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1.
Doklady Earth Sciences - The Ermakovo F–Be deposit, the largest Be deposit in Russia and one of the world’s largest deposits, is located in West Transbaikalia. The ores of the deposit...  相似文献   

2.
Doklady Earth Sciences - An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X22340013  相似文献   

3.
Located along the southern part of the Yarlung Zangbo suture zone in southern Tibet, Bangbu is one of the largest gold deposits in Tibet. Auriferous sulfide-bearing quartz veins are controlled by second- or third-order brittle fractures associated with the regional Qusong–Cuogu–Zhemulang brittle-ductile shear zone. Fluid inclusion studies show that the auriferous quartz contains aqueous inclusions, two-phase and three-phase CO2-bearing inclusions, and pure gaseous hydrocarbon inclusions. The CO2-bearing inclusions have salinities of 2.2–9.5% NaCleq, and homogenization temperatures (Th) of 167–336 °C. The δD, δ18O, and δ13C compositions of the Bangbu ore-forming fluids are − 105.5 to − 44.4‰, 4.7 to 9.0‰ and − 5.1 to − 2.2‰, respectively, indicating that the ore-forming fluid is mainly of metamorphic origin, with also a mantle-derived contribution. The 3He/4He ratio of the ore-forming fluids is 0.174 to 1.010 Ra, and 40Ar/36Ar ranges from 311.9 to 1724.9. Calculations indicate that the percentage of mantle-derived He in fluid inclusions from Bangbu is 2.7–16.7%. These geochemical features are similar to those of most orogenic gold deposits. Dating by 40Ar/39Ar of hydrothermal sericite collected from auriferous quartz veins at Bangbu yielded a plateau age of 44.8 ± 1.0 Ma, with normal and inverse isochronal ages of 43.6 ± 3.2 Ma and 44 ± 3 Ma, respectively. This indicates that the gold mineralization was contemporaneous with the main collisional stage between India and Eurasia along the Yarlung Zangbo suture, which resulted in the development of near-vertical lithospheric shear zones. A deep metamorphic fluid was channeled upward along the shear zone, mixing with a mantle fluid. The mixed fluids migrated into the brittle structures along the shear zone and precipitated gold, sulfides, and quartz because of declining temperature and pressure or fluid immiscibility. The Bangbu is a large-scale Cenozoic syn-collisional orogenic gold deposit  相似文献   

4.
Mafic rocks of a Permian crust to mantle section in Val Malenco (Italy) display a multi-stage evolution: pre-Alpine exhumation to the ocean floor, followed by burial and re-exhumation during Alpine convergence. Four prominent generations of amphiboles were formed during these stages. On the basis of microstructural investigations combined with electron microprobe analyses two amphibole generations can be assigned to the pre-Alpine decompression and two to the Alpine metamorphic P–T evolution. The different amphiboles have distinct NaM4, Ca, K and Cl contents according to different P–T conditions and fluid chemistry. Analysing these mixed amphiboles by the 39Ar−40Ar stepwise heating technique yielded very complex age spectra. However, by correlating amphibole compositions directly obtained from the electron microprobe with the components deduced from the release of Ar isotopes during stepwise heating, obtained ages were consistent with the geological history deduced from field and petrological studies. The two generations of pre-Alpine amphiboles gave distinguishable Triassic to Late Jurassic/Early Cretaceous ages (≈225 and 130–140 Ma respectively). High-NaM4 amphiboles have higher isotopic ages than low-NaM4 ones, in agreement with their decompressional evolution. The exhumation of the Permian crust to mantle section is represented by the former age. The latter age concerns Cl-dominated amphibole related to an Early Cretaceous oceanic stage. For the early Alpine, pressure-dominated metamorphism we obtained a Late Cretaceous age (83–91 Ma). The later, temperature-dominated overprint is significantly younger, as indicated by 39Ar−40Ar ages of 67–73 Ma. These Late Cretaceous ages favour an Adriatic origin for the Malenco unit. Our data show that 39Ar−40Ar dating combined with detailed microprobe analysis can exploit the potential to relate conditions of amphibole formation to their respective ages. Received: 1 March 1999 / Accepted: 18 August 2000  相似文献   

