Diamond Fields International has received a revised resource estimate from MRDI, a division of AGRA Simons, for the main Marshall Fork feature on its 100-per-cent-owned sea diamond concessions near Luderitz, Namibia. The revised resource estimate contains 437,000 carats in the indicated category and 132,000 carats in the inferred category for a total of 569,000 carats representing a 20-per-cent increase in the indicated carats and a 43-per-cent increase over the previous resource estimate announced in Stockwatch Jan. 25, 2000. This revised estimate is based on an increase from 1.01 to 1.36 square kilometres in the interpreted area of the main Marshall Fork channel feature as determined by the recent high-resolution geophysical survey conducted by Marine & Coastal Geoscience of South Africa. Advancements in the survey technology and significant enhancements in the data interpretation techniques provide a much more accurate picture of the Marshall Fork feature as compared with previous surveys.
Revised Marshall Fork Feature Resource
Estimate Summary April, 2000
Area Basis
Resource Feature Area Grade Total
Category (sq m) (ct/sq m) ct
Indicated 865,000 0.50 437,000
Inferred 491,000 0.27 132,000
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Total 1,356,000 0.42 569,000
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Previous Marshall Fork Feature Resource
Estimate Summary, January, 2000
Area Basis
Resource Feature Area Grade Total
Category (sq m) (ct/sq m) ct
Indicated 770,000 0.47 365,000
Inferred 239,000 0.14 33,000
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Total 1,009,000 0.39 398,000
The resource estimate for the Marshall Fork feature was compiled by MRDI, a division of AGRA Simons, (senior author and qualified person: M. Thurston, PhD) based on geophysical and sampling data provided by the company and using the resource classification in accordance with the Toronto Stock Exchange guidelines and the Australasian code for reporting mineral resources and ore reserves (JORC, 1999). The indicated resource is based on sampling carried out by De Beers Marine and is unadjusted for differences that might exist between the sampling and potential future mining processes. The inferred resource refers to those parts of the Marshall Fork feature that are less well sampled than the indicated resource and for which the estimates of grade and thickness are considered less well known. Given the design and operating characteristics of the sampling tool and the irregular surface of the footwall in the Marshall Fork feature, MRDI believes it is likely that the sample grade, and therefore total number of carats, have been underestimated and estimates this suspected bias to be 740,000 carats (517,000 carats for January, 2000, estimate). The estimate was made by comparing sampling and production data in a similar geological environment. If the carats associated with the sampling bias are added to the resources the total average grade would be 0.97 of a carat per square metre. The carats associated with the suspected sampling bias carry a high level of uncertainty. The actual difference in carats between sampling and mining can only be accurately assessed once mining has begun. Marine & Coastal Geoscience conducted the latest geophysical survey on the feature in 1999 with the data interpretation being completed in 2000.
Diamond grades for marine and beach alluvial deposits in southern Africa
are normally reported in carats per square metre. In the Marshall Fork feature, all diamond recoveries are associated with the basal gravel horizons, which average 1.0 metre thick. Moving from north to south in the feature, the basal gravel layer becomes overlain with layers of clay, shell and mud. These non-diamond bearing overburden layers get progressively thicker toward the southern end of the feature. The average thickness of sediment material including the gravel and overburden in the Marshall Fork feature is 1.4 metres.
Revised Marshall Fork Feature Resource
Estimate Summary – April, 2000
Volume Basis Gravel
Resource Gravel Volume Grade Total
Category (m3) (ct/m3) ct
Indicated 904,000 0.48 437,000
Inferred 413,000 0.32 132,000
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Total 1,317,000 0.43 569,000
For improved disclosure and in compliance with TSE guidelines the resource is also reported on a volume basis. The volume reported is the volume of gravel and not the full sediment thickness. The method used to record gravel thickness is approximate and as such the volume and grade of the gravel horizon should be taken as indicative. The resource tables assume a nominal bottom cutoff of 1.6 millimetres (square mesh).
Over 10,000 carats of diamonds recovered from the sampling and test-mining activities in Marshall Fork were sold in 1999 for an average value of $160 (U.S.)/carat. Diamond market conditions remain robust and in general prices for similar sizes and quality of stones as those found in the Diamond Fields concession, have increased since the parcels were sold.
The new resource estimates are being incorporated into the geological model and mine planning activities as part of the feasibility study. Feasibility work is under way and is scheduled for completion in July, 2000. The expanded resource base at Marshall Fork is expected to support a highly profitable mining operation. The operating design criterion for the mining system capacity in the feasibility study is 500,000 square metres per year (1.0 million cubic metres per year). The scoping study previously indicated that the project could be developed and production could be achieved within 12 months of a formal decision to proceed.
