bY
Gieter h t o n Krewedl.
1974
STATEYEIT EY AUTHOR
T h i s d i s s e r t a t i o n has been submitted i n p a r t i a l f u l f i l l m e n t of
r e q u i r e a e n t s f o r an advanced degree a t The University of Arizona and
i s deposited i n the University Library t o be made a v a i l a b l e t o borrowers under rules of the Library,
Erief quotations from t h i s d i s s e r t a t i o n are allowable without
of source
special permission, provided that accurate acknowledgnent
i s made. Requests f o r permission f o r extended quotation from or
reproduction of t h i s manuscript i n whole o r i n p a r t may be granted by
the copyright holder.
COPYRIGETED
BY
.. ..
DIETER ANTOX KRF??ZDL
1974.
iii
The author became i n t e r e s t e d i n the c e n t r a l KagdalenaI.!ountains
whil e doing geologic
mapping f o r Exxon Corp. i n the Nagdalena mining
d i s t r i c t as a f i e l d a s s i s t a n t t o C h a r l e s
F. Park, Jr.
Gratefulappre-
c i a t i o n i s extended t o D r . Park f o r h i s i n i t i a l ' e n c o u r a g e m e n t t o undert a k e t h i s p r o j e c t and
t o Exxon f o r i t s financial support
andpermission
to publish this dissertation.
I acknowledge with thanks the support
of b5.nes.
I am especially indebted to Charles
. Mexico Zrureau ofMines
w i t h whom the author
of t h e New Nexico Bureau
E. Chapin of the
New
had many informative dis-
cussions,
The author extends foremost appreciation to
Dr. Spencer R.
Titley f o r h i s guidance and assistance throughout the dissertation.
His h e l p f u l a d v i c e a n d c o n s t r u c t i v e c r i t i c i s m s ' a r e g r a t e f u l l y
edged,
acknowl-
I am i n d e b t e d t o Drs. George E. Davis and Richard F. Wilson
for their critical reading
of themanuscript.Daniel
a s s i s t e d i n t h e photographyand
The constant support
f i n a l p r e p a r a t i o n of the manuscript.
andencouragementfrom
assured the successful completion
Lynch generously
my wife, Eeth,
of t h e d i s s e r t a t i o n .
iv
TABLE OF
CONTELTS
Page
.....................
............................
..........................
.... .. .. ....... .. ....... .. .. .... . .
.
.
.
. . . ....... .. .. .. .. ......... .. .. .. .. .... . .
........................
GEOLCGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LIST OF ILLUSTMTIORS
vii
AFSTRACT
ix
IETRODUCTION
1
Location and A c c e s s i b i l i t y
Topography
and
Grainage
Purpose
and
Scope
Hethod o f I n v e s t i g a t i o n
PreviousFork
Precambrian Rocks
......................
.....
. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ....................
.......................
. .. .. .. .. .. ............. .. .. ..
.
...................
.......................
. .. .. .. .. .. .. .. .. .. .. .. .. .. .........
. . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
...........................
. . . . . . . . .. ... ...................... ... ... ... .. .. ..
. . . ..... .. .. ....... .. .. ....... .. .. . . .
XLGIOKAL
.......................
.......................
Breillite
Granite
Paleozoic Rocks
I<ississippian
Kelly
Limestone
Pennsylvanian
Kagdalena
Group
Permian Ab0 Fornation
CenozoicRocks
Tertiary Volcanic Rocks
T e r t i aIrnyt r u s i v e
Rocks
Tertiary
Sedimentary
Rocks
GuaternarySediments
STRUCTUE
Precambrian and Paleozoic
Structure
Laramide S t r u c t u r e
LarlytoKiddleOligoceneFaults
Late
Oligocene
Faults
Late
Cenozoic
Block
Faults
ALTLXATIOK
Propylitization
2
2
6
7
0
11
13
13
15
16
16
19
25
25
25
53
71
75
78
78
80
. 80
82
84
88
e9
*
vi
TAELE OF COMTEMTS.
Continued
Page
.. ..........................
.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
........................
Silicification
Lime-Silicate
Argillization
Sericitieation
.......................
XineralCccurrence . . . . . . . . . . . . . . . . . . . . .
Controls of bIineralization . . . . . . . . . . . . . . . . .
EISTCRY . . . . . . . . . . . . . . . . . . . . . . .
Precambrian
IliddleCenozoic . . . . . . . . . . . . . . .
Late Cenozoic . . . . . . . . . . . . . . . . . . . . . . . .
LATE CE:MOZOIC TECTONIC SETTING . . . . . . . . . . . . . . . . . .
ColoradoPlateau ......................
Yasin and Kange Frovince . . . . . . . . . . . . . . . . . . . .
kCONOKIC GF.OLGSY
GEOLOGIC
to
..
.
.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
.........................
......................
Historical Sketch
Rio Grande Graben
Co~cLusIoMs.
LIST OF WFEP>JXES
..
90
92
93
93
95
95
100
106
106
111
116
116
117
119
120
123
125
.
*
LIST OF ILLUS?”RATIT%OI,!S
Page
Figure
1. Index map showing t h e l o c a t i o n of t h e c e n t r a l Xagdalena
Kountains,SocorroCounty,
Kew Kexico
.........
.............
.................
........
of
..........
.
........
ERTS photograph of west-central New Nexicoshowing
inentphysiographicfeatures.
2.
3
prom-
3.
Landmarks and drainage systems of t h e central and northe r n XagdalenaMountains
4.
Geologic map and cross s e c t i o n s of t h e c e n t r a l K a i d a l e n a
mountains....^........^..
4
5
i n pocket
5.
he-Cenozoic stratigraphy
t h e c e n t r a l Kagdalena Hount a i n s . . . , . . . . . . . . . . .
12
6.
Precambrian a r g i l l i t e (1%) contact with Kissi s s i p p i a n
Kelly Limestone (M) l o c a t e d east of North Baldy Peak.
17
7.
8.
9
.’
10.
11.
12.
-
13
West-dipping Pennsylvanian Sandia Formation
I.:adera LiRestone, (M)i n NorthFork Canyon
( S ) and
23
Cenozoic stratigraphy of t h e c e n t r a l Kagdalena Mount a i n s . . . . . . . . . . . . . . . . . . . . . . . . .
27
C o r r e l a t i o n c h a r t of equivalent Tertiary volcanic and
sedinentary units in the southern Eear Kountains and the
i<agc!alena i?ountains
29
Lower Spears Formation containing c l a s t s of Abo Format i o n (A), Paleozoiclimestone (L) and porphyritic
andesite(FA)...
32
..................
..................
Photomicrograph
a porphyritic andesite from the
dleSpearsFormation.
. . . . . . . . . . . . . . . mid...
Fhotonicrograph of a l a t i t e from the upper Spears Formation.. . . . . . . . . . . . . . . . . . . . . . . . .
of
Photomicrograph o f a q u a r t z l a t i t e from t h e IIells Kesa
Formation.......................
.......................
9
36
41
14. Photomicrograph 3f an andesite f r o n the Sixmile Canyon
andesite.
vii
45
viii
LIST OF ILLUSTRI1?'IOMS--Continued
Figure
.......................
....................
.....
Photomicrograph of
formation
a r h y o l i t e from t h e Sawmill Canyon
Photomicrographofan
Peakandesite,
a n d e s i t e from the South Ealdy
Photomicrographof a r h y o l i t e from t h e Timber Peak
r h y o l i t e . . . . . . . . . . . . . . . . . . .
Photomicrogra2hof a mafic dike of andesite
comp o s i t i o n . . . . . . . . . . . . . . . . . . . . . . . .
Photomicrographof
n i t i c composition
.a .latite-monzonite
. . . . . . . .dike. .of. . monzo.....
..................
.........
.............
Highly flow-banded.white rhyolite dike exposed
21,T.3S+,R.3b!.
i n sec.
Photomicrographofwhiterhyolitedike.
K e l l i n d u r a t e d and conglomeratic Popotosa Formation
exposed a t Kater Canyon Fesa.
58
61
64
65
74
%
24.
25.
Generalized geologic map of t h e c e n t r a l Magdalena
I4ountains showing f o l d s and f a u l t s developed during
variousperiods
.n pocket
A l t e r a t i o n and m i n e r a l i z a t i o n i n t h e c e n t r a l Plagdal e n a Mountains.
.n pocket
....................
....................
West-central Mew Hexico during Middle to Late Xiocene
time showing t h e d i s t r i b u t i o n o f volcanic rocks and
f a c i e s of t h e Popotosa Formation according t o Eruning
(1973).
26.
........................
The majorLateCenozoic
s t r u c t u r a l t r e n d s which i n fluenced the formation of the Holocene physiography of
west-central Xew Kexico
114
Major physiographic features within the Colorado Plat e a u and t h e Kio Grande graben of west-central
Kew
biexico.
118
................
27
112
........................
AESTRACT
The Fagdalena Fountains of
west-central Kew Yexico are a
north-trending block-faulted mountain range situated within the Rio
Grande grabenoftheRasin
and Range physiographicprovince.Mapphg
i n t h e c e n t r a l Kagdalena l.!ountains was undert,aken t o determine the
geology and tectonic history
of the range.
The o l d e s t s t r a t a exposed i n t h e c e n t r a l MagdalenaNountains
are Precambrian argillite and granite,
which are unconformably o v e r l a i n
strata were deposited
by upperPaleozoicsedimentaryrocks.Eesozoic
but,weresubsequentlyeroded.UpliftduringtheLaramideorogeny
..
,
was
.
followed by extensive erosion and 1evelir.g during the Eocene
Volcanismbegandu-ring
the Oligocene 1:;poch w i t h t h e deposition of
volcanoclastic sediments, lava flows, and ash flows of the
0
I4ovement along a E. 80 \.!.-trending,
steeply dipping
D a t i l Group.
f a u l t zone i n Early
Oligocene time r e s u l t e d i n u p l i f t of t h e northern portion
dal.enaNountainsandcaused
t h e strata.
Epoch.
2.5 miles of strike
Theemplacementof
positsfollowedtheformation
of t h e Mag-
s l i p displacement of
ash f l o w s e p a r a t e d b y c a l d e r a
of t h e
h'. 80'
f i l l de-
W.-trending f a u l t zone.
The
source areas f o r t h e E e l l s Mesa Formation ash flow and possibly the
Sawmill Canyon formation ash flow
area.
are at the southern
The Timber Peak rhyoliteashflow
limit of t h e study
i s t h e youngestvolcanicunit
and i t s source area lies in the northern San Kateo Mountains, southwest
o f t h e Nagdalena Kountains.
ix
X
Following the
emplacement of t h e l i a t i l Group, the Eagdalena
a r e a was f a u l t e d and t i l t e d a l o n g a north-northwest-trending zone
which
l o c a l i z e d t h e emplacement o f d i k e s and stocks dated a t 28 t o 30.5 m.y.
The LateOligocene
Eorth-northwest-trending s t r u c t u r e s a l s o s e r v e d
the conduit for the hydrothema1 solutions
placementdepositsadjacenttothefault
as
which formed l i n e s t o n e Yezones.
The a n c e s t r a l !.!agdaien.a
Mountains were a topographic h i g h during the Miocene Spoch,andsuppli3d
detritustotheadjacentlowlands.
a r e a was nearly corcpletely buried
Ey Late Miocene t i m e t h e Kagdalena
by i t s own debris. Elock faulting
began during Late Hiocene time and resulted
r e l i e f between the Fagdalena Eiountains
Zinc-lead mineralization
i n 5000 f e e t o f s t r u c t u r a l
and t h e surrounding basins.
i n the basal E!ississippian limestone
..
.
g e n e t i c a l l y and s p a t i a l l y r e l a t e d t o t h e O l i g o c e n e s t o c k s .
somatic replacement and mineralizatj.on
Peak'mines along Late
taldy
Oligocene,,north-northwest-trending s t r u c t u r e s
t h e area.
a l i z a t i o n and a l t e r a t i o n p r o g r e s s i v e l y d e c r e a s e t o
Peak a r e a .
a buried stock underlying
where s i l l s , d i k e s , and plugsarevery
z a t i o n e i t h e r i n the stocks,
t h e south of the
exposed s t a c k s s u g g e s t s t h e
a portion of K o r t h Fork Canyon
common.
The p o t e n t i a l m i n e r a l i -
o r i n the wall rock surrounding
makes t h e Linchburg-l,!orth Ealdy Peak andKorth
able for buried ore deposits.
Bothminer-
The s p a t i a l a s s o c i a t i o n of dike rocks,
particularlythe white rhyolite dikes, to
presence of
is
Fyrometa-
i n the Linchburg and North
may b e r e l a t e d t o a known buried stock underlying
Linchburg-biorthBaldy
'
t h c stocks,
Fork Canyon areas favor-
e
INTRODUCTION
Although t h e geology of t h e Magdalena mining district is generand Koschmann, 1942). l i t t l e i s known
ally well understood (Loughlin
about the geology
thenselves.
and tectonic developnent
of t h e Nagdalena 3 o u n t a i n s
The lack of geologicinformationregardingthemountain
mass i n t o which t h e o r e d e p o s i t s
unsolved.Theseinclude
have been emplaced leaves many problems
1) d e f i n i t i o n of thePaleozoicstratigraphy,
2) s t u d y i n g t h e T e r t i a r y D a t i l v o l c a n i c s
for t h e ashflows,
and locating the source
areas
3) determining guidelines for mineral exploration
and evaluating the mineral potential
of the area' south
of t h e Magdalena
mining district, including the location of possible base-metal-associated
stocks, and 4 ) i n t e r p r e t i n g t h e t e c t o n i c h i s t o r y
of t h e Magdalena
Xountains and e s t a b l i s h i n g t h e i r r e l a t i o n s h i p t o t h e R i o
and the Basin and
Range physiographic province.
Stratigraphy, structure,
and magmatic i n t r u s i o n i n t h e c e n t r a l
3agdalena Xountains were studied to determine
t e c t o n i c developmentof
therange.
of the s t r a t i g r a p h i c sequencefrom
results of which havebeen
t h e geologic history and
The central area provides exposures
t h e Precambrian t o t h e Holocene,
t e n s i o n s of s t r u c t u r e from t h e Nagdalenamining
ied, the
Grcande graben
Ex-
d i s t r i c t have been stud-
utilized to outline the geologic
h i s t o r y of t h e XagdalenaXountains.
KLthough less concentrated than
t h a t of the Gagdalena mining d i s t r i c t a t t h e p r e s e n t s u r f a c e , t h e m i n e r alization in the central part
of t h e mountains r e v e a l s manyof
c o n t r o l s and a l t e r a t i o n .
1
t h e same
2
Location and A c c e s s i b i l i t x
The >!agdalena I4ountains a r e l o c a t e d i n S o c o r r o County, New
Mexico, approximately 17 milesvestofSocorro(Fig.
ied i s the central portion of the
north-south from
%
1). The a r e a s t u d -
Nagdalena 1,:ountains extending 6 miles,
of North Baldy Peak' t o approximately 1%
mile north
miles south of SouthBaldy Peak and 5 miles east-west, thus covering
3). The centralllagdalenaMountains are a l s o
square miles (Figs. 2 and
r e f e r r e d t o a s t h e I < a t e r Canyon a r e a a f t e r t h e
drainagethattransectsthearea.
Themapped
southeastern corner of t h e Hagdalena mining
calledtheKelly
30
mining d i s t r i c t .
15-minute topographic quadrangle,
major northeast-trending
area slightly overlaps the
d i s t r i c t , which is a l s o
The a r e a l i e s w i t h i n t h e
and t h e MolinoPeak
Magdalena
and South Ealdy
,
7&ninute
topographic quadrangles.
Access t o t h e a r e a
Highway 60 (Fig. 3).
i s by t h e Water Canyon road turnoff
S t a r t i n g a t t h e campgrounds i n !:Tater Canyon, t h e
road is unpaved and climbs approximately
NagdalenaI4ountains
from U.S.
9 miles to the crest of
the
on which i s s i t u a t e d Langmuir Laboratory.Jeep
trails o f f e r a c c e s s u p
Copper Canyons.
NorthForkand
NorthBaldyPeak
is a l s o a c c e s s i b l e by four-wheel drive vehicles along the crest road,
which s t a r t s a t t h e abandonedmining
town of Kelly.
'
Topographx and Drainage
Physiography of t h e c e n t r a l Magdalena Mountains is c h a r a c t e r i z e d
by steepslopes
and p r e c i p i t o u s r e l i e f .
trendingcrestalridgetransectsthearea.
f e e t , and South BaldyPeak,
h narrow,6-mile-longnorthNorthBaldyPeak,
a t 9858
t h e highest peak i n t h e Eagdalena Flountains,
a t 10,783 f e e t , a r e l o c a t e d a l o n g
t h i s crestalridge.Steep
slopes of
3
108'
106'
1
1
. .
104O
,
i
. .
36O
36'
OF ERTS PHOTOGRAPH
340
e'Roswell
...
Q,
32'
Carlsbad
I
I
I
32'
104O
106O
Dotil-Mogollon Volcanic
Province
0
.
50
(
I
t
Miles
..
Figure 1. Index map showing t h e location'ofthecentral14agdalena
Kountains,SocorroCounty,
I;ew Xexico.
5
<
-ri
Ti
?
...
-T
1
-
Figure
3 . Landmarks and drainage systems of t h e c e n t r a l andnorthern
Eiagdalena Kountains.
i
almost 2000 f e e t p e r m i h e x t e n d t o t h e . w e s t o f t h i s c r e s t a l r i d g e ,
whereas gentler slopes
east.
of less than 1000 feet per mile extend
t o the
t h e region mapped, 6458 f e e t , i s i n t h e
The l o w e s t e l e v a t i o n i n
northeast corner of t h e a r e a a t t h e mouth of Water Canyon.
The areastudiedcontains
Canyon i s the major drainage
Canyonand
numerous steep-sidedcanyons.Water
North Fork Canyon, Copper
in the area, with
Ealdy Canyon s e r v i n g a s i t s t r i b u t a r i e s ( F i g .
major drainages include South
3).
Other
Canyon, Sixmile Canyon, Ryan H i l l Canyon,
Sawmill Canyon, M
i
l
l Canyon, Hop Canyon and Patterson Canyon.
manent streams exist
i n the area.
No per-
Runoff i s mainly during t h e r a i n y
months of July, AugustandSeptember.
. Purpose -.
and Scope
A detailed study
of t h e c e n t r a l Magdalena Mountains w a s under-
taken for the following reasons:
The s t r a t i g r a p h i c s e c t i o n p r e s e n t i n
t h e ItagdalenaPIountains
well exposed i n t h e c e n t r a l p o r t i o n of therange.
and structural relationships are
area than in the Fagdalena
is
As t h e s t r a t i g r a p h i c
more c l e a r l y d i s c e r n a b l e i n t h e c e n t r a l
mining d i s t r i c t , a n a c c u r a t e i n t e r p r e t a t i o n
of t h e s t r a t i g r a p h i c and s t r u c t u r a l g e o l o w of the range can
A study of t h e Datil Groupexposed
in the study area
be made.
would aid i n t h e
understanding of the volcano-tectonic history of the Datil4iogollon volcanic field.
The Xagdalenamining
district, located
of t h e range, was a majorproducer
b i l i t y of buried stocks
i n the northwest portion
of lead,zinc,andcopper.
i n the southern portion
The possi-
of t h e d i s t r i c t as
7
postulated byLoughlinand
Koschmann (1942) and Titley (1958), and
southward extension of the
main ore zone can be assessed
the
from t h e
r e s u l t s of work i n t h e c e n t r a l Magdalena Mountains.
The Magdalena itountains are located near the juncture
Colorado Plateau Frovince, the Easin
Grandegraben.
of t h e
and Range Province, and the
Rio
The a d d i t i o n of f i e l d d a t a from t h e c e n t r a l Magdalena
Nountains would a l l o w t h e i n t e r p r e t a t i o n
of s t r a t i g r a p h i c , s t r u c t u r a l ,
and temporal relationships between these provinces,
and assist i n t h e
placement of the range into a particular physiographic province.
of 1nvesti.ration
Nethod -
Eleven monthsof
o f 1970,
f i e l d work during the spring and
summer months
1971, and 1972 were spent i n t h e Kagdalenabiountains.
Recon-
naissance mapping was done i n t h e northern and southern Hagdalena
Nountains, detailed
range.
mapping was confined t o t h e c e n t r a l p o r t i o n
The geologic map of thepresentstudyoverlaps
eastern corn-?r of t h e Xagdalena mining
data,
into the central portion
3 ) . Aerialphotographs,enlarged
imately 500 f e e t t o t h e i n c h ,
The r e s u l t s havebeen
wereused
t o a s c a l e of approx-
t r a n s f e r r e d t o a 1" = 2,000' composite
t h e 1-lolino Peak and SouthEaldy
e
of
as a base f o r p l o t t i n g t h e f i e l d
map consisting of portions of the Pagdalena
pocket)
w i t h t h e south-
d i s t r i c t , a s mapped by Loughlin
and Koschmann (1942)andextendssouthward
therange(Fig.
of the
15-minute quadrangle, and
Peak '&minute
quadrangles (Fig.
4, i n
e
8
Previous __
work
The e a r l y l i t e r a t u r e d e s c r i b i n g t h e
Hagdalena Flountains was
i n t h e Ragdalena mining d i s -
primarily concerned with the mineralization
t r i c t and d e a l t l i t t l e w i t h t h e geology o r tectonic development of the
range.Earlyworkers
such as Jones(1904)
and Gordon, l9lO), provided
andGordon
a brief account
(Lindgren,Graton,
of t h e g e n e r a l g e o l o g y ' o f
.
the
-
Ilagdalena mining d i s t r i c t and noted the occurrences and characteristics
p. 258) r e f e r r e d t o
of oredeposits,Lindgren,andothers,(1910,
Plagdalena Range a s t h e S i l v e r Mountain o r
the central portion of the
t h e Water Canyon d i s t r i c t and discussed the.mining activity
i n the area.
Wells (191.8, p. 69-75), i n h i s d e s c r i p t i o n of t h e manganese dep o s i t s i n t h e Tilater Canyon d i s t r i c t , d e s c r i b e d t h e g e o l o g y o f
.
t r a l KagdalenaXour.tains.
'
Lasky's(1932,
t h e cen-
. ,.
p. 33-91) study of
t h e mineral
d e p o s i t s i n t h e Hagdalena mining d i s t r i c t a l s o i n c l u d e d a general discussion.of the geology
of b.!ater Canyon and Hop Canyon.
I n both reports
only a c u r s o r y d e s c r i p t i o n of t h e s t r a t i g r a p h y alid structure was given.
Loughlin and Koschmann's (1942) description
of t h e geology and
o r e d e p o s i t s o f the iiagdalena mining d i s t r i c t i s one of the major contributions to the
the range to
geologyofthe
be within
KagdalenaI4ountains.TheyConsidered
a southeast. extensior.
physiographicprovince.Loughlin
of the Easin and
Range
and Koschmann (1942) a d m i t t e d t h i s
placement was based on meager data covering a small portion of t h e
Kagdalena Fountains and considered any conclusions tentative until
a
much larger area has been investigated.
Two a d d i t i o n a l s t u d i e s
been made.
of the central Fagdalena Eountains
have
A poption of t h e 1Vater.Canyon area was s t u d i e d by Kalish
.
!
!
~
9
(1953); and t h e geology around Langmuir Labpratory was described by
Stacy(1968).Eecause
of e r r o r s i n d e s c r i b i n g t h e v o l c a n i c s t r a t i g r a p h y .
in their respective arcas;they did not contribute to
of the regional volcanic stratigraphy or tectonic
t h e understanding
..
development of t h e
range.
Brown (1972) presented data
on the volcanic stratigraphy
t e c t o n i c s of the southern Bear llountains, located north
Kagdalenas(Fig.
scribed byTonking
2).
He redefined andexpanded
(1957).
and
of t h e
t h e Datil Group a s de-
Brown (1972)suggested
t h a t thesouthern
Eear Mountains a r e a Hasin and Range feature developed as a response t o
t h e opening of the Rio Grande rift.
A study of the San Nateo Kountains southwest
..
Nountains by Deal
of t h e Magdalena
and Rhodes ( i n p r e s s ) will a i d i n t h e c o r r e l a t i o n
similar v o l c a n i c u n i t s between t h e two ranges.
The San MateoMountains
i n composi-
c o n s i s t e s s e n t i a l l y of mid-Tertiary volcanic rocks, ranging
t i o n from a n d e s i t e t o r h y o l i t e .
I n t h e I 4 t . Ffithingtonarea
northern SanMateo Kountains, Deal and
dron 30-40
of
of t h e
Rhodes ( i n p r e s s ) d e s c r i b e
km. i n diameter which they consider to be the source
a c:tularea f o r
t h e A . L. Peak Formation and the Potato Canyon Formation.Theseformat i o n s a r e l i t h o l o g i c a l l y and s t r a t i g r a p h i c a l l y s i m i l a r t o
i n t h e Magdalena 14ountains.lieal
and Rhodes ( i n p r e s s ) d e s c r i b e t h e S a n
Mateo Kountains a s an eastward dipping block
post-volcanic tectonism related to the opening
A compilation report
u n i t s present
which was t i l t e d d u r i n g
of the Rio Grande rift,
on t h e f i e l d work c u r r e n t l y i n p r o g r e s s i n
t h e Magdalena-Tres Kontosaarea(Chapin,
and o t h e r s , i n p r e p a r a t i o n )
add p e a t l y t o t h e l e v e l of understanding of t h e r e g i o n a l geologyof
will
the
lo
area as w e l l as i t s mineral potential. 'Furthermore, contributions
regional geology of the Datil-Fogollon volcanic province (Fig.
E l s t o n (19721 Llston, Rilcerman, and Uamon
t o t.he
1)'by
(1968). andElston, Coney,
andRhodes (1970) will add t o t h e u n d e r s t a n d h e of t h e Tertiary vol.canotectonic fraxetrork of the Hogollon Plateau area.
e
GEOLCGY
The s t r a t i g r a p h i c u n i t s exposed i n t h e c e n t r a l H a g d a l e n a
Mountains can be divided into four
typeandage.
main groups according t o t h e r o c k
These includePrecambrianargirLite
s i p p i a n t o Permian limestone, shale,
canic,intrusive,
and g r a n i t e ; Kissis-
and sandstone; mid-Tertiary
vol-
and sedimentaryrocks;andtalus,pedimentgravels,
and a l l u v i a l d e p o s i t s
of
A generalizedcolumnarsection
Quaternaryage.
of the pre-Cenozoic stratigraphic sequence
i s presented i n Figure
t h e Cenozoic s t r a t i g r a p h i c sequence i n F i g u r e 8.
a t least 5 soparate periods
5
and
The area hasundergone
of f a u l t i n g and t i l t i n g s i n c e P r e c a m b r i a n
..
time r e s u l t i n g i n t h e formation of unconformities, fault blocks, and
complex s u r f a c e g e o l o u .
The bedrock u n i t s c r o p o u t i n
of the Frecanbrian rocks
area (Fig. 4).
a semi-domal, configuration south
exposed i n t h e n o r t h e a s t p o r t i o n o f t h e s t u d y
Paleozoic andCenozoic
formations,dippingsouthwest
to
southeast, become progressively younger south of the Precambrian exposures.
The ?:iocenePopotosaFormation,
t h e crest betweenSouthBaldy
t h e youngest T e r t i a r y u n i t , c a p s
Peak and Langmuir Laboratory. Farther
the north,
i n t h e Magdalenamining
east slope
of t h e range; sedimentary rocks, steeply dipping
cover most of
to
d i s t r i c t , Precambrian r o c k s form t h e
t o t h e West,
t h e west slope; and Oligocene volcanic rocks form the
foothills.
