Hydrothermal gold mineralization at the Hira Buddini gold mine,India: constraints on fluid evolution and fluid sources from boron isotopic compositions of tourmaline     

M. -S. Krienitz  R. B. Trumbull  A. Hellmann  J. Kolb  F. M. Meyer  M. Wiedenbeck 《Mineralium Deposita》2008,43(4):421-434

We determined the boron isotope and chemical compositions of tourmaline from the Hira Buddini gold deposit within the Archean Hutti-Maski greenstone belt in southern India to investigate the evolution of the hydrothermal system and to constrain its fluid sources. Tourmaline is a minor but widespread constituent in the inner and distal alteration zones of metabasaltic and metadacite host rocks associated with the hydrothermal gold mineralization. The Hira Buddini tourmaline belongs to the dravite–schorl series with variations in Al, Fe/(Fe+Mg), Ca, Ti, and Cr contents that can be related to their host lithology. The total range of δ¹¹B values determined is extreme, from −13.3‰ to +9.0‰, but 95% of the values are between −4 and +9‰. The boron isotope compositions of metabasalt-hosted tourmaline show a bimodal distribution with peak δ¹¹B values at about −2‰ and +6‰. The wide range and bimodal distribution of boron isotope ratios in tourmaline require an origin from at least two isotopically distinct fluid sources, which entered the hydrothermal system separately and were subsequently mixed. The estimated δ¹¹B values of the hydrothermal fluids, based on the peak tourmaline compositions and a mineralization temperature of 550°C, are around +1 and +10‰. The isotopically lighter of the two fluids is consistent with boron released by metamorphic devolatilization reactions from the greenstone lithologies, whereas the ¹¹B-rich fluid is attributed to degassing of I-type granitic magmas that intruded the greenstone sequence, providing heat and fluids to the hydrothermal system. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Metamorphic fluid origins in the Osborne Fe oxide–Cu–Au deposit,Australia: evidence from noble gases and halogens   总被引：1，自引：1，他引：0  

L. A. Fisher  M. A. Kendrick 《Mineralium Deposita》2008,43(5):483-497

The Osborne iron oxide–copper–gold (IOCG) deposit is hosted by amphibolite facies metasedimentary rocks and associated with pegmatite sheets formed by anatexis during peak metamorphism. Eleven samples of ore-related hydrothermal quartz and two pegmatitic quartz–feldspar samples contain similarly complex fluid inclusion assemblages that include variably saline (<12–65 wt% salts) aqueous and liquid carbon dioxide varieties that are typical of IOCG mineralisation. The diverse fluid inclusion types present in each of these different samples have been investigated by neutron-activated noble gas analysis using a combination of semi-selective thermal and mechanical decrepitation techniques. Ore-related quartz contains aqueous and carbonic fluid inclusions that have similar ⁴⁰Ar/³⁶Ar values of between 300 and 2,200. The highest-salinity fluid inclusions (47–65 wt% salts) have calculated ³⁶Ar concentrations of approximately 1–5 ppb, which are more variable than air-saturated water (ASW = 1.3–2.7 ppb). These fluid inclusions have extremely variable Br/Cl values of between 3.8 × 10⁻³ and 0.3 × 10⁻³, and I/Cl values of between 27 × 10⁻⁶ and 2.4 × 10⁻⁶ (all ratios are molar). Fluid inclusions in the two pegmatite samples have similar ⁴⁰Ar/³⁶Ar values of ≤1,700 and an overlapping range of Br/Cl and I/Cl values. High-salinity fluid inclusions in the pegmatite samples have 2.5–21 ppb ³⁶Ar, that overlap the range determined for ore-related samples in only one case. The fluid inclusions in both sample groups have ⁸⁴Kr/³⁶Ar and ¹²⁹Xe/³⁶Ar ratios that are mainly in the range of air and air-saturated water and are similar to mid-crustal rocks and fluids from other settings. The uniformly low ⁴⁰Ar/³⁶Ar values (<2,200) and extremely variable Br/Cl and I/Cl values do not favour a singular or dominant fluid origin from basement- or mantle-derived magmatic fluids related to A-type magmatism. Instead, the data are compatible with the involvement of metamorphic fluids that have interacted with anatectic melts to variable extents. The ‘metamorphic’ fluids probably represent a mixture of (1) inherited sedimentary pore fluids and (2) locally derived metamorphic volatilisation products. The lowest Br/Cl and I/Cl values and the ultra-high salinities are most easily explained by the dissolution of evaporites. The data demonstrate that externally derived magmatic fluids are not a ubiquitous component of IOCG ore-forming systems, but are compatible with models in which IOCG mineralisation is localised at sites of mixing between fluids of different origin. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.  相似文献   

