Mining-Prospecting Dictionary

• Macroscopic: Visible to the unaided eye.
• Magma: A mass of molten rock.
• Magmatic Ore Deposit: Formed by differentiation of mineral in magma.
  Magnetic separator: A device that uses a strong magnetic field to extract magnetic material from sands or concentrates.
• Malleable: Easily hammered and flattened when cold; refers to metals.
• Mallet: Wooden hammer for driving stakes.
• Margin: Money deposited as a guarantee of performance on the purchase or sale of a futures contract. On hedge markets, these deposits are called original or initial margins. If the market later fluctuates against the holder of the contract, he is required to make up the difference between his contract price and the current market price by paying additional funds called variation margins, also known as maintenance margins. When prices fluctuate in the trader's favor, excess variation margins may be withdrawn. (On NYMEX and COMEX markets, not on the LME.)
• Matrix rock: Gangue or rock that contains minerals or ores.
• Merrill Crowe Circuit or Merrill Crowe Process: Removal of gold from pregnant cyanide solution by deoxygenating, followed by precipitation on zinc dust, followed by filtration to recover the resultant auriferous gold slimes.
• Mesh: Related to the openings in a sieve or screen.
• Metallurgy: Science of ore processing and metals.
• Metaluminous: Said of an igneous rock in which the molecular proportion of aluminum oxide is greater than that of sodium and potassium oxides combined but generally less than of sodium, potassium, and calcium oxides combined.
• Metamorphism: Alteration of rocks subsequent to their deposition.
• Meteoric water: Surface water that sinks into cracks and fissures.
• Methane: An explosive mine gas composed of hydrogen and carbon.
• Metric tonne: Equal to 1.102 standard short ton (U.S.).
• Mill: Facility for processing ores or gravels. A plant where ore is ground, usually to fine powder, and the valuable metals are extracted by physical and/or chemical processes.
• Miner's inch: Water measure equal to 12.5 gallons per minute.
• Mineral: Solid substance having a regular and definite chemical composition.
• Mineralizatio n: Mineral-bearing rock. Mineralization generally refers to the presence of gold and silver established by widely spaced Drilling.
• Mining claim: A portion of the public lands claimed for the valuable minerals occurring in those lands; obtaining mineral rights under mining law.
• Molecule: Smallest atomic combination that comprises a certain compound.
• Monitor: Device for measuring equipment or processing operations.
• Monolith: A single, large block of stone.
• Monument: An object placed or erected to mark boundaries of a mining claim
• Mother lode: A gold-bearing district in California over 100 miles long. Also refers to very rich placer in ore deposits.
• Muck: A common term for waste rock in a mine; also sticky mud.
• Mudstone: 1. An indurated mud having the texture and composition of shale, but lacking its fine lamination or fissility; a blocky or massive, fine-grained sedimentary rock in which the proportions of clay and silt are approximately equal; a nonfissile mud shale. See also siltstone. 2. A general term that includes clay, silt, clay stone, siltstone, shael, and argillite, and that should be used only when the amounts of clay and silt are not known or specified or cannot be precisely identified. 3. A term used for a mud-supported carbonate sedimentary rock containing less than 10% grains (particles with diameters greater than 20 microns); e.g. a calcilutite. The term specifies neither mineralogical composition nor mud of clastic origin.