The trace element zonation in vent chimneys from the Silurian Yaman-Kasy VHMS deposit in the Southern Ural, Russia: insights from laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS)

摘要

The combination of high sensitivity ICP-MS and Nd-YAG UV laser ablation was utilised to determine the distribution of trace elements (Mn, Tl, As, Pb, Au, Ag, Bi) within the Silurian black smoker vent chimneys from Yaman-Kasy copper-zinc-massive sulphide deposit in the Southern Urals. The study has shown systematic distribution patterns within the chimneys for two groups of trace elements. Group 1 elements (Mn, As, Pb, Ag and Au) are enriched in colloform pyrite in the outer-most section of the chinmey wall. This enrichment probably results from rapid precipitation of colloform pyrite under low temperature conditions. Pyrite euhedra, which result from the recrystallization of colloform pyrite toward the inner wall, are depleted in the Group 1 elements. Group 2 elements (Bi, Ag and Au) are enriched in chalcopyrite along the boundary between the chalcopyrite inner wall and the sphalerite filled central conduit, where Bi, Ag, Au, Pb tellurides have been precipitated in a zone of strong temperature gradients. The main zone of chalcopyrite within the central inner wall is depleted in Group 2 elements, probably due to the high temperature of formation which is unsuitable for telluride precipitation. Generally, trace element concentrations of chimneys increase with the decrease in chalcopyrite content from pyrite-chalcopyrite- to marcasite-chalcopyrite-sphalerite- to marcasite-quartz-rich chimneys, due to decrease in temperature and increase in Eh of the black smoker fluids.