UPPER DEVONIAN STRATIFORM

BARITE-LEAD-ZINC-SILVER MINERALIZATION

AT TOM CLAIMS,

MACMILLAN PASS, YUKON TERRITORY

by

ROBERT CLIFTON CARNE

B.Sc, University of British Columbia, 1974

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

in

THE FACULTY OF GRADUATE STUDIES

(Department of Geological Sciences)

We accept this thesis as conforming

to the required standard

THE UNIVERSITY OF BRITISH COLUMBIA

© Robert Clifton Carne, 1979 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.

R.C. Carne

Department nf Geological Sciences

The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5

Date April 20, 1979 ABSTRACT

The Macmillan Pass area is underlain by Hadrynian to Middle Devonian fine grained sedimentary strata and volcanic rocks,of Selwyn Basin. Wide• spread occurrences of Upper Devonian debris flows and turbidites record uplift and erosion of older rocks to the west or northwest. Deposition of overlying, locally derived coarse clastic assemblages are related to subsequent formation of a graben-like, fault-bounded trough in the study area. Continued slow subsidence of the down dropped basin is reflected by anomalously large thicknesses of an overlying siliceous black shale unit. Upper Devonian strata are unconformably overlain by Mississippian(?) peri-tidal or shallow water clastic sedimentary rocks which record a grad• ual, northward sea level transgression. Paleozoic and older rocks are intruded by Cretaceous granitic bodies.

Stratiform barite-lead-zinc mineralization on the Tom claims is contained in two tabular zones separated by a fault. Both zones occur at the transition between Upper Devonian locally derived coarse clastic rocks and overlying basinal shales. The two mineralized bodies together contain nine million tons of ore grade material averaging 8.6% Pb, 8.4% Zn and

2.8 oz/ton Ag, based on initial development work.

The Tom West Zone, studied in detail, consists of seven stratiform mineral horizons, each with distinctly different characteristics. Ore textures vary from massive quantities of poorly bedded galena, sphalerite and pyrite to finely laminated barite and cherty argil lite with disseminated sulphide minerals. A mineralized and altered breccia body underlies the stratiform massive sulphide mineralization.

Time-stratigraphic reconstructions of a cross-section through the -iii-

Tom West Zone, with accompanying mineralogical and assay data, predicate

a multi-stage genetic model. Each mineralizing event is time related to

localized tectonic activity which resulted in the formation of depressions

on the seafloor. Ore forming constituents were carried by geothermal fluids,

ascending along cross-stratal permeability provided by deep-seated faults

and venting to the seafloor through the breccia body. Exhalative fluids were initially relatively high temperature, cooling gradually through the

life of the geothermal system. Observed metal and mineralogical zonation within the stratiform mineralization reflects these processes. -i v-

TABLE OF CONTENTS

Paoe ABSTRACT ii ACKNOWLEDGEMENTS ix INTRODUCTION 1

Objectives 1

Location and Access 2

. General Description of the.Area 5 Previous Geological Work 5 Exploration History 6 GEOLOGIC SETTING OF THE MACMILLAN PASS AREA 8 Regional Tectonic Setting 8 Geology of the Selwyn Mountains 16 GEOLOGY OF MACMILLAN PASS AREA 22 Stratigraphy 22 Canol Formation: Unit 1 24 Unit 2 31 Unit 3a 52 Unit 3b 61 Imperial Formation: Unit 4a 78 Unit 4b 83 Quartz-feldspar porphyry dykes 85 Structural Geology 86 ECONOMIC GEOLOGY OF MACMILLAN PASS AREA 92

General Statement 92

Tom West Zone Mineralization 93 Method of Study 93

Ore Stratigraphy, Petrology, Mineral Textures and Metal Distribution 94 GENESIS OF STRATIFORM BARITE AND BARITE-LEAD-ZINC DEPOSITS OF MACMILLAN PASS AREA T....1 114 Review of Current Theories on Genesis of "Sedimentary- Exhalative" Deposits with Reference to Tom West Zone 114 Probable Genetic History of Tom West Zone "125 SUMMARY AND CONCLUSIONS 129 REFERENCES "140 -V-

LIST OF FIGURES

Page Figure 1: Map of Yukon Territory and western District of Mackenzie showing location of the Macmillan Pass area with respect to major settlements and highways 3

Figure 2: Location of the study area with respect to Tom and Jason claim groups 4 Figure 3: Tectonic elements of Yukon Territory and northern British Columbia 9 Figure 4: Tectonic elements of Yukon Territory and northern British Columbia before 450 km of post-Paleozoic right-lateral movement along Tintina Fault 10

Figure 5: Regional geology of southern Selwyn Mountains us—tbe_p.Q€tefe.^f&l Figure 6: Geology of Macmillan Pass area 4fi-#ie--pockFt SfCtll Figure 7: Generalized stratigraphy of Macmillan Pass area 23 Figure 8: Generalized stratigraphy of the upper part of Unit 1 (Canol Formation) 25

Figure 9: Stratigraphy of Unit 2 (Canol Formation) 34 Figure 10: Frequency vs grain size for Unit 2 (Canol Formation) massive conglomerate 37 Figure 11: Detailed stratigraphy of Unit 3a (Canol Formation) from an area immediately under• lying Tom West Zone stratiform mineralization 54 Figure 12: Typical section of framboidal pyritic and "blebby" shales of Unit 3b (Canol Formation) 69 Figure 13: Stratigraphy of upper Unit 3b (Canol Formation), Unit 4a and Unit 4b (Imperial Formation) 71 Figure 14: Reconstructed cross-section through the Tom deposit..at the close of Canol Formation time 88

Figure 15: Structurally restored, true stratigraphic c r \\ section of the Tom West Zone (south half) 4fr-^ne~pud^ f^''

Figure 16: Diagrammatic underground drill sections with C C \\ N assay values, Tom West Zone (south half) +ir-*h€-p eeket f u>" Figure 1.7: Theoretical behavior of four types of exhalative fluid in sea water 120 Figure 18: Successive mineralizing events, Tom West Zone o / /i (south half) in tho-poeket -vi-

LIST 0£ TABLES

Table I: Characteristics of coarse framework grains of Unit 2 (Canol Formation) conglomerate Table II: Characteristics of fine framework grains of Unit 2 (Canol Formation) conglomerate 36 Table III: Characteristics of some stratiform barite and base metal deposits 115

LIST OF PLATES Plate A: Photomicrograph of Unit 1 (Canol Formation) sandy siltstone showing limonite staining resulting from oxidation of constituent pyrite 27 Plate B: Photograph of groove and flute casts on the basal surface of a Unit 1 (Canol Formation) turbidite 27 Plate C: Photograph of the basal contact of the Unit 2 (Canol Formation) massive conglomerate 32 Plate D: Photograph showing detail of Unit 2 (Canol Formation) massive conglomerate 32 Plate E: Photomicrograph (plane light) of a well rounded, mottled grey chert pebble (Clast Type I) from Unit 2 conglomerate (Canol Formation) 39 Plate F: Photomicrograph (plane light) of Unit 2 conglomerate (Canol Formation) showing radiolarian chert pebble (Clast Type II) and angular black shale fragment (Clast Type V) 39 Plate G: Photomicrograph (plane light) showing detail of bleached and oxidized rim of oblate dark chert pebble (Clast Type III) from Unit 2 (Canol Formation) massive conglomerate.... 41 Plate H: Photomicrograph (plane light) of radiolarian chert pebble (Clast Type VI) from Unit 2 (Canol Formation massive conglomerate 41 Plate I: Photomicrograph (crossed nicols) of Unit 2 (Canol Formation) conglomerate showing well rounded quartzite pebble (Clast Type VII) and polycrystal1ine quartz grain (Clast Type X) 44

Plate J: Photograph of a 25 cm thick, poorly sorted slump debris deposit near the base of Unit 3a (Canol Formation) on the Tom claims 56

Plate K: Photomicrograph (plane light) of pebbly mudstone (Unit 3a, Canol Formation) 56

Plate L: Photograph showing typical exposure of recessive, silvery grey weathering shales of Unit 3b (Canol Formation), Jason claims 62 -vii-

Page Plate M: Photomicrograph (crossed nicols) of Unit 3b (Canol Formation) black fetid limestone 62

Plate N: Photograph of flat pebble conglomerate (Unit 4a, Imperial Formation) 82

Plate 0: Photomicrograph (crossed nicols) of bioturbated siltstone (Unit 4a, Imperial Formation 82 Plate P: Photograph of cross-laminated silty mudstone from the base of Unit 4b (Imperial Formation) 84 Plate Q: Photomicrograph (crossed nicols) of cross- laminated silty mudstone from the base of Unit 4b (Imperial Formation) 84 Plate R: Photomicrograph (plane light) of sheared turbidites of Unit 1 (Canol Formation) beneath the decollement surface, east edge of the study area 90 Plate S: Photomicrograph (reflected light) of massive sphalerite occurring in Horizon mineralization (Tom West Zone), showing chalcopyrite exsolution blebs 97

Plate T: Photomicrograph (reflected light) of laminated barite and sphalerite with interstitial galena of Horizon A (Tom West Zone), showing partially euhedral outlines of barite masses 97

Plate U: Photograph of silicified footwall fragments in Horizon A (Tom West Zone) massive galena 98 Plate V: Photograph of evenly laminated black cherty argillite and sulphide minerals of Horizon B, Tom West Zone 98

Plate W: Photomicrograph (reflected light) of euhedral barite crystals cemented by sphalerite and galena, Horizon C (Tom West Zone) 101 Plate X: Photograph of Horizon C (Tom West Zone) laminated mineralization exhibiting strong soft-sediment deformation 101

Plate Y: Photograph of finely laminated sphalerite, galena and barite of Horizon D, Tom West Zone 103 Plate Z: Photograph of Horizon F (Tom West Zone) mineralization showing dehydration cracks in cherty argillite beds 107

Plate AA: Photomicrograph (reflected light) of framboidal pyrite from the immediate footwall of the Tom West Zone 109

Plate BB: Photomicrograph (reflected light) of pyrite- bournonite intergrowth from epigenetic breccia mineralization underlying the south end of the Tom West Zone Ill -vi i i-

Page Plate CC: Photomicrograph (reflected light) of calcispheres replaced by pyrite and tetrahedrite. 113 Plate DD: Photomicrograph (plane light) of siderite replacing chert clast in Unit 2 massive conglomerate (Canol Formation).. 113 -ix-

ACKNOWLEDGEMENTS

The writer acknowledges the kind co-operation of the staff of Hudson

Bay Exploration and Development Co. Ltd., in particular, R.A. Freberg and

R. Macintosh who extended permission to examine underground drill core

and who provided copies of plans and diamond drill records for the Tom

deposit. Ogilvie Joint Venture personnel aided in permitting examination

of diamond drill core from the Jason property and providing copies of a one inch to one thousand foot scale, contoured orthophoto of the Tom and

Jason properties on which mapping control for this study was based. In

addition, C.L. Smith was most helpful in discussions on the stratigraphy

of the study area.

I further wish to express sincere appreciation to C.I. Godwin, under

whose supervision this thesis was written, and to A.J. Sinclair for his

help with the mineralogical work. W.C. Barnes and W.R. Danner provided

help and stimulated discussion on sedimentology and stratigraphy. S.L.

Blusson and K.M. Dawson of the Geological Survey of Canada offered constant

encouragement and elucidated correlations with regional stratigraphy.

Analysis of samples for microfossils and whole-rock geochemistry whteh were

carried out by the Geological Survey were submitted to K.M. Dawson and

D.F. Sangster respectively.

Field work for this project was carried out while the writer was

employed by the Geology Section of the Department of Indian and Northern

Affairs, Whitehorse. Their support is gratefully acknowledged. Minor

financial support was contributed by the Department of Geological Sciences,

University of British Columbia. - 1 -

INTRODUCTION

The thesis area, located near Macmillan Pass along the Yukon-Northwest

Territories border, has been of economic interest since the discovery of

stratiform barite-lead-zinc-silver mineralization and subsequent staking of the Tom mineral claims by Hudson Bay Exploration and Development Co.

Ltd. prospectors in 1951. Interest in the area was renewed with the recent discovery of similar mineralization six km west of the original Tom showings.

In addition to barite-hosted base metal mineralization of^.economic potential

in the Macmillan Pass area, Upper Devonian to Mississippian black shales and associated clastic rocks of the Canol Formation and its time equivalents in southeast Yukon and northeast British Columbia contain perhaps the world's largest known accumulations of sedimentary barite.

Objectives

Purpose of the present work is to study in detail the petrology,

stratigraphy and depositional setting of the Upper Devonian and Mississippian

Canol and Imperial Formations, informally known as the "Black Clastic Unit", in the Macmillan Pass area and to describe in detail the mineralogy, ore textures and mineral zonation of the Tom barite-lead-zinc-silver deposit.

In combining the determination of the tectono-stratigraphic setting of the deposit with detailed studies of the mode of ore deposition, it is hoped that a tenable genetic model for the Tom deposit can be outlined. A genetic model, by analogy, could be applied to other stratiform base metal deposits which have similar features. To this end, a 24 square kilometre area of the Tom and adjoining Jason claims was mapped by the author in - 2 -

July and August of 1976 and during a short visit to the area in the late summer of 1977. Detailed logging of underground diamond drill core from the Tom deposit was carried out in Whitehorse during May and December, 1976.

The author benefitted from a ten week period of employment with Archer,

Cathro and Associates in July and August, 1977 during which he was responsible for detailed mapping of Upper Devonian and Lower Mississippian sedimentary

rocks of a large area..immediately south of the Tom claims. The present

study incorporates some of the results of that work.

Location and Access

Tom and adjacent Jason claim groups are located approximately nine

kilometres southwest of Macmillan Pass at the Yukon-Northwest Territories

border (Figures 1 and 2). Vehicle access to the area is by the North Canol

Road which crosses both claim groups. The road is not presently maintained

during winter months (October to April). A gravel surfaced, 600 metre

airstrip which is located on the north part of the Tom property serves

both camps. A permanent trailer camp on the Tom property is accessible

by a 3 km gravel road leaving the Canol Road at Kilometre 440. The main

showing area on the Jason property is served by a four-wheel-drive and

bulldozer tote road that crosses the Macmillan River. Ross River, the

closest community, is accessible by the Canol Road (160 km) or by wheel-

equipped fixed wing aircraft. Following local convention, the area of the

Tom and Jason claims is referred to as the "Macmillan Pass area" in the

present work. - 3 -

Alaska Highway Klondike Highway ® Canol Road / ® Robert Campell Highway ® Dempster Highway /

Alaska

Territory 'Dawson

Norman Wells

V Northwest V i '' Territories

Macmillan Pass Area

British

Columbia

miles 150 J T I 0 km 150

Figure 1. Map of Yukon Territory and western District of Mackenzie showing location of the Macmillan Pass area with respect to major settlements and highways. Figure 2. Location of the study area with respect to Tom and Jason claim groups. - 5 -

General Description of the Area

Macmillan Pass lies within the Selwyn Mountains physiographic province

(Bostock, 1948). Relief is moderate, elevations range from 1160 m (3800 ft) to over 2010 m (6600 ft). The dominant physiographic feature of the area

is the Macmillan River valley which crosses the central map area in a northeast to southwest direction. Bedrock outcroppings are scarce, with the exception of steep-sided ridges and peaks which are often craggy when capped by resistant rock. Flat-topped ridges and hills, which are almost devoid of outcrop, are usually covered by blocks of felsenmeer locally derived from frost riven bedrock. Valley bottoms are covered by a thick mantle of drift, colluvium and alluvium.

Although hunting in recent years has diminished populations of the larger mammals, moose, grizzly bear, caribou and wolves are still commonly

seen in the region. Areas with elevations less than 1500 m (5000 ft)

support a dense vegetation cover, including alpine fir on well drained

slopes and stunted black spruce, willow and Arctic black birch on poorly drained valley bottoms (Porsild, 1945).

Previous Geological Work

Earliest work by the Geological Survey in the region was by Kindle

(1945) who carried out reconnaissance geological mapping during the summers

of 1944 and 1945 along the route of the then recently completed Canol Road.

Regional mapping by Blusson (1974), which includes the study area, was

released on Open File by the Geological Survey of Canada in 1974. Recent

studies by Geological Survey of Canada workers Blusson (1976) and Dawson - 6 -

(1977) have aided in defining the strati graphic setting,.of the Tom deposit.

This report draws heavily on unpublished diamond drill data supplied by

Hudson Bay Exploration and Development Co. Ltd. A summary of the author's field work in the area during the summer of 1976 has been published

(Carne, 1976).

Exploration History

The Tom mineralization was discovered in 1951 by Hudson Bay Exploration and Development Co. Ltd. prospectors. Development work by the company, primarily on the discovery or "West" zone, during the period 1951 to 1953 consisted of geological mapping, sampling and trenching as well as 5436 m of EX diamond drilling in 39 holes (R.A. Freberg, oral communication, 1976).

