Abstract: The Chating copper-gold ore in Xuancheng region is a newly discovered large ore deposit in the Mesozoic-Cenozoic volcanic-sedimentary Nanling-Xuancheng basin in recent years, where the deposits are located at shallow depths of the Middle-Lower Yangtze River. This study is focused on the cryptoexplosive breccia pipe developed in the intrusives of quartz-dioriticporphyrite in the Chating copper-gold ore deposits. Based on the detailed core observations and petrographic analysis, characteristics and types of cryptoexplosive breccia are determined, and the relationship between the cryptoexplosive breccia and the copper-gold mineralization is discussed. The cryptoexplosive breccia in the ore deposits can be divided into three types: cryptoexplosivemelt-crystal-lithicbreccia, cryptoexplosive hydrothermal breccia, and cryptoexplosive fracture breccia based on its textures, compositions and abundance of rubbles. The cryptoexplosive breccia appears as an irregular pipe enveloped by the quartz-dioriticporphyrite and shows a regular spatial distribution. From the center of breccia to wall-rock are quartz-dioriticporphyrite, cryptoexplosivemelt-crystal-lithicbreccia, the cryptoexplosive hydrothermal breccia, and the cryptoexplosive fracture breccia, respectively. The spatial relationship between the alterated, mineralized and the cryptoexplosive breccia pipe shows that there exists a genetic link between formation of cryptoexplosive breccia and mineralization. The cryptoexplosion of the melt, liquid and gas originated from intermediate-acid magma induced the
formation of large amount rubbles and fractures which can cause sudden temperature and pressure changes of ore-forming fluids. In addition, the cryptoexplosive breccia may provide room for migrating, mixing, and ore-forming material unloading for ore-forming hydrothermal fluid that arose from magmatic hydrothermal fluid. The geological features of the Chating copper-gold deposit are similar to those of the porphyry deposits including the intermediate-acid porphyrite host rocks, the alteration types, and zonation of wall rocks, as well as fine-grained dissemination and fine-veined, and net-veined mineralization. However, the mineralization enrichment site is consistent with the cryptoexplosive breccia pipe. Also, the geological features such as breccia, veined, agglomerated mineralization and hydrothermal anhydrite developed intensively in the vein are distinctly different from typical porphyry deposits. Therefore, based on these characteristics, we suggest that the Chating copper-gold ore deposit is a cryptoexplosive breccia type deposit closely related to intermediate-acidic hypabyssal intrusion.

Key words: Chating, Xuancheng City, Anhui Province, copper-gold ore deposits, cryptoexplosive breccia pipe, cryptoexplosive breccia type deposit