吉林省兰家金矿南泉眼闪长岩U-Pb年代学和地球化学特征

南泉眼闪长岩是兰家矽卡岩型金矿的成矿岩体,研究程度极低.通过岩石地球化学和LA-ICP-MSU-Pb年代学研究,讨论了岩石成因、来源和构造背景.研究表明,南泉眼闪长岩为准铝质的钙碱性岩石;岩石明显富集大离子亲石元素(如Rb、K、Sr)、活泼的不相容元素(如Th、U)和轻稀土元素,相对亏损高场强元素(如Nb、Ta、Ti、P)和重稀土元素,具有明显的负Eu异常,Nb/Ta、La/Nb、Th/La比值显示岩石具壳源特征,Al2O3+MgO+FeOt图解显示岩浆具弧型活动大陆边缘特征.闪长岩岩浆锆石LA-ICP-MSU-Pb加权平均年龄为170.21±0.73Ma(MSWD=0.14);谐和年龄值为170.21±0.39Ma(MSWD=0.018),为中侏罗世.成岩构造背景为燕山早期太平洋板块俯冲引起大陆弧伸展和岩石圈减薄,软流圈物质上涌、底侵提供热动力,不成熟下地壳物质部分熔融形成南泉眼闪长岩.     

北祁连造山带红石泉岩体地球化学特征及其构造意义

红石泉岩体地处北祁连造山带的龙首山成矿带西南缘,区内发育伟晶岩型铀矿床。本文对红石泉岩体进行岩相学、岩石地球化学研究,探讨其岩石成因、岩浆来源,厘定其构造环境。元素地球化学结果显示：岩体具中硅、富铝,富钠特征,为准铝质高钾碱性正长岩系列。在微量元素图解中,样品富集Rb、U、K、Nd等元素,亏损高场强元素Nb、Ta、Ti及元素P等;在稀土元素球粒陨石标准化图解中,样品富集轻稀土,轻重稀土分馏明显,Eu显示正异常。样品显示高的Zr+Nb+Ce+Y的值,属A型花岗岩。结合其元素地球化学特征及区域内岩浆岩的演化,厘定岩体为祁连板块与阿拉善板块碰撞后拉张环境下,壳源岩浆与幔源岩浆混合形成。     

长江中下游地区燕山晚期基性岩浆活动的记录

江苏省宁镇地区位于长江中下游沿江成矿带的最东端,是长江中下游成矿带的重要组成部分,蒋庙岩体是宁镇地区唯一的基性岩体.对此岩体进行了锆石U-Pb年代学、矿物化学、岩石地球化学和Sr-Nd-Hf同位素研究,讨论了其成因及地幔源区性质.岩体主要由橄榄辉长岩、角闪辉长岩和辉石闪长岩组成,其中辉石闪长岩的锆石LA-ICP-MS(laser ablation inductively coupled plasma mass spectrometry) U-Pb年龄为121±1 Ma.锆石ε_Hf(t)值介于-2.9~-6.4.全岩地球化学研究显示岩石样品富钠低钾,富集轻稀土元素,重稀土元素亏损不明显,富集大离子亲石元素(如K、Ba、Sr等),亏损高场强元素(如Nb、Ta、Ti、Zr、Hf等).蒋庙基性侵入岩在长江中下游地区中生代岩浆岩中具有最高的ε_Nd(t)值以及最低的(87Sr/86Sr)_i值,其Sr-Nd同位素组成介于软流圈地幔(depleted MORB mantle,DMM)-富集岩石圈地幔(enriched mantle Ⅱ,EMⅡ)之间.研究认为,蒋庙岩体应来源于软流圈地幔和富集岩石圈地幔的混合组分,可能有少量的俯冲板片物质加入源区,并在成岩过程中经历了一定程度的结晶分异.结合区域地质、年代学、矿物学和地球化学资料,表明蒋庙岩体的形成可能与古太平洋板块俯冲事件密切相关.      

小兴安岭二龙山林场堆晶辉长岩地球化学特征及构造环境

小兴安岭北部二龙山林场辉长岩的主量、微量和稀土元素的测试分析结果显示: 二龙山辉长岩为钙碱性系列、偏铝质岩石; δEu 正异常,Sr 元素含量富集明显,具有堆晶辉长岩特征; Rb /Sr、Nb / Ta、LILE/HFSE、Th /Ta、Nb /U 和Nb /La 比值特征均显示,辉长岩岩浆来自受到俯冲流体交代的地幔源区。Nb /Zr、Th /Nb、Th /Ta 和Ta /Hf 比值特征及对Th /Hf --Ta /Hf 构造环境判别图解投点表明,二龙山辉长岩形成于陆内拉张环境。     

