The White Pine news. [volume], April 17, 1910, Page SIX, Image 6

About The White Pine news. [volume] (Ely, Nev.) 1906-1910

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Report of Geological Survey on Nevada Camps
(By William H. Emmonds.)
(Continued from last Sunday.)
At Gold Circle the andesite is rela
tively rich in augite and magnetite.
Andesine predominates, but some of
the plagioclase is labradorite. The
andesite is mainly younger than the
rhyolite, for dikes of andesite cut the
rhyolite and flows of andesite which
are presumably connected with the
dikes overlie the rhyolite flow. At
one place in this district a rhyolite
flow caps the andesite and an in
trusive mass of quartz porphyry
which has the same composition as
rhyolite was noted cutting andesite.
It appears that the eruptions of the
rhyolite took place in the main be
fore the andesite was formed, but
that some hryolite eruptions follow
ed thooe of andesite.
The contact relations between the
andesite and the basals have not been
determined. No andesite intrusions
have been noted in the Pliocene lake
beds (Humboldt formation) and the
andesitic eruptions are therefore
probably older than these beds. As
the basalt effusive rocks are closely
associated with these beds, it is high
ly probabable that the andesite er
uptions ceased before the basalts
were extravasated.
Andesites cut the sedimentary
rocks in the Shoshone Range and are
exposed in the Gem mine, at T enabo,
and in tne Lovie mine, at Lander.
They have a dense glassy ground
mass and at some places are vesicular
and so it is assumed that they repre
sent flows or intrusives formed near
the surface. They are dark dense
rocks which an altered glassy ground
mass containing phenocrysts of acidic
plagioclase and some orthodase.
Dacite.
When andesite contains a few
phenocrysts of quartz it is termed
quartz-bearing andesite, but if there
is a considerable proportion of quartz
—as much as 3 or 4 per cent of the
volume—‘then the rock Is dacite.
The groundmass of dacite is glassy
or fine grained, and the phenocrysts
commonly present are feldspar,
quartz, hornblaue, blotite, and augite. j
The feldspars are mainly plagiodase i
and may lie a little richer In soda
than the plagiodases of andesite. The
andesite at the Zenoll mine in the
Saqord district, near Palisade, is
richer in quartz than ,.ie other ande
sites which form the country rock
for the ore deposits. Northeast of
this region there is a body of typical
dacite containing a noticeable propor
tion of quartz. Another body of
dacite is in the Cortez Range and ex
tends southward rfom Palisade a dis
tance of several miles. The dacites
are closely related to andesites in
composition and occurrence and are
believed to have been erupted at
aoout the same time.
Succession of the Tertiary Eruptive
Rocks.
The order of eruption or the suc
cession of iertiary igneous rocks in
the Great Basin, as given by Baron
von Richthofen, is propylite, andesite,
trachyte, rhyolite, basalt. This se
quence in an amplified form was ac
cepted by the geologists of the For
tieth Parallel Survey, but for rhyo
lite and basalt the term neolite was
substantiated. Subsequently, it was
proved by G. F. Becker that propy
lite is in the Washoe district an al
tered phase of andesite. Later still
this form of alteration was shown to
be common and so the term propy
lite has ceased to be used for the
primary rock, but “propylitization"
has been accepted for a certain kind
of hydrothermal metamorphism. The
trachytes, as determined by Zirkel ,
for the Fortieth Parallel Survey,
have been shown by Hague and hi
dings to be in tne main andesites and
dacites. Spurr, who has studied the
Tertiary lavas throughout a large
part of the Great Basin, gives this
general succession: (1) Rhyolite,
(2) andesite, (3) rhyolite, (4) ande
site, and (5) basalt.
In the area heer considered the
rhyolites were the first rocks erupt
ed. They were the most extensive,
for they cover a large part of the sur
face and their thickness Is very great.
