EP 177 | Rethinking Grade Control: When Ordinary Kriging Isn't Enough

In Part 2 of Snowden Optiro's Fresh Thinking tungsten series, Senzeni Mandava Matondi, Laurie Hassall and Melanie Bulley discuss the key technical considerations for tungsten projects from a resource geology perspective. Building on Part 1's exploration of tungsten markets, pricing and global supply chains, this episode shifts the focus to deposit geology, mineralogy, assaying, metallurgical recovery and geometallurgy. The discussion explores: Tungsten deposit types: The geological characteristics of skarn, quartz vein, stockwork, granite-related and stratabound deposits. Scheelite and wolframite: Why identifying the dominant tungsten mineral is important for exploration, processing and recovery. Exploration and assaying: The use and limitations of fluorescence, analytical methods, quality control and historical assay data. Tungsten grade reporting: The distinction between elemental tungsten (W) and tungsten trioxide (WO₃), and why consistent reporting is important. Metallurgical recovery: How mineralogy, grain size, liberation and ore sorting can influence processing. Geometallurgy and resource classification: The importance of understanding geological and metallurgical variability when evaluating tungsten projects. The episode highlights why tungsten grade alone does not provide a complete picture of a project's technical characteristics, and why geology, mineralogy and metallurgical recovery need to be considered together.

In this episode of Snowden Optiro's Fresh Thinking podcast, Julian Aldridge, Regional Director – EMEAA, is joined by Melanie Bulley, Senior Consultant, and Laurie Hassall, Principal Consultant, for the first discussion in a two-part series on tungsten. The discussion examines tungsten from a market and supply chain perspective, with particular attention to the recent rise in APT prices and the factors affecting the availability of tungsten products. Topics discussed include: Ammonium paratungstate (APT), its role as an intermediate tungsten product and its use as a market price reference. The relationship between APT prices, tungsten concentrate and mine revenue, including payability considerations. China's role in tungsten mine production, concentrate consumption and downstream processing. The effects of Chinese export controls, US tariffs and defence procurement restrictions. Tungsten's strategic applications and the challenges associated with substitution. Responsible sourcing, conflict minerals requirements and 3TG traceability. Processing capacity outside China and its importance in developing non-Chinese tungsten supply chains. The contribution and limitations of tungsten recycling. The implications of recent APT price movements for new tungsten projects and long-term price assumptions. Part 2 will explore the technical aspects of tungsten projects, including deposit types, geology, mineralogy, assaying, metallurgy and Mineral Resource estimation.

Inferred Mineral Resources are the lowest-confidence Mineral Resource category, but what role should they play in mine planning? In this episode of Fresh Thinking, Tarrant Elkington is joined by Allan Earl, Executive Consultant at Snowden Optiro, to discuss the practical and regulatory considerations around including Inferred Resources in mine plans. Tarrant and Allan explore the distinction between mine plans developed for operational and strategic purposes and those used for public reporting. They discuss how Inferred Resources are treated under different reporting frameworks, including JORC, NI 43-101 and S-K 1300, and some of the challenges this creates for mine planners. The discussion also considers the practical implications of including or excluding Inferred Resources, particularly for long-term and underground mine planning, and the potential for companies to maintain different plans for internal, strategic and public reporting purposes. Subscribe to Fresh Thinking by Snowden Optiro for more technical discussions from across the mining industry. 

When does ordinary kriging stop being the best approach for grade control? In this episode of Fresh Thinking, Ian Glacken, Executive Consultant, and Dr Gregory Zhang, Senior Consultant at  @SnowdenOptiro , explore direct SMU estimation and the circumstances where conventional ordinary kriging may not provide the best result. They discuss the challenges presented by highly skewed grade distributions, mixed populations and complex anisotropy, and consider alternative approaches including categorical indicator kriging (CIK), multiple indicator kriging (MIK) and localised MIK. Drawing on a case study, Ian and Gregory examine why different estimation methods should be tested and assessed against reconciliation results, rather than assuming a single approach will work for every deposit. They also emphasise an important point: more sophisticated estimation techniques are not a substitute for appropriate drilling and good-quality data.  Listen to Fresh Thinking for technical insights and practical perspectives from Snowden Optiro's mining and geology experts.

Changing workplace exposure limits could become an important driver of battery electric vehicle adoption in underground mining. In this episode of Fresh Thinking by ‪@SnowdenOptiro‬, Hamish Guthrie is joined by Sarah de Vries to discuss Sarah's recent presentation at The Electric Mine Conference 2026, "Evolving Air Quality Regulations: A Catalyst for Electric Machine Adoption." Sarah explores the changing regulatory environment for diesel particulate matter (DPM) and other airborne contaminants, and what tighter exposure limits could mean for underground mine ventilation, operating costs, productivity and equipment selection. The discussion also considers the growing role of battery electric vehicles (BEVs) in underground mining, including current technology limitations, ventilation and infrastructure considerations, and the importance of evaluating BEVs within the specific operating and financial context of each mine. Sarah also shares key takeaways from The Electric Mine Conference, including emerging operating data from mines trialing and operating full BEV fleets underground. In this episode: Changes to workplace exposure limits for DPM Implications for underground mine ventilation Options for reducing diesel emissions underground The role of BEVs in meeting changing air quality requirements Current limitations and considerations for BEV adoption Emerging operational data from underground BEV fleets Subscribe to the ‪@SnowdenOptiro‬ YouTube channel for more technical discussions from our mining and geology specialists.

