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八卦庙金矿床位于秦岭造山带凤太铅锌多金属矿田北部,是陕西省规模较大的金矿床之一,已探明金储量约106 t.赋矿围岩是上泥盆统星红铺组浅变质泥质碎屑岩和碳酸盐岩,其成矿过程可划分为3期,分别是①顺层磁黄铁矿-石英成矿期;②NE向黄铁矿-石英成矿期;③裂隙硫化物-方解石成矿期.目前关于NE向黄铁矿-石英成矿期成矿物质来源和成矿机制仍存在争议.本文通过矿相学观察,将NE向黄铁矿-石英成矿期划分为自形磁黄铁矿-黄铁矿-粗粒石英阶段(Ⅰ)、他形黄铁矿-银金矿-细粒石英阶段(Ⅱ)、他形磁黄铁矿-自然金-方解石阶段(Ⅲ)和黑云母阶段(IV),并在此基础上采用激光剥蚀-多接收等离子体质谱(LA-MC-ICP-MS)分析方法对千枚岩围岩中以及不同阶段形成的硫化物进行了原位S同位素测试,结果显示围岩中原生磁黄铁矿的δ34 S值集中于11.6‰～13.0‰之间,介于前人报道的原生黄铁矿δ34 S值变化范围(3.3‰～16.0‰);阶段I形成的黄铁矿的δ34 S值为8.4‰～10.1‰,磁黄铁矿为7.6‰～8.0‰;阶段II黄铁矿的δ34 S值相对较高,为14.0‰～15.9‰;阶段Ⅲ磁黄铁矿的δ34 S值介于6.4‰～8.3‰之间.八卦庙金矿NE向黄铁矿-石英成矿期总体相对富集重硫同位素、离散程度较大,各阶段硫化物的硫同位素值介于矿集区花岗岩和围岩硫之间,显示其具有岩浆硫与地层硫混合的特征.结合阶段I到阶段Ⅲ矿物组合的变化(黄铁矿+磁黄铁矿→黄铁矿→磁黄铁矿),推断阶段IIδ34 S值增高是水岩反应引起的硫化作用所致,而阶段Ⅲ硫同位素值降低可能与岩浆水的加入密切相关.结合成矿物理化学条件,推断该成矿期成矿热液中金主要以Au(HS)2-的形式迁移,阶段I到阶段Ⅱ由水岩反应引起的硫化作用是导致他形黄铁矿-银金矿-细粒石英阶段(Ⅱ)金矿化的主要原因,而岩浆水的混入可能是导致他形磁黄铁矿-自然金-方解石阶段(Ⅲ)金沉淀的主要机理. 相似文献
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云南香格里拉红山铜矿石硫化物环带及地质意义 总被引：3，自引：3，他引：0
云南香格里拉县红山铜矿是三江义敦岛弧带南端重要铜矿床,颇受关注,成因认识分歧大.矿区出露上三叠统板岩、变碎屑岩和灰岩夹中基性火山岩、火山碎屑岩以及少量侵入其中的中酸性和超基性岩脉、岩株,透镜状铜硫化物矿体产在顺层状矽卡岩体内或边部,成矿后断裂明显.矿石中普遍发育以黄铁矿为核部、黄铜矿为中间带、磁黄铁矿为边部带的硫化物环带,其中核部黄铁矿呈立方体自形-半自形晶,黄铜矿呈他形晶围绕黄铁矿沉淀,磁黄铁矿呈他形分布在黄铜矿外围,内带常被外带硫化物溶蚀交代.环带从内到外硫化物先后沉淀,矿物生成顺序为黄铁矿-黄铜矿-磁黄铁矿.环带中三种硫化物矿物的REE配分曲线和微量元素蛛网图极为相似,负Eu异常显著,富集U、Th、Zr、Hf,亏损Rb、Sr、Ba,与矿区超基性岩表现出较高相似性;环带从内到外,∑REE(0.17371×10-6、1.22626×10-6、5.25925×10-6)和微量元素含量依次升高,Co/Ni和Se/Te比值降低,指示矿石硫化物沉淀过程中,可能伴随热液体系内地壳物质不断增加.环带中硫化物矿物δ34SV-CDT=3.81‰～5.23‰,具有岩浆硫源特征,δ34SV-CDT边部带磁黄铁矿 (4.47‰)＜δ34SV-CDT中间带黄铜矿(4.58‰)＜ δ34SV-CDT核部黄铁矿(4.65‰),三种硫化物间没有达到同位素平衡分馏.红山铜矿石环带结构是岩浆热液为主成矿流体中黄铁矿、黄铜矿、磁黄铁矿先后晶出成因,伴随硫化物环带的形成,热液系统从早到晚H2S和O2逸度降低或pH升高过程. 相似文献
