About the Groundwater Driven Mineralization Display
University of Waterloo alumnus Jim Reimer donated funds to install these showcases and purchase specimens to enhance his personal mineral collection, which was also donated to the University. This display shows specimens from hydrothermal mineral deposits and will be used to describe how they are formed.
Some of the localities represented are known for economic lead and zinc deposits. Lafarge Quarry, Dundas, Ontario; Pine Point, Northwest Territories; and Nanisivik, Nunavut are Canadian examples of the type of mineralization known as Mississippi Valley Deposits. These deposits form as enormous quantities of hot brine migrate through the rock, opening cavities and depositing minerals, oil and gas.
Low Temperature Minerals
Malachite is a green copper carbonate which forms when copper ore weathers, meaning it is changed by air, water, and other environmental factors. Malachite is often used as an ornamental mineral.
Crocoite is lead chromate, which makes striking red crystals. It forms by oxidation (addition of oxygen from the air) of lead ore, along with the addition of chromium, which is carried by water from other rocks. It is sometimes used in paint as a yellow pigment.
Petrified wood forms when mineral-bearing water percolates through buried trees, depositing quartz in fluid-filled openings in the wood or replacing the wood with quartz. This preserves the wood’s structure, leaving what look like stone trees behind. The logs were replaced by silica, coloured with oxides of iron and manganese. The most common of the fossil trees in the Petrified Forest is Araucarioxylon arizonicum. Some of the logs, although broken into segments, represent substantial trees which would be over 50 metres tall when they were alive. They are relatives of the modern “Monkey Puzzle” Tree.
Agate forms when water, which contains dissolved quartz, flows into cavities in lava and leaves behind a thin layer of quartz. A sequence of these layers of quartz creates the stone called agate.
When water, which is trapped in sediment, rises to the surface and evaporates it can leave behind its dissolved minerals, which crystallize to form gypsum or barite roses. Sometimes sand gets embedded in the crystals as they form. This can be seen in the Gypsum crystals from Mexico.
Stalactites grow from the ceiling of a cave and stalagmites grow from the floor. They are formed when water, continuously dripping from the ceiling, leaves small traces of minerals behind.
Geodes are cavities, left when the rock cooled, in which minerals are deposited from solution. Okenite is a silicate mineral, meaning that it contains the element silicon. It forms clusters of crystals, which look like fluffy white balls, in geodes in volcanic rock.
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Medium temperature minerals
Gypsum is a common mineral. It can be deposited from lake and sea water, as well as from hot springs, from volcanic vapours, and from sulphate solutions in veins. It is typically abundant wherever extensive sedimentary beds occur, predominantly those rich in saline precipitates where there the water contains a lot of sulphate.
Celestine is a strontium sulphate mineral which occurs as crystals and as masses. It is commonly associated with minerals like gypsum and halite. It mainly forms in sedimentary rocks of carbonate marine origin, particularly limestones, where it fills vents and other openings. It can also form as a primary hydrothermal mineral, as is the case with the specimens below
Strontium ions are thrown out into the solution as aragonite alters to calcite. The strontoum then enters low-temperature hydrothermal solutions and combines with oxidized sulphur to form Celestine.
Galena is present in practically all hydrothermal sulphide ore bodies. It is associated with pyrite, chalcopyrite and sphalerite, calcite and fluorite. Galena precipitates out of hydrothermal solutions easily when lead ions combine with sulphur ions, which is more likely to occur with decreasing temperature and pressure. The lead ions likely come from deeply buried sedimentary and metamorphic rocks and are carried closer to the surface by high-temperature aqueous fluids.
Fluorite, calcium fluoride, is a very common mineral found in many kinds of deposits. It is abundant as both masses and crystals in hydrothermal ore veins. Fluorite is normally found among limestones, and is often associated with galena, barite, quartz, calcite and dolomite. The calcium ions come from waters close to limestones, because limestone is so soluble. The calcium ions combine with fluoride ions, found in small quantities in deep seated spring waters, forming fluorite. Pale-coloured octahedral crystals form at higher temperatures, darker coloured cubic crystals at lower temperatures.
Calcite is very common and abundant in all classes of rocks except granitic types and pegmatites. It is found as a gangue mineral in many kinds of hydrothermal veins, in caverns in limestone formations, or deposited from warm or cold springs. Hydrothermal alteration occurs when hot waters free calcium and carbonate ions from separate sources, and these ions combine and precipitate calcite.
Sphalerite occurs with other sulphides in hydrothermal ore veins (as with the specimens below), in disseminated deposits, in veins in igneous rocks or in contact metasomatic deposits. Sphalerite forms in hydrothermal veins when zinc ions combine with sulphate ions.
Dolomite also occurs in hydrothermal veins and is often associated with quartz, calcite, barite, fluorite, etc. Hydrothermal dolomitization occurs when hot (75-250°C) magnesium-rich brine flows up active faults, hot sealing shales, evaporates, or other low permeability strata, and then flows laterally into permeable carbonates that are typically less than 1km from the surface.
