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Blanket mine, Zimbabwe

6th November 2015

By: Sheila Barradas

Creamer Media Research Coordinator & Senior Deputy Editor

  

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Name: Blanket mine.

Location: The Blanket Mine is located in the south-west of Zimbabwe about 15 km west of Gwanda, the provincial capital of Matabeleland South.

Controlling Company: Caledonia Mining Corporation.

Brief History: The Blanket mine started production in 1904. In 1965, Falconbridge acquired the property. Kinross took over the mine in 1993 and built an enlarged carbon-in-leach plant with a 3 800 t/d capacity to treat an old tailings dump together with the run-of-mine ore.

Caledonia acquired the Blanket mine from Kinross in April 2006. Following the implementation of indigenisation, effective from September 2012, Caledonia now owns 49% of the mine.

Caledonia has made considerable capital investments in Blanket’s underground, surface and township facilities. These investments culminated in the commissioning of the No 4 Shaft expansion project at the end of September 2010, which increased the mine’s hoisting capacity from the No 4 Shaft from 500 t/d to 3 000 t/d.

Caledonia is further developing the Blanket mine by installing and equipping the No 6 Winze to access deeper level resources, by completing a tramming loop on the 22 level in June 2015 to allow for increased movement of waste and ore tonnage underground and sinking the 6-m-diameter Central Shaft to a depth of 1 080 m. First production is targeted for January 2016. This will provide access to the current inferred resources below 750 m and enable further exploration, development and mining in these sections along the known Blanket strike.

Brief Description: The Blanket mine is a well-established Zimbabwean gold mine, which currently operates at a depth of about 750 m below surface. Blanket also holds brownfield exploration and development projects on the existing mine area and on its satellite properties, which are within trucking distance of the Blanket metallurgical recovery plant.

Products: Gold.

Geology/Mineralisation: The Blanket mine is part of the Sabiwa group of mines. The mine is a cluster of mines extending from Jethro in the south, through Blanket itself, Feudal, AR South, AR Main, Sheet, Eroica and Lima in the north. These ore shoots occur in the Blanket shear zone, a low-angle transgressive shear characterised by the presence of biotite relative to the massive amphibolites forming the country rocks.

A regional subhorizontal dolerite sill intrudes the above sequence and is emplaced about 500 m below surface. The sill does not cause a significant displacement and, although it truncates all the ore shoots, the mineralised shoots continue undisturbed below the sill.
Active mining at the Blanket mine is conducted over a 3 km strike that includes eight discrete ore shoots.

Mineralisation occurs in near vertical shoots aligned along a north-south axis.

Two main types of mineralisation are recognised: disseminated sulphide replacement reefs and quartz-filled reefs and shears.

Reserves: Total proven and probable reserves, as at October 2014 were estimated at 2.93-million tonnes grading 3.67 g/t of gold.

Resources: Total measured and indicated resources as at August 2014 were 4.05-million tonnes grading 3.82 g/t of gold. Inferred resources of 3.34-million tonnes grading 5.11 g/t of gold are present.

Mining Method: Underground – long-hole open stoping and underhand stoping methods.

Major Infrastructure and Equipment: Following the successful commissioning of Blanket’s No 4 Shaft expansion project in September 2010, the underground workings have increased production to about 1 200t/d. Broken ore is trammed along the 22 level rail system by battery locomotives and the ore car trains are self-tipped onto one of three grizzlys above the ore bins, which are located between 22 level and the 765 m level crushing station. The minus 300 mm rock is held in three underground storage bins.

Payable ore and waste ore are held in separate storage bins and handled accordingly. Ore is gravity fed from these ore bins onto the 765-m-level crushing station conveyor, which deposits the ore onto a vibrating grizzly feeder that, in turn, offloads the oversize ore into a 30 × 20 Telsmith jaw crusher.

The underground crushing station ensures that all the run-of-mine ore is reduced to minus 150 mm in size. This provides for the optimisation and greater efficiency of the automated skip-loading and hoisting operations. This allows mining and hoisting activity to continue without interruption. Blanket No 4 Shaft has been equipped with the first automated loading system in Zimbabwe, which sequentially fills the two 6 t ore skips that are hoisted from the 789 m level to surface.

The Jethro and Eroica shafts and the No 5 and No 6 Winzes are used for transporting personnel and materials underground, and the No 2 and Lima shafts are also used for hoisting ore to surface.

The Blanket gold plant comprises crushing, milling, carbon-in-leach and batch elution electrowinning circuits.

Prospects: In November 2014, Caledonia announced a revised investment plan for the Blanket mine, in terms of which production is expected to increase to an estimated 80 000 oz of gold by 2021, following the investment of about $70-million. This money has been invested in the completion of the tramming loop and installation of the No 6 Winze, which will increase production from January 2016 onwards, as well as facilitate the ongoing sinking of the main Central Shaft to 1 080 m that is well under way. The investment is expected to be funded from internal cash generation and existing cash resources.

Caledonia will also continue to improve its confidence in its resource base and convert resources into mineable reserves and investigate alternative expansion opportunities.

Contact Person: Mark Learmonth.
Contact Details:
Caledonia Mining Corporation,
tel +27 11 447 2499,
fax +27 11 447 2554,
email info@caledoniamining.com or marklearmonth@caledoniamining.com, and
website http://www.caledoniamining.com.

Edited by Leandi Kolver
Creamer Media Deputy Editor

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