,'
a
12
f
Dark-red, fine-grained sandstone.
dadero
200- 1800'
fine-grained,
dark-gray, of saquance
Thick
b l a c k , c h e r t - b e a r i n gl i m e s t o n e sw i t hi n t e r bedded quartzite and shale
bed near the base.
i
Gray to blackcorbonqceousshalewithinterb e d d e ds a n d s t o n e sa n df o s s i l i f e r o u s
limesfane.
Reddish-brown,fine-grained quartzite and subo r d i n a t ei n t e r b c d d e ds h a l e .
Gray, c r y s t a I I i n o , w h i t ec h e r tb e a r i n gl i m e s t o n e l o c a l l y i n c l u d i n g a sandsloneatthe
Pink, coarse-grained granite.
L i g h t - p r e e n ,f i n e - g r o i n e da r g i l l i t ew i t h
m o r es c h i s t o s ez o n a sl o c o l l y .
0
500
1000
V e r t i c aFl e a t
Figure
5.
-Pre-Cenozoicstratigraphy
Mountai.ns.
of t h e c e n t r a l Eagdalena
base.
Precambrian __.
Rocks
The o l d e s t r o c k s i n t h e
mountain range are.Precambrian
argil-
l i t e and g r a n i t e .
Although no radiometric age determinations have been
made on the rocks,
a Precambrianage
ofseverallinesofevidence.
Mississippian limestones
face suggesting
may be i n f e r r e d from a combination
T h i s evidenceincludesthedeposition
upon a subhorizontal granite
and a r g i l l i t e s u r -
a long period of erosion: pre-li!ississippian regional
metamorphism as evidenced by t h e l a c k of it i n t h e post-Devonian
tiary rocks:
of
01
Ter-
and according t o Loughlin and Xoschmann ( 1 9 4 2 ) . s t r u c t u r a l
s i m i l a r i t y t o Precambrian rocks elsewhere
i n New Vexico,
The Precambrian terrain consists predominately
of a r g i l l i t e .
Precambrian granite i s l i m i t e d t o a c i r c u l a r o u t c r o p east of North Baldy
..-
Peak.
According t o Loughlin and Koschmann (1942, p. 9-11) i n t h e
Magdalena mining d i s t r i c t , t h e Precambrian g r a n i t e i s more common relative to the argillite in the
Precambrian t e r r a i n .
Argillite
-
D i s t r i b u t i o n andOccurrence.
and i s , b e s t exposed e a s t of North Baldy
e r n p o r t i o n of the study area,
Peak,where
rocks,
Nississippian limestone unconformably overlies Precambrian
N . 80'
The a r g i l l i t e i s bounded on the south by the
North Fork
i n t h e north-
Argillitecropsout
Canyon f a u l t zoneand
The a r g i l l i t e a l s o c r o p s o u t i n s e c .
silicified horst block within
t o t h e e a s t by a N.
18, T.
3S.,
35'
W. fault, zone.
R. 'Jd., i n a h i g h l y
a north-northwest-trending
C o r r e l a t i v e r o c k s i n t h e I.!agdalenaRange
W.-trending
havebeen
f a u l t zones
called greenstone
e
s c h i s t i n Lindgren, and others (1910,
p.
by Loughlin and Koschmann (194%. p. 7-8),
(1953,
14
%43-244), a r g i l l i t e and s c h i s t
and greenstone by K a l i s h
P* 6-8).
The a r g i l l i t e i s the oldest rock
by the Becambrian granite,
lite.
*
i n t h e area.
which contains many inclusions of t h e a r g i l -
The i n t r u s i o n of t h e g r a n i t e a p p e a r s t o
e f f e c t on t h e a r g i l l i t e .
d i p s 40-60°
southeast.
It i s intruded
havehad
no a l t e r a t i o n
The a r g i l l i t e g e n e r a l l y s t r i k e s
The contact of t h e a r g i l l i t e w i t h
N.
4.5'
E. and
t h e overlying
Mississippian limestone i s a prominent angular unconformity that gener-
ally strikes north
and d i p s 25O t o
under t h e g e n e r a l
Loughlin and Koschmann
(194.2, p. 8 ) s t a t e t h a t
. .
argillite.
the rocks becomemore
t o t h e west.
of mica schist are includerl
Minoramounts
headingof
35'
schistose in the north
endof
c r e a s e of s c h i s t t o t h e n o r t h c o u l d r e f l e c t e i t h e r
the range.
The i n -
a regionalmeta-
morphic zonation, a l a t e r a l s t r a t i g r a p h i c f a c i e s changeof
the rock
before metamorphism, o r a d i f f e r e n c e i n s t r a t i g r a p h i c o r s t r u c t u r a l
l e v e l s exposed i n t h e n o r t h and c e n t r a l . p o r t i o n of the range.
Litho1op.y.
The a r g i l l i t e i s t y p i c a l l y l i g h t gray-greenand
weathers t o a buff o r gray.
It i s f i n e g r a i n e d and has a distinctive
s i l i c e o u s appearance.Thinlight-to-dark-greenbandsgenerally
than 1 cm. t h i c k and rarely over
3 cm. t h i c k a r e common i n t h e a r g i l l i t e .
The argillite weathers into small, angular fragments that cover
erable portions
less
con.sid-
of t h e Precambrian t e r r a i n .
In thin section,
t h e major minerals are quartz
minor amounts of chlorite,magnetite,
and orthoclase.
and s e r i c i t e , and
Subround g r a i n s
of quartz as l a r g e a s 2 m, i n diameter are imbedded i n a fine-grained
15
q u a r t z ,s e r i c i t e ,
and c h l o r i t e groundmass.
aroundthecoarserquartzgrains,
Fine-grainedlaminaecurve
which a r e e l o n g a t e p z r a l l e l t o t h e
.
bedding.
A pebble conglomerate
place i n the study area,
i n t h e a r g i l l i t e i s exposed from place
and i s w e l l exposed i n Korth Fork Chnyon 2 u s t
east of the contact with the Kelly
(Fig. 4).
to
Elongatepebbles,
33.
Limestone i n sec. 22, T. 3S.,.R.
1 cm. t o 3 cm. i n length; are p a r a l l e l t o
t h e bedding and a r e cemented i n a fine-grained matrix.
Granite
D i s t r i b u t i o n and Occurrence.
I
Precambrian g r a n i t e c r o p s o u t e a s t
R e Yri. (Fig. 4) and covers
lite.
In the central Hagdalena Mountains,
of NorthBaldy
.a much smaller .surface area t h a n t h e a r g i l -
The predominance of t h e a r g i l l i t e i n
that the east slope
Peak i n sec. 17, T. 3 . .
t h e study area suggests
of the range may n o t b e e n t i r e l y
composed o f g r a n i t e
as speculated by Loughlin and Koschmann (1942, p. lo), based on t h e i r
study i n t h e Xagdalena mining d i s t r i c t , and underscores the need
more mapping i n t h e n o r t h e a s t p o r t i o n
The youngerage
demonstrated by
of the range.
of t h e g r a n i t e r e l a t i v e t o t h e a r g i l l i t e
t h e i n t r u s i v e r e l a t i o n s h i p of t h e g r a n i t e a n d t h e
ous i n c l u s i o n s of a r g i l l i t e i n t h e g r a n i t e . S m a l l d i k e s
t h e a r g i l l i t e east ofNorth
numer-
of g r a n i t e c u t
less t h a n
commonly p a r a l l e l t h e a r g i l l i t e l a y e r s .
Litholoq,.
pinkcolor
is
Ealdy Peak and a r e t r u n c a t e d a t t h e b a s a l
c o n t a c t of theKellyLimestone.Thesedikesaregenerally
1 0 cm. wideand
for
The Precambrian g r a n i t e i s c h a r a c t e r i z e d by i t s
and fine-t2-medium-grained
texture.Microscopicexamination.
16
shows microperthitic orthoclase
Hicrographicintergrowth
and q u a r t z t o be the essential minerals.
of quartzandorthoclase
c l a s e i s subhedral, fresh, .and ranges as long
5
Oligoclase composes l e s s t h a n
'
i s common.
as 4
mm.
percent of the rock.
The ortho-
i n length.
Green b i o t i t e i s
clusters w i t h o t h e r m i n e r a l s , i n
a d i s t i n c t i v e mineral. t h a t o c c u r s a s
v e i n l e t s , and i n t e r s t i t a l t o q u a r t z
and feldspar.Magnetite
associatedwiththebiotite.Apatite
i s commonly
and z i r c o n a r e minor constituents.
Paleozoic Rocks
Rocks of E a r l y andMiddle
centralxagdalena Itountains.
Paleozoic age are not present
The first record of deposition
in the
on thePre-
cambriansurface
i s the Kississippian Kelly
Sandia Formation
and hiadera Limestone a n d - t h e Permian Ab0 Formation
constitute the remainder
Limestone.
The Pennsylvanian
of t h e P a l e o z o i c s e c t i o n i n t h e c e n t r a l
Kagdalena Jlountains.
Mississippian Kelly Limestone
K i s s i s s i p p i a n s t r a t a i n t h e Magdalenn Mountains l i e unconfomn-
ably upon a gently undulating surface
and granite (Fig.
6).
of truncated Precambrian argillite
The Mississippian limestone i n c e n t r a l New Fexico
i s considered by Kottlowski (1965)
t o be a t h i n remnant of the original
t o t a l s e c t i o n owing to erosion during Late Mississippian
time.
The K i s s i s s i p p i a n s e c t i o n i n t h e Magdalena mining d i s t r i c t was
o r i g i n a l l y named t h e Graphic-Kelly Limestone by Herrick (1904)
two leading mines.
Lindgren,and'others
t h e Kelly Limestone a f t e r t h e
after the
(1910) renamed theHississippian
t a m of Kelly.
Armstrong (1958) divided
t h e K i s s i s s i p p i a n of west-central New !.!exico, including the Magdalena
Figure 6.
Precambrian a r g i l l i t e (E)
contact with t h e Mississippian
Kelly Limestone (14) l o c a t e d e a s t of North BaldyPeak.
la
Kountains, i n t o t h e Cal.osa Formation of Early Osagian age
LimestoneofLateOsagianage
and the Kelly
on t h e b a s i s of t h e f a u n a l assemblage.
The e n t i r e K i s s i s s i p p i a n s t r a t a i n t h e c e n t r a l Magdalena Fountains are
designated the Kelly Limestone since the stratigraphic section
t h i n t o be subdivided on t h e s c a l e
of mapping (1"=
is too
in
2,000')used
t h i s study.
DLstribution and Occurrence.
t h e c r e s t of the range a t NorthEaldy
o v e r l i e s t h e Precambrianfrom
southward across the
Canyon (Fig.
Kelly Limestone i s exposedbetween
composing thet.ransverse
.4),A small outcrop of th"
t h e two p a r a l l e l n o r t h and s o u t h f a u l t s
North Fork Canyon f a u l t zone i n sec.21,
.
R.
becausetheuppermostportionofthelimestone
i s silicified.
f a u l t zone, t h e K e l l y Limestone does not crop out
I n the
E!ort.h Fork Canyon
as r e s i s t a n t r i d g e s
i t s l a c k of s i l i c i f i c a t i o n .
s t r i k e from northwest
from 20'. t o
0
45
1/J.,
and v a r i e s i n
t o n o r t h e a s t owing t o t h e f o l d i n g
i n t h e t!ater Canyon area.
of t h e s t r a t a
The r e s u l t i n g a n t i c l i n e s and synclinesgive
t h e K e l l y Limestone a sinuous outcrop pattern
trict.
o f the range
of t h e K . 80° W.-trending
The Kelly Limestone dips
i n t h e I.!aterCanyon
Vhere t h e d i p i s g e n t l e r , o r theoverlyingrockshave'teen
moved, the width of the exposures
considerably.
bearing horizon
'
E l Tigre mine.The
Kelly Limestone crops out as steep cliffs along the crest
Water Canyon d i s t r i c t , s o u t h
T.
.
72.'.approximately $ of a milewestofthe
becauseof
Peak
E!orth.E'ork Canyon f a u l t zone, where it i s displaced
2.5 m i l e s t o t h e e a s t i n \ r a t e r
3s..
The Kelly Limestone unconformably
disre-
of the Kelly Limestonebroadens
?he importanceoftheKellyLimestoneasthemajorore-
i n t h e Hagdalena mining d i s t r i c t i s r e f l e c t e d b y t h e
19
numerous p r o s p e c t p i t s ,
i n t h e Water.Canyonarea.
which outline the exposures
The southernmostexposureoftheKelly
Limestone i s a t t h e Euckeye mine i n sec. 27,
a t the junction
of t h e limestone
T. 3 . . R. Tv:., (Fig. 4)
of Water Canyon and Copper Canyon a t which place i t ' i s
truncated by t h e Water Canyon fault zoneand
surface on t h e e a s t s i d e
Litholoa.
i s dropped i n t o t h e sub-
of t h e fault.
The Kelly Limestone i s a lightbluish-gray,
to-coarse-grainedcrinoidallimestone.White
present,particularlytowardsthetop
t o gray chert
of theformation.
varies from 80 t o 100 f e e t , which i s thinner than the
r e p o r t e d by Loughlin
medium-
bands a r e ..:
The thickness
130 f e e t t h i c k n e s s
and Koschmann (1942) i n t h e Magdalena mining
dis-
trict. Locally, a t t h e b a s e of t h e K e l l y Limestone, a zone, up t o 8 f e e t
. ).
and a r g i l l i t e f r a g m e n t s as l o n g a s
thick, contains quartz, feldspar
embedded i n a fine-grained calcite matrix.
a l e n t of the Calosa Formation
5 cm*
T h i s b a s a l zone i s theequiv-
as described by Armstrong (1963).
Loughlin and Koschmann (1942, p. 14-16)were
able to subdivide
t h e K e l l y Limestone i n t o a lower and upper limestone by the "silver pipe"
member, a bed of fine-grained, argillaceous dolomitic limestone,
they describe as the
ever, the "silver pipe"
which
most r e l i a b l e marker horizon i n t h e d i s t r i c t ,
member was recognized only
Water Canyon area and could not be used
Hou-
i n a few p l a c e s i n t h e
f o r mapping purposes.
Pennsylvanian Magdalena Group
The Pennsylvanian System
i s represented by t h e Magdalena Group,
which was named a f t e r t h e MagdalenaMountainsby
Gordon (1907).
Kagdalena Group rests unconformably upon the Hississippian Kelly
The
20
and KaderaLimestone.
Limestone and c o n s i s t s of t h e Sandia Formation
The t o t a l t h i c k n e s s of thePennsylvaniansection
in the central
'
Kagdalena ?.!oamtains i s 2350 f e e t .
SandiaFormation.
"
by Herrick(1899)
The SandiaFormation
was o r i g i n a l l y named
after the Sandia Xountains, Eernalilla
County, New
It i s composed predominately of s h a l e w i t h l e s s e r
Hexico.
amounts of
limestone and q u a r t z i t e , and forms the lower h a l f of t h e Hagdalena
Group.
The t o t a l t h i c k n e s s of the Sandia Formation
i n t h e Water Canyon
a r e a i s 550 f e e t , which compares with the 600 f e e t measured by Loughlin
and Koschmann (1942) i n t h e Nagdalenamining
Formationappears
t o thicken very
2300 f e e t of section reported
district.
rap5.dI.y northward
The Sandia
as evidenced by t h e
i n Lindgren, and others (1910) a t the
north end of t h e ltagdalena mining
district.
Loughlin and Koschmann (1942, p. 16-18) subdivided t h e Sandia
Formation i n t o six members which, beginning with the oldest, are desig-natedlowerquartzite,lowerlimestone,middlequartzite,shale,upper
limestone, and u p p r q u a r t z i t e members.However,
as notedbyLoughlin
and Koschmann (1942), the members vary considerably in thickness
some a r e l e n t i c u l a r and l o c a l l y a b s e n t .
and
The' lowerlimestone,middle
q u a r t z i t e , upperlimestone,andupperquartzite
members a r e p a r t i c u l a r y
noted f o r t h e i r t h i n n e s s or absence i n p a r t s of t h e Nagdalena mining
district.
I n t h e c e n t r a l Magdalena Nountains,thedivision
SandiaFormation
i n t o six members was notpossible.Rather,for
purposes, the formation
of the
mapping
was d i v i d e d i n t o two members, a lower q u a r t z i t e
21
member containing minoramountsof
t a i n i n g minorur,ounts
shale and an upper shale
member con-
of limestone and q u a r t z i t e .
The Sandia Formation i s characterized by t h e abundance of shale:
medium-to-coarsely-crystallinelimestonecontainingbrachiopods,bryozoan, and algae: and t h e fine-to-medium-grain,cross-bedded,reddishbrown q u a r t z i t e .
The highly variable lithology
of theSandiaFormation
Madera Lime-
c o n t r a s t s w i t h t h e uniform fine-grained limestone of the
stone s
Lower o u a r t z i t e member; The
overliestheKelly
lower quartzite member p e r s i s t e n t l y
Limestone i n t h e c e n t r a l Hagdalena Range.
Thecon-
t a c t i s s t r u c t u r a l l y confonr,able, but does represent a hiatus from
MississippiantoEarlyPennsylvanian
q u a r t z i t e member v a r i e s from100
time.
Thickness of thelower
..
t o 150feet.Characteristicfeatures
o f t h e lower q u a r t z i t e member include a fine-to-medium-grain
roundquartzgrains,andcross-bedding.
presentlocally.
Late
Reddish-brown,
Fauna are lacking, but Loughlin and
p. 17) describe some Pennsylvanian plant
size,
s i l t y shale. i s
Koschmann (1942,
remains i n t h e lover q u a r t z i t e
menber.
Shale menber;
The shale member, which makes up t h e g r e a t e r p o r t i o n
of the Sandia Formation,
Canyon area.
i s approximately 400 f e e t t h i c k i n t h e P!ater
The shale member i n c l u d e s t h e lowerlimestone,middle
quartzite,shale,
upperlimestone,
and upper q u a r t z i t e members from
Loughlin and Koschmann's (1942) study of
Magdalenamining
district. Shale
.
t h e SandiaFormation
in the
i s dominant throughout, b u t i s l o c a l l y
interbedded w i t h limestone and q u a r t z i t e beds.
l o w e r q u a r t z i t e member and the shale
The contact between the
member i n some p l a c e s i s gradational,
22
b u t t h e two members a r e commonly separated by a m o t t l e d , c o a r s e l y
crystalline limestone,
2 t o 8 f e e t i n thickness, with.abundant
Pr0ductu.s
brachiopods and bryozoans.,
The shale i s adark-gray
It i s carbona-
t o black f i s s i l e rock.
ceous, and c o n t a i n s s e v e r a l t h i n , i n t a r b e d d e d , l e n t i c u l a r l p y e r s
q u a r t z i t e and limestone.
The limestoilesarebluish-gray,
of
medium-to-
c o a r s e l y c r y s t a l l i n e and fossiliferous, containing brachipods, bryozoans,
andalgae,
The q u a r t z i t e s a r e brown t o gray and f i n e g r a i n e d .
HaderaLimestone.
The NaderaLimestone
Formation i n t h e c e n t r a l HagdalenaEountains.
name MaderaLimestone
overlies the Sandia
Gordon (1907)adopted
the
for the dark-blue limestone conformably overly-
i n g t h e s h a k r Sandia Formation
i n Socorro and E e r n a l i l l o c o u n t i e s .
..
The t r u e t h i c k n e s s
of t h e Madera Limestone i n t h e Magdalena
mining district. i s d i f f i c u l t t o e s t i m a t e because of
movalof
the upper portion
f a u l t i n g and re-
by erosion,Loughlinand
Koschmann (1942)
estimated the Madera Limestone t o be a t l e a s t 600 f e e t and a maxinlum
of 1000 feet thick. Kottlowski
included strata only
(1963)consideredthattheformation
as young as Xissourian and predicted the Kadera
1 mile west
Limestone t o be much thicker. Recent drilling approximately
of Korth Baldy Peak penetrated an apparently unfaulted section
Madera Limestone,1800
feetthick.
of
The outcropofthe
Madera L'xestone
i n t h e c e n t r a l Kagdalena Xountains further support the
1800 f o o t . t h i c k -
ness.
Distribution and occurrence:
The Madera Limestone i s exposed i n
see. 18 T. 3S., R. 3!.1. a s t h e continuation of the Paleozoic exposures
southward from t h e Xagdalena mining d i s t r i c t ( F i g .
7).
h'orth Ealdy Peak
Figure
7. West dippingPennsylvanianSandiaFormation
Limestone (1.1) i n Morth Fork Canyon.
(S) and Nadera
24
i s cap?ed by a t h i n remnantof
North Fork
The N . 80'
:,;adera Limestone.
W.-trending
Canyon f a u l t zone has displaced the Xadera Limestone east
i n t o Water Canyon a r e a where it i s well exposed i n florth Fork Canyon
Y
and Copper Canyon,
An i s o l a t e d h o r s t b l o c k
Group i s exposed i n secs. 20 and
basalt. Spears Formation of the Datil
29, T. 3 S . ,
I?.y:!.
Fork Canyon.
southof
North Ealdy Peak near t h e headofRorth
The uplifted block
trending outcrop of approximately
f e e t i n width.
of ?.ladera Limestoneoccurs
i n a north-
6500 f e e t i n l e n g t h and 300 t o 600
The iiaderaLimestone
northwest-trending zoneof
of EaderaLimestoneand
h o r s t i s a continuation of a north-
u p l i f t e d b l o c k s of Precambrian rocks,
extend from the Hagdalena mining
which
district into the central1Jagdalena
ICowtains.
. ...
Lithologx;
The 1;adera Limestone i s a blue-gray,fine-grained
lime-.
stonethatcontainsblackchertnodules.Fusilinids,brachiopods,
solitary corals occur throughout the formation.
A few t h i n b e d s o f
whitetogreenish-grayquartzitearepresentnearthebase.
beds are mottled, shaley,
and
and a r e s t a i n e d r e d d i s h
The upper
by the overlying
Ab0
Formation.
T b lower 300 f e e t of the XaderaLimestone
s h a l e and white t o g r a y , medium-to-coarse-grain
similar to the Sandia Formation.
contain bluish-gray
quartzite beds very
The contact between the Sandia Forma-
t i o n and t h e Madera Limestone i s gradational and i s p l a c e d a r b i t r a r i l y
upon t h e doninance and greater thickness of the fine-grained limestone
with a subsequentdecrease
i n theshale
remainderoftheEaderaLimestone
and q u a r t z i t e b e d s ,
The
i s a very uniform, fine-grained micrite.
25
Permian Abo Fornation
G i s t r i b u t i o n, - and Occurrence.
'
The Abo Formation is t h e youngest
Paleozoic unit i n t h e Nagdalena !4ountains and
stone with a slightangularunconformity.
Formation i n t h e s t u d y a r e a
o v e r l i e s t h e Nadera Lime-
The onlyexposureofthe
i s a t t h e head of Patterson Canyon, north-
west of Morth Ealdy Peak (Fig. 4).
I n t h e !:'ater Canyon a r e a , a l l t h e
Ab0 Formation was removed p r i o r t o t h e d e p o s i t i o n
canics
.
Lithology.
The Ab0 Formationhas
a t the head of Patterson
Ab0
Canyon.
fine-to-coarse-grainedsandstone
of the Oligocene vol-
a maximum thickness of
100 f e e t
The formation consists of dark-red,
and minor.amounts of interbedded red
sandyshale.Cross-bedding,ripplemarks,
and mud c r a c k s are common.
Locally, limestone pebbles appa;-ently derived from the underlying Xadera
Limestone a r e i n t h e b a s a l b e d s
found,butLoughlinand
of t h e Abo Formation.
No f o s s i l s were
Koschmann (1942, p. 21)describe
some Pernian
p l a n t f o s s i l s from t h e f o m a t i o n i n t h e XagdaXena mining d i s t r i c t .
Cenozoic
Oligocene volcanic rocks
on Paleozoicsedimentaryrocks
Pocks
were deposited i n angular unconformity
i n t h e centpalEagdalenaKountains.Dikes
and s t o c k s i n t r u d e d t h e area f o l l o w i n g t h e c e s s a t i o n of volcanism.
Sedimentary processes became dominant during Pliocene
time w i t h t h e de-
p o s i t i o n of t h e PopotosaFormation.
Tertiary Volcanic itocks
Lava flows, ash flows,
longing to the Oligocene
and volcanocl.astic sedimentary rocks be-
D a t i l Group cover t h e l a r g e s t area i n t h e
.
26
c e n t r a l FagdalenaXountains.
The volcanic rocks dip
20°-250 southwest
t o s o u t h e a s t from thePaleozoic-Frecambriancore(Fig.4).
The D a t i l p e r i o d o f volcanism lasted from 37.1 m.y.
as determined by age dating
by various workers (Eurke
Smithand
Weber, 1971).
others,inpress;
t o 30.5 m.y.
and o t h e r s , 1963;
The combined thickness of t h e
volcanic rocks i n t h e c e n t r a l ?lagdaler,aHountains i s a m a x i m u m of
12,000 f e e t and on theaveragedips
Paleozoicsedimer.taryrocks,Figure
10'-15
0
less than the subjacent
8 i s a generalizedcompositestrat-
i g r a p h i c column of t h e T e r t i a r y sequence i n t h e c e n t r a l llagdalena Mountains.
'
The need t o d e f i n e t h e s t r a t i g r a p h i c sequence of t h e D a t i l
Group h a s e x i s t e d s i n c e
l*!inchester(1920)
f i r s t named t h e C a t i l Fonna..
tion as interbedded volcanics
and sedimentary rocks outcropping
Datil Kountains, 36 miles v e s t of Hagdalena.Loughlinand
i n the
Koschmann's
( 1 9 4 2 ) i n t e r p r e t a t i o n of the volcanic sequence i n t h e Nagdalenamining
t h e complex s t r u c t u r e and a l t e r a t i o n i n t h e
d i s t r i c t was hamperedby
. .
a r e a , making any c o r r e l a t i o n of t h e i r work i n t h i s s t u d y d i f f i c u l t .
Tonking(1957)
who studied the Puertecito quadrangle,
north of Nagdalena, divided the
ascending order, the Spears
Jara Peak Kember.Weber
15 miles
Datil Formation i n t o t h r e e membersr
Member, t h e H e l l s MesaMember,
(1971, p. 35)recognized
i1:
and t h e La
thecomplexity of t h e
D a t i l and r a i s e d i t t o group status and the Spears, Hells
Nesa. and t h e
La Jara Peak Nembers were e l e v a t e d t o f o r m a t i o n a l s t a t u s ,
The La J a r a
Peak Formatinn has since been
structural evidence (Chapin,
of 23.8 m.y. (Chapin1971-a).
shown t o be a post-Datil event based
on
and o t h e r s , i n preparation) and a K-Ar d:~,te
0-50'
Slreom grovel
D e b r i s slides dominoledbyOlh
llor tuffs.
u n c o o r o l t d o l e d d e b r i s 01 I h e n o r g i n r 01 I h e range.
?_-
Red, w e l l i n d u r a t e d longlomerate
episode o f $lock i n l r w i o n a n d m i n e r a l i z o l i d n a t
followed by exlensive erosion.
-Major
2am.y.
Reddirh-purple,cryrlaI-rich t o p o o r r h y o l i t e a s h flows.
Gloy,ophonilic,vesieul.r onderile rilh minor interbedded
l l oawo sn darnl odn r .
PeOk arnohdryheosl i lt lec
C o m p o a i l e Sheet of gray,crystal poor r h p l i l i c t u f f s wilh
interbedded
andesite
flows..
