THE PAMPEAN PEGMATITE PROVINCE, ARGENTINA:
A REVIEW
Miguel Angel Galliski
1
IANIGLA, CCT MENDOZA (CONICET), Avda. Ruiz Leal s/n,ParqueGralSan Martín; C.C.330
(5.500) Mendoza, Argentina. [email protected]
Keywords: rare-element pegmatites, Sierras Pampeanas, Argentina.
INTRODUCTION
The Pampean pegmatite province
contains most of the granitic pegmatites
of Argentina. It has economic mineral
resources that had been mined during the
past 80 years, producing in excess of 1
Mt of feldspar of ceramic grade, 1Mt of
quartz, 50,000 t of mica, 25,000 t of beryl,
10,000 t of spodumene, 45 t of tantalum
minerals, and 10 t of bismuth minerals. It
extends discontinuously for more that 800
km N-S and 200 km E-W, from 24º30´ to
33º30´S, mostly in the Sierras Pampeanas
of northwestern and central Argentina. Its
possible extension to the South could be
even more than 400 km as indicated by
discontinuous outcrops under recent cover.
The present review updates previous
interpretations (Galliski 1994a, b).
TECTONIC SETTING
The orogenic pegmatite fields of the
Pampean pegmatite province developed
mainly in the early Paleozoic, during the
Pampean (~550-520 Ma) and especially
Famatinian (~500-435 Ma) orogenic
cycles, along a pericratonic mobile belt
located in the western proto-margin of
Gondwana. The tectonic evolution of this
mobile belt is complex and it includes
the accretion of several terranes (Cf.
Collo et al. 2009). Significant facts in
the geological evolution of the pegmatite
30
province include: (1) the ensialic
deposition of several thousand meters thick
psammopelitic succession of sediments,
represented by the Puncoviscana Formation
and equivalent protoliths, during the Late
Proterozoic - Early Cambrian, and (2)
the Upper Ordovician collision of the
Precordillera terrane. The present tectonic
setting that exposes the pegmatite province
results from the flat subduction geometry
of the Nazca plate under this segment of
the South America plate.
THE
OROGENIC
FIELDS
PEGMATITE
The orogenic pegmatite fields
encompass pegmatites of muscovite,
muscovite–rare-element and rare-element
classes using the classification of Cerný
& Ercit (2005). The distribution of the
economic pegmatite fields is plotted in
Fig. 1. The muscovite class pegmatites
are dominant in three fields aligned in
the western side of the province, and one
in the eastern side. From north to south
the (1) Centenario district is placed in
amphibolite facies of medium pressure and
comprises pegmatites hundred meters long
and 1-3 m wide that have muscovite of
grade 2. The (2) Ambato district is hosted
in micaschists and migmatites intruded by
small tonalite and granodiorite stocks. The
pegmatites are medium sized bodies with
biotite, muscovite, garnet and schorl that
Estudos Geológicos v. 19 (2), 2009
Miguel Angel Galliski
Estudos Geológicos v. 19 (2), 2009
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THE PAMPEAN PEGMATITE PROVINCE, ARGENTINA: A REVIEW
produced some hundred of tons of good
quality mica graded 4 to 5. The (3) Valle
Fértil district comprises more than 50
pegmatites emplaced in medium- to highgrade metamafic and metapsammitic
rocks,
that
have
undergone
metamorphism during the Famatinian
cycle, at peak conditions of 600-700
MPa and 700-800 ºC. The pegmatites
are tabular or equidimensional bodies
with simple zoning. They have biotite,
muscovite and, occasionally, allanite,
monazite or magnetite as accessory
phases and they are not visibly linked
with granite intrusives. The (4) Alta
Gracia district is located in the eastern
border of the province and comprises
pegmatites 100-200 m long and 5-20 m
wide that have commercial muscovite in
the intermediate zone. They are placed in
gneisses and amphibolites of medium- to
high-metamorphic grade.
