Preliminary Investigations Into the Style, Setting and Timing of Uranium Mineralization, Jacques Lake Deposit, Central Mineral Belt, Labrador (original) (raw)
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Ore Geology Reviews, 2020
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Mineralium Deposita, 2011
The Athabasca Basin hosts many world-class unconformity-related uranium deposits. Recently, uranium reserves for the Eagle Point basement-hosted deposit have increased with the discovery of new mineralized zones within secondary structures. A paragenetic study of Eagle Point reveals the presence of three temporally distinct alteration stages: a pre-Athabasca alteration, a main alteration and mineralization comprised of three substages, and a post-main alteration and mineralization stage that culminated in remobilization of uraninite from primary to secondary structures. The pre-Athabasca alteration stage consists of minor amounts of clinochlore, followed by dolomite and calcite alteration in the hanging wall of major fault zones and kaolinitization of plagioclase and Kfeldspar caused by surface weathering. The main alteration and uranium mineralization stage is related to three temporally distinct substages, all of which were produced by isotopically similar fluids. A major early alteration substage characterized by muscovite alteration and by precipitation Ca-Sr-LREE-rich aluminum phosphatesulfate minerals, both from basinal fluids at temperatures around 240°C prior to 1,600 Ma. The mineralization substage involved uraninite and hematite precipitated in primary structures. The late alteration substage consists of dravite, uranophane-beta veins, calcite veins, and sudoite alteration from Mg-Ca-rich chemically modified basinal fluids with temperatures around 180°C. The post-main alteration and mineralization stage is characterized by remobilization of main stage uraninite from primary to secondary structures at a minimum age of ca. 535 Ma. U-Pb resetting events recorded on primary and remobilized uraninites are coincident with fluid flow induced by distal orogenies, remobilizing radiogenic Pb to a distance of at least 225 m above the mineralized zones.
Ore Geology Reviews
Uranium mineralization in the Kiggavik area, on the eastern border of the Thelon basin (Nunavut, Canada), hosts significant uranium resources within the basement and its understanding is critical to comprehending the genesis of unconformity-related deposits' structural controls and therefore exploration of these types of deposits in this prospective district. This article deciphers the complex multiphase fracture network associated with uranium mineralization of the most recently discovered, basement-hosted prospect in the Kiggavik area, named Contact. The Contact prospect is located along the Andrew Lake Fault (ALF), a major NE-SW fault corridor in the area. This study combines field work, drillcore logging, sampling, and macro-to micro-petro-structural analyses. Key results from this study highlight that the NEtrending ALF, along with the ENE-trending Thelon (TF) and Judge Sissons (JSF) faults, formed early during intracratonic rifting and deposition of the Baker Lake and Wharton groups (ca. 1850-1750 Ma) in response to the Thelon and Trans-Hudsonian orogeny. The ALF was affected by a strong silicification-brecciation event that likely developed at ca. 1750 Ma, and partitioned later deformation and fluid circulation. In the Contact prospect, the ALF was reactivated multiple times and mineralized in three stages with distinctive secondary fracture patterns, alteration, and mineralization types. Ten fracture stages have been identified at the Contact prospect, f1 to f10. The first stage of mineralization, coeval with f5, is related to fluids of unconstrained origin that circulated through E-W faults in the area that locally reactivated quartz veins of the brecciation event at the intersection with the ALF. Mineralization at this stage is polymetallic and associated with weak clay alteration. The second stage of uranium mineralization occurred coeval with transtensional reactivation of the NE-SW trending ALF (f6c) and in relation to circulation of oxidizing basinal brines within the fault zone. Mineralization at this stage is monometallic and associated with illite and sudoite alteration. Later reactivation of the inherited fracture network (f8) led to strong illitization and bleaching of the host rock, with local reworking of the ore body. Finally, reactivation of the fracture network during f9 and 10 lead to circulation of meteoric fluids that remobilized mineralization in a third stage of uranium re-concentration along redox fronts, with strong illitization and bleaching of the host rock. Unlike the classic unconformity-related uranium deposits in the Athabasca Basin where clay alteration halos occur around the ore bodies related to mineralizing processes, in the Contact prospect the strongest clay alteration event (f8) postdates both main stages of mineralization. Along with uranium remobilization, the basement-hosted Contact prospect is likely a relict of what was once a larger deposit.
The Paleoproterozoic (Statherian) Thelon Basin is located in the Churchill Province of the Canadian Shield, formed following theTrans-Hudson Orogeny. Basin formation followed an interval of felsic volcanism and weathering of underlying bedrock.The diagenetic evolution of theThelon lasted about one billion years and was punctuated by £uid movement in£uenced by tectonic events. Early quartz cements formed in well-sorted, quartz-rich facies during diagenetic stage 1; £uids in which these overgrowths formed had d 18 O values near 0% (Vienna Standard Mean Ocean Water). Uranium-rich apatite cement (P1) also formed during diagenetic stage 1 indicating that oxygenated, uraniumbearing pore water was present in the basin early in its diagenetic history. Syntaxial quartz cement (Q1) formed in water with d 18 O from À 4 to À 0.8% in diagenetic stage 2. Diagenetic stage 3 occurred when theThelon Formation was at ca. 5 km depth, and was marked by extensive illitization, alteration of detrital grains, and uranium mineralization. Basin-wide, illite crystallized at $200 1C by £uids with d 18 O values of 5^9% and dD values of À 60 to À 31%, consistent with evolved basinal brines. Tectonism caused by the accretion of Nena at ca.1600 Ma may have provided the mechanism for brine movement during deep burial. Diagenetic stage 4 is associated with fracturing and emplacement of ma¢c dikes at ca. 1300 Ma, quartz cement (Q3) in fractures and vugs, further illitization, and recrystallization of uraninite (U2). Q3 cements have £uid inclusions that suggest variable salinities, d 18 O values of1.5^9%, and dD values of À 97 to À 83% for stage 4 brines. K-feldspar and Mg-chlorite formed during diagenetic stage 5 at ca. 1000 Ma in upper stratigraphic sequences, and in the west. These phases precipitated from low-temperature, isotopically distinct £uids.Their distribution indicates that the basin hydrostratigraphy remained partitioned for 4600 Ma.
