Igneous

Intrusive Ore Deposit

Intrusive ore Deposits

Chromite "Chromium ore deposit types"
Both olivine and chromite deposits are closely associated with ultramafic plutonic rocks. The bulk of chromite reserves occur in the large, laterally extensive stratiform where tabular seams prevail or Bushveld-type form occurring in stable shield areas as exemplified by the Bushveld Igneous Complex in South Africa, the Great Dyke of Zimbabwe, northern Finland, and Bahia State, Brazil. In contrast, the smaller podiform or Alpine-type deposits occur in mobile belts "in the mantle section of ophiolites" such as the Urals of the former U.S.S.R.; the Tethyian mountain chain of the Balkans, Turkey, and Iran; and the Circum-Pacific belt. Overall, significant chromite reserves and production are restricted to fewer than 10 countries, and nonmetallurgical grades to still fewer, namely South Africa, the Philippines, Turkey, Greece, Finland, Albania, and India.

Global Chromite Resources Map
Source: Department of Mineral Resources, South Africa, Heinz H. Pariser

The Bushveld contains giant exploitable resources of 2300Mt of mainly metallurgical chromite at >50% Cr2O3 (Vermaak 1986). Genetically similar but much smaller deposits occur in the Great Dyke, Zimbabwe and the Stillwater Complex, Montana. In the Great Dyke, massive chromitite dykes (offsets) extend 100m downwards into footwall sandstone and conglomerate.

Chromite resources are very large and sufficient for centuries of consumption. However, only two countries control 90% of the resources (South Africa and Kazakhstan), implying a certain geopolitical risk.

Exploration for podiform chromite is challenging. Outcropping ore has been found and exploited long ago. Deep orebodies are sought by a combination of detailed geological mapping, structural geology and geophysical methods for locating high-density or magnetic material at depth (gravimetric and magnetic methods). Seismic methods may help to locate massive ore. Stratiform chromite seams are found by geological and petrological investigations. Note that it is always advisable to examine any chromitite for possible by-product platinum element contents.

World Chromite Ore Reserve Base / Mine Production
Source: Department of Mineral Resources, South Africa, Heinz H. Pariser

Global Chromite Supply
Source: Department of Mineral Resources, South Africa, Heinz H. Pariser

Ore & Concentrate Trade Flow
Source: Department of Mineral Resources, South Africa, Heinz H. Pariser

Olivine

Olivine Forsterite (Mg) and fayalite (Fe2) are end members of a continuous solid solution series. Manganese and calcium may substitute part of Mg and Fe. Valuable olivine is generally forsteritic. Already in antiquity, it was mined as a semiprecious, clear and translucent mineral (peridote) on tiny Zebirget Island (St Johns) in the Red Sea, Egypt. About 100 years ago, nearly monomineralic olivine rocks (dunite) were first used as a refractory material. With a melting point of 1890C, Mg-rich forsterite is understandably preferred to Fe-rich fayalite (1205C).

Olivine is in demand for manufacturing special refractories, but mainly (75% of total consumption) as a slag conditioner similar to dolomite in pig iron production. In this sector, iron content of olivine is accepted. The use of olivine is advantageous because it replaces dolomite and reduces coke consumption, thereby diminishing CO2 emissions. Olivine is also used for sintered heatstorage elements in electrical heating appliances where it competes with magnesia made from magnesite. 

Commercial olivine and dunite deposits are common in alpine-type ultrabasic terrains. A limited market restricts production to Norway"The world’s largest olivine mine is Aheim in western Norway", with 80% of world production; smaller producers are Spain, Italy, Japan, and the United States. The modest U.S. production is from North Carolina and Washington. Nepheline Syenite Nepheline syenite is a relatively common, silica-deficient, magmatic intrusive rock. Commercial production, however, is limited to large operations in Canada, Norway, and the former U.S.S.R. because of the limited market size, competition from feldspar, and the requirement for a consistently low iron content. Production from Canada and Norway is virtually all exported; this accounts for 70% and 30%, respectively, of world production, excluding the former U.S.S.R.
International statistics on olivine (dunite) production are incomplete and most is probably comprised in the giant class of “crushed stone and aggregates”. A large seaside quarry at Atammik between the capital Nuuk and Maniitsoq in Greenland, with an annual production of 1 Mt, was put on hold in 2009.

Nepheline syenite 

Nepheline syenite is a relatively common, silica-deficient, magmatic intrusive rock. Commercial production, however, is limited to large operations in Canada, Norway, and the former U.S.S.R. because of the limited market size, competition from feldspar, and the requirement for a consistently low iron content. Production from Canada and Norway is virtually all exported; this accounts for 70% and 30%, respectively, of world production, excluding the former U.S.S.R.

