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Alteration of rocks and localization of uranium mineralization in the northwestern Strel’tsovka caldera are exemplified in
the Dal’nee deposit. In the main parameters of hydrothermal mineralization (temperature, pH, pressure, and composition of
solution), the Dal’nee deposit differs from the deposits of the Strel’tsovka ore field located in the central part of the
caldera. The localization of high-grade stratiform orebodies are interpreted in light of kinematic relations between steeply
and gently dipping faults that formed in the tectonic setting of the NE-SW-trending, long-living, right-lateral, strike-slip
faulting. The wide halos of argillic alteration and the structural control of uranium mineralization are caused by the fact
that the deposit is located at the margin of the geological block, which has developed since the Late Triassic in a regime
of extension (pull-apart) to form a depression, which is arranged en echelon relative to the main caldera and comparable to
it in area. Currently, this depression is overlapped by sediments of the Sukhoi Urulyungui Basin. Such a structure markedly
increases the probability of finding hidden uranium ores associated with low-temperature argillic alteration in the volcanosedimantary
rocks and granitoid basement of the northwestern Strel’tsovka caldera. 相似文献
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Nicolas Coppo Pierre-André Schnegg Pierik Falco Roberto Costa Martin Burkhard 《Swiss Journal of Geoscience》2008,101(2):409-413
The local and regional structural pattern of volcanic edifices strongly controls the space distribution of electrical resistivity. Here we report on the structural context of the western part of the Las Cañadas caldera of Tenerife (LCC) thought to have initiated the formation of the caldera. Using a new dataset of 11 audiomagnetotelluric tensors we emphasize the resistivity distribution of Ucanca caldera and propose a major revision of its extension. We find that Ucanca caldera has a limited westwards extent and that El Cedro sector is a depression margin of the caldera. According to the extent of hydrothermalized rocks at the base of the LCC wall and the distribution of Pico Teide – Pico Viejo vents, we constrain the location and size of Ucanca caldera. The interpretation of these results also constrains the extension of the Icod Valley and proposes a headwall located below the Pico Teide – Pico Viejo Complex. 相似文献
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《Applied Geochemistry》2004,19(6):819-834
Spatial distribution of soil Hg, B and NH4 was investigated in the soils of Cañadas caldera, Canary Islands, in the summer of 1992. Soil Hg, B and NH4 were also studied over several transects intersecting structural features. Soil Hg concentration ranged from 10.83 to 45,000 μg kg−1 whereas those of B and NH4 ranged from 8.45 to 4512 μg kg−1 and from 0.31 to 181 mg kg−1, respectively. Probability plot analysis identified 3 geochemical populations for Hg and B whereas only 2 were detected for NH4. Multivariate analysis (cluster, factor and multiple regression analysis) was used to identify subtle geochemical characteristics of the groups and factors and to determine the relationship between Hg, B and NH4 and the soil secondary parameters. High soil Hg, B and NH4 concentrations are interpreted as being related to areas where a convection system has developed, coinciding with the most recent volcanic centers located along the basaltic rift zones and with the main features inside Cañadas caldera: Teide volcano and Roques de Garcı́a. Background levels of soil volatiles are present in locations where no indication of subsurface thermal activity occurs. Generally, the secondary controls on Hg, B and NH4 are subtle and are overwhelmed in areas characterized by subsurface geothermal activity. 相似文献
