Yanshanian gold metallogenic system and metallogenic model of the Guilaizhuang gold ore field, western Shandong

The Guilaizhuang gold ore field is one of the essential tellurium-rich goldfields in eastern China and the only super-large goldfield in western Shandong so far. These gold deposits controlled by the Tongshi subvolcanic dome occur in different depths, geological structures, and geological bodies. Though their mineralization types are diverse, their host wall rocks, formation environment, geological background, and metallogenic characteristics are generally consistent: (1) The Guilaizhuang gold ore field, mainly composed of Precambrian basement rocks and early Paleozoic carbonate cap rocks, is an endogenous medium−low hydrothermal gold concentration area of relatively developed Mesozoic tectonic magmatism. (2) Yangan fault, a derivative structure of the Tanlu Fault Zone, controls the distribution of strata, magmatic rocks, secondary structures, and gold deposits (points) in this area. The sub-faults of the Yangan fault and the radial and circular structures of subvolcanic domes are good places for ore fluid migration and sedimentation. (3) The mineralization types are mainly cryptoexplosive breccia, magnesian carbonate micro-disseminated, porphyry, skarn superposition, and altered fracture zone. The ores generally develop into disseminated, veinlet disseminated, stockwork, crumb, and block structures, reflecting that they were formed in the post-magmatic hydrothermal environment. (4) It shows a distinguished character of coexistence of tellurium and gold super concentration. In addition to common native gold and electrum, there are also tellurium-containing minerals such as bessmertnovite, petzite, hessite, calaverite, etc. (5) The early Jurassic intermediate alkaline magma initially started the gold mineralization process in this area and provided parent rock and material source for the early Cretaceous alkaline magmatic activities. The main mineralization period of the Guilaizhuang gold ore field in western Shandong may be in the early Cretaceous. (6) The ore-forming fluid has the characteristics of low temperature and low salinity. The isotopic characteristics are multi-sourced. They are dominated by magmatic water and atmospheric precipitation, with a small amount of metamorphic water. (7) Au likely combines with Te and S to form transportable complexes for migration in the ore-forming hydrothermal fluid. There is a high tellurium fugacity in the ore-forming hydrothermal fluid. Under medium- and low- temperature conditions, tellurium can easily replace sulfur and enter the sulfide lattice. Under high tellurium fugacity conditions, tellurium is prone to form telluride with elements such as gold, silver and lead to mineralization. The consistency of the regional metallogenic characteristics indicates that the Mesozoic large-scale gold mineralization in the Guilaizhuang area of western Shandong is controlled by a unified geological event and can be classified into a unified subvolcanic medium-low hydrothermal gold metallogenic system.