冀北蓟县系铁岭组古风化壳稀土元素富集规律及古环境意义.pdf

矿床地质MINERAL DEPOSITS2023年10月October，2023第 42 卷第 5 期42（5）：10341047张运强等：冀北蓟县系铁岭组古风化壳稀土元素富集规律及古环境意义*本文得到中国地质调查局地质调查项目（编号：DD20230383 和 DD20230060）、河北省高层次人才资助项目（编号：A202001056）和河北地矿局综合研究项目（编号：454-0502-JBN-G43D）共同资助第一作者简介张运强，男，1982 年生，高级工程师，主要从事战略性矿产资源调查评价工作。Email：*通讯作者陈海燕，女，1983 年生，高级工程师，主要从事区域地质矿产调查及科普工作。Email：收稿日期2023-01-05；改回日期2023-08-03。赵海杰编辑。文章编号：0258-7106（2023）05-1034-14Doi:10.16111/j.0258-7106.2023.05.012冀北蓟县系铁岭组古风化壳稀土元素富集规律及古环境意义*张运强1，陈海燕1*，杨鑫朋2，王志民1，郝森1，李朋伟1(1 中国地质调查局廊坊自然资源综合调查中心，河北 廊坊065000；2 河北省区域地质调查院，河北 廊坊065000)摘要冀北地区蓟县系铁岭组顶部普遍发育一套古风化壳，该层位轻稀土元素和 Rb 均出现显著的富集现象。为了进一步探讨风化过程中元素的迁移规律以及古环境特征，文章对该套古风化壳开展了详细的地球化学研究。结果表明，古风化壳中轻稀土元素、Rb 和 Ti 等含量自下而上表现为“先升高，后降低”的分布规律，且随着风化层中黏土物质的增加而升高，在中上部黏土岩中达到富集的峰值，推测与黏土矿物的吸附作用相关；古风化壳 Ce正异常、Eu 明显的负异常等特征指示轻稀土元素主要富集于中上部的氧化环境，且氧化作用越强越富集；化学蚀变指数 CIA 介于 53.5479.50，风化淋滤指数 BA 变化范围为 0.391.08，共同指示了风化壳形成于温暖湿润的气候环境。综合稀土元素、微量元素和 La/Yb-REE 图解显示，风化壳稀土元素和微量元素主要来源于下伏铁岭组碳酸盐岩以及火山岩浆活动。关键词稀土元素；富集机理；古风化壳；铁岭组；冀北中图分类号：P618.7；P618.77文献标志码：AREE enrichment and palaeoenvironmental significance of paleo-weatheringcrust of Tieling Formation of Jixian System,northern Hebei ProvinceZHANG YunQiang1,CHEN HaiYan1,YANG XinPeng2,WANG ZhiMin1,HAO Sen1and LI PengWei1(1 Langfang Center for General Survey of Natural Resources,China Geological Survey,Langfang 065000,Hebei,China;2 Hebei Regional Geological Survey Institute,Langfang 065000,Heibei,China)AbstractA set of paleo-weathering crust is widely developed on the top of Tieling Formation in the Middle Proterozoicin northern Hebei Province,it is found that both the light rare earth and the associated Rb have reached enrichment.The paper studies migration of elements during weathering and the characteristics of paleoenvironmentbased on detailed geochemistry study，the results show that the contents of LREE、Rb and Ti in the paleo-weathering crust increase first and then decrease,and enhance with the increase of clay material in the paleo-weathe-ring layer,in the middle and upper part of the clay rock reached the peak value,presumably related to the adsorption of clay minerals.The light rare earths in the paleo-weathering crust begin to be