Most orebodies have cross-sections of less than 1 km2 and hence do not
offer a particularly large target for exploration. Fortunately, although in
the geological record ore deposits are small and rare and result from the
exceptional coincidence of certain geological processes, these processes
are mappable on a much larger, district to regional scale and constitute a
mineral system in which the ore deposit is the central feature. A mineral
system can therefore be defined as `all geological factors that control the
generation and preservation of mineral deposits, and stress the processes
that are involved in mobilising ore components from a source,
transporting and accumulating them in more concentrated fonn and then
preserving them throughout the subsequent geological history'. The
mineral system concept emphasises that for many ore deposit types,
although economically viable mineralisation may only occur on a scale of
say, hundreds of metres, the total system of fluid-rock interactions that led
to ore formation can extend over a distance of tens to hundreds of
kilometres around the deposit. When mapped out, the total mineral
system provides a far larger exploration target than the actual ore deposit
itself. Important geological factors defining the characteristics of any
mineralising system include: 1. sources of the mineralising fluids and transporting ligands;
2. sources of the metals and other ore components; 3. migration pathway;
4. thermal gradient; 5. energy source; 6. a mechanical and structural focusing mechanism at the trap site;
7. chemical and/or physical traps for ore precipitation. Many of these factors individually are common throughout time and
space and are mappable on a regional scale. The delineation and
empirical prediction of mineral systems can thus be approached by
combining two components of metallogenic research. Firstly, the
development of maps of regional geoscientific data and data sets of the
distribution of factors significant for mineral systems in general.
Secondly, the determination of the essential ingredients of particular
styles or types of deposits in terms of mappable elements that any
exploration program could focus on.