This operation is believed to be the first use of helicopter-supported diamond drilling in the Yukon Territory (Freberg, 1976). Estimated reserves at this time were 10.47 million tons of material averaging 5% zinc and some lead (Green, 1965). Because of low zinc prices and its remote location, the property lay idle until 1966 when a small crew resurveyed the original grid set up in 1951 and conducted geological mapping, geochemical soil surveys and a magnetometer survey (R.A. Freberg, oral communication, 1976). Late in the 1967 season, an additional 1675 m of BQ diamond drilling was carried out to evaluate a new soil geochemical anomaly discovered upslope and east of the discovery zone. The results of this work were encouraging and the company continued drilling in 1968 on the lead-rich new discovery, or

"East" zone as it became known. A total of 3271 m of BQ diamond drilling

in 16 holes was completed in conjunction with additional geochemical

sampling and geological mapping. Reserves at this time were quoted at - 7 -

5.1 million tons grading about 8% zinc, 8% lead and 2.7 oz/ton silver

(Findlay, 1969).

During the summer of 1969, the company rebuilt the Canol Road from

Ross River to the property and upgraded an existing airstrip (Craig and

Laporte, 1970). A mining camp was established late in the season;,and an adit was collared west of and downslope from the two showings. During

1970 and 1971 the two mineralized zones were further defined by a total of 1887 m of underground development in conjunction with 2363 m of AQ underground diamond drilling. Additional AQ underground drilling early in 1972 increased the total diamond drilling on the property to 11,853 m

(Archer, Cathro and Associates, 1972). Ore reserves are currently estimated at 9 million tons averaging 8.6% lead, 8.4% zinc and 2.8 oz/ton silver using an 8% combined lead and zinc cutoff grade. Ten million tons of sub-ore grade material averaging 4.6% zinc, 0.9% lead and trace amounts of silver have been outlined (Archer, Cathro and Associates, 1972).

Very little further physical work has been carried out on the property since culmination of the drilling program in 1972. A small crew was employed during August of 1976 to repair damage to the permanant trailer camp caused by an avalanche the previous spring. Additional soil sampling, trenching and geophysical surveys were carried out late in the 1977 field season..

The Jason claims, owned by Ogilvie Joint Venture*, adjoin the Tom property to the west (Figure 2), and were staked in August, 1974 and July,

1975 following discovery of significant lead, zinc and barium soil geo• chemical anomalies. During June and July of 1975, geological mapping as

* C.L. Smith, Brinex, Mitsubishi Canada Ltd. and Ventures West Capital Ltd. - 8 -

well as geochemical and gravity surveys were conducted on the property. Zinc and barium soil anomalies coincident with a gravity high led to definition of targets that were followed up by exploratory

BQ diamond drilling in October, 1975. Seven holes were drilled, totalling 640 m in length.,. During the summer of 1976, an additional

2163 m of drilling in 14 holes was completed. Midway through the 1976 drilling program, diamond drill size was increased from BQ to NQ in an effort to combat excess flattening of deep holes with no apparent positive effects. Rotary drilling methods employed for deep drilling during the summer of 1977 also proved unsatisfactory because of poor ground conditions. Controlled diamond drilling using HQ-size equipment, carried out in the late summer and fall of 1977, resolved the flattening problem to the satisfaction of OJV geologists.

Rumours of the discovery of stratiform barite-lead-zinc mineralization on the Jason property precipitated a claim staking rush late in the summer of 1976. Most of the remaining favourable ground in the Macmillan Pass area was staked.

GEOLOGIC SETTING OF MACMILLAN PASS AREA

Regional Tectonic Setting

The regional tectonic setting of southern Yukon Territory, southeastern Northwest Territories and northern British Columbia is shown dm Figure 3. Distribution of tectonic elements before 450 km of dextral transcurrent movement along Tintiha Fault is shown in

Figure 4. The principal tectonic subdivisions are: - 9 -

ANVIL-CAMPBELL ALLOCHTHON

Yukon SYLVESTER ALLOCHTHON Territory

Alaska

Northwest

Territories

acmillan Pass Area

i

O, British

^ O Columbia

NORTHERN ROCKY MTN TRENCH

Figure 3. Tectonic elements of Yukon Territory and northern British Columbia (after Tempelman-Kluit, 1977 and Gordey, 1978). - 10 -

Figure 4. Tectonic elements of Yukon Territory and. northern British . Columbia before 450 km of right-lateral movement along Tintina Fault (refer to Figure 3).. - 11 -

Mackenzie Arch (Douglas ejt a]_., 1970) and Macdonald Platform

(Gabrielse, 1967; Douglas ejt al_., 1970)-^..regions of dominantly shallow-water carbonate sedimentation from Early Cambrian to

Middle Devonian time;

Pelly-Cassiar Platform (Gabrielse, 1967; Gordey, 1977; Tempelman-

Kluit and Blusson, 1977) - a northwest trending belt of shallow- water carbonate sedimentation during the Siluraan and Devonian which was built upon a platform of extensive Late Cambrian andesitic submarine volcanism;

Selwyn Basin (Gabrielse, 1967; Tempelman-Kluit and Blusson, 1977)

- a northwest trending epicontinental trough which was partially bounded on its seaward side by the Pelly-Cassiar Platform and to the east and northeast by shallow-water carbonates of Mackenzie

Arch. Selwyn Basin sedimentation was characterized by shale and chert accumulation from Early Cambrian to Middle Devonian time.

During the Late Devonian and Lower Mississippian coarse clastic rocks and shale derived from erosion of uplifted blocks within the basin finally filled it, lapping across Pelly-Cassiar Platform and onto the miogeoclinal sequence to the east and northeast;

Kechika Trough (Douglas etaiL^ 1970; Gabrielse et a]_., 1977).-.a linear trough of dominately shale accumulation from Early Cambrian to Middle Devonian time. It is continuous with southern Selwyn

Basin and separates southern PelTy-Cassiar Platform from Macdonald

Platform. During the Upper Devonian a flood of coarse clastic rocks and associated shales derived from the west covered

1eptosynclinal shales of Kechika Trough and lapped onto the - 12 -

the carbonates of Macdonald Platform;

(5) Omineca Crystalline Belt (Douglas et a]_., 1970; Wheeler et al_. , 1972;

Tempelman-KIuit, 1978) - a belt of crystalline rocks that includes

metamorphosed lithologies of Proterozoic and Paleozoic shelf edge

rocks correlative with shallow-water carbonates of Pelly-Cassiar

Platform. Metamorphic rocks are intruded by discordant high level

plutons. Omineca Crystalline Belt is continuous with Yukon

Crystalline Terrane;

(6) Yukon Crystalline Terrane (Tempelman-Kluit, 1976 and 1978, Tempelman-

Kluit ejt al_. , 1976) - a region of metamorphic rocks ranging from

Proterozoic to late Paleozoic which are generally correlative with

unmetamorphosed equivalents in Pelly-Cassiar Platform to the south•

east and in Selwyn Basin to the northwest. Metamorphic rocks, which

are intruded by late Mesozoic and Tertiary plutons, can also be

correlated.with metamorphic rocks of Omineca Crystalline Belt on the

basis of gross lithological similarities;

(7) Coast Plutonic Complex (Roddick and Hutchinson, 1974; Wheeler et al.,

1972) - an extensive belt of dominately pluton^and metamorphic rocks.

Mesozoic to Tertiary magmatism was essentially synchronous with

metamorphism so that many granitic bodies are concordant with

metamorphic culminations;

(8) Whitehorse Trough (Tempelman-Kluit, 1978) - a partially fault bounded

late Triassic to Middle Jurassic back-arc basin into which clastic

debris was shed from a volcanic arc lying to the southwest;

(9) Tantalus Basin (Wheeler e_t al_., 1972) - a successor basin which formed

from segmentation of Whitehorse Trough and in which Upper Jurassic and - 13 -

Lower Cretaceous non-marine clastic sediments accumulated;

(10) Atlin Terrane (Monger, 1975) - a northwest trending, fault bounded

complex composed of weakly metamorphosed Upper Paleozoic marine

sediments, basic volcanic rocks and ultramafic rocks;

(11) Anvil-Campbell Allochthon (Tempelman-Kluit et al., 1976; Tempelman-

Kluit, 1977) - an assemblage of Permian ocean floor cherts, basalts

and associated ultramafic rocks presumed to have been thrust upon

southeast Selwyn basin, Pelly-Cassiar Platform, Yukon Crystalline

Terrane and Omenica Crystalline Belt during the Late Triassic. A

number of isolated bodies of mafic and ultramafic rocks scattered

through Yukon Crystalline Terrane are probable klippen of the same

allochthon. Batholith sized bodies of plutonic rocks, now preserved

. .as klippen, were thrust over the mafic and ultramafic rocks at a .

later time;

(12) Sylvester Allochthon (Wheeler et a]_., 1972; Tempelman-Kl uit et al.,

1976; Gabrielse, 1978) - an allochthonous assemblage of Mississippian

to Permian basic volcanics, ultramafics and chert emplaced upon

carbonate strata of southern Pelly-Cassiar Platform;

(13) Tintina Trench (Tempelman-Kluit, 1977) - a major topographic lineament

which extends northwestward from southeast Yukon into Alaska. Mid-

Late Cretaceous right lateral transcurrent movement of 450 km along

this lineament has been proposed (Tempelman-Kluit, 1977);

(14) Northern Rocky Mountain Trench (Gabrielse and Dodds, 1977); Gabrielse

et al_., 1977) - a major topographic lineament which forms a southerly

continuation of Tintina Trench and along which at least 125 km of

Eocene or later dextral transcurrent movement has occurred (Gabrielse - 14 -

et al_., 1977). Additional movement on subparallel faults may bring

the total right lateral transcurrent movement on the fault system to

about 450 km;

(15:)'Teslin Lineament (Tempelman-Kluit, 1978) - a west^dipping fault,which

has brought rocks of Atlin Terrane and Tantalus Basin next to, and

over Omineca Crystalline Terrane; and

(16) Denali Fault (Campbell and Dodds, 1978) - a major fault system along

which major dextral transcurrent movement occurred during Tertiary

time with sporadic minor movement continuing up to Recent time.

From early to middle Paleozoic time, shallow water carbonate sediments

accumulated on Mackenzie Arch and MacDonald Platform while in Selwyn Basin

and Kechika Trough, fine grained clastic sediments and cherts were deposited.

At its inception in Early Cambrian time, the basin was a comparatively

shallow area where calcareous shales were deposited while limestone

accumulated near the shelf-slope break along the site of the future Pelly-

Cassiar Platform. Later shallow water carbonate sediments of the platform

were built on a base of extensive Late Cambrian andesitic volcanism and

Selwyn Basin became truly restricted from the ocean. Shale, often

calcareous, accumulated along its margins while thick sequences of chert

were deposited in its deeper central parts. During Late Devonian time,

coarse clastic rocks which were derived from erosion of uplifted fault

blocks from within Selwyn Basin covered most of the basin and Pelly-Cassiar

Platform and lapped onto the miogeoclinal sequence on Mackenzie and

MacDonald Platforms. In early and Middle Mississippian time, central

parts of Pelly-Cassiar Platform were the loci of extensive marine acid - 15 -

volcanism while east-central and northeastern Yukon were covered by coarse clastic sediments derived from the uplift of northern parts of the Yukon. The record of latest Paleozoic sedimentation is incomplete but a return to more normal sedimentation by this time is indicated.

Early and Middle Triassic time was characterized by widespread tectonic activity. Metamorphism of Yukon Crystalline Terrane and northern Omineca

Crystalline Belt, and the^ emplacement of Anvi1-Campbel1 allochthon took place in this interval. By the late Triassic, Yukon Crystalline Terrane,

Omineca Crystalline Belt and Coast Plutonic Complex were emergent or shallow areas; the metamorphosed basement of Whitehorse Trough had subsided along a partially fault bounded margin, and at this time was a back-arc basin into which clastic debris was shed from a volcanic arc which lay to the southwest. As progressive erosion of the arc continued, granitic material from the eros.i.on of the Coast Plutonic Complex accumulated in the trough during Early and Middle Jurassic time. By Late Jurassic or Early

Cretaceous, sedimentation in Whitehorse Trough consisted of minor shale and coal in small basins or lakes while non-marine successor basin sedimentation continued in the adjacent Tantalus Basin. About mid- or

Late Cretaceous time, Whitehorse Trough, Tantalus Basin and At!in Terrane were uplifted and transposed eastward against Omineca Crystalline Belt along Teslin Lineament. The Coast Plutonic Complex, Omineca Crystalline

Belt, and to a lesser extent, Yukon Crystalline Terrane and Selwyn Basin were affected by widespread Mesozoic plutonism. Mid- to Late Cretaceous

and Tertiary dextral transcurrent movemement along Tintina and Northern

Rocky Mountain Trenches displaced the earlier formed tectonic elements. - 16 -

Geology of the Selwyn Mountains

The study area:is located near the east side of the Selwyn Basin tectonic province in the southern Selwyn Mountains. Geology of this area is shown in Figure 5. Sedimentary rocks, ranging in age from Hadrynian to Mississippian, are divided into five major sequences which are intruded by Cretaceous granitic rocks:

(1) Cambrian and earlier: "Grit Unit" and "Phyllite Unit" (Blusson, 1971;

Gabrielse et aj_., 1973; Gordey, 1978)

"Grit Unit" is an informal name coined by Roddick and Green (1961),

to describe Hadrynian clastic rocks which consist mainly of gritty

quartzite, black and dark green shale and slate, calcarenite, con•

glomerates and sandstone with lesser limestone, varicoloured shale

and slate. Quartzites and sandstones contain distinctive bluish,

opalescent rutilated quartz grains which are typically fractured and,

in many places, consist of a patchy mosaic of areas with slightly

different extinction. Large (granule sized) quartz grains are

generally well rounded while smaller grains usually have subangular

to subrounded outlines.

Gabrielse et_ al_. , (1973) use the term "Phyllite Unit" for a

succession of late Proterozoic to Lower Cambrian fine grained clastic

rocks which conformably overly the older "Grit Unit". Lithologies

consist of greyish green, non-calcareous phyllitic slates with minor

interbedded very fine grained quartzite and limestone.

(2) Lower Cambrian: Sekwi Formation (Blusson, 1971; Gabrielse et al.,

1973; Fritz, 1976; Gordey, 1978) - 17 -

The Sekwi Formation is characterized by an assemblage of brightly

coloured, orange and yellow weathering dolomites, silty limestone and

quartzite, with interbedded dark recessive shale and argillaceous

limestone. Basic submarine volcanic flows and associated tuffs are

an important component of the upper part of the formation in south

Selwyn Mountains. Platformal rocks of the Sekwi Formation are probable

time equivalents of the "Phyllite Unit". The facies boundary between

these two rockstypes occurs along a belt which passes approximately

through the centre of Figure 5.in a northwest to southeast direction.

Both the Sekwi Formation and the "Phyllite Unit" are partially eroded

and, in places, entirely removed beneath a mid-Franconian (middle

Upper Cambrian) unconformity of regional extent.

(3) Ordovician to Middle Devonian: Road River Formation (Roddick and Green,

1961; Gabrielse, 1967; Green et al_., 1967; Blusson, 1971; Gabrielse et

aj_., 1973; Gordey, 1978)

Ordovician to Middle Devonian argillaceous graptolitic rocks

throughout northern Yukon, easternmost Alaska and Selwyn Basin are

referred to as the Road River Formation. Lithologies consist largely

of recessive, platy, thin bedded argillaceous limestone, calcareous

shale and chert. In southern Selwyn Mountains Road River calcareous

shales change facies eastward to platformal carbonate rocks along a

northwest-southeast trending belt which passes through the northeast

corner of Figure 5. Southwest of Selwyn Mountains, Road River shales

grade rapidly into sequences of varicoloured basinal cherts which

underlie much of central Selwyn Basin. In the area of Figure 5 and - 18 -

to the southwest, Road River lithologies lie unconformably on the

Proterozoic "Grit Unit", Lower Cambrian "Phyllite Unit" and probable

facies equivalents in Sekwi Formation. To the east and southeast,

where no significant hiatus is indicated, middle Paleozoic platformal

carbonate rocks and basinal shales are conformable with carbonate

rocks of the underlying Upper Cambrian Rabbitkettle Formation. Black,

carbonaceous shales of Road River Formation host the large Howards::

Pass stratiform zinc-lead deposit located about 100 km south of

Macmillan Pass in Nahanni map area (105 1/6, 11, 12).

(4) Upper Devonian: Canol Formation (Roddick and Green, 1916; Blusson,

1971; Gabrielse et al_., 1973)

The name Canol Formation was originally applied to black, siliceous,

pyritic and non-fossiliferous Upper Devonian shales which occur near

Norman Wells on the Mackenzie River (Bassett, 1961). Rocks of the

same age and similar lithology which occur in the Macmillan Pass area

have been grouped with overlying clastic rocks and informally referred

to as the "Black Clastic Group". The lower black shale member of the

"Black Clastic Group" has recently been tentatively assigned to the

Canol Formation by Blusson (1976, cited in Dawson, 1977). Shales of

the "Black Clastic Group" blanket much of Selwyn Basin, Kechika Trough

and northern Yukon. Canol Formation attains its greatest known thickness

and lithological complexity in the Macmillan Pass area where it was

deposited in a graben-like, east-west trending trough described by

Blusson (1974 and 1976). Canol shales unconformably overlie Road River

Formation shales in Selwyn Mountains; however, no apparent unconformity

of this age exists to the southeast in southern Mackenzie Mountains - 19 -

where the shales conformably overlie carbonate strata of Nahanni and

Headless Formations. According to Gabrielse (1967) and Tempelman-

Kluit and Blusson (1977), deposition of widespread Upper Devonian clastic rocks may have resulted from erosion of uplifted fault blocks within Selwyn Basin. The Tom and Jason stratiform barite-lead-zinc- silver deposits are contained within Canol Formation near its base and above a massive, locally occurring chert pebble conglomerate.

