Genesis Of The Chromitite In Cuobuzha Ophiolite In The Western Part Of Yarlung Zangbo Suture Zone,Tibet

Chromitite is the main source for the metal chromium,which is of great importance in industrial production.Chromitite is a rare but extremely important strategic resource in China.The reserves of chromite in China account for only 1‰of the reserves of the world.The raw chromitite ore for producing chromiumin China is dependent on import.There are about more than 9000 ultrmafic massifs in China,but few of them contain chromitites.Therefore,it is urgent to find chromitites with industrial value.Although the study on podiform chromitite started early and a lot of data have accumulated,the origin of podiform chromitite is still controversia and is difficult to be converted into a mine exploration model.Therefore,it is of great importance to discuss the formation process of podiform chromitite.We choose the Cuobuzha ophiolitic chromitite in the western segment of Yarlung Zangbo Suture Zone?YZSZ?as the object of this study.And we have carried detailed petrographic,mineralogical and geochemical research work on it.As unusual minerals such as diamonds,moissanites,have been recovered from several ophiolites in the YZSZ,we have also carried mineral separation work on the Cuobuzha chromitite to test the existence of these unsual minerals in the Cuobuzha ophiolite.The following progresses have been obtained:?1?The Cuobuzha chromitite is typical high-Cr chromitite,with Cr₂O₃ contents of 56.01-58.43%,and Cr#[=100×Cr/?Cr+Al?]of 75-78.MORB-normalized spidergrams of chromite show depletions in Al,Ga,V,Mg and Zn,but enrichments in Mn and Cr.Ti contents of the chromite show a wide range.In the Cr#-TiO2,Al₂O₃-TiO₂ and Cr#-Mg#diagrams,the chromite showed the boninitic affinity.But the MORB-normalized pattern was distinctly different from the boninite,obviously enriched in Ti,and depleted in V and Sc.?2?The chemical compositions of the chromites from the chromitite and those from the surrounding rock are significantly different from each other.?3?The discovery of a large number of crystal groups in the chromite,including metal alloys?Os-Ir,Fe-Ni,Fe-Cr?,natural elements?natural and natural silver?and clinopyroxene dissolution,and platinum group minerals,corundum,quartz,cassiterite,serpentine,chlorite and other minerals,indicates that the system is not ideal but a complex system.?4?In combination with previous studies,we believe that the geological,petrological and mineralogical characteristics of the Cuobuzha podiform chromitite support the melt-fluid flow model.