Underground hard-rock mining

Underground hard-rock mining refers to various underground

1. Planning and Preparation

Planning and preparation are crucial initial steps in the core drilling process. This stage involves conducting a comprehensive assessment of the site and establishing the necessary groundwork for a successful drilling operation. Here's a breakdown of the key aspects involved:

A)   Site Assessment

Before drilling can begin, a thorough site assessment is conducted to determine the optimal drilling locations. This assessment involves evaluating factors such as the type of material to be drilled, subsurface conditions, potential obstacles (e.g., underground utilities), and structural integrity. This information helps identify suitable areas for drilling that minimize risks and ensure accurate results.

B)   Permits and Permissions

Depending on the location and regulations governing the site, it may be necessary to obtain permits and permissions before commencing drilling activities. This involves understanding and complying with local regulations, environmental guidelines, and any specific requirements for drilling in certain areas.

C)   Safety Considerations

Safety is paramount in any drilling operation. During the planning stage, safety protocols and measures are established to protect personnel, equipment, and the surrounding environment. This includes assessing potential hazards, developing emergency response plans, and ensuring the availability of necessary safety equipment.

D)   Equipment and Resources

Planning also involves determining the equipment and resources required for the core drilling operation. This includes selecting the appropriate drilling rig, drill bits, and accessories based on factors such as the material being drilled, desired core diameter, and drilling depth. Adequate resources such as water supply, drilling mud, and coolants are also considered to ensure smooth drilling operations.

E)   Timeline and Logistics

Establishing a timeline for the core drilling project is essential for effective project management. This includes setting deadlines, scheduling equipment and personnel, and coordinating with other stakeholders involved in the project. Logistics, such as transportation of equipment and materials to the site, are also planned during this stage.

1. By carefully planning and preparing for core drilling, professionals can mitigate risks, ensure compliance with regulations, and streamline the drilling process. Thorough site assessments, obtaining necessary permits, and considering safety measures and equipment requirements contribute to a successful and efficient core drilling operation.
2. Declines can be a spiral tunnel which circles either the flank of the deposit or circles around the deposit. The decline begins with a
   open cut
   mine
3. Shafts are vertical excavations sunk adjacent to an ore body. Shafts are sunk for ore bodies where haulage to surface via truck is not economical. Shaft haulage is more economical than truck haulage at depth, and a mine may have both a decline and a ramp
4. Adits are horizontal excavations into the side of a hill or mountain. Adits are used for horizontal or near-horizontal ore bodies where there is no need for a ramp or shaft.

Declines are often started from the side of the high wall of an

Ore access

Levels are excavated horizontally off the decline or shaft to access the ore body.

Development mining vs. production mining

There are two principal phases of underground mining: development mining and production mining.

Development mining is composed of excavation almost entirely in (non-valuable) waste rock in order to gain access to the orebody. There are six steps in development mining: remove previously blasted material (muck out round), scaling (removing any unstable slabs of rock hanging from the roof and sidewalls to protect workers and equipment from damage), installing support or/and reinforcement using shotcrete etceteras, drill face rock, load explosives, and blast explosives. To start the mining, the first step is to make the path to go down. The path is defined as 'Decline' as describe above. Before the start of a decline, all pre-planning of the power facility, drilling arrangement, de-watering, ventilation and, muck withdrawal facilities are required.^[2]

Production mining is further broken down into two methods, long hole and short hole. Short hole mining is similar to development mining, except that it occurs in ore. There are several different methods of long hole mining. Typically, long hole mining requires two excavations within the ore at different elevations below surface, (15 m – 30 m apart). Holes are drilled between the two excavations and loaded with explosives. The holes are blasted and the ore is removed from the bottom excavation.

Ventilation

One of the most important aspects of underground hard rock mining is ventilation. Ventilation is the primary method of clearing hazardous gases and/or dust which are created from drilling and blasting activity (e.g., silica dust, NOx), diesel equipment (e.g., diesel particulate, carbon monoxide), or to protect against gases that are naturally emanating from the rock (e.g., radon gas). Ventilation is also used to manage underground temperatures for the workers. In deep, hot mines ventilation is used to cool the workplace; however, in very cold locations the air is heated to just above freezing before it enters the mine. Ventilation raises are typically used to transfer ventilation from surface to the workplaces, and can be modified for use as emergency escape routes. The primary sources of heat in underground hard rock mines are virgin rock temperature, machinery, auto compression, and fissure water. Other small contributing factors are human body heat and blasting.

