Chemostratigraphy and Elemental Zoning Studies in the Ore-Bearing Facies of the Nudeh Besshi-Type Volcanogenic Massive Sulfide Deposits (VMS), Southwest Sabzevar

The Late Cretaceous volcano-sedimentary sequences that bear Cu (Zn) mineralization compose of four units (Unit1, Unit2, Unit3, and Unit 4). The copper (Zn) mineralization on the unit 2 occurred in two distinct horizons. The host rock includes olivine basalt flow and tuffaceous silty sandstone. In this deposit, mineralization occurred in three different facies (stringer zone, massive ore facies and bedded ore facies). The Nudeh deposit has a strongly horizontal geochemical zonation from Massive ore facies to bedded facies (decreasing of ore grade and Cu:Zn ratios, increasing of Ba:Zn ratios, and increasing of Fe and Mn) and vertical zonation, specially within massive ore facies (upward increasing of Cu:Fe and Cu:Ti ratios, and decreasing of Cu:Zn ratio). The lithogeochemica studies show that maximum copper grade in massive ore facies is about 11.2%, which is decreased to the bedded ore facies. This grade in the bedded ore facies changes from 4 to 5 percent. The base metal overall grade (Cu/Zn+Pb) of the Nudeh deposit in massive ore facies is more than the stringer zone and bedded ore facies. Some parameters such as changing in hydrothermal and sedimentary components ratio, variation of temperature, Eh and pH, the role of refinement process in massive ore facies and dominants of sedimentary conditions in bedded ore facies, control this geochemical zonation of the Nudeh deposit.