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首页> 外文期刊>Ore Geology Reviews: Journal for Comprehensive Studies of Ore Genesis and Ore Exploration >P-T conditions of mineralization in the Jonnagiri granitoid-hosted gold deposit, eastern Dharwar Craton, southern India: Constraints from fluid inclusions and chlorite thermometry
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P-T conditions of mineralization in the Jonnagiri granitoid-hosted gold deposit, eastern Dharwar Craton, southern India: Constraints from fluid inclusions and chlorite thermometry

机译：印度南部Dharwar Craton东部Jonnagiri粒状金矿床的成矿条件：流体包裹体和亚氯酸盐温度计的制约

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摘要

Gold mineralization at Jonnagiri, Dharwar Craton, southern India, is hosted in laminated quartz veins within sheared granodiorite that occur with other rock units, typical of Archean greenstone-granite ensembles. The proximal alteration assemblage comprises of muscovite, plagioclase, and chlorite with minor biotite (and carbonate), which is distinctive of low- to mid-greenschist fades. The laminated quartz veins that constitute the inner alteration zone, contain muscovite, chlorite, albite and calcite. Using various calibrations, chlorite compositions in the inner and proximal zones yielded comparable temperature ranges of 263 to 323 deg C and 268 to 324 deg C, respectively. Gold occurs in the laminated quartz veins both as free-milling native metal and enclosed within sulfides. Fluid inclusion microthermometry and Raman spectroscopy in quartz veins within the sheared granodiorite in the proximal zone and laminated auriferous quartz veins in inner zone reveal the existence of a metamorphogenic aqueous-gaseous (H_2O-CO_2-CH4-l-salt) fluid that underwent phase separation and gave rise to gaseous (CO_2-CH4), low saline (~5 wt. percent NaCl equiv.) aqueous fluids. Quartz veins within the mylonitized granodiorites and the laminated veins show broad similarity in fluid compositions and P-T regime. Although the estimated P-T range (1.39 to 2.57 kbar at 263 to 323 deg C) compare well with the published P-T values of other orogenic gold deposits in general, considerable pressure fluctuation characterize gold mineralization at Jonnagiri. Factors such as fluid phase separation and fluid-rock interaction, along with a decrease in f(O_2), were collectively responsible for gold precipitation, from an initial low-saline metamorphogenic fluid. Comparison of the Jonnagiri ore fluid with other lode gold deposits in the Dharwar Craton and major granitoid-hosted gold deposits in Australia and Canada confirms that fluids of low saline aqueous-carbonic composition with metamorphic parentage played the most dominant role in the formation of the Archean lode gold systems.
机译：印度南部Dharwar Craton的Jonnagiri的金矿化位于剪切的花岗闪长岩中的层状石英脉中，该脉状与其他岩石单元（典型的太古宙绿岩-花岗岩群）一起出现。近端蚀变组合包括白云母，斜长石和绿泥石以及少量的黑云母（和碳酸盐），这是低至中绿片期褪色的特征。构成内部蚀变带的层状石英脉包含白云母，绿泥石，钠长石和方解石。使用各种校准，内部和近端区域中的亚氯酸盐成分分别产生了263至323摄氏度和268至324摄氏度的可比较温度范围。金以自由研磨的天然金属形式存在于层状石英脉中，并包裹在硫化物中。近区剪切花岗闪长岩内石英脉和内层叠层含金石英脉的流体包裹体热计量法和拉曼光谱显示，存在发生相分离的变质含水气态（H_2O-CO_2-CH4-l-盐）流体并生成气态（CO_2-CH4），低盐分（约5重量％NaCl当量）的水性流体。髓质化花岗闪长岩中的石英脉和层状脉在流体成分和P-T模式方面显示出广泛的相似性。尽管估计的P-T范围（263至323摄氏度时为1.39至2.57 kbar）与一般已公布的其他造山金矿床的P-T值相比具有很好的对比，但是，宽大的压力波动是Jonnagiri的金矿化特征。流体相分离和流体-岩石相互作用以及f（O_2）减少等因素共同导致了金矿从最初的低盐变质流体中析出。将Jonnagiri矿液与Dharwar Craton中的其他矿床金矿床以及澳大利亚和加拿大的主要花岗岩类金矿床进行比较，证实了低盐含量的含水碳质流体与变质的亲本质在太古宙岩的形成中起着最主要的作用。洛德金系统。

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