GEOLOGY OF THE PERLITE DEPOSITS
OF THE NO AGUA PEAKS
TAOS COUNTY, NEW MEXICO
'
Karl A. Naert*
Lauren A. Wright**
and
C h a r l e s P.Thornton**
*Patino, N.V.,
7 Kings East, Toronto,Ontario,
Canada MSClA6
""Department of Geosciences, The P e n n s y l v a n i a S t a t e U n i v e r s i t y ,
16801, U.S.A.
U n i v e r s i t yP a r k ,P e n n s y l v a n i a
Abstract
i s obtained from
Most of t h e p e r l i t e produced i n t h e u n i t e d S t a t e s
an accumulation of rhyolitic rock
County, New Mexico.
which u n d e r l i e s t h e
No Agua Peaks, Taos
8 m i l l i o nt o n s
Two quarryingoperationsyieldedabout
1950-79.
o fc r u d ep e r l i t ei n
The p e r l i t e , mostof
i t devoid of onionskin
2nd lithic rhyO\itC
'texture,formsdiscretebodies,associatedwithbodies
A l l of t h e u n i t s a r e
of glassyrhyolite,,
mappable,showingwelldefined,although
g r a d a t i o n a l ,c o n t a c t s .
The u n i t sa r ed i s t i n g u i s h a b l em e g a s c o p i c a l l y
marked d i f f e r e n c e s i n v e s i c u l a r i t y , . c r y s t a l l i n i t y
mileSwh$re i t f o r m s f o u r h i l l s .
by
and c o l o r .
is confined to an area
The r h y o l i t i c a c c u m u l a t i o n
of about+W&square
The p e r l i t e and g l a s s y r h y o l i t e
units
On eachhil.1,the
of each h i l l show a c r u d e l y a n n u l a r p a t t e r n i n p l a n .
contacts between the
commonly
two rock -types, as well as the flow banding within
individualbodies,tendtodipinward,apparentlytowardacentralvent.
W
e thusinterpreteach
h i l l as t h e s i t e of a n i n d i v i d u a l e x t r u s i o n
The bodies of l i t h i c r h y o l i t e ,
Exposed a t t h e c r e s t
The lowerslopes
.of glassy rhyolite
p e r l i t e .L o c a l l y
and s i z e s , c u t a c r o s s
and a r e i n t e r p r e t a b l e as dome b u r s t s .
the annular pattern
perlite.
of v a r i o u s s h a p e s
dome.
anda
ofeach
h i l l is a body of r e l a t i v e l y compact
of e a c h a r e u n d e r l a i n s u c c e s s i v e l y
bodycomposed
by a body
mostly of r e l a t i v e l y v e s i c u l a r
and s u c c e s s i v e l ye x p o s e db e n e a t ht h el a t t e ra r eu n i t s
of g l a s s yr h y o l i t e ,p e r l i t e ,a n d f p e r l i t 2 \ - b r e c c i a .A n a l y s e s
samples of 27 p e r l i t e show anaverage
of
H20 content of 2 . 7 6 w t . p e r c e n t ;
2.33 w t . percent H20.
samples of g l a s s y r h y o l i t e a v e r a g e d
M0541L(
The H 0 may have been derived
2
continuedcirculation
6
by h y d r a t i o n of o b s i d i a n bylong-
of m e t e o r i t e w a t e r a f t e r t h e f o r m a t i o n :
of t h e
7
e
-
domes, o r i t may have.beenmagmaticwaterexsolvedfrom
..
'rhyolite melts during vesiculation
of t h e magma.
1~
and l a t e r r e a b s o r b e d d u r i n g t h e c o o l i n g
W
e favorthelaterinterpretationfor
most of t h e h y d r a t i o n
til
as t h e water a p p a r e n t l y i s u n i f o r m l y d i s t r i b u t e d i n t h e v e s i c u l a r u n i t s ,
a
10
L
6
of h y d r a t i o n b e b g u n r e l a t e d
both p e r l i t e and g l a s s y r h y o l i t e , t h e d e g r e e
W J i L t ? j hhc ' p n \ i k c k . ~ t + c k , . ~ $ ~ c ~ U l
.a
!,&.$
.hu, ,,-&+.sk&
+CY&#.
a s s o c l a k U i h h%L\cyrQla&
t o proximitytothesurfaceortozones
of f r a c t u r i n g andbrecciation_,,, W
e
also i n t e r p r e t e a c h
body of p e r l i t e and g l a s s y r h y o l i t e a s
s e p a r a t e flow, b e c a u s e f e a t u r e s i n d i c a t i v e
a t t h e t o p of t h e u p p e r g l a s s y r h y o l i t e u n i t .
emplaced a s a
of f l o w surfaces were observed
Introduction
and
Acknowledgments
The principal source of perlite-in the western hemisphere, and perhaps
..
the world, comprises
a group of depositsin the No Agua.Peaks
of northern
'
New Mexico. The deposits form part of an accumulation of rhyolitic volcanic
rocks which form the peaks. They were first worked
in 1950.
Through 1979,
they probably had yielded a total
of about 8 million tons of commercial
. .
perlite, nearly all obtained from two properties. is.
One
now owned and
~.
Corbordtrbn
seffttwfty, and the other by the
operated by the Johns-Manville Products
.
General Refraciories Company (Grefco)
This report is concerned primarily with the economic ofgeology
the No
Agua perlit$ deposits., but it also includes a brief description of the
15 miles east of the No Agua Peaks.
Brushy Mountain perlite deposit, about
The report consists mainly of.materia1 contained in the doctoral
o f thesis
the senior author (Naert,
1974) and is basedon field and laboratory
investigations pursued during the period
1971-1974.
The field work involved the preparation
o f the geologic map
of Plate 1
and the sampling reported herein. It was confined largely to the summers
of 1971 and 1972 when the project was supported by two successive grants
from the New Mexico Bureau of Mines and Mineral Resources. Another phase
of the investigation of the No Agua perlite deposits concerned variations
of the perlite and their possible
in the thermal expansion characteristics
relation
to
variations
in
certain
physical
and
.chemical
of
characteristics
perlite, specifically chemical composition, bulk density, and percentage
by volume of glass, crystallites, and vesicles. A brief summary
of the
'
measurement of these variations and
of a statistical analysis of the results
is included herein.
.,
4
Most of t h e f i e l d workand
Chemicalanalyseswere
a l l o.f the petrography
was done by Naert.
made, a l s o by N a e r t , i n t h e M i n e r a l C o n s t i t u t i o n
of thepro-
Laboratories,PennsylvaniaStateUniversity.Wrightconceived
ject, arranged for the grants
from t h e New MexicoBureau
of,Mines and
M i n e r a l . R e s o u r c e s ,c o n t r i b u t e da b o u ts e v e nd a y st ot h ei n i t i a l
stages.of the field
work,field-checkedthe
andend
map a n d s e r v e d a s t h e s i s
on Naert'sthesiscommittee,alsofield-checked
advisor.Thorntonserved
t h e map, and c o n t r i b u t e d t o t h e o r e t i c a l p a r t s
of t h er e p o r t .
its present.form.
i n v i t a t i o n ,W r i g h ta s s e m b l e dt h er e p o r ti n
7, 1 2 , 28, and 29.
Proddcb
Personfie1 of theJohns-ManvilleCorporation
A t Naert's
He a l s o
preparedFigures
E.
I
Greqco
and t h e S i l b r i c o
?A
of t h erier s p e c t i vper o p e r-t i e s.
authorized
the
examination
Company
and a s s i s t ei n
d
?%d&k
many ' o t h e r 'ways.
The.Johns-Manville4Corporation, i n ' p a r t i c u l a r ,g e n e r o u s l y
suppliedfundsfortheanalyticalpart
of t h e s t u d y
topographic map ( s c a l e 1 i n . : . 4 0 0 f t . )
of i t s p r o p e r t y .
rwiews of themanuscript,
F. L. Kady and I r v i n g F r i e d m a n , i n c r i t i c a l
c o n t r i b u t e d numerous h e l p f u l s u g g e s t i o n s
and o b s e r v a t i o n s , a s w e l l
p r e f e r r e d i n t e r p r ' e t a t i o n ' of t h e i n t e r n a l s t r u c t u r e
t i o n of t h e No Agua Peaksandtheorigin
also helpfully reviewed the manuscript
on t h e t h e o r e t i c a l r o l e
and a n a l y t i c a l d a t a
of t h e r h y o l i t i c
of t h e p e r l i t e .
as
their
accumula-
C. W. Burnhaio
andprovided,forquotation,observations
of water i n t h e f o r m a t i o n
Naert,WrightandThornton,however,
and made a v a i l a b l e a
of t h e No Agua d e p o s i t s .
aresolelyresponsibleforthefield
and f o r t h e i n t e r p r e t a t i o n s p l a c e d
uponthem.
D e f i n i t i o n s of P e r l i t e , . O r i g i n s o f t h e
Uses of P e r l i t e
P e r l i t e I n d u s t r y andTreatmentand
Theterm
" p e r l s t e i n " was f i r s t used by F i c h t e l (1791) who defined i t
as g l a s s y v o l c a n i c r o c k w i t h
a pearlyluster.
employed by Esmark (1798),Beudant
T h i s d e f i n i t i o n was a l s o
i n 1822 i n t r o d u c e dt h et e r m" p e r l i t e "
c
as a synonym for perlstein. The observation that volcanic glass
will expand
if heated to suitable temperatures apparently
was first made by
J.W. Judd
(1886).
Concerning the heating of obsidian nodules, he stated, "If the
temperature be now raised to whiteness the whole mass swells up to
cauliflower-like excrescences, till it has attained eight or ten times'its
original bulk".
From the early definition of perlite and from the observation of the
thermal expansion of obsidian have evolved the two presently used definitions
of perlite, one petrologic and the other copiercial.
In a petrologic sense,
I
the term is commonly applied to glassy volcanic rock of rhyolitic to dacitic
composition, containing two to five percent combined water, and displaying
an onionskin texture and a pearly luster. The perlite of commerce is
ordinaeily definedas any glassy volcanic rock which, upon heating, expands
to at least ten times its original volume without the production of excessive
fines or excessive unexpansible material. .Although commercia1,perlite is
defined very broadly,it has proved tobe chemically similar to the material
that fits the petrological definition.A s commercial perlite commonly lacks
in this report the term "onionskin
the pearly luster or onionskin texture,
perlite" will designate rock that falls within the petrologic definition
of perlite. Rock to which the
comercial definition applied will
be termed
simply "perlite".
The perlite deposits of commrce occur mainly in three geologic settings:
(1) borders of rhyolitic flows,(2) full thicknesses of rhyolitic flows,
ail,of
or rhyolitic domes.
and (3) variously shaped bodies that form parts
The largest and most uniform perlite deposits. have proved
be associated
to
No Agua deposits being a noteworthy example.
with the rhyolitic domes, the
6
Expanded p e r l i t e a p p a r e n t l y was f i r s t u sed commerc i a l l y i n Germany wher
i n 1924, i t was employed as an i n g r e d i e n t i n a b r a s i v e b r i c k s ( J a s t e r ,
P e r l i t e i s reported t o havebeen'firstused
In t h a t y e a r ,
1956).
in theUnitedStatesin
1940.
expanded p e r l i t e was employed as a n a g g r e g a t e i n ' p l a s t e r
at
a p l a n t near Las Vegas,Nevada;
i t was a l s o u s e d e x p e r i m e n t a l l y
as an
at.
AnonqMoVS,
i n g r e d i e n t i n enamel iA SuperiorArizona (Chem. and Met. Eng., 1945; Taylor,
0
1950).
1946, and was
w a s f i r s t r e c o r d e di n
Domesticproductionofperlite
In t h e , l a t e 1 9 4 0 ' s a n d e a r l y
obtainedmostlyfromdepositsinArizona.
interest in perlite.as an industrial material
grew r a p i d l y , and much e f f o r t
was devotedltoprospecting,testing,andthedevelopmentof'uses.
At
s c o r e s of l o c a l i t i e s i n t h e w e s t e r n U n i t e d S t a t e s d e p o s i t s
were exploredandtested
as p o s s i b l es o u r c e s
'
Butnomore
of v o l c a n i c g l a s s
of p e r l i t e ( F i g .
1).
Hundreds
were made t o p l a c e many o f . t h e d e p o s i t s
of claims were staked, and attempts
i n operation.
1950's
than 25 were r e p o r t e d active i n a given year
.
The crude material was s h i p p e d t o v a r i o u s p o i n t s , m o s t l y i n t h e w e s t e r n . U n i t e d
as a l i g h t -
S t a t e s , where it w a s expanded and sold to local markets, mafnly
weight aggregate.
.
The valueof
a givendepositprovedtodependmainly
(1) the e x p a n s i o n c h a r a c t e r i s t i c s
(3) physicalaccessibility
location of the deposit with
of t h e p e r l i t e ,
on f o u r f a c t o r s :
(2) s i z e of t h e d e p o s i t ,
and ease of o p e r a t i o n of t h e d e p o s i t ,
and ( 4 )
reference t o a c t u a l o r p o t e n t i a l m a r k e t s .
