A gaping hole in the ground yawns behind the ruined palace. A faint purple glow illuminates this area at night, but there are few here to see it. This city has been dead for centuries, still cursed by some terrible doom. Interlopers find themselves in the arms of Death before they find this quarry. The wizard does his work in peace, away from the worlds of men and beasts alike.
He thinks back to when he found the toxic ore. His colleagues had always thought the city devoid of any worth, and said as much whenever they had the opportunity. For all their braggadocio, they were truly ignorant. The wizard would not believe in tales. He would find out for himself what treasures that ancient doom had left intact, for him alone to uncover. And he would leave the others to their blindness, and keep his just rewards all to himself.
At least, so long as these minions prove reliable. He could not, of course, mine the toxic ore himself. A preposterous idea! Nor could he refine it. He had tried cajoling adventurers into coming here, to aid him in acquiring this blighted fruit. But they had died, horribly, screaming. The wizard can hear them still, on cold, windless nights. These new friends of his, summoned from another world entirely, were not so weak.
The Building Blocks are from a plane of existence very different than this terrestrial one. They are masters of cube-like shapes, reworking all that surrounds them into images of themselves, just without limbs. For these square-shaped creatures are used to a world of cubes and right angles, and so they forge the matter of this world into shapes they know as best they can. And they do so easily, for they are immune to the toxic effects of the magic that infuses this strange, unique ore. They pull it from the ground both day and night, never weakening beneath its emerald glow. They put it through the refining procedures, stacking the final product — still toxic, but in a form the wizard can work with — into luminous piles of blocks.