诸广棉花坑铀矿床花岗岩中黑云母成分特征及其成岩成矿意义

诸广棉花坑铀矿床围岩是中粒斑状二云母花岗岩和中粗粒斑状黑云母花岗岩,本文通过对其中的黑云母进行了岩相学观察和详细的矿物化学分析以探讨黑云母的形成条件及其成岩成矿意义。电子探针分析结果表明,本区黑云母富铁贫镁,属于铁叶黑云母,指示诸广花岗岩体为过铝质岩系,起源于地壳。黑云母结晶的温度为650~700℃,logfO2为-15~-16,压力为159~247MPa,对应的侵位深度为5.2~7.2km。与非产铀花岗岩对比,本区岩浆具有相对较低的温度和氧逸度。     

粤北产铀与不产铀花岗岩中黑云母和绿泥石矿物化学特征及其与铀成矿的关系

长江岩体和九峰岩体同为粤北诸广山复式岩体中的燕山期花岗岩体,它们的矿化特征具有显著差异,是诸广山地区典型的产铀岩体和不产铀岩体。本文利用电子探针对两岩体中黑云母和绿泥石开展了详细的矿物化学研究。结果显示,长江岩体中黑云母富铁贫镁,为铁叶云母,黑云母绿泥石化较为严重,绿泥石类型主要是蠕绿泥石和铁镁绿泥石,偏铁质绿泥石,主要形成于较还原环境;九峰岩体中黑云母为铁质黑云母,绿泥石化较弱,绿泥石类型多为蠕绿泥石、铁镁绿泥石和密绿泥石,偏镁质绿泥石。黑云母的成分特征显示,长江岩体结晶温度为600~650℃,氧逸度lgf(O2)为-16~-17,挥发分组成显示出相对高F、低Cl的特征;九峰岩体结晶温度为680~720℃,氧逸度lgf(O2)为-14~-15,挥发分组成显示出相对低F、高Cl的特征。综合地质特征和矿物化学特征可知,较低的温度和氧逸度、较高的挥发分F含量是岩体产铀的有利因素。     

云南腾冲大松坡锡矿成矿年代学研究:锆石 LA-ICP-MS U-Pb年龄和锡石LA-MC-ICP-MS U-Pb年龄证据

大松坡锡矿床是三江特提斯成矿域腾冲-梁河锡-钨多金属矿带内的典型锡矿床之一,与古永岩基有密切的成生联系.本文利用LA-ICP-MS锆石U-Pb定年手段对大松坡锡矿床小龙河含锡黑云母花岗岩和二长花岗岩进行制约,两件黑云母花岗岩样品分析结果分别为70.3±3.2Ma和75.3±4.2Ma,一件二长花岗岩样品结果为71.5±2.1Ma,代表了岩浆结晶年龄.LA-MC-ICP-MS U-Pb方法直接对锡石进行年龄测试在国内外研究报道尚少,本文首次对该矿床云英岩型锡矿石中锡石进行定年尝试,结果为75.5±2.6Ma,与岩体年龄在误差范围内一致.小龙河锡矿床含锡岩体与古永岩基年龄一致,表明该含锡岩体可能是古永岩基的一部分.大松坡锡矿床的成矿年龄与含锡岩体年龄一致,表明二者同时形成,共系新特提斯洋俯冲构造背景的产物.     

云南个旧卡房锡矿田花岗岩黑云母矿物化学特征及其成岩成矿意义

黑云母作为花岗岩中含量最高的暗色矿物,其成分特征对指示岩石成因与成矿起着重要作用。云南个旧卡房锡多 金属矿床的形成与花岗质岩浆活动密切相关,卡房花岗岩包含有大量黑云母,通过电子探针测试方法,对该花岗岩中的 黑云母成分进行了系统的研究。结果显示,黑云母为富铁黑云母,具有富硅、铁、铝、钾、钛,贫锰、镁、钙、钠等特 征,含铁指数为0.67~0.83。黑云母的成分特征暗示其结晶温度为500~708 ℃,结晶压力为202~538 MPa,对应的结晶深度为 7.64~20.35 km,表明卡房花岗岩形成于中低温环境、属于中深成相。综合研究认为,卡房锡矿田花岗岩具有高铁指数以及 氧逸度由高到低变化趋势等特征是锡成矿的有利条件,可以作为在本区寻找锡矿的重要标志。     

