• Home
  • Ispat Digest
  • United Nations Framework Classification of Mineral Reserves/Resources

United Nations Framework Classification of Mineral Reserves/Resources

United Nations Framework Classification of Mineral Reserves/Resources

United Nations Framework Classification (UNFC) of Mineral Reserves/Resources consists of a three dimensional system with the following three axes: Geological assessment, Feasibility assessment and Economic viability. The process of geological assessment is generally conducted in stages of increasing details (Fig 1)

UNFC of minerals

Fig 1 Classification of minerals

The typical successive stages of geological investigation i.e. reconnaissance, prospecting, general exploration and detailed exploration, generate resource data with a clearly defined degrees of geological assurance. These four stages are therefore used as geological assessment categories in the classification. Feasibility assessment studies form an essential part of the process of assessing a mining prospect. The typical successive stages of feasibility assessment i.e. geological study as initial stage followed by prefeasibility study and feasibility study/mining report as well defined. The degree of economic viability (economic or sub economic) is assessed in the course of prefeasibility and feasibility studies. A prefeasibility study provides a preliminary assessment with a lower level of accuracy than that of a feasibility study, by which economic viability is assessed in detail. The various terms used in this classification and their definitions are as follows:

Total Mineral Resource

It is a concentration(or occurrence) of material of intrinsic economic interest. It has resonable prospects for eventual economic extraction. Its location, grade, quantity, geological chracteristic is known, estimated or interpreted from specific geological evidence and knowledge. Total mineral resource are of three types.

  • Measured Mineral Resouce – Itm is that part of mineral resource for which tonnage, density, shape, physical characteristics, grade and mineral content can be estimatedwith a high level of confidence i.e. based on detailed exploration.
  • Inducated Mineral Resource – In this category tonnage, densities, shape, physical characteristic, grade and mineal content can be estimated with reasonable level of confidence based on exploration, sampling and testing information, location of borehole, pits etc. too widely placed.
  • Inferred Mineral Resource –In this type tonnage, grade and mineral content can be estimated with low level of confidence inferred from geological evidence.

Mineral Reserve

It is economically mineable part of measured and/or indicated mineral resource. It is of two types.

  • Proved Mineral Reserve – It is economicallly mineable part of Measured Mineral Resource.
  • Probable Mineral Reserve – It is economically mineable part of indicated or in some cases a Measured Mineral Resource.

Reconnaissane Mineral Resource

It is estimates based on regional geological studies and mapping, airborne and indirect methods, preliminary field inspections as well as geological inference and extrapolation.

Prefeasibility Mineral Resource

It is that part of an indicated and in some circumstances Measured Mineral Resource that has been shown by prefeasibility study to be not economically mineable. It also indicates possibly economically viable resource subject to changes in technological, economic, environmental and/or other relevant condition.

Feasibility Mineral Resource

It is that part of Measured Mineral Resource, which after feasibility study has been found to be economically not mineable. It also indicates possibly economically viable resource subject to changes in technological, economic, environmental and/or other relevant condition.


Various terms are defined as follows.

