Regional multi-sources of Carboniferous karstic bauxite deposits in North China Craton: Insights from multi-proxy provenance systems

Abstract

The sources of karstic bauxite are complex and have not been so far addressed by multi-proxy provenance studies that interrogate bauxite sources. The Carboniferous bauxite in the North China Craton, which is the largest karstic bauxite area in the world, contains considerable quantities of detrital heavy minerals, including zircon, rutile, tourmaline, and moissanite, allowing multi-proxy provenance studies. In this study, geological, mineralogical, geochemical analyses, and detrital heavy mineral analyses were conducted for the Jiagou and Kuancaoping bauxite deposits located in the southern and northern parts of the North China Craton, respectively. Coupled with previously published geological, geochemical, and detrital mineral data, this study aims to thoroughly clarify the provenance of karstic bauxites in the North China Craton. In general, the ore-bearing rock series contains three units: lower iron-bearing claystone consisting of illite, chamosite, and goethite; middle bauxite ore dominated by diaspore, kaolinite, illite, chamosite, and anatase; and upper bauxitic claystone composed of kaolinite, diaspore, and anatase. Immobile trace element ratios and Rare Earth Element patterns of the bauxites throughout the North China Craton revealed that the lower iron-bearing claystone was autochthonous and directly sourced from the underlying limestone. The isotope data of detrital zircon along with chemical compositions and morphological features of detrital rutile, tourmaline, and moissanite in the bauxite ores revealed that the bauxite ore and bauxitic claystone were mainly para-allochthonous and derived from regional multi-sources. The multi-sources origin is also shared by other karst bauxites in the world. The results indicate that the bauxite deposits in the northern and southern parts of the North China Craton have distinct source materials. The provenance of the bauxite in the northern part of the North China Craton is mainly from the northern margin craton orogenic belt and the adjacent intraplate paleo-uplifts, whereas in the southern part, it is dominated by the North Qinling orogenic belt and the nearby paleo-uplifts. Consequently, the Carboniferous karstic bauxites in the North China Craton are characterized by the autochthonous origin of the lower iron-bearing claystone and the para-allochthonous origin of the upper bauxite ore and bauxitic claystone. This clearly illustrates the dependence of provenance information on mineral proxy choice and underlines the preponderance of multiproxy provenance studies to solve the complex source issue of karst bauxites in North China Craton.