Geochemistry of Heavy Minerals from Wang River, Lampang Province, Thailand

Wang River, known as Mae Nam Wang, is located in Northern part of Thailand. It is 440km long and has a catchment area 10,791km². It originates from Mt. Phi Pannam and flows south-westward to join Ping River at Tak Province. The study area is the upper part of Wang River, which is located in the Wang Nua District, Lampang Province. The upper part of Wang River has been mined for gold placer deposit for a long time by local residents. Previous studies, dealing with gold grain morphology and chemistry of this area, reported several heavy mineral assemblages. In this study, we focused on geochemistry of detrital heavy mineral assemblage occurring within placer gold deposit of the study area to trace the provenances of the detrital heavy minerals and to evaluate the economic value of the detrital heavy mineral deposits on upper part of Wang River.

The samples from the study area were prepared by panning and heavy liquid separation for analyses. An Energy Dispersive System (EDS) in Scanning Electron Microscope (SEM) was used for identification and image analysis of the detrital grains. The assemblage of heavy minerals in this area consists of ilmenite, zircon, hematite, magnetite, garnet, and rutile. Ilmenite (>21.5%) is the most common heavy mineral in the prepared heavy mineral sample. The proportion of zircon, hematite, magnetite, garnet, and rutile are approximately 15.0%, 14.7%, 10.5%, 5.8%, and 5.1% respectively. A plot of FeO-TiO₂-Fe₂O₃ ternary diagram shows that most of iron-titanium oxides are plotted near or above the line of ilmenite (FeTiO₃) – hematite (Fe₂O₃) solid solution, which is continuous solid solution above 800℃. It provides useful information about forming condition of the source rock. Furthermore, the combination of the chemical analyses results with detailed geologic setting of the study area can be a tool to trace the provenances of the detrital heavy minerals.