  • Uneconomic Occurrence – This consists of materials of estimated quantity, that are too low in grade or for other resons are not considered potentially economic. Thus, Uneconomic Occurrence is not part of a Mineral Resource. If quantity and quality are considered worthy of reporting, it should be recognied that an Uneconomic Occurrence cannot be exploited without major technological and/or economic cahanges, which are not currently predictable.
  • Mineral Occurrence – A mineral Occurrence is an indication of mineralisation, that is worthy of further investigation. The term Mineral Occurrence does not imply any measure of volume/tonnage or grade/quality and is thus not part of a Mineral Resource.
  • Mining Report – A Mining Report is understood as the current documentation of the state of development and exploitation of a deposit during its economic life including current mining plans. It is generally made by the operator of the mine. The study takes into consideration the quantity and quality of the minerals extracted during the reporting time, changes in Economic Viability categories due to changes in prices and costs, development of relevant technolgy, newly imposed environmental or other regulations, and data on exploration conducted concurrently with mining. It presents current status of deposits, providing a detailed and accrate, uo to date statement on the reserves and theremaining resources.
  • Feasibility studies – A feasibility study assesses in detail the technical soundness and Economic Viability of a mining project, and serves as the basis for the investment decision and as a bankable document for project financing. The study constitutes an audit of all geological, engineering, environmental, legal and economic information accumulated on the project. Generally, a separate environmental impact study is required. Cost data must be reasonably accurate (usually within +/- 10 %), and no further investigation should be necessary to make the investment decision. The information basis associated with this level of accuracy comprises the reserve figures based on the results of Detailed Exploration, technological, pilot tests and capital and operating cost calculations such as quotation of equipment suppliers. A sensitivity study may require independent verification in certain circumstances.
  • Prefeasibility studies – A prefeasibility study provides a preliminary assessment of the Economic Viability of a deposit and forms the basis of justifying further investigations (Detailed Exploration and Feasibility Study). It usually follows a successful exploration campaign, and summarizes all geological, engineering, wnvironmental, legal and economic information accumulated todate on the project. In projects that have reached a relatively advanced stage, the prefeasibility study should have error limits of +/- 25 %. In less advanced projects higher errors are to be expected. Various items are in use internationally for prefeasibility studies reflecting the actual accuracy level. The data required to achieve this level of accuracy are reserves/resources figures based on Detailed and General Exploration, technological tests at laboratory scale and cost estimates e.g. from catalogues or based on comparable mining operations. The prefeasibility study addresses the items listed under the feasibility study, although not in as much details.
  • Geological Study – A geological study is an initial evaluation of Economic Viability. This is obtained by applying meaningful cut-off values for grade, thickness, depth and costs estimated from comparable mining operations. Economic Viability categories, however, cannot in general be defined from the geological study because of the lack of detail necessary for an Economic Viability evaluation. The resource quantities estimated may indiate that the deposit is of intrinsic economic interest, i.e. in the range of economic to potential economic. A geological study is carried out in the following four stages: Reconnaissance, Prospecting, General Exploration and Detailed Exploration. The purpose of the geological study is to identify mineraliation, to establish continuity, qquantity, and quality of a mineal deposit, and thereby define an investment opportunity.
  • Reconnaissance – A 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, as well as geological inference and extrapolation. The objective is to identify mineralised areas worthy of further investigation towards deposit identification. Estimates of quantities should only be made if sufficient data are available and when an analogy with known deposits of similar geological character is possible, and then only within an order of magnitude.
  • Prospecting – It is the systematic process of searching for a mineral deposit by narrowing down areas of promising enhanced mineral potential. The methods utilized are outcrop identification, geological mapping and indirect methods such as geophysical and geochemical studies. Limited trenching, drilling and sampling may be carried out. The objective is to identify a deposit which will be the target for further exploration. Estimates of quantities are inferred, based on interpretation of geological, geophysical and geochemical results.
  • General Exploration – It involves the initial delineation of an identified deposit. Methods used include surface mapping, widely spaced sampling, trenching and drilling for preliminary evaluation of mineral quantity and quality (including mineralogical tests on laboratory scale if required), and limited interpolation based on indirect methods of investigation. The objective is to establish the main geological features of a deposit, giving a reasonable indication of continuity and providing an initial estimate of size, shape, structure and grade. The degree of accuracy should be sufficient for deciding whether a prefeasibility study and detailed exploration are warranted.
  • Detailed Exploration – it involves the detailed three dimensional delineation of a known deposit achieved through sampling, such as from outcrops, tranches, boreholes, shafts and tunnels. sampling grids are closely spaced such that size, shape, structure, grade, and other relevant characteristicsof the deposit are established with a high degree of accuracy. Processing tests involving bulk sampling may be required. A decision whether to conduct a feasibility study can be made from the information provided by Detailed Exploration.

Leave a Comment