东昆仑阿克楚克塞地区辉长岩地球化学特征、锆石U-Pb年龄及其构造意义

东昆仑地区基性-超基性岩石的研究较薄弱,缺乏对东昆仑幔源岩浆活动及岩浆演化的整体认识。对阿克楚克塞辉长岩进行了地球化学、锆石U-Pb年代学及Hf同位素研究,结果显示,该岩石形成于晚三叠世早期(219.3±1.1Ma,MSWD=0.80);岩石SiO2含量为49.03%~57.26%,Mg#值为49~57,属于钙碱性系列岩石;稀土元素配分曲线为轻稀土元素富集的右倾型,富集大离子亲石元素Rb、Ba、K,相对亏损高场强元素Nb、Ta、Ti;εHf(t)=-1.81~3.25,锆石Hf模式年龄大于锆石结晶年龄。地球化学特征显示,阿克楚克塞辉长岩岩浆源区应为受俯冲板片流体交代的岩石圈地幔。结合区域构造背景分析,阿克楚克塞辉长岩形成于印支期造山后伸展的构造环境,继承了早期板片俯冲改造的地幔源区特征。     

辽东桓仁西部古元古代侵入岩年代学及岩石地球化学

华北克拉通东部辽东地区出露古元古代侵入岩,为准确认识辽东地区古元古代构造演化过程,选取北沟岩体、正岔岩体和树柳林子岩体的岩相学、岩石地球化学及年代学特征,探讨了岩体的形成时代、岩石成因及其构造环境。锆石SHRIMP U-Pb年代学研究表明,柳林子岩体年龄为(2 490±8) Ma,北沟岩体年龄为(2 457±11) Ma。北沟岩体高硅富钾,富集Rb、U、Th、K等大离子亲石元素,亏损Nb、Ti、P等高场强元素,为过铝质高钾钙碱性I型花岗岩,Nb/Ta平均值5. 75,Rb/Nb平均值4. 21,源于太古宙古老地壳的部分熔融;正岔岩体高硅富钾,富集Rb、Ba、U、Th、K等大离子亲石元素,亏损Nb、Ti、P等高场强元素,为弱过铝质高钾钙碱性A型花岗岩,Nb/Ta平均值16. 06,Rb/Nb平均值4. 81,源区可能由幔源岩浆底侵带来的热量加热地壳,导致其重熔并与之混合后形成的。柳林子岩体为变质角闪辉长岩,呈亚碱性,富集Rb、Ba、K等大离子亲石元素,亏损Nb、Ti、P等高场强元素,显示其岩浆可能形成于受陆壳微弱混染的软流圈地幔或岩石圈地幔。认为研究区古元古代侵入岩形成于东、西陆块碰撞拼合后的后造山挤压向板内伸展转换的构造环境,为构造体质转换的产物。     

青海省东昆仑大水沟金矿英云闪长岩锆石U-Pb测年、岩石地球化学及其找矿意义

大水沟金矿位于东昆仑中段,目前矿区西部共圈定金矿(化)体9条,结合化探异常和区域地质背景对比,认为该区具有良好的找矿前景。本文利用LA-MC-ICPMS锆石U-Pb定年技术,首次获得与金矿成矿有密切关系的英云闪长岩加权平均年龄为(239.5±0.9)Ma,厘定为中三叠世;岩石地球化学研究表明,英云闪长岩为钙碱性系列岩石,轻稀土富集,轻重稀土分馏明显,具弱的负铕异常,岩体明显富集大离子亲石元素(Rb、K)、活泼不相容元素Th、轻稀土元素和Pb,相对亏损高场强元素(Nb、Ta、P、Ti),Rb/Sr、Nb/Ta等特征反映出岩石具有壳幔混合岩浆的特点。结合东昆仑地区已有的年代学资料、岩石地球化学和区域地质构造演化分析,本文认为英云闪长岩形成构造环境为俯冲阶段;俯冲作用促进了幔源流体的运移,在构造有利部位沉淀形成金矿。     

新疆牛毛泉磁铁矿含矿岩体岩浆演化过程及源区特征

牛毛泉基性杂岩体位于准噶尔古板块博格达-哈尔里克晚古生代岛弧东段,赋存磁铁矿。研究表明,该岩体具有明显成层性和韵律构造特征,主要岩石类型有橄榄辉长岩、含橄榄辉长岩、辉长岩和角闪辉长岩。岩石地球化学特征表明,该套岩石属拉斑玄武岩系列,m/f值介于0.65~1.44之间,属铁质基性-超基性岩。岩石稀土元素总量相对较低,稀土元素配分曲线为轻稀土元素略富集的右倾型;岩石富集大离子亲石元素(Rb、Ba、Sr、U),相对亏损高场强元素(Zr、Hf),具有明显的Nb、Ta负异常和弱的Ti正异常。岩石εNd(t)=-3.4~-0.50,εSr(t)=-3.4~8.5,具有向EMⅠ方向演化的趋势,表明岩浆源区可能为受俯冲流体交代改造的富集岩石圈地幔,是新疆北部早二叠世时期后碰撞伸展阶段的产物,由拆沉的富集岩石圈地幔被软流圈加热后发生部分熔融并上侵形成。     

