Study On Genesis And Deep Ore Prediction Of Baolun Gold Deposit, Hainan Province

The Large-scale Baolun gold-ore deposit, located in Ledong County Hainai Province, is a high-grade deposit found in South China in recent years. However, due to its poor research work and nearly 20 years large-scale exploitation, some key questions about genesis of deposit is still on controversial,the upper part of the main ore mined,the prospect of deep and peripheral resources is unknown,in order to ensoure the sustainable development of mine,looking for new resources to succeed,it is necessary to further study the metallogenic geological conditions、 deposit genesis and metalloenic regularities,and provide the basis for the Baolun gold deposit in deep part and surrounding the delineation of ore prospecting target area.Based on detailed research on geological characteristics of Baolun gold deposit, this paper has carried out a systematic study on the origins of the ore-forming fluids and metals, and a detailed discussion on the relationship between Jianfengling granites and the gold depost, and established a genesis model at last. Moreover, based on the zoning model of the primary halo in hydrothermal gold deposit, we put forward the prospecting potential area in the futher.(1) Electron probe analysis of pyrite in quartz veins shows that the S/Fe of pyrite is below 2(1.5 on the average) and the Au/Ag is above 0.5(2.3 on the average), this suggests that the pyrite maybe belong to magmatic hydrothermal genesis. The electron probe analysis of natural gold shows that it has quite high fineness(962 on the average), suggest the genesis of the deposit maybe associated with the medium-high temperature fluid activity.(2) The Jianfengling granites belong to peralumious type on ACNK-ANK diagram(ACNK=1.07～1.16), and belong to alkaline series on alkine vs silica diagram. The trace elements is rich in Rb, Th, U, Pb, Sm, Nd, and depleted Rb, Sr, Ti, Nb, Ta, Zr, Hf, Eu, the REE pattern diagram. The REE pattern shows that they are rich in LREE (LREE/HTEE=8.9 on the average), with strong negative Eu anomaly (8Eu=0.09～0.38). Isotopic analysis shows it has high initial strotium(0.725783～0.728520), and low initial neodymium (0.511944～0.511952). All of these characters indicate that the Jianfengling granties belong to the transition type between S-type and aluminous A-type, and form in the continental collisional orogeny environment.(3) The zircon U-Pb dating of Jianfengling medium-fine grained biotitic syenogranite yields 235.6+3.5Ma, which suggests that it was produced in the Indosinian magmatism event. The previous researches show that the metallogenic epoch of Baolun gold deposit formed in 236-205Ma, which is consistent with the the magmatism evolution of Jianfengling granites.(4) Study on the fluid inclusions of three types of veins shows that the gold-bearing quartz veins forming in the early mineralization stage are predominated by the rich-CO2 fluid inclusions, and the peak homogenous temperatures is 320℃, the gold-polymetallic sulfide quartz veins are richer in H2O than the early mineralization stage veins, the peak homogenous temperatures are reduced to 280℃, the carbonate-quartz vein are prodeominated by H2O-rich fluid inclusions, the peak homogenous temperatures are further reduced to 180℃. The mechanisms for gold deposition during the early mineralization stage was controlled by reduced pressre-boiling, and was related to the temperature decreased and the PH and oxygen fugacity increased during the middle-late stage. Moreover, the calculation of mineralization depth shows that the Baolun gold deposit formed in 10.2km.(5) Based on the distribution of gold anomalies and the location of concentration center of frontal indicator elements of As, Hg, Ag ect, indicate that the gold mineralization is most likely in the depth of 7 and 11 exploration lines in south mining area, and in the east and lower of 130 horizontal plane in Haogangling mining area. Meanwhile, because the concentration center of Hg in the 103 exploration lines in Haogangling area appers in Surface and 130 horizontal plane, and the mineralization intensity of Au and Hg in Haogangling is larger than the south part of mining area, suggests the denudation degree of Haogangling mining area is lower than south mining area, that is to say, the prospecting potential in Haogangling area is better than the south mining area.