| 1. |
- Allen, Rodney, et al.
(författare)
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Setting of Zn-Cu-Au-Ag massive sulfide deposits in the evolution and facies architecture of a 1.9 Ga marine volcanic arc : Skellefte district, Sweden
- 1996
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 91:6, s. 1022-1053
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Tidskriftsartikel (refereegranskat)abstract
- Skellefte mining district occurs in an Early Proterozoic, mainly 1.90-1.87 Ga (Svecofennian) magmatic province of low to medium metamorphic grade in the Baltic Shield in northern Sweden. The district contains over 85 pyritic Zn-Cu-Au-Ag massive sulfide deposits and a few vein Au deposits and subeconomic porphyry Cu-Au-Mo deposits, The massive sulfide deposits mainly occur within, and especially along the top of: a regional felsic-dominant volcanic unit attributed to a stage of intense, extensional, continental margin are volcanism. From facies analysis we interpret the paleogeography of this stage to have comprised many scattered islands and shallow-water areas. surrounded by deeper seas. All the major massive sulfide ores occur in below-wave base facies associations: however, some ores occur close to stratigraphic intervals of above-wave base facies associations, and the summits of some volcanoes that host massive sulfides emerged above sea level. Intense marine volcanism was superceded at different times in different parts of tile district by a stage of reduced volcanism, uplift resulting in subregional disconformities, and then differential uplift and subsidence resulting in a complex horst and graben paleogeography. Uplift of the are is attributed to the relaxation of crustal extension and the emplacement of granitoids to shallow crustal levels. A few massive sulfide ores formed within the basal strata of this second stage. The horst and graben system was filled by prograding fluvial-deltaic sediments and mainly mafic lavas, and during this stage the Skellefte district was a transitional area between renewed are volcanism of more continental character to the north, and subsidence and basinal mudstone-turbidite sedimentation to the south. This whole volcanotectonic cycle occurred within 10 to 15 m.y. We define 26 main volcanic, sedimentary, and intrusive facies in the Skellefte district. The most abundant facies are (1) normal-graded pumiceous breccias, which are interpreted as syneruptive subaqueous mass flow units of pyroclastic debris, (2) porphyritic intrusions, and (3) mudstone and sandstone turbidites. Facies associations define seven main volcano types, which range from basaltic shields to andesite cones and rhyolite calderas. Despite this diversity of volcano types, most massive sulfide ol es are associated with one volcano type: subaqueous rhyolite cryptodome-tuff volcanoes. These rhyolite volcanoes are 2 to 10 km in diameter, 250 to 1,200 m thick at the center, and are characterized by a small to moderate volume rhyolitic pyroclastic unit, intruded by rhyolite cryptodomes, sills, and dikes. Massive sulfide ores occur near the top of the proximal (near vent) facies association The remarkable coincidence in space and time between the ores and this volcano type indicates an intimate, genetic relationship between the ores and the magmatic evolution of the volcanoes.Many of the massive sulfide ores occur within rapidly emplaced volcaniclastic facies and are interpreted to have formed by infiltration and replacement of these facies. Some of the ore deposits have characteristics of both marine massive sulfides and subaerial epithelial deposits. We suggest that massive sulfides in the Skellefte district span a range in ore deposit style from deep-water sea floor ores, to subsea-floor replacements, to shallow-water and possible subaerial synvolcanic replacements. Facies models are provided for the mineralized rhyolite volcanoes and volcanological guides are provided for exploration for blind ores within these volcanoes.
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| 2. |
- Andersson, Joel B.H., et al.