The different fields from the rareelement pegmatite belt belong to the
LCT (Li, Cs, Ta) petrogenetic family.
They are aligned N-S and mostly hosted
in medium-grade metamorphic rocks,
preferentially in amphibolite facies from
an Abukuma-type metamorphic belt, that
suffered polyphase deformation during the
Pampean and Famatinian orogenic cycles.
From north to south the pegmatite fields
are (5) Cerro Blanco, (6) El Quemado,
(7) Quilmes, (8) Calchaquí, (9) Ancasti,
(10) Sierra Brava, (11) Conlara, (12)
Totoral (13) La Estanzuela, (14) Altautina,
(15) Comechingones. The Cerro Blanco
comprises pegmatites of rare-element
class emplaced in sillimanite-bearing
gneisses that have beryl and muscovite as
main minerals. El Quemado is a district
hosted in mottled hornfels and micaschists
that has pegmatites of petalite and berylcolumbite-phosphate
subtypes.
The
Quilmes district, emplaced in gneisses
of medium- to high-metamorphic grade,
32
contains pegmatites mined for ruby
mica that contains minor beryl. They are
considered as of the muscovite–rareelement class. The Calchaquí is a poorly
studied district located in phyllites and
cordierite-bearing micaschists that has
rare-element pegmatites with beryl. The
Ancasti pegmatite field comprises a
population of pegmatites of rare-element
class that are contained in micaschists and
gneisses. The pegmatites are distributed in
several groups with predominantly berylcolumbite-phosphate and spodumene
subtypes. The Sierra Brava district hosted
in metamorphic rocks of slightly higher
grade is southward located. It comprises
pegmatites, possibly of muscovite–rareelement class, that were mined by muscovite
and beryl. The Conlara, Totoral and La
Estanzuela pegmatite fields are located in
the San Luis ranges and have a past record
of producing mica, beryl, spodumene,
tantalite and lastly K-feldspar, albite
and quartz. These districts are hosted in
metamorphic complexes of medium grade,
intruded by orogenic and postorogenic
granites. The medium-sized pegmatites
are representative of several types and
subtypes as beryl-columbite-phosphate,
spodumene, albite-spodumene and albite.
The pegmatite fields of Córdoba ranges,
Altautina and Comechingones, contain
pegmatites of beryl-columbite-phosphate
and subordinate spodumene subtypes
placed in a crystalline rock basement,
possibly older than the Famatinian one,
and developed mostly during the Pampean
orogenic cycle. Columbite of the orogenic
rare-element pegmatites bears the highest
contents of Ta. The common primary
phosphates belong to the triphylite group.
The K-Ar ages of the pegmatites from
this belt, except for the Córdoba districts,
are grouped in the Lower Paleozoic, in good
correlation with the granitic magmatism of
the Famatinian orogenic cycle. They are
Estudos Geológicos v. 19 (2), 2009
Miguel Angel Galliski
genetically linked to a suite of two mica,
or muscovite-tourmaline leucogranites,
which usually are small to medium size
composite intrusives of variable fabric,
within the aplite to pegmatite range. They
are peraluminous, low-Ca calcalkaline
rocks, that have high LILE and volatile
contents, especially B and P. They have
total REE depleted contents and high
initial 87Sr/86Sr ratios (≥ 0.71). Most of
these S-type leucogranites and associated
pegmatites are syn- to late-kinematic
and were slighly or strongly deformed
during the late-stage phases of Famatinian
deformation. The most favored model for
the origin of this suite comprises episodic
crustal anatexis, produced by muscovite ±
biotite dehydration melting, of dominant
Puncoviscana protholiths by shear-heating
during a collisional orogeny, as proposed
by Nabelek & Liu (2004) for other regions.
This collisional leucogranite suite
is space-related to another suite of TTG
dominant lithology, which includes
some more basic intrusives; it is also
calcalkaline, peraluminous, and have lower
87
Sr/86Sri ratios (~ 0.706). This last suite
has been considered of I-type and related
to a subduction setting, with variable lower
crust component and possible assimilation
of supracrustal protoliths (Pankhurst et al.
