共查询到20条相似文献,搜索用时 46 毫秒
1.
Isotope geochemistry of ore fluids for the Dongsheng sandstone-type uranium deposit, China 总被引:2,自引:1,他引:2
The Dongsheng sandstone-type uranium deposit is one of the large-sized sandstone-type uranium deposits discovered in the northern part of the Ordos Basin of China in recent years. Geochemical characteristics of the Dongsheng uranium deposit are significantly different from those of the typical interlayered oxidized sandstone-type uranium ore deposits in the region of Middle Asia. Fluid inclusion studies of the uranium deposit showed that the uranium ore-forming temperatures are within the range of 150–160℃. Their 3He/4He ratios are within the range of 0.02–1.00 R/Ra, about 5–40 times those of the crust. Their 40Ar/36Ar ratios vary from 584 to 1243, much higher than the values of atmospheric argon. The δ18OH2O and δD values of fluid inclusions from the uranium deposit are -3.0‰– -8.75‰ and -55.8‰– -71.3‰, respectively, reflecting the characteristics of mixed fluid of meteoric water and magmatic water. The δ18OH2O and δD values of kaolinite layer at the bottom of the uranium ore deposit are 6.1‰ and -77‰, respectively, showing the characteristics of magmatic water. The δ13CV-PDB and δ18OH2O values of calcite veins in uranium ores are -8.0‰ and 5.76‰, respectively, showing the characteristics of mantle source. Geochemical characteristics of fluid inclusions indicated that the ore-formation fluid for the Dongsheng uranium deposit was a mixed fluid of meteoric water and deep-source fluid from the crust. It was proposed that the Jurassic-Cretaceous U-rich metamorphic rocks and granites widespread in the northern uplift area of the Ordos Basin had been weathered and denudated and the ore-forming elements, mainly uranium, were transported by meteoric waters to the Dongsheng region, where uranium ores were formed. Tectonothermal events and magmatic activities in the Ordos Basin during the Mesozoic made fluids in the deep interior and oil/gas at shallow levels upwarp along the fault zone and activated fractures, filling into U-bearing clastic sandstones, thus providing necessary energy for the formation of uranium ores. 相似文献
2.
The Ordovician-Lower Carboniferous sequence of slightly metamorphosed gray carbonate-terrigenous rocks contains the Silurian
black cherty shales enriched in carbon (6–9%), pyrite (6–7%), and uranium (∼30 ppm). The uranium ore is localized at the pinch-out
of areal and linear zones of the Early Permian supergene (exogenic) oxidation of rocks expressed in reddening (hematitization).
U, As, Sb, Cu, Ni, Mo, and Ag have been removed from the oxidized black shales and concentrated in the cementation zone in
form of pitchblende and sulfides in wall-rock disseminations and veinlets largely hosted in carbonate-bearing rocks. In the
Late Permian, during deposition of the upper Rotliegende and Zechstein, the fractures in the basement were filled with carbonates
and sulfates; uranium was partly redeposited along with enrichment in Pb and Zn. Mesozoic and Cenozoic supergene processes
altered uranium ore insignificantly. 相似文献
3.
A. F. Redkin V. I. Velichkin A. P. Aleshin G. P. Borodulin 《Geology of Ore Deposits》2009,51(4):290-304
The experimental study of an F-bearing silicic melt—U, Nb, Ta minerals—chloride-fluoride fluid system is focused on ascertaining
the origin of uranium deposits spatially related to intraplate silicic volcanism. The first series of experiments on uranium
solubility in silicic melts close in composition to ore-bearing rhyolite of the unique Strel’tsovka Mo-U ore field has been
performed in order to determine more precisely the ore genesis. As starting solid phases, model homogeneous glass of the chemical
composition (wt %) 72.18 SiO2, 12.19 Al2O3, 1.02 FeO, 0.20 MgO, 0.33 CaO, 4.78 Na2O, 3.82 K2O, 1.44 Li2O, and 2.4 F (LiF, NaF, KF, CaF2, MgF2); synthetic UO2 and UO3·0.33H2O; and natural columbite were used. The starting solutions contained 1.0 m Cl and 10−2
m F. The runs were conducted in a gas vessel at a pressure of 1000 bar and in a high-pressure hydrothermal vessel at 2000 bar.
