Take a magnet and see if it sticks to the fireplace metal. If it sticks its iron (not pewter) and the mantle fixture can be removed and sand blasted. Id then take it and have it coated withan electrostatic coating that cn be color coded. The process is called "powder Coating" and its really will restore the fireplace surround and the mantle. Id tick with a color that is either neutral or will enhance the room, (no pinks or flaming oranges). Id suggest a powder coating of a semi gloss black. When you get the fireplace all disassembled, take it to a powder coating company and they will usually clean it for coating.
Coating is an electrostatic powder pigment that is then baked on at a high temp. (Pewter would never make it in a fireplace, its too "meltable" in high temps and would easily dent when a log hit it.