriftsartikel (refereegranskat)abstract
- Northern Sweden is currently experiencing active exploration within a new gold ore province, the so called Gold Line, situated southwest of the well-known Skellefte VMS District. The largest known deposit in the Gold Line is the hypozonal Fäboliden orogenic gold deposit. Mineralization at Fäboliden is hosted by arsenopyrite-rich quartz veins, in a reverse, mainly dip-slip, high-angle shear zone, in amphibolite facies supracrustal host rocks. The timing of mineralization is estimated, from field relationships, at ca. 1.8 Ga.The gold mineralization is hosted by two sets of mineralized quartz veins, one steep fault-fill vein set and one relatively flat-lying extensional vein set. Ore shoots occur at the intersections between the two vein sets, and both sets could have been generated from the same stress field, during the late stages of the Svecofennian orogen.The tectonic evolution during the 1.9–1.8 Ga Svecofennian orogen is complex, as features typical of both internal and external orogens are indicated. The similarity in geodynamic setting between the contemporary Svecofennian and Trans-Hudson orogens indicate a potential for world-class orogenic gold provinces also in the Svecofennian domain.The Swedish deposits discussed in this paper are all structurally associated with roughly N-S striking shear zones that were active at around 1.8 Ga, when gold-bearing fluids infiltrated structures related to conditions of E-W shortening.
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| 7. |
- Bark, Glenn, et al.
(författare)
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Orogenic gold in the new Lycksele-Storuman ore province, northern Sweden : the Palaeoproterozoic Fäboliden deposit
- 2007
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 32:1-2, s. 431-451
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Tidskriftsartikel (refereegranskat)abstract
- Southwest of the well-known Skellefte District, northern Sweden, a new gold ore province, the so called Gold Line, is presently being explored. During the past decade a number of gold occurrences have been discovered in this area. The largest known gold occurrence is the Fäboliden deposit. Late-to post-orogenic, ca. 1.81 to 1.77 Ga, Revsund granite constitutes the main rock type in the Fäboliden area and surrounds a narrow belt of mineralized metagreywackes and metavolcanic rocks. The supracrustal rocks are strongly deformed within a roughly N-S trending subvertical shear zone. The mineralization constitutes a 30 to 50 m wide, N-S striking, steeply dipping zone. The mineralization is commonly hosted by arsenopyrite-bearing quartz-veins within the supracrustal rocks. The quartz veins parallel the main foliation in the shear zone. Gold is closely associated with arsenopyrite-löllingite and stibnite and found in fractures and as intergrowths in the arsenopyrite-löllingite. Gold is also seen as free grains in the silicate matrix of the host rock. The proximal alteration zone displays positive correlation with Ca, S, As, Ag, Sb, Sn, W, Pb, Bi, Cd, Se, and Hg, whereas K and Na show a slightly negative correlation. The hydrothermal mineral assemblage in the proximal alteration zone is diopside, calcic amphibole, biotite, and minor andalusite and tourmaline. This type of assemblage is commonly recognized in hypozonal orogenic gold deposits worldwide. Garnet-biotite geothermometry indicates amphibolite facies in the Fäboliden area. The ductile fabric that hosts the mineralization is also found in the margin of the surrounding Revsund granitoid. It is therefore suggested that at least the final stages of the gold mineralization are syn- to late-kinematic, and the minimum age for the mineralization is thus constrained at ca. 1.80 Ga (Revsund age).
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| 8. |
- Bauer, Tobias, Associate professor, 1982-, et al.
(författare)
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Regional structural setting of late-orogenic IOCG mineralization along the northern Nautanen deformation zone, Norrbotten, Sweden
- 2023
-
Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 163
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Tidskriftsartikel (refereegranskat)abstract
- The northern Norrbotten ore province in Sweden is one of the most mineralized areas in Europe. Iron, gold and/or copper deposits occur as iron oxide-apatite-style mineralization (IOA, Kiruna-type) as well as iron oxide-copper–gold (IOCG) style. Regardless of mineralization style, most deposits appear to be spatially controlled by a set of crustal-scale Palaeoproterozoic shear zones which share similar structural characteristics and deformation histories.Reappraisal of regional geological and geophysical data, coupled with structural mapping, suggests crustal-scale shear zones form continuous c. N-S-trending zones extending from the Skellefte district in the south into the northern Norrbotten ore province. One example from Norrbotten is a zone that extends SSW from Karesuando in the north towards Svappavaara. While this structure has traditionally been inferred to continue SW towards Arjeplog (i.e. the Karesuando – Arjeplog Deformation Zone; KADZ), we favour its deflection SSE into the Nautanen-Aitik trend, making it a continuous, IOCG-bearing, crustal-scale deformation zone. Similar shear zone geometries can be observed in analogous zones to the west. Most of these crustal scale structures record at least two time-separated deformation events of regional significance. IOA and IOCG deposits form in different tectonic environments, separated in time and overprinting each other.
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| 9. |
- Bernet, Matthias, et al.
(författare)
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Multidisciplinary petro-geo-thermochronological approach to ore deposit exploration
- 2019
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368. ; 112:Sept.
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Forskningsöversikt (refereegranskat)abstract
- The continuous search for mineral resources such as gold, copper and base metals etc. requires a refined understanding of the thermal evolution and exhumation history of potential exploration targets, as only ore deposits can be exploited that have been exhumed to the surface or near to the surface. In order to better understand the exhumation history of the ore deposits a multidisciplinary approach using single grain geo- and thermochronology double/triple dating in combination with other geochemical, fluid inclusion and petrological analyses, can significantly support prospecting for such resources, particularly in frontier areas, where little geological information exists. Geo-thermochronology provides information on the timing of initial host rock crystallization, ore deposit formation and subsequent exhumation as the thermal history can be modelled and exhumation rates can be determined. Here we present a methodological outline on which single-grain double/triple-dating techniques can be used, what sampling strategies may be applied, and how the data may be interpreted.
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| 10. |
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| 11. |
- Billström, Kjell, et al.
(författare)
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Sandstone-hosted Pb-Zn deposits along the margin of the Scandinavian Caledonides and their possible relationship with nearby Pb-Zn vein mineralisation
- 2020
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 127
-
Forskningsöversikt (refereegranskat)abstract
- Numerous sandstone-hosted Pb-Zn deposits occur along the present-day erosional front of the eastern Scandinavian Caledonides. The largest deposit is Laisvall (64.3 Mt at 4.0% Pb, 0.6% Zn and 9.0 g/t Ag) and since mineralisations generally share similar characteristics (reminding of both SEDEX and MVT-style) the term Laisvall-type has often been used. Typically, mineralised zones occur along sedimentary bedding and consist of disseminated galena and sphalerite and lesser amounts of calcite, fluorite, baryte, pyrite and sericite forming a cement that fill interstitial pores in Neoproterozoic/Eocambrian (e.g. Laisvall) to Cambrian (e.g. Vassbo) sandstones. Deposits occur both in autochtonous and allochtonous sedimentary rocks, and a broad consensus exists about their epigenetic nature, their spatial relationships to syn-sedimentary faults and that ore fluids have scavenged metals from the crystalline basement. However, the detailed ore depositional history and the timing of ore deposition have remained more controversial. New analyses aimed to complement earlier Rb-Sr data (crush-leach technique using sphalerite) fail to support a published three-point isochron age of 467 +/- 5 Ma. This is probably due to syn-ore mixing between fluids carrying isotopically variable strontium and inherited problems to analyse sphalerite grains that strictly were deposited from a single ore pulse. Tentatively, strontium in the ores originate from a mix of components derived from the basement, seawater and the local sedimentary host sequences. The lead component has highly radiogenic compositions, and data define sub-parallel linear arrays interpreted to essentially represent mixing of isotopically different types of lead released from regional basement rocks. There are obvious similarities when comparing features of deposits representing two Pb-Zn ore styles, the sandstone-hosted dissemination and the fracture-controlled mineralisation in the granite-dominated basement occurring further east of the Caledonian margin. These include low temperature brines responsible for mineral deposition, the mineralogy and the nature of Rb-Sr and Pb isotope data. We suggest that these types of mineralisation have a common origin and time of emplacement, but it is elusive to propose a well-constrained age. Nonetheless, field observations and other evidence suggest that ore formation is due to large-scale fluid flow triggered by the transition from an extensional to compressional tectonic setting at about 500 Ma. Connected to this mid-Cambrian stage was the development of syn-sedimentary faults and fractures in the basement and in overlying consolidated sandstones. The opening of such zones of weakness enabled a movement of ore-forming fluids infilling pore space in sandstones (disseminated ore) and fractures in the basement (vein ore).
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| 12. |
- Cave, Ben J., et al.
(författare)
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Multi-stage precipitation and redistribution of gold, and its collection by lead-bismuth and lead immiscible liquids in a reduced-intrusion related gold system (RIRGS); Dublin Gulch, western Canada
- 2019
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 106, s. 28-55
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Tidskriftsartikel (refereegranskat)abstract
- Dublin Gulch reduced intrusion-related gold system (RIRGS), located in the Selwyn Basin area of western Canada, represents one of the best examples of RIRGS mineralization globally and hence can be studied to unravel genesis and evolution of these types of deposits. Based on textural relationships, mineralogy, and trace element mineral chemistry, three auriferous vein stages were identified. The paragenetic sequence for the auriferous vein stages are: 1) Eagle Style (ES), quartz-albite, low sulfide and sulfosalt content ( < 5% vol.), As-Fe-Mo-W-Pb-Bi-Au-Ag veins; 2) Potato Hills Style-1 (PHS-1), quartz, high sulfide and sulfosalt content ( > 30% vol.), As-Fe-W-Pb-Bi-Au-Ag veins; and, 3) Potato Hills Style-2 (PHS-2), high sulfide and sulfosalt content ( > 30% vol.), Fe-Pb-Sb-Zn-Cu-Au-Ag veins. In the ES and PHS-1 veins, Au is present both as native gold (Au, Ag) and as invisible gold in arsenopyrite, whilst in the PHS-2 veins, Au is present as invisible gold in pyrite. Native gold micrograins (individual grains, 1-100's mu m in size) are observed associated with Pb minerals (in anhedral-toglobular cosalite (Pb2Bi2S5) in ES veins, or galena (PbS) in the PHS-1 veins]. Native gold is also observed as micrograins along arsenopyrite margins and in quartz fractures. We suggest a variation on the hydrothermal Bi melt collector model to explain the Au-Pb +/- Bi association. The Au, Ag, Pb, and Bi are interpreted to have been locally remobilized from arsenopyrite, which shows textures and trace element distribution patterns consistent with fluid-and-deformation assisted recrystallization. We suggest Pb and Bi were mobilized either as immiscible nanodroplets that coalesced to form larger Pb +/- Bi liquid accumulations or into the hydrothermal fluid and subsequently exsolved to form immiscible Pb +/- Bi liquids. We propose that remobilized Au and Ag were collected by these Pb +/-Bi immiscible liquids. Subsequent retrograde alteration (sulfidation) is interpreted to have converted the Au-Ag-Pb +/- Bi alloys to native gold and cosalite (ES), and native gold and galena mineral assemblages (PHS-1). The similarity of the Au/Ag ratios in native gold and arsenopyrite supports a local source for the native gold micrograins. Temperatures required to attain liquid Pb-0.Bi-5(0).(5) ( > 145.2 degrees C) and Pb (> 327.5 degrees C), are consistent with arsenopyrite geothermometry (ES 345-405 degrees C; PHS-1 approximate to 380 degrees C). These suggested new variations (Pb-Bi and Pb) on the hydrothermal melt (Bi) collector model are important, given the common association of native gold with Pb +/- Bi sulfosalts in many gold deposits, and the relatively low temperatures required to maintain these liquids and collect Au from the hydrothermal fluid.
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| 13. |
- Decree, S., et al.
