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Assessing aggregate deposits

January 5, 2023  By Bill Gowdy

One More Load: Proper procedure is key for producer success

Proper assessment of aggregate deposits is fundamental to the viability of aggregate companies, long-term sustainability and, best utilization of this rapidly depleting resource. Proper resource assessment drives all business evaluation for an operation, and it is critical to have sufficient fundamental information on a deposit to de-risk decision making and improve profitability.

Most aggregate deposits, by nature, are geometrically complex.

As most operators can attest, when opening a pit face, deposits are typically not continuous flat stratigraphy but are a variable array of irregular swirling and cut masses of sand and gravel. One of the biggest deficiencies in aggregate assessment is having the appropriate density of test hole data to properly understand a deposit configuration. For perspective, one test hole per hectare is a hole spacing every 100 metres (328 ft.).

While there is no hard and fast rule to the number of test holes required, it is dependent on the geological complexity of a deposit. Something like a glacial outwash deposit, or fluvial (river lain) deposit can be more continuous requiring less information.


However, a deposition taking place in proximity to a glacial source can have extreme variability in the geometry, grain size distribution and require substantially higher density of information to assess. Having an understanding of the geological deposit environment in which a particular deposit is formed will assist in guiding the amount of testing required.

Test hole logging and documentation is also critical of a deposit. Ensure that the person supervising a test hole program has sufficient expertise in assessing the material (knowledge of basic rock types, what materials are deleterious to aggregate production, etc., are key).

Field logging can be quite subjective (one person’s good material, may be classified by another person’s mediocre aggregate).

In addition to field logging, analytical information should be collected when conducting test holes as lab data removes subjectivity from the assessment process. Samples collected when completing test holes can be used for further work such as sieve analysis, petrographics, alkali reactivity, abrasion resistance, soundness, impurities, density, and absorption etc., depending on the application the deposit is intended.

Sufficient testing data aids in providing a better resource estimate (knowing how much material an operation has), and in providing a better prediction on operating costs: improved estimates of stripping and crushing costs, what material can be produced, and ultimate mine life. Ideally, if an aggregate resource is a premium material, a company will want to reserve that material for its highest and best use, both maximizing profitability and reserving that material for its optimal and best available usage.

Industry is seeing protracted timelines in securing regulatory approvals and it is becoming increasingly complex and expensive. It is best to fully understand the geometry of a deposit so that a company is going through an application process once – not amending an approval several times throughout the life of an operation because a deposit configuration was not initially understood fully.

Proper aggregate testing information upfront will aid in guiding the regulatory approval submission and will also provide a lot more credibility to a company, with regulators and the public.

There is an enormous investment in an aggregate business. The critical first step is ensuring that a deposit is assessed sufficiently.

Bill Gowdy is the technical director of aggregates for SLR Consulting. He has 35 years of experience in the geology and environmental fields, including 22 years based in Edmonton managing aggregate resource assessments, geological modelling, permitting, reclamation, environmental management systems, groundwater monitoring, community relations and biodiversity projects.

One More Load is a recurring column in Rock to Road magazine.

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