This is the first paper to study the market response to “Joint Ore Reserve Committee” –compliant announcements made by Australian mining firms. Results from an event study based on matched firms suggest that these announcements are highly value relevant, with the market reacting in a significantly positive way to both exploration and resource announcements. Larger abnormal returns are found to accrue to smaller firms, to firms that use positive adjectives in their announcement headlines and to firms whose announcements imply larger percentage increases in resource levels. We also find evidence of markets anticipating both exploration and resource announcements a few days before they are released, which may be suggestive of some insider trading.