The ultramafic rock located on the northern slope of Lüliang Mountain in the northwestern region of North Qaidam Orogen is altered to serpentinite. The occurrence of disseminated chromite within the serpentinite holds significant implications for understanding the petrogenesis of the protolith. This work provides strong evidence of a distinct zonal texture in the chromite found in the ultramafic rock, using petrographic microstructure and electron probe composition analysis. The core of the chromite is characterized by high contents of Cr^#, with enrichment in Fe^3+# (Fe³⁺/(Cr + Al + Fe³⁺)) and depletion in Al₂O₃ and TiO₂. The Cr₂O₃ content ranges from 51.64% to 53.72%, while the Cr^# values range from 0.80 to 0.84. The FeO content varies from 24.9% to 27.8%, while the Fe₂O₃ content ranges from 5.19% to 8.74%. The Al₂O₃ content ranges from 6.70% to 9.20%, and the TiO₂ content is below the detection limit (<0.1%). Furthermore, the rocks exhibit Mg^# values ranging from 0.13 to 0.25 and Fe^3+# values ranging from 0.07 to 0.12. The mineral chemistry of the chromite core in the ultramafic rock suggests it to be from an ophiolite. This ophiolite originated from the fore-arc deficit asthenosphere in a supra-subduction zone. The estimated average crystallization temperature and pressure of the chromite are 1306.02 °C and 3.41 GPa, respectively. These values suggest that the chromite formed at a depth of approximately 110 km, which is comparable to that of the asthenosphere. The chromite grains are surrounded by thick rims composed of Cr-rich magnetite characterized by enrichment in Fe^3+# contents and depletions in Cr₂O₃, Al₂O₃, TiO₂, and Cr^#. The FeO content ranges from 28.25% to 31.15%, while the Fe₂O₃ content ranges from 44.94% to 68.92%. The Cr₂O₃ content ranges from 0.18% to 23.59%, and the Al₂O₃ and TiO₂ contents are below the detection limit (<0.1%). Moreover, the rim of the Cr-rich magnetite exhibits Cr^# values ranging from 0.90 to 1.00, Mg^# values ranging from 0.01 to 0.06, and Fe^3+# values ranging from 0.64 to 1.00, indicating late-stage alteration processes. The LA-ICP-MS zircon U-Pb dating of the ultramafic rock yielded an age of 480.6 ± 2.4 Ma (MSWD = 0.46, n = 18), representing the crystallization age of the ultramafic rock. This evidence suggests that the host rock of chromite is an ultramafic cumulate, which is part of the ophiolite suite. It originated from the fore-arc deficit asthenosphere in a supra-subduction zone during the northward subduction of the North Qaidam Ocean in the Ordovician period. Furthermore, clear evidence of Fe-hydrothermal alteration during the post-uplift-denudation stage is observed.