Platinum is one of the world's rarest and most geographically concentrated metals, with applications spanning the automotive, industrial, jewellery and emerging hydrogen sectors. But what does its evolving supply and demand outlook mean for the mining industry? In this episode of Fresh Thinking by Snowden Optiro, Senzeni Mandava Matondi and Julian Aldridge explore platinum's geology, market dynamics and strategic importance. They discuss the concentration of global platinum supply, changing automotive demand, the potential role of hydrogen technology, substitution between platinum group metals (PGMs), supply constraints and the challenges of bringing new mines into production. The conversation also considers what these trends could mean from a mining perspective, including the potential for renewed exploration, mine life extensions and new project development. Subscribe to Fresh Thinking by Snowden Optiro for more technical discussions covering geology, resource estimation, mining and the commodities shaping the industry.

Was the sample representative? Every geological model, resource estimate, grade control decision and reconciliation result ultimately depends on the quality of the samples behind it. In this episode of Fresh Thinking by Snowden Optiro, Melanie Bulley is joined by Senzeni Mandava Matondi to explore the Theory of Sampling and why representative sampling is fundamental to reliable decision-making throughout the mining value chain. They discuss why natural heterogeneity makes sampling challenging, the difference between correct and incorrect sampling errors, why precision should not be confused with representativity, and why even highly precise laboratory analysis cannot correct a sample that was unrepresentative from the beginning. The episode also explores the practical consequences of poor sampling, including ore loss, dilution, poor reconciliation and unreliable resource estimates. In this episode: Why sampling is the foundation of mining data Understanding representativity and natural heterogeneity Correct vs. incorrect sampling errors Precision vs. representativity Why laboratories cannot fix poor sampling The impact of sampling on grade control and reconciliation Principles of good sampling practice

Tailings Mineral Resource Estimates can appear straightforward. The material has already been mined, crushed, processed and deposited in one location — but tailings facilities present their own unique set of technical challenges. In this episode of Fresh Thinking by @SnowdenOptiro  , Senzeni Mandava and Melanie Bulley explore the nuances of estimating Mineral Resources within tailings facilities. They discuss how tailings differ from conventional in situ deposits and why depositional engineering, rather than natural geological controls, can become fundamental to understanding continuity. opics covered include: Density and moisture uncertainty Sampling unconsolidated and saturated material Variography and spatial continuity in tailings • Depositional history and hydraulic segregation The importance of the phreatic surface and hydrogeology Metallurgical recoverability and project economics Mineral Resource classification Tailings reprocessing, critical minerals and ESG considerations As Senzeni and Melanie discuss, a tailings facility is not simply a relocated orebody. It is an engineered, evolving sedimentary system with its own geotechnical, hydrogeological, metallurgical and operational complexities.

In Part 2 of our Fresh Thinking by @SnowdenOptiro  two-part series, host Melanie Bully is joined by Senzeni Matondi to continue the discussion on why the most expensive mistake in grade control isn't necessarily mining low-grade material — it's making the wrong decision about whether material is ore or waste. Following on from Part 1, this episode explores how mining operations can make better grade control decisions by understanding and managing uncertainty. Melanie and Senzeni discuss why average grade alone doesn't tell the full story, how conditional bias and grade smoothing can affect ore and waste classification, and why local accuracy around the cut-off grade is so important. They also explore grade control as a complete value chain — from sampling, QA/QC and geological logging through to estimation, dig planning, mining execution, stockpile management and mine-to-mill reconciliation. The conversation then turns to modern approaches to uncertainty and risk, including conditional simulation, probability-based ore classification and risk-based digline optimisation. In this episode Melanie and Senzeni discuss: Why two models with similar average grades can deliver very different operational outcomes Conditional bias and the impact of grade smoothing The importance of local accuracy around the cut-off grade How ore loss and dilution result from misclassification • Why reconciliation reflects the performance of the entire grade control system Moving from deterministic estimates to risk-informed decision-making What best-practice grade control looks like at high-performing operations The key message from this two-part series is simple: grade control isn't about producing the perfect block model — it's about consistently making better mining decisions.

In this episode of Fresh Thinking by Snowden Optiro, Rayleen Hargreaves, Principal Consultant at Datamine and Product Owner of Reconcilor, talks with Ian Glacken, Executive Consultant at Snowden Optiro, about the importance of reconciling mineral resources and reserves across the mine value chain. Resource and reserve reconciliation is often given less attention than the production stages of the mining process, yet it provides an important link between what a company reports, what it plans to mine, and what is ultimately produced.  Rayleen and Ian discuss: The role of resources and reserves in the mine value chain The differences between mineral resources and mineral reserves • Why resource and reserve reconciliation is important The value of monthly reconciliation and early warning indicators Why reserves need to be represented as a model that can be depleted How to approach reconciliation when mining occurs outside the reported reserve The relationship between resource, reserve and grade control reconciliation The growing importance of transparency and reconciliation in reporting codes The discussion also considers potential changes to the JORC Code and the role that resource and reserve reconciliation could play in improving transparency for companies, shareholders and other stakeholders.