2<)o mu>\v\ & HERON : GEOLOGY and ore deposits of tavot. 



Owing to the softness of the rocks in the decomposed zone. 

 underground production work lias been carried on to a great extent 

 without the aid of machinery, though an air compressor with an 

 equipment of machine drills is used in the development work now 

 being undertaken on Big Hill. Here, helow the limit of alteration. 

 both granite and sedimentaries are exceedingly hard. 



Bands of greisen form borders to the veins in the granite and 

 both granite and greisen from the altered zone rapidly break down 

 on exposure to the air. The granite is an exceptionally white 

 and fine-grained rock and is practically devoid of hlack micas or 

 of iron ores. It is decomposed to a greater depth on Tin Hill than 

 011 Big Hill. The veins, with one or two notable exceptions, do 

 not carry through from one section to the other and were perhaps 

 for ned in different fissure systems. The vein quartz is of the 

 opaque, white, massive variety as a- rule ; glassy quartz and good 

 crystalline structures are rare. All the veins carry mica.. In the 

 deeper parts of the veins galena, pyrite. chalcopyrite. molybdenite 

 and zinc blende are found with wolfram and cassiterite. In the 

 upper portions the sulphides have been leached away and the 

 wolfram is often partially changed into tungstite. Molybdenite 

 is commonest in the Waterfall vein. Oxidised Compounds of 

 bismuth, derived from the sulphide, are found in the hill-side detrital 

 deposits on the eastern end of Big Hill. Fluorite is not uncommon 

 in small quantities. 



Lvi-dences of movement such as slickensides, crushed quartz and 

 contorted micas are often seen. In the. Kanban chaung section 

 oi the mine there is an extraordinary occurrence of a tluorite-topaz 

 rock bordeiing a wolfram-molybdenite-cassiterite vein in sediments. 

 If is described in detail in another chapter (p. 58). 



The detrital deposits of the hill sides are of great extent and 

 value and are extensively worked in the rainy season by water 

 which is led on to them by an elaborate and lengthy system of water 

 races and flumes. In the bottom of the valley there occurs a thick- 

 deposit of clay, pebble and boulder beds partly, in our opinion, of 

 detrital origin and partly the result of torrential stream action. 

 This is worked by means of a monitor. An old river terrace with 

 rich wolfram and cassiterite-bearing gravels has recently been 

 Uncovered at a height of 75 feet above the present level of the 

 Maungmeshaung chaung. It owes its preservation to an over- 



