Intermediate Mining interview questions

150 questions with answers (MIN-151 to MIN-300). Try each one aloud before reading the answer.

Mining Geology & Exploration

MIN-151 · How is the true thickness of a bed found from a vertical borehole?

For a vertical hole cutting a bed dipping at θ, true thickness = vertical intersection length × cos θ. For example, a 10 m intersection in a bed dipping 30° gives 10 × 0.866 ≈ 8.7 m true thickness.

MIN-152 · How does the induced polarisation (IP) method detect disseminated sulphides?

IP measures the chargeability of the ground: after a current is switched off, disseminated metallic grains discharge slowly, giving a decaying voltage. It detects low-grade disseminated sulphides (such as porphyry copper) that resistivity alone may miss.

MIN-153 · Why are magnetic surveys effective for iron ore exploration?

Magnetite-bearing banded iron formations have high magnetic susceptibility, producing strong anomalies in the Earth's field. Airborne and ground magnetometers map these anomalies quickly over large areas; hematite ores give weaker responses and need gravity support.

MIN-154 · What are pathfinder elements in geochemical exploration?

Pathfinders are elements associated with an ore type that disperse more widely or are easier to detect than the target metal. Examples are arsenic and antimony for gold, and mercury for some base-metal deposits.

MIN-155 · What are the key features of a porphyry copper deposit?

Porphyry deposits are large, low-grade (often 0.3–1% Cu), disseminated and stockwork Cu–Mo–Au ores associated with intermediate intrusions. Their size and uniform grade make them ideal for large open pits or block caving. Malanjkhand in India is a porphyry-type copper deposit.

MIN-156 · What is a volcanogenic massive sulphide (VMS) deposit?

VMS deposits are lenses of massive Cu–Zn–Pb sulphides formed by hydrothermal fluids venting onto the seafloor in volcanic settings. They are compact and high-grade, often mined underground.

MIN-157 · Where are India's main iron ore deposits and what type are they?

Most are hematite ores in Precambrian banded iron formations, in Odisha and Jharkhand (Singhbhum–Keonjhar belt), Chhattisgarh (Bailadila) and Karnataka (Bellary–Hospet). Magnetite ores occur mainly in Karnataka and Andhra Pradesh.

MIN-158 · How do Gondwana and Tertiary coals of India differ?

Gondwana coals (Damodar, Mahanadi, Son, Godavari valleys) hold the bulk of India's reserves; they are high-ash and low-sulphur. Tertiary coals (north-east India) are younger, low-ash but high-sulphur. Lignite occurs mainly in Tamil Nadu, Rajasthan and Gujarat.

MIN-159 · How is exploratory borehole spacing decided?

Spacing depends on deposit continuity, grade variability, structural complexity and the resource category required. It is often refined using variography so that holes are close enough to estimate grade within acceptable error; closer grids give measured-category confidence.

MIN-160 · How is channel sampling done?

A channel of uniform width and depth is cut across the full width of the ore body, perpendicular to its strike, and all material is collected. Uniform cross-section ensures each part of the vein is represented proportionally.

MIN-161 · What QA/QC samples are inserted in an assay programme?

Certified reference materials (standards) to check accuracy, blanks to detect contamination, field and laboratory duplicates to check precision, and check assays at an umpire laboratory. Results are tracked on control charts.

MIN-162 · How is remote sensing used in mineral exploration?

Satellite and airborne multispectral or hyperspectral imagery maps lithology, alteration minerals (clays, iron oxides) and structures over large areas. It helps target ground surveys and reduces reconnaissance cost.

MIN-163 · How is geophysical borehole logging used in coal exploration?

Natural gamma, density (gamma–gamma) and resistivity logs identify coal seams, which have low density and low gamma. Logs define seam depths and thicknesses precisely and correlate seams between holes, even where core recovery is poor.

Mine Development

MIN-164 · What factors decide the location of a shaft?

Position relative to the ore body (usually footwall side, outside the zone of subsidence), ground conditions, water, surface topography and infrastructure, haulage distances and the need for a protective shaft pillar.

MIN-165 · When is a decline preferred to a vertical shaft?

A decline is preferred for shallower deposits (roughly up to 300–500 m) and moderate outputs, where trackless equipment can drive directly to the workings. Shafts become cheaper to operate at greater depth and high hoisting rates.

MIN-166 · How does ground freezing work in shaft sinking?

Boreholes around the shaft circle circulate chilled brine or liquid nitrogen to freeze the water-bearing ground into a strong, impermeable ice wall. The shaft is then sunk and lined inside the frozen cylinder.

MIN-167 · What is the cementation method of shaft sinking?

Cement grout is injected under pressure through holes drilled ahead of the shaft bottom to seal fissures in water-bearing rock. It reduces water inflow before the ground is excavated.

MIN-168 · What is raise boring?