enriched under the conditionof oxidation,and enriched with the increase of oxidation.Positive abnormality of Ce and obvious negativeanomaly of Eu indicate that the light rare earths are mainly enriched in the oxidation environment of the middleand upper part,and gradually reach mineralization with the increase of oxidation.The CIA of chemical alteration第 42 卷 第 5 期张运强等：冀北蓟县系铁岭组古风化壳稀土元素富集规律及古环境意义1035近年来，中国相继在川南沐川、滇东北宣威、黔西等西南地区发现了古风化壳型稀土、铌等稀有金属矿，此类矿床具有层位稳定、厚度较大、矿化元素众多等特征，具有很好的成矿前景和找矿潜力（衮民汕等，2021；文俊等，2021；刘阳等，2021）。但北方地区却鲜有古风化壳型矿床报道，前人仅在晋中南沁源、平陆以及豫西郁山等地的奥陶纪顶部的古风化壳中发现有轻稀土、镓等稀有及稀散金属富集（王银喜等，2000；李中明等，2007）。作者通过对冀北地区系统调查发现，中元古界蓟县系铁岭组顶部碳酸盐岩古风化壳中广泛存在稀土和铷等稀有元素的高度富集现象。已有古地磁资料表明，至少在1200700Ma期间，华北地块位于近赤道低纬度地区（黄宝春，2008），具备碳酸盐岩风化壳发育的湿热气候条件，野外调查已发现冀北多地保存了一定规模的该层位古风化壳。基于此，本文对铁岭组顶部古风化壳开展了地球化学研究，探讨了稀土元素富集特征、迁移规律、古风化环境、物质来源等，以期为下一步在冀北地区寻找古风化壳型“三稀”找矿突破提供优选层位和靶区。1区域地质背景研究区位于华北陆块中北部的冀北张家口、承德及保定等地区，区内中元古界蓟县系铁岭组顶部普遍发育一套古风化壳，与上覆地层青白口系下马岭组之间形成一个广泛分布的平行不整合或微角度不整合界面，代表了乔秀夫最早命名的“芹峪运动”或“芹峪上升”（乔秀夫，1976）地壳运动的产物，不整合面上发育黏土、铝土矿、褐铁矿和赤铁矿层，充填于岩溶构造中，厚度变化大，指示铁岭组沉积后一次明显沉积间断，代表了铁岭组沉积后的区域性地壳抬升。该古风化壳呈北东-南西方向展布，向西至宣化-涞源，东至平泉一带，是本次古风化壳研究的目标层位（图1）。2富集剖面特征该古风化壳属于典型的碳酸盐岩古风化壳型，下伏原岩为蓟县系铁岭组泥晶白云岩，局部发育燧石结核和叠层石。古风化壳底部由于长期风化剥蚀造成顶部不整合面凹凸不平，局部残留有小型的“岩溶漏斗”。风化壳主要由各类风化产物经后期压实固结而成的杂色泥岩、黏土岩和少量的褐铁矿层组成（图2ad）。古风化壳顶部被下马岭组正常沉积的杂色含粉砂页岩覆盖。以涞水县紫石口剖面为例，风化壳总厚约420m不等，底部和中部层厚不等，横向延伸长度大于2km。古风化壳新鲜露头岩性以黄白色、黄褐色和砖红色（铁质）黏土岩为主，下伏为铁岭组泥晶白云岩，局部含叠层石及燧石条带，风化壳之上进入青白口系下马岭组灰黄色薄板状含粉砂页岩，自上而下可以划分如下：青白口系下马岭组：灰黄色、浅灰绿色含粉砂页岩，薄层状，厚度300 cm：12.灰白色含砂黏土岩，中等风化，厚度 288cm；11.黄褐色粉砂质黏土岩，偶见黄铁矿颗粒，已经褐铁矿化，厚度235 cm；10.红褐色铁质含粉砂黏土岩，网纹状构造，风化强烈，厚度210 cm；9.红褐色黏土岩，疏松多孔，质地较轻，厚度183 cm；8.灰黄色黏土岩，含少量褐铁矿化黄铁矿颗粒，厚度165 cm；7.灰黄色黏土岩，质地较轻，厚度160 cm；6.灰白色黏土岩，偶含黄铁矿（多风化为褐铁矿），风化较强，厚度153 cm；5.黄褐色含粉砂黏土岩，风化面网纹状褐铁矿化明显，厚度113 cm；index is between 53.54 and 79.50,and the BA of weathering shower index varied from 0.39 to 1.08,indicatingthat the weathering crust was formed in a warm and humid climate conditions.The spider-web Diagram,REE distribution curve and the diagram analysis of La/Yb-REE of the micronutrient indicate that the rare earth elements and micronutrient are mainly derived from the carbonate rocks of the underlying Tieling Formation andvolcanic