B I Y e - g f o y ,p o r p h y r i l i co n d e r i l e
rocks l o c o l l y neor bore.
f l o w s c o n t a i n i n qv o l ~ o n i ~
i
.. .
Groy l o p i n k , c t y s t o l r i c h . l i t h i c - r i c h l o l i l e
lulfs al
ond YOICanOCImLIiC rocks o t bose.
P o r p h y r i t i c" t a r k e y
lrOCk*' o n d s r i l s f l o u r .
P u r p l i s h to g r e e n i s h - g r a ye o d e s i l e
l o l o l i t ed e b r i s
bcoringsandstone ond c o n g l o m e r o l e .
D o r k - r e d l,i n e - g t o i n e d
. o
1000
rondrtone.
2000
7
"
V e l l i c o l Feel
Figure 8.
Cenozoic s t r a t i g r a p h y o f t h e c e n t r a l F a g d a l e n a Hountains.
28
A study by E r o m (1972) of t hhe volcanic rock:s i n t h.esouthern
BearMountains,
3 miles north
of D a t i l Group i n t o
of I.Tagdalena, permitted,thesubdivision
13 separate u n i t s totaling approximately
i n thickness. Figure
9 i s a c o r r e l a t i o n c h a r t of equivalent units de-
scribed by Brown (1972) north of the
Loughlinand
4000 f e e t
1jlagda7ena mining d i s t r i c t ,
Koschmann's (1942) effusive sequence i n t h e Kagdalena
mining d i s t r i c t , and t h e u n i t s used i n the present study
from t h e cen-
t r a l Kagdalena Range e
SpearsFormation.
The deposition of SpearsFormation,
lowermost u n i t of t h e D a t i l Group, represent the beginning
a c t i v i t y i n t h e Magdalena a r e a i n 1Carly Oligocenetime.
others (1963) obtained
the
of volcanic
Burke and
a 37.1 m.y. K-Ar d a t e on b i o t i t e i n a l a t i t e
tuff breccia i n t h e J o y i t a Hills, 30 miles 'east of the Lemitar Mountains.
The SpearsFormation
i s considered by Chapiq and o t h e r s , ( i n
p r e p a r a t i o n ) t o be s t r a t i g r a p h i c a l l y e q u i v a l e n t t o t h e . l a t i t e - t u f f
breccia in the Joyita
Hills based on l i t h o l o g i c and s t r a t i g r a p h i c
similarity.
The Spears Formation unconformably overlies the
i n t h e c e n t r a l EIagdalena Nountains.
Only l o c a l l y a t t h e
Patterson Canyon does the Spears Formation overlie
MaderaLimestone
head of
t h e Abo Formation.
The. Spears Formation i s composed of volcanoclastic sedimentary
rocks,volcanic
It canbedividedinto
a s h flows,andlavaflows.
mappable members.The
middle member, which i s a d i s t i n c t i v e p o r p h y r i t i c
l a v a f l o w o r "turkey track" porphyry, separates
l y t h i c k sequenceof
3
epiclasticrocks.
which i s a member of the Spears Formation
thk? otherwise monotonous-
The tuff ofNippleMountain,
exposed i n the southern Bear
Southern Bear Mountains
lzrown (1972)
Fanglomerate of Dry Lake Canyon
La J a r a Peak Formation
Timber Peak r h y o l i t e
South Laldy Peak a n d e s i t e
Sawmill Canyon formation
- - - - Eianded r h y o l i t e - - - -
s
Tuff of Allen 'Jell
Andesiteflows
Upper t u f f of Eear Springs
Andesite flows
Lower tuff of Pear Springs
Porphyritic andesite flows
2
+
I2
H e l l s Mesa Formation
-
----
Rhyoliteporphyry
sill
---
a,
Tuff o f Goat Spring
Upper l a t i t e
Upper member
- - - - - - - Lower a n d e s i t e - - - - Lower lt au tfift' e
n o
.rl
c, i*iid.dle member
&i
d
(Ok
o
Lower member
Figure 9.
I:
0
.rl
c,
Upper member
d
- - - - - - - - - - - - - - - - - - - :dEo
a h
- - - - - - Purpleandesite - - - - *a
Porphyritic andesite flows
Lower menher
Correlation chart of equivalent Tertiary volcar?ic
and sedimentary units used by
workers i n the southern Eear Mountains
and the Fagdalena $fountains. .
h,
W
30
Kountains (arown, 1972), i s not present
.
tains.
i n t h e c e n t r a l Magdalena I4oun-
i s of v a r i a b l e
Erown (1972)reportsthattheSpearsFormation
a t H e l l s Mesa, i n
l i t h o l o g y , from dominantly fine-grained fluvial rocks
the Eear MountaiRs, t o a t h i c k s e c t i o n of l a v a f l o w s and a s h f l o w t u f f s
o v e r l y i n g r e l a t i v e l y t h i n volcanic conglomerates i n t h e s o u t h e r n Eear
Mountains.These
lithologicvariatiorisarealsopresentinthecentral
Magdnlena Motmtains.
I n NorthFork
Canyon, the Spears Formation consists
of 3500 f e e t o f conglomerate,sandstone,lavaflows
flows.
and l a t i t i c ash
Furthertothesouth,thelatiticashflowsdecreaseinthick-
nesse but
s t i l l o v e r l i e a thick volcanoclastic section.
Lowermember;
The lower member of the Spears Formation consists of
volcanic siltstone, sandstone,
thickness.
and conglomerate a s much as 1200 f e e t i n
i s the
The lower member contains no ash or lava flows and
equivalent of Loughlinand
Magdalenamining
Koschmnnn's (1942) Purple Andesite
in the
district (Fig. 9).
Field exposures 'of the lower Spears Formation reveal
a monoto-
nous sequence of well-indurated, volcanoclastic sedimentary rocks
con-
or
t a i n i n g no marker horizons that can be used for correlation purposes
stratigraphicposition,Attitudedeterminationscan
thefiner-grainedlayers.
be taken only from
The c o l o r v a r i e s from a grayish-purple i n t h e
rocks of Patterson Canyon on the northwest t o a greenish-gray i n t h e
rocksofRorthFork
Canyon and Copper Canyon.
common c o l o r and r e p r e s e n t s t h e f r e s h , g e n e r a l l y
portion of t h e lowerSpearsFornation.
Grayish-purple i s t h e most
more conglomeratic
The greenish-gray color
t o replacement of the ferromagnesian minerals to
i s due
c h l o r i t e and epidote.
i n t h e sequence and contains unsorted
Conglomeratepredominates
10 cm.
and subrounded p o r p h y r i t i c l a t i t i c t o a n d e s i t i c c l a s t s a v e r a g i n g
i nl e n g t h( F i g .
10).
The ,phenocrysts i n t h e c l a s t s
of chalky white to gray feldspar
ceous,aphanitic
uniformly. c o n s i s t
and dark-green hornblende
groundmass.Subrounded
i n a sili-
fragments of t h e d i s t i n c t i v e l y
r e d Jib0 Formation and Piadera Limestone a s l o n g a51 meter are common i n
.
I
the basal portion. Imbrication directions taken from clasts of
Ab0
of t r a n s p o r t from t h e
Formation within the unit indicate a direction
southwest.
Viewed microscopically, the clasts are
similar m i n e r a l o g i c a l l y
and c o n s i s t of a s much a s 40 percent plagioclase, saniiline, and hornblendephenocrysts.
The c r y s t a l s a r e a s l o n g
.
h e d r a l t o euhedral.
...
as
1.5
mm.
and a r e sub-
The groundmass i s afine-grainedaggregate
feldspar,hornblende,biotite,quartz,apatite
Middle member:The
of
and magnetite,
middle member of the Spears Formation
is a
blue-gray t o reddish-gray vesicular, "turkey track" porphyry, andesite
flow.
The middleSpearsFormationoverlies
Spears Formation throughout
t h e volcanoclastic lower
t h e c e n t r a l MagdalenaMountains.
The ex-
t r u s i o n of t h e andesite flows represents the oldest Cenozoic volcanism
i n t h e Nagdalena area.
The middle Spears Formation
i s mapped separately because of i t s
, d i s t i n c t i v e n e s s , i t s m a x i m u m 500 f e e t thickness, and i t s u s e f u l n e s s as a
markerhorizon
in separating the lower
andupperSpearsFormation.
one "turkey track" porphyry occurs within the Spears Formation
Only
in the
c e n t r a l Nagdalena Mountains, separating
the volcanoclastics of the lower
Spears Formation from the volcznoclastic
and l a t i t i c a s h f l o w s of t h e
Figure 10.
Lower Spears Formation containing clasts
of Ab0 Formation
( A ) Paleozoic limestone (L) and porphyritic andesite (?A).
.
.
e
33
A "turkey track" andesite flow
upperSpearsFormation.
w i t h i n the Spears
Formation i s a l s o exposed i n the Eear Mountains (Erowp, 1972;Tonking,
1957)and
i s equivalent to the middle
described i n southeastern Arizona by
the "turkey track" porphyry be used as
member.
Similar flows
Cooper(1961)
have been
who suggested t h a t
a guide for the correlation of
Miocene rocks.
i s characterized by
Viewed microscopically, the andesite flow
abundanteuhedralphenocrysts
of plagioclase (An
55) .as long as
10
mm.i n
diameter i n a f i n e - g r a i n e d f e l t y groundmass of plagioclase and magnetite
(Fig. 11). The plagioclase commonly shows c l a ya l t e r a t i o n ,C a l c i t e ,
epidote, chlorite,
-
and s i l i c a a r e p r e s e n t i n a l t e r e d
f a u l t s or intrusions.
zones adjacent
to
The v e s i c l e s commonly a r e f i l l e d w i t h s e c o n d a r y
c a l c i t e o r silica. Xagnetite oxidized to .hematite gives the characteri s t i c r e d d i s h s t a i n t o the rock.
member;
A sequence of interbeddedconglomeratic
mud flowsand
andes5t.e flows of t h e middle Spears For-
l a t i t i c ash flows overlies the
mation and i s i n angular unconformity w i t h the overlying Fells
Formation.
strike.
Yesa
its
The l i t h o l o g y of t h e upper Spears Formation varies along
South of NorthSaldyPeak,theupperSpearsFormation
posedofvolcanoclasticsand
some l a t i t i c ashflows.Further
s c ~ t t hi n Baldy Canyon, t h e l a t i t i c a s h f l o w s
c l a s t i c s and some l a t i t i c a s h
flows.
i s com-
to the
dominate over the volcano-
L a t i t i c ash flows becomemore
inant higher in the stratigraphic section
dom-
of the upper Spears Formation
i n t h e c e n t r a l Xagdalena Kountains.
The apparent thickness
o€ t h e upper Spears Formation
from t h e geologic map and cross
c r o s s sections
s e c t i o n s(Fig.
(Fig,
>
4) a l s o v a r i e s
a s measured
..
...
Figure
11.
Photomicrograph of a porphyritic andesite from t h e middle
Spears Formation.--Plagioclase (P) phenocrysts
and
c a l c i t e (C) f i l l e d v e s i c l e s i n a fine-grained;ironstained,grounchass
of f e l d s p a r andmagnetite.Crossed
3.
nicols,
x
35
considerable.
A t NorthBaldy
Teak t h e upper member i s a t a maximum
thickness of 1700 feet, but t h i n s r a p i d l y t o a more c o n s i s t e n t 700 f e e t
southward.
exposed i n the southernmost
The conglomeratic mud flows are best
i n secs. 33 and 3 4 , T. 3s.. R.
exposuresoftheupperSpearsFormation
3M.
Thay are very
similar t o the conglomerates of t h e lowerSpears
Formation,beingpurple-gray,
underlyingandesiteflows
and containing subrounded clL:s’ts of t h e
as w e l l a s l a t i t i c a s h f l o w s .
range from 1 cm. t o 1 2 cm. and l o c a l l y a s l o n g
The c l a s t s
as 1meter i n length.
The conglomerate exhibits neither sorting nor stratification.
The l a t i t i c a s h f l o w s a r e
r i c h tuffs.
compact,welded,
The ash flows are characterized by
brown color, chalky
.
c r y s t a l and l i t h i c an overall grayish-
,..
w h i t e f e l d s p a r s , and red-brown t o grayish-red,
subrounded l i t h i c fragments.
The t u f f s contain few pumice fragments.
Quartz crystals generally are absent, but
common towards the top
become increasingly more
of t h e section thovgh never exceeding
3 percent
by volume of the rock.
Petrographically,feldspar
and hornblendephenocrysts,
compos-
i n g as much a s 40 percent of t h e ash flow i n t h e upper Spears Formation,
are i n a n a p h a n i t i c , a r g i l l i z e d
from An3,
as
5
matrix (Fig. 12).
t o An36, dominatesoversanidine.
percent and has been replaced
hedral to euhedral,
O.5.mm.
Plagioclase,varying
Hornblende ranges t o as much
by magnetite.
The f e l d s p a r s are sub-
and range i n s i z e from 0.2 mm. t o 2 mm- but average
The groundmass i s glassy, w i t h l i t t l e d e v i t r i f i c a t i o n ,
or calcite.
Flow bandi.ng i s ex-
and the groundmass.
Accessoryminerals
shows a g e n e r a l a l t e r a t i o n t o c l a y
h i b i t e d by thephenocrysts
and . .
36
Figure
12.
Photomicrograph of a latite from the upper Spears Formation.--Flagioclase ( F ), sanidine (S) and hornblende (H) .
crystals in a glassy matrix. Crossed nicols, X 3.
37
i n c l u d eb i o t i t e ,q u a r t z ,a p a t i t e ,
and clinopyroxene.
fragments, which a r e g e n e r a l l y less than
t a l s of plagioclase, l e s s than 0.1
The l a t i t i c l i t h i c
3 cm. i n length, contain crys-
mm.
long i n a fine-grained, siliceous
matrix.
The contact of t h e upperSpearsFormation
H e l l s Mesa Formation can be
w i t h the overlying
easily placed on t h e b a s i s o f c o n t r a s t s i n
color and l i t h o l o g y between t h e two formations andincrease in the steepness of t h e s l o p , which i s underlain by H e l l s Kesa Formation.
(1972, p. 17) r e p o r t e d t h a t
Brown
a distinctive hematite-stained conglomerate
provides a u s e f u l marker bed a t t h e t o p of t h e S p e a r s i n t h e s o u t h e r n
BearNountains.
T h i s conglomerate i s n o t p r e s e n t i n t h e c e n t r a l
A 0.5 meter thick regolith, developed
a t thetop
.
of the Spears Formation,
i s present only i n t h e s o u t h p o r t i o n of ‘the
NagdalenaFountains.
study area and represents subaerial weathering before deposition of the
Hells KesaFormation.
The a c t u a l c o n t a c t i n many places i s obscured
owing t o t h e mantl.ing by
d e b r i s from t h e Hells Mesa Formation.
H e l l s Xesa Formation.
”
The H e l l s Mesa Formation
Group i s a t h i c k sequenceofquartz
o t h e r s , (1963)obtained
l a t i t e ash flow tuffs.
a K-Ar d a t e from b i o t i t e of 32.4 m.y.
sample taken from the basal portion
.
of t h e D a t i l
Burke and
from a
of the Hells Hesa Formation exposed
i n J o y i t a Hills northeast of t h e MagdalenaMountains.Tonking(1957,
pa 29-30,
56) o r i g i n a l l y named t h e Hells Mesa a member of t h e D a t i l
Formation a f t e r a conspicuous landform a t t h e e a s t e r n edge of Bear
tain(secs.
7 and 26, T. lN., R. 451.).Weber
Houn-
(1971) r a i s e d t h e Datil t o
g r o u p s t a t u s making t h e Hells Xesa a formation.
The Hells Hesa Forma-
t i o n was m i s t a k e n l y i d e n t i f i e d , by Loughlin and Koschmann (1942,
38
p. 33-35) i n the P!agdalena mining d i s t r i c t and'Kalish (1953, p. 26-27)
i n the\later.Canyonarea,as
a rhyoliteporphyry
s i l l (Fig. 9 ) .
i n t o 7 members i n t h e
(1972, p. 18-50) divided the k!ells XesaFormation
9 ) . Regional mapping i n t h e I.!agdalena
southernEearKountains(Fig.
i n redefining
d i s t r i c t (Chapin, and o t h e r s , i n p r e p a r a t i o n ) r e s u l t e d
Erown's (1972) Hells Hesa Formation.
Formation i s the equivalent
of t h e H e l l s F e s a
Erom
I n t h i s studytheHells
Nesa
of Eroprn's (1972, p. 19-30) lowest merzber
9 ) , on
Formatj-on, t h e t u f f of Goat Spring (Fig.
t h e b a s i s of continuous exposure
from the Bear,I.Iountains t o t h e Magda-
l e n a Mountains.
The H e l l s Nesa Formation covers a s u r f a c e a r e a g r e a t e r t h a n
square miles
in the central
10
The formation i s ex-
Kagdalsna14ountains.
,.
posed i n a wide crescent shaped pattern beginning near
southeast to South
I:'aterCanyonMesa
Canyon, and t h e n n o r t h e a s t t o t h e w e s t e r n s l o p e s o f
e a s t of t h e Water Canyon campground (Fig. 4).
steep, talus-mantled
slopes i n t h e h i g h e r e l e v a t i o n s
c r e s t of the range for over
Baldy Peak.
IJorih Ealdy Peak,
It forms
and makesup
the
3 miles between North Ealdy Peak and South
I j i s t i n c t i v e w h i t e c l i f f s near North Ealdy Peak and a pro-
nounced n e a r l y v e r t i c a l , f a u l t
escarpment on t h e e a s t s i d e
Canyon are composed of the )!ells
of!.!ater
Nesa Formation.
The Hells Kesa Formation i s a multiple flow, simple cooling untt
ofcrystal-rich,quartzlatite
tuff.
i t s gray color, pink sanidine,
w h i t e plagioclase and round quartz
The formation i s d i s t i n g u i s h e d by
embedded i n a microgranular groundmass.
1 f o o t i n the poorly welded,
!:'eathered
eyes
c a v i t i e s as long as
upper portions of the Elells Mesa Formation
9
along t h e c r e s t of therangeinsee.30,
>
T.
3S.,
Et. 3k7. give the rock
~~
.
~~
e
39
a pitted texture.
fragments.
As much a s 2 psrcent of the rock
i s rr.ade up of l i t h i c
The rockweathersintoangular,blockyboulders,forming
tensivetalusslopes.
ex-
Slopes developed on ,the H e l l s Mesa Formation are
steeper than those developed
on the underlying Spears Formation.
The thickness of t h e H e l l s Nesa Formation varies considerably
w i t h i n a short distance.
Baldy Peak theformation
miles south
A t thenorthernmostexposurewestof
i s approximately 200 f e e t t h i c k .
of NorthBaldyPeak
formation is 3850 f e e t t h i c k ,
t h a t may i n c l u d e r e p e t i t i o n
North
However,
3
i n Copper Canyon and Mill Canyon, t h e
The l a t e r f i g u r e i s a m a x i m u m thickness
of t h e strata by unrecognized
normal fault-
ing*
The H e l l s Nesa Formation i s a densely welded, gray
where i n t h e c e n t r a l Magdalena Nountains except
NorthBaldy
Peak.
and southwest
farther to the
west and southwest of
The formation i s Tqhite andpoorly'welded
of KorthEaldyPeak,
t o t h e west
becoming grayer and densely welded
south.
Thin volcanoclastic conglomerates
and minor "turkey track"
porphyry andesite flows are interbedded with the Hells
flow tuffs in an area between
Northbaldy
tuff ever:r-
Peak.
Mesa Formation ash
North Faldy Peak and 2.5 miles south
of
The epiclasticsedimentaryrockscontainfragments
very similar to the Spears
Formation and the andesite flows resemble t h e
middle member of t h e SpearsFormation.
They appear t o b e r e s t r i c t e d t o
t h e upper portion of t h e Hells Hesa Formation and a r e l i m i t e d i n a e r i a l
e x t e n t fromNorth
Canyon (Fig. 4).
Ealdy Peak t o t h e north side
of Copper Canyon and Mill
40
Furthermore, the Eells
Nesa Formation overlies the lower
i n s,ec. 18, T.
of the Spears Formation west of Korth Ealdy Peak'
T;J.
on the upthrolm side
f a u l t zone (Fig. 4).
of t h e N . 80'
3.5.. R.
Fork Canyon
\;,-trendingNorth
There i s no middle o r upperSpearsFormation
underlying the Hells IiesaFormation
Canyon f a u l t zone.
member
on the north side
On t h e downthrown side of
of t h e North Fork
t h e NorthFork
Canyon
f a u l t zone, t h e B e l l s 14esa Formation o v e r l i e s t h e upper Spears Formation.
Becauseof
the lack
foliation, attitudes
ofpumice,
l i t h i c fragments,megascopic
on t h e Hells Mesa Formation a r e d i f f i c u l t t o o b t a i n .
The blocky, debris-mantled slopes
of the Hells )lesa Formation make it
d i f f i c u l t t o find outcrops. Attitudes are determinable
fragments are more abundant o r the rock
The a t t i t u d e s o b t a i n e d i n d i c a t e
exists between the upper Spears Formation
where l i t h i c
i s poorly welded.
tha; an angular unconformity
and t h e Bells Mesa Formation.
The d i s p a r i t y i n d i p i s very pronounced south
20, T. X., 3.
Yd.
west vhile the
Hells Nesa Formation only dips
of .Worth E d d y Peak i n sec.
vheretheupperSpearsFormationdips
as much a s 49'
lQo west (Fig, 4 ) . The
formations appoach structural conformity farther to the south as the
d i s p a r i t y i n d i p s becomes less.
Viewed m i c r o s c o p i c a l l y t h e q u a r t z l a t i t e
of t h e Hells Kesa For-
mation i s distinctly porphyritic, phenocrysts.making up
percent of therock(Fig.
q u a r t z , andminor
edges.
The c r y s t a l s r a n g e i n s i z e
show p a r t i a l refrom
3 m. t o
l e s s t h a n 0.1 nv. The groundmass h a s d e v i t r i f i e d t o m i c r o g r a n u l a r
c r i s t o b a l i t e ,g l a s s ,
50
13). Phenocrystsofsanidine,plagioclase,
hornblende are comnonly broken and
sorptionalong'their
from 20 t o
and feldspar.
e
Figure 13.
e
Fhotomicrograph of a quartz latite from the Hells Mesa
Formation.--Plagioclase ( P ) , sanidine (S), and quartz
(Q)crystals in fine-grained groundmass of cristobalite,
glass, and feldspar. Crossed nicols, X 3.
42
Sanidine i s t h e most abundant feldspar and.varies
30 percent of therock.
from 2
mm.
t o 0.1
The sanidine i s subhedralto'euhedral,varies
mm.
and averagesaround
m
l m
. in size.
t h e more intensely altered zones, sanidine
more r a r e l y by c h l o r i t e o r epidote.
Plagioclase phenocrysts
i s replaced by c a l c i t e , and
Nany of t h e g r a i n s appear t o have
been broken and partly resorbed during
emplacement of the ash flow sheet.
make upfrom
5 t o 20 percent of t h e
The plagioclase i s subhedral t oe u h e d r a l ,b u t
smaller in size than the sanidine, ranging
anaverage
of 0.8
mm.
1.5 .m.,
The plagioclase i s andesine, An3z t o An36.
.. ...
g e n e r a l l yn e a rf a u l t
i s slightly
from O , l . m m t o
g r a i n s show i n c i p i e n t t o a l m o s t t o t a l r e p l a c e m e n t
Calcite,chlorite,
The sanidine
shows c l a y o r h e m i t i t e a l t e r a t i o n . I n
generally i s f r e s h , b u t l o c a l l y
rock.
from 10 t o
o r epidotereplacement
with
The
by c l a y and s e r i c i t e .
of theplagioclaseoccurs
zones o r intrusive bodies.
The plagioclase pheno-
c r y s t s are a l s o broken o r r e s o r b e d , b u t n o t t o t h e
same degree as t h e
sanidine grains.
Quartz composes from
grains are as
5 t o 15 percentof
t h e rock.
much a s 3 m.. i n size averaging around
slightlygreaterthanthefeldspars.Quartz
breakage, as demonstrated
1.2
The rounded
mm,.
which i s
i s f r e s h and shows rare
by c a v i t i e s and h o l e s t h a t are f i l l e d w i t h
c r i s t o b a l i t e and glass.
The ferromagnesian minerals, represented
b i o t i t e , nevercomprise
finegrained
by hornblende and
more than 2 percent of the rock.
and subhedral.
The b i o t i t e i s
The hornblende i s euhedral and a s much a s
1m
m
, i nl e n g t h .A l t e r a t i o nt oc h l o r i t e ,m a g n e t i t e ,
and, l e s s commonly,
43
c a l c i t e i s present i n most grains.
The minor a c c e s s o r i e s a r e m a g n e t i t e ,
a p a t i t e , and zircon.
Lithic fragments i n t h e H e l l s f.!esa Formation a r e l i g h t brown
l e s s t h a n 4 cm. long. Alteration
pieces ofporphyry
chlorite, calcite
and clay give the fragments
i n t h e form of
a greenish color.
The groundmass, which i s g e n e r a l l y h i g h l y a r g i l l i z e d ,
of t h e
quartz latite i s cornonly devitrified to cristobalite
and f e l d s p a r .
Flow banding of the
i s only slightly
groundmass around the phenocrysts
developed and can only be observed microscopically.
i n the upper portion
Volcanoclastic sedimentary rocks interbedded
o f H e l l s Nesa Formation a r e r e s t r i c t e d t o w i t h i n a
and southeastof
X o r t h EaldyPeak.
rocks are approximately
t o the south.
'
%.5
mile area south
A t North k l d y Peak thesedimentary
..
30 f e e t t h i c k , and become p r o g r e s s i v e l y t h i n n e r
The b o u l d e r - s i z e c l a s t s a t
sizeclastsatthesouthern
NorthBaldy
limit ofexposure
Sixmile Canyon Andesite.
insec.
Peak grade t o sand-
31, T . 3 S . , R.
The Sixmile Canyon a n d e s i t e i s a t h i c k
sequenceofblue-gray,amygdaloidal,porphyriticandesiteflows
.
local,interbeddedsedimentaryrocksnearthebase.
a n d e s i t e i s the equivalent
i t e flows.
3:d.
with
The Sixmile Canyon
of Brown's (1972, p. 46-47) porphyritic andes-
The plagioclasephenocrystsaverage
i s slight'ly smaller than the average
0.8
m
m
. i n length,which
of the plagioclase phenocrysts
t h e middleSpearsFornation.Volcanoclasticconglomerate
in
and mud f l o w
breccia at the base
of the Sixmile Canyon a n d e s i t e a r e a h e t e r o l i t h i c
composite of quartz
l a t i t e , I a t i t e and andesite fragments w i t h no obvious
sorting or bedding.
Buck Peak.
They a r e exposed o n l y i n South Canyon northwest of
44
An i s o l a t e d o u t c r o p of finely laminated limestone
e a s t of Timber Peak i n sec. 9, T . 4S.,
R.
3W.
i s exposed
The stratigraphic
p o s i t i o n of the limestone i s d i f f i c u l t t o d e t e r m i n e b e c a u s e
it appears to be interbedded with the andesites.
and plant coverage, but
The limestone outcrop
and i s notexposed
i s small, covers an area
of 50 f e e t by
anywhere e l s e i n thestudyarea.
the limestone contains laminae
0.1
of t h e t a l u s
mm.
15 f e e t ,
I n t h i n section,
of subround q u a r t z g r a i n s l e s s t h a n
inlengthinterbedded
w i t h micritic limestone.
No f o s s i l s o r
organic material are present.