(författare)
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In-situ trace element and Sr isotope signature of apatite: A new key to unravelling the genesis of polymetallic mineralisation in black shales of the Early Cambrian Niutitang Formation, Southern China
- 2022
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368. ; 150
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Tidskriftsartikel (refereegranskat)abstract
- The Early Cambrian Mo-Ni-PGE sulphidic black shale in the Niutitang Formation on the margin of the Yangtze Craton (Southern China) is known for its extremely high metal concentrations. It is also very rich in phosphate that formed contemporaneously with the sulphides. Detailed petrological as well as in-situ trace element and Sr isotope analyses of authigenic apatite revealed new information on the metallogenesis of this enigmatic rock unit. In the ore bed, apatite forms nodules or is found in phosphatic (phoslithoclasts) and sulphide clasts. In the latter, the replacement of organic matter and sulphides by apatite microspherules suggests a microbially mediated phosphogenesis. Enrichment in middle rare earth elements emphasizes the role played by Fe-oxyhydroxides and organic matter in element scavenging. Moderately reducing conditions are supported by a lack of Ce and Eu anomalies. The trace element signature of apatite and its initial 87Sr/86Sr (0.7032-0.7190), which is -for a group of analyses -well below the signature of Lower Cambrian seawater, points to some contribution from mafic rock-sourced hydrothermal brines. This effectively explains the exceptional enrichment of Ni and PGE in the sulphides. Seawater remains, however, the preferred source for other elements such as P and Mo.
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| 14. |
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| 15. |
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| 16. |
- García-Tudela, Matías, et al.
(författare)
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The chromitites of the Herbeira massif (Cabo Ortegal Complex, Spain) revisited
- 2024
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Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 170
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Tidskriftsartikel (refereegranskat)abstract
- The ultramafic rocks of the Herbeira Massif in the Cabo Ortegal Complex (NW Iberia) host chromitite bodies. The textural and compositional study of the host rocks and the chromitites classified them into: (1) Type-I chromitites, forming massive pods of intermediate-Cr chromite (Cr# = 0.60–0.66) within dunites; and (2) Type-II chromitites forming semi-massive horizons of high-Cr chromite (Cr# = 0.75–0.82) interlayered with dunites and pyroxenites. Minor and trace elements (Ga, Ti, Ni, Zn, Co, Mn, V and Sc) contents in the unaltered chromite cores from both types show patterns very similar to fore-arc chromitites, mimicked by the host dunites and pyroxenites. Calculated parental melt compositions suggest that Type-I chromitites crystallized from a melt akin to fore-arc basalt (FAB), while Type-II chromitites originated from a boninite-like parental melt. Both melts are characteristic of a fore-arc setting affected by extension during rollback subduction and have been related to the development of a Cambrian-Ordovician arc. These chromitites are extremely enriched in platinum-group elements (PGE), with bulk-rock PGE contents between 2,460 and 3,600 ppb. Also, the host dunites and pyroxenites exhibit high PGE contents (167 and 324 ppb, respectively), which are higher than those from the primitive mantle and global ophiolitic mantle peridotites. The PGE enrichment is expressed in positively-sloped chondrite-normalized PGE patterns, characterized by an enrichment in Pd-group PGE (PPGE: Rh, Pt and Pd) over the Ir-group PGE (IPGE: Os, Ir and Ru) and abundant platinum-group minerals (PGM) dominated by Rh-Pt-Pd phases (i.e. Rh-Ir-Pt-bearing arsenides and sulfarsenides, Pt-Ir-Pd-base-metal-bearing alloys, and Pt-Pd-bearing sulfides). The PGM assemblage is associated with base-metal sulfides (mostly pentlandite and chalcopyrite) and occurs at the edges of chromite or embedded within the interstitial (serpentinized) silicate groundmass. Their origin has been linked to direct crystallization from a S-As-rich melt(s), segregated by immiscibility from evolved volatile-rich small volume melts during subduction. At c. 380 Ma, retrograde amphibolite-facies metamorphism occurred during the exhumation of the HP-HT rocks of the Capelada Unit, which affected chromitites and their host rocks but preserved the primary composition of chromite cores of the chromitites. This event contributed to local remobilization of PGE as suggested by the negative slope between Pt and Pd and high Pt/Pd ratios in the studied chromitites, and host dunites and pyroxenites. In addition, it promoted the alteration of primary PGM assemblage and the formation of secondary PGM. Nanoscale observations made by focused ion beam high-resolution transmission electron microscopy (FIB/HRTEM) analysis of a composite grain of Rh-bearing arsenide with PGE-base-metal bearing alloys suggest the mobilization and accumulation of small nanoparticles of PGE and base-metals that precipitated from metamorphic fluids forming PGE-alloys. Finally, we offer a comparison of the Cabo Ortegal chromitites with other ophiolitic chromitites involved in the Variscan orogeny, from the Iberian Peninsula to the Polish Sudetes. The studied Cabo Ortegal chromitites are similar to the Variscan chromitites documented in the Bragança (northern Portugal) and Kraubath (Styria, Austria) ophiolitic massifs.
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| 17. |
- Garcia, Victor B., et al.
(författare)
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The Neoarchean GT-34 Ni deposit, Carajás mineral Province, Brazil : An atypical IOCG-related Ni sulfide mineralization
- 2020
-
Ingår i: Ore Geology Reviews. - 0169-1368 .- 1872-7360. ; 127
-
Tidskriftsartikel (refereegranskat)abstract
- The GT-34 deposit, located 12 km to the SW of the Sossego copper–gold mine in the Carajás Province, northern Brazil, represents an unusual Ni sulfide mineralization. The deposit occurs along a NE-SW-trending sub-vertical shear zone marked by progressive Mg-alkalic alteration zones, predominantly hosted in granitic and locally in granodioritic to tonalitic orthogneisses. Initial alteration zones result in unique scapolite-orthopyroxene assemblage, which is partially preserved within pervasive hornblende-chlorapatite ± plagioclase replacement zones. Nickel mineralization occurs mainly as matrix-supported breccias characterized by a pentlandite-pyrrhotite-rich matrix and rounded fragments chiefly of hornblende and chlorapatite. Irregular stockworks and net textured veins containing chalcopyrite-pentlandite are less common. Phlogopite ± talc ± actinolite alteration and late-stage veinlets crosscut the previous alteration zones and the mineralization. The phlogopite ± talc ± actinolite alteration occurs as irregular veins and chalcopyrite-pyrrhotite-magnetite are commonly observed where such alteration intersects the Ni mineralization. Late-stage veinlets are represented by K feldspar-epidote-chlorite-calcite and quartz-albite-chlorite-calcite-epidote veins, both containing minor amounts of millerite, pyrite and F-OH-apatite. High-resolution SIMS U-Pb zircon geochronology obtained for the GT-34 deposit revealed an age of 2828 ± 4 Ma for zircon grains inherited from the host orthogneisses. The timing of the mineralization altered zircon grains from the scapolite-orthopyroxene and phlogopite ± talc ± actinolite alteration zones, is attributed to an age interval between 2751 and 2720 Ma. Although poorly constrained, the geochronological data corroborate a Neoarchean age for the GT-34 Ni mineralization, similar to that of other IOCG deposits in the Carajás Province and coeval with the bimodal magmatism in the area. The atypical orthopyroxene-marialite mineral chemistry support a metasomatic crystallization at high temperatures (>700 °C), low aH2O (<0.5) and pressures between 5 and 7 kbar. Hypersaline fluids, as the ones described for the IOCG deposits in Carajás at such PxT conditions, would enable the orthopyroxene-marialite crystallization, as supported by experimental studies available in the literature. Mineralogical and geochemical considerations on the nature of the Ni sulfide mineralization points toward a metasomatic origin, feasible with the predicted P-T-fluid scenario for the hydrothermal alteration. Such conditions raise the initial temperature and pressure estimates of the IOCG metasomatic alteration by at least 200 °C and pressure up to 7 kbar, making it the hottest and probably deepest IOCG-related metasomatic alteration known to date for Carajás.
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| 18. |
- Gil de la Iglesia, Alba, et al.
(författare)
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Reflection seismic imaging to unravel subsurface geological structures of the Zinkgruvan mining area, central Sweden
- 2021
-
Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 137
-
Tidskriftsartikel (refereegranskat)abstract
- The Zinkgruvan mining area is located on the south-eastern part of the Bergslagen district, one of the three major mineral producing regions in Sweden. In this study, we present the results from three (P1, P2 and P8) reflection seismic profiles each approximately 3000 m-long crossing the Zinkgruvan Zn-Pb-Ag-(Cu) mining area. P1 was acquired using cabled geophones with 10 m receiver and source interval and crossed major geological features. The other two profiles (P2 and P8) were acquired by wireless recorders with 20 m receiver and 10 m source interval and ran perpendicular to P1. Through a special data processing workflow adapted to this dataset, good quality seismic sections were obtained along these profiles, although a high noise level due to high voltage electric power lines was present. The interpretations were constrained by (1) seismic P-wave velocity and density data from a series of downhole logging measurements, (2) 3D forward reflection traveltime modelling in both pre- and post-stack domains, and (3) other geophysical and geological observations available from the site. Despite the notably complex geology, the processed seismic sections clearly reveal a series of horizontal to gently dipping reflections associated with known geological formations. Results indicate that most structures and lithological contacts dip or plunge to the northeast, including the targeted Zinkgruvan Formation. The results from this seismic survey are encouraging regarding the potential of the seismic method for base-metal exploration in Sweden and in particular in the Bergslagen district. It shows the high resolving power of the reflection seismic methods for imaging complex geological structures in a cost-effective and environmentally-friendly way.
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| 19. |
- González-Jiménez, José M., et al.
(författare)
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Precious metals in magmatic Fe-Ni-Cu sulfides from the Potosí chromitite deposit, eastern Cuba
- 2020
-
Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 118
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Tidskriftsartikel (refereegranskat)abstract
- The Moa-Baracoa ophiolite in eastern Cuba is one of the few known ophiolites that display sulfide mineralization attributable to a magmatic origin in association with podiform-chromite ores hosted in the mantle-crust transition. These sulfide ores chiefly consist of Fe-Ni-Cu sulfides, namely pyrrhotite, pentlandite, chalcopyrite and cubanite partly altered to valleriite. The sulfide mineralization is located along the contact between the podiform-like chromite ores and intruding pegmatitic gabroic dykes. The detailed mineralogical study of the sulfide mineralization coupled with the first ever laser ablation ICP-MS analysis reveals that this sulfide mineralization show contents of the precious metals (Os, Ir, Ru, Pt, Re, Au, Ag) and other (semi)-metals (Co, Ni, Cu, Se, Te, Bi, Pb, As Sb) comparable to those sulfides from the magmatic sulfide deposits associated with mafic complexes hosted in the continental crust. The results obtained from this study confirm that Fe-Ni-Cu sulfides at Potosí are magmatic in origin, and very likely derived from the solidification of droplets of sulfide melt segregated by immiscibility from the intruding mafic melts once they interacted with the pre-existing chromitite at the mantle-crust transition zone of the ophiolite. The immiscibility of sulfide melt was achieved as a result of a progressive increase of fS2, very likely triggered by a set of circumstances, including the progressive fractionation of the intruding mafic melt leading to increase of aSiO2 and accumulation of volatiles as well as the crystallization of oxides. Two main generations of pentlandite were observed. One generation is primary in origin and it was locally exsolved along with pyrrhotite from monosulfide solid solution (MSS) during low-temperature cooling. The second type of pentlandite resulted from the reaction of MSS with coexisting droplets of Cu-and Ni-rich sulfide melt. LA-ICP-MS analysis reveals that most precious metals (Ru, Os, Ir, Re, Au, Ag) were concentrated along with the base-metal sulfides (BMS), although their distribution among the different BMS (pyrrhotite, pentlandite, chalcopyrite and cubanite) does not strictly follow the expected distribution according to the known melt-solid and solid-solid partition coefficients. Unlike the other analyzed PGEs, Pt was not preferentially concentrated in BMS but as discrete micrometer-sized sperrylite grains. The crystallization of sperrylite took place before and contemporaneous to sulfide segregation, and Pt-As nanoparticles probably played an important role in the Pt uptake as nucleation seeds for the formation of micron-sized sperrylite grains. These observations highlight the open-system nature of the ore forming system as well as the important role of arsenic in concentrating PGE in high-temperature silicate and sulfide melts.
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| 20. |
- Goodenough, K. M., et al.
