yofe on the Formation of Gold Ore. — vott Kraatz. 105 
set, but deteriorate rapidly in depth. As a result of the rot- 
ting of the pyrites, brown and black veins are common. One 
vein is rich in stibnite, which carries gold in the form of 
coarse lenticular grains. Where the antimony mineral is de- 
cayed the native gold is found embedded in the yellow 
antimony oxide. Occasionally the gold is found in the bor- 
ders of intrusive dykes. The veins which occur in the granite 
(underlying the Swazi formation) decrease rapidly in gold 
c(»ntent as depth increases, even though they may be very 
rich near the surface. 
Auriferous conglomerates are characteristic of the Cape 
formation, which rests unconformably upon the Swazi beds. 
The conglomerate strata carry a variable quantity of gold. 
They consist essentially of quartz pebbles which are held to- 
gether by a siliceous cement. The gold is found almost wholly 
between the pebbles. When it occurs in them it seems to have 
been squeezed into small crevices. The greenish gray matrix 
that binds the pebbles together shows niacroscopically ])yrite 
and small quartz fragments, with occasionally some chlorite. 
Oold is seldom visible to the unaided eye: but it is also a 
rare thing to see gold in the matrix under the microscope. 
Dr. Koch found that pyrite, magnetite, zircon, rutile, musco- 
vite, chlorite, secondary quartz and gold constitute the ce- 
menting matrix. The pyrite is usually rolled or rounded and 
seldom occurs in the usual combinations, qc 02 (210), oo (210) 
(100) or (111). Dr. Koch determined and I can corrobo- 
rate it, that the gold is always later than the pyrite and 
nearly always united with or completely grown around the 
latter. Since gold in small quantity is not always easily dis- 
tinguished from the sulphitls, a larger quantity of the so-called 
concentrates,* i. e. the pyrite liberated b}^ the stamps, was 
examined. Under the microscope are seen numerous small 
crystals, which are partly recognizable as (juartz and ])artly 
a>* small gold crystallites. If the pyrite be now digested for 
several hours in a very dilute solution of potassium cyanide 
the small metallic crystals disappear and in their places re- 
main only small irregular shaped cavities. Since pyrite which 
contains no gold is not attacked, even by 24 hours of treat- 
ment with the same potassium cyanide solution, the micro- 
*Furnished bv Dr. Kossler of Frankfurt a. M. 