Ground support

Some means of support is required in order to maintain the stability of the openings that are excavated. This support comes in two forms; local support and area support.

Area ground support

Area ground support is used to prevent major ground failure. Holes are drilled into the back (ceiling) and walls and a long steel rod (or rock bolt) is installed to hold the ground together. There are three categories of rock bolt, differentiated by how they engage the host rock.^[3] They are:

Mechanical bolts

• Point anchor bolts (or expansion shell bolts) are a common style of area ground support. A point anchor bolt is a metal bar between 20 mm – 25 mm in diameter, and between 1 m – 4 m long (the size is determined by the mine's engineering department). There is an expansion shell at the end of the bolt which is inserted into the hole. As the bolt is tightened by the installation drill the expansion shell expands and the bolt tightens holding the rock together. Mechanical bolts are considered temporary support as their lifespan is reduced by corrosion as they are not grouted.^[3]

Grouted bolts

• Resin grouted rebar is used in areas which require more support than a point anchor bolt can give. The rebar used is of similar size as a point anchor bolt but does not have an expansion shell. Once the hole for the rebar is drilled, cartridges of polyester resin are installed in the hole. The rebar bolt is installed after the resin and spun by the installation drill. This opens the resin cartridge and mixes it. Once the resin hardens, the drill spinning tightens the rebar bolt holding the rock together. Resin grouted rebar is considered a permanent ground support with a lifespan of 20–30 years.^[3]
• Cable bolts are used to bind large masses of rock in the hanging wall and around large excavations. Cable bolts are much larger than standard rock bolts and rebar, usually between 10 and 25 metres long. Cable bolts are grouted with a cement grout.^[3]

Friction bolts

• Friction stabilizer (frequently called by the
  genericized trademark Split Set) are much easier to install than mechanical bolts or grouted bolts. The bolt is hammered into the drill hole, which has a smaller diameter than the bolt. Pressure from the bolt on the wall holds the rock together. Friction stabilizers are particularly susceptible to corrosion and rust from water unless they are grouted. Once grouted the friction increases by a factor of 3–4.^[3]
• Swellex is similar to Friction stabilizers, except the bolt diameter is smaller than the hole diameter. High pressure water is injected into the bolt to expand the bolt diameter to hold the rock together. Like the friction stabilizer, swellex is poorly protected from corrosion and rust.[3]

Local ground support

Local ground support is used to prevent smaller rocks from falling from the back and ribs. Not all excavations require local ground support.

• Welded Wire Mesh is a metal screen with 10 cm x 10 cm (4 inch) openings. The mesh is held to the back using point anchor bolts or resin grouted rebar.
• Shotcrete is fibre-reinforced spray-on concrete which coats the back and ribs preventing smaller rocks from falling. Shotcrete thickness can be between 50 mm – 100 mm.
• Latex Membranes can be sprayed on the backs and ribs similar to shotcrete, but in smaller amounts.

Stope and retreat vs. stope and fill

Stope and retreat

Using this method, mining is planned to extract rock from the stopes without filling the voids; this allows the wall rocks to cave in to the extracted stope after all the ore has been removed. The stope is then sealed to prevent access.

Stope and fill

Where large bulk ore bodies are to be mined at great depth, or where leaving pillars of ore is uneconomical, the open stope is filled with backfill, which can be a cement and rock mixture, a cement and sand mixture or a cement and tailings mixture. This method is popular as the refilled stopes provide support for the adjacent stopes, allowing total extraction of economic resources.

