摘要
陕西大西沟铁矿床位于秦岭造山带山-柞盆地西北部,与银洞子大型银铅矿床毗邻。矿体主要赋存在泥盆系青石垭组中上段,容矿岩石为一套海相复理石碎屑岩和碳酸盐岩建造。矿床的金属矿物主要有菱铁矿、磁铁矿、黄铁矿,其次为黄铜矿、磁黄铁矿等;非金属矿物主要是重晶石、石英、铁白云石,其次为方解石、绢云母、绿泥石、黑云母、斜长石、钠长石、堇青石等,局部地段由于表生氧化和次生富集作用而形成针铁矿、赤铁矿、蓝辉铜矿等。与矿化有关的围岩蚀变较弱,主要有硅化、绢云母化、绿泥石化和碳酸盐化。基于野外地质观察、矿物共生组合和矿石结构构造的系统研究,将大西沟铁矿床的形成划分为3期6阶段,分别是:①喷流沉积期:硅质岩-黄铁矿-菱铁矿阶段(Ⅰ)、重晶石-磁铁矿阶段(Ⅱ);②热液改造期:堇青石-黄铁矿-磁铁矿阶段(Ⅲ)、石英-碳酸盐阶段(Ⅳ)、碳酸盐-硫化物-磁铁矿阶段(Ⅴ);③表生氧化期(Ⅵ)。流体包裹体显微测温结果表明,喷流沉积期Ⅰ阶段菱铁矿完全均一温度和盐度w(NaCl_(eq))峰值区间分别为230~270℃和13%~14.5%,Ⅱ阶段重晶石中流体包裹体的完全均一温度和盐度w(NaCl_(eq))峰值区间分别为220~290℃和9%~13%;热液改造期Ⅳ阶段菱铁矿和石英中气液两相包裹体均一温度峰值区间为240~300℃,盐度w(NaCl_(eq))为2.6%~15.7%;热液改造期Ⅴ阶段菱铁矿与石英中流体包裹体,除大量气液两相包裹体外,还发育有含子矿物多相包裹体,其中,气液两相包裹体均一温度峰值区间为290~340℃,盐度w(NaCl_(eq))为5.1%~13.4%,含子矿物多相包裹体均一温度峰值区间为380~440℃,盐度w(NaCl_(eq))为40.6%~59.7%。含子晶流体包裹体可能是流体不混溶或/和高盐度流体加入的反映。矿区内不同产状碳酸盐矿物的C、O同位素组成比较均一,δ~(13)C_(PDB)值集中在-3.58‰~-1.15‰之间,δ~(18)O_(SMOW)值为21.22‰~21.82‰,均表现出海相碳酸盐或海底喷流热液溶解海相碳酸盐的特征。大西沟矿床的地质、矿化和流体特征与海底热液喷流沉积型矿床一致,可能属于典型的喷流沉积型菱铁矿床,但后期受到秦岭造山作用的影响及热液叠加改造并形成磁铁矿和少量硫化物。大西沟菱铁矿矿床与邻近的银洞子铅锌矿组成一个较完整的喷流沉积成矿系统,两者可能分别代表了喷流沉积的边缘相和中心相。
The Daxigou iron deposit is located in the northwest of Shan-Zha Basin in the Qinling Orogen, adjacent to the Yindongzi Ag-Pb deposit. The orebodies are hosted in the upper section of Devonian Qingshiya Group, which is a set of flysch clastic-carbonate sedimentary formations of marine facies. The metallic minerals consist mainly of siderite, magnetite, pyrite, and chalcopyrite with minor pyrrhotite, hematite, goethite, and digenite. The nonmetallic minerals are dominated by barite, quartz, and ankerite, with a little calcite, sericite, chlorite, biotite, plagioclase, albite, and cordierite. Supergene oxidation has formed some iron and copper supergene minerals, such as goethite, hematite, and digenite. Wall rock alteration associated with mineralization is weakly developed, and is mostly characterized by silicification, sericitization, chloritization, and carbonatization. On the basis of a systematic study of field geological features, mineral paragenesis, ore texture and structure, the mineralization process can be divided into six stages: SEDEX period: the silicolite-pyrite-siderite stage(Ⅰ) and the barite-magnetite stage( Ⅱ); hydrothermal alteration period: the cordierite-pyrite-magnetite stage( Ⅲ), the quartz-carbonate stage(Ⅳ) and the carbonate-sulfide-magnetite stage(Ⅴ), and supergene period(Ⅵ). Fluid inclusion study shows that the temperature and salinity w(NaCl_(eq)) of siderite from stage Ⅰ focus on 230~270℃ and 13%~14.5%, respectively; the temperature and salinity w(NaCl_(eq)) of barite from stage 2 are mainly distributed in 220~290℃and 9%~13%, respectively. The fluid inclusions in siderite and quartz from stage Ⅳ in hydrothermal alteration period mostly are gas-liquid two-phase inclusions, with the temperature and salinity w(NaCl_(eq)) distributed