Trace Element Characteristics of Zircon: A Means of Assessing Mineralization Potential of Granitoid Intrusions and Porphyries

智力优势。在全球范围内，会聚边缘环境中的含水和富硫弧岩浆在成因上与产生斑岩Cu（-Mo-Au）、浅成热液Au（-Ag）和各种其他类型矿床类型的岩浆热液流体相关。虽然理论上一个平均的弧型花岗闪长岩可以产生这样的存款，大多数侵入弧壳不产生矿床和经济贫瘠。中到中岩浆都是强烈氧化的，尽管它们在上陆壳中侵位和结晶，但它们最终来自更深的幔源玄武质到安山质岩浆。系统研究了典型矿化和非矿化侵入体中锆石的微量元素组成和年龄，以评价该矿物作为矿化示踪剂的实用性。来自美国西部和南美洲一系列特征良好的斑岩和相关系统的样品将被作为研究的目标。众所周知，锆石是一种坚固的矿物，通过随后的冷却，再加热或热液事件保持其岩浆成分。采用离子探针（SHRIMP-RG）和激光烧蚀-电感耦合等离子体质谱（LC-MS）技术，可以对锆石中Hf、Y、Sc、V、Ti等微量元素和稀土元素进行准确的原位分析。此外，U-Th-Pb同位素年龄信息可以同时或顺序收集。Hf/Zr比值在岩浆结晶过程中增加，温度可以用锆石中钛地质温度计监测。因此，锆石提供了机会，以限制时间-温度-成分路径的侵入系统。锆石中的稀土元素系统学也将作为侵入岩浆中氧化还原条件的示踪剂进行评价。例如，对智利萨尔瓦多萨尔瓦多侵入体的初步研究表明，与无矿侵入体相比，矿化侵入体中锆石中测得的Eu异常较小，这可能是由于在不存在斜长石的中地壳或地壳深部，氧化态较高和岩浆分异共同作用的结果。这一提议将有助于了解导致斑岩型矿床形成的过程，斑岩型矿床是全球铜和钼的主要来源，也是重要的副产品金、银和其他金属，全球年产量超过1 000亿美元。该项目还将支持一个博士后研究人员和支持教学工作的PI？在经济地质学和地球化学在俄勒冈州立大学，是必要的培训，为地球科学家需要寻找，开采和修复矿床。这项工作还将涉及与工业界的合作，为学生获得矿业实践经验提供新的途径，并为未来的合作努力开辟道路。

Intellectual Merit. Globally, hydrous and sulfur-rich arc magmas in convergent margin settings are genetically related to magmatic-hydrothermal fluids that produce porphyry Cu(-Mo-Au), epithermal Au(-Ag), and a variety of other types of mineral deposits types. Although in theory an average arc-type granodiorite can generate such a deposit, most intrusions in arc crust do not produce mineral deposits and are economically barren. intermediate to silicic magmas are both strongly oxidized and, although they are emplaced and crystallized in the upper continental crust, they ultimately derive from deeper seated mantle-sourced basaltic to andesitic magmas. A systematic study of the trace element compositions and ages of zircons from representative mineralized and barren intrusions is proposed to evaluate the utility of this mineral as a tracer for mineralization. Samples from a range of well characterized porphyry and related systems in the Western USA and South America will be targeted for study. Zircon is well-known as a robust mineral that retains its magmatic composition through subsequent cooling, reheating, or hydrothermal events. A suite of trace elements including Hf, Y, Sc, V, Ti, and the rare earth elements can be accurately analyzed in situ in zircon via the ion microprobe (SHRIMP-RG) and laser ablation-ICP-MS methods. Additionally, U-Th-Pb isotopic age information can be collected simultaneous or sequentially. The Hf/Zr ratio increases during crystallization of magma, and temperature can be monitored using the Ti-in-zircon geothermometer. Thus, zircon offers the opportunity to constrain time-temperature-composition paths for intrusive systems. The rare earth element systematics in zircons will also be evaluated as a tracer of redox conditions in the intrusive magmas. For example, initial work on porphyry intrusions at El Salvador, Chile, indicates that the Eu anomaly measured in zircons from mineralized intrusions is small compared to barren intrusions, and likely results from a combination of higher oxidation state and magmatic differentiation in the middle or deep crust where plagioclase is absent.Broader Impacts. This proposal will contribute to understanding of the processes that lead to formation of porphyry-type mineral deposits, which are the principal global sources of copper and molybdenum, and significant byproduct gold, silver, and other metals with annual global production in excess of $100 billion. The project will also support one post-doctoral researcher and support teaching efforts by both PI?s in economic geology and geochemistry at OSU that are essential training for geoscientists required to find, exploit and remediate mineral deposits. The work will also involve collaboration with industry, providing new pathways for students to obtain practical experience in the minerals industry and opening the way for future collaborative efforts.