Similar occurrences of barren bedded barite are present in numerous locations.over a wide area extending from southern Kechika Trough to northern Mackenzie Mountains (Blusson, 1976; R.J. Cathro, oral communication, 1977). Barite deposits, which range in thickness from a few centimetres to 150 m or more, may attain a strike length of over 8 km.

Mississippian and later(?): Imperial Formation (Roddick and Green,

1961; Blusson, 1971; Gabrielse et al_., 1973)

The youngest sedimentary rocks exposed in the southern Selwyn

Mountains are the upper part of the "Black Clastic Group" which has been correlated with the Imperial Formation (Hume and Link, 1945) of northern Mackenzie and Richardson Mountains (Blusson, 1976, cited

in Dawson, 1977). In Selwyn Mountains, Imperial Formation lithologies consist of resistant, massive siltstones, quartzites, conglomerates and shales. Basal members are separated from the Canol Formation by a sharp lithological break which is locally an angular unconformity.

Deposition of relatively shallow water siltstones and quartzites in the Macmillan Pass area and contemporaneous deposition of turbidites

in the Howards Pass area, 100 km to the south, is consistent with - 20 -

with southerly paleocurrent indicators in the turbidites (T. Bremner,

oral communication, 1977). Imperial Formation sediments are thought

to have been derived, in part, from uplifted areas in the Barn and

British Mountains near the Arctic Coast but in southern Selwyn Mountains

they may include complexly interfingered material derived from local

sources as well (J.6. Abbott, oral communication, 1978). Gordey (1978

and oral communication, 1978) has mapped a fault near the Howards Pass

area where Imperial Formation unconformably overlies both the Canol

and Road River Formations where they are juxtaposed by a high angle

normal fault.

(6) Cretaceous: Granitic stocks and dykes (Blusson, 1971; Gabrielse et

al_. , 1973)

Granitic stocks which occur in Selwyn Mountains are a part of a

belt of post-tectonic granitic intrusive rocks which fringe Selwyn

Basin along its east and northeast edge. Dominantly granodioritic

and quartz-monzonitic in composition, they are characterized by

hornblende as the principal mafic mineral. Stocks generally lack

foliation, have sharply defined contacts with few apophyses and are

finer grained or, in part, porphyritic near contacts. Hornblende

granodiorites of the Itsi Range (Figure 5) have been dated by potassium-

argon means as 96 million years old (Bassdsgaard et, al_., 1961) while

biotite quartz-monzonites in southern Mackenzie Mountains (Flat River

map area) yield a potassium-argon age of 110 million years (Leech et

al_., 1963).

Rusty weathering contact aureoles up to 600 m wide are most

strikingly developed in fine grained clastic rocks. Pelitic hornfels - 2 1 -

consist primarily of sericite, muscovite, quartz and biotite with

rare andalusite and graphite. Impure limestones are relatively

unchanged in appearance by contact metamorphism except that differential

weathering in silty banded limestones is accentuated by growth of new

minerals, commonly diopside, tremolite, idocrase, garnet, epidote, and

rarely, potash feldspar, plagioclase, sphene and biotite. Sandy and

silty dolomite and dolomitic sandstones are altered to mixtures of

tremolite, diopside, quartz and carbonates. The Targe Mactung tungsten

deposit, located along the Yukon-Northwest Territories border (Figure 5),

is contained within a skarn developed in probable Sewki Formation

limestone-shale breccias (Dawson and Dick, 1978).

Northwesterly trending, northerly plunging open folds are the dominant structures developed in rocks of southern Selwyn Mountains. Isoclinal folding is more commonly developed in peilitic rocks of Selwyn Basin than in carbonate platformal equivalents to the northeast. Steeply dipping reverse faults, which parallel the regional fold trend, commonly die out in the cores of anticlines and are probably related in time to the regional deformation. Axial plane cleavage is best developed in pelitic rocks and to a lesser degree in carbonate rocks while only relatively competent sandstone and conglomerate beds lack cleavage. Steeply dipping, north• easterly trending normal faults cross-cut and displace earlier regional structures. Axial plane cleavage associated with regional deformation predates mid-Cretaceous granitic intrusions. Minor, small scale doming, folding and block faulting of country rock accompanied intrusion of the

stocks. - 22 -

A belt of east-west trending, isoclinal folds and vertical faults cross-cuts northwesterly trending structuresoof central Selwyn Mountains in the area of Macmillan Pass. Fold axes and well developed axial plane cleavage are steeply dipping to slightly overturned. This structural belt is terminated by northerly trending normal faults in a region located about

40 km east of the study area. Although this deformation is likely post-

Paleozoic in age, it may coincide with an Upper Devonian graben-like trough.

Its trend and location, then, may be inherited from this earlier structure.

GEOLOGY OF MACMILLAN PASS AREA

Stratigraphy

The study area is underlain by clastic sedimentary rocks of the Upper

Devonian to Mississippian and(?) later "Black Clastic Group". Lower part of the "Black Clastic Group" is correlative with the Canol Formation of the Normal Wells area, N.W.T. while the upper part is similar to Imperial

Formation of northern Yukon Territory. Formational names, although not officially accepted for these rocks, are applied here at the suggestion of S.L. Blusson (oral communication, 1977) on the basis of preliminary

regional studies by the Geological Survey of Canada. Geology of Macmillan

Pass area is shown in Figure 6. Stratigraphy is summarized in Figure 7.

Units 1, 2, 3a and 3b of Figures 6 and 7 are assigned to Canol Formation while map units 4a and 4b are assigned to Imperial Formation. Paleozoic

sedimentary rocks are intruded by Cretaceous quartz-feldspar porphyry dykes

genetically related to a large hprnblende-biotite granodiorite stock which

lies a few kilometres south of the study area (Figure 5). - 23 -

APPROXIMATE DESCRIPTION THICKNESS (m)

Calcareous and non-colcareous siltstones and silty IOOO mudstones local unconformity or facies change 0—100 Mudstone, shale and siltstone local unconformity

Black pyritic shales and mudstones, minor calcarenite 30—1300 turbidites and black fetid limestone, chert pebble • conglomerate turbidites near base on Jason property

0—20 Stratiform barite-leod-zinc-silver deposits 4—40 Pyritic shales and siUstones, slump deposits 70-240 Massive chert pebble conglomerate debris flow and turbidites

Siltstones and. shales (turbidites), occasional thin chert 120 pebble debris flows , disconformity Carbonaceous, slightly calcareous black shales, black chert and black shaly limestone

Figure 7. Generalized stratigraphy of Macmillan Pass area. - 24 -

Canol Formation: Unit 1

Relatively recessive lithologies of Unit 1 are well exposed in steeply dipping beds forming the core of an anticline which borders the northwest edge of the study area (Figure 6). Unit 1 is poorly exposed in uplifted fault blocks in the southwestern portion of the map area and near the east edge of the map area where the core of an anticline is cut by a cirque.

Only the uppermost 45 m of Unit 1 were observed. Generalized stratigraphy is shown in Figure 8.

Four distinct lithologies are recognized in the upper 45 m of Unit 1:

(a) finely interbedded silty shales and sandy siltstones (contourites);

(b) thick bedded silty sandstones (turbidites);

(c) medium to thick bedded sandy siltstones (grain flows); and

(d) chert pebble conglomerate bodies with lenticular cross-sections

(debris flows).

Grey weathering, black silty shales which are finely interbedded with brown weathering, grey sandy siltstones make up about 80% of the map unit.

Shale beds range:.from 1 cm to 4 cm in thickness and average about 2 cm.

On the other hand, sandy siltstone interbeds are much more variable in thickness, ranging from a few grains thick to accumulations over 5 cm thick.

Overall shale-siltstone ratio of these rocks is approximately 5:1. This ratio decreases slightly toward the top of the observed section of Unit 1 due to an increase in overall thickness of the sandy siltstone component with respect to shale.

Silty shales consist of a fine grained mixture of clay minerals and

opaque organic matter. A few silt-sized grains of sericite averaging 0.05

mm in length are present as are a few well rounded silt-sized grains of quartz. - 25 -

Figure 8. Generalized stratigraphy of the upper part of Unit 1 (Canol Formation). - 26 -

Framework of sandy siltstone interbeds is predominately composed of subangular to subrounded quartz grains which range in size from less than

0.01 mm to 0.5 mm in long diameter. Quartz grains make up about 35% of the rock. Approixmately 15% of the sandy siltstones is composed of sub- rounded to well rounded argillaceous chert grains ranging in size from

0.02 mm to 0.8 mm in long diameter. A few masses of matted kaolinite with subequant: to subrounded outlines are present, probably as alterations of detrital feldspars. Less than 5% of the rock is composed of opaque to semi- opaque, irregular patches of organic(?) matter segregated in laminae with finer constituents. Angular fragments of black shale make up less than

5% of the rock. Nearly 40% of the rock is composed of a matrix of clay minerals and opaque organic(?) matter cemented by cryptocrystal1ine quartz.

The amount of matrix materials varies considerably; in places quartz and chert framework grains are in point contact,/.while a majority of the grains are "floating" in matrix and cement. Limonite casts after pyrite are common in sandy siltstone beds, especially in finer grained laminae.

Limonite staining of the rock, resulting from oxidation of this pyrite, is conspicuous as brown bands aligned parallel to bedding (Plate A). Oxidation of pyrite is not a surface weathering effect since limonite and pyrite crystal casts are present in diamond drill core of Unit 1 taken from several hundreds of metres below surface.

Sandy siltstone beds do not generally show well developed graded bedding although a general concentration of sand size grains is noted at the basal portions of thicker units. Basal contacts are sharp and seldom have features indicative of erosive deposition although flute casts and sole marks are present on exposed bases of some of the thicker beds. Flute cast Plate A: Photomicrograph of Unit 1 (Canol Formation) sandy siltstone showing limonite staining resulting from oxidation of constituent pyrite. Sedimentary tops is to the right.

Plate B: Photograph of groove and flute casts on the basal surface of a Unit 1 (Canol Formation) turbidite. - 28 -

orientations were not measured due to the rubbly nature of most exposures of these 1ithologies. Load casting of sandy siltstones into underlying silty shales is common, grading into incipient ball and pillow structure, with increasing thickness of sandy siltstone units. Parallel lamination is commonly well developed near the base of thicker beds while upper parts commonly display well developed low angle cross-lamination. Upper surfaces of sandy siltstone beds are sharp and frequently rippled.

Finely interbedded silty shales and sandy siltstones with sand/shale ratios of 1 or greater are characteristic of the deep water, distal turbidite facies as proposed by Walker and Mutti (1973) and as described by Valdiya

(1970) and Cromwell et aj_. (1966). Load and flute casts are also commonly characteristic of turbidity current deposits (Davies and Williamson, 1976).

However, the absence of well defined graded bedding and the presence of parallel lamination, small scale cross-lamination and abrupt rippled tops in sandy siltstone beds is more characteristic of distal turbidity current deposits which have been reworked by bottom-flowing currents. These deposits are called contourites, as defined by Bouma (1973). Following these considerations, it is likely that.normal pelite deposition was interrupted periodically by silt and sand influxes carried by turbidity currents.

Reworking and redistribution of coarse material was effected by contour- following bottom currents.

Medium to thick bedded, grey silty sandstone beds occur near the top of the observed section of Unit 1. Thickness of these beds ranges from about 2 cm to over 2 m. Subrounded to well rounded, bluish opalescent quartz grains which range in size from 0.04 mm to 0.5 mm, with a modal diameter of approximately 0.3 mm, make up about 40% of the rock. Eighty - 29 -

percent of these grains have non-undulose extinction; all show strong, optically continuous quartz overgrowths. Subrounded to well rounded! chert grains comprise about 20% of the rock. Chert grains range in size from 0.06 mm to 0.5 mm with an approximate model diameter of 0.3 mm.

Most of these are argillaceous cherts composed of microcrystal1ine quartz and clay minerals. A few grains contain abundant radiolarian(?) "ghosts"..

Iron oxides are conspicuous, comprising 2% to 5% of the rock as pore fillings and cement. Organic matter, present as irregular bodies of black, semi- opaque material, forms less than 5% of the rock. Angular black shale fragments, commonly less than 0.06 mm in size, make up 2% to 3% of the rock.

Although about 25% of the silty sandstones is composed of a matrix of clay minerals and microcrystal1ine quartz cement. Cementation is incomplete resulting in a fairly high permeability.

Size grading in silty sandstone beds is present only as a vague concentration of medium sand size (greater than 0.25 mm) quartz and chert grains at bases of the beds. Finer sand and silt size clasts are distributed evenly through the rock. Vague bedding is discernable in the middle and upper portions of the beds as a diffuse concentration of organic matter along subparallel planes. Prominent asymmetrical, climbing ripple cross- lamination is usually present in the upper portions of beds. Ripples are anastomosing and subparallel when viewed on exposed upper bedding surfaces.

Distinctive, buff weathering sandy siltstone beds are distributed throughout the section of Unit 1 which occurs on the ridges paralleling the northwest edge of the study area (Figure 6). Subrounded quartz and chert grains, ranging in size from 0.01 mm to 0.07 mm with a modal diameter of 0.05 mm (coarse silt) compose about 45% of the rock. Granule size - 30 -

chert grains commonly are present near the bases of thickest beds. Very few angular, silt sized shale fragments are distributed evenly throughout the beds. Framework grains are supported by a matrix of clay minerals and a cement of microcrystal1ine quartz with subordinate iron-oxides which makes up about 45% of the rock. In some thin sections,, porosity makes up as much as 15% of the sandy siltstones. Porosity occurs mainly in the form of intergranular euhedral limonite casts after pyrite crystals.

The:sandy siltstone beds, although quite variable in thickness, appear to be otherwise identical. Size grading of framework grains is generally absent. Diffuse parallel lamination of iron-oxide accumulations are related to oxidation of pyrite as shown by the cocurrent concentrations of limonite casts. Sharp, featureless upper and lower contacts are usually present.

Thickness of individual beds varies markedly and several appear to lens out along strike over a distance of a few hundred metres. Stauffer (1967) gives an excellent account of similar features observed from beds in the Santa

Ynez Mountains of California. He proposes a classification as grain flows for the transportation and deposition of these fine sandy sediments.

Characteristics of grain flow deposits indicate deposition by pseudo-laminar flow of granular material, possibly initiated by tectonism in the source area. Walker and Mutti (1973) point out, however, that in the absence of excess pore pressures, relatively large slopes (18° to 37°) are required for true grain flow. This observation effectively argues against the inclusion of grain flow deposits in normal turbidite successions which are considered to be indicative of very gentle depositional slopes. The high percentage of intergranular porosity of sandy siltstone beds of Unit 1 may be indicative of relatively high initial pore pressure, enabling deposition on low angle slopes. - 31 -

Tabular bodies of chert pebble conglomerate with lensoid cross-sections occur near the top of Unit 1. Sedimentary structures, other than broadly scoured basal contacts, were not seen in these rocks. Their petrology, fabric and, presumably, their mode of deposition are similar to those of the massive chert pebble conglomerate discussed in following sections.

No fossils or trace fossils were seen in rocks of Unit 1 other than a few fibrous, wood-1ikeoongahi^"fragments which were observed in thin sections of silty sandstone beds. An ammonite was collected in 1976 by J.A. Morin from a dense, black, non-calcareous mudstone which underlies beds of Unit 1 about one kilometre east of the Tom deposit (J.A. Morin, oral communication,

1976). The fossil was subsequently identified as Ponticeras cf. P_. tschernyschewi (Hozapfel) of Upper Devonian (Frasnian) age by W.W. Nassichuk of the Institute of Sedimentary and Petroleum Geology in Calgary (Report

No. l-WWN-1977). The species has been previously identified from above the Kee Scarp Formation on Carcajou Ridge, Norman Wells area, N.W.T., where it occurs in "unnamed beds" just below the Canol Formation (W.W.^Nassichuk, written communication, 1977).

Canol Formation: Unit 2

Relatively resistant lithologies of Unit 2 are well exposed on both the Tom and Jason properties, forming prominent ridges and scarps on rugged hillsides and low g.laciated ridges and hills in lowlands of the Macmillan

River valley. Lithologies consist mainly of massive, resistant chert pebble conglomerate (Plates C and D). Less resistant, coarse grained chert turbidites with interbedded recessive black silty shales cap the thick conglomerate. Although both the conglomerate and coarser members of the turbidite sequence are extremely well indurated, they are commonly Plate D: Photograph showing detail of Unit 2 (Canol Formation massive conglomerate. - 33 -

well jointed and consequently, very susceptible to frost heaving. All but the steepest exposures are covered with a variable thickness of locally derived felsenmeer. The massive conglomerate exhibits considerable local variation in thickness, ranging from 70 to 240 metres. A complete section of the capping turbidites and shales was only seen on the Tom property, where it is 6.4 m thick. Lithologies of Unit 2 are summarized in Figure 9.

