Using a gold wash plant, exposed gold-bearing gravels are mined using a bulldozer that pushes and stockpiles the gravel near a wash plant. The stockpiled gold-bearing gravel is then fed into the wash plant by a front-end loader or large backhoe. This practice promotes equipment efficiency by allowing the bulldozer to continue mining while the loader or backhoe feeds the wash plant at a steady rate. When the mined gravel is fed into the washplant. It is classified by particle size using various stationary or vibrating screens. Classifying gravels provides for more efficient gold recovery, reduced water consumption, and facilitation of mine site rehabilitation, and is practiced by most operators. The oversize material, usually larger than two inches, slides out of the washplant into a pile where it can be moved by a front-end loader or bulldozer. The undersize material and gold-bearing gravel is mixed with water and flows through the sluicebox where the gold and heavy black sands are concentrated. Tailings are gravel, sand, and other materials accumulated at the end of the sluicebox. Tailings are routinely moved away from the sluicebox by a loader or bulldozer.
The water that carries the gold-bearing gravel through the sluicebox becomes sediment-laden and turbid. This muddy process water flows from the end of the sluicebox over a pile of fresh tailings into a series of settling ponds. These ponds are designed to hold the muddy water long enough for the fine sediments to settle. The physical design of the ponds depends upon the amount of water flowing through the system, the sediment characteristics of the gravels being worked, and the physical characteristics of the site. Most mines use a series of small settling ponds to permit more flexible water management. Small ponds are usually easier to build, repair, dean, replace, bypass, and rehabilitate than larger ponds. The use of pre-settling ponds is encouraged. A pre-settling pond is located in the tail race between the sluice and the first settling pond. Sands and other heavy settleable solids are collected here where they are easy to wash.
However, some zero-discharge systems do have occasional discharges, usually due to water seepage through pond dikes. This seepage almost always meets the settleable solids effluent standards, and in most cases, Is probably of better quality than the water discharged from typically operated settling ponds. I.e., less settleable solids and lower turbidity. Carefully designed and Implemented water management practices are required to achieve zero discharge of muddy water into adjacent streams. Water used in the sluicing process Is pumped from the nearby stream through the washplant and into the settling ponds. Water Intake from the stream Is suspended when the ponds contain adequate water to support continued sluicing operations by recycling pond water to the washplant. In some cases, groundwater seepage Into the settling ponds may be sufficient to eliminate the need for adding stream water to the system. The practice of zero discharge and the recycling of mine water contributes to compliance with federal effluent limitations and State water quality standards.
Placer mining involves equipment ranging from a simple gold pan all the way up to trucks, excavators, and a gold wash plant.This type of gold prospecting usually involves less investment and will consistently yield small amounts of gold, with occasional bonanzas for those who are persistent. If you can learn to reliably return from every trip with decent concentrates, so that over time you fill a five-gallon bucket, and then maybe even a fifty-five-gallon drum, with black sands, magnetite, ilmenite, rare earth elements (REEs), and gold, you will be rewarded in the long run.
Either way, your long-term goals are your own.Very few prospectors are simply in it for the money, looking at this as a way to become a millionaire overnight. Some of us just like to get out of town, camp in the mountains, and enjoy the spirit of the outdoors. Some people like to work up a little sweat and appetite, improve their health, and learn a little. Some of us like to solve problems and run machinery, and enjoy the challenge of keeping a pump going or making sure the sluice is running right. Still others like the wildlife, the scenery, and the historical importance of the Wild West, and bring back their riches as photos and videos. In each case, if you toss in a little gold fever as motivation and stay scientific about your sampling and exploration, you will prosper far and above the value of your recovered material.
Still, a nice payday is always a treat. One sure way to reach that goal is to keep trying. Keep practicing, keep exploring, and keep getting out in the field. Another truism that seems to hold is that the farther away from civilization you get. the better your chances.
