rock brought to surface during gold mining

extraction of resources | geology

Mining is the extraction of valuable minerals or other geological materials from the earth from an orebody, lode, vein, seam, or reef, which forms the mineralized package of economic interest to the miner.

Ores recovered by mining include metals, coal, oil shale, gemstones, limestone, dimension stone, rock salt, potash, gravel, and clay. Mining is required to obtain any material that cannot be grown through agricultural processes, or created artificially in a laboratory or factory. Mining in a wider sense includes extraction of any non-renewable resource such as petroleum, natural gas, or even water.

Mining of stone and metal has been done since pre-historic times. Modern mining processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials, and final reclamation of the land after the mine is closed.

The nature of mining processes creates a potential negative impact on the environment both during the mining operations and for years after the mine is closed. This impact has led most of the worlds nations to adopt regulations designed to moderate the negative effects of mining operations. Safety has long been a concern as well, and modern practices have improved safety in mines significantly.

The process of mining from discovery of an ore body through extraction of minerals and finally to returning the land to its natural state consists of several distinct steps. The first is discovery of the ore body, which is carried out through prospecting or exploration to find and then define the extent, location and value of the ore body. This leads to a mathematical resource estimation to estimate the size and grade of the deposit.

This estimation is used to conduct a pre-feasibility study to determine the theoretical economics of the ore deposit. This identifies, early on, whether further investment in estimation and engineering studies is warranted and identifies key risks and areas for further work. The next step is to conduct a feasibility study to evaluate the financial viability, the technical and financial risks, and the robustness of the project.

This is when the mining company makes the decision whether to develop the mine or to walk away from the project. This includes mine planning to evaluate the economically recoverable portion of the deposit, the metallurgy and ore recoverability, marketability and payability of the ore concentrates, engineering concerns, milling and infrastructure costs, finance and equity requirements, and an analysis of the proposed mine from the initial excavation all the way through to reclamation. The proportion of a deposit that is economically recoverable is dependent on the enrichment factor of the ore in the area.

To gain access to the mineral deposit within an area it is often necessary to mine through or remove waste material which is not of immediate interest to the miner. The total movement of ore and waste constitutes the mining process. Often more waste than ore is mined during the life of a mine, depending on the nature and location of the ore body. Waste removal and placement is a major cost to the mining operator, so a detailed characterization of the waste material forms an essential part of the geological exploration program for a mining operation.

Once the analysis determines a given ore body is worth recovering, development begins to create access to the ore body. The mine buildings and processing plants are built, and any necessary equipment is obtained. The operation of the mine to recover the ore begins and continues as long as the company operating the mine finds it economical to do so. Once all the ore that the mine can produce profitably is recovered, reclamation begins to make the land used by the mine suitable for future use.

Mining techniques can be divided into two common excavation types: surface mining and sub-surface (underground) mining. Today, surface mining is much more common, and produces, for example, 85% of minerals (excluding petroleum and natural gas) in the United States, including 98% of metallic ores.

Targets are divided into two general categories of materials: placer deposits, consisting of valuable minerals contained within river gravels, beach sands, and other unconsolidated materials; and lode deposits, where valuable minerals are found in veins, in layers, or in mineral grains generally distributed throughout a mass of actual rock. Both types of ore deposit, placer or lode, are mined by both surface and underground methods.

Some mining, including much of the rare earth elements and uranium mining, is done by less-common methods, such as in-situ leaching: this technique involves digging neither at the surface nor underground. The extraction of target minerals by this technique requires that they be soluble, e.g., potash, potassium chloride, sodium chloride, sodium sulfate, which dissolve in water. Some minerals, such as copper minerals and uranium oxide, require acid or carbonate solutions to dissolve.

Surface mining is done by removing (stripping) surface vegetation, dirt, and, if necessary, layers of bedrock in order to reach buried ore deposits. Techniques of surface mining include: open-pit mining, which is the recovery of materials from an open pit in the ground, quarrying or gathering building materials from an open-pit mine; strip mining, which consists of stripping surface layers off to reveal ore/seams underneath; and mountaintop removal, commonly associated with coal mining, which involves taking the top of a mountain off to reach ore deposits at depth. Most (but not all) placer deposits, because of their shallowly buried nature, are mined by surface methods. Finally, landfill mining involves sites where landfills are excavated and processed.

This form of mining differs from extractive methods that require tunneling into the earth, such as long wall mining. Open-pit mines are used when deposits of commercially useful minerals or rocks are found near the surface; that is, where the overburden (surface material covering the valuable deposit) is relatively thin or the material of interest is structurally unsuitable for tunneling (as would be the case for sand, cinder, and gravel). For minerals that occur deep below the surfacewhere the overburden is thick or the mineral occurs as veins in hard rockunderground mining methods extract the valued material.

Open-pit mines are typically enlarged until either the mineral resource is exhausted, or an increasing ratio of overburden to ore makes further mining uneconomic. When this occurs, the exhausted mines are sometimes converted to landfills for disposal of solid wastes. However, some form of water control is usually required to keep the mine pit from becoming a lake, if the mine is situated in a climate of considerable precipitation or if any layers of the pit forming the mine border productive aquifers.

Open-cast mines are dug on benches, which describe vertical levels of the hole. These benches are usually on four to sixty meter intervals, depending on the size of the machinery that is being used. Many quarries do not use benches, as they are usually shallow.

Most walls of the pit are generally dug on an angle less than vertical, to prevent and minimize damage and danger from rock falls. This depends on how weathered the rocks are, and the type of rock, and also how many structural weaknesses occur within the rocks, such as a faults, shears, joints orfoliations.

The walls are stepped. The inclined section of the wall is known as the batter, and the flat part of the step is known as the bench or berm. The steps in the walls help prevent rock falls continuing down the entire face of the wall. In some instances additional ground support is required and rock bolts, cable bolts and shotcrete are used. De-watering bores may be used to relieve water pressure by drilling horizontally into the wall, which is often enough to cause failures in the wall by itself.

Ore which has been processed is known as tailings, and is generally a slurry. This is pumped to a tailings dam or settling pond, where the water evaporates. Tailings dams can often be toxic due to the presence of unextracted sulfide minerals, some forms of toxic minerals in the gangue, and oftencyanide which is used to treat gold ore via the cyanide leach process. This toxicity can harm the surrounding environment.

Gold is generally extracted in open-pit mines at 1 to 2ppm (parts per million) but in certain cases, 0.75ppm gold is economical. This was achieved by bulk heap leaching at the Peak Hill mine in western New South Wales, near Dubbo, Australia.

Nickel, generally as laterite, is extracted via open-pit down to 0.2%. Copper is extracted at grades as low as 0.15% to 0.2%, generally in massive open-pit mines in Chile, where the size of the resources and favorable metallurgy allows economies of scale.

Sub-surface mining consists of digging tunnels or shafts into the earth to reach buried ore deposits. Ore, for processing, and waste rock, for disposal, are brought to the surface through the tunnels and shafts. Sub-surface mining can be classified by the type of access shafts used, the extraction method or the technique used to reach the mineral deposit. Drift mining utilizes horizontal access tunnels, slope mining uses diagonally sloping access shafts, and shaft mining utilizes vertical access shafts. Mining in hard and soft rock formations require different techniques.

Other methods include shrinkage stope mining, which is mining upward, creating a sloping underground room, long wall mining, which is grinding a long ore surface underground, and room and pillar mining, which is removing ore from rooms while leaving pillars in place to support the roof of the room. Room and pillar mining often leads to retreat mining, in which supporting pillars are removed as miners retreat, allowing the room to cave in, thereby loosening more ore. Additional sub-surface mining methods include hard rock mining, which is mining of hard rock (igneous, metamorphic or sedimentary) materials, bore hole mining, drift and fill mining, long hole slope mining, sub level caving, and block caving.

Heavy machinery is used in mining to explore and develop sites, to remove and stockpile overburden, to break and remove rocks of various hardness and toughness, to process the ore, and to carry out reclamation projects after the mine is closed. Bulldozers, drills, explosives and trucks are all necessary for excavating the land. In the case of placer mining, unconsolidated gravel, or alluvium, is fed into machinery consisting of a hopper and a shaking screen or trommel which frees the desired minerals from the waste gravel. The minerals are then concentrated using sluices or jigs.

Large drills are used to sink shafts, excavate stopes, and obtain samples for analysis. Trams are used to transport miners, minerals and waste. Lifts carry miners into and out of mines, and move rock and ore out, and machinery in and out, of underground mines. Huge trucks, shovels and cranes are employed in surface mining to move large quantities of overburden and ore. Processing plants utilize large crushers, mills, reactors, roasters and other equipment to consolidate the mineral-rich material and extract the desired compounds and metals from the ore.

Once the mineral is extracted, it is often then processed. The science of extractive metallurgy is a specialized area in the science of metallurgy that studies the extraction of valuable metals from their ores, especially through chemical or mechanical means.

Mineral processing (or mineral dressing) is a specialized area in the science of metallurgy that studies the mechanical means of crushing, grinding, and washing that enable the separation (extractive metallurgy) of valuable metals or minerals from their gangue (waste material). Processing of placer ore material consists of gravity-dependent methods of separation, such as sluice boxes. Only minor shaking or washing may be necessary to disaggregate (unclump) the sands or gravels before processing. Processing of ore from a lode mine, whether it is a surface or subsurface mine, requires that the rock ore be crushed and pulverized before extraction of the valuable minerals begins. After lode ore is crushed, recovery of the valuable minerals is done by one, or a combination of several, mechanical and chemical techniques.

Since most metals are present in ores as oxides or sulfides, the metal needs to be reduced to its metallic form. This can be accomplished through chemical means such as smelting or through electrolytic reduction, as in the case of aluminium. Geometallurgy combines the geologic sciences with extractive metallurgy and mining.

Mining exists in many countries. London is known as the capital of global mining houses such as Rio Tinto Group, BHP Billiton, and Anglo American PLC.The US mining industry is also large, but it is dominated by the coal and other nonmetal minerals (e.g., rock and sand), and various regulations have worked to reduce the significance of mining in the United States.In 2007 the totalmarket capitalization of mining companies was reported at US$962 billion, which compares to a total global market cap of publicly traded companies of about US$50 trillion in 2007.In 2002, Chile and Peru were reportedly the major mining countries of South America.The mineral industry of Africa includes the mining of various minerals; it produces relatively little of the industrial metals copper, lead, and zinc, but according to one estimate has as a percent of world reserves 40% of gold, 60% of cobalt, and 90% of the worlds platinum group metals.Mining in India is a significant part of that countrys economy. In the developed world, mining in Australia, with BHP Billiton founded and headquartered in the country, and mining in Canada are particularly significant. For rare earth minerals mining, China reportedly controlled 95% of production in 2013.

