Stable isotope study of antimony deposits in the Muratdagi region,western Turkey

The Muratdagi region is rich in antimony deposits having the following common characteristics: post Miocene age, location on the down-thrown blocks next to normal faults, in the vicinity of active or fossil thermal springs, and in contact with carbonate rocks. The isotopic composition of — 7. SMOW of the mineralizing fluid calculated from the measured ° ¹⁸O of quartz and the fluid inclusion microthermometry, is indicative of meteoric water origin. The ° ¹³C of the inclusion CO₂ of — 19.1 to — 25.4 PDB is indicative of interaction with organic material-graphite. The ° ³⁴S of stibnite — 3.6 to — 0.7 is, in view of the mineral assemblage, indicative of magmatic origin of the sulphur. A tightly confined set of structural, lithological, hydrological and geochemical features define a sequence of geochemical processes; formation of acid and reducing fluid, leaching and transport of antimony complexes and precipitation of stibnite within defined lithological units. The set of processes seems to have taken place within a space of 5000 m lateral and 1000 m vertical extension.     

A sulfur isotope study of volcanogenic massive sulfide deposits of the Eastern Black Sea province,Turkey

Kuroko-type massive sulfide deposits of the Eastern Black Sea province of Turkey are related to the Upper Cretaceous felsic lavas and pyroclastic rocks, and associated with clay and carbonate alteration zones in the footwall and hangingwall lithologies. A complete upward-vertical section of a typical orebody consists of a stringer-disseminated sulfide zone composed mainly of pyrite and chalcopyrite; a massive pyrite zone; a massive yellow ore consisting mainly of chalcopyrite and pyrite; a black ore made up mainly of galena and sphalerite with minor amounts of chalcopyrite, bornite, pyrite and various sulfosalts; and a barite zone. Most of the deposits in the province are associated with gypsum in the footwall or hangingwall. The paragenetic sequence in the massive ore is pyrite, sphalerite, chalcopyrite, bornite, galena and various sulfosalts, with some overlap between the mineral phases. Massive, stringer and disseminated sulfides from eight kuroko-type VMS deposits of the Eastern Black Sea province have a ³⁴S range of 0–7 per mil, consistent with the ³⁴S range of felsic igneous rocks. Sulfides in the massive ore at Madenköy (4.3–6.1 per mil) differ isotopically from sulfides in the stringer zone (6.3–7.2 per mil) suggesting a slightly increased input of H₂S derived from marine sulfate with time. Barite and coarse-grained gypsum have a ³⁴S range of 17.7–21.5 per mil, a few per mil higher than the ³⁴S value of contemporaneous seawater sulfate. The deposits may, therefore, have formed in restricted basins in which bacterial reduction of sulfate was taking place. Fine-grained, disseminated gypsum at Kutlular and Tunca has ³⁴S values (2.6–6.1 per mil) overlapping those of ore sulfides, indicating sulfide oxidation during waning stages of hydrothermal activity.     

Sulfur isotopes and the origin of stibnite mineralisation in New England,Australia

Stibnite mineralisation in the antimony province of New England can be divided into Central type ores (veins of stibnite + quartz ± berthierite) and Peripheral type ores of stibnite + quartz + native antimony ± berthierite. The Central stibnites have ³⁴S_CDT values of –5±2 (1) which may represent equilibrium precipitation from mantle sulfur at about 200°C. Peripheral stibnites have ³⁴S values between 0 and –25, with a large group at 0±2. They represent precipitation from a limited supply of mantle sulfur and the acquisition of sedimentary sulfur. We consider that the different ore types were produced from distinct ore solutions derived from two immiscible melts. These originated in the deep mantle, were mobilised by tectonic activity and supplied the antimony and most of the sulfur to the ores.     

