Paleomagnetic Directions as Indicators of Fluid Movement in the
Athabasca Basin 1
J.C. Dobrohoczki 2, T.K. Kyser 2, and J. Baker 3
Dobrohoczki, J.C., Kyser, T .K., and Baker J. (1993): Paleomagnetic directions as indicators of fluid movement in the Athabasca
Basin; in Summary of Investigations 1993, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 93-4.
The Athabasca Basin has been extensively explored for
uranium following the discovery of high-grade unconformity-type uranium deposits in the late 1960s. A wide
range of techniques has been applied in the search for
new deposits and in developing a model for deposit formation. Of great importance to any model is documentation of the fluid history of the basin. Minerals deposited
coevally from a mineralizing fluid may provide a more
widespread indication of uranium deposit formation than
the metal itself. One such mineral is hematite, which is
pervasive throughout the sandstones of the Athabasca
Basin as well as the underlying regolithic basement (Hoeve and Sibbald, 1978). Hematite has been deposited
by various fluid events including diagenesis, uranium
mineralization, and later events (Kotzer et al. , 1992).
Hematite can record the paleomagnetic direction due to
its high coercivity which allows it to acquire the declination (horizontal component) and inclination (vertical component) of the paleomagnetic field at the time of crystallization (Tarling, 1971; Irving, 1964). This property
serves to characterize the hematite formed in a particular fluid event.
Athabasca Group unconformably overlies Archean and
Early Proterozoic gneisses and metasedimentary rocks
within which there is a well developed paleoregolith several metres thick (Hoeve and Sibbald, 1978).
2. Previous Work
The first investigation of paleomagnetism in the
Athabasca Basin was by Fahrig et al. (1978) who examined numerous samples of essentially vertical, unoriented (no declination) drill core samples from throughout the basin. Both reverse and normal inclinations
were found distributed throughout numerous drill holes.
Fahrig et al. (1978) indicated the possibility of using paleomagnetism to correlate lithologies, assuming the polarity of reversals occurred during deposition of the formation and had not been altered since. Later investigations showed that the hematite carrying the magnetization had been extensively remobilized by later post-depositional fluid events (Ramaekers 1979b, 1980b; Lar·
son and Walker, 1975).
1. Regional Geology
Additional paleomagnetic studies did not occur until extensive work had been done on determining the fluid
history of the Athabasca Basin through petrology, fluid
inclusions, and stable and radiogenic isotope analyses
(Hoeve and Quirt, 1984; Wilson and Kyser, 1987;
Kotzer and Kyser, 1990a and b, 1991 , 1992). Only after, was it possible to relate fluid events, hematite paragenesis, and paleomagnetism (Kotzer et al., 1992)
(Figure 1).
The Athabasca Basin, located in the Churchill Province
of northern Saskatchewan, is the youngest of a series
of intracratonic basins that formed after the Huclsonian
Orogeny (Aamaekers, 1981). In the study area, the
Helikian Athabasca Group comprises the Manitou Falls,
Wolverine Point, and Locker lake formations. The basal Manitou Falls Formation is an eastward thickening
wedge of fluvial and marine mature quartz sandstones
and alluvial fan conglomerates (Aamaekers, 1979a;
1980a). Conformably overlying the Manitou Falls Formation are the sandstones, siltstones, and mudstones of
the Wolverine Point Formation (Ramaekers, 1981 ). The
Locker Lake Formation overlies the Wolverine Point Formation and consists of pebbly sandstones interbedded
with a few thin siltstones (Ramaekers, 1981). The
Kotzer et al. (1992) determined that, Early Proterozoic
(1600 to 1700 Ma) magnetization (A-magnetization) has
a normal polarity and is associated with local fluid migration during early diagenesis. Middle Proterozoic (1450
to 1600 Ma) magnetization (B-magnetization) has a reverse polarity, and is associated with regional fluid migration during peak burial diagenesis, and is coeval
with formation of unconformity-type uranium mineralization that resulted from the mixing of saline, metal-bearing oxidizing basin fluids with reducing basement fluids.
Late Precambrian (- 900 Ma) magnetization (C-magneti·
zation) has a high-angle normal polarity and is associated with a fluid pulse probably initiated by early uplifting and faulting of the basin. Extensive remobilization
and deposition of uranium in some areas, such as at
This report presents some of the preliminary paleomagnetic data obtained from unoriented drill core (no declination) from various sites in the eastern half of the
Athabasca Basin and a general interpretation and discussion of the results.