Mining operations can be grouped into five major categories in terms of their respective resources. These are oil and gas extraction, coal mining, metal ore mining, nonmetallic mineral mining and quarrying, and mining support activities.Of all of these categories, oil and gas extraction remains one of the largest in terms of its global economic importance. Prospecting potential mining sites, a vital area of concern for the mining industry, is now done using sophisticated new technologies such as seismic prospecting and remote-sensing satellites. Mining is heavily affected by the prices of the commodity minerals, which are often volatile. The 2000s commodities boom (commodities supercycle) increased the prices of commodities, driving aggressive mining. In addition, the price of gold increased dramatically in the 2000s, which increasedgold mining; for example, one study found that conversion of forest in the Amazon increased six-fold from the period 20032006 (292 ha/yr) to the period 20062009 (1,915 ha/yr), largely due to artisanal mining.

Safety has long been a concern in the mining business especially in sub-surface mining. The Courrires mine disaster, Europes worst mining accident, involved the death of 1,099 miners in Northern France on March 10, 1906. This disaster was surpassed only by the Benxihu Colliery accident in China on April 26, 1942, which killed 1,549 miners.While mining today is substantially safer than it was in previous decades, mining accidents still occur. Government figures indicate that 5,000 Chinese miners die in accidents each year, while other reports have suggested a figure as high as 20,000.Mining accidents continue worldwide, including accidents causing dozens of fatalities at a time such as the 2007 Ulyanovskaya Mine disaster in Russia, the2009 Heilongjiang mine explosion in China, and the 2010 Upper Big Branch Mine disaster in the United States.

Mining ventilation is a significant safety concern for many miners. Poor ventilation inside sub-surface mines causes exposure to harmful gases, heat, and dust, which can cause illness, injury, and death. The concentration of methane and other airborne contaminants underground can generally be controlled by dilution (ventilation), capture before entering the host air stream (methane drainage), or isolation (seals and stoppings).Rock dusts, including coal dust and silicon dust, can cause long-term lung problems including silicosis, asbestosis, and pneumoconiosis (also known as miners lung or black lungdisease). A ventilation system is set up to force a stream of air through the working areas of the mine. The air circulation necessary for effective ventilation of a mine is generated by one or more large mine fans, usually located above ground. Air flows in one direction only, making circuits through the mine such that each main work area constantly receives a supply of fresh air. Watering down in coal mines also helps to keep dust levels down: by spraying the machine with water and filtering the dust-laden water with a scrubber fan, miners can successfully trap the dust.

Gases in mines can poison the workers or displace the oxygen in the mine, causing asphyxiation.For this reason, the U.S. Mine Safety and Health Administration requires that groups of miners in the United States carry gas detection equipment that can detect common gases, such as CO, O2, H2S, CH4, as well as calculate% Lower Explosive Limit. Regulation requires that all production stop if there is a concentration of 1.4% of flammable gas present. Additionally, further regulation is being requested for more gas detection as newer technology such as nanotechnology is introduced.

Ignited methane gas is a common source of explosions in coal mines, which in turn can initiate more extensive coal dust explosions. For this reason, rock dusts such as limestone dust are spread throughout coal mines to diminish the chances of coal dust explosions as well as to limit the extent of potential explosions, in a process known as rock dusting. Coal dust explosions can also begin independently of methane gas explosions. Frictional heat and sparks generated by mining equipment can ignite both methane gas and coal dust. For this reason, water is often used to cool rock-cutting sites.

Miners utilize equipment strong enough to break through extremely hard layers of the Earths crust. This equipment, combined with the closed work space in which underground miners work, can cause hearing loss.For example, a roof bolter (commonly used by mine roof bolter operators) can reach sound power levels of up to 115dB.Combined with the reverberant effects of underground mines, a miner without proper hearing protection is at a high risk forhearing loss.By age 50, nearly 90% of U.S. coal miners have some hearing loss, compared to only 10% among workers not exposed to loud noises.Roof bolters are among the loudest machines, but auger miners, bulldozers, continuous mining machines, front end loaders, and shuttle cars and trucks are also among those machines most responsible for excessive noise in mine work.

Since mining entails removing dirt and rock from its natural location, thereby creating large empty pits, rooms, and tunnels, cave-ins as well as ground and rock falls are a major concern within mines. Modern techniques for timbering and bracing walls and ceilings within sub-surface mines have reduced the number of fatalities due to cave-ins, but ground falls continue to represent up to 50% of mining fatalities.Even in cases where mine collapses are not instantly fatal, they can trap mine workers deep underground. Cases such as these often lead to high-profile rescue efforts, such as when 33 Chilean miners were trapped deep underground for 69 days in 2010.

High temperatures and humidity may result in heat-related illnesses, including heat stroke, which can be fatal. The presence of heavy equipment in confined spaces also poses a risk to miners. To improve the safety of mine workers, modern mines use automation and remote operation including, for example, such equipment as automated loaders and remotely operated rockbreakers. However, despite modern improvements to safety practices, mining remains a dangerous occupation throughout the world.

Environmental issues can include erosion, formation of sinkholes, loss of biodiversity, and contamination of soil, groundwater and surface water by chemicals from mining processes. In some cases, additional forest logging is done in the vicinity of mines to create space for the storage of the created debris and soil.Contamination resulting from leakage of chemicals can also affect the health of the local population if not properly controlled.Extreme examples of pollution from mining activities include coal fires, which can last for years or even decades, producing massive amounts of environmental damage.

Mining companies in most countries are required to follow stringent environmental and rehabilitation codes in order to minimize environmental impact and avoid impacting human health. These codes and regulations all require the common steps of environmental impact assessment, development of environmental management plans, mine closure planning (which must be done before the start of mining operations), and environmental monitoring during operation and after closure. However, in some areas, particularly in the developing world, government regulations may not be well enforced.

Ore mills generate large amounts of waste, called tailings. For example, 99 tons of waste are generated per ton of copper, with even higher ratios in gold mining. These tailings can be toxic. Tailings, which are usually produced as a slurry, are most commonly dumped into ponds made from naturally existing valleys.These ponds are secured by impoundments (dams orembankment dams).In 2000 it was estimated that 3,500 tailings impoundments existed, and that every year, 2 to 5 major failures and 35 minor failures occurred;for example, in the Marcopper mining disaster at least 2 million tons of tailings were released into a local river.Subaqueous tailings disposal is another option.The mining industry has argued that submarine tailings disposal (STD), which disposes of tailings in the sea, is ideal because it avoids the risks of tailings ponds; although the practice is illegal in the United States and Canada, it is used in the developing world.

The waste is classified as either sterile or mineralised, with acid generating potential, and the movement and storage of this material forms a major part of the mine planning process. When the mineralised package is determined by an economic cut-off, the near-grade mineralised waste is usually dumped separately with view to later treatment should market conditions change and it becomes economically viable. Civil engineering design parameters are used in the design of the waste dumps, and special conditions apply to high-rainfall areas and to seismically active areas. Waste dump designs must meet all regulatory requirements of the country in whose jurisdiction the mine is located. It is also common practice to rehabilitate dumps to an internationally acceptable standard, which in some cases means that higher standards than the local regulatory standard are applied.

After mining finishes, the mine area must undergo rehabilitation. Waste dumps are contoured to flatten them out, to further stabilise them. If the ore contains sulfides it is usually covered with a layer of clay to prevent access of rain and oxygen from the air, which can oxidise the sulfides to producesulfuric acid, a phenomenon known as acid mine drainage. This is then generally covered with soil, and vegetation is planted to help consolidate the material. Eventually this layer will erode, but it is generally hoped that the rate of leaching or acid will be slowed by the cover such that the environment can handle the load of acid and associated heavy metals. There are no long term studies on the success of these covers due to the relatively short time in which large scale open pit mining has existed. It may take hundreds to thousands of years for some waste dumps to become acid neutral and stop leaching to the environment. The dumps are usually fenced off to prevent livestock denuding them of vegetation. The open pit is then surrounded with afence, to prevent access, and it generally eventually fills up with ground water. In arid areas it may not fill due to deep groundwater levels.

During the twentieth century, the variety of metals used in society grew rapidly. Today, the development of major nations such as China and India and advances in technologies are fueling an ever greater demand. The result is that metal mining activities are expanding and more and more of the worlds metal stocks are above ground in use rather than below ground as unused reserves. An example is the in-use stock of copper. Between 1932 and 1999, copper in use in the USA rose from 73 kilograms (161lb) to 238 kilograms (525lb) per person.

95% of the energy used to make aluminum from bauxite ore is saved by using recycled material.However, levels of metals recycling are generally low. In 2010, the International Resource Panel, hosted by the United Nations Environment Programme (UNEP), published reports on metal stocks that exist within societyand their recycling rates.

The reports authors observed that the metal stocks in society can serve as huge mines above ground. However, they warned that the recycling rates of some rare metals used in applications such as mobile phones, battery packs for hybrid cars, and fuel cells are so low that unless future end-of-life recycling rates are dramatically stepped up these critical metals will become unavailable for use in modern technology.

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basic gold prospecting & exploration methods

Prospecting and exploration that is a search for precious metals deposits is not a simple process because big deposits were discovered a long time ago. There are several places with important content of precious metals waiting for skill prospectors. The large mining companies of the world are focused in big deposits and the small deposits are attractive for small miners and perhaps their interest for gold is the most valuable tool for exploring new deposits.

Gold is a very widely disseminated throughout nature and may be found in any geological formation from the oldest rocks to the deposits that are still being formed, but in common with other metals, it is more likely to be found in the oldest rocks and in those places where the earth crust has undergone the most extensive changes such as elevations, folding, tilting, faults, fissuring and also volcanic action, with resulting changes in the composition and texture of the rocks.

The current technology is very important in development new project and exploration of new deposits begins with the selection of a target area. This is followed by reconnaissance exploration in which satellite remote sensing; geological mapping and seismic techniques are used. In turn, this is followed by detailed geophysical studies and later, a detailed drilling, sampling, assaying and mineralogical study. Gold deposits are sought with many techniques, but they are based on geochemical studies. Commonly more than one method is employed. With these methods, the geologist is looking for anomalies. Perhaps, the most important techniques are photogeology and seismic techniques.

Photogeology is a very important of gold deposit exploration. It gives complete information of high altitude photography and satellite photography. Images are recorded either on films or by recording the image digitally. Films used include black & white, true color, and Infra-red. In color photos, the red areas indicate live vegetation. This makes them useful for locating outcrops in highly vegetated areas.Also least affected by fog, and is effective in cloudy environment. It is also good for determining moisture content of soils. The typical aerial photos are those which are taken with the camera lens vertical due to oblique photos could exaggerate the relief.

In general, photogeology involves the interpretation of an areas geology from analysis of landforms, drainage and vegetation. Basically, there are four types of information, fracture and trace analysis, fracture identification, seep detection and channel change study. When a fracture is observed in cross section, it seems to be vertical or near vertical breaks in the bedrock. Gold particles can be deposited into fractures. Other important information is the called lithological mapping, which involves the interpretation of surface features so that can be obtained a more exact map.

