In the Edong District, intrusive rocks related to the Yanshanian tectono-magmatic event cover about 17% of the area. The early Yanshanian magmatism is associated with the Indosinian uplifts and characterized by diorite-granodiorite batholiths. The four largest intrusions include the Yangxin quartz diorite-granodiorite (outcrop area: 215 km2, K-Ar ages of 118-157 Ma), the Yinzu quartz diorite (90 km2, 150-189 Ma), the Lingxiang diorite (54 km2, 101-145 Ma), and the Tieshan diorite-quartz diorite (140 km2, 120-150 Ma). There are many small stocks of granodiorite and granodiorite porphyry that are also related to early Yanshanian magmatism. The late Yanshanian magmatism in the Edong District occurs mainly within the down-faulted basin and includes both intrusive and volcanic rocks. Examples include the Echeng granite-diorite intrusion (85 km2, 94-126 Ma), associated with the Chengchao deposit, and the Jinshandian quartz monzonite-monzogranite stock (16 km2, 94-142 Ma), associated with the Zhangfushan deposit. The accompanying volcanic rocks mainly belong to the basalt-andesite-dacite-rhyolite series and host only a few small hydrothermal Fe deposits.
Host rocks to most of the deposits are those of the Lower Triassic Daye formation. The main types of mineralization are Fe, Cu, Fe-Cu and Cu-Fe skarn deposits, whereas porphyry and stratabound massive sulphide deposits are minor. The Cu-(Au,W,Mo) deposits are mainly associated with the early Yanshanian diorite-granodiorite intrusions in the eastern part of the district. The Fe skarn deposits are generally associated with the late Yanshanian volcanic rocks or gabbro-diorite-granodiorite-granite intrusions in the western part of the district, and occur in the contact zones between the intrusions and Triassic gypsum-bearing carbonates and shale-carbonate sequences. Transitional Cu-Fe and Fe-Cu skarn deposits, which account for more than 50% of the copper reserves, occur in the central Edong District. Contact metasomatism is well developed in the district, and formed calcic, magnesian or transitional skarns, depending on the composition of the country rocks.
Ref.:
- Yuanming Pan and Ping Dong (1999): The Lower Changjiang (Yangzi/Yangtze River) metallogenic belt, east central China: intrusion and wall rock-hosted Cu-Fe-Au, Mo, Zn, Pb, Ag deposits. Ore Geology Reviews 15, 177-242.
