Mineral Resource Estimation in Kenya

Every mining project rests on one number: how much valuable material is in the ground, and at what concentration. That number is not simply measured. It is estimated from limited samples, using geological interpretation and statistics, then reported according to strict professional standards. Understanding how resource estimation works helps investors, licence holders, and lenders judge the reliability of what they are being told.

Resources vs. Reserves

These terms are often confused:

• Mineral Resource: A concentration of material of intrinsic economic interest, with reasonable prospects for eventual economic extraction. Classified as Inferred, Indicated, or Measured according to geological confidence.
• Ore Reserve: The economically mineable part of an Indicated or Measured Resource, after applying “modifying factors” such as mining, processing, metallurgical, economic, marketing, legal, environmental, social, and governmental considerations.

A resource is a geological statement. A reserve is a statement that includes engineering and economic evidence.

Reporting Standards

Internationally recognised codes govern public reporting. The JORC Code (Australasia), NI 43-101 (Canada), and the CRIRSCO-aligned family of standards require that estimates be prepared or supervised by a Competent Person (or Qualified Person) with relevant experience. The codes also demand transparency about data, methods, assumptions, and risks. Kenyan projects seeking international finance or listing typically follow one of these standards.

Step 1: Data Collection and Validation

Reliable estimation begins with reliable data:

• Drill hole collar surveys that accurately record locations.
• Downhole surveys that record hole deviation.
• Geological logs describing lithology, alteration, and mineralisation.
• Assay data from accredited laboratories with documented QA/QC.
• Density measurements, essential for converting volume to tonnes.

Errors in any of these propagate into the final estimate. Data validation, including checks for duplicates, overlapping intervals, and unrealistic values, is therefore a critical step.

Step 2: Geological Interpretation and Domaining

Geologists interpret the shape and continuity of mineralisation using sections and plans. Mineralised bodies are outlined as three-dimensional wireframes, often based on grade thresholds, lithology, alteration, or structural controls. The deposit may be divided into domains with similar characteristics, since mixing different populations leads to biased estimates.

Step 3: Compositing and Statistical Analysis

Assay samples are usually of different lengths, so they are standardised into composites of equal length. Statistical analysis then examines grade distribution, outliers, and relationships between variables. Extremely high grades can disproportionately influence results, so they may be capped (cut) after careful analysis.

Step 4: Variography and Spatial Continuity

Variography quantifies how grade changes with distance and direction. A variogram describes how similar two samples are as the distance between them increases. This spatial model underpins geostatistical estimation and indicates how far sample information can reliably be extended.

Step 5: Block Modelling and Grade Estimation

The deposit is divided into a three-dimensional grid of blocks. Grades are estimated for each block using methods such as:

• Inverse distance weighting, which weights nearby samples more heavily.
• Ordinary kriging, a geostatistical method that uses the variogram to calculate optimal weights and provide an estimation error.
• Indicator or conditional simulation methods for complex or high-variability deposits.

Search parameters, minimum and maximum samples, and block size must reflect drill spacing and mining selectivity.

Step 6: Validation of the Model

Models are checked against the input data through visual comparison, swath plots, global statistical comparison, and, where possible, reconciliation with test mining or bulk samples. A model that has not been validated should not be used for financial decisions.

Step 7: Classification

Resources are classified by confidence, based on drill spacing, geological continuity, data quality, and estimation quality:

• Measured: High confidence in tonnage, grade, and geometry.
• Indicated: Reasonable confidence, sufficient for mine planning.
• Inferred: Lower confidence, with geological evidence implying but not verifying continuity.

Inferred resources cannot be converted to reserves, and should be treated cautiously in economic studies.

Special Challenges in Kenya

• Nugget effect in gold deposits: Coarse, erratic gold produces high variability, so larger sample volumes and tighter drill spacing may be needed.
• Weathering profiles: Oxide, transition, and fresh zones differ in density and recovery, requiring separate domains.
• Limited historic data: Older datasets may lack QA/QC, requiring verification drilling.
• Complex structure: Folded or faulted mineralisation demands careful modelling.
• Industrial and construction minerals: These often require quality parameters such as chemistry, particle size, or strength, not just a single grade.

Common Errors

• Using inadequate sample numbers for the claimed confidence.
• Ignoring QA/QC failures.
• Extrapolating far beyond drilling.
• Using inappropriate density values.
• Failing to document cut-off grade and assumptions.

Why Independent Estimation Adds Value

An independent resource estimate gives lenders, buyers, and partners confidence that figures are reliable and transparent. It also helps owners understand where additional drilling will most efficiently improve confidence and value.

Conclusion

Resource estimation blends geology, statistics, and professional judgement. Done properly, it provides a defensible basis for mine planning, financing, and negotiation. Done poorly, it creates false confidence.

Innercore Geoconsultants Services Limited supports Kenyan projects with data validation, geological modelling, and resource estimation aligned to recognised reporting standards. Contact us to review or develop your resource estimate.