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- Lundmark, Christina, et al.
(författare)
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The geology and Re-Os geochronology of the Palaeoproterozoic Vaikijaur Cu-Au-(Mo) porphyry style deposit in the Jokkmokk granitoid, northern Sweden
- 2005
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Ingår i: Mineralium Deposita. - : Springer Science and Business Media LLC. - 0026-4598 .- 1432-1866. ; 40:4, s. 396-408
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Tidskriftsartikel (refereegranskat)abstract
- The Vaikijaur Cu–Au–(Mo) deposit is located in the ca. 1.88 Ga calc-alkaline Jokkmokk granitoid near the Archaean–Proterozoic palaeoboundary within the Fennoscandian shield of northern Sweden. The Skellefte VMS district lies immediately to the south and the northern Norrbotten Fe-oxide–Cu–Au deposits to the north. The Vaikijaur deposit occupies an area of 2×3 km within the Jokkmokk granitoid and includes stockwork quartz-sulphide veinlets and disseminated chalcopyrite, pyrite, gold, molybdenite, magnetite, and pyrrhotite. Porphyritic mafic dykes were emplaced along fractures in a ring dyke pattern. The Jokkmokk granitoid, dykes, and the mineralized area are foliated, indicating that mineralization predated the main regional deformation. The mineralized area is characterized by strong potassic alteration. Phyllic and propylitic alteration zones are also present. A pyrite-rich inner core is surrounded by a concentric zone with pyrite, chalcopyrite, and gold. Molybdenite is distributed irregularly throughout the chalcopyrite zone. Geophysical data indicate a strongly conductive central zone in the mineralized area bordered by conductive and high magnetic zones. Five high precision Re–Os age determinations for three molybdenite occurrences from outcrop and drill core samples constrain the age of porphyry-style Cu–Au–(Mo) mineralization to between 1889±10 and 1868±6 Ma. A younger molybdenite is associated with a much later metamorphic event at about 1750 Ma. These data suggest that primary porphyry-style mineralization was associated with calc-alkaline magmatism within the Archaean–Proterozoic boundary zone at ca. 1.89–1.87 Ga.
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| 3. |
- Lundmark, Christina, et al.
(författare)
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The Jokkmokk granitoid, an example of 1.88 Ga juvenile magmatism at the Archaean-Proterozoic border in northern Sweden
- 2005
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 127:2, s. 83-98
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Tidskriftsartikel (refereegranskat)abstract
- The Jokkmokk granitoid is exposed in a large plutonic massif northwest of Jokkmokk in northern Sweden. It is light grey to white, fine-grained, with megacrysts of feldspar and glomeroporphyritic hornblende and biotite. Small enclaves of mafic rocks and synplutonic mafic dykes are products of mingling with a coeval and possibly cogenetic mafic magma. The Jokkmokk granitoid was previously considered to belong to the c. 1.8 Ga Lina S-type intrusive suite, but the Jokkmokk granitoid has a unique calc-alkaline to alkali-calcic, metaluminous to weakly peraluminous, character with a moderate LREE enrichment and a flat HREE pattern, and a flat to slightly positive Eu-anomaly. U–Pb TIMS zircon dating of the Jokkmokk granitoid gives an age of 1883±15 Ma which is coeval with the emplacement of the Haparanda suite, but contrary to the Haparanda suite it displays a positive _Nd(t) value of 2.8, indicating a more juvenile Palaeoproterozoic character similar to the Jörn suite in the Skellefte district. This type of magma seems to be restricted to the palaeoboundary between the Archaean craton in the north and Palaeoproterozoic juvenile crust in the south. Spatial correlation with low angle, south dipping, WNW-trending shear zones and NNE-trending subvertical shear zones, highlight the possibility that this unique magma type is related to transtension in the overriding plate and partial melting in a sub-arc mantle wedge during NE-directed subduction processes related to the early stages of the Svecokarelian orogen. This type of setting has been advocated as the potentially most favourable tectonic setting for porphyry copper formation.
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- Weihed, Pär, 1959-, et al.
(författare)
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Vaikijaur Cu-Au-(Mo) deposit, northern Sweden : preliminary results from fluid inclusion and (O, H) isotope studies
- 2006
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Ingår i: The 27th Nordic Geological Winter Meeting, January 9-12, 2006, Oulu, Finland. - Helsinki : Geological Society of Finland. ; , s. 95-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Vaikijaur Cu-Au-(Mo) deposit is located in the ca. 1.88 Ga calc-alkaline Jokkmokk granitoid near the Archaean-Proterozoic palaeoboundary within the Fennoscandian shield in northern Sweden. The Vaikijaur deposit occupies an area of 2×3 km within the Jokkmokk granitoid and includes stockwork quartz-sulphide veinlets and disseminated sulphides and gold. The mineralized area is characterized by potassic, phyllic and propylitic alteration. A conductive pyrite-rich central part is surrounded by a conductive and magnetic zone with pyrite, chalcopyrite, and gold. Analyses of one metre drill core sections have shown up to 5% Cu and 7 ppm Au. Molybdenite is distributed irregularly in the deposit. Re-Os age data suggest that primary porphyry-style mineralization was associated with the calc-alkaline magmatism at ca. 1.89-1.87 Ga. Molybdenite records also a later metamorphic event at about 1750 Ma (Lundmark et al., 2005).Preliminary fluid inclusion data reveal no evidence for the involvement of high-salinity fluids typically for the Norrbotten Fe oxide-Cu-Au ores. By contrast, fluid inclusions in quartz veinlets associated with the sulphides at Vaikijaur indicate deposition from inflowing low- to medium-salinity aqueous and carbon dioxide-rich fluids. Oxygen and hydrogen isotope compositions of quartz, biotite, chlorite and amphibole in ore-related samples have mixed magmatic and seawater signatures.
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