Antimony mineralization superimposed by late gold mineralization: A case study of the Miaolong Au-Sb deposit, Guizhou Province, China

The coexistence of Au and Sb mineralization is common in orogenic and Carlin-type deposits because of their similar geochemical behavior. Herein, we conducted detailed mineral texture, chemistry, and S isotope analyses of the Miaolong Au-Sb deposit using microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (Fs-LA-MC-ICP-MS), focusing on investigating the paragenesis of Au and Sb mineralization. The results indicate two separate mineralization events at Miaolong: Sb mineralization overlain by subsequent Au mineralization. During Sb mineralization, minerals such as stibnite, quartz, calcite, chalcostibite, and native antimony precipitated in the fault-controlled open space. Antimony occurs predominantly in stibnite, with lower amounts of chalcostibite and native antimony. During Au mineralization, arsenian pyrite, arsenopyrite, dolomite, quartz, and illite were formed. Gold is mainly found as invisible Au within arsenian pyrite and arsenopyrite. During the late-ore stage, calcite (with minor realgar) crystallized in open spaces. Minerals from the Au-mineralization stage typically crosscut, overgrew, and replaced minerals from the Sb-mineralization stage. Additionally, stibnite, arsenian pyrite, and arsenopyrite show δ34S values of 17.56–19.81 ‰, 17.81–28.37 ‰, and 17.74–23.21 ‰, respectively. The heavy S isotopes in ore-related sulfides suggest that S most likely originated from the strata through a thermal-chemical sulfate reduction (TSR) process. A comparison reflects the similarities in Au mineralization in the Sandu-Danzhai metallogenic belt (SDMB) and Carlin-type Au deposits (CTGDs) in the Youjiang Basin, suggesting that the Au deposits in the SDMB are CTGDs and that the Au deposits in the two districts could have originated from the same extensive metallogenic event. This study shows that although the coexistence of Au and Sb mineralization is common, it could result from the superimposition of distinct hydrothermal events. This finding suggests the relationships between Au and Sb in the SDMB, as well as in other CTGDs, should be reassessed.