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隋延辉 《吉林大学学报(地球科学版)》1990,(3)
辽宁省浑河断裂以北(浑北)地区的诸块状硫化物矿床遭受了强烈变形-变质作用影响。本文论述硫化物矿体的变质-变形,以及硫化物矿物的物理迁移。阐明黄铁矿发生塑性变形的影响因素;指出磁黄铁矿由六方相转变为单斜相是其发生塑性变形的重要机制;讨论了硫化物塑性变形序列;测得Cu型矿床变形温度为450～500℃,变形压力为0.7～0.8GPa;S型矿床变型温度为600～650℃,相应的压力为1.0～1.2GPa。 相似文献
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捕虏体麻粒岩是了解下地壳形成和演化的重要样品。汉诺坝新生代玄武岩中的二辉麻粒岩捕虏体样品中富含各种硫化物相,主要类型有:①孤立产出的球状出溶硫化物;②矿物颗粒之间或颗粒内的粗晶硫化物;③次生硫化物包裹体群;④裂隙充填硫化物。电子探针分析表明,硫化物的矿物成分均为贫镍磁黄铁矿,(Ni+Co+Cu)/Fe(原子比)远小于0.2;(Fe+Cu+Co+Ni)/S(原子比)比地幔岩的磁黄铁矿小,多小于0.875,反映了一种S过饱和环境。各种产状的磁黄铁矿中Au、Ag都有一定的含量,其平均值分别为0.19%～0.22%(Au)、0.01%～0.02%(Ag),反映下地壳的麻粒岩化与金矿化的成因联系。磁黄铁矿的Ni、Co、Cu含量与S正相关,说明微量重金属元素与S具有同源的关系,由于地幔去气伴随S而进入下地壳。 相似文献
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捕虏体麻粒岩是了解下地壳形成和演化的重要样品.汉诺坝新生代玄武岩中的二辉麻粒岩捕虏体样品中富含各种硫化物相,主要类型有:①孤立产出的球状出溶硫化物;②矿物颗粒之间或颗粒内的粗晶硫化物;③次生硫化物包裹体群;④裂隙充填硫化物.电子探针分析表明,硫化物的矿物成分均为贫镍磁黄铁矿,(Ni Co Cu)/Fe(原子比)远小于0.2;(Fe Cu Co Ni)/S(原子比)比地幔岩的磁黄铁矿小,多小于0.875,反映了一种S过饱和环境.各种产状的磁黄铁矿中Au、Ag都有一定的含量,其平均值分别为0.19%～0.22%(Au)、0.01%～0.02%(Ag),反映下地壳的麻粒岩化与金矿化的成因联系.磁黄铁矿的Ni、Co、Cu含量与S正相关,说明微量重金属元素与S具有同源的关系,由于地幔去气伴随S而进入下地壳. 相似文献
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东天山主要铜镍矿床中磁黄铁矿的矿物标型特征及其成矿意义 总被引：7，自引：4，他引：3
东天山是中国最重要的岩浆铜镍硫化物矿带之一,产有黄山东、黄山、香山、葫芦等大中型铜镍矿床。图拉尔根、白石泉两处镍铜矿床为近年来在新疆地区铜镍找矿中的重大发现,两者均属于与镁铁质-超镁铁质杂岩有关的岩浆熔离-贯入型矿床。矿物共生组合以磁黄铁矿 镍黄铁矿 黄铜矿为特征,磁黄铁矿系矿石中最主要组成部分。文章以X射线衍射、扫描电镜、电子探针分析并辅以常规显微镜,查明这些矿床中磁黄铁矿均系Co、Ni的最主要载体矿物,Co、Ni元素主要以游离状态的硫化物(或硫砷化物)形式存在,如镍辉砷钴矿、钴辉砷镍矿、镍黄铁矿及紫硫镍矿等矿物。它们多以微细包裹体或出溶体形式随机地分布于磁黄铁矿内部,而少量的Co、Ni元素则以类质同像方式存在于磁黄铁矿晶格之中。图拉尔根、白石泉、葫芦三矿床中磁黄铁矿在多型结构以及微量元素地球化学方面均表现出一定的差异,系由两矿床容矿岩石基性程度及成矿温度之差异引起。 相似文献
