Syngenetic Pb‐Zn‐Cu sulphide mineralization in 1.8 Ga subaerial volcanic rocks, southeastern Sweden

Abstract

A Pb‐Zn‐Cu‐(As‐W)‐bearing sulphide mineralization, hosted by the 1800 Ma Småland volcanics, has been investigated at Ålatorp, 40 km ENE of Växjö in southeastern Sweden. The Ålatorp deposit was subject to small‐scale mining for silver in the 18th century, but due to very low silver contents it has never been economically viable. Galena, sphalerite, and chalcopyrite occur in a dense network of quartz‐carbonate veinlets, hosted by intensely hydrothermally altered volcanic rocks, which are strongly depleted in sodium, calcium, and strontium, and strongly enriched in lead, zinc, copper, tin, and tungsten when compared to unmineralized and unaltered equivalents. The lead isotopic ratios of galena suggest that the hydrothermal process leached metals from the volcanic rocks immediately after their deposition. The Ålatorp Pb‐Zn‐Cu mineralization is thus a typical example of a synvolcanic ore‐forming system, which may be compared to the much larger porphyry‐type systems in Cretaceous and Tertiary subaerial volcanic rocks elsewhere in the world. Significant geochemical anomalies of Pb, Zn, Cu, W, and As in Quaternary till indicate that several (or many) other sulphide occurrences of comparable character exist in the Ålatorp area and elsewhere in the Småland volcanics. Sundblad, K., 1997: Syngenetic Pb‐Zn‐Cu sulphide mineralization in 1.8 Ga subaerial volcanic rocks, southeastern Sweden. GFF, Vol. 119 (Pt. 2, June), pp. 103–108. Stockholm. ISSN 1103–5897.