揚(yáng)子陸塊北緣馬元鉛鋅礦床地質(zhì)和地球化學(xué)特征

1、2008年2月Feb.,2008礦床地質(zhì)MIN ERAL DEPOSITS第27卷第1期Vol.27No.1文章編號(hào):025827106(20080120037212揚(yáng)子陸塊北緣馬元鉛鋅礦床地質(zhì)和地球化學(xué)特征王曉虎1,薛春紀(jì)2,333,李智明1,4,李強(qiáng)5,楊榮進(jìn)6(1長(zhǎng)安大學(xué)資源學(xué)院,陜西西安710054;2中國地質(zhì)大學(xué)地質(zhì)過程與礦產(chǎn)資源國家重點(diǎn)實(shí)驗(yàn)室,北京100083;3中國地質(zhì)大學(xué)地學(xué)院,北京100083;4西安地質(zhì)礦產(chǎn)研究所,陜西西安710054;5長(zhǎng)江大學(xué)地球科學(xué)學(xué)院,湖北荊州434023;6陜西地礦局漢中地質(zhì)大隊(duì),陜西漢中723000摘要馬元鉛鋅礦床是近年在揚(yáng)子陸塊北緣鉛鋅找礦的新

2、突破。礦床主要形成于邊緣基底隆起翼部震旦系燈影組中,礦體呈層狀、似層狀產(chǎn)于角礫化白云巖層間構(gòu)造帶中,圍巖蝕變很弱。礦石中硫化物以閃鋅礦、方鉛礦為主,礦物成分簡(jiǎn)單,中粗粒晶質(zhì)結(jié)構(gòu),充填于白云巖角礫間。礦石中礦物流體包裹體記錄的成礦流體溫度為100 320,密度為0185011068g/cm3,估算成礦流體壓力為24193117MPa,相應(yīng)成礦深度9001198m。礦石中硫化物的34S V2CDT為121941914,且34S黃鐵礦>34S閃鋅礦>34S方鉛礦;硫酸鹽礦物的34S為321233148, H2S來自海相硫酸鹽的還原。礦石硫化物206Pb/204Pb為1716218102,

3、207Pb/204Pb為1514915163,208Pb/204Pb為3715738135,成礦金屬來源于震旦紀(jì)寒武紀(jì)地層。礦石中熱液脈石礦物的13C V2PDB為-312-112,18O V2SMOW為19142114,成礦流體中CO2為震旦系碳酸鹽巖的溶解成因。馬元鉛鋅礦床成礦流體可能為起,伴隨碑壩穹隆構(gòu)造過程,成礦流體沿?zé)粲敖M白云巖層間(滑脫或溶塌構(gòu)造從蓋層沉積中心向隆起邊部運(yùn)動(dòng)并發(fā)生熱液充填成礦,在成因上為MV T鉛鋅礦床。關(guān)鍵詞地球化學(xué);鉛鋅礦床;礦床地質(zhì);馬元;揚(yáng)子陸塊北緣中圖分類號(hào):P618142;P618143文獻(xiàn)標(biāo)識(shí)碼:AG eological and geochemical

4、 characteristics of Mayuan Pb2Zn ore deposit onnorthern margin of Yangtze landmassWAN G Xiao Hu1,XU E ChunJi2,3,L I ZhiMing1,4,L I Qiang5and YAN G RongJin6(1School of Earth Sciences and Land Resources,Changan University,Xian710054,Shaanxi,China;2State K ey Laboratory of G eological Processes and Min

5、eral Resources,School of Earth Sciences and Resources,China Universit y of G eosciences,Beijing 100083,China;3China University of G eosciences,Beijing100083,China;4Xian Institute of G eology and Mineral Resources, Xian710054,Shaanxi,China;5School of Earth Sciences,Y an gtze University,Jingzhou434023

6、,Hubei,China;6HanzhongG eological Party,Shaanxi Bureau of G eology and Mineral Resources,Hanzhong723000,Shaanxi,ChinaAbstractMayuan is a newly discovered Zn2Pb ore deposit on the northern margin of Yangtze landmass.The ore de2 posit mainly occurs in the Sinian Dengying Formation around an old baseme

7、nt dome.The ore body is bedded and stratoid in form and lies in a structural zone of dolomite breccias along the stratification,and the wall2rock alter2 ation is weak.The sulfide minerals sphalerite and galena are simple and assume medium to coarse grained crys2 tals in the ore,and fill the dolomite

8、 breccias.Studies of fluid inclusions in some gangue minerals and sphalerite本文得到中國地質(zhì)調(diào)查局綜合研究項(xiàng)目(1212010511807和教育部?jī)?yōu)秀青年教師資助計(jì)劃的聯(lián)合資助第一作者簡(jiǎn)介王曉虎,男,1983年生,在讀碩士研究生,研究方向?yàn)榈V床地球化學(xué)。E2mail:wangzykc33通訊作者薛春紀(jì),男,1962年生,博士,教授,從事礦床學(xué)、礦產(chǎn)普查與勘探教學(xué)的研究工作。E2mail:chun ji.xue 收稿日期2007209221;改回日期2007210223。李德先、張綺玲編輯。show that the o

