The Geology, Petrography and Geochemistry of Gabbroic Rocks of the Pants Lake Intrusive Suite on the Donner/Teck South Voisey's Bay Property, North-Central Labrador, Canada

Heather E. MacDonald

A thesis submitted in conformity with the requirements for the degree of Mastet's of Science Graduate Department of the Department of Geology University of Toronto

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Heather E. MacDonald

Master's of Science, 1999 Department of Geology University of Toronto

Abstract

The South Voisey's Bay property held by Donner Minerals Limited in North-Central

Labrador hosts Ni-Cu-Co mineralization within gabbroic rocks of the Pants Lake

Intrusive Suite (PLIS). Three drill holes from across the property were seiected for study. Samples were analyzed for major, trace, rare earth elements and examined by petrographic microscope. The data suggests that two distinct intrusions make up the

PLIS denoted as the North and South Intrusions. Geochemical cornparisons to the

Voisey's Bay troctolites indicates similar major element contents reflecting plagioclase- rich mineralogy, and trace element contents of Voisey's Bay are similar to the South gabbro units. Contamination sources are not obvious corn data collected. Al1 gabbros are chalcophile-element depleted when plotted on CdZr and Cu/Hf diagrams.

Sulphides would have settled out of a silicate melt, due to a contrast in density, perhaps in a previous charnber or feeder conduit. Acknowledgments

First and foremost, 1 would like to give thanks to Dr. A.J. Naldrett for his supervision, instruction and insight. Without his invaluable support this project would not have been possible. Also indispensable was the help of one cornmittee member, Dr. M.P. Gorton, for his assistance and instruction of neutron activation analysis, interpretation of geochemical data, and reviews of my thesis. Dr. Chusi Li also provided guidance and information regarding the Voisey's Bay deposit. Several other members of the department were a great source of information and advice: Dr. Steve Scott, another cornmittee member who added sorne important ideas; Dr. James Brenan, who added his critical reviews of this thesis; and Dr. Claudio Cermignani completed the microprobe analysis of my samples as a contract to Teck. Thanks to Jim for aiding (and sometimes rescuing files) in computer technical difficulties! Karen Gorra took some great photos of several of rny sarnples. Dr. James Scoates from the Universite Libre de Bruxelles was open to discussion and helpful hints. 1 also gratefully acknowledge the financial assistance of a University of Toronto Open Scholarship.

Instrumental to this project was the generous support of Teck Exploration Limited and

Donner Minerals Limited. They provided two summers of employment and limitless, extremely valuable help from a great crew that 1 had the privilege to work with: Paul

Moore, Harvey Keats, Kerry Sparkes, Tom Lane, Denis, Guy, Kellie, Steve, Floyd,

Trevor, Mike, Bing, and the rest of the Pants Lake Crews of 1997 and 1998! Andy

Kerr, Bruce Ryan and Dick Bailey of the Newfoundland Department of Mines and Energy were al1 extremely approachable and enthusiastic, and greatly assisted in my understanding of regional and local geology.

My good fnend and room-mate, Michelle Joyette crushed my samples and helped maintain my sanity by providing recreational breaks. Troy Small deserves a reaIly big thank-you for bolstering my confidence and managing to put up with me during the final stages of this project! My oflice-mate Andrew, and fnends, including the many graduate students of yesterday and today, GSU-goers, and Sleeman Breweries Honey

Brown Lager were also much needed stress relievers. Ed and Harry of the GSU should also recognized for providing al1 us grad snidents with a place to blow off steam.

My grandmother (December 8, 1908-July 22, 1999) was always very supportive even though she didn't quite understand why her pndaughter was interested in rocks!

Unfortunately, she didn't get to see the final product, but 1 would like to thank her anyway. Finally, 1 would like also to extend my gratitude to my family for their unconditional support, and, who encouraged the completion of my tirne at U. of T. with such loving inquiries as: "Are you done yet?" Table of Contents

Page Title Page 1 .* Abstract Il *-a Acknowledments 111 vi i List of Tables .-. List of Plates Vlll

List of Firmres- lx List of Appendices xi Map: Regional Geoloav Survev of the South Voisev's Bav Proiect 1 :50 000 back pocket

Chapter 1. Introduction 1.1 General Statement 1.2 Obiectives 1.3 Methods 1.4 Location and Access

Cha~ter2. Regional Geolow 2.1 Regional Settinp; 2.1.1 Makkovik Province 2.1.2 Grenville Province 2.1 -3 Superior Province 2.1 -4 Southeastern Churchill Province 2.1.5 Nain Province 2.1.6 Nain Plutonic Suite 2.1.7 Ham Lake Intrusive Suite 2.1.8 Flowers River Imeous Suite 2-2 Nain-Churchill Boundarv 2.3 Sequence of Intrusive Events 2-4 The Voisey's Bay Deposit

Chapter 3. Local Geolorry 3.1 Pants Lake Property Description 3.2 Local Unit Descriptions 3.3 Field Relationshi~s 3.4 Sample Collection

Chapter 4. Petroera~hv 4.1 Upper seauence gabbro 4.2 Coarse-mained gabbro 4.3 Black gabbro 4.4 Fine-mained olivine gabbro 4.5 Peridotite 4.6 Discussion Page

Chapter 5. Rock Geochemistrv 5.1 Analytical Techniques 5.2 Ma-ior Element Anal-ytical Results 5.2. t Upper sequence gabbro 5.2.2 Coarse-mined gabbro 5.2.3 Black gabbro 5.2.4 Fine-grained olivine gabbro 5.2.4.1 North Intrusion (VBS-97-77) 5.2.4.2 South Intrusion (VBS-97-79] 5.2.5 Peridotite 5.3 Rare Earth and Trace Eiement Analvtical Results 5.3.1 Pants Lake Gabbros-S~idermarns 5.3.2 Pants Lake Gabbros. Tasiuvak and Nain Gneiss and Lower Crust-Soidermams:- Com~arison 5 -3-3 Pants Lake-Voisev's Bay S~idermams: Cornparison 5.3.4 Ratio Profiles 5.3.5 Modeling of Estimated Parental Liciuid of North and South Gabbros with Possible Contaminant: Diamms 5.3.6 Sul~hideDevletion: Histograms 5.4 Discussion

Chapter 6. Mineral Chemistrv 6.1 Plagioclase 6.2 Olivine 6.2.1 Black Gabbro and Coarse-mained Gabbro 6.2.2 Fine-grained olivine Gabbro 6.2.3 Peridotite 6.3 Discussion

Cha~ter7. Discussion and Conclusions Geological Mode1 and Ex~iorationRecomrnendations North Gabbro South Gabbro

References

Appendices List of Tables Page Chapter 2: 2.1 Sequence of intrusive events in North-Central Labrador 13 (Arnelin et al., 1999; Fitzpatrick et al., 1998; Wardle, 1993; Wardle et al., 1997).

Chapter 3: 3.1 Summary of significant mineralization intersections (Donner Minerals, press release, November 18, 1998)

Chapter 4: 4.1 Petrographic summaries of al1 units.

Chapter 5: 5.1 a Whole rock major elements. 5.1 b Recalculated whole rock major elements with standard deviations. 5.2 Statistical analysis of identicality between units 40-42 and 41-42. 5.3 Whole rock trace and rare earth elements. 5.4 Original melt composition for the North and South Intrusions.

Cha~ter6 6.1 Microprobe olivine compositions.

vii List of Plates (Unless otherwise specified, al1 photos by H.MacDonald) Page Chapter 3 3.1 Scenic Pants Lake, taken fiom the helicopter. 3.2 Rapakivi-texture granite (photo by K-Gorra, University of Toronto). 3.3 Contaminated core. 3.4 Breccia unit with magnet/scriber for scale. 3.5 Minera1 Hill with K-Emon for scale. 3.6 "Oatmeal" texture, sample from Mineral Hill (photo by K-Gorra, University of Toronto). 3.7 Coarse-grained xenolith or dyke in fine-grained olivine gabbro fiom NDT area (photo by K-Gorra, University of Toronto). Close up of Plate 3.12. 3.8a Small scale layering in the NDT area. 3.8b Small scale Iayering in the NDT area. 3.9 Black gabbro vs. coarse-grained gabbro drill core (photo by K-Goma, University of Toronto). 3.10a Coarse-grained, fine-grained olivine gabbro contact with hammer for scale. 3.10b Coarse-grained, fine-grained olivine gabbro contact with hand for scale. 85 3.1 1 Chill zone of fine-grained olivine gabbro against coarse-grained gabbro 86 from isolated gabbro outcrop, south of Sarah Lake with pen for scale. 3-12 Coarse-grained xenolith/dyke in fine-grained olivine gabbro in NDT area 86 with C-Fitzgerald for scale. 3.13 Intrusive contact between rapakivi granite and fine-grained olivine 87 gabbro in the South Intrusion.

Chapter 4 4.1 Thin section of coarse-grained gabbro with interstitial olivine grains. 87 4.2 Thin section of black gabbro. 88 4.3 Thin section of euhedral olivine grains in fine-grained olivine gabbro. 88 4.4 Thin section of small scale Iayering. 89 4.5 Thin section of peridotite altered to serpentine. 89

Chapter 6 6.1 SEM photornicrograph of dusty plagioclase, sample #75066. Page Cha~ter1 1.1 Location map of Labrador, Canada (after Wardle et al., 1997). 91 1.2 Geology map of Labrador, Canada. 92 13 Claim map of the South Voisey's Bay project. 93

Chapter 2 2.1 Local geology map of the Voisey's Bay deposit (Li and Naldrett, 1999). 94 2.2 Mode1 of the Voisey's Bay deposit (Li and Naldrett, 1999). 95

Chapter 3 3.1 Names and location of gabbro bodies and study drill holes on the South 96 Voisey's Bay property. 3.2 Idealized profiles of gabbro intrusions if al1 units are present. 97 3.3 Profiles of the mineralized sequences (adapted fiom Kerr, 1999). 98 3.4 Profiles of study drill holes. 99 3.5 Expanded profile of upper portion of VBS-97-79. 1O0

Chapter 5 5.1 Diagrarn of Al203 vs. Si02 for al1 samples. 101 5.2 Diagram of Mg0 vs. Si02 for al1 samples. 102 5.3 Diagram of Mg0 vs. A1203 for al1 samples. 1O3 5.4a VBS-97-77, Profile of MgO, A1203 and Fe0 vs. Depth. 104 5.4b VBS-97-77, Profile of Na20, K20 and Mg# vs. Depth. 105 5.5a VBS-97-75, Profile of MgO, A1203 and Fe0 vs. Depth. 1O6 5Sb VBS-97-75, Profile of Na20, K20 and Mg# vs. Depth. 1O7 5.6a VBS-97-79, Profile of MgO, A1203 and Fe0 vs. Depth. 108 5.6b VBS-97-79, Profile of Na20, K20 and Mg# vs. Depth. 1O9 5.7 Spidergram of OIB, MORB, and Upper, Lower and Average Crust. 110 5.8 Spidergram of the North Intrusion units. 111 5.9 Spidergram of the South Intrusion units. 112 5.10 Spidergram of the North Intrusion units plus the Tasiuyak and Nain 113 gneisses. 5.1 1 Spidergram of the South Intrusion units plus the Tasiuyak and Nain 114 gneisses. 5.12 Spidergram of the North Intrusion units plus the Voisey's Bay VT and NT. 1 15 5.13 Spidergram of the South Intrusion units plus the Voisey's Bay VT and NT. 1 16 5.14 Profiles of Hf and LdSm vs. Depth. 117 5.15 Profiles of Zr, CerYb and Th/Ta vs. Depth. 118 5.16 Discrimination diagram of Th/Ta vs. Ce/Yb for al1 samples. 119 5.17 Discrimination diagram of LdSm vs. CeNb for al1 samples. 120 5.18 Discrimination diagram of La/Sm vs. Th/Nb for al1 samples. 121 5.19a Histogram of CdZr for Noril'sk basalts (Li and Naldrett, 1999). 122 Page

5.1 9b Histogram of Cu/Zr for Nonl'sk basôlts (data fiom Lightfoot et al., 1994). 5.20 Histogram of Cu/Zr for al1 sarnples. 5.21 Histogram of CuMf for al1 samples.

Chapter 6 6.1 VBS-97-75, Depth vs. Fo in olivine. 6.2 VBS-97-77, Depth vs. Fo in olivine. 63VBS-97-79, Depth vs. Fo in olivine.

Chapter 7 7.1 Mode1 of the Voisey's Bay South property. List of Anendices

Page

A. Petrographic descriptions. B. Original melt compositions-calculations. C. R-factor calculation. 1. Introduction

I .l. General Statement

The Donner Resources Limited (now Donner Minerals Limited) Voisey's Bay South property in Labrador, Canada (see Figure 1.1) hosts a mafic layered intrusion with several gossanous Ni-Cu showings. This property lies approximately 90 km south of the well-known Voisey's Bay nickel-copper-cobalt deposit that is hosted by a troctolitic intrusion belonging to the Nain Plutonic Suite (sue Figure 1.2). Atier the Voisey's Bay massive sulphide discovery by Archean Resources Limited and Diamond Fields

Resources Incorporated just south of Nain in 1993, a staking rush overtook northern

Labrador. Donner managed to acquire a block of daims covenng an area of 1500 km' in conjunction with 13 junior pmers (see Figure 1.3). Over the summers of 1995 and

1996, Stream sampling, airbome geophysical surveys, regional reconnaissance mapping, and the drilling of 50 shallow holes were accomplished. Core was sent to the

University of Toronto for petrographic analysis fiom these drill holes.

Encouraging results arose from the first two summers of field work and an agreement was forged between Donner Resources and Teck Exploration in the fa11 of

1996. Teck Exploration became the operator of the Voisey's Bay South property for the field seasons of 1997, 1998, and 1999 to date. The sumrner field programs of 1997 and 1998 were focused on detailed reconnaissance mapping over the entire project area; detailed grid mapping of al1 known gabbro bodies; ground electromagnetic, magnetic, and gravity surveys; and drilling on selected targets. 1.2. Obiectives

The petrographic report written by C.Li at the University of Toronto in 1996 spawned the idea of a Master's of Science project based on sumrner field work, petrography and Iaboratory geochernical analysis at the University of Toronto.

Originally, it was thought that an investigation of various showings throughout the property would be a worthy topic for study. However, most of the showings proved to contain only minor quantities of sulphide and it was decided that a systematic petrological and geochemical analysis of the gabbroic body that hosts the mineralization, the Pants Lake Intrusive Suite (PLIS), would be geologically insightfil as well as helpfiil in tems of exploration needs. This can be supported by the fact that the generation of magmatic sulphide deposits depend on the pressure, temperature, and the fbgacities of O and S of the whole magmatic system. The gabbroic rocks therefore should not be regarded as a separate system since the silicate mineralogy is an integral part of the complex process required in the formation of a magmatic sulphide deposit.

As the culmination of two summers spent mapping on the property and research at the University of Toronto based on the collected samples and subsequent data acquired, the goal of this study is to characterize the geology, petrography, geochemistry, and develop a working mode1 of the gabbroic intrusion.

1 -3. Methods

Three drill holes representative of the spectrum of known igneous rocks belonging to the Pants Lake Suite were selected. The drill holes were sampled at 10 m or 20 m intervals depending on the depth of hole. Al1 zones of alteration, veins, dykes, etc. were avoided in the sampling. These 25cm core samples had a small section removed for a polished thin section, then were crushed and analyzed for major, trace and rare earth elernents. This data is then to be compared with data fiom the Voisey's

Bay deposit in order to assess the econornic potential of the Pants Lake area.

