Interviewer view · keep this screen to yourself

Unit economics of a copper mine

You run the case. Read the prompt, answer questions from the notes below, and share data only when the candidate asks for it or gets stuck. Score at the end.

Case timer

00:00

Target length:

1. Read the prompt aloud

Read it slowly, then pause. Let the candidate ask questions before they structure.

Ridgecrest Copper (a fictional company) runs an open-pit mine in Chile. It processes 25 million tonnes of ore a year at a grade of 0.8 percent copper, with 90 percent recovery. Mining and processing cost USD 24 per tonne of ore. Transport, smelting charges and site overheads add USD 210 million a year. The copper price is USD 9,500 per tonne. What is the cash cost per tonne of copper and the yearly cash margin?

2. Answers to clarifying questions

This case has no scripted clarifying answers. Answer from the prompt, and say "assume what you think is reasonable" if the prompt does not cover it.

3. A model structure

Compare the candidate's structure with this one. A different split can be just as good if it is clean and fits the problem.

Cash margin = copper produced x (price minus cash cost per tonne)
- Copper produced = ore x grade x recovery
- Total cash cost = ore x cost per tonne of ore + other costs
- Cash cost per tonne = total cash cost divided by copper produced

4. The working, step by step

Each step shows how a strong candidate works it out. Share a new fact from it only when the candidate asks or is stuck, and let them do the math: the result in the dark box is what they should reach.

Step 1: Copper produced
What a strong candidate does: 25 million tonnes of ore, 0.8 percent copper, 90 percent recovered.
Copper produced (tonnes): 25,000,000 × 0.008 × 0.9 = 180,000
Step 2: Total cash cost
What a strong candidate does: USD 24 on 25 million tonnes is 600 million, plus 210 million.
Total cash cost (USD million): 25 × 24 + 210 = 810
Step 3: Cash cost per tonne
What a strong candidate does: USD 810 million divided by 180,000 tonnes.
Cash cost (USD per tonne of copper): 810,000,000 ÷ 180,000 = 4,500
Step 4: Yearly cash margin
What a strong candidate does: Margin of 5,000 dollars per tonne on 180,000 tonnes.
Yearly cash margin (USD million): (9,500 - 4,500) × 180,000 ÷ 1,000,000 = 900

The recommendation to listen for

At the end, say: "The CEO walks in. What is your recommendation?"

Ridgecrest should keep the mine running and protect its grade, because it produces 180,000 tonnes of copper at a cash cost of USD 4,500 per tonne, earning about USD 900 million a year at USD 9,500. First, the margin of USD 5,000 per tonne gives a large cushion against a lower price. Second, cost per tonne of copper depends on the 0.8 percent grade and 90 percent recovery, since mining cost is paid per tonne of ore. The risk is a falling grade, which raises cost per tonne. As a next step, add royalties, taxes and sustaining capex before any investment decision.

Score the candidate

Score each criterion from 1 to 5. A 2 or a 4 sits between the descriptions.

This case has no exhibit. Score Exhibit reading on how the candidate used the data you gave them: did they pick out the number that matters and say what it means?

Structuring

1: No clear structure, or a memorized framework that does not fit the problem.
3: A sensible structure, but with some overlap, a gap, or no clear priority.
5: A structure built for this problem, with no overlap and no gaps, a stated hypothesis, and a clear first step.

Math

1: Frequent errors, no units, or needed heavy help to finish.
3: Right answers but slow or messy working, or one error caught late.
5: Accurate and clearly narrated, with units, a sense check, and what the number means.

Exhibit reading

1: Read the chart aloud without finding the number that matters.
3: Found the key number but gave only part of the so-what.
5: Pulled the right number quickly and said what it means for the case.

Synthesis

1: Summarized what was done, with no clear answer.
3: Gave an answer, but with weak reasons or no next step.
5: Answer first, then two or three reasons with numbers, the main risk, and next steps.

Communication

1: Hard to follow: long silences, no signposting.
3: Clear most of the time, with some rambling.
5: Calm and concise, signposted each step, and checked in with the interviewer.

Total

0 out of 25

Score all five criteria to see the band and the feedback template.