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

摘要

Mesozoic granitoids in East Shandong ~1 containsome 30 Moz gold, making East Shandong the largest granitoid-hosted gold province in the world. The gold province is locatedalong the northern boundary of the suture zone between theNorth China and South China cratons. According to theirmineralogical, geochemical and geochronological characteristics,two groups of Mesozoic granitoids are recognised in EastShandong, 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 northof the suture zone, whereas the second group of granitoids occuron both sides of the suture zone. These characteristics suggestthat the two groups of granitoids were associated with differenttectonic events. A tectonic analysis suggests that the MYgranitoids are the result of collision and suturing of the Northand South China cratons during the Triassic to Jurassic, whereasformation of the LY granitoids is attributed to the distal (inland)influence of subduction of the Pacific-Izanagi plate underneaththe Eurasian continent during the Cretaceous. The major golddeposits are spatially associated with the MY granitoids in EastShandong. Most of the gold occurs either as quartz-veins in thegranitoids or disseminated in altered shear zones along theboundary of the granitoids and Archaean metamorphic rocks. Themajor gold mineralization and alteration generally display thecharacteristics of gold-only provinces, namely CO_2-rich, lowsalinity and reduced fluids and proximal mica and sulfidealteration. These characteristics are different from those ofPhanerozoic granitoid-related skarn-porphyry systems.Accordingly, the gold mineralization may be more tectonicallyand structurally controlled rather than have a direct geneticrelationship with the granitoid itself. According to therelationships between tectonics, granitoids, distribution of golddeposits and fluid geochemistry, the major gold in East Shandongmay have been formed during the subsequent exhumation stageafter the collision of the North and South China cratons.