1 -4. Location and Access

The South Voisey's Bay property is located on the easternmost part of the

Canadian Shield, in north-central Labrador (see Figure l.2), famous for its mgged terrain and weather that approaches fkom the Labrador Sea to the east. The area corresponds to 55" 30' N degrees latitude and 62" 00' W degrees longitude or centred about 6 150 OOON and 571 OOOE UTM on NTS maps 13K, 13L, 13M, 13N. The location of the property places it between the Nain Intrusive Suite to the north and the

Harp Lake Intrusive Suite to the south.

Access to the property is fiom Happy Valley-Goose Bay by fixed-wing aircrafi on wheels to Luc's Airstrip approximately 25 km southeast of camp, or float plane directly to Pants Lake. Access fi-om Goose Bay is also available by helicopter. 2. Reeional Ceolow

2.1. Regional Setting

North-central Labrador displays barren terrain, with the exception of protected valleys,

providing excellent outcrop exposure. Elevations extend to more than 600 m, and the

terrain has been subjected to Pleistocene glaciation (Thomas and Monison, 1991 ;

Wardle 1995).

Labrador is the easternrnost extent of the exposed Canadian Shield. Included

within Labrador are five structural provinces (see Figure 1.2): Nain (3800-2500 Ma),

Southeastern Churc hiIl (SECP)(2780- 1740 Ma), Supenor (2700-2650 Ma), Grenville

(2700-950 Ma) and Makkovik (2800- 1800 Ma) respectively (Wardle et al., 1997). The

youngest rocks in Labrador are melt rocks and breccias associated with the Mistastin

impact Crater at 38 * 4 Ma (Wardle, 1993).

In the irnmediate area of the South Voisey's Bay property only the Nain and

Churchill structural provinces are present.

2.1.1. Makkovik Province

Within the Makkovik Province there have been at least two deformation and metamorphic events of approximately 2500- 1890 Ma and 1800 Ma in age (Wardle and

Bailey, 198 1). These events produced nurnerous migrnatization and mylonitic shear zones. The northwest Makkovik province contains reworked Archean basement of the

Nain Tectonic Province that is in tum overiain by Proterozoic sedimentary and volcanic cover rocks. The central region comprises Paleoproterozoic sequences of sedimentary,

rnafic volcanic, felsic volcanic (1 860- 18 10 Ma) and granitoid intrusive rocks ( 1840-

1720 Ma). The southern and easternmost zone of this province is underlain mainly by

cornptex, polyphase, syn- to post-tectonic granitoid plutons ( 1840- 1720 Ma) and

rernnant gneissic crustal materials of approximately 2000 Ma. The gneisses fiom the

eastem part of the Makkovik Province consist of juvenile crust accreted to the Nain

craton (Wardle et al., 1997).

The southem border is in contact with the Grenville deformation. Although it is

thought to have once been continuous with the Churchill Province, it is now separated

by Helikian rocks (Wardle and Bailey, 198 1).

2.1.2. Grenville Province

The northern Grenville Province consists of a thrust belt of rock that predominantly

formed during the Labradorian Orogeny, 17 10- 1620 Ma, as part of a major period of j uvenile crustal accretion along the southeastern margin of the Precarnbrian Shield

(Wardle, 1993). This region tmncates the mobile belts of the Churchill and Makkovik

Provinces and also contains vestiges of reworked Archean pre-Labradorian crustal

gneisses and granitoids. The eastern and western terranes of the northern zone of this

province comprise rnixed assemblages of mafic, calc-alkaline granitoid intrusions and

metasedimentary gneisses (Wardle et al., 1997).

The southem Grenville Province is a younger belt of post-orogenic plutons that

are products of the ca. 1080-960 Ma GrenviIlian magmatism. The eastern terrane of

this region boasts granitic and anorthosite-mangerite-charnoclcite-granite(.4MCG) suites. The western zone also displays AMCG suites and gneisses of unknown age

(Wardle et al., 1997).

2.1.3. Sttperior Province

Only a small fragment of the eastern Superior Province is present in Labrador, and it is underlain by Archean granulite facies granitic plutons, metasedimentary and orthogneisses and less common meta-volcanic and intrusive mafic rocks. The granitic

plutons include diatexite of granodiorite-monzogranite composition. This is hown as the Ashuanipi Complex and foms al1 of the Superior Province in Western Labrador.

The magmatic activity is thought to have occurred prier to a regional tectonothermal event approximately 2680 to 2065 Ma. To the east, the gneissic domain is overlain by

Proterozoic sedirnentary rocks (Wardle et al., 1997).

2.1.4. Sort theasiern Churchill Province

The Southeastern Churchill Province is a mobile belt and comprises the southern and eastern extension of the province that underlies northern Saskatchewan, Manitoba, the

Northwest Temtories and Nunavut. It was formed by a collision between two Archean cratons. the Superior and the Nain (Wardle et al., 1997). As witnessed throughout the

Voisey's Bay South property, structural trends within this province are mainly northwest-southeast.

The south end of the New Québec Orogen (Labrador Trough) or Circum-

Ungava Geosyncline, comprising shallow to deep water sedimentary, mafic and ultramafic plutonic and mafic volcanic rocks, lies within Labrador. These rocks have been thrusted over the Archean Superior Province to the West (Wardle et al.. 1990).

The central region of this province, to the east of the Labrador Trough is largely

underlain by gneisses and supracmstal rocks that are intmded by Proterozoic granitoid

batholiths. These gneissic assemblages are thought to represent reworked Archean

basement (Wardle and Bailey, 198 1). The northeastem margin of the Churchill is

characterized by eastwards thnisting and overtuming ont0 the Nain craton that is the

result of the Torngat Orogen. The Torngat sequences include the distinctive Tasiuyak

gneiss as the axis unit and the Abloviak shear zone that denote the cotlisional boundary

between this province and the Nain Structural Province (Wardle et al., 1997).

This province is intruded by large Proterozoic AMCG complexes of the

Mistastin, Michikarnau and Harp complexes. The Nain Plutonic Suite inmides between the Southeastern Churchill Province and the Nain (Wardle et al., 1997).

Of interest to the South Voisey's Bay property and on a much more detailed scaIe, one of the main units of the Churchill Structural Province is composed of gamet- si11 imani te and sulphide-grap hite bearing quartzo-feldspathic paragneiss, the above mentioned Tasiuyak gneiss. This province also possesses a gamet-bearïng quartzo- feldspathic orthogneiss that is thoüght to intrude the paragneiss (Fitzpatrick et al.,

1998).

2.1.5. Nain Province

The Nain Province is a stable Archean craton that is in contact with the Churchill

Province on the western boundary and with the Makkovik Province on it's southern boundary. This province is separated fiom the southeastem Churchill (SECP) and

Makkovik provinces by Paleoproterozoic shear zones (James, 1997). One block of the

Nain Province, located geographically south of the Nain Plutonic Suite and the Flowers

River Igneous Suite is called the Hopedale Block (3 100-2800 Ma). The other and

northern component of this province is named the Saglek Block (3800-3600 Ma), and

lies north of the Mesoproterozoic intrusions. The two Nain blocks are similiar in

appearance and in geological units and were separated ca. 2500 Ma by ductile shearing,

granulite facies metamorphism and intrusive events (James, 1997). The western margin

of the Hopedale Block is intruded by the Proterozoic Harp Lake Intrusive Suite.

The Nain block within the region of study is the Hopedale. The Hopedale Block

consists of two greenstone belts characterized by lenticular geometries with a northeast

trend. The Florence Lake and Hunt River greenstone belts are mainly greenschist to

amphibolite-facies volcanic belts. These are intruded by Archean tonalite and

granodiorite plutons and are surrounded and also intruded by orthogneiss units (Wardle

et al., 1997).

Included within this province is the Ingrid Group, Ca. 1900 Ma, that unconforrnably overlies rocks in the Hopedale Block (James, 1997). Wardle et al.

( 1997) placed the Ingrid in the SECP as did Do~er/Teckinitially. However, Company mapping has indicated the location of the tectonic province boundary zone (see

Regional Geology Survey-Map) is different to that assumed by Wardle et al. (1997). If this new boundary location is to be believed the Ingrid unit would then lie within the

Nain Province, as in James ( 1997). in the South Voisey's Bay project area, the unit contains rnafic to intermediate volcanics and derived sedimentary rocks with greenschist to lower amphibolite facies metamorphic grade (Fitzpatrick et. al, 1998).

2.1.6. Nain Plutonic Suite

The Nain Plutonic Suite is a Mesoproterozoic plutonic suite Ca. 1350-1290 Ma, comprising basic and silicic magmas and covering 20 000 km' (Ryan, 1997). This grand intrusion obscures the boundary zone between the Southeastern Churc hi11

Province and the Nain Province in northem Labrador.

The Nain intnisive suite is an AMCG complex and consists of four main geological units: anorthosite, granite, diorite and troctolite. The anorthosite units are thought to intrude as cumulates and crystal-rich melts. Granites produced by crustal melting, appear as rapakivi-style intrusions. The troctolitic rocks are the least fractionated units fiom this suite and thus ascended fkom their parental region quickly.

Layering is observed within several of these olivine-rich intrusions. The highly fractionated end-member of this complex is the ferrodiorite that is believed to be a rernnant of anorthositic crystallization. Due to density differences, these rocks did not ascend as high in the crust as the other units and hence are not as plentifùl at the present surface level. Young mafic dykes ca. 1280 cut through the intrusion (Ryan, 1997).

Suiphide mineralization is present within this complex. The world class Ni-Cu-

Co Voisey's Bay Deposit was discovered in a troctolitic intrusion, called the Voisey's

Bay Intrusion (discussed later).

Within the South Voisey's Bay mapping area several of the basic to silicic intrusive units are present. 2.1.7. Harp Lake Intrusive Suite

Similar to the Nain Plutonic Suite, the Harp Lake Complex that borders the south of the

property is a Mesoproterozoic intrusion comprising basic to silicic magmas, although

the rnajority of the complex is an anorthositic intrusion. This large AMCG intrusion

covers approximately 10 000 km' and has been found to be 1.46- 1.45 Ga (Emslie,

1980). Ernslie et al. (1994) proposes a mode1 for the complex in which large volumes

of mafic magma caused melting of crustal materials and subsequent episodic intrusions.

The interpreted geometry of the intrusion is a flat sheet or lopolith (Wardle, 1993).

The Harp complex is older than the Nain Plutonic Suite but has sirnilar rock

units with three broad compositional groups: mafic, intermediate and pyroxene-bearing

granitic (adamellite). As previously mentioned, the interior of the suite is dorninated by

anorthosite, with leuconorite and leucotroctolite. Gabbroic bodies, some layered, are

found at the margins of the anorthosite. Youngest within this complex are adamellite or

rapakivi-style granites. Ferrodiorite dykes and west-southwest striking mafic dykes, called the Harp Dykes, are comrnon throughout the intrusion and the Nain Province

(Emslie, 1980).

Sulphide mineralization, mainty Ni and Cu showings, are found within this complex that has been explored since the 1970s (Kerr and Hinchey, 1998). The mineralization usually consists of disseminated sulphides in small, low-grade stratiforrn showings within anorthositic and gabbroic rocks and appears to be primary (Kerr and

Smith, 1998). Massive sulphides in a few showings are also found to occur in recrystallized anorthositic rocks (Kerr and Hinchey, 1998). The PGEs are also present in small quantity found in association with Ni and Fe sulphide showings, and hematite- rnagnetite disseminations are also present within anorthositic rocks (Wardle, 1993).

2.1.8. FZo rvers River Igneous Suite

The eastern edge of the South Voisey's Bay property exhibits the ca. 1.27 Ma

(Thomas and Morrison, 199 1) perdkaline granites of the Flowers River Suite (See

Regional GeoIogy Survey-Map, unit 59) that lies within the Nain Province (Wardle et al., 1997). The aeromagnetic pattern of this complex suggests a ring complex with a central core of subaerial volcanic rocks that may have been the result of a caldera-fil1 sequence (Wardle, 1993).

Small proportions of Be, Nb, Th, REES, Y, and Zr have been found in this intrusion (Wardle, 1993).

2.2 Nain-Churchill Boundary

The junction between the Nain and Churchill structural provinces has been found to be mainly tectonic (Ryan, 1996). This is a Paleoproterozoic continental near-vertical but slightly east-dipping 1.86 Ga suture zone. The last movement recorded along the suture is known as the Abloviak shear zone and dated at 1.73-1.75Ga (van Kronendank, 1993).

In northem Labrador, the distinctive marker used for locating the boundary zone is the eastem-most unit of the Southeastern Churchill Province, the Tasiuyak gneiss, that has been mylonitically foliated, lineated and contains purple gamets. In nonhem

Labrador especially, the boundaïy between Archean and Proterozoic rocks can be reliably constrained and determined on the basis of known continuous stratigraphie markers and structures. It is less certain and clearly not sharp however, from Nain Bay

to Harp Lake. The zone between the two provinces in many places is unclear due to an

imprint of tectonism on oider tectonized rocks (Ryan, 1996). The younger intrusions of

the Nain Plutonic Suite and Harp Lake Intrusive Suite also obscure this junction. The

process of locating the junction in the remainder of Labrador is based on known

relationships in northern Labrador and age dating.

In the Voisey's Bay area, samples of the Nain Plutonic Suite were dated by Nd,

Sr, and Pb methods and were found to show a significant difference fiom one side of

the extrapolated junction to the other according to the province through which the

intrusion was emplaced. This has resulted in an undulating collisional junction (Ryan,

1996). It is not known whether the suture was important as a conduit in the formation

of the Voisey's Bay Deposit, allowing metal-rich magma ascend, since the collisional

zone predates the deposit by 400 million years.

On the Pants Lake property the location of the supposed contact has been moved

further West (see Regional Geology Suwey-Map) of it's position show on earlier

regional geology rnaps. This change was based on detailed geological mapping by the

Company and geophysical data. In the property area the recently located boundary

corresponds to the eastern extent of the Tasiuyak gneiss. Wardle (personal

communication} is confident that this gneissic unit corresponds to the unit found in

northem Labrador. The diflerence in Archean and Proterozoic gneissic units is quite distinct on the detailed scale. The junction in this area is not accompanied by severe deformation. Although a few mylonitic zones have been observed, the rock units do display a strong pervasive foliation. 2.3. Sequence of Intrusive Events

Table 2.1 lists the series of major intrusive events in north-central Labrador including the North Intrusion of the PLIS.

Table 2.1. Dates of intrusions within north-central Labrador (Amelin et al., 1999; Fitzpatrick et al.. 1998: Wardle. 1993; Wardle et al.. 1997). Date /Ma) Intrusive Suite or Tectonic Rock Tpe Dated Province Michikarnau Intrusion granitoid rocks Harp Lake Intrusive Suite *Arc Lake and Fazy *granitoid plutons Lake * Snegamook Lake *granitoid pluton Grenville Province Michael Gabbro sheets gabbroic rocks Mistastin Lake Batholith granitic rocks Red Wine Igneous Suite peralkaline volcano- &tonic and alkaline ~lutonicrocks - N% Plutonic suite *Voiseyls Bay Intrusion *troctolitic *Pants Lake Suite *gabbroic rocks (North Gabbro) *Makhavinekh Lake and 'rapakivi granite Umiakovik *Jonathan Intrusion *layered gabbroic *Kglapait Intrusion *layered gabbroic *Goodnews/Newark * layered gabbroic Island *Voisey Bay- 'granitic batholith Notakwanon Nain dvke swarm mafic Harp dyke swann mafic, ferrodioritic Flowers River Suite peralkaline plutono- voicanic rocks ------Strange Lake Intrusion peralkaline plutonics 2.3. The Voisev's Bav De~osit

The magrnatic Ni-Cu-Co Voisey's Bay Deposit was discovered approximately 30 km south of Nain by two prospectors in 1993. It is located in the collision zone between

Archean orthogneisses of the Nain Province to the east and the sulphide- and graphite- bearing paragneiss of the Churchill Province to the West. Current estimates of the reserves and resources of the deposit are 124.4 x 106 tonnes grading 1.66 W.% Ni (Li and Naldrett, 1999). The mineralization is hosted in a mafic troctolitic intrusion of the

Nain Plutonic Suite called the Voisey's Bay Intrusion dated at 1333 * 1 Ma (Amelin et al., 1999) by U-Pb dating of coexisting zircon, apatite and baddeleyite- The feeder system to the West of this intrusion that hosts the sulphide mineralization is called the

Reid Brook zone.

