Peru

Atacocha Mine

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Overview

Mine TypeOpen Pit
Commodities
  • Zinc
  • Silver
  • Lead
  • Gold
  • Copper
Mining Method
  • Truck & Shovel / Loader
Production Start1938
Mine Life2033
ShapshotThe El Porvenir, Atacocha Underground and Atacocha Open Pit mines are part of the Cerro Pasco Complex.

The Atacocha site includes two mines: the Atacocha underground mine and the San Gerardo open pit mine. The underground mine is suspended and remains under care and maintenance, but mining continues in the San Gerardo open pit mine.

Once the San Gerardo pit is depleted, operations at the Atacocha underground mine will be re-started. The Atacocha processing plant is expected to be decommissioned by 2027. The underground mine will be integrated with the El Porvenir underground mine, with both mines feeding the El Porvenir processing plant.

Owners

SourceSource
CompanyInterestOwnership
Nexa Resources S.A. 75.96 % Indirect
Nexa Resources Atacocha S.A.A. (operator) 100 % Direct
The mine is wholly-owned and operated by Nexa Resources Atacocha S.A.A., which is controlled 91% by Nexa Resources El Pornevir S.A.C., a 99.99% subsidiary of Nexa Resources Peru S.A.A.

Nexa Resources S.A. owns 83.55% interest in Nexa Peru and therefore holds 75.96% of Atacocha mine.

Contractors

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Deposit type

  • Breccia pipe / Stockwork
  • Vein / narrow vein
  • Skarn
  • Replacement
  • Porphyry

Summary:

Three types of mineral deposits are recognized at Atacocha, described as either: skarn (Exo and Endo Skarn); replacement (lithological and structurally controlled); or hydrothermal veins (and collapse breccias).

Mineralization
At Atacocha, mineralization is characterized as a skarn, intermediate sulphidation epithermal vein/breccia-style, or porphyry mineralization.

Skarn/metasomatic-related mineralization spatially associated with the Santa Bárbara stock or San Gerardo stock is paragenetically earlier, followed by the hydrothermal mineralization. Skarn-related mineralization is commonly associated with the garnet and silica-skarn-chlorite assemblages, comprising pyrite, chalcopyrite, sphalerite, galena, and lesser pyrrhotite, pyrite, bournonite, covelite, orpiment, and realgar occurring within the Pucará Group sediments around the Santa Bárbara stock.

Skarn-related mineralization is characterized by pyrite, chalcopyrite, sphalerite, galena, with lesser bismuthinite and a variety of sulphosalts (Bi-bearing) and pyrrhotite, bornite, and covellite at lower elevation. Molybdenite may occur proximal to the skarn-related mineralization. Elevated Bi and Au are reported to be associated with skarn-related mineralization. Veins and veinlets with pyrite, chalcopyrite, sphalerite, galena, with quartz and carbonate occur within marble units, and are spatially associated with skarn bodies.

The intermediate sulphidation epithermal mineralization occurs in the upper part of the system (i.e., at higher elevations) as veins and breccias, characterized by galena, Ag-bearing sulphosalts, sphalerite, and free Au. Gangue mineralogy comprises quartz (silica), pyrite, specularite/hematite, adularia, rhodochrosite, rhodonite, and alabandite. The silica-sericite halloysite alteration assemblage is generally associated with this epithermal system. These veins and breccias are mostly between the San Gerardo stock and Fault 1, appearing to be at least partly controlled by the northwest-trending Fault 13. Breccias have been grouped into either Ag-Pb-Zn hydrothermal breccias or siliceous breccias based on their mineralogical assemblages and textural characteristics.

Siliceous breccias are further sub-divided into three groups: silica, granular (“terrosa”), and massive. Collectively the siliceous breccias may form large, relatively continuous bodies based on various interpretations; some appear to be spatially associated with the San Gerardo and Santa Bárbara intrusives and structurally controlled by the Milpo-Atacocha, Longreras, 13, 1, and Laquia faults. Veinlets of pyrite, galena, sphalerite, and possibly other fine undistinguished sulphides may occur within the variable silica-sericite-clay matrix.

