Ore-forming age and material sources of the North Santonggou manganese deposit in East Kunlun of Qinghai:Constrained by Re-Os isotopic chronology and geochemistry
The North Santonggou manganese deposit in East Kunlun is the largest marine sedimentary manganese deposit discovered in Qinghai Province in recent years.This deposit is located on the northern margin of the southern structural belt of the East Kunlun mountains,and the manganese-forming basin is closely related to the tectonic evolution of the Proto-Tethys ocean.So far,few studies have been conducted on this manganese deposit,and as a result,there remain some controversies,especially the formation age of its ore-bearing sequence(Meso-Neoproterozoic versus Ordovician-Silurian)as well as its manganese sources(dominated by seafloor hydrothermal fluid or jointly contributed by seafloor hydrothermal fluid and continental weathering).In order to solve these problems,on the basis of detailed geological investigation and drill observation,11 manganese ore samples were selected for Re-Os isotope analysis which yielded a Re-Os isochron age of 442±15 Ma.This age suggests that the North Santonggou manganese deposit was formed in the Late Ordovician rather than the Meso-Neoproterozoic as previously thought,and is consistent with the formation age of the sedimentary rocks of the Ordovician Nachitai Group in this region.In addition,the initial 187Os/188Os ratio obtained from Re-Os isotope analysis is 0.67±0.02,which is significantly lower than that of coeval seawater(～0.72).This ratio indicates that the manganese of the North Santonggou manganese deposit was mainly derived from submarine hydrothermal fluid.In the discrimination diagrams of SiO2-Al2O3,Al/(Al+Fe+Mn)-Fe/Ti,Fe-Mn-(Ni+Cu+Co)× 10 and lgU-lgTh,all samples fall into submarine hydrothermal-sedimentary area.The distribution patterns of rare earth elements in ores also have the characteristics of submarine hydrothermal sources.Overall,it is indicated that the metal source of the North Santonggou manganese deposit is closely associated with submarine hydrothermal activity.
East KunlunSedimentary manganese depositNachitai GroupRe-Os isotope ageGeochemistry
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维普
