Geology and mineralogy of ore at the hidden Engteri Au-Ag deposit,the Magadan Region

The Engteri is a new hidden Au-Ag deposit in the Russian segment of the Pacific ore belt. The discovery of this deposit merits special attention, because it involves repeated attempts to reappraise a lowprospective ore occurrence, which were crowned with success as a result of fulfillment of large-scale drilling project. The average Au grade is 18.6 gpt. The deposit is classified as the gold geochemical type of Au-Ag deposits. The major ore mineral is pyrite, which amounts to no less than 95% of the total ore minerals. The native phases comprise electrum and to a lesser extent native gold of low fineness (730). The homogenization temperature of fluid inclusions is 125–255°C with a distinct maximum at 145–150°C. Despite blind localization of some orebodies, the Engteri deposits bears evidence for a deep erosion level: (1) small vertical range of economic mineralization (50–100 m); (2) predominant occurrence of massive sugarlike quartz with a low sulfide content; (3) prevalence of massive and brecciated textures above rhythmically banded textures; and (4) lack of low-temperature propylites. The southern part of the ore field distinguished by occurrence of rhythmically banded, framework-tabular, and brecciated texture has the best prospect for revealing new orebodies. The Engteri deposit allowed us to outline the following prospecting guides and methods of prospecting for hidden Au-Ag deposits: (1) these deposits are regularly arranged in ore clusters between heavy concentrate anomalies of cinnabar and gold-silver or silver-base-metal occurrences (method of missed link); (2) findings of fragments of ore mineral assemblages with sporadically high Au and Ag contents in barren calcite-quartz veins (method of indicators); (3) linear zones of ankeritization in the fields of low- and mediumtemperature propylites (mapping of metasomatic rocks); and (4) pyrite-quartz veinlets with rhythmically banded pockets (mineralogical mapping of halos of stringer-disseminated mineralization).     

Mass,volume and chemical changes in the alteration zone at the Norbec mine,Noranda, Quebec

A funnel-shaped alteration pipe in Archean rhyolite and andesite below massive sulphide Zn-Cu ores at the Norbec mine in northwestern Quebec was outlined from drill core samples, geochemical parameters, and normative alteration mineralogy. The pipe has a mass of 37.9 million tonnes giving a volume of 13 × 10⁶ m³, which represents volume increase of 10% relative to the unaltered host volcanic rocks. A bulk chemical composition was calculated using weighting procedures for volumes of influence for the samples. Net mobile mass change, or chemical flux, for the alteration pipe was + 5.8 × 10⁶ tonnes; inclusion of the massive ore lens yields a flux of + 9.6 × 10⁶ tonnes for the whole hydrothermal system. The largest additions to the system in millions of tonnes were: FeO(+4.2), SiO₂(+3.8), S(+1.8), K₂O(+0.55), and MgO(+0.5); the only depletions were Na₂O (–1.4), and CaO(–0.44). Base and precious metals accounted for 3.4% of the total element flux.     

Secondary copper enrichment in tailings at the Laver mine, northern Sweden

 Field and laboratory studies of the sulphide-bearing tailings at Laver, northern Sweden, show that the present release of metals from the tailings is low, especially with regard to Cu. A large part of the Cu released by sulphide oxidation is enriched in a distinct zone just below the oxidation front. The enrichment zone occurs almost all over the tailings area except in areas with a shallow groundwater table. The Cu enrichment is caused by formation of covellite and adsorption onto mineral surfaces. The transport of Zn, Co, Cd, Ni and S seems to be controlled mainly by adsorption. No secondary zone or secondary minerals containing these metals have been found. Just below the groundwater table, metals are released into solution when the enrichment zone reaches the groundwater due to the low pH. An increased release of metals, especially Cu, can be expected in the future, since the enrichment zone is moving towards the groundwater table. Received: 4 December 1997 · Accepted: 17 December 1998     

Geology and ore genesis of the manganese ore deposits of the Postmasburg manganese-field,South Africa

The Postmasburg Mn/Fe-ores occur exclusively in dolomitic Precambrian sinkhole structures with siliceous breccias and shales as hostrocks. The main manganese minerals are braunite and bixbyite, apart from secondary alteration products of the psilomelane-manganomelane family. Various generations of ore minerals could be identified. The ore mineralization is subdivided into three different genetic types. They are classified either as pure karst deposits or as combined formations of karst origin and shallow marine sedimentation due to the transgression of the Banded Iron Formation (BIF) sea. Post-sedimentary metamorphism is identified as very low grade. The development of the different ore types is illustrated schematically.     