in240~300℃ and 2.6%~15.7%, respectively. The siderite and quartz from stage Ⅴ have many gas-liquid twophase inclusions and polyphase inclusions containing daughter minerals. The temperature of gas-liquid twophase inclusions ranges from 290 to 340℃, with the salinity w(NaCl_(eq)) distributed in 5.1%~13.4%; the temperature and salinity w(NaCl_(eq)) of polyphase inclusions are distributed in 380~440℃ and 40.6%~59.7%, respectively. The polyphase inclusions containing daughter minerals in the siderite and quartz may represent the nonmiscibility of fluids or the participation of high salinity fluids. Carbon and oxygen isotopes of different types of carbonate minerals are relatively homogeneous. The δ~(13) C_(PDB)and δ~(18) O_(SMOW)of the carbonate minerals are-3.58‰~-1.15‰ and21.22‰~21.82‰, respectively, showing the characteristics of marine carbonates or marine carbonate dissolved by seafloor hydrothermal fluids. The geology, mineralization and fluid characteristics of the Daxigou deposit are consistent with features of SEDEX(Sedimentary Exhalative) deposit, and hence it may belong to SEDEX siderite deposit. Subsequently, parts of magnetite and sulfide minerals might have been formed under the influence of Qinling Orogeny and hydrothermal modification. The Daxigou siderite deposit and its adjacent Yindongzi lead and zinc deposit have formed a whole sedimentary deposit system, and may represent the edge phase and the center phase of the sedimentary exhalative system, respectively.
引文
Carne R C and Cathro R J.1982.Sedimentary Exhalative(SEDEX)zinc-lead-silver deposits,northern Canadian cordillera[J].Cim Bulletin,75:66-78.
Chen H L.2007.Ore forming conditions of copper deposit in vicinity of Yindongzi silver-lead polymetallic deposit in Shaanxi Province and its ore prediction[J].Mineral Resources and Geology,21(3):257-261(in Chinese with English abstract).
Coplen T B,Kendall C and Hopple J.1983.Comparison of stable isotope reference samples[J].Nature,302(17):236-238.
Cui J T,Zhao C Y and Wang J C.1999.The rock-lineage units classification and evolution of Dongjiangkou and Zhashui rockbodies in southern Qinling[J].Geology of Shaanxi,17(2):7-15(in Chinese with English abstract).
Du D H.1986.Devonian study in Qinba area,Shaanxi[M].Xi’an:Xi’an Jiaotong University Press(in Chinese).
Espana S,Velasco F,Boyce A J and Fallick A E.2003.Source and evolution of ore-forming hydrothermal fluids in the northern Iberian Pyrite Belt massive sulphide deposits(SW Spain):Evidence from fluid inclusions and stable isotopes[J].Mineralium Deposita,38:519-537.
Fan X R.2001.The study of tectonic evolution and sedmentary-exhalative metallization of the western Qinling Orogenic Belt(Doctoral thesis)[D].Supervisor:Wu Y Z.Changsha:Central South University.1-98(in Chinese with English abstract).
