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1.
The subsurface temperature field was studied on a set of 46 borehole logs measured in the vicinity of uranium deposits in the Bohemian Cretaceous Basin. Vertical variations of the steady state temperature and the temperature gradient are governed by thermal conductivity which strongly varies in dependence on lithology. Large departures from undisturbed temperature detected in many holes are associated with uranium mining. A positive anomaly is observed in leaching fields where large amounts of acid are injected into the uranium-bearing Cenomanian. A negative anomaly is linked to the operation of hydraulic barriers which enclose the mining area and helps to contain pollution by pumping clean water into the Cenomanian aquifer. The spatial distribution of the observed temperature anomalies helps to map the migration of the fluids used in both processes. The temperature disturbance is propagated from the Cenomanian aquifer up through overlying impermeable sediments. The good fit of transient conductive models to the measured temperatures rules out heat advection and hence upward water flow towards and contamination of the upper Middle Turonian aquifer in the vicinity of the holes studied.  相似文献   

2.
Hydrothermal sulfide-sulfate deposits were sampled from eight active and inactive vent sites along the East Pacific Rise at 21°N during the RISE expedition of April, 1979. The mineralogy of the samples has been determined by X-ray diffractometry, scanning electron microscopy, and X-ray energy dispersive analysis. Mounds of Zn, Fe, and Cu sulfides, dominated by sphalerite, pyrite, and lesser chalcopyrite, are topped by inactive and active chimneys, spouting fluids ≤350°C. The outer zones of active chimneys bear abundant anhydrite precipitated from heated ambient seawater, in addition to hydrothermal pyrite and sphalerite. Mg-hydroxysulfate-hydrate, a phase identified in seawater heating experiments, but previously not observed in nature, is intimately intergrown with anhydrite. Hottest chimneys contain massive chalcopyrite±bornite in their interior zones and belch fluids blackened by a presumably non-equilibrium assemblage of pyrrhotite plus minor sphalerite and pyrite. The early, outer walls of chimneys form from sulfates and the sulfide minerals in black smoke, but metastable pyrrhotite in outer zones is rapidly recrystallized to pyrite or marcasite. Reduction in the permeability of the outer walls permits a high-temperature (>～250°C), low-pH environment within chimneys that enhances precipitation of Cu-Fe sulfides in the central zones. Cooler, worm-covered chimneys emit white fluids bearing particulates of amorphous silica, barite, and pyrite. Amorphous silica and barite are also widely associated with fossilized worm-tubes. Two inactive chimneys are filled with sphalerite, wurtzite, sulfur, pyrite, and marcasite. Anhydrite has been dissolved from these dead chimneys, and the sulfate assemblage is dominated by barite and alteration products such as jarosite and natrojarosite. Silicates other than amorphous silica are not abundant in these deposits, although talc forms in hot chimneys from seawater Mg and hydrothermal silica, and nontronite is found in sediments on the crest of the East Pacific Rise. Other accessory phases identified include copper-rich sulfides such as cubanite, chalcocite, covellite, and digenite; galena; Fe-oxyhydroxides, including goethite; and gypsum. Chimney debris accumulates to form basal mounds, and the mineralogical differences between mounds and chimneys are attributable to weathering of mounds. Mn-oxyhydroxides form crusts within a few meters of the vents, but are not coprecipitating with the sulfide/sulfate minerals.  相似文献   

3.
Since its development some thirty years ago, the airborne electromagnetic (AEM) method has been primarily used as a tool for mineral prospecting. However, advanced AEM systems are capable of other tasks, such as geological mapping and groundwater exploration. Excellent correlation between maps of apparent conductivity and geological maps was observed in several regions of Brazil where AEM surveys were performed. The degree of correlation seems to depend on the local climate. In humid and subhumid tropical regions, a weathered layer develops whose thickness and conductivity depend upon bedrock lithology. Therefore certain lithological types can be recognized from their conductivity signature; e.g., granites and Precambrian coarse clastic rocks are resistive, metavolcanic (particularly mafic) and volcanic rocks are conductive, Phanerozoic sediments are generally highly conductive. Two geophysical surveys are analyzed in the paper. The first was conducted with the time-domain, towed-bird AEM system in the Itapicuru greenstone belt in the state of Bahia. The apparent conductivity map correlated better with the local lithology than the magnetic map. Results of the AEM survey were successfully used to improve the regional geological map. A helicopter EM system was used in the second survey, which covered a portion of the Precambrian shield of Rio Grande do Sul. Also in this region ground checks confirmed the usefulness of conductivity surveys in geological mapping. The technique outlined in the paper holds great promise for countries of humid tropical climate, where few outcrops exist and access is often difficult. The tests performed in Brazil indicate that by executing AEM/aeromagnetic surveys during initial stages of mapping and exploration programs, time and expenditure required for geological field work can be considerably reduced. The resulting geological maps are more accurate and the inventory of mineral occurrences becomes more complete.  相似文献   

