内蒙古黑鹰山富铁矿床磷灰石钐-钕同位素年龄及其地质意义

黑鹰山富铁矿床地处北山造山带西伯利亚板块与哈萨克斯坦_北山板块汇聚地带,是中国西北地区规模最大和品位最高的富铁矿床之一,其独特的产出环境和地质特征为国内外地质学界所关注。为了查明该矿床的形成过程,笔者首次对致密块状铁矿体中的6件磷灰石样品和脉状铁矿体中的2件磷灰石样品进行了钐_钕同位素测定。块状矿体的6件样品所获等时线年龄为(32 2 .0±4 .3)Ma,MSWD值为0 .0 9,14 3 Nd/14 4 Nd初始比值为(0 .5 12 30 8±0 .0 0 0 0 0 3) ,εNd(t)为(1.6 6±0 .0 1)。脉状矿体中2件样品的εNd(t)值分别为7.2 0和7.2 6 ,明显高于块状矿体磷灰石样品。依据上述同位素分析数据和特征比值,结合容矿围岩和矿体地质特征,推测黑鹰山富铁矿床的形成与海西早期富碱岩浆流体多期次活动有关,成矿物质主要来自地幔物质占优势比例的壳_幔混源岩浆房。     

浙江八面山特大型萤石矿床成因研究

通过成矿地质背景,矿体地质特征,矿石特征,矿床稀土元素,流体包裹体地球化学,氢氧同位素地球化学特征等研究,认为八面山萤石矿床,按矿体赋存于岩体与灰岩接触带、灰岩层间及构造破碎带;岩石有细粒及粗粒-巨晶两类;矿床成矿温度主要集中在120°～240°之间;氢氧同位素特征反应成矿流体具有多来源多成因的特征;成矿物质Ca主要来源于寒武系中的灰岩与泥质灰岩,F主要来源于寒武系泥质灰岩,部分可能为岩浆热液从地表深部携带而来,萤石矿床成矿流体水具有多源性;成矿流体具有大气降水,变质水和岩浆水共同混合作用的结果,在岩浆侵入热源的作用下,三种水混合后被加热,形成了成矿溶液的重要载体。研究认为八面山萤石矿床是受地层-岩体-断裂共同控制"三位一体"的中低温热液成因矿床。     

北京密云沙厂环斑花岗岩杂岩体黑钨矿钐—钕同位素研究

鉴于缺少可直接用于同位素测年的金属矿物,许多钨矿床的成矿时代大多数是悬而未决的地质难题。本文以我国著名北京密云沙厂环斑花岗质杂岩体内产出的黑钨矿为研究对象,对钨矿床的形成年龄进行了测定,8件黑钨矿Sm-Nd同位素等时线年龄为1430±93Ma(2σ),Nd初始比值为0.510992±3(2σ)和ε_(Nd)(1430Ma)为-10.5±0.84(2σ),这是迄今在我国测定到的最老的钨矿床成矿年龄。通过对全国已有钨矿床同位素年龄数据的对比分析,并且结合它们的地质与地球化学特征,可以认为,我国最古老的钨矿床很可能形成于中元古代,而并非是古生代。另外,密云沙厂地区钨矿床的成矿作用与中元古代富矿碱性岩浆活动有关。     

豫西陈楼萤石矿床地质特征及Sm-Nd同位素年龄

对陈楼萤石矿床地质特征进行归纳总结,并测定萤石的Sm-Nd同位素等时线年龄,为矿床成矿年龄、物质来源的研究及进一步找矿提供依据。陈楼萤石矿床是典型的中—低温热液裂隙充填型矿床,矿体严格受构造带控制,F2,F3,F4,F5为其主要容矿构造;主矿体自上而下具上陡—中缓—下陡的趋势,矿体平均厚度2.97 m,平均品位63.99%;矿石主要有块状、胶结状、条带状和玉髓萤石矿四种类型;围岩中常见硅化、高岭石化、绿泥石化、绢云母化等,且含矿构造自中心向两侧蚀变具有明显分带特征。测得萤石Sm-Nd同位素等时线年龄为(120±17) Ma,~(143)Nd/~(144)Nd初始比值0.512 031±0.000 026,εNd(t)=-8.8,对比前人测得太山庙岩体的SHRIMP锆石U-Pb年龄112～125 Ma,~(143)Nd/~(144)Nd初始比值0.511 653～0.512 506,εNd(t)值-16.1～-7.5,说明成矿作用发生在燕山晚期早白垩世,指示萤石成矿物质可能来源于地壳,且与太山庙岩体的成矿物质来源应一致或相近。     

