The mineralogical and chemical characteristics of As solid phases in arsenic-rich mine tailings from the Nakdong As-Bi mine in Korea was investigated. The tailings generated from the ore roasting process contained 4.36% of As whereas the concentration was up to 20.2% in some tailings from the cyanidation process for the Au extraction. Thin indurated layers and other secondary precipitates had formed at the surfaces of the tailings piles and the As contents of the hardened layers varied from 2.87 to 16.0%. Scorodite and iron arsenate (Fe3AsO7) were the primary As-bearing crystalline minerals. Others such as arsenolamprite, bernardite and titanium oxide arsenate were also found. The amorphous As-Fe phases often showed framboidal aggregates and gel type textures with desiccation cracks. Sequential extraction results also showed that 55.7-91.1% of the As in tailings were NH(4)-oxalate extractable As, further confirmed the predominance of amorphous As-Fe solid phases. When the tailings were equilibrated with de-ionized water, the solution exhibited extremely acidic conditions (pH 2.01-3.10) and high concentrations of dissolved As (up to 29.5 mg L(-1)), indicating high potentials for As to be released during rainfall events. The downstream water was affected by drainage from tailings and contained 12.7-522 microg L(-1) of As. The amorphous As-Fe phases in tailings have not entirely been stabilized through the long term natural weathering processes. To remediate the environmental harms they had caused, anthropogenic interventions to stabilize or immobilize As in the tailings pile should be explored.

Geochemical characteristics of As contamination in the Myungbong gold mine area in Korea were investigated, and the mine tailings were found to contain high concentrations of As (2,500-6,420 mg/kg). The mine tailings are an obvious candidate for the source of contamination in the study area. From the sequential, and oxalate, extraction analyses the majority of the As in the tailings was found to be associated with Fe oxides produced when sulfide minerals are oxidised. Mineralogical examinations showed the formation of poorly crystalline Fe oxides on a rim of pyrite, onto which the As was retained. The sediments of two ponds affected by the tailings also contained significant levels of As. High concentrations of dissolved As were also found in pond and stream waters. It has been suggested that the mobility of the As was increased by the reductive dissolution of Fe oxides under reducing conditions in the pond. Agricultural fields, located beneath the tailing dumps, have been contaminated by the continuous use of contaminated stream water and groundwater for irrigation.

Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon dates and geochemical and isotopic (Sr and Nd) data were obtained for Middle Jurassic granitoids from the Buyeo area along the southwestern margin of the Gyeonggi Massif, South Korea. Foliated 179 Ma granitoids are dominated by granite and diorite, non-foliated 167 Ma granitoids include granite to alkalifeldspar granite, and the youngest, non-foliated 165 Ma granitoids consist of alkali-feldspar granite. The 179 Ma and 167 Ma rocks are geochemically typical of I-type granitoids, and their LILE enrichment and negative Nb-Ta-Ti-P anomalies are common features of subduction-related granitoids. In contrast, 165 Ma rocks are A-type granitoids that show HREE-enriched patterns with significant depletions of Sr, P, Eu, and Ti. I-type granitoids dated at 179 Ma and 167 Ma have I Sr = 0.7092-0.7158, 0.7206-0.7263 and ε Nd (T) = -13.96 to -13.55, -21.47 to -19.51, respectively. A-type, 165 Ma granitoids have relatively lower I Sr (0.7052) and strongly negative ε Nd (T) (-20.47), reflecting melt derivation from the lower crust. These results suggest that the formation of granitoids along the southwestern boundary between the Gyeonggi Massif and the Okcheon Belt took place at ca. 179-167 Ma by the subduction of the paleo-Pacific plate. The 165 Ma post-orogenic A-type granites intruded in an extensional setting, providing a critical time constraint on the termination of Jurassic plutonism in South Korea. The 179 Ma foliated granitoids are similar to syn-kinematic granitoids in and around the Honam shear zone, indicating that ductile shear movement may have occurred at ca. 179 Ma. Biotite K-Ar ages of deformed Precambrian rocks and Middle Jurassic granitoids from the Buyeo area generally yield ages of 144-152 Ma and 124-135 Ma. These results probably reflect pervasive reactivation during Latest Jurassic to Early Cretaceous deformation that postdated the main ductile shearing event along the southern boundary of the Gyeonggi Massif.