Subsequently the andesites were
erupted, but in much smaller
amounts. They took the form of
dikes and large intrusive masses as
well as flows, and in that they dif
fered from the rhyolites, which are
flows. The eruption of the basalts
followed that of the andesites and
seems to have closed the period of
volcanism in northern Nevada. The
Pliocene lake beds (Humboldt forma
tion), whose deposition followed the
bulk of the rhyolite eruptions, were
formed during the eruptions of the
basalts, for basa't flows occur under
them and interbedded with them.
Some of the rhyolite appears also to
have been erupted during the depo
sition of the Humboldt beds, for
rhyolite pumice is interbedded with
them, and this does not seem to be
a sand washed from older rhyolites,
but volcanic dust which settled di
rectly in water. The periods of the
. extravasation of the various lavas are
thus shown to have been to some ex
tent overlapping, but the general suc
cession is ( 1) rhyo’ite, (2) andesite,
(3) basalt.
Age of the Tertiary Eruptive Itocks.
In Eocene time the area covered
by this reconnaissance was, as al
ready stated, dry land, but Just east
of it there was a great lake in which
the Eocene beds were deposited. In
the Dixie Hills, east of the Pinyon
Range, some 25 miles southwest of
Elko, these beds, according to S. F.
Emmons, are for the most part fine
ly bedded calcareous shales contain
ing carbonaceous members which
carry seams of impure coal. Similar
beds are found in Penn canyon, 14
miles north of Oslno, and on the
northwest slope of the Elko range, 4
miles east of Elko. There is no rec
ord of volcanic ejectamenta inter
stratified with these beds, and It Is
inferred that the coutnry to the west
of this lake was free from valcanism
throughout the Eocene.
Tne area here discussed was dry land
also during Miocene time, when there
was a large lake to the west of it in
which the Truckee formation was de
posited. As already stated, typical
exposures of these beds with fresh
water mollusks are found in the
Kawsoh mountains and along the
south end of the Montezuma range,
and beds of similar lithologic com
position occur in the Reese river can
yon about 12 miles southwest of the
southwest corner of the area. These j
beds contain much volcanic material
of rhyolitic character and nearly
everywhere are overlain by rhyolite.
Wherever observed in connection
with basaltic eruptions they are cut
through or overlain by the basalt.
In Pliocene time a age occupied al
most the whole territory between
the Wasatch range and the Sierra. In
this lake were deposited the Hum
boldt beds, which contain abundant
volcanic material, mainly of a rhyo
lite character. These beds rest above
basalts and flows of basalt are In
cluded in them.
The general succession of the
.eruptive rocks was, as already stated,
ill) rhyolite, (2) andesite, (3) ba
! salt. The rhyolite eruptions prob
ably began in early Miocene time
( soon after the deposition of the Eo
! eene lake beds, and continued
through the Pliocene, for there are
rhyolitic tuffs and apilli in these lake
beds. The andesites weer intruded
after there had been very extensive
rhyolite eruptions, for great thick
nesses of rhyolite are cut by ande
site. As few if any andesites intrude
the Pliocene lake beds, it Is believed
that the andesites were erupted
mainly, if not altogether, late in
Miocene time, probably at its close.
The basalts were erupted during
Pliocene time, for they are interbed
ded with the Pliocene lake beds.
Deformation of the Bocks.
The sedimentary rocks and lava
flows are in few places found in the
horizontal position, but nearly every
where are tilted and faulted. In all
the ranges where they are exposed
the Paleozoic rocks are thrown into
broad open folds and have dips which
for the most part range from 1 •> de
gress to 4 5 degrees. As shown by
the atlas of the Fortieth Parallel Sur
vey, the Cortez and Pinyon ranges
are in the main anti-clinal, the Seet
o.va or Jacq Creek range is synclinal
and the Shoshone range is an east
ward-dipping monocline modified by
profound faulting. The Centennial
range is a northward-dipping fault
ed monocline modified by subordinate
anticlines and synclines.
