hard rock mining for gold

geology of hard rock gold deposits

geology of hard rock gold deposits

Man knew more about gold itself and lusted for it much before he understood the geology of hard rock gold or its deposits. Man had to learn about hard rock extraction methods and how to locate those gold deposits just to satisfy the thirst for that yellow metal. Gold has been the most highly esteemed and sought after precious commodity since the times of antiquity It has spurred on numerous expeditions and conquests dating back to Alexander the Great, to Caesar of Rome and to Cortezs conquests of Central and South America. The greed for gold throughout history has led to the enslavement of nations, conflict between nations and appalling treatment of men. Golds beauty, unique density, relatively low melting point and ability to form coinage made it a natural trading medium.

Gold as a currency dates back to ancient Greece. Various forms of gold-backed currencies developed throughout history. The last gold standard developed was the Bretton Woods Agreement after WWII. Under this agreement, the US dollar alone was pegged to gold and all other currencies were related to the USD. This was eliminated by President Nixon (US) in 1971, thus ending a very long history of the reliance of the gold standard for trade. Up until recently, gold was considered as a safe haven for investment in times of economic and geopolitical turmoil.

Gold is soft, yellow, has a relatively high melting point of 1,064oC and is the most ductile and malleable of all metals. Its atomic number is 79 and is a member of the group 1B metals which is a subgroup of the larger transitional group of metals. The other metals of the 1B group are silver copper and roentgenium. With the exception of roentgenium, the other metals in this group were known as coinage metals. Again with the exception of roentgenium, the 1B group have a similar electron configuration with one electron in their outer shell. Like all other transitional metals, including silver and copper, golds valence electrons the electrons that combine with other elements are present in more than one shell. All 1B metals are relatively inert and are corrosion resistant gold is very dense and has a specific gravity of 19.3 and an atomic weight of 197. Golds high electrical and thermal conductivity, are only superseded by that of by two other 1B elements -silver and copper.

It exists in nature in its native form, and alloyed, most often with silver and to a lesser extent with copper. It rarely occurs in nature in compounds, but when it does it occurs in tellurides such as AuTe2 and selenides (AUSe). Many pyrite and pyrrhotite minerals contain gold, which is often recovered when extracting copper from lode vein deposits. The purity of gold is stated in terms of fineness and carats (ct). Fineness is defined as the parts per 1000. For example gold with a fineness of 800 means it is 80% pure gold. Alternatively, gold that is 100% pure is 24ct.

Subduction Zones: These zones occur where the heavier oceanic plate pushes under the lighter continental plate and slides beneath it. Volcanoes are often formed in these zones thus explaining the Ring of Fire around the Pacific Ocean subduction zone. Water can percolate down towards the magma or connate water (water coming from the magma) can be enriched in metals and then deposited in the surrounding rock.

Up until 2006, South Africa was the largest producing nation of gold. However, since then South Africas gold production has been eclipsed by China, Australia, Russia, United States, Canada and Peru. Other major gold producing countries include, Uzbekistan, Mexico, Ghana, Papua New Guinea and Chile. The largest gold deposit that is currently being mined is the Grasberg Mine in Papua, Indonesia. This mine which is owned by gold miner Freeport McMoRan has known reserves of 100 million ounces. The largest undeveloped gold deposit is the Pebble deposit located near the foot of the Aleutian Peninsula in Alaska. It has reserves of 107 million oz. The development of this deposit is currently on hold due to environmental concerns, specifically due to being the home of the worlds largest sockeye salmon runs.

These, then are some of the attributes of gold and the characteristics of some of its occurrences. Hopefully, it can be seen that gold has played a key role in the discovery of the New World and other historical events and continues to play a role in the economic vicissitudes of the world economy.

prospecting for gold ore - techniques to find rocks with gold

prospecting for gold ore - techniques to find rocks with gold

Most prospectors spend their time looking for placer gold. These are the solid pieces of gold that have eroded from a vein and have formed in a concentration. Most prospectors look for placer gold in creeks and rivers (although this isnt the only place they are found).

