Mineable Inventory

Mineable inventory is used here as an engineering term for material selected for extraction under a stated mine design and set of assumptions. It connects the geological model with quantities that a production plan can organize, allowing for practical extraction geometry, exclusions, mining losses and dilution. Its meaning depends on the stated reference point: material selected in situ, material expected to be recovered by mining, and material delivered to a plant are different quantities.

This terminology does not establish a Mineral Resource or Mineral Reserve category. Under the Australasian JORC Code, 2012 edition, internal tonnage and grade estimates outside its reporting categories may support evaluation, but cannot simply be presented as additional public reporting categories. An inventory therefore needs both an engineering definition and a separate statement of any applicable reporting classification.^[1]

Define the Inventory Before Counting It

The inventory boundary determines what the total can answer. A design inventory might support comparisons between extraction layouts. A schedule inventory identifies material assigned to particular periods and destinations. An operational inventory may describe material already broken or stockpiled. Combining these without distinguishing their states can count the same material repeatedly.

A useful inventory statement identifies:

• Purpose and date: the decision being supported and the date to which depletion and available information relate.
• Spatial basis: the geological model version, mining shapes, exclusions and coordinate system.
• Material basis: tonnes and grade or quality, density and moisture conventions, and whether dilution and losses are already included.
• Reference point: the physical stage represented, such as selected in situ material or plant feed.
• Eligibility and status: geological confidence categories, selection criteria, destinations and remaining engineering conditions.

These are proposed accounting fields, not a new classification system. Their practical test is whether another engineer could reproduce the total and explain why a particular parcel is included. A number without this basis cannot establish whether an apparent increase represents new geological information, a wider excavation, additional dilution or a changed reporting boundary.

Translate Geological Shapes into Mining Shapes

A block selected by a grade or value criterion is not automatically an independently extractable parcel. The CIM 2019 best practice guidelines connect reserve estimation to mine designs and schedules, with geotechnical conditions influencing excavation geometry. Practical mining shapes can include lower-grade material that cannot be separated. Underground stopes may extend beyond mineralized outlines; open-pit extraction can incorporate contact dilution and internal waste. The same guidelines distinguish mining losses from processing recovery and identify material left for stability or operational reasons as possible losses.^[2]

The inventory calculation should expose the decisions between the model and the excavation. For each mining unit, ask whether the material is accessible, whether the proposed extraction boundary is physically achievable, and what must remain unmined. Keep excluded material identifiable so that a later design change can be evaluated without rebuilding its history from a single reduced total.

An exclusion and a loss allowance need distinct accounting roles. If a pillar has already been removed from the selected shape, subtracting it again through a mining-loss factor counts the exclusion twice. A design that includes the pillar must identify where its non-extraction enters the calculation. Each exclusion needs one complete accounting treatment.

The underlying resource classifications should remain visible through these transformations. Geometrical selection, reblocking, computational resampling of an existing model and scheduling assignments do not themselves generate new geological evidence. An internal planning scenario containing material of different confidence levels needs identifiable components; the inventory label cannot resolve their different suitability for the decision being made.

Account for Loss and Dilution on a Consistent Basis

Mining loss removes selected material from recovery. Diluting material is mined with the selected ore, but internal waste may already be represented in the selected shape and grade. Ebrahimi's open-pit analysis distinguishes internal from external dilution and retains diluent grade in its balance.^[3]

For one selected parcel, a transparent accounting identity is:

T_feed = T_selected - T_loss + T_added
M_feed = M_selected - M_loss + M_added
g_feed = M_feed / T_feed

Here T is dry material mass in tonnes, M is one contained commodity's mass in tonnes, and g_feed is its mass fraction. Subscripts identify selected material, mining losses, additional diluent and resulting plant feed. The balance assumes a common parcel boundary, T_feed > 0, no inventory accumulation, and delivery of all retained material to the plant without other diversions. Sorting rejects and other diverted streams require separate terms. Material already in T_selected must not be added again; lost material and diluent may have different grades. The grade relationship follows Ebrahimi's weighted-mass principle.^[3]

State the denominator of a dilution percentage: initial selected tonnes and final diluted tonnes give different ratios. Retain the underlying masses when transferring assumptions between models; an unidentified denominator prevents reproduction of the calculation.

Connect Inventory with Destinations and Time

An inventory has spatial content; a schedule adds timing and prerequisites. Consider a conceptual comparison between two inventories containing equal plant-feed tonnes. In one, the material is accessible through existing workings. In the other, much of it depends on an unfinished access connection. The totals match, but their ability to support the next production period does not. The difference is revealed by readiness and dependency information, not by another aggregate tonnage.

For a planning application, distinguish material available within the period, material dependent on identified development, and material retained only in an alternative scenario. Keep the scenario identities separate: two alternative extraction layouts cannot both contribute their overlapping tonnes to one production schedule.

Destination is equally important. Material assigned to immediate treatment, a blending stockpile or a deferred stockpile represents different delivery commitments. A schedule should demonstrate when deferred material can be reclaimed and processed. If the plan has no remaining treatment capacity, calling that material future plant feed conceals an unresolved assumption. This is a planning consistency check; it does not by itself decide public reporting eligibility.

Keep Stockpiles and Reporting Totals Distinct

JORC 2012 clause 41 applies resource and reserve criteria to stockpiles and other previously mined material; physical accessibility alone does not establish economic extraction. It includes underground broken ore within its stockpile discussion and separates material already undergoing processing. Clause 36 also requires clarity about whether Resources include the material converted to Reserves and prohibits adding the two reported estimates into one combined figure.^[1]

For an internal inventory register, assign each physical parcel one location and material state at the accounting date. A transfer from a stope to a stockpile changes that state; it does not create additional material. When the stockpile is reclaimed, its decrease and the receiving stream's increase should refer to the same transfer. Keep revisions to estimated quantity or quality identifiable separately from physical movements.

Macfarlane's reconciliation framework follows material between defined measurement boundaries, including mine-to-plant transfers and stockpiles. It calls for explicit stocktake methods, inventory measurements, control points and an auditable record of material movement. These principles support comparison of like quantities over matched periods, rather than treating every disagreement as a geological-model error.^[4]

Revise the Inventory Without Losing Its History

When totals change, preserve the previous basis and distinguish depletion, model updates, revised designs, changed loss or dilution assumptions, and destination changes. These explanations answer different engineering questions. More tonnes caused by additional diluent do not establish more valuable mineralization; fewer available tonnes caused by an access delay do not necessarily indicate a geological loss.

As a qualitative example, suppose new mapping changes a proposed stope boundary. Re-evaluate the selected shape and its contained commodity, identify any changed exclusion, and check which dilution allowance already captures the boundary change. Then update dependent development and delivery assignments. Record the changes against the earlier version so that their combined effect remains traceable. The inventory becomes useful when its components explain the plan, rather than merely supply a headline total.