A fluidinclusion
study
oftheWaldo-Graphic
mine,
Magdalena
district,
NewMexico
by JoseManrique
andAndrew
Canpbell,
Department
of Geosciences,
NewMexico
Institute
of Mining
andTechnology,
Socorro,
NM87801
Introduction
The Magdalena mining district is located
in Socorro County, central New Mexico, 30
mi west of Socorroand 1..5mi southeastof
zl
ol
trl
a
i
oi
Mining and Technology.
I
Previous sfudies
FIGUREl-Index map of Magdalenamining district.
enceof silicatemineralson depositionof ore
minerals at the Linchburg mine in the southern part of the district, and he concludedthat
both chemicaland structural controls were
important in the formation of the sulfide and
skarn minerals.Park (1971)made a detailed
the MagdalenaMountains (Fig. 1). The mineralizedareasare locatednear the structural
margins of two overlapping cauldrons: the
Socorrocauldron,which is locatedat the south
end of the distric! and the Magdalena-Sawmill Canyoncauldron,which is locatedsouth
and wesi of the district (Fig. 2). The agesof
the tuffs associatedwith the developmentof
the two cauldrons have been estimated at
30-32 Ma (Weber, 197!; Burke et al., 1963)
and27-29Ma (Blakestad
,1978),respectively.
Rock types
ture measurementsof fluid inclusions in
barite, calcite,qvartz, and fluorite from vuggy
cavities and fractures in the jasperoid. He
concludedthat the temperaturesof deposibionwere in the rangeof 165-285'Cand found
no evidenceofboiling. Blakestad(1978)used
the concept of cauldron subsidence and
stratigraphicnomenclatureof Cenozoicvolcanicrocks at that time to make a large-scale
map of the district and a structural interpretation of the area.
Regional and local geology
The Magdalenamining district is located
immediately south of the Colorado Plateau
physiographicprovince, on the west side of
include argillite and schist, gabbro or diabase,felsite,and granite.
On the west side of the MagdalenaMountains sedimentsof the Carboniferoussystem
were depositedupon a Precambriansurface
of low relief. Theseare the Calosoand Lad-
silicifiedin the southern part of the district
(Loughlin and Koschmann, 7942;Iovenetti,
1977).
At the Waldo-Graphic mine, on level 9 between the Maderaand Waldo faults, the Madera Limestone changesstrike and dip
chaotically.It has been interpretedas a zone
of cauldron margin megabreccia(Fig. 2) by
Blakestad(1978)and Chapin et al. (1978).
However, reinterpretationof the location of
cauldron margins suggeststhat the nearest
cauldronmargin is more than 3 mi southwest
of the district (G. R. Osburn, pers. comm.
7986).
Cenozoicvolcanic rocks of basaltic-andesitic, latitic, and rhyolitic compositionrange
in age from 39 to 26 Ma (Blakestad, 7978).
Theserocksinclude Datil Group (39-33Ma),
Hells MesaTuff, and La JenciaTuff (Loughlin
and Koschmann, 1942;Blakestad, 1978;Eggleston,1982;Osbum and Chapin, 1983).The
Alsoin thisissue
Useof sullatesto identify
weathered
coal
o.7
Geotechnical
siteinvestigation,
Estancia
Basin
o. 11
p.12
Pointof RocksCanyon
Fluvialdeposition
and
paleoenvironment
of Cutler
Formation
red beds
o. 14
p.
Service/News
19
Mineral
symposium
abstracts p.20
Staffnotes
o.24
Goming
soon
conspicuousmarker bed of a dark-gray to
black,denseargillaceouslimestone.Thisbed
is known as "silver pipe" or "indicator" becauseof its closeassociationwith ore shoots.
The Ladron Member has been extensively
Crosssectionthroughthe EngleBasin
Petroleum
exploration
targets
Applications
for cathodoluminescence
Ultraviolet
mineralsin NewMexico
Geologicinvestigations
in NewMexico
thicknessof Cenozoicvolcanic rocks in the
Magdalenaareahasbeenestimatedto be 2,000
ft (Blakestad,1978).
In the Magdalena district several dikes,
stocks,and dikelike intrusive bodiesare exposedwith compositionsranging from granite to gabbro. The main intrusive bodies,
which crop out on the surface,are Anchor
Canyonstock(28.3Ma), Nitt monzonitestock
(28.0Ma), and latite porphyry of Mistletoe
Gulch. Additionallv. four concealedintrusive bodies have been reported (Blakestad,
1978).The Linchburgporphyry quartz monzonite is exposedin underground workings
of the Linchburg mine. A porphyritic monzonitebody, which intrudes the Precambrian
rocks, Kelly Limestone, and Sandia Formation, was discoveredas a result of drilling at
the North Baldy Peakarea.A latite porphyry
has been mapped on the L4th level and below in the Waldo-Graphic mine, which
Chapin et al. (1978)reported to be similar to
the latite porphyry of Mistletoe Gulch. A
porphyry granite or quartz monzonitebody
was also discovered(as a result of drilling
during explorationwork) 500 ft south of the
Vindicator shaft (Fig. 2).