( 1) Funded by a joint NSERC University-Industry (Cameco and Uranerz) CAD grant.
(2) Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, S7N OWO.
(3) Pacific Geoscience Centre, Sidney, British Columbia, V8L 482.
Saskatchewan Geological Survey
161
Petrology
Stqr. Hydrothermal A ltrration J
quart,ovcrgrowth
QI
ht m.(A mog.)
diag. kaol.+illitc
insst. +•lln.halo
Ill
~.:1!7~~1~halo
h•.i.(IJmag.)
11
.1<
-r
1
Cl
112
~ : f ~ !t drav
Q2,Tl
111
copper
t Ni·As·S
hem.((:
mog.)
_1s113
1
I
,·
1
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,·····
/
j
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-
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:1 I
-+-
I
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Late meteor ic t "·ents
J~···
j
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I
1
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1
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)
J
1
· I'
15'170
· iI-t:W
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/
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,
I .. •••• .... . I I
I I I I
I
/
I
lluid
(reducing)
mid-latitude
b•11in bri~
(oxidizing)
3. New Work
ha,\.-, ncnt
I
I II II II
I
Hematite is altered to goethite
(G1), which looses its magnetic
susceptibility giving an incoherent
D-magnetization. Uplift is likely to
have occurred periodically between - 800 Ma and the present.
Fluid
pore fluids
(IS-20wt"/o
NaCl)
Ii
240
I
(J0-3_1 Wt%
NaCl)
a) Sampling and Analysis
The 130 samples used in this
study are from vertically drilled, un,.
,
I
. _J. •••·•· .·
2> high- latiludo oriented (no declination) drill core
~
1
from: McArthur River P2 North·
50
KJ
j
Sue Zones A, B, C, D, and E; Tele·
goe!hito alln. or hem G 1
,11
i
/
/
D-incohcrent ma,:.
I
phone
Lake (located a few km
1
southwest of the Sue Zone); and
1800
1400
woo
AG~: (Ma)
WO
200
Rumple Lake (located in the mid·
die of the Athabasca Basin). The
Figure 1 - Proposed mineral paragenesis-fluid history in the Athabasca Basin, developed from petrographi~, fluid inclusion, and stable and radiogenic isotope systematics.
Rumple Lake drill core was used
Pa:agenes1s of hematite has been established using field and petrographic relationas a control hole to study the
ships and Pf:!leo~gnet~sm (mo:1ified from Kotzer et al., 1992). Abbreviations are:
deeper part of the basin because it
altn.=alterafton; d1ag.=d1agenet1c; mag.=magnetization; drav.=dravite· h em. =hematite·
was located far from any known
'
'
kaol.=kaolinite; sst.=sandstone; and qtz.=quartz.
mineralization and major faulting.
As the drill core samples had to be
t~e Eagle Point deposit, is associated with C-magnetiza·
re-cored for paleomagnetic analysis, samples were set1on. ln~oh~rent magnetization of Phanerozoic age (D·
lected that had no fractures. All the samples were from
magnetization) was caused by the incursion of low temthe Manitou Falls Formation or the underlying regolith
perature meteoric waters which altered hematite to
and basement, except for two samples from Rumple
goethite.
Lake which are from the upper Wolverine Point Formation. Two oriented surface hand specimens were also
In the initial stages of diagenesis, heavy-mineral suites
collected from the Maw zone.
within the Manitou Falls Formation were strongly altered
to hematite (H1), and early quartz (01) overgrowths
Paleomagnetic analysis of the drill core was done at the
were formed (Kotzer et al., 1992). The H1 -hematite carPacific Geoscience Centre (PGC) in Sidney, B.C.
ries the A-magnetization. Coeval apatite gives a U-Pb
Where possible, drill core samples were re-cored to ob·
age of 1650 to 1700 Ma (Cummings et al., 1987).
tai~ two one-inch diameter by one-inch high paleomag~ellc
cores. Analyses of the natural remnant magnetizaPrograde peak burial diagenesis at -200°C, involving
tion and thermal demagnetization were made on the
the mixing of saline, oxidizing basin fluids with reducing
PGC's automated Schoenstadt SSM1 fluxgate spinner
basement fluids resulted in the remobilization of hemamagnetometer.
tite (H2) and formation of diagenetic clays (K1 , 11 , C1 ).
euhedral quartz (02), dravite (T1), and polymetallic urab) Results
nium mineralization (S1 . U1) (Kotzer and Kyser, 1992).
