Explanation on AS 6 needed for Coal Mine

While going through the definition of AS 6, it said about its applicability except: 1) Forests, Plantation etc 2) Wasting assets like Extraction  of Minerals, Oil and Gas etc 3) Expenditure on R&D 4) Livestock. Since, Coal mines come under Wasting asset, hence, this standard should not be applicable to it. But still we use 'Depletion Method' for calculating depreciation of a Coal mine. Why?