Dyno Nobel Drill to Leach: Transforming Gold Recovery in Heap Leach Mining

The Invisible Variable in Gold Recovery That Most Operations Never Measure

Heap leach gold mining has been refined over decades. Solution chemistry is monitored continuously. Pad design is engineered to precise tolerances. Irrigation rates are calibrated to optimise cyanide contact time. Yet across the industry, a consistent gap persists between the theoretical recoverable gold in ore and what actually reports to the pregnant solution pond. The missing variable rarely appears on any metallurgical dashboard, and it is determined not on the leach pad, but at the moment of detonation.

The structural integrity of individual ore particles after blasting governs how effectively cyanide solution can penetrate, percolate, and dissolve gold from within the rock matrix. This is not a function of how finely the ore is crushed or how evenly it is stacked. It is a function of the internal micro-fracture network created during the blast event itself, a property invisible to standard particle size distribution analysis and one that most operations have never systematically measured or optimised.

This is precisely the gap that Dyno Nobel Drill to Leach was designed to address.

What Dyno Nobel Drill to Leach Actually Is

The Dyno Nobel Drill to Leach process emerged as a specialised adaptation of the company's established Drill to Mill methodology. Where Drill to Mill targets operations with grinding circuits, optimising fragmentation to improve mill throughput and reduce specific energy consumption, Drill to Leach is purpose-built for heap leach operations where no milling stage exists. The performance objective shifts entirely: rather than reducing particle size, the goal is to engineer controlled micro-fracture networks within ore particles at the point of blasting, maximising the internal surface area available for cyanide contact on the leach pad.

The program is delivered through Dyno Nobel's DynoConsult team, which develops customised, site-specific blast design solutions rather than applying standardised product recommendations. Every component of the blast design is evaluated and potentially modified, including explosive product selection, detonator type, burden-to-spacing geometry, subdrill depth, stemming height, and timing sequence.

How Drill to Leach Differs From Conventional Blast Optimisation

The distinction between conventional blast optimisation and the Drill to Leach approach is more fundamental than it might appear on the surface.

Most blast optimisation programs are evaluated by what the muck pile looks like and how quickly the crusher processes the material. Drill to Leach shifts the measurement point entirely downstream, to the leach pad, where the financial consequences of blast design decisions are ultimately realised. Furthermore, understanding drill results interpretation at the operational level can help mine teams better contextualise what these blast-driven metrics are actually telling them.

The Science of Micro-Fracturing and Why It Governs Leach Kinetics

Understanding why Drill to Leach works requires a basic understanding of how cyanide leaching actually functions at the particle scale. Gold dissolution in alkaline cyanide solution is a surface reaction. The rate at which gold reports to solution is directly proportional to the reactive surface area available for contact. In a conventional heap leach operation, this surface area is largely defined by the external geometry of the ore particles.

In an operation using optimised micro-fracture blasting, the internal crack network within each particle dramatically expands the total reactive surface, allowing cyanide solution to penetrate into the rock rather than merely washing over its exterior.

The mechanism through which micro-fractures are generated is detonation pressure and velocity of detonation (VOD). High-VOD explosive products generate shock wave intensities that propagate fracture networks through the ore matrix well beyond the immediate blast zone. Lower-energy or blended emulsion products may produce visually comparable muck piles while generating fundamentally weaker internal damage profiles.

TITAN Gassed Emulsion: Why Explosive Selection Determines Internal Rock Damage

Dyno Nobel's TITAN gassed emulsion product is central to the Drill to Leach technical case. The product is characterised by elevated detonation pressure and high associated VOD, properties that translate mechanically into greater micro-fracture propagation through the ore matrix compared to conventional blended emulsion alternatives.

A critically important and widely underappreciated fact: two blasts can produce nearly identical particle size distributions while generating entirely different internal fracture networks, depending solely on the energy profile of the explosive used. Standard fragmentation analysis cannot distinguish between these outcomes.

This has a direct implication for operations currently using blended emulsions with non-electric initiators. The recovery performance they observe on their leach pads may reflect not just their ore characteristics or solution chemistry, but the cumulative effect of under-fracturing every tonne of ore that has ever been blasted under their baseline program. For investors and operators alike, interpreting drill results in this context means looking well beyond surface-level fragmentation data.

The Two-Phase Trial Program: Design, Challenges, and Results

Dyno Nobel has conducted two structured trial phases at a U.S. gold mining operation, with a third phase planned. The trial site specification involved 6¾-inch blastholes, a 20-foot bench height, a 3-foot subdrill, and individual blasts comprising 200 to 300 holes. The operation had been running a consistent blasting program using blended emulsion with non-electric detonators for several years, providing a robust historical dataset from which a reliable performance baseline could be established.

