Study On The Cobalt Enrichment Mechanism Of Zhongba Cobalt-manganese Deposit In Shiqian, Guizho

The global geotectonic pattern and paleoclimatic environment changed dramatically in the middle and late Neogene,and the representative events include global glacial events represented by"Snowball Earth",Rodinia supercontinent rifting and Gondwana supercontinent convergence,and large-scale mineralization events.After the end of the ice age,during the rapid change of climate from cold to hot,a large number of"cap carbonates"were developed globally,and more manganese-bearing dolomites and manganese deposits were deposited.The cobalt-manganese deposit of Shiqianzhongba is one of the representative deposits with a maximum cobalt content of 537×10^-6.However,the research on the state of cobalt in the cobalt-manganese deposit of Shiqianzhongba,its enrichment mechanism and its coupling relationship with the material circulation among the Earth’s circles after the ice age is very shallow.In this paper,we investigate the sedimentology,mineralogy and elemental geochemistry of the Shiqianzhongba cobalt-manganese deposit,and integrate the relevant studies with the global geotectonic evolution,paleoclimate,paleomarine environment and microbial effects in the middle and late Neogene,with the aim of explaining the material source,enrichment process and key control factors of cobalt.The following results and insights were obtained in this paper:1.The ore minerals in the cobalt-manganese deposit mainly include barium manganese ore and hydromanganese ore,etc.The vein minerals include calcite,kaolinite,quartz,feldspar,etc.Next,barite,sphalerite,monazite and other minerals are also developed.2.By examining the SiO₂/Al₂O₃ratio,Fe/Ti-Al/（Al+Fe+Mn）diagram,Mn/Fe ratio,Co/Zn vs.Co+Ni+Cu diagram,LogTh-LogU,La/Ce ratio of the cobalt-manganese deposit rocks/ore,and combining with the time frame of occurrence and influence of contemporaneous volcanic activities around the study area,it is concluded that the mineralization of Shiqianzhongba cobalt-manganese ore The source of cobalt-manganese ore in Shiqianzhongba is likely to be closely related to the hydrothermal activity of the seafloor.The study of the cobalt endowment shows that no independent minerals of cobalt have been found in the Shiqianzhongba cobalt-manganese deposit.Elemental surface scanning and correlation analysis show that cobalt may be assigned to manganese-bearing minerals such as barium manganese ore and hydromanganese ore in the form of homogeneous or adsorption.4.Preliminarily,the enrichment mechanism of cobalt in Shiqianzhongba cobalt-manganese deposit is divided into three stages:（1）During the snowball Earth period,a large amount of cobalt and manganese elements were brought to the marine system due to submarine volcanic/hydrothermal activities,and the initial reservoir of cobalt and manganese was formed in the seawater.（2）With the melting of glaciers,the snowball Earth ended,which accelerated the weathering rate of surface rocks and increased the flux of weathering products input to the ocean,causing an increase in seawater alkalinity.In this process,a large amount of dissolved Mn²⁺in the reducing water body is affected by sea level rise or redox interface fluctuations,and manganese mostly precipitates with carbonate rocks in the form of oxides.During the precipitation of manganese oxides,cobalt will be adsorbed continuously,and eventually cobalt-bearing manganese dolomite will be formed.（3）With the continuation of crustal uplift or weathering,the cobalt-bearing manganese dolomite deposited in advance is continuously weathered to form cobalt-bearing manganese claystone,causing secondary enrichment and mineralization of cobalt.