(författare)
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Structural Evolution of the Central Kiruna Area, Northern Norrbotten, Sweden : Implications on the Geologic Setting Generating Iron Oxide-Apatite and Epigenetic Iron and Copper Sulfides
- 2021
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 116:8, s. 1981-2009
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Tidskriftsartikel (refereegranskat)abstract
- To guide future exploration, this predominantly field based study has investigated the structural evolution of the central Kiruna area, the type locality for iron oxide-apatite deposits that stands for a significant amount of the European iron ore production. Using a combination of geologic mapping focusing on structures and stratigraphy, petrography with focus on microstructures, X-ray computed tomography imaging of sulfide-structure relationships, and structural 2D-forward modeling, a structural framework is provided including spatial-temporal relationships between iron oxide-apatite emplacement, subeconomic Fe and Cu sulfide mineralization, and deformation. These relationships are important to constrain as a guidance for exploration in iron oxide-apatite and iron oxide copper-gold prospective terrains and may help to understand the genesis of these deposit types. Results suggest that the iron oxide-apatite deposits were emplaced in an intracontinental back-arc basin, and they formed precrustal shortening under shallow crustal conditions. Subsequent east-west crustal shortening under greenschist facies metamorphism inverted the basin along steep to moderately steep E-dipping structures, often subparallel with bedding and lithological contacts, with reverse, oblique to dip-slip, east-block-up sense of shears. Fe and Cu sulfides associated with Fe oxides are hosted by structures formed during the basin inversion and are spatially related to the iron oxide-apatite deposits but formed in fundamentally different structural settings and are separated in time. The inverted basin was gently refolded and later affected by hydraulic fracturing, which represent the last recorded deformation-hydrothermal events affecting the crustal architecture of central Kiruna.
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| 3. |
- Bauer, Tobias, Associate professor, 1982-, et al.
(författare)
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Structural Controls on Iron Oxide Copper-Gold Mineralization and Related Alteration in a Paleoproterozoic Supracrustal Belt: Insights from the Nautanen Deformation Zone and Surroundings, Northern Sweden
- 2022
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 117:2, s. 327-359
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Tidskriftsartikel (refereegranskat)abstract
- The Nautanen deformation zone in the Gällivare area of northern Sweden is a highly Cu-mineralized, magnetite-rich, large-scale shear zone with a long-lived (~100 m.y.) deformation, hydrothermal alteration, and mineralization history. This composite structure hosts the Aitik porphyry Cu-Au-Ag ± Mo deposit and several Cu-Au ± Fe ± Ag ± Mo occurrences assigned to the iron oxide copper-gold (IOCG) deposit class. The Nautanen deformation zone was a locus for polyphase deformation and intermittent metasomatic-hydrothermal activity that overprinted middle Orosirian (ca. 1.90–1.88 Ga) continental arc-related volcanic-plutonic rocks. The deformation zone is characterized by intense shearing fabrics that form a series of subvertical to moderately W-dipping, NNW-SSE–trending, first-order shear zones with oblique reverse kinematics and related NNE-SSW–oriented second-order shear zones that control hydrothermal alteration patterns and Cu-Au mineralization.Hydrothermal alteration in the study area formed during several phases. Volcanic-volcaniclastic rocks to the east and west of the Nautanen deformation zone display low to moderately intense, pervasive to selectively pervasive (i.e., patchy zones or bands, disseminations) sericite ± feldspar, amphibole + biotite + magnetite ± tourmaline, and K-feldspar + hematite alteration. Both the amphibole + biotite and K-feldspar + hematite associations occur adjacent to NNW- and NE-oriented deformation zones and are locally associated with minor sulfide. Within the deformation zone, a moderate to intense biotite + amphibole + garnet + magnetite + tourmaline + sericite alteration assemblage is typically associated with chalcopyrite + pyrrhotite + pyrite and forms linear and subparallel, mainly NNW-oriented seams, bands, and zones that locally appear to overprint possibly earlier scapolite + sericite ± feldspar alteration. Late-stage epidote ± quartz ± feldspar alteration (retrograde saussuritization) forms selectively pervasive zones and epidote veinlets across the area and is partly related to brittle faulting.A magnetite-amphibole-biotite–rich, penetrative S1 foliation records shortening during early Svecokarelian-related deformation (D1) and can be related to ca. 1.88 to 1.87 Ga arc accretion processes and basin inversion that overlaps with regional peak metamorphism to near mid-amphibolite facies conditions and a potential initial Cu mineralization event. Folding and repeated shearing along the Nautanen deformation zone can be assigned to a second, late-Svecokarelian deformation event (D2 stage, ca. 1.82–1.79 Ga) taking place at a higher crustal level. This D2 deformation phase is related to late-stage accretionary processes active during a transition to a stage of postorogenic collapse, and it was accompanied by abundant, syntectonic intrusions. D2-related magmatism produced high-temperature and low-pressure conditions and represents a regional magmatic-hydrothermal event that controlled the recrystallization/remobilization of magnetite, biotite, and amphibole. Associated shear zone reactivation during D2 favors the utilization of the Nautanen deformation zone as a fluid conduit, which preferentially controlled the siting and formation of epigenetic Cu-Au mineralization with distinctive IOCG characteristics within second-order shear zones.
