曹华文, 裴秋明, 张寿庭, 张林奎, 郑 硌, 胡昕凯

(1.中国地质调查局 成都地质调查中心，成都610081; 2.中国地质大学 地球科学与资源学院，北京 100083)



豫西栾川中鱼库锌(铅)矿床闪锌矿Rb-Sr年龄及其地质意义

曹华文1,2, 裴秋明2, 张寿庭2, 张林奎1, 郑 硌2, 胡昕凯2

(1.中国地质调查局 成都地质调查中心，成都610081; 2.中国地质大学 地球科学与资源学院，北京 100083)

中鱼库矽卡岩型锌(铅)矿床位于华北陆块南缘河南省西部栾川Mo-W-Pb-Zn-Ag多金属矿集区南部，矿体呈层状-似层状赋存于新元古界栾川群三川组碎屑岩、碳酸盐岩地层中。因缺乏精确的成矿年代学研究，对该矿床成因的争议较大。本文在矿床地质背景和岩石矿物学研究的基础上，对13件矿石样品中的闪锌矿进行Rb-Sr同位素年代学研究。闪锌矿87Rb/86Sr和87Sr/86Sr同位素比值分别集中在0.802～18.98和0.713 359～0.748 684，二者具有良好的线性关系；其等时线年龄为(136.4±0.8) Ma (2σ，MSWD=3.6)，(87Sr/86Sr)t=0.711 913±0.000 074。Rb-Sr同位素年龄反映该矿床形成于早白垩世，稍晚于研究区内的斑岩-矽卡岩型Mo-W矿床(146±2 Ma B.P.)，与区内最后一阶段花岗质岩浆活动(142～136 Ma B.P.)有关，属于栾川Mo-W-Pb-Zn-Ag多金属成矿系统。结合区域资料，认为该矿床形成于中生代陆-陆碰撞过程中由挤压向伸展转变的阶段，或碰撞后造山的局部伸展背景。

锌(铅)矿床；闪锌矿；Rb-Sr同位素；中鱼库；成矿系统

矿床成矿时代的厘定对探讨成矿物质来源、建立矿床成因模式和指导找矿勘查等具有重要的意义[1-5]。铅锌矿床的精确测龄一直是一个科学难题，前人进行过较多的探索性工作[6-11]。近年来，随着测试技术的提高与理论方法的完善，硫化物Rb-Sr同位素已成为一种直接测定铅锌矿床矿化年龄的有效方法，在实际研究中取得了许多进展[12-15]。其中，闪锌矿Rb-Sr测龄已被较为广泛地用于Pb-Zn-Ag多金属矿床成因解释[16]。

豫西栾川Mo-W-Pb-Zn-Ag多金属矿集区位于华北陆块南缘(图1-A)。近年来，该地区Mo-W矿床(147～139 Ma B.P.)的成因[17-21]、晚中生代(157～135 Ma B.P.)花岗岩的成岩过程[22-25]和区域大地构造背景[26-28]的研究较详细；但区域内的Pb-Zn-Ag多金属矿床的研究较少，且成因争议较大。部分学者认为区内Pb-Zn-Ag矿床为MVT型[29]、SEDEX型[30]或同沉积改造成因型矿床[31]；也有学者认为属热液脉型Pb-Zn-Ag矿床，受层间断裂控制，且与研究区内晚中生代花岗岩浆活动有关[32-35]。

栾川多金属矿集区北部为南泥湖-三道庄矿田，南部为近几年探明的鱼库-石宝沟矿田(图1-B)[33]。中鱼库锌(铅)矿床相对富锌，贫铅，位于鱼库矿田西端，即蜚声中外的南泥湖-三道庄矿床的南部(图1-B)。中鱼库矿床东南的银洞沟和西沟矿床属层间断裂控矿的脉状铅锌银矿床(图1-C)，发现较早且研究较为详细[30,34, 36-37]；但对新近发现的中鱼库矿床的研究较为薄弱，前人仅对中鱼库矿床的闪锌矿痕量元素[38]和隐伏岩体[22]做过部分研究。本文在中鱼库矿床地质特征研究的基础上，采用闪锌矿Rb-Sr测龄方法，厘定该矿床的成矿时代，并与研究区内晚中生代花岗岩成岩时代、斑岩-矽卡岩型Mo-W矿床成矿时代进行对比，探讨中鱼库锌(铅)矿床的成因和构造背景。