Fang W X,Zhang G W and Huang Z Y.1999.Characteristics of bariteolites and diagenism-metallogenesis for superlarge,silver-poly tmetallic deposits in Yingdongzi and Daxigou,Shaanxi[J].Acta Petrologica Sinica,15(3):484-491(in Chinese with English abstract).
Fang W X and Lu J Y.2000.Genesis and characteristics of hydrothermal sedimentary facies forsiderite-silver-polymetallic deposits in Yindongzi and Daxigou,Shanxi,China[J].Acta Sedimentologica Sinica,18(3):431-438(in Chinese with English abstract).
Fang W X and Liu J J.2013.Dynamics of the late Paleozozic apartpull basin and its relationgship with mineralization of gold-silverpolymetallic-barite-siderite deposits in Zha-Shan-Shang,Shaanxi Province[J].Acta Sedimentologica Sinica,31(2):193-209(in Chinese with English abstract).
Gong H J,Zhu L M,Sun B Y,Li B and Guo B.2009a.Zircon U-Pb ages and Hf isotope characterisitics and their geological significance of the Shahewan,Caoping and Zhashui granitic plutons in the South Qinling Orogen[J].Acta Petrologica Sinica,25(2):248-264(in Chinese with English abstract).
Gong H J,Zhu L M,Sun B Y,Li B,Guo B and Wang J Q.2009b.Zircon U-Pb ages and Hf isotopic composition of the Dongjiangkou grantic pluton and its mafic enclaves in South Qinling terrain[J].Acta Petrologica Sinica,25(11):3029-3045(in Chinese with English abstract).
Gusstafson L B and Williams N.1981.Sediment-hosted stratiform deposits of copper,lead and zinc[J].Econ.Geol,75:139-178.
Hall D L,Sterner S M and Bodnar R J.1988.Freezing point depression of NaCl-KCl-H2O solutions[J].Econ.Geol.,83(1):197-202.
Jia R X,Guo J,He Y and Wei H M.2004.Ore fluid geochemistry of gold polymetallic deposits in the Fengtai ore district,Qinling mountains[J].Geology in China,31(2):192-200(in Chinese with English abstract).
Leach D,Sangster D,Kelley K,Large R R,Garven G,Allen C,Gutzmer J and Walters S G.2005.Sediment-hosted lead-zinc deposit:A global perspective[C].Economic Geology 100th Anniversary Volume.561-607.
Leach D,Bradley D,Huston D,Pisarevsky S,Taylor R and Gardoll S.2010.Sediment-hosted lead-zinc deposits in earth history[J].Econ.Geol.,105:593-625.
Li Q,Wang B Q,Ma G Z and Wang X H.2007.Space time relationship of gold deposit to lead-zinc deposit in Fengtai ore field in South Qinling[J].Journal of Earth Sciences and Environment,29(1):15-21(in Chinese with English abstract).
Li T.1979.Metallogenic geochemistry of marine sedimentary type of siderite deposit[J].Geology and Exploration,1:1-8(in Chinese).
Li Y and Gao F M.1989.Characteristics of Pb-Zn ore deposits in Zhenxun metallogennic belt in Shanxi and their genesis[J].Contributions to Geology and mineral Resources Research,4(2):54-66(in Chinese with English abstract).
Liu Z D,Sun F Y,Ma F F and Zhang B L.2013.Zircon U-Pb ages and petrochemical characteristics of Zhashui granitic plutons in South Qinling Orogen of Shaanxi and their geological significance[J].Global Geology,32(2):236-243(in Chinese with English abstract).
Ma G L,Qi S J,Li Y and Xue C J.1996.A study of the exhalative orgin of the Changba lead-zinc deposit,Gansu Province[J].Contributions to Geology and Mineral Resources Research,11(3):36-44(in Chinese with English abstract).