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| 4. |
- Bauer, Tobias, 1982-, et al.
(författare)
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Structural controls on the setting, shape and hydrothermal alteration of the Malmberget IOA deposit, northern Sweden
- 2018
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 113:2, s. 377-395
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Tidskriftsartikel (refereegranskat)abstract
- The Malmberget iron oxide-apatite (IOA) deposit in northern Sweden is one of the largest underground iron ore mine operations in the world with estimated ore reserves in 2015 of 346 million metric tons (Mt) at 42.5% Fe. The underground operation is concentrated in 10 orebodies of 5 to 245 Mt each, which currently produce 17.4 Mt of apatite iron ore per year. Structural investigations were combined with data on hydrothermal mineral assemblages in order to reconstruct the relative timing of ore-forming, deformation, and overprinting hydrothermal events. The results improve the understanding of structural geometries, relationships, and control on orebody transposition in the deposit. A first compressional event (D1) around 1.88 Ga represents the main metamorphic event (M1) in the area and was responsible for a strong transposition of potential primary layering and the orebodies and led to the formation of a composite S0/1 fabric. A subsequent F2 folding event around 1.80 Ga resulted in the formation of an open, slightly asymmetric synform with a steeper southeast limb and a roughly SW-plunging fold axis. The result of structural modeling implies that the ore formed at two separate horizons. The folding was accompanied by stretching, resulting in boudinage of the iron orebodies. D2-related high-strain zones and syntectonic granites triggered the remobilization of amphibole, biotite, magnetite, and hematite and controlled the formation of iron oxide-copper-gold (IOCG)-type hydrothermal alteration, including an extensive K-feldspar alteration accompanied with sulfides, scapolite, and epidote. This shows a distinct time gap of at least 80 m.y. between the formation of iron oxides and sulfides. Brittle structures and the lack of an axial planar parallel fabric in conjunction with previous results suggest upper crustal, low-pressure, and high-temperature conditions during this D2 deformation phase, indicating a hydrothermal event rather than a purely regional metamorphic compression. It is proposed in the present study that the Malmberget IOA deposit was deformed and metamorphosed during a 1.88 Ga crustal shortening event. Moreover, the Malmberget IOA deposit was affected by a 1.8 Ga folding and hydrothermal event that is related to a regional IOCG overprint.
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| 5. |
- Billström, Kjell, et al.
