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

地壳中的岩浆热液流体在某些情况下运输和沉积矿石金属，而在其他情况下，它们将热水输送到用于发电的高温地热系统中。矿物究竟是如何在这些环境中沉淀的还不太清楚，因为这个过程在深度和时间尺度上运作，无法直接观察。为了了解岩石裂缝是如何、何时以及在哪里形成的，然后被矿物质（尤其是石英）填满，这项研究的研究人员正在检查地球表面暴露的大型矿床中的矿脉。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Butte的大型和特征良好的热液系统作为研究岩浆热液脉如何充满石英，硫化物和磁铁矿的天然实验室。通过(1)绘制石英占主导地位的矿脉的分布图和邻近矿脉的主岩蚀变变化，(2)利用一套分析工具（SEM、SEM- cl、SEM- ebsd和EPMA）分析石英矿脉的结构和成分，(3)利用微量元素和流体包裹体测温法估算矿物形成的温度和压力，研究矿脉形成的机制和时间尺度。(4)在实验室进行热液石英生长实验，评估晶体生长速率对ti -in-石英温度计的影响。结合SEM-CL结构（斑纹与带状自面体）、EBSD（定位晶体取向）、流体包裹体均一温度，以及EPMA中ti -in-石英、zr -in-金红石和ti -in-黑云母的P-T解释，这些数据集将约束流体流动、传热和石英沉淀的相互作用，为岩浆热液系统的工作方式提供新的见解。

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.