南坑萤石矿床萤石包裹体特征及成因研究

对南坑萤石包裹体研究发现,成矿热液温度、压力、盐度低;成分以F~-,Ca~(2+)为主;CO_2/H_2O比值小;fo_2低;氢氧同位素组成与当地大气降水同位素组成特征相同,表明南坑产于花岗岩断裂破碎带中的萤石矿床,成矿热液与物质来源都与花岗岩岩浆期后热液活动没有发生直接联系,属于与大气降水活动密切相关的脉状萤石矿床。     

东秦岭钼矿Re-Os同位素年龄及其成矿动力学背景

东秦岭钼矿带位于华北克拉通南缘 ,集中分布于陕西省的金堆城地区、河南省栾川县南泥湖 -三道庄 -上房沟、嵩县雷门沟地区。钼矿床类型主要为斑岩型、斑岩 -矽卡岩型 ,少量热液碳酸盐岩脉型。采用电感耦合等离子体质谱仪法对南泥湖钼矿田、雷门沟钼矿床等 4个矿床 8件辉钼矿进行了 Re-Os同位素年龄测定 ,获得南泥湖矿床的辉钼矿 Re- Os模式年龄为 14 1.8± 2 .1Ma;三道庄矿床的辉钼矿 Re- Os模式年龄为 14 4 .5± 2 .2～ 14 5 .0± 2 .2 Ma,平均为 14 5 .0± 2 .2 Ma;上房沟矿床的辉钼矿 Re- Os模式年龄为 14 3.8± 2 .1～ 14 5 .8± 2 .1Ma,平均为 14 4 .8± 2 .1Ma;6件样品的等时线年龄为 14 1.5±7.8Ma(2σ) ;雷门沟钼矿床的 2件辉钼矿样品的 Re- Os模式年龄为 131.6± 2 .0～ 133.1± 1.9Ma,平均为 132 .4± 2 .0 Ma。结合前人资料 ,认为东秦岭钼矿的形成时代局限于 2 2 1.5± 0 .3～ 132 .4± 2 .0 Ma之间 ,主要出现在 2 2 1.5± 0 .3Ma左右和 14 4 .8± 2 .1～ 132 .4± 2 .0 Ma时限之间 ,其对应的地球动力学背景分别为华北克拉通与扬子克拉通的碰撞造山后陆内造山和伸展过程、中国东部构造体制大转换时期     

阜平群下部太古代变质岩石的REE、Rb-Sr和Sm-Nd年龄及其意义

对采自阜平群下部16个变质岩石样品进行了Sm-Nd年龄测定,部分样品还进行了Rb-Sr年龄测定和REE分析。Sm-Nd同位素结果形成两条等时线。一条等时线具有年龄为:2790±171(2σ)Ma,I_(Nd)=0.50917±16(2σ),ε_(Nd)(t)=±1.6;另一条等时线,t=1949±84(2σ)Ma,I_(Nd)=0.50986±5(2σ),ε_(Nd)(t)=-5.0±1.0。Rb-Sr同位素数据分散,参考等时线年龄为2070Ma。     

福建建阳回潭萤石矿床地质特征及成因探讨

建阳回潭萤石矿床位于闽西北隆起带武夷山成矿带,整体受北东向的五夫—兴田断裂控制,矿体贮存于构造破碎带中,围岩为加里东期中细粒白云母二长花岗岩。矿体形态简单,顶底界面沿走、倾向上均呈舒缓波状,总体形态呈长透镜体状,属单脉型的大型萤石矿床。萤石Sm-Nd年代学揭露矿床的形成时代大致为(110±15.6) Ma。微量元素、Sr同位素、H-O同位素与流体包裹体测温显示成矿流体来源于同期岩浆期后热液与天水的混合,具有低温、低盐度特征,分析认为回潭萤石矿床的成因类型属于低温热液充填型。     