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现代海底烟囱中流体包裹体的研究 总被引：8，自引：2，他引：8
大洋中脊的海底块状硫化物矿床是当前地球科学的一个热点。因为他不仅具有经济效益,而且可以直接观测到这些矿床的形成过程。这些矿床均有许多黑烟囱和白烟囱。在这些烟囱中成矿流体不断地流过,并同时沉淀出Cu,Pb,Zn硫化物和脉石矿物。本研究的样品是取自北纬21°N的太平洋洋脊中现代大洋海底的Zn(Cu)型硫化物烟囱。对这些烟囱的矿物共生组合进行研究发现其矿物组合相当简单,分硫化物和脉石矿物两种。硫化物中以其含量多少排列为闪锌矿,黄铁矿,黄铜矿和磁黄铁矿。脉石矿物以硬石膏为主,见少量重晶石。在烟囱中这些硫化物和脉石矿物的分布是有分带性的。从外到内为硬石膏带,黄铁矿带,闪锌矿带。闪锌矿带向里可见到少量黄铜矿和磁黄铜矿,及硬石膏,但它们尚未构成一个带。烟囱的中心常常是空的,因为是原来的热液通道。 发现两类流体包裹体:一类为水溶液相包裹体。另一类为CH_4的包裹体。其均一温度是从180～265℃。最外面的硬石膏带,均一温度从180～245℃(平均212℃)。黄铁矿带均一温度从185～260℃(平均218℃)。闪锌矿带均一温度从190～265℃(平均229℃)。从平均的均一温度看似乎从边上到中心从212—218—229℃向上升,说明一个趋势,中间的温度较高,边上的较低。成矿溶液的盐度与海水相差不大,但略大於海水 相似文献
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捕虏体麻粒岩是了解下地壳形成和演化的重要样品。汉诺坝新生代玄武岩中的二辉麻粒岩捕虏体样品中富含各种硫化物相，主要类型有：①孤立产出的球状出溶硫化物；②矿物颗粒之间或颗粒内的粗晶硫化物；③次生硫化物包裹体群；④裂隙充填硫化物。电子探针分析表明，硫化物的矿物成分均为贫镍磁黄铁矿，（Ni＋Co＋Cu）／Fe（原子比）远小于0．2；（Fe＋Cu＋Co＋Ni）／S（原子比）比地幔岩的磁黄铁矿小，多小于0．875，反映了一种S过饱和环境。各种产状的磁黄铁矿中Au、Ag都有一定的含量，其平均值分别为0．19％～0.22％（Au）、0．01％～0．02％（Ag），反映下地壳的麻粒岩化与金矿化的成因联系。磁黄铁矿的Ni、Co、Cu含量与S正相关，说明微量重金属元素与S具有同源的关系，由于地幔去气伴随S而进入下地壳。 相似文献
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金川岩浆铜镍（铂）硫化物矿床是我国最主要的铂族等战略性关键金属宝库。金川矿床中铂族金属的富集过程和富集机制还存在很多争论。本文通过详细的矿物学及矿床学研究,厘定了金川矿床成矿阶段。成矿阶段可划分为硫化物矿浆结晶阶段、挥发分流体作用阶段及热液改造阶段。其中硫化物矿浆结晶阶段的主要矿物组合为镍黄铁矿（Pn- a）- 磁黄铁矿（Po- a）- 黄铜矿（Ccp- a）;挥发分流体作用阶段的主要矿物组合为镍黄铁矿（Pn- b）- 磁黄铁矿（Po- b）- 黄铜矿（Ccp- b）- 黄铁矿（Py- Ⅰ）- 磁铁矿（Mag- Ⅰ）- 菱铁矿- 叶蛇纹石- 磷灰石- 铬铁矿- 白云石- 方解石（Cal- Ⅰ）- 金云母。热液改造阶段的矿物组合为透闪石- 绿泥石- 蛇纹石- 方解石（Cal- Ⅱ）- 磁铁矿（Mag- Ⅱ）。