| 1. |
|
|
| 2. |
- Jonsson, Erik, et al.
(författare)
-
Apatite-iron oxide-hosted REE mineralisation at Kopslahyttan, NW Bergslagen, Sweden
- 2015
-
Ingår i: Mineral Resources In A Sustainable World. - 9782855550664 ; , s. 781-784
-
Konferensbidrag (refereegranskat)abstract
- Of the different types of REE mineralisation known from the Fennoscandian shield, the Palaeoproterozoic apatite-iron oxide ores of Kiruna type represent one resource type with significant potential. Here we describe an REE-rich apatite-magnetite mineralisation from the classic Bergslagen ore province in south central Sweden. Associated with moderately to weakly REE-enriched magnetite mineralisation of banded and vein types, the most apatite-rich occurrence at Kopslahyttan shows REE enrichment that is similar in both magnitude and pattern to other Kiruna type deposits. Yet, the present REE mineralogy is wholly dominated by monazite-(Ce), allanite-(Ce) and LREE-enriched epidote, the latter two often occurring as zoned crystals or aggregates. Minor xenotime-(Y) also occurs, and titanite locally hosts minor Y+HREE. The abundant fluorapatite is suggested to have been an additional, original host for REE, prior to fluid-mediated alteration leading to wholesale remobilisation of REE from the apatite. This remobilisation included dissolution-reprecipitation processes that lead to the nucleation of monazite in fluorapatite, but probably also further transport and precipitation as e.g. allanite/REE-epidote, through reactions with locally common silicates. In addition, we suggest that very coarse grained, variably Th-bearing monazite present in the mineralisation may have been a primary REE phase, in marked contrast to most other deposits of this type.
|
|
| 3. |
- Kathol, Benno
(författare)
-
U–Pb zircon age of a granodioritic gneiss from Rimokojan at Stora Luleälven, Norrbotten County, northern Sweden
- 2018
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A granodioritic gneiss from Rimokojan at Stora Luleälven north of Jokkmokk in the central part of Norrbotten County, has been dated using U–Pb SIMS analyses of zircon. The sampled gneiss occurs within a massif of granodioric to tonalitic gneisses together with strongly deformed basic dykes and intrusions of almost undeformed gabbro to diorite of the Haparanda suite. This rock association occurs in the southern part of a distinct magnetic anomaly in the area of the Muddus National Park. Analyses of oscillatory zoned zircon domains from the Rimokojan gneiss sample yielded a weighted average 207Pb/206Pb age of 2668 ± 3 Ma (2σ) which is interpreted to date the protolith at c. 2.67 Ga. This figure is similar to other age determinations of Archaean rocks in southeastern Norrbotten County (2.70–2.64 Ga). Field relations suggest that the gneiss protolith has been deformed during at least two different deformational events which both predate the emplacement of the 1.91–1.87 Ga Haparanda suite. Two analyses of low Th/U, cathodoluminescence (CL)-dark unzoned zircon rims from the same sample are interpreted to date a metamorphic event at c. 2.61 Ga.
|
|
| 4. |
- Lynch, Edward, et al.
(författare)
-
Geology, lithostratigraphy and petrogenesis of c. 2.14 Ga greenstones in the Nunasvaara and Masugnsbyn areas, northernmost Sweden
- 2018
-
Ingår i: SGU Rapporter och meddelanden. - Uppsala : Sveriges geologiska undersökning. - 0349-2176. ; 141, s. 19-77
-
Tidskriftsartikel (refereegranskat)abstract
- Two Palaeoproterozoic greenstone successions in the Nunasvaara and Masugnsbyn areas of north-central Norrbotten (northernmost Sweden) have been investigated to (1) characterise their primary depositional features; (2) establish lithostratigraphic correlations between both areas; and (3) gain insights into the petrogenesis of greenstone-type volcano-sedimentary successions in this sector of the Fennoscandian Shield.In the Nunasvaara area (Vittangi greenstone group), a partly conformable, polydeformed, approximately 2.4 km thick greenstone sequence mainly consists of basaltic (tholeiitic) metavolcanic and metavolcaniclastic rocks (amygdaloidal lava, laminated tuff). Intercalated metasedimentary units include graphite-bearing black schist, and pelite. The uppermost part consists of amphibolitic pelite with intercalated metacarbonate layers and rare meta-ironstone, metachert and meta-ultrabasic horizons. Numerous metadoleritic sills occur throughout the package.In the Masugnsbyn area (Veikkavaara greenstone group) a relatively conformable approximately 3.4 km thick greenstone sequence displays