Genesis Of The Ershiyizhan Copper(Gold) Deposit In The Upper Heilongjiang Basin

The Ershiyizhan copper?gold?deposit is located in the eastern part of the upper Heilongjiang metallogenic belt in the north of the Great Xing'an Mountains,and has been in the prospecting and exploration stage in recent years.This work passed the geological characteristics of the Ershiyizhan copper?gold?deposit,detrital zircon U-Pb chronology and Hf isotopes of the Ershierzhan Formation,all-rock geochemistry,potash feldspar ⁴⁰Ar-³⁹Ar chronology,micro-temperature measurement of fluid inclusions,and isotope geochemistry clarify the genesis of this deposit and propose a possible metallogenic model of the deposit.The main knowledge gained is as follows:?1?The lower sedimentary limit of the Ershierzhan Formation is early period of early Cretaceous,and the tectonic background of the source area of the Ershierzhan Formation is the continental island arc environment at the edge of the active continent.The sediments of the Ershierzhan Formation were mainly formed in four periods:Neoarchean?2711±10Ma??Middle Proterozoic-Paleoproterozoic?1238?2428Ma??Neoproterozoic?561?921Ma??Mesozoic-Late Paleozoic?134?540Ma?,and the Phanerozoic granite magma provided the most abundant source for the Ershierzhan Formation.?2?The Ershiyizhan copper?gold?mineralization are closely related to the early Cretaceous quartz feldspar porphyry.The hydrothermal mineralization process can be divided into three ore stages:quartz-potash feldspar-polymetal sulfide stage?S??,quartz-polymetal sulfide stage?SII?,quartz-carbonate mineral±pyrite stage?S??.Among them,S?and S?are the main metallogenic stages,and the gold and copper enrichment positions are different.Copper is mainly concentrated in the cement of ore-bearing porphyry breccia,and gold is mainly concentrated in the ore-bearing porphyry surrounding rocks.?3?The Ershiyizhan copper?gold?deposit develops Potassium silicification alteration,propylitization alteration,and feldspar decomposition alteration.PIMA test results show that copper and gold mineralization are closely related to dolomite and illite alteration;the analysis of major and trace element factors of altered rocks shows that copper and gold mineralization are different,and gold mineralization is closely related to silicification and feldspar decomposition alteration,while copper mineralization is related to molybdenum and zinc mineralization,and also bring In,Cd,Co and Sb.?4?The early ore-forming fluids of the Ershiyizhan copper?gold?deposit originated from the fluids dissolved in the ore-bearing porphyry,and the boiling of the fluids in the early metallogenic stage is widespread.As the ore-forming process progressed,meteoric water was gradually added,until the late mineralization stage,the ore-forming fluids changed into low temperature and low salinity fluid.The ore-forming pressure of early stage is 100bars-500bars,and the estimated ore-forming depth is mainly 1?5Km.Early fluid boiling was the main precipitation mechanism of copper,and temperature reduction was the main precipitation mechanism of gold.?5?The sulfur isotope in the Ershiyizhan copper?gold?deposit is a deep-source magma sulfur with crust-mantle mixed source,and the source of lead is also a crust-mantle mixed source,and magmatic rocks and surrounding rock strata formed before ore formation were extracted during fluid evolution.so the ore-forming material is multi-source,which may come from both ore-bearing porphyry and various surrounding rocks of the ore-bearing porphyry.The hydrothermal fluids extracted from the Early Cretaceous magma activated the minerals in the surrounding rocks,and groundwater circulated under the driving of the thermal energy of the rock mass,leached the minerals in various surrounding rocks,and precipitated in the appropriate structural location.