| The Great Wall gold deposit,located in Qian'an City,Hebei Province,was discovered by No.2 Geological Brigade of Hebei Geology and Mineral Exporation Bureauin 1990 based on geochemical exploration anomalies.After several years of exploration,seven ore belts including ?,?,?,?,?,? and ? have been discovered so far.The total amount of mineral resources identified throughout the region was 2180.85 kt of ore reserves and 10007.75 kg metals of gold obtained.The Great Wall gold deposit is located in the middle segment of the northern margin of the North ChinaCraton(NCC),and the combining site of NCC,the Siberian and the Pacific Plate.By Mesozoic,this regionhad the characteristics of the intra-continental orogeny,which falls into compression and extension alternate environment with frequent tectonic-magmatic activity.However,the stretching became stronger by early Cretaceous.Three large-scale mineralization in North China had a greater impact on the NCC.The Great Wall gold deposit was controlled by tensional setting due to lithosphere thinning during 130-110 Ma.On the scale of the deposit,it is mainly controlled by the exposed F1 fracture and its secondary fractures.Based on field operation,this paper analyzes themetallogenic background and the geological features of deposit,and through thethe study of ore-controlling structures,chemical composition of metal sulfides,fluid inclusions and S isotopes,proving the process of fluid evolution.Comparedwith the basic characteristics of typical deposit,the Great Walll is a Carlin-type gold deposit.The host strata of the Great Wall gold deposit are the Yangzhuang Formation and the Wumishan Formation of the JixianGroup,and diorite igneous rocks,and are hosted in the vermiculite dolomite and sandy muddy dolomite,and the dolomite.The dolomite containing chert and sand-shale as the most important host rocks provide a good ore-forming environment and ore-bearing space for the gold orebody.The ore bodies in Great Wall deposit are mainly hosted within the NW-trending structure fractured zone,and the intersection between strata-dissectiing fault and fault is the ore-containing position.The ore bodies are deposited in the ore belts in a layered,lenticular,and vein-like.The main ore minerals of the Great Wall gold depositare pyrite,limonite and natural gold;gangue minerals mainly includedolomite,calcite,and quartz.Ore structure are mainly automorphic,hypidiomorphic,xenomorphic texture and replacement structure.Ore structures are disseminated,vein-like,and mass-like.Wall rock alterations includedecar bonation,silicification,argillization and dolomitization.Mineralization is divided into three stages: quartz-pyrite(stage ?),polymetallic sulfide stage(stage ?),and carbonate(stage ?).The ore-forming fluid is all gas-liquid two-phase fluid.The pressure of the main metallogenic stage(stage ?)is mainly 13 to 17 MPa,corresponding to estimated metallogenic depths of 1.3 to 1.7 km.The metallogenicfluid associated withthe Great Wall depositis characterized by moderate to low temperatures(concentrated in 145 ~ 160 °C),low salinity(concentrated in 8 ~ 11wt% NaCl),and low density(0.94 ~ 1.01g/cm3)fluid.The electron probe analysis of pyrite shows that the Great Wall gold deposit is characterizedas hydrothermal genesis.The accompanying elements of the gold deposit and the occurrence state of the gold both have the characteristics of a Carlin-type gold deposit.S isotope analysis shows that the ore-forming materials were mainly derived from magma mixed with sulfur from strata.The study of H-O isotopes shows that the ore-forming fluid was derived from the mixing of magmatic water and atmospheric water.In summary,the metallogenesis of the Great Wall deposit was controlled by the F1 fault and its secondary faults exposed in this region(Lengkou faults).The Great Wall gold deposit is the Carlin-type gold deposit. |
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