Applied Geochemistry, 1997
Abatract--The Cigar Lake unconformity-type U deposit is one of the largest and highest grade U deposits in the Proterozoic Athabasca Basin, northern Saskatchewan, Canada. Cigar Lake has recently been the focus of an international, 3-a, collaborative program in which this U deposit was studied as a natural analogue for a spent nuclear fuel repository• The deposit is located near the eastern margin of the Athabasca Basin, 430 m below the surface, at the intersection between Hudsonian-age faults and the unconformity between Athabasca group sandstones and Aphebian metasediments. Three stages of U mineralization have been identified based on cross-cutting relationships and textures observed in thin section and back-scattered electron (BSE) images, O isotope data and chemical compositions. All stages of U mineralization have been variably altered to Ca-rich, U-hydrate minerals or uranyl oxide hydrate minerals and coft:inite.
The Fraser Lakes uranium and thorium showings are located immediately southeast of the Athabasca Basin, Saskatchewan. The mineralized granitic pegmatites/leucogranites occur within the contact zone between Wollaston Group metasediments and underlying Archean orthogneisses, and are interpreted to outcrop ~200m below the eroded, uplifted paleo-unconformity with overlying Athabasca Group sandstones. They are composed mainly of quartz, feldspars, and biotite, with subordinate amounts of apatite, monazite, allanite, U-rich zircon, uraninite-uranothorite-thorite, and ilmenite. Some uraninite grains are zoned. Uraninite alteration is greatest along grain boundaries and fractures with significant U loss and Pb gain/loss. U-Th-Pb chemical age dating of the uraninite grains yielded a crystallization age of 1770 ±90 Ma (i.e. the pegmatite age) and some younger age clusters. These younger ages correlate to U-mineralization events documented for unconformity-type uranium deposits in the Athabasc...
Canadian Mineralogist, 2016
The P2 fault, a 13 km-long steeply dipping reverse fault, is the main structural control of the McArthur River uranium deposit in the eastern Athabasca Basin, northern Saskatchewan, Canada. Three types of tourmaline were observed in the metasedimentary basement rocks along the P2 fault: early oxy-schörl [(Na 0.47 A 0.37 Ca 0.16)(Fe 2þ 1.30 Al 0.91 Mg 0.72 Ti 0.07) Al 6 (Si 5.79 Al 0.21 O 18)(BO 3) 3 OH 3 (O 0.63 OH 0.29 F 0.08), where A ¼ vacancy] of metamorphic-anatectic origin, hydrothermal oxydravite [(Na 0.57 Ca 0.23 A 0.18 K 0.02)(Mg 1.93 Fe 2þ 0.62 Al 0.29 Ti 0.15)Al 6 (Si 5.93 Al 0.07 O 18)(BO 3) 3 OH 3 (O 0.57 OH 0.23 F 0.20)], and magnesiofoitite [(A 0.77 Na 0.20 Ca 0.02 K 0.01)(Mg 1.99 Al 0.92 Fe 3þ 0.07)Al 6 (Si 6 O 18)(BO 3) 3 (OH 3)(OH 0.71 O 0.25 F 0.04)]. Oxy-schörl formed in granitic pegmatites, a partial melt product of the metasediments during peak metamorphism. Oxy-dravite formed from hydrothermal fluids after the peak metamorphism but before deposition of the Athabasca sandstones, whereas magnesio-foitite is a product of later, low-temperature hydrothermal activity. Both oxy-schörl and oxy-dravite are coarse-grained (from 500 lm up to 1 cm), whereas magnesio-foitite occurs as radial aggregates of fine, prismatic crystals (,15 lm in width). Magnesiofoitite crystallized together with sudoite, illite, and ''APS'' minerals (alunite supergroup LREE-rich aluminum phosphate-sulfate minerals) along the entire studied length (~7 km) of the P2 fault and is abundant in proximity to the Zone 2 ore body of the McArthur River deposit. In the ore zone, the assemblage occurs with uraninite and is partially overprinted by late, remobilized uraninite and sudoite. Therefore, magnesio-foitite is likely contemporaneous with the main stage of uranium mineralization. It is characterized by a high vacancy at its X-site (0.70-0.85 apfu) and high Al at its Y-site (0.70-1.12 apfu), suggesting that magnesio-foitite likely replaced pre-existing high-Al phases, such as kaolin and sudoite. The occurrence of magnesio-foitite along the entire P2 fault, in both areas of mineralization and apparently barren areas, suggests chemically similar fluids travelled along the entire P2 fault, but only produced ore in localized areas.