首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 62 毫秒
1.
宝山铜铅锌多金属矿床是湖南重要的铅锌生产基地。矿床内矽卡岩型铜(钼)矿化受侏罗纪花岗闪长斑岩的控制,而主要的铅锌矿体则产于远离岩体的碳酸盐地层中,且缺乏可靠的矿化年龄限制。为了查明宝山铅锌矿体与花岗闪长斑岩之间的成因关系,文章对宝山花岗岩类中浸染状黄铁矿的硫同位素和钾长石的铅同位素,以及铅锌矿石萤石脉石的流体包裹体进行了测试和研究,并与前人报道的铅锌硫化物矿石的硫、铅同位素进行了对比,尝试为宝山铅锌矿化的物质来源及成因提供依据。研究表明,花岗闪长斑岩中浸染状黄铁矿的δ34S值为+1.5‰~+3.5‰,与铅锌矿石硫化物(方铅矿、闪锌矿及黄铁矿)相一致;同时,花岗岩类中钾长石的铅同位素组成206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.4789~18.7668、15.6835~15.7220和38.7903~39.1035,具有壳源的特征,且与铅锌矿石硫化物的铅同位素分布范围相吻合。宝山矿床的硫、铅同位素特征表明,花岗闪长斑岩应是铅锌矿化的主要硫源及金属来源。宝山矿床铅锌矿石萤石中的流体包裹体具有低温(130~150℃)、低盐度(8%)的特征,可能是岩浆热液演化到晚期的产物。结合已有的有关资料加以对比和分析,研究认为,宝山铅锌矿床的成矿物质应来源于花岗闪长岩的岩浆期后热液,在热液演化晚期迁移到远端地层中沉淀,形成了宝山的主要铅锌矿体。  相似文献   

2.
驱龙铜矿是西藏陆陆碰撞造山带冈底斯斑岩铜矿带内代表性矿床之一。本文对其含矿斑岩和矿石矿物进行了S、Pb同位素组成分析。驱龙矿床含矿斑岩与矿石矿物的硫同位素组成比较一致,含矿斑岩δ34S为-2.1‰~-1.1‰,黄铜矿δ34S为-6.3‰~-1.0‰,均值-2.76‰;硬石膏δ34S为 12.5‰~ 14.4‰,平均 13.4‰。成矿热液中的硫同位素基本达到了平衡,显示出岩浆硫组成特点。含矿斑岩的206Pb/204Pb范围为18.5104~18.6083,207Pb/204Pb变化于15.5946~15.7329之间,208Pb/204Pb为38.6821~39.1531之间;矿石矿物黄铜矿的206Pb/204Pb、207Pb/204Pb、208Pb/204Pb分别为18.4426~18.5909、15.5762~15.6145、38.5569~38.8568。含矿斑岩与矿石矿物的铅同位素组成比较一致,它们的变化幅度较小,应具有相同的起源与演化历史。无论是岩石铅还是矿石铅,在铅构造模式图上均位于造山带铅演化曲线上。驱龙矿床硫、铅同位素数据暗示,成矿物质主要来自深源岩浆,含矿斑岩起源于西藏造山带加厚的下地壳熔融,具有幔源成分的混染。  相似文献   

3.
湖南祁东清水塘铅锌矿床成矿物质来源同位素示踪   总被引：3，自引：0，他引：3       下载免费PDF全文
清水塘铅锌矿床位于湖南省祁东县北东部,是一个中型矿床。在详细的野外地质调查基础上,本文通过矿石硫、铅同位素,含矿石英氢、氧同位素和含矿方解石碳、氧同位素等综合研究,探讨清水塘铅锌矿床成矿物质来源和成因。硫同位素研究结果表明,清水塘铅锌矿床中黄铁矿、方铅矿和闪锌矿的硫同位素δ~(34)S介于-7.41‰~2.91‰之间,重晶石的硫同位素δ~(34)S介于11.49‰~12.34‰之间,表明矿石中的硫主要来源于深源岩浆,并受到上部地壳物质的混染。黄铁矿、方铅矿和闪锌矿的Pb同位素~(206)Pb/~(204)Pb介于17.810~18.710之间,~(207)Pb/~(204)Pb介于15.497~15.726之间,~(208)Pb/~(204)Pb介于37.858~38.834之间;其中闪锌矿变化范围略偏大,表明矿石中的铅主要来源于地壳,可能混有少量地幔物质。含矿石英的氢、氧同位素δD_(SMOW)介于-87.4‰~-79.3‰之间,δ~(18)O_(H_2O)介于-8.10‰~0.63‰之间,表明成矿流体以岩浆水为主,晚期有大气降水的混入。含矿方解石的碳、氧同位素δ~(13)C_(VPDB)介于-5.3‰~-4.6‰之间,δ~(18)O_(SMOW)介于12.30‰~13.48‰之间;与地层灰岩的δ~(13)C_(VPDB)(0.9‰~2.6‰),δ~(18)O_(SMOW)(21.86‰~23.39‰)不一致;说明成矿流体中的碳主要来自深源岩浆。以上研究表明,清水塘铅锌矿床的成矿物质主要来自地壳熔融形成的岩浆,混合作用是成矿的主要机制。  相似文献   

