鄂尔多斯盆地北部纳岭沟铀矿直罗组含铀岩系蚀源区识别

【研究目的】纳岭沟铀矿是鄂尔多斯盆地北部最重要铀矿床之一,识别其含铀岩系物源区对于深化成矿作用和找矿预测具有实际意义。【研究方法】笔者通过岩石学、重矿物学、地球化学和沉积相分析等方法,识别了纳岭沟铀矿床中侏罗统直罗组含铀岩系的蚀源区。【研究结果】含铀岩系岩石类型主要为中粗长石砂岩,碎屑成分有长石、石英、黑云母和花岗岩岩屑、变质岩岩屑等,分选中等至差;碎屑多呈棱角状、次棱角状,少数为次滚圆状,磨圆度差至中等。重矿物分布极不均匀,呈棱角状、次棱角状、次滚圆状,磨圆度差至中等;ZTR(锆石+电气石+金红石)指数2%~10%。电气石、尖晶石、锐钛矿、角闪石、碳硅石等呈集簇状分布;碎屑锆石延长系数主要为1~2.2,其次2.2~3.2。稀土元素球粒陨石配分曲线形态相似,ΣREE值104.75×10^(-6)~283.86×10^(-6),LREE/HREE值0.13~0.47,La/Yb值9.60~32.66,元素含量变化幅度大。纳岭沟地区含铀岩系砾质、砂质辫状河沉积相由矿区北东方向至南西方向延展,与高厚度砂体、高含砂率砂体分布规律一致。【结论】纳岭沟铀矿直罗组含铀岩系蚀源区为矿区北东缘的晋蒙交界地带的前中侏罗世隆起区的太古代片麻岩、古元古代孔兹岩、二长花岗岩和古生代岩浆岩、沉积岩和中生代沉积岩、火山岩。

柴西北缘跃进二号地区晚新生代沉积特征及沉积相演化

柴西北缘跃进二号地区沉积相特征精细研究对油气及铀矿勘查意义重大。笔者通过收集柴西北缘典型油气矿区200余孔典型钻孔资料,结合区域古地理及构造特征,分析砂体等厚度图,绘制柴西北缘晚新生代上油砂山组、狮子沟组及七个泉组沉积相平面图,揭示柴西北缘在晚新生代主要发育辫状河三角洲前缘、扇三角洲平原、辫状河三角洲平原、滩坝、扇三角洲前缘、洪泛泛滥平原及滨浅湖等沉积亚相及沉积相。通过对跃进二号地区ZK8-20、跃Ⅱ5-21、ZKⅡ1-10、跃Ⅱ4-11下、跃Ⅱ2-6等钻孔不同地层岩性、颜色、沉积序列、测井曲线、沉积结构构造等的综合分析,根据沉积学原理,认为该区在上油砂山组及狮子沟组主要发育辫状河三角洲平原,表现为水上分流河道及分流河道间沉积特征;第四系七个泉组主要发育辫状河三角洲前缘沉积相,表现为河口坝沉积微相、分流间湾微相及水下分流河道微相等。识别出研究区在晚新生代沉积相主要表现为退积式分布特征,湖水平面在狮子沟组有轻微下降,在七个泉组上升;研究区垂向上从下向上发育辫状河三角洲前缘亚相、辫状河三角洲平原亚相、滨浅湖亚相,形成了上部湖相,下部辫状河三角洲相的沉积模式。

Origin and circulation of saline springs in the Kuqa Basin of the Tarim Basin,Northwest China