图1 鱼库-赤土店锌铅银矿带地质简图Fig.1 Simplified geological map of the Yuku-Chitudian Zn-Pb-Ag belt(A)秦岭造山带大地构造背景简图(据文献[22]修编)；(B)栾川钼钨铅锌银矿集区地质简图(据文献[22]修编)；(C)中鱼库锌(铅)矿床矿体分布简图(据文献[31]修编)。Pz1s.三岔口组; Pt3y.鱼库组; Pt3d.大红口组; Pt3m.煤窑沟组; Pt3n.南泥湖组; Pt3s.三川组; Pt2b.白术沟组; 5.燕山早期花岗岩; ν3.加里东期变辉长岩-变正长斑岩

1 区域地质背景

秦岭造山带从北到南，包括华北板块南缘(即华熊地体)，北秦岭造山带、南秦岭造山带和扬子板块北缘；分别被栾川断裂、商丹缝合带和勉略缝合带分割。豫西栾川矿集区在大地构造位置上位于华北克拉通南缘与北秦岭造山带东段的结合部位(图1-A)。栾川矿集区内一系列金属矿床围绕中酸性小岩体呈规律性分布，构成了一个从中心到外围的斑岩型-矽卡岩型Mo-W矿床(内带)→矽卡岩型Mo-Pb-Zn矿床(过渡带)→中低温热液脉型Pb-Zn-Ag矿床(外带)的成矿系列。中鱼库锌(铅)矿床被认为是过渡带的典型代表[33, 39]。

研究区内主要出露地层为长城系熊耳群、蓟县系官道口群、新元古界栾川群和下古生界陶湾群(图1)。其中官道口群白术沟组，栾川群三川组、煤窑沟组为区域主要赋矿层位，层控性明显。区内主体构造格局的形成主要受控于华北板块与扬子板块的碰撞，以及太平洋板块向欧亚板块的俯冲。整体构造线方向以北西西向为主，同时发育北东向、近南北向断裂构造。区内岩浆活动频繁而强烈，岩浆岩比较发育，主要有新元古代前加里东期变正长斑岩、变辉长岩和中生代燕山期花岗岩。其中，以燕山期上房沟、南泥湖、黄背岭、鱼库、石宝沟及火神庙等中酸性岩体与成矿作用的关系最为密切；多呈小岩株、岩脉状产于区域断裂交汇部位。

2 矿床地质特征

中鱼库锌(铅)矿床位于河南省栾川县陶湾镇鱼库村，赋矿地层为新元古界栾川群三川组(Pt3s)，主要为一套碳酸盐岩夹少量碎屑岩沉积(图1，图2)。三川组可分为上、下两段，下段(Pt3s1)以灰白色变石英砂岩为主，夹钙质粉砂岩及薄层炭质板岩，岩石致密坚硬，底部含燧石，厚度326.55 m；上段(Pt3s2)以大理岩为主，不同地段存在一定差异，其中上部主要为灰白色-青灰色中厚层状大理岩、黑云母大理岩，下部则以条带状大理岩夹钙质粉砂岩薄层为主，厚度289.86 m(图2)。矿区东南部出露燕山期鱼库二长花岗岩，西南部出露黄背岭黑云母二长花岗岩[22]。近期在中鱼库矿区钻孔中发现隐伏岩体——黑云母二长花岗岩，属壳幔混源的I型花岗岩，主要矿物为斜长石、钾长石、石英和黑云母，副矿物有磁铁矿、钛铁矿、磷灰石、金红石和锆石等。

矿区围岩蚀变类型主要为矽卡岩化，另发育角岩化，蚀变围岩为透辉石矽卡岩、石榴子石透辉石矽卡岩、透辉石角岩等。矽卡岩化可以分为石榴石-透辉石矽卡岩，主要形成硅灰石、钙铝榴石和透辉石等；阳起石-绿帘石矽卡岩，形成大量含水硅酸盐矿物[38]。矿区内共发现3条锌铅金属矿体，呈层状-似层状赋存于矽卡岩及角岩中。其中，S068是中鱼库矿床规模最大的矿体，分布于榆木沟-札子沟一带(图2)，延伸近2.2 km；沿走向厚度变化较大，最厚处可达16.32 m，最薄处仅1.10 m；产状与地层近于一致，倾向355°～50°，倾角15°～65°。

图2 中鱼库锌(铅)矿床S068矿脉实测剖面图Fig.2 Geological cross section of S068 vein in the Zhongyuku Zn-Pb deposit(据文献[31]修编)

矿石结构主要呈半自形-自形粒状结构，少量交代残余结构等(图3)。矿石构造有块状构造、条带状构造、浸染状构造、团块状构造及少量蜂窝状构造、土状构造等。矿石矿物主要为黄铁矿、铁闪锌矿、磁黄铁矿、黄铜矿及方铅矿等，脉石矿物为石英、白云石、透辉石和石榴子石等，还可见少量方解石和白云母等。Zn品位(质量分数：w)为0.35%～4.21%，平均3.43%；Pb品位为0.01%～1.10%，平均0.08%；Ag品位为(2.79～16.40)×10-6，平均9.18×10-6[31]。

