Discovery and geological significance of gas-liquid spouting expulsion and effusion depositional structures at Xialei manganese deposit in Guangxi

Abstract

The Daxin Xialei Devonian manganese deposit in Guangxi is the first super-massive manganese ore deposit ever discovered in China. Here we conducted detailed petrographic studies on manganese-bearing sequence, ore mineral assemblages and their textures and structures. Our work reveal that the brecciated, vein-bearing and stockwork manganese ore minerals may form correspondingly to the expulsion and effusion of the gas and liquid-rich fluid. In addition, prevailing manganese-bearing silicate and sulfide minerals (rhodonite, manganese-iron chlorophyllite, pyrite, chalcopyrite, manganite, etc.) of hydrothermal origin are observed among the ores. Further comprehensive examinations of the original borehole data of the mining area lead to two major outcomes.First, three syndepositional faults are successfully recovered and identified in Late Devonian Xialei-Tuhu Ⅳ-graben basins, which controls the formation and spatial distribution of the manganese ore deposit.Second, brecciated manganese ore minerals appear to be clustered in space, and the localities of which may correspond to the locations of the ancient gas-liquid expulsion and effusion centers that give rise to the formation of manganese ore. Notably, the spatial distribution of the fossilized gas-liquid centers is controlled by the syndepositional faults developed during the formation of manganese ore deposit. Given the observation that Xalei Devonian manganese ore deposit shares comparable expulsion and effusion depositional features to Nanhua Datangpo gas-liquid depositional manganese ore deposit at Songtao of Guizhou Province, it is therefore argued that both Xialei and Datangpo manganese ore developed by similar mechanisms. This study sheds light on a better understanding of the metallogenic mechanism(s) and will place better constraints on the future explorations of Xialei manganese ore deposit.

Keywords

• gas-liquid expulsion and effusion sedimentary structure
• syngenetic syndepositional fault
• discovery
• xialei manganese deposit
• guangxi