Geological,Geochemical Characteristics And Genesis Of Jinchanggouliang Gold Deposit, Chifeng, Inner Mongolia Autonomous Region

Jinchanggouliang gold deposit is located in the Longtan block of the northeasternNuluerhu uplifted belt, which stands at the east of Zhangjiakou – Chifeng gold ore-belt,the northern edge of Huabei platform. Longtan block is surrounded by faults, theEW-directed Chifeng-Kaiyuan ultra-lithosphere fracture-belt is its north edge, theNE-NNE-directed Lingyuan-Beipiao ultra-lithosphere fracture-belt is its southeast edge,the NNE-directed Linjiadi-Zhongsanjia fracture is its west edge, which underwentLvliang movement, Caledonian event, Variscan event and Yanshan movement etc.multiperiodic tectonic and magmatic activities. The outcropping strata are very complexin this area, the basal stratum is Archean mesometamorphic supracrustal rock type,Mesoproterozoic epicontinental marine clastic sedmentary rock series, Palezoic marinefacies clastic sedmentary rock series, Mesozoic continental facies volcanic lava,clasticsedmentary rock series and Cenozoic terrigenous clastic sedmentary rock seriesrespectively overlapped the basal stratum. The lower member of the Xiaotazigoucomplement, which belongs to Jianping Group, Neoarchean, is the wallrock ofJinchanggouliang gold deposit.After cratonization, the area remained stable for a long time, until Neopaleozoic,especially Mesozoic Yanshan movement activated tectonic movement in this area. Thetotal tectonic framework is made up of basement tectonics and fracture structures. Thedeep fault which cut through the whole lithosphere in this area, is the uprising andtravelling channels of ore-forming materials and fluids derived from mantle. Theintroduced NW-directed,SN-directed faults and their intersection position formsfavorable points for deposition of ore-forming materials. The NW-directedFangshengou– Jinchanggouliang fault which went through Jinchnaggouliang goldore-field, is the ore-controlling structure.The magma activity was very frequent in this ore-field, the magmatic rock locatedin the mean axis of Nuluerhu uplift belt occupied over 50% of Longtan block, and therewas also plenty of magmatic rock in Aohanqi composite downfault, which was in thenorth of the ore-field. The magmatic activity of uplift belt was mostly granite, and therewere minor basic rock and ultrabasic rock occupied the lower member of Neoarchean.After Yanshan movement, all kinds of dike rocks widely distributed in the ore-field, suchas diorite porphyrite,quartz porphyry,granite porphyry,biotite trachyandesite,andesitporphyrite,rhyolite porphyry etc. The relation of between dike rocks and mineralizationwas rather close, field and underground investigation demonstrates that the formation ofdike rocks was earlier than mineralization, or latter than mineralization, or synchronally.Jinchanggouliang gold ore-field is was divided into east and west ore-field byNE-directed Toudaogou fault, vein-like ore body was dominant, the total number ofveins is about 70, lens-shaped ore body and lenlenticulated ore body is minor. Accordingto the strike direction, ore veins can be separate into three group, the NW-directed orevein is dominant, NE-directed and SN-directed ore veins are minor. The metallizationpattern are sulfide quartz vein and sulfide alteration rock pattern, and the former isprimary. The industrial mineral veins are pyrite-sulfide quartz vein,chalcopyrity-sulfidequartz vein,pyrrhotite-sulfide quartz vein and their sulfide alteration rock patternrespectively. According to our microscopical identification, pyrite,chalcopyrite andpyrrhotite are dominant ore minerals, secondary ore minerals are sphalerite,tetrahedrite,galena,bornite,chalcocite and goethite etc. The gold ore minerals are electrum,nativegold and native silver etc. Quartz is primary gangue mineral, and secdonary gangueminerals are chlorite , sericite , potassic feldspar and carbonate. We separatemetallogenesis of Jinchanggouliang into four stages of mineralization according to orefabric and the relation of minerals: the first stage, quartz vein stage;the second one,quartz-pyrite stage;the third one, polymetallic sulfide stage;the last one, carbonatestage.The research of hydrogen and oxygen from the fluid inclusions indicates thatore-forming fluid mostly derived from magmatic water, organic water entered intoore-forming fluid later. The homogenization temperature of the fluid inclusion vary from202.8℃ to 416.8℃, which can be divided into four obvious stage, and they are250~280℃, 290~310℃, 320~350℃, 360~400℃. The stage of 360~400℃ is the mostimportant temperature stage, indicating that the formational temperature is very high.The components of ore-forming fluid are mostly H2O+CO2(+CO)+X1-2SO4+XCl1-2H2S+N2+H2+CH4 (H2S,C6H6,C2H4,C2H6,CH4,C3H8), and its chemical componentsis similar with the characteristic of high sulfidation gold deposit which is related withvolcanoic-subvolcanoic magmatism.The range of δ34S of Jinchanggouliang gold deposit is from -5‰ to + 1.508‰, andthe peak of δ34S is between -1‰ and +1‰, the average of δ34S is -0.031‰, which issimilar with the δ34S of uranolite. The histogram of δ34S indicates that it has single peak,which demonstrates the source of sulfur of the ore deposit is single, the sulfur wasderived from mantle or lower crust. Accroding to Zartman's Pb isotopic scheme, the pbisotope has two plotted area. Most Pb isotope value plot in the area between lower crustevolutionary thread and mantle evolutionary thread and their exterior, part of Pb isotopevalue plot in the area of upper crust, the characteristic of Pb isotope indicate that mostPb isotope derived from lower crust or mantle, part of Pb derived from upper crust orcontaminated by materials of upper crust through which ore-forming fluid ascended.Chalcophile-elements, iron-group elements , platinum-group elements and the ratio ofrelated elements have identified that the ore-forming materials were derived from richedmantle.As for the tectonic settings, the geochemical characteristics of dark dikes whichwas related with mineralization in Jinchanggouliang gold deposit indicate that it hassimilar attributes with adakites rock. Dark dikes might were formed by certain partialmelted oceanic crust. So the ore-forming environments was continental margin whichwas induced by the long-distance effect of the paleopacific plate's underriding, and thecharacteristic of Pd and Pt have proved it. During this period, the large-scale ascendingof the sathenosphere, underplating of the basalt magma and the delamination of thelithosphere in the eastern China occurred, which induced the third large-scalemineralization in the eastern China. So, we conclude that Jinchanggouliang gold(-copper)deposit is a mesothermal Au(Cu)deposit that is related with volcanic-subvolcanic action,which was formed in the continental margin environment, and its direct thermodynamicsource was underplating basaltic magma.