Question 1 of 4: Mine Life-Cycle Stages & Ana Paula Project DCF Analysis

Question 1: Mine Life-Cycle Stages & Ana Paula Project DCF Analysis (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

a) The five stages in the life of a mine

A mining project runs through five broad stages between initial discovery and final walk-away. 1 — Exploration. Regional prospecting followed by progressively more targeted geological mapping, geochemical sampling, geophysical surveys and diamond drilling, aimed at discovering and then delineating a mineralized zone well enough to estimate a resource. 2 — Evaluation and Development. The resource is converted to a mineable reserve through pre-feasibility and feasibility studies (geotechnical, metallurgical, environmental and economic work), the mine and mill are engineered in detail, permits are obtained, and project financing is arranged. 3 — Construction. The bulk of the capital program is spent building the mine access, pit or shaft, processing plant, tailings facility, power and water infrastructure, and completing pre-production stripping/development, so the operation is ready to produce. 4 — Operation (Production). Ore is extracted, processed and sold on a sustained basis; this is the only stage that generates revenue and is where the capital invested in stages 1–3 is recovered and (if the project is economic) turned into profit. 5 — Closure and Reclamation. Once reserves are exhausted, infrastructure is decommissioned, the pit/waste-dump/tailings landforms are re-graded and re-vegetated, water treatment and long-term monitoring commitments are established, and the site is eventually relinquished to a stable, walk-away condition.

b) Typical cash flows through the five stages

Each stage has a characteristic cash-flow signature. Exploration is a small, sustained cash outflow spread over the years it takes to find and delineate a deposit — most exploration projects never reach a discovery, so this spend is high-risk with no assurance of return. Evaluation/Development is a larger outflow: feasibility studies, detailed engineering and permitting are expensive but still produce no revenue. Construction is the single largest cash outflow, concentrated into a short (here, 4-year) capital-intensive window as the mine and mill are built. Operation is the only stage with net cash inflow — revenue less operating cost, sustained for the whole production life — and must be large enough, for long enough, to repay the preceding three stages of outflow and still return a profit. Closure is a final outflow (decommissioning and reclamation cost) with no offsetting revenue. The resulting cash-flow diagram is a deep, widening valley (exploration → development → construction) followed by a sustained plateau of positive cash flow during production, ending in a small terminal dip at closure.

c) “Mines are designed for closure”

This statement means that the end-state landform, water-management and reclamation objectives are built into the mine plan and permit application from the very start of design — concurrently with the pit, waste-dump and tailings engineering — rather than being addressed only after production ends as a separate, bolt-on closure project. It reflects both a regulatory shift (BC's Health, Safety and Reclamation Code and Mines Act permitting now require an approved, funded closure plan before construction is authorized) and an economic one: retrofitting closure onto infrastructure that was never designed for it is far more expensive, and sometimes technically impossible, than designing for it up front. Two examples of this design philosophy: (1) progressive (concurrent) backfilling — waste rock is placed back into mined-out pit areas as mining advances rather than stockpiled separately, so the final void volume, pit-lake flooding risk and long-term slope stability are minimized without a large, separate end-of-life earthmoving campaign; and (2) engineered co-disposal of tailings and waste rock to a stable, self-draining final landform designed from day one (a “walk-away” closure design), which avoids leaving a legacy stand-alone tailings dam that would otherwise require indefinite water treatment and monitoring after mine life ends.

Discounted Cash Flow Analysis — Ana Paula Project

Given. Values interpreted from the press release, with the assumptions stated in the callout below.

Find. (i) the gross and net value of the ore per tonne; (ii) NPV, PVR and before-tax payback period at i = 10%; (iii) a recommendation on whether the project should proceed.

Approach. Value the contained metal at spot price to get the gross (in-situ) value per tonne, apply the metallurgical recovery and deduct the combined operating cost to get the net value per tonne credited to the mine; build the annual before-tax cash-flow timeline (capital outlay, production net cash flow, closure outlay) and discount every year at 10% for NPV and the profitability ratio; track the undiscounted cumulative cash flow for the simple payback period; then judge viability from the sign of NPV/PVR together with the payback profile.

