Trace element zonation in marbles hosting Cu-Zn-Fe-Pb-As sulphides at Gruvåsen, south central Sweden

Abstract

Abstract The mid-Proterozoic sulphide skarn mineralization of the Gruvåsen area, Hällefors, Bergslagen Ore District, Sweden, shows a zonal distribution with Cu-Zn-Fe-W-Mo-Bi-Sn in a central zone, and Zn-Fe-Pb-As-Sb in the peripheral zones. This zonation crosscuts lithological boundaries. Trace element concentrations in the sulphide-free, silicate-poor marbles between the mineralizations also show zonal patterns corresponding to that of the sulphide skarns. K, Na, Fe, Sc, Rb, Sb, Y, Zr, REE, Hf, W, and Th show the highest concentrations in the marbles of the central zone. The high K and W concentrations in the central zone marbles coincide with the occurrence of coarse grained scheelite-microcline rock in the same central zone, indicating that the trace element zonation in the marbles is related to the same hydrothermal event that has caused potassic alteration and tungsten and sulphide mineralization. Therefore, it is suggested that the elevated trace element concentrations may be used as an exploration tool for marble-hosted sulphide mineralizations. Metavolcanites, underlying the sulphide skarns, have been affected by local potassic alteration and consequently depleted in W, Th, U, Y, and REE. This local depletion in the metavolcanites, and enrichment of the same elements in marbles hosting the mineralizations, suggest that the so-called immobile elements such as Ti, Y, Zr, Nb, and REE have been mobilized towards higher levels. It is therefore concluded that under the conditions of local potassic alteration the word ‘immobile’, characterizing element behaviour, should be used with the utmost care.