magmatism during this geological period.Key words:rare earth elements,enrichment mechanism,paleo-weathering crust,Tieling Formation,NorthHebei1036矿床地质2023 年图 1冀北中元古界蓟县系铁岭组顶部古风化壳分布图1蓟县系铁岭组；2青白口系下马岭组；3不整合界线；4剖位置面；5行政区界线Fig.1Distribution of the paleo-weathering crust on the top of the Tieling Formation of Jixian System in the northern Hebei1Tieling Formation of Jixian System;2Xiamaling Formation of Qingbaikou System;3Unconformity;4Section point;5Administrative boundaries4.灰黄色黏土岩，风化中等，厚度63 cm；3.红褐色铁质黏土岩，中等风化，厚度44 cm；2.黄褐色黏土质粉砂岩，含少量褐铁矿，厚度35 cm；1.红褐色粉砂质黏土岩，厚度15 cm；蓟县系铁岭组：泥晶白云岩，局部可见含叠层石和燧石条带，厚度500 cm；古风化壳黏土岩多呈灰黄色，成分由黏土、陆源碎屑，局部含少量黄钾铁矾。黏土呈隐微鳞片状，多变为绢云母，杂乱分布，粒径一般0.004 mm，局部与铁质混杂，颜色较深。陆源碎屑主由石英、长石、岩屑组成，零星分布，粒径一般为0.0040.06 mm的粉砂，石英表面较干净。长石主为斜长石，具高岭土化等。岩屑多具黏土化等。黄钾铁矾呈粒状、鳞片状等，薄片中显黄色，多呈集合体状产出或呈土状、皮壳状等产出（图2e、f）。3样品采集及测试文章选取涞水县紫石口、蓬头和涿鹿县郝家坡3个典型的古风化壳剖面新鲜样品进行逐层取样。主量、微量及稀土元素送至河北省区域地质矿产调查研究所实验室分析，其中主量元素FeO采用硫酸-氢氟酸溶矿-重铬酸钾滴定法，其他元素采用四硼酸锂熔片 XRF 法(X 射线荧光光谱法)分析，仪器为Axios mAX X 射线荧光光谱仪，分析误差小于2%；稀土元素（包括 La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu、Y）和微量元素（包括Ge、Ga、In、Tl、Re、Cd、Se、Te，稀有元素：Nb、Ta、Be、Li、Zr、Sr、Hf、Rb、Cs）使用电感耦合等离子体质谱法(ICP-MS)测定，仪器为X Serise2 等离子体质谱仪，分析过程中用标样控制结果的可靠性，测定平均标准偏差小于10%，平均相对标准偏差小于5%。4地球化学特征（1）常量元素根据18组主量元素数据（表1）分析可知，古风化壳剖面相比于新鲜基岩，其上部的风化层表现出：w(Al2O3)=9.83%22.08%（新 鲜 基 岩 为 0.66%第 42 卷 第 5 期张运强等：冀北蓟县系铁岭组古风化壳稀土元素富集规律及古环境意义1037图2蓟县系铁岭组顶部古风化壳野外特征（ad）及岩矿石特征（e、f）a.古风化壳产状；b.古风化壳风化特征；c.小型岩溶漏斗；d.风化壳底部的褐铁矿；e.粉砂质黏土岩手标本照片；f.粉砂质黏土岩显微照片(正交偏光)Pt23x 下马岭组；Pt22t铁岭组；PW古风化壳；Ser黏土矿物；Qz石英；Jr黄钾铁矾Fig.2Field characteristics of paleo-weathering crust of Tieling Formation of Jixian System(ad)and characteristics of rocks andores(e,f)a.Field occurrence of paleo-weathering crust;b.Weathering features of paleo-weathering crust;c.Small karst funnel;d.Limonite at the bottom ofthe paleo-weathering crust;e.Photographs of hand specimens of silty clay rocks;f.Microphotographs of silty clay rocks(orthogonal polarizing)Pt23xXiamaling Formation;Pt22tTieling Formation;PWPaleo-weathering crust;SerClay mineral；QzQuartz;JrJarosite1038矿床地质2023 年表1蓟县系铁岭组顶部古风化壳常量元素分析结果(w(B)/%)及相关参数Table 1Major elements analysis results(w(B)/%)and the related parameters of the