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

评估蒙大拿州斯蒂尔沃特杂岩地壳硫污染在 PGE 矿化生成中的作用：多重硫和铼锇同位素研究

• 批准号: 1249702
• 负责人: Edward Ripley
• 金额: $ 30万
• 依托单位: Indiana University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-04-01 至 2017-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1249702&HistoricalAwards=false
• 关键词: Assessing; Role; Crustal; Contamination; Generation

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.

铂金的大部分供应是由礁石类型提供的？沉积物。 这些沉积物是在火成岩中发现的薄层，其特征是存在1-5体积百分比的硫化物矿物质，主要是富含铁，铜和镍的矿物质。 PGE（铂？组元素）硫化物矿物质的浓度较小，但提供了经济上重要的金属，例如铂和钯。 我们对白金组元素的需求预计将在未来几年内增加，特别是由于汽车行业的进步。铂金的最大储量是在南非和津巴布韦发现的，在布什维尔德建筑群和大堤坝中发现了沉积物。在俄罗斯（西伯利亚）也发现了大量储量，与富含硫化物矿物质的火成岩组合有些不同（有时几乎是100％硫化物）。蒙大拿州斯蒂尔沃特建筑群的火成岩岩石占美国仅有的两个PGE矿山。来自矿山的钯产量占全球总数的百分之几。由于我们对PGES的利用，美国需要增加我们的储量并减少我们对外国资源的依赖。需要对本提示中描述的类型进行研究来改善模型来探索和开发珊瑚礁型PGE沉积物，类似于在斯蒂尔沃特综合体中发现的模型。从地球的沉积岩石中得出的硫的重要性，以前尚未强调s s sulf of sulf of Sulfer sulfer sulfer sulfer sulfory sulfory，因为硫磺是固定的，因为硫磺的价值是固定的，因为这是硫磺的价值，因为硫磺的价值是硫磺属于硫磺。地面的地幔。由于到斯蒂尔沃特综合体的国家岩石超过26亿年（称为大古龄），因此涉及33S和34S值的同位素比的利用提供了另一种方法，可以测试是否对PGE-Enriched Magmas的产生产生是否至关重要。大将沉积岩的硫可能与涉及33秒和34秒的比率图明显不同。该关系定义了所谓的陆地分级线（TFL）。 异常偏离TFL的起源仍然是一个辩论问题，但是在火成岩中，异常的硫同位素值的存在证实了乡村岩石起源的Archean当代硫的同化或成立。为了检验以下假设：源自大帝乡村岩石的地壳硫参与了Stillwater综合体中的J-M珊瑚礁和其他富含硫化物的区域的形成，我们建议从在遍历中通过Stillwater建筑群中收集的多个样品收集的多个硫同位素数据，包括两个位置，包括当前工作的静止水域和东部的bolderersees和East Boulderers Minees。 静水矿山最近的映射清楚地定义了许多富含硫化物的镜头，这些镜头构成了J-M礁中的PGE矿化。我们的抽样将包括各个镜片，并进行了详细的岩石学（显微镜）分析，以解释矿化和非矿化域之间的界面。也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，该计算将用于量化地壳硫参与在Stillwater复合物中的重要性。拟议的工作需要评估大型PGE沉积物是否归功于其起源于岩浆与沉积物岩石的相互作用，这些岩石岩石提供的硫磺远远超出了岩浆的地幔来源的含量。我们的结果将限制模型，以进一步探索PGE，并阐明岩浆国家岩石相互作用的过程，这在几种类型的金属矿床的产生中可能具有重要意义。