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1.
The paper reports the results of Pb isotope study of several gold deposits of the Russia’s largest metallogenic province of Northern Transbaikalia. Potential sources of the ore material are considered by the example of new and previously published Pb–Pb data on nine deposits and occurrences of different scales. The comparison of Pb–Pb isotope-geochemical characteristics of ores, Paleozoic granitoids, as well as metamorphic pyrite from barren metasedimentary sequences shows that the Neoproterozoic terrigenous–carbonate rocks of the Baikal–Patom fold belt (BPB) served as the main source of lead and other components in the mineral-forming systems of the deposits. Significant variations of Pb isotope ratios typical in general of the considered deposits of the BPB reflect the initial isotopic heterogeneity of Pb source. This heterogeneity is caused by mixing of two geochemical types of continental crust during sedimentation: old (Early Precambrian) crust of the Siberian craton with long-term geochemical evolution and newly formed Late Precambrian crust. Pb–Pb data serve in support of the hydrothermal–metamorphogenic hypothesis of the formation of gold deposits of the BPB. 相似文献
2.
Sr-Nd-Pb-Hf isotope mapping combined with U-Pb zircon SHRIMP ages of granitoids from four sampling profiles across terrane boundaries in Uzbekistan reveal distinct reservoir types (cratonic and accretionary), witnessed by the diverse nature and origin of the predominant Paleozoic granitic magmatism that provided hosts for major ore-bodies. The study region comprises four major terranes, including 1) the Sultan-Uvais terrane, 2) the Kyzylkum-Nurata Segment and 3) the Gissar Segment of the South Tien Shan and 4) the Chatkal-Kurama terrane of the Middle Tien Shan. Sr-Nd isotope analyses show a wide range of εNdt (− 5 to + 7) and (87Sr/86Sr)t of 0.704–0.707, indicating involvement of both mantle-derived material and older crustal sources. A wide range of Hf-isotope compositions found in zircons of Chatkal-Kurama granites, Middle Tien Shan (εHf mainly ~ − 5 to + 5), could be due to recycling of older crustal protolith(s); in particular, the earliest (Silurian) granites may be directly derived from 1.5 to 1.7 Ga lower crust. In the Southern Tien Shan, some involvement of subducted oceanic crust is evidenced by strongly juvenile εHft values of up to + 14 and + 16 (Sultan-Uvais, Teskuduk-Kyzylkum). Permo-Carboniferous granitoids, which occur across all terranes also exhibit a wide range of isotope signatures, corresponding to Mesoproterozoic–Neoproterozoic crustal protoliths with a westward increase in juvenile contributions. Pb isotopes (whole-rock) imply the dominance of a crustal component and crust-mantle mixing processes. New age data confirmed: 1) old age of the Turkestan Ocean (505 Ma in Sultan-Uvais), 2) fragments of Silurian island arcs in the accretionary complex of the Chatkal-Kurama terrane (granites of 429–416 Ma) and in the upper allochthon of the South Tien Shan (gabbro 438 Ma in Tamdytau), and 3) a significant volume of granitoid magmatism of subduction or early-collisional stages (around 320–310 Ma) in the Chatkal-Kurama Segment and especially in the Gissar Segment. The westernmost part of the Tien Shan is characterized by multiple subduction processes responsible for 300 million years of geodynamic evolution history (accretionary collage, crustal growth) with the pre-Mesozoic crust formation concluded by Permian post-collisional extensional magmatism. 相似文献
3.
