共查询到19条相似文献，搜索用时 390 毫秒
1.
湘西沃溪W-Sb-Au矿床白钨矿Nd-Sr-Pb同位素对成矿流体的示踪 总被引：10，自引：3，他引：10
本文对湘西沃溪W-Sb-Au矿床白钨矿进行了系统的Nd-Sr-Pb同位素分析。结果表明,白钨矿的Sm、Nd含量较低,147Sm/144Nd(0.64~1.27)值和Sm/Nd值(1.11~2.22)变化较大,其εNd(t=199Ma)值也很低,平均为-25.5(n=9);白钨矿的87Sr/86Sr值(0.7476~0.7504)高,平均为0.74961(n=11),代表白钨矿形成时的初始87Sr/86Sr(t=199Ma)值;逐级分离Pb同位素分析结果显示白钨矿的206Pb/204Pb、207Pb/204Pb、208Pb/204Pb值变化范围小,平均依次分别为18.11、15.61、38.6,与含金石英脉中黄铁矿、蚀变围岩及区域板溪群板岩等的相应Pb同位素比值基本一致。白钨矿Nd-Sr-Pb同位素组成和闪锌矿等其他矿物的Sr同位素特征指示成矿流体来自板溪群下伏成熟陆壳、深部花岗质岩浆、浅部赋矿围岩等源区。成矿流体是这些来自不同源区的流体相作用而形成的混合流体。成矿作用则是这些不同源区的流体混合作用并演化的结果。且成矿流体演化早期是来自下伏成熟陆壳的流体与来自赋矿围岩的流体混合,导致早期W成矿;晚期是来自深部花岗质岩浆的流体与浅部赋矿围岩的流体混合作用,导致晚期Sb-Au成矿。W-Sb-Au成矿则是中生代陆内碰撞造山体制下不同期次的流体演化和叠加作用的结果。 相似文献
2.
渣滓溪W-Sb矿床位于湘西雪峰山弧形构造带的中段,是典型脉状W-Sb矿床.本文对渣滓溪矿区的白钨矿进行了Sm-Nd同位素研究.研究表明,其白钨矿的Sm/Nd变化范围为0.2175～0.3485,在白钨矿的147Sm/144Nd-1433Nd/144Nd图解中,对应的等时线年龄为(227.3±6.2)Ma,MSWD=1.6,是白钨矿的形成年龄,代表了渣滓溪W-Sb矿床的主成矿年龄,属于晚三叠纪.渣滓溪W-Sb矿床白钨矿的εMd(t)值为-11.81～-11.91,不同于沃溪W-Sb-Au矿床白钨矿的εNd(t),暗示两者在成矿物质来源上具有一定差异.本次白钨矿Sm-Nd同位素等时线年龄研究结果进一步明确了渣滓溪W-Sb矿成矿年龄,为研究湘西W-Sb多金属矿床成矿年龄及湘西的成矿时空特征提供了可靠和有用的数据,而渣滓溪W-Sb矿床晚三叠纪成矿时代的确定对于区域找矿也具有重要意义. 相似文献
3.