The O2 (H2) fugacity was set by Ni-NiO, Co-CoO, Fe3O4-Fe2O3, and Cu-Cu2O buffers. The equilibrium between melt and solution for major elements is reached during the first day, whereas 5–7 days
are required for ore elements (U, Nb, Ta) to come into equilibrium. The solubility of Nb and especially Ta in Cl-F solutions
equilibrated with F-bearing melt is extremely low. The solubility of U is much higher (10−4−10−5 mol/kg H2O). The energy dispersive spectroscopy of run products allowed us to establish that columbite dissolved incongruently with
formation of U- and F-bearing pyrochlores. The performed experiments have shown that a silicic melt close to the rhyolitic
magma of the Strel’tsovka caldera in composition is not able to generate postmagmatic ore-forming solutions containing more
than 10−6−10−5 mol U/kg H2O under the relatively low pressure necessary for the existence of the first type of fluid. The amount of uranium that could
have precipitated from this fluid in the zone of ore deposition is estimated at 216–9000 t. This estimate is two orders of
magnitude lower than the total uranium resources of the deposits localized in the Strel’tsovka caldera. Thus, the upper crustal
silicic magma chamber hardly was a source of uranium for Mo-U deposits of the Strel’tsovka ore field. 相似文献
4.
Most altered clay minerals in uranium ore deposits in granites in the selected provinces of South China haveδ
18O
m
values ranging from 6.22 to 7.24,δDm from −60 to −70,δ
18O
from +3.05 to −3.07, and
from −20.2 to −37.5‰. Relative enrichment of32S in the uranium ore deposits and greater variations in Pb isotopic composition of galenas from them show that uranium ores
in the granites were formed in such a way that uranium in shallow-source granites had been mobilized by heated meteoric waters
and then migrated to local favourable locations along great faults to form uranium ore deposits.
Zhang Shaoli, Yang Wenjin, Tang Chunjing and Xu Wenxin did part of this work. 相似文献
5.
Bohdan Kříbek Karel Žák Petr Dobeš Jaromír Leichmann Marta Pudilová Miloš René Bohdan Scharm Marta Scharmová Antonín Hájek Daniel Holeczy Ulrich F. Hein Bernd Lehmann 《Mineralium Deposita》2009,44(1):99-128
Three major mineralization events are recorded at the Rožná uranium deposit (total mine production of 23,000 t U, average
grade of 0.24% U): (1) pre-uranium quartz-sulfide and carbonate-sulfide mineralization, (2) uranium, and (3) post-uranium
quartz-carbonate-sulfide mineralization. (1) K–Ar ages for white mica from wall rock alteration of the pre-uranium mineralization
style range from 304.5 ± 5.8 to 307.6 ± 6.0 Ma coinciding with the post-orogenic exhumation of the Moldanubian orogenic root
and retrograde-metamorphic equilibration of the high-grade metamorphic host rocks. The fluid inclusion record consists of
low-salinity aqueous inclusions, together with H2O-CO2-CH4, CO2-CH4, and pure CH4 inclusions. The fluid inclusion, paragenetic, and isotope data suggest that the pre-uranium mineralization formed from a
reduced low-salinity aqueous fluid at temperatures close to 300°C. (2) The uraniferous hydrothermal event is subdivided into
the pre-ore, ore, and post-ore substages. K–Ar ages of pre-ore authigenic K-feldspar range from 296.3 ± 7.5 to 281.0 ± 5.4 Ma
and coincide with the transcurrent reorganization of crustal blocks of the Bohemian Massif and with Late Stephanian to Early
Permian rifting. Massive hematitization, albitization, and desilicification of the pre-ore altered rocks indicate an influx
of oxidized basinal fluids to the crystalline rocks of the Moldanubian domain. The wide range of salinities of fluid inclusions
is interpreted as a result of the large-scale mixing of basinal brines with meteoric water. The cationic composition of these
fluids indicates extensive interaction with crystalline rocks. Chlorite thermometry yielded temperatures of 260°C to 310°C.
During this substage, uranium was probably leached from the Moldanubian crystalline rocks. The hydrothermal alteration of
the ore substage followed, or partly overlapped in time, the pre-ore substage alteration. K–Ar ages of illite from ore substage
alteration range from 277.2 ± 5.5 to 264.0 ± 4.3 Ma and roughly correspond with the results of chemical U–Pb dating of authigenic
monazite (268 ± 50 Ma). The uranium ore deposition was accompanied by large-scale decomposition of biotite and pre-ore chlorite
to Fe-rich illite and iron hydrooxides. Therefore, it is proposed that the deposition of uranium ore was mostly in response
to the reduction of the ore-bearing fluid by interaction with ferrous iron-bearing silicates (biotite and pre-ore chlorite).