Geochemical and temperature controls on ore mineralization at the Emperor gold mine, Vatukoula, Fiji

Emperor is a large epithermal gold-tellurium deposit which occurs at the margin of the Tavua caldera and is associated with high-level mineralized tuffs, breccias and silicious sinters. The deposit consists of mainly narrow, steep “shear” and shallow dipping “flatmake” mineralized vein structures. Mineralization spanned a period during which different veins and dyke intrusions occurred so that some early structures are offset by later ones. High Au values and high Au/Ag ratios, corresponding to the intersection of shear and flatmake structures, generally correlate with high Ag, Te and Ba values in some structures (Crown Shear) and high Hg in others (166 Flatmake). Other elements commonly anomalous in the high-grade ore zones are As, Mo and Cu. Thallium, Se and Sb are commonly high below ore zones while Hg may be high above (e.g., Crown Shear), in (166 Flatmake) or even below (e.g., Prince of Wales Shear) ore zones.Gold precipitated in a temperature interval of 180–210°C; higher temperatures commonly occur at depth in some flatmakes (166 N, 608) and lower temperatures nearer the surface. In the two steep shears analyzed, higher temperatures correspond to where they are intersected by flatmakes. Temperatures may decrease below such intersections in which case Hg, Sb, etc., commonly increase with depth.Evidence of boiling, characterized by coexisting gas- and liquid-rich fluid inclusions, is minor and spatially sporadic. Quartz and carbonate found in ore containing bonanza concentrations of Au contain few to no gas-rich fluid inclusions. The intensity of wall-rock alteration is unrelated to gold grades.Ore deposition is inferred to have been caused mainly in response to fluid mixing rather than extensive boiling and/or wall-rock alteration, although these processes occurred. The source of the Au, Ag, Te, etc. is inferred to be near a neutral, relatively reduced, bisulphide-rich, ore solution at near 300°C and derived in some way from the shoshonitic volcanics or associated monzonitic intrusions. The second non-ore solution necessary for mixing, is inferred to have been an acid, oxidized solution at 150°C and having a large meteoric component. The result of fluid mixing was ore genesis, and a telluride, minor sulphide and very minor sulphate (barite) and anhydrite ore assemblage.     

Geology of the San Isidro iron ore deposit,Venezuela

The iron ore deposits of Cuadrilatero Ferrifero de San Isidro represent the largest iron ore reserves in Venezuela. The district is a part of the iron metallogenic province of northern Guayana, one of the richest iron-bearing regions of the world. All presently known iron ore deposits of Venezuela are situated within this province: Cerro Bolivar, Altamira, Rondon, San Isidro, María Luisa, El Pao and others. Their total ore reserves amount to 2,000 million tons (disregarding the unenriched or slightly enriched iron-formation). The Imataca belt to which the iron ore deposits are confined consists of metamorphosed sedimentary and igneous rocks of Early Precambrian age, the oldest rocks presently known in South America. This belt extends some 450 km from the Orinoco delta southwesterly to the Cauro River. Iron ore is formed from banded iron-formation, a member of the Imataca complex, by removal of silica. The process of supergene enrichment is controlled to a certain degree by structural elements. There are five ore bodies in the San Isidro district, extremely varied in shape and size. Single bodies extend up to 3–4 km in length, approximately parallel to the regional structure pattern, and a few hundred meters in width. The morphology of the bottom of the ore bodies is rather irregular, particularly in transversal sections. Contacts between ore and the unaltered iron-formation beneath are gradational. Maximum vertical section through ore is 260 m; the average is 60 m approximately. The stratigraphic thickness of iron formation has been magnified by structural deformations. The primary stratigraphic thickness is estimated to be some 50–150 m. The iron ore is classified into two main types: a) hard, crustal ore, b) soft, friable ore. Hematite grains which remained after the leaching of silica, and goethite (as cement) are the two main constituents of crustal ore. Hematite and magnetite and a minor amount of quartz are almost the only constituents of friable ore. The crustal ore forms a 15–60 m thick mantle covering friable ore. The overall volume ratio between the friable and the crustal ore is about 2:1. However, it varies in different zones. The mean composition of iron ore on the basis of 10,800 chemical analyses is 64.41% Fe, 2.62% SiO₂, 0.6% Al₂O₃. The ore contains a minor amount of Mn, P, Ti (no S, As, Ba). The ore reserves amount to 750 million tons; in addition, 180–300 million tons of possible ore reserves are estimated.