《矿物学报》2016,(3)
苗龙金锑矿床位于贵州三都-丹寨金锑汞成矿带,矿体赋存于上寒武统三都组海相碳酸盐岩中。本文对该矿床的成矿期方解石微量元素含量、Sr-Nd同位素组成进行了研究。结果表明,该矿床成矿期方解石稀土元素总量变化范围大(5.98~139μg/g,平均值为43.7μg/g),在球粒陨石标准化稀土元素配分模式图中大多数方解石样品具有轻稀土富集特征((La/Yb)_N=1.84~9.18,(Gd/Yb)_N=2.55~6.14),少量样品表现为中稀土富集特征((La/Yb)_N=0.33~1.39,(Gd/Yb)_N=1.29~2.24)。该矿床成矿期方解石样品不具有Ce异常(δCe=0.97~1.19),但具有Eu异常(δEu=0.61~1.72),指示其形成于相对还原条件下。方解石样品的~(87)Sr/~(86)Sr值为0.7108~0.7144,平均值为0.7119,高于赋矿围岩的~(87)Sr/~(86)Sr值(0.7090),表明成矿流体相对富放射成因锶,其不可能主要由赋矿的三都组灰岩提供,而可能来自富放射成因锶的前寒武纪基底。Sm-Nd同位素研究表明,该矿床成矿期方解石样品可构筑两条Sm-Nd等时线,其对应的等时线年龄分别为273±14 Ma和272±43 Ma,但与地质背景不符,因此该次方解石Sm-Nd同位素定年等时线无地质意义。这种假等时线现象可能是由成矿流体初始~(143)Nd/~(144)Nd不均一造成的。方解石ε_(Nd)(0)(-14.02~-9.48)远小于0,指示成矿流体中的Sm和Nd来源于陆壳。 相似文献
4.
包金山金钨矿床位于湘中白马山-龙山-紫云山金矿带的东段,是近年新发现的一个赋存于前寒武纪浅变质岩中的金矿床。在野外调研和室内镜下研究的基础上,本文利用XRD、EMPA、ICP-MS、ID-MS等多种分析手段,对其进行了元素地球化学和同位素地球化学研究,进而揭示了该区金矿床的形成时代和矿床成因。研究表明,该区白钨矿的化学成分较均一,其WO_3含量大体与理论值一致,但Ca O含量稍低于其理论值,这可能与Sr、REE、Na等微量元素对白钨矿晶格中Ca的类质同象置换有关。除Sr、REE、As以外,该区白钨矿中的微量元素,特别是Mo、Bi、Sn、Be、Nb、Ta等均低于1×10~(-6),明显有别于华南与燕山期花岗岩有关钨矿床中的白钨矿。该区白钨矿的稀土元素含量为484.5×10~(-6)~972.9×10~(-6)(平均721.3×10~(-6)),显著高于湘西、湘中一带其它矿床中的白钨矿;其稀土元素配分模式均表现出向上拱曲的富MREE特征。该区白钨矿的~(147)Sm/~(144)Nd比值为0.2079~0.4070,~(143)Nd/~(144)Nd为0.512126~0.512398,在Sm-Nd同位素图解中构成了一条很好的等时线,其对应的等时线年龄为207.8±1.5Ma(MSWD=1.03),表明该矿形成于晚三叠世。该区白钨矿的~(87)Sr/~(86)Sr值较高(0.73164~0.73974),大体与渣滓溪矿区的白钨矿一致,高于廖家坪和龙山矿区的白钨矿,但明显低于沃溪和西安矿区的白钨矿,这暗示湘中、湘西一带不同时代形成的金钨矿床,其成矿物质来源和成矿机制可能存在差异。Sr-Nd同位素联合示踪显示,包金山矿区白钨矿的Sr-Nd同位素组成,明显不同于新元古界板溪群和紫云山岩体的主体,而是与紫云山补体花岗岩较吻合,暗示该区金钨成矿可能与紫云山晚期岩浆活动有关。结合区域年代学资料,可进一步推断出,晚三叠世金、钨成矿作用在湘中地区广泛存在,这些成矿作用均与印支期花岗质岩浆活动有关。湘中一带前寒武纪浅变质岩中的金矿床,在成因上是属与还原性侵入岩有关的金矿类型(IRGS型)。 相似文献
5.
湘西沃溪Au-Sb-W矿床中富放射成因锶的成矿流体及其指示意义 总被引：8，自引：0，他引：8
研究表明，湘西沃溪Au-Sb-W矿床白钨矿的Sr含量很高，为1455—6810μg／g；^87Sr／^86Sr为0．74675～0．75003，明显不同于国外金矿中的白钨矿，表现出显富放射成因锶。沃溪矿床的成矿流体为一种显富放射成因锶的热水溶液，暗示成矿流体不可能是类似于现代大洋中脊喷出的热液或古海水，其矿床成因并非前人所认为的“海底热泉(卤水)沉积成因”或“海底喷流沉积成因”。矿床中这种显富放射成因锶的成矿流体。很可能是热水溶液对下伏古老基底淋滤或是对元古界赋矿地层中的碎屑岩选择性优先淋滤所致。 相似文献
6.
