From Command and Conquer Wiki

A Ore Refinery was a facility used in the Great World War II to separate the ore gathered by Ore Trucks. It could store up to 1000 units of ore, storing additional ore required Ore Silos to be built. When built it deployed a single Ore Truck to gather ore for it, more Ore Trucks could be built from a War Factory.

With the introduction of Tiberium as the planets major resourece, Ore refineries became inadiquate because they did not selter their workers from the effects of Tiberium. Tiberium Refineries replaced them by the time of the First Tiberium War.