Marcasite is also found in abundance in sulphide veins, and is exceptionally abundant in lead-zinc deposits. It is precipitated by the slow addition of iron to a sulphate solution around 75°C.
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High Temperature Minerals
Galena is present in practically all hydrothermal sulphide ore bodies. It is associated with pyrite, chalcopyrite and sphalerite, calcite and fluorite. Galena precipitates out of hydrothermal solutions easily when lead ions combine with sulphur ions, which is more likely to occur with reducing temperature and pressure. The lead ions likely come from deeply buried sedimentary and metamorphic rocks and are carried closer to the surface by high-temperature aqueous fluids.
Sphalerite occurs with other sulphides in hydrothermal ore veins (as with the specimens below), in disseminated deposits, in veins in igneous rocks or in contact metasomatic deposits. Sphalerite forms in hydrothermal veins when zinc ions combine with sulphate ions. Calcite is very common and abundant in all classes of rocks except granitic types and pegmatites. It is found as a gangue mineral in many kinds of hydrothermal veins, in caverns in limestone formations, or deposited from warm or cold springs. Hydrothermal alteration occurs when hot waters free calcium and carbonate ions from separate sources, and then the ions combine to precipitate calcite.
Galena is present in practically all hydrothermal sulphide ore bodies. It is associated with pyrite, chalcopyrite and sphalerite, calcite and fluorite. Galena precipitates out of hydrothermal solutions easily when lead ions combine with sulphur ions, which is more likely to occur with declining temperature and pressure. The lead likely comes from deeply buried sedimentary and metamorphic rocks and is carried closer to the surface by high-temperature aqueous fluids. Calcite is very common and abundant in all classes of rocks except granitic types and pegmatites. It is found as a gangue mineral in many kinds of hydrothermal veins, in caverns in limestone formations, or deposited from warm or cold springs. Hydrothermal alteration occurs when hot waters free calcium and carbonate ions from separate sources, and then the ions combine to precipitate calcite.Siderite is typically found in large deposits in sedimentary rocks, but good crystallized specimens are obtained mainly from sulphide ore veins where it forms hydrothermally (though it may also be found in some pegmatites and in metamorphosed sedimentary rocks). Siderite is an iron carbonate mineral, likely formed when iron ions were present near a source of carbonate ions and combined with them.
Sphalerite occurs with other sulphides in hydrothermal ore veins (as with the specimens below), in disseminated deposits, in veins in igneous rocks or in contact metasomatic deposits. Sphalerite forms in hydrothermal veins when zinc ions combine with sulphate ions. Calcite is very common and abundant in all classes of rocks except granitic types and pegmatites. It is found as a gangue mineral in many kinds of hydrothermal veins, in caverns in limestone formations, or deposited from warm or cold springs. Hydrothermal alteration occurs when hot waters free calcium and carbonate ions from separate sources, and then the ions combine to precipitate calcite. Dolomite also occurs in hydrothermal veins and is often associated with quartz, calcite, barite, fluorite, etc. Hydrothermal dolomitization occurs when hot (75-250°C) magnesium-rich brine flows up active faults, hot sealing shales, evaporates, or other low permeability strata and then flows laterally into permeable carbonates that are typically less than 1km from the surface.
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Nanisivik Baffin Island collection
Nanisivik Mine was high in Canada’s Arctic. The Nanisivik mine operated from 1976 until 2002 in one of the world’s most inhospitable environments. Located on Northern Baffin Island, almost 800 km above the Arctic Circle, in the territory of Nunavut, Nanisivik experiences daily average temperatures as low as -30°C in February, but only as high as 5°C in July. The town was built in 1975 to support the mining and processing of lead-zinc ore from the Nanisivik Mine. The deposit is a Mississippi Valley Type (MVT) carbonate–hosted lead-zinc deposit. The mine was closed in 2002 due to failing metal prices and declining resources. Nanisivik had a population of 287 in 1996, but that had fallen to 77 in 2001, as the mine wound down, and is now zero.
Despite the mine closure, Nanisivik will live on because of plans by the Canadian government to use the town’s port as a naval station, which will help maintain Canada’s presence in the Arctic.
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Galena Deposits
Galena (lead sulphide, PbS) is the main ore mineral of lead. Found throughout the world, Galena is one of the most abundant minerals. Its structure consists of alternating lead and sulphur atoms packed in cubes, resulting in the cubic crystal form in which galena is often found.
Lead beads, dating to more than 6,000 years ago, have been found in Turkey, suggesting that galena was known at that time since naturally-occurring metallic lead is rare. To produce lead, galena is ground up and roasted, producing lead oxide, which is heated with carbon in a blast furnace, to make metallic lead. Silver is a common constituent of galena deposits, making them an important silver ore as well.
Other uses of galena:
While galena is primarily important as lead ore, there are a few uses for this mineral in its unrefined form. Crystals of galena are used as detectors, to convert radio signals to sound, in simple, early radios called crystal sets. Since ancient times, galena has been ground to produce Kohl, which is used as eye make-up. Because lead ore is toxic, modern kohl make up retains the name and look of its ancient counterpart, but contains no lead.