There are many Mineral Resource & Ore Reserve classification systems followed worldwide. At present there is no single classification system which is universally accepted or followed. UNFC is universally valid, and followed mostly in Asian and European countries.
There are 3 axes (can be understood as 3 steps in evaluation) in UNFC classification:
A. Economic axis (It indicates whether mining a deposit is profitable or not)
B. Feasibility axis (It indicates if a deposit can be mined or not)
C. Geological axis (It indicates the progress and status of exploration)
They are progressive upwards (Like stratigraphic succession, advances upwards with time & the addition of information). The Geological study is preliminary stage, and the Feasibility study is secondary, which indicates if a deposit is economically mineable or not. In short, they can be expressed as the presence (GA), feasibility (FA) and profitability (EA) of a deposit.
A. Economic Axis:
1. Economic – Deposit is economically mineable under the competitive market conditions.
2. Potentially economic – Deposits at the time of classification are not economic, but they may become economic in near future with changes in technology, increase in demand for the commodity, development of new mining methods which can result in profit etc.
3. Intrinsically economic – Deposits with preliminary evaluation of economic viability (can be understood as the economic viability unknown).
B. Feasibility Axis:
1. Mining Report and/or Feasibility Study – Mining Report is the detailed status report of the mine which is generally made by the operator of the mine. The study takes into consideration production, changes in classification categories, status of exploration, mining methods etc. Feasibility study assesses in detail the technical soundness and economical viability of the deposit. Cost data must be reasonably accurate (+/- 10%). It serves as the basis for investment decision.
2. Prefeasibility study – Preliminary assessment of the economic viability of a deposit. Cost data must be considerably accurate (+/- 25%). It serves as the basis for further investigations.
3. Geological study – It is an initial evaluation of economic viability of the deposit. Cut-off values for grade, thickness, depth and costs estimated from comparable mining operations.
C. Geological Axis:
1. Detailed Exploration – Detailed close spaced drilling (requirement varies from type of deposit, for e.g., Gold deposits need to be drilled on around 10m x 10m grid, and Coal deposits can give sufficient information from 200m to 500m grids), exploratory drive development or trenching, bulk sampling, structural analysis, alteration study etc.
2. General exploration – Widely spaced drilling, small scale geological mapping, trenching, outcrop sampling etc. The degree of accuracy should be sufficient for deciding whether a Prefeasibility Study and Detailed Exploration are required.
3. Prospecting – The study is carried out to identify potential prospects within large areas for further exploration. It includes outcrop identification, large scale geological mapping, and indirect methods such as geophysical and geochemical studies. Limited trenching, drilling, and sampling may be carried out.
4. Reconnaissance - Study identifies areas of enhanced mineral potential on a regional scale based primarily on results of regional geological studies, regional geological mapping, airborne and indirect methods, preliminary field inspection, and extrapolation.
The categories are represented in 3 digit format (EFG) which represents Economic, Feasibility and Geological axes. The sorting can be easily done in ascending order to get the categories in decreasing order of the economic viability.
The entire classification can be broadly categorized into 3 divisions:
1. The Geological study is in progress, but no considerable feasibility study or economic analysis is conducted.
(i) 334 – Reconnaissance Mineral resource
(ii) 333 – Inferred Mineral resource
(iii) 332 – Indicated Mineral resource
(iv) 331 – Measured Mineral resource
2. The feasibility studies and economic analysis indicates no profitability at present conditions, but has a potential to be mined in future.
(i) 222 & 221 – Prefeasibility Mineral resource
(ii) 211 – Feasibility Mineral resource
3. The feasibility studies and economic analysis indicates that the deposit is economic and can be classified as a reserve.
(i) 121 & 122 – Probable Mineral reserve
(ii) 111 – Proved Mineral reserve