Reserve Estimation in Mining

📘 Reserve Estimation 

 1. Introduction

• Reserve estimation means calculating the quantity and quality of mineral/coal present in a mine.
• It is the basis for mine planning, feasibility studies, and statutory reporting.
• Correct reserve estimation ensures safe, economic and scientific mining.

2. Basic Terms

• Resource: Total mineral present in nature (economic + uneconomic).
• Reserve: That part of resource which is economically mineable with current technology & legislation.
• Tonnage Factor: Volume (m³) to tonnage (tonnes) conversion using density or specific gravity.
• Grade: Average quality of ore (e.g., % Fe in iron ore, calorific value in coal).

3. Classification of Reserves (A) Indian System (Coal/Metal Mines)

1. Proved Reserves – High confidence, confirmed by detailed drilling, sampling, exposure in mine.
2. Probable Reserves – Reasonably assumed from limited boreholes or sampling.
3. Possible/Inference Reserves – Based on assumptions, least reliable.

(B) International (UNFC / JORC)

• Measured → Indicated → Inferred (similar to Proved → Probable → Possible).

👉 Exam Tip: Proved = Highest confidence, Inferred = Lowest confidence. 4. Factors Affecting Reserve Estimation

• Size, shape & geometry of deposit.
• Sampling density (number & spacing of boreholes).
• Geological complexity (folds, faults, intrusions).
• Specific gravity/density of mineral.
• Accuracy of survey and borehole logs.

5. Methods of Reserve Estimation (A) Geometrical/Conventional Methods

1. Cross-Section Method
• Area of ore in different vertical sections × Average strike length.
• Best for coal seams with uniform thickness.
2. Polygon Method
• Each borehole surrounded by polygon → ore assigned equally.
• Quick but less accurate.
3. Triangular Method
• Triangles drawn between 3 boreholes → reserves within triangle calculated.
• More accurate than polygon.
4. Block Method
• Orebody divided into regular blocks, each block calculated separately.
• Used in mine planning.

(B) Mathematical/Statistical Methods

1. Inverse Distance Method (IDW)
• Nearby samples have more influence than distant ones.
2. Geostatistical Methods (Kriging, Variogram analysis)
• Most advanced & accurate, used in modern software (Datamine, Surpac).

6. Coal Reserve Estimation (Special Points)

• Specific Gravity (G) of coal needed for weight conversion.
• Formula:

Tonnage=Area(m2)×Thickness(m)×SpecificGravity×1,000Tonnage = Area (m²) × Thickness (m) × Specific Gravity × 1,000Tonnage=Area(m2)×Thickness(m)×SpecificGravity×1,000

• Thickness of seam = measured at true dip (not apparent dip).
• Corrections required for geological losses (faults, washouts, dykes).

7. Practical Considerations in Reserve Estimation

• Borehole log accuracy → Coal seams, band thickness, partings.
• Sampling → Proper channel/bituminous sampling.
• Safety factor → Always reduce reserves by 10–15% for losses in coal mines.
• Statutory reporting → As per Indian Bureau of Mines (IBM) & CMPDI formats.

8. Importance for DGMS Exam

• Direct questions often asked:
• Which method suits uniform coal seams? (Cross-section)
• Which reserves are least reliable? (Possible/Inferred)
• Formula for converting volume to tonnage.
• Practical viva may include:
• Demonstration of borehole correlation.
• Explaining reserve calculation using borehole data.

9. One-Line Key Takeaways

• Reserve = Economically mineable resource.
• Proved > Probable > Possible.
• Cross-section method → coal seams.
• Polygon method → fast, less accurate.
• Triangular method → more accurate than polygon.
• Inverse distance → nearer points matter more.
• Geostatistics → most advanced.
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  Reserve Estimation — 30 MCQs with memory hacks (DGMS exam style)

Q1  The primary aim of reserve estimation is to determine:

A) Mine ventilation needs
B) Quantity and quality of mineral economically extractable
C) Number of workers required
D) Market price of mineral
E) Transport routes
Answer: B — Reserves = how much + what quality can be mined.
Memory hack: Q+Q → Quantity + Quality (reserves = Q+Q).

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Q2 Which category has the lowest confidence?

A) Proved
B) Indicated
C) Inferred
D) Measured
E) Probable
Answer: C — Inferred = least reliable data.
Memory hack: Inferred = Iffy (lowest confidence).

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Q3 Which category has the highest confidence?