It is widely accepted that hydrogeochemistry of saline springs is extremely important to understand the water circulation and evolution of saline basins and to evaluate the potential of potassium-rich evaporites.The Kuqa Basin,located in the northern part of the Tarim Basin in Northwest China,is a saline basin regarded as the most potential potash-seeking area.However,the origin and water circulation processes of saline springs have yet to be fully characterized in this saline basin.In this study,a total of 30 saline spring samples and 11 river water samples were collected from the Qiulitage Structural Belt(QSB)of the Kuqa Basin.They were analyzed for major(K^+,Ca2^+,Na^+,Mg2^+,SO42-,Cl-and HCO3-)and trace(Sr2^+and Br-)ion concentrations,stable H-O-Sr isotopes and tritium concentrations in combination with previously published hydrogeochemical and isotopic(H-O)data in the same area.It is found that the water chemical type of saline springs in the study area belonged to the Na-Cl type,and that of river water belonged to the Ca-Mg-HCO3-SO4 type.The total dissolved solid(TDS)of saline springs in the QSB ranged from 117.77 to 314.92 g/L,reaching the brine level.On the basis of the general chemical compositions and the characteristics of the stable H-O-Sr isotopes of saline springs,we infer that those saline springs mainly originated from precipitation following river water recharging.In addition,we found that saline springs were not formed by evapo-concentration because it is unlikely that the high chloride concentration of saline springs resulted in evapo-concentration and high salinity.Therefore,we conclude that saline spring water may have experienced intense evapo-concentration before dissolving the salty minerals or after returning to the surface.The results show that the origin of salinity was mainly dominated by dissolving salty minerals due to the river water and/or precipitation that passed through the halite-rich stratum.Moreover,there are two possible origins of saline springs in the QSB:one is the infiltration of the meteoric water(river water),which then circulates deep into the earth,wherein it dissolves salty minerals,travels along the fault and returns to the surface;another is the mixture of formation water,or the mixture of seawater or marine evaporate sources and its subsequent discharge to the surface under fault conditions.Our findings provide new insight into the possible saltwater circulation and evolution of saline basins in the Tarim Basin.

豫西卢氏五里川地区柳树湾铀矿碱交代成矿作用

豫西卢氏五里川地区新发现的柳树湾铀矿碱交代成矿作用明显,对于豫西成矿带新一轮找矿战略行动具有直接指示意义.通过岩石学、岩石化学和同位素定年等研究,认为早古生代中期,深源岩浆上侵、熔融、交代中元古代秦岭微陆块,形成富碱含铀的灰池子岩体(429.4±5.3 Ma)和花岗伟晶岩(417.4±2.3 Ma);早古生代晚期,混有幔源成分的含U、Na、Zr、Hf流体和含U、K、Nb、Ta流体富碱流体交代花岗伟晶岩,塑造了柳树湾花岗伟晶岩铀矿床;富碱流体在改变了岩体及伟晶岩的碱质(K+Na)、硅质(SiO_(2))、REE和Zr、Hf、Ti等元素分布环境的过程中,导致锆石U-Pb、白云母Ar-Ar和辉钼矿Re-Os同位素封闭体系受损.碱交代作用是岩体、花岗伟晶岩成岩以及柳树湾铀成矿的根本原因.

内蒙古额仁淖尔凹陷赛汉组砂(泥)岩地球化学特征及其对铀成矿作用的制约

【研究目的】查明二连盆地额仁淖尔凹陷赛汉组含铀砂(泥)岩的岩石矿物及地球化学特征,探讨铀成矿作用。【研究方法】包括野外地质编录、偏光显微镜、电子探针能谱分析、主微元素、环境地球化学及铀的价态分析等。【研究结果】(1)铀矿物以吸附态和独立铀矿物的形式存在,常与炭屑和黄铁矿共(伴)生并发现闪锌矿。(2)矿石具有高C_(有)、S、CO_(2)的特征,泥岩U^(6+)/U^(4+)平均为1.01,砂岩U^(6+)/U^(4+)平均为0.57。(3)砂(泥)岩的CIA值为50.83~66.34,稀土元素特征与蚀源区花岗岩一致,主微量元素特征均显示存在明显的后期沉积-成岩阶段的水岩作用。【结论】(1)海西期花岗岩是赛汉组砂(泥)岩的主要物源,沉积环境为半干旱—半湿润古气候。(2)吸附作用和氧化还原作用是研究区铀富集的主要机理,泥岩型铀矿以吸附作用为主,砂岩型铀矿以氧化还原作用为主。(3)深部流体可能参与了成矿作用。