9、re2forming fluid temperatures are100320,the ore fluid densities are0185011068g/cm3, the fluid pressures are24193117MPa and the corresponding metallogenic depths are9001198m.The 34SV2CD Tof sulfides are121941914and34S pyrite>34S sphalerite>34S galena,and the34S of barite are 321233148.The miner

10、alization H2S resulted from marine sulfate reduction.The206Pb/204Pb of ore sul2 fide are1716218102,207Pb/204Pb are1514915163,208Pb/204Pb are3715738135,and the ore metals were derived from the Sinian2Cambrian strata.13C V2PDB of the hydrothermal gangue mineral calcite are-312-112,18O V2SMOW are191421

11、14,and the CO2in the ore2forming fluid was derived from the disso2 lution of Sinian carbonates.The ore2forming fluid was a basin brine of middle2lower temperature and might have originated from Sinian2Cambrian sediments.With the Beiba dome2structure process,the fluid migrated from the sedimentary ce

12、nter to the margin of the dome along the structure zone between the stratifications and,as a re2 sult,the hydrothermal space2filling mineralization occurred.The Mayuan Zn2Pb ore deposit is genetically a MV T deposit.K ey w ords:geochemistry,Zn2Pb ore deposit,geology,Mayuan,northern margin of Yangtze

13、 landmass大型盆地或古陸邊緣盆地是鉛鋅礦床形成的重要地質(zhì)環(huán)境,沉積巖為主巖的鉛鋅礦床金屬儲(chǔ)量占世界鉛鋅總儲(chǔ)量的80%左右(Deb et al.,2004。揚(yáng)子陸塊西南邊緣震旦系、古生界和三疊系中產(chǎn)有許多重要鉛鋅礦床(邵世才等,1997;周朝憲,1998;韓潤生等,2001;黃智龍等,2001a;2001b;王獎(jiǎng)?wù)榈? 2001;方維萱等,2001;芮宗瑤等,2004;付紹洪等, 2004;林方成,2005;張長(zhǎng)青等,2005,東部邊緣也形成重要礦床(謝樹成等,1997;葉水泉等,2000;芮宗瑤等,2004;徐忠發(fā)等,2006,揚(yáng)子陸塊周邊地區(qū)沉積巖中鉛鋅礦的資源潛力受到高度關(guān)注。近年

14、,在揚(yáng)子陸塊北緣震旦系中發(fā)現(xiàn)了馬元等鉛鋅礦床,它們層控特征明顯,鉛鋅礦資源潛力大,引起關(guān)注。齊文等(2004;2006從礦床的發(fā)現(xiàn)角度探討了馬元鉛鋅礦的地質(zhì)特征,薛春紀(jì)等(2006; 2007探討了馬元鉛鋅礦的成礦模式,侯滿堂等(2006;2007a;2007b分析了馬元鉛鋅礦的地質(zhì)特征和找礦的方向及遠(yuǎn)景,李厚民等(2007研究了馬元鉛鋅礦的地球化學(xué)特征,指出馬元鉛鋅礦的成礦時(shí)代為早奧陶世(486±12Ma。本文擬較系統(tǒng)地研究馬元鉛鋅礦床地質(zhì)和地球化學(xué)性質(zhì),分析礦床類型和勘查方向,以期服務(wù)于揚(yáng)子周緣相關(guān)鉛鋅礦床的勘查和研究。1區(qū)域地質(zhì)馬元鉛鋅礦床位于揚(yáng)子陸塊北緣,陜西漢中南部碑壩(雜

15、巖穹隆的周邊。區(qū)域基底由中2上元古界火地埡群和晉寧2澄江期變中酸性侵入巖2基性雜巖等構(gòu)成,火地埡群由中2深變質(zhì)火山碎屑巖夾中基性火山熔巖、大理巖及混合巖組成。蓋層由震旦系上統(tǒng)寒武系下統(tǒng)被動(dòng)大陸邊緣碳酸鹽巖2碎屑巖系組成,震旦系上統(tǒng)為燈影組,底部有底礫巖,下段為砂巖、含礫砂巖,上段為層紋狀藻屑白云巖夾中厚層狀白云巖、厚層白云巖、礫屑白云巖、角礫狀白云巖、含燧石條帶白云巖和薄層白云巖;寒武系下統(tǒng)為郭家壩組,底部零星分布有含鈷鋁土礦層,下段是炭質(zhì)板巖、含炭粉砂質(zhì)板巖,上段是粉砂質(zhì)板巖、泥質(zhì)板巖、泥灰?guī)r。基底與蓋層之間不整合接觸。震旦系上統(tǒng)是區(qū)域上重要的鉛鋅賦礦層位。在漢南碑壩地區(qū),蓋層圍繞基底環(huán)形分

