Geological and geochemical characteristics and genesis of the Shaxi porphyry copper (gold) deposits, Anhui province

The Shaxi porphyry copper (gold) deposits are a typical example of porphyry copper deposits associated with diorite in eastern China. Quartz diorite, which hosts the deposits, has a Rb-Sr isochron age of 127.9+/-1.6 Ma. Geoch emically, the rock is rich in alkalis (especially sodium), light rare earth elements (LREE) and large-ion lithophile elements (LILE), and has a relati vely low initial strontium isotopic ratio (I-Sr=0.7058); thus it is the pro duct of differentiation of crust-mantle mixing source magma. The model of a lteration and mineralization zoning is similar to the Hollister(1974) diori te model. The ore fluids have a relatively high salinity and contain signif icant amounts of CO2, Ca2+, Na+ and Cl-. The homogenization temperatures of fluid inclusions for the main mineralization stage range from 280 to 420 d egrees C, the delta(18)O values of the ore fluids vary from 3.51 to 5.52 pa rts per thousand, the delta D values are in the range between -82.4 and -59 .8 parts per thousand, the delta(34)S values of sulphides vary from -0.3 to 2.49 parts per thousand, and the delta(13)C values of CO2 in inclusions ra nge between -2.66 and -6.53 parts per thousand. Isotope data indicate that the hydrothermal ore fluids and ore substances of the Shaxi porphyry copper (gold) deposits were mainly derived from magmatic systems.