The Tertiary java flows are at no
place closely folded. The contorted
bands of some of the shalelike rhyo
lites suggest that these rocks have
been deformed by compression, but
a close inspection shows that their
convolutions are the result of move
ments which took place before the
rocks had completely cooled, and are
not caused by subsequent deforma
tion. The lava beds are nearly
everywhere in a tilted position, how
ever, and at many places they are
faulted. The tilting movements
were evidently accomplished after
the Paleozoic sedimentary rocks had
been folded, and the lavas do not
show so large an element of hori
zontal compression as the sediments.
The present attitude of the Paleo
zoic sedimentary rocks is doubtless
due to various processes which oper
ated at different times. As already
stated, there are in the area no bed
ded rocks which were laid down be
tween the close of the Carboniferous
and the beginning of the Miocene,
and consequently there is no
evidence within the area itself which
will show the time at which the de
forming movements took place. In
formation respecting what happened
during this time must therefore be
gained outside of the area, at
places where rocks of suitable age
are known.
In California there is a general
unconformity between the folded
Jurassic beds and the Cretaceous
beds, which are not so greatly fold
ed. The time of the folding is there
fore known to be at the end of the
Jurassic. Folded Jurassic beds are
found in northern Nevada as far
east as the Pahute Range, and, al
though these beds are not covered by
the Cretaceous, they were probably
deformed at the time of the extens
ive mountain-making movements in
(California. It. is not known wheth
er this movement extended eastward
across the Great Rasin as far as the
Wasatch mountains, but at any rate
' the Wasatch and Uinta mountains
and the country extending far to the
east of them were strongly uplifted
at the close of Cretaceous time. The
effect of the movement at this time
was probably felt also in northern
Nevada.
A few miles east of Elko the
Eocene beds are highly tilted and
overlain by volcanic materials of
Pliocene age. In the Dixie Hills,
southwest of Elko, and in Penn Can
yon, 14 miles north of Osino, beds
of the same age are highly tilted.
The Miocene lavas are not so greatly
deformed, so It is supposed that the
movement took place before Miocene
time, or near the close of the Eocene,
i ne mountain-making movements
which are recorded In the folded
, Paleozoic sedimentary rocks seem
! therefore to have taken place at the
[end of the Jurassic, at the end of the
Cretaceous, and at the end of the
Eocene, but the extent and relative
Importance of each can not be shown.
A period of deformation followed
the eruption of the Miocene lavas,
for these rocks at many places are
highly tilted and fautled. This
movement seems to have taken place
without the strong compressional
stresses which produced the pre-Mio
cene folds, and practically all the
faultB are of the normal type, In
which the hanging wall appears to
have dropped. Some of the mountain
ranges were doubtless elevated at
this time. Blocks of the Paleozoic
sedimentary rocks which had been
deformed by folding in pre-Miocene
time were left in relatively exalted
positions when other blocks sank
away from them and formed the val
leys. Since that time profound ero
sion has oblterated the fault scarps,
but has not everywhere obliterated
the entire effects of faulting, for the
elevated block is still at a higher al
titude than the depressed block.
A period of less intense crustal de
formation followed the deposition of
Pliocene ake beds, which are in
places gently warped and faulted.
Resume of Geologic History.
In the area studied there is no
record of pre-Cambrian events. The
oldest rocks exposed are the quartz
ites and grits which outcrop on the
crest of the Ptnyon range. Through
out Cambrian and early and middle
Ordovician time this part of Nevada
was the floor of a sea upon which
quartzites, limestone, and shales were
deposited, the whole series of pre
Silurian rocks having a thickness of
more than 10,000 feet. Near the
middle of the Ordovician period the
sea became shallower and the Eureka
was deposited. Subsequently the sea
bottom was lifted above the water
level without tilting the beds. The
land mass did not remain long abov£
the water, but sank slowly and grad
ually through late Ordovician time,
and was again elevated at the close
of the Ordovician, and throughout
the Silurian remained above sea lev
el. In Devonian time approximate
ly 6,000 feet of limestone, sandstone,
and shale were deposited. Sedi
mentation was uninterrupted be
tween the Deconian and the Carbon
iferous, but in the early Carbonifer
ous there was a shallowing of the
j waters, and at some places as much
I as 3,000 feet of sandstone was de
I posited. The was followed by the
! deposition of 3,800 feet of limestone
and shales, above which was laid
down the Webed conglomerate, hav
ing a thickness of 2,000 to 6,000
feet. This was followed by the de
position of the upper Carboniferous
limestone, up to 2,u00 feet thick.
