Mineralization And Metallogenic Prediction Of The Jinchang Cu-Au Deposit In Dongning,Heilongjiang Province

The Jinchang deposit,as a large representative porphyry Cu-Au deposit in the Yanbian-Dongning metallogenic belt,is located in Dongning town,Heilongjiang Province.The deposit is mainly controlled by breccia pipe structures,annular-radial faults and microcracks in late Indosinian diorite and early Yanshanian monzogranite,whcih thus displays four types of mineralization:breccia pipe type Cu-Au,breccia pipe type Au,quartz-sulfide vein type Au,and veinlet-dissemination type Au.According to the geochronology and characteristics of mineral assemblage,the Jinchang deposit can be divided into two epochs of mineralization process,that is,Cu-Au metallogenic epoch and Au metallogenic epoch.The studies of fluid inclusion and H-O isotopes show that daughter-mineral-bearing multi-phase,vapor-rich,and NaCl-bearing three-phase fluid inclusions were identified in quartz crystals in the early stages of Cu-Au and Au metallogenic epochs.By contrast,fluid inclusions in quartz crystals of the late stages from the two metallogenic epochs are only of the liquid-rich,with minor NaCl-bearing three-phase fluid inclusions.In addition,the values of?D and?¹⁸O_H2O2O obtained from quartz samples in Cu-Au and Au mineralization plot in the fields of Au–Cu series of magmatic water,which reflect that the ore-forming fluids for the Cu-Au and Au mineralization were derived from magmatic water.Taken together,the ore-forming fluids in the early stages from Cu-Au and Au metallogenic epochs belonged to magmatic-hydrothermal transitional fluids that gradually evolved into homogeneous NaCl-H₂O system magmatic fluids in the late stages.The results of S,Pb and Re-Os isotopes indicate that the ore-forming materials for the Jinchang deposit originated from typhonic magmas.Based on petrography and magmatic zircon LA-ICP-MS U-Pb dating,this paper established the emplacement sequence of magmatic rocks in the Jinchang ore district:late Indosinian medium-to fine-grained diorite?209.5±1.4Ma??early Yanshanian medium-to coarse-grained monzogranite?195.8±1.3²01.5±1.5Ma?,medium-to fine-grained biotite granodiorite?197.0±6.0Ma?and fine-grained syenogranite?191.8±2.2Ma??late Yanshanian fine-grained quartz monzonite?114.7±3.1Ma?,dioritic porphyrite?112.7±0.8¹18.2±0.8Ma?,granite porphyry?112.6±0.9¹13.5±3.8Ma?and fine-grained biotite granodiorite?106.8±2.0Ma?.Sulfide Re-Os dating shows that the metallogenic ages for four types of mineralization including breccia pipe type Cu-Au,breccia pipe type Au,quartz-sulfide vein type Au and veinlet-dissemination type Au are 114.0±3.0 Ma,102.9±2.7Ma,99.3±7.9 Ma and 101.2±4.2 Ma,respectively.Comprehensive studies on chronology and deposit show that the two epochs of mineralization for the Jinchang deposit occurred in late Yanshanian,in which the Cu-Au mineralization was closely related to quartz monzonite while the Au mineralization was most likely as product of the biotite granodiorite magmatic activity.Using the basic theory of geotectonics and regional metallogeny,this paper collected predecessors'zircon U-Pb ages of main magmatic rocks in Yanbian-Dongning metallogenic belt and summed up regional tectonic evolution history of late Paleozoic-Mesozoic to six stages:?1?the late Paleozoic tectonic evolution that was dominated by the subduction and closure of the Paleo-Asian Ocean;?2?continental collision orogeny of theYanbian and Dongning areas in the Early-Middle Triassic;?3?postorogenic collapse and extension during the Late Triassic;?4?tectonic evolution that was controlled mainly by the circum-Pacific tectonic regime during the Early-Middle Jurassic;?5?interval period of the Paleo-Pacific Ocean tectonic evolution from the Late Triassic to earliest Early Cretaceous;?6?active continental margin related to the subduction of the Paleo-Pacific Ocean during latest Early Cretaceous.Combined with the rock geochemical analysis,this paper conclude that two epochs of mineralization in the Jinchang Cu-Au deposit were products of comagmatic emplacements with different epochs in the late Yanshanian,and that the metallogenic dynamics background was active continental margin environment related to the subduction of the Paleo-Pacific Plate.In terms of deposit and metallogenic regularity,combined with induced polarization anomaly,high magnetic anomaly and soil geochemical anomaly,the author considers that the Heixiazigou-Xingjiagou-Qiongbangzigou belt in the eastern of Jinchang ore district boasts good prospecting potentiality,in which three prospecting target areas named I,II and III have been enclosed.On that basis,a primary rock geochemical survey for deep part of the key work area have been carried out.This paper established primary halo prospecting model of different types of mineralization.For the breccia pipe type mineralization,front halo indicator elements include As-Sb-Hg;mineralization halo indicator elements include Au-Ag-Cu-Co-Pb-Zn,tail halo indicator elements include Mo-Ni-Bi;For the veinlet-dissemination type mineralization,front halo indicator elements include As-Sb-Hg-Pb-Zn,mineralization halo indicator elements include Au-Ag-Cu-Co,tail halo indicator elements include Mo-Ni-Bi;For the quartz-sulfide vein type mineralization,front halo indicator elements include As-Sb-Hg-Pb-Zn,mineralization halo indicator elements include Au-Ag-Cu-Co,tail halo indicator elements include Mo-Ni-Bi.The above results cooperate with primary rock geochemical anomaly,further delineating four prospecting target areas named A-1,A-2,B,and C in deep part of the key work area.