(författare)
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Age and provenance of host rocks and ores in the Paleoproterozoic Skellefte District, northern Sweden
- 1996
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 91:6, s. 1054-1072
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Tidskriftsartikel (refereegranskat)abstract
- The Skellefte district in northern Sweden is a ca. 1.9 Ga, extensively mineralized, mainly felsic, submarine volcanic belt. Within the district, the volcanic rocks (Skellefte Group) are overlain by turbiditic sedimentary rocks and coarser clastic rocks, as well as younger, mainly mafic, volcanic rocks (Vargfors Group). To the north, subaerial volcanic rocks of the Arvidsjaur Group are probably coeval with the Vargfors Group. The sedimentation in the Bothnian basin, south of the Skellefte district, appears to have started at ca. 2.0 Ga and continued until ca. 1.86 Ga, as indicated by the presence of granitoids spanning this time interval. The first main magmatic episode in the Skellefte district was a felsic stage at around 1.89 Ga as confirmed by two new U-Pb zircon ages from volcanic rocks situated in the central and eastern part of the district (Bjurvattnet, 1884 + or - 6 Ma; Melestj rn, 1889 + or - 4 Ma). No basement is known to the felsic magmatism, but granitoids occurring to the south of the district, which have been dated at 2.0 to 1.9 Ga, could constitute remnants of a basement which was destroyed by 1.89 Ga arc volcanism within the Skellefte district. The Vargfors Group overlies the Skellefte Group with no major unconformity, and one new age from an ignimbrite in the Vargfors Group (1875 + or - 4 Ma) confirms the temporal relationship with the deposition of subaerial volcanic rocks of the Arvidsjaur Group.An evaluation of age data for the early, synvolcanic (ca. 1890 Ma) Joern-type granitoids suggests that these should be further subdivided. Three different generations of Joern-type granitoids may exist. The GI phase has an age of about 1.89 Ga, the GII and GIII phases within the major Joern batholith probably formed at around 1.87 Ga, and the Siktr sk intrusion in the southern part of the district, has a crystallization age of ca. 1.86 Ga.A number of distinctive isotopic characteristics have been observed, e.g., significant data scatter for Sr whole-rock data, reversely discordant zircon data, and unusually young lower intercept ages for zircon discordia. These features seem to relate preferentially to volcanic rocks, and it is suggested that this behavior is due to Phanerozoic hydrothermal processes that have mobilized elements at different scales. Upper intercepts for zircon discordia, however, are with one exception thought to represent true crystallization ages. The 1847 + or - 3 Ma age for a mass flow at Petiktr sk, as defined by a three-point discordia, is for geologic reasons too young, but a considerably higher (super 207) Pb/ (super 206) Pb age at 1890 Ma for one zircon fraction is more consistent with the field relationships.Volcanic-hosted massive sulfide ores occur in the upper part of the volcanic sequence of the Skellefte Group and, in some cases, also in the lower part of the Vargfors Group. A good approximation of the age of massive ore formation is provided by the age of the host rocks. It is suggested that two main depositional stages of massive ore occurred at ca. 1885 to 1880 Ma and at ca. 1875 Ma. Gold occurs in two principal settings, as a constituent in the volcanic-hosted massive sulfide ores, and related to quartz veins found both in intrusive and supracrustal rocks. In the massive ores, gold was probably emplaced in connection with the hydrothermal processes which concentrated the base metals. Gold in some major intrusive-related Au deposits (e.g., Bjoerkdal) is likely to have concentrated at a premetamorphic stage, tentatively at 1.87 Ga, and still other Au ores (e.g., Boliden) may be epithermal in origin and were possibly formed at a relatively late stage at ca. 1.85 Ga. Later, during peak metamorphic conditions, some mesothermal Au-As vein deposits (e.g., Grundfors) formed at ca. 1.84 to 1.82 Ga.
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| 6. |
- Boström, K., et al.
(författare)
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Langban - Exhalative Sedimentary Deposit
- 1979
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 74:5, s. 1002-1011
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Tidskriftsartikel (refereegranskat)abstract
- Chemical, mineralogical, and isotope analyses of hausmannite, braunite, and hematite ores from Laangban, Sweden, show that the precursor of this deposit has several similarities in its mineralogy, chemistry, and oxidation state with many deposits of Devonian and Recent ages, such as some deposits in Kazakhstan, in the Red Sea hot brine depressions, and in the East Pacific Rise. Possibly Rammelsberg, Meggen, Franklin Furnace, and Sterling Hill also belong to this type of deposit, for which an exhalative-sedimentary origin is proposed.
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| 7. |
- Cabral, A. R., et al.
(författare)
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Distinguishing high-from low-temperature platinum nuggets through their trace-element pattern
- 2019
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Ingår i: Economic Geology and The Bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128. ; 114:2, s. 201-206
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Tidskriftsartikel (refereegranskat)abstract
- High- and lowerature platinum nuggets from two historical localities, Chocó in Colombia and Córrego Bom Sucesso in Brazil, are compared with respect to trace elements. Supergene platinum nuggets from Córrego Bom Sucesso are enriched in Se and Hg, but depleted in siderophile and chalcophile elements, and have fractionated platinum group element patterns, in comparison with magmatic platinum nuggets from Chocó. In particular, Se concentrations over ∼100 g/g Se and S/Se ratios above unity indicate Se recycling in a supergene environment with abundant organic matter. © 2019 Society of Economic Geologists; Economic Geology.
