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MECHANIZED MINING IN NARROW VEINS: HUARÓN MINE

Por: John Olivera Agama, Ingeniero de Planeamiento Mina Senior, Pan American Silver Huarón.


Abstract

Huarón is a hydrothermal deposit with a zoned distribution of high temperature mineralization in its central zone (copper bearing sulfides) and mineralized lead and zinc towards the edges with high silver contents. 

The geological, morphological and geomechanical characteristics of mineralized structures in the Huarón mine. From 2020 to 2022, there has been an increase in production of narrow veins from 0.4m to 1.8m, increasing from 27% to 42%, with dip from 75° to 89° and RMR ranging from 25 to 35. This required a different and adaptable mining method to those that were usually performed, such as the conventional overhand cut and fill mining with electric winches and Jack Leg machine until 2015, year in which the traditional Sub Level Stoping mining method was mechanized and started, with preparation sections of 3.5 m wide by 3.8 m high. The sections were adapted to the equipment available in the market. In the preparations, the over dilution increased up to 20% creating openings and instability in the mining and safety problems for our personnel and equipment, in addition to the cost overruns that this implies, obtaining margins similar to those of conventional mining.

Our main objective is to improve the preparation and mechanized mining of Operations. From the mining results of the Sub Level Stoping variant, the AVOCA method is generated, which is a combination of traditional Cut and Fill Stoping and the use of electronic detonators in the advances with the objective of performing a segregation method in the sub levels (2.8m wide x 3.8m high) that is adapted to mining in narrow veins, with an improvement consisting in the use of Micro - Trackless Equipment (low profile equipment less than 2.0 m wide) in each process of the unit operation. With this mining method and equipment designed for narrow mine workings, a maximum opening limit is maintained and controlled in preparation and in mining. 

Their implementation is planned to reduce over dilution and maintain mining widths that are economically feasible, profitable and safe. For this reason, the acquisition of trackless micro equipment for narrow veins was carried out, including: Muki Front-Face Mini-Jumbo, Small Bolter, Shotcrete Minin Robot, Mini Mixer. For long-hole drilling, the Jumbo Mini Raptor and for cleaning, the 2.2 yd3 remote-controlled scooptram. All equipment under 2.0 m wide.

In addition, a geomechanical design was made for the dimensioning of openings and panels, obtaining an ideal bench of 10 m to 12m with 20-meter mining panels. A mining strategy was considered in each unit operation (drilling, blasting, support, cleaning and filling) and mining control parameters (safety, deviation, fragmentation, dilution, width factor, secondary blasting and recovery).

The tests gave positive results, so its use was intensified, achieving the mechanization of mini equipment for the whole mining process in narrow veins. Rockfall accidents dropped to zero, the Unit's safety indicators improved in recent years, pit production increased from 2,000 tons/month to 4,000 tons/month, over dilution was reduced from 20% to 10%, thus reducing the cost of mining from 67 $/ton in conventional mining to 35 $/ton in mechanized mining.

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