lithological, geochemical and geophysical characteristics similar to that at Nunasvaara. This succession consists of a dominant basaltic metatuff sequence overlain by metasedimentary units towards the top (e.g. meta-ironstone, metachert, amphibolitic schist, calcitic and dolomitic marbles). Minor metadolerite sills occur in the metatuffs. Near the base of the metatuff package, a graphitic black schist horizon occupies a similar stratigraphic position to a prominent black schist layer at Nunasvaara (here named the Nunasvaara member). This unit is a key marker horizon providing lateral correlation between both successions and also acts as a useful strain marker for reconstructing deformational events.Both greenstone successions record the effects of overprinting syn-to late-orogenic (Svecokarelian) tectonothermal events. These include complex, polyphase ductile deformation (D1 to D3 events at Nunasvaara, forming the Nunasvaara dome), peak amphibolite facies metamorphism, metasomatic-hydrothermal alteration and late-stage retrogression and brittle faulting (composite D4 at Nunasvaara). Locally, these overprinting processes formed metamorphic graphite, skarn-related Fe ± Cu and hydrothermal Cu ± Pb ± Mo mineralisation.U-Pb SIMS zircon dating of a metadolerite dyke from Nunasvaara and a metadolerite sill from Masugnsbyn have yielded mean weighted 207Pb/206Pb ages of 2 144 ±5 Ma (2σ, n = 10) and 2 139 ±4 Ma (2σ, n = 5) Ma, respectively. These precise dates constrain the timing of hypabyssal mafic magmatism, provide a minimum age for the deposition of the volcanic and sedimentary rocks, and identify a new approximetly 2.14 Ga episode of tholeiitic magmatism in this sector of the Fennoscandian Shield. Whole-rock initial εNd values for greenstone meta-igneous units range from +0.4 to +4.0 at Nunasvaara (n = 11) and +0.4 to +3.7 at Masugnsbyn (n = 7). These data indicate a juvenile depleted to partly enriched mantle (asthenospheric or lithospheric) as a major source of the tholeiitic melts. Corresponding trace element systematics have enriched mid-ocean ridge (E-MORB)-type signatures, and indicate minor assimilation of Archaean continental crust (i.e. Norrbotten craton) during magma ascent and storage. Overall, the combined geological, geochemical and isotopic characteristics of the greenstones are consistent with protolith formation within an incipient oceanic basin (epieric Norrbotten Seaway) during approximetly 2.14 Ga rifting and sagging of the Norrbotten craton.
|
|
| 5. |
- Martinsson, Olof, et al.
(författare)
-
Age and character of late-Svecokarelian monzonitic intrusions in northeastern Norrbotten, northern Sweden
- 2018
-
Ingår i: SGU Rapporter och meddelanden. - Uppsala : Sveriges geologiska undersökning. - 0349-2176. ; 141, s. 381-400
-
Tidskriftsartikel (refereegranskat)abstract
- Palaeoproterozoic magmatism in northern Norrbotten shows a complex evolution, with several different plutonic suites ranging in age 1.93–1.70 Ga. Here we present data for three monzonitic intrusions from different parts of the area. They are petrographically and chemically similar, consisting mainly of perthite, augite and orthopyroxene, with megacrysts of poikilitic biotite as a characteristic minor component, and with high Sr and Ba. The intrusions have been dated at 1.80 Ga and may be part of a more extensive magmatic event in northern Sweden, including other chemically similar monzonitic and gabbroic intrusions, which often occur as ring dykes at the Merasjärvi gravity high (MGH) in northeastern Norrbotten. The monzonitic intrusions have A-type signatures and chemical characteristics overlapping those of rocks in arc and within-plate settings. These intrusions may thus have formed in either a back arc setting related to eastward subduction associated with the Transscandinavian Igneous Belt further west (TIB 1), or through a separate igneous event caused by a mantle plume.
|
|
| 6. |
- Nysten,, Per
(författare)
-
Age of the rhyolite hosting the Ultevis Mn-Fe-Ba-As mineralisation, northern Sweden
- 2018
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A feldspar-porphyric Svecofennian rhyolite associated with Mn-mineralisations at Ultevis, west of Jokkmokk, northern Sweden, has been dated to 1872 ± 9 Ma. This figure also gives a maximum age of deposition of the stratigraphically overlaying sedimentary rock sequence (the Snavva–Sjöfall group). The position of Mn-Fe-Ba-As-F-U-(W-Mo) mineralisations is discussed in relation to the transition from volcanic to sedimentary environments in the Tjåmotis–Ultevis area.
|
|
