Bronze is an alloy from the Industrial Craft 2 mod which is required for many things. It is made with the dusts from Copper and Tin in a 3:1 ratio. Bronze Tools are 30% more durable than Iron, having approximately 350 uses before breaking. With the abundance of Copper and Tin, about twice as much of each Ore can be found in the world over Iron Ore, making Bronze Tools is a good way to keep mining while saving your Iron for important Machinery, Weapons or Tracks.
Bronze has an EMC value of 256, (same as Iron) so if you have an Energy Condensor or Transmution Tablet then making your iron into bronze then making tools is 30% more effecient.