TIN 



645 



ally has a large length-to-width ratio, a placer of 

 transgressive origin may consist of a sheet of heavy 

 minerals buried beneath marine sediments (Aus- 

 tralia). Placers of this type have yielded large 

 amounts of cassiterite in Indonesia (Bangka and 

 Billiton Islands) and will continue to do so. 



FOSSIL PLACERS 



Any or all of the preceding four types of placers 

 may become fossil placers by burial beneath younger 

 sediments or lava. Uplift and renewed erosion along 

 disrupted drainages may expose such placers irregu- 

 larly, and second-cycle alluvial placers may be gen- 

 erated (Nigeria). Depending in part on the geologic 

 age, the gravels of some fossil placers may be lithi- 

 fied to such an extent that they must be mined by 

 lode-mining methods. In others, major postdeposi- 

 tional changes, such as partial solution of cassiter- 

 ite, may affect the value. 



RESOURCES 



IDENTIFIED RESOURCES 



Tin resources of the world were computed by 

 Robertson (1965) ; his figures were incorporated 

 with some modifications and additions into a report 

 by Sainsbury (1969). These two reports contain the 

 facts and presumptions of the calculations of re- 

 serves and brief descriptions of the main tin-pro- 

 ducing deposits of the world. 



In the present report, new calculations have been 

 made, principally to accommodate this volume's 

 classification of undiscovered resources in both 

 known and unknown districts. Such geologic calcu- 

 lations require a bold and optimistic approach, and 

 new figures are presented herein (table 135). Fac- 

 tors which can be used to estimate undiscovered 

 resources are largely geologic and partly intuitive 

 and include: 



1. History of production. 



2. Rapid rise of reserve figures in newly discovered 



districts, such as Rondonia, in Brazil. 



3. Potential favorability of parts of the world in 



which even basic geologic mapping is lacking. 



4. Unexpected new developments in old districts, 



such as the major ore bodies opened recently 

 in Cornwall. 



5. Comparison of tonnages mined in countries hav- 



ing a long production history, such as Malaysia, 

 with other countries having a substantial pro- 

 duction but with higher grade known reserves, 

 such as Indonesia and Thailand. 

 When these factors are applied optimistically, the 

 potential resources of tin in undiscovered districts 

 seem to be large, and reserves and resources in 

 known districts are increased substantially over the 



previous estimates by Robertson (1965) and Sains- 

 bury (1969). 



The tin reserves and resources of China, Russia, 

 and other Communist countries cannot be assessed 

 accurately from published data. Even the Interna- 

 tional Tin Council has not attempted a tabular sum- 

 mary. For this report, however, we have estimated 

 the magnitude of tin reserves and resources of China 

 and Russia. 



As can be seen from table 135, all the identified 

 tin resources lie within the established tin-producing 

 countries. The figures given for these resources do 

 not differ greatly from those of the previous re- 

 source calculations mentioned above. In this report, 

 inferred reserves for countries with revived mining 

 of substantial amounts of tin, such as England or 

 Australia, are assumed to be equal to or greater than 

 their measured and indicated reserves. In other 

 countries, such as Zaire (the Congo) and Thailand, 

 inferred reserves must be much greater than the 

 figures for measured and indicated ore. 



Probably the greatest departure from earlier 

 reserve estimates is the assignment of substantial 

 proved and inferred reserves for England and Aus- 

 tralia and greater inferred reserves for Indonesia 

 and Thailand. The greater inferred reserves for In- 

 donesia and Thailand are based directly upon a com- 

 parison of grade of material being mined by dredges. 

 Inasmuch as the tin-producing areas in Thailand, 

 Malaysia, and Indonesia are roughly comparable in 

 size, a large amount of tin will no doubt be mined in 

 Thailand and Indonesia before the grade of their 

 alluvial deposits drops to that being mined today in 

 Malaysia. 



Because classes of reserves in this report differ 

 from those in all previous reports, no direct compari- 

 son can be made beyond the figures for identified 

 resources, which roughly correspond to the total in 

 categories historically called measured, indicated, 

 and inferred. 



HYPOTHETICAL RESOURCES 



Evaluation of hypothetical resources can be based 

 in part on the past mining history of an area. 

 Countries such as Malaysia and Indonesia, which 

 have produced large amounts of tin for nearly a 

 hundred years and which can expand their produc- 

 tion greatly if a slight price increase and an ade- 

 quate market warrant, are going to continue to 

 produce tin for nearly as long as they have already 

 done. Other countries, such as Nigeria, have well- 

 known limiting factors which suggest that they may 

 not be able to produce for extended periods of time. 

 Hence, their subeconomic resources must be smaller. 



