Mineralogical and geochemical characteristics of waste rocks and tailings from a gold mine in northeastern Thailand: application for environmental impact protection

Abstract

Gold mining activities have raised seriously concern on environment and health in the local communities, particularly in the northeastern Thailand. Although, gold mines in Thailand have been operated longer than decade, potentials of acid mine drainage (AMD) generation and toxic element releasing have not been investigated in detail. Various mining wastes may contain hazardous elements such as arsenic, lead, zinc, cadmium and cyanide. These elements may be released under AMD environment. Therefore, AMD is a severe environmental impact which often occurs in metal sulfide mines including gold mine. Mine wastes (i.e. tailings and waste rocks) from the study area in the northeastern Thailand are collected and investigated. Mineralogical and geochemical characteristics of these mine wastes were carried out using microscope, XRD, Raman, FTIR, EPMA, XRF and ICP-MS. The tailing samples can be divided into upper gray tailings and lower ocher tailings. The upper gray tailings mainly contain sulfide minerals (pyrrhotite, pyrite ± chalcopyrite) and silicate minerals; consequently, they are defined as potential acid forming (PAF). On the other hand, the lower ocher tailings mainly contain goethite, quartz, chlorite, muscovite, calcite and hematite with minor pyrrhotite which they are classified as non-acid forming (NAF). However, the lower ocher tailings contain high contents of As (238–2870 mg kg-1), Cu (750–2608 mg kg-1) and Pb (10–1506 mg kg-1). Regarding to the waste rocks, they are characterized by sandstone, siltstone, gossan, skarn, skarn-sulfide, massive sulfide, diorite and limestone/marble. Among these rocks, the massive sulfide and skarn-sulfide rocks mainly consist of pyrrhotite, pyrite, arsenopyrite and chalcopyrite that are actual source of AMD. Moreover, the gossan rocks are composed of As (334–810 mg kg-1), Cu (500–7500 mg kg-1) and Zn (45–350 mg kg-1), which they can be used as a natural adsorbent (under controlled oxidizing condition and pH > 2) with high potential for remediation of As and Cu contamination within the surrounding areas. In conclusions, the upper tailings and the massive sulfide/skarn-sulfide rocks have potential of AMD generation whereas the lower tailings and gossan waste rock contain high contents of toxic elements. These toxic elements are unstable under acid drainage and they may be released into the environment. Therefore, the tailing storage is recommended to be covered to prevent the oxidizing processes of the upper tailings. For the waste rock dumping sites, particularly sulfide and transition dumps containing massive sulfide and skarn-sulfide rocks, they should also be cover by layer of compacted clay after the mine closure.