Exploration history and geology of disseminated gold deposit at Maoling in Proterozoic sedimentary rocks in North China Platform

Abstract

The Maoling deposit, with average grade of 2 g/t Au and reserves of over 45 m.t., is a disseminated Au deposit hosted in Proterozoic sedimentary rocks in the Southern Liaoning Province of the North China Platform. The hidden ore bodies at Maoling were discovered in 1985 through a combination of geophysical and geochemical studies in the area which showed anomalies during the reconnaissance soil geochemical survey. The ore bodies show high magnetic susceptibility, low resistivity and high chargeability compared to unaltered host rocks and they are enriched in As, Ag, Pb, Co, Ni and Sb. The soils overlying the deposit show secondary halos of Au, As, Ag, Pb and Sb. All Au deposits in the area are in and around Mesozoic granitic intrusions and the Maoling deposit is underlain by the Wo-Longquan batholith. The occurrences of Au deposits and cross-cutting relationships between alteration zones and dykes suggest that the Au mineralization took place after the peak intrusive event during the Jurassic tectonic activity. The ore bodies at Maoling are composed mostly of fine dissemination of arsenopyrite and pyrrhotite and they are accompanied by intense sericitization and silicification with minor biotitization. The characteristics of the deposit are akin to those of Carlin-type Au deposits in North America, including intense regional silification, high tonnage/grade ratio, high As and Ag, low base metal contents, and dissemination of fine-grained metallic minerals in sedimentary rocks. Whereas the host rocks of North American Carlin-type deposits are unmetamorphosed, those of the Maoling deposit have undergone greenschist- to amphibolite-facies regional metamorphism and some ores occur within the andalusite-grade contact metamorphic rocks of the intrusion. The lack of cristobalite, opaline silica, clays, and cinnabar which are common in Carlin-type deposits together with the evidence of brittle-ductile deformation in the Maoling deposit is consistent with the mineralization at Maoling at higher temperatures and deeper crustal level than Carlin-type deposits.