Trace element geochemistry and genesis of the copper ore deposits of the Singhbhum shear zone,Eastern India

The genesis of the copper ore deposits of the Singhbhum shear zone, India, has been worked out through a detailed geochemical examination of the ores and the country rocks. Following different techniques of atomic absorption, the abundances of Cu, Co, Ni, Pb, Zn, Cd, Ag, Mn and Hg were determined and the trace element characteristics of the principal rock units in and outside the shear zone have been compiled and critically evaluated. The data suggest that the ore deposits are the result of a sequence of long-continued and over-lapping geological processes culminating in intense shearing, syntectonic granitization and considerable mobilization of the ore elements. The Precambrian metasedimentary and metavolcanic rocks of the shear zone, as well as those enclosing it, served as the source, while diffusion of the ore constituents and their precipitation in physicochemically favourable structural traps, formed in response to shearing, resulted in the formation of the deposits.

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Zusammenfassung Als Beitrag zur Klärung der Genese der Kupferlagerstätten in der Singhbhum Shear Zone, Indien, wurden geochemische Untersuchungen an Erzen und Nebengestein durchgeführt. Spurengehalte von Cu, Co, Ni, Pb, Zn, Cd, Ag, Mn, Hg wurden mit Hilfe der AAS bestimmt, ihre Verteilung innerhalb der Zone und der angrenzenden Gesteinstypen wird diskutiert. Auf Grund der vorliegenden geochemischen Daten wird folgende Deutung zur Entstehung der Erzlagerstätten gegeben: Die Bildung der Singhbhum-Erzvorkommen ist das Ergebnis einer Folge langandauernder und sich überschneidender geologischer Prozesse, wie intensiver Scherung, syntektonischer Granitisation und damit verbundener Mobilisierung der oben genannten Elemente. Die präkambrischen Metasedimente und Metavulkanite innerhalb der Scherzone und ihrer näheren Umgebung sind als Muttergesteine der erzbildenden Elemente anzusehen. Die Bildung der Lagerstätte ist das Resultat der Diffusion von Lösungen und ihres Absatzes in physikalisch-chemisch günstigen Struktur-Fallen, gebildet im Anschluß an die Scherung.

     

Reworked manganese ore bodies in Bonai-Keonjhar belt,Singhbhum Craton,India: Petrology and genetic study

The genetic evolution of three types of reworked manganese ore bodies namely: Detrital, Concretionary (Mangcrete) and Wad in the Precambrian Iron Ore Group occurring in Bonai-Keonjahr belt, Singhbhum Craton, India are reported. All the reworked Mn-ore bodies are developed in a restricted area and have a limited resource. Mangcrete and wad are commonly exposed at the surface and extend to a maximum depth of 10 m while detrital ores are observed below 10–20 m from the surface.Detrital ore bodies occur as large boulders and are buried under a thick zone of laterite. Mangcrete is concretionary in nature; oolitic, spherulitic and nodular in shape. Broken fragmented of ooloids and pisoloids, often observed in mangcrete, are indications of reworking. Wad exposures are noticed above low to medium-grade bedded manganese ore bodies. Among three reworked ore types, the detrital is of low to medium-grade having Mn:Fe ratio > 5, while wad and mangcrete are of sub-grade (Mn:Fe ~ 1) and off-grade type (Mn:Fe < 1) respectively.Detrital ore bodies are of allochthonous nature and developed through several stages such as fragmentation of pre-existing ore, leaching and cementation followed by transportation and deep burial. Mangcrete represent chemogenic precipitates at several stages of contemporary Mn-Fe-Al rich fluid under supergene environment. Wad is of bio-chemogenic origin and developed in a swampy region under marine environment due to slow chemical precipitation of Mn-Fe enriched fluid, in several stages nucleating quartz/hematite/cryptomelane detritals.     