滇西来利山与小龙河云英岩型锡矿成矿流体氧逸度特征对比

来利山锡矿床与小龙河锡矿床是滇西地区典型的云英岩型锡矿床。为揭示它们在成因上深层次的差异性,对来利山锡矿和小龙河锡矿的锡石进行了电子探针成分分析、镜下观察以及成矿环境对比分析。结果表明,锡石中的铁多以Fe~(3+)的形式与Sn~(4+)发生类质同象,氧逸度越高,锡石中Fe~(3+)越多,宏观上表现为锡石的颜色越深。来利山矿区锡石中Fe含量明显低于小龙河矿区,且锡石颜色明显比小龙河矿区颜色浅,反映了来利山锡矿成矿环境相对开放,成矿流体氧逸度偏低,流体中Sn络合物迁移能力较强,在花岗岩体外接触带的围岩裂隙中形成外云英岩型锡矿床;而小龙河锡矿成矿环境相对封闭,成矿流体氧逸度偏高,流体中Sn络合物迁移能力较弱,多在花岗岩体顶部的构造裂隙中形成内云英岩型锡矿床。     

河南栾川南泥湖和上房沟花岗岩体黑云母成分特征及其成岩成矿意义

河南栾川南泥湖和上房沟花岗岩体与钼多金属成矿作用密切相关。本文用电子探针测试方法,分析了南泥湖岩体和上房沟岩体中黑云母的成分特征。结果表明,2个岩体中黑云母均具有高硅、富镁、低铝和贫铁的特征,属镁质黑云母。2个岩体的结晶温度分别为730~830℃和750~860℃,氧逸度(logfO2)分别为-8.5~-7.0和-8.0~-6.5,结晶压力和深度分别为72~120MPa、54~127MPa和2.62~4.37km、1.97~4.63km,有利于南泥湖-三道庄和上房沟超大型钼矿床的形成,地球化学特征显示2个岩体均属壳幔混源的Ⅰ型花岗岩,属深源中浅成花岗岩。     