The silica breccia comprises clasts of milky white to grey opaline silica, sub-rounded to sub angular, from millimetre to centimetre size; as well as less common sandstone and limestone clasts. The silica-breccia clasts are cemented by a white granular silica, with occasional cross cutting thin white silica veinlets.
The massive (siliceous) breccia forms zones of pervasive alteration comprising predominantly fine grained and massive white silica.

The granular-(siliceous) breccia comprises loose white to grey silica grains, within a poorly cemented clay (undifferentiated) matrix.

The Ag-Pb-Zn breccias are sub-divided into calcareous, polymictic-monomictic, and karst/collapse. Breccia clasts include limestone, marble, silica (massive), and skarn; the composition of the clasts indicates that brecciation occurred later than skarn development. Massive silica alteration may cross-cut skarns.
The calcareous breccia comprises sub-angular to sub-rounded clasts of limestone and marble; cemented by a grey to dark grey calcareous matrix, with occasional bituminous material and rare pyrite. Pyrite, sphalerite, galena, and other sulphides/sulphosalts including orpiment, realgar, tetrahedrite, alabandite, stannite, as well as quartz, calcite, rhodochrosite, and rhodonite occur within the matrix. Minor mineralization may occur within marble where the calcareous breccias cross-cut these units. Geochemical/mineralogical zonation is apparent whereby galena (Pb) and Mn-bearing minerals are more abundant distally relative to sphalerite (Zn). Bi- and Sn-bearing minerals are more elevated proximally.

The polymictic to monomictic breccias are overall grey, and comprise sub-angular clasts of black limestone, mudstone, white silica with silica-pyrite veinlets, and marble with silica wollastonite and calcite. Monomictic breccias comprise sub-angular clasts of limestone or predominantly intrusive rocks. Both polymictic and monomictic breccias clasts vary in size and are cemented with a black amorphous material with disseminated pyrite. Pyrite, chalcopyrite, sphalerite, galena, and possibly other sulphides occur within the matrix forming veins/veinlets, pockets, or disseminations.

Karst/collapse breccias contain clasts of limestone, marble, silica, skarn, and intrusive rocks, are sub-angular to sub-rounded, within a matrix of sub-horizontal laminated limestone and silica-sericite-clay material.

The Cu-Au±Mo porphyry mineralization is found in the Santa Bárbara stock. It consists of porphyry quartz monzodiorite with potentially economic grades (i.e., 0.3% Cu, 0.3 g/t Au) of Cu Au ± Mo. The San Gerardo stock is made of the same quartz monzodiorite, but with weaker alteration and much lower grades of all metals of interest. In the Milpo stock, the porphyry potential was poorly investigated, however, A- and B-type stockwork veinlets with low Cu grades were recorded in the past and the stock warrants future investigation.

Reserves

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Mining Methods

  • Truck & Shovel / Loader

Summary:

Atacocha operates two mines: the Atacocha underground mine and the San Gerardo open pit mine. The underground mine is currently suspended, but mining continues in the San Gerardo open pit mine. The underground mine is planned to restart production in 2027 at which point the open pit mine will be depleted.

Once the pit is depleted in 2027, operations at the underground Atacocha mine will be re-started. The underground mine will be integrated with the El Porvenir underground mine, with both mines feeding the El Porvenir processing plant. The Atacocha processing plant and mine site will be shut down and all operations will be transferred to the El Porvenir mine site.

