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The role of hydrothermal processes and the formation of the J-M reef and associated rocks of olivine-bearing zone I of the Stillwater Complex, Montana
Mineralium Deposita ( IF 4.8 ) Pub Date : 2024-05-07 , DOI: 10.1007/s00126-024-01267-2
A. R. Gupta , Alan E. Boudreau

Several lines of evidence, including hydrous melt inclusions and unusually Cl-rich apatite, have been used to suggest that the reappearance of olivine and PGE-sulfide of the J-M Reef in the Stillwater Complex, Montana, is due to fluid infiltration and hydration melting. This study builds upon the hydration melting model using the programs MELTS and PELE with Stillwater bulk rock compositions for the original protolith. Cl-bearing phases are not modeled by MELTS and thus simple oxide mixtures of either a pure H2O or a H2O + Na2O “faux brine” are added to norite, gabbronorite, and melanorite protoliths at 1050 °C at 2 kbar pressure, conditions for which the nominally “dry” protolith is > 95% solid. Incongruent hydration melting results in up to 37% olivine produced in the melanorite. The olivine Fo content is a function of the partial melt retained on cooling, and ranges between 76 and 86, overlapping the natural range of olivine compositions observed in the rocks. Modeling with the PELE program, which includes a silicate liquid Cl component, sulfur species, and a more complex C-O–H-S fluid, suggests that, for CO2-rich fluids, fluid metal concentrations on the order of 25 ppm Pt, 75 ppm Pd, 0.03 wt.% Cu, and 0.20 wt.% Ni at a fluid/rock mass ratio of ~ 0.25 are needed to account for the observed ore grades. Sulfide and ore metals are readily remobilized for more H2O-rich fluids, consistent with heterogeneous distribution of sulfide and regionally variable ore grades.



中文翻译:

热液过程的作用以及蒙大拿州斯蒂尔沃特杂岩含橄榄石带 I 的 JM 礁和伴生岩的形成

包括含水熔体包裹体和异常富含 Cl 的磷灰石在内的几条证据表明,蒙大拿州斯蒂尔沃特杂岩区 JM 礁石中橄榄石和铂族元素硫化物的重新出现是由于流体渗透和水化融化造成的。这项研究建立在水合熔融模型的基础上,使用 MELTS 和 PELE 程序以及斯蒂尔沃特块状岩石成分作为原始原岩。熔体不模拟含 Cl 相,因此纯 H 2 O 或 H 2 O + Na 2 O“人造盐水”的简单氧化物混合物在 1050 °C、2 ℃下添加到苏长岩、辉长岩和黑长岩原岩中。 kbar 压力,名义上“干燥”原岩固体含量 > 95% 的条件。不一致的水合熔化导致黑云母中产生高达 37% 的橄榄石。橄榄石 Fo 含量是冷却时保留的部分熔体的函数,范围在 76 到 86 之间,与岩石中观察到的橄榄石成分的自然范围重叠。使用 PELE 程序(包括硅酸盐液体 Cl 成分、硫物质和更复杂的 CO-HS 流体)进行建模表明,对于富含 CO 2的流体,流体金属浓度约为 25 ppm Pt、75 ppm Pd 、0.03 wt.% Cu 和 0.20 wt.% Ni(流体/岩体比约为 0.25)需要考虑到观察到的矿石品位。硫化物和矿石金属很容易重新流动成富含H 2 O的流体,这与硫化物的不均匀分布和区域性矿石品位的变化相一致。

更新日期:2024-05-08
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