The Fresnillo underground mine is located in the eponymous municipality in the central state of Mexico, Zacatecas, an area with rich mining resources.
This mine, located at 2.200 m.a.s.l., was discovered in 1554 and is property of the mining company Fresnillo Plc, the division for precious metals of the Mexican company Peñoles since its reorganization in 2004, listed at the London stock exchange.
In the Fresnillo mine, silver and gold are being extracted primarily, and to a lesser extent lead and zinc. Its processing plant has a capacity of 8000 t per day (2.640.000 t annually). The reserves of the mine amount to 277,55 million ounces of silver, accounting for 96 % of the Peñoles group's reserves and making it the most productive silver mine of the world. The gold reserves account for 667.000 ounces, making it the second most productive gold mine of Mexico.*
Rock support with mechanized, wet-mix shotcreting
One of the contractors in charge of the exploitation of the Fresnillo mine is Diseños y Construcciones Martínez (DICOM), one of the big Latin American construction companies headquartered in Fresnillo, Zacatecas. Being a specialist in the integral mine development process, DICOM takes care of drilling and blasting, ground support and mucking out, as well as electrical, water and ventilation installations and mine infrastructure. Apart from mining, DICOM is also present in other fields related to infrastructure construction and architectural design.
Depending on the meters of advance per day and type of rock, rock support in the Fresnillo mine is carried out by means of anchor bolts, wire mesh and shotcrete. DICOM applies mechanized, wet-mix shotcrete, working with Putzmeister machinery.
Previously, DICOM used the dry-mix method for shotcreting, but switched to wet spraying not only to comply with current regulations, but also because of the multiple advantages associated with this method:
- The security of the operator is increased as he does not work in the yet unstabilized area
- The reduced quantity of dust leads to a healthier working environment
- With the wet spraying process a higher level of support is achieved
- Mechanized concrete spraying is more efficient
- Maintenance costs are reduced
- There is less rebound than with dry spraying
- The working cycles are shorter
- Less manpower is required
As far as additives for the shotcrete mix are concerned, DICOM mainly works with SIKA products. For example, the use of retardants is required for transport, as the concrete plant is located outside the mine, and the excavation face is situated approximately 10 km away from the entrance. Additionally, plasticizers and accelerants are added for spraying. The fibers usually used are macro-synthetic (high density) polyethylene -fibers.
Putzmeister SPM 4210 WETKRET DUAL DRIVE and MIXKRET 4 in the machine park of DICOM
DICOM owns four SPM 4210 WETKRET Dual Drive concrete spraying systems, which can be operated both electrically and by the diesel engine to be able to work in areas without electrical supply.
The SPM 4210 WETKRET series has a spraying arm with a vertical spraying reach of 10 m, as well as a concrete pump with a capacity of 20m3/h. Its proportional remote control (cable and wireless) permits full regulation of the concrete output as well as adjustments to the predefined additive dosage. In this way, the machine operator can cope with the changing working conditions in the mine.
The equipment features a heavy-duty chassis with state-of-the-art axles as well as a reinforced turning system which facilitates working in the harsh conditions of mining, as for example in Fresnillo where the machines descend until levels of 1.270 m of depth by their own means.
The hydraulically-operated synchronized peristaltic additive pump is equipped with an automatic dosing device proportional to the concrete flow, thereby assuring spraying accuracy and quality.
Besides, DICOM possesses four low-profile concrete mixers of the Mixkret 4 series, with a capacity of 4 m3 for transporting the pre-mixed shotcrete from the concrete plant to the excavation face located 10 km from the entrance.
Mixkret 4 is equipped with an Integrated Continuously Variable Drive (ICVD) system without gear shift, taking full advantage of the engine power at any time without interruptions in traction, making operation easier for the driver.
The heavy-duty axles, four steering and driving wheels (4x4) as well as a powerful 6-cylinder 130 kW / 174 HP motor provide great climbing and movement power. The engine features an AAC (Automatic Altitude Compensation) system that enables its operation at high altitude offering the same performance. The Mixkret equipment used by DICOM incorporates the optional additive discharging system with a deposit of 120 l, to optimize shotcrete additive logistics.