5.
Summary K–Ar and Ar–Ar whole rock and mineral ages are presented for 25 samples of metamorphic rocks from the Mid-Bosnian Schist Mts., representing one of the largest allochthonous Palaeozoic terranes incorporated within the Internal Dinarides. Four main age groups can be distinguished: 1) Variscan (343Ma), 2) post-Variscan (288–238Ma), 3) Early Cretaceous (mainly 121–92Ma), and 4) Eocene (59–35Ma) ages. Apart from this, an Oligocene (31Ma) age was obtained on Alpine vein hyalophane. The radiometric dating indicates a polyphase metamorphic evolution of the Palaeozoic formations and suggests a pre-Carboniferous age of the volcano-sedimentary protoliths, an Early Carboniferous age of Variscan metamorphism and deformation, post-Variscan volcanism, an Early Cretaceous metamorphic overprint related to out-of-sequence thrusting of the Palaeozoic complex, and an Eocene and Oligocene metamorphic overprint related to the main Alpine compressional deformation and subsequent strike-slip faulting, and uplift of the metamorphic core. Accordingly, the Mid-Bosnian Schist Mts. can be correlated in its multistage geodynamic evolution with some Palaeozoic tectonostratigraphic units from the Austroalpine domain in the Eastern Alps.Deceased  相似文献   

6.

40Ar‐39Ar age spectra on minerals from granitic, metamorphic and hydrothermal rocks confirm that the Early Proterozoic Tennant Creek Block was affected by two thermal events during its evolution. Although extensive alteration of biotite and feldspar within the granites precludes the direct determination of their cooling history, 40Ar‐39Ar analyses for hydrothermal muscovite from several nearby gold‐copper deposits indicate that regional cooling to below ～ 300°C was not prolonged. Flat, uniform muscovite age spectra were obtained from gold deposits east of the Tennant Creek town site and indicate a minimum age of 1825–1830 Ma for their formation. These ages are within error of those for the felsic volcanism of the Flynn Subgroup, and a genetic relationship between the two may exist. Samples from gold deposits elsewhere in the area indicate disturbance of the K‐Ar isotope system. The second thermal event to affect the region occurred at around 1700 Ma, and is confirmed by the 40Ar‐39Ar muscovite ages for the ‘Warrego’ granite (1677 ± 4 Ma) and for the metamorphism of the Wundirgi Formation (1696 ± 4 Ma).  相似文献   

