Sm-Nd geochronology, REE geochemistry and C and O isotope characteristics of calcites and stibnites from the Banian antimony deposit, Guizhou Province, China

抄録

The Banian sediment-hosted antimony deposit is a medium-sized deposit located in the Dushan County, South Guizhou, China. Calcite is the dominant gangue mineral and can be divided into two types: white and pink. Pink calcite is intimately associated with mineralization. Sm-Nd dating of five white calcites yield an isochron age of 128.2 ± 3.2 Ma, with initial ε_Nd = -4.3 and MSWD = 0.54, while six pink calcites yield an identical age of 126.4 ± 2.7 Ma with initial ε_Nd = -6.0 and MSWD = 0.68. These new age constraints suggest that the Banian deposit formed during the late Yanshanian. Negative initial ε_Nd values, C (-0.5 to -1.8), O (12.5 to 14.6) isotopic characteristics of calcites, and field observations of abundance of vuggy open spaces, all suggest significant interaction between fluid and wall rocks. Calcites are characterized by strongly LREE-depleted and MREE- and HREE-enriched (LREE/HREE = 0.11-0.61). Stibnites are LREE-enriched, and MREE- and HREE-depleted (LREE/HREE = 105-500). Wall rocks are characterized by moderate LREE-enriched (LREE/HREE = 6.2-12). Pink calcites are more enriched in LREE (LREE/HREE = 0.11-0.61) than white calcites (LREE/HREE = 0.11-0.23), while the concentration of HREE remains nearly constant in both. The high contents of Fe and Mn in calcites and the negative correlation between Fe+Mn (ppm) and LREE/HREE ratios suggest that the Fe-Mn impurities in calcites may dominate the enrichment of MREE and HREE in calcites from the Banian deposit.