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（PGE：铂（Pt）、钯（Pd）、铑、铱、钌和锇（Os））对美国的经济增长至关重要。镍和铂族元素几乎只存在于富含铁和镁的火成岩中。铜可能存在于各种岩石类型中，但也发现与镍和铂族元素有关。矿石元素通常与硫化物矿物中的硫键合，或者在某些情况下，发现铂族元素与砷（As）、碲（Te）或锑（Sb）键合。虽然这些矿床中的大多数都是在火成岩体中发现的，但有一类矿化是由几乎纯的硫化物矿物组成的，位于火成岩之外和周围的沉积岩中。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，随着我们对原材料的全球需求增加，我们努力维护一个可持续的地球，这种资源将具有国家重要性。由于矿石很大，可开采的尺寸相对较小，因此环境足迹相应较小;任何必要的回收都很容易完成。镍是一种战略铁合金，对不锈钢的制造至关重要。Pt和Pd都用作催化转化器内的活性金属。美国只有一个活跃的镍矿，只有两个生产铂和钯的矿（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块状硫化物矿点如何在空间相关的火成岩之外形成的理解。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。这项研究的一个重要的更广泛的含义是，来自IU教育系的学生经常在我们的实验室进行研究项目;这种经验是有益的，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。尽管与火成岩有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积累来解释，一些与镍铜铂族元素矿床有关的块状硫化物矿化现象更难以用这种机制来解释。在沃西湾（拉布拉多）、伊格尔（密歇根州）和新发现的塔马拉克存款（明尼苏达州）发现的矿化作用与岩浆通道有关;随着通道变宽，岩浆速度降低，块状硫化物可能积聚在那里，也许变平。然而，在这些地方发现的变质沉积围岩中的块状硫化物并不容易用这种机制来解释。围岩中的Cu-Ni-（PGE）块状硫化物矿化也与较大的片状层状侵入体有关，包括杜卢斯杂岩体（明尼苏达州）和斯蒂尔沃特杂岩体（蒙大拿州）。在这两个地区，在接触带的泥质岩中发现了块状硫化物，与火成岩的连通性有限或没有。与杜卢斯杂岩接触面附近弗吉尼亚组块状硫化物矿化的初步地球化学数据显示，S、Os、Cu和铅（Pb）的部分地壳来源具有很强的特征。在许多地方，围岩中的块状硫化物穿透并横切浸染状含硫化物火成岩。围岩托管的块状硫化物矿点的起源知之甚少;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。我们计划对中大陆地区三个此类矿床的物理和结构形式进行详细研究（杜卢斯杂岩的Eagle、塔马拉克和Mesaba（Babalac）存款，以及Stillwater杂岩），沿着关键地球化学特征的确定（Ni/Co、S/Se、PGE、Sb和As的含量和比值以及Os、Pb、Cu、Ni和S同位素组成的变化），这将有助于解释地幔熔体地壳熔融或热液控制了它们的形成。西伯利亚著名的Noril'sk Ni-Cu-PGE矿床也含有大量硫化物矿化，这些硫化物矿化发生在沉积围岩中，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研究，包括具有特殊经济意义的围岩型矿化。他们的研究与我们提出的工作平行，并提供了一个机会，对一个知之甚少的矿石类型进行比较评估。该项目部分得到了NSF FY 15可持续化学，工程和材料（SusChEM）倡议的支持。

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.