4.
铜山岭铜多金属矿床是湘南W、Sn、Pb、Zn、Cu多金属矿集区的代表性矿床,本文对其不同类型岩石和矿石矿物进行了S、Pb、C同位素组成对比研究。矿石硫化物的δ34 S值变化范围为-1.9‰~5.7‰,平均值为2.6‰,硫主要来源于硫同位素组成均一化的岩浆。硫化物硫同位素平衡温度表明,矿床主要成矿温度为134~339℃。矿石铅的206 Pb/204 Pb、207 Pb/204 Pb、208 Pb/204 Pb比值分别为18.256~18.856、15.726~15.877、38.352~39.430;岩体岩石铅的206Pb/204Pb、207Pb/204Pb、208Pb/204Pb比值分别为18.617~18.805、15.721~15.786、38.923~39.073;两者铅同位素组成相同,都主要为上地壳铅,是由同一岩浆体系分异形成,可能来源于古老基底岩石。不同类型岩石、方解石矿物的δ13 CPDB值为-9.88‰~1.32‰,δ18 OSMOW值为11.67‰~17.68‰,从矽卡岩矿体到距岩体稍远的围岩地层,方解石矿物的δ13 CPDB、δ18 OSMOW值逐渐增大,成矿流体中的碳早期可能主要来源于岩浆,在成矿过程中有部分碳酸盐岩地层碳的加入。铜山岭矿床成矿物质主要来源于岩浆,赋矿地层对矿床成矿物质来源作用不显著,仅提供了少量成矿物质。  相似文献   

5.
湖南黄沙坪铅锌多金属矿床铅、硫同位素地球化学特征   总被引：7，自引：0，他引：7  
黄沙坪铅锌多金属矿床是湘南的代表性矿床之一, 矿床受SN向宝岭倒转背斜和观音打座倒转背斜的控制,赋存围岩以花岗斑岩与石英斑岩为主,矿石以铅锌硫化物矿石为主,对该矿床S同位素研究表明,δ34S值为-2.2‰～17.2‰。矿石Pb同位素组成206Pb/204Pb为17.893～18.772; 207Pb/204Pb为15.580～16.045;208Pb/204Pb为38.490～41.560。研究表明,该矿床的硫源可能是岩浆来源与海水(地层)硫混合作用形成;矿床中异常铅矿化的铅是岩源来源。  相似文献   

6.
雪鸡坪斑岩铜矿位于西南三江构造火成岩带义敦岛弧带,其成矿斑岩为印支期石英闪长玢岩和石英二长斑岩。研究对该矿区安山岩、矿化斑岩和矿石矿物系统进行S,Pb同位素分析结果表明:金属硫化物的δ34S值为-3.1‰～ 0.7‰,平均值为-1.1‰,与矿化斑岩的硫同位素组成(-1.4‰和-1.5‰)一致,均落入幔源硫范围,表明硫主要来自岩浆;δ34S黄铁矿(-1.8‰～ 0.7‰,平均-0.5‰)>δ34S黄铜矿(-2.2‰～0.0‰,平均-1.2‰)>δ34S方铅矿(-3.1‰～-1.3‰,平均-2.4‰),硫同位素分馏基本达到平衡。矿石矿物(208Pb/204Pb=37.917～38.230,平均值38.075;207Pb/204Pb=15.528～15.614,平均值15.571;206Pb/204Pb=17.929～18.082,平均值17.981)与矿化斑岩(208Pb/204Pb=37.832、37.883,207Pb/204Pb=15.529、15.538,206Pb/204Pb=17.906、17.910)以及安山岩(208Pb/204Pb=37.816～37.884,207Pb/204Pb=15.549～15.562,206Pb/204Pb=17.845～17.919)的初始铅组成基本一致,变化范围较小,表明三者具有相同的来源;在铅构造模式图上,所有样品铅同位素均位于造山带演化线上或附近,在铅同位素源区判别图中,均落入造山带和下地壳区域,这表明Pb主要来源于壳幔混合。雪鸡坪铜矿S,Pb同位素组成共同指示成矿物质主要来自于深部岩浆,这种岩浆可能主要起源于俯冲洋壳板片的部分熔融并受到少量地壳物质的混染。  相似文献   