(författare)
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Europe's rare earth element resource potential : An overview of REE metallogenetic provinces and their geodynamic setting
- 2016
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 72, s. 838-856
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Tidskriftsartikel (refereegranskat)abstract
- Security of supply of a number of raw materials is of concern for the European Union; foremost among these are the rare earth elements (REE), which are used in a range of modern technologies. A number of research projects, including the EURARE and ASTER projects, have been funded in Europe to investigate various steps along the REE supply chain. This paper addresses the initial part of that supply chain, namely the potential geological resources of the REE in Europe. Although the REE are not currently mined in Europe, potential resources are known to be widespread, and many are being explored. The most important European resources are associated with alkaline igneous rocks and carbonatites, although REE deposits are also known from a range of other settings. Within Europe, a number of REE metallogenetic belts can be identified on the basis of age, tectonic setting, lithological association and known REE enrichments. This paper reviews those metallogenetic belts and sets them in their geodynamic context. The most well-known of the REE belts are of Precambrian to Palaeozoic age and occur in Greenland and the Fennoscandian Shield. Of particular importance for their REE potential are the Gardar Province of SW Greenland, the Svecofennian Belt and subsequent Mesoproterozoic rifts in Sweden, and the carbonatites of the Central Iapetus Magmatic Province. However, several zones with significant potential for REE deposits are also identified in central, southern and eastern Europe, including examples in the Bohemian Massif, the Iberian Massif, and the Carpathians.
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| 21. |
- Horn, S., et al.
(författare)
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Cobalt resources in Europe and the potential for new discoveries
- 2021
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Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 130
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Tidskriftsartikel (refereegranskat)abstract
- Global demand for cobalt is increasing rapidly as we transition to a low-carbon economy. In order to ensure secure and sustainable supplies of this critical metal there is considerable interest in Europe in understanding the availability of cobalt from indigenous resources. This study reviews information on cobalt resources in Europe and evaluates the potential for additional discoveries. Based on published information and a survey of national mineral resource agencies, 509 cobalt-bearing deposits and occurrences have been identified in 25 countries in Europe. Harmonised cobalt resources, classified using the United Nations Framework Classification (UNFC), have been estimated for 151 deposits in 12 countries where data are available. The calculated total resource comprises 1 342 649 tonnes of contained cobalt metal. This includes: 114 638 tonnes in commercial projects with current cobalt extraction; 370 409 tonnes in potentially commercial projects; 111 107 tonnes in historic estimates compliant with modern reporting; and 746 495 tonnes in non-compliant historic estimates. Analysis of these data reveals that cobalt resources are widely distributed across Europe in deposits of several different types. Global mine production of cobalt is dominated by stratiform sediment-hosted copper deposits, magmatic nickel-copper deposits and nickel laterite deposits, but other deposit types may also be significantly enriched in cobalt. In Europe, current cobalt production is derived from three mines in Finland: the magmatic sulfide deposit at Kevitsa; the Kylylahti deposit of volcanogenic massive sulfide (VMS) affinity; and the black shale-hosted deposit at Sotkamo (Talvivaara). This study has identified 104 deposits in Europe that are currently being explored for cobalt, of which 79 are located in Finland, Norway and Sweden. The Fennoscandian Shield and the Caledonian Belt in these countries are high priority exploration terrains for a variety of cobalt-bearing deposits, notably magmatic Ni-Cu-Co deposits. The Svecofennian, Sveconorwegian and the Caledonian orogenies in Fennoscandia also resulted in the formation of several other cobalt-enriched deposit types. These include chiefly metasedimentand metavolcanichosted Co-Cu-Au, VMS, skarn and polymetallic vein deposits. The Kupferschiefer deposits in Poland and Germany are stratiform sediment-hosted Cu deposits with some similarities to the Central African Copperbelt, which is the predominant global producer. However, the cobalt grade in the Kupferschiefer deposits is relatively low (0.005-0.008% Co) and not currently economic to exploit without significant improvement in extraction technology. In the Balkans and Turkey cobalt grades and tonnages are known in 27 nickel laterite deposits, with several containing more than 10 000 tonnes of cobalt metal. Only nickel is currently recovered from these deposits, but new processing technologies such as high-pressure acid leaching could enable cobalt recovery in the future. Small polymetallic cobalt-bearing vein deposits in several European countries have been historic producers of cobalt. Today most are uneconomic, but new technologies and the drive towards locally-sourced raw materials could make them viable future sources of cobalt.
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| 22. |
- Jansson, Nils F., et al.
(författare)
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Multistage ore formation at the Ryllshyttan marble and skarn-hosted Zn-Pb-Ag-(Cu) + magnetite deposit, Bergslagen, Sweden
- 2015
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 69, s. 217-242
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Tidskriftsartikel (refereegranskat)abstract
- Numerous magnetite skarn deposits and marble- and skarn-hosted base metal sulphide deposits occur in polydeformed and metamorphosed, felsic-dominated metavolcanic inliers in the Palaeoproterozoic Bergslagen region of south-central Sweden, including the Ryllshyttan magnetite and Zn-Pb-Ag-(Cu) sulphide deposit, approximately 2.5 km SW of the large Garpenberg Zn-Pb-Ag-(Cu-Au) deposit. The Ryllshyttan deposit, from which approximately 1 Mt of Zn-rich massive sulphide ore and 0.2 Mt of semi-massive magnetite were extracted, is located near a transition between magnesian skarn and dolomitic marble. The host unit consists of a 10-20 m-thick former calcitic limestone of likely stromatolitic origin that is commonly pervasively altered to skarn, locally hosting magnetite skarn deposits. The ore-bearing unit is one of several mineralised marble units within a more than 1 km-thick, felsic-dominated metavolcanic succession that includes a metamorphosed, large caldera-fill pyroclastic deposit, 800 m stratigraphically above the Ryllshyttan host succession. The Garpenberg stratabound Zn-Pb-Ag-(Cu)-(Au) deposit is located higher in the stratigraphy, just below the caldera fill deposits. The metavolcanic succession is bounded to the NW by a large granitoid batholith and intruded by a microgranodiorite pluton less than a 100 m from the Ryllshyttan deposit. Magnetite laminae in bedded skarns and metavolcanic rocks in the hanging wall of Ryllshyttan indicate an early (syngenetic) accumulation of Fe-rich exhalites. In contrast, the sulphide mineralisation consists of stratabound replacement-style ore associated with dolomitisation of the host and with discordant K-Mg-Fe±Si alteration of volcanic rocks and early porphyritic intrusions in the footwall and hanging wall. The microgranodiorite that intrudes the host succession crosscuts the K-Mg-Fe±Si alteration envelope and is overprinted by Na-Ca alteration (diopside and plagioclase-bearing mineral associations) that also overprints K-Mg-Fe±Si-altered rocks. The Na-Ca alteration is interpreted to be associated with the formation of calcic and magnesian iron skarn deposits semi-regionally at a similar stratigraphic position. Despite superimposed amphibolite facies regional metamorphism and substantial syn-D2-D3 remobilisation of sulphides concurrent with retrograde alteration of skarn assemblages, cross-cutting field relationships indicate that the Ryllshyttan magnetite and Zn-Pb-Ag-(Cu) sulphide deposit results from protracted VMS-style hydrothermal activity including early seafloor mineralisation (Fe-rich exhalites), closely followed by sub-seafloor carbonate-replacement-style mineralisation (base metal-bearing massive sulphides). Both mineralisation styles were overprinted by contact metasomatism associated with the formation of abundant magnetite skarn deposits during the emplacement of granitoid intrusions. As for other deposits in the Bergslagen region, the ore-forming system at Ryllshyttan thus has similarities to both metamorphosed VMS deposits and metasomatic Fe and Zn skarn deposits. Our results suggest that the sequence of volcanic, intrusive and hydrothermal events in this region is compatible with prograde heating of a long-lived hydrothermal system, wherein a shift from a convective seawater-dominated system to a contact metamorphic and/or metasomatic environment occurred during the early stage of the 1.9-1.8 Ga Svecokarelian orogeny. This model partly resolves the controversy regarding genesis of the iron oxide and base metal sulphide deposits in Bergslagen, as we recognise that these deposits have a complex history of alteration, metamorphism, deformation and (re)mobilisation, and no unique established genetic model can account for all their features.
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| 23. |
- Jansson, Nils, et al.
(författare)
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Genesis of the Zinkgruvan stratiform Zn-Pb-Ag deposit and associated dolomite-hosted Cu ore, Bergslagen, Sweden
- 2016
-
Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 82, s. 285-308
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Tidskriftsartikel (refereegranskat)abstract
- Zinkgruvan, a major stratiform Zn-Pb-Ag deposit in the Paleoproterozoic Bergslagen region, south-central Sweden, was overprinted by polyphase ductile deformation and high-grade metamorphism (including partial melting of the host succession) during the 1.9-1.8 Ga Svecokarelian orogeny. This complex history of post-ore modification has made classification of the deposit difficult. General consensus exists on a syngenetic-exhalative origin, yet the deposit has been variably classified as a volcanogenic massive sulfide (VMS) deposit, a sediment-hosted Zn (SEDEX) deposit, and a Broken Hill-type (BHT) deposit. Since 2010, stratabound, cobaltiferous and nickeliferous Cu ore, comprising schlieren and impregnations of Cu, Co and Ni sulfide minerals in dolomitic marble, is mined from the stratigraphic footwall to the stratiform Zn-Pb-Ag ore. This ore type has not been fully integrated into any of the existing genetic models. Based on a combination of 1) widespread hematite-staining and oxidizing conditions (Fe2O3>FeO) in the stratigraphic footwall, 2) presence of graphite and reducing conditions (Fe2O3 5 km) Zn-Pb-Ag ore was precipitated.Both ore types are characterized by significant spread in δ34S, with the sulphur in the Cu ore and associate marble-hosted Zn mineralization on average being somewhat heavier (δ34S = -4.7 to +10.5 ‰, average 3.9 ‰) than that in the stratiform Zn-Pb-Ag ore (δ34S = -6 to +17 ‰, average 2.0 ‰). The ranges in δ34S are significantly larger than those observed in syn-volcanic massive sulphide deposits in Bergslagen, for which simple magmatic/volcanic sulphur sources have been invoked. Mixing of magmatic-volcanic sulfur leached from underlying volcanic rocks and sulfur sourced from abiotic or bacterial sulfate reduction in a mixing zone at the seafloor could explain the range observed at Zinkgruvan.A distinct discontinuity in the stratigraphy, at which key stratigraphic units stop abruptly, is interpreted as a syn-sedimentary fault. Metal zonation in the stratiform ore (decreasing Zn/Pb from distal to proximal) and the spatial distribution of Cu mineralization in underlying dolomitic marble suggest that this fault was a major feeder to the mineralization. Our interpretation of ore-forming fluid composition and a dominant redox trap rather than a pH and/or temperature trap differs from most VMS models, with Selwyn-type SEDEX models, and most BHT models. Zinkgruvan has similarities to both McArthur-type SEDEX deposits and sediment-hosted Cu deposits in terms of the inferred ore fluid chemistry, yet the basinal setting has more similarities to BHT and felsic-bimodal VMS districts. We speculate that besides an oxidized footwall stratigraphy, regionally extensive banded iron formations and limestone horizons in the Bergslagen stratigraphy may have aided in buffering ore-forming brines to oxidized, near-neutral conditions. In terms of fluid chemistry, Zinkgruvan could comprise one of the oldest known manifestations of Zn and Cu ore-forming systems involving oxidized near-neutral brines following oxygenation of the Earth’s atmosphere.
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| 24. |
- Jian, W., et al.
(författare)
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Late Triassic Au-Mo mineralization in the Xiaoqinling region and a genetic connection to carbonatitic magmatism
- 2022
-
Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368. ; 145
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Tidskriftsartikel (refereegranskat)abstract
- The southern margin of the North China craton hosts a number of quartz vein-style deposits of the unusual AuMo ore spectrum, including the Dahu deposit in the Xiaoqinling region. Pristine euhedral monazite and rutile crystals from the Dahu Au-Mo mineralized veins yield LA-ICP-MS weighted mean 206Pb/238U ages of 212.1 +/- 1.7 Ma (1 s, MSWD = 1.13) and 209.7 +/- 2.7 Ma (2 s, MSWD = 1.7), respectively. These ages point to a Late Triassic gold mineralization event in the Xiaoqinling region, aside from the regionally well-recognized Early Cretaceous gold mineralization event. Tectonic setting, mineral association, elemental and isotopic signatures, and fluid characteristics of the Dahu deposit suggest that the Late Triassic Au-Mo mineralization represents a carbonatiteassociated hydrothermal system, with ore fluids exsolved from a late-stage carbonatite system. Mineralogically, the Dahu deposit is enriched in hydrothermal minerals common to carbonatite systems, such as carbonates, sulfates, and REE minerals. Trace element and isotope compositions of vein minerals also show similarities to those of carbonatites. Monazite displays a pronounced LREE-enriched and smooth pattern (no Eu anomaly), with epsilon Nd(t) values ranging from -14.9 to -13.3. Rutile is characterized by high Nb concentrations (6 to 18 wt%) and extremely high Nb/Ta ratios of 236 to 2044. Fluid inclusions in the Dahu Au-Mo mineralized veins and the regionally distributed coeval carbonatites are all dominated by low to moderate salinity H2O-CO2 fluids that contain sulfates as trapped solids/daughter minerals. Our study suggests that the southern margin of the North China craton has potential for the exploration of polymetallic hydrothermal mineralization related to hidden carbonatites.
