02 kleimansandfinal

IAEA Technical Meeting on Origin of sandstone type uranium deposits: A global perspective, Vienna, May 2012

Geologic setting and mineralization controls at the
Sierra Pintada uranium district, Mendoza, Argentina

Laura E. Kleiman

División Geología del Uranio,
Gerencia Exploración de Materias Primas
Comisión Nacional de Energía Atómica,
Avenida del Libertador 8250, 1429 Buenos Aires, Argentina.
kleiman@cnea.gov.ar


Sierra Pintada uranium district
Permian sandstones of the Cochicó Group
Main factors controlling mineralization
• Stratigraphy
• Structures and palaeogeography of the
basin
• Sandstone provenance
• Sandstone geochemistry
• Palaeoclimate
• Source rocks for uranium
• Agents causing uranium precipitation


MAIN URANIUM DISTRICTS


URANIUM PRODUCTION IN ARGENTINA
(1952 to 1995)

10% 3% Sandstones

Vein-type and
granitoids
Surficial and
87% others

Total production: 2582 tn U
Kleiman and Ramos, 2006


GONDWANA BASINS

Cu
en
ca
a
a
a
de
e
e
e
Sa
n
Ra
fa
el

Kleiman and Ramos, 2006


CHOIYOI RHYOLITIC PROVINCE

~280-250 Ma

Kleiman and Japas, 2009



•Inland arc-migration due to
shallowing of the slab;
subduction angle was oblique
to the margin.
•Volcanism and sedimentation
were syntectonic with the San
Rafael Orogeny, a major
episode of transpressional
deformation.
•Deformation controlled both
the paleogeography of the
basin and the emplacement of
the mineralizations .


GEOLOGICAL MAP OF THE
SAN RAFAEL MASSIF
Carrizalito Deposit

Triassic Puesto Viejo Fm: continental
San Rafael
rifting sandstones, basalts, rhyolites
Los Reyunos
Cerro Carrizalito Fm: rhyolitic
Dr Baulíes Deposit ignimbrites,subvolcanic bodies,
La Pintada Deposit garnet rhyolites
El Potrerito Upper Quebrada del Pimiento Fm:
Choiyoi andesites
35º S Agua de los Burros Fm: rhyolitic
ignimbrites, subvolcanic bodies.

Nihuil Dam Lower Cochicó Group: dacitic
Choiyoi ignimbrites, andesites,
continental sandstones

U mineralization in sandstones

Scale (approx.)1:500000
(


STRATIGRAPHY OF THE SAN RAFAEL MASSIF
Age Phase Diastrofism Lithology Stratigraphy
Cycle Phase
227.4 TRIASSIC Middle Synrift Continental sediments, rhyolitic Puesto Viejo Formation
248,2 Lower Huarpic ignimbrites, basalts

G Rhyolitic lavas, subvolcanic Cerro Carrizalito Formation
Upper Choiyoi O bodies and ignimbrites
P Upper N Quebrada del Pimiento Formation
256,0 andesitic lavas and dykes
E Section D Pre- Rhyolitic ignimbrites,
R W Huarpic subvolcanic bodies, sediments Agua de los Burros Formation
M Lower A Andesitic breccias, dacitic
I Choiyoi N ignimbrites sandstones Arroyo Punta del Agua Formation
A Lower I Cochicó
N Section C Dacitic and rhyolitic Group Yacimiento Toba Vieja Gorda
ignimbrites Los Areniscas Atigradas
Sandstones and conglomerates Reyunos
Formation Psefític Member
Sanrafa Rhyodacitic subvolcanic Cerro Agua de las Yeguas Formation
290,0 bodies
elic
323,0 Upper Sandstones and shales El Imperial Formation
Marine platform sedimentation
CARBONIFEROUS Lower
354,0
DEVONIAN FA Chanic Greenschist facies La Horqueta Formation
MA metamorphic rocks
TI
417,0 SILURIAN Gabbros, milonites Loma Alta Formation (El Nihuil Gabbro)
NI
443,0 ORDOVICIAN Marine sediments and Ponon Trehue and Lindero Formations
AN
limestones
495,0 CAMBRIAN
545,0 PRECAMBRIAN GRENV Amphibolites, aplites Cerro La Ventana Formation
ILLIAN


SIERRA PINTADA DISTRICT

Yacimiento Los Reyunos Formation:
Aeolian and fluvial sandstones interbedded with ignimbrites
the sandstones are reworked from the pyroclastic flows


SIERRA PINTADA DISTRICT

Pérez and Solís, 1984


STRUCTURES RELATED TO THE SAN RAFAEL OROGENY
Development of growth folds and faults and colapse of the structures

Moreno Peral and Salvarredi, 1984.


#

Carrizalito deposit

P
PS #
R
RO

Dr. Baulíes deposit
SR
R
SR

La Pintada deposit
O
PSR

#

#

Sketch showing San Rafaelic WNW sinistral Schematic distribution of main structures related to the San
transpressional and post-Sanrafaelic WNW Rafael orogeny in the three domains with the location of the
dextral transtensional structures five measured areas. 1: Agua del Toro, 2: Yacimiento Dr.
Baulíes, 3: El Nihuil, 4. Valle Grande, 5: Ponón Trehué.



Japas et al., 2008


Stratigraphy of the Cochicó Group

Arroyo Punta del Agua Fm.