The map scale towards the center of the photo is different from the map scale toward the edges of the photo. Orthophotos are images which have the distortion rectified, and can be used directly for mapping purposes.There are many applications of photogeological methods in mineral exploration work as well as in the studies of environmental geology and geologic hazards. Most importantly, they are used to make accurate topographic base maps. In mineral exploration work, accurate topographic base maps are essential for recording geological observations. Rock and soil color changes, or color anomalies, can be delineated and possibly investigated with ground traverses.

Photogeologic analysis provides data on local geology conditions which help to detect possible gold zones. Even, it is possible to get information on ground water movement, and this is influenced by fracture traces, karst features and aquifer recharge and discharge points such as springs. It is possible to get information on lithology, alteration and structures. When the work was performed properly, there will be possible to know the structural features in a specific area, such as the direction and dip of the beds, fold direction, and fault plane dip. Color contrasts in exposed bedrock due to changes in rock type, or lithology, and can be traced on the photograph, to map out the contact. The information can be gathered more efficiently and safely than a ground traverse, although there is no substitute for direct observations.

Photographic surveys follow specified flight routes and take the photographs at regular spacing along the path. The overlap between adjoining photos in a sequence along the line is about 55-60 %. The overlapped area is detected by the camera from two different views in two different photos. The two adjoining photos used together make what are called a stereo pair. The two photos can be placed side by side and observed with a stereoscope.

Once the need for Photogeologic support is identified, the place is screened for suitability. A preliminary determination is made to insure that the site is located within the appropriate geologic terrene for the requested Photogeologic work. Government and private sources of overhead imagery are searched for available coverage and information on geology, hydrology and soils is compiled. Close contact with prospectors and gold companies assures that the results of the study will provide the information required. The results of the Photogeologic study are compiled into a bound report that includes figures, maps, and interpretation.

Surface seismic techniques used in gold exploration are restricted to seismic refraction and seismic reflection methods. Probably, the first one is the most employed. The equipment employed for both techniques is very similar and assure the travel time of acoustic waves propagating through the subsurface. In the seismic refraction method, the travel time of waves refracted along an acoustic interface is measured. In the other technique, the travel time of a wave which reflects off an interface is measured.

The information to be obtained is dependent on the acoustic properties of the subsurface material. Specifically, their properties can identify various geological materials. In this way, the interpretation of seismic indicates changes in lithology or stratigraphy, geologic structures and water saturation zones. These techniques are commonly employed to know the depth and structure of geologic and hydrological areas.

The seismic refraction technique is a geophysical method widely used to explore the ground. Basically, seismic waves travel outward from a source and reach a detector. The detector first senses the waves that went directly to it along the ground surface, and then it senses waves that went downward, were refracted at a deep layer, then left the deep layer and came back to the surface. Due to the waves move faster in the deep layer, they take the surface waves. At a certain distance exists a crossover point, the refracted waves reach the detector first. With this initial information, a few assumptions can be considered about the place and we can know the thickness of the surface layers and its possible composition.

The information obtained can be used to make a map on bedrock topography, determine the depth of gravel or sand, delineate perched water tables, detect subsurface caverns, identify shallow faults and fracture zones, and detect large boulders.

Seismic refraction explorations are based on the time required for a seismic wave to travel from a source to a receiving point. Basically, a sound can be used for the seismic source and twelve or more vertical geophones are used for the receiving points. The selection of the seismic source depends on the seismic line, the resolution required, and the environmental properties. A signal enhancement seismograph records signals from the geophones. By analyzing the arrival time of the seismic wave as a function of distance from the seismic source, the seismic velocities of the underlying soil/rock units and the depth to geologic contacts can be determined. The geophone spacing and the distance between the seismic source and the first geophone are designed to obtain the needed penetration and resolution. The method is usually employed to areas where seismic velocity increases or is constant with depth.

The seismic data are studied by plotting the arrival time of the wave at each geophone versus the distance from the seismic source to the geophone. These charts are commonly known as travel-time plots. The data have to be fitted with straight-line segments. Each line segment corresponds to a different stratus or layer. The reciprocal of the slope of the line is the apparent wave velocity of the layer. Current state-of-the-art analyses use forward and inverse modeling and ray tracing that seek to minimize discrepancies between field measured arrival times and corresponding times traced through the velocity model.

The seismic velocity of a geologic stratus can be known by the refraction method and a relative estimate of the depth to different acoustic interfaces. Seismic refraction surveys are very useful to obtain information on depth at different locations. Refraction surveys are useful in buried valley areas to map the depth to bedrock thickness of overburden. The information obtained can be related to various physical properties of the bedrock; rock types have specific ranges of velocities. For example, dolomites and granites have different seismic velocities. A key aspect of this method is the line length to me measured. It is recommended that the distance from the seismic source to the geophone station or reception point have to be three or more times the desired depth of exploration.

It is essential in the evaluation of a gold deposit to have, as accurately as possible, a model of the mineralized zone geometry, shape, size, quality, variability, and limits. Physical, chemical and geological characteristics may vary greatly within a single deposit and from deposit to deposit. Critical data can be collected in a variety of ways, including drilling, surface and/or underground mapping, geophysical or geochemical surveys, or studies of rock mechanics properties, mineralogical types and relations.

The initial prospecting work is conducted on the potential place and consists in taking samples. The first samples are grab as single pieces and later can be composited if were necessary in nature, lacking any definite width characteristics, but useful in identifying local mineralization and possible geochemically anomalous zones. The rock sampling can be done by regular people, but ideally a geologist must oversee this task. It is important to determine sample station using handheld GPS devices, usually accurate to within 5-10 m. As was mentioned samples are initially grab in nature, but also, it is important to take chip samples across structures and veins in order to determine widths of mineralization and the presence of any wall rock mineralization near to these structures.

If the sampling program is detailed, the initial number of samples is more than 500 and this can be composited according to the first mineralogical assessment. For example, it is good practice to prepare at least 100 composites from grab samples in 1-4 m2 areas along 50 m and spaced lines at 10 m spaced sample locations. The samples can be assayed for several elements if there is not any economical restriction, otherwise the assays must include at least gold and silver. In this way we can know a preliminary distribution of metals. For example, of 100 samples collected the average gold value can be 2 g/t, with 40 samples reporting more than 1 g/t gold. Usually, the silver content is higher than gold content. If other metals were assayed, it is possible to establish a correlation between base metals and precious metals. In some places, local high sulphidation epithermal overprints within a predominantly polymetallic style hydrothermal system.

Other initial information to be obtained is the possible occurrence of anomalous to significant contents of precious metals in the different zones where grab samples were taken. If more information is required, part of the samples can be submitted for Whole Rock Analysis and X-Rays. It must be mentioned that samples usually vary from fresh to altered ores. The results to be obtained can confirm the existence of several populations among different rocks such as volcanic and andesite. Then, we can infer can some rock were formed or derived from the chemical reaction or weathering of other rocks. Essentially, it is possible to establish a preliminary paragenesis of the deposit.

Other points to be sampled are stream sediment. These samples have to be collected in different stations along each drainage and theirs positions can be determined by using a GPS. Results of the survey provide information on potential areas of anomalous base and precious metal values throughout the place. By performing statistical analysis is possible to know what zone or zones are more important and basically the gold and silver distribution.

Soils must not be overlooked. It is important to take collected samples over 2.0 km x 2.0 km areas. Samples can be taken at 40 m station along 150 m spaced grid lines, each line approximately 2 km in length. One more time, sample stations are located using a GPS device. Results of this survey let identify precious metals within the grid area.

Preliminary exploration can be performed by trenching. This method needs a backhoe or bulldozer, which makes possible to observe and take bulk samples on a continuous basis across the mineralized zone. Several ore types are weathered easily at the surface and these layers have to be removed in order to have good information on mineralogy and lithology. Preliminary trenching and pitting may be done with the objective of providing initial information to geologists in order to improve the parameters estimated for this sampling program.

Normally, trenches are excavated by hand employing picks and shovels until the bedrock is visible, most the time at depths of 1 to 3 metres. Trench sampling can be carried out by channelling a sample along the floor of the trench. Each channel is between 10 to 20 cm wide and 5 to 10 cm depth. Samples are taken for geological purposes. In this way, veins, altered zones or different mineralized zones can be sampled so that the contacts can be 2-4 cm within the sample boundaries. Sample weights are usually between four to eight kilos.

In serious and big trenching programs, bulldozers are employed to explore the different areas at different depths. That kind of equipment is easily available when is necessary to move huge tonnes of waste material to access the place. Mechanical or hydraulic rippers are employed in difficult mineralized zones. If extra depth is required, a shallow shaft is sunk at lower cost and with less damage to the surface. The face or uphill side of the trench is a zone of geological information and sampling point due to these zones are virgin and clean of broken material. Trenching programs are useful when they are planned properly, but they could be a waste of money and time when the program was prepared without technical considerations.

If the grab sample gave interesting results, a drilling program must be planed in order to have a better knowledge on the deposit. The drilling program can involve one or more types of drilling, conditioned by the material to be sampled, rock environment, and the reason of the sampling. Basically, there are two types of drilling, one involves core drilling and the other one is reversed circulation.

The core drilling is employed for most the mining companies. The main disadvantages are the cost and the time required to complete the programs, however the information to be obtained is excellent. Essentially, provides accurate samples of a mineral deposit, the rock types, mineral types, and rock structures. By employing this method, the core is removed from the hole. There are some variations of this technique than improve the time required to extract the core. This greatly accelerates the drilling process and improves core recovery. However, it yields a smaller diameter core. Some drilling techniques often produce poor core recovery, but with improved core barrels, a good design, the total core recovery can be improved. Disadvantages of diamond core drilling are its high cost, small size of sample and slow penetration rate. Bulk sampling for metallurgical testing or placer deposit testing are generally obtained by the drilling of large diameter holes (plus 6-inches in diameter), or by sinking winzes.

During the drilling program the core has to be stored and extracted for geological and metallurgical purposes, which reduces cost and time. There are five main sizes of diamond core employed for mining projects,

The cost is influenced by rock type, terrain conditions, environmental conditions, and time required to complete the program. The time depends on ore body size, diamond core diameter required, geology department and the previous information obtained at the beginning of the project. For instance, if the objective is to have complete information on mineralization and perform metallurgical tests (e.g. comminution, concentration, leaching), the time required is around eight weeks. Obviously, there are several activities involved such as mobilisation of the drill team on site, drilling, geological mapping, core splitting, core logging, and core packing. Finally, the samples are delivered to different laboratories.