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| 25. |
- Kampmann, Tobias Christoph, 1987-, et al.
(författare)
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Syn-tectonic sulphide remobilization and trace element redistribution at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, Bergslagen, Sweden
- 2018
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Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 96, s. 48-71
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Tidskriftsartikel (refereegranskat)abstract
- Mineralization types at the Palaeoproterozoic Falun base metal sulphide deposit are predominantly pyritic Zn-Pb-Cu-rich massive sulphide mineralization, disseminated to semi-massive Cu-Au mineralization, auriferous quartz veins, and mineralized shear zones of talc-chlorite-dominated schist. The massive and disseminated to semi-massive sulphide mineralization types were subject to polyphase ductile deformation (D1 and D2) and metamorphism under low-P, lower-amphibolite facies conditions, which led to the development of ore textures and paragenetic relationships indicating both mechanical and chemical remobilization of sulphides. In the massive sulphide mineralization, rare inclusion-rich pyrite occurs as relic cores inside inclusion-poor metamorphosed pyrite. Imaging and spot analysis using multielement laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) reveal that inclusion-poor pyrite was depleted in trace elements, which were originally present as non-stoichiometric lattice substitutions or in mineral inclusions. The inclusion-rich pyrite was shielded from depletion and, at least partly, retained its initially higher trace element concentrations, including Au.Gold is also associated with chalcopyrite in the disseminated to semi-massive Cu-Au mineralization and in the system of auriferous quartz veins hosted therein, the latter being also affected by the D2 ductile strain. It is inferred that emplacement of the vein system took place after the peak of metamorphism, which occurred between D1 and D2, but prior to and possibly even shortly after completion of the D2 deformational event. Similarities in trace element signatures in chalcopyrite are compatible with the interpretation that the quartz veins formed by local chemical remobilization of components from the Cu-Au mineralization. Transport of liberated Au from pyrite during grain growth in the massive sulphide mineralization may have upgraded the Au endowment in the quartz veins, leading to the additional formation of native gold in the veins. A strong correspondence between elements liberated from pyrite (e.g. Pb, Bi, Se and Au) and those forming discrete and characteristic mineral phases in the quartz veins (Pb-Bi sulphosalts, native gold) supports this hypothesis.Trace element signatures for the main sulphide minerals pyrite, chalcopyrite, sphalerite and galena are similar to previously published data from other metamorphosed massive sulphide deposits. The association of the Falun mineralization with elevated Bi is reflected by its occurrence in sulphide minerals (e.g. galena) and in abundant mineral inclusions of Pb-Bi sulphosalts (e.g. weibullite), especially in the disseminated to semi-massive Cu-Au mineralization. Elevated Sn concentrations in the lattice and/or as cassiterite inclusions in chalcopyrite, sphalerite and galena are compatible with a hot, acidic and reducing fluid during formation of the syn-volcanic, base metal sulphide mineralization and associated host-rock alteration.
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| 26. |
- Konopelko, D., et al.
(författare)
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Precambrian gold mineralization at Djamgyr in the Kyrgyz Tien Shan : Tectonic and metallogenic implications
- 2017
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368. ; 86, s. 537-547
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Tidskriftsartikel (refereegranskat)abstract
- The Djamgyr gold deposit is located within the Neoproterozoic basement of the Middle Tien Shan terrane immediately west of the Talas-Fergana fault. The deposit comprises a system of auriferous quartz veins cross-cutting the Beshtor plagiogranite. The veins are surrounded by hydrothermal alteration aureoles and are oriented parallel to the Talas-Fergana fault. The Beshtor granite sampled in the vicinity of the deposit yielded a Neoproterozoic (Tonian) U-Pb zircon age of 815 ± 6 Ma, which is the first single grain zircon age of the Middle Tien Shan basement west of the Talas-Fergana fault. Ar-Ar dating of two muscovite fractions from the alteration aureoles of the auriferous quartz veins yielded ages of 804 ± 3 and 805 ± 3 Ma suggesting that the mineralization in the Djamgyr deposit occurred during the Neoproterozoic ca. 10 m.y. after emplacement of the Beshtor granite. The structural pattern of the auriferous quartz veins and the new geochronological data, combined with the results of previous structural studies, may tentatively constrain the age of pre-existing major fault possibly marking an inherited terrane boundary in the northern part of the present-day Talas-Fergana strike-slip fault. The discovery of Precambrian gold mineralization in the Middle Tien Shan suggests re-evaluation of the metallogenic potential of its Precambrian basement that occupies significant areas west and east of the Talas-Fergana fault.
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| 27. |
- Li, Nuo, et al.
(författare)
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Fluid evolution of the Yuchiling porphyry Mo deposit, East Qinling, China
- 2012
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 48, s. 442-459
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Forskningsöversikt (refereegranskat)abstract
- The Yuchiling Mo deposit, East Qinling, China, belongs to a typical porphyry Mo system associated with high-K calc-alkaline intrusions. The pure CO2 (PC), CO2-bearing (C), aqueous H2O-NaCI (W), and daughter mineral-bearing (S) fluid inclusions were observed in the hydrothermal quartz. Based on field investigations, petrographic, microthermometric and LA-ICP-MS studies of fluid inclusions, we develop a five-stage fluid evolution model to understand the ore-forming processes of the Yuchiling deposit. The earliest barren quartz +/- potassic feldspar veins, developed in intensively potassic alteration, were crystallized from carbonic-dominant fluids at high temperature (>416 degrees C) and high pressure (>133 MPa). Following the barren quartz potassic feldspar veins are quartz-pyrite veins occasionally containing minor K-feldspar and molybdenite, which were formed by immiscible fluids at pressures of 47-159 MPa and temperatures of 360-400 degrees C. The fluids were characterized by high CO2 contents (approximately 8 mol%) and variable salinities, as well as the highest Mo contents that resulted in the development of quartz-molybdenite veins. The quartz-molybdenite veins, accounting for >90% Mo in the orebody, were also formed by immiscible fluids with lower salinity and lower CO2 content of 7 mol%, at temperatures of 340-380 degrees C and pressures of 39-137 MPa, as constrained by fluid inclusion assemblages. After the main Mo-mineralization, the uneconomic Cu-Pb-Zn mineralization occurred, as represented by quartz-polymetallic sulfides veins consisting of pyrite, molybdenite, chalcopyrite, digenite, galena, sphalerite and quartz. The quartz-polymetallic sulfide veins were formed by fluids containing 5 mol% CO2, with minimum pressures of 32-110 MPa and temperatures of 260-300 degrees C. Finally, the fluids became dilute (5 wt.% NaCI equiv) and CO2-poor, which caused the formation of late barren quartz+ carbonate fluorite veins at 140-180 degrees C and 18-82 MPa. It is clear that the fluids became more dilute, CO2-poor, and less fertile, with decreasing temperature and pressure from quartz-pyrite to late barren veins. Molybdenite and other sulfides can only be observed in the middle three stages, i.e., quartz-pyrite, quartz-molybdenite and quartz-polymetallic sulfide veins. These three kinds of veins are generally hosted in potassic altered rocks with remarkable K-feldspathization, but always partly overprinted by phyllic alteration. The traditional porphyry-style potassic-phyllic-propylitic alteration zoning is not conspicuous at Yuchiling, which may be related to, and characteristic of, the CO2-rich fluids derived from the magmas generated in intercontinental collision orogens. Among the fluid inclusions at Yuchiling, only the C-type contains maximum detectable Mo that gradationally decreases from 73 ppm in quartz-pyrite veins, through 19 ppm in quartz-molybdenite veins, and to 13 ppm in quartz-polymetallic sulfide veins, coinciding well with the decreasing CO2 contents from 8 mol%, through 7 mol%, to 5 mol%, respectively. Hence it is suggested that decreasing CO2 possibly results in decreasing Mo concentration in the fluids, as well as the precipitation of molybdenite from the fluids. This direct relationship might be a common characteristic for other porphyry Mo systems in the world. The Yuchiling Mo deposit represents a new type Mo mineralization, with features of collision-related setting, high-K calc-alkaline intrusion, CO2-rich fluid, and unique wall-rock alterations characterized by strong K-feldspathization and fluoritization.
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| 28. |
- Lisitsin, Vladimir A., et al.
(författare)
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Orogenic gold mineral systems of the Western Lachlan Orogen (Victoria) and the Hodgkinson Province (Queensland) : Crustal metal sources and cryptic zones of regional fluid flow
- 2016
-
Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 76, s. 280-295
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Tidskriftsartikel (refereegranskat)abstract
- Orogenic gold mineral systems in the Western Lachlan Orogen (Victoria) and the Hodgkinson Province (Queensland) produced gold provinces characterised by vastly different scales of gold endowment and strongly uneven distribution of gold mineralisation within each province. The volume of hydrous pyrite-bearing rocks undergoing metamorphic devolatilisation during thermo-tectonic events driving orogenic gold mineral systems represents a fundamental first-order constraint on the total gold endowment and its broad spatial distribution, both between and within the provinces. Most of the largest gold deposits in both regions occur in linear, richly-endowed metallogenic zones, oblique to the dominant regional structures and related to deep crustal domain boundaries. These boundaries, with only subtle surface expressions, were the major regional structural controls which promoted focused near-vertical flow of mineralising metamorphic fluids above the outer margins of cratonic blocks in the lower crust. Recognised major faults represented only more local scale and often indirect controls on the focused fluid flow, particularly effective above the deep cratonic block boundaries overlain by relatively thick crustal source rocks.
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| 29. |
- Mahdy, Nasser M., et al.
(författare)
-
Petrogenesis of U- and Mo-bearing A(2)-type granite of the Gattar batholith in the Arabian Nubian Shield, Northeastern Desert, Egypt : Evidence for the favorability of host rocks for the origin of associated ore deposits
- 2015
-
Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 71, s. 57-81
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrothermal ore deposits associated with granitic rocks are the result of combinations and series of successive processes, events and conditions in a magma system and at post-magmatic stage. The metal content of a granitic magma as well as fractional crystallization, metal-ligand complexation, emplacement mechanisms and tectonic processes influence the metal precipitation and content of a hydrothermal ore deposit. The present study of the Gattar batholith evaluates how these processes contribute to the generation of an ore deposit. Gattar batholith in the north Eastern Desert of Egypt as part of the northern region of the Arabian-Nubian Shield (ANS) is geographically, mineralogically and geochemically divided into two distinctive areas. The southern part mainly consists of syenogranite while the northern part is dominated by highly evolved alkali-feldspar granite. Uranium and Mo mineralization occurring here is mostly limited to the margin of the highly evolved alkali-feldspar granites. New U-Pb zircon geochronology within this study indicates an age of similar to 620-600 Ma, although high common Pb and discordant age data of many zircon grains reflect alteration by F-rich fluids. Some zircons with distinct older U/Pb ages were considered to be inherited from the wall rocks representing juvenile crust of the ANS. The two different granitic rocks are comagmatic in origin and have A-type characteristics generated by partial melting of lower juvenile crust of the ANS. Geochemical data are in good agreement with a magmatic origin of the alkali-feldspar granites, suggesting fractional crystallization of a syenogranitic source as the most favorable process of their formation. Petrography, geochemistry, and geochronology studies of the Gattar granites along with field observations provide evidence for multiple intrusions as a result of successive magma pulses with different chemical composition. This led to the formation of reverse zoning within the intrusive complex. This kind of magma emplacement promotes the escape of exsolved metal-bearing volatile-rich fluids into the boundary of the Hammamat Sedimentary Rocks (HSR) and Gattar granite at the northern part of the batholith. Build-up of volatiles is a common phenomenon in granitic rocks and typically results in enhanced contents of F, alkalis and ore metals released at subsolidus stage.
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| 30. |
- Malehmir, Alireza, et al.
