Carbon–oxygen isotopic covariations of calcite from Langdu skarn copper deposit, China: implications for sulfide precipitation  

作　　者：Tao Ren Xingchun Zhang Runsheng Han Baohong Hou 

机构地区：[1]Faculty of Land and Resource Engineering, Kunming University of Science and Technology [2]State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Science [3]Minerals & Energy Division, Primary Industries and Resources SA,GPO Box 1671, Adelaide,SA 95000, Australia

出　　处：《Chinese Journal Of Geochemistry》2015年第1期21-27,共7页中国地球化学学报

基　　金：supported by the National Science Foundation of China (NSFC) project (40372049)

摘　　要：The Langdu skarn copper deposit in the Zhongdian area, Yunnan Province, China, has an average Cu grade of 6.49 %. The deposit is related to a porphyry intrusion(*216 Ma), which was emplaced in the Upper Triassic sedimentary rocks of the Tumugou and Qugasi Formations.At the Langdu skarn copper deposit, carbon and oxygen isotope ratios of fresh limestones(d18O = 3.0–5.6 % relative to V-SMOW; d13 C = 24.5–25.7 % relative to PDB)and partly altered limestones(d18O = 27–7.2 to-1.9 %;d13C = 11.8–15.2 %) indicated that the deposit was a typical marine carbonate source. Oxygen and carbon isotope values for calcites formed at different hydrothermal stages are-9.1 to 0.2 and 10.1–16.3 %, respectively. Moreover,the carbon–oxygen isotopic composition of an ore-forming fluid(d18O = 5.0–9.5 %, d13 C =-7.3 to-5.3 %) suggested the presence of magmatic water, which most likely came from the differentiation or melting of a homologous magma chamber. The deposition of Calcite I may arise from metasomatism in an open system with a progressively decreasing temperature.Later, the minerals chalcopyrite, pyrrhotite, quartz and Calcite II were precipitated due to immiscibility. Water–rock interaction could potentially be responsible for Calcite III precipitation in the post-ore stage.The Langdu skarn copper deposit in the Zhongdian area, Yunnan Province, China, has an average Cu grade of 6.49 %. The deposit is related to a porphyry intrusion （- 216 Ma）, which was emplaced in the Upper Triassic sedimentary rocks of the Tumugou and Qugasi Formations. At the Langdu skarn copper deposit, carbon and oxygen isotope ratios of fresh limestones （δ^18O= 3.0-5.6 ‰ relative to V-SMOW; δ13C = 24.5-25.7 ‰ relative to PDB） and partly altered limestones （δ18O = 27-7.2 to -1.9‰; δ13C = 11.8-15.2 ‰） indicated that the deposit was a typ- ical marine carbonate source. Oxygen and carbon isotope values for calcites formed at different hydrothermal stages are -9.1 to 0.2 and 10.1-16.3 ‰, respectively. Moreover, the carbon-oxygen isotopic composition of an ore-forming fluid （δ13O = 5.0-9.5‰, δ13C = -7.3 to -5.3‰） suggested the presence of magmatic water, which most likely came from the differentiation or melting of a homologous magma chamber. The deposition of Calcite I may arise from metasomatism in an open system with a progressively decreasing temperature. Later, the minerals chalcopyrite, pyrrhotite, quartz and Calcite II were precipitated due to immiscibility. Water-rock interaction could potentially be responsible for Calcite III precipitation in the post-ore stage.

关 键 词：氧同位素比率 海相碳酸盐 热液方解石 夕卡岩型 铜矿床 沉淀 中国 硫化物 

分 类 号：P618.41[天文地球—矿床学]