small scale mining - an overview | sciencedirect topics
ASM refers to the low-tech, labour intensive mineral extraction and processing found across the developing world (Hilson and McQuilken, 2014), encompassing varying degrees of formality and legality, characterised by low levels of environmental, health and safety awareness (Hilson, 2002: 4), and usually located in remote rural areas (Hilson, 2002).
Artisanal and small-scale mining (ASM) is one of the most important economic activity in many of the sub-Saharan Africa rural communities (Hein and Funyufunyu, 2014). Widespread artisanal, alongside small-scale mining operations are currently increasing in intensity in Nigeria. These activities are causing immeasurable damage to the environment and populations that live in the vicinity of these mine fields. The discharges of potentially harmful elements from the exposed mine-out/mineral processing sites and their subsequent remobilization into the soils and natural water bodies constitute serious human health problems (Lar etal., 2015). Artisanal mining in Nigeria and especially in its south-western sector is reported to be at best unplanned and haphazard with attendant negative impact on the environment (Okunlola and Omitogun, 2014).
The northern part of Nigeria viz Bin Yauri, Iperindo, Kebbi State, Maru, and Tsohon is rich in gold deposits. Gold mining started in these areas in 1913. However, by the time of World War II gold production stalled. The Imperial companies involved in gold mining gave up gold exploration. The resurgence of interest to mine gold was once began in the 1960s, but the Nigerian Civil War thwarted those efforts.
Then during the 1980s, the search for gold resumed by the Nigerian Mining Corporation (NMC). The NMC was not successful in part because of poor funding of the venture. Mining in general was abounding with problems because of government impassivity. This indifference was due to government focus on the discovery of oil in 1956. Oil remains the most valuable commodity in Nigeria today. However, in 2015, the government issued gold mining licenses to the two companies for exploration.
Three technologies are discussed in this chapter, together with some notes about the use of computers in the Third World. The technologies are: provision of telephone service to villages, land mine detection, and small-scale mining.
In Europe and the United States, cell phones are inexpensive and the coverage extends nearly everywhere in the country. In the Third World, cell phones are moderately expensive and coverage is spotty. Where coverage exists, cell phones can make a significant improvement to the lives of village people. One person in a village owning a cell phone can serve as the equivalent of a telephone company, answering the telephone, finding the called party, or taking a message, connecting wage earners in cities with their families in villages. However, because the density of traffic in rural areas in the Third World is low, so it will be a long time before either cell phones or land lines are generally available there. Two problems with landlines are that copper wire is prized for jewelry and that large animalslike elephantsknock over the poles over. The article describes alternatives less expensive than either cell phones or landlines.
Unfortunately, many buried land mines remain in the Third World and serious accidents continue to occur. In some places large areas of arable land are not usable because they contain land mines. One of the articles in this chapter reviews the technology of land mines and another discusses a way of detecting their presence.
Many small-scale mines are functioning in the Third World. They are often dangerous and polluting but earn cash for people who have only worse alternatives. The article gives the rudiments of the technologies used and suggests ways of making the process more benign.
Computers are potentially of significant value in the Third World, and it is recommended that volunteers bring laptops with them. Volunteers should know word processing and use of spreadsheets. These can be learned quickly; while an instruction book can be helpful, many people have learned to use both word processors and spreadsheets by experimenting. Basic modern software is nearly always user-friendly. It is advisable to bring backup disks of all software, including the operating system, and any manuals supplied with hardware or software. The number of people one can turn to for advice about computer problems will be much fewer than in the United States and Europe; the author, however, has found some very capable computer experts in the Third World who are often associated with universities.