During the Paleozoic era there
were thus deposited between 30,000
and 40.000 feet of sedimentary rocks.
These beds carried a considerable
portion of conglomerates, sandstones
and shales and must have been de
posited, in part at least, in relatively
shallow water and not far from the
shore. According to Clarence King,
the Paleozoic sea was east of a land
mass whose shore was in northern
Nevada near longitude 117 deg. 30
min'. West of that meridian and
north of the fortieth parallel there
are no Paleozoic rocks in northern
Nevada, but pre-Cambrian or post
Paleozolc rocks instead. As already
stated, the sea bottom did not re
main stationary, but oscillated from
time to time and permitted a very
great thickness of beds to be deposit
ed. At the close of the Ordovician
period parts of it rose and. were not
submerged again until the beginning
of the Devonian. The close of
Paleozoic time was marked by pro
found but relatively gentle conti
nental movements. In the vicinity
of the Havallah Range, about 117
deg. 30 min. west longitude, there
was, according to King, a pivotal
line. The area to the east of this
line remained submerged in Paleo
zoic time, and that to the west was
above sea leve\ In Mesozoic time
the conditions were reversed—the
country to the east became dry land
and that to the west sank below the
level of the sea and received thick
contributions of Triassic Jurassic
sediments. According to Ping, im
mediately after the deposition of the
Jurassic sediments they were folded
with much horizontal compression,
producing great north-south moun
tain ranges. The westernmost of
these ranges was the Sierra Nevada,
and the Great llasin ranges were
formed probably at the same time.
The reason for this conclusion is
that many of the mountain ranges
parallel to the mountains In the area
studied, but west of It. are composed
of folded Jurassic rocks. The fold
ing at this time was most intense in
the Sierra Nevada and decreased east
ward toward the Wasatch Range. At
about this time, or else near the close
or the Cretaceous, the granitic rocks,
in the main granodlorites, were in
truded in the Paleozoic beds. Many
of the ore deposits were formed at
the time of this intrusion.
With the advent of Tertiary time
began a period marked by extensive
Inland lakes. The earliest of these
in this region was the Goshute Lake,
in which were laid down the Eocene
beds. ItB western shore extended
nearly to the eastern border of the
area studied, this area constituting a
land mass from which the sediments
were derived. In this lake were de
posited up to 2,000 feet of shales,
clnys, and limestones, with some beds
of impure coal. The deposition of
these beds was followed by moun
tain-making movements, in which
they were tilted at some place as
much as 45 deg. In Miocene time
a great lake was formed west of the
area. King has called this the Pa
hute I^ake and the beds are called
the Truckee formation. They con
tain much volcanic debris and record
a time of great volcanic activity.
This period of igneous activity dif
fered from that of the post-Jurassic,
as the rocks recording it are not
granular rocks but are mainly lava
flows and andesites, formed relative
ly near the surface. The rhyolites
were first extravasated, and later
these intruded by andesites. Many
of the ore deposits were formed in
connection with the andesitic In
trusions.
In Pliocene time, when volcanlstn
was still at Its height, an extensive
lake was formed which covered near
y the whole of the Great Basin.
King has called this Shoshone Lake
and the beds that were laid down in
the Humboldt formation. In the
lake, which may have contained lofty
islands, a great thickness of sand
stones, clays, and calcareous and
dlatomaceous shales was deposited,
with a mass of volcanic material,
principally of a rhyolitic character,
which was blown out of volcanic
vents and settled in the water of the
lake. Extensive flows of basalt oc
curred at about this time.