(författare)
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A Review of Reflection Seismic Investigations in Three Major Metallogenic Regions : The Kevitsa Ni-Cu-PGE district (Finland), Witwatersrand Goldfields (South Africa), and the Bathurst Mining Camp (Canada)
- 2014
-
Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 56, s. 423-441
-
Forskningsöversikt (refereegranskat)abstract
- Effective exploration for mineral deposits depends on a sound understanding of the processes and geological structures that contributed to their formation. The reflection seismic method has proven to be a powerful tool that provides a high-resolution image of the subsurface and information about structural and lithological relationships that control mineral deposits. The method has also become an attractive geophysical tool for deep exploration and mine planning. In this paper, we review the use of reflection seismic methods to obtain a better understanding of the architecture and ore-forming processes of three diverse mineral regions: the Kevitsa Ni-Cu-PGE district in Finland, the goldfields of the Witwatersrand Basin South Africa, and the Bathurst Mining Camp, Canada. Seismic data, both 2D and 3D, from the Kevitsa deposit clearly image the 3D geometry of the ore-bearing intrusion and provide information about its relationship to the host rock units and nearby intrusions within a larger tectonic framework. 3D seismic data from the Witwatersrand Basin not only provide clear images of major structures, including a distinct reflection that acts as a marker horizon for the gold-bearing reef, but also provide information that may be useful in resolving a long-standing controversy regarding the origin of the gold in the Basin. For example, it might be possible to show that dykes formed impermeable barriers, thereby falsifying the epigenetic hydrothermal models. 2D and 3D seismic data from the Brunswick No. 6 area in the Bathurst Mining Camp suggest that the Brunswick horizon (which contains the bulk of the massive sulfide and associated iron deposits) occurs within a reflective package that extends down to at least 6-7 km depth.
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| 31. |
- Malehmir, Alireza, et al.
(författare)
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Reflection seismic imaging and physical properties of base-metal and associated iron deposits in the Bathurst Mining Camp, New Brunswick, Canada
- 2010
-
Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 38:4, s. 319-333
-
Forskningsöversikt (refereegranskat)abstract
- The Bathurst Mining Camp, northern New Brunswick, Canada is a major base-metal producing region that includes the Brunswick No. 12 and smaller past-producing Brunswick No. 6 deposit. Sustaining mining activity in the camp requires exploration of orebodies near and adjacent to existing mines. In this paper, we recovered, re-processed, modeled and interpreted a 2D high-resolution reflection seismic profile in the vicinity of the Brunswick No. 6 open pit with the aim of providing key information on the geological structures associated with mineral deposits at depth. The seismic data quality is good to excellent with numerous strong reflections in raw shot gathers, resulting from a careful survey design that included test shots and a priori considerations for the geological environment. Physical properties of lithological units and mineralized zones including gamma–gamma, conductivity, magnetic susceptibility, density and sonic data were studied from borehole geophysical measurements conducted near the mine. This helped to correlate seismic data and shows that the Brunswick Horizon, a key ore-prospecting horizon, and associated lithological contacts are strongly reflective. The results demonstrate that reflection seismic imaging has been particularly effective for imaging steeply dipping structures of the Brunswick No. 6 deposit many of which intersect the surface and thus allow for correlation with surface geology. Massive sulfides and iron formation of the Brunswick Horizon are identifiable locally within a distinctive reflective package that can be used as a broad guide in the region for the exploration of deep base-metal deposits. In several locations, a change from highly reflective to semi-transparent seismic character is explained by the presence of faults that juxtapose highly reflective lithological units with seismically transparent lithologies.
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| 32. |
- Maraszewska, Maria, et al.
(författare)
-
Multi-stage metamorphic and metasomatic imprints on apatite-monazite-xenotime assemblages in a set of small iron oxide-apatite (IOA) ore bodies, Prins Karls Forland, Svalbard
- 2023
-
Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 155
-
Tidskriftsartikel (refereegranskat)abstract
- On Prins Karls Forland, Svalbard Archipelago, a set of small iron oxide-apatite (IOA) ore bodies have been discovered within a crustal shear zone, which deformed the polymetamorphosed Neoproterozoic metasedimentary rocks. The ores have various styles and grades of deformation and distinct mineral assemblages whose compositions record a multi-stage tectonothermal and metasomatic history. These IOA ore bodies can be subdivided into fluorapatite-bearing and predominant low-Th monazite in the upper section of the shear zone and FCl apatite-bearing and predominant high Th-monazite in the structurally lower higher-grade deformed part. The first stage of alteration for these ore bodies resulted in metasomatic alteration of the apatite and liberation of REE and P redeposited as monazite and xenotime. The transport of dissolved REE and P was likely enhanced by deformation. The second stage of alteration had a distinct impact on the individual ore bodies, which resulted in the Th-enrichment of a small subset of the monazite grains in the upper section of the shear zone. In the lower section of the shear zone most of the monazite was replaced by high Th monazite. Here the original fluorapatite is enriched in Cl, Mn, and Sr, most probably due to interaction with CaCl2-rich fluids enriched in Sr and Mn that was scavenged from the hosting metasediments and altered metagabbros. Contrasting textures, mineral assemblages, and the geochemistry of the ores from distinct localities reflect involvement of compositionally different fluids from the gabbroic rocks and surrounding metasedimentary rocks during the protracted tectonothermal evolution of Prins Karls Forland. Therefore, it is concluded that the IOA ore bodies most likely resulted due to the fractionation of Fe, P, Ca, and REE from hypersaline fluids associated with the gabbros. Once deposited, these IOA ore bodies were subsequently altered during at least one and perhaps two later metamorphic events.
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| 33. |
- Maries, Georgiana, et al.
(författare)
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Downhole physical property logging for iron-oxide exploration, rock quality, and mining : An example from central Sweden
- 2017
-
Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 90, s. 1-13
-
Tidskriftsartikel (refereegranskat)abstract
- Several physical properties obtained from geophysical logging and laboratory measurements were analyzed in order to characterize iron-oxide mineralization and host rocks in the Blotberget mining area of central Sweden. Seven boreholes intersecting the mineralization between 300 and 600 m depth in a volcano-sedimentary setting were downhole logged for this purpose. The downhole logging included full-waveform triple sonic, natural gamma, magnetic susceptibility, formation resistivity, fluid temperature and conductivity while laboratory measurements consisted of density, rock quality designation and magnetite content measurements. Full-waveform sonic data were used for rock quality assessments of the mineralized zones and their host rocks and proved their potential to be used for mine planning purposes. The ore-bearing rocks are primarily distinguished by increased density and dynamic elastic moduli estimated from the full-waveform sonic logging. Although seismic velocities do not follow a linear increase with the density for the mineralized rocks, as expected for igneous rocks, it is observed that a strong seismic signal from the mineralization can be expected primarily due to their high density. In addition, the full-waveform sonic data could be used as a proxy for fracture delineations and in situ rock quality assessment. For example, zones of washed-up amplitudes in these data correlate well with zones of poor quality rocks, identified by core logging. Based on the full-waveform sonic data, seismic attenuation and its reciprocal, the seismic quality factor, were calculated. A decrease in the seismic quality factor was observed at zones with low rock quality designation, but also correlated with the mineralized zones suggesting several fracture zones in the mineralization and that the ore-bearing rocks might be less competent than the surrounding host rocks. Eventual rock support and reinforcement might be required for future mining operations. Full-waveform sonic data have the potential to improve rock quality assessments for mine planning and exploration purposes.
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| 34. |
- Martinsson, Olof, et al.
(författare)
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Metallogeny of the Northern Norrbotten Ore Province, northern Fennoscandian Shield with emphasis on IOCG and apatite-iron ore deposits
- 2016
-
Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 78, s. 447-492
-
Forskningsöversikt (refereegranskat)abstract
- The Northern Norrbotten Ore Province in northernmost Sweden includes the type localities for Kiruna-type apatite iron deposits and has been the focus for intense exploration and research related to Fe oxide-Cu-Au mineralisation during the last decades. Several different types of Fe-oxide and Cu-Au +/- Fe oxide mineralisation occur in the region and include: stratiform Cu +/- Zn +/- Pb +/- Fe oxide type, iron formations (including BIF's), Kiruna-type apatite iron ore, and epigenetic Cu +/- Au +/- Fe oxide type which may be further subdivided into different styles of mineralisation, some of them with typical IOCG (Iron Oxide-Copper-Gold) characteristics. Generally, the formation of Fe oxide +/- Cu +/- Au mineralisation is directly or indirectly dated'between-2.1 and 1.75 Ga, thus spanning about 350 m.y. of geological evolution. The current paper will present in more detail the characteristics of certain key deposits, and aims to put the global concepts of Fe-oxide Cu-Au mineralisation into a regional context. The focus will be on iron deposits and various types of deposits containing Fe-oxides and Cu-sulphides in different proportions which generally have some characteristics in common with the IOCG style. In particular, ore fluid characteristics (magmatic versus non magmatic) and new geochronological data are used to link the ore-forming processes with the overall crustal evolution to generate a metallogenetic model. Rift bounded shallow marine basins developed at similar to 2.1-2.0 Ga following a long period of extensional tectonics within the Greenstone-dominated, 2.5-2.0 Ga Karelian craton. The similar to 1.9-1.8 Ga Svecofennian Orogen is characterised by subduction and accretion from the southwest. An initial emplacement of calc-alkaline magmas into similar to 1.9 Ga continental arcs led to the formation of the Haparanda Suite and the Porphyrite Group volcanic rocks. Following this early stage of magmatic activity, and separated from it by the earliest deformation and metamorphism, more alkali-rich magmas of the Perthite Monzonite Suite and the Kiirunavaara Group volcanic rocks were formed at similar to 1.88 Ga. Subsequently, partial melting of the middle crust produced large volumes of similar to 1.85 and 1.8 Ga S-type granites in conjunction with subduction related A-/I-type magmatism and associated deformation and metamorphism. In our metallogenetic model the ore formation is considered to relate to the geological evolution as follows. Iron formations and a few stratiform sulphide deposits were deposited in relation to exhalative processes in rift bounded marine basins. The iron formations may be sub-divided into BIF-(banded iron formations) and Mg rich types, and at several locations these types grade into each other. There is no direct age evidence to constrain the deposition of iron formations, but stable isotope data and stratigraphic correlations suggest a formation within the 2.1-2.0 Ga age range. The major Kiruna-type ores formed from an iron-rich magma (generally with a hydrothermal over-print) and are restricted to areas occupied by volcanic rocks of the Kiirunavaara Group. It is suggested here that 1.89-1.88 Ga tholeiitic magmas underwent magma liquid immiscibility reactions during fractionation and interaction with crustal rocks, including metaevaporites, generating more felsic magmatic rocks and Kiruna-type iron deposits. A second generation of this ore type, with a minor economic importance, appears to have been formed about 100 Ma later. The epigenetic Cu-Au +/- Fe oxide mineralisation formed during two stages of the Svecofennian evolution in association with magmatic and metamorphic events and crustal scale shear zones. During the first stage of mineralisation, from 1.89-1.88 Ga, intrusion-related (porphyry style) mineralisation and Cu-Au deposits of IOCG affinity formed from magmatic-hydrothermal systems, whereas vein-style and shear zone deposits largely formed at c. 1.78 Ga. The large range of different Fe oxide and Cu-Au +/- Fe oxide deposits in Northern Norrbotten is associated with various alteration systems, involving e.g. scapolite, albite, K feldspar, biotite, carbonates, tourmaline and sericite. However, among the apatite iron ores and the epigenetic Cu-Au +/- Fe oxide deposits the character of mineralisation, type of ore- and alteration minerals and metal associations are partly controlled by stratigraphic position (i.e. depth of emplacement). Highly saline, NaCl + CaCl2 dominated fluids, commonly also including a CO2-rich population, appear to be a common characteristic feature irrespective of type and age of deposits. Thus, fluids with similar characteristics appear to have been active during quite different stages of the geological evolution. Ore fluids related to epigenetic Cu-Au Fe oxides display a trend with decreasing salinity, which probably was caused by mixing with meteoric water. Tentatively, this can be linked to different Cu-Au ore paragenesis, including an initial (magnetite)-pyrite-chalcopyrite stage, a main chalcopyrite stage, and a late bornite stage. Based on the anion composition and the Br/Cl ratio of ore related fluids bittern brines and metaevaporites (including scapolite) seem to be important sources to the high salinity hydrothermal systems generating most of the deposits in Norrbotten. Depending on local conditions and position in the crust these fluids generated a variety of Cu-Au deposits. These include typical IOCG-deposits (Fe-oxides and Cu-Au are part of the same process), IOCG of iron stone type (pre-existing Fe-oxide deposit with later addition of Cu-Au), IOCG of reduced type (lacking Fe-oxides due to local reducing conditions) and vein-style Cu-Au deposits. From a strict genetic point of view, IOCG deposits that formed from fluids of a mainly magmatic origin should be considered to be a different type than those deposits associated with mainly non-magmatic fluids. The former tend to overlap with porphyry systems, whereas those of a mainly non-magmatic origin overlap with sediment hosted Cu-deposits with respect to their origin and character of the ore fluids.