16、布,表現(xiàn)為一大型穹隆構(gòu)造,核部為火地埡群及晉寧2澄江期中酸性2基性雜巖體,翼部為震旦系上統(tǒng)寒武系下統(tǒng),震旦系寒武系本身發(fā)育舒緩復(fù)式向斜和背斜構(gòu)造。受燈影組角礫狀白云巖層位控制,鉛鋅礦體也圍繞穹隆核部呈帶狀展布(圖1。漢中南部碑壩穹隆構(gòu)造是重要的控礦構(gòu)造,不僅控制了本區(qū)基底和蓋層的分布,而且穹隆化過程很可能引起翼部燈影組厚層白云巖發(fā)生層間滑動(dòng)而形成滑脫構(gòu)造,并可能伴隨網(wǎng)狀張性裂隙和角礫化,為鉛鋅硫化物沉淀提供了良好場(chǎng)所。區(qū)域巖漿活動(dòng)主要是作為基底組成部分的中新元古界火地埡群英安巖、流紋巖、玄武巖和晉寧2澄江期侵入的黑云母花崗巖、花崗斑巖、斜長(zhǎng)花崗巖、閃長(zhǎng)巖、輝長(zhǎng)巖、輝綠巖及超基性巖等,它們不同程

17、度發(fā)生了變質(zhì)。震旦系上統(tǒng)寒武系下統(tǒng)蓋層沉積區(qū)無巖漿巖出露。83礦床地質(zhì)2007年2礦床地質(zhì)馬元鉛鋅礦床位于漢中南部碑壩穹隆構(gòu)造南翼的孔隙溝2楠木樹2尖硐子溝一帶(圖1,N EE 向或近EW 向展布。沿震旦系燈影組層位順層勘查,先后在穹隆東翼麻地坪2松坪2安山一帶發(fā)現(xiàn)SN 向礦帶,在穹隆北翼西河2地坪一帶發(fā)現(xiàn)N EE 走向的礦帶。本文以南翼礦帶為重點(diǎn)揭示礦床地質(zhì)特征。礦體呈層狀、似層狀產(chǎn)于燈影組角礫狀白云巖層中,與上下盤巖層基本整合(圖2。礦體局部有分枝復(fù)合及膨大狹縮,膨大處往往形成礦囊,厚度增大,礦石品位增高。從地表到深部,礦石品位與厚度有增大的趨勢(shì) 。圖1馬元鉛鋅礦田地質(zhì)圖(據(jù)齊文等,200

18、4Fig.1G eological map of the Mayuan lead 2zinc orefield ,Hanzhong ,Shaanxi Province (after Qi et al.,200411g 寒武系下統(tǒng)郭家壩組炭質(zhì)板巖;2Z 2dn 震旦系燈影組白云巖夾砂巖;3Pt 223h 中2上元古界火地埡群火山碎屑巖夾中基性火山熔巖;4223b 2花崗斑巖;5223b 2黑云母花崗巖;62222閃長(zhǎng)巖;7223a 2黑云母斜長(zhǎng)花崗巖、斜長(zhǎng)花崗巖;8v 2222輝長(zhǎng)巖;9鉛鋅礦帶;10地質(zhì)界線;11斷裂1Carbonaceous slate of Lower Cambrian G

19、uojiaba Formation ;2Dolimite intercalated with sandstone of Upper Sinian Dengying Formation ;3Volcanic clastic rocks intercalated with intermediate 2basic lava of Middle 2Upper Proterozoic Huodiya Group ;42-3b 2Granite porphyry ;52-3b 2Granitite ;62-22Diorite ;72-3a 2Biotite plagiogranite ,plagiogra

20、nite ;8v 2-22G abbro ;9Lead 2zinc ore belt ;10G eological boundary ;11Fault.93第27卷第1期王曉虎等:揚(yáng)子陸塊北緣馬元鉛鋅礦床地質(zhì)和地球化學(xué)特征圖2馬元鉛鋅礦床楠木樹礦段勘探線剖面圖(齊文等,2004Fig.2Exploration section of Nanmushu ore block in the Mayuan lead2zinc deposit礦石自然類型為鉛鋅礦化角礫狀白云巖,氧化礦石呈灰黃色,原生礦石呈深紅2灰白色。鉛鋅硫化物礦化主要發(fā)生在角礫狀白云巖的礫間空洞或膠結(jié)物中,呈空隙、裂隙充填狀產(chǎn)出,白云巖

21、角礫比較干凈,無礦化及明顯蝕變現(xiàn)象。賦存在角礫之間膠結(jié)物中的礦石礦物主要為閃鋅礦,次為方鉛礦。角礫化強(qiáng)烈的白云巖中礦化強(qiáng)度高,往往形成富礦體,而碎裂化程度低的白云巖中脈狀、網(wǎng)脈狀礦化較弱,鉛鋅品位較低。礦石礦物成分簡(jiǎn)單,以閃鋅礦、方鉛礦為主,表生礦物包括少量菱鋅礦、水鋅礦、紅鋅礦、異極礦、鋅釩、白鉛礦;脈石礦物以白云石、方解石、黃鐵礦、磁鐵礦為主,另見石英、重晶石、螢石、瀝青、粘土質(zhì)、碳質(zhì)等。礦石中硫化物礦物以不規(guī)則中粒晶質(zhì)結(jié)構(gòu)為主,也見他形粒狀結(jié)構(gòu)、包含結(jié)構(gòu)及黃鐵礦的草莓狀結(jié)構(gòu);礦石以白云巖角礫空隙、裂隙充填構(gòu)造為主,也見網(wǎng)脈狀及浸染狀構(gòu)造,角礫多為白云巖(圖3,大小不等,呈不規(guī)則狀分布,棱

