Ore Genesis And Prognosis Of Wulaga Gold Deposit, Jiayin County, Heilongjiang Province

Wulaga gold deposit is the main gold deposit in Northeast China. It mothball resources are faced with troubles of deficiency; some new reserves must be searched in order to postpone fixed number of years of service.It lies in Jiayin county Heilongjiang Province. Geotectonically, the Deposit lies at the joint of Taipinggou upwarping and Jiayin down-warping belt which belongs to the northern Jamusi upheaval belt. The Jamusi upheaval belt is located at Jilin-Heilongjiang geosynclinal system which is in the east segment of Tianshan-Inner Mountain fold belt. It is affected by the geological developing and evolvement of Central Asia- Mongolia Plate and Pacific Plate. The structure is complicated in the diggings. The nearly EW trend fold and fault are the basement structures. Pacific Plate subduct to Eurasia Continent, which formed the NNE trend Wulaga deep-seated fault in Mesozoic era.The strata outcropping in the area include Proterozoic Heilongjiang Group which are metamorphic rocks. Its lithology characterize is mainly chlorite-albite-schist, chlorite-tremolite-schist, quartz-schist. The strata also include Mesozoic and Cenozoic volcanic sediment rocks: Lower Cretaceous Ningyuancun Formation, Taoqihe Formation, upper Cretaceous Yuliangzi Formation, Cenozoic Miocene, Pliocene and Pleistocene. The gold content is high (the average grade is 28.8 ppb) in the metamorphic rocks. It is supposed that the metamorphic rocks provided several mineral matters. The magmatic intruding activities are mainly plagioclase-granite porphyry in the Yanshan period. Orebodies lie in plagioclase-granite porphyry structural breccia belt mostly, others in the porphyry and schist fragmentation alteration belt.NNE trend Wulaga deep-seated fault is the ore-leading and rock-leading structure. It controlled the magmatic activities and hydrothermal fluid movement. NWW trend fault which is sub-structure of Wulaga deep-seated fault is the mainore-controlling structure.The ore minerals in the Wulaga gold deposit are mainly composed of natural gold, pyrite, marcasite, stibnite; gangue is mainly colloid calcedony quartz, calcite, kaolin. The texture of the ore bodies are colloidal texture, fine grain-dissemination texture. The main structure of the ore bodies are vein structure, stockwerke structure. There are many types of wall-rock alteration, such as chloritization and epidotization, berecitization, carbonatization, silicification; pyritization, pyrite-beresitization, propylitization. Mineralized silicification is linear distributed and controlled by structure. It is closely related to gold mineralization.According to the analyzing of liquid component of fluid inclusions, the deposit has characteristics of low salinity and low temperature. The temperature ranges from 152.2℃to 329.6℃. The main value is between 150℃and 220℃. The salinity value is from 1.22wt%NaCl to 5.4wt%NaCl, with the average 3.3wt%NaCl. The value of density is between 0. 75 and 0. 94 g/ cm3. The average value of pressure is 23.24×105 Pa. On the base of the relationship between depth and pressure (Sun Fengyue et al, 2000), a 2.32km average metallogenic depth is worked out. The ore-forming fluids were composed of major H2O, and minor CH4, H2S, CO, CO2 (Wang Keyong, 2004). The value ofδ18OH2O is between–2.73‰and 5.81‰,whileδDH2O is from-78.25‰to–132.64‰. The metallogenic fluid of Wulaga gold deposit was main atmospheric condensation and it was formed in the environment of low temperature. There is not ore genesis relationship between the gold mineralation and plagioclase-granite porphyry. The plagioclase-granite is the wallrock of the ore bodies.The early stage of ore-forming, the magmatic water is the main ore-forming fluid. And magmatic thermal up-welling leads to the rock cryptoexploded on the top and side. It formed a ringy cryptoexplosive ore-bearing breccia belt. This is the first stage porphyry-like mineralization. The main ore-forming stage of Wulaga gold deposit is the epithermal one. Buried magmatic rock provided the heat and driving force. Atmospheric water infiltrated deep through the fissure, and the hot fluid went up. Atmospheric water and hot fluid composed of the fluid circulation system. The fluid leached the mineral matters of Proterozoic Heilongjiang Group when it rised. Then the value of Eh and pH changed when the pressure reduced in shallow and fluid boiled, which resulted in the gold precipitation and low temperature mineral assemblage formed, such aschalcedony-quartz and adularia et al. It is formed the low sulfurdation epithermal deposits.The ore bodies in the No.1 vein were the main ore bodies in the diggings. They lie in plagioclase-granite porphyry structural breccia belt mostly. Ore-controlling faults characterized undulating varies in strike and dip. So the ore bodies occur will recur between enrichment segment and barren interval. Ore bodies NWW-trend diagonal distributed, and the pitch angle is 7°±. In the dip, orebodies occurred in local extensional place when the ore-controlling fault dip steeper. And there is no orebodies when dips slighter.On the base of the summarizion and study on the ore-forming condition and the rule of enrichment, effective method is adopted to prognosticate orebodies in deep(side) in the diggings. The polarizability is rather low and the resistivity is high in plagioclase-granite porphyry. There is relative high polarizability and strong Hg anomal in ore-bearing alteration fragmentized zones. According to the measure of induced polarization and mercury vapor along the pitch and dip of ore bodies, the bodies of high polarizability and the place of high Hg content were found. Metallized bodies was discovered by the new borehole project verification. It is concluded that a buried ore body in deep. But if along NWW-trend deeper, the buried ore bodies was probably cut by late intrusion. There is still bigger potential of prospection along dip of the main ore bodies.