根据矿体野外地质特征和矿物镜下鉴定，可以将区内成矿作用划分为3个阶段：(1)矽卡岩阶段，早期主要形成硅灰石，钙铝榴石和透辉石等；晚期则形成大量含水硅酸盐矿物，如阳起石、绿帘石以及钾长石等。(2)石英-硫化物阶段，为成矿主阶段，形成大量的闪锌矿、磁黄铁矿等。(3)石英-碳酸盐阶段，形成大量的热液石英和方解石等。其中石英-硫化物阶段可以细分为早阶段闪锌矿+黄铁矿+黄铜矿+磁黄铁矿组合(图3-D、E)；中阶段闪锌矿+黄铁矿+(黄铜矿)组合(图3-F、G);晚阶段形成闪锌矿+磁黄铁矿+黄铜矿+(黄铁矿)+(方铅矿)+(辉钼矿)组合(图3-H、I)。

图3 中鱼库锌(铅)矿床矿石典型结构构造特征Fig.3 Typical textures and structures of sulfide ores from the Zhongyuku Zn-Pb deposit(A)块状矽卡岩化矿石; (B)矽卡岩化矿体; (C)3个阶段的矿化作用; (D)成矿早阶段，闪锌矿(sph1)与黄铜矿(cp1)，黄铜矿(cp1)与磁黄铁矿(po1)，黄铁矿(py1)与磁黄铁矿(po1)分别具有共结边结构，四者近同期形成; (E)成矿早阶段，闪锌矿(sph1)与黄铜矿(cp1)、黄铁矿(py1)具有共结边结构，三者近同期形成; (F)成矿中阶段，黄铁矿(py2)交代早阶段磁黄铁矿(po1)，并穿插破碎的脉石矿物(gn); (G)成矿中阶段，形成大量的黄铁矿(py2)，交代早阶段磁黄铁矿(po1); (H)成矿晚阶段，形成大量的磁黄铁矿(po2)， 交代中阶段黄铁矿(py2); (I)成矿晚阶段，大量磁黄铁矿(po2)、闪锌矿(sph3)和黄铜矿(cp2)交代中阶段黄铁矿(py2)。图(D)-(I)均为反射光单偏光镜下照片，红色标尺长50 μm

3 分析测试

本次研究的13件闪锌矿样品均采自中鱼库矿区斜井以及坑道中的新鲜未经风化的矿石，主要采集矽卡岩阶段和石英-硫化物阶段的矿石样品。矿石样品挑纯至纯度99%以上，研磨至粒度<200目。闪锌矿单矿物粉末样品经过如下处理：①Teflon高压密闭熔样法熔样；②稀盐酸-硝酸溶解稀释；③Rb、Sr化学分离和提纯等。其Rb、Sr含量和同位素比值在南京大学现代分析中心同位素分析室的VG 354同位素质谱仪上完成。详细实验测试方法和流程参见文献[40-42]。

美国同位素标样(NBS987)87Sr/86Sr比值测试结果为0.710 233±6 (2σ)，与标准值(0.710 340±260)误差<0.015%。Sr和Rb的实验背景值分别为0.2×10-9g和0.3×10-9g。87Rb/86Sr和87Sr/86Sr比值不确定度(2σ)分别为1%和0.01%，置信度95%。Rb-Sr等时线年龄采用Isoplot(4.15)程序计算[43]，其中λRb=1.42×10-11a-1。

中鱼库闪锌矿Rb和Sr同位素组成见表1。其Rb的质量分数(wRb)为(0.0853～12.86)×10-6，wSr为(0.2834～1.989)×10-6，87Rb/86Sr和87Sr/86Sr比值分别为0.802～18.98和0.713 359～0.748 684。获得等时线年龄为(136.4±0.8) Ma (2σ，MSWD=3.6)，(87Sr/86Sr)t=0.711 913±0.000 074(图4)，地质时代为早白垩世。

图4 中鱼库锌(铅)矿床闪锌矿87Rb/86Sr和87Sr/86Sr关系及等时线年龄Fig.4 Rb-Sr isochron age of sphalerites from the Zhongyuku Zn-Pb deposit

