From the RuneScape Wiki, the wiki for all things RuneScape
Iron ore is unrefined iron. A player with a Mining level of 15 or higher can mine iron ore from iron rocks found in various mines, granting 35 Mining experience for each ore mined. A player with 15 or higher Smithing can smelt iron ore into an iron bar by using it on a furnace, granting 12.5 Smithing experience, although there is a 50% chance that it will be too impure to smelt unless a player is wearing a ring of forging or is using the Super Heat spell from a normal spell book, in which case the chance will be 100%. Note: A ring of forging only lasts for 140 smelts.
A player with 30 or higher Smithing can smelt iron ore into a steel bar by using it on a furnace along with 2 coal or just one using the Blast Furnace, granting 17.5 Smithing experience. It can also be used with level 16 Summoning, 7 spirit shards, and 1 gold charm to summon a Granite Crab.
Another way to get iron ore is as a drop. The Flesh crawler is known to drop iron ore regularly.
A player can smelt an Iron ore into an Iron bar through the Smithing skill by using it on a furnace, granting 12.5 Smithing experience, but has a 50% success rate. This requires level 15 Smithing. Iron bars can then be used on Anvils to create Iron items. A player can also smelt a iron ore into a steel bar by using it on a furnace along with 2 coal or just one using the Blast Furnace, granting 17.5 Smithing experience. This requires level 30 Smithing.
If a player were to mine his own iron ore and smelt it into iron bars with a Ring of forging at a furnace near a bank the player would be able to make a lot of money in a short period.
A free player, though unable to use any enchanted rings, can still mine the iron ore for direct selling. The current price of iron ore should be taken care, though. The selling of these ores is relatively quick, usually complete after 1 second-5 hours of exchange placement.
A player can efficiently collect iron ore by one of a few methods:
1. Use a Spirit kyatt to teleport to the Piscatoris Fishing Colony and mine iron ore, then use a ring of dueling to teleport to Castle Wars. Bank, and repeat.
2. Teleport to Ardougne by means of a player owned house portal (it is cheaper than the regular teleport), and then run to the mine south of the Legends' Guild. Mine Iron Ore at the three rock formation. Use a ring of dueling to teleport to castle wars, bank, and repeat.