The lead isotopic composition of galena from the Neoproterozoic sediment-hosted Zn-Pb sulphide deposit at Rosh Pinah and the oxidised Zn deposit at Skorpion in the Pan-African Gariep Belt, southwestern Namibia, as well as that of galena from minor occurrences in the wider Rosh Pinah ore province was investigated and is compared with that of other major sediment-hosted base metal ore deposits hosted by Neoproterozoic strata in southwestern Africa and Brazil. The isotope data were supplemented by a geochemical provenance study of the argillitic host rock to the Rosh Pinah deposit and its stratigraphic equivalents. The pre-orogenic Rosh Pinah deposit and the inferred progenitor for the secondary Skorpion deposits have very similar Pb isotopic compositions. In contrast, syn-orogenic deposits (e.g. Tsumeb-type) show a larger proportion of radiogenic Pb from the country rocks that were infiltrated by orogenic ore fluids.In all examples studied, the ore Pb has elevated 207Pb/204Pb ratios compared to Pb that evolved according to average crustal Pb growth models. The isotopic composition of the ore Pb is in agreement with that of the oldest crustal component known from the pre-Gariep basement, i.e. an Eburnean (c. 2.0 Ga) volcanic arc, best preserved in the Richtersveld Terrane, that represents the largest volume of post-Archaean juvenile crust in southern Africa. Erosion of that arc provided the main sediment source for the metasedimentary siliciclastic host to the Rosh Pinah deposit. Derivation of the Pb, and by analogy Zn, from this Eburnean volcanic arc is therefore inferred for the formation of Rosh Pinah-type syn-rift, early diagenetic replacement mineralisation.The calculated 2- and 2-values for the Rosh Pinah ore province (around 10.2 and 42, respectively) are higher than predicted by conventional Pb crustal growth models and are similar to those found in the wider region of southern Africa (Otavi Mountain Land) and eastern Brazil. The obtained data highlight not only that calculated Pb model ages may have no geochronological significance but might also point to a common crustal evolution of this part of SW-Gondwana.Editorial handling: M. Chiaradia 相似文献
4.
接触交代夕卡岩型多金属矿床铅源新认识 总被引：1，自引：0，他引：1
本文研究的接触交代夕代岩型多金属（铜－铅－锌）矿床是与燕山期中－酸性岩浆作用有密切关系的矿床工业类型，传统上认为成矿物质是岩浆分异的产物。文中用矿石铅、岩浆岩铅及围岩铅同位素组成，探讨了三者之间的关系，阐明了该类矿床矿石铅的三种来源，即单一的岩浆源，岩浆与围岩混合源及多元（三种以上）混合源，认为在运用铅同位素研究矿石成因时，既要研究矿石铅，也要研究岩浆岩长石铅和围岩（沉积岩）铅的同位素组成，并考虑 相似文献
5.
Isotope Tracing and Prospecting Assessment of Gold-Silver Deposits in Zhejiang Province 总被引：1，自引：0，他引：1
Chen Haoshou Xu Butai Department of Earth Sciences Zhejiang University Hangzhou Zhejiang Zhejiang Institute of Geology Mineral Resources Hangzhou Zhejiang Liu Xinzhu 《《地质学报》英文版》1997,71(3):293-304
Three different types of gold and silver deposits in Zhejiang Province(Huangshan gold deposit, Zhilingtou gold-silver deposit and Haoshi silver deposit) showmarked differences in lead and strontium isotopic composition, suggesting three differentsources and geneses of these deposits. The Huangshan gold deposit features low initial Srisotope ratios and low μ values or low content of radiogenic Pb and its ore-forming materialscame primarily from the upper mantle; the Zhilingtou gold-silver deposit shows high initial Srisotope ratios and high μ values or high content of radiogenic Pb and the ore-forming materialswere derived mainly from the upper crust; and the Haoshi silver deposit has its Pb and Srisotope ratios between the above two cases with the ore-forming materials stemming from boththe mantle and the crust. The characteristic Pb isotopic composition may serve as an indicatorfor prospecting for different types of ore deposits. 相似文献
6.
