THE WITWATERSRAND GOLD REGION . 745 
and marcasite, which vary somewhat in amount in different places. 
Though the sulphides are usually abundant where the ore is rich in 
gold, yet they are also often abundant where the ore carries very little 
gold, so that the quantity of them is not necessarily an indication of the 
richness of the ore. They are sometimes very finely disseminated 
in minute particles, at other times in a coarser condition, generally 
crystalline, and sometimes in -concretionary or radiating nodules. 
They are generally oxidized for a few hundred feet from the surface, 
giving the ore a brown, rusty appearance, while at a greater depth the 
ore assumes a gray or greenish-gray color. 
The gold is finely disseminated in the ore and is rarely noticeable 
to the naked eye, though it can sometimes be seen in thin flakes 
incrusting the pebbles, or in small particles in the siliceous matrix. 
The gold is not uniformly distributed through the reefs. There 
are rich places and poor places, but in spite of this, it may be said that 
the gold is much less irregular over long distances than in most gold 
deposits, and in no other part of the world can so many mines be seen 
on the same ore body. 
Most of the ores mined in the Witwatersrand district are of low 
grade, though bodies of higher-grade ore occur, and more rarely 
small amounts of very rich ore are found. The value usually varies 
from a grade too low to work profitably up to about $25 per ton and 
sometimes to very much more. Under the ordinary conditions exist- 
ing in the district, ore of $6 per ton is about as low-grade material as it 
pays to work, and most of the ore at present being treated ranges 
from about that value up to $12 or $15 per ton. The average value 
of the ore mined in the Witwatersrand district in the year ending June 
30, 1905, was from 36.888 to 37.123 shillings, or a little less than $9 
per ton. 
In the early days only the higher-grade ores were worked, but 
with the increased facilities for mining and milling, the cost was 
diminished, and the tendency is, therefore, to save the lower-grade 
ores which were once thrown away, and to mix them with the higher- 
grade ores, thus bringing down the average value of the ore treated, 
but adding to the aggregate amount of gold produced. 
The mines vary in depth from a few feet to over 4,000 feet, quite a 
t “Transvaal Mines Department,” Annual Report of the Government Engineer 
for the Year Ending June 30, 1905, p. 8. 
