Objective As a newly discovered skarn−type Cu−polymetallic deposit within the Zashui−Shanyang ore cluster, the Yuannenlou deposit lacks precise constraints on the timing of magmatism and mineralization, and the genetic relationship between these two processes remains unclear, which hinders a comprehensive understanding of regional metallogeny. This study employs isotopic geochronology to precisely determine the ages of magmatism and mineralization, elucidate their genetic linkage, and discuss the implications for regional ore prospecting.

Methods Based on detailed investigations of deposit geology and petrographic characteristics, this study integrates LA–ICP–MS U–Pb dating of zircon and garnet with zircon trace element analysis. An integrated comparative analysis was conducted to constrain the petrogenesis and metallogeny of the deposit.

Results The multiphase porphyritic intrusions in the Yuanmenlou deposit occur as small stocks (controlled by the intersection of N–S−trending fault zones and NWW–trending fold belts) and dikes (controlled by NWW−trending interlayered structural zones). The primary lithologies are granodiorite porphyry, granite porphyry, and quartz diorite porphyry. Zircon U–Pb dating of five dike samples yields ages ranging from 147.2 Ma to 148.0 Ma, while hydrothermal garnet from the skarn yields a U–Pb age of 151.5 ± 3.4 Ma. Zircon rare earth element (REE) compositions indicate high magmatic oxygen fugacity, with calculated oxygen fugacity values relative to the FMQ buffer ranging from +0.49 to +1.01 and averaging +0.84 (n=91). The zircons display strong positive Ce anomalies (Ce/Ce* = 152~251), weak negative Eu anomalies (Eu/Eu* = 0.68~0.76), and relatively high (Ce/Nd)/Y ratios.

Conclusions The porphyritic intrusions with varying lithofacies in the Yuanmenlou area formed from a single magmatic system, with compositional variations attributed to magma differentiation and wall−rock assimilation. The timing of magmatism and mineralization is Late Jurassic. The ore−forming magma was moderately oxidized and hydrous. The emplacement of multiphase dikes was closely associated with the formation of thick skarn zones and multilayered copper orebodies. These findings expand the exploration potential of the Zhashui–Shanyang ore cluster and provide significant implications for future prospecting.