夏日哈木超大型镍矿I号岩体地幔源区性质和硫化物熔离过程:来自橄榄石成分、亲铜元素和硫同位素的约束
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本文为国家自然科学基金项目(编号 41972057)、中央高校基本科研业务费专项资金项目(编号 300102271208)、中国地质调查项目(编号 DD20221696)和陕西省自然科学基金一般项目(面上)(编号 2021JM- 160)联合资助的成果


The nature of mantle source and the process of sulfide segregation of the Xiarihamu No.I intrusion: Insights from olivine, chalcophile elemental and sulfur isotopic compositions
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    摘要:

    夏日哈木超大型镍矿I号岩体的地幔源区目前仍存在软流圈、大陆下岩石圈地幔和辉石岩地幔三种不同认识。本次研究通过对该岩体西段新近发现的隐伏矿体ZK3109钻孔中斜方辉石岩和浸染状矿石中的橄榄石进行原位成分分析,识别地幔源区性质,并结合硫化物原位S同位素和全岩亲铜元素组成,探讨硫化物熔离过程。样品中橄榄石均具有较低的Mn/Zn比值(基本小于13. 5),而且斜方辉石岩中橄榄石具有较低的100×Mn/Fe比值(基本小于1. 35),指示岩体源区有辉石岩地幔组分加入,与前人根据硫化物矿体富Ni特征的推测一致。橄榄石低Ca(小于300. 00×10-6)、高Li(平均9. 83×10-6)以及Sc与Ni正相关指示辉石岩地幔组分可能是俯冲洋壳物质交代大陆下岩石圈地幔的产物。另一方面,斜方辉石岩中橄榄石Ni、Fo值均与Co负相关且全岩S和铂族元素(PGE)相关性不明显,说明浅部岩浆房硫化物熔离发生在斜方辉石岩形成之后。浸染状矿石中橄榄石Co和Ni正相关且全岩S和PGE正相关,暗示橄榄石成分受控于硫化物熔离。样品中镍黄铁矿、磁黄铁矿和黄铜矿δ34S值(2. 28‰~6. 11‰)高于地幔值(0 ± 2‰),指示壳源硫化物的选择性加入导致母岩浆在浅部岩浆房S饱和。模拟计算表明岩体东、西两段浸染状矿石和网脉状矿石中亲铜元素的差异是母岩浆在硫化物熔离过程中二者R值(硅酸盐熔体和硫化物熔体质量比)不同造成的,分别为30~3000和3000~15000。本次研究表明综合运用矿物原位成分、S同位素和全岩亲铜元素组成能够有效识别铜镍硫化物矿床赋矿岩体地幔源区性质并刻画硫化物熔离过程。

    Abstract:

    The nature of mantle source of the Xiarihamu Ni deposit is still under debate, with three possible source regions from asthenosphere, sub- continental lithospheric mantle or pyroxenite mantle. In this study, we collected orthopyroxenite and disseminated ore samples from the drill hole ZK3109, and carried out the in- situ analysis on olivine composition of the No. I intrusion to identify the nature of mantle source, and analyzed the in- situ S isotopic composition of sulfide and whole- rock chalcophile elements to portray the processes of sulfide saturation and segregation. Most olivine grains of orthopyroxenite and disseminated ores have low Mn/Zn ratio (<13. 5), and most of those from orthopyroxenite have low 100×Mn/Fe ratio (<1. 35), indicating a pyroxenite mantle component in the source origin. Moreover, the low Ca(<300. 00×10-6) and high Li with an average value of ~9. 83×10-6 in olivine from orthopyroxenite and disseminated ores, and the positive correlation of Sc and Ni for olivine from orthopyroxenite, suggests that the pyroxenite mantle was formed by the metasomatism of sub- continental lithospheric mantle by materials from the subducted oceanic crust. On the other hand, the negative correlations of Co concentration with Ni concentration, and Fo value of olivine from orthopyroxenite and the ambiguous correlation of S and PGE indicate that the sulfide segregation occurred after the formation of orthopyroxenite. In contrast, the positive correlation of Co and Ni of olivine and the positive correlation of S and PGE of disseminated ores suggest that the olivine composition is mainly controlled by the sulfide segregation. Pentlandite, pyrrhotite and chalcopyrite of orthopyroxenite and disseminated ore have δ34S ranging from 2.28‰ to 6.11‰, distinctly higher than the mantle value (0±2‰), indicating that the S saturation of parental magma in the shallow magma chamber was triggered by the selective addition of crustal S. The modeling results suggest that the different chalcophile elemental compositions of disseminated ores and net- textured ores in the west and east segments of the No. I intrusion were ascribed to different R- values (the mass ratio of the silicate melt to sulfide melt) during sulfide segregation of the parental magma, ranging from 30~3000 and 3000~15000, respectively. Therefore, the combination of mineral, S isotopic and whole- rock chalcophile elemental compositions can be a comprehensive way to effectively identify the nature of mantle source and describe the processes of sulfide segregation of the Cu- Ni sulfide deposits.

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李中州,王亚磊,王梦玺,焦建刚,夏明哲.2023.夏日哈木超大型镍矿I号岩体地幔源区性质和硫化物熔离过程:来自橄榄石成分、亲铜元素和硫同位素的约束[J].地质学报,97(10):3326-3346.
LI Zhongzhou, WANG Yalei, WANG Mengxi, JIAO Jiangang, XIA Mingzhe.2023. The nature of mantle source and the process of sulfide segregation of the Xiarihamu No. I intrusion: Insights from olivine, chalcophile elemental and sulfur isotopic compositions[J]. Acta Geologica Sinica,97(10):3326-3346.

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  • 收稿日期:2022-07-10
  • 最后修改日期:2022-10-28
  • 录用日期:2022-10-28
  • 在线发布日期: 2023-10-16
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