The Goblin Diplomacy quest is required. This quest brings you into contact with the Cave Goblins (the Lost Tribe in question) living below Lumbridge Castle and also involves the mysterious HAM clan (the only NPC clan currently in existence). After finishing the quest, players can access the Dorgeshuun mines. These mines contain iron and silver rocks and one of the goblins there buys both of them so it is a very good place to powermine and still make some money. The mines also provide a shortcut to the Lumbridge slayer caves as well as often being used for the Wanted! quest.
From StrategyWiki, the video game walkthrough and strategy guide wiki