Peter Marchev Majka Kaiser-Rohrmeier Christoph Heinrich Maria Ovtcharova Albrecht von Quadt Raya Raicheva 《Ore Geology Reviews》2005,27(1-4):53
The Rhodope Massif in southern Bulgaria and northern Greece hosts a range of Pb–Zn–Ag, Cu–Mo and Au–Ag deposits in high-grade metamorphic, continental sedimentary and igneous rocks. Following a protracted thrusting history as part of the Alpine–Himalayan collision, major late orogenic extension led to the formation of metamorphic core complexes, block faulting, sedimentary basin formation, acid to basic magmatism and hydrothermal activity within a relatively short period of time during the Early Tertiary. Large vein and carbonate replacement Pb–Zn deposits hosted by high-grade metamorphic rocks in the Central Rhodopean Dome (e.g., the Madan ore field) are spatially associated with low-angle detachment faults as well as local silicic dyke swarms and/or ignimbrites. Ore formation is essentially synchronous with post-extensional dome uplift and magmatism, which has a dominant crustal magma component according to Pb and Sr isotope data. Intermediate- and high-sulphidation Pb–Zn–Ag–Au deposits and minor porphyry Cu–Mo mineralization in the Eastern Rhodopes are predominantly hosted by veins in shoshonitic to high-K calc-alkaline volcanic rocks of closely similar age. Base-metal-poor, high-grade gold deposits of low sulphidation character occurring in continental sedimentary rocks of synextensional basins (e.g., Ada Tepe) show a close spatial and temporal relation to detachment faulting prior and during metamorphic core complex formation. Their formation predates local magmatism but may involve fluids from deep mantle magmas.The change in geochemical signatures of Palaeogene magmatic rocks, from predominantly silicic types in the Central Rhodopes to strongly fractionated shoshonitic (Bulgaria) to calc-alkaline and high-K calc-alkaline (Greece) magmas in the Eastern Rhodopes, coincides with the enrichment in Cu and Au relative to Pb and Zn of the associated ore deposits. This trend also correlates with a decrease in the radiogenic Pb and Sr isotope components of the magmatic rocks from west to east, reflecting a reduced crustal contamination of mantle magmas, which in turn correlates with a decreasing crustal thickness that can be observed today. Hydrogen and oxygen isotopic compositions of the related hydrothermal systems show a concomitant increase of magmatic relative to meteoric fluids, from the Pb–Zn–Ag deposits of the Central Rhodopes to the magmatic rock-hosted polymetallic gold deposits of the Eastern Rhodopes. 相似文献
7.
8.
Lead isotope signatures of epithermal and porphyry-type ore deposits from the Romanian Carpathian Mountains 总被引：3，自引：0，他引：3
Lead isotope analyses have been performed on the two major Miocene mining districts of Romania, Baia Mare and Apuseni Mountains. These two districts have different non-overlapping 206Pb/204Pb isotopic signatures ranging from 18.752 to 18.876 and 18.497 to 18.740. In the Baia Mare district, epithermal deposits are overall homogeneous in their lead isotopic compositions and have values similar to the average of the calc-alkaline volcanic rocks. These results suggest a magmatic signature for the Pb (and possibly other metals) in the hydrothermal fluids. However, magmas in this district show isotopic evidence of crustal assimilation. In the southern Apuseni Mountains, the lead isotope compositions of sulfide minerals in porphyry copper deposits are clustered, confirming that Pb, and probably other metals, were derived principally from associated porphyry stocks. On the other hand, lead isotope data on sulfides in epithermal ore deposits are much more scattered, indicating a notable contribution of Pb from local country rocks. In the Apuseni Mountains, 'fertile' volcanics are few and appear to come from a more primitive mantle-derived source. Most of the analysed volcanic rocks seem 'barren'. Differences in lead isotopic compositions between the Baia Mare district and the Apuseni Mountains are due to a different basement, and probably to variations in crustal assimilation superimposed on variations in the mantle source composition. In the Apuseni Mountains, Pb may be partly inherited from the previous Mesozoic magmatic-hydrothermal stage. From a geodynamic point of view, it seems that the nature and the source of volcanic rocks and their position related to the collision area of the Carpathian arc are not the only factors controlling the 'fertility' of a volcanic district. 相似文献
9.
河南桐柏围山城金银成矿系统矿床地球化学特征 总被引：4，自引：1，他引：4
河南桐柏围山城的金银矿床形成于印支—燕山期碰撞造山的动力学背景。对矿床地球化学的研究表明 ,各矿床围岩均发生大规模的成矿元素活化迁移 ,稀土元素和硫同位素资料均指示矿化主要源自早期的矿源层 ;Pb同位素资料指示俯冲下插的南秦岭构造岩片部分融熔形成的花岗岩浆和深源流体提供了部分成矿物质 ;H、O同位素资料指示成矿流体主要由大气降水、部分岩浆热液和变质热液混合演化而成。工业矿体的形成与后期的构造及热流体的叠加改造有关。矿化带内金银矿床具有共同的成矿地质背景和成矿地质特征 ,构成了一个完整的以沉积初始富集、构造及岩浆热液改造的成矿系统 相似文献
10.
