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

Dilles，J./里德，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。比尤特是巨型斑岩铜钼岩浆热液存款的绝佳范例，100多年地下开采的数据和样品加上数百个钻孔，包括11个1.5至2.3公里深的垂直孔，为系统提供了特殊的访问。 Butte已成为现代对成矿过程的许多理解的基础，我们的目标是通过应用新的和最先进的分析技术，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了产生矿化作用的斑岩岩浆大约在7600万至6800万年前就位，但热液矿石流体和岩石在6400万至6100万年前冷却到低于300摄氏度。 应用额外的同位素测年（使用U-Pb，Ar-Ar和Re-Os）将使我们能够理解这种年龄差异。 我们早期对氢和氧同位素的研究表明，岩浆卤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）。 这些发现将通过应用最先进的技术（激光-ICP-MS和阴极发光）对石英中捕获的矿石流体的微米级样品进行放大，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剖面图，说明一个巨大的岩浆-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.