It also provides a source of unusual mineral specimens and rare earth elements (REE) extraction. The industrial use of Nepheline syenite includes refractories, glass making, ceramics and, in pigments and fillers. It is also used as construction facade, interior wall texture, and countertops.

Diamonds

Most diamonds formed in the Earth’s lithospheric mantle, at high pressures and relatively moderate temperatures. Diamonds are brought to the surface by volcanic eruptions that originate from these source regions defined by the “cool” 40mW/m2 mantle geotherm of Pollack & Chapman (1977).The primary geological habitat for natural diamond is kimberlite, an ultrabasic intrusive rock associated with stable shield regions. Diamondiferous kimberlites are concentrated in southern Africa, the Siberian Platform, Brazil, and Western Australia. Ages range from Precambrian in South Africa to Recent in Tanzania. Diamonds are also produced commercially from placer deposits such as in Namibia (see Sedimentary section ). Overall, Africa is a prime region for diamond production, in particular South Africa, Botswana, Namibia, Lesotho, Swaziland, and Angola.

Industrial diamond is foremost an abrasive that is used for drilling, grinding, sawing and polishing. Useful properties apart from its hardness include toughness, resilience against aggressive chemicals and high-temperature stability. Applications are numerous, ranging from microsurgery to deep drilling for petroleum and cutting large monolithic dimension stones. Most of this market is served by synthetic diamonds.

World's top 17 diamond producing countries for 2011 and 2012

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Lithium

Lithium tends to concentrate in silicic rocks and pegmatites containing feldspar, quartz, and mica in places such as Bernic Lake, Manitoba, Canada (spodumene, lepidolite); Greenbushes, Western Australia (spodumene); and Bikita, Zimbabwe (petalite, spodumene, lepidolite, eucryptite). Although lithium-rich pegmatites are separated to form a lithium concentrate plus by-product feldspar, quartz, or mica, these pegmatitic sources of lithium have been strongly challenged by lithium extracted from brines in Chile and Argentina (in fact, the availability of lithium from brines forced the closure of a hard-rock operation in the Kings Mountain area of North Carolina).
Dentified lithium resources total 5.5 million tons in the U.S and approximately 34 million tons in other countries. Identified lithium resources for Bolivia and Chile are 9 million tons and in excess of 7.5 million tons, respectively. Identified lithium resources for Argentina, China, and Australia are 6.5 million tons, 5.4 million tons, and 1.7 million tons, respectively. Canada, Congo (Kinshasa), Russia, and Serbia have resources of approximately 1 million tons each. Identified lithium resources for Brazil total 180,000 tons.

World map of Lithium Distribution Source"USGS"

Lithium minerals may be associated with pollucite CsAlSi2O6.H2O, which is the main carrier of caesium (crustal abundance 3 ppm, density 1.892 g/cm3, melting point 28.64 C), as in the Bernic Lake rare metal pegmatite (Tanco mine, Manitoba), which contains 300,000 t pollucite with an average Cs2O content of 24% (USGS 2010). Other sources include caesium beryl exploited from Li-rich pegmatites and lithium brines. Caesium is part of X-ray tubes, atomic clocks, scintillometers, magnetometers and special glasses. Most of it is processed into caesium formate (CsOOH) brine, which is non-toxic and displays a high density (2.3 g/cm3) making it a useful ingredient of high-pressure and high-temperature drilling fluids (e.g. ultra-deep holes in hydrocarbon exploration).

Mining for Lithium:

Most lithium is recovered from brine, or water with a high concentration of lithium carbonate. Subsurface brines trapped in the Earth’s crust are the major source material for lithium carbonate. These sources are less expensive to mine than from rock such as spodumene, petalite, and other lithium-bearing minerals.

Brine production of lithium begins by first pumping the brine into evaporative ponds. Over 12 to 18 months, concentration of the brine increases to 6,000 ppm Li through solar evaporation. When the lithium chloride reaches optimum concentration, the liquid is pumped to a recovery plant and treated with soda ash, precipitating lithium carbonate, which is then filtrated, dried, and shipped.

Beryllium

One of the most important industrial metals in the world. Although beryl is also associated with pegmatites in locations such as Brazil, the former U.S.S.R., and western Canada, production of bertrandite in Utah now accounts for 80% of the world’s beryllium supply.