上黑龙江盆地二十一站岩体角闪石和黑云母成分特征及成岩成矿意义

二十一站岩体位于黑龙江省东北部大兴安岭地区塔河县境内,该岩体产出的岩石类型包括早白垩世二长岩和石英二长斑岩及早侏罗世花岗岩和二长岩等,在该岩体中已发现斑岩型铜金矿床,但是该岩体形成的物理化学条件和岩石成因尚不清楚,不同岩性岩浆岩的成矿潜力也不明确。鉴于此,本文以二十一站岩体中不同时代的花岗岩、二长岩、石英二长斑岩的黑云母和角闪石为研究对象,结合偏光显微镜、电子探针背散射图像和电子探针化学成分,对该岩体的岩石学、矿物学特征进行了研究,并对岩浆结晶的物理化学条件、岩石成因和成矿意义进行了探讨。结果显示:早白垩世二长岩中角闪石化学成分显示:角闪石富钙(CaO 11.21%~11.78%)、富镁(MgO 13.61%~14.85%)、贫钠(Na2O 0.80%~1.11%)和贫钾(K2O 0.40%~0.54%),属于镁角闪石,结晶温度为704.92~805.58℃,平均温度为761.82℃,压力为73.83~115.93MPa,对应岩浆侵位深度为2.8~4.4km,结晶时岩浆氧逸度为△NNO+1.63,含水量为H2O=4.92%,反映出岩浆结晶时高温、高氧逸度、富含水分、浅侵位的特征。黑云母的Fe2+/(Fe2++Mg)比值比较均一,反映黑云母未遭受后期流体改造,均为原生岩浆成因的黑云母。其中早侏罗世花岗岩和二长岩所代表的A类黑云母化学成分上富铁(TFeO 19.92%~22.42%)贫镁(MgO 7.99%~10.46%),属于铁质黑云母,早白垩世二长岩和石英二长斑岩所代表的B类黑云母相比于A类黑云母更富镁(MgO 12.38%~14.45%)和钛(TiO21.90%~2.75%),贫铁(TFeO 16.64%~17.97%)和铝(Al2O315.00%~16%.79),属于镁质黑云母。A类和B类黑云母对应岩浆结晶温度分别为720~740℃和750~780℃;压力为202.20~443.49MPa和158~231MPa,对应岩浆侵位深度为6.67~14.64km和5.24~7.24km;结晶时岩浆氧逸度分别为10-15~10-16和10-12~10-13;岩浆来源为壳源,且B类黑云母对应岩浆有地幔物质参与。因此,可以认为二十一站岩体中早白垩世二长岩和石英二长斑岩具有中高温,高氧逸度应含水量,岩浆主要来源于地壳物质的部分熔融,并有部分地幔物质参与,侵位深度较浅的特点,具有形成大型斑岩矿床的潜力。早侏罗世花岗岩和二长岩氧逸度相对较低,侵位较深,物质来源为地壳,因此不具备成矿潜力。     

赣中紫云山岩体含矿花岗岩黑云母成分特征及其成岩成矿意义

通过对紫云山花岗岩中的黑云母进行详细的岩相学观察和矿物化学成分分析,讨论黑云母的形成环境以及其成岩成矿的意义,电子探针分析发现紫云山花岗岩中黑云母富铁贫铝高钛低镁,属于典型的铁质黑云母。其FeOTot为20.34%~21.81%,w(Al2O3)为17.11%~17.67%,w(TiO2)为3.26%~3.91%,w(MgO)为6.33%~7.26%,FeO/(FeO+MgO)为0.74~0.76,指示紫云山花岗岩属于壳源的S型花岗岩。黑云母成分还指示紫云山花岗岩形成于相对较高的温度和氧逸度环境,黑云母结晶温度为760℃~780℃,logfO2为-135 MPa~-125 MPa,压力为253 MPa~322 MPa,对应侵入深度为9.56km~12.18km。此外,黑云母具有富F的特征,F质量分数为0.47%~1.73%,为铀、钨矿床的形成提供了有利条件。     

云南马厂箐铜钼矿成矿岩体的角闪石和黑云母矿物学特征及其意义

马厂箐铜钼矿床位于扬子克拉通西缘,是三江成矿带内典型的大陆碰撞型斑岩铜-钼矿床,其成矿作用与矿区内的斑状花岗岩密切相关。在详细的岩相学观察基础上,对成矿岩体的造岩矿物角闪石和黑云母开展了电子探针成分分析,厘定了斑状花岗岩结晶的温压条件、岩浆氧逸度和含水量等要素,为解析马厂箐富碱侵入岩体的演化和成矿作用提供了矿物学尺度的制约。实验数据显示,岩体内角闪石富镁(w(Mg O)14.1%~16.3%)、富钙(w(Ca O)11.0%~11.6%)、贫钾(w(K2O)0.3%~0.6%)、富钠(Na2O/K2O1.0),属于阳起石和镁角闪石。黑云母Fe2+/(Fe2++Mg)比值较为均一,集中分布在0.35~0.38之间,且显示出富镁(w(Mg O)13.6%~16.2%)、铝(w(Al2O3)12.9%~13.7%),贫钛(w(Ti O2)1.9%~3.0%)、钙(w(Ca O)0.06%)的特征,属镁质黑云母。由角闪石和黑云母阳离子数计算的矿物结晶温度分别为687~770℃和660~713℃,结晶压力为38~82 MPa和55~80 MPa,相应侵位深度为1.3~2.7km和1.8~2.6 km。同时,通过角闪石成分计算岩浆氧逸度为ΔNNO+1.56~+2.41,并且根据岩石地球化学特征及矿物相稳定组合限定岩浆源区具有较高的含水量(w(H2O)10%)。结合矿物组合中角闪石的大量存在,分析可知马厂箐斑状花岗岩具有高氧逸度、富水、侵位浅的特点,符合形成大型-超大型斑岩Cu-Mo矿床岩浆岩的基本特征。因此,继北衙超大型斑岩Au矿取得重大突破后,推测三江成矿带南段扬子克拉通一侧斑岩型Cu-Mo矿床仍有较大的找矿潜力。     

