New insight into the source of metals in Hg deposits at the southwestern margin of the Yangtze Platform, China: Evidence from mercury stable isotope compositions

Abstract

The genesis of the typical Hg-Au-Sb metallogenic district in the southwestern margin of the Yangtze Craton, Southwestern China, remains controversial. A systematic study of the mercury (Hg) concentrations and Hg isotopic compositions of the Hg deposit at Paiting was conducted to constrain the sources of metals. Mass-independent fractionation (MIF) of Hg isotopes with slight positive Δ199Hg (0.03‰ to 0.22‰) was observed in the Hg ore samples, indicating that Hg transported by the ore fluids was primarily derived from the Cambrian black shale as these rocks show similar Δ199Hg signatures (−0.02‰ to 0.08‰). Based on these newly obtained Hg isotope ratios, we propose that deep hydrothermal fluids promoted the mobilization of Hg in Hg-bearing strata (i.e., Cambrian Niutitang Formation black shale) in the paleo-basin sedimentary strata to form Hg-enriched fluids. The Hg-enriched fluids flowed and permeated from the lower to the upper strata during mineralization and were transported to the platform margin slope facies along faults, followed by Hg precipitation to form Hg deposits. Hg isotope ratios could be a robust tracer to distinguish the metal sources of hydrothermal Hg deposits.