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《Acta Geologica Sinica》 2018-06
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Genesis of Rutile from Metallogenic Porphyry in the Zhunuo Porphyry-type Cu-Mo Deposit,Tibet,China,and Its Significance for Prospecting

DAI Jie;NI Shijun;HUANG Yong;DING Jun;Chou I-Ming;Chengdu Center,China Geological Survey;Key Laboratory of Sedimentary Basin and Oil and Gas Resources,MLR;Chengdu University of technology;Sanya Institute of Deep-sea Science and Eengneering,Chinese Academy of Science;  
Zhunuo porphyry deposit,newly discovered in the west of southern Gangdase metallgoenic belt,Tibet,is a typical porphyry-type Cu-Mo deposit with a very large Cu reserves.Rutile is one of the typical accessory minerals for porphyry copper deposits.Therefore,its composition and texture can deduce the evolution process of ore-forming fluids and determine the main orebodies.Based on detailed field geological work,metallogenic porphyry(biotite granodiorite)samples from the potassic alteration zone were studied.The results indicate that the rutiles usually coexist with magnetite(Ⅰ kind)and hematite(Ⅲ kind),both of which occur in and around biotites.Striped(long10~0μm,with 3~10μm),granular(diameter 10~40μm),or irregular rutiles occur within quartz-pyrite veins(Ⅱ kind).The three occurrences of rutiles formed in three conditions:the I kind of rutiles was formed by the reaction of titanic magnetite under the condition of S-rich environment during or after the alteration of biotite or titanite;the Ⅱ kind of rutiles was formed by reaction of ilmenite in the O-rich environment during or after the alteration of biotite or titanite;and the Ⅲ kind of rutiles directly precipitated from the Ti-bearing fluid.The metallogenic porphyry has the high concentration(0.66 wt.%)of TiO_2,which provided abundant ore-forming material source.Electron microscope analyses show that rutiles are dominantly TiO_2 of 94%,but relatively enriched in V_2O_3,Nb_2O_5,FeO,WO_3,CaO,SiO_2,Al_2O_3 and ZrO_2,with few or without MgO and MgO.The compositions of V_2O_3 and Nb_2O_5 range from 0.20 ot 2.39 wt%(with an average of 0.49 wt%)and from0.20 to 4.63 wt%(with an average of 1.25 wt%)respectively.And average compositions of WO_3 and FeO are 1.92 wt% and 1.81 wt%respectively,with about 0.05 wt.% of ZrO_2 in rutiles.When carrying out exploration outside the Zhunou deposit using rutiles,the first consideration should be the composition of V_2O_3 in retiles above 0.2 wt.%(Ⅱ kind should be above 0.5 wt.%),and then the composition of Nb_2O_5 should be considered above 0.2 wt.%(Ⅲ kind of retiles should above 2.6 wt.%).And the high concentration of W,Fe,the anomaly of Zr should also be considered.Furthermore,the grain size of theⅡ kind of rutiles should be above 10μm.
【Fund】: 西藏朱诺-厅宫-努日大型矿床成矿专属性研究项目(项目编号:1212011221073);; 羌塘盆地金星湖—隆鄂尼地区油气资源战略调查项目(121201010000161110)联合资助资助的成果
【CateGory Index】: P618.41;P618.65
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