Other intrusive occurrencesin the Magdalena mining district are mafic dikes, andesitic intrusive bodies, and white rhyolite
dikes.All of theseintrusive rocks are hydrothermally altered and some white rhyolite
dikes show a spatial relationship with the
mineralization(Titley,1958;Blakestad,1978).
The white rhyolite dikes are consideredto
be younger than the emplacement of the
stocks (Loughlin and Koschmann, 1942;
Blakestad,1978).
Thereis a spatialrelationshipbetweenthe
main stocksand the mineralizedzones (Fig.
2). The Nitt and Waldo-Graphic mines are
locatednear the contactof the Nitt monzonite stock and limestones.For the most part
this stock lacks conspicuoushydrothermal
alterationin contrastto the concealedintrusions that show consistentalteration.
Waldo-Graphic mineralization
The Waldo-Graphic zinc-lead deposits are
hosted by the limestones of the Pennsylvanian Madera and Mississippian Kelly Formations. The replacementand skarn bodies
were localizedby the intersectionof northtrending fractures with favorable horizons
within the limestones(Loughlin and Koschmann, 1942).The relative age of the mineralization is younger than the Nitt monzonite
stock and latite porphyry dikes based on
crosscuttingrelations seenin the field.
Mineralogy
A complete list of the primary and secondary minerals found in the Magdalena
district, together with detailed macroscopic
and microscopicdescriptions,was published
by Loughlin and Koschmann (1942); the
readeris directedto it for details.In the WaldoGraphic mine the gangue and ore minerals
occur as open-space fillings and replacements in limestone. Loughtn and Koschmann (1942)reported that most mineralization
was deposited by replacementof the limestones.That quantitativerelationshipcannot
be confirmed becausesubsequentobservations have only been made on remnants of
the ore deposit.
The principal sulfide minerals consist of
pyrite, sphalerite,galena,and chalcopyrite.
ganguemineralsinclude calcOre-associated
silicateskarn minerals (diopside-hedenbergite and actinolite),iron oxides (specularite
New AAexnc@
L.ln;
Monzonile
ffi
Lotitedikes
GEOLOGY
o Science
andSeruice
Volume 9, No. 1, February 1987
P o l e o z o i cs e d i m e n l o r ryo c k s
ond Quoternorycover
17..t'Tl
Precombr ion rocks
Couldron morgin
In{erredconloci
Poleozoic-Precombrion
rocks
Edifor;Deborah A Shaw
Dralters:Cherie Pelletier and Becky Titus
Publishedquarterly by
New Mexico Bureau of Mines and Mineral Resources
a division of New Mqico Instihrte of Mining & lbclnology
BOARD OF REGENTS
Ex Officio
Garrey Camthers, Gooernorof Nru Mexico
ol PublicInstruction
Alan Morgan, Superintendent
Appointed
Pres
,19n-1987, Iis Cruces
Judy Floyd,
Gilbert L Cano, SeclTreas,1985-1991, Albuquerque
Lenton Malry, 1985-1989,Albuquerque
Donald W Morris, 1983-1989,Ips Alamos
SteveTones, 1967-191, Socorro
New Mexico lnstitute of Minint & Technology
Laurence H Lattman
Presidilt,
New Mexico Bureau of Mines & Mineral Resources
Frank E Kottlowski
Dirntor
George S Austin
DeputyDirector
lssued quarterlt February May, August,
Subscrrptions:
November; subscriPtion price $6 00/calendaryear
Editoial mottq: Articles submitted for publication should
be in the editor's hands a minimum of five (5) months
before date of publication (February, Mat August, or
November) and should be no longer than 20 tyPewritten, double-spacedpages. All scientific PaPerswill be
reviewed by at least two PeoPlein the apProPriatefield
of study. Address inquiries to DeborahA Shaw, Editor
oI Nru Menco Geology,New Mexico Bureau of Mines &
Mineral Resources,Socoto, NM 87801
uithouf pq
Published
as publicdomain,therelorereproducible
mission Sourcecreditrequested
FIGURE 2-Structural map of Magdalena mining district and the major mines; modified
from Blakestad (1978).
February 1987
Nm Mexico Geology
Circulation:1,6N
P/iulerr University of New Mexico Printing Plant
and magnetite), quartz, calcite, and minor magnetic. Magnetite was found mainly in changed in color from dark in the sulfide
barite.
the Graphic zone as massiveto fine-grained stageto light in the carbonatestage. It is not
The most common minerals of the oxi- blebs and as specularite-magnetite aggre- known whether this is due to a continually
dized zone are smithsonite, anglesite, cer- gates.
evolving deposition or to two distinct epiussite,chrysocolla,malachite,chalcocite,and
sodesof deposition.As a whole, pyrite formed
"limonite" (goethite-hematite). Silver min- Gangue minerals-Quartz grains are en- after the specularite-magnetite(Loughlin and
eralsand native gold alsohavebeenreported closedby skam mineralsand intergrown with Koschmann, 7942,pIs. 24, 25) and, although
sphalerite. Quartz veinlets crosscut dark it formed earlierthan sphalerite,it was formed
(Loughlin and Koschmann, 1942).
sphaleriteand larger veins at igneous rocks later than galena.