赋存于变质岩中的层控（层状）型钨矿床的成因在国际矿床学界一直存在争议,白钨矿的元素和同位素地球化学研究是解决其成因争议的有效手段。位于雪峰弧形构造带中的西安钨矿床是该类矿床的典型代表,其矿床成因也存在着很大争议。本文利用EMPA、ICP- MS、ID- MS等多种分析手段,对该矿白钨矿的主量元素、微量元素、及Sm- Nd和Sr同位素进行了研究。研究表明,该区白钨矿中CaO含量小于其理论值,这可能与热液流体中的REE、Sr、Pb、Ba等元素与白钨矿中的Ca发生类质同象置换有关;该区白钨矿微量元素组成具有富Sr、而亏损Mo、Bi、Sn、Nb、Ta等特征,类似于西澳绿岩带型金矿、云南大坪和湘西沃溪等造山型金矿床中的白钨矿,其Mo含量和Sr/Mo值均显示其具变质热液成因特征,而与岩浆热液无关;该区白钨矿的稀土元素配分模式相当一致,均表现为LREE亏损、HREE相对富集、MREE最为富集的特征,其分配行为主要表现为REE3+与Na+以电价补偿形式替代Ca2+而选择性进入白钨矿晶格中;该区白钨矿n(87Sr)/n(86Sr)测定值为0. 75412~0. 78231,表明形成该区白钨矿的成矿流体并非来自海水或岩浆热液,其矿床成因也并非前人所认为的“海底热泉（卤水）沉积成因”、“海底同生喷流沉积成因”或“岩浆期后热液成因”。在LREE—MREE—HREE三角判别图解中,西安矿区白钨矿样品点均落入加拿大、澳大利亚和湘西造山型金矿区域,明显不同于与岩浆活动有关的钨矿床,该矿是属于造山型钨矿;在Sr—Nd同位素组成图解中,该区白钨矿与湘西一带出露的新元古代地层明显分布在不同区域,但部分样品点与华南最老地层—太古宇崆岭群重叠,暗示该矿成矿物质可能来自深部的太古宇崆岭群,而非来自赋矿的新元古界变质岩。 相似文献
7.
安徽东顾山钨矿床白钨矿主微量元素和Sr-Nd同位素特征及其对成矿作用的指示 总被引：7，自引：3，他引：4
安徽东顾山矿床是长江中下游成矿带长江以北发现的首例大型矽卡岩型钨矿床。该矿床的成矿岩浆岩为黑云母花岗岩,成矿时代为97.22Ma,成矿作用明显不同区内140Ma斑岩型铜金矿床和130Ma玢岩型铁矿床。本文通过对东顾山矿床中矽卡岩阶段和氧化物阶段白钨矿开展EPMA矿物主量元素、LA-ICP MS微量元素分析和Sr-Nd同位素测试分析,对矿床成矿流体的演化和成矿物质来源进行了系统研究。矿床中两类白钨矿稀土元素和Mo~(6+)含量演化特征均指示成矿流体氧逸度逐渐减弱。两类白钨矿的εNd(t)范围为-17.7~-16.2,~(87)Sr/~(86)Sr值为0.70956~0.71113,指示东顾山矿床的成矿物质来自地壳,并由董岭群变质基底提供了部分成矿物质。东顾山矿床与长江中下游成矿带及邻区鸡头山矿床、大湖塘矿床中的白钨矿同位素特征差别较大,指示钨矿床的成矿物质来源除了江南式基底和双桥山群基底外,董岭式基底可以为钨矿床提供成矿物质,因此南钨北移的界限可以越过长江深断裂。 相似文献
8.