A pilot hole is drilled downward between two levels, then a large reamer head is attached and pulled upward to enlarge the hole to full diameter. Cuttings fall to the lower level. It gives a smooth, safe raise without people working in it.

MIN-169 · What is an Alimak raise climber?

An Alimak is a cage platform that climbs a rack-and-pinion guide rail fixed to the raise wall. Miners drill and charge from the platform, then lower it before blasting. It allows long raises in hard rock without a pilot hole.

MIN-170 · How do drill-and-blast, roadheaders and TBMs compare for drivage?

Drill-and-blast is flexible for any shape and hard rock. Roadheaders cut soft to medium rock (up to about 100 MPa) with low vibration and profile control. TBMs give the fastest advance in long, straight, circular tunnels but have high capital cost and little flexibility.

MIN-171 · What are the principles of the New Austrian Tunnelling Method (NATM)?

NATM mobilises the strength of the surrounding rock by allowing controlled deformation, using a thin flexible primary support (shotcrete and rock bolts) installed promptly. Deformation monitoring guides additional support.

MIN-172 · How are declines designed for trackless equipment?

Gradients are typically around 1 in 7 to 1 in 9, with cross-section sized to the largest vehicle plus clearances for ventilation ducts and services. Curves, passing bays, drainage and roadway surface are designed for safe truck operation.

MIN-173 · What are rigid guides and rope guides in shafts?

Rigid guides are steel or timber rails fixed to buntons across the shaft; they suit high speeds and many levels. Rope guides are tensioned wire ropes; they are cheaper and need no buntons but require larger clearances between conveyances.

MIN-174 · Why is footwall development often preferred in metal mines?

Footwall drifts and crosscuts lie in rock not disturbed by stoping or caving of the hanging wall, so they stay stable for longer. They also allow access to multiple stopes and draw points.

MIN-175 · What is the shaft sinking cycle?

The cycle is drilling the bottom, charging and blasting, ventilating, mucking (often with a cactus grab into kibbles), and installing temporary support, followed by permanent lining at intervals.

MIN-176 · What are the trade-offs between inclined and vertical shafts?

Inclined shafts follow the ore body dip and shorten crosscuts but are longer for the same depth, harder to maintain and slower for hoisting. Vertical shafts are shorter, more stable and give faster hoisting but need longer crosscuts.

Surface Mining

MIN-177 · What factors govern bench height selection?

Reach and size of the loading equipment, rock strength and slope stability, blasthole diameter and fragmentation, ore selectivity and dilution, and statutory requirements.

MIN-178 · What is the break-even stripping ratio?

It is the maximum stripping ratio at which mining a unit of ore just breaks even: BESR = (recoverable value per tonne of ore − cost of mining and processing per tonne of ore) ÷ cost of stripping per unit of waste.

MIN-179 · What are common dragline operating methods?

Simple side casting, extended bench (dragline sits on a bench built from spoil to increase reach), and pull-back or tandem operations. The method is chosen based on overburden depth and dragline reach.

MIN-180 · What factors affect the stability of overburden dumps?

Dump height and slope, foundation strength, material shear strength, water and pore pressure, rate of dumping, drainage and seismic loads. Weak foundation clay and rainfall are common causes of dump failures.

MIN-181 · How is the stability of a pit slope assessed?

Using geotechnical mapping, kinematic analysis of discontinuities (planar, wedge, toppling), and limit equilibrium methods (Bishop, Janbu, Morgenstern–Price) to calculate a factor of safety. Numerical modelling is used for complex cases.

MIN-182 · What are basic haul road design rules?

A common rule is a running width of at least 3.5 times the widest vehicle for two-way traffic, safety berms at least half the wheel height, gentle sustained gradients (often 8–10%) and adequate curve radius, drainage and cross-slope.

MIN-183 · What are rolling resistance and grade resistance?

Rolling resistance is the force to overcome tyre flexing and penetration, often about 2% of vehicle weight plus extra for soft roads. Grade resistance is about 1% of vehicle weight per 1% grade (about 10 kg per tonne per %). Their sum is total resistance.

MIN-184 · What is the match factor in truck–shovel systems?

MF = (number of trucks × loading time per truck) ÷ (number of loaders × truck cycle time). MF = 1 is a perfect match; MF < 1 means loaders wait, MF > 1 means trucks queue.

MIN-185 · What is in-pit crushing and conveying (IPCC)?

IPCC places a mobile or semi-mobile crusher in the pit and conveys crushed material out by belt, replacing long truck hauls. It cuts diesel use, labour and cost per tonne in deep pits but reduces flexibility.

MIN-186 · How are pit slopes monitored?

By survey prisms with robotic total stations, slope stability radar, extensometers, inclinometers, piezometers and visual inspection. Trends in displacement velocity give early warning of failure.

MIN-187 · What is a pushback (phase) in open-pit mining?

A pushback is a sequential expansion of the pit wall that removes a slice of waste and ore to progress from the initial pit to the ultimate pit. Phasing brings higher-value ore forward and smooths stripping.

