Metallogenesis of the Late Carboniferous Karst Bauxite in the North China Craton: A Review.

The metallogenesis of the Late Carboniferous karst bauxite of the Benxi Formation in the North China Craton has long been debated, particularly regarding the relative roles of in situ weathering and residual accumulation of the underlying carbonate rocks, allochthonous Al-rich materials input, paleokarst geomorphological control, and postdepositional modification. Within a tectonic paleogeographic framework, this study integrates published petrological, mineralogical, major, trace, and rare earth elements (REEs) geochemical data, detrital zircon and rutile U-Pb geochronological data, and Hg-isotope data, and evaluates these data sets within an evidence framework. The basal Fe-bearing claystone shows continuity with the carbonate basement in immobile element weathering trends and REE affinities, which strongly supports an origin principally by in situ weathering and residual accumulation of the basement. The main bauxite and overlying claystone deviate from this trend, a pattern more consistent with input from multiple peripheral and intracratonic sources, with possible contributions from contemporaneous volcanic ash. Long-distance aeolian and regional fluvial transport, convergence within negative paleokarst geomorphic units, and deposition in a terrestrial-marine continuum setting are interpreted as likely components of the metallogenic system. On this basis, the genesis of the Benxi Formation karst bauxite can be interpreted, within a regional synthesis framework, as a continuously coupled, multistage process.