Many o f t h e e a r l y a t t e m p t s t o q u a r r y p e r l i t e p r o f i t a l j l y
ended i n f a i l u r e ,
as o p e r a t o r s e x p e r i e n c e d d i f f i c u l t y i n p r o d u c i n g p e r l i t e w i t h u n i f o r m
e x p a n s i o nc h a r a c t e r i s t i c s .T h i sp r o b l e m
i n the composition and texture
was caused, i n p a r t ,
by v a r i a t i o n s
of t h e r o c k q u a r r i e d a n d , i n p a r t ,
J
s e l e c t i v em i n i n gp r a c t i c e s .D i f f i c u l t i e sa l s o
were e x p e r i e n c e di n
by non-
7
~
~
perfecting the technique of expanding perlite. Consequently, in the mid-1950's
the mining of perlite
in the U.S. became dominated by a few large companies
'
which controlled large deposits and were capable of producing marketable
871,000 tons of crude
perlite of uniform quality. In 1977, a total of
perlite was quarried in the United States. Eighty-nine percent bf this
production
was
obtained
from
New
Mexico
and
principally
the
No
Agua
deposits.
At present, perlite is expanded in two types of furnaces, one horizontal
and the other vertical. Each is operated at temperatures
in the general range
of 1400° to 1800°F (60O0C-10OO0C). Crude perlite, ground to specified sizes,
is retainedionly a short time in the furnace. Upon expansion, it is carried
it is separated into
away with the hot gases an
toair classifie, where
several sizes and the excessively fine material is removed.
In the milling
and expanding process, care
is takento produce a minimum of fines.
The usefulness of expanded perlite stems mainly from a combination of
physical and chemical properties,
most.notably (1) low bulk density,(2)
,
low thermal conductivity, (3) high heat resistance, ( 4 ) low sound trans-
(6) chemical
mission, (5) large surface'area of individual particles and
inertness. The four first-listed properties have led to the principal use
of expanded
perlite, namely
as an aggregate in insulation boards, plaster,
and portland cement concrete. Between50 and 60 percent of the expanded
perlite produced in the United States is used for these purposes.
It is
also used as a filter, low-temperature insulating material, filler,
abrasive, foundry castable and bonding agent and fpr numerous other purposes.'
History of Discovery and Development ofNo the
Agua
and Brushy Mountain Perlite Deposits
The historical summary that follows was .based
on informal conversations
with MIB. Mickelson, J. Graham, and D. Griffiths who,
in 1971 and 1972,were
I
managers of Johns-Manville, General Refractories and Silbrico perlite
o p e r a t i o n so fn o r t h e r n
of potentially
M.B.
New Mexico.These
economic d e p o s i t s of p e r l i t e i n t h e No Agua Peaks area t o
MickelsonofAntonito,Colorado.
ofcommercial
In 1948Mickelsonobtained
a sample
I n August
p e r l i t e fromthedepositnearSuperior,Arizona.
No Agua Peaks,henoted
of that year, while picnicking in the
between the sample and
peaks.
a c c o u n t sa t t r i b u t et h er e c o g n i t i o n
a similarity
area o f t h e
a rock unit extensively exposed in the
He had p r e v i o u s l yp r o s p e c t e dt h e
No Agua Peaks area f o r v o l c a n i c
c i n d e r s unaware t h a t h e was w a l k i n g a c r o s s o n e o f t h e w o r l d ' s l a r g e s t
A few d a y sa f t e rt h ep i c n i ch es t a k e d
d e p o s i t so fp e r l i t e .
) and e a s t p a r t of t h e area.
much o f t h e n o r t h ( F i g . 3
A t n e a r l y the same time c l a i m s c o v e r i n g t h e
of the mountains(Fig.3
west and 'southwest parts
) were s t a k e d f o r t h e G r e a t L a k e s
now a D i v i s i o no ft h eG e n e r a lR e f r a c t o r i e s
Minesofrfaos.Also
a t nearlythe
governmenttrapper,discoveredandclaimed
32) here referred to
Carbon Comap,ny,
Company (Grefco).
owned by t h e S i l b r i c o Company, on.t h e s o u t h s l o p e
f o rU n i t e d
claims covering
The claimnow
of east h i l l , were' s t a k e d
same time Mercedes O r t i z , 'a
a perlitedeposit(Figs.31
as t h e B r u s h y M o u n t a i n d e p o s i t , j u s t n o r t h
and
of Cerro
Montoso 15 miles east of t h e No Agua Peaks.
The p e r l i t e claims of t h e No Agua area t h u s compose t h r e e p r o p e r t i e s
(Fig.'3 ), e a c h s e p a r a t e l y
owners,consisting
owned s i n c e t h e claims were s t a k e d .
The p r e s e n t
of theJohns-ManvilleCorporation,theGrefcoandthe
S i l b r i c o Company, a c q u i r e d t h e s e p r o p e r t i e s t h r o u g h t h e
shown i n F i g u r e 4 . S i n c e
sales andmergers
1965 a l l of t h e p e r l i t e producedfromthe
Agua deposits has been obtained from the Johns-Manville
No
and Grefco quarries.
w a s operated only. i n 1965 when about 500 t o n s o f p e r l i t e
The S i l b r i c o q u a r r ;
. was removed by a formerowner,the
P e r l i t e from t h e p r o p e r t y
U.S.
P e r l i t e Company.
i s s t o c k p i l e d near a mill on t h e p r o p e r t y .
by b l a s t i n g a n d
i s quarried
of the Johns-Manville Corporation
The crude
p e r l i t e i s c r u s h e d ,d r i e d ,s c r e e n e da n dd i s t r i b u t e dt os t o r a g eb i n s .
prepared perlite
The
i s t r a n s p o r t e d 25 miles i n covered hopper trucks to storage
a n db l e n d i n gf d c i l i t i e s . a t
a r a i l h e a di nA n t o n i t o ,C o l o r a d o .
A t t h eG r e f c o
i s scrapedfromthequarrywithoutblastingand
property, perlite
similarly to the perlite quarried
is m i l l e d
by the Johns-Manville Corporation.
I
In both operations the milling produces
composes
a minus 120-mesh f r a c t i o n t h a t
as much a s t e np e r c e n to ft h ec r u s h e dp e r l i t e .T h i sf r a c t i o n
no p r e s e n t v a l u e a n d
i s p l a c e d i n waste p i l e s on t h e p r o p e r t y .
fraction,producedduringthesizinganddrying,
i s of
A still finer
i s c o l l e c t e d i n baghouses
and i s a l s o p i l e d on t h e p r o p e r t y .
A l l of t h e p e r l i t e produced i n . t h e Johns-Manville operation and most of
the perlite produced
byGrefco
is shipped in bulk or in bags to expansion
p l i n t st h r o u g h o u tt h eU n i t e dS t a t e sa n d
Canada.Grefcoexpands
some of i t s
product i n a p l a n t a t t h e A n t o n i t o r a i l h e a d .
GeneralTopographicandGeologicFeatures
of t h e No Agua Peaks and Vicinity
The No Agua Peaks occupy an area. of about five square miles which
athwart the
common boundary of t h e La Seguita Peaks and
quadranglesof
New Mexico.
U.S.
lies
Tres P i e d r a s 715 minute
Highway 285 p a s s e s c l o s e t o t h e w e s t e r n
marginofthepeaks,connectingtheperliteoperationswithAntonito,
Colorado, ' 2 5 miles t o t h e n o r t h
tothesouth.
and w i t h Tres P i e d r a s , New Mexico, 7 miles
The No Agua
Peaks
rise
(FI? 6 1
above
the' surface of the Taos
PlateauAwhich,
at that locality,is about 8000 feet above sea level. The peaks
are actually
four relatively large hills (West, North, East and South Hills) asspaced
to
form the corners of a square about
4000 feet on a side. The hills crest
at elevations 900 to 1200 feet higher than the surrounding plateau. The
western part of this topographic high is lower
comonly
and referred to as
(FI?* b) *
the "LowHill area". The No Agua Peaks are dwarfedSanbyAntonio Peak, a
A
dome-strato vokano whose crest is about seven miles northeast of them and
is 10,833 feet above sea level.
The
general
geological
features
of
the
o f . the No Agua
Peaks
vicinity
I
(Fig.7 ) were described by Butler
(1971) in a paper whichc0vers.a much
larger area extending mainly to the west and south of the peaks. As noted
by him, the'dome-forming rhyolitic bodies
of the No Agua .Peaks are part of
a successionof late Cenozoic volcanic and sedimentary rocks which, in
north-western Taos County and northeastern Rio Arriba County, rest depositionally upon.Precambrian metamorphic and ignepus rocks. This succession is
broadly
divisable
into
an older part and a younger part.
The older part was originally termed "Los
the Pinos gravel" (Atwood and
Mather, 1932).
It was renamed the Los Pinos Formation by'Butler
(1971) who,
in the. area of
Figure7, recognized.threemembers.
In upward order these
are (1) the coarsely porphyritic quartz latite
member.composed.oftuffaceous
sandstone, tuff; and conglomerate containing clasts
of porphyritic quartz
latite, (2) the La Jarita Basalt Member, and(3) the rhyolite member com- .
posed of sandstone, conglomerate, tuff', and flows, the volcanic units being
mostly rhyolitic. The younger partof the late Cenozoic succession, comprising the Hinsdale Formation and the overlying Servilleta Formation, consists
mainly of basalt flows interlayered with subordinate sand and gravel.
Volcanic
domes
which
form
San
Antonio
Peak
and
Cerro
Aire
are
composed
of
hypersthene-bearing quartz-latite,a unit which predates the Servilleta
formation and may be younger than the lower part of the Hinsdale Formation (Butler, 1971).
The
rhyolitic
units
of
the
No
Agua
Mountains
are
older
than
the
Hinsdale
Formation and younger than much of the Los Pinos Formation, although the
uppermost strata in exposures of the Los Pinos Formation, along 285
Highway
about one mile northwest of the northwest border
of the No Agua Peaks,
contain clastsof glassy, rhyolitic rock which were derived from the No
Agua domes ,(Figs.
hole (R.D.H. 2),
8 and 9).
Logs af .'.-ill
from a 1147-foot rotary drill
lo), indicate
collared near the Johns-Manville plant (Fig.
that successively beneath the.rhyolitic units ofNo.Agua
the
Peak area
170-foot thickness of basalt (probably the
La Jarita Basalt Member of '
the Los Pinos Formation) and
a 450-foot thickness of sandstone, shale and
conglomerate.
The rhyolite bodies of the No Agua Peaks have ayielded
3.5 m.y. radiometric' date (analysis of potassium and argon isotopes from feldspar
phenocrysts by W.A. Bassett) and4.8 m.y. fission track date (Lipman and
others, 1970). Another fission track analysis, this one of
a sample of
the upper glassy rhyolite, indicated an age within 11 to 13 million year
'
interval (analysis by M.G. Seitz, Geophysical Laboratory, Carnegie Institue,
Washington, D.C., 1972). The volcanic rocks of the Hinsdale Formation in
the vicinity of the No Agua Peaks have yet to be dated radiometrically, but
they probably were deposited near the end of Hinsdale volcanism (Butler,
1971).
The
terranes where bodies of rhyplitic and basaltic rock are closely associated.
Such a relationship between lavas of bimodal compositions has been explained
in various ways. One explanation would derive the acidic lavas through the
partial melting of earlier felsic rocks and involves a heat source related
to the basaltic rocks. The acidic lavas
of the.No Agua Peaksmay have been
derived iri such a fashion from the Precambrfan basement rocks, presumed to
consist 'largely of granitic gneiss, that lie at shallow depths beneath the
. .
accumulation of rhyolitic rocks. .
I
1nvestigations.of Other Perlite Deposits and of
the 0rigin.of Perlite
Although.the origin of perlite has been treated
a,number
in of
papers, published mainly in the period 1958-1966, relatively little has
been written concerning the petrologic and stru'ctural features of large
deposits of perlite. The available descriptions indicate that most or
all of the perlite bodies
of present'or potential commercial interest
occur as parts of rhyolitic domes. Individual domes range
in diameter
from a few tens of meters to as much as one kilometer.
of.the
Some
domes
consist simply of a centrally located body of perlite surrounded,
in plan,
by rhyolite or glassy rhyolite and.'featured by inward dipping flow banding. Examples include the Cedar Top perlite deposit, San Bernandino
County, California .(Wright and others, 1954), and the Fish Springs perlite
0..
deposit, Inyo County, California (Chesterman',
1953).
Other domes, such as
'
the Ardov dome,U.S.S.R.
(Nasedkin, 1963), consist of alternating layers
of perlite, glassy rhyolite, and lithic rhyolitic, but also arranged concentrically in plan. Brief descriptions of still other perlite deposits
also implya concentric structure. These include the Puketara Tholoid and
Opal Deposits, Tairua district, New Zealand (Thompson and1954),
Reed,
deposits near socorro, New Mexico (Weber,
1963), and the Numinbah Valley
deposit, New South Wales, Australia (Hamilton,.
1966).
The conical internal
structure, implied by the in-dipping flow banding and concentric plan
1
common in perlite-bearing rhyolitic domes also has been shown in idealized
representations of rhyolitic domes in general (Fig.
11 ; von Leyden, 1936).
..
The perlite bodies of the rhyolitic domes ordinarily show gradational
contacts with the glassy rhyolite. Analyses of the associated glassy
rhyollte,
as
well as analyses of the perlite, commonly show
water-content
a
in excess of two percent. Characteristically included in the bodies of
perlite and glassy rhyolite, are occurrence&
of massive obsidian which
clearly predate the bordering water-rich glassy rock and which only
analyze
a small fraction of a percent
of water. Much of the obsidian is in the form
of black
nodule
diameter,
surrounded
perlitic
by material
with an onionsk
ally
termed
"marekanites"
"Apache
or
3
That perlite, as defined petrologically, forms by hydration of
obsidian was first proposed by Chesterman
(1954).