MIN-188 · What are the advantages of a surface miner over drill and blast?

No blasting vibration, flyrock or fumes, selective mining of thin bands to control dilution, sized product that may avoid primary crushing, and a level floor. It is limited to softer rock and has high pick wear in hard rock.

MIN-189 · How is shovel productivity estimated?

Output (bank m³/h) = bucket capacity × fill factor × (3600 ÷ cycle time in s) × job efficiency ÷ swell factor (loose/bank). For a 10 m³ bucket, fill 0.9, 30 s cycle, 0.83 efficiency and swell 1.4: ≈ 10 × 0.9 × 120 × 0.83 ÷ 1.4 ≈ 640 bank m³/h.

Underground Coal Mining

MIN-190 · What factors determine pillar size in bord and pillar working?

Depth of cover, seam height, gallery width, coal strength, roof and floor conditions, and whether the pillars will be extracted later. Indian regulations prescribe minimum pillar dimensions against depth and gallery width.

MIN-191 · What are local falls and main fall in depillaring?

Local falls are partial roof collapses in the goaf near the extraction line. The main fall is the first large collapse of the main roof over the panel; before it, heavy weighting can cause pillar crushing, air blasts and accidents, so it is closely monitored.

MIN-192 · What is periodic weighting in longwall mining?

After the first main roof caving, the main roof cantilevers over the goaf and breaks at regular intervals as the face advances. Each break transfers a peak load to the powered supports, called periodic weighting.

MIN-193 · How does hydraulic sand stowing work?

Sand is mixed with water at the surface and the slurry is pumped or gravity-fed through pipelines into the goaf behind barricades. The water drains away and the sand compacts to support the roof and reduce subsidence.

MIN-194 · What is the blasting gallery method?

It is an Indian technique for thick coal seams, in which developed galleries are used to drill long ring holes upward into the seam, blast the full thickness and load coal remotely with LHDs. It gives high recovery from seams too thick for conventional bord and pillar.

MIN-195 · What is longwall top coal caving (LTCC)?

In LTCC, a longwall shearer cuts the lower part of a thick seam while the top coal above the supports caves and is drawn through openings at the rear of special supports onto a rear conveyor. It allows extraction of seams of about 5–12 m thickness.

MIN-196 · What causes spontaneous heating of coal?

Coal oxidises slowly at low temperature, releasing heat. If heat is not dissipated (crushed coal, low ventilation leakage through goaf, high moisture changes, pyrite), the temperature rises until it may ignite. Low-rank, high-volatile coals are most susceptible.

MIN-197 · What are crossing point temperature and incubation period?

Crossing point temperature is the temperature at which coal heated at a controlled rate exceeds the surrounding bath temperature, indicating its susceptibility; lower values mean higher risk. Incubation period is the time from exposure to air until the coal heats to ignition.

MIN-198 · What is Graham's ratio?

Graham's ratio = 100 × CO produced ÷ O₂ deficiency, computed from analysis of return air or sealed-area samples. A rising value indicates developing spontaneous heating.

MIN-199 · How are coal dust explosions prevented?

By suppressing dust at source (water sprays, wet cutting), removing accumulations, stone dusting roadways to keep incombustible content high, and installing stone dust or water barriers to stop flame propagation.

MIN-200 · What is methane drainage?

Methane drainage captures gas from coal seams and goafs through boreholes before or after mining and pipes it to the surface. It reduces the ventilation load and the gas can be used for power or sold.

MIN-201 · How is depillaring done with a continuous miner?

The miner splits pillars into smaller stooks and extracts them in slices or fenders, typically in a retreat sequence, with breaker-line support such as mobile roof supports. It gives faster extraction and better safety than manual or semi-mechanised methods.

MIN-202 · Why is face length a critical design parameter in longwall mining?

Longer faces give more coal per web and fewer gate roads, raising productivity, but they increase support and conveyor loads, gas emission, face cycle time and ventilation demand. Face length is optimised for equipment capacity and geology.

Underground Metal Mining

MIN-203 · What factors control the choice of an underground metal mining method?

Ore body geometry (thickness, dip, shape, depth), ore and wall rock strength, grade distribution, value, dilution tolerance, subsidence restrictions, production rate and cost. Methods such as Nicholas' approach rank these systematically.

MIN-204 · What is vertical crater retreat (VCR) mining?

Large-diameter holes are drilled down from an upper level to the stope bottom, and spherical charges are fired in the lower part of the holes to break horizontal slices upward toward the drilling level. Broken ore is drawn from below.

MIN-205 · How does sublevel open stoping differ from sublevel caving?

In sublevel open stoping, the stope remains open and self-supporting until filled or abandoned, giving low dilution but needing strong walls. In sublevel caving, the hanging wall caves into the void, accepting higher dilution in exchange for low cost.

MIN-206 · What are the undercut and extraction levels in block caving?

