Sulfide-olivine Fe-Ni exchange and the origin of anomalously Ni rich magmatic sulfides
Sulfide-olivine Fe-Ni exchange and the origin of anomalously Ni rich magmatic sulfides
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DOI：
10.2113/econgeo.108.8.1971
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发表时间：
2013-12
期刊：
影响因子：
5.8
通讯作者：
S. Barnes;B. Godel;D. Gürer;J. Brenan;J. Robertson;D. Paterson
中科院分区：
文献类型：
--
作者：
S. Barnes;B. Godel;D. Gürer;J. Brenan;J. Robertson;D. Paterson
硫化物液体与橄榄石之间的平衡用Fe和Ni的交换系数表示，KD =（XNiS/XFeS）硫化物液体/（XNiO/XFeO）橄榄石。的积极依赖K D上的Ni + Cu含量的硫化物液体，以及对F O 2，已被实验证明，并引起硫化物和橄榄石饱和的硅酸盐液体组合物之间的关系的临界非线性。测得的K D值橄榄石硫化物对浸染岩浆硫化物矿石在Betheno（西澳大利亚州）和Mirabela（巴西）是一致的独立估计的F O 2，并落在范围内的组合物的依赖K D是强的。这种效应已被定量建模，使用与可用实验数据的经验最佳拟合作为KD变异性的参数化，并计算共存橄榄石、硅酸盐熔体和硫化物液体之间Fe、Ni和Mg的平衡分布作为硅酸盐/硫化物质量比R的函数。结果表明，K D的组成依赖性是一个关键因素，在产生非常富镍硫化物的例子Betheno和Mirabela，其中共存的橄榄石也是富镍。具有异常高的Ni/Cu比的高度富Ni硫化物在自然界中可能比通常认识到的更常见，并且不需要用热液蚀变过程来解释。
Equilibration between sulfide liquid and olivine is expressed in terms of the exchange coefficient for Fe and Ni, K D = (X NiS /X FeS ) sulfide_liquid /(X NiO /X FeO ) olivine . The positive dependence of K D on Ni + Cu content of sulfide liquid, as well as on f O 2 , has been demonstrated experimentally and gives rise to a critical nonlinearity in the relationship between sulfide and olivine-saturated silicate liquid compositions. Measured K D values for olivine-sulfide pairs from disseminated magmatic sulfide ores at Betheno (Western Australia) and Mirabela (Brazil) are consistent with independent estimates of f O 2 , and fall within the range where the composition dependence of K D is strong. This effect has been modeled quantitatively, using an empirical best fit to available experimental data as a parameterization of the K D variability, and calculating the equilibrium distribution of Fe, Ni, and Mg between coexisting olivine, silicate melt, and sulfide liquid as a function of the silicate/sulfide mass ratio R. It is shown that the composition dependence of K D is a key factor in giving rise to extremely Ni rich sulfides as exemplified by Betheno and Mirabela, where coexisting olivine is also Ni rich. Highly Ni enriched sulfides with anomalously high Ni/Cu ratios may be more common in nature than is commonly recognized and do not need to be explained by hydrothermal alteration processes.