CMF模式的排他性依据和造山型银矿实例:东秦岭铁炉坪银矿同位素地球化学  

Exclusive evidences for CMF model and a case of orogenic silver deposits: Isotope geochemistry of the Tieluping silver deposit, east Qinling orogen.

作　　者：陈衍景[1] 隋颖慧[2] Franco PIRAJNO 

机构地区：[1]北京大学造山带与地壳演化实验室 [2]北京大学地质学系 [3]西澳大利亚地质调查所

出　　处：《岩石学报》2003年第3期551-568,共18页Acta Petrologica Sinica

基　　金：科学院百人计划;教育部跨世纪人才培养计划;国家攀登预研(95-Pre-39-04);国家自然科学基金(49972035)

摘　　要：河南熊耳山区的铁炉坪银矿定位于高级变质基底中的NE向断裂带中,是熊耳山脉状造山型金、银、铅锌矿床的重要组成部分。成矿作用包括了早、中、晚3个阶段,分别形成石英-黄铁矿,多金属硫化物和碳酸盐脉3类矿物组合。早阶段成 矿温度大约为373℃左右,成矿流体δD=-90‰,δ^(13)C_(co_2)=2.0‰,δ^(18)O=9‰,来源较深;晚阶段流体温度<203℃,δD=70‰,δ^(13)C_(co_2)=-1.3‰,δ^(18)O=-2‰,属于浅源大气降水热液;中阶段流体均一温度210～249℃,δD=-109‰,δ^(13)C_(co_2)=0.1‰,δ^(18)O=2‰,是深源与浅源流体的混合。对比讨论表明,熊耳山区的早前寒武纪变质基底、熊耳群火山岩和燕山期花岗岩类的三者之一或它们的混合物,均无法提供具有早阶段流体D-O-c同位素组成(高δ^(18)O和δ^(13)C,低δD)的成矿流体,表明早阶段流体来自栾川群和管道口群的碳酸盐-页岩-硅质岩建造的变质脱水作用。矿石硫同位素组成较低,铅同位素比值较高,同样不可能来自熊耳山的主要地质体,更不可能来自其下伏的地幔和下地壳,指示成矿物质和流体应主要来自栾川群和管道口群。尽管栾川群和管道口群地层的同位素地球化学研究尚待补充,铁炉坪银矿的同位素地球化学特征似乎只能借助碰撞造山成岩成矿与流体作用模式才能合理解释。The Tieluping silver deposit is a recently discovered Mesozoic orogenic-type Ag-Pb-Au deposit in East Qinling Orogen. Its ore formation includes three stages: early, middle and late, which include quartz-pyrite, polymetallic sulfides and carbonates, respectively. The early stage fluids are characterized by deltaD -90parts per thousand, delta(13) C-CO2 = 2.0parts per thousand and delta(18) O = 9parts per thousand at 373 degreesC, and are deeply sourced; the late stage fluids, with deltaD = -70parts per thousand, delta(13) C-CO2 = -1.3parts per thousand, delta(18) O = -2parts per thousand, are shallow-sourced meteoric water; whereas the middle stage fluids, with deltaD = -109parts per thousand, delta(13) C-CO2 = 0.1parts per thousand, delta(18) O = 2parts per thousand, are a mix of deep-sourced and shallow-sourced fluids. Comparisons of the D-O-C isotopic systematics of the early stage ore-forming fluids with the fluids derived from Mesozoic granites, Early Precambrian metamorphic basement and Mesoproterozoic Xionger Group, shows that these units cannot generate fluids with the isotopic composition (high delta(18) O and delta(13) C ratios and low deltaD ratios) characteristic of the ore-forming fluids. This suggests that the E-stage ore-forming fluids originated from metamorphic devolatilisation of a carbonate-shale-chert lithological association, locally rich in organic matter, of the Luanchuan and Guandaokou Groups. In addition, sulfur and lead isotope data show that the ore-forming fluids must originate from a source abundant with radiogenic lead and low delta(34) S, that differs significantly from geologic units in the Xiong'er Terrane, the lower crust and the mantle. This supports the view that the Luanchuan and Guandaokou Groups south of the Machaoying fault might be the favorable sources, although little is known about their isotopic compositions. A tectonic model for collisional orogeny, metallogeny and hydrothermal fluid flow is employed here to explain the formation of the Tieluping silver deposit. During

关 键 词：铁炉坪造山型银矿 稳定同位素 秦岭造山带 CMF模式 排他性依据 

分 类 号：P597.2[天文地球—地球化学] P618.52[天文地球—地质学]