He based this conclusion
on 'the contrast in water content, gradational contacts between the massive
obsidian and onionskin perlite, and the observation that the perlite is concentrated along fractures that extend into the obsidian. "Perlitization"
according to Chesterman (195%) occurs when "volcanic glass, originally
I
containing only a few hundreths percent water, becomes fractured and
brecciated, and hydrated to perlite". He observed that the necessary
water could have been derived
in part
from
ground'water
and.
in
part
from
extrusive bodies emplaced nearby.
Ross and Smith (1955) also concluded that the onionskin perlite that
encloses cores of water-poor obsidian has formed by secondary hydration of
the obsidian. They attributed the onionskin texture to volume change
produced by hydration of the surface layer of obsidian. Nasedkin and
Petrov (1962) observed that volcanic glass, when partial1y.hydrated
experimentally,
acquired the concentric cracks characteristic
of onionskin
I
texture. They concluded that the crackswere the result of stresses be..
'
tween layers of.differing degrees of hydratibn. Friedman and Smith
(1958)
measured the relative deuterium concentrations
in eleven samples of coexisting
obsidian
and
onionskin
perlite
and
compared'
them
with
deuterium
concentrations in meteoric waters. They concluded that the meteoric waters
in the obsidian,but were related to the water
were unrelated to the water
in the perlite, and that the hydration thus occurred in the presence of
meteoric waters.
Geological Features and Rock
of theNo Agua Mountains
Units
Previous Investigations
The perlite deposits of No
theAgua Peaks have been described only in
a very general way by previous workers. Two chemical analyses of the glassy
(1938).
rocks were reported by Shepherd
Butler ( 1 9 4 6 ) , in reference to the
peaks, described themas anerosional remnant ofan extinct volcano. He
noted a rangein lithology from "black, spherulite-bearing obsidian to
purple-gray, finely. flow-layered, spherulite-bearing pitchstone" and estimated
an
age
of
late
Middle
Tertiary.
In a brief reporton the economic geology of the
No Agua perlite
deposits, Schilling (1960) described thein as a volcanic dome extruded from
several
vents
during
the
late
stages
of,thePliocene-Pleistocene
volcanism.
9
He estimated the reserveKof commercial perliteat several millions of tons.
The possibility of the presence
of several domes, rather than a single dome,
d
was suggested by Weber
(1963').May (1965)
suggested that the rhyolitic bodies
are parts ofa,single, extensive flow, almost1000 feet thick, which has
been erodedlinto several hill-forming remnants.In 1971, the No Agua Peaks
were referred to by Butler
as anerosional remnant of a local mass of
rhyolite which was extruded after all or nearly all of the uppermost member
of the Los Pinos Formation
had been deposited and before the Lower Basalt
S
Member of the Hiniale Formation was emplaced.
General
.Features
Most of the rhyolitic material of Nothe
Agua Peaksis separable
into; (1) perlite, (2) glassy rhyolite, and(3) lithic (stony) rhyolite.
These compose mappable units distinguishable by differences in the ratio
of glass to crystalline and cryptocrystalline material, and by differences
in the degree of vesicularity. Contacts between perlite and glassy rhyolite
are ordinarily gradational, but the gradation generally occurs within a
few feet, permitting well exposed contacts to be shown as solid lines
on the geologic map. The mapping also was aided by persistent differences
in color. Locally exposed within the rhyolitic terrane is a fourth mappable
.unit which qualifies as a "tuff-perlite breccia".
The perlite.is persistently the most vesicular of the three.
Its
vesicularity, however, ranges widely from body to body and, to a lesser
degree, from place to place within a given body. The perlite specimens
examined in th@n
section proved tobe withinthe,range of 5 to 20 percent
of 2 to 5
vesicles. Specimens of glassy rhyolite showed a vesicularity
percent. Specimens of lithic rhyolite were non-vesicular. The contacts
of glassy rhyolite, although gradational,
between bodiesof perlite and bodies
consistently
markan abrupt
change
in
vesicularity,
The watercont'ent ( H - 0 expelled in the range llO°C
of
to 95OoC) of. the
2
major rock types, as indicated by analysis 60
of samples (Table 1
) , de-
creases froman average 2.76 percent in the perlite to
an average of2 . 3 3
percent in the glassy rhyolite, and thence antounmeasured, but obviously
no other signifimuch lower percent in the lithic rhyolite. We can detect
cant differencesin chemical composition from rock type to rock type (Table
I ) within a g5ven dome. A s indicated below, however, systematic differences
have been detected
in a
comparisonof.the composition
of
the
western
part
of the
of the volcanic pile with the composition of the
rest pile.
,
Much or all of the cryptocrystalline material in the glass-bearing
units apparently has formed by the devitrification of glass. The coarser
crystalline'material consists predominantly of plagioclase which, where
identifiable in thin section,proved to inbethe albite-oligoclase range.
Phenocrysts of quartz and biotite are minor constituents of all of the
rhyolitic units. Black'obsidian, in the form of semi-angular nodules
(marekanites) generally 1 to 3 cm in diameter, are present, but uncommon,
in allof the bodies of glassy rhyolite. They are persistently surrounded
by perlite. Nearly all of the,observed marekanites are in the upper
glassy rhyoliteunit
The perlite, glassy rhyolite, and lithic rhyolite are characteristically
flow banded. The'individual bands of all three rock types are generally
thin, most of them within the
.5 mm to 2 mm range and rarely exceeding
1 cm inthickness. The banding is expressed by differences in the
proportions of glass to cryptocrystalline and microcrystalline material,
and, in the perlite units,by differences in the abundance of vesicles.
It
SPECINENS RECOVERED F1:Ol.l
6, 04 'P 7 ~ . 51 03 . 3 5
0.075
0.78
6 0 ' M P 73.30
13.15
0.075
0.75
0.060
100'NP 73.37 1 2 . S 2 0.070
0.85
160'flP
73.37
13.05
0.215
0.73
0.SO
230'i'l?72.00
13.00
0,130
3 2 O f ~ P 7 O . 4 j 12.92 0.052 0.SO
4lO'/lPS3.00
9.00
0.215
0.77
0.040
Table 1.
Chemicalanalyses
0.b60
0.080
0.070
0.070
0.065
0.080 0.79
4.17
4.65
0.110 0.83
3.80
4.50
0.100 0.91
3.58
4.37
0.080 0.77
4.00
4.67
124.0
0.120 0.77
4.02
4.60
0.420 1.10 2.95
4.09
123.0
2.60
0.310
0.89
.1.90
of v o l c a n i cu n i t s
t o Sample l o c a t i o n s o n P l a t e 1.
(Diamond Drill Hcle shown on P l a t e 1)
RDll-2
115.0
115.0
128.0
110.0
37 .O
of t h e No Agua Peaks.Number-letterdesignations
Wif
TF'B = t u f f p e r l i t e b r e c c i a ;
LP
=
lower p e r l i t e u n i t ;
refer
LGR = lower
&
glassy rhylite unit;
MP = m i d d l e p e r l i t e u n i t ;
u n i t ; LR = l i t h i c r h y o l i t e u n i t .
H20-450
=
H20 released between
Percentages 'of Si02, A1203,
UGR = u p p e r g l a s s y r h y o l i t e u n i t ;
combined FeO and Fe 0 ; H. 0-Min = H 0 releasedbelow l l O ° C ;
2 3
2
llO°C and 450'12; H20-950 = H20 released between 450°C and 95OOC.
FeOX
Ti02,Fe203,
_-
='
MnO, M30 and ppm of Rb were obtained
303 and 403atomicabsorptionspectroscopes.Percentagesof
photometer 1L143.
A n a l y t i c a l . p r e c i s i o n ,e s t a b l i s h e d
f o r a l l componentsexceptTi0and
f
5 percent.
2
up = upper perlite
Rb.
by meansof
Perkin Elmer
N a 0 and K20 were determinedwith a flame
2
. .
by r e p l i c a t e a n a l y s i s , i s w i t h i n 2 1.5 p e r c e n t
Accuracy oY T i 0
2
i s w i t h i n 2 10 p e r c e n ta n df o r
Rb i s w i t h i n
n26-450
!;us;bcr a d
rock ur.i.k
Si0
A1203
2-
73.60
75.10
73.60
73.00
72.35
4-9 OGR 73.45
4-10 U 6 R 7 4 . 2 5
4-11 L R 73.60
4-12 "(re 73.10
4-13 flP 7 L .OO
4-14 VGR 73.40
4-15 MP 7 5 .OO
4-16 PIP 74.10
4-17 TPB 74,lO
5-1 V P 76.90
5-2
74.00
5-3 "GR 73 .OO
5-4 t A Q 73.60
5-5 PlP 73.90
5-6 M P 73.75
5-? *If 71.00
13.27
13.34
13.24
13.35
4-L V P
4-5" UP
4-6 V P
4-7 OP
4-8 U P
13.1.2
13.20
13.35
12.95
12.47
13.22
13.35
13.42
13.30
13.34
13.68
12.68
1 2 . E6
13 .OO
12.90
13 . I 3
'f)
G-ITPB
G-2 AP
72.10
7 4 .OG
G-3 MI" 7 L . 0 0
G-4 M P 74.60
C-5 I'V 73.70
G-6 f i Q 73.55
C-7 nP 72.60
G-C #P 74.70
G-9 p p i3.6.3
G-10 PI" 7 4 ,lo
c-11 mp 73.75
G-.l2 p\F 25.50
G-13 f l P 73.75
S-14 L6L.R 7 4 .OO
G-15 L p 72.00
C-iG LP 75.20
G-17 A:' 74.25
.
12.82
MnO
Ti0
2
FeOX
0.070
0.070
0.065
0.065
0.065
0.070
0.70
u.75
0.67
0.76
0 .78
0.G8
u.74
0.70
0.77
0.67
0.67
0.65
0.67
0.65
0.73
0.70
0.67
0.67
0.68
0.55
0.70
0.07i
0.066
0.069
0.079
0.065
0.065
0.073
0.073
0.074
0.071
0.071
0.071
0.071
0.073
0.072
0.070
0.075
0.073
0.070
0.076
0.067
0~127
0.043
0.032
0.040
0.075
0.040
0.050
0.60
0.61
0.62
0.59
0.59
0.58
0 .61
0.61
0.55
0.1.42
0.145
0.140
0.150
0.140
0. IJi5
0.1hO
0.145
0.144
0 . s.45,
0.1h7
0.140
0.145
0.150
0.147
0 . 150
1.470
0.015
0.080
0.075
0.090
0.070
0.080
0.060
0.070
0.070
0.095
0.062
0 .080
0.065
0.075
0 .OiO
0.095
12.70 0.050
12.95 O.OG0
1 2 . 9 0 0.215
1 2 .9E 0.100
12.70 0 .I45
1 2 . 74 0 .os0
12.60 0 . 0 5 2
13 .OO 0.052
12.62 0.060
1 2 . 7 7 0.015
12.70 0:OGO
0.070
1 2 .!lo
12.77 0:OG5
1 2 .9a 0 ,065
12.62 0.70
12..77 0.015
12.85 0.100
O.GO
0.57
1 .GO
0.59
0.59
0.5G
0.62
11.61
LfgO.
O.OGO
0.115
0.030
0.020
0.045
0.057
0.025
0.040
0.130.
0.030
0.040
0.035
0.035
0.040
Cxc)
0.67
O'.i3
0.8.;
0.85
0.85
0.85
0.89
0.85
1.30
0.87
0.84
3.82
4.53.
?<a 0
2
3.78
3.35
3.79
3.81
3.8Q
3.89
3.86
3.91
3.82
3.82
0.91 3.87
0.88
0.91
0.93
0.82
0.64
0.92
0.64
0.67
0.86
0.52
0.010 0.52
0.060 0.52
0.017 0 . 5 5
0.030 0.45
0.025 0.53
0.020 0.54
0.020 0.54
0.030 0.7L
0.020 0.60
0.01.5 0 . 5 2
0.030 0.47
0.005 0.51
0.015 0.53
0.020 0.76
0.020 0.53
0.050 0.51
3.58
3.85
3.95
3.95
4.84
3.85
3.93
3.96
4.06
3.88
4.33
(1.25
4.50
4.14
4.60
b.24
4.10
4.07
4.23
4.03
4.32
4.45
4.27
4.44
4.27
4.1.2
4.25
K20
4.48
4.36
4.48
4.50
4.53
4.57
4.50
4.54
4.22
4.54
4.49
4.77
4.54
4.70
4.90
4.69
4.67
4.97
4.52
4.54
4.67
4.32
4.45
4.60
4.70
4.27
jb.27
4.hl
4'15
4.52
4.A2
4.35
4.53
4.46
4.27
4.47
Rb-PPN
137.0
135 .O
132
134 .O
128 .O
138.0
132 .O
141.0
130.0
126.0
130.0
132 .O
:137.0
137 .O
;.
157 .O
142.0
137 .O
130.0
137 .O
136.0
l i 7 .o
267 .O
262.0
255 .O
256 .O
250 .O
255.0
267 .O
257.0
252.0
263.0
265.0
250.0
247.0
240.0
251.0
264.0
272.0
€1 0-Elin
2
0 .G9Oi)
0.5.873
0.095s
O.Oti73
0.27%
0.113i
0.2119
0.0999
0.0916
0.1438
.
1:.,0-450
H 0-950
2
'
p Lus
U 2 0-750
0.3440
0.h876
0.3730
0.3238
0.3145
0.2631
2:Si83'
2.9772
2.9311
3.0111
2.9744
..
