摘要
绿柱石是重要的铍矿石矿物,记录了花岗伟晶岩型稀有金属矿床的成岩成矿过程。东秦岭伟晶岩区是我国重要的稀有金属产地之一。本文调查了东秦岭卢氏伟晶岩区中的南阳山矿区(703号脉锂矿化伟晶岩和302号脉铍矿化伟晶岩)、七里沟-前台矿区(前台锂矿化伟晶岩)、蔡家沟矿区(大西沟和韭菜沟锂矿化伟晶岩)和瓦窑沟矿区(西山沟和瓦窑沟铍矿化伟晶岩)的伟晶岩内部结构分带,认为东秦岭稀有金属伟晶岩主要为过铝质LCT型伟晶岩,属于稀有金属(REL)类REL-Li亚类。其中,703号脉、韭菜沟和大西沟伟晶岩属复杂型锂辉石亚型,前台伟晶岩属钠长石-锂辉石型,302号脉、瓦窑沟和西山沟伟晶岩属绿柱石型绿柱石-铌铁矿亚型。电子探针结果表明绿柱石富碱金属,贫铁和镁。绿柱石元素替代机制包括通道-八面体替代、通道-四面体替代以及通道中碱金属阳离子间的置换。西山沟和瓦窑沟绿柱石的替代机制分别是Na(Fe2+,Mg)-1Al-1和NaLi-1Be-1。302号脉、前台、大西沟和韭菜沟绿柱石的替代机制为(Na,Cs) Li-1Be-1。703号脉绿柱石的替代机制包括NaFe2+-1Al-1、NaCs-1和(Na,Cs)Li-1Be-1。绿柱石的Cs2O含量和Na/Cs值揭示伟晶岩分异演化程度序列(由低至高)为瓦窑沟矿区→302号脉铍矿化伟晶岩→蔡家沟矿区→前台→703号脉锂矿化伟晶岩。铍矿化伟晶岩岩浆分异演化程度低于锂矿化伟晶岩岩浆。背散射图像显示绿柱石内部分带多样,包括均一结构、条带状、正/反蚀变边、补丁分带和复杂不规则分带。与铍矿化伟晶岩相比,锂矿化伟晶岩产出的绿柱石内部分带复杂多样,反映更为强烈的液相不混溶和交代作用。随伟晶岩岩浆分异演化程度升高,绿柱石FeO含量降低,内部分带更为复杂,发育蚀变边结构、补丁分带和不规则分带等。绿柱石FeO含量和内部分带特征可作为花岗伟晶岩分异演化程度的潜在
Beryl which is one of the most important beryllium minerals records the rock-forming process and rare-element( REL)mineralization of granitic pegmatites. East Qinling Lushi pegmatite district is a famous rare-element producing area in China. This study investigated the internal zonation patterns of the pegmatite dykes from the East Qinling,including No. 703 Li-mineralized pegmatite and No. 302 Be-mineralized pegmatites in Nanyangshan,Qiantai Li-mineralized pegmatite in Qiligou-Qiantai,Daxigou and Jiucaigou Limineralized pegmatites in Caijiagou,Xishan’gou and Wayaogou Be-mineralized pegmatites in Wayaogou. These pegmatites belong to peraluminous LCT-family and REL-Li subtype. The Nanyangshan No. 703,Jiucaigou and Daxigou pegmatites belong to complex type and spodumene subtype,while the Qiantai pegmatite belong to albite-spodumene type. The Nanyangshan No. 302,Wayaogou and Xishan’gou pegmatites belong to beryl type and beryl-columbite subtype. The EMPA results show that beryls are enriched in alkali and poor in iron and magnesium. The substitution mechanisms of beryl from the REL pegmatites in the East Qinling are channel-octahedral,channel-tetrahedral and alkali cations in channel. The substitutions of beryl from the Xishan’gou and Wayaogou are Na( Fe2+,Mg)-1 Al-1 and NaLi-1Be-1,respectively. The beryls from the No. 302,Qiantai,Daxigou and Jiucaigou pegmatites mainly display substitution of( Na,Cs) Li-1Be-1,while the substitutions:( 1) NaFe2+-1Al-1,(2) NaCs-1 and( 3)( Na,Cs) Li-1Be-1 were revealed for the No. 703 pegmatite. The Cs2O contents and Na/Cs values indicate a sequence of the decreasing degree of fractionation and evolution of pegmatites,which is No. 703 → Qiantai →( Daxigou and Caijiagou)→ No. 302 →( Xishan’gou and Wayaogou). Li-mineralized pegmatitic magma is more highly fractionated than those of beryllium mineralization. The internal zonation patterns of beryls are homogeneous grain,layered zoning,alteration borders,patches and complex irregular zoning in BSE images.Compared with the B
作者
周起凤
秦克章
唐冬梅
王春龙
马留锁
ZHOU QiFeng;QIN KeZhang;TANG DongMei;WANG ChunLong;MA LiuSuo(Key Laboratory of Mineral Resources t Institute of Geology and Geophysics t Chinese Academy of Sciences, Beijing 100029, China;Institute of Mineral Resources Research, China Metallurgical Geology Bureau, Beijing 101300, China;Institutions of Earth Science ^ Chinese Academy of Sciences, Beijing 100029, China;College of Earth and. Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;Faculty of Earth Resources 1 China University of Geosciences, Wuhan 430074, China;Bureau of Natural Resources of Lushi County, Sanmenxia 472200, China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2019年第7期1999-2012,共14页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41602095)
岩石圈演化国家重点实验室开放课题(201304)联合资助
关键词
绿柱石
元素替代机制
花岗伟晶岩演化程度指示标志
稀有金属矿化
卢氏县
东秦岭
Beryl
Element substitution
Indicators of the degree of evolution of granitic pegmatite
Rare-element mineralization
Lushi County
East Qinling
