Multiphase methane-rich fluid inclusions in gold-bearing quartz as illustrated at Pontal (Goias, Brazil)
Multiphase methane-rich fluid inclusions in gold-bearing quartz as illustrated at Pontal (Goias, Brazil)
复制标题
含金石英中的多相富甲烷流体包裹体，如庞塔尔（巴西戈亚斯）所示
DOI：
10.1180/minmag.1990.054.375.11
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发表时间：
1990
影响因子：
2.7
通讯作者：
M. Dardenne
中科院分区：
文献类型：
--
作者：
N. Guilhaumou;M. Santos;J. Touray;C. Bény;M. Dardenne
摘要 在Pontal金矿脉中，主要的糖质石英与寡长石、黑云母、角闪石、透闪石-阳起石、硫化物（小于2%）和浸染状天然金伴生。根据流体包裹体的习性、分布以及与金颗粒的空间关系，区分了四种主要类型的流体包裹体。 S 型是原生多相大尺寸（100 至 200 µm）夹杂物，均质化温度（V + L → L）在 350 至 450°C 之间。它们含有菱铁矿和/或方解石和类石墨微晶作为子相。通常与这些内含物相关的是微小（50 至 100 µm）的黑云母或阳起石固体内含物。在大多数这些包裹体中，仅在气相中检测到 CH4。然而，观察到了一些明显的例外情况（CO2/CH4 比率接近 0.85）。 C 型夹杂物晚于金，并且浸染在石英中或沿着横切石英晶界的轨迹出现。它们可能含有苏打石子晶体。 CO2/CH4 比率范围为 0.0 至 0.5。均质温度为 150 至 300°C。 V型主要是气态CH4-H2O包裹体。它们可能以与金颗粒直接相关的小尺寸夹杂物的形式出现。 L 型是晚次生起源的水性两相包裹体。 CO2/CH4 比率的分散可能与捕获时引发金沉淀的氧逸度波动有关。 f O2 随时间的变化可以反映石英沉积过程中氧化还原条件下无缓冲的流体-岩石相互作用。最后，金沉积被解释为发生在高温（500°C）和高压下，与绿片岩和角闪岩相之间的边界条件相一致。
Abstract In the Pontal auriferous lode, dominant saccharoidal quartz is associated with oligoclase, biotite, hornblende, tremolite-actinolite, sulphides (less than 2%), and disseminated native gold. Four main types of fluid inclusion have been distinguished based on their habit, distribution and spatial relation-ship with gold particles. Type S are primary multiphase large sized (100 to 200 µm) inclusions with homogenization temperatures (V + L → L) between 350 and 450°C. They contain siderite and/or calcite and graphite-like microcrystals as daughter phases. Commonly associated with these inclusions are tiny (50 to 100 µm) solid inclusions of biotite or actinolite. In most of these inclusions, only CH4 has been detected in the vapour phase. However some noticeable exceptions were observed (CO2/CH4 ratio near 0.85). Type C inclusions are later than gold and occur disseminated in quartz or along trails that crosscut quartz grain boundaries. They may contain nahcolite daughter crystals. CO2/CH4 ratios range from 0.0 to 0.5. Homogenization temperatures vary from 150 to 300°C. Type V are mainly gaseous CH4-H2O inclusions. They may occur as small-sized inclusions directly associated with gold particles. Type L are aqueous two-phase inclusions of late secondary origin. The scattering of the CO2/CH4 ratios could be related to fluctuations of the oxygen fugacity that triggered gold precipitation at the time of trapping. These variations of f O2 with time could reflect unbuffered fluid-rock interaction with respect to redox conditions during quartz deposition. Finally, gold deposition is interpreted to have occurred at elevated temperature (500°C) and pressure, compatible with boundary conditions between greenschist and amphibolites facies.