Geology and Geochemical Characteristics of Gevaş Listwaenites (van-Turkey)

Abstract

This study investigates the geological, mineralogical, and geochemical characteristics, and the precious metal contents of the listwaenite in the Gevaş ophiolite. Gevaş listwaenites are found to be mainly composed of dolomite/ankerite, quartz and chalcedony. Calcite, magnesite, chlorite, fuchsite, magnetite, pyrite, hematite and chromite were found as the primary minerals, and tetrahedrite, chalcopyrite, galena, pyrite, millerite, sphalerite, argentite, gold and magnetite were determined as opaque minerals in ore bearing listwaenite (OBL). Covellite, chalcosite, malachite, azurite, anglesite, cerussite, violoarite, bindheimite and limonite were found as secondary minerals. The listwaenites formed by alteration of the serpentinites (n=23 sample) were depleted in MgO, Fe2O3, Na2O and enriched in K2O, CaO and H2O with respect to serpentinite. The values of SiO2 and Al2O3 were variable in serpentinite and listwaenite, with respect to their average content, and the MnO values were enriched only in OBL. Listwaenites were classified into two groups based on their SiO2 content: (i) Silica-rich listwaenites being named as Type I, SiO2>35.52wt.%, and (ii) SiO2≤35.52 wt. % carbonate-rich listwaenites being named as Type II. The Cr, Ni and Co contents of listwaenites (OBL) were depleted according to serpentinite, but the listwaenites wenriched in Au, Ag, Cu, Zn, Sb, As, K, Rb, Ba, Sr, P, Ti, U and Pb contents. The geological, mineralogical and geochemical studies revealed that those listwaenites that have limited cracks and fissures do not show metal enrichment, whereas well sheared and thrust related listwaenite zones are enriched in Au, Ag, Cu, Sb, Zn and Pb metals. While gold and silver show positive correlations with As, Ba, Cu and Sb (i.e. r>0.93), Pb, Zn and Ni show lower correlations. A limited number of analyses indicate that the Au value of Gevaş listwaenites is 53 times more gold-enriched than the serpentinized peridotites.