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Updated mineral resource for Karowe mine (Botswana)

Published by , Assistant Editor
Global Mining Review,

Lucara Diamond Corp. (Lucara) has shared the results of a recent Mineral Resource Update prepared in accordance with National Instrument 43-101 (NI43-101). According to the the diamond exploration and mining company, these up-to-date results will be used for mine planning and will support the preparation of current feasibility-level studies for the potential development of an underground mine, after the completion of the current opencast mine, at its Karowe mine.

CEO of Lucara, Eira Thomas commented: "Going forward, the Karowe mine plan is dominated by South Lobe ore, with the high grade, high value EM/PK(S) unit becoming increasingly prevalent as we mine deeper. We now understand that some of Karowe's large, high value diamonds originated from the EM/PK(S) unit including the historic 1109 carat Lesedi La Rona and the 813 carat Constellation which sold for a record US$63 million. This resource update supports the continued recovery of large high value diamonds from the South Lobe throughout its remaining opencast mine life and the likelihood for underground mining until at least 2036. Feasibility work assessing the potential for underground mining, including hydrogeological and geotechnical drilling together with several mining trade off studies is ongoing."

The Karowe mine has been operating commercially since July 2012. The mine has produced and sold over 2 million carats from 13.9 million t of processed kimberlite at an average sales price of US$606/carat. 

The updated mineral resource estimate was completed by Mineral Services Canada Inc. The estimate is based on historical evaluation data combined with new sampling results (microdiamond, bulk density and petrography) from recent deep core drilling and from historical drill cores. New delineation drill coverage and review of historical drill cores supported an update of the internal geological model.

According to the company, the updated Mineral Resource, valid at the cut-off date of 26 December 2017, includes a recoverable Indicated Mineral Resource at a 1.25 mm bottom cut off size of 7.9 million carats hosted in 57.85 million t at an average grade of 13.7 cpht with an average modeled diamond value of US$673 per carat. The new base of the Indicated Mineral Resource is 400 masl (600 m below surface). The updated Mineral Resource also includes a recoverable Inferred Mineral Resource of approximately 1.17 million carats hosted in 5.84 million t at an average grade of 20 cpht with an average modeled diamond value of US$716 per carat between 400 masl to 256 masl (base of current geological model).

The mineral resource estimate for AK06 above 600 masl is restated with minor modifications from the previous project Technical Report (see Lucara press release of 15 December 2017). A high confidence geological model and comprehensive bulk density dataset constrain estimates of volume and tonnage. Grade estimates are based on a well distributed large diameter drilling (LDD) sample dataset that supports the interpolation of local grade estimates. Modifications to the previous estimate include revisions to the geological model, more aggressive capping of outlier LDD grade values used for interpolation and updated diamond values for the South Lobe to reflect the current production and sales dataset.

The mineral resource estimate for AK06 below 600 masl has been significantly revised from the previous estimate based on the results of core drilling and microdiamond sampling work carried out in 2017/18. Volume and tonnage estimates are similarly based on the AK06 geological model and a spatially representative broad bulk density sample coverage. Grade has been estimated using a microdiamond-based approach that is based on a calibration of the ratio of microdiamond stone frequency (stones per kilogram) to + 1 mm LDD macrodiamond grade.

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