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Mexico
Cusi Mine Expansion Project (Cusi Mine)

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 Location:
86 km SW from Ciudad Cuauhtemoc, Chihuahua, Mexico

  Project Contacts:
Blas Cano de los Rios #500 Col. San Felipe
Chihuahua
Chihuahua, Mexico
C.P. 31203
Phone  ...  Subscription required
WebsiteWeb
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  • Overview
  • Owners
  • Geology
  • Mining
  • Processing
  • Production
  • Reserves
  • Costs & Financials
  • Fleet
  • Personnel
  • Filings & News

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Overview

StagePreliminary Economic Assessment
Mine TypeUnderground
Commodities
  • Silver
  • Lead
  • Zinc
  • Gold
Mining Method
  • Bench & Fill
  • Sub-level Retreat
  • Room-and-pillar
Processing
  • Dewatering
  • Flotation
Mine Life16 years (as of Jan 1, 2020)
Latest NewsRokmaster Files PEA Technical Report for The Revel Ridge Project     January 22, 2021


Owners

Source: p. 5
CompanyInterestOwnership
Sierra Metals Inc. 100 % Indirect

Deposit Type

  • Epithermal
  • Vein / narrow vein


Summary:

Mineral Deposit
Mineralization at the Cusi Mine has been variously described as a) low-sulfidation epithermal (Ciesielski, 2007), b) high-sulfidation epithermal (SGS, 2008) and linked epithermal-base metal system (Meinhert, 2006). Meinhert (2006) notes that although shallow (<100 m) historic mining is reported to have encountered grades exceeding 1,000 oz/ton Ag, the veins currently exposed are more base-metal rich than would be expected in an epithermal system. However, Sierra Metals geologists consider the abundance of base metals on the property to be primarily a function of depth of exposure and SRK agrees with this interpretation. Mineralization occurs along narrow fractures containing quartz, sphalerite and galena, and wall rock alteration consists primarily of silicification and the development of clays and iron oxides. The veins contain quartz with crustiform and banded textures typical of epithermal systems.

The current geologic model for the Cusi property is described as follows:

The country rock on the property consists primarily of felsic volcanics interpreted to represent a caldera with a resurgent dome. Magma is interpreted to have intruded along the Cusi fault, a regional NW-trending, right-lateral strike-slip fault, and a subsequent eruption produced the collapsed caldera and Upper Volcanic Series felsic tuffs. A resurgent dome then arose within the caldera on the western side of the Cusi fault. This dome was then dissected by numerous northeast-trending, left-lateral faults, which acted as conduits for hydrothermal fluids and now host mineralized veins.

Two of the vein sets at Cusi are relatively large and have been mapped along strike for nearly a kilometre each. These vein sets, dilatational areas and structural intersections have historically been found to be reliable targets for mineralization. The veins are composed of both wide, continuous areas of mineralization as well as zones of numerous smaller swarms of veins or stockwork veinlets. The mineralization is predominately Ag and Pb-rich with lesser amounts of Au, Zn and Cu present in some areas.

SRK is of the opinion that the geologic model developed by Sierra Metals, which focuses primarily on the interpretation of the discrete veins and their related splays/stockwork zones, is appropriate for the deposit type and mining method, and that this has been borne out by a history of production.

Mineralization and Alteration
Numerous epithermal mineralized veins exist on the property. Typically, these are moderately to steeply dipping to the southeast, southwest, and north, ranging from less than 0.5 m to 2 m thick, and extend 100 m to 200 m along strike and up to 400 m down-dip. Small open pits were typically developed at vein intersections.

The epithermal mineralization associated to structures, breccias and filling fractures ranging from less than 1 m to 10 m thick, with a polymetallic filling of Ag-Pb-Zn sulphides and minor contents of copper and variable contents of gold. Crustiform and banded epithermal textures are common, and there is pervasive silicification with some sericite and disseminated pyrite. Zones with argillic alteration are common at the borders of the pervasive silicification, including kaolinite and montmorillonite. Oxidation is characterized by hematite, limonite and manganese oxides.

Zones of micro-veinlets and dissemination associated to intense fracturing related to the main structures are observed in the area of Promontorio. In Eduwiges, veins and zones of “stockwork” of quartz with pyrite and silicification alteration of 60 m to 150 m width and 200 m to 250 m extension are observed (Geomaps, 2012).


