Download Unraveling the alteration history of the basement rocks along the P2

Unraveling the alteration history of
the basement rocks along the P2
Fault Zone and in the McArthur
River uranium deposit
E. Adlakha1; K. Hattori1, G. Zaluski2, T. Kotzer2 & E. Potter3
1Department
of Earth Sciences, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada
2Cameco Corporation, Exploration Office, Saskatoon, SK. Canada, S7M 1J3
3Geological Survey of Canada, Booth Street Complex, Ottawa, Ontario
SK Open House 2013
Introduction
• McArthur River uranium deposit
• Unconformity-hosted
• World’s largest high-grade uranium deposit
• 385.5 Mlbs U3O8 (Total Reserves)1
• Structurally controlled by the P2 reverse fault
• Zone 2 ore body
• Located in the basement
• 500 - 640 m below surface1
• P2 reverse fault (045/45-60SW)
• Constrained to chloritized graphitic metapelite in the basement
• Extensively altered and brecciated, especially in proximity to the ore
zone
• Conduit for fluid flow during mineralization
12012
McArthur River Technical Report
Motivation for study
i.
Establish a sequence of alteration minerals in the basement
rocks at McArthur River and the P2 fault.
ii. To evaluate the degree to which the P2 fault served as a fluid
pathway for uraniferous fluids or reducing fluids to permeate
the basement rocks and precipitate the ore during
mineralization.
iii. Discriminate fertile alteration (e.g. chemically or
crystallographically) and/or geochemical fingerprints to aid
exploration for deep-rooted high-grade unconformity-type
uranium deposits.
iv. Ascertain the role of the basement rocks (ie. a reductant and/or
a structurally viable environment) below the Athabasca
sandstones in the main mineralizing event.
v. Constrain the composition and source of the mineralizing fluid.
Outline
• Study-area & sampling
• Preliminary results
• Describe alteration in the basement:
• Outside the P2
• Along strike of the P2 fault
• In areas of mineralization
economic
mineralization
sub-economic
mineralization
no mineralization
sub-economic
mineralization
Sampling
Sampling
Regional sandstone anomalies
• Earl & Sopuck, 1989, as shown in Jefferson, 2007
Regional basement alteration
Modified from Macdonald, 1985
Least altered rocks
Crd-Gt bearing paragneisses
locally intruded by pegmatite lenses
•
•
•
•
•
Cordierite (altered by sudoite & illite),
Garnet (Fe-Mg chlorite)
Biotite (chloritization by Fe-Mg chlorite),
K-Feldspar (illitized)
Quartz (± dravite, amphibole, sulfide)
• accessory Zircon, Monazite & Apatite
Least altered rocks
Least altered rocks
• Early alteration
• Fe-Mg chlorite
• Altered Gt & Bt
• Illite
• Altered K-feldspar
Ill
Least altered rocks
• Early alteration
• Fe-Mg chlorite
• Altered Gt & Bt
• Illite
• Altered K-feldspar
Early retrograde chlorite
Ill
Green Zone alteration
• Sudoite replaced garnet
• Mixed sudoite & illite matrix
• Plus minor Fe-Mg chlorite
Wall rock alteration: Green Zone
• Sudoite replaced garnet
• Mixed sudoite & illite matrix
• Plus minor Fe-Mg chlorite
Red Zone alteration
• Hematite overprints sudoite
• Hematite, kaolinite & illite
• At least two generations of hematite
Sud
Red Zone alteration
• Hematite overprints sudoite
• Hematite, kaolinite & illite
• At least two generations of hematite
Conglomerate alteration
• Sudoite occurs with hematite in
basal conglomerate
• Event is post sandstone
deposition
Red Zone type alteration in conglomerate
• Sudoite occurs with hematite in
basal conglomerate
• Event is post sandstone
deposition
Wall rock alteration: Bleached Zone
• Illite & kaolinite with relict
hematite
Alteration profile summary
• Formed by multiple fluid events:
• Pre-sandstone deposition
• Ill1 early alteration of
Kfs
• Chl1 (Fe-Mg chlorite)
chloritization of Bt
• Hem1 (preserved in
quartz overgrowths
±kaolinite)
• Post sandstone deposition
• Sudoite
• Hem2
• Ill2 (±kaolinite)
Modified from Macdonald, 1985
Alteration along the P2 fault
• Predominately in chloritized, graphitic metapelite
• Localized hematite alteration along fractures
Alteration along the P2 fault