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Zusammenfassung Die Eisenerzlagerstätten der Cuadrilatero Ferrifero de San Isidro beinhalten die größten Eisenerzreserven in Venezuela. Der Erzbezirk ist ein Teil der reichsten Eisenerzregionen der Welt. Alle bekannten Eisenerzvorkommen Venezuelas befinden sich in dieser Provinz (Cerro Bolivar, Altamira, Rondon, San Isidro, Maria Luisa, El Pao und andere). Die Gesamtvorräte werden auf etwa zwei Milliarden Tonnen geschätzt (ohne die nichtangereicherten oder nur wenig angereicherten Eisenquarzite). Die Imataca-Zone, an die die Eisenerzvorkommen angrenzen, besteht aus metamorphosierten sedimentären und magmatischen Gesteine des Archaikums, die ältesten bisher in Südamerika bekannten Gesteine. Die Imataca-Zone erstreckt sich ungefähr 450 km vom Delta des Orinoco in südwestlicher Richtung bis Rio Cauro. Die Eisenerze entstanden aus feingeschichteten (gebänderten) Eisenquarziten (Itabirite). Die Prozesse der deszendenten Anreicherung werden teilweise durch strukturelle Elemente bedingt. Fünf Erzkörper des San Isidro-Bezirks sind bekannt. Die Lagerstätten sind 3 bis 4 km lang und einige Hunderte Meter breit. Sie sind den regionalen Strukturen vorwiegend parallel gelagert. Die Morphologie der Erzkörperunterlage ist ziemlich unregelmäßig, besonders senkrecht zum Streichen. Der Kontakt zwischen dem Erz und den unterliegenden unveränderten Eisenquarziten ist stufenförmig. Das Erz ist durchschnittlich etwa 60 m mächtig, mit maximalen vertikalen Mächtigkeiten von 260 m. Die primäre stratigraphische Mächtigkeit des Eisenquarzites wurde durch strukturelle Deformationen vergrößert. Man kann die primäre Mächtigkeit auf 50–150 m schätzen. Das Eisenerz wird in zwei Typen klassifiziert: a) hartes Krustenerz, b) weiches, bröckeliges Erz. Die Hämatitkörner, die nach der Entfernung der Kieselsäure übrig blieben nebst Goethit (als Zement), sind die zwei wichtigsten Komponenten des Krustenerzes. Das weiche Erz enthält Hämatit, Magnetit und etwas Quarz. Das Krustenerz bildet eine 15–60 m mächtige Decke über dem bröckeligen, weichen Erz. Das Gesamtvolumenverhältnis zwischen dem weichen und harten Erz ist ungefähr 2:1. In anderen Zonen ist es jedoch unterschiedlich. Die durchschnittliche Zusammensetzung des Eisenerzes ist: Fe 64,41%, SiO₂ 2,62%, Al₂O₃ 0,6%; das Erz enthält auch etwas Mn, P, Ti (kein S, As, Ba). Die Eisenerzvorräte wurden auf 750 Millionen Tonnen berechnet, wozu wahrscheinlich weitere 180–300 Millionen Tonnen kommen.