2000).
THE POST-OROGENIC PEGMATITE
FIELDS
The granitic pegmatites of this
kind form distinctive units in the (16)
El Portezuelo (Papachacra) and (19)
Potrerillos groups, and (17) Velasco and
(18) Punilla districts. The pegmatites of the
El Portezuelo group belong to the miarolitic
class, miarolitic-rare-element subclass,
possibly of gadolinite-fergusonite type and
NYF (Nb,Y,F) signature (Colombo 2006).
The pegmatites from the Velasco district
Estudos Geológicos v. 19 (2), 2009
are units of beryl-columbite-phosphate
subtype contained in the Huaco sienoto monzogranite, dated at 350-358 Ma
(Grosse et al. 2008). The pegmatites of the
Punilla field are rounded bodies, similar to
the Velasco ones, but generally larger, with
more varied mineralogy, and contained
in porphyritic granites of the Achala
batholith, dated at 368± 2 Ma (Dorais et al.
1997). The columbite in these pegmatites
is usually columbite-(Fe) enriched in
Y. The most common primary Fe-Mn
phosphate is triplite. The pegmatites of
the Potrerillos group are medium sized
pegmatites with biotite, muscovite,
tourmaline, beryl and, occasionally,
primary fluorite contained in a biotite
porphyritic granite, dated at 352-362 Ma.
Except for the El Portezuelo miarolitic
pegmatites that have a diagnostic NYF
mineralogy, and the Potrerillos pegmatites
that locally have primary fluorite,
monazite and ilmenorutile suggesting the
same signature, the pegmatites of the other
districts are difficult to classify because
they lack typical diagnostic paragenesis.
In general, the parental granites of
these pegmatites form composite batholiths
or stocks lacking post-emplacement
deformation, that were intruded in
upper- to medium upper crust levels (P
150-250 MPa), mostly during the Lower
Carboniferous. Petrographically, they are
generally biotite porphyritic granites to
monzo- or sienogranites, locally showing
K-feldspars with incipient rapakivi-like
textures. They are usually high silica,
meta to mildly peraluminous, high-K
calc-alcaline granites, with Fe-, Mg-,
and Ca-contents higher than the orogenic
leucogranites. Commonly, these granites
are moderately LIL and HFSE enriched.
The initial 87Sr/86Sr ratios, if not disturbed,
are generally low to medium (0.7030.706); the contents and normalized REE
patterns, and  18O values are most likely
33
THE PAMPEAN PEGMATITE PROVINCE, ARGENTINA: A REVIEW
comparable to those of the NYF signature.
These attributes suggest that this is a postorogenic suite probably of aluminous A-type
granites, intruded in an intraplate tectonic
setting. In the El Portezuelo and Huaco
granites the genetic interpretation favor a
mixed source with melting of crustal I-type
granite protoliths, previously metasomatized
by a mantle fluid component (Colombo 2006,
Grosse et al. 2008).
CONCLUSIONS
The framework for the geological
evolution of at least the Famatinian
representatives of the Pampean pegmatite
province comprises basically three major
episodes: (1) intrusion of muscovite class
pegmatites, poorly or non-connected
with parental granites, in a MP-MT
metamorphic environment generally
westward of, (2) a LCT rare-element
pegmatite belt and the parental collisional
leucogranites placed at the axis of a LPMT metamorphic belt developed in the
Upper Ordovician during the Famatinian
tectonic cycle, and (3) occurrence of a suite
of rare-element pegmatites locally with
definite NYF signature, mostly contained
in post-orogenic granites that form major
composite batholiths or minor plutons,
possibly of aluminous A-type granites
intruded during the Lower Carboniferous
in an intraplate tectonic setting.
Acknowledgements
This paper is a contribution to PIP
5907 of CONICET and PICT 21638 of
FONCYT.
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