The Ni-Cu-Co deposit is compartmentalized into an upper chamber called The

Eastem Deeps, that is separated fiom a lower charnber named the Reid Brook chamber by a feeder sheet approximately 1 km in length (See Figure 2.1; Li and Naldrett, 1999).

Specific rock types of the intrusion include Leuco-troctolite (LUT) in the lower chamber, Feeder Breccia (FB) in the Reid Brook zone, Feeder Olivine Gabbro (FOG),

Leopard Troctolite (LT) and Basal Breccia Sequence (BBS) in the feeder sheet, and in the Eastem Dceps Olivine Gabbro (OG), Normal Troctolite (NT) and Varied-textured

Troctolite are present (Li and Naldrett, 1999).

Massive sulphide mineralization is present in the "Ovoid" deposit

(600 m x 300 m x 110 m ) that occurs at the present erosional sudace level, and has been interpreted by Li and Naldrett (1 999) to be a topographic pool neighbouring the entrance to the Eastern Deeps upper chamber. Stringers of massive sulphides have also been found in the surrounding gneisses adjacent to the feeder sheet. Additional

sulphide mineralization has also been located along the entry line of a feeder into the

Eastern Deeps. The mineralizat ion comprises pyrrhotite (both hexagonal and troilite in

various proportions), pentlandi te, chalcopyrite, magnetite and minor quantities of

cubanite. These sulphides and oxide are found in or in close proximity to the BBS or

FB sequences. In both breccia units, considerable evidence indicates that substantial

interaction occurred between the mafic melt and the gneissic host rocks; the latter

appear as fiagrnents in the breccia sequences (Li and Naldrett, 1998).

Extensive olivine analysis has been performed on al1 gabbroic units and indicate

that olivines in the LUT,OG and FOG have low Ni values with respect to their

forsterite values. The NT and VT units show a large scatter although generally possess

higher Ni concentrations. The Ni content values Vary inversely to the forsterite values

in the LT unit. Al1 variations in the Ni in olivine analyses have been explained by

fractional c~ystallizationand sulphide segregation of the melt, shifis in the olivine

composition due to interaction with trapped liquid, and the re-equilibration of olivines

in the presence of sulphides (Li and Naldrett, 1999). Consequently, these analyses have

aided in constraining a mode1 of the deposit.

Sulphur isotopic values found by Ripley et al. ( 1999) indicate that the gabbroic

rocks in the Reid Brook zone could have undergone a 50% sulphur contribution fiom the Tasiuyak gneiss. Less contamination is called for in the east, which is consistent

with the lower sulphur contents of the Nain gneisses. Oxygen isotopic work also performed by Ripley et al. (1999) on the gneissic fi-agments in the breccia sequences also suggest that more contamination of the Tasiuyak gneiss in the western part of the intmsion. Together this information indicates that in the western portion of the deposit,

the Tasiuyak gneiss was definitely involved in the process of ore genesis. However, the

contribution of sulphur was probably not the sole process responsible for

mineralization. The Nain gneisses have also contributed to the melt and the subsequent

increase in silica content may have depressed the sulphide solubility in the melt (Riplsy

et al., 1999).

Re-Os isotopic data fiom the sulphide ores suggest that the parental magma was

basaltic in composition rather than picritic, and that this rnelt achieved sulphide saturation as a consequence of ingestion of radiogenic crustal units. Two percent contamination by the Tasiuyak gneiss and sixteen percent contamination by the Nain gneisses is suggested as a cause of the radiogenic Os, followed by R-factor equilibrations that upgraded the sulphide tenor during transport and especially in the

Eastern Deeps (Lambert, et al.. 1999).

The current mode1 proposed for this magmatic massive sulphide deposit (see

Figure 2.2; Li and Naldrett, 1999) is that a pulse of magma ascended fiom the source region to a lower charnber (the Reid Brook) where it fractionated to form mafic and ultra-mafic cumulates. The melt became sulphur saturated as a result of interaction with the flanking gneissic material. This magma then became depleted in chalcophile elements as olivine grains crystallized and fractionated and sulphides segregated. A second wave of magma moved into the chamber forcing the depleted meit and some sulphides upwards into an upper chamber (the Eastern Deeps) through a feeder system.

Flow within the feeder zone was most likely rapid and turbulent. Sulphides were deposited in thicker areas of the fccdcr sheet and in the entrance to the upper charnber where the flow velocity would have lessened. This second undepleted wave of magma picked up and enriched sulphides before redepositing them along the system in physical traps.

Several factors are emerging fiom recent work completed on the deposit. The

Voisey's Bay intrusion is the oldest mafic intrusion in the Nain Plutonic Suite at 1334-

1332 Ma. The intrusion involves two waves of magma with contamination of the basaltic parent melt from country rocks attributed as an important element in the onset of sulphide saturation both as a source of sulphur and by an addition of silica. Sulphide mineralization is found in a feeder system entenng a large chamber, deposited in topographie traps and due to a rapid decrease in flow velocity. 3. Local Geology

3.1. Pants Lake Pro~ertvDescription

Scenic Pants Lake (see Plate 3.1) features rolling hills, with more mgged terrain to the southem and northem extents of the property reaching heights of 600 m above sea level.

Barren hi11 tops provide excellent outcrop exposure on the property.

The Pants Lake Intrusion encompasses anorogenic plutonic rocks that were emplaced between the Churchill Structural Province to the West and the Archean Nain

Structural Province to the east (see Figure 13 and Regional Geology Survey-Map).

The two structural provinces were welded together along a tectonic junction

Paleoproterozoic in age. South of the Nain Plutonic Suite however, the contact zone is dificult to accurately identiw due to glacial overburden and does not resemble a high strain sector in the Pants Lake region. The suture zone in the South Voisey's Bay property is characterized by highly foliated and infiequent mylonitized gneisses.

3.2. Local Unit Descriptions

The intrusions in the northem area of the property belong to the Nain Plutonic

Suite and comprise granitoid rocks (unit 49), mafic dykes (unit 47), intermediate units comprising monzodiorites to monzonites and diodes (unit 46), anorthosites (unit 45) and an olivine leucogabbro (unit 43) on the Regional Geology Survey-Map. These units, notably the anorthosite, are very similar in appearance to the members of the

Harp Lake cornplex. Two units of the Mid-Proterozoic Harp Lake Intrusive Suite have been mapped

on the southem border the propem. These include a rapakivi-style granite (unit 39) of

rounded centimetre-scale potassium feldspar grains mantled by plagioclase with an amphibole matrix (see Plate 3.2) and morthositic rocks (unit 35).

Locally, the Churchill Structural Province includes a hornblende-biotite mafic tonalite gneiss (unit 2c) that occasionally possesses relict granulite facies minera1

assemblages (Fitzpatrick et aI., 1998), and a foliated granitoid (unit 2d). Also present is the graphite and sulphide-bearing Tasiuyak paragneiss (unit 2b) and a quartzo-

feldspathic orthogneiss with megacrysts of potassium feldspar (unit 2a). The Ingrid

Group (unit 2i) of metamorphosed volcanics and sedimentary rocks is located on the eastern boundary of the property

In the vicinity of the study area, the Nain Province comprises Archean gneissic components of an orthogneiss (unit 1 a), paragneiss (unit 1b) and a melanocratic to leucocratic tonalite gneiss (unit lc), al1 of which display excellent banding and gneissosi ty.

The host rocks for the nickel-copper-cobalt rnineralization on the Voisey's Bay

South property belong to the Pants Lake Intrusive Suite. This mafic suite consists of two areas of gabbroic rocks with a long, thin gabbroic body in-between. For ease of discussion, the gabbroic members in the property area have been denoted as the North

Intrusion, South Intrusion, Worm Gabbro and the Doughnut Gabbro (see Figure 3.1).

The Worm and Doughnut gabbros are similar in appearance and believed to belong to the North intrusion but these names will be retained as geographical locators. The

Northem intrusion is fiirther subdivided into the NDT, Northern Abititi and Happy Face, GG areas. To the north-west of the South gabbro is the Mineral Hill showing.

From the results in this study, the North and South gabbros appear to be separate

intrusions.

The PLIS comprises a series of layered intrusions, which when fiilly developed consist of an upper sequence of altered gabbro (unit 42hbl), coarse-grained gabbro also refex-red to as a leucogabbro (unit 42), "black gabbro" (unit 40), fine-grained olivine gabbro (unit 4 1), and peridotite (also unit 4 1). In this study unit 4 1 has been separated into 4 1s and 4 1n indicating the South gabbro and the North gabbro respectively. Unit

4 1s also contains an upper and lower unit denoted as 4 1su and 4 1sl. Within the intrusion sequence, contarninated units (unit 4 1corn) (see Plate 3.3) and brecciated units (unit 42bx, 41bx) (see Plate 3.4) with a fine-grained mafic matrix, gneissic clasts and occasional amydules filled with quartz and calcite crystals are found. Pegmatitic zones are also found anywhere in the sequence however, mainly seem to be concentrated in the coarse-grained gabbro unit (see Figure 3.2). The pegrnatitic zones are thought to represent late-stage crystaliization of trapped intercumulus liquid, perhaps volatile-rich.

The rnineralized sequence found in the North intrusion is generally broken down into an upper and lower sequence consisting of a matrix containing sulphides and gneissic fragments (see Figure 3.3). The upper unit typically has a coarse-grained matrix with elliptical gneissic fragments that form bands parallel to the basal contact.

The lower sequence includes a leopard-texnired gabbro (sulphides surrounding clinopyroxene oikocrysts), fine grained olivine gabbro with fragments and at the base a barren unit either overlying sulphides or the footwall gneisses. The South intrusion does not have the complex mineralized sequence of the north but does contain a

pendotite unit that occurs above sulphide mineralization.

Gossanous outcrops are abundant across the property (see Plate 3.5) and at the

time of writing several significant intersections of mineralization have been found in

drill core (see Table 3.1). The mineralization consists of massive and semi-massive

pyrrhotite, a significant quantity of the pyrrhotite is troilite (Naldrett et al., 2000),

pentlandite, cubanite and chalcopyrite. Cobalt is included in the pentlandite crystal

structure. Mineralization seems to have a propensity to occur where gabbro is underlain

by the Tasiuyak gneiss as opposed to the orthogneiss. The contaminated and

mineralized units of the Pants Lake Intrusion is the topic of a Master's of Science

project undertaken by Rod Smith at Mernorial University that began in the surnmer of

1998.

1 Table 3.1. Surnmary of significant mineralization intersections found in ddlcore. Source is *essrelease fiom Donner Minerals Limited, November 18, 1998. Drill Descript ion Mineralization

at the base of gabbro, semi-massive, 0.2m 4.5% Ni, 2.6% Cu, 028% Co in the footwall gneisses, massive, 0.3m 3.4% Ni, 0.5% Cu. 0-46%

in gabbro/troctolite, massive, 1 5.7m 1.13% Ni, 0.78% Cu, 0.2%Co in footwall gneisses, massive, 1.1 m 1 1.8% Ni, 9.7% Cu, 0.43%Co in gabbro/troctolite, massive, 1m 1.93% Ni, 1.64% Cu, 0.3%Co The upper sequence gabbro is composed of highly altered minerals, plagioclase and hornblende. In outcrop this unit has distinctive colouration with bright green alteration minerals after clinopyroxene and chalk-white plagioclase. As this unit is very similar in many aspects to the coarse-grained unit, it is suspected that the alteration of this unit is due to the movement of fluids to the top contact of the gabbro body. Kerr

( 1999) has noted that in drill core, this sequence is especially prevalent beneath a gneissic cap rock.

The coarse-grained gabbro is light-grey coloured in outcrop with white plagioclase; it may have a slightly msty colour in olivine-rich zones. Outcrops of this unit display an "oatmeal" texture (aggregates of plagioclase grains surrounded by cpx grains *olivine) (see Piate 3.6). This unit contains approximately 75% plagioclase

(andesine-labradorite), 520% clinopyroxene, 5- 15% olivine with minor arnounts of biotite, rnagnetite, ilmenite, and apatite.

The percentages of the main components in the fine-grained olivine gabbro are distinct fiom those of the coarse-grained gabbro, being 60-75% plagioclase, 20-40% olivine, 1-5 % clinopyroxene and rninor biotite, magnetite, ilmenite and apatite. This unit appears red/orange in outcrop due to the high percentage of olivine (see Plate 3.7).

The fine-grained olivine gabbro in the NDT area displays layenng on the centimetre scale (see Plates 3.81 and 3.8b). This kind of layering is not observed elsewhere on the property except for a small area of non-uniforrn, chaotic layering found on the banks of the Adlatok River in the fine-grained olivine unit of the south gabbro. The NDT layers are defined by a darker-coloured layer at the base grading upwards into lighter-coloured minerals. Larger metre scale layering is seen in the coarse-grained unit in some areas, for example NDT and Mineral Hill (see Plate 3.5). The layering for al1 units of the

North intrusion dips at approximately 20" to the north and north-east.

The black gabbro appears to have the same composition as the coarse-grained gabbro but the mafic minerals appear to have undergone slightly enhanced alteration.

The outcrops of this unit appear black or dark grey with dark green alteration rirns around olivine grains (see Plate 3.9). For reasons unknown, this unit hosts the most significant intersections of sulphide rnineralization.

The pendotite unit, by definition, contains 40% or greater olivine (Streckeisen,

1976) with minor clinopyroxene, plagioclase and sulphides and is fairly extensively altered to serpentine and iron-oxides. No peridotite units have been found in the north gabbro drill holes, and no outcrops of this unit have been observed to date in either gabbro body.

3 -3. Field Relationships

A zircon U/Pb age of the northem intrusion has been found by Dr. G. Dunning at the

Mernorial University of Newfoundland to be 1322.2 * 2 Ma (Fitzpatrick et al., 1998).

This result establishes that the northem intrusion is within the span of ages found for the Nain Plutonic Suite. This date is younger than the Voisey's Bay intrusion that crystallized at 1333 * 1 Ma (Amelin et al., 1999), and older than the Mushua Intrusion, 13 17 * 1.4 Ma (Amelin et al., 1997) that is located north of the Voisey's Bay intrusion.

An age date for the South Intrusion of the PLIS is not available at the present time.

The upper contact of the North Gabbro outcrops immediately adjacent to the intermediate intrusive units of diorites and anorthosites belonging to the Nain Plutonic Suite, but is not seen in direct contact. The northern gabbro body is thought to dip below the gneisses to the east- The basal contact is seen in the NDT area and perhaps along the eastern limb of the body where the Happy Face, GG and Major General showings occur. The Worm Gabbro body is most Iikely a basal contact as sulphide rnineralization is visible on the north end of the body; on the West side of the "worm".

The Worm Gabbro appears to dip beneath gneisses to the east but exposure of this contact is covered by till.

In places an intrusive contact separates the fine-grained olivine gabbro and the coarse-grained gabbro (see Plates 3.10a and 3.10b) in the NDT area of the North

Gabbro but chi11 zones are not present in order to indicate which unit is younger.

Closer to the suture zone to the east, isolated outcrops display chi11 margins of the fme- grained gabbro against and intmding into the coarse-grained upper gabbro (see Plate

3.1 1). Xenoliths or dykes of the coarse-grained gabbro also occur in the fine-grained red gabbro (see Plate 3.12). In drill core the coarse-grained unit has been observed to intrude the fine-grained unit within the northern intrusion. It is assumed from the field relationships, geochemistry and textures observed in thin section that the coarse-grained gabbro is a fiactionated, derivative of the magma that gave rise to the fine-grained unit.