表1 中鱼库锌(铅)矿床闪锌矿Rb-Sr同位素分析结果

4 讨 论

4.1 成矿时代

中鱼库闪锌矿(87Rb/86Sr)-(87Sr/86Sr)等时线年龄图上(图4)，所有的样品点均落在等时线上，且13个数据点加权平均方差(MSWD)为3.6,说明数据点离散程度较低，等时线可信度较高，闪锌矿形成过程中Sr同位素均一、封闭。其(87Sr/86Sr)-(1/Rb)(图5-A)和(87Rb/86Sr)-(1/Rb)之间不存在线性关系，表明不同阶段闪锌矿形成期间(87Rb/86Sr)t基本上保持不变[14]。其(Rb/Sr)-(87Sr/86Sr)值(图5-B)和(Rb/Sr)-(87Rb/86Sr)之间呈正相关关系，表明样品中87Rb和放射性成因的87Sr与样品的初始Rb含量有关[44]。因此，本次研究测定的闪锌矿Rb-Sr同位素等时线年龄(136.4±0.8 Ma)应代表其结晶成矿的年龄。

图5 中鱼库锌(铅)矿床闪锌矿Rb、Sr及其同位素关系图Fig.5 Covariant diagrams of sphalerite Rb and Sr concentrations and its isotopes for Zhongyuku Zn-Pb deposit

4.2 矿床成因

栾川Mo-W-Pb-Zn-Ag矿集区内，中鱼库北部的冷水北沟Pb-Zn-Ag矿床石英Ar-Ar年龄为138 Ma[32]，东南部的西沟和西北部的三道沟Pb-Zn矿床Rb-Sr年龄分别为137 Ma和138 Ma[33]。本次研究的中鱼库锌(铅)矿床成矿年龄(136 Ma)与上述三者在误差范围内一致，表明研究区内Pb-Zn-Ag矿化时代集中在(137±1) Ma B.P.(表2，图6)。中鱼库矿区隐伏的黑云母二长花岗岩锆石U-Pb年龄为(154.1±1.8) Ma[22]，辉钼矿Re-Os年龄为(146.2±0.9) Ma[22](表2)，早于中鱼库铅锌矿化时代。

从栾川矿集区内花岗岩成岩年龄、Mo-W矿床及Pb-Zn-Ag多金属矿床成矿年龄统计中(表2，图6)可以发现，研究区内花岗岩岩浆活动可以细分为3个阶段：158～152 Ma B.P.、150～144 Ma B.P.、142～136 Ma B.P.；斑岩-矽卡岩型Mo-W矿床的成矿年龄为147～139 Ma，峰值为146 Ma，与第二阶段晚侏罗世晚期岩浆活动有关(图6)；热液脉型Pb-Zn-Ag矿床主要形成于137 Ma B.P.，与第三阶段早白垩世早期岩浆活动时代接近。

矿集区内花岗岩(87Sr/86Sr)t值为0.706 1～0.709 8(均值为0.707 9)[45-46]；赋矿围岩地层(87Sr/86Sr)t值分散，为0.712 2～0.835 7(均值为0.761 3)[47]。而西沟Pb-Zn矿床(87Sr/86Sr)t为0.709 9～0.748 3(均值为0.720 8)[33,47]；百炉沟Pb-Zn矿床(87Sr/86Sr)t为0.713 8～0.721 3(均值为0.716 9)[33]；三道沟Pb-Zn矿床(87Sr/86Sr)t为0.710 5～0.712 6(均值为0.711 6)[33]；本次研究的中鱼库Zn-Pb矿床(87Sr/86Sr)t为0.711～0.712 8(均值为0.711 9)：矿集区内Pb-Zn矿床Sr同位素比值与研究区内花岗岩的值接近，远小于赋矿地层(图7)，表明Pb-Zn矿床的物质来源主要为燕山期花岗岩。

中鱼库锌(铅)矿床为典型的矽卡岩型矿化特征(图2和图3)；闪锌矿痕量元素与岩浆热液脉型Pb-Zn矿床特征符合[38]；闪锌矿(87Sr/86Sr)t值与花岗岩接近；且成岩成矿年龄相近，远小于赋矿围岩地层年龄：这些证据表明中鱼库矿床属于与区内岩浆岩(如中鱼库隐伏岩体[22]，图1-C)有关的矽卡岩型铅锌矿床。研究区内热液脉型-矽卡岩型Pb-Zn矿床[32,34]、斑岩-矽卡岩型Mo-W矿床[17-18]与区内晚侏罗世-早白垩世花岗岩活动构成一个统一的岩浆-热液-成矿系统。

