Skip to main content
Register
Get StartedSign In

Geological Models

Deposit models

Every mineral gets its own deposit model — with deposit-specific evidence layers, spectral signatures, and weight configurations drawn from the published deposit-model literature.

Gold

6 deposit models are applied to a gold analysis. Africa's major gold deposit types — from Archean greenstone-hosted orogenic systems through intrusion-related and epithermal veins to laterite-hosted supergene enrichment. Listed in descending order of the prior weight each model carries in the mixture.

Orogenic Gold

Structural-controlled

The dominant gold deposit type across Africa. Shear zone-hosted gold in metamorphic terranes — responsible for most production in West and East African greenstone belts. It carries the largest prior of any gold model here.

Key Indicators

  • + Structural lineaments and shear zones
  • + Iron oxide alteration (gossan)
  • + Sericite-carbonate alteration
  • + Topographic edges

Evidence Layers Weighted

Alteration composite, hydroxyl, gold evidence, topographic edge density, iron oxide, argillic, propylitic

Supergene Gold

Weathering-enriched

Laterite-hosted gold enriched by tropical weathering — common across the West African laterite plateau and increasingly targeted by juniors.

Key Indicators

  • + Laterite/ferricrete surfaces
  • + Strong iron oxide signature
  • + Flat terrain
  • + Proximity to primary sources

Evidence Layers Weighted

Iron oxide — weighted more heavily here than in any other gold model — then gold evidence, argillic, hydroxyl, topographic edge density

Epithermal Low-Sulfidation

Volcanic-hosted

Formed from near-neutral pH fluids. Quartz-adularia-sericite gangue. Less intense alteration footprint than HS.

Key Indicators

  • + Sericite-illite alteration
  • + Chalcedonic silica
  • + Propylitic halo
  • + Structural corridors

Evidence Layers Weighted

Alteration composite, gold evidence, hydroxyl, argillic, propylitic (true Mg-OH where EMIT is available)

Epithermal High-Sulfidation

Volcanic-hosted

Near-surface deposits in volcanic arcs with advanced argillic alteration (alunite, kaolinite, pyrophyllite).

Key Indicators

  • + Advanced argillic alteration
  • + Silicic core with argillic halo
  • + Volcanic vent proximity
  • + Iron oxide staining

Evidence Layers Weighted

Alteration composite, argillic (kaolinite doublet where ASTER or EMIT is available), gold evidence, iron oxide, hydroxyl

Intrusion-Related Gold

Intrusion-proximal

Gold in sheeted vein arrays around the margins and cupolas of felsic to intermediate intrusions, rather than in a single structurally-focused lode.

Key Indicators

  • + Proximity to felsic/intermediate intrusions
  • + Concentric alteration zoning
  • + Sheeted vein arrays
  • + Intrusive contacts

Evidence Layers Weighted

Iron oxide, hydroxyl and topographic edge density weighted equally, then gold evidence and alteration composite

Porphyry Gold-Copper

Intrusion-related

Large-tonnage, low-grade gold disseminated through altered intrusions, with copper as a co-product. It carries the smallest gold prior on this list — the model is included for completeness across intrusive terranes, not because it is expected to dominate an African gold search.

Key Indicators

  • + Concentric alteration (potassic to phyllic to propylitic)
  • + Structure-controlled veining
  • + Circular structural patterns
  • + Intrusive centres

Evidence Layers Weighted

Hydroxyl, topographic edge density and gold evidence weighted equally, then alteration composite and iron oxide

Recognised for gold, deliberately not scored

This model is part of the gold deposit-model set, but it is held out of the mixture rather than scored on a basis we are not yet prepared to defend. Each reason is given below, and its share of the prior weight is redistributed across the models that are scored — never counted as evidence that was there.

  • Placer (Alluvial) Gold — Resolved for gold but not scored, because Madini has no validated retrieval for the placer deposit class. That is deliberately narrower than "placers cannot be seen from orbit", which would be wrong — placer workings are detectable in free satellite imagery. What we will not do is score the model on its primary discriminator: placer favourability turns on valley-bottom, drainage and wetness classes that hinge on a 2–5 m vertical distinction, and our own GEDI-referenced measurement over a Congo area of interest put the canopy-induced vertical noise in SRTM elevation at roughly four times that signal there. Slope and edge-density classes, which turn on the full local relief, are unaffected. Placer's prior is dropped and the remaining gold models are renormalised over the mass that is scored.

Scientific References

Deposit model classifications and criteria are based on established economic geology literature:

  1. Groves, D.I., Goldfarb, R.J., Gebre-Mariam, M., Hagemann, S.G., & Robert, F. (1998). Orogenic gold deposits: A proposed classification in the context of their crustal distribution and relationship to other gold deposit types. Ore Geology Reviews, 13(1-5), 7–27. DOI
  2. Hitzman, M.W., Oreskes, N., & Einaudi, M.T. (1992). Geological characteristics and tectonic setting of Proterozoic iron oxide (Cu-U-Au-REE) deposits. Precambrian Research, 58(1-4), 241–287. DOI
  3. Sillitoe, R.H. (2010). Porphyry copper systems. Economic Geology, 105(1), 3–41. DOI
  4. Hedenquist, J.W. & Lowenstern, J.B. (1994). The role of magmas in the formation of hydrothermal ore deposits. Nature, 370, 519–527. DOI
  5. Kesler, S.E. (2010). Geologic stocks and prospects of non-renewable natural resources. Geological Society of America Special Paper 468. DOI
  6. Bradley, D.C., McCauley, A.D., & Stillings, L.L. (2017). Mineral-deposit model for lithium-cesium-tantalum pegmatites. USGS Scientific Investigations Report 2010-5070-O. DOI

Last updated: August 14, 2026

Try these models on your ground

Get Started How It Works