In this contribution, we analyze 30 years of mine development data and quantitatively identify the processes that control the grade and tenor of the mineralized rock. An assay database of more than 60,000 samples was used to examine variations in ore grade and tenor of the sulfide mineralization in the J-M reef horizon of the Stillwater Complex along the strike and down the dip of the deposit in the area of the Stillwater mine. We compare these results with data from the East Boulder mine and whole-rock lithogeochemistry of samples collected along the entire strike length of the complex. We find significant variation in the composition of the reef sulfides in different spatial domains of the Stillwater mine area and between the Stillwater and East Boulder mines. Most of the variation in the grade and tenor can be explained by a variation in the mass of silicate magma with which the sulfide liquid equilibrated (i.e., R factor); however, geochemical and textural evidence suggests that parts of the reef may have experienced significant S loss following initial sulfide melt segregation. Some variability in the reef tenor and grade can be attributed to variable amounts of sulfur loss due to low-temperature hydrothermal fluids and the overestimation or underestimation of metal concentrations in reef assays due to the nugget effect. Furthermore, we address the Pd/Pt ratio of the reef samples and suggest that the lower solubility of Pt in the parental silicate melt may have caused the crystallization and removal of Pt alloys at some point before the melt reached sulfide saturation and Pt could partition into the sulfide liquid. This disparity between the prior evolution of Pt and Pd in the silicate melt resulted in the observed Pd/Pt ratio of ~3.65 across all areas of the reef—a value significantly larger than anticipated for primitive mantle-derived magmas.

中文翻译：

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美国蒙大拿州斯蒂尔沃特综合大楼JM礁的性质和组成

在此贡献中，我们分析了30年的矿山开发数据，并定量确定了控制矿化岩石品位和年限的过程。分析数据库包含60,000多个样本，用于检查Stillwater矿区罢工和下沉沿斯蒂尔沃特复杂区JM礁层的矿石品位和硫化物矿化度的变化。我们将这些结果与来自East Boulder矿山的数据以及沿该综合体整个走向长度收集的样品的全岩石岩性化学进行了比较。我们发现，在斯蒂尔沃特矿区的不同空间区域以及斯蒂尔沃特矿和东博尔德矿之间，礁石硫化物的组成存在明显差异。品位和年限的大部分变化可以用与硫化物液体平衡的硅酸盐岩浆质量变化（即R因子）来解释。然而，地球化学和质地的证据表明，在最初的硫化物熔体偏析之后，礁石的某些部分可能经历了明显的S损失。礁石年限和品位的某些变化可以归因于由于低温热液引起的硫损失量的变化以及礁石化验中金块效应导致金属浓度的高估或低估。此外，我们研究了礁石样品中Pd / Pt的比率，并指出在母体硅酸盐熔体中Pt较低的溶解度可能导致熔体达到硫化物饱和之前的某个时刻，Pt合金的结晶和去除，并且Pt可以分配到硫化物中液体。硅酸盐熔体中Pt和Pd的先验演化之间的这种差异导致在整个礁石区域观察到的Pd / Pt比约为3.65，该值明显大于原始地幔衍生岩浆的预期值。