Mining Methods

  • Bench & Fill
  • Sub-level Retreat
  • Room-and-pillar


Summary:

Bench and fill mining method is currently used in the main areas of the mine and to a lesser extent, room and pillar mining is also used. The mining method used varies depending on geotechnical constraints, mineralization trends, dimensions, and mine production targets.

Using the updated Mineral Resource estimate, Sierra Metals performed an expansion analysis to determine how the Cusi mine could achieve higher sustainable production rates. The analysis indicated that higher production rates are achievable through the massification of the bench and fill mining method in the new production areas, which will allow the sustainability of the operation. A new configuration of the mining method will allow obtaining a greater recovery of mining resources and increasing productivity.

Current production at Cusi comes from the Promontorio and Santa Rosa de Lima mineralized zones. Mineralized material is currently hauled to the surface using one of several adits or declines accessing the mineralized zones, and is then dumped onto small pads outside of the portals.

The mining sequence through this method is of a descending type, that is, the upper levels are mined, while in the lower ones the necessary preparations are made to start mining once the mineralized material has been extracted from the upper stopes. Within a sublevel, mining is carried out in retreat, starting at the ends of the stope and retreating towards the entrance.

In Cusi, mining sublevels are vertically spaced 16 meters from floor to floor, with a 3.5 m sill pillar left in-situ.

The conceptual mine plan developed was based on the implementation of bench and fill throughout the Cusi mine. Sierra evaluated the relative advantages of using the bench and fill mining method and determined improved mine production could be achieved for the following mineralized zones: Santa Rosa de Lima, Santa Eduwiges, Promontorio, San Nicolas, San Juan, San Ignacio, La Gloria, La Durana and Candelaria.

The extracted mineral is taken to the Mal Paso processing plant located 36 km from the mine, where lead and zinc concentrates are produced.

A base case Life of Mine (LOM) production and development schedule was generated for the Cusi
mine based on 1,200 tpd (432,000 tonnes per year).

The start date of this schedule is January 2021. Typical mining rates of 1,200 t/day mineralized
material and 560 t/day waste were applied as these are the rates the mine has been reportedly
operating at in early 2020.


Crushing and Grinding
Crusher / Mill TypeModelSizePowerQuantity
Jaw crusher ....................... Subscription required 1
Cone crusher ....................... Subscription required 2
Ball mill 7' x 10' 250 HP 1
Ball mill 8' x 7' 250 HP 1
Ball mill 8' x 14' 600 HP 1

Summary:

The concentrator's processing facilities include a crushing circuit consisting of a 50 t bulk hopper, a Metso TK9-32-22V vibratory feeder, a C96 Metso jaw crusher, an HP300 secondary cone crusher, a tertiary cone crusher HP300, a 6’x 20’ Trio double-bed primary vibrating screen, a 6’x20’ Trio double-bed secondary vibrating screen and a 5’x14’ double-bed secondary vibrating screen. The material is crushed to 90% passing -5/16" and is then deposited into three fine hoppers with an aggregate storage capacity of 1000 t.

The grinding circuit consists of a 7’x 10’ ball mill with a 250 HP motor, an 8’x 7’ ball mill with a 250HP motor and an 8’x14’ ball mill with a 600HP motor, and the classification system consists of D20 hydrocyclones.


Processing

  • Dewatering
  • Flotation

Flow Sheet: Subscription required

Summary:

The Cusi processing facilities include two interconnected process plants, which are the Mal Paso mill purchased from Rio Tinto, and the El Triunfo (Triungo) mill. Both mills are conventional ball mill and flotation plants fed from a single crushing circuit. The flotation circuit has the ability to produce lead concentrate and zinc concentrate, although the Pb circuit represents a comparably higher percentage of concentrate production.

El Triunfo includes a cyanide leach plant that has been used to process legacy tailings and, at times, fresh tails from Mal Paso. The leach plant was idled in mid2012 with no indication that it is scheduled to restart.

Cusi’s Mal Paso processing facility consists of a conventional concentration plant including crushing, grinding, flotation, dewatering of final concentrate, and a tailings disposal facility.

The Triungo circuit, which has a capacity of 400 tpd, produces a copper concentrate and a zinc concentrate. The Mal ........