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| 35. |
- Molnár, F., et al.
(författare)
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Boron, sulphur and copper isotope systematics in the orogenic gold deposits of the Archaean Hattu schist belt, eastern Finland
- 2016
-
Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 77, s. 133-162
-
Tidskriftsartikel (refereegranskat)abstract
- The Hattu schist belt is located in the western part of the Archaean Karelian domain of the Fennoscandian Shield. The orogenic gold deposits with Au–Bi–Te geochemical signatures are hosted by NE–SW, N–S and NW–SE oriented shear zones that deform 2.76–2.73 Ga volcanic and sedimentary sequences, as well as 2.75–2.72 Ga tonalite–granodiorite intrusions and diverse felsic porphyry dykes. Mo–W mineralization is also present in some tonalite intrusions, both separate from, and associated with Au mineralization. Somewhat younger, unmineralized leucogranite intrusions (2.70 Ga) also intrude the belt. Lower amphibolite facies peak metamorphism at 3–5 kbar pressures and at 500–600 °C temperatures affected the belt at around 2.70 Ga and post-date hydrothermal alteration and ore formation. In this study, we investigated the potential influence of magmatic-hydrothermal processes on the formation of orogenic gold deposits on the basis of multiple stable isotope (B, S, Cu) studies of tourmaline and sulphide minerals by application of in situ SIMS and LA ICP MS analytical techniques.Crystal chemistry of tourmaline from a Mo–W mineralization hosted by a tonalite intrusion in the Hattu schist belt is characterized by Fe3 +–Al3 +-substitution indicating relatively oxidizing conditions of hydrothermal processes. The range of δ11B data for this kind of tourmaline is from − 17.2‰ to − 12.2‰. The hydrothermal tourmaline from felsic porphyry dyke swith gold mineralization has similar crystal chemistry (e.g. dravite–povondraite compositional trend with Fe3 +–Al3 + substitution) and δ11B values between − 19.0‰ and − 9.6‰. The uvite–foitite compositional trend and δ11B ‰ values between − 24.1% and − 13.6% characterize metasomatic–hydrothermal tourmaline from the metasediment-hosted gold deposits. Composition of hydrothermal vein-filling and disseminated tourmaline from the gold-bearing shear zones in metavolcanic rocks is transitional between the felsic intrusion and metasedimentary rock hosted hydrothermal tourmaline but the range of average boron isotope data is essentially identical with that of the metasediment-hosted tourmaline. Rock-forming (magmatic) tourmaline from leucogranite has δ11B values between − 14.5‰ and − 10.8‰ and the major element composition is similar to that of the metasediment-hosted tourmaline.The range of δ34SVCDT values measured in pyrite, chalcopyrite and pyrrhotite is from − 9.1 to + 8.5‰, which falls within the typical range of sulphur isotope data for Archaean orogenic gold deposits. In the Hattu schist belt, positive δ34SVCDT values characterize metasediment-hosted gold ores with sulphide parageneses dominated by pyrrhotite and arsenopyrite. The δ34SVCDT values are both positive and negative in ore mineral parageneses within felsic intrusive rocks in which variable amounts of pyrrhotite are associated with pyrite. Purely negative values were only recorded from the pyrite-dominated gold mineralization within metavolcanic units. Therefore the shift of δ34SVCDT values to the negative values reflects precipitation of sulphide minerals from relatively oxidizing fluids. The range of measured δ65CuNBS978 values from chalcopyrite is from − 1.11 to 1.19‰. Positive values are common for mineralization in felsic intrusive rocks and negative values are more typical for deposits confined to metasedimentary rocks. Positive and negative δ65CuNBS978 values occur in the ores hosted by metavolcanic rocks. There is no correlation between sulphur and copper isotope data obtained in the same chalcopyrite grains.Evaluation of sulphur and boron isotope data together and comparisons with other Archaean orogenic gold provinces supports the hypothesis that the metasedimentary rocks were the major sources of sulphur and boron in the orogenic gold deposits in the Hattu schist belt. Variations in major element and boron isotope compositions in tourmaline, as well as in the δ34SVCDT values in sulphide minerals are attributed to localized involvement of magmatic fluids in the hydrothermal processes. The results of copper isotope studies indicate that local sources of copper in orogenic gold deposits may potentially be recognized if the original, distinct signatures of the sources have not been homogenized by widespread interaction of fluids with a large variety of rocks and provided that local chemical variations have been too small to trigger changes in the oxidation state of copper during hydrothermal processes.
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| 36. |
- Murton, Bramley J., et al.
(författare)
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Geological fate of seafloor massive sulphides at the TAG hydrothermal field (Mid-Atlantic Ridge)
- 2019
-
Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 107, s. 903-925
-
Forskningsöversikt (refereegranskat)abstract
- Deep-sea mineral deposits potentially represent vast metal resources that could make a major contribution to future global raw material supply. Increasing demand for these metals, many of which are required to enable a low-carbon and high-technology society and to relieve pressure on land-based resources, may result in deep sea mining within the next decade. Seafloor massive sulphide (SMS) deposits, containing abundant copper, zinc, gold and silver, have been the subject of recent and ongoing commercial interest. Although many seafloor hydrothermally systems have been studied, inactive SMS deposits are likely more accessible to future mining and far more abundant, but are often obscured by pelagic sediment and hence difficult tolocate. Furthermore, SMS deposits are three dimensional. Yet, to date, very few have been explored or sampled below the seafloor. Here, we describe the most comprehensive study to date of hydrothermally extinct seafloor massive sulphide (eSMS) deposits formed at a slow spreading ridge. Our approach involved two research cruises in the summer of 2016 to the Trans-Atlantic Geotraverse (TAG) hydrothermal field at 26 N on the Mid-Atlantic Ridge. These expeditions mapped a number of hydrothermally extinct SMS deposits using an autonomous underwater vehicle and remotely operated vehicle, acquired a combination of geophysical data including sub-seafloor seismic reflection and refraction data from 25 ocean bottom instruments, and recovered core using a robotic lander-type seafloor drilling rig. Together, these results that have allowed us to construct a new generic model for extinct seafloor massive sulphide deposits indicate the presence of up to five times more massive sulphide at and below the seafloor than was previously thought.
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| 37. |
- Myint, Aung Zaw, et al.
(författare)
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Stable isotope and geochronological study of the Mawchi Sn-W deposit, Myanmar : Implications for timing of mineralization and ore genesis
- 2018
-
Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368. ; 95, s. 663-679
-
Tidskriftsartikel (refereegranskat)abstract
- Myanmar is endowed with abundant Sn-W mineralization, pre-eminent amongst which is the world-class Mawchi deposit. In the Mawchi area, N-S trending vertical or steeply dipping quartz veins are hosted by both Eocene granite and Carboniferous to Early Permian metasediments. Three stages of ore formation are recognized; (i) tourmaline-cassiterite stage (ii) main ore stage and (iii) sulfide stage. Tourmaline, cassiterite and pyrite-I are early-formed minerals and are representative of the first stage. Their deposition continued together with wolframite, scheelite, molybdenite, arsenopyrite, pyrite-II, fluorite and danalite, which form the second stage. This was followed by the successive deposition of sulfides such as chalcopyrite, sphalerite, galena and Pb-Bi sulfides. A 40Ar/39Ar magmatic biotite plateau age of 41.50 ± 0.16 Ma (MSWD = 2.5) is determined for the Mawchi biotite granite which we interpret as the time the granite cooled through the biotite blocking temperature, and is consistent with a previously reported LA-ICP-MS U-Pb zircon concordia age of 42.72 ± 0.94 Ma (MSWD = 2). A molybdenite Re-Os model age of 42.4 ± 1.2 Ma indicates that Sn-W mineralization was synchronous with late Eocene granitic magmatism. Our 40Ar/39Ar hydrothermal muscovite plateau ages from the tourmaline granite (40.14 ± 0.14 Ma; MSWD = 1.48) and quartz vein selvages (40.80 ± 0.12 Ma; MSWD = 0.47) define the timing of hydrothermal alteration and simultaneous veining that accompanied the late stage of ore forming at Mawchi. Fluid inclusion microthermometry from cassiterite, scheelite, quartz, and fluorite reveals that ore fluids in the cassiterite-tourmaline stage and main ore stage are characterized by moderate homogenization temperatures (Th = 260–345 °C) and salinities (4.5–15.7 wt% NaCl equiv), while the sulfide stage is characterized by lower temperatures (Th = 175–260 °C) and moderate to low salinity (2.5–13 wt% NaCl equiv). The mean δ34S of all sulfides is 2.9 ± 2.9‰ which is suggestive that the overall system is dominated by magmatic sulfur. The similarity of δ34S values in galena and Pb-Bi sulfides (−1.3 to 2.7‰) suggest that sulfur, and inference the Pb and Bi were transported by a common fluid, probably of magmatic origin. The calculated δ18OH2O of the hydrothermal fluid associated with cassiterite and tourmaline is 7.3–8.4‰. Scheelite and quartz deposition is characterized by lighter δ18OH2O values (2.1–4.9‰) indicating that the ore fluid might be mixed with another source of water, perhaps, meteoric. Hydrogen isotopic compositions (δD = −51 to −121‰) again indicate that origin of the ore fluid is magmatic, but δD (∼−120‰) is low enough to support the δ18OH2O data that suggests, in part, a meteoric water component to the hydrothermal fluids at Mawchi.
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| 38. |
- Parvaresh Darbandi, Mahboobeh, et al.
(författare)
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Textures and chemical compositions of the Narm iron oxide-apatite deposit in Kuh-e-Sarhangi district (Central Iran) : Insights into the magmatic-hydrothermal mineralization
- 2022
-
Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 141
-
Tidskriftsartikel (refereegranskat)abstract
- The Narm deposit is located in the Kuh-e-Sarhangi district which is a main part of the most significant Iranian iron mineralization belt, the Kashmar-Kerman Tectonic Zone (KKTZ) in Central Iran. The Narm deposit comprises an estimated total of ∼ 135000 tons of iron ore with an average grade of ∼ 55% Fe and is hosted in Early Cambrian volcano sedimentary rocks of the Rizu formation. Ore occurrences in this deposit consist of lens-shaped magnetite ore bodies, magnetite-apatite-actinolite veins and locally rare brecciated dolomite with magnetite clasts. Magnetite, pyrite, chalcopyrite and specularite associated with apatite, actinolite, biotite and carbonate minerals form the primary main mineral assemblage which is accompanied by hematite and goethite as the secondary minerals. Magnetite as the most current mineral of Narm deposit reveal the magmatic to hydrothermal evolution of mineralization. Magmatic magnetite minerals (Mag I) are dark-gray inclusion-rich magnetite spatially correlated with high temperature Ca-Fe alteration. The brighter inclusion-free hydrothermal magnetite groups (Mag II and Mag III) form during the temperature decreasing of the mineralizing fluid. According to the magnetite chemistry examination, most magnetite fall into the field for magnetite from iron-oxide apatite (IOA) deposits. Apatite minerals with F/Cl >2, belong geochemically to the fluorapatite type. In addition to the primary dolomite, there are some hydrothermal Fe-rich dolomites and Mn bearing ones, indicating the hydrothermal fluid playing the important role for Fe-rich mineralization. In respect to fluid evolution, fluid inclusion analysis of calcite and apatite minerals form the magnetite paragenesis assemblage represent homogenization temperature range for fluid between 325-557℃. The salinity of fluid varied from 7.7 to 11.6 wt % NaCl equivalent and a cooling trend with the dominant chlorine complex as an agent for deposition of the Fe-rich ores. The geochemical characteristics of the δ18Ofluid values of magnetite (from +6.1 to +10.4‰) and δ18Ofluid values of actinolite (from +7.7 to +12.5‰) represent the magmatic-hydrothermal (δ18Ofluid > + 0.9 ‰) formation process. The iron rich Al-clinochlore composition from the alteration zone indicates a temperature range between 250 and 330℃ which points to a temperature reduction of hydrothermal fluids in this mineralizing zone. The integrated geochemical data from this investigation, including mineral chemistry, microthermometry of fluid inclusions and oxygen isotope data all reveal a magmatic-hydrothermal genesis for this deposit.
