The Cu-Au Mineralization Characteristics And Prospecting Direction In The Sanfengshan Area,Nenjiang County,Heilongjiang Province

Sanfengshan area in Nenjiang County,Heilongjiang Province is located in the eastern part of the Central Asian orogenic belt and the west side of the Hegenshan-Heihe fault zone.The strata exposed in the study area are dominated by Early Paleozoic Ordovician and Silurian,and the magmatic rocks are mainly Yanshanian igneous rocks.The area is characterized by simple structure,mainly NW and NE trending faults,folds and ductile shear zones.The Cu and Au mineralization in the area is mainly veinlike and occurs in the sandstone of Silurian Huanghuagou formation and is controlled by NW trending faults.The wall rock alteration include silicification,propylitization,sericitization,carbonatization and kaolinization.According to the mineral assemblage and vein cutting relationship,the hydrothermal mineralization can be divided into three stages:(I)quartz pyrite stage;(II)quartz polysulfide stage;(III)calcite poor sulfide stage.The mineralization belongs to medium sulfur epithermal vein type.Studies on fluid inclusions in Sanfengshan region show that two types of inclusions,gas-liquid two-phase inclusions(L)and gas-rich inclusions(V),are mainly developed in stage I.The homogenized temperature of the inclusions is 167.7?263.3?,and the salinity is 2.6?5.1wt.%Na Cl eqv.Stage II,III main development L-type inclusions,homogenized temperature is 110.3?216.6?,salinity is 1.3?5.4 wt.%Na Cl eqv.;The microscopic temperature measurement results showed that the fluid gradually evolved from H₂O-Na Cl hydrothermal fluid with medium temperature and low salinity to H₂O-Na Cl hydrothermal fluid with low salinity and low temperature.H-O isotope results show that the ore-forming fluid in Sanfengshan area may be a mixture of magmatic water and meteoric water,but mainly meteoric water(?¹⁸O_H2Oand?D values are 11.4‰?16.9‰and-82.1‰?-74.7‰,respectively).The ore-forming fluid is characterized by low salinity(1.3%?5.4%)and low density(0.75?0.97 g/cm³).The ore-forming pressure in the main mineralization stage is low,which is 22.5?30.6MPa.The ore-forming depth in the main mineralization stage is 0.75?1.02 km.The mineralization in Sanfengshan area mainly occurs in the Huanghuagou formation,which is controlled by NW fault and magmatic activity,and is the necessary metallogenic condition for the study area.The prospecting indicators in Sanfengshan area mainly include:Huanghuagou formation;NW-trending fault structure;Silicification and sericinization;High magnetic gradient zone with low resistivity and high polarization anomaly;Soil Association anomalies of elements such as Ag,Cu,Au,Zn,as,Sb and single element anomalies of Au.Based on the comprehensive analysis of the geological characteristics and mineralization causes of Sanfengshan area,combined with the data of geophysical and geochemical anomalies,the mineral resources evaluation system was used to delineate 5 prospecting target areas,which provided the basis for the next step of prospecting work.