Metallogeny of the Hunjiang basin, northeastern North China block

Abstract

The Hunjiang basin in the northeastern North China block is host to a wide range of ore deposit types that are currently exploited by more than 100 past and producing mines. Extensive field and laboratory investigations were conducted to summarize the regional metallogeny, classify the different deposit types, and to place the deposits within a regional geologic and tectonic context. The Archean basement of the basin is host to magnetite deposits that have been affected by high-grade metamorphism. In addition, Proterozoic magmatic Cu-Ni deposit and orogenic Au deposits that are likely of Mesozoic age are located in the metamorphic basement rocks. Polymetallic Co-Cu and Ni-Co-Cu deposits are located in Proterozoic schists within the basin and are of pre- to syn-metamorphic origin. However, most deposits in Hunjiang basin can be related to Mesozoic igneous activity. This includes porphyry Cu and Cu-Mo deposits as well as associated skarns and carbonate replacement deposits. Economically most significant are Au deposits hosted in Proterozoic limestone and dolomite that are located distal to the Mesozoic igneous intrusive centers. This includes the White Mountain deposit near Baishan City, which contains an endowment of more than 50 tonnes Au. There are no known high-sulfidation epithermal deposits within the Hunjiang basin, which is consistent with fluid inclusion evidence demonstrating that emplacement of the porphyry intrusions occurred at significant depth below the paleosurface. Geochronological constraints indicate that Mesozoic igneous activity and associated deposit formation in the Hunjiang basin occurred as a result of Jurassic subduction processes and subsequent extension after slab rollback and lithospheric delamination under the Eastern North China Block in the Cretaceous. Future mineral exploration efforts in the Hunjiang basin should focus on the distal sedimentary rock-hosted Au deposits associated with Mesozoic intrusions, with special emphasis on the northern part of the basin where these deposits occur preferentially at the intersection of extensional faults with a vanished evaporite unit that is distinctly enriched in Fe oxides providing a chemical trap.