The undercut level is where a horizontal slot is blasted beneath the block to start caving. The extraction (production) level, below it, holds drawbells and drawpoints from which LHDs load caved ore.

MIN-207 · Why is draw control important in caving methods?

Uneven drawing lets waste from above reach drawpoints early, causing dilution and ore loss, and can create stress concentrations or air gaps. Controlled, uniform draw keeps the ore–waste interface level.

MIN-208 · How does paste fill compare with hydraulic fill?

Paste fill is dewatered, full-size tailings with a small amount of binder; it does not bleed water, needs no drainage barricades and gives higher strength with less cement. Hydraulic fill uses deslimed sand and must drain water, which can cause barricade failure.

MIN-209 · What are primary and secondary stopes?

In a two-stage sequence, primary stopes are mined first between ore pillars and filled with cemented fill. Secondary stopes are then mined between the cured primary fill masses, which must stand unsupported.

MIN-210 · What are crown pillars and sill pillars?

A crown pillar is ore left above a stope (often below a level or the surface) to support the overlying ground. A sill pillar is left at the base of a stope above a haulage level to protect it.

MIN-211 · What is post-pillar cut and fill?

It is a variant of cut and fill for wider ore bodies, in which pillars of ore are left in a regular pattern and run up through successive slices, surrounded and supported by fill.

MIN-212 · What is square-set stoping?

Square-set stoping supports the stope with rectangular timber frames as ore is removed, then fills the sets. It allows very selective mining of weak, irregular, high-grade ore but is labour-intensive and now rarely used.

MIN-213 · How does dilution affect grade? Give a numerical example.

Diluted grade = (ore tonnes × ore grade + waste tonnes × waste grade) ÷ total tonnes. Mining 100,000 t at 5% Zn with 15,000 t of barren waste gives 500,000 ÷ 115,000 ≈ 4.35% Zn, and dilution of 15,000/115,000 ≈ 13%.

MIN-214 · What problems occur in ore passes?

Hang-ups (arching of large or sticky material), wall wear and enlargement, pass collapse, water causing mud rushes, and over-sized boulders. Grizzlies, controlled water content and correct inclination (usually steeper than about 55–60°) reduce them.

MIN-215 · What is in-situ leaching (solution mining)?

A leaching solution is injected through wells into a permeable ore body, dissolves the mineral and is pumped back through recovery wells for processing. It is used for uranium, copper and some salts; it avoids excavation but needs good permeability and groundwater control.

Rock Mechanics & Ground Control

MIN-216 · What is RMR and how is it calculated?

Rock Mass Rating (Bieniawski) sums ratings for UCS, RQD, joint spacing, joint condition and groundwater, then applies an adjustment for joint orientation. The total (0–100) places the rock in five classes and is used to estimate stand-up time and support.

MIN-217 · What is the Q-system?

Barton's Q = (RQD/Jn) × (Jr/Ja) × (Jw/SRF), representing block size, inter-block shear strength and active stress. Q ranges from about 0.001 to 1000 and, with the excavation span and support ratio, gives support requirements.

MIN-218 · What is the stress around a circular opening in a hydrostatic stress field?

By the Kirsch solution, the tangential stress at the boundary is 2p and radial stress is zero, where p is the field stress. For a non-hydrostatic field, the maximum boundary stress is 3σ₁ − σ₃.

MIN-219 · What is the tributary area method of pillar stress?

It assumes each pillar carries the full overburden over its own area plus half the surrounding openings. For square pillars of width w and opening width B: σp = γH × (w + B)²/w².

MIN-220 · What is subsidence?

Subsidence is the downward movement of the ground surface caused by underground extraction. It produces vertical lowering, tilt, curvature and horizontal strain that can damage structures, roads and drainage, and is greatest over total extraction methods such as longwall and caving.

MIN-221 · How does the width-to-height ratio affect pillar strength?

Pillar strength rises as width-to-height ratio increases, because the confined core grows and the pillar fails less by spalling. Slender pillars (w/h below about 3) can fail suddenly, while squat pillars (w/h above about 8–10) behave strongly and stably.

MIN-222 · What is the Hoek–Brown failure criterion?

It is an empirical, non-linear criterion for rock: σ₁ = σ₃ + σc(mb·σ₃/σc + s)ᵃ. Parameters mb, s and a are derived from the intact constant mi, the Geological Strength Index (GSI) and a disturbance factor D.

MIN-223 · What are the mechanisms by which rock bolts support ground?

Suspension (hanging weak layers from strong strata), beam building (clamping thin layers into a thicker composite beam), keying (pinning blocks) and general reinforcement of a jointed rock mass to increase its strength.

MIN-224 · What is the point load test?

A rock core or lump is loaded between two conical platens until it breaks. The point load index Is(50), corrected to 50 mm size, is quick to obtain in the field; UCS is roughly 20–25 times Is(50), though the factor varies with rock type.