4.
Chemical interaction of thermal fluids with reservoir rock in the Roosevelt Hot Springs thermal area, Utah, has resulted in the development of characteristic trace-element dispersion patterns. Multielement analyses of surface rock samples, soil samples and drill cuttings from deep exploration wells provide a three-dimensional perspective of chemical redistribution within this structurally-controlled hot-water geothermal system.Five distinctive elemental suites of chemical enrichment are recognized, each characteristic of a particular combination of physical and chemical conditions within the geothermal system. These are: (1) concentrations of As, Sb, Be, and Hg associated with siliceous material at locations of liquid discharge, fluid mixing or boiling; (2) concentrations of Mn, Ba, W, Be, Cu, Co, As, Sb and Hg in manganese and iron oxide deposits; (3) high concentrations of Hg in argillized rock near fumaroles and lower concentrations in a broad diffuse halo surrounding the thermal center; (4) concentrations of As in sulfides and Li in silicate alteration minerals immediately surrounding high-temperature fluid flow-controlling fractures; (5) deposits of CaCO3 at depth where flashing of brine to steam has occurred due to pressure release. The geochemical enrichments are not, in general, widespread, pervasively developed zones of regular form and dimension as are typical in many ore-forming hydrothermal systems.As the geothermal system develops, changes and eventually declines through time, the chemical deposits are developed, remobilized or superimposed upon each other, thus preserving within the rocks a record of the history of the geothermal system. Recognition of trace-element distribution patterns during the exploration of a geothermal system may aid definition of the present geometry and interpretation of the history of the system.  相似文献   

5.
The Volcanic Sedimentary Complex (VSC) of the Iberian Pyrite Belt (IPB) in southern Portugal and Spain, comprises an Upper Devonian to Lower Carboniferous submarine succession with a variety of felsic volcanic lithofacies. The architecture of the felsic volcanic centres includes felsic lavas/domes, pyroclastic units, intrusions and minor mafic units that define lava–cryptodome–pumice cone volcanoes. The diversity of volcanic lithofacies recognized in different areas of the IPB mainly reflects variations in proximity to source, but also differences in the eruption style. The IPB volcanoes are intrabasinal, range in length from 2 km to > 8 km and their thickest sections vary from ∼ 400 m to > 800 m. These volcanoes are dominated by felsic lavas/domes that occur at several stratigraphic positions within the volcanic centre, however the pyroclastic units are also abundant and are spatially related to the lavas/domes. The intrusions are minor, and define cryptodomes and partly-extrusive cryptodomes. The hydrothermal systems that formed the Neves Corvo and Lousal massive sulfide ore deposits are associated with effusive units of felsic volcanic centres. At Neves Corvo, the massive sulfide orebodies are associated to rhyolitic lavas that overlie relatively thick fiamme-rich pyroclastic unit. In several other locations within the belt, pyroclastic units contain sulfide clasts that may have been derived from yet to be discovered coeval massive sulfide deposits at or below the sea floor, which enhances the exploration potential of these pyroclastic units and demonstrates the need for volcanic facies analysis in exploration.  相似文献   