天柱大河边重晶石矿床铅同位素特征及来源探讨

对取自天柱大河边重晶石矿床的重晶石样品和含方铅矿黑色页岩样品进行了铅同位素测定与研究.结果表明,在 Zartman铅构造模式图中,重晶石矿石、含方铅矿黑色页岩和黑色页岩有大致相同的铅同位素分布区,均沿上地壳铅演化线分布,表明它们之间具有同源关系;重晶石矿石及其赋矿黑色页岩的铅同位素组成与基底地层的铅同位素组成在 Zartman铅构造模式图中具有完全不同的分布范围,表明重晶石矿石中的铅不大可能来源于基底地层;结合重晶石矿石及其赋矿黑色页岩的铅同位素组成在 Zartman铅构造模式图和Δγ-Δβ铅来源分类图的分布,天柱大河边重晶石矿床的铅主要具上地壳铅、壳幔混合的俯冲带铅和热水沉积作用铅的混合来源特点,这为天柱大河边重晶石矿床的热水沉积成因提供了铅同位素证据.     

Sr Isotope Constraints on the Age and Source of Ore—Forming Materials of Gold Deposits,Southwestern Hunan

We have measured Rb and Sr concentrations in fluid inclusions of quartz in gold deposits, southwestern Hunan. The Rb-Sr isochron ages of 435±9Ma and 412±33Ma are respectively determined, revealing that gold mineralization in this area took place in the Caledonian period rather than in the Wuling-Xuefeng period as traditionally considered. Sr isotope geochemistry of the hydrothermal fluid indicates that the ore-forming materials are of crust origin, derived largely from the ore-hosting strata rather than from the basic dikes.     

Oxygen isotope study of the Kamioka Zn-Pb skarn deposits,Central Japan

The Kamioka Zn-Pb deposits consist of clinopyroxene-rich skarns replacing limestone lenses in Hida gneissose rocks. Paleozoic metabasite, early Jurassic Funatsu granitic rocks and late Cretaceous porphyritic dikes and stocks, are the known igneous rocks in the mining area. Oxygen isotopic compositions of eight separates each of clinopyroxene and quartz from the deposits (Table 1), and some minerals and rocks from the major rock units around the deposits (Table 2), have been analyzed. The estimated oxygen isotopic ratios of the fluids responsible for the formation of the deposits, range as low as -4 to +3 (SMOW). These values are considerably lower than expected from magmatic waters, and demonstrate that none of the igneous rocks in the area could be a direct source of the skarn- and ore-forming fluids. The data instead show that the deposits are formed by a huge convective circulation of solutions of meteoric water origin, promoted by a hidden batholithic intrusion at the time of the late Cretaceous.     

云南兰坪盆地西缘脉状铜多金属矿床硫、铅同位素组成及成矿示踪

云南兰坪盆地西缘脉状铜多金属矿床主要赋存于由砂岩、粉砂岩和页岩组成的碎屑岩建造中.为了查明兰坪盆地西缘脉状铜多金属矿床成矿物质来源,对盆地西缘四个典型脉状铜多金属矿床(科登涧、连城、金满和水泄)的硫、铅同位素的组成进行了分析和对比研究.结果表明,这些矿床的铅同位素组成总体变化较小,且大部分落在盆地沉积地层铅范围内,金满、连城铜矿床可能有部分深源铅的加入.硫同位素特征表明,兰坪盆地西缘脉状铜多金属矿床的硫主要来源于地层硫酸盐的还原作用,其中金满铜矿床和连城铜钼多金属矿床可能有深源硫的混入.各矿床硫同位素不同的特点,除反映各矿床源区硫同位素组成的差异外,可能还与各矿床成矿时不同的物理化学条件(温度、氧逸度、pH 值和离子强度等)差异有关     

The source of calcium in wet atmospheric deposits: Ca-Sr isotope evidence

Tracing the origin of calcium in wet atmospheric deposits is important for environmental studies since it is a dominant acid neutralising cation and an essential nutrient. Here we present the first calcium isotope ratio measurements for rain and snow. Samples from northeastern and southern locations (France, Switzerland, Luxembourg, California and Japan) suggest a carbonate origin. Only at a local scale in a forested watershed (Vosges mountains, France) the Ca isotopic compositions of rainwater indicate that the rainwater becomes admixed with throughfall solution, which is a mixing product of Ca from dissolved atmospheric dust particles and leave excretions. If this proves to be widely true, the contribution of Ca from the canopy could be very important for the neutralisation of acid rain and of the corresponding soil system in forested watersheds. In such cases Ca and Sr cycles are decoupled in the lower atmosphere. In contrast to Sr isotopes, Ca isotopes can be applied to tracing processes occurring in the biosphere.     

