An Experimental Study to Elucidate PGE, Base Metal Sulfide and Au Fractionation in Mafic Layered Intrusions

智力上的优点。与镁铁质层状侵入体有关的铂族元素（PGE）矿床的形成有两种相互竞争的模式：1）硫化物沉降“下行"模式; 2）水流体”上行"模式。模型1假设，铂族元素从熔体分配到早期形成的硫化物相，通过岩浆沉淀，产生显着的富铂族元素的硫化物的岩浆体的地板上的积累。这一假说受到了批评，因为特征铂族元素，贱金属硫化物（BMS）和Au补偿是不一致的硫化物液体分馏。模型2假设从岩浆中析出的水溶性挥发相提取矿石金属作为溶解物质。模型2是有吸引力的，因为它提供了一个机制，所观察到的金属相对丰度，但尚未进行定量测试，由于不提供高质量的分配数据的PGE，BMS和Au在适当的压力-温度-组成（PTX）的条件出席侵位，凝固和脱气的镁铁质侵入体。本项目建议进行实验和建模，以定量测试这些假设。该项目将产生数据约束：1）Pt、Pd、Cu和Au在不含S和含S的粗玄岩熔体、含水超临界流体、+/-硫化物晶体、+/-硅酸盐晶体之间的分配，以及2）Pt、Pd、Cu和Au在不含S和含S的粗玄岩熔体、共存的水蒸气和盐水、+/-硫化物之间的分配，岩浆PTX处的+/-硅酸盐晶体。实验将在100 MPa和800-1100 C下进行，PT范围是大多数层状侵入体固化和脱气的范围。水相的氧逸度和硫逸度、总盐度和HCl将系统地变化。与Alan Boudreau（杜克大学）合作，使用PALLADIUM程序的修改形式，测量元素分配系数，并用于模拟在含水流体饱和的镁铁质硅酸盐岩浆凝固过程中Pt、Pd、Cu和Au的色谱分离。这些数据和建模将限制含水岩浆流体是否能够从结晶镁铁质硅酸盐熔体中富集和运输经济数量的PGE、BMS和Au，以及含水流体的沉淀是否能够产生天然矿床的PGE、BMS和Au特征。该研究将有助于加深对镁铁质层状侵入体演化过程中铂族元素、铂族金属硫化物和Au行为的认识，提高发现新铂族元素矿床的预测技术。私家侦探将在实验技术，分析化学和计算建模方面培训一名研究生，并通过与UNLV，杜克大学，ETH和UCLA的教师合作，将研究生暴露给不同的科学家群体。学生将参与本科教学和指导，并通过在专业会议上介绍她/他的研究来获得曝光。学生将获得宝贵的技术写作技能，同时准备在科学期刊上发表的论文和手稿。私家侦探计划将至少一名本科生纳入该项目，以执行一些分析化学任务，微量测温和样品制备。鼓励本科生在研究项目中发挥积极作用，并完成本科论文。

Intellectual merit. Two competing models for formation of platinum-group-element (PGE) deposits associated with mafic layered intrusions have been widely considered: 1) the sulfide-settling 'downers' model; and 2) the aqueous fluid 'uppers' model. Model 1 hypothesizes that PGEs are partitioned from melt into early-formed sulfide phases that settle through the magma to yield significant accumulation of PGE-rich sulfides on the floor of the magma body. This hypothesis receives criticism because the characteristic PGEs, base-metal sulfides (BMS) and Au offsets are inconsistent with sulfide liquid fractionation. Model 2 hypothesizes that an aqueous volatile phase exsolved from the magmas extracts the ore metal as dissolved species. Model 2 is attractive in that it provides a mechanism for the observed metal relative abundances, but has not been tested quantitatively owing to unavailability of high-quality partitioning data for the PGE, BMS and Au at the appropriate pressure-temperature-composition (PTX) conditions attending emplacement, solidification and degassing of mafic intrusions. This project proposes to perform experiments and modeling to quantitatively test these hypotheses. The project will produce data constraining: 1) the partitioning of Pt, Pd, Cu and Au between S-free and S-bearing dolerite melt, aqueous supercritical fluid, +/- sulfide crystals, +/- silicate crystals at magmatic PTX, and 2) the partitioning of Pt, Pd, Cu and Au between S-free and S-bearing dolerite melt, co-existing aqueous vapor and brine, +/- sulfide, +/- silicate crystals at magmatic PTX. Experiments will be performed at 100 MPa and 800-1100 C, the PT range over which most layered intrusions solidify and degas. Oxygen and sulfur fugacities, total salinity and HCl of the aqueous phase(s) will be varied systematically. Element partition coefficiencts and will be measured and used to model the chromatographic separation of Pt, Pd, Cu and Au during solidification of an aqueous fluidsaturated mafic silicate magma using a modified form of the program PALLADIUM in collaboration with Alan Boudreau (Duke U.). The data and modeling will constrain whether aqueous magmatic fluids can or can not scavenge and transport economic quantities of PGE, BMS and Au from crystallizing mafic silicate melts and if precipitation from aqueous fluid can produce PGE, BMS and Au characteristics of natural ore deposits.Broader impacts. The study will advance our understanding of the behavior of PGEs, BMS and Au during the evolution of mafic layered intrusions and improve predicative techniques for the discovery of new PGE deposits. The P.I. will train one graduate student in experimental techniques, analytical chemistry and computational modeling and expose the graduate student to a diverse group of scientists through collaboration with faculty at UNLV, Duke University, ETH, and UCLA. The student will be involved in undergraduate teaching and mentoring and gain exposure through presentations of her/his research at professional meetings. The student will gain invaluable technical writing skills while preparing a dissertation and manuscripts for publication in scientific journals. The P.I. plans to incorporate at least one undergraduate student into this project to perform some of the analytical chemistry tasks, microthermometry and sample preparation. The undergraduate student(s) will be encouraged to take an active role in the research project and complete an undergraduate thesis.