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首页> 外文期刊>Contributions to Mineralogy and Petrology >The effect of pressure on sulphur speciation in mid-to deep-crustal arc magmas and implications for the formation of porphyry copper deposits
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The effect of pressure on sulphur speciation in mid-to deep-crustal arc magmas and implications for the formation of porphyry copper deposits

机译：压力对中-深地壳弧岩浆中硫形态的影响及其对斑岩型铜矿床形成的影响

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Piston cylinder experiments are used to investigate the effect of oxygen fugacity (fO(2)) on sulphur speciation and phase relations in arc magmas at 0.5-1.5 GPa and 840-950 degrees C. The experimental starting composition is a synthetic trachyandesite containing 6.0 wt% H2O, 2880 ppm S, 1500 ppm Cl and 3800 ppm C. Redox conditions ranging from 1.7 log units below the Ni-NiO buffer (NNO -1.7) to NNO + 4.7 were imposed by solid-state buffers: Co-CoO, Ni-NiO, Re-ReO2 and haematite-magnetite. All experiments are saturated with a COH fluid. Experiments produced crystal-bearing trachydacitic melts (SiO2 from 60 to 69 wt%) for which major and volatile element concentrations were measured. Experimental results demonstrate a powerful effect of oxidation state on phase relations. For example, plagioclase was stable above NNO, but absent at more reduced conditions. Suppression of plagioclase stability produces higher Al2O3 and CaO melts. The solid sulphur-bearing phases and sulphur speciation in the melt are strong functions of fO(2), as expected, but also of pressure. At 0.5 GPa, the anhydrite stability field is intersected at NNO >= +2, but at 1.0 and 1.5 GPa, experiments at the same fO(2) produce sulphides and the stability field of sulphate moves towards higher fO(2) by similar to 1 log unit at 1.0 GPa and similar to 1.5 log units at 1.5 GPa. As a result, models that appeal to high oxidation state as an important control on the mobility of Cu (and other chalcophiles) during crustal differentiation must also consider the enhanced stability of sulphide in deep-to mid-crustal cumulates even for relatively oxidized (NNO + 2) magmas. Experimental glasses reproduce the commonly observed minimum in sulphur solubility between the S-2 -and S6+ stability fields. The solubility minimum is not related to the Fe content (Fe2+/Fe3+ or total) of the melt. Instead, we propose this minimum results from an unidentified, but relatively insoluble, S-species of intermediate oxidation state.
机译：活塞缸实验用于研究氧逸度（fO（2））在0.5-1.5 GPa和840-950摄氏度下对弧形岩浆中硫的形态和相关系的影响。实验的起始成分是含有6.0 wt％的合成菱锰矿％H2O，2880 ppm S，1500 ppm Cl和3800 ppm C.氧化还原条件是由固态缓冲液施加的，范围从Ni-NiO缓冲液以下1.7 log单位（NNO -1.7）到NNO + 4.7 -NiO，Re-ReO2和赤铁矿-磁铁矿。所有实验均用COH液饱和。实验产生了含晶体的菱锰矿熔体（SiO2为60至69 wt％），并测量了主要和挥发性元素的浓度。实验结果证明了氧化态对相关系的强大影响。例如，斜长石蜡在NNO以上是稳定的，但在更还原的条件下不存在。斜长石稳定性的抑制产生较高的Al2O3和CaO熔体。固态含硫相和熔体中的硫形态是fO（2）的强大功能，正如预期的那样，也是压力的强大功能。在0.5 GPa时，硬石膏稳定性场在NNO> = +2时相交，但是在1.0和1.5 GPa时，在相同的fO（2）上进行的实验会产生硫化物，而硫酸盐的稳定性场则向着更高的fO（2）移动，类似于1.0 GPa时为1 log单位，而1.5 GPa时为1.5 log单位。结果，呼吁高氧化态作为对地壳分化过程中Cu（及其他嗜碱性微生物）迁移率的重要控制的模型，还必须考虑到即使是相对氧化（NNO），硫化物在深至中地壳累积物中的稳定性也有所提高。 + 2）岩浆。实验玻璃重现了S-2和S6 +稳定性场之间通常观察到的硫溶解度最小值。溶解度最小值与熔体的Fe含量（Fe2 + / Fe3 +或总含量）无关。取而代之的是，我们提出了这种最低限度的结果，这是由中间氧化态的一个未知但相对不溶的S物种引起的。

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