南秦岭十里坪锑矿床成矿时代及成因的初步研究

十里坪锑矿床受赵川陆缘隆_滑构造的主滑脱拆离带的控制。矿体呈脉状赋存于韧_脆性主滑脱带上部的脆性次级断层_节理中,矿石类型主要为萤石石英辉锑矿型。围岩为太古宙_元古宙变质岩系,围岩蚀变弱。成矿流体属H2O_CO2_NaCl体系,流体包裹体盐度w(NaCleq)为3.6%～11.3%,均一温度为109～232℃,形成压力大致为800×105Pa。硫、铅同位素研究表明,矿质主要来源于变火山岩围岩;氢、氧同位素显示,成矿流体以大气降水为主,初步将该矿床定为变质岩源就地式大气降水热液矿床。矿石中萤石Sm_Nd等时线年龄为(392±24)Ma,与南秦岭北部晚古生代拗陷区热水喷流_沉积成矿时代相一致,它们都形成于秦岭微板块泥盆纪非造山裂解阶段。     

内蒙古苏莫查干敖包特大型萤石矿床地质特征及成因

苏莫查干敖包矿床是迄今为正在全球范围内找到的最大规模单一萤石矿床.萤石矿体大多呈层状、似层状和透镜状沿下二叠统碳泥质板岩(夹灰岩透镜体)与流纹质火山岩接触带分布,并且与中生代花岗岩类侵入岩体具有密切的空间分布关系.流纹质火山岩和花岗岩的锆石SHRIMP U-Pb年龄值分别为(276±10)Ma和(138±4)Ma,它们分别是海西晚期和燕山中期酸性岩浆活动的产物.萤石矿体主要由4种类型矿石所构成,即石英-萤石型、石英-硫化物-萤石型、萤石-石英型和方解石-石英-萤石型.矿物组分有萤石、石英(蛋白石、玉髓)、方解石、绢云母和绿泥石,个别样品中有磁铁矿、黄铁矿、磁黄铁矿、黄铜矿、闪锌矿、毒砂和锡石.围岩蚀变自矿体中心向外分别为绢云母化、硅化、碳酸盐化和高岭石化.钕、锶和铅同位素分析结果表明,萤石矿床是多期次和多阶段岩浆热液活动的产物,成矿作用分别发生在海西晚期和燕山中期,并以后者为主.海西晚期富碱质酸性岩浆喷发活动为层纹状和条带状矿体以及矿源层的形成创造了有利条件.相比之下,燕山中期花岗质岩浆侵入活动不仅为细晶质、伟晶质和角砾状矿体的形成提供了物质、动力和热力来源,而且是成矿流体对流循环的"发动机".苏莫查干敖包矿床属于与花岗岩类深成侵入岩体有关的热液型萤石矿床,成岩(矿)物质来自壳、幔混合源,其中壳源组分占有绝对优势.     

江西宁都坎田萤石矿床稀土元素地球化学特征及其指示意义

赣南地区萤石资源丰富, 坎田萤石矿位于赣南地区的兴国—宁都萤石成矿带上, 矿体赋存于晚侏罗世黑云母花岗岩内。本文结合研究区的区域地质背景, 对江西宁都坎田萤石矿床的萤石及围岩进行了稀土元素地球化学特征研究, 以探讨坎田萤石矿床的成矿流体来源和矿床成因。其研究结果表明, 萤石的稀土元素总量为34.11×10–6~78.12×10–6, 属于轻稀土富集型, 稀土元素配分曲线形态基本一致; 围岩的稀土元素总量为94.14×10–6~175.72×10–6, 其配分模式与萤石具有相似同步性, 且萤石与围岩具有相近的Sm/Nd比值, 均表明萤石的成矿流体来源与围岩密切相关。结合前人在赣南地区对萤石气液包裹体进行氢氧同位素特征的研究, 认为成矿流体主要来源于大气降水, 成矿物质Ca和F元素主要来自于大气降水对燕山早期的黑云母花岗岩的淋滤和萃取。通过研究区的地质背景、萤石的强烈负Eu异常特征以及Tb/Ca-Tb/La关系图, 认为研究区萤石矿属于还原环境下的中低温热液充填型萤石矿床。     

Fluorite deposition in hydrothermal systems

During the formation of fluorite deposits fluorite is precipitated either as a consequence of changes in temperature and pressure along the flow path of hydrothermal solutions or due to fluid mixing, or as the result of the interaction of hydrothermal solutions with wall rocks.A decrease in temperature in the flow direction is the most appealing, though still unproven, mechanism of fluorite deposition in Mississippi Valley fluorite deposits.Mixing can produce solutions which are either undersaturated or supersaturated with respect to fluorite. The most important parameters are the temperature, the salinity, and the calcium and fluoride concentration of the fluids prior to mixing.A variety of wall rock reactions can lead to fluorite precipitation. Among these reactions which increase the pH of initially rather acid (pH ≤ 3) hydrothermal solutions are apt to be particularly important.     