Phase 1: The Split-Bench Method and What It Revealed

The first trial used a split-bench design, firing one half of a given bench under baseline parameters and the other half under the optimised Drill to Leach design. The logic was straightforward: compare two blast approaches side by side within the same geological environment.

The results were directionally encouraging but less definitive than expected. Post-trial investigation identified the reason: lateral geological variability across the bench was introducing inconsistency into the controlled comparison. The ore characteristics differed meaningfully from one side of the bench to the other, making it impossible to attribute performance differences with confidence to the blast design rather than the geology.

This Phase 1 finding was itself a significant methodological insight. It established that vertical geological consistency typically exceeds lateral consistency in this deposit, a factor that fundamentally reshaped the Phase 2 trial design.

Phase 2: The Stacked-Bench Method and Its Superior Results

In the second trial, the team applied baseline parameters to an upper bench and the optimised Drill to Leach design to the directly underlying bench. By exploiting the more consistent vertical geology, the comparison became substantially cleaner.

The results from Phase 2 were described as very encouraging. Laboratory testing indicated:

• An overall increase in total gold recovery compared to baseline performance
• A measurable reduction in the time required to achieve peak recovery levels
• Minimal change in particle size distribution between baseline and optimised blasts
• An improvement in crusher throughput despite the limited PSD shift

That last data point carries particular significance. The absence of meaningful PSD change combined with a throughput improvement is a strong corroborating signal that micro-fracture network enhancement is occurring. Micro-fractures reduce inter-granular bond strength within ore particles, lowering mechanical resistance at the crusher even when visible particle sizes remain comparable. This is a mechanism that conventional blast performance metrics would never detect.

The convergence of three independent data signals (improved gold recovery, faster recovery kinetics, and throughput uplift without fragmentation change) creates a robust multi-dimensional case for the micro-fracturing hypothesis that no single metric alone could establish.

The Role of Electronic Detonators in Timing Precision

A key modification in the optimised blast design was the full transition from non-electric detonators to electronic detonators. Non-electric systems are subject to cap scatter, meaning the actual firing time of individual detonators can deviate from nominal timing by variable amounts, introducing uncontrolled energy sequencing across the blast pattern. Electronic detonators eliminate this variability, ensuring that the timing applied to the blast design is the timing that actually fires.

The mine had independently been evaluating a transition to electronic detonators before the trial program commenced, driven in part by highwall stability requirements and community noise compliance considerations. This alignment made the timing upgrade a natural operational fit rather than a trial-imposed constraint, and it simultaneously delivered blast vibration management as a co-benefit of the Drill to Leach program.

Phase 3: Moving From Laboratory to Field-Scale Validation

Laboratory bottle roll tests provided rapid directional confirmation. Leach column tests, which more accurately simulate heap leach percolation dynamics, took approximately eight months to return results in Phase 1, with turnaround improving in Phase 2 through better testing protocol management. Both methods, however, operate under controlled conditions that cannot fully replicate the hydrodynamic complexity of a real heap leach pad.

Phase 3 addresses this limitation directly by constructing dedicated field test leach cells. One cell will receive baseline-blasted ore; the other will receive optimised-blasted ore. Both cells will operate under identical solution application conditions, with results measured over a real leach cycle.

A critical operational learning from Phases 1 and 2 will be implemented in Phase 3: full material traceability. The trial site, like many heap leach operations, used a stockpile system at the crusher where intermittent ore loads were blended across multiple shifts before being placed on the leach pad. This practice severed the direct chain of custody between blast design and pad placement, obscuring the relationship between what was blasted and what was leaching.

For Phase 3, the team will implement rigorous tracking of:

1. Blast parameters applied to each specific ore parcel
2. Ore grade and source location for each parcel
3. Crusher feed sequence and stacking position on the test cell
4. Solution application conditions across the full leach cycle

Preliminary field recovery results are anticipated approximately three months after ore placement on the test pad, though full leach cycle completion may extend this measurement window further.

Blasting as a Value Chain Lever: Rethinking the Economics

The traditional view of blasting in open-pit mining positions it as a cost centre, a necessary operational step evaluated primarily on rock movement efficiency and safety compliance. The Drill to Leach framework challenges this framing fundamentally, repositioning blast design as a value-generation function with measurable financial consequences across every downstream process.

In heap leach operations, the compounding effect of blast decisions is particularly pronounced because there is no milling circuit to partially correct suboptimal fragmentation. The ore goes from the blast directly to the pad. The internal structural properties of the rock at the moment of detonation are essentially locked in for the duration of the leach cycle. Moreover, the relationship between cut-off grade economics and blast-induced recovery improvement means that operations running marginal ore grades may find Drill to Leach disproportionately valuable.

