| 1. |
- Dias, Pedro, et al.
(författare)
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Geophysical investigation of the down-dip extension of the Lombador massive sulphide deposit, Neves-Corvo, Portugal
- 2021
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Ingår i: International journal of earth sciences. - : Springer Nature. - 1437-3254 .- 1437-3262. ; 110:3, s. 911-922
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Tidskriftsartikel (refereegranskat)abstract
- The 150 Mt Lombador massive sulphide deposit is one of the seven known deposits of the Neves-Corvo mine. The deposit dips approximately 30o-35o to the NE and is open down dip, with current exploitation reaching down at 1 km depth. To investigate the possible downwards continuation of the deposit, a 1D constrained inversion of time-domain electromagnetic (TEM) ground loop data was conducted, followed by 3D electromagnetic (EM) forward modeling and a constrained 3D gravimetric inversion over the same area. To perform the EM and gravity modeling/inversion, a 3D geologic model was built using a density database comprising of approximately 300 drill-holes, and an electrical conductivity database with measurements from resistivity surveys and 1D inversion of the TEM data. The EM modeling shows that the Neves Formation shales are a regional conductive layer extending down to approximately 1.6 km depth in the Lombador area. This layer, often topped by massive sulphides, has an average density of 2.83 g/cm(3), whereas stockwork and massive sulphide reach on average 3.1 g/cm(3) and 4.5 g/cm(3), respectively. The 3D constrained gravity inversion results do not support the hypothesis of the presence of massive sulphides located in the down-dip direction of the Lombador deposit in the immediate vicinity of the known deposit. The lack of spatial resolution of the gravity grid, the study area limited size and the lack of information from within the basement suggest further studies are required to confirm the presence and amount of stockwork mineralization down-dip the Lombador deposit inside the Neves-Formation or the Phyllite-Quartzite basement.
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| 2. |
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| 3. |
- Lundberg, Angela, et al.
(författare)
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Impulse Radar Snow Surveys – Influence of Snow Density
- 2000
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Ingår i: Nordic Hydrology. - : IWA Publishing. - 0029-1277 .- 1996-9694. ; 31:1, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- Snow cover water equivalent (SWE) is of major importance for planning of e.g. hydropower production in areas where a large proportion of the annual precipitation falls as snow. Radar technique can be used to determine SWE from the two-way travel time (twt) of a radar-wave propagation through a snowpack. SWE is usually related to twt through an empirical relationship, SWE = -b+a twt, where the values of a and b are determined by linear regression from simultaneous measurements of SWE (with snow-courses) and twt (with radar technology). In this paper a theoretical relationship between twt and SWE is developed showing the need for introducing the density when relating twt to SWE. Use of different empirical relationships for the real dielectric constant showed that the a-value for dry snow with a density of 350 kg m-3 (a typical value at the end of the accumulation season in the Nordic countries) is 0.040 m ns-1 (twt given in nanoseconds). When the snow density deviates considerably from this value a corrected a-value has to be used. A density of 300 and 400 kg m-3 gives a = 0.036 and 0.045 m ns-1 respectively. The b-value should theoretically be zero for measurements at the snow surface, non-zero values are probably due to the use of the direct wave between transmitter and receiver antennas as reference. The theoretically derived equations were confirmed by laboratory and field measurements as well as by measurements taken from literature.
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| 4. |
- Lundberg, Angela, et al.
(författare)
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Impulse radar surveys - influence of liquid water : remote sensing and hydrology 2000
- 2001
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Ingår i: Remote Sensing and Hydrology 2000. - Wallingford, Oxfordshire : IAHS Press. - 1901502465 - 9781901502466 ; , s. 136-138
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Konferensbidrag (refereegranskat)abstract
- Snow water equivalent (SWE) of snow is of great importance for hydropower production in areas where a large proportion of the reservoir water comes from snow. Impulse radar to estimate the SWE is now in operational use in some Scandinavian basins. With radar technology the radar wave propagation time in the snow pack is converted into SWE with the help of a parameter usually termed the a value. Use of radar technology during late winter brings about risk for measurements of wet snow. The a value for dry snow cannot be used directly for wet snow. A liquid-water content of 5% (by volume) reduces the a value by » 20%.
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| 5. |
- Lundberg, Angela, et al.