7.
湖南常宁康家湾铅锌矿床同位素地球化学研究   总被引：2，自引：0，他引：2  
在详细的野外地质工作基础上,本文通过矿石硫、铅同位素,含矿石英的氢、氧同位素,以及含矿方解石的碳、氧同位素组成等综合研究,探讨康家湾铅锌矿床成矿物质来源和形成机制。结果显示矿石的δ34SVCDT介于-2.71‰~-0.90‰之间,均值为-1.42‰,表明矿石中的硫主要来自深部岩浆,可能受到地壳物质混染。矿石铅同位素206Pb/204Pb介于18.227~18.573之间,均值为18.485;207Pb/204Pb介于15.661~15.695之间,均值为15.682;208Pb/204Pb介于38.673~38.964之间,均值为38.820;铅同位素组成比较均一,具有放射铅的特征,表明成矿物质主要来源地壳,混有少量地幔物质。含矿石英中的δDSMOW介于-68.00‰~﹣60.00‰之间,均值为-64.00‰;δ18OH2O介于-7.25‰~-5.17‰之间,均值为-6.23‰;氢、氧同位素组成研究显示,成矿流体早期以岩浆水为主,后期混有大气降水。含矿方解石中的δC VPDB介于-0.50‰~0.30‰之间,均值为0‰;δ18OSMOW介于14.10‰~16.80‰之间,均值为14.40‰;含矿方解石中的碳、氧同位素与地层灰岩中的碳、氧同位素值大致相近,表明矿石中碳主要来源于晚古生代地层中的灰岩。以上研究表明,康家湾铅锌矿床的成矿物质主要来自地壳,混有少量地幔物质,混合作用可能是矿床形成的主要机制。  相似文献   

8.
青海沱沱河地区多才玛铅锌矿床是西南三江特提斯北段新生代铅锌矿集区的典型矿床之一,本文首次应用飞秒激光剥蚀多接受器等离子体质谱法对多才玛铅锌矿床中金属硫化物的原位S和Pb同位素进行了测定。结果显示:黄铁矿、方铅矿和闪锌矿的原位S同位素的δ~(34)S_(V-CDT)值介于-26.34‰～4.24‰之间,均值-12.15‰(n=20),其中闪锌矿的δ~(34)S_(V-CDT)值介于-10.30‰～-3.52‰,均值-7.39‰(n=9);方铅矿的δ~(34)S_(V-CDT)值为-26.34‰～-11.74‰,均值-20.36‰(n=9);黄铁矿的δ~(34)S_(V-CDT)值分别为2.50‰,4.24‰。矿床δ~(34)S数据范围较宽,总体表现为富集负值硫的特征,说明有机质可能参与成矿。岩浆热液期发育的黄铁矿δ~(34)S值具有深源特征,沉积热液期发育的方铅矿和闪锌矿的δ~(34)S值表明成矿过程存在还原作用,指示盆地地层还原流体的混入,综上可认为多才玛铅锌矿床硫具有混合来源的特征。方铅矿原位Pb同位素结果为~(206)Pb/~(204)Pb=18.866～18.929,~(207)Pb/~(204)Pb=15.674～15.689,~(208)Pb/~(204)Pb=39.052～39.174。方铅矿与地层的Pb同位素组成一致,位于上地壳平均Pb演化线之上,具上地壳和地幔混合俯冲带铅的特征,表明其成矿物质的来源多样。结合矿床学、矿物学及同位素数据,本文认为多才玛铅锌矿床S元素主要来源于赋矿围岩,Pb金属元素主要来源于藏北钾质火山岩,侵入地层岩浆与盆地流体的混合是金属硫化物沉淀的重要机制。  相似文献   

