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
