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

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 .6.199Hg values. The group 2 OGDs and mafic dikes from the margin that witnessed complex oceanic and continental subductions have mixed positive to negative .6.199Hg values. The group 3 OGDs on the margin that experienced continental subduction have dominantly negative .6.199Hg 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 .6.199Hg of both recycled marine sediments and seawater during oceanic subduction, whereas group 3 with negative .6.199Hg 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.

Automated summary

This study investigates the mercury isotope ratios of gold-related sulfides and mafic dikes from four orogenic gold provinces on the margins of the North China Craton and Yangtze Craton, revealing the presence of three different orogenic gold deposit (OGD) groups. The analysis indicates that the subduction histories play a major role in determining the sources of the OGDs.