Connecting a computer or other electrical device to power is not difficult overseas, but does require attention. The plugs going into electrical outlets will usually be a different shape from those in the United States. One can buy plug adaptors in the United States or in cities worldwide. It is probably cheaper, though, to purchase plugs and replace the ones on the equipmenta knife and screwdriver will be required. Of course, replacing a plug does not affect the amplitude of the voltage, which is 240 volts in much of the world but 120 volts in the United States. Generally, electrical appliances will be damaged if plugged into the wrong size voltage. Most laptops, however, can be powered with either 120 volts or 240 volts, so one can usually use the voltage available. It goes without saying, however, that one should be prudent and check the label on the power supply. If it does not indicate INPUT 100240 volts, or similar, be careful. Printers, however, are normally designed for either 120 or 240 volts so the input voltage will probably have to be changed to use a printer designed for the U.S. in the Third World. Big cities in the Third World usually have electrical supply stores where suitable voltage adapters can be purchased. Transformers are used to convert from one voltage to another and are the basis of the best adaptors. The current rating of the adaptor should be higher than the nominal current specified on the printer because peak current demand can be several times the nominal current. Lightly loaded electrical power systemsas many are in the Third Worldare likely to have large voltage surges that can damage a computer. A surge protector is worth having. It is also wise to unplug a computer during a lightning storm.
The Internet is a valuable resource both in the Third World and the U.S., but not available in much of the world, and when nominally available may be too slow to be really useful. The bandwidth of the telephone lines is often too small. E-mail is more likely to be available if one has access to the local telephone service. A volunteer may have to do some searching to find an e-mail provider but most volunteers will agree the search is worth it. The details of making a connection will depend on local conditions. It is safest to have a widely used modem and computer, that is, one made by a well-known company, so the appropriate software can be easily installed.
The products of mining are the largest contributors to export earnings in Ghana, with gold mining accounting for 90% of the value of mineral exports, and 44% of total export earnings in 2017. Mining occurs on both large and small scale, and both are linked to land degradation and air and water pollution. The environmental health risks of gold mining have emerged as a key topic in public discourse in Ghana. Water logging, increased sediment load in rivers, acid mine drainage, arsenic and cyanide pollution, and mercury poisoning of rivers by the large mining companies have been reported in the major gold mining areas of Obuasi, Prestea, Tarkwa, and others, as underground and surface mining and ore processing activities continue to intensify to earn more foreign exchange. Extraction of gold through roasting in the major gold producing center of Obuasi by the large capital companies releases 1419 tons of arsenic daily into the atmosphere, water, and soils. Small-scale mining by the artisanal and small-scale mining sector (ASM) has expanded rapidly in Ghana. More than 60% of the total mining labor force is in this sector. The ASM in 2014 produced about 34% of exported gold (compared to 9% in 2000) making it a major sector of the Ghanaian economy and an important source of livelihood and income for more than a million Ghanaians. Yet, an estimated 85% of ASM operations are illegal. The local idiom for such operations is galamsey (literally gather them [minerals] and sell). The unprecedented national public outcry against such operations is driven by alarming warnings, such as the one expressed by the Ghana Water Company that the country is at risk of importing water for consumption as early as 2020 if the galamsey-driven pollution of water sources continues on its current track. Most ASM activities focus on alluvial gold, which is exploited along the banks of rivers and in rivers. The rapidly expanding small-scale gold mining and the burning of mercury amalgams over open fires and kitchen stoves by small-scale operators to produce the final gold product is estimated to release approximately 5 tons of mercury into the biophysical environment. Analysis of hair and other samples from workers indicate the high levels of mercury contamination. In one study, the total arsenic in food samples (raw and cooked) from Obuasi were observed to be higher than for those in Kumasi, with little arsenic pollution. Neurological disorders, disturbed functions of the liver, kidney ailments, arthritis, miscarriages, respiratory failure, motor control problems, visual impairment, and weight and memory loss are among the health problems reported. Furthermore, mining activities remove surface vegetation and scar landscapes with large potholes in which water accumulates and become breeding grounds for mosquitoes. Thus, exposures to health risk from mining operations go well beyond the workers of concessionaries to include whole communities. The most vulnerable individuals to the health hazards are migrants from the impoverished northern regions of Ghana and locals who view mining as more attractive than the low-income activity of farming. The causes of unregulated ASM go beyond poverty. The causes lie as well in networks of powerful actors with political and economic interests in sustaining illegal activities, and the nature of land-based interests and the challenges of regulating them where illegal ASM occurs. Chinese immigrants, involved in illegal mining, are among the economic interests. In response to grave public concerns, the government placed a temporary ban on ASM activities in January2017, but faced equally intense pressure to lift it. And, indeed, the government announced a plan, on August 16, 2018, to lift the ban.
