Collaborative Research: Magmatism and Mineralization in the Owyhee Mountains, ID: A Case Study of Mid-Miocene Au-Ag Ores and the Emergence of the Yellowstone Hotspot

合作研究：Owyhee山脉的岩浆作用和成矿作用：以中中新世金银矿石和黄石热点的出现为例。俄勒冈州东部、华盛顿州、爱达荷州西南部和内华达州北部的哥伦比亚河-斯蒂恩斯洪水玄武岩火山作用发生在新生的黄石热点的轨道启动时间约16.7 Ma期间。这一岩浆事件与影响泛滥玄武岩省南部(例如俄勒冈高原)的三个现象不谋而合：[1)全区范围内伸展构造活动的焦点地带的发展±泛滥玄武岩岩浆的喷发(例如，内华达裂谷北部和俄勒冈-爱达荷州地块)；[2)众多硅质主导的岩浆系统(例如，McDermitt和Santa Rosa-Calico火山田)；以及[3]丰富的浅成热液金银矿化，(例如，Buckkin-National，Sleeper，Delamar)。PI领导最近的工作表明，以双峰为主的玄武岩-流纹岩岩浆作用和集中伸展作用相结合，导致岩浆系统不仅形成火山口，而且具有多个离散的喷发轨迹和多样化的喷发产品和风格的特征。推测局部的喷发产物和喷发类型包括与镁铁质岩浆一起从地幔运出并就位于浅成热液系统的金银矿石。该模型的有效性将在两个重点地区进行检验，即奥威希山脉(ID)和贾比奇地区(内华达州贾比奇山脉)，那里有极好的暴露中中新世洪水玄武岩熔岩流和浅侵入体、硅质火山和浅成岩产品以及具有重要经济和历史意义的金银矿。将获得野外、岩石学、地球化学、同位素和年代学数据，以评价浅成热液Au-Ag成矿作用与相关岩浆活动的关系。拟议的研究将具体检查局部矿化和硅质岩浆的产生是否受到镁铁质岩浆活动增强时期的刺激。野外、地球化学和地质年代学结果将为人们对中新世中期俄勒冈高原火山活动的时空模式(S)和类型提供额外的约束，这是充分了解这一岩浆事件如何影响北美岩石圈所必需的。这个项目解决了一个根本性的问题，即贵金属来自什么地球储藏库？浅成热液贵金属矿化与镁铁质岩浆活动(特别是泛滥玄武岩)密切相关的假设具有世界范围内的经济意义，并可指导全球贵金属勘探工作。这项拟议的研究将使来自两个EPSCoR机构的学生接触到基本的地质野外工作以及基于实验室的详细分析工作。此外，这项工作将为Owyhee油田地区的动态数字地图提供基础，该地图将用于本科生和研究生课程，以及一系列关于火山学、岩石学和矿石成因的实验室练习。最后，这个项目将为一位年轻的科学家(首席PI)提供宝贵的指导。

Collaborative Research: Magmatism and mineralization in the Owyhee Mountains, ID: A case study of mid-Miocene Au-Ag ores and the emergence of the Yellowstone HotspotIntellectual Merit. Voluminous Columbia River-Steens flood basalt volcanism in eastern Oregon and Washington, southwestern Idaho, and northern Nevada occurred during the proposed ~16.7 Ma initiation of the track for the nascent Yellowstone hotspot. This magmatic event coincided with three phenomena that affected the southern portion of the flood basalt province (e.g. the Oregon Plateau): [1] region-wide development of focused zones of extensional tectonism ± eruption of flood basalt magmas (e.g. the northern Nevada rift and Oregon-Idaho graben); [2] development of numerous silicic dominated magmatic systems (e.g. the McDermitt and Santa Rosa- Calico volcanic fields); and [3] abundant epithermal Au-Ag mineralization, (e.g. Buckskin-National, Sleeper, DeLamar). Recent work by the lead PI suggests that the combination of dominantly bimodal basalt-rhyolite magmatism and focused extension resulted in magmatic systems that were not just caldera-forming, but instead were characterized by multiple discrete eruptive loci and a diversity of eruptive products and styles. It is hypothesized that the eruptive products and styles locally included Au-Ag ores that were transported from the mantle with mafic magmas and emplaced locally in epithermal systems. The validity of this model will be tested in two focus regions, the Owyhee Mountains (ID) and the Jarbidge district (Jarbidge Mountains, NV), where there are excellent exposures of mid-Miocene flood basalt lava flows and shallow intrusive bodies, silicic volcanic and hypabyssal products, and Au-Ag mines that are economically and historically significant. Field, petrographic, geochemical, isotopic, and geochronologic data will be obtained to evaluate the relation of epithermal Au-Ag mineralization to the associated magmatic activity. The proposed research will specifically examine whether local mineralization and silicic magma production was stimulated by periods of enhanced mafic magmatism. The field, geochemical, and geochronologic results will provide additional constraints on the poorly understood spatial-temporal pattern(s) and styles of mid-Miocene Oregon Plateau volcanism, which are needed to fully understand how this magmatic event affected the North American lithosphere.Broader Impacts. This project addresses a fundamental question, namely, in what Earth reservoir do precious metals originate? The hypothesis that epithermal precious metal mineralization is intimately related to mafic magmatism (specifically, flood basalts) has worldwide economic implications, and could guide global precious metal exploration efforts. The proposed research will expose students from two EPSCoR institutions to basic geologic field work as well as detailed, laboratory-based analytical work. Additionally, this work will provide the basis for a dynamic digital map of the Owyhee field area that will be used in undergraduate and graduate courses, as well as a series of laboratory exercises regarding volcanology, petrology, and ore genesis. Finally, this project will provide invaluable mentoring aspects to a young scientist (lead PI).