The Treatment of Cryptocurrencies is treated the same as shares and any other derivatives such as CFD's.
If they held for long term capital appreciation they will classified as Capital Gains Tax, if it is used for speculation purposes the gain or loss will be included in your taxable income.
See this article: http://www.sars.gov....urrencies-.aspx
If you need any advice, contact me, I have been successful in many such tax objections.
Mark Vorster CA(SA)