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

智力上的功绩。在全球范围内，汇聚边缘环境中的含水富硫弧状岩浆与岩浆热液有关，这些热液产生斑岩铜(-Mo-Au)、浅成热液Au(-Ag)和各种其他类型的矿藏。虽然理论上一个普通的弧型花岗闪长岩可以产生这样的矿床，但弧形地壳中的大多数侵入体不会产生矿藏，经济上是贫瘠的。中至硅质岩浆都是强氧化的，虽然它们是在上陆壳侵位和结晶的，但它们最终来自更深的地幔来源的玄武岩到安山质岩浆。对典型矿化和贫化侵入体锆石的微量元素组成和年龄进行了系统的研究，以评价该矿物作为矿化示踪剂的作用。来自美国西部和南美洲一系列具有良好特征的斑岩和相关系统的样本将成为研究的目标。众所周知，锆石是一种坚固的矿物，通过随后的冷却、重新加热或热液事件保留其岩浆成分。采用离子探针(SHRIMP-RG)和激光烧蚀-电感耦合等离子体质谱(ICPS-MS)方法，可对锆石中的Hf、Y、Sc、V、Ti等一系列痕量元素和稀土元素进行现场准确分析。此外，还可以同时或顺序收集U-Th-Pb同位素年龄信息。在岩浆结晶过程中，Hf/Zr比值增大，温度可用钛锆石地质温度计监测。因此，锆石提供了限制侵入系统的时间-温度-组成路径的机会。锆石中的稀土元素系统学也将被评估为侵入岩浆中氧化还原条件的示踪剂。例如，智利萨尔瓦多斑岩侵入岩的初步工作表明，与贫瘠的侵入岩相比，以矿化侵入体中的锆石测量的Eu异常较小，可能是由于缺乏斜长石的中地壳或深部地壳中较高的氧化态和岩浆分异所致。这一提议将有助于理解导致斑岩型矿藏形成的过程，斑岩型矿藏是铜和钼的主要全球来源，以及重要的副产金、银和其他金属，全球年产量超过1000亿美元。该项目还将支持一名博士后研究人员，并支持S在俄亥俄州立大学经济地质学和地球化学方面的教学工作，这是对需要寻找、开采和补救矿藏的地球科学家的基本培训。这项工作还将涉及与行业的合作，为学生提供获得矿产行业实践经验的新途径，并为未来的合作努力铺平道路。

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.