The Anatomy of a Mine - Mining and the Environment: From Ore to Metal - page 174

series of steps from examination of large areas to progressively smaller and smaller areas,
until further exploration locates the deposit. This type of survey depends on the current
state of geo-chemical and geological knowledge, the nature of the area investigated, and
the exploration philosophy of the organization involved.

Stream Sediment Sampling
Stream sediment sampling involves the systematic collection of small samples of sediment
from the active beds of rivers and creeks. In combination with geological mapping and
reconnaissance remote sensing methods, it can provide insight into the mineral potential
of a large area. In rugged areas, locating sampling sites can be difi cult, but exploration
personnel are aided by using high quality aerial photos, satellite-based global position-
ing systems and experienced ground crews. Sediment at a sample point may be sieved to
obtain the most sensitive size fraction, or panned in the traditional way to determine if
gold or other heavy minerals are present. It is not advisable to rely on panning alone as it is
easy to miss very i ne-grained gold. Sample size ranges from 100 grams to i ve kilograms.
The number of stream sediment samples taken can vary substantially but one to four sam-
ples per square kilometre is typical. The environmental impact of stream sediment surveys
is minor and temporary. No special access developments are required. The small sample
holes in stream beds are self-repairing through normal river action. Flagging tape used to
temporarily mark sample sites is often biodegradable.

Rock Sampling
The geochemical halo associated with some mineral deposits may be detected by chemical
analysis of rocks. Such halos are typically larger than the actual ore deposit, making them
an easier target to locate. Rock sampling involves the taking of small hand-sized samples
generally of less that one kilogram. Once an anomalous concentration of the target ele-
ments is detected, more detailed sampling and careful geological mapping is required to
locate the actual deposit.

The geochemical halo associated
with some mineral deposits are
typically larger than the actual
ore deposit.

Soil Sampling
A geochemical indication of a nearby mineral deposit may be obtained by sampling and
analyzing the soil. Under some weathering conditions, elements present in the ore body
may be widely dispersed in a geochemical halo that is much larger than the source deposit.
It is this enlarged halo that is the target for many soil sampling programmes. Geochemical
soil sampling programmes are usually conducted over relatively small areas and the location
of the sample sites is controlled by a surveyed grid established on the ground or by tempo-
rary location techniques. Soil samples are typically collected by hand from a small hole dug
to a depth of about ten centimetres. They are generally less than one kilogram in weight. In
some l at, open environments, a small hand or vehicle mounted auger drill may be used to
obtain a deeper sample. Appropriate rehabilitation of sample sites is carried out during the
survey. Soil samples are transferred directly to a laboratory for geochemical analysis.

Other Geo-chemical Methods
A variety of other geochemical methods have been developed in recent years, often in
response to specii c needs. Minerals deposits may emit a variety of gases that leak to the sur-
face and either accumulate in soils or are emitted to the atmosphere in very low concentra-
tions. Radon emanating from uranium deposits is an example. Attempts have been made to
collect and analyze these gases, both with ground and airborne collection systems. Results
to date vary. Techniques employing the direct analysis of water samples have similarly