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某些情况下运输和存款矿石金属，在其他情况下，它们将热水送入用于发电的高温地热系统。 矿物在这些环境中沉淀的确切方式尚不清楚，因为这些过程在深度和时间尺度上进行，无法直接观察。为了了解岩石裂缝如何、何时、何地形成，然后填充矿物，特别是石英，这项研究的调查人员正在检查暴露在地球表面的一个大型矿床存款的矿脉。 该奖项支持的研究包括绘制矿脉图案，确定矿物组合，然后对晶体的纹理进行成像，测量晶体中捕获的流体的性质，并确定这些晶体中微量元素的丰度。 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且特征良好的热液系统作为一个天然实验室，用于研究岩浆热液脉如何填充石英、硫化物和磁铁矿。通过（1）绘制石英脉的分布图和与这些脉相邻的围岩蚀变的变化，（2）使用一套分析工具分析石英脉的结构和成分，来解决脉形成的机制和时间尺度（3）利用微量元素和流体包裹体测温技术估算成矿温度和压力;（4）在实验室中进行热液石英生长实验以评估晶体生长速率对石英中钛温度计的影响。结合数据集解决SEM-CL纹理（斑驳与带状自形），EBSD（解决晶体取向），流体包裹体均一化温度，和P-T解释的钛石英，锆金红石和钛黑云母从EPMA将限制流体流动，热传递和石英沉淀的相互作用的方式，提供新的见解如何岩浆热液系统的工作。

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.