Fluorite stability in silicic magmas

Recent experimental evidence is used to assess the conditions under which fluorite forms an early crystallising phase in silicic magmas. Fluorite solubility primarily depends on the (Na + K)/Al balance in the coexisting silicic melt, reaching a minimum in metaluminous melts. It can display reaction relationships with topaz and titanite, depending on changes in melt composition during crystallisation. An empirical model of fluorite stability in Ca-poor peralkaline rhyolite melts is derived and applied to selected rocks:

内蒙古东七一山萤石矿床的稀土元素地球化学特征及成因

运用等离子质谱和等离子体光谱对内蒙古东七一山萤石矿的萤石矿石和围岩样品的稀土元素进行了系统分析.结果表明,矿石的∑REE<30×10-6,LREE为5×10-6～15×10-6,HREE<5×10-6,Y<20 ×10-6;而围岩的∑REE>290×10-6,LREE>240×10-6,HREE>40×10-6,Y>70×10-6.可将萤石矿石的稀土元素的分布型式分为轻、重稀土富集型两类一类矿石的∑REE多小于29×10-6,LREE/HREE和La/Yb分别大于7和12,δEu、δCe的变化范围分别为0.85～1.10,Ce、Eu基本不显异常;另一类的∑REE 约18×10-6 ,LREE/HREE和La/Yb分别小于3和2,δEu为0.45～0.70,δCe为0.70～0.90,具明显的负Eu异常,Ce微具负异常.矿石与围岩的稀土地球化学研究显示,该萤石矿系岩浆热液成因.     

Standard Reference Material of Fluorite FM

Standard reference material of fluorite FM, consisting chiefly of fluorite, quartz and baryte, was prepared by the Institute of Mineral Raw Materials in Kutná Hora (Czechoslovakia). The homogeneity of the pulverised SRM was checked by X-ray fluorescence spectrometry from counts corresponding to the amounts of iron, copper, barium, strontium and titanium. The SRM was considered homogeneous if the "between bottles" variance was not significantly greater than the "within bottles" variance and further, if the error caused by heterogeneity of the SRM was less than one third of the error of an analytical determination carried out in a routine manner. Analytical results from 26 laboratories were processed following the recommended procedure of CMEA-countries which includes: Testing the normality of results, eliminating out-lying results and computing the arithmetic means, estimates of standard deviations and the confidence intervals of the means. Attested values for 17 components and non-attested values for 30 components and/or elements are reported.     

Isotopic Geochemistry of Chinese Fluorite Deposits

China is one of the richest countries in the world in terms of fluorite resources. On the basis of host rocks and mineralization patterns, the fluorite deposits in China have been classified into three types: (1) those occurring in Mesozoic volcanic regions, mainly consisting of veinfilling deposits of the quartz-fluorite association (Type I); (2) those occurring in granite areas, chiefly belonging to veinfilling deposits of the quartz-fluorite association or veinfilling or altered-rock deposits associated with Pb, Zn, W, Sn, etc. (Type II); and (3) those occurring in carbonate rocks as bedded deposits of quartz-fluorite, sulfide-fluorite, and quartz-barite-calcite-fluorite assemblages (Type III).

This paper summarizes the characteristics of fluorite deposits in China on the basis of strontium-, hydrogen-, and oxygen-isotopic and geochronological data, as well as geological investigations of deposits from 22 mining districts. δ¹⁸O and δD values of ore-forming fluids are ?10.2 to +3.7‰ and ?77.9 to 41.0‰, respectively, for Type-I deposits, ?13.1 to ?4.9‰ and ?65.5 to ?41.7‰ for Type-II deposits, and -5.6 to +4.3‰ and ?80 to ?29‰ for Type-Ill deposits. Study of the isotopic water-rock exchange indicates that the mineralizing fluids for these types of deposits have been derived mostly from circulating geothermal water that originated from Mesozoic meteoric water. The differences in the isotopic characteristics of hydrothermal systems for various types of deposits depend mainly on isotopic exchange between water and rocks, the water/rock values being 0.05 to 2.0 for Type-I deposits, generally more than 2.0 for Type-II deposits, and 0.5 to 3.0 for Type-Ill deposits.

