Hydrothermal fluid evolution and structural control of the Guarim gold mineralisation, Tapajós Province, Amazonian Craton, Brazil     

Evandro Luiz Klein  Reginaldo Alves dos Santos  Kazuo Fuzikawa  Rômulo Simões Angélica 《Mineralium Deposita》2001,36(2):149-164

Fluid inclusion and structural studies were carried out at the Guarim gold deposit in the Palaeoproterozoic Tapajós province of the Amazonian craton. Guarim is a fault-hosted gold deposit cutting basement granitoids. It consists of a quartz vein, which is massive in its inner portions, grading laterally either to a massive or to cavity-bearing quartz vein associated with hydrothermal breccias. The wallrock alteration comprises chlorite, carbonate, white mica and sulphide minerals, with free gold occurring within quartz grains and spatially associated with sulphide mineral grains. Petrographic, microthermometric and Laser Raman investigations recognised CO₂-rich, mixed H₂O–CO₂, and H₂O fluid inclusions. The coexisting CO₂ and H₂O–CO₂ inclusions were interpreted as primary immiscible fluids that formed the gold-bearing vein. The H₂O inclusions were considered a product of later infiltration of fluids unrelated to the mineralising episode. The mineralising fluid has CO₂ ranging typically from 5–10 mol%, contains traces of N₂, has salinities of ∼5 wt% NaCl equiv., and densities varying between 0.85 and 0.95 g/cm³. The P–T estimations bracket gold deposition between 270–320 °C and 0.86–2.9 kb; ƒ_O2–ƒ_S2–pH estimates suggest a reduced, near-neutral character for the fluid. Variations in the physico-chemical properties, as demonstrated by the fluid inclusion study, resulted from a combination of fluid immiscibility and pressure fluctuation. This interpretation, combined with textural and structural evidence, suggests the emplacement of the mineralised vein in an active fault and at a rather shallow level (4–7 km). The geological and structural setting, deposit-scale textures and structures, wallrock alteration and physico-chemical fluid properties are compatible with those of epizonal to mesozonal orogenic lode gold deposits. Received: 3 March 2000 / Accepted: 21 October 2000  相似文献   

Construction of underground caverns for petroleum storage in orogenic areas: Geological stability     

Kazuo Hoshino   《Engineering Geology》1993,35(3-4):199-205

Japan is located at the boundary between three continental and oceanic plates, and there is a great variety and complexity of geological features as a result of tectonic activities. The possibility of excavating large underground tunnels in the seemingly “fragile” rocks in orogenic areas was considered as a national project for the underground storage of petroleum. One hundred and seventy sites in 57 areas were selected based on a comprehensive survey over the whole country. After a successful experiment with a test tunnel, 112 m long and 250 m² in cross-section area, excavated in Cretaceous granite, three sites in granites and pyroclastic rocks were selected for construction. The largest of these storage tunnels is 550 m in length and20 × 30 m in cross-section.

Before construction, a detailed survey of the subsurface geology was carried out, taking into consideration the structural geology, the mechanical properties of the rocks and the hydrogeology. It was concluded that even in active orogenic areas, there are many suitable sites for large underground excavations and that these can be detected by detailed, planned surveys.  相似文献   

MECHANISM OF ARMORING PHENOMENA     

Shinji Egathira  Kazuo Ashida Associate Professor  Disaster Prevention Research institute  Kyoto University. Professor  Disaster Prevention Research Institute  Kyoto University. 《国际泥沙研究》1990,(1)

I. INTRODUCTIONArmor coats, which are comPOSed of particles coarser than those of the under layers, are usually foundon the bed surfaces of mountain streams or gravel bed rivers. A large number of P8pers have been publishedon armor coats. Most of them emphasize that the selective entrainment or transportation plays an imPOrtantrole on the armoring processes.Some recent studies indicate that the difficulty arises in describing the propagation of armor coats interms of selective entrainm…  相似文献   

Geochemical significance of lipids and lipid-derived substructures interlaced in kerogen     

Kazuo Fukushima  Ryoshi Ishiwatari 《Organic Geochemistry》1988,12(6)

