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1.
江西金山金矿含金黄铁矿的Rb-Sr年龄   总被引：8，自引：0，他引：8  
前人对江西金山金矿的成矿时代有许多不同的认识,笔者通过对江西金山蚀变岩型矿石中的含金黄铁矿Rb-Sr年龄的测定得出,含金黄铁矿的Rb-Sr等时线年龄为(838±110)Ma,initial87Sr/86Sr=0.7045±0.0020。由此可以推测晋宁期是蚀变岩型金矿体形成的主要时期。黄铁矿Rb-Sr所得的Sr同位素初始比(87Sr/86Sr)i小于陆源硅酸盐的值(0.720),而与玄武岩的值(0.704)接近,结合前人有关的同位素及稀土、微量元素研究,笔者认为金山金矿变质岩型矿体的成矿物质源于变质围岩,成矿流体为来源于深部的变质水。  相似文献   

2.
祁进平  宋要武  李双庆  陈福坤 《岩石学报》2009,25(11):2843-2854
河南栾川西沟铅锌银矿床位于华北克拉通南缘栾川断裂北侧,为赋存于中-晚元古代浅变质碳酸盐建造中的层控矿床,被认为是晚元古代的热水沉积型矿床.从成矿早阶段至晚阶段,矿物共生组合依次为;细粒黄铁矿、粗粒黄铁矿-闪锌矿-白云石-石英组合、多金属硫化物-白云石-石英组合、黄铁矿-石英-碳酸盐组合.本文对其矿石硫化物和黑云母进行了单颗粒矿物Rb-Sr同位素分析和研究.1件赋矿钙质二云片岩样品的5个黑云母颗粒样品给出Rb-Sr等时线年龄为366.0±10Ma,代表赋矿围岩的区域变质年龄.由于黄铁矿-碳酸盐细脉切穿了钙质二云片岩的片理,闪锌矿细脉切穿大理岩条带,矿体未遭受区域变质作用,可推断矿化发生于366Ma之后.考虑到区域内的构造变形事件和大规模花岗岩类侵入和成矿作用的年龄数据集中在156～134Ma,峰值在138 Ma左右,认为西沟铅锌银矿床形成于晚侏罗世-早白垩世.5件成矿早阶段细粒黄铁矿具有较低的I_(Sr-138Ma0值(按138Ma计算的锶同位素初始比值),变化范围为0.7100～0.7151,平均0.7127,该值略高于晚侏罗-早白垩斑岩类和花岗岩基,明显低于太古代太华群变质基底、中元古代熊耳群安山质火山盖层和中-晚元古代栾川群和官道口群的片岩地层,但与赋矿围岩栾川群大理岩地层接近,表明碳酸盐地层变质脱水和晚侏罗-早白垩岩浆岩均有可能为早阶段成矿提供成矿流体.相比之下,主成矿阶段硫化物则更加富含放射成因锶;14个主成矿阶段粗粒黄铁矿测点的I_(Sr-138Ma)值范围为0.7152～0.7344,平均0.7247,13个闪锌矿测点的I_(Sr-138Ma)值范围为0.7108～0.7398,平均0.7283,这些硫化物I_(Sr-138Ma)值接近于或低于太古宙太华群、中元古代熊耳群和中-晚元古代官道口群和栾川群,表明这些地层的锶都有可能混入成矿流体.因此,上述研究表明成矿早阶段流体主要为壳源岩石的变质脱水流体或燕山期岩浆热液,而在主成矿阶段,通过水岩相互作用与浅源循环的大气水或建造水的混入,浅部盖层栾川群地层的成分较多地加入了成矿系统.  相似文献   

