Geological and geochemical characteristics and vanadium enrichment regularity of the Qianjiaping vanadium deposit in southern Qinling Mountain

Abstract：The Qianjiaping vanadium deposit occurs in the black rock series of lower Cambrian Shuigoukou Formation in southern Qinling region. The black rock series is composed of black carbonaceous siliceous rocks, black carbonaceous siliceous rocks interbedded with argillite and argillite. The vanadium ore bodies are layered in form. The ore type is mainly black carbon-bearing siliceous rocks interbedded with argillite. The vanadium mineral is mainly roscoelite. The main components of the black rock series are SiO2, Al2O3 and K2O, with the enrichment of such elements as Fe, Ba, Zn, P, Cu, Ni, Cr, Sr, Zr, Ag, Ti, Mn and V. The values of the black rock series n(V)/n(Cr)=5.92—30.64, n(V)/n(V+Ni)=0.88-0.99, and δU>1 indicate that the sedimentary environment might have been under an anoxic condition. The values of the black carbonaceous siliceous rock n(SiO2)/n(Al2O3)=238.81, U/Th>1 and δ30Si=-0.1‰-0.5‰, and δ18O=20.2‰—25.8‰ indicate that the ore deposit was probably a hydrothermal deposit in the closed semi-deep ocean basin. The values of the argillite n(SiO2)/n(Al2O3)=5.69，n(Al)/n(Al+Fe+Mn)=0.63，and n(Si)/n(Si+Al+Fe)=0.74-0.76 indicate that the material sources were probably of continental origin, affected by hydrothermal solution. The vanadium mineralization is hosted in the black rock series deposited originally in the fault basin near the margin of the isolated paleo-uplift. The vanadium obviously tends to be concentrated in the argillite inside or near the black carbonaceous siliceous rock. The vanadium content is the highest in the transitional strata between the carbonaceous siliceous rocks interbedded with argillite and argillite, so is the content of such elements as Cu, Pb, Zn, As, W and Mo. The metallogenic materials of the vanadium deposit might have been derived from deep hydrothermal solution. The absorption of the argillite is very important for the vanadium enrichment. It is concluded that the vanadium deposit should be of exhalative hydrothermal sedimentary origin.