Metasomatized mantle sources for orogenic gold deposits hosted in high-grade metamorphic rocks: Evidence from Hg isotopes

Geology Pub Date : 2023-11-29 DOI:10.1130/g51593.1
Qingfei Wang, Xuefei Liu, Runsheng Yin, Weijun Weng, Hesen Zhao, Lin Yang, D. Zhai, Dapeng Li, Yao Ma, D. Groves, Jun Deng
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Abstract

Investigation of Hg isotope ratios of gold-related sulfides and penecontemporaneous mafic dikes from four orogenic gold provinces on the margins of the North China Craton and Yangtze Craton identifies three orogenic gold deposit (OGD) groups from different tectonic regimes. Ore-related sulfides of group 1 OGDs and mafic dikes from the craton margin reworked via oceanic subduction mostly have positive Δ199Hg values. The group 2 OGDs and mafic dikes from the margin that witnessed complex oceanic and continental subductions have mixed positive to negative Δ199Hg values. The group 3 OGDs on the margin that experienced continental subduction have dominantly negative Δ199Hg values. These isotopic differences indicate subduction histories have a first-order control on the distinct sources for the OGDs. It indicates that OGDs were derived from fluids from the mantle lithosphere metasomatized by contrasting subduction components, not from metamorphic fluids as is widely accepted. Group 1 OGDs and dikes were sourced from metasomatized mantle, which inherited the positive Δ199Hg of both recycled marine sediments and seawater during oceanic subduction, whereas group 3 with negative Δ199Hg was derived from mantle lithosphere metasomatized by subduction of mainly continental components. This genetic model identifies regions with high-grade metamorphic rocks above metasomatized mantle lithosphere as promising new OGD exploration targets.
高品位变质岩中蕴藏的成因金矿床的变质地幔源:来自汞同位素的证据
通过对华北克拉通和扬子克拉通边缘四个成因金矿床群的金相关硫化物和五叠纪岩浆岩的汞同位素比值的研究,确定了不同构造体系的三个成因金矿床群。第一组成因金矿床和来自克拉通边缘经大洋俯冲再造的岩浆岩长岩的矿石相关硫化物大多具有正Δ199Hg值。来自经历了复杂的大洋和大陆俯冲的边缘的第 2 组 OGDs 和岩浆岩尖峰的 Δ199Hg 值由正到负不等。经历过大陆俯冲的边缘第 3 组 OGD 的 Δ199Hg 值主要为负值。这些同位素差异表明,俯冲历史对 OGDs 的不同来源具有一阶控制作用。这表明OGDs来源于地幔岩石圈的流体,这些流体经过对比强烈的俯冲作用后发生了变质,而不是像人们普遍认为的那样来源于变质流体。第 1 组 OGD 和岩穴来源于变质地幔,在大洋俯冲过程中继承了循环海洋沉积物和海水的正Δ199Hg,而第Δ199Hg 为负的第 3 组则来源于主要由大陆成分俯冲变质的地幔岩石圈。这一基因模型确定了在变质地幔岩石圈之上具有高品位变质岩的区域为有希望的新的海洋地球化学数据勘探目标。
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