U mineralogy an its distribution in the rocks
A practical approach for the knowledge of the
main U minerals and their meaning as U sources
Michel CUNEY
UNIVERSITE DE LORRAINE – GEORESSOURCES - CREGU – CNRS
54 506, Vandoeuvre les NANCY France
[email protected]
U, Th sites in the nature
P. : U, Th minerals
S. : Substitution in accessory minerals
T. : Traces the main rock forming minerals
A. : Adsorption on mineral surfaces
O. : Associated with organic matter
D. : Dissolved state in geologic fluids
U, Th sites in the nature
P. SITES : U, Th minerals
Uraninite
UO2+x (cubic) euhedral shapes
U308 = 85 wt % U
Pechblende
UO2+x (cubic) (collomorph)
Coffinite
U[SiO4]
Ningyoite
U[PO4]
Brannerite
(U,Ca,Ce,Y,Th)(Ti,Fe)2O6
Uranothorianite
(Th,U)O2+x
Uranothorite
(Th,U)[SiO4]
[1 – x (OH) 4x]
See also http://www.uraniumminerals.com, http://www.webmineral.com
Uraninite crystal from St Sylvestre two mica peraluminous leucogranite
50 µm
Optical microscope transmitted light
Uraninite crystals "Trebilcock Mine", Topsham, Sagadahoc Co., Maine, USA
Photo courtesy of IROCKS.com
Botryoidal - Collomorph
PITCHBLENDE = Pech – Blende (in German)
Except
the crystal form
its properties
are the same
as uraninite :
occurs as irregular
masses
rounded, layered,
or botryoidal
structure
PITCHBLENDE
Botryoidal pitchblende up to 2 cm
overgrown by pyrite, Jánská vein 15th level
(Mining Museum Příbram, 853) photo P. Škácha
100 µm
SEM
backscattered
electron images
120 µm
Syngenetic zoning, kku-pitchblende. BSE-images Epigenetic alteration, kku-pitchblende
Golubev
PITCHBLENDE
UO2,x
Pechblende and Gummites
(« Limonites of Pitchblende »
Pitchblende + Gummite
Texture : ''Oeil de Perdrix''
REE patterns
of U-oxides
from various
deposit types
Parameters controlling REE incorporation in U-oxides
ALTERATION OF PITCHBLENDE TO COFFINITE
Coffinite
USiO4
SiO2
microcristalline
hematite/pyrite
Pitchblende
Reflected light microscopy
BOIS NOIRS LIMOUZAT, FOREZ
Uranothorianite (Th,U)O2 in clinopyroxene & calcite
Seydoux-Guillaume et al. 2008
Uranothorianite in clinopyroxene and calcite
Seydoux-Guillaume et al. 2008
BRANNERITE (U,Ca,Y,Ce)(Ti,Fe)2O6
Monoclinic, Black, brownish, Vitreous, Resinous, Dull Hardness: 4½ - 5½
Name: For Dr. John Casper Branner (1850-1922), American geologist
Brannerite, with inclusions of arsenopyrite(white). Size crystals up to 10mm. Pol. section,
refl. light. Photo Kjell Gatedal (Hakansboda, Lindesberg, Västmanland, Sweden)
BRANNERITE (U,Ca,Y,Ce)(Ti,Fe)2O6
Photo Copyright © Daniele Respino Locality: Lodrino, Riviera, Ticino (Tessin), Switzerland
A steel-grey 6 mm prismatic crystal of brannerite perched on a 4x2 cm matrix. Photo D. Respino.