Theres a good reason for this. Placer gold is easier to locate than gold that is contained in a hard rock deposit. However, there are some miners that specialize in located gold within hard rock. While it is harder to find, the payoffs can be huge.

If an area has a lot of soil, then these rock changes arent always easy to see. In this case, vegetation will be a good indicator. Different plants will generally grow in different types of host rock.

Soil is comprised of small particles of rock and mineral, so a chance in soil color is a good indicator for gold, just like a change in rock type. Often, changing soils that are yellowish or reddish in color will indicate a high iron content, which is a very good sign in gold country.

In places where different rock types come together, the contact point will sometimes have material that has a very loose structure. This rock will crumble easily. If quartz is present, it will often be very rotten and crumbly.

Iron staining is another excellent indicator that hard rock gold may be present. As mentioned already, reddish soils are a good indicator of this. If you are finding quartz pieces that have dark red or black attached to it, this is also a good sign that there is high iron content, and you may want to crush and sample some of the nearby rocks.

If you are exploring new spots with little evidence of mining or prospecting in the past, then it is a good idea to first look at nearby gold areas and compare geology. Sometimes you can identify similar geological indicators that can help you find gold.

First, I always recommend that you carry a gold pan and sample the gravels in the area. Even in a desert, you can dig down into a dry wash and pack in some water to use while panning. If you are able to locate even some very fine gold, this will tell you that you are in a good area.

Second, you can collect promising rock samples and crush them up to release any potential gold. We detail this process in this article. It is a relatively simple method, and will give you an idea of what types of samples are worth collecting and processing.

Third, and perhaps the most popular method used by small-scale gold prospectors is to use a gold detector. By scanning mining tailings and ore samples with a metal detector, you can locate samples that contain visible veins of gold.

how to recognize hard rock gold ores | icmjs prospecting and mining journal

how to recognize hard rock gold ores | icmjs prospecting and mining journal

I regularly get inquiries along the line of: Hey, I found this rock, and I think it might be gold ore. How can I tell? Prospectors are always on the lookout for gold-bearing rocks that may be the source of any nearby placer gold.

Data mining involves processing huge amounts of digital information to find hidden patterns and financial relationships. To executives, the findings are like gold, but on the weekends, I prefer seeing the real thing in the bottom of my pan.

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portable hard rock gold mining equipment | crushing plants | hard rock mining equipment | dove

portable hard rock gold mining equipment | crushing plants | hard rock mining equipment | dove

DOVE is a major manufacturer of Hard rock Gold mining equipment, crushing plants, and portable Hard rock mining equipmentfor recovery of Gold, Platinum, Silver, Manganese, Zinc, Nickel, Tin, Lead, Zircon and other metals contained in hard rock deposits (Primary deposits) and quartz rocks.

SPEEDMINER Portable Hard Rock Plants are designed and engineered with expertise, for complete size reduction of the rocks, and efficient processing and recovery of the liberated metals and minerals production contained in a hard rock deposit.

DOVE Portable Hard Rock Plants are engineered for complete communition of the material through multiple stages of crushing and grinding cycles, and efficient processing and recover of the liberated metals and minerals through an effective and advanced separation and concentration circuit.

DOVE Portable Hard Rock Plants are designed for the highest recovery in the industry of the liberated particles of gold, platinum, light metals, base metals, ferrous metals, sand, gravel, and coal, down to micron.

DOVE Portable Hard Rock Plants and recovery methods vary depending on several factors, including the size of the rock, the rocks condition, the hardness of the materials, minerals composition in the ore, specific gravity and other characteristics and specification of the elements to insure the efficient recovery of 100% of the minerals Production, with no loss.

Hard rock mining is the process of extracting metals and minerals encased in rocks (primary deposit). Hard rock ore can contain metals, minerals such as gold, platinum, silver, iron, copper, manganese, zinc, nickel, tin and lead, zircon, etc.

The feed hopper described as a large bin above the crusher into which the ore is dumped prior to being discharge into the primary crusher. In Certain cases the feed hopper will be configured with static or vibrating grizzly.

