asked the Minister for Energy if he will state, in respect of the exercise on the ore reserves in the Navan orebody carried out by the Geological Survey, circa 1972, the calculated result arrived at.
37.
Written Answers. - Navan Orebody.
36.
asked the Minister for Energy if he will state, in respect of the exercises on the ore reserves in the Bula portion of the Navan orebody carried out by the Geological Survey in 1980 and 1981, the estimated reserve figures arrived at and their category.
38.
asked the Minister for Energy if, in respect of the written answer of 11 June 1986 he will define each of the terms "proven ore reserves" and "probable ore reserves" as referred to and used by Tara to derive the calculated figures furnished to the House for the Tara leasehold.
39.
asked the Minister for Energy if, in respect of the written answer of 11 June 1986 he will define the terms "proven ore reserves" and "probable ore reserves" as referred to and used by Bula Limited to derive the calculated figures furnished to the House for the Bula property.
40.
asked the Minister for Energy if, in respect of the ore reserve figures ascribed to Tara Mines, in his reply of 5 June 1986, he will disclose, having carried out the necessary investigations, if any part of the ore in the ground to which the figures referred was either: (a) extracted prior to 31 December 1985 or, (b) occurring outside the Tara leasehold area.
I propose to take Questions Nos. 36 to 40, inclusive, together.
In 1980 the Geological Survey carried out a study of the in-situ ore reserves of Bula Limited and concluded that there were 7.8 million tonnes demonstrated (combined proven and probable reserves) in the orebody at 5 per cent combined lead and zinc cut-off grade. In 1981 the survey concluded that the mineable Bula ore reserves were 6.5 million tonnes at 5 per cent combined lead and zinc cut-off grade. As I informed the Deputy in reply to a question on 11 June the Geological Survey did not break down the Bula reserves into separate proven and probable categories.
The survey's figures differ significantly from the figures furnished to me by Bula Limited. There can be variations of significance in calculations of ore reserves by different experts, depending, among other factors, on the methods of calculation used. For instance the Geological Survey calculations were done on the basis of a 5 per cent conbined lead and zinc cut-off grade whereas the figures furnished by Bula Limited were calculated on the basis of a 4 per cent zinc equivalent cut-off grade.
During 1972 and 1973 the Geological Survey had carried out on-going assessments of the Navan ore reserves in the light of emerging information from intensive drilling. In September 1973 the survey's assessment was that in-situ reserves totalled 69.9 million tonnes of which proven and probably reserves amounted to 24.7 million tonnes at a combined lead and zinc cut-off grade of 4 per cent. Tara Mines Limited and Bula Limited referred to and used the US Bureau of Mines definitions of proven and probable ore in calculating the ore reserve figures which I furnished to the Deputy in reply to a question on 11 June 1986. The definitions are as follows:—
Measured (Proven): Material for which estimates of the quality and quantity have been computed, within a margin of error of less than 20 per cent from sample analyses and measurements from closely spaced and geologically well known sample sites.
Indicated (Probable): Material for which estimates of the quality and quantity have been computed partly from sample analyses and measurements and partly from reasonable geologic projections.
I do not understand the first part of the Deputy's question as regards the figures for Tara Mines ore reserves which I gave in my reply to the Deputy's question of 5 June 1986. The figures I quoted were in respect of ore reserves as at 31 December 1985 which obviously could not have been extracted prior to that date.
I have been assured by Tara Mines Limited that none of the Tara ore reserves quoted in my reply of 5 June 1986 occurred outside the Tara leasehold area.