龙首山芨岭岩体北带正长岩型铀矿的矿化特征及成矿规律
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摘要
龙首山成矿带芨岭岩体北带广泛出露加里东晚期形成的正长岩,前人对及其与铀矿化关系研究程度偏低。通过对芨岭岩体北带正长岩及其围岩黑云母石英片岩的岩石学、地球化学和铀矿化特征进行综合研究,认为区内正长岩具有准铝质碱性A型花岗岩特征,在晚志留世—早泥盆世祁连山—龙首山造山运动晚期进入伸展环境下形成。根据形成的铀矿物以及发育的蚀变组合,认为存在两个阶段的铀成矿作用:第一个阶段主要在正长岩内部形成钍石、铀方钍石等铀矿物;第二阶段在正长岩与黑云母石英片岩接触带两侧均形成了沥青铀矿为主的铀矿物。正长岩与黑云母石英片岩接触破碎部位为含矿热液减压区,形成了高反差的地球化学还原环境,为铀矿沉淀的有利部位。
The late Caledonian syenite is widespread in the northern of Jiling rock mass of the Longshoushan metallogenic belt.Previous studies on the relationship between syenite and uranium mineralization are low.By comprehensive study on the petrology,geochemistry,chronology and uranium mineralization characteristics of syenite and biotite-quartz schist in the area,conclude that the syenite has the character of A-type granite,formed in late-orogenic extensional environment of Qilian-Longshoushan Mountain during SilurianEarly Devonian period.U enrichment is influenced by magmatic differentiation,the later metallogenic the epoch is,the higher the U content is.Two stages of uranium mineralization was divided according to the uranium minerals formed and alteration combinations.In the first stage,uranium minerals such as thorite and uranium galena-thorite were formed mainly in syenite;In the second stage,pitchblende-dominated minerals of pitchblende-dominated were formed on both sides of the contact zone between syenite and biotite quartzschist.Therefore,it was considered that the contact fragmentation area between syenite and biotite quartzschist is the decompression zone of ore-bearing,forming a high contrast geochemical reduction environment,which is the favorable part for uranium deposit.
The late Caledonian syenite is widespread in the northern of Jiling rock mass of the Longshoushan metallogenic belt.Previous studies on the relationship between syenite and uranium mineralization are low.By comprehensive study on the petrology,geochemistry,chronology and uranium mineralization characteristics of syenite and biotite-quartz schist in the area,conclude that the syenite has the character of A-type granite,formed in late-orogenic extensional environment of Qilian-Longshoushan Mountain during SilurianEarly Devonian period.U enrichment is influenced by magmatic differentiation,the later metallogenic the epoch is,the higher the U content is.Two stages of uranium mineralization was divided according to the uranium minerals formed and alteration combinations.In the first stage,uranium minerals such as thorite and uranium galena-thorite were formed mainly in syenite;In the second stage,pitchblende-dominated minerals of pitchblende-dominated were formed on both sides of the contact zone between syenite and biotite quartzschist.Therefore,it was considered that the contact fragmentation area between syenite and biotite quartzschist is the decompression zone of ore-bearing,forming a high contrast geochemical reduction environment,which is the favorable part for uranium deposit.
引文
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[3]柴宝民,杨瑞木,孙延怀.龙首山花岗岩基本特征及成因探讨[R].西北地勘局203研究所,1987.
[4]张甲民,赵如意,王刚,等.甘肃龙首山芨岭铀矿区A型似斑状花岗岩地质特征及其地质意义[J].矿物岩石地球化学通报,2017,36(5):813-823.
[5]陈金勇,范洪海,王生云,等.纳米比亚欢乐谷地区白岗岩微量元素、稀土元素地球化学特征及其与铀矿化关系[J].地球化学,2016,45(5):486-498.
[6]许保良,阎国翰,张臣,等.A型花岗岩的岩石学亚类及其物质来源[J].地学前缘,1998(3):113-124.
[7]张志强,王凯兴,王刚,等.甘肃龙首山芨岭地区古生代正长岩成因及构造意义[J].地质论评,2018,64(4):1017-1029.
[8]刘正义,王生云,顾大钊,等.龙首山芨岭铀矿床含矿主岩特征及铀矿床成因讨论[J].西北地质,2018,51(2):160-170.
[9]钟军,范洪海,陈金勇,等.辽宁赛马霓霞正长岩黑云母地球化学特征、40 Ar-39 Ar年龄及其地质意义[J].地球科学,网络首发:2018-08-22.http://kns.cnki.net.
[10]杜乐天.碱交代作用地球化学原理[J].中国科学:B辑,1986(1):81-90.