MINING
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Primary non-sulphide zinc deposits formed the initial targets for the company. Most deposits of zinc are formed of zinc sulphide, sphalerite (ZnS2) and the zinc grade of the ore is generally between 5% and 8%. Following crushing and milling individual mineral grains are liberated and those containing zinc are separated from the other minerals and a concentrate of the zinc bearing minerals, running from 53% to 58%, is obtained. The zinc concentrate is then shipped to an electro-refinery where zinc metal is produced.
When zinc sulphide is near the surface, it is unstable and will over millions of years react with air and water to form a variety of minerals, including: oxides, carbonates, silicates and aluminium silicates. Most commonly a mixture of these minerals is formed. However, as oxidation is generally the prime reaction, they are collectively referred to as “oxides”.
These “oxide” minerals each have different properties so that a process designed to concentrate one mineral may not work for another. The mixed mineralogy of oxide deposits frequently requires complex processes to recover a high proportion of the zinc, and as each process has its own costs, such an approach is rarely economically viable. A process that recovers all the zinc, irrespective of its mineralogy is likely to be more attractive. This may be achieved either by hydrometallurgical techniques that dissolve out the zinc or by pyrometallurgical techniques that “boil” off the zinc, the latter, however, tend to be very energy intensive.
The hydrometallurgical approach enables the zinc to be recovered either as metal or some other refined product. However such processing requires substantial capital expenditure, and to justify this only larger deposits are likely to be economic.
ZincOx undertook a global literature search for oxide deposits. This found that zinc deposits frequently consist of several small high grade pods of mineralisation. The extent of those pods near the surface is generally small and therefore the potential to generate large tonnages of oxide zinc minerals is very limited. The study concluded that higher grade deposits had generally been processed by pyrometallurgical methods at a time when energy was relatively cheap, and so these deposits are generally exhausted. The lower grade deposits may remain unexploited but are generally too small to justify hydrometallurgical treatment.
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To date the company has successfully obtained interests in two major zinc oxide deposits: Jabali, in Yemen and Shaimerden, in Kazakhstan.
There are, in addition, a small number of other substantial zinc deposits in which the company would be interested to participate. While attempts to date to secure an interest in these projects has not been successful, they remain potential targets.
 Constructing crushers on site at Jabali
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