Misplaced Pages

#784215

83-620: Chromite grains are commonly found in large mafic igneous intrusions such as the Bushveld in South Africa and India. Chromite is iron-black in color with a metallic luster , a dark brown streak and a hardness on the Mohs scale of 5.5. Chromite minerals are mainly found in mafic-ultramafic igneous intrusions and are also sometimes found in metamorphic rocks . The chromite minerals occur in layered formations that can be hundreds of kilometres long and

166-510: A Johnson Matthey 2013 estimate. The demand of platinum has somewhat steadily been increasing, driven by the more intensive use per capita with developing area and urbanization, the demand reached an all-time high in 2005 of 208.3 metric tons. From 1975 to 2013, the autocatalytic and jewellery industry dominated the market with more than 70% of the gross demand. Jewellery was barely ahead of autocatalysts prior to 2002 with brute gross demand values being somewhat similar or higher. From 2002 to 2003,

249-405: A definitive control approach and distinct mitigation techniques can provide importance related to the safety of human health. When chromite ore is exposed to surface conditions, weathering and oxidation can occur. The element chromium is most abundant in chromite in the form of trivalent (Cr-III). When chromite ore is exposed to aboveground conditions, Cr-III can be converted to Cr-VI , which

332-403: A few meters thick. Chromite is also common in iron meteorites and form in association with silicates and troilite minerals. The chemical composition of chromite can be represented as FeCr 2 O 4 , with the iron in the +2 oxidation state and the chromium in the +3 oxidation state. bauxite, when presented as an ore , or in massive form, forms as fine granular aggregates. The structure of

415-483: A focus on PGEs (primarily platinum and palladium), vanadium, iron (generally from magnetite), chromium, uranium, tin, ... There are multiple major mining companies that are heavily involved within this area, particularly AngloAmerican , African Rainbow Minerals , Impala Platinum , Northam Platinum Ltd. , Lonmin plc , and more recently Bushveld Minerals . It has been reported that more than 20 billion metric tons of PGE ore rock has been indicated in South Africa by

498-617: A non-exhaustive list: The three largest ore bodies are the Merensky Reef , the UG2 Chromitite Reef and the Platreef : * Table modified from USGS , 2010. Most of the identified mineral inventory is from the three described reefs, most of it is located within the eastern limb but most of the reserves are found within the western limb. The chrome deposits of the Bushveld forms

581-461: A significant impact on the global environment. The environmental costs for platinum mines are only slightly higher in energy, somewhat lower in water and moderately higher in greenhouse gas emissions when compared to gold mining. South Africa's economy is heavily tied to its mining industry and has been greatly affected by low metal prices. Mining companies have had to cut costs by lowering production, closing mines, selling off projects, and reducing

664-495: A silica content between 45 and 55 wt% , corresponding to the silica content of basalt in the TAS classification . Such rocks are enriched in iron, magnesium and calcium and typically dark in color. In contrast, the felsic rocks are typically light in color and enriched in aluminium and silicon along with potassium and sodium . The mafic rocks also typically have a higher density than felsic rocks. The term roughly corresponds to

747-441: A size range of 5–20 mm. Other minerals that are seen in podiform deposits are olivine , orthopyroxene , clinopyroxene , pargasite , Na-mica , albite , and jadeite . Chromium extracted from chromite is used on a large scale in many industries, including metallurgy, electroplating, paints, tanning, and paper production. Environmental contamination with hexavalent chromium is a major health and environmental concern. Chromium

830-575: Is a portmanteau of "magnesium" and "ferric" and was coined by Charles Whitman Cross , Joseph P. Iddings , Louis V. Pirsson , and Henry Stephens Washington in 1912. Cross' group had previously divided the major rock-forming minerals found in igneous rocks into salic minerals, such as quartz , feldspars , or feldspathoids , and femic minerals, such as olivine and pyroxene . However, micas and aluminium-rich amphiboles were excluded, while some calcium minerals containing little iron or magnesium, such as wollastonite or apatite , were included in

913-431: Is a silicate mineral or igneous rock rich in magnesium and iron . Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine , pyroxene , amphibole , and biotite . Common mafic rocks include basalt , diabase and gabbro . Mafic rocks often also contain calcium -rich varieties of plagioclase feldspar. Mafic materials can also be described as ferromagnesian . The term mafic

