Mineralogic and Isotopic Studies of Cu-Ni Sulfide Mineralization Associated with the Duke Island Ultramafic Complex, Southeastern Alaska

杜克岛综合体是位于阿拉斯加狭长地带的30多个白垩纪超镁铁质矿体之一。最近的钻探作业发现大量低品位块状和浸染性硫化物矿化赋存于橄榄石-斜方辉石岩体中。分析表明，最高含量为1.95%的铜、0.25%的镍和1克/吨的铂和钯。在此之前，阿拉斯加型超镁铁质杂岩被认为是铜-镍-铂族元素(PGE)硫化物沉积前景不佳的矿体。PGE矿化似乎主要与杂岩中富铬矿化有关，大多数PGE赋存于合金、碲化物或锑化物中。由于这些原因，这些络合物被认为是在非常低的FS2环境中形成的。阿拉斯加型杂岩被认为是在与俯冲过程有关的挤压状态下形成的。很少有大型岩浆铜镍(PGE)硫化物矿床与俯冲带有关，对杜克岛杂岩的构造和岩石学环境的分析表明，邻近的围岩含有硫化物，可能是与弧有关的火山活动的馈送系统。因此，在过去可能被忽视的硫化物潜力的构造环境中，该杂岩可能是铜-镍-(PGE)矿化定位的良好靶点。将对硫化物矿化进行详细的岩相学、电子探针、PGE、稳定同位素和Re/Os同位素研究，以评价其岩石成因演化。2001年和2003年收集的钻芯将用于我们的项目。地球化学研究将评估硫化物熔融和从硅酸盐岩浆中分离的性质和原因(如果有的话)，成矿过程中涉及的硫的来源，成矿过程中围岩污染的总体性质，热液作用在硫化物成因中的可能重要性，以及硫化物系统中Os(和潜在的相关金属)的来源和演化。初步分析表明，与围岩的相互作用在硫化物的形成中起到了重要作用，热液作用也可能起到了重要作用。这项研究的结果不仅适用于其他阿拉斯加类型的杂岩，而且将在构造环境方面与其他世界级铜镍(PGE)矿床进行有趣的比较。拟议研究的更广泛影响包括为将参与研究领域和分析部分的研究生和本科生提供的教育机会。与行业合作伙伴的合作将是这项研究取得成功的必要条件。Quaterra Resources将提供钻芯和化学分析，并将在阿拉斯加提供实地运输。这项研究的结果将对阿拉斯加东南部的进一步勘探和潜在的经济发展产生影响，并将对美国有限的镍和PGE资源进行评估。

The Duke Island complex is one of more than thirty ultramafic bodies of Cretaceous age located in the Alaskan panhandle. Recent drilling operations detected large volumes of low-grade massive and disseminated sulfide mineralization hosted within an olivine-clinopyroxenite body. Assays show a maximum of 1.95% Cu, 0.25% Ni, and 1 gram/ton combined Pt + Pd. Prior to this discovery, Alaskan-type ultramafic complexes were considered poor prospects for Cu-Ni-platinum group element (PGE) sulfide deposition. PGE mineralization appears to be primarily associated with chromite-rich occurrences in dunitic portions of the complexes, and most of the PGEs are housed in alloys, tellurides, or antimonides. For these reasons the complexes are thought to have formed in very low fS2 environments. Alaskan-type complexes are thought to have formed in compressive regimes related to subduction processes. Very few large magmatic Cu-Ni-(PGE) sulfide deposits are associated with subduction zones, and an analysis of the tectonic and petrologic environments of the Duke Island complex suggests that immediate country rocks are sulfide-bearing and probably served as feeder systems for arc-related volcanic activity. Thus the complex may represent an excellent target for the localization of Cu-Ni-(PGE) mineralization in a tectonic environment that in the past may have been overlooked in terms of sulfide potential. Detailed petrographic, electron-microprobe, PGE, stable isotopic, and Re/Os isotopic studies of the sulfide mineralization will be undertaken to evaluate its petrogenetic evolution. Drill cores collected in 2001 and 2003 will be available for our project. Geochemical studies will assess the nature and causes of sulfide liquation and separation from a silicate magma (and if this process occurred at all), the source of sulfur involved in the mineralization, the overall nature of country rock contamination in the ore-forming processes, the possible importance of hydrothermal processes in sulfide genesis, and the source and evolution of Os (and potentially related metals) in the sulfide system. Preliminary analyses indicate that interaction with country rocks has been important in sulfide formation, and that hydrothermal processes may have played a significant role as well. Results of this study will be applicable not only to other Alaskan-type complexes, but will offer an interesting comparison in terms of tectonic environments relative to other world-class Cu-Ni-(PGE) deposits. Broader implications of the proposed research include the educational opportunities presented to both graduate and undergraduate students who will be involved in the field and analytical portions of the research. Collaboration with industry partners will be imperative for the success of the research. Quaterra Resources will provide access to drill cores and chemical analyses, and will provide field transportation in Alaska. Results from this study will have an impact on further exploration and potential economic development in southeastern Alaska, and will be important for the assessment of limited Ni and PGE resources in the United States.