You can find relics without having to raid tombs, I have yet to go to a tomb, although I am planning in doing so later, and I find lots of relics. As I travel to a specific location, such as find mercury, along the way I tilt my screen as if my sim is standing on his head. You can see better through the trees to spot more gems, rocks and sites to excuvate.
At the base camp, in China, take all the books the first time there and you can make a lot of money from selling them "back home".
It't a good way to get some extra money, generally never come home with less than 7,000. When you accept an adventure to find metals or gems, you are shown their locations and as you go to collect them you find lots of other goodies.