MIN-225 · What instruments are used to monitor ground behaviour underground?

Extensometers for roof and wall displacement, convergence indicators, load cells on bolts and props, stress cells, telltales for roof sag and microseismic systems for rock fracturing.

MIN-226 · What is the angle of draw?

The angle of draw is the angle between the vertical at the edge of the extraction and the line to the limit of surface subsidence. It is used to size protective pillars for surface structures and shafts.

MIN-227 · What is squeezing ground?

Squeezing is large, time-dependent inward deformation of weak rock (such as shale, clay-rich or highly stressed rock) when stress exceeds its strength. It needs yielding support systems that can accept deformation.

MIN-228 · What is the slake durability test?

It measures the resistance of weak rocks (such as shale and mudstone) to breakdown under wetting and drying cycles in a rotating drum. Low slake durability indicates roof or floor that will deteriorate on exposure to mine water or humidity.

Drilling & Blasting

MIN-229 · What parameters control blast design?

Hole diameter, burden, spacing, bench height, subdrill, stemming length, explosive type and density, charge distribution, delay timing and initiation sequence, together with rock mass properties and the desired fragmentation.

MIN-230 · What rules of thumb relate burden and spacing to hole diameter?

Burden is typically about 25–40 times the hole diameter, depending on rock and explosive. Spacing is usually 1.0–1.5 times the burden, and stemming about 0.7–1.0 times the burden.

MIN-231 · What is the stiffness ratio in bench blasting?

Stiffness ratio = bench height ÷ burden. Ratios above about 3 give good fragmentation and low flyrock; low ratios (below about 2) give a stiff burden that breaks poorly, with more back-break and toe problems.

MIN-232 · Why are delays used in blasting?

Delays fire holes in sequence so each hole has a free face, improving fragmentation and muck movement. They also reduce the maximum charge per delay, lowering ground vibration and airblast.

MIN-233 · What is scaled distance and how is it used for vibration control?

Scaled distance SD = D ÷ √Q, where D is distance (m) and Q the maximum charge per delay (kg). Peak particle velocity is predicted as PPV = K·(SD)⁻ᵝ, with site constants K and β found by regression of monitored blasts.

MIN-234 · What is the difference between pre-splitting and smooth blasting?

Pre-splitting fires a row of closely spaced, lightly charged holes along the final wall before the main blast, creating a crack that shields the wall. Smooth blasting fires the perimeter holes last, after the main blast, to trim the profile with minimal damage.

MIN-235 · What are the advantages of emulsion explosives?

Excellent water resistance, high density and velocity of detonation, good energy per hole, safer handling (non-cap-sensitive bulk forms) and fewer toxic fumes than ANFO. They can be pumped into wet holes.

MIN-236 · Why is velocity of detonation (VOD) important?

High VOD explosives produce strong shock energy and suit hard, massive rock. Lower VOD explosives produce more heave (gas energy) and suit softer or fractured rock and displacement of muck. Matching explosive to rock impedance improves energy transfer.

MIN-237 · What is the Kuz–Ram fragmentation model?

It combines Kuznetsov's equation for mean fragment size (from rock factor, powder factor, charge mass and explosive strength) with a Rosin–Rammler distribution whose uniformity index depends on blast geometry. It predicts the size distribution of blasted rock.

MIN-238 · What causes air overpressure (airblast) from blasting?

Gases venting through inadequate stemming, unconfined surface detonating cord, blown-out faces with insufficient burden, and rock movement. It is controlled by proper stemming, covering cord, correct timing and avoiding blasting in adverse weather.

MIN-239 · What is back-break?

Back-break is rock fractured beyond the last row of holes into the new bench wall. It damages crests, weakens slopes and makes drilling of the next blast difficult; excessive burden, long delays and overcharging the back row cause it.

MIN-240 · Calculate the powder factor for a hole with 4 m burden, 5 m spacing, 10 m bench height and 100 kg of explosive.

Rock volume per hole = B × S × H = 4 × 5 × 10 = 200 m³. Powder factor = 100 ÷ 200 = 0.5 kg/m³, or about 0.19 kg/t for rock of 2.6 t/m³.

Mine Ventilation & Gases

MIN-241 · Why is mine ventilation critical?

It supplies oxygen for people and engines, dilutes and removes methane, CO, blasting fumes and diesel exhaust to safe levels, controls dust and removes heat and humidity to keep working conditions safe.

MIN-242 · What is Atkinson's equation?

Frictional pressure drop in an airway is p = k·C·L·Q² ÷ A³, where k is the friction factor (kg/m³), C perimeter (m), L length (m), Q quantity (m³/s) and A area (m²). It shows pressure is very sensitive to airway area.

MIN-243 · What is the square law of mine ventilation?

For a given airway, p = R·Q², where R = kCL/A³ is the resistance (N·s²/m⁸). Doubling the air quantity needs four times the pressure and eight times the air power.

