Mica chemistry as an indicator of oxygen and halogen fugacities in the CanTung and other W-related granitoids in the North American Cordillera
Mica chemistry as an indicator of oxygen and halogen fugacities in the CanTung and other W-related granitoids in the North American Cordillera
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DOI：
10.1130/spe246-p205
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发表时间：
1990
期刊：
影响因子：
--
通讯作者：
W. T. V. Middelaar;J. D. Keith
中科院分区：
文献类型：
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作者：
W. T. V. Middelaar;J. D. Keith
在本章中，我们报告的使用和限制氧和卤素逸度来表征与钨矿床有关的花岗岩类。与钨有关的花岗岩类一般处于中间地球化学地位，演化程度低于锡花岗岩，但比斑岩型铜、钼花岗闪长岩分化程度更高。电子探针分析表明，广东系统中不同族群的黑云母（花岗岩、细晶岩、层状岩、脉岩和矽卡岩）在主元素化学上存在差异。然而，氟-氯截距值表明黑云母中的卤素与一种流体重新平衡。这种再平衡可能是在相对较低的温度（300至350 ℃），但如果流体在冷却过程中没有改变其卤素逸度，则可能是在较高的温度（500 ℃）下。在这两种情况下，这意味着岩浆黑云母的初始卤素含量被热液流体覆盖。细晶岩，远离矿化，具有较低的截距值（较高的氟逸度）的观察可能表明，成矿流体演化的主要黑云母花岗岩体，而不是从浅色相。黑云母中的高亚铁/铁比值、花岗岩中磁铁矿和钛铁矿的缺失以及矽卡岩矿物学特征表明了广东等高品位矿床岩浆热液流体的还原条件。认为岩浆的氧化状态、初始水量和侵位深度对大型钨矿床的形成起着重要作用。
In this chapter we report on the use and limitations of oxygen and halogen fugacities to characterize granitoids associated with tungsten deposits. Tungsten-related granitoids generally occupy an intermediate geochemical position, less evolved than tin granites, but more differentiated than porphyry copper and molybdenum granodiorites. Microprobe analyses of the different populations of biotite in the CanTung system (in granite, aplite, lamprophyre, vein, and skarn) show differences in major-element chemistry. Fluorine-chlorine intercept values, however, indicate that the halogens in the biotites reequilibrated with one fluid. This reequilibration probably was at relatively low temperatures (300 to 350 C), but might have been at higher temperatures (500 C) if the fluid did not change its halogen fugacity during cooling. In both cases, this implies that the initial halogen content of the magmatic biotites is overprinted by the hydrothermal fluid. The observation that an aplite, away from the mineralization, has a lower intercept value (higher fluorine fugacity) may indicate that the mineralizing fluid evolved from the main biotite granite body and not from the leucocratic phase. High ferrous/ferric ratios in biotites, the absence of magnetite and titanite in the granite, and the skarn mineralogy indicate reducing conditions of the magmatichydrothermal fluids of the CanTung and some other high-grade deposits. We propose that the oxidation state of the magma, the amount of initial water, and the depth of emplacement play an important role in the formation of large tungsten deposits.