collier.] TIN ORES OF TASMANIA. 49 
character of the pay gravel. The contents of each hole is carefully 
washed and the tin ore weighed, and from these results calculations as 
to the probable yield of the ground arc made. On the basis of this 
estimate the fields are let to Chinamen. 
AUSTRALIA. 
In Australia tin ore has been found very widely distributed, and is 
mined in New South Wales, Queensland, South Australia, Tasmania, 
Victoria, and West Australia. The occurences present considerable 
variety, and both alluvial and vein deposits have been worked, though 
the greater part of the tin is produced from alluvial deposits. The 
two best-known localities of stream tin are Vegetable Creek in New 
South Wales, and Bischoff Mountain in Tasmania." All the tin gravels 
of Vegetable Creek are derived from masses of granite that are per- 
meated b}^ numerous tin veins. The width of the channel deposits of 
this creek varies from 5 to 15 chains, or from 330 to 990 feet, but 
the richest portions are reported to be from 1 to 5 chains wide. The 
average thickness of the deposit is reported to be 7 feet, while the 
thickness of the pay gravel averages 2^ feet. The average yield per 
cubic yard of pay gravel is said to be about 20 pounds of tin ore, equal 
to about 0.8 per cent. In this district the mining is done by hydraulic 
monitors and other modern mining appliances. 
The tin deposits of the Mount Bischoff region in Tasmania are largely 
residual gravels derived from decomposition in situ of the bed rock. 
The bed rock of this mountain consists of Paleozoic clay slates and 
quartz, and to a less extent of sandstones and dolomites. The slates 
are traversed by numerous veins of quartz-porphyry. The porphyry 
and also the slates have undergone great transformations, so that all 
of the original feldspar and mica, as well as the primary quartz, have 
been replaced by topaz, tourmaline, secondary quartz, tinstone, and to a 
less extent by fluorspar, arsenious pyrites, and magnetite. The gravels 
are sometimes astonishingly rich in tin. In one instance 2-10 tons-of 
concentrated ore were taken from an area of 60 square feet. Masses 
containing 6 hundredweight, almost free from the matrix, have been 
found. The accumulation of tin ore in the gravel is exceedingly patchy, 
as might be expected in deposits of this nature. Frequently within 
60 feet of the richest deposits the wash dirt is found to contain only 
traces of tin. The ore is first concentrated by sluicing, then crushed 
and further concentrated; 5,500,000 tons of material handled previous 
to 1899 is reported to have } T ielded 41,560 tons of black tin, or 0.81 
per cent of the total material treated. The value of a ton of gravel 
probably averaged about 6s. 10d., or $1.70. The total cost of mining, 
crushing, dressing, and bagging the concentrates amounted to Is. 2^d., 
aRolker, C. M., Production of tin in various parts of the world: Sixteenth Ann. Rept. U. S. Geol. 
Survey, pt. 3, 1895, p. 497. 
Bull. 229—04 4 
