Omitiomire Copper Project

The Omitiomire Copper Project is located 140 km by road northeast of Windhoek in central Namibia, in semi-arid savannah-type grazing land.

Omitiomire project area

IBML has planned a two-stage approach to bring Omitiomire into production:

  • Phase 1: The initial project is based on near-surface oxide and mixed oxide-sulphide copper.  In 2013, Craton completed a Definitive Feasibility Study (‘DFS’), a Social and Environmental Impact Assessment (‘SEIA’) and an Environmental Management Plan (‘EMP’) for the Phase 1 project.

 

  • Phase 2: During Phase 2 Craton expects to be able to develop a larger project based on the deeper sulphide copper resource at Omitiomire plus other copper resources which might be discovered within trucking distance of Omitiomire.

 

Geology of the Omitiomire Deposit

Drilling has defined a broadly tabular copper deposit, striking north-south and dipping at a shallow angle (around 20º-30º) to the east.  The deposit forms sub–outcrop, beneath shallow sand cover, over several hundred metres; at depth, drilling has shown a strike length of over 3,500 metres (‘m’).  The deposit is about 10m thick near surface but thickens to the east, where some drill holes have intersected over 100m of copper mineralisation. 

The deposit consists of a number of stacked parallel tabular bodies (“lenses”) which partly merge.  

drill section

Drill section showing stacked ore lenses.  The numbers on the right-hand side of the figure show elevation above sea level

In August 2014, Bloy Resource Evaluation (‘Bloy’) provided an updated resource estimate of 137 million tonnes (‘Mt’) at an average grade of 0.54% copper (‘Cu’) at a cut-off grade of 0.25% Cu.  The resources are reported in accordance with the guidelines set out by the Joint Ore Reserves Committee (JORC, 2012).  The Measured and Indicated categories constitute 71% of the deposit.  

omitiomire resource

Table 2.  Omitiomire resource at a cut-off grade of 0.25% Cu (Bloy, 2014).
Note: The resource figures are not constrained within any form of resource limiting pit shell

In addition, Bloy reported Exploration Target material, also at a cut-off grade of 0.25% Cu, in the range 76 Mt – 155 Mt for 430,000t – 650,000t of metal grading between 0.4% and 0.6% Cu.  Caution: Exploration Target material remains conceptual in nature and might or might not be realised in the future.

Note:  The technical information relating to the Omitiomire resource has been summarised from a report, dated 31 August 2014, provided to Craton by Ms Carrie Nicholls and Mr Michael Rohwer of Bloy Resource Evaluation.  Both Ms Nicholls and Mr Rohwer are Members of the Australasian Institute of Mining and Metallurgy and have sufficient experience to qualify as Competent Persons as defined in the September 2012 edition of the “Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves”.  Ms Nicholls and Mr Rohwer consent to the inclusion of the information in the form and context in which it appears.

Primary copper mineralisation occurs mainly as the mineral chalcocite (Cu2S) with minor bornite (Cu5FeS4) within bands of mafic (amphibole-biotite-plagioclase) schist.  There are no iron sulphides (pyrite or pyrrhotite).  The highest copper grades are associated with bands of strongly-deformed epidote-biotite schist.  Inter-banded felsic (quartz-plagioclase-biotite) gneiss is barren.  Banding is on a scale of centimetres to metres in thickness.

sawn nq dril core

Sawn NQ drill core showing the banded nature of Omitiomire ore.  
The steel-grey mineral is chalcocite and the brown-coloured mineral is chrome-epidote

Primary sulphide copper is oxidised to 20m depth and partly oxidised to 40m depth.  Oxide copper occurs mainly as the mineral malachite (green hydrated copper carbonate) with subordinate chrysocolla (blue hydrated copper silicate) and minor tenorite (black copper oxide).  The proportion of primary chalcocite increases with depth.

omitiomire oxide copper ore

Omitiomire oxide copper ore.  The green mineral is malachite; the blue-green mineral is chrysocolla

Phase 1: Oxide Copper Project

The Company plans initial mining based on three small pits, up to 50m deep, located on near-surface oxide and mixed oxide-sulphide copper.  A Life of Mine open pit plan has been developed by Perth-based Cube Consulting.  The plan is to mine slightly more than 3 Mt averaging 0.6% Cu as oxide copper and 0.33% Cu as sulphide copper.

Plan showing location of initial pits and associated infrastructure

The planned processing plant throughput is 40,000 tonnes per month (‘tpm’).  The initial ore feed will be entirely oxide copper material, which will be processed via acid leach – solvent extraction – electro-winning to produce cathode copper (mainly 99.99% Cu).  Increasing amounts of chalcocite will be extracted as mining progresses; this will be processed via flotation to produce copper concentrate (about 30% Cu).

Phase 1 oxide copper project:  Planned processing flow sheet

The total copper produced during the operation is planned to be 25,570 t.  The project can be expanded by extending and deepening the pits to mine in excess of 6 Mt at 0.86% Cu.  This upside potential scenario was not the subject of the DFS.

Proposed Phase 2 Sulphide Copper Project

The entire copper deposit (oxide and sulphide copper) was the subject of a Pre-Feasibility Study (‘PFS’) which was completed in 2010.  Although that study has not subsequently been updated, many of the conclusions from the PFS remain valid.

The banded orebody is amenable to simple beneficiation.  Copper is concentrated in dark (mafic) bands whereas pale-coloured (felsic) bands are largely barren.

Drill core showing copper-bearing mafic bands and barren felsic bands

The copper-bearing mafic schist bands are soft and heavy whereas the barren felsic gneiss bands are hard and light.  This difference in physical characteristics between copper-bearing and barren bands permits low-cost and effective pre-concentration by dense medium separation (‘DMS’).  Testwork carried out at Mintek Laboratories near Johannesburg has shown that this process doubles the grade of mill feed to +1% Cu.

The main copper mineral, chalcocite, contains 79% Cu.  Bench-scale metallurgical studies have shown 90% recovery from the sulphide zone, to produce a high grade (+50% Cu) concentrate with no deleterious elements such as arsenic and bismuth.  

Phase 2 project:  Proposed process flow chart

The PFS identified the following infrastructure requirements for the Phase 2 operation:

  • A 90 km water pipeline to connect the project to the Namibian water supply network;
  • A 115 km power line to connect the project to the Namibian power grid;
  • Road upgrades either to transport copper concentrate to the existing railway at Nossob siding, or to connect to existing sealed roads to the port at Walvis Bay on the Atlantic coast;
  • An on-site village to accommodate the workforce;
  • A river diversion around the proposed open-cut mine.

 

Infrastructure upgrades proposed for the Phase 2 operation (from 2010 PFS)

Craton has not yet committed to a Phase 2 feasibility study.  It is anticipated that the larger project would be based on the deeper sulphide copper resource at Omitiomire plus other copper resources which might be discovered within trucking distance of Omitiomire.  This project will require a separate SEIA and Environmental Management Plan.

Note:  The technical information contained in this document was compiled by Dr Ken Maiden (MAIG, FAusIMM), a Director of International Base Metals Limited.  Dr Maiden is a Member of the Australian Institute of Geoscientists and a Fellow of the Australasian Institute of Mining and Metallurgy.  He has sufficient experience to qualify as a Competent Person as defined in the September 2012 edition of the “Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves”.  Dr Maiden consents to the inclusion of the matters in the form and context in which they appear.