Metallogenic System Of Jiaojia Gold Oreifeld, Shandong Province, China

Jiaojia gold field is the nomenclature spot of the Jiaojia-type gold deposits, withidentified gold resources/reserves of over 500 tonnages. The tectonic setting andmetallogenic geodynamic setting of Jiaojia gold field is unique among the global golddeposits, and the source and enrichment mechanism of huge gold resources areattractive key scientific problems. The thesis focuses on the metallogenic system ofJiaojia gold field, and the following conclusions were made through detailed field andlaboratory research.1. The gold deposit formed in the geodynamic setting of large-scale lithospherethinning during tectonic regime transformation from continent-continent collision tosubduction collision. The regional principal compressive stress in the ore stage isNNE-NE striking, and the ore-controlling fault belt is dominated by dextral tensoshear activities. The rhombic ore-controlling fault system, which is composed ofJiaojia fault belt and secondary faults and fractures on its footwall, controlls theformation and distribution of the mineralization network.2. Altered-mineralized rocks inherit from Linglong biotite granite andmetamorphic rocks of Jiaodong Group, and the gold grade in Linglong granite andJiaodong Group is inversely proportional to the deposit scale. Though lamprophyre islocated near the mineralization belt, its geological-geochemical characteristics areobviously distinct from those of ores, and its gold grade is directly proportional to thegold grade of geologic bodies that the lamprophyre intruded into, and the lamprophyre scale is inversely proportional to the deposit scale. In conclusion, thegold originates from Linglong biotite granite and metamorphic rocks of JiaodongGroup instead of lamprophyre.3. The ore fluid is a H2O-CO2-K+-C1-system which is of medium-lowtemperature (200℃-330℃), low salinity (3.15-8.99wt%NaCl), and similar isotopecompositions with metamorphic/magmatic fluids, with minor late-ore stage fluiddrifts to the meteoric water line. During metallogenic processes, the total content ofrare earth elements in the gold-bearing pyrite increases first and decreases afterwards,withδ18O in the fluids decreases gradually, indicating that the ore fluid mainlyoriginates from metamorphic fluid, while the metamorphic grade and water-rockreaction are the main factors that affect gold deposition.4. The 3D zonation structure of gold mineralization is evident. In horizontaldirection, away from the main fault plane on the footwall of Jiaojia fault, themineralization varies from pyrite-sericite-quartz altered rocks mineralization toquartz-sulfides veins -pyrite-sericite-quartz altered rocks- silicified rocksmineralization. In vertical direction, the altered rocks mineralizations overlie the veintype mineralizations in deposit scale, while the vein type mineralizations overlie thealtered rocks mineralizations in ore body scale. Weathering and denudation aftermineralization are the main factors affecting the transformation and preservation ofgold deposits. The denudation depth increases from NE to SW of the Jiaojia fault, andthe denudation of Wangershan gold ore bodies is shallower than that of Jiaojia goldore bodies.5. Gold field is the product of structure-fluid coupling ore formation. The fluidsmigrated along the strikes of ore-controlling faults, meanwhile, due to the outwarddevelopment of fractures caused by accumulation of periodic pressure, part of thefluids migrated laterally. The changing of ore fluids from alkaline-oxidative-hightemperature fluids to acidic-weak reductive-medium-high temperature fluids to weakacidic-reductive-medium-high temperature fluids made the gold in host rocks becomehighly charged ions, reactivate and flow into fluids. Afterwards, the changes ofphysical-chemical conditions caused the stability decrease of AuH3SiO4and AuHSiO4, the solubility decrease of [AuCl2]-and Au(HS)2-, the consumption of Fe2+,Fe3+,Cu2+,the formation of pyrite, chalcopyrite and other sulfides, the break down ofgold-sulfur/chlorine complex compound, and accumulation and deposition of hugegold resources.6. Exploration system model was established according to the analysis results ofspace-time structure of metallogenic system and prospecting potential at the footwallwas pointed at areas of 500~1000m away from the Jiaojia fault. Aiming at theimportant prospecting potential areas, prediction model of blind ore body wasestablished and 20 prediction targets were defined. A total proved newly increasedgold resource is 10.04t by the end of the year of 2011.