1. Gross (in-situ) value per tonne of ore. Converting each grade to troy ounces per tonne (31.1035 g/oz) and valuing at spot price: $$v_{Au} = \frac{1.56}{31.1035}\times 1450 = 72.71\ \text{US\$/t}, \qquad v_{Ag} = \frac{7.5}{31.1035}\times 28 = 6.75\ \text{US\$/t}$$ $$\boxed{v_{gross} = v_{Au}+v_{Ag} = 72.71+6.75 = 79.48\ \text{US\$/t}}$$
2. Net value per tonne after recovery and operating cost. Applying the assumed 94.5% flotation recovery and deducting the combined US$70/t mining+milling+overhead cost: $$v_{rec} = v_{gross}\times R = 79.48\times 0.945 = 75.11\ \text{US\$/t}$$ $$\boxed{v_{net} = v_{rec}-70 = 75.11-70.00 = 5.11\ \text{US\$/t}}$$ — a thin operating margin, only about 7% of the recovered value, worth flagging before the NPV result even appears.
3. Annual cash flows. Producing the 44.8 Mt reserve over 10 years gives an annual mining/milling rate of $$\dot{T} = 44.8/10 = 4.48\ \text{Mt/yr}$$ so each production year nets $4.48\times 10^{6}\times 5.11 = \text{US\$}22.87\ \text{M/yr}$ before tax.
4. Spread the capital and closure costs over their own periods. The preproduction capital is spread evenly over the 4 preproduction years and the closure cost evenly over the 2 closure years, with production cash flow running years 5–14: capital outlay US$54.75 M/yr (years 1–4), production net cash flow US$22.87 M/yr (years 5–14), closure outlay US$30.0 M/yr (years 15–16).
5. Net Present Value at i = 10%. Discounting each year's cash flow with $PVF_n = (1+i)^{-n}$ and summing (capex negative, production positive, closure negative): $$NPV = -\sum_{t=1}^{4}\frac{54.75}{1.1^{t}} + \sum_{t=5}^{14}\frac{22.87}{1.1^{t}} - \sum_{t=15}^{16}\frac{30.0}{1.1^{t}}$$ $$\boxed{NPV = -\text{US\$}91.3\ \text{M}}$$
6. Present Value Ratio. The present value of the capital invested (years 1–4, discounted the same way) is $PV_{capex} = 54.75\times CPVF(10\%,4) = 54.75\times 3.1699 = \text{US\$}173.5\ \text{M}$, so $$\boxed{PVR = \frac{NPV}{PV_{capex}} = \frac{-91.3}{173.5} = -0.53}$$
7. Payback period (simple, before-tax). Tracking the undiscounted cumulative cash flow: it is US$−219.0 M at the end of year 4, recovers through the US$22.87 M/yr production inflow, and first turns positive at $$\boxed{t_{payback} \approx 13.6\ \text{years from project start}\ (\approx 9.6\ \text{years into production})}$$ However the cumulative position peaks at only about +US$9.7 M (end of year 14) before the two closure years pull it back to about −US$50 M by the end of the project — the payback is real but shallow, and does not survive the closure cost.

iii) Recommendation. On the stated assumptions the project does not clear a 10% hurdle rate: NPV is negative (−US$91.3 M), PVR is negative (−0.53, meaning every dollar of capital invested destroys about 53¢ of value in present-value terms), and while the undiscounted cash flow does eventually recover the initial capital, it does so only after 13.6 years and the gain is then given back by the closure cost. The root cause is visible in step 2: the recovered value of the ore (US$75.11/t) is barely above the US$70/t operating cost, leaving almost no margin to service a US$219 M capital program. Recommendation: do not proceed to mine development on this analysis — unless a more detailed feasibility study can credibly improve metallurgical recovery, lower operating cost, or shows metal prices materially above the press release's assumptions, the project as scoped is not an attractive use of capital at a 10% discount rate.