Petrogenesis of the Tiegeshan diorite porphyry in the Duolong ore district, Tibet: Implications for porphyry mineralization

Porphyry deposits are genetically linked to intermediate-acid hypabyssal intrusions, yet their metallogenic districts frequently contain barren diorite porphyries whose petrogenetic relationships to mineralization remain poorly understood. This study presents integrated analyses of zircon U-Pb geochronology and trace element geochemistry, whole-rock major and trace element compositions, Sr-Nd isotopic systematics, and electron probe microanalysis (EPMA) on amphibole for the Tiegeshan diorite porphyry in Tibet. This is complemented by comparative EPMA studies on the Gerze diorite porphyry, to elucidate their petrogenetic evolution and metallogenic implications. The Tiegeshan diorite porphyry exhibits detrital zircon inheritance patterns, yielding a crystallization age of 122 ± 0.5 Ma. The diorite porphyry exhibits low SiO 2 (55.75–58.05 wt%), total alkalis (Na 2 O + K 2 O = 3.72–4.45 wt%), and MgO (2.79–3.28 wt%), with metaluminous characteristics (A/CNK = 0.84–0.91) and sodic (Na-rich and K-poor) affinity (K 2 O/Na 2 O = 0.12–0.29), classifying as calc-alkaline rocks. Its chondrite-normalized REE patterns display LREE enrichment, flat HREE trends, and subtle negative Eu anomalies (δEu = 0.36–0.39), coupled with primitive mantle-normalized enrichment in LILEs (Ba, Sr) and depletion in HFSEs (Nb, Ta, Ti), consistent with arc-related signatures. Sr-Nd isotopic compositions reveal hybrid magma sources involving mantle-derived components and crustal assimilation. The presence of amphibole phenocrysts in the Tiegeshan diorite porphyry indicate hydrous conditions in the shallow magma chamber. Notably, the amphibole at Tiegeshan contains significantly higher water contents (mean: 6.26 wt%) compared to the Gerze porphyry (4.53 wt%). Petrogenetic constraints suggest that the Tiegeshan diorite porphyry originated through partial melting of lower crustal sources with amphibole-dominated residues, experiencing limited fractional crystallization but moderate crustal contamination during ascent. Its tectonic setting corresponds to a continental arc environment during the transitional phase between terminal subduction and incipient collision, with slab rollback triggering large-scale magmatism in Duolong. Ore-forming intrusions in the district represent more evolved porphyritic phases of the magma chamber, highlighting the importance of identifying the distribution patterns of these evolved porphyritic intrusions for regional exploration targeting.