4.3 成矿构造背景

晚古生代晚期至三叠纪末期，秦岭洋(商丹洋+勉略洋)逐渐俯冲、消减和闭合[54]，南、北秦岭微地块(造山带)分别与扬子板块和华北板块拼合，形成勉略缝合带和商丹缝合带[55](图1-A)，至此，研究区进入板内陆-陆碰撞造山环境[28,56-57]。在强烈的碰撞挤压背景下，晚侏罗世-白垩纪(150～100 Ma B.P.)时期，华北板块沿鲁山-淮南断裂(图1-A中F1断裂)向南俯冲于华雄地体下[28]；同时，在栾川断裂(图1-A中F2

断裂)以北的研究区内(即华北板块南缘或华雄地体)，由于发生挤压向伸展转变的过程[23]，形成大量的I型和A型花岗岩，并伴生大量的Mo-W-Pb-Zn-Ag-Au矿床[24,26,58-60]。研究区内Pb-Zn-Ag矿化时代集中在(137±1) Ma B.P.，即形成于秦岭造山带中生代陆-陆碰撞过程中由挤压向伸展转变的阶段，或碰撞后造山的局部伸展背景。

5 结 论

a.中鱼库Zn-Pb矿床13件闪锌矿Rb-Sr等时线年龄为(136.4±0.8) Ma，指示该矿床形成于早白垩世，矿床成因为与岩浆活动有关的矽卡岩型矿床。

b.栾川矿集区内矽卡岩型-热液脉型Pb-Zn-Ag矿成矿年龄(137±1 Ma)晚于区内斑岩-矽卡岩型Mo-W矿床的成矿年龄(146±2 Ma)，与区内最后一阶段花岗岩浆活动(142～136 Ma B.P.)有关；它们共同构成Mo-W-Pb-Zn-Ag多金属成矿系统。

c.该矿床形成于中生代陆-陆碰撞过程中由挤压向伸展转变的阶段，或碰撞后造山的局部伸展背景。

野外工作期间得到河南省地质调查院和栾川县地质矿产局的大力支持，成文过程中得到燕长海教授级高工悉心指导和修改，使本文得以完善，在此一并致以诚挚的感谢！

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Rb-Sr dating and geological significance of sphalerites from the Zhongyuku Zn(Pb) deposit in Luanchuan, West Henan, China

CAO Hua-wen1,2, PEI Qiu-ming2, ZHANG Shou-ting2, ZHANG Lin-kui1, ZHENG Luo2，HU Xin-kai2

1.ChengduCenter,ChinaGeologicalSurvey,Chengdu610081,China; 2.SchoolofEarthSciencesandResources,ChinaUniversityofGeosciences,Beijing100083,China

Zhongyuku skarn type Zn (Pb) deposit is located in the southern part of Luanchuan Mo-W-Pb-Zn-Ag polymetallic ore district, southern margin of the North China Block. Bedded ore bodies occur in clastic and carbonate strata in the Sanchuan Formation of the Neoproterozoic Luanchuan Group. However, the genesis of this deposit is controversial, because of the lack of accurate metallogenic geochronology. Based on the study of geological setting, petrology and mineralogy of the deposit, the Rb-Sr isotopic compositions of sphalerite from 13 ore samples are analyzed. It shows that87Rb/86Sr and87Sr/86Sr isotopic compositions have a linear correlation, ranging from 0.802 to 18.980 and 0.713 359 to 0.748 684 respectively, and it reveals that the isochron age is (136.4±0.8) Ma (2σ, MSWD=3.6), and (87Sr/86Sr)tis 0.711 913±0.000 074, indicating that the Zhongyuku deposit formed in early Cretaceous period, slightly later than porphyry-skarn type molybdenum-tungsten deposits in the Luanchuan ore district. It is considered that the formation of the Zhongyuku deposit associates with the last stage of granitic magma activities (142～136 Ma B.P.) in the ore district. The porphyry-skarn-type Mo-W deposits and skarn-type Zn-Pb deposit constitute a Mo-W-Pb-Zn-Ag polymetallic metallogenic system. The study indicates that the Zhongyuku deposit possibly formed in a transition stage from compression to extension setting during continent-continent collision process in Mesozoic, or locally extension setting of post-collision orogenic process.

Zn (Pb) deposit; sphalerite; Rb-Sr isotope; Zhongyuku; metallogenic system

10.3969/j.issn.1671-9727.2016.05.03

1671-9727(2016)05-0528-11

2015-08-13。

国家“十二五”科技支撑计划项目(2011BAB04B06); 中国地质调查局地质调查项目(12120115022701; 1212011220925)。

曹华文(1988-)，男，博士，助理研究员，研究方向：矿产资源勘查与评价，E-mail:caohuawen1988@126.com。

裴秋明(1989-)，男，博士研究生，研究方向：矿产资源勘查与评价，E-mail:peiqm2010@163.com。

P597

A