LEAD 



327 



result in a loss of the lead resources (A. L. Clark, 

 oral commun., 1972). 



Known and partly explored lead deposits of pre- 

 sumably large size also occur in strata-bound ore 

 bodies in central Tennessee, central and south- 

 central Missouri, northern Arkansas, central Texas, 

 northeast Washington, and central Kentucky in the 

 United States; in several areas in western Canada; 

 in central Europe; in North Africa; and in the 

 U.S.S.R. Other low-grade deposits are known in 

 several mining districts in the Rocky Mountains and 

 Great Basin, and in numerous districts that contain 

 vein and replacement deposits in other parts of the 

 world. Similarly, many low-grade, lead-bearing mas- 

 sive sulfide deposits in the Eastern United States 

 have not been fully explored or developed, at least 

 during recent decades, and some may contain sig- 

 nificant recoverable resources. Eventual exploration 

 and development of some of these low-grade depos- 

 its are expected to disclose, from time to time, sec- 

 tions that are of fairly high grade. 



Another conditional, but perhaps unconventional 

 resource of lead and other metals is the mineralized 

 sediments that occur in the thermal deeps of the 

 Red Sea basin (Degens and Ross, 1969). According 

 to Bischoff and Manheim (1969, p. 535), the upper- 

 most 10 meters of the Atlantis Deep in this basin 

 contains 50 million metric tons of mineral-bearing 

 sediment containing 3.4 percent of zinc, 1.3 percent 

 of copper, 0.10 percent of lead, and about 1.6 

 ounces per ton of silver. The adjacent Discovery 

 and Chain Deeps contain similar sediments of lower 

 concentration, and presumably other undiscovered 

 thermal areas in the world's ocean basins are the 

 sites of metal-enriched sediments. Like the man- 

 ganese nodules, exploitation of these deposits will 

 pose many problems. 



HYPOTHETICAL RESOURCES 



Throughout the history of mining and exploration, 

 only a few of the larger mining districts have been 

 totally worked out and abandoned. Successive gen- 

 erations, armed with new concepts, new techniques, 

 and new-found optimism, have successfully rede- 

 veloped old mines and discovered new deposits that 

 were somehow overlooked by their predecessors. In 

 many areas throughout the world, small or unim- 

 portant districts have also been developed into ma- 

 jor producers. With the passage of time, mining 

 has been carried to greater and greater depths, and 

 new, totally concealed ore shoots and even centers 

 of ore deposition have been discovered. Areas that 

 hold promise for the discovery of new ore centers 

 in active or formerly active mining districts in- 



clude, among many examples, the central plateau 

 of Mexico, the Cordillera of Peru and adjacent coun- 

 tries, the districts of Kazakhstan that are under- 

 going accelerated development, and even the classic 

 districts of Europe, United States, and Canada. 



Like the "Identified Resources," the "Hypothetical 

 Resources" include ores that are technologically 

 recoverable as well as those that are subeconomic. 

 Any attempt to quantify the amount of lead that 

 may be contained in them would be perilous, but it 

 may be generally estimated to be equal to half or 

 more of the known world reserves. 



SPECULATIVE RESOURCES 



The volume of recoverable and subeconomic lead 

 ores in undiscovered districts cannot be estimated, 

 but they may equal or exceed all of the reserves cur- 

 rently known throughout the world. During the past 

 few decades, new mines and ore centers that rank 

 among the largest that are known have been dis- 

 covered in Canada, Australia, United States, and 

 other countries throughout the world. These depos- 

 its occur in a variety of geologic terranes, but had 

 remained undiscovered because they were totally 

 concealed by barren rocks or because insignificant 

 exposures did not indicate their true size or grade. 

 Inasmuch as vast areas of possible mineral-bearing 

 rocks underlie glacial debris in North America, 

 Europe, and Asia, deep soil and other surficial de- 

 posits in the tropic, temperate, and arid regions of 

 the world, and even the marine waters of the con- 

 tinental shelves, it is certain that similar deposits 

 will continue to be discovered during the indefinite 

 future. Many of these deposits are amenable to dis- 

 covery through geophysical and geochemical explora- 

 tion ; others, such as those that are thoroughly oxi- 

 dized or deeply buried, will be discovered only as a 

 result of imaginative geologic analysis and coura- 

 geous physical exploration. Inasmuch as lead de- 

 posits are widely distributed in many different geo- 

 logic environments throughout the world, such 

 geologic analysis will be applied most successfully 

 to specific types of lead deposits in specific geologic 

 terranes. As in the past, it will be chiefly based on 

 continuing studies of the genesis of ore deposits and 

 the features that determine their distribution and 

 localization in the earth's crust, and it must be 

 coupled with a willingness to consider and test 

 pioneering concepts of ore deposition and distribu- 

 tion. 



PROSPECTING TECHNIQUES 



The principal new discoveries of lead deposits 

 like most other types of mineral deposits, have been 