高倍电子探针镜下发现,金川矿床铂族矿物与磁铁矿（Mag- Ⅰ）、黄铁矿（Py- Ⅰ）、铬铁矿、磷灰石、黄铜矿、磁黄铁矿、镍黄铁矿及菱铁矿等共生。金川铜镍硫化物矿床中铂族元素(PGM)矿物主要包括硫砷铱矿（IrAsS）、钯的铋化物、碲化物和硒化物、钯的金属互化物（PdAu2）、砷铂矿（PtAs2）、铂单质以及铂的金属合金（Pt- Fe）。其中大量的PGM分布于镍黄铁矿的裂隙中,或产于镍黄铁矿、磁黄铁矿及蛇纹石裂隙中。与磁铁矿、菱铁矿、铬铁矿、黄铜矿、磷灰石以及叶蛇纹石等矿物共生,指示PGE富集与氧化性流体加入密切相关。金川矿石镍黄铁矿（Pn- b）、磁黄铁矿（Po- b）、黄铜矿（Ccp- b）、黄铁矿（Py- Ⅰ）、磁铁矿（Mag- Ⅰ）以及菱铁矿中高Co含量,表明流体在Co的超常富集过程中也起到了决定性作用。金川矿石中大量碳酸盐矿物、叶蛇纹石、金云母、磁铁矿、黄铁矿、铬铁矿以及富Cl磷灰石的出现;S、Mg元素呈网脉状分布于蚀变橄榄石和硫化物中,推测流体组分可能是一种富C富Cl的富含挥发分的高氧逸度流体。金川铬铁矿、磁铁矿（Ⅰ）、菱铁矿等矿物中高Ti、高Nb含量和高Nb/Ta比值,暗示此流体可能是一种高温的超临界流体。以上特征综合表明该特征流体对金川铜镍硫化物矿床中铂族元素等关键金属的超常富集起到了关键控制作用。当挥发分流体与残余硫化物矿浆相互作用及改造先存硫化物及橄榄石时,不仅会促使Os、Ir、Ru、Rh、Pt、Pd进一步活化、富集,还会导致流体中PGE强烈富集,使得流体中的Pd、Se、Te、Bi、Pt含量不断提高,最终形成大量的PGM。综上所述,本文认为在岩浆演化晚期可能存在一种高氧逸度的富Cl富C的深源流体注入岩浆房,该深源挥发分流体对PGE及Co的迁移和超常富集起到了关键控制作用。 相似文献
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江苏六合新生代玄武岩中地幔捕虏体的硫化物相研究 总被引：13，自引：3，他引：10
江苏六合一带碱性玄武岩中的出露有以尖晶石二辉橄榄岩为主的地幔捕虏体,这些地幔矿物中普遍有硫化物相出现：（１）被寄主矿物捕获的早期硫化物颗粒。（２）产于矿物晶粒边界或次生裂隙充填物,（３）硫化物包裹体,包括单相硫的包裹体、硫化物－玻璃两相熔体包裹体和ＣＯ／２－硫化物－玻璃（含硅酸盐子矿物）的多相包裹体,电子探针分析表明,硫化物包裹体比例隙中硫化物具有更高的相对Ｆｅ和Ｓ含量,较低的Ｎｉ含量。硫化物包裹 相似文献
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地幔岩中不同产状的流体-熔体包裹体及地幔流体交代作用 总被引：1，自引：0，他引：1
地幔捕虏体中存在不同产状的熔体包裹体和各种硅酸盐玻璃相,包括主矿物内部的蠕虫状、长圆形、圆形、不规则状包裹体(I型)、边部的连通的管状包裹体(T型)、主矿物边部和粒间的片状熔融体——“浆胞”(C型),三者可见明显过渡关系,它们是地幔流体交代地幔岩石过程中由交代重熔形成的,是研究地幔流体的特征和地幔交代作用的对象之一,从I型、T型到C型,其成分呈规律变化,其中S、Cu、Ni,K、Na含量呈明显的降低趋势．包裹体中玻璃相的成分较主矿物富Si、Al、S、Cu、Ni、K和Na,再加上C02包裹体的发现,表明地幔流体的成分富碱金属、Si、Al、S、Cu、Ni和CO2,地幔交代作用可以使交代产物中Si、Al含量升高而形成中酸性岩浆,也可由于硫化物熔体聚集而形成矿浆．不同地区的地幔流体性质可能存在差异,这些不同性质的地幔流体町能与不同类型的地幔成矿作用有关． 相似文献
13.
