Correspondence — J". Coggin Brown. 45 



Wolfram and cassiterite are nearly always associated together, 

 though lodes containing one of these minerals, especially wolfram, 

 to the entire exclusion of the other, are known. The mineral associa- 

 tion in order of deposition is as follows : molybdenite, wolfram, 

 cassiterite, native bismuth, bismuthiuite, chalcopyrite, arseffopyrite, 

 pyrrhotite, galena, and blende. Scheelite also occurs in small 

 quantities. In Mr. ltastall's classification of tungsten occurrences 

 into paragenetic sub-types Burma should be associated with Queens- 

 land rather than with Etta Knob and Ivigtut. 



In a paper read before the fourth Indian Science Congress at 

 Madras in January, 1916, of which only an incomplete summary has 

 been published (see Journ. As. Soc. Bengal, n.s., vol. xiii, No. 2, 

 pp. ccii-iii, 1917), I have suggested that the place of fluorine and 

 boron may have been taken by sulphur and arsenic in the pneuraato- 

 lytic stages of ore formation here. I am driven to this conclusion by 

 the universal presence of sulphides, generally in the form of pyrite, 

 in the Tavoyan lodes and the relative absence of minerals containing 

 fluorine and boron. 



Some of our lodes are pegmatites. They contain felspar as well as 

 quartz. They have the composition, structure, texture, and other 

 characteristic features of normal pegmatites, but they carry wolfram 

 and cassiterite as well. I have suggested that others in which the 

 pegmatitic origin is not so clear may represent a hydrothermal phase 

 of pegmatite development resulting in the production of quartz with 

 the ore minerals. There are cases here where true wolfram and 

 cassiterite-bearing pegmatites pass in short distances along their 

 strike directions into pure quartz veins with wolfram and tinstone. 



I do not deny the part played by pneumatolytic reactions as they 

 are generally understood. I cannot account for the greisens which 

 sometimes border the walls of lodes in granite and also carry 

 valuable quantities of ore minerals by any other theory, but I doubt 

 whether fluorine and boron played much part in the reactions. 



It is pleasing to note that Mr. Bastall concludes that there is no 

 real distinction between magmatic segregations and veins in this 

 type of ore-deposit, for if it is correct to regard the pegmatite-aplite 

 group of rocks as differentiation products of granites, it is reasonable 

 to regard their metallic ores as segregations from acid magmas to the 

 same extent. 



The wolfram occurrences in other parts of Burma are not identical 

 with those of Tavoy, though this district produces by far the greater 

 proportion of Burma's output. Tourmaline is present in the Mergui 

 lodes and also in those of the Thaton district. Beryl is a common 

 mineral in the lodes of the Tamethin district. 



Mr. Bastall has alluded to the widely scattered literature on the 

 subject, and to his bibliography on this district the following 

 published papers may be added : " Economic Geology of Tavoy," by 

 J. Coggin Brown; "The Origin of Wolfram and a Preliminary 

 Investigation as to its persistence at depth in the Tavoy District," 

 by Dr. W. 11. Jones. Both these papers are published in a work 

 entitled Lectures delivered at Tavoy under the auspices of the Mining 

 Advisory Board, Superintendent Government Printing, Kangoon, 



