摘要
牛苦头矿床位于东昆仑造山带祁漫塔格地区中段,目前已探明Pb+Zn资源量116万吨(推断及以上),为祁漫塔格地区探明的最大矽卡岩型铅锌矿床之一。M1、M4以及M2三个磁异常区(矿段)为牛苦头矿区主要的矿段(点),矿区发育大量与铅锌多金属矿成矿密切相关的花岗质岩体。本文通过对M1、M4以及M2三个矿段典型矿床地质特征、蚀变与矿化分带空间关系的研究,初步确定了M1和M4矿段钻孔底部的花岗闪长岩、M2矿段钻孔底部的二长花岗岩为成矿岩体。LA-ICPMS锆石U-Pb定年结果表明,牛苦头矿区花岗质岩浆岩主要分为两期:M1和M4矿段的花岗闪长岩,其时代为375~353Ma,对应于海西期;M2矿段钻孔底部的二长花岗岩,其时代为216~212Ma,对应于印支期。全岩主微量元素地球化学研究表明,M1和M4矿段海西期花岗闪长岩为钙碱性系列-高钾钙碱性系列I型花岗岩,Mg^#值相对较高(平均44.23),含有大量暗色包体,具有弱的δEu负异常(0.68~0.87),以上特征暗示其源区形成过程中存在地幔物质的参与,类似于变玄武质角闪岩源区。其富集LREE和大离子亲石元素,亏损HREE和高场强元素,显示出后碰撞岩浆岩的地球化学性质。M2矿段钻孔底部的印支期二长花岗岩,属于高钾钙碱性-钾玄岩系列I型花岗岩,Mg^#值相对较低(平均27.05),不含暗色包体,较为明显的δEu负异常(0.11~0.56),∑REE为113×10^(-6)~512×10^(-6),富集LREE和大离子亲石元素、亏损HREE和高场强元素,Rb/Sr比值高,代表了较高分异的岩体,其源区类似于变砂岩源区。综合区域构造-岩浆演化地质背景,本文认为牛苦头海西期花岗闪长岩形成于晚泥盆世始特提斯洋闭合后的后碰撞阶段背景下,地幔底侵古老陆壳,由幔源岩浆与壳源岩浆混合而形成。而晚期印支期二长花岗岩则形成于晚古生代古特提斯洋闭合后的后碰撞环境,类似于变砂岩岩性地壳的部分熔融并经历了较强分异演化而成。结合矿床地质及矿物学特征,本文初步将牛苦头矿区划分为两个成矿系统:即M1、M4海西期成矿系统和M2印支期成矿系统,分别对应海西和印支两期岩浆成矿作用。
The Niukutou deposit,located in the central-western part of Qimantagh area,East Kunlun orogenic belt,is one of the most potential Pb-Zn skarn deposits in Qimantagh area with a proven Pb+Zn resource of 1.15 million tons(inference or above).M1,M4 and M2 magnetic anomaly areas(ore blocks)are the main ore blocks(points)in this district.Large volume of granitic rocks are closely related to the mineralization of Pb-Zn polymetallic deposit.Based on the study of geological characteristics,alteration and mineralization zonation of typical deposits in M1,M4 and M2 ore blocks,it is preliminarily concluded that granodiorite and monzonitic granite at the bottom of drill holes are the ore forming rock bodies.LA-ICP-MS analysis shows that the granitic rocks in Niukutou ore district could be divided into two stages:(1)the granodiorite in M1 and M4 ore blocks,with ages of 375 Ma and 353 Ma,corresponding to Hercynian;and(2)the monzonitic granite at the bottom of borehole in M2 ore block is 216 Ma to 212 Ma,corresponding to Indosinian.The whole rock geochemical studies show that the Hercynian granodiorites in M1 and M4 ore blocks belong to calc alkaline series–high-K calc alkaline series I-type granites,with relatively high Mg#(average=44.23),a large number of dark enclaves and weakδEu negative anomaly(0.68~0.87).The above characteristics suggest that mantle material participated in the formation of the source area,similar to meta-basaltic amphibolite source.They are enriched in LREE and large ion lithophile elements,depleted in HREE and high field strength elements,showing the geochemical features of post-collisional magmatic rocks.The Indosinian monzonitic granite at the bottom of drill hole in M2 ore block belongs to high-K calc-alkaline to shoshonite I-type granites,with relatively low Mg#value(average=27.05),no dark enclaves,obvious negativeδEu anomaly(0.11~0.56),andΣREE varying from 113×10-6 to 512×10-6.It is rich in LREE and large ion lithophile elements,depleted in HREE and high field strength elements,and high Rb/Sr values,representing a highly differentiated rock.Its source area is similar to that of meta-sandstone source.Based on regional tectonic-magmatic evolutionary geological backgrounds,we suggest that the Niukutou Hercynian granodiorites were formed in the post collisional setting after the closure of the Eo-Tethyan Ocean in Late Devonian,when the mantle underplated the ancient continental crust,and the ore deposit was formed by the mixed mineralization of mantle derived magma and crust derived magma.The Late Indosinian monzogranite was formed in the post collisional environment after the closure of the Paleo-Tethys in the Late Paleozoic,similar to the partial melting of metamorphic sandstone lithosphere and experienced strong differentiation and evolution.Combined with the geological and mineralogical characteristics of the deposit,the Niukutou ore district is preliminarily divided into two metallogenic systems:the M1 and M4 Hercynian metallogenic system and the M2 Indosinian metallogenic system,corresponding to Hercynian and Indosinian magmatic ore-forming processes respectively.
作者
王新雨
祝新友
李加多
王玉往
蒋斌斌
吴锦荣
黄行凯
赵子烨
WANG XinYu;ZHU XinYou;LI JiaDuo;WANG YuWang;JIANG Binbin;WU JinRong;HUANG XingKai;ZHAO ZiYe(Beijing Instituta of Geology for Mineral Resources Co.,Lta,Beijing 100012,China;The Qinghai Hongxin Mining Co.,Ltd.,Golmud 816099,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2021年第5期1567-1586,共20页
Acta Petrologica Sinica
基金
国家重点研发计划项目(2017YFC0602403)
中国地质调查局国家二级项目(DD20190815、DD20160072)
中国铜业重点科技项目(QHHXKCZYB007、QHHX-KZ-JF2020-001)联合资助。