22、角明顯,無方向性,顯示了原地碎裂等張性構(gòu)造特點(diǎn)。鋅礦物呈不規(guī)則的、大小不等的團(tuán)塊狀,也有呈似條紋狀或條帶狀、網(wǎng)脈狀,還有的沿角礫或方解石2石英脈、重晶石脈的邊部斷續(xù)呈似脈狀充填在角礫之間。在脈內(nèi)偶爾見到不規(guī)則狀的閃鋅礦、方鉛礦團(tuán)塊,并可見到少量的閃鋅礦呈薄膜狀附著在節(jié)理面上。礦石中黃鐵礦的電子探針分析表明(表1,本區(qū)黃鐵礦中鐵含量為45104%46127%,平均為45165%;硫含量為52116%53114%,平均為52161%;S/Se比值為10628。與黃鐵礦的理論值(Fe=46155%、S=53145%相比,硫和鐵均顯虧損,這些化學(xué)成分特點(diǎn)與熱液成因黃鐵礦的相應(yīng)特征相似。礦石中閃鋅礦的C

23、d含量變化于(5405120×10-6(表1,晶體不同部位Cd含量有明顯變化,從中心到邊部,Cd的含量逐漸增大,中心540×10-6,中間1630×10-6,邊部5120×10-6。鉛鋅礦床中閃鋅礦富Cd,富集程度受成礦流體的硫離子活度、成礦溫度、p H和Cd/Zn比值等物理化學(xué)條件的制約,硫離子活度低、成礦溫度低、p H值低和Cd/Zn 比值高,有利于Cd在閃鋅礦中的富集(Schwartz, 2000。閃鋅礦Cd含量及變化反映出,從礦化早階段到晚階段可能伴隨著成礦流體的硫離子活度、成礦溫度和p H值的降低和Cd/Zn比值的增高。04礦床地質(zhì)2007年

24、圖3馬元鉛鋅礦床礦石構(gòu)造照片F(xiàn)ig.3Photos of Ore fabrics of the Mayuan lead 2zinc deposit ,Hanzhong ,Shaanxi表1馬元鉛鋅礦石中金屬礦物的電子探針分析結(jié)果(w B /%T able 1E lectric microprobe analyses of metallic minerals in the Mayu an Z n 2Pb deposit ,H anzhong ,Shaanxi(w B /%樣品號(hào)礦物As SInSeZn SnG ePbSbCuC oFeCdNiAgAu 總和PD22B2磁鐵礦0.0210.0360

25、.017 3.260-0.1200.0230.0690.03353.150-0.008-56.737PD22B3黃鐵礦-52.160-0.001-0.0550.0060.0360.07245.1800.019-0.035-97.563PD22B3閃鋅礦-31.8200.012-66.6200.039-0.0510.053-0.2660.029-0.01098.900K XG 25黃鐵礦0.20452.4900.009-0.122-0. 0580.09445.040-0.11498.131K XG 25閃鋅礦-32.610-0.00766.5000.0020.093-0.136-0.0810.0

26、54-0.02099.503K XG 25閃鋅礦0.00932.640-65.840-0.1060.026-0.2450.0400.1090.163-99.179K XG 25閃鋅礦-31.840-65.460-0.0100.0980.1250.512-98.045MY 216黃鐵礦-53.140-0.005-0.04146.2700.007-99.464MY 217黃鐵礦0.20552.650-0.0860.004-0.032-0.0700.08046.1100.027-0.03299.297測(cè)試單位:國土資源部成礦作用及其動(dòng)力學(xué)開放研究實(shí)驗(yàn)室。儀器型號(hào)為J XA 28100?！?”為未檢測(cè)

27、出。圖4馬元鉛鋅礦石及其中的瀝青Fig.4Ore and asphalt in the Mayuan Zn 2Pb deposit ,Hanzhong ,Shaanxi礦區(qū)內(nèi)圍巖蝕變較弱,與鉛鋅礦化有關(guān)的蝕變主要有硅化、重晶石化,其次為白云石化、螢石化、瀝青化。硅化和重晶石化主要以膠結(jié)物形式與閃鋅礦等同時(shí)充填于角礫間及裂隙內(nèi),對(duì)白云巖角礫無明顯的交代現(xiàn)象。瀝青充填于白云巖的角礫之間或呈水滴狀嵌布于沿洞壁生長(zhǎng)的水晶晶簇之間(圖4。14第27卷第1期王曉虎等:揚(yáng)子陸塊北緣馬元鉛鋅礦床地質(zhì)和地球化學(xué)特征 圖5馬元鉛鋅礦石中石英(左和方解石(右內(nèi)流體包裹體Fig.5Fluid inclusions i

28、n quartz(leftand calcite(rightfrom the Mayuan Pb2Zn deposit,Hanzhong,Shaanxi3礦床地球化學(xué)特征流體包裹體的顯微鏡下觀察發(fā)現(xiàn),馬元鉛鋅礦石中石英、重晶石、方解石、閃鋅礦等礦物晶體內(nèi),流體包裹體大小一般小于10m,呈米粒狀、長(zhǎng)條形、橢圓形或不規(guī)則狀(圖5中左圖,多為氣2液兩相和單液相包裹體,次生包裹體一般沿裂隙發(fā)育(圖5中右圖,不作為本次研究對(duì)象。采用Linkam2THMSG600型冷熱臺(tái),測(cè)得礦石中脈石礦物均一溫度變化于100320之間(表2,平均溫度約250,屬中低溫性質(zhì);測(cè)得流體包裹體的冰點(diǎn)溫度范圍為-1515-51

