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

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商之一。Butte是巨型斑岩铜钼岩浆热液矿床的极佳例子，来自100多年地下开采的数据和样品以及数百个钻孔(包括11个1.5至2.3公里深的垂直钻孔)提供了进入该系统的特殊通道。巴特一直是现代许多成矿过程理解的基础，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。在完成的研究阶段，我们使用同位素测年技术确定，产生矿化的斑岩岩浆大约在7600万到6800万年前侵位，但在和6100万年前之间，热液成矿流体和岩石冷却到不到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，岩浆卤水产生了高温铜钼矿(黑云母蚀变)和后来的铁硫化物(绢云母蚀变)。这些发现将通过对困在石英中的微米级矿液样本应用最先进的技术(激光-电感耦合等离子体质谱和阴极发光)来扩大，以确定各种矿液的温度、压力和化学成分。我们计划将地质学、地球化学学、热液蚀变矿物学和矿石矿物学综合成一系列的地图和横截面，以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.