6.
本文利用藏北地区三口天然气水合物钻孔测温数据,在分析样品热导率测试结果基础上,计算了藏北地区的热流值.对于样品热导率值,首先根据样品孔隙度对实验室测试结果进行了饱水校正,计算热流时采用的是对应井段的岩石热导率饱水校正值的厚度加权平均值.地温梯度以三口钻孔48 h的测温数据为基础,回归三口井的地温梯度,计算时去除了浅部受地表温度和冻土带对温度影响的数值.A钻孔地温梯度分为200~438 m和438~882 m两段回归,分段热流的加权平均值作为钻孔热流值,计算结果为42.7 mW·m-2; B钻孔和C钻孔回归地温梯度时未分段,热流计算结果分别为58.3 mW·m-2、70 mW·m-2.综合分析认为,岩石圈断裂、地幔上涌、碰撞造山过程中的剪切生热等因素可能造成了班公湖—怒江缝合带以南热流值较高,而北部羌塘地块热流值相对较低.  相似文献   

7.
We have studied the scaling behavior of compressional-wave velocity and density logs from an exploration borehole that extends down to about 700 m depth in the Brunswick No. 6 mining area, Bathurst Mining Camp, Canada. Using statistical methods, vertical and horizontal scale lengths of heterogeneity were estimated. Vertical scale length estimates from the velocity, density and calculated acoustic impedance are 14 m, 33 m, and about 20 m, respectively. Although the estimated scale length for the acoustic impedance implies a weak scattering environment, elastic finite difference modeling of seismic wave propagation in 2D heterogeneous media demonstrates that even this weak scattering medium can mask seismic signals from small, but yet economically feasible, massive sulfide deposits. Further analysis of the synthetic seismic data suggests that in the presence of heterogeneity, lenticular-shaped targets may only exhibit incomplete diffraction signals whereby the down-dip tails of these diffractions are mainly visible on the stacked sections. Therefore, identification of orebody generated diffractions is much easier on the unmigrated stacked sections than on migrated stacked sections. The numerical seismic modeling in 2D heterogeneous media indicates that in the presence of large horizontal, but small vertical scale lengths (structural anisotropy), identification of massive sulfide deposits is possible, but their delineation at depth requires detailed velocity modeling and processing algorithms which can handle the anisotropy.  相似文献   

8.
Seafloor massive sulfide (SMS) deposits are generated by high-temperature hydrothermal systems. Their precious resources have attracted global interest. A number of investigations with controlled-source electromagnetic (CSEM) methods have been implemented in recent years. There are three major problems with SMS surveying using EM methods. First, SMS imaging techniques for hydrothermal systems have a limited range. Simulations and applications have validated only simple layered models. Second, their inversion efficiencies must be improved further. Laterally constrained inversions and spatially constrained inversions are usually used to map geological structures. However, choosing their suitable weighting parameters is inefficient. Third, the effects of induced polarization (IP) on ore deposits are not considered in such inversions. A non-polarizable model is unable to accurately depict a polarizable model. To resolve these problems, an advanced strategy is used to improve the efficiency of the pseudo-3D inversion process. The proposed imaging method has the ability to map complex 3D geoelectrical structures, and therefore, it can both obtain information regarding surface ore deposits and distinguish between active and inactive hydrothermal systems. However, this method can also be used to depict the distributions of alteration zones and buried deposits. Furthermore, the influences of IP on the inversion are discussed with respect to the Cole- Cole model, and it is shown that the effects of IP on polarizable deposits cannot be ignored during the inversion.  相似文献   

9.
Electromagnetic (EM) logging provides an efficient method for high-resolution, vertical delineation of electrically conductive contamination in glacial sand-and-gravel aquifers. LM. gamma, and lithologic logs and specific conductance data from sand-and-gravel aquifers at five sites in the northeastern United States were analyzed to define the relation of KM conductivity to aquifer lithology and water quality. Municipal waste disposal, septic waste discharge, or highway deicing salt application at these sites has caused contaminant plumes in which the dissolved solids concentration and specific conductance of ground water exceed background levels by as much as 10 to 20 limes.
The major hydrogeologic factors that affected KM log response at the five sites were the dissolved solids concentration of the ground water and the silt and clay content in the aquifer. KM conductivity of sand and gravel with uncontaminated water ranged from less than 5 to about 10 millisiemens per meter (mS/m); that of silt and clay zones ranged from about 15 to 45 mS/m: and that of the more highly contaminated zones in sand and gravel ranged from about 10 to more than 80 mS/m. Specific conductance of water samples from screened intervals in sand and gravel at selected monitoring well installations was significantly correlated with KM conductivity.
CM logging can be used in glacial sand-and-gravel aquifer investigations to (1) determine optimum depths for the placement of monitoring well screens: (2) provide a nearly continuous vertical profile of specific conductance to complement depth-specific water quality samples; and (3) identify temporal changes in water quality through sequential logging. Detailed lithologic or gamma logs, preferably both, need to be collected along with the F.M logs to define zones in which elevated EM conductivity is caused by the presence of sill and clay beds rather than contamination.  相似文献   

