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Namibia
Otjihase Mine (Central)

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 Location:
0 km from Otjihase, Namibia

  Regional Office:
Windhoek, Office O2A South Block Maerua Mall Centaurus Road
Windhoe
Namibia
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Fax264 61 249 138
WebsiteWeb
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  • Overview
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  • Geology
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  • Processing
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  • Reserves
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Overview

StatusCare and Maintenance
Mine TypeUnderground
Commodities
  • Copper
  • Silver
  • Gold
Mining Method
  • Room-and-pillar
Processing
  • Flotation
Otjihase consists of two underground mines (Otjihase and Matchless) and an 800ktpa copper concentrator, currently on care and maintenance. The operations were in production until September 2015, producing high quality concentrate sought after for blending.


Owners

 
CompanyInterestOwnership
Labour Investment Holdings 2.5 % Indirect
Weatherly International plc 97.5 % Direct

Deposit Type

  • VMS


Summary:

The Otjihase deposit comprises five sub parallel, spatula-shaped, mineralised zones namely Shoot A, Shoot B, Shoot 2, Shoot 3 and Shoot 4. Shoots A and B are known collectively as the Main Shoot in mine terminology because of their close proximity, but geologically they are separate entities. The shoots consist of massive sulphides composed primarily of chalcopyrite and pyrite, hosted in a magnetite rich quartzite. Of the five, only Shoot A is consistently mineralised and forms the bulk of the mineral resources.

With the exception of Shoot B, which is slightly elevated above the southern margin of Shoot A, the westerly-plunging mineralised shoots occur at approximately the same stratigraphic level and are separated by more than 150m of barren or weakly mineralised quartz-mica schists that dip north westerly at 16°.

The northern margins of the shoots are abrupt, whereas the southern margins are gradational, consisting of thin bands and lenses of mineralisation, or disseminated mineralisation, in the quartz-mica schist country rocks. The footwall contact between the lowermost mineralised band and the underlying quartz-mica schists is usually sharp. The hangingwall contact is often gradational due to the presence of zones of disseminated mineralisation.

Each of the shoots has a gossanous outcrop and extends down plunge for more than eight kilometres. The mineralised shoots are cut by a series of sub-vertical northerly trending normal faults that down-throw the shoots progressively deeper towards the west. The faults separate the deposit into a number of blocks (or compartments) named after the faults that occur along the western margin of each block.

The Otjihase deposit lies in quartz-biotite chlorite and quartz-biotite schists and consists of a shoot of massive and disseminated sulphides about 200m wide plunging to the west at about 6°. The deposit dips to the northwest at about 16°. The shoot thickness varies between 4m and 12m with an average between 6m and 8m. The hanging wall is a quartzbiotite chlorite schist with distinct schistosity which sometimes spalls. It is competent if supported. The declines and other development are usually excavated in competent quartzmica schists.

The mineralisation stretches from near surface to depths of 800m and more and is divided into compartments by north-south trending faults. These faults are water bearing and contain flowing material and are thus difficult to traverse.


Mining Methods

  • Room-and-pillar


Summary:

Historically, mining has been by means of room and pillar with primary extraction rates ranging from around 80% to 85% in the upper Otjihase compartment to 45% in the Kuruma compartment.

The Otjihase compartment extends from the surface down to a depth of approximately 260m below surface. The upper area, down to around 180m below surface was mined by JCI using a room and pillar system based on 5m by 5m square pillars with 15m wide rooms on dip and strike.

The ore is trucked to an underground crusher station immediately east of the Hoffnung East fault from where it is transported by means of 10 conveyor belt sections to a point where it is tipped into kibbles pulled by locomotives which take the ore the last 1.5km to the mill receiving bins on surface.


Crushing and Grinding


Processing

  • Flotation

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Summary:

The following sections of the process plant were examined:
• Concentrator plant;
• Electrical sub-station for the plant complex;
• Standby generator setup;
• Ore receiving;
• Crushing and storage;
• Compressor house;
• Milling plant;
• Copper flotation;
• Pyrite flotation;
• Concentrate thickening;
• Concentrate storage and filtration;
• Drying and loading area;
• Water storage and management;
• Lime plant;
• Workshop areas;
• Laboratory;
• 61m thickener tailings handling;
• Backfill plant; and
• Tailings dam.

The Otjihase concentrator is designed as a sequential flotation plant treating a base metal sulphide mineral deposit. The economic metals in the ore are copper and silver with pyrite and small amounts of gold. Historically, the flotation plant sequentially produced copper concentrate, and pyrite concentrate with silver being primarily contained in the copper concentrate.


Combined production numbers are reported under Central


Reserves at December 31, 2014:

CategoryTonnage CommodityGradeContained Metal
Proven 921,064 t Copper 1.74 % 16,084 t
Proven 921,064 t Silver 7.06 g/t 6,508 kg
Proven 921,064 t Gold 0.4 g/t 374 kg
Probable 1,230,754 t Copper 1.28 % 15,762 t
Probable 1,230,754 t Silver 0.18 g/t 8,801 kg
Probable 1,230,754 t Gold 0.18 g/t 218 kg
Proven & Probable 2,151,818 t Copper 1.48 % 31,846 t
Proven & Probable 2,151,818 t Silver 7.11 g/t 15,309 kg
Proven & Probable 2,151,818 t Gold 0.28 g/t 592 kg
Measured 1,279,257 t Copper 2.32 % 29,786 t
Measured 1,279,257 t Silver 9.42 % 12,053 kg
Measured 1,279,257 t Gold 0.54 g/t 693 kg
Indicated 4,190,379 t Copper 1.95 % 81,619 t
Indicated 4,190,379 t Silver 7.7 g/t 32,275 kg
Indicated 4,190,379 t Gold 0.32 g/t 1,330 kg
Inferred 3,402,131 t Copper 1.38 % 46,841 t
Inferred 3,402,131 t Silver 5.73 g/t 19,483 kg
Inferred 3,402,131 t Gold 0.23 g/t 775 kg


Heavy Mobile Equipment:

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Corporate Filings & Presentations:

DocumentYear
Annual Report 2016
Project Description 2013
Annual Report 2012
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Aerial view:

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