Combined production numbers are reported under Cusi Mine

Operational Metrics:

Metrics
Daily ore mining rate  ......  Subscription required
Waste tonnes, LOM  ......  Subscription required
Ore tonnes mined, LOM  ......  Subscription required
Total tonnes mined, LOM  ......  Subscription required
Annual ore mining rate  ......  Subscription required
* According to 2020 study.
Subscription required - Subscription is required.

Reserves at August 31, 2020:
Mineral resources are reported at a single cut-off grade of 95 g/t AgEq.

CategoryTonnage CommodityGradeContained Metal
Measured & Indicated 5,356 kt Silver 182 g/t 31.3 M oz
Measured & Indicated 5,356 kt Lead 0.49 % 58.3 M lbs
Measured & Indicated 5,356 kt Zinc 0.58 % 68 M lbs
Measured & Indicated 5,356 kt Gold 0.12 g/t 20.2 koz
Measured & Indicated 5,356 kt Silver Equivalent 215 g/t 37 M oz
Inferred 4,893 kt Silver 146 g/t 23 M oz
Inferred 4,893 kt Lead 0.43 % 46.1 M lbs
Inferred 4,893 kt Zinc 0.69 % 74.8 M lbs
Inferred 4,893 kt Gold 0.18 g/t 27.7 koz
Inferred 4,893 kt Silver Equivalent 183 g/t 28.8 M oz

Commodity Production Costs:

CommodityUnitsAverage
Assumed price Lead USD  ......  Subscription required *
Assumed price Zinc USD  ......  Subscription required *
Assumed price Silver USD  ......  Subscription required *
Assumed price Gold USD  ......  Subscription required *
* According to 2020 study / presentation.
Subscription required - Subscription is required.

2020 Study Costs and Valuation Metrics :

MetricsUnitsLOM Total
Expansion CapEx $M USD  ......  Subscription required
Sustaining CapEx $M USD  ......  Subscription required
Closure costs $M USD  ......  Subscription required
Total CapEx $M USD  ......  Subscription required
UG OpEx $M USD  ......  Subscription required
Processing OpEx $M USD 116.1
G&A costs $M USD 16.5
Total OpEx $M USD  ......  Subscription required
Income Taxes $M USD  ......  Subscription required
Royalty payments $M USD  ......  Subscription required
Gross revenue (LOM) $M USD  ......  Subscription required
EBITDA (LOM) $M USD  ......  Subscription required
Pre-tax Cash Flow (LOM) $M USD  ......  Subscription required
After-tax Cash Flow (LOM) $M USD  ......  Subscription required
After-tax NPV @ 5% $M USD  ......  Subscription required
After-tax NPV @ 10% $M USD  ......  Subscription required
After-tax NPV @ 8% $M USD  ......  Subscription required
Subscription required - Subscription is required.

Proposed Heavy Mobile Equipment as of August 31, 2020:
HME TypeSizeQuantity
ANFO Loader 1
....................... Subscription required 1
....................... Subscription required 3
....................... Subscription required 4
....................... Subscription required 1
....................... Subscription required ....................... Subscription required 2
....................... Subscription required 1
....................... Subscription required 1
....................... Subscription required 7
Subscription required - Subscription is required.

Mine Management:

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Aug 31, 2020
....................... Subscription required ....................... Subscription required Subscription required Aug 31, 2020
Subscription required - Subscription is required.

Staff:

Total WorkforceYear
Subscription required 2020

Corporate Filings & Presentations:

DocumentYear
................................... Subscription required 2020
Subscription required - Subscription is required.

News:

NewsDate
Rokmaster Files PEA Technical Report for The Revel Ridge Project January 22, 2021
Rokmaster Closes C$9.1 Million Non-brokered Private Placement December 31, 2020
Rokmaster Increases Private Placement Financing December 16, 2020
Rokmaster Announces $8.5M Financing with a Strategic Investment by Crescat Capital December 15, 2020
Rokmaster Drills Strong Gold Mineralization of 5.09 g/t AuEq over 8.37 Metres Down Dip Of Historical Revel Ridge Resource Areas December 11, 2020
Rokmaster Delivers Robust Economics for Revel Ridge: After-Tax NPV(5.0%) of C$423M, 29.5% IRR and 2.6 Years Payback December 8, 2020

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