MIN-244 · How are airway resistances combined in series and parallel?

In series, resistances add: R = R₁ + R₂ + … In parallel, 1/√R = 1/√R₁ + 1/√R₂ + … Parallel splits greatly reduce total resistance.

MIN-245 · What is the equivalent orifice of a mine?

It is the area of a sharp-edged orifice that would pass the same quantity at the same pressure as the mine: A ≈ 1.19·Q/√p (A in m², Q in m³/s, p in Pa, ρ ≈ 1.2 kg/m³). A larger orifice means an easier-to-ventilate mine.

MIN-246 · What are the fan laws?

For a given fan and air density: Q ∝ N, p ∝ N² and power ∝ N³, where N is rotational speed. Pressure and power also vary directly with air density.

MIN-247 · How is natural ventilation pressure calculated?

NVP = g·H·(ρ_d − ρ_u), where H is shaft depth and ρ_d, ρ_u are the mean air densities in the downcast and upcast columns. Colder, denser air in the downcast drives flow down that shaft.

MIN-248 · How is the operating point of a mine fan found?

It is the intersection of the fan's pressure–quantity characteristic curve with the mine resistance curve p = RQ². Changes in mine resistance or fan blade angle shift the operating point.

MIN-249 · What are Kirchhoff's laws in ventilation networks?

First law: the algebraic sum of airflows at a junction is zero. Second law: the algebraic sum of pressure drops around any closed mesh is zero, after allowing for fans and natural ventilation. Network solvers such as the Hardy Cross method use them.

MIN-250 · What is methane layering and how is it prevented?

Methane, being lighter, forms a layer along the roof where air velocity is low. It is prevented by keeping sufficient air velocity (often at least about 0.5 m/s near the roof) and by using air movers or brattice to create turbulence.

MIN-251 · How is heat stress assessed in deep mines?

By wet-bulb temperature, effective temperature (combining dry-bulb, wet-bulb and air velocity) or thermal work limits. Heat sources include auto-compression of air, virgin rock temperature, machinery and groundwater; control is by more air, higher velocity and refrigeration.

MIN-252 · Find the fan input power for 200 m³/s at 1.5 kPa with 75% efficiency.

Air power = p × Q = 1500 × 200 = 300 kW. Input power = 300 ÷ 0.75 = 400 kW.

Mine Machinery & Transport

MIN-253 · How is belt conveyor capacity calculated?

Capacity (t/h) = 3600 × A × v × ρ, where A is the load cross-section on the belt (m²), v belt speed (m/s) and ρ loose bulk density (t/m³). A depends on belt width, troughing angle and surcharge angle.

MIN-254 · What makes up the power needed by a belt conveyor?

Power to move the empty belt, to move the load horizontally (friction), to lift or lower the load (± m·g·H), and for accessories such as skirts and scrapers, divided by drive efficiency.

MIN-255 · What is rimpull and why is retarding important?

Rimpull is the tractive force available at the tyre–ground contact for propulsion. On downhill hauls, retarders (electric dynamic braking or hydraulic) control speed without overheating service brakes, which is critical for safe haulage.

MIN-256 · How is mine pump power calculated?

Pump power P = ρ·g·Q·H ÷ η. For 0.1 m³/s against 300 m total head at 70% efficiency: 1000 × 9.81 × 0.1 × 300 ÷ 0.7 ≈ 420 kW.

MIN-257 · What is the difference between ordinary lay and Lang's lay ropes?

In ordinary lay, wires in a strand are laid opposite to the strands in the rope; it resists kinking and crushing. In Lang's lay, wires and strands are laid the same way, giving more wearing surface and flexibility, but it tends to untwist and must have both ends fixed.

MIN-258 · What safety devices are fitted to mine winders?

Overwind and overspeed protection (automatic contrivance), depth indicator, slack-rope detection, mechanical brakes that apply on power failure, safety catches or arresters in the headframe, and signalling interlocks.

MIN-259 · What limits the load on a Koepe winder?

The rope must not slip on the friction wheel. By the capstan relation, T₁/T₂ ≤ e^(μθ), where T₁ and T₂ are the rope tensions on each side, μ the coefficient of friction of the tread and θ the angle of wrap.

MIN-260 · How do electric and diesel LHDs compare?

Electric LHDs (cable or battery) have no exhaust, less heat and lower ventilation and running costs, but cable units have limited range. Diesel LHDs are flexible but need more ventilation for exhaust and heat. Battery-electric units are increasingly used.

MIN-261 · Why are draglines often preferred over shovel–truck for overburden in strip mines?

A dragline digs and casts overburden directly into the void with no haulage, giving very low cost per cubic metre for flat-lying seams. Its limitations are high capital, limited reach and depth, and poor flexibility.

MIN-262 · What are availability and utilisation of mining equipment?

Mechanical availability = hours available for work ÷ scheduled hours. Utilisation = hours actually worked ÷ hours available. Their product gives effective use and directly affects production.

