Reducing Mechanisms Potentially Involved in Formation of Athabasca Basin Uranium Deposits: Relevance to Exploration

Transcription

1 Reducing Mechanisms Potentially Involved in Formation of Athabasca Basin Uranium Deposits: Relevance to Exploration Gary Yeo 1 & Eric Potter 2 1 Denison Mines Corp. 2 Geological Survey of Canada 1

2 Original Title this would take a lot more than 20 minutes to cover! Reducing Mechanisms Potentially Involved in Formation of Basin- Related Uranium Deposits: Relevance to Athabasca Basin Gary Yeo 1 & Eric Potter 2 1 Denison Mines Corp. 2 Geological Survey of Canada 2

3 We re just a couple of geologists Us geochemists? Narf! Note that this is not a geochemist s review of the Athabasca reductant problem 3

4 The Athabasca Basin Deposit Model Three components in the conventional model for Athabasca deposits: 1. At sub-athabasca unconformity, 2. Associated with reverse faults 3. Associated with graphitic pelites Question (Mike Gunning): Are graphitic pelites essential to this model? If Yes: focus exploration along the Key Lake Rabbit Lake corridor associated with basal Wollaston graphitic pelites; ; drill conductors If No: much more of Athabasca basin is prospective; deposits not necessarily associated with graphitic pelite conductors 4

5 From Cuney (2009) 5

6 Hoeve & Sibbald (1978) Diagenetic- Hydrothermal Model oxidizing diagenetic solutions reacted with graphitic rocks to yield reducing solutions containing carbon dioxide and methane. Mineralization resulted from interaction of flows of methane-bearing reducing solutions and of oxidizing diagenetic solutions carrying ore constituents. 6

7 Importance of Graphitic Pelites Structural Basement graphitic pelites localized Trans-Hudson ductile deformation as well as syn- and post- Athabasca brittle faulting Potential reducing mechanism Graphite, or CH 4 /CO 2 generated from graphite, considered the reductant for U 6+ in oxidizing basinal fluids (Hoeve( & Sibbald,, 1978; Cuney,, 2009; IAEA, 2009; Belyck,, 2010) Many recent reviews, however, are (deliberately?) not specific about the reducing mechanism (e.g., Jefferson et al., 2007; Kyser & Cuney,, 2008; Skirrow et al., 2009; Burrows, 2010) 7

8 Why the western Wollaston graphitic pelites? What is special about the Key L Eagle Point corridor? 8

9 Why the western Wollaston graphitic pelites? Wollaston Structural Cross-section section (Tran, 2001) Structurally, Wollaston Domain is a broad synclinorium; hence basal Wollaston strata are structurally elevated along its western extent 9

10 Why the western Wollaston graphitic pelites? Wollaston Chronostratigraphy Wollaston Supergroup is a classic foreland basin succession: 1. Starved basin facies: black shales, ironstone, carbonates & marls; 2. Flysch (pelites and psammopelites) 3. Molasse (meta-arkose) (Yeo & Delaney, 2007) 10

11 Reducing Mechanisms suggested for Athabasca deposits Carbon-based based reducing mechanisms Intrabasinal fluid hydrocarbons (Alexandre( & Kyser, 2006) Basement graphite or graphite-derived CH 4 or CO 2 (Hoeve & Sibbald,, 1978; Wallis et al., 1985; Alexandre et al., 2005) Inorganic-based reducing mechanisms H 2 S from pyrite (Cheney, 1985; Ruzicka,, 1993) Fe 2+ from chloritization of biotite or illitization of hornblende (Wallis et al., 1985; Alexandre et al., 2005) 11

12 Intrabasinal hydrocarbons (fluid hydrocarbons) Fluid hydrocarbons considered potential reductants in many sandstone-hosted deposits South Texas coastal plain (Adams & Smith, 1981) Ordos & Tarim basins, China Late Cret.-Cenozoic Cenozoic Chu-Sarya & Syr-Darya basins in Kazakhstan (Jaireth( et al., 2008) Proterozoic hydrocarbons (from 1.54 Ga Douglas Fm) common in Athabasca Basin, but post-date 1.59 Ga U1 mineralization (Wilson et al, 2007) Exception: At Dufferin Lake, 1.54 Ga hydrocarbons are intimately associated with 1.54 Ga uranium (Alexandre & Kyser,, 2006) 12

13 Basement-derived hydrocarbons: 1. CH 4 or CO 2 associated with graphitic pelite CH 4 stable in C-CHC CH 4 -H 2 O-CO 2 system >800C (Price, 1997) Survival of pre-metamorphic CH 4 in high-t metamorphism favoured by: Presence of water High fluid pressure Closed system Could sufficient CH 4 survive metamorphism to be a significant reductant? If CH 4 survived metamorphism, could it be released from graphite to act as a reductant? 13