However, they are close in age and contact relationships in the field remain ambiguous.

The contact between the fine-grained olivine gabbro and the black gabbro is intrusive in the Northern Abitibi area, but the 1998 drilling program did not conclusively indicate that the black gabbro is a younger unit. Kerr (1999) summarized the relationship by describing the black gabbro as a distinct unit that is in close temporal association with the fine-grained unit. The southem extent of the black gabbro unit in contact with the coarse-grained gabbro may be gradua1 as outcrop exposure of the relationship between the two units was not found.

The upper contact for the fuie grained olivine gabbro of the south intrusion is visible in outcrop as an intrusive contact with the Harp rapakivi granites (see Plate

3.13) in the southern part of the property, attesting to the younger age of the gabbro.

The basal contact of the south gabbro has only been observed in drill core approximately 760 m below the present surface. Sulphide accumulations are present as at the base of the northern intrusion. Another zone of sulphide occurs in drill hole 79, above the basal contact of the sill. This probably marks the base of a si11 that has intruded along the upper contact of the southern gabbro.

Rocks younger than the Harp Suite within that complex inchde a dyke swarm of olivine diabase Harp Dykes. Ernslie (1980) describes the Harp dykes that transect the complex as sub-vertica1 however, one is described as "[a] sheetlike body [that] intrudes the northwestem part of the Arc Lake adamellite north of Border River and dips northerly at 20 to 25 degrees". This particular Harp dyke corresponds to the Cartaway

Intrusion (Kerr, 1999) approxirnately 3 km south of Pants Lake that is supposed to resemble Pants gabbro texturally (A-Kerr, persona1 communication) and shares the common dip angle. This description also applies to the Doughnut Gabbro which was mapped in the sumrner of 1998 within the rapakivi textured granites of the Harp Lake

Complex, approximately 5 km south-east of the south limb of Pants Lake (see Figure

3.1). This intrusion actually more closely resembles a "Y" or sling-shot shape, but the name remains. This intrusion also displays the "oatmeal" texture associated with the

Pants gabbros and shows a gentle dip to the north. Structural trends in the gneisses are generally northwest-southeast to north- south. Throughout the gneisses on the property mylonite, and shear zones are observed with north-south and younger east-west orientations. Late-stage, high angle faults are also observed throughout the property, clearly post-dating the crystallization of the gabbroic bodies.

Synthesizing al1 field relationships and the newly-rendered age dates of the

North gabbro indicates that the North Intrusion could be associated with the Nain

Plutonic Suite. The relationship is not so clear with the South Intrusion. It is not known if the South Intrusion is older/younger or contemporaneous with the North

Intrusion. tt could also be part of the NPS to the north but rnay also be a late component of the Harp complex. This is the first suggestion that the two intrusions are distinct. In al1 previous work the intrusions were considered to be part of the same system.

3.4. Sample Collection

The three drill holes chosen for this study span the property and contain variable thicknesses of gabbro. Holes VBS-97-75 and VBS-97-77 (see Figure 3.1) are fiom the northem intrusion of the property, in the Northern Abitibi and NDT areas respectively.

The third study hole, VBS-97-79,is fiom the southem intrusion (sec Figure 3.1). In the

Northem Abitibi area, hole VBS-97-75 collared in black gabbro, hole VBS-97-77 in the northern NDT area collared in upper sequence gabbro. VBS-97-79, just over 1km east of Mineral Hill, collared in quarto-feldspathic paragneiss and intenected olivine gabbro at depth. Whole core samples of 25cm were taken up to depths of 139m, 428m and 695m from the drill holes respectively (see Figures 3.4 and 3.5). Holes 75 and 77 were sampled at 10m intervals, while due to the depth, hole 79 was sampled at 20m intervals for a total of 88 samples. This sampling method was thought to be the best technique in order to achieve a systematic stratigraphie interpretation of the gabbroic intrusion. 4. Petroeraahv

Ninety polished thin sections were examined. Results of the gabbroic units are surnmarized in Table 4.1. Modal proportions are based on visual estirnates and may be slightly different to field estimates given the limited size of a thin section. See

Appendix A for individual sample petrographic descriptions.

4.1. Umer seauence gabbro (unit 42hbl)

The upper sequence gabbro displays the same textures as the coarse-grained gabbro and is therefore considered to be a highly altered counterpart of this unit. Originally a plagioclase cumulate, alteration to amphibole as well as serpentine, chlorite and sericite is observed. Some minerals are difficult to identi* due to the alteration however the originally texture can still be observed and is identical, except for alteration, with unit

42.

4.2. Coarse-grained gabbro (unit 42)

Unit 42 crystallized as a plagioclase orthocumuIate with late intercumulus clinopyroxene, a second generation of plagioclase, and olivine (see Plate 4.1).

Pegmatitic patches pervade the unit. Plagioclase is present as euhedral to subhedral tabular crystals and anhedral grains that can be concentrically zoned as well as posessing poIysynthetic twins. The clinopyroxene grains display a pink to light-green pleochroism which may be indicative of elevated Ti02. Olivine grains are anhedral interstitial grains that crystallized late in the evolution of the melt. The rocks are

reasonably fiesh, although sericitization of plagioclase and the sli@t serpentization of

olivine grains is noticeable in a small nurnber of sarnples. Magnetite is a rninor

constituent. This rock may be classified a leucogabbro by the high proportion of

plagioclase.

4.3. Black gabbro (unit 40)

The coarse-grained gabbro unit and the black gabbro unit share many characteristics

(see Plate 4.2) This unit is a plagioclase orthocumulate with late stage clinopyroxene and olivine grains. Pegmatitic patches also occur throughout as in the coarse-grained gabbro unit. Brown biotite is a rninor component, in close association with the minor magnetite constituent, or altered to chlorite. Minor serpentinization and sericitization is seen as reaction rims around olivine and plagioclase grains. Below 80 m, although the rock remains coarse grained, ohvine grains are euhedral and occur as clusters in

interstitial spaces. Strain fractures are apparent in clinopyroxene, and plagioclase grains possess strained and folded polysynthetic twins close to the bottom of the drill hole.

The "black" colour witnessed in outcrop is seen in thin section to be derived

from the inclusion of rnicroscopic black specs within the plagioclase and pyroxene grains giving these grains a "dusty" appearance. It is not possible to identiQ the inclusions by petrographic microscope. A scaming electron microscope study of the black gabbro will be discussed in Chapter 6. 4.4. Fine-mained olivine gabbro (unit 41 1

The distinctive mineralogy and petrography of units 41 and 42 was very helpfiil in detailed mapping of the gabbro body. Units 4 1south and 4 1north are a fine-grained olivine gabbro with fairly unifom texture. The rock is an olivine-plagioclase orthocumulate in which euhedral, early-formed olivine grains appears to have been succeeded by the crystal lization of olivine and plagioclase and then late clinopyroxene

(see Plate 4.3). Minor constituents include: biotite, magnetite, ilmenite and apatite.

Most of the samples are very fiesh. The textures of the north and south gabbros are identical, although the south unit generally is finer-grained. Plagioclase laths displays polysynthetic twinning and zoning. Clinopyroxene lacks zoning and cleavage and is a pink-brown colour suggesting that it is titaniferous. Biotite "shadows" surround oxide grains. In a strict sense, several of the fine-grained olivine gabbro samples should be classified as troctolite but for lack of confision they are classified by this unit name.

The 400 m mark of VBS-97-79 is highly altered. This separation coincides with a fault or shear zone as 8 m of serpentine veins and highly sheared rocks are visible in drill core. Slickenslides are also apparent in the drill core on the surfaces of serpentinized fractures indicative of minor strike-slip motion.

Layering observed in outcrop is the result of higher concentrations of mafic minerals, olivine and clinopyroxene, that have undergone serpentinization and alteration to oxides (see Plate 4.4). 4.5. Peridotite (unit 41)

The peridotite unit is assigned to unit 41south and is the most primative rock type witnessed in this collection. This unit in thin section is quite distinct from the fine- grained olivine gabbro and consists primanly of 2-3 mm cumulate olivine grains that have been subsequently heavily altered to serpentine, chlorite and epidote (See Plate

4.5). For these reasons the author has distinguished this rock type as a subunit of unit

41.

This is a mesocumulate rock; interstitial plagioclase and clinopyroxene are minor components. Plagioclase grains display undulose extinction and polysynthetic twins, and subsequently have undergone sericitization and saussuritization. Fractures are evident that continue through pyroxene and olivine grains. Accessory minerals consist of: orange biotite, magnetite, ilmenite, pyrrhotite, pentlandite and chalcopyrite.

The sulphide and oxide minerals comprise less than 5 modal % of the rock. Troilite is present and imparts a weave-like texture to the grains. Pentlandite also occurs as granular masses a1 ongside chalcopyri te and pyrrhotite; along grain boundaries.

Lamellar twinning is observed in both pyrrhotite and magnetite. Ilmenite is present as lameilae within magnetite grains. - - Table 4.1. Chari )f petrographic sides of gabbroic units. Rock Type Mineralogy Pro~ortion Grain Size Texture UPP~~ chlorite patches of high fine 'plagioclase Sequence plagioclase proportion of 5- 15- cumulate Gabbro sericite alteration fine * highly altered (Unit 42alt) serpentine (2') minerals, fine magnetite (2') otherwise same 2mm amphibole (2') as unit 42 1-2mm Coarse-grained plagioclase 75% and up S-l5mm,l- 'plagioclase Gabbro clinopyroxene 5-20% 2mm cumulate (Unit 42) olivine 5- 15% 2- 1Ornrn 'interstitial biotite minor 2- I Omm olivine + cpx magnetite minor fine 'pegmatitic ilmenite minor fine pa tc hes fine Fine-grained plagioclase 2-Sm. *cumulus Olivine Gabbro olivine 0.5mrn euhedral (Unit 4 1 ) c 1inopyroxene 2-5mm olivine + plag biotite fine *late cpx magnetite fine ilmenite fine Black Gabbro plagioclase 5- 15mm *cg same (Unit 40) clinopyroxene 2-10mm texture as 42, olivine 2-5mm some as 4 1 opaques (Fe- microscopic oxides) (fraction of pm)

. - ~eridotite olivine >40% 2mm *ohvine (Unit 41) plagioclase 10% 1mm cumulate cl inopyroxene rninor OSmm 'altered to biotite trace fine serpentine pyrrhotite 5% 1-2mm sementine high fine - - -

4.6. Discussion

The thin section analysis was iùrther evidence to support field-based hypotheses that the fine-grained and coarse-grained gabbro were separate units. The samples were detected to include ortho- to mesocumulate rocks and comprise leucogabbros, gabbros, olivine gabbros, troctolites and peridotites. For simplicity, the unit names are retained. 5.1 . Analvtical Techniques

Al1 samples were crushed and prepared at the University of Toronto. Whole rock major

elernents along with six trace elements: Rb, Sr, Y, Zr, Nb and Ni, were detemiined at

Activation Laboratories using x-ray fluorescence. Copper was also determined at the

Activation Labs by aqua regia extraction in order to find the concentration in ppm

levels. Though the samples for this study contain mainly silicate minerals, the aqua

regia method was selected as the appropriate method to achieve the desired detection

level as it would measure the amount of Cu in the sulphide minerals. The amount of Cu

that would be retained in silicate minerals is neglible. The trace and rare earth element

concentrations were determined by neutron activation analysis at the University of

Toronto.

X-ray fluorescence involves a solid sample process of analysis. A small arnount of each cmshed and powdered sample is compressed into a powdered pellet for major elernent analysis or is fused into a glass disk for the analysis of trace elements (Jenner,

1996). An x-ray tube is used to irradiate the sample and produces secondary x-rays

(Klein and Hurlbut, 1993). The emission of x-radiation fiom the secondary x-rays is called x-ray fluorescence. An x-ray emission spectrum is produced fiom the energy that is absorbed by atoms of the elements present within each sample. As the samples absorb energy, electrons leave the inner shells which are then re-filled. Electrons emit energy in the form of x-radiation as they move fiom higher to lower energy levels. Individual elements have characteristic spectral lines that correspond with specific

wavelengths superimposed on a low-intensity continuous background spectnim where

the peak height is proportional to intensity. Quantitative analysis involves the

cornparison of x-ray intensities (ie. height of peak) for each elernent of a known

standard, with the elemental x-ray intensities on the spectnim from the given samples.

Peak heights are calculated by counting the intensities of the background near the peak

and the peak itself. The peak height represents the intensity of the elements present,

which is then used to determine the concentrations with appropriate corrections for the

matrix effects. This method of chemical analysis is usehl for the detennination of

major elements and is sensitive to some trace elements in the ppm range (eg. in this

study Rb, Sr, Y, Zr, Nb and Ni) because of low background intensities (Klein and

Hurlbut, 1993).

Neutron activation analysis is extremely usefùl for the determination of the

concentration of trace and rare earth elements due to the high degree of sensitivity and

lack of matrix effects, especially for elements that have historically been difficult to

analyze using solution chemistry or XRF, for example Th, Hf and Ta (Potts, 1987).

Samples are uncomplicated to prepare as they only have to be crushed to powder and

for this study weighed out to approxirnately 250 mg and packaged.

Instrumental neutron activation analysis involves first irradiating the samples in

a nuclear reactor, in this case, the Slowpoke nuclear reactor at the University of

Toronto. This activation produces a number of radioactive isotopes as a result of

various neutron-absorbing nuclear reactions. Given the variance of half-lives of particular elements, measurement of the gamma-ray spectra takes place in two stages, 7 days and 40 days after irradiation. A solid-state germanium gamma-ray detector is used to identiQ specific isotopes by their gamma-rays of characteristic energy and quantitative determinations can be obtained by measuring the area under the photopeaks in the spectra in conjunction with a signal accumulation counting system. The spectra is compared to known standards that are prepared and treated in the same manner as the other samples.

5.2. Major Element Analyticai Results

ïhe detection lirnits, as quoted by Activation Labs, for the whole rock major element analysis by XRF is 0.01%. The same analytical technique has detection limits for Rb,

Sr, Y, and Nb at 2 ppm, 5 ppm for Zr, and 1 pprn for Ni. Aqua regia extraction provided detection lirnits for Cu of 1 ppm. instrumental neutron activation analysis has the following standard detection iimits for a coaxial detector: La 0.5 ppm, Ce 1.5 ppm,

Nd 15 ppm, Sm 0.2 ppm, Eu 0.5 ppm, Tb 0.17 ppm, Yb 0.34 pprn and Lu 0.07 pprn

(Jenner, 1996). Results of major element analyses for each geological unit are listed in

Table 5.la along with 2 standard deviation errors (Table 5.lb). For al1 calculations and graphing, the whole rock major element data were normalized to 100% anhydrous shown in Table 5.lb. The Fe203 and Fe0 concentrations were calculated from

Fe203total concentrations in the ratio of 0.10: 1.

Figure 5.1 of Al203 vs. Si02 displays a positive association between Si02 and

A1203 contents. The most primitive rocks have the lowest contents of both oxides as exemplified by the peridotite unit. Figure 5.2 exhibits an increase in Si02 content with decreasing Mg0 content. Figure 53 shows, as expected, that A1203 decreases with

increasing Mg0 concentrations.

5.2.1. Upper Sequence Gabbro

The upper sequence gabbro sample has the highest Si02 content at 49.86 wt%, but is

only 1 wt% highter than the couse-grained gabbro unit and black gabbro. The

concentration of other major elements of the upper sequence gabbro are again generally

comparable to the coarse-grained and black gabbro units. Of al1 the gabbro units, this

sample posesses the highest Na20 and K20 concentrations and the lowest Fe203 and

FeO.