Qi W and Hou M T.2005.Types and prospecting trend of lead and zinc ores in Shaanxi Province[J].Geology of Shaanxi,23(2):1-19(in Chinese with English abstract).
Ren P,Liang T,Niu L,Lu L,Zhang W J,Yang Z,Wang C and Cheng Y L.2013.Geological characteristic and geodynamic process from Pb-Zn deposit in Qinling of Shaanxi[J].Journal of Earth Sciences and Environment,35(1):34-47(in Chinese with English abstract).
Song X W,Hou M T and Chen R Y.2003.The compartmentalization of minerals sequence of mineral deposits in Shaanxi Province[J].Geology of Shaanxi,21(2):1-18(in Chinese with English abstract).
Valdes E L.1998.Pb-Zn“SEDEX”deposits and their copper stockwork roots,western Cuba[J].Mineralium Deposita,33:560-567.
Wang D S,Wang R T,Dai J Z,Wang C A,Li J H and Chen L X.2009.“Dual ore-controlling factors”characteristics of metallic deposits in the Qinling Orogenic belt[J].Acta Geologica Sinica,83(11):1719-1729(in Chinese with English abstract).
Wang G Y.1986.Oxygen and carbon isotopic compositions of stratabound siderites and their genetic significances[J].Acta Sedimentologica Sinica,4(2):27-38(in Chinese with English abstract).
Wang R T,Ren T,Li J B,Dai J Z,Wang D S,Wang Y T and Yan Z.2010.Geochemical characteristics,metallogenetic model and exploration predicting of Yindongzi Ag-Pb polymetallic deposit,Zhashui County,Shaanxi Province,China[J].Acta Geologica Sinica,84(3):418-430(in Chinese with English abstract).
Wang Y and Bai X R.1994.Study of genetic mineralogy in Yindongzi silver-lead polymetallic deposit in Zhashui County,Shanxi Province[J].Contributions to Geology and Mineral Resources Research,9(3):83-92(in Chinese with English abstract).
Wang Z Q,Yan Q R,Yan Z,Wang T,Jiang C F,Gao L D,Li Q G,Chen J L,Zhang Y L,Liu P,Xie C L and Xiang Z J.2009.New division of the main tectonic units of the Qinling Orogenic Belt,Central China[J].Acta Geologica Sinica,83(11):1527-1546(in Chinese with English abstract).
Yan Z,Wang Z Q,Wang T,Yan Q R,Xiao W J,Li J L,Han F L and Chen J L.2007.Tectonic setting of Devonian sediments in the Qinling Orogeny:Constraints from detrital modes and geochemistry of clastic rocks[J].Acta Petrologica Sinica,23(5):1023-1042(in Chinese with English abstract).
Yan Z,Wang Z Q,Chen L,Liu S W,Ren T,Xu X Y and Wang R T.2014.Tectono magmatism and metallogeneses of ShanyangZhashui ore concentration area in Qinling Orogen[J].Acta Petrologica Sinica,30(2):401-414(in Chinese with English abstract).
Yang K,Liu S W,Li Q G,Wang Z Q,Han Y G,Wu F H and Zhang F.2009.LA-ICP-MS Zircon U-Pb geochronology and geological significance of Zhashui granitoids and Dongjiangkou granitoids from Qinling,Central China[J].Acta Scientiarum Naturalium Universitatis Pekinensis,1:36-42(in Chinese with English abstract).
Yang Y M and Fang W X.1999.Metallogenic model and halo-forming pattern of the Daxigou-Yindongzi silver polymetallic deposit in Shaanxi[J].Geological Exploration for Non-ferrous Metals,8(6):598-603(in Chinese with English abstract).
Yang Y M and Fang W X.2000.Sources of mineralization constituents and accumulation environment of ore-forming in Daxigou-Yindongzi siderite-silver polymetallic superlarge ore deposit[J].Northwest Geoscience,21(1):53-61(in Chinese with English abstract).