Sulfides-In the Waldo-Graphic mine, py- and recrystallizedlimestone.
From texfural relationshipsobservedin this
rite occursas: disseminationsin the altered
Calciteoccursas long pointed crystals or studv.it is concludedthat chalcopyriteformed
country rocks;veinlets and lensesin specu- scalenohedronsand as short prisms with latei than pyrite and sphaleriti, but the relarite-magnetite aggregates;pyritic bodies rhombohedral terminations thit fill vugs. lationship between chalcopyrite and galena
with minor associatedinterstitial chalcopv- Calcite has also been reported to occur as is ambiguous. However, based on the parrite; crystalline massesassociatedwith dis- platy radial aggregates,
ageneticsequenceof Loughlin and Koschtinctive zones or bands of sphalerite and
Bariteoccursas white platy crystals,mostly mann (1942),chalcopyriteis believedto have
galenathat have replacedlimestone;and py- in fractures bounding the "silver pipe" and formed early with respect to galena.
rite-bearing quartz and calcite veinlets that away from the orebodies.
Quartz and calcite were deposited
cut other sulfides, dikes, and wall rocks.
throughout much of the paragenesis,but the
Most of the sphaleritein the orebodiesof
calcitepredominated in the final stagesof ore
WaldeGraphic mine is dark brown to black, Paragenesis
deposition.
showslittle internal reflectance,and is probThe parageneticsequencewas determined
ably iron rich. It occursas aggregatesof an- on the basis of field relationships of the minhedral grains associatedwith speculariteor erals and a limited study of polished secFluid inclusion study
other sulfides (galena-pyrite). In the north- tions. Becausethe orebodiesabovethe water
More than 50 doubly-polished thick seceastareasof the mine sphaleritereportedly level have been mined out, observationand tions of quartz, calclte,sphalerite, and barite
forms massive orebodies with minor pyrite sampling were confined to remnants of the were prepared; in most of them no useful
and galena. In the western portion of the ore. Resultsfrom this study were compared fluid inclusions were found becauseof small
mine sphalerite is light greenish to yellow with Loughlin and Koschmann's(1942)study, size or poor optical characteristics.
and shows a distinctive color banding. In which was done when the mine was active.
The temperaturesof phasechangesin fluid
this area of the mine it does not appear to As a whole our observationsare in agree- inclusions during freezing and heating tests
be associatedwith specularite.The dark-col- ment with the previous work.
were measured on a Linkham TH600 dualored sphaleritecontains chalcopyriteincluOre formation may be grouped into three purpose heating/freezingstage. Reproducisions.This texture,known asemuliion texture major stages(Fig. 3). The first stagewas the bility of the melting temperature (Tm) was
or chalcopyrite disease (Barton, 1978), has growth of skarn minerals, recrystallization +0.2'C. Measurementsof homogenization
been interpreted as a product of: L) exoso- and/or marbleization of the limestone, and
temperaturehad a reproducibilityof + 1.0'C
lution, 2) replacementor epitaxialgrowth, 3) depositionof specularite-magnetiteand miexceptfor inclusionsin dark sphalerite,which,
mechanicalmitng (Kojima and Sugaki,1985 nor quartz. The second stage consisted of
due to poor visibiliry, were only good to about
and referencescited therein), or 4) a product deposition of pyrite, dark sphalerite, chal- + 5 0 c .
of supergeneprocesses(DeWaaland John- copyrite, galena,and quartz. The final stage
son, 1981).Its formation may imply move- was characterizedby the deposition of carment of copper within the sphaleritecrystal bonates, barite, and minor light-colored Freezingand heating observations
itself or an addition of copper and iron from sphalerite.
During the freezing runs, inclusions exan externalsource.The effectsof these proThe temporal relationship between spec- hibited different kinds of behavior: in some
cesseson the fluids trapped at the time of ularite and magnetite was not determined inclusions the size of the gas bubble desphaleriteformation are unknown.
conclusively in this study, but Loughlin and creasedsuddenly, but the inclusions reChalcopyrite occurs as small interstitial KoschmannQ9a2,pl.2) suggestedthat mag- mained relatively transparent a secondgroup
grainsin pyrite and as microscopicblebsen- netite was formed after specularite.Sphal- showed similar behavior but turned "grainy"
closedin sphalerite.Galenais generallyless erite was depositedin both the sulfide and and dull gray; in a third group the gasbubble
abundantthan sphalerite,and occursas fine- c a r b o n a t es t a g e s o f m i n e r a l i z a t i o n a n d
grained, interstitial blebs between grains of
sphalerite.Loughlin and Koschmann(1942)
reportedthat the ratio of galenato other sulColc-silicotes
fides increased with the distance from the
Hemotiie
Nitt monzonite contact.
Mognetite
Skam minerals--Dopside-hedenbergite and
7r(Pa
3t7- 205"C
at47"_C
actinolite occur as replacement minerals in
Quortz
limestonesand to a minor extent in intrusive
Colcite
rocks. These minerals occur as columnar
sheaves,as much as 6 cm long, and as finePyrite
grainedmasses.They have beenpartially reDork 3lO-175"C -!r!l Spholerite
placed by calcite and quartz due to late
hydrothermal activity.