The reason this metal is so important is because of its physical properties.  It is twice as light as aluminum, has an incredibly high melting point at 1287°C, it is not affected by air or water even when it is red hot, and it is many times stronger that other metals, even engineered metals such as titanium and steel alloys.It is used in a wide range of tools including chisels.  It is used in high-end clock and watch movements.  It is used for making bearings that will resist extreme heat.  It is also very corrosion resistant when alloyed with copper. Because of its high strength and light weight it is used to hold the guidance systems in many missiles and rockets.

Economic sources of beryllium are only: epithermal stratiform volcanogenic beryllium impregnations in rhyolite tuffite; rare element pegmatites of the lithium-caesiumtantalum (LCT) type.Several epithermal stratiform volcanogenic beryllium deposits occur in the area of Spor Mountain in Utah, USA.

Bertrandite Mining:

Unlike beryl, in which the mineral can be identified by color and crystal structure, bertrandite mineralization cannot be recognized by the naked eye. Consequently geologic and geochemical evaluations are conducted on a specific area, followed by a drilling program to determine if an economic ore body exists.After delineating an ore body, overburden is removed to within 2 m of the ore.  In the 2-m cover remaining, drill benches are constructed on 7.5-m centers to take samples of the ore body at 0.6-m intervals. Information obtained from analyzing the samples allows cross sections and contour maps to be developed. These maps are used to plan the mining and processing operations.

After the maps are prepared, the remainder of the overburden is removed, and the ore is mined, typically with a self-loading scraper. Because of the irregular ore-grade distribution in the ground, the ore is mined from areas defined by drill data and placed in a stockpile in layers to obtain a more homogeneous blend. Further drilling, sampling, and assaying of the stockpiled ore is then performed to generate a map that delineates ore-grade distribution throughout the stockpile. On the basis of the grade distribution, stockpiled ore is selectively trucked to the mill for further processing.

Fluorspar

Fluorite is commercially named fluorspar composed of calcium fluoride (CaF2).  It is the principal source of fluorine. The same is used in production of hydrofluoric acid, which is used in a wide variety of industrial applications including glass etching. Fluorite tends to occur in well-formed isometric crystals, forming cubes and octahedrons. It also occurs in both massive and earthy forms, and as crusts or globular aggregates with radial fibrous texture.
Fluorspar is a “persistent” mineral occurring in various ore deposits, including Mississippi Valley (lead/zinc) type deposits, hydrothermal veins, stratabound or Manto deposits, contact metamorphic terrains, and alkali rock complexes. More than 50% of world production comes from China, with Mexico, Mongolia, South Africa, and Russia adding another 30%. Much of this production is exported, and the availability of attractively priced exports has forced the closure of smaller operations in North America and Europe. Other producers, largely for export, include Brazil, Kenya, Morocco, and Uzbekistan.

Sources:

In some areas, fluorite rich veins may be weathered to depths of as much as 75 m. Such weathered ore, a mixture of clay and fragments of fluorite and detached wall rock, may be mined open pit with draglines, scrapers, or power shovels to depths of as much as 50 m. Below that, underground mining methods, involving modified top slicing or overhead shrinkage stoping, are used.

Vein Mining:

Vein mining is commonly done by shrinkage stoping, cut-andfill, and open stoping where strong walls occur. Closely spaced shrinkage stope bins may give way to widely spaced bins, with electric and air slushers being used in the tops of stopes to transport the overbreak to the ore pass. Air-operated, rubber-tired, muckhaul units can be adapted to in-stope work. Where shrinkage stoping is used, broken ore is commonly moved to the shaft by track haulage using battery-powered locomotives and 1- or 2-t side-dump cars.

With the introduction of diesel haul units of less than 1.5 m in width, mining can be changed from shrinkage stoping to ramp subleveling in veins. Loaders can be served by small diesel trucks carrying 3 to 4 t. Ventilation for the diesel equipment is usually handled by lines of woven plastic tubing. In shafts, bucket hoisting is supplanted by lifting in larger skips. In larger mines, crushers are installed over skip-loading pockets at the shaft bottom, which improves skip loading.

Room and Pillar:

In bedded deposits, room-and-pillar patterns are used, with the widths of rooms governed by roof conditions. Newer equipment has rubber tires and is diesel operated, including the muckhaul units—which have buckets ranging in size from 0.9- to 4.6-m3 capacity—and rubber-tired diesel trucks with 3- to 18-t capacity. Drilling is done by diesel-propelled jumbos in the bedded ore mines, but the jackleg drills are still used in narrower working places and drifts. In multileveled ore bodies, haulage ramps on 12% to 15% grades connect the levels. Vertical raises are used to facilitate ventilation requirements.