Bronze ores can be gathered while mining with a pickaxe or a shovel. There is a 2.5% chance to find this colored ore. You'll need level 80 mining skill to begin smelting bronze into ingots. Using these Bronze Ingots to craft weapons will give you 40% fire dmg. And 14 total resistance when crafting armor.
Armor crafted with bronze ingots:
Physical resist: 3
Fire resist: 0
Cold resist: 7
Poison resist: 2
Energy resist: 2