Fluid Inclusions And H-O-C-S-Pb Isotope Studies Of The Xinmin Cu-Au-Ag Polymetallic Deposit In The Qinzhou-Hangzhou Metallogenic Belt, South China: Constraints On Fluid Origin And Evolution

Qinzhou-Hangzhou metallogenic belt is an important polymetallic (Cu, Mo, W, Sn, Pb, Zn, Au, and Ag) belt in South China. The Xinmin polymetallic deposit is located in the southwestern segment of this belt, which ore bodies hosted in the contact zone of granite and Lower Devonian sedimentary strata and in the structure fractured zone within the strata. Three hydrothermal stages can be distinguished: quartz+tourmaline+pyrite (early stage), tourmaline+pyrite+galena+bismuthinite+sphalerite+chalcopyrite+pyrrhotite (main stage), and quartz+calcite+dolomite (late stage). The mineralizing fluid system can be described as aqueous with medium-high salinity (2.7-50.7 wt.parts per thousand NaCl equiv. in the main stage and 0.18-8.81 wt.parts per thousand NaCl equiv. in the late stage) and medium-high temperature of 485 degrees C to 205 degrees C (main stage) and 300 degrees C to 116 degrees C (late stage). The trapping pressures varied from 2 MPa to 30 MPa (main stage) and 0.4 MPa to 9 MPa (late stage). The delta O-18 values of quartz range from 6.7 parts per thousand to 8.5 parts per thousand, and the delta D values for fluid inclusions in quartz range from -45 parts per thousand to -52 parts per thousand. The calcite has C-isotopes ranging from -5.8 parts per thousand to +0.7 parts per thousand and O-isotopes from +12.7 parts per thousand to 21.4 parts per thousand. H-O-C isotope data are consistent with a hydrothermal fluid derived from the Cretaceous granitoid magma. The delta S-34 values of sulfides are -3.3 parts per thousand to +1.9 parts per thousand. Sulfides have Pb-206/Pb-204 ratios of 18.377 to 18.473, Pb-207/Pb-204 ratios of 15.606 to 16.684, and Pb-208/Pb-204 ratios of 38.613 to 38.902. The S-Pb isotope data suggest derivation of S and Pb mainly from the Cretaceous granitic magma. It is concluded that the Xinmin deposit is a medium-high temperature, medium-high salinity hydrothermal polymetallic deposit, related to the granitic magmatism and strictly controlled by the fault and shattered zones.