Multiple mineralization events in the eastern Central Asian orogenic belt: Insights from geology, geochronology, and geochemistry of the giant Tongshan porphyry Cu deposit, NE China

The Tongshan deposit is a giant porphyry Cu system in the eastern Central Asian orogenic belt where complex alteration and mineralization processes have remained poorly constrained. This study elucidated its evolution through integrated field geology, Re-Os geochronology, and sulfur isotope analysis. Mineralization in the western segment of Tongshan is hosted in granodiorite porphyry and tonalite and is associated with phyllic and localized potassic alteration. In the eastern segment, mineralization occurs within Ordovician Duobaoshan Formation volcanic rocks and the roof pendants of granodiorite and dacite porphyry, where propylitic alteration overprints earlier alteration assemblages. Two distinct mineralization episodes were identified: an initial porphyry-style mineralization (episode A) and a later overprinting porphyry(-epithermal) mineralization (episode B). Episode A comprises three stages (A-I, A-II, and A-III), with the main Cu mineralization in stage A-II forming quartz-chalcopyrite ± molybdenite ± pyrite veinlets with K-feldspar halos. Episode B veins overprinted earlier veins and contributed significant additional Cu through four stages (B-I, B-II, B-III, and B-IV) of wider quartz-sulfide veining. Systematic logging showed a positive correlation between the density of overprinting veins and Cu(-Mo-Au) grades. Molybdenite Re-Os dating suggests that episode A and B veins likely occurred at 475.6 ± 2.3 Ma and 228.1 ± 2.9 Ma, respectively. These ages suggest that the porphyry-style mineralization corresponds to the Ordovician granodiorite porphyry intrusions, whereas the overprinting porphyry(-epithermal) mineralization was associated with Triassic granodiorite and dacite porphyry. A significant characteristic at Tongshan is the prolonged interval of more than 200 m.y. between the two mineralization episodes. The δ34S values of the episode A sulfides range from −2.1‰ to −0.5‰, which is consistent with a magmatic source. The episode B sulfide δ34S signatures of −5.6‰ to +0.9‰ are analogous to those of a mantle-crust mixed source, indicating the Duobaoshan Formation may have been a potential sulfur reservoir. These results provide a refined genetic model for Tongshan and valuable insights for exploring other Paleozoic porphyry Cu deposits in the Central Asian orogenic belt.