Back - The ceiling or roof of an underground opening. Backfill - Waste material used to fill the void created by mining an ore- body. Background - Minor amounts of radioactivity due not to abnormal amounts of radioactive minerals nearby, but to cosmic rays and minor residual radioactivity in the vicinity. Back sample - Rock chips collected from the roof or back of an underground opening for the purpose of determining grade. Backwardation - A situation when the cash or spot price of a metal stands at a premium over the price of the metal for delivery at a forward date. Balance sheet - A formal statement of the financial position of a company on a particular day, normally presented to shareholders once a year. Ball mill - A steel cylinder filled with steel balls into which crushed ore is fed. The ball mill is rotated, causing the balls to cascade and grind the ore. Banded iron formation - A bedded deposit of iron minerals. Basalt - An extrusive volcanic rock composed primarily of plagioclase, pyroxene and some olivine. Basal till - Unsorted glacial debris at the base of the soil column where it comes into contact with the bedrock below. Basement rocks - The underlying or older rock mass. Often refers to rocks of Precambrian age which may be covered by younger rocks. Base camp - Center of operations from which exploration activity is conducted. Base metal - Any non-precious metal (eg. copper, lead, zinc, nickel, etc.). Basic rocks - Igneous rocks that are relatively low in silica and composed mostly of dark-colored minerals. Batholith - A large mass of igneous rock extending to great depth with its upper portion dome-like in shape. Similar, smaller masses of igneous rocks are known as bosses or plugs. Bauxite - A rock made up of hydrous aluminum oxides; the most common aluminum ore. Bear market - Term used to describe market conditions when share prices are declining. Bedding - The arrangement of sedimentary rocks in layers. Beneficiate - To concentrate or enrich; often applied to the preparation of iron ore for smelting. Benlonite - A clay with great ability to absorb water and which swells accordingly. Bessemer - An iron ore with a very low phosphorus content. Bio-leaching - A process for recovering metals from low-grade ores by dissolving them in solution, the dissolution being aided by bacterial action. Biotite - A platy magnesium-iron mica, common in igneous rocks. Bit - The cutting end of a drill frequently made of an extremely hard material such as industrial diamonds or tungsten carbide. Blackjack - A miners term for sphalerite (zinc sulphide). Black smoker - Volcanic vent found in areas of active ocean floor spreading, through which sulphide-laden fluids escape. Blaster - A mine employee responsible for loading, priming and detonating blastholes. Blast furnace - A reaction vessel in which mixed charges of oxide ores, fluxes and fuels are blown with continuous blast of hot air and oxygen-enriched air for the chemical reduction of metals to their metallic state. Blasthole - A drill hole in a mine that is filled with explosives in order to blast loose a quantity of rock. Blister copper - A crude form of copper (assaying about 99%) produced in a smelter, which requires further refining before being used for industrial purposes. Block caving - An inexpensive method of mining in which large blocks of ore are undercut, causing the ore to break or cave under its own weight. Board lot - One hundred shares. Bond - An agreement to pay a certain amount of interest over a given period of time. Boom - A telescoping, hydraulically powered steel arm on which drifters, manbaskets and hydraulic hammers are mounted. Box hole - A short raise or opening driven above a drift for the purpose of drawing ore from a stope, or to permit access. Break - Loosely used to describe a large-scale regional shear zone or structural fault. Breast- A working face in a mine, usually restricted to a stope. Breccia - A rock in which angular fragments are surrounded by a mass of fine-grained minerals. Broken reserves - The ore in a mine which has been broken by blasting but which has not yet been transported to surface. Brunton compass - A pocket compass equipped with sights and a reflector, used for sighting lines, measuring dip and carrying out preliminary surveys. Bulk mining - Any large-scale, mechanized method of mining involving many thousands of tonnes of ore being brought to surface per day. Bulk sample - A large sample of mineralized rock, frequently hundreds of tonnes, selected in such a manner as to be representative of the potential orebody being sampled. Used to determine metallurgical characteristics. Bullion - Metal formed into bars or ingots. Bull market - Term used to describe financial market conditions when share prices are going up. Bull quartz - A prospectors term for white, coarse-grained, barren quartz. Byproduct - A secondary metal or mineral product recovered in the milling process.   Prospecting &  Mining Basics