274 BROWN A HERON : GEOLOGY AND ORE DEPOSITS OK TAVOY. 



Heinze Basin and consists of intrusive granite of the ordinary type. 

 Wolfram was discovered in it in the open season of 1916 by native 

 prospectors and, although the region was most difficult of access, 

 numerous concessions were applied for in L917 and great hopes 

 were entertained that a large extension of the main mineral-bearing 

 zone of the district had been discovered. Extensive prospecting 

 has however shown that the actual bearing area is small and is 

 confined to the two concessions of Messrs. Steel Bros. & Co., Ltd., and 

 Mating Sein Khine. They are situated near the contact of the 

 granite and the Mergni sediments above the bend which the Zinba 

 stream makes to the south-west. 



Steel Bros. Zinba. — This concession was granted to The Burma 

 Minerals, Ltd., in 191(5 and at a later date it was sold to Messrs. 

 Steel Bros. & Co.. Ltd. In 1917 it produced 25 tons of concentrates 

 and in 1918 77 tons. It contains several thin veins which are believed 

 to be of pegmatitic origin and to strike north and south, though 

 this observation is uncertain. A good deal of the production, which 

 is won entirely by hand labour, comes from the detrital deposits. 

 The concentrates are practically tin free, the average content being 

 about .] per cent, of metallic tin. Molybdenite, bismuthinite, 

 oxidised bismuth compounds and fluorite also occur. 



According to Dr. Morrow Campbell the order of deposition is 

 molybdenite, bismuthinite, fluor spar and quartz, commencing with 

 the first ; the minerals have been observed in thin bands in this 

 order commencing from the outer granite wall of the vein. In 

 other veins there are intimate intergrowths of molybdenite and 

 bismuthinite and both are sometimes found in the form of rounded 

 pebbles completely enclosed in quartz. Antimonite has also been 

 found in small quantities. Hair-like crystals of bismuthinite 

 enclosed in quartz crystals are known and interesting greisens con- 

 taining wolfram, scheelite, molybdenite, bismuthinite, chalcopyrite 

 and pyrite. In one place Dr. Campbell discovered a tourmaline 

 pegmatite on the wall of a wolfram-bearing vein, while the same 

 authority reports a very large quantity of tourmaline in large quartz 

 veins right on the Siamese frontier at an altitude of about 3.300 

 feet. There are remains of a former covering of sedimentary rocks 

 at about 2,700 feet above sea level on the BpUT west of the mine, and 

 within a mile of the frontier, so that the evidence is strong that 

 the hearing veins occur riear a dome as well as near a marginal 

 contact. 