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| 39. |
- Patten, Clifford G. C., et al.
(författare)
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Hydrothermal mobilisation of Au and other metals in supra-subduction oceanic crust : Insights from the Troodos ophiolite
- 2017
-
Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 86, s. 487-508
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Forskningsöversikt (refereegranskat)abstract
- The Troodos ophiolite is an ideal location to investigate the relationships between the mobilisation of metals by hydrothermal fluids from the lower oceanic crust and the formation of volcanogenic massive sulphide (VMS) deposits. The ophiolite hosts the classic Cyprus-type Cu-rich VMS deposits as well as abundant zones of epidosite alteration in the lower sheeted dyke section that are significantly depleted in base metals including Cu and Zn, and are considered to be the source of the metals enriched in the overlying deposits. Previous research indicates that the Troodos VMS deposits are irregularly enriched in Au and related elements As, Sb, and Se, but the behaviour of these elements during the hydrothermal alteration of the Troodos ophiolite hitherto has been poorly investigated. Low detection limit whole rock analyses of fresh glass samples reveal that the Troodos primitive crust has a similar metal content and distribution to modern-day arc-related environments such as the Manus Basin. Compared to mid oceanic ridge basalt (MORB), the Troodos primitive crust is enriched in As, Sb and Pb most likely due to addition from a subducting slab during crustal formation. During early stages of magmatic differentiation (9-3.5 wt% MgO) Au, As, Sb, Se, Cu, Zn and Pb behave as incompatible elements due to the sulphide-undersaturated nature of the melt. The onset of magnetite crystallisation, however, at similar to 3.5 wt% MgO leads to sulphide segregation and depletion of strongly chalcophile elements (Au, Cu and Se) during continued differentiation (<3.5 wt% MgO) whereas poorly chalcophile elements (As, Sb, Zn and Pb) remain incompatible. These differences in metal behaviour can account for the Cu-rich, Zn-Pb-poor of the Cyprus-type VMS deposits as the source area rocks show high Cu fertility compared to Zn and Pb. Mobilisation of metals during hydrothermal alteration of the Troodos ophiolite is more extensive than observed in hydrothermally altered MORB. Mass balance calculations show that the epidosite zones are significantly depleted in Au (-88 +/- 16%), As (-89 +/- 23%), Sb (-60 +/- 12%), Se (-91 +/- 20%), Cu (-84 +/- 18%), Zn (-63 +/- 9%) and Pb (-60 +/- 8%). Background altered diabase from outside epidosite zones shows similar metal depletions which suggests that the source areas of VMS are not restricted to epidosite zones but are extended to the lower sheeted dyke section. The masses of metals mobilised from a source area of 10.9 km(3), (composed of a 5 km(3) epidosite zone and 5.9 km(3) of background altered diabase) in the Solea graben are 47 t Au, 21 kt As, 1200 t Sb, 3100 t Se, 2.4 Mt Cu, 1.8 Mt Zn and 27 kt Pb. Comparison of metal quantities mobilised from lower sheeted dike section in the Solea graben with those hosted in VMS deposits shows trapping efficiencies ranging from 4 to 37% indicating that most of the metals is lost by other processes.
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| 40. |
- Pitcairn, Iain K., et al.
(författare)
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The gold conveyor belt : Large-scale gold mobility in an active orogen
- 2014
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 62, s. 129-142
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Tidskriftsartikel (refereegranskat)abstract
- The Southern Alps of New Zealand are part of an active collisional orogen where metamorphism, hydrothermal fluid flow and the formation of orogenic gold deposits are ongoing. The Southern Alps are forming due to transpressional collision between continental crust fragments on the Pacific and Australian tectonic plates. The plate tectonic rates and geometries, the sources of fluid and broad-scale fluid pathways in the hydrogeological system, and the geochemical compositions of the Torlesse Terrane rock that is being advected through the orogen are well defined so that a mass balance of metal mobility during active orogenic processing in the Southern Alps of New Zealand can be calculated. Advection of a 10 km wide x 5 km deep section of Torlesse rock through the orogen at tectonic rates (0.01 m/yr) that is then metamorphosed up to amphibolite fades causes mobilisation of over 11,27 t Au, 10.1 Mt As, 47,000 t Hg, 560,000 t Sb and 14,000 Mt H2O in 1 Myrs. The masses of elements mobilised at the same rate along the length of the Southern Alps (>200 km) for 5 Myrs would be more than 100 times greater. The metals were mobilised by the metamorphic fluid produced during the orogenic processing of the Torlesse Terrane rocks and the concentrations of Au, As, Hg and Sb in this fluid are calculated to be 0.08, 711, 3, and 40 mg/kg, respectively. The mobilised metals form the orogenic gold deposits that occur in the Southern Alps. Different styles of gold deposits form contemporaneously during the active orogenesis of the Southern Alps, including those with a fluid temperature > rock temperature that may appear to have formed after the peak of metamorphism but are instead just the product hydrothermal fluid mineralising rocks on their retrograde metamorphic path. The mass balance shows that there has been orders of magnitude more metal mobilised in the orogen than resides in the currently known deposits. There is a clear potential for large gold deposits occurring in the yet to be uplifted parts of the Southern Alps if there have been efficient enough fluid focusing and metal precipitation mechanisms occurring under the Southern Alps.
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| 41. |
- Sadeghi, Martiya, et al.
(författare)
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Principal components analysis and K-means clustering of till geochemical data: Mapping and targeting of prospective areas for lithium exploration in Västernorrland Region, Sweden
- 2024
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Ingår i: Ore Geology Reviews. - : Elsevier B.V.. - 0169-1368 .- 1872-7360. ; 167
-
Tidskriftsartikel (refereegranskat)abstract
- To achieve the demand for elements used for the green transition energy, such as lithium, it is necessary to recognize the spatial distribution of the concentrations of these elements in different earth materials such as bedrock and soil and to identify areas with anomalous concentrations of such elements (i.e., mineralization) for further exploration and hopefully exploitation. This study carried out multivariate statistical analyses on compositional (i.e., element concentration) data from till samples to recognize areas that likely contain lithium pegmatite mineralization in the Västernorrland region, central Sweden. We applied principal components analysis (PCA) and K-means clustering techniques to reveal regional-scale patterns in the till geochemical data. We demonstrate that these two methods have potential for recognition of geochemical anomalies related to the underlying bedrock geology as well as to mineralization. The results of PCA- and K-means clustering were validated using known occurrences of lithium mineralization. Two different datasets were compared; one containing all available geochemical data and the second containing only available trace elements in the dataset and it was found that anomalous clusters of samples defined by K-means clustering have anomalous multi-element signatures defined by robust PCA. This demonstrated that principal components are the continuous solutions to the discrete cluster members for the K-means clustering. The results show that both PCA and K-means clustering of till geochemical datasets at the early stages of exploration and target generation may reveal useful information that can be used to identify potential areas for more detailed mapping or exploration activities.
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| 42. |
- Sandrin, Alessandro, et al.
(författare)
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Geophysical and petrophysical study of an iron oxide copper gold deposit in northern Sweden
- 2006
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Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 29:1, s. 1-18
-
Tidskriftsartikel (refereegranskat)abstract
- A geophysical-petrophysical study has been performed in an area WSW of the city of Kiruna, northern Sweden. The sub-regional tectonic setting is dominated by two important shear zones, which define the boundary of a granitic body. Many Cu-Fe-occurrences are located in proximity of faults related to these major deformation zones. Particular attention has been given to the Tjårrojåkka iron oxide copper gold (IOCG) deposit. Here the bedrock is characterised by intermediate to mafic meta-volcanics, metamorphosed intermediate to mafic dykes, and gabbroic-dioritic intrusions of Svecofennian ages (1.96-1.75 Ga). The major Cu- and Fe-occurrences are hosted by the meta-andesites. The aim of the study is to put the deposits into a tectonic framework and test existing hypotheses for their occurrences.Glacial deposits cover almost the entire area, leading to a scarcity of outcrops and inferring that geophysical data are fundamental for geological understanding. In addition to this, petrophysical analysis is vital for the interpretation of geophysical data (gravity, airborne magnetics and radiometrics, very low frequency) and for the definition of geophysical signatures of the deposits. The anisotropy of magnetic susceptibility (AMS) was also studied for the tectonic analysis. More than 150 oriented samples were collected in a number of outcrops along a profile intersecting the major structures in the Tjårrojåkka area.From the airborne magnetic data, two major linear features are interpreted as deformation zones. The strike of these deformation zones is approximately NW-SE and E-W, respectively. The same trends have been defined from other geophysical data such as airborne VLF and ground gravity data. A third important structural trend striking SW-NE has been defined by K/Th data and ground magnetic data. Very good agreement has been found between geophysical lineaments and AMS directions. Magnetic foliations determined by AMS measurements confirm the existence of three major trends in the study area: SW-NE, E-W and NW-SE. The major Fe-orebody shows approximately a SW-NE strike direction as defined from ground magnetic data. This is parallel to the strike of magnetic foliation determined in outcrops 1 km NW of the deposit. The epigenetic nature of the Cu and Fe occurrences in Tjårrojåkka and their spatial relationship with deformation zones suggest a connection between the formation of the deposits and a tectonic event. A later tectonic episode resulted in E-W trending deformation in the central area, affecting the orebodies themselves. Other, probable, compressive deformations have been indicated from petrophysical and geophysical analyses.Thermomagnetic measurements indicate that Fe-oxides (Ti-magnetite) are common in the area, while Fe-sulphides are almost absent. Multi-domain magnetite has been identified as the most common Fe-oxide in different rock types, while an unstable magnetic mineral has been detected in metamorphosed volcanics. A good spatial correlation has been observed between Cu-deposits and high K/Th values from radiometric data, values that are expressions of potassic alteration.
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| 43. |
- Sandrin, Alessandro, et al.
(författare)
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Physical properties of rocks from borehole TJ71305 and geophysical outline of the Tjårrajåkka Cu-prospect, northern Sweden
- 2007
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Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 30:1, s. 56-73
-
Tidskriftsartikel (refereegranskat)abstract
- In the last decades Fe-oxide Cu–Au (IOCG) deposits attracted the interest of exploration geologists and geophysicists. General geophysical descriptions of IOCG deposits have been published in the recent past, but there is still a lack of detailed geophysical investigations. We present a petrophysical study of rock samples from exploration borehole TJ71305, which intersects the Cu-prospect in the Tjårrojåkka IOCG mineralised area, northern Sweden. Furthermore geophysical data are compiled and analysed to tentatively define a geophysical signature, at local scale, for this type of deposit. The study area is dominated by intrusive and volcanic rocks of Middle Proterozoic age, the latter hosting the Cu and Fe occurrences. The Fe occurrences are clearly defined from both aeromagnetic and ground magnetic data, and are also indicated by gravity, geoelectric and electromagnetic data. Enrichment in ferromagnetic minerals in the area is suggested by the high values of magnetic susceptibility commonly obtained for different rock types; magnetite and Ti-magnetite are the dominant magnetic minerals. Haematite with variable contents of Ti was detected and it is probably a result of oxidation of magnetite in alteration zones. In Tjårrojåkka a clear spatial relationship is noted between Cu occurrences and high K/Th ratios. This ratio is calculated from airborne radiometric data and is an expression of enrichment in potassium, due to alteration. The Cu-prospect is also indicated by high gravity and magnetic anomalies, by clear positive anomalies in induced polarisation data and by negative anomalies for the imaginary part of ground electromagnetic (Slingram) data. However, high-density/high-susceptibility/low-resistivity (Ti)-magnetite is associated with the Cu-prospect and this may lead to misinterpretation of potential field, electromagnetic and geoelectric data.
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| 44. |
- Sosnicka, Marta, et al.
