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

杜克岛杂岩体是位于阿拉斯加狭长地带的30多个白垩纪超镁铁质岩体之一。最近的钻探作业发现大量的低品位块状和浸染状硫化物矿化在橄榄石单斜辉石体内。分析显示最大值为1.95%的Cu、0.25%的Ni和1克/吨的Pt + Pd组合。在此发现之前，阿拉斯加型超镁铁络合物被认为是铜镍铂族元素（PGE）硫化物沉积的不良前景。铂族元素矿化似乎主要与富铬铁矿发生在纯橄榄岩部分的复杂，和大多数的铂族元素是安置在合金，碲化物，或锑化物。由于这些原因，复合物被认为是在非常低的fS 2环境中形成的。阿拉斯加型复合体被认为是在与俯冲过程有关的挤压机制中形成的。很少有大型岩浆铜镍（铂族元素）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，直接围岩含硫化物，可能是与弧有关的火山活动的馈线系统。因此，复杂的可能是一个很好的目标定位的Cu-Ni-（PGE）矿化的构造环境，在过去可能被忽视的硫化物潜力。详细的岩相学，电子探针，铂族元素，稳定同位素和Re/Os同位素的硫化物矿化将进行研究，以评估其成岩演化。2001年和2003年收集的岩心将可用于我们的项目。地球化学研究将评估硫化物从硅酸盐岩浆中熔离和分离的性质和原因（以及是否发生了这一过程）、矿化所涉及的硫的来源、成矿过程中围岩污染的总体性质、热液过程在硫化物成因中的可能重要性以及硫化物系统中Os（和潜在相关金属）的来源和演变。初步分析表明，与围岩的相互作用在硫化物形成中起着重要作用，热液过程也可能发挥了重要作用。本研究的结果将不仅适用于其他阿拉斯加型复合体，但将提供一个有趣的比较，在构造环境相对于其他世界级的Cu-Ni-（PGE）矿床。拟议的研究的更广泛的影响，包括教育机会，研究生和本科生谁将参与该领域和分析部分的研究。与行业合作伙伴的合作对于研究的成功至关重要。该公司将提供岩心和化学分析，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，并对美国有限的镍和铂族元素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.