The Th data on primary, mostly aqueous, inclusions trapped in carbonates of the ore substage range between 152°C and 174°C
and total salinity ranges over a relatively wide interval of 3.1 to 23.1 wt% NaCl eq. Gradual reduction of the fluid system
during the post-ore substage is manifested by the appearance of a new generation of authigenic chlorite and pyrite. Chlorite
thermometry yielded temperatures of 150°C to 170°C. Solid bitumens that post-date uranium mineralization indicate radiolytic
polymerization of gaseous and liquid hydrocarbons and their derivatives. The origin of the organic compounds can be related
to the diagenetic and catagenetic transformation of organic matter in Upper Stephanian and Permian sediments. (3) K–Ar ages
on illite from post-uranium quartz-carbonate-sulfide mineralization range from 233.7 ± 4.7 to 227.5 ± 4.6 Ma and are consistent
with the early Tethys-Central Atlantic rifting and tectonic reactivation of the Variscan structures of the Bohemian Massif.
A minor part of the late Variscan uranium mineralization was remobilized during this hydrothermal event. 相似文献
6.
The eastern Dharwar Craton of southern India includes at least three ∼ 2700Ma supracrustal belts (schist belts) which have
mesothermal, quartz-carbonate vein gold mineralization emplaced within the sheared metabasalts. In the Hutti and the Kolar
schist belts, the host rocks are amphibolites and the ore veins have been flanked by only a thin zone of biotitic alteration;
in the Ramagiri belt, however, the host rocks to the veins have been affected by more extensive but lower temperature alteration
by fluids. The rare earth element (REE) geochemistry of the host metabasalts, alteration zones, ore veins and the bulk sulfides
separated from the ore veins and the alteration zones suggest that
Because alteration and mineralization involved addition of REE, more LREE compared to HREE, the fluids could be of higher
temperature origin. The initial Nd isotope ratios in the host rocks (εNd calculated at 2700 Ma) showed a large variation (+8 to -4) and a deep crustal source for the fluid REE seems likely. A crustal
source for Pb and Os in the ore samples of Kolar belt has previously been suggested (Krogstadet al 1995; Walkeret al 1989). Such a source for ore fluids is consistent with a late Archean (2500Ma) accretionary origin for the terrains of the
eastern Dharwar Craton. 相似文献
– | •the REE chemistry of the immediate host rocks has been modified by fluids which added LREE, |
– | •the REE abundance of the ore veins vary with the amount of host rock fragments included in the veins, |
– | •the sulfides formed during mineralization have significant REE concentration with patterns nearly identical to the ore veins and alteration zones and |
– | •therefore the ore fluids involved in gold mineralization here could be LREE enriched. |
7.
The interaction of columbite and uraninite with a fluid-magma system consisting of a melt of Li-F-granite and fluoride fluid
at 750°C and P = 2300 bar causes the formation of zonal pyrochlores being considerably different in uranium and fluorine contents. Fluorine-rich
pyrochlores (to 7–12 at %) preserve the Nb/U ratio of the initial columbite (15–30). Uranium-bearing pyrochlores contain 2–4
times less amounts of fluorine, above 2 at % of uranium, and the Nb/U molar ratio decreases to 5–15. The analysis of Ca, U,
and F variation trends points to the influence of temperature on the reactions of Ca2+ to U4+ cation exchange. The statistical analysis (250 measurements) showed that the maximum uranium content in pyrochlores amounted
to 16 ± 5 wt % for the magmatic system saturated with uraninite. 相似文献
8.
The Strel’tsovka and Antei uranium deposits located in the Strel’tsovka caldera are unique in ore resources. According to
the considered mathematical model, the uranium source of these deposits was related to the middle-lower crustal silicic magma
chambers or had mantle origin. Boundary conditions of the model are based on modern views of physicochemical conditions of
hydrothermal process in the Strel’tsovka ore field and factors governing ore deposition therein. Modeling results are consistent
with morphology of orebodies and ultimate uranium resources of the deposits and thus confirm indirectly that the physicochemical
parameters of the ore-forming system are coherent. The maximal duration of uranium ore deposition is estimated at 500 ka. 相似文献
9.
