Mining Glossary M

• Mafic - Igneous rocks composed mostly of dark, iron- and magnesium-rich minerals.

• Magma - The molten material deep in the Earth from which rocks are formed.

• Magmatic segregation - An ore-forming process whereby valuable minerals are concentrated by settling out of a cooling magma.

• Magnetic gradient survey - A geophysical survey using a pair of magnetometers a fixed distance apart, to measure the difference in the magnetic field with height above the ground.

• Magnetic separation - A process in which a magnetically susceptible mineral is separated from gangue minerals by applying a strong magnetic field; ores of iron are commonly treated in this way.

• Magnetic susceptibility - A measure of the degree to which a rock is attracted to a magnet.

• Magnetic survey - A geophysical survey that measures the intensity of the Earth's magnetic field.

• Magnetite - Black, magnetic iron ore, an iron oxide.

• Magnetometer - An instrument used to measure the magnetic attraction of underlying rocks.

• Map-staking - A form of claim-staking practised in some jurisdictions whereby claims are staked by drawing lines around the claim on claim maps at a government office.

• Marble - A metamorphic rock derived from the recrystallization of limestone under intense heat and pressure.

• Margin - Cash deposited with a broker as partial payment of the purchase price for any type of listed stock. The stock is held by the broker as security for the loan.

• Marginal deposit - An orebody of minimal profitability.

• Market order - An order to buy or sell at the best price available. In absence of any specified price or limit, an order is considered to be "at the market".

• Matte - A product of a smelter, containing metal and some sulphur, which must be refined further to obtain pure metal.

• Metalurgical coal - coal used to make steel.

• Metallurgy - The study of extracting metals from their ores.

• Metamorphic rocks - Rocks which have undergone a change in texture or composition as the result of heat and/or pressure.

• Metamorphism - The process by which the form or structure of rocks is changed by heat and pressure.

• Migmatite - Rock consisting of thin, alternating layers of granite and schist.

• Mill - A plant in which ore is treated and metals are recovered or prepared for smelting; also a revolving drum used for the grinding of ores in preparation for treatment.

• Milling ore - Ore that contains sufficient valuable mineral to be treated by milling process.

• Millivolts - A measure of the voltage of an electric current, specifically, one-thousandth of a volt.

• Minable reserves - Ore reserves that are known to be extractable using a given mining plan.

• Mineral - A naturally occurring homogeneous substance having definite physical properties and chemical composition and, if formed under favorable conditions, a definite crystal form.

• Muck - Ore or rock that has been broken by blasting.

• Muck Sample - A representative piece of ore that is taken from a muck pile and then assayed to determine the grade of the pile.