INTERPRETATION OF CURVES

Referring therefore to Fig. 1, it can be deduced that if the above-mentioned constraints are accepted and a US $50 000 000 gross revenue regarded as the

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ORE IN MILLIONS OF TONNES

FIG.3. Family of curves showing gross revenue of US $1000 X 106 over a life-of-mine for deposits containing up to 30 X 106 t ore and less than 2 kg/ U3Os.

minimum figure, then it is possible to construct a family of curves, using tonnage/

grade combination which would give this revenue at various price categories in terms of $/kg U. At an upper limit of US $200/kg U, for example, and with the constraints mentioned above, no deposit lying within the stippled area would be included in the international resource inventory up to the year 2025.

Figures 2 and 3 illustrate the effect of higher levels of the gross-revenue constraints of US $400 000 000 and US $1 000 000 000 respectively. From Fig. 2 it will be seen that to meet a gross-revenue requirement of US $400 000 000 within the 10 000 000 t reserve, and a U³0⁸ grade up to 1 kg/t U³0⁸, the constraints are considerably higher. The lower U³ 0⁸ grade limit is now about

144 TOENS

ORE RESERVES (xlO6)

FIG. 4. Family of curves showing gross revenue of US $50 X 106 to 1000 X 106 over a life-of-mine for deposits containing up to 30 X 106 t ore and less than 2 kg/t U308.

0.2 kg/t, and the minimum tonnage requirement about 3 X 106 t. Figure 3 illustrates that for a gross revenue of US $1 000 000 000 and given a U³ 0⁸ grade up to 1 kg/t U3 08 and maximum tonnage of 10 X 106 t, the constraints are still higher. The lower-grade limit is about 0.6 kg/t U308 and minimum tonnage requirement is 6 X 10⁶ t. If higher grades and lower tonnages are considered, the constraints obviously change as illustrated on the graphs. Figure 4 is an onion-peel diagram which attempts to put together Figs 1—3 in a 3-dimensional representation of the various constraints and their combinations, and illustrates how reserve and grade demands increase with the escalation of gross-revenue requirements.

3 RECOMMENDATIONS

Should the concept presented above meet with the general approval of the Working Group, it is suggested that the proposals presented here may serve as a basis for establishing an internationally acceptable norm for categorizing uranium resources which contain less than 1 kg U³0⁸/ t ore and with a reserve of up to

10 X 106 t.

Assuming that a US $50 000 000 gross-revenue requirement is acceptable, it is then suggested that the deposits could be categorized as illustrated in Fig. 1, and that within each category the price requirement could be stated. For example, a deposit containing 2 X 10⁶ t ore and with a U³0⁸ grade of 0.5 kg/t would be classified as B/50/75.

ACKNOWLEDGEMENTS

The author would like to thank Mrs. Erika Viljoen for writing the computer program and for her assistance in constructing the curves. Thanks are also due to Mr. H. E. James, Mr. H. A. Simonsen, Dr. D. W. Boydell, Mr. B. Corner and Mr. К. Т. Brown for useful discussions and comment.

DISCUSSION

M. V. HANSEN: What sparked off the idea of performing this experiment?

P. D. TOENS: In my opinion it is becoming necessary to attempt to define, in broad terms, the low-grade/low-tonnage package for the Red Book and other studies in order to provide guidelines on what should and what should not be included in a global inventory. It is obvious to those of us involved in these studies that there are some deposits which are not, but should be, included in resource estimates; conversely, some which are included should not be.

M. V. HANSEN: Have you had any opportunity of testing this theory in a real case?

P. D. TOENS: Apart from carrying out a number of theoretical exercises it has not been possible to test this concept. It is not particularly important what figures are used to define the lower limits. What is important, however, is that these limits be defined so that uniformity may be achieved in global resource estimates when dealing with the low-grade/low-tonnage package, which collectively could assume considerable significance.

J. J. SCHANZ: Are your figures expressed in terms of current or constant dollars?

146 ^TOENS P. D. TOENS: We use 1978 US dollars.

J. J. SCHANZ: What price change limits do you assume for the future?

P. D. TOENS: We work on the assumption that the price of uranium will not exceed US $200/kg U.

J. J. SCHANZ: Do you assume that there will be technological changes in the foreseeable future?

P. D. TOENS: Yes, I think the technology will have to improve if the lower limit of my model is to be realistic.

D. M. TAYLOR: Have you studied similar families of curves using cost instead of price, and gross expenditure instead of gross revenue?

P. D. TOENS: No, we have not. This is something which the Joint NEA/

IAEA Steering Group could look into if it is decided to adopt a classification system. However, in my model cost of production and gross expenditure over a given period are very closely linked and could mean the same thing.

J.A. PATTERSON (General Chairman): What is the significance of the lettered categories А, В, С and D shown in Fig. 1 ?

P. D. TOENS: They are used for dividing the low-grade package into various arbitrary grade categories.

J. A. PATTERSON (General Chairman): The use of these grade groups implies that there would be no consideration of minimum grades — or costs — when classifying a deposit. The diagram thus represents only a preliminary or partial step towards the evaluation or classification of a deposit. It would have been more useful if it had shown the tonnage and average grade calculated after application of a minimum thickness and grade cut-off.