     

法国比利牛斯山Trimouns滑石-绿泥石矿床地质与成因

位于法国比利牛斯山的Trimouns矿床是世界上最大的滑石-绿泥石矿床之一。对该矿床形成的条件及滑石和绿泥石矿石的含量已较清楚。它是由不同类型的岩石通过热液交代蚀变而形成的，主要包括白云岩蚀变为滑石为主的矿石和硅铝质岩石(云母片岩和伟晶岩)蚀变为绿泥石为主的矿石。滑石矿石显示片理化结构(滑石片岩)或压实块状结构(块滑石)。由伟晶岩蚀变而来的绿泥石矿石为呈绿色的球状矿体，而由云母片岩蚀变而来的绿泥石矿石呈块状或片理状、颜色为灰绿色和深灰色。本文对欧洲这个独一无二的滑石和绿泥石矿床的地质特征和成因进行了总结和讨论。流体包裹体研究表明成矿流体为高盐度(20to30％eq．wt％NaCl)、中温(320℃)、压为为2．5kbars。磷钇矿和独居石的U—Ph定年结果表明，成矿年代为112—97Ma，成矿作用可能持续了16Ma以上。     

Mercury in subsurface and mine waters at Aktash ore deposit

In a weakly mineralized, weakly alkaline aqueous halo of mercury ores, Hg migrates mainly as a hydroxide and also as complexes from which it cannot be precipitated by H₂S. This latter form of “bound mercury” may broaden the halo and dissipate the metal over long distances.     

Oxygen and hydrogen isotopic studies of ore deposition and metamorphism at the Raul mine,Peru

The volcano-sedimentary sequence at the Raul mine, central Peru, consists of andesitic volcanics, graywackes, and siltstones, and has been metamorphosed to the upper greenschist-lower amphibolite facies at temperatures of 400–500°C. Isotopic data (O and H) have been collected from: (a) quartz and magnetite from stratiform ores, (b) amphiboles from amphibolite units that host stratiform ores, (c) calcite from late veins, (d) detrital quartz from graywackes, and (e) whole rocks.Interunit differences in quartz and magnetite δ¹⁸O values suggest that these minerals have resisted isotopic exchange during metamorphism, and that quartz-magnetite isotopic temperatures (380–414°C) represent primary formational temperatures. Calculated δ¹⁸O values of water in equilibrium with quartz and magnetite range from 9.1 to 12.6%..Amphibole δ¹⁸O and δD values show no interunit differences and suggest that the amphiboles have exchanged isotopes with a large metamorphic fluid reservoir. Calculated δ¹⁸O_H2O and δD_H2O values range from 8 to 12%. and ?3 to +42%., respectively.δ¹⁸O_H2O values calculated from δ¹⁸O calcite and fluid inclusion filling temperatures range from 7.5 to 10%.. Water extracted from fluid inclusions in calcite has a δD value of ?20%..δ¹⁸O values of metamorphosed graywackes and volcanic sediments are not atypical, but andesitic lavas are ¹⁸O-rich (8–10%.) compared to normal andesites.Waters involved in ore deposition, metamorphism, and late vein formation at Raul are all thought to have a common source, principally seawater. The δ¹⁸O_H2O and δD_H2O values could be produced by evaporation of seawater, shale ultrafiltration, and isotopic exchange with host rocks during deep circulation through the volcano-sedimentary pile.A model is proposed whereby coastal ocean water is restricted from the open sea by volcanic island arcs, and subsequently undergoes evaporation. Circulation of this water is initiated by heat associated with seafloor volcanism. ¹⁸O-enrichment in andesites may be produced by isotopic exchange with high ¹⁸O waters at elevated temperatures and sufficiently high water/rock ratios.     