Reversed circulation drilling is a fast and cheap method. Unfortunately, the samples obtained provide no much information on mineralogy and the metal content can be no very reliable. Since the sample are not very deeper, information and data have to analyzed and studied carefully. A hammer transmitting its force through drill rods to a rotating drill bit which does the penetration. Air or water is circulated through the drill rods to cool the bit and carry out the rock cuttings to the collar of the hole, where they are collected and prepared for study and assay. The method works well where the wall rock is competent, dry and impermeable. It has a practical depth limit of 45 to 90 m. Metal values may be lost by seepage into the wall rock, or added or diluted by caving or seepage into the drill hole. Reverse circulation of the drill water down the hole and up the drill rods greatly improves the accuracy of the sample. Sometime, mining companies during the first months of operation employ this method to study zones that were not studied well during the exploration program. Results are different. For example, by employing a core drilling program the average gold content was 5 g/t. however, the second method on the same place gave higher values, 10 g/t. This situation creates doubt and conflict between the design criteria and the new values. For this reason, results obtained by reversed circulation need a special study and interpretation.

There is other option called Rotary drilling. This technique is inexpensive and fast and similarly to the reverse circulation drilling, there is some disadvantages such as samples are broken into small chips that dont show the structure of the bedrock and the samples submitted for assaying are not very realistic. Most of the rigs are truck mounted and completely self contained, including the air compressor. Standard tri-cone bit can drill a hole four inches in diameter and the drill cuttings are blown out of the hole with compressor air. Samples are piled on the ground in rows, each pile represents approximately 0.50 to 3.0 meters of advance and each row from 6.0 to 30.0 meters of hole. Ideally, the sample must be collect in appropriate containers. This method is preferred by people who want to perform the sampling and logging in the same drilling hole.

Sometime, the drilling can be performed in two parts if the first program didnt cover all the mineralized area. This additional drilling program can be complemented with geophysical methods in order to define the objectives of the program. For example, magnetic surveys identify magnetic zones that are related to silica cap areas. If the deposit presents high sulphidisation in areas far from the main ore body, the extra drilling is recommended. This can occur in deposits with structural and stratigraphic control and consequently some areas could be occulted. If the mineralization is close to the surface, at deeper areas may be or not possible to find high mineralization.

The drilling procedure can be designed under several considerations such as the geology team set out the holes in an area close to the drill rigs, drilling pads are done with bulldozers and the geologist oversee the work, cores are laid out for inspection, the final hole depth is decided by the geologists, hole location is recorded by GPS system, and geologist performs logging and coordinate the sample storage. There are other considerations that depend on the drilling target.

There are two types of samples to be studied. The first group is formed by the grab samples taken at the beginning of the project. These samples are basically rock chips. These samples must be bagged and sent to the lab for assays and metallurgical tests. The second group is constituted by cores from drill holes, cut channel samples or bulk samples from trenches, or underground workings. Similarly to the first group, the samples need to be assayed and tested metallurgically. For assays, these samples must be reduced in volume and size of particles without dilution or enrichment of metal values.

Field samples are sent to the sample preparation facility where the samples will be divided for geology and metallurgical information. In order to deliver the sample in the best condition to the laboratory facility is necessary to consider some factors such as use appropriate labels and names to identify the samples, define the procedure to be employed for bagging and sample collection, assure the sample preservation, manipulate the sample when is necessary, and minimize the movement of the sample in and out of the container. The storage and transportation must consider the oxidation conditions to be exposed the samples and more even if the presence of sulphides is important. Under this consideration, samples must be stored in a freezer. If the samples need to be logged and cut, they must be taken from the freezer. When the samples have to travel a long distance is good practice to wrap the samples in a bag which air was purged with nitrogen. In this way the sample will stay in inert atmosphere and the possible risk of oxidation will be minimized.

Normally, drill core samples are split in half with a diamond core saw. One half is submitted for analysis and/ore metallurgical tests and the other half is stored. The core has to be photographed at the site, geologically logged and geotechnically logged. The core samples are selected by the geologist based on logging information and must be labelled with the right code and name. Samples range in length from 0.20 m to 2.5 m and their weight is variable, 1.5 to 6.0 kilos. The half core samples are bagged and placed in sacks, security sealed and shipped to the laboratory for sample preparation according to the testwork program.

When the samples arrive to the laboratory for assays, they are codified according to the laboratory system and weighed. Each core sample is entirely crushed to almost 100% passing 1.7 mm (10 mesh). Samples are homogenized and one kilo is split and pulverized to approximately 90% passing 0.075 mm (200 mesh). Then, 200 to 300 grams are split. If the samples are wet, it will necessary to dry the samples without using any heating system in order to avoid any physiochemical change in the samples.

In order to control the sample preparation procedure, approximately 5 to 10% of the crushed and pulverized samples are submitted for a regular particle size analysis by using lab screens. Blank samples are included into this control so that the sample preparation procedure can be done properly. These samples can be added into the core samples at a frequency of 1 in 30.

In order to perform assays for gold and silver, 40-60 grams aliquots are taken for fire assay. This assay method employs fluxes according to the minerals present in the sample due to the fluxes are variable and there is not a unique recipe. Some assays for other elements are performed by atomic absorption. For example, we can have 1,000 to 50,000 samples to be submitted for 20-30 elements. Sometimes, assays for almost all the elements can be done by Inductively Coupled Plasma (ICP). Gold is always assayed by fire assay using 25-35 g charges.

Certificated laboratories have a quality control procedure that includes the sample to be assayed, standard, blanks and duplicate samples into every assay. For example this procedure can consider three standards, two blanks and three repeats in every batch of 80 samples. If any discrepancy is found, the whole batch has to be re-assayed.

Prospecting is to search valuable mineral deposits and is the focus of many people around the world. Gold prospecting is a very special case due to is suitable for many speculations and potential objectives. Gold deposits are variable and the prospector needs few tools in order to detect potential mines. The modern equipment enables people to transform an obligatory task into a challenge. There is a question very important, where to look for gold? Try to answer this question is not simple, but there some clues to be considered.

Since gold is widely disseminated in the nature, it can be found in any geological formation, from the oldest rocks to the deposits that are still in formation. However, gold can be found in old regions and places where the earth surface has experienced many changes such as elevations, folding, tilting, faults and volcanic action, with resulting modifications and alterations in metal composition and crystalline structures.

Geological exploration is developed by steps, starting with studies in small scale and finishing with studies in big scale. In this way, the prospector has to analyze progressively the territories with important potential or perspectives to find the desired metal. This consideration obliges to evaluate different places with variable interest until find the right place so that it can be evaluated and verified as economical resource. Obviously, each step needs more detailed studies. Basically, there are four prospecting steps: regional, identification, local, and detailed exploration.

Regional exploration considers a region determined by geological, economical and accessibility factors. The limits of this sped are not necessarily associated to geological elements. Few times are carried out geochemical studies due to the main source of information are cosmic images, photogeological information and aerophysical data. The main objective is to define one or several districts within the region under study. The difference between district and region is arbitrary under special considerations. However, a district can be considered a discrete unit due to the identification and limits are conditioned by a special mineralization or geological considerations favorable to find any special mineralization.

It is necessary to perform studies on active sediments present in fluvial points. Typically, one sample per five square meters can be studied. In this way, the district will be defined. The geochemical study of rocks oriented to identify mineralized and sterile zones is appropriate.

Prospecting is the first exploration oriented to study a specific district, which was defined previously. The objective is to detect potential areas and not necessarily to find a mineralized place. The areas detected will be studied in detail according to the first results. This study is designed to define anomalies in a specific district or region. In order to do this is necessary to know the work scale that allows identifying the areas with major potential.

The sampling procedure must assure a detailed geological interpretation of the place, even to get information on the location of the geological contacts. In areas where there are prominent outcrops, the samples can be taken in areas of two square kilometers. The number of elements to be studied can be selected considering the previous study (regional study).

Local exploration tries to detect geochemical answers in small areas. The objective must be selected con precision and its location has to be very exact. Although the objective is not to locate a deposit, the development of the study could identify one. Basically, the objective is to define the mineralogy associated to anomalies of specific elements or group of elements. The sampling procedure and the expected answer are related to the type of mineralization required in the study. For example, sulphide deposits produce anomalous aureoles of hundreds of meters, and narrow veins are associated to anomalies developed in dozens of meters around them.

A detailed sampling of sediments at 20-200 m intervals is useful to define the location of any anomalous object. If the drainage system is poor, rocks can be studied only if the mineralization produces an extensive dispersion system. The number of samples is based on the drainage system and could be expensive.

Once the objective was defined, the next step is to locate the mineralized zone and its extension. Normally, studies of rocks and soils are the geochemical techniques more employed during a detailed exploration. It is common to take samples 150-400 m extensions with 30-90 m intervals. When the mineralized zone was located, samples will be taken with much more detail such 40-90 m with 5-10 m intervals in order to create a map with all the mineralization. The only way to identify the mineralization and all the changes into the zone is to perform a drilling program. Sometimes, trenching is an option. When the object was identified, the exploration process continues if the previous results were acceptable.

This term makes reference to the character of a rock described in terms of its structure, color, mineralization, grain size, and arrangement of its components. These parameters give a special characterization to the rocks contained into the deposit. For example is the prospection team identified a hydrothermal ore body, basically all the drill cores and outcrops around the deposit must have specific properties to this type of deposit.

Gold deposits can be located within breccias defined by multiple phases of breccias and associated to air fall pyroclastics. In this case, they could be divided in a sequence of bedded lithic, crystal and anomalous tuffs that overlie a massive basement. Basically, the host rocks are a sequence of lithic formations with fragmental texture and rapid changes during its formation. Then the prospector must be able to detect and/or identify these characteristics with information proportioned by the geologist. In this way, these lithic zones define a stratigraphy which special orientation. For example, they could deep between 5 to 15 towards the northeast, steeping and thickening proximal to the contact with the breccias.

The rock formation can stay beneath the lithic sequence and the contact could be unconformable. Then, it can be considered a modified mineralized zone with appreciable change into its structure. Sometimes, some rock formations formed a pre-existing land surface upon which the new formation was deposited. Probably, this kind of surface is related to breccia formation. A breccia formation is identified in the drilling program and/or trenching sampling program and the rock formation may to be in a large bowl shaped depression and could be constituted by two or more phases that form a new body. For example, if there are two phases, the first one is an early formation with consistent assemblages characterized by fine grained rocks. And the second one could have rounded particles with empty spaces formed during the cooling process. A typical example of the second phase is the presence of vughy silica.

It is important to identify the structure because the mineralized zone has a special orientation. Sometimes is difficult to recognize the right orientation, but the initial emplacement is the first reference point due to control the alteration and mineralization. The structures are characterized specific alterations, presence of stockworks with variable content of sulphides and brecciation. For example, some structures can be 1-3 m in width, but zones can be 30-50 m wide. This variation is an indication on the mineralogy into the deposits. For this reason, during the blasting sometimes is difficult to take a decision about the points to be drilled. This behavior is explained by the presence of hydrothermal fluids with subsequent mineralization.

There are some stockworks formed in areas very close to the mineralized zone or under special circumstances formed only in specific places. For example, some siliceous zones with important content of vughy silica can be detected in areas no very close to the main structure, which can be characterized by the presence of fractured stockworks. Certainly, this zone probably is influenced by combination of structures and breccias with different orientation. However, the mineralization is useful to detect these changes into the structures.