Methods

The mining method selected is determined by the size, shape, orientation and type of orebody to be mined. The orebody can be narrow vein such as a gold mine in the Witwatersrand, the orebody can be massive similar to the

• Cut and fill mining is a method of short-hole mining used in steeply dipping or irregular ore zones, in particular where the
  unconsolidated. Cut and fill mining is an expensive but selective method, with the advantages of low ore loss and dilution.^[4]
• Drift and fill is similar to cut and fill, except that it is used in ore zones, which are wider than the method of drifting will allow to be mined. In this case, the first drift is developed in the ore, and is backfilled using consolidated fill. The second drift is driven adjacent to the first drift. This carries on until the ore zone is mined out to its full width, at which time the second cut is started atop of the first cut.
• Shrinkage stoping is a short-hole mining method which is suitable for steeply dipping orebodies. This method is similar to cut and fill mining with the exception that after being blasted, broken ore is left in the stope where it is used to support the surrounding rock and as a platform from which to work. Only enough ore is removed from the stope to allow for drilling and blasting the next slice. The stope is emptied when all of the ore has been blasted. Although it is very selective and allows for low dilution, since most of the ore stays in the stope until mining is completed, there is a delayed return on capital investments.^[4]
• VRM/ VCR: Vertical retreat mining (VRM) also known as Vertical crater retreat (VCR) is a method where mine is divided in vertical zones^[clarification needed] with depth of about 50 meters using open stoping, bottom-up mining. Long-hole large-diameter holes are drilled vertically into the ore body from the top using in-the-hole (ITH)^{[5][clarification needed]} drills, and then blasting horizontal slices of the ore body into an undercut. Ore blasted in retrieval taken in phase. This retrieval is done from bottom of the section developed. Last cleaning of ore is done through remote controlled LHD machines. A system of primary and secondary stopes is often used in VCR mining, where primary stopes are mined in the first stage and then backfilled with cemented fill to provide wall support for the blasting of successive stopes. Side chambers will be mined in pre-planned sequence after the fill has solidified.^[6]

^[7]

Bulk mining methods

• Block caving is used to mine massive steeply
  better source needed] Where caving does continue, the ground surface may collapse into a surface depression such as those at the Climax and Henderson molybdenum mines in Colorado
  . Such a configuration is one of several to which miners apply the term "glory hole".

The ore is then dumped into a truck to be hauled to the surface (in shallower mines). In deeper mines, the ore is dumped down an ore pass (a vertical or near vertical excavation) where it falls to a collection level. On the collection level, it may receive primary

• The deepest mines in the world are the
  TauTona (Western Deep Levels) gold mines in the Witwatersrand region of South Africa, which are currently working at depths exceeding 3,900 m (12,800 ft).^[10]
• The deepest inactive mine in Asia is the Kolar in the Karnataka region of India. Closed in 2001, the main shaft had reached a depth of 10,560 ft (3,220 m).
  This region is also the location of the harshest conditions for hard rock mining, with air temperatures of up to 45 °C (113 °F). However, massive refrigeration plants are used to bring the temperature down to around 28 °C (82 °F).
• The deepest inactive hard rock mine in North America is the Empire mine in Grass Valley California. Closed in 1956 the main shaft had reached an incline depth of 11,007 ft (3,355 m). The combined length of all shafts is 367 miles (591 km).
• The deepest active hard rock mine in North America is Kidd Mine in Canada, which mines zinc and copper in Timmins, Ontario. At the maximum depth of 9,889 feet (3,014 m) this mine is the deepest base metal mine in the world, and its low surface elevation means that the bottom of the mine is the deepest accessible non-marine point on earth.^[11][12]
• LaRonde's Penna shaft (#3 shaft) is believed to be the deepest single lift shaft in the Western Hemisphere. The new #4 shaft bottoms out at 2,840 m (9,320 ft) down. LaRonde mine expansion was completed in June 2016 at the depth of 3,008 m (9,869 ft), the deepest longhole open stopes in the world.^[13]
• The deepest active mine in Eurasia and in Asia is Skalisty Mine of
  Nornickel, located in Talnakh. In September 2018 it reaches depth of 2,056 m (6,745 ft) below surface.^[14]
• The deepest mine in Europe is the 16th shaft of the uranium mines in Příbram, Czech Republic at 1,838 m (6,030 ft).^[15]
• The deepest hard rock mines in Australia are the copper and zinc lead mines in Mount Isa, Queensland at 1,800 m (5,900 ft). ^{[citation needed]}
• The deepest
  troy ounces, currently worked to a depth of approximately 2,200 m (7,200 ft).^{[citation needed}
  ]
• The deepest
  extreme point of Earth
  .

• Adit
• Gold mining
• Mining
• Pinge
• Shaft Mining
• Mining Act of 1872
• Stoping

References