Sulfur isotope study of a modern intertidal environment,and the interpretation of ancient sulfides

Extensive sulfur isotope distribution data for sulfides precipitated in an intertidal environment show no distinctive features when compared with isotope values for other marine, sedimentary sulfides. The fractionation ranges from α = 1.030 to α = 1.048. The pattern is characteristic for a system essentially open to sulfate, and isotope analyses of interstitial sulfates are corroborative. A population of sulfate-reducing bacteria of the order of 10⁹ organisms per cc of interstitial water is indicated. Seasonal variation of the isotope distribution reflects a transient sulfide composition and a bacterial population in which the fractionation effect is indirectly controlled by temperature. The data presented for this modern shallow water environment are at variance with an earlier assessment of isotopic distributions in ancient sulfides which linked shallow water environments with limited fractionation (α ? 1.025) in a closed system.     

胶东金矿成矿系列硫同位素研究

胶东金矿的早晚两期成矿系列中，岩浆成因或在岩浆期即有天然水和表生矿质加入的矿床，δ＾３４Ｓ值均有自早而晚依次降低的规律。为重熔岩浆分异成矿理论和成矿系列的建立提供了重要证据。焦家式和某些晚期矿床，在形成矿液后有表生硫加入，扰乱了这一规律性。胶东群中的硫同位素没有达到均匀化，副变质岩偏重，而斜长角闪岩偏轻，接近陨石硫值，是近似原始岩浆的产物。     

西秦岭阳山金矿带硫同位素特征:成矿环境与物质来源约束

阳山金矿带成岩期的黄铁矿主要为立方体-他形,反映出一种较低温度(<200℃)、成岩流体的过饱和度低、快速冷却、氧逸度和硫逸度低、物质供应不足的成岩条件,δ³⁴S值变化范围较大(-4.2‰～12.5‰),反映了硫源自于泥盆系地层,其中灰岩中黄铁矿硫源自于海水中硫酸根离子的还原作用,千枚岩中黄铁矿经历了细菌还原作用。成矿期黄铁矿具有多种晶形,但立方体单晶较少,指示成矿系统处于中-低温(200～300℃)、成矿流体的过饱和度高、缓慢冷却、氧逸度和硫逸度高、物质供应充分的成矿有利条件。成矿早阶段和主阶段硫化物的δ³⁴S值变化范围为-4.2‰～3‰,接近于岩浆硫范围,其中成矿主阶段的黄铁矿以五角十二面体、八面体和立方体形成的聚形更常见,且聚形黄铁矿的硫同位素值变化范围更窄(-2.1‰～1.2‰),更符合岩浆硫来源特征;成矿晚阶段辉锑矿的δ³⁴S值变化范围为-6.6‰～-4.5‰,而与其共生的黄铁矿δ³⁴S值分别是7.6‰和-12.1‰,反映晚阶段除岩浆岩硫源外,浅变质的泥盆系地层也提供了部分硫源。     

