U · V
Compound Bleaching
Roll-front oxidation boundary
Best single U-V indicator. Maps hematite dissolution and clay enrichment at the oxidation-reduction interface — the direct spectral expression of the bleaching front immediately up-dip of the ore zone.
Fe³⁺ → Fe²⁺ reduction · U-V-Cu sandstone · Roll-front U targets
U · V
Redox Boundary
V⁵⁺ / V⁴⁺ transition zone
Locates the vanadium geochemical transition. V and U co-precipitate under equivalent redox conditions, bracketing the ore-hosting roll-front from the reducing side. Strong SWIR absorption yields a characteristically dark image.
V⁵⁺ vanadate (oxidised) → V⁴⁺ roscoelite/montroseite (reduced)
U · V
Clay Hydroxyl
Alteration clay in host rock
Detects hydroxyl-bearing clay minerals — kaolinite, illite, montmorillonite — formed by diagenetic and hydrothermal alteration of uraniferous host sandstones. Confirms conditions favorable for U precipitation.
Al-OH and Mg-OH stretch in clay minerals (SWIR)
U · V
Ferrous Iron
Reducing zone indicator
Detects ferrous iron (Fe²⁺) in silicates and oxides. Reducing conditions are required for uranium precipitation from soluble uranyl complexes. Dark zones in the basin interior reflect organic-rich reducing sediments.
Fe²⁺ absorptions in silicates and oxides · Roll-front reducing side
U · V
Normalized Clay
Vegetation-corrected clay mapping
Vegetation-normalized clay index removes the photosynthesis contribution, isolating clay mineral signal in exposed sedimentary rock. Produces improved anomaly contrast in areas of sparse plant cover.
Clay SWIR absorption normalized against vegetation red-edge
U · V
Fe Oxide Ratio
Oxidation-state gradient mapping
Ratio of hematite (Fe³⁺) to goethite zones providing a proxy for lateral oxidation-state gradient across the roll-front. Bright = oxidised red-bed margins; dark = reducing organic-rich basin interior.
Hematite vs. goethite discrimination via visible band ratios
U · V
Gossan / Fe Enrichment
Supergene iron capping
Maps supergene iron capping above mineralized zones. Strongest anomalies cluster at basin-flank outcrop belts. Use in combination with the bleaching index to filter false positives from iron-rich Mesozoic red beds.
Gossanous Fe-hydroxide surface expression above buried mineralization
U · V
Geobotanical Stress
Indirect U/V toxicity indicator
Vegetation stress response over uranium-enriched soils as a geobotanical indicator. Performance limited in arid, sparse-vegetation study areas. Use only as a low-weight tie-breaker for existing Tier 1 candidates.
Vegetation spectral stress signatures (red/NIR ratio)
Zn · Pb
Zn / Fe Gossan
Surface oxidized polymetallic cap
Targets zinc-enriched, iron-stained gossanous material from supergene oxidation of polymetallic sulfide assemblages. Intense anomalies occur along anticlinal crests. Gossan without co-incident bleaching indicates polymetallic targets distinct from roll-front U systems.
Fe-hydroxide + Zn-carbonate spectral blend in visible-NIR
Zn · Pb
Zn-Pb Carbonate / Gossan
Secondary Zn-Pb carbonate zone
Targets smithsonite and cerussite secondary Zn-Pb carbonate zones in gossanous waste rock. Elevated values at anticlinal crests confirm supergene enrichment of a polymetallic sulfide source.
Zn-carbonate + Pb-carbonate SWIR absorption
Cu
Cu Carbonate (Malachite)
Copper mineral detection
Detects malachite and torbernite staining at Cu-U sites on bare rock surfaces. Characteristic bright green signature provides a direct outcrop-scale indicator for copper carbonate minerals in the supergene zone.
Malachite/torbernite staining · Cu-U co-precipitation sites
Cu
Azurite Detection
Rare but highly diagnostic
Maps azurite (blue copper carbonate) surface indicator. Rare occurrence means each anomaly is highly diagnostic — a direct confirmation of near-surface copper mineralization wherever detected.
Azurite blue carbonate absorption feature (visible)
Cu
Ferrous Alteration (Chalcocite)
Cu/chalcocite reducing zone
Near-zero or negative values indicate dark Cu sulphide-bearing reduced sandstone. Identifies chalcocite-zone alteration characteristic of sandstone-hosted Cu-U systems at the roll-front reducing margin.
Dark Cu sulphide spectral suppression (low reflectance)
REE
Carbonaceous Shale / Coal
Organic-rich sediment REE proxy
Maps carbonaceous shale and coal outcrops as a proxy for REE enrichment. Also serves as an organic reductant indicator for uranium exploration — carbonaceous material is the principal driver of U precipitation at roll-front interfaces.
Low reflectance of carbonaceous material across VNIR-SWIR
REE
Mafic Silicate Index
Mafic provenance indicator
Identifies mafic-intermediate igneous and metasedimentary rocks as Sc sources. Most informative as a provenance constraint and lithological discriminator rather than a direct mineralization indicator.
Mafic silicate absorptions (pyroxene, amphibole) in NIR-SWIR
Ti · HM
Silicate Host-Rock Proxy
Permeable silicate host lithology
Titanium is immobile during weathering and diagenesis, making it a reliable proxy for silicate host-rock composition. Confirms permeable coarse-clastic facies favorable for roll-front development. Used to eliminate mudstone-dominated areas.
Ti-bearing mineral absorptions (ilmenite, rutile, titanite) in NIR-SWIR
Ti · HM
Ilmenite / Titanite Proxy
Heavy mineral distribution
Targets ilmenite (FeTiO₃) and titanite (CaTiSiO₅) via their combined Fe-Ti spectral signature. Both are heavy minerals concentrated in placer deposits. Strong response on basin margins consistent with igneous and metamorphic source rocks.
Combined Fe-Ti absorptions distinguishing ilmenite from other Fe-oxides
General
As Jarosite / Acid Drainage
Jarosite enrichment indicator
On bare waste surfaces, maps jarosite enrichment indicating arsenic mobility and active acid rock drainage. Identifies scorodite and arsenate-jarosite assemblages at mine waste pile candidates.
Jarosite Fe-SO₄ absorptions in visible-SWIR · acid drainage proxy
Composite
Alteration Composite
Optimal for U-V targeting
Combines Fe oxide, clay hydroxyl, and ferrous iron indices into a single RGB composite. Yellow-orange areas indicate Fe + clay co-occurrence (ore-roll target). Red indicates unaltered background. The primary reconnaissance output.
Weighted multi-index composite · Tier 1 candidate generation
Base
Natural Colour
Baseline reference image
True-colour B04/B03/B02 composite providing the baseline geological context for interpreting spectral index anomalies. Used to verify field-observable features and identify bare rock vs. vegetation vs. soil backgrounds.
B4-B3-B2 (R-G-B) · context baseline for anomaly interpretation