10.
Hydrothermal systems in regions of high relief may not have obvious thermal features indicative of their central upflow zone at depth. Investigation of such areas for geothermal energy production in the Philippines has, however, encountered relatively large ( > 10,000 m2) areas of volumetrically significant but diffuse, cold-gas emission and associated intense argillic alteration. These features are likely to be best developed above, or close to, hydrothermal upflow zones. The identification of such features is important for interpreting the hydrology of active geothermal systems in the course of exploration for power development, or when interpreting the paleohydrology of fossil geothermal systems which host epithermal mineral deposits. Such zones of argillic alteration are likely to be barren of precious metals or other elements (except mercury) which are commonly used as pathfinders for precious-metal deposits, but are indicative of subsurface processes significant in ore genesis.It is proposed that the term “kaipohan” be used for such features. Their existence depends on the presence of either a low-permeability geologic formation or where a suitable relationship exists between the hydrology of the deep geothermal reservoir and that of the shallow groundwater system. Such a situation occurs in steep terrain, where much of the area supplying meteoric recharge to the geothermal system is at a lower elevation than the area overlying the centre of the system, and where there is a high annual rainfall. These conditions are typical of andesitic stratovolcanoes in tropical or subtropical island arcs.  相似文献   

11.
Characterization of the hydraulic properties of fractures in chalk   总被引：3，自引：0，他引：3  
Nativ R  Adar E  Assaf L  Nygaard E 《Ground water》2003,41(4):532-543
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12.
The mineralogy of five groups of hydrothermal chimneys from the East Pacific Rise has been examined. Three of the chimneys, where the exit temperature of the hydrothermal fluids was close to 350°C, are rich in copper sulfides. Exit temperatures from the other two chimneys were less than 300°C; in these, the chimney walls are rich in zinc sulfide. The major sulfides in the chimneys as a whole were found to be wurtzite, chalcopyrite, pyrite, and cubanite. Anhydrite is always the dominant sulfate, and is present in all the deposits. Silicates are also present but in relatively minor amounts. There are considerable differences in the mineralogy of sulfides, sulfates, and silicates between the active and inactive vent deposits.The isotopic composition of sulfur in anhydrites from active vents is close to that of seawater; the δ34S values of the sulfides range from +1.3 to +4.1‰. The isotopic composition of sulfur in the anhydrites is consistent with a derivation predominantly from seawater sulfate. The sulfur in the sulfides must have a complex origin including contributions from both sulfur in basalts and sulfide produced by reduction of sulfate in seawater. Mixing of H2S-dominated hydrothermal fluids with cold seawater near the seafloor resulted in the precipitation of non-equilibrium assemblages of sulfides and sulfates.  相似文献   

13.
In fractured rocks, well temperature logs often exhibit abrupt temperature changes over a small distance, typically surging or dropping several degrees over several tens of meters. The abrupt temperature changes usually occur in localized fracture zones or small faults. Away from these zones, temperature quickly restores itself to the background linear conductive profile. A theoretical model is presented herein to interpret the pattern of such abrupt temperature changes. I illustrate that this type of temperature profile originates from a different physical process than the physical processes found in some other typical temperature patterns in large scales. I also demonstrate that, using the field data, the theoretical model can be effectively used to estimate fluid flow velocity in fracture zones or local faults. Using the temperature profiles from two boreholes, fluid flow velocity in fracture zones is estimated to be as high as 1.1×10−6 m/s. Although fracture flow is a highly localized feature, it can reach three orders of magnitude higher than fluid flow in the hosting rock matrices.  相似文献   