Young kerogens isolated from seven freshwater lakes, six river mouths and four marine surface sediments were subjected to pyrolysis in vacuo. Their pyrolysates were trapped and separated subsequently for determination of hydrocarbons, fatty acids and alcohols. The abundances, carbon number distributions of long (C₁₂) polymethylene chain lipid compounds and relative abundances of pristenes are proposed as possible indices applicable to discrimination between young kerogens from freshwater lacustrine and marine sediments. Some oil-shale kerogens of Eocene and Permian age were pyrolyzed in the same way, where the chain-length distributions of the pyrolysis products showed similar trends as those observed for the pyrolysis of young kerogens.  相似文献   

The Japan Trench and its juncture with the Kuril Trench: cruise results of the Kaiko project, Leg 3     

Jean-Paul Cadet  Kazuo Kobayashi  Jean Aubouin  Jacques Boulgue  Christine Deplus  Jacques Dubois  Roland von Huene  Laurent Jolivet  Toshihiko Kanazawa  Junzo Kasahara  Kinichiro Koizumi  Serge Lallemand  Yasuo Nakamura  Guy Pautot  Kiyoshi Suyehiro  Shin Tani  Hidekazu Tokuyama  Toshitsugu Yamazaki 《Earth and Planetary Science Letters》1987,83(1-4)

This paper presents the results of a detailed survey combining Seabeam mapping, gravity and geomagnetic measurements as well as single-channel seismic reflection observations in the Japan Trench and the juncture with the Kuril Trench during the French-Japanese Kaiko project (northern sector of the Leg 3) on the R/V “Jean Charcot”. The main data acquired during the cruise, such as the Seabeam maps, magnetic anomalies pattern, and preliminary interpretations are discussed. These new data cover an area of 18,000 km² and provide for the first time a detailed three-dimensional image of the Japan Trench. Combined with the previous results, the data indicate new structural interpretations. A comparative study of Seabeam morphology, single-channel and reprocessed multichannel records lead to the conclusion that along the northern Japan Trench there is little evidence of accretion but, instead, a tectonic erosion of the overriding plate. The tectonic pattern on the oceanic side of the trench is controlled by the creation of new normal faults parallel to the Japan Trench axis, which is a direct consequence of the downward flexure of the Pacific plate. In addition to these new faults, ancient normal faults trending parallel to the N65° oceanic magnetic anomalies and oblique to the Japan trench axis are reactivated, so that two directions of normal faulting are observed seaward of the Japan Trench. Only one direction of faulting is observed seaward of the Kuril Trench because of the parallelism between the trench axis and the magnetic anomalies. The convergent front of the Kuril Trench is offset left-laterally by 20 km relative to those of the Japan Trench. This transform fault and the lower slope of the southernmost Kuril Trench are represented by very steep scarps more than 2 km high. Slightly south of the juncture, the Erimo Seamount riding on the Pacific plate, is now entering the subduction zone. It has been preceded by at least another seamount as revealed by magnetic anomalies across the landward slope of the trench. Deeper future studies will be necessary to discriminate between the two following hypothesis about the origin of the curvature between both trenches: Is it due to the collision of an already subducted chain of seamounts? or does it correspond to one of the failure lines of the America/Eurasia plate boundary?  相似文献   

On the sensitivity characteristics of Lacoste & Romberg gravimeter (model G)     

Ichiro Nakagawa  Sinzi Nakai  Ryūichi Shichi  Hirokazu Tajima  Sadakatu Izutuya  Yoshiteru Kono  Toshihiro Higashi  Hiromi Fujimoto  Makoto Murakami  Kazuo Tajima  Minoru Funaki 《Journal of Geodesy》1985,59(1):55-67

  相似文献   

Geodetic observations of ice flow velocities over the southern part of subglacial Lake Vostok, Antarctica, and their glaciological implications   总被引：1，自引：0，他引：1  

Jens Wendt  Reinhard Dietrich  Mathias Fritsche  Anja Wendt  Alexander Yuskevich  rey Kokhanov  Anton Senatorov  Valery Lukin  Kazuo Shibuya  Koichiro Doi 《Geophysical Journal International》2006,166(3):991-998