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The development of vertical zoning of wall-rock metasomatic alteration is considered with the Mesozoic Strel’tsovka caldera as an example. This caldera hosts Russia’s largest uranium ore field. Metasomatic rocks with the participation of various phyllosilicates, carbonates, albite, and zeolites are widespread in the ore field. In the eastern block of the caldera, where the main uranium reserves are accommodated, hydromica metasomatic alteration gives way to beresitization with depth. Argillic alteration, which is typical of the western block, is replaced with hydromica and beresite alteration only at a significant depth. Postore argillic alteration is superposed on beresitized rocks in the lower part of the section. Two styles of vertical metasomatic zoning are caused by different modes of deformation in the western and eastern parts of the caldera. Variations of the most important petrophysical properties of host rocks—density, apparent porosity, velocities of P- and S-waves, dynamic Young’s modulus, and Poisson coefficient—have been determined by sonic testing of samples taken from different depths. It is suggested that downward migration of the brittle-ductile transition zone could have been a factor controlling facies diversity of metasomatic rocks. Such a migration was caused by a new phase of tectonothermal impact accompanied by an increase in the strain rate or by emplacement of a new portion of heated fluid. Transient subsidence of the brittle-ductile boundary increases the depth of the hydrodynamically open zone related to the Earth’s surface and accelerates percolation of cold meteoric water to a greater depth. As a result, the temperature of the hydrothermal solution falls down, increasing the vertical extent of argillic alteration. High-grade uranium mineralization is also localized more deeply than elsewhere. 相似文献
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Peter Koděra Jaroslav Lexa Andrew Hugh Rankin Anthony Edward Fallick 《Mineralium Deposita》2005,39(8):921-943
The central zone of the large Miocene tiavnica stratovolcano in the Western Carpathians hosts epithermal Au mineralization of intermediate-sulfidation type, located at deep levels of the historic Rozália base-metal mine at Banská Hodrua. The Au mineralization occurs as subhorizontal veins at the base of pre-caldera andesites, close to the roof of a subvolcanic granodiorite intrusion. The veins are dismembered by a set of quartz–diorite porphyry sills and displaced by the younger, steeply dipping, Rozália base-metal vein, and parallel structures. The base-metal vein structures are related to resurgent horst uplift in the caldera center. The Au mineralization formed during two stages. Based on fluid inclusion evidence, both stages formed from fluids of low salinity (0–3 wt% NaCl eq.), which underwent extensive boiling at moderate temperatures (280–330°C). Variable pressure conditions (39–95 bars, neglecting the effect of CO2) indicate continual opening of the system and a transition from suprahydrostatic towards hydrodynamic conditions at shallow depths (~550 m). The fluid inclusions of the Rozália base-metal vein show homogenization temperature peaks at ~285 and 187°C and salinities between 1 and 4 wt% NaCl eq. Precipitation of Au is considered to be the result of prolonged boiling of fluids and associated decrease in Au solubility. Oxygen and hydrogen isotope data for quartz and carbonate from the Au veins show a relatively homogeneous fluid composition (–2.7 to 1.118O, –78 to –62D). The combined 18Ofluid and Dfluid values suggest a mixed character of fluids, falling between the fields of typical magmatic and meteoric water influenced by 18Ofluid shift due to fluid–rock isotopic exchange. End stages of open-system boiling and fractionation could have been reached, at least locally. Significantly lower isotopic composition of meteoric fluids associated with Au mineralization compared to those associated with the intrusion-related mineralizations could have resulted from changing paleoclimate and/or analytical problems of extraction of water from fluid inclusions. The proposed genetic model for the Au deposit at Rozália mine highlights the importance of hydrothermal activity during the early stage of caldera collapse. Caldera subsidence established new, convective, fluid-flow paths along marginal caldera faults, which acted as infiltration zones. Major metal precipitation occurred within subhorizontal structures that formed as the result of a collapse-related stress field. A shallow, differentiated magma chamber at the base of the volcano was the likely source of heat and magmatic components for the mineralizing fluids.Editorial handling: S. Nicolescu 相似文献
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V. I. Mal’kovsky A. A. Pek A. P. Aleshin V. I. Velichkin 《Geology of Ore Deposits》2008,50(3):192-198
