JOHANNESBURG (Reuters) - Shares of South Africa's Merafe Resources were up more than 4 percent on Monday after the ferrochrome producer said it expected earnings to more than double for the six months to June, boosted by higher production and better sales. South Africa's largest producer of ferrochrome, an ingredient used to make stainless steel, said headline earnings per share could to climb up as much as 142 percent to between 8.6 and 9.2 cents per share from 3.8 cents last year. Headline EPS, the main measure of profit in South Africa, excludes certain one-time items. Merafe, which supplies stainless steel mills in Europe, America, China and Japan said it also benefited from the weakening of the rand against the U.S dollar. Sales of its main metal ferrochrome rose by 25 percent in the period. The company's shares were up 4.35 percent to 1.44 rand by 0844 GMT, their highest level in more than three years.