Maximum grain size measurements for individual constituents of the conglomerate were recorded from seventeen thin sections, diamond drill core from both Tom and Jason properties, as well as from numerous outcrop exposures and hand specimens. The range of maximum cross-sectional diameters for each constituent was taken as its size range. A summary of these observations and others is given in Table I and II.

A matrix of clay sized particles and microcrystal1ine quartz cement usually make up less than 10% of the rock. Both matrix and cement are occasionally partially replaced by siderite. Chalcedonic quartz cement rarely occurs where chert or quartz grains are in contact with each other.

Intergranular porosity is generally much less than one percent of the total volume.

Two extremes of grain size distribution are present: a "coarse" end member in which 65% of the rock is composed of pebble sized clasts (4 mm to 6 mm in maximum diameter); and a "fine" end member in which 50% of the clasts are classed as sand sized. Frequency histograms for each end member are given in Figure 10. Although both end members represent a dramatic variability in grain size, each are overwhelmingly trimodal. Three grain sizespopulations are present:

(a) gravel, consisting predominately of pebbles with a modal maximum - 34 -

Figure 9. Stratigraphy of Unit 2 (Canol Formation). TABLE I: Description of Coarse ( 4 mm) Framework Grains of Unit 2 Conglomerate (Canol Formation),

CLAST7 MEGASCOPIC MICROSCOPIC MAXIMUM PERCENT PERCENT ROUNDNESS. • SPHERICITY TYPE DESCRIPTION DESCRIPTION SIZE RANGE OF CLASS OF ROCK 1-10 SCALE* 10-10 SCALE*

I mottled light grey 97% cryptoxt. QZ 10 mm to 16 .to 29 8 8 and dark grey 2% microxt. SE 40 mm 45 well rounded .;spheroidal chert 1% silt size QZ (pebble)

II dark grey chert 30% Radiol aria 5 mm to 3 3 60% cryptoxt. QZ 10 mm 20 7 to 13 subangular elongate 0-15% SE? (pebble)

III dark grey chert 95% cryptoxt. QZ 5 mm to 9 5 with light grey 3% organics? 40 mm 16 6 to 10 very well obi ate rims 2% sericite? (pebble) rounded

IV white chert mosaic of 4 mm to 7 7 microxt. and 6 mm 7 2 to 5 well rounded subspheriodal cryptoxt. QZ (pebble)

V pyritic black pyritic, si lie. 4 mm to 2 3 shale carbonaceous 8 mm 5 2 to 3 angular elongate shale (pebble)

VI banded 1ight grey almost totally 35 mm to 3 2 chert Radiolaria(?), 40 mm 5 2 to 3 subangular equant carbonaceous (pebble)

VII white quartzite very well 12 mm to 9 8 sorted, clean 42 mm 2 1 very well spheroidal quartzite (pebble) rounded

Abbreviations: QZ = quartz cryptoxt. = cryptocrystall ine silic. = siliceous SE = sericite microxt. = microcrystalline * Roundness and sphericity were estimated visually using a numeric scale of 1 to 10 TABLE II: Description of Fine (0.0625 mm to 2 mm) Framework Grains of Unit 2 Conglomerate (Canol Formation).

CLAST MEGASCOPIC MICROSCOPIC MAXIMUM PERCENT PERCENT ROUNDNESS SPHERICITY TYPE • DESCRIPTION DESCRIPTION SIZE RANGE OF CLASS OF ROCK 1-10 SCALE*- 1-10 SCALE*

I mottled light grey 97% cryptoxt. QZ 0.4 mm to 7 6 and dark grey 2% microxt SE? 2 mm 60 12 to 30 subrounded subsequant chert 1% silt size QZ (med.-cse xsand)

VIII clear quartz monoxt. QZ 0.2 mm to 9 8 60% strained 1.1 mm 15 3 to 8 very well spheroidal 40% unstrained (fin-cse sand) rounded

IX white quartz monoxt. QZ with 0.1 mm to 6 3-7 fluid inclusions 0.3 mm 10 2 to 5 subrounded sphericity 90% strained (fin-med sand) varies

II dary grey chert 25% Radiol aria 0.08. mm to 3 4 60% cryptoxt. QZ 1.1 mm 10 2 to 5 subangular elongate 15% microxt. SE? (fine sand) to equant

X white quartz polyxt. QZ 0.2 mm to 8 6 strong undulose 2.0 mm 3 1 to 2 well rounded subequant extinction (med sand)

XI Miscellaneous biotite,zircon 0.1 mm to less general euhedral crystals igneous accessory hornblende 2.0 mm than 1 slightly rounded outlines minerals (fin-med sand) 2

Abbreviations: QZ = quartz cse = coarse cryptoxt. = cryptocrystalline

SE = sericite med = medium microxt. = microcrystalline polyxt. = polycrystalline fin = fine monoxt. = monocrystal1ine * Roundess and sphericity were estimated visually using a numeric scale of 1 to 10 Fine" end member

'Coarse* end member

Mean grain sizes of Juniper Ridge Conglomerate (Lowe. 1976)

co

t Scale

mm Scale

GRAIN SIZE

for Unit massive conglomerate.(Canol Formation). Figure 10. Frequency vs grain size 2 - 38 -

diameter of -4 on the 0 scale (63 mm);

(b) sand, mainly coarse sand with a modal maximum diameter of approximately 1 on the 0 scale (0.5 mm); and,

(c) minor amounts (less than 5%) of clay sized material.

Both the granule classification, ranging in size from -1 to -2 0'(2 mm to

4 mm), and the silt sized fraction, ranging in 0 from 8 to 4 (0.0039 mm to 0.0625 mm) are missing from the distributions.

This phenomenon may be due to four factors:

(a) bias introduced by grain size measurement procedures;

(b) presorting in the source area of the grains;

(c) sorting by the mode of transportation to the site of deposition; or,

(d) preferential abrasion of these grain sizes in transportation.

Since the measurement of maximum grain size was conducted rather rigorously, it is unlikely that the measurement bias is responsible for the trimodality of the size distributions. The remaining three factors will be evaluated in the discussion of the provenance, transportation and deposition of the chert pebble conglomerate in the following page's.

The coarse grained nature of the conglomerate permits a detailed examination of its constituents. The rock is composed of at least eleven types of framework grains whose characteristics are summarized below.

Clast Type I: Mottled, light grey and dark grey chert grains (primarily composed of cryptocrystal1ine quartz (97%), 2% to 3% clay mineral particles, and less than 1% silt size detrital quartz grains) make up about 45% of the coarse framework clasts and 60% of the fine framework clasts of the conglomerate (Plate E). Clay mineral particles have random orientation and are relatively-uniform in size. The mottled appearance of the chert is due to patchy areas of microcrystal!ine quartz, due to recrystal1ization - 39 -

Plate E: Photomicrograph (plane light) of well rounded, mottled grey chert pebble (Clast Type I) from Unit 2 conglomerate (Canol Formation).

Plate F: Photomicrograph (plane light) of Canol Formation Unit 2 conglom• erate Clast Type II radiolarian chert pebble (II) and angular black shale fragment (Clast Type V). - 40 -

of cryptocrystalline quartz. These grains originated from erosion of relatively pure bedded chert.

Clast Type II: Dark grey chert clasts with subangular, elongate outlines form about 20% of the coarse framework grains and 10% of the fine framework grains. Twenty-five to thirty percent of the chert is composed of spheriodal masses of microcrystal1ine quartz, probably recrystallized radiolaria (Plate F). A matrix of predominant crypto• crystall ine quartz and minute clay mineral flakes with subparallel alignment makes up the remainder of the grains. Clasts of Type II were derived from erosion of impure or argillaceous radiolarian cherts.

Clast Type III: Dark grey to black cherts with conspicuous light grey peripheral rims form 16% of the coarse framework grains. They are not present in sizes smaller than 5 mm in maximum diameter. These clasts are composed of cryptocrystalline quartz (95%), up to 3% sub-opaque to opaque organic(?) matter, and approximately 2% clay mineral flakes which have subparallel alignment. They are commonly pyritic and rarely contain

"ghosts" of radiolaria. Light grey rims which range in width from 0.6 mm to 8.5 mm appear to be primarily due to bleaching or oxidation of organic matter and pyrite (Plate G). This type of clast has the most uniform shape of all framework grain types in the conglomerate. Although their size ranges from 5 mm to 40 mm in maximum diameter, they are well rounded and oblate in shape (where more than one dimension was observed). Bedding(?) in the clasts, represented by subparallel alignment of micaceous minerals, invariably parallels the long axes of the clasts. The morphology of the altered rims of the clasts, combined with their relatively coarse grain size and markedly uniform shape, suggests a common source for the grains. - 41 -

Plate G: Photomicrograph (plane light) showing detail of bleached and oxidized rim of oblate dark grey chert pebble (Clast Type III) from Unit 2 massive conglomerate (Canol Formation).

Plate H: Photomicrograph (plane light) of radiolarian chert pebble (Clast Type VI) from Canol Formation Unit 2 massive conglomerate. - 42 -

They may have been derived from argillaceous chert nodules in carbonate rocks or by abrasion of argillaceous chert fragments by a process peculiar to the resultant oblate shape. Chert nodules in carbonate rocks are commonly structureless and very irregular in shape, although disc shapes predominate. Such chert nodules, however, invariably contain appreciable amounts of carbonate (Pettijohn, 1975, p. 435). Blatt (1959) showed.that pebbles larger than 6 mm in diameter tend to abrade to disc-shaped pebbles in a beach environment and to spherical or rod-shaped grains in fluvial environments. Thus the disc shape and the organic-free rims on these pebbles might then be due to prolonged exposure in a partially subaerial, intertidal beach environment,or, more probably, may be an artifact of bed thickness and fracture spacing in the source rock.

Clast Type IV: Well rounded, white chert pebbles composed of a patchy mosaic of microcrystal 1 ine and cryptoc.rystal 1 ine quartz make up 1% of the coarse framework grains. They are not present in sizes smaller than 4 mm.

The grains were probably derived from relatively pure bedded cherts.

Clast Type V: Pyritic, carbonaceous and siliceous black shale fragments with elongate, angular outlines are often plastically deformed around other framework grains (Plate F). They comprise approximately 5% of the coarse fraction. The black shale fragments are not present in sizes smaller than

4 mm in length. Their relatively large size and angular outlines in con• junction with their apparently poorly lithified nature when deposited suggests that they may have been plucked from underlying sediments during

transportation of the conglomerate.

Clast Type VI: Subangular, equant-shaped grains of banded, light grey chert are almost totally composed of "ghosts" of Radiolaria(?) 0.006 mm to - 43 -

0.03 mm in diameter (Plate H). Megascopic banding is due to the presence of a small amount of carbonaceous material concentrated in zones parallel to bedding(?) in the clasts. Grains of this type make up approximately

5% of the coarseffraction.

Clast Type VII: Less than 2% of the coarse framework grains consist of well rounded pebbles of white quartzite. Quartz grains which make up most of the quartzite clasts are dominantly monocrystalline and range in size from 0.1 mm to 2.2 mm (Plate I). Most are quartz which shows straight to slightly undulose extinction and which has relatively few fluid .inclusions; grains with highly undulose extinction are relatively rare. Grain shapes have been altered by the addition of small amounts of quartz overgrowths in optical continuity with the grains or by pressure solution along contacts with adjacent quartz grains. Clay minerals are present as matrix material and compose an estimated 5% to 8% of the clasts. Silt sized detrital biotite, hornblende and zircon are present in trace amounts. These clasts represent second generation material, that is, metamorphosed sandstones whose ultimate source terrane might have been granitic igneous rocks.

Clast Type VIII: Monocrystalline grains of very well rounded and subspherical, sand size, clear quartz make up 15% of the fine framework grains. In hand specimens, these grains have a distinctive, opalescent, bluish colour. Approximately 60% of these clasts show straight extinction while the remainder show slightly undulose extinction. Most of the grains typically have minor overgrowths of quartz cement in optical continuity with the original fabric. A slight dominance of non-undulatory grains may be considered to be indicative of grain maturity because undulatory quartz has a greater dislocation density (Lobo and Osborne, 1976). Due to their - 44 -

Plate I: Photomicrograph (crossed nicols) of Canol Formation Unit 2 conglomerate showing well rounded quartzite pebble (Clast Type VII) and Clast Type X polycrystalline quartz grain (X). - 45 -

advanced maturity, a provenance for the quartz grains cannot be speculated upon although they may have been immediately derived from the degradation of quartzites which make up Clast Type VII.

Clast Type IX: White, monocrystal1ine quartz grains with subrounded outlines and very low to moderate sphericity comprise approximately 10% of the fine framework grains. Minute, fluid-filled inclusions are ubiquitous throughout, imparting a cloudiness or while colour to the quartz. These grains, in view of their apparently lesser maturity than clear quartz grains, probably reflect a different provenance; perhaps from the erosion of vein quartz rather than the erosion of second generation quartz from metamorphosed sedimentary rocks.

Clast Type X: Polycrystal1ine quartz grains with well rounded, subequant shapes and strongly undulose extinction make up approximately 3% of the fine framework grains (Plate I). This type of quartz is commonly characteristic of gneisses and schists (Blatt e_t aj_., 1972).

Clast Type XI: Less than 2% of the fine framework grains of the chert pebble conglomerate is composed of miscellaneous igneous accessory minerals such as biotite, zircon and hornblende. Since these minerals are minor constituents of quartzite pebbles of Clast Type VII, it is likely that they too were derived from erosion of metamorphosed sedimentary rocks in the.source area of the chert pebble conglomerate.

On the basis of grain shape, two broad classifications of framework grains in the chert pebble conglomerate can be made:

(a) grains whose quantitative roundness and sphericity totals less than ten on a scane of ten for maximum degree of development for each factor

(Clast Types I, III, IV, VII, VIII, IX, X, and possibly XI); and, - 46 -

(b) grains whose quantitative roundness and sphericity totals less than ten (Clast Types II, V and VI).

Using percentage ranges listed for these grain types in Tables I and II,

64% ("fine" end member) to 71% ("coarse" end member) of the rock is composed of well rounded grains with high sphericity and roundness while 16% ("fine" end member) to 21% ("coarse" end member) of the chert pebble conglomerate is composed of grains of low sphericity with relatively angular outlines.

Well rounded pebbles with high sphericity are indicative of abrasion by stream erosion (McBride., 1966). As previously stated, pebbles of Clast

Type III may have been modified by coastline processes. Angular clasts are less mature and may have been modified by coastline processes. Angular clasts are less mature and may represent rip-up clasts of material picked up and incorporated into the conglomerate during transportation to the site of deposition.

No preferred orientation of clasts in the conglomerate, such as imbrication, is present. The only sorting of grain size is an apparently random differentiation between a predominance of relatively coarse, pebble sized clasts and a predominance of sand sized framework grains. Coarser clasts "float" in a matrix of finer grains and subordinate clay. Sutured grain contacts are present only where packing of coarser grains is sufficiently close to allow pressure solution of adjacent grains.

The basal contact of the massive conglomerate with underlying beds is only exposed along a ridge paralleling the northwesterly edge of the study area. Here the contact is abrupt and roughly conformable. The only evidence of erosive deposition being east to southeasterly trending, broad, shallow scours with depths less than one metre. - 47 -

The massive conglomerate of Unit 2 displays; most of the characteristics

peculiar to debris flow deposits. Debris flows are described as thick grain

flows of gravel sized material modified by the presence of interstitial

plastic mud (Lowe, 1976). They typically consist of three grain size

populations:

(a) gravel;

(b) sand; and,

(c) interstitial silt and clay of subordinate importance.

The Juniper Ridge Conglomerate, a submarine debris flow of Upper Cret•

aceous age which occurs in California, consists of gravel, sand and clay

(Lowe, 1976). The mean diameters of the Unit 2 chert pebble conglomerate

are almost identical to the Juniper Ridge debris flow (Figure 10).

Compositional ly, the Unit 2 conglomerate .-has a much higher percentage of

sand sized material for both the "coarse" end member and "fine" end member.

According to Lowe (1976) fine, cohesionless material mixed with the fluid

interstitial to a dispersion of coarser grains has two effects:

(a) it reduces the immersed weight of larger grains and, hence, the dispersive pressure required to maintain the suspension; and,

(b) it promotes higher flow velocities by increasing the density contrast between the flow and the ambient fluid (in this case, sea water).

The higher overall proportion of fines in the Unit 2 conglomerate would have had the effect of increasing flow velocities with respect to mechanisms responsible for similar deposits (e.g. sand flows, mud flows, etc.)

Debris flow deposits generally lack internal bedding and commonly show unsupported framework grains (Fisher, 1976). Experimental work and theoretical analyses suggest that clasts, if sufficiently supported, can - 48 -

comprise more than 95% of the debris volume and yet have essentially no influence on the gross strength of the mixture (Rodine and Johnson, 1976).