Southern Cross was one of the earliest gold mining centres in Western Australia. Over 142 tonnes of gold have been produced
from the district, and, on a gold per hectare basis, the Southern Cross greenstone belt in the southwestern Yilgarn Craton
is the most productive of Western Australia's Archaean greenstone belts. The SW Yilgarn Craton is characterised by high-grade
(amphibolite- to granulite-facies) metamorphism, extensive granitoid magmatism and older greenstone volcanism ages, compared
to the well-known greenschist-facies metamorphism and younger (2.7 Ga) eruption ages which dominate in the Eastern Goldfields
Province. The Pb-isotope compositions of deep-seated granitoids in the SW Archaean Yilgarn Craton, which were emplaced coeval
with a craton-wide major orogenic lode-gold mineralization event at about 2.64–2.63 Ga, have been determined for 96 whole-rock
and 24 K-feldspar samples. The Pb isotope data of the granitoids are consistent with a crustal origin for their genesis, probably
by reworking (partial melting) of older continental crust. The Pb isotope composition of greenstones, which are the main host
rocks for gold mineralisation, and pyrites from the komatiite-hosted syngenetic Ni deposits in the amphibolite-facies Forrestania
greenstone belt, have also been determined, with initial Pb-isotope ratios higher than that for the Eastern Goldfields Province.
The Pb isotopic character of the orogenic lode-gold deposits in the region is intermediate between coeval granitoid and greenstone
Pb, indicating that the ore fluids contained metals from both reservoirs. The Pb in the ore fluid of the most deeply formed
deposit, Griffin's Find, overlaps the isotopic composition of coeval granitoids, indicating the deep-seated granitoid magmatism
was the primary source for Pb in the ore fluids.
Received: 8 October 1998 / Accepted 22 December 1998 相似文献
11.
K. E. Degtyarev 《Geotectonics》2011,45(1):23-50
The extended Saryarka and Shyngyz-North Tien Shan volcanic belts that underwent secondary deformation are traced in the Caledonides
of Kazakhstan and the North Tien Shan. These belts are composed of igneous rocks pertaining to Early Paleozoic island-arc
systems of various types and the conjugated basins with oceanic crust. The Saryarka volcanic belt has a complex fold-nappe
structure formed in the middle Arenigian-middle Llanvirnian as a result of the tectonic juxtaposition of Early-Middle Cambrian
and Late Cambrian-Early Ordovician complexes of ensimatic island arcs and basins with oceanic crust. The Shyngyz-North Tien
Shan volcanic belt is characterized by a rather simple fold structure and consists of Middle-Late Ordovician volcanic and
plutonic associations of ensialic island arcs developing on heterogeneous basement, which is composed of complexes belonging
to the Saryarka belt and Precambrian sialic massifs. The structure and isotopic composition of the Paleozoic igneous complexes
provide evidence for the heterogeneous structure of the continental crust in various segments of the Kazakh Caledonides. The
upper crust of the Shyngyz segment consists of Early Paleozoic island-arc complexes and basins with oceanic crust related
to the Saryarka and Shyngyz-North Tien Shan volcanic belts in combination with Middle and Late Paleozoic continental igneous
rocks. The deep crustal units of this segment are dominated by mafic rocks of Early Paleozoic suprasubduction complexes. The
upper continental crust of the Stepnyak segment is composed of Middle-Late Ordovician island-arc complexes of the Shyngyz-North
Tien Shan volcanic belt and Early Ordovician rift-related volcanics. The middle crustal units are composed of Riphean, Paleoproterozoic,
and probably Archean sialic rocks, whereas the lower crustal units are composed of Neoproterozoic mafic rocks. 相似文献
12.
Pb isotope fingerprinting of mesothermal gold deposits from central Victoria, Australia: implications for ore genesis 总被引：2，自引：0，他引：2
New Pb isotope data from three major mesothermal lode gold deposits (Ballarat West, Tarnagulla, Maldon) in central Victoria
support a model whereby the metals derived from a large reservoir with a long residence time in the crust below the Palaeozoic
Lachlan Fold Belt. The Pb isotopic ratios of least radiogenic samples from these deposits are in close agreement with published
Pb signatures for turbidite-hosted gold deposits, and for Devonian granites, elsewhere in the Lachlan Fold Belt. Despite their
spatial distribution and variations in the geological setting, the Pb signatures point to the extraction and transport of
metals from a crustal source area by long-lasting, large-scale hydrothermal systems, resulting in the prominent homogenisation
of Pb isotopic ratios. The enduring interaction between large hydrothermal systems and an extensive crustal source reservoir
were a vital pre-requisite in the formation of the Victorian gold province. In this regard, the prospectivity of Victoria
is analogous to world-class ore provinces elsewhere, such as the Archaean Yilgarn Block in Western Australia.