MIN-263 · What is TKPH in haul truck operation?

Tonne-kilometre-per-hour is the tyre's heat-generating capacity. Working TKPH = average tyre load × average speed over a shift; it must not exceed the tyre's rated TKPH or the tyre overheats and fails.

MIN-264 · What are autonomous haulage systems?

Driverless haul trucks guided by GPS, sensors and a central control system. They improve safety and utilisation and reduce operating cost but need high capital, robust communications and segregation from manned equipment.

Mine Planning, Valuation & Economics

MIN-265 · What are the nugget, sill and range of a variogram?

The nugget is the variance at near-zero distance due to sampling error and micro-scale variability. The sill is the plateau of variance where samples become uncorrelated, and the range is the distance at which the sill is reached.

MIN-266 · How does kriging differ from inverse distance weighting?

IDW assigns weights based only on distance. Kriging uses the variogram to give unbiased, minimum-variance weights that account for spatial correlation and data clustering, and it also estimates the error of each estimate.

MIN-267 · What is Taylor's rule?

An empirical guide to mine life: life (years) ≈ 0.2 × (expected ore tonnes)^0.25. For 100 Mt it gives 0.2 × 100 = 20 years, so about 5 Mt/year.

MIN-268 · What is internal rate of return (IRR)?

IRR is the discount rate at which the project NPV equals zero. A project is attractive if its IRR exceeds the company's hurdle rate or cost of capital.

MIN-269 · What is the payback period and its limitation?

Payback is the time for cumulative cash flow to repay the initial investment. It is simple and indicates risk but ignores the time value of money and cash flows after payback.

MIN-270 · What is Hoskold's formula?

It values a wasting mining asset by assuming part of annual income gives a speculative return on capital while the rest goes into a sinking fund at a safe rate to recover capital: V = A ÷ [r + s/((1+s)ⁿ − 1)], with A annual income, r speculative rate, s safe rate and n life.

MIN-271 · How is the discount rate chosen for a mining project?

It is based on the company's weighted average cost of capital, adjusted for project-specific risks such as country risk, commodity price volatility, technical uncertainty and project stage.

MIN-272 · What is the difference between capex and opex in mining?

Capex is the investment in fixed assets such as shafts, equipment, plant and infrastructure, including sustaining capital. Opex is the recurring cost of mining, processing, labour, energy and consumables, usually expressed per tonne.

MIN-273 · What are long-, medium- and short-term mine plans?

Long-term plans cover the life of mine and strategy. Medium-term plans (yearly to a few years) set budgets, equipment and pushbacks. Short-term plans (weekly to monthly) schedule specific blocks to meet grade and tonnage targets.

MIN-274 · What changes did the MMDR Amendment Act 2015 bring?

It made auction the method of granting mineral concessions, extended mining lease tenure to 50 years, and created the District Mineral Foundation (DMF) for welfare of mining-affected people and the National Mineral Exploration Trust (NMET) to fund exploration.

MIN-275 · What are the stages of a mining feasibility study?

Scoping (conceptual) study, pre-feasibility study (comparing options to select one) and definitive or bankable feasibility study. Accuracy improves from roughly ±30–50% to ±10–15% while detail and cost increase.

MIN-276 · What is sensitivity analysis in mine evaluation?

It changes one input at a time, such as price, grade, recovery, opex or capex, to see the effect on NPV or IRR, usually shown as a spider diagram. It identifies the variables to which the project is most sensitive.

Mine Safety & Legislation

MIN-277 · How are mine accidents reported in India?

Under Section 23 of the Mines Act 1952, the owner, agent or manager must notify fatal and serious accidents and dangerous occurrences to DGMS and other authorities in the prescribed form and time. Fatal accidents are investigated by DGMS.

MIN-278 · What are frequency rate and severity rate?

Frequency rate is the number of lost-time injuries per million man-hours worked. Severity rate is the number of man-days lost per million (or thousand) man-hours worked. Mining also uses fatality rates per 1000 persons employed or per million tonnes.

MIN-279 · What is the hierarchy of controls?

In decreasing effectiveness: elimination, substitution, engineering controls, administrative controls and personal protective equipment. Risk control should start at the top, with PPE as the last resort.

MIN-280 · What precautions are needed when approaching old waterlogged workings?

Accurate, updated mine plans, statutory barriers, DGMS permission to work within the prescribed distance, advance and flank probe boreholes, water dams and pumping capacity, and trained workers aware of warning signs such as sweating strata and increased seepage.

MIN-281 · How are underground mine fires dealt with?

Small fires are attacked directly with water, extinguishers or foam. Larger fires are isolated by sealing with stoppings, followed by inertisation with nitrogen or CO₂ and monitoring of sealed-area gases before reopening.

MIN-282 · What is a principal hazard in mining?

A principal hazard is one that can cause multiple fatalities or a major incident, such as inundation, fire, explosion, roof or slope failure, outburst, winding failure or major equipment collision. Each needs a Principal Hazard Management Plan.