paleo-weathering crust on the top of Tieling Formation of Jixian System组分SiO2Al2O3TiO2Fe2O3FeOCaOMgOK2ONa2OMnOP2O5烧失量总数Fe3+/Fe2+CIABASiO2TiO2Fe2O3CaOMgOK2ONa2O铁岭组泥晶白云岩PTD-018.961.990.0810.3723.7916.610.310.080.070.0136.6999.962.4577.0521.62古风化壳黄褐色黏土岩PTD-158.7819.5717.990.320.291.195.610.0900.074.7999.7022.7175.40.48-0.690.27-0.19-1-0.990.84-0.89白色黏土岩PTD-263.1920.121.252.990.480.141.136.040.100.074.1599.665.5774.530.492.2414.21-0.64-0.99-0.9317.940.2黄褐色黏土岩PTD-356.7619.210.9410.410.530.190.995.60.080.010.054.9699.7317.5875.170.462.1411.262.65-0.99-0.9417.920.07铁岭组泥晶白云岩5-20-1*1.420.660.032.150.0730.3220.540.140.040.590.0143.9799.9427.6469.9579.79古风化壳粉砂质泥岩5-20-2*60.5517.630.878.470.460.171.015.020.10.010.075.2999.6516.5775.320.470.60.09-0.85-1-10.34-0.91泥质粉砂岩5-20-3*53.3416.820.9160.460.130.834.820.100.076.0899.5531.375.160.460.470.18-0.71-1-10.35-0.9褐铁矿5-20-4*32.0910.270.5340.840.240.110.553.520.10.010.0611.4199.73153.1571.050.540.450.140.22-1-10.62-0.84泥岩5-20-5*26.679.830.5829.040.250.170.727.060.3400.0624.6799.39104.5453.541.080.260.3-0.09-1-12.39-0.43含粉砂泥岩5-20-6-1*42.4113.970.8627.250.290.130.734.440.1500.079.4399.7384.5772.490.510.410.35-0.4-1-10.5-0.82泥岩5-20-6-2*65.7517.171.23.240.380.110.795.190.1100.085.6499.667.6774.060.470.780.54-0.94-1-10.42-0.89泥岩（疏松多孔）5-20-6-3*66.2918.841.11.570.430.140.925.550.0900.064.6199.603.2974.890.460.640.28-0.97-1-10.39-0.92含褐铁矿泥岩5-20-6-4*63.5719.971.112.720.480.120.975.860.100.074.7399.705.174.760.460.480.22-0.96-1-10.38-0.92泥岩5-20-7-1*49.0714.550.9322.380.430.090.74.230.0800.077.199.6346.8474.860.460.570.41-0.53-1-10.37-0.91含粉砂泥岩5-20-7-2*57.2315.041.0814.760.410.10.714.410.0800.075.7899.6732.474.870.460.770.58-0.7-1-10.38-0.91粉砂质泥岩5-20-8*63.5218.131.283.870.480.150.865.240.100.064.5798.267.2675.090.450.630.55-0.93-1-10.36-0.91含泥砂岩5-20-9*55.4322.081.037.180.620.160.945.610.10.010.076.5299.7510.4277.480.40.170.03-0.9-1-10.2-0.93下马岭组含粉砂泥岩6-15-12*54.2821.260.758.721.440.361.134.750.10.010.036.6199.445.4579.50.390.19-0.22-0.87-1-10.05-0.92注:“*”为紫石口剖面数据，下同（据郭文琳等，2014）；CIA=Al2O3/(Al2O3+CaO+Na2O+K2O)100%;BA=(K2O+CaO+Na2O+MgO)/Al2O3100%，比值单位为1。