2.8386.
2.9682
3.164L
3.0169
3.0754
3.2311,
-2.51523
2.7777
2.8932
2.5946
2 .I475
0.6509
0.3126
0.2597
0.2720
3.4286
3.2058'
2.8544
2.4196
3.6405
3.5057
2.9461
2.5633
2.4037
1.9868
2.0427
1.9566
1.8381
2.3841
0.1936 1.6356
0.05?6 2.3101
0.3161 ,2.719-$
0.2137 2;2324
0.1974 2.2392
0.2090 2.1656
0.2416 2.0797
0.3862 2.7123
0.1665 1.8221
0.3236 2.6336
0.3500
0.2969.
0.2605
0.3444
0.30h4
0.2943
0.2555
0.2758
0.3001
0.3303
0.3252
0.3155
0 * 3059
0,2599
0.091s
0.4560
0 .29!!h
0.5646
0. 3942
0 3ld19
0.3680
0.3966
0.2695
0..32:;7
0.2927
0.3503
2.3075
1.3032
2.4830
2.5667
2.2aso
0.451s
0.$2,6
2.33112
2 .X63
2.5698
.2.4546
2 . so12
2.5705
2.19G8
2.5154
1.2166
2.5L34
0.274;
2.6903
.
1
2.5342
2.4895
2.5581
2.6873
2.6099
2.5755
0.1L59
0.1692
0.1766
0.3966
0.0603
O.hA35
ti,O-TOi:LL
' .
2 . E113
2.3i8i
2 -4063.
2.3422
2.4753
2 .8326
2.0207
2.6933
2.6045
1.5655
2.6274
2.6911
2.5813
2.6198
2.8442
2.8899
2.7650
3.6264
2.8362
2.fi057
2.7751
I).205s 1 . 4 2 5 5
0.301s '2.SjOi
. ..
2 - 9j
i
i
2 .yj<?
3.1,SL:L
3.2355
3.1L5? .
3.Oi3i'
3,13?O
3.25i9
3.1817
3 .S959
3.2145
2.90:s
3.1253
;.27;2
3 .:?Ls
0.2S59
3.2599
2.9763
20
is accentuated by an elongation of the vesicles. Where present, the marekanites tend to occur in rows parallel with the flow banding and clearly represent .remnants of unusually thick (as much
as flow bandsof original,
10 cm)
water-poor obsidiannow partly altered to perlite.
In basic geologic features the four hills
are similar in that the
crest of eachis underlain by a body of relatively compact perlite, the
higher slopes largely by glassy rhyolite, and the lower slopes largely by
vesicular perlite. Additional support for the separate dome interpretation
exists in the observation, elaborated upon in a following section of this
Low the
Hills
report, tha; all of the perlite and glassy rhyolite units of
-
West Hill area contain lower percentagesof A 1 0 Ti02,Fe 0 M 0 CaO, and
2 3'
23'g'
K20 and higher percentages of.Mn0, 20Naand Rb, than do the rhyolite units
of the rest of the
No Agua Peaks.
Upon observing the consistent distribution of the same rock types,
from dome to dome, Naert based his designation of mappable units upon two
factors, lithology and position in the domes. Thus the names "upper perlite",
"middle perlite", and "lower perlite" are applied,
in that order, to the
bodies of compact perlite
exposed'on the crest of each hill, to the vesicular
perlite of the lower slopes, and to the vesicular perlite beneath the glassy
rhyolite of the Low Hill area. The two units of glassy rhyolite are
designated as "upper glassy rhyolite". and "lower glassy rhyolite", whereas
the two other rhyolitic units are simply termed "tuff-perlite breccia"
and "lithic rhyolite". Because the "lower perlite" is exposed only
in the
LOW Hill area and the lower parts of the four domes are hidden beneath talus
each of thefour
and alluvium, the designation of a "middle perliteon body"
.
.
necessari. l y i m p l y t h a t ' e a c h
domes does not
of p e r l i t e now hiddenfrom
view.
Indeed, .e r o t a r y d r i l l h o l e ,
+lu. roo-$+ C1LS-m)
Johns Manville m i l l , passed through
directly into Tertiary basalt
i s f e aitured by a s t i l l lower body
J
b
i
near the
a"m t h i c k n e s s of t h e m i d d l e p e r l i t e
andsedimentaryunits,indicatingtheabsencethere
).
H i l l a r e a . (Fig.
of t h el o w e ru n i t so ft h eN o r t h
General Features and Petrology
oftheRhyoliticUnits
Tuff-vitrophyre
shown on t h e g e o l o g i c
T u f f - d e r l i t eb r e c c i a ,a s
limitedexposure.
i s of v e r y
Low H i l l a r e a , i t
Where noted a t t h e l o c a l i t y i n t h e
apparently underlies
a westward extension of the lower glassy rhyolite
West H i l l .
u n i to ft h e
map (Pl. I),
The t u f f - p e r l i t eb r e c c i a , e x p o s e d
Manville p l a n t , a p p e a r s t o
ofthewest-trendingridge.westoftheJohns
u n d e r l i et h em i d d l ep e r l i t eu n i t
on t h e s o u t h s i d e
of theNorth
Hill.
On t h es o u t h w e s ts i d e
of the E a s t H i l l , t u f f - p e r l i t e b r e c c i a a l s o u n d e r l i e s p e r l i t e . o f t h e m i d d l e
perlite unit, but
its position with respect to the structure of the
East
H i l l dome i s u n c l e a r .
,
The t u f f - p e r l i t e b r e c c i a
is typically gray to reddish
o ff r a g m e n t so fo n i o n s k i np e r l i t e .
rangeof
5
t o 15 cm i nd i a m e t e r .
ofpowdery,redtuffaceous
Most of t h ef r a g m e n t s
They a r ec o n t a i n e di n
material (Fig.13).
brown and c o n s i s t s
are w i t h i n t h e
a m a t r i x composed
The unitranges.frompoor.ly
t o well bedded.
Becauseof
i t s limited exposure and obscure pattern
t h e p o s i t i o n of t h e t u f f - p e r l i t e b r e c c i a
of d i s t r i b u t i o n ,
i n the internal structure
of t h e
glassy
I=
domes p e also obshure. Much of this unit may have formed
in frontof
. advancing flows of perlite
and.have
involved in part, the mixing of
fragmented perlite with ash from
an underlying layer. Underlying ash was
observed at the locality-northeast of the Grefco plant and may record the
initial eventof the rhyolitic volcanism.
Lower perlite unit
The lower perlite unit, which was recognizedin only
the Low
Hill
area
of the western part of the mountains,
is nonresistant and commonly covered
by talus. ;Where the unitis exposed, Its lower part is consistently hidden
beneath Quaternary alluvium. It is exposed well enough laterally, however,
the
to indicate that it probably.continuously underlies the western ofpart
Low Hill area and thus forms
a body that is about
2000 m in north-south
dimension.
It is generally overlain by the lower glassy rhyolite unit and,
in a place west and northwest of the Grefco quarry, by the lithic rhyolite
unit. Quarrying of the lower rhyolite unit would require the' removal of
much overburden of glassy rhyolite and lithic rhyolite and thus would be
uneconomic at present.
The lower perlite unit is gray to pale brown and very vesicular, the
vesicles composing about20 percent of.the rock. The ratio of glass to
OM,>'"%*+
crystalline and cryptocrystalline,+ppears
to be slightly greater than
Flow banding is common.
1:l.
Lower
.
The lower glassy rhyolite unit which
is exposed only in
the
Low
.
Hill
in color and weathers a dark gray.
area, is resistant, ledge-forming, gray
It ranges in estimated thickness from
10 m to 50 m.
It is much more
extensively exposed than the underlying lower perlite and tuff-perlite breccia
units.
'
It forms.most of the footwall of.the middle perlite unit
in the Low
Hill-West Hill area.
It is essentially coextensive with the overlying middle
perlite unit, the two units extending, coulee-like,
well to the west of the
central part of the West
Hill dome. The lower glassy rhyolite is unexposed
east of 'the Low Hill area. If present in the areaof the four domes
it is
hidden beneath alluvium and overlying volcanic units. Where exposed, the
lower and upper contacts of the lower glassy rhyolite unit tend to parallel
the topographic contours, indicating a generally horizontal attitude.
The lotrer glassy
. . rhyolite unit, is strongly flow banded. Along the
lower contact the banding, genera4is
in
parallel with the contact
and dips gently inward. In the higher parts of body the banding shows a
wide rangein orientation, apparently resulting from flowage
in a viscous
lava.
The lower glassy rhyolite
is much less vesicular than the overlying
no more than two percent
of the
middle perlite unit, the vesicles forming
volume of the specimens examined. Approximately two thirds of the solid
material consists of cryptocrystalline and microcrystalline material, considerably more than contained in the overlying perlite. The glassy fraction,
which forms the remaining third shows a pearly luster in hand specimen and
an onionskin texturein thin section. The relatively high proportion of
non-glassy, unexpansible material makes the glassy rhyolite unusuable
as
perlite.
Middle perlite unit
The middle perlite unit, immediately underlies most of the area of the
Low Hills to form there the aforementioned oreonbody
the Grefco property.
It also underlies most of the lower slopes of each of the four hills where,
is commonly hidden beneath
unlike its occurrence in the Low Hills it
area,
talus derived from'the overlying upper glassy rhyolite member. Where the
unit is exposed, it displays
flowbanding that, in the vicinity of the domes,
commonly dips inward toward the centers of the hills, although less obviously
than does the flow banding in the upper glassy rhyolite and upper perlite.
.Thus, we tentatively interpret the middle perlite unit
as issuing from
vents ateach'of the four domes, the contacts between the four bodies being
obscured by popr exposures and relatively uniform lithology.
The middle perlite unit is gray to pale brown and weathers mostly to
pale brown. Like the lower perlite unit,it averages about 20 percent
I
vesicles, but displays a considerable range in vesicularily. The solid
1:l to 6:5 ratios
fraction, as is typical of the No Agua perlites, displays
in the proportion of glass to cryptocrystalline and crystalline material.
The vesicles are,
in general, larger thanin the lower perlite layer,
are abundant enough to
commonly about5 mm in maximum dimension, and they
permit the perlite to be quarried without blasting.
In some places, including the south side of the East Hill, the middle
perlite contains zonesof less vesicular and more crystalline rock that
resemble'the middle glassy rhyolite.An interlayering of glassy rhyolite
and perlite of the middle perlite unit
is shownin a generalized way(P. 1)
on the southside of the North
Hill.
Recent excavationon the south side of the West Hill have shown that
the middle perlite
unit.there
is
strongly and irregularly brecciated through
.
.much of its thickness.Asitresembles brecciation that commonly features
the fronts of rhyolite flows,
we interpret it in this way.
Upper glassy rhyolite unit
The upper glaksy rhyolite unit, which underlies the middle to high
slopes of each of the four hills and forms bodies that tend to be annular
WJ. ISJ
4
in plan, is generally resistant and well exposed. The bodies range in
'
P
estimated thickness from about
50 to 150 m.
The rock isgray,on fresh
surfaces and weathers to reddish gray.
It is locally vesicular, but,
like the lower glassy rhyolite,much less
so than the bordering bodies of
perlite. Some.is distinctly flow banded (F.ig.lb), some only faintly so.
The configurationof the flow banding
of the upper glassy rhyolite
unit provides 'the principal evidence that each of theis hills
the site of
I
PI.1,
an extrusion dome (Fig.\%).
Although variously oriented in detail, the
>
.flow banding, in,general,dips inward toward the centers
of the hills
and parallelwith contacts between the upper glassy rhyolite and the
overlying and underlying units.
The flow banded facies closely resembles the lower glassy rhyolite,
being characterized by alternating laminae
of glass-rich and glass-poor
material (Fig.17 ) . The onionskin texture,so common in the lower unit
of the upper glassy rhyolite,
is generally undetectable in handspecimens
but is commonly observable
in thin sections of the upper unit. About
two thirds of both the well banded and poorly .banded rock;like the
lower glassy rhyolite unit, consists
of cryptocrystalline and crystalline
material (Figs.18, l9,L.O)
.
Where especially well exposed
on the North and East
Hills, the upper
part of the upper glassy' rhyolite unit is shown to consist of a zone
(6;s.21)
Lolor
characterized byan onionskin texture of the glass, a pink, a clay-size
n
4
,
alteration mineral, and scattered cores of obsidian (marekanites)
an
26
inch or less in diameter. Locally the zone also contains scattered
masses of pumice as much as
20 cm. long. Downward from the overlying unit
of perlite
the onionskin texture disappears.
Upper perlite unit
As the
upper perlite unit underlies
much of the crest' of each of the
four hills and is underlain by the inward-dipping upper glassy rhyolite
unit, we interpret it as occupying the central and highest part
of each of
the domes. The domes of the North and East Hills contain the two bodies of
greatest ar'eal extent, each being irregulariy ovoid
in plan,700 m and 900 m
long and 400 m and 500 m in maximum width respectively, The upper perlite
body of the, WestHill is of comparable dimensions;but is transected.and
made very irregular by two intrusive bodies
the-lithic
of
rhyolite. The
upper,perlite body of the South
Hill ispoorly exposed, but is apparently by
far the smallest of the four, as mapped being only350about
m long.
The
upper
hill to hill.
perlite
unit
displays
a relatively uniform lithology from
It is colored grayish brown and weathers pale brown.It is
5 to 15 percent of the volume of
vesicular but the vesicles compose only
rock, compared with the
20.percent average vesicularityof middle and
of the upper bodyis thus much more
lower perlite bodies. The perlite
compact than the perlite of the other two. The vesicles
are elongate and
.generally 1 to 3 mm long.
