Cooling and exhumation of the oldest Sanqiliu uranium ore system in Motianling district, South China Block

Abstract

The Sanqiliu uranium deposit belongs to a uranium ore system in Motianling district. It is the oldest uranium deposit in South China. Primary uranium mineralization occurred almost simultaneously with the emplacement of the host granites and subsequent dykes, and it has a relatively high grade of uranium (0.421%). We clarify the age of mineralization and investigate the cooling history through new pitchblende U-Pb and apatite fission-track thermochronology. The pitchblende U-Pb results indicate that uranium mineralization occurred at 801-759 Ma. Fractionation of uranium and lead at~374-295 Ma is interpreted as remobilization and resetting of the original uranium. The Motianling area has apatite fission-track ages of 57 to 18 Ma. By combining our results with previous work, we conclude that the deposit cooled slowly and was exposed at the surface during the Cenozoic. The timing and depth of exhumation helped to preserve and avoid erosion of the uranium deposit, and highlight the potential for regional uranium exploration.

Geochronology of early Mesozoic diabase units in southwestern China: metallogenic and tectonic implications

“…However, potential overprinting by widespread early and late Mesozoic tectonothermal events (e.g. the Indosinian and Yanshanian events; Wang, Y. J. et al 2013;Qiu, L. et al 2014Qiu, L. et al , 2015aDong et al 2015) suggests that the K-Ar ages for these diabase units may be unreliable. As such, precise ages are necessary to constrain the timing of emplacement of these sills.…”

“…The Badu diabase formed in a non-arc setting (Qiu et al 2015a(Qiu et al ,b, 2016. If the diabase was generated directly from the mantle and underwent fractional crystallization then it should have formed under magma oxygen fugacity conditions similar to that of typical Hawaiian basalts (∼FMQ +1; Jackson, Weis & Huang, 2012).…”

“…These metals were subsequently concentrated to form the Au deposits in the SW South China Block (SCB). However, rare magmatic rocks have been identified in the Youjiang fold-and-thrust belt (Wang, Y. J. et al 2013;Qiu, L. et al 2015aQiu, L. et al ,b, 2016. In addition, the recent discovery of an Au deposit hosted by the Badu diabase (Dong et al 2013;Li, P. et al 2015) implies a genetic relationship between mafic magmatism (e.g.…”

“…Yan et al 2003Yan et al , 2006Yan et al , 2016Wang, Y. J. et al 2013;Qiu et al 2017). The basement in this region consists of metamorphosed Neoproterozoic shallow-marine sandy to argillaceous detrital flysch units that are intercalated with volcanic rocks Qiu et al (2015a). The basement is overlain by a Palaeozoic to lower Mesozoic marine and Middle Triassic to Cretaceous clastic sedimentary cover sequence (Li et al 2014;Tang et al 2014;Qiu et al 2017).…”

“…Deprat, 1914;Fromaget, 1932Fromaget, , 1941, foreland basins, foldand-thrust belts and large-scale granitic magmatism within the southwestern SCB (e.g. Wang, Y. J. et al 2007aWang, Y. J. et al ,b, 2013Lepvrier et al 2011;Faure et al 2014Faure et al , 2016aQiu, L. et al 2014Qiu, L. et al , 2015aQiu, L. et al ,b, 2016Qiu, L. et al , 2017. The Triassic magmatism is characterized by voluminous felsic intrusions that are distal from continental margins and occur as dispersed batholiths and sporadic plutons within the SCB ( Fig.…”