新疆西天山喇嘛萨依铜矿床地质和C、O、S、Pb同位素地球化学

摘要

The Lamasayi copper deposit is a representative copper deposit in the Sailimu massif in Western Tianshan,Xinjiang,China.However,the genesis of this ore deposit is controversial.This study tries to discuss the problem through tracing the origin of ore forming material using stable isotopes of C,O,S and Pb and inves-tigating the geological characteristics of the Lamasayi copper deposit.The δ1 3 C values of gangue calcite vary be-tween -1.04‰and -0.87‰which are lower than those of wall-rock limestone (δ13C =3.51‰-5.47‰);the δ1 8 O values of gangue calcite are from 9.33‰ to 9.61‰ and are quite lower than those of normal marine carbonate (δ1 8 O =20‰-26‰).The C and O isotopic compositions reflect that the ore-forming fluid may be a mixture of magmatic water and ground water.The δ34 S values of sulfides mainly vary from 3.75‰ to 8.64‰ which is close to the sulfur isotope composition of the Hercynian porphyries (for example,theδ34 S values of sul-fides from the Dabate porphyry copper-molybdenum deposit are from 4.9‰to 7.9‰)and which reflects that the sulfur may be originated mainly from porphyry.The Pb isotope compositions of chalcopyrite are from 1 8.264 to 1 9.544 for 206 Pb/204 Pb,from 1 5.575 to 1 5.656 for 207 Pb/204 Pb,and from 38.1 03 to 38.705 for 208 Pb/204 Pb, respectively,which shows characteristic of two-stage abnormal lead and being rich in radiogenic lead,similar to the Pb isotope composition of the Hercynian porphyries (for example,the Dabate rhyolitic porphyry)and which also indicates that the ore-forming metal may be derived from the porphyry.In summary,the Lamasayi copper deposit may be skarn type deposit related to porphyry.%喇嘛萨依铜矿是新疆西天山赛里木微地块内的一处典型铜矿床，关于其成因类型尚存争议。总结了该铜矿床的地质特征，测试围岩、脉石碳酸盐的C、O同位素和硫化物的S、Pb同位素组成，探讨其成因类型。研究表明，喇嘛萨依铜矿床具有后生矿床特征，发育矽卡岩化蚀变，脉石方解石的δ13 C值变化范围为-1.04‰～-0.87‰，低于围岩灰岩的δ13C值（变化范围为3.51‰～5.47‰），δ18O值变化范围为9.33‰～9.61‰，明显低于正常的海相碳酸盐岩的O同位素（δ18 O＝20‰～26‰），C、O同位素组成反映喇嘛萨依铜矿成矿晚阶段流体来自岩浆水和地下水的混合水；硫化物的δ34 S值主要变化范围为3.75‰～8.64‰，与区域上海西期斑岩的硫同位素组成（如达巴特斑岩铜钼矿床硫化物的δ34 S变化范围为4.9‰～7.9‰）接近，反映硫来源于斑岩；黄铜矿的铅同位素为206 Pb/204 Pb＝18.264～19.544，207 Pb/204 Pb＝15.575～15.656，208Pb/204Pb＝38.103～38.705，具有富含放射成因铅、两阶段异常铅特征，与区域上海西期斑岩（达巴特流纹斑岩）的铅同位素组成特征相似，反映成矿金属物质部分来源于斑岩。通过综合分析认为，喇嘛萨依铜矿是与斑岩有关的矽卡岩型矿床。