Mantle xenoliths are common in the Cenozoic basalts of the Changbaishan District,Jilin Province,China.Sulfide assemblages in mantle minerals can be divided into three types:isolated sulfide grains,sulfide-meh inclusions and filling sulfides in fractures.Sulfide-meh inclusions occur as single-phase sulfides,sulfide-silicate melt,and CO_2-sulfide-silicate melt inclusions. Isolated sulfide grains are mainly composed of pyrrhotite,but cubanite was found occasionally.Sulfide-meh inclusions are mainly composed of pontlandite and MSS,with small amounts of chalcopyrite and talnakhite.The calculated distribution coefficient K_(D3)for lherzolite are similar to that of mean experimental value.The bulk sulfides in lherzolite were in equilibrium with the enclosing minerals, indicating immiscible sulfide melts captured in partial melting of upper mantle.Sulfide in fractures has higher Ni/Fe and(Fe Ni)/S than those of sulfide melt inclusions.They might represent later metasomatizing fluids in the mantle.Ni/Fe and(Fe Ni)/S increase from isolated grains,sulfide inclusions to sulfides in fractures.These changes were not only affected by temperature and pressure,hut by geochemistry of Ni,Fe and Cu,and sulfur fugacity as well. 相似文献
14.
坡一含铜镍基性-超基性岩体是新疆北山西段早二叠世幔源岩浆活动产物之一。本文主要对该岩体中铬铁矿及内部固体包裹物进行了电子探针分析。坡一岩体铬铁矿主要成分呈线性变化并具低Zn、Ti和Fe3+的特征。铬铁矿内部固体包裹物由橄榄石、辉石等无水单矿物相包裹物,角闪石、金云母等含水多矿物相包裹物以及硫化物三类组成,硅酸盐包裹物化学成分上表现出富镁高铬的特点,其中云母具有富碱高镁的特征。估算得到铬铁矿结晶温度在1340~1411℃之间,结晶压力在2.56~3.33 GPa之间,坡一岩体原始岩浆Al2O3含量约为14.13%,Ti O2含量约为1.57%。结合已有研究成果,认为坡一岩体原始岩浆早期属于低钛苦橄质岩浆,可能是软流圈地幔环境下经历了15.5%~18.9%程度的部分熔融产物。原始岩浆早期存在含水富挥发份流(熔)体相且达到了硫饱和,铬铁矿结晶可能是导致硫饱和的重要原因。 相似文献
15.
地幔捕虏体中的流体-熔体包裹体 总被引：3，自引：0，他引：3
地幔流体的研究现已成为国内外前沿课题。地幔岩捕虏体中的流体-熔体包裹体是地幔流体的直接证据,通过对它们的研究可以直接获取地授流体的信息。包裹体按相态特征主要有三类：二氧化碳流体包裹体、二氧化碳-硅酸盐熔体包裹体、硫化物-熔体流体包裹体。本总结了地幔岩中流体-熔体包裹体的基本特征、微量元素地球化学、硫化物-熔体包裹体和二氧化碳流体包裹体稳定同位素特征的研究进展状况。讨论认为：地幔流体是由C、H、O、S等元素的挥发份和硅酸盐熔体组成;上地幔流体在化学成分上明显富含CO2、硫化物、LILE和BEE,它引起地幔交代作用和地授部分熔融;上地授流体的分布存在不均匀性,其组成也存在地区性差异。 相似文献
16.
The extreme depletion of the Earth’s mantle in sulfur is commonly seen as a signature of metal segregation from Earth’s mantle to Earth’s core. However, in addition to S, the mantle contains other elements as volatile as S that are hardly depleted relative to the lithophile volatility trend although they are potentially as siderophile as sulfur. We report experiments in metal-sulfide–silicate systems to show that the CI normalized abundances of S, Pb, and Sn in Earth’s mantle cannot be reproduced by element partitioning in Fe ± S–silicate systems, neither at low nor at high pressure. Much of the volatile inventory of the Earth’s mantle must have been added late in the accretion history, when metal melt segregation to the core had become largely inactive. The great depletion in S is attributed to the selective segregation of a late sulfide matte from an oxidized and largely crystalline mantle. Apparently, the volatile abundances of Earth’s mantle are not in redox equilibrium with Earth’s core. 相似文献
17.
