Zhao Jian Jian*
Zimasco Private Limited, Zimbabwe
*Corresponding author:Zhao Jian-Jian, Zimasco Private Limited, 00263 Harare, Zimbabwe
Submission: September 10, 2024: Published: September 25, 2024
ISSN 2578-0255Volume12 Issue4
The Great Dyke is a narrow, linear NNE trending body of mafic and ultramafic rocks 550km in length and between 4km and 11km wide that intrudes Archaean granitoids and greenstone belts of the Zimbabwe Craton [1]. The claims are distributed over a 550km stretch of the Great Dyke, from Tengenenge in the north to the CSC area south West of Zvishavane in the South. There are totally 11 seams of chromite mineralization in great dyke. Seams 1 and 2 are mostly exposed in Middle and South Dyke. The Middle Dyke has seam 1 up to seam 4 exposed. Seam 2 to 10 is better exposed in the North dyke [2]. Conventional mining method employed currently for Dyke underground mines in Zimbabwe is Resue Breast Stoping. This method is done using handheld pneumatic jackhammers for drilling the stope face, with waste packing, stope chrome cleaning and tramming by manual methods. Zimasco is the largest ferrochrome producer in Zimbabwe, as well as chrome ore. This was practiced on a number of Zimasco shafts namely at Rhodesdale 1 Shaft in Lalapanzi, Ngezi Mine, Pedlin mine, Hocberg mine all in Ngezi and Section 19 Shaft, Ivo 50 and Royal 3 in Mutorashanga. However, to improve on productivity, a number of initiatives were adopted which include use of Battery Locomotives for tramming mainly at Rhodesdale 1 Shaft and Section 19 Shaft. An idealised underground mining layout complete with shaft, drives and box holes would look similar to the schematic below (Figure 1). The essential considerations in the extraction of chrome seams are the removal of the seam with minimum fragmentation of the material and with minimum contamination by waste. The method of exploitation almost universally employed is that of Resue Stoping on breast faces (for dips ≤30°) and up-dip faces (for dips >30°).
Figure 1:Resue breast stoping method for dyke underground chrome mining.
The generally adopted technique is shown in the Figure 2.
a. Drilling and blasting the hanging wall waste down the
full length of the stope face. The waste derived from the blast is
packed between timber props to fill the stope from footwall to
hanging wall. Excessive waste (30%) due to swell is lashed into
the seam drive for tramming to a waste pass and subsequent
hoisting to surface for dumping. The stope floor is swept clean
before breaking the chrome.
b. The chrome seam exposed on the footwall is broken to
induce separation and lifted with as much care as possible to
avoid fragmentation.
c. Support consists of 2 rows of support close to the face,
and back filling behind.
Figure 2:Operation step of reuse stoping method.
Resue stoping on breast faces is in most cases practiced on advance stoping with retreat mining only employed in areas where the ground is considered blocky and unstable. Up-dip stoping is seldom applied where dips are less than 30 . In such cases, local faulting/jointing will be the determining factor. Up to now, there is no other efficiency mining method for this ultrathin seam chrome ore. While more than 95% chrome resources in Zimbabwe belongs to this type. So the best way is to develop as much as shaft to enhance the production across the whole dyke.
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