SECTION 10

#1732884116785

996-475: Is a norite with extensive chromitite and sulfide layers or zones containing the ore. The Reef contains an average of 10 ppm platinum group metals in pyrrhotite , pentlandite , and pyrite as well as in rare platinum group minerals and alloys . The Merensky and UG2 reefs contain approximately 90% of the world's known PGM reserves. About 80% of the platinum and 20% of the palladium mined each year are produced from these horizons. The formation mechanisms of

1079-556: Is a part of the spinel group , which means that it is able to form a complete solid solution series with other members in the same group. These include minerals such as chenmingite (FeCr 2 O 4 ), xieite (FeCr 2 O 4 ), magnesiochromite (MgCr 2 O 4 ) and magnetite (FeFe 2 O 4 ). Chenmingite and xieite are polymorphs of chromite while magnesiochromite and magnetite are isostructural with chromite. Chromite occurs as massive and granular crystals and very rarely as octahedral crystals. Twinning for this mineral occurs on

1162-520: Is also quarried from parts of the complex and rendered into dimension stone . There have been more than 20 mine operations. There have been studies of potential uranium deposits. The complex is well known for its chromitite reef deposits, particularly the Merensky reef and the UG2 reef. It represents about 75 percent of the world's platinum and about 50 percent of the world's palladium resources. In this respect,

1245-400: Is black (Fe,Cr) 2 O 3 pigment, which is fairly expensive and is synthetic . Natural chromite allows for an inexpensive and inorganic pigmentation alternative to the expensive (Fe,Cr) 2 O 3 and allows for the microstructure and mechanical properties of the tiles to not be substantially altered or modified when introduced. Mafic A mafic mineral or rock

1328-754: Is defined by the Melinda Fault, which dips to the west and is situated within the Pietersburg terrane. The Melinda Fault extends in an eastern direction along the Palala Shear Zone (PSZ). This Fault and the PSZ are collectively designated as the Palala-Zoetfontein Lineament. The TML represents the boundary between the southern portion of the Northern Limb and the remainder of the Bushveld. It demarcates

1411-636: Is displaced 500 m to the south by the Makweng Fault. The Sekhukhune Fault trends in a north-south direction and has a throw of up to 2 km to the west. The Sekhukhune Fault is situated to the east of the Fortdraai Anticline. The Laersdrift Fault is located to the NW of the eastern Bushveld Complex. The Pilanesberg Complex is situated in the western lobe of the Bushveld Complex. The southern part of

1494-411: Is facing a lack of education, high crime levels, and health problems within the workforce. Additionally, they are facing high poverty levels, government deficits, and are still heavily dependent on the platinum mining industry which is "responsible for more than 65% of local GDP and 50% of all direct jobs" (over 70,000 jobs). The accommodations and housing are lacking and have seen little to no effort from

1577-421: Is found in metamorphic rocks such as some serpentinites . Ore deposits of chromite form as early magmatic differentiates. It is commonly associated with olivine , magnetite , serpentine and corundum . The vast Bushveld Igneous Complex of South Africa is a large layered mafic to ultramafic igneous body with some layers consisting of 90% chromite, forming the rare rock type chromitite (cf. chromite

1660-750: Is independent from chromium speciation. Plant studies have shown that toxic effects on plants from chromium include things such as wilting, narrow leaves, delayed or reduced growth, a decrease in chlorophyll production, damage to root membranes, small root systems, death and many more. Chromium's structure is similar to other essential elements which means that it can impact the mineral nutrition of plants. During industrial activities and production things such as sediment, water, soil, and air all become polluted and contaminated with chromium. Hexavalent chromium has negative impacts towards soil ecology because it decreases soil micro-organism presence, function, and diversity. Chromium concentrations in soil diversify depending on

1743-493: Is mined, it is aimed for the production of ferrochrome and produces a chromite concentrate of a high chromium to iron ratio. It can also be crushed and processed. Chromite concentrate, when combined with a reductant such as coal or coke and a high temperature furnace can produce ferrochrome . Ferrochrome is a type of ferroalloy that is an alloy in between chromium and iron. This ferroalloy, as well as chromite concentrate can introduce various health effects. Introducing