29、1。利用Hall 等(1988的冰點(diǎn)下降溫度計(jì)算鹽度的公式得出,馬元鉛鋅礦床鹽度w(NaCl eq變化范圍為719% 1716%,具有盆地鹵水特點(diǎn)。礦物流體包裹體反映的成礦流體主要為NaCl2 H2O2MgCl2、NaCl2H2O2CaCl2和NaCl2H2O三種化學(xué)體系(姚書振等,2006。流體包裹體記錄的成礦流體密度通過Bodnar(1983的NaCl2H2O2MgCl2、Na2 Cl2H2O2CaCl2、NaCl2H2O體系的t2W2相圖得出,變化范圍在0185011068g/cm3之間(表2。馬元鉛鋅礦床成礦流體在已存的張性開放空間內(nèi)充填,是主要的成礦方式。成礦壓力和成礦深度的估算采用

30、邵潔漣(1988的經(jīng)驗(yàn)公式,即p=p0×T/T0其中p0=219+2620S,T0=374+920S(T為流體均一溫度,S為流體鹽度。表3馬元鉛鋅礦床硫同位素組成T able3Sulfur isotopic compositions of the Mayu anPb2Z n deposit樣品編號(hào)樣品名稱34S V2C DT/樣品來源S21閃鋅礦17.8采自楠木樹礦段S22閃鋅礦18.0采自楠木樹礦段F21方鉛礦16.8采自楠木樹礦段F22方鉛礦16.6采自楠木樹礦段F23方鉛礦15.6采自楠木樹礦段H21黃鐵礦18.8采自楠木樹礦段H22黃鐵礦18.6采自楠木樹礦段M Y28閃鋅礦

31、17.0采自楠木樹礦段KXG29閃鋅礦16.0采自孔隙溝礦段MA YN21閃鋅礦18.9據(jù)李厚民等(2007 MA YN22閃鋅礦17.7據(jù)李厚民等(2007 MA YN23閃鋅礦17.7據(jù)李厚民等(2007 MA YN24閃鋅礦18.5據(jù)李厚民等(2007 MA YN25閃鋅礦18.1據(jù)李厚民等(2007 MA YN26閃鋅礦18.5據(jù)李厚民等(2007 MA YN27閃鋅礦19.4據(jù)李厚民等(2007MWT1閃鋅礦18.22侯滿堂等(2007bMWT3閃鋅礦17.94侯滿堂等(2007bMWT4方鉛礦12.94侯滿堂等(2007bMWT2重晶石32.2侯滿堂等(2007bMWT5重晶石33

32、.33侯滿堂等(2007bMWT5重晶石33.48侯滿堂等(2007b測(cè)試單位:中國地質(zhì)科學(xué)院礦產(chǎn)資源研究所同位素實(shí)驗(yàn)室。質(zhì)譜儀型號(hào):MAT251。測(cè)試精度0.2。姚書振等,秦嶺地區(qū)重大找礦疑難問題研究報(bào)告R,2006. 估算結(jié)果成礦壓力介于24193117MPa之間,對(duì)應(yīng)的成礦深度介于9001198m之間,平均約912m,成礦深度屬于淺成環(huán)境。對(duì)馬元鉛鋅礦石中的黃鐵礦、閃鋅礦、方鉛礦、重晶石做了硫同位素測(cè)定(表3。礦區(qū)19件硫化物樣品34S=121941914,平均值18151;3件重晶石樣品34S=321233148,平均值3310。研究表明震旦紀(jì)燈影期古海水硫酸鹽的34S=2012381

33、7(張同鋼等,2004,早寒武世海相硫酸鹽的34S=30(福爾,1983。對(duì)比這些事實(shí),可能指示了導(dǎo)致硫化物沉淀的H2S由海相硫酸鹽還原形成,硫源于震旦系寒武系或盆地鹵水。礦石中硫化物表現(xiàn)出34S黃鐵礦>34S閃鋅礦>34S方鉛礦的明顯趨勢(shì)(圖6,反映成礦流體中硫同位素達(dá)到平衡,屬于同期礦化的產(chǎn)物。利用礦石中共生硫化物礦物對(duì)黃鐵礦2閃鋅礦的硫同位素進(jìn)行的平衡溫度估算,結(jié)果為274(1000ln=(3×105/ T2,與流體包裹體平均溫度接近,應(yīng)代表了主成礦的溫度。馬元鉛鋅礦石5個(gè)硫化物樣品的鉛同位素組成206Pb/204Pb=1716218102,207Pb/204Pb=

34、15149 15163,208Pb/204Pb=3715738135,侯滿堂等(2007b基于此,用豪特曼斯公式計(jì)算的模式年齡值為41206137億年?？赡苤甘境傻V金屬來源于震旦系寒武系地層。馬元鉛鋅礦區(qū)3件礦石樣品中熱液方解石礦物的13C V2PDB=-211-112,平均為-116,相應(yīng)樣品方解石的18O V2SMOW=19141918,平均為1916;熱液白云石13C V2PDB值為-312,18OV2SMOW值為2114;圍巖白云巖中13C V2PDB值為011,18O V2SMOW值為2612(李厚民等,2007(表4。研究證明,海相碳酸鹽巖的13C值變化范圍很小(-12,平均為0(

