Geology, Geochemistry And Genesis Of The Liaotun Gold Depisit, Bama County, Guangxi,China

The Liaotun gold deposit, located in northwestern Guangxi, is the only one gold deposit for sure spatially closely related to quartz porphyry. The ore field is located at the contact zone between platform and basin on the southwest of Longtian isolated carbonate platform. The bearing strata and rocks in the ore field include politic siltstone and hraywacke of Triassic. The ore bodies are structurally controlled by faults. The mineralization took place include the diagenetic stage, the hydrothermal stage, the weathering stage. The hydrothermal stage is divided into early and late stage.The pyrites include framboidal, veinlet, grainy. Trace elements suggest that there is a negative correlation between As and S content in the pyrites, the correlation between As and Au is no obvious. Analysis of Co and Ni in pyrite suggest that the framboidal pyrites are formed the process of sedimentary, the veinlet and grainy pyrite are formed the process of hydrothermal. The form of Au are solid solution and nanoparticles in pyrite, the dominant form of Au is nanoparticles in framboidal pyrite, whereas the dominant form of Au is solid solution in veinlet and grainy, some Au of nanoparticles are probably dissolution from solid solution in arsenian pyrite of mrtastable state.Fluid inclusions of quartz in ore stage shows that the homogenization temperatures range from 160 to 240?, The freezing point temperatures range from-7 to-4?, The salinity ranges from 1.57 to 12.28 wt%NaCl, The density ranges from 0.77 to 1.01 g/cm3, The pressure ranges from 8.90 to 20.92 Mpa, The estimation of metallogenic depth ranges from 3.36 to 7.91 km. The main component of gas phase is H2 O, CO2, CH4. Above all, the ore-forming fluids are moderate to low temperature, low salinity, low density and contain CO2 and CH4.The gold of the strata varied from 10-9 to 16×10-9, which are higher than the clarke value of the continental crust, it is probably to provides the ore-forming material sources. The average content of Au in the fresh quartz porphyry are slightly higher than similar rock in this area, it has a probably that providing minerals for mineralization.The distribution curves of orebody and wallrocks are very similar, indicating that the ore-forming materials probably mainly derived from strata.The distribution curves of orebody and fresh quartz porphyry are similar, infering that the ore-forming materials probably derived from strata. The distribution curves and ?REE of orebody and the quartz porphyry orebody are similar, however, it shows negative of ?Ce, which inferred that the fluid of the quartz porphyry orebody mineralization probably different from the orebody in different stages or even different sources.The hydrogen and oxygen isotopes of quartz and pyrite is mainly falls in the magmatic water area, some near the meteoric water line. The argon isotope of pyrite is mainly from atmospheric argon(40Ar/36 Ar ratios is 308.40), it indicate that the ore-forming fluids derived from magmatic fluids and meteoric water. The ?34S value varies of orebody and wallrocks are very similar, infer that sulfer main derived from strata. A part of the ?34S value varies similar of gold ores and the mineralized quartz porphyry, some part of similar to quartz porphyry, owing to the later ore-bearing thermal solution mineralization along the quartz porphyry fractured zone after the form of quartz porphyry. The sulfur sources of the early stages is probably different from the late stages, and probably superimposed by deep source also involved.the lead isotopes suggest that the lead mainly comes from the upper crustal rocks.The gold mainly derived from the triassic strata, but the quartz porphyry in the region probably provided some gold. The ore-forming fluids are probably derived from magmatic fluid and meteoric water. It can be deduced that there developed gold pre-encichment in sedimentary diagenetic stage. The magmatic fluid mixed with the meteoric water during the hydrothermal metallogenesis stage, the mixing fluid leached the pre-encichment gold, which resulted in the formation of ore-forming fluid, it rised and migration, the ore-forming fluid unload and mineralization at the suitable sites. The ore-bearing hydrothermal fluid in later stage removed, enrichment and mineralization along tectonic and shear fractures. During the weathering stage, the orebody weathered and leached, and formed the oxidized orebody which is easy to benefication.