I am an avid metal detector user. I found four of these ingots on the site of a Civil War fort. In the same area we found a period belt buckle, musket trigger assembly, buttons and musket balls. The ingots I found are in pretty rough shape compared to the ones you have pictured. I have had them tested and they are silver.

The location where the Confederate fort stood has now been developed. The area has been developed for over a century. Concrete was being torn up and we went out and searched the area. I am going to respectfully decline to divulge the location. My state is notorious for taking custody of historical artifacts found on public land by hobbyists.