试论玉龙斑岩铜矿带内矿床的蚀变和矿化分带

西藏东部玉龙斑岩铜矿带(以下简称矿带),由玉龙、马那松多、多霞松多、莽总和扎那朵等已查明的矿床及一系列有远景的待查矿点组成的,该矿带,系我国目前所知较大的斑岩铜矿带。笔者曾在玉龙矿带进行过十余年地质工作,现将个人对矿床蚀变和矿化分带之浅见介绍如下。     

南岭成矿带大湾铀矿田铀成矿环境与找矿前景

湖南省大湾铀矿田位于南岭成矿带九嶷山杂岩体中段,有利的成矿环境使该地区成为华南重要的产铀区及稀有金属和有色金属矿集区。岩体外接触带寒武系为矿田的主要铀源层之一和成矿有利部位,已探明的铀矿床均产于九嶷山杂岩体中部金鸡岭岩体外接触带。九嶷山杂岩体分别由东、西两个完全独立的岩浆演化中心演化而来,西部岩浆演化中心的金鸡岭岩体与铀成矿作用关系密切,形成了岩浆演化中心、热流体活动中心与矿化中心三位一体的基本构造格局。深大断裂带为成矿流体循环运移提供了通道和热动力来源。铀成矿作用主要发生在晚白垩世早期地应力转向期,矿化与NW向伸展断裂及其相伴的深源热流体有关。岩体接触带为铀沉淀富集的有利地球化学障。重力、航磁及航空γ能谱异常及放射性水化学异常是找铀的重要判据之一。在区域铀成矿环境分析基础上,对该区找矿前景进行了展望。     

西藏班公湖-怒江成矿带上的碰撞后铜矿床

地处藏北高原的班公湖-怒江铜矿带是继藏东的玉龙斑岩铜矿带和藏南的冈底斯斑岩铜矿带之后,在青藏高原上发现的第三条铜矿带。与前两条斑岩铜矿带不同的是,班公湖-怒江铜矿带的铜矿床类型具有多样性,包括:1多龙、雄梅斑岩型铜金矿床;2尕尔穷-嘎拉勒斑岩-矽卡岩型铜金矿床;3拨拉扎斑岩型铜钼矿床;4舍索矽卡岩型铜(铅锌)多金属矿床。不同类型铜矿床的成矿时代集中在120~90 Ma之间,约30 Ma间隔内。文章通过沉积岩岩相学、火成岩岩石地球化学以及锆石U-Pb与辉钼矿Re-Os同位素年代学的综合研究,指出班公湖-怒江中特提斯洋盆的闭合时间为早白垩世初(140~130 Ma之间),班公湖-怒江成矿带上的铜矿床都形成于碰撞后造山环境。该成矿带与铜矿化有关的侵入岩主要为花岗闪长(斑)岩和石英闪长(玢)岩,在岩石地球化学上,富集大离子亲石元素(Rb、Th、U、Ba、K、Pb),亏损高场强元素(Nb、Ta、Ti),显示出俯冲组分对岩浆生成过程产生的重要影响,与碰撞后岩浆作用特征相吻合。除了班公湖-怒江铜矿带外,青藏高原上的另外两条斑岩铜矿带(即藏东的玉龙斑岩铜矿带和藏南的冈底斯斑岩铜矿带),也是形成于洋盆闭合之后的造山带碰撞后环境,因此,青藏高原可以说是地球上碰撞后铜矿床的天堂。     

A multivariate statistical study of copper mineralization in the central section of Mosaboni Mine, Eastern Singhbhum, India