Received: 10 February 1998 / Accepted: 28 April 1998 相似文献
13.
云南格咱岛弧岩浆成矿带铅同位素特征及成矿物质来源示踪 总被引：8，自引：1，他引：7
云南格咱岛弧成矿带是西南三江构造岩浆岩带的重要组成部分,是我国近年来新发现的铜多金属矿集区,产出有普朗超大型斑岩型铜矿、雪鸡坪中型斑岩型铜矿、红山大型矽卡岩-斑岩型铜矿等。测试结果表明,典型成矿斑岩体的矿石矿物铅同位素组成:206Pb/204Pb为17.680～19.165,207Pb/204Pb为15.453～15.773,208Pb/204Pb为37.730～39.654,铅同位素组成较为稳定,具有贫铀铅、富钍铅的特征。铅同位素组成与特征参数(Δβ与Δγ、V1与V2)之间具有明显的正相关性,依据铅构造模式判别和成因分类的综合分析,格咱岛弧成矿带的铅主要来源于地幔和下地壳,具壳幔混合来源的特征,其成矿作用与岩浆岩活动存在较为密切的关系。 相似文献
14.
The mantle metasomatites (fluidized magmatic rocks) of the Pamir-Tien Shan region show extremely high contents of lithophile and chalcophile trace elements, which often exceeds the regional average abundances of the Earth’s crust. Geochemical relations were established between mantle and crustal rocks, and it was shown that the compositions of magmatic rocks of different age and formation depth and polychronous mineralization are relatively stable. These data and some other facts indicate the possible influence of mantle fluids (melts) on the crustal rocks and processes. An alternative model implies the geochemical influence of crustal rocks on the geochemical characteristics of the regional mantle. The ore material of alkali basic rocks and some hydrothermal and rare metal deposits shows a geochemical affinity to the supposed mantle (mantle-crustal) sources. The ore-bearing fluids (melts) were presumably related to the evolution of ultradeep “hot” material of mantle plumes and “daughter” diapirs carrying alkaline, trace, and ore elements. 相似文献
15.
西天山浅成低温金矿容矿火山岩地球化学及成矿环境初探 总被引：5，自引：0，他引：5
20世纪90年代,在新疆西天山北段晚古生代火山岩区内相继发现了阿希大型金矿床及其外围的伊尔曼得、恰布坎卓它等金矿床(点),并进一步确定了其系产于晚古生代火山岩内的浅成低温矿床.矿床赋存于伊犁晚古生代火山岩区的吐拉苏-也里莫墩火山岩带中.矿床围岩为下石炭统大哈拉军山组中基性-中酸性陆相火山岩系,以钙碱性为主,少量碱性系列岩石,具有富硅、钠、贫钾、铝、镁、钙成分和里特曼指数偏高的特点;岩石稀土元素含量中等(ΣREE=41.59×10-6~135.83×10-6),属于轻稀土富集型(含量29.05×10-6~95.37×10-6),分镏程度较高;容矿火山岩以K、Rb、Ba、Th等大离子元素富集和Ti、Y、Yb、Sc等亏损为特征,接近于板内过渡型玄武岩系列岩石;火山岩和矿石206Pb/204Pb值为17.5269~18.6644,207Pb/204Pb值为15.1073~16.0108,208Pb/204Pb值为37.3670~38.1958,具壳幔混合源特征;含金石英脉锶同位素初始值与区内容矿火山岩、矿化有关蚀变矿物十分接近,介于0.705~0.709之间,显示成矿作用与火山岩系的密切成因联系;文中结合容矿火山岩时空分布和成矿地球化学特征的讨论分析,揭示了金矿成矿与容矿火山岩的内在联系,确立了金矿化的陆内裂谷环境特点,建立了浅成低温热液型金矿的第三种成矿背景,拓宽了找矿区域. 相似文献
16.