A t h i n s e c t i o n of typical andesite reveals phenocrysts
g i o c l a s e composing a s much a s 60 percent of the rock,
felty, fine-grained matrix
eneandmagnetite(Fig.
l a b r a d o r i t e (An57),which
0.8
embedded i n a
of plagioclase w .i t h 1.esser amounts of pyrox’:
i
14). The euhedralplagioclasephenocrystsare
a r e as much as 3 mm. i n length hut average
mm. The g r a i n s haveundergone
calcite.
alterationtoclay,sericite,
The pyroxene i s as much a s 2 mm. i n size,averaging
and i s a l t e r e d t o m a g n e t i t e , c h l o r i t e ,
Sawmill Canyon Formation.
multiple flow,
of pla-
and
0.5 mm.,
and c a l c i t e .
The Sawmill Canyon formation i s a
compound c o o l i n g u n i t c o n s i s t i n g
of crystal-poor,
r h y o l i t i c a s h flow t u f f s interbedded w i t h . andesite flows and a k a s a l
volcanoclasticsandstone.
The unit, crops out i n a discontinuousband
on the western and southern flanks
of t h e study area fromwest
o f Rorth
E d d y Peak. s o u t h t o Sawmill Canyon and e a s t t o S i x m i l e Canyon (Fig. 4).
It o v e r l i e s t h e €!ells Mesa Formation t o t h e n o r t h and the Sixmile Canyon
ande;-.;.-Let o t h e s o u t h .
The Sawmill Canyon formation is l i t h o l o g i c a l l y
45
Figure 14. Photomicrograph of an andesite from the Sixniile Canyon
andesite.--Plagioclase (P) crystals in a fine-grained
groundrnass of feldspar, magnetite and pyroxene.
Crossed nicols, X 3.
.46
similar to the tuffs
of Eezr Springs and the
thesouthern,EearKountains
Dealand
(Erown, 1972, p. 31-49).
Rhodes ( i n p r e s s ) d e s c r i b e
Mountains t h a t t h e y c o n s i d e r t o
NagdalenaMountains
a 2100 f o o t t h i c k s e c t i o n
A . L. Peak area of the northern
of rhyolitic ash flows in the
t h e A . L. Peak Formation.
t u f f of Allen ' d e l l i n
be the source area for
a t l e a s t p a r t of
The Sawmill Canyon formation i n t h e c e n t r a l
i s a sequence of gray, crystal-poor ash flow
that are 1ithologically.and stratigraphically similar to the
i n t h e SanKateoMountains.Exposures
Formationexposed
San >!ate0
A. L. Peak
f r o m the San
Nateo Mountains t o t h e KagdalenaMountains are not continuous
. Late Cenozoic block faulting,
tuffs
due t o
downdropping the Nulligan Gulch a r e a ( F i g .
2), and subsequent cover of the volcanic rocks by Quaternary sediments.
Fission track dates
the
A. L. Peak Formationfrom t h e San Mateo Nountains a t 31.8
age of the
may.
i n press) place
from sphenes (Smith and .others,
* 1.7
m.y.
Age d a t i n g of t h e Sawmill Canyon formationfrom t h e
Nagdalena Mountains will be necessary i n order t o d e f i n i t e l y c o r r e l a t e
with the
A. L.
Peak Formationofthe
San KateoKountains.Therefore,
t h e Sawmill Canyon formation i n t h e c e n t r a l Kagdalena Mountains i s
tentatively correlated with the
A. L. Peak Formation of
the San Kateo
Hountains until their equivalency can be established,
The Sawmill Canyon formation i s poorly exposed i n t h e c e n t r a l
Hagdalena Kountains w i t h -the best outcrops occurring
on t h e r i d g e be-
tween Eop Canyon and Patterson Canyon, west of North Baldy Peak i n sec.
18, T.
x., 13.
3W.
The thickness of t h e Sawmill Canyon formation i n t h e
c e n t r a l Kagdalena Range i s from 800 t o 1200 f e e t .
.
The u n i t t h i c k e n s
47
considerably i n Sawmill Canyon and a t t h e head of Ryan I I i l l Canyon,
south of the study area.
The Sawmill Canyon .formation west of Horth Ealdy Peak
i n sec.
,C."1
18, T.
p.,R. T!.
{li, scLim'i*iary
contains 125 f e e t of dark-gray volcania rocks that
A
were a t l e a s t p a r t l y d e r i v e d from the underlying Eells
The sand-size fragments of quartz, lithic fragments,
Kesa Formation.
and f e l d s p a r are
w e l l bedded and show cross-beddingandgradedbedding.Kinorchanneling
into the Bells
Mesa Formationsuggests
a fluvial origin.
In Simile
3 ) . similar sedimentary rocks are also
Canyon west of Buck Peak (Fig.
a t the base of t h e Sawmill Canyon formation overlying the Sinnnile
andesite.
The sandstonecontainsquartz,feldspar,
Canyon
and a v a r i e t y of
l i t h i c fragments embedded i n a fine-grain, iron-stained, quartz-rich
.. ..^
matrix.
Fine-grained andesite flows,
volcanoclasticrocks
i n sec. 18, T.
50 f e e t t h i c k , o v e r l i e t h e
x.,
R. 3 1 .
Samples o ft h ea n d e s i t e
much a s 1 cm. i n l e n g t h i n
flows contain phenocrysts of plagioclase as
a matrixoffine-grainedplagioclase,pyroxene,andmagnetite.
s i l i c a v e i n l e t s c u t the andesite.
The andesite flow
crystal-poor, quartz-poor, highly foliated
500 f e e t t h i c k .
The ashflow
welded with flattened
p a t t e r n (Fi::;.
15).
i s o v e r l a i n by a
ash f l o w t h a t
i s 200 t o
i s gray and i s moderately t o densely
pumice t h a t g i v e s t h e r o c k
T o t a lc r y s t a lc o n t e n t
The rockweathersto
gruss.
The
2 mnx+ i n l e n g t h w i t h minor
amounts of quartzorplagioclase.Lineationdue
pumice o r flaw f o l d s around phenocrysts
a strong foliation
i s less than 10 percent,
phenocrysts are euhedral sanidine less than
developed.
Minor
totheelongationof
o r pmice fragments
i s well
48
Figure 15. Photomicrograph of a rhyolite from the Sawmill Canyon
formation.--Sanidine (S) crystals in a fine-grained,
highly foliated groundmass. Crossed nicols, X 3.
e
e
.
.
49
A dark-gray, fine-grained to prophyritic andesite flow unit,
400 t o 600 f e e t t h i c k , o v e r l i e s t h e
ash flows,
The a p h a n i t i c f l o w s a r e
compact with an abundance of small, red hematitizgd phenocrysts of
pyroxene.
The porp!yr%ticflows
a r e v e s i c u l a r and contain up t o
cent plagioclase phenocrysts as long
ES
50 per-
mm. The uppermost a s h f l o x
3
u n i t of the Sawmill Canyon Formation i s a f o l i a t e d r h y o l i t e c o n t a i n i n g
as much a s
15 p e r c e n t c r y s t a l s of quartz, sanidine, plagioclase and
biotite. Limited exposures
and weatheringof
t h e ash flow t o n e a r l y
v e r t i c a l c l i f f s make a n y d e t a i l e d s t u d y d i f f i c u l t .
~
South
Peak Andesite.
The SouthEaldy
Peak z n d e s i t e con-
I
_
”
sists predominately of vesicular, fine-grained andesite flows,
interboddedashflows
and epiclastic sediments.
..
SouthEaldyPeak,thehighest
andminor
The u n i t crops out
at
.
peak i n t h e ihgdalena Range.
The expo-
sures a r e r e s t r i c t e d t o t h e s o u t h w e s t e r n p o r t i o n o f t h e s t u d y a r e a . i n
Sawmill Canyon, where talus slopes and complex f a u l t i n g make any i n t e r p r e t a t i o n of t h e s t r a t i g r a p h y d i f f i c u l t .
The thicknessoftheSouth
Baldy Peak a d e s i t e may be a m a x i m u m of1500
however, could represent
This thickness,
a n exaggerated thickness because
f a u l t i n g i n t h e Sawmill Canyon area.
SouthEaldy
feet.
Peak andesite can
The s t r a t i g r a p h i c p o s i t i o n o f t h e
beseensouthof
Langmuir Laboratory, a t
which place it o v e r l i e s t h e SawmillCawonformation.
limit of exposure
i n Baldy Canyon the andesite flows
w i t h t h e Hells Xesa Formation.
of normal
A t t h e northern
are i n f a u l t c o n t a c t
The Timber Peak r h y o l i t e o v e r l i e s t h e
South Baldy Peak andesite.
The aphanitic, dark-gray andesite flows are best exposed
S o u t h E d d y Peak and on the slopes west of
Timber Peak.
at
The a n d e s i t e s
.,
Figure 16.
...
Photomicrograph of an andesite from the'south Baldy Peak
andesite.--Fine-grained plagioclase, pyroxene, and magnetite
and calcite-filled (C) vesicle. Crossed nicols, X 3.
52
Timber ”
Peak Rh.youngest volcanic rock
The Timber Peak r h y o l i t e
i n t h e c e n t r a l Hagdalena Xange, and forms
Q
c r e s c e n t shaped outcrop
1 mile west of North Ealdy Peak, south
pattern beginning at the ridge
t o Langrr;uir L a b o r a t o r y , e a s t t o
Timbel. Peak and Euck Peak, and north
Kater Canyon Xesa (Fig. 4, i n pocket).
-andesitetothesouthat
the
It caps the highest. elevations
i n t h e study area.
Canyon formation t o t h e n o r t h
represents
to
The unit overlies the Sawmill
i n Iiop Canyon and the South Baldy Peak
Langmuir Laboratory.
The PopotosaFormation
unconformably o v e r l i e s t h e Timber Peak r h y o l i t e a t Water Canyon Kesa
and near Langmuir Laboratory.
The Timber Peak r h y o l i t e i s t e n t a t i v e l y c o r r e l a t e d w i t h t h e
Potato Canyon Formation exposed
i n t h e San Mateo Hountains (Deal and
Rhodes, i n p r e s s ) based on l i t h o l o g i c s i m i l a r i t y
position.
Late Cenozoic block faulting
and s t r a t i g r a p h i c
and cover by Quaternary sedi-
ments prevent direct correlation by continuous outcrops between the
San Mateo Range and t h e MagdalenaMountains.
* 1.6
m.y.
An a g e d a t e of
30.3 m.y.
by f i s s i o n t r a c k from sphenes h a s been obtained from the
Potato Canyon Formation i n t h e San Nateo I.!ountains (Deal a n d Rhodes,
in press), but
no dating has been
done on t h e Timber Peak r h y o l i t e i n
t h e Magdalena Mountains.
The Timber Peak r.hyolite i n t h e c e n t r a l Magdalena Mountai’ns i s
a multiple flow sequenceofcompactlywelded
rhyolitic ash flows.
rock i s characterized by i t s grayish-red-purple color,
sanidine,bronze-coloredbiotite,
and f o l i a t i o n .
The
”moonstone”
The f o l i a t i o n i s t h e
r e s u l t of bands of light-colored, coarse-grained mixtures of cristob a l i t e and feldspar surrounded
by finer-grained, reddish-purple layers
e
53
ofgl !ass.
The form;t t i.on v a r i e s from a cry$;tal-poor t o crjrs, t a l --1-ich t u f f
with quartz, sanidine,
and b i o t i t e b e i n g t h e
most common phenocrysts.
tuff a t the
Fine-grained andesite flows locally interfinger with the
northwest limit of exposureof
.
3N., R.
3W.
t h e Timber Peak lthyolite i n sec. 18, T.
of t h e Timber Peak r h y o l i t e i n t h e
The t o t a l t h i c k n e s s
c e n t r a l Iiagdalena14ountains
i s as much as 650 f e e t and may be consider,
a b"_l y t h.~i c k e r i n t h e .Xater-.Ca.nyon
- ~.~Kesa area. .
Viewed microscopically, the
."
I
,
Timber Peak r h y o l i t e i s composed
p r i n a r i l y o f a c r i s t o b a l i t e and sanidine matrix ar,d 20 t o 40 percent
phenocrysts(Fig.
17).
Sanidine and q u a r t za r et h e
and compose a s much as
dominant c r y s t a l s
38 percent of t h e r o c k w i t h b i o t i t e
plagioclase making up theremainder
of thephenocrysts.
range i n s i z e from l e s s t h a n 0.1
mm.
mately 0.e m.
subroundedandbroken.
b a l i t e and f e l d s p a r .
L i t h i cf r a g -
of rocks composed of intergrowths of cristo-
Some of t h e s a n i d i n e e x h i b i t s
a n d l o c a l l y forms spherulites. Inclusions of South
are present locally near
The phenocrysts
t o le>''&.
and average'approxi-
The c r y s t a l s a r e
ments a r e r a r e , b u t c o n s i s t
and t r a c e s of
a perthitic texture
Baldy Peak a n d e s i t e
t i e base of t h e u n i t . E i o t i t e
s t a g e s of a l t e r a t i o n t o m a g n e t i t e .
but locally are altered to clay
banding i s displayed by the
is in various
The f e l d s p a r s as a whole a r e f r e s h ,
and minor s e r i c i t e . E x c e l l e n t f l o w
bands of hematized glassy zones alternating
with light colored, coarser-grained zones
of c r i s t o b a l i t e and f e l d s p a r .
T e r t i a r y I n t r u s i v e Rocks
The o l d e s t T e r t i a r y i n t r u s i v e r o c k
i s a volcanic neck, which
intrud:.+d t h e Hells Nesa FormationduringOligocene
time.
Followingthe.
Figure 17. Fhotonicrograph of a rhyolite from the Timber Peak
rhyolite.--Individual flow bandsconsisting mainly of
sanidine (S) and quartz (Q)are distinguished by the
presence or absence of hematized groundmass. Crossed
nicols,
3.
'
x
55
u n i t i n the
emplacement of the Timber Peak rhyolite, the youngest
D a t i l Group, the Kagdalena a r e a underwent a period, of extensional faulting along a 1:orth-northwesttrendingstructural
intruded the north-northwest-trending fault
zone.
Stocks and d i k e s
zone during Late Oligocene
i n t h e c e n t r a l Nagdalena Kountains a s w e l l as i n t h e Kagdalena mining
district.
The s t o c k s a r e monzonite t o g r a n i t e i n composition and have
from 28 t o 30.5 m.y. i n age (Weber, 1971).
beendatedasrar.ging
which i n order of
dike rocks can be classified into three major types,
1) mafic 2)
decreasingageare$
rhyolite.
latite-monzonite,
The aplite dikes reported by Loughlin and
p. 40) i n t h e Nagdalena mining
The
and
3) w h i t e
Koschmann (1942,
d i s t r i c t were not found i n t h e c e n t r a l
Magdalena ?,fountains.
i n t h e Magdalena
Dikes are spatially associated with..stocks
Hountains.
The mafic dikes
i n t h e Xagdalenamining
d i s t r i c t a r e con-
c e n t r a t e d w i t h i n 1 mile of t h e exposed stocks (Chapin, personal cornunication).
The latite-monzonitedikes/stockassociation
i s best
i l l u s t r a t e d i n t h e c e n t r a l Hagdalena Hountains where t h e d i k e s a r e
abundant adjacent to the
$!aterCanyon
dikes are restricted to the
stock (Fig. 4). !.kite rhyolite
Nitt and Anchor Canyon stocks i n t h e
Nagdalena mining d i s t r i c t (Loughlin and Koschmann, 1942, P l a t e
d i e o u t beyond the southern
.Volcanic Keck.
”
neckcropsout
i n sec.
limits of t h e exposed stocks.
A topographically prominent rhyolitic volcanic
33, T. 3N., X. 3V. (Fig.4).
i n t r u d e s and extends 90 f e e t above t h e exposed surface
Mesa Formation.
21, and
The volcanicneck
of t h e f i e l l s
The r h y o l i t e i s cornposed ofquartzphenocrysts
fine-grained,highlyfoliatedmatrix.Excellent
in a
columnar j o i n t i n g i s
56
exhibited by the volcanic neckand
outward-dipping a t t i t u d e s of t h e
foliation are present near the base changing to 'nearly vertical dips
The neck i s c r u d e l y c y l i n d r i c a l and has a maximum diameter
a t t h e top.
of 900 f e e t .
KO
radialdikesareassociatedwiththevolcanic
An age of Kiddle Oligocene
neck.
o r younger i s suggested by cross-
in
c u t t i n g r e l a t i o n s h i p s and possible Hells Kesa Formation inclusions
the volcanic
present.
neck.Gray
t o black, fine-grained volcanic fragments are
as 3 em.,
The volcanicfragmentsareaslong
a r e most common near the base
wards the top.
of the volcanic neck,
The alignmentofthe
the rock w i t h a flow structure.
The i n t r u d e d H e l l s KesaFormation
e f f e c t s were noticed surrounding the
Fine-grained
"
Mountainswere
becoming r a r e t o -
more elongatefragmentsprovides
shows very l i t t l e d i s r u p t i o n , d i s t o r t i o n
Hafic Dikes.
subrounded,and
or compaction.
No thermal
..
neck.
dikes
i n the
mafic
intruded along a north-northwest-trending
c e n t r aMagdalena
l
f a u l t zone
before and a f t e r t h e emplacement of theLateOligocenestocks.
mafic dikes are equivalent
t h e Kagdalenamining
The
i n conposition to.the lamprophyre dikes in
d i s t r i c t (Loughlinand
Koschmann, 1942, p. 43).
where t h e d i k e s a r e most abundant within and near exposed stocks.
The mafic dikes are
exposedstocks
most common within a 1 m i l e r a d i u s of t h e
i n t h e Nagdalenamining
district.
The a r e a o f
abundant mafic'dikes i n t h e c e n t r a l HagdalenaMountains
T.
x.,X.
7~'.(Fig. 4) on t h en o r t hs i d e
is also the area
ofNorthFork
of the greatest concentration
and w h i t e r h y o l i t e d i k e s .
most
i s i n sec. 21,
Canyon.
This
of latite-monzonite dikes
57
i n widthfrom
The mafic dikes range
a l l y l e s s t h a n 200 f e e t l o n g ,
from K e '5
E. t o
If.45'
The average trend
the dips are
1.1.:
2 t o 20 f e e t and a r e gener-
from 70'
Topographically, the dikes are depressed slightly
i s N.. 10'
1.f. b u t v a r i e s
east to vertical.
owing t o t h e i r more
rapid weathering relative to the surrounding country rock.
The w a l l
rocks adjacent to the dikes are characteristically bleached
and a r a
r a r e l ys i l i c i f i e d .G o e t h i t es t a i n i n g
t h e mafic dikes, e4tending locally
common occurrence, particularly
I n handspecimen,
and g o e t h i t e - c a l c i t e v e i n l e t s
in
some 30 f e e t i n t o w a l l r o c k s , a r e
i n t h e NorthFork
a
Canyon area.
t h e mafic dike rocks are dark 'green, fine
grained, rarely porphyritic,
and c o n t a i n a s much as 10 percent magnetite.
The oxidation of t h e m a g n e t i t e t o g o e t h i t e
h a s r e s u l t e d i n a r u s t y brown
i n the
s t a i n on theweatheredsurfaces.Plagioclasegrainsarepresent
s l i g h t l y c o a r s e r samples.
The porphyriticvarietiescontainphenocrysts
c o n s i s t i n g of plagioclase, pyroxene,hornblende,and
b i o t i t e .Q u a r t z
i s present i
n some dikes.
Viewed microscopically, t h e groundmass consists predominately
of f e l t y p l a g i o c l a s e m i c r o l i t e s w i t h i n t e r s t i t i a l m a g n e t i t e ,
and a p a t i t e ( F i g . 1 8 ) .
'
Alteration of the plagioclase to clay
pyroxene t o c a l c i t e and c h l o r i t e i s common.
as
3
m
m
. i n length and euhedral.
toclay,sericite,
pyToxene,
and c a l c i t e .
and t h e
The phenocrysts are as
much
The labradorite phenocrysts are altered
The ferromagnesianphenocrystsare
totally to partially replaced by calcite, chlorite,
o r magnetite.
Zatite-MonzoniteDikes.Porphyriticlatite-monzonitedikesare
the next youngest
i n t h e c e n t r a l Magdalena Mountains and
d i k e s a t a number of l o c a l i t i e s i n KorthFork
Canyon.
cut the mafic
The
Figure 18.
Fhotonicrograph of a maficdike of and.esiticconposition.-Plagioclase (?) c r y s t a l s w i t h l e s s e r amounts of pyroxene
andmagnetite i n a fine-grained matrix. Crossed nicols,
x 3.
59
w i t h t h e !.later Canyon
latite-monzonite dikes are spatially associated
stock, becoming l e s s abundant with increased distance from.the stock
(Fig. 4 ) . The latite-monzonite dikes crop
o u t from
3 miles southof
t h e Water Canyon s t o c k i n Copper Canyon and ?plater Canyon t o 2.5 miles
north of the stock
i n Garcia Canyon ard Jordan Canyon.
The d i k e s are
exposed 2 miles west of t h e ',later Canyon stock, which i s bordered on
t h e east by t h e I+.
zone.
35' \,I.-trending f a u l t zoneand t h e Water Canyon fault
Latite-monzonite dikes as well.as white rhyolite and mafic dikes
are p r e s e n t i n t h e n o r t h e a s t p o r t i o n of t h e Magdalena Xountains.
The latite-monzonite dikes intrude the Late Oligocene northnorthwest-trending fault
ously.for over
dipping 70'
zoneand
1 mile i n NorthFork
east t o vertical.
25 t o 75 f e e t .
some of t h e d i k e s c r o p o u t c o n t i n u Canyon.
The d i k e s a r e s i n u o u s ,
The thickness.of
t h e d i k e s varies from
The outcrop breadth of sone of the dikes adjacent
Water Canyon stock i s g r e a t e r t h a n 75 f e e t .
.dikes stand out in
t o the
Elany of t h e l a t i t e - m o n z o n i t e
r e l i e f b y . a s much as 30 f e e t above the surrounding
countryrock,especially
i n b!orth Fork Canyon.
Silicification,
a r g i l l i z a t i o n , and l i m o n i t e s t a i n i n g of t h e i n t r u d e d c o u n t r y r o c k a r e
sporadic and l i m i t e d t o a few f e e t from the dike.
A large isolated latite-monzonite dike crops out
west portion of the study
area i n sec. 18, T. 3 . . R. 3!J.
Patterson Canyon and continues N. 10'
Nagdalenamirdng d i s t r i c t .
s i l l byLoughlinand
i n t h e north-
a t t h e head of
E. t o Chihuahua Gulch i n t h e
The i n t r u s i o n was o r i g i n a l l y mappea as a
Koschmann(19'42).However,
trusion crcss-cuts both the Spears Formation
t h e n e a r l y vertical i n and the Paleozoic
e
60
sedimentary rocks substantiate
and t h e r e f o r e must be considered
a dike.
a
The dike i s a s wide a s 300 ' f e e t and. i s truncated on the south by
north-trending Late Cenozoic fault.
Hand specimens of the latite-monzonite dikes
by their grayish-green color weathering
crysts of f e l d s p a r commonly over 10
are c h a r a c t e r i z e d
t o a yellow brown: by pheno-
mm.i n length; by c h l o r i t i z e d
b i o t i t e and hornblende; by rounded, glassy, quartz grains: and by
fine-to-medium-grainedmatrix.
The rockweathers
to spheroidal forms,
d i f f e r e n t from the blocky character of the weathered
d i k e s .Q u a r t z
andcomposes
a
white rhyolite
i s p r e s e n t i n t e r s t i t i a l l y and a s subround d i s c r e t e g r a i n s
as much a s
5
Some orthoclase i s
percentoftherock.
graphically intergrown with the quartz. Xagnetite
,
t o limonite and gives the rock
i s commonly oxidized
...
a yellow-brown color.
I n t h i n section, the texture of the latite-monzonite dikes
is
p o r p h y r i t i c , w i t h a groundmass t h a t v a r i e s from f e l t y i n t h e l a t i t i c
types to a finephaneriticinthemonzonitictypes(Fig.
19).
The
o r clinopyroxene composing as
phenocrysts are orthoclase, plagioclase,
much as 20 percent of the rock. Orthoclase crystals are as long
30
mm,. subhedral,
and commonlyshow
their boundaries. Alteration
norrcalzoningand
resorption along
of t h e o r t h o c l a s e i n c l u d e s b o t h c l a y
and
i n t h e plagioclase grains.
s e r i c i t e , and i s generally not as intense as
The andesine phenocrysts are
as
as much a s 4 mm..in length, euhedral,
show strong alterZi;',.on t o c l a y , s e r i c i t e ,
and c a l c i t e . . A u g i t e ,
and
which
occurs i n t h e l a t i t i c v a r i e t i e s b o t h as phenocrysts and as a'component
of t h e groundmass, i s a s much a s
a l t e r e dt oc a l c i ~ t e ,c h l o r i t e ,
3
mm. i n length and g e n e r a l l y h i g h l y
and magnetite.
The f e l d s p a r s compose
61
Figure 19.
Photomicrograph of a latite-monzonite dike of monzonitic
composition.--Crthoclase (0), plagioclase (P), and
quartz (Q) in a chloritized groundmass. Crossed nicols,
x
3-
62
approximately 80 percent of t h e r o c k w i t h p l a g i o c l a s e i n e x c e s s
potashfeldspar.Eiotite',
which a l t e r s t o c h l o r i t e
t h e dominant ferromagnesian mineral
up t o
of
andmagnetite,
is
i n t h e monzonitic varieties making
1-5 percentoftherock.Accessorymineralsincludezircon,
a p a t i t e and euhedral sphene
as l o n g a s 2 mm.
Wh5,te Rhyolite bikes.
Vhite
rhyolite
i n t r u s i o n s i n t h e c e n t r a l Magdalena Eountains.
latite-monzonite dikes as well as the
dikes
are
the
youngest
They cut the mafic and
Water Canyon stock.The
white
rhyolite dikes also intrude the Late Oligocene, north-northwest-trending
f a u l t zone, l o c a l l y u s i n g t h e
monzonite dikes.
same conduits as the mafic
The white rhyoklte dikes
fiagdalena mining d i s t r i c t (Loughlinand
they occupy the roof zones
have been described i n t h e
Koschmann, 1942, p.
of t h e exposed'stocks.
i n t h e c e n t r a l Eagdalena Kountains
or latite-
43-a) where
T h e d i k e s are common
where t h e y a r e l o c a l i z e d p r i m a r i l y
faults, and t h e N. EOo bJ.-trending
along north-northwest-trending
Fork Canyon f a u l t zone (Fig: 4)
I
Worth
The w h i t e r h y o l i t e d i k e s e x h i b i t ,
as
well, a northeast-trending zone beginning north of South EaPdy Peak and
e x t e n d i n g t o t h e k!aterCanyon
stock as defined by
a number of s h o r t ,
sinuous.north-trendingdikes.
The most pro1ific.whit.e rhyolite diking
i n t h e c e n t r a l Eiagdalena
Mountains i s i n Eorth Fork Canyon; p a r t i c u l a r l y i n secs. 21 and 28, T.
3 S . , H. 3.'. (Fig.4).
I n North Fork Canyon, t h ew h i t er h y o l i t ei n t r u s i o n s
have penetrated parallel to the bedding
c i r c u l a rp l u g s .P a r a l l e ld i k e
f r o n h'orth Ealdy
of t h e s t r a t a or c r o p o u t a s
Swarms a r e exposedalmostcontinuously
Peak t o t h e southern limit of mapping a t t h e head of
Ryan Hill Canyon, a d i s t a n c e of 6 miles.
