SusChEM: Geochemical and Mineralogical Constraints on the Genesis of Country Rock-hosted Massive Sulfide Mineralization Associated with Mafic Rock-related Cu-Ni-PGE Deposits

镍（Ni）、铜（Cu）和铂族元素（PGEs：铂（Pt）、钯（Pd）、铑、铱、钌和锇（Os））对美国的经济增长至关重要。Ni和pge几乎只存在于富含铁和镁的火成岩中。铜可能出现在各种岩石类型中，但也与Ni和PGEs伴生。矿石元素通常与硫化物矿物中的硫结合，或者在某些情况下，PGEs可能与砷（As），碲（Te）或锑（Sb）结合。虽然这些矿床大多是在火成岩体内发现的，但也有一类矿化是由几乎纯的硫化物矿物组成的，这些矿物位于火成岩外部和封闭的沉积岩内部。这些事件的等级可能很高，它们代表了一种鲜为人知的资源，随着我们全球对原材料需求的增加和我们努力维持一个可持续发展的地球，这种资源将具有国家重要性。由于矿石体积大，可开采面积相对较小，因此对环境的影响也相对较小；任何必要的开垦都很容易完成。镍是一种重要的铁合金，对制造不锈钢至关重要。铂和钯都用作催化转化器中的活性金属。美国只有一个在生产镍矿，只有两个在生产铂和钯矿（都在同一个火成岩体内）。作为该项目的一部分，将开展的工作将增加我们对在空间相关的火成岩之外形成大规模硫化物的理解。为了使该项目取得成功，需要公司地质学家和学术机构科学家之间的合作努力。这项研究的一个关键的更广泛的含义是，来自印第安纳大学教育系的学生经常在我们的实验室进行研究项目；这一经验是有益的，因为教师准备促进学生在科学、数学和可持续性方面的培训。虽然与火成岩相关的块状硫化物矿化通常可以通过岩浆系统中不混溶硫化物液体的重力聚集来解释，但与Ni-Cu-PGE矿床相关的一些块状硫化物矿化现象则很难用这种机制来解释。在沃伊塞湾（拉布拉多）、伊格尔（密歇根州）和新发现的塔玛拉克矿床（明尼苏达州）发现的矿化与岩浆导管有关；大量的硫化物可能积聚在岩浆速度随着管道变宽或变平而下降的地方。然而，在这些由变质沉积的乡村岩石承载的块状硫化物的每一个地方的发现都不容易用这种机制来解释。Cu-Ni-(PGE)块状硫化物矿化也被发现与较大的片状层状侵入体有关，包括Duluth杂岩（明尼苏达州）和Stillwater杂岩（蒙大拿州）的侵入体。在这两个地方，在接触环的泥质岩石中发现大量硫化物，与火成岩的连通性有限或没有。在靠近德卢斯杂岩接触的Virginia组块状硫化物矿化的初步地球化学数据显示出S、Os、Cu和铅（Pb）的部分地壳衍生特征。在许多地方，块状硫化物渗透并横切浸染的含硫化物火成岩。我国岩石含矿块状硫化物矿床的成因尚不清楚；显然，更好地了解有限的自然资源的未来发展是必不可少的。我们计划进行的详细研究物理和结构形式的三个这样的存款Midcontinent地区(老鹰,落叶松,Mesaba(巴氏合金)存款德卢斯的复杂,在静复杂),以及一个决心的主要地球化学特徵(Ni / Co的变异,S / Se,铂族元素,某人浓度和比例,和操作系统,铅、铜、镍和S同位素组成),阐明解释的幔源是否融化,地壳融化,或者是热液流体控制了它们的形成。西伯利亚著名的诺里尔斯克镍铜铂矿床也含有大量硫化物矿化，这些矿化发生在沉积岩中，与含硫化物的火成岩相隔数米。我们的俄罗斯同事正在对诺里尔斯克的矿化进行详细的研究，包括具有特别经济意义的乡村岩石承载类型。他们的研究与我们提出的工作相似，并为对一种知之甚少的矿石类型进行比较评估提供了机会。本项目得到了NSF 2015财年可持续化学、工程和材料（SusChEM）计划的部分支持。

Nickel (Ni), copper (Cu) and platinum-group elements (PGEs: platinum (Pt), palladium (Pd), rhodium, iridium, ruthenium, and osmium (Os)) are vital to the economic growth of the United States. Ni and PGEs are found almost exclusively in igneous rocks that are rich in iron and magnesium. Copper may occur in a variety of rock types but is also found in association with Ni and PGEs. The ore elements typically occur bonded to sulfur in sulfide minerals, or in some cases PGEs may be found bonded to arsenic (As), tellurium (Te) or antimony (Sb). Although most of these deposits are found within igneous rock bodies, there is a category of mineralization that is composed of nearly pure sulfide minerals that is located outside of the igneous rocks and within enclosing sedimentary rocks. The grade of these occurrences may be high and they represent a poorly understood resource that will be of national importance as our global need for raw materials increases and we strive to maintain a sustainable earth. Because the ore is massive the mineable dimensions are relatively small and hence the environmental footprint is correspondingly small; any necessary reclamation is readily accomplished. Nickel is a strategic ferro-alloy which is essential to the manufacture of stainless steel. Both Pt and Pd are used as active metals within catalytic converters. The United States has only one actively producing Ni mine and only two mines that produce Pt and Pd (both within the same igneous body). The work that will be undertaken as part of this project will increase our understanding of how massive sulfide occurrences form outside of the spatially associated igneous rocks. In order