direction as well. The discovery of new, rich, ore

bodies can put a lower yielding one out of business, or

the development of techniques for concentrating lower

grades may reduce the final cost of processing them to

less than that of processing higher grades by other

means. Nonetheless, the highest yielding (lowest cost)

ore bodies almost always are exploited first, and

mining becomes progressively more costly as a result.

 The principal factors relating to metals

acquisition, thus, are the nature of the ore body itself

(size, depth, richness, chemical and physical composition,

and location) and the techniques available for its

discovery and exploitation. But metals acquisition

consists of more than locating ores, gaining access to

them, separating the richest ores and hauling them to

the surface; once at the surface, ore must be worked

into an almost pure form. Separating the process into

mining and refining is useful mostly for definitional

purposes; the process is a continuous one from mine to

factory and any technological change reducing the cost

of acquisition, or refining, tends also to reduce the

cost of the metal delivered at point of use.

 Technological change at all points, coupled with

rich and accessible ore deposits have allowed metals

costs to remain low since 1860; but the existence of