(författare)
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Fluid types and their genetic meaning for the BIF-hosted iron ores, Krivoy Rog, Ukraine
- 2015
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 68, s. 171-194
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Tidskriftsartikel (refereegranskat)abstract
- This paper contributes to the understanding of the genesis of epigenetic, hypogene BIF-hosted iron deposits situated in the eastern part of Ukrainian Shield. It presents new data from the Krivoy Rog iron mining district (Skelevatske-Magnetitove deposit, Frunze underground mine and Balka Severnaya Krasnaya outcrop) and focuses on the investigation of ore genesis through application of fluid inclusion petrography, micro-thermometry, Raman spectroscopy and baro-acoustic decrepitation of fluid inclusions. The study investigates inclusions preserved in quartz and magnetite associated with the low-grade iron ores (31-37% Fe) and iron-rich quartzites (38-45% Fe) of the Saksaganskaya Suite, as well as magnetite from the locally named high-grade iron ores (52-56% Fe). These high-grade ores resulted from alteration of iron quartzites in the Saksaganskiy thrust footwall (Saksaganskiy tectonic block) and were a precursor to supergene martite, high-grade ores (60-70% Fe). Based on the new data two stages of iron ore formation (metamorphic and metasomatic) are proposed. The metamorphic stage, resulting in formation of quartz veins within the low-grade iron ore and iron-rich quartzites, involved fluids of four different compositions: CO2-rich, H2O, H2O-CO2(+/- N-2-CH4)-NaCl(+/- NaHCO3) and H2O-CO2(+/- N-2-CH4)-NaCl. The salinities of these fluids were relatively low (up to 7 mass% NaCl equiv.) as these fluids were derived from dehydration and decarbonation of the BIF rocks, however the origin of the nahcolite (NaHCO3) remains unresolved. The minimum P-T conditions for the formation of these veins, inferred from microthermometry are T-min = 219-246 degrees C and P-min = 130-158 MPa. The baro-acoustic decrepitation analyses of magnetite bands indicated that the low-grade iron ore from the Skelevatske-Magnetitove deposit was metamorphosed at T = similar to 530 degrees C. The metasomatic stage post-dated and partially overlapped the metamorphic stage and led to the upgrade of iron quartzites to the high-grade iron ores. The genesis of these ores, which are located in the Saksaganskiy tectonic block (Saksaganskiy ore field), and the factors controlling iron ore-forming processes are highly controversial. According to the study of quartz-hosted fluid inclusions from the thrust zone the metasomatic stage involved at least three different episodes of the fluid flow, simultaneous with thrusting and deformation. During the 1st episode three types of fluids were introduced: CO2-CH4-N-2(+/- C), CO2(+/- N-2-CH4) and low salinity H2O-N-2-CH4-NaCl (6.38-7.1 mass% NaCl equiv.). The 2nd episode included expulsion of the aqueous fluids H2O-N2CH4-NaCl(+/- CO2, +/- C) of moderate salinities (15.22-16.76 mass% NaCl equiv.), whereas the 3rd event involved high salinity fluids H2O-NaCl(+/- C) (20-35 mass% NaCl equiv.). The fluids most probably interacted with country rocks (e.g. schists) supplying them with CH4 and N-2. The high salinity fluids were most likely either magmatic-hydrothermal fluids derived from the Saksaganskiy igneous body or heated basinal brines, and they may have caused pervasive leaching of Fe from metavolcanic and/or the BIF rocks. The baro-acoustic decrepitation analyses of magnetite comprising the high-grade iron ore showed formation T = similar to 430-500 degrees C. The fluid inclusion data suggest that the upgrade to high-grade Fe ores might be a result of the Krivoy Rog BIF alteration by multiple flows of structurally controlled, metamorphic and magmatic-hydrothermal fluids or heated basinal brines.
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| 45. |
- Subías, I., et al.
(författare)
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Isotopic constraints on the age and source of ore-forming fluids of the Bou Azzer arsenide ores (Morocco)
- 2022
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 143, s. 104769-104769
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Tidskriftsartikel (refereegranskat)abstract
- The Bou Azzer district in Morocco has a long mining history since the beginning of the XXst century during which it has become the only world producer of Co from primary, hydrothermal Co arsenide ores. Orebodies are structurally controlled, and mainly distributed along fault contacts between Cryogenian ophiolite-related serpentinite bodies and intrusive quartz diorite or, locally, ophiolitic gabbros or Ediacaran volcanic rocks. Ore formation took place through a multi-stage mineralizing process that included an early stage composed by gold, quartz, chlorite, muscovite and calcite, followed by the main arsenide and sulfarsenide stage (subdivided into three substages, IIa: Ni-rich, Co ores, IIb: Co-Fe ores and IIc: Fe-Co ores), and ending with an epithermal stage characterized by the precipitation of sulfides along with quartz and calcite. Field relations and most previous geochronologic dating pointed to a post Pan-African age of ore formation, mainly coincident with the Hercynian orogeny.The isotopic study presented in this paper includes S, Pb, Rb/Sr and Sm/Nd data of a set of ore mineral samples from three deposits (Aghbar, Tamdrost and Aït Ahmane), as well as of regional samples representative of the different lithologies occurring in the Bou Azzer area. The isotope data set was completed with S isotope analyses of arsenide and sulfarsenide minerals from five ore deposits (Filon 7/5, Aghbar, Tamdrost, Ightem and Aït-Ahmane) and of some whole-rock regional samples. Results show that ores formed during multi-episodic hydrothermal events connected with hercynian reactivation of Devonian-Carboniferous faults, supporting previous geochronologic dating. The obtained Pb, Sr, Nd and S isotopic signatures of ore minerals and regional rocks further show that ophiolite-related lithologies became isotopically modified by interaction with crustal material and afterwards acted as the main source of ore-forming elements. Nevertheless, isotopic data do not fully concur with such a simple scenario but are quite consistent with a rather complex interpretation based on multi-source origin of some elements and isotopes scavenged from a number of isotopically different lithologies both from the inferred basement and the volcanic and sedimentary cover.
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| 46. |
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| 47. |
- Talbot, Christopher J., et al.
(författare)
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Potash in a salt mushroom at Hormoz Island, Hormoz Strait, Iran
- 2009
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 35:3-4, s. 317-332
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Forskningsöversikt (refereegranskat)abstract
- Increasing volumes of potash are currently being discovered in a cluster of diapirs of Hormoz (formerly Hormuz) salt near Bandar Abbas, Iran. Most of the potash beds studied so far occur in complex recumbent folds in a salt mountain that would be difficult to exploit safely. However, Holocene marine erosion removed any salt mountains from a sub-group of near-shore Zagros diapirs and exposed their deeper structural levels. Even though these diapirs are still active, their potash deposits are likely more tractable to safe exploitation than in a salt mountain - as we make clear here for Hormoz Island. Geochemical surveys on Hormoz Island reveal two separate potash anomalies that are valuable pseudostratigraphic markers. Integrating field measurements of the attitudes of bedding with lineaments on air photos suggests that Hormoz Island consists of a mature bell- or plume-shaped mushroom diapir with potash beds wound around a toroidal axis of rotation near current exposure levels. 2D numerical models simulate the salt mushroom on Hormoz Island and its internal circulation. They also suggest that the diapir has a wide overhand above a narrow stem in this gas-rich region. We use the mushroom diapir model to outline a regional exploration strategy that has the potential of influencing the world potash market thereafter.
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| 48. |
- Talbot, Christopher J., et al.
(författare)
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Potash in salt extruded at Sar Pohl diapir, Southern Iran
- 2009
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 35:3-4, s. 352-366
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Forskningsöversikt (refereegranskat)abstract
- Recent progress in the search for potassium salts in Iran is outlined. After reviewing how most potassium ores form by the evaporation of seawater +/- hydrothermal brines, we focus on how most ores are deformed within salt diapirs. We summarise the history of the 150 or so diapirs of Hormoz salt emergent in the Zagros Mountains of Iran and then consider in detail the nature of potash at Sar Pohl, 60 km west of Bandar Abbas. These deposits are unique in that they occur in salt that extruded sub-aerially and spread over the surrounding ground surface via gravity-driven collapse. Mapping and drilling of the complex structural geology of Sar Pohl found the potash beds to be dispersed in distal salt but concentrated in piles of recumbent folds with axes circumferential to the mountain over lows in the vent rim. Equivalents of the curtain folds surviving in the stems of German diapirs presumably still exist beneath Sar Pohl and would be safer to mine than the recumbent folds in this soluble mountain. However, it should be possible to continuously pump water onto the exposed salt and guide the resulting brines through evaporation ponds and then a crystallization plant on the adjacent plains. This approach would accelerate natural degradation processes but harvest potash currently draining into the gulf.
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| 49. |
- Tindell, Thomas, et al.
(författare)
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The Kago low-sulfidation gold and silver deposit : A peripheral mineralisation to the Nansatsu high-sulfidation system, southern Kyushu, Japan
- 2018
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368. ; 102, s. 951-966
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Tidskriftsartikel (refereegranskat)abstract
- The Kago deposit is a small deposit located at the southern tip of the Satsuma Peninsula of Southern Kyushu, Japan. It lies proximal to the well-known Nansatsu-type mineralisation province dominated by high-sulfidation type epithermal deposits. The deposit was heavily mined in the 18 th Century, largely for its relatively higher gold compared to that of surrounding and regional deposits. The Kago deposit is a typical low-sulfidation deposit, characterised by adularia-quartz veins, composed of electrum, Ag-tetrahedrite, polybasite, chalcopyrite and pyrite. Based on mine records, the grade ranged from 4.1 to 13.3 g/t Au and 2.6-6.6 g/t Ag. Alteration grades from low to high temperature argillic into a propylitic zone at the extremes of the vein exposures. Carbonate is absent. Fluid inclusion microthermometry reveals a typical temperature range of 220-240 °C with salinity of 0.7-2.6 NaCl eq. wt%. Electrum from high-grade ore ranges from 66 to 69 wt% Au. 40Ar/39Ar age dating of adularia bearing colloform/crustiform and brecciated veins, suggests a mineralisation event from 4.23 to 4.0 Ma. δ18O of veined and silicified quartz ranges from +4.0 to +18.4‰. δ18OH2O of fluids in equilibrium with quartz, in the dominant range of measured fluid inclusion temperatures, ranges from -6.5‰ to -0.2‰. δ34S of pyrite has a narrow range from -1.8 to 2.7‰. The deposit lies at the northern extent of the classic Nansatsu high-sulfidation epithermal area, in which a number of silicified bodies punctuate the region in a roughly semi-circular shape. The Kago deposit lies within the principle mineralisation age range of the high-sulfidation deposits, which range from 5.5 to 3.7 Ma. The structural displacement of the Kago deposit from the Nansatsu mineralisation and the differing host rocks has greatly influenced alteration, ore and rock-water interaction of the ore depositing fluids. Here we seek to establish the relationship that this extended mineral province has between the differing styles of mineralisation.
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| 50. |
- Tiu, Glacialle, et al.
(författare)
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Ore mineralogy and trace element (re)distribution at the metamorphosed Lappberget Zn-Pb-Ag-(Cu-Au) deposit, Garpenberg, Sweden
- 2021
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Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 135
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Tidskriftsartikel (refereegranskat)abstract
- Qualitative and quantitative mineralogical and textural investigations were undertaken for the different sulfide minerals in the 1.89 Ga Lappberget deposit, with a focus on sphalerite and pyrite. Three sphalerite types were identified and associated with: (1) main massive sulfide mineralization, (2) Fe-Mn skarn ore, and (3) Ag-rich fissure veins. Sphalerite-1 contained a relatively higher amount of trace elements (Fe, Co, Ge, Cu, Sn, and Au) but is lower in Mn/Fe, Ga, and Hg compared to sphalerite-2. Evidence of tectono-metamorphic modification of sulfides is observed throughout the deposit, such as the formation of growth twins and deformation twins in sulfides, the development of high-angled triple-point junctions in recrystallized pyrite and sphalerite, and the formation of ‘ball ore’ or ‘durchbewegung’ textures within mineralized shear zones. The recrystallization of pyrite and galena may have led to the re-distribution of fluid-mobile elements (As, Cu, Zn, Pb, Ag, and Au), some of which were deposited in discordant Ag-rich fissure veins peripheral to the main massive sulfide lenses. Trace element signatures of sulfides in Lappberget are compatible with the other metamorphosed and deformed, subseafloor volcanogenic carbonate replacement (SVALS)-type deposits in the Bergslagen mining district.
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