When are detected several fractures is important to try to determine how were formed because we can know the possible final orientation of the mineralized structures. Normally, the combination of these structures can provide the host rock into the ore body.

This parameter can be considered as a physical and/or chemical variation in a rock or mineral during its formation. These changes have influence in the type of mineralization to be found into any structure. it is important to mention that alteration or changes and mineralization and processes developed in different periods. For example, an acid fluid leaches a rock producing a rock with many holes or empty spaces (vughy silica) and around this formation can be developed alunite and kaolinite zone.

According to the structure sequence and location is necessary different amounts of acid leaching agent to aggressively dissolve the rocks and the acid fluid formation are formed in water saturated places close to the structures. This creates zones with alterations into stratigraphic horizons. These zones can be characterized by containing variable amounts of different rock types whose alteration or leachability is different according to the stratigraphic horizons. In this way is expected to find zones of different level of porosity and permeability. For this reason, there are different types of vughy silica.

It is important to establish a relationship between altered zones and stratigraphic zones due to its formation and deposition is influenced by the leaching conditions. This is totally valid for gold deposit formation and especially when there are free gold particles deposited into the empty spaces of some minerals.

Alteration has influence on gold mineralization. For example, intense leaching creates pathways or routes for metal bearing fluids and some spaces or positions are created to host gold and heavy metal sulphides. For this reason, some underground operation can produce copper and lead concentrates with variable contents of gold. Obviously, is expected to find some undesirable elements.

Ore bodies present mineralization at different depths and they are characterized by variable contents of gold. Probably, some zones have higher content than the others and they were influenced by the leaching fluids and the type of mineralized structures. For example, some intersections the mineralization is disseminated and distributed by stratus.

Hydrothermal fluids run along different rock formation and produce dipping mineralization that can be detected a variable distance from the main structures. Probably, important gold contents can be detected in some structures due to some lithologies were leached with more intensity than others. This can be explained by the stratigraphy and gold content near to the surface. Then, metal content in sulphide areas are related to the degree of alteration and structure formation.

The geologist or prospector must have a knowledge on the ore types are most likely to carry gold; otherwise the time employed will be unfruitful. In most deposits is possible to identify the rock; volcanic, sedimentary, metamorphic, or even the river streams that transport gold. The valuable gold ores are brought in by different system of transportation such as percolating waters and gasses from cooling systems. The first one is probably the most important because they are charged with different heavy metals or base metals. The second one is other important source of gold ores and is characterized by special fluids locked into the rock in chemical combination. These fluids are extremely important in the formation of valuable ore bodies. They pass through different rock formations on their way to the surface dissolving several minerals and carry them in solution for large or short distances. These mineral loaded waters reach a space in the rock where they deposit their valuable charge. These spaces are open and formed by earth movements or large open spaces formed by dissolution of other minerals. In open fissures, vein deposits can be identified. Fluids may leave their metallic minerals into porous formation like granite to form disseminated deposits.

Gold is not very soluble and high pressures and under the presence of some chemical agents is possible to be transported in solution. Percolating fluids are mainly acid ground waters that penetrates rocks, dissolved the matrix and transport metals to different parts. These metals could be lead or copper. For these reason some polymetallic deposits contains important amounts of gold.

When we have to talk about gold mining, everybody thinks on free gold. This idea started at the first days of gold deposit processing. The gold from original veins was gradually disintegrated through the time. Gold being heavy and resistant to weathering has been concentrated in sand, gravel and different rock formations. Probably placer deposits have been mined for most miners since the first days on mining.

Placer deposits have been formed by the mechanical concentration of heavy minerals and the product to be extracted are of very important commercial value. This means the marketability is totally successful. Basically, the minerals to be present in marketable products include all the material characterized by high specific gravity and resistance to wear and weathering. Precious metals belong to this group and may be possible to find other heavy material such as magnetite, chromite, rutile, monazite, zircon or gem stones. The big alluvial placers have been formed after a long time. Placers deposits are easy to prospect and estimated in qualitative form. A gold pan is the first tool to be employed at the moment of find out the values minerals present in the deposit. The heavy concentrate collected is examined with great detail. For example, if magnetite is present, a magnet can removed this material and the remaining product can be examined by using a magnifier glass and reactivity to some chemical reagents. Even is good idea to evaluate radioactivity. If the results are positive, the material can be sent to a special laboratory in order to confirm and get more information on the material.

Placers are located in or adjacent to a river stream. The material has been formed by the action of running water, ocean, lake waves or winds. For many years, aquatic deposits have been mined, and most people overlooked deserts places. The main obstacle has been the lack of water at these places, but the technology has developed dry concentrators capable of recovering gold. These methods are the best alternative. The main examples of this type of deposits are located in Nevada and some areas of Australia. For some time, quicksilver was used, but results were not satisfactory and some operative problems were experimented by the amalgamation equipment.

In general, important values of precious metals may be found in any place, but they must be of practical level and quantity. Some small pieces may contain important values of gold, but the project must evaluate of the deposit. Normally, these cases are good for recreational activities or very small mining operations. In this way, the particle size and amount of material to be handled have an effect on the project. Sluices and rockers are good options for small miners.

Gold deposits may be located on the side of a mountain or on any bench removed from any body of water. These are ancient water deposits left by the flowing stream or probably the beach of a very old aquatic formation. Many times, formations are not accessible and the geologist or field prospector must remove material such as plants, rocks or ground. Some zones may report high gold contents, but the mineralogy is not always the same and the deposits could be extremely small. For this reason the metallurgical evaluation is complement with the deposit volume, otherwise, the project could not have the level of profit expected considering the first results.

It is well known that mountains and volcanic areas are more favorable for metallic deposits due to these places are characterized by faults and fractures in the rock formations that are appropriate for gold minerals concentration. In hilly or mountainous areas are favorable for the contact or outcrops, which indicate that values are under the surface. These are places where the vein could be exposed on the surface due to the action of different agents such as fluids or weathering. The first indications are mineral fragments or some material loose that look like a floating material. The last indication means that the ore source could be found in a slope.

Similarly to the placers, some outcrops can be covered by other undesirable material which has to be removed. Then, the prospector must be able to clean the area and follow the vein so that he can recognize the deposit orientation and possible volume. In general, outcrops are different in size and appearance. Some of them are characterized by silica rocks and standing notoriously on the surface. Other outcrops cannot be detected easily and apparently are small; however, many times they are big. It is well know that silica in limestone develops an obvious outcrop due to silica is more resistant to weathering conditions. In this way, many base metals and its mineral are weather easily and can be detected in outcrops. This is important to mention due to base metal minerals are potential gold carriers.

Outcrops may stay in an oxidation zone and the mineralization at deeper points could be totally different. Basically, the oxidation zone is influenced by the terrain, climate and geographical location. There may also be considerable enrichment in the oxidation areas, derived from the surface values. As the surfaces are weathered, eroded, leached and percolated by fluids, the valuable minerals are transported and deposited downstream. These processes proceed down to the groundwater level where oxidation disappears and sulphides appear.

Dry places are potential places where gold must be prospected. Normally these areas are dry, but in any moment a fluvial precipitation happen and the ground is eroded. A gold prospector must observe the zone and look for dry rivers.

gold rises with molten rock | live science

Gold, as well as other rare metals, can be brought to the surface by plumes of molten rock from deep within the mantle, the layer underneath Earth's crust, producing background levels of gold up to 13 times higher than elsewhere, according to research published Oct. 19 in the journal Geology.

"In practical terms, what this means is that in areas like this, gold deposits might be more common and/or bigger than they would have been if the rocks were not plume-derived," said Alex Webber, a geochemist from the University of Southampton in England who led the study. "So whilst the process we've studied does not directly create a mineral deposit, it helps greatly to increase the likelihood that economical deposits would be found in the area."

Other areas that may have high background concentrations of gold include large igneous provinces vast accumulations of igneous, or volcanically produced, rocks in the Earth's crust such as the East African Rift, the Deccan Traps in central India, and the Siberian Traps in northern Russia. The Hawaiian Islands, which were formed over a mantle hotspot and are composed of igneous rocks, also are likely to have higher concentrations of gold and other rare metals, Webber said.

During the Earth's early years, as its molten mass began to separate into the core, mantle and crust, different elements accumulated in different layers. Iron, copper, platinum, gold and certain other metals that are dense and compatible with iron moved toward the core, which is why theyre relatively rare at the Earth's surface and of higher economic value.

"The deeper mantle probably contains more gold and other iron-loving metals than rocks closer to the surface," Webber told OurAmazingPlanet. "Any mechanism that can bring any of that 'lost' gold closer to the surface creates the potential for very large enrichments over the background gold concentration of normal crustal rocks."

california gold rush - students | britannica kids | homework help

Early in 1848 James W. Marshall, a carpenter from New Jersey, picked up some glittering flakes from the American River at the site of a sawmill he was building near Coloma, California. He gathered up the pieces and sped to the office of the mills owner, John Sutter. Urging Sutter to secrecy, Marshall showed him his findings. Sutter tested the flakes and confirmed Marshalls suspicion: gold had been found in California. Within months, Marshalls discovery was made public, bringing a flood of fortune seekers to the region. The California Gold Rush would transform California and fuel the westward push of the United States.

In the years that followed Marshalls discovery, Californias population exploded. The promise of wealth and a new life lured people from around the world to California. American gold seekers traveled west from the Eastern states, migrating in such vast numbers that their passage stimulated advancements in transcontinental travel. People of diverse backgrounds and ethnicities came to California, selling their property and getting loans to afford the journey. Along the way, they risked danger and disease for a chance at gaining riches.

In 1849 alone, $10 million worth of gold was pulled from the ground, and over the next few years this number grew. In view of the huge amounts of money that could be made, and the rising lawlessness in mining settlements, politicians pushed to speed up the process of statehood. In 1850 California became the 31st state. The Gold Rush peaked in 1852, when $81 million worth of gold was extracted in California. Afterward, the number slowly declined. By the end of the 1850s the Gold Rush was over, but its legacy would continue to influence Californiaand the countryin the years to come.

Word of Marshalls find was carried by overland travelers and by ships that stopped at the California coast. The earliest gold seekers came from Oregon, Mexico, and South America, especially Chile and Peru. Then news spread across the Pacific, drawing hopeful miners from the Sandwich Islands (now Hawaii), China, and Australia. Later they were joined by Europeans, particularly from Germany, Ireland, and France.

Back in the United States, the first accounts of California gold in East Coast newspapers were skeptical. It was not until President James K. Polk confirmed the early discoveries in late 1848 that the Gold Rush ignited in the United States. The tens of thousands who rushed to California in 1849 came to be called the Forty-niners. Altogether, they numbered about 80,000. By 1853 the number of fortune seekers would rise to 250,000.

About 95 percent of the Forty-niners were men, typically white men from the Eastern states. Married men usually left their families at home in the East, with the promise of returning with riches. In 1850 women made up less than 10 percent of Californias population.