A feeder at the bottom of the hopper helps transfer the ore to the crusher evenly and continuously. It can simultaneously screen materials roughly and increase the practical handling capacity of the whole production line.

The first step of rock reduction process from large particles into small pieces is running them through a DOVE primary Jaw Crusher, a crusher that takes the rocks and crushes it smaller. DOVE Jaw Crushers have two opposing ribbed panels, or jaws, with one jaw moving forward and back to crush raw material against the fixed jaw. Only material that has been crushed to a size equivalent to the opening at the bottom of the jaws falls through the bottom of the machine. This sizing is determined by the closed side setting of the jaw panels. Jaw Crushers exert more crushing power and are the best choice for very hard rock like granite and abrasive rock.

A secondary crusher is one that takes crushed material out of a primary crusher and reduces the product further. DOVE Jaw crusher or DOVE cone crusher depending on the hardness and rock condition can perform as the secondary crusher stage. After materials are crushed into the desired output size, it will go further on the next stage, which is grinding part.

The DOVE ball mill is the key grinding equipment after material is crushed. It is used to grind and blend bulk material into powder form using different sized balls. The working principle is simple, impact and attrition size reduction take place as the ball drops from near the top of the rotating hollow cylindrical shell. The output materials will be feed to the processing and recovery machines.

Depending on project requirement DOVE incorporate advanced DOVE Vibrating Screen,Concentrators,Magnetic Separators,Shaking Tables,Rotary Dryers,and Flotation Processfor recovery of minerals with no loss.

DOVE laboratory will assay your ore samples rapidly and analyze your raw materials and recommend the most efficient processing plant according to the ore specifications, minerals composition, and ore assay results, and your project size and the geologic and topographic conditions of your mine.

mining : what is gold mining? how is gold mined? | geology page

mining : what is gold mining? how is gold mined? | geology page

Placer mining is the technique of extracting gold accumulated in a placer deposit. Placer deposits are composed of relatively loose material that makes tunneling difficult, so most extraction methods involve water or dredging.

Gold panning is mainly a manual gold separation technique from other materials. Large, shallow pans are filled with gold-containing sand and gravel. The pan is submerged and shaken in water, sorting the gravel gold and other material. It quickly settles down to the bottom of the pan as gold is much denser than rock.

Usually the panning material is removed from stream beds, often at the inside turn in the stream, or from the streams bedrock shelf, where gold density allows it to concentrate, a type called placer deposits.

It has long been a very common practice for prospecting and small-scale mining to use a sluice box to extract gold from placer deposits. Essentially, a sluice box is a man-made channel with riffles at the bottom. In order to allow gold to drop out of suspension, the riffles are designed to create dead zones.

In order to channel water flow, the box is placed in the stream. At the top of the box is placed gold-bearing material. The material is transported by the current through the volt where behind the riffles settles gold and other dense material. Less dense material flows like tailings out of the box.

While this method has been largely replaced by modern methods, small-scale miners use suction dredges to make some dredging. Small machines that float on the water are typically operated by one or two people. A suction dredge consists of a pontoon-supported sluice box attached to a suction hose controlled by an underwater miner.

State dredging permits specify a seasonal time period and area closures in many of the U.S. gold dredging areas to avoid conflicts between dredgers and fish populations spawning time. Some states, like Montana, need a comprehensive licensing procedure, including U.S. permits. Engineering corps, Montana Environmental Quality Department and local county water quality boards.

Also called a cradle, it uses riffles to trap gold similarly to the sluice box in a high-walled box. A rocker box uses less water than a sluice box and is suitable for areas with limited water. A rocking motion provides the movement of water needed to separate gold in placer material from gravity.

Hard rock gold mining extracts gold in rock instead of fragments in loose sediment, producing most of the gold in the world. Open-pit mining is sometimes used, for example in central Alaskas Fort Knox Mine. Barrick Gold Corporation has one of the largest open-pit gold mines in North America located on its Goldstrike mine property in north eastern Nevada.

