Tectonic and district to deposit-scale structural controls on the Ge'erke orogenic gold deposit within the Dashui-Zhongqu District, West Qinling Belt, China

Ge'erke (>100 t gold) is one of six Mesozoic gold deposits within the Dashui-Zhongqu District, that collectively have a non-JORC resource of about 150 tonnes gold out of a total of >1100 tonnes gold for the host West Qinling Belt. The deposits in the Dashui-Zhonggu District are deeply weathered to depths of up to 400 m, with secondary Fe-oxides having replaced pyrite and other sulfides. This makes traditional ore deposit studies involving mineralogical, geochemical and isotopic analysis difficult. Thus, their association has been controversial with correlations to deposits that include Carlin and intrusion-related types postulated. However, these associations can be discounted in favour of their classification as epizonal orogenic gold deposits. At Ge'erke, gold mineralization was focused in the hangingwall of a broadly south-dipping southern margin of a granite pluton in a wide variety of fault trends. This complexity was caused by heterogeneous stresses developed around the rigid pluton by the broadly NE-SW directed regional principal maximum stress responsible for the sinistral movement along the crustal-scale faults which control the regional alignment of the West Qinling gold deposits. At the orebody and ore shoot scale, gold mineralization is controlled by rheology contrasts, particularly the fault contacts between crystalline limestone units and granite dykes, which are themselves in a variety of orientations because of inhomogeneous strain around the parent granite pluton. In this region the secondary faults that subparallel the Mianlue Suture and associated crustal-scale faults are poorly gold mineralized in the absence of granite plutons. During exploration, such buried plutons and the orientations of their margins can best be detected by gravity surveys, although magnetic surveys may also be useful.