URANO-THORITE (Th,U)SiO4 & URANINITE
100 µm
Transmitted light microscopy
Uranothorite : (Th,U)Si04
Scanning electron microscopy (backscattered electron image)
U content of a mineral does not
determine whether it is a U ore mineral
If U is present in a mineral
in complex combinations with other elements
It may be too costly to extract
that mineral is not a U ore mineral
ex : Nb-Ta-Ti minerals
General classification of Ta-Nb-Ti oxides (Černý et Ercit, 1989)
Group
General formula
Crystal System
Minerals
Chemical formula
Orthorhombic
Brannerite
Thorutite
Orthorhombic
Columbite
Tantalite
Orthorhombic
(Y,Ca,Ce,U,Th,)(Ti,Nb,Ta)2O6
Polycrase
(Y,Ca,Ce)(Nb,Ta,Ti)2O6
Euxenite
Tantaeuxenite (Y,Ca,Ce)(Ta,Nb,Ti)2O6
Orthorhombic
(Y,U,Th,Ca)(Nb,Ta,Ti)O6
Samarskite
(U,Th,Y,Ca)(Nb,Ta,Ti)O6
Ishikawaite
Ca-Samarskite (Ca,Y,U,Th)(Nb,Ta,Ti)O6
AB2O6
Brannerite A=U,Th
Columbite
B=Ti,Fe
A=Mn,Fe,Mg
B=Ta,Nb>Ti,U,Th
Polycrase
A=Y,Ca,Ce,U,Th
B=Ti,Ta,Nb
ABO4
Samarskite A=Y,U,Th
B=Nb>Ta
Fergusonite A=REE,Y,U,Th,Zr,Ca
B=Nb,Ta, Ti,Sn,W
Monoclinic
Orthorhombic
Tetragonal
A1-2B2O6(O,OH,F)
Pyrochlore A=Ca,K,Na,Ba,Y,REE,U,Th Cubic
B=Ta,Nb,Ti,Fe,Sn,W,Sb
Davidite
M2O3 type
Rhomboedral
(U,)(Ti,)2O6
(Th)(Ti)2O6
(Mn,Fe,Mg)(Nb,Ta,U,Th)2O6
(Mn,Fe,Mg)(Ta,Nb,U,Th)2O6
Nd-Fergusonite (REE,U,Th)(Nb,Ta)O6
Y-Fergusonite (Y,REE,U,Th)(Nb,Ta)O6
Pyrochlore (Ca,U,REE)(Nb,Ta,Ti)2O6(O,OH,F)
Microlite (Ca,U,REE)(Ta,Nb,Ti)2O6(O,OH,F)
(Ca,U,REE)(Ti,Nb,Ta)2O6(O,OH,F)
Betafite
Davidite
(REE,Ca)(Y,U)(Ti,Fe)20O38
Finch and Murakami,1999. Systematics and paragenesis of uraniuum minerals in Burns and Finch, Uranium, mineralogy,
geochemistry and the environment, Mineralogical Society of America,, Review in Mineralogy, v. 39, p. 91-179
Nb-Ta-Ti TETRAVALENT URANIUM MINERALS
DAVIDITE
(La,Ce,Ca)(Y,U)(Ti,Fe3+)20O38
BETAFITE (cubique)
(Ca,Na,U)2(Ti,Nb,Ta)2O6(OH,F)
U, Th sites in the nature
P. SITES : hexavalent U minerals
More than 200 species
The most spectacular in appearance of U(VI) minerals is their color :
- bright yellow, orange, green, & all combinations
-some of them fluoresce under UV light
important factor in their recognition in the field
Occur : - as earthy or powdery materials or
- as fine, delicate, needle-like or platy, flake-like crystals
Only a small proportion of the total world U production to date
Two major modes of occurrence:
1. weathered or oxidized zones of primary deposits,
alteration of the primary minerals in place
called secondary minerals
2. primary concentrations in sedimentary rocks = calcretes
HEXAVALENT URANIUM MINERALS
INCREASING
precipitation
pH
precipitation
dissolved
2UO2[SO42-]n complexes UO2[CO3 ]n
DECREASING SOLUBILITY
Sulfate
s
SO42-
+ H2O
Carbonate
s
CO32Dissolved
UO22+
+ SiO44-
Oxy-hydroxides
+ AsO43+ VO43Arsenate
s
Vanadates
+ PO43Phosphate
s
Silicate
s
modified from Garrels & Christ, 1959
HEXAVALENT URANIUM MINERALS
Oxy-hydroxides : Mn[(UO2)xOy(OH)2](H2O)m
M = Ca2+, Pb2+, Ba2+, Sr2+, 2K+
[(UO2)8O2(OH)12](H2O)12
Schoepite
K2[(UO2)6O4(OH)6](H2O)8
Compreignacite
Pb[(UO2)4O3(OH)4](H2O)4
Fourmarierite
Carbonates :
(UO2)(CO3)
Rutherfordine
Pb2 (UO2)(CO3)3
Widenmannite
Silicate :
Ca (UO2)2[SiO3OH]2, 5H2O
Uranophane
55 wt% U
Phosphates
Cu(UO2)2(PO4)2-10H2O
Torbernite & Meta-torbernite : 50 wt% U
Ca(UO2)2(PO4)2-10H2O
Autunite & Meta-autunite :
50 wt% U
Vanadates
Ca(UO2)2(VO4)2- 5-8H2O
Tyuyamunite :
40-48 wt% U
K2(UO2)2(VO4)2- 1-3H2O
Carnotite :
40-45 wt% U
(Ba,Pb) (UO2)2 (VO4)2, 5H2O
Francevillite :
K+ can be replaced by : Na, Rb, Cs, Tl, Ag - Ca2+ by : Pb, Ba, Mn, Ca …
TORBERNITE & Meta-torbernite (Chalcolite) (CuO*2UO3*P2O5* nH20; 60 wt % U3O8)
only difference between the 2 being the number of water molecules present
