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首页> 外文期刊>Journal of Asian earth sciences >Ore fluids associated with the Wynad gold mineralization, southern India: evidence from fluid inclusion microthermometry and gas analysis
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Ore fluids associated with the Wynad gold mineralization, southern India: evidence from fluid inclusion microthermometry and gas analysis

机译：与印度南部Wynad金矿化有关的矿浆：流体包裹体热计量法和气体分析的证据

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摘要

In southern India, major gold deposits occur in the Archean granite-greenstone terrain of Kolar, Hutti, Ramagiri, and within Proterozoic granulite terrain in Wynad. The Wynad Gold Field (WGF) which is located within the Moyar-Bhavani lineament—a Proterozoic transcrustal shear zone hosts gold within quartz veins, which are emplaced along the mesoscopic faults and shears in the region. The quartz veins cut the regional fabric of the country rocks, suggesting that the veins were formed in post-tectonic and post-metamorphic episode of crustal shearing. Gold as visible specks or interstitial grains and veinlets are seen within quartz and associated sulfide minerals, indicative of multiple mineralizing events. Fluid inclusion studies carried out on gold-quartz veins showed the frequent occurrence of bi-phase primary inclusions of H_2O-CO_2, pseudosecondary inclusions of H_2O-CO_2 and aqueous secondary inclusions. Microthermometric studies of different samples revealed a near pure CO_2 composition, associated with the aqueous phase, with melting temperatures close to - 56.6 ℃. Clathrate melting temperatures of primary and pseudosecondary inclusions show that the fluids were low to moderately saline (2-14 wt% NaCl equiv.). Homogenization temperatures of primary and pseudosecondary inclusions range between 250-330 ℃ and 230-300 ℃, respectively. The secondary aqueous inclusions have much lower homogenization temperatures between 130 and 220 ℃. Fluid densities calculated from the microthermometric data were between 0.8 and 1.0 g/cm~3. The isochores pertaining to these fluid densities intercept, the trapping temperatures, within pressure ranges of 0.5 and 2.9 kbars. Fluid inclusion gas analyses were carried out on selected samples using a quadrupole mass spectrometer. The analysis shows that the fluid inclusions were mainly of H_2O and CO_2 with minor quantities of N_2 and CH_4, which was in close correlation with our visual analytical data. We envisage that the fluids responsible for the Wynad gold mineralization evolved from an H_2O-CO_2 fluid and precipitated gold at temperatures of 300-350 ℃, due to the sudden pressure and temperature decrease as the fluids entered the shear zone.
机译：在印度南部，主要的金矿床分布在Kolar，Hutti，Ramagiri的太古代花岗岩绿岩地带以及Wynad的元古代花岗石地带。位于Moyar-Bhavani界线内的Wynad金矿田（WGF）-一个元古代的跨壳剪切带中的石英脉内蕴藏着金，这些石英脉沿该区域的介观断层和剪切带布置。石英脉切开了乡村岩石的区域结构，表明这些脉形成于地壳剪切的后构造和后变质期。在石英和伴生的硫化物矿物中可以看到作为可见斑点的金或间隙晶粒和细纹，这表明发生了多个矿化事件。在金-石英脉上进行的流体包裹体研究表明，H_2O-CO_2的两相一次夹杂物，H_2O-CO_2的假二次夹杂物和水性次生夹杂物频繁发生。对不同样品进行的显微热学研究表明，与水相相关的CO_2成分接近纯，熔融温度接近-56.6℃。一次和二次次生包裹体的包合物熔融温度表明，流体的盐度低至中度（2-14 wt％NaCl当量）。一次和二次次生夹杂物的均质温度分别在250-330℃和230-300℃之间。次级含水夹杂物的均质温度低得多，介于130和220℃之间。由微热测量数据计算的流体密度在0.8和1.0g / cm〜3之间。与这些流体密度有关的等渗线在0.5和2.9 kbars的压力范围内截留了俘获温度。使用四极质谱仪对选定的样品进行了流体包裹体气体分析。分析表明，流体包裹体主要为H_2O和CO_2，少量N_2和CH_4，与我们的目测分析数据密切相关。我们认为，负责Wynad金矿化的流体是从H_2O-CO_2流体演化而来，并在300-350℃的温度下析出了金，这是由于流体进入剪切区时压力和温度突然下降所致。

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