for the project to be successful a collaborative effort between company geologists and scientists at academic institutions is required. A key broader implication of the research is that students from the IU Department of Education frequently undertake research projects in our lab; the experience is beneficial as teachers are prepared to promote student training in science, mathematics and sustainability.Although massive sulfide mineralization associated with igneous can often be explained via gravitational accumulation of immiscible sulfide liquid in a magmatic system, some occurrences of massive sulfide mineralization associated with Ni-Cu-PGE deposits are more difficult to explain by this mechanism. Mineralization such as that found at Voisey's Bay (Labrador), Eagle (Michigan) and the newly discovered Tamarack deposit (Minnesota) are associated with magma conduits; massive sulfides may have accumulated where magma velocity decreased as the conduit widened, and perhaps flattened. However, discoveries at each of these localities of massive sulfide hosted by metamorphosed sedimentary country rocks are not easily accounted for by such a mechanism. Cu-Ni-(PGE) massive sulfide mineralization hosted by country rocks is also found in association with larger, sheet-like layered intrusions, including intrusions of the Duluth Complex (Minnesota) and the Stillwater Complex (Montana). In both of these localities massive sulfides are found in pelitic rocks of the contact aureoles, with limited or no connectivity with the igneous rocks. Preliminary geochemical data from the massive sulfide mineralization in the Virginia Formation near the contact with the Duluth Complex show strong signatures for partial crustal derivation of S, Os, Cu and lead (Pb). In many localities the country rock-hosted massive sulfides penetrate and crosscut disseminated sulfide-bearing igneous rocks. The origin of the country rock-hosted massive sulfide occurrences is poorly understood; clearly a better understanding is essential for future development of limited natural resources. We plan to undertake a detailed study of the physical and textural form of three such deposits in the Midcontinent region (Eagle, Tamarack, and the Mesaba (Babbitt) deposit of the Duluth Complex, and at the Stillwater Complex), along with a determination of key geochemical characteristics (variations of Ni/Co, S/Se, PGE, Sb and As concentrations and ratios, and Os, Pb, Cu, Ni and S isotopic compositions), that will shed light on the interpretation of whether mantle-derived melts, crustal melts, or hydrothermal fluids have controlled their formation. The well-known Noril'sk Ni-Cu-PGE deposits in Siberia also contain massive sulfide mineralization that occurs in the sedimentary country rocks, separated by several meters from sulfide-bearing igneous rocks. Our Russian colleagues are in the midst of a detailed study of the mineralization at Noril'sk, including the country rock - hosted type which is of particular economic significance. Their study parallels our proposed work and provides an opportunity for comparative evaluation of a poorly understood ore type.This project is supported in part via the NSF FY15 Sustainable Chemistry, Engineering, and Materials (SusChEM) initiative.