H2-hematite from this fluid mixing event carries the B·
Of the 130 drill core samples that were analyzed, 58
magnetization. lllite intergrown with H2-hematite has a
had thermal demagnetizations that were reasonably
Rb-Sr age of 14n ±57 Ma (Kotzer and Kyser, 1990b).
strong and coherent enough to be classified as A, B or
C. The remainder of the samples gave incoherent direcA late, high-temperature fluid pulse, probably initiated
tions and are tentatively classified as D-incoherent magby early uplifting and fracturing of the basin, formed the
netization.
The two oriented surface hand specimens
~oung~st hematite (H3) which carries the C-magnetizatton. llhte, formed together with H3-hematite, gives a Rb- from the Maw zone gave D-incoherent magnetizations.
The majority of the D-incoherent samples are from the
Sr and K-Ar age of about 900 Ma (Kotzer and Kyser,
upper units of the drill holes; in the Maw zone hand
1990b).
samples, hematite has been partially or entirely altered
to low temperature goethite.
Uplift and fracturing of the basin resulted in incursion of
low temperature oxidizing meteoric fluids, formation of
For a few samples, the magnetization changes over a
r~trograde mineral assemblages, and destruction of pre·
core length of only a few centimeters from a reverse 8v1ously formed unconformity-type uranium deposits.
to ~ n~rmal A- or C-magnetization or from A- to C-magT~is proc_ess is ~anifested by pervasive kaolinite (K2)
net1zat1on. These changes occur even in drill core samwith drav1te (T2) in fractures, followed by remobilization
ples of the same lithology and hematite staining and inof uranium (U2) and pyrite ($2), which were redepodicate that the fluid movement is permeability controlled.
sited in late fault fractures, and late kaolinite (K3) forma·
tion in reactivated fractures (Kotzer and Kyser, 1991 ).
dravite in fractures
perva~ive 1-:aol.
pyrite in fraclW'cs
uranium in fractures
kaol. in fractures
t(T2
2
s2
112
,·
I
I I I -. + ,,.
1
162
,l.... ~.. .. ..
::~c
Summary of Investigations 1993
The inclinations of the reasonably stable magnetizations
(at 500°C thermal demagnetization) were combined
with inclinations of the stable magnetizations of Fahrig
et al. (1978) (at 560°C) to give a histogram of paleomagnetic inclinations (Figure 2). The inclinations normally can be separated into the A-, 8 -, and C-magnetization events.
Athabasca Basin
Ont
Paleomagnetism
sn:zo.~t:
l niAII. ~HII
•
U
"1....$
The Maw zone drill hole ZQ-11 (Figure 3) contains D-incoherent magnetization throughout the core, except for
some A and C directions and very strong 8-magnetization within about 1O m of the unconformity. Core samples from Sue Zone A, B, C, D, and E yielded predominantly 0-incoherent magnetization, except samples
from Sue Zone A (A 114 at 52.0 m) and B (8118 at
30.2 m) that are near uranium mineralization and which
give 8-magnetizations. The few samples collected from
Telephone Lake drill hole SP-66 are of A-magnetization
(52.7 m and 69.0 m) and C-magnetization (64.0 m).
The Rumple Lake drill core (74-J) has a mixture of A-,
8-, and C-magnetizations throughout the drill core, with
8-magnetization occurring in the regolithic basement.
Petrographic relations indicate that the two D-incoherent magnetizations may occur in sandstones leached of
hematite during the early diagenesis of the basin before
quartz overgrowth (Figure 1).
McArthur River P2 North samples (Figure 4) are from
the drill holes along a northeast-trending reverse fault
that has uranium mineralization at or near the unconformity. At drill hole MAC204, which intersects the mineralized zone at about 500 m depth, the magnetization
above the unconformity is predominantly D-incoherent
magnetization with a few B-magnetizations. Well below
the mineralization and the unconformity, in the fault fractured basement, are numerous B· and C-magnetizations. MAC214 is predominantly 0 -incoherent magnetization with some 8-magnetizations throughout the drill
hole along with some A-magnetizations near the base.
MAC206 is a mixture of A-, 8-, and D-incoherent magnetizations throughout the drill hole, with some C-magnetizations. MAC138 is predominantly D-incoherent and
1•
i
I
I
12
I
10
~
8
!
18
16
f
l
Amagnet1srn
I
..I
s
Bmagrelrsm
I
2
I
.1.•.1
IOOm · .· ··..
