云南大坪金矿白钨矿微量元素、稀土元素和Sr-Nd同位素组成特征及其意义  

Trace elements,rare earth elements(REE)and Nd-Sr isotopic compositions in scheelites and their implications for the mineralization in Daping gold mine in Yunnan province,China.

作　　者：熊德信[1] 孙晓明[1] 石贵勇[1] 王生伟[1] 高剑锋[2] 薛婷[1] 

机构地区：[1]中山大学地球科学系 [2]南京大学成矿作用国家重点实验室,南京210093

出　　处：《岩石学报》2006年第3期733-741,共9页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划(973)项目(No.2002CB412610);国家自然科学基金(编号:40173025);国家教育部跨世纪优秀人才培养计划基金资助。

摘　　要：利用ICP-MS和同位素质谱分析了大坪金矿含金石英脉中白钨矿的微量元素、稀土元素和Sm-Nd、Rb-Sr同位素组成,结果显示大坪白钨矿中富Sr、Ba,而亏损Mo、Bi、Sn、Nb、Ta等,指示原始成矿流体与岩浆的结晶分异作用无关,并非前人普遍认为的岩浆水和大气降水的混合流体;样品的REE球粒陨石标准化配分曲线为高度一致的右倾和MREE富集型,Eu出现正异常,表明白钨矿与流体之间REE元素发生了强烈分异,白钨矿中REE的配分行为主要表现为REE^(3+)与Na^+成化合价补偿形式替代Ca^(2+)选择性进入白钨矿晶格中,成矿流体是相对封闭的高温、富Na^+的还原性热液体系;Sr-Nd同位素组成显示本区原始成矿流体主要来自下地壳,但不排除有幔源物质加入。原始成矿流体的形成与区域性剪切带的活动有关,韧性剪切作用导致下地壳富CO_2流体上升,并与闪长岩发生强烈的水岩反应,而剪切带中脆性断裂的形成是成矿流体迁移、集中、沸腾和矿质沉淀的触发因素。Scheelite is a widely-distributed accessory mineral in auriferous quartz veins in Daping gold deposit, China. Trace elements, rare earth elements（REE） and Nd-Sr isotopic compositions of the scheelite were determined respectively by ICP-MS and mass spectrograph in this work. The results show that the scheelite is enriched with Sr, Ba and depleted with Mo, Bi, Sn, Nb and Ta, indicating that primitive ore-forming fluid of the Daping mine probably didnl derive from magmatic crystallization and differentiation, and was not a mixed fluid of magmatic and meteoric water proposed by many previous researchers. The scheelites picked from different samples possess very similar MREE-enriched and dextral-inclined chondrite-normalied patterns and positive Eu anomaly, suggesting that intensive REE differentiation occurred between the scheelites and the ore-forming fluid, REE were substituted in Ca^2 ＋ site of the scheelites by charge compensation mechanism （ REE^3 ＋ Na ^＋ = 2Ca^2＋ ） , and the primitive ore-forming fluid was a relative high temperature, Na ^＋ enriched and reducing hydrothermal system. High correlation of trace elements and REE compositions in scheelites and diorite around rocks and their alterations suggests that relative intensive fluid-rock interaction occurred before the scheelites precipitation. Sr-Nd isotopic composition of the scheelites indicates the primitive mineralizing fluid derived predominantly from the lower crust, but interfusion of the mantle-derived fluid could not be excluded. The primitive mineralizing fluid had close relationship with the regional ductile deformation in the mining district, the ductile shear zone penetrated the crust, induced CO2 enriched fluid ascended from the lower crust, and gave birth to intensive fluid-rock interaction with the diorite rock. Formation of the brittle fractures in the shear zone triggered transportation, concentration and boiling of the ore-forming fluid and precipitation of the ore minerals.

关 键 词：白钨矿 微量元素 稀土元素 Sr—Nd同位素 成矿流体 闪长岩 大坪金矿 

分 类 号：P618.67[天文地球—矿床学] P618.51[天文地球—地质学]