This planet consists of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%); the remaining 1.2% are "trace amounts" of the 80 or so remaining elements. Most of that iron constitutes the core of the planet but we will not run out of iron compounds or iron ore found near to the surface for some time to come.

Why is iron so prominent in this planet and others? Because planets were formed from the stuff bred inside the first stars. The reaction chain for generating energy by nuclear fusion starts with hydrogen and stops after iron has been bred. Iron, if you like, is the ash eventually produced by fusing hydrogen to helium, helium and hydrogen to lithium, and so on. When those first stars "burnt out" after a few billon years, some of them coughed up their ashes in a mighty supernova explosion. In time, new stars were formed. Some of these are still burning and visible at night. One is only visible during the day from a clumped-together iron-rich ash ball called earth.
From the viewpoint of chemistry, iron (like copper) is a tricky element that can form many oxides, sulfides, carbonates, and so on. All these compounds could be used for smelting iron but some are better for that purpose than others.
Sulfides are usually bad news. We know that from smelting copper and expect similar problems when smelting iron. Moreover, sulfur in iron is really bad news, and I therefore will only mention iron sulfides briefly in what follows.
        Rich ores are better then poor ores. What makes an ore rich? In the first place, the relative amount of iron it contains. I will give that number in percent (%). One kilogram of magnetite, for example, contains 0.724 kg of iron. If you get about 700 g of iron for every kilogram of magnetite ore you put into your smelter, you have a smelting efficiency of almost 100 %. That is far from the reality of ancient smelting, however.