Idea - When you get your base, it's small, and you need to make it bigger! And to do so, you need to purchase expansions, and like in Diamond/pearl, there are large, tough, unminable boulders that can only be removed via special procedure!{Which, in diamond/pearl, is getting the flag of a rival player} This "special procedure" should be like, buying extremely expensive dynamite/TNT/generic explosive, and placing it on the large boulder to explode!
And there's a chance that the boulder is actually a massive geode/has extremely valuable forms of gemstones!