Analysis of the distribution patterns of Pb isotope data from mineralised samples using the plumbotectonic model of Carr et al. (1995), which invokes mixing between crustal and mantle reservoirs, indicates systematic spatial patterns that reflect major metallogenic and tectonic boundaries in the Paleozoic Lachlan and Delamerian orogens in New South Wales and Victoria, Australia. This distribution pattern accurately maps the boundary between the Central and Eastern Lachlan subprovinces. The Central Lachlan Subprovince is characterised by Pb isotope characteristics with a strong crustal signature, whereas the Eastern Lachlan Subprovince is characterised by variable crustal and mantle signatures. The Macquarie Volcanic Province is dominated by Pb with a mantle signature: known porphyry Cu–Au and high sulphidation epithermal Au–Cu deposits in the province are associated with a zone characterised by the strongest mantle signatures. In contrast, granite-related Sn deposits in the Central Lachlan Subprovince are characterised by the strongest crustal signatures. The Pb isotope patterns are broadly similar to Nd isotope model age patterns derived from felsic magmatic rocks, although a lower density of Nd isotope data locations makes direct comparison difficult.The two reservoirs identified by Carr et al. (1995) do not appear to be isotopically linked: the crustal source was not formed via extraction from the mantle source. Rather, the two reservoirs formed separately. The mantle reservoir may have been sourced from a subducting proto-Pacific plate, whereas the crustal reservoir is most likely to be extended Australian crust. The data allow the possibility that the proto-Pacific mantle source was isotopically linked to the western Tasmanian crustal source.Comparison of Pb isotope data from the Girilambone district, Central Lachlan Subprovince, (e.g., Tritton and Avoca Tank Cu deposits) with those from the Cobar Cu–Au–Zn–Pb district, Eastern Lachlan Subprovince, in north central New South Wales indicates a less radiogenic signature, and probably older age, for deposits in the Girilambone district. Hence, a syngenetic volcanic-associated massive sulphide origin for these deposits is preferred over a syn-tectonic origin. The data are also consistent with formation of the Girilambone deposits in a back-arc basin inboard from the earliest phase of the Macquarie Volcanic Province. 相似文献
17.
The crustal continuum model for late-Archaean lode-gold deposits of the Yilgarn Block,Western Australia 总被引：19，自引：0，他引：19
D. I. Groves 《Mineralium Deposita》1993,28(6):366-374
Most Archaean gold ores belong to a coherent genetic group of structurally controlled lode-deposits that are characteristically
enriched in Au with variable enrichments in Ag, As, W, Sb, Bi, Te, B and Pb, but rarely Cu or Zn, and are surrounded by wallrock
alteration haloes enriched in K, LILE and CO2, with variable Na and/or Ca addition. Evidence from the Yilgarn Block of Western Australia, combined with similar evidence
from Canada and elsewhere, indicates that such deposits represent a crustal continuum that formed under a variety of crustal
régimes over at least a 15 km crustal profile at PT conditions ranging from 180°C at <1 kb to 700°C at 5 kb. Individual deposits,
separated by tens to hundreds of kilometres, collectively show transitional variations in structural style of mineralisation,
vein textures, and mineralogy of wallrock alteration that relate to the PT conditions of their formation at varying crustal
depths. Specific transitions within the total spectrum may be shown also by deposits within gold camps, although nowhere is
the entire continuum of deposits recorded from a single gold camp or even greenstone belt.
Recognition of the crustal continuum of deposits implicates the existence of giant late-Archaean hydrothermal systems with
a deep source for the primary ore fluid. A number of deep fluid and solute reservoirs are possible, including the basal segments
of greenstone belts, deep-level intrusive granitoids, mid-to lower-crustal granitoidgneisses, mantle lithosphere, or even
subducted oceanic lithosphere, given the probable convergent-margin setting of the host greenstone terranes. Individual stable
and radiogenic isotope ratios of fluid and solute components implicate fluid evolution from, or equilibrium with, a number
of these reservoirs, stressing the potential complexity of pathways for fluid advection to depositional sites. Lead and strontium
isotope ratios of ore-associated minerals provide the most persuasive evidence for fluid advection through deep-level intrusive
granitoids or granitoid-gneiss crust, whereas preliminary oxygen isotope data show that mixing of deeply sourced fluid and
surface waters only occurred at the highest crustal levels recorded by the lode gold deposits. 相似文献
18.