North of the study area
i n the
63
Nagdalena m i n i n g d i s t r i c t , t h e w h i t e r h y o l i t e d i k e s a r e
north-northwest-trending dikes
northern part
rare, b u t t h r e e
have penetrated t h e exposed stocks'in t h e
of t h e d i s t r i c t .
10
The white rhyollte dikes range from
t o 200 f e e t i n width and commonly stand out as "Chinese wall", topographicfeaturesrisipgas
much a s
sistance to erosion generally
of the white rhyolite dikes
Fork Canyon f a u l t zonewhich
75 f e e t above t h e t e r r a i n .
The r e -
i s t h e r e s u l t of t h e h i g h s i l i c a c o n t e n t
such a s t h e d i k e
which intruded the Korth
contains 76 p e r c e n t s i l i c a .
The w h i t e r h y o l i t e d i k e s a r e d i s t i n g u i s h e d i n t h e f i e l d
grayish-whitecolor:
texture (Pig.
by a compact, fine-grained, locally flow
2 0 ) ; by round quartz
by t h e i r
banded
g r a i n s ; and by feldspar phenocrysts.
m i t e i s present, commonly a s much a s 0.3 percent.Weatheringofthe
..
p y r i t e produces limonite psuedomorphsand
rock.Phenocrystsofquartz
a yellow-brown s t a i n on t h e
and f e l d s p a r , up t o 2 cnt. long, make up
a s much a s 20 percent of the white rhyolite dikes.
I n thin section, the white rhyolite dikes
porphyritic to glomeroporphyritic texture
groundmass (Fig. 21).
i n a compact,microgranular
The phenocrystsaregenerallyorthoclaseand
q u a r t z and compose 10 t o 20 percentoftherock.
hedral to euhedral,
have a d i s t i n c t i v e
as much a s
moderate a l t e r a t i o n t o c l a y
quartzarecomon.Quartz
shows minor resorption along
The orthoclase i s sub-
1.5 mm. i n length, and shorn weak t o
and sericite. Graphic intergrowths with
i s subround, a s much as 2 mm. i n l e n g t h , a n d
i t s edges.
Minor subhed.ra1 t o e u h e d r a l
plagioclase of An8 t o An12 composition also forms phenocrysts
as 1 mm.
The plagioclase i s a l t e r e d t o c l a y
and s e r i c i t e .
as l a r g e
The
Figure 20.
Highlyflowbandedwhiterhyolitedikeexposed
21, T. 3S.S R. 3We
i n sec.
.. ,..
Figure 21.
Photomicrograph of awhiterhyolitedike.--Orthoclase
(0)
and quartz (a) phenocrysts i n a fine-grained groundmass.
Crossednicols, X 3.
66
groundmass i s a fine-grained mixture of qu.artz
highly sericitized. Silicification
and f e l d s p a r and i s
i s a l s o a common a l t e r a t i o n e f f e c t .
Eydrothermal alteration and mineralization, which followed the
emplacement of t h e w h i t e r h y o l i t e d i k e s , a r e s p a t i a l l y r e l a t e d t o t h e
i n t r u s i o n s .A l t e r a t i o ni n c l u d e st h es i l i c i f i c a t i o n
s i l i c a t i o n of the adjacent country rock,
truded rocks
and on the walls
of t h e s t u d y a r e a . S i l i c a t i o n
i n the Kelly Limestone adjacent
and lead-zinc-copper mineralization
bearing pyrite occurs
and mineralization i n t h e i n -
of t h e d i k e s . S i l i c i f i c a t i o n o f t h e d i k e s
primarily i s seen i n t h e n o r t h e r n p a r t
a white rhyolite dike occurs
of t h e d i k e s ,
i n t h e NorthBaldy
Peak area.
Gold i n gold-
on t h e w a l l s of t h e w h i t e r h y o l i t e d i k e s a t t h e
d i v i d e batween Kill Canyon andCopper
Canyon.
The presence of w h i t e
rhyolite dikes in mineralized areas has previously been reported
Loughlin and
to
by
Koschmann (1942) i n t h e Magdalena mining d i s t r i c t and by
T i t l e y (1958) i n the Linchburg mine.
Water Canyon Stock.
north side
of t h e mouth ofWater
Baldy Peak i n secs. 14,
The stock i s exposeddue
M.
Canyon, 2.5 t o 3 miles east ofIJorth
15, 22,and23,
dimensions of t h e s t o c k a r e
N e 35'
The Water Canyon stock i s l o c a t e d on t h e
T. 3 S , , K.
3700 feet east-west
t o Late Cenozoic block
m a r g i n a l f a u l t zoneand
the
An age date obtained
New NexicoEureau
The
by 3000 feet north-south.
f a u l t i n g along the
0
N. 25 E. Water Canyon f a u l t zone.
K a l i s h (1953, p. 8) considered the stock to be
s i m i l a r t o t h e basement rocks exposed
yhf. (Fig. 4).
a Precambrian granite
i n t h e Magdalena mining d i s t r i c t .
by the author and Charles Chapin of t h e
of Hines supports a Late Oligocene age
The K-Ar d a t e was obtained from biotite
for the stock.
i n a sample taken fron t h e
.:
67
c e n t e r of t h e Water Canyon stock.
The date of
+- 1.2
30.5 m.y.
m.y.
corresponds closely with t h e d a t e s on t h e exposed s t o c k s i n t h e
Kagdalenamining
d i s t r i c t and suggests a major episode
t r u s i o n from 28.0 t o 30.5 m.y.
of stock in-
affecting the central and northern
Kagdalena Rountains.
a Late 3ligocene age for the
Field data supporting
s t o c k a r e as follows.
Water Canyon
Ejitt
The stock i s compositionally similar to the
and Anchor Canyon stocks i n t h e Kagdalena mining d i s t r i c t , whichhave
been dated
1963).
a t 28.0 and 28.3 m.y.,
r e s p e c t i v e l y (Weber and Bassett,
The stockdoesnotintrudePaleozoicsedimentaryrocks
or t h e
which are compo-
Oligocene volcanic rocks, but latite-monzonite dikes,
s i t i o n a l l y similm and g e n e t i c a l l y r e l a t e d t o t h e Vater Canyon stock,
.. ...
penetratetheentirestratigraphicsection.
zone, which i s EarlyOligocene
Canyon stock.Furthermore,
The BorthFork
Canyon f a u l t
i n age, h a s beentruncatedbythe
t h e graytobuffcolor
V!ater
and t h e rounded-
terrain of t h e Vyater Canyon stock i s i n c o n t r a s t t o t h e pink t o r e d
c o l o r and angular terrain
of the Frecambrian granite.
B mafic dike cuts the Yater
the grayish-green type
The maficdike
is
commonly found i n the centraltlagdalena Eountains.
The feley groundnass as well
as t h e few phenocrysts of plagioclase have
beenalteredtocarbonate,chlorite,
also has intruded the
Canyon stock.
or epidote.
A whiterhyolitedike
Water Canyon stock.
There i s no a p p a r e n t a l t e r a t i o n of the Precambrian country rock
surrounding the stock, possibly reflecting the unreactive nature
argillite.
The onlymineralizationpresent
s i l i c i f i e d zone t h a t c u t s t h e s t o c k
of t h e
0
i s along a N . 40 !$“.-trending
w i t h minor lead, zinc and copper.
.
68
There i s )Tb n o r m i n e r a l i z a t i o n i n the Kelly Limestone adjacent
t c .he
Water Canyon stock,
The \later Canyon stock i s a fresh, coarse-grained,
q u a r t z monzonite porphyry
systam.Epidote
huff t o pink
w i t h a well-developed north-trending joint
commonly i s developedalong
these j o i n t surfaces.
Numerous i n c l u s i o n s of Precambrian a r g i l l i t e are i n t h e s t o c k , p a r t i c u l a r l ya l o n gt h ec o n t a c t .
The stock is f i n e - g r a i n e da d j a c e n tt ot h e
'
Precambriancontact.Kicroscopically,thequartzmonzoniteconsists
(Anz5 t o An
p r i m a r i l y of orthoclase,plagioclase
33
) and quartz.
Horn-
blende and
b i o t i t e a r e t h e common ferromagnesian minerals with minor
pyroxene.
The rockhas
orthoclaseaslong
a porphyritic texture with phenocrysts
as 5 cm.
of
The orthoclase shows zoningandonlyminor
..
a l t e r a t i o n t o s e r i c i t e o r .carbonate.
Buried Stocks. Field evidence suggests the presence ofburied
"
stocks underlying t h e Linchburg-NorthBaldy
Canyon a r e a i n s e c s .
and evidence
21 and 28, T. 3S., R.
i s presented supporting
Peak area and t h e North Fork
3kr.
Each area i s discussed
t h e a s s e r t i o n o f t h e presence of t h e
buried stocks.
The presence of
a buried stock underlying the Linchburg
a r e a i n the southern portion
of t h e Magdalena mining d i s t r i c t h a s b e e n
and Koschmann (1942, p. 32, 48, 105)
previouslypredicted.Loughlin
noted the extensive silicification
limestone along fault zones
of Frecambrian a r g i l l i t e and Paleozoic
and the high temperature mineral assemblage
i n t h e Linchburg mine as suggestive of a stock underlying
Austin(1960,p,16)considered
mine
t h e area.
t h e abundance of s c h e e l i t e i n t h e v i c i n -
i t y of t h e Linchburg mine along the north-northwest-trending
Young
69
American'fault zone as strongly suggestive
area.Titley
(1958) studied
the
skarnmineralassemblageadjacent
to
i n the Linchburg mine and suggested
the north-northwest-trending faults
that the area
of a'stock underlying t h e
i s underlain by a buried stock.
A similar skarn-type
a l t e r a t i o n and s i l i c i f i c a t i o n i s present a t North Ealdy Peak southeast
of t h e Linchburg mine i n the study area.
Mafic, latite-monzonite, and particularly
white rhyolite dikes
a r e s p a t i a l l y a s s o c i a t e d w i t h t h e exposed stocks and may be f u r t h e r
evidence for buried stocks
i n t h e KagdalenaMountains.
described a white rhyolite dike in the Linchhurg
has mapped w h i t e r h y o l i t e d i k e s i n t h e
T i t l e y (19.58)
mine,and
t h e miter
North Baldy Peak area, suggesting
t h e p o s s i b i l i t y of a buried stock.
The Linchburg-North Ealdy
Peak a r e a ' i s w i t h i n a north-northwest-
trending zone of h o r s t b l o c k s exfRnding from t h e Kagdalena mining
trict into the central
Magdalena Mountains.Loughlinand
dii-
Koschmann
(1942) c a l l e d ' t h i s zone of h o r s t s t h e ma-in ore zone a s it contained the
g r e a t e s t c o n c e n t r a t i o n of metals
i n t h e Kagdalenamining d i s t r i c t .
Horst blocks of Precambrian argillite uplifted against Paleozoic sesimentary rocks outline the
main ore zone i n t h e Ilagdalena mining d i s t r i c t
and t h i s zone of horstscontinuessouth-southeastward.
Magdalenabiountains a long, narrow block of
Spears Formation has been uplifted
I n thecentral
Madera Limestone and lower
w i t h i n t h e H e l l s Mesa Formation and
t h e upper Spears Formation and i s a continuation of t h e h o r s t b l o c k s
from t h e biagdalena mining d i s t r i c t .
The presence of
a buried stock underlying the
Linchburg-Morth
Baldy Peak area has been verified recently,by the release of information
70
previouslyheldconfidential
i n preparation).
by miningcompanies(Chapin,and
Drill holesand
penetratedtheoutermostportion
of the size
of a n igneous rock. Little
event.According
i s known
it i s s i m i l a r i n t e x t u r e
t o t h e exposed stocks,and suggests that
t h e samemagv.atic
it i s p a r t of
t o Chapin and o t h e r s ( i n p r e p a r a t i o n ) ,
i n the Linchburg nine
t h e i n t r u s i o n exposed i n t h e c r o s s c u t
i s a quartz
monzonite porphyry containing argill.ized plagioclase phenocrysts
fresh, romded grains
and quartz; Chlorite
are common i n t h e i n t r u s i o n .
and
and q u a r t z i n a granophyric
of potash feldspar
matrix ofpotashfeldspar
..
a crosscut i n t h e Linchburg mine
o r shape of t h e i n t r u s i o n , h u t
andcomposition
others,
and c a l c i t e a l t e r a t i o n
The presence of disseminatedpyriteand
sparse coppsr mineralization in the Linchburg stock differs from the
..
exposed stocks
i n t h e Nagdalena I~<ountains.
Another stock nay underly the liorth
and 28, T.
Peak,
3N., R.
31. approximately
1.5 miles southeast ofNorthEaldy
The proposedexistenceofthestock
l a r g e number of d i k e s i n t h e
Fork Canyon a r e a i n secs. 21,
NorthFork
i s basedprimarily
on t h e
Canyon a r e a , d i f f e r i n g from t h e
Nowhere i n t h e
Linchburg mine a r e a where d i k e s a r e r a r e a t t h e s u r f a c e .
1.lagdalena mining d i s t r i c t o r i n t h e c e n t r a l Kagdalena Mountains i s t h e
d i k i n g as p r o l i f i c a s i n t h e h'orthFork
Canyon area.
"-Ate r h y o l i t e d i k e s a s w e l l a s m a f i c
arepresent
i n h'orthFork
locally present in
Canyon.
NorthFork
White r h y o l i t e s i l l s and plugs are
Canyon.
i n nunerous stream channels suggesting
I
rocks and the Tertiary volcanic rocks
thin veneer overlying
and latite-monzonite dikes
The i n t r u s i v e r o c k s
are exposed
t h a t the Paleozoic sedimentary
exposed on t h e s u r f a c e a r e o n l y
a largerintrusionatdepth.In
a
a l l directions .
*
e
71
from t h e a r e a of g r e a t e s t i n t r u s i o n i n t h e south half of sec.
R.
21, T.
x.,
T:J., t h e exposed i n t r u s i o n s d e c r e a s e i n number and occurrence.. South
ofsee.
21, T. 3S., R ,
7;f. a few latite-mo>lzoniteand w h i t e r h y o l i t e
dikes trend north-northwest for
3 miles (Fig. 4).
exposed stocks i n
Dike r o c k s a r e s p a t i a l l y a s s o c i a t e d w i t h t h e
t h e NagdalenaKountains.
The existence of t h e r e c e n t l y v e r i f i e d b u r i e d
stock i n t h e Linchburg-North Baldy
Peak a r e a w a s suggested by the white
rhyolite dikes as well as the high temperature mineralization and alteration present i n thearea.Intensefaulting
may haveallowed
ment and concentration of magma from a distant source area.
diking i n Korth Fork
Canyon, and particul.arly the
Furthermore, the white rhyolite dike swarms'exposed
The abundant
white rhyolite dikes,
2 1 and28,
may suggest a buried stock underlying secs.
t h e move-
T. 3S.,
?M.
R.
t o the. southern
limits of mapping may suggest a l a r g e r i n t r u s i o n u n d e r l y i n g t h e c e n t r a l
Hagdalena Mountains.
'Tertiary Sedimentary Rocks
PopotosaFormation.
east
~2.uof
The prominent r e d c l i f f s t h a t
?later Canyon f o r more than
1.5
form t h e
miles a r e made up of Hiocene
sedimentaryrocksofthePopotosaFormation.Kalish
(1953, p. 22)
c a l l e d t h i s u n i t a rhyolite agglomerate i n t h e Water Canyon Nesa area.
Also, much o f t h e f l a t , r u h b l y a r e a
betweenSouthEaldyand
Langmuir
Laboratory i s underlain by t h e PopotosaFomation.Stacy(1968,
called the rock between South Ealdy
laharicbreccia.
p. 42)
Peak andLangmuir Laboratory a
The PopotosaFormation
l i e s unconformably on t h e
Timber Peak r h y o l i t e and represents the beginning
of T e r t i a r y
72
sedimentation i n t h e c e n t r a l Nagdalena Fountains fqllowing Late Cligoc e n e f a u l t i n g and i n t r u s i o n ,
Popotosa Zormation
Denny (1940) originally 'described the
a s a basal unit ofsthe Sante
p o s i t e d i n middle Niocene
to Pliocene time.
The Popotosa Formation
district.
Fe Group which was de-
i n t h e Nagdalenamining
i s not present
I n thesouthernEearKountains,theFopotosaFormation
interbedded w i t h t h e upper one-third of the
u n i t which Chapin(1971-a)dated
in the southern Eear
is
La J a r a Feak Formation, a
a t 23.8 m.y.
The PopotosaFormation
14ountains c o n s i s t s of s i l t s t o n e s and mud flow
b r e c c i a s composed mainly of
d e t r i t u s from t h e La J a r a Peak Formation,
&own (1972, p. 66) c a l l e d t h e u n i t the fanglomerate
of Dry LakeCanyon
a f a c i e s of t h e PopotosaFormation ( E r u n i n g , 1973):
~....
southern part of the Puertecito quadrangle, north of the Kagdalena
(Fig.9),
Mountains,Tonking(1957,
In .the
p. 34)designatedtheextensivelyexposed
series of poorly sorted volcanic-rich siltstone, sandstone,
andcon-
glomerate as t h e I'opotosaFormation.
According t o Eruning(1973,
Popotosa Formation began about 24
p. 107) the deposition
m.y.
during the emplacement of t h e
u p p e r t h i r d of t h e La J a r a Peak Formation.Cepositionof
Formation continued locally
of t h e
t h e Popotosa
i n the Socorro, New Nexico area to approxi-
mately 11 m.y. a s d a t e d by a trachyandesite flow
overlying the Popotosa Formation
and a s s o c i a t e d t u f f s
on Socorro Peak (Eurke and others,
1963). The PopotosaFormation
i s overlainby
{Weber and Eassett, 1963) west
of t h e c e n t r a l Magdalena Kountains i n -
14 m.y. r h y o l i t e f l o w s
dicating depositior. of t h e Popotosa Formation ceased
Kagdalena area.
e a r l i e r i n the
73
Kottlowski, k!eber, and blillard (1969) considered the Santa
Group of c e n t r a l f:ew I;exico t o haveformedunder
environment t o t h e G i l a
Conglomerateof
a similar depositional
southwestern New Mexico and
southeastern Arizona. Eoth rock units resulted
from erosion of the
and deposition i n adjacent basins.
istinghighlands
Conglomerate a s determined by vertebrate fossils
of Benson,Arizona
Fe
The age of the Gila
from lake beds south
1962).
i s Late Pliocene to Early Pleistocene (Heindl.
The Popotosa Formation
alluvialfandepositconsisting
ex-
i n t h e c e n t r a l Nagdalena Kountains i s an
of wellinduratedsandstone,conglomerate,
and breccia. Exposures of the Popotosa Formation are limited to the
Water Canyon Xesa (Fig. 22) and t o t h e a r e a
betweenSouthEaldy
Peak and
Langmuir Laboratory.
.. . .
KO c l a s t s o f La J a r a Peak Formation,Paleozoicsedimentaryrocks,
o r Precambrian a r g i l l i t e and g r a n i t e have been found
Formationof
t h e c e n t r a l Magdalena Fountains.
Mountains the Popotosa Formation
i n t h e Fopotosa
I n t h e central Kagdalena
i s r e d , t o reddish-brown and
i s com-
posed of a n g u l a r t o subrounded c l a s t s o f Liatil volcanic rock, primarily
the Tinber Peak r h y o l i t e .
The c l a s t s r a n g e i n s i z e from l e s s t h a n 1 inch
t o over 2.5 f e e t and a r e cemented by an iron-stained, siliceous
mass.
The rock has
ground-
a vuggy or f r o t h y t e x t u r e and c o n t a i n s c a v i t i e s as
much as 9 f e e t i n diameter i n Vater Canyon Plesa.
The PopotosaFormation
i s approximately 400 f e e t t h i c k a t 'Water Canyon Nesa, b u t t h i n s r a p i d l y
eastward w i t h i n
rhyc:lite surface.
0.5
miles t o a depositional pinchout
A t t h e c r e s t of t h e rangebetweenSouthBaldyPeak
and Langmuir Laboratory,thePopotosaFormationforms
blocky fragments.
on t h e TimberPeak
a t h i n veneerof
'
Figure 22.
Well indurated and conglo~neraticPopotosaFornation
exposed a t Kater Canyon Mesa.
75
I n t h e Wat,er Canyon l,!esa a r e a , a thin, reddish-black, vesicu1ar.k
lava flow
i s interbedded w i t h thePopotosaFormation.Kinorplagioclase
a r e i n the aphanitic
andpyroxenephenocrysts
groundmass.
The lava flow
i n a few stream beds and cannot be traced laterally.
i s exposed only
The size, shape,
andcomposition
I’opotosa Formation v a r i e s fromplace
of t h e d e t r i t u s composing t h e
to place,
Between SouthBaldy
and Langmuir Laboratory the Popotosa Formation contains subround
much a s 2.5 f e e t i n length of TimberPeak
angular fragments as
theSouthEaldyandesite,
and mino:
Sawmill Canyon formation.
these volcanic u n i t s crop out i n the adjacent area.
i n the Popotosa Formation are
Mesa a r e a , t h e c l a s t s
Peak
to
rhyolite,
A
l
l of
I n t h e Water Canyon
muchmore
heter-
o l i t h i c and v a r i a b l e i n s i z e androundness.
. ,.
’
Rocks s i m i l a r t o t h e PopotosaFormationcropout
westofSouthEaldy
Peak i n t h e 14ule Shoe Ranch area.
southwest of South Ealdy
PopotosaFormation
Peak a r e n o t a s c o a r s e
a t t h e c r e s t of the range.
fragrcefits i n the clastic rocks southwest
h e t e r o l i t h i c and does not contain as
a n d e s i t e andTimberPeak
of the range.
The c l a s t i c r o c k s
or angular as t h e
The l i t h o l o g y o f t h e
of South Ealdy
Peak i s more
many c l a s t s of South Baldy
r h y o l i t e as the Popotosa Formation
Peak
a t t h e crest,
The c l a s t i c r o c k s i n t h e Kule Shoe Ranch a r e a a r e i n t e r -
bedded with Late Oligocene volcanic
age and
3 milessouth-
---”
r’l\
r m k s approximately
30 m.y. i n
29
are considered correlative with the
described by Oeal and *odes
u
Eear Trap Canyon Formation
(in press).
Quaternary Sediments
The Quaternary sediments of t h e c e n t r a l Hagdalenab!ountains
c o n s i s t of pediment g r a v e l s ,t a l u s ,
andalluvium.
The unconsolidated
2b
PzI‘
76
i n t h e SouthEaldy Peak-
sediments cover large areas, particularly
Langmuir Laboratoryarea,concealingtheunderlying
geology.
Pediment Gravel.Poorlyconsolidatedmaterial
mapped a s pedi-
ment gravel i s exposed on t h e e a s t e r n f l a n k
of t h e Magdalena Range and
i n a considerable portion
The pediment gravel includes
ofWater
gently sloping alluvial fans
eastward into the
covered slopes
Canyon.
on the margins
SEalteRanch
of the range that dip
F l a t s (La Jencia Easin),
and the beulder-
i n 'Jater Canyon,
The bedrock areas demonstrably influence the type
found i n t h e pediment gravels.
ana westofr,later
To the north
Precambrian a r g i l l i t e , Oligocenevolcanicrocks,
tary rocks predoninate in the gravel.
,..
Canyon eroded material from t h e Popotosa Formation
Canyon,
and Paleozoic sedimen-'
To the south
..
of d e b r i s
and e a s t of b!ater
and Oligocene vol-
c a n i c r o c k s make up t h e d e b r i s .
!:'here
t h e pediment gravel i s only a t h i n veneer covering
underlyingformations,
windows of possiblebedrockarepresent.
example i s t h e I.!ater Canyon manganese mine on t h e e a s t s l o p e s
the
A good
of Water
Canyon (Fig. 4) t h a t was developed i n the Timber Teak r h y o l i t e ancl i s
surrounded by pediment gravels.
l;!hether suchanexposure
o r a slurpblock from higher elevations
T
T aa ll u
u ss ..
i s bedrock
i s d i f f i c u l t t o determine.
H
ee ss
H aa tt ee rr ii aa ll mapped
mapped aa ss tt aa ll u
u ss ii n
n cc ll u
ud
d ee ss d
d ee b
b rr ii ss .. ss ll ii d
dand
and
l a n d s l i d e s t h a t are extensively developed at the higher elevations,
p a r t i c u l a r l y i n thesouthernportion
of Timber Peak rhyolite, over
s t a b l es l o p e s .
of thestudyarea.Largeblocks
300 f e e t i n length, slump down .steep, un-
Rock g l a c i e r s , some up t o
0.5 mile i n length,cover
77
i n South,Sixmile,Sawmill,
considerable portions of the slopes
Bear, Kill, Hop, and Patterson Canyons (Fig. 3).
C l a s t s of ash flow
Fiardy,
'
t u f f s d e r i v e d f o r t h e most p a r t from t h e
f i e l l s Itesa Formation and
t h e Timber Peak r h y o l i t e a r e t h e
main con-
s t i t u e n t s of t h e t a l u s .
The Timber Peak r h y o l i t e s u p p l i e d m a t e r i a l
t o t h e t a l u s cones covering many of the southern and western slopes of
the range,
House-sizeblocks
Laboratoryhave
of Timber Peak r h y o l i t e around Langmuir
slumped i n t o Sawmill Canyon,
dipping slopes between Rorth Ealdy
posed of Hells
Peak and South Ealdy
Feak a r e com-
Mesa Formation.
Alluvium.
been deposited
Ta1.u~ covered, westward-
Alluvium comprises !Iolocene streamgravels
i n t h e major drainages cutting bedrock,
pediment gravels.
has beenentrenched
I n 'dater Canyon westof
t h a t have
talus, and
k t e r Canyon Mesa, t h e stream
intoanolderstreamterrace.Intermittentrunoff
still s u p p l i e s m a t e r i a l , which i s deposited i n the valleys today.
~~~
STKUCTUFG
I n t e r p r e t a t i o n of t h e s t r u c t u r e s i n the Eagdalena Kountains has
been hampered by a l a c k of field data, Reconnaissance
mappingand t r a v -
erses were made o u t s i d e t h e c e n t r a l Magdalena Mountains i n o r d e r t o
b e t t e ru n d e r s t a n dt h es t r u c t u r e
of therange.
The a d d i t i o n a l d a t a
available from Frown (1972) in the southern Pear Yountains, the compilationstudy
by Chapinand
others(inpreparation)ofthe
Magdalena-Tres
Montosac: area as well is Loughlin and Xoschmann's (1942) study
on t h e
Xagdalena mining d i s t r i c t a l l o w f o r a better understanding of the local
and regional structures.
. ...
S t r u c t u r a l f e a t u r e s i n t h e c e n t r a l Magdalena!*lountains can be
consideredunderfivemajorheadings:PrecambrianandPaleozoicstruc-
t u r e , Laramide s t r u c t u r e , Early t o PliddleOligocene
cene f a u l t s , andLateCenozoicblock
faults.
f a u l t s , LateOligo-
Each t y p eh a s
been
'
i n f l u e n t i a l i n t h e s t r u c t u r a l h i s t o r y of t h e c e n t r a l Plagdalena I.!ountains
and i s discussed separately.
Precambrian and Pal.eozoic S t r u c t u r e
"
The Precambrian a r g i l l i t e i n g e n e r a l s t r i k e s n o r t h w e s t a n d d i p s
s t e e p l yt ot h ee a s t .
No f o l d s are p r e s e n ti n , t . h e a r g i l l i t e .
Cambrian g r a n i t e c r o s s c u t s t h e d i p
The h e -
of t h e a r g i l l i t e . G r a n i t e d i k e s
g e n e r a l l y less than 2 f e e t wide f i l l northeast-trending fractures and
comnonly i n t r u d e p a r a l l e l t o t h e bedding
_c
of t h e a r g i l l i t e .
