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Eritrea
Bisha Mine

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 Location:
40 km W from Akordat, Eritrea

  Address:
61, Mariam Gimby PO Box 4276
Asmara
Eritrea
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  • Overview
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  • Mining
  • Processing
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  • Filings & News

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Overview

StageProduction
Mine TypeOpen Pit
Commodities
  • Copper
  • Zinc
Mining Method
  • Truck & Shovel / Loader
Processing
  • Flotation
Mine Life8 years (as of Jan 1, 2019)
Latest NewsNevsun Resources Extends Mine Life at Bisha Zinc-Copper Mine     June 14, 2018


Owners

Source: p. 60, 265
CompanyInterestOwnership
Eritrean National Mining Corp. 45 % Indirect
Zijin Mining Group Co., Ltd 55 % Indirect
On 30 April 2019, Nevsun Resources (Eritrea) Ltd. (“Nevsun Eritrea”), a subsidiary of the Company, entered into an equity transfer agreement with Eritrean National Mining Corporation and Bisha Mining Share Company (“Bisha”). Nevsun Eritrea transferred its 5% equity interest in Bisha to Eritrean National Mining Corporation at a consideration of USD10 million. The registration change of the above equity transfer was completed on 30 May 2019. The Company ultimately owns 55% equity interest in Bisha through Nevsun Eritrea, while Eritrean National Mining Corporation owns 45% equity interest in BMSC.

Deposit Type

  • VMS


Summary:

The Property is underlain by Neoproterozoic upper green schist to lower amphibolite facies volcanics and sedimentary units of the Augaro Adobha Belt.

The Bisha Main deposit is a series of four massive sulphide lenses that occur over a 1.2 km north- south trending strike extent. The thickness of the lenses is variable up to 70 m. Mineralisation extends to a depth of 600 m below surface.

The massive sulphide bodies comprise a southern zone and a northern zone. The main part of the southern zone strikes approximately 345° and dips steeply to the west, with strike and dip lengths of some 600 m and 500 m respectively. The main part of the northern zone strikes approximately 0° and dips steeply to the west, with strike and dip lengths of some 500 m and 100 m respectively. The southern zone plunges 45° to the south. In the hanging walls of both the southern and northern zones, there are two smaller massive sulphide pods interpreted to be folded limbs of the two main zones.

The Gossan varies in composition from highly siliceous and ferruginous to massive goethite– hematite–jarosite. The Oxide Zone is up to 50 m deep and is composed of hematite, quartz and clays; in places, original rock textures are preserved. The Oxide zone is enriched in Au, Pb, Ba and Mo and depleted in Cu, Zn, Cd and Co.

The Soap Zone is a white, light yellow or light brown zone, and consists of clay, quartz, barite and possibly anglesite. The Acid Zone is dark grey, and consists of clay, quartz, galena and pyrite. Faint original textures of the protolith may be preserved in both. Both the Acid and the Soap are depleted in Cu, Zn, Cd, Co, Fe and Mn and strongly enriched in Au, Ag, Pb and Ba; they are poorly consolidated and drill recoveries in these zones are generally poor.

The Supergene Zone is up to 20 m thick, and has elevated Cu and Ba and depleted Zn, Cd and Mn. Sphalerite and chalcopyrite are replaced by chalcocite, covellite, digenite and native copper. The Pyrite Sand lies directly above the Supergene Zone and consists of unconsolidated recrystallised pyrite grains; Cu from this Zone has been remobilised and deposited in the Supergene Zone.

Some remobilisation of Cu and Ba from the Primary Zone upwards into the Supergene zone has occurred along steeply dipping basement structures.

The Primary Zone represents the original massive sulphide deposit. The mineralogy is comprised of pyrite and sphalerite, with minor chalcopyrite, covellite, pyrrhotite and galena.

The Harena massive sulphide mineralisation is a tabular body up to 60 m thick that strikes 040° true, dips approximately 60° to the northwest, and plunges shallowly to the southwest. It is defined by diamond and minor RC drilling along a strike length of approximately 900 m; the deposit is closed down dip but is open down- plunge to the southwest.

The primary massive sulphide units comprise mainly massive sulphide mineralisation with subordinate semi-massive sulphide and volcanic lithologies, and are predominantly made-up of fine to medium-grained subhedral to anhedral pyrite with interstitial and/or enriched layers of sphalerite and chalcopyrite and range from 0.4 m to 100 m thick, averaging 19.8 m. The massive sulphide units have a tabular to lensoidal shape, with the thicker parts of the mineralisation in elongated shallowly SW- plunging shoots. In each massive sulphide unit there is a typical volcanic hosted massive sulphide (VMS) zonation from a Cu-Au-Ag rich base to a Zn-Ba rich top. The associated stringer mineralisation below the massive sulphide occurs in about half the drillholes; where present it is up to 58 m thick and averages 6.6 m. The total mineralised package (massive sulphide plus stringer) averages 23 m thick.