35、鄭永飛等,2000,分析與綜合研究不同學(xué)者(Veizer et al.,1976;郝立波等,2004的成果,可見海相碳酸鹽巖的13C V2PDB= -61395120,平均為-0190。馬元礦石中熱液脈石礦物13C V2PDB平均值為-210,可能反映了碳來自震旦系 寒武系地層中的碳酸鹽巖。結(jié)合相應(yīng)熱液脈石礦物樣品中18O V2SMOW平均值為2010的事實(shí),推測(cè)礦石中熱液方解石和熱液白云石應(yīng)是本地區(qū)震旦系寒武系地層中,碳酸鹽巖礦物溶解形成,成礦流體應(yīng)屬于盆地流體系統(tǒng)。礦石圖6馬元鉛鋅礦床硫同位素直方圖Fig.6Sulfur isotopic histogram of the MayuanPb

36、2Zn deposit表4馬元鉛鋅礦床中熱液方解石、熱液白云石、圍巖白云巖碳氧同位素組成及瀝青的C同位素組成T able4C arbon and oxygen isotopic compositions of hy2 drothermal calcite and dolomite,host rock dolomite and carbon isotopic composition of bitumen in the Mayu an Pb2Z n deposit 樣品編號(hào)樣品名稱18O V2S MOW/18O V2S MOW/18O V2S MOW/S23方解石-1.6-11.119.4M Y2

37、14方解石-1.2-10.819.7M Y215方解石-2.1-10.819.8MA YN233白云巖0.1-4.626.2MA YN243白云石-3.2-9.221.4MA YN223瀝青-33.0MA YN233瀝青-33.4MA YN283瀝青-32.1測(cè)試單位:中國地質(zhì)科學(xué)院礦產(chǎn)資源研究所同位素實(shí)驗(yàn)室。3樣品據(jù)李厚民等(2007。中瀝青的C同位素組成是典型的沉積有機(jī)質(zhì)來源,鋅成礦作用與盆地的有機(jī)質(zhì)有密切關(guān)系(李厚民等, 2007。4礦床基本特征及對(duì)比分析綜上所述,根據(jù)馬元鉛鋅礦床的基本特征(表5,該礦床應(yīng)屬于白云巖等沉積巖為主巖的后生層控礦床。世界上有可能以沉積碳酸鹽巖為主巖的重要鉛鋅

38、礦床主要有MV T和Sedex兩種類型(Deb et al.,2004,馬元鉛鋅礦床與MV T鉛鋅礦床和Sedex 型鉛鋅礦床的一般特征對(duì)比分析見表5。馬元鉛鋅礦床出露于揚(yáng)子陸塊北緣被動(dòng)大陸邊緣碑壩古隆起周邊,鉛鋅礦大部分產(chǎn)于震旦系燈影表5馬元鉛鋅礦床基本特征及與MVT、Sedex鉛鋅礦床對(duì)比T able5B asic characteristics of the Mayu an Z n2Pb deposit in comparison with MVT and Sedex deposits 礦床類型馬元鉛鋅礦床特征MV T鉛鋅礦床特征SEDEX型鉛鋅礦床特征容礦巖石角礫狀白云巖以白云巖為主的

39、碳酸鹽巖碎屑巖2碳酸鹽巖(含蒸發(fā)巖,多種沉積巖容礦地層成礦時(shí)代震旦系上統(tǒng)燈影組角礫化白云巖3,早奧陶世(486±12Ma 古生界,少量三疊系和元古界成礦作用發(fā)生于容礦地層形成之后中2上元古界和泥盆系為主成礦時(shí)代與容礦地層時(shí)代相同(同生礦床礦體形態(tài)基本是層控的,礦體呈層狀、似層狀、脈狀層控的。與圍巖不整合的似層狀、透鏡狀、筒狀、脈狀層控的。層狀、透鏡狀、堆垛狀與圍巖整合,也見層狀礦體底部伴有脈狀、網(wǎng)脈狀或浸染狀礦化帶礦石的礦物組合簡(jiǎn)單,閃鋅礦、方鉛礦、黃鐵礦、白云石、方解石、石英、重晶石,見瀝青黃鐵礦、白鐵礦、閃鋅礦、方鉛礦,有的礦床重晶石和螢石為主要脈石礦物,見瀝青黃鐵礦、磁黃鐵礦、

40、閃鋅礦、方鉛礦,有的礦床含大量重晶石和硅質(zhì)巖熱水沉積巖無無硅質(zhì)巖、鈉長(zhǎng)石巖、鐵白云巖、電氣石巖、重晶石巖礦石組構(gòu)粗晶結(jié)構(gòu)、硫化物和熱液碳酸鹽巖礦物膠結(jié)白云巖角礫、網(wǎng)脈狀構(gòu)造、浸染構(gòu)造塊狀、浸染狀、脈狀構(gòu)造。常見硫化物和熱液粗晶白云石膠結(jié)碳酸鹽巖角礫塊狀構(gòu)造、微細(xì)晶硫化物與上下地層構(gòu)成紋層狀構(gòu)造、浸染狀構(gòu)造圍巖蝕變硅化、重晶石化、白云石化、螢石化硅化、碳酸鹽化、黃鐵礦化、重晶石化、螢石化等發(fā)育層狀礦體的圍巖蝕變不發(fā)育,下部蝕變浸染狀礦體礦床規(guī)模礦床規(guī)模不大,但礦田資源遠(yuǎn)景好單個(gè)礦床規(guī)模較小(30300萬噸,但可成群分布.礦田Pb+Zn金屬量可達(dá)1000萬噸以上呈單個(gè)礦床或小群礦床產(chǎn)出,礦床規(guī)模非

