Fluid inclusion characteristics and stable isotope geochemistry of the Dongleiwan skarn Cu polymetallic deposit in the Jiujiang-Ruichang metallogenic area, Jiangxi Province
JIA Li-qiong;XU Wen-yi;YANG Dan;MO Xuan-xue;YANG Zhu-sen;CHEN Wei-shi;WANG Liang;State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Sciences and Resources,China University of Geosciences;MRL Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources,Chinese Academy of Geological Sciences;Gold Geology Institute of Chinese Armed Police Force;
Located in northwestern Jiujiang-Ruichang metallogenic area, the Dongleiwan skarn Cu-Mo-Au polymetallic deposit belongs to Jiujiang-Ruichang Cu-Au orefield, which is a component part of the Middle-Lower Yangtze River Cu-Au metallogenic belt and the Daye-Jiujiang metallogenic subzone. Petrographic and microthermometric studies of fluid inclusions in quartz from the main metallogenic phase( quartz-polymetallic sulfide phase)show that the inclusions related to mineralization include mainly four types. Homogenization temperature and salinity w( Na Cleq) of the ore-forming fluids are concentrated in 210 ~ 350℃ and 1% ~ 9% respectively, suggesting medium-high temperature and medium-low salinity. Gases of fluid inclusions mostly contain H2 O and CO2, followed by N2, CO and O2, with a small amount of CH4 and C2H2. Cations of liquid composition mostly consist of Ca2 +,K+and Na+, followed by a small amount of Mg2 +, while anions are mainly Cl-, SO2-4, followed by NO-3and NO-2, and the fluid is of the CO2-H2O-Na Cl-Ca Cl2( KCl) system, with the calculated ion concentrations ranging from 3. 1% to 34. 5%. Hydrogen-oxygen isotope characteristics show that the δ18OH2Ovalues of the ore-forming fluids in the main metallogenic stage are in the range of 0. 93‰ ~ 5. 20‰, and δDV-SMOWvalues vary between- 81‰and- 64‰, which implies that the ore-forming fluids were mainly derived from magmatic fluids, with the mixture of a small amount of meteoric water. The δ34SV-CDT‰ values of sulfides range from- 2. 2‰ to 3. 4‰. Lead and rhenium isotopic composition of the ore indicates that the ore-forming materials of the Dongleiwan deposit were derived mostly from the upper mantle, and partially from the crustal materials. The Dongleiwan deposit is a hydrothermal metasomatic skarn type deposit. The folds and fractures of this area provided the migration pathway for mineralization, and magmatic emplacement developed skarn type magmatic fluid subsystems, accompanied by Cu( Mo,Au, etc.) mineralization. These factors eventually led to the formation of the ore deposit.