Provenance of Nanhuan Datangpo Formation Manganese Mn Deposit in Songtao Area,East Guizhou Province:Evidence from Sr Isotope

Yu Wenchao; Du Yuansheng; Zhou Qi; Peng Touping; Wang Ping; Yuan Liangjun; Xu Yuan; Pan Wen; Xie Xiaofeng; Qi Liang

doi:10.3799/dqkx.2016.092

Abstract：Provenance of manganese deposit is a key problem in the manganese metallogenic study.For a better understanding on the metallogenic process of the Nanhuan manganese deposit in Songtao area,East Guizhou Province,we need to gain a clear idea of the provenance of this manganese deposit.The Sr isotope study on the Mn deposit in Lower Nanhuan Datangpo Formation in Songtao,East Guizhou Province indicates that 87 Sr/86 Sr ratios in 15 samples vary in 0.705 727-0.732 536.Studied samples include Mn ore,Mn shale and black shale in the Mn-bearing layer and the highest 87 Sr/86 Sr ratio appears in the black shale sample.With Al (%)increasing in samples,87 Sr/86 Sr ratios show two changing trends:the rising trend indicates terrigenous materials input and the falling trend indicates the deep hydrothermal sources input.As to 87 Sr/86 Sr ratios via Mn (%),there is no significant correlation coefficient,but 87 Sr/86 Sr ra-tios decrease when Mn (%)increase generally,according to residual analysis,we find that this is caused by the convergence fluctuation of 87 Sr/86 Sr ratios against the Mn(%)changes.The broad variation of 87 Sr/86 Sr ratios in Mn layer is caused by the dual inputs from terrigenous materials and hydrothermal sources.Compared with the contemporary (about 660 Ma)Sr isotope ratio in paleoseawater and the Sr isotope data from different ages Mn deposit world wide,we find that the broad variation of 87 Sr/86 Sr ratios in the Datangpo For-mation.Mn layer does not conform to the feature of hydrogenetic Mn deposit.Considered with the specific geological background,we believe that the accumulation and precipitation of manganese are separated processes:the accumulation of Mn had finished in the anoxic basin during the Sturtian glaciation,whereas the Mn deposit precipitated in an unstable paleoceanographic environment at the beginning of interglaciation.