Lithospheric mantle as a metal storage reservoir for orogenic gold deposits in active continental margins: Evidence from Hg isotopes

Geology Pub Date : 2024-03-01 DOI:10.1130/g51871.1
Jing-Yuan Zhang, Kun-Feng Qiu, Runsheng Yin, Zheng-Yu Long, Yue-Chuan Feng, Hao-Cheng Yu, Zi-Yue Gao, Jun Deng
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Abstract

The subcontinental lithospheric mantle (SCLM) is now suggested by many workers to play a role in the formation of orogenic gold deposits in active continental margins, given that the gold and volatiles may be introduced into the SCLM during plate subduction. The giant Cretaceous Jiaodong gold province within the North China block occurs in a convergent margin setting where there is no terrane accretion, thus eliminating from consideration the commonly accepted metal and fluid source reservoir for orogenic gold—the metamorphosed upper crust of an active orogenic belt. Thus, the auriferous fluids were released below the high-grade Archean cratonic rocks from either enriched SCLM or directly from the subducted oceanic slab. Mercury (Hg) isotopes allow fingerprinting of isotopically distinct reservoirs, discriminating between the two possibilities. We present Hg isotope data for a set of pyrite grains, native gold, and lamprophyres from six main gold districts in the Jiaodong gold province. These samples dominantly yielded near-zero Δ199Hg (0‰ ± 0.1‰), within uncertainty of the mantle Δ199Hg value. The results provide novel evidence that the SCLM predominantly controlled the Hg budget of the Jiaodong gold deposits, implying that the SCLM acted as a buffer for the crustal mass-independent fractionation Hg signatures and a storage reservoir for gold and volatiles. Consequently, during slab subduction, gold and volatiles were recycled and stored within the SCLM and were later released from the mantle during uplift and relaxation of compressional tectonics.
岩石圈地幔作为活动大陆边缘造山运动金矿床的金属储存库:来自汞同位素的证据
鉴于金和挥发物可能是在板块俯冲过程中被引入大陆下岩石圈地幔(SCLM)的,因此许多研究人员认为大陆下岩石圈地幔在活动大陆边缘造山型金矿床的形成过程中发挥了作用。华北地块内的白垩纪胶东巨型金矿床发生在一个汇聚边缘环境中,这里没有地层增生,因此不存在公认的成因金的金属和流体源储层--活动造山带的变质上地壳。因此,含金流体是从富集的SCLM或直接从俯冲的大洋板块释放到高品位的Archean碎屑岩之下的。汞(Hg)同位素可以对同位素不同的储层进行指纹识别,从而区分这两种可能性。我们展示了一组来自胶东金省六个主要金矿区的黄铁矿颗粒、原生金和灯泡岩的汞同位素数据。这些样品的主要Δ199Hg值接近零(0‰ ± 0.1‰),在地幔Δ199Hg值的不确定性范围内。这些结果提供了新的证据,表明SCLM主要控制着胶东金矿床的汞预算,意味着SCLM是地壳质量无关分馏汞特征的缓冲区,也是金和挥发物的储存库。因此,在板块俯冲过程中,金和挥发物被回收并储存在SCLM中,随后在隆升和压缩构造松弛过程中从地幔中释放出来。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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