玲珑黑云母花岗岩成因:矿物学特征约束

晚侏罗世玲珑黑云母花岗岩广泛分布于胶东半岛西北部,是胶东半岛众多中生代侵入岩中出露面积最大的岩体,为区内主要赋矿围岩。有关其成岩物理化学条件、岩石成因类型和源区特征却一直存在争议。本文在系统的岩石学和岩相学研究基础上,对钾长石、斜长石、黑云母和角闪石等主要造岩矿物进行了成分分析,以期厘定成岩物理化学条件,并进一步约束岩石成因。研究结果表明:钾长石K_2O含量为14.17%~15.85%,平均15.14%,Na_2O含量为0.62%~1.50%,平均1.04%,属于正长石(Or=86.51~94.35);斜长石Na_2O含量为8.41%~10.02%,平均9.11%,CaO含量为3.05%~4.54%,平均3.99%,属于更长石(Ab=74.97~84.56);黑云母相对富铁(FeO为18.49%~21.64%,平均20.13%)、贫镁(Mg O为8.06%~10.89%,平均9.50%),为镁铁黑云母或富铁黑云母;角闪石富铁(FeO为21.24%~22.24%,平均21.68%)、贫镁(Mg O为5.75%~6.57%,平均6.11%),均为含铁韭闪石质普通角闪石。花岗岩不同温压条件下的水逸度图解显示岩体形成压力为2.7~3.2kbar,深度为10~12km;锆石饱和温度计(综合前人数据计算得到)、角闪石-斜长石温度计和二长石温度计结果分别表明岩浆侵位温度为728~795℃,结晶温度为614~682℃,最后在531~565℃温度下固结成岩;黑云母和角闪石成分表明岩体形成时氧逸度较低,为-21.67~-16.73。黑云母化学成分Mg O与Al_2O_3呈现负相关性,说明其结晶过程中可能发生了Mg~(2+)和Al~(3+)的置换反应,结合黑云母Mg O-FeO-Al_2O_3图解可知岩体具有钙碱性花岗岩的特征。黑云母的含铁系数、MF值、AlⅥ值和较低的氧逸度指示玲珑黑云母花岗岩为S型花岗岩。黑云母具有由核部到边部FeO、Mg O和K_2O含量均一的特征,结合黑云母FeO/(FeO+Mg O)-Mg O图解、黑云母MF值以及角闪石Mg#值说明岩石物质来源为壳源。玲珑黑云母花岗岩中斜长石和黑云母的种属,岩体内大量太古宙继承锆石和产出方向与区域胶东群一致的胶东群残留体进一步说明其可能是胶东群部分熔融的产物,形成过程中没有明显幔源物质的参与。     

Isotopic systematics of He,Ar, S,Cu, Ni,Re, Os,Pb, U,Sm, Nd,Rb, Sr,Lu, and Hf in the rocks and ores of the Norilsk deposits

This paper reports the first results of a study of 11 isotope systems (³He/⁴He, ⁴⁰Ar/³⁶Ar, ³⁴S/³²S, ⁶⁵Cu/⁶³Cu, ⁶²Ni/⁶⁰Ni, ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ^206–208Pb/²⁰⁴Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others.     