Cholcopyrite
Iron Oxides-Specularite is the most abunts
Goleno
dant of the hypogeneiron oxidesand occurs
t85-t45.C
Borite
as micaceous aggregates and interwoven
bladelike crystals. Most of this specularite
is magnetic,probably due to the presenceof
Skorn
Sulfide
Corbonote
Stoge
microscopicor submicroscopicmagnetite. In
some polished sectionsmagnetite was not
observed,even though the specularitewas
FIGURE 3-Paragenesis diagram with fluid inclusion temperatures
Nm Mexico Ceology February 1987
disappeared.Tm was obtained by warming
the inclusionsslowly, especiallyabove - 30'C,
and when the amounts of ice in the inclusion
became small the warming up was stopped
to ensure equilibration. The temperature at
which the last ice melted (Tm) was recorded.
The first appearanceof liquid was not detectedand, therefore,not recorded. Several
fluidinclusions exhibitedTm above0'C; when
this occurred and when freezing of the fluid
inclusion was not observed,a careful check
for the presenceof CO, gas and for clathrate
formation was performed by applying the
techniques and criteria used by Collins (1979).
However, CO, gas and clathrates were not
observed. Each freezing run was performed
at least twice in order to check the reproducibility of Tm. When Tm was not reproducible
within the range stated, stretching upon
cooling was assumedand the measurement
was not recorded.The suspectedstretching
during cooling was detectedonly a few times
in fluid inclusions in calcite and sPhalerite'
A{ter Tm was determined, experimental
heating runs were performed for each mineral to determine the range of homogenization temperatures(Th). Eachchip was heated
at rates of 30'C Per minute until temPeratures near the range of homogenization were
reached,then the rate of heating was slowed
to rates of 1-2'Clmin, and the temperature
was registeredwhen the gas bubble disappeareq.
The fluid inclusions in sphalerite Presented special problems in determining homogenization temperatures because the
bubble disappeared in dark border areas of
the inclusions. To obtain Th, the heating run
was stopped as soon as the bubble disappeared in the areas of total reflection, and
ihe temperature was dropped a few degrees
centigrade. If the gas bubble immediately
reappeared,then the temperature was raised
2-3be above the temperature at which the
run was stopped. The cyclesof raising and
lowering the temperaturewere repeateduntil the vapor bubble reappeared only after
the inclusion was supercooled. This indicated that the fluid inclusion had indeed homogenized during the previous heating.
TABLE1-Fluid inclusion homogenizationtemperaturesand salinitiesfrom the Waldo-Graphicmrne;
*
P = primary; S : secondary; : number of measurements'
Sample
Salinity
Temperature ('C) of
homogenization (Th)
welO-sw(P)
-2w (P)
w900-s0 (P)
7.44-r33(6)"
367-269 (17)-
w600-25 (P)
w300-1 (P)
s.4(ry
3170r
Observation
Quartz in recrystalfized
Iimestone
303-216(4).
Quartz intergrown with
sphalerite
4.48-4.32(2)"
317-205(5)-
Quartz hosted by skarn
4.01-3.53(3).
2.56-2.06(3)*
341J09 (4)r7n_tnqr?t*
Quartz vein in intrusive
w900-1 (P)
0.87-0.18(7).
270-147(8)"
Quartz postmineralization
w900-50 (P)
_10 (P)
5.25-3.21(3)*
2.40-r.90 (3)*
362-232(5)"
335-200(5)*
Sphalerite with quartz,
hematite, and
chalcopyrite
w920-7 (P)
w300-3 (P)
3.21-7.56(6)*
(10r
0.70-0.18
185-110(7).
185-145(r0)*
Sphalerite (light colored)
(s)
Barite
calcitewithout fluid inclusions. Secondary
fluid inclusionsin calcitewere not abundant.
The presenceof fluid inclusionswith variable gis-liquid ratios may be interpreted in
a varietyof ways such as the trappingof an
immiscible fluid, true boiling or effervescence,sequentialtrapping of different fluids
at different times, necking down after formation, or leakage(Roedder,1979).The variable gasJiquid ratio in calcite observed in
this studvisassumedto be the resultof neckdown for the following reasons:1) no
ing
fluid
incluA
type
primary
Quartz-Only
was identified by optical means; 2) alCO,
samPles.
quartz
sions were measured in
However, sample 900-1 showed both type A most complete absenceof gas-rich fluid inand type B fluid inclusions. The coexistence clusions;3) lack of zonal distribution of fluid
of liquid- and vapor-rich inclusions suggests inclusions; and 4) no textural evidence of
the tlapping of immiscible fluids caused by trapping of differentfluids at different times.
boiling at the time of formation of this quartz. Thiiefoie, Th is not representativeof the
temperature of trapping and, therefore, is
Sphalerite-Primary fluid inclusions mea- not presentedhere.