The Northwest deposit comprises a series of poly- metallic massive sulphide lodes that have been defined over a strike length of 800 m, striking northeast, and dipping from 70° northwest to sub- vertical. The deposit is thickest at the centre, tapering to widths of less than 8 m at its strike limits. The central portion of the deposit is over 85 m wide. In cross-section, the deposit is a wedge that narrows down-dip. Resource drilling has effectively defined the deposit to a maximum of 250 m below surface. Exploration drilling indicates that a mineralised stringer vein system still exists at depths of 350 m below surface.

The Hambok deposit lies within the Western Nakfa terrane, and is part of a sequence of Late Proterozoic mafic to felsic volcanic rocks, and sedimentary rocks, including pelite, chert, and carbonate units. The deposit comprises a primary copper/zinc sulphide zone, representing the majority of the deposit, and a minor oxide gold component. The primary massive sulphide mineralisation is a single body, with a faulted displacement interpreted at depth in the northeast of the deposit. The massive sulphide zones strike at approximately 015°, dipping steeply to the east, with overall strike and dip lengths of some 975 m and 400 m, respectively. The thickness of the massive sulphide varies from about 5.0 m to 75 m.

The Asheli massive sulphide deposit is located within the felsic volcanic sequence. It is a tabular, steeply north-plunging body 400 m long by 100 m wide and up to 30 m thick composed of pyrite, sphalerite and chalcopyrite. The top of the deposit is 60 m below surface.


Mining Methods

  • Truck & Shovel / Loader


Summary:

The Bisha Main and Harena deposits are mined as a conventional open pit operation. At Bisha Main, most of the in-pit haulage for waste will be carried out using 65-tonne haulage trucks and 10 m3 excavators, in 5 m benches. To control mining dilution and to increase selectivity smaller excavators will be utilised for ore mining. Harena pit will be mined using the same mining fleet and also in 5 m benches.

Waste rock will be moved and hauled to multiple rock storage facilities based on their geochemical characteristics and period of operation. Some of the mineralised waste will be stockpiled near the pit so that it can be recovered if commodity prices increase from current levels.

Mine design criteria:
- Bench height (final wall) - 10 m. Ore and waste will be mined in 5.0 m working benches.
- Bench face angle - 63°, 67°, 70°. Mainly 70°.
- Catch bench width - 6 m to 8.3 m. Varies based on the geotechnical zone, on final walls.
- Geotechnical berm - 16 m. At 140 m vertical intervals.
- Inter-Ramp angle - 39° to 46°. Varies by zone.
- Haulage road width - 32.5 m. Two way roads, includes berm and ditch.
- Maximum road slope 10%.
- Rock dump face angle - 34°. 25 m lifts and overall slope of 26°.

The Bisha Main ultimate pit is oriented in south-north direction. It broadly consists of two adjoining sections, a smaller pit in the north and the main pit to the south. The pit is ~1,400 m long (south to north) and ~700 m wide (east to west). The lowest bench in this pit is at 325 m amsl. The main haulage road reaches to the surface at 460 m amsl. The highest wall of the main pit is on the north- east side and is 240 m high. This high wall is broken into five sections by four passes of haulage ramp.

The in-pit haul road is mainly an anticlockwise spiral ramp beginning at the bottom of the pit and reaching to the natural topography at 460 m bench. The road is designed at 25 m width and 10% gradient. The road for the deepest 12 benches (60 m) at the bottom of the pit is reduced to 15 m wide and is considered to be a single lane road for 65 tonne trucks. The last 40 m of the pit has very little waste to be moved and will therefore accommodate less traffic. The pit has a second access road on the west side of the pit for safety and also to help reduce waste mining cycle time.

Harena pit is located to the southwest of the Bisha Main pit, about 10 km from the crusher. The pit is approximately 530 m by 450 m with the long axis of the pit oriented in a north- easterly direction. To minimise the strip ratio and to avoid mining the northeast high wall, the ramp is designed to be only on the northwest wall. The Harena pit extends to 475 m amsl, for a total depth of ~155 m. The highest wall at Harena is about 155 m. Part of this wall was mined while mining the oxide ore in the past.

Harena pit is a small pit and will also be mined in two phases. Phase 1 of Harena will be focused on pre-strip and preparation. Its development is scheduled to be synchronised with the Bisha Main pit when it approaches its final stages of life.

Harena pit commences in 2019 Q4 when waste mining in Bisha Main is substantially completed. In 2020, some ore will be mined in Bisha Main, however the majority of mining activity will be focused in Harena. Ore mining in Harena will be completed in 2021 Q3.


Crushing and Grinding


Processing

  • Flotation

Flow Sheet: Subscription required

Summary:

The 2.4 Mtpa BMSC (Bisha Mining Share Company) process plant Phase III expansion was commissioned in mid-2016 to process Primary material from the Bisha Main and Harena pits. The Phase III expansion now includes separate copper and zinc flotation circuits, concentrate dewatering/handling and tailings thickening prior to pumping and disposal in the tailings management facility.

