Re-Os Isotopic Systematics Accompanying the Conversion of Organic-Rich, Pelitic Country Rocks to Hornfels, Magma Contamination and Sulfide Ore-Genesis, Duluth Complex

由于幔源玄武质部分熔体中Re相对于Os的富集，以及地壳岩石的高Re/Os比值，Re/Os同位素体系已被证明是评价壳幔基性岩浆动力学相互作用过程的灵敏示踪剂。 在围岩污染评价中，Re-Os同位素体系作为岩石学示踪剂的应用取决于对污染岩石中开放或封闭体系行为的正确评价，以及火成岩或富硫化物矿石材料结晶后Re和Os的固定性。 本项目将评估富含有机物的沉积岩中Re和Os的分布和同位素特征、接触变质作用和这些岩石向角岩转化过程中同位素特征的变化以及由于围岩同化或释放的流体相而产生的含硫化物火成岩中发现的同位素变化。 杜卢斯杂岩和元古代围岩的地质背景提供了一个极好的机会，通过接触变质和脱水的过程中跟踪的Re-Os系统的演化，和基性岩浆同化的围岩。 在巴伯托铜镍存款地区存在地壳污染和未污染的辉长岩和troctolitic岩石，系统的Re-Os分析将允许深入评价同位素变异的原因，这种变异可能源于围岩的变质和热液过程，以及与硅酸盐岩浆和硫化物岩浆比例变化有关的岩浆过程。

9814204RipleyBecause of the enrichment of Re relative to Os in mantle-derived, basaltic partial melts, and the high Re/Os ratio of crustal rocks, the Re/Os isotopic system has proven to be a sensitive tracer in the evaluation of dynamic interaction processes between crust and mantle-derived mafic magmas. In the assessment of country rock contamination the application of the Re-Os isotopic system as a petrologic tracer is dependent upon the proper evaluation of open- or closed-system behavior in the contaminant rock, and immobility of Re and Os after crystallization of the igneous rock or sulfide-rich ore material. This project will evaluate the distribution and isotopic characteristics of Re and Os in organic-rich sedimentary rocks, changes in isotopic characteristics during contact metamorphism and conversion of these rocks to hornfels, and isotopic variation found in sulfide-bearing igneous rocks produced as a result of assimilation of country rocks or a released fluid phase. The geologic setting of the Duluth Complex and Proterozoic country rocks presents an excellent opportunity to trace the evolution of the Re-Os system through the processes of contact metamorphism and dehydration, and assimilation of country rocks by mafic magma. Both crustally-contaminated and uncontaminated gabbroic and troctolitic rocks are present in the area of the Babbitt Cu-Ni deposit, and systematic Re-Os analyses will permit an in-depth evaluation of the causes of isotopic variability that may originate as a result of metamorphic and hydrothermal processes in the country rocks, and magmatic processes related to changes in the ratio of silicate magma to sulfide magma.