41、常大,平均礦石量7000萬噸成礦背景揚(yáng)子陸塊北緣,漢中南部碑壩古隆起邊緣克拉通盆地邊緣的碳酸鹽巖臺(tái)地,部分產(chǎn)于裂谷帶伸展背景,克拉通及其邊緣(裂陷海槽容礦構(gòu)造張性層間滑脫、角礫巖化帶和斷裂裂隙不整合面、溶塌角礫巖帶/巖筒為主,次為斷裂裂隙同沉積構(gòu)造作用形成的次級(jí)盆地與巖漿巖關(guān)系無關(guān)無關(guān)無關(guān)成礦方式熱液充填先存開放式空間角礫之間的開放孔隙充填和對(duì)碎屑和圍巖的交代作用地表(海底或湖底熱水沉積作用賦礦地層巖相古地理淺水碳酸鹽巖臺(tái)地(白云巖淺水碳酸鹽巖相,包括碳酸鹽巖層、礁體、頁巖2碳酸鹽巖相變帶深水相黑色頁巖、粉砂巖、淺水相砂巖、碳酸鹽和燕發(fā)巖,甚至是巨大的陸相湖泊等鉛同位素指示成礦金屬來自震旦2寒

42、武系組成變化大,與賦礦地層關(guān)系密切組成均勻,指示成礦金屬來自盆地巨厚沉積柱或基底硫同位素富重硫,硫來源于地層硫酸鹽的還原富重硫,硫來源于海水硫酸鹽的還原富集重硫,硫來源于海相硫酸鹽的還原3據(jù)李厚民等,2007組中。區(qū)域上地層控制鉛鋅礦產(chǎn)出,礦體呈層狀、似層狀產(chǎn)于角礫狀白云巖或厚層礫屑白云巖中,張性層間滑脫、角礫巖化帶和斷裂裂隙為主要聚礦容礦構(gòu)造。礦區(qū)圍巖蝕變較弱,發(fā)育白云石化、重晶石化、硅化、螢石化等,溶蝕角礫表現(xiàn)為由重晶石、方解石等膠結(jié)物包圍白云巖質(zhì)角礫,角礫呈棱角狀、次圓狀,磨圓度較差,顯示出原地破碎的特點(diǎn)。礦區(qū)礦石礦物組合簡(jiǎn)單,以閃鋅礦、方鉛礦為主,脈石礦物主要為重晶石、石英等。礦石具有

43、角礫狀、網(wǎng)脈狀構(gòu)造,中、粗粒狀結(jié)構(gòu),具有低溫?zé)嵋汉笊涮畛傻V特點(diǎn)。整個(gè)礦區(qū)未見巖漿巖活動(dòng)。從一系列地質(zhì)特征看,馬元鉛鋅礦床在地質(zhì)特征和地球化學(xué)性質(zhì)方面與MV T型鉛鋅礦床具有明顯的相似性。5結(jié)論馬元鉛鋅礦床形成于揚(yáng)子陸塊北緣基底(漢中南部碑壩隆起翼部震旦系角礫化白云巖中,區(qū)域基底由中上元古界火地埡群和晉寧2澄江期變中酸性侵入巖2基性雜巖構(gòu)成,蓋層為震旦系寒武系被動(dòng)陸緣碳酸鹽巖2碎屑巖系。礦體呈層狀、似層狀產(chǎn)于燈影組角礫化白云巖層間構(gòu)造帶中,圍巖蝕變很弱。礦石中硫化物以閃鋅礦、方鉛礦為主,并含瀝青。礦物成分簡(jiǎn)單,中粗粒晶質(zhì)結(jié)構(gòu),充填于白云巖角礫間,閃鋅礦晶體中Cd含量從晶核到邊部增加趨勢(shì)明顯。馬

44、元鉛鋅礦床成礦流體溫度為100320,平均溫度約250,利用礦石中共生硫化物礦物對(duì)黃鐵礦2閃鋅礦的硫同位素進(jìn)行的平衡溫度估算結(jié)果為274,兩者溫度接近,可能代表主成礦溫度。馬元鉛鋅礦床成礦流體密度為0185011068g/cm3,估算成礦流體壓力為24193117MPa,相應(yīng)成礦深度9001198m。礦石中硫化物的34S V2CD T=12194 1914,且34S黃鐵礦>34S閃鋅礦>34S方鉛礦,硫酸鹽礦物的34S=321233148,H2S來自海相硫酸鹽的還原。礦石硫化物206Pb/204Pb=17162 18102,207Pb/204Pb=1514915163,208Pb/

