Geological Characteristics And Genesis Of The Tangba Gold Deposit In Wudu,Gansu

The Qinling mountains extend from east to west across central China,and the Qinling orogenic belt has attracted the attention of geologists at home and abroad for its special geological structure.The long and complex history of geological evolution has fascinated researchers hoping to find out.The western Qinling orogenic belt is the western part of the Qinling orogenic belt and is one of the important parts of the central orogenic belt in China.The western Qinling orogenic belt is located in the paleoasian tectonic domain.The special section where the tethys tectonic domain meets the coastal Pacific tectonic domain is a key part of the central orogenic belt in China.In this study,the Wudu Tangba gold deposit in Gansu province is located in the eastern part of Yangshan-Shijiba gold deposit belt in the south of the west Qinling mountains,south of the Xinguan-Hejiaba-Liping fault,and the Tangba?Zhoujiagou double anticline.Due to the special tectonic evolution history of the west Qinling mountains,it has become a rich and active gathering area of mineralizing materials and fluids.Therefore,the geological tectonic environment and metallogenic conditions of Tangba gold deposit are relatively complex compared with other areas.In addition,previous studies on this subject are not high,so there is still a lack of in-depth research and discussion on the geological characteristics of the deposit,source of metallogenic materials,metallogenic fluid,ore-controlling factors and genesis of the deposit,and there is a lack of certain experimental data support in the classification of deposit types.On the basis of collecting the regional geological data and the geological data of the research area,this paper makes a more systematic investigation and analysis on the geological characteristics,geochemical characteristics,ore-controlling factors and the genesis of the tangba gold deposit.The following main achievements and understandings have been achieved:(1)The strata exposed in the Tangba Gold Mine are mainly the Sinian Guanjiagou Formation of the Sinian in the Proterozoic and the Qiaotou Formation in the Lower Devonian of the Paleozoic.The rock is quartz sericite phyllite with thin layered limestone,medium-thick layered limestone,sandy slate with metamorphic sandstone,etc.The intrusive rocks are relatively monotonous,basically granite porphyry veins,concentrated in distribution and appearing in groups in the middle of the mining area.Two large fault structures,F1 and F2,control the distribution of granite porphyry veins,which are consistent with the regional tectonic lines.The distribution of the deposit is closely related to the rock mass in space.(2)There are four main types of wall rock alteration in the mining area:carbonate,sericite,silicification and pyrite mineralization,among which the alteration closely related to gold mineralization is mainly pyrite mineralization and silicification.The relationship between silicification and mineralization is the closest,and occurs at all stages of mineralization.Pyrite mineralization is the main carrier mineral of gold.(3)The deposit has 6 main gold ore bodies.Among them,Au1 ore body is a representative ore body,which is a hidden ore body,controlled by the fracture zone of F1fault,and the ore body is located in the lower plate of the granite porphyry vein.(4)The ore structure in the mining area mainly consists of automorphic-semi-automorphic grain structure,heteromorphic grain structure,interstitial structure,crushing structure,metasomatism dissolution structure,inclusion structure,internal fragmentation structure,internal band structure,etc.The ore structure is mainly disseminated structure,vein-like structure,strip-like structure,star-point structure and so on.(5)According to the interpenetration relationship between the ore veins and the structural characteristics of the ore,the mineralization in this area can be divided into two phases,namely hydrothermal period and epigenetic period.The hydrothermal phase can be further divided into four stages:(1)Sericite petrolization stage;(2)quartz-natural gold-polymetallic sulfide stage,is the main mineralization stage of gold;(3)the natural gold-pyrite-quartz stage,superimposed on the second stage of mineralization,forming high grade ore;(4)quartz-carbonate stage,the last stage of hydrothermal activity,weak mineralization.Supergene oxidation usually occurs in the developed area of surface and shallow fissure.(6)According to H,O and S stable isotope experiments,the variation range of pyrite?³⁴S(‰)is-1.9‰?0.8‰,and the average is-0.23‰.The variation range is relatively small,showing the characteristics of deep source sulfur on the whole.The variation range of the main ore-forming fluid?¹⁸O_H2O(V-SMOW)was 7.89‰?9.97‰,and the variation range of?D_(V-SMOW)was-81.3‰?-77.0‰,It shows that magmatic water is the main ore-forming fluid,which is consistent with sulfur isotopes.(7)The results of fluid inclusion test in the mining area show that the ore-forming hydrothermal fluid has the characteristics of medium and low temperature and medium and low salinity.The complete uniform temperature range of CO₂ phase in quartz during the main mineralization period was 252.6?342.8?,with an average value of 279.72?.The average temperature of aqueous two-phase inclusions ranged from 156.9?to 307.6?,and the average temperature was 256.7?.The ore-forming hydrothermal fluid is characterized by medium and low temperature and medium and low salinity.(8)Based on the comprehensive analysis of the above metallogenic factors,it is concluded that the deposit type is a medium-low temperature magmatic hydrothermal deposit related to magmatism in the late indo-chinese period.