Sulphide ores of metals are usually concentrated by forth floation proces. Which one of the following sulphide ores offers an exception and is conventrated by chemical leaching'

Sulphide ores of metals are usually concentrated by both floatation process. Which of the following sulphide ores offers an exception and is concentrated by chemical leaching ?

Sulphide ores, of metáls are usually concentrated by froth floatation process. Which óne of the following sulphíde ores offers an "exception and is concèntrated by chemical leaching.