*Data extracted from the official website of Fresnillo Plc: www.fresnilloplc.com/...
This mine, located at 2.200 m.a.s.l., was discovered in 1554 and is property of the mining company Fresnillo Plc, the division for precious metals of the Mexican company Peñoles since its reorganization in 2004, listed at the London stock exchange.
In the Fresnillo mine, silver and gold are being extracted primarily, and to a lesser extent lead and zinc. Its processing plant has a capacity of 8000 t per day (2.640.000 t annually). The reserves of the mine amount to 277,55 million ounces of silver, accounting for 96 % of the Peñoles group's reserves and making it the most productive silver mine of the world. The gold reserves account for 667.000 ounces, making it the second most productive gold mine of Mexico.*
Rock support with mechanized, wet-mix shotcreting
One of the contractors in charge of the exploitation of the Fresnillo mine is Diseños y Construcciones Martínez (DICOM), one of the big Latin American construction companies headquartered in Fresnillo, Zacatecas. Being a specialist in the integral mine development process, DICOM takes care of drilling and blasting, ground support and mucking out, as well as electrical, water and ventilation installations and mine infrastructure. Apart from mining, DICOM is also present in other fields related to infrastructure construction and architectural design.
Depending on the meters of advance per day and type of rock, rock support in the Fresnillo mine is carried out by means of anchor bolts, wire mesh and shotcrete. DICOM applies mechanized, wet-mix shotcrete, working with Putzmeister machinery.
Previously, DICOM used the dry-mix method for shotcreting, but switched to wet spraying not only to comply with current regulations, but also because of the multiple advantages associated with this method:
- The security of the operator is increased as he does not work in the yet unstabilized area
- The reduced quantity of dust leads to a healthier working environment
- With the wet spraying process a higher level of support is achieved
- Mechanized concrete spraying is more efficient
- Maintenance costs are reduced
- There is less rebound than with dry spraying
- The working cycles are shorter
- Less manpower is required
As far as additives for the shotcrete mix are concerned, DICOM mainly works with SIKA products. For example, the use of retardants is required for transport, as the concrete plant is located outside the mine, and the excavation face is situated approximately 10 km away from the entrance. Additionally, plasticizers and accelerants are added for spraying. The fibers usually used are macro-synthetic (high density) polyethylene -fibers.
Putzmeister SPM 4210 WETKRET DUAL DRIVE and MIXKRET 4 in the machine park of DICOM
DICOM owns four SPM 4210 WETKRET Dual Drive concrete spraying systems, which can be operated both electrically and by the diesel engine to be able to work in areas without electrical supply.
The SPM 4210 WETKRET series has a spraying arm with a vertical spraying reach of 10 m, as well as a concrete pump with a capacity of 20m3/h. Its proportional remote control (cable and wireless) permits full regulation of the concrete output as well as adjustments to the predefined additive dosage. In this way, the machine operator can cope with the changing working conditions in the mine.
The equipment features a heavy-duty chassis with state-of-the-art axles as well as a reinforced turning system which facilitates working in the harsh conditions of mining, as for example in Fresnillo where the machines descend until levels of 1.270 m of depth by their own means.
The hydraulically-operated synchronized peristaltic additive pump is equipped with an automatic dosing device proportional to the concrete flow, thereby assuring spraying accuracy and quality.
Besides, DICOM possesses four low-profile concrete mixers of the Mixkret 4 series, with a capacity of 4 m3 for transporting the pre-mixed shotcrete from the concrete plant to the excavation face located 10 km from the entrance.
Mixkret 4 is equipped with an Integrated Continuously Variable Drive (ICVD) system without gear shift, taking full advantage of the engine power at any time without interruptions in traction, making operation easier for the driver.
The heavy-duty axles, four steering and driving wheels (4x4) as well as a powerful 6-cylinder 130 kW / 174 HP motor provide great climbing and movement power. The engine features an AAC (Automatic Altitude Compensation) system that enables its operation at high altitude offering the same performance. The Mixkret equipment used by DICOM incorporates the optional additive discharging system with a deposit of 120 l, to optimize shotcrete additive logistics.
*Data extracted from the official website of Fresnillo Plc: www.fresnilloplc.com/...