A) Indicated
B) Probable
C) Proved
D) Inferred
E) Possible
Answer: C — Proved = highest certainty (measured data).
Memory hack: Proved = Professional certainty.

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Q4 The method dividing deposit into triangles between boreholes is:

A) Cross-sectional
B) Polygonal
C) Triangular
D) Block method
E) Kriging
Answer: C — Triangular uses triangles for interpolation.
Memory hack: Triangular → Triangle between three boreholes.

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Q5 Area = 0.5 km², thickness = 4 m, density = 1.5 t/m³. Reserve = ?

A) 2 Mt

B) 3 Mt

C) 4 Mt

D) 5 Mt

E) 6 Mt


Answer: B — 0.5×1,000,000×4×1.5 = 3,000,000 t (3 Mt).
Memory hack: km² → multiply by 1,000,000; 0.5×4×1.5 = 3 → 3 Mt.

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Q6 Why prefer weighted average over simple arithmetic?

A) Easier
B) Equal weight to samples
C) Considers thickness/area influence
D) No data needed
E) Ignores grade
Answer: C — Weights reflect thickness/area impact on grade.
Memory hack: Weight = Worth — thicker/wider samples carry more worth.

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Q7 Borehole spacing 1200 m indicates which category?

A) Proved

B) Indicated

C) Inferred

D) Probable

E) Possible


Answer: C — 1200 m spacing → inferred resource.
Memory hack: 1.2 km = Inferred (1.2 → Inferred).

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Q8 Main difference between geological and mineable reserves is:

A) Dip & strike only
B) Grade variation only
C) Losses & dilution considered in mineable
D) Seismic data
E) Ventilation design

Answer: C — Mineable = geological minus losses & dilution.

Memory hack: Mineable = Minus losses (both start with M).

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Q9 Which method uses polygons of influence?

A) Cross-sectional

B) Block

C) Polygonal

D) Kriging

E) Triangular


Answer: C — Polygonal method assigns area to each borehole.
Memory hack: Polygon = Polygonal (each borehole gets a polygon).

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Q10 Which Act mainly governs reserve reporting in India?

A) Mines Act 1952

B) MMDR Act 1957

C) CMR 2017

D) MMR 1961

E) DGMS circulars


Answer: B — MMDR Act (1957) for mineral reporting & regulation.
Memory hack: MMDR = Mineral Management & Data Reporting (think reporting).

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Q11 Thicknesses 2 m (18%) and 4 m (28%). Weighted average ash % = ?

A) 18%

B) 22%

C) 24.67%

D) 26%

E) 28%


Answer: C — ((2×18)+(4×28))/6 = (36+112)/6 = 148/6 = 24.666… ≈ 24.67%.
Memory hack: Total weight / total thickness — do quick multiply & divide.

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Q12 Boreholes near suspected waterlogged workings must be spaced at:

A) 3 m

B) 6 m

C) 9 m

D) 12 m

E) 15 m


Answer: B — Spacing ≤ 6 m (CMR requirement).
Memory hack: Water danger → 6 (think “six for safety”).

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Q13 Advance boreholes must be kept how far ahead of the face?

A) 1 m

B) 2 m

C) 3 m

D) 4 m

E) 5 m


Answer: C — 3 m ahead of the working face.
Memory hack: 3 ahead — three is safety step.

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Q14 Typical bulk density range for metallic ore:

A) 1.0–1.5 t/m³

B) 2.5–3.0 t/m³

C) 3.5–4.0 t/m³

D) 4.0–5.0 t/m³

E) 1.8–2.0 t/m³


Answer: B — Ore ~2.5–3.0 t/m³.
Memory hack: Ore ≈ 2.5–3 (ore heavier than coal).

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Q15 Most accurate statistical estimation method:

A) Arithmetic average

B) Weighted average

C) Inverse distance

D) Kriging

E) Polygonal


Answer: D — Kriging (geostatistics) uses spatial correlation.
Memory hack: Kriging = King of geostatistics.

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Q16 Mineable = 6 Mt. Losses = 10%, dilution = 5%. Geological reserves = ?

A) 6.5 Mt

B) 7.0 Mt

C) 7.0588 Mt

D) 7.5 Mt

E) 8.0 Mt


Answer: C — Geological = 6 ÷ (1−0.10−0.05) = 6 / 0.85 = 7.0588 Mt.
Memory hack: Divide by 0.85 (1 − total loss) → 6/0.85 ≈ 7.06.

