Formation of Magmatic-hydrothermal Veins: Interpreting Quartz Textures and Vein Mineral Assemblages in the Butte, Montana porphyry Copper System

地壳中的岩浆热液在一些环境中运输和储存矿石金属，在其他环境中，它们将热水输送到用于发电的高温地热系统中。矿物在这些环境中究竟是如何沉淀的还不是很清楚，因为这些过程是在无法直接观察到的深度和时间尺度上进行操作的。为了了解岩石破裂是如何形成的，何时何地形成，然后填充矿物，特别是石英，这项研究中的研究人员正在检查地球表面暴露的一个大型矿藏中的矿脉。该奖项支持的研究包括绘制矿脉模式和确定矿物组合，然后成像晶体的结构，测量晶体中流体的性质，以及确定这些晶体中的微量元素丰度。这些测量揭示了晶体的温度、深度和生长历史。在这项研究中，蒙大拿州巴特的大型热液系统作为一个天然实验室，研究岩浆热液矿脉如何充填石英、硫化物和磁铁矿。通过(1)填图以石英为主的脉的分布和与这些脉相邻的围岩蚀变的变化，(2)利用一套分析工具(扫描电子显微镜、扫描电子显微镜、扫描电子显微镜和电子探针)分析石英脉的结构和成分，(3)利用微量元素和流体包裹体测温法估计成矿的温度和压力，以及(4)在实验室进行热液石英生长实验，以评估晶体生长速度对钛In-石英温度计的影响。来自EPMA的扫描电子显微镜-化学发光结构(斑点状与条带状)、EBSD(解决晶体取向)、流体包裹体均一化温度以及钛在石英、钛在金红石和钛在黑云母中的P-T解释的组合数据集将限制流体流动、热传递和石英沉淀的相互作用，从而为岩浆热液系统的工作提供新的见解。

Magmatic-hydrothermal fluids in the crust transport and deposit ore metals in some settings, and in other settings, they feed hot water into high-temperature geothermal systems used to produce electricity. Exactly how minerals precipitate in these environments is not well understood because the processes operate at depths and on timescales that are not accessible to direct observation. To understand how, when, and where rock fractures form and then fill with minerals, especially quartz, the investigators in this study are examining veins in a large ore deposit exposed on Earth's surface. Studies supported by this award consist of mapping the vein pattern, and determining the mineral assemblages, then imaging the textures of crystals, measuring the properties of fluids trapped in the crystals, and determining the abundances of trace elements within those crystals. These measurements reveal the temperature, depth and growth histories of the crystals.In this study, the large and well characterized hydrothermal system in Butte, Montana serves as a natural laboratory for investigating how magmatic-hydrothermal veins fill with quartz, sulfides and magnetite. The mechanisms and timescales of vein formation are addressed by (1) mapping the distribution of quartz-dominated veins and variations in alteration of the host rock adjacent to these veins, (2) analyzing quartz vein textures and compositions using a suite of analytical tools (SEM, SEM-CL, SEM-EBSD, and EPMA), (3) estimating temperature and pressure of mineral formation using trace element and fluid inclusion thermometry, and (4) conducting hydrothermal quartz growth experiments in the laboratory to assess the influence of crystal growth rate on the Ti-in-quartz thermometer. The combined data set addressing SEM-CL textures (mottled vs. banded euhedral), EBSD (addressing crystal orientations), fluid inclusion homogenization temperatures, and the P-T interpretations of Ti-in-quartz, Zr-in-rutile and Ti-in-biotite from EPMA will constrain the interplay of fluid flow, heat transfer, and quartz precipitation in ways that provide new insights into how magmatic hydrothermal systems work.