Uranium ore-forming systems of the - Geoscience Australia

Uranium ore-forming systems of the Lake Frome regionTable 8.1: Basin-hosted uranium mineral systems of the Lake Frome region: exploration criteriaMineral syscomponentSources -metalsSources -fluidsSources -ligandsSources –fluids, metals,ligandsPermeabilityand chemicalarchitecturePermeabilityand chemicalarchitecturePermeabilityand chemicalarchitecturePermeabilityand chemicalarchitectureQuestion # Ingredients Importance Mappable/measurable features ScaleQ3Q3Q3Q3,Q4Q3,Q4Leachable U-enriched source, including one ormore of the following: U-rich felsic rocks rimming and/orunderlying the basin. Lithic fragments of felsic rocks (includingvolcanic ash) in the sandstone aquifer. Leachable detrital U-rich minerals (zircon,monazite, allanite, apatite etc) insandstone Felsic volcanics in and/or close proximityto the sandstone aquifer Uranium mineralisation occurrences inhinterland Deeply weathered U-rich source rocksLarge volumes of highly oxidised (initially airsaturated)fluids, e.g. meteoric water, lakewater, requiring sub-aerial conditions andmoist climate (at least seasonally)Leachable U:essential; Uenrichment: highlydesirable; deepweathering: highlydesirableU enrichment indicated by γ-ray spectrometricdata, geochemical analyses of potential sources; Udistribution in source minerals; history of deepweathering and its spatial distributionEssential Oxidised alteration/weathering/diageneticassemblages in source areas and pathways;paleoclimate data; sub-aerial sedimentsPhosphate, bicarbonate, F or Cl ions Desirable Phosphate-, carbonate-, F- or Cl-bearing mineralsin source areas or pathways, altered/leachedLeached U sources (from fresh or weathered Desirable U depletion zones as indicated by γ-raysource rock areas), requiring fluids ofspectrometric data, wire-line logs and geochemicalappropriate compositionanalyses; U-leached paleoweathering profilesPreservation of high redox state (and low pH?,high ligand activity, etc) of fluids alongpathways, requiring subaerial setting of fluidrechargePreservation of low pH?, high ligand activity,etc of fluids along pathwaysQ1 Permeable clastic sediments / rocksinterstratified with aquitards or aquicludesQ2,Q4Fluid confinement and focussing geometrieswithin basinEnergy driver Q4, Q1 Topography causing hydraulic head in preexistingaquifersEnergy,Permeabilityand chemicalarchitectureDepositionalgradientDepositionalgradientDepositionalgradientDepositionalgradientDepositionalgradientQ4, Q2 Gentle slope of aquifers away from basinmargin at times of fluid flow, resulting from: Primary depositional dip Tilting of sequence due to reactivation ofbasin margin faults Change in continental stress fields (e.g.compression or extension) Basinal subsidence DomingQ1-Q5 Evidence of uranium (and related) mineralsystem activityQ4,Q5 Regional gradation from oxidized (upstream)to reduced conditions (downstream) in aquifersQ5Q5Q5EssentialEssentialEssentialDesirableEssentialEvidence of subaerial setting of fluid recharge;extensive oxidised alteration zones in reducedaquifers; low feldspar content (mature seds); lowCa content?Low feldspar content (mature seds); low Cacontent; high phosphate mineral contentClastic sediments / rocks with high primary orsecondary permeabilities, typically mature sands,silts, sandstones, siltstones in continental fluvialand/or mixed fluvial-shallow marine environmentsEmbayment geometry of basin at 10-100km scale;paleochannel systems; constrictions in channels;lateral facies variations in permeability; onlaps ofaquifers on aquitards; some fault and foldgeometriesEvidence for uplift and exhumation of basinmargins or basement and history of events, e.g. v.coarse piedmont clastics, fission track dating, etcGeometry of basin at times of fluid flow, asdetermined from field mapping, sedimentaryfacies, structural measurements, seismic, gravity,MT and AEM data; tectonic historyDesirableDistribution of mineral occurrences (U, Cu, V, Co,Pb-Zn, etc)EssentialRegional-district-deposit scale mapping of redoxvariations and geochemistry in aquifers; mappingof hydrogeochemical gradients in groundwatersfrom regional aquifers; AEM may map reducedzonesPresence of in-situ reductants in aquifers or Essential Bends in paleochannels may have concentrations Bacteria colonies capable of reducing U 6+aquitards, including:of organic matter; some carbonaceous materials Solid carbonaceous material (e.g. woodymay be mappable using EM; drill hole logs frommaterial, coal, humic/humate componentswater and exploration drill holes; sedimentary Locally derived reduced waters (e.g. withfacies analysisH 2 S etc from bacterial activity) Inorganic reductants (e.g., Fe 2+ -rich rocks& minerals, sulfides (particularly pyrite)Presence of mobile reductants in aquifers and EssentialHydrocarbon shows in drilling and at surface;along faults, including:petroleum systems analysis of underlying basins; Gaseous or liquid hydrocarbons and/orgroundwater chemistry (e.g., low Eh)H 2 S that have migrated along faults oraquifers from underlying reservoirs orcoal seams Reduced groundwatersU deposition and changes in fluid chemistrycaused by gradients in: Redox pH silica saturation vanadium saturationEssential# Five Questions (Walshe, et al., 2005; Barnicoat, 2007) are as follows:Q1: What is the geodynamic and P-T-t history of the system?Q2: What is the architecture of the system?Q3: What are the characteristics and sources (reservoirs) of water, metals, lagands and sulfur?Q4: What are the fluid flow drivers and pathways?Q5: What are the transport and depositional processes for metals, ligands and sulfur?Alteration mineral zoning about ore as follows:oxidized (brown/red) sandstone with total oxidationof pre-existing sulfide minerals→ Se enrichment →U ores±silcrete → Mo and sulfide mineralenrichment/replacement of Fe-bearing silicatesand silicates → reduced (green/gray) sandstone±silcrete. Groundwater zonation from upstream todownstream as follows: high (oxidized) Eh → ore→ low (reduced) Eh. Redox and related reactionsmay also be reflected in δD, δ 13 C, δ 18 O, δ 34 S andU-series disequilibria variations in rock and ingroundwater.Terrane (basin)District (camp) and depositDistrict (camp) and terrane(basin)District (camp)District (camp)Terrane (basin)District (camp)District (camp)Continental to terrane(basin)Terrane (basin) to depositDistrict (camp)District (camp)District (camp) and depositPage 113 of 151