7.
<正>Thus far,our understanding of the emplacement of Xuebaoding granite and the occurrence and evolution of the Songpan-Garze Orogenic Belt has been complicated by differing age spectra results.Therefore,in this study,the ~(40)Ar/~(39)Ar and sensitive high resolution ion micro-probe(SHRIMP) U-Pb dating methods were both used and the results compared,particularly with respect to dating data for Pankou and Pukouling granites from Xuebaoding,to establish ages that are close to the real emplacements.The results of SHRIMP U-Pb dating for zircon showed a high amount of U,but a very low value for Th/U.The high U amount,coupled with characteristics of inclusions in zircons,indicates that Xuebaoding granites are not suitable for U-Pb dating.Therefore,muscovite in the same granite samples was selected for ~(40)Ar/~(39)Ar dating.The ~(40)Ar/~(39)Ar age spectrum obtained on bulk muscovite from Pukouling granite in the Xuebaoding,gave a plateau age of 200.1±1.2 Ma and an inverse isochron age of 200.6±1.2 Ma.The ~(40)Ar/~(39)Ar age spectrum obtained on bulk muscovite from Pankou granite in the Xuebaoding gave another plateau age of 193.4±1.1 Ma and an inverse isochron age of 193.7±1.1 Ma. The ~(40)Ar/~(36)Ar intercept of 277.0±23.4(2σ) was very close to the air ratio,indicating that no apparent excess argon contamination was present.These age dating spectra indicate that both granites were emplaced at 200.6±1.3 Ma and 193.7±1.1 Ma,respectively.Through comparison of both dating methods and their results,we can conclude that it is feasible that the muscovite in the granite bearing high U could be used for ~(40)Ar/~(39)Ar dating without extra Ar.Based on this evidence,as well as the geological characteristics of the Xuebaoding W-Sn-Be deposit and petrology of granites,it can be concluded that the material origin of the Xuebaoding W-Sn-Be deposit might partially originate from the Xuebaoding granite group emplacement at about 200 Ma.Moreover,compared with other granites and deposits distributed in various positions in the Songpan-Garze Orogenic Belt,the Xuebaoding emplacement ages further show that the main rare metal deposits and granites in peripheral regions occurred earlier than those in the inner Songpan-Garze.Therefore,~(40)Ar/~(39)Ar dating of Xuebaoding granite will lay a solid foundation for studying the occurrence and evolution of granite and rare earth element deposits in the Songpan-Garze Orogenic Belt.  相似文献   

8.
A Cu-bearing skarn zone occurs north of the Shayvar Mountain in northwestern Iran. Skarn-type metasomatic alteration and mineralization occur along the contact between Upper Cretaceous impure carbonates and a Miocene Cu-bearing granitic stock. Both endoskarn and exoskarn developed in the rocks. Exoskarn is the principal skarn zone and is enclosed by a skarnoid–hornfelsic zone. Skarn formation occured during stages: (1) prograde, (2) middle stage and (3) late stage. In the prograde stage, there were two main processes: (a) metamorphic–bimetasomatic and (b) prograde metasomatic. The metamorphic process began immediately after intrusion of the pluton into the enclosing impure carbonates. The prograde metasomatic stage commenced with segregation and evolution of a fluid phase in the pluton and movement into fractures and micro-fractures in the skarnoid–hornfelsic rocks developed in a metamorphic zone. The introduction of considerable amounts of Fe, Si and Mg led to the development of voluminous medium- to coarse-grained anhydrous calc-silicates. During the middle stage, the previously formed skarn zones were affected by intense multiple hydrofracturing in the Cu-bearing stock. In addition to Fe, Si and Mg, substantial amounts of Cu, Pb and Zn, along with volatile components such as H2S and CO2 were added to the skarn system. Consequently, substantial amounts of hydrous calc-silicates (epidote, tremolite–actinolite), sulfides (pyrite, chalcopyrite and molybdenite), oxides (magnetite, hematite) and carbonates (calcite) replaced the anhydrous calc-silicates. The retrograde stage was synchronous with the incursion of relatively low-temperature, more oxidized fluids into skarn system, resulting in partial alteration of the early-formed calc-silicates and development of a series of very fine-grained aggregates of chlorite, clay, hematite and calcite. Zircon grains from the endoskarn zone provide constraints on the timing of solidification of the granite stock (9.91 ± 0.31 Ma) that caused mineralization in the Anjerd area. One sample of primary hornblende from the monzogranitic Shayvar batholith has an 40Ar/39Ar age of 26.54 ± 0.65 Ma and indicates that intrusion of the Miocene stock and associated Cu skarn formation occurred a considerable time after intrusion of the batholith.  相似文献   

