372 Reviews — Geology of the Bawdwin Mines, Burma. 



contaminated with dolomite, and when the mixed rock is heated to 

 about 1,000° C. in an electric furnace the magnesite becomes darker 

 in colour. On slaking the magnesite material forms a Tery coarse 

 gritty powder, while the dolomite lime forms a milky paste which 

 can be easily removed by washing; hence a separation can be readily 

 effected. The fuel-testing and ore-dressing sections of the Depart- 

 ment have also conducted much useful work in various special 

 directions, and the whole report gives evidence of much energy and 

 activity. 



R. H. K. 



III. — Geology and Oee-deposits of the Bawdwin Mines, Burma. 

 By J. CoGGiN Brown, llec. Geol. Surv. India, vol. xlviii, pt. iii, 

 pp. 121-80, with 8 plates, 1917. 



fllHE Bawdwin ore-deposits are enclosed in a series of rhy elites and 

 J_ rhyolitic tuffs, which form a kind of dome protruding through 

 the younger Pangyung (Cambrian or Ordovician) strata. Above 

 these is a regular sequence to the Devonian, and then an uncon- 

 formable series of Jurassic sandstones, clays, and limestones. At one 

 horizon in the Silurian many specimens of Monograptus have been 

 found. The rocks of the volcanic series are much weathered, and 

 their original character is not always easy to determine, but all the 

 ore-bodies seem to lie in the tuffs rather than in the rhyolites. The 

 ore-bodies all lie in a well-marked zone or channel about 8,000 feet 

 long and 400 or 500 feet wide, possibly connected with an ancient 

 fault system. 



There are three distinct lodes of lead-silver-zinc ore, but of much 

 more importance is the Chinaman ore-body, which is an enormous 

 replacement deposit of zinc-lead-silver ore, lying on the hanging- 

 wall side of the ore-channel. The essential constituents of the 

 ores are galena and zinc-blende with a little pyrite and chalco- 

 pyrite. The ore is always argentiferous, showing on the average 

 about 19 oz. to the ton. The gangue consists of metamorphosed 

 country rock and a little quartz. The zinc ore appears to be as 

 a rule of earlier formation than the galena, while the copper and 

 iron sulphides are intermediate. Carbonates, sulphates, and other 

 oxidized ores of lead and zinc have long been worked by the Chinese, 

 but are now nearly exhausted. 



The author considers that the origin of the ores is to be attributed 

 to the intrusion of granite masses into the ancient volcanic rocks, 

 hot solutions having risen along shattered fault-planes previously 

 produced and replacing rocks readily susceptible of mineralization, 

 such as these rhyolitic tuffs would appear to be. The reserves of 

 sulphide ores are very large, and after many vicissitudes the mines 

 appear to be now in a flourishing condition, largely owing to the 

 construction of a narrow-gauge railway 50 miles long, and bid fair 

 to become one of the great zinc-lead producers of the world. 



E. H. R. 