Oceanography in northwestern Europe during the last interglacial from intrashell δO ranges in Littorina littorea gastropods     

Johan Burman  Tore Psse 《Quaternary Research》2008,70(1):121-128

Coastal sea-surface temperature (SST) and sea-surface salinity (SSS), including seasonality, in northwest (NW) Europe during the early phase of the Eemian interglacial ca. 125 ka ago were reconstructed from Littorina littorea (common periwinkle) gastropods. The results were based on intra-annual δ¹⁸O analyses in recent and fossil shells, mainly originating from the sea of Kattegat (Sweden) and the English Channel (United Kingdom), and confined to intertidal settings. The Eemian L. littorea shells indicated annual SSTs in the range 8–18°C for the English Channel and 8–26°C for Kattegat. All specimens from the Eemian sites experienced summer SSTs of ca. 1–3°C above recent conditions. The estimated winter SST in the English Channel during the Eemian was comparable to modern measurements of ca. 8°C. However, the Kattegat region displayed Eemian winter SST approximately 8°C warmer than today, and similar to conditions in the western English Channel. The recent-fossil isotope analogue approach indicated high SSS above 35 practical salinity units (psu) for a channel south of England in full contact with the North Atlantic Ocean during the last interglacial. In addition, the Kattegat shells indicated a SSS of ca. 29 psu, which points out a North Sea affinity for this region during the Eemian.  相似文献   

岩石样品中低含量铂族元素和锇同位素比值的高精度测量方法   总被引：9，自引：1，他引：9  

杨竞红  GerharBRUGMANN 《岩石学报》2001,17(2):325-331

铂族元素（Os,Ir,Pt,Ru,Rh,Pd)具有强亲铁性和强亲铜性，为一组地球化学性质相近的相容元素，铂族元素包含两个同位素衰变体系（^190Pt-^186Os和^187Re-^187Os)。近年来，铂族元素和Re-Os同位素在研究各类不同地持作用过程中，尤其是在地幔岩石的研究中，作用独特，效果显著。由于地幔岩石的铂族元素含量较低，因此高精度，高灵敏度的分析测试方法的研究就显得十分重要。以往的分析方法（如常规的ICP－MS和中子活化分析方法），对含10^-9-10^012级低含量铂族元素的产品分析精度一般较差（＞15％－100％）。所采用的分析流程通常也无法同时获得样品的铂族元素含量和Os同位素比值。本文采用新的熔样方法（HAP－S高温高压釜酸溶法），新的化学流程（溶剂萃取和阴离子交换树脂柱）和新的分析仪器（多接收等离子体质谱MC－ICPMS和负离子热电离质谱N－TIMS）。用同位素稀释法对低含量地幔橄榄岩样品同时测定的铂族元素含量和Os同位素比值，获得了高精度的分析结果。对所分析的地橄榄样品中的铂族元素分配曲线和Os同位素组成的地质意义进行了初步探讨。  相似文献   

The Role of Organic Matter in the Formation of Siderite from Xuanlong Area,Hebei Province     

刘敏  陈志明等 《中国地球化学学报》1997,16(1):86-94

Based on the analysis of siderite distribution,occurrence,chemical compositionk,structureal characteristics,carbon-oxygen isotopic characteristics and relationship between siderite and hematite,this paper presents a systematic study of siderite in the region studied.suggesting that the siderite in the Xuanlong area genetically resulted from organically reduced primary hematite during the diagenesis.The ferric and ferrous relations directly depend on organic contents.In the presence of organic matter ferrous iron can be converted to ferric iron through or ganic reduction.The above conclusion has also been proved by organic geochemistry.data.  相似文献   

