| Abstract:The Mojiang gold-nickel deposit in the Yunnan province was identified through exploration efforts in the 1980s. However, after more than forty years of development and exploitation, the resources are now experiencing depletion. Through exploration and research in collaborative with the mining company, new breccia-type ores have been reidentified, which generally shows high gold grades, reaching up to 12 g/t. The gold-bearing breccia can be classified into at least two types: tectonic breccia and volcanic breccia. The tectonic breccia is located in the thrust zone between the Jinchang intrusive rock, the Lower Devonian Jinchang Formation, and the Upper Triassic Yiwanshui Formation. Volcanic breccia is found in the open pit and drill holes ZK74-52 and ZK76-9 of the Dishuikan section. The breccia-type gold orebodies are distributed near the line 68 of the Dishuikan section and line 94 of the Maobiliangzi section. The breccia components mainly consist of siltstone, carbonaceous mudstone, and quartz, with a sandy and mudstone cement. Gold mineralization also occurs in volcanic breccias, which have a more complex composition, including ultrabasic rocks, gray-white silicified siltstones, liver-colored quartz sandstones, serpentinite, and quartz. The matrix contains ripped-up vitroclast and plastic shard, suggesting a volcanic genesis. Volcanic breccia has been strongly affected by silicification and carbonation. The breccia components indicate that the volcanic breccia formed after the emplacement of the Jinchang intrusive rock and before the diagenesis of the red sandstone of the Upper Triassic Yiwanshui Formation. Identifying the distribution characteristics and genesis of breccia-type gold orebodies is crucial for increasing the reserves and production capacity of Mojiang deposit. It also facilitates the exploration of new deep-level mineralization and open up new prospects for mineral exploration. |