5.2.2. Coarse-gruined gabbro

The whole rock major elements of unit 42 generally show a high dispersion of values due to the coarse grain size and cumulate nature of these samples. The major element concentrations are consistent with the petrography which indicates that the rock is a plagioclase cumulate with minor mafic rninerals (See Figure 5.4a). Figure 5.4b displays fairly constant contents of K20 and Na20 W.%. A low concentration of

Na20 W.% is visible at 30 m. This point corresponds to a low value of Al203 and high values of Mg0 and Fe0 W.%, indicating that the sample is rich in mafic minerals and poorer in plagioclase than the rest of the unit. The fractionation trend represented by Mg #, seen on Figure Wb,decreases in value fiom 0.5 at the base of the coarse- grained unit to 0.3. This would suggest a roughly normal fractionation process with the top-most samples displaying the highest degree of fractionation, since the Mg # decreases as fractionation proceeds. Samples numbered 75 1 l8,75 1 19,75 124 and 75 125 fiom VBS-97-79 have been alocated with unit 42 as their chemistry is more akin to this panicular unit.

5.2.3. Black gabbro

The black gabbro and coarse-grained gabbro units share many sirnilarities in their chemical make-up. The major elements of the two units are in close accord for the compounds A1203, Fe203, FeO, Mg0 and Cao. The high A1203 + Ca0 4 Na20 values indicate that unit 40 is plagioclase-rich. The A1203 wt% values are at the low end of the anorthosite range and are slightly higher than the other gabbro units, reflecting the high modal percent of plagioclase (See Figure SSa). Concentrations of the other oxides are ail within the gabbroic range but also reflect the plagioclase-rich mineralogy (See Figures 5.Sa and SSb). The Mg # seen on Figure SSb, is fairly constant at 0.4 fiorn the base of the hole up to 70 m depth where the value decreases to

0.3 towards the top. The low numbers imply a reasonably fiactionated magma.

A statistical test of identicality performed on the black gabbro and coarse- grained gabbro confirmed the sunilarility of chemical constituents. An F test was performed in order to substantiate that the variances of the two units were equal. The critical value for one group having 13 samples and the other having 10, at 1 % significance level is 5.1 1 (Davis, 1986) with a one-tailed distribution. The values had a range of 0.09 to 84.9 (See Table 5.2), therefore the T test of identicality coutd only be performed for MnO, P205 and Ti02. This serves to illustrate that the two units are not identical and that the black gabbro rnay then be a separate pulse within the northem gabbro. 5.2.4. Fine-grained olivine gabbro

The sub-units of this categorization, with the exception of the peridotite, al1 contain similar abundances of major elements that is the consequence of the major phases cornprising the rocks.

5.2.4.1. North Intrusion (VBS-9 7-77)

The unit 4 ln averages 46.98 W.% Si02 and 9.19 wt.% MgO, consistent with the plagioclase and olivine abundances. In a plot of Mg0 W.% versus depth (Figure 5.4a), this unit shows increasing values tiom approximately 400 m depth up to 275 m where the trend abruptly reverses over 50 m, then illustrates decreasing Mg0 values from 225 m up to the top of this unit. Figure 5.4b displays a wide range of values for Na20

W.% that correlate to scatter exhibited on the A1203, Fe0 and Mg0 wt.% profiles, indicating that variations are due to change in the plagioclase/mafic mineral ratio.

The Mg # increases fiom the base of hole 77 from a value of approximately 0.35 to approximately 0.55 about 175 m depth (Figure 5.4b). This is a reverse fractionation trend since the Mg # decreases as fractionation proceeds. Upwards, to the top of the drill hole, the value of the Mg # decreases in a normal fractionation trend to a low number of 0.3. The bottom 200 m of this drill hole appears to have had a constant influx of new magma. Only slight scatter in the values are present in the upper portion of the hole indicating that perhaps a few pulses of new magma occurred.

5.2.4.2. Sourh Intrusion (VBS-97-79)

The major element contents on Figures 5.6a and 5.6b reflect the plagioclase and olivine mineralogy for units 4 1su, 4 1sl and the pendotite subunit. A roughly normal fractionation trend represented by the Mg # is seen on Figure 5.6b. From the top of the peridotite unit to approximately 500 m depth the Mg # decreases to 0.5. This number then increases very slightly up to the 400 m division, followed by a gradational decrease to 0.4 at 275 m depth, where it remains fairly constant to the top of the drill hole. The srnall scatter may be the result of influxes of new magma. At approximately

250 m in the upper zone, an anomalous point is obvious in al1 plots. It appean to be a very different, highly fractionated magma (Mg # of 0.3) that is intmding this less fractionated body. Pulses of new magma are minor fluctuations in the fiactionation trend unlike the anomalous point at 250 m depth.

5.2.5. Peridotite

The highest concentration of iron and magnesiurn oxides are found in the peridotite unit indicative of the olivine-rich composition. Consequently, the contents of the other oxides are lower than al1 other units notably Si02 and A1203 (See Figures 5.6a and

5.6b). The Mg # plotted on Figure 5.6b shows the highest value averaging 0.6. This is the highest and thus least fractionated value of al1 study samples.

5.3. Rare Earth and Trace Element Analytical Results

Table 53 lists the whole rock trace and rare earth element compositions. Figure 5.7 displays average trace elements concentrations for the upper crust, lower cmst, average cmst, MORB and OIB (Taylor and McLeman, 198 1; Weaver and Tamey, 1984;

Saunders and Tarney, 1984; and Sun, 1980). 5.3. I Pants Lake Gabbros-Spidergrams

Average values for each of the units associated with the North Gabbro, units 40,42 and

4 ln are ploned on Figure 5.8. The four samples fiom VBS-97-79 classified as unit 42

are plotted along with the North Gabbro units. These four units al1 have very similar

spidergram patterns. Looking at the patterns overall, striking positive Sr and Eu

anomalies are evident for each pattern implying a significant addition of plagioclase.

Very low concentrations of U imply that the element was oxidized to a +6 valence state

where, as it is soluble, it was leached out with respect to Th. The units al1 show

approximately 20 times the primitive mantle values of alkali elements which may be

due to contamination with crustal matenal; indicative of continental tholeiites. The

right, least incompatible, end of the pattern is flat with low concentrations of the heavy

REEs. Niobium and Ta values are also very Iow.

The spiderplots patterns for averages of the South Intrusion units including:

4 1 su, 41 sl and 4lperid al1 possess similar characteristics as seen Figure 5.9. This plot

exhibits the low U concentrations witnessed in the spiderplot for the North Intrusion.

Units 4 1su and 4 1 SI have the sarne shape of pattem although 4 1su is higher indicating

that it has not been dhted with as much plagioclase as 41sl. The two fine-grained

gabbro units display high Sr values but only 4 1 sl exhibits a positive anomaly indicative

of the presence of plagioclase. The peridotite unit has a slight Eu anomaly but a

negative Sr anomaly that agrees with the less plagioclase-rich mineralogy. The main difference between the two spiderplots is witnessed on the right end of the figures,

where the south gabbro units depict a steeper pattern than the north gabbro units, fiom

P205 through to Lu. 5.3.2. Pan ts Lake Gabbros, Tasiuyak and Nain Gneiss and Lorver Crut-Spidergrarns:

Cornparison

Gneissic data used to establish a possible contamination source for the gabbros in this study is from the Voisey's Bay area; ie. not local and may have slightly different compositions than those of the South Voisey's Bay area.

The north gabbro units plotted against the two gneiss units are displayed in

Figure 5.1 0. No similarities are immediately obvious however, the Tasiuyak gneiss does not appear to be a contender for a conmbution of Th with values close to 300 times that of the primitive mantle compared to 4- 10 tirnes as exhibited in the gabbroic units. The Nain gneiss does have similar Th concentrations as the other unit. One interesting observation of the Nain gneiss pattern is the positive Sr and Eu anomalies that indicate that this may be a metarnorphosed anorthosite unit since felsic rocks do not have a positive Eu anomaly. The lower cmst values of U and Th are similar to the PLIS sarnples.

The South Intrusion samples plotted along with the Tasiuyak and Nain gneisses in Figure 5.1 1 again shows that no sources of contamination are imrnediately obvious except that again the Tasiuyak gneiss has too high a concentration of Th to be a contributer of that element. Both gneissic units are sirnilar to the south gabbro concentrations of elements on the right end of the pattern, specifically: Zr, Eu, Y, Tb,

Yb, and Lu. The five units al1 share the steeper dope displayed on the more compatible end of the pattern unlike the north gabbro samples. The lower crust again displays similar values of U and Th to the Pants gabbros. 5.3.3. Pants Lake- Voisey 's Bay Spidergram: Cornparison

Figure 5.12 displays pattems for averages of Voisey's Bay varied-texture troctolite and normal troctolite plotted with the North Intrusion samples. The patterns have similar positive Sr and Eu anomalies indicative of plagioclase accumulation. The VT unit does not appear to be as depleted in U as the Pants Lake units, but the Voisey's samples have lower Th values. The North Intrusion units have almost identical P205 contents as the

VT and NT but they do not share the dope of the nght end of the spidergram.

South Intrusion samples plotted with the Voisey's Bay average values for the W and NT units are seen in Figure 5.13. The Voisey's Bay samples again have positive Sr and Eu anomalies and share the shape of the pattern with the south gabbro units, from

Nd to Lu. Low U concentrations are present in the NT unit but, unlike the Pants samples, is accompanied by low Th.

5.3.4. Ratio Profies

Zirconium and Hf are incompatible elements into the main phases which are fractionating in the study gabbros; plagioclase and olivine. Therefore, the concentrations of the incompatible elements should increase as fiactionation proceeds.

However, as the study samples are cumulates, napped liquid will reequilibrate with crystallized minerals and alter their initial composition. Profiles of these two element versus depth shows the high degree of scatter (Figures 5.14 and 5.15). These trends do not represent fiactionation trends due to the et'fect of trapped liquid.

The value of ratios of trace elernents should not vary significantly throughout a given unit, as the ratios do not depend on the amount of trapped liquid. The ratio of

La6m versus depth for the three drill holes is plotted in Figure 5.14. This figure displays fairly constant trends for each hole with a value of approximately 2.2 for the

north gabbro (VBS-97-75 and VBS-97-77) and 3.0 for the south gabbro (VBS-97-79).

Figure 5.15 displays the ratios of CelYb and Maversus depth. The value of CeNb

is approximately 7.0 for the north gabbro units and 22.0 for the south gabbro except for

the four sarnples that have been classified as north intrusion sarnptes. These four

samples also have a CeNb value of approximately 7.0 with no indication of mixing in-

between the two sills. The ratio of Maalso gives a constant value for the north

gabbro samples including the four samples fiom drill hole 79 with a value of

approximately 4.0. This value is approximately twice that of the south gabbro value

that displays a value of 2.0.

5.3.5. Modelling of Estimated Parental Liquid of North and South Gabbros with

Possible Conraminanf: Diagrams

As indicated in the ratio profile plots of the previous section, discrimination diagrarns of

Th/Ta versus Ce/Yb (Figure 5.16), La/Srn versus Ce/Yb (Figure 5.17) and LaiSm

versus Th/Nb (Figure 5.18) al1 indicate that the North Intrusion had a distinct

contamination history or parental source than the South Intrusion. In each of the above

figures, the north intrusion samples form a discrete cluster from the south body. The

trace elernent chemistry of the South Intrusion gabbros is sirnilar to the Voisey's Bay samples on these discrimination figures, unlike the north gabbros.

One goal of this study was to attempt to identiQ sources of contamination. In order to infer possible contarninants for the PLIS samples, the staning material must be known and compared with data of possible contaminants in the area. To estimate a parental melt composition for the study rocks, plagioclase was removed fiom the bulk rock's major element compostions. It was assurned that the curnulate rocks consisted of

50 % plagioclase and 50 % melt. The resulting major element contents most closely resembled a ferropicnte (See Table 5.4). The estimated parental composition of the

PLIS sarnples are modelled with potential contaminants. Picrites from published

Iiterature were also used as starting points on the discrimination plots since the calcuiations performed to estimate the original composition of the study rocks did not encompass trace and rare earth elements. The picrites chosen from literature were dependent on the trace element data available.

Hypothetical mixing trends were plotted on three of the above figures starting fiom either a selected picrite, or a point which appeared to correspond to the data plotted, and ending at the Tasiuyak and Nain gneisses. Due to the differences in the trace element geochemistry of the starting picntes, the results are very different.

Figure 5-17 displays a theoretical mixing Iine in which the study sampies lie at approximately 30% Tasiuyak gneiss and 70% Amisk picrite for the ratios of La/Sm versus Ce/Yb. The Nain gneiss contamination path was close to approximately 40% gneiss to 60% picrite. Figure 5.16 of Th/Ta versus Ce/Yb illustrates a mixing trend from perhaps an original composition of the Pants magma to the Nain gneiss, with the south intrusion samples at approximately 10-20% gneiss to 80% picnte. The north gabbro samples lie on the mixing line at approximately 5% Tasiuyak gneiss. In this diagram, the mixing trends were extrapolated fiom a starting point which appeared to corresponded to the two di fferent locations of the respective gabbro bodies and the two gneissic end points. A picrite fiom literature was not chosen as a starting point in this figure. Figure 5.18 produced even different results with the Tasiuyak gneiss appearing to contribute approxïmately 5% and the Nain gneiss including more or less 10%

material to the Archean ferropicrite. This ferropicrite fiom the literature most closely

resembles the estimated liquid composition of the PLIS rocks (See Table 5.4), and may

produce the most reasonable results on the above figures. Interestingly, these values

are similar to those suggested by Lambert et al. (1 999) of 2% contamination fiom the

Tasiuyak gneiss and 16% fiom the Nain gneiss for the Voisey's Bay samples based on

Re-Os modelling.

5.3.6. Srtlphide Depletion: ffistogmms

In the estimation of sulphide depletion, the ratios of Cu/Zr and Cu/Hf are used. These

were reliable elements to use since their concentrations are much higher in the study

rocks than the individual detection limits for their respective method of analysis. As

previously mentioned, the concentration of Zr and Hf increases in the melt as

fractionation progresses. This is also tnie of Cu since it is an incomptible element into the fractionating phases, unlike Ni which partitions into olivine readily. The copper content will only increase in the melt until sulphide saturation is reached, whereupon as

it is a chalocophile element, it will partition into sulphide liquid. The Cu/Hf and CulZr ratios would then serve as favorable ratios to detect sulphide depletion. Lightfoot et al.

(1994) have also observed that these elernent ratios are usehl in charactenzing rocks

from di fferent units or formations.

Li and Naldrett (1999) have found that the chalcophiIe element depleted basalts of the Nadezhdinsky lavas fiom Noril'sk have Cu/Zr ratios of less than one (See Figure

5.19a). Figure 5.19b (data fiom Lightfoot et al., 1994), resembles the pattern observed in Figure 5.19a in that the Lower Nadezhdinsky (ndl), Middle Nadezhdinsky (nd2), and Upper Nadezhdinsky (nd3) basalts have show the greatest degree of chalcophiie depletion. The Mokulaevsky (rnk) and Tuklonsky basalts (tk) lavas are chalcophile un- depleted and display an evolution of less depletion fiom left to right. The Lower and

Upper Morongovsky (mrl and mr2; mr on the figure) show the result of mixing of depleted magma with fiesh magma.

In Figure 5.20, the samples of the North and South Intrusions of the PLIS are al1 below the value of one and therefore have experienced a high degree of chalcophile element depletion. The few samples that plotted above the vatue of one are associated with a mineralized sequence. Figure 5.21 of fiequency versus CulHf was used alongside the Cu/Zr figure because of uncertainties attached to Zr analyses at low concentration. The Cu/Hf plot agreed with the results of the previous figure, however the values are difierent due to different concentrations of Hf and Zr found in nature.