9.
The KAr isochron method is an attempt to obtain the initial age or reset age and the extraneous argon isotopic ratio of a suite of cogenetic samples of different K-contents. Some samples contain excess argon-40 and others lose argon-40. The resultant ages on single samples are not significant geologically. We have discussed the principles of three types of isochrons commonly used, the 40Ar vs 40K isochron, the 40Ar/36Ar vs 40K/30Ar isochron, and the 40Ar/36Ar vs 39Ar/36Ar isochron, and evaluated the first two types for ten different hypothetical cases. If a straight line is obtained in the 40Ar vs 40K isochron, a positive intercept indicates an approximately constant amount of excess argon, whereas a negative intercept indicates argon loss. A curved line or scattering of points indicates that the basic assumptions are not valid for the set of samples under consideration. The 40Ar/36Ar vs 40K/36Ar isochron method is valid, rigorously, only when all samples of the system under consideration have the same non-radiogenic argon isotope composition. This requires that either no excess argon is present in the system, or else each analysis contains the same proportion of excess and atmospheric argon. If these conditions do not hold, approximately, invalid ages and invalid intercepts are obtained. Any KAr isochron needs to be used with caution.  相似文献   

10.
Recent investigations reveal that the ultrahigh-pressure metamorphic (UHPM) rocks in the Donghai region of East China underwent ductile and transitional ductile-brittle structural events during their exhumation. The earlier ductile deformation took place under the condition of amphibolite facies and the later transitional ductile-brittle deformation under the condition of greenschist facies. The hanging walls moved southeastward during both of these two events. The 40Ar/39Ar dating of muscovites from muscovite-plagioclase schists in the Haizhou phosphorous mine, which are structurally overlain by UHPM rocks, yields a plateau age of 218.0±2.9 Ma and isochron age of 219.8Ma, indicating that the earlier event of the ampibolite-facies deformation probably took place about 220 Ma ago. The 40Ar/39Ar dating of oriented amphiboles parallel to the movement direction of the hanging wall on a decollement plane yields a plateau age of 213.1±0.3 Ma and isochron age of 213.4±4.1 Ma, probably representing the age o  相似文献   

11.
Doklady Earth Sciences - The original and published geochronological data and the geological position of different granitoid complexes of the Main (Kolyma) Batholith Belt of Northeast Asia have...  相似文献   

12.
Daraban Leucogranite dykes intruded discordantly into the basal serpentinized harzburgite of the Mawat Ophiolite, Kurdistan region, NE Iraq. These coarse grained muscovite-tourmaline leucogranites are the first leucogranite dykes identified within the Mawat Ophiolite. They are mainly composed of quartz, K-feldspar, plagioclase, tourmaline, muscovite, and secondary phologopite, while zircon, xenotime, corundum, mangano-ilemnite and cassiterite occur as accessories.The A/CNK value of the granite dyke samples varies from 1.10 to 1.22 indicating a strongly peraluminous composition. CaO/Na2O ranges from 0.11 to 0.15 and Al2O3/TiO2 from 264 to 463, similar to the strongly peraluminous (SP) granites exposed in ‘high-pressure’ collision zones such as the Himalayas.Ar–Ar muscovite step-heating dating yields 37.57 ± 0.25 and 38.02 ± 0.53 Ma plateau ages for two samples which are thought to reflect either their magmatic emplacement or resetting during collision-related metamorphism. Mineral chemistry shows evidence of both primary and secondary types of muscovite, with cores favouring the magmatic interpretation and slight effects of a late syn-serpentinization fluid seen at the rims.Geochemical features of Daraban Leucogranite dykes favour a syn-collisional tectonic setting. They probably formed in response to the continental collision between Eurasia and Arabia during the initial stage of the opening of the Gulf of Aden at 37 Ma. The muscovite ages and geochemical features of Daraban Leucogranite are strong evidence for the timing of the continental collision between northeastern Arabia and Eurasia in Kurdistan region of Iraq.  相似文献   

