Optimising concentrate specs over the LOM:

A Whittle SIMO case study

Presented by: Olga Abdrashitova,Mining Engineer, Technical Services Group

Mt Carlton Overview

Evolution Ownership 100%

Location 150km south of Townsville, QLD

Production commenced July 2013

Design treatment capacity of 800ktpa

Ore Reserves (Dec 2017) 4.50Mt @ 4.92g/t gold

Owner miner since 2015

Mine planning software Surpac, MineSched, Whittle, Leapfrog

Mr Carlton Overview - Geology

Geology High‐sulphidation epithermal style deposit  Arsenic sulphides and some native gold (within pyrite)Contained Metals Gold, silver and copperProcessing Method Crushing, grinding and bulk sulphide flotation to produce a polymetallic concentrate

Scheduling Task

Compare various schedule options and suitable mining capacities for: 2 Open Pit Stages & UG 3 Open Pit Stages with no UG

Test each schedule under different concentrate payabilityscenarios:HG Con MG Con LG ConVariable payability over the LOMPayability specs are based on Au, Cu, Ag, As

Tool utilized: Simultaneous Optimization – SIMO

GEOVIA Whittle advanced Strategic Scheduling software Optimises inputs simultaneously over life of mine Maximises the value (NPV) under given constraints

SIMO InputsFinancials Prices & CostsProcessing Process recoveries Concentrate specs (blending constraints) Concentrate PayabilitiesMining Schedule Quarterly Schedule Pit Stage designs Au grade bins same as material classes Base Mining & Process Capacity Capex & start date of increasing mining capacity Vertical Advance Rate UG Stope sequence & Start date 

Challenge 1 – Blending Scenario Limitation

Whittle interface only allows for either Extractive or Bulk Blending

Extractive Blending:min-max constraints on input grades prior to processing

Bulk Blending:min-max constraints on output product grades, no processing(DSO bulk products only)

Blending Scenario Limitation

Concentrates involve both processing AND product blending based on output grades. Workaround: pre-calculate concentrate grades for each as block model elements

and use as extractive scenario input grades:

Issue: Discrepancy between pre-calculated and actual output concentrate grades:

block1 block2 average block1 block2 averageAU, g/t 2 10 6 6 10 8S, % 4 6 5 12 6 9AU Con grade calc (input to blend) 29 78 53 20 78 49AU flotation output, gram 1.59       7.65       9.24          4.5        7.7         12.2         Concentrate tonnes 0.05       0.10       0.15          0.2        0.1         0.33         AU Con grade recalc (output con grade) 60 37

Similar S grades High and low S grades

Challenge 2 – OP & UG hybrid scheduleWhittle is an open pit only strategic scheduler Solution Convert UG Schedule Stope sequence into an ASCII model Use as a separate Mine Add UG Mining costs as extra ‘processing costs’LimitationNo flexibility in UG stoping sequence

= Stope 1= Stope 2

Challenge 3 – continuity of UG contribution

UG inventory is randomly mined over the LOM to optimise the value – not sustainable due to associated fixed costs

Solution Use CAPEX optimisation to ‘buy’ sustaining capex as mining capacity for a certain period, then ‘expire’ the capacity by raising the capex cost later:

= Stope 2

Challenge 4 – Variable payability concentrate

Payability, i.e. price adjustment is applied per output element rather than blend feed:

Solution Use payability as process recovery*, use separate process method for each concentrate blend/payability, create a process group for process capacity limit:

= Stope 2

*This will reduce output metal, keep this in mind when re‐calculating output concentrate grade

Scenario outputs summary - Cashflow Comparison

Example Schedule Output: Variable Concentrate, OP&UG Scenario

Note: This is a high level strategic example only and doesn’t reflect and actual LOM schedule

*Process feed excludes existing stockpiles

Conclusions SIMO is a useful tool for high level strategic schedules that

involve concentrates production, it allows to:Assess different concentrate spec and payability options Assess various pit staging and sequencing optionsOptimise mining capacity using capex optimisationPossible to include UG feed (limited application)

Suggestions: Enable the 3-step ‘Processing > Blend feed > Product’ option

rather than 2-step Bulk or Extractive blending – concentrates require both! Additional flexibility to ‘pushback’ sequencing would give more

freedom to UG sequence (also useful for laterite deposits)

Other tips

Collaboration is the key!

Talk to the Metallurgist, Geologist, Geotechnical engineer,

Mine Manager, Commercial Manager, GM

Keep everyone in the loop

Question everything

Don’t assume, try all What If’s