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| 8. |
- Frank, Katherine, et al.
(författare)
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Variability in the Geological, Mineralogical, and Geochemical Characteristics of Base Metal Sulfide Deposits in the Stollberg Ore Field, Bergslagen District, Sweden
- 2019
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - Littleton, Colorado : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 114:3, s. 473-512
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Tidskriftsartikel (refereegranskat)abstract
- The Stollberg ore field occurs in the Bergslagen region of south-central Sweden, a polydeformed ca. 1.9 Ga igneous province dominated by bimodal felsic and mafic rocks. Sulfide mineralization is hosted by metavolcanic rocks, marble, and skarn and consists of massive to semimassive polymetallic sulfides and iron oxide in a semiregional F2 syncline termed the Stollberg syncline. The dominant country rocks are rhyolitic pumice breccia and rhyolitic ash-siltstone with minor mafic sills metamorphosed to the amphibolite facies. On the eastern limb of the Stollberg syncline, sulfide mineralization occurs as stratabound premetamorphic replacement of volcaniclastic rocks and limestone that grades into iron formation. The development of skarn assemblages is the result of low-temperature replacement of limestone and volcaniclastic rocks rather than formation by high-temperature metasomatism or synmetamorphic or late hydrothermal replacement of marble. Metamorphosed, hydrothermally altered rocks on the eastern limb are dominated by the assemblages garnet-biotite and gedrite-albite. Silica-altered rocks are generally subordinate in the Stollberg ore field; however, sulfides at Gränsgruvan, on the western limb of the syncline, are located in a silicified zone along with metamorphosed, altered rocks dominated by sericite and the assemblage quartz-garnet-pyroxene. Although the Tvistbo and Norrgruvan prospects along the northern end of the syncline are small, they show geologic characteristics that are transitional to deposits found on the western and eastern limbs of the syncline. Ore at Tvistbo is hosted by skarn and is spatially associated with quartz-garnet-pyroxene rocks, whereas sulfides at Norrgruvan are hosted by quartz-fluorite rocks that are similar to those hosting the Brusgruvan deposit on the eastern limb of the syncline.Whole-rock analyses of variably altered host rocks in the Stollberg ore field suggest that most components were sourced from felsic volcaniclastic rocks and that Zr, Ti, Al, Hf, Nb, Sc, Th, Ga, U, and rare-earth elements (REEs) were immobile during alteration. These rocks are enriched in light REEs, depleted in heavy REEs, and have negative Eu anomalies, whereas sulfide-bearing rocks (Fe- and base metal-rich) and altered rocks in the ore zone show the same REE pattern but with positive Eu anomalies. Indicators of proximity to sulfides in altered rocks in the Stollberg ore field include positive Eu anomalies, an increase in the concentration of Pb, Sb, As, Tl, Ba, Ba/Sr, and K2O, as well as an increase in a modified version of the Ishikawa alteration index, which accounts for the presence of primary Ca in an original limestone component. Garnet and pyroxene enriched in either Ca or Mn are also considered to be pathfinders to ore. Cooling of an acidic, reduced hydrothermal fluid that carried sulfur and metals, which became neutralized as it reacted with limestone, is likely responsible for the formation of sulfides in the Stollberg ore field. The nature of the host rock types, the style of the alteration spatially associated with sulfide mineralization, and the spatial association with iron formation bear some resemblance to volcanogenic massive sulfide and Broken Hill-type deposits. However, the stratabound replacement of limestone by sulfides distinguishes it from these deposit types and is a so-called SVALS-type ore system, which is a class of stratabound, volcanic-hosted, limestone-skarn deposits restricted to the Bergslagen district.
