DEEP Iron Furnaces

Adds DEEP furnace variants for the Iron Furnaces mod.

Furnace Tier	Fuel Yield	Speed	Block IDs
Lead	50	200	1676,1677
Silver	150	100	1678,1679
Amethyst	75	400	1680,1681

Note: Fuel Yield here is in terms of items smelt per fuel used, not in terms of time burning per fuel used

Known bugs and issues None so far :3