Collaborative Research on Fluid Pathways, and Metal Transport and Deposition in Carlin-Type Gold Deposits: Insights From the Getchell System

这项由内华达大学拉斯维加斯分校和内华达大学雷诺分校的研究人员开展的合作研究旨在利用矿业公司钻探的12,000多个孔的数据和复杂的3D建模软件，为最先进的原位微观分析技术识别样品，从而开发内华达州北部盖彻尔区经典卡林型金矿的时空地质和地球化学框架。利用钻孔和模拟软件，我们将建立一个全面的三维模型，从中我们将解释含金热液所走的流体路径。然后，我们将在模型中添加第四个维度，即时间，通过整合对沿解释的流体路径位置的不同阶段的石英、黄铁矿和其他硫化物矿物的详细微观分析研究。具体地说，研究人员将利用阴极发光、电子探针化学分析、激光烧蚀电感耦合等离子体质谱化学分析和原位离子探针同位素分析，记录石英和黄铁矿的结构以及同位素和微量元素组成如何随着时间和空间的任何给定时间点发生变化。石英和黄铁矿的同位素和微量元素组成基本上是热液的指纹，对各种矿物的分析将使更好地追踪成矿流体的通道和演化。通过比较流体路径上不同位置的不同样品中的这些“指纹”，可以推断形成含金黄铁矿和石英的热液的组成在时间和空间上是如何变化的。还计划研究以流体包裹体形式捕获在石英中的热液样品，以推断成矿流体的温度和成分如何沿流体路径在时间和空间上变化。根据这些数据，研究人员将能够通过确定流体进入、穿过和离开高品位矿带时的物理和化学演化，来约束矿体高品位部分的沉积机制。内华达州的卡林型金矿约占全球黄金年产量的8%，使美国成为世界第二大黄金生产国。尽管它们很重要，但它们的起源的几个方面仍然是个谜。这项研究的结果不仅将有助于更好地了解卡林型矿床的成因，还将有助于对更广泛的地球过程的洞察。这个项目将促进我们对地壳上部岩石中被加热和伸展的热液循环所涉及的水文和质量传递的理解。重要的新知识将通过采矿业和研究人员之间的研究伙伴关系产生，采矿业是内华达州第二重要的行业，研究人员包括一名博士后研究员以及研究生和本科生。这一知识将改善内华达州和世界其他地区类似金矿的勘探。项目成果还将有助于政府机构和矿业公司进行矿产潜力评估，并改善政府机构的土地使用决策。

This collaborative study by researchers at the University of Nevada Las Vegas and the University of Nevada Reno aims to develop a time-space geological and geochemical framework of the classic Carlin-type gold deposits of the Getchell district in northern Nevada by utilizing data from more than 12,000 holes drilled by mining companies and sophisticated 3D modeling software to identify samples for state-of-the art in situ micro analytical techniques. With the drill holes and modeling software we will build a comprehensive 3-dimensional model from which we will interpret fluid pathways taken by the gold-bearing hydrothermal fluids. We will then add the fourth dimension, time, to the model by integrating detailed micro analytical studies of various stages of quartz, pyrite, and other sulfide minerals at locations along interpreted fluid pathways. Specifically, the investigators will document how the textures and isotopic and trace element compositions of quartz and pyrite vary with time and at any given point in space, using cathodoluminescence, electron microprobe chemical analyses, laser ablation ICP-MS chemical analyses, and in situ ion probe isotope analyses. The isotopic and trace element composition of the quartz and pyrite are essentially fingerprints of the hydrothermal fluid and analyses of various minerals will allow better tracking of the passage and evolution of the ore fluid. By comparing these "fingerprints" in different samples from different locations along fluid pathways it will be possible to deduce how the composition of the hydrothermal fluid, which formed the gold-bearing pyrite and quartz, varied both in time and space. It is also planned to study samples of the hydrothermal fluid trapped as fluid inclusions in the quartz to deduce how temperatures and compositions of the ore-forming fluid varied in time and space along fluid pathways. From these data the investigators will be able to constrain depositional mechanisms in high-grade portions of the ore bodies by identifying how fluids physically and chemically evolved as they traveled into, through, and out of high-grade ore zones. Carlin-type gold deposits in Nevada account for about 8% of the annual worldwide gold production, making the United States the second largest gold producer in the world. Despite their importance, several aspects of their origin remain enigmatic. The results of this research will not only lead to better understanding of the origin of Carlin-type deposits, but will also lend insights into broader earth processes. This project will advance our understanding of hydrology and mass transfer involved with hydrothermal circulation in upper crustal rocks that were being heated and extended. Important new knowledge will be generated through a research partnership between the mining industry, Nevada's second most important industry, and the researchers, including a post doctoral fellow and graduate and undergraduate students. This knowledge will improve exploration for similar gold deposits in Nevada and other parts of the world. Project results will also contribute to mineral potential assessment by government agencies and mining companies, and improved land use decisions by government agencies.