13.
Amphibole concentrates from four samples of variably retrogressed eclogite from the Tsäkkok Lens of the Seve Nappe Complex display discordant40Ar/39Ar age spectra suggestive of extraneous argon contamination.36Ar/40Ar vs.39Ar/40Ar isotope correlations are well-defined for two samples and yield ages of 464.7 ± 1.3 Ma and 463.2 + 6.3 Ma. Inverse ordinate intercepts are very much larger than 295 and confirm significant extraneous argon components. Two white mica concentrates from metasedimentary units of the Tsäkkok Lens display internally concordant40Ar/39Ar age spectra which define plateau ages of 448.2 ± 1.6 Ma and 468.4 ± 0.9 Ma. An amphibole concentrate from a metamorphosed basic dike within the Sarek Lens of the Seve Nappe Complex yields an isotope correlation age of 463.8 ± 12.3 Ma, suggesting a post-metamorphic thermal evolution similar to that of the Tsäkkok Lens. The amphibolite and white mica ages are interpreted to date post-metamorphic cooling through appropriate temperatures for intracrystalline retention of argon following amphibolite facies retrogression of the eclogite facies assemblages. The Seve Nappe Complex appears to have originated within distal facies of the late Proterozoic-early Paleozoic miogeocline of Baltica. The present40Ar/39Ar results provide a record of early Paleozoic (pre-Middle Ordovician) tectonothermal activity and therefore are compatible with previous suggestions of significant early Caledonian orogenesis within the Scandinavian Caledonides.
Zusammenfassung Die Amphibolitkonzentrate aus vier Proben unterschiedlich regressiver Eklogite aus der Tsäkkok-Linse des Seve-Deckenkomplexes spiegeln diskordante40Ar/39Ar Altersspektren wieder. Diese deuten an, daß eine Argonkontamination von außen stattgefunden hat.36Ar/40Ar gegen39Ar/40Ar Isotopen sind für zwei Proben genau bestimmt und liefern Alter von 464,7 ± 1,3 Mio. und 463,2 ± 6,3 Mio. Jahre. Inverse Ordinatenabschnitte sind sehr viel größer als 295 und bestätigen erhebliche Argon-Fremdkomponenten. Zwei Hellglimmerkonzentrate aus metasedimentären Einheiten der Tsäkkok-Linse zeigen intern konkordante40Ar/39Ar Altersspektren, welche Plateaualter von 448,2 ± 1,6 Mio. und 468,4 ± 0,9 Mio. Jahre besitzen. Ein Amphibolkonzentrat aus einem metamorphen basischen Gang innerhalb der Sarek-Linse des Seve-Deckenkomplexes liefert ein Isotopenkorrelationsalter von 463,8 ±12,3 Mio. Jahre, welches eine postmetamorphe thermale Entwicklung andeutet, die ähnlich der Tsäkkok-Linse ist. Die Amphibol- und Hellglimmeralter werden dahingehend interpretiert, daß sie die postmetamorphe thermale Abkühlung durch entsprechende Temperaturen für das intrakristalline Zurückhalten des Argons datieren, die im Anschluß an die Amphibolitfaziesregression der Eklogitfaziesvergesellschaftung folgte. Der Seve-Deckenkomplex scheint aus einer distalen Fazies spätprotero- bis frühpalaeozoischen Miogeosynklinale von Baltika hervorgegangen zu sein. Die jetzigen40Ar/39Ar Ergebnisse liefern eine Aufzeichnung von frühpaleozoischen (Vor-Mittelordovizium) tektono-thermalen Aktivitäten, und sie sind daher vergleichbar mit früheren Vermutungen von einer bedeutenden frühkaledonischen Orogenese innerhalb der skandinavischen Kaledoniden.
Résumé Les concentrés d'amphiboles de quatre échantillons d'éclogites, rétromorphosés à des degrés divers, provenant de la lentille de Träkkok («Seve Nappe Complex») montre un spectre discordant d'âges40Ar/39Ar, ce qui suggère une contamination par un apport d'argon. Les corrélations entre36Ar/40Ar et39Ar/40Ar sont bien définies pour deux échantillons et fournissent des âges de 464,7 ± 1,3 Ma et 463,2 ±6,3 Ma. Les rapports40Ar/36Ar sont beaucoup plus élevés que 295 et confirment un apport extérieur d'argon significatif. Deux concentrés de mica blanc provenant des unités métasédimentaires de la lentille de Tsäkkok présentent des spectres d'âges40Ar/39Ar concordants, qui définissent des âges-plateau de 448,2 ± 1,6 Ma et 468,4 ± 0,9 Ma. Un concentré d'amphibole provenant d'un dyke basique métamorphisé dans la lentille des Sarek du «Seve Nappe Complex» fournit par corrélation isotopique un âge de 463,8 ± 12,9 Ma, ce qui suggère une évolution thermique post-métamorphique similaire à celle de la lentille de Tsäkkok. Les âges fournis par les amphiboles et les micas blancs sont interprétés comme correspondant au refroidissement post-métamorphique, à travers des températures permettant la rétention intracristalline de l'argon, à la suite de la rétromorphose des éclogites dans le faciès des amphiboles. Le «Seve Nappe Complex» a dû être engendré dans les faciès distaux du miogéosynclinal tardi-protérozoïque à éo-paléozoïque de la Baltique. Les valeurs actuelles de40Ar/39Ar enregistrent l'activité tectonothermique du Paléozoïque inférieur (pré-Ordovicien moyen); elles sont donc en accord avec l'hypothèse antérieurement émise d'une orogenèse éo-calédonienne au sein des Calédonides Scandinaves.
Tsäkkok Seve, , 40Ar/39Ar. , -. 36Ar/40Ar 39Ar/40Ar 464,7±1,3 , 463,2±6,3 . 295 , . Tsäkkok , 448,2±1,6 468,4±0,9 . Sarek Seve 463,8±12,3 ., , Tsäkkok. , , , coxpa . Seve, , - . 40Ar/39Ar - , .. . .
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14.
A 2000 km long dextral Talas-Fergana strike–slip fault separates eastern terranes in the Kyrgyz Tien Shan from western terranes. The aim of this study was to constrain an age of dextral shearing in the central part of the fault utilizing Ar–Ar dating of micas. We also carried out a U–Pb–Hf zircon study of two different deformed granitoid complexes in the fault zone from which the micas for Ar dating were separated. Two samples of the oldest deformed Neoproterozoic granitoids in the area of study yielded U–Pb zircon SHRIMP ages 728 ± 11 Ma and 778 ± 11 Ma, characteristic for the Cryogenian Bolshoi Naryn Formation, and zircon grains analyzed for their Lu–Hf isotopic compositions yielded εHf(t) values from −11.43 to −16.73, and their calculated tHfc ages varied from 2.42 to 2.71 Ga. Thus varying Cryogenian ages and noticeable heterogeneity of Meso- to Paleoproterozoic crustal sources was established for mylonitic granites of the Bolshoi Naryn Formation. Two samples of mylonitized pegmatoidal granites of the Kyrgysh Complex yielded identical 206Pb/238U ages of 279 ± 5 Ma corresponding to the main peak of Late-Paleozoic post-collisional magmatism in the Tien Shan (Seltmann et al., 2011), and zircon grains analyzed for their Lu–Hf isotopic compositions yielded εHf(t) values from −11.43 to −16.73, and calculated tHfc ages from 2.42 to 2.71 Ga indicating derivation from a Paleoproterozoic crustal source. Microstructural studies showed that ductile/brittle deformation of pegmatoidal granites of the Kyrgysh Complex occurred at temperatures of 300–400 °C and caused resetting of the K–Ar isotope system of primary muscovite. Deformation of mylonitized granites of the Bolshoi Naryn Formation occurred under high temperature conditions and resulted in protracted growth and recrystallization of micas. The oldest Ar–Ar muscovite age of 241 Ma with a well defined plateau from a pegmatoidal granite of the Kyrgysh Complex is considered as a “minimum” age of dextral motions along this section of the fault in the Triassic while younger ages varying from 227 Ma to 199 Ma with typical staircase patterns indicate protracted growth and recrystallization of micas during ductile deformations which continued until the end of the Triassic.  相似文献   