3.
The intrusive rocks associated with the large Nezhdaninka gold deposit (Au > 470 t) hosted in the Permian carbonaceous terrigenous sequence have been dated on zircon and rock-forming minerals with precision U-Pb (ID-TIMS) and Rb-Sr methods. The lamprophyre of the dike complex that occurs in the ore field and spatially is related to gold mineralization has concordant U-Pb zircon age (121 ± 1 Ma) and the same isochron Rb-Sr age (121.0 ± 2.8 Ma). The concordant U-Pb zircon age of granodiorite that dominates in the Kurum pluton is 94 ± 1 Ma, whereas the Rb-Sr isochron age of various intrusive rocks from this pluton is 1–4 Ma younger. This difference is caused by long-term cooling of the Kurum pluton and later closure of Rb-Sr isotopic system of biotite (300–350°C) and other rock-forming minerals as compared with U-Pb isotopic system of zircon (～ 900°C). The Rb-Sr age of quartz diorite from the Gel’dy group of stocks (92.6 ± 0.8 Ma) coincides within uncertainty limits with the age of the Kurum pluton. Thus, the rocks pertaining to two epochs of magmatic activity, which developed in the South Verkhoyansk Foldbelt and divided by a time span of 25–28 Ma, are documented in the Nezhdaninka ore field. Taking into account that the age of gold mineralization is no less than 120 Ma, the data obtained allow us to specify the previously proposed formation model of the Nezhdaninka deposit. These data give grounds to rule out the Late Cretaceous Kurum pluton and the Gel’dy group of stocks from constituents of the ore-magmatic system, and to suggest that an Early Cretaceous deep-seated magma source existed beneath the deposit. Along with host terrigenous rocks, this magma source participated in the supply of matter to the hydrothermal system. The Nd, Sr, and Pb isotopic systematics of igneous rocks and ore mineralization in the Nezhdaninka ore field show that the Early and Late Cretaceous magma sources were formed in the Precambrian crust dated at ～1.8 Ga.  相似文献   

4.
中亚盆地钾盐矿床的形成时代目前被限定为晚侏罗世至早白垩世,较为宽泛.盐类矿物沉积之后若未被改造,可测定其形成时代;若被改造则可利用同位素测年研究其沉积后作用.为了得到中亚盆地钾盐矿床的形成时代和/或了解盐类矿物受到的后期改造过程,利用Rb-Sr同位素定年对矿床中的盐类矿物进行了测定.结果表明,无法形成可靠的Rb-Sr等...  相似文献   

5.
硫化物Rb-Sr同位素定年研究进展   总被引：4，自引：0，他引：4  
针对金属矿床成矿年代确定混乱的问题,国内外许多矿床学家和同位素地球化学家对金属矿物常规同位素定年方法进行了有益的探索研究,尤其是对于矿石矿物以闪锌矿、方铅矿和黄铁矿为主的铅锌矿床,硫化物矿物Rb-Sr同位素定年方法显示出了其独特的优势。结合近几年开展的工作,总结国内外硫化物Rb-Sr同位素定年研究取得的成果、闪锌矿中Rb、Sr的赋存状态与定年机理以及定年适应性问题。采用闪锌矿Rb-Sr同位素组成数据拟合成等时线源自热液流体与闪锌矿之间Rb和Sr的不同分异作用,但并不是所有的闪锌矿均适合该定年技术。要成功获得年龄,需结合野外地质特征采集代表性的矿石样品,并在镜下鉴定基础上挑选合适的单矿物;在分析测试过程中,需尽可能去除次生包裹体和粘土矿物。  相似文献   

6.
广东天堂铜铅锌多金属矿床Rb-Sr等时线年龄及其地质意义   总被引：19，自引：7，他引：12  
文章选取8件闪锌矿、3件方铅矿和1件黄铁矿样品,采用Rb-Sr等时线定年方法测定天堂铜铅锌多金属矿床的成矿时代.获得闪锌矿等时线年龄为(98.1±1.6) Ma,闪锌矿+方铅矿等时线年龄为(99±2)Ma,闪锌矿+方铅矿+黄铁矿等时线年龄为(98.2±1.3) Ma,闪锌矿+黄铁矿等时线年龄为(97.87±0.96) Ma,方铅矿+黄铁矿等时线年龄为(98.6±4.2) Ma.Rb-Sr定年结果表明,天堂铜铅锌多金属矿床的成矿时代为98 Ma左右,矿床形成于晚白垩世早期,可能与135Ma之后太平洋板块的运动方向发生转向,使得中国大陆包括华南板块在内均处于持续伸展阶段有关.硫化物矿石Rb-Sr所得的Sr同位素初始比(87Sr/86Sr)i平均值为0.7117,小于陆源硅酸盐的值(0.720),高于地幔Sr的初始值0.707,结合笔者对该矿床所做的S、Pb等同位素组成特征研究,显示成矿物质来源于壳幔混合.研究表明,利用特定矿床的主要矿石矿物,采用Rb-Sr等时线定年方法通过共生矿物组合和单矿物相互约束,可以有效地确定成矿时代,这对了解矿床的成矿背景等具有一定的指示意义.  相似文献   

