Assessing the Role of Crustal S Contamination in the Generation of PGE Mineralization in the Stillwater Complex, Montana: A multiple S and Re-Os Isotopic Study

世界的大部分？铂金的供应是由所谓的“礁型”提供的。存款。这些矿床是在火成岩中发现的薄层，其特征是存在1 - 5%体积的浸染硫化物矿物，主要是那些富含铁、铜和镍的矿物。铂族元素(白金?族元素)硫化物矿物的浓度要小得多，但提供了经济上重要的金属，如铂和钯。我们对铂族元素的需求预计将在未来几年增加，特别是在汽车工业的进步的推动下。最大的铂储量在南非和津巴布韦，在Bushveld Complex和Great Dyke发现了矿藏。在俄罗斯（西伯利亚）也发现了大量的储量，与一些不同的火成岩组合有关，这些火成岩富含硫化物矿物（有时接近100%硫化物）。蒙大拿州斯蒂尔沃特（Stillwater）综合体的火成岩是美国仅有的两个PGE矿，位于所谓的J-M礁（J-M Reef）。这些矿山的钯产量占世界总产量的百分之几。由于我们对PGEs的利用，美国需要增加我们的储备，减少我们对外国资源的依赖。需要对该提案中描述的类型进行研究，以改进珊瑚礁型PGE矿床的勘探和开发模式，类似于在静水复合体中发现的那些。地球沉积岩中硫的重要性？在处理礁型矿床形成的模型中，S地壳以前没有得到强调，主要是因为硫同位素值接近那些通常分配给来自地球的硫的值。地幔。由于静水杂岩的乡村岩石超过26亿年（称为太古宙），因此利用包含33S和34S值的同位素比值提供了另一种方法来测试乡村岩石衍生硫是否对富含pge的岩浆的生产至关重要。太古宙沉积岩中的硫在33S和34S比值图上可能明显偏离~ 0.515的斜率；这个关系定义了所谓的地面分割线（TFL）。异常偏离TFL的成因仍有争议，但火成岩中异常硫同位素值的存在证实了太古宙岩石硫的同化或合并。为了验证来自太古宙岩石的地壳硫参与了J-M礁和静水杂岩中其他富硫化物带形成的假设，我们建议从两个地点（包括静水和东博尔德矿的当前工作）穿过静水杂岩的样品中收集多个硫同位素数据。最近在静水矿的测绘中，已经明确定义了构成J-M礁PGE矿化的一些富硫化物透镜体。我们的采样将包括单个透镜，并进行详细的岩石学（微观）分析，以解释矿化和非矿化域之间的界面。还将收集所有样品的硫浓度；合并的数据集将允许严格的质量平衡计算，用于量化地壳硫在静水复合体中的重要性。建议的工作是评估大型PGE矿床的起源是否归因于岩浆与沉积岩的相互作用，这些沉积岩提供的硫远远超过了可能从岩浆的地幔源隔离的硫。我们的结果将约束进一步的PGE勘探模型，并阐明岩浆-乡村岩石相互作用的过程，这可能对几种类型的金属矿床的生成具有重要意义。

The bulk of the world?s supply of platinum is provided by what are known as ?reef-type? deposits. These deposits are thin layers that are found in igneous rocks and are characterized by the presence of 1 to 5 volume percent of disseminated sulfide minerals, principally those rich in iron, copper and nickel. PGE (platinum?group element) sulfide minerals occur in much smaller concentrations but provide the economically important metals such as platinum, and also palladium. Our need for platinum-group elements is projected to increase in coming years, driven particularly by advances in the automotive industry. The largest reserves of platinum are found in South Africa and Zimbabwe, with deposits found in the Bushveld Complex and the Great Dyke. Large reserves are also found in Russia (Siberia) associated with a somewhat different assemblage of igneous rocks that are very rich in sulfide minerals (sometimes nearly 100 % sulfides). The igneous rocks of the Stillwater Complex in Montana host the only two PGE mines in the United States in what is called the J-M Reef. The palladium production from the mines accounts for a few percent of the world total. Because of our utilization of PGEs the United States needs to increase our reserves and reduce our dependence on foreign sources. Research of the type described in this proposal is needed to improve models for both exploration and development of reef-type PGE deposits, similar to those found in the Stillwater Complex.The importance of sulfur derived from sedimentary rocks of the earth?s crust has not been previously emphasized in models dealing with the generation of reef-type deposits, largely because sulfur isotopic values are near those typically assigned to sulfur derived from the earth?s mantle. Because country rocks to the Stillwater Complex are in excess of 2.6 billion years (referred to as Archean age), the utilization of isotopic ratios that involve both 33S and 34S values provides another method to test if country rock derived sulfur has been essential for the production of PGE-enriched magmas. Sulfur from Archean sedimentary rocks may show a distinct departure from a slope of ~ 0.515 in ratio plots involving 33S and 34S; the relation defines what is known as the Terrestrial Fractionation Line (TFL). The origin of the anomalous departure from the TFL is still a matter of debate, but the presence of anomalous sulfur isotopic values in igneous rocks confirms the assimilation, or incorporation, of Archean-aged sulfur of country rock origin. In order to test the hypothesis that crustal sulfur derived from Archean country rocks was involved in the formation of the J-M Reef and other sulfide-rich zones in the Stillwater Complex we propose to collect multiple sulfur isotope data from samples collected in traverses through the Stillwater Complex in two locations that include the current workings at the Stillwater and East Boulder mines. Recent mapping in the Stillwater Mine has clearly defined a number of sulfide-rich lenses that constitute the PGE mineralization in the J-M Reef. Our sampling will include the individual lenses, with detailed petrographic (microscopic) analyses done to interpret interfaces between mineralized and non-mineralized domains. Sulfur concentrations from all samples will also be collected; the combined data set will permit rigorous mass balance calculations that will be used to quantify the importance of crustal sulfur involvement in the Stillwater Complex. The proposed work is required to evaluate if large PGE deposits owe their origins to the interaction of magmas with sedimentary country rocks that supplied sulfur far in excess of that which could have been sequestered from the mantle source of the magmas. Our results will constrain models for further PGE exploration and shed light on the processes of magma-country rock interaction that may be of significance in the generation of several types of metallic ore deposits.