贵州晴隆锑矿床中萤石的Sr同位素地球化学 总被引：11，自引：0，他引：11
对黔西南晴隆锑矿床中的萤石进行了Sr同位素分析，得到其Sr同位素比值为0．70766-0．70932。这个比值明显高于赋矿的二叠系茅口组灰岩(0．70672—0．70821)和蛾眉山玄武岩(0．70441—0．70638)，表明成矿流体相对富集放射成因^87Sr。由于该矿成矿流体的Sr同位素比值明显高于蛾眉山玄武岩，因此将其成矿作用仅仅简单归结于与玄武岩火山活动有关的岩浆热液是不妥的。同时，成矿流体Sr同位素比值也高于二叠纪灰岩的Sr同位素比值，指示成矿流体不可能为单纯的二叠纪海水，而应该有更为富集放射成因Sr的岩石的贡献，可能是这些二叠系岩石下伏的地壳基底。先前对矿床稀土元素地球化学研究得到，成矿物质有外部地壳岩石参与；氢氧同位素地球化学研究发现，成矿流体为大气降水演化产物而不是海水;成矿物质(F和Sb)具有赋矿围岩以外的来源。结合萤石的Sr同位素分析，可以认为晴隆锑矿不是简单的“海相火山喷流沉积成因”或“原地改造产物”，成矿流体和成矿物质均具有外部来源参与而不单单是来自赋矿围岩，可能与下伏基底岩石有关。 相似文献
9.
湘中锡矿山锑矿床的Sr同位素地球化学 总被引：21，自引：3，他引：21
对湘中锡矿山锑矿床围岩灰岩、硅化灰岩、煌斑岩和脉石矿物进行了系统的Sr同位素研究。结果表明，矿区围岩发生了隐性蚀变，灰岩中Sr亏损，而^87Sr/^86Sr高于同时代的海相碳酸盐，这种隐性蚀变很可能是水／岩反应所致。矿体附近的硅化灰岩中Sr更加亏损，而^87Sr/^86Sr明显增加。成矿期方解石的^87Sr/^86Sr较高，成矿体系中变化的W／R比造成了方解石中^87Sr/^86Sr值的明显波动。成矿流体为一富放射成因^87Sr的溶液。成矿流体来自或流经基底地层，流体中的Sr由基底碎屑岩提供，矿质Sb也可能主要来自富Sb的元古宇基底。水／岩反应的理论模拟显示，锡矿山成矿流体中的Sr约为3．0μg/g，^87Sr/^86Sr为０．７１７；蚀变－成矿体系为一开放体系，矿石的沉淀机制主要为水／岩反应，成矿体系中W／R 比较高。 相似文献
10.
古台山矿床是雪峰弧形构造带中段颇具代表性的石英脉型金锑矿床。矿床位于白马山复式岩体的外接触带,主要赋存于南华系长安组和板溪群五强溪组。本文对古台山矿床载金矿物毒砂流体包裹体氦、氩同位素和含矿石英流体包裹体铷、锶同位素进行了分析。He-Ar同位素分析显示,成矿流体的3He/4He为0.011~0.038 Ra,40Ar/36Ar值为414.4~732.6,表明成矿流体主要为地壳流体,同时有部分大气降水的加入。Sr同位素分析显示,含矿石英流体包裹体87Rb/86Sr变化于0.013~0.956,87Sr/86Sr变化于0.72529~0.73245;利用前人获得的成矿年龄(223.6 Ma)进行了初始锶同位素组成的返算,获得其ISr-223.6变化于0.72360~0.73167,平均0.72744。通过与印支期白马山岩体、板溪群等相关地质体锶同位素组成对比,认为古台山矿床成矿流体不可能单独来源于岩浆,而是岩浆流体运移过程中与来自基底具有高锶同位素比值的碎屑岩水岩相互作用的结果。He-Ar同位素揭示矿区深部及周缘地区板溪群具有更好的资源潜力。 相似文献
11.
