1.2 Design Basis & Constraints

The design basis records the objectives, requirements, inputs and assumptions used to develop and check an engineering design. It provides a reference for comparing alternatives and reviewing changes.^[1]

For a mine, that reference must connect the deposit and its setting with a practicable development case. Constraints restrict the available solutions. Some are physical; others arise from applicable permissions, agreements, environmental conditions or project decisions. A coherent basis lets mining, processing and infrastructure teams work toward compatible outcomes while keeping uncertainty visible.

Separate Objectives, Requirements and Assumptions

The following distinctions help a project team explain the status of information it uses:

Confusing these roles can prevent a fair comparison. A preferred access arrangement is not necessarily a fixed requirement. Equally, a favourable cost estimate cannot remove a binding land restriction. The review should identify where a condition comes from, who can clarify or change it, and what evidence would justify reconsideration.

Requirements need an identifiable purpose and a way to check compliance. NASA's systems-engineering handbook connects technical requirements with stakeholder expectations, operational scenarios, interfaces and constraints. That general relationship is useful for mine engineering, although NASA's programme procedures are not mining regulations.^[1]

Define a Complete Development Case

A design basis needs information about the mineralization, extraction approach, processing response and facilities that support them. CRIRSCO's advisory June 2024 reporting template illustrates these connections through its technical-study criteria: mining assumptions, production schedules, ground and water conditions, testwork, infrastructure and closure provisions. The template supports mineral reporting; actual disclosure obligations depend on the applicable national or regional system.^[2]

The emphasis differs between mines. In an open pit, slope conditions, waste movement and access geometry constrain the operating arrangement. Underground, extraction geometry, development access and ventilation or cooling can be decisive. Both cases require a consistent relationship between the material to be mined, the means of extracting it and the facilities needed through time.^[2]

The boundary of the case should also be explicit. Identify facilities included in the project, existing assets assumed to remain available, and services expected from outside parties. A design that relies on an external facility has an interface to resolve even when that facility is outside the owner's construction scope. A short boundary description can prevent a necessary connection or supporting activity from disappearing between discipline estimates.

Connect Production Targets to Operating Conditions

Production assumptions enter the engineering and economic case together. Nell and Burks' mining-study discussion links schedules, grades, recoveries, prices and expenditure timing in the financial model. Its infrastructure discussion also distinguishes project-funded facilities from utility investment recovered through operating charges. A service arrangement therefore influences both the physical design and the economic basis.^[3]

The design basis should make clear what each production quantity describes. A target for saleable product, a plant-feed rate and total material movement answer different questions. For any adopted rate, identify its measurement point, time basis, material condition and assumed operating circumstances. These are practical safeguards against comparing quantities that look similar but represent different work.

Consider a proposed increase in plant feed. The connected review asks whether the mine can expose and deliver the material, whether development or stripping must change, and whether the supporting services can accommodate the revised case. If one discipline retains the previous production profile, its work may be internally consistent yet incompatible with the rest of the study.

The relevant conditions also change through the mine life. Initial production, an expansion and the final extraction period may require different arrangements. A design basis can distinguish facilities required at the outset from later additions, including the assumptions on which those additions depend. Mine life then provides a planning horizon for those commitments, rather than a single number applied unchanged to every asset.

Make Constraints Specific to Place and Time

Environmental and social information affects the definition of a feasible project. For projects within its financing framework, IFC's 2012 Performance Standard 1 links assessment scope to project type, scale and location, and calls for suitable baseline information. Its area-of-influence concept also includes relevant associated facilities and impacts beyond the immediate site. This provides a reason to examine connected corridors and facilities when defining the project boundary.^[4]

A spatial limit should be supported by the information needed to use it: location, reference system, origin, scope and review status. A mapped feature, an interpreted hazard zone and a confirmed restriction have different evidential and decision-making roles. Recording those differences allows the design team to act on an established limit while investigating an unresolved one.

Timing matters as much as location. An existing service might become available after the period in which the mine plan needs it. A location that suits a temporary construction use could obstruct a later permanent facility. These situations require a sequence of compatible arrangements, rather than a single layout that ignores when each area or service is occupied.

Closure objectives should enter this discussion early. Brock, Weeks and Heyes describe integrated closure planning as an iterative process informed by a developing knowledge base, stakeholder engagement and intended land use after mining. The resulting objectives influence the work to be provided for during operation as well as at closure. Closure cost estimates and responsibilities also need review as the mine changes.^[5]

Match Confidence to the Decision

The basis should show which inputs are observed, which are interpreted and which remain assumed. The practical test is whether the available evidence supports the commitment being considered. A preliminary comparison can retain competing possibilities; a decision that fixes a major interface needs a clearer account of what could invalidate it.

This does not mean collecting every possible measurement before progressing. Additional work should be linked to a decision: would it change the preferred arrangement, resolve a decisive constraint or materially change the confidence in the proposed commitment? Where it would not, refining a minor parameter may be less useful than resolving an uncertain dependency between systems.

Reviews also need consistent economic conventions. Nell and Burks identify taxes, prices, production and operating-cost information among financial-model inputs. A comparison should preserve an identifiable set of assumptions so that a change in engineering scope is distinguishable from a change in commercial expectations.^[3]

Revise the Basis as a Connected Whole

As a qualitative example, suppose an external power connection is now expected later than the design assumed. The immediate change concerns one service date. Its consequences may include the development sequence, construction services, commissioning arrangements and production timing. A revised cost estimate alone would not show whether the resulting operating case remains coherent.

The review should identify the affected requirements, analyses, schedules and decisions; record the revised assumption; and establish which work must be reconsidered. NASA's requirements-management guidance emphasizes traceability and evaluation of the consequences of changes before their approval. A maintained baseline gives this review an identifiable starting point.^[1]

An effective design basis remains concise enough to use while retaining links to the supporting evidence. Its value is the ability to explain why the current design is appropriate, where its limits lie and which changes require another engineering decision.