Abstract
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.‰ NaCl equiv. in the main stage and 0.18-8.81 wt.‰ NaCl equiv. in the late stage) and medium-high temperature of 485°C to 205°C (main stage) and 300°C to 116°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 δ 18 O values of quartz range from 6.7‰ to 8.5‰, and the δ D values for fluid inclusions in quartz range from -45‰ to -52‰. The calcite has C-isotopes ranging from -5.8‰ to +0.7‰ and O-isotopes from +12.7‰ to 21.4‰. H-O-C isotope data are consistent with a hydrothermal fluid derived from the Cretaceous granitoid magma. The δ 34 S values of sulfides are -3.3‰ to +1.9‰. Sulfides have 206Pb/204Pb ratios of 18.377 to 18.473, 207Pb/204Pb ratios of 15.606 to 16.684, and 208Pb/204Pb 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.
Highlights
Knowledge of the sources of ore-forming components can provide valuable background information in evaluating mineral potential and target area selection in regional exploration programs [1, 2]
We identified three hydrothermal stages and presented a detailed sulfide and fluid inclusions study from different stages to characterize the nature of the ore-forming fluids of the Xinmin deposit and to reconstruct the temperature-pressure condition for the mineralization
The isotopic composition of H2S in ore fluids equilibrated with PyI was calculated using a temperature of 350°C, and PoII, PyII, SpII, CcpII, GnII, and BmII using a temperature of 250°C, and the fractionation equations of [31]
Summary
Knowledge of the sources of ore-forming components can provide valuable background information in evaluating mineral potential and target area selection in regional exploration programs [1, 2]. Numerous studies on the O, H, C, S, and Pb isotope systematics in polymetallic deposits have been applied to trace the origin of ore-forming fluids [3,4,5,6,7,8]. The target deposit of our studies, the Xinmin polymetallic is not endowed with world-class ore resources, and Geofluids (a). It is an interesting area for study because it is a part of magmatic rock-related hydrothermal Cu-Au-Ag polymetallic ore system, with great potential for future exploration. We identified three hydrothermal stages and presented a detailed sulfide and fluid inclusions study from different stages to characterize the nature of the ore-forming fluids of the Xinmin deposit and to reconstruct the temperature-pressure condition for the mineralization. Based on the isotopic compositions (C-H-O-S-Pb), we try to trace the sources for ore materials and fluids and to unravel the ore-forming conditions and ore genesis
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