东昆仑埃坑德勒斯特二长花岗岩岩石地球化学特征及岩石成因

埃坑德勒斯特铜(钼)矿是近年来在东昆仑地区发现的斑岩型铜(钼)矿,矿区位于东昆南复合拼贴带内,花岗斑岩及外围碎裂的二长花岗岩是主要的赋矿围岩。对二长花岗岩进行了岩石地球化学和Sr-Nd同位素研究,讨论了岩浆来源、岩石成因和构造背景。研究表明,岩石富硅,相对富钠贫钙和镁,属钙碱性过铝质系列岩石。岩石明显富集大离子亲石元素(K、Ba、Rb)和活泼的不相容元素(如Th、U),相对亏损高场强元素(Nb、Ta、P、Ti)。样品的ISr值为0.707 05～0.707 37,εNd(t)为-2.2～-1.6,Rb/Sr为0.17～0.32,反映岩浆来源具壳幔混合特点。根据Y+Nb-Rb、La/NbBa/Nb等判别图解及与俯冲有关的蛇绿岩带发育特征,表明该岩体形成于安第斯型活动大陆边缘环境。俯冲作用导致俯冲板片的流体降低熔点和直接交代地幔,使地幔部分熔融形成基性岩浆。幔源岩浆底侵作用提供热能,使基性下地壳物质部分熔融形成花岗质岩浆,其中混入了少量幔源岩浆。     

胶东招掖地区滦家河花岗岩锆石U-Pb年代学、岩石地球化学及其地质意义

滦家河花岗岩体是胶东金矿区内的重要岩体,其岩性主要为中粗粒黑云母二长花岗岩。锆石LA—ICP—MS U—Pb年代学研究表明,滦家河花岗岩形成于149±2 Ma,属晚侏罗世。滦家河花岗岩Si O2的含量为64.58%~72.05%,相对较高;A/CNK值为0.98~1.22。微量元素特征显示,滦家河花岗岩富集大离子亲石元素(LILE)Rb、Ba、K,强烈亏损高场强元素(HFSE)Nb、Ta、Ti、P;稀土元素特征显示轻稀土强烈富集,重稀土极度亏损,轻微正铕异常。岩石的Nb/La和Nd/Th比值显示壳源花岗岩的特征,Rb/Sr比值暗示可能有部分幔源物质混入。结合区域地质分析认为,侏罗纪开始,太平洋板块向欧亚大陆的俯冲引发大规模幔源岩浆底侵,导致地壳物质部分熔融形成滦家河花岗岩。     

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.     

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.     

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).     

Petrographic, mineralogy, and geochemistry of coals of Pabedana, Kerman Province, Central Iran

This paper discusses the result of the detailed investigations carried out on the coal characteristics, including coal petrography and its geochemistry of the Pabedana region. A total of 16 samples were collected from four coal seams d2, d4, d5, and d6 of the Pabedana underground mine which is located in the central part of the Central-East Iranian Microcontinent. These samples were reduced to four samples through composite sampling of each seam and were analyzed for their petrographic, mineralogical, and geochemical compositions. Proximate analysis data of the Pabedana coals indicate no major variations in the moisture, ash, volatile matter, and fixed carbon contents in the coals of different seams. Based on sulfur content, the Pabedana coals may be classified as low-sulfur coals. The low-sulfur contents in the Pabedana coal and relatively low proportion of pyritic sulfur suggest a possible fresh water environment during the deposition of the peat of the Pabedana coal. X-ray diffraction and petrographic analyses indicate the presence of pyrite in coal samples. The Pabedana coals have been classified as a high volatile, bituminous coal in accordance with the vitrinite reflectance values (58.75–74.32 %) and other rank parameters (carbon, calorific value, and volatile matter content). The maceral analysis and reflectance study suggest that the coals in all the four seams are of good quality with low maceral matter association. Mineralogical investigations indicate that the inorganic fraction in the Pabedana coal samples is dominated by carbonates; thus, constituting the major inorganic fraction of the coal samples. Illite, kaolinite, muscovite, quartz, feldspar, apatite, and hematite occur as minor or trace phases. The variation in major elements content is relatively narrow between different coal seams. Elements Sc,, Zr, Ga, Ge, La, As, W, Ce, Sb, Nb, Th, Pb, Se, Tl, Bi, Hg, Re, Li, Zn, Mo, and Ba show varying negative correlation with ash yield. These elements possibly have an organic affinity and may be present as primary biological concentrations either with tissues in living condition and/or through sorption and formation of organometallic compounds.     

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.