Fluid characteristics of vein and altered wall rock in Archean mesothermal gold deposits
Fluid characteristics of vein and altered wall rock in Archean mesothermal gold deposits
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太古宙中温温金矿脉及蚀变围岩流体特征
DOI：
10.2113/gsecongeo.86.3.667
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发表时间：
1991
期刊：
影响因子：
--
通讯作者：
M. Gagnon
中科院分区：
文献类型：
--
作者：
J. Guha;H. Lu;B. Dubé;F. Robert;M. Gagnon
在太古代中生代金矿床附近常观察到某些蚀变趋势。本研究旨在通过固体探针质谱法监测流体包裹体成分的变化：（1）建立和验证流体-岩石相互作用期间流体成分的系统变化，（2）表征矿脉和围岩中流体的成分和行为，以便建立它们之间的联系，（3）阐明流体不可渗透性在金沉积中的作用的新认识，（4）仔细研究结果以供勘探使用。一个含有大量游离黄金的大型存款（瓦尔d9奥尔的西格玛矿），第二个存款，游离金含量较少（奇布加毛的Norbeau矿）和第三个金矿化区，围岩蚀变，几乎没有矿脉（奇布加毛的Tadd前景）。对不同的蚀变带和每个地点的金矿化进行了仔细的流体包裹体取样。在大多数情况下，CO2-H2O的不混合程度不同。质谱结果表明，在蚀变过程中，所有站点的所有世代的包裹体都含有CO2和H2O。对于蚀变容存款的减少X（分CO2）可以映射向外的矿化带。最引人注目的结果是，流体包裹体与主矿化幕在西格玛表现出几乎完全分离成CO2和H2O端成员。这可以解释为极端流体压力波动的结果。这一特征在Norbeau矿脉中是不存在的，那里的游离金含量非常有限。对Doyon矿的高品位矿石进行的一次测试产生了类似于Sigma的模式。我们认为，极端压力波动是有限的脉托管矿床，如Norbeau和金沉淀基本上从流体-岩石矿物相互作用。不混合是最可能的原因，自由金沉积。成矿系统在游离金沉积时可能经历了重大的断裂事件，本研究表明，高CO2/H2O比值与蚀变岩型矿床中的金矿化有关，但由于CO2-H2O流体的不混合模式不同，该比值在脉型矿床中可能是不可靠的指标。递减法是一种快速、有效的确定CO2-H2O不混合和富金矿化潜力的方法.
Certain trends in alteration are commonly observed near Archean mesothermal gold deposits. This study was designed to monitor the changes in composition of fluid inclusions using solid probe mass spectrometry by: (1) establishing and verifying systematic changes in the composition of the fluid during fluid-rock interaction, (2) characterizing the composition and behavior of fluids in the vein and the wall rock in order to establish a link between them, (3) elucidating new insights on the role of fluid immiscibility in gold deposition, and (4) scrutinizing the results for potential use in exploration.Three representative sites of gold mineralization were chosen: a large deposit with appreciable amounts of free gold (Sigma mine in Val d9Or), a second deposit with a smaller amount of free gold (Norbeau mine in Chibougamau), and a third area of gold mineralization with altered wall rock and little veining (Tadd prospect in Chibougamau). Fluid inclusions were carefully selected to sample different alteration zones and the gold mineralization at each site. In most of the cases, varying degrees of unmixing of CO 2 -H 2 O were noted.Mass spectra results show that during alteration all generations of inclusions at all sites contained CO 2 and H 2 O. For the alteration-hosted deposit a decrease in X (sub CO 2 ) could be mapped outward from the mineralized zone. The most striking result was that fluid inclusions associated with the main mineralizing episode at Sigma showed a nearly complete segregation into CO 2 and H 2 O end members. This can be interpreted as the result of extreme fluid pressure fluctuations. This characteristic was absent from the Norbeau veins where free gold exists in very limited amounts. A test on a high-grade ore shoot from the Doyon mine resulted in a pattern similar to Sigma. We suggest extreme pressure fluctuations were limited in vein-hosted deposits like Norbeau and gold was precipitated essentially from fluid-rock mineral interaction. Unmixing was the most likely cause of free gold deposition. Mineralizing systems may have undergone major fracturing events at time of free gold deposition.This study suggests high CO 2 /H 2 O ratios are related to gold mineralization in altered rock-hosted deposits but that the ratio may be an unreliable guide in vein-hosted deposits because of the variable unmixing pattern of CO 2 -H 2 O fluids. Decrepitometry may prove a useful and rapid method for identifying CO 2 -H 2 O unmixing and bonanza gold potential.