14.
塔河油田碳酸盐岩缝洞型储层的测井识别与评价方法研究   总被引：12，自引：4，他引：12  
塔河油田奥陶系以碳酸盐岩为主，油气的主要储渗空间为裂缝和溶蚀孔洞，具有很强的非均质性．本文利用常规及成像测井资料，对碳酸盐岩缝洞型储层的识别与评价方法进行研究．为了综合各种测井方法识别裂缝，建立了综合裂缝概率模型，计算综合裂缝概率指示裂缝的发育程度．利用地层微电阻率扫描成像测井资料进行裂缝和溶蚀孔洞的定性、定量解释．定量计算的裂缝参数为：裂缝密度、裂缝长度、裂缝平均宽度、平均水动力宽度、裂缝视孔隙度；定量计算的溶蚀孔洞参数有：面孔率、孔洞密度．根据缝洞型储层孔隙空间类型及其中子孔隙度、补偿密度、声波、双侧向电阻率的测井响应物性特征，建立缝洞型碳酸盐岩储层复杂孔隙介质解释模型，用于确定裂缝、溶蚀孔洞孔隙度和评价储层．  相似文献   

15.
A suite of electrical, radiation, and mechanical borehole probes were run in a 76-mm-diameter borehole drilled to a slant depth of 380 m in leptite and granite. The hole is located in Precambrian bedrock in central Sweden where a site is dedicated to in-situ experiments pertaining to the disposal of radioactive wastes. The challenge to borehole logging methods for such site investigations is to resolve geological features and fluid flow parameters in geological sites which are initially chosen for their homogeneity, low porosity, and minimal fracturing. The Stripa borehole is characterized by high electrical resistivity values in the 20–100 kΩm range, by acoustic velocities around 5800 m s-1 (which is close to laboratory values on intact specimens), and by total porosity of around one volume percent. In this context, probe resolution was adequate to produce interpretable information on almost all of the logs. Two principal rock types were encountered in the hole: granite, of quartz monzonitic composition, and leptite. The granite and leptite intercepts are subdivided into units characterized by mafic mineral content, sulfide mineral content, and electrical and radiation properties. Iron-rich zones in the leptite are highly anomalous on the gamma-gamma and neutron logs; thin mafic zones in the granite can also be distinguished. Occurrences of a few percent pyrite are detected by the electrical, gamma-gamma, and neutron logs. Although overall porosity is quite low throughout the hole, analysis of the resistivity and neutron logs indicates the porosity increases by a few volume percent at fracture zones. The differential resistance and caliper probes detect borehole diameter roughness of less than 1 mm, helping to confirm acoustic waveform anomalies which are indicative of fracture zones. Compres-sional wave transit time and shear-wave interference patterns usually occur coincident with open fractures observed in core, the correlation being especially good at major fracture zones.  相似文献   

16.
Lead isotope data of sulfides and host volcanic rocks from the Bukit Botol and Bukit Ketaya deposits, the two representative deposits of the Tasik Chini volcanic‐hosted massive sulfide (VHMS) deposit, Central Belt of Peninsular Malaysia, are reported. Lead isotope compositions of the associated sulfide minerals and volcanic rocks from the Bukit Botol deposit exhibit homogeneous and less radiogenic values (206Pb/204Pb showing a range of composition from 18.14 to 18.20, 207Pb/204Pb between 15.52 and 15.59 and 208Pb/204Pb from 37.96 to 38.35). Similarly, the Pb isotopic compositions of the host volcanic rocks from the Bukit Ketaya deposit yielded a narrow range to those of the sulfide samples (206Pb/204Pb from 18.04 to 18.20, 207Pb/204Pb between 15.43 and 15.57 and 208Pb/204Pb of 37.96 to 38.30). The uniform Pb‐isotope compositions of the sulfides in the ore horizon and the host volcanic rocks from both deposits suggest a derivation from a similar source reservoir and mineralization processes. In the framework of the tectonic model for the Central Belt of Peninsular Malaysia, both deposits display a range of lead isotopic compositions originated from mixing of bulk crust/juvenile arc and minor mantle sources, which are typical for VHMS deposits in an island arc–back arc setting.  相似文献   