The hydrothermal Mo-U deposits of the Strel’tsovka ore field, unique in reserves, are localized in the Late Mesozoic caldera of the same name. The consideration of geochemical processes that controlled uranium transfer by ore-bearing fluids and its precipitation in orebodies has shown that a nonstationary temperature distribution could have exerted a substantial effect on ore formation. The temperature field in the Strel’tsovka caldera, which was caused by a shallow-seated magma chamber that existed beneath the caldera by the onset of the ore stage, was simulated by mathematical modeling. A one-dimensional nonstationary model of conductive heat transfer taking into account the latent heat of magmatic melt crystallization was used. The problem was solved with the finite difference method. It has been established that, at optimal parameters of the model, the magma chamber would have completely crystallized in 56 ka; the maximum estimate is 133 ka. Three million years after emplacement of the granitic intrusion, the related thermal anomaly in the upper crust should have disappeared. The results obtained indicate that granitic melt of this chamber could not have been a source of uranium-bearing solutions that formed deposits 5 Ma after the cessation of magmatic activity. 相似文献
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《International Geology Review》2012,54(2):246-262
AbstractThe Cenozoic stratigraphy of the southern Guanajuato Mining District (GMD) was established 40 years ago. The existence of a caldera structure that produced the Cenozoic volcanic cover was postulated and the world-class silver ore deposit of the Oligocene age has been closely related to magmatism. In this context, we present a new geological map of the southern GMD, U–Pb and Ar–Ar ages of the volcanic units, and structural data for the Cenozoic faults. Our results document that the volcanic centre was active between ca. 33.5 Ma and ca. 31.3 Ma, coeval with NW–SE normal faulting. We propose that the Bufa, Calderones, and Cedro formations are stratigraphic units directly related to the volcanic centre. Although the younger Chichíndaro Rhyolite scarcely crops out within the study area, it appears to be more extensive outside of the study area, forming part of the rhyolitic volcanism of the Mesa Central of Mexico. In the study area, the Chichíndaro Rhyolite buries major faults, demonstrating that it was emplaced after the peak of faulting. The two main structures are the El Cubo and Veta Madre grabens; also there are several faulted and brecciated zones where silver–gold mineralization was emplaced. The extension direction changed from NE to NW producing normal faulting, reactivating older structures and allowing dike intrusion. The extensional phase continued to be active throughout the Oligocene. The age of the volcanic event and a new K–Ar age of the Veta Madre vein of 29.8 ± 0.8 Ma (K–Ar in adularia) indicate that the hydrothermal event began immediately after the emplacement of the Cedro Formation. The emplacement of the Chichíndaro Rhyolite allowed hydrothermal activity to be active for two million years or more. 相似文献
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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
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Pillow lavas in Bompoka island of the Andaman–Nicobar islands, forming a part of Sunda–Burmese forearc, are composed of plagioclase and clinopyroxene microphenocrysts in a fine-grained ferruginous groundmass along with glass. They are also characterized by several quench plagioclase and clinopyroxene morphologies. Zr/TiO2 versus Nb/Y relationship of these pillow lavas show that these are tholeiitic basalts in composition. These basalts have low MgO (5.19–6.12 wt%), Ni (84–118 ppm), and Cr (144–175 ppm) abundance and high FeO(T)/MgO (1.71–1.92) ratios, reflecting their fractionated nature. In Th/Yb versus Nb/Yb and Ti/Yb versus Nb/Yb binary diagrams, they show N-MORB affinity. However, La/Nb–Y and Ce/Nb–Th/Nb relationships along with a slight LREE depleted (LaN/YbN = 0.75–0.82) pattern and high Ba/Zr (0.28–0.40) ratios and LILE (K, Rb, Ba, Sr and Th) enrichment relative to N-MORB, suggest their back-arc basin basalt affinity. It is inferred that these pillow basalts have been derived from a metasomatised N-MORB-like mantle source in a trench-distal (wider) back-arc basin, probably near the leading edge of the Eurasian continent during Early to Late Cretaceous times, prior to the currently active Andaman–Java subduction system. 相似文献
