GATE MN key terms

A numerical classification of rock mass quality obtained by summing ratings for uniaxial compressive strength, RQD, joint spacing, joint condition, groundwater and orientation adjustment; used to select support systems.

The percentage of a borehole core consisting of intact pieces 100 mm or longer, measured along the core axis, used as an index of rock mass fracturing.

A rock mass classification developed at NGI that rates rock quality from RQD, joint set number, joint roughness, joint alteration, water inflow and stress conditions, giving a value used for tunnel support design.

The ratio, usually expressed as a percentage, of core length actually recovered in drilling to the length of the drilled run; low values indicate weak or highly fractured ground.

The original system by which the six RMR parameters are rated and weighted, with ratings adjusted for discontinuity orientation, to give a rock mass class from very poor to very good.

The continuous recording of geophysical or geological properties along a borehole, such as natural gamma, resistivity, density or caliper, used to infer strata, grade and rock properties.

The branch of statistics applied to spatially correlated data, using variograms and kriging to estimate grade or other properties at unsampled locations and to quantify estimation variance.

A geostatistical estimation method that predicts values at unsampled locations as weighted averages of nearby samples, with weights derived from a fitted variogram model.

A plot of the variance of differences between sample pairs against separation distance, characterising spatial continuity and providing the model used in kriging.

The minimum grade at which material is classified as ore rather than waste, determined by economic and metallurgical factors and directly affecting ore tonnage and mine life.

The part of a mineral resource that can be economically and legally extracted at the time of estimation, reported with grade, tonnage and modifying factors.

The ratio of waste material to ore mined, usually expressed as volume or mass of overburden per unit of ore, and a key determinant of open-pit economics.

The vertical height of a single mining bench or lift in an open-pit or quarry, governed by equipment reach, blasthole depth and slope stability requirements.

The size distribution of rock fragments produced by a blast, controlled by burden, spacing, explosive type, charge concentration and delay timing, and affecting loading and crushing costs.

The distance from a blasthole to the nearest free face (burden) and the distance between adjacent blastholes (spacing); the two primary drill pattern parameters controlling blast outcome.

The mass of explosive used per unit mass or volume of rock broken, a standard index for comparing blast designs and explosive consumption.

The controlled interval between detonation of successive blastholes or rows, which governs relief, fragmentation, muckpile shape and vibration control.

Self-generated temperature rise in coal or sulphide-bearing material caused by low-temperature oxidation when heat generation exceeds heat dissipation, potentially leading to spontaneous combustion.

The exothermic reaction of coal with oxygen at ambient temperature, producing heat and gases such as carbon monoxide and carbon dioxide, and the precursor to spontaneous combustion.

An uncontrolled combustion in a mine, either open or sealed, that threatens personnel, equipment and reserves and may require sealing, inertisation or direct extinguishing.

The introduction of inert gas, usually nitrogen or combustion products, into a sealed area to lower oxygen concentration and suppress combustion or explosion risk.

The controlled supply and distribution of air underground to provide oxygen, dilute and remove gases and dust, and control temperature and humidity.

The opposition of a mine airway to air flow, described by the Atkinson equation and depending on friction factor, perimeter, length and the square of airflow quantity.

The plot of pressure developed by a fan against airflow quantity at fixed speed, used with the mine resistance curve to find the operating point.

The deliberate extraction of methane from coal seams or surrounding strata through boreholes before, during or after mining, to reduce gas content and improve safety.

A sudden, violent release of gas, often with coal or rock, from a working face or seam, driven by gas pressure and stress, and requiring prediction and control measures.

A sudden violent failure of highly stressed rock that ejects material into an excavation, driven by strain energy release rather than by gas pressure.

The downward displacement of the ground surface caused by underground extraction, governed by seam thickness, depth, extraction method and strata behaviour.

A block of unmined rock or ore left in place to support overlying strata, protect surface features or separate workings, designed against compressive and shear failure.

An underground mining method in which ore is extracted in rooms separated by regularly spaced pillars, suitable for flat-lying, relatively competent deposits.

A stoping method in which ore is blasted into open stopes from sublevels and drawn from below, requiring competent wall rock and ore.

A mass mining method in which ore is undercut so it fractures and caves under gravity, then drawn through drawpoints, suited to large, weak, low-grade deposits.

The management of ore and waste draw from drawpoints or loading units to minimise dilution and ore loss and to maintain the required grade.

The unintentional mixing of waste or low-grade material with ore during mining, which lowers the grade delivered to the mill and must be estimated and controlled.

The excavation of a vertical or inclined access shaft from the surface, involving drilling, blasting, mucking, lining and hoisting operations in a restricted working space.

The raising of ore, waste, personnel and materials through a shaft by means of a winder, rope and conveyance, whose capacity and safety govern shaft output.

The condition in which a rock or soil slope resists failure, assessed by comparing shear strength with shear stress along potential slip surfaces and expressed as a factor of safety.

The formation of acidic, metal-bearing water when sulphide minerals, especially pyrite, oxidise on exposure to air and water in mine workings or waste dumps.

The finely ground waste material remaining after valuable minerals are extracted from ore, stored in engineered impoundments or used as backfill.