Maslows hierarchy of needs explains the motivation of human behavior unless a basic need is not met, higher needs cannot work as motivators. Thus, it is necessary to know at what stage of Maslows framework people are living. In developing countries especially, small-scale mining is undertaken in the most poor and remote areas. Thus, miners in this environment are at the base of Maslows framework, satisfying their basic physiological needs: food, clothing, and shelter. They are not likely to operate in an environmentally friendly manner(Aryee,2003) unless poverty is alleviated. Maslows concept of motivation may be used to help improve workforce motivation.
A formal strategy for employee engagement on sustainability is required, and should be tied in with broader business goals (Weeme,2012). Preferably, employees should be involved in developing this strategy with the support of senior management. This will give them a sense of belonging and help the organization grow. This process also assists with staff development. There should be programs available to support individual skill sets or needs. Mutual support among coworkers will result in an increased commitment to the organization. In addition to engagement of employees, all stakeholders concerned should be involved in sustainability projects. Their feedback is essential for progressive improvement.
The process of mineral concentration and cleaning was conceptualized centuries earlier by selective hand sorting of desired or undesired particles of lumpy size by mere appearance, color, texture, heaviness, etc. Hand sorting was common practice to separate rich ore as concentrate and wood or iron pieces as a cleaning process from ROM ore. Hand sorting is still a popular method in small-scale mining operations for the separation of waste rock and specific sizing of ore for commercial purposes (Fig.13.26).
The sorting techniques are changed to mechanical mode by adopting optical, electronic, and radioactive properties for large-scale industrial applications. This is possible due to the distinct contract between the valuable ore and waste gangue minerals with respect to their physical properties. The critical attributes are light reflectance (base metals and gold ore, limestone, magnesite, barite, talc, and coal), ultraviolet ray (wolframite and sheltie), gamma radiation (uranium and thorium), magnetism (magnetite and pyrrhotite), conductivity (sulfide ores), and X-ray luminescence (diamond). The main objective of mechanical sorting is to reduce the bulk of the raw ROM ore by rejecting large volumes of waste material at an early stage. The process utilizes a two-stage separation process. The first stage involves primary crushing of feed that liberates preconcentrate and barren rejects. The second stage performs recrushing, grinding, and processing to produce final concentrates and tailings. This two-stage operation will substantially lower the cost of large volumes of crushing and grinding, and the subsequent process of upgradation to produce marketable final concentrates.
A fully automatic electronic sorting device is comprised of an integrated circuit of an energy source, a process computer, a detector, and an ejector (Fig.13.27). ROM ore at desired fragment size, preferably washed, moves on a conveyor belt or vibrating feeders at uniform speed and is released, maintaining a natural flow of the stream of ore particles. The energy elements like light rays, laser beams, and X-rays converge from the source and reflect from the surface of the rocks passing through the sorting zone. The nature of reflectance is sensed by the detector system, which sends signals to the computer. The amplified signal activates an air jet at the right instant and intensity to eject the particle from the stream. The accepted and rejected particles are dropped in separate stacks around a conical splitter.
Mining projects and associated environmental conflicts are widespread in Latin America, with high concentration of mining ores extraction in Central America, across the Andean Ranges, and in Brazil (Temper et al., 2015; SNL, 2015, Fig. 12.2K). Given the global increase in mineral demand and the concentration of mineral deposits in Latin America (SNL, 2015), extensive mining is expected to increase all over the region. Mining pollution has been recorded in stream ecosystems from the Mxico-US border (Razo et al., 2004) to Patagonia (Bustos et al., 2014); some areas have been exploited for over 400years in Mexico (Chapa-Vargas et al., 2010) and Bolivia.
