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

锆石的微量元素特征：评估花岗岩侵入体和斑岩成矿潜力的一种方法

• 批准号: 1049792
• 负责人: John Dilles
• 金额: $ 22.7万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-10-01 至 2014-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1049792&HistoricalAwards=false
• 关键词: Trace; Element; Characteristics; Zircon; Means

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.

知识价值。在全球范围内，汇聚边缘环境中的含水和富硫弧岩浆与岩浆热液流体有关，这些岩浆热液流体产生斑岩型Cu（-Mo-Au）、浅热液型Au（-Ag）以及各种其他类型的矿床类型。虽然理论上一般的弧型花岗闪长岩可以形成这样的矿床，但弧壳中的大多数侵入体不能形成矿床，在经济上是贫瘠的。中-硅质岩浆均为强氧化岩浆，虽然它们位于上大陆地壳中并结晶，但它们最终来源于深部幔源玄武岩-安山岩岩浆。本文提出对代表性矿化侵入体和贫化侵入体中锆石的微量元素组成和年龄进行系统研究，以评价其作为矿化示踪剂的应用价值。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、再加热或热液事件保持其岩浆成分。利用离子探针（SHRIMP-RG）和激光烧蚀- icp - ms方法，可以在原位准确分析锆石中的微量元素Hf、Y、Sc、V、Ti和稀土元素。此外，U-Th-Pb同位素年龄信息可以同时或顺序收集。岩浆结晶过程中Hf/Zr比值增大，温度可采用ti -in-锆石地温计监测。因此，锆石为限制侵入系统的时间-温度-组成路径提供了机会。锆石中的稀土元素系统也将作为侵入岩浆氧化还原条件的示踪剂进行评价。例如，对智利萨尔瓦多斑岩侵入体的初步研究表明，矿化侵入体中锆石的Eu异常与无矿化侵入体相比较小，这可能是由于中深部没有斜长石的地壳中氧化态较高和岩浆分异共同作用的结果。更广泛的影响。这一建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，也是全球年产量超过1000亿美元的重要副产品金、银和其他金属。该项目还将资助一名博士后研究人员，并支持两位PI？在俄勒冈州立大学攻读经济地质学和地球化学，这是对寻找、开发和修复矿藏所需的地球科学家必不可少的培训。这项工作还将涉及与工业界的合作，为学生提供获得矿物工业实际经验的新途径，并为今后的合作努力开辟道路。