bright emerald color, a pearly luster, hardness of 2-2 1/2 (same as the fingernail)
specific gravity = 3.5 : flat, square, translucent crystals, usually fluoresce with a faint green c
Lemon or sulfur-yellow, occasionally apple-green,
brilliant yellow to greenish-yellow fluorescence in UV light
hardness = 2-2 1/2, specific gravity, 3.1
has a colorless to pale yellow or green streak
occurs in small square, rectangular, or octagonal flat
translucent crystals or as thin coatings or stains on rock
5 x 4 x 3cm Daybreak Mine
Mount Spokane, Washington
Autunite : Ca(UO2)2 (PO4)2,10H2O
alpha-Uranophane
: Ca (UO2)2Si03(OH)2,5H20
beta-Uranophane : (H3O)Ca (UO2)2 (SiO4)2,3H2O
Carnotite : K2(UO2)2(VO4)2- 1-3H2O
A 2-cm thick layer in Mancos Shale (Mesa Verde Comb Wash, SW Utah)
lemon-yellow mineral
yellow streak
powdery aggregates
thin films or stains
First identified in 1898 in the Colorado Plateau area (USA)
not fluorescent
Major U production from W. of the Black Hills, S. Dakota
specific gravity = 4
Tyuyamunite
Marie Mine, Carbon Co., Montana, USA
Ca(UO2)2(VO4)2- 5-8H2O
first occurrence: SE Turkmenistan
near the town of Tyuya Muyun
Crystal size approx. 0.25mm
slightly more greenish color than carnotite
in some cases, very weak yellow-green fluorescence
not found in carnotite
U, Th sites in the nature
S. SITES : substitution
Accessory minerals
Zircon
Monazite
(Zr,Hf,U,Th)[SiO4]
(LREE,Th,U)[PO4]
Xénotime
Allanite
Titanite
Apatite
(Y,HREE,U)[PO4]
(Ca,LREE,Th,U…)(Al,Fe)[Al2Si6O12]
(Ca,U)[TiSiO5]
(Ca,U)5[PO4]3 (OH, F, Cl, CO2)
solid solution with britholite
Metamict ZIRCONS
MONAZITE
Extremely stable phase :
can preserve crystallization ages through the geological cycle
chosen as possible matrices for high level nuclear waste diposal
Monazite
Zircons
Plain light
500 µm
Crossed nicols
500 µm
ALLANITE
+
URANINITE
U, Th sites in the nature
T. : Traces the main rock forming minerals
U content in main rock forming minerals (Qz, fldsp, micas …)
is generally very low :
ppb levels
when higher U contents are reported
contamination with U in fissures
U adsorbed at their surface
U, Th sites in the nature
A. : Adsorption on mineral surfaces
U can be easily adsorbed at the surface of a number of minerals :
Ferrihydrite (the most significant U-sorbing phases in
weathering of the Koongarra U deposit (Payne & Airey, 2006)
Ti – Fe oxides - hydroxides >>
clays minerals : interstratified > illite > kaolinite
according to the importance of their specific surface
very weakly on other silicates
Relative adsorption of various minerals in a composite sample
Koongarra sample
U, Th sites in the nature
O. : Associated with organic matter
U Has several relations with organic matter :
O.M. trapped around U minerals
= polymerisation of hydrocarbons from geologic fluids
O.M. used as a reductant for U deposition :
= plants in tabular sandstone deposits
= graphite at Rössing …
O.M.-U complexes for U transport in solution
Organic matter trapped around uraninite crystals
bitumen
UO2
OKLO, Gabon
Gauthier-Lafaye
SEM-BSE) images of bitumen nodules from the
Permo-triassic Dongara sandstone (Perth basin,
with monazite cores at various stages of
mechanical breakup.
Migrating liquid hydrocarbons are immobilized
and solidified to form bitumen envelopes around
the detrital grains of monazite because of
emitted alpha and beta particles (Rasmussen
and Glover, 1990). Continued radiation resulted
in greater crosslinking and branching, thereby
producing complex insoluble polymers (bitumen)
U, Th sites in the nature
D. : Dissolved state in geologic fluids
U in see water : 3.3ppb
4 billions U tons dissolved !
Rivers, lakes
0.1-0.4 ppb