Why do oxide copper ores sometimes need less grinding before leaching than sulfide ores?

In mineral processing, the extent of grinding required depends on the subsequent extraction method. For oxide copper ores, which are frequently processed via leaching, complete liberation of the copper minerals from the gangue is not always necessary. The ore needs to be crushed and ground only to the degree required to expose the surface of the minerals to the leaching agent.1

In contrast, sulfide ores typically undergo selective flotation following the grinding stage. This process relies on reagents to create an attraction between the copper mineral surfaces and air bubbles to separate them from waste materials. Because flotation requires an optimal degree of mineral liberation to be effective, sulfide ores generally require more intensive grinding than oxide ores destined for leaching.1