Here is the full list of all 12 Lost Artifacts: Golden Island achievements worth 1,000 gamerscore.
For constructing a building
For summoning the tortoise
For getting rid of the Wicked Thief
For restoring the mechanisms
For restoring the water wheel
For activating an altar
For speeding up archaeologists
For stopping time
For speeding up construction
For completing all levels with 3 stars
For collecting all rewards
For defeating the Villain