Causes of Re-Os Isotopic Variations in High-Temperature Sulfide Mineral Assemblages: Insights From the Duluth Complex-Virginia Formation System

智力优势：该项目将评估解释地壳侵入岩浆中硫化物沉淀的假设-这可能解释与杜卢斯侵入杂岩相关的某些重要矿床的形成。围岩混染被认为是幔源玄武岩浆中硫化物饱和的必要条件，可以通过同化地壳硫，也可以通过同化硅质物质，导致镁铁质岩浆中硫化物溶解度降低。Re-Os同位素体系在评价岩浆矿床和幔源岩中地壳混染的作用方面特别有用。由于铼和锇的亲铜性质，该系统非常适合作为硫化物矿化中壳源金属的指示剂。然而，最近的研究表明，Re-Os同位素系统可能特别容易受到与流体相互作用有关的扰动。以前对可能的围岩污染物的硫同位素研究表明，这些岩石是与杜卢斯杂岩有关的岩浆硫化物矿化的主要硫源。 然而，初步的Re-Os同位素研究表明，接触晕中的硫化物矿物的特点是由非放射成因的Os，而块状硫化物矿化在杜卢斯的特点是由放射成因的Os-指示广泛的Os污染。这些岩石中硫化物系统的极端Re-Os同位素变化反映了基性岩浆与地壳岩石相互作用的基本过程。接触晕中的脉含有石英和硫化物组合（磁黄铁矿立方镍黄铁矿），这是非常相似的岩浆硫化物矿化中发现的。为了检验接触带中Re/Os同位素体系的扰动与含Re-Os流体和硫化物矿物之间的反应有关的前提，计划对脉体材料以及空间相关的沉积硫化物进行流体包裹体、稳定同位素和Re-Os同位素研究。这些数据将允许评估流体的起源和成分，以及它与杜卢斯杂岩岩浆的关系。由于大型捕虏体的围岩，保持低品位的矿物组合在其核心是目前在侵入岩的复杂，我们也将能够系统地评估负责Re-Os和S同位素变化的机制，从捕虏体核心通过变质边缘和周围的浸染含硫化物的火成岩。研究结果将有助于揭示与镁铁质岩浆-地壳相互作用有关的硫化物体系中Re-Os同位素变化的原因，并对评价岩浆硫化物成矿作用的Re-Os同位素体系具有重要价值。拟议的研究的更广泛的方面包括培训研究生和本科生在系统的实地采样和使用国家的，在三个国家科学基金会资助的实验室建立了用于化学和同位素分析的现代分析设施。与明尼苏达州自然资源研究所的合作对项目的成功至关重要。随着第三世界经济的加强，对岩浆系统中发现的金属资源的勘探和利用继续增长。了解经常使用的放射性同位素系统如何对涉及岩浆和流体的高温事件作出反应，对于开发未来勘探模型至关重要。

Intellectual Merit: This project will evaluate hypotheses to explain precipitation of sulfide minerals from crustally intruded magmas - that may explain the formation of certain important ore deposits associated with the Duluth intrusive complex. Country rock contamination has been proposed as a requirement to produce sulfide saturation in mantle-derived basaltic magmas, either through assimilation of crustal sulfur, or by assimilation of siliceous material that results in a decrease in the sulfide solubility of the mafic magma. The Re-Os isotopic system has proven particularly useful in evaluating the role of crustal contamination in magmatic ore deposits and in mantle-derived rocks in general. Because of the chalcophile nature of both Re and Os, the system is well-suited as an indicator of crustally derived metals in sulfide mineralization. However, recent studies have shown that the Re-Os isotopic system may be particularly prone to perturbations related to later interaction with fluids. Previous S isotopic studies of likely country rock contaminants suggest that these rocks were the principal source of sulfur for the magmatic sulfide mineralization associated with the Duluth complex. However, preliminary Re-Os isotopic studies indicate that sulfide minerals in the contact aureole are characterized by unradiogenic Os whereas the massive sulfide mineralization at Duluth is characterized by radiogenic Os - indicative of extensive Os contamination. Extreme Re-Os isotopic variations in the sulfide systems in these rocks are reflective of fundamental processes that must accompany the interaction of mafic magmas with crustal rocks. Veins in the contact aureole contain quartz and a sulfide assemblage (pyrrhotitecubainte-pentlandite) that is very similar to that found in the magmatic sulfide mineralization. In order to test the premise that the perturbation of the Re/Os isotopic system in the contact aureole is related to the reaction between Re-Os-bearing fluids and sulfide minerals, fluid inclusion, stable isotopic, and Re-Os isotopic studies of the vein material, as well as spatially associated sedimentary sulfides, are planned. These data will allow assessment of the origin and composition of the fluid, and its relationship to the magmas of the Duluth Complex. Because large xenoliths of country rocks that preserve low-grade mineral assemblages in their cores are present in the intrusive rocks of the Complex, we will also be able to systematically evaluate the mechanisms responsible for Re-Os and S isotopic variations from xenolith cores through metamorphosed margins and surrounding disseminated sulfide-bearing igneous rocks. The results of this study will shed light on the causes of Re-Os isotopic variations in sulfide systems related to mafic magma-crust interaction, and will be of particular value in the evaluation of Re-Os isotopic systematics associated with magmatic sulfide ore formation.Broader Impacts: Broader aspects of the proposed research include the training of both graduate and undergraduate students in systematic field sampling and in the use of state-of-theart analytical facilities for chemical and isotopic analyses at three NSF-funded laboratories. Cooperation with the Minnesota Natural Resources Research Institute will be essential for the project to succeed. Exploration for, and utilization of, metallic resources found in magmatic systems continues to grow as third-world economies strengthen. Knowledge of how an often utilized radiogenic isotopic system may respond to high-temperature events involving magmas and fluids is essential to the development of future exploration models.