The shape of the two plots is fbndamentally identical and advocates that the study rocks are al1 chalcophile depleted.

5.4. Discussion

It is important to realize that the study rocks are cumulates and therefore the major elements reflect varying proportions of cumuius and intercumulus phases. Al1 major element compositions are within the limits expected for gabbros and peridotites, and reflect the observed rnineralogy. Although A1203 contents are high (average 16.72-

2 1.48 W.%) for al1 units except the peridotite, simply representing the plagioclase-rich nature of most of the study samples. In the literature, high-Al basalts and gabbros supposedly occur by the absorption of previously-forrned plagioclase grains during

contamination. Iron-rich source regions have been suspected to produce high-Al

gabbros in the Adirondacks and in the Harp Lake Complex and are charactenstic of

a~orthosite-bearingterranes (Olsen and Morse, 1990). The high-Al basaltic parental

liquids are also thought to fractionate to ferrodiontes (Mark1 and Frost, 1999). This

idea may apply to the gabbros of the North Intrusion since it is most likely associated

with the Nain Plutonic Suite, and possibly parental to the morthosite to the north of the

property, as small areas of ferrodionte are also present.

The ratio of MgOl(Mg0 + FeO) or Mg #, found from the major elernent

geochemistry, generall y reflects a very slightly higher degree of fractionation in the

coarse-grained units than in the fine-grained units, and different fractionation trends in

the lower fine-grained units. The coarse-grained units are very similar chernically with

identical spiderplot patterns. These iinits represent crystallization in which, fiom the

textural evidence, plagioclase seerns to have appeared on the liquidus ahead of olivine.

This is possible if the magma is contarninated with either A1203 or Si02, as is

suspected in the study area (J-Brenan, persona1 cornmunciation). The major element

compositions of the fine-grained units are also similar reflecting the mineral

compositions. but marked differences are apparent between the north and south gabbros

in the trace and rare earth element constituents.

Comrnon to al1 spidergrams is low Rb, possibty stripped out by alteration, but

low Rb values are also a characteristic of the NPS and cumulate rocks (Emslie, 1996).

Low U values may be due to this element having been oxidized and removed during alteration. Under reducing conditions Eu can be reduced fiom a 3+ to a 2+ valence state that is strongly preferred by plagioclase. The presence of cumulus plagioclase would increase the Eu content giving rise to a positive Eu anomaly on spiderplots, as is evident in nearly al1 the PLIS samples. The high Sr anomaly is connected to the elevated plagioclase content as it also has a +2 valence state and therefore partitions easi 1y into Ca-bearing minerals such as feldspars,

The difference in trace elements abundances between the North and South

Intrusions implies different contamination histories or reflects different original melts.

This data supports the hypothesis that these are indeed two independent intrusions that do not share a cornrnon plumbing system. The unit 42 samples fiom VBS-97-79 may represent an injection of northem type sill that intnided the already crystallized south chamber as rnixing did not occur, given the evidence of trace element ratio profiles on

Figure 5.15. The lower si11 at 254 m depth is associated with sulphides.

Postulating that the Nain and Tasiuyak gneisses andor the lower cmst could be contaminants is dificult given the unreasonableness of bulk assimilation. However, the

Tasiuyak does not seem to be a large contributer of elements due to a very high content of Th, not witnessed in the PLIS rocks. Both the Nain and Tasiuyak gneisses have very similar patterns, on the right end of the spidergrams, to the south gabbro units. The gneisses do share a few of the points with the north gabbro on the right end of the plots, although have a different pattern. Values of U and Th are similar in al1 the study samples to those ploned for the lower crust. ïhe Voisey's Bay troctolites show a remarked similarïty to the south gabbros of hole 79 on the spidergrams, except for

PZ05 and U. in order to speculate on a possible contamination path, an original magma composition of a ferropicrite (or picrite) was chosen. Mixing trends plotted on discrimination diagrams produced highly different results. Of the three figures, approximately 5 % Tasiuyak gneiss with 10 % Nain gneiss (Figure 5-18), most closely resembles the proportions that are suggested for Voisey's Bay. This is not to Say that the proportions would be the same for the Pants Lake gabbros given the geographical distance between the two locations, it is merely stated as a point of interest. The exact contamination history of the Pants Lake samples is not and may not ever be known.

The ratios of CulZr and Cu/Hf were used to detect any chalcophile element depletion in the study samples. In the literature, it is stated that Zr and Hf will partition into clinopyroxene modestly with a low partition coefficient of -O. 1 (Fujimaki et al.,

1984) however, this is not a problem in the PLIS samples as clinopyroxene is not a fractionating phase. The majority of samples are chalcophile element depleted as they have values of CulZr < 1 and CdHf < 50.

As the study samples are al1 cumulate rocks, the presence of trapped liquid must be taken into account when deliberating the trace and rare earth element concentrations and the fractionation process. The concentrations of incompatible elements can not be taken at face value, rather, the use of ratios is warranted as the value of the ratio is unchanged with the addition of trapped liquid. Figures 5.14 and 5-15 show a significant dispersion for Zr and Hf ploned against various trace and rare earth element ratios. The values of the ratios provide further evidence in the distinction between the south and north gabbroic bodies. The geochemistry points to two distinct intrusions of gabbroic cumulate rocks, the North and South Intnisions, with two separate contamination histories or parental magmas. Generally, the coarse-grained units of 40 and 42 are have the lowest Mg #.

The peridotite unit is the most primitive with the highest Mg # found in the study sampies. As these are cumulate rocks, trapped liquid is present and must be taken into account when interpreting concentration and fiactionation evolution. From a parental melt composition of a ferropicrite, contamination sources may be both the Tasiuyak and

Nain çneisses, or another contaminant. The South Intrusion gabbros are chernically very sirnilar to Voisey's Bay VT and NT units except for Th, U and P205. With the exception of samples associated with mineralized sequences, al1 PLIS samples have been chalcophile-element depleted. 6. Mineral Chemistrv

6.1. Plagioclase

As previously discussed, the plagioclase and clinopyroxene grains of the black gabbro

appear "dusty" in thin section. This is due to dark coloured inclusions within these

grains. In outcrop and in drill core this gabbro unit resembles the coarse-grained gabbro

unit however is much darker in colour. The inclusions were too minute to be identified

by petrographic microscope, therefore an examination of several thin sections in the SEM

(Scanning Electron Micrograph) was deemed necessary.

The query was to investigate the possiblity of the PLIS incorporating graphite of

the Tasiuyak gneiss into the plagioclase and clinopyroxene grains or to recognize the

inclusions as an Fe-oxide. Clinopyroxene may contain Fe in the chernical composition,

(Ca. Mg. ~e'+.~e~' , Ti, A1)z [(Si, Al)&] (Deer et al., 1993) and plagioclase

Na[AiSi30s]-Ca[A12Si&] (Deer et al., 1993) rnay have divalent iron enter as Ca(Mg,

Fe)Si30sand trivalent iron can substitute for AI)' (Smith and Brown, 1988).

Plagioclase grains were chosen for examination. The electron beam was centred on small dark blebs within plagioclase grains which appear as bright dots on the image

(see Plate 6.1). This proved a difficult exercise due to the extremely small size of the inclusions however, a Fe peak did appear on the spectrum fiom the EDS analyzer of elements present. When the beam was centred off-dot, a Fe peak did not occur on the histogram. Pending fûrther study, it is assumed that the dusty nature of the black gabbro plagioclase and clinopyroxene grains is caused by inclusions of extremely fine-grained iron-oxides. Fine-grained oxide in plagioclase, probably resulting from exsolution, is present in many igneous bodies (eg. Voisey's Bay and Sudbury). Smith and Brown

(1988) state that exsolved Fe metal in lunar and meteoritic plagioclases requires a reduction mechanism if the Fe exsolved out of the plagioclase, but the details of the chernical processes remain obscure. What is not understood as yet, is why it occurs in onIy some of the gabbros of the northem intrusion, and what this implies as to the genesis of these rocks.

Following the Michel-Lévy approach to plagioclase compositions, plagioclase grains exhibiting albite-law twins with uniform illumination were studied. Glamer

(1 980) found that this method gave highly reproducibile results as a set of ten measurements gives a 95 % probability of predicting a composition to within 5 mole percent An. A range of An40-An64 appeared throughout the gabbroic units. This falls on the Ca-end of andesine to labradorite compositions. This result corresponds to the microprobe analysis performed by Hodder (1 997) that had a range of An46-An77. In contrast, Kerr (1998) did not find any plagioclase grains more calcic than approximately

An55.

6.2. Olivine

Analyses of olivine grains for the collected thesis samples was contracted to University of Toronto and analyzed by Dr. C. Cedgnani on the CAMECA SX50 microprobe in the spring of 1998. Euhedral olivine grains were found to be fairly homogeneous and therefore one point per grain, five grains per thin-section (ie. sample) were analyzed.

The anhedral olivine grains of units 40 and 42 were found to be zoned but the analyses were taken from various locations within the grains and results were averaged. Due to confidentiality, only the forsterite compositions will be used in this study (see Table

6.1).

Olivine grains in the upper sequence unit were found to be too altered to be analyzed as the grains in this thin section are mainly serpentine.

6.2.1. Black Gabbro and Coarse-grained Gabbro

Forsterite values for the olivine grains in the black gabbro and coarse-grained gabbro were similar with combined averages for low, mean and high values found to be: 41 -8 Fo, 47-7 Fo, and 53.6 Fo. Normally, these values would suggest that these grains have undergone a significant amount of fiactionation. However, these grains are normally zoned, suggesting that they crystallized with a significant amount of trapped liquid. In Figures 6.1 and 6.2, both of these units show a high scatter, in line with the interstitial and zoned nature of these grains. However, a roughly normal hctionation trend could be implied as the values in the highest levels have the lowest forstente numbers.

62.2. Fine-grained olivine gabbro

On al1 figures representing these units. the olivine Fo values form a much tighter grouping than observed in the coarse-grained units with zoned anhedral olivine grains.

Unit 4 ln gabbro fiom VBS-97-77 has olivine grains that have low, mean and high values of 56.6 Fo, 57.7 Fo, and 58.7 Fo, averaged. Drill hole 79, unit 4 1su samples have comparable values to those of hole 77 with a mean average of 54.2 Fo. Unit 41sl olivine grains have elevated values with the range of averages comprising: 66.1, 66.6 and 67.0 Fo. The trends for the two holes are quite different as seen in Figures 6.2 and 63.

Hole 77 exhibits a reverse trend (increasing forsterite content) fiom the base up to

approximately 200m depth. The upper portion of this unit has a normal trend. Unit

414 of hole VBS-97-79 displays a normal trend with two slight reversais above 500 m.

A normal differentiation path is displayed for unit 4 1su up to the mineralized zone.

6.2.3. Per-idotite

The peridotite unit again displays the most primitive values. The low, mean and

high averaged forsterite nurnbers for samples in this unit are: 72.7 Fo, 73.1 Fo, and

73.4 Fo. In Figure 6.3, the peridotite unit has a reverse hctionation trend indicative of

a fresh pulse of magma.

6.3. Discussion

The upward variations in Fo content of olivine produce two different types of

fractionation trends, normal and reverse. The upward enrichent in Fo is expressed by

a reverse trend and could be due to interaction with primitive magma. The hotter and

more primative magma would have higher Mg0 contents and therefore Fo values than

the fractionated magma. If injections of this new magma occurred, this would cause

mixing and the result would be a lower Fo content than the fresh magma but a higher Fo

number than the fractionated magma. The upward depletion in Fo is classified as a

normal fractionation trend of mafic magma crystallizing olivine. In other words, as the

mafic magma crystallizes Mg-rich olivine the remaining melt becomes enriched in Fe.

Consequently, the later-fonning olivines will contain more Fe relative to Mg and therefore will have lower Fo values. Using high forsterite values to represent more primitive magma, influxes of new

melt can be inferred from Figures 6.2 and 6.3. From 390 m up to 150 m in VBS-97-77

the reverse fkactionation of olivine grains is apparent. This suggests that this bore hole

is in close proximity to a plumbing system and is flushed with fiesher, more primitive

magma thoughout this interval. Slight reversals in the differentiation paths in this

same hole are exhibited at approximately 275 m and 225 m indicating influx of a very

primitive composition. Once crystallized above 150 m, the incoming flow ebbs and

allows the body to hctionate in a normal Mg-depletion progression. Weak infimes of

new magma to VBS-97-79 are visible in Figure 6.3 at 620 m and for the interval of 500

to 400 m. A fauit zone at 400 m obscures the olivine differentiation pattern. An

anomalously low Fo value at approximately 230 m is indicative of a different highly

fractionated magma intmding the already crystallized south chamber. This is implied as

the forsterite values above this intrusion fa11 back into the fkactionation path suggesting

that mixing did not occur. Figure 6.1 is not as enlightening as this unit is highly

fractionated with a large scatter in points, although a vaguely normal trend could be

inferred.

No significant differences appear in the chemistry of rocks which show upward depletion and enrichment in Fo. For example, in VBS-97-79 unit 4 1su has an upward depletion in Fo but has the same profile as unit 41sl on the spidergram in Figure 5.8; the 4 I su profile lies above that for 4 1si. The peridotite unit has a reverse hctionation path, upward enrichment in Fo, but has the sarne spiderplot pattern as unit 4 1SI that displays a normal hctionation trend with a couple slight reversals. The only difference between these two patterns on the spidergram is the positive Sr anomaly due to the difference in plagioclase content, The trace element geochemistry of both gabbroic

units in drill hole 77 are very comparable in Figure 5.7, but unit 41 exhibits a reverse

fractionation trend in Figure 6.2 while unit 42 does not.

ïhe determined olivine forsterite values compare with units of the Voisey's Bay

deposit. The average forstente values for Unit 42 has a mean of 48.6 Fo and unit 40 has

a mean of 46.8 Fo that corresponds to compositions of the FOG that has an average

value of 46.3 Fo (Li and Naldrett, 1999). The mean of the average forsterite values for

Unit 4 1n has a value of 57.7 Fo that is roughly equivalent to the olivine gabbro (OG)

average of 58.3 Fo (Li and Naldren, 1999). Unit 41su has a value of 55.6 Fo that is in-

between the LT of 52 Fo and OG of 58.3 Fo. Unit 4 1SI corresponds to the NT unit as

the hvo values are 66.6 Fo and 66.8 Fo, respectively. The high forsterite content of 73.1

Fo found in the peridotite unit of the PLIS similar to values found in the Voisey's Bay's

ultramafic inclusions of 74.1 Fo (Li and Natdrett, 1999). Therefore, it can be assumed

that the upper units are more fractionated, except in drill hole 77 where the Fo values

increase upwards so that the most primative olivine grains are close to the top of the

intrusion.

The forsterite values of olivine grains should not be considered entirely accurate

in representing primary liquid compositions. Olivine grains will reequilibrate with

trapped liquid (Chalokwu and Grant, 1987; Barnes, 1986). Bames (1986) graphs

calculated curves for the determination of initial olivine composition in a cumulate rock

with various cumulate phases and associated trapped liquid. Units 42 and 40 roughly

correspond to a plot for a cumulate with the composition of 60% plagioclase, 20% olivine and 20% clinopyroxene. The cornbined mean olivine composition is alrnost off scale for these units but could give a shifi fiom a final 47.7 Fo content to an initial 60

Fo composition, and the high value of 53.6 Fo for these units with a trapped liquid

estimate of 50% results in an olivine original composition of approximately 66 Fo. This

is a 13 mol % shifi in olivine composition. The gabbroic members of unit 41 roughly

correspond to a plot of 50% plagioclase and 50% olivine. From a combined mean

average of 58 Fo and 50% trapped liquid, the original olivine grain would have a 67 Fo

composition. The peridotite unit with a mean composition of 73 Fo plotted on an

olivine cumulate composition graph at 10% trapped liquid has an shift to an original

composition of 74 Fo; at 30% trapped liquid a shifi to 76 Fo and; at 50% trapped liquid

gives an original composition of 79 Fo. These results probably display the smallest

amount of trapped liquid shifi as this unit has the highest olivine content and most

likely the lowest intercumulate liquid which would help preserve Mg-rich compositons.

