Ringosis

I found that note and took the minecart. Are the ingots in the same room as the Shield Sigil? How many were in there?

I've just cleared the battery, checked everywhere thoroughly and I've only got 8 ingots. I've heard there are 20...what have I missed? The only thing I can see that even might have some is the minecart. I pushed the level first time and ended up in that little room with the shield sigil. Now when I go back I can't choose to not push the lever. Did I miss a bunch down there?