The Atacocha underground mine is mined by the overhand Cut and Fill (C&F) and Sub-Level Stoping (SLS) mining methods. C&F stopes are 20.0m high consisting of 4.0m high cuts and a minimum mining width of 4.0m. C&F stopes are located 55 m from the main ramps and accessed by stope access ramps with grades varying from -15% to +15%. Production is achieved by horizontal drill and blast, and backfilled using unconsolidated waste fill or hydraulic backfill. The SLS mining method has demonstrated increased productivities and reduced unit costs as compared to the C&F mining method. SLS stopes are located a minimum of 40m from infrastructure, are 20.0m high, 30.0m long and have a minimum mining width of 4.0m. Production is achieved by vertical blastholes and backfilled using unconsolidated waste fill. Mined-out stopes are backfilled using unconsolidated backfill and hydraulic fill using tailings.

San Gerardo is an open pit operation located at the top of mineralized zone and is mined by 6.0m high benches. Since the temporally suspension of Atacocha underground mine, the open pit production is responsible by the metallurgical plant feed. Operations are carried out by contractor with a mining fleet that allows selectivity in the loading process.

Atacocha Open Pit (San Gerardo)
San Gerardo is a conventional open pit drill and blast operation using excavators and trucks operating on bench heights of six metres. The open pit is operated by a contractor, that provides operators, equipment, and ancillary facilities required for the mining operation.

Mill feed material produced by San Gerardo is hauled to the orepass at the east of the pit that reports to the 3600 Level of Atacocha UG, where it is trammed by locomotive and rail car to the Atacocha plant. Waste is hauled to the San Gerardo waste dump, which is adjacent to the Atacocha TSF dam. Average single direction haul distances for ore and waste are approximately 1.0 km and 4.7 km, respectively.

Open Pit Design
The San Gerardo pit is excavated with variable pit floor elevations and an ultimate pit bottom at 4,114 MASL. Ramps are 12 m wide at a 10% gradient that allow bi-directional haul truck travel. The mine is designed with a six-metre bench height, utilizing 127 mm vertical drill holes on 4.8 m x 5.8 m drill pattern with 0.5 m of sub-drilling.

Open Pit LOM Production Schedule
The open pit Mineral Reserve estimate supports an open pit LOM production plan of approximately four years before the underground mine starts production in 2027. Total material mined does not exceed 10 Mtpa (approximately 27 ktpd).

The LOM plan assumes that Atacocha UG will be operational starting in 2027 and will ramp up from 0.5 Mtpa in 2027 to 1.0 Mtpa in 2029.

Comminution

Crushers and Mills

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Processing

  • Crush & Screen plant
  • Flotation
  • Dewatering

Summary:

The Atacocha concentrator utilizes a conventional crushing, grinding, and sequential flotation scheme to produce lead and zinc concentrates with an average daily processing rate of approximately 4,400 tonnes. A flash flotation step is included in the grinding circuit that recovers lead at a grade sufficiently high to report directly to the final lead concentrate. The majority of gold and silver report are into the lead concentrate. Despite the plant having capacity to produce copper concentrate, the circuit of the plant has been bypassed and the Atacocha metallurgical plant produces only zinc and lead concentrates.

Flotation
The flotation plant consists of three circuits that are controlled by a Courier 6SL inline analyzer that was installed in September 2004 (currently only the multiplexer operates). The bulk rougher circuit produces a bulk copper-lead concentrate that is then separated in the lead circuit to produce the copper and lead concentrates. The zinc circuit processes the tailings from the copper and lead circuits, and including a regrinding stage, produces the zinc concentrate and the final tails.

Bulk Rougher Circuit
The bulk rougher flotation circuit treats the whole ore, obtaining lead concentrates, made up of the concentrates of the grinding circuit SK-80 flash flotation cells plus the OK-8 and OK-20 cleaner concentrates and the OK-30 I and 1st OK-8 scavenger concentrates. To this are added the concentrates of the RCS-30 and 2nd + 3rd OK-8 scavenger cells (may or may not include cleaners); the cleaner tailings are recycled to the bulk rougher feed. The feed to the cleaners is made up of rougher concentrates. The concentrates from the OK-30 I cells are fed to the OK-3 cells (lead cleaning), the concentrate from these cells also forms the lead concentrate and the tailings returns to the rougher feed.