The development of a load/placer mine and the selection of the proper gravity recovery plant is more difficult than most people realize. Television shows have glamorized mining making it look like anybody can start a mine with little to no experience. What people dont realize is that mining is a structured engineering discipline taught at university. Just as you should not build your own bridge without knowledge of civil engineering, you should not think becoming a miner is a simple task. If you have no experience in the mining field you need to get educated about the process before you embark on this adventure. We have compiled a basic guide to assist in that process.
The terminology used for this type of mining is often interchanged. The term for the type of deposit under consideration is alluvial. Alluvial deposits are formed when the gold has migrated from its original deposition by weathering to a new location often inactive stream beds or in historic watercourses now overlain by sediments or glacial sediments.
In general Placer Mining is typically the recovery of gold from stream sediments through the use of dredges and sluices or other gravity means. Load mining generally involves the stripping of an overburden layer (soil) to uncover the underlying gravels that contain the gold. These deposits are often mined with mobile equipment and the ore trucked to a gravity treatment plant.
1. Permitting am I allowed to disturb the land excavating pits, leaving tailings behind, water usage, noise, air quality. In most cases you are not allowed to simply start mining even on your own land without the proper permits.
2. Resource estimation how much gold is present (grade and tonnage) and what does the deposit look like over burden depth, ore depth, gravel size. Generally, a placer resource is established by drilling or augering holes around the deposit to delineate the extent of the gold. This is often combined with field gravity recovery testing to provide an estimate of the recoverable grade.
6. Mine plan do you have a mine plan where are you going to mine first, where is the overburden going to be placed, where are the tailings going to be placed, is the plant going to be in one spot or moved during the mine life, what are the haulage distances. Is this a seasonal operation?
Mine Conditions Where is your project located? terrain, climate, infrastructure variables How large is your concession? Is a mobile or fixed plant right for this application? How many yards/hour (m/hr or tons per hour) do you want to process? How much water do you have available (GPM or m/hr)? Is there power available from the grid or do you required generation?
Plant Characteristics Are you looking for a mobile machine that you move regularly or a stationary plant that you haul your ore to? What type/size of equipment will you be feeding the plant with (front end loader, dredge pump, other)?
Feed Characteristics Ore consistency: What is the estimated maximum boulder size (in, mm)? Is there significant clay present? What is your maximum gold size (mm or um)? Is there fine gold present, what is the typical size (um)?
8. Economic Model Once you have made some initial assumptions you need to develop an economic model (even a basic one) so that you know if the project is viable before you start. No matter what type of project you should try and establish some basic economics unless this is just going to be a small hobby operation where profit does not matter. There are a lot of assumptions required to develop the model and you need to be realistic in your assessment. Add contingencies for operating costs of 10-15% and 20-30% for capital costs.
Found in Bulgaria are some of the oldest gold artifacts known to mankind, in the Varna Necropolis, a collection of graves built between 4700 and 4200 BC. This finding, dating back nearly 7000 years, provides evidence of the first civilization to use gold mining equipment. Some archeologists claim the Sakdrisi site in southern Georgia, which dates to roughly 4000 BC, is the worlds first gold mine.
In the 19th century, gold rushes occurred around the globe and people migrated to different regions hoping to strike it rich. The Victorian Gold Rush took place in Victoria, Australia, between 1851 and the late 1860s, and the Second Boer War took place in South Africa between 1899 and 1902. In America, the famous California Gold Rush took place in 1949, and discovery of Nevada's Carlin Trend,North America's largest gold depository,took placein 1961.
Since the beginning of civilization, humans have mined around 6 billions troy ounces of gold. Today, 2.5 percent of all gold production happens in Nevada, making it one of the primary regions on earth. As of 2017, China produced the most gold per year at 429 metric tons, followed by Australia, and then Russia. However, there's still a lot of gold out there, and you can join in the gold mining industry by investing in basic gold mining equipment.