7.
《Resource Geology》2018,68(3):275-286
The volcanic‐hosted Xiangshan uranium orefield is the largest uranium deposit in South China. Recent exploration has discovered extensive Pb–Zn mineralization beneath the uranium orebodies. Detailed geological investigation reveals that the major metallic minerals include pyrite, sphalerite, galena, and chalcopyrite, whilst the major non‐metallic minerals include quartz, sericite, and calcite. New δ18Ofluid and δDfluid data indicate that the ore‐forming fluids were mainly derived from magmatic, and the sulfide δ34S values (2.2–6.9‰) suggest a dominantly magmatic sulfur source. The Pb isotope compositions are homogeneous (206Pb/204Pb = 18.120–18.233, 207Pb/204Pb = 15.575–15.698, and 208Pb/204Pb = 37.047–38.446). The 87Sr/86Sr ratios of sulfide minerals range from 0.7197 to 0.7204, which is much higher than volcanic rocks and fall into the range of metamorphic basement. Lead and strontium isotopic compositions indicate that the metallogenic materials probably were derived from metamorphic basement. Pyrite Rb–Sr dating of the ores yielded 131.3 ± 4.0 Ma, indicating that the Pb–Zn mineralization occurred in the Early Cretaceous.  相似文献   

8.
Rb-Sr isotope systematics have been investigated of epidote, actinolite, albite and biotite concentrates from 4 spilite samples from the Precambrian basement directly W of lake Vänern in SW Sweden. The rocks belong to the Dalsland Supracrustal Group whose basal conglomerate was deposited on an erosion surface with a maximum age of c. 1,200 Ma. Epidote-WR and actinolite-WR tie lines in a Nicolaysen diagram give ages with an average of 990±10 (la) Ma, which is thought to represent the metamorphic culmination. Biotite-WR lines yield an average age of 900±15 (1σ) Ma, which indicates the time at which the rock complex cooled through the isotopic closure temperature of biotite, estimated at c. 250° C. The average cooling rate in this period was very low, 1–2° C/Ma. Initial Sr isotopic ratios of the 4 spilite samples vary from 0.7040 to 0.7080 and are thought to reflect interaction of mantle-derived basalts with seawater.  相似文献   

9.
甲乌拉铅锌银矿床位于内蒙古自治区满洲里市南西150km。矿床产于中蒙古-额尔古纳兴凯造山带南东缘之得尔布干断裂北西侧。本文在甲乌拉矿床选取7件闪锌矿和6件黄铁矿样品开展了Rb-Sr定年。获得闪锌矿的Rb-Sr等时线年龄为143.0±2.0Ma(MSWD=3.2),锶同位素初始值I Sr=0.71265;黄铁矿的Rb-Sr等时线年龄为142.0±3.0Ma(MSWD=5.7),锶同位素初始值ISr=0.71267;闪锌矿与黄铁矿的Rb-Sr等时线年龄为142.7±1.3Ma(MSWD=3.8),锶同位素初始值ISr=0.71266。上述定年结果表明,甲乌拉矿床形成于早白垩世初期。甲乌拉矿床硫化物的Rb和Sr含量分别介于0.1034×10-6～7.367×10-6和1.301×10-6～7.148×10-6之间,Sr同位素初始比值(87Sr/86Sr)i介于0.71238～0.71277之间,平均值为0.71264,暗示甲乌拉矿床的成矿物质主要来源于地壳。甲乌拉矿床形成于蒙古-鄂霍茨克造山过程的后碰撞阶段。  相似文献   

