岩浆作用对岩浆热液金铜成矿制约的元素地球化学和锆石CL图像记录——以延边小西南岔富金铜矿床为例

CONSTRAINTS OF MAGMATISM ON THE ORE-FORMING PROCESS OF MAGMATIC HYDROTHERMAL GOLD-RICH COPPER DEPOSITS AS RECORDED FROM THE ELEMENT GEOCHEMISTRY AND ZIRCON CL IMAGE FEATURES:——A CASE STUDY OF THE XIAOXINANCHA GOLD-RICH COPPER DEPOSIT,YANBIAN,JININ PROVIN

通过对延边小西南岔大型富金铜床矿区产出的与成矿密切的角闪花岗闪长岩、黑云花岗闪长岩、黑云二长花岗岩(花岗杂岩)侵入体和闪长玢岩岩脉的地质、岩相学和元素地球化学研究,结合单颗粒锆石CL图象特征及精细测年结果,初步确定:它们的岩浆就位发生在晚中生代早白垩世末期(112 Ma^102 Ma),适值伊泽奈崎板块向古亚洲板块俯冲的大陆边缘环境;金铜矿化发生在角闪花岗闪长岩(111.7 Ma±2.8 Ma)、黑云花岗闪长岩(106.7 Ma±1.6 Ma)、黑云二长花岗岩(104.6 Ma±2.5 Ma)与闪长玢岩(102.1Ma±2.2 Ma)的就位之间;花岗杂岩是先存的岩石圈地幔受到俯冲大洋板片提供流体的交代,形成的次生岩石圈地幔,次生岩石圈地幔的部分熔融产生的埃达克质岩浆在MOSH面附近与下地壳重熔产生的钾质熔体混合,混合后的岩浆经以斜长石为主的矿物相分离结晶作用先后上侵就位形成;而闪长玢岩岩脉则是埃达克质岩浆直接上侵就位形成;矿质主要来自俯冲大洋板块,埃达克岩浆和地壳重熔岩浆的形成以及两者的混合作用、混合岩浆的结晶分离作用是导致成矿物质活化、迁移、富集的根源。

Based on the study of geology, petrography and element geochemistry of hornblende granodiorite,biotite granodiorite and biotite monzonitic granite intrusions （the granitic complex） and dioritic porphyrite dikes which are closely associated with output by the Xiaoxinancha goldrich copper deposit in Yanbian,Jinin Province and combined with the CL image features of single grain zircon and precise fine dating results,it is suggested that magma emplacement took place at the end of the early Cretaceous （112 Ma-102 Ma） of late Mesozoic in accordance with continental margin environment when hanaqi plate was subducted beneath the Paleo-Asian plate. Goldcopper mineralization occurred between the emplacement of hornblende granodiorite （111.2 Ma± 2.8 Ma）,biotite granodiorite （106. 7 Ma±1.6 Ma）,biotite granite （104. 6 Ma±2.5 Ma） and that of diorite porphyry （102.1 Ma±2.2 Ma）. It is indicated that the pre-existing lithospheric mantle was metasomatized by fluids supplied by a subduction oceanic slab,forming the secondary lithospheric mantle. Partial melting of this secondary lithospheric mantle produced adackitic magma which was then mixed with the potassic magma generated by remelting of the lower crust at the Moho discontinuity. The mixed magma underwent fractional crystallization with plagioclase as a main separated mineral phase,and then ascended and emplaced to form the intrusive granitic complex. In addition,the dioritic porphyrite veins were formed directly by adakitic magma. Metallogenic materials come from the subducted oceanic plate,whereas formation and mixing of the adakitic magma and remehed crustal magma as well as crystallization of the mixed magma have resulted in activation, migration and enrichment of metallogenic materials.