大兴安岭南段白音诺尔铅锌矿床成矿时代确定及其找矿意义

Determination of metallogenic age and prospecting significance of the Baiyinnuoer lead-zinc deposit in the southern Da Hinggan Mountains

内蒙古白音诺尔铅锌矿床是我国北方著名的超大型矽卡岩型铅锌矿。矿区出露的岩浆岩主要有花岗闪长岩、晶屑凝灰熔岩、石英斑岩、闪长玢岩、花岗岩。矿体呈脉状和囊状,产于中二叠统哲斯组大理岩中,受硅钙面及北东向断裂构造的控制。关于白音诺尔铅锌矿床的成矿时代存在燕山期成矿和印支期成矿两种不同的观点。本文通过厘定与矿体空间位置关系密切的岩浆岩的成岩年龄推测矿体的形成时代,坑道地质调查发现矿体切穿了区内晚侏罗世满克头鄂博组的火山岩后又被闪长玢岩切穿,因此可推测矿体的形成时代介于两种岩浆岩之间,通过锆石LA-ICP-MS U-Pb定年,获得了火山岩的年龄为149.9±2.5Ma,闪长玢岩的年龄为140.3±2.6Ma,由此限定成矿年龄在140.3±2.6~149.9±2.5Ma之间,属于晚侏罗-早白垩世,与区域上锡多金属矿床的形成时代一致。在白音诺尔铅锌矿床中已有锡的显示并在其周边地区发现了锡矿体的存在,区域上锡多金属矿床的形成与晚侏罗-早白垩世的高演化花岗岩关系密切,因此认为白音诺尔铅锌矿的成矿地质体可能为同期隐伏高演化花岗岩,暗示矿床深部仍存在巨大找矿前景。

Baiyinnuoer Lead-Zinc deposit in Inner Mongolia is a famous superlarge skarn type lead zinc deposit in North China.The magmatic rocks exposed in the mining area mainly include granodiorite,crystalline tuff lava,quartz porphyry,diorite porphyrite and granite.The ore body is vein and saccate,occurring in the marble of the Zhesi Formation of Middle Permian age,and controlled by the silicalcium surface and NE trending fault structure.There are two different views on the metallogenic age of Baiyinnuoer Lead-Zinc deposit:the Yanshanian and the Indosinian ages.In this paper,the age of the ore body is inferred by determining the diagenetic age of the magmatic rocks closely related to the spatial location of the ore body.Through the geological survey of the tunnel,it is found that the ore body cut through the volcanic rocks of the late Jurassic Manketouebo Formation in the area and then was cut through by the diorite porphyrite.Therefore,it can be inferred that the age of the ore body lies between the ages of both kinds of magmatic rocks.Through LA-ICP-MS U-Pb dating of zircon,the age of the volcanic rocks is obtained as 149.9±2.5 Ma,and the age of diorite porphyrite is 140.3±2.6 Ma,which limits the mineralization age to 140.3±2.6~149.9±2.5 Ma,i.e.to late Jurassic-Early Cretaceous which is consistent with the formation age of tin polymetallic deposits in the region.Tin-rich minerals have been found in Baiyinnuoer Lead-Zinc deposit and tin ore bodies have been found in its surrounding areas.The formation of tin polymetallic deposit in the area is closely related to the high evolution granite in the late Jurassic Early Cretaceous.Therefore,it is proposed that the metallogenic body of Baiyinnuoer Lead-zinc Deposit may be the concealed under the high evolution granite of the same period,suggesting that there is still a huge prospecting prospect in the deeper part of the deposit.