The Bijiashan Rb-rich granitic porphyry is situated on the southern flank of the Dahongliutan-Quanshuigou fault in the West Kunlun orogenic belt. This intrusion directly forms the orebody, and this orebody represents a newly discovered superlarge rubidium deposit. Systematic geochronological, whole-rock geochemical, and mineralogical analyses on this intrusion were performed, aiming to clarify the petrogenesis of the Bijiashan porphyry and the rare-metal metallogenic mechanisms of the associated rubidium deposit. Zircon LA-ICP-MS U-Pb dating yielded an age of (5.88±0.06) Ma (MSWD = 2.2), thereby confirming its emplacement in the Pliocene. The Bijiashan granitic porphyry was characterized by high silica and high potassium content, belonging to the high-K calc-alkaline series. The rocks have total rare earth element (ΣREE) contents of (131-202) × 10^-6, with a composition marked by significant light rare earth element (LREE) enrichment and a right-sloping REE pattern. Notably, it exhibits a discernible “tetrad effect” and a significant negative Eu anomaly, suggesting that it is a highly fractionated granite of pure crustal derivation. Within the deposit, rubidium is primarily hosted in alkali feldspar and biotite. Rb⁺ isomorphously substitutes for K⁺ in K-feldspar or occupies the interlayer sites of biotite/sericite. High fluorine (F) content in mica exhibits a significant positive correlation with rubidium (Rb) enrichment. The formation of the Bijiashan Rb deposit was dominated by crystallization differentiation of a crust-derived, highly fractionated granitic magma, with subsequent overprinting by late-stage, fluorine-rich hydrothermal fluids. Early magmatic differentiation was responsible for the preconcentration of rubidium in the residual melt. This process was followed by further extreme enrichment through subsequent fluid activity, culminating in the final fixation of rubidium via isomorphism in alkali feldspar and sheet silicate host minerals.