Breccia, hydrothermal alteration and structural geology of the Huangtun porphyry Au-Cu deposit in the Middle-Lower Yangtze Metallogenic Belt, eastern China

• Published in: Ore geology reviews Vol. 120; p. 103414
• Main Authors: Wang, Biao, Zhou, Tao-Fa, Fan, Yu, Chen, Jing, Liu, Yi-Nan, Chen, Yang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2020
• Subjects: Alteration zone; Breccia facies; Geological characteristics; Gold and copper deposits; Luzong basin; Structure activities; Geological characteristics; Gold and copper deposits; Breccia facies; Structure activities; Alteration zone; Luzong basin
• ISSN: 0169-1368; 1872-7360
• DOI: 10.1016/j.oregeorev.2020.103414

There were two stages of structure activity in the mining area. The pre-mineralisation structure activity formed F1 and F2 faults, and these faults also controlled location of the emplacement of Au-Cu mineralisation later. Subsequently, the intrusion related to gold and copper mineralisation was emplaced and released fluids, which formed K-Na silicate to illite-smectite altered magmatic-hydrothermal breccia, from the deep to shallow. Hydrothermal breccia with a high matrix/cement ratio then formed when mineralizing fluid permeated the fracture zone. During post-mineralisation activity, the sinistral strike-slip F1 and F2 faults were reactivated, forming tectonic breccia containing some massive carbonate ± quartz ± pyrite clusters clasts. [Display omitted] •The Huangtun porphyry deposit is a newly discovered deposit in the Luzong Basin.•A sub-vertical breccia pipe hosted the main gold-copper mineralization.•Alteration varied from ab, bt-ab, chl and ser zones from deep to shallow. Luzong Basin is an important part of the Middle-Lower Yangtze Metallogenic Belt in eastern China, in which the dominant types of deposits are iron-oxide-apatite and skarn iron deposits. However, a new porphyry gold-copper deposit, Huangtun deposit, has recently been discovered in the north-eastern margin of the basin. Detailed studies of geological characteristics and metallogenic processes of Huangtun gold-copper deposit are needed to supplement the mineralisation type of the Luzong Basin. Based on drill core logging and petrology observations of thin sections and polished sections, a north-striking sinistrial strike-slip major fault and a series of secondary NE-striking sinistrial strike-slip faults have been identified in the mining area. A mineralised breccia pipe at the intersection of the two groups of faults is the main host of the Au ore body. The alteration types in the mining area, from deep to shallow, include an albite alteration zone, a biotite-albite alteration zone, a chlorite alteration zone and a sericite-pyrite alteration zone. A detailed mapping of the breccia pipe has been provided in the mining area. Seven different breccias facies have been divided according to the internal structure, composition, morphology, matrix content and alteration assemblages. Genesis of the different breccia facies have been identified based on crosscutting relationships and clast-in-clast textures, which revealed that there are two different faulting and brecciation stages. During the first stage, matrix-supported breccia formed near the fracture zone. Gold-copper mineralisation then occurred along the intersection of the two groups of fracture zones, which formed K-Na silicate to sericite altered magmatic-hydrothermal breccia, from deep to shallow. In addition, these different facies of breccia correspond to four stages of fluid evolution: the albite stage, biotite-albite stage, chlorite stage and sericite-pyrite stage. Hydrothermal breccia with a high matrix/cement ratio then formed when mineralizing fluid permeated the fracture zone. During the second stage, the ore bodies were faulted to form tectonic breccia containing some massive carbonate ± quartz ± pyrite clusters as clasts. Based on the current study, we conclude that the locations of the intersection of fault zones in the northern part of the Luzong Basin and the northern part of the mining area have potential for further gold mineralisation.