HFSE, REE, and PGE geochemistry of three sedimentary rock-hosted disseminated gold deposits in southwestern Guizhou Province, China

Abstract

The sedimentary rock-hosted disseminated gold (SRHDG) deposits in southwest Guizhou Province, China, are located near the buried edge of the Yangtze Craton. Three deposits, Lannigou, Getang and Zimudang, were chosen for this study. The deposits are hosted by fine-grained clastic and calcareous sedimentary rocks and formed at low temperatures from low salinity solutions of low to intermediate pH and low f_O2 . Chemical analyses of the ores and host rocks show that high field strength elements, such as Nb, Ta, Zr and Hf, were immobile during hydrothermal alteration. However, rare earth elements (REE) were mobile. Light rare earth elements (LREE) were depleted, whereas heavy rare earth elements (HREE) were enriched. A differentiation of platinum group elements (PGE) concentrations was documented. The ores are enriched in Pd and Pt, consistent with the higher solubility of these two elements in ore fluids. The Pd/Ir ratios of the ores are lower than those of the ultramafic rocks and the Emeishan basalts in the region. Thus, the ultramafic intrusives and basalts could not have been the main source of the PGEs and gold in the SRHDG deposits. Rather, these metals were derived mainly from the sedimentary host rocks as evidenced by the trace element and stable isotopic characteristics of the ores. Our data suggest that the SRHDG deposits in southwest Guizhou are most likely of amagmatic origin, which is consistent with the lack of igneous intrusives in the vicinity of the deposits, the very weak metamorphic grade of the rocks, the lack of metamorphic effects within the time range of the SRHDG deposits, and coincidence in time of gold mineralization with regional extension.