| Baolun gold deposit is the highest grade gold deposit, located in Baolun Farm of Ledong County, Hainan Province. The fracture zone formed by NNW parallel compression-shear fracture is the main ore-controlling structure in Baolun gold deposit, and mining area-related granites are mainly biotite syenogranite in Jianfengling. The ore body in Baolun gold mining area are mainly distributed in Haogangling area,21ore body has been delineated, contain auriferous quartz veins and auriferous altered rock. Predecessors have paid highly attention to Baolun gold deposit, but the study of fluid inclusions is relatively weak, and there are different understanding about forming material source of Baolun gold deposit. On the basis of detailed indoor data compilation and field geological survey, through detailed analysis of major elements, trace elements and rare earth elements of rock and ore, and the study of fluid inclusions in different stages, we have a deeper understanding on forming material source and ore-forming fluids properties of Baolun gold deposit. Combined with the results of previous studies, we drawn the metallogenic model diagram of Baolun gold deposit. The main results and understanding are as follows:1. Gold bearing quartz vein type is the main type in ore, while gold-bearing altered rock type is the secondary. The independent mineral of natural gold is the main status in gold occurrence, while gold bismuth compounds is the secondary. Natural gold particles are filled in smoky gray quartz grains irregularly, while partial natural gold particles are wrapped in quartz grains and pyrite.2.The SiO2, K2O and ALK (total soda) content of granite rocks are very high in Jianfengling, the average content of SiO2 is 75.23%, which belongs to high-K calc-alkaline series; ACNK (aluminized index) is 1.33 to 1.98, which belongs to peraluminous granite. The granite rocks in Jianfengling are magmatic highly differentiated products, the differentiation index DI is 88.64-98.28, with an average of 93.97.3. There are significant differences between the REE geochemical characteristics of Indosinian granites and Yanshanian granites, the REE pattern of Yanshanian granites is different from other samples, the former shows "V" shape while the latter shows right slant enriched V-shaped (LREE enrichment type), and ZREE, LREE, HREE, LREE/ HREE of Yanshanian granites are lower than the other samples. These features suggest that the mineralization of Baolun gold deposit have close space-time relation to Indosinian granites; and the Au, Bi content of Yanshanian fine-grained granite in mining area are very high, indicating that the ore has been reconstructed by fluid related to Yanshanian rock. The gold content of wall rock far from ore in mining area is 20.1×10-9, and ore REE and trace element distribution curve are very similar to wall rock, reflecting the inheritance of ore to formation material.4. Gold-quartz veins phase fluid inclusions are mainly CO2 inclusions, mainly as Ⅰa, Ⅰc type inclusions, the CO2 content in fluid is high, with a small amount of CH4; Ⅱb type inclusions and I b type inclusions growed in quartz mineral of gold-polymetallic sulphides stage, the CO2 content of fluid in this stage decreased, the CH4, H2O content increased, and appear a small amount of C2H4; in quartz-carbonate stage, the fluid inclusions types are basically Ⅱb. The fluid in Baolun gold deposit is CO2-NaCl-H2O system with middle temperature, low salinity fluid properties. Metallogenic temperature is between 255～337℃, metallogenic pressure in gold-quartz vein stage is 66.5～74.7 Mpa, metallogenic depth is between 4.6～5.0Km. And with the evolution of the fluid, the CO2 content of fluid composition decreased, CH4, H2O content increased, the temperature and pressure gradually decreased.5. In the fluid inclusion, the value of δ18O and δD is -2.4%o～+9.8‰ and -62%o～-30‰ respectively, which indicate ore-forming fluids are mainly magmatic water-based, and mixed with metamorphic water, the influence of atmospheric precipitation is relatively small.6.According to the geological characteristics, geochemical characteristics and ore-forming fluid characteristics of the deposit, we can inferred that Baolun gold deposit is magmatic hydrothermal quartz vein deposits which controlled by faulted structure, its forming process is broadly divided into three stages. Caledonian tectonic movement form Haogangling anticline. With the formation of the anticline, tectonic fissures are formed in the turn end of anticline, metamorphic differentiation hydrothermal penetrated along fractures, forming poor gold quartz veins; Strong tectonic-magmatic activity in Indosinian lead to the emplacement of Jianfengling pluton. On the one hand, post-magmatic hydrothermal is wealthy of Au, S, Cl, F, etc; On the other hand, magmatic hydrothermal and heat fluid extract actively Au, S, Fe and other components of the surrounding rock, they migrate upward together along with the tectonic fracture zone, in the structural fissures expansion space parts, due to the rapid change of oxidation-reduction potential, to form acontinuous large-scale mineralization. Middle Tuolie group is carbonaceous phyllite, which plays the role of kicker layer, so gold ore body is located in NNW trending tectonic fractures of below Tuolie group; this area was subjected to intense tectonic again during Yanshan period, with the thrust deformation and magmatic activity, make the break of auriferous quartz veins which formed in early stage, and structural differentiation hydrothermal and magmatic hydrothermal were filled into broken quartz veins again, to transform the gold mineralization formed in the early stage and to be further enriched. |
PDF Full Text Request