15.
The early Permian Xiaomiao mafic dike swarm in the East Kunlun orogenic belt (EKOB) provides an excellent opportunity to study the petrogenesis of such swarms developed in supra-subduction zone environments, and to investigate the early plate tectonic history of the Palaeo-Tethyan Ocean. Hornblende 40Ar–39Ar dating results indicate that the mafic dikes formed in the early Permian (277.76 ± 2.72 Ma). The Xiaomiao mafic hypabyssals have the following compositional range: SiO2 = 46.55–55.75%, MgO = 2.80–7.38%, Mg# = 36–61, and (Na2O + K2O) = 2.87–4.95%. Chemically, they display calc-alkali affinities, ranging in composition from gabbro to gabbroic diorite. All analysed dikes are enriched in light rare earth elements and large-ion lithophile elements (e.g. Rb and Ba), but are depleted in heavy rare earth elements and high field strength elements (e.g. Nb, Ta, and Ti). Their ISr and ?Nd(t) values range from 0.707 to 0.715 and –2.60 to +2.91, respectively. They are geochemically similar to subduction-related basaltic rocks (e.g. island arc basalt), but differ from E-MORB and N-MORB. Petrographic and major element data reveal that fractional crystallizations of clinopyroxene, olivine, hornblende, and Fe–Ti oxides may have occurred during magma evolution, but that crustal contamination was minor. Based on geochemical and Sr–Nd isotopic bulk-rock compositions, we suggest that the mafic dikes were likely generated by 10–20% partial melting of a spinel + minor garnet lherzolite mantle source metasomatized by subducted, slab-derived fluids, and minor sediments. Based on our results, we propose that the early evolution of the Palaeo-Tethyan Ocean involved the spreading and initial subduction of the Carboniferous to early Permian ocean basin followed by late Permian subduction, which generated the magmatic arc.  相似文献   