:k
.>
..
78
~~
~
79
X i s s i s s i p p i a ns t r a t a
unconformably overliethePrecambrian.
Kississippian-Pennsylvanian contact
i s a conformable surface that
no s t r u c t u r a l d i s r u p t i o n . U n c o n f o r m i t i e s i n
tary rocks we reported by
Kagdalenamining
district,
The
t h e Pennsylvanian sedimen-
Loughlinand Koschnann (1.942, p.
Loughlinand
shows
56) i n t h e
Koschmann (1942) stated there
i s an angular unconf'ormity between the Fadera Limestone of Pennsylvanian
age and the
Ab0 Formation of Permian age i n t h e Eagdalena mining dis-
trict.
The P a l e o z o i c s t r a t a s t r i k e n o r t h w e s t
and d i p 1
0
'
North Baldy Peak b u t change t o a west-trending strike and
Of
30
0
to
0
55
lena Hountains.
attheirsouthern
vest near
a southward d i p
limit of exposure ir, t h e c e n t r a l Hagda-
A s e r i e s of u p r i g h t a n t i c l i n e s a n d s y n c l i n e s w i t h
nor-th-
i n the Paleozoic sedimentary
west to northeast trends are developed
in the central
t o 30'
KagdalenaKountains(Fig.
p r e s e n t i n theOligoceneSpearsFormation.
2 3 , i n pocket).Folds
NorthFork
rocks
are also
Canyon andCopper
Canyon occupy the hinge zone o f a n t i c l i n e s and are separated by topographic ridges which are structuralsynclines.Spacingbetweenthe
a n t i c l i z e s i s approximately 1 mile.
The structuresplungeapproximately
0
30 t o t h e west beneath t h e unfolded Fells Kesa Formation.
Folds in. the Paleozoic rocks
and the Oligocene Spears Formation
are r e s t r i c t e d t o t h e c e n t r a l Kagdalena Xountains and
are not present
t h e I.!agdalena mining d i s t r i c t ( L o u g h l i n and Koschmann, 1942, p.
Spatially, folds in the Paleozoic rocks are limited to
and t o t h e south i n t h e c e n t r a l k g d a l e n a
,
. ..,-..
:v
ti'orthFork
2
Canyon f a u l t zone,along
57).
Mortli Ealdy Peak
PIountains.
The f o l d s a r e
3:.
80 W.-trending
developed on t h e downthrotrn side and south of t h e
in
0
.
which o b l i q u e s l i p movement occurred.
80
Laramide S t r u c t u r e
The term"Laramide"
has been applied
t o a period oT large-scale,
c r u s t a l d i s t u r b a n c e s d u r i n g which many o f the mountains and b a s i n s of
t h e Rocky Hountainregion
(1933, p. ll@)
wereformed.blilmarth
t h e Laramide a s beginning i n Late Cretaceous time and ending
defined
i n Early
As more s t r u c t u r a l d a t a accumulrrte, i t i s i n c r e a s i n g l y
T e r t i a r yt i r r e .
evident t h a t o r o g e n i c e v e n t s p r e s e n t l y a s c r i b e d t o t h e
Laramide d i d n o t
end simultaneously i n a l l p a r t s of t h e Rocky Mountains.
beginnor
limits and scope of t h e Laramideorogeny
i n west-central Rew &lexico.can
i n terms of the time following
b e s t be defined
t h e d e p o s i t i o n of t h e
Cretaceous Xesa Verde Group and before the deposition of.the
I
Formation.
The
Eocene Paca
.
.. . ..
The Laramide u p l i f t a p p e a r s t o
have the.shapeof
dome o r a n t i c l i n e whose axis trends north-northwest
Loughlinand
om elongate
'
'
i n t h e Hagdalena area.
Koschmann (1942, p. 57) noted the general change
i n strike
from N. 30° E. i n t h e G r s n i t e
of the west-dipping pre-volcanic rocks,
Mountain a r e a n o r t h of the lvlagdalena mining d i s t r i c t t o N. 15O 1;l. i n t h e
main portion of the
I-lagdalenamining
district..
exposure i n t h e c e n t r a l KagdalenaMountains,
east-westanddipsouth.
h a s beendropped
of
the Paleozoic rocks strike
The east-dippinglimb
into the subsurface by
A t the southern Zinit
of t h e P a l e o z o i c s t r a t a
Late Cenozoic block faulting.
E a r l y t o Middle Oligocme Faults
A N. 80' W.-trending
posedfromNorthBaldy
s i d e ofKorth
f a u l t zone of Early Oligocene age
is ex-
Peak e a s t t o Water Canyon p a r a l l e l i n g t h e n o r t h
Fork Can:,on (Fig. 23). The f a u l t zone d i p s from s t e e p l y
81
to the south to vertical.
Canyon f a u l t zone i s composed
l'heNorthFork
of two west-trending, parallel,
normal f a u l t s with the south side
upf'2<r.li-
;,!
The s t r i k e - s l i p conponent of o f f s e t a l o n g t h e North Fork
A
f a u l t zone i s determined by t h e Kelly Limestone, which
Korth E d d y Peak and crops out
area.
Canyon
i s truncated 'at
2.5 miles t o t h e east i n t h e V a t e r Canyon
The s t r i k e - s l i p d i s p l a c e m e n t a l o n g t h e n o r t h f a u l t
Fork Canyon f a u l t zone i s g r e a t e r t h a n t h e south fault.
component o f o f f s e t a c r o s s t h e
down.
of theh'orth
The d i p - s l i p
Canyon fault zone i s 1400 f e e t
NorthFork
Kelly Limestone a t
as measured by t h e d i f f e r e n c e i n e l e v a t i o n o f t h e
North Ealdy Peak and i n Water Canyon.
The h'orth Fork
Canyon f a u l t zone i s covered by younger volcanic
r o c k s west and southofRorth
h'orthFork
3S.,
Baldy Peak.
The northern f a u l t of t h e
Canyon f a u l t zone i s exposed i n t h e west h a l f o f
K. 7;). a t thesouthforkofPatterson
Ca.nyon (Pig. 4).
h a s removed t h e younger volcanic roclcs and exposed
and the f a u l t zone.
To t h e w e s t t h e
NorthFork
Erosion
the Spears Formation
Canyon f a u l t zone i s
truncated by a LateCenozoic,north-trendingblock
Wlk$nson (Chapin,
sec. 18, T.
fault.
Mapping by
and o t h e r s , i n preparation) i n t h e T r e s ?!ontos2s area
o f t h e G a l l i n a s Range, approximately 10 miles west of Magdalena, has
resulted in the recognition of
a west-northwest-trending f a u l t zone,
which may be a westerly continuation of
t h e Korth Fork Canyon f a u l t zone.
The Sorth Fork Canyon f a u l t zone developed before the deposition
of t h e Elells Nesa Formation and a f t e r t h e emplacement o f t h e S p e a r s
Formation.
The SpearsFormation was truncated by the North'Fork Canyon
f a u l t zone whereas the
Eells tksa Formation overlaps t h e Iiorth Fork Can-
yon f a u l t zone v e s t andsouth
of North Ealdy Peak.
Furthermore,dikes
82
related to the Late Oligocene intrusions,
KagdalenaMountains,
which a f f e c t e d t h e e n t i r e
wez-e intruded across as
Fork Canyon f a u l t zone.
well as &long the Korth
.
Following t h e emplacement of the Hells NesaFormati.on,
trending, south-dipping,
a west-
normal f a u l t develcpedfromSouthEaldy
e a s t t o South Canyon (Fig. 2 3 ) .
Evidence f o r t h e existence of t h e South
Canyon f a u l t i s based on topography,displacementof
tionadjacenttothefault.
Peak
s t r a t a , and a l t e r a -
lu'orth of t h e fault i n S o u t h Canyon, t h e
H e l l s Nesa Formation i s exposed and truncated against the younger
mile Canyon andesite. Pyrite
Nesa Formation adjacent
Six-
and q u a r t z v e i n l e t s o c c u r i n t h e E e l l s
t o t h e South Canyon faxlt b u t are not present
i n t h e S i m i l e Canyon andesite.
The South Canyon f a u l t is truncated
.
...
by a north-trending, Late Cenozoic block fault to the
east and i s
covered by t h e Timber Peak r h y o l i t e ,
The South Canyon f a u l t was reactivated between South Ealdy
Peak
and Timber Peak a f t e r t h e emplacement of t h e Sawmill Canyon formaticn.
The displacement of s t r a t a i s evidence for the
Hells iiesa Formation north
second p e r i o d of f a u l t i n g .
of t h e f a u l t i s truncated against South fialdy
The South Canyon fault west of
Peak a n d e s i t e on the south.
Peak i s covered by Timber Peak
Souti.: Ealdy
rhyolite.
Late
Oligocene
Faults
Following t h e .emplacement o f t h e Datil Group, t h e c e n t r a l &lag:;:;lena Piountains were c u t by a s e t of north-northwest-trending
LateOligoceneage(Fig.
0
N. 30 b!.
23).
These f a u l t s t r e n d from
w i t h a dominant t r e n d o f
M. 10'
12J.
hi.
10'
f a u l t s of
E. to
The north-northwest-trending.
exposed from the southern limit of t h e Ki.tt stock through the LinchburgGrand Ledge area (Loughlin
and Koschmann, 1942,' P l a t e . 2 ) .
The north-northwest-trending faults continue north and south
of t h e c e n t r a l
I'iagdalena Mountains.
The f a u l t s e x t e n d
southward i n t o
Sawmill Canyon and Ryan 1 5 1 1 Canyon, both of which have a pronounced
north-narthwesttopographictrend.
continue northward into the
The north-northwest-trending
faults
Magdalena mining d i s t r i c t as expressed by
h o r s t s and f a u l t s a l o n g which the Kelly Limestone h a s been mineralized.
fieplacement d e p o s i t s i n the Kelly Limestone along north-northwesttrending f a u l t s occur i n t h e Linchburg mine and t h e North Raldy-Peak
mine, 4 miles s o u t h of the
trict.
exposed s t o c k s i n t h e Magdalenamining d i s -
Also, dikes and t h e Nitt and AnchorCanyon
.. ...
.
.
stocks i n t h e Kagda-
l e n a mining d i s t r i c t have a north-northwest orientation.
I n the southern Eear
Mountains north of the Nagdalena Kountains,
Brown (1972) recognized the continuation
f a u l t s , which have c u t t h e a r e a i n t o
of the north-northwest-trending
a number of westward
progressivelystepped
down t o t h e e a s t ?
Tonking's(1957)
Puertocitoquadrangle
shows thenorth-northwest-trending
tilted blocks
map of t h e
f a u l t s con-
.
t i n u i n g northwardfromErown'sarea.
Late CenozoicBlock
-F a u l t s
The major u p l i f t of the central13agdalena Kountains occurred
alongLate
Cenozoic block faults.
f a u l t zones (Fig.
t h e N,
2 3 ) ; t h e N. 25'
35' H.-trendingboundary
Novement occurred along three major
E.-trendingWater
Canyon f a u l t zone,
f a u l t zone on t h e n o r t h e a s t s i d e o f t h e
Nagdalena Xange, and a n o r t h - t r e n d i n s f a u l t
zone on the west s i d e of t h e
85
Plagdalena Range.
The north-trending fault
zone,borderingthewestside
of the central Xagdalena Kountains, caused large,
displacements, and forms the east border
down t o t h e w e s t
of the Mulligan Gulch.graben.
0
N. 35 ltJ.-trending f a u l t zone,borderingthenorth-
Movement alongthe
east s i d e of t h e c e n t r a l Magdalena Mountains,caused
placementand
formed t h e Snake3anch
down t o , e a s t d i s The N.
F l a t s graben.
25' E. Water
Canyon f a u l t zone s e p a r a t e s t h e upthrown Precambrian t o T e r t i a r y r o c k s
t o t h e n o r t h w e s t from t h e downthrown T e r t i a r y r o c k a t Water Canyon Mesa
to the southeast.
The north-trending fault
zone on t h e west s i d e o f t h e c e n t r a l
i*lagdalena Range i s distinguished by the alignment
ment o f s t r a t a , s i l i c i f i e d f a u l t
of springs, displace-
zones,andsteepslopegradients.
Two
.. ,..
p a r a l l e l f a u l t s make up the north-trending fault
The e a s t f a u l t l i e s within the study area,
s i d e o€ t h e range.
west f a u l t i s
0.5
mile outside the study area.
of the north-trending
along the east flank of Granite
from t h e c e n t r a l
town of Kelly and continues
Mountain(Chapin,and
o t h e r s , i n prep-
of s t r a t a along t h i s f a u l t i n sec. 18, T. 3S.,
aration).Displacenent
R. 3?.i s e s t i m a t e d t o befrom
1000 t o 1500 f e e t .
The Water Canyon f a u l t zone consists of
f a u l t s drop2ingblocks
but the
The e a s t e r r m o s t fault
f a u l t zone continuesnorthward
MagdalenaI*;ountains passing through the
t o t h e southwest i n s e c .
3, T. 4s.. R.
two p a r a l l e l normal
The f a u l t s t r e n d W. 250 E.. i n
down t o t h e e a s t .
Water Canyon and c o n t r o l t h e d r a i n a g e p a t t e r n ,
frombiater
zone b o r d e r i n g t h e w e s t
3l.
The w e s t f a u l t d i e s o u t
The east f a u l t i s continuous
Canyon t o t h e head of Ryan Hill Canyon a t the southern limit
86
ofmapping.
Aerialphotographsindicatethatthis,fault
may continue
s o u t h i n t o Ryan t i i l l Canyon and into the southern portion of the ran&e.
The 13iocene Popotosa Formation i s truncated and exposed on the
downthrown s i d e of t h e Water Canyon f a u l t zone..
o f t h e Datil vo1canios;and
Popotosa Formation contains only fragments
not of Paleozoic
andupthrown
Furthermore,the
o r Precambrian rocks presently exposed
s i d e of the \rater
Canyon f a u l t zone.
on the northwest
Thissuggests t h a t
the Paleozoic and Precambrian rocks were not exposed during
Fopotosa sedimentation,
and ,that present day exposure
Cenozoic u p l i f t a l o n g t h e \ , l a t e r
t h e time of
i s due t o Late
Canyon f a u l t zone a f t e r t h e a e p o s i t i o n
'
of the Popotosa Formation.
t h e Water Canyon f a u l t zone i s
.. .
Water Canyon and decreases .southward.
A t the
The amount of displacement along
,
g r e a t e s t a t t h e mouthof
mouth of Water Canyon i n sec. 14, T. 3S., R. 3W,, Precambrian rocks are
exposed on t h e upthrown s i d e , and Tertiary rock are exposedon
in
thrown s i d e .F a r t h e rt ot h es o u t h ,a s
sec.
3, T. 3K.) R. 3N.:Terti-
ary r o c k s o f d i f f e r e n t a g e a r e ' i n f a u l t c o n t a c t .
displacement a t t h e mouth ofWater
N. 35'
!:'.-trending
The s t r a t i g r a p h i c
Canyon i s i n excess of 3000 f e e t .
The n o r t h e a s t p o r t i o n o f t h e c e n t r a l
bordered by a
Xagdalena Nountains
is
f a u l t zone, which has dropped the ad-
j o i n i n g Snake Ranch F l a t s down t o t h e e a s t . S a n f o r d
of gravity studies,
t h e down-
(1968), on t h e b a s i s
interpreted t h e Snake R a n c h - F l a t s t o b e n northwest-
trendingstructuraldepressionprobablyresultingfromnormalstep-faulti n g and p o s s i b l e t i l t i n g a l o n g
a northwest-trendingfaultzone.
.
The
presence of scarplets cutting alluvial fans as evidenced in the field,
and p a r t i c u l a r l y from a e r i a l photographs,indicate
movement hasbeen
87
continuing. Aerial photographs also indicate the
f a u l t zone a p p e a r s t o t r u n c a t e t h e
It. 25
0
N. 35O $[.-trending
E. b!ater Canyon f a u l t z o n e ' .
and continues to the southenst forming the eastern boundary of Ilater
Canyon Xesa.
The displacement on t h e N.
cult to deternine
estimate i s made.
35' $1.-trending f a u l t zone i s d i f f i -
and v a r i e s depending on t h e l o c a t i o n where t h e
North of 1t1atel- Canyon, Precambrianrocksareexposed
on t h e upthrown s i d e of t h e N. 35' 1.1. f a u l t zone a t t h e n o r t h e r n end of
the range, whereas
fromWater
sedimentaryrocksareexposed
Canyon south, Tertiary volcanic
on t h e upthrown s i d e o f t h e
f a u l t o z o n e . The area north of Vater
IJater Canyon f a u l t zone.
N,
t h e N.
The best estimate
minate, but probably exceeds
W
.
of d k p l a c e n e n t f o r t h e
made' south of
A s alluvium c o v e r s t h e s t r a t a
35' IJ. trending fault zone,
0
35
Canyon was a l s o u p l i f t e d b y t h e
35' W.-trending f a u l t zone should be
f a u l t zone.
N.
and
t h e islater Canyon
on the downthrown s i d e of
t h e exact displacement
2000 f e e t ,
is indeter-
REGIONAL A L m T I O N
Alteration in the centrallhgdalena Xountains
and i s closely confined t o intrusive
the composition of the host rock,
contactsalong
i s dependentupon
Altera-
which a l t e r i n g s o l u t i o n s were able t o migrate.
t i o n i s of t h e same t y p e a s found i n t h e Etagdalena mining d i s t r i c t , b u t
is not as intense
of a l t e r a t i o n a r e
nor aswidespread.Fivetypes
p r e s e n ti nt h ec e n t r a l
I4agdalena.Nountains;propylitization,silicifi-
c a t i o n ,l i r t e - s i l i c a t e ,a r g i l l i z a t i o n ,
and s e r i c i t i z a t i o n ,H e m a t i t e
t e r a t i o n , which i s so s t r i k i n g i n t h e southern Flagdalenamining
(Loughlinand
al-
district
Koschnann, 1942), i s r a r e l y p r e s e n t i n t h e c e n t r a l Magda.,
l&aKountains.Variation's
indistribution,controls,
mineralization will be discussed under each type
andimportance
to
of alteration.
Rock exposed w i t h i n and along the Late Oligocene, north-north-
west-trending s t r u c t u r a l zone r e v e a l t h e g r e a t e s t amoltnt and development
of a l t e r a t i o n .
Along t h i s zone t v o a r e a s haveundergone
alteration i n the central portion
One a r e a t o t h e n o r t h
of the range (Fig.
t h e major
24, i n pocket).
i s a d j a c e n t t o t h e Magdalena mining d i s t r i c t and
o v e r l i e s one known b u r i e d i n t r u s i o n i n t h e
and a postulated buried stock
Linchburg-North Ealdy
area
i n t h e North Fork Canyon a r e a . A l t e r a t i o n
d i e s o u t southward b u t i n c r e a s e s i n i n t e n s i t y
of t h e study a r e a i n sec. 33, T.
x , , R.
3b!.,
i n the southernmost part
and secs. 4 and
5, T. 4s..
R. p. a t t h e i n t e r s e c t i o n of t h e north-northwest-trending zone with
transverse South Canyon f a u l t zone.
the
89
-P r o p l i t i z a t i o n
Fropylitic alteration occurs over
a wide a r e a and a t g r e a t d i s -
tances from icnolwn a r e a s of mineralization.CaLcite,chlorite,
e p i d o t ec h a r a c t e r i z ep r o p y l i t i ca l t e r a t i o n .P y r i t e
and
i s r a r e l yp r e s e n t .
P r o p y l i t i c a l t e r a t i o n i n t h e c e n t r a l Magdalena Mountains i s b e s t developed i n the Spears and H e l l s Mesa Formations w i t h i n the north-northwestt r e n d i n gs t r u c t u r a lz o n e ,C a l c i t ev e i n l e t sw i t hg e o t h i t ea r ep r e s e n t
l o c a l l y i n the Paleozoic rocks, particularly in
the area overlying t h e
postulated Korth kork Canyon stock.
The Spears Formation, consisting of sedimentary rocks, andesite
flows, and l a t i t i c ashflows,
alteration.Feldspar
i s t h e most s u s c e p t i b l e t o p r o p y l i t i c
andferromagnesianminerals
i n t h e S p e a r s Formation
a r e commonly a l t e r e d t o c a l c i t e and l o c a l l y t o epidote or c h l o r i t e ,
P r o p y l i t i c a l t e r a t i o n i s p a r t i c u l a r l y common a d j a c e n t t o a f a u l t zone o r
an i n t r u s i v e c o n t a c t .
The a l t e r a t i o n of the Spears Formation
i s not as
i n t e n s e as described by Erown (1972) i n the southern Eear Fountains
or
i n t h e KagdalenaNining d i s t r i c t , where t h e p e r v a s i v e p r o p y l i t i z a t i o n
l e d Loughlin and
Koschmann (1942) t o b e l i e v e t h a t f o u r s e p a r a t e b u t
laterallyequivalent
normally purple
tered.
u n i t s e x i s t e d (Fig. 9 ) .
The lowerSpearsFormation,
i n c o l o r , is a greenish gray where p r o p y l i t i c a l l y al-
The middle o r “turkeytrack”
member of theSpearsFormation
appears to be very reactive to altering solutions, probably because of
i t s v e s i c u l a r or porous nature and chemicalcomposition.Calcite,
epidote, and c h l o r i t e a r e common a l t e r a t i o n p r o d u c t s o f p l a g i o c l a s e a n d
ferromagnesian minerals of the middle Spears Formation throughout
study area.
the
The upper Spears and the Hells Mesa Formation 'show p r o p y l i t i c
b!orth Baldy Peak i n
a l t e r a t i o n most corrmonly south and southeast of
secs. 1 7 and20,
of the hells
T, 3 S . , R.
"J.
KesaFormation,
(Fig.24),
i n secs.
3 and 4,
undergone p r o p y l i t i c a l t e r a t l o n . C h l o r i t e
more intense zones of alteration
The southernmostexposure
T. 4S.,
R.
jY..
has also
i n the
and epidoteoccur
and give the ash flows of the upper
Spears and E e l l s Kesa Formation a greenish tinge.
Silicification
The a d d i t i o n of s i l i c a t o t h e c o u n t r y r o c k o f t h e
Hagdalena
in-
Nountains i s c o n t r o l l e d by the proximity of t h e a l t e r e d r o c k s t o
trusions o r f a u l t zones,Silicificationoccurseitheraspartial
t o t a l replacementofthehostrock
or a s v e i n s .
The jasperoidtype
replacement i n t h e K e l l y Limestone a t North Baldy Peak and
dalenamiringdistricthasundergom
to
i n t h e Kag-
two p e r i o d s o f s i l i c i f i c a t i o n .
The
f i r s t period was characterized by t h e massive replacement of the Kelly
Limestone by s i l i c a , formingthejasperoid.
The rock was l a t e r f r a c -
t u r e d , and t h e n d r u s y q u a r t z f i l l e d t h e f r a c t u r e s .
30
mineralization
accompanied the massive replacement, but barite, fluorite,
f i d e s , andgold
were i n t r o d u c e d w i t h t h e s e c o n d s t a g e - o f s i l i c i f i c a t i o n .
Jasperoid replacement
i s r e s t r i c t e d t o t h e I.!orth Baldy Peak a r e a
and i s a continuation ofwidespread
e r n Nagdalenamining
uppamost portion
silicification present
x., R.
i n t h e south-
d i s t r i c t ( L o u g h l i n and Xoschmann, 1942).
of the Kelly Limestone
jasperoid along the crest of the range north
17, T.
minor sul-
3';:. and northoftheliorth
The
i s preferentially replaced by
of Korth Ealdy
Peak i n sec.
Fork Canyon fault. zone.South
of the Korth.Fork Canyon f a u l t zoneand
trending f a u l t zone i n sec. 20,
along the north-northwest-
T. 3S., R. 7r.f., themiddleSpears
For-
mation i s . t o t a l l y r e p l a c e d by jasperoid i n a zone 150 f e e t east-west
by
2.50 f e e t north-south(Fig.
24).
Hematiteaccompanies
i s no mineralization present.
alteration,butthere
t h ej a s p e r o i d
The hematite as-
s o c i a t , i o n w i t h s i l i c i f i c a t i o n was also recognized by Loughlin and
Koschmann (1942, p.
mining d i s t r i c t .
lifted along the
t h e southernKagdalena
up-
A horstblockexposingI-recambrianargillite,
Grand Ledge fault (Loughlin and
west of NorthEaldy
by s i l i c a .
5b) i n t h e v o l c a n i c r o c k s o f
Peak i n sec. 18, T.
Koschmann, 1942)north-
3s.. R. yd., i s t o t a l l y r e p l a c e d
The jasperoid replacement of the Frecambrian argillite only
Koschmann (1942),
occurs i n t h e Korth Saldy Peak area.Loughlinand
T i t l e y (1958), andLovering(1962)statedthat
t h e jasperoid replacements
i n t h e Kagdalena mining d i s t r i c t were equivalent i n time and c r i g i n t o
the lime-silicate alteration,
b u t were f a r t h e r away from t h e source of
the fldds.
S i l i c i f i c a t i o n i s a l s o p r e s e n t i n t h e Timber Peakmine
4 and
5, T. 4S., R. p!.) i n
SpearsFormationandthe
t h e form o f v e i n l e t s p e n e t r a t i n g
Iiells Kesa Formation(Fig.
24).
as much as 0.5 percent, i s found i n t h e q u a r t z v e i n l e t s .
within the north-northwest structural
east-westSouth
area (sees.
t h e upper
Pyrite,locally
The area is
zone a t i t s i n t e r s e c t i o n w i t h t h e
Canyon f a u l t . S i l i c a v e i n l e t s c u t o n l y t h e S p e a r s a n d
Hells Mesa Formations on t h e upthrown s i d e of the South Canyon f a u l t and
not the younger Sixmile
the fault.
Canyon andesite exposed on t h e downthrown side of
92
A second period
of s i l i c i f i c a t i o n i s i n d i c a t e d by s i l i c a v e i n s
occurringalongLateCenozoicblockfaultzones.
boundary f a u l t of t h e NagdalenaKountains
localities along the western
The main western
i s s i l i c i f i e d i n a number of
edge of the central Magdalenaltountains.
The Popotosa Formation has been
s i l i c i f i e d a d j a c e n t t o t h e Late Cenozoic
Hesa Formation i s re-
f a u l t s o u t h of South Zaldy Feak, and the Eells
placed by s i l i c a a l o n g t h e
Water Canyon f a u l t zone.
Lime-Silicate
A small pyrometasomatic deposit developed
i s located 0.2 milesoutheastof
located at the intersection
KorthBaldy
i n t h e K e l l y Limestone
Peak (Fig. 24).
It i s
of the north-northwest-trending structural
zone w i t h the Sorth Fork Canyon f a u l t zone. "The minerals present
are
diopside,andradite,quartz,allophane,galena,sphalerite,pyrit.e,
chalcopyrite andmalachite.
A white rhyolite dike
present and appears t o havepreceded
minor
i s theonlyintrusive
the alteration and the m
. i.n e r a l i -
zation.