SECTION 20

#1732884116785

1826-498: Is most stable in its trivalent (Cr(III)) form, seen in stable compounds such as natural ores. Cr(III) is an essential nutrient, required for lipid and glucose metabolism in animals and humans. In contrast, the second most stable form, hexavalent chromium (Cr(VI)), is generally produced through human activity and rarely seen in nature (as in crocoite ), and is a highly toxic carcinogen that may kill animals and humans if ingested in large doses. Health effects When chromite ore

1909-462: Is not used as a rock classification in the IUGS classification scheme. Mafic rocks are sometimes more precisely defined as igneous rocks with a high proportion of pyroxene and olivine, so that their color index (the volume fraction of dark mafic minerals) is between 50 and 90. Most mafic volcanic rocks are more precisely classified as basalts . Chemically, mafic rocks are sometimes defined as rocks with

1992-435: Is observed to emit pollutants into the air such as nitrogen oxides , carbon oxides and sulfur oxides , as well as dust particulates with a high concentration of heavy metals such as chromium , zinc , lead , nickel and cadmium . During high temperature smelting of chromite ore to produce Ferrochrome , Cr-III is converted to Cr-VI. As with chromite ore, Ferrochrome is milled and therefore produces Cr-VI. Cr-VI

2075-580: Is separated from the others by structural boundaries. The southern and central zones are separated by the Steelpoort Fault. The eastern lobe is further subdivided by the presence of the Stofpoort and Wonderkop Faults, which serve to differentiate the northeast from the central zone. The Stofpoort Fault is situated in close proximity to the Olifants River. The western zone is separated from the remainder of

2158-407: Is the hexavalent state of chromium. Cr-VI is produced from Cr-III by means of dry milling or grinding of the ore. This is due to the moistness of the milling process as well as the atmosphere in which the milling is taking place. A wet environment and a non-oxygenated atmosphere are ideal conditions to produce less Cr-VI, while the opposite is known to create more Cr-VI. Production of ferrochrome

2241-624: Is the largest layered igneous intrusion within the Earth's crust . It has been tilted and eroded forming the outcrops around what appears to be the edge of a great geological basin : the Transvaal Basin . It is approximately two billion years old and is divided into four limbs: northern, eastern, southern and western. It comprises the Rustenburg Layered suite, the Lebowa Granites and

2324-703: Is the only country that contains notable chromite reserves in both stratiform and podiform deposits. Stratiform deposits are formed as large sheet-like bodies, usually formed in layered mafic to ultramafic igneous complexes. This type of deposit is used to obtain 98% of the worldwide chromite reserves. Stratiform deposits are typically seen to be of Precambrian in age and are found in cratons . The mafic to ultramafic igneous provinces that these deposits are formed in were likely intruded into continental crust , which may have contained granites or gneisses . The shapes of these intrusions are described as tabular or funnel-shaped. The tabular intrusions were placed in

2407-651: Is therefore introduced into the dust when the Ferrochrome is produced. This introduces health risks such as inhalation potential and leaching of toxins into the environment. Human exposure to chromium is ingestion, skin contact, and inhalation. Chromium-III and VI will accumulate in the tissues of humans and animals. The excretion of this type of chromium from the body tends to be very slow which means that elevated concentrations of chromium can be seen decades later in human tissues. Environmental effects Chromite mining, chromium, and ferrochrome production can toxically effect

2490-479: Is used as a pigment for glass, glazes, and paint, and as an oxidizing agent for tanning leather. It is also sometimes used as a gemstone . Usually known as chrome, it is a very essential industrial metal. It is hard and resistant to corrosion. This is used for things such as nonferrous alloys, the production of stainless steel, chemicals that process leather, and the creation of pigments. Stainless steel usually contains about 18 percent of chromium. The chromium in

2573-430: The 2014 South African platinum strike . Platinum is more likely to be affected by social, environmental, political and economic issues where as gold not as much. This is because platinum has large mineral resources already identified and is not expected to be depleted for many decades (potentially up to year 2040). Furthermore, platinum is geographically restricted to the three by far the most significant resources, namely