16.
The Fujiawu porphyry Cu–Mo deposit is one of several porphyry Cu–Mo deposits in the Dexing district, Jiangxi Province, Southeast China. New zircon SHRIMP U–Pb data yield a weighted mean 206Pb/238U age of 172.0 ± 2.1 and 168.5 ± 1.4 Ma from weakly altered granodiorite porphyry and quartz diorite porphyry, respectively. Two hydrothermal biotites from granodiorite porphyry give an Ar–Ar step-heating plateau age of 169.9 ± 1.8 and 168.7 ± 1.8 Ma. Hydrothermal apatite exsolved from altered biotite yields an isotope dilution thermal ionization mass spectrometry isochron age of 164.4 ± 0.9 Ma. The apatite age is similar to the ages obtained from hydrothermal rutile (165.0 ± 1.1 and 164.8 ± 1.6 Ma) and indicates that the magmatism and hydrothermal activity in the Fujiawu deposit occurred in the Middle Jurassic. Hydrothermal fluid circulation related to multiple stages of magma emplacement resulted in Cu–Mo mineralization in the Fujiawu porphyry deposit. The zircon SHRIMP U–Pb ages and the published molybdenite Re–Os age (170.9 ± 1.5 Ma) represent the timing of magma crystallization and Mo mineralization, whereas the rutile and apatite U–Pb ages reflect the timing of Cu mineralization following quartz diorite emplacement. The data suggest slow cooling after emplacement of the quartz diorite porphyry.  相似文献   

17.
International Journal of Earth Sciences - This study is based upon a stratigraphic and structural revision of a Middle Jurassic–Upper Cretaceous mostly continental succession exposed between...  相似文献   

