Geology and Ore no. 2, 2003

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No. 2

The Black Angel lead-zincmine at Maarmorilik inWest Greenland

The Black Angel lead-zincmine at Maarmorilik inWest Greenland

The Black Angel mine took its namefrom a pelite outcrop that forms adark angel-like figure on a precipitouscliff face of marble above Affarlikas-saa fjord. The mineralised zone actu-ally crops out just above the angelfigure about 700 m above fjord level.The 1100 m high Angel mountain issituated at the margin of the Green-land ice cap at 71°N lat. on the westcoast of Greenland, about 500 kmnorth of the Arctic Circle, where thereis two months of winter darkness.The peninsula across the fjord housedthe mining camp, concentrator and allservices and received its nameMaarmorilik from a former marblequarry situated there from the 1930s.The only access to the mine fromthese facilities was by two aerialtramways.

The Black Angel deposit comprisedten ore bodies totalling 13.6 milliontons grading 12.3% Zn, 4.0% Pb and29 ppm Ag. Of these 11.2 million tonswere extracted in the period 1973–90.The mining operations ceased whenthe extractable ore reserves wereexhausted, leaving 2.4 million tons ofore tied up in pillars and other areasinaccessible to mining.

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GreenlandCanada

InlandIce

HudsonBay

Maarmorilik

SUPERIORCRATON

NORTHATLANTICCRATON

Foxe-

Rinkian

belt

500 km

Lower Proterozoicsupracrustal rocks

Middle Proterozoic-Tertiaryplatform rocks

Archaean

Hudsonian (includingreworked Archaean)

Pre-drift map of West Greenland and NE Canada showing the Foxe-Rinkian mobile belt andMaarmorilik. Modified from Grocott & Pulvertaft (1990).

View from north-west of the Angel mountain with the Greenland Inland Ice in the background. The former mining town of Maarmorilik wassituated on the peninsula to the right. Summer 1992.

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The Black Angel lead-zinc mine at Maarmorilik in West Greenland

Regional geology

The ores are hosted in the MârmorilikFormation of the Palaeoproterozoic KarratGroup. This Group belongs to the Foxe–Rinkian mobile belt of NE Canada andcentral West Greenland, which constitutesa component of the Trans-Hudson Orogenof North America. In Greenland, exposuresof the Karrat Group are known over anorth–south distance of c. 550 km cover-ing some 10,000 km2. The Group, thatrests unconformably on an Archaeangneiss complex, is intruded by a major1860 Ma syn-tectonic granite complexand is overlain by Cretaceous–Tertiary sed-iments and volcanics. The Karrat Group,several kilometres thick, is composed oflower shelf units of carbonates andquartzites, and an upper unit of deep-water turbidites and minor volcanic rocks.The basement and the cover sequencewere subjected to several phases of strongfolding and thrusting during theHudsonian orogenesis and variably affect-ed by regional metamorphism.

The Mârmorilik Formation consists of cal-citic and dolomitic marbles with a basalquartzitic unit and intercalations of anhy-drite-bearing marbles and semipelitic

schists. The formation is believed to havebeen deposited on a carbonate shelf in anepicontinental marginal basin c. 2 Ga ago.In the mine area, where the formation hasbeen tectonically thickened to c. 1000 m,three main phases of folding and thrust-ing have been distinguished, and meta-morphism reached upper greenschistfacies.

Mineralisation and ore

Carbonate-hosted lead-zinc mineralisationis common in the Mârmorilik Formationand in the mine area stratabound sulphidemineralisation occurs at various levels. Themain ore bodies are located 600–700 ma.s.l. in the upper part of the sequencewhich is dominated by calcitic marble,whereas the satellite ores of Nunngarut tothe south are hosted in the lower part ofthe sequence dominated by dolomite mar-ble. The distribution of ore bodies is con-trolled by a major z-fold with a 070°-strik-ing near-horizontal axis. The ore formsflat-lying, highly deformed, massive lensesup to 30 m thick, of which ten reach eco-

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T H E B L A C K A N G E L L E A D - Z I N C M I N E A T M A A R M O R I L I K

Inland IceQaamarujuk

Maarmorilik

Uummannaq

Nuussuaq

Nunngarut 2

Angel

I South

I

V 16

Cover

Banana

Tributary

Nunngarut 1

DeepIce

Map

500 m

500 m

500 m

Affarlikassaa

2

1

34★

★

★

★25 km

1 km

71°07´N

71°N

51°15´W

51°15´W 52°W

Map of the Maarmorilik area with ore bod-ies shown in red. Stars in inset map showmain prospects of Black Angel type; thecross marks a shale-hosted zinc prospect.

