The geology and structural setting of the Hakansboda Cu-Co-As-Sb-Bi-Au deposit and associated Pb-Zn-Cu-Ag-Sb mineralisation, Bergslagen, Central Sweden

Abstract

A complex sulphide mineralisation occurs within calc-silicate rich dolomite-calcite marble at Håkansboda, Bergslagen, Central Sweden. Exploration during 1980-86 has defined the distribution and nature of the mineralisation and its structural setting. Three zones of mineralisation are identified. The central or B zone, with up to 900 m strike length and 80 m wide, is proven to a depth of 600 m. It forms an envelope around previously mined massive and streaky chalcopyrite-pyrrhotite and chalcopyrite-arsenopyrite-tennantite ore shoots, containing minor antimony, bismuth, gold and molybdenum. A similar, but lower grade mineralisation forms the A and C zones. The deposit is spatially associated with strongly altered felsic volcanic rocks and volcaniclastics, especially in the stratigraphic footwall, and areally extensive exhalite horizons with Pb-Zn-Cu-Ag-Sb sulphides and Mn-rich magnetite ores in the stratigraphic hangingwall. The 'ore'-hosting sequence occurs on the overturned limb of a regional F, syncline and is refolded by steeply plunging F, folds. Brecciated host rock-sulphide lenses and the geometry of individual ore shoots indicate remobilisation and extension of the sulphides into pipe-like bodies parallel to local F, fold axes.