Genesis history of iron ore from Mesoarchean BIF at the Wodgina mine,Western Australia

Several iron-ore deposits hosted within Mesoarchean banded iron formations (BIFs) are mined throughout the North Pilbara Craton, Western Australia. Among these, significant goethite±martite deposits (total resources >50 Mt at 55.8 wt% Fe) are distributed in the Wodgina district within 2 km of the world-class pegmatite-hosted, tantalum Wodgina deposits. In this study, we investigate the dominant controls on iron mineralisation at Wodgina and test the potential role of felsic magma-derived fluids in early alteration and upgrade of nearby BIF units. Camp-scale distribution and geochemistry of iron ore at Wodgina argue against any significant influence of identified felsic intrusions in the upgrade of BIF. Whereas, the formation of BIF-hosted goethite±martite iron ore at Wodgina involves: (i) early (ca 2950 Ma) metamorphism of BIF causing camp-scale recrystallisation of pre-existing iron oxides to form euhedral magnetite, with local enrichment to sub-economic grades (～40 wt% Fe) within or proximal to metre-wide, bedding-parallel shear zones, and (ii) later supergene lateritic enrichment of the magnetite-bearing BIF and shear zones, forming near-surface goethite±martite ore. The supergene alteration sequence includes: (i) downward progression of the oxidation front and replacement of magnetite by martite, (ii) local development of silcrete at ～40 m below the modern surface caused by the lowering of the water-table, (iii) intensive replacement of quartz by goethite, resulting in the goethite±martite ore bodies at Wodgina, and (iv) late formation of ferricrete and ochreous goethite. Goethitisation most likely took place within the hot and very wet climate that prevailed from the Paleocene to the mid-Eocene. Goethite precipitation was accompanied by the incorporation of trace elements P, Zn, As, Ni and Co, which were likely derived from supergene fluid interaction with nearby shales. Enrichment of these elements in goethite-rich ore indicates that they are potentially useful pathfinder elements for concealed ore bodies covered by trace element-depleted pedogenic silcrete and siliciclastic rocks located throughout the Wodgina mine.     

紫金山矿集区地质特征、矿床模型与勘查实践

紫金山矿集区位于福建省上杭县城北约15 km处,是一个典型的与陆相火山活动有关的斑岩-浅成低温热液型铜钼金矿床成矿系统,分布于长14 km、宽4km范围中,已探明高硫化浅成中低温热液型特大型金、铜矿床各1处,低硫化热液型大型银多金属矿床2处,斑岩型铜钼矿床1处,中小型铜、金矿床3处.文章结合近年来在该矿集区找矿取得的重大进展,介绍了创新性地质找矿的实践经验:一是开展三维地质建模;二是开展蚀变矿物短波红外光谱测试和解译,建立蚀变找矿模型;三是注重物化探资料的应用和二次开发,建立物化探找矿模型;四是以大量真实的生产技术经济指标为基础,以资源利用最大化为原则,开展矿床动态评价,指导成矿预测,提高找矿效率.     

山东昌邑莲花山铁矿矿床地质与矿石稀土、微量元素特征

莲花山铁矿位于昌邑-安丘铁成矿带的中部,铁矿体赋存于古元古代粉子山群小宋组中。本文通过矿石地球化学特征及其与矽卡岩矿物组合和赋矿围岩结构特征的对比研究,证明了莲花山铁矿与条带状铁矿相似。莲花山铁矿矿石稀土元素含量较低,经页岩标准化的稀土元素配分模式呈现轻稀土元素亏损、重稀土元素富集的特征,具有明显的Eu、Y、La异常,为无明显Ce异常,Y/Ho比值反映了在其沉积时受到海水作用的影响,表明莲花山铁矿的稀土元素来源于火山热液和海水的混合溶液。微量元素中Ti、V、Co、Ni、Mn、Sr、Ba等含量较低,原始地幔标准化的微量元素配分曲线显示,U、La、Hf呈正异常,Ba、Nb、Ta、Sr呈负异常,SiO2/Al2O3、Ti/V、Ni/Co、和Sr/Ba的比值指示了莲花山铁矿成矿物质来源于火山物质的沉积。研究结果表明,莲花山铁矿成矿作用源于火山热液与海水的混合,成矿物质来自火山沉积物,其地质与地球化学特征与五台山铁矿一致,为火山沉积变质型铁矿床。     