The ore-forming ages for Type-I and Type-II deposits are roughly separated into three groups—230 to 180 Ma, 120 Ma, and 90 to 60 Ma. These ages successively decrease from northwestern China to southeastern coastal areas.

⁸⁷Sr/⁸⁶Sr values of 0.7306 to 0.7710 (mean 0.7513) from fluorite in the early stage (main mineralization) for Type-I deposits are higher than those from host rocks (0.7081 to 0.7260) during the mineralizing event, and mostly fall in the range of ⁸⁷Sr/⁸⁶Sr values from basement metamorphic rocks (from 0.7455 to 0.9094) during the epoch of mineralization. But the ⁸⁷Sr/⁸⁶Sr values of 0.7102 to 0.7137 (mean 0.7122) for late-stage fluorite and calcite are similar to those of surrounding host rocks. This indicates that the mineralizing materials of early stages in the formation of deposits (Type-I) originated mostly from Precambrian basement metamorphic rocks; those of later stages (Type II) were derived chiefly from host rocks. Type-II and Type-Ill deposits from different mining areas exhibit great variations in ⁸⁷Sr/⁸⁶Sr values, but are quite similar to their host rocks, indicating that the mineralizing materials in Type-II and Type-Ill deposits were derived chiefly from their host rocks.     

Fluorite deposits in China: Geological features,metallogenic regularity,and research progress

Fluorite is one of the important mineral raw materials in the industry. In China, it is mainly distributed in the provinces and regions such as Hunan, Zhejiang, Jiangxi, Inner Mongolia, Fujian, and Henan provinces, boasting huge reserves and large numbers of deposits. However, most of the fluorite deposits are on a small or medium scale. The main fluorite deposits in China were studied in this paper. Their geological features and metallogenic regularity were summarized and compared. Meanwhile, based on their main genetic factors including metallogenic fluid sources and main metallogenic geological processes, they were divided into two groups, namely meso-epithermal deposits and magmatic-hydrothermal deposits. Furthermore, based on the prospecting achievements and research progress obtained in fluorite deposits in recent years, prospecting potential predictions were made for the metallogenic prospect areas and major prospecting areas of fluorite in China. This aims to provide a theoretical basis and direction for future fluorite prospecting in China.     

塔里木盆地西克尔萤石地球化学特征及成因讨论

通过对塔里木盆地西克尔地区萤石矿及赋矿围岩进行地球化学分析,探讨该区萤石矿成因。研究表明,萤石矿物稀土元素配分模式图表现出轻稀土元素相对富集,正铕异常特点;微量元素分析显示Eu、Sr、Ba具有相关性;Sr同位素比值与围岩相近。最终认为萤石矿成矿流体主要来自于加热的盆地卤水,微量（包括稀土）元素来自下伏地层及围岩,Ba、Eu、F等元素可能来自下寒武统硅质岩及磷块岩。     

试述福建顺昌南舟萤石矿地质特征

顺昌南舟萤石矿位于顺昌县埔上镇南舟村境内，1996年福建省区域地质调查队开展1：5万埔上幅区调时发现矿体，后开展普查工作表明该矿床规模大、交通方便，易于开采，现已投入开发利用。南舟萤石矿成矿地质特征在闽北丰富的萤石资源中具有一定代表性。     

Fluorite solubility equilibria in selected geothermal waters

Calculation of chemical equilibria in 351 hot springs and surface waters from selected geothermal areas in the western United States indicate that the solubility of the mineral fluorite, CaF₂, provides an equilibrium control on dissolved fluoride activity. Waters that are undersaturated have undergone dilution by non-thermal waters as shown by decreased conductivity and temperature values, and only 2% of the samples are supersaturated by more than the expected error. Calculations also demonstrate that simultaneous chemical equilibria between the thermal waters and calcite as well as fluorite minerals exist under a variety of conditions.Testing for fluorite solubility required a critical review of the thermodynamic data for fluorite. By applying multiple regression of a mathematical model to selected published data we have obtained revised estimates of the pK (10,96), ΔG^o_f (?280.08 kcal/mole), ΔH^o_f (?292.59 kcal/mole), S° (16.39 cal/deg/mole) and C^o_P (16.16 cal/deg/mole) for CaF₂ at 25°C and 1 atm. Association constants and reaction enthalpies for fluoride complexes with boron, calcium and iron are included in this review. The excellent agreement between the computer-based activity products and the revised pK suggests that the chemistry of geothermal waters may also be a guide to evaluating mineral solubility data where major discrepancies are evident.