10.
江西相山铀矿田科学深钻3号孔在深部-700 m发现大量铅锌多金属矿化脉,垂向上呈"上铀下多金属"的分布特征。本文选取深部多金属矿脉主成矿阶段(S3)自形闪锌矿样品6件和不同阶段的毒砂、黄铁矿、方铅矿、方解石等样品12件,以及围岩全岩样品17件,进行了Rb、Sr同位素组成研究。结果表明:(1)由闪锌矿Rb-Sr等时线法确定的相山铀矿田深部多金属矿化形成于121. 0±3. 5Ma,与围岩火山岩存在较大时差,可能与晚于围岩的深部次火山有关。根据穿插关系,多金属矿化略晚于碱性交代铀矿化,但明显早于酸性交代铀矿化;(2)多金属矿化脉体中金属矿物的Rb和Sr含量分别介于0. 041×10~(-6)～1. 38×10-6和2. 35×10-6～23. 11×10-6之间,Sr同位素初始比值(87Sr/86Sr)i变化较大,介于0. 706114～0. 718814之间,平均值为0. 713579,暗示相山铀矿田深部多金属矿化的成矿物质主要来源于地壳。初始流体Sr同位素值(0. 718665)明显高于成矿时赋矿围岩(流纹英安岩为0. 714581,碎斑流纹岩为0. 714417)的Sr同位素组成,表明多金属成矿流体和物质并非来自围岩火山岩;(3)由早到晚阶段的(87Sr/86Sr)i呈明显降低的演化趋势,表明成矿流体演化过程中受到大气降水的不断稀释作用。相山矿田的铀矿和深部多金属矿化同形成于华南中生代板内伸展构造背景。  相似文献   

11.
The age of the main productive phase of ore formation at the large Solnechnoe tin deposit has been estimated for the first time based on the study of the Rb-Sr isotopic system of hydrothermal quartz and adularia from ore veins and metasomatic rocks. The Rb-Sr isochron age (84 ± 1 Ma) of mineralization coincides with the age of intrusive rocks pertaining to the third phase of the Silinka Complex, which control tin mineralization. The 87Sr/86Sr ratios of ore-forming solution and granitic rocks of the final intrusive phase are close to each other, indicating that the granitic melt was most likely one of the main sources of metals. The long and multistage formation history of the deposit could have been caused by complex geodynamic evolution of the Sikhote-Alin accretionary fold region in the Cretaceous.  相似文献   

12.
The Tiemurt Pb-Zn-Cu deposit (metal reserve: 0.29 Mt (Pb + Zn) and 0.14 Mt Cu) is hosted in the Kangbutiebao Formation volcanic-sedimentary rocks in the Chinese Altay Orogen, NW China. Although some geological and geochemical characteristics of primary seafloor sedimentary mineralization are preserved, major fault-controlled Pb-Zn-Cu orebodies are adjacent to the Sarekbuobu orogenic gold deposit, and therefore it is also interpreted to be closely related to regional deformational-metamorphic processes. The seafloor sedimentary mineralization is evidenced by the occurrence of the banded ores and marine sulfate-originated sulfur isotopic compositions of the sulfides (bimodal δ34S values of 17.29–18.67‰ and −25.03 to −17.58‰). The lead isotope compositions accord with the evolution line of mantle, implying that the Pb were chiefly sourced from the mantle-reservoir. The later deformational and metamorphic overprinting are recorded by the fault-controlled lodes with ore textures of epigenetic infilling and replacement. Besides well-developed CO2-rich fluid inclusions, the D-O isotopic data of the overprinting fluids fall into the area between metamorphic fluids and meteoric water line, indicative of metamorphic fluids origin with meteoric water involvement. To further trace the Pb-Zn-Cu accumulation and remobilization processes, systematic in-situ trace elements in sulfides of different generations are analyzed using LA-ICP-MS. Ti-Mn-Cu-Pb-Zn-Bi concentrations in pyrite show a trend of progressive decrease from early to late generations. Similar decreasing trends of trace element concentrations are also present in sphalerite, galena, chalcopyrite and pyrrhotite, although the combinations of trace element are slightly different. This indicates that the ore-forming metals (esp. Cu, Pb and Zn) were initially locked up in the crystal lattice of the VMS sulfides (especially pyrite). Deformational and metamorphic processes of the primary ores during the Permian-Triassic collisional orogeny have likely led to trace element remobilization and sulfides purification, which redistributed the metals and upgraded the ores. Combined with previous studies, we proposed that the Pb-Zn-Cu of Tiemurt had been accumulated from seafloor sedimentation (ca. 400 Ma) to deformation-metamorphism processes (ca. 240 Ma).  相似文献   