Despite their small numbers, women participated in the Gold Rush in many ways. Because many of the men who came west were accustomed to having their wives clean and cook for them, they paid women to perform these tasks. Some women made a living by running boardinghouses, where they housed and cooked for miners. With so few women in California, those who did live there found their skills and company to be in high demand.

Gold Rush women were divided socially and labeled as either bad or good. They were held to a different moral standard than men. Women who had nontraditional lifestyles or jobs were thought of as immoral and labeled bad. One of the most famous bad women of the Gold Rush was Miss Ah Toy, a Chinese prostitute and businesswoman who lived in San Francisco.

The influx of gold seekers had serious consequences for the many Native American peoples of California. The people whose ancestors had lived on the land for thousands of years shared little of the prosperity brought to California by the Gold Rush. Many American Indians were involved in the Gold Rush from its earliest days but were mistreated by white settlers and forced to work for them.

Californias Indians were devastated by the many diseases that were brought by migrants during the late 1840s and throughout the 1850s. Smallpox, measles, and cholera spread quickly because the Indians had no immunity to them. Before the Gold Rush, Indians made up most of Californias population, numbering about 150,000. By 1870, however, only 30,000 Indians remained. It has been estimated that disease was responsible for 60 percent of the American Indian population losses during the mid-1800s. Those who survived still felt the impact of the Gold Rush. The settlements that arose and the environmental impact of gold mining made traditional Native American lifestyles very difficult or impossible to maintain.

Whether coming from within the United States or from abroad, those who made the journey to California faced many risks. There were a number of routes to take to California. Chinese miners sailed across the Pacific Ocean, spending up to two months making the trip in small boats. The three main routes used by American gold seekers were the Oregon -California Trail, the Cape Horn route, and the Panama shortcut.

None of the routes to California was free from challenges or expense. Trips could cost $400 or more (a substantial sum at the time) and lasted several months. Each of the routes attracted a different demographic of gold seekers. Those traveling with families usually made the journey overland because it was too expensive or too cramped to do so on a ship. People traveling overland could expect six months of hardship and many unpredictable accidents along the way. Thousands of people died before reaching their destination. The sea voyage around Cape Horn could last up to eight months. Although the route through Panama offered the shortest travel time (as little as a month), it required braving the many threats of the Panama jungle.

The Oregon-California Trail stretched more than 2,000 miles (3,200 kilometers) from Missouri to Oregon and California. By wagon, the journey could take upwards of six months to complete. The starting point of the trail was Independence, Missouri. Heavy wagons pulled by oxen, mules, or horses usually set off in wagon trains. These were groups of wagons that made the long, hard journey together. Banding together as a team offered advantages in terms of safety along the trail. A large wagon train could intimidate bandits or hostile American Indians who might consider attacking a lone wagon.

People in wagon trains also relied on each other for support when problems arose. The varied terrain across the country was a constant challenge for travelers. In wagon trains people could share supplies or lend a hand pushing the wagon or carrying loads across tough passes. In good conditions, a wagon could cover 12 to 20 miles (19 to 32 kilometers) in a day. However, if the roads were muddy or there were rivers to cross, they were lucky to cover 5 miles (8 kilometers). Other difficulties of the journey included accidents and illness. Among the common trail diseases were cholera, smallpox, tuberculosis, diphtheria, typhoid fever, and scurvy.

The longest route to California was the sea voyage around Cape Horn, at the southern tip of South America. Gold seekers first boarded a ship on the East Coast of the United States, in New York City or Boston, Massachusetts. The ship traveled south around Cape Horn and then north to California, where passengers would get off at San Francisco. The voyage took about six months. The Cape Horn route covered 18,000 nautical miles (33,000 kilometers). During this lengthy trip, passengers faced illness, hunger, and poor nutrition. Ships traveling the Cape Horn route were often very crowded, which caused sickness to spread quickly.

A third route involved both sea and overland travel. The first step of the journey was to board a ship departing from the East Coast of the United States and sailing to the Atlantic coast of Panama, in Central America. Then travelers crossed the Isthmus of Panama, the strip of land that connects North America and South America. They canoed up the Chagres River, in central Panama. Then they rode a mule through the jungle to reach Panama City on the Pacific coast. There they boarded a ship to San Francisco.

By taking the Panama shortcut, gold seekers could cut about 8,000 miles (13,000 kilometers) and a few months off the Cape Horn route. Unfortunately, the advantages of the Panama shortcut came at a very steep price. Diseases such as yellow fever and malaria were a huge threat to travelers through Panama.

The huge demand for transportation to California gave rise to important developments in transcontinental travel. The influx of travelers through Panama inspired the creation of the Panama Railroad. Stretching from the Atlantic coast to the Pacific, it was the worlds first transcontinental railroad. Construction began in 1850 and was completed five years later. In 1863, a few years after the end of the Gold Rush, workers began building the first transcontinental railroad in the United States. It was completed in 1869. When the Panama Canal was built in the early 20th century, it closely followed the route of the Panama Railroad. Though only about 51 miles (82 kilometers) long, the canal had a huge impact on world trade.

The drive to get to California as quickly as possible was spurred by the fact that people were claiming mining territories on a first-come-first-served basis. Before it achieved statehood, California had no laws or government. In 1848 there was also no federal law to regulate mining. People came to California thinking that gold was free for the taking.

Rules about rights to property and how miners interacted were governed by a miners code. This code was a system for managing property rights through the staking of claims. Miners did not own the property they claimed. However, the first person to get to a site, discover gold, and mine it was entitled to the gold he found. A person could maintain his claim to a site only if he notified other miners that it belonged to him. A miners claim to a site lasted only as long as the miner continued to work it. If a person left his mining site, he lost his claim to it. The site was considered free to be claimed by a new miner. Taking over a marked site that was not being worked was called claim jumping.

Miners usually claimed a site and left within a short period of time. The California Gold Rush was truly a race to find the site that would yield the most gold. Since no one knew exactly where the gold was or how much could be found, a miner would typically abandon an unproductive site quickly and then claim another.

As mining camps began to form, each district established a set of rules. Without a government or other authority to enforce these rules, however, property claims were not very secure. The miners code worked only if people were willing to follow it. Many property rights were maintained only with the threat of violence, and disputes over claims were frequently settled with weapons rather than diplomacy. Californias mining districts were thought of as lawless, violent, and immoral places.

Many men came to California with the attitude that the laws that governed their behavior at home did not apply to them out west. Miners could spend 12 to 16 hours a day, six days a week doing hard physical labor at their claim sites. They spent their Sundays off in mining towns, playing as hard as they worked. Alcohol was readily available in mining towns and so was opium. Without authorities to keep people in check, drunken bar brawls and petty fights could end in murder. Mining towns also presented men with plenty of opportunities to gamble.

Men in mining towns outnumbered women nine to one. The lack of women meant that mining town society was rougher and rowdier than in the East. Mining towns were, however, far more ethnically diverse than most towns in the United States during the mid-1800s. Chinese, Mexican, African American, and American Indian people interacted with each other and with white Americans to a degree that was unmatched in the East. Prejudice and racism were common, however, and some of the violence that occurred in mining towns was racially driven.

By early 1849 an estimated 6,000 Mexicans had come to California seeking gold. California had been part of Mexico until the United States took control at the end of the Mexican-American War just a year earlier. Nevertheless, Mexican miners were treated as outsiders and often suffered discrimination. The tension between Mexican and American miners was heightened by the fact that many Mexican miners were more experienced and successful than the Americans. In 1850 California passed a Foreign Miners Tax, which forced non-American miners to pay $20 a month to the state. This tax targeted Mexican miners in an effort to drive them out of California.

In 1852 the government imposed a new Foreign Miners Tax, this time aimed at removing the Chinese. Many people had left China because of the poor economic conditions that followed the first Opium War (183942). The number of Chinese immigrants grew so much during the 1850s that they made up a fifth of the population in Californias mining towns.

Some African American Forty-niners arrived in California as free people looking to make their own fortunes. Others were slaves brought by their owners. Free African American miners did not have full rights as American citizens and were often mistreated by white American miners. In 1850 California joined the Union as a free state, and many slaves gained their freedom. Nevertheless, slavery continued in some areas.

In 1848 American Indians made up about half of the gold diggers in California. They were expected to perform the hardest labor for the lowest price. In 1850 the California legislature passed the Act for the Government and Protection of Indians. The act created a list of American Indian crimes and punishments and denied Indians the right to testify in court. Under the terms of the act, American Indians could be seized and forced to do involuntary labor. In effect, the act allowed white people to enslave Indians. An amendment to the act in 1860 allowed whites to take orphaned Indian children as slaves and force them to serve until they reached 35 to 40 years of age.

The Indians suffered the worst of the racial violence that occurred during the Gold Rush. When the Forty-niners flooded California, they overran Indian lands. Most white Americans felt that the Indians stood in the way of progress. They believed in Manifest Destinythe idea that it was their divine right and duty to spread Protestant and democratic ideals across the continent. Indian communities were attacked by groups of miners who wanted to stake claims on their land. In some instances, entire villages were murdered. Many Indians were forced to march to reservations, where conditions were dismal and many people starved.

Tragically, the abuse of American Indians was widely accepted and even encouraged. In certain California districts, miners were paid for Indians body parts and scalps. The popular attitude among whites was that Indian lives were worthless. Gold Rush miners did not just deny American Indians their right to land, they denied their right to life. The belief in white superiority and Manifest Destiny was supported by the U.S. governments brutal treatment of American Indians across the country.

Immigrants and American settlers were lured west by newspaper advertisements claiming that California was a land of inexhaustible gold mines where anybody could strike it rich. These ads often made light of the challenges that miners would face when they arrived. Few of the people who came to California were prepared for the grueling realities of gold mining. Some men spent hours standing knee-deep in frigid creeks as they hopefully panned for gold. Others faced extreme risks digging and blasting for gold. Most of the Forty-niners had no mining experience or skills and had to learn through trial and error. Even with very hard work, few miners actually achieved the success they dreamed of.

During the 1850s the amount of available gold began to decline. New mining techniques evolved to reach the gold that remained further below the surface. As mining technology advanced, the character of gold mining in California changed. Mining by individuals who worked their own claims was replaced by large-scale industrial mining. Rather than seeking their own fortunes, miners were hired to work in mines owned by corporations. The new mining techniques employed by these companies had a devastating impact on Californias environment and landscape.

Panning was the simplest way of collecting gold. It involved scooping soil or gravel from the bottom of a stream into a shallow pan. The miner would then swirl the water in the pan so that the heavier pieces of gold would sink to the bottom while the lighter materialdirt and gravelwould come to the surface. The miner tilted the pan to allow the dirt and gravel to wash away, leaving only the gold behind. Panning was the slowest and least effective method of collecting gold. Miners could typically get through 50 pans in a day and collect only a small amount of gold.

