Mineralogical and chemical characteristics of the allanite-rich copper and iron ores from the Sin Quyen mine, northern Vietnam

Abstract

Selected ores from the Sin Quyen allanite-rich Au-bearing chalcopyrite-magnetite deposits were studied microscopically and chemically. The ore minerals tend to occur along the NW-SE-trending sheared zone of altered host rocks; yet the ore minerals show no stress effect, implying the mineralization later than the regional shearing. The ore minerals occur associated with the metasomatic minerals consisting mainly of clinopyroxene, hastingsite, allanite, epidote, biotite, titanite, carbonate minerals and rarely quartz. Allanites containing almost all of the rare earth element (REE) components of the ores occur in disseminated manner and are euhedral to subhedral. The mineral is an early crystallized mineral replaced by magnetite and chalcopyrite. The allanite contains around 16 wt.% REE and is low in mafic components having chemical composition of Mn-poor type, which tends to occur in the magnetite-series granitic rocks in Japan. The REE components could have been derived from an oxidized alkaline granitic activity of mid-Tertiary. Both chalcopyrite and magnetite are well separated by the mineral dressing, and all the allanites moved to the tailings. Therefore, the tailing pond turns out to be an excellent LREE reservoir in future.