Geological Characteristics And Genesis Of Zhongbao Tungsten Deposit And Prediction Of Its Surrounding Prospecting Objects, Tuokexun, Xinjiang Prov

Middle tianshan block, a microcontinent between junggar and tarim block, is located in the middle of tianshan belt and pinches out at the east of Kumishi area. The oceanic crust of south tianshan subducted norwards under the middle tianshan block,which lead to the formation of series of volcanic and intrusive rocks related to the subduction and collision at the south of middle tianshan block in the late Paleozoic and control the formation of different types of deposits. Zhongbao tungsten deposit is located in the NWW-trending granite belt at the south of middle tianshan block.On the basis of geological works in the field and previous data,this paper firstly discussed the regional geological setting, tectonic evolution of Kumishi area and the genesis of Zhongbao granite and detailedly studied the geological characteristics of deposit and orebody and its genesis and then summarized the metallogenic model of Zhongbao tungsten deposit.At last,we gave the conclusion about the prospect of tungsten mineralization in Kumishi area combining with the analyse of geochemical exploration and remote sensing.The tectonic evolution of Kumishi area successively experience back-arc extension-subdction-collision-post collision processes which compose a typical wilson cycle and later a pull-apart basin was formed by strike-slip tectonic processes.The stage of subdction and collision between the oceanic crust of south tianshan and middle tianshan block is the main mineralization stage which control the formation of Cu-Pb-Zn polymetallic deposits and W-Sn deposites in this area.Zhongbao two-mica monzogranite is closely related to the tungsten mineralization.U-Pb Zircon dating for the Zhongbao granite yield a weighted mean age of 298±3.5 Ma, belonging to late-devonian carboniferous. geochemical characteristics indicate that Zhongbao granite is potassium-rich calc-alkaline and peraluminous granite which experienced a medium-high degree differential evolution process.lt belongs to Crustal melting S-type granite which formed in the collision setting and its source rock is Precambrian basement of middle tianshan block.The rock body is tungsten-rich and provides main metal source for Zhongbao tungsten deposit.Field observations and studies show that Zhongbao tungsten deposit belongs to skarn-type scheelite deposit with the superposition of greisen mineralization and late quartz vein mineralization. The orebodies are located in the east plunging crown of Kumishi anticline.As the Turn end and the two wings of anticline always form a number of secondary folds, The relative sliding of adjacent strata usually leads to the layered, like layered, saddle-shaped peeling space at the fold hinge and two wings which is advantageous to skarn metasomatism between the granite and wall rock.The strata at the south wing which is damaged by the NE-trending fracture provide the channel and intrusive space for the magma and the later SN-trending fracture mostly cause the later transformation of the ore body. The morphological characteristics of zhongbao tungsten deposit ore body are controlled by the affects of the multiple ore-controlling factors.Ore types in the district are mainly Gt-Di-Ep skarn type, Act-Di-Ves skarn type, greisen type, and skarnised marble tpye. Hypidiomorphic granular texture, nematoblastic texture, and lepido-granular blastic texture are developed and the ores are massive or banded. The ore mineral is sheelite disseminated in the all ores types and minor cassiterite and pyrite. Gangue minerals are mainly diopside, idocrase, epidote, garnet, wollastonite, tremolite, quartz, fluorite, muscovite, biotite and calcite.Mineralization is divided into skarn period and greisen-quartz scheelite period in Chronol-ogical order, in which the skarn period is divided into early stage and late stage, and the greisen-quartz scheelite period is divided into greisen stage and quartz scheelite stage. The late three stages is the main mineralization stage. Quartz carbonate stage doesn't form the Tungsten ore. The study of the content of tungsten in rock mass and country rock indicates that tungsten is mainly originated from the mineralization granitic intrusion, infering that precambrian system basement from middle Tianshan land mass is a beneficial ore bearing formation for tungsten, and stratum from Lower Devonian is to provide partial material source as a poor source bed. Oxygen and hydrogen isotope studies from quartz make clear that ore-forming fluid devided from the magmatic water, closely related to the Zhongbao rock mass. Hydrogen isotope study from scheelite shows that belongs to skarn type.After the study of the fluid inclusions in the sheelite, diopside, quartz, fluorite, and calcite, we obtained the following knowledge of ore-forming P-T conditions.(1)All tested data show that the homogeneous tempetature is between 140-440℃, while the main mineralizing stage of sheelite happened between 250-360℃with mean temperature of 309℃. It is belonging to the scope of high to medium temperature. Ore-forming temperature gradually descending from early skarn stage, late skarn stage, quartz-sheelite stage to quartz-carbonaite stage, among which the late skarn stage and the quartz-sheelite stage are the main ore-forming stage. (2) The salinity of the ore-forming fluid is between 6% to 22%. The salinity of the fluid inclusions in sheelite is between 12% to 15% with the mean salinity of 13.41%. It is belonging to middle to high salilinty settings. During the mineralization, it gradully descending.(3) The desity of the ore-forming fluid is between 0.792g/cm3 and 0.967g/cm3. The desity of the fluid captured in sheelite is 0.844g/cm3. Influenced by the volatiles and temperature, the fluid desity increases during the mineralizing process.(4) The ore-forming pressure is between 146 and 461 bar. The sheelite is formed at 353 bar. The depressing of ore-forming pressure from early stage to late stage reflects the movement of ore-forming fluid to shallow depth and deposit the minerals in the fractures and crused zones.(5) The minerals are formed at the depth of 1.1-4.5 km. Sheelite is formed at the depth of 2.7-4km, which is moderate.With the study of the ore types, wall rock alteration, geochemistry of ore-bearing pluton, fluid inclusions and H-O isotope of the fluid at Zongbao Tungsten deposit, we believe it is a typical skarn-type sheelite deposit which is formed during the subduction to the Middle Tian and close of South Tianshan ocean. The deposit is genetical associated with the co-collisional granite. The ore substances are derived from the melting of deep crust. The ore-forming fluid is deep drived magmatic water. P-T condition of the deposit is obtained with high to middle temperature (250-360℃), high salinity (12%-15%), middle depth (2.7-4km) and relatively high pressure (353 bar).Multispectral, hyperspectral remote sense and geochemical anomaly show that tungsten anomaly in Kumux region is characterized by apparently distributing in the southern edge of middle Tianshan land mass and inner of that along the NWW direction, which resulted from the subduction from south Tianshan ocean to middle Tianshan land mass forming Subduction-collision type tungsten-rich granite in the late Paleozoic telophase, being NWW direction under the control of regional fault. Comprehensive analyzing of various anomalies related to mineraliz- ation and the geological interpretation, this article considered Collision granites from the southern edge of middle Tianshan land mass and the religion in agreement with the anomalies has bright future for tungsten ore propects, inner of middle Tianshan land mass and the north edge of Tarim is also the favorable direction for the tungsten ore.