A multivariate statistical analysis was carried out with log-transformed values of Cu, Ni, Co, Pb, Zn, Ag, Cr, Mn, Ca, and Sr in several sets of samples collected across the mineralized base metal zone in sheared soda granite, feldspathic schist, and chlorite schist from the central section of Mosaboni Mine of the famous Singhbhum Copper Belt of eastern India. Linear correlation coefficient matrices of two sets of ore samples (>0.5% Cu)—one from levels 18 and 21 and the other from levels 25 and 28—indicate two well-defined and distinct clusters comprising Cu, Ni, Co, Pb, and Zn on one hand and Ca, Sr, and Mn on the other. Varimax-rotatedR-mode factor analysis of two above-noted sample sets, taken along with available geologic information, indicates that over 80% of the variability in data matrices for 9–10 elements can be accounted for by four distinct processes: (a) an early phase of copper mineralization which apparently replaced Mn, Ca, and Sr in the host rock; (b) a silicate-cum-oxide phase of crystallization/recrystallization of host rock; (c) remobilization of sulfide-forming ore elements (Cu, Ni, Co, Pb, and Zn); and (d) a phase of mineralization of Ag which appears to have replaced Cr, Ca and Cu. Process (c) was quantitatively most important. Factor score studies are suggestive of preferred introduction of Ni, Co, Pb, and Zn along central parts of preexisting copper-mineralized zones.     

Himalayan magmatism and porphyry copper–molybdenum mineralization in the Yulong ore belt, East Tibet

Summary ?The NW–SE-trending Yulong porphyry Cu–Mo ore belt, situated in the Sanjiang0 area of eastern Tibet, is approximately 400 km long and 35 to 70 km wide. Complex tectonic and magmatic processes during the Himalayan epoch have given rise to favorable conditions for porphyry-type Cu–Mo mineralization. Porphyry masses of the Himalayan epoch in the Yulong ore belt are distributed in groups along regional NW–SE striking tectonic lineaments. They were emplaced mainly into Triassic and Lower Permian sedimentary-volcanic rocks. K–Ar und U–Pb isotopic datings give an intrusion age range of 57–26 Ma. The porphyries are mainly of biotite monzogranitic and biotite syenogranitic compositions. Geological and geochemical data indicate that the various porphyritic intrusions in the belt had a common or similar magma source, are metaluminous to peraluminous, Nb–Y–Ba-depleted, I-type granitoids, and belong to the high-K calc-alkaline series. Within the Yulong subvolcanic belt a number of porphyry stocks bear typical porphyry type Cu–Mo alteration and mineralization. The most prominent porphyry Co–Mo deposits include Yulong, Malasongduo, Duoxiasongduo, Mangzong and Zhanaga, of which Yulong is one of the largest porphyry Cu (Mo) deposits in China with approximately 8 × 10⁶ tons of contained Cu metal. Hydrothermal alteration at Yulong developed around a biotite–monzogranitic porphyry stock that was emplaced within Upper Triassic limestone, siltstone and mudstone. The earliest alteration was due to the effects of contact metamorphism of the country rocks and alkali metasomatism (potassic alteration) within and around the porphyry body. The alteration of this stage was accompanied by a small amount of disseminated and veinlet Cu–Mo sulfide mineralization. Later alteration–mineralization zones form more or less concentric shells around the potassic zone, around which are distributed a phyllic or quartz–sericite–pyrite zone, a silicification and argillic zone, and a propylitic zone. Fluid inclusion data indicate that three types of fluids were involved in the alteration–mineralization processes: (1) early high temperature (660–420 °C) and high salinity (30–51 wt% NaCl equiv) fluids responsible for the potassic alteration and the earliest disseminated and/or veinlet Cu–Mo sulfide mineralization; (2) intermediate unmixed fluids corresponding to phyllic alteration and most Cu–Mo sulfide mineralization, with salinities of 30–50 wt% NaCl equiv and homogenization temperatures of 460–280 °C; and (3) late low to moderate temperature (300–160 °C) and low salinity (6–13 wt% NaCl equiv) fluids responsible for argillic and propylitic alteration. Hydrogen and oxygen isotopic studies show that the early hydrothermal fluids are of magmatic origin and were succeeded by increasing amounts of meteoric-derived convective waters. Sulfur isotopes also indicate a magmatic source for the sulfur in the early sulfide mineralization, with the increasing addition of sedimentary sulfur outward from the porphyry stock. Received August 29, 2001; revised version accepted May 1, 2002 Published online: November 29, 2002     