Erosional remnants of chert pebble conglomerate similar to Unit 2 blanket much of Selwyn Basin,(Blusson, 1976 and Gabrielse, 1977). Detailed studies of lithified debris flows have identified individual deposits which cover only hundreds of square kilometres rather than the much larger size indicated for the Unit 2 conglomerate. However, none of the deposits described have the high proportion of fines developed in the chert pebble conglomerate, consequently, they may not have attained the higher velocities of transport which might have lead to larger depositional areas. Conversely, initial regional studies of the conglomerate give no indication of the number of individual flows involved or whether they were not formed by some other process such asudeposition by turbidity currents. Embly (1976) describes a late Pleistocene debris flow which occurs off the continental rise west of the Canary Islands. Material in this conglomerate travelled up to 700 km from its source over slopes as low as 0.1°, eventually covering an area of 2 3 over 30,000 km with a total estimated volume of 600 km .

No paleocurrent determinations were made for the Unit 2 chert pebble conglomerate because of its massive nature, but broad scours present along basal contact indicate an east to southeasterly direction of transport. In addition, regional studies indicate a westerly provenance (Blusson, 1974 and 1976).

Relatively resistant, thick bedded turbidites which cap the massive chert pebble conglomerate of Unit 2 are best exposed near the southeastern corner of the study area (Figure 6). A complete section from the conglomerate to overlying beds of Unit 3a is not present. The generalized section shown - 49 -

in Figure 9 is pieced together from diamond drill hole logs and field observations of several incompletely exposed sections. Thickness of the turbidites appears to be a fairly consistent 6 m. Bouma (1962) turbidite divisions A, B, C, D and E are generally present.

Division A rocks are composed of quartz, chert and shale fragments.

Well rounded, subspherical quartz grains are the dominant component of the rock, comprising approximately 20% of the volume. Quartz grains range in size from 0.1 mm to 1.1 mm. Eighty to ninety percent are unstrained, most show extensive quartz overgrowths in optical continuity with the grains. Radiolarian cherts, argillaceous radiolarian cherts and fragments of black shale each make up about 15% of the rock. Radio• larian chert grains are pebble sized, well rounded and subspherical in shape. They are composed of Radiolaria "ghosts" with a cryptocrystalline quartz matrix containing only minor amounts of clay minerals. Argillaceous cherts occur as subangular, subequant silt and granule sized particles.

Angular black shale clasts, ranging from silt to pebble size, are often plastically deformed and bent around other framework grains. Relatively pure microcrystal1ine chert grains, fairly well rounded and ranging in size from 0.3 mm to 0.6 mm in diameter, form approximately 5% of the

Division A rocks. Matrix and cement make up about 30% of the rock, yielding a partially matrix supported texture. Only a few percentage of framework grains are in point contact; here minor pressure solution of siliceous cTasts occurs.

Division B and C are petrogr^aphically indistinguishable. Very well rounded grains of quartz, 0.06 mm to 0.3 mm in size with a modal diameter of 0.1 mm, form about 25% of the rocks. Eighty percent of the quartz . - 50 -

grains are unstrained, over 90% are monocrystalline. All/shave well developed, optically continuous quartz overgrowths. Relatively pure, very well rounded, fine sand sized chert grains comprise approximately

20% of the Division B and C rocks. Ten percent is composed of well rounded, subspherical clasts of argillaceous chert. In contrast to rocks which form Division A, angular clasts of argillaceous chert and shale are absent. Approximately 7% of the framework grains is irregular, sand sized patches of textureless organic matter(?). This material, which forms about 25% of the total volume of the rock, forms irregular masses with boundaries which are subsiduary to adjacent framework grains.

Clay matrix material is only present in amounts less than 3% of the total volume.

Division D beds are predominately composed of a dense mixture of clay mineral particles and organic matter with minor amounts of cryptocrystalline quartz cement. Well rounded, silt sized detrital quartz grains which are concentrated in thin parallel laminae make-up less than 2% of the rock.

Division E is comprised of uniformly clay sized material. Mineralogy is dominated by clay minerals with subordinate opaque organic(?) matter and minor silica cement.

All turbidites in the observed sections of Unit 2 begin with Bouma's

(1962) Divsion A. ABCDE beds predominate over beds with one or more division missing. Division E is considered by most authors to represent interturbidite, or normal, pelagic sedimentation (Bouma, 1962; Middleton and Hampton, 1973). Beds of this type are missing from several turbidite units (turbidite units 4, 6, 9 and 14 of Figure 9). Normal pelagic sedimentation suceeding the deposition of these turbidites might have - 51 -

been minimized through erosion by deposition of overlying turbidites and/or deposition of overlying turbidites might have occurred before accumulation of appreciable amounts of pelagic sediments.

Bed 11 of Figure 9 does not display features characteristic of normal turbidity current deposits. Its basal surface is devoid of erosional features other than broad scour casts. The upper surface of the bed is flat and featureless. Internally, the rock is massive and ungraded but diffuse parallel lamination is present in lower parts of the bed. Vague

dish structures are present above the diffuse;:parallei lamination. No convolute lamination, cross-lamination or ripple marks are present. This hontzont-islsimilar to supposed grain flows in marine Tertiary rocks of

California described by Stauffer (1967). Walker and Mutti (1973) point out that, in the absence of excess pore pressures, relatively large slopes (18° to 37°) are required for true grain flow. This observation effectively precludes the inclusion of grain flow deposits in normal turbidity current deposit sequences which are generally considered to be typical of much flatter slopes. Unfortunately, no specimens of this bed were obtained for thin section analysis; however, based on field observations, intergranular porosity of this rock is much higher than in enclosing turbidites. This feature may be a remnant of high primary intergranular porosity which would enable a low depositional slope angle for the sediment.

Beds of the turbidite succession which caps Unit 2 are best exposed in outcrop along a small scarp face which occurs near the southeastern corner of the map area (Figure 6). Elsewhere, their presence is indicated by float and felsenmeer typical of the constituent lithologies. At the - 52 -

described location, many beds are very contorted. Grossly convolute bedding is present at one locality where large fragments of the sequence are rotated with concurrent extensive deformation of Division E shales by injection between competent blocks of coarser material. In a nearby area, a 4 m thick section of the turbidite sequence is folded into an eastward verging, isoclinal, overturned fold. Local folds and faults of larger scale trend north-south and are upright with near vertical axial orientation. The local deformation of the turbidites seems to be plastic; that is, beds are tightly folded and rotated, injections of finer material occurs without extensive shearing and fracturing of the rocks. In contrast, sections of the underlying debris flow conglomerate

(which apparently has a similar structural competency) were observed to have abundant brittle fractures and micro-faults in tight folds and near faults. These points, considered in conjunction with the discordant nature of the local deformation, suggest that the disruption of the Unit

2 turbidite succession occurred by large scale soft sediment deformation such as slumping or sliding. Disruption was, then, caused by instability of the sequence following its deposition.

Paleocurrent measurements for the turbidites based on asymmetrical ripple mark and flute cast orientations measured from apparently undisturbed beds indicates that they were deposited from southeasterly flowing turbidity current (C.L. Smith, oral communication, 1978).

Canol Formation: Unit 3a

Lithologies of Unit 3a are best exposed'in the beds of westerly flowing creeks which drain the eastern part of the Tom property (Figure

6). Well exposed sections of the unit are also present on the north limb of the large sync!ine which borders the northwest edge of the map area. - 53 -

Sub-outcrop and float of Unit 3a define the south limb of the syncline.

Felsenmeer and talus float are typical of exposures along the northeast edge of the map area. Lithologies underlying the mineralized .horizon on the Jason property were interpreted from diamond drill core. Although exposures of Unit 3a commonly exhibit a high degree of lithological variability, these rocks are best distinguished in the field from similar appearing lithologies of Unit 1 by their deep brown weathering colour and their very pyniltiic nature.

A section through Unit 3a, measured in the bed of a creek flowing down a steep slope immediately east of the Tom West Zone stratiform mineralization, is shown in Figure 11. At this location, the majority of the map unit consists of finely interbedded porous, silty sandstones and.-.;fair:lyrlaminated black, pyritic shale. Silty sandstone interbeds range from a few millimetres to nearly oneihalf metre thick. Thicknesses of beds and laminae are locally variable, pinching and swelling along strike, and commonly lenticular in cross-section. Deposition of even relatively thin beds was mildly erosive as illustrated by commonly occurring scour marks and flute casts. Tops of these beds are sharp and featureless. Size gradation of clasts within the sandy siltstone beds is not present. The highest proportion of silty sandstone with respect to shale is present at the base of the section where sandy portions are relatively thick and where ihdiixfduail thick lenticular bodies of sandy siltstone are common. Sand and silt size clasts are composed predominantly of well rounded abundant quartz and subordinate chert grains. Matrix of the rock is composed of clay mineral particles, cement is cryptocrystalline quartz. Intergranular porosity is very high, - 54 -

Figure 11. Detailed stratigraphy of Unit 3a (Canol Formation) in an area immediately underlying Tom West Zone stratiform mineralization. - 55 -

frequently making up as much as 30% of the total volume of the rock.

Shale interbeds are composed of a very fine grained accumulation of clay minerals, carbonaceous material, minor silt sized detrital quartz and minor quartz cement.

A thick sequence of contorted, interbedded silty sandstone and shale is present in the lower half of the observed section of Unit 3a. Bedding near the base of this sequence is extremely convoluted and disrupted.

Deposition of this sequence appears to have been weakly erosive, as illustrated by scour marks on underlying rocks. The top of the contorted bedding is abrupt, perhaps due in part to erosion by deposition of over• lying intraformational conglomerate. A similar occurrence of convolute bedding is located approximately 300 m north of the described section.

Here, convolute bedding is contained within an elongate body about 10 m in maximum thickness and approximately lenticular in cross section.

Two thick sequences of pebbly mudstone appear stratigraphically above the convolute bedding. Pebble and sand sized framework grains are imbedded in a very fine grained, carbonaceous mudstone matrix (Plate

K). Upward fining of pebble sized clasts is well developed with reverse grading occasionally present. Pebbles are composed of well rounded chert grains of several types, all of which are present as framework clasts in the underlying Unit 2 massive chert pebble conglomerate. Sand sized clasts are predominately well rounded quartz grains while well rounded chert grains are present in subordinate amounts. Bases of both pebbly mudstone sequences are marked by beds of intraformational conglomerate which contain contorted angular clasts of the underlying silty sandstones and shales (Plate J). - 56

Plate K: Photomicrograph (plane light) of pebbly mudstone (Unit 3a, Canol Formation). - 57 -

Two series of beds marked by bases of sand and silt sized material which grade rapidly upward to material of uniform clay size are present: one set lies between the two sequences of pebbly mudstone; the other occurs near the upper part of the measured section of Unit 3a (Figure 11).

These beds are characterized by a complete lack of identifiable sedimentary textures other than gradual upward fining, and by thicker accumulations than similarity appearing interbedded silty sandstones and shales that form the bulk of Unit 3a. Sand and silt sized ffnact-fons are predominately composed of well rounded quartz grains. Sand sized, well rounded chert grains are present in subordinate amounts.

A 12 cm thick bed of porous, black rock is present immediately above the uppermost beds of sandy siltstone and shale. The rock is composed of approximately 65% to 70% pore space, occurring as 0.6 mm to 1.8 mm, rough.Ty spherical voids. Cavities are lined by a very thin layer of tangentially arrayed, finely fibrous chalcedony crystals. Groundmass of the rocks is composed of a dense admixture of cryptocrystalline quartz and opaque, textureless carbonaceous(?) material. The porous texture is apparently the result of solution of spherical grains which were formerly the major constituent of the rock. Petrographic examination does not offer any insight into the source of this phenomena.

A 1.4 m thick sequence of uniformly fine grained sedimentary rock caps?,theccoarse clastic section of Unit 3a observed on the Tom property

(Figure 11). Carbonaceous, black, very fine grained shales grade abruptly into extremely siliceous, carbonaceous black shales. Pyrite content, as bedded concentrations of euhedral cubes and pyritohedrons and as ubiquitous disseminated polyframboids, increases upsection paralleling the increase - 58 -

in silica content of the rock as based on hardness. Thickness of bedding in the shales increases upward with the increase in silica content.

Sections of Unit 3a observed elsewhere are more 1ithologically and texturely uniform. For example, a section measured in a creek bed 400 metres south of the previously described location contains very few contorted beds and no pebbly mudstones. In addition, beds of intra- formational conglomerate are thin and few in number. Shale horizons also cap the section of Unit 3a in this area but they are not as extensively silicified as shales which immediately underlie the Tom West Zone mineralization. The significance of this observation will be discussed in a later section dealing with economic geology.

Near the easterly margin of the study area((Figure 6), lithologies of Unit 3a are exposed only as frost-heaved blocks of felsenmeer and talus float. Here the unit consists of rocks similar in lithology to those previously described except that pebbly mudstones, intraformational congolomerates and contorted bedding are absent.

On the north limb of the large syncline which occurs in the northwest half of the map area (Figure 6), Unit 3a consists of finely interlaminated siltstone and shale described in the field as "pinstripe shales". Silt• stone laminae are very thin, commonly less than 0.5 mm thick. Shale interbeds are a fairly consistent three to four cm thick. Siltstone laminae are too thin to determine presence of graded bedding. A general upward decrease in the si 1tstone/shale ratio of the unit at this location was observed in the field. South of these exposures, on the opposite limb of the syncline, beds of Units3a are very similar in nature with exception of the inclusion of numerous, relatively thin beds of pebbly mudstone - 59 -

and lesser intraformational conglomerate.

Inspection of drill core from rocks stratigraphically underlying the Jason barite-lead-zinc horizon reveals that lithologies of Unit 3a are radically different in this locality. Pebbly mudstones and chert pebble conglomerate beds up to 2 m thick dominate the section. In places, the muddy matrix material of the rock makes up over 50% of its volume; more commonly, matrix is subordinate in proportion to well rounded framework grains of chert, yielding an almost entirely grain supported texture. Clast types are varied, most are various types of chert (pebbles) and well rounded quartz (sand) very similar in nature to those forming the bulk of Unit 2 chert pebble conglomerate. According to detailed studies of diamond drill core from the Jason claiims by

Ogilvie Joint Venture geologists, both the thickness of these beds and the average grain size of their constituents locally decrease rapidly to the northeast (C.L. Smith, oral communication, 1977). In contrast, the thickness of Unit 3a on the Tom claims, as measured from diamond drill sections, increases systematically to the north accompanied by a general decrease in overall grain size.

Beds of Units 1 and 2 are relatively constant in texture and lithology across the study area. Their lateral continuity and uniformity is inferred to be a consequence of the regional uniformity of their depositional setting. In contrast, characteristics of overlying Unit 3a are highly variable. Correlation between exposures is difficult to make and would be virtually impossible if not for their distinctive brown weathering colour and well defined strati graphic position, overlying - 60 -

very resistant beds of Unit 2 conglomerate and turbidites and underlying silvery grey weathering shales of Unit 3b.

A majority of the rocks of Unit 3a consists of finely interbedded silty sandstones and shales. Sandy siltstone laminae and beds are variable in thickness and lateral extent while relative uniform in internal texture. Their unsorted yet relatively thin bedded nature and their lateral irregularity are interpreted to be indicative of local derivation.

Interbedded shales probably reflect periods of normal pelagic sedimentation.

Pebbly mudstones and intraformational conglomerates are present in all but the most northerly sections of Unit 3a. Similar pebbly mudstones which have been described by Crowell (1957) are associated with slump structures and interbedded with other varied, poorly sorted clastic rocks.

Origin of pebbly mudstones is ascribed to downslope movement of material resulting from mixing of coarse grained turbidites with interbedded muds after metastability is initiated by mechanisms such as earthquake shocks or oversteepening of depositional slopes. Pebbly mudstones will not form unless slopes are steep enough to permit slumping of the pebble-mud mixture which has a higher viscosity than other mixtures, such as those which form turbidites, debris flows and grain flows (Crowell, 1957).

Intraformational conglomerates and convolute bedding are formed when viscosity of down-slope moving debris is sufficiently high enough to rip-up and incorporate slabs of underlying sediment (Crowell, 1957).

Intraformational conglomerate and occasional contorted bedding locally underlie each bed of pebbly mudstone (Figure 11). The two sequences of siltstone beds grading to shale which are present in the upper half of of Unit 3a (Figure 11) are interpreted as turbidity current deposits - 61 -

because of their relatively thick bedded and regularly stratified nature with well developed upward fining of coarse constituents.

Chaotic accumulations of slump deposits, mudflows, grain flows and

turbidites are defined as olistostromes (Abbato et al_., 1970; Hsu, 1974).

In the strictest sense, however, true olistrostrome deposits are more

regional in extent than the scattered slump and slide debris present in

the Macmillan Pass area although a sriimilar depositional setting may be

inferred. Instability of sediments caused by local tectonic activity

such as rapid uplift of the seafloor accompanied by earthquake shocks

may be responsible for the locally variable and disrupted lithologies

of Unit 3a. The interpreted derivation of coarse material from Unit 2

sediments and its subsequent incorporation into pebbly mudstones and

grain flows of Unit 3a is critical in this context. In addition,

indicated current directions of transport for this material are

diametrically opposed to those determined for underlying beds of Unit:2,

suggesting a rapid change in depositional regimes. Deposition of the

fine grained clastic rocks capping the Unit 3a section beneathr.the Tom

mineralization is interpreted as a return to local basin stability.