Other gold mines use underground mining where tunnels or shafts extract the ore. South Africa has up to 3,900 meters (12,800 ft) underground deepest hard rock gold mine in the world. The heat is unbearable for humans at such depths, and air conditioning is necessary for workers safety.

Gold is also produced through mining, where it is not the main product. Large copper mines, such as the Bingham Canyon mine in Utah, often recover together with copper considerable amounts of gold and other metals. Some sand and gravel pits, such as those around Denver, Colorado, in their washing operations may recover small amounts of gold.

Cyanide extraction of gold may be used in areas where fine gold-bearing rocks are found. Sodium cyanide solution is mixed with finely ground rock that has been proven to contain gold or silver and is then separated as a gold cyanide or silver cyanide solution from ground rock. To precipitate residual zinc and silver and gold metals, zinc is added. Zinc is removed with sulfuric acid, leaving a silver or gold sludge that is generally smelted into an ingot and then shipped to a metal refinery for final processing into pure metals of 99,9999 percent.

In recent years, the technique of alkaline cyanide dissolution has been highly developed. It is especially suitable for processing low-grade gold and silver ore (e.g. less than 5 ppm gold), but its use is not limited to such ores. This extraction method involves many environmental hazards, largely due to the high acute toxicity of the involved cyanide compounds.

Historically, mercury has been widely used in placer gold mining to form mercury-gold amalgam with smaller gold particles, thereby increasing the rate of gold recovery. In the 1960s, large-scale mercury use stopped. In artisanal and small-scale gold mining (ASGM), however, mercury is still used, often clandestine, gold prospecting. It is estimated that 45,000 metric tons of mercury used in California for placer mining have not been recovered.

hard rock mining equipment | crushing plants | dove

hard rock mining equipment | crushing plants | dove

DOVE is the worlds major manufacturer of an unmatched range of Semi-stationary Hard Rock mining equipment and crushing plants, for gold, platinum metals, base metals, and ferrous metals, producing high quality Ball Mills, Jaw Crushers, Cone Crushers, Magnetic Separators, Shaking Tables, Gold Concentrators, Rotary Dryers and Flotation Process.

GOLDROCKMINERPlantsare designed exclusively by DOVE and are combination of hard rock crushing and processing plant. Each plant is tailor made and designed based on mineral composition of the ore and specification of each mining site. DOVE mineral laboratory provides detailed mineral analysis on your ore samples.

DOVE is the leader and powerhouse in the mining equipment manufacturing industry and over the last 50 years has produced the largest range of Semi-stationary Hard Rock Plants (GOLDROCKMINERHard Rock Processing Plants)for small, medium and large-scale hard rock mining operations, with the capacity to handle material ranging from 2-600 Tons/Hour solids.

Semi-stationary hard rock processing plants, also known as Semi-stationary Crushing Plants, Crushing and Grinding Plants are processing plants designed for the efficient processing of the valuable minerals contained in a Hard Rock (Primary) deposit, for the recovery of Gold, Platinum metals, Base metals, Ferrous metals and Light metals.

DOVE Semi-stationary Hard Rock Plants are the most advanced processing plants in the mining industry, with unique features and designs, and the highest recovery rate. DOVE Semi-stationary hard rock processing plants are economical, with the highest and fastest return on investment.

DOVE Portable Hard Rock Plants and recovery methods vary depending on several factors, including the size of the rock, the rocks condition, the hardness of the materials, minerals composition in the ore, specific gravity and other characteristics and specification of the elements to insure the efficient recovery of 100% of the minerals Production, with no loss.

Hard rock mining is the process of extracting metals and minerals encased in rocks (primary deposit). Hard rock ore can contain metals, minerals such as gold, platinum, silver, iron, copper, manganese, zinc, nickel, tin and lead, zircon, etc.

DOVE Semi-stationary Hard Rock Plants unique designs are embedded in every single one of their components to insure efficient operations and 100% recovery of the Gold, Tin, Iron, Tantalite, Manganese and other metals and minerals production, with no loss.

