Magmatic Evolution and Layered Chromitite Formation in the Gayahe Ultramafic Complex, East Kunlun Orogenic Belt, Western China

Field investigations in the Gayahe ultramafic complex have revealed a well-defined stratigraphic sequence, characterized by a vertical succession of ultramafic rocks from base to top: pyroxenite, serpentinite, olivine pyroxenite, and dunite. Minor siliceous units, volcanic rocks, and intrusive dikes of syenitic granite and dioritic porphyrite are also present. Two distinct chromitite layers have been identified: (1) The 5.6m-thick chromite enrichment zone comprises a nearly 1m-thick massive chromitite seam interbedded with upper and lower chromite veinlets, with grades varying between 11.66 wt. % and 45 wt. %; (2) A thinner chromitite layer (~1.3 m), for which grade data is not available. The thicker chromitite layer overlies olivine pyroxenite, which is serpentinized and grades into a dunite shell at the chromitite contact. In high-grade layers, the dunite is notably thin, while the massive chromitite transitions into banded chromitite with decreasing grade. Overlying pyroxenite is similarly serpentinized. In this dataset, samples were collected from the thick massive chromitite layer and associated ultramafic rocks.