average level in the earth's crust as a whole, 10,000

tons of material would have to be handled to obtain each

ton of copper. Technology would be sorely pressed and

costs could be expected to rise substantially.

 Clearly, the situation confronting the miner,

and hence the rest of the economy, is not the sudden and

complete exhaustion of ore bodies, but rather the steady

worsening of the yield of ore concentrations, and the

necessity, in underground operations particularly, to

incur greater costs as the works expand and the mines

deepen. In that case, ore must be hauled further,

ventilation and water removal problems become more

difficult, and finally a point is reached at which the

cost of extracting ore from the given mine, given

the price at which ore is selling at the time, is so

high that operations are no longer profitable. Thus,

a considerable amount of ore may be left in the ground

unexploited and the mine closed, possibly to be reopened

should ore prices increase or should new and cheaper

methods of extraction particularly favorable to the

specific mine be developed--provided the mine has not

deteriorated too greatly in the interim.

 So it is also with new, unmined deposits. A

deposit not rich enough to be exploited when discovered

may later be developed as new techniques become available

or as the yields of formerly richer deposits become

poorer. Of course, the situation works in the opposite