西藏那茶淌铅锌矿床S-Pb同位素组成及其示踪成矿物质来源

那茶淌矿床位于西藏冈底斯–念青唐古拉成矿带东段,为近年发现的具中—大型远景规模的矽卡岩型铅锌矿床,其成矿物质来源及其成矿背景还缺乏详细调查,制约了矿床成因的深入研究。本文在矿床地质特征研究基础上,对矽卡岩型矿石中主要金属矿物闪锌矿、方铅矿、磁黄铁矿的S、Pb同位素组成进行分析,探讨矿床成矿物质来源,并与区域上典型铅锌矿床进行对比,总结区域成矿规律。结果显示,那茶淌矿床金属硫化物的δ³⁴S（‰）值变化于－1.6‰～4.2‰之间,平均值为1.4‰,其频率直方图呈正太分布形式,具幔源硫特征。金属硫化物的²⁰⁶Pb/²⁰⁴Pb值为18.548～18.792,平均值为18.691;²⁰⁷Pb/²⁰⁴Pb值为15.683～15.856,平均值为15.755;²⁰⁸Pb/²⁰⁴Pb值为39.049～39.685,平均值为39.331;铅同位素特征值μ的变化范围为9.61～9.93,平均值为9.74,所有样品μ值均高于9.58,显示铅源具有上地壳源区物质的特征。通过区域成矿作用对比研究,那茶淌矿床S、Pb同位素组成与念青唐古拉带东段典型矽卡岩型铅锌矿床具有相似的特征,成矿物质主要来源于念青唐古拉群结晶基底物质的重熔。

     

A sulfur isotope study on pyrite deposits of Southern Tuscany,Italy

The S-isotope composition (δ³⁴S_CDT) of 213 samples of sulfides, sulfates and native sulfur from the pyrite mineralizations of southern Tuscany and associated country rocks were determined. The sulfur isotopic composition of pyrite is quite homogeneous and similar for all studied ore bodies, with an average δ³⁴S value near +9,5‰. Pyrite disseminated within the Filladi di Boccheggiano formation, and thought to be authigenic, shows a much larger range of δ³⁴S values (-13.1 to +14.5‰). The isotopic compositions of other sulfides associated with pyrite in the deposits show that isotopic equilibrium among sulfides was approached on a regional scale, but seldom fully attained. Isotopic data suggest that sedimentary marine sulfate was the ultimate source of sulfur in ores. Sulfates (mostly anhydrite) from the sulfate-carbonate lenses associated with both the Filladi di Boccheggiano and the Calcare Cavernoso formations also have similar and homogeneous compositions (average δ³⁴S=+15–16‰). Coexisting sulfates and sulfides are not in isotopic equilibrium. In the light of the isotopic data, among the many proposed genetic models for the largest stratabound pyrite bodies the two following alternatives appear the most likely: 1) in agreement with recently suggested hypotheses, the ore bodies are older than the emplacement of the Mio-Pliocenic granitoids in the area, and are probably hydrothermal-sedimentary in origin, coeval with associated country rocks; 2) the ore bodies were formed as a consequence of bacterial reduction of anhydrite in low-temperature convection systems related to the early stages of the Mio-Pliocenic thermal anomaly. In both cases, the emplacement of the Mio-Pliocenic granitoids caused metamorphism and remobilization of the pre-existing ores, producing smaller discordant mineralized bodies.     

中国不同时代主要类型铜矿床硫同位素特征及其成因意义

硫同位素是示踪矿床成矿物质来源的重要手段,对于揭示硫的物质循环也具有参考意义。笔者等选择我国不同类型、不同时间、不同空间的8个大型、超大型铜矿床,系统搜集和整理了1415个硫同位素数据资料,结果发现：①空间上,矽卡岩型、斑岩型和海相火山沉积型三类铜矿硫同位素组成显示“上重下轻”、“中轻边重”的规律。②时间上,矿床尺度从成矿早期到成矿晚期,不同类型矿石的δ34S值逐渐增大;全国尺度不同类型铜矿中黄铜矿的硫同位素组成,从老到新,δ34S值由正变负,与矿床尺度的变化规律相反。③对找矿的指示,甲玛和大宝山矿床中富矿体中硫化δ34S值偏高,在阿舍勒矿床靠近矿化中心的黄铁矿δ34S值偏低,胡篦型铜矿早期富钴黄铁矿δ34S值高于晚期贫钴黄铁矿δ34S值。总体上,除新太古代红透山铜矿之外,其他时代不同类型铜矿中黄铜矿δ34S值从元古宙到古生代到中生代再到新生代,明显降低,与地球演化有关。     