Pbconcentrate

1000 t

1973197419751976197719781979198019811982198319841985198619871988198919901996

Total

83732383942454238373126262430343625

-

590

4616815314313214815115114014113612211910512013612987

-

2,327

-336429478387332592520683653754723542456440779843507

-

9,454

-16

11112

1122633756333

-321

591579916

556

-47691973316

12885

109717971

-2315553

14918492

-

1,154

Znconcentrate

1000 tGross salesmill. DKK

Taxesmill. DKK

Net earningsmill. DKK

Key economic figures for the Black Angel mine

nomic size and were mined. The massiveore consists of pyrite, sphalerite and gale-na, with abundant rotated marble frag-ments and quartz inclusions. The mainaccessory ore minerals are pyrrhotite, chal-copyrite, tennantite and arsenopyrite.Cherty horizons and disseminatedgraphite are quite common in the wallrocks whereas minor fluorite and baryteare restricted to a few of the ore bodies.Various ore tectonites have been distin-guished – massive ore, banded ore, por-phyroclastic ore or "buck shot ore" andremobilised ore.

The sulphides are strongly tectonised and

metamorphosed and the origin of the oresis uncertain; their present distribution isstructurally controlled. It is perhaps mostlikely that the ores have been formed bysedimentary-exhalative processes on thesea floor (SEDEX-type) but they could alsohave formed at a later stage (MississippiValley-type).

Sphalerite-galena-pyrite occurrences of theBlack Angel type are known from marbleoutcrops at three localities south of Maar-morilik. It appears that this type of sul-phide deposit only occur in areas ofintense folding and major structural thick-ening of the marbles.

Zinc mineralisation is also known from theclastic metasediments of the KarratGroup. At one locality north of Maar-morilik, stratabound sphalerite-galena-pyrrhotite mineralisation occurs over astrike-length of some 9 km near the baseof the turbidite sequence. The clastic rocksalso have a potential for epigenetic ‘tur-bidite–hosted gold deposits’.

History of the mine

Sulphide samples leading to the discoveryof the Black Angel deposit were found inconnection with marble quarrying in the1930s and investigated by Danish geolo-

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Elev. 600 m

Elev. 0 m

Affarlikassaa

1.7 km

Elev. 1000 m

A simplified cross-section through the Black Angel mine

Angel zone

Finee ore bin

The millTh

Crusher

Maarmorilik

W

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gists in the 1930s and 1940s. Commercialinvestigations including diamond drillingwere carried out in the 1960s by a syndi-cate led by Cominco Ltd. of Canada. In1971 the Danish mining company Green-ex A/S (established in 1964 and 62.5%owned by Cominco Ltd. through the sub-sidiary Vestgron Mines Ltd.) obtained a25-year exploitation concession. Financialterms were favourable at that time, withonly a resource tax of yearly earnings tobe paid after recovery of all pre-produc-tion costs and capital investments. Theinvestment of c. 333 mill. DKK had beenrecovered in 1977, after which the com-pany started to pay concession fees.

Underground exploration in 1971–72 indi-cated a probable ore reserve of 4.1 milliontons grading 15.0% Zn, 5.0% Pb and 28ppm Ag. Based on this and after a hecticconstruction period of only 15 months,production started in 1973. During themine's 17-year lifespan, it was possible tomore than triple the original minablereserves. In 1985 a major operating losswas incurred, and due to growing finan-cial losses and dwindling ore reserves,Cominco scheduled Black Angel mine forclosure in early 1986. Boliden Mineral ABtook over Greenex from Cominco in mid-1986. Boliden managed to keep the minein operation and ensure sufficient mill

throughput for profitable operation untilmid-1990. Boliden cut operation costs,which peaked at about 1,700 DDK/t in1985 by about 30% to 1,200 DDK/t.Among other things, personnel werereduced from 335 at the end of 1984 toaround 250 in late 1987. Greenex was liq-uidated in 1995.

Infrastructure and personnel

The Maarmorilik townsite comprised astorage hall for stockpiles, workshops,harbour and shipping facilities, offices,residences, dining hall, heliport andhangar, as well as medical facilities.

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Black Angel mountain

Banana zoneI zone

Cover zone

Inland Ice

4.0 km

E

Massive ore

Pelite

Grey banded marble

White/light grey banded marble

LEGEND

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A simplified cross-section through the Black Angel mine. Not to scale.