sured in sphalerite were tyPe A. Most exhibited negative crystal shape in which Barite--Barite exhibited few clear areas that
inclusionborderswere dark. In extremecases/ containedusablefluid inclusions.In general
whole inclusions were almost completely dark the fluid inclusions in barite were small and
because of the high internal reflectivity of difficult to measure.In addition, many of the
sphalerite.It was possibleto distinguish the inclusions appeared to be secondary or t9'
bubble in several of these dark inclusions. have leaked.Severaltype C secondaryfluid
Secondaryfluid inclusions are related to frac- inclusionswere filled with a colorlesssoluClassificationand description of fluid
tures or as aligned arrays of negative crystal- tion. All the measurements were made in
inclusions
shapedinclusionswith no apParentrelation- what were assumed to be primary type A
According to phase relationshipsat room ship to actual fractures. Of this last group/ fluid inclusions.
temperature, fluid inclusions of Waldo- some were measured and reported as Tm/
Graphic mineralizationmay be separatedinto Th of secondaryfluid inclusions.Type C inFluid inclusion results
three groups. Type A [(I-V)L], the most clusions appeareddark and empty, and they
The homogenizationtemperaturesand sacommon, are two-phase liquid-rich fluid in- were generally associatedwith fractures'
measuredfrom the Waldo-Graphicmine
when
linitv
no
chanqe
exhibited
clusionsin which the gas phase is less than These inclusions
are iummarized in Table1.
50Voby volume and homogenizedby vapor cooledor heated.
disappearance.Type B [(L-V)U are gas-rich
fluid inclusions in which the gas phase fills Calcite-Fluid inclusions in calcitewere type Quartz-Because the fluid inclusion study
more than 95% of the volume of the cavity. A with variable gas-liquid ratio and random was done with quartz samplesfrom different
In one type B inclusion, it was possible to distribution. In some inclusions the bubble stagesof paragenesis,the range of lomogobserve that the inclusion homogenized to appeared gray to dark and was conspicu- eni2ation temperatures was broad (147gas.Type C (L), are composedof one-phase ouily larger than the other group of inclu- 367"C).However, the data may be divided
liquid-rich fluid inclusions that exhibited no sions with small, clear bubbles. In all cases, into three temperature populations that corchangewhen cooled or heated. No fluid in- the bubble was not greater than 50Voby vol- respond fairly well with the parageneticasclusions were observed to contain daughter ume. There was a general scarcity of type B sociationof the quartz (Fig.a). Temperatures
fluid inclusions.Many areasapPearedas clear ofthe highestgroup ranged from 280to 380"C,
minerals.
February 1,987 Nm MexicoGeology
Many inclusions located along fracture
planes were interpreted to be of secondary
origin. Isolatedinclusionsof large size,variable shape, and with no apparent relationship to fracfureswere assumedto be primary.
In general, most of the samples contained
few type A inclusions. The small size andior
the optical characteristicsof many inclusions
precluded observation of fluid behavior during cooling and heating.
with a peak of 320"C. Most of this data is
from inclusionsin quartz associatedwith recrystallizedlimestoneand from primary fluid
inclusionsin vein quartz within an intrusive
body. The intermediate temperature group
ranged from 200 to 260'C. Inclusions in this
group were mainly from quartz intergrown
with sphalerite or skarn minerals and from
secondary fluid inclusions from the intrusion-hostedvein quartz. Temperaturesin the
lowest group ranged from 140to 200"C.These
inclusions were in samples from the postmineralizationstage.
Fluid inclusion salinitiesranged from 0.2
to 7.4 eq wt% NaCl. Figure 5 shows that
early-stagequartz fluid inclusionshave higher
salinities than the salinities measured in
samples of the later stages (post-mineralization).
Barite-The fluid inclusions measured in
barite have homogenization temperatures
from 145 to 185"C (Fig. a). Salinity values
rangefrom 0.2 to 0.7 eqwt% NaCl (Fig.5).
Again, the barite is thought to have formed
in the last stage.
Discussion
The salinity valueshave been plotted versus homogenization temperatures in Figure
6. The data may be grouped in three populations: 1) inclusions in pre-ore quartz associatedwith recrystallized limestone and
primary fluid inclusionsfrom a quartz veini
2) inclusionsin dark- and light-colored
sphalerite,inclusions in quartz intergrown
with sphalerite or occurring in skarn, and
secondaryfluid inclusionsin vein quartz; and
3) inclusionsfrom barite and quartz thought
to be post-oreminerals.
Sphalerite-The range of Th of primary inThe salinity-homogenizationtemperature
clusions in sphalerite was 110-362"C.The diagram(Fig. 6) shows a progressivecooling
distribution of Th values on a histogram of the solutions through time, which began
shows two distinct populations (Fig. 4)IThe with early quartz and ended with late barite
first ranged from 110 to 190'C and is com- and quartz. Fluid salinity showed a sympaposed of fluid inclusions from light-colored thetic trend. Fluids trapped in mineralsfrom
sphalerite.In this group Th values cluster the early stage had a higher salinity than
around 150to 190'C.The secondpopulation those from later parageneticstages.At the
consistedof datafrom dark-brown sphalerite time of sphalerite deposition a decreaseof
and rangedfrom 190to 370'Cwith most tem- the fluid temperatureoccurred,but there was
peraturesgrouped between 230to 310"C(Fig. no conspicuousvariation of fluid saliniW.