第 42 卷 第 5 期张运强等：冀北蓟县系铁岭组古风化壳稀土元素富集规律及古环境意义1039表2蓟县系铁岭组顶部古风化壳稀土元素分析结果(w(B)/10-6)及相关参数Table 2Rare earth elements analysis results(w(B)/10-6)and the related parameters of the paleo-weathering crust on the top of Tieling Formation of Jixian System组分LaCePrNdSmEuGdTbDyHoErTmYbLuYREECe2O3(La/Yb)N(La/Sm)N(Gd/Yb)NCeEuLaCePrNdSmEuPTD-0泥晶白云岩7.4013.421.686.111.120.220.960.150.900.180.540.090.570.096.5139.9435.898.794.171.350.910.60PTD-1黄褐色黏土岩102.44206.2625.0493.4217.792.7113.391.9410.702.035.910.925.760.8852.01541.20536.4812.003.651.860.980.512.112.452.352.432.571.76PTD-2白色黏土岩106.21213.1325.9594.8016.503.0213.041.9010.932.116.281.016.400.9953.86556.13550.9411.214.081.630.970.591.802.102.022.031.881.68PTD-3黄褐色黏土岩62.10115.2614.9154.9410.161.558.781.367.951.524.450.734.620.7238.63327.68310.099.073.871.520.910.471.051.101.161.191.210.72HJP-2含燧石结核白云岩3.909.590.883.880.950.211.080.181.020.190.500.070.480.077.5330.5323.2968.421.232.290.113.01HJP-3褐铁矿26.4042.637.1734.258.931.737.761.226.561.213.130.473.130.4331.21176.23144.3145.160.582.970.173.353.662.064.615.085.484.67HJP-4灰黄色黏土岩110.32156.8920.3798.0617.923.2318.373.0717.763.389.181.399.331.3285.61556.20485.6141.450.551.860.232.903.371.532.582.911.911.38HJP-5灰白色黏土岩111.97172.8420.6198.5014.792.3512.901.9310.562.055.930.936.540.9246.44509.26503.2933.530.302.010.302.814.002.143.083.421.710.955-20-1泥晶白云岩5.409.491.214.801.070.341.160.191.120.230.590.100.550.0910.3736.7126.696.633.191.690.890.885-20-2粉砂质泥岩67.73144.7016.6662.3512.922.4810.941.7610.762.125.951.065.991.0565.75412.22367.897.633.321.461.030.60-0.010.200.080.02-0.05-0.435-20-3泥质粉砂岩78.20201.3019.7075.5916.603.1813.492.1012.242.456.521.126.381.1773.74513.78473.898.272.981.691.230.610.060.550.190.150.13-0.325-20-4褐铁矿38.0683.5310.1941.369.281.848.721.478.821.664.170.703.900.6750.20264.57220.696.592.601.791.020.59-0.030.220.160.190.20-0.255-20-5泥岩26.3265.398.4936.479.532.0410.392.0012.032.195.410.864.670.8466.19252.82177.403.801.751.781.050.59-0.33-0.05-0.030.050.23-0.175-20-6-1含粉砂泥岩85.51225.5021.8782.6815.532.6710.711.528.781.724.710.804.680.8446.75514.27521.2512.343.481.831.250.600.521.280.730.650.39-0.255-20-6-2泥岩138.00427.3037.70144.9028.334.2119.232.8616.643.228.851.508.561