The Yuanmenlou Cu polymetallic deposit is located in the central Zhashui—Shanyang ore concentration area, South Qinling Belt, and is closely associated with multiphase intermediate- felsic porphyritic intrusions. Previous geochronological studies indicate that these intrusions were emplaced at 147.2～148.0 Ma, broadly coeval with skarn- related Cu mineralization, and were derived from moderately oxidized and hydrous magmas. However, their magmatic evolution, volatile behavior, and metallogenic potential remain insufficiently constrained. This study aims to evaluate whether the Yuanmenlou intrusions belong to the regional Late Mesozoic high Ba—Sr magmatic system and whether apatite compositions record the transition from a Cl- rich fertile magmatic stage to an F- rich residual melt stage.Methods: Representative samples were collected from drill holes ZK801 and ZK001 and from exposed porphyritic intrusions in the Yuanmenlou mining area, including granodiorite porphyry, fine- grained quartz diorite porphyrite, quartz monzonite porphyry, granite porphyry, and altered granite porphyry. Twelve samples were analyzed for whole- rock major, trace, and rare earth elements. Apatite grains from five representative samples were analyzed for major and volatile components by EPMA and for trace elements by LA—ICP—MS. Petrographic observations, whole- rock Sr—Y—Ba—REE systematics, and apatite F—Cl—S—Sr—Y—REE compositions were integrated to constrain magmatic differentiation, volatile evolution, and Cu polymetallic metallogenic potential.Results: The Yuanmenlou porphyritic intrusions are intermediate to felsic in composition, with SiO2 contents mainly concentrated at 66%～72%, and belong to the high- K calc- alkaline to shoshonitic series. They are characterized by high Ba—Sr contents, relatively high Sr/Y and La/Yb ratios, light rare earth element enrichment, weak Eu anomalies, and depletion in Nb, Ta, Ti, and P. These features are comparable to those of Late Mesozoic high Ba—Sr granitoids in the Shanyang area, suggesting that the Yuanmenlou intrusions represent shallow- level phases of a regional hydrous, high Ba—Sr intermediate- felsic magmatic system. Decreasing MgO, TiO2, CaO, and P2O5 with increasing SiO2 indicates fractional crystallization of hornblende, biotite, Fe—Ti oxides, apatite, and feldspar- group minerals. Apatite compositions vary among different intrusive phases. Apatite from fine- grained quartz diorite porphyrite and part of the granodiorite porphyry is relatively Cl- rich, with low F/Cl ratios, high Sr/Y ratios, and low REY contents. In contrast, apatite from granite porphyry and part of the quartz monzonite porphyry is F- rich and Cl- poor, with high F/Cl ratios, low Sr/Y ratios, and high REY contents. Most apatite SO3 contents are low, but some analyses show elevated SO2 values; calculated melt sulfur contents are mainly 10～17×10-6.Conclusions: Whole- rock and apatite geochemical features indicate that the Yuanmenlou porphyritic intrusions belong to the Late Mesozoic high Ba—Sr intermediate- felsic magmatic system of the Zhashui—Shanyang district. Their high Sr/Y and high Ba—Sr signatures were likely controlled by hydrous deep- level differentiation and multistage magma evolution rather than by a single slab- melting process. Whole- rock and apatite compositions jointly record an evolution from a relatively weakly differentiated, Cl- rich, high- Sr/Y magmatic stage to a more evolved, F- rich, Cl- poor, and REY- enriched residual melt stage. The Cl- rich, SO3- bearing, high- Sr/Y apatite in fine- grained quartz diorite porphyrite and granodiorite porphyry may indicate a magmatic stage favorable for Cu- bearing fluid release. Therefore, combined whole- rock Ba—Sr—Sr/Y—La/Yb signatures and apatite F—Cl—S—Sr—Y—REE indicators provide a useful mineral- geochemical approach for evaluating concealed porphyry- skarn Cu polymetallic mineralization in the Zhashui—Shanyang ore concentration area.