dilleb] COPPER DEPOSITS OF REDDING REGION, CAL. 129 
all washed away and the original sulphides be near the surface. The 
gold from the gossan washed away in past ages accumulated in Town 
Creek and afforded the rich placer mines of the early days. 
Zone of enrichment. — Next below the gossan occur the dark ores 
which the miners usually designate " black oxide," but in reality they 
appear to be chiefly dark sulphides, chalcocite, and sphalerite, gen- 
erally mixed with pyrite, chalcopyrite, and barite. In some places 
there is only a thin film of this material between the gossan and the 
yellow sulphides, but generally in the Bully Hill district it extends 
for 10 feet or more to the predominantly yellowish sulphides. Chal- 
cocite is most abundant near the borders of the pyritous ore mass, 
and small nodules of it are found in the adjacent fissile clays at much 
greater depths. Bornite occurs locally near the gossan with black 
sulphides; also at greater depths with chalcopyrite, pyrite, and sphale- 
rite. While its secondary origin in the enriched zone not far beneath 
the gossan is evident, that at greater depths is more doubtful. 
Fresh chalcopyrite was found in the zone of enrichment incrusting 
secondary chalcocite ; hence it is evident that some of the chalcopy- 
rite must be secondary. The lower limit of the zone of enrichment 
is not sharply defined, and it will be discovered only by detailed 
investigations. 
Zone of primary sulphides. — The workings in the Bully Hill mine 
in October, 1902, had attained a depth of about 512 feet, which is 
considerably below the lowest level where the writer saw any of the 
secondary ores. 
However, some of the miners report local "black oxides" at that 
depth. The ore in this zone is chiefly pyrite, with some chalcopyrite 
and a varying amount of sphalerite. 
Gang ue. — The gangue mineral of a large part of the Bully Hill ore 
is barite. It is rarely abundant, and often is so finely disseminated 
as to be invisible in the ore, yet greatly increases its weight. The 
source of the barite is most likely to be found in the metarhyolite, 
whose feldspar appears to contain a notable amount of barium. 
Selvage. — On the east wall there is generally a white selvage-like 
material which ranges from a mere film to 12 feet in thickness. A 
hemical examination by George Steiger shows it to contain Na 2 20, 
K 2 3.28, and H 2 11.87, from which it appears to be a mixture of 
I J (kaolin and sericite. It affords an excellent material for lining the 
converters. This white selvage is sometimes found on both sides of 
jhe ore, and, combining, cuts off the ore. The selvage may be wholly 
bsent, in which case the ore is directly attached to the wall rock. 
he wall rock of metarhyolite on the west side is usually much fresher 
han that opposite, and shows the hard, knotted, flinty character of 
nil |ihe surface. 
.ml Prospecting. — It is evident that gossan, and to some extent also the 
;ii.j peculiar knotted or brecciated metarhyolite, is to be the main guide 
Bull. 213—03 9 