The late Tertiary was marked by
very extensive normal faulting, a
large part of which took place after
the lava flows were extravasted and
after the second period of ore de
position. Many of the old mountain
ranges were probably raised, and new
ones may have been formed. In the
Quaternary, mountain glaciers form
ed in the higher ranges during the
glacial period. Small lakes occupied
some of the depressions between the
mountains, and extensive accumula
tions of debris, eroded from the
mountains, filled the valleys.
Ore Deposits.
GENRAL STATEMENT.
It has been shown that the Igneous
rocks of the area studied belong to
two distinct periods of volcanism. j
The first of these was probably in
Cretaceous time, and the rocks form- (
ed during that period are intrusive
granular rocks and deep-seated por- j
phyryies, in the main granodlorites
and granodiorite porphyries. All
these rocks were formed at consider
able depth, and since they were in
truded this country has been greatly
eroded and the capping which must
have covered them when they solidi
fied has been removed. These early
intrusive rocks do not cut the Terti
ary lake beds or lavas, but are con
fined to the Paleozoic sedimentary
formations.
A large number of the ore deposits
are in or near the early intrusives.
These include deposits at Bullion
(Railroad district.) Lone Mountain,
Edgemount, Columbia, Aura, Moun
tain City. Cortez, Mill Canyon, Grey
, Eagle, Dean, and Lewis, and some of
the deposits at Tenabo. The deposits
at Mineral Hill may also belong to
this group.
The Tertiary lavas and associated
rocks are in the main rhyolites,
andesites, and basalts. These rocks
are younger than the granodiorites
and associated rocks and for reasons,
thought to be of Miocene and
Pliocene age. The ore bodies associ
ated with the later eruptlves include
the deposits at Tuscarora, Cornuco
pia, Good Hope, Burner, Falcon,
Stafford, Lynn, and Gold Circle, and
probably some of those at Tenabo
and Lander.
With respect to metal contents, the
deposits of both groups carry silver,
gold, copper, and lead. Silver and
gold are the most Important metals
of both groups, but the proportion
of gold to silver is greater In the
earlier deposits than in those of the
later group. The deposits at Edge
mont and at Dean belong to the
earlier group, and at these places the
only metal won in important quanti
ty is gold. The copper and lead de
posits are associated mainly with the
older Intrusive rocks. These metalR
occur also with the silver and gold
ores of the later group, but in smaller
proportion.
Earlier l>c|M>*.i(s (Cretaceous?.)
The deposits associated with the
older intrusive rocks are conserva
tively estimated to have produced
$22,000,000.
With respect to the Intrusive rocks
the Cretaceous ore deposits show
various relations. The gold-bearing
fissure veins at Edgemont and Bull
Hun are more than a mile away from
the nearest granodiorite intrusions,
but most of the deposits, especially
those in limestone, are but a few
rods away from the deep-seated in
trusive rocks, or else they are as
sociated with dikes which are prob
ably connected with the larger intru
sive bodies. The deposits of this
group are eontaetB-metamoruhic de
posits, irregular replacements de
posits or chambers In limestone, re
placement veins and sheeted zones in
limestone and shales, fissure veins
in quartzites, and fissure veins in
igneous rocks.
Con tact-Met amorphic l»i |Mciis.
The eontart-metamorphic deposits
are represented at Bullion ( Railroad
district,) Lone Mountain, Lime
Mounaln, and Cortez. In point of
production these deposits are not so
important as other deposits which are
usually associated with them, but
with respect to genesis they form a
distinct and Interesting type. At
Bullion the eontart-metamorphic 1
ore consists of garnet, calcite, actl
nolite, tremolite, epldote, quartz,
pyroxene, chalcopyrite, bonlte, ga
lena, and zinc blende. The metals
are copper, silver, and lead. All the j
minerals are Intergrown and were
formed at the same time. They are
in limestone not more than a few
rods from the contact with the ig
neous rock and formed by gaseous
solutions from that rock at the time
of the intrusion. At Lone Mountain
contact-metamorphic deposits occur
near ganodlorite but are not exten
sively developed. The ore consists
of calcite, garnet, actinollte, mag
netite, pyrlte, chalcopyrite, and
other minerals and carries values in
copper and silver. At Lime Moun
tain some ore composed of calclte,
white and black mien, tremollte, and
copper-bearing sulphides Is presum
ably of contact-metamorphlc origin.