Presented in this paper is an approach to the analysis of “series-stage“division.The processes of hydrothermal evolution involved in ore deposition,the factors affecting the enrichment of uranium and the source of ore forming elements in uranium deposit 720 are also discussed .In addition,the ore-forming tem-perature and pressure as well as the pH,Eh and chemical composition of ore-forming medium are studied with reference to the fluid inclusion data available.A double solution-mixing model has been proposed to explain the genesis of the uranium deposit studied. 相似文献
10.
The Sakharjok Y-Zr deposit in Kola Peninsula is related to the fissure alkaline intrusion of the same name. The intrusion
∼7 km in extent and 4–5 km2 in area of its exposed part is composed of Neoarchean (2.68–2.61 Ma) alkali and nepheline syenites, which cut through the
Archean alkali granite and gneissic granodiorite. Mineralization is localized in the nepheline syenite body as linear zones
200–1350 m in extent and 3–30 m in thickness, which strike conformably to primary magmatic banding and trachytoid texture
of nepheline syenite. The ore is similar to the host rocks in petrography and chemistry and only differs from them in enrichment
in zircon, britholite-(Y), and pyrochlore. Judging from geochemical attributes (high HSFE and some incompatible element contents
(1000–5000 ppm Zr, 200–600 ppm Nb, 100–500 ppm Y, 0.1–0.3 wt % REE, 400–900 ppm Rb), REE pattern, Th/U, Y/Nb, and Yb/Ta ratios),
nepheline syenite was derived from an enriched mantle source similar to that of contemporary OIB and was formed as an evolved
product of long-term fractional crystallization of primary alkali basaltic melt. The ore concentrations are caused by unique
composition of nepheline syenite magma (high Zr, Y, REE, Nb contents), which underwent subsequent intrachamber fractionation.
Mineralogical features of zircon-the main ore mineral—demonstrate its long multistage crystallization. The inner zones of
prismatic crystals with high ZrO2/HfO2 ratio (90, on average) grew during early magmatic stage at a temperature of 900–850°C. The inner zones of dipyramidal crystals
with average ZrO2/HfO2 = 63 formed during late magmatic stage at a temperature of ∼500°C. The zircon pertaining to the postmagmatic hydrothermal
stage is distinguished by the lowest ZrO2/HfO2 ratio (29, on average), porous fabric, abundant inclusions, and crystallization temperature below 500°C. The progressive
decrease in ZrO2/HfO2 ratio was caused by evolution of melt and postmagmatic solution. The metamorphic zircon rims relics of earlier crystals and
occurs as individual rhythmically zoned grains with an averaged ZrO2/HfO2 ratio (45, on average) similar to that of the bulk ore composition. The metamorphic zircon is depleted in uranium in comparison
with magmatic zircon, owing to selective removal of U by aqueous metamorphic solutions. Zircon from the Sakharjok deposit
is characterized by low concentrations of detrimental impurities, in particular, contains only 10–90 ppm U and 10–80 ppm Th,
and thus can be used in various fields of application. 相似文献
11.
N. A. Goryachev G. N. Gamyanin V. Yu. Prokof’ev T. A. Velivetskaya A. V. Ignat’ev N. V. Leskova 《Russian Journal of Pacific Geology》2011,5(2):97-110
The mineral assemblages of the Ag-Sb deposits from the Yana-Kolyma Foldbelt were studied. The compositions of ore minerals,
the isotopic compositions of sulfur in ore minerals, and the carbon and oxygen in carbonates are given. Arsenopyrite of the
deposits is significantly enriched in Sb (1–16 wt %), which is related to the primary enrichment of the ore-hosting sequences
in Sb and the ore formation at shallow depths. Based on the fluid inclusions study, the deposits were formed at T = 329–149°C and P = 0.30–1.04 kb from low-salinity chloride-sulfate-bicarbonate solutions enriched in Sb and Ag. The sequence of precipitation
of Ag-Sb minerals was mainly controlled by the Sb concentration and the sulfur fugacity and potential in the fluid. 相似文献
12.