The rocker, or cradle, was a machine developed to speed up this process. A rocker was a long wooden box mounted on two curved pieces of wood similar to the curved runners of a rocking chair or babys cradle. The box was set at a downward angle. The miner shoveled dirt into the box and then poured water over it. The material was sifted by rocking the box from side to side. As the material was washed along, barriers called riffles captured pieces of gold, which were then collected by hand.

Later devices used the same concept as the rocker but improved on it. The long tom was bigger than the rocker and therefore could handle more material. It also contained a sheet of metal with holes in it to aid the sifting process. The long tom evolved into the sluice box, an even longer version of the same device. A sluice box was placed in a running stream, making it more efficient than devices in which water had to be supplied by hand.

Hydraulic mining involved using jets of water to break apart hard rock to reach the gold ore inside. The water was piped through a hose and blasted out through a nozzle. The powerful stream was shot at a hillside, breaking the hard rock into pieces. The water and blasted rock flowed through sluice boxes to collect the gold. The unwanted material was washed or dumped into nearby streams and rivers.

Hydraulic mining permanently changed the landscape of northern California. The debris left behind from blasting the Sierra Nevada mountains clogged rivers and streams flowing toward San Francisco Bay. Along with blocking navigation on these rivers, the debris caused them to frequently overflow their banks. Flooding spread silt and sand over farmland in the Sacramento Valley, which was disastrous for many farmers. Mining debris also killed wildlife in the rivers and upset the natural balance of ecosystems.

Hydraulic mining was very profitable, and for some time the environmental damage it caused was overlooked because of the gold that it yielded. In time, however, the mounting issues it created led to an outcry against its use. Hydraulic mining was eventually ended as it became too problematic and too expensive.

The Gold Rush transformed the people, culture, economy, and landscape of California in profound ways. California was rapidly converted from a rural, inaccessible region to a populous territory filled with booming towns and cities. The Gold Rush spurred advancements in transportation, which made transcontinental travel in the United States easier than ever before. The influx of immigrants to California made it a place of multiculturalism and ethnic diversity.

In the years that followed the Gold Rush, the period and the changes it brought about were somewhat romanticized by white Americans. This chapter of U.S. history was often told as the story of single, white, American men risking everything to go west and claim their fortunes. The American miners were portrayed as daring, hardworking, and admirable symbols of Manifest Destiny. However, white American miners represented only one version of the Gold Rush story.

For many white Americans, the Gold Rush represented the fulfillment of Manifest Destiny. The West was civilized according to the common ideals of their society at the time: the American Indians were almost entirely removed, the environment was dominated and its resources plundered, and the American way of life was spread from coast to coast.

To understand the Gold Rush more fully, however, it is necessary to acknowledge alternative perspectives on the era. The discovery of gold in California fueled the regions growth and economy. However, destructive mining techniques permanently damaged the environment. The Gold Rush drew enormous numbers of immigrants from around the world, making California one of the most culturally diverse places in the United States. However, competition between ethnic groups gave rise to oppression and violence.

Government-sanctioned discrimination against Mexican and Chinese miners and the exploitation of American Indians are clear evidence that the period was not a golden age for everyone involved. Discriminatory laws against immigrant miners and the taxes that were demanded of them illustrate how minority groups were denied social, political, and economic equality. For Californias Indians in particular, the Gold Rush was a tragedy. In the stampede to stake claims, Indians were systematically murdered and driven off their lands. Diseases wreaked havoc on their populations, and laws allowed white Americans to enslave them. The romanticized picture of the era has to be balanced with the viewpoints of the Indians and other groups who suffered because of the miners lust for gold.

The Gold Rush, and the growth it brought, thrust California into the heated national debate over slavery. At the start of the 1850s, the African American population in California numbered fewer than 1,000. Nevertheless, Californias position regarding slavery would weigh heavily in the tense relationship between the Northern and Southern states.

On September 9, 1850, California joined the United States as the 31st state. The process of granting statehood to California had been accelerated in light of the population explosion brought on by the Gold Rush. Another factor was the lawlessness that was growing there in the absence of an official state government. Although there was much momentum to bring California into the Union, there was also much controversy over its status in regard to slavery. At the time, the country had equal numbers of free states, where slavery was illegal, and slave states, where slavery was allowed. California petitioned Congress to enter the Union as a free state, which would have upset the balance of free and slave states. The dispute threatened to break up the Union.

After months of debate, Congress finally passed the Compromise of 1850. The South agreed to allow California to enter the Union as a free state and accepted the prohibition of the slave trade in the District of Columbia. In return, the North allowed New Mexico and Utah to organize as territories with no mention of slavery and gave the South a stronger fugitive slave law.

The Compromise of 1850 postponed but could not prevent war between the North and the South. After the American Civil War began in 1861, Californias gold proved to be an important resource for the Union. In that time of crisis, gold shipments from the Sierra Nevada funded the U.S. government and its war effort. This contribution to the Union victory was yet another legacy of the Gold Rush.

Benoit, Peter. The California Gold Rush. New York, NY: Childrens Press, 2013.Collins, Terry. Stake a Claim!: Nickolas Flux and the California Gold Rush. Mankato, MN: Capstone Press, 2014.Hall, Brianna. Strike It Rich! The Story of the California Gold Rush. Mankato, MN: Capstone Press, 2015.Maxwell-Long, Thomas. Daily Life During the California Gold Rush. Santa Barbara, CA: Greenwood Publishing Group, Inc., 2014.Micklos, John, Jr. A Primary Source History of the Gold Rush. Mankato, MN: Capstone Press, 2016.Onsgard, Bethany. Life During the California Gold Rush. Minneapolis, MN: Core Library, 2015.Raum, Elizabeth. The California Gold Rush: An Interactive History Adventure. Mankato, MN: Capstone Press, 2016.

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gold mining process | introduction | integrated report 2013 | anglogold ashanti

To conduct our business and produce gold, certain inputs such as ore-bearing resources, people and machinery are required. We invest in skills enhancement, technology development and application, and in prospecting for and developing our mineral resources and ore reserves, to ensure the economic viability and sustainability of our business.

Vertical shafts and decline ramps are sunk into the ground to transport people and equipment to and from deep-level ore bodies (many are more than 1,000m below surface) and to bring the ore mined to surface.

Gold ore is processed and smelted into dor (unrefined gold bars) at our operations and dispatched to various metal refineries, including our Queiroz refinery in Brazil and Rand Refinery in South Africa.

Overarching this business model is our sustainability strategy which has as its primary aim zero harm to people and the environment. We endeavour to ensure that the communities with which we engage and society are better off for our presence.

This is integral to mine planning and development, from the start of exploration to the end of mining activity. Closure planning, which takes into account community livelihoods and land rehabilitation, continues throughout the life of an operation.

gold mining process | who we are, what we do | sustainability report 2013 | anglogold ashanti

To conduct our business and produce gold, certain inputs such as ore-bearing resources, people and machinery are required. We invest in skills enhancement, technology development and application, and in prospecting for and developing our mineral resources and ore reserves, to ensure the economic viability and sustainability of our business.

Vertical shafts and decline ramps are sunk into the ground to transport people and equipment to and from deep-level ore bodies (many are more than 1,000m below surface) and to bring the ore mined to surface.

Gold ore is processed and smelted into dor (unrefined gold bars) at our operations and dispatched to various metal refineries, including our Queiroz refinery in Brazil and Rand Refinery in South Africa.

Overarching this business model is our sustainability strategy which has as its primary aim zero harm to people and the environment. We endeavour to ensure that the communities with which we engage and society are better off for our presence.

This is integral to mine planning and development, from the start of exploration to the end of mining activity. Closure planning, which takes into account community livelihoods and land rehabilitation, continues throughout the life of an operation.

bodie, california | hard rock mining

Bodies source of gold came from hard rock mining mining that requires breaking apart ore to extract gold thats intermingled with the rock. There are many steps to this kind of mining; here are some of the steps:

Basically, ore extraction means digging. Digging for A LOT of solid rock out of mountains. The way you get to that rock is by digging hallways to the rocks that have the most gold in them. Those hallways are called tunnels and mine shafts. Bodie has hundreds of miles of mine shafts. Some that connect to others, some that are short, others that are long and some that are so deep, they fill with water from the water table. Those shafts need to be pumped out so the miners can do their work.

When a suitable location is found for recovering gold-rich ore, a horizontal shaft is excavated, then a vertical shaft is drilled. The ore is then cut out of the mountain by using large drills and black powder or dynamite, then hoisting those chunks of rock to the surface with ore carts and other bucket rigs. As the ore is removed from the mountain, the tunnels and shafts can become unstable and can cave-in, so they must be shored up to keep the men safe and the tunnels open.

Shoring up a tunnel or shaft means building a frame structure that pushes against the rock walls to keep them from moving. Sometimes blasting with dynamite or earthquakes would cause a small cave-in that could create even more shaking that could bring other walls crashing down. When that happened, miners were killed or trapped without food or water. That was just one of the many dangers a Bodie miner took for getting paid $4 a day.

Once the ore was extracted from the mountain, it had to be crushed into a sand-like consistency. A stamp mill has several areas for handling different parts of the process. Stamp mills were usually built on a hillside, located lower than the mines so that the operators wouldnt have to haul the heavy rocks up to the top of the building thats where the process starts

At the top of a mill the big pieces of rock, sometimes the size of a soccer ball, were fed into a giant metal jaw that would crush them up until the smaller pieces fell between a metal grating called a grizzly; so-called because the spacing between the grating was about the width between the claws of a grizzly bear (about 2 inches). There were sometimes a succession of these crushers that would reduce the size of the ore to the needed gravel sized pieces. The gravel would be mixed with water and fed to the stamp battery.

The stamp battery would further crush the gravel into a sand or cinnamon consistency, and was then called slurry. That slurry would flow out of the stamp batteries through a fine mesh screen onto amalgamation tables. These tables were long and lined with large metal sheets made of zinc. A mill worker would use a brush to paint a chemical mixture of liquid mercury onto the zinc sheets before the sluice was opened on the stamp battery. Then, as the slurry flowed across the zinc and mercury, the gold would become stuck to the plates, while the tailings (the crushed ore that didnt have enough gold to stick to the plates) would be funneled to tanks, tailing ponds and other holding areas.

When enough gold stuck to the plates, the mill worker would scrape the amalgam of gold (and sometimes silver) and mercury into a big ball, put that into a bucket and give it to the supervisor. The worker would then re-paint the zinc plates with mercury to start the process over. Throughout the day, the stamp battery screens or the stamp die would get clogged and need to be cleaned, so one at a time, stamps would be locked from falling while debris was removed. This process of crushing the ore and collecting it by chemical means would get about 90% of the gold out of the rock.

Bodie had a dozen or more stamp mills, with the largest being the Standard Mill. Working in the mill was extremely loud. With 20 stamps pounding away 24 hours a day, 7 days a week (except when a battery was being cleaned) and steam engines roaring and pumping, jaw crushers shattering rocks, millwrights pounding on metal and many other noisy jobs, mill workers were likely to lose their hearing before losing an appendage. One trick workers used was to press bees wax with cotton into their ears. But, with an ever present danger from every direction working in such a large building with so many people, so much machinery and moving parts, it might have been more important to hear someone yell duck, than it was to keep your hearing.

