南秦岭大巴山大型钡成矿带中锶同位素组成及其成因意义  

Strontium isotopic composition and its genetic significance of the Dabashan large barium metallogenic belt in southern Qinling Mountains

作　　者：刘家军[1,2] 吕志成[3] 吴胜华[1,2] 柳振江[1,2] 翟德高[1,2] 王银宏[1,2] 陶银龙[1,2] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]中国地质大学(北京)地球科学与资源学院,北京100083 [3]中国地质调查局发展研究中心,北京100037

出　　处：《地学前缘》2014年第5期23-30,共8页Earth Science Frontiers

基　　金：国家自然科学基金项目(41173062);教育部博士点基金项目(20130022110001);国家重点基础研究发展计划'973'项目(2014CB440903);高等学校学科创新引智计划项目(B07011)

摘　　要：为探讨南秦岭大巴山大型钡成矿带中毒重石矿床与重晶石矿床的差异性,文中对大型钡成矿带的锶同位素组成特点进行了研究。结果表明,寒武系地层钡矿床中23件钡解石、毒重石、重晶石样品的87 Sr/86 Sr比值集中在0.707 771～0.708 869,平均值为0.708 379,低于寒武纪海水87Sr/86Sr比值（0.709）,反映了成矿流体中有幔源物质的混入,锶同位素组成可能是海水与海底热卤水混合的结果,该过程类似于造成重晶石在海底沉积物中富集的现代洋底热水活动。志留系地层钡矿床中12件钡解石、毒重石、重晶石样品87Sr/86Sr比值集中在0.708 242～0.708 809,平均值为0.708 447,高于志留纪海水87Sr/86Sr比值（0.707 93）,可能是同时代海水与深部热水混合所致,并有较高放射性成因壳源锶的混染。锶同位素组成可能是海水与海底热卤水混合的结果。文中锶同位素的研究为南秦岭大巴山大型钡成矿带的海底热水沉积成因提供了新的证据。In order to compare the differences between witherite and barite deposits occurred in the Dabashan large barium metallogenic belt in southern Qinling Mountains, this study initially investigates their strontium isotopic compositions. The obtained 87Sr/86 Sr values of various barium-bearing minerals collected from the Cambrian layers generally range from 0. 707771 to 0. 708869, with an average value of 0. 708379（n：23）. This isotopic value is typically lower than the average value of the coeval seawater（0. 709） but significantly higher than the mantle＇s values, which most likely suggests the existence of a mantle-originated fluid in the hydrothermal system In contrast, the detemlined 87Sr/S6Sr values of various barium-bearing minerals from the Silurian layers generally vary from 0. 708242 to 0. 708809, with an average value of 0. 708447（n=12）. This value is higher than the average value of the coeval seawater（0. 70793） but significantly lower than the crust＇s values, which mostly indicates a mixed origin for the ore-forming fluid, i. e. , the coeval seawater and deep hydrotherrnal water. Meanwhile, this value is also indicative of variable contamination of crust-originated strontium, which is characterized by relatively high radiogenetic 87Sr/86Sr ratios. The strontium isotopic compositions provide new constraints for the fluid origins and support the submarine hydrothermal exhalative genesis for those barium deposits widely occurred in the Dabashan large barium metallogenic belt in southern Qinling Mountains.

关 键 词：锶同位素 热水沉积 大型钡成矿带 大巴山 南秦岭 

分 类 号：P618.7[天文地球—矿床学] P597[天文地球—地质学]