Geology of bogala mine,ceylon and the origin of vein-type graphite

The unique vein-type graphite deposits of Ceylon occur in high-grade metamorphic terrain of Early Precambrian metasedimentary series. At the Bogala graphite mine, the rocks are of the granulite and almandine amphibolite metamorphic facies. The direction of veins is strongly controlled by the two major regional lineation directions; veins with a third direction are also present. The veins are very irregular in length, width, and local attitude and contain only minor amounts of other minerals than pure graphite. Each vein is made up of a number of parallel graphite sheets oriented parallel to the vein. It is suggested that the Ceylon graphite veins, and possibly all similar deposits, form by lateral secretion. The graphite is obtained from the surrounding carbon-rich sediments and transported in the solid phase as the slippery graphite grains move along grain boundaries down a pressure gradient. The graphite accumulates along the relatively low-pressure zones of fractures. Each graphite sheet within the vein represents a period of pressure release along the fracture.

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Zusammenfassung Die einzigartigen gangförmigen Graphitlagerstätten von Ceylon befinden sich in einem hochgradig metamorphen Gebiet präkambrischer Sedimente. Die Bogala Grube liegt in einer Granulit- und Almandin-Amphibolitzone. Die Richtung der Gänge wird weitgehend bestimmt durch die beiden regionalen Gesteins-Hauptrichtungen; doch gibt es auch Gänge, die einer dritten Richtung folgen. Länge, Breite und lokaler Verlauf der Gänge sind sehr unregelmäßig. Neben reinem Graphit weisen sie nur geringe Mengen anderer Mineralien auf. Jeder einzelne Gang besteht aus einer Reihe gangparalleler Graphitzonen. Es besteht die Vermutung, daß die ceylonesischen Graphitgänge und möglicherweise alle ähnlichen Lagerstätten durch Lateralsekretion entstanden sind. Der Graphit stammt aus den stark karbonhaltigen Sedimenten der Umgebung und wird im festen Zustand umgelagert, indem die Graphitblättchen sich auf Korngrenzen in Richtung des Druckabfalls bewegen. Der Graphit sammelt sich entlang den Bruchzonen mit relativ niedrigem Druck an. Jedes Graphitband im Gang ist auf eine Druckentlastung entlang der Bruchzone zurückzuführen.

     

陕西省马鞍桥金矿床地质特征、同位素地球化学与矿床成因

马鞍桥金矿床产于西秦岭造山带商丹断裂带南缘的E-W向脆-韧性剪切带中,矿体定位受剪切带控制并集中于变形强烈的部位,赋矿围岩为泥盆系浅变质沉积建造。出露于矿区的香沟花岗斑岩脉发生蚀变和金矿化,但未达工业品位。矿化岩石和矿石的铅同位素比值与地层接近,而与香沟花岗岩相异,暗示矿石铅不可能来自花岗岩。碳-氧同位素组成特征显示,成矿流体来源于碳酸盐地层或相似岩石建造的变质或改造脱水作用;从成矿早阶段经主阶段到晚阶段,成矿流体的δ¹⁸O及δD值逐渐降低,指示成矿流体从早阶段的变质热液或地层改造热液向晚阶段的大气降水热液演化。马鞍桥金矿分布于大陆内部造山带中,成矿作用与始于印支晚期的陆内造山作用有关,后者以陆内俯冲、推覆叠置和陆壳变质变形等为特点。马鞍桥金矿床地质特征和同位素地球化学组成与阳山超大型金矿床相似,应为类卡林型金矿床或属介于造山型和卡林型之间的过渡类型金矿床。     

Prediction of local ore recoveries and ore-waste ratios at the silver bell uranium mine

Geostatistical estimation techniques were customized to allow forecasting of production figures at the Silver Bell uranium mine (Uravan District).Surface drill hole data were used to provide a block model of kriged estimators of average uranium grades. Figures for recoverable ore grade and the ore-waste ratio are then deduced from regressive curves previously obtained from underground information and production data. Cross-validations of the entire model were performed and were found positive.     

