Résumé
Artisanal and small-scale gold mining (ASGM) is a major source of mercury (Hg) contamination in tropical ecosystems, yet tracing Hg sources and transformations remains challenging. This study investigates Hg dynamics in the Yanomami Indigenous Territory (Brazil), a remote and ecologically sensitive region severely affected by illegal ASGM and a recent humanitarian-environmental crisis. We integrate mineralogical, geochemical, and total Hg data with Hg stable isotope analyses (δ²⁰²Hg and Δ¹⁹⁹Hg) from soils, sediments, suspended particulate matter (SPM), and liquid Hg to assess contamination sources and biogeochemical behavior. Hg concentrations reach up to 8,470 ng•g⁻¹ in SPM, with isotopic signatures reflecting both natural and anthropogenic inputs. A binary isotope mixing model based on δ²⁰²Hg reveals variable ASGM-derived contributions. Three distinct groups emerge: (1) a Source Mixing Group showing a continuum between natural and ASGM inputs; (2) a Hotspot Group with high Hg concentrations and isotopic signatures resembling ASGM liquid Hg; and (3) a Redox-Process Group with isotopic deviations indicative of in situ redox-driven transformations under oxic-anoxic gradients. To support interpretation in complex settings, we propose a simplified, semi-quantitative framework integrating source apportionment and environmental processes. This tool enhances environmental forensics and risk assessment in ASGM-impacted areas.