Problems in oxygen isotope geothermometry in mafic granulite facies rocks from near Einasleigh,northern Queensland     

N.J. McNaughton  Allan F. Wilson 《Precambrian Research》1980,13(1):77-86

Oxygen isotope geothermometry of coexisting minerals from five mafic granulites does not reflect the peak temperature of metamorphism as determined by other methods. Exchange of ¹⁸O between phases during slow cooling has (a) lowered the δ ¹⁸O of clinopyroxene relative to orthopyroxene in the presence of hornblende, (b) raised the δ ¹⁸O of quartz in a manner which is partly dependent on quartz abundance, and (c) lowered the δ ¹⁸O of plagioclase in some rocks.  相似文献   

The world-class Wallaby gold deposit,Laverton, Western Australia: An orogenic-style overprint on a magmatic-hydrothermal magnetite-calcite alteration pipe?     

Brock?P.?Salier  David?I.?GrovesEmail author  Neal?J.?McNaughton  Ian?R.?Fletcher 《Mineralium Deposita》2004,39(4):473-494

Gold mineralisation at the Wallaby gold deposit is hosted by a 1,200 m thick mafic conglomerate. The conglomerate is intruded by an apparently comagmatic alkaline dyke suite displaying increasing fractionation through mafic-monzonite, monzonite, syenite, syenite porphyry to late-stage carbonatite. In the mine area, a pipe-shaped zone of actinolite-magnetite-epidote-calcite (AMEC) alteration overprints the conglomerate. Gold mineralisation, associated with dolomite-albite-quartz-pyrite alteration, is hosted in a series of sub-horizontal, structurally controlled zones that are largely confined within the magnetite-rich pipe. The deposit has a current ore reserve of 2.0 Moz Au, and a total resource of 7.1 Moz Au.TIMS U–Pb analysis of magmatic titanite and SHRIMP U–Pb analysis of gold-related phosphate minerals are used to constrain the timing of magmatism and gold mineralisation at Wallaby. Monzogranite and carbonatite dykes of the Wallaby syenite intruded at 2,664±3 Ma, at least 5 m.y. and probably 14 m.y. before gold mineralisation at 2,650±6 Ma. The significant hiatus between proximal magmatism and gold mineralisation suggests that gold-bearing fluids were not derived from magmas associated with the Wallaby syenite, particularly since intrusive events are unlikely to drive hydrothermal systems for more than 1 m.y.Analysis of the C and O isotopic compositions of carbonates from regional pre-syenite alteration and AMEC alteration at the Wallaby gold deposit suggests that AMEC alteration formed via interaction between magmatic fluids and the pre-syenite wallrock carbonate. The C and O isotopic composition of gold-bearing fluids, as inferred from ore-carbonate, are isotopically distinct from proximal magmatic fluids, as inferred from magmatic carbonate in carbonatite dykes.Thus, detailed isotopic and geochronological studies negate any direct genetic link between proximal magmatic activity related to the Wallaby syenite and gold mineralisation at Wallaby. The gold endowment of the Wallaby gold deposit, combined with the relatively low solubility of gold as thiosulfide complexes in low-salinity ore fluids at temperatures of about 300°C, implicates the influx of very large volumes of auriferous hydrothermal fluids. No large-scale shear-zones nor faults through which such large fluid-volumes could pass have been identified within the immediate ore environment, so fluid influx most probably occurred largely in a unit-confined, brittle-ductile fracture system. This was the ~500-m diameter AMEC alteration pipe, which was a brittle, iron-enriched zone in an otherwise massive conglomerate. During compressional deformation, the competency contrast between unaltered and AMEC-altered conglomerate created a zone of increased fracture permeability, and geochemically favourable conditions (high Fe/Fe+Mg ratio), for gold mineralisation from a distal source.Editorial Handling: C. Brauhart  相似文献   

New data on the Neoproterozoic – Cambrian geotectonic setting of the Teplá-Barrandian volcano-sedimentary successions: geochemistry,U-Pb zircon ages,and provenance (Bohemian Massif,Czech Republic)     

Kerstin?DrostEmail author  Ulf?Linnemann  Neal?McNaughton  Old?ich?Fatka  Petr?Kraft  Michael?Gehmlich  Christian?Tonk  Jaroslav?Marek 《International Journal of Earth Sciences》2004,93(5):742-757

