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 MELBOURNE, Australia, Aug. 16 /PRNewswire/ -- Great Central Mines N.L. (ADRs -- NASDAQ: GTCMY), an Australian corporation, advised that the Australian Stock Exchange Limited released the following reply today by Great Central Mines N.L. to a letter from the Australian Stock Exchange Limited.
 1. Yes. The McDonald Speijers' mineral resource estimate of 6.8 million tons at 3.5 grams per ton (g/t) after using a bottom cut of 1 g/t and a top cut of 45 g/t based on data received by them up to July 12, 1993 is the resource estimate.
 However, it should be stressed that this is the first global mineral resource estimate and since July 12, 1993 drilling has continued to intersect significant mineralization. The resource estimate takes no account of the Western Zone mineralization.
 The directors also point out that
 -- coarse visible gold is commonly present in drill core;
 -- these drill hole sections with coarse gold are subjected to screen fire assays to achieve the most reliable assay results;
 -- considerable checking of routine fire assays has also been carried out to verify assays.
 2. No, the directors do not believe that reference to the 6.8 million tons at 5.2 g/t uncut for 1,130,000 ounces in the table page 3 is likely to be interpreted as an over estimate of the resource. The figure was given as a comparison for each of the resource categories on an uncut basis and would be fully understood by investors when read with paragraph 1 on page 3.
 3. Yes. Underground mining is being considered as an option for some of the resource and studies are in progress. A cutoff grade of 1 g/t gold is considered to be reasonably appropriate for potential open cut mining and 3 g/t is the approximate cut off grade likely to be required for underground mining.
 4. McDonald Speijers did agree to the release. In McDonald Speijers' view the uncut figure is not a resource estimate and the uncut estimate reported by the directors was given simply to indicate the sensitivity of grade estimates to assay cutting as detailed in point 1.
 5. The depth of the mineralization intersected has been provided in previous reports issued to the market on a hole-by-hole basis. In summary, the mineral resource estimate is to a depth of 400 meters for the Discovery Zone, 350 meters in the Central Zone and to a maximum depth of 17 meters in the Laterite Zone.
 The depth to which the mineral resource estimate is to be mined by open cut operations is dependent on the grade, stripping ratios and mining costs when compared with likely underground development and mining costs. These costs and factors are being addressed by the feasibility study presently in progress.
 6.1. A macrodiamond is a diamond with a dimension greater than 0.5mm.
 6.2. The macrodiamonds were 1.2mm respectively in size and had a total weight of 0.01 carat. The diamonds were recovered from a gravel sample with an approximate weight of 54 tons.
 6.3. The chromites were recovered from a bulk sample of approximately 12 tons.
 6.4 The kimberlitic nature of the chromites was determined by electron microscope probing of 42 chromites, for major and trace elements, and comparing the chemistry of the grains, with other chromites known to be derived from kimberlites.
 This report has been prepared by a person who is a corporate member of The Australian Institute of Mining and Metallurgy, has had a minimum of five years experience in this field of activity and has consented in writing to the report in the form and context in which it appears.
 The letter from the Australian Stock Exchange follows:
 Re: Quarterly Report for Period Ending June 30, 1993
 We refer to your company's quarterly report (report) which was released to the market on July 29, 1993. In reviewing the report we have the following queries which we would appreciate your company clarify, namely:
 1. On page 3 of the report, your company has stated that the global mineral resource estimate for Bronzewing is 6.8 million tons at 3.5 g/t, with all high assays cut to 45 g/t, and a bottom cut of 1 g/t, for 760,000 ounces. In interpreting this information one is left with the impression that all grades below 1 g/t have been ignored, because they could not be mined profitably in an open pit. The consultants (McDonald Speijers) have recognized that there is some very course gold mineralization present, and this would result in a significant bias to the resource calculation. Accordingly, the have come to the conclusion (by means unstated) that a more realistic determination of the gold resource can be calculated by cutting the high values back to a maximum of 4.5 g/t.
 In our view it seems that the consultants are saying that 6.8 million tons at 3.5 g/t (i.e. 760,000 ounces) is the most likely estimate of the resource present. Do you agree with this interpretation? If not, please explain the basis of your calculation of the resource.
 2. In reviewing the table on page 3, we are concerned that the reference to the 6.8 million tons at 3.5 g/t with no topcut, and a bottom cut of 1 g/t for 1.13 million ounces is likely to be interpreted as an overestimate of the resource. Do you agree? If not, please explain.
 3. On page 4, the company has also provided a mineral resource estimate of 2.9 million tons at 6.5 g/t with all high assays cut to 45 g/t, and a bottom cut of 3 g/t, for 610,000 ounces. This implies that in 3 g/t cut-off would presumably represent the marginal grade which could be mined in an underground mining operation. This suggests that underground mining would need to be considered as an option for some of the ore. Do you agree with this view? If not, please explain.
 4. Could you please advise whether your consultants approved the release of the resource figures in the manner in which they have been presented in the report? Could the consultants specifically indicate what inferences should be drawn from the cut and uncut global resource figures?
 5. It is appreciated that although it is probably too early for your company to indicate any definite plans and give a split between open pit resources and underground resources, it would however be of assistance to the reader if you could indicate the depth to which the resources have been calculated.
 6. With regard to the statements on diamonds, could you please explain the following:
 6.1 What is the definition of "macrodiamond"?;
 6.2 How many carats did the 2 "macrodiamonds" weigh? And, what weight of sample did they come from?;
 6.3 What weight of sample is involved in the "thousands of kimberlitic chromites" reported?; and
 6.4 How has the kimberlitic nature of the chromites been determined?
 We look forward to your early response and clarification in respect to the above matters. ASX reserves the right to release this letter, and any reply to the market.
 (Signed) Greg Nankin, assistant manager-companies, of the Australian Stock Exchange.
 -0- 8/16/93
 /CONTACT: J. H. Barry, director and company secretary of Great Central Mines, 011-613-276-7888/

CO: Great Central Mines N.L. ST: IN: MNG SU:

LG-TS -- NY020 -- 2917 08/16/93 09:12 EDT
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Date:Aug 16, 1993

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