13.
花垣矿集区位于我国湘西-黔东成矿带,作为世界级的超大型铅锌矿床之一,预测储量超过千万吨,位于花垣矿集区中部渔塘矿田的柔先山铅锌矿床是区内典型的铅锌矿床.采用闪锌矿Rb-Sr分相法获得了柔先山铅锌矿床的Rb-Sr等时线年龄为412±6 Ma（MSWD=1.5,初始86Sr/87Sr=0.709 32）,地质时代为早泥盆世,这一年龄限定了花垣地区铅锌矿床的时代.柔先山矿床的铅锌矿矿石流体包裹体、Sr-S-Pb同位素示踪研究显示,成矿流体可能是地层封存水与后期迁移流体的混合,成矿元素中的铅主要来源于围岩,硫由赋矿层位之上的含膏岩层经历热化学还原过程供给,铅和锶同位素特征都指示上地壳来源.   相似文献   

14.
Abstract. The petrography, chemical, fluid inclusion and isotope analyses (O, Rb-Sr) were conducted for the shale samples of the Mount McRae Shale collected from the Tom Price, Newman, and Paraburdoo mines in the Hamersley Basin, Western Australia. The Mount McRae Shale at these mines occurs as a footwall unit of the secondary, hematite-rich iron ores derived from the Brockman Iron Formation, one of the largest banded iron formations (BIFs) in the world. Unusually low contents of Na, Ca, and Sr in the shales suggest that these elements were leached away from the shale after deposition. The δ18O (SMOW) values fall in the range of + 15.0 to +17.9 per mil and show the positive correlation with calculated quartz/sericite ratios of the shale samples. This suggests that the oxygen isotopic compositions of shale samples were homogenized and equilibrated by postdepositional event. The pyrite nodules hosted by shales are often rimmed by thin layers of silica of varying crystallinity. Fluid inclusions in quartz crystals rimming a pyrite nodule show homogenization temperatures ranging from 100 to 240C for 47 inclusions and salinities ranging from 0.4 to 12.3 wt% NaCl equivalent for 18 inclusions. These fluid inclusion data give direct evidence for the hydrothermal activity and are comparable to those of the vein quartz collected from the BIF-derived secondary iron ores (Taylor et al, 2001). The Rb-Sr age for the Mount McRae Shale is 1,952 ± 289 Ma and at least 200 million years younger than the depositional age of the Brockman Iron Formation of ∼ 2.5 Ga in age. All the data obtained in this study are consistent with the suggestion that high temperature hydrothermal fluids were responsible for both the secondary iron ore formation and the alteration of the Mount McRae Shale.  相似文献   

15.
The behaviour of the Rb-Sr and Sm-Nd isotopic systems with increasing degree of Hercynian metamorphic overprint was studied along a transect in Cambrian shales of northwestern Morocco. Clay fractions of < 0.2 to 2–6 μm size from five samples were investigated, representing a range from nonmetamorphic to epizonal metamorphic conditions. The samples were washed in cold l N HC1 prior to digestion to separate soluble/exchangeable Rb, Sr, Sm, and Nd from amounts of these elements fixed in the crystallographic sites of the minerals and to analyze both components separately.The results reveal that the Rb-Sr isotopic system is dominated by Sr hosted by clay mineral phases (both detrital and authigenic illite and chlorite) and carbonate-hosted soluble Sr. Isotopic homogenization of Sr occurred during Hercynian metamorphism, yielding ages between 309 and 349 Ma.The Sm-Nd isotopic system, on the other hand, is dominated by cogenetic apatite and Fe oxide/ hydroxide, both having high contents of leachable REEs. The leachates yield a Sm-Nd isochron age of 523 ± 72 Ma, indicating diagenetic equilibrium between apatite and Fe-oxide/hydroxide. Fine-grained clay fractions of < 0.2 μm size plot onto this reference line, suggesting isotopic equilibrium with the leachates. Size fractions > 0.2 μm show inheritance of a detrital Nd component. The study demonstrates that the diagenesis of the investigated argillaceous sediments can be dated by the Sm-Nd chronometer in authigenic cement phases. The isotopic system of these minerals (apatite, Fe hydroxide/oxide) was homogenized during authigenic mineral growth in a sediment that was flushed by diagenetic fluids and had abundant primary or secondary interconnected pore space.The Hercynian metamorphic overprint caused partial isotopic rehomogenization of the adsorbed and clay-hosted portion of the Sr as well as of the carbonate-hosted Sr. The Sm-Nd system in the cement phases survived this metamorphism. This results in decoupling of the two isotopic systems and allows the dating of diagenesis on the one hand (Sm-Nd) and metamorphism on the other hand (Rb-Sr).  相似文献   

