Magmatism And Mineralization Of The Haigou Gold Deposit,Jilin

The Haigou gold deposit is located in Antu County,Jilin Province,which is a large scale orogenic gold deposit.Electron microprobe,whole rock geochemistry,sulfide Re-Os isotopic dating and zircon U-Pb isotopic dating are utilized to reveal the relationship between magmatic and mineralization events.Based on microscopic examination and electron probing analysis,common ore minerals including native gold,pyrite,molybdenite,galena,chalcopyrite,magnetite,hematite and minor electrum,altaite and melonite have been identified in the Haigou gold deposit.At least three distinct magmatic stages in the studied area have been constrained based on field relationship and geochronological data.The early phase consists of monzonitic granite and monzonite with zircon U-Pb ages of 329Ma and 327Ma,respectively.Diorite and porphyrite intruded into the Haigou complex at 311Ma,which was followed by granodiorite,dated at 260Ma.The late stage is dominated by diorite porphyry,formed at around 135Ma.The hydrothermal sericite from gold-bearing altered rocks has a ⁴⁰Ar/³⁹Ar age of 165.3±1.2 Ma,which mostly indicates that the gold deposit formed during the Middle Jurassic.Molybdenite Re-Os isotope analysis shows a model age of 310.7±4.8Ma,demonstrating that there is a molybdenum mineralization occured³10Ma in the Haigou gold deposit.The relationship between molybdenum mineralization and the Haigou granites are not close,whereas the early diorite and porphyrite intrusions show temporal and spatial relationships with Mo mineraliztion.The REE distribution patterns of the Haigou granites and dikes are LREE-enriched.The REE distribution patterns of rocks with different ages are quite different,whereas the REE distribution patterns of rocks with similar ages are almost identical.This may imply that there are different sources of magmatic rocks in different periods,but the magmatic rocks during the same period is related to homologous evolution.The normalized trace element distribution curves reveal that monzonitic granite and monozonite have similar characteristics,showing relative enrichment of large ion lithophile elements?LILE,i.e.,Rb,Ba,K?.Trace elements indicate the Haigou complex formed under the continental margin arc setting.The obtained Sr isotopic compositions of monzonitic granite may suggest a mixed source of crust and mantle,whileas Sr isotopic compositions of diorite reflects a mantle source.The evident Nd isotopic distinctions between the Haigou granites and dikes likely show different magma sources.The former with a crust source may be related to the partial melting of the ancient crust,whileas the latter with a mixed crust-mantle source may be formed by partial melting of the mantle or the new crust.