Abstract

The Garpenberg deposit of central Sweden is a metamorphosed, strata-bound Zn-Pb-Cu-Ag sulfide deposit intercalated in an early Proterozoic supracrustal sequence of felsic metavolcanics and subordinate metasedimentary rocks, which have been folded, metamorphosed, and intruded by synorogenic granitoids. The magmatism is calc-alkaline and most of the volcanic activity occurred as explosive submarine volcanism.The Garpenberg deposit is emplaced at the contact between metasedimentary and metavolcanic rocks and consists of 32 lens-shaped orebodies. Stratiform Zn-Pb-Cu mineralization is underlain by Cu-bearing stockwork ore with an extensive alteration zone of quartz-phlogopite rocks with minor chlorite, cordierite, garnet, staurolite, and andalusite. Chemically, the altered zone is enriched in magnesium, iron, ore metals, manganese, and volatiles, and is depleted in sodium and calcium.The proposed volcanogenic origin, related to calc-alkaline magmatism, is supported by the morphology, wall-rock alteration, and ore mineralogy. The similarity of the Garpenberg deposit to the Archean massive sulfide deposits of Canada and the Kuroko deposits of Japan supports this theory but also reveals possible differences between the compositions of Precambrian and Phanerozoic seawater. Dissimilarities in the metal ratios (Cu:Pb:Zn) of the different deposits and their associated lithologies suggest differences in their tectonic setting. The Garpenberg deposit is thought to have formed in an active continental margin setting rather than in an island arc.

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