高压微波消解法测定醋酸纤维过滤器采集的微尘粒子中的砷镉钴铬铜铁锰镍铅钒锌

最新的流行病学研究表明,空气中较高浓度的悬浮细颗粒可能对人类的健康有不利的影响。根据该项研究显示,由于心脏病、慢性呼吸问题和肺功能指标恶化而导致死亡率的升高与细尘粒子有关。这些研究结果已经促使欧盟于1999年4月出台了限制空气中二氧化硫、二氧化氮、氧化氮、铅和颗粒物含量的法案(1999/30/EC),对各项指标包括对可吸入PM10颗粒的浓度提出了新的限制性指标。PM10颗粒是指可以通过预分级器分离采集的气体动力学直径小于10μm的细颗粒。目前研究的兴趣重点逐步偏向PM2.5这些更细微颗粒物,PM2.5这种颗粒物对健康有明显的不利影响。在欧盟指令2008/50/EC中,对PM10和PM2.5都提     

Wavelength-dispersive X-ray fluorescence spectrometric determination of Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites

Komatiites are mantle-derived ultramafic volcanic rocks. Komatiites have been discovered in several States of India, notably in Karnataka. Studies on the distribution of trace-elements in the komatiites of India are very few. This paper proposes a simple, accurate, precise, rapid, and non-destructive wavelength-dispersive x-ray fluorescence (WDXRF) spectrometric technique for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites, and discusses the accuracy, precision, limits of detection, x-ray spectral-line interferences, inter-element effects, speed, advantages, and limitations of the technique. The accuracy of the technique is excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Ba, Pb, and Th and very good (within 4%) for Y. The precision is also excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th. The limits of detection are: 1 ppm for Sc and V; 2 ppm for Cr, Co, and Ni; 3 ppm for Cu, Zn, Rb, and Sr; 4 ppm for Y and Zr; 6 ppm for Nb; 10 ppm for Ba; 13 ppm for Pb; and 14 ppm for Th. The time taken for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in a batch of 24 samples of komatiites, for a replication of four analyses per sample, by one operator, using a manual WDXRF spectrometer, is only 60 hours.     

Roles of xenomelts,xenoliths, xenocrysts,xenovolatiles, residues,and skarns in the genesis,transport, and localization of magmatic Fe-Ni-Cu-PGE sulfides and chromite

Most sulfide-rich magmatic Ni-Cu-(PGE) deposits form in dynamic magmatic systems by partial melting S-bearing wall rocks with variable degrees of assimilation of miscible silicate and volatile components, and generation of barren to weakly-mineralized immiscible Fe sulfide xenomelts into which Ni-Cu-Co-PGE partition from the magma. Some exceptionally-thick magmatic Cr deposits may form by partial melting oxide-bearing wall rocks with variable degrees of assimilation of the miscible silicate and volatile components, and generation of barren Fe ± Ti oxide xenocrysts into which Cr-Mg-V ± Ti partition from the magma. The products of these processes are variably preserved as skarns, residues, xenoliths, xenocrysts, xenomelts, and xenovolatiles, which play important to critical roles in ore genesis, transport, localization, and/or modification. Incorporation of barren xenoliths/autoliths may induce small amounts of sulfide/chromite to segregate, but incorporation of sulfide xenomelts or oxide xenocrysts with dynamic upgrading of metal tenors (PGE > Cu > Ni > Co and Cr > V > Ti, respectively) is required to make significant ore deposits. Silicate xenomelts are only rarely preserved, but will be variably depleted in chalcophile and ferrous metals. Less dense felsic xenoliths may aid upward sulfide transport by increasing the effective viscosity and decreasing the bulk density of the magma. Denser mafic or metamorphosed xenoliths may also increase the effective viscosity of the magma, but may aid downward sulfide transport by increasing the bulk density of the magma. Sulfide wets olivine, so olivine xenocrysts may act as filter beds to collect advected finely dispersed sulfide droplets, but other silicates and xenoliths may not be wetted by sulfides. Xenovolatiles may retard settling of – or in some cases float – dense sulfide droplets. Reactions of sulfide melts with felsic country rocks may generate Fe-rich skarns that may allow sulfide melts to fractionate to more extreme Cu-Ni-rich compositions. Xenoliths, xenocrysts, xenomelts, and xenovolatiles are more likely to be preserved in cooler basaltic magmas than in hotter komatiitic magmas, and are more likely to be preserved in less dynamic (less turbulent) systems/domain/phases than in more dynamic (more turbulent) systems/domains/phases. Massive to semi-massive Ni-Cu-PGE and Cr mineralization and xenoliths are often localized within footwall embayments, dilations/jogs in dikes, throats of magma conduits, and the horizontal segments of dike-chonolith and dike-sill complexes, which represent fluid dynamic traps for both ascending and descending sulfides/oxides. If skarns, residues, xenoliths, xenocrysts, xenomelts, and/or xenovolatiles are present, they provide important constraints on ore genesis and they are valuable exploration indicators, but they must be included in elemental and isotopic mass balance calculations.     