The mafic-ultramafic complex near Finero (Ivrea-Verbano Zone), II. Geochronology and isotope geochemistry   总被引：1，自引：0，他引：1  

Meihua Lu  Albrecht W. Hofmann  Maurizio Mazzucchelli  Giorgio Rivalenti 《Chemical Geology》1997,140(3-4):223-235

Whole-rock Nd and Sr isotopic compositions of the mafic-ultramafic complex near Finero demonstrate that the magma was derived from a depleted, perhaps MORB-type mantle reservoir. The Sm-Nd data for the Amphibole Peridotite unit can be interpreted as an isochron with an apparent age of 533 ± 20 Ma, which is consistent with a ²⁰⁷Pb/²⁰⁶Pb evaporation age of 549 ± 12 Ma of a single zircon grain from the Internal Gabbro unit. However, the interpretation of these apparent ages remains open to question. We therefore retain the alternative hypotheses that the intrusion occurred either about 533 or 270 Ma ago, the latter being the most likely age of emplacement of the much larger magma body near Balmuccia (Val Sesia). The implication of the older emplacement age (if correct) would be that the igneous complex may be related to the numerous amphibolite units, which are intercalated with the metapelites of the overlying Kinzigite Formation, and together with them may constitute an accretionary complex. In this case, the mafic-ultramafic complex itself might also be part of such an accretionary complex (as has been proposed for the Balmuccia peridotite).

Internal Sm-Nd isochrons involving grt, cpx, plag and amph from the Internal Gabbro unit yield concordant ages of 231 ± 23, 226 ± 7, 223 ± 10, 214 ± 17, and 203 ± 13 Ma. These results confirm published evidence for a separate, regional heating event about 215 ± 15 Ma ago.

Initial _Nd(533) values average +6.3 ± 0.4 for six samples of the Amphibole Peridotite unit and +6.0 ± 1.2 for ten samples of the External Gabbro unit. ⁸⁷Sr/⁸⁶Sr ratios require little or no age correction and range from 0.7026 to 0.7047 (with two outliers at 0.7053 and 0.7071). Strong correlations between ⁸⁷Sr/⁸⁶Sr and K₂O and weaker correlations between initial _Nd and K₂O imply a comparatively minor (≤ 10%) contamination of the External Gabbro magma by crustal material and a later alteration by a crustal or seawater-derived fluid. These results contrast sharply with the isotopic composition (negative _Nd and high ⁸⁷Sr/⁸⁶Sr values) of the associated mantle rocks, the Phlogopite Peridotite unit, which has been pervasively metasomatized by crustal fluids. This type of metasomatism and its isotopic signature are never seen in the magmatic complex. This evidence rules out any direct genetic relationship between the igneous complex and the mantle peridotite. The crust-mantle interaction is the opposite of that seen at Balmuccia, where the mantle peridotite is essentially ‘pristine’ and the magmatic body has been extensively contaminated by assimilation of crustal rocks.  相似文献   

Crust-mantle interaction in the evolution of the Ilímaussaq Complex, South Greenland: Nd isotopic studies     

Ross Stevenson  B.G.J. Upton  A. Steenfelt 《Lithos》1997,40(2-4):189-202

Sm-Nd isotopic compositions were determined for the peralkaline Ilímaussaq Complex of the Gardar Province of southern Greenland. The majority of the samples in the agpaitic and augite syenitic units have near chondritic initial _Nd(≈ 0), whereas a few samples trend towards _Nd values as low as − 6 at the time of intrusion (1143 Ma). This latter value, from a sample taken from the margin of the complex, lying on the evolutionary trend for Ketilidian country-rock granitoids, suggests that large-scale contamination took place only at the margins of the complex. The similarity of the Nd isotopic compositions of the augite syenite and agpaitic units suggests that their parental magmas were derived from the same reservoir. A comparison of the Nd with existing Sr and Hf isotopic data for the complex suggests an origin by combined assimilation fractionation processes. Assimilation-fractional crystallization modeling of the isotopic compositions indicates that the Ilímaussaq magmas could have formed through fractional crystallization of a basaltic melt while assimilating granitic crust. The model requires initially higher assimilation rates from basalt to augite syenite composition with subsequent decreasing assimilation rates from augite syenite to agpaitic compositions. Alkali granites, which formed after the intrusion of the augite syenites, have isotopic compositions intermediate between those of the augite syenites and the surrounding Ketilidian basement. This implies even greater amounts of assimilation and is interpreted as evidence for an origin through fractionation of a basaltic or augite syenite magma with concurrent assimilation of Ketilidian crust.  相似文献   

