The billionaire claims Vale is misleading investors by claiming local prosecutors had closed an investigation into alleged illegal practices related to Simandou.
Higher imports by the world's second-biggest bullion consumer could support benchmark gold prices, which have corrected nearly 17% from an all-time high of $2,072 in August.
Scientists say coal ash from the Punta Catalina power plant revealed high concentrations of arsenic, selenium and other potentially harmful heavy metals.