Tectonics, granitoids and mesozoic gold deposits in East Shandong, China

Abstract

Mesozoic granitoids in East Shandong 1 East Shandong gold province is also called Jiaodong gold province, where “Jiao” refers to the Jiaozhou Peninsula, and “dong” stands for east. 1 contain some 30 Moz gold, making East Shandong the largest granitoid-hosted gold province in the world. The gold province is located along the northern boundary of the suture zone between the North China and South China cratons. According to their mineralogical, geochemical and geochronological characteristics, two groups of Mesozoic granitoids are recognised in East Shandong, namely the Middle Yanshanian (MY) (ca. 160–150/130? Ma) and the Late Yanshanian (LY) (ca. 117–85 Ma) granitoids. The first group of granitoids only occur to the north of the suture zone, whereas the second group of granitoids occur on both sides of the suture zone. These characteristics suggest that the two groups of granitoids were associated with different tectonic events. A tectonic analysis suggests that the MY granitoids are the result of collision and suturing of the North and South China cratons during the Triassic to Jurassic, whereas formation of the LY granitoids is attributed to the distal (inland) influence of subduction of the Pacific–Izanagi plate underneath the Eurasian continent during the Cretaceous. The major gold deposits are spatially associated with the MY granitoids in East Shandong. Most of the gold occurs either as quartz-veins in the granitoids or disseminated in altered shear zones along the boundary of the granitoids and Archaean metamorphic rocks. The major gold mineralization and alteration generally display the characteristics of gold-only provinces, namely CO 2-rich, low salinity and reduced fluids and proximal mica and sulfide alteration. These characteristics are different from those of Phanerozoic granitoid-related skarn–porphyry systems. Accordingly, the gold mineralization may be more tectonically and structurally controlled rather than have a direct genetic relationship with the granitoid itself. According to the relationships between tectonics, granitoids, distribution of gold deposits and fluid geochemistry, the major gold in East Shandong may have been formed during the subsequent exhumation stage after the collision of the North and South China cratons.