Collaboration: Temporal Evolution of Hydrothermal Fluid Compositions and Construction of a 3 Dimensional Geologic Model for the Giant Butte Magmatic-Hydrothermal Ore Deposit

EAR-0001230 和 0001272Dilles, J./Reed, M. 蒙大拿州巴特区拥有北美最大的铜储量，也是世界上最大的铜和银生产国之一。 Butte 是巨型斑岩铜钼岩浆热液矿床的绝佳范例，其中来自 100 多年地下采矿的数据和样本以及数百个钻孔（包括 11 个深度为 1.5 至 2.3 公里的垂直孔），为进入该系统提供了特殊的途径。 比尤特已成为现代理解成矿过程的基础，我们的目标是通过应用新的最先进的分析技术来建立改进的假设，包括热液矿石与岩浆的联系。 在研究的完成阶段，我们使用同位素测年技术确定，产生矿化的斑岩岩浆形成于大约 76 至 6800 万年前，但热液矿石流体和岩石在 64 至 6100 万年前冷却至 300 摄氏度以下。 额外同位素测年（使用 U-Pb、Ar-Ar 和 Re-Os）的应用将使我们能够了解这种年龄差异。 我们早期对氢和氧同位素的研究表明，岩浆盐水产生了高温铜钼矿石（黑云母蚀变）以及后来的铁硫化物（绢云母蚀变）。 通过对石英中捕获的矿石流体的微米级样品应用最先进的技术（激光ICP-MS和阴极发光）来扩大这些发现，以确定各种矿石流体的温度、压力和化学成分。我们计划将地质学、地球化学、热液蚀变矿物学和矿石矿物学综合成一系列地图和横截面，以说明巨大岩浆-热液系统的三维空间和时间演化。

EAR-0001230 & 0001272Dilles, J./Reed, M.The Butte district, Montana, contains North America's largest copper reserves and is among the world's largest producers of copper and silver. Butte is a superb example of a giant porphyry Cu-Mo magmatic-hydrothermal ore deposit where data and samples from more than 100 years of underground mining plus hundreds of drill holes, including 11 vertical holes of 1.5 to 2.3 km depth, provide exceptional access to the system. Butte has served as the basis for much of modern understanding of ore formation processes, and our goal is to build improved hypotheses, that include the links of hydrothermal ores to magmas, via application of new and state-of-art analytical techniques. In the completed phase of research, we used isotopic dating techniques to establish that porphyry magmas that produced mineralization were emplaced about 76 to 68 million years ago, but that hydrothermal ore fluids and rocks cooled to less than 300 degrees C between 64 and 61 million years ago. Application of additional isotopic dating (using U-Pb, Ar-Ar and Re-Os) will enable us to understand this age difference. Our earlier work with isotopes of hydrogen and oxygen shows that magmatic brines produced high-temperature copper-molybdenum ores (biotite alteration) as well as later iron-sulfides (sericitic alteration). Those findings will be enlarged by application of state-of-the-art techniques (laser-ICP-MS and cathodoluminescence) on micrometer-scale samples of ore fluids trapped in quartz to establish temperature, pressure, and chemical composition of various ore fluids. We plan to synthesize the geology, geochemistry, and hydrothermal alteration mineralogy, and ore mineralogy into a series of maps and cross-sections that illustrate the three-dimensional spatial and temporal evolution of a giant magmatic-hydrothermal system.