The forsterite values may therefore be slightly inaccurate in representing primary compositions especially when dealing with the more fiactionated or late crystallizing units.

Olivine compositions provide a great deal of information fiom which many

inferences may be made. From this data and associated trace element data, difierences

in magma chambers and influxes of fiesh magmas may be supposed. ne South

Intrusion hosts a more primitive magma with many pulses of fiesh magma that entered and reequilibrated. Perhaps a different, more fiactionated siIl intruded an already crystallized intrusion of the south-type magma at the upper mineralized sequence in hole 79. The North Intrusion has a reverse differentiation trend for one drill hole that may imply it is proximal to a plwnbing system. Hotter and newer magma definitely entered this chamber and produced this reverse trend. In the Northern Abitibi area, the olivine grains showed a normal fractionation process. 7. Discussion and Conclusions

Several conclusions are evident regarding the Pants Lake Intrusive Suite. The property clearly has two different mafic cumulate intrusions in attendance with dissirnilar contamination histones or originating fiom different sources. Therefore, the two bodies may have taken similar paths to their present level of emplacement, but have "rested" and fiactionated at different levels. The contamination occurring during the "rest" periods resulted in the different chernistry of the bodies. The mafic ortho- to mesocumulate rocks include: leucogabbros, gabbros, olivine gabbros, troctolites and peridotites but for simplification are classified as: coarse-grained gabbros, fine-grained olivine gabbros, and peridotites. Trapped liquid is present and rnay affect the olivine compositions and necessitates caution when interpreting incompatible element concentrations. Even so, hctionation trends can be identified as well as influxes of new magma into the respective chambers. The chemistry of al1 units resembles the

Voisey's Bay deposit rocks and may have similar contamination histories. The original magmas of the North and South Intrusions conceivably could have had compositions akin to a ferropicnte which then hctionated to high-Al gabbros. Contamination sources seemingly include a small arnount of Tasiuyak gneiss constituents and perhaps a slightly larger proportion of Nain gneissic components. ALI units are sulphide depleted which occurred preceding emplacement in the two chambers. Geological Mode1 and Exploration Recommendations

Many items must be taken into account when exploring for magmatic Ni deposits.

These systems undergo complex processes where factors other than constant values of sulfide melt-silicate melt distribution coeficients are important (Peach and Mathez,

1993). Also required are a MgO-rich, sulphur under-saturated magma and a sulphur- bearing and/or siliceous contaminant (as in Sudbury and Nonl'sk), to drive the magma to sulphide saturation- The R-factor (ratio of mass of silicate to mass of sulphide magma) of the deposit and a collection site for the sulphide liquid must also be considered during exploration. This ratio also helps to predict the concentrations of

PGEs.

Equation (1) is used to calculate the value of the R factor (R) where Y= Ni concentration in sulphides, D=distribution coefficient for Ni, and X= initial Ni concentration in silicate magma (Naldrett, 1997). In estimating R for the Pants Lake property the following values were used: Y=2% or 20000 ppm Ni , D4100 (Peach and

Mathez, 1993; for magma with approx. 48 wt% Si02 and IO wt% MgO), and X=150 ppm (See Calculation in Appendix C). The Voisey's Bay South property has a low R value at approximately 150. Low R factor deposits range from 100-2000 and contain

Ni and Co values of most Ni sulphide ores that have reiatively low Pt concentrations

(Naldrett, 1997). Voisey's Bay also is a low R factor deposit (A-Naldrett, personal communication). Therefore, a small amount of silicate magma interacted with sulphides and the new and as yet undiscovered South Voisey's Bay deposit is most likely going to be a large low grade deposit without significant PGE concentrations. Low oxygen fugacity values are possible but not necessarily present for this

property as graphite is abundant in one of the possible sources of contamination, the

Tasiuyak gneiss. The oxygen fugacity of the developing system is dependent upon

pressure. As the oxygen fugacity increases the ability to dissolve sulphur decreases.

Also, an increase in temperature increases the ability of S to dissolve, which is means

that an olivine-rich (high temperature) magma interacting with a sulphur source, could

dissolve a relatively large amount of S (Naldrett, 1997).

It has been shown fiom the geochemistry and field relationships that the North

Gabbro and South Gabbro have had different contamination histories and ascended up different feeder systems, or evolved fiom dissimilar source material. Therefore, different exploration critena must be applied to the two areas.

North Gabbro (See Figure 7.1): One likely feeder area is in the vicinity of the black gabbro (the Northern Abitibi area) as thick intersections of basal contaminated breccias are located in this region. Northwest of Taheke Lake may also be a possiblity as it is not known where the intrusion lies under the lake. Either location could have utilized the same feeder as the anorthosites and ferrodiorites to the north or stiil have been associated with the NPS but employed a different plumbing systern.

One mode1 is that sulphur undersaturated magma produced by mantle melting moved through a lower chamber, crystallizing mafic silicates and giving rise to an Al- rich, possibly ferropicritic melt, that reacted with sulphur fiom the Tasiuyak gneiss and silica fiom the Nain gneiss at depth. Dense sulphides then senled fiom this magma. This origin is similar to that proposed for the Kiglapait mafic intrusion of the NPS, that

is thought to have had an anhydrous alurninous basaltic parent melt (Emslie, 1996).

The liquid then crystallized plagioclase which eventually floated due to it's

buoyancy. The gabbroic liquid moved through to the area now occupied by the north

gabbro from the chamber at depth and deposited cumulus olivine grains. In the

interstitial spaces of forming plagioclase grains, the cumulus olivine grains collect and

fom clusters. The accumulation of plagioclase explains the positive Eu anomaly

exhibited on spidergrams. The magma kept moving through the northern gabbro

chamber and into other areas (now removed by erosion) as sills. This produced the

reverse crystallization trend seen in hole 77. As the magma moved into this new

chamber, layering and in some cases cross-bedding developed. Flow of new magma

ebbs and the remaining magma in the north gabbro chamber fractionates with a normal

trend.

The black gabbro is close in age to the fine-grained gabbro, and is most likely a

separate pulse in which Fe-oxides exsolved out of the plagioclase and clinopyroxene

crystal structures. This unit is texturally and chemically very similar to the coarse-

grained gabbro and does have an intrusive contact with the red-coloured, fine-grained olivine gabbro without any evidence of chill zones. If the fine-grained olivine gabbro was already hot, as it is assurned that these units are close in age, this could explain the

lack of a fine-grained zone at the contact. In studying drill holes 97-93,97- 1 O6 and 97-

108, Kerr (1 999) speculates that the black gabbro is indeed a separate unit that has a close temporal relationship with the fine-grained unit. Unfominately, the black gabbro does not show any significant sulphide enrichment. Interestingly, this unit does host the most noteworthy intersections to-date. The relationship between the northern gabbroic units is arnbiguous at best, however, they are al1 similar in age.

More sulphide liquid fonned at the base of the north gabbro chamber since this is closer to the source of the sulphur and silica. This magma would have soldified quickly thus blocking the transfer of sulphur and silica from the country rocks into the rest of the gabbro body (Barnes et al., 1997). As discussed previously, field observations imply that sulphide mineralization tends to overly the sulphur-bearing paragneiss rather than the quartzofeldspathic orthogneiss. However, it has been postulated by Kerr (1 999) that the rnineralized sequence including gneissic inclusions is a separate pulse of magma and being denser, flowed along the bottom of the chambers.

This may have been an earlier pulse of magma that preceded the fractionated liquid into the chamber. The influx of silicate magma would not have interacted with the country rocks as the earlier sulphide and gneissic clast-bearing pulse was intervening. As well, the sulphide pulse would not have had a chance to interact with the overlying gabbroic melt and increase the value of R. However, it is not known if the mineralized sequence is in fact younger than the gabbroic units.

In this mode1 the favoured place for sulphide accumulation would be a topographic depression along the base of the chamber. This is the likeliest location as the sulphide minerais would be much denser than the silicate counterparts and wouId therefore senle. Sulphides may have also been pushed close to the entrace to the chamber by the sulphide-laden pulse. Discouragingly, a pulse of non-depleted magma is conspicuously absent fkom this intrusion suggesting that the sulphides could not have been significantly e~chedsubsequent to their initial formation. Since significant intersections of mineratization occur along the northern tip of the northern gabbro body

this would be a target area to search for a feeder system. To the northwest of Taheke

Lake may also be a possible locale for a plumbing system as the gabbroic body is not

present at surface. Except for closely spaced dnlling in close proximity to drill hole

VBS-97-75 the exact nature of contacts with other units to the north are not well

known.

South Gabbro: The feeder system may be from the south undemeath and possibly

utilizing the same system as the Harp. Perhaps this intrusion may be a late-stage

component of the Harp. The central region, in the vicinity of VBS-97-79, rnay also be

a possible location for the feeder as large anomalies are indicated by gravity surveys.

This intrusion has a much different and steeper geornetry than the northern intrusion.

Primitive cumulate layers of peridotite have been observed in drill core. Chaotic

layering has been observed in fine-grained olivine gabbro on the bank of the Adlatok

River at the southern extent of the intrusion. This body intnides the rapakivi granite

therefore establishing that it is unmistakably younger than the felsic unit.

A normal hctionation trend implies a fractionation chamber rather than the

"rnoving through" chamber of the north, although an approximately hundred metre

reverse fractionation trend is observed in drill hole 79 between 500 rn and 400 m depth.

This would imply that pulses of new and hotter magma were injected into the chamber after the initial impulses. The batches of fiesh melt entered the chamber for an extended period during the course of the evolution of the charnber and caused some amount of mixing. A fault zone situated at and about 400 m with minor strike-slip displacement obscures the remainder of this reverse crystallization trend. The remainder of the upper chamber crystallized with a normal fiactionation trend.

However, the forsterite composition of olivine grains generally decreases up-hole with the most primitive values belonging to the pendotite at the base of the intrusion. The shear zone at approximately 400 m does not seem to affect the olivine composition significantly.

From the gathered information, it could be theorized that a ferropicritic high-A1 melt entered the chamber fiom a lower source area where sulphides had dropped out due to interaction with a sulphur or silica source. Peridotite layers are the most primitive rock type present and most likely were among the first to crystallize. This unit also exhibits chalcophile depletion in the histogram that uses the Cu/Hf or CdZr ratio as a gauge of sulphide interaction (Figures 5.20 and 5.21) except for a few sarnples that belong to part of the mineralized sequence. The chalcophile-enriched samples associated with the mineralized distribution in VBS-97-79 are in contact with a thin screen of paragneiss at 250 rn (upper mineraiized sequence) and footwall paragneiss (lower minerdized sequence) at 700 m. The upper mineralized sequence is associated with one of the samples of the four that were classified as belonging to the north gabbro since they possess the sarne trace element chemistry. This unit is interpreted to be thin sills which intrude the south gabbro; geochemical plots indicate that mixing of the two did not occur. For the north gabbro to be intruding the south it would seem to be younger. Once again however, age relationships are not clear-cut.

In this model, one piace to investigate for the accumulation of sulphides would again be an input area into this chamber or a topographie trap. This magma was once again chalcophile depleted suggesting that the sulphides have already been stripped out and perhaps amassed somewhere pnor to the gabbroic emplacement in this chamber.

As this chamber has not been drilled extensively it may possess some magma that was not so chalcophile-element depleted and which served to enrich previously formed sulphides. This idea is somewhat analogous to the Voisey's Bay mode1 although evidence for a less-depleted melt is required.

Two separate intrusions require two different sets of exploration criteria. In the northem gabbro, the probable practice would be to look for a physical trap in the base of the chamber where accumulation of sulphides could occur. A feeder channel or entrance to the northem gabbro chamber could also be benficial. In this area the black gabbro unit seems to be the preferential unit for sulphide development. It has hosted the most significant intersections of sulphide mineralization to date for unknown reasons except that perhaps it is in close proximity to a inlet channel fiom a lower chamber.

The whole rock data indicated higher concentrations of nickel in the South intrusion, panicularly in the pendotite unit that averages approximately 900 ppm, than found in the north gabbro. Perhaps this is indicative of chalcophile-enrichment in at least one magma pulse that would upgrade the low R factor sulphides. Any kind of topographic trough such as a feeder system and entrance to the magma chamber would be sulphide collection sites and consequent exploration targets. Despite the southem intrusion not having such a clear definition as the north, a number of possibilities exist. nierefore, a new deposit would lie at great depth in the south gabbro chamber where the first magma became sulphur saturated and deposited suiphide droplets. Any subsequent influxes fkom the source region could have enricheci these sulphides and transported them close to an entry point of the south chamber. The other occurrence of massive sulphide would be in the northern tip of the North Gabbro where significant sulphide mineralkation has accumuiated. References

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Li, C. and Naldrett, A.J. 1998. Melting reaction of gneiss xenoliths in the Voisey's Bay troctolite complex: evidence for crustal assimilation (abs). GAC/MAC Meeting, Québec City, Québec, Vol. A 109

Li, C. and Naldrett, A.J. 1999. Geology and petrology of the Voisey's Bay intrusion: reaction of olivine with sulfide and silicate liquids. Lithos, 47, 1-3 1

Lightfoot, P.C., Naldrett, A.J., Gorbachev, N.S., Fedorenko, V.A., Hawkesworth, C.J., and Doherty, W. 1994. Chemostratigraphy of the Siberian Trap lava, Noril'sk district, Russia: Implications and source of flood basalt magma and their associated Ni-Cu mineralisation. Proceedings of the Sudbury-Nonl'sk symposium. Ontario Geological Survey Special Publication, No. 5,283-3 12

Markl, G., and Frost, B.R. 1999. The origin of anorthosites and related rocks fiorn the Lofoten Islands, Northern Nonvay: II. Calculation of parental liquid compositions for anorthosites. Journal of Petrology, 40, 1,61-77

Naldrett, A.J. 1997. Magmatic Sulphides: Seventeenth Ore Deposits Workshop, Volume 1. Department of Geology, University of Toronto, December 15- 18, 1997.

Naldrett, A.J., Asif Mohammed, Krstic Sasa and Li Chusi. 2000. The composition of ore at the Voisey's Bay Ni-Cu sulphide deposit, with special reference to platinum- group elements. Economic Geology (in press).

Naldrett, A.J., Singh Jagrnohan, Krstic Sasa and Li Chusi. 2000. The rnineralogy of the Voisey's Bay Ni-Cu-Co deposit, Northem Labrador, Canada: Influence of oxidation state on textures and minera1 compositions. Economic Geology (in press).

Olsen, K.E. and Morse, S.A. 1990. Regional AI-Fe mafic magmas associated with anorthosite-bearing terranes. Nature, 344,760-762 Peach, C.L. and Mathez, E.A. 1993, Sulfide melt-silicate melt distribution coefficients for nickel and iron and implications for the distribution of other chalcophile elements. Geochimica et Cosmochirnica Acta, 57,3013-3021

Potts, P.J. 1987. A Handbook of Silicate Rock Analvsis. Blackie & Son Ltd., Glasgow, Chapman and Hall, New York, 622 pp.

