马达加斯加北部绿岩带石英脉型金矿流体包裹体特征及成矿作用分析

Characteristics of fluid inclusions and mineralization of lode gold deposits in the greenstone belt of northern Madagascar

为探讨马达加斯加北部绿岩带石英脉型金矿的成矿温度和物质来源,对Maevatanana和Andriamena两个绿岩带石英脉型金矿的石英脉流体包裹体的研究表明,这两条绿岩带金矿流体包裹体较为发育,有H_(2)O-NaCl包裹体,即水溶液型(Ⅰ类);CO_(2)-H_(2)O-NaCl包裹体,即LH_(2)O+VCO_(2)型(Ⅱ类);富CO_(2)包裹体,即LH_(2)O+L CO_(2)+VCO_(2)型(Ⅲ类)和少量含子晶的H_(2)O-NaCl包裹体,即含NaCl子矿物型(Ⅳ类)等4种类型;成矿阶段可分为早期成矿、主成矿、后期成矿阶段,早期成矿阶段以I和部分Ⅱ类包裹体为主,偶见少量Ⅳ类含NaCl子晶包裹体,主成矿阶段以大部分Ⅱ类和Ⅲ类包裹体为主,后期成矿阶段以Ⅰ类包裹体为主;Maev和Adm金矿成矿流体以CO_(2)-NaCl-H_(2)O型为主,同时含有不同程度的CH_(4)、N_(2)和H_(2),以及少量的H_(2)S等挥发分,表现为富CO_(2)、中-低盐度、中高温和不混溶。结合已有区域地质背景和成岩成矿特点,推断流体成矿作用与过程中大量花岗质岩浆经过同熔或重熔作用生成及上侵定位有密切关系,矿床形成与陆内碰撞造山过程,并且有深部来源物质参与成矿。

To investigate the mineralization temperature and material source of quartz vein type gold deposits in the northern Greenstone belt of Madagascar,relatively well developed fluid inclusions were studied in the Maevatananaand the Andriamena quartz vein type gold deposits in the greenstone belt.There are H_(2)O-NaCl inclusions,namely aqueous solution type(ClassⅠ);CO_(2)-H_(2)O-NaCl inclusion,namely LH_(2)O+VCO_(2)type(ClassⅡ);CO_(2)-rich inclusions,namely LH_(2)O+LCO_(2)+VCO_(2)type(ClassⅢ),and a small amount of H_(2)O-NaCl containing daughter crystals,namely NaCl daughter mineral type(ClassⅣ).The metallogenic stage can be divided into the early metallogenic stage,the main metallogenic stage and the late metallogenic stage.The early metallogenic stage is dominated by ClassⅠand ClassⅡinclusions,and occasionally a few ClassⅣNaCl subcrystalline inclusions.The main metallogenic stage is mostly dominated by ClassⅡand ClassⅢinclusions,while the late metallogenic stage is dominated by ClassⅠinclusions.The mineralization fluids of Maev and Adm gold deposits are dominated by CO_(2)-NaCl-H_(2)O,and contain different degrees of CH_(4),N_(2)and H_(2),as well as a small amount of H2S volatilization,showing CO_(2)rich,medium and low salinity,medium and high temperature immiscibility.Combined with the existing regional geological background and diagenetic ore-forming characteristics,it is inferred that the fluid mineralization is closely related to the formation of a large number of granitic magmas through co-melting or re-melting and the location of upper emplacement;the deposit formation is related to the intrauterine collision orogenic process,and the deep source material is involved in the mineralization.