Recreational facilities included a radio/TVstation, library, sports hall, post office,recreation centre and guest apartments.An 8.4-MW diesel generator station pro-vided all the power needed for the mine'soperations and the community. By desali-nating the fjord water through use ofwaste heat from the diesels, the powerplant also produced all the fresh waterrequired. The saline-enriched water fromthe desalination plant was used as drillingfluid in the mine; strong brine would notfreeze when drilling in permafrost. Thebrine for drilling had to be transported intanks up to the mine via the aerialtramway, as had all other equipment.

Supplies had to be shipped in and concen-trate shipped out during the 6 monthsice-free period from June to November.Personnel were ferried by helicopterbetween the mine and the nearest airportat Ilulissat, 200 km to the south.The Black Angel mine provided employ-ment opportunities and was important to

the local economy. Of the c. 350 employ-ees, up to 44% were Greenlanders, therest mainly Danes and Swedes. The em-ployees worked a 10-hour shift, with 2shifts a day, six days a week. Four workingmonths at the mine earned one month'svacation, travel included.

When mining was discontinued, Greenexundertook in 1990–91 an extensive clean-up, partly of buildings, plant, installationsetc. and partly targeting the sources ofheavy-metal contamination in the area.Final abandonment involved the removalof all surface structures (except two) andthe cable ways. Very little infrastructurewas removed from the mine.

Exploration in the mine area

In the period 1966–85, 17 major surfacedrilling programs were conducted aroundMaarmorilik and a total of 160,000 m wasdrilled in 400 holes. Most of the drillingwas on top of the Angel mountain where

it was performed systematically in a gridalong the 070° corridor hosting the ores.Much of this was through the ice cap, sothat 200–300 m of ice had to be pene-trated and then several hundred metres ofrock to intersect the target areas. New orebodies located by surface drilling wereinvestigated further by undergrounddrilling. Primary exploration drilling wasalso accomplished underground, thus con-tinually adding new tonnage to the orereserves.

High-grade ore intersections below the icecap were encountered in three areas. Onlythe westernmost of these, the Deep Icezone, was reached by primary develop-ment and mined, whereas the two east-ernmost targets remain. This was partlydue to delays created by water inflow dueto the lack of permafrost below the icecap.

Immediately south of the mine area, sev-eral lead-zinc prospects of Black Angel

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Mining town seen from the mine portal. Summer 1990.

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type exist, and farther away, lead-zincprospects of the same type occur in threeareas. Some of these were drill tested butall were rejected as viable prospects byGreenex. However, the zinc prospects inthe turbidite basin north of Maarmorilikwere found after the mine closure andnever drilled.

Mining and ore treatment

The main mining equipment was electro-hydraulic 2 and 3 boom jumbos, front-endloaders (scooptrams) and trucks, and themine housed an underground workshopfor repair and maintenance. After drillingby hydraulic jumbos and blasting, the bro-ken ore was hauled by truck to ore passesand then by locomotive haulage to theprimary crusher bin just inside thetramway portal. Parts of the Angel zonenear the portal were declared off limits to

mining to protect major access and trans-port routes in this area from possible dam-age from rock instability. The crushed orewas skipped across the fjord to the oredressing plant by an aerial tramway with afree span of 1500 m. The tramway had acapacity of 12 skips per hour; skip capaci-ty was 10 tons. One skip was fitted with acabin to transport personnel. There was asecond, smaller tramway for transporta-tion of material. Ore from Nunngarut was

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Car on foot-wall ramp in marble below mined-out stopes in ore dipping to the left.

Sketch of thin irregular ore which must bemined selectively.

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10

20

30

40

50

60

70

80

90

Year

10.000 t

Pb%

Zn%

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

Annual oreproduction at the BlackAngel mine.

trucked directly to a crusher inMaarmorilik.

The concentrating process was conven-tional selective flotation of galena andsphalerite using sea water. In most yearsthe recovery was c. 96% for zinc, 90%for lead and 75% for silver. Annual pro-duction averaged 135,000 tons of 57.6%zinc concentrate and 35,000 tons of69.7% lead, 420 ppm silver concentrate.

Tailings were discarded through a pipelineto the bottom of the adjacent Affarlikas-saa fjord. The concentrate was storedunder cover and shipped to WestEuropean smelters, normally by three ship-ments between June and November.

