Multi-satge formation of the podiform chromitite

Abstract：Podiform chromitite serves as the main source of chromium and is also the shortage ore species in China; therefore, the discovery of large chromitite deposits has become the first way to solve the long-term dependence on imports. But there is disagreement about the genesis of podiform chromite. With the discovery of many abnormal mantle minerals in podiform chromite and its host mantle peridotite, geologists have rethought the genesis of the podiform chromitite. This paper focuses on the latest achievements and progress in the study of the podiform chromitite both in China and abroad, which include the morphological characteristics of podiform chromitite, output feature, mineral chemistry, the distribution pattern of the platinum group elements (PGE), the UHP minerals in the chromitite, and the host harzburgite evolution. The chromium of podiform chromitite was derived from the incongruent melting of the two types of pyroxene and associated mineral spinel, which might have been formed in an environment of the lower mantle or transition zone. Platinum group element minerals exist as inclusions and fissures in the podiform chromitite, and the content of platinum group elements is related to the S saturation level formation in the process and has multi-phase characteristics. The authors hold that the process of the formation of podiform chromitite consisted of four stages, which were the stage of chromium source derivation, the crystallization stage of spinel and UHP minerals, the chromitite ore-forming stage, and the stage of chromitite seating. It is thought that the characteristics of each stage require further refinement and investigation, and the detailed comparison between different podiform chromitite deposits is necessary.