Indicative Value Sensitivity Framework

The following table illustrates the potential economic range of recovery improvement across different operating scenarios. These figures are indicative only and depend heavily on head grade, gold price, and site-specific recovery baselines.

Indicative estimates only. Actual outcomes vary significantly by operation.

Two distinct value streams exist within this framework. The first is straightforward: higher total recovery means more gold extracted per tonne of ore processed, directly improving revenue per unit of mining cost. The second is subtler but equally important: faster recovery reduces the working capital tied up in ore sitting on the pad awaiting target recovery thresholds. Consequently, for operations running large, slow-leaching pads with extended cycle times, the cash flow acceleration benefit of speed-of-recovery improvement can be financially material independent of any change in total recovery. How gold price and miners respond to improved recovery rates also amplifies the commercial case considerably.

Which Operations Are the Best Candidates?

Not every heap leach operation will present an equally compelling case for Drill to Leach. The program is best suited to operations that share certain characteristics.

From a geological standpoint, sites where vertical consistency exceeds lateral variability are particularly well-suited to the stacked-bench trial methodology validated in Phase 2. Understanding the three-dimensional geological variability of a potential trial site is now considered foundational to trial design, a direct product of the Phase 1 experience.

Frequently Asked Questions: Dyno Nobel Drill to Leach

What is the core difference between Drill to Leach and Drill to Mill?

Drill to Mill targets operations with grinding circuits, where the objective is improving throughput, reducing specific energy consumption in grinding, and lowering grinding media wear through better upstream fragmentation. Drill to Leach is engineered specifically for operations with no milling stage. The performance target shifts from external particle size to internal micro-fracture density, because in a heap leach environment it is the internal crack network, not the particle dimensions, that governs cyanide penetration and gold dissolution rates.

Why does Phase 3 require field test pads rather than additional column tests?

Column tests provide controlled, reproducible data but they cannot replicate the full complexity of a working heap leach pad. Variables including solution channelling driven by local compaction differences, spatial variability in ore stacking density, and the hydrodynamic effects of large-scale irrigation systems all influence real-world recovery in ways that bench-scale apparatus cannot capture. The field test pad represents the definitive validation environment, bridging the gap between laboratory proof-of-concept and commercial deployment confidence.

Does the Drill to Leach optimisation require significant changes to existing blast infrastructure?

The optimised design applied in the U.S. trial involved modifications to explosive product, detonator type, subdrill depth, burden-to-spacing ratio, and stemming height. The transition to electronic detonators is a meaningful infrastructure step, but for operations already evaluating this change for independent operational reasons, the upgrade aligns naturally with Drill to Leach trial requirements. It simultaneously delivers vibration management and timing precision benefits, making it an operationally coherent investment.

How should operations interpret the absence of PSD change alongside recovery improvement?

This combination is actually the clearest possible signal that micro-fracturing is the active mechanism. If recovery improved alongside a significant PSD reduction, the cause could plausibly be attributed to finer fragmentation increasing external surface area. However, when PSD remains essentially unchanged while recovery improves and crusher throughput increases, the only consistent explanation is enhanced internal fracture network density. This data pattern is technically more valuable than a result that confounds micro-fracturing with fragmentation change.

The Broader Implication for Heap Leach Industry Practice

The advancement of Dyno Nobel Drill to Leach raises a question that extends well beyond any single trial program. If blast-induced micro-fracturing is a material driver of leach kinetics, and if standard fragmentation analysis systematically fails to measure it, then an unknown proportion of the heap leach industry may be making blast design decisions with an incomplete performance model.

The KPI frameworks that govern most blasting operations are built around lagging indicators: muck pile geometry, crusher throughput, and pad recovery measured weeks or months after the blast event. The Drill to Leach philosophy positions blast design as a leading indicator in the value chain, one that can be engineered proactively and tracked in near real-time as part of an integrated operational optimisation program. In addition, for operations conducting longer-range feasibility work, the definitive feasibility study process should arguably incorporate blast design as a recovery lever from the outset rather than treating it as a secondary variable.

For heap leach gold producers evaluating where marginal improvement dollars generate the greatest return, the blast face may represent the most underleveraged intervention point in the entire recovery system. Teams seeking practical guidance on blast design capabilities and training can also explore Dyno Nobel's drill and blast academies, which provide structured professional development aligned with these emerging optimisation methodologies.

This article contains forward-looking statements and indicative value projections based on trial data from a single U.S. gold operation. Results may vary materially across different geological settings, ore types, and operational configurations. The economic figures presented are illustrative only and should not be relied upon as predictions of outcomes at any specific operation. Readers seeking additional technical perspectives on blast optimisation and heap leach processing may find relevant industry case studies through the Engineering and Mining Journal's Operating Strategies section at e-mj.com.

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