Geochemical Characteristics of Granite in the Xiaopingba Deposit of Wenshan,Yunnan Province and Its Implications for Petrogenesis
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摘要: 小平坝接触交代矽卡岩型白钨矿床位于滇东南薄竹山岩体东缘,矿体主要产于第一期中粒黑云母二长花岗岩与寒武系碳酸盐岩接触部位,对区内花岗岩的主量、微量、稀土元素分析结果显示:其w(SiO2)变化于67.69%~76.98%之间,平均为70.96%,w(K2O+Na2O)较高,平均为8.06%,K2O/Na2O、A/CNK、里特曼指数σ平均值分别为2.04,1.03,2.36,具铝过饱和、高钾钙碱性特征;富集Rb、Pb、Th、U、La、Zr等大离子亲石元素,而亏损Nb、Ta、Sr、Ba、Ti等高场强元素和不相容元素;稀土元素总量较高,平均为288.01×10-6,轻重稀土元素分馏明显,LREE富集,δEu为0.36~0.69,平均为0.57,具中等负异常;CaO/Na2O-Al2O3/TiO2图解、Rb/Ba-Rb/Sr图解暗示其源岩为砂泥质沉积岩;综合分析认为其为地壳重熔S型花岗岩,且经历了高度分异演化,形成于同碰撞构造环境。Abstract: Xiaopingba contact metasomatic scheelite skarn deposit is located in the eastern margin of Bozhushan granite,southeastern Yunnan province.The orebodies are mainly produced in the contacts between medium grained biotite monzogranite of the first intrusion and Cambrian carbonatite.Major trace and rare element analysis of the granite shows that its SiO2 contents range from 67.69%-76.98%(average 70.96%),the average total alkaline contents,K2O/Na2 O,A/CNK and Rittmann index are 8.06%,2.04,1.03,and 2.36 respectively.The rockbody is characterized by highly-enriched kalium cale-alkaline and belongs to peraluminous granite.The trace elements are characterized by enrichment of large-ion lithophile elements such as Rb,Pb,Th,U,La and Zr depletion of high field strength element and incompatible elements such as Nb,Ta,Sr,Ba,Ti.It has high total rare earths(average 288.01×10-6),medium strong negative Eu anomalies(δEu=0.36-0.69,average 0.57) and the right-declining of rare earth elements distribution patterns.CaO/Na2O vs Al2O3/TiO2 and Rb/Ba vs Rb/Sr all indicate the granite originated from the magma formed by argillite rocks.Its geochemical characteristics imply that the Xiaopingba granite is mainly derived in the crust,and experienced a crystal process.Hence,it belongs to the S-type granite and should be formed in a continental collision tectonic setting.
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Key words:
- granite /
- geochemistry /
- petrogenesis /
- Bozhushan /
- Wenshan in Yunnan
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