.5892.96935.84939.0310.883.081.801.420.520.852.261.261.190.92-0.105-20-6-3泥岩（疏松多孔）94.78285.4024.8691.1716.653.2012.831.9611.932.396.721.196.921.2965.57626.86621.139.253.601.481.410.630.351.310.580.460.19-0.285-20-6-4含褐铁矿泥岩96.40292.4025.1392.6016.893.2812.611.9111.522.296.531.166.702.3363.46635.21634.009.713.611.511.420.650.361.350.580.470.20-0.275-20-7-1泥岩89.10271.3023.8988.5016.102.9411.831.7510.282.015.600.955.431.0154.72585.41591.9311.083.501.741.410.610.521.630.810.690.38-0.215-20-7-2含粉砂泥岩102.00309.8026.89100.5019.313.6214.572.2112.972.607.151.257.141.3169.76681.08676.489.643.341.631.420.620.481.550.740.640.41-0.175-20-8粉砂质泥岩49.31189.7018.4574.6815.052.8610.791.7510.892.196.031.086.231.2358.40448.64421.025.342.071.391.510.65-0.380.370.040.06-0.04-0.425-20-9含泥砂岩85.79242.6022.1480.6215.002.8112.902.1012.762.506.841.196.951.2664.04559.50540.068.333.621.481.330.580.311.110.510.380.15-0.326-15-12含粉砂泥岩55.54108.5512.7647.218.771.819.691.559.071.595.050.815.210.8544.14312.60281.237.204.011.490.980.57注:比值单位为1，球粒陨石标准化数值引自Taylor et al.，1985；Ce=CeN/（LaN+PrN）0.5;Eu=EuN/（SmN+GdN）0.5。1040矿床地质2023 年1.99%），w(Fe2O3）=1.57%40.84%（新 鲜 基 岩 为1.0%2.15%），w(K2O）=3.52%7.06%（新鲜基岩为0.14%0.31%）和 w(SiO2)=26.67%66.29%（新鲜基岩为 1.42%18.16%）总体均呈现增加趋势；尤其是w(K2O)和 w(SiO2)则较新鲜基岩急剧上升。与之相反，w(CaO)（0.10%0.36%）和w(MgO)（0.55%1.19%）则急剧降低，推测与古风化壳剖面中白云石迅速淋失以及长英质和黏土等“不溶物”的逐渐堆积密切相关（王世杰等，1999）。（2）稀土元素分析结果显示（表 2），古风化壳中稀土元素总量REE 为（145.02935.84）10-6，明显高于新鲜基岩。(La/Yb)N值在 3.8068.42 之间，(La/Sm)N值在 0.304.08之间，(Gd/Yb)N值在 1.392.97之间，属于轻稀土元素相对富集型，配分曲线平滑右倾（图 3）。Eu 在铁岭组新鲜基岩为弱的负异常，进入风化层后下降至 0.520.65 之间，表现为明显的负异常。Ce在铁岭组白云岩中值均为负异常，而在古风化壳中大部分大于 1，指示了风化淋滤导致Ce3+离子在表生环境中氧化为不活泼 Ce4+后沉淀富集，显示正异常。5讨论5.1轻稀土元素、铷和钛元素富集特征铁岭组古风化壳剖面垂向上轻稀土元素、铷和钛元素的氧化物（分别为Ce2O3、Rb2O 和 TiO2，下同）含量总体表现为“先升高，后降低”的趋势。以紫石口剖面为例，分布规律如下：（1）Ce2O3在底部铁质黏土岩中首先出现富集，在粉砂质黏土岩中由下而上逐渐升高；向黏土岩渐变过程中随岩性中黏土物质含量的增加，而在中上部黏土岩中达到最高值（939.0310-6）。但由于陆源碎屑物质的加入，到达剖面顶部后Ce2O3含量逐渐降低，最终在进入下马岭组正常沉积层后Ce2O3含量下降至最低（图4），作者推测轻稀土元素的富集可能主要与黏土矿物的吸附作用密切相关（郭文琳等，2014）。此外，古风化壳中的铁质黏土岩Ce2O3含量明显低于黏土含量更高的黏土岩，可能是风化使黏土岩持续发生脱硅、去铁、降硫、富铝的化学反应，因此使轻稀土元素逐渐富集（金中国等，2019）。（2）Rb2O 和 TiO2显示出与Ce2O3总体协调一致的变化趋势。相关性分析(表 3)显示，Rb2O 与Ce2O3相关系数(R1)为0.72，呈现中度相关；TiO2与Ce2O3相关系数(R2)为0.84，呈现高度相关；Rb2O与TiO2相关系数(R3)为0.93，呈现显著相关。