Exclusive evidences for CMF model and a case of orogenic silver deposits: Isotope geochemistry of the Tieluping silver deposit, east Qinling orogen.
Exclusive evidences for CMF model and a case of orogenic silver deposits: Isotope geochemistry of the Tieluping silver deposit, east Qinling orogen.
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发表时间：
2003
影响因子：
1.8
通讯作者：
Pirajno Key
中科院分区：
文献类型：
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作者：
Pirajno Key
铁鲁坪银矿是东秦岭造山带新近发现的一个中生代造山带型银铅金矿床。成矿分为早、中、晚三个阶段，分别为石英-黄铁矿、多金属硫化物和碳酸盐。早期流体特征为δD = -90‰，δ13CCO2 = 2。δ18O =9‰，373℃，来源较深；晚期流体δD=-70‰，δ13CCO2 =- 1.3‰，δ18O =- 2‰为浅源大气水；中期流体δD = - 109‰，δ13CCO2 =0。1‰，δ18 O = 2‰，为深源和浅源混合流体。早期成矿流体与中生代花岗岩、早前寒武纪变质基底和中元古代雄儿群成矿流体的D-O-C同位素系统对比表明，这些单元不可能产生具有成矿流体同位素组成特征（高δ18O和δ13C比值和低δD比值）的流体。表明e期成矿流体来源于栾川组和官道口组局部有机质富集的碳酸盐岩-页岩-燧石岩性组合的变质脱挥发作用。此外，硫、铅同位素数据表明，成矿流体必须来自一个富含放射性成因铅和低δ34S的来源，这与雄耳地体、下地壳和地幔的地质单元有明显不同。这支持了马超营断裂带以南的栾川群和官道口群可能是有利源区的观点，尽管对它们的同位素组成知之甚少。本文采用碰撞造山作用、成矿作用和热液流动的构造模型来解释铁鲁坪银矿床的形成。在华南古陆与华北古陆的中生代碰撞过程中，一块含碳酸盐岩-页岩-燧石岩性组合的地壳板块沿马朝营断裂向北俯冲至熊耳地体之下，局部富含有机质（碳质页岩）。下冲栾川群和关道口群变质脱挥发作用为金银（铅锌）矿带发育提供了成矿流体，其中包括铁鲁坪银矿床。
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 δD = -90‰, δ13CCO2 = 2. 0‰ and δ18O =9‰ at 373℃, and are deeply sourced; the late stage fluids, with δD=-70‰, δ13CCO2 =- 1.3‰, δ18O = -2‰, are shallow-sourced meteoric water; whereas the middle stage fluids, with δD = - 109‰, δ13CCO2 =0. 1‰, δ18 O = 2‰, 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 δ18O and δ13C ratios and low δD 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 δ34S, that differs significantly from geologic units in the Xionger 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 the Mesozoic collision between the South and North China paleocontinents, a crustal slab containing a lithological association consisting of carbonate-shale-chert, locally rich in organic matter (carbonaceous shale) was subducted northwards beneath the Xiong'er Terrane along the Machaoying fault. Metamorphic devolatilisation of the underthrusted Luanchuan and Guandaokou Groups provided the ore-forming fluids to develop the Au-Ag-(Pb-Zn) ore belt, which includes the Tieluping silver deposit.