陕西小秦岭地区碳酸岩时空分布、地球化学特征及其与铀稀土成矿作用的关系  

Spatial and temporal distribution,geochemical characteristics of carbonatites and their relationship with U–REE mineralization in the Xiaoqinling area,Shaanxi Province

作　　者：康清清 陈正乐[1,3] 潘家永[1] 李鹏 刘玉龙[4] 李雷 江宏君 高成 KANG Qingqing;CHEN Zhengle;PAN Jiayong;LI Peng;LIU Yulong;LI Lei;JIANG Hongjun;GAO Cheng(State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,Jiangxi,China;Team 224 of Sino Shaanxi Nuclear Industry Group,Xi’an 710024,Shaanxi,China;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China;Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;Team 214 of Sino Shaanxi Nuclear Industry Group,Xi’an 710100,Shaanxi,China)

机构地区：[1]东华理工大学核资源与环境国家重点实验室,江西南昌330013 [2]中陕核工业集团二二四大队有限公司,陕西西安710024 [3]中国地质科学院地质力学研究所,北京100081 [4]中国科学院广州地球化学研究所,广东广州510640 [5]中陕核工业集团二一四大队有限公司,陕西西安710100

出　　处：《地质力学学报》2024年第1期147-167,共21页Journal of Geomechanics

基　　金：国家重点研发计划(2017YFC0602205);中国铀业与东华理工大学核资源与环境国家重点实验室联合创新基金项目(NRE2021-01);中陕核工业集团有限公司科技攻关项目(61230101)。

摘　　要：碳酸岩作为一种岩浆成因的岩石类型,是铀、稀土等矿产的重要含矿母岩。陕西小秦岭地区广泛分布着碳酸岩,呈大脉状、群脉状、网脉状沿断裂构造侵入太古代变质基底、长城系熊耳群火山沉积岩及蓟县系高山河群碎屑岩中。基于野外穿插关系,结合碳酸岩主要矿物组合特征,将小秦岭碳酸岩划分为5个阶段,由老到新分别为:霓辉石正长岩阶段、霓辉石碳酸岩阶段、钾长石碳酸岩阶段、石英碳酸岩阶段和含沸石碳酸岩阶段,碳酸岩由早期铁碳酸岩向晚期钙碳酸岩演化。在空间上碳酸岩大致以近东西向小河断裂为界,南北部碳酸岩脉的主要类型存在明显的差异;在时间上碳酸岩总体形成于晚三叠世,但不同地段不同类型碳酸岩存在较为明显的时间差异性。碳酸岩地球化学特征显示高硅、富碱、低镁、高钡锶−稀土元素的特征,以及异常高的钾钠比值;CaO含量、TiO_(2)含量、Al_(2)O_(3)含量、铁镁质含量、全碱含量、稀土元素总量及分馏程度均有自早期碳酸岩到晚期碳酸岩逐渐降低的趋势;MnO含量与重稀土元素含量变化相反,且两者呈线性相关特征;与国内其他地区碳酸岩地球化学特征具有明显的差异性。不同类型碳酸岩具有显著的成矿专属性:早期的霓辉石正长岩、霓辉石碳酸岩、钾长石碳酸岩主要富集铀(铌),钾长石碳酸岩还富集钼;晚期的石英碳酸岩主要富集钼、重稀土元素。碳酸岩的侵入致使围岩发生了普遍的霓长岩化作用,由此导致的钾钠元素的迁移可能是碳酸岩成矿专属特征的重要指标和原因。研究结果为小秦岭地区碳酸岩型铀、稀土等多金属矿的区域勘探提供了有价值的信息。[Objective]Carbonatites,as magmatic-origin rocks,are crucial source rocks for uranium,rare earth,and other minerals.They are widely distributed in the Xiaoqinling region of Shaanxi,giving rise to numerous large to super-large carbonatite deposits of uranium,molybdenum,and rare earth,represented by Huayangchuan and Dashigou,attracting attention from scholars in recent years.Previous studies on carbonatite deposits in the area focused on petrology,mineralogy,genesis,and mineralization chronology.However,they were often limited to individual deposits,needing more regional cross-sectional comparative studies.[Methods]This study employs field geological surveys,petrographic analysis,and geochemical characterization of typical rocks and ores to reclassify different types and stages of Xiaoqinling carbonatites.It analyzes the geochemical characteristics of various carbonatite types and explores the mineralization processes of uranium and rare earth elements associated with carbonatites.[Results]Xiaoqinling carbonatites exhibit a large vein,vein group,and vein network morphology,intruding into the Archean metamorphic basement,Xiong'er Group volcanic sedimentary rocks of the Changchengian System,and Gaoshanhe Group clastic rocks of the Jixianian System along fault structures.Based on field crosscutting relationships and primary mineral assemblage characteristics,Xiaoqinling carbonate rocks can be re-divided into five stages from old to new:aegirine syenite stage(I),aegirine carbonatite stage(II),potassium feldspar carbonatite stage(III),quartz carbonatite stage(IV)and zeolite-bearing carbonatite stage(V).Spatially,the division is roughly along the nearly EW-striking Xiaohe Fault,with northern carbonatite veins dominated by aegirine syenite and aegirine carbonatite,rich in aegirine,biotite and other dark minerals,distributed in the Archean gneiss basement.The southern part is mainly composed of light-colored potassic feldspar carbonatites and quartz carbonatites,almost devoid of dark minerals,with surrounding rocks consist

关 键 词：陕西小秦岭 碳酸岩 类型划分 地球化学 成矿指示 

分 类 号：P584[天文地球—岩石学]