Can magma degassing at depth donate the metal budget of large hydrothermal Sb deposits?
Can magma degassing at depth donate the metal budget of large hydrothermal Sb deposits?
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岩浆深度脱气能否贡献大型热液锑矿床的金属预算？
DOI：
10.1016/j.gca.2020.08.029
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发表时间：
2020-12
影响因子：
5
通讯作者：
Ruizhong Hu
中科院分区：
文献类型：
--
作者：
Shanling Fu;Zoltan Zajacz;Alex;ra Tsay;Ruizhong Hu
锑成矿作用与岩浆作用之间的成因联系已被提出，但对岩浆脱气过程中锑的活动性知之甚少。我们进行了一系列的实验，以了解流体成分，氧逸度（fO 2），压力和温度对锑之间的岩浆流体和流纹岩熔体在地壳条件下（T= 850 °C，P= 200 MPa）的分配的影响。实验在钼-碳化铪（MHC）压力容器组件中在T = 850至1000 °C、P= 100至200 MPa和logfO 2从低于Ni-NiO缓冲层的1.64 log单位到高于Ni-NiO缓冲层的1.78 log单位进行。Sb在含氯流体中的分配较弱，当流体中总氯浓度从0.99增加到16.24 m时，Sb的流体/硅酸盐熔体分配系数（DSb流体/熔体）从0.48 ± 0.11（1σ）增加到0.85 ± 0.17（1σ），表明流体中没有明显的Sb-氯化物物种。相比之下，随着熔体的铝饱和指数（ASI）从1.02增加到1.24，DSb流体/熔体从0.89 ± 0.19增加到1.49 ± 0.19。适度增加DSbfluid/meltis与增加ASI的熔体（和HCl/金属氯化物在流体中）最有可能涉及到降低锑在熔体中的溶解度，并进一步证明了缺乏显着的氯化物络合Sb。我们还发现，DSbfluid/meltis只有轻微的影响fO 2表明锑不改变氧化态（Sb 3+）在氧化还原条件下典型的弧岩浆作用。此外，在流体相中的还原S物种的存在下，仅导致DSbfluid/melt的轻微增加，表明Sb-硫化物络合物在岩浆流体中不是特别稳定。我们的数据还表明，在100至200 MPa和850至1000 °C范围内的压力和温度不会显著影响DSb流体/熔体。因此，很明显，在大多数可能的条件下，流纹质熔体脱气在上地壳中，锑将只有微弱的分配到流体相，它很可能是大型浅成热液锑矿床的锑预算不是直接来自原始岩浆流体。
A genetic link between Sb mineralization and magmatism has previously been proposed, yet little is known about the mobility of Sb during magma degassing. We have carried out a series of experiments to understand the effects of fluid composition, oxygen fugacity (fO2), pressure and temperature on the partitioning of Sb between magmatic fluids and a rhyolitic melt at crustal conditions (T= 850 °C,P= 200 MPa). The experiments were carried out in Molybdenum - Hafnium Carbide (MHC) pressure vessel assemblies atT= 850 to 1000 °C,P= 100 to 200 MPa and logfO2from 1.64 log units below to 1.78 log units above the Ni-NiO buffer. Antimony partitions into aqueous chloride-bearing fluids weakly, with the fluid/silicate melt partition coefficient of Sb (DSbfluid/melt) increasing from 0.48 ± 0.11 (1σ) to only 0.85 ± 0.17 (1σ) as the total chlorine concentration in the fluid increases from 0.99 to 16.24 m, indicating the lack of significant Sb-chloride species in the fluid. In contrast, DSbfluid/meltincreased from 0.89 ± 0.19 to 1.49 ± 0.19 as the aluminum saturation index (ASI) of the melt increased from 1.02 to 1.24. The moderate increase in DSbfluid/meltwith increasing ASI of the melt (and HCl/metal chloride in the fluid) most likely relates to decreasing Sb solubility in the melt and further demonstrates the lack of significant chloride complexing of Sb. We also found that DSbfluid/meltis only slightly influenced byfO2suggesting that Sb does not change oxidation state (Sb3+) at redox conditions typical of arc magmatism. Furthermore, the presence of reduced S species in the fluid phase caused only a minor increase in DSbfluid/meltindicating that Sb-sulfide complexes are not particularly stable in magmatic fluids. Our data also show that pressure and temperature, within the range of 100 to 200 MPa and 850 to 1000 °C, do not significantly influence DSbfluid/melt. Thus it is apparent that at most possible conditions at which rhyolitic melts degas in the upper crust, Sb will only weakly partition into the fluid phase and it is likely that the Sb budget of large epithermal Sb deposits is not directly derived from primary magmatic fluids.
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