4). Salinity values for both dark and light
The cbmbined analyses of the maximum
sphaleriteare in the range 1.5 to 5.2 eqwt% and minimum temperaturesof trapping of
NaCl (Fig. s).
each mineral, the homogenization-temper-
ature histograms, the temperature-salinity
diagram, and the parageneticstudy suggest
that the skarn stagewas formed at temperatures greater than 320'C becausethe temperature of quartz formation associatedwith
the recrystallized limestonesranges from259
to 367"C,and most fluid inclusions homogenized at about 320"C. Most of the sulfide
mineralization probably formed in the range
from 175 to 310"Cbecauseall the homogenization temDeraturesmeasuredin dark-colo r e d s p h a l e r i t ea r e i n t h i s r a n g e . T h e
measured values below this range correspond to fluid inclusions in light-colored
sphalerite.Minor sphalerite deposition occurredafter the main stageof mineralization.
The third (gangue)stagewas depositedbelow 200"C.This interpretationhas been plotted on the parageneticdiagram (Fig. 3).
Genetic model for ore deposition
The WaldeGraphic deposit is typified by
its associationwith shallow mid-Tertiary stock
and volcaniccauldron-relatedsequences.Its
primary mineralogy is specularite-magnetite, sphalerite,galena,and pyrite with subordinant chalcopvrite and barite. It forms
replacementsand skam orebodiesin the Kelly
and Madera Limestones.
The fluids resDonsiblefor the mineralization in the WaldeGraphic zone were HrOrich, low salinity (<7.4 eq wt% NaCl) with
a
C
-a
f
.C
(D
E
f
z.
AAAAA
200
300
Homogenizotion
temperoture
"C (Th)
Quortz:
400
123456
Solinity
eq wt o/. NoCl
16o) Post ore
Hostedby
ffi
Recrystollized
limestoneFl-J Skorn
liFl Intrusive
I
Spholerite
FIGURE 4-Histogram of homogenization temperatures
Spholerite:
I
l--l
Dork
Light
FIGURE S-Histogram of salinity measurements.
Nao Mexico Geology February 1987
temperaturesin the range of L10 to 367"C.
Boiling may have occurred but only in the
final stagesof quartz deposition.
To interpret the genesisof Waldo-Graphic
deposits,it is necessaryto build a hypothesis
that explainsthe origin of mineralizationon
a district-wide scale.There is a spatial relationship between the fine-grainedNitt monzonite and the mineralization at Nitt and
Waldo-Graphic mines, but the degree of
hydrothermal alterationof the stock and the
fluid inclusion study resultssuggestthat the
mineralizationpostdatesthe emplacementof
the intrusive body. The spatial distribution
of intrusive rocks (including those found in
the subsurface)suggeststhat underneaththe
Magdalenadistrict is a concealedpluton that
may be of regionaldimensions.The exposed
fine-grained intrusions would represent the
earliest magmatic activity and the porphyritic phases,the latest.
In agreementwith Elston (1975),the age
of the Magdalena mining district mineralization is estimatedto be between28 Ma and
20 Ma becausethe ores were formed after
cauldron collapse, after the intrusion of the
Anchor Canyonand Nitt monzonite(28Ma),
and probablybeforethe inception of basaltic
volcinism into the region.
Tentatively, the ore deposit genesis is interpreted to be related to the episodic emplacementof a concealedpluton, which acted
as a heat engine. This createdepisodic epithermal ground-water convection cells, lo-
Q u o r t zi n :
izedlimeslone* primory
Recrystoll
quortz veininclusions
ond secondory
Skorn,spholerite,
inclusions
Posl ore
Spholerite:
Dork
Lighf
'- -1
Borite
I
o
o
o
r
D
A
,'I
6
o
tsr-:
=
ao
nt\
lFJ
d
4
ci
o
Il , l iI o
I1 f l )
6--
E
o
c.
o
a
3
I
t
trc
=
tr
o
I
I
I
tr
I
o
I
I
tti-
,/r.
/-\t \ )
t-t
i,t
o
,--::
\--:;::l)--"
a
/
/
l^/
va
o
roo
oo
,
\t
S^oo
i""
t'--g9""'
300
200
temperoture
Homogenizotion
"C (Th)
FIGURE 5-Salinity-homogenization temPerature diagram.
February1987 NewMexicoGeology
has been
References
I
o
ol
paper
o
o
, I
_t
--a
ACKNOWLEDGMENTS-ThiS
improved from comments and suggestions
made by David Norman, William Chavez,
jr., Ted Eggleston,and Bob North. The New
Mexico Geological Society and the Latin
American ScholarshipProgram of American
Universities (LASPAU) provided funding for
this research.We are grateful to all of them.
Mr. Manrique thanks TacpaUniversity in Peru
for leave of absenceduring this period.