The Teplá-Barrandian unit (TBU) of the Bohemian Massif was a part of the Avalonian-Cadomian belt at the northern margin of Gondwana during Neoproterozoic and Early Cambrian times. New detrital zircon ages and geochemical compositions of Late Neoproterozoic siliciclastic sediments confirm a deposition of the volcano-sedimentary successions of the TBU in a back-arc basin. A change in the geotectonic regime from convergence to transtension was completed by the time of the Precambrian-Cambrian boundary. The accumulation of around 2,500 m Lower Cambrian continental siliciclastics in a Basin-and-Range-type setting was accompanied by magmatism, which shows within-plate features in a few cases, but is predominantly derived from anatectic melts displaying the inherited island arc signature of their Cadomian source rocks. The geochemistry of clastic sediments suggests a deposition in a rift or strike-slip-related basin, respectively. A marine transgression during Middle Cambrian times indicates markedly thinned crust after the Cadomian orogeny. Upper Cambrian magmatism is represented by 1,500 m of subaerial andesites and rhyolites demonstrating several geochemical characteristics of an intra-plate setting. Zircons from a rhyolite give a U-Pb-SHRIMP age of 499±4 Ma. The Cambrian sedimentary and magmatic succession of the TBU records the beginning of an important rifting event at the northern margin of Gondwana.

Kerstin DrostEmail:

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West African provenance for Saxo-Thuringia (Bohemian Massif): Did Armorica ever leave pre-Pangean Gondwana? – U/Pb-SHRIMP zircon evidence and the Nd-isotopic record     

Ulf?LinnemannEmail author  Neal?J.?McNaughton  Rolf?L.?Romer  Michael?Gehmlich  Kerstin?Drost  Christian?Tonk 《International Journal of Earth Sciences》2004,93(5):683-705

Neoproterozoic rocks in the Saxo-Thuringian part of Armorica formed in an active margin setting and were overprinted during Cadomian orogenic processes at the northern margin of Gondwana. The Early Palaeozoic overstep sequence in Saxo-Thuringia was deposited in a Cambro-Ordovician rift setting that reflects the separation of Avalonia and other terranes from the Gondwana mainland. Upper Ordovician and Silurian to Early Carboniferous shelf sediments of Saxo-Thuringia were deposited at the southern passive margin of the Rheic Ocean. SHRIMP U/Pb geochronology on detrital and inherited zircon grains from pre-Variscan basement rocks of the northern part of the Bohemian Massif (Saxo-Thuringia, Germany) demonstrates a distinct West African provenance for sediments and magmatic rocks in this part of peri-Gondwana. Nd-isotope data of Late Neoproterozoic to Early Carboniferous sedimentary rocks show no change in sediment provenance from the Neoproterozoic to the Lower Carboniferous, which implies that Saxo-Thuringia did not leave its West African source before the Variscan Orogeny leading to the Lower Carboniferous configuration of Pangea. Hence, large parts of the pre-Variscan basement of Western and Central Europe often referred to as Armorica or Armorican Terrane Assemblage may have remained with Africa in pre-Pangean time, which makes Armorica a remnant of a Greater Africa in Gondwanan Europe. The separation of Armorica from the Gondwana mainland and a long drift during the Palaeozoic is not supported by the presented data.  相似文献   

Reply to the discussion on "Gold deposits of the Tapajós and Alta Floresta domains,Tapajós–Parima orogenic belt,Amazon Craton,Brazil" (<Emphasis Type="Italic">Mineralium Deposita</Emphasis> 36:278–299, 2001) by Dreher AM,Mach SRF,Martini SL     

Jo?o?SantosEmail author  David?Groves  Léo?Hartmann  Márcia?Moura  Neal?McNaughton 《Mineralium Deposita》2002,37(8):785-787

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Uraniferous diagenetic xenotime in northern Australia and its relationship to unconformity-associated uranium mineralisation     

Daniela A. Vallini  David I. Groves  Neal J. McNaughton  Ian R. Fletcher 《Mineralium Deposita》2007,42(1-2):51-64

