Origin of the carbonaceous debris and its implication for mineralization within the Qianjiadian uranium deposit, southern Songliao Basin

Abstract

Appearance and coal petrology of the carbonaceous debris (CD) from the Qianjiadian uranium deposit, southern Songliao Basin are illustrated in order to reveal the relationship between the CD and uranium mineralization, response of the CD and uranium mineralization to diabase dikes, and origin of the CD. Three types of CD have been identified in the Yaojia Formation: CD serving as trapped sediments, CD serving as laminae of cross bedding, and CD occurring in lumpy sandstones. With an average content of 91.2% in the CD, organic macerals are primarily composed of homoeollinite, desmocollinite and inertinite. Inorganic macerals of the CD mainly include pyrite with an average content of 8.8%. Average contents of the desmocollinite, inertinite and pyrite from the CD in the ore bearing section are higher than that in the non-ore bearing section, respectively. The study demonstrates that the CD rich in inertinite and desmocollinite facilitates uranium mineralization. Uranium is frequently adsorbed in the desmocollinite and inertinite, and coffinite is embedded in the inertinite, inferring that roles of the CD in uranium mineralization are both adsorption and reduction. Vitrinite reflectance (VR) of the CD ranges from 0.24% to 0.513% with an average value of 0.335%. The VR of the CD in the ore bearing section is generally larger than that in the non-ore bearing section. Uranium mineralization and enlargement of the VR are both attributed to the diabase dikes. The CD originated from the Late Cretaceous wildfire-related woody plants, and it has been transported into fluvial channels and preserved in sandstones.