There is growing evidence that the budget of Pb in mantle peridotites is largely contained in sulfide, and that Pb partitions strongly into sulfide relative to silicate melt. In addition, there is evidence to suggest that diffusion rates of Pb in sulfide (solid or melt) are very fast. Given the possibility that sulfide melt “wets” sub-solidus mantle silicates, and has very low viscosity, the implications for Pb behavior during mantle melting are profound. There is only sparse experimental data relating to Pb partitioning between sulfide and silicate, and no data on Pb diffusion rates in sulfides. A full understanding of Pb behavior in sulfide may hold the key to several long-standing and important Pb paradoxes and enigmas. The classical Pb isotope paradox arises from the fact that all known mantle reservoirs lie to the right of the Geochron, with no consensus as to the identity of the “balancing” reservoir. We propose that long-term segregation of sulfide (containing Pb) to the core may resolve this paradox. Another Pb paradox arises from the fact that the Ce/Pb ratio of both OIB and MORB is greater than bulk earth, and constant at a value of 25. The constancy of this “canonical ratio” implies similar partition coefficients for Ce and Pb during magmatic processes (Hofmann et al. in Earth Planet Sci Lett 79:33–45, 1986), whereas most experimental studies show that Pb is more incompatible in silicates than Ce. Retention of Pb in residual mantle sulfide during melting has the potential to bring the bulk partitioning of Ce into equality with Pb if the sulfide melt/silicate melt partition coefficient for Pb has a value of ∼ 14. Modeling shows that the Ce/Pb (or Nd/Pb) of such melts will still accurately reflect that of the source, thus enforcing the paradox that OIB and MORB mantles have markedly higher Ce/Pb (and Nd/Pb) than the bulk silicate earth. This implies large deficiencies of Pb in the mantle sources for these basalts. Sulfide may play other important roles during magmagenesis: (1) advective/diffusive sulfide networks may form potent metasomatic agents (in both introducing and obliterating Pb isotopic heterogeneities in the mantle); (2) silicate melt networks may easily exchange Pb with ambient mantle sulfides (by diffusion or assimilation), thus “sampling” Pb in isotopically heterogeneous mantle domains differently from the silicate-controlled isotope tracer systems (Sr, Nd, Hf), with an apparent “de-coupling” of these systems. 相似文献
18.
J. P. Lorand 《Lithos》1989,23(4):281-298
The orogenic-type spinel peridotite massifs of Lherz and Freychinède (Northeastern Pyrenees, Ariège, France) were tectonically emplaced along the North Pyrenean fault. They have been cross-cut by Cretaceous alkali basalts, a few kilometres below the Moho. These magmas crystallized at about 1.0–1.5 GPa as veins of amphibole-rich pyroxenites, containing garnet, and also occasionally as phlogopite hornblendites. In spite of the low volume of trapped silicate liquid, the veins contain up to 1900 ppm S, up to 140 ppm Cu and up to 10 ppb Pd. Under the microscope, the sulfides occur as isolated inclusions within magmatic phases (orthopyroxene, clinopyroxene, amphibole, garnet, spinel, ilmenite), irrespective of parting, cleavage or exsolution planes, or as interstitial grains among the major phases, showing signs of textural equilibration. The sulfide inclusions are interpreted as resulting from entrapment of an immiscible sulfide liquid during magmatic crystallization of the veins. However, a detailed comparison with sulfide inclusions from Cpx- and Al-augite megacrysts entrained in continental basalts shows that post-trapping structural and compositional rearrangements have probaly occurred, in response to cooling, deformation and recrystallization of the veins in the lithospheric mantle.
Except in the thinnest veins where subsolidus re-equilibration of the Ni partitioning has occurred between the veins and their host peridotites, the sulfide inclusions are predominantly composed of slightly nickeliferous pyrrhotite, coexisting with subordinate amounts of pentlandite and chalcopyrite. Bulk chemistry recomputed from modal proportions and microprobe analyses of each individual sulfide in 500 inclusions is as follows: 54% Fe, 5.5% Ni, 2.0% Cu and 38.0% S. A calculation combining this composition and the experimentally determined distribution coefficients for Ni and Cu between sulfide melt and silicate melt leads to < 200 ppm Ni and > 85 ppm Cu in the silicate melt at the time at which the sulfide liquid became immiscible. It is concluded that the alkalic basaltic magma parent to the amphibole-rich veins reached sulfide saturation at depth of 30–40 km, i.e. after some differentiation occurred in the uppermost lithospheric mantle. 相似文献
19.
