Petrographic- and chemical characteristics of alteration associated with Au-bearing quartz veins at the Bjorkdal gold deposit, skellefte district, northern Sweden

摘要

The Bjorkdal gold lode deposit is situated in the eastern part of the Skellefte district; a Palaeoproterozoic volcanic belt, mainly known for its pyritic Zn-Cu-Au-Ag massive sulphide deposits. The deposit consits of gold-bearing quartz veins, situated at the margin of a quartz-monzodioritic pluton. Structurally the quartz veins are related to ductile shear zones that enabled quart veining during ductile-brittle deformation. This study presents petrographic observations together with mass balance calculations for the alteration zone of two quartz veins within the mine and one quartz vein outside the mine. Preliminary results show that Si, Ca, Na, K, Fe, LILE, V, Cr, Co, Ni, Cu, Zn, and W were mobilized during quartz veining and fluid-rock interaction. Si, Ba, and Cu are enriched in the hydrothermal alteration zones within the deposit and depleted outside the deposit, suggesting that some elements may have been mobilized over larger areas within the pluton during the ore-forming event.