Petrochemistry of the lavas from proterozoic dalma volcanic belt,Singhbhum, eastern India

The Dalma volcanic belt of the Singhbhum Precambrian terrain in eastern India is developed along the median zone of a linear basin flanked by Archaean cratonic basement to the south. The lavas, in a low grade metamorphic environment, preserve a strong compositional bimodality, with highly magnesian picritic volcanics developed at the base and low-K basalt flows above, constituting the bulk of the lava pile. The ultrabasic lavas have low concentrations of immobile incompatible elements, ratios of which are probably controlled by the source character. Dalma mafic flows are closely comparable in geochemical character to modern day mid-oceanic ridge basalts (MORB) with a dominance of light-REE-depleted basalts and ferrobasalts. However, in terms of certain element ratios (Th/Ta), deviation from MORB characteristics toward island arc tholeiites is apparent. In this respect the Dalma basalts appear to have a modified MORB composition and the closest chemical analogy may be basalts from back-arc basins, i. e. a supra-subduction zone environment. The bimodality of ultrabasic and mafic lavas is reminiscent of Archaean komatiitic provinces. The geochemical signature of the Dalma lavas, and the geological framework of the terrain, strongly point to a marginal basin domain developed in this crustal segment during the Proterozoic.

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Zusammenfassung Der Vulkangürtel von Dalma liegt in der präkambrischen Region Singhbhum in Ostindien. Aufgeschlossen ist der Dalma-Gürtel im mittleren Bereich eines geradlinigen Bekkens, das im Süden durch Basement des Archaikums begrenzt wird. Die Laven befinden sich in einer geringmetamorphen Umgebung und weisen eine bimodale Zusammensetzung auf. An der Basis sind Magnesium-reiche und darüber Kalium-arme Basalte entwickelt, die repräsentativ für den Durchschnitt der Laven sind. Die ultrabasischen Laven enthalten niedrige Konzentrationen an immobilen nicht kompatiblen Elementen, deren Verhältnis wahrscheinlich von den Eigenschaften der Lavaquelle gesteuert wird. Der geochemische Charakter der mafischen Dalma-Vulkanite entspricht weitgehend den heutigen Basalten der ozeanischen Rücken (MORB). Dabei dominieren leicht abgereicherte REE-Basalte sowie eisenreiche Basalte. Vergleicht man allerdings Elementverhältnisse wie das von Th/Ta, wird eine Abweichung von dem typischen MORB-Charakter hin zu Inselbögen-Tholeiten deutlich. Berücksichtigt man diese Beobachtungen, scheinen die Dalma-Basalte eine modifizierte MORB-Zusammensetzung zu haben, die in ihrem Chemismus am ehesten den Basalten von Back-Arc-Becken, z. B. in einem Gebiet einer Supra-Subduktionszone, zu entsprechen. Die Bimodalität der ultrabasischen und mafischen Laven erinnert an archaische komatiitische Regionen. Die geochemische Zusammensetzung der Dalma-Laven sowie der geologische Rahmen des Gebietes deuten auf ein randliches Becken hin, das sich während des Proterozoikums entwickelt haben könnte.