A pyrometasomatic d e p o s i t s i m i l a r t o t h e I ~ l o r t h E d d y
i s l o c a t e d i n the Linchburg nine
i n t h e Kagdalena mining
T i t l e y (1958) s t u d i e d s i l i c a t i o n a s
Feak skarn
d i s t r i c t where
a controloforedeposition.Titley
(1958) d e t e r m i m d t h e l i m e - s i l i c a t e a l t e r a t i o n t o b e s p a t i a l l y a s s o c i ated to fault
zones t h a t were t h e c o n d u i t s f o r t h e m i n e r a l i z i n g
teringsolutions.Silicate
outward a r e :
15 f e e t
and sulfidezonesdevelopedfrom
1) 1-2 f e e t of i n t e n s e s i l i c i f i c a t i o n :
of gametized limestone (andradite);
o f andradite,hedenjergite,sphalerite,
and ala fault
2 ) approximately
3) a wide t r a n s i t i o n zone
and galena constituting the
main
93
ore bodies; 4 ) a narrower zone ofpyroxenatedlimestonecontaining
galena and s p h a l e r i t e ; and
5)
a broad fringe
of hematizedlimestone
which generally gives way t o marbleized limestone (Titley,
78).
1958, p. 58-
Zone 3 from theLinchburg mine most closely resembles the skarn
d e p o s i t a t t h e I t o r t h E d d y Peak mine.
Argillization
Clay a l t e r a t i o n of f e l d s p a r i s common throughout the study area.
Hypogene a l t e r a t i o n of f e l d s p a r i s g e n e r a l l y r e s t r i c t e d t o r o c k s c l o s e
t o f a u l t s or intrusive contacts whereas supergene alteration occurs
o r a r g i l l i z e d z o n e s are a d j a c e n t t o f a u l t
a wider area. Local bleached
zones o r next to mafic
o r white rhyolite dikes
a t the surface.
The most i n t e n s e a r g i l l i c a l t e r a t i o n . i . 5
west by 750 feet north-south
over
a zone 400 f e e t e a s t -
i n sec. 21, 'T. 3S., R. 3W., 1.5 milessouth-
e a s t of North Ijaldy Peak (Fig. 24).
The nort.hwcst-trendingzone
a l m o s t e n t i r e l y w i t h i n t h e middleSpearsFormation.
boxwork s t r u c t u r e s a f t e r p y r i t e
:
is
The presence o f
as well as goethite staining of the
rock
i n d i c a t e t h e r e was a high amount of iron sulfide present before oxidation.
The a c i d i c s o l u t i o n s r e s u l t i n g
may have r e s u l t e d i n c l a y a l t e r a t i o n
from t h e o x i d a t i o n o f t h e p y r i t e
of the rocks.
Sericitization
S e r i c i t e a l t e r a t i o n of f e l d s p a r i s common i n t h e i n t r u s i v e a n d
volcanicrocks
i n thestudyarea,
ular, are characterized
The w h i t e r h y o l i t e d i k e , s , i n p a r t i c -
by a q u a r t z - s e r i c i t i c groundmassand
s e r i c i t e replacementofthefeldspars.
As much
a s s o c i a t e d w i t h t h eq u a r t z - s e r i c i t ea l t e r a t i o n .
quartz-
as 0.5 p e r c e n t p y r i t e
The a s s o c i a t i o n of
is
94
white rhyolite dikes with the
they used the
exposed s t o c k s a n d t h e s u g g e s t i o n t h a t
same conduits as the mineralizink and a l t e r i n g s o l u t i o n s
would a r g u e f o r t h e a l t e r a t i o n t o be hydrothermal.
4
ECONOFEC GEOLOGY
The study area overlaps
Xagdalenamining
by
p
mile the southeast corner
d i s t r i c t , whichproducedover
$52 m i l l i o n i n z i n c , l e a d ,
copper and s i l v e r (Chapin and others,inprepara.tion).
production came frorn limestone replacenent deposits
stone adjacent to
t h e southernexposure
of t h e
Mostof
i..~
n t h e Kelly Lime-
of the Oligocene stocks
adjacent to the Late Oligocene north-northwest-trending fault
wherein l i e s t h e main orezones.Kostofthecopperore
from the northern part of the Eagdalena
the
and
zone
was produced.
mining d i s t r i c t between t h e .
Mtt stock and t h e town of Kelly.Zinc-leadreplacementdepositsoccur
along the north-northwest
main ore zone i n t h e Linchburgmine,
2 miles
south of any ex-psed stock.
The presence of a buried stock underlying the southern portion
of t h e d i s t r i c t h a s b e e n p r e d i c t e d
Koschmann,
f o r many years (Loughlin
and
1942, T i t l e y , 1958, and Austin, 1960). One of thepurposes
f o r mapping i n t h e c e n t r a l Nagdalena:,Iountains
t h e p o s s i b i l i t y of the presence
Lena mining d i s t r i c t .
the southern portion
was t o b e t t e r e v a l u a t e
of a buried stock
in the southern
Kagda-
The presence of anothermineralizingcenter
in
of t h e d i s t r i c t would make limestone replacement
deposits o r a porphyry copper deposit definite targets for exploration.
- Occurrence
Mineral
Although mining
in
1869 (Jones, 1901L,p.
i n t e r e s t i n t h e c e n t r a l Ifagdalena Mountains began
126), therehas
95
been onlyminormineral
,
96
1953) r e p o r t e d a s of 19.52 only a
production.Smith(privatereport,
t o t a l of 784 t o n s of ore, which included0.21
o f Ag/ton, C.e.1 percent Cu, 7.09 percent Fb,and
producedfrom
no mining.
39 percent Zn, being
I n recent years there
t h e c e n t r a l HagdalenaKountains.
has been virtually
of Au/ton,2.26'02.
02.
The occurrence of m i n e r a l i z a t i o n i n t h e
c e n t r a l I,!agdalena Kountains has been briefly described
p. 71-74)andLasky
(1932, p.
by Xells (1918,
46-53), who c a l l e d it t h e X a t e r Canyon
mining d i s t r i c t .
f o u r genetic types:
. Mneralization present can be divided into
1) zinc,lead- and copper,2)gold,3)
fluorite.
manganese,and
4) b a r i t e and
The Mater Canyon stock i s barren of m i n e r a l i z a t i o n a s a r e t h e
rocks i n corkact w i t h t h e i n t r u s i o n .
The base metal deposits of zinc, lead, copper and silver occur
a s limestone replacement deposits, primarily
along fault zones.
bearing horizon
i n t h e K e l l y Limestone
The reputation of the Kelly Limestone as the orei n t h e Hagdalenamining
mostly non-productive prospect pits
d i s t r i c t r e s u l t e d i n nwmrous,
i n t h e K e l l y Limestone throughont
t h e c e n t r a l Kagdalena Fountains.
H i n e r a l i z a t i o n and a l t e r a t i o n i n t h e c e n t r a l Magdalena Kountains
are b e s t developed i n t h e h'orthEaldy
Peak area.
The Morth EaldyFeak
17,
mine l o c a t e d on t h e southeast shoulder
of North Ealdy Feak i n sec.
T. p . eR. Y,I.,
is developed i n a n a n d r a d i t e - ~
diopside skarn
coppersulfides.
(Figure24,in.pocket)
of the Kelly Limestone with associated
KO estimate of t h e tonnageproduced
t h e e x t e n t of theworkings would indicate production
zinc, l e a d , and
i s a v a i l a b l e , but
was minor.
skarn occurs a t t h e . i n t e r s e c t i o n w i t h t h e n o r t h e r n f a u l t o f t h e
The
North
97
Fork Canyon f a u l t zoneand
a north-northwest-trending fault,
which i s
occupied t y a wkite rhyolite dike.
The E l Tigre mine i s located i n sec. 21, .T. y., R. 3'-J. (Fig.
24), approximately 1 mile southeast
of North h l d y Peak.
The mine was
a small scale operation developed along the southern fault
Fork Canyon f a u l t zone.There
of t h e 8 o r t h
i s no s k a r n a l t e r a t i o n p r e s e n t
i f i e d f a u l t zones a t t h e c o n t a c t
of t h e HaderaLimestonewith
b u t silicthe
Frecambrian a r g i l l i t e a r e p r e s e n t . M i n e r a l i z a t i o n c o n s i s t s o f g a l e n a .
sphalerite,barite,
and r a r e l y c h a l c o p y r i t e .
monzonite dikes are
common.in t h e a r e a b u t
White r h y o l i t e and l a t i t e no major i n t r u s i v e body is
exposed.
The southermost exposure
of any appreciable amount of minerali-
z a t i o n i s found i n t h e Euckeye mine developed i n t h e K e l l y Limestone 'and
l o c a t e d on t h e d i v i d e between Copper Canyon and !dater Canyon i n see. 27,
T.
3.5.. R.
7;:.' ( F i g , 24).
Southeast of t h e Euckeyemine.
theKelly
Limestone i s truncated and downthrown on t h e e a s t side of t h e Water Canyon fault zone.According
of o r e c o n f i n e d t o t h e
t o Smith (privatereport,l953),smallpockets
Kelly Limestone were produced along
i n t h e Buckeye mine.
S i l i c i f i c a t i o n o f the limestone
ation present. There
i s only one recordofshipment
containing 0.02
02.
Au/ton, 2.79
No other records of shipments can
02.
Ag/ton, and
i n 191.7 of
be t r a c e d d i r e c t l y t o t h e
1.5 m i l e s t o t h e n o r t h
latite-monzonite dikes,
is t h e only alter-
53 t o n s
5.57 percentcopper.
although minor production may havecontinued.Except
yon stock located
fault awes
Buckeye mine
f o r t h e Water Gan-
and l o c a l w h i t e r h y o l i t e
and
there aTe no major i n t r u s i o n s i n t h e mine area.
98
is
South of the Paleo,zoic exposures, base metal .mineralization
almostabsent.Localtraces
of mal.achite a r e foundalongthenorth-
northwest-trending faults, but,
thestudyarea.Kinor
become absent i n the southern part
Igneous intrusion
Peak along fault zones,
and mineralization followed the
of the EatilG?oup during Late Oligocene time,
dalena mining
i n prospect
amounts ofchrysocollaarefound
p i t s southwest of South Ealdy
district penetrated the volcanic
t o w i t h i n 1000 f e e t of the surface.
To the south the Water Canyon s t o c k
only sparse mineralization
Kithburiedstocks
Peak a r e a
rock surface.
and t h e s p a t i a l l y a s s o c i a t e d
mineralization i n t h e Xagdalenamining
not uncovered the buried stocks
Xag-
rocks and may have r i s e n
Canyon stopped within the pre-volcanic
Erosion has uncovered both the stocks
emplacement
The s t o c k s i n t h e
and the buried stocks underlying the iinchburg-North Saldy
and North Fork
of
district.
However, e r o s i o n h a s
i n t h e c e n t r a l Nagdalena Xountains where
i s present. Kineralization
may be associated
and e x i s t i n greaterquantitywithdepth
Paleozoic rocks underlying the volcanic rocks
2n t h e
.
.
i n t h e c e n t r a l Xagdalena
Nountains.
Goldand
manganese occur i n t h e s o u t h a n d
c e n t r a l Magdalena Kountains t o t h e s o u t h
copper mineralization. Siliceous gold
t h e range
(Fig. 24),
than 2
3 miles south of North Ealdy
east p o r t i o n of the
and e a s t of t h e z i n c , l e a d , a c d
veins a r e . p r e s e n t a t t h e crest of
Peak i n sec. 31, T. 3S.,
The gold o c c w s a s a traceelement
H.
and l o c a l l y a s s p e c k s
3
W
.
less
mm.i n s i z e w i t h i n p y r i t e cubes t h a t are on t h e s i l i c i f i e d w a l l s
of a white rhyolite dike.
99
Reportedly, gold has
a l s o been mined from t h e Timber Peak mine
3’/1.,(I%%. 24)
i n secs. 4 and 5 , T . bS., R.
east-southeast ofSouthBaldy
Peak.
approximately
1.5
miles
According t o Jones (1904, p. 127.)
gold and s i l v e r v a l u e s were obtained. i n t h e e a r l y l9OO’s from limfted
production along fault
zo;?es.
of the cast-trending South
fault.
The mine i s l o c a t e d a t t h e i n t e r s e c t i o n
Canyon f a u l t and a north-northwest-trending
No v i s i b l e m i n e r a l i z a t i o n
i s presentbutcross-cuttingsilica
veinlets with pyrite oxidizing to goethite are present and restricted
t o t h e I i e l l s Xesa Formation on t h e n o r t h s i d e
of the South Canyon fault..
The l a c k of s i l i c a v e i n l e t s or goethite i n t h e younger S i m i l e Canyon
formation on t h e s o u t h s i d e
of the South Canyon f a u l t s u g g e s t s t h a t
t h e s i l i c a and p y r i t e may havebeen
Formation before the
introduced into tn? H e l l s Kesa
emplacement of the younger Sixmile Canyon volcanics.
The South Canyon f a u l t developed a f t e r t h e e x t r u s i o n
Hells Xesa ash flow.Fumarolic
of t h e
activityassociatedwiththeterminal
a c t i v i t y of t h e H e l l s Nesa ash flow eruption may have r e s u l t e d i n t h e
. .
emplacement o f s i l i c a v e i n l e t s , p y r i t e ,
and possiblygold.
difficult to Setermine whether the gold mineralization
during the fumarolic activity along the South
It i s
was introduced
Canyon f a u l t o r during t h e
main period of Oligocene mineralization along the north-northwest-trendingstructure.
The mine workings a r e p a r a l l e l t o
t h e north-northwest-
trending strccture suggesting that the gold mineralization
was locali7,ed
along the north-northwest-trending fault.
Manganese occurrences are common.in t h e e a s t e r n
por.tion of the central
P!agdalena Kountains.
and southern
A number of manganese mi.::es
davelo1:.d along north-northwest-trending structures occur
i n the southern
100
h a l f of therange
k. y;:.
as well.
(Fig. 24) of\,later
40 percent
Canyon produced 8 9 tonsofover
manganese from 1914 t o l9lE ( t ? e l l s , 1918, p. 72).
b u t a l s oc o n t a i n s
26, T , 3S.,
A mazganese mine l o c a t e d i n s e c .
The o r e i s mostly waci,
some psilomelane and manganiferousc$lcite.
The mine
i s developed i n a block of Timber Peak rhyolite surrounded by Popotosa
Formation d e b r i s f a l l e n from theoverhanging
cliffs.
The m i n e r a l i z a t i o n
was emplaced along a Late Cenozoicnorthwest-trending
of t h e \,!ater Canyon mine.
placedtheFopotosaFormationsoutheast
i n t e r p r e t a t i o n i s correct, then’ the
than the
main perioj of Late
The younger age
manganese mineralization obtained
(1971) i n t h e L u i s Lopez manganese d i s t r i c t l o c a t e d
ChupederaKountains,
10 m i l e s e a s t
If t h i s
manganese m i n e r a l i z a t i o n i s younger
Oligocenemineralization.
corresponds with Pliocene dates for
byNeber
fault that dis-
of t h e Nagdalena3!ountains.
i?lt h e
Only more
d e t a i l e d mapping and c o r r e l a t i o n of dated events w i l l h e l p t o d e t e r m i n e
whether both areas
were affected by the
same period of
manganese mineral$.-
z:!tion.
Earite occurs along
l e n a l!ountains.
f a u l t planes throughout the central
3 a r i t e i s most comvon i n t h e North Ealdy Peak m e a
where it i s associated w i t h minoramountsof
of barite occur along Late Oligocene faults
r h y o l i t ed i k e s
as
Hagda-
fluorite.
IEinor amounts
and t h e w a l l s of w h i t e
s o u t h of thePaleozoicexposurcs.
i3arite veins, as wide
3 f e e t , 2nd quartz veinlets occur along the Water
Csnyon f a u l t zone.
of Nineralization
Controls The f a c t o r s which controlled mineralization i n t h e c e n t r a l
MagdalenaXountains
we:*e t h e same t h a t a f f e c t e d
t h e Xagdalenamiping
.
101
district.
A' r e v i e x of t h e s e f a c t o r s is now presentt.,? i n o r d e r t o a i d
futura mineral exploration.
The age of, mineralization i s Late' 01igOCenO \.ased on i t s as30.5 m.y.
sociation with the 28 to
stocks i n t h e i"I+::,lalena Mountains.
I G n e r a l i z a t i o n , w i t h the possible exception
ofmangcrrtwse,
event to affect the area prior to the uplift
Chapin(1971-a)
was t h e l a s t
of t h o k g d d l e n a I4ountains.
reported a younger period of l e a d - s l l v e r m i n e r a l i z a t i o n
c u t t i n g t h e 23.8 n.y. La J a r a Peak Formation i n t h e s o u t h e r n XearNomtains.This
secondperiod
of mineralization appears to be minor, and
t h e r e i s no evidence of i t a f f e c t i n g t h e Magdalena Xountains.
.Wineralization occurs primarily as limestono replacement deposits
in.the Rississippian Kelly Limestone, the
t h e Precambrianrocksconducive
first favowble horizon above
t o s u l f l d e minerali::nt,ion.
lying Pennsylvanian quartzites, shales,
The over-
and l i m e s t o n w l o c a l l y c o n t a i n e d
minor o r e and may have acted as a r e l a t i v e l y inlpermtvthle capping forcing
the solutions to
move l a t e r a l l y through the Kelly Llwstone.
The mair. s t r u c t u r a l c o n t r o l was t h e Late Olit:ocene,
northwest-trending fault
north-
zone which c o n t r o l l e d t h e eanplacement of t h e
Oligocene stocks and d i k e s and provided the conduits for the ascent
thehydrothermalsolutions,
trendingfault
zoneand
The stocksintrude
arenotfaulted
northwest-trending zonecaused
by it.
t h e north-northwest-
Intrusionintothenorth-
the northerly alignnont
t h e Plagdalena m i n i n g d i s t r i c t (Loughlinand
of
of t h e s t o c k s i n
Koschmann, 1942, p l a t e 2 )
:
and t'..c N, 10'
3.
dikes that are
common i n t h e c e n t r a l Kagdalena EoUntn-l.ns; The main o r e
alignment of dike rocks, particularly
zone containing zinc-lead mineralization
t h e white rhyolite
i n the Lincht,urg mine, 2 miles
102
south of t h e exposed Oligocene stocks, para.llels the north-northvest0
t h e X. '80
trendingstructure.Otherpre-existingstructuressuchas
NorthFork
Canyon s t r u c t u r e a p p e a r t o
'2.
have aided i n stock and dike
emplacement.
The s p a t i a l a s s o c i a t i o n of the mineralization with
stocksdemonstratesthe
t h e Oligocene
magmatic controloforedeposition.Future
eral exploration should be directed
toward the finding of
because of p o s s i b l e m i n e r a l i z a t i o n i n
min-
more s t o c k s
t h e adjacent bedrock
or i n the
intrusion itself.
Eased on t h e s e c o n t r o l s c e r t a i n g u i d e l i n e s c a n
f i n e areasunderlain by thesestocks.
The north-northwest-trending
s t r u c t u r a l zone c o n t r o l l e d t h e emplacenentof
should b e c a r r i e d o u t a l o n g t h i s
White rhyolite dikes, because
the stocks
and e x p l o r a t i d n
zone f o r potential bu-ried stocks.
of t h e i r s p a t i a l a s s o c i a t i o n w i t h
posed stocks i n t i e Kagdalena mining
Alteration of the volcanic
ex-
d i s t r i c t (Loughlin and Xoschmann,
194.2, p l a t e Z ) , nay be surface indicators
c r i b e dt ot h e ' e x p o s e d
be used t o de-
o f buried stocks.
can be as-
and sedimentary rocks
o r p o s t u l a t e db u r i e di n t r u s i o n s .P r o p y l i t i c
a l t e r a t i o n i s hidespread i n t h e S p e a r s Formation i n t h e Elagdalena min-
i n g d i s t r i c t b u t becomes more restricted along the north-northwesttrending structures in the central
Magdalena Kountains. This decrease
i n a l t e r a t i o n i n t h e c e n t r a l NagdalenaF!ountains
from the source area
of the
could signify distance
o r contrastingrocktypes.Jasperoidreplacement
Kelly Limestone i s common i n t h e !.iagdalena mining d i s t r i c t b s t
i s present only in the
Kountains.
KorthEaldy
Peak a r e a o f t h e centrali.:agdaIena
!he Precambrian a r g i l l i t e exposed i n sec.
le,
T.
x., R.
3!.
103
i s p a r t of a north-northwest-trending horst block $hat
i s almost t o t a l l y
. .
replaced by s i l i c a . T h i s
i s t h e most complete a l t e r a t i o n o f t h e a r g i l -
l i t e anywhere i n t h e Plagdalena Kountains.Farther
tothesouth,silica
veinstrendingnorth-northwestcutthevolcani.csandlocallytotally
17, T.
replacethem,(sec.
Peak,Fig.
24).
3S.,
.
R . 3W.. 0.5 n i l e s o u t h e a s t o f
Xorth Ealdy
S i l i c i f i c a t i o n becomes 1 e s s . c o n n o nf a r t h e rt o
S i l i c a t i o n i s possibly another indicator of
Pyrometasonatic deposits occur adjacent
a buried stock.
t o north-northwest-trending
s t r u c t u r e s i n t h e Linchburg-Morth Ealdy Peak a r e a , 2
t h e exposedstocks
t h e south.
i n t h e Hagdalenamining
t D
district.
d e p o s i t i n t h e Linchburg mine north of the study area
3 miles south of
The pyrometasomatic
and a small skarn
d e p o s i t on the southeast
limb ofNorthBaldyPeak
suggest a possible
. .. ,..
localsourceforthealteringsolutions.
Hoth d e p o s i t s may bethe re-
s u l t of hydrothermal solutions emitted
from an intrusion underlying the
Linchburg-EorthBaldy
and southoftheLinchburg-Eorth
Peak a r e a . E a s t
Baldy Peak a r e a s i l i c a t i o n
i s absent.
s e n t i n these areas suggesting
Iiowever, s i l i c i f i c a t i o n i s pre-
a g r e a t e r d i s t a n c e from t h e source of
the
altering solutions.
Zinc-lead-copper-silver mineralization occurs predominately
the northwest portion of the Hagdalena Mountains whereas gold
manganese are mainly i n t h e central:.!agdalenaMountains.
and
Any zoning
model i s complicated by the presence of multiple plutons, exposed
inferred, each of
in
or
which could be the source for local hydrothermal
solutions.Konetheless,
a generalzonationdoesappear
Most of the copper mineralization
t h e Kagdalenamining
t o bepresent.
i s a d j a c e n t t o t h e exposed s t o c k s i n
d i s t r i c t w i t h l o c a l , minor o c c u r r e n c e s f a r t h e r t o
104
i n lime-
i n t h e c e n t r a l Kagdalenab!ountains.Zinc-leadoccur
thesouth
stone replacernent &posits
as f a r s o u t h a s t h e
c e n t r a l Magddenalcountains.?heareas
Euclceyemine
in the
of g r e a t e s t c o n c e n t r a t i o n o f
lead-zinc mineralization are adjacent to the Oligocene stocks
Linchburg mine.
Tungsten i s anomalouslyhigh
i n t h e v i c i n i t y of t h e
Linchbwg mine ( A u s t i n , 1 9 6 0 ) o c c u r r i n g a s s c h e e l i t e i n
somaticoresalong
and i n t h e
a north-northwest-trendingfault.
t h e pyrometa-
I4inor valuesof
gold,occur i n t h e o r e and jasperoid deposits i n t h e Mzgdalenamining
district.
Gold also occurs
i n siliceousveinscuttingvolcanicrocks
i n t h e c e n t r a l Xagdalena Kountains, peripheral
copper d e p o s i t s i n t h e northwest portion
s o c i a t e d with the galena
t o t h e major zinc-lead-
i n t h e Magdalena mining
district.
. ,.
mineralization i s p e r i p h e r a l t o t h e Kagdalena mining
volcanic rocks
Kountains.
i s as-
of t h e r a n g e . S i l v e r
district cutting
i n t h e e a s t e r n and southern foothills of the
Some of t h e manganese may be younger than the
of zinc-lead-copper mineralization and, therefore,
Hanganese
Magdalena
main period
may r e p r e s e n t a
separate period of mineralization.
Two d i f f e r e n t s o u r c e a r e a s f o r m i n e r a l i z i n g f l u i d s a r e d e f i n a G l e
on t h e b a s i s o f a l t e r a t i o n
andmineralassemblages.
i s a d j a c e n t t o t h e Nitt stock i n t h e Kagdalenamining
The northern area
d i s t r i c t where a
pyrometasonatic mineral assemblage with associated sulfide minerals
ex-
tends from the Linchburg mine t o t h e North Ealdy Feak area overlapping
into the central
KagdalenaMountains.
The Linchburg-P!orth
EaldyFeak
a r e a i s considered t o be a continuation of the main o r e zone from the
XagdaleRa mining d i s t r i c t . F l u i d s
from a buriedstockunderlying
the
Linchburg-Korth Baldjr Peak a r e a rose along t h e n o r t h - n o r t h H e s t - t r e n d i n g
105
f a u l t s m i n e r a l i z i n g t h e K e l l y Limestone much'the same way as i n t h e
northern area a d j a c e n t to t h e Nitt stock.
..
. .~ ..
GEOLOGIC HISTOZY
Precambrian t o Middle Cenozoic
”
”
The deposition of impure a r g i l l a c e o u s and quartzose sediments
during Precambrian time was followed by a r e g i o n a l metamorphism r e s u l t ing i n theformationofargillite
metamorphism could have been
granite.Tilting
i n t h e Magdalena area.
The low-grade
a t l e a s t i n p a r t due t o t h e i n t r u s i o n o f a
of t h e metasediments t o t h e n o r t h e a s t
marked the end
of Precambrian orogenic activity.
1s.opachand f a c i e s maps drawn by Kottlowski
during i;;arly and Xiddle Paleozoic
area.
(1965) show
that
time, c e n t r a l New Kexico was a p o s i t i v e
It i s presurned t h a t t h e extensive erosion and levelling
Precambrian terrain took place during
t h i s time.
of t h e
A n a r i n e b a s i n ex-
i s t e d i n s o u t h w s s t e r n Xew Mexico during the Early and
Hi&dle Paleozoic,
but n o t u n t i l t h e Kississippian Period did shallow epicontinental seas
transgress northward across the
Limest0r.e (hrmstrong, 1963).
stone, Hississippian
.
Magdalena area, d e p o s i t i n g t h e Kelly
F o l l o i ~ n g t h e d e p o s i t i o n of the Kelly Lime-
seas withdrewtoward
the south, alloxing
wide-
spread erosion to occur during Late Nississippian to Early Pennsylvanian tine,
The geography o f west-central h’ew !,lexica changed g r e a t l y i n
Pennsylvanian time (Kottlowski,
1965). Seastransgressedfromthenorth
depositing marine limestone, quartzose sandstone, and shale of the
dalena Group.
The 2350 f o o t t h i c k n e s s of MagdalenaGroup
Kagdalena Kountains suggests that the
Lucero-Sanbiateo
106
t4ag-
i n the central
Easin was one
107
large, north-trecding
channelway i n s t e a d of two d i s t i n c t b a s i n s s e p a r a t e d
i n t h e Magdalena a r e a a s proposedbyKottlowski
(1965).
I n Early Perm-i-
a n time, terrestrial sedimentation ensued with the deposition
shale,siltstone
of red
and sandstone of t h e Ab0 Formation.
Eo sedimentary record of Kesozoic s t r a t a e x i s t s i n t h e Kagdal’ena
Hountains.Lithofacies
and isopach maps (Kottlowski, 1965) i n d i c a t e
t h a t L a t e Permian, T r i a s s i c , and Late Cretaceous strata
i n t h e Magdalena area, but erosion during
Mesozoicand
were deposited
Tertiary time
has removed them,
The Kagdalena a r e a i s s i t u a t e d on the northwest flank
and o t h e r s , i n
major Late Cretaceous-Early Tertiary uplift (Chapin,
preparation).
of a
The o u t l i n e of t h i s major Laramide uplijCt,ispooaly known
and i s determined by locating areas
where t h e Eocene Oaca Formation
o v e r l i e s t h e Upper Cretaceous !a!esa Verde Group.
present data indicate
Using t h i s evidence,
t h e major Laramide u p l i f t i s hordered t o t h e
north i n t h e J o y i t a llills, t o t h e west i n southern Gallinas Range, t o
t h e e a s t i n the Socorro Mountains
and t o t h e s o u t h
f l a n k of t h e SanMateo Mountains(Chapin,
on the southwest
and o t h e r s , i n p r e p a r a t i o n ) .