Yacimiento Los Reyunos Fm.
Toba Vieja Gorda Mb.
Areniscas Atigradas Mb.
aeolian and fluvial
sandstones

Psefitic Mb.
alluvial fan
deposits, interbedded
dacitic ignimbrite flows


Sandstone Petrology
Four sandstone levels within the Yacimiento Los Reyunos Formation
Modal analysis:
Psefitic Member : abundant rock fragments from the substratum
Areniscas Atigradas Member: plagioclase, quartz, micas and volcanic rock
fragments

Stratigraphic level

upper level sandstones

Areniscas Atigradas
Member

lower level sandstones

Psefitic Member


Sandstone Petrology: Psefitic and Areniscas Atigradas Members
• Sandstone provenance:
• Metamorphic and sedimentary substratum for older sandstones of
the Psefitic Mb.
• Intermediate to acid volcanic rocks for sandstones of the Areniscas
Atigradas Mb.

Lv

0.5 mm
Lm
0.4 mm


Sandstone Petrology

Montmorillonite, caolinite, illite, and Fe chlorite cements

Lv
Carbonate cement
0.5 mm

Carbonate cement predominates above the mineralized
horizons in the deposits


Sandstone Geochemistry
2

Psefitic Member

1 Fe-shale Fe-sand
log(Fe2O3/K2O)

lower level sandstones

Wacke
Litharenite Sublitharenite
Shale
Areniscas Atigradas
0 sandstones
Quartz arenite

Arkose Subarkose upper level sandstones

-1
0 0.5 1 1.5 2 2.5
log(SiO2/Al2O3)


Sandstone provenance:Geochemistry of sandstones and ignimbrites
Puesto Abra and Las Moras, sandstones and ignimbrites Dr. Baulíes deposit, sandstones and ignimbrites
100
100

189
Rock/chondrite

186 167

Rock/chondrite
180 168

169
10 171/85Fr
10
164/85
179/85
165/85

166/85

1 1
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Carrizalito deposit: sandstones and ignimbrites
La Pintada deposit, sandstones and ignimbrites
100

100

184
190
Rock/chondrite

Rock/chondrite

182

10 191/85 177
10
174
102/06
181/85

1 103/06 178/85
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

1
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
0.1


Sandstone Geochemistry

CIA= 100*[Al2O3/(Al2O3+CaO*+Na2O+K2O)] >55<71


Uranium source rocks
Cochicó Group ignimbrites
Crystal-rich ignimbrites , monotonous sequence
Quartz Plag. FK Biot. Lv Lm+Ls Pumice Matrix
7-21 17-44 1-9 2-11 0.1-20 0.1-12 0.5-20 25-40
Accesory minerals: Apatite, zircon, titanomagnetites
Dacites and rhyolites ( up to 72% SiO2 ),
subalkalines (mol Na + K / Al = 0.5 to 0.7)
meta to peraluminous (mol Al / Na + K + Ca = 0.8 to 1.25)
medium to high K series
La/Yb = 20.5 to 43.8
U (average content) = 1.32 ppm (n = 55, S = 0.57)
Th/U (average) = 5.95 (n = 23, S = 2.47)


100.0
Th (ppm)

10.0

1.0
0.1 1.0 10.0 100.0
U (ppm)

Lower Choiyoi San Rafael Upper Choiyoi San Rafael
Lower Choiyoi Agua Escondida Upper Choiyoi Agua Escondida


DR. BAULÍES

Lardone and Giordano, 1984


DR. BAULÍES

Deposit size (t U): 6000 and grade (%U): 0. 11 - 0.13

Uranium mineralization:
uraninite, coffinite, brannerite,uranophane and
liebegite
Uraninite with excess of SiO2 and Ca2O, contains MnO
Brannerite contains Zr

Fe, As, Pb, Cu, and Zn sulphides

Pb, Ba, Zr, As, S, Li increase in the mineralized
sandstones.


DR. BAULÍES

Uranium mineralization Uranium mineralization filling
following stratification, SS fractures crosscuting bedding
planes, dilatant fractures


DR. BAULÍES

Sulphide Volcanic chloritized
minerals rock fragment adsorb U

uraninite uraninite
cement cement


DR. BAULÍES
Subhedral coloform
uraninite uraninite

uraninite + uraninite
coffinite replacing micas


DR. BAULÍES

Anatase Brannerite


DR. BAULÍES
Agents causing uranium precipitation
•Organic carbon in the sandstones : 0.21 - 0.41%
•Organic matter is amourfous and extrinsec, humic acids?
•Sulphur total : 0.07 - 0.22 %
•Fe, As, Pb, Cu, and Zn sulphides
•Barite cement in the mineralized sandstones
•Uranium is adsorbed in secondary titanium minerals:
anatase (Ti-sponges) which formed by disolution of
titanomagnetites
•Uranium is also adsorbed in clay minerals, in chlorites, in
altered lithic volcanic fragments, in chloritized biotites, in
feldspars and in iron hydroxides


Conclusions

Several factors controlled the mineralization at the
Sierra Pintada uranium district:
•Aeolian sandstones from the Areniscas Atigradas Member
are the host rocks for the uranium mineralizations
•Structures conditioned the paleogeography of the basin,
the distribution of host and source rocks and groundwater
circulation
•Dacitic to rhyolitic volcanism play a major role as the
source for both the sandstones and for the uranium.
• U precipitation was related to the addition of reducing
agents such as organic matter and sulphides and the
presence of certain minerals in the sandstones.


THANKS FOR YOUR ATTENTION

02 kleimansandfinal

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