Gold mineralization associated with Emeishan basaltic rocks: Mineralogical, geochemical, and isotopic evidences from the Lianhuashan ore field, southwestern Guizhou Province, China

Abstract

A number of gold deposits are newly discovered in the Lianhuashan ore field, southwestern Guizhou Province, China. The gold orebodies are restricted to the Emeishan basaltic rocks and the interlayer fractures between the Emeishan basaltic rocks and the limestone of the Maokou Formation. Three generations of pyrite (Py0, Py1, and Py2) have been recognized in these deposits based on morphology and paragenetic relationships. Electron microprobe (EMP), laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and laser-ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analyses were carried out to characterize their chemical and sulfur isotopic compositions.The framboidal Py0 is enriched in As but depleted in most of the other trace elements. It has negative δ34S values of −14.5–−1.9‰, which are typical of diagenetic pyrites resulted from bacterial reduction of marine sulfate. Py1 and arsenopyrite exhibit high concentrations of Au and As, making them the most dominant auriferous minerals. They yield comparable δ34S values of −2.8– + 2.1‰, consistent with the derivation of sulfur from the Emeishan basaltic rocks. Py2 is characterized by well developed oscillatory-zoned textures, that are interpreted in terms of internal self-organization processes. It contains low concentrations of Au and highly variable concentrations of As, Sb, Co, and Ni. The Py2 grains show slightly positive δ34S values of + 0.4– + 7.0‰, indicating that the sulfur was mainly sourced from the Emeishan basaltic rocks with variable amounts of contamination from reduced marine sulfate.The Emeishan basaltic rocks may have provided not only ore-hosting space but also Au, S, and other associated elements for gold mineralization in the Lianhuashan ore field. Similar gold deposits are expected to be discovered in the areas of Emeishan basaltic rocks with high Au backgrounds and small thicknesses.