中国不同时代主要类型铜矿床硫同位素特征及其成因意义

硫同位素是示踪矿床成矿物质来源的重要手段,对于揭示硫的物质循环也具有参考意义。本文选择我国不同类型、不同时间、不同空间的8个大型、超大型铜矿床,系统搜集和整理了1415个硫同位素数据资料,结果发现：① 空间上,矽卡岩型、斑岩型和海相火山沉积型三类铜矿硫同位素组成显示“上重下轻”、“中轻边重”的规律。② 时间上,矿床尺度从成矿早期到成矿晚期,不同类型矿石的δ34S值逐渐增大;全国尺度不同类型铜矿中黄铜矿的硫同位素组成,从老到新,δ34S值由正变负,与矿床尺度的变化规律相反。③ 对找矿的指示,甲玛和大宝山矿床中富矿体中硫化δ34S值偏高,在阿舍勒矿床靠近矿化中心的黄铁矿δ34S值偏低,胡篦型铜矿早期富钴黄铁矿δ34S值高于晚期贫钴黄铁矿δ34S值。总体上,除新太古代红透山铜矿之外,其他时代不同类型铜矿中黄铜矿δ34S值从元古宙到古生代到中生代再到新生代,明显降低,与地球演化有关。     

Sulfur and carbon isotope compositions in the stratiform Zn-Pb-Cu sulfide deposits of the Rajpura-Dariba belt,Rajasthan, NW India: A model of ore genesis

The sulfur isotope composition of 86 sulfide minerals from the Middle Proterozoic, metamorphosed, stratiform, sediment-hosted Zn-Pb-CU sulfide deposits of Dariba and Sindeswar Kalan located within the Rajpura-Dariba belt in Rajasthan, NW India, have been determined. In addition, 16 carbonaceous and 2 carbonate rock samples from the ore zone have been analyzed for their C_tot and C_org contents and carbon isotope compositions. The sulfur isotope compositions range from 9.1 to –6.7 (mean value of 1.9). Increasing ³⁴S values stratigraphically upward are observed, particularly for pyrite and pyrrhotite suggesting a syngenetic origin for the sulfur. No marked lateral isotopic variations or isotopic variation in minerals from successive laminae in banded ore samples occur. Fractionation of sulfur isotopes between coexisting sulfides suggests that the original isotopic pattern was basically preserved during the amphibolite-facies metamorphism suffered by the deposits. C_org in carbonaceous rocks ranges 0.5–9.3 wt%, with ¹³C values between –21 and –31 (mean of –25.4) in keeping with the biogenic derivation of the carbon. Recrystallized dolostones have ¹³C values close to –14.4Geological evidence and isotopic features are consistant with the following genetic scheme: (a) base-metal ores along the belt formed from geothermal emanations carrying H₂S, produced by the chemical reduction of seawater sulfates and leaching of mafic volcanics, in a semiclosed (with respect to SO₄), shallow-water, rift-related basin with high biological activity; (b) pyrite and pyrrhotite formed diagenetically by bacterial reduction of sulfate in pore seawater in a system open to H₂S, thus bringing about the gradual enrichment of ³⁴S in these minerals stratigraphically upward; and (c) northward in the belt, at Sindeswar Kalan, the basin of ore deposition was relatively more open.     

Iron isotope constraints on the metal source and depositional environment of the Neoproterozoic banded iron- and manganese deposits in Urucum,Brazil

