244 BROWN & HERON: GEOLOGY AND ORE DEPOSITS OP TAVOY. 



This theory has been criticised severely by Dr. Morrow Campbell, 



whose views regarding the relative order of deposition of cassiterite 

 and wolfram in mixed intergrowths are much like ours, but in fair- 

 ness to Dr. Jones it must be pointed out that he referred more 

 to the order of deposition as the mineralizers travelled and not so 

 much to the order of deposition in the parts of a vein where both 

 occurred together. He holds that in an intermediate zone, under suit- 

 able temperature conditions, both wolfram and cassiterite would be 

 deposited more or less simultaneously and an occasional specimen 

 showing cassiterite in wolfram in no way detracts from his view 

 that cassiterite deposits at higher temperatures than wolfram does. 

 According to Dr. Campbell :— " In general in such tin-wolfram areas 

 on the contact, the ratio of cassiterite to wolfram is greater in veins 

 in the sedimentary rocks than in those in the granite below. When 

 in granite the ratio of tin to wolfram appears to fall as we move 

 down from the vicinity of the contact." 1 



Our experience is the reverse of this. As a general rule we find 

 that cassiterite is present in relatively larger amounts in veins 

 traversing the granite, than in others which pierce sedimentary 

 rocks. The highest grade wolfram concentrates, i.e., those which 

 contain the greatest percentages of W0 3 , come from mines working 

 in veins at high horizons in the sediments, the richest tinny concen- 

 trates from veins in granite, though there are exceptions to both 

 statements. We are not aware of the existence of any evidence 

 regarding a change in the relative ratio of the two minerals at 

 various levels in the granite. 



With regard to the intermediate character of the ore from Mergui, 

 it is true that, in the aggregate, that district produces a greater 

 proportion of cassiterite than Tavoy, but most of it comes from 

 wolfram-free tourmaline pegmatites— a type absent from the Tavoyan 

 field. In the wolfram-cassiterite quartz veins themselves the pro- 

 portion of cassiterite to wolfram is lower than in many Tavoyan 

 veins. 



It is impossible for geologists unacquainted with the Malayan 

 tin fields to pass an opinion on the validity of Dr. Jones' theory. 

 We note that no physiographical evidence has been brought forward 

 to prove conclusively the contention that the Peninsula has suffered 

 greater denudation than Lower Burma. The existence of the 



1 J. Morrow Campboll (9), pp. 18—20. 



