Operating A Mine And Ore Processing Newmont Mine

       The first part of the mining process involves finding the minerals and collected core samples from various depths. The core samples were assayed (tested) to determine the mineral content. Material mined from the open pit or from underground is either ore (containing gold and silver) or waste rock (little or no gold and silver). To find out which is which, samples of rock are collected. The samples are sent to an assay laboratory where the rock is tested for its gold content. Geologists use the results to mark out the sampled areas into zones of ore and waste rock so they can be mined separately. Research of a different sort followed; investigation and monitoring was carried out to assess potential environmental and social effects of a mining operation Newmont has both operational and closed tailings impoundments in a variety of climatic and topographic settings. 

      Newmont Mining Corporation, based in Greenwood Village, Colorado, USA, is one of the world's largest producers of gold, with active mines in Nevada, Indonesia, Australia, New Zealand, Ghana and Peru. Holdings include Santa Fe Gold, Battle Mountain Gold, Normandy Mining, Franco-Nevada Corp and Fronteer Gold. Newmont conducts extensive siting, engineering, environmental and social studies to support the specific selection and design of each facility. In 2013, Newmont managed the safe handling and disposal of 173 million tonnes of tailings that consisted of 142.1 million tonnes placed within surface facilities or used for backfilling of pits. An additional 31.9 million tonnes of tailings were deposited offshore in a deep sea canyon

There are two types of mineral mining designs for operating a mine from newmont mine :

•  Surface (open pit) and 
• Underground. Surface

1. Surface (open pit)  

       

    Surface mines are generally preferred if the ore body is relatively shallow and uniform, and are made by digging into the Earth’s surface one layer at a time. The final mine is cone-shaped.First, drilling holes in the ground and fill them with explosive. After the rock has been broken up by blasting, it is loaded into giant haul trucks using large shovels and front-end loaders. Each truck used in the open pit can carry about 90 - 100 tonnes of rock. The rock is hauled to the primary crushers. Rock containing gold, copper and other valuable minerals is hauled away for processing and waste rock is taken to a separate area for storage. Areas of waste rock are later rehabilitated.

      As dig farther down, it is necessary to dewater the mine to ensure that the water level remains below the pit floor. Each day, pump thousands of gallons of water from the pit. Some of this water is used on site to wash vehicles and to spray the haul roads to dampen dust. Excess water is piped over to the water treatment plant near the processing plant to be treated before it is discharged to nearby rivers or lakes.

 2. Underground 

      

       Underground mines are used to extract minerals or metals from deep in the Earth. When building an underground mine, dig a tunnel to get to the minerals, this can be a straight vertical tunnel called a shaft or a tunnel that spirals gradually downwards, called a decline. To access the ore from the shaft or decline, dig other tunnels. also mine out tunnels to provide proper ventilation and emergency exits. mine the tunnels and the ore bodies by drilling and blasting. The broken-up ore is then transported to the surface for processing. Waste rock may be transported to the surface or left in the mine and used to fill empty space.The type of ground support needed depends on how stable the ground is and how long the tunnel is going to be used for. These factors are identified in advance so that engineers can design the mine for maximum safety and value.

      

Ground support may be provided by rock bolts or split sets, which are forced into drilled holes to exert pressure on the surrounding rock, which keeps it intact. Chemicals or grouts are sometimes added with rock bolts to give them greater strength and install wire mesh to keep smaller rocks from falling down.High-pressure spraying of Shotcrete (a mortar/concrete mix) onto the tunnels’ walls and backs provides more support. As complete mining in each stope, backfill it with a cement mixture as well.Underground mines pose a greater safety risk and limit the size of equipment that can be used; however, they cause less environmental disturbance.

Ore Processing Newmont Mine

Basic Ore Processing 

Haul trucks transport the ore from open pits or underground operations to processing operations. Some ores may be stockpiled for later processing. Rock that is not economical to mine is stored in waste rock storage areas. The grade and type of ore determine the processing method used. Additionally, the geochemical makeup of the ore, including its hardness, sulfur content, carbon content and other minerals found within, impact the cost and methods used to extract gold.

Processing methods 
In mineral processing, newmont depending on the mineral ore, they process it using the following methods:

Removing the gold-bearing rock from the ground is just the first step. To isolate pure gold, mining companies use a complex extraction process. The first step in this process is breaking down large chunks of rock into smaller pieces. At a mill, large machines known as crushers reduce the ore to pieces no larger than road gravel.

The gravel-like material then enters rotating drums filled with steel balls. In these drums, feed ore into a series of crushers and grinding mills to reduce the size of the ore particles and expose the mineral.

Next, mill operators thicken the slurry with water to form pulp and run the pulp through a series of leaching tanks. Leaching dissolves the gold out of the ore using a chemical solvent. The most common solvent is cyanide, which must be combined with oxygen in a process known as carbon-in-pulp. As the cyanide and oxygen react chemically, gold in the pulp dissolves. When workers introduce small carbon grains to the tank, the gold adheres to the carbon. Filtering the pulp through screens separates the gold-bearing carbon.

The carbon moves to a stripping vessel where a hot caustic solution separates the gold from the carbon. Another set of screens filters out the carbon grains, which can be recycled for future processing. Finally, the gold-bearing solution is ready for electrowinning, which recovers the gold from the leaching chemicals. In electrowinning, operators pour the gold-bearing solution into a special container known as a cell. Positive and negative terminals in the cell deliver a strong electric current to the solution. This causes gold to collect on the negative terminals.

Alternative Ore Processing

Newmont mine use alternative gold recovery methods in some processing plants to accommodate different ore characteristics or other requirements. For example, ore that has a high level of sulfide minerals or carbon (or both) is called refractory ore. Refractory ore resists normal processing methods as the high sulfide minerals trap gold particles, making it difficult for the cyanide to reach the gold and leach it.

Heating

To leach gold from refractory ore, it must be subjected to high temperature, high pressure and/or oxygen. Newmont treats refractory ore in two ways: by using an autoclave or a roaster.

An autoclave is used before leaching occurs. First, the slurry is heated and fed into an autoclave, where high-pressure steam, water and oxygen are applied to oxidize the sulfide material by a chemical reaction. The slurry is then cooled and sent back into the process to be leached.

An alternative to an autoclave is a roaster, a very high temperature oven that is often used instead of an autoclave if the ore to process contains a large amount of organic carbon. Roasting uses heat and air to burn the organic carbon into fuel and to burn the sulfur off ore, which heat to 932 to 1,202 degrees F. 

Heap leaching

In heap leaching, newmont mine dump crushed ore into piles called heaps, to which apply a weak cyanide solution, using drip feeders. The gold dissolves into the cyanide solution. The entire heap leach area is lined with heavy duty liners to ensure no solution leaks into the environment. Next, collect the gold-cyanide solution in ditches and ponds, and then transport it to a recovery plant.

 
Flotation 

Flotation is a method of separating minerals depending on their ability to attach to air bubbles. Flotation can be used for a number of materials by adjusting the chemicals. At Newmont, it is used for copper recovery and, in a very limited number of cases, for gold processing. 

introduce air bubbles to the slurry while it is in small tanks, called flotation cells. With add some chemicals to the slurry to assist the process. The desired minerals stick to the bubbles and rise to the top, resulting in froth. The froth overflows from the tank, and is removed and sent to the next step in processing.

Gravity circuit

A gravity circuit recovers coarse gold before it is leached. Gravity circuits use the same principles as gold panning: coarse gold is heavier than other material and will settle to the bottom so that it can be removed (gold is 19.3 times heavier than an equal volume of water).