中亚成矿域锂矿床成矿规律及成矿模式

Lithium deposits in the Central Asian Metallogenic Domain:Metallogenic regularity and model

中亚成矿域发育一系列锂矿床,这些矿床主要分布在西伯利亚克拉通南部的造山带中,矿床的形成具有多期性,包括前寒武纪(1.85~1.83Ga)、晚寒武世-早奥陶世(494~483Ma)、早二叠世(294~272Ma)、晚三叠世-早白垩世(220~180Ma)和早白垩世(139~121Ma)等5个成矿期,矿床类型主要为伟晶岩型和花岗岩型。基于成矿构造背景和锂成矿特征的研究,以重要构造线为界,将成矿域划分为2个成矿省和7个成矿带:(1)阿尔泰-东萨彦成矿省,位于成矿域的西部,包括阿尔泰、桑吉伦高地和东萨彦等3个成矿带,主要发育伟晶岩型锂矿床,成矿作用集中在上述前4个成矿期,矿床形成与西伯利亚克拉通和古亚洲洋2个构造体系有关。(2)蒙古-鄂霍茨克成矿省,位于成矿域的东部,包括东外贝加尔成矿带以及Gobi Ugtaal-Baruun Urt和大兴安岭等2个锂远景成矿带,主要发育早白垩世花岗岩型锂矿床,矿床形成主要与蒙古-鄂霍次克构造体系有关。此外,在中国东天山发育少量晚三叠世伟晶岩型锂矿床,构成东天山锂远景成矿带,矿床形成与哈萨克斯坦-准噶尔板块和塔里木板块碰撞有关。中亚成矿域稀有金属花岗岩和大多数稀有金属伟晶岩为花岗质岩浆高分异结晶的产物,其结晶分异的驱动机制主要是热驱动。富含稀有金属的花岗岩和伟晶岩岩浆的形成温度偏低(~650℃),压力变化较大(500~170MPa);锂富集机理为岩浆结晶分异作用和流体不混溶作用。本次研究分别提出了阿尔泰伟晶岩型锂矿床的成矿模式“地壳熔融→深部花岗岩岩基→浅部稀有金属花岗岩岩枝-伟晶岩岩脉”和东外贝加尔花岗岩型锂矿床的成矿模式“地壳熔融→深部花岗岩岩基→浅部花岗岩-稀有金属花岗岩岩株”。

A series of lithium deposits occur in the Central Asian Metallogenic Domain(CAMD).These lithium deposits are mainly located in the orogenic belts in the southern Siberian Craton,and their formation has multiple stages,including the Precambrian(1.85~1.83Ga),Late Cambrian-Early Ordovician(494~483Ma),Early Permian(294~272Ma),Late Triassic-Early Cretaceous(220~180Ma) and Cretaceous(139~121Ma).The main types of lithium deposits are pegmatite-and granite-type.On the basis of the metallogenic tectonic backgrounds and rare-metal mineralization characteristics,the CAMD can be subdivided into 2 provinces and 7 metallogenic belts according to the tectonic line coundaries:(1) The Altay-Eastern Sayan metallogenic province is located in the western part of the CAMD,which includes three lithium metallogenic belts:the Altay,the Sangilen Highlands and the Eastern Sayan.It is mainly composed of pegmatite-type Li deposits,with mineralization concentrated in first four peak periods.The formation of Li deposits is related to the Siberian Craton and the Paleo-Asian Ocean tectonic systems.(2) The Mongolian-Okhotsk metallogenic province is located in the eastern part of the CAMD,which includes the Eastern Transbaikalia Li metallogenic belt as well as the Gobi Ugtaal-Baruun Urt and Daxing'an Mountains Li prospective belts.It is mainly composed of Cretaceous(139~121Ma) granite-type Li deposits.The formation of these Li deposits is mainly related to the Mongolian-Okhotsk tectonic system.In addition,there is a prospective belt in the Eastern Tianshan Mountains of China in which the Late Triassic pegmatite-type Li deposits occurred.The formation of the deposit is related to the collision between the Kazakhstan-Junggar and Tarim plates.The rare-metal granites and most rare-metal pegmatites in the CAMD are the products of the high differentiation of granitic magma which is triggered by the thermal-driven.The magmtic temperature is relatively low(~650℃),and its pressure change is significant(500~170MPa).The mechanism of Li enrichment mainly includes magmatic crystallization differentiation and fluid immiscibility.This study proposes a metallogenic model of “crustal melting→deep granite pluton→shallow rare metal granite apophyse-pegmatite vein” for the pegmatite-type Li deposit in the Altai belt and a “crustal melting→deep granite pluton→shallow granite-rare metal granite stock” model for the granite-type Li deposit in the Eastern Transbaikalia belt.