Canol Formation: Unit 3b

Unit 3b undenTvi.es most of the map area (Figure 6). The majority of

the rocks of this map unit are distinctively silvery grey weathering,

very siliceous and carbonaceous black shales. Lithologies weather

recessively and outcrop is generally limited to siliceous members.

Non-siliceous shale are exposed as small,, and usually slumped, outcrops

on the sides of avalanche gullies or as small talus fragments and

felsenmeer (Plate L). The base of Unit 3b is best exposed in beds of Plate M: Photomicrograph (crossed nicols) of Unit 3b (Canol Formation) black fetid limestone. - 63 -

creeks draining the Tom property and in diamond drill core from the Jason claims. Unfortunately, because of the structural complexity of rocks in the area immediately adjacent to the Jason mineralization, direct correlation of lithologies between diamond drill holes is difficult at this stage and will not be attempted for the present study. Detailed examination of diamond drill core from this area, however, has provided insight into the general nature of the stratigraphy of otherwise poorly exposed sections of Unit 3b.

The lowermost 400 m of Unit 3b are best observed in core from Jason

Diamond Drill Hole 8 (JDDH8), collared approximately 100 m south of the

Canol Road near the Tom - Jason property boundary (Figure 6). Here lithologies consist predominately of very siliceous and pyritic, carbonaceous black shales. Minor rock types include interbedded chert and quartz pebble debris flows and turbidites, pyritic calcarenites deposited as turbidites and debris flows, and thin bedded black fetid limestones.

The basal 175 m of Unit 3b as seen in core from JDDH8 (Figure.-6) consists of noncalcareous, moderately to highly siliceous, very fine grained black shales interbedded with poorly sorted debris flows and coarse grained turbidites with well developed A-E Bouma divisions.

Coarse framework grains are moderately well rounded to very well rounded chert pebbles similar to those which make up the bulk of Unit 2 rocks and coarse clastic members of Unit 3a. Finer framework grains are mostly subangular to well rounded quartz with subordinate amounts of well rounded chert sand. Minor intraformational :Gong,l:omera.te and contorted bedding are also present. Thickness of individual coarse clastic beds ranges from a few centimetres to several metres, usually separated by varying - 64 -

thicknesses of uniformly fine grained, pyritic black shale. A general thinning and overall upward fining of coarse clastic beds is present.

Similar coarse clastic horizons are not present in exposures of lower

Unit 3b on the Tom property a few kilometres to the east. Minor intra• formational conglomerates seen interbedded with gritty black shale on the north Jason claims are probably correlative.

Black shales of the overlying 250 m of Unit 3b, as seen in JDDH8, are interbedded with pyritic calcarenites. Coarse clastic beds are thin and frequently clustered with thickest beds at the base, fining and thinning upsection., These turbidites, in contrast to underlying coarse clastic rocks, consist of Bouma divisions C and D (rippled or wavy laminae and upper parellei laminae). Divisions A and B are weakly developed in a few of the thickest laminae. Framework clasts consist of pyrite, micrite, shale fragments, quartz grains and organic debris including calcisphere and radiolaria fragments. Pyrite is present as sand sized detritus with partially broken euhedral outlines. Detrital pyrite makes up as much as 20% of the coarse materal in division A and

B of the thickest beds. Approximately 10% of the framework grains are angular, elongate clasts of very fine grained black shale 0.1 mm to

3 mm in length (sand to granule size). Shale clasts are imbricated with long axes aligned at a low angle to bedding. As much as 40% of the framework grains are angular clasts of siliceous, very fine grained, brown micrite with very finely disseminated silica making up less than

20% of the material. Larger coarse sand sized micrite grains have very thin recrystallized rims. Carbonate grains, although relatively large in size, occur near the tops of weakly developed B divisions; perhaps - 65 -

because of their lesser relative density than either shale or pyrite clasts. About 10% of the coarse framework grains of division B in the turbidites consists of subrounded to moderately well rounded, mono- crystalline quartz grains. Detrital grains of divisions C and D consist predominately of recrystallized Radiolaria and calcisphere(?) fragments in addition to lesser fine detrital quartz and carbonate. Very small elongate fragments in the matrix may be detached Radiolaria spines or sponge spicules. Most beds are poorly cemented. Minor calcareous cement is subordinate to microcrystal1ine quartz cement. Voids, conspicuous in the coarse fractions of the turbidites, form up to 10% of the total rock vol ume.

A 1.1 m thick, poorly graded, pyritic and calcareous clastic horizon is present near the base of the calcareni.te turbidite section observed in JDDH8. The lower part of this bed is marked by large pebbles of well rounded chert and angular black shale. Smaller, angular grains of siliceous,!'micritic limestone and detrital pyrite form the bulk of upper framework clasts. Approximately 33% of the framework material is organic; 15% consists of recrystall ized Radiolaria up to O'JI mm in diameter, some with intact spines and remarkedly well preserved inner spheres; an additional 15% consists of silicified calcispheres, many of which have very well preserved inner walls and septa; 2% of the framework clasts are elongate siliceous needles which could be either silicified calcareous sponge spicules or recrystallized siliceous sponge spicules. Less than 1% of the framework grains are unclassifiable foraminiferal (?) fragments. The massive and poorly sorted nature of this bed suggests a classification as a debris flow.deposit in contrast to the enclosing turbidites. - 66 -

The lower 400 m of Unit 3b are well exposed in creek beds draining the east half of the Tom property (Figure 6). The unit here, on the whole, consists of uniformly fine grained, carbonaceous black shales.

Coarse clastic beds are not present to the degree seen in JDDH8. Shales vary in bedding thickness from thin and platy (less than 2 cm) to very thick and massive (as much as 1 m). Thickest beds tend to be very carbonaceous and non-siliceous, as demonstrated in the field by their soft "sooty" nature. Thinnest beds arejgenerally harder to the knife blade, perhaps indicative of a higher degree of silica content.

A sequence of very porous arid siliceous rock was observed in the bed of a creek draining the south part of the Tom property, near the adit entrance and about 320 m stratigraphically above the base of Unit

3b. The beds outcrop over a strike length of 1200 m and the thickness of the whole sequence ranges from 0.3 m to 1.2 m. Individual beds are composed of upward fining, silt to granule sized angularbblack shale fragments. Minor moderately well rounded detrital quartz grains and trace amounts of recrystal1ized radiolaria are also present. Basal parts of the beds are heavily stained with iron oxides. Approximately

40% of the total rock volume is pore space. Voids are roughly equant with angular outlines. They appear near the base of each bed and "fine"

upward, increasing in frequency until the beds take';on the appearance of pumice. These porous beds probably represent the surface weathered equivalents of pyritic, calcareous turbidites seen in core from JDDH8.

Void space is likely representative of micritic limestone clasts, leached and dissolved as acidic groundwaters are released by the oxidation of detrital pyrite in the rock. - 67 -

Basal sections of Unit 3a, exposed in the northwest part of the study area (Figure 6), consist of uniformly fine grained, black, carbonaceous and weakly siliceous shale. A few beds of pebbly mudstone and intraformational conglomerate are present but thick successions of coarse clastic material were not seen. A few thin, porous shale horizons are likely the weathered and fine grained equivalents of calcareous clastic horizons observed to the southeast in JDDH8.

At least four distinct beds of black weathering, dark grey, fetid limestone lie within the lower half of Unit 3b. Bed thickness ranges from 10 cm to 35 cm. The limestone is almost pure calcium carbonate.

Microcrystal1ine quartz and very finely disseminated euhedral pyrite are present in trace amounts. Calcite occurs as irregularily shaped, monocrystalline masses with grainisizes ranging up to 3 mm in long diameter. Individual crystals have undulose extinction and unusually curved cleavage traces (Plate M). Since cleavage directions and undulose extinction are randomly oriented, it is likely that these phenomena are not inherited from strain induced recrystal1ization of the limestone.

Jason Diamond Drill Hole 8 (Figure 6) intersected a 250 m section of black, pyritic and very siliceous shale which contains conspicuous

"blebs" or flattened nodules of quartz-carbonate composition. An additional 220 m of similar "blebby" shale is exposed upsection in

sporadic outcrop directly south of the drill hole collar. Composition

of the blebs is uniformly about 80% microcrystalline calcite, the

remainder being composed of microcrystal1ine quartz. Quartz-calcite

blebs are flattened along bedding planes, averaging 4 mm across and

0.6 mm thick. The blebs occur in "cycles" with pyritic siliceous - 68 -

laminae. The base of each cycle is marked by a very siliceous and pyritic horizon (Figure 12). Pyrite occurs as framboids in diffuse and often non-continuous laminae ranging in thickness from the width of a few framboids to accumulations of over 3 cm. Framboids are occasionally concentrated in large masses along betiding. Cryptocrystal1ine quartz cementation is pervasive, enveloping the pyrite laminae and extending above them for a distance of a few centimetres. Contacts with underlying and overlying moderately siliceous "blebby" shales are sharp. Pyrite framboids are occasionally recrystal1ized into cubic euhedral crystals, especially where siliceous cementation is weakly developed. Intact Radiolaria are commonly very abundant in the siliceous zones, forming as much as 30% of the rock and decreasing rapidly in concentration towards the top of each cycle. Appearance of quartz- carbonate blebs in each cycle is abrupt, usually 2 to 10 cm above the pyrite accumulations. Concentration and size of the blebs decreases towards the top of each cycle. Framboidal pyrite is usually very finely disseminated throughout the "blebby" shales.

Individual cycles range in thickness from 0.6 m to 1.5 m and

repetatively occur in 4 to 8 m successions of five or more cycles.

Five such successions or zones are present in the 480 m section of Unit

3b observed in JDDH8 and immediately overlying, rocks. Similar and

probably co-relative lithologies are present in Unit 3b exposures on

the Tom property and on the north Jason claims. At both locations,

individual zones can be traced along strike for distances exceeding

3000 m. - 69 -

Relative silica content

- —Quartz-carbonate blebs

^•/J^^- Framboidal pyrite

one metre

low high

Figure 12. Typical section of framboidal pyritic and "blebby" shale of Unit 3b (Canol Formation). - 70 -

Overlying rocks, comprising the upper three-fourths of Unit 3b, areiuaiiformly fine grained and very carbonaceous black shales. Radiolaria are present in trace amounts only., The uppermost 150 m of these rocks consists of rhythmic alterations of very siliceous black mudstone and non-siliceous, gritty black shale (Figure 13). Cherty mudstone beds, ranging in thickness from 3 cm to over 40 cm, are distinguished by their massive, non-fissile nature and their blocky, subconchoidal fracture.

In thin section they are uniformly very fine grained and carbonaceous.

Silica presumably occurs as abundant cryptocrystal1ine quartz cement.

Bases of cherty mudstone beds are smooth andt'featureless while basal surfaces of non-siliceous gritty shales are commonly load casted into underlying mudstones. This phenomenon may be due to much higher depositional rates for shales than for the mudstones. Shales are much too friable to be examined petrographically but their gritty nature is indicative of a fairly high content of silt-sized material.

No identifiable diagnostic fossils were observed either during field investigations or during petrographic examination of Unit 3b rocks.

Fragments of carbonized material seen in some specimens of silvery grey weathering shale on the Tom property are probably similar to "younger than Devonian" fossilized woody plant fragments collected from the same rocks by Sangster (1971 and pers. comm., 1976). Samples of the fetid limestone beds were submitted to the Geological Survey of Canada for microfossil analysis but proved to be unfossi1iferous. No microfossils were/.noted in thin sections of the limestone.

Radiolaria can be used for dating purposes if their external morphology is preserved. The recrystallized nature of radiolaria in - 71 -

Reddish brown siltstone and silty shale

Grey silty shale and mudstone Black siliceous mudstone •^•^ Siltstone, conglomerate with anhydrite nodules

Grey silty mudstone and shale, anhydrite nodules and gypsum crystal casts

Reddish brown laminated siltstone

Grey tuffaceoust?) silty shale

Cross-bedded brown silty mudstone, coarsening

upward to muddy siltstone Black mudstone with barite nodules, and 'E black shale 3 •.—• —• unconformity

Massive to thick bedded black siliceous mudstone with interbedded black shale

.. . — unconformity (?) Grey shale

Black mudstone

Reddish brown flat pebble conglomerate

All lithologies of Unit 4a, Unit 4b and the upper four metres ot Unit 3b are bioturbated

metres

Figure 13. Stratigraphy of upper Unit 3b (Canol Formation) and Units 4a and 4b (Imperial Formation). - 72 -

Unit 3b rocks as well as the commonly lacking or poorly preserved

nature of spines prohibits this type of study.

Calcispheres are common in sedimentary rocks ranging in age from

Silurian to Recent. Specimens from rocks of Units 3a and 3b are very

similar to Radiosphaera described by Stanton (1963). On the basis of

limited data, he indicated that this type of calcisphere is restricted

to Upper Devonian sediments in North America although its range extends

through Lower Carboniferous in Russia.

Brachiopods and conodonts collected from the Tea barite deposit,

located 20 km west of the study area, give^an^Upper Devonian age for

the bedded barite. Barite at this location occupies the same strati- graphic position as the Tom and Jason barite-lead-zinc-silver horizons

(Came, 1976-.aarid Dawson, 1977).

Lower coarse clastic beds of Unit 3b are most common in rocks which directly overlie the Jason barite-lead-zinc-silver stratiform mineralization. Their petrology and mode of deposition as proximal turbidites and debris flows, and their direction of transport from the south, are comparable to similar rocks of underlying Unit 3a which may be indicative of deposition in a continuous sedimentologic regime.

Rocks of lower Unit 3b exposed elsewhere in the study area are predominantly uniformly fine grained shales easily distinguished from underlying beds of Unit 3a which inevitably contain appreciable amounts of moderate to coarse clastic interbeds. Within the context of this study, it is a moot point whether the deposition of these coarse beds is a reflection of local tectonic activity or of an unstable sediment source to the south. Their locally variable and discontinuous nature within the - 73 -

study area suggests that they have at least a local source.

Source rocks for the overlying pyritic calcarenites which were deposited as turbidites and debris flows are more problematic. Their major constituents, pyrite and micritic limestone clasts, are present as constituents of immediately underlying rocks. Pyritic shales are commonly formed in basins with restricted circulation although they may be deposited in deep water or shallow water, up to the intertidal zone (Dimroth, 1975). The absence of any in situ bioturbation in these rocks is testament to the restricted nature of their depositonal environment as dissolved oxygen in the sediment and overlying waters was depleted by the decay of organic matter. Non-fossiliferous, organic rich, fetid black limestones are also characteristic of this environment

(Krumbein and Sloss, 1963, p. 507).

Depth of provenance constraints are imposed on the pyritic calcarenite beds by the presence of calcispheres as a major component of the rock.

Calcispheres are also present as a minor constituent of uppermost Unit

3a beds where they form the footwall to the Tom barite-1ead-zinc silver mineralization. Silicified calcispheres observed in these rocks consist of a spherical outer wall ranging up to 0.1 mm in diameter and may also contain an inner chamber connected to the outer wall by radially oriented spines. Outer spines are usually broken off, especially in detrital specimens. Calcispheres were first described by Williamson in 1880.

Since that time, various classification schemes have been set up on the basis of spine morphology. Paleo-environments of calcispheres have been described by several authors including Baxter (1960), Rupp (1960), Stanton

(1963), and Machielse (1972). In all cases, calcispheres were reported - 74 -

to occur in reefoid accumulations and bioherms as well as associated fore-reef and back-reef calcarenites and calcilutites. Since studies were generally confined to these lithologies, the previously unreported occurrence of calcispheres in black shale cannot be taken as precluding the deposition of these organic remains in this type of sedimentary setting.

Calcispheres have long been theorized to be the fossilized spores or reproductive organs of algae. This hypothesis was confirmed by

Marszalek (1975) who reported that modern calcispheres are being produced as the spores of Acetabularia antillana, an encrusting dasycladacean green alga found in the Florida Keys. These organisms live only in shallow protected waters with restricted or semi-restricted circulation.

Their environments are subjected to a wide variation in temperature and salinity but a maximum water depth of only 2.5 m can be tolerated.

Marszalek (1975) noted that sediment samples collected from areas surrounding centres of calcisphere production indicate that calcispheres do not survive transportation over any appreciable distance, and that rapid burial or entrapment is necessary for their preservation. The presence of a significant number of these organic remains in uppermost beds of Unit 3a and lower members of Unit 3b implies that shallow water environments must have locally existed during their deposition.

Since calcispheres are originally composed of aragonite, and providing that si 1icification of these organisms did not occur before their deposition, the maximum water depth of Unit 3a and lower 3b sedimentary environments would have been limited by the aragonite compensation depth (ACD). Rapid dissolution of aragonite occurs below - 75 -

the ACD both at and immediately below the sediment-water interface. A

Pleistocene to Recent open ocean ACD of 1000 to 3000 m is indicated from the work of Chen (1968) and Me.Tguen and Thede (1975). Bernoulli and Winterer (1975) suggest an ACD ranging from 1700 m to 2100 m for

Mesozoic Tethyan assemblages. A high concentration of decaying organic matter, causing an intense CO^ production and a corresponding lowering of the pH of interstitial and overlying waters, will significantly raise the ACD. Other factors such as variation in climate, water temperature, salinity and in the rate of terriginous influx will exert minor regulation on the ACD (Heese and Butt, 1976). The presence of calci• spheres in relatively carbonaceous and pyritic shales such as those of upper Uniti;3aiand lower Unit 3b may suggest a maximum water depth of about 2000 m for their deposition.

