Usually I wouldn't recommend Extracting Materials in The Upper Abyss since it is a gankfest. However, this area is out of the way and very good for Platinum, Adamantium and Garnet. On each of these islands you will find 5-6 Adamantium Deposits at any given time. You will also find 3-4 Platinum Deposits. Usually there is only 1 or 2 Garnet per island if you're lucky.
The only mobs that are on these two islands are Wriggots, they are roughly level 32 and don't pose much of a threat. If you run out of Adamantium and Platinum Deposits on these islands head just a tad west to the main island and Extract some goodies there.
Items of Interest
Greater Adamantium Ore
Pure Platinum Ore
Big Garnet Ore