First... congratulations!
You've dug your first "Cast I" button ...so called because the whole thing is one solid piece of cast high-copper-content brass. (That metal's color is "orange-ish" rather than the yellow of typical brass. Strictly Confederate-made, and a product of the Deep South. Many were apparently manufactured at the Atlanta Arsenal. They start showing up in the second half of 1863, and were issued almost exclusively to the Army of Tennessee and other Deep South CS troops. Few are found in Virginia ...and those few got there on the uniforms of Longstreet's Corps, who received the Cast I buttons while on detached service with the Army of Tennessee in late 1863.