U p l i f t and t i l t i n g of t h e Kagdalena area during the
Laramide
orogenywre followed by erosion and beveling of the area:during
time.
The removalof
the variable thickness
Eocene
t h e Ab0 Formation i n t h e \,later Canyon a r e a and
of t h e Madera Limestone r e s u l t e d from erosion
during Loccne time.
Cenozoic volcanism began
Oligocene time with the deposition
i n t h e Magdalena area during Early
of Spears Formation, the basal
of t h e D a t i l Group, approximately 37 m.y.
ago.
unit
The lower member i s a
108
volcanoclastic deposit consisting entire1.y of debris derived
I.!ogollon Plateau volcanic piro-
l a t i t i c ar.d andesitic flow rocks of the
v i n c et ot h es o u t h
from
andsouthwest.IRbricationdirectionstaken
c l a s t s o f Abo Formation within the unit indicate
p o r t from thesouthwest.
a direction of trans-
The deposition of the porphyritic andesite
i n t h e Eagda-
flow, which i s the middle'memhr of the Spears Formation
lena area, represents
i n the sedimentation process
a temporary break
t h a t was renewed again i n t h e upperSpearsFormation.
The l a t i t i c
volcanic rocks i n t h e upper Spears Formation represent the
placement of ash flows
from
first em-
upon t h e Hagdalena area.
Following the deposition of the upper Spears Formation,
0
N. 80 V,-trending fault
zonedeveloped,
calledthe
f a u l t , which uplifted the northern portion of
by 1400 f e e t .
formation
of
the
Iiorth
a
NorthFork
Canyon
t h e Magdalena Kountains
The emplacement of the !iells Nesa Formationfollowedthe
!,I' f '
Fork Canyon f a u l tQ. u a r tlza t i taes fhl o w s
probably moved northwardfrom
( J ~ $~'
?<-,
<'
2",.
a sourcelocatedsouthofthe.studyare2
.
\'" .
-\
and possibly overlapping the southeast portion of the central
!,!agdalena
1.lountains i n t h e a r e a between Timber Peak and Ruck Peak (Pig.
3). The
H e l l s Resa volcanics filled the paleovalley south
yon f a u l t zone,eventuallycoveringtheescarpment.
of t h e North Fork CanThe e r o s i o n of t h e
Spears Formation on t h e Upthrown s i d e of the escarpment resulted
deposition of volcanoclastic sediments
in the
between t h e i n d i v i d u a l a s h f l o w s
of t h e t i e l l s PIesa Formation.
The speculated source area of the Hells
KesaFormationbetween
Timber Fedc and Euck Peak, which i s covered by younger volcanics,
based on thefollowingobservations,
The r a p i d i n c r e a s e
is
i n thickness
'
,I
leg
o f t h e Zells Kesa ashflowssouthward,from
KorthEaldy
south of
Peak a t s e e I 18, T . 3K., K. 3!. t o 3850 feet. t h r e e miles
icorth Ealdy Peak,.may indicate proximity
southernportion
flOV7S
l e s s t h a n 200 f e e t west of
of the study area.
occurred along ring fractures
to the source i n the
The extrusionof
t h e voluminousash
which developed i n t o f a u l t s follow-
i n g t h e c o l l a p s e of the roof overlying the
Hells Nesa magma chamber.
The South Canyon f a u l t i s considered t o be a r i n g f a u l t which t r u n c a t e s
t h e E e l l s Hesa Formation and allows volcanoclastics and andesite.flows
of the Sixmile Canyon a n d e s i t e t o fill the collapsed caldera overlying
the source area of the
Hells Elesa Formation.
The lack of megascopic l i n e a t i o n i n t h e I j e l l s Mesa Formation exposed i n t h e c e n t r a l Nagdalena Mountains prevented flow
directions to
. ...
bedetermined.
However, i n t h e s o u t h e r n
Kagdalena Kountains,
rear Wountains, n o r t h o f t h e
brown (1972) determined from flow
structures t h a t
Eells Kesa Formation may have been t o t h e s o u t h
the source area for the
o f t h e town of biagdalena.
The Sixmile Canyon a n d e s i t e was probably deposited i n a caldera
t h a t forired by collapse along ring faults
following the eruption of the Hells
walls o f t h e c a l d e r a
such as t h e South Canyon f a u l t
Xesa ashflow.
T h e s t e e p , unstable
and
underwent caving and avalanching, depositing
fillingthecalderawithvolcanoclasticsediments.
A 'shallow, calm l a k e
of limited a e r i a l extent formed during t h i s time on the caldera floor
d e p o s i t i n g minor limestone. Kost of the filling of the caldera,
was t h e r e s u l t o f t h e d e p o s i t i o n
evidence for resurgency
P
of andesiticflows.There
i n t h e 1':ells Kesa caldera.
however,
i s no
110
Fyroclastic volcanism i n the c e n t r a l ?,fagdalena Fountains was
renewed w i t h t h e emplacementof
the Sawmill Canyon formation, and
i n the northern San
p a r t d e r i v e d from a source area located
tains, southwest of the
was i n
Mateo Foun-
Rhodes, i n p r e s s ) .
Magdalena Kountains (Deal and
I n t h e S a r n i l l Canyon area of the central and southern Kagdalena
tains, the
S a m i l l Canyon formation i s exposedover
I,[, r ?'
creases greatly in thickness.
g e n e r a l l yn o r t h ,
a l a r g e area and in-
3,
The d i p oftheSawmill
Sawmill Canyon v a r i e s from 45'
?!om-
Canyon formation i n
east t o nearly v e r t i c a l a n d t h e s t r i k e
The widespread a e r i a l d i s t r i b u t i o n , t h e g r e a t
ness, and the steep dips of the Sawmill
is
thick- .
Canyon formation could indicate
another source area located.in the southern
Magdalena I.:oun?.ains and over-
lappino, i n t o t h e southwest.ern portion of t h e c e n t r a l Magdalena Fountains
between Langmuir Laboratory and TjmberPeak
('Fig. 3 ) .
Following t h e emplacement of Sawmill Canyon formation, the South
Canyon f a u l t between Timber Feak and South Baldy Peak
and downdropped t h e areasouth
with minor ash flow
of t h e f a u l t .
was r e a c t i v a t e d
Andesite lava flows coupled
t u f f s and volcanoclastic sedimentary rocks coxposing
the South E d d y Peak a n d e s i t e f i l l e d t h e d e p r e s s i o n s o u t h o f t h e ' r e a c t i vated South Canyon f a u l t .
The South Faldy andesite
p o s i t e d i n a caldera formed by t h e c o l l a p s e o f t h e
may havebeen
de-
roof overlying the
Sawmill Canyon formation magma chamber l o c a t e d i n t h e s o u t h w e s t p o r t i o n
of the central
Xagdalena Yountains and
i n t o t h e southern IHagdalena Noun-
tains.
The f i n a l p y r o c l a s t i c e v e n t t h a t e f f e c t e d
hountains was t h e emplacementof
t h e c e n t r a l Hagdalena.
t h e Timber Peak r h y o l i t e , whose source
a r e a i s i n t h e b!t. Withington area of the northern San Hateo Nountains
I
~~
~
a
a
121
(]Seal and Iihodes, i n press).
During LateOligocenetimethecentral
Kagdalena Nountains were faulted
and t i l t e d along a north-nor'thvest-
trending zone along which dikes and stocksintruded.Thesestocksrange
i n age from 28 t o 30.5 m.y. giving a minimum age f o r t h e f o r m a t i o n
of
the fault
As-
zone a s w e l l a s t h e c e s s a t i o n o f p y r o c l a s t i c v o l c a n i s m .
sociated w i t h the Oligocene igneous activity
alteration that affected the
was the mineralization and
l,!agdalena mining d i s t r i c t and t h e c e n t r a l
Kagdalena Fountains.
Late Cenozoic
The Late Cenozoic geologic history
of t h e MagdalenaI*loun'iains
can best be determined by the depositional
ofthePopotosaFormation.
and p o s t - d e p o s i t i o n a l h i s t o r y
The PopotosaFormation
r e s u l t e d from t h e
erosion of the highlands, producing the bordering coarse-grained
sedi-
ments'of a l l u v i a l fan deposits intertonguing with the finer-grained sedi-
25). The o r i g i n a l s z z e and shapeof
mentsofplayadeposits(Fig.
Fopotosa Pasin can be only partially reconstructed, but according
Eruning
(1973, p. 108), it
t h e NagdalenaMountains
a n east-west direction.
about 24 m.y.
extendednorth-south
to
a t l e a s t 30 miles from
t o t h e Ladron Kountains and
at least
35 miles i n
The d e p o s i t i o n of thePopotosaFormationbegan
ago during the
t h e BearI,!ountainsand
the
emplacement of t h e La Jara PeakFormation
ceased i n t h e S o c o r r o Peak a r e a b e f o r e t h e
t r u s i o n of flows approximately 11m.y.
The o r i g i n a l Fopotosa Easin
u p l i f t of the ancos-
of Yopotosa deposition.
of t h e a n c e s t r a l i-:ao,dalena Kountains began
.. .-...
ex-
ago.
was modified by
t r a l Magdalena 1.iountains duringthetime
in
Uplift
a f t e r t h e emplacement, of t h e
e
112
COLORADO
PLATEAU
.
?.
Mopdoleno Peak v o I c o n i c s
Figure 25.
Vest-central Keu l,!exico during l.!iddle t o L a t e t4iocenetime
showing t h e d i s t r i b u t i o n of volcanic rocks a n d f a c i e s of
t h e Popotosa Formation according t o Sruning (1973).
113
La Jara Peak Formation.
D e t r i t u s d e r i v e d from t h e d i p s l o p e
Peak Fomation capping the north
a f a c i e so ft h e
Hountains(Fig.
25).
A longperi-
Xagdalena1,iountainswere
own debris. Rhyolite lavas
overlie fanglonerates
Dry Lake Canyon,
1973, p. 94).
PopotosaFormation(Eruning,
od of erosion ensued until finally the
beneath their
was shed
end of the Pagdalena [Nowtains
north and west forming the distinctive fanglomerate of
Sarz
ofLa
buried
from a vent a t 1k.gdalena Peak
of t h e PopotosaFormationwestof
These 14 m,y. flows (Weber,
gradation of t h e Kagdalena Nountains occurred
t h e Eagclalena
1971) s u g g e s tt h a t
de-
a t l e a s t up u n t i l t h a t time,
Following the deposition of the Fopotosa Ii'ormation i n Ieiocene
time, west-central
New Nexico underyent
a tectonic adjustment after the
. c e s s a t i o n of v o l c a n i c ( . c t i v i t y i n t h e S o c o r r o. . Peak area about 1
1m.y.
(Fig. 2 6 ) .
The o r i g i n a l PopotosaEasin
number o f i n t r a b a s i n h o r s t s
Mountains,and
was subsequentlydisrupted
such as t h e Magdalena Nountains, the Eear
theSocorro-Lemitar
!.!ountains.
U p l i f t of t h e Xagdalena Kountains may have begun
tihe emplacementof
by a
shortly after
t h e 14. m.y. Magdalena Peak r h y o l i t i c l a v a s ,
almost c e r t a i n l y after the llrn.y. Socorro Peak.lavas.
t o s a Formation was removed from the northern
Paleozoic and Precambrianrocks.
and
The e n t i r e Popo- , .
14agdalena Nountains exposing
The north end of the Nagdalena
Xoun-
t a i n s was l o c a t e d z t . l e a s t as far north as Bear Springs canyon along the
east s i d e of the present Dear Nountains (Eruning,
1973) b u t was down-
f a u l t e d n o r t h of U S , Highway 60 along the San Augustin lineament
(Fig. 26)
Continued u p l i f t i n Pliocene and Quaternary time has allowed the
erosion of m w h of t h e Popotosa Fornation
..
'
. .... . .
. ,,. ...'I.?.. :
-...
.r.,
~
'
,
.
.
i n t h e c e n t r a l Magdalena
3.14
COLORADO
RIO GRAfdDE
GRABEN
PLATEAU
ACOMA
EMBAYMENT
Figure 26.
.
LUCERO
U P L l FT
The m j o r Late Cenozoic structural trends which influenced
theformationofthe
Fiolocene physiographyofwest-central
Ke7.r i.;exicor---i;ata outside t h e E?gddalcria area compiled fro?
Eruning (1973)and Ch;ipin, and o t h e r s ( i n p r e p a r a t i o n ) .
Kountains.
The fanglomerates, which crop o u t het%zeen South Eildy Peak
and Langmuir Laboratory, and
a t Ciater Canyon Piesa, r e p r e s e n t t h e rem-
nants of thePopotosaFormation.
PiagdalenaMountains
The PopotosaFormation
has been greatly reduced
i n t h e central
i n volumne and a e r i a l ex-
t e n t . . U p l i f t of' t h e Xagdalena Kountains since Pliocene time along
basin-rar.ge faults has been as
t o the bordering basins.
much a s 5,000 f e e t i n e l e v a t i o n . r e l a t i v e
LATE CEROZOIC TECTONIC SETTING
The purpose of a physiographic classification
i s the ready
c h a r a c t e r i z a t i o n of large areas for identification, comparison,
trast.
Such a c l a s s i f i c a t i o n i s based on geologic structure
morphicstage.
A physiographic classification
i n t o i t s correct structural
and geo-
t h a t d o e sn o ts e ta na r e a
o r topographic setting defeats
If the physiographic province includes areas
and con-
i t s purpose.
of s t r o n g l y c o n t r a s t i n g
s t r u c t u r e s , it becomes misleading.
\*Jest-central New Kexico has been divided into the Colorado
Plat.eau physiographic province
Easinand
and t h e Mexican 17ighland section of t h e
Range physiographicprovince(Eardley,1962).
Itountains are located within the Easin and
i n c e and a r e a d j a c e n t t o t h e e a s t e r n
physiographicprovince.
The Kagdalena
Range ,physiographic'prov-
edgeof
the Colorado Plateau
The Easin and Range province i n west-central
New Nexico i s characterized by generally north-trending mountain ranges
and b a s i n s forming a s t r u c t u r a l and topographic depression known as
t h e Rio Grande graben.
Colorado Plateau
The Colorado Plateau province
i s located west and north of the
Kagdalena Kountains and occupies a rectangular area
of almost l 5 O , O O O
square miles w i t h i n northwestern Cew Xexico, northeastern Arizona, southeasternUtah,
and southwesternColorado.
The ColoradoPlateau
acterized by flat-lying sedimentary rocks greater than
116
i s char-
10,000 f e e t t h i c k
117
and i s bordered on
a l l s i d e s by belts of Cretaceous and Early
f o l d s and t i n r u s t s ( G i l l u l y ,
Tertiary
1963, p. 156).
Fitzsimmons (1959) differentiated
t h e Colorado Plateau province
of west-central Kew Nexico i n t o t h e Lucero u p l i f t , t h e Alcoma embayment,
and theNogollonslope(Pig.
slope i s n o t a s i n g l e
TheMogollon
27).
geomorphic feature b u t i s r a t h e r an area of individual ranges, 5ncluding
the Gallinas Hountains and the
San hlateo Fountains.
A l l of west-central i?ew Mexico underwent
development through the Kiddle
similar t e c t o n i c
Tertiary, including t h e emplacement of
Oligocenevolcanicsandintrusives.Eeginning
the present physiographic separation
from the Colorado Flateau acting
a
i n L a t e Cenozoic time,
of west-central Kew Xexico r e s u l t e d
as a r e l a t i v e l y s t a b l e c r u s t a l block
w h i l e t h e Easin and Range’ province underwent’ d i f f e r e n t i a l movement and
block faulting.
Easin and Range Province
”
The Easin and Range province has become t h e t y p e area f o r a
structural pattern comonly called basin-range
or fault-block structure.
What i s commonly r e f e r r e d t o as t h e Easin and Range t y p e o f s t r u c t u r e s
i s a c t u a l l y o n l y one of v a r i o u s t y p e s of structures found i n t h e prov-
ince.
Kountainrapgesresulting
from s t r u c t u r a la n t i c l i n e sw i t ha d j a -
c e n tb a s i n sb e i n gs t r u c t u r a ls y n c l i n e s
are a l s op r e s e n t .
Domal
i n t r u s i o n s formed othermountainranges.tiorstandgrabentypeof
s t r u c t u r e s c h a r a c t e r i z e d p a r t i c u l a r l y by the Rio Grande graben occur
withintheEasin
and Range province.
From t h e d i v e r s e s t r u c t u r e p r e s e n t ,
c
GRABEN
COLORADO
PLATEAU
ACOMA
EMBAYMENJ
Figure 27.
GRANDE
/ RIO
’
LUCERO
UPLIFT
I~iajorphysiogl*aphicfeatures w i t h i n theColoradoFlateau
and the Rio Grande graben of west-central New BIexico.--Data
outside the biagdalena area compiledfromBruning
(1973).
Chapin, and o t h e r s ( i n p r e p a r a t i o n ) andFitzsimmons (1959).
119
the tern Pasin
and Flange t r u l y d e s c r i b e s a gross physiographic aspect,
and no general explanation
of t h e s t r u c t u r e
i s possible.
Historical Sketch
The origin of the Easin
and Range topography and i t s structural
implications have longbeendebated
among geologist.
King(1870)
inter-
preted the mountains i n Nevada and western Utah a s e r o s i o n a l remnantsof
Late Jurassic folds.
Iie assumed t h a t t h e
Range province were similar
mountainsof
t h e F,asinand
t o t h o s e i n the Valley and Ridge province
the Applachian Hountains i n appearance, but
of
he a t t r i b u t e d t h e d i f f e r e n c e s
i n topography t o di€ferent climate conditions
under which
t h e two moun-
t a i n a r e a s developed.
G i l b e r t (1874) concluded from t h e geomorphic
..
evidence i n Nevada
on o n e ' o r b o t h s i d e s by
and western Utah that the mountains are bordered
f a u l t s and havebeen
raised and/or rotated
i n relatively recent geologic 'time,
above t h e i n t e r v e n i n g basins
He i n f e r r e d t h a t b a s i n
and Range
topography was caused d i r e c t l y by Late Cenozoic f a u l t i n g , t h e e f f e c t s o f
which a r e s t i l l manifest . i n t h e modern landscape.
Davis (1903)supported
G i l b e r t ' s t h e o r i e s and systematized observations €or t h e r e c o g n i t i o n of
an area's
geomorphic stage ofdevelopxent.
The genesis of t h e mountain ranges i n t h e Kexican Highland sect i o n of theEasin
and Range province i s e q u a l l y c o n t r o v e r s i a l .
(1969) considerec! the
Cserna
overwhelming majority o f t h e mountain ranges i n the
north-central Chihuahua t o be cornplex anticlines whereas the intermontane
basinsaresynclinesfilled
w i t h LateTertiarysedhents.
map evidence i s s c a r c e t o prove thepresence
fie noted t h a t
of faultedblocks.
However,
*
120
Yuan (1962) characterized the Easin
and Range province of Arizona and
iiew I+xico a s f a u l t e d mountain ranges separated
developedsincepost-Pliocenetime.
by s t r u c t u r a l t r o u g h s
He suggestedthepresence
e r o s i o n a l s u r f a c e s i n correlatable layers across the San Pedro
southeastern Arizona and the Rio
of
River i n
Grande i n New Xexico i n d i c a t e t h e
t e c t o n i c i n s t a b i l i t y and a c t i v e u p l i f t of the Rasin and
Range province.
Rio Grande Graben
The Rio Grande graben
i s t h e dominant f e a t u r e o f t h e Basin and
Range province of west-central Eew Kexico.
The RioGrandegraben
is a
s t r u c t u r a l l y and topographic low a r e a t h a t d i v i d e s h’ew Mexico i n h a l f .
It trends north-northeast for about
600 miles from northern Chihuahua.
Nexico t o n o r t h ofLeadviZle,Colorado(Chapin,
characterizes the Eio
. ,.
1971-b).
b l o c kf a u l t i n g
Grande graben which consists of generally north-
trending mountain ranges and basins arranged
i n a n % echelon manner.
hryan (1938) described the geology of the Rio Grande valley and
noted the offset
of t h e Miocene Satlte Fe Group by Late Cenozoic
Kellq (1952) showed thedepression
trending grabens along the course
Eiexico Kelley
t o be a series of
of t h e RioGrande.
echelonnorthI n c e n t r a l flew
(1952) r e s t r i c t e d t h e R i o Grandegrahen t o a narrow con-
s t r i c t i o n , which 2id not include the
Magdalena Mountains.
Chapin (1971-h) noted that the south
a p p e a r s t o widenand
splay out into the Fasin
southern New Hexicoand
that the north
along t h e upperArkansasValley
Grandegraben
faults.
endof
t h e Rio Grande graben
and Range province of
end t a p e r s t o a narrow depression
i n Colorado.
may r e p r e s e n t a rift formedby
He s u g g e s t e d t h a t t h e Rio
c r u s t a l . a t t e n u a t i o n as t h e .
121
Colorado Plateau moved west-nortnwestward away from t h e c o n t i n e n t a l i c terior.
Eased on f o s s i l s i n b a s a l a l l u v i a l
interbedded volcanic rocks Chapin
f i l l and K-Ar d a t e s on
(1971-b)argued
that block faulting
began a t least 18 m i l l i o n y e a r s ago.
Results of t h e a u t h o r ' s s t u d y
placement of
t h e Eagdalena Kountains
have e s t a b l i s h e d a basis f o r t h e
i n t o t h e R i o Grandegrabenof
b a s i n and Range physiographicprovince.
north-northwest-trendinguplift
approximately 14 m.y. ago.
The Magdalena ?fountains are. a
formed by Late Cenozoicblockfaulting,
The renewal of upli.ft of the
t a i n s i n Holocene time i s suggested by scarps
and l a n d s l i d e s .
stream i n ?dater Canyon,
The h o r s t i s boundedon
east by Snake Ranch F l a t s , on the north-northwest
andonthe
Magdalena 1-ioun-
i n t h e pediment g r a v e l s on
the northeast side of the range, the entrenchecl
and t h e s t e e p s l o p e s
the
the north-
by t h e Eear Mountains,
west by t h e Mulligan Gulch graben (Fig. 27).
A topographic
relief of 5,000 f e e t by t h e Kagdalena Kountains i s t h e g r e a t e s t i n westc e n t r a l Xew 14exico.
Other prominent
features i n t h e Magdalena area included wtthin
t h e X i 0 Grande graben are t h e Eear Mountains, a westward t i l t e d b l o c k upl i f t e d by Late Cenozoic f a u l t i n g (Frown, 1972).
has been downfaulted against the
The Snake Ranch F l a t s
Eear Nountains and t h e Magdalena Moun-
t a i n s on t h e west and t h e Socorro-Lemitar14ountainson
t h e east.
Cenozoic sediments eroded from the neighboring uplifts have
basin (Gebrine,Spiegel,
and Williams,
1963).
filled the
MulliganGulchgraben
s e p a r a t e s t h e San Eateo Kountains and the Gallinas Piountains
from t h e b e a r MountainsandKagdalenaI4ountains
Late
on t h e west
on t h e east (Chapin and
.
122
others,inpreparation).
The graben was formed by Late Cenozoic fault-
i n g and contains sediments derived
from the bordering uplifts.
CONCLUSIONS
Kississippian limestones unconformably overlie Precambrian
a r g i l l i t e and g r a n i t e i n t h e Nagdalenaarea.I:uringPennsylvanian
a t h i c k sequence of quartzose sandstone, shale,
posited i n the Lucero-SanPlate0
time
and limestone werede-
Easin. Terrestrial sandstone
and s i l t -
st0r.e were deposited during Permian time.
U p l i f t and t i l t i n g of the Kagdalena area during t h e Laramide
orogeny was followed by l e v e l i n g of the highlands during
Eocene time.
Erosion removed a l l of t h e Xesozoic s t r a t a and l e f t o n l y i s o l a t e d r e m - ,
n a n t s of t h e Permian s t r a t a .
.. ...
Volcanismbegan aproxirnately 37 m.y.
Six distinct volcanic formations
volcanoclastics,ashflows
Kesa Formation ash flows
and ceased
30.5 m.y. ago.
make up t h e C a t i l Group and consist of
and lavaflows.
A sourcearea
for t h e h ' e l l s
may overlap the southeastern portion
c e n t r a l Magdalena Nountains and
a source area for the Sawmill
o f the
Canyon
formation may overlap the southwestern portion.
Following t h e emplacement of the youngest ash flow, the
l e n a a r e a was f a u l t e d and t i l t e d by a north-northwest-trending
hydrothermal solutions,
rock.
zone of
a major r o l e i n t h e emplacement
Late Oligocene age. These faults played
of the Late Oligocene stocks, dikes,
Hagda-
and served as t h e c o n d u i t s f o r
which a l t e r e d or mineralized t h e adjacent county
The dikes and stocks may be the surface expressions of
larger intrusion underlying the northern
123
a much
and c e n t r a l Xagdalena E.!ountains.
124
Euried plutons including the North Laldy
Peak-Linchburg stock
may contain mineralization o r replacement deposits adjacent to
Possible buried stocks
may be defined by
them.
a l t e r a t i o n and m i n e r a l i z a t i o n ,
structural control, and diking. particularly the white rhyolite dikes.
The a n c e s t r a l Kagdalena Mountains were degraded
during Kiocene
time u n t i l they were nearly o r completely buried teneath their
debris.
The FopotosaFormation
areas are remnants
,.
own
i n t h e Water Canyon andSouthEaldy
Peak
of a l l u v i a l fans t h a t once covered a much wider area.
The biagdalena Xountains have been
f e e t along bordering block faults.
uplifted approximately 5,000
The ?lagdalenaFlountaim
the Easin and Range physiographic province and are part
graben of west-central
New Hexico.
. ..
are within
'of t h e RioGrande
bY
C i e t e r Anton Krewedl
..
....
A Cissertation Submitted to the Faculty
DEPART?EKT
OF
of t h e
GEOSCIENCZS
I n P a r t i a l F u l f i l l m e n t of t h e Requirements
For the Degree of
DOCTO2 OF PEILCSOPI.:Y
I n the Graduate College
T I S UNIE3RSITY OF ARIZOXA
A.
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'
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.
depression i n Coloradoand h'ew ;Xexico, j . ~
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pt.2,
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p. 224.
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Chapin, C. 3., 1971-a, K-Ar ageofthe
La J a r a Feak Andesite and i t s
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..
126
Cooper, J . R., 1961, Turkey-trackporphyry-apossibleguide
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~
Debrine, E . , Spiegel, Z . , and Villiams, D., 1963, CenozoZc sedimentary
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...
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'
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Precambrian
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DIETER A . K R E W E D L
re 2 3 : Generolizedgeologic
map of t h ec e n t r o lM o g d o l e n oM b u n t o i n s
f o l d so n df a u l t sd e v e l o p e dd u r i n gv a r i o u sp e r i o d s .
showing
G E O S C I E N C E S , I974
P h . D. D I S S E R T A T I O N
0
A'
9, and S o u t h B a l d y and M o l i n oP e a k
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1965.
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54
LEGEND
X
- Copper
0-
Lead
- Zinc
0 - Siticn
0 - Manganese
A - Borite
A
i c n i e I"
:2
,000'