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

杜克岛是位于阿拉斯加狭长地带的30多个白垩纪超镁铁体之一。最近的钻井作业在橄榄斜辉石岩体内发现了大量低品位块状浸染状硫化物矿化。测定结果显示铜含量最高为1.95%，镍含量为0.25%，铂+钯含量最高为1克/吨。在此发现之前，阿拉斯加型超镁铁性配合物被认为是cu - ni -铂族元素（PGE）硫化物沉积的不良前景。PGE矿化似乎主要与在配合物的二元部分的富铬铁矿有关，并且大多数PGE被安置在合金、碲化物或锑化物中。由于这些原因，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作用有关的压缩环境中形成的。很少有大型岩浆Cu-Ni-(PGE)硫化物矿床与俯冲带有关，对杜克岛杂岩的构造和岩石环境的分析表明，邻近的岩石含有硫化物，可能是弧相关火山活动的支线系统。因此，该络合物可能是在构造环境中定位Cu-Ni-(PGE)矿化的一个极好的目标，而在过去，这种构造环境在硫化物潜力方面可能被忽视。对硫化物矿化进行详细的岩石学、电子显微、PGE、稳定同位素和Re/Os同位素研究，以评价其成岩演化。2001年和2003年收集的岩心将用于我们的项目。地球化学研究将评估硫化物从硅酸盐岩浆中液化和分离的性质和原因（如果这一过程发生的话），矿化过程中硫的来源，成矿过程中农村岩石污染的总体性质，热液过程在硫化物形成中的可能重要性，以及硫化物系统中Os（和潜在相关金属）的来源和演化。初步分析表明，与乡村岩石的相互作用在硫化物形成中起着重要作用，热液作用也可能起着重要作用。该研究结果不仅适用于其他阿拉斯加型杂岩，而且将为与其他世界级铜镍矿床的构造环境进行有趣的比较提供参考。拟议研究的更广泛含义包括为研究生和本科生提供教育机会，他们将参与该领域和研究的分析部分。与行业伙伴的合作对于研究的成功至关重要。Quaterra Resources将提供钻探岩心和化学分析，并将在阿拉斯加提供现场运输。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，并对美国有限的Ni和PGE资源的评估具有重要意义。

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.