16.
The paper reports Rb-Sr isotopic data obtained by the authors on ore-hosting rocks from the Kairagach epithermal Au-Ag deposit in the Kurama ore district in the Central Tien Shan, Uzbekistan. The influence of mineralizing hydrothermal solutions on the host volcanic rocks of andesite-dacite composition and the metasomatic alterations of these rocks are proved to have been resulted in with the homogenization of the Sr isotopic composition, i.e., its equalization between various modes of Sr occurrence. This offers additional possibilities of the application of the Rb-Sr isochron method in dating hydrothermal processes. The application of Rb-Sr isotopic methods in studying samples from the Kairagach deposit allowed the authors to obtain dates whose reliability corresponds to isochron one (291 ± 3 Ma) or is very close to it (290 ± 6 Ma). The data thus obtained provide good reasons to believe that the corresponding epithermal mineral deposits in the Kurama ore district (Kairagach, Kochbulak, and others) were genetically related to and simultaneous with the emplacement subvolcanic porphyry intrusions.  相似文献   

17.
从内蒙古包头至白云鄂博地区,横跨高、中、低级变质岩区,都发现有金矿及金矿化点。对三个主要金矿床的Pb、S、Rb—Sr、K—Ar等同位素的研究表明,成矿物质来自变质岩和花岗岩,成矿时代与古生代晚期华北陆台活化的岩浆作用有关。铅的混合模型说明在不同变质岩区变质岩和花岗岩对矿源的贡献不同。  相似文献   

18.
The sequence of rock and ore formation at the Yermakovsky beryllium deposit is established on the basis of geological relationships and Rb-Sr and U-Pb isotopic dating. The Rb-Sr age of amphibolitefacies regional metamorphism is determined for quartz-biotite-plagioclase schist (266 ± 18 Ma) and dolomitized limestone (271 ± 12 Ma) of the Zun-Morino Formation. The U-Pb zircon age of premineral gabbro is 332 ± 1 Ma. The Rb-Sr age of gabbro is somewhat younger (316 ± 8.3 Ma), probably owing to the effect of Hercynian metamorphism on sedimentary rocks of the Zun-Morino Formation and gabbroic intrusion that cuts through it. The U-Pb zircon age of gneissose granite of the Tsagan Complex at the Yermakovsky deposit is 316 ± 2 Ma, i.e., close to the age of metamorphism superimposed on gabbro rocks. The U-Pb zircon age of preore granitic dikes, estimated at 325 ± 3 and 333 ± 10 Ma, is close to the age of gabbro. The Ar/Ar age of amphibole from a granitic dike (302.5 ± 0.9 Ma) probably displays a later closure of this isotopic system or the effect of superimposed processes. The Rb-Sr age of alkali syenite intrusion is 227 ± 1.9 Ma. The U-Pb zircon age of alkali leucogranite stock pertaining to the Lesser Kunalei Complex is 226 ± 1 Ma, while the Rb-Sr age of beryllium ore is 225.9 ± 1.2 Ma. These data indicate that beryllium ore mineralization is closely related in space and time to igneous rocks of the Lesser Kunalei Complex dated at 224 ± 5 Ma and varying from gabbro to alkali granite in composition. Thus, the preore Hercynian magmatism at the Yermakovsky deposit took place ∼330 Ma ago and was completed by metamorphism dated at 271–266 Ma. The ore-forming magmatism and beryllium ore mineralization are dated at 224 ± 5 Ma. Postore magmatic activity is scarce and probably correlated with tectonic melange of host rocks.  相似文献   

