| 西藏铁格隆南铜(金银)矿床地质特征及勘查模型——西藏首例千万吨级斑岩-浅成低温热液型矿床 |
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| 关键词:geological characteristics exploration model porphyry-epithermal Cu (Au, Ag) Tiegelongnan Duolong Tibet |
| 基金项目:国土资源部公益性行业科研专项(编号: 201511017);中国地质科学院院基本科研业务费(编号: YYWF201608);国家自然科学基金项目(编号: 41172077; 41402178);中国地质调查局青藏高原专项项目(编号: 12120113037400);中铝资源西藏金龙矿业股份有限公司项目(编号: XZJL-2013-JS03) |
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| Geological Characteristics and Exploration Model of the Tiegelongnan Cu (Au-Ag) Deposit: The First Ten Million Tons Metal Resources of a Porphyry-epithermal Deposit in Tibet |
| The Tiegelongnan deposit is located in the middle of the northwest Duobuza porphyry Cu-Au deposit, and its primary ore host rock are Early Cretaceous porphyries and a suite of flysch formation or fly-schoid formation of Middle-Lower Jurassic strata, named Sewa Formation (J1-2s). A suite of Meiriqiecuo intermediate-basic volcanic formation (K1m), which was formed at 110 Ma in the post metallogenic period, lies upon the porphyry metallogenic system and is proved to be an essential element of ore preservation. With such means as detailed geological mapping, geological logging, lithogeochemical measurements, microscope observation, electron microprobe analysis, fluid-inclusion analysis, isotopic geochronology, audio magnetotelluric sounding and comprehensive research, the authors detected that the Cu-Au-Ag deposit is generally like a cylinder, trending northeast and stretching for about 2 000 meters in the northeast-southwest direction and 1 200 meters in the northwest-southeast direction. The average grade of Cu is greater than 0.5 percent and the average grade of associated Au and Ag is about 0.08 g/t and 2 g/t, separately. The resource of Cu is estimated to be about 11 megatons, and the prospective resources could be more than 15 megatons. Ores are mainly of typical veinlet disseminated structures. From top to bottom, the metallic minerals vary in a certain sequence, i.e., covellite, digenite, spionkopite, yarrowit, djurleite, anilite, chalcopyrite, bornite and a small amount of molybdenite, and the nonmetallic minerals vary in the same way, i.e., from top to bottom there are alunite, dickite, kaolinite, diaspore, sericite, quartz, anhedritite and so on. The typical minerals and the alteration mineral assemblage indicate that the deposit belongs to a porphyry-epithermal metallogenic system. The isotopic dating of different minerals gives us a clear mineralization sequence that the mineralization of epithermal system is later than porphyry’s. To be specifically, the data of granodiorite-porphyry yields a diagenesis age of 120 Ma, which is older than the Re-Os age of molybdenite of the porphyry stage which is about 119 Ma, and the Ar-Ar age of alunite of the epithermal stage is about 116 Ma which is younger than the two ages mentioned above. The location of epithermal deposits was likely to move to a lower altitude continually due to the continual uplifting of the south side of Qiangtang Terrane, which could make a contribution to the formation of the typical extremely thick orebodies of the epithermal type. Two different kinds of fluid were recognized through the homogenization temperature in fluid inclusion study. The porphyry metallogenic system is characterized by high temperature and high salinity fluid, whereas the epithermal metallogenic system is characterized by low temperature and low salinity fluid. The emplacement location of the intrusions in the Tiegelongnan deposit is fairly shallow and the boundaries between the intrusions and the upper strata of Meiriqiecuo Formation are unconformable in the drill hole of ZK1604, which could be an evidence of the outcropping of the orebodies in the post ore-forming period, and in the meantime it is probable that the猠獵数獰獥敲搠?瑡潲?戠敯?洠潥牰敩?瑨桥慲湭????浵攠杯慲瑥潢湯獤?楥湳?瑯桦攠??略漠汰潯湲杰?潹牲敹?捥潰湩捴敨湥瑲牭慡瑬攠搠?慥牰敯慳?t system was eroded, which is based on the metallogenic depth estimation that the upper orebodies exposed at surface had formed at the depth of about 1.2 km. The characteristics of the trace elements and the rare earth elements in the intrusions indicate that the intrusions belong to high-potassium calc-alkaline series, which are enriched in LILE and depleted in HFSE and can represent the geochemical characteristics of arc magma. In the Duolong ore concentration area, almost all the samples fall in the active continental margin zone in Y-Th/Ta and Ta/Yb-Th/Yb diagrams, and most of the samples fall in the continental marginal arc zone in Th-Co-Zr/10 and Th-Sc-Zr/10 trace element tectonic diagrams. The tectonic-magmatic activities also suggest that the formation of Duolong intrusions was closely related to the southward subduction of Bangong-Nujiang Tethys Ocean toward the Qiangtang terrane in Early Cretaceous, which was similar to the situation of tectonic setting of Andes metallogenic belt. The fact that the magma originated from depleted mantle and was contaminated by the crustal materials is primarily based on the Hf isotopic studies, which could be known from the Hf isotope data that they fall between chondrite and depleted mantle evolutionary lines and the Hf crustal modal ages are approximately the same as the intrusions there. Besides, it is likely that the hornblende might have been the main source of the melt magma, which indicates that the Bangong-Nujiang Tethys Ocean crust might have undergone a phase transition in the 50~70 km depth, which could induce the partial melting of the mantle by dehydration of such water-rich minerals as hornblende. It turns out that more deposits resemble Tiegelongnan or Rongna type could be uncovered in Gaerqin and Dibiaonamugang according to the short infrared spectra mapping and petrogeochemical profile measurement. There is a great potential for finding more Cu and the resource quantity of Cu is a????????????????????????????????????????????????????????????????????????? |
| TANG Ju-xing,SONG Yang,WANG Qin,LIN Bin,YANG Chao,GUO Na,FANG Xiang,YANG Huan-huan,WANG Yi-yun,GAO Ke,DING Shuai,ZHANG Zhi,DUAN Ji-lin,CHEN Hong-qi,SU Deng-kui,FENG Jun,LIU Zhi-bo,WEI Shao-gang,HE Wen,SONG Jun-long,LI Yan-bo,WEI Lu-jie.2016.Geological Characteristics and Exploration Model of the Tiegelongnan Cu (Au-Ag) Deposit: The First Ten Million Tons Metal Resources of a Porphyry-epithermal Deposit in Tibet[J].Acta Geoscientica Sinica,37(6):663-690. |
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