蒙古国查夫银多金属矿床含矿花岗闪长岩锆石U-Pb年代学、地球化学及岩石成因

中蒙边境查夫-甲乌拉银多金属矿集区内与成矿相关的岩浆岩研究薄弱. 以查夫银多金属矿床含矿花岗闪长岩及其闪长质包裹体为研究对象, 进行了岩石学、锆石U-Pb年代学、地球化学和原位Lu-Hf同位素研究. 花岗闪长岩及闪长质包裹体的锆石206Pb/238U加权平均年龄分别为195.7±1.3 Ma和196.5±2.4 Ma, 在误差范围内一致, 为早侏罗世岩浆作用的产物. 寄主花岗闪长岩为准铝质-弱过铝质、高钾钙碱性-钙碱性系列的I型花岗岩, 闪长质包裹体为同源岩浆混合成因包裹体. 寄主花岗闪长岩具有宽泛的εHf(t)值(4.4~10.7), 其二阶段Hf模式年龄介于550~960 Ma, 表明寄主花岗闪长岩的初始岩浆起源于新元古代从亏损地幔增生的新生地壳的部分熔融, 并存在幔源物质的混入. 基于以上研究, 结合区域构造演化资料, 认为查夫银多金属矿床含矿花岗闪长岩形成于蒙古-鄂霍次克洋板块俯冲的活动大陆边缘背景.

ZIRCON U-Pb CHRONOLOGY,GEOCHEMISTRY AND PETROGENESIS OF ORE-BEARING GRANODIORITE IN TSAV SILVER POLYMETALLIC DEPOSIT,MONGOLIA

The research on magmatic rocks related to mineralization was weak in Tsav-Jiawula Ag polymetallic ore concentration area on the China-Mongolia border. Taking the ore-bearing granodiorite and its dioritic enclaves in Tsav Ag polymetallic deposit as object, the paper studies the petrology, zircon U-Pb chronology, geochemistry and in-situ Lu-Hf isotopes. The zircon 206Pb/238U weighted average ages of 195.7±1.3 Ma and 196.5±2.4 Ma for granodiorite and diorite enclaves respectively are consistent within the error range, indicating that both were products of the Early Jurassic magmatism. The host granodiorite belongs to I-type granite of quasi aluminous-weakly peraluminous and high K calc alkaline-calc alkaline series. The diorite enclaves are of consanguineous magma mixing origin. The host granodiorite has broad εHf(t) values (4.4-10.7) with the two-stage Hf model ages ranging from 550 to 960 Ma, reflecting the primary magma of host granodiorites originated from the partial melting of new crustal accretion from depleted mantle in Neoproterozoic with mantle-derived materials mixed. Combined with the regional tectonic evolution data, it is considered that the Tsav Ag polymetallic deposit was formed in the active continental margin setting caused by the subduction of Mongolia-Okhotsk oceanic plate.