War Eagle Mountain : Geology
The Oro Fino Vein system is known to extend at least some 12,000 feet in a NS direction and has been
observed to vary greatly in thickness ( 1 ft to 25 ft ) with mill grades of 0.5 to 1.25 Troy ounces of gold per
ton on average, and Silver values of 5 to 40 Troy ounces per ton. The ratio of Silver to Gold is generally
14 :1. As is typical for this kind of precious metal bearing quartz vein system, several large "pockets" of very
rich ore concentration occur scattered throughout. These are the so-called "Hot Spot" locations where mill
grades of up to 25 Troy ounces of Gold per ton are encountered, and some areas showing grades as high as
90 to 300 oz Gold / ton. The depth of the vein system is known to be in the 2,000 ft area, with only about the
first 500 to 1100 feet of depth actually mined on about 15 % of the vein.
The Cumberland mine, also part of the War Eagle Mountain structure, sits on top of a clearly separate
vein system. This vein is 100 to 200 feet east of the Oro Fino Vein. The Cumberland Vein is oriented N-S,
dips 60 degrees to the east, and is one to twelve inches thick. Very rich ore, some as high as 9 ounces of gold
to 40 ounces of silver exists within this vein.
The Poorman mine, also on the War Eagle Mountain, sits on top of an identical vein to the Oro Fino
vein, but about 1,000 feet to the west of the Golden Chariot shaft. This vein is mostly silver.
The main veins on the Mountain are the Oro Fino, Central, and Poorman veins. An additional 40
offshoot veins are associated with the ( 3 ) main veins. The Oro Vino Vein system is located close to the top
and on the east flank of the 8,051 ft War Eagle Mountain, which is one of the main peaks of the Owyhee
Mountains, some 50 air mile SSW of Boise, capital of the state of Idaho. The Poorman Vein system is
located close to the top and on the west flank of War Eagle Mountain. The Central Vein system connects the
Oro Fino and the Poorman. The mining district is being referred to variously as The Carson and French
districts or the Silver City district. War Eagle Mountain is the easternmost known accumulation of precious
metals in a seven mile E-W trending mining area which includes the Poorman, Central, and Oro Fino
complexes on War Eagle Mountain, the Silver City complex on Florida Mountain, and the Delamar complex
on DeLamar Mountain.
Estimates of reserves range from 500,000 ounces of Gold, to 3,000,000 ounces of Gold on War Eagle
Mountain, although this is based purely on historical records. Recent surveys and drilling activities have
tended to confirm these historical records. A best-guess estimate of 5,000,000 Troy ounces of Gold
equivalent is generally accepted, based upon drilling, sampling, and existing production records.
The core of War Eagle Mountain is a large dome-like structure made up of intrusive granodiorites or
quartz-monzonites, probably several thousand feet thick. The rocks are similar to those of the Cretaceous
Idaho batholith which occupies a large portion of central Idaho. The general consensus is that the War Eagle
is an outlier of the batholith, separated by extentional tectonics and displaced southwest ward to its present
position. The Oro Fino Vein system is found within this lithologic unit.
A number of late Oligocene dacite and quartz latite dykes intruded the granodiorites accompanied by
latite flows of thickness sometimes exceeding 100 feet.Following the intrusion of the latites, the area was
sujected to erosion. This is evidenced by a sedge of early-to-mid-Tertiary sediments on the southern flank of
War Easgle Mountain. This deposit, which in turn is covered basalts, has only recently been recognized as a
stratigraphic unit. Most of the rocks in this unit can best be described as a poorly sorted, very coarse dirty
sandstone. Macerated carbonized plant debris is common and some black paleosoil zones have been
observed. This is an indication of a reducing depositional environment and may have important implications
for the accumulation of disseminated precious metal. Elements such as gold and silver can be strongly
absorbed in the complex carbon compounds derived from plant cellulose degradation. Indeed, reports of
significant enrichment of gold and silver at the base of this sedimentary unit immediately above the
Cretaceous quartz monzonite is published.
The gold and silver bearing veins of War Eagle Mountain, including the Oro Fino, are steeply dipping
to subvertical in attitude and are generally oriented in a NS to NW-SE direction. The vein structures cut the
youngest widespread lithologic unit, dated by potassium-argon at 15.6-15.7 million years. Potassium-argon
dates on the vein material in the Florida mine and War Eagle Mountain area indicate an age range between
14.8-15.2 million years. Their origin is probably related to a Middle Miocene eruptive episode, representing
the last and waning stages of activity. The textures, mineralogy and geometry of the veins all indicate that
they are "epithermal" deposits. This means that, according to the current interpretations, the minerals were
deposited by hydrothermal fluids at relatively shallow depths and low to moderate pressures. Temperatures
were originally thought to be around 50-200 degrees Celcius, but it has been realized since that many of the
"epithermal" deposits were formed at temperatures well above 200 degrees C. The effect of the so-called
"hyper-enrichment" is to produce multiple pockets of bonanza ore, or highly-enriched spots.
The regional geology surrounding the Carson mining district is contained within three physiographic
provinces, the northern Basin and Range, the western and the central Snake River Plain. Adjoining the
western front of the Owyhee Mountains, the northern Basin and Range province imposes northwest listric
fault patterns upon lowland flood basalts, latites, rhyolites ( flows and ash-flows ) and sedimentary units. To
the north and northeast, faulting associated with the formation of the western Snake River Plain province has
displaced the granodiorite core of the Owyhee Mountains out of contact with the Idaho batholith to the
southwest. Separating the batholith by extensional tectonics, the northwest trending rift-like fault system has
formed a basin filled with intercalated flood basalts, rhyolites and sedimentary units. Additionally, the basin
forms the erosional channel for the modern Snake River near Boise, Idaho. The central Snake River Plain
province abuts the eastern and southern borders of the Owyhee Mountains. The lithologic units occurring
within this generally northeast trending province are flood basalt dominated bimodal volcanic associations
containing locally thick sedimentary units.