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Q17 Which method is used heavily in modern mine software?

A) Cross-section

B) Block method

C) Kriging

D) Polygonal

E) Triangular


Answer: C — Kriging + block modeling integrate in software.
Memory hack: Modern = Komplicated → Kriging.

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Q18 Safety barriers affect which reserve count?

A) Geological reserves

B) Mineable reserves

C) Indicated reserves

D) Measured reserves

E) Resources


Answer: B — Barriers reduce what can actually be mined.
Memory hack: Barrier = Blocked mineable.

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Q19 Best source to correlate seams across area:

A) Cross-section maps

B) Borehole logs

C) Seismic surveys

D) Pit mapping

E) Resistivity survey


Answer: B — Borehole logs give direct seam data for correlation.
Memory hack: Logs = Real record (trust borehole logs).

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Q20 Mineable reserves are normally reported in:

A) m³

B) tonnes

C) % grade

D) kg/m²

E) MT/hr


Answer: B — Tonnes (or million tonnes).
Memory hack: Reserves = Rupees? No — Tonnes.

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Q21 Cross-sectional method best suits:

A) Steep seams

B) Shallow seams

C) Complex folds

D) Flat tabular deposits

E) Irregular ore bodies


Answer: D — Flat tabular bodies give simpler cross-sections.
Memory hack: Cross-section → think flat slice.

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Q22 Why triangular method is preferred to polygonal?

A) Fewer boreholes needed

B) Less math

C) More accuracy

D) No survey required

E) No samples needed


Answer: C — Triangular interpolation reduces local error.
Memory hack: Triangles = tighter fit between points.

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Q23 “Indicated resource” confidence is:

A) Low

B) Moderate

C) High

D) None

E) Variable


Answer: B — Indicated = moderate confidence.
Memory hack: I = Indicated = Intermediate confidence.

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Q24 Area = 2 km², thickness = 4 m, density = 1.5 t/m³. Reserve = ?

A) 8 Mt

B) 10 Mt

C) 12 Mt

D) 15 Mt

E) 18 Mt


Answer: C — 2,000,000×4×1.5 = 12,000,000 t = 12 Mt.
Memory hack: 2×4×1.5 = 12 → add million = 12 Mt.

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Q25 Seam = 2 Mt with 30% ash. Quantity of clean coal (~non-ash) = ?

A) 0.6 Mt

B) 1.0 Mt

C) 1.4 Mt

D) 1.6 Mt

E) 2.0 Mt


Answer: C — Non-ash = 70% of 2 Mt = 1.4 Mt.
Memory hack: 100−ash% = clean% → 70% × 2 = 1.4.

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Q26 Proved reserves are derived from which resource class?

A) Inferred

B) Indicated

C) Measured

D) Possible

E) Probable


Answer: C — Proved ← measured resource.
Memory hack: Measured → Proved (measure = prove).

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Q27 Proving waterlogged old workings by boreholes is specified in:

A) MMR 1961

B) CMR 2017 Reg.127

C) Mines Act 1952

D) IBM rules

E) DGMS circular


Answer: B — CMR 2017 Reg.127 (borehole proving for inundation).
Memory hack: CMR 127 → think Careful Mine Rules → 127 for water.

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Q28 Geological reserves generally do not account for:

A) Grade

B) Volume

C) Density

D) Mine losses

E) Seam thickness


Answer: D — Losses are considered later (mineable reserves).
Memory hack: Geological = Ground data only; losses are later.

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Q29 Mineable reserves definition:

A) Geological only

B) Geological minus losses & dilution

C) Inferred resources

D) Probable only

E) Seismic estimate


Answer: B — Extractable after deducting losses/dilution.
Memory hack: Mineable = Mine-able after deductions.

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Q30  Which DOES NOT affect reserve estimation accuracy?

A) Borehole spacing

B) Core recovery

C) Geological complexity

D) Sampling error

E) Mine ventilation


Answer: E — Ventilation is operational, not reserve estimation factor.
Memory hack: Reserve accuracy = B-C-G-S (Borehole, Core, Geology, Sampling) — ventilation is out.

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Quick study tip (memory technique)

• Group facts into small clusters and use tiny phrases:
• "400-800-1200" = proved-indicated-inferred spacing (remember as “4-8-12 hundred”).
• “Area×Thick×Density” = always recite the tonnage formula 3 times aloud.
• For losses/dilution: visualize a cake and slice out losses (leftover = mineable).
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