There are two basic steps to gold mining: prospecting and production. "Prospecting" refers to the actual search in a certain area for valuable minerals, and "production," also known as mining, is the physical act of removing the gold from where you found it. Since different equipment exists for prospecting and mining, this article explores, briefly, equipment used for prospecting, and then focuses, primarily, on gold mining equipment.
How do you find gold? In the gold mining industry, theres a lot of value in learning from others who have gone before you. No one ever gets all the gold out of any one location. So, try going to where gold exists in abundance. Consider this: the California Gold Rush only removed a small percentage of the gold thats out there. That's right.
There are areas in California that are still open to recreational prospecting, including the Auburn State Recreation Area and the South Yuba Recreation lands. Once you get your feet wet in an area proven to have gold, you can move on to other areas closer to home. After mastering prospecting and gold-mining techniques, you might even want to look for gold in your own back yard.
Some people say, Gold is where you find it. What this means is you have to learn what to look for. First, understand that the way water moves in rivers and streams determines where gold deposits might settle. Next, you need to learn why gold concentrates in certain areas, and then search those areas.
Once youve selected a specific waterway for mining, youll want to pick specific points to search. Since it is impractical to search the entire stream or river, there are ways to read a waterway to determine the most likely places to find gold. The following describes how to find those places.
The first thing to know is gold is heavy. Its about 19 times heavier than the same amount of water and 6 times heavier than solid material found in streams and rivers. So, anything that slows the movement of water is likely to trap gold deposits. Things that slow down moving water are:
Water on the downriver side of obstacles will move slower, and this is where heavier gold will settle. When looking at a chosen waterway, begin by searching for natural dams where gold may have collected. Another place that collects heavier objects in a waterway is inside bends, places where water naturally slows down. Heavy objects will often form a bar at these points, and the upside of a bar inside bends is a great place to look for gold.
Once gold has settled in a stream, over time, it works its way down layers of soil and settles in bedrock. A great location for gold is in the material coating bedrock under a stream. Choose a location on the inside a bend where there is an obstruction and then dig to the bedrock. Sifting the soil coating bedrock, usually, will produce gold.
Learn to delay the excitement of seeing gold for the first time and you will have more gold-filled dirt to take home with you. Once you get better at choosing locations, and especially if you find a proven location, its best to spend your time digging and removing dirt, rather than sifting and cleaning it on site. Delay celebrating and get as much dirt as possible to take home. Once you get home, sift and clean the gold youve found.
Another great place to look for gold is in tall grass growing above an inside bend. Grass acts like a sieve and the largest gold pieces end up at the roots of grass. They often call this kind of gold oat gold. The pieces might be smaller than gold found in other places, but there could be a lot.
If you want to invest a little in your endeavor, you can purchase a metal detector designed to find gold. This gold mining equipment can cut down on the time spend hunting, but a mid-level detector can cost about $600.
When considering getting involved in gold prospecting and mining, make sure you learn and follow the rules. There are certain places where prospecting is legal and others where it is not. Many prospecting clubs exist and joining one can help ensure you are following rules. For examples, most sites require that you refill any holes you have dug, and that you do not destroy local plant life. Learn the rules before you head out with your gold mining equipment.
Once youve finished prospecting and have a location where you know there is gold, you will need gold mining equipment. What you use will depend on the size of your operation. If you are working in the gold industry, you will have industrial gold mining equipment. If you are mining on your own as a hobby, youll need smaller, personal gold mining equipment. Lets look at both.
If you want to use industrial mining equipment, make sure you have the proper training. If working for a business, they should provide needed training. However, if you purchased industrial gold mining equipment for a personal claim, be certain you know what you are doing. Safety should always come first.
Miners use drills for underground mining to create access holes for descending underground, or to place explosive charges to bring material to the surface. The drill miners choose depends on how and what is being mined.
Blasting tools create an explosion to blast away chunks of material to access minerals. Blasting can also remove chunks of unwanted materials that are keeping other machines or people from getting to a seam of wanted materials. In underground and open pit mines, miners use both drilling and blasting tools, often together. They use drills to place blasting tools at the right depth and in the right place.
