南泥湖-三道庄钼(钨)矿床中矽卡岩的形成过程及其与钼钨矿化的关系
The formation process and Mo (W) mineralizaton of the skarn in the Nannihu-Sandaozhuang Mo (W) deposit
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摘要: 通过野外地质、光学显微镜以及背散射（BSE）电子图像的观察，南泥湖-三道庄钼（钨）矿床中矽卡岩的形成过程为：第一期流体首先与靠近岩体的大理岩发生反应生成硅灰石、钙铁榴石、钙铝榴石、钙铁辉石和透辉石，当流体继续向外运移遇到灰岩时，直接将其交代形成透辉石矽卡岩或曲卷纹层状透辉石矽卡岩；第二期流体则沿裂隙向围岩中呈面型分布，叠加交代第一期矽卡岩化过程。据此，石榴子石和辉石可以划分为两个世代，第一世代石榴子石（Gro3-82And15-96）呈斑点状，第一世代辉石（Di18-86Hd13-70Jo0-13）可与斑点状石榴子石共生，也可与斜长石（Ab55-70An30-44）共生；第二世代石榴子石（Gro23-58And37-74）呈面型分布，第二世代辉石（Di0-68Hd28-84Jo3-16）沿裂隙呈面型向围岩中展布。第一世代石榴子石和辉石在空间上分布范围较第二世代广。钼钨矿化在矽卡岩的最早阶段即已开始，贯穿整个矽卡岩的形成过程，引起钼钨沉淀的原因可能是具有较高钼钨含量的流体与围岩发生反应时引起的局部还原性环境。Abstract: Based on field observation and microscopic and backscattered electron (BSE) images, the authors recognized a two-stage formation process of the skarn in the Nannihu-Sandaozhuang Mo (W) deposit. At the first stage, the fluid reacted with marble to form wollastonite, andradite, grossularite, hedenbergite and diopside. As the fluid migrated outward, the dark limestone was replaced by diopside skarn or wrigglite diopside skarn. At the second stage, the fluid spread into the wall rock along fractures to form new skarn which was superimposed on the earlier skarn. According to these observations, the skarn minerals such as garnet and pyroxene could be divided into two generations. The first generation of garnet GrtI) (Gro3-82And15-96) is spot-like in wollastonite marble or skarn, and the first generation of pyroxene (PxI) (Di18-86Hd13-70Jo0-13) could intergrow with GrtI in wollastonite marble or skarn and with plagioclase (Ab55-70An30-44) in wrigglite diopside skarn. The second generation of garnet (GrtII) (Gro23-58And37-74) and the second generation of pyroxene (PxII) (Di0-68Hd28-84Jo3-16) were superimposed on GrtI and PxI with smaller space area. The mineralization of molybdenite and scheelite commenced at the very beginning of skarnization and covered the whole skarn formation process. The local reducing environment, induced by the reaction between the fluid with adequate concentration of Mo and W elements and the wall rocks might have triggered metal precipitation.
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Key words:
- eastern Qinling /
- western Henan Province /
- Sandaozhuang /
- skarn /
- molybdenite
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