As with the other.perlite units, fifty to sixty
percent of the solid fraction
o f the rock consists of glass; the remainder
).
is cryptocrystalline and crystalline material (Fig.23
The flow banding of the upper perlite isunit
generally well defined,
but in some places is indistinct.It ranges widely in attitude within an
i n d i v i d u a l body..
A largeproportionofthemeasuredattitudes,however,
trace of t h ec o n t a c tw i t ht h e
s t r i k ea p p r o x i m a t e l yp a r a l l e lw i t ht h e
(Pl. 1, F i g . 7 ) .
u n d e r l y i n gg l a s s yr h y o l i t e
inwardtoward
t h ec e n t e r s
of t h e domes.
Most o ft h e s ea l s od i p
during the end s t a g e so fc o n s o l i d a t i o n .
the upper perliteanit, like those
The p h y s i c a l c h a r a c t e r i s t i c s
problems of q u a l i t y c o n t r o l .
of
of t h e m i d d l e p e r l i t e u n i t , d i f f e r f r o m
within a given dome andfrom
dome t o dome, and i n t r o d u c e
The d i f f e r e n c e sa p p e a rt ob em a i n l yi nt h e
i s developed.
abundance of v e s i c l e s and t h e d e g r e e t o w h i c h o n i o n s k i n t e x t u r e
Although mo4tof
2
T e n s i o nf r a c t u r e s ,o r d i n a r i l y
i n echelon, are comon,andapparentlyformed
t o 20 cm longandarranged
place to place
'
theupperperlitelackstheonionskintexture,Johns-
Manville p e r s o n n e l r e p o r t
i t s presence i n p e r l i t e q u a r r i e d s o u t h
faultontheNorth
Hill.
i n themainquarry
on t h e N o r t h H i l l ,
It i s c r u d e l y circular i n p l a n ,
material.
and contains pink clay-like
The o p e r a t o r s o b s e r v e t h a t p e r l i t e
of o n i o n s k i n t e x t u r e p r o d u c e s
h i g hp e r c e n t a g eo ff i n e sd u r i n gp r o c e s s i n g .
recovered from shallow drill holes
depth..Nevertheless,
was encountered
A body'ofonionskinperlitealso
a few t e n s o f , m e t e r s i n d i a m e t e r
of t h e
a relatively
They a l s o r e p o r t t h a t p e r l i t e
shows a d e c r e a s e i n v e s i c u l a r i t y w i t h
the upper p e r l i t e u n i t a p p e a r s t o c o n s i s t a l m o s t
e n t i r e l y of rock of p r o v e d o r p o t e n t i a l v a l u e a s e x p a n s i b l e p e r l i t e .
Lithic rhyolite unit
The i n t r u s i v e b o d i e s of l i t h i c r h y o l i t e are i r r e g u l a r i n o u t l i n e
c u t a l l of t h e o t h e r m a j o r l i t h o l o g i c u n i t s .
o c c u r r i n gi ne a c h
No Aguadomes.
These are w i d e l y d i s t r i b u t e d ,
of t h e - f o u r domes and i n t h e Low H i l l a r e a .
them as dome b u r s t s m a r k i n g t h e f i n a l
They r a n g e i n
We i n t e r p r e t
event i n t h e v o l c a n i c h i s t o r y o f t h e
exposed lengthfromabout
l i t h i c r h y o l i t e i s colored a c h a r a c t e r i s t i cb l u i s hg r a y .
i s d e v e l o p e dt ov a r i o u s
and
100 m t o 1800 m.
A s flowbanding
The
degrees,therockrangesfrom
w e l l laminatedtomassive.
Both t h e l a m i n a t e d ' a n d m a s s i v e f a c i e s c o n s i s t m o s t l y o f c r y p t o c r y s t a l l i n e
CF'9 25)
8
. a n dc r y s t a l l i n e
material.
They c o n t a i nv a r i o u sp r o p o r t i o n s
of g l a s s ,b u t
,+-
alsoanoverallhigherproportionofthenonglassyconstituentsthanthe
Where g l a s s i s l o c a l l y a b u n d a n t , t h e u n i t ' i s d i f f i c u l t
g l a s s yr h y o l i t e .
or impossible to distinguish
i n outcropfromtheupperglassyrhyolite.
is variously oriented,
The f l o w b a n d i n g d i s p l a y e d i n t h e l a m i n a t e d r o c k
but i s general2yconcordantwiththeoutlines
of t h e b o d i e s .
Breccias
I n additiontothetuff-perlite,breccia,andtheflowbreccias,
two
1
were n o t e d i n t h e
o t h e rt y p e so fb r e c c i a
No Agua r h y o l i t e t e r r a n e .
is a fault breccia.and the other apparently
s p i n e s (Fig-
2b
shown on P l a t e 1 .
).
formed a t t h e s i t e s of e x t r u s i o n
The f a u l t b r e c c i a c h a r a c t e r i z e s a l l
It i s e s p e c i a l l y well exposedandabout
i t consists of angular fragments of the bordering units in
a west-striking fault
A similarlylarge
of t h e f s u l t s
10 meters wide
of North .Hills.
a l o n gt h ew e s t - s t r i k i n gf a u l tt h a tc u t st h ec e n t e r
matrix of the same u n i t .
One
There
a finelycrushed
zone of b r e c c i a c h a r a c t e r i z e s
which c u t s t h e s o u t h e r n p a r t
of t h e Low H i l l area.
Geochemical Evidence f o r Magmatic D i f f e r e n t i a t i o n
i n t h e No AguaRock U n i t s
Thechemicalanalyses
of t h e 72 r o c k s a m p l e s , . r e p r e s e n t i n g
u n i t s exposed i n . each dome (Table 1
), show a p p a r e n t l ys i g n i f i c a n t
d i f f e r e n c e sb e t w e e ns a m p l e sc o l l e c t e di n
samplesgathered
a l l of t h e
in the other three hills,
the West Hill-Low H i l l a r e a and
.
29
Frequency distributions demonstrate the presence
i s intherubidiumcontent,onepopulation
The most obvious difference
140 ppm
Rb,
c o n t a i n i n g1 2 0t o
t h eo t h e r
240 t o 280 ppm.
All of t h e low
East andSouth
Hills; a l l of t h e
Rb samples were obtainedfromthe.North,
high Rb samples were obtained from the
A duster analysis, devised
West H i l l and t h e Low H i l l area.
by FriedmanandRubin
formed on t h ec h e m i c a la n a l y s e so ft h e
analysisalsoidentifies
of two populations.
72samfiles(Table
two d i s t i n c t g r o u p s ( F i g .
a l l the samplesfromtheNorth,
(19G7), was per-
East andSouth
comprising sal1 of the samples from the
I
).
..
This
.
27 ), onecomprising
Hills a n d . t h e o t h e r
West H i l l and t h e Low H i l l a r e a .
1
Themeans
for A1 0
Ti0
2 3'
2'
Fe203, MgO, CaO, .and K 0 a r ec o n s i s t e n t l yh i g h e r
2
and t h e means f o r MnO, Na 0, and Rb are c o n s i s t e n t l y l o w e r i n t h e a n a l y s e s
2 '.
..
of samples 'from the North,
of samplesfromthe
East, andSouth
H i l l s as compared w i t h a n a l y s e s
West H i l l and Low H i l l area.
An i d e n t i c a l s e p a r a t i o n
is indicated in a plot of the values for the Crystallization Index versus
t h eA l k a l iI n d e x
on a v a r i a t i o n d i a g r a m . I n
a closedsystem,Fe,
C a are g e n e r a l l y removed from the magma a t a n e a r l y s t a g e
w h i l e Mn, Na and Rb become r e l a t i v e l y . e n r i c h e d i n
,
are a reshit. ofmagmatic
thatthevariousbodies
North, East, andSouth
H i l l .and Low H i l l area.
i f r h y o l i t e of
a s i n g l e magma chamber, t h e d i f f e r e n c e s
t h e No Agua domes.wasextrudedfrom
and indicat.e
of c r y s t a l l i z a t i o n ,
the remaining magma.
Thus the c o m p o s i t i o n a l d i f f e r e n c e s s t r o n g l y s u g g e s t t h a t ,
i n thecompositionoftherocks
Mg and
differentiation,
of r h y o l i t i c r o c k i n t h e . a r e a
Hills.were emplacedbeforethebodies
of t h e
of t h e West
.
.
:
&
./ "$
Extruskion History of the
No Agua Domes
Models
In attempting to reconstruct the extrusion history ofNo the
Agua
.
rhyolitic terrane,we have considered the four models of Figure
2g
They are based upon observations in the
No Agua rhyolitic terrane, and
on descriptions and interpretationsof'typical rhyolitic domes elsewhere
(Williams, 1932; von Leyden,1936; Putnam, 1938; Chelikosky, 1940; Smith,
1973.).
The mddels pertain especially to the lower glassy rhyolite, middle
perlite, upper glassy rhyolite, and upper perlite units NoofAgua
the Peaks.
Model A featyres a single, laterally extensive flow, bounded top and bottom
i
at rests
be, perlitic outer zones and a more crysta'lline inner part. It
least in part, upon an earlier flow of glassy rhyolite.
c d m sThe
flow
is deeply eroded, and the hills are erosional remnants.
Model B involves smaller domes coincident with the hills. Each dome
is formed
by a single flow which has grown upward and outward from beneath
the center of the dome. Each consists an
of outer perlitic zone andan
inner core of the more crystalline glassy rhyolite. Flow banding in the
lower part of the domes dip inward toward the conduit and, in the ,upper
parts, is concordant with the outlines.of the domes.
It is much less
eroded than dome of Model
A.
. .
Model C also involves hill-forming domes
.of about the dimensions of
the domes of model
B, but constructe'd of two flows extruded from the same
vent. Each flow comprises two cooling units; a vesicular,very glassy
4+eC
upper part (the perlite unit) and a less vesicular and less glassy lower
A
part (the glassy rhyolite unit). Flow banding in the inner part of each
flow dips inward.
Model D resembles modelC, but instead,of involving two flows,it would
make each of the four units a separate flow contrasting with the underlying
and overlying units in degree. vesicularity and proportion of crystals.
Some of the flows form bodies of perlite, others form bodies of glassy
rhyolite. A s i n model C, the flow banding of the inner part of each flow
dips inward.
The term "endogenous extrusion dome" has been
commonly~appliedto
features like .thoseportrayedinmodel B.
It isdefined by Williams (1932)
as a "volcanic dome that has grown primarily by expansion from within and
is characterized'by a concentric arrangement of flow 'layers". The type
of dome illdstrated
in model C has been termed
an "exogenous extrusion.dome"
and defined by Williams(1932) as "a volcanic dome that is built by surface
a central vent or crater." Model
D is best
effusions of.viscous lava from
described as partly endogenous and partly exogenous, the highest and latest
flow
being
essentially
endogenous
and
the
others
exogenous(
F13.l9
1
Origin of the perlite
Pertinent to an evaluation of the four models, is the question of the
in same
origin of the perlite. Was it formed by the process, well documented
perlite occurrences, involving the perlitization of obsidian through hydration by meteoric waters and over a lengthy well
periodafter solidification
of the glass; or did No
theAgua perlite form in the course of the volcanic
event?
<
'
I
&
The abundaneof obsidian nodules (marekfnites)
, a-ze&&&
in the
onionskin perlite-bearing zone at the top of the upper.glassy of
rhyolite
the North and East Hills, demonstrate that at least some of the dome-forming
rhyolitic rock originally solidified
as nonvesicular obsidian which was
later p a r t l yp e r l i t i z e d .
of t h e g l a s s y r h y o l i t e
The p r i m a r yv e s i c u l e s ,
and i n t h e p e r l i t e
of t h e No Aguadomes
point against
were once composed of 'nonvesicular
the possibility that these rocks also
i s e v i d e n c et h a tt h e
obsidian.Alsolacking
so p e r s i s t e n t i n t h e r e s t
was introduced by surfaceorground
waters.
water i n t h e v e s i c u l a r r o c k
The v a r i a t i o n s i n w a t e r c o n t e n t
are r e i a t i v e l y s m a l l ( T a b l e
of the perlite and glassy rhyolite samples
and apparently unrelated in space to the pre-quarry ground surface
zonesof
2)
h r to
severe f r a c t u r i n g o r b r e c c i a t i o n .
An a l t e r n a t e i n t e r p r e t a t i o n , which we view as more c o n s i s t e n t w i t h t h e
a v a i l a b l ef i e l d ,p e t r o g r a p h i c ,
and a n a l y t i c a l o b s e r v a t i o n s , h o l d s t h a t
most
i s magmatic i n o r i g i n , was p r e s e n t as a .
o f ' t h e watei i n t h e g l a s s y r o c k s
v o l a t i l e i n the v e s i c l e s , and was reabsorbed by t h e g l a s s upon cooling.
We d i s c u s s e d t h i s p o s s i b i l i t y . w i t h
the
C.W. Burnham who h e l p f u l l y p r o v i d e d
following observations."
11
of water t h a t p r e v i o u s l y e x s o l v e d
Perlitization through reabsorption
from t h e r h y o l i t e melts d u r i n g v e s i c u l a t i o n
i s compatible with the
H 0 s o l u b i l i t yr e l a t i o n s
2
(Burnham, 1979, Fig. 3 . 1 ) .
present in the perlites,
whichaverages
is r e s t o r e d t o t h e o r i g i n a l
a depth ofapproximately
.
i n excess ofapproximately
i nv e s i c u l a t i o n .
