Geological and geochemical characteristics and genesis of the Cishan gold deposit in Tongling ore cluster area, Anhui Province

Abstract

The Cishan gold deposit is a newly discovered medium-scale independent skarn gold deposit located in the Tongling ore cluster area of the Middle-Lower Yangtze Metallogenic Belt, and the ore-related intrusion is the Cishan pyroxene diorite. In this study, we investigated the zircon U–Pb Geochronology, whole-rock geochemistry of the Cishan ore-related pyroxene diorite, and C–O–S isotope compositions of hydrothermal calcites and metal sulfides in the ores. The pyroxene diorite was emplaced at ca. 141.7 ± 0.36 Ma. They are metaluminous and record high-K calc alkaline and shoshonite series with the characteristics of high Al and alkali (K, Na), enriched in LREEs and LILEs (Rb, K, Ba, Sr), depleted in HREEs and HFSEs (Th, U), without significant Eu anomalies. We suggest that the magma of the Cishan pyroxene diorite was probably derived from partial melting of the enriched lithospheric mantle mixed with a small amount of crustal derived melts, and then underwent crystallization differentiation and weakly upper crustal contamination during the magmatic ascending. The δ13CV-PDB and δ18OV-SMOW values of the hydrothermal calcites range from −5.1‰ to −0.5‰ and 11.7‰ to 16.2‰ respectively, and the δ34SV-CDT values of sulfide ore minerals range from −0.7‰ to 6.0‰, showing that the ore-forming fluids and materials were derived from the magma. Combined with previous studies, we proposed that both the Cishan intrusion and skarn gold deposit were formed under the tectonic transition period from compressional to extensional setting, and the Middle–Lower Yangtze Metallogenic Belt was located in the inland side of the continental margin arc under the subduction of the paleo-Pacific plate.