The provenance of late Permian karstic bauxite deposits in SW China, constrained by the geochemistry of interbedded clastic rocks, and U–Pb–Hf–O isotopes of detrital zircons

Abstract

The provenance of karstic bauxite deposits is difficult to constrain as such deposits are the products of intensively weathered rocks. We have studied the geochemistry of interbedded clastic rocks and isotopic characteristics of detrital zircons in late Permian karstic bauxite deposits in SW China to understand their provenance. The U–Pb ages of detrital zircons from both clastic rocks and bauxite ores show a peak at ~260Ma. This peak age is within error of the sedimentary age (259.8±0.4Ma) of the bauxite ores and the age of emplacement of the Emeishan large igneous province in SW China. The peak age, together with abundant fragments of volcanic quartz crystals in the clastic rocks, suggests that the bauxite deposit was derived from volcanic rocks. Further, the clastic rocks yield Al2O3/TiO2 values of 25–132 and δEu=0.23–0.58, showing arc-like REE trends and indicating that the source rocks were felsic. The εNd(T) values of the bauxite ores and clastic rocks typically range from −7.6 to −3.5, with 130 out of 140 detrital zircons yielding εHf(T) values of −26.7 to −0.6 and δ18O values of +5.6‰ to +10.3‰, consistent with a dominantly crustal provenance. Based on the paleogeography and distribution of Permian magmatic rocks in SW China, it is likely that the karstic bauxite deposits were derived from the felsic volcanic rocks of a Permian magmatic arc at the northern margin of the Paleo-Tethys, rather than from the Emeishan large igneous province. This study provides a new perspective on the provenance of karstic bauxite deposits worldwide and yields insights into element mobility during extreme weathering.