Nd-Sr-Pb isotopic constraints on metal and fluid sources in W-Sb-Au mineralization at Woxi and Liaojiaping (Western Hunan,China) 总被引：9，自引：0，他引：9
This paper presents Nd-Sr-Pb isotope data on scheelite, inclusion fluids and residues of gangue quartz, and sulfides from the W-Sb-Au ore deposits at Woxi and Liaojiaping (LJP) in the Xuefeng Uplift Belt (XUB), Western Hunan, China. Sm and Nd concentrations in scheelite from Woxi are much lower than in scheelite from LJP and can be distinguished by their high 147Sm/144Nd ratios of ~1.25 from the much lower ratios around 0.26 in scheelites from the LJP. Nd values (compared to values at 200 Ma, which is the average timing of granitoid emplacement during the Indosinian-Yanshanian periods in the XUB) are around –10 for the LJP and compare well with the range of –5 to –11 defined by the granitoids, whereas they are around –27 for scheelite from Woxi. This might indicate that REEs in the mineralizing fluids at LJP originated from granitoids that are concentrated along the southern border of the XUB, whereas in the case of Woxi, the original fluids might have been masked by REEs released during intense high-temperature wall rock alteration of unexposed Precambrian basement rocks at depth. Sr isotopes of scheelite from these two deposits show similar relations to host / nearby rocks, in that 87Sr/86Sr (T=200 Ma) ratios of ~0.721 for LJP scheelite agree with values ranging between 0.718 – 0.726 for granitoids, whereas these ratios are much higher (i.e. 0.745) for scheelite from Woxi and correspond to the 87Sr/86Sr (T=200 Ma) ratio range of 0.743 – 0.749 for Precambrian host slates. Crushing experiments to release inclusion fluids from gangue quartz and sulfides deposited during later stages of ore deposition in both deposits failed to provide accurate and geologically meaningful two-point (fluid-residue) tie lines in Rb-Sr isochron diagrams. However, Sr released from fluid inclusions generally reveals lower initial 87Sr/86Sr ratios than the respective residues and shows affinities to 87Sr/86Sr (T=200 Ma) values of Indosinian-Yanshanian granitoids, both at Woxi and LJP. Pb stepwise leaching of scheelite and sulfides did not result in sufficient spreads in Pb isotope diagrams and therefore no information regarding exact mineralization ages in the two deposits could be deduced. Overall, ore Pb isotopes reveal upper crustal signatures and are compatible with Pb isotope signatures of the predominant Precambrian slates in the Woxi area. Steep trajectories through late stage quartz-sulfide mineralization in Pb isotope diagrams may hint at mixing scenarios involving Pb from the host rocks and a component with lower 207Pb/204Pb and 208Pb/204Pb ratios relative to 206Pb/204Pb ratios, which cannot be linked to any known reservoir in the XUB mining district. Sr isotopes of four out of seven residual sulfide samples from Woxi plot along a paleomixing line at an age of 199 ± 8 Ma, supporting a mixing scenario for the fluids indicated by the Pb isotopes and pointing to a possible genetic relationship with the emplacement of Indosinian—Yanshanian granitoids. The budgets of REEs, Rb-Sr and Pb in the original fluids were severely affected by contamination of these elements apparently during intense wall rock alteration but, after sealing of the major pathways, the mineralizing fluids tend to have better preserved their original signatures. These attest a genetic relationship between the metallogeny in the XUB W-Sb-Au province and the emplacement of Indosinian-Yanshanian granitoids during Mesozoic intracontinental tectonic uplift and thrusting.Electronic Supplementary Material Supplementary material is available in the online version of this article at Editorial handling: B. Lehmann 相似文献
12.
