摘要
三江北段青海草陇、川西扎乌龙(或卡亚吉)伟晶岩型锂铍矿床与西部的喀喇昆仑白龙山、大红柳滩、肖尔布隆锂铍矿床以及东部的川西甲基卡、可尔因、雪宝顶等锂铍矿床,一起构成了青藏高原北缘一条近东西向的古特提斯巨型锂成矿带。但在草陇(青海南部玉树)以西到喀喇昆仑白龙山(新疆南部)之间一直还没有其他锂铍矿的报道。本次研究在青海省玉树地区草陇锂铍矿床以西72 km的尕朵‒扎朵地区发现了92条花岗伟晶岩,其中22条含(绿柱石‒锂云母)锂辉石花岗伟晶岩脉含矿性较好,另有不含矿伟晶岩脉15条,含矿性不明伟晶岩55条。本文对尕朵‒扎朵地区新发现的含(绿柱石‒锂云母)锂辉石花岗伟晶岩(含矿)和白云母花岗伟晶岩(不含矿)开展了系统的岩石学、地球化学及年代学研究。结果显示,含矿伟晶岩具有高SiO_(2)(72.87%~75.01%)、Al2O3(14.81%~17.18%)含量,低MgO(0.02%~0.03%)、CaO(0.32%~0.48%)、TiO_(2)(0.001%~0.007%)、P_(2)O_(5)(0.30%~0.42%)含量,及富钠( Na_(2)O/K_(2)O=2.05~12.92)的地球化学特征;白云母花岗伟晶岩(不含矿)亦具有高SiO_(2)(69.97%~73.75%)、Al_(2)O_(3)(15.18%~16.18%)含量,低MgO(0.01%~0.02%)、CaO(0.22%~0.38%)、TiO_(2)(0.001%~0.003%)、P_(2)O_(5)(0.35%~0.46%)含量,及变化的 Na_(2)O/K_(2)O值(0.35~2.04,平均1.0)。含矿和不含矿花岗伟晶岩的微量元素均富集大离子亲石元素Rb、K和高场强元素Nb、Ta、Hf,亏损Ba、Nd、Zr、Ti和稀土元素,且Zr/Hf值(7.85~18.44)低和Rb/Sr值(2.98~74.21)高;稀土元素总量较低,轻稀土元素富集,轻、重稀土元素分馏弱,发育负Ce异常,正‒负Eu异常,显示出岩浆演化晚期高度分异特性。含矿伟晶岩Li_(2)O品位为0.18%~2.33%,平均品位0.76%;BeO品位为0.04%~0.05%,平均品位0.043%,显示了良好的含矿性。年代学研究显示,含矿和不含矿伟晶岩的铌钽铁矿和锡石U-Pb年龄分布在194~178 Ma区间内,代表岩浆结晶和成矿时代,是燕山早期早侏罗世晚期产物;其白云母Ar-Ar年龄为158~153 Ma,可能为后期热液改造或侵入体冷却年龄。尕朵‒扎朵地区成矿伟晶岩的形成最有可能与早侏罗世陆内背景下可可西里‒松潘‒甘孜地块巨厚的三叠纪复理石沉积物发生熔融和随后的岩浆与热演化以及锂铍等稀有金属富集有关。该区含(绿柱石‒锂云母)锂辉石花岗伟晶岩的发现具有十分重要的成矿、找矿意义:①玉树地区锂铍多金属矿化带从草陇向西延伸70多公里到尕朵‒扎朵地区,构成一个具有重大潜力的矿集区(N:33°20′~33°50′;E:96°30′~97°30′),本研究将其定名为“草陇‒尕朵锂铍多金属矿集区”,该矿集区将是未来伟晶岩型锂铍多金属矿找矿工作的重点靶区;②前人的研究显示,古特提斯巨型锂成矿带中的锂铍多金属矿床主要形成于晚三叠世‒早侏罗世早期(218~194 Ma),本次研究发现了该巨型锂矿带中最年轻的成矿伟晶岩形成于早侏罗世晚期(194~178 Ma)。这表明该成矿带除晚三叠世‒早侏罗世早期伟晶岩外,早侏罗世晚期伟晶岩也具有良好的成矿潜力,拓展了青藏高原北部伟晶岩型锂铍矿的找矿时间和空间范围。
The Caolong and Zawulong lithium-beryllium mineralized pegmatites in the northern section of the Sanjiang River Tectonic Zone,together with the Bailongshan,Dahongliu,Xiaoerbulong lithium-beryllium deposits of the Karakoram area in the west and the Jiajika,Keeryin,Xuebaoding deposits of west Sichuan in the east,constitute an approximately west-east trending giant lithium belt of Paleo-Tethys Suture in the northern Tibet Pateau.However,no Li-Be-rich pegmatite has been reported between the Caolong(Yushu of southern Qinghai)and Bailongshan(Karakoram area of southern Xinjiang)pegmatites.This study reports newly discovered more than 92 pegmatite dikes to the west of the Caolong pegmatites(about 72 km)in the Yushu Regions,southern Qinghai province.There are more than 22 pegmatite dikes containing spodumene,lepidolite or beryl,15 ore-free pegmatite dikes,and 55 pegmatite dikes of unknown ore-bearing potential.In this paper,a systematic study on petrology,geochemistry and chronology has been carried out on the(lepidolite or beryl)spodumene(ore-bearing)and muscovite(ore-free)granitic pegmatites newly discovered in the Gado-Zaduo area of the Yushu region in the middle part of the Paleo-Tethys metallogenic belt.The ore-bearing pegmatites have high contents of SiO_(2)(72.87%–75.01%)and Al_(2)O_(3)(14.81%–17.18%),and low MgO(0.02%–0.03%),CaO(0.32%–0.48%),TiO_(2)(0.001%–0.007%),and P_(2)O_(5)(0.30%–0.42%)with high Na_(2)O/K_(2)O ratios ranging from 2.05 to 12.92,indicating sodium-rich geochemical characteristics.The ore-free muscovite pegmatites have similar high contents of SiO_(2)(69.97%–73.75%)and Al_(2)O_(3)(15.18%–16.18%),and low MgO(0.01%–0.02%),CaO(0.22%–0.38%),TiO_(2)(0.001%–0.003%),and P_(2)O_(5)(0.35%–0.46%),but exhibt varible Na_(2)O/K_(2)O ratios ranging from 0.35 to 2.04.The trace elements of ore-bearing or-free granitic pegomatites show the