Yang Z R.Studies on the mineralization system of large ore-cluster areas in Qinling Orogenic Belt(Doctoral thesis)[D].Supervisor:Liu J C.Xi’an:Chang’an University.1-119(in Chinese with English abstract).
Yao S Z,Zhou Z G,LüX B,Chen S Y,Ding Z J and Wang P.2006.Mineralization characteristics and prospecting potential in the Qinling Metallogenic Belt[J].Northwestern Geology,39(2):156-178(in Chinese with English abstract).
Zhang B R,Chen D X,Li Z J,et al.1989.Regional geochemistry of the Shanyang-Zhashui metallogenic belt,Shaanxi[M].Wuhan:China University of Geosciences Press.1-221(in Chinese).
Zhang C L,Wang T and Wang X X.2008.Origin and tectonic setting of the early Mesozoic granitoids in Qinling Orogenic Belt[J].Geological Journal of China Universities,14(3):304-316(in Chinese with English abstract).
Zhang G W,Meng Q R and Yu Z P.1996.The orogenic process and dynamic characteristics of the Qinling Orogenic Belt[J].Chinese science:D series,26(3):193-200(in Chinese).
Zhu H P,Guo J,Zhu H Z and Zhang R.1998.The carbon and oxygen isotopes geochemistry of sedimentary formation of the Fengtai Basin,Qinling[J].Geological Exploration for Non-ferrous Metals,7(6):321-325(in Chinese with English abstract).
Zhu H P.2004.Geology and geochemistry for copper and zinc deposits of Zhashui-Shanyang area-the importance of epigenetic minera lization[M].Chinese Academy of Geological Sciences(in Chinese with English abstract).
陈连红.2007.陕西省银洞子银-铅多金属矿床外围铜矿成矿条件与找矿预测[J].矿产与地质,21(3):257-261.
崔建堂,赵长缨,王炬川.1999.南秦岭东江口、柞水岩体岩石谱系单位划分及演化[J].陕西地质,17(2):7-15.
杜定汉.1986.陕西秦巴地区泥盆系研究[M].西安:西安交通大学出版社.1-230.
范效仁.2001.西秦岭构造演化与喷流成矿研究(博士论文)[D].导师:吴延之.长沙:中南大学.1-98.
方维萱,张国伟,黄转莹.1999.银硐子-大西沟特大型银多金属矿床中重晶石岩类特征及成岩成矿作用[J].岩石学报,15(3):484-491.
方维萱,芦继英.2000.陕西银硐子-大西沟菱铁银多金属矿床热水沉积岩相特征及成因[J].沉积学报,18(3):431-438.
方维萱,刘家军.2013.陕西柞-山-商晚古生代拉分断陷盆地动力学与成矿作用[J].沉积学报,31(2):193-209.
弓虎军,朱赖民,孙博亚,李犇,郭波.2009a.南秦岭沙河湾、曹坪和柞水岩体锆石U-Pb年龄、Hf同位素特征及其地质意义[J].岩石学报,25(2):248-264.
弓虎军,朱赖民,孙博亚,李犇,郭波,王建其.2009b.南秦岭地体东江口花岗岩及其基性包体的锆石U-Pb年龄和Hf同位素组成[J].岩石学报,25(11):3029-3045.
贾润幸,郭键,赫英,隗合明.2004.秦岭凤太成矿区金多金属矿床成矿流体地球化学研究[J].中国地质,31(2):192-200.
黎彤.1979.海相沉积型菱铁矿矿床的成矿地球化学[J].地质与勘探,1:1-8.
李强,王兵岐,马治国,王晓虎.2007.南秦岭凤太盆地金矿与铅锌矿的成矿模式[J].地球科学与环境学报,29(1):15-21.
李英,高福模.1989.陕南镇旬矿田铅锌矿化特征及成因[J].地质找矿论丛,4(2):54-66.
刘哲东,孙丰月,马芳芳,张本龙.2013.陕西南秦岭柞水岩体锆石U-Pb年龄、岩石地球化学特征及其地质意义[J].世界地质,32(2):236-243.
