How many drillholes do I need to upgrade my Inferred Resource? Andrew Fowler Kathy Zunica

How many drillholes do I need to upgrade my Inferred Resource? Andrew Fowler Kathy Zunica

The Idea Overheard in a boardroom in Canada You typically upgrade 30 % of your resource from an in-fill drilling programme - Very experienced geologist

Now that the challenge was accepted Was there actually any truth in the premise? How were we going to isolate the data to ensure we were only looking at in-fill drilling? What sort of factors might influence the success of an in-fill drilling programme? Could we possibly investigate all of these factors? How were we going to measure it?

We needed to focus our attention Could we answer these questions. Do in-fill drilling programmes meet the resource upgrade expectations? Do factors such as the commodity type, change in competent person or resource size influence whether the in-fill drilling programme will achieve the desired outcome? How does the grade change when the resource is upgraded?

The Aim Establish a benchmark for how many drillholes are required to upgrade a desired proportion of a Mineral Resource from Inferred to higher resource categories.

Case Studies Deposit Type Commodity Group Number Shear/Breccia hosted Precious Metal (Shear/Breccia) 12 Shear/Breccia hosted Base Metal 1 Porphyry Base Metal 7 Porphyry Precious Metal (Epithermal/Porphyry) 3 Epithermal Precious Metal (Epithermal/Porphyry) 7 Skarn Base Metal 3 Iron Formation Bulk Commodities 4 Carlin-type gold Precious Metal (Shear/Breccia) 2 Stratiform Copper Base Metal 2 Ultramafic Ni-Cu sulphide Base Metal 2 Iron Oxide Copper Gold Base Metal 1 Mineral sand: Zircon Titanium Bulk Commodities 1 Nickel Laterite Base Metal 1 Pegmatite Lithium Base Metal 1 Phosphate: upwelling type Bulk Commodities 1 Sedimentary Lead-Zinc-Silver Base Metal 1 Volcanogenic Massive Sulphide Base Metal 1

Case Studies

The Method Information Collected Created a giant spread sheet. Comparison of 2 consecutive mineral resource reports. Distilled the following information: Number of drillholes. Grade, tonnes and cut-off grade used for reporting. Reasons for change in classification geological interpretation, estimation method. Competent person.

The Method How to Measure it 2012 estimate 2014 estimate Tonnage (Mt) Ag (g/t) Tonnage (Mt) Ag (g/t) Inferred 4.3 513 5.1 372 Indicated 5.7 702 10.1 511 Indicated proportion 0.64 0.73 proportion change +0.09 Drillhole number 222 262 Increase in drilling 18% Grouped the Measured and Indicated categories together. Used contained metal to determine proportion. Plotted proportion change versus increase in drilling to investigate the relationship between in-fill drilling and resource upgrade.

The Investigation Initial Results

Optimal and Sub-optimal

Commodity Type

Resource Size

Change in Competent/Qualifed Person

Grade change

The Benchmark? Based on the results for the optimal population, if a company wishes to obtain a proportion change of 0.2, the company should increase drilling by 25 %. An optimal drilling programme will upgrade the resource with the least amount of drillholes. If the proposed drill programme is not expected to produce the resource upgrade predicted by the optimal population, it might be pertinent to consider if there is redundancy in the drilling programme. Consultation between the CP/QP and the designer of the in-fill drillhole programme is paramount. Further work is required to confirm the existence of the optimal and sub-optimal populations and investigate other factors that influence the success of in-fill drilling programmes.

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AMC capability and experience AMC Consultants (AMC) is a leading mining industry consultancy, providing a broad range of high-quality, professional services to the global exploration, mining and financial services industries. AMC currently employs more than 170 professional geologists, engineers, metallurgists and support staff working from offices in Australia, Canada, Singapore and the United Kingdom. AMC is a reliable business partner that has built trusted relationships with the minerals sector over 30 years. AMC has completed more than 7,000 assignments for major mining companies and financial institutions in more than 100 countries in Oceania, the Americas, Africa, Europe, Asia, the South Pacific, and countries of the former Soviet Union.

Andrew Fowler PhD, AusIMM CP (Geo) Senior Geologist afowler@amcconsultants.com Kathy Zunica BSc (Hons), MAusIMM Senior Geologist kzunica@amcconsultants.com

GRACIAS.