9.
贵州独山巴年锑矿床是华南锑矿带代表性锑矿床之一。矿体赋存于中泥盆统独山组地层之中。本文对该矿床辉锑矿的硫、铅同位素组成进行了系统分析。结果表明,辉锑矿的δ34S值变化范围为-5.4‰～-1.2‰,平均-4.2‰,计算获得成矿流体中总硫的δ34SΣS=0.1‰,显示岩浆来源硫的同位素特征。辉锑矿铅同位素组成变化范围较窄:206Pb/204Pb为18.561～19.156,平均18.813;207Pb/204Pb为15.703～15.769,平均15.734;208Pb/204Pb为38.573～39.207,平均38.906。绝大多数样品中矿石铅为正常铅,具有华南区域性铅同位素组成特征。我们认为巴年锑矿床成矿金属元素锑除主要来源于赋矿围岩泥盆系外,基底地层也可能提供了部分成矿物质。  相似文献   

10.
鱼库锌多金属矿床位于豫西栾川钼钨铅锌银矿集区内的鱼库—赤土店铅锌矿带的北西端。矿床赋存于新元古界栾川群三川组碳酸盐岩夹碎屑岩地层中,矿体呈似层状、透镜状产于透辉石-石榴石矽卡岩中,受矽卡岩带控制。硫化物的硫同位素组成比较稳定,δ~(34)S变化范围为2.3‰~3.9‰,平均3.2‰。硫同位素组成与区域内斑岩-矽卡岩型矿床的硫同位素组成一致,反映硫的主要来源为深部岩浆;金属硫化物样品的~(206)Pb/~(204)Pb变化范围为17.781~18.455,平均值18.043;~(207)Pb/~(204)Pb变化范围为15.502~15.590,平均值15.545;~(208)Pb/~(204)Pb变化范围为38.232~38.624,平均值38.438,矿石铅同位素组成稳定,矿石铅主要来源于地幔,成矿作用与构造岩浆作用相关的热液过程关系密切。综合分析认为矿床成因应属于岩浆热液接触交代矽卡岩型矿床。  相似文献   

11.
Pelagic deposits at Abadeh represent a complete biostratigraphic record across the Permian/Triassic boundary (PTB). The presumed water depth during deposition of these sediments was between 60 and 90 m. Similar to other Permian/Triassic boundary sections, the succession at Abadeh is characterised by a negative carbon isotope shift of approximately 4. The values start to decrease in the lower C. changxingensis - C. deflecta s.l. Zone, reach –0.12 (V-PDB) in the uppermost Permian just below the PTB, remain low to the early I. isarcica Zone (–0.32) and increase subsequently in the upper I. isarcica Zone. For the time interval of the PTB negative carbon isotope excursion, between the C. iranica and the I. isarcica Zones, no correlation exists between the 13Ccarb and the 18Ocarb. The above observations argue against the conclusion of Heydari et al. (2001) that the carbon isotope event at the P/T transition is an alteration artefact and not a global signal. The decrease in 13Ccarb is accompanied by a ~5 (and potentially up to 10) increase in 34SSSS. Together, these features are thought to reflect a complex global event, notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves. For the carbon isotope drop, other factors, such as the collapse of ocean primary productivity may also have played a role. The 87Sr/86Sr ratios of Dzhulfian seawater show only a minor increase from 0.70705 to 0.70710, reaching 0.70720 in the Dorashamian. The increase becomes steeper in the Early Triassic reaching 0.70754 in the N. dieneri Zone. The rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost Permian (C. meishanensis - H. praeparvus Zone) and the lack of a dense land vegetation in the Early Triassic, prior to the Spathian (Upper Olenekian).  相似文献   

12.
M Ohta  T Mock  Y Ogasawara  D Rumble   《Lithos》2003,70(3-4):77-90
Diamond-bearing carbonate rocks from Kumdy-Kol, Kokchetav massif, Kazakhstan, were strongly altered by fluids flowing through fractures and infiltrating along grain boundaries during exhumation. Alteration includes retrogradation of high-grade silicate assemblages by hydrous minerals, replacement of diamond by graphite and of dolomite by calcite. Diamond-bearing carbonate rocks are among the most intensely altered isotopically with δ18OVSMOW values as low as +9‰, δ13CVPDB=−9‰, and 87Sr/86Sr as high as 0.8050. Evidence of isotopic equilibration between coexisting dolomite and high-Mg calcite during ultrahigh-pressure metamorphism (UHPM) is preserved only rarely in samples isolated from infiltrating fluids by distance from fractures. Isotopic heterogeneity and isotopic disequilibrium are widespread on a hand-specimen scale. Because of this lack of homogeneity, bulk analyses cannot provide definitive measurements of 13C/12C fractionation between coexisting diamond and carbonate. Our study adequately documents alteration on a scale commensurate with observed vein structures. But, testing the hypothesis of metamorphic origin of microdiamonds has not fully succeeded because our analytical spatial resolution, limited to 0.5 mm, is not small enough to measure individual dolomite inclusions or individual diamond crystals.  相似文献   

