Trace Metal Distribution in Sulfide Minerals from Ultramafic-Hosted Hydrothermal Systems: Examples from the Kairei Vent Field, Central Indian Ridge
Trace Metal Distribution in Sulfide Minerals from Ultramafic-Hosted Hydrothermal Systems: Examples from the Kairei Vent Field, Central Indian Ridge
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DOI：
10.3390/min8110526
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发表时间：
2018-11
期刊：
影响因子：
2.5
通讯作者：
Yejian Wang;Xiqiu Han;S. Petersen;M. Frische;Z. Qiu;Yi-Tao Cai;P. Zhou
中科院分区：
文献类型：
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作者：
Yejian Wang;Xiqiu Han;S. Petersen;M. Frische;Z. Qiu;Yi-Tao Cai;P. Zhou
超镁铁质凯雷喷口场位于南纬 25°19′、东经 70°02′，靠近中印度洋中脊 (CIR-S1) 第 1 段的北端，水深约为 2450 m。本研究旨在研究不同质地的硫化物矿物中微量元素的分布，并使用 LA-ICP-MS 点扫描和线扫描分析来研究控制这些矿物中微量元素分布的可能因素。我们的研究结果表明，不同矿物的微量元素分布存在明显的系统差异，如下：（1）凯雷黄铁矿分为三种类型，包括早期自形黄铁矿（py-I）、亚自形黄铁矿（py-II）和胶状黄铁矿（py-III）。黄铁矿通常富含Mo、Au、As、Tl、Mn和U。与其他类型相比，黄铁矿-I具有较高的Se、Te、Bi和Ni含量； py-II相对于py-I和py-III富含Au，但缺乏Ni；相对于 py-I 和 py-II，py-III 富含 Mo、Pb 和 U，但缺乏 Se、Te、Bi 和 Au。黄铁矿中 Se、Te 和 Bi 浓度的变化很可能受强温度梯度的影响。黄铁矿中镍的浓度通常低于钴的浓度，这表明我们的样品在高温下沉淀，而钴的极端富集可能来自岩浆热源和蛇纹石化反应的影响。 (2)黄铜矿的特点是Co、Se、Te含量较高。黄铜矿中 Se 和 Te 的丰度高于其他矿物，这被解释为高温下 Se 和 Te 在黄铜矿晶格中的高溶解度造成的。 Kairei 喷口区黄铜矿中的 Sb、As 和 Au 浓度相对较低。 (3) 富锌烟囱闪锌矿的特点是 Sn、Co、Ga、Ge、Ag、Pb、Sb、As 和 Cd 含量较高，但与其他矿物相比，Se、Te、Bi、Mo、Au、Ni、Tl、Mn、Ba、V 和 U 含量较低。高浓度的 Cd 和 Co 可能是由于闪锌矿中的 Zn2+ 被 Cd2+ 和 Co2+ 取代所致。闪锌矿中高浓度的 Pb 伴随着高浓度的 Ag 表明 Ag 以 Pb-Ag 磺盐形式存在。金的闪锌矿含量通常较低，并且与铅密切相关，表明其存在于方铅矿的微包裹体中。 Kairei 闪锌矿中 As 与 Ge 的强相关性表明它们可能在中等温度和适度还原的条件下沉淀。 (4) 斑铜矿-二辉岩中除钴、硒和铋外，大多数微量元素的浓度都非常低。超镁铁质热液系统中的蛇纹石化可能对低砷黄铁矿中金的富集发挥重要作用。与长英质海底块状硫化物矿床相比，超镁铁质矿床的硫化物矿物中 Se 和 Te 浓度较高，但 As、Sb 和 Au 浓度较低，后者通常归因于岩浆挥发物的贡献。与典型的超镁铁质海底块状硫化物矿床一样，Kairei 黄铜矿中 Se 的富集表明，控制 Se 富集的主要因素是喷口流体中温度控制的流动性。
The ultramafic-hosted Kairei vent field is located at 25°19′ S, 70°02′ E, towards the Northern end of segment 1 of the Central Indian Ridge (CIR-S1) at a water depth of ~2450 m. This study aims to investigate the distribution of trace elements among sulfide minerals of differing textures and to examine the possible factors controlling the trace element distribution in those minerals using LA-ICP-MS spot and line scan analyses. Our results show that there are distinct systematic differences in trace element distributions throughout the different minerals, as follows: (1) pyrite is divided into three types at Kairei, including early-stage euhedral pyrite (py-I), sub-euhedral pyrite (py-II), and colloform pyrite (py-III). Pyrite is generally enriched with Mo, Au, As, Tl, Mn, and U. Pyrite-I has high contents of Se, Te, Bi, and Ni when compared to the other types; py-II is enriched in Au relative to py-I and py-III, but poor in Ni; py-III is enriched in Mo, Pb, and U but is poor in Se, Te, Bi, and Au relative to py-I and py-II. Variations in the concentrations of Se, Te, and Bi in pyrite are most likely governed by the strong temperature gradient. There is generally a lower concentration of nickel than Co in pyrite, indicating that our samples precipitated at high temperatures, whereas the extreme Co enrichment is likely from a magmatic heat source combined with an influence of serpentinization reactions. (2) Chalcopyrite is characterized by high concentrations of Co, Se, and Te. The abundance of Se and Te in chalcopyrite over the other minerals is interpreted to have been caused by the high solubilities of Se and Te in the chalcopyrite lattice at high temperatures. The concentrations of Sb, As, and Au are relatively low in chalcopyrite from the Kairei vent field. (3) Sphalerite from Zn-rich chimneys is characterized by high concentrations of Sn, Co, Ga, Ge, Ag, Pb, Sb, As, and Cd, but is depleted in Se, Te, Bi, Mo, Au, Ni, Tl, Mn, Ba, V, and U in comparison with the other minerals. The high concentrations of Cd and Co are likely caused by the substitution of Cd2+ and Co2+ for Zn2+ in sphalerite. A high concentration of Pb accompanied by a high Ag concentration in sphalerite indicates that Ag occurs as Pb–Ag sulfosalts. Gold is generally low in sphalerite and strongly correlates with Pb, suggesting its presence in microinclusions of galena. The strong correlation of As with Ge in sphalerite from Kairei suggests that they might precipitate at medium temperatures and under moderately reduced conditions. (4) Bornite–digenite has very low concentrations of most trace elements, except for Co, Se, and Bi. Serpentinization in ultramafic-hosted hydrothermal systems might play an important role in Au enrichment in pyrite with low As contents. Compared to felsic-hosted seafloor massive sulfide deposits, sulfide minerals from ultramafic-hosted deposits show higher concentrations of Se and Te, but lower As, Sb, and Au concentrations, the latter often attributed to the contribution of magmatic volatiles. As with typical ultramafic-hosted seafloor massive sulfide deposits, Se enrichment in chalcopyrite from Kairei indicates that the primary factor that controls the Se enrichment is temperature-controlled mobility in vent fluids.