Chromite - Misplaced Pages Continue

2656-456: The Great Dyke . Chromite can be seen in stratiform deposits as multiple layers which consist of chromitite . Thicknesses for these layers range between 1 cm and 1 m. Lateral depths can reach lengths of 70 km. Chromitite is the main rock in these layers, with 50–95% of it being made of chromite and the rest being composed of olivine , orthopyroxene , plagioclase , clinopyroxene , and

2739-524: The International Union of Geological Sciences (IUGS) classification of igneous rocks, include some light-colored ferromagnesian minerals, such as melilite , in the mafic mineral fraction. Accessory minerals , such as zircon or apatite, may also be included in the mafic mineral fraction for purposes of precise classification. When applied to rocks, the term mafic is used primarily as a field term to describe dark-colored igneous rocks. The term

2822-546: The Platinum Group Elements (PGEs) and Platinum Group Metals (PGMs), chromium , copper , nickel , gold and vanadium concentrates, reef formation and orientation , and affect the type of mineralization, for example magmatic and hydrothermal deposits . Tectonic controls and effects can be seen or indicated by stratigraphic and crustal thickening and thinning, record of tectonic activity by type of structure such as collision and rifting , and influence on

2905-560: The Steelpoort Shear Zone (SSZ). These shear structures control several factors and have major geological implications within the Bushveld Igneous Complex, including structural, mineralogical , tectonic , metamorphic and economic . Some structural controls include the direction and flow of magma and intrusions , structural traps for mineralization and the structural evolution of the complex. Mineralization controls

2988-403: The ore can be seen as platy, with breakages along planes of weakness. Chromite can also be presented in a thin section. The grains seen in thin sections are disseminated with crystals that are euhedral to subhedral . Chromite contains Mg, ferrous iron [Fe(II)], Al and trace amounts of Ti. Chromite can change into different minerals based on the amounts of each element in the mineral. Chromite

3071-403: The Bushveld Complex still remains as one of the prime sources of PGE ore. There have been many strikes for unfair pay and working conditions, illegal miners (so-called " zama-zamas "), gun-fire conflicts , political swindles and legal fights. The prime use of platinum is for auto-catalytic converters (in cars) and jewellery. The total net demand of PGE in 2012 was 197.4 metric tons according to

3154-475: The Bushveld complex is unique and one of the most economically significant mineral deposit complexes in the world. The Bushveld Igneous Complex covers a pear-shaped area in the central Transvaal . It is divided into an eastern and western lobe, with a further northern extension. All three sections of the system were formed around the same time—about 2 billion years ago—and are remarkably similar. Vast quantities of molten rock from Earth's mantle were brought to

3237-558: The Bushveld igneous complex. Similarly, another study has found high concentrations of microscopic (<63 μm) PGE airborne dust particles near the mining areas. These have been found to be transported surface runoff and atmospherically, then further concentrated into soils and rivers such as the Hex River which flows directly into Rustenburg, the most populated municipality of North West Province of South Africa. A study from Maboeta et al. in 2006, has revealed through chemical analysis that

3320-690: The Jagersfontein, Klerksdorp and Potgietersrus shear zones and the Thabazimbi-Murchison lineament, chromium with the Rustenburg Layered Suites (RLS) critical zone and the TML, and gold with the Jagersfontein and Klerksdorp shear zones. Vanadium deposits are associated with the vanadium-rich magnetite deposits of the Bushveld, such as the TML, some of which may be associated with shear zones, and copper and nickel deposits, which often occur together in

3403-651: The PSZ is located in the northern part of the BIC, trends EW and can be 5–10 km wide. Two distinct fault orientations have been identified within the Pietersburg terrane: a NE–SW orientation and an ENE–WSW orientation. The most conspicuous faults with these orientations are the YPF and the Zebediela Faults. Different mineral occurrences are more strongly associated in the BIC in specific shear zones. PGEs are generally associated with

Chromite - Misplaced Pages Continue

3486-663: The Pilanesberg Complex exhibits NW–SE isopach lines that trend parallel to the Rustenburg Fault, which dips in the same direction towards the center of the Western Bushveld Complex. The Brits Graben is situated in the eastern region, in close proximity to Hartebeespoort . This Graben is delimited by a series of parallel faults, among which the most prominent is the Brits Fault, which trends NW–SE and intersects

