Metallogenic regularity of antimony-gold deposits in Longlin-Xilin district in western Guangxi, South China

Antimony deposits are characterized by simple minerals assemblage, and often lack minerals suitable for testing and analysis. Therefore, the metallogenic ages, sources of ore-forming materials, and genesis of antimony deposits are controversial. The antimony metallogenic province in South China accounts for over 83% of China's antimony resources. The Dian-Qian-Gui antimony metallogenic belt is located in the western of the South China antimony metallogenic province. In this study, we summarized ore-bearing stratums, rock lithologies, host structures, and the relationship between gold and antimony of 86 deposits in the Longlin-Xilin antimony-gold district, the middle segment of the Dian-Qian-Gui antimony metallogenic belt. Combined with the geological investigation of typical deposits and the distribution of magmatic rocks, the relationships among antimony mineralization with clastic rocks and magmatic rocks were discussed. We concluded that: (1) nonographitic black shales and pyritiferous sandstones and siltstones are favorable  for antimony mineralization. These strata have high antimony background values, which may have provided ore-forming materials. (2) The felsick intrusions may provide heat or Sb and S for the antimony mineralization. (3) Statistical results show that independent antimony and gold deposits dominate in the Longlin-Xilin district, and few deposits are characterized by intergrowth features of antimony with gold. These indicate that antimony deposits in the study area may be the superposition of fluids from different sources, and a small number of deposits maybe resulting by the Sb-Au separation from same ore-forming fluid. In the latter case, the precipitation of stibnite consumed H₂S in the ore-forming fluid, resulting in other metals that migrated in the form of complexes (such as Au and Hg) to precipitate at the same time. The competitive relationship between Sb and Au led to that the contents of Sb, Au show a negative correlation in antimony-gold deposits. (4) The district has experienced NS-striking compression in the Indosinian, followed by the NW-SE-striking compression in the middle-late Jurassic. The intersection of NWW-SEE-striking and NE-SW-striking faults is the favorable ore-bearing space. The NWW-SEE-striking faults were strike slip in response to the NW-SE-striking shortening deformation, whereas the NE-SW-striking faults exhibited transpression. As a result, the NE-SW-striking faults are not beneficial than the NWW-SEE-striking faults. Based on these studies, we proposed the ideal direction for prospecting in Longlin-Xilin district: (1) Black shale and pyritiferous siltstones of the Yujiang Formation that in the core of the Xinzhou anticline are the favorable stratums for antimony prospecting. (2) Concealed intrusion in the NWW-SEE-striking Nongsang-Shijaizhai fault (the Longlin County) and the intersection area of the NWW-SEE-striking Douhuang-Xilin fault and the NE-SW-striking fault (the Xilin County) are the favorable spaces for antimony exploration. The abovementioned discussion will enhance our understanding of the genesis and metallogenic regularity of antimony deposits and provide the directions for exploration.