Modern Mining June 2016

MINING News

Marthinusen & Coutts, a division of Actom, has again demonstrated its ability to undertake challenging work on rotating machinery. The division was recently called upon to assist Gold Fields’ South Deep Twin Shafts when the mine experienced a failure on one of the stators on its main winder installation. Marthinusen & Coutts rewinds South Deep stator

Rob Melaia, Engineering and Technical Executive at Marthinusen & Coutts, explains that the sheer physical size of the stator alone is quite unique – especially in terms of the challenges of rewinding such a large unit. “The 65-ton stator mass driving a squir- rel cage induction motor very probably makes this the largest motor of its type in the world,” he says. “While there are many larger synchronous motors, it is highly unlikely that there are larger squirrel cage rotor machines.” He says that the 6 MW, 3,3 Hz, eight- pole design of the stator makes it greater than a 90 MW, 50 Hz, 750 RPM equivalent, and that when one adds in the fact that these are driven by cycloconverters, the uniqueness of the installation is apparent. Following a thorough assessment by Marthinusen & Coutts, it was ascertained that the stator insulation had failed prema- turely after approximately eight years, when one would normally expect a 30-year ser- vice life from this machine. This failure was unusual in that there was no physical exter- nal damage and no signs of overheating. Furthermore, with two parallel connected motors one would expect both to fail if a severe external transient was the root cause. The prevailing root cause remained cyclical stresses on the stator insulation due to ther- mal expansion and contraction cycles. 2013, Kibo carried out additional resource drilling in late 2013 leading to the publica- tion of a new mineral resource statement of 16,48 Mt at 1,14 g/t (550 000 oz) in February 2014. Kibo announced the com- mencement of a Definitive Feasibility Study (DFS) on the project in October 2014. Since then it has completed a Preliminary Economic Assessment and commenced a Prefeasibility Study which together will comprise the first stage of the DFS. Lake Victoria Gold’s Imwelo gold project is located along strike and contiguous with the Imweru project. It effectively forms an extension of Kibo’s Imweru East Mineralised Zone and has a published JORC mineral resource of 205 200 oz at a grade of 2,3 g/t (of which 90 800 oz is in the measured and indicated categories). Lake Victoria was granted a mining licence over the project in January 2015 which should enable mine development to progress rapidly. 

Pictured with the stator are (from left) Richard Botton, Divisional CEO at Marthinusen & Coutts, Michael Olivier, Engineering Manager at South Deep, Chris van Heeswijk, electrical consultant to South Deep, and Rob Melaia, Engineering Executive at Marthinusen & Coutts.

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Gold projects in Tanzania to be amalgamated Kibo Mining, listed on AIM, has signed a Memorandum of Understanding (MOU) with Lake Victoria Gold to amalgamate the companies’ respective Imweru and Imwelo gold projects into a new com- pany (NEWCO). The board of NEWCO will comprise a mix of Kibo and Lake Victoria management combining significant experience across exploration and mine development.

within 12 to 18 months of forming NEWCO, targeting 100 000 oz per annum within 24 to 30 months. “The past two years’ steady work on the Imweru DFS advanced the Imweru project to a level where we could come to an arrangement with Lake Victoria Gold, which will see the amalgamation of the respective projects on a like for like basis, to create a project with critical mass and a clear path to near-term production,” com- ments Louis Coetzee, CEO of Kibo. The Imweru and Imwelo projects are located in the Lake Victoria goldfield of northern Tanzania, approximately 35 km west of AngloGold Ashanti’s Geita mine and within a similar geological setting, prospective for Archaean age ‘greenstone’ hosted gold mineralisation. After acquiring the Imweru project in

T h e p r o j e c t s h a v e c omb i n e d JORC-compliant stated resources of approximately 755 300 ounces. Based on upside potential identified in the exist- ing Imweru CPR, the combined project will provide NEWCO with the potential to achieve a plus 1 million ounce resource in a relatively short time frame. The two companies have a production target of 50 000 oz of gold per annum

14  MODERN MINING  June 2016