马国良,祁思敬,李英,薛春纪.1996.甘肃厂坝铅锌矿床喷气沉积成因研究[J].地质找矿论丛,11(3):36-44.
齐文,侯满堂.2005.陕西铅锌矿类型及其找矿方向[J].陕西地质,23(2):1-19.
任鹏,梁婷,牛亮,鲁麟,张文璟,杨钊,王婵,程玉龙.2013.陕西秦岭铅锌矿床的地质特征及成矿动力学过程[J].地球科学与环境学报,35(1):34-47.
宋小文,侯满堂,陈如意.2003.陕西省矿床成矿系列的初步划分[J].陕西地质,21(2):1-18.
王东生,王瑞廷,代军治,王长安,李建华,陈荔湘.2009.秦岭造山带金属矿床的“二元控矿”特征[J].地质学报,83(11):1719-1729.
王关玉.1986.层控菱铁矿的氧、碳同位素组成及其成因意义[J].沉积学报,4(2):27-38.
王瑞廷,任涛,李建斌,代军治,王东生,王义天,闫臻.2010.柞水银洞子银铅多金属矿床地球化学特征/成矿模式及找矿预测[J].地质学报,84(3):418-430.
王焰,白学让.1994.陕西柞水银硐子银铅多金属矿床成因矿物学研究[J].地质找矿论丛,9(3):83-92.
王宗起,闫全人,闫臻,王涛,姜春发,高联达,李秋根,陈隽璐,张英利,刘平,谢春林,向忠金.2009.秦岭造山带主要大地构造单元的新划分[J].地质学报,83(11):1527-1546.
闫臻,王宗起,王涛,闫全人,肖文交,李继亮,韩芳林,陈隽璐.2007.秦岭造山带泥盆系形成构造环境:来自碎屑岩组成和地球化学方面的约束[J].岩石学报,23(5):1023-1042.
闫臻,王宗起,陈雷,刘树文,任涛,徐学义,王瑞廷.2014.南秦岭山阳-柞水矿集区构造-岩浆-成矿作用[J].岩石学报,30(2):401-414.
杨恺,刘树文,李秋根,王宗起,韩以贵,吴峰辉,张帆.2009.秦岭柞水岩体和东江口岩体的锆石U-Pb年代学及其意义[J].北京大学学报,1:36-42.
杨耀民,方维萱.1999.陕西大西沟重晶石菱铁矿-银硐子银铜铅多金属特大型矿床成矿成晕模式[J].有色金属矿产与勘查,8(6):598-603.
杨耀民,方维萱.2000.大西沟-银硐子超大型矿床成矿物质来源、成矿堆积环境及成矿作用多阶段性[J].西北地质科学,21(1):53-61.
杨志华.1991.边缘转换盆地的构造岩相与成矿[M].北京:科学出版社.1-228.
杨宗让.2012.秦岭造山带大型矿集区成矿系统研究(博士论文)[D].导师:刘建朝.西安:长安大学.1-119.
姚书振,周宗桂,吕新彪,陈守余,丁振举,王苹.2006.秦岭成矿带成矿特征和找矿方向[J].西北地质,39(2):156-178.
张本仁,陈德兴,李泽九等.1989.陕西柞水山阳成矿带区域地球化学[M].武汉:中国地质大学出版社.1-221.
张成立,王涛,王晓霞.2008.秦岭造山带早中生代花岗岩成因及其构造环境[J].高校地质学报,14(3):304-316.
张国伟,孟庆任,于在平.1996.秦岭造山带的造山过程及其动力学特征[J].中国科学:D辑,26(3):193-200.
朱华平,郭健,朱宏洲,张蓉.1998.秦岭凤太盆地沉积建造的C、O同位素特征[J].有色金属矿产与勘查,7(6):321-325.
朱华平.2004.柞山地区铜锌多金属矿床地质-地球化学-后生成矿作用的重要性[M].中国地质科学院矿产资源研究所.