For the ore reserve calculations – comput-erised from the early 1980s – a dilutedcut-off grade of 8% combined lead andzinc was used. The ore was mainly mined

by the room-and-pillar method; onlysmaller steep ore bodies were mined bycut-and-fill methods. In thin parts of theore, selective mining (resuing) was prac-tised. The full face was drilled over, keep-ing the ore horizon in the top of the face.The lower part of the face containing the

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in 1000 t

AngelCoverTributaryIBananaNunngarut 1Deep IceNunngarut 2I SouthV 16

Total

6,6453,992

76768445034731619711936

13,557

4.82.82.04.62.93.85.53.14.31.9

4.0

14.210.59.1

12.38.38.7

14.87.2

11.15.3

12.3

5,2833,343

68362233532731215011228

11,196

5.03.02.04.73.23.85.53.24.42.0

4.1

Pb% Zn% in 1000 t Pb%

14.611.09.2

12.79.18.8

14.97.5

11.25.4

12.6

83848991739499769579

83

85889094829599799581

85

Zn% Ore Metal

Tonnage Production Recovery %

Ore zone

Tonnage and production of individual ore bodies of the Black Angel mine

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Maarmorilik after the removal of the mining town. Summer 1997.

View of the mining town and the Angelmountain from the west. Summer 1985.

waste was blasted and mucked out first.The upper ore section was then mined.Ore bands down to 0.4 m thick weremined by this method.

Remnant mining – guided by a carefulregistration of metal contents in the pillarsaiming at maximal metal recovery andsupervised by an extensive rock mechanicsprogramme – led to a high metal extrac-tion rate of 85%. In one section of theAngel zone, the stopes were totally back-filled with waste and a number of high-grade pillars were recovered by long holemining from drifts underneath the orehorizon.

All ten ore zones, except the Deep Icezone, are in permafrost. On the whole,the permafost proved to be an asset formine stability and it contributed to thehigh extraction rate. Close to the surfacethe rock temperature is minus 4°C andthis rises by 1°C per 150 m from surface.However, under the ice cap, the tempera-ture rises more rapidly so that the easternpart of the mine is not in permafrost –hence water flows in from fissures in the

marble. During development of the accessramp to the Deep Ice zone, drifting wasstopped in 1984 for more than a yearbecause of high water inflow. It was final-ly continued through the water-bearingzone under cover of grout injection anddraining of the water.

Pollution and environmentalmonitoring

After the first few years of mining, pollu-tion was found to be a bigger problemthan anticipated. Increasing amounts ofdissolved lead, zinc and cadmium weremeasured in the fjord water aroundMaarmorilik. A comprehensive monitoringof heavy metals in the biota showed thatlead pollution of blue mussels and sea-weed in the intertidal zone of the coastalareas near Maarmorilik was the most seri-ous problem. As a result, the authoritiesrequested Greenex to improve the envi-ronmental situation, the main culprits ofthe pollution being tailings and wastedumps.

The tailings were discharged at a depth of

30 m through a pipeline, from where theysettled on the bottom of the Affarlikassaafjord at 50–60 m. A number of measures were undertaken,and from 1978 to 1985 lead content ofthe tailings fell from 0.44% to 0.15%,zinc content from 1.10% to 0.23% andcadmium content from 57 to 14 ppm.

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Typical face to be mined selectively: ore on top of white marble.

“Buck shot ore” with marble rafts left in pillar.

Four waste dumps totalling 2–3 milliontons with 0.1–0.8% Pb and 0.3–2.3% Znhad been disposed outside the mine in itsfirst 10 years of operation. One of thesedumps of c. 400,000 tons reached intothe tidal zone, and the highest lead- andzinc values in seaweed and musselsoccurred in this area. After mine closurethis dump was removed and partly placedon the bottom of the Affarlikassaa fjordand partly in the former concentrate stor-age.

Rib pillar with high grade banded ore.

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Scooptram shifting broken rock.

Waste dump rea-ching from 345 ma.s.l. into the fjordon north side ofthe Angel moun-tain, summer1989. The orehorizon is seen justabove the dumphole (arrow) in theuppermost part ofthe 900 m highcliff. The dumpwas removed aftermine closure.

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Prior to abandonment, an environmentalagreement was in place to ensure theongoing monitoring of the fjords aroundMaarmorilik by the NationalEnvironmental Research Institute (NERI).Thus, since closure the environmentaround the site has been monitored annu-ally by analysing for lead and zinc in seawater, lichens, seaweed and marine ani-mals. As anticipated, these studies show amarked decline in heavy metal concentra-tions compared to earlier. Environmentalmonitoring will be continued until 2005.

Resumption of mining activity?

In spring 1997, Canadian companyPlatinova A/S was granted an explorationlicence for the Maarmorilik area in orderto examine the possibilities for re-openingthe mine. The Platinova plan was basedon mining about half of the remainingzinc from the highest value pillars in theAngel and Cover zones (800,000 tonsaveraging 14% Zn and 4.5% Pb). The orewas to be crushed on site and shipped by

bulk ocean carrier during three shippingseasons to a concentrator for custommilling.