17.
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18.
An integrated study using geophysical method in combination with pumping tests and geochemical method was carried out to delineate groundwater potential zones in Mian Channu area of Pakistan. Vertical electrical soundings (VES) using Schlumberger configuration with maximum current electrode spacing (AB/2 = 200 m) were conducted at 50 stations and 10 pumping tests at borehole sites were performed in close proximity to 10 of the VES stations. The aim of this study is to establish a correlation between the hydraulic parameters obtained from geophysical method and pumping tests so that the aquifer potential can be estimated from the geoelectrical surface measurements where no pumping tests exist. The aquifer parameters, namely, transmissivity and hydraulic conductivity were estimated from Dar Zarrouyk parameters by interpreting the layer parameters such as true resistivities and thicknesses. Geoelectrical succession of five‐layer strata (i.e., topsoil, clay, clay sand, sand, and sand gravel) with sand as a dominant lithology was found in the study area. Physicochemical parameters interpreted by World Health Organization and Food and Agriculture Organization were well correlated with the aquifer parameters obtained by geoelectrical method and pumping tests. The aquifer potential zones identified by modeled resistivity, Dar Zarrouk parameters, pumped aquifer parameters, and physicochemical parameters reveal that sand and gravel sand with high values of transmissivity and hydraulic conductivity are highly promising water bearing layers in northwest of the study area. Strong correlation between estimated and pumped aquifer parameters suggest that, in case of sparse well data, geophysical technique is useful to estimate the hydraulic potential of the aquifer with varying lithology.  相似文献   

19.
The Chinkuashih district at northern Taiwan hosts one of the largest Au deposits in the western Pacific gold province. Gold were precipitated from hydrothermal solutions as native gold or incorporated into sulfides at a temperature range of 200-350 °C. The sulfides in ore mines have 187Os/188Os ratios varying from 0.139 to 0.249. The positive 187Os/188Os-1/Os correlation is consistent with derivation from the hybrid fluids containing various proportions of mantle and crustal components. The crustal component was the meteoric water that had acquired its Sr and Os isotopic signatures from the local sedimentary formations and dacitic intrusions. The mantle component was the magmatic fluid segregated from the dacitic magma by fractional crystallization. Based on the 187Os/188Os-1/Os correlation, the hybrid fluids forming the Chinkuashih sulfides contained less than 30% magmatic fluid, except for one sulfide sample from Hsumei, which required >40% magmatic fluid. Compared to meteoric water, the magmatic fluid contained a higher Os content (130 times higher) and was enriched in Os relative to Sr with an Os/Sr ratio two orders higher than that of the crustal fluid. Consequently, the Os budget in the hybrid fluids was controlled by the magmatic fluid, although the meteoric water was volumetrically dominated. If gold and Os behave similarly in chemistry, the Chinkuashih gold deposits are of mantle origin and the area where sulfides with the greatest mantle Os signature may host undiscovered gold deposits. Finally, the 187Os/188Os ratios of sulfides show no relationship with the mineral assemblages of sulfides, implying that the sulfide mineral assemblages reflect local surfacial redox conditions rather than the chemical characteristics of parental fluids.  相似文献   

20.
Thermal models are developed and temperature-depth profiles computed to account for the development of sharply inverted metamorphic zonations and estimatedP-T conditions beneath deep-seated thrust faults, with particular reference to the metamorphism of the Pelona Schist-Vincent Thrust system of southern California.Models dependent only upon conductive redistribution of heat from an initially hot upper plate are inadequate to account for the observed temperature distributions and theP-T time constraints can only be satisfied if a total shear heating of 3 hfu or more occurs in the region of the thrusts. These heating rates are consistent with known rates of plate movement, shear stresses along major fault zones, and shear strengths of rocks.Petrological constraints indicate the likelihood of buffering of the maximum temperature attained by shear heating due to marked reduction of shear strengths of rocks upon increase of temperature and release of water during metamorphic dehydration reactions.These models may be of general applicability to inverted metamorphic zonations, notably those beneath obducted Newfoundland ophiolites, and are consistent with our present understanding of the thermal properties of the upper parts of subduction zones.  相似文献   

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