The Dragset copper-zinc deposit: a deformed, volcanogenic sulphide occurrence in the L√łkken greenstones, Central Norway
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Brittle-ductile deformation of a primary, volcanogenic sul phi de deposit at Dragset has produced a stack of folded and faulted massive sulphide layers now underlying a ftattened and elongated stringer ore zone. The orebody was overturned, deformed and metamorphosed under mid-greenschist facies conditions during at !east two major phases of deformation. The host rocks are mostly massive. sheet-ftow and pillowed greenstones which retain the geochemical signature of tholeiitic ocean-ftoor basalts. Metabasalts in the stringer zone show ore-related hydrothermal alteration marked by enrichment in Fe and MgO, and depletion in CaO and Na20. Ore types include: massive. fine-grained pyritic and siliceous ores with minor Cu and Zn: chalcopyrite- and sphalerite-rich pyritic ores; and chalcopyrite-pyrrhotite stringer ores. Primary ore fabrics are only preserved on a macroscale and include compositional layering in sphaleriterich ores, and possibly some replacement and relict fragmentary textures. Textures in massive pyritic ores mostly reftect cataclastic ftow and recrystallization during early isoclinal folding and axial plane shearing of the ore layers. This style of deformation is probably typical for massive pyritic ores subjected to high shear stress under low grade metamorphic conditions (350-450C)