Geological And Geochemistry Characters Of Ni-bao Gold Deposit Of Pu-an County In Gui-zhou Province And The Discussion On Its Genesis

The Nibao gold deposit in Puan county, Guizhou province locates in the middle part of Chelang-Sandaogou mineralized zone in the western of Panjiazhuang fault zone, which situated in Lianhuashan gold metallogenic province pertain to southwest Guizhou. Based deep analysis on geological background of the research area, mining geological and deposit geological characteristics, this paper analyzed the source of ore-forming materials, the properties, source and evolution of ore-forming fluid deeply from geochemistry and ore-forming fluid via sampling and testing relevant research specimen of Nibao deposit, from which the writter put forward a new understanding of the mineralization enrichment regularity, metallogenic model and the genesis of the deposit.The Nibao gold deposit is divided into two types of "fault type" ore body and "stratabound type" ore body according to the ore body occurrence, spatial locations and the main ore-controlling factors. The ore bodies show some differences in both macro and microscopic characteristics. The "fault type" ore body exhibit brecciated and vine like mainly controlled by fault zone and its host rock is breccia which exist in fault fracture, the main Au bearing minerals of which are Pyrite and arsenopyrite occuring together as vines in ore body, and the main gangue mineral is calcite. On the other hand, the "stratabound type" ore body giving priorities of massive and banded structure distribute along strata and its host rock is siliceous breccia belonging to tectonic erosion variations, the Au bearing mineral of which are pyrite and arsenopyrite, and the main gangue of which are quartz and fluorite. Most of the pyrite is disseminated distribution, and arsenopyrite aggregated distribution. From results of element geochemistry and inclusion analysis, the "fault type" ore body shows weak silicification with characteristics of δCe＞1、δEu＜1. The fluid inclusions of calcite are manily gas-liquid aqueoue solution (W type), two-phase containing CO2(C2type), and three-phase containing daughter minerals (H type). The uniform temperature, salinity, and density respectively100～200℃,3.00%～6%NaCleqv and0.69～1.00g/cm3corresponding to the pressure and depth of the mineralization of30-40MPa and1.0-2.5km. Otherwise, the "stratabound type" ore body shows strong silicification with characteristics of δCe＜1、δEu＞1. The fluid inclusions of fluorite are mainly two-phase (W type and C2type) and occasionally three-phase containing CO2(C1type) can be seen. The uniform temperature, salinity, and density are respectively220～260℃,0.00%～2%NaCleqv and0.54～1.03g/cm3corresponding to the pressure and depth of the mineralization of40-80MPa and1.5～3.0km.The "fault type" ore bodies and "stratabound type" ore bodies are considered as the same product of different ore-forming environment through comparison and analysis of them. The salinity of ore-forming fluid increased, the metallogenic environment changed (reduction to oxidation) from "stratabound type" ore body to "fault type" ore body. The characteristics of fluid inclusion indicate that the fluid of "fault type" ore body experienced boiling, leading to a large number of mineral deposits. REE and sulfur isotope of Au bearing pyrite in ore body that reveal metallogenic material mainly might mainly derived from Emeishan basalt. The source of ore-forming fluid which is meso-epithermal, low salinity and low density including H2O-CO2-NaCl hydrothermal system major from the mixture of metamorphic fluid and formation water. Combining with the metallogenic chronology study posted by predecessors, we conclude that the genesis of Nibao gold deposit is orogenic-formation water epigenetic hydrothermal type gold deposit releated to Yanshanian orogeny, from which the model of orogenic drive-formation water mineralization is put forward.