Ore feeding, Crushing (Coarse and Fine), Grinding (or milling), Sizing (screening and classification) and Concentration (separation and recovery) are the three most important steps that are involved in ore processing by Hard Rock Plants. Overlooking any short of these steps will result in lack or reduction of recovery, as well as the loss of the valuable minerals.

In a hard rock plant, the concentration (recovery and separation) stage is achieved by a method scientifically called Gravity Separation. The separation occurs when the metals and mineral are subjected to a variety of forces in a medium (e.g. water, air, other heavy medium) to trigger a response, which is usually enhanced resistance or accelerated settling time of said metals and minerals, depending on their specific gravity.

consists of a large hopper designed to feed the ore to the rest of the hard rock plant plant. The hopper, in a hard rock, usually allows for dry feed of the rocks to the plant. It is designed for a direct feed by earth moving equipment. The size of the feed will depend on the plants capacity (Tons Per Hour).

DOVE Ore Feed Hoppers are supplied in wide range of capacities, and are designed and engineered as parts that fit to make the hopper. This feature allows the hopper to easily be shipped in standard containers and rapidly be assembled and installed once on site.

it is a device set between the hopper and belt conveyor, or any equipment fed by the hopper. This device will ensure that the material coming from the feed hopper is efficiently and smoothly fed to the next equipment. The vibrating feeder prevents the hopper from being clogged by the accumulation of rocks and allows the next equipment to be safely fed without having to endure the stress of rocks falling directly on it, which could accelerate wear and tear, and result in damage.

DOVE Feeders are a wide variety of vibrating feeders that can be configured with grizzly bars to screen the oversized rocks contained in the ore to insure efficient processing and recovery of the minerals in the next stages, and to protect the next equipment from the potential damages that could occur from an impact with said rock. The screening sizes vary depending on the ore characteristics and project specifications.

works as the means by which the ore, rocks or dry sand in a solid form, is efficiently transported throughout the processing plant. DOVE Belt Conveyors are in various dimensions to cater to the ore logistics capacity requirements of the processing plant as well as the mining site characteristics.

DOVE Conveyors belts are built with high quality thick rubber that can withstand the weight of material with minimum. DOVE Belt Conveyors are supplied with high resistance support stand, with reinforced structure.

is a device designed to reduce the size of a rock. It breaks the particles by applying a compressive force to them. The two jaws applying a mechanical pressure to the particles achieve this. A jaw crusher consists of a set of vertical jaws, one of which is stationary, while the other jaw called swings back and forth, relatively to the stationary jaw. The crusher acts like a nutcracker on the particles.

DOVE Jaw Crushers come in various designs and capacities, aimed to handle all stages of crushing, from primary to tertiary, of various types of rocks such as granite, quartz, gravel, and many more. DOVE Jaw Crushers are configured with optimum cavities. Their height is designed in relation to the feed opening to ensure minimum clogging of the material, resulting in higher crushing efficiency, all in a compact design.

is a device designed to reduce rocks into smaller rocks or dust. It operates using a mantle that rotates within a bowl. The material is compressed between an eccentrically rotating piece of steel, called the mantle, and a stationary piece of steel, called the bowl. The material works its way down along the crushing chamber, as it gets smaller, until the crushed material is discharged at the bottom of the machine.

DOVE Cone Crushers are designed to handle various capacities and material hardness, in secondary and tertiary crushing operations, for limestone, granite, basalt, quartzite, river gravel, and many more. DOVE Cone Crushers are designed for rapid Field Adjustment and Continuous Lubrication. They are configured with Hydraulic Cleaning units and Hydraulic Lifting Arm. The latter allows for the operator to remove the top shell and empty the crushing of all

is a device that breaks up material by either striking it with a bowl bar that moves rapidly, or by throwing the material into a stationary anvil where it will break upon impact. They are utilized in aggregates operation, mining operations and recycling operations.