Earth-moving machines move around large amounts of materials. They might haul material after blasting, move other materials allowing access to seams of minerals, dig underground mines, or get down to the bedrock where minerals might exist.
Crushing equipment moves materials around an underground mine. Miners use this equipment to keep the flow of materials going at an efficient rate, and to save money. It is easier to remove crushed rocks rather than heavy chunks, so crushing equipment saves time and effort.
A sluice box is a way to sift through raw material more quickly. Essentially, its automated panning. These machines used to be large and heavy in the early days of panning, but are now lightweight and easier to use. If youre serious about mining, they are worth checking out.
A higher quality sluice box, high banker boxes have a water pump allowing more material to move through faster. These boxes recycle water so you dont have to rely on water flow in the river. They recover more gold than basic models.
If you arent going into the professional gold mining industry, but are looking for a hobby or a part-time job to bring in a little extra money, consider joining a mining club to help you once you begin your prospecting journey. The club will help you learn about personal gold mining equipment, but, for now, lets take a quick look at what you will need.
There are lots of different sizes, colors, and options in gold pans. Essentially, a 14-inch plastic pan is the best size, by far. Color does not matter, however gold shows up better in black. Black sand shows up better in blue or green. There are many new kinds of pans, but a basic pan with sharp, undercut riffles is all you need. Make sure the bottom of the pan is as wide as possible to catch more gold.
You will need a place to store the gold you find. All you need is a waterproof container you can close tightly, such as a 35mm film container. You can purchase containers on the internet, specifically made for holding gold.
The last thing to consider is investing in Gold Lab, a personal system that recovers gold from the concentrate you have refined. A good gold panner can get most of the gold from refined dirt, but a Gold Lab kit will allow you to further refine and recover 100% of your gold.
Once you have your equipment, its time to get in the river to pan for gold. This simple technique mimics what the river does naturally. You recover material, or dirt and place it in the pan, from a river location where you think there might be gold. Then, you shake it in a left-to-right motion underwater to sweep away light materials while causing heavier materials to go to the bottom of the pan.
Take the pan with the riffles on the far side and shake it, vigorously, left and right. This breaks up materials sending heavier items to the bottom. Do not slosh water out of the pan. If you need to, repeat the previous step and break up larger chunks again.
Continue shaking the pan back and forth and keep removing the top layer of lighter materials until you are down to only the heaviest materials, such as coins, BBs, old bullets, buckshot, nails, garnets, black iron rocks and black sand. You should now be able to see gold in the pan when shaking and tilting it forward slightly.
Use a magnet to remove black sand and other metal objects. Keep removing things until only gold remains. Remove the larger gold pieces and save any leftover concentrate. Let it sit for a while so you can recover any remaining pieces of gold that settle.
If you have enjoy the outdoors, and have just a little ambition, you can make a hobby out of gold prospecting and mining. All you need are basic tools that as your gold mining equipment and the willingness to do a little research. Once you decide where to go, or join a mining club to help you find locations, pack up your tools and prospect. It may take practice at panning before you find anything, but once you do, youll love the feeling of satisfaction and discovery. If you find you enjoy the hobby, invest in semi-professional gold mining equipment and see if you can up the amount you discover. Even if you only discover a few flakes, prospecting can be a great way to make new friends, learn about the gold industry, and understand a little about gold prospectors of old. Its an inexpensive hobby, so grab basic gold mining equipment and get started today.
911MPE has for target market what mining professionals consider the pilot-plant scale mining operation or artisanal mining operations with a focus around under 500TPD. Metals you can extract include: gold, silver or other of the precious group as well as the classic base metals; copper, lead, zinc, nickel, molybdenum. Much of our ultra-small scale equipment allows you to process from just a few kilo (pounds) per day and work on your passion for a small budget.
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.
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