Metallogenesis of Devonian—Carboniferous Strata—bound Carbonate—type Uranium Deposits in South China
庞玉蕙 《中国地球化学学报》1990,9(3):264-274
This paper deais with the geological conditions.mineralization characteristics,genetic types and space-time distribution of the Devonian-Carboniferous strata-bound carbonate-type uranium deposits in South China.These ore deposits are genetically classified as the leaching type and the leaching-hydrothermal superimposed type,These ore deposits are confined mainly to the strata (D2-3,C1)of platform-lagoon carbonate facies.Unique tectonic settings are a vital factor leading to the formation of these uranium deposits.A metallogenetic model for these uranium deposits has been proposed. 相似文献
13.
In order to ascertain the forms in which uranium is present in ores of the Melovoe rare metal sedimentary deposit of uranium
and rare earth minerals (South Mangyshlak), we investigated a series of typical ore samples that were collected earlier; both
the uranium content and the total content of rare earth metals in them lay within 0.1–0.3%. The study was carried out by analytical
electron microscopy using transmission electron microscopy and scanning electron microscopy, electron microdiffraction, and
microprobing. It was ascertained that both uranium and rare earth elements are present in ore mostly associated with biogenic
phosphate in the form of natural minerals, such as uraninite, ningyoite, coffinite, autenite, and churchite. Iron hydroxides
and graphitized organic matter are present in some samples. It is assumed that the co-occurrence of uranium and rare earth
elements, which is nontypical for the sedimentary process, resulted from secondary epigenetic processes and alternation of
reducing and oxidizing environmental conditions. 相似文献
14.
冀北张麻井铀钼矿床叠加成矿:矿石地球化学质量 平衡迁移计算的制约 总被引:1,自引:1,他引:0
张麻井铀钼矿床位于沽源-红山子铀成矿带西南段,是中国重要的与火山岩有关的热液铀矿床,其铀、钼储量均达到大型矿床的标准。铀-钼矿矿体主要分布于流纹斑岩岩体的内外接触带,钼矿化的分布范围略大于铀矿化,两者在空间上高度重叠。在铀-钼矿矿体外发育一层单钼矿体,与铀-钼矿矿体界限清晰,两者为截然分开的接触关系。为了研究该矿床铀成矿与钼成矿的关系,对张麻井的铀矿石、钼矿石进行主微量元素分析,采用质量平衡迁移计算方法,选择Yb元素作为不活动组分,使用Grant公式对其组分迁移定量计算。地球化学数据显示,铀矿石的平均w(U)、w(Mo)为1589×10-6、3837×10-6;钼矿石的平均w(U)、w(Mo)为493×10-6、5706×10-6,显示钼矿石具有更高的Mo含量,更低的U含量。计算结果显示铀矿石的Isocon均小于以1(分别为0.48、0.58、0.46、0.53),相较流纹斑岩整体发生了组分带入,其中最明显的特点是带入大量SiO2,还带入Mo、U、Zn、Cu、Ni、V、Pb、Co等成矿元素,K2O、Na2O、Rb、Cs等碱金属,以及Ba、Sr等大离子亲石元素,Cd、Bi、Sc、Eu等组分也表现出较大程度的带入,仅碱金属Li,MnO等少量组分显示带出;钼矿石的Isocon均小于以1(分别为0.73、0.67、0.90、0.39),相较于流纹斑岩整体也发生了组分带入,带入的主要有成矿元素Mo、U、Ni、Zn、V、Co、Cu、Pb,碱金属K2O、Na2O、Rb、Li,大离子亲石元素Ba、Sr,以及TFeO、Cd、Bi、Sc等组分,仅Cr、MnO组分显示带出。质量平衡迁移计算之后,铀、钼矿石平均w(Mo)分别增加到7217×10-6、7759×10-6,显示两者增加的Mo基本一致。铀、钼矿石平均w(U)分别增加到3131×10-6、604×10-6,显示前者增加的U远远大于后者。在标准化Isocon图解中,铀矿石和钼矿石的组分迁移具有一定相似性,但具体迁移特征也有一定的差异,整体上表现出相似而不相同的特点。结合矿石从铀-钼矿矿体到外侧的单钼矿体,U含量迅速下降的地球化学特征,铀、钼矿体的空间分布特征以及其接触关系,文章认为两者极有可能是不同的成矿过程,而且可能是后期富铀成矿流体叠加在早期的钼矿之上。 相似文献
15.