Stratabound, uraniferous diagenetic xenotime cements provide a minimum depositional age of 1,632±3 Ma for the sedimentary Birrindudu Group in the Killi Killi Hills, Tanami Region in northern Australia. The age of xenotime formation is broadly coeval with that recently proposed (1,650–1,600 Ma) for uranium mineralisation in the unconformity-associated deposits of the Pine Creek Inlier, northern Australia, and Athabasca Basin, Canada. The geological setting and formation model for the uraniferous xenotime crystals are similar to those widely proposed for unconformity-associated uranium deposits, suggesting a genetic link between the two. However, xenotime formation in the Birrindudu Group occurred during an apparently earlier stage of diagenesis, compared to late diagenetic formation of unconformity-associated uranium deposits. This could be explained by variations in the thickness of sediment cover and diachronous diagenesis across the basin, at the time of the basin-wide uranium mobilisation event, herein dated at ca. 1,630 Ma. In such a scenario, stratabound uraniferous xenotime cements could represent the remote distal zones of a more deeply buried, uranium mineralising system. Alternatively, the xenotime layer represents a precursor to, or a source for, later unconformity-associated ore deposition. In this case, the presence of diagenetic uraniferous xenotime in an area prospective for unconformity-associated uranium mineralisation would be an indication of, and still provide an approximate age for, uranium mobilisation within the cover sequence. Xenotime is a far more robust mineral than uraninite for U–Pb geochronology and can potentially provide a more reliable and precise timeframe for uranium mineralisation and subsequent recrystallisation events if present in the immediate uranium-ore environment.  相似文献   

冀东金厂峪金矿区钠长岩脉及青山口花岗岩体SHRIMP锆石U-Pb定年及其意义   总被引：20，自引：0，他引：20       下载免费PDF全文

罗镇宽  关康  裘有守  苗来成  Y. M. Qiu  N .J. McNaughton  D. I. Groves 《地质找矿论丛》2001,16(4):226-231

金厂峪金矿床是冀东最大的金矿床 ,具有早期复脉型和晚期石英大脉型两种矿石类型。矿区产有多期钠长岩脉 ,且与含金矿脉有密切的时间和空间关系。青山口花岗岩体位于矿区西约 2～ 3km,有研究者认为金矿床成因上与花岗岩体有关。应用先进的 SHRIMP测年技术 ,测得肉红色钠长岩脉的锆石 w (2 0 7Pb) / w (2 0 6Pb)年龄为 (185 8± 8) Ma,青山口花岗岩体锆石 w(2 0 6Pb) / w(2 3 8U )年龄为 (199± 2 ) Ma。金厂峪金矿床的的复脉型矿化早于肉红色钠长岩脉 ,故其矿化的时代应在晚元古代。青山口岩体的年龄和区域上与辉钼矿化有关的花岗岩年龄一致 ,均为燕山早期。推测金厂峪金矿床晚期石英大脉型矿化中的辉钼矿化可能与青山口花岗岩体有关 ,石英大脉型金矿化时代为中生代燕山期  相似文献   

Archaean Au−Ag mineralisation at Racetrack,near Kalgoorlie,Western Australia: a high crustal-level expression of the Archaean composite lode-gold system     

M. Gebre-Mariam  D. I. Groves  N. J. McNaughton  E. J. Mikucki  J. R. Vearncombe 《Mineralium Deposita》1993,28(6):375-387

The Racetrack Au−Ag deposit, in the Archaean Yilgarn Block, Western Australia, is hosted by a porphyritic basalt in a low greenschist facies setting and is associated with a brittle strike-slip fault system. Three distinct and successive stages of hydrothermal activity and late quartz-carbonate veining resulted in multiple veining and/or brecciation: Stages I and II are Au-bearing, whereas Stage III and late veins are barren. The ore shows features of both classic epithermal and mesothermal deposits. Alteration assemblages, typified by sericitization, carbonization, silicification and chloritization, are similar to those of mesothermal gold deposits, wheras the quartz vein-textures including comb, rosette, plumose and banded, ore mineralogyof arsenopyrite, pyrite, chalcopyrite, sphalerite, galena, freibergite, tetrahedrite, tennantite, fahlore, electrum and gold, and metal associations (Cu, As, Ag, Sn, Sb, W, Au and Pb) are more characteristics of epithermal deposits. Fluid inclusions related to Stage II are two phase and aqueous with 1–8 (average 4) wt. % NaCl equiv. and CO₂ content of <0.85 molal. Pressure-corrected homogenisation temperatures range from 190°C to 260°C. Mineral assemblages indicate that ore fluid pH ranged between 4.2 and 5.3, f_{O 2} between 10^−38.8 and 10^−39.6 bars, and m_Σs between 10^−3.2 and 10^−3.6. Calculated chemical and stable isotope compositions require a component of surface water in the ore fluid depositing the mineralisation, but evidence for deep crustal Pb indicates that deeply sourced fluids were also involved. The deposit is interpreted to have formed in a shallow environment via mixing of deeply sourced fluids, from at least as deep as the base of the greenstone belt, with surface waters. It therefore represents the upper crustal end-member of the crustal depth spectrum of Archaean lode-gold mineralisation.  相似文献   

