Gemstone Production Records, Recovery Calculations and Operating Costs | Level 2 Lesson 9

Level 2 · Lesson 9
Complete Gemstone Mining and Extraction Learning Program
Suggested study: 60–90 minutes, including the exercise.

Go to exercise · Go to quiz · Continue learning

In this lesson — open the contents
  1. At a glance: Choose the right denominator
  2. Learning outcomes
  3. 2.9.1 Record material and time consistently
  4. 2.9.2 Recovered grade
  5. 2.9.3 Recovery efficiency and mass yield
  6. 2.9.4 Weighted results and balances
  7. 2.9.5 Throughput and downtime
  8. 2.9.6 Costs and interpretation
  9. Illustrated learning guide
  10. Practical learning exercise
  11. Review points
  12. Lesson summary
  13. Practice quiz: 10 MCQs
  14. Assignment
  15. References and further reading

Good production records turn observations into useful indicators. Each indicator needs a clear numerator, denominator, unit and time period. Similar-looking percentages can mean very different things.

At a glance: Choose the right denominator

01 Recovered gradeRecovered carats ÷ feed mass
02 Test recoveryRecovered test items ÷ introduced test items
03 Operating cost per caratIncluded period costs ÷ recovered carats

Key idea: Every performance number needs units, a defined basis and a statement of exclusions.

Learning outcomes

  • Convert grams, carats, kilograms and tonnes.
  • Calculate recovered grade, mass yield and controlled recovery.
  • Use weighted totals correctly.
  • Interpret throughput and costs without promising profitability.

2.9.1 Record material and time consistently

A daily record should identify date, work area, material batch, feed quantity, processed quantity, recovered targets, rejects, useful output, downtime and measurement method. Use dry or wet mass consistently and state the basis. Volume requires a suitable density basis before conversion to mass.

One metric tonne is 1,000 kg; one kg is 1,000 g; one carat is 0.2 g. Therefore 10 ct is 2 g. Check that a balance and its precision are suitable for the actual task. Excessive decimal places do not create accuracy.

2.9.2 Recovered grade

Recovered grade is target output divided by the amount of feed processed, on a stated basis. A fictional sample yielding 12 ct from 60 kg has recovered grade 12 ÷ 60 = 0.20 ct/kg, equivalent to 200 ct/t.

This describes those tests under those conditions. It is not automatically an in-situ grade, a representative deposit grade or a reserve. It includes the effects of the recovery method and any losses in that trial.

2.9.3 Recovery efficiency and mass yield

Recovery compares recovered target material with the target originally present or independently estimated. In a controlled exercise, 18 ct recovered from a known starting 24 ct is 75% recovery by target mass. The independent starting amount is essential.

Mass yield compares a specified product mass with feed mass. If 2 kg of concentrate comes from 100 kg of feed, concentrate mass yield is 2%. That does not mean 2% gemstone recovery. The concentrate may contain non-target material.

2.9.4 Weighted results and balances

Sample A produces 5 ct from 20 kg, while B produces 3 ct from 60 kg. Combined recovered grade is total output divided by total feed: 8 ÷ 80 = 0.10 ct/kg. The unweighted average of 0.25 and 0.05 is 0.15 ct/kg and is wrong for the combined feed.

A mass balance accounts for all measured streams on compatible bases. For a dry teaching example, 100 kg feed equals 2 kg concentrate plus 97 kg rejects plus 1 kg unaccounted. The discrepancy is 1%; investigate weighing, retained material and handling losses rather than assuming its cause.

2.9.5 Throughput and downtime

Distinguish scheduled hours from operating hours. If 12 tonnes are processed during 6 actual operating hours within an 8-hour shift, operating throughput is 2 t/h. Average output over the scheduled shift is 1.5 t/h. Both can be valid when labelled correctly.

Operating-time fraction in this simplified record is 6 ÷ 8 = 75%. Formal availability and utilization definitions can differ between organizations, so define the terms before comparison. Do not multiply inconsistent indicators and call the result a standard performance measure.

2.9.6 Costs and interpretation

If the fictional shift has recorded operating costs of PKR 90,000 and produces 30 saleable carats, the recorded operating cost is PKR 3,000 per saleable carat. State what is included and excluded. This is not necessarily a fully loaded cost.

Revenue depends on quality distribution, actual selling prices, fees and sale conditions. Unsold stock is not cash revenue. A low cost per carat does not prove profit, and a few valuable stones can make a short period unrepresentative. Use scenario analysis and transparent records.

Illustrated learning guide

1. Feed
What quantity and measurement basis?
2. Output
Target, concentrate or saleable product?
3. Time
Operating hours or scheduled hours?
4. Indicator
Formula, units, limitations and decision.

Always name the numerator and denominator. The same dataset can support several different, correctly labelled indicators.

Practical learning exercise

Recalculate each worked example independently with a calculator. Make a table containing formula, substituted numbers, answer, unit and one interpretation limit. Use only the fictional datasets supplied.

Review points

  • Separate observations, assumptions and interpretations.
  • State units, method, sample context and limits before using a result.
  • Field and equipment competence require suitable supervised assessment.

Lesson summary

Recovered grade, recovery efficiency and mass yield differ. Combine unequal samples with weighted totals. Define time and cost boundaries, investigate discrepancies and separate indicators from profit claims.

Practice quiz: 10 MCQs

Select one answer for each question and press “Check my answers.” This self-check collects no name or email and does not verify professional competence.

1. 10 ct equals:

2. 12 ct from 60 kg gives:

3. 0.20 ct/kg is equivalent to:

4. 18 ct recovered from known 24 ct is:

5. 2 kg concentrate from 100 kg feed gives:

6. 5 ct/20 kg and 3 ct/60 kg combine to:

7. 12 t in 6 operating hours gives:

8. 12 t over an 8-hour shift gives:

9. PKR 90,000 divided by 30 saleable ct gives:

10. A low operating cost per carat alone proves:

Answer key and explanations
  1. B. 10 × 0.2 g = 2 g.
  2. C. 12 ÷ 60 = 0.20 ct/kg.
  3. D. Multiply by 1,000 kg per tonne.
  4. A. 18 ÷ 24 × 100 = 75%.
  5. B. This ratio compares concentrate mass with feed mass.
  6. C. (5 + 3) ÷ (20 + 60) = 0.10 ct/kg.
  7. D. 12 ÷ 6 = 2 t per operating hour.
  8. A. 12 ÷ 8 = 1.5 t per scheduled hour.
  9. B. 90,000 ÷ 30 = 3,000 per saleable carat.
  10. C. Revenue, other costs and uncertainty must also be assessed.

Assignment

Prepare a one-shift production sheet with compatible quantities, a balance, operating and shift throughput, recovered grade and recorded cost per saleable carat. Include one uncertainty and one check for each indicator.

References and further reading

Sources provide subject background. Cases, numbers, exercises and illustrated guides are course-created teaching material unless stated otherwise. International guidance is not a substitute for current local requirements, manufacturer instructions or professional design.

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