MIN-283 · What is bow-tie analysis?

Bow-tie analysis shows a top event with its causes and preventive controls on the left and consequences with mitigating controls on the right. It helps visualise and verify critical controls for major hazards.

MIN-284 · What is environmental telemonitoring in coal mines?

It is a networked system of fixed sensors for methane, CO, oxygen, air velocity and temperature that transmits data continuously to a surface control room, with alarms and automatic power trips when limits are exceeded.

MIN-285 · What changed regarding employment of women in Indian mines in 2019?

A 2019 notification under the Mines Act permitted women to work above ground at night and below ground in technical, supervisory and managerial roles, subject to written consent, safety, facilities and group deployment safeguards.

MIN-286 · What breathing apparatus do mine rescue teams use?

Closed-circuit, self-contained breathing apparatus that supplies oxygen from a cylinder and scrubs exhaled CO₂, giving several hours of protection in irrespirable atmospheres. Teams also use gas detectors and resuscitators.

MIN-287 · What occupational diseases are common in mining and how are they controlled?

Coal workers' pneumoconiosis, silicosis, asbestosis, noise-induced hearing loss and manganese poisoning. Control is through dust suppression, ventilation, respirators, noise control and initial and periodic medical examinations under the Mines Rules 1955.

MIN-288 · What are the roles of owner, agent and manager under the Mines Act?

The owner has overall control and responsibility. The agent acts for the owner in management of the mine. The manager, holding the required certificate, is responsible for day-to-day control, management, supervision and direction of the mine.

Mineral Processing & Mine Environment

MIN-289 · What is beneficiation?

Beneficiation is upgrading ore to a higher-grade concentrate by physical or physico-chemical methods such as crushing, grinding, screening, gravity, magnetic, electrostatic separation and flotation, without changing the chemical identity of the mineral.

MIN-290 · What is Bond's law of comminution?

W = 10·Wi·(1/√P₈₀ − 1/√F₈₀), where W is energy (kWh/t), Wi Bond work index (kWh/t), and F₈₀, P₈₀ the 80% passing sizes of feed and product in micrometres.

MIN-291 · What is reduction ratio?

Reduction ratio is the ratio of feed size to product size of a crusher or mill, often using F₈₀/P₈₀. Jaw crushers typically achieve about 4–8 and cone crushers about 3–6.

MIN-292 · How is recovery calculated from assays (two-product formula)?

Recovery R = 100 × c(f − t) ÷ [f(c − t)], where f, c and t are the grades of feed, concentrate and tailings. For f = 2%, c = 25% and t = 0.2%: R = 100 × 25 × 1.8 ÷ (2 × 24.8) ≈ 90.7%.

MIN-293 · What are the main flotation reagents?

Collectors (e.g. xanthates) make target minerals hydrophobic; frothers (e.g. MIBC, pine oil) stabilise froth; activators (e.g. copper sulphate for sphalerite) and depressants (e.g. cyanide, lime) control selectivity; pH modifiers (lime, soda ash) set pulp chemistry.

MIN-294 · How does a hydrocyclone work?

Slurry enters tangentially and spins; coarse and dense particles move to the wall and exit at the apex (underflow), while fine particles and most water leave through the vortex finder (overflow). It is widely used in closed-circuit grinding.

MIN-295 · What are washability curves of coal?

Float–sink tests separate coal into density fractions; plotting cumulative yield against ash gives washability curves (primary, cumulative float, cumulative sink and densimetric). They predict yield and ash at any separation density and show the near-gravity material.

MIN-296 · How are concentrates and tailings dewatered?

By thickeners (gravity settling aided by flocculants), followed by filters (vacuum disc or drum, pressure filters) and sometimes thermal drying. Dewatering recovers process water and produces transportable concentrate.

MIN-297 · What are the upstream, downstream and centreline methods of tailings dam construction?

In upstream construction, each raise is built on deposited tailings, which is cheapest but least stable. Downstream raises are built outward on the dam's own fill, which is most stable. The centreline method keeps the crest axis fixed and is intermediate.

MIN-298 · How is dust controlled in opencast mines?

Water sprinkling of haul roads (often with chemical suppressants), wet drilling or dust collectors on drills, water sprays at crushers and transfer points, covered conveyors, green belts and wind barriers.

MIN-299 · How is acid mine drainage treated?

Active treatment adds lime or other alkalis to neutralise acidity and precipitate metals as hydroxides. Passive systems use constructed wetlands, anoxic limestone drains and bioreactors. Prevention by covering or flooding sulphide waste is better than treatment.

MIN-300 · Why is topsoil managed separately in surface mining?

Topsoil holds organic matter, nutrients and seed bank needed for revegetation. It is stripped before mining, stored in low stockpiles (or placed directly on reshaped dumps) and protected from erosion so it can be reused in reclamation.

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