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

Abstract

The assemblage of heavy minerals of alluvial sand from the study area, upper part of Wang River, consists mainly of rutile, ilmenite, zircon, garnet, spinel, hematite and magnetite. Fe-Ti oxide (ilmenite, ferrianilmenite, peseudobrookite, ferropseudo-brookite and ulvöspinel) is the most common heavy mineral type, which measured over than 21%, in the prepared heavy mineral samples. Morphological analysis results indicate that the most of the detrital grains have undergone advanced mechanical abrasive weathering processes during transportation. Mineral indices (RZi and ATi) suggest that the detrital grains have unimodal source lithology and an implication of some effect of chemical condition which could be cause for the loss of apatite grains. Rutile geochemistry indicates that its internal homogeneity in trace element abundances, and the most of rutile grains might be composed under amphibolite/eclogite – granulite phases condition (700 - 900℃). The majority of rutile grains were possibly derived from felsic intrusive rock which is exposed eastern side of the river. The trace element contents of the detrital zircon grains represents that the zircon grains were also have felsic intrusive rocks (such as granitoids) as a plausible source lithology and its Ce anomaly reveals that the zircon grains could be crystallized under relatively high oxidizing condition. Discriminant function analysis results for magnetite grains show that the detrital grains are might be derived from metasedimentary rocks, which are exposed upper most part of the river and Cretaceous granitic intrusive rocks, which are same candidates with other detrital grains (rutile and zircon), and the contribution of mafic volcanic rocks, which are exposed western side of the river, is none ore negligible. There, probably, was a topographical setting which enabled to make the weathering debris, including magnetite grains from the felsic intrusive rocks, generally flowing into and having an effect on this fluvial system in the past.