Vito Coppola Maria Boni H. Albert Gilg Bozena Strzelska-Smakowska 《Mineralium Deposita》2009,44(5):559-580
The Silesia–Cracow district in Poland has been one of the world’s principal sources of zinc from nonsulfide zinc ore (Polish:
galman). The still remaining nonsulfide ore resources can be estimated at 57 Mt at 5.6% Zn and 1.4% Pb. Nonsulfide mineralization
is mainly hosted by Lower Muschelkalk (Triassic) limestone and is associated with different generations of the hydrothermal
ore-bearing dolomite (OBD I, II, III). A fundamental ore control is believed to have been exerted by the basement faults,
which were repeatedly reactivated during the Alpine tectonic cycle, leading to the formation of horst-and-graben structures: these dislocations may have caused short periods of emersion and the circulation of meteoric waters during the
Cenozoic. Nonsulfide ores show a wide range of morphological characteristics and textures. They occur as earthy masses, crystalline
aggregates, and concretions in cavities. Breccia and replacement textures are also very common. The most important mineral
phases are: smithsonite, Fe–smithsonite, Zn–dolomite, goethite, and Fe–Mn(hydr)oxides. Minor hemimorphite and hydrozincite
have also been detected. Two distinct nonsulfide ore types occur: the predominant red galman and the rare white galman. In the white galman, Fe–smithsonite and Zn–dolomite are particularly abundant. This ore type is commonly considered as a peripheral hydrothermal
alteration product related to the same fluids that precipitated both the OBD II–III and the sulfides. In contrast, a supergene
origin is commonly assumed for the red galman. Evidence of the petrographic and mineralogical difference between white and red galman is also found in stable isotope data. Smithsonite from red galman shows a limited range of δ
13CVPDB values (−10.1 to −11.4‰), and δ
18OVSMOW values (25.3‰ to 28.5‰, mean 26.8 ± 0.3‰). The uniform and low carbon isotope values of red galman smithsonite are unusual for supergene carbonate-hosted deposits and indicate the predominance of a single organic carbon
source. Smithsonite from white galman has a more variable, slightly more positive carbon isotope (−2.9‰ to −7.4‰), but broadly similar oxygen isotope composition
(26.8‰ to 28.9‰). The relationship of the white galman ore with the hydrothermal system responsible for OBD II and sulfide generation is still uncertain. The most important paleoweathering
events took place in both Lower and Upper Silesia during Late Cretaceous up to Paleogene and early Neogene time. During this
period, several short-lasting emersions and intense weathering episodes facilitated the formation of sinkholes in the Triassic
carbonate rocks and the oxidation of sulfide orebodies through percolating meteoric waters. These phenomena may have lasted
until the Middle Miocene. 相似文献
16.
The Tuwaishan, Baoban, Erjia, Bumo and other gold deposits in western Hainan occur in Precambrian metamorphic clastic rocks
and are structurally controlled by the Gezhen shear zone. Fluid inclusion studies have been carried out of the gold deposits
mentioned above. The homogenization temperatures of the whole fluid inclusion population range from 140°C to 370°C, indicating
that gold was precipitated mainly at 240–250°C. The salinities are within the range of 2.0–9.2 wt% NaCl equiv. and the pressure
of formation of the deposits was estimated at about 270×105−500×105Pa, corresponding to a depth of about 1.1–2.0 km under lithostatic confinement. Chemical studies show that the ore fluid is
of the Na+(K+)-Ca2+-Cl−(F−) type. Theδ
18O andδD values of the fluid vary from −2.7‰- +4.4‰ and −50‰–−87‰ Evidence developed from fluid inclusions and geological setting
indicates that the ore fluid was a mixture of magmatic and meteoric-hydrothermal waters. Changes in chemical composition andδ
18O andδD of fluid inclusions from one ore field to another seem to be related with regional tectonism, metamorphism and magmatism. 相似文献
17.
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
18.
