Ms. Mimbs,
Can you tell us were you found this reference to the "North Georgia Volunteers." There are numerous references to companies in various counties being referred to as (name your county) "Volunteers" and there were several as Company D from several regiments.
The only Barney Casteel that I found was in Company A, 59th Tennessee Infantry Regiment. This company was mustered in at Firestones, McMinn County, Tennessee on 23 NOV 1861. I found no Barney Castel's.
I hope this helps. Please let me know if you have any questions.
Respectfully,
Gerald D. Hodge, Jr.
War Between the States Historian
Historian: 39th Georgia Volunteer Infantry Regiment
http://39thgavolinfrgt.homestead.com/39thHomepage.html