Lithology within the district is composed of various units including the basement unit of Cretaceous
intermediate intrusives of quartz monzanite to granodiorite composition. Flood basalts unconformably
blanket the western flanks of the mountain range and extend as far east as War Eagle Mountain. Capping and
intercalated with the basalts are latite units that can be found district-wide and within erosional windows
throughout the region. The baslat-latite sequence is interrupted by an erosional disconformity followed by
localized units of eruptive quartz latite which commonly forms the base for rhyolite domes. The rhyolite
domes are composed of volcanic breccias, flows and plugs of variable thicknesses and geometry.
The primary ore host on War Eagle Mountain is Cretaceous Granite, followed by Tertiary Tuff ( a pale
green to black lapilli tuff/reglith ) of up to 50 % granite.
Idaho Bureau of Mines and Geology
"Report on the Geology and Metalliferous Resources of the Region About Silver City, Idaho"
Dec 1926
"The size, characteristics, extent, and probable persistence of the veins have been discussed in the
descriptions of the individual mines. However, since this question is the factor upon which the entire future
of the district depends, it is desirable that a brief summary be given here.
All of the larger veins, such as the Oro Fino, Golden Chariot, and others on War Eagle Mountain, are
remarkable for their continuity along both strike and dip so far as developments have gone. The Black JackTrade Dollar vein has been developed for 6,000 feet along its strike and for 1,800 feet in depth without
notable decrease in strength. The Oro Fino - Golden Chariot Vein has a development along its strike of
nearly 4,000 feet, and is strong and well developed where the Sinker Tunnel cut it, 2,500 feet below the
outcrop. These facts seem to preclude any adverse conclusions as to the persistence of the main veins in the
direction of stike and dip. The fissuring and fracturing which made possible the development of the veins,
are certainly continuous for long distances.
Although all the veins of the region are in one way or another filled fissures, they belong in four
different groups or classes. The classification is based both on the kind of fissuring and the kind or type of
filling. The Oro Fino - Golden Chariot Vein is an example of the "Cemented Breccia" ( the cementing
material being either massive and crystallized quartz, or pseudomorphic quartz ). The Breccia veins consist
of fragments of the country rock cemented by vein matter. The ore minerals, except those of superficial
origin, are all apparently contemporaneous with the gangue matter, there having been periods during the long
process of mineralization when little but gangue was deposited, and others when the deposition of the ore
minerals was important. That this type of vein is persistent is evident when one realizes that the Oro Fino Golden Chariot vein has been actually mined for more than 3,000 feet in length, and where intersected by
the Sinker Tunnel, some 2,500 feet below the surface, it is as strong as in the upper levels.
The Oro Fino - Golden Chariot vein enclosed a large persistent ore body of medium precious metal
content, a condition which gives distinct promise of further extension within the limitations created by the
activity of supergene agents. The known ore body is developed in that portion of the vein fissures ( crossfracturing ), and it is very possible that the conditions which pertain at the Poorman mine are also effective in
the Oro Fino - Golden Chariot vein. If this is the case, the ore body might have a considerable pitch
( length ) in the vein, although this pitch may or may not be northward, like the Poorman.
The Sinker Tunnel constitutes an ideal site for mining and milling operations. It has already been
shown in the preceding discussion of ore deposits that the zone of primary ore bodies of the Silver City
region may be expected to persist without great change in tenor to a depth considerably below any attained
by the past mining activity. If it is true that the ore developed on the lowest levels of the mines of the
Oro Fino group is hypogene or primary, which seems to be likely, and if it has the reported tenor cited in the
preceding discussion, there is considerable promise of future activity.
The Golden Chariot shaft is sunk in the granite wall rock, striking the vein at the ninth level, below
which it has been sunk about 350 feet. It is probable that this shaft, although caved at the collar, is in good
condition for the greater part of its depth, particularly below the water level. Opening and un-watering it
sufficiently to permit accurate surveying should not, if the expected condition prevails, be an extremely
difficult task and should not be shirked. As has been pointed out already, the base of the shaft and the tope of
the raise are not much more than 150 feet apart vertically and perhaps even less horizontally. This program
offers the most expeditious and economical solution of the problem. Should this development prove the
existence of workable primary ore, the Sinker Tunnel should be extended to cross cut the entire vein system
to the Poorman, since the maximum of economy and efficiency may be gained by working the system as a
unit.
The re-examination of the Silver City mining region , upon which this report is based, has established
two fundamental facts : first, the veins of the Silver City region have contained large persistent ore bodies of
medium and rather uniform tenor ; second, there is no reason to expect that the ore bodies will fail to
continue in depth."
Ore has been extracted almost without interruption for an incredible horizontal length of about 3.600
feet, and to depths between 300 and 1,100 feet on the Oro Fino Vein. Between the Ida Elmore and the South
Chariot shafts, a distance of about 1,400 feet, stoping has ceased uniformly at the eighth level of the
Minnesota.
The sudden cessation in mining has caught the War Eagle Mountain vein system in a time-warp,
caused by the failure of the major banks in the United States at the time, and the subsequent flooding of the
entire shaft system. If the true condition is accurately depicted in the available documents of the time, the ore
body was not bottomed by any mining operations, prior to 1876.