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Sequence Stratigraphy of the Permian--Triassia Boundary Section of Changxing, Zhejiang, Southern China 总被引：1，自引：0，他引：1
Zhang Kexin Tong Jinnan Yin Hongfu Wu Shunbao China University of Geosciences Wuhan Hubei 《《地质学报》英文版》1997,71(1):90-103
Three third-order sequences and about one hundred high-frequency cycles or Milankovitchcycles within the Late Permian Changxingian to Early Triassic Griesbachian are identified in theMeishan Section of Changxing, Zhejiang Province, southern China, the candidate stratotype sec-tion of the global Permo-Triassic boundary, based on a detailed study of the biological,ecological and high-resolution allochthonous cyclic events, microfacies and depositional systems.Furthermore, the stacking pattern of the depositional systems across various Changxingian andGriesbachian sedimentary facies of the Lower Yangtze and the sequence stratigraphic frameworkare outlined with the Meishan section as the principal section. In this paper the habitat types offossil biota are applied to semiquantitative palaeobathymetry and the study of relative sea levelchanges. 相似文献
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DING Xiaozhong GUO Xianpu PENG Yang JI Yunlong WANG Yineng Institute of Geology Chinese Academy of Geological Sciences Beijing China University of Geosciences Beijing Northwestern Bureau of Petroleum Geology SINOPEC Urumqi 《Continental Dynamics》2001,(2)
1. IntroductionThe Tarim basin, one of the most developed and important areas of marine Cretaceous-Tertiary in China except for south Tibet, is very rich in oil and gas, such as Kekeya oilfield in southwestern Tarim and Kela2 gas field in northeastern Tarim. Because of the expansion, subduction of the oceanic crust of the Tethys and the collision between the India plate and the Eurasia plate during the Cretaceous-Tertiary, the Tethys transgressed into the Tarim basin from west to east fr… 相似文献
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In terms of major element, trace element and REE geochemical characteristics ofvolcanic rocks in the area studied and by making use of the TiO2-K2O-P2O5,The-Hf-Ta and Zr-Nb-Y trianglar diagrams and the environmental discrimination diagrams of incompatible ele-ment distribution pattems,the authors have drawn some conclusions that are different from those by previous workers.It is concluded that volcanic rocks in the Laochang Ag polymetallic deposit at Lancang,Yunnan belong to continental within-plate alkali basalts, and that their geotectonic setting seems to be at the northeastern margin of East Gondwana Land. 相似文献
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O. S. Yakovleva I. V. Pekov L. Horváth I. A. Bryzgalov V. O. Yapaskurt E. V. Guseva 《Geology of Ore Deposits》2010,52(8):725-735
High-alumina fenites in the Mont Saint-Hilaire alkaline complex, Québec, Canada, form bodies at the contact of peralkaline
nepheline syenite. Fenites are subdivided into four types: corundum-spessartine-biotite-feldspar, muscovite-corundum-hercynite-biotite-feldspar,
carbonated muscovite-biotite-hercynite-feldspar, and spessartine-hercynite-feldspar. Accessory minerals of the ilmenite-pyrophanite
series, columbites, zircon, thorite, pyrrhotite, Fe, Mn, Mg, Ca, Ba, and REE carbonates, uedaite-(Ce), etc. are identified.
Three stages are suggested in the formation of these rocks. In mineralogy and geochemistry, the Mont Saint-Hilaire high-alumina
fenites are similar to Al-rich fenites replacing xenoliths in the Khibiny alkaline complex, Russia. In both cases, fenites
are related to peralkaline rocks and replace high-alumina protoliths: granite at Mont Saint-Hilaire and metapelites in the
Khibiny Mountains. These fenites are regarded as a specific type of fenites with rock-forming Mg-depleted hercynite. 相似文献
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The Tongfeng mercury zone is an important producer of mercury in China.The underlying Lower Cambrian black rock series is strongly depleted in mercury and is thought to be the major source bed for mercury mineralization .The Catian deposit ,as the representative of the zone, was formed at low temperature,which is characterized by a meteoric chlorine-rich and sulfur-poor ore-forming solution of high salinity.A geochemical genetic model of buried hydrothermal explosion is proposed. 相似文献