Chromite prospects in the Daba-Xiugugabu ophiolite zone southwestern Tibet

Abstract：The Yarlung Zangbo ophiolite belt is >1500 km long and may be divided into three segments: the east (Qüxü-Mêdog), central (Ngamring-Rinbung) and west (from west Saga to the Sino-India national border) segments. The west segment is further divided into the Dajiweng-Saga ophiolite zone in the north and Daba-Xiugugabu ophiolite zone in the south. The previous research focused on the east and central segments and very limited work has been done in the west segment. Ophiolite masses (blocks) in the Daba-Xiugugabu ophiolite zone are composed of mantle peridotite. The main rock types are harzburgite and dunite with rare lherzolite, while oceanic crust is lacking in the typical ophiolite section. The ophiolite masses are large and have pronounced facies zoning with extensive dunite facies. Many chromite mineralization occurrences have been found in the La'nga Co, Dongpo, Dangqiong and Xiugugabu masses. Orebodies occur in lenticular (podiform), short-vein and irregular shapes. Ore is mostly massive in structure and in a few cases disseminated, generally with a Cr2O3 content of over 40%. The chromite deposits are of podiform type. Comparative study indicates that the rock masses in this ophiolite belt are similar to the mineralized rock bodies hosting large podiform chromite deposits in the world in respect to the tectonic setting, ophiolite type, size of rock masses, rock composition, location of preservation, degree of partial fusion, geochemical characteristics of rocks and minerals and chromite mineralization characteristics. The Daba-Xiugugabu ophiolite zone has good metallogenic conditions and better ore prospects. The authors suggest that: dunite facies in the northwest part of La'nga Co mass is the target with the best ore prospects, and next are dunite facies and dunite-harzburgite facies of the Dongpo mass and dunite-harzburgite facies of the Dangqiong mass.