Structural characteristics of the Wulong shear zone and related gold mineralization in the Wulong Gold Camp, southeastern Liaoning Province, China

Dijiang Guo, Thèse de Doctorat.

Projet de Doctorat en ressources minérales sous la supervision du Dr Huan-Zhang Lu.

Description du projet

The Wulong shear zone is composed of approximately parallel NNE striking faults and it traverses different rock types, varying from early Proterozoic gneiss to late Mesozoic sediments. The Wulong gold camp, structurally controlled by the Wulong shear zone, is located near the Dandong City, southeastern Liaoning province, China. This gold camp is composed of three gold mines: the Wulong gold mine, the Sidaogou gold mine and the Jielishu gold-copper mine. In the Wulong mine area, the Wulong shear zone is developed in late Archean gneiss. Ductile deformation is demonstrated by elongated quartz grains, mica-fish and pressure shadow. Finite strain measurement indicates that the shear is flattened ellipsoid type in the Wulong mine area. Paleopiezometer measurements indicate that differential stress in shear zone ranges from 81.5 MPa to 144.6 MPa in the Wulong mine, and strain rates vary from 9.428 x 10 -23 to 4.284 x 10-21 sec-1 . In the Sidaogou gold mine, The Wulong shear zone is developed in the early Proterozoic Liaohe group metamorphosed sandstone rocks. Zonation of tectonites is not well developed in this area. Ductile deformation structures developed in the Sidaogou area include mylonite foliation, gliding lineation, intrafolial folds, lenses and boudinages. Finite strain measurements suggest that deformation type is near plain-strain ellipsoid, differential stress measured in Sidaogou mine area is 71.5 MPa, corresponding to a strain rate of 4.026 x 10-23 sec-1. In the Jielishu mine, both gold and copper are economically valuable. The deposit is hosted in marble. Observed sulfides in the Jielishu deposit include pyrite, chalcopyrite, chalcocite, malachite and minor sphalerite and galena. Free gold was frequently observed in chalcopyrite and pyrite. The Jielishu gold-copper deposit is characterized by vug structure developed in ore bodies, which was not observed in the other two deposits. Au contents have intimate relationships with Bi contents in these deposits. REE signatures suggest that ores developed in the Wulong gold camp have similar sources. Pb isotope data indicate that the ore materials were obtained from upper crust. Sulfur isotope data of ores suggest that sulfur was probably of magmatic origin (+1.55‰ ∼ +2.5‰), but host rock/fluid reactions contributed additional sulfur to ores of the Sidaogou deposit (+11.33‰). Based on geological and geochemical features in the three gold deposits, the author proposes that the three gold deposits are structurally controlled by the Wulong shear zone, and the gold deposit is genetically related with the Sanguliu intrusion and a descriptive model of gold mineralization, magmatic intrusion and the Wulong shear zone is proposed.