DOVE Impact Crushers are designed and supplied in various models, and are used for hard material crushing operation. The material can be bauxite, coal, coke, magnetite, mica, salt, slate, and many more. DOVE Impact Crushers rolls are made of various alloys, from manganese or Tacm, and can be easily adjusted by increasing or decreasing the shims.

are devices, used in mineral dressing processes and other operations (paints, pyrotechnics, ceramics, and selective laser sintering, for the grinding of materials. This device is used in DOVE Semi-Stationary Hard Rock plants to grind the ore until the liberation size of valuable minerals is reached. The size reduction is achieved by impact and attrition. When the shell rotates, the balls are dragged to almost the top of the shell, and from there, they fall unto the material, which breaks due to impact, DOVE Ball Mills are deigned for either wet or dry grinding of materials, in various models, to cater to the liberation size of the minerals and the hardness of the ore. DOVE Ball Mills can be used in various industries such as mining, construction and aggregate, chemical, pyrotechnics, ceramics, waste processing, food processing, and many more.

are used in DOVE Hard Rock Processing Plants to classify the different ranges of particles contained in the ore and ensure that the right sizes of materials goes the right processing stages, insuring a high efficiency delivered during said processing stages. The screen sizes depend on the ore characteristics, project specifications and on the plant configuration.

DOVE Vibrating Screens can be configured with multiple decks to efficiently and simultaneously separate various sizes of material from one another. DOVE offers a wide range of Vibrating Screens, with different mesh sizes, number of decks and various capacities. The parameters of the DOVE Vibrating Screens are tailor-made to cater to each mining projects, individually.

are a type of gravity concentration apparatus, predominantly used in the gold mining industry. It is used for the recovery of fine particles of free gold, meaning gold that does not require gold cyanidation for recovery.

Gold centrifugal concentrators have been developed over the past century and allow for mining operations to trap a higher percentage of the fine gold and other precious metals in black sands that used to be lost into the tailing ponds. Centrifugal gold concentrators operate using G-forces which allow for separation of the heavier particulate including fine gold and other metals.

DOVE Centrifugal Concentrators are configured for automatic and continuous recovery, using only recycled water only to process and to recover 100%, down to 40 microns (0.004 mm), of all fine the gold, silver, platinum group metals, and other precious metals contained in the processed ore.

DOVE Gold Concentrators are integrated with locking mechanism, a complete hydraulic system, as well as feed and moisture adjustment mechanism, to eliminate freezing conditions and regulate the flow of the material.

can be considered a thin film, shear flow process equipment, that separates particle of the material being fed to it based on the differences in their specific gravity, density, size and shape. Mineral rich particles, from light to heavy and fine to coarse will be effectively sorted by net effective weight on the Concentrating Table.

Concentrating Tables have been used are recognized as the most effective and selective machines for wet gravity separation, and have been proving their efficiency in producing a high-grade concentrate, while handling a wide range of specific gravities, for many years. They are mostly used for the final cleaning stages to produce final concentrates.

DOVE Concentrating Tables are designed with rectangular or diagonal wooden or aluminum decks, covered with one-piece of ultra-smooth rubber riffle surface. The riffle pattern can be sand riffling, slime riffling, or individual riffle patterns, depending on the individual separation requirements. DOVE Concentrating Tables are extremely selective wet gravity separation devices that offer exceptional efficiency in material separation that other existing tables in the industry, with rough-surface covering, cannot achieve.

DOVE Concentrating Tables are designed with rectangular or diagonal wooden or aluminum decks, covered with one-piece of ultra-smooth rubber riffle surface. The riffle pattern can be sand riffling, slime riffling, or individual riffle patterns, depending on the individual separation requirements.

DOVE Concentrating Tables are extremely selective wet gravity separation devices that offer exceptional efficiency in material separation that other existing tables in the industry, with rough-surface covering, cannot achieve.

DOVE laboratory will assay your ore samples rapidly and analyze your raw materials and recommend the most efficient processing plant according to the ore specifications, minerals composition, and ore assay results, and your project size and the geologic and topographic conditions of your mine.

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