3569-833: The Rooiberg Felsics, that are overlain by the Karoo sediments. The site was first publicised around 1897 by Gustaaf Molengraaff who found the native South African tribes residing in and around the area. Located in South Africa , the BIC contains some of the richest ore deposits on Earth. It contains the world's largest reserves of platinum-group metals (PGMs) and platinum group elements (PGEs) — platinum , palladium , osmium , iridium , rhodium and ruthenium — along with vast quantities of iron , tin , chromium , titanium and vanadium . These are used in, but not limited to, jewellery, automobiles and electronics. Gabbro or norite

3652-673: The Rustenburg Layered Suite, the Transvaal Supergroup and the Pretoria Group. The BSZ is NW–SE trending and is located within the Brits Fault. The NE–SW trending Ysterberg–Planknek Fault (YPF) is situated within the northern lobe of the Bushveld Complex. An additional ENE–WSW trending fault is situated within the northern lobe and is designated the Grasvally Fault. The boundary between the northern and southern lobes

3735-542: The UG2 chomitites is dominated by granular orthopyroxene, interstitial plagioclase and clinopyroxene with minor variable amounts accessory minerals such as phlogopite. The UG2 chromitites are underlain by pyroxenite footwall that is distinct from hanging wall pyroxenite. Chromite subhedral to subrounded (less than 0.5 mm in size) grains are a minor (c. 4%) but constant phase that is embedded with orthopyroxene (and other interstitial phases such as mentioned) throughout this footwall pyroxenite. Large oikocrysts are visible within

3818-523: The abundance of podiform deposits increase towards the top of the tectonites. Podiform deposits are irregular in shape. "Pod" is a term given by geologists to express the uncertain morphology of this deposit. This deposit shows foliation that is parallel to the foliation of the host rock. Podiform deposits are described as discordant, subconcordant and concordant. Chromite in podiform deposits form as anhedral grains. The ores seen in this type of deposit have nodular texture and are loosely-packed nodules with

3901-452: The alteration effects of high temperatures and pressures seen in the metamorphic series. It is able to progress through the metamorphic series unaltered. Other minerals with a lower resistance are seen to alter in this series to minerals such as serpentine , biotite and garnet . Chromite is found as orthocumulate lenses in peridotite from the Earth's mantle . It also occurs in layered , ultramafic intrusive rocks. In addition, it

3984-581: The boundary between the Pietersburg terrane and the central portion of the Kaapvaal Craton . In general, the TML is a large EW trending shear zone that forms a boundary between the Bushveld Complex and the Limpopo Belt and is 20 and 30 km wide. The JSZ is located within the TML, it trends NE–SW and is between 10 and 15 km wide. The KSZ runs parallel to the JSZ, trends NS and can be up to 10 km thick in places, while

4067-574: The chromitite seams in the Bushveld Igneous Complex are highly debated: numerous mechanisms have been proposed. The following is a non-exhaustive list of chromitite formations process. There has been a proposal of the origins of at least three different processes used to model the PGE mineralization in the area: The Bushveld Igneous Complex is a layered mafic intrusion (LMI) with well-defined ore bodies of stratiform chromitite layers concentrated with

4150-473: The conditions that rocks form. It can have reactions with various gases such as CO and CO 2 . The reaction between these gases and the solid chromite grains results in the reduction of the chromite and allows for the formation of iron and chromium alloys . There could also be a formation of metal carbides from the interaction with chromite and the gases. Chromite is seen to form early in the crystallization process. This allows for chromite to be resistant to

4233-460: The development stage of an organism may vary. Things such as the temperature of the water, its alkalinity, salinity, pH, and other contaminants will also impact these toxic effects on organisms. Chromite can be used as a refractory material because it has a high heat stability . The chromium extracted from chromite is used in chrome plating and alloying for production of corrosion resistant superalloys , nichrome , and stainless steel . Chromium

SECTION 50

#1732884116785

4316-722: The different compositions of the sediments and rocks that the soil is made from. The chromium present in soil is a mixture of both Cr(VI) and Cr(III). Certain types of chromium such as Chromium-VI has the capability to pass into the cells of organisms. Dust particles from industry operations and industrial wastewater contaminate and pollute surface water, groundwater, and soils. In aquatic environments, chromium could experience things such as dissolution , sorption , precipitation , oxidation , reduction , and desorption . In aquatic ecosystems chromium bioaccumulates in invertebrates, aquatic plants, fish, and algae. These toxic effects will operate differently because things such as sex, size, and

