Molybdenum deposits in the eastern Qinling,central China: constraints on the geodynamics

More than a dozen molybdenum prospects, distributed within a zone about 200 km long and 20 km wide, have been discovered in the Eastern Qinling orogenic belt, central China. These deposits are mainly hosted within small, dominantly granoporphyritic and quartz monzonitic intrusions of Cretaceous age. They can be classified into five groups based on spatial relationships between the ores and intrusions: porphyry-type, transitional-type (between porphyry and skarn), skarn-type, vent breccia-type, and hydrothermal vein-type Mo deposits. Regional geologic relations and deep-seated structures define the presence of the Luanchuan syncline, an EW-striking west-dipping depression located beneath the Mo-bearing metallogenic zone. Because the axis of the syncline is west-dipping in the study area and the crust overlying it is thickened, the stress is inhomogeneous, resulting in a S–N compressive stress in the deep crust and development of a set of NE-oriented extension-shear faults. These faults are superimposed on the W–E-striking deep-seated faults parallel to the ancient continental margin. The two groups form a chequerboard-like assemblage of deep-seated faults, providing channels for ascending ore fluids derived from crust–mantle interaction and space for subsequent ore precipitation. These faults controlled the emplacement of a series of intermediate-acid granite magmas and also contributed significantly to the distribution of the various Eastern Qinling ore deposits.