Regional distribution of Al,B, Ba,Ca, K,La, Mg,Mn, Na,P, Rb,Si, Sr,Th, U and Y in terrestrial moss within a 188,000 km2 area of the central Barents region: influence of geology,seaspray and human activity

Five hundred and ninety-eight samples of terrestrial moss (Hylocomium splendens and Pleurozium schreberi) collected from a 188,000 km² area of the central Barents region (NE Norway, N Finland, NW Russia) were analysed by ICP-AES and ICP-MS. Analytical results for Al, B, Ba, Ca, K, La, Mg, Mn, Na, P, Rb, Si, Sr, Th, U and Y concentrations are reported here. Graphical methods of data analysis, such as geochemical maps, cumulative frequency diagrams, boxplots and scatterplots, are used to interpret the origin of the patterns for these elements. None of the elements reported here are emitted in significant amounts from the smelting industry on the Kola Peninsula. Despite the conventional view that moss chemistry reflects atmospheric element input, the nature of the underlying mineral substrate (regolith or bedrock) is found to have a considerable influence on moss composition for several elements. This influence of the chemistry of the mineral substrate can take place in a variety of ways. (1) It can be completely natural, reflecting the ability of higher plants to take up elements from deep soil horizons and shed them with litterfall onto the surface. (2) It can result from naturally increased soil dust input where vegetation is scarce due to harsh climatic conditions for instance. Alternatively, substrate influence can be enhanced by human activity, such as open-cast mining, creation of ‘technogenic deserts’, or handling, transport and storage of ore and ore products, all of which magnify the natural elemental flux from bedrock to ground vegetation. Seaspray is another natural process affecting moss composition in the area (Mg, Na), and this is most visible in the Norwegian part of the study area. Presence or absence of some plant species, e.g., lichens, seems to influence moss chemistry. This is shown by the low concentrations of B or K in moss on the Finnish and Norwegian side of the (fenced) border with Russia, contrasting with high concentrations on the other side (intensive reindeer husbandry west of the border has selectively depleted the lichen population).     

Mercury,arsenic, antimony,and selenium contents of sediment from the Kuskokwim River,Bethel, Alaska,USA

The Kuskokwim River at Bethel, Alaska, drains a major mercury-antimony metallogenic province in its upper reaches and tributaries. Bethel (population 4000) is situated on the Kuskokwim floodplain and also draws its water supply from wells located in river-deposited sediment. A boring through overbank and floodplain sediment has provided material to establish a baseline datum for sediment-hosted heavy metals. Mercury (total), arsenic, antimony, and selenium contents were determined; aluminum was also determined and used as normalizing factor. The contents of the heavy metals were relatively constant with depth and do not reflect any potential enrichment from upstream contaminant sources.     