II
I}
.:··:
M A\\' ZO S t:
'I.Q ll
Om
A.'("
IO Okm
--
!OOm
,\ · m.agn.t.:n 1..i1tfM,
11· m•ncti/~lic,n
c·-magnct.o,.. 111on
l)· incN'l.cn:nlmitA~ti,~lon
Figure 3 - Paleomagnetism data from drill holes in the
Athabasca Basin. Magnetizations separated by a slash are
samples where the two paleomagnetic cores have two distinct
magnetic inclinations.
C-magnetizations, with 8-magnetizations occurring near
the unconformity.
4. Discussion
A-, 8-, C-, and incoherent D-magnetizations are generally present throughout the entire basin. These magnetizations are intermixed throughout the drill core with incoherent D-magnetizations typically present in the upper
sections of the drill core as a result of pervasive alteratfon of hematite to goethite by late,
C maynet1srn
low-temperature meteoric waters.
In very late fault fracture zones, Dincoherent magnetization is the predominant magnetization throughout
drill core (Figure 5).
i....1. .1.• l
Fluid flow was permeability controlled as indicated by the change in
magnetization of samples within a
few centimeters of each other. This
is the result of partial overprinting
by later fluids constrained by the
permeability of the rock altered by
previous fluid and diagenetic
events or fracture episodes.
The 8-magnetization appears to be
present
throughout the basin near
":
"'
th e unconformity. This indicates
Paleomagnetic inc!inations
that this was a basin wide event.
Figure 2 - Histogram of paleomagnetic inclinations a t soo•c thermal demagnetization, inThe 8-magnetization also occurs
cluding the data from Fahrig et al. (1978) at 560°C thermal demagnetization.
0
'
0
«/
0
"
0
0
"I
Saskatchewan Geological Survey
..
0
ii?
R
0
0
o,
163
MAC104
MA<.'2@6
McArthur River
P2 North
Um
""'
•0
•
e
.....
..
',. ,
/ / ~~
_ _ _ _ (1979): The paleolatitude and paleomagnetic age
of the Athabasca Formation, northern Saskatchewan·reply;
Discussions and Communications in Current Research,
Part C, Gaol. Surv. Can., Pap. 79-1C, p119-120.
/
~
-~
4r
•
•••
••••
M.\Cl14
Cini
M,\('138
· ... -'"eadLakc
Pt«>}C:~ ~
--J(.~- -.,; ,~_
~
.,.(a-.._-. •
Q
_,, - c.....-on
J.>._._..,.lioo
/~
non-m -
Figure 4 • Paleomagnetism data from drill holes at McArthur
River P2 North. Magnetizations separated by a slash are samples where the two paleomagnetic cores have two distinct magnetic inclinations.
in the upper sections of the Rumple Lake drill core, indicating that fluids associated with B-magnetization occurred both near the unconformity and in horizons in
the Athabasca Group sediments well above the unconformity. Since the fluids associated with 8-magnetization seem to be a basin wide event, major fluid movement and mixing occurred during tectonic activity that reactivated basin fault fractures. Uranium mineralization,
generally located at the intersection of major basement
fault zones with the basinal sediments, occurred because these fault zones allowed horizontally controlled
saline, metal-bearing oxidizing fluids to mix with reducing basement fluids. Fracturing in the fault zone controlled the permeability and thereby the flow rates and mixing ratios between oxidizing and reducing fluids, thus
determining whether mineralization occurred at, above
or below the unconformity.
5. Acknowledgments
J.C.D. thanks T.K. Kyser and M. Fayek for collecting
the first batch of samples from the Athabasca Basin
and the staff at the Pacific Geoscience Centre; E. Irving
and J. Wyne for helpful advice. Also thanks are extended to Cameco and Uranerz for their assistance and
funding through a joint NSERC University-Industry grant.
164
Cummings, G., Krstic D., and Wilson J. (1987): Age of the
Athabasca Group, northern Alberta; Geol. Assoc. Can.,
Prog. Abstr. 12, pA35.
Fahrig W.F., Christe K.W., and Freda G. (1978) : The paleolatitude and paleomagnetic age of the Athabasca Formation,
northern Saskatchewan; in Current Research, Part C,
Geol. Surv. Can., Pap. 78-1C, p1-6.
McArtbor R.i~cr
Proj ect / '
•
6. References
Hoeve J . and Quirt D. (1984): Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution
of the Middle-Proterozoic, Athabasca Basin, northern Saskatchewan, Canada; Sask. Research Council, Tech. Rep .
187, 187p.