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Résumé La ceinture volcanique de Dalma, dans le Précambrien de Singhbhum (Inde Orientale) est située dans la partie médiane d'un bassin linéaire bordé au Sud par un socle cratonique archéen. Les laves se trouvent dans un environnement de faible degré de métamorphisme et présentent une composition nettement bimodale: volcanites picritiques très magnésiennes à la base, surmontées de coulées basaltiques pauvres en K, qui constituent l'essentiel de l'ensemble. Les laves ultrabasiques montrent de faibles concentrations en éléments immobiles incompatibles dont les rapports sont probablement déterminés par le caractère de la source. Les coulées basiques de Dalma sont très comparables, dans leurs propriétés géochimiques, aux basaltes récents des rides océaniques (MORB), avec une dominante de basaltes pauvres en terres rares légères et de ferro-basaltes. Toutefois, les rapport de certains éléments (Th/Ta) font apparaître, par rapport au MORB, une déviation vers les tholéiites d'arcs insulaires. A ce point de vue, les basaltes de Dalma montrent une composition de MORB modifée et une analogie avec les basaltes de bassins d'arrière-arc, c'est-à-dire en situation de supra-subduction. La bimodalité laves ultrabasiques/laves basiques est une réminiscence des provinces komatiitiques archéennes. Le signalement géochimiques des laves de Dalma et leur situation géologique plaident en faveur d'un domaine de bassin marginal développé dans ce segment central au cours du Protérozoïque.

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山东招掖金矿带花岗岩成因及与金矿床的关系

著名招掖金矿带中金矿床的形成与本区玲珑、滦家河和郭家岭花岗岩有着密不可分的成因联系。根据这些花岗岩的地质和岩石特征,以及主要元素、微量元素、稀土元素的演化特点和黑云母成分分析,认为它们均为地壳深部部分熔融形成的花岗岩。玲珑花岗岩和滦家河花岗岩是同一岩浆源经分异作用形成的不同岩体,郭家岭花岗岩则为晚期侵入岩体。总体为燕山早期同一构造岩浆演化旋回形成的复式岩体。金的成矿作用与郭家岭花岗岩有关。     

云南牟定戌街地区铀矿化特征及成因探讨

云南牟定戌街1101铀矿区位于扬子地台西南缘,康滇地轴中南段,是我国西南地区产于元古界变质岩中的铀矿之一。通过对矿化区岩石及矿石的岩石学、矿物学、地球化学及年代学特征进行研究,分析了铀矿的形成条件,揭示了铀成矿规律。研究发现:①牟定戌街地区铀矿化赋存于斜长角闪岩、角闪斜长片麻岩和二云母石英片岩等变质混合岩中,主要铀矿物为晶质铀矿、钛铀矿及次生铀矿,含铀矿物有榍石、锆石,硫化物丰富,围岩蚀变主要为硅化、赤铁矿化、碱交代等;②牟定1101铀矿化地区混合岩化岩石的地球化学特征表现为高钾钙碱性-钙碱性系列岩石;③研究区混合岩形成于1 056 Ma左右,铀矿形成于845 Ma左右,为新元古代产物;④牟定1101地区铀成矿受构造、岩性控制,与混合岩化作用、构造热液活动及碱交代作用关系密切,属热液成因铀矿。     

滇东南锡矿带矿床类型及其组合特征

本文从矿床地质特征出发,以矿床的矿石类型为基础,考虑成因,强调矿床的工业意义,将滇东南锡矿带的矿床类型划分为两类、四组合、十四型。锡矿床围绕花岗岩突呈现规律性的空间组合,同时以成矿地质条件的差异、成矿作用的多样性,形成矿床类型的不同组合形式。     

河南围山城金银成矿带铅同位素地球化学及矿床成因

桐柏山区的围山城金银成矿带包括破山特大型银矿、银洞坡大型金矿、银洞岭大型银多金属矿床及一些矿点,所有矿床赋存于上元古界歪头山组地层,并具有层控特征。矿石矿物的铅同位素组成为²⁰⁶Pb/²⁰⁴Pb=16.753~17.216,²⁰⁷Pb/²⁰⁴Pb=15.417~15.638,²⁰⁸Pb/²⁰⁴Pb=38.251~39.050;与歪头山组地层的铅同位素组成一致,而与桐柏地区的其他地层、岩体差别较大,表明成矿物质来自赋矿地层歪头山组。围山城成矿带应属于典型的层控造山型金银成矿系统,它形成于中生代扬子与华北板块的陆陆碰撞造山过程,碰撞造山期间的下插板片变质脱水诱发了矿带内流体成矿系统的发育,强烈的流体-岩石相互作用使歪头山组内的成矿物质被萃取、迁移、聚集到碳质绢云片岩层。     

