Experiment · mineral prospecting

Mineral alteration, mapped from orbit

Six Sentinel-2 band ratios that geologists use to find hydrothermal alteration, iron-oxide caps and gossans. Pick an area of bare ground up to 1,500 km² and the engine maps it from the clearest valid scene in under a minute.

Prospecting map

Layers

Opacity

Show targets on top of any layer

Scene & coverage

Ranked targets

#	Location	Density	Clay / OH	Iron oxide	Actions

Experimental. Layers are relative to the area's own bare ground, so they show anomalies, not mineral abundance or grade. Field-check every target before drawing conclusions.

MethodS2 L2A · 10–20 m

What each layer reads

Ratio composite: Clay/hydroxyl in red, iron oxide in green, ferrous iron in blue. Red to yellow marks clay plus iron, the signature of argillic alteration and gossans. Blue marks fresh, ferrous rock.
Targets: Pixels where clay/hydroxyl and iron oxide both sit in the area's top decile. Ranked on a ~300 m grid by how densely they cluster.
Iron oxide · B4/B2: Hematite, goethite and jarosite. Oxidised caps over sulphides and lateritic soils.
Clay / hydroxyl · B11/B12: Al-OH minerals: kaolinite, alunite, sericite, illite. The core of hydrothermal alteration halos.
Ferrous iron · B12/B8 + B3/B4: Fe²⁺ in mafic rocks, chlorite and amphibole, often the unaltered background.
Gossan · B11/B4: Weathered sulphide cappings, rich in iron and depleted in everything else.
Ferric iron · B4/B3: Fe³⁺ staining, a sharper view of oxidation than the iron oxide ratio.
Ferrous silicates · B12/B11: Biotite, chlorite and amphibole in fresh crystalline rock.

Limitsread before drilling

Ratios read the top millimetres of rock and soil. Vegetation, cloud, water and deep shadow are masked out.
Sentinel-2 has two short-wave infrared bands, so it separates clay from iron but cannot tell kaolinite from alunite. That needs hyperspectral data such as EnMAP.
Dry riverbeds, sand sheets, tailings and quarries can mimic alteration. Read targets against the imagery and the geology.