4399-668: The different exploration and mining companies of which contains about 38.1 kilotons of platinum metal in mineral reserves and resources in the Bushveld. The sum of PGEs and Gold resources and reserves equates to a total of about 72 kilotons from the Bushveld Complex alone. Most are underground mines (such as Longhole Stoping, Drift-and-Fill mining, etc. ), fewer are open pit like the large Mogalakwena mine . Mining feasibility studies have identified impacts on surface water , groundwater , wetlands , flora , fauna and related social issues. Additionally, these impacts include increased drainage of salts, sediments thought channels and streams near

4482-652: The earliest phase of the Complex. The Complex includes layered mafic intrusions (the Rustenburg Layered Suite) and a felsic phase. The complex has its geographic centre located north of Pretoria in South Africa at about 25° S and 29° E . It covers over 66,000 km (25,000 sq mi), an area the size of Ireland . The complex varies in thickness, in places reaching 9 kilometres (5.6 mi) thick. Lithologies vary from largely ultramafic peridotite , chromitite , harzburgite , and bronzitite in

4565-436: The environment. Chromite mining is necessary when it comes to the production of economic commodities . As a result of leaching of soils and the explicit discharge from industrial activities, weathering of rocks that contain chromium will enter the water column. The route of chromium uptake in plants is still ambiguous, but because it is a nonessential element, chromium will not have a distinct mechanism for that uptake which

4648-464: The evolution of the BIC. Metamorphic controls are localised metamorphism and alteration in shear zones, they affect mineral formation and stability, and they may show evidence of pressure - temperature - time (P-T-T) paths. Economic controls include, mineral deposits, they help to guide mining and exploration and with resource and reserve estimation and extraction. The eastern lobe of the Bushveld Complex comprises three distinct zones, each of which

4731-455: The femic minerals. Cross and his coinvestigators later clarified that micas and aluminium amphiboles belonged to a separate category of alferric minerals. They then introduced the term mafic for ferromagnesian minerals of all types, in preference to the term femag coined by A. Johannsen in 1911, whose sound they disliked. The term mafic is still widely used for dark-colored ferromagnesian minerals. Modern classification schemes, such as

4814-444: The form of PGE-Chloride in the liver, kidneys, bones and lungs. The intake is generally through metallic or oxide dust that is inhaled or is absorbed through the skin causing contact dermatitis , on the long term causing sensitization and can eventually to lead to cancers. A study from January 2013, has shown an increasing trend of the development of silicosis caused by silica dust and asbestos fibers related to workers mining in

4897-482: The form of sills with the layering of these intrusions being parallel. Examples of these tabular intrusions can be seen in the Stillwater Igneous Complex and Bird River . The funnel-shaped intrusions are seen to be dipping towards the center of the intrusion. This gives the layers in this intrusion a syncline formation. Examples of this type of intrusion can be seen in the Bushveld Igneous Complex and

4980-480: The formation of a structure rather like a layered cake consisting of distinct rock strata, including three PGM-bearing layers, referred to as reefs. Large portions of the central area are covered by younger rocks. The extrusions were emplaced over an early diabasic sill, outcrops of which are visible on the southeastern side of the Complex. These are typically greenish in colour and composed of clinopyroxene , altered to hornblende and plagioclase , and are regarded as

5063-399: The gross demand significantly decreased in jewellery (87.7 to 78.1 tons), but has largely increased in autocatalysts (80.6 to 101.7 tons) and has since then almost consistently dominated the market (with 2009 being the one exception linked to weak car sales). In 2016, the platinum market continued to be in deficit for the 5th consecutive year, just barely reaching a demand 200,000 oz. In 2017,

SECTION 60

#1732884116785

5146-482: The lower sections to mafic norite , anorthosite , and gabbro toward the top, and the mafic Rustenburg Layered Suite is followed by a felsic phase (the Lebowa Granite Suite). The orebodies within the complex include the UG2 (Upper Group 2) reef containing up to 43.5% chromite , and the platinum-bearing horizons Merensky Reef and Platreef . The Merensky Reef varies from 30 to 90 cm in thickness. It

