The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1915-02-04

tude than around the Snowstorm and
National mines The dip in the south
divisions are far the steepest, which
coupled with the movement, has mao
an important influence on the depth
To which the ore will proceed, the
kind of minerals, and the enrichment
effect. also the oxidation.
The structural features Of the Gran
tie peak syneline are ably dealt with
in Prof. paper 81. U. s. geological sur
vey DID, 66-67, and admirably shown
on the plate map of the report,
The Copper Beds.
AS mentioned, there are three as
tinct occurrences of copper beds, one
each In the wallace, st. Regis. and
Reyett formations Of the east syncline
limb. The first two groups are In
wallace and st. Regis rocks, with
large amount of sericitic and other
matter, which originally, no doubt
was sandstone or sandy shale, thln
bedded, and affording very moderate
opportunities for circulation of under
ground solutions Infiltrations closed
the pore space during the time OF
metamorphism. Subsequent move
ment due to pressure has not operated
to release mineral, as the rocks smash
into gouge a condition antagonistic 70
free circulation. The principal copper
mineral is chalcopyrite Galena oc-
ours, and rarely little sphalerite. The
rock carrying the minerals has almost
the appearance of a hornstone, and the
degree Of impregnation is vastly less
than with the Revett occurrence.
The copper beds in Revett are thick
err strata, brittle. and composed en-
tirely of quartzose matter plus the
copper minerals. In crushing or I'M
der pressure, they have tendency to
break down like loaf sugar. This
structure, favoring free circulation
explains the reason for this enrich
ment to commercial value. Along the
seven miles observed, the Revett group
originally contained copper in sui
phide form of apparently one-fiftieth
to one-tenth of one per cent per ton
of rock. It was in intimate dissemin
alton of chalcopyrite seemingly witt
the rock matrix. Silver to the extent
of 21a ounces or more to each Y
pounds of copper prevailed, with
very small amount of gold. Along
small portion, silicification proceeded
to the degree of excluding the coppel
minerals, but the portion Is insignif1
cant and may be a secondary feature
N the upper parts of the dip after tn
rock has been robbed of its copper con
tent. Enrichment has occurred witt
change of a greater or less degree Il
the volume and kind of mineral, at in
tervals where favorable geologic con
Editions allow.
Copper lmpregnation.
The deposits are unique in that tn
nearest igneous rocks are miles away
and there are none whatever in tn
syncline. There is much to supper
the theory that the impregnation tool
place concident with the metamor
phisn, the silcous and copper solu
lions travelling together to fill the por
space in the original sandstone, con
verting it into the present quartzitf
with recurring intervals of pressure
crushing and cementation.
Weathered quartzite from the Snow
storm mine outcrops shows typics
coarse grains of quartz, around Whic
were deposited the silica and cope
cements. The rock suggests an earl
very open circulatory condition, witt
changes in copper minerals, mad
through breaking down under pressure
The latter would indicate that tn
change took place after the faultin
land that originally the type of miner
allzation in the south division wa
similar to that in the north. The fault
ing movement steepened the dip, IN
creased through this the concentrativ
effect and gave copper minerals
greater content and density. VIVA
became of by-products will be note
later. Weathering of exposed STRAIT
contributed by sending the release
mineral below the plane of the dip, be
ing the easiest path Of travel, as tn
, mineralized strata were the weake
and were thus kept open.
The syncline fault | interpret a
; constituting dam which held bac
the solutions, while faults across tn
strike assisted in checking the flo'
and thus caused deposition. The evi
Itlence is that cross faults in comhin
alton with the dip are responsible 70
the areas Of commercial enrichment
The source Of the copper can only b
conjectured.
The copper beds are normally yer
dry; in fact, the presence of waite
quickly robs them of the soluble min
erals, transporting them elsewhere
Water Is bad sign for the prospectoi
! Chalcopyrite is seemingly the prlm
AIRY mineral Chalcocite is a derive
mineral, being found in all stages o
formation and transition. Bornite !
present Pyrite Is absent over the en-
tire area, only one instance of its oc
currence coming under observation, II
4