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TitleFluid evolution recorded by alteration minerals along the P2 reverse fault and associated with the McArthur River U-deposit
AuthorAdlakha, E E; Hattori, K; Potter, E G
SourceGoldschmidt 2013 conference abstracts; Mineralogical Magazine vol. 77, no. 5, 2013 p. 558, (Open Access)
Alt SeriesEarth Sciences Sector, Contribution Series 20130167
PublisherMineralogical Society
MeetingGoldschmidt 2013 conference; Florence; IT; August 25-30, 2013
Mediapaper; on-line; digital
File formatpdf; html
AreaMcArthur River
Lat/Long WENS-105.0000 -104.5000 58.0000 57.7500
Subjectseconomic geology; structural geology; mineralization; uranium; uranium deposits; mineral deposits; alteration; structural features; faults; basement geology; Athabasca Basin; McArthur River Deposit; McArthur River Zone
ProgramTargeted Geoscience Initiative (TGI-4), Uranium Ore Systems
AbstractThe basement rocks along the P2 fault are extensively altered, particularly where they host the McArthur River Zone 2 uranium ore body. Two generations of tourmaline occur along the P2: i) early, euhedral-subhedral, coarse-grain (>0.5 mm), 1-2 cm wide veins and isolated grains of dravite (Mgtourmaline), and ii) later fine-grain (<0.2 mm), radial magnesiofoitite (alkali-deficient dravite) forms veinlets (< 2
mm), overgrowths on earlier dravite, and grains disseminated within fine-grain illite. Fe-clinochlore, coarse-grain illite, rutile and hematite are ubiquitous along the P2 and occur as pervasive replacement minerals or veins, and post-date dravite crystallization. To ensure minerals were free of inclusions, individual grains were first inspected with BSE-SEM at highest magnification and elemental peaks were then carefully monitored during trace element analysis (LA-ICPMS). Dravite [(square0.4Na0.6)(square0.2Mg1.9Fe0.5Ca0.2Ti0.2)(Al5.9Fe0.1)(Si5.7 Al0.3O18)(BO3)3(OH3.8F0.2)] contains 1.24 (± 0.09, 1&) wt% TiO2, 89 - 280 ppm Zn, 51 - 630 ppm Cr, 190 - 1500 ppm V, and atomic F/Cl ratios range 98 - 11000. Magnesiofoitite [(square0.7K0.1Na0.2)(square0.4Fe0.1Mg2.0Al0.5)Al6(Al0.1Si5.9O18)(BO3)3(F0.02O H3.98)] contains 65 - 260 ppm V, 2.9 - 110 ppm Cr, 0.2 - 3.7 ppm U, and 0.2 - 34 ppm Th, and ranges 3.2 - 80 atomic F/Cl. Dravite and magnesiofoitite contain low Li (< 12 ppm) and high Ni (1 - 28, 13 - 250 ppm, respectively); however, they also show contrasting trace element behaviours: dravite is enriched in LREE relative to HREE ([Ce]N/[Ce]*N) > 1, and has a positive Eu anomaly, whereas, magnesiofoitite is enriched in HREE relative to LREE ([Ce]N/[Ce]*N) < 1, and has a negative Eu anomaly. Chlorite [(Fe1.9Mg2.6Al1.4)(Si2.7 Al1.3O10)(OH)8] contains significant Li (40 - 669 ppm), and Mn (803 - 4083 ppm); illite [(K0.9) (Al1.8Mg0.1Fe0.1)(Si3.2Al 0.8O10)(OH)2] contains significant B (17 - 250 ppm), Li (<4.9 - 144 ppm), Ti (36 - 14500 ppm), Rb (343 - 692 ppm), U (<0.01 - 0.6 ppm), Sn (1.2 - 148 ppm), and Ba (78 - 1670 ppm); and both minerals show atomic F/Cl ratios > 10. High F/Cl, U, Th and B, and a negative Eu anomaly in alteration phases suggests a contribution of pegmatite to the fluid.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. Currently, all of Canada's uranium production comes from the Athabasca Basin. The McArthur River and nearby Millennium deposits within the basin are spatially associated with a regional fault system termed the P2 structure and the local VQ fault. This publication uses changes in mineralogy and mineral chemistry along the fault structures and basement rocks to infer changes in the ore-forming fluid characteristics proximal to mineralization. The preliminary results indicate that the P2 structure was critical in focusing ore-forming fluids and that the fluids extensively interacted with the basement rocks.