* indicates further definition within glossary
Agglomerate - a coarse pyroclastics deposit, or its lithified equivalent, containing a large proportion of rounded, fluidly shaped *volcanic bombs.
Argillic Alteration - *hydrothermal alteration of certain minerals within a rock, to clay minerals (e.g. *alunite and *kaolinite).
Advanced Argillic Alteration - *feldspar-destructive *hydrothermal alteration in which *kaolinite-*quartz dominate at low temperatures (below 300 degrees C). Implies very low pH and low alkalis content of the *hydrothermal fluid.
Alteration - changes in the chemical composition of a rock affected by external causes such as hydrothermal fluids or weathering.
Alunite - a mineral with the chemical composition KAl3(SO4)2(OH)6, typically formed by *hydrothermal *alteration associated with *epithermal systems.
Andesite - a fine-grained, intermediate volcanic rock.
Bottle Leach - pulped material is agitated by rolling bottles on a set of rollers, continuously for 72 hours. The leach (pregnant) solution and the washed tailings are then assayed for gold values. This test can be used to compute the reagent requirements of the sample.
Breccia - a coarse-grained rock composed of broken angular rock fragments enclosed in a fine-grained matrix or held together by a cement comprising fine grained minerals. A rock that has formed by this process is said to be 'brecciated'.
Chalcedony - a *cryptocrystalline variety of silica with a compact fibrous structure and waxy lustre. It may be translucent or semi-transparent and occurs in a variety of colours. It is often found as a deposit, lining or filling cavities in rocks.
Chalcopyrite - a copper mineral with the chemical composition CuFeS2.
Chip Sampling - rock particles chipped from a surface, either along a line or over an area. It is used as an inexpensive reconnaissance tool to see if mineralization is of sufficient interest to warrant the more expensive channel sampling.
Channel Sampling - a channel is cut in an outcrop, usually the same diameter as the core being collected, to maintain the volume-variance relationships. Samples are normally 0.5-5 kg in weight, mostly 1-2 kg, and each is rarely taken over 2 m or so in length.
Column Leach - crushed material is put into lab-sized columns (6-12 inches diameter by 4-8 feet high) and leached with cyanide solution, over a number of days. The tests are intended to indicate the gold and silver recoveries obtainable by heap leaching.
Cryptocrystalline - a crystalline aggregate so finely divided that individual crystals cannot be distinguished under a normal microscope.
Dacite - a coarse-grained silica-rich volcanic rock.
Epithermal - said of a *hydrothermal mineral deposit formed within ~1 km of the Earth's surface and in the temperature range of 50oC-200oC, occurring mainly as veins. Also said of that environment. See *Low-Sulphidation and *High-Sulphidation.
Fault - a fracture in earth materials along which the opposite sides have been displaced parallel to the plane of movement. The surface along which movement takes place is known as a fault plane.
Footwall - the mass of rock below a fault plane, mineralized zone or mine working, in particular the wall rock beneath a fault or inclined vein. Compare *Hanging Wall.
Grab Sampling - samples are representative handfuls or shovelfuls of broken rock, picked at random. It is a low cost and rapid method and best used where the mineralization and waste break into particles of about the same size. It is particularly useful as a means of quality control of mineralization at strategic sampling points.
Hanging Wall - The overlying side of a fault, mineral deposit or mine working, in particular the wall rock above a fault or inclined vein (Compare *Footwall).
High Sulphidation (HS) - high sulphidation deposits are one of three principal types of *epithermal deposits, formed from high-temperature magmatic fluids. Their defining features include *pyrite-rich, high sulphidation state sulphide assemblages typified by copper sulphides (enargite, luzonite, digenite, chalcocite and covellite); and *advanced argillic alteration assemblages typified by *quartz and clay minerals (*alunite, *pyrophyllite, and *kaolonite/dickite).
Hydrothermal - of or pertaining to hot water, to the action of hot water, or the products of this action, such as a mineral deposit precipitated from a hot aqueous solution, with or without demonstrable association with *igneous processes.
Hypogene - a term applied to mineral deposits formed by ascending fluids within the Earth. These deposits are primary and formed beneath the Earth's surface.
Igneous - said of a rock or mineral that solidified from molten or partially molten material, i.e. from magma; also applied to processes leading to, related to, or resulting from the formation of such rocks.
Intermediate Sulphidation (IS) - transitional between *high sulphidation and *low sulphidation and typified by *sulphide assemblages of tennantite tetrahedrite, hematite-*pyrite-magnetite, pyrite, chalcopyrite and iron-poor sphalerite.
JORC - Joint Ore Reserves Committee. The Code for Reporting of Mineral Resources and Ore Reserves (the JORC Code) is widely accepted as a standard for professional reporting purposes.