Hoeve J. and Sibbald T.1.1. (1978): Uranium metallogenesis
and its significance to exploration in the Athabasca Basin;
in G. R. Parslow (ed.), Uranium Exploration Techniques,
Sask. Geol. Soc. , Spec. Publ. 4, p161-188.
Irving E. (1964): Paleomagnetism and its Application to Geological and Geophysical Problems; John Wiley and Sons
Inc.
Kotzer T. and Kyser T.K. (1990a): The use of stable and radiogenic isotopes in the identification of fluids and processes
associated with the unconformity-type deposits; in Beck ,
L.S. and Harper, C.T. (eds.), Modern Exploration Techniques, Sask. Geol. Soc., Spec. Publ. 10, p115-131 .
_ __ _ (1990b): Fluid history of the Athabasca Basin and
its relation to uranium deposits; in Summary of Investigations 1990, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 90-4, p153-57.
_ _ _ _ (1991): Retrograde alteration of clay minerals in
uranium deposits; Chem. Geo!. (Isotope Geosci. Sec.),
v86, p307-321.
_ _ _ _ (1992}: Isotopic, mineralogical, and chemical evidence for multiple episodes of fluid movement during prograde and retrog rade diagenesis in a Proterozoic basin; in
Kharaka, Y.K. and Maest, A.S. (eds.), Water-Rock Interaction, p1177-1181 .
Kotzer T .. Kyser T.K., and Irving E. (1992): Paleomagnetism
and evolution of fluids in the Proterozoic Athabasca Basin,
northern Saskatchewan, Canada; Can. J . Earth Sci. , v29,
p1474-1491 .
Larson E.E. and Walker T.R. (1975): Development of chemical
remnant magnetization during ear1y stages of red-bed formation in Late Cenozoic Sediment, Baja California; Geol.
Soc. Amer. Bull., v86, p639-650.
Ramaekers, P. (1979a): Stratigraphy of the Athabasca Basin;
In Summary of Investigations 1979, Saskatchewan Geological Survey, Sask. Miner. Resour., Misc. Rep. 79-10, p154160.
_ __ _ (1979b): The paleolatitude and paleomagnetic
age of the Athabasca Formation, northern SaskatchewanOiscussion; Discussions and Communications in Current
Research, Part C, Geo!. Surv. Can., Pap. 79-1C, p117-119.
Summary of Investigations 1993
w
MAC206
MAC138
MAC204
MAC214
MAWrone
Rurnple Lake
E
SUE zone
U/C
...
.
.
- -· -- ....
·---.
--
--.
--- --.
.......... -·· .
,
··
... ..._.,...--.
··-- . ..,,,..--··--· ..,,,..--- .
I ltt St i I t
-----
. _.,...,. . .,,,. ... -.__
__....
_.,,..
-- --.
.-~-.
.
.,..
·-
·-
·-
--
.,,,....
- . ...
-... .,,,,-
_,,,..
A-magnetism
Minerillizafion
B-magnetism
Fault/shear zone
•c-magnetiSffi
.. ----.... _.,,.._,.. _,,,..
r:;; :1
Athabasca Formation
(_.:::.';'~.,:::j
BASEMENT
-
Profile not to scale
Figure 5 - Profile of the eastern part of the Athabasca Basin showing the general movement and distribution of fluids over time as
indicated by paleomagnetic evidence to date.
_ _ _ _ (1980a): Stratigraphy and tectonic history of the
Athabasca Group (Helikian) of northern Saskatchewan; in
Summary of Investigations 1980, Saskatchewan Geological Survey, Sask. Miner. Resour., Misc. Rep. 80-4, p99-
_ _ _ _ (1981 ): Hudsonian and Helikian basins of the
Athabasca region, northern Saskatchewan; in Campbell,
F.H.A. (ed.), Proterozoic Basins of Canada, Gaol. Surv.
Can., Pap. 81-10, p219·233.
106.
_ _ _ _ (1980b): The paleolatitude and paleomagnetic
age of the Athabasca Formation, northern SaskatchewanFurther discussion; Discussions and Communications in
Current Research, Part B, Geol. Surv. Can., Pap. 80-18,
p297-299.
Saskatchewan Geological Survey
Tarling D.H. (1971): Principles and Applications of Paleomagnetism; Chapman and Hall Publishing.
Wilson M.A. and Kyser T.K. (1987): Stable Isotope geochemistry of alteration associated with the Key Lake uranium deposit, Canada; Econ. Geo!. v82, p1540·1557.
165