Timing of Gold and Arsenic Sulfide Mineral Deposition at the Getchell Carlin-Type Gold Deposit, North-Central Nevada
Timing of Gold and Arsenic Sulfide Mineral Deposition at the Getchell Carlin-Type Gold Deposit, North-Central Nevada
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DOI：
10.2113/gsecongeo.96.1.75
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发表时间：
2001
期刊：
影响因子：
5.8
通讯作者：
J. Cline
中科院分区：
文献类型：
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作者：
J. Cline
在盖特沃勒卡林型金矿存款的预金矿化包括石英和基本金属脉矿化与侵入白垩纪花岗闪长岩股票。矿脉含有少量黄铁矿和微量黄铜矿、毒砂、方铅矿和闪锌矿。黄铁矿中等粗，在薄片上，具有高起伏，抛光良好，破碎，并被金矿组合局部胶结。白色云母与花岗闪长岩侵入体附近的脉有关。通过样品的火试金分析或黄铁矿的电子探针分析，没有观察到或检测到金。微探针分析表明，前黄铁矿具有近化学计量的组成。可变的，低砷存在于黄铁矿中的样品叠加了金矿化。二次离子质谱（西姆斯）分析检测到微量金的粗，近化学计量的黄铁矿叠印样品。金矿阶段矿化作用使前金矿脉组合破碎并胶结。金矿阶段组合由富金、砷黄铁矿和白铁矿组成，周围包裹有碧玉状石英和晶簇状石英，以及局部晚期的萤石、雌黄和硅锌矿。碧玉和矿石黄铁矿一致的空间组合反映了它们的近同期形成。矿石中的黄铁矿以细小、不规则的颗粒或在早期的无金黄铁矿上的边缘出现。在薄片中，黄铁矿明显清晰，具有低抛光浮雕和差抛光。西姆斯和电子探针分析表明，黄铁矿通常含有8至11%（重量）的砷和多达2,400 ppm的金。在矿石阶段接近尾声时，萤石、雌黄和镓铁矿在断层或石灰岩溶解形成的开阔空间中局部沉淀。成矿后期矿化主要为充填在开阔空间中的雄黄和方解石，少量石英、辉锑矿和草莓状黄铁矿。雄黄与成矿期石英、萤石和硅铝石的自形晶面一致。方解石填充了大部分剩余的开放空间，并符合自形晶面的石英，萤石和雄黄。重要的纹理观察反驳了早期的解释，即金矿化和砷矿物形成为两个独立的事件，相隔4000万年。在少数含金黄铁矿的矿期石英与方解石、雄黄接触的地区，雄黄、方解石包裹着含金黄铁矿颗粒。远离这些接触带的块状雄黄和方解石不含含金黄铁矿。雄黄、方解石和碧玉中的黄铁矿矿石的存在需要这些矿物的紧密计时，并表明没有主要的时间中断来分隔矿石阶段和晚期矿石阶段的矿物沉积。相反，纹理表明，成矿阶段和晚期成矿阶段是作为一个单一的、不断演化的热液系统的一部分形成的。较年轻矿物在较老矿物保存完好的自形面上的连续过度生长支持了金矿阶段向晚期矿石阶段的连续演化。这些结果是一致的流体包裹体，表明共生连续矿物沉淀的含水成矿流体具有一致的盐度和气体含量，但在下降的温度。结果表明，在误差范围内，34，39，和42 Ma的年龄测定的萤石和galkhaite在Gettera和冰长石在附近的Twin Creeks矿，分别最接近的时间在Gettera的金沉积。
Pregold mineralization at the Getchell Carlin-type gold deposit includes quartz and base metal vein mineralization associated with intrusion of a Cretaceous granodiorite stock. The veins contain minor pyrite and trace chalcopyrite, arsenopyrite, galena, and sphalerite. The pyrite is moderately coarse and, in thin section, has high relief, is well polished, and is fractured and locally cemented by the gold ore assemblage. White micas are associated with veins near the granodiorite intrusion. Gold was not observed or detected by fire assay analyses of samples or electron microprobe analyses of pyrites. Microprobe analyses show that pregold pyrites have near-stoichiometric compositions. Variable, low arsenic is present in pyrite in samples overprinted by gold mineralization. Secondary ion mass spectrometry (SIMS) analyses detected trace gold in the coarse, near-stoichiometric pyrite in overprinted samples. The pregold vein assemblage was fractured and cemented by gold ore-stage mineralization The gold ore-stage assemblage consists of gold- and arsenic-enriched pyrite and marcasite encompassed by jasperoid and drusy quartz, and local late fluorite, orpiment, and galkhaite. The consistent spatial association of jasperoid and ore pyrite reflects their near-contemporaneous formation. The ore pyrite occurs as either fine, irregularly shaped grains, or rims on earlier, gold-free pyrite. In thin section, the pyrite is visibly distinct and has a low polishing relief and a poor polish. SIMS and electron microprobe analyses show that ore pyrites commonly contain 8 to 11 wt percent arsenic and as much as 2,400 ppm gold. Near the end of the ore stage, fluorite, orpiment, and galkhaite precipitated locally in open space created by faulting or limestone dissolution. Late ore-stage mineralization consists dominantly of open space-filling realgar and calcite, with minor quartz, stibnite, and framboidal pyrite. Realgar conforms to euhedral crystal faces of ore-stage quartz, fluorite, and galkhaite. Calcite filled most remaining open space and conforms to euhedral crystal faces of quartz, fluorite, and realgar. Significant textural observations argue against an earlier interpretation that the gold mineralization and arsenic minerals formed as two discrete events separated by 40 m.y. In a few areas where calcite and realgar are in contact with ore-stage quartz containing gold-bearing pyrite, realgar and calcite enclose gold-bearing pyrite grains. Massive realgar and calcite distal from these contacts do not contain the gold-bearing pyrite. The presence of ore pyrite in realgar, calcite, and jasperoid requires close timing of these minerals and shows that there is no major time break separating ore-stage and late ore-stage mineral deposition. Textures indicate, instead, that the ore stage and late ore stage formed as part of a single, evolving hydrothermal system. The consistent successive overgrowth of younger minerals on perfectly preserved euhedral faces of older minerals supports the continuous evolution of the gold ore stage into the late ore stage. These results are consistent with fluid inclusions that indicate that paragenetically successive minerals precipitated from an aqueous ore fluid with consistent salinity and gas contents but at declining temperatures. Results show that, within error, the 34, 39, and 42 Ma ages determined for fluorite and galkhaite at Getchell and adularia at the nearby Twin Creeks mine, respectively, most closely approximate the timing of gold deposition at Getchell.