What is a mineral that occurs in a quantity that is economically worthwhile to mine?

The correct option is ORE.

An ore is a type of rock which contains sufficient minerals with important elements which can be economically extracted from the rock. Ore are usually extracted through mining, they are then extracted to remove impurities and to refine the valuable minerals.

This would be an ore. An ore is a substance with metals and other materials that can be used therefore it is worthwhile to mine.