'
containing more
Theend
2
Ian.
now
27 analyzedsamples,
with H 0 a t
2
Upon e x t r u s i o n of t h e s e melts a t temperatures
,
7OO0C, more than 90 percent of t h e H 0 would exsolve,
2
p r o d u c t ,i nt h i s
C
90 p e r c e n t vesi&4es,
4
t\
maximum v e s i c u l a r i t y of 20 p e r c e n t .
case, however,wouldbepumice
***
which i s not i n a c c o r q w i t h a n o b s e r v e d
The vesicles wouldundergo
some compression
is
a load of overburden,ofcourse,butthed'iscrepancy
much t o o l a r g e t o b e a c c o u n t e d f o r
1,
2.7 p e r c e n t i n t h e
of t h ew a t e r
melts, t h e s e melts w o u l d . b e s a t u r a t e d
+ha.u-
duringcoolingunder
Ifall
'known
by t h i s mechanism.
An a l t e r n a t i v e e x p l a n a t i o n i n v o l v i n g
as t h e magmas ascendedfromdepths
magmatic"water"
is t o assume t h a t ,
of approximately 2 km o r g r e a t e r ,
and
33
underwent p a r t i a l v e s i c u l a t i o n , t e m p e r a t u r e s d e c l i n e d
belowapproximately
7OO0C p r i o r t o e x t r u s i o n , t h e r e b y m e t a s t a b l y " f r e e z i n g " i n t o t h e g l a s s
of i h e o r i g i n a l
H20 content.Accordingly,
would be produced
800 and.900
ut.
less exsolved
most
a v e s i c u l a r i t y of 20 p e r c e n t
by e x s o l u t i o n of only 0 ; 5 w t . p e r c e n t H20 a t a depth between
Lower v e s i c u l a r i t i e s wouid beproduced
H20 a t g r e a t e r d e p t h s . "
by correspondingly
Evaluation of the models.
If we have correctly interpreted the markenite-bearing zone at the top
of the upper glassy
rhyolite,unit
as
also
the top ofan.individua1 flow
and
thus the upper perlite unit aas
later flow, model
C must be preferred, as
the other three are nonpermissive of the two asunits
separate flows.
We reject modelA, partly for this reason, but also because
it is
inconsistent with the generally inward dipping'configurations of flow
banding and of the geological contacts which characterize each of the
hills, an observation made in a precedfng section of this report. The
I
single flow interpretation also is incompatible with the compositional
differences, cited earlier, between the specimens from the Low Hill-West
Hill area and those from the other hills.
In addition, the topographic
low, between the four hills is
also
.difficult to explain by erosion of
a single flow. Post-flow collapse is a possibility,.but the mapping
shows no evidence for this.
Model B, although more compatible with the observed geological data
than modelA, lacks evidence for a connection between the upper and
middle perlite units. It also is apparently inconsistent with the
configuration of the flow banding of the upper perlite unit,
2\50and
w i s h "k*- b r e s e m c e
+L
++b
OF
ut.t..-
OF ibstki>h
\u.~t'-
5\hssq r\u_./Dl;.\Tc
unit.
~k
++M
;LC
Model C more c l e a r l y accommodates t h e f l o w b a n d i n g p a t t e r n o f
Plate 1
al w
t h a n domodels A and B. But i t doesnotexplain
the d i s t r i b u t i o n of
m.&$&2&aC ~ V r n l i e
4
w
&
e
&
&
w
n o n?
v,
esicular bodies of obsidian
a+ & bb. o
"1
b J \ a s q a \ i k uai+,
f
nnrt n
ow.
(1.1
q
t h a t , i n thesubsurface
E
+kc
and the middle perlite unit
Model D, w e f e e l , f a c e s
in
i s the-observation
Also
unexplained,
mill a r e a ,
(RDH-2; F i g . l b ) of the JohnsManville
in addition to the lower units,
the middle glassy rhyolite unit,
t h r e e models.,But
i n a well-defined layer
i s missing,
rests d i r e c t l y ypon T e r t i a r y b a s a l t .
noneof
theobjectionscitedfor'theother
i no u rc o n v e r s a t i o n sw i t ho t h e rg e o l o g i s t sc o n c e r n i n g
I
of model D , some h a v e s u g g e s t e d t h a t i n d i v i d u a l f l o w s
the credibility
should not
show g r a d a t i o n a l c o n t a c t s w i t h t h e u n d e r l y i n g a n d o v e r l y i n g
v o l c a n i c u n i t s and should display flow breccias and other evidences of
c o o l i n ga l o n g
their uppersurfaces.
Some g e o l o g i s t s a l s o
i n textur'eand
that the differences
have suggested
water c o n t e n t , f r o m u n i t t o u n i t , a r e
difficult t o explain theoretically in
a modelbased
on i n d i v i d u a l f l o w s ,
magma a r e i m p l i e d .
particularly if variations in the water content of the
A gradationalcontact,however,canbeexplainedifanindividualflow
was c o m p l e t e l ys o l i d i f i e d .A l s o ,
was emplacedbeforetheunderlyingflow
lO*uO
phenomena.Moreover,
as c o n t r o l l e d , i n l a r g e p a r t ,
$L"W
~.,a~',~
a g i v e nu n i t
t h ep e r c e n t a g eo fw a t e rc o n t a i n e di n
seems b e s t i n t e r p r e t e d
q u a l i f y a5
i t s contained b&eeIes ofpdmice
themarekanite-bearingzone,and
by t h e a v a i l a b i l i t y
of water vapor i n t h e v e s i c l e s and t h e a v a i l a b i l i t y of g l a s s t o a b s o r b
it
a
.
~
d
a
E
b
W
S
"
p
i
.
~
n
%
i
?
+
~
p
~
~
&
~
a
t
e
;
n
n
n
e
n
inrl ivFdual
r
t
&
-
i
I
36
ANALYSIS OF'THE CHARACTERISTICS OF PERLITE
An attempt was made by Naert(1974) to devise a method of predicting the
expansion characteristics of perlite by relating them to variations
in the
physico-chemical characteristics of the crude material. Numerous earlier
attempts have been aimed at the same objectives. These include research and
observations by Judd (1896), Kozu (1929), Wilson and Roseveare (1945), King
. .
and others (194&), Murdock and Stein (1950), Taylor (19501, Wilfey and Taylor
(1950), Keller and Pickett (1954), Weber (1955), Albert (1958), Leineweber
(1961), Yavip (1962), Nasedkin (1963), Kadey (1963), Salat and Oncacova (1964),
I
and May (1965).
Each suggested that expansion characteristicscan be predicted
by observing variations inone or more of the following:(1) luster, ( 2 ) abun( 3 ) specific.gravity, (4) percentage of combined
dance of obsidian nodules,
(6) chemical
water, (5) percentages of microscopic inclusions and phenocrysts,
composition, (7) texrure of the rock, ( 8 ) color, '(9) degree of devitrification,
(10) temperature of expansion, and
(11) retention time in the furnace.
A statistical
analysis.of 106 chemical analyses of perlite samples gathered
throughout the world showed that,
with regard to chemical composition, the No
Agua perlites are a random sample of this world population (Naert,
1974).
The
following characteristicswere measured on 153 samples of the No Agua perlites:
1. Chemical composition (Si02, A1203, Ti02, Fe203 (total iron) CaO,
MgO, MnO, Na20,
K20, Rb in ppm, and H20 released at llO°C,
450'C
and 950°C);
2.
Proportions of glass, crystallites and vesicles
as determined by
point count under the microscope;
3. Eulk density of the rockas measured with a mercury balance; and
4.
Ranking on the basis of presence of. banding, relative size of
crystallites, presence and degree
of development of onionskin
texture, and degree .of devitrification.
Attempts were
madeto
measure
the
crystallinity
of
the
glass
by
X-Ray
diffraction, to determine
H 0 bonding characteristics of the water by
2
infrared absorption, and to measure differences in the refraction indices of
glass,
but
,these
pr&ed
unsuccessful.
. .
At the Lompoc, California, laboratories'of the Celite Division of the
Johns-Manville Corporation,22 expansion characteristics were measured
on 47
of the 72 samples of perlite from the No Agua domes. Samples from the Low
Hill area,as well as samples
of lithic rhyolite, were excluded from the tests.
The tests included data
on feed rate, temperature, expanded density,
loss' on
ignition, sieve analyses
of the expanded material (percent retained by weight
and volume), expanded density of the various size fractions, percent weight of
the various size fractions
of the expanded material, percent by weight
@f
yield (percent 'of the crude. that expanded) and sinks (unexpansible material),
the densityof the sinks and the necessary temperature to obtain
a
7-8 pcf.
expanded density. Data on at least 18 of these 22 variables were obtained for
each sample.
Statistical control of the observations was established by employing
several designson replicate analysis. The data were processes and examined
with the aid ofthe following statistical computer programs:
NORMSTAT, The Pennsylvania State University
Dept. of Geosciences
STATPAC,
,
Statistical Package Program, Verity, 1970,
The Pennsylvania State University, Computation
Center
CLUS,
A Cluster Analysis, and Taxonomy. System for
Grouping and ClassifyingData, Rubin and Friedman,
1968 IBM Corp.
FSCORE Kohr,
1969, The Pennsylvania State University,
Computation Center.
When all of the measured variables
were related to the expanded density
values, the expansion characteristics were found to be unrelated to differences
in the chemical-compositions of the perlite samples.
On the other hand, more
than 85 percknt of the variation in expanded density
was found to be attributable to the combined effects 1of
) the percentage of volatiles released between
110°C and 45OoC, 2) the bulk density of the rock,
3) the crystallite and vesicle
content (log basee).
characteristis
of
The combined effects of.these varibles upon the expansion
perlites differ from perlite to perlite. The.discriminant
functions, obtained from the classification of a set of perlite samples of
known expansion behavior, permit one to assign a given sample of unknown expansion behavior toone or three groups based
on expandability (good, medium, and
poor).
Classification of a sample of unknown expansion characteristics first
requires the transformation of the.four variables into a standardized form
using the following formula:
X i ? / r IC,
.
2
X . is the value of the individual variable for the
i is the standardized value;
1
-
unknown sample:X is the mean value of the individual vairable from a set of
h
samples of known expansion behavior;
(J is,the standard,deviationof
the
individual variable from a set of samples of known expansion behavior.
StandardhDeviation
Variable
(0)
Percentage of volatiles
r e l e a s e da e
450PC (H450)
Bulk density
Percentage ~ P c r y ’ s t a ~ ~ i t e s
Vesicle c o n t(belaon)sgte
2’.335
3.3478
2.022
1.6167
44.9698
83.279
1.777
6.453
i s m u l t i p l i e d by t h e d i s c r i m i n a n t v a l u e f o r t h e
Each s t a n d a r d i z e d v a l u e
correspondingvariableobtainedfromtheclusteranalysis
of known e x p a n s i o nb e h a v i o r .F o rt h et h r e eg r o u p sa sr e c o g n i z e d
on t h e set ofsamples
by t h e c l u s t e i
I
analysis.and corresponding
t o thecommercialclassification
a r e two d i s c r i m i n a n tf u n c t i o n s .
The Z v a l u e s( d i s c r i m i n a n tc o e f f i c i e n t s )f o r
eachofthevariablesforbothfunctions
’
Variable
H 450
of p e r l i t e s , t , h e r e
are l i s t e d below.
1.3038
=2
-1.3100
Bulk density
-1.8682
-1.1416
Vesiclecontent
-0.8232
-0..3758
Crystallite content
-0.6768
-0.4757
Eigenvalue
of
;+ita\
5 .9874
0: 7238
Vdriatiol,
%,explaLnedby
discriminant
the
89.215
10.785
roups
0,1208
.T h e s u m ' of t h e p r o d u c t s of t h e s t a n d a r d i z e d v a l u e of e a c h of t h e
characteristics and the corresponding discriminant coefficient will, giv.e
. .
the Z-value for the corresponding
Example:
axis of t h e k n o w n sample .gkoupings
z1
H 4 5 0 :( - 0 . 2 6 1 8 ) ( 1 . 3 0 3 9 )
='
Bulkdensity:(0.1045)(-1.8682)
=
Crystallite content: (-0.0856)(-06768)
=
V e s i c lceo n t e n (t :0 . 0 4 6 9 ) ( - 0 . 8 2 3 2 )
I
-0.2826.
-0.1952
= 0.0579
0,0386
J
II
I
I
S u m = -0.4585
6vl
I
I
h
B e c . a u s e Z 2 e A y a c c o u n t s f o r A I O % of t h e d i s c r i m i n a t i o n , i t i s . n o t
necessary tq calculate the
by Z
1
2
2
i
v a l u e , a s a s a m p l e will b e c l e a r l y d e f i n e d
!
alone
I
P l o t of t h e U n k n o w n S a m p l e
I
T h e v a l u e of Z1 is p l o t t e d o n t h e Z 1 a x i s
this particular sample into group
C
I
50
of F i g u r e 38 a n d p l a c e s
i
the hard or poorly expahding
._
.
perlite group.
R e g i o n of U n c e r t a i n t y i n t h e C l a s s i f i c a t i o n
(at t h e . 0 5 l e v e l
of
- 2c). .
significance
B e t w e eR
n a n g e of Z 1
to
B and C
-0,2765
0.1569 t o
A and B
0.2207
On the basis
a percentage
of t h e b o u n d a r i e s b e t w e e n g r o u p s ,
-misclassification in the present g r o u p i n g s m a y b e c a l c u l a t e d .