Effects on aquatic ecosystems and freshwater biota are reported from small-scale mining projects (Brosse et al., 2011) to open-pit, large-scale projects (Alvarez-Berros and Mitchell Aide, 2015). Gold mining has been identified as a major threat for freshwater South American fish due to the severe dredging of rivers, which modifies habitats, and mercury pollution associated with gold extraction (Reis, 2013), even when gold mining is performed on a small scale (Brosse et al., 2011). Also, gold mining coincides with important Neotropical conservation areas in South America, including all of its tropical and subtropical forest (Alvarez-Berros and Mitchell Aide, 2015). Pollution with organic methyl-mercury is associated with not only gold mining, but also with deforestation and forest fires (Roulet et al., 2000); additionally, it has major effects on fish communities as well as on humans consuming those resources in several parts of South America, especially in Amazonian communities (Webb et al., 2004). In addition the long history of oil exploitation with the liberation of formation waters with high concentrations of heavy metals have polluted waters in several parts of the Amazonia (O'Rourke and Connolly, 2003), as well as several locations in the Caribbean (Guzmn and Jimnez, 1992). Studies in Brazil have shown adverse ecosystem effects of coal mining including: the toxic concentration of metals in lakes (Moschini-Carlos et al., 2011); effects on biota, such as the bioaccumulation of Al and Fe in freshwater clams (Fernandes de Oliveira et al., 2016); and even in insectivorous bats feeding on emerging insects, which also showed damage at DNA level (Zocche et al., 2010). Copper mines have produced toxic levels of heavy metals in waters impacted by acid mine drainages in Mexico (Gmez-Alvarez et al., 2008). Iron mining in Brazil has reduced aquatic insect diversity and modified community composition (Gomes-Rodrigues and de Padua Bueno, 2016). Multimetal and sand exploitation are a serious threat for fish in the Magdalena river basin in Colombia, as well as in the Los Patos Lagoon drainage system in Brazil and Uruguay (Barletta et al., 2010).
Most of the region affected by the Exxon Valdez oil spill was pristine wilderness. About 7000 people lived in PWS in 1989, almost all of them in Cordova, Valdez, and Whittier. Less than 200 people resided within the spill trajectory inside the sound, mainly Alaska natives in the village of Chenega, and residents of a fish hatchery at Sawmill Bay. Few people lived along the coasts of the Kenai and Alaska peninsulas and Kodiak and adjacent islands, except for the 8000 residents in the city of Kodiak. The primary industry in the spill region was commercial fishing, which introduced negligible contamination to shoreline sediments and biota. Small-scale mining and land-based fish processing were important industries historically within PWS, but these were few and scattered (Lethcoe and Lethcoe, 1994). Contaminant effects of these activities on shorelines were attenuated by the 1964 Great Alaska Earthquake, which uplifted most shorelines within the spill trajectory from 1 to 10 m into the supratidal (the zone immediately above the highest reach of the tides). Although contaminants from these human activities were occasionally found in inter- and shallow subtidal sediments, they were quite localized, affecting a very small fraction of the shoreline (Karinen et al., 1993). Human activities occur on 0.2% of the shoreline of PWS (Boehm et al., 2004).
Prior to the spill, the most likely sources of hydrocarbons on shorelines and shallow subtidal sediments within the spill region were asphalt and fuels from storage tanks in Valdez and elsewhere that ruptured during the 1964 earthquake (Kvenvolden et al., 1995), and a natural regional background of hydrocarbons from eroded organic-rich shales and siltstones east of PWS. The high viscosity of the asphalt (> 10,000 centipoise) prevented it from penetrating into subsurface intertidal sediments, so patches became stranded by high tides on surface rocks. Small asphalt patches may still be found firmly adhered to cobbles, boulders, and bedrock above +3 m tidal elevation, but they were a small amount (<3%) relative to the Exxon Valdez oil remaining in PWS by 2001 (Short et al., 2004a).
