Collect Sourcestone Ore from the Spectral Harvesters. You may also find some unharvested ore in the remains of the fallen constructs. Once you've collected the Sourcestone Ore, deliver it to Kain Sunsworn in Lastlight.
When this location was attacked, our soldiers bled out their lives and our machines bled out their sourcestone. So now the harvesters are collecting it to make Regulos the Destroyer even more powerful.