The source of lead in Archaean lode gold deposits of the Menzies-Kalgoorlie-Kambalda region,Yilgarn Block,Western Australia     

N. J. McNaughton  D. I. Groves  W. K. Witt 《Mineralium Deposita》1993,28(6):495-502

The Archaean greenstone terrane between Menzies and Kambalda exhibits a coherent, although deformed, stratigraphic sequence intruded by granitoids and bounded by major NNW-trending shear and/or fault zones. The greenstone terrane hosts a large number of lode gold prospects and deposits, including the giant Kalgoorlie deposits. The initial Pb isotope compositions of lode gold deposits, as determined from ore related galena and pyrite, vary systematically in a linear trend on a²⁰⁷Pb/²⁰⁴Pb versus²⁰⁶Pb/²⁰⁴Pb diagram which reflects crustal heterogeneity at the time of mineralisation. Deposits hosted within a 90 km section of the Menzies-Boorara Shear Zone have a uniform, radiogenic initial Pb isotope composition irrespective of temperature of mineralisation and proximity to granitoid-gneiss in plan view. The Pb in these deposits is considered to be derived largely from older felsic crust underlying the greenstone belt and was accessed via this major shear-zone system. Deposits in a transect unrelated to a major shear zone show a systematic correlation between initial Pb isotope compositions and proximity to granitoid-gneiss and/or to mineralisation temperature. These compositions are less radiogenic than those within the Menzies-Boorara Shear Zone, but trend on a²⁰⁷Pb/²⁰⁴Pb versus⁶⁰⁶Pb/²⁰⁴Pb diagram between this isotope signature and the uniform Pb isotope signature which characterises the >100 km greenstone transect from the Mt Pleasant area through Kalgoorlie to Kambalda. These data are interpreted to reflect Pb derivation from discrete crustal segments within and below the greenstones, and require that mineralisation was related to crustal-scale hydrothermal systems that accessed both sialic mid- to lower-crust and the greenstone succession.  相似文献   

The age and origin of younger granitic plutons of the Shaw Batholith in the Archaean Pilbara Block,Western Australia   总被引：1，自引：0，他引：1  

M. J. Bickle  L. F. Bettenay  H. J. Chapman  D. I. Groves  N. J. McNaughton  I. H. Campbell  J. R. de Laeter 《Contributions to Mineralogy and Petrology》1989,101(3):361-376

The whole-rock Pb-Pb method has been used to date four of the younger, mainly adamellite, late-tectonic plutonic phases within the ca. 3.5 Ga Shaw Batholith of the Archaean east Pilbara Block. Three suites give ages within error of 2966 Ma (Porphyritic Granites at 2948±50 Ma, Leuco-adamellites at 2943±46 Ma and Garden Creek Adamellite at 3007±48 Ma). The post-tectonic Cooglegong Adamellite gives an age of 2847±34 Ma. The Sm-Nd model isotopic systematics of all four suites indicate derivation from crust ranging between ca. 3200 and 3600 Ma in age. The sources for these four younger plutonic phases were heterogeneous and, although exhibiting some isotopic characteristics of the older (3.5–3.3 Ga) calc-alkali plutonic suites, were more depleted in the LIL elements Rb, U and Th. In addition, the Garden Creek Adamellite and the Cooglegong Adamellite lack the very fractionated and HREE-depleted REE patterns characteristic of both the older calc-alkali plutonic rocks and the Porphyritic Granites and Leuco-adamellites. The crust underlying the Shaw Batholith at ca. 2950 Ma must have been both markedly heterogeneous and variably depleted, a conclusion consistent with the complex tectonic and plutonic evolution of this region.  相似文献