I
;I l
It l
Ir l
Il l
I I
I I
I I
I I
, I
atto
z
-€
i;--'
calized by the structure developed during
cauldron collapse.In this sense the skarn
bodiesare the result of the interactionof the
limestones with fluids of appropriate compositionand temperature.However,it is also
possiblethat this deposit developedin two
stages:1) skarn formation associatedwith
the Nitt monzonite intrusion as a ground
preparation followed by; 2) an epithermal
stageto which the sulfide oreswere related.
With the Dresentinformation it is difficult
to determini the source of the ore metals.
However, because we suggest that mineralization is related to epithermal activity and
not directly related to igneous rock emplacement, derivation of the metals by leaching
of plutonic and volcanic rocks seems more
likely than a direct magmatic source. This is
in agreementwith the genesispostulated for
the silica in the jasperoid (Iovenetti, 1977).
In addition, Ewing (1978)proposed, as one
of the possiblesourcesof the lead, the leaching of Tertiary volcanic rocks based on the
refiterpretatioh of the lead isotopic data from
the mineral depositsof southern New Mexico. Nine of Ewing's lead isotopic analyses
were from the Magdalena mining district.
I
I
I
I
Barton, P. 8., 1978,Someore texturesinvolving sphalerite
from Furotobe mine, Aikta Prefecture, Japan: Mining
Geology, v. 28, pp. 293-j00.
Blakestad,R. B., Jr., 1978, Geology of the Kelly mining
dishict, SoconoCounty, New Mexico:UnpublishedM.S.
thesis, University of Colorado, Boulder; New Mexico
Bureau of Mines and Mineral Resources,Open-file Report 43, 139pp., 2 Pls.
Burke, W. H., Kenny, G. S., Otto, J. B., and Walker,
R. D., 1953,Potassium-argondates, Socorroand Siena
Counties, New Mexico: New Mexico Geological Societv, Guidebook to 14th Field Conference,p. 224.
. ., and
C t r a f i n , C . E . , J a h n s ,R . H . , C h a m b e r l i n , - RM
Oibum, G. R., 1978;in Chapin, C. E., and Elston,
W. E. (eds.),Fieldguide to selectedcauldronsand minins districts of the Datil-Mogollon volcanic field, New
MExico:New Mexico GeologicalSociety,SpecialPublication7, pp.70-12.
Collins, L. F., 1979, Gas hydrates in CO2-bearingfluid
inclusions and the use of freezing data for estimation
of saliniry:EconomicGeology,v.1+, pp. 1435-'1444.
DeWaal, S. A., and Johnson, J. A., 1'981',Chemical heterogeneifyof sphaleritein a base-metalsulfide deposit:
EconomicGeology,v.76, pp. 594-705.
't982,
T.,
Geology of the central Chupadera
Eggleston,
-Mountains,
Socono County, New Mexico: Unpublished M.S. thesis, New Mexico Institute of Mining and
Technology,Socorro, 154 pp.; New Mexico Bureau of
Mines and Mineral Resources,Open-file report 141,162
pp., 2 maps.
Elston,W E.,1976,Tectonicsignificanceof mid-Tertiary
volcanismin the Basinand RangeProvincewith special
referenceto New Mexico; in Elston, W. E., and Northrup, S. A. (eds.),Cenozoicvolcanismin southwestern
New Mexico: New Mexico Geological Society, Special
Publication 5, pp. 93-1.02.
Continuedon pageL0
estimateda reservebase for the Salt Lake coal field of 347 million
tons within 250 ft of the surface. Using sulfates as a factor, this
reservebasecan be recalculatedas approximately69 million tons of
oxidized,lower rank coal and 278million tons of unoxidizedreserve
base.
Conclusions
The formation of sulfatesis due to an increasein the amount of
oxygen-richsurfacewater reachingthe coal.The oxygen then reacts
with the sulfides, pyrite, and marcasiteto form sulfates.Although
the maximum depth at which sulfateis found is 180ft, most of the
sulfatesare found within 50-60 ft of the surface.Coals containing
sulfatesthat are deeper than this 50-60-ft interval are overlain b|
greateramounts of porous sandstonesor alluvium. In either case,
surfacemoisture,carrying oxygen,penetrateddeeperthan coalsnot
overlain by the same thicknessesof these porous lithologies. Conversely,severalcoalsthat have no sulfatedevelopment,yet are within
50-60-ftof the surface,are overlain by impermeablematerialssuch
as mudstone and claystone.In this caie, the impermeablenature of
the overburden prevents oxygen-bearingwatei from reaching the
coal.The shallowestcoal in which no sulfatedevelopmentoccursis
40 ft.
When analyzingthe combustioncharacteristics
and estimatingthe
resourcesof a coal-bearingarea, attention should be paid to the
distribution of sulfatevaluesin the coals.Coalsin the Salt Lake coal
field within 40 ft of the surfacehave sulfates,high moisture, low
Bfu, and increasedoxygen values. The range of values for those
parameters is much greater than for deeper coals. In the Salt Lake
coal field all coals within 40 ft of the surface can be considered
oxidized.None of thesefeaturesis desirablefor a steamcoal.These
data, if figured with the rest of the analyses,will tend to bias the
coal negatively. Likewise, exgluding these data from an area-wide
appraisal would bias the results positively. Reporting both sets of
data and noting the maximum, minimum, and average depths of
oxidation will allow a better assessmentof area coals.
wish to thank Lynn Brandvold and William
ACKNOWLEDGMENTS-I
Stone for helpful comments and Orin Anderson, Louie Martinez,
and Ralph Wilcox for reviewing a version of this paper.