• Predominately in chloritized, graphitic metapelite
• Localized hematite alteration along fractures
• Alteration profile is preserved near the P2 but not
it’s lateral continuity
• Alteration species and textural relationships at a localized
scale are consistent with wall rock alteration
• Green & Red Zones are intermingled with sporadic
bleaching
Alteration along the P2 fault
• Predominately in chloritized, graphitic metapelite
• Alteration profile is preserved but it’s lateral
continuity is not
• Ie. mixing of Green & Red Zones with sporadic bleaching
• Occurs at depths of up to 200 m below the unconformity
Alteration profile proximate to the P2
fault: mingling of the Red & Green Zones
• Predominately in chloritized, graphitic metapelite
• Alteration profile is preserved but it’s lateral
continuity is not
• Ie. mixing of Green & Red Zones with sporadic bleaching
• Occurs at depths of up to 200 m below the unconformity
Alteration along the P2 fault
• Predominately in chloritized, graphitic metapelite
• Localized hematite alteration along fractures
• Alteration profile is preserved near the P2 but not
it’s lateral continuity
• Alteration species and textural relationships at a localized
scale are consistent with wall rock alteration
• Green & Red Zones are mixed with sporadic bleaching
• Occurs at depths of up to 200 m below the unconformity
(north-east extension of P2)
1 cm
Alteration along the P2 fault
• Predominately in chloritized, graphitic metapelite
• Alteration profile is preserved but it’s lateral
continuity
is not
1 cm
• Ie. mixing of Green & Red Zones with sporadic bleaching
• Occurs at depths of up to 200 m below the unconformity
Alteration along the P2 fault
• Predominately in chloritized, graphitic metapelite
• Alteration profile is preserved but it’s lateral continuity
is not
• Ie. mixing of Green & Red Zones with sporadic bleaching
• Occurs at depths of up to 200 m below the unconformity
• Magnesiofoitite
• Observed only along the P2 fault in the basement
• Abundant proximal to mineralization
• Zone 2 in the basement or “perched” mineralization in sandstone
• Late in alteration paragenesis
• Cross-cuts and/or replaces Bleached, Red & Green Zone-type
alteration
• Alters metamorphic tourmaline (Dravite)
Alteration along the P2 fault
Mgf
Mgf
Trace elements in tourmaline
APS
Trace elements in tourmaline
APS
Trace elements in tourmaline
• Uranium detected in
magnesiofoitite
• Low LREE in magnesiofoitite
Contemporaneous with Al-PSO4 (APS) minerals??
Alteration along the P2 fault:
• Proximal to mineralization
Alteration along the P2 fault
• Proximal to mineralization
• APS minerals
• Hosted in Mgf
• Sr-Ce-Nd
Mgf
Qtz
APS
Alteration along the P2 fault
• Proximal to mineralization
• APS minerals
• In sudoite
• Ce-La-Nd rich
1 µm
APS
Alteration along the P2 fault:
• Mineralization
Alteration along the P2 fault:
U
• Mineralization
• Arsenian pyrite (1-2.5 wt% As)
occurs with uraninite
• Inclusions of Mg-rich chlorite in
As-pyrite
• Pyrite and ore hosted in Fe-rich
chlorite
As-py
Fe-chl
Mg-chl
As-py
As-py
Alteration along the P2 fault:
U
• Mineralization
• Arsenian pyrite (1-2.5 wt% As)
occurs with uraninite
• Inclusions of Mg-rich chlorite in
As-pyrite
• Pyrite and ore hosted in Fe-rich
chlorite
As-py
Al (VI)
Fe-chl
Mg-chl
As-py
As-py
Summary
• Alteration profile
• Red Zone formed from multiple fluid events
• Paleo-weathering
• Diagenesis
• Alteration along the P2 fault
• Alteration proximal &/or occurring with mineralization
• Magnesiofoitite & sudoite occur with APS minerals
• As-pyrite contemporaneous with uranium ore (Zone B)
• Contains inclusions of clinochlore
• Uranium ore in sandstone (ZONE B) hosted by chamosite
Acknowledgements
• Glenn Poirier of the Museum of Nature for his help during SEM
& EMPA analysis;
• Cameco Geologists: Aaron Brown (Project Geologist), Doug
Adams, Remi Labelle, and Brian McGill (Chief Mine Geologist)
for all of their assistance during field work at McArthur River.
• We acknowledge the RAP bursary to EEA and a grant to KH from
NRCan through TGI-4 program.