Origin of the cyclic alteration of siliceous pyritic shales with non-siliceous "blebby" shales of Unit 3b is not readily explained. The genesis of framboidal pyrite has been discussed recently by Berner (1969),

Farrand (1970), Rickard (1970), Lougheed and Mancuso (1973), Sweeney and

Kaplan (1973), and Kalliokoski (1974). These authors are in agreement that framboid formation might be related to the presence of organic matter, proceeding within the bounds of an organic membrane or sheath; either the skeletons or degraded bodies of micro-organisms, or in droplets or coatings of hydrophobic organic residues. Javor and Mountjoy (1976) reviewed the literature in conjunction with detailed studies of framboids from the organic-rich, Proterozoic Mount Robson shales and concluded that pyrite framboids originated from diagenetic replacement of blue- green alga spores, bacterial colonies, eukaryotic algae cells, or as - 76 -

pseudo-fossils diagenetically formed within the bounds of hydrophobic residues within the sediments. Since organic remains of these types are rarely preserved, the relatively high content of carbonaceous matter in the Unit 3b shales must be taken to infer that a suitable environment for formation of pyrite framboids, or any or all of the described mechanisms, was present.

Detrital 1 iron minerals serve as themain.source of iron in modern marine sediments. Dissolution of these minerals and reduction of ferric oxides takes place after deposition through both organic and inorganic processes. Bacterial reduction of seawater sulphate is the main.;source of sulphide, with the breakdown of organic sulphur compounds providing a lesser source. Thus, the limiting factors on framboidal pyrite formation are:

(a) the concentration and reactivity of detrital iron bearing minerals;

(b) the availability of dissolved sulphate which can be utilized by

sulphate reducing bacteria; and,

(c) the concentration of organic compounds or the "metabolized organic

matter" of Berner (1970).

Berner (1971) suggests that the concentration of metabolized organic matter, which hosts the growth of framboids, is the most important single limiting factors since iron-bearing minerals and dissolved sulphate are common constituents of most marine sediments. However in euxinic marine basins, such as the Black Sea, sediments and overlying waters contain abundant dissolved ti^S and presumably excess metabolized organic matter. Pyrite framboid formation in these environments is controlled mainly by the distribution of reactive detrital iron minerals (Ostroumov ejt aj_., 1961, - 77 -

cited in Berner, 1971). In order to apply this observation to the pyritic Unit 3b shales, a cyclical supply of reactive detrital iron minerals is implied since the other factors appear to have been in constant supply while the occurrence of framboidal pyrite is episodic.

Since the pyrite occurs in uniformly fine grained shale, rapid influx of these minerals by turbidity currents or other similar mechanisms can be ruled out. A possible source for detrital iron minerals may have been the submarine weathering (halmyrolysis) of volcanic ash (Calvert,

1974). Direct evidence is not present for any local volcanic activity during the deposition of Unit 3b. However, Tempelman-Kluit (1976 and oral communication, 1978) reports that acid volcanism on Pelly-Cassiar

Platform was contemporaneous, in part, with the deposition of Canol

Formation rocks in the Macmillan Pass area.

Pyrite in weakly silicified laminae of Unit 3b black shales is often euhedral and probably represents recrystal1ized framboids. Framboidal pyrite will rapidly recrystal1ize to cubic crystals if not protected by a sufficiently well developed siliceous envelope (Massaad, 1974).

Unit 3b is thin or locally missing along the eastern margin of the study area (Figure 6). Because of poor outcrop character, it is difficult to tell whether rocks mapped as Unit 3a in this area are not, in fact, interbedded clastic rocks and shales of the type commonly seen elsewhere near the base of Unit 3b. In any case, the maximum thickness of Unit 3b along the eastern margin of the study area is Hess ..than 30m. Thickness of the unit undergoes a dramatic increase from the east central margin of the study area to the central part of the study area where it attains a minimum thickness of at least 1430 m. This phenomenum is illustrated

in cross-section ABC shown in Figure 6. - 78 -

Tentative correlation of four fetid limestone markerchorizons observed in JDDH8 and in outcrops of Unit 3b shales in the central part of the map area with similar limestones on the Tom property suggests that rapid differential subsidence of the central map area accompanied deposition of Unit 3b. Unit 4a lies unconformably on

Unit 3b along the eastern margin of the map area while the contact between Units 3b and 4a in the central map area is apparently conformable.

Uplift and erosion of part of upper Canol Formation lithologies might have occurred prior to, and probably concurrent with, deposition of basal lithologies of Imperial Formation east of the thrust fault shown on Figure 6. Timing and mechanism of thrust faulting and uplift is discussed in more detail in the following section dealing with structural geology. Rapid thickening of Unit 3b across the study area is then probably due to a combination of initial deposition .in.a„

rapidly subsiding basin with further erosion of the basin margins after tectonic uplift and exposure.

Imperial Formation: Unit 4a

Strata of Unit 4a are well exposed as talus and felsenmeer along

ridge tops and scree slopes in eastern and southeastern parts of the

study area (Figure 6). Although exposure is excellent, the relatively

recessive and poorly indurated natures" most lithologies contributes to

their poor outcrop characteristics. The generalized stratigraphic

section through Unit 4a and lower part of Unit 4b, shown in Figure 13,

is a compilation of field observations and several incomplete measured

sections taken in the;;southeast corner of the study area. Although most

lithological components of Unit 4a exhibit considerable lateral variation - 79 -

in thickness and extent, their distinctive lithologies and weathering characteristics serve to identify them in the field. Unit 4a, as a whole, weathers a distinctive buff brown colour which distinguish it from underlying silver grey weathering black shales of Unit 3b and from overlying dark brown weathering, resistant muddy.., siltstones of Unit 4b.

Unit 4a consists of cyclic alterations of reddish brown and grey coloured shallow water clastic sedimentary rocks. Total thickness of the package varies from 0 m to over 100 m.

The lowest member of Unit 4a consists of a succession of interbedded very fine grained black mudstones and black shales which range in thickness from 1 m to 2.5 m. Two cm to 5 cm thick, massive mudstone beds are separated by 25 cm to 60 cm thicknesses of very carbonaceous, non-pyritic black shale. Mudstone beds contain distinctive spherical anhydrite-barite nodules which range from a few millimetres to over two centimetres in diameter. Central parts of nodules consist of randomly oriented, prismatic anhydrite crystals in an argillaceous matrix which is cemented by microcrystal1ine quartz. Barite occurs as prismatic crystals within a similar matrix and cement along the outer rims of the nodules. Gradational zonation between barite crystals in the rims and anhydrite in the cores of the nodules suggests that barite might be progressively replacing anhydrite nodules in a manner proposed by

Laznicka (1976) for barite nodules which occur in correlative platformal carbonates and shales of Mackenzie Arch.

Variable thicknesses of soft, grey silty shale overlie nodule-

bearing black mudstones and shales in most exposure of Unit 4a. Matted masses and individual particles of clay minerals make up ten to twenty - 80 -

percent of the rock. Matrix and cementing material are uniformly too fine grained to be determined microscopically but the very earthy odour of wetted specimens of grey shale indicates that kaolinite probably makes up a major part of the clay mineral content of the rock. Poor development of silica cementation in the grey shale is often shown by their very soft and recessive nature.

Siltstones, mudstones and shales of Unit 4a generally exhibit marked cyclic colouration; that is, alterations of grey and black fine grained rocks with coarser reddish brown siltstones. Reddish colouration of siltstones is,due to thin iron-oxide coatings on grains or to iron- oxide cementation of grains. Because diagenetic silica cementation and overgrowths on quartz grains formed after iron-oxide coatings and cement, iron-oxide formation proceeded very early in the diagenetic history of the siltstones in an oxidizing environment. Furthermore, the presence of grey shales is usually indicative of well aerated depositional environments where oxygen reached bottom muds and aerobic bacterial oxidation of organic matter is facilitated (Huang, 1962).

Thin and infrequent, carbonaceous, black mudstone horizons may reflect periodic accumulation of organic-rich sediments in localized stagnant tidal or supratidal lagoons.

Evidence of diagenetic evaporite mineral formation is common in most Unit 4a lithologies. In addition to anhydrite-barite nodules in

black mudstones, distinctive bladed gypsum crystal casts make up about

30% of the total rock volume of finely interbedded grey silty mudstones and shales which occur near the middle part of the section of Unit 4a

(Figure 13). Casts of euhedral gypsum crystals are occasionally filled - 81 -

or partially filled with coarsely crystalline anhydrite. Vacant casts are usually rimmed by a thin layer of tangentially arrayed, fibrous chalcedony which is unusual in its optically length-slow character.

Secondary nodular, replacement or pore filling gypsum and anhydrite are usually indicative of shallow marine intertidal and supratidal environments (Lucia, 1969). Length-slow chalcedony is inevitably associated with sulphates and evaporite minerals, often replacing gypsum or anhydrite (Folk and Pittman, 1971). A reddish brown flat pebble congolomerate bed, which varies in thickness from a few centimetres to over one metre, forms a distinctive marker horizon near the top of Unit 4a in the study area (Figure 13). "Pebbles" are irregularly shaped, plate-like fragments of hematitic, siliceous

si 1tstone,.which are laterally separated by vertically oriented bodies of poorly cemented mixtures of siltstone and lithic shale fragments

(Plate N). The pebbles are vertically separated by elongate, flattened

bodies of fibrous, length-slow chalcedony which is, oriented with crystal

long axes,perpendicular to bedding in the rock. Roughly polygonal out•

lines of the plate-like "pebbles" suggests that their lateral separation

by thin bodies of poorly sorted sediment may have resulted from infilling of dehydration cracks. Flat pebble conglomerates of this type are

generally thought be have resulted from l.ithification of intertidal

sediments into thin crusts which are subsequently broken by dehydration

and wave action (Kinsman, 1969).

All lithologies of Unit 4a show evidence of bioturbation. Biologic

activity is reflected in numerous feeding tunnels of burrowing organisms which are commonly filled with porous sandstone and siltstone partially - 82 -

Plate 0: Photomicrograph (crossed nicols) of bioturbated siltstone (Unit 4a, Imperial Formation). - 83 -

cemented by iron-oxides and silica (Plate 0). Small, semi-opaque and structureless spherical bodies in most burrow fillings may be fecal pellets.

Thickness of Unit 4a decreases in a general manner from a maximum

in the northeast study area to absence in the southeast (Figure 6).

Variable thickness of the unit as a whole may simply be due to partial

removal by erosion before or during deposition of Unit 4b sediments.

The lateral lithological and thickness variability of Unit 4a sedimentary rocks in conjunction with their shallow water environment of deposition suggest that they may represent a relict shoreline deposit. The thinning and eventual disappearance of these rocks may be due to an unrecognized facies change to deeper water equivalents in the.south part of the map area. Correlative rocks, 25 km southwest of the study area on the Tea claims, consist of an assemblage of brown weathering calcareous and non- calcareous shales, silty mudstones, sandstones and clean, cross-bedded, well sorted quartzites which are interpreted as shallow water lagoonal, barrier bar and beach deposits (Carne, 1976; T. Bremner , oral communication,

1976).

Imperial Formation: Unit 4b

In the study area, Unit 4b generally consists of a monotonous assemblage of resistant, cliff forming, brown weathering, silty mudstones and muddy siltstones with thin shaly mudstone intervals. Stratigraphy of the lower part of Unit 4b is illustrated in Figure 13. Well developed, small scale climbing ripple crosslamination in most lithologies indicates a southerly direction of transport for sediments of Unit 4b (Plate P). - 84 -

Plate Q: Photomicrograph (crossed nicols) of cross-laminated silty mudstone from the base of Unit 4a, Imperial Formation. - 85 -

Cross-lamination is outlined by thin accumulations of carbonaceous material.

Over 70 percent of siltstone framework clasts are dominantly silt size or finer, subangular to subrounded, well sorted quartz grains with slightly undulose extinction. Carbonaceous material, detrital muscovite- sericite grains and opaque minerals make up the remainder of framework grains. Poorly developed silica cementation is present in most lithologies

(Plate Q).

A general upwards coarsening from muddy siltstone to silty mudstone is present in the section of Unit 4b exposed in the area of Figure 6.

In the northeast corner of the study area, the upper part of Unit 4b consists of coarse, poorly sorted and poorly cemented, dark brown, rusty brown weathering chert pebble congolomerate. Initial field investigations of these rocks indicate that they are channel-fill deposits. Higher in

Unit 4b, south of the study area, lithologies consist of thick to massive bedded, well laminated, calcareous quartzose siltstones and arenites with lesser interbedded calcareous shales and thick bedded, cross-laminated calcareous and non-calcareous quartzites. Regional studies of Imperial

Formation stratigraphy suggest that silty mudstones, muddy siltstones and channel congolomerates of Unit 4b which occur within the study area were deposited at the leading edge of a southerly prograding delta front

(T. Bremner, oral communication, 1976).

Quartz-feldspar Porphyry Dykes

Distinctive, light grey to buff-orange weathering quartz-feldspar porphyry dykes cut sedimentary rocks of Canol and Imperial Formations in the south-central study area (Figure 6). Macroscopic examination of - 86 -

these rocks shows that their composition, although highly variable,

consists of equal amounts of subhedral quartz, euhedral potash feldspar

and lesser euhedral biotite phenocrysts in a fine grained matrix. Strong

surface alteration has completely kaolinized feldspar phenocrysts and

fine grained matrix of the rock. Chilled margins of dykes are commonly

thin and show evidence of flow banding. Thin, hornfelsed contact aureoles

in intruded pelitic rocks are commonly less than one metre wide. Dykes

are nearly vertical or steeply dipping and are oriented in an approximately

radial fashion about a hornblende-biotite granodiorite stock which lies

about one kilometre south of the study area (Figures 5 and 6).

An area of weakly hornfelsed shales, mudstones and siltstones of

Units 3b, 4a and 4b occurs in the southeast corner of the study area

(Figure 6). Weak contact metamorphism of pelitic rocks has resulted in

rusty weathering, resistant slates. The contact metamorphism is not

spacially related to dyke intrusion and might be due to an unexposed small granodiorite stock.

Structural Geology

Four independent tectonic events have shaped the Middle Paleozoic to Upper Mesozoic structural evolution of the Macmillan Pass area.

Rapid local tfif ferentira.1 subsidence within the Macmillan Pass area followed deposition of Unit 2 massive chert pebble conglomerate debris flow and proximal to intermediate facies turbidites. Slumping of Unit 2 unconsolidated sediments and deposition of chaotic debris and olistostrome deposits of Unit 3a into a local basin reflect the high degree of sedimentary - 87 -

instability at this time. Stable depositional regimes returned to the east part of the study area by the end of Unit 3a time. Depositional instability in the southwest .study area continued to early Unit 3b time, as shown by the accumulation of thick, chaotic, intraformational and debris fan conglomerates. Passive differential subsidence probably continued through'Unnit 3b deposition as indicated by "fanning" of fetid limestone marker horizons (Figure 14). Subsidence in the east half of the area was "hinged" along an approximately north-south trending zone of flexure which occurs near the eastern margin of the study area.

At the end of Unit 3b time, easterly directed compressional forces resulted in thrust faulting and folding of the eastern basin margin. A plate of middle and upper Canol Formation sediments, riding on a decollement surface beneath massive Unit 2 chert pebble conglomerate, over-rode Canol sediments to the east while, during the same event, overthrust sediments were deformed into easterly verging, recumbent folds.

Overthrusting was, in places, accomplished by imbricate thrust faulting

(Figure 6). Mylonitized and brecciated zones marking decollement surfaces were seen in drill core recovered from surface diamond drilling in this area.

Rocks of Units Land 3a within the zone of detachment and imbricate faulting are very strongly sheared. Shear planes, which are outlined by alignment of platy minerals and lamellar concentrations of carbonaceous material, commonly cross-cut bedding at low angles in the drill core. Micro-folds and rapid alteration of upright and overturned graded beds in the footwall of the thrust fault suggest that shearing and tight isoclinal folding locally accompanied fault movement. In this zone, finer grained pelitic sediments were commonly injected plastically along shear planes into more Upper limit of Unit 3b "blebby'•' shales

Road River Formation and older sedimentary rocks

Laminated barite and sulphides Massive sulphides

WW Epigenetic "stockwork" mineralization

Direction of soft sediment slumping

metres

Figure 14. Reconstructed cross-section (looking north) through the Tom West Zone mineral deposit at the close of Canol Formation time. The reconstructed section is located approximately along section line A-B of Figure 6. - 89 -

competent, well cemented coarser clastic rocks (Plate R). Foliation of

peletic rocks does not cut detrital quartz grains nor does it cut earlier

formed quartz overgrowths on these grains. Coarse, well cemented silt•

stones do not display foliation or, at best, foliation is very poorly

developed. These features suggest that this deformation occurred prior

to complete 1 Unification of the sediments but after the formation of

diagenetic silica overgrowths on quartz grains. Erosion of uplifted and

folded sediments before deposition of Unit 4a places an upper time limit

on initial deformation. Mild folding of the unconformity between Units

3b and 4a suggests that this deformation may have continued or reactivated

at a later time (see cross section ABC of Figure 6). An easterly trending

normal fault which is inferred to displace folded strata and the thrust

fault in the eastern part of the area does not appear to cut the basal

Imperial Formation unconformity (Figure 6).