江西相山铀矿田成矿物质来源的Nd、Sr、Rb同位素证据 总被引：14，自引：0，他引：14
对相山大型火山岩型铀矿田中邹家山和沙洲铀矿床及其赋矿围岩（碎斑熔岩及次花岗闪长斑岩）进行了Nd、Sr、Pb同位素研究。结果表明：成矿期萤石的εNd(t)值（－6．7～-8．3）和初始^87Sr/^86Sr比值（0．7145－0．7207）与赋矿围岩的εNd(t) 值（－6．2～－9．4）和初始^87Sr/^86Sr比值（0．7121－0．7192）相似。在εNd(t)-tl图上，成矿期萤石数据点的投影域与赋矿围岩的基本吻合，均落在相山元古宙基底演化域范围内。成矿期黄铁矿的铅组成在^206Rb/^204Pb-^207Pb/^204Pb关系图上呈线性分布，而火山岩的铅同位素组成位于此相关线低值一端。利用异常铅线的斜率及成矿年龄计算出富铀体质体的形成年龄为144Ma，这与赋矿围岩的成岩年龄（135－140Ma)接近。因此，相山铀矿田成矿物质主要来自富铀的火山－侵入杂岩,而火山－侵入杂岩则是由类似于地表出露的元古宙基底变质岩部分熔融形成的。由引可见，相山铀矿田的成矿物质主要来源于地壳。 相似文献
13.
The DUPAL anomaly, a radiogenic isotope anomaly discovered in the Indian Ocean mantle, has been interpreted as due to a large-scale mantle heterogeneity. To provide new constraints on the DUPAL origin, we analyzed isotope ratios of Li, Sr, and Nd in fresh N-MORB glasses recovered from the Rodrigues Triple Junction in the Indian Ocean, and from the North Atlantic. The Li isotopic compositions of the Indian Ocean DUPAL N-MORBs were comparable to those of the North Atlantic non-DUPAL N-MORBs. The source of the DUPAL signature in Indian Ocean MORBs and the E-MORB-type enriched mantle source have quite different Li isotopic compositions. The 143Nd/144Nd values of both sources are significantly lower than those of the North Atlantic N-MORBs. The δ7Li values of most oceanic island basalts with similar low 143Nd/144Nd signatures are also higher than those of the North Atlantic N-MORBs, except for several Koolau lavas. The Li isotope results support the recent proposal that significant amounts of recycled lower continental crust might produce the radiogenic isotope signatures of the Indian Ocean DUPAL source. 相似文献
14.
河南大湖金钼矿床成矿物质来源的锶钕铅同位素约束 总被引：10，自引：6，他引：4
河南灵宝大湖金钼矿床位于小秦岭金矿田北缘,属典型的断控脉状矿床.前人较好研究了矿床流体包裹体和成矿年代,但对成矿物质来源研究薄弱.本文对16件矿石硫化物及5件赋矿围岩样品进行了Sr-Nd-Pb同位素分析,金属硫化物I_(Sr)=0.70470～0.71312,平均0.70854;(~(143)Nd/~(144)Nd)_i=0.51143-0.51215,平均0.51162;(~(206)Pb/~(204)Pb)_i=17.033～17.285,(~(207)Pb/~(204)Pb)_i=15.358～15.438,(~(208)Pb/~(204)Pb)_i=37.307-37.582,平均值分别是17.162,15.405,37.440.5件太华超群样品I_(Sr)=0.70947～0.73201,平均0.72294;(~(143)Nd/~(144)Nd)_i=0.51076～0.51133,平均0.51107;(~(206)Pb/~(204)Pb)_i=17.127～18.392,(~(207P)b/~(204)Pb)_i=15.416～15.604,(~(208)Pb/~(204)Pb)_i=37.498～37.814,平均值分别是17.547,15.470,37.616.Sr-Nd-Pb同位素特征表明成矿物质来源具壳幔混合特征,初始成矿流体可能来源于亏损的残余洋壳,并通过成矿过程的水岩相互作用与太华超群混合;据此认为,在218Ma年左右,秦岭地区的陆陆碰撞造山作用并没有结束,而仍在进行之中. 相似文献
15.