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| 9. |
- Frietsch, Rudyard
(författare)
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On the magmatic origin of iron ores of the Kiruna type : reply
- 1984
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 79:8, s. 1949-1951
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Jansson, Nils, et al.
(författare)
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Evolution of the paleoproterozoic volcanic-limestone-hydrothermal sediment succession and Zn-Pb-Ag and iron oxide deposits at Stollberg, Bergslagen region, Sweden
- 2013
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 108:2, s. 309-335
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Tidskriftsartikel (refereegranskat)abstract
- The Stollberg Zn-Pb-Ag and magnetite mining field is located in the Bergslagen region of the Fenno -scandian Shield. The main Stollberg ore deposits comprise a chain of orebodies that occur discontinuously for5 km along a prominent marble and skarn horizon. Orebodies mainly contain magnetite and combinations ofsphalerite, galena, pyrrhotite, and lesser pyrite and chalcopyrite within marble and skarn. Previously, the twomain limestone (marble) units in the Stollberg area were regarded as structural repetitions of one single horizon.Based on sedimentary and volcanic facies and structural analysis, the mineralized Stollberg limestone isnow shown to be the uppermost of two different limestone units within a ca. 3-km-thick Paleoproterozoic (∼1.9Ga) volcanosedimentary succession. Approximately 2 km of preserved footwall stratigraphy is recognized belowthe Stollberg limestone, as opposed to ca. 500 m in previous structural models. This new interpretation hasallowed the stratigraphic evolution prior to the mineralizing event and extent of the Stollberg hydrothermal systemto be investigated in detail.After formation of the Staren limestone ca. 1 km below Stollberg, the depositional basin subsided to belowwave base, while adjacent areas were uplifted and eroded. This led to the deposition of a ca. 600-m-thick, shallowing-upward sedimentary sequence in which normal-graded subaqueous mass flow deposits pass upward topolymict limestone-volcanic breccia-conglomerates. This sequence is attributed to progradation of a fan deltadepositional system. The breccia-conglomerates are overlain by ca. 500 m of juvenile rhyolitic pumice brecciathat is interpreted as a major pyroclastic deposit. Conformably above is the Stollberg ore host, which comprisesplanar-stratified, rhyolitic ash-siltstone interbedded with Fe-Mn-rich hydrothermal sedimentary rocks andlimestone, all deposited below wave base. This ore host package is extensively altered to skarn and mica schist.The thickness, extent, and homogeneous composition of the rhyolitic pumice breccia below the ore host suggestthat volcanism was accompanied by caldera subsidence and that the Stollberg ore deposits formed withinthe caldera structure. The ore host is overlain by planar-stratified, rhyolitic ash-siltstone and subordinate sedimentarybreccias deposited below wave base from turbidity currents and suspension.Skarns in the Stollberg ore host unit are interpreted as metamorphosed mixtures of variably altered rhyolite,limestone, and hydrothermal sediments. Whole-rock contents of Al, Ti, Zr, Hf, Nb, Sc, Th, Ta, U, and heavyrare-earth elements are highly correlated in skarns, limestone, magnetite mineralization, and variably alteredrhyolites in the Stollberg succession, suggesting that these elements were supplied by a felsic volcaniclasticcomponent and were immobile during alteration. The felsic volcaniclastic component is calc-alkaline and characterizedby negative Eu anomalies and light rare-earth element enrichment. Strong positive Eu anomalies areonly observed in limestone, skarn, and iron ore in the Stollberg ore host, i.e., in samples rich in Mn, Ca, andFe.The Stollberg ore deposits are interpreted as metamorphosed, hydrothermal-exhalative and carbonate replacement-type mineralization. The hydrothermal-exhalative component formed first by accumulation of sedimentsrich in Mn and Fe, coeval with limestone formation during waning volcanism. Burial of the hydrothermal systemby sediments of the stratigraphic hanging wall led to a gradual shift to more reducing conditions. At thisstage, the Stollberg limestone interacted with more sulfur rich hydrothermal fluids below the sea floor, producingstrata-bound, replacement-type Zn-Pb-Ag sulfide and additional iron oxide mineralization
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