Kaolinite - a clay mineral formed by the breakdown of feldspar, usually by *hydrothermal *alteration.
Lithocap - lithocaps are large masses of pyritic, advanced argillic and silicic (leached) alteration that are located between the subvolcanic intrusive environment and the *Palaeosurface.
Low Sulphidation (LS) - low sulphidation deposits are one of three principal types of *epithermal deposits, formed through the mixture of magmatic fluids and meteoric water. They are typified by pyrite-pyrrhotite-asenopyrite assemblages and Fe-rich sphalerite.
Mesozoic - an era ranging from 230 to 70 million years before present that includes the Triassic, Jurassic and Cretaceous periods.
Miocene - an epoch of the *Tertiary period from 24.6 to 5.1 million years before present.
Molybdenite - a mineral with the chemical composition MoS2.
Opal - a hydrated, amorphous form of silica, characteristic of very high level *epithermal systems and hot spring deposits.
Orogenic belt - a linear region that has been subjected to deformation, including folding, during a mountain-building episode.
Oxide - a mineral compound of oxygen and one or more metallic element (Compare *Sulphide).
Oxide Zone - the upper portion of a mineralized zone that has been modified by a solution of surface waters bearing oxygen, soil acids and carbon dioxide. It extends from the surface to the water table. Primary ore minerals in this zone react with this solution to produce various secondary minerals containing oxygen (Compare *Sulphide Zone).
Palaeo - a prefix indicating pre-*Tertiary origin, and generally altered character, of a rock or feature to the name of which it is added, e.g. palaeosurface.
Phenocryst - a relatively large, conspicuous crystal in a finer grained groundmass in a *porphyritic rock.
Pliocene - an epoch of the Tertiary period from 5.1 to 2 million years before present.
Porphyritic - the texture of an igneous rock in which larger crystals (*phenocrysts) are set in a finer-grained groundmass, which may be crystalline or glassy or both; a rock with such texture.
Porphyry - an igneous rock of any composition that contains conspicuous *phenocrysts in a fine grained groundmass.
Porphyry deposits - low-grade, large-tonnage deposits, principally mined for copper, molybdenum and gold or tin, normally intimately associated with intermediate to acid igneous rocks and characterised by intense and extensive *hydrothermal *alteration of the host rocks.
Pyrite - an iron bearing *sulphide mineral with the chemical composition FeS2. Its yellow-gold colour has often led to it being mistaken for gold, hence its more common name, "fool's gold".
Pyroclastic - fragmented rock material formed by a volcanic explosion or ejection from a volcanic vent.
Pyrophyllite - yellowish white, grey or pale-green mineral, Al2Si4O10(OH)2 *hydrothermal *alteration associated with *epithermal systems.
Quartz - a mineral with the chemical composition SiO2.
Schist - a yellowish metamorphic rock that is not defined by mineral composition but by the well-developed parallel orientation of more than 50 per cent of the minerals present, in particular those minerals of lamellar or elongate prismatic habit, much as mica and hornblende.
Stockwork - a mineral deposit in the form of a branching network of veinlets associated with a plutonic intrusion, particularly one of acid to intermediate composition. Typical of a *porphyry deposit.
Subduction - the process whereby one *tectonic plate slides beneath another.
Sulphide - a term referring to several types of chemical compounds in which sulphur is combined with one or more metals (Compare *Oxide).
Sulphide Zone - the lower portion of a mineralized zone that lies below the water table and therefore has not been modified by oxygen-bearing surface waters (Compare *Oxide Zone).
Supergene - a term applied to minerals formed by processes that almost always involve water, with or without dissolved material, descending from the surface. These fluids may cause secondary enrichment of minerals within the mineralized zone.
Talus - rock fragments derived from and lying at the base of a cliff or steep rocky slope.
Tectonic plate - an areally extensive section of the Earth's crust that behaves as a rigid coherent block.
Tertiary - a time period 65-1.8 million years ago. The term Tertiary corresponds to all the rocks and fossils formed during this period.
Thrust - a low-angle reverse *fault. The displacement on a thrust may be very large, for example the horizontal displacement of about 16 kilometres on the Moine Thrust in the northwest of Scotland.
Tuff - a *pyroclastic rock composed mainly of volcanic ash (fragments more than two millimetres in diameter).
Volcanic bomb - a clot of lava ejected from a volcanic vent while still molten. Bombs range in size from 64 millimetres to several metres in diameter and show great variation in shape; they are normally vesicular, at least to some extent, and occasionally hollow.
Vug - a cavity in a rock, usually lined by crystalline material. Also a cavity in a mineral vein.
Vuggy Silica - the texture produced by the dissolving of minerals and rock fragments, and the replacement of the remaining matrix of the rock by silica minerals, usually *quartz. This texture is common in *high-sulphidation epithermal systems.
