Mining prospection

Various techniques are used in the search for a mineral deposit, an activity called prospecting. Once a discovery has been made, the property containing a deposit, called the prospect, is explored to determine some of the more important characteristics of the deposit. Among these are its size, shape, orientation in space, and location with respect to the surface, as well as the mineral quality and quality distribution and the quantities of these different qualities.

Prospecting

In searching for valuable minerals, the traditional prospector relied primarily on the direct observation of mineralization in outcrops, sediments, and soil. Although direct observation is still widely practiced, the modern prospector also employs a combination of geologic, geophysical, and geochemical tools to provide indirect indications for reducing the search radius. The object of modern techniques is to find anomalies—i.e., differences between what is observed at a particular location and what would normally be expected. Aerial and satellite imagery provides one means of quickly examining large land areas and of identifying mineralizations that may be indicated by differences in geologic structure or in rock, soil, and vegetation type. In geophysical prospecting gravity, magnetic, electrical, seismic, and radiometric methods are used to distinguish such rock properties as density, magnetic susceptibility, natural remanent magnetization, electrical conductivity, dielectric permittivity, magnetic permeability, seismic wave velocity, and radioactive decay. In geochemical prospecting the search for anomalies is based on the systematic measurement of trace elements or chemically influenced properties. Samples of soils, lake sediments and water, glacial deposits, rocks, vegetation and humus, animal tissues, microorganisms, gases and air, and particulates are collected and tested so that unusual concentrations can be identified.

Exploration

On the basis of such studies, a number of prospects are identified. The most promising of these becomes the focus of a field exploration program. Several exploration techniques are used, depending on the type of deposit and its proximity to the surface. When the top of a deposit intersects the surface, or outcrops, shallow trenches may be excavated with a bulldozer or backhoe. Trenching provides accurate near-surface data and the possibility of collecting samples of large volume for testing. The technique is obviously limited to the cutting depth of the equipment involved. Sometimes special drifts are driven in order to explore a deposit, but this is a very expensive and time-consuming practice. In general, the purpose of driving such drifts is to provide drilling sites from which a large volume can be explored and a three-dimensional model of the potential ore body developed. Old shafts and drifts often provide a valuable and convenient way of sampling existing reserves and exploring extensions.