藏西班公湖斑岩铜矿带成矿斑岩地球化学及Pb、Sr、Nd同位素特征 总被引：9，自引：1，他引：8
对班公湖铜矿带2个具有代表性的斑岩铜矿床--多不杂铜矿床和尕尔穷铜矿床进行了详细的岩石地球化学和Pb、Sr、Nd同位素特征研究表明,与冈底斯铜矿带相比,该铜矿带含矿斑岩大离子不相容元素的富集程度相对减弱,而高场强元素和重稀土元素的亏损程度明显减轻,轻、重稀土元素的分馏程度减弱,且具有Eu的弱正异常,岩石在氧化性上更强一些;从Pb、Sr、Nd同位素特征来看,班公湖铜矿带含矿斑岩更富含放射性成因铅,~(143)Nd/~(144)Nd比值明显降低,其源区更接近印度洋沉积物区域,表明该铜矿带含矿斑岩的岩浆源区更浅,有更多的地壳物质加入;班公湖铜矿带含矿斑岩形成的构造环境属于活动大陆边缘区域,而冈底斯铜矿带明显偏离了活动大陆边缘区域,表明班公湖斑岩铜矿带形成于碰撞后地壳隆升阶段,而冈底斯铜矿带则形成于碰撞后地壳伸展阶段. 相似文献
16.
Omai is a high tonnage, low-grade, world-class gold deposit located in the Paleoproterozoic Guiana Shield. It is the second
most important gold deposit in the Guiana Shield (after Las Cristinas, Venezuela), and one of the largest in South America
(4.0 million oz.). Sm-Nd and Sr isotope data are presented for host rocks and for scheelite from auriferous quartz-carbonate-scheelite-sulfide-telluride
veins from the Omai deposit. Gold-bearing veins are hosted by the Paleoproterozoic Barama-Mazaruni Supergroup, a greenstone
belt sequence consisting of mafic volcanic rocks interbedded with sedimentary rocks that are intruded by quartz-feldspar porphyry
and rhyolite dikes. This lithologic sequence was folded and metamorphosed to lower greenschist facies during the Paleoproterozoic
Trans-Amazonian orogeny. The volcano-sedimentary unit was intruded by a post-tectonic quartz monzodiorite-diorite-hornblendite
stock. Initial Nd isotope ratios for the Omai volcanic rocks range from ɛNd=+2.1 to +4.2. These values suggest that this part of the Guiana Shield was a site of new crust formation during the Paleoproterozoic
and was not contaminated by older (Archean), reworked continental crust. Initial Nd isotope ratios for the Omai stock range
between +0.5 and +2.3, which suggest limited contamination with previously formed continental crust. Although the Nd isotopic
ratios of gold-related scheelites overlap with those of the host rocks, particularly the tholeiitic basalts at the interpreted
time of vein emplacement, the lack of both isotopic mixing and significant Nd movement during the hydrothermal process suggest
that the Nd isotope composition can be used to determine the isotopic characteristics of the ore fluid source area. At Omai,
the ore fluid is largely derived from a radiogenic Nd source, represented by mantle or lower crustal reservoirs. Strontium
isotope ratios for the scheelites cluster tightly between 0.7019 and 0.7021. The Sr isotope data suggest that unlike Nd, Sr
was significantly mobile during the hydrothermal process. The fluids responsible for the Omai deposit may have picked up Sr
along the flow path. The constant low Sr isotope values of scheelites probably reflect the key role that the local tholeiitic
basalts played as the main source of Sr in the fluids. Whereas Nd isotopes identify the fluid source area, the Sr isotopes
map the fluid flow paths.
Received: 11 February 1999 / Accepted: 1 November 1999 相似文献
17.