(författare)
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Radar snow surveys : influence of snow density
- 1998
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Ingår i: XX Nordic Hydrological Conference. - Helsinki : Nordic Association for Hydrology. - 9521103221 ; , s. 679-
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Konferensbidrag (refereegranskat)
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| 6. |
- Lundberg, Angela, et al.
(författare)
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Snow accumulation in forests from ground and remote sensing data
- 2004
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 18:10, s. 1941-1955
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Tidskriftsartikel (refereegranskat)abstract
- Winter-forest processes affect global and local climates. The interception-sublimation fraction (F) of snowfall in forests is a substantial part of the winter water budget (up to 40%). Climate, weather-forecast and hydrological modellers incorporate increasingly realistic surface schemes into their models, and algorithms describing snow accumulation and snow-interception sublimation are now finding their way into these schemes. Spatially variable data for calibration and verification of wintertime dynamics therefore are needed for such modelling schemes. The value of F was determined from snow courses in open and forested areas in Hokkaido, Japan. The value of F was related to species and canopy-structure measures such as closure, sky-view fraction (SVF) and leaf-area index (LAI). Forest structure was deduced from fish-eye photographs. The value of F showed a strong linear correlation to structure: F = 0·44 - 0·6 × SVF for SVF < 0·72 and F = 0 for SVF > 0·72, and F = 0·11 LAI. These relationships seemed valid for evergreen conifers, larch trees, alder, birch and mixed deciduous stands. Forest snow accumulation (SF) could be estimated from snowfall in open fields (So) and to LAI according to SF = So (1 - 0·11 LAI) as well as from SVF according to SF = So (0·56 + 0·6 SVF) for SVF < 0·72. The value of SF was equal to So for SVF values above 0·72. The value of sky-view fraction was correlated to the normalized difference snow index (NDSI) using a Landsat-TM image for observation plots exceeding 1 ha. Variables F and SF were related to NDSI for these plots according to: F = -0·37NDSI + 0·29 and SF = So (0·81 + 0·37NDSI). These relationships are somewhat hypothetical because plot-size limitation only allowed one sparse-forest observation of NDSI to be used. There is, therefore, a need to confirm these relationships with further studies.
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| 7. |
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| 8. |
- Lundberg, Angela, et al.
(författare)
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Snow Wetness Influence on Impulse Radar Snow Surveys Theoretical and Laboratory Study
- 2000
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Ingår i: Nordic Hydrology. - : IWA Publishing. - 0029-1277 .- 1996-9694. ; 31:2, s. 89-106
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Tidskriftsartikel (refereegranskat)abstract
- The snow-water equivalent of late-winter snowpack is of utmost importance for hydropower production in areas where a large proportion of the reservoir water emanates from snowmelt. Impulse radar can be used to estimate the snow-water equivalent of the snowpack and thus the expected snowmelt discharge. Impulse radar is now in operational use in some Scandinavian basins. With radar technology the radar wave propagation time in the snowpack is converted into snow-water equivalent with help of a parameter usually termed the a-value. Use of radar technology during late winter brings about risk for measurements on wet snow. The a-value for dry snow cannot be used directly for wet snow. We have found that a liquid-water content of 5% (by volume) reduces the a-value by approximately 20%. In this paper an equation, based on snow density and snow liquid water content, for calculation of wet-snow a-value is presented.
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| 9. |
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| 10. |
- Mainali, Ganesh, et al.
(författare)
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Tailings dams monitoring in Swedish mines using self-potential and electrical resistivity methods
- 2015
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Ingår i: Electronic Journal of Geotechnical Engineering. - : Mete Öner. - 1089-3032. ; 20:13, s. 5859-5875
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Tidskriftsartikel (refereegranskat)abstract
- Tailings dam failures have been occurring in recent years. Many of these failures have caused human casualties, destruction of property, and damage to environment and huge economic loss to the mining industry. The monitoring of the dam is essential to know the existing state of the dams and to ensure the safety of the dam over its life time. The present study has been conducted to test the applicability of electrical resistivity and self-potential (SP), for detecting anomalous seepage through mine tailings dams in Sweden and monitoring the physical condition of the dam. This study has demonstrated the potential of using geoelectrical methods for monitoring the conditions of the tailing dams related to seepage.
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