Natural oil seeps were proposed as the source of natural hydrocarbons found throughout the shelf sediments of the northern Gulf of Alaska (Bence et al., 1996; Page et al., 1995), but appear now to be negligible sources, with eroded shelf rock being the major source (Short et al., 2004b). These hydrocarbons are not bioavailable because they are sequestered within coal or rock matrixes (Short et al., 2004b). The hydrocarbon source rocks are eroded by streams and by glaciers from outcrops of the Kulthieth and Poul Creek formations along the southern coast of the Gulf of Alaska from Katalla to Yakutat Bay (Van Kooten et al., 2002). Finely eroded sediments become entrained by the Alaska Coastal Current and transported to PWS and westward, where they settle on subtidal sediments. Concentrations of source rock PAH tend to increase with depth, ranging from less than 100 ng g1 dry sediment in the intertidal of the spill-affected region to 1500 ng g1 in benthic sediments of the deepest parts of the sound (O'Clair et al., 1996; Page et al., 1995).
Deposition of PAH from forest fires on Kenai Peninsula has also been reported (Page et al., 1999), but hydrocarbon signatures indicative of combustion sources are at trace levels except near former or present human habitation sites (Carls et al., 2004a), which are widely scattered.
Australia hosts rich zinc-lead-silver deposits in the Middle Proterozoic metasediments with exhalative association (SEDEX). The deposits are mainly located in McArthur-Mount Isa basin in the Northern Territory, Broken Hill in New South Wales, medium size mines in Tasmania and small deposits in Western Region. The former intracontinental sedimentary basin system exposed over 1200km in NW-SE trend with Mount Isa in the south and McArthur in the north. The 5- to 10-km-thick basin formation was active through a series of rift-sag cycles between 1800 and 1550Ma. The basin hosts five world-class stratiform deposits [from south to north: Mount Isa, Hilton, George Fisher (1653Ma), Century (~1575Ma) and HYC (Here is Your Chance) (1640Ma)] each with over 100Mt of ore reserves at +10%, Zn+Pb. There are few other deposits namely Lady Loretta, Dugald River, Cannington, Grevillea, Mt Novit, Kamarga and Walford Creek either with low tonnage and high-grade or no published reserve available (Large et al., 2004) . The Broken Hill Zn-Pb deposit consists of a cluster of orebodies within Willyama Supergroup having large global reserves of +300Mt. Rosebery silver-lead-zinc deposit was discovered in 1893 at Tasmania's west coast on the slopes of Mt Black.
Broken Hill deposit (3156S:14125E) is located 511km northeast of Adelaide (NH-A32) and 1160km west of Sydney (NH-32). Broken Hill (The Silver City) is an isolated mining city, far west of New South Wales Province, Australia.
The deposit was discovered by Charles Rasp, a boundary rider, while mustering sheep around Broken Hill area in 1883. Being trained in chemistry he was fascinated by the mineral appearance and formation (gossans). Rasp, joined by others, submitted ML and initiated prospecting for tin in gossans. The initial assaying from small shaft indicated low-grade lead and silver and finally reported finding of massive galena, sphalerite, cerussite and rich silver. Small scale mining was gradually accelerated to increase in tenure, mine size and efficiencies by consolidation of claims during last part of twentieth century. The Broken Hill Proprietary Company Limited (BHP Co. Ltd) was incorporated in 1985 for operating zinc, silver and lead mines. BHP Billiton merged in 2001 and became the largest global mining company measured by revenue in 2011.
The Willyama Supergroup (7-9km thick) has been divided into six principal packages defined by litho-stratigraphy (Table 15.2) probably deposited on existing continental crust. The mineralized packages from an arcuate belt of deformed, high-grade amphibole granulite rocks of Paleoproterozoic age represent the regional setting of Broken Hill deposits.
The Broken Hill mineralization occurs within the Broken Hill Group. This is marked by a widespread development of metasediments, interpreted as sudden deepening of the rift and the onset of more significant hydrothermal activity giving an interpretative magnetic age of 1680-1690Ma (Page and Laing, 1996)  which is widely quoted as inferred age of mineralization.