During a site visit in 1997, the mine wasfound to be completely dry with few signsof loose rock falling from the back ineither stoping areas or travel ways.Measurements of previously establishedrock mechanical control points revealedno detectable ground movement sinceshutdown in 1990. Much of the equip-ment, including crushing facilities, was inexcellent condition with virtually no signsof rust. In January 1998, however, due tolow zinc prices Platinova gave up the proj-ect and the company has since aban-doned its license.

The future of the 'Black Angel'

At mine closure, Greenex depositedimportant geological records at theGeological Survey of Greenland,Copenhagen – now the GeologicalSurvey of Denmark and Greenland

(GEUS). This included data files comprisingthe ore reserves data base, geological sec-tions and mine maps, a collection of typi-cal ore specimens and 23 km of drill core.In 1999, the cores were relocated at theBureau of Minerals and Petrolems's drillcore archive in Kangerlussuaq, WestGreenland. A complete set of surfaceexploration reports was already housed atthe Survey. The collections in Denmarkand Greenland make it possible to contin-ue studies of the Black Angel ores withthe possibility of gaining new understand-ing about the distribution of possible addi-tional ore in the area.

The existence of an additional ore poten-tial in the mine area is indicated by oregrade intersections known from surfacedrillings in two areas to the east. It is tobe hoped that research in the Black Angelrecords and continued field exploration ofthe Mârmorilik Formation and the KarratGroup will ultimately result in renewedmining.

11Mining town seen from the cable car with ore skip in the foreground. Spring 1986.

Key references

Alm, L., Christensen, K. & Ekenberg, R. 1987:

Room and pillar mining in Maarmorilik, Greenland.

In: Almgren, G., Berg, I. & Matikainen, R. (eds):

Improvement of mine productivity and overall econ-

omy by modern technology, 895–904. Rotterdam:

A. A. Balkema.

Garde, A.A. 1978: The Lower Proterozoic

Marmorilik Formation, east of Mârmorilik, West

Greenland. Meddelelser om Grønland 200(3),

71 pp.

Grocott, J. & Pulvertaft, T.C.R. 1990: The

Early Proterozoic Rinkian Belt of central West

Greenland. In: Lewry, J.F. & Stauffer, M.R. (eds):

The Early Proterozoic Trans-Hudson Orogen of

North America. Geological Association of Cana-

da Special Paper 37, 443–463.

Krauland, N. & Söder, P.E. 1987: Determining

pillar strength from pillar failure observation.

Engineering and Mining Journal 188, 34–40.

Pedersen, F.D. 1980: Remobilization of the

massive sulphide ore of the Black Angel mine,

central West Greenland. Economic Geology 75,

1022–1041.

Pedersen, F.D. 1981: Polyphase deformation of

the massive sulphide ore of the Black Angel

mine, central West Greenland. Mineralium

Deposita 16, 157–176.

Thomassen, B. 1991: The Black Angel lead-zinc

mine 1973–90. Rapport Grønlands Geologiske

Undersøgelse 152, 46–50.

Thomassen, B. 1992: The gold and base metal

potential of the Lower Proterozoic Karrat

Group, West Greenland. Rapport Grønlands

Geologiske Undersøgelse 155, 57–66.

Wyllie, R.J.M. 1988: Boliden coaxes a few

more years out of Greenland's Black Angel

mine. Engineering and Mining Journal 189(2),

26–33.

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Greenland Resources A/SVandsøvej 5P.O. Box 821

DK-3900 NuukGreenland

Tel: (+299) 32 79 13Fax.: (+299) 32 79 14

E-mail: [email protected]: www.resources.gl

Bureau of Minerals and Petroleum(BMP)

Government of GreenlandP.O. Box 930

DK-3900 NuukGreenland

Tel: (+299) 34 68 00Fax.: (+299) 32 43 02

E-mail: [email protected]: www.bmp.gl

Author:Bjørn Thomassen, GEUS

Editor: Karsten Secher, GEUS

Graphic Production: Annabeth Andersen, GEUS

Printed: April 2003

Printers: Schultz grafisk

Geological Survey of Denmark and Greenland (GEUS)

Øster Voldgade 10DK-1350 Copenhagen K

Denmark

Tel: (+45) 38 14 20 00Fax.: (+45) 38 14 20 50E-mail: [email protected]: www.geus.dk

Front cover photograph:

The Black Angel mountain with mine portals and

angel figure, with traditional Greenland dog

sledges in the foreground. Spring 1980.

Depot of drill cores from surface exploration on top of the Angle mountain. Summer 1989.

Geology and Ore no. 2, 2003

Documents

Transcript of Geology and Ore no. 2, 2003