Geological, geochemical features and geochronology of Au-Cu deposits in Gonzha terrane, Russian Far East area

Gonzha terrane is located in the southern part of Mongolo-Okhotsk fold belt, within the northern part of Argun terrane. A large number of superlarge-large gold deposits lie in Gonzha terrane, such as Pionernoe, Burinda, Pokrovskoe and Borgulikan. These deposits are closely related to the intrusions and subaerial volcanic accumulations. Petrogeochemical studies indicate that the granodiorite-diorite assemblage is enriched in LILE (such as K, Rb, Ba), mobile incompatible elements (such as U, Th, Pb) and light rare earth elements (LREE), relatively depleted in HFSE (such as Ta, Nb, P, Sr, Ti) and heavy rare earth elements (HREE). The chondrite-normalized REE patterns display pronounced LREE enrichment and HREE depletion, slightly negative or no Eu anomalies (δEu=0.78~0.93, averagely 0.86), and no Ce anomalies (δCe=0.89~0.97). Geochemical characteristics of elements imply that the granodiorite-diorite assemblage was formed in an island-arc environment on continental margin, with characteristics of obvious crust-mantle mixing. LA-ICP-MS zircon U-Pb studies indicate that ore-bearing diorite porphyry in the Pionernoe Au-Ag deposit has a weighted mean 206Pb/238U age of 113.8±2.0Ma, whereas ore-bearing monzodioritic porphyrite in the Borgulikan Au-Cu-Mo deposit has a weighted mean 206Pb/238U age of 112.7±2.8Ma. The LA-ICP-MS zircon U-Pb ages for granodiorites related to metallogenesis in Pionernoe and Borgulikan are 117.2±1.3Ma and 117.0±3.6Ma, suggesting that the Pionernoe Au-Ag deposit and the Borgulikan Au-Cu-Mo deposit were formed in Early Yanshanian period, and their formation ages are consistent with formation ages of Sandaowanzi and Doan gold deposits in Heilongjiang Province.