19.
康定杂岩Rb-Sr、Sm-Nd同位素系统及其意义   总被引：1，自引：0，他引：1  
通过对康定—冕宁地区出露的英云闪长岩、黑云角闪斜长片麻岩、角闪变粒岩全岩及其中所分离出的角闪石、黑云母、斜长石、钾长石的Rb-Sr、Sm-Nd同位素的系统测定,结合岩石的锆石U-Pb年龄结果,确定这些变质杂岩由于经历了复杂的形成过程与变质历史,Rb-Sr、Sm-Nd同位素体系难以确定其结晶年龄。由单矿物与全岩Rb-Sr、Sm-Nd体系拟合的~700 M a的等时线年龄反映了角闪岩相-高角闪岩相的变质作用年龄。Sm-Nd同位素体系由于在变质作用过程中的部分开放性,很容易给出无意义的较老的混合年龄。康定杂岩结晶后并没有经历麻粒岩相变质作用,区域上所含的麻粒岩透镜体可能是新元古代(773~721 M a)期间由Rod in ia超大陆裂解产生的新生洋壳向扬子克拉通陆块俯冲消减过程的变质产物。俯冲到一定深度后,由于板片被拉断,软流圈上涌导致变质洋壳板片岩石、先前底侵变质的镁铁质岩石及扬子陆块长英质基底岩石发生部分熔融,以镁铁质岩石熔融产生的熔浆为主(>70%),与长英质基底岩石熔融产生的熔浆混合形成w(Na2O)/w(K2O)>1的TTG组合。  相似文献   

20.
The formation conditions and age of the Sukhoi Log gold deposit are considered on the basis of new isotopic-geochemical data. The U-Pb isotopic study of zircon and monazite from high-grade ore and host black slates at the Sukhoi Log deposit was carried out with SIMS technique using a SHRIMP II instrument. Two generations of monazite are distinguished on the basis of optical and scanning electron microscopy, cathodoluminescence, and micro X-ray spectroscopy. Monazite I is characterized by black opaque porphyroblasts with microinclusions of minerals pertaining to metamorphic slates and structural attributes of pre- and synkinematic formation. Monazite II occurs only within the ore zone as transparent crystals practically free of inclusions and as rims around monazite I. The REE contents are widely variable in both generations. Porphyroblastic monazite I differs in low U and Th (0.01–0.7 wt % ThO2) contents, whereas transparent monazite II contains up to 4 wt % ThO2. The average weighted U-Pb isotopic age of monazite I is 650 ± 8.1 Ma (MSWD = 1.6; n = 9) and marks the time of metamorphism or catagenesis. The U-Pb age estimates of synore monazite II cover the interval of 486 ± 18 to 439 ± 17 Ma. Zircons of several populations from 0.5 to 2.6 Ga in age are contained in the ore. Most detrital zircon grains have porous outer rims composed of zircon and less frequent xenotime with numerous inclusions of minerals derived from slates. The peaks of 206Pb/238U ages in the most abundant zircon populations fall on 570 and 630 Ma and correspond to the age of newly formed metamorphic mineral phases. The discordant isotopic ages indicate that the U-ThPb isotopic system of ancient detrital zircons was disturbed 470–440 Ma ago in agreement with isotopic age of monazite II and the Rb-Sr whole -rock isochron age of black slates (447 ± 6 Ma). The new data confirm the superimposed character of the gold-quartz-sulfide mineralization at the deposit. Black shales of the Khomolkho Formation of the Bodaibo Synclinorium were affected by metamorphism over a long period; the peaks of metamorphism and catagenesis are dated at 570 and 650–630 Ma. The high-temperature ore formation was probably related to a hidden granitic pluton emplaced 450–440 Ma ago, that is, 200 Ma later than the events of greenschist metamorphism. Hercynian granitoid magmatism (320–270 Ma) did not exert a substantial effect on the U-Th-Pb isotopic system in accessory minerals from the ore and could not have been a major source of ore-forming fluids.  相似文献   

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