Francesca Castorina Umberto Masi Giorgio Padalino Marcella Palomba 《Mineralium Deposita》2006,41(4):323-338
Major- and trace-element contents and Sr–Nd isotope ratios were determined in albitite, albitized and unaltered late-Variscan granitoid samples from the world-class Na-feldspar deposits of central Sardinia, Italy. The albite deposit of high economic grade has geological, textural, and chemical features typical of metasomatic alteration affecting the host granitoids. Albitization, locally accompanied by chloritization and epidotization, was characterized by strong leaching of Mg, Fe, K, and geochemically similar trace elements, and by a significant increase of Na. Ca, and P were moderately leached in the most metasomatized rocks. Other major (Si, Ti, Ca) and trace elements (U, Th, Y, and Zr), along with light (LREE) and middle (MREE) rare-earth elements, behaved essentially immobile at the deposit scale. The Nd-isotope ratios (0.512098 to 0.512248) do not provide information on the emplacement age of the unaltered late-Variscan granitoids. On the other hand, their Sr-isotope ratios fit an errorchron of 274±29 Ma (1σ error), in fair agreement with all published ages of Sardinian Variscan granitoids. The very low Rb content of albitized rocks precludes application of the Rb–Sr radiometric system to determine the age of albitization. The Sm–Nd system is not applicable either, because the 143Nd/144Nd ratios of albitized rocks and unaltered granitoids overlap. The overlap confirms that Sm and Nd were substantially immobile during albitization. On the other hand, the measured 87Sr/86Sr ratios of the albitized rocks are appreciably lower than those of the unaltered host granitoids, whereas, their initial Sr-isotope ratios are higher. This seems to suggest that a) albitization was induced by non-magmatic fluids rich in radiogenic Sr, and b) albitization occurred shortly after the granitoid emplacement. This conclusion is supported by Nd isotopes, because unaltered granitoids and albitites fit the same reference isochron at 274 Ma. The fluids acquired radiogenic Sr by circulation through the Lower Paleozoic metasedimentary basement. Specifically, it is estimated that Sr supplied by the non-carbonatic basement represents about 22 wt% of total Sr in albitite. 相似文献
18.
岩石学、地球化学和Nd、Sr、Pb同位素研究表明,西藏冈底斯铜矿带雄村特大型铜金矿床的容矿火山岩为一套具超浅成侵入特点的英安斑岩,SiO2含量集中在61.97%~64.31%之间,富Na2O、低K2O,Na2O/K2O比值平均为5.25。地球化学上明显富集大离子不相容元素Rb、Ba、K、Sr、Pb,同时高场强元素Nb、Ta、Ti处于亏损状态。Sr、Nd同位素组成变化范围小(87Sr/86Sr=0.705154~0.708267,ISr=0.704299~0.705357;143Nd/144Nd=0.512730~0.512931),具有富集地幔特征;Pb同位素组成显示出地幔铅与造山带铅的双重特性(206Pb/204Pb=18.170~18.432,207Pb/204Pb=15.485~15.546,208Pb/207Pb=37.993~38.392)。研究指出它们是早侏罗世(195Ma)由雅鲁藏布江洋壳向欧亚大陆之下俯冲形成的岛弧火山岩,岩浆源区具有EM1型原始地幔富集特征,同时有一定数量的俯冲沉积物加入了地幔源区的部分熔融。根据雄村矿床的成矿时代和矿化特征,笔者认为该矿床的成因类型与胶东焦家式金矿一致,为破碎带蚀变岩型。旦狮庭组容矿火山岩对成矿的贡献在于作为矿源层为矿床提供了成矿金属元素。 相似文献
19.
山东蓬莱、临朐新生代碱性玄武岩的钕、锶同位素组成 总被引：16，自引：0，他引：16
本文报道了鲁东和鲁西新生代碱性玄武岩13个样品的Nd、Sr同位素组成,~(143)Nd/~(144)Nd=0.512967—0.512744,~(87)Sr/(86)Sr=0.70349—0.70450。它们在地质剖面上呈现规律性变化,可能与其地幔源区同位素组成的层状分带有关。鲁西地幔源区具有较鲁东更加亏损的组份。两地地幔源区在演化中都曾发生过地幔交代(或富集)作用,根据玄武岩Nd同位素模式年龄估计地幔交代作用发生的时间为0.45Ga。 相似文献