东准噶尔北缘老山口铁铜金矿区侵入岩LA-ICP-MS锆石U-Pb定年及地质意义

老山口铁铜金矿区位于准噶尔北缘的喀拉通克—卡拉先格尔成矿带南段,矿化与岩浆侵入活动有关。本文利用LA-ICP-MS锆石U-Pb定年方法对老山口铁铜金矿区的中粒闪长岩、正长岩、黑云母闪长岩和闪长玢岩进行了年代学研究,获得其年龄分别为353.8±1.9Ma、366.3±1.9Ma、3±2.3Ma和379.7±3Ma,表明矿区存在三期岩浆活动。其中黑云母闪长岩和闪长玢岩的年龄,在误差范围内一致,它们可能为中泥盆世同源岩浆演化的产物,且岩体侵入时代与准噶尔洋俯冲阶段花岗岩及卡拉先格尔斑岩铜矿带含矿斑岩年龄较一致,表明其可能是板块俯冲阶段的产物。闪长岩和正长岩的年龄分别为353.8±1.9Ma和366.3±1.9Ma,与东准噶尔北部青格里河下游一带后碰撞花岗岩类和布尔根一带后造山伸展A型花岗岩的年龄接近,而地球化学特征却存在差异,说明老山口正长岩和闪长岩体是俯冲晚期阶段的产物。根据地质特征,老山口铁铜金矿的形成与闪长岩及闪长玢岩侵入有关,因此岩体年龄也限定了矿区存在两期铁铜金矿化,即379Ma左右和354Ma左右。

Zircon U-Pb Dating for Intrusions in Laoshankou Ore District in Northern Margin of East Junggar and Their Significances

The Laoshankou ore district is located in the northern margin of Junggar and the southern side of the Kalatongke—Kalaxiange′er porphyry copper belt. The mineralization associated with the magma intrusion activities. After performance of LA-ICP-MS zircon U-Pb dating, we respectively obtained 353.8±1.9Ma, 366.3±1.9Ma, 379.3±2.3Ma and 379.7±3Ma for the diorite, syenite, biotite diorite and diorite porphyrite in the Laoshankou ore district, which represent three distinguishing magma intrusive activities. The ages of biotite diorite and diorite porphyrite are consistent in the error limits, those are comagmatic in the Middle Devonian. Furthermore, the time of pluton intrusions is consistent with granites of the subduction stage of Junggar Ocean and the ore-forming porphyries in Kalaxiange’er porphyry copper metallogenic belt. Those are the products in the subduction stage of Junggar plate. The ages of diorite and syenite are consistent with the dating of post-collision granitic plutons in the Lower Reaches of the Qinggeli River and Buergen extensional A-type granites in the Northern Part of East Junggar. However, their geochemistry is differential. The diorite and syenite plutons in Laoshankou are the products in the subduction advanced stage of Junggar plate. Based on field geological properties, The formation of Laoshankou deposit associated with diorite and diorite porphyrite pluton intrusion. So their ages also limit two period of iron—copper—gold mineralization, which are about 379Ma and 354Ma.