ORES OF TIN AND TUNGSTEN 73 
Cornwall, Malaysia, including the islands of Billiton and 
Banka, and adjacent areas in southern Burma, Siam, and 
Yunnan; also in north-western Tasmania, Bolivia, and 
Nigeria ; small deposits have been found in Germany, New 
South Wales, and Alaska. No important supplies have been 
found in North America. 
Cornisa Mines—The tin-field of greatest historic interest 
is Cornwall, which was worked by the Pheenicians about 
1000 or 600 B.c. They cast the tin into cross-shaped ingots 
weighing about 150 Ib. each, that were well adapted for 
transport on horseback and on the floor of a boat. The 
stream tin is derived from lodes which are generally associated 
with masses of Carboniferous or Lower Permian granite 
and quartz-porphyry dykes, both of which were injected 
when the Lower Paleozoic rocks of Cornwall and Devon 
were folded by mountain-forming movements. The pre- 
dominant rock is slate, locally known as killas, in which the 
lodes contain ores of copper ; but when the lodes pass down 
Into granite the copper is replaced by tin (Fig. 9, p. 21). Dol- 
oath Mine, which was 3 miles long and 3000 feet deep and 
1 the deepest of British metal mines, was begun for copper ; 
the workings entered granite at the depth of between 120 
and 1500 feet, and were continued for tin. The primary 
tin ore occurs mainly in the vein-quartz of the lode; but it 
In places impregnates the granite walls thus forming the 
Capel.” 
The significant minerals associated with tin ores contain 
boron and fluorine; they include tourmaline, a complex 
Variable borosilicate ((AlB),SiO, + %), topaz, the fluo- 
silicate of aluminium ((AlF),Si0,), and fluor-spar (CaFy). 
The felspar beside the tourmaline veins has been altered to 
kaolinite (p- 169). The Cornish tin lodes were formed under 
Pneumatolytic conditions by the attack of superheated 
steam with boric and fluoric acids upon the felspars and 
their conversion into tourmaline, topaz, and kaolinite, while 
the quartz was corroded, and cassiterite deposited. Where 
lime was present the fluoric acid formed fluorite. Primary 
tin ores throughout the world have this pneumatolytic 
Origin, with local variations. 
Mz. Biscuorr, Tasmania—The Mt. Bischoff tin mine in 
northern Tasmania was discovered in 1871; mining was