Metallogenic Model And Prospecting Direction Research Of Qingchengzi Polymetallic Ore Field In Liaoning Province

The Qingchengzi ore field is an important super-large Pb-Zn-Ag-Mo polymetallic ore district located in the Liaodong rift zone,north margin of the North China Craton.Based on the references of previous mineral exploration and scientific researches,a series of modern methods,especially genetic and prospecting mineralogical methods are used to analyze the geodynamic backgrounds,tectonic setting,ages and petrogenesis,magma and ore-forming fluids as well as ore materials sources of the ore systems.LA-ICP-MS U-Pb zircon dating of the Dadingzi plagiogranite,Shuangdinggou granite,Xinling granite,Zhenzigou granite,and Yaojiagou granite porphyry yields ages of 1988±31 Ma,224.8±1.5 Ma 226.8±1.5 Ma,224.6±1.4 Ma and 167.0±1.1 Ma,respectively.The age of Zhenzigou Pb-Zn deposit is constrained by the zircon U-Pb isotopes of the related porphyry to be about 224.6±1.4Ma.Molybdenite Re-Os isotopic analyses of the Yaojiagou and Xinling deposit yield ages of 164.7±2.3 Ma,164.3±2.4 Ma and 221.3±3.2 Ma 221.7±3.4 Ma,respectively.The ages of the Mo-Pb-Zn mineralization are consistent with the ages of the associated Mesozoic granites,suggesting a close relationship between magmatism and mineralization in this region.The geochronology,whole-rock geochemistry and Sr-Nd-Pb isotopic characteristics of the Mesozoic granite show that these rocks are of adakitic affinity,?-type and sourced from melting of the ancient lower crust mixed with mantle and upper crust materials.The Indosinian magmatism and mineralization occurred in a stretch background during delamination of the lithosphere after the collision between the Siberian Plate and North China Craton,whereas,the Yanshanian magmatism and mineralization were controlled by the retreating of the subduction zone of the PaleoPacific Plate.The sulfur isotope of the stratiform,stratoid and vein-like ore bodies in the Qingchengzi district show similar sources of ore-forming materials which were mainly derived from the strata mixed with magmatic sulfur.The lead isotope data indicate that the ore-forming metals were mainly generated from the magmas sourced from the mixtures between the crust and mantle with a small amount of lead from the strata.The ore-forming fluids for the Mo mineralization were of middle to high temperatures and low density,whereas the Pb-Zn-Ag-Au mineralization fluids were middle to low temperatures.The data of the homogenous temperatures,salinities and densities of the ore-forming fluids show gradual decreasing trend from the Xinling granite outward to the Xinling Mo deposit,the Zhenzigou vein-like Pb-Zn deposit and the Gaojiabaozi Pb-Zn-Ag deposits.Although the Proterozoic mineralization marks were mostly removed by the magmatic hydrothermal alteration related with the Indosinian magmatism,a multiple superposition signatures are still clear for the Qingchengzi Pb-Zn deposits which can be classified as sedmentary-metamorphic-magmatic hydrothermal transformation type.Based on the systemically studies of the geological and geochemical as well as mineral typomorphic characteristics of the ore deposits,the exploration directions of the Qingchengzi Mo-Pb-Zn deposits are summarized in this thesis.