汉诺坝玄武岩中辉石岩类包体Nd、Sr、Pb同位素及其成因信息   总被引：13，自引：1，他引：13  

陈道公  支霞臣  李彬贤  王银喜  杨杰东 《地球化学》1997,26(1):1-12

对汉诺坝地区的１２个辉石岩和１个麻粒岩包体进行了Ｎｄ、Ｓｒ、Ｐｂ同位素测定，发现辉石岩组成有很大变化，１４３Ｎｄ／１４４Ｎｄ比值为０．５１１６０—０．５１３１４，８７Ｓｒ／８６Ｓｒ比值为０．７０２９—０．７０８６，２０６Ｐｂ／２０４Ｐｂ比值为１５．９４２—１８．６８３，２０７Ｐｂ／２０４Ｐｂ比值为１５．２６４—１５．５６９，２０８Ｐｂ／２０４Ｐｂ比值为３６．２１３—３８．７４４，显示了其复杂成因ｑ推测具有高Ｓｒ、低Ｎｄ和低Ｐｂ同位素组成的辉石岩是地幔早期富集的产物，与麻粒岩、辉长岩包体有类似成因；具有弱至中等亏损的Ｎｄ、Ｓｒ同位素和高放射成因Ｐｂ的辉石岩是亏损地幔近期富集或交代的产物  相似文献   

西南极长城湾NG93-1沉积柱样碳、氧、锶、铅同位素地球化学研究及其古环境意义   总被引：1，自引：1，他引：1  

陈毓蔚  桂训唐  韦刚健  罗又郎 《地球化学》1997,(3)

对西南极西北海域乔治王岛和纳尔逊岛之间长城湾浅水海区柱长８３ｃｍ的沉积柱样ＮＧ９３－１进行了矿物学、Ｓｒ、Ｐｂ、Ｏ、Ｃ等同位素地球化学研究。揭示了沉积物以陆源碎屑物为主，证实南设德兰群岛火山岩是该海区沉积物的重要控制源。Ｏ、Ｃ同位素记录了早全新世以来两次冰期，一次高温的气候变动信息，并指出Ｓｒ、Ｐｂ同位素组成的剖面变化具有气候演变的示踪意义。  相似文献   

Chemical and environmental isotope study of precipitation in Syria   总被引：1，自引：0，他引：1  

Z. Kattan 《Journal of Arid Environments》1997,35(4):601-615

Waters from a network of rainfall collection covering nine meteorological stations distributed mainly in the western part of Syria have been assayed using chemical and environmental isotope techniques for a period of 5 months from Dec 1989 to Apr 1990. The chemistry of rain waters falling over the mountainous stations shows a low solute concentration (20–105 mg⁻¹/L) compared with those falling over the coastal and anterior stations (50–210 mg⁻¹/L). The rain waters are generally characterized by a high deuterium excess (d = 19 ‰) compared with that of typical global meteoric waters (d = 10 ‰). The estimated deuterium excess is lower than that for the eastern Mediterranean meteoric waters (d = 22 ‰). The altitude effect is shown up by a depletion of heavy stable isotopes of about −0·23 ‰ and −1·65 ‰ per 100 m elevation of δ¹⁸O and δD, respectively. The spatial distribution pattern of tritium contents shows a gradual build up with increasing distance from the Syrian coast. The weighted mean tritium content in rain waters falling over the country is estimated to amount to 9·5 tritium units (TU) during the period of observation.  相似文献