Bulk-Scavenger Flotation Circuit
The tailings from the bulk rougher OK-30 II cells feed the bulk scavenger flotation circuit consisting of an OK-20 cell followed by a bank of six OK-8 cells and one OK-16 cells. The OK 20 scavenger concentrate flows to a bank of five cleaner scavenger OK-8 cells. The bulk scavenger tailings feed the zinc circuit.

Pb/Cu Separation Circuit
Since July 2019, no Pb/Cu separation has been carried out due to a copper head grade of less than 0.10%, ranging from 0.06% to 0.08%. The Pb/Cu separation can be resumed when the copper head grade improves.

Zinc Circuit
The zinc rougher circuit processes the tailings from the bulk lead-copper scavenger circuit with conditioning in two 16 ft dia. x16 ft agitated tanks operated in series. The zinc rougher circuit consists of one OK-100 cell and one OK-50 cell operated in series. The scavenger circuit consists of a bank of three OK-16 cells, a bank of four OK-16 cells and one OK-50 cells, and the cleaning circuit consists of one stage using an OK-10 cell and a bank of five OK-3 cells. The zinc scavenger tailings are final tailings. The first rougher concentrate and the cleaner concentrate are the final zinc concentrates.

The scavenger concentrates return to the second scavenger feed (OK-16) and tailings from the first scavenger are recycled to the second rougher feed.

Thickeners and Filters
Lead an zinc flotation concentrate are pumped to two parallel concentrate thickeners for each metal for dewatering. The thickener underflow slurry from the lead and zinc thickener underflows are pumped to the lead and zinc concentrate storage tanks respectively for density control. The slurry is then pumped to a CC-45 ceramic disc filter, which reduces the moisture in each of the concentrates to approximately 8.2% for transportation. Filter aid at 20 g/t is added to improve the filtration process. There are two drum filters that can be used for either lead or copper concentrate dewatering. The filtered concentrates are discharged to the concentrate storage areas for shipping. The concentrates are loaded into trucks by front end loader when being despatched to customers.

Tailings Pumping System
Atacocha's tailings transport system is a high pressure pumping system using Geho positive displacement pumps designed to pump thickened tailings at a density 55%-65% solids to the Atacocha tailings dam. A project is being developed for a treatment rate of 5,000 dry tpd, i.e. 4,500 tpd of tailings.

The concentrator's general tailings are fed to the 125 ft thickener at a density of 1,250 g/L to reduce the total volume of material that must be transported to the Atacocha TSF. The tailings pulp is temporarily stored in the thickener-clarifier. Flocculant is dosed at a rate of 30 L/min at a concentration of 0.025%. The underflow of the thickener is recirculated with HR-200 pumps until it reaches 55% to 65% solids. When the pulp reaches the appropriate density, it is fed into the linear sieve, to store clean pulp of adequate granulometry in the storage tanks, and when the density decreases, the pulp is recirculated to the thickener until it reaches the adequate density again. The overflow with < 50 ppm solids is stored in a tank and then recirculated to the concentrator, and excess water is sent to the settling ponds.

The pumped tailings are disposed of in the basin of the Atacocha TSF.

Recoveries & Grades:

CommodityParameter2023202220212020201920182017
Zinc Recovery Rate, % 75.979.176.375.377.577.979
Zinc Head Grade, % 0.770.890.881.21.431.431.43
Zinc Concentrate Grade, % 50.750.850.450.6495051.4
Silver Recovery Rate, % 82.777.77676.4
Silver Head Grade, g/t 37.632.731.443.247.344.244.5
Silver Concentrate Grade, g/t 2,0061,6581,8021,844
Lead Recovery Rate, % 85.785.583.3838485.386.7
Lead Head Grade, % 0.930.970.821.151.31.181.22
Lead Concentrate Grade, % 52.953.951.753.553.755.355.8
Gold Recovery Rate, % 56.267.969.654
Gold Head Grade, g/t 0.310.310.310.310.370.470.59
Gold Concentrate Grade, g/t 11.220.222.110.3
Copper Head Grade, % 0.050.080.10.09
Copper Recovery Rate, % 5.999.618.46
Copper Concentrate Grade, % 18.520.718.8