The deposits of the Garrison mine, !
at Cortez, are In the main chambers
of siliceous ore In limestone, but a |
small amount of contact-metamorph-!
lc ore Is found near a dike of de- j
composed porphyry. This ore con
sists of calclte, tremollte, acttinollte,
quartz, and serlclte, Intergrown with
which Is a small amount of pyrlte.
The contact-metamorphlc silicates
are developed at Mill Canyon, In the
Cortez Range, and also at Mountain
Bcastoria
For Infanta and Children.
The Kind You Have
Always Bought
-n__ iVa
Bears 1110
Signature
of
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% In
111
_ Use
££> fi Aperfprt Remedy for CrmsHp*
tlon. Sour Stomach.DUrrtoa P_,. ft n n p
Worms,ConvulsionsJeverisk P (l f II V R I
& * ness and LOSS OF SLEET. BUI U f U I
f*2S|e2« I Thirty Years
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Exact Copy o» Wrapper. TM, omt.uk comm.kt. «rw nm e.rr
City, but no contart-metamorptaic ore
has been found at these places. 80
far 8b known there are no contact
metamorp. ic zones in the Shoshone
Range along the border of the in
trusive grundiorite. which nearly
everywhere breaks throngh quartzite,
a rock that is not favorable for con
tact metamorphism. Why the gran
diorites of the central part of the
Centennial Range did not cause con
tact metamorpbism is not easily un
derstood, for all the conditions so
far as known seem to be similar to
those prevailing where contact met*
amorphism has taken place.
Irregular Replacement Ik'iHsitM in
Limestone.
The irregular replacement deposits
or chambers In limestone are among
the most important ore bodies in the
area studied. They Include the sli
ver-lead deposits at Bullion, the sil
ver deposits at Cortez and Mineral
Hill, some of those at Mill Canyon,
and probably some of the inaccessible
deposits at Lewis and Lone Mountain.
These deposits are found in areas
which are intruded by the granitic
rocks or the related porphyries, and
for the most part tney have the form
of chimneys or ribbons that are re
lated to the intrsectlons of Assures
rather than to bedding planes. In
all these deposits sliver Is the most
important metal, but there are Im
portant amounts of lead and copper
In the deposits at Bullion. Gold Is
usually present, but always In sub
ordinate quantity. As a rule the ore
Is highly siliceous. The gangue min
erals are quartz, barite, and calclte.
The principal sulphides are pyrite,
gelena, zinc blende, argentlte, and
chalcopyrlte. Stlbnlte, Btromeyerlte,
gray copper, polybaslte, stephanlte.
and other minerals containing arsenic
or antimony are present In some of
the ore. Contact-metamorphlc sili
cates are wanting. The ore bodies of
this group are without exception near
the deep-seated lntruslves and are
believed to have been deposited by
solutions which were given off from
these rocks as they cooled.
Contiuned next Sunday.)
Cholljr—“Well, I bear that you
and Grace are to become life part
ners.”
George—"Yen, she puts In the
capital and I put in the experience.”
— Boston Record.
"Did he fare his illness with a
good heart?”
“Yes; It was his liver that bother
ed him.”—New York Kvenlng Tele
gram.
Low Rates East
Summer excursion round-trip
tickets at greatly reduced
prices to Eastern points:
SOLD ON
May 11, 12, 13, 14, 23, 26, 27
June 2, 3, 4, 24, 25, 26, 30
July 1,2,3, 4, 5, 6, 25, 26, 27
Aug. 1, 2, 3, 4
Sept. 1,2, 3, 11, 12, 13, 14
Southern Pacific
District Passenger Agent’s Office
Room 207, Odd Fellow Bldg.,
RENO - - - NEVADA