380 
PROCEEDINGS OF SECTION C. 
first two mentioned. The stone crushed has been about 140,000 tons, 
yielding a product of 144 per cent, of “black tin.” The tin ore 
obtained lias been worth, on the average, about £45 per ton on the 
ground. 
After the stone is taken from the mines, owing to the low yield 
of the general mass of the vein stuff, and the comparatively heavy 
charges for carting to the mills and crushing, it is usually subjected to 
a process of hand-dressing before sending it to the mills, and hence 
the high average yield of ore from the stone crushed. 
The yield of metal from the ore produced by the following rock 
and alluvial formations in the district may be approximately stated as 
follows, the lode ore not having been put through any process of calcina- 
tion : — Herberton porphyry : Crushed lode ore, 69 per cent. Irvine- 
bank sedimentary rock : Crushed lode ore, 62 per cent. Herberton 
porphyry : Deep lead alluvial tin, 73 per cent. Herberton porphyry, 
ranges : Alluvial tin lode detritus, 71 per cent. Tate and CoolgaYra, 
granite: Alluvial tin, 74 percent. 
Until about a year ago it was the custom to crush and prepare all 
the lode tin for the market without washing, the oxide being sufficiently 
clean to dress out therefrom a marketable product ; but at Irvine- 
bank, where the sedimentary rock prevails, calcination and lixiviation 
have recently been adopted, by which the volatile and soluble products 
are got rid of, and the ore raised up to a value of 70 per cent, for 
metal. 
Stream tin taken from the old deep drift beds is of a purer quality 
than that obtained from lodes in the same locality, whether it be in the 
form of detritus from the open gullies or crushed ore from the mine. 
It will be noticed from the list of assays just given that granite 
stream tin yields a larger percentage of metal than either porphyry or 
sedimentary rock; also that ore mined from the porphyry produces a 
higher percentage than ore, in an unroasted state, taken from rocks of 
aqueous origin, being less impregnated with minerals which lower its 
value, such as copper, arsenical pyrites, and bismuth. 
Stream tin from the granite has mostly a ruby tinge, and has been 
ascertained to be slightly impregnated with nickel, iron, and lime. 
The bluish-grey ore from the porphyry contains iron and lime, but no 
nickel. Mr. Henderson, Government Analyst, in a recent report on 
the subject, considers that the difference in the colour of the ore is not 
the result of chemical composition, but is more probably due to its 
deposition under different physical conditions. 
DRESSING MACHINERY. 
At present there are in operation and in course of erection in the 
district five stamping mills of from five to fifteen heads each. They 
are all driven by steam power, except the Bischoff Mill, which is 
worked by a turbine, operated by water from the Walsh River. The 
mills are all of the usual type. 
The process of dressing the ore varies in the different mills, but 
in all cases the advantage of hydraulic classification, and the cleaning 
of the rougher portion of the sand by the process of jigging, is recog- 
nised. The treatment of the slimes is different in different mills. At 
