Laws pertaining to private lands distinguish between surface collecting (picking up objects laying on top of the ground) and any ground-disturbing, or digging for artifacts. Laws pertaining to state and federal lands do not distinguish between surface collecting and any type of digging for artifacts.
It is legal to collect artifacts from the surface of private property, IF you have written permission from the landowner. Be sure not to trespass, though.
On private land, it is legal to dig or metal detect for artifacts IF you have written permission from the landowner, and IF you have notified the Georgia Department of Natural Resources in writing five (5) business days before you begin. This includes all ground-disturbing activities, including on Civil War sites.
It is generally illegal to dig human burials and/or collect human skeletal remains or burial objects. Additionally, it is unlawful to receive, retain, dispose of, or possess any human body part (including bones), knowing it to have been removed from a grave unlawfully.
To surface collect, metal detect, or to legally dig on any state property, you must have a permit from the Georgia Department of Natural Resources. State property includes state parks, historic sites, wildlife management areas, and state forests, as well as state highway rights-of way, navigable river and stream bottoms, and the Atlantic coast all the way to the three mile limit.
Generally, it is illegal to surface collect, metal detect, or dig on any federal lands without a federal permit. Federal lands in Georgia include Corps of Engineers lakes and the lands around them managed by the Corps, U.S. Forests, National Parks, National Wildlife Refuges, and military bases.