enrichment of large ion lithophile elements Rb,K and high field strength elements Nb,Ta,and Hf,while the depletion of Ba,Nd,Zr,Ti and rare earth elements.Their Zr/Hf ratios(7.85–18.44)are low and the Rb/Sr ratios(2.98–74.21)are high.The total amount of rare earth elements is low,and there is enrichment and partitioning curve of light rare earth elements.The fractionation of light and heavy rare earth elements is weak.The negative Ce and positive to negative Eu anomalies are developed.All geochemical signatures indicate the highly differentiated characteristics of late magmatic evolution.The Li_(2)O grade of spodumene(or beryl-limica)-bearing granitic pegmatites ranges from 0.18%to 2.33%,with an average grade of 0.76%.The grade of BeO is 0.04%–0.05%,with an average grade of 0.043%,showing great economic potential.The age dating for beryl spodumene-bearing(ore-bearing)and muscovite-bearing(ore-poor)granitic pegmatites suggests that the niobium-tantalite and cassiterite U-Pb ages of the granitic pegmatites range from 194 Ma to 178 Ma,which represent the crystallization or mineraliztion age of magmatic rocks,indicating that they could be formed at early Yanshanian.The Ar-Ar age of muscovite ranges from 158 Ma to 153 Ma,which may be the result of late hydrothermal modification or cooling age of the intrusions.The formation of the Gaduo-Zaduo granitic pegmatites was most probably related to partial melting of Triassic flysch from the Hohxil-Songpan-Ganzi Block and subsequent magma evolution and lithium-beryllium enrichment in an intracontinental setting.The discovery of spodumene-bearing granitic pegmatites in the Gaduo-Zaduo area of the Yushu region has a great significance in ore deposit exploration,including:(1)it means that there is a ore concentration area from the Caolong pegmatites to the Gaduo pegmatites(N:33°20′-33°50′;E:96°30′-97°30′).We call it“the Caolong-Gaduo Li-Be polymetallic ore concentration area”and this area will be a very important target for Li polymetallic exploration;(2)Previous studies have shown that the lithium-beryllium polymetallic deposits in the Paleo-Tethys giant lithium metallogenic belt were mainly formed in the Late Triassic-Early Jurassic(218-194 Ma).However,this study shows that the youngest metallogenic pegmatites in the metallogenic belt were formed in the late Early Jurassic(194-178 Ma).It expands the time and space of prospecting for pegmatite-type lithium-beryllium deposits in northern Tibet.
作者
李五福
刘金恒
李善平
贾春兴
王成武
周金胜
王春涛
许传兵
谈生祥
胡继春
章荣清
龚林
王秉璋
王强
LI Wufu;LIU Jinheng;LI Shanping;JIA Chunxing;WANG Chengwu;ZHOU Jinsheng;WANG Chuntao;XU Chuanbing;TAN Shengxiang;HU Jichun;ZHANG Rongqing;GONG Lin;WANG Bingzhang;WANG Qiang(Key Laboratory of the Northern Qinghai-Tibet Plateau Geological Processes and Mineral Resources,Qinghai Geological Survey Institute,Xining 810012,Qinghai,China;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,Jiangsu,China)
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2022年第5期924-950,共27页
Geotectonica et Metallogenia
基金
第二次青藏高原综合科学考察研究(STEP)项目(2019QZKK0702)
青海省地质矿产勘查开发局项目(青地矿科[2021]59号)联合资助。
关键词
含(绿柱石-锂云母)锂辉石伟晶岩
锂铍成矿
成矿时代
尕朵-扎朵
草陇-尕朵矿集区
青海玉树
青藏北部
(beryl-lepidolite)spodumene-bearing pegmatites
Li-Be mineralization
mineralogenetic epoch
Gaduo-Zaduo area
Caolong-Gaduo ore concentration area
Yushu region of Qinghai province
northern Tibet
