emmons] PLATINUM IN COPPER ORES IN WYOMING. 97 
Thus far three large bodies, about 40 to 50 feet iu diameter aud 12 
to 30 feet high, have been opened. The upper one immediately below 
the wash was a gossan of iron oxide carrying about 9 ounces of silver 
per ton, with a trace of gold, from which the copper had been pretty 
completely leached out. Below this came silicates and carbonates 
of copper. The zone of enriched sulphide below the oxidized body, 
which alone was accessible, is apparently larger and certainly richer, 
and extends 30 feet or more above the level. It shows two large ore 
bodies of no definite outline inclosed in highly decomposed diorite. 
The latter, in its extreme form called " talc" by the miners, is a white 
kaolinized mass of the consistency of soft clay, but often retaining 
something of the original granular structure of the rock. Near the 
ore bodies covellite grains are so uniformly distributed through it as 
to give the appearance at a little distance of basic silicates in a white 
feldspathic rock. The remarkable feature of the ore is the abun- 
dance of the rather uncommon indigo-blue copper sulphide, covellite 
(CuS). The upper part of the body is slightly stained with iron oxide, 
while in the lower part some pyrite is visible, but not in relatively 
large proportion. Cuprite occurs here and there in brilliant ver- 
milion red crystals, and is sometimes reduced to native copper. The 
covellite is rather irregularly distributed through the kaolin-like 
mass, but sometimes occurs in massive lenses up to 2 feet thick. In 
so plastic a mass no definite structure could be observed in the mine, 
but some of the pyritous ore on the dump showed a certain vein-like 
structure. A specimen of this, which was examined microscopically 
by Mr. Lindgren, shows that the covellite replaces the pyrite directly, 
without the formation of intermediate minerals; that the ore has a 
cellular structure, apparently resulting from reduction in volume 
during its conversion, and that the roughly rounded cavities are 
often lined with soft white silica in mammillary crusts, the manner of 
occurrence indicating that it was formed by solution, either simulta- 
neously with or immediately after the formation of the covellite. 
In two places secondary pyrite of later formation than some of the 
! covellite was observed. 
Sperrylite could not be distinguished in the thin section. From 
the description given by Wells and Penfield of that which they were 
able to separate, it probably occurred in ore similar in character to 
this, and from its fresh appearance it seems probable that the sper- 
rylite was an original constituent of the sulphide ore. More definite 
knowledge as to its manner of occurrence will probably be obtained 
when the deposit has been opened at greater depths and beyond the 
reach of surface alteration. 
Bull. 213—03 7 