小秦岭文峪金矿床流体包裹体研究及矿床成因

文峪金矿位于小秦岭矿田南部,其产出受脆-韧性剪切带控制,赋矿围岩为太华群变质杂岩.根据脉体穿切关系和矿物交代关系,可以将文峪金矿流体成矿过程分为早、中、晚三个阶段,其热液石英中发育CO2-H2O型、纯CO2型和H2O溶液型三种类型流体包裹体.平阶段石英中原生包裹体主要是CO2-H2O型和纯CO2型,其成分为CO2+H2O±N2±CH4,均一温度集中在290～330℃,盐度为1.02％～9.59％ NaCleqv;中阶段为主成矿阶段,该阶段石英中包含了所有3种类型的包裹体,其中以CO2-H2O型包裹体为主,获得CO2-H2O和水溶液包裹体均一温度集中在250～290℃,盐度为0.02％～12.81％NaCleqv;晚阶段石英仅发育水溶液型包裹体,具有较低的均一温度(114～239℃)和盐度(4.18％～8.95％ NaCleqv).根据CO2-H2O型包裹体计算早、中阶段压力分别为130 ～ 178MPa和85 ～ 150MPa,对应的成矿深度分别为4.7～6.5km和3.1～5.5km.总体而言,文峪金矿的初始流体具有中高温、富CO2、低盐度的变质流体特征,晚成矿阶段流体演化为低温、低盐度水溶液流体,流体的不混溶导致了主成矿期矿质的大量沉淀,文峪金矿为中浅成的造山型矿床.     

江西城门山铜矿地质特征及矿床成因

江西城门山铜矿床的形成与长山-城门湖背斜和NEE向、NW向、NNE向三组断裂有关,矿床主要产于燕山期花岗闪长斑岩与石炭系、二叠系、三叠系碳酸盐岩的接触带上,部分矿体产于花岗闪长斑岩中.成矿物质具有多源、深源性.矿床为似层状、豆荚状、透镜状、带状及席状.通过对矿体形态、矿石组成、矿石结构构造、围岩蚀变等矿床特征的研究,进一步分析了矿床的成因.其结果认为,城门山铜矿床为燕山早期晚阶段及晚期早阶段中酸性钙碱系列岩浆的多次上侵作用形成的矽卡岩型、块状硫化物型、斑岩型“三位一体”的铜矿床,为岩浆期后中低温热液矿床.     

大兴安岭成矿带找矿工作新进展

内蒙古自治区地质调查院近年在大兴安岭成矿带中段西坡,通过开展1∶5万矿产资源远景调查和矿产资源评价工作,发现了一批非常有前景的矿产地。选择其中5处较好的矿产地进行了部分地段详查,4处达中型矿床规模,1处可达大型矿床规模。选择2处进行了普查,见矿较好,目前正在工作,均有望成型。根据成矿地质条件、物化探异常特征及普查孔控制情况分析,各矿床均有扩大规模的可能。综合分析各矿产地成矿地质条件,二连-东乌旗和阿尔山-梨子山-博克图2个成矿远景区均具有较好的找矿前景,进一步开展地质勘查工作有望实现找矿工作的重大突破。     

Geologic setting,genesis and transformation of sulfide deposits in the northern part of Khetri copper belt,Rajasthan, India — an outline