That big amalgam ball of hardened mercury, gold and silver would eventually be delivered to the retort room, where the mixture was heated to melt the mercury to a gaseous form, where it would again liquefy and be recycled back to the amalgamation table in the mill for painting the tables. What remained (hopefully) was raw gold, ready for the smelting process.

Smelting is the process of further refining the gold and melting it into bullion for sale and transportation. Many gold mining towns were targeted by bad men and would hold up the stage coaches hauling the gold ingots. Some mine owners in Bodie were smart and poured such large ingots, that a single rider on horseback could not carry a single ingot alone. That helped in reducing stage hold-ups. Another trick by Bodie smelters was to leave gold and silver mixed in a single pour, requiring that it be separated and processed at a mint facility something robbers wouldnt be able to do on their own, and if they were looking for facilities to do that kind of work, would surely be discovered.

The battery itself was a large, odd looking iron box with an opening at the top for the stems and an opening on the front that held the fine mesh screens. On the back side of the battery are the cams. The cam shaft was turned by a large wheel, driven by a belt that was turned by a steam engine.A stamp battery is the name for a collection of stamps, usually is sets of 5. Each individual stamp is a heavy round cylinder between 250 and 1,000 pounds each, covered with a shoe on the bottom, which is easier to replace than the entire stamp.

The stamp is connected to a long stem that can also weigh several hundred pounds alone. Around one portion of the stem is a tappet; a large piece of metal that looks similar to a spool, about 12-16 inches tall. It acted as a lever, which would come in contact with the passing cam and cause the entire stamp and stem to be raised, until it reached the end of the cam and fell. The stem is connected to the stamp, which was covered by a shoe, which drops and strikes the die (or more hopefully, the ore thats on the die). The die was a flat, hard, round piece of metal, mostly matching the stamp shoe in diameter, where the slurry mix of water and ore would sit until the stamp dropped down and pulverized it.

mining techniques | geology for investors

Once a potentially economic mineral deposit has been found many different challenges face the company preparing to open a mine. One of the most important factors in determining whether a depositcan be economically extracted isthe type of mine that will be required.

Mining techniques can be divided into two broad categories: surface mining and subsurface mining (See Figure 1). Surface mining consists of stripping soil and vegetation away and possibly a limited amount of rock and then removing ore in large quantities. Conversely, subsurface mining involves sinking a mineshaft and digging tunnels to reach a deposit at depth. These two broad categories encompass almost all mining techniques and will be discussed in detail. As a general rule surface mining is more cost effective than subsurface mining.

The most common surface mining technique is open-pit mining (Figure 1), where a commodity is extracted via an open pit in the ground. This is an extremely cost effect way of removing a resource because large quantities can be removed with minimal effort. Other surface techniques include quarrying and strip mining.

Subsurface mining can be done in many ways with a vast number of terms to describe each type. However all types involve digging tunnels or shafts to access a resource that is too far below the surface or too spread out to use a surface technique and remain economical. The tunnels that are offshoots of the main shaft are termed drifts. The commodity is extracted in the subsurface and then brought to the surface for processing and waste rock disposal. Subsurface extraction requires vast amounts of planning because of the increased safety concerns of working underground. A collapse can be costly in more ways than one. Digging tunnels designed to intersect ore bodies isnt easy either. Complex geometry is used to determine the orientation of the ore body and drifts are constructed to maximize the amount of ore removed, a miss can lead to loss of revenue because large amounts of host rock are removed that do not contain any ore. The smaller volumes extracted only prove to increase extraction costs, which is why higher grades are needed to open a subsurface mine.

The first, and sometimes only, question to ask is how close is the deposit to the surface? Proximity to the surface plays a major role in determining which mining technique will be used. A small deposit near the surface may very well be economical if open-pit mining can be utilized. However, the same deposit a few hundreds of meters below the surface may prove to be uneconomical due to costs associated with subsurface extraction.

Another factor is the geometry of the deposit(s). For instance there may be multiple small deposits in an area where the construction of a single mineshaft allows for the extraction of more than one small deposit. The deposits may not be horizontally spaced but vertically spaced making the open-pit technique economical for only the upper deposit. Alternatively, the deposit might have a very complex shape, where open-pit mining would involve the removal off a tremendous amount of waste rock. This waste rock candilute the grade of the depositand render the deposit uneconomical. In this case subsurface mining could be used because of the precision of the technique but at a much higher cost.

Host rock can play a key role in mine economics. Subsurface mining techniques may not be possible in a very weak and unconsolidated host rock. Cost associated with stabilizing drifts and risk of collapse may over shadow any potential revenue.On the other hand, unconsolidated and soft host rock is ideal for open-pit style mining because it favors the bottom line (i.e. The less money it takes to extract the resource, the more profitable the operation.)

A high water table and a highly permeable host rock can alsocreate problems when it comes to the de-watering of a mine. In order to combat this, some companies have employed the use of frozen barriers, or ground freezingto literally freeze the groundwater around the mine using refrigeration units and underground piping. Again, this is only appropriate where the deposit is rich enough to warrant the expense.

Another more specialized mining technique is in-situ leaching (Figure 2), also referred to as in-situ recovery, or solution mining. This is perhaps the most economical of all techniques, but is only appropriate under certain conditions. In-situ leaching can be conducted without removing any rock at all, but the commodity of interest must be soluble. This technique is used to extract resources such as potash, uranium and copper by pumping leaching solution down holes drilled into the deposit and pumping the solution back to the subsurface. The solution travels through fractures that are either naturally occurring in the rock or produced artificially by hydraulic fracturing. The chemistry of the solution varies depending on what is being extracted. For instance, water is used for potash, acids or carbonates for uranium and acids for copper.

Heap leaching works on the same principle as in-situ leaching except that the rock is mined, crushed then piled before the solution is pumped through the rock. Itis perhaps most famously used for extracting gold from mines along the Carlin Trend in Nevada. With recent advances in technology heap leaching practices have even been applied to waste rock and tailings sites to extract any remaining ore. A company planning to perform leaching (whether in-situ or heap) does not require very high grade ores and facesfewer logistical problems than a company planning on using any other technique.

Leaching is not without risk and controversy though. The use of acids to extract uranium and copper, and cyanide to extract gold in heap operationshas environmental implications. Groundwater contamination and surface run-off are potential problemsthat need consideration during the mine design process.

environmental impacts of gold mining | brilliant earth

Dirty gold mining has ravaged landscapes, contaminated water supplies, and contributed to the destruction of vital ecosystems. Cyanide, mercury, and other toxic substances are regularly released into the environment due to dirty gold mining.

Modern industrial gold mining destroys landscapes and creates huge amountsof toxic waste. Due to the use of dirty practices such as open pit mining and cyanide heap leaching, mining companies generate about 20 tons of toxic waste for every 0.333-ounce gold ring. The waste, usually a gray liquid sludge, is laden with deadly cyanide and toxic heavy metals.

Many gold mines dump their toxic waste directly into natural water bodies. The Lihir gold mine in Papua New Guinea dumps over 5 million tons of toxic waste into the Pacific Ocean each year, destroying corals and other ocean life. Companies mining for gold and other metals in total dump at least 180 million tons of toxic waste into rivers, lakes, and oceans each yearmore than 1.5 times the waste that U.S. cities send to landfills on a yearly basis.

To limit the environmental damage, mines often construct dams and place the toxic waste inside. But these dams do not necessarily prevent contamination of the surrounding environment. Toxic waste can easily seep into soil and groundwater, or be released in catastrophic spills. At the worlds estimated 3,500 dams built to hold mine waste, one or two major spills occur every year.

Toxic waste spills have had devastating consequences in Romania, China, Ghana, Russia, Peru, South Africa, and other countries. In 2014, a dam collapsed at the Mount Polley gold and copper mine in British Columbia, sending about 25 million cubic meters of cyanide-laden waste into nearby rivers and lakesenough to fill about 9,800 Olympic-sized swimming pools. The spill poisoned water supplies, killed fish, and harmed local tourism.

Dirty gold mining often leads to a persistent problem known as acid mine drainage. The problem results when underground rock disturbed by mining is newly exposed to air and water. Iron sulfides (often called fools gold) in the rock can react with oxygen to form sulfuric acid. Acidic water draining from mine sites can be 20 to 300 times more concentrated than acid rain, and it is toxic to living organisms.

The dangers increase when this acidic water runs over rocks and strips out other embedded heavy metals. Rivers and streams can become contaminated with metals such as cadmium, arsenic, lead, and iron. Cadmium has been linked to liver disease, while arsenic can cause skin cancer and tumors. Lead poisoning can cause learning disabilities and impaired development in children. Iron is less dangerous, although it gives rivers and streams a slimy orange coating and the smell of rotten eggs.

Once acid mine drainage starts, it is difficult to stop. Acidic waters flowing from abandoned mines can raise acidity levels and destroy aquatic life for generations. Roman mining sites in England are still causing acid mine drainage more than 2000 years later.

The use of mercury in gold mining is causing a global health and environmental crisis. Mercury, a liquid metal, is used in artisanal and small-scale gold mining to extract gold from rock and sediment. Unfortunately, mercury is a toxic substance that wreaks havoc on miners health, not to mention the health of the planet.

For every gram of gold produced, artisanal gold miners release about two grams of mercury into the environment. Together, the worlds 10 to 15 million artisanal gold miners release about 1000 tons of mercury into the environment each year, or 35 percent of man-made mercury pollution. Artisanal gold mining is actually among the leading causes of global mercury pollution, ahead of coal-fired power plants.

When mercury enters the atmosphere or reaches rivers, lakes, and oceans, it can travel across great distances. About 70 percent of the mercury deposited in the United States is from international sources. Still more mercury reaches the United States through imported fish. Once it reaches a resting place, mercury is not easily removed. Sediments on the floor of San Francisco Bay remain contaminatedwith mercury left by the California gold rush of the 19th century.

Mercury is extremely harmful to human health. The amount of vapor released by mining activities has been proven to damage the kidneys, liver, brain, heart, lungs, colon, and immune system. Chronic exposure to mercury may result in fatigue, weight loss, tremors, and shifts in behavior. In children and developing fetuses, mercury can impair neurological development.

A gold mining boom is accelerating the destruction of the Amazon rainforest, a biologically diverse ecosystem that acts as a check on global warming. Artisanal, or small-scale, gold miners are tearing down the forest to access the rich gold deposits beneath. One study found that deforestation rates in the Madre de Dios region of the Peruvian Amazon have increased six-fold due to gold mining.

Gold mining is also responsible for releasing large amounts of mercury into the Amazons air and water. The mercury is poisoning plants, animals, fish, and people. In one city in the Peruvian Amazon, unsafe mercury levels were recorded in 80 percent of local residents. The gold mining boom does not bode well for the Amazon or the people, both locally and globally, who depend on it.