Identification and significance of CH4-rich fluid inclusions in Langdu skarn Cu deposit, Yunnan Province, China
Identification and significance of CH4-rich fluid inclusions in Langdu skarn Cu deposit, Yunnan Province, China
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DOI：
10.1007/s12594-015-0336-y
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发表时间：
2015-10
影响因子：
1.3
通讯作者：
Tao Ren;M. Ma
中科院分区：
文献类型：
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作者：
Tao Ren;M. Ma
在中甸地区浪都矽卡岩型铜存款矿床中，发现了单相和两相富CH 4流体包裹体。显微测温结果证实，单相CH 4流体包裹体在-118.3 ℃ ~-114.2 ℃之间均质化为液态，而两相富CH 4流体包裹体在-87.5 ℃ ~-84.7 ℃之间部分均质化。激光拉曼显微光谱分析表明，包裹体中的气体成分以CH 4为主，N2含量较少。富CH 4两相流体包裹体可确定成矿过程中的流体温度（300°C ~ 400°C）和压力（1014 bar ~ 1484 bar），表明成矿作用发生在3.8 ~ 4.8 km深处的岩石静压力下。流体包裹体中的CH 4可能是热液与曲嘎寺组碳质板岩发生2C +2 H2O = CH 4 + CO2反应而形成的。CH 4（和/或N2）将极大地扩展气/液不相容性的范围，并将作为还原剂将SO 42-转化为硫化物沉积所必需的阴离子S2-。大量的块状硫化物矿床（黄铜矿、磁黄铁矿）反映了热液流体的物理化学条件，甲烷会引起热液流体的显著变化。
Single-phase CH4and two-phase CH4-rich fluid inclusions were identified at Langdu skarn Cu deposit in Zhongdian area, southwest China. Microthermometric results confirm that the single-phase CH4fluid inclusions are homogenized to liquid from -118.3ºC to -114.2ºC, and two-phase CH4-rich fluid inclusions partly homogenized from -87.5 ºC to -84.7 ºC. Laser Raman micospectroscopic analyses show that vapors of the fluid inclusions are dominant of CH4with minor N2. The two-phase CH4-rich fluid inclusions allow the determination of the fluid temperature (300°C to 400°C) and pressure (1014 bars to 1484 bars) during mineralization, suggesting that ore formation took place at 3.8 to 4.8 km depth under lithostatic pressure. CH4contained in the fluid inclusions most likely formed by the reaction 2C + 2H2O=CH4+CO2between carbonaceous slate from Qugasi Formation and hydrothermal fluids either in situ or during migration. CH4(and/or N2) will greatly expand the field of vapor/liquid immiscibility and will act as reducing agent which transforms SO42–to S2–that is essential anion for sulfide deposition. Numerous massive sulfide deposits (chalcopyrite and pyrrhotite) reflect that physical and chemical condition of hydrothermal fluid and significant change would be caused by CH4.