Mesothermal-epithermal altered rock type gold deposit, associated with gold-bearing crypto-explosive breccias and minor quartz veins.

Classified as a subepithermal deposit, representing the transitional mineralization between porphyry and epithermal deposits. Its Au orebodies are hosted in the Xiongcun Formation tuff. The surrounding tuff is intensely altered, and the textures and compositions of the protolith are difficult to constrain. The tuff consists mainly of quartz and sericite, and is bedded and fine- to medium-grained. The orebodies consist of several parallel ore veins that dip to the NE at 56°–67° and strike E–W (∼313°), and thus were likely structurally controlled by NW–SE-trending faults and fractures . The ore veins are 1–3 m wide and locally up to 5 m, and generally have strike lengths of 5–15 m and extend 280 m vertically. The Dongga Au deposit has total Au resources of 9.55 tons with a variable grade of 0.13–61.6 g/t (average = 6.9 g/t). Hydrothermal alteration in the deposit was phyllic, with abundant quartz, sericite, and pyrite, with no Au in the pyrite.
One supergene and three major mineralization (I, II, and III) stages, based on petrographic observations. The earlier mineralization stage (I) is disseminated and also formed veins, whereas the later mineralization stages (II and III) only formed veins. The earlier mineral assemblage (I) is dominated by quartz and sericite, along with minor pyrite, which was typically replaced by late chalcopyrite, pyrrhotite, and sphalerite. In stage II, which was the main stage of Au mineralization, the ore minerals are pyrite, chalcopyrite, pyrrhotite, Au-bearing minerals (i.e., native Au and electrum), and minor sphalerite. The gangue minerals are chlorite, epidote, and minor sericite. In stage III, minor sericite, epidote, and chlorite were formed along with quartz, actinolite, and pyrite. The supergene stage formed hematite, limonite, and malachite by oxidation of primary sulfides.

The exposed strata in the Xiongcun ore district mainly comprise the Lower–Middle Jurassic Xiongcun Formation and Quaternary. The Xiongcun Formation (195 to 165 Ma) mainly consists of volcanic conglomerate, volcanic breccia, tuff, shale, sandstone, siltstones and limestone, with orebodies predominantly hosted in tuff. The Xiongcun ore district records intense magmatism, marked by multiple intrusive phases emplaced during the Early Carboniferous, Jurassic, and Eocene, including Early Carboniferous hornblende gabbro (~354.9 ± 0.9 Ma), amphibolite (~354.9 ± 0.9 Ma) and diorite (~354.3 ± 1.4 Ma); Early Jurassic quartz diorite porphyry (~175.7 Ma); Early–Middle Jurassic quartz diorite porphyry (174 ± 1.6 Ma); Middle Jurassic quartz diorite porphyry (~161.8 Ma) and diabase dike (165.3 ± 1.0 Ma); and Eocene quartz diorite pluton (50 Ma), biotite granodiorite (48 Ma) and lamprophyre dike (47.0 ± 0.6 Ma). The Dongga Au deposit is located in the central part of the Xiongcun ore district, in close proximity to the No. 2 porphyry Cu-Au deposit, and they constitute a porphyry–epithermal mineral system. Five types of veins were identified in the Dongga Au deposit: quartz–sulfide veins, chlorite–sulfide veins, pyrite veins, actinolite veins, and late quartz veins.

Other Regions, Features and Areas containing this locality

References