Important copper-gold (± molybdenum) porphyry deposits occur in the northwest region of Argentina, part of the Central Andes. This paper provides new isotope information on two of these deposits, Bajo de la Alumbrera and Agua Rica, the latter having an epithermal overprint event. The two deposits are genetically associated with the Miocene Farallón Negro Volcanic Complex. Whole rock and sulfide samples were analyzed for Pb, Sr and Nd isotopes to characterize the sources of magma and mineralization of both deposits. Sr and εNd data made it possible to divide the samples into three distinct groups. Most samples are slightly differentiated, have OIB (Ocean Island Basalts) isotope characteristics, and show some Nd fractionation. Lead isotope also shows distinct groups with an enrichment trend in radiogenic lead. In both deposits, the sulfides are more radiogenic than the host rocks, but are clearly related to them because all plot on a single trend. A crustal contribution to the deposits is suggested on the basis of lead isotope signatures. The similarity on the Pb isotope signatures suggests the same magmatic fluid source, although at Agua Rica the crustal component is more evident than at Bajo de la Alumbrera, possibly because of the assimilation of Paleozoic country rocks at Agua Rica. 相似文献
19.
Lead isotope analyses of 25 sulfide samples (galenas, iron sulfides, and sulfosalts) from five different mines of the Skellefte district, northern Sweden, demonstrate that the Pb-isotopic composition of galenas and other sulfides rich in lead varies between individual deposits within the district. This contrasts with many other base-metal districts, where ore lead is isotopically homogeneous on a regional basis. Although all of the Skellefte leads are depleted in 207Pb relative to average global lead evolution models, thus suggesting a large mantle-derived component in their sources, the Nasliden deposit lying at the contact of the host volcanic rocks and the overlying metasediments contains a significant component of crustal lead. It is concluded that while the Pb-isotope data are consistent with a volcanic exhalative origin of the ores of the Skellefte district, they also demonstrate that older crustal lead was incorporated into the sulfides during their emplacement and the subsequent period of magmatic and metamorphic activity which followed their deposition. 相似文献
20.
Cripple Creek and other alkaline-related gold deposits in the southern Rocky Mountains, USA: influence of regional tectonics 总被引：1，自引：0，他引：1
Alkaline-related epithermal vein, breccia, disseminated, skarn, and porphyry gold deposits form a belt in the southern Rocky Mountains along the eastern edge of the North American Cordillera. Alkaline igneous rocks and associated hydrothermal deposits formed at two times. The first was during the Laramide orogeny (about 70-40 Ma), with deposits restricted spatially to the Colorado mineral belt (CMB). Other alkaline igneous rocks and associated gold deposits formed later, during the transition from a compressional to an extensional regime (about 35-27 Ma). These younger rocks and associated deposits are more widespread, following the Rocky Mountain front southward, from Cripple Creek in Colorado through New Mexico. All of these deposits are on the eastern margin of the Cordillera, with voluminous calc-alkaline rocks to the west. The largest deposits in the belt include Cripple Creek and those in the CMB. The most important factor in the formation of all of the gold deposits was the near-surface emplacement of relatively oxidized volatile-rich alkaline magmas. Strontium and lead isotope compositions suggest that the source of the magmas was subduction-modified subcontinental lithosphere. However, Cripple Creek alkaline rocks and older Laramide alkaline rocks in the CMB that were emplaced through hydrously altered LREE-enriched rocks of the Colorado (Yavapai) province have 208Pb/204Pb ratios that suggest these magmas assimilated and mixed with significant amounts of lower crust. The anomalously hot, thick, and light crust beneath Colorado may have been a catalyst for large-scale transfer of volatiles and crustal melting. Increased dissolved H2O (and CO2, F, Cl) of these magmas may have resulted in more productive gold deposits due to more efficient magmatic-hydrothermal systems. High volatile contents may also have promoted Te and V enrichment, explaining the presence of fluorite, roscoelite (vanadium-rich mica) and tellurides in the CMB deposits and Cripple Creek as opposed to deposits to the south. Deep-seated structures of regional extent that formed during the Proterozoic allowed the magmas to rise to shallow crustal levels. Proterozoic sites of intrusions at 1.65, 1.4, and 1.1 Ga were also important precursors to alkaline-related gold deposits. Many of the larger gold deposits are located at sites of Proterozoic intrusions, and are localized at the intersection of northeast-trending ductile shear zones formed during Mesoproterozoic deformation, and an important north-trending fault formed during 1.1 Ga rifting. 相似文献