452 



UNITED STATES MINERAL RESOURCES 



Table 92. — Summary of identified resources of niobium and 

 tantalum, in the world 



[Identified resources: Specific, identified mineral deposits that may or 

 niay not be evaluated as to extent and Rrade, and whose contained miner- 

 als may or may not be profitably recoverable with existing technology 

 and economic conditions] 



Nb205 content Ta205 content 

 (tons) (tons) 



Reserves^ (see table 89): 



North America 1,918,600 6,470 



South America 9,050,500 5,450 



Europe 142,250 



Africa 2,744,500 60,000 



Total reserves 13,855,850 71,920 



Total reserves rounded 14,000,000 72,000 



Total conditional ^ resources 



(see text) 14,000,000 72,000 



Total identified resources 28,000,000 144,000 



1 Reserves: Identified deposits from which minerals can be extracted 

 profitably with existing technology and under present economic condi- 

 tions. 



^Conditional resources: Specific, identified mineral deposits whose con- 

 tained minerals are not profitably recoverable with existing technology 

 and economic conditions. 



About 14 million tons can be identified as a mini- 

 mal figure for reserves of NbzOs in deposits in the 

 world, and similarly a figure of 73,000 tons is mini- 

 mal for reserves of TaaOj. Additional resources of 

 probable lower grade exist at many of the explored 

 deposits as unevaluated protore bedrock beneath 

 some surficial weathered deposits in some carbonatite 

 complexes and in some weathered pegmatite and 

 granite deposits. Some deposits also contain lower 

 grade material that was not included in reserve 

 calculations because it was below the grade of ma- 

 terial being considered at the time of evaluation, 

 and some deposits have been identified as containing 

 niobium and tantalum minerals but have not been 

 sufficiently explored or evaluated. These materials 

 in these deposits all constitute conditional resources. 

 The distribution and extent of known low-grade or 

 unevaluated deposits suggest that such conditional 

 resources are at least equal to the computed reserves 

 or 14,000,000 tons NbaOs and 70,000 tons TajOa. 



UNDISCOVERED RESOURCES 



Undiscovered resources no doubt occur as blind 

 ore bodies in known carbonatites or as ore bodies in 

 undiscovered carbonatites in known carbonatite 

 provinces. These hypothetical resources will con- 

 tinue to be discovered through continuing geologic 

 and exploration activities and constitute probably 

 several times the amount of currently known 

 resources. 



Some undiscovered resources termed speculative 

 resources might lie in undiscovered carbonatite 

 provinces or in new geochemical and geologic en- 

 vironments for these elements. For example, until 



the post-World War II era, commercial niobium 

 deposits were considered to be restricted to peg- 

 matites and related placers; the discovery of low- 

 grade large-tonnage carbonatite-pyrochlore deposits, 

 however, changed the whole resource picture for 

 niobium. 



One might speculate that such a low-grade large- 

 tonnage type of source lies undiscovered for tanta- 

 lum and that additional new types of sources exist 

 for niobium. Conceivably, unknown fossil placers 

 exist that are large low-grade resources. Discoveries 

 of such resources will depend on future scientific 

 and technological advancements in exploration and 

 geologic knowledge in order to discover the deposits 

 that lie beneath great areas of volcanics, younger 

 sedimentary rocks, and unconsolidated materials. 



PROSPECTING TECHNIQUES 



Inasmuch as alkalic-rock complexes and associ- 

 ated carbonatites at the present time are the chief 

 targets for large low-grade niobium deposits, their 

 recognition is the first step in exploration. Recogni- 

 tion has been made in the process of geologic map- 

 ping, through aerial observation and photography, 

 and through geophysical surveying. The common 

 circular plan and concentric arrangement of rocks 

 constituting alkalic complexes can be distinguished 

 and rock types can be identified by the usual 

 geologic-mapping techniques, and these discordant 

 structures are sometimes evident on aerial photo- 

 graphs in areas of surface exposure. 



Where these structures are covered with overbur- 

 den or younger rocks, their magnetite content can 

 be a factor in their detection. Both airborne and 

 ground magnetic surveys have been employed to 

 successfully detect magnetic anomalies, some of 

 which have been shown to be caused by carbonatite 

 niobium deposits. The natural association of nio- 

 bium with uranium and thorium makes radiation 

 detectors a useful exploration tool. Many occurrences 

 of niobium have been found with the aid of these 

 detectors, and new improved airborne radiometric 

 detectors have great potential for prospecting. Seis- 

 mic surveying and gravity measuring techniques 

 have proved useful where information on depth of 

 overburden or information on differences in rock 

 densities was desired. Future prospecting methods 

 no doubt will employ combinations of these tech- 

 niques, both airborne and on the surface, to outline 

 the basic targets for exploration. 



Once the target is identified, it must be evaluated 

 by conventional exploration procedures. Niobium 

 and tantalum minerals are not easily identified, and 

 niobium and tantalum are not easily detected with- 



