Tectonic-alteration-mineralization of the Xindigou-Maoduqing gold deposits in the Daqing Mountains, Inner Mongolia, China

The Xindigou and Maoduqing gold deposits, occurring in the Liushugou Formation of Neoarchean Serteng Shan Group, are typical greenstone-type gold deposits related to ductile-brittle shear deformation. Tectonic-altered rocks are mainly phyllonitic quartz-sericite schist, phyllonitized chlorite-sericite schist, mylonitized chlorite-quartz schist, sericite-chlorite felsic mylonitic schist, felsic cataclasite and pyrite-sericite-quartz tectonic schist. The geochemical characteristics of tectonic-altered rocks are similar to those of intermediate-basic volcanic rocks. Their ∑REE (44.9-155.4×10-6), LREE/HREE (7.0-26.1) and δEu (0.6-1.2) of tectonic-altered rocks also resemble those of intermediate-basic volcanic rocks. Tectonic-alteration-mineralizing fluids are characterized by low salinity, high density and CO2-rich fluids, with typical features of orogenic gold deposits. The important prospecting areas are zones of strong tectonic alteration in regions where metamorphic mafic volcanic rocks in Precambrian greenstone formations are widely distributed.