Flowsheet modifications have been recently introduced, including the redirection of the concentrate from the first two copper and zinc rougher flotation cells to final concentrate.

The BMSC process plant has undergone a number of modifications/expansions as the feed has changed from Oxide to Supergene and now, Primary material for both the Bisha Main and Harena pits.

Following two-stage grinding and classification to an 80% passing (P80) size of 75 µm, copper flotation is completed nine, 100 m3 rougher cells followed by three stages of copper cleaning in a range of 100 m3, 30 m ........

Recoveries & Grades:

CommodityParameter2017201620152014
Copper Recovery Rate, %  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required
Copper Head Grade, % 12.83.95.9
Zinc Recovery Rate, %  ......  Subscription required  ......  Subscription required
Zinc Head Grade, % 6.25.7
Subscription required - Subscription is required.

Production:

CommodityUnits201920182017201620152014
Copper M lbs  ......  Subscription required  ......  Subscription required1856136196
Zinc M lbs  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required
Silver koz  ......  Subscription required  ......  Subscription required
Gold oz  ......  Subscription required
All production numbers are expressed as metal in concentrate.
Subscription required - Subscription is required.

Operational Metrics:

Metrics201920182017201620152014
Annual processing capacity  ......  Subscription required  ......  Subscription required
Annual mining capacity  ......  Subscription required  ......  Subscription required
Ore tonnes mined  ......  Subscription required  ......  Subscription required  ......  Subscription required3,643,000 t3,150,000 t2,282,000 t
Waste  ......  Subscription required  ......  Subscription required  ......  Subscription required9,367,000 t10,654,000 t12,277,000 t
Tonnes milled  ......  Subscription required  ......  Subscription required  ......  Subscription required2,278,000 t1,929,000 t1,789,000 t
Stripping / waste ratio  ......  Subscription required  ......  Subscription required  ......  Subscription required2.6 3.4 5.4
Subscription required - Subscription is required.

Reserves at December 31, 2019:

CategoryTonnage CommodityGradeContained Metal
Proven & Probable t Copper 0.94 % 144,384 t
Proven & Probable t Zinc 5.41 % 830,976 t
Total Resource t Copper 1.02 % 663,797 t
Total Resource t Zinc 4.85 % 3,173,252 t

Commodity Production Costs:

CommodityUnits20172016
C1 cash costs Zinc USD 0.97 / lb
C1 cash costs Copper USD 1.72 / lb 1.04 / lb
C1 cash costs Zinc USD 0.88 / lb†
† Net of By-Product.

Financials:

Units2019201820172016
Sustaining costs M USD  ......  Subscription required
Capital expenditures M USD  ......  Subscription required  ......  Subscription required
Operating Income M  ......  Subscription required
Gross profit M  ......  Subscription required
After-tax Income M  ......  Subscription required
Operating Cash Flow M  ......  Subscription required
Subscription required - Subscription is required


Heavy Mobile Equipment as of December 31, 2016:
HME TypeModelSizeQuantity
Dozer (crawler) ....................... Subscription required 2
Dozer (crawler) ....................... Subscription required 2
Dozer (rubber tire) ....................... Subscription required 4.633 m blade width 1
Drill ....................... Subscription required 229 mm 2
Drill ....................... Subscription required 150 mm 5
Excavator ....................... Subscription required 1
Excavator ....................... Subscription required 4
Excavator ....................... Subscription required 2
Grader ....................... Subscription required 4.677 m blade width 1
Grader ....................... Subscription required 4.267 m blade width 1
Loader ....................... Subscription required 2
Loader ....................... Subscription required 1
Truck (haul) 65 t 23
Truck (water) 56781 l 1
Truck (water) 30283 l 2
Subscription required - Subscription is required.

Mine Management:

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required May 30, 2020
....................... Subscription required ....................... Subscription required Subscription required May 30, 2020
....................... Subscription required ....................... Subscription required Subscription required May 30, 2020
....................... Subscription required ....................... Subscription required Subscription required May 30, 2020
....................... Subscription required ....................... Subscription required Subscription required May 30, 2020
....................... Subscription required ....................... Subscription required Subscription required May 30, 2020
Subscription required - Subscription is required.

Staff:

Total WorkforceYear
Subscription required 2018
Subscription required 2017
Subscription required 2016

Corporate Filings & Presentations:

DocumentYear
................................... Subscription required 2019
................................... Subscription required 2019
................................... Subscription required 2018
Annual Information Form 2017
Management Discussion & Analysis 2017
Annual Information Form 2016
Management Discussion & Analysis 2016
Technical Report 2016
Subscription required - Subscription is required.

News:

NewsDate
Nevsun Resources Extends Mine Life at Bisha Zinc-Copper Mine June 14, 2018
Nevsun Resources Provides 2018 Outlook and Guidance January 31, 2018

Aerial view:

Subscription required - Subscription is required.

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