5229-542: The majority in terms of the proportion of all the known chrome reserves of the world. This area is very strategic as it is easy and cheap for mining; this is because their continuity in thick seams over scores of miles of strike and their persistence in depth, which has all been proved via deep drilling. Just like the chrome seams, Bushveld's titano-magnetite seams of the Main Zone illustrates similar continuity and persistence though, have not been extracted to date. Contained within

5312-525: The mentioned lobes. As for the center area, it is dominated by granites and other related rocks. A large metamorphic contact aureole is observed within the northern limb, the Potgietersrus area. The Vredefort impact structure is predated by the BIC intrusion and has been shown to be likely unrelated to the BIC's mineralization. The Merensky Reef can be subdivided into five layers (from bottom to top): The UG2 Pyroxenite (Reef): The host rock of

5395-660: The mine sites. There has been an increased fleeting dust generation contaminating air and water, surface water runoff is leading to a decrease in water recharge for downstream users, possibly the loss of certain vulnerable flora and fauna species, soil compaction and land erosion; the contamination and quality deterioration of the surface and ground water is driven by seepage from waste rock dumps, stockpiles, gas spills, etc. The mining activities that make large use of water could potentially lead to dewatering of local aquifers. Moreover, construction activity impacts such as removal of natural land and noise from machinery and vehicles may disrupt

5478-695: The mineral and chromitite, a rock containing chromite). The Stillwater Igneous Complex in Montana also contains significant chromite. Chromite suitable for commercial mining is found in just a handful of very substantial deposits. There are 2 main types of chromite deposits: stratiform deposits and podiform deposits. Stratiform deposits in layered intrusions are the main source of chromite resources and are found in South Africa , Canada , Finland , and Madagascar . Chromite resources from podiform deposits are mainly found in Kazakhstan , Turkey , and Albania . Zimbabwe

5561-580: The mining companies to improve them. Between 2013 and 2016, the platinum companies contributed more than ZAR 370 million into the city; funding local infrastructure, water supply and treatment centres, sporting programmes, tourism, public road expansions, sewage treatment plants, cultural activities. The primary concern is the combination of high poverty rates and social injustice. There have been much more than 30 individual mine operations mostly mining for PGEs, some chrome, tin, and others (of which most are underground, few are open cut). These are shown below as

5644-722: The older basic rock class. Mafic lava , before cooling, has a low viscosity , in comparison with felsic lava, due to the lower silica content in mafic magma . Water and other volatiles can more easily and gradually escape from mafic lava. As a result, eruptions of volcanoes made of mafic lavas are less explosively violent than felsic-lava eruptions. Volcanic rocks : Subvolcanic rocks : Plutonic rocks : Picrite basalt Peridotite Basalt Diabase (Dolerite) Gabbro Andesite Microdiorite Diorite Dacite Microgranodiorite Granodiorite Rhyolite Microgranite Granite Bushveld igneous complex The Bushveld Igneous Complex ( BIC )

5727-809: The outcrops and on mine walls. The Platreef : this reef structure is divided into three sections: The BIC contains several shear zones , some are within known faults , the most important of which are the Jagersfontein Shear Zone (JSZ), the Klerksdorp Shear Zone (KSZ), the Potgietersrus Shear Zone (PSZ), the Thabazimbi -Murchison Lineament (TML), the Brits Shear Zone (BSZ), the Olifants River Shear Zone (ORSZ) and

5810-651: The region by two anticlines, namely the Katloof and Phosiri. The Merensky Reef has been displaced by 2 km to the south in the vicinity of Zebediela , as a consequence of the Madika Fault. The Madika Fault is sub-parallel to the Wonderkop Fault, which is located in the Bojanala Platinum District Municipality in the vicinity of the town of Wonderkop. The critical zone of the Rustenburg Layered Suite

5893-444: The same deposit, are associated with mafic and ultramafic intrusions and shear zones, such as the JSZ. The general mineral assemblage of the chromitite seams in the Bushveld Complex consists of olivine + chromite, chromite +/- bronzite + plagioclase, chromite + plagioclase, and chromite + clinopyroxene. The BIC's layered sequence is commonly divided into five different zones: The area has many different ore deposits, but mostly with