45、204Pb =3715738135,成礦金屬來源于震旦系寒武系或基底。礦石中熱液脈石礦物方解石的13C V2PDB =-312-112,18O V2SMOW=1914 2114,成礦流體中CO2為震旦系碳酸鹽巖溶解成因。成礦流體可能為起源于蓋層沉積的中低溫盆地鹵水,伴隨碑壩穹隆構(gòu)造過程,成礦流體沿?zé)粲敖M白云巖層間(滑脫或溶塌構(gòu)造從蓋層沉積中心向隆起邊部運(yùn)動(dòng),并發(fā)生熱液充填為主的成礦作用。馬元鉛鋅礦床是揚(yáng)子陸塊北緣比較典型且資源前景良好的MV T鉛鋅礦床。R eferencesBodnar R J.1983.A method of calculating fluid inclusion volu

46、mes based on vapor bubble diameters and PV TX properties of inclusion fluids J.Econ.G eol.,78:535542.Deb M and G oodfellow W D.2004.Sediment2hosted lead2zinc sulphide deposits.Attributes and models of some major deposits in India, Australia and CanadaM.Narosa Publishing House.1367. Fang W X,Hu R Z,S

47、u W C and G ao Z M.2001.On characteristics of the metallogenic systems of continental dynamics and metallogenic series as well as prospecting orientations at the southern margin ofthe Y angtze massif and its vicinitiesJ.Acta Mineralogica Sinica, 21(4:561570(in Chinese with English abstract.Fowle G.1

48、983.Isotope geology principleM.Pan S L and Qiao G S, translates.Beijing:Science Press.326332(in Chinese.Fu S H,Gu X X,Wang Q,Li F Y and Zhang M.2004.A preliminary study on the enrichment regularity of dispersed elements in lead2 zinc deposits in the SW margin of the Y angtze platformJ.Bul2 letin of

49、Mineralogy,Petrology and G eochemist,23(2:105108 (in Chinese with English abstract.Hall D L,Sterner S M and Bodnar R J.1988.Freezing point depression of NaCl2KCl2H2O solutionsJ.Econ.G eol.,83:197202.Han R S,Liu C Q,Huang Z L,Chen J,Ma D Y and Li Y.2001.G enesis modeling of Huize lead2zinc ore deposi

50、t in YunnanJ.Acta Mineralogica Sinica,21(4:674680(in Chinese with English abstract.Hao L B and Qi C M.2004.G eochemistry principleM.Beijing:G eol.Pub.House.1120(in Chinese.Hou M T,Wang D G,Deng S B,Y ang Z R and Xu T.2006.G eology of lead2zinc mineralization in Mayuan area of Shaanxi ProvinceJ.G eol

51、ogy of Shaanxi,24(1:4556(in Chinese with Englishabstract.Hou M T,Wang D G,Y ang Z R and G ao J.2007a.G eological charac2 teristics of lead2zinc mineralized zones in the Mayuan area,Shaanx2 i,and their ore prospectsJ.G eology in China,34(1:101109 (in Chinese with English abstract.Hou M T,Wang D G,Den

52、g S B and Y ang Z R.2007b.G eology and genesis of the Mayuan lead2zinc mineralization belt in Shaanxi ProvinceJ.Northwestern G eology,40(1:4260(in Chinese with English abstract.Huang Z L,Chen J,Liu C Q,Han R S,Li W B,Zhao D S,G ao D R and Feng Z H.2001a.A preliminary discussion in the genetic rela2

53、tionship between Emeishan basalts and Pb2Zn deposits as exempli2 fied by the Huize Pb2Zn deposit,Yunnan ProvinceJ.Acta Mineralogica Sinica,21(4:681688(in Chinese with English abstract.Huang Z L,Chen J,Han R S,Li W B,G ao D R,Zhao D S and Liu C Q.2001b.REE geochemistry of calcite a gangue mineral in

54、the Huize ore deposit,YunnanJ.Acta Mineralogica Sinica,21(4: 659666(in Chinese with English abstract.Li H M,Chen Y C,Wang D H and Li H Q.2007.G eochemistry and mineralization age of the Mayuan zinc deposit,Nanzheng,south2 ern Shaanxi,ChinaJ.G eological Bulletin of China,26(5:546 552(in Chinese with

55、English abstract.Lin F C.2005.G eological and geochemical characteristics and genesis of supper2large2scale Sedex2type stratiform lead2zinc deposits in the Dadu river valley on the western margin of the Y angtze cratonJ.Acta G eologica Sinaca,79(4:540558(in Chinese with English abstract.Qi W,Hou M T

56、,Wang K M,Y ang Z R and Wang D G.2004.A large2scale stratabound lead2zinc metallogenic belt discovered in the Mayuan area,Nanzheng County,ShaanxiJ.G eological Bulletin 27 卷 1 期 第 第 王曉虎等 : 揚(yáng)子陸塊北緣馬元鉛鋅礦床地質(zhì)和地球化學(xué)特征 47 of China , 23 ( 11 : 1139 1142 ( in Chinese wit h English abstract . Qi W , Hou M T and Wang G B. 2006. Sinian system Pb2Zn deposit types and prospecting direction of upper Yangtze plateform J . Chinese wit h English abstract . wit h English abstract . 469. China Univ. Geosci. Press. 3845 (in Chinese . Geochemistry , 16 (1 :3034 (in Chinese