Abstract:The Jilongshan skarn Au-Cu deposit is a representative skarn deposit in southeastern Hubei Province. Its orebodies are mainly hosted in the contact zone between the carbonate of the Lower Triassic Daye Group and the granite diorite porphyry. The ore-forming process can be divided into four stages, namely prograde skarn stage, retrograde skarn stage, quartz-sulfides stage and carbonate stage, and the precipitation of Au and Cu occurred at the quartz-sulfides stage. Microscopic observation and electron microprobe analysis suggest that Au and Ag occur mainly as visible Au minerals(native gold, electrum) and visible Ag minerals(hessite, matildite), respectively, and Au minerals occur mainly as inclusions in chalcopyrite and tetrahedrite or micro-fracture fillings in pyrite. Abundant Te-Bi minerals, such as tetradymite and aikinite, were observed in the Jilongshan Au-Cu deposit. In high temperature hydrothermal fluids, Au and Ag elements were probaboy transported as chloride complexes. With the decreasing temperature of the fluid and the variation of compositions, Au and Ag elements might have been transported as sulfide complexes and bismuth-telluride melts or complexes. At the quartz-sulfides stage, fluid boiling and sulfurization resulted in the decrease of fS2 and the increase of fTe2. When fluids lay in the oxygen fugacity range of pyrite-pyrrhotite buffer, pH values assumed neutral-to-alkaline nature, -10.7 < logfTe2 < -8.4 and -11.4 < logfS2 < -10.6, there existed the transfer and enrichment of Au by Te, Bi and As elements, which resulted in the formation of the Jilongshan skarn Au-Cu deposit.
