Sources of Ore-forming Materials in the Jiaodong Gold Deposits:Constraints on Gold Content from Geological Units Related to Gold Mineralization
Jiaodong is recognized as the third largest concentration of gold deposits globally.Recent advancements have been achieved in the exploration of gold deposits and the associated metallogenic theories.However,significant gaps remain in the understanding of the genesis of these deposits and the sources of mineralizing materials.A critical question that persists is how to scientifically and coherently elucidate the enrichment of gold(Au)in deposits that exceed the concentrations found in the surrounding rocks.In this study,we systematically collected and analyzed samples of Late Mesozoic granite and Early Cambrian metamorphic rocks from Jiaodong that have not undergone mineralized alteration to determine their gold(Au)content.The average Au content of 97 granite samples was found to be 0.31×10-9.Specifically,the average Au contents for Linglong-type,Guojialing-type,and Weideshan-type granites were 0.25×10-9,0.28×10-9,and 0.35×10-9,respectively.Additionally,the average Au content of 397 samples of Early Precambrian metamorphic rocks was determined to be 1.05×10-9.The abundance of gold in all geological units in Jiaodong is comparable to or lower than that in the Earth's crust and the average gold content in the North China Plate.However,the gold content in early Precambrian metamorphic rocks is 3.39 times higher than in late Mesozoic granite.Based on previous studies,it is inferred that there is no source area or ore-source rock(layer)with anomalous gold enrichment in Jiaodong.Instead,the substantial gold mineralization is attributed to the partial melting of the ancient metamorphic basement during the Late Mesozoic.During the formation of granitic magma via partial melting of basement metamorphic rocks in the lower crust,over 70%of the gold(Au)precipitates in a comparable"melting"process with in the ultra-high temperature environment,resulting in the production of Au-poor granites.The fluids associated with the magmatic activity of pre-mineralization Linglong and Guojialing-type granites facilitated the migration and enrichment of Au.The substantial alterations in the geochemical com-position of Weideshan and Laoshan-type granites during and subsequent to the mineralization period disrupted the chemical equilibrium of the fluids,thereby creating favorable conditions for the precipitation of gold(Au).
source of ore-forming materialsJiaodong gold depositsLate MesozoicAu-poor granitespartial melting
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