Metallogenic Environment And Prediction For Baguamiao Gold Deposit Type In Qinling Region, China

The Baguamiao is the largest gold deposit found so far in Devonian sediments in Qinling Region, which located in Fengxian, Shaanxi near Gansu province. The Baguamiao deposit is hosted in the Xinghongpu group of lower Devonian, which consists low-grade fined-grained clasts, with striped Na- and Ca-bearing silicates and laminated albite. It is showed to be hydrothermal sediments on seabed.The natrium- calcium-silicalites with strip structure is gradually changing into phyllite. The thickness of the rocks is thinner than 1 cm in general and the minority reaches several cm. The rock types include the iron-bearing carbonate silicalite, the iron-bearing carbonate albite silicalite, and quartz albite, quartz- and iron-bearing carbonate. On the section in the field, there is depositional cycle with the change of the strip rock zone → the spot slate zone → carbon-bearing phyllite from the bottom upward.. There is a series of lamina change interbedded by iron-riching carbonate lamina, albite-bearing lamina and argillaceous lamina in thin section. The thickness of the lamina is from 0.1 to 1.2 mm.The albite, shaped in lense, is located in the northern of the deposit and the ratio of Sr/Ba is smaller than 1, which was identified to be sedimentary genesis rather than intrude.The ratios of Fe₂O₃/FeO, SiO₂/Al₂O₃, SiO₂/ MgO and SiO₂/(Na₂O+K₂O) of the two type rocks above are similar to those of the hydrothermal sedimentary rock of the lead-zinc deposits in Devonian, Qinling and the hydrothermal sediments on the sea floor. The projection pots locate in the area of the lead-zinc deposits in Devonian, Qinling and the modern hydrothermal sediment on the sea floor in the triangle diagrammatize of Fe-Mn- (Co+Ni+Cu)× 10. According to the synthesis study by their REE element and H, O, C, Si isotope, they belong to the hydrothermal sedimentary origin. Along with forming of the Qinling crack and sink trough in Devonian and the movement of the syngenetic rupture, the hydrothermal sedimentary rock series with gold-riching are formed, which is close relative to gold mineralization.The orebodies in Baguamiao gold deposit occurred as lens-like and bed-like orebodies along the fault zone with showing approximately comfortable attitudes with the host rocks. There are 30 various minerals about in ores. Of which, about 10 various minerals are common. The metal minerals less than 3%. Pyrotite, pyrite and native gold are common. Binerite, chalcopyrite, galena, sphalerite and ilmenite can be seen also. The element assemblage is Au-Hg-Ag-B-Zn-Cu-Pb-Sb -As, in which the Au-Ag assemblage is the most important. Baguamiao gold deposit is characteristic with the alone pyrotite and pyrite assemblage, altered and depigment of wall rock, spot structure and the quartz veins occur along or cut the stratum, which is different with the typical Carlin type or similar Carlin type gold deposits.The gold mineral of Baguamiao gold deposit is independent gold. The gold is usually in middle-, fine and micro- size. Gold is mainly occurred as intercrystal—gold and Crach—gold, and inclusion—gold is little. The gold mainly hosted in quartz, pyrotite and pyrite. It is shown by the gold ore selectation that Baguamiao gold deposit can be developed and utilized. The gold content in Baguamiao giant gold deposit is in direct proportion to the development and folded broken degree of quartz vein and to the content of co-existed sulphide, and is in inverse proportion to vein thickness and the grain size of co-existed sulphide. The gold content in joint vein is higher than that in bedding vein.the gold content is several to more than ten times of the content in surrounding rock nearby. Nevertheless industrial ore body isn't alone consisted of gold-quartz vein. In view of the points mentioned above, the authors put forward that the gold mineralization type is...