Mineral resource is definable (US Geological Survey Circular 831, 1980) as “a concentration of naturally occurring solid, liquid or gaseous material in or on the Earth’s crust in such form and amount that economic extraction of a commodity from the concentration is currently or potentially feasible”
In other words, the mineral resource includes minerals existing in possibility and therefore capable of development into actuality as well as those only surmised to exist. Figure 4a is a schematic classification of resource (U.S.G.S. and US Bureau of Mines) based on the foregoing definition, popularly referred to as the McKelvey Box. The large box represents the resources and within this box, a smaller one represents the reserves.
MINERAL EXPLORATION AND RESERVE EVALUATION
This is that part of the resource whose existence is demonstrated and recoverable at profit under the prevailing deposit knowledge and economic conditions. This figure brings out an important feature of a nation’s mineral resources. It is a dynamic entity and we can see that a resource that is not a reserve today may be upgraded to that rank in time to come depending on variables. These controlling factors, often known as follows:
- Existence of a deposit
- Extractability of the mineral values
- Energy and material requirements for extraction
- Environmental acceptability requirements and
- Economics of a possible operation
- Including availability of capital market demand,
- Political and societal constraints.
The point to note is the inter-relationship among the components of mineral endowment, amplified in Figure 1b. In response to variations in the five E’s listed above, deposits are continually moving from the “undiscovered” category to the “identified” category as our geological information on the deposit gets better and more complete.
More On mineral exploration
Also deposits or parts of deposits are continually moving in either direction between the “economically feasible” and the “subeconomic” categories in response to economic and technological factors. And so, if we now superimpose, we see clearly that the value of any mineral commodity can be greatly altered by technology and research.
With increased technological activity in the area of the commodity, there will be concomitant increase in the demand of the commodity conceived. The converse is also true and we can quickly illustrate this with the story of cassiterite in Nigeria. Cassiterite is the ore from which the metal tin is extracted
Cassiterite production and export from Nigeria reached its all-time high during World War II. According to C. J. Evans of International Tin Research Council (ITRC), this was the time when tin usage was put on a sound scientific footing. With the major tin producing countries of the world overwhelmed by the war, the Institute was committed to maximizing effective use of the metal towards war effort.
The activities in tin production were consequently at its maximum in those parts of the world free from hostilities. Nigeria turned out to be Britain’s principal source of tin for her war effort. The world war over the tin success story has since been reversed, as is demonstrated by the drastic and systematic drop in tin production in Nigeria.
Adequate knowledge of the nation’s mineral reserves is essential for planning. With respect to any specific mineral commodity considered to be a reserve, three sub-groupings are possible depending on our knowledge of the mineral deposit, the current mining status and the current market value of the metal sought. Hence, mineral reserve can be;
(a) Proved: in which all information on the ore grade or tenor, cut-off grade and depth of ore formation are known for the deposit.
(b) Probable in which one or two of the above facts in (a) are lacking.
(c) Possible in which the deposit is merely known to be present but no other details are available.
According to Taylor and Steven (1983) the mineral resource potential of any locality can be identified as high, moderate or low. It implies that the resource concept exists with respect to an economic and technological reference. As these references change, the magnitude of the resources and the reserves concomitantly change. Hence, while the on-going exploitation of mineral deposits results in depletion of the mineral resources, technological innovation in recovery and discovery, improved geologic understanding of the ore genesis and better commodity prices, all together may increase the mineral resource base. Figure 3 illustrates the economic dynamics of mineral resources of a nation.
A change in economic reference from ‘eo’ to ‘e*’ (e* > eo) displaces downward the boundary separating resources from non-resources, thereby increasing the magnitude of resources. Thus a statement on mineral resources is also a statement of relevant economic and technogeologic circumstances. The combination of technology, geology and economics in appraisal of resources calls for yet other resource terms.