18.
The Qingchengzi orefield is a large polymetallic ore concentration area in the Liaodong peninsula,northeastern China,that includes twelve Pb-Zn deposits and five Au-Ag deposits along its periphery.The ore-forming age remains much disputed,which prevents the identification of the relationship between the mineralization and the associated magmatism.In this paper,we quantitatively present the feasibility of making ore mineral ~(40)Ar/~(39)Ar dating and report reliable ~(40)Ar/~(39)Ar ages of lamprophyre groundmass,K-feldspar and sphalerite from the Zhenzigou deposit.Direct and indirect methods are applied to constrain the timing of mineralization,which plays a vital role in discussing the contribution of multistage magmatism to ore formation.The low-potassium sphalerite yielded an inverse isochron age of 232.8±41.5 Ma,which features a relatively large uncertainty.Two lamprophyre groundmasses got reliable inverse isochron ages of 193.2±1.3 Ma and 152.3±1.5 Ma,respectively.K-feldspar yielded a precise inverse isochron age of 134.9±0.9 Ma.These four ages indicate that the mineralization is closely associated with Mesozoic magmatism.Consequently,regarding the cooling age of the earliest Mesozoic Shuangdinggou intrusion(224.2±1.2 Ma)as the initial time of mineralization,we can further constrain the age of the sphalerite to 224–191 Ma.These new and existing geochronological data,combined with the interaction cutting or symbiotic relationship between the lamprophyre veins and ore veins,suggest that the Pb-Zn-Au-Ag mineralization in the Qingchengzi orefield mainly occurred during three periods:the late Triassic(ca.224–193 Ma),the late Jurassic(ca.167–152 Ma)and the early Cretaceous(ca.138–134 Ma).This polymetallic deposits are shown to have been formed during multiple events coinciding with periods of the Mesozoic magmatic activity.In contrast,the Proterozoic magmatism and submarine exhalative and hydrothermal sedimentation in the Liaolaomo paleorift served mainly to transport and concentrate the ore-forming substances at the Liaohe Group with no associated Pb-Zn-Au-Ag mineralization.  相似文献   

19.
The Sanshandao Au deposit is located in the famous Sanshandao metallogenic belt, Jiaodong area. To date, accumulative Au resources of 1000 t have been identified from the belt. Sanshandao is a world-class gold deposit with Au mineralization hosted in Early Cretaceous Guojialing-type granites. Thus, studies on the genesis and ore-forming element sources of the Sanshandao Au deposit are crucial. He and Ar isotopic analyses of fluid inclusions from pyrite(the carrier of Au) indicate that the fluid inclusions have 3 He/4 He=0.043–0.21 Ra with an average of 0.096 Ra and 40 Ar/36 Ar=488–664 with an average of 570.8. These values represent the initial He and Ar isotopic compositions of ore-forming fluids for trapped fluid inclusions. The comparison of H–O isotopic characteristics combined with deposit geology and wall rock alteration reveals that the ore-forming fluids of the Sanshandao Au deposit show mixed crust–mantle origin characteristics, and they mainly comprise crust-derived fluid mixed with minor mantle-derived fluid and meteoric water during the uprising process. The ore-forming elements were generally sourced from pre-Cambrian meta-basement rocks formed by Mesozoic reactivation and mixed with minor shallow crustal and mantle components.  相似文献   

20.
Four samples of plagioclase and biotite from the Shaxi porphyry in the lower part of the Yangtze metallogenic belt were analyzed for age determination with the 40Ar/39Ar method. The results yield reproducible ages of 126 Ma to 135 Ma with a high level of confidence according to the agreement between isochron and plateau ages. The four Ar-Ar ages are relatively consistent within the analytical error. These ages are also consistent with, but more precise than, previous K-Ar and Rb-Sr ages and thus provide better constraints on the time of porphyry formation and associated Cu-Au mineralization along the middle to lower part of the Yangtze metaliogenic belt. The ages of 126 to 135 Ma are interpreted to represent the intrusive time of the Shaxi porphyry, so that the Cu-Au mineralization should have occurred later due to the post-magmatic hydrothermal event.  相似文献   

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