Summary:
The Laoling uplift zone, situated within the Liaoning-Jilin orogenic belt, is a significant tectonic-magmatic belt associated with Au-polymetallic mineralization. The Banmiaozi gold deposit was formed in a tectonic setting involving the subduction of the Palaeo-Pacific Plate beneath the North China Craton. Its characteristics indicate that it can be classified as a collisional orogenic gold deposit.
The Banmiaozi gold deposit is hosted within an irregular stratiform-like silicified tectonic breccia belt that generally consists of at least two stages of breccia formation. The first stage formed along the unconformity before mineralization, and the second stage formed coevally with mineralization, and there is a superposition between the two.
The composition of the breccias is complex and includes haematite-quartz sandstone, silicified quartz sandstone, silicified dolomite marble, minor quartzite, shale, diorite porphyry, haematite, and baryte. The cement is mainly a mixture of powdered rocks and minerals, including silica, calcium-iron, and baryte. The metallogenic belt hosts several gold orebodies, which show stratiform-like or lenticular shapes. The hanging wall of the ore body shows distinct alterations as silicification and pyritization. Weak silicification is evident in the footwall marble, but the alteration zone is much narrower than in the hanging wall. The main mineralization occurs with the alteration of silicified-pyritized-baryte. The ore minerals are predominantly native gold with minor silver-bearing native gold and electrum, which occur in pyrite, quartz, chalcedony, baryte, dolomite, minor iron dolomite, sericite, and chlorite. Studies of fluid inclusions within baryte indicate that the initial ore-forming fluids were medium to low temperature, low density, and composed mainly of H2O and CO2. Mixing with metamorphic fluids during the ore-forming process was the main mechanism of mineralization.
Mineralization
A total of 9 major ore bodies, numbered I, II, II-1, II-2, III, IV, IV-1, V, and VI have been recognized. Among them, I, II, III, and IV are the main ore bodies, and all 9 ore bodies have a stratiform-like shape and are distributed in a northeast direction of 40°-60°, with a total discontinuous extension of 1,970 m, trending southeast at an inclination angle of 48°-61°. Three ore bodies, I, II, and VI, are exposed on the surface, while the remaining 6 ore bodies, II-1, II-2, III, IV, IV-1, and V, are concealed. I, II, III, and IV are partially connected and dip to the northeast. II, II-1, II-2, V, and VI are independent ore bodies. Among them, I, II, III, and IV are the main ore bodies, while the other 5 are minor ore bodies.