In the austral summer seasons 2001/02 and 2002/03, Global Positioning System (GPS) data were collected in the vicinity of Vostok Station to determine ice flow velocities over Lake Vostok. Ten GPS sites are located within a radius of 30 km around Vostok Station on floating ice as well as on grounded ice to the east and to the west of the lake. Additionally, a local deformation network around the ice core drilling site 5G-1 was installed.
The derived ice flow velocity for Vostok Station is  2.00 m a⁻¹± 0.01 m a⁻¹  . Along the flowline of Vostok Station an extension rate of about 10⁻⁵ a⁻¹ (equivalent to 1 cm km⁻¹ a⁻¹) was determined. This significant velocity gradient results in a new estimate of 28 700 years for the transit time of an ice particle along the Vostok flowline from the bedrock ridge in the southwest of the lake to the eastern shoreline. With these lower velocities compared to earlier studies and, hence, larger transit times the basal accretion rate is estimated to be 4 mm a⁻¹ along a portion of the Vostok flowline. An assessment of the local accretion rate at Vostok Station using the observed geodetic quantities yields an accretion rate in the same order of magnitude. Furthermore, the comparison of our geodetic observations with results inferred from ice-penetrating radar data indicates that the ice flow may not have changed significantly for several thousand years.  相似文献   

Numerical analysis of nonlinear soil–pile group interaction under lateral loads     

Hossein Tahghighi  Kazuo Konagai   《Soil Dynamics and Earthquake Engineering》2007,27(5):463-474

A nonlinear p–y element was provided which can simply model the behavior of a pile group foundation subjected to lateral loading. Its elasto-plastic side soil is expressed as a Winkler-type distributed model. Despite the simplification involved in modeling such a complex phenomenon the proposed nonlinear soil model can reproduce the system behavior as computed by more rigorous 3D finite element methods. The numerical results are also compared with those from available physical model data to confirm that our simulations can predict the behavior of pile groups with good accuracy.  相似文献   

On unbiased backtransform of lognormal kriging estimates   总被引：4，自引：0，他引：4  

Jorge Kazuo Yamamoto 《Computational Geosciences》2007,11(3):219-234

Lognormal kriging is an estimation technique that was devised for handling highly skewed data distributions. This technique takes advantage of a logarithmic transformation that reduces the data variance. However, backtransformed lognormal kriging estimates are biased because the nonbias term is totally dependent on a semivariogram model. This paper proposes a new approach for backtransforming lognormal kriging estimates that not only presents none of the problems reported in the literature but also reproduces the sample histogram and, consequently, the sample mean.  相似文献   

Mass balance and sources of mercury in Tokyo Bay   总被引：1，自引：0，他引：1  

Masahiro Sakata  Kohji Marumoto  Masahiro Narukawa  Kazuo Asakura 《Journal of Oceanography》2006,62(6):767-775

The mass balance and sources of mercury in Tokyo Bay were investigated on the basis of observations from December 2003 to January 2005. Estimated input terms included river discharge (70 kg yr⁻¹) and atmospheric deposition (37 kg yr⁻¹), and output terms were evasion (49 kg yr⁻¹), export (13 kg yr⁻¹) and sedimentation (495 kg yr⁻¹). Thus, the outputs (557 kg yr⁻¹) considerably exceeded the inputs (107 kg yr⁻¹). In addition, the imbalance between the inputs and outputs of mercury was much larger than that of other trace metals (Cd, Cr, Cu, Pb and Zn), which suggests that there are other major inputs of mercury to Tokyo Bay. The mercury concentrations in rivers correlated significantly with the concentrations of Al and Fe, major components of soil. In Japan, large amounts of organomercurous fungicides (about 2500 tons as Hg) were used extensively in fields in the past, and most of the mercury was retained in the soil. In this study, the mercury concentration in rivers was measured primarily in ordinary runoff. These observations lead to the hypothesis that field soil discharged into stormwater runoff is a major source of mercury in Tokyo Bay. As a preliminary approach to validating this hypothesis, we measured the concentrations of mercury and other trace metals in river water during a typhoon. The mercury concentrations in stormwater runoff increased to 16–50 times the mean value in ordinary runoff, which is much higher than the increases for other metals. This tends to support the hypothesis.  相似文献