Geochemical characteristics of ores and surface waters for environmental risk assessment in the Pinpet iron deposit, southern Shan State, Myanmar

• Published in: Resource geology 2020-07, Vol.70 (3), p.296-308
• Main Authors: Zay Ya, Kyaw, Otake, Tsubasa, Koide, Aoi, Sanematsu, Kenzo, Sato, Tsutomu
• Format: Article
• Language: English
• Subjects: Aquatic environment; Arsenic; Bedrock; Beneficiation; Carbonates; Chemical analysis; Chemical composition; Clay; Contamination; Copper; Drinking water; Dry season; Environmental assessment; environmental impact; Geochemistry; Haematite; Heavy metals; Hematite; Hydroxides; Iron; iron mine; Iron ores; limestone bedrock; Limonite; Metal concentrations; Mine tailings; Minerals; Mining; Myanmar; Ores; Pinpet; Public concern; Quality standards; Risk assessment; Rivers; Sediment; Sediments; sequential extraction; Speciation; Stream pollution; Streambeds; Streams; Surface water; Tributaries; Water pollution; Water quality; Water quality standards; Zinc
• ISSN: 1344-1698; 1751-3928
• DOI: 10.1111/rge.12231

Mining operations in the Pinpet Fe deposit, which is the second‐largest Fe deposit in Myanmar, are currently suspended, in part because of possible contamination of heavy metals and hazardous elements (e.g., Fe, As, Cu, Zn, and U) into the surrounding aquatic environment and associated public concern. However, a scientific investigation of the source and degree of contamination in streams near the deposit has not yet been conducted. Therefore, we quantified heavy‐metal and hazardous‐element concentrations of stream waters and sediments in stream beds, and measured the speciation and concentration of these metals in deposit Fe ores using the sequential extraction method, to better understand the influence of mining activities on the surrounding environment. Geochemical results for Nan‐tank‐pauk stream and its tributaries indicate that the chemical compositions of their waters are controlled by carbonate bedrock and that no detectable contamination has occurred as a result of mining activity or hematite and limonite ore beneficiation processes in either the wet or dry seasons. All measured heavy‐metal and hazardous‐element concentrations were below the World Health Organization standards for drinking water and the proposed national drinking water quality standards in Myanmar. Bulk chemical compositions of stream‐bed and tailings dam sediments show that As, Zn, and Cu concentrations are similar to those in uncontaminated sediments. Results of bulk mineralogical and chemical analyses of ore samples reveal that some limonite ore samples contain substantial amounts of As (up to 2 wt%). However, sequential extraction results indicate that most (>90%) of the As in these As‐rich ores is hosted in insoluble fractions (e.g., crystalline Fe hydroxides and clays). Therefore, arsenic is unlikely to be released into the aquatic environment by interacting with water during ore beneficiation processes should the mine resume operations. Geochemical results indicate no significant contamination occurred in the surface water due to the mining activity and beneficiation process of hematite and limonite ores in Pipet iron deposit, Myanmar. Bulk mineralogical and chemical analyses of ore samples demonstrated that some limonite ore samples contain significant amounts of Arsenic (up to 2 wt%). However, most arsenic in the arsenic‐rich ores is hosted in insoluble fractions.