Prospectivity
cu-v3.2
Sediment-hosted copper, Kalahari Copperbelt
All runs Ranks ground
Mineral system
Cu Copper Definition 2.1
Sediment-hosted copper, Kalahari Copperbelt
Signed by T. Kgosi, Pr.Sci.Nat on 04 Aug 2026
Gradient-boosted trees, redox-constrained · 250 m
Ran 08 Sept 2026, 272 min
Run by: Amini modelling team · Accepted by: T. Kgosi, Pr.Sci.Nat
Supersedes cu-v3.1 Capture efficiency
The top 10% of ranked ground holds 79% of the known deposits.
Search-space reduction 95.8%
The share of the modelled area a competent person can set aside for this commodity.
Validation
Blind-site hit rate 100%
Threshold agreed at MS1 70%
Block cross-validation 6 folds, 40 km blocks
AUC 0.87 ± 0.04
Physical constraints
- Prediction is confined to the D'Kar / Ngwako Pan redox contact and its permissible stratigraphy; ground outside it cannot score high regardless of geophysical response.
- Cover thicker than 120 m caps the class at medium: the evidence beneath is not resolved.
- Structural blocks north of the Ghanzi ridge are excluded pending the revised stratigraphic model.
Features and importance
| Feature | Critical process | System role | Importance |
|---|---|---|---|
| Distance to interpreted redox contact | Trap: reduced host against oxidised red-bed source rock | Trap | |
| Magnetic low, graben margin | Transport: basin-margin faults route brine to the contact | Transport | |
| Cu-Ag-Co pathfinder residual | Source and transport: leakage of metal-bearing brine to surface | Transport | |
| Red-bed thickness, modelled | Source: oxidised sediment supplying copper to solution | Source | |
| Kalahari cover thickness | Preservation and detectability: cover attenuates every surface proxy | Preservation | |
| Tilt-derivative structural density | Transport: fracture permeability at the contact | Transport |
Inputs
| Dataset | Version | Confidence filter | Coverage |
|---|---|---|---|
| Ghanzi aeromagnetics | 2004 levelled, 2026 re-grid | A and B only | 94% |
| National gravity | 2021 | A and B only | 71% |
| KCB regional soil geochemistry | 2019 | B or better, levelled | 38% |
| Geology 1:250k with Pre-Kalahari interpretation | 2023 | all, lineage recorded | 100% |
| Boseto drilling, petrophysical calibration | 2024 batch | assayed intervals only | 12% |
Boseto drilling, petrophysical calibration covers 12% of the modelled area and is the layer that governs the bounds.
Validation
| Withheld site | Withheld by | Class | In the high class |
|---|---|---|---|
| BS-CU-01 Zone 5 extension | T. Kgosi, Pr.Sci.Nat | High | In the high class |
| BS-CU-02 Boseto west | T. Kgosi, Pr.Sci.Nat | High | In the high class |
| BS-CU-03 Ghanzi ridge south | T. Kgosi, Pr.Sci.Nat | High | In the high class |
| BS-CU-04 Mahumo | T. Kgosi, Pr.Sci.Nat | High | In the high class |
| BS-CU-05 Plutus | T. Kgosi, Pr.Sci.Nat | High | In the high class |
| BS-CU-06 Banana Zone north | T. Kgosi, Pr.Sci.Nat | High | In the high class |
Outputs
- Prospectivity surface 3.2 · COG, 250 m
- Confidence surface 3.2 · COG, 250 m
- Feature-importance maps 3.2 · COG per feature
- Against historical exploration 3.2 · COG, 250 m
- Difference against cu-v3.1 3.2 · COG, 250 m
Parameters
- learningRate
- 0.05
- maxDepth
- 5
- trees
- 900
- classCut
- high ≥ 0.78, medium ≥ 0.52
- negatives
- 3:1, drawn outside permissible stratigraphy
Limitations and completeness
- Gravity coverage is 71% of the modelled area; the north-west gap widens the bounds there.
- Soil geochemistry covers 38% of the belt, all of it south of the Ghanzi ridge.
- Petrophysical calibration rests on one drilling campaign.
Against the previous edition
| cu-v3.1 | cu-v3.2 | Change | ||
|---|---|---|---|---|
| Blind-site hit rate | 83.3% | 100% | +16.7% | Improved |
| Capture at 10% of area | 68% | 79% | +11% | Improved |
| Block-CV AUC | 0.83 | 0.87 | +0.04 | Improved |
| AUC spread across folds | 0.06 | 0.04 | -0.02 | Improved |
| High-class ground | 7,980 km² | 6,240 km² | -1,740 km² | Improved |
| Search-space reduction | 94.6% | 95.8% | +1.2% | Improved |
| Grid resolution | 250 | 250 | 0 | Unchanged |
Inputs that arrived
- Boseto drilling, petrophysical calibration · 2024 batch
Inputs revised
- Ghanzi aeromagnetics: 2004 levelled → 2004 levelled, 2026 re-grid
What moved the model
- Tilt-derivative structural density 0% → 8%
- Magnetic low, graben margin 24% → 19%
- Cu-Ag-Co pathfinder residual 20% → 17%
- Distance to interpreted redox contact 29% → 31%
- Kalahari cover thickness 12% → 11%
- Red-bed thickness, modelled 15% → 14%
Difference against cu-v3.1 COG, 250 m
Targets from this run
3 targets are ranked from this run.
| Target | Score | Class | Competent person |
|---|---|---|---|
| KCB-CU-014 Ngwako Pan West | 0.91 | High | T. Kgosi, Pr.Sci.Nat |
| KCB-CU-021 Boseto South Extension | 0.87 | High | T. Kgosi, Pr.Sci.Nat |
| KCB-CU-033 Ghanzi Ridge Central | 0.58 | Medium | T. Kgosi, Pr.Sci.Nat |