云南富乐铅锌矿床地质、地球化学及成因

富乐铅锌矿床位于扬子陆块西南缘的川滇黔铅锌成矿域东南部,受弥勒-师宗-水城区域性深大断裂构造控制,矿体呈似层状隐伏于中二叠统阳新组层间构造带内,赋矿围岩为白云岩。矿石矿物主要为闪锌矿,方铅矿和黄铁矿次之,含少量黄铜矿和黝铜矿等,脉石矿物主要为方解石和白云石。矿石构造主要有致密块状、浸染状和网脉状,金属矿物主要呈自形、半自形或他形粒状结构,其次为交代残余结构。已累计探明Pb+Zn金属资源量超过50万吨,平均品位大于10%Pb+Zn,最高达60%Pb+Zn,并伴随大量Cu和分散元素(如Cd、Ga、Ge等),显示其成矿环境极为特殊。本次工作通过详细的矿床地质和C-O、S及Pb同位素地球化学研究,旨在揭示该矿床的成矿物质来源及矿床成因。方解石的δ~(13)C值介于1.25‰~2.01‰之间,均值为1.64‰,与海相碳酸盐岩相似,而高于地幔和沉积有机质;δ~(18)O值为17.21‰~17.74‰,均值为17.49‰,介于海相碳酸盐岩(沉积有机质)和地幔之间。这表明方解石的C很可能来自碳酸盐岩围岩,而O同位素很可能受到流体与围岩间的水/岩相互作用影响。硫化物的δ~(34)S值介于10.04‰~16.43‰之间,均值为14.12‰,显示富集重S同位素的特征,表明成矿流体中S主要来源于沉积地层中的膏岩层,是海水硫酸盐岩热化学还原作用的产物。单颗粒方铅矿的~(206)Pb/~(204)Pb=18.5295~18.6100(均值为18.5640),~(207)Pb/~(204)Pb=15.6938~15.7024(均值为15.6974),~(208)Pb/~(204)Pb=38.5690~38.6568(均值为38.6008),其变化范围很窄,且与区域沉积岩和基底变质岩范围重叠,表明成矿金属Pb主要由沉积地层和基底岩石共同提供。综合矿床地质以及C-O、S和Pb同位素资料,本文认为富乐是一个形成于三叠纪拉张向挤压再向伸展的构造体制转换背景下、以碳酸盐岩为容矿围岩、受背斜和层间构造控制的层控、后生、富分散元素和高品位铅锌矿床,其成矿特征很可能是峨眉山岩浆作用和印支造山运动共同作用的结果。     

黔东南州那哥铜多金属矿床地质地球化学

贵州黔东南州从江那哥铜多金属矿床位于扬子陆块与华夏陆块过渡带的江南造山带西南段。矿床赋存于青白口系甲路组(Qbj)和乌叶组(Qbw)的浅变质沉积岩中,受近南北向宰便区域断层F1和近东西向F2断层控制,矿体产在F2断裂破碎带内。区内新元古代岩浆活动频繁,超基性、基性和酸性岩浆广泛发育,以摩天岭花岗岩为规模最大;岩浆活动与成矿关系密切,铜多金属矿床就产于那哥、加榜辉绿岩旁。热液矿物石英包裹体H、O同位素组成表明,成矿流体来源于岩浆水,并有部分变质水参与,矿石硫化物S同位素组成暗示物质可能来源于深部,矿石、地层及岩体Pb同位素组成表明那哥、加榜基性侵入岩和赋矿变质沉积岩地层均为成矿提供了部分物质,岩浆活动为成矿提供了热源。综合该矿床地质地球化学特征,初步认为该矿床应为岩浆热液型多金属硫化物矿床。