Production

CommodityUnits2024202320222021202020192018
Zinc t 0000000000000000000000000000017,323
Silver koz 00000000000000000000000000001,679
Lead t 000000000000000000000000000000000015,595
Gold oz 000000000000000000000015,431
Zinc Equivalent M lbs 00000000000100
Copper t 000125
All production numbers are expressed as metal in concentrate. ^ Guidance / Forecast.

Operational metrics

Metrics202320222021202020192018
Daily processing capacity 4,400 t4,300 t4,300 t4,500 t4,500 t4,500 t
Annual processing capacity 1.68 Mt
Ore tonnes mined 1,394 kt1,354 kt1,271 kt
Tonnes processed 1,397,192 t1,353,681 t1,271,107 t1,065 kt1,505 kt1,551 kt

Production Costs

CommodityUnits2024202320222021202020192018
Cash costs (sold) Zinc USD 0000000 0000000 0000000 0000000 000000 0.48 / lb   0.51 / lb  
^ Guidance / Forecast.
Net of By-Product.

Operating Costs

Currency2023202220212020201920182017
Total operating costs ($/t milled) USD 32.9  36.7  32.4  33.2  50.8  44  42.8  

Financials

Units2023202220212020201920182017
Sustaining costs M USD 16.1  4.4  11.1  15.3   11.8   16.9   5.9  
Capital expenditures M USD 16.2  4.5  11.6  15.3   11.8   16.9   5.9  
Revenue M USD 77.3  95.2  66.9  55.5   95.8   90.1   112  
Operating Income M USD 3  9.8  0.5  -54.8   -23.4   0.3   16  
Gross profit M USD 16.7  27.6  21.7  1.6   -1.2   9.3   28.3  
Pre-tax Income M USD -3.7  3.2  -0.7  -56.9   -25.3  
After-tax Income M USD -5.7  1.3  -1  -75.2   -20.7   -2.1   10.7  
EBITDA M USD 13  25  4.9  -11.3   1.1   12.8   29.3  

Heavy Mobile Equipment

Ref. Date: December 31, 2023

SourceSource
HME TypeModelSizeQuantityLeased or
Contractor
Drill Sandvik DP1500i 2 Leased
Excavator Caterpillar 395JC 6 m3 1 Leased
Excavator Caterpillar 349D 3.4 m3 1 Leased
Excavator Caterpillar 374FL 4.2 m3 1 Leased
Truck (haul) Volvo FMX 84R 26 m3 8 Leased
Truck (haul) Mercedes Benz Actros 4140-B 8x4 24 m3 7 Leased

Personnel

Mine Management

Source Source
Job TitleNameProfileRef. Date
Consultant - Costs Jason Cox LinkedIn Dec 31, 2023
Consultant - Mining Varun Bhundhoo LinkedIn Dec 31, 2023
Consultant - Recovery Methods Paul Hampton LinkedIn Dec 31, 2023
General Manager - Operations Development Cristovão Teofilo Dos Santos LinkedIn Apr 1, 2024
Infrastructure Superintendent Roy Petty Durand LinkedIn Apr 1, 2024
Logistics Manager Evelyn Serrano Moromisato LinkedIn Apr 1, 2024
Metallurgical Manager James Refulio LinkedIn Apr 1, 2024

EmployeesContractorsTotal WorkforceYear
170 1,105 1,275 2023
177 621 798 2022
186 944 1,130 2021
200 710 910 2020
390 1,042 1,432 2019
398 937 1,335 2018
421 991 1,412 2017
417 2016
421 2015

Aerial view:

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