The Urucum area of Brazil hosts a series of Cryogenian ironstones intercalated by oxide-dominated manganese layers. The Urucum iron and manganese formations (IF-MnF) are among the largest sedimentary iron and associated manganese deposits of the Neoproterozoic, however, the depositional model and the source of metals for the IF-MnF in this area are highly controversial. In this study, we performed systematic Fe isotope analysis on fresh and geochemically characterized drill core samples of the Urucum iron and manganese formation deposited in the center of the ancient Urucum graben system. The samples have a large variation in Fe isotope composition, with a δ⁵⁶Fe range of −2.04‰ to +0.75‰, and exhibit a general trend of decreasing δ⁵⁶Fe values with increasing manganese contents. The low δ⁵⁶Fe values of the IF and MnF samples reflect Rayleigh fractionation processes of contineous partial oxidation of aqueous Fe(II) prior to deposition at the sampling site. Using a mixing model and previously published Nd isotope data on the same samples, we estimated that benthic (i.e., porewaters released from submarine sediments in the Urucum basin) Fe fluxes provided 7–50% of total Fe in the Urucum IF-MnF, and the rest of Fe source was from low-temperature hydrothermal vents. Based on combined Fe and Nd isotope data of the Urucum IF-MnF, we propose that low-temperature hydrothermal fluids and benthic fluxes of pore waters were mixed and transported by an upwelling current. The fluid subsequently experienced partial oxidation during the transportation process and became enriched in light Fe isotopes. In the Urucum graben basin, the iron- and manganese-rich oxides deposition occurred progressively under increasingly oxidizing conditions, and such process could have operated repeatedly to produce the alternation of iron and manganese formations. The chemical sediments of the Urucum IF-MnF deposits thus reflect the existence of a sharp redox gradient in the marine environment during the late Cryogenian period.     

Stable isotope study of base metal deposits from the Eastern High Atlas,Morocco

Tertiary epigenetic lead ± zinc and copper mineralizations occur in the Mesozoic carbonate cover and stibnite, barite and copper mineralization in the Precambrian to Palaezoic basement in the Eastern High Atlas, Morocco. The carbon isotope data from host carbonates range from +3 to -1‰ PDB. The data are typical for marine carbon. There is no difference between surrounding dolomites and younger vein dolomites. The oxygen isotopic composition of the samples is enriched in ¹⁶O; the range is from -3 to -11‰ PDB with respect to that of carbonates in equilibrium with marine water. It is postulated that the isotopic composition was changed during dolomitization being caused by transition of connate formation waters diluted to some degree by meteoritic water. The bacteriogenically reduced sulphur from syngenetic sulphides and Mesozoic marine sulphate mobilized during Tertiary orogenesis are thought to be the source of H₂S and SO₄. Cambro-Ordovicien sulphate is also supposed to be the source of sulphur in the Jebel Zelmou barite deposit in the basement. Isotopic composition of lead from galenas in the Tertiary deposits from the Mesozoic cover are strikingly homogenous. Model ages vary between 230–180 Ma. It is suggested that important mobilization processes are responsible for Tertiary metallogeny in Morocco.

     

稀有气体同位素地球化学在矿床学研究中的应用进展

稀有气体因其化学惰性以及在不同来源地质体中的同位素组成差异很大,在研究成矿流体来源、演化和壳-幔相互作用过程中具有非常重要的意义。另外,由于⁴He、⁴⁰Ar是放射成因子体同位素,具有年代积累效应,因此,它们常被用于同位素测年。本文简要回顾了流体包裹体中稀有气体同位素的后生影响和样品、分析方法选择注意事项,以及近年来稀有气体同位素在成矿流体示踪,⁴⁰K-⁴⁰Ar、⁴⁰Ar-³⁹Ar定年及（U-Th）/He定年方面的研究进展。已有研究证实流体包裹体中的稀有气体可能受后期扩散丢失、后生叠加和同位素分馏的影响,要根据目的选择不同的分析方法;稀有气体同位素可以示踪不同类型矿床的流体来源、演化及壳-幔相互作用、稀有气体同位素与卤素联合运用可以用来指示流体和盐度来源、演化过程以及矿物沉淀机制等,³He/热的研究可以追溯流体的热源及其运移方式;流体包裹体⁴⁰Ar-³⁹Ar可以用于矿床直接定年,表生含钾矿物的⁴⁰K-⁴⁰Ar、⁴⁰Ar-³⁹Ar定年以及锆石、磷灰石和铁氧化物（U-Th）/He定年可为矿床及氧化带的形成时间、矿床形成后的抬升、剥露历史、古气候演化等重大地质问题讨论提供大量有意义的信息。