14 Basement-derived hydrocarbons: 2. CH 4 or CO 2 derived from graphitic pelite CH 4 and CO2 potentially also generated by hydrolysis of graphite by basin-derived fluids: 2C + 2H 2 O = CH 4 +CO 2 2H 2 O +CO 2 = CH 4 +2O 2 low δ 13 C values in graphite and pyrobitumen at Athabasca deposits suggest bitumen was formed by radiolysis of graphite; not from CH 4 (Kyser et al., 1989) 14

15 Basement-derived hydrocarbons: 2. CH 4 or CO 2 derived from graphitic pelite At McArthur River, CH 4 (ca. 1 m from ore) and C 2 H 6 & CO 2 (ca. 10 m from ore) were interpreted to be from post-ore ore radiolysis of C (Derome et al., 2003) Kyser et al. (1989) and Derome et al. (2003) concluded graphite and potentially derived hydrocarbons did not have a major role in reducing uranium, but 15

16 Basement-derived hydrocarbons: 3. Direct reduction of U 6+ by graphite Alexandre et al. (2005) suggested that U 6+ was directly reduced by radiolysis of graphite: U H 2 O + 1 2C 1 UO CO H + If this is the case, we should commonly see an intimate association between graphitic pelite and uranium. Do we see this? 16

17 Basement-derived hydrocarbons: 3. Direct reduction of U 6+ by graphite Little or no graphitic pelite at Rabbit Lake (graphitic arkose present), Eagle Point, Raven-Horseshoe, Cluff Lake, Centennial Uranium more strongly associated with other lithologies at Key Lake & Shea Creek This suggests graphite is not a direct reductant for U 6+ 17

18 Basement-derived hydrocarbons: 3. Direct reduction of U 6+ by graphite Key Lake: Deilmann Pit (Harvey, 2007) Ore zone Graphitic zone Ore zone restricted to SE side of graphitic pelite Associated with Key Lake Fault 18

19 Basement-derived hydrocarbons: 3. Direct reduction of U 6+ by graphite Graphitic pelites Key Lake: Gartner Pit (Wheatley et al, 2006) Ore zone mainly SE of graphitic pelites Associated with Key Lake Fault 19

20 Inorganic reductants: H 2 S from pyrite H 2 S from breakdown of pyrite (e.g. pyrite to pyrrhotite) ) is a potential reductant: FeS 2 + H 2 = FeS +H 2 S H 2 S from pyrite suggested as the reductant in: Boomerang Lake prospect, NWT (Beyer et al., 2010) Athabasca deposits (Cheney, 1985) Wollaston graphitic schists are favourable because they are sulphide-rich (pyritic black shale protolith) 20

21 Inorganic reductants: Fe 2+ from pyrite Fe 2+ from oxidation of pyrite is a potential reductant: 1. FeS 2 +7/20 2 +H 2 O = Fe 2+ + SO H + 2. U H 2 O + 2Fe 2+ = UO 2 + Fe 2 O H + On reduction of Fe 2+ to Fe 3+, the latter goes to hematite, but where does the sulphate go? Aluminium phosphate sulphate minerals? δ 34 S values of ore zone sulphides at McClean Lake are comparable to those of basement pyrite, suggesting derivation of ore zone sulphur from basement (Bray et al., 1982) Ore zone sulphides,, however, occur late in paragenetic sequence 21

22 Inorganic reductants: Fe 2+ from silicates Fe 2+ from chloritization of biotite or illitization of hornblende is a potential reductant (Alexandre et al., 2005) : or biotite + H + + H 2 O + Mg 2+ => chlorite + K + + SiO 2 + Fe 2+ hornblende + K + + H + => illite +Na + + Ca 2+ + Fe 2+ Mg 2+ + SiO 2 +H 2 O and then U H 2 O + 2Fe 2+ = UO 2 + Fe 2 O H

23 Inorganic reductants: Fe 2+ from silicates Chloritization of biotite results in significant volume loss (via replacement of K layers by Mg(OH) 2 layers; Kogure & Banfield,, 2000) creating potential space for an ore zone Chlorite, illite and hematite alteration typically closely associated with primary uranium mineralization at Athabasca deposits, both spatially and paragenetically 23