二者在古风化壳底部的粉砂质黏土岩中开始出现富集，同样向上伴随黏土质增加而进一步富集（图 4），反映了Rb和Ti与轻稀土存在密切的共伴生关系，其中Rb元素的富集可能与长石、云母及黏土化相关，由富Rb矿物分解释放和次生黏土矿物的吸附滞留两个相互竞争过程的共同控制（马英军等，1999）；而Ti元素则可能由于风化作用使原岩中分解出来的钛和稀土元素等被黏土矿物吸附而富集于风化淋滤残留物中（张彬等，2019）。5.2元素迁移规律为了精准分析古风化壳常量元素和微量稀土元素在风化过程中的迁移规律，本次运用元素质量迁移系数(j)来定量地反映元素的净迁移量（季宏兵等，1999；李艳丽等，2005），常量和稀土、微量元素分别选取Al2O3和ZrO2作为不活化元素进行计算。相应公式为：常量：j,w=(j,w/j,p)/(Al2O3,w/Al2O3,p)-1；稀土、微量：j,w=(j,w/j,p)/(Zr,w/Zr,p)-1，式中j,w,j,p代表元素 j 在风化残积层和基岩中的浓度；Al2O3,w、Al2O3,p、Zr,w和 Zr,p分 别 表 示 参 比 元 素Al2O3和Zr在风化层和基岩中的浓度。j,w值大于0代表了积累富集，反之则显示了淋滤迁出的特征。选取紫石口剖面为例，SiO2值均大于0，变化范围为 0.170.78，由底到顶表现为“降低升高降低”的变化趋势，总体显示了石英、长石等酸不溶物图3蓟县系铁岭组顶部古风化壳稀土元素球粒陨石标准化配分模式图Fig 3Chondrite normalized REE patterns of the paleo-weathering crust on the top of Tieling Formation of Jixian System第 42 卷 第 5 期张运强等：冀北蓟县系铁岭组古风化壳稀土元素富集规律及古环境意义1041图4蓟县系铁岭组顶部古风化壳Ce2O3、Rb2O和TiO2量元素含量变化趋势图1铁岭组；2古风化壳；3下马岭组；4白云岩；5含砂黏土岩；6粉砂质黏土岩；7粉砂质页岩；8黏土岩；9褐铁矿化；10紫石口剖面样品；11蓬头剖面样品；12郝家坡剖面样品；13取样位置和编号Fig.4Variation of Ce2O3，Rb2O and TiO2in the paleo-weathering crust of Tieling Formation of Jixian System1Tieling Formation;2Paleo-weathering crust;3Xiamaling Formation;4Dolomite;5Arenaceous clay;6Silty clay;7Silty shale;8Clay;9Ferruginous;10Samples from the Zishikou section;11Samples from the Pengtou section;12Samples from the Haojiapo section;13Sampling position and number质的富集特征（王世杰等，2002）；TiO2值均大于0，变化范围为0.030.58，且在垂向上总体表现出先升高再降低的趋势，总体也显示了积累富集；而Fe2O3值均小于0，大部分数值接近-1，反映了Fe元素大部分迁出；CaO和 Na2O值均小于 0，且大部分数值接近-1，反映了碳酸盐岩物质的快速风化淋滤流失（季宏兵等，1999）；值得注意的是，K2O值均大于0，除局部数值偏大以外，大部分数值较接近，可能代表了风化过程中伊利石等含 K 元素的黏土类矿物的增加（图5）。La、Ce、Pr、Nd和Sm的值基本都大于0，且数值波动较大，则反映了风化过程中轻稀土发生沉淀或被吸附，与南方现代碳酸盐岩风化壳规律较一致（图6）。此外，Ce与TiO2的净迁移量显示出近乎一致的变化规律，且最高值点附近可能是重要的风化淋滤物理化学界面；Rb与K2O也表现出很好的协调一致性，可能指示了Rb元素是以类质同象形式赋存于富K的伊利石、伊蒙混层等黏土矿物中，从而达到了显著富集。1042矿床地质2023 年表3蓟县系铁岭组顶部古风化壳微量元素分析结果(w(B)/10-6)及相关参数Table 3The trace elements analysis results(w(B)/10-6)and the related parameters of the paleo-weathering crust on the top of Tieling Formation of Jixian System组分RbSrZrNbBaHfTaThURb2OR1R2R3PTD-0泥晶白云岩11.0951.3962.641.9066.431.580.911.660.6712.130.720.840.93PTD-1黄褐色黏土岩224.8285.30278.8324.231465.048.501.9227.415.45245.98PTD-2白色黏土岩249.4