13.
In an effort to constrain the mechanism of dolomitization in Neogene dolomites in the Bahamas and improve understanding of the use of chemostratigraphic tracers in shallow‐water carbonate sediments the δ34S, Δ47, δ13C, δ18O, δ44/40Ca and δ26Mg values and Sr concentrations have been measured in dolomitized intervals from the Clino core, drilled on the margin of Great Bahama Bank and two other cores (Unda and San Salvador) in the Bahamas. The Unda and San Salvador cores have massively dolomitized intervals that have carbonate associated sulphate δ34S values similar to those found in contemporaneous seawater and δ44/40Ca, δ26Mg values, Sr contents and Δ47 temperatures (25 to 30°C) indicating relatively shallow dolomitization in a fluid‐buffered system. In contrast, dolomitized intervals in the Clino core have elevated values of carbonate associated sulphate δ34S values indicating dolomitization in a more sediment‐buffered diagenetic system where bacterial sulphate reduction enriches the residual in 34S, consistent with high sediment Sr concentrations and low δ44/40Ca and high δ26Mg values. Only dolomites associated with hardgrounds in the Clino core have carbonate associated δ34S values similar to seawater, indicating continuous flushing of the upper layers of the sediment by seawater during sedimentary hiatuses. This interpretation is supported by changes to more positive δ44/40Ca values at hardground surfaces. All dolomites, whether they formed in an open fluid‐buffered or closed sediment‐buffered diagenetic system have similar δ26Mg values suggesting that the HMC transformed to dolomite. The clumped isotope derived temperatures in the dolomitized intervals in Clino yield temperatures that are higher than normal, possibly indicating a kinetic isotope effect on dolomite Δ47 values associated with carbonate formation through bacterial sulphate reduction. The findings of this study highlight the utility of applying multiple geochemical proxies to disentangle the diagenetic history of shallow‐water carbonate sediments and caution against simple interpretations of stratigraphic variability in these geochemical proxies as indicating changes in the global geochemical cycling of these elements in seawater.  相似文献   

14.
Iron is one of the most abundant transition metal in higher plants and variations in its isotopic compositions can be used to trace its utilization. In order to better understand the effect of plant-induced isotopic fractionation on the global Fe cycling, we have estimated by quantum chemical calculations the magnitude of the isotopic fractionation between different Fe species relevant to the transport and storage of Fe in higher plants: Fe(II)-citrate, Fe(III)-citrate, Fe(II)-nicotianamine, and Fe(III)-phytosiderophore. The ab initio calculations show firstly, that Fe(II)-nicotianamine is ～3‰ (56Fe/54Fe) isotopically lighter than Fe(III)-phytosiderophore; secondly, even in the absence of redox changes of Fe, change in the speciation alone can create up to ～1.5‰ isotopic fractionation. For example, Fe(III)-phytosiderophore is up to 1.5‰ heavier than Fe(III)-citrate2 and Fe(II)-nicotianamine is up to 1‰ heavier than Fe(II)-citrate. In addition, in order to better understand the Fe isotopic fractionation between different plant components, we have analyzed the iron isotopic composition of different organs (roots, seeds, germinated seeds, leaves and stems) from six species of higher plants: the dicot lentil (Lens culinaris), and the graminaceous monocots Virginia wild rye (Elymus virginicus), Johnsongrass (Sorghum halepense), Kentucky bluegrass (Poa pratensis), river oat (Uniola latifolia), and Indian goosegrass (Eleusine indica). The calculations may explain that the roots of strategy-II plants (Fe(III)-phytosiderophore) are isotopically heavier (by about 1‰ for the δ56Fe) than the upper parts of the plants (Fe transported as Fe(III)-citrate in the xylem or Fe(II)-nicotianamine in the phloem). In addition, we suggest that the isotopic variations observed between younger and older leaves could be explained by mixing of Fe received from the xylem and the phloem.  相似文献   