5976-501: The so-called Critical Zone; these are referred to as reefs . The three main reef deposits are the Merensky reef , UG2 Reef, and the Platreef. These reefs are mostly continuous to discontinuous chromite layers with amounts of PGE mineralization. The surface rocks are exposed as separate lobes or limbs (the main ones being eastern, western and northern limbs) spans an area of approximately 66,000 km . This large igneous province comprises

6059-439: The soil from a tailings disposal facility had higher levels of C, N, NH 4 and K in comparison to the other general sampling sites. The difference was attributed to rehabilitation regimes being implemented reducing the abundance of these microbial and bacterial nutrients . Mining operations in general consume much energy and water, producing much waste rock, trailings and greenhouse gases. A study has shown that PGM mining has

6142-439: The soil, atmosphere and vegetation. Since some of the food production activities are located near these areas, the primary concern is that the local population (several towns and cities, including Rustenburg with more than 500,000 inhabitants ) will ultimately be exposed to the contaminants either by skin contact, dietary intake or inhalation. PGEs such as platinum, palladium, and rhodium have been shown to bioaccumulate under

6225-428: The stainless steel is the material which hardens making it resilient to corrosion. Most shiny car trim is chromium plated. Superalloys that contain chromium allow jet engines to run under high stress, in a chemically oxidizing environment, and in high-temperature situations. Porcelain tiles are often produced with many different colours and pigmentations . The usual contributor to colour in fast-fired porcelain tiles

6308-452: The surface through long vertical cracks in Earth's crust—huge arcuate differentiated lopolithic intrusions—creating the geological intrusion known as the Bushveld Igneous Complex. These intrusions are thought to predate the nearby Vredefort impact to the south, by some 30 million years. The effects of these injections of molten rock over time, combined with the crystallisation of different minerals at different temperatures, resulted in

6391-457: The surrounding ecosystems . Depending on the beneficiation and concentration methods, there are different impacts plausible such acid runoff from leaching and metal slimes . Hexavalent chromium from mine wastes has been shown to be highly toxic. A study has shown that up to 5% of the world total production of PGEs is lost and emitted as dust entering the global biogeochemical cycle . Nearby towns have shown elevated levels of platinum within

6474-590: The three main igneous suites the Lebowa Granite Suite (large A-type granitic intrusions), Rustenburg Layered Suite (c. 8 km-thick layered mafic-ultramafic cumulate sequence), and the Rashoop Granophyre Suite (granophyric rocks). These are exposed as layered sequences of sheet like intrusions that are commonly subdivided as five main zones (from bottom to surface): Marginal, Lower, Critical, Main, and Upper Zones. These can be seen in sequence within

6557-468: The titano-magnetite ore is a persistent fractional percentage of vanadium. Reserves of the titanium and vanadium in these iron ores could potentially be very large. With that being said, it is evident that the ores existing in Bushveld occupy an important place in the world of mineral resources. Although other major platinum deposits have been found in places like the Sudbury Basin or Norilsk (Russia),

6640-430: The two still dominate the market gross demand by far. That being said, the global platinum demand is still expected to increase in subsequent years to 2017. The price of platinum is quite volatile in comparison to gold, but both have greatly increased over the last century. Despite platinum being far much rarer than gold, 2014 was the last year platinum was valued at a higher price than gold (2018). This coincides with

6723-443: The various alteration products of these minerals. An indication of water in the magma is determined by the presence of brown mica . Podiform deposits are seen to occur within the ophiolite sequences. The stratigraphy of the ophiolite sequence is deep-ocean sediments, pillow lavas , sheeted dykes , gabbros and ultramafic tectonites . These deposits are found in ultramafic rocks, most notably in tectonites. It can be seen that

6806-405: The work force. Miners are quite often on strike asking to get the minimum salary, and mines continue to fail safety standards and face labour unrest. A research study in 2016 by eunomix showed that Rustenburg, one of the fastest-growing cities in South Africa, has an "abnormally high concentration of young men who are separated from their families due to the migrant labour system". The population

6889-445: The {III} plane as described by the spinel law . Grains of minerals are generally small in size. However, chromite grains up to 3 cm have been found. These grains are seen to crystallize from the liquid of a meteorite body where there are low amounts of chromium and oxygen. The large grains are associated with stable supersaturated conditions seen from the meteorite body. Chromite is an important mineral in helping to determine

#784215