Research On Mineralization And Geological Model Of Prospecting And Prediction Of The Zaozigou Gold Deposit In The Xiahe-Hezuo Ore Concentration Area,Gansu Province,China

Zaozigou gold deposit is located in the northwest of West Qinling orogenic belt,and it's one of the Xiahe-Hezuo ore concentrated area's super-large gold deposits.Its host rock is sedimentary rock of Triassic Gulangdi Formation,which is dominated by microclastic rocks.The fracture structure of the gold deposit is well developed,and the intermediate-acidic vein is widely distributed in the gold deposit.The mineralization closes to fracture structure and magma intrusion effect.In full summarizing on the basis of previous research achivements,through the massive field geological investigation,systematic sampling,microscopic observation,indoor analysis and test,comprehensive research,with the knowledge of petrology,petrogeochemistry,ore deposit geology,fluid inclusion,isotopic geochronology,isotopic geochemistry,etc.,this paper achieves the following main understandings and achievements:(1)Clarifying the evolutive time sequence of the intrusive rocks is quartz diorite porphyrite to quartz biotite diorite porphyrite to granite porphyry preliminarily.The intrusive rocks are related to the mineralization of the deposit.The paper holds that the three kinds of rock have the same cause of formation and magmatic process.They were formed in the continental margin-arc environment which was related to the Paleo-Tethys Ocean's subduction.They mainly came from the granulite facies' lower crust melting partly,which was caused by the earth mantle basaltic magma upwelling,and there was a little mantle material mixed.(2)Getting the LA-ICP-MS zircon's U-Pb ages of quartz diorite porphyrite,quartz biotite diorite porphyrite and granite porphyries are 241.4±2.0Ma,241.2±2.3Ma and 238.9±1.6Ma,and the emplacement age is Early Indosinian.Combined with previous research achievements,limiting the diagenetic age of Zaozigou gold deposit is between238.9±1.6Ma and 230 ± 2.3 Ma.(3)The paper discusses the cause of two mineralization types' difference in Zaozigou gold deposit,and holds that it's the coupling effect's result of fluid evolution and tectonic evolution.(4)The researches of hydrogen and oxygen isotopes,carbon and oxygen isotopes show that the main source of Zaozigou gold deposit's metallogenic fluid was magmatic water,and it mixed with atmospheric water later.The research of fluid inclusion shows that the metallogenic fluid's property is Na Cl-H2 O system which has the characteristics of medium-low temperature,low salinity and low density.(5)The deposit's genetic type of Zaozigou gold deposit is a far low-temperature hydrothermal type which is related to intermediate-acidic intrusive rock.(6)The paper builds Zaozigou gold deposit's Trinity model of geological prospecting and prediction: Determining the mineralized geological body is an Early Indosinian concealed intermediate-acidic rock mass which was in large emplacement.The metallogenic structure is mainly fracture structure system,and its metallogenic structural surfaces are mainly fracture structure and intrusive contact structural surface.Making systematical summaries of metallogenic characteristic sign from orebody characteristic,surrounding rock alteration,Mineralization zoning,mineral assemblage and typical mineral characteristic,mineralization stage,fluid inclusion characteristic and stable isotope characteristic,etc.