Regional Geology Survey: South Voisey's Bay, 150 000 Map, Donner Minerals Ltd. and Teck Exploration Ltd,

Ripley, E.M., Park, Y.-R., Li, C. and Naldrett, A.J. 1997. Sulphur and Oxygen Isotopic Studies of the Voisey's Bay Ni-Cu-Co Deposit, Labrador, Canada- (abs.) AGU Fa11 Meeting

Ripley, E.M., Park, Y.-R., Li, C., and Naldrett, A.J. 1999. Sulfûr and oxygen isotopic evidence of country rock contamination in the Voisey's Bay Ni-Cu-Co deposit, Labrador, Canada. Lithos, 47, 53-68

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Mn 4986 ma6 U O 776 012 4% rom 3 orr OB oit 97za miJ 4947 21 43 a% LU 012 lm IOIP 1re am cm a12 T~P (192n 100 Y

2 a15 7m Oz 114 QI4 in in llU 016 1104 a26 a am 121 in 10% 015 1013 026 om a09 1- 1- IJI 1234 017 1256 O24 063 OC9 1- 1- 126 >la 0.15 11 71 023 os O07 11ST 416 1284 Oz0 052 006 Irn 999 asl 014 ctm al9 09 005 11) Il6 1042 0.14 11 69 O18 0% a06 tan il0 989 413 lia 045 0- 1i.n I 12 1007 O14 11 17 417 052 O07 11- Il0 992 014 11 a 016 035 006 la9 los 943 a13 9m 074 OU 001 a74 am 7.57 OIT azs a21 O am LIl 0% au a12 7~ a23 046 oœ 1- 1- 149 1342 019 1ZM on a78 oc9 1- 1- 140 113. 019 llr3 027 081 OûE 11- 110 990 014 7n OJ) 0- a11 11 la, 1016 O 16 am as om 011 11s 115 101) 016 a13 a33 os a10 ~sn in 14 15 021 1I'rO a21 066 O06 tasr 105 946 O14 CG! O36 101 O12 137 iu6 oie a9o 431 097 010 101 915 014 5.24 Or) 8 O13 1- -1- 106 9 014 545 OU) 127 O15 trm 1 ta 1063 (Li6 561 O39 a a14 l?m 122 1101 016 557 015 130 016 1W 125 1124 076 578 019 IZ? O13

... . . 75113 4769 1787 UV7 IP 11s 017 6% 9% 293 OU 129 014 3114 r6~n)~ WU 11s 1068 ais 642 OR 2m 0.5 112 avc

75118 a4i 1633 1 132 11 92 017 a67 (1.5 279 071 1 il 014 ni19 am 160s tu irt izrs oia 73 am zsl os lu 01s Ti124 ibJ5 1274 127 1146 O17 461 9W 119 OW 19 O22 Table 5.2 Statistical analysis of identicality between units 40-42 and 41 -42. Units 40 and 42 Units 41 and 42 Ftest 1 Ftest 1

Units 40-42 F-test: nl=13, vl=12 n2=10, v2=9 at 1% significance, critical value=5.11 (one-tailed)

T-test: v=2 1 (n 1+n2-2) at Ioh significance level, critical value= +/- 2.518 (two-tailed) Table 5.3 Whole rock trace and rare earth elements.

5 Ml09e 1 0.002551 3MOfb63 1 0.0025 6 am53M 2 4- 1 aOOprr 1 0.041215 4 a014545 4 mZYD 5 0.015m 1- 4 0.012m2 1 ao03155 1 0.002435 3 0-7.6 4 Mltem 1 0.ooZfJoB 1 aOCZ1100 17 OBMeW 3 O~mm 106 0.- 3 0.01m 4 0.n13ss 3 O.aw6% 5 aolrm s ao1sia 1 0na3534 3 aM16UI 4 M12al 3 am12 6 a016304 5 om- 5 0.01497 7OB204a 4 ao1w11 5 0.014w7 5 Qo1s337 8 a023739 10 amass Table 5.3 continuecl.

1 Table 5.4 Calculated original melt compositions for the North and South Intrusions. 78

"Archean' fenopicritc 42.86 7.72

20.91 14.33 8.77 0.57 0.1 5 Ti02 0.99 0.02 1.96 0.62 4.18 Mn0 0.1 5 0.1 5 0.1 8 0.2 P205 0.12 0.12 0.03 0.3 1 Total 99.74 95.97 100.00

SOUTH INTRUSION assumina 50 made% daaioclase

Amisk picrite: Leybourne et al., 1997 Archean ferropicrite: Francis et al., 1999 Table 6.1 Microprobe anaiysis of olivine grains. Plate 3.1. Scenic Pants Lake, photo taken fiom the helicopter.

Teck Camp /

Plate 3.2 Rapakivi-texture granite. Scale bar is 2 cm (photo by K-Gorra, University of Toronto). Plate 3.3 Contaminated core of the mineralized sequence.

Plate 3.4 Breccia unit of gabbroic matrix and gneissic clasts, with magnetkcriber for scale. Plate 3.5 Minerai Hill showing with K. Emon for scale. Large-scale layering is also evident.

Plate 3.6 "Oatrneal" texture of coarse-grained gabbro; sample fiom Mineral Hill (photo by K-Gorra, University of Toronto). Plate 3.7 Contact zone of coarse-grained xenolith/dyke in fine grained olivine gabbro. Close-up of Plate 3.12 (Photo by K-Gorra, University of Toronto).

Plate 3.9 Black gabbro versus coane-grained gabbro (photo by K.Gorra, University of Toronto).

black gabbro coarse-grained gabbro Plate 3.8a. Small scale layering in the NDT area, along strike, perpendicular to dip surface.

Plate 3.8b. Small scale layering in the NDT area, surface angle close to dipping surface. Plate 3.1 0a. Coarse-grained, fine- grained olivine gabbro contact in the NDT area, with hammer for scale.

Plate 3.1 Ob. Corne-grained, fine-grained olivine gabbro contact in the NDT area. Plate 3.1 1 Chill zone of the fine-grained olivine gabbro against the coarse-grained gabbro displaying the "oatmeal texture", isolated outcrop close to suture area.

Plate 3.12 Coarse-grained xenolitlddyke within the fine-grained olivine gabbro in the NDT area. Plate 3.13 Fine-grained olivine gabbro intruding the rapakivi granite.

Plate 4.1 Thin section of couse-grained gabbro with interstitial olivine grains (Sample 75077 fiom VBS-97-77). Plate 4.2 Thin section of black gabbro (Sample 7506 1 fiom VBS-97-75).

Plate 4.3 Thin section of euhedral olivine grains- in fine-grained- olivine gabbro (Sample 75 140 from VBS-97-79). Plate 4.4 Thin section of small scale layeting (Sample HM-03-0 1).

Plate 4.5 Thin section of pendotite altered to serpentine, crossed polars (Sample75 144 fiom VBS-97-79). Plate 6.1 SEM photomicrograph of plagioclase grain fiom sample 75066 fiom VBS-97-75.Scale bar is 100 Pm. Inclusion contains an Fe-phase. Figure 1. t Location map of Labrador, Canada (after Wardle et al., 1997). Figure 1.2 Regional geology of Labrador and the location of the Voisey's Bay South Project.

Figu~2.2 Mode1 of the Voisey's Bay deposit (Li and Naldrctt, 1999). Figure 3.1 Narnes aiid locatioris of the gabbro bodies and study drill iioles on the South Voisey's Bay property.

I'liitonic Silitt .iic :iiitl niiortliosiic Nain-Churchill boundary '-b - 6km INTRUSION

Einslic, 1980 not part of Figure 3.2 Cartoon displaying idealized profiles of intrusions if al1 units are present.

NORTH INTRUSION SOUTH INTRUSION

paraforthogneiss 1 altered 42 I

47 SU (occasicnal pegrnatitic patches)

fault? 1 41 n

(occasional pegrnati tic I

patches j l

41 SI (occasionai pegmatiiic patches)

peridotite

41 s mineraiized sequence

pa rdorthogneiss Figure 3.3 Profiles of the mineralized sequences.

NORTH INTRUSION SOUTH IN1RUSlON (adapted from Ken, 1999)

peridotite cumulate

increasinç 3-5% gneissic dissernimated clasts su1 phides

fine- grained gabbro with diss. sulphides

1520% sulphide leopard blebs texture sulphides

barren gabbro

barren gabbro decreasing in grain size to a chill zone sulphide blebs Figure 3.4 Profile of study drill holes. Diamonds to the left of profiles denote sample locations.

(-1 km [O the wcst is the Mineml Hill showing of the Sorih Inuusion) -. -. V BS-97-75 black 1 1 tonalite @bm it I, I, contaminami b&ro/rnineraI~d 1 guence , 02 r ! massive ,suiphides

shearlfault zone

adphide-rich zone

neissic inclusions

ironounced chill zone

pangneiss Figure3.5 Expanded profile of the upper portion of VBS-97-79. Diamonds to the left of the profile denote sample locations and numbers. The sample numben outlined in red, have the North Intrusion chemistry.

paragneiss - with inclusions of partially -e- NiMg tonalite [melted graphite plus -- CuWf A oliune Fo-high * oliune Fo-a*. oliwne Fo-low

. -A ,>- ,/ ,-'/,K.- /.-- .--ij lis-

-

ite feldspathic peridotite- -10.00 10.00 30.00 50.00 70.00 90.00 CulHf and Forstente Figure 5.1 Diagram of AI203 vs. SIOZ for al1 samples.

+ VBS-97-75, Unit 40 rn VBS-97-77, Unit 42

A VBS-97 -77, Unit 41

x VBS-97-79, Unit 42 r VOS-97-79, Unit 41su

0 VBS-87-79, Unit 41sl

+ VBS-97-79, Unit 4lperid Figure 5.2 Diagrarn of Mg0 vs. Si02 for al1 samples.

VBS-97-75, Unit 40

iVBS-97-77, Unit 42

A VBS-97-77, Unit 41

x VBS-97-79, Unit 41su

mVBS-97-79, Unit 4 1SI + VBS=97-79, Unit 4lpend

x VBS-97-78, Unit 42 Figure 5.3 Diagram of Mg0 vs. AI203 for al1 samples.

VBS-97-75, Unit 40 1 I

+ + WBS-87-77, Unit 42 I l

A VBS-97-77, Unit 41 I l x VBS-97-79, Unit 42 1 x VBS-97-79, Unit 41su 1 WBS-97-79, Unit 41SI

+ VBS-97-79, Unit 4lperid 1 Figure S.& Profik of MgO, Ai203 and Fe0 m. Oepth, VBS-97-77.

Figure 5.- Profile of Mm, AI203 and Fe0 vs. Depth, VBS-97-75.

Figure5.8 Spidergram of the North Intrusion units (primitive mantle values from Suri and McDonough, 1989).

. . +VBS-97-75, Unit 40 +VBS-97-77, Unit 42 +VBS-97-77, Unit 41 *VBS-97-79, Unit 42 . - - - . - ---

Figure 5.10 Spidergram of the North Intrusion units with the Tasiuyak and Nain gneisses and Lower Cmst (primitive mantle values from Sun and McDonough, 1989).

+VBS-97-75, Unit 40 +VBS-97-77, Unit 42 +VBS-97-77, Unit 41 +VBS-97-79, Unit 42 43- Ave. Tasiuyak Gneiss 4Ave. Nain Gneiss Figure 5.1 1 Spidergram of South Intrusion units with the Tasiuyak and Nain gneisses and Lower Cmst (primitive mantle values from Sun and McDonough, 1988). Figure 5.12 Spidergram of North lnt~sionunits with Voisey's Bay VT and NT (primitive mantle values from Sun and McDonough, 1989).

+VBS-97-75, Unit 40

+VBS-97-77, Unit 42

-t-VBS-97-77, Unit 41

*VBS-97-79, Unit 42 -Voisey's Bay, Ave.VT --a- Voisey's Bay, Ave.NT - .- - Figure 5.13 Spidergram of the South Intrusion units with Voisey's Bay VTand NT (primitive mantle values from Sun and McDonough, 1989).

+VBS-97-79, Unit 41 SI +- VBS-97-79, Unit dlperid -Voisey's Bay, Ave,VT

-+ Voisey's Bay, Ave.NT 1 -

Figure 5.16 Discrimination diagram of ThlTa vs. CelYb, with mixing trends.

50% Tasiuyak Gneiss 100% Tasiuyak Gneissyb - a 50% Picrite 0 -- 13- O + Ave. Tasiuyak Gneiss O - \ - .a Ave. Nain Gneiss A Perid, VBS-79

O Unit 41sul VBS-79 l O 1 X Unit 41~1,VBS-79 l 1 .Unit 4ln. VBS-77 + Unit 42, VBS-77

0 Unit 40, VBS-75 100% 0 Unit 42, VBS-79 50% Nain Gneiss Nain 50% Picrite Gneiss Voisey's Bay VT Original composition A Voisey's Bay NT of Pants magma? A A mixing trend A A A 0 mixing trend .A A/ - a.,

p.AA1 1 , 1 1 1 - I 1 1 1 1 + Average Tasiuyak Gneiss 4 Average Nain Gneiss A Peridotite X Picrite (Amisk) 100% Tasiuyak ~neis// Unit 41su, VBS-79 + Unit 41~1,VBS-79 - Unit 41, VBS-77 4 - Unit 42, VBS-77 d 4 Unit 40, VBS-75 Tasiuyak Gneiss P I / O Voisey's Bay VT and NT 50% Picrite X Reid Brook, leuco-troc. Reid Brook, ave. mela-troc. - a mixing trend x p .A Nain - A mixing trend Gneiss Unit 42, VOS-79 - - . . . . . - -

, a, A - 4- A 50% Nain Gneiss O 5Q% Picrite - .A - 100% Picrite (Amisk) Figure 5.18 Discrimination diagram of LalSm vs. ThlNb, with mixing trends.

.- - rverage Tasiuyak Gneiss

Average Nain Gneiss

Perid, VBS-79 ,..- -'7 100% Tasiuyak Gneiss I Picrite (Archean) 100% Nain Gneiss Unit 41 su, VBS-79

Unit 41 sl, VBS-79

/a Unit 41 n, VBS-77 pw Unit 42, VBS-77 50% Nain Gneiss ,a ' 50% Picrite Unit 40, WS-75 O 50% Tasiuyak Gneiss 50% Picrite Unit 42, VBS-79 .O rnixing trend a + A m mixing trend -- - -

100% Picrite (Archean)

Figum 6.1 Dipth vr. Forsîmrite in olivine, VBS-97-7s. +am. valucs 42 -t-low values 42 +h@hvakios42 ' +ave. MW4ln ' ~Lowvaiues41~1 Figun 6.3 0.pth m. Forrtwite in divine, VBS-97-79.

APPENDIX B

Parental Melt Calculation:

Labradorite in gabbro compositions (Best, 1982): Si02 53.44 W.% A1203 29.58 W.% Fe203 0.13 W.% Fe0 0.14 W.% Mg0 0.06 W.% Ca0 11.83 W.% Na20 4.5 1 W.% K20 0.26 W.% Ti02 0.02 wt.%

Sample calcuIation:

Curnulate rocks: 50 % mode plag + 50 % liquid (approximately)

48.2 wt.%(north gabbro) = 53.44 W.% Si02 (0.5 mode) + x (0.5)

48.2 W.% = 26.72 wt. % + x (0.5) APPENDlX C

R-factor calculation:

Y = 20 000 ppm (2% Ni, rough estimate taken from Table 3.1) X = 150 ppm (rough estimate taken from Table 53) D = 1 100 (the author chose 1 100 as values were 1000- 1300 for 48 wt% SiO2; 10 wt% Mg0 in Peach and Mathez, 1993)

20 OOOR + (22 x 106 )= 165 000 + 165 OOOR

(22 x 106 ) - 165 000 = 165 OOOR - 20 OOOR

2 1 835 000 = 145 OOOR . NOTE 10 USERS

Oversize maps and charts are microfilmed in sections in the following manner:

LEFT TO RIGHT, TOP TO BOTTOM, WlTH SMALL OVERLAPS

Donner -- - - liners [.id O 1 2 3 4 5 III Kilometers Donner Minerals Ltd 1 Teck Exdoration Lt-d South Voisey's Bay Project,