STRUCT IRES AND CHARACTERISTICS OF TUNGSTEN DEPOSITS. 231 



main granite intrusions arc longer than those running across them, 

 and the fractures of the granite itself are longer and better determined 

 than those in the overlying covering of sedimentary strata. 



The Tavoy field is not an old one. Mining of a sort commenced 

 in l'.)0 ( .) and since then has been, with rare exceptions, carried on 

 under a particularly pernicious tribute system. Exploration has 

 in a great measure been left to the cooly, who, quite naturally, 

 only concerns himself with rich mineralized patches. The denscness 

 of the forests and the thickness of the soil cap have added to the 

 difliculty, and mine plans are not compulsory until leases have 

 been granted. It is only in tin; past three years that systematic 

 working plans have been available, and these have reference to the 

 larger mines alone. It is safe to say that the majority of the larger 

 veins have not as yet been explored from end to end, and. when to 

 these facts are added complications introduced by faulting and other 

 geological anomalies, it will be seen that it is not easy to arrive at 

 accurate data on this important subject. 



There are several large and well-defined veins in the Paungdaw 

 granite with strike extensions of at least 1,200 feet and possibly 

 they continue very much further than this. In the Hermyingyi 

 section of the field the outcrops of veins in granite have been traced 

 for many hundreds of feet without their limits being determined exactly. 

 Again, bands or /ones of mineralised country are sometimes met 

 with which contain irregular veins throughout their length, though 

 it may be impossible to trace any particular one for a great distance. 

 For example, there are more or less continuous workings on the main 

 " A " zone at Pagaye over a distance of 3,200 feet, and it is probable 

 that this by no means limits the extensions of the zone. 



From these large and well-formed veins on the one hand, to small 

 insignificant stringers on the other, every gradation exists, and it is 

 not uncommon to find examples of them all on a single mine. As 

 a general rule veins are larger and longer in the granite than they 

 are in the sedimentaries away from it. 



Both wolfram and cassiterite show a tendency to deposit in thin 

 stringers or leaders, and little veinlets, half an inch or so in thick- 

 ness, are to be found which reproduce the internal structures of 

 large veins. Such stringers are, for their size, often excessively 

 rich in the metallic minerals and patches of ore occur in them which 

 are practically solid, without the admixture of any other mineral. 

 instances occur at Yanmazu, Pagaye, Pa-in and other mines. When 



