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Lucara Diamond Corp. Completes PEA for Karowe Underground Mine, Botswana

Published: November 15, 2017 |

[Click image to enlarge]

Lucara Diamond Corp. has completed the preliminary economic assessment (PEA) prepared in accordance with National Instrument 43-101 for the development of an underground mine to commence production, after the completion of the current open pit mine, at its Karowe Mine in Botswana.

Based on the positive PEA results, the company has continued with the development of a pre-feasibility study (PFS), with an anticipated release in Q2, 2018.

“The results of the PEA demonstrate the potential economic viability for the development of an underground mine at Karowe. Underground operations are focused on the high value south lobe, which remains open at depth below the current design, and is a further indication of the potential longevity of the resource and cashflow generation at Karowe,” said William Lamb, president and CEO.

“We have seen on-going improvement in the value of diamonds from the south lobe and the development of an underground mine has the potential to add significantly to the Life of Mine at Karowe,” added Lamb.

PEA APPROACH AND PROJECT OVERVIEW

The PEA for the Karowe Underground project and together with the Karowe Mine, presents a stand-alone scenario that does not factor in or modify in any way the economics of the open pit operations of the Karowe Mine, except where taxes are affected based on capital expenditures. The PEA does, however, assume that the Karowe Underground will seamlessly integrate into current operations with kimberlite sourced from underground being stockpiled in the latter years of the open cast operations to ensure sufficient availability to the processing facilities to maintain the current 2.5 million tonnes per annum (mtpa) throughput.

The Karowe Underground targets the South Lobe kimberlite resource below the current planned bottom of the open pit, expected to be at approximately 690 meters above mean sea level and 320 meters below surface (mbs), to a depth of 420mamsl (590mbs). The lower portion 200m vertical from 600 to 400mamsl is composed of inferred mineral resource, which the PEA considered to be too speculative geologically to have the economic considerations applied to them that would enable them to be categorized as mineral reserves. The PEA is preliminary in nature and there is no certainty that the PEA will be realized.

The Karowe Underground benefits from the brownfields nature of the existing operations at the Karowe Mine. Since declaring commercial production in July 2012, the Karowe Mine has produced an average of 320,000 carats per annum from three kimberlite lobes, from the treatment of 2.5mtpa. These open pit operations are scheduled to continue until 2026 with the originally planned processing of low grade stockpiles in 2027 being moved to 2036, the end of the current planned underground operations.

The Karowe Mine process plant and other site facilities and equipment required to support an underground mining operation have recently been upgraded to accommodate the treatment of harder and higher density material at depth. Existing on-site infrastructure includes offices, warehouses, laydown areas, maintenance facilities, a crushed kimberlite stockpile and reclaim, access and service roads, an airstrip, explosives magazines, and water and electrical infrastructure.

The bulk underground mining method selected to mine the diamond kimberlite pipe measuring some 200m in diameter is SLC. Initially the pipe will be partially offset from the pit bottom, resulting in the top four sublevels being slightly offset from the pit bottom. These top levels plus two levels below the pit bottom will be mined by a derivation of sub-level open stoping (SLOS) daylighting into the pit bottom.

For the purpose of the PEA, SLC was considered due to its lower initial capital cost. On completion of the current PFS geotechnical program, further consideration will be given to a block caving option. This trade-off study will be completed as part of the PFS initial pre-feasibility work program.

The mine design for both the upper levels SLOS and the following SLC mining once general caving of the host rocks commences, will be similar. The sublevel interval will be 25m, which is the international norm for the method. Owing to the reported hardness and strength of the kimberlite at 156 Mpa, the mine design is intended to evaluate increasing the sub level interval to 30m at the PFS stage. The assumed competence of the kimberlite also allows the size of the extraction crosscuts to be developed 5.0m wide and 5.0m high. The spacing of the crosscuts skin to skin are set at 8.0m to optimise the draw ellipsoids. The flexibility of the method allows adjustments to be made to the sub level intervals and crosscut spacing to suit localized geotechnical conditions. This will apply particularly to the upper level SLOS access levels.

Access and ventilation will be provided by two ramps developed from surface boxcuts. The ramps will traverse poor ground conditions over some 2000m each to reach the first underground mining levels. The mine design contemplates the development of twin 6.0m wide and 6.3m high ramps to cater to larger haul trucks. The twin ramp system will be required to facilitate the planned production rate of approximately 7,500 tonnes per day (tpd) of kimberlite and country rock.

Following extraction from the Karowe Underground sub-level, kimberlite will be trammed to the Karowe Mine process plant where it will be processed at an average rate of 7,000tpd (~2.5mtpa) using existing crushing, milling, XRT, DMS concentration and final recovery facilities.

MINING AND PROCESSING

The Karowe Underground SLOS and SLC design and schedule were derived using Datamine’s Studio 5D Planner software. The main development ends were sequenced in 5D Planner and this information was sent to the EPS Scheduler for the mine schedule. The design was also evaluated against the geological block model to determine the grade, tonnes and dollar per tonne. Total LOM development requirements are estimated to be 43,700m lateral and 2,635m vertical development.

Processing mined kimberlite at a rate of approximately 2.5mtpa will be achieved using the existing milling and diamond recovery circuit. The existing crushing, milling, XRT, DMS concentration and final recovery facilities will be used and confirmatory metallurgical testwork will be conducted to confirm the applicability of the existing comminution circuit for the processing of the harder kimberlite from depth.

Existing coarse and fine tailings facilities will need to be expanded to accommodate the additional volume of material generated from the mining and processing of underground mined kimberlite.

To read more details in the company’s press release, CLICK HERE


About Lucara
Lucara is a leading independent producer of large exceptional quality Type IIa diamonds from its 100% owned Karowe Mine in Botswana. The Company has an experienced board and management team with extensive diamond development and operations expertise. The Company operates transparently and in accordance with international best practices in the areas of sustainability, health and safety, environment and community relations.

To Stop by Lucara’s website, CLICK HERE


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