The present study is confined to the northern part of the Khetri copper belt that extends for about 100 km in northern Rajasthan. Mineralization is more or less strata-bound and is confined to the garnetiferous chlorite schist and banded amphibolite quartzite, occurring towards the middle of the Proterozoic Delhi Supergroup. Preserved sedimentary features and re-estimation of the composition of the pre-metamorphic rocks suggest that the latter were deposited in shallow marine environment characterized by tidal activity. Cordierite-orthoamphibole-cummingtonite rock occurring in the neighbourhood of the ores is discussed, and is suggested to be isochemically metamorphosed sediment. The rocks together with the ores were deformed in two phases and metamorphosed in two progressive and one retrogressive events of metamorphism. Study of the host rocks suggests that the maximum temperature and pressure attained during metamorphism are respectively 550–600°C and < 5.5 kb. Principal ore minerals in Madan Kudan are chalcopyrite, pyrrhotite, pyrite and locally magnetite. In Kolihan these are chalcophyrite, pyrrhotite and cubanite. Subordinate phases are sphalerite, ilmenite, arsenopyrite, mackinawite, molybdenite, cobaltite and pentlandite. The last two are very rare. Gangue minerals comprise quartz, chlorite, garnet, amphiboles, biotite, scapolite, plagioclase and graphite. The ores are metamorphosed at temperatures > 491°C. Sulfide assemblages are explained in terms of f_{S 2} during metamorphism. Co-folding of the ore zone with the host rocks, confinement of the ores to the carbonaceous pelites or semi-pelitic rocks, strata-bound and locally even stratiform nature of the orebodies, lack of finite wall rock alteration, metamorphism of the ores in the thermal range similar to that for the host rocks, absence of spatial and temporal relationship with the granitic rocks of the region led the authors to conclude that the entire mineralization was originally sedimentary-diagenetic. Any loss of primitive features and development of incongruency are due to subsequent deformation and metamorphism to which the ores and their hosts were together subjected.     

西藏冈底斯银多金属矿化带的基本特征与成矿远景分析

在冈底斯斑岩铜矿带的北侧,发育一条与之平行的银多金属矿化带。文章对该银多金属矿化带的成矿构造背景、矿床类型及矿化特点进行了初步分析与总结。研究结果表明,该矿化带受旁多—措勤逆冲系的控制,呈近EW向带状展布,带内矿床多位于EW向逆冲断裂与近NS向张性构造的交汇部位;主要矿化类型为矽卡岩型和热液脉型;据矿化特点差异,以念青唐古拉为界,可分为东、西2段,东段以矽卡岩型Cu-Pb-Zn-Ag矿化为主,西段以热液脉型Ag-Pb-Zn矿化为主,西段矿床的银含量明显高于东段。该矿化带是大陆碰撞造山晚期或后碰撞伸展早期(25～15Ma)热液活动的产物。综合对比分析显示,该矿化带具有良好的成矿条件及巨大的成矿潜力,有望发展成为一条规模巨大的银多金属成矿带。     

Coexisting chloritoid-staurolite from the Sillimanite (fibrolite) zone,Sini, district Singhbhum,India

Microprobe analyses of the minerals from an unusual chloritoid-staurolite-garnet (+ muscovite + quartz + ilmenite) assemblage from the sillimanite (fibrolite) zone of Sini, India are presented and the petrological significance of the paragenesis is discussed. The X Mg in the different minerals from the chloritoid-staurolite-bearing rock varies in the order, muscovite > chlorite > chloritoid > staurolite > garnet > ilmenite, and from the associated sillimanite-bearing schists: muscovite > biotite > staurolite > garnet rim > garnet core > ilmenite. A graphical representation of the mineral compositions in an AFM projection displays a consistent topology if the effects of non-AFM components such as Zn in the staurolite and Mn in the garnet are taken into account. Petrographic and mineralogical data are consistent with a prograde formation of the chloritoid-staurolite-garnet assemblage. It is suggested that the paragenesis has been formed at similar PT conditions to the associated sillimanite (fibrolite)-staurolite-garnet-mica schists. These conditions are estimated to be 600–625°C/6±0.5 Kb.