Tobias Christoph Kampmann

3D modelling and sheath folding at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit and implications for exploration in a 1.9 Ga ore district, Fennoscandian Shield, Sweden

Altered and mineralized rocks at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, situated in the Palaeoproterozoic Bergslagen ore district in the south-western part of the Fennoscandian Shield, have been metamorphosed at low-pressure, amphibolite-facies conditions and affected by ductile deformation. Using combined surface mapping of lithology and structure, drill core logging and microstructural work, the polyphase (D1 and D2) ductile deformation is demonstrated and a 3D model for the deposit created. Mineral associations include quartz, biotite, cordierite, anthophyllite, and minor almandine, andalusite and chlorite in silicate-rich altered rock, calcite or dolomite in marble and tremolite-actinolite or diopside-hedenbergite in skarn. The silicate minerals show varying growth patterns during the different phases of the tectonothermal evolution, with considerable static grain growth occurring between D1 and D2, and even after D2. F2 sheath folding along axes that plunge steeply to the SSE, parallel to a mineral stretching lineation and the dip direction of the S2 foliation, is suggested as a key deformation mechanism forming steeply plunging, cone- to rod-shaped mineralized bodies. This contrasts with a previous structural model invoking fold interference. A major shear zone with talc-chlorite-(quartz-biotite) mineral association separates the northern and southern structural domains at the deposit and bounds the polymetallic massive sulphides to the north.

SIMS U-Pb zircon geochronology at the Kuså Ni-Cu deposit, south-central Sweden

Abstract The Kuså orthomagmatic Ni-Cu sulphide deposit is situated c. 13 km west of Falun in Bergslagen, south-central Sweden. Ion probe data on zircon from the mafic to ultra-mafic host rocks yield a 207Pb/206Pb weighted average age of 1798 ± 4 Ma, suggesting a genetic connection to intrusive activity forming the Transscandinavian Igneous Belt (TIB-1 phase). TIB-1 ages have recently been reported also for the Kleva deposit of similar type in Southern Sweden. The presence of these two occurrences suggests prospectivity potential for Ni-Cu mineralisation in mafic to ultramafic members of the areally extensive TIB.