Boundary Between Groups
A a n d B,
(z,t z B ) / 2 , =
B and C
GB t
0.2032
Z c- 0) /. 2 =
297
(z = m e a n d i s c r i m i n a n t v a l u e f o r t h e v a r i o u s g r o u p s )
On t h e b a s i s of t h e s e v a l u e s o n l y t w o s a m p l e s o r
the samples were misclassified between groups
between groups B and A were misclassified.
6 . 2 p e r c e n t of
-
B and C while none
.
E S
"
s b W % i\F\5UrC
"
30J
~
"
.
__
Brushy Mountains.Deposit
TheBrushyMountain
p e r l i t e d e p o s i t was i n v e s t i g a t e d by Naert,
b u t i n much less d e t a i l t h a n t h e
No Agua p e r l i t e domes.The
deposit
l i e s a b o u t . 1 5 miles e a s t of t h e No Agua d e p o s i t s and 1 6 miles westof
I t i s cotinected with U.S.
the.Canyon of theRioGrande.
by a well-graded d i r t r o a d .
been operated
aboutonesquare
31).
The d e p d s i t was opened c i r c a 1965andhas
by S i l b r i c o . s i n c e t h e n .
BrushyMountain
'
Highway285
a c t u a l l y c o n s i s t s of two low h i l l s , c o n f i n e d t o
mile, which rise abovetheTaosPlateau(Figs.30and
The h i l l s and thehigherCerro
Montoso t ot h es o u t ha r eu n d e r l a i n
I
mainly by flows of theRioGrande
of b a s a l t andandesite.
Basalt, which i s , i n f a c t , a mixture
In t h e v i c i n i t y ofBrushyMountain
i s exposed i n
a n d e s i t e i s covered by Q u a t e r n a r ya l l u v i u m .P e r l i t e
t h r e ep l a c e s ;
a t each i t i s o v e r l a i n by the basaltfflows.
e x t e n s i v eo ft h et h r e ee x p o s u r e s
i s about 4000 f e e t l o n g
of t h e more s o u t h e r l y o f t h e
lowersouthwestslope
smaller exposure i s low on t h e s o u t h s l o p e
third has been uncovered
to the'north margin
thebasalt=
Themost
and forms t h e
two h i l l s .
A much
of t h e n o r t h e r n h i l l .
The
by trenching through the alluvium adjacent
of CerroMontoso.
A t eachlocality,thecontact
of t h e p e r l i t e with t h e o v e r l y i n g
b a s a l t . i s i n t r u s i v e and d i p s m o d e r a t e l y t o w a r d t h e h i l l .
A t e a c ha l s o ,
.
t h e b a s a l t i s deformedwhereas
g e n t l e ,a p p a r e n t l yi n i t i a ld i p .
pushedupward
inthesurroundingarea
Thus, t h eb a s a l ta p p e a r st oh a v eb e e n
by t h e i n t r u d i n g a c i d i c r o c k .
The b a s a l t rests upon a n i r r e g u l a r l a y e r
a soilthat
claylayer
.
i t displays a
ofbaked
formedbeforethebasaltflows.wereemplaced.
and t h e p e r l i t e body,and
c l a y ,p o s s i b l y
Between t h e
w e l l exposed i n t h e main quarry,
i s a t r a n s i t i o n zone composed of p e r l i t e f r a g m e n t s i n
a matrix of baked
'I?
1
Y3
/+
clay,thematrixgradingincolorfromdarktolightredtowardtheperlite.
&, is e v e r y w h e r e h i g h l y b r e c c i a t e d a n d c o n t a i n s r e l a t i v e l y l a r g e p r o p o r t i o n s
4, ' c r l
4''
oqf u a r t z
and f e l d s p a pr h e n o c r y s t si;nt h e s er e s p e c t sp, a r t i c u l a r l yt,h e
N o Agua d e p o s i t s .
Brushy Mountain deposits differ from the
were o r i g i n a l l y c o n f i n e d t o t h e w e s t e r n h a l f
The q u a r r y i n g o p e r a t i o n s
But i n 1976,quarrying
o ft h es i n g l el a r g ee x p o s u r e( F i g .
31):
on anexposurenearthenorthedge
of CerroMontdso.
was about 3000 f e e t long, 500 f e e t wideand
mull4
In 1975,the,quarry
was bordered on t h e e a s t by
a wall t h a t r a n g e d i n h e i g h t f r o m a b o u t 1 0 f e e t t o a b o u t
Low i n t h e q u a r r y , n e a r
about 150 f e e t i nd i a m e t e r ,
i t s southernedge,
100 f e e t .
i s a . s u b c i r c u l a re x p o s u r e ,
of p o r p h y r i t i cr h y o l i t e .
i s r e d d i s h . b r o w na n du n b r e c c i a t e d ,h a se s s e n t i a l l yt h e
composition as t h e p e r l i r e ( T a b l e
was begun
The r h y o l i t e , which
same chemical
3 ) , and appears to be
a feederpipe
f o r t h e p e r l i t e mass.
The o u t c r o p o f ' p e r l i t e a t t h e n o r t h
representtheerodedremnantof
t hs eo u thhi l l
a pa.rt of t h e p e r l i t e body exposedon'
o r i t could
represent
a separate body.
q u a r r y i n g of t h e s o u t h e r n d e p o s i t s h o u l d
e x p o s u r eo fp e r l i t ea p p e a r st o
edge of CerroMountaincould
CenJr;wUC'
t e l l which.Themorenortherly
mark a s e p a r a t e dome.
Quartzporphyry,
which underlies
two s m a l l h i l l s n o r t h e a s t
ofBrushyMountain,
essentiallythe
same chemicalcomposition
as t h e p e r l i t e ,
probably.geneticallyrelated.
also has
and t h e two are
'
B1
B2
B3
B4
B5
sio2
61.12
77.3
74.13
75.57
75.0
*'Z03
15.10
10.90
11.91
12.15
12.30
Ti02
.905
5.80
Fe203
.19
.125
.16
.13
1.50
.'7'9
.81
-80
MnO
.085
.097
.071
.061
.070
MgO
.179
.058
.152
*
10
.122
CaO
.4.96.
.44
.38
Na20
4.31
3.83
.3.35
3.68
3.70
K2°
2.92
4.48
5.03
5.01
5.0.7
Rb
PPm
Sr
48
.31
. * 49
114
155
164
142
*
*
lOPPm
<5ppm
*
H20(+1100C). .*
x
2.40
*
*
*
*
.49
x
*
H20(-llO°C)
X
'
Not determined
(Flsa. 31
E ~ U ~ L L J
I
i
Table 2 , Chemical analyses of samples of rock units
of the Brushy Mountain
perlite-bearing area. B1 is andesite from exposure on northwest
slope of Brushy Mountain;B2 is from bpdyof porphyritic rhyolite
east of Brushy Mountain . '
; B3 is perlite from main quarry.
B4 and,B5are rhyolfte from
an apparent feeder dike.
List of References
Albert, Janos, 1958, Geblxhter Perlit, seine.Herste1lung und Verwendung als
Zuschlagstoff: Silicat Technik.
v. 9, Verlag Technik, Berlin, p. 453-
457.
Amonymous news item, 1945. Chem. and Met.Eng.,
V.
52, p. 142.
Atwood, W. W., and Mather, K. F., 1932, Physiography and Quaternary geology
of the San Juan Mountains Colorado:
U.S. Geol. Survey Prof. Paper166,
176 p .
Beudant, F. S.;1922,
Butler, A:P.,
I
Voyage MineralogiqueFA Geologique' en Hongrie., Paris.
Jr., 1946, Tertiary and Quaternary geology
of the Tusas-Tres
Piedras area, New Mexico (Ph.D. thesis), Cambridge, Harvard Univeristy,
183 p. .
Butler, A. P., 1971, Tertiary volcanic stratigraphyof the eastern Tusas
Mountains,
southwest
of
the
San
Luis
Valley,
Colorado-New
.i n Mexico:
pha fleriru
Guidebook of the San Luis Basin, Colorado,
M. Geol. Soc.,An~$. Field
n
Conf. Guide b., No. 22, p. 289-300.
...-. .. ...
.
Burnham, C. W., 1979, Magma"and hydrothermal fluids; & Geochemistry of hydro"
thernial ore deposits, H.L. Barnes ed., John Wiley& Sons, New York,
p. 71-136.
Chelikowsky, J. R., 1940, Tectonicsof the rhyo1ite.h the Mammoth embayment:
.Jour. Geol., v. 48, p . 421-435.
of the west: Mining Cong. Jour.,
Chesterman, C. W., 1954, Lightweight aggregates
V.
40, p. 67-69.
Chesteman, C. W., 1957a, Volcanic 1ightwei.ght aggregates of western United
in Tom0 1 of
States, -
Volcanologia
del
20th Mexico, D.F., sec. 1, p. 205-229.
Cenozoico:
Internat.
Geol.
Cong.,
%
. .
Chesterman, C. W., 1957b, Pumice, pumicite and volcanic cinders: California
Div. Mines Bull. 176, p. 433-448.
'Esmark, J., 1799, Kurze Bescrieibung einer Mineralogischen Reise durch Ungarn,
Siebungen und das Banat: Neves Berpann, J . ,
V.
2, p. 63-70.
Fichtel, J. E. von, 1791, Mineralogische Bemerkungen von der Karbathen: Wein,.
V.
1, p. 365.
Friedman, B. P., and Rubin,J., 1967, On some invariant criteria for grouping
data:
.
Jour:
Am.
Stat. Assoc.,' v. 62, p. 1152-1178.
.
Friedman, I. I., and Smith, R L., 1958, The deuterium content
of water in
some vo+canic glasses: Geochim. et Cosmochim. Acta, v. '15,
p. 218-228.
Hamilton, J. K . , ,1966, Reportof perlite deposit investigation, northern. New
South Wales:' Courtesy of.Australian Gypsum, Ltd.,
22 p.
Jaster, M. C., 1956, Perlite resources
in the United States: U.S. Geol. Survey
Bull. 1027 H, 28 p.
Judd, J. W., 1886, On marekanite and its allies: Geol. Mag.,new ser., v. 3,
p. 241-248.
Keller, W. D., and Pickett, E. E., 1954, Hydroxyl and water from Superior,
Arizona:
Am.
Jour. Sci., v. 252;p. 87-98.
S., and Kelley, K.. K., 1948, Perlite: thermal data and
energy required for expansion: U.S. Bur. Mines Rept. Inv. 4394, 15 p.
a
Kedey, F. L., 1963, Petrographic techniques in perlite evaluation: Trans.
Am.
Inst.,Mining Metall. Petroleum Engineers,v. 226, p. 332-336.
Kozu, Shukusuke, '1929, Thermal studies
of obsidian, pitchstone and perlite from
Japan: Sci. Rept., TEhoku Imp. Univ., (Sendai, Japan), Ser.
3, v. 3,
p. 225-238.
Leineweber, J. P., 1961, The dryingof perlite:. Johns-kanville Research Dept.,
Confid, Rept. no. 412-7740, 25 p.
.
i
Leyden, Rudolf von;1936, Staukuppen und verwandte Bildungen: Zeit. Vulk., v.
16,
p. 225-247.
May,
T.
C.,
1965,
in Mineral
Perlite,
Facts
and
Problems,
U.S. Bur.
Mines
Bull.
630, p. 655-651.
Murdock, J. B., and Stein, H. A., 1950, Comparative furnace designs for the
expansion of perlite: Min. Eng., v. .187, p. 111-119.
Naert, K. A., 1974, Geology, extrusion history and analysis of characteristics
...
of perlite from No Agua, New Mexico
(Ph.D. thesis): University Park, The
Pennsylvania State University, 236
p.
Nasedkin, V.'V., 1963, Water-bearing volcanic glasses of acid composition,
their genesis and alteration: Trudy Inst. Geol. Rudnykh..Mestor., Petrog.,
Mineral.,.iGeokh.,
98,
V.
p. 39-43.
Nasedkin, V. V., and Petrov, V. P., 1962, Experimental production of perlitic
structure [in vo.lcanic glass]: Dokl.AN SSSR, v. 145.,abstract in Min.
Abst.,
V.
17, p. 375.
Putnam, W. C., 1938;The
Mono Craters California: Geog. Rev., V. 28, p. 68-82.
Ross, C. S., and Smith, R.L., 1955, Water and other volatiles
in volcanic
glasses:
Am. Mineralogist, V.
40., p. 1871-1089.
Salat, J. and Oncakora, P., 1964, Perlity, ich vyskyt, petrochemia a prakticke
pouzitie: Vydivatelstva Slovenskey Akademie Vied. Acad. Sc., Bratislava,
110 p.
Schilling, J. H., 1960, Mineral resources of Taos County, New.Mexico: New Mexico
Bur. Mines and Min. Res. Bull., v.71, 124 p.
Am.
Shepherd, E. S., 1938, The gases in rocks and some related problems:
Sci. 5th ser., v. 35-A, p. 311-351.
of the
Smith, E. I., 1973, Mono Craters, California: a new interpretation
eruptive sequence: Geol. SOC. Am., Bull.,
V.
84, p. 2685-269.0.
Jour.
Taylor, C. W., 1950,.Perlite popping from a shaky start, a new solid industry:
Chem. Eng., V. 57, p . 90-94.