24 Typical Athabasca sandstone alteration (Thomas et al., 2006) 24

25 Typical Athabasca basement alteration (Thomas et al., 2006) 25

26 Alteration at Key Lake Chloritized pelite & pegmatite Ore zone 26

27 Hematite cap above ore & grey chlorite-illite alteration at Roughrider Hathor Exploration news release 21 Oct.,

28 Paragenesis: : Athabasca Basin (Hiatt & Kyser,, 2007) Minerals associated with U1 event: Formation of C1/C2 chlorite (and I1 illite*) is potential Fe 2+ source; H2 hematite (and I1 illite*) is Fe 3+ sink * hornblende => illite + Fe 2+ ; plagioclase + Fe 2+ => illite 28

29 Paragenesis: : Athabasca, Thelon & Kombolgie basins (Jefferson et al., 2007) U1 Mineralization Athabasca U1 mineralization : Formation of C1/C2 chlorite (& illite?) is potential Fe 2+ source; H3/H4 hematite (& illite?) is Fe 3+ sink 29

30 Conclusions Reducing mechanisms involving Fe 2+ are more likely than those involving graphite Close spatial and paragenetic association of chlorite, illite & hematite alteration with ore suggests Fe 2+ from silicates; not pyrite 30

31 Conclusions Biotite-rich rocks (pelites( pelites) ) are the key favourable lithology for localization of unconformity-type type deposits In answer to Mike Gunning s s question: graphitic pelites are not essential to create a chemical trap much more of Athabasca Basin is prospective than just the Key L Rabbit L corridor Graphitic pelites are still important as controls on reactivated faults which acted as fluid conduits, but their presence is not essential 31

32 Thank you maybe someone in the crowd will take our bait and explain the whole mess for us! 32

33 References Alexandre,, P. and Kyser,, K., 2006: Geochemistry of uraniferous bitumen in the southwest Athabasca Basin, Saskatchewan, Canada; Economic Geology; vol. 101, p Alexandre,, P., Kyser,, K., Polito,, P. and Thomas, D., 2005: Alteration mineralogy and stable isotope ope geochemistry of Paleoproterozoic basement- hosted unconformity-type type uranium deposits in the Athabasca Basin, Canada; Economic Geology, G vol. 100, p Belyck,, C., 2010: Uranium Ore Deposits: Geology and Processing Implications; Uranium Proceedings of the 3rd International Conference on Uranium, 40th Annual Hydrometallurgy Meeting, Metallurgical Society, Canadian Institute for Mining and Metallurgy, Saskatoon, Canada; Edited by E.K. Lam, J.W. Rowson and E. Ozberk,, p Beyer, S.R., Kyser,, K., Hiatt, E.E., and Fraser, I., 2010: Geological evolution and d exploration geochemistry of the Boomerang Lake unconformity-type type uranium prospect, Northwest Territories, Canada; SEG Special l Publication 15, p Bray, C.J., Spooner, E.T.C., Golightly,, J.P. and Saracoglu,, N., 1982: Carbon and sulphur isotope geochemistry of unconformity-related related uranium mineralization, McClean Lake deposits, N. Saskatchewan, Canada; Abstracts with Programs,, Geological Society of America, August 1982, Vol. 14, Issue 7, p Burrows, D.R., 2010: Uranium exploration in the past 15 years and d recent advances in uranium metallogenic models; SEG Special Publication 15, p Cheney, E.S., 1985: Similarities between roll-front and Athabasca unconformity-type type uranium deposits and the possible role of sulphides in their origin; in Geology of Uranium Deposits, Edited by T.I.I. Sibbald and W. Petruk,, CIM Special Volume 32, 268p. Cuney,, M., 2009: Quels modeles pour les gisements d uranium au Quebec nordique et au Labrador; Quebec Exploration 2009, Quebec (24 Nov 2009) ppt presentation. Cuney,, M., 2009: The extreme diversity of uranium deposits; Mineralium Deposita,, vol. 44, p Derome,, D., Cathelineau,, M., Lhomme,, T. and Cuney,, M., 2003: Fluid inclusion evidence of the differential migration of H2 and O2 in the McArthur River unconformity-type type uranium deposit (Saskatchewan, Canada). Possible role on postp ost-ore ore modifications of the host rocks; Journal of Geochemical Exploration, vol , 79, p Harvey, 530.Harvey, 2007 Harvey, S.E. and Bethune, K.M., 2007: Context of the Deilmann Orebody,, Key Lake mine, Saskatchewan; in EXTECH IV: Geology and Uranium Exploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta, (ed.) C.W. Jefferson and G. Delaney; Geological Survey of Canada, Bulletin 588, p Hiatt, E.E. and Kyser,, T.K., 2007: Sequence stratigraphy, hydrostratigraphy,, and mineralizing fluid flow in th eproterozoic Manitou Falls formation, eastern Athabasca Basin, Saskatchewan; in EXTECH IV: Geology and Uranium Exploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta, (ed.) C.W. Jefferson and G. Delaney; Geological Survey of Canada, Bulletin 588, p Hoeve,, J. and Sibbald,, T.I.I., 1978: Uranium mineralization and its significance to exploration e in the Athabasca Basin; In Uranium Exploration Techniques, Edited by G.R. Parslow,, Saskatchewan Geological Society Special Publication 4, p IAEA, 2010: Uranium 2009: Resources, Production and Demand, 425p. 33

