Ore-controlling Characteristics and Metallogenic Model of Brittle Ductile Shear Zones of Baguamiao Gold Deposit in Fengxian County, Shaanxi

Located on the north wing of the Baguamiao secondary inverted syncline of north Sujiagou-Kongguangou composite syncline, the Baguamiao super-large gold deposit is the unique of the west Qinling area. The major hosted rocks are dolomitic silty phyllite and stripped marbleized limestone of the lower Xinghongpu formation. Gold orebodies are controlled by ductile shear zones under the northwest-trending F₁³ great fault and develops into three types of gold mineralization which are quartz vein type, structural altered type and altered mylonite type, with structural altered type dominating the mineralization. From surface to deep, ductile shear zones are fragile to fragile-ductile to ductile in order, which are corresponding with the three types of gold mineralization. Due to the orogenesis and crust uplift in Indosinian, ductile shear deformed mylonite of the ductile zone is uplifted, superimposed to the fragile-ductile and ductile shearing zones, thus constituting different types of gold mineralization superposition enrichment, then forming deficient gold orebodies. During Indosinian-Yanshanian, magmatism became active and intruded along the northeast-trending F₂² fault, which drives the gold ions of deep and both sides of the surrounding rocks activate, migrate to west of F₂² and east F₂³ fault and enrich. By superposition, transformation and enrichment on the former deficient gold bodies, the gold orebodies took the place and are finally formed.