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Rock & Soil Sampling – The Key to Most Exploration Projects

By: JS in Exploration Basics, Exploration Methods

Soil sampling is a basic technique of mineral exploration. Cheaper than drilling, sampling can be used to
quickly establish the existence and extent of hoped for mineralization.

Initial geophysical and other remote sensing methods are used to target a geological structure which
may contain mineralization. Soil sampling can either stop a project dead in its tracks, or give the green
line for further expenditure including drilling.

Why Is Soil Sampling Important?

Soil sampling is undertaken to define the location and shape of an obscured mineralized structure and
to identify any higher grade sections within the structure. A successful soil sampling program will
result in accurate drill-hole targeting. Many structures are not mineralized to the same degree along
their length. A great deal of money can be wasted drilling along a geophysical anomaly only to realize
later that the highest grade zones are confined to narrow steeply plunging zones in the plane of the
structure.

All too often, drilling doesn’t intersect any of these zones and the prospect is subsequently abandoned
or relinquished. Opportunities are missed because a thorough chip and soil sampling programme was
not undertaken.

Rock Chip Sampling

Rock chip sampling is sampling of exposed potentially mineral-bearing rocks. Chips are taken during
initial mapping, and if promising results are returned, a subsequent soil sampling survey undertaken.
Alternatively, in many cases, outcrops maybe either minor or non-existent, and soil sampling is a
key next step for an exploration programme.

Designing a Soil Sampling Programme

A soil sampling programme
must be designed to ensure
that it tests the structure
which is causing the
geophysical anomaly. In the
example below, the plan
consists of seven lines each
separated by 120m. These
lines cross, at right angles,
the structure that was
identified using a ground
magnetic survey. Each
sampling site along the lines
is spaced 20m apart, a total
of 147 samples. Surface rock chips may provide evidence as to where the high grade zones lie along the
structure. The geologist take these into account when planning the soil sampling programme. When the
geologist is happy with the plan, the sample points are entered into a GPS in readiness for the survey.

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