俄罗斯远东岗仁地体金铜矿床地质、地球化学特征及其LA-ICP-MS锆石U-Pb年龄

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

岗仁地体位于额尔古纳超地体北部边缘,蒙古—鄂霍茨克构造带南部,该区分布着大量的大型、超大型金矿床,这些矿床在成因上与中酸性侵入岩和浅成次火山岩关系密切。岩石地球化学研究表明,花岗闪长岩-闪长岩组合明显富集大离子亲石元素、不相容元素和轻稀土元素,亏损高场强元素和重稀土元素。球粒陨石标准化稀土配分模式为轻稀土元素富集、重稀土元素亏损的右倾型,具有微弱的负Eu异常或基本无Eu异常,无Ce异常,元素地球化学性质反映出花岗闪长岩-闪长岩组岩浆具有壳幔混合的特征,且形成于大陆边缘的火山弧环境。LA-ICP-MS锆石U-Pb测年结果揭示,皮奥涅尔金银矿床含矿闪长玢岩的206Pb/238U年龄加权平均值为113.8±2.0Ma,博尔古利坎铜金钼矿床赋矿二长闪长斑岩的206Pb/238U年龄加权平均值为112.7±2.8Ma,与皮奥涅尔金银矿床和博尔古利坎铜金钼矿床成矿有关的奥列佳花岗闪长岩体的年龄分别为117.2±1.3Ma和117.0±3.6Ma。由此可知,皮奥涅尔金银矿床和博尔古利坎铜金钼矿床形成于燕山早期,与中国黑龙江地区三道湾子金矿、东安金矿等金矿床形成时代一致。

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.