Mineralogy and Geochemistry Characteristics and Genetic Implications for Stratabound Carlin-Type Gold Deposits in Southwest Guizhou, China

The southwest of Guizhou Province is considered to be one of the most important areas of the Carlin-type gold deposits in China. Three deposits, Shuiyindong, Nibao and Getang which are all stratabound but with different lithology, were chosen to compare the characteristics of host strata and the source of ore-forming materials. Geochemical analyses and petrographic observation were carried out on the ores and representative minerals from the three gold deposits. Abundant pyrite in all samples can be divided into depositional pyrite and hydrothermal pyrite based on the textures and trace elements. Arsenian pyrite is the major gold-bearing minerals and mainly formed during hydrothermal processes. The involvement of the hydrothermal pyrites is closely related to the enrichment of gold, in which the fluid should be enriched in Au and As, but depleted in Fe. Specially, the gold element presented in these Carlin-type gold deposits often occurred in invisible forms including nanoparticles, submicroscopic particles and crystal lattice. Nanoparticles and submicroscopic particles of Au mostly emerged in the arsenian pyrite and quartz voids, which suggested that pyritization and silicification take place during the main mineralization stage. High contents of lattice Au mainly exist in the overgrowth rims of arsenian pyrite. In addition, mineralized rocks of the Shuiyindong, Nibao and Getang deposits display LREE enrichment patterns. And the samples from Shuiyindong and Nibao deposits exhibit similar geochemical behavior as those from the samples of typical Emeishan basalt, indicating that these two deposits may be affected by basic volcanic clastic material during sedimentation. However, the ore-forming materials of the two deposits are different. The Shuiyindong deposit likely result from the mixtures of magmatic source with minor contribution of sedimentary rocks, whereas the Nibao deposit might have a magmatic source. The element geochemistry of samples from Getang deposit is much different from the other two deposits, and the sedimentary rocks may be the major contribution. As a consequence, the synthesized studies on these three deposits significantly contribute to a better understanding of the ore-forming materials source and the formation process of these nano-and submicron gold particles of Carlin-type gold deposits in the southwest Guizhou Province, China.