Coprecipitation of Ti,Mo, Sn and Sb with fluorides and application to determination of B,Ti, Zr,Nb, Mo,Sn, Sb,Hf and Ta by ICP-MS

We examined the coprecipitation behavior of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides under two different fluoride forming conditions: at < 70 °C in an ultrasonic bath (denoted as the ultrasonic method) and at 245 °C using a Teflon bomb (denoted as the bomb method). In the ultrasonic method, small amounts of Ti, Mo and Sn coprecipitation were observed with 100% Ca and 100% Mg fluorides. No coprecipitation of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides occurred when the sample was decomposed by the bomb method except for 100% Ca fluoride. Based on our coprecipitation observations, we have developed a simultaneous determination method for B, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta by Q-pole type ICP-MS (ICP-QMS) and sector field type ICP-MS (ICP-SFMS). 9–50 mg of samples with Zr–Mo–Sn–Sb–Hf spikes were decomposed by HF using the bomb method and the ultrasonic method with B spike. The sample was then evaporated and re-dissolved into 0.5 mol l^− 1 HF, followed by the removal of fluorides by centrifuging. B, Zr, Mo, Sn, Sb and Hf were measured by ID method. Nb and Ta were measured by the ID-internal standardization method, based on Nb/Mo and Ta/Mo ratios using ICP-QMS, for which pseudo-FI was developed and applied. When 100% recovery yields of Zr and Hf are expected, Nb/Zr and Ta/Hf ratios may also be used. Ti was determined by the ID-internal standardization method, based on the Ti/Nb ratio from ICP-SFMS. Only 0.053 ml sample solution was required for measurement of all 9 elements. Dilution factors of ≤ 340 were aspirated without matrix effects. To demonstrate the applicability of our method, 4 carbonaceous chondrites (Ivuna, Orgueil, Cold Bokkeveld and Allende) as well as GSJ and USGS silicate reference materials of basalts, andesites and peridotites were analyzed. Our analytical results are consistent with previous studies, and the mean reproducibility of each element is 1.0–4.6% for basalts and andesites, and 6.7–11% for peridotites except for TiO₂.     

Alkaline rocks of Samchampi-Samteran, District Karbi-Anglong, Assam, India

The Samchampi-Samteran alkaline igneous complex (SAC) is a near circular, plug-like body approximately 12 km² area and is emplaced into the Precambrian gneissic terrain of the Karbi Anglong district of Assam. The host rocks, which are exposed in immediate vicinity of the intrusion, comprise granite gneiss, migmatite, granodiorite, amphibolite, pegmatite and quartz veins. The SAC is composed of a wide variety of lithologies identified as syenitic fenite, magnetite ± perovskite ± apatite rock, alkali pyroxenite, ijolite-melteigite, carbonatite, nepheline syenite with leucocratic and mesocratic variants, phonolite, volcanic tuff, phosphatic rock and chert breccia. The magnetite ± perovskite ± apatite rock was generated as a cumulus phase owing to the partitioning of Ti, Fe at a shallow level magma chamber (not evolved DI = O1). The highly alkaline hydrous fluid activity indicated by the presence of strongly alkalic minerals in carbonatites and associated alkaline rocks suggests that the composition of original melt was more alkalic than those now found and represent a silica undersaturated ultramafic rock of carbonated olivine-poor nephelinite which splits with falling temperature into two immiscible fractions—one ultimately crystallises as alkali pyroxenite/ijolite and the other as carbonatite. The spatial distribution of varied lithotypes of SAC and their genetic relationships suggests that the silicate and carbonate melts, produced through liquid immiscibility, during ascent generated into an array of lithotypes and also reaction with the country rocks by alkali emanations produced fenitic aureoles (nephelinisation process). Isotopic studies (δ¹⁸O and δ¹³C) on carbonatites of Samchampi have indicated that the δ¹³C of the source magma is related to contamination from recycled carbon.