LEAD 



329 



may be somewhat limited, or have special applica- 

 tions, when used in the search for specific types of 

 ore bodies. In general, the surface EM systems have 

 been most successfully applied in the exploration for 

 massive sulfides beneath thin glacial overburden ; the 

 IP systems are widely used in the exploration for 

 disseminated sulfides of the porphyry copper or Miss- 

 issippi Valley types, although disseminated barren 

 pyrite, graphite, and some clay minerals also give IP 

 responses. The AFMAG system is useful in locating 

 deep conductive features and can be used to trace 

 major faults and belts of rocks that have a wide 

 range of conductivity. 



Many important lead-producing deposits have been 

 discovered as a result of geophysical prospecting. 

 These include the Brunswick, Heath Steele, Kidd 

 Creek, and many others in eastern Canada, the Lady 

 Evelyn in northern Australia, the Gortdrum and 

 Silvermines deposits in Ireland, deposits in the Skel- 

 lefte area, Sweden, the Vihanti district in Finland 

 and others (for a more complete list see Pemberton, 

 1966, and other sources) . 



PROBLEMS FOR RESEARCH 



The reserves and identified world resources of lead, 

 unlike resources of many other mineral commodities, 

 appear to be adequate for the foreseeable future. 

 Despite an accelerating rate of consumption since 

 World War II, these reserves and resources have not 

 only kept pace with extraction but have been sub- 

 stantially increased as a result of highly successful 

 exploration in many countries. Enormous submargin- 

 al resources have been recognized in the ocean basins 

 in the form of heavy-metal-rich manganese nodules, 

 which eventually may become a competitive source 

 of lead. It would appear that the main problems con- 

 cerning lead are related not so much to the avail- 

 ability of resources as to mining, processing, and use 

 of lead in our modem mechanized society. As these 

 aspects are beyond the scope of this paper, they are 

 noted here only briefly. 



Of chief concern is the toxicity of lead to humans, 

 resulting in a variety of health hazards, particularly 

 in the urban environment, and the resultant loss of 

 markets for some lead products as selected uses of 

 lead are restricted or prohibited. For example, recent 

 legislation has virtually eliminated the use of lead 

 pigments in interior paints and greatly restricted 

 their use in many exterior and industrial applications. 

 Similarly, legislative action has been directed toward 

 reducing or eliminating lead in high-octane gasoline. 

 Although such action may be required to bring about 

 the adoption and use of some catalytic exhaust-con- 



trol devices and to prevent atmospheric contamina- 

 tion, the advantages of tetraethyl lead in controlling 

 the burning rate of gasoline in high-compression 

 engines, which greatly decreases the consumption of 

 gasoline under conditions of constant performance, 

 may force the adoption of smog-reducing exhaust 

 systems that are compatible with at least a small 

 quantity of lead in most gasolines, or that remove 

 lead along with carbon monoxide, nitrogen oxides, 

 and unbumed hydrocarbons. Other factors leading to 

 decreased use of lead include the expanding use of 

 plastic cable sheaths and caulking compounds and 

 the use of alternate compounds in solder, type metal, 

 and coatings. 



Despite these restrictions on the use of lead, in- 

 creased consumption is anticipated as a result of the 

 accelerating use of automobiles and trucks through- 

 out the world, the development of battery-operated 

 vehicles for delivery and commuter transport, the 

 growing demand for lead as an additive to improve 

 the machinability of steel, brass, and other alloys, 

 and the small but possibly increasing use as radia- 

 tion shielding that will be required in the wider 

 adoption of atomic energy. 



More directly related to the problems of reserves 

 and resources are the many difficulties inherent in 

 utilization of fine-grained, complexly intergrown 

 massive ores that constitute an important part of 

 the reserves of lead and other metals in southeastern 

 Canada, Eastern United States, Japan, and else- 

 where. Despite many attempts, some of these ores 

 have not been amenable to processing efficiently or 

 profitably by conventional milling and smelting tech- 

 niques. Continued development of chemical ore- 

 processing methods and of continuous-smelting tech- 

 niques that do not require clean separation of galena, 

 sphalerite, pyrite, and copper sulfide minerals should 

 lead to greater development of these massive sulfide 

 ore bodies. 



REFERENCES CITED 



Agard, J., 1967, Conclusions genetiques, tirees de I'etude 

 des gites strataformes de plomb, zinc, baryte, dans les 

 formations carbonatees du Maroc, in Brown, J. S., ed., 

 Genesis of strataform lead-zinc-barite-fluorite deposits 

 (Mississippi Valley type deposits) — A symposium, New 

 York 1966: Econ. Geology Mon. 3, p. 316-321. 



Anderson, C. A., 1969, Massive sulfide deposits and volcanism: 

 Econ. Geology, v. 64, no. 2, p. 129-146. 



Bauchau, Christian, 1971, Essai de typologie quantitative des 

 gisements de plomb et de zinc avec la repartition de 

 I'argent: Bur. Recherches Geol. et Minieres Bull., sec. 

 2, no. 3, p. 1-72; no. 4, p. 1-47. 



Behrend, Von F., 1950, Die Blei-und Zinkerz Fuhrenden 

 Impregnations Lagerstatten im Buntsandstein am 

 Nordrand der Eifel und ihre Entstehung, in Dunham, 