References
American Society of Testing Materials, 1983, Gaseous fuels; iz Coal and coke: v 05 05,
D3775, pp. 402-405.
Anderson, O. J.,7981,,Geology and coal resourcesof Cantaralo Spring 7rl:-min quadrangle: New Medco Bureau of Mines and Mineral Resources,Open-file RePort 142,
13 pp.,2 maps, scale1.:24,000.
Anderson, O. J., and Frost, S. I ,1982, Geology and coal resources of Twenty-Two
Spring quadrangle: New Mexico Bureau of Mines and Mineral Resources,Open-file
Report 143,6 pp., 1 map, scale1:24,000.
Campbell, n W., 1981,Geology and coal resourcesof Ceno Prieto and The Dyke quadrangles: New Mexico Bureau of Mines and Mineral Resources,Open-file Report 1<K,
68 pp.,2 maps, scaleL:24,000.
Campbell, F. W., and Roybal, G. H., 1982, Geology and coal resourcesof ihe Fence
Lake 1:50,000quadrangle, Catron and Cibola Counties, New Mexico: New Mexico
Bureau of Mines and Mineral Resources,Open-file Report 207, 37 pp ,2 maps
Kottlowski, F E., Campbell, F. W, Roybal, G. H , Hatton, K S., 1985,New Mexico; ln
1985Keystone coal industry manual: McGraw-Hill, Inc., pp. 531-540.
Mclellan, M. W, Biewick, L. R., and Landis, E. R., 1984,Stratigraphicframework,
stru*ure, and generalgeology of the Salt Lake coal field, Cibola and Catron Counties,
New Mexico: U S. GeologicalSuruey,MiscellaneousField StudiesMap MF-1689,scale
1.:24,000
Roybal, G. H., and Campbell, F. W., 1981,Stratigraphic sequencein drilling data from
Fence Lake area: New Mexico Bureau of Mines and Mineral Resources,Open-file
Report 145,59 pp., 11 maps, scale1:50,000.
Wood, G H., Kehn, T. M., Carter, M. D., and Culbertson, W C , 1983,Coal resource
classificationsystem of the U S. Geological Suruey: U S GeoiogicalSuruey, Circular
891.,55 pp
!
Continuedfrom page5
Ewing, T. E ,1978, Lead isotope data from mineral deposits of southern New Mexicea reinterpretation:
Economic Geology, v.73, pp. 578-6M
Gordon, C H, 1910,Magdalenadistric| in Lindgren,
W, Graton, L , and Gordon, C H., The ore deposits
o{ New Mexico: U S. Geological Survey, Professional
Penpt
6R
nn
J41-)4n
Iovenetti, | , 7977, Hydrothermal silicification of the Kelly
Limestone in the eastem portion of the Kelly nining
district, Socono County, New Mexico: Unpublished M S
thesis, New Mexico Institute of Mining and Technology, Socorro, 153 pp
Kolima, S., and Sugaki,A, 1985,Phaserelationsin the
Cu-Fe-Zn-S system between 500 and 300"C under
hydrothermal conditions: EconomicGeology,v 80, pp
758-1.7't
Lasky, S G , 1932,The ore deposits of Socorro Counry
New Mexico:New Mexico Bureau of Mines and Mineral
Resources,Bulletin 8, 139 pp
Loughlin, G F, and Koschmann,A H ,7942, Geology
and ore deposits of the Magdalena district, New Mexico: U S GeologicalSuruey,ProfessionalPaper200, 168
PP
Osbum, G. R, and Chapin, C E , 1983,Ash-flow tuffs
and cauldronsin the northeastMogollon-Datil volcanic
field-a summary: New Mexico Geological Society,
Guidebook to 14th Field Conference,pp 797-204.
Park, D E., 1971,Petrology of the Tertiary Anchor Canyon stock, MagdalenaMountains, central New Mexico:
Unpublished M S. thesis,New Mexico Institute of Mining-and Technology,Socono,92 pp
Roedder,E , 1979,Fluid inclusions as samplesof ore fluid;
ln Barnes, H. L. (ed ), Geochemistry of hydrothermal
ore deposits, John Wiley and Sons, 2nd ed, pp 634737
Titley, S R , 1958,Silication as an ore control, Linchburg
mine, Socono County, New Mexico: Unpublished M S
thesis, University of Arizona, Tucson, 153 pp
Weber, R. H., 1977, K-Ar ages of Tertiary volcanic and
intrusive rocks in Socorro,Catron, and Grant Counties,
New Mexico: New Mexico Geological Society, Guidebook to 14th Field Conference, pp.220-223
!
February
'1.987
New Mexico Geology