15.
P.R. Castillo  P. Scarsi  H. Craig   《Chemical Geology》2007,240(3-4):205-221
The classic hotspot hypothesis [Morgan, W. J., 1971. Convection plumes in the lower mantle. Nature 230, 42–43], which posits that linear volcanic chains are traces of fixed plumes in the mantle on moving lithospheric plates, was instrumental in elevating the plate tectonics paradigm in the 1960s into a modern Earth Science theory. The hypothesis itself, however, remains conjectural because many of its predictions, particularly the simple age-progressive type of volcanism, are not observed in many linear volcanic chains. As an alternative explanation, it is proposed that linear volcanic chains are formed through magmatism along pre-existing lines of weakness such as transform zones and old sutures, or along cracks created by stresses on lithospheric plates. The Marquesas linear volcanic chain in south-central Pacific has geologic features that are consistent with some of the predictions of both hypotheses. To better constrain the origin of this volcanic chain, we collected major and trace element and Sr, Nd, Pb, and He isotopic data from several Marquesan lavas. Our new analyses combined with literature data classify the samples into the well established tholeiitic to mildly alkalic, low 87Sr/86Sr, high 143Nd/144Nd, shield-building volcanic phase lava group and highly alkalic, high 87Sr/86Sr, low 143Nd/144Nd, post-shield phase group. Lead isotopes show generally higher 206Pb/204Pb ratios and suggest evidence of crustal assimilation for the shield-building phase lavas, consistent with the argument that the shield-building phase volcanism has a lithospheric source component. On the other hand, post-shield phase lavas that are predicted to represent the true composition of the mantle source by the hotspot hypothesis have higher 3He/4He ratios and these are coupled to other geochemical tracers. Thus our results show that the Marquesas volcanic chain, similar to many other linear volcanic chains, has a high 3He/4He component in its mantle source. The presence of such a distinct source component cannot be easily explained by dispersed upper mantle heterogeneities, but provides a powerful constraint for the hotspot origin of many linear volcanic chains.  相似文献   

16.
Mineralogical, textural and geochemical investigations were made to determine the post-depositional evolution of Devonian and Early Carboniferous carbonates from Valle de Tena. The carbonate association is made up of low-Mg calcite, which occurs as micrite, spar cements, neomorphic patches and spar filling veinlets. Non-stoichiometric dolomite and ankerite occur as cements (dolomite also as replacements) in the Middle Devonian, post-dating calcite types. All these phases pre-date tectonic stylolites, indicating compaction after stabilization of the carbonate minerals. Strontium concentrations indicate that Early Devonian and Early Carboniferous micrites initially precipitated as aragonite; Middle and Late Devonian micrites precipitated as high-Mg calcites. Both precursors were diagenetically stabilized to low-Mg calcites through interaction with meteoric waters in phreatic environments. Trace elements in dolomite and ankerite indicate precipitation from Sr-enriched meteoric water. All studied carbonates, except Middle Devonian limestones, precipitated in reducing environments, which favoured incorporation of Fe and Mn. Late calcite generations precipitated from more saline waters than micrites. Light 18O values in micrites suggest alteration mainly in meteoric-phreatic environments. The dolomites and ankerites precipitated from more 18O-depleted fluids than the calcites, suggesting a greater contribution from meteoric waters. Variations in 13C of micrites represent primary secular trends, according to published 13C variations. The 13C oscillations within each succession probably relate to sea-level oscillations. Strontium isotopes also point to a meteoric origin of diagenetic fluids. Model calculations suggest that O and Sr isotopes equilibrated between calcites and fluid at relatively low water/rock ratios, whereas C isotopic signatures are inherited from limestones.  相似文献   

17.
Geochemical observations, including major ion and trace element analysis, and isotopic tracing have been carried out in the Subarnarekha River system (northeastern India) during a surface-water- and groundwater-monitoring program aimed at evaluating impacts of mining. The aquifer is of fracture type. Groundwater flow conditions and pollutant transfer were observed through a network of 69 wells. δ18O and δ2H results suggest that transfer from rainfall towards groundwater storage through soils and the unsaturated zone is fast, without any major transformation like evaporation. The scatter of 87Sr/86Sr signatures in surface water and groundwater are explained by three end-members. One is compatible with rainwater inputs. The most mineralised end-member represents anthropogenic inputs (agricultural practices and ore processing). The third end-member, characterised by a high 87Sr/86Sr signature, is believed to be controlled by natural geochemical processes, although affected by human activities (e.g. drainage of mine waste). Potential flow paths, investigated north of the area, reveal that all groundwater types seem to evolve more in pockets than along a flow path. The limited extent of transfer and the predominance of natural phenomena help to explain the moderate level of groundwater contamination and the characteristics of surface water contamination by mining and the metallurgy industry.  相似文献   

