Evolution Of Au Ore-forming Fluid And Metallogenetic Regularity Research In Eastern Shandong

As one of the most famous gold producing area in China,Jiaodong Gold Province has approximately one-third of the country's total gold resource reserves.Both densely distributed large or super-large gold deposits and concentrated mineralization age in Jiaodong made it a major eruption of Mesozoic metallogenesis in Jiaodong by geologists with a lot of accumulated research results.Ore-forming fluid research in Jiaodong mainly includes:(1)Fluid inclusions,gold ore-forming fluids source,gold ore-forming materials source and Au mineralization basic researches of specific gold-forming fluids.(2)A comparative study of different types of gold deposits,orogenic gold deposits in Xiaoqinling area and Jiaodong area.(3)Partial achievements have been made in the innovative research of ore-forming fluids combined with 3D technology for deep prospecting,fluid evolution,and interdisciplinary integration.However,most of the specific gold-forming fluids studies are limited in basic study of fluid inclusions without enough further study.There is still some controversy on the source,nature and evolution process of different types of gold deposits in Jiaodong and still huge research space for innovative research on gold-forming fluids.In addition,there are so many research results in Jiaodong that with the increasing demand for the effective combination of"single specific"and"regional systems",the systematic(comparative)studies of ore-forming fluids have been continuously improved.Continuously improving the ore-forming fluids systematic(contrast)study has laid a solid foundation for the study of geological exploration,regional modeling and metallogenetic regularity.Si O₂solubility is an important parameter for studying the activation,migration and precipitation,hydrothermal composition,properties and evolution of elements in water-solid interaction within the earth.It is of great significance to understand the genesis of quartz-related deposits as well.This study is based on the project of“Survey of Tectonic Alteration and Reasarch of Mineralization in Laizhou-Zhaoyuan Area,Shandong Province”by Shandong Geological Survey and Chang'an University.Typical gold deposits were selected for gold-forming fluids properties within Si O₂solubility and discussing the ore-forming fluid sources,properties and evolution.Ore-forming fluid evolution and metallogenic regularity in Jiaodong had been analyzed from"longitudinal evolution"and"horizontal comparison".The main results obtained are as follows.(1)CH₄-CO₂inclusions(F_Itype),CO₂-H₂O-X inclusions(F_IItype),CO₂-H₂O inclusions(F_IIItype)and H₂O inclusions(F_IVtype)are the four types of fluid inclusion.Ore-forming fluid in Jiaodong is a CO₂-Na Cl-H₂O±CH₄(±N₂)system characterized by low-medium temperature,low-medium salinity,rich CO₂and containing certain hydrocarbons,within a main metallogenic temperature range of 166.7?363.8?and pressure range of 90?242MPa.(2)The source of ore-forming fluids in Jiaodong is characterized by a combination of magmatic water,atmospheric water(and metamorphic water).Atmospheric water has the most significant effect on ore-forming fluid of quartz vein type gold deposits,and gradually weakened in altered cataclastic type gold deposits from Zhao Ping Fault to Jiaojia Fault to Sanshandao Fault.(3)The source of ore-forming materials in Jiaodong has the characteristics of mixed sources mainly inherited from old strata.The influence of seawater sulfur and superficial sulfur on the metallogenic process gradually increases from Mou Ru Fault to Zhao Ping Fault to Jiaojia Fault to Sanshandao Fault.(4)Si O₂solubility is controlled both by temperature,pressure,fluid flux and fluid properties in gold deposit,showing as Xiadian>Jiaojia>Sanshandao>Jinqingding and cataclastic type-sulfide quartz vein type>altered cataclastic type>quartz vein type.Smoky-gray and milky-white quartz which related to immiscible and ore-forming fluid cooling are important symbol of mineralization.Although Si O₂solubility viration does not directly affect the gold precipitation process,it promotes the gold precipitation.(5)Temperature of ore-forming fluids gradually increases from Mou Ru Fault to Zhao Ping Fault to Jiaojia Fault to Sanshandao Fault as well as pressure and depth gradually increase generally.Immiscibility and fluid cooling are the mainly two mechanisms of gold precipitation in Jiaodong,immiscibility mainly exists in altered cataclastic type gold deposits,both immiscibility and fluid cooling exist in quartz vein type gold deposits.The comparative analysis of the metallogenic depth and the estimated denudation depth shows that Jiaodong still has good potential for deep prospecting.