Collaborative Research: Pressure Decrease as a Cause of Quartz and Molybdenite Vein Mineral Precipitation in Magmatic-Hydrothermal Systems

合作研究：压力降低是岩浆热液系统中石英和辉钼矿脉矿物沉淀的原因

• 批准号: 0440324
• 负责人: Scott Wood
• 金额: $ 15.13万
• 依托单位: Regents of the University of Idaho
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-02-01 至 2008-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0440324&HistoricalAwards=false
• 关键词: Collaborative; Research; Pressure; Decrease; Cause

In high temperature geothermal systems, and magmatic hydrothermal systems such as the porphyry copper deposit at Butte, Montana, sharp decreases in pressure from lithostatic toward hydrostatic are a likely process for producing quartz veins. The nearly universal occurrence of molybdenite (MoS2) in such quartz veins that likely form by pressure drop and the scarcity of molybdenite in other vein types suggest that molybdenite, like quartz, precipitates by pressure reduction, as opposed to a decrease in temperature. Previous molybdenite solubility experiments have not addressed the role of pressure, thus we do not know a chemical mechanism that would cause molybdenite to precipitate upon a drop in pressure. For quartz, we know its solubility as a function of pressure, but we do not know the origin of quartz mineral and trace element compositions that distinguish pressure-drop vein quartz from other types of quartz. This research addresses pressure decrease as a key process in magmatic hydrothermal systems in three coordinated sub-projects: (1) experiments in the Wood laboratory (U. Idaho) to explore molybdenite solubility as a function of pressure and temperature, (2) in the Reed laboratory (U. Oregon), determine the SEM-cathodoluminescence textures and related trace element compositions, 18O/16O ratios and fluid inclusion properties in natural vein quartz formed by pressure drop and other processes; and (3) apply numerical modeling methods (program CHILLER) to explore the role of pressure-decrease in magmatic hydrothermal systems. Benefits beyond the research itself include the following: a) graduate students and two undergraduates would be trained in the analytical, experimental, and computational methods involved in modern geochemical research; b) the Reed-Wood research collaboration joins complementary strengths in experimental, analytical and numerical modeling geochemistry that would aid future developments in geochemistry; c) a deeper understanding of magmatic hydrothermal processes is important for mineral exploration and for future energy extraction from high-temperature (400 degrees C), high-yield geothermal systems, such as that now being drilled in Iceland.

在高温地热系统和岩浆热液系统中，例如蒙大拿州比尤特的斑岩铜矿床，压力从静岩到静水的急剧下降是产生石英脉的可能过程。 在此类石英脉中，辉钼矿 (MoS2) 几乎普遍存在，很可能是由压降形成的，而其他脉类型中辉钼矿的稀缺表明，辉钼矿与石英一样，是通过压力降低而不是温度降低而沉淀的。 以前的辉钼矿溶解度实验没有解决压力的作用，因此我们不知道在压力下降时导致辉钼矿沉淀的化学机制。 对于石英，我们知道其溶解度与压力的函数关系，但我们不知道石英矿物的起源和微量元素成分，这些成分将压降脉石英与其他类型的石英区分开来。这项研究将压力降低作为岩浆热液系统中的一个关键过程，通过三个协调的子项目来解决：（1）在伍德实验室（美国爱达荷州）进行的实验，探索辉钼矿溶解度与压力和温度的函数关系，（2）在Reed实验室（美国俄勒冈州），测定压降等过程形成的天然脉石英的SEM-阴极发光结构和相关微量元素组成、18O/16O比值和流体包裹体性质； (3)应用数值模拟方法（程序CHILLER）探索岩浆热液系统中压力降低的作用。 研究本身之外的好处包括： a) 研究生和两名本科生将接受现代地球化学研究中涉及的分析、实验和计算方法的培训； b) Reed-Wood 研究合作结合了实验、分析和数值模拟地球化学方面的互补优势，这将有助于地球化学的未来发展； c) 更深入地了解岩浆热液过程对于矿物勘探和未来从高温（400 摄氏度）、高产地热系统（例如目前在冰岛钻探的地热系统）中提取能源非常重要。