The Wittichen Co–Ag–Bi–U mining area (Schwarzwald ore district, SW Germany) hosts several unconformity-related vein-type mineralizations
within Variscan leucogranite and Permian to Triassic redbeds. The multistage mineralization formed at the intersection of
two fault systems in the last 250 Ma. A Permo-Triassic ore stage I with minor U–Bi–quartz–fluorite mineralization is followed
by a Jurassic to Cretaceous ore stage II with the main Ag and Co mineralization consisting of several generations of gangue
minerals that host the sub-stages of U–Bi, Bi–Ag, Ni–As–Bi and Co–As–Bi. Important ore minerals are native elements, Co and
Ni arsenides, and pitchblende; sulphides are absent. The Miocene ore stage III comprises barite with the Cu–Bi sulfosalts
emplectite, wittichenite and aikinite, and the sulphides anilite and djurleite besides native Bi, chalcopyrite, sphalerite,
galena and tennantite. The mineral-forming fluid system changed from low salinity (<5 wt.% NaCl) at high temperature (around
300°C) in Permian to highly saline (around 25 wt.% NaCl + CaCl2) at lower temperatures (50–150°C) in Triassic to Cretaceous times. Thermodynamic calculations and comparison with similar
mineralizations worldwide show that the Mesozoic ore-forming fluid was alkaline with redox conditions above the hematite–magnetite
buffer. We suggest that the precipitation mechanism for native elements, pitchblende and arsenides is a decrease in pH during
fluid mixing processes. REE patterns in fluorite and the occurrence of Bi in all stages suggest a granitic source of some
ore-forming elements, whereas, e.g. Ag, Co and Ni probably have been leached from the redbeds. The greater importance of Cu
and isotope data indicates that the Miocene ore stage III is more influenced by fluids from the overlying redbeds and limestones
than the earlier mineralization stages. 相似文献
19.
Vikt. L. Barsukov 《Geochemistry International》2006,44(12):1191-1214
By means of computer modeling, it was shown that the pre-uranium quartz and quartz-sulfide veins of the Schlema deposit with
their typomorphic assemblages could be formed at the expense of cooling of hot pore solutions from the Aue granite cupola
underlying the mineralized zones. As was shown previously [1], the ore metal content of these pore solutions changes with
decreasing temperature and pressure in the granite-water system and an increase in the intensity of granite “flushing” with
a water phase. The dependence of the composition of precipitated material on the proportions of chlorides and carbon dioxide
in the pore solutions was evaluated in the models. It was shown that silica mobilization from the granite and redeposition
were accompanied by the oxidation of ferrous iron in the granite and extraction of sulfide sulfur in molal amounts similar
to or even higher than those of silica. This provided conditions for uranium migration after these stages and formation of
hydrothermal uranium ores.
Original Russian Text ? Vikt.L. Barsukov. 2006, published in Geokhimiya, 2006, No. 12, pp. 1290–1314. 相似文献
20.
粤北长江花岗岩型铀矿田沥青铀矿原位U-Pb年代学研究及其地质意义 总被引:4,自引:2,他引:2
花岗岩型铀矿床是我国重要的工业铀矿床类型,广泛分布于南岭地区。粤北长江铀矿田位于南岭中段诸广山岩体中南部,是我国典型的花岗岩型铀矿田。由于铀矿物在化学组成和成因上的固有属性,前人通过传统的铀矿物U-Pb同位素定年获得的成矿年龄(157~52Ma)变化范围较大且分散,难以有效约束精确的铀成矿时代。本文在精细矿物学研究的基础上,对长江铀矿田棉花坑、书楼坵和长排三个铀矿床的沥青铀矿开展了LA-ICP-MS原位微区U-Pb同位素定年研究。结果表明,棉花坑矿床成矿年龄为60. 8±0. 6Ma和66. 8±1. 6Ma,书楼坵矿床成矿年龄为71. 4±1. 3Ma和74. 4±1. 7Ma,长排矿床成矿年龄为62. 4±2. 5Ma和70. 2±0. 5Ma,总体分为~75Ma、~70Ma和~60Ma三期成矿年龄,代表了华南花岗岩型铀矿的晚期铀矿化。长江铀矿田成矿时代与诸广地区北东向断裂带、断陷盆地的强烈拉张时期(80~60Ma)同步,指示区内铀矿化与南岭地区晚白垩世-古近纪地壳拉张作用有关,区内铀成矿的幔源矿化剂CO_2来自区域性北东向断裂带的拉张作用。综合前人资料,认为诸广地区的铀成矿具同时性和多期性特征,成矿峰期为~140Ma、~125Ma、~105Ma、~90Ma和80~60Ma,成矿统一受制于华南岩石圈伸展的动力学背景,诸广山-南雄盆山体系白垩-古近纪的构造演化可能是促使区域铀矿化形成的主要因素。 相似文献