Today's is a brief lesson in geology and geography, fields in which your humble Corpse is no expert (though I'm pretty good at finding places on a world map).
yù chū kūn gāng
"Jade comes from the Kunlun Mountains."
The two varieties of gemstone collectively known as jade, nephrite and jadeite, come from a number of sources, not just the Kunlun Mountains. Jadeite, for example, can be collected on the beaches of Big Sur in California, which I may or may not have done. (It's unclear because I never had the greenish rocks I collected there properly identified.) China's historical and ongoing love of jade is well-known and, in my opinion, righteous, because jade is amazing. There are a number of characters for jade of different kinds: 玉， 翠， 翡， 玖, and plenty more, but that's beyond the scope of this post.
崑 is a reference to the Kunlun Mountains that run through central Asia; their western end is in Tajikistan (Chinese: 塔吉克) and their eastern/Chinese terminus is in 青海 Qinghai province. There's also a lot of mythology surrounding 崑崙山 Kunlun Mountain, which is not necessarily related spatially to the Kunlun Mountains themselves. I leave it up to you, dear reader, to delve into this mythology on your own.
岡 means "hill" or "ridge", and thus is a metonym of sorts for 山, the usual Chinese character for "mountain."
So now you've all been given the general locations of precious stones and metals in China. If a couple thousand years' exploitation hasn't utterly exhausted these sources, which it almost certainly has, you might be in luck if you go to China seeking a fortune in gold and jade. If, you know, the locals, 仙人 immortals, or the Chinese government don't mind.