The orebodies are confined within a single unit of the mine sequence i.e. the Lode Horizon which is subdivided into four units such as the clastic and calc-silicate, garnet quartzite, C-lode and mineralization horizon. Orebodies are rich in calcite, fluorite, lead and rhodonite and to a lesser extent within clastic and calc-silicate horizon, a unit dominated by clastic psammopelitic to pelitic rocks with some well-developed calc-silicate layers, weak amphibolites and Potosi gneiss.
The mineralization is essentially strata-bound and stratiform and has been traced for 25km along strike and up to a depth of 2000m. The Broken Hill mineralization is interacted with exhalites like Qtz-mgtFe, Cu sulfides, Qtz-Fe oxide/sulfideCu and stratiform and strata-bound scheelite. The orebodies have been divided in two categories i.e. lead lode and zinc lode, based on Pb:Zn ratio. The former type is the calcitic orebodies that contain calcite, rhodonite-bustamite, apatite, garnet and fluorite, abundant lead and largely hosted within clastic metasediments. The second type is the primary quartz orebodies rich in primary quartz and garnet, gahnite and cummingtonite, little or no calcite or barium-rich calc-silicate component and rich zinc metal. The primary quartz orebodies mostly lie in the upper part of the sequence while the calcitic orebodies lie in the lower part (Fig. 15.3). The Thackaringa Group primarily hosts the Banded Iron Tourmaline ore.
The regional field relationships have established an essentially strata-bound and stratiform syn-SEDEX model of Broken Hill type. The metal deposition has been conceptualized as a result of high heat flow within the sedimentary basin in which the Willyama Supergroup was being deposited. This high heat flow eventually led to the high-grade regional metamorphism of the enclosing sediments.
There are nine separate but closely related orebodies stacked within a single package of stratigraphy. The preproduction reserve has been estimated as 300Mt at 12.0% Zn, 13.0% Pb, and 175g/t Ag. There are seven mine blocks from SW to NE as Southern Operations, North Mine, Potosi North, Silver Peak, Central block, Flying Doctor and Henry George.
The combined Mineral Resource (Measured, Indicated and Inferred) of Broken Hill Operation as on June 2011 stands at ~22.7Mt at 9.0% Zn, 7.0% Pb and 86g/t Ag. The Ore Reserve, which only applies to the Southern Operations, stands at 14.7Mt at 5.3% Zn, 4.0% Pb and 43g/t Ag. The statement is based on JORC Code and expected mine life is more than 10 years. Resource and Reserve Drilling is now recommenced to increase confidence around existing resources and reserves and potentially enhancement. (Source: ASX and Media Release 28 December 2011.)
Sources of potential exposure to Hg vapor are mainly those from unintentional accidents, take-home exposure and, with a controversial findings, dental amalgam restorations. In developed countries, involuntary damage of Hg-devices (e.g., from broken thermometers, fluorescent light bulbs or liquid metal used in school laboratories), or specific products (e.g., mercury-containing paints) are the main routes of childrens exposure by inhalation (Figs.1 and 2). Some larger biomonitoring studies involving mother-child couples in Norway and 6- to 10-year-old children in New England suggested that dental amalgam outgassing may raise the Hg levels slightly, but without practical or clinical significance for prenatal and children exposure. On the contrary, based on epidemiological studies a recent review reported that the safety of Hg released from dental amalgam fillings is questionable. Within EU, the use of Hg for amalgam fillings in 2010 represented the second largest use after that used for chlorine compounds production. To deal with this issue and in the view of precautionary principle, the EU commission established a ban on the use of Hg as constituent of dental amalgams (and in electronic medical measuring devices) for treatment of deciduous teeth, for children under 15years of age, for pregnant and breastfeeding women (Regulation EU, 2017/852). Although children are not exposed in active workplaces, some former industrial facilities that used Hg and converted to residences or take-home exposure (from parents job exposure, Hg-containing devices, cultural and folk remedies) can lead to remarkable elemental Hg exposure. In developing countries, children and/or pregnant women involved in gold extraction process (artisanal and small-scale mining) can be exposed through inhalation of Hg vapors or by dermal contact through the skin.