After the discovery of the Aguablanca ore deposit (the unique Ni–Cu mine operating in SW Europe), a number of mafic‐ultramafic intrusions bearing Ni–Cu magmatic sulfides have been found in the Ossa–Morena Zone of the Iberian Massif (SW Iberian Peninsula). The Tejadillas prospect is one of these intrusions, situated close to the border between the Ossa–Morena Zone and the South Portuguese Zone of the Iberian Massif. This prospect contains an average grade of 0.16 wt % Ni and 0.08 wt % Cu with peaks of 1.2 wt % Ni and 0.2 wt % Cu. It forms part of the Cortegana Igneous Complex, a group of small mafic‐ultramafic igneous bodies located 65 km west of the Aguablanca deposit. In spite of good initial results, exploration work has revealed that sulfide mineralization is much less abundant than in Aguablanca. A comparative study using whole‐rock geochemical data between Aguablanca and Tejadillas shows that the Tejadillas igneous rocks present a lower degree of crustal contamination than those of Aguablanca. The low crustal contamination of the Tejadillas magmas inhibited the assimilation of significant amounts of crustal sulfur to the silicate magmas, resulting in the sparse formation of sulfides. In addition, Tejadillas sulfides are strongly depleted in PGE, with total PGE contents ranging from 14 to 81 ppb, the sum of Pd and Pt, since Os, Ir, Ru and Rh are usually below or close to the detection limit (2 ppb). High Cu/Pd ratios (9700–146,000) and depleted mantle‐normalized PGE patterns suggest that the Tejadillas sulfides formed from PGE‐depleted silicate magmas. Modeling has led us to establish that these sulfides segregated under R‐factors between 1000 and 10,000 from a silicate melt that previously experienced 0.015% of sulfide extraction. All these results highlight the importance of contamination processes with S‐rich crustal rocks and multiple episodes of sulfide segregations in the genesis of high‐tenor Ni–Cu–PGE ore deposits in mafic‐ultramafic intrusions of the region. 相似文献
20.
Sulfide and platinum mineralization in the Merensky Reef: evidence from hydrous silicates and fluid inclusions 总被引：5，自引：1，他引：5
Christian G. Ballhaus Eugen F. Stumpfl 《Contributions to Mineralogy and Petrology》1986,94(2):193-204
The base metal sulfides of the Merensky Reef are associated with hydrous silicates and intense deuteric hydrous alteration of cumulus and postcumulus silicates. Biotite and phlogopite crystallized in the vicinity of sulfides from a volatile-enriched highly fractionated intercumulus melt. Amphibole, chlorite, and talc are later alteration phases of cumulus pyroxene and intercumulus plagioclase. Biotite is often accompanied by zircon, rutile, and quartz. Accessory quartz hosts a complex suite of H2O-NaCl-(CaCl2)-CO2-CH4 fluid inclusions which have thus far not been described from the Merensky Reef. The earliest fluid inclusion compositions are NaCl-(H2O) with less than 10 vol.% water; CO2 coexisting with a halite daughter crystal and brine; and polyphase inclusions with up to six daughter and accidental phases and high contents of divalent cations. The maximum trapping temperature is around 730° C at 4 to 5 kb pressure. Later inclusion generations are H2O-NaCl, CO2-H2O, and pure CO2 and CH4. The presence of Cl-rich fluids during the intercumulus stage of the crystallizing Merensky Reef is directly related to the mode of sulfide precipitation. Prior to sulfide unmixing in a hydrous magma sulfur is likely to be present as H2S. Sulfur saturation causes reaction of H2S with oxides of the silicate melt to form a sulfide melt plus water. During reaction the magma is enriched in water until a separate fluid unmixes. It carries all compounds with high fluid/melt partition coefficients, as well as metals capable of forming OH- and Cl-complexes. Precious metals are assumed to have fractionated into the Cl-rich fluid as Cl-complexes rather than being dissolved in the sulfide melt. During the cooling evolution of the fluid the precious elements precipitate around the periphery of sulfide melt droplets. The model proposed explains the distribution pattern of platinum-group minerals in the Merensky Reef better than any orthomagmatic mineralization concept offered so far. 相似文献