18.
Increasing evidence shows that Mesoproterozoic rocks are widespread in the Río de la Plata Craton. Carbon and strontium isotope analyses were carried out for three different, carbonate-bearing successions in the southern Nico Pérez Terrane. The Parque UTE Group is erected, comprising (from base to top) the mainly volcanogenic Cañada Espinillo Formation, the dolomitic Mina Valencia Formation and the mixed carbonate-siliciclastic Cerro del Mástil Formation. A δ13C curve was obtained for carbonates of the Parque UTE Group, which is characterized by a plateau at +1 to +1.6‰ V-PDB, bracketed between two negative excursions (−1.8‰ V-PDB at the base and −3.3‰ V-PDB at the top). These values are consistent with a Mesoproterozoic depositional age for the unit, as indicated by U–Pb ages of synsedimentary volcanics and gabbros of 1429 ± 21 and 1492 ± 4 Ma, respectively.  相似文献   

19.
A carbon and oxygen isotope survey based on 42 samples from the Amba Dongar carbonatite complex of Gujarat, India, indicates that the magmatic differentiation series sövite → alvikite → ankeritic carbonatite is beset with a distinct isotope trend characterized by a moderate rise in 13C coupled with a sizeable increase in 18O. From an average of −4.6 ± 0.4 ‰ [PDB] for the least differentiated (coarse) sövite member, δ13C values slowly increase in the alvikite (−3.7 ± 0.6 ‰) and ankeritic fractions (−3.0 ± 1.1 ‰), whereas δ18O rises from 10.3 ± 1.7 ‰ [SMOW] to 17.5 ± 5.8 ‰ over the same sequence, reaching extremes between 20 and 28 ‰ in the latest generation of ankeritic carbonatite. While an apparent correlation between δ13C and δ18O over the δ18O range of 7–13 ‰ conforms with similar findings from other carbonatite complexes and probably reflects a Rayleigh fractionation process, the observed upsurge of 18O notably in the ankeritic member is demonstrably related to a late phase of low-temperature hydrothermal activity involving large-scale participation of 18O-depleted groundwaters. As a whole, the Amba Dongar carbonatite province displays the characteristic 13C/12C label of deep-seated (primordial) carbon, reflecting the carbon isotope composition of the subcontinental upper mantle below the Narmada Rift Zone of the Indian subcontinent.  相似文献   

20.
The Emarat deposit, with a total proved reserve of 10 Mt ore grading 6% Zn and 2.26% Pb, is one of the largest Zn–Pb deposits in the Malayer–Esfahan belt. The mineralization is stratabound and restricted to Early Cretaceous limestones and dolomites. The ore consists mainly of sphalerite and galena with small amounts of pyrite, chalcopyrite, calcite, quartz, and dolomite. Textural evidence shows that the ore has replaced the host rocks and thus is epigenetic.Sulfur isotopes indicate that the sulfur in sphalerite and galena has been derived from Cretaceous seawater through thermochemical sulfate reduction. Sulfur isotope compositions of four apparently coprecipitated sphalerite–galena pairs suggest their precipitation was under equilibrium conditions. The sulfur isotopic fractionation observed for the sphalerite–galena pairs corresponds to formation temperatures between 77 °C and 168 °C, which agree with homogenization temperatures of fluid inclusions.Lead-isotope studies indicate that the lead in galena has been derived from heterogeneous sources including orogenic and crustal reservoirs with high 238U/204Pb and 232Th/204Pb ratios. Ages derived from the Pb-isotope model give meaningless ages, ranging from Early Carboniferous to future. It is probable that the Pb-isotope model ages that point to an earlier origin than the Early Cretaceous host rocks are derived from older reservoirs in the underlying Carboniferous or Jurassic units, either from the host rocks or from earlier-formed ore deposits within these units.This research and other available data show that the Emarat Zn–Pb deposit has many important features of Mississippi Valley-type (MVT) lead–zinc deposits and thus we argue that it is an MVT-type ore deposit.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号