<p>The formation of Caosiyao giant porphyry Mo deposit is related to three granitic porphyries: coarse-grained granite porphyry (CG), fine-grained granite porphyry (FG), and giant plagioclase phenocryst bearing granite porphyry (PG). To investigate the mineralization significance of three porphyries, Microthermometry, Laser micro-Raman Spectra, and H-O-He-Ar isotope analyses of fluid inclusions were conducted. Intermediate density with high temperatures (&gt; 550 °C) and moderate-low salinities (~10 wt.%) characterizes CG-related initial exsolved fluids. Vapor-rich and brine phases separated from the initial fluid following a continuous decrease in pressure and temperature, inducing molybdenite precipitation. FG-related initial fluids are characterized by high temperatures (&gt; 550 °C) and salinities (&gt; 65 wt.%). The mixing of low-salinity fluids led to a rapid decrease in the salinity of FG-related fluid, promoting the deposit of the Mo element. The lead-zinc mineralization is closely related to the FG-related fluid, and the addition of meteoric fluid induced the formation of galena and sphalerite. The ore-forming fluid related to the PG is CO₂-rich and accompanied by the addition of mantle-derived He-Ar. The presence of CO₂ did not contribute to the solubility of Mo, resulting in the absence of a considerable amount of molybdenite.</p>