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Gold Prospecting Methods -Borehole Surveying
Ground penetrating radar is effective in rapidly profiling shallow subsurface layering based on the reflection of electromagnetic waves from subsurface interfaces. It is commonly applied to mapping soil layers, depths to bedrock, buried stream channels, rock fracture zones and cavities, buried waste materials and buried metallic features. The tool can be used on land, overwater in freshwater lakes and rivers and in boreholes, either in the downhole or crosshole modes.
Borehole geophysical methods are used to provide high resolution information on lithology, bulk density, porosity, fracturing, fluid flow, oxidation, and susceptibility. New technology allows multiple logs to be recorded simultaneously. Borehole seismic methods either downhole or crosshole provide information on layering, elastic modulo of layers and bedrock, voids or anomalies in geological layering using tomography mapping, and assist in determining design parameters for structures. Crosshole and tomographic surveys are also carried out with resistivity and electromagnetic methods to provide high resolution images of anomalous conditions having contrasting resistivity or conductivity properties.
The results are utilized for a wide range of applications, some of which are listed below:
- The search for resources, Gravel, sand and quarry sites. Mineralized weathered zones, location of buried alluvial channels with gold, diamond or tin.
- The Alluvial gold, diamond or platinum exploration, the seismic survey, before the sampling stage, leads to the cost effective exploration. One must know where the paleochannels are, before any drill or pit sampling can take place.
The seismic profile-section costs much less than drilling, while provide more information. The drill, pit or bulk sampling is then reduced to testing significant areas. If these areas are promising, more involved examination can take place. Saprolite hosted gold deposits are also targets for seismic investigation.
- The oil & gas pipelines, The prevention of oil spills: the survey of soil stability, depth to bedrock, and fault location under existing or planned pipelines.
- The civil engineering geology, Geotechnic surveys, rippability surveys, landslides prevention.
- The environmental remediation, Ground water table and bedrock depths, site tomography. The drill does not provides the detail necessary to solve many problems; besides in hazardous waste disposal sites one does not want to poke holes into it.
- The excavation, Harbor basins and entrances, pipelines, canals, roads, railways. The seismic provides depth to the bedrock which helps calculating the volumes of excavation.
- The foundations, The survey of soil stability before constructing heavy industrial buildings, bridges, harbor quays and breakwaters, dams, piling, airfields.
- The water prospecting, Ground water table in the overburden, water-bearing sections of rock.
A shallow seismic survey provides:
- A 2D length-depth profile at a reasonable cost.
- A full image of underground geological conditions. It reduces the risk of overlooking critical or promising areas.
- A terrain-independence. The jungle, rough terrain, urban sites and water- covered swamps can all be surveyed with equal ease.
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