The most common route of exposure to elemental Hg is through inhalation because it volatizes at ambient temperature (25C). According to human studies, about 70%85% of inhaled Hg vapor can be absorbed by the lungs and, then, distributed to the red blood cells (RBCs), central nervous system (CNS) and renal system. In the case of children, the greater lung surface areas respect to the body weight and the faster breath resulted in a higher dose of Hg absorbed per unit of b.w. Rat study showed that Hg vapor is poorly absorbed by gastrointestinal tract (0.01% of the dose), therefore, if ingested, it exerts little toxicological effects. While the average rate of absorption through human skin were estimated to be 0.024ng/cm2 for every 1mg/m3 in air. Due to lipophilic characteristic and uncharged monatomic form, Hg vapor can be easily crossby diffusionthe lipid bilayers of cellular and intracellular organellar membranes, the blood-brain and the placental barriers. Within the RBCs and in tissues, Hg0 is rapidly oxidized to divalent form (Hg2+) by the action of ubiquitous H2O2-catalase. However, part of the Hg vapor remains in the blood circulating system long enough for reaching other tissues, including the bloodbrain and placental barriers. The capability of fetal tissue to take up the nonionized Hg as well the accumulation in fetal brain have been shown in animal and human studies; the uptake of Hg in fetus increases with the gestational age in pregnant rats. In any case, the amount of Hg0 that cross the brain barrier can be slowly converted and trapped within the brain cells in a divalent form, becoming bound with different proteins like metallothionein (MT), and so less able to diffuse out of the brain (molecular mechanisms of Hg-MT interaction are further discussed). Metallothionein is a cysteine-rich low-molecular-weight intracellular protein involved in the homeostasis regulation of essential metals and in metal detoxification processes (i.e., modifying both kinetics and toxicity of Hg). Regarding kinetics, studies on mice demonstrated that the presence of MTs in the placenta have the role to modulate the maternal-to-fetal transfer of essential and nonessential metals. About toxicity, neurobehavioral changes (i.e., locomotor activity and learning ability) and significantly accumulation of MT have been observed in mice and in rats intrauterine exposed to Hg vapor than those not exposed. Accumulation of this form of Hg has also been localized in the renal proximal tubule of monkeys exposed to elemental mercury from dental amalgams.
how big are millions, billions, and trillions?
The Piraha tribe is a group living in the jungles of South America. They are well known because they do not have a way to count past two. According to Daniel L. Everett, a linguist and professor who spent decades living among and studying the tribe, the Piraha have no number words to distinguish between these two numbers. Anything more than two is a big number.
Most people are similar to the Piraha tribe. We may be able to count past two, but there comes a point where we lose our grasp of numbers. When the numbers get big enough, intuition is gone and all we can say is that a number is "really big." In English, the words "million" and "billion" differ by only one letter, yet that letter means that one of the words signifies something that is a thousand times larger than the other.
Do we really know how big these numbers are? The trick to thinking about large numbers is to relate them to something that is meaningful. How big is a trillion? Unless weve thought of some concrete ways to picture this number in relation to a billion, all that we can say is, "A billion is big and a trillion is even bigger."
Numbers higher than a trillion are not talked about as frequently, but there are names for these numbers. More important than the names is knowing how to think about large numbers. To be a well-informed member of society, we really should be able to know how big numbers like a billion and trillion really are.
Everett, Daniel. (2005). "Cultural Constraints on Grammar and Cognition in Piraha: Another Look at the Design Features of Human Language." Current Anthropology, vol. 46, no. 4, 2005, pp. 621-646, doi:10.1086/431525
metro bullion | small scale mining | mining supply
We aim to ensure the communities where we operate remain strong and long into the future.This means working with local people, organizations and governments to invest in and create programs that benefit the entire community.
Metro Bullion Inc. overall corporate objective is to consistently evolve value by using the free cash flow generated via its gold ore-processing business to increase its processing capacity and to support sustainable community development projects