Thompson, B. N., and Reed,
J. J., 1954, Perlite deposits in New Zealand, Part
1,
Geology: New Zealand Jour. Sci. and:Techn., v. 36, p. 208-226.
lAcbLT,
il,
~,I?Gb>
Pt~1f-k
JLbvtl.67
Weber, R; H., 1963, Geologic features of the Scocorro perlite deposit:&
New Mexico Geol. SOC. Guide Book, 14th Ann. Field Conference: Socorro,
p. '144-145.
New Mexico Bur. Mines and Mineral Resources,
Weber, R.
V.
H., 1955,
Processing perlite, the technologic problems: Min. Eng.,
7, p. 174-176.
Wilfey, R.D: and'Taylor, C. W., 1850, Perlite mining and processing
- a new
industry for the west: Eng. and Min. Jour., v. 151,
p. 80-83.
Williams, Howell, 1932, The history and character
of volcanic domes: Univ.
Calif. Bull. Dept. Geol. Sci.,V. 21, p. 51-146.
Wilson, E. D., and Roseveare, G.H., 1945, Arizona perlite: Ariz. State Bur.
Mines Circ. no. 12, 10 p.
Wright;L.
A;,
Chesterman, C. W., and Norman,L. A . , 1954, Occurrence and use of
non-metallic commosities in southern California; Geology of Southern
California, R. H. Jahns, editor, California Div. Mines Bull. 170, ch.
VIII, p. 59-74.
of certain.
Yavits, I. N., 1962, Investigation of the viscosity and fusibility
water-bearing volcanic glasses: Sborn. Trudov 'ROSNIIMS'.1962, no. 25, P.
54-62, translated in Geochem. Intern.,1964, no. 2, p. 331-335.
CAPTIONS FOR ILLUSTRATIONS
NO AGUA PEAKS
/
Geologic map and fence diagram of perlite deposits of the No Agua
Mountains, Taos County, New Mexico.
Figure
$I:
Perlite-bearing localitiesin the United States, modified from
A
Jaster (1957),
w
&ported
Figure 2.
1975.
in U. S . Bur. Mines Minerals Yearbook,
Graph’ showing data
o n production of perlite in the United States,
1946-1975,
Figure 3 .
showing locationof quarries activein 1974 as
from U.S. Bur.
Mines
Minerals
Yearbook.
7
Map of No Agua Peaks showing principal topographic features and
I
property boundaries.
Figure 4 .
Diagram showing history of ownership of the three perlite properties
of the No Agua Peaks.
Figure 5.
View, looking southeastward,of No Agua Peaks, showing facilities
.
.
of the Johns-Manville Products Company (right-center), North and
East Hills (left), and West Hill (far right).
Figure 6 .
View of Low Hill area, looking southwestward from West Hill, showing
main quarry of General Refractories Company (Grefco).
Figure 7.
Generalized geologic map of the region of the No Agua. Modified
from Butler (1977).
Figure 8.
Exposure alongU.S. Highway 285, and about 2 miles northwest of No
Agua Peaks, showing contact between basalt of Hinsdale Formation and
an underlying conglomerate probably of the rhyolite member
of the
Los Pinos Formation (Butler,1971).
of perlite
Figure 9.
The conglomerate contains clasts
apparently erodedfromdomes of the No Agua Mountains.
9.
Detail of conglomerate in exposure from Figure
Figure 10. Logs of diamond drill hole R.D.H.-2, about
400 feet north-northeast
of mill ofJohns-Manville Company (Plate1).
t
'
Figure 1%
Sketch of a radially fissured dome (after Leyden, 1936)
'C = crust, P= primary dome rock,
Rf = filling of radial
fissures, R s = unfilled radial.fissure, Cs = central
summit depression between the hills.
Figure 11B.
Sketch of an extrusion dome (after Leyden,1936).
Cc = collapse crater, Sp= structural pattern,C = crust,
T = talus. . .
..
.
....
. ._"
_.
I
~
~
~
Figure 12. Map showing distribution of rotk bodies and general structural
features of the rhyolitic domes of No
theAgua Peaks.
Figure 13. Photomicrograph of tuff-perlite breccia, showing fragments of
perlite (light) in a microcrystalline matrix. Length of field
mm.
is 2
Figure 14. Photomicrograph of ves,icular perlite from middle perlite unit
vesicles. Length of field is 1.3'mm.
Figure 15. Cliff-forming upper glassy rhyolite unit overlying the middle
U.S. perlite (Silbrico) quarry of Plate
1.
perlite unit near the
Figure 16. Exposure of upper glassy rhyolite showing irregularities in
flow
banding.
Figure 17. Photomicrograph of glassy rhyolite of upper' glassy rhyolite unit
showing bands of microcrystalline and cryptocrystalline material
-(light) in glass (dark); biotite phenocryst lower left. Length
of field is 0.7 mm.
,
Figure 18. Photomicrograph of glassy rhyolite of upper glassy rhyolite unit
showing phenocrysts of plagioclase (light) .in a ground mass of
glass (dark) and microcrystalline and cryptocrystalline material;
(light); crossed nicols. Length of field is 2
mm.
Figure 19. Photomicrograph of glassy rhyolite of upper glassy rhyolite unit
in a ground mass of
glass-and
showing phenocrysts of plagioclase
,microcrystalline material; partly crossed nicols. Length
of'
field is 2 mm.
.
'
Figure 20:Photomicrography of glassy rhyolite of upper glassy rhyolite unit
showing glass-rich layers (light) alternating with layers rich
*
in microcrystalline and cryptocrystalline matieral. Glass displays
onionskin texture. Length of fieid is 2 mm.
'Figure 2 1 . Photomicrograph of glass (light)in upper part of upper glassy rhyolite
unit with typical onionskin texture. Length of field0.4ismm.
Figure 2 2 . Exposure of upper part of upper glassy rhyolite unit of Hill
North
containing nodular remnants black obsidian (marenkanites). The
larger light, lenticular masses consist of pumiceous material.
Figure 23. Photomicrograph of perlite from upper perlite unit showing irregular
distributed cryptocrystalline material (light)in the glassy ground
mgss. Length of field is 2
mm.
Figure 2 4 . Exposure of upper perlite unit
on top of the West Hill; Perlite
displays horizontal.flow banding.
Figure 25. Photomicrograph of glassy facies of lithic rhyolite unit which is
composed mostly of layers of cryptocrystalline material (dark)
which alternate with glass-rich layers (light). Length of field
is 2
mm.
Figure 26. Exposure of rhyolitic
rock interpretable as eroded remnant of
extrusion spine.
Figure 2 7 . Graph showing partitioningof samples of rhyolitic material from
deposits of No Agua Peaks. Partitioning is determined by,a cluster
(62
analysis based on chemical analysis ofa representative suite(62
samples) of rocks from theNo Agua.Peaks. The C1 and C2 represent
the first two factors in the statistical analysis.
1
Figure 28. H y p o t h e t i c a l c r o s s s e c t i o n s ' s h o w i n g f o u r i n t e r p r e t a t i o n s
ofth.e
r h y o l i t i c ' f l o w s of t h e No Agua Peaks and involving the four major
u n i t s exposedthere.
LGR = l o w e r g l a s s y r h y o l i t e u n i t ;
p e r l i t e unit;.UGR = u p p e r g l a s s y r h y o l i t e u n i t ;
u n i t .S o l i dl i n e s
u n i tb o u n d a r i e s .
MP = . m i d d l e
UP = u p p e r p e r l i t e
dash lines a r ec o o l i n g
are flowboundaries;
the same a r e a l d i s t r i b u t i o n
A l l sectionsimply
A was drawn without
of perli.te and glassy rhyolite, but cross section
r e f e r ' e n c et oa t t i t u d e so ff l o wb a n d i n g .O t h e rc r o s ss e c t i o n s . s h o w
g e n e r a l i z e d p a t t e r n offlowbandingrepresented
. P l a t e 1.
by a t t i t u d e s of
are e v a l u a t e di nt e x t .
C r o s ss e c t i o n s
F i g u r e 29. I d e a l i z e d s k e t c h o f t y p i c a l r h y o l i t e
dome of t h e No Agua Peaks,
based on model D of F i g u r e 11 andshowing
the five principal
u n i t s and t h e i r g e o l o g i c s e t t i n g : ( a ) c r y s t a l l i n e r o c k s
Precambrianbasement;(b)cover
of T e r t i a r ys e d i m e n t a r yr o c k s
of p e r l i t e ; (d)'flow
includingbasaltflow(c)initialflow
g l a s s yr h y o l i t e ;( e )
r h y o l i t e ,i n t r u s i v e
of the
l a t e r f l o wo fp e r l i t e ;( f )
of
body of l i t h i c
a n dp r o b a b l ya l s oe x t r u s i v e .D o t t e dl i n e
shows approximate location
of present topographic surface.
Diameter of dome i s 2000 t o 3000 f e e t .
F i g u r e 30. P l o t o f t h e
pdtd
7
No Agua s a m p l e s p a r t i t i o n e d i n t h r e e g r o u p s d e s i g n a t e d
1
by circles, s q u a r e s and t r i a n g l e s . , The p a r t i t i o n i n g i s based on
a cluster analysis of a-matrix based
0
a t 450 C , t h e c r y s t a l l i n e and v e s i c l e .
amountof
volatiles released
content.
P representstheplotforan
i n t h e accompanying t e x t .
on v a l u e s f o r b u l k d e n s i t y ,
unknown sample as c a l c u l a t e d
The axes z1 and z2 r e p r e s e n t t h e f i r s t
two f a c t o r s from t h e s t a t i s t i c a l a n a l y s i s .
F i g u r e 31. Geologicsketch-mapofBrushyMountainareashowingdeposits
of t h e S i l b r i c o Company.
F i g u r e 32. V i e w looking northward of BrushyMountainand
perlite quarry of
..
S i l b r i c o Company, s h o w i n gc r u s h i n gp l a n t( e x t r e m el e f t ) .
Basalt-andesite flow caps perlite
on upper slopes
Impure p e r l i t e u n d e r l i e s l o w e r s l o p e s
F i g u r e 33:Photomicrograph
ofmountain.
t o rightofquarry.
of p e r l i t e from Brushy Mountain deposit showing
phenocrysts of p l a g i o c l a s e i n a groundmass
of g l a s s and m i c r o c r y s t a l l i n em a t e r i a l .L e n g t h
composed of l a y e r s
of f i e l d is 1.6
mm.
0
0
a
O
0
w
0
*
0
0
o
VI
0
0
0)
0
-J
0
Operations
Production in tons x 103
0
0
nY
Number of Producersand
Antonito
25 miles
i
Co:o.
2000 ft
c"-l
\
L
Property I
P r o p e r t y I1
P r o p e r t y I11
l n o,oerafion since
about 1950
ln operation since
about 1 9 5 0
Operated b r i e f l y
1965
Located 1948
Great Lakes
L o c a t e d1 9 4 8
UnitedMines
of Taos
Merged
Sold 1959
L o c a t e d1 9 4 8
Sold 7950
I F. E. Schundler Col
I
Merged 1959
Company
U.S. Perlite
Company
I
Johns-Manville
Sales Corp
Merged 1963
Susquehanna
Company
Merged
I
I Silbrico
Corp.
I
I
EXPLANATION
Alluvium
(TS),
ServilletoFormation
flows of medium to coarse grained
basalt enclosing interbeds of
sand and grovel.
HinsdaleFormation
(Th)
mainly flows of basalt. ,
,
Hypersthene-bearing quartz-lotite (Tq),
flows form same volcanic domes
'
relotton to Hlnsdale Formatton unclear.
i
i!
Los Pinos Formation
,
Rhyolite member (Tlr)
tuffaceous
sandstone. conglomerate of rhyolite
fragments.
Rhyolite of No Aqua Mountains (Tim),
bodies of commercial perlite
associated withflows of lossy rhyolite
ond intrusive l i t h i c rhyoiiqe.
Jarito Bosolt member of Barker (Tij),
flows of basalt.
I
Coarsely porphyriticquartz-latite
member (Tic), tuffoceous sondstpne,
tuff and conglomerate ofporphyritic
quar'tz-ratite.
i
Precambrian ignequs and mefamorphlorocks
1
"
"
1
"
Geologiccontact,
approximate
I
dashed where
lillivoits
0
a”i
5
;
’
’
1
Geologiclog
200 A P I units
111111111I
Spontaneous
Gamma-ray
Potential
.
..
c
c
7
r 27
-
-
r
1.64 1.09 -
c 2 0.55 0.0 0.54 -0.54
-1
0.0
0.55 1.64 1.09
C'l
2.19
~~
~
-
I
I
..........
-0
."
7
e7
A.
-
.........-1....lZ7-, ....... =.......
-
*..
"7
F1
-3
-UP
UGR
MP
"
-0.
.
? *
..
-.e
..*-.......................
.;:TIL
*.............
-1I I
A
i
Genera Iized D'rof ile
1'B.
of present topography
"y
UP
I
1
. . . .,
,
UGR
I
! :
.
1
I
. ;
.
i
UP
..
."................
,
UGR
IMP
"
"
.
' I
c
0
0
0
0
0
*_.
LOO
0
0
a
"
"
"
"
"
"
. .
0
0,
Y
0 0
0 0
00 O U R
0
0
..
o
.
0
..
.
.
. .
F.
EXPLANATION
0
Quaternary
alluvlum-colluvium
Basalt and
andesite-basalt
A
L
A
-
Perlite
breccia
0
Porphyritic
rhyolite
0
I000
ZOO0
500
3000 feet
.IOOO meters