The Anatomy of a Mine - Mining and the Environment: From Ore to Metal - page 173

Figure 4.5 . In the short term, planned exploration spending for the rest of the world, par-
ticular China and India, has grown rapidly.
At any stage of exploration, results are assessed to decide whether to proceed with fur-
ther work. A decision to abandon the search is not proof that ore deposits do not exist in
the area. There are many examples of major mineral deposits being discovered in areas
explored on previous occasions. Re-evaluation of previously explored areas is very impor-
tant in the search for minerals.
Exploration geology is a well-researched topic and ample literature is available for
detailed subject coverage (Sheriff and Geldart 1995, Robb 2005, Moon et al . 2005, and
McDonald 2007). The following text is limited to a brief illustration of reconnaissance
exploration, geological mapping, geo-chemical and geo-physical exploration, and drilling.
These activities normally do not require the preparation of environmental impact assess-
ment studies, but good industry environmental practices and standard operating proce-
dures apply (see also Chapter Thirteen).

Reconnaissance Exploration

In the reconnaissance or early exploration phase, remote sensing methods such as satellite
imagery and various types of aerial photography are used as a 'i rst-pass' to home-in on possi-
ble mineralization sites worthy of more detailed, and hence more expensive ground appraisal.
Digital satellite and aerial imageries are commercially available, but generally require com-
puter enhancement techniques for effective use. Selected geophysical data such as magnetic
intensity and radiometry are often in the form of remotely sensed data, acquired by specially
equipped aircraft over-l ying the reconnaissance area in a grid pattern. Reconnaissance explo-
ration can cover large areas of hundreds or even thousands of square kilometres.

Geological Mapping

The next step in exploration data gathering is normally the production of suitable geo-
logical maps of target areas identii ed in the reconnaissance phase. Field geologists explore
a target area, typically tens of square kilometres in size, accurately recording the nature,
location, and structure of various rock units. Small hand-sized samples may be collected
for mineralogical and textural studies by microscope or chemical analysis in the laboratory.
It is normal for an area to be mapped by different geologists at different times. As geo-
logical concepts change over time, repeated mapping improves the understanding of an
area. The i nal product of geological mapping is a map which accurately documents rock
types, alteration mineralogy, and structural data such as faults, folds, and stress patterns.
Geological mapping is of vital importance in deducing the location of hidden ore deposits.

Geo-chemical Exploration

Geochemical exploration is the
scientifi c process of locating geo-
chemical haloes by systematic
sampling and chemical analysis of
rock, soil, water, or vegetation.

When an ore deposit is formed, elevated concentrations of metals and other elements are
often dispersed in the surrounding host rock. Further dispersion of metals and elements
may occur when the deposit weathers in a near surface environment. This dispersion fea-
ture is known as a geo-chemical halo, which eventually may lead towards the origin of the
anomalies; in concentration these may indicate a concealed mineral deposit. Geochemical
exploration is the scientii c process of locating geo-chemical haloes by systematic sampling
and chemical analysis of rock, soil, water, or vegetation. The survey typically follows a