34 References Jaireth,, S., McKay, A. and Lambert, I., 2008: Sandstone uranium deposits s associated with hydrocarbon-bearing bearing basins: implications for uranium exploration in Australia; AUSIMM 2008 presentation Jefferson, C.W., Thomas, D.J., Gandhi, S.S., Ramaekers,, P., Delaney, G., Brisbin,, D., Cutts,, C., Portella,, P. and Olson, R.A., 2007: Unconformity-associated uranium deposits of the Athabasca Basin, Saskatchewan and Alberta; in EXTECH IV: Geology and Uranium Exploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta, (ed.) C.W. Jefferson and G. Delaney; Geological Survey of Canada, Bulletin 588, p Kogure,, T. and Banfield,, J.F., 2000: New insights into the mechanism for chloritization of biotite using polytype analysis; American Mineralogist, vol. 85, p Kyser,, T.K., Wilson, M.R. and Ruhrmann,, G., 1989: Stable isotope constraints on the role of graphite in the genesis of unconformity-type type uranium deposits; Canadian Journal of Earth Science, vol. 26, p Kyser,, K. and Cuney,, M., 2008: Unconformity-related related uranium deposits; in Recent and Not-so so-recent Developments in Uranium Deposits and Implications for Exploration; MAC Short Course 39, p Price, L.C., 1997: Minimum Thermal Stability Levels and Controlling Parameters of Methane, as determined by C15+ Hydrocarbon Thermal Stabilities, USGS Bulletin 2146-K, p Ruzicka,, V., 1993: Unconformity-type type uranium deposits; in Kirkham, R.V., Sinclair, W.D., Thorpe, R.I. and Duke, J.M., eds., Mineral Deposit Modelling: : Geological Association of Canada, special Paper 40, p Skirrow,, R.G., Jaireth,, S., Huston, D.L., Bastrakov,, E.N., Schofield, A., van der Wielen,, S.E. and Barnicoat,, A.C., 2009: Uranium Mineral Systems: Processes, Exploration Criteria and a New Deposit Framework; Geoscience Australia Record 2009/20, 44p. Thomas, D., Brisbin,, D., Drever,, G., and Zaluski,, G., 2006: Uranium Deposit Types: Within the Context of 2006 Global Exploration Activity; Uranium: Athabasca Deposits and Analogues, 2006 CIM Field Conference, ence, Saskatoon, Sept 2006, powerpoint presentation Tran, H.T., 2001: Tectonic Evolution of the Paleoproterozoic Wollaston Group in the Cree Lake Zone, northern Saskatchewan; PhD P thesis, University of Regina, Regina, Saskatchewan, 458p. Wallis, R.H., Saracoglu,, N., Brummer,, J.J. and Golighltly,, J.P., 1985: The geology of the McClean uranium deposits, northern Saskatchewan; in Geology of Uranium Deposits, CIM-SEG Uranium Symposium, September 1981, edited by T.I. Sibbald and W. Petruk,, CIM Special Volume 32, p Wilson, N.S.F., Stasiuk,, L.D. and Fowler, M.G., 2007: Origin of organic matter in the Proterozoic Athabasca Basin of Saskatchewan and Alberta, and significance to unconformity uranium deposits; EXTECH volume,, p Wheatley, K., Bell, G., Kinar,, D. and Calayan,, N., 2006: Geology of the Key Lake deposits; Uranium: Athabasca Deposits and Analogues, 2006 CIM Field Conference, Saskatoon, Sept 2006, powerpoint presentation Yeo, G.M. and Delaney, G., 2007: The Wollaston Supergroup, stratigraphy and metallogeny of a Paleoproterozoic Wilson cycle in the Trans- Hudson Orogen,, Saskatchewan; in EXTECH IV: Geology and Uranium Exploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta, (ed.) C.W. Jefferson and G. Delaney; Geological G Survey of Canada, Bulletin 588, p