| 冷水坑斑岩型铅锌矿床地质特征 |
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| 引用本文：.1985.Geological characteristics of the Lengshuikeng porphyry type Pb-Zn deposit in Guixi county, Jiangxi province[J].Mineral Deposits,4(4):15~24 |
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| Geological characteristics of the Lengshuikeng porphyry type Pb-Zn deposit in Guixi county, Jiangxi province |
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| Abstract:Ore-forming processes of the Lengshuikeng Pb-Zn deposit are controlled mainly by the granite porphyry genetically related to Upper Jurassic volcanic rocks. The Pb-Zn orebodies occur within the porphyry body, especially near the upper contact zone, with the attitude of the orebody consistent with that of the rock body. The ore deposit is characterized by planar alteration zonation, i. e., from the center of the rock body towards the wall rock, there appear successively chloritization zone→sericitization zone→carbonatization zone. Ore minerals are mainly galena and sphalerite, with a less amount of argentite, pyrite, etc. Ores have dissemination and veinlet-dissemination structures and occur as cryptonlerous aggregates. Orebodies are stratoid, lenticulal and veinlike in shape, and orebeds have great thickness. Ore grade is relatively low with Pb/Zn ratio being 1/1.5. Mineralizations are correspondent with wall rock alterations, with Cu-S(Pb-Zn)association at the center. Ag-Pb-Zn outwards, and Fe-Mn(Pb-Zn)in the wall rock. Sulfur isotopic compositions of the deposit are quite similar to those of Yulong, Xizang and Tongchang, Jiangxi, indicating that sulfur is mainly derived from the depth. The average metallogenic temperature is 380℃, implying that the ore deposit is formed at middle-high temperatures．From the ore characteristics it is considered that the Lengshuikeng Pb-Zn deposit not only is a typical porphyry deposit, but has its own peculiarities as well. The peculiarities are shown in two aspects: (1)．The granite porphyry is ultra-acidic, rich in K, and poor in NaSiO2 content of the rock body is more than 72％, averaging 74.32％, obviously high compared with SiO2 content of other rocks of the same kind, indicating an acidic-ultra-acidic rock body. Its total alkali content is 6.97％, while its K2O/Na2O ratio reaches 14.15 on the average, far much higher than that of the other ore-bearing porphyry bodies. (2)．Mineralization and alteration are unique: galena and sphalerite replace selectively feldspar phenocrysts or crystalloclastics, and matrices or cements are only weakly mineralized, thus forming peculiar dissemination ores. Such selective replacements are also seen in chloritization and Fe-Mn carbonatization. The vein-like and veinlet mineralizations are characterized by sparse distribution, relatively large width, regular shapes and steep dips. Mineralized veinlets are rarely seen extending into the mineralized phenocrysts. Such a structure, made up of dissemination and veinlet(or veinlike)nlineraljzation, is called veinJet-dissemination structure, which bears some obvious differences from structures of other porphyry deposits. |
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