The study area is located along the southern margin of a structurally

anomalous, 20 km wide belt, which extends at least 100 km to the west and

approximately 30 km to the east of the Macmillan Pass area (Figure 5 and

Blusson, 1971 and 1974). Within this belt, Paleozoic and earlier sedimentary and volcanic strata are generally deformed into tight, slightly overturned,

isoclinal, east-west trending folds. Northerly to northwesterly trending, open, upright folds are the most common structures in the Mackenzie

Mountains (Gabrielse et_ aJL , 1973). Since overprinting of the two contrasting structural fabrics does not seem to occur, the two structural styles might have resulted from the same orogenic event. According to Gabrielse et al.

(1973), northerly to northwesterly trending structures of the Mackenzie

Mountains have a pre mid-Cretaceous age of formation because of the cross- - 90 -

Plate R: Photomicrograph (plane light) of sheared turbidites of Unit 1 (Canol Formation) beneath the decollement surface, east edge of the study area. - 91 -

cutting relationship of Middle and Late Cretaceous granitic plutons.

East-west trending structures in the study area are represented by the easterly plunging syncline and anticline pair in the west and by vertical to steeply dipping slaty cleavage in rocks south of the Macmillan

River (Figure 6). Arching of earlier northerly trending folds and the thrust plate along the eastern margin of the area might be related to east-west trending anticlinal folding of these rocks.

Minor open folds with cresentic axial trends are present in the south- central map area (Figure 6). These folds have amplitudes of less than

10 m and dips on fold limbs are commonly gentle. Regional mapping in the

Macmillan Pass area has shown that these fold axes are concentric about a granitic stock which lies about 1200 m south of the map area (C.L. Smith, oral communication, 1976). These structures are probably related to deformation of country rock by emplacement of the granitic body.

Major faults may parallel valleys which form conspicuous topographic lineaments along the southwest edge of the map area and along the Macmillan

River (Figures 5 and 6). Southeasterly and easterly trending faults which cut the south limb of the large syncline in the west part of Figure 6 might be related to either of these proposed fault systems although no concrete evidence for the existence of major faults is seen in the present study. 92 -

ECONOMIC GEOLOGY OF MACMILLAN PASS AREA

General Statement

Jason, Tom West Zone and Tom East Zone mineral .deposits are syngenetic, stratiform accumulations principally composed of finely laminated sphalerite, galena, pyrite, barite and black siliceous argillite. The three deposits occur at the same approximate stratigraphic interval, marking the sedimentary transition between locally derived slide and slump debris deposits of Unit 3a with finer grained black shales and minor conglomerates of Unit 3b. Because of the preliminary status and confidential nature of the results of geological investigations into the mode and tenor of mineralization in the Jason deposit, discussion in the present work is limited to the Tom deposits.

Stratiform, barite-lead-zinc-silver mineralization on the Tom claims occurs in two tabular bodies (Figure 6). The East Zone is 160 m long,

3 m to 20 m thick and dips steeply west. The West Zone, a much larger body about 1200 m long and 3 m to 60 m thick, dips 50° to 70° west. East

Zone mineralization has been explored in its entirety by surface and underground diamond drilling to a depth of 350 m. Only the higher grade south half of the West Zone has been explored in detail by underground diamond drilling where ore grade material has been outlined to a depth of 260 m. Tenor and mode of mineralization continues down-dip beyond this depth but difficulties encountered in drilling deep holes have precluded further exploration of the West Zone to this time. The two deposits on the Tom property together total nine million tons of ore grade material averaging 8.6% Pb, 8.4% Zn and 2.8 oz/ton Ag using an 8% combined lead and zinc cutoff grade. Ten million tons of sub-ore grade - 93 -

material which averages 4.6% Zn, 0.9% Pb and trace amounts of silver have been outlined by surface drilling in the north half of the West Zone.

Its remote location, poor zinc prices and lack of power development in the area have held back further exploration of the deposit.

Detailed study of East Zone ore textures and metal zonation is inhibited by the highly tectonized nature of the deposit. Stratiform mineralization and enclosing sedimentary strata have been severely disrupted by the action of shear stresses associated with post-ore thrust faulting

(refer to cross section, Figure 6) resulting in massive recrystallization of ore minerals and obliteration of primary textures by shearing, micro- faulting and small scale isoclinal folding. In contrast, primary textures and other depositional features of the West Zone mineralization appear to be unaffected by this and later events.

Tom West Zone Mineralization

Method of Study:

The south half of the Tom West Zone mineralization was selected for detailed study. Following its discovery in 1951 by Hudson Bay Exploration and Development Co. Ltd., the deposit was delineated by surface prospecting, trenching and diamond drilling during the periods 1951 to 1953 and 1966 to

1968. From 1969 to 1972 the extent of mineralization was further defined by a total of 1887 m of underground workings in conjunction with over

4762 m of underground AQ diamond drilling. Much of the underground diamond drill core from the Tom property was stored at the company's facilities in Whitehorse until 1976 when it was donated to the H.S.

Bostock Core Library in Whitehorse, operated by the Department of Indian - 94 -

and Northern Affairs. Surface diamond drill core which is stored on the property has since succumbed to the ravages of time and specimen collections.

Underground workings were unfortunately unavailable for inspection by the author because of bad air and the possibility of caving. Study of the

West Zone mineralization was primarily accomplished through data collected by detailed logging of 525 m of underground diamond drill core. For expediency only those holes which were drilled along a horizontal plane at adit level and at approximately right angles to strike of the minerali• zation were logged. Accompanying assay records were kindly provided for the use of the writer by Hudson Bay Exploration and Development Co. Ltd.

Small samples of drill core were systematically taken for petrographic analysis.

In order to best utilize textural, assay and mineralogical data, information derived from the diamond drill core logs was used to reconstruct a cross-section through the south half of the West Zone as it would have appeared at the culmination of ore deposition. This was accomplished by assignation of the top of the stratiform mineralization as an arbitrary horizontal datum plane. Measured bedding attitudes of laminated ore in drill core were rotated to horizontal. Distances measured from the collar of the hole were adjusted accordingly and converted to metric units for conformity. Figure 15 illustrates the reconstructed cross sectional profile of the south part of the West Zone at the 4750 (adit) level.

Ore Stratigraphy, Petrology, Mineral Textures and Metal Distribution :

A structurally restored,true stratigraphic section of the south half of the Tom West Zone deposit is shown in Figure 15. Ore stratigraphy is - 95 -

derived from detailed logging of diamond drill core and from petrographic

determinations on over 50 polished sections and 25 thin sections. Seven

distinct types of stratiform mineralization are recognized (Horizons A

to G). Lateral ore horizon contacts shown on Figure 15 are extrapolated

between diamond drill holes where possible but in most cases they are

arbitrarily located. Vertical contacts seen in diamond drill cores are

remarkably consistent in their occurrences when plotted on the reconstructed

section. Assay values are plotted on Figure 16.

Massive, poorly laminated galena, sphalerite, pyrite, siderite, minor barite and quartz of ore Horizon A form the highest grade of mineralization yet discovered in the Macmillan Pass area. Assays range as high as 31% Pb, 14% Zn and 11 oz/ton Ag (Figure 16). Sulphide and

sulfosalt minerals which occur in minor amounts include chalcopyrite,

boulangerite, bournonite and tetrahedrite. Thickness of the horizon ranges from 2.5 m to 3.5 m.

Lower part of Horizon A is primarily composed of bedded pyrite and siderite. Coarsely crystalline pyrite, which occasionally contains very small irregular siderite masses, occurs in laminations or beds up to 2 cm thick. Crystalline quartz fills the interstices between pyrite grains.

Interlaminated siderite is coarsely crystalline and relatively uncontaminated by the inclusion of other minerals. Galena and sphalerite occur in minor amounts subsidiary to pyrite, siderite and quartz. Chalcopyrite, boulangerite, bournonite and tetrahedrite are often found as minute blebs along pyrite grain boundaries. Barite is not present here. Pyrite content decreases abruptly towards the top of Horizon A where siderite is present only in trace amounts. Here galena and sphalerite are the most common - 96 -

minerals, making up over 70% of the rock. A general increase in zinc

content with respect to lead occurs towards the top and towards the

northern lateral limit of the massive sulphide zone (Figure 16). A

corresponding decrease in barite content of the ore accompanies the

zonation from lead to zinc enrichment. Chalcopyrite in middle and

upper parts of Horizon A occurs as small, rounded exsolution(?) blebs

in dark brown sphalerite (PlateS).

At the top of and in northernmost parts of the Horizon A, vaguely

interlamiriated tan coloured sphalerite and light grey barite gangue are

the dominant mineral species. Barite grains have almost euhedral outlines

and commonly enclose minute galena masses and :blebs in fractures and

along cleavage planes (Plate T). Minor discrete bodies of finely

crystalline galena also occur in sphalerite laminae. Chalcopyrite and

sulfosalt minerals are not present in appreciable quantities. Pyrite

occurrence is limited to minor amounts of disseminated framboids in

sphalerite. Angular, silicified fragments of footwall Unit 3b silty

shale and siltstone which "float" in a massive sulphide matrix occur

throughout Horizon A (Plate U). Footwall breccia fragments range from

silt to cobble size.

Horizon B, which underlies most of the West Zone (Figure 15), consists

of evenly laminated black cherty argillite, dark grey chert and lesser

barite with interlaminated and disseminated sphalerite, galena and pyrite

(Plate V). Strata of Horizon B are likely facies or time equivalents of

Horizon A massive sulphides.

Sulphide mineral, barite, siliceous argillite and chert laminae or

- beds of Horizon B display a high degree of both vertical and lateral - 97 -

Plate S: Photomicrograph (reflected light) of massive sphalerite occurring in Horizon A mineralization (Tom West Zone), showing chalcopyrite exsolution blebs (qz = quartz, si = sphalerite, cp = chalcopyrite)

Plate T: Photomicrograph (reflected light) of laminated barite and sphalerite with interstitial galena of Horizon A (Tom West Zone). Note partially euhedral outlines of barite masses, (ba = barite, si = sphalerite, gl = galena). - 98 -

Plate U: Photograph of silicified and altered footwall fragments (black) in Tom West Zone Horizon A massive galena.

Plate V: Photograph of evenly laminated black cherty argillite and sulphide minerals of Horizon B (Tom West Zone). - 99 -

thickness variation. In general, black cherty argillite and dark chert laminae vary in thickness from less than 1 mm to about

2 cm while sulphide and barite laminae range from less than 1 mm to about

5 mm thick. Sulphide laminae are usually monomineralic; that is, sphalerite laminae contain very little or no included pyrite and galena, and vice versa. Lesser amounts of galena and sphalerite occur as minute disseminations in black cherty argillite laminae. Pyrite is usually present as monomineralic, stratified concentrations of framboids or nearly idiomorphic recrystal1ized framboids. Minor amounts of framboidal pyrite are also scattered throughout cherty argillite laminae or beds.

Assay values of Horizon B are erratic, ranging from trace amounts of lead, zinc and silver to 22% Zn, 26% Pb and 10 oz/ton Ag (Figure 16).

An overall northerly decrease in the combined', lead-zinc grade, with increasing distance from massive sulphide mineralization of Horizon A, is accompanied by a general increase in the Zn/Pb ratio of the ore. Lead/ silver ratios increase from about 2;:.l (2% pb to 1 oz/ton Ag) to about 4:1 in a like manner. Sub-microscopic inclusions of silver bearing minerals in galena might carry the bulk of silver present since no discrete silver bearing sulphide or sulfosalt minerals were identified in polished section examination of drill core samples. No copper bearing species were seen in specimens of Horizon B. Thickness of Horizon B is relatively constant, averaging about 2.4 m.

Horizon C, contained within a small body, lens-shaped in cross- section, which concordantly overlies massive sulphide mineralization of

Horizon A (Figure 15). Interlaminated sulphide minerals, barite and - 100 -

cherty argillitesaressimilar in appearance to mineralization of Horizon B.

Horizon C, however, contains significantly higher amounts of barite and mineral lamination is generally much more contorted and disrupted.

Sulphide mineral laminae range from less than 1 mm to over 1 cm thick while thicknesses of argillite laminae are much more variable, ranging

up to 2 cm. Barite laminae are generally about 2 mm thick. Metal values

of Horizon C are somewhat lower than those of the underlying massive

sulphide body but higher than similar appearing mineralization of Horizon

B. Grades range up to. 7% Pb, 20% Zn and 1 to 2 oz/ton Ag (Figure 16).

Galena and honey coloured sphalerite occur in separate, almost mono=

mineralic laminae. Sphalerite laminae are generally thicker and more

common than galena laminae. Discrete barite laminations are composed

of roughly euhedral barite crystals which are cemented by a matrix of

galena and sphalerite (Plate W). Trace amounts of very'small, elongate

chalcopyrite exsolution grains are concentrated along sphalerite grain

boundaries and cleavage planes. Chalcopyrite also occurs as discrete

mineral segregations interstitial to galena and barite grains. Eudedral

pyrite crystals are present in trace amounts in sulphide mineral and

barite laminae. Massive concentrations of framboidal pyrite are very

common .in siliceous black argillite laminae and beds. No identifiable

silver minerals were seen.

Most specimens of Horizon C observed in drill core were'.at least

mildly deformed. Brecciation and contortion of laminated ores appears

to have occurred before their complete 1 Unification as demonstrated by

the "soft sediment" nature of their deformation (Plate X). Angular,

silt to pebble sized grains of black, silty shale are scattered through- - 101-

Plate X: Photograph of Horizon C (Tom West Zone) laminated mineralization. Note extreme soft-sediment deformation. - 102 -

out Horizon C. Shale clasts are silicified, often carbonatized and commonly contain a variety of sulfosalt minerals which are foreign to surrounding banded sulphides, barite and argillite.

Horizon C displays well developed vertical metal zonation (Figure

16). At the base of the unit, zinc and lead occur in approximately equal amounts. Relative zinc enrichment towards the top of the horizon

increases the zinc to lead ratio to almost 3:1. Similarily, the lead

to silver ratio increases rapidly upward from about 1:1 (1% Pb per 1 oz/

ton Ag) to about 6:1 at the top. Thickness of Horizon C varies from 2.2 m at the south end to 6.4 m near the northern limit.

Horizon D, which contains the bulk of West Zone tonnage, appears to

grade laterally from Horizon C (Figure 15). Gangue consists principally

of finely laminated, light grey to white barite and lesser siliceous

black argillite with minor dark grey chert (Plate Y). Grade varies from

1% to 9% Pb and 3.5% to 10% Zn (Figure 16). Only trace amounts of

silver are present. Thicknesses of barite laminae range from about 0.5

mm to 1 cm while averaging about 2 mm. They attain their greatest

thickness at the northern limit of the West Zone cross-section shown in

Figure 15. Barite in Horizon D occurs as cryptocrystal1ine, massive

bedded concentrations in contrast to Horizons A and C where barite is

generally present as roughly lamellar occurrences of nearly euhedral

crystals embedded in a matrix of galena and sphalerite. Black, cherty

argillite laminations range from 0.1 mm /to 1 cm thick, averaging about

6 mm. Minor dark grey chert laminae, which average about 6 mm in

thickness, are scattered thoughout the section. Argillite and chert - 103 -

•

Plate Y: Photograph of laminated barite (light grey), sphalerite (medium grey) and galena (dark grey) typical of Horizon D mineralization, Tom West Zone. Note the stratified concentration of small, angular lithic fragments (black) near the base of the specimen. - 104 -

laminae appear to have little lateral thickness variability although both exhibit marked variation in vertical thickness and frequency of occurrence.

Both Horizons C and D are capped by a 2 cm to 4 cm thickness of massive, grey pyritic chert which serves as a distinctive marker horizon (Figure 15).

Honey coloured sphalerite and galena of Horizon D occur in discrete laminae and as disseminations along grain boundaries in barite. Sulphide mineral laminae are essentially monomineralic; that is, sphalerite laminations contain little or no galena and vice versa. Framboidal pyrite is disseminated throughout chert and siliceous argillite laminae while it is present in trace amounts only in barite, sphalerite and

galena laminae. Chert and argillite laminae, as well as the occasional

barite ilai.mination, contain no sphaerlite or galena. Both barren barite

laimae and sulphide-bearing barite laminae as well as chert laminae contain

subangular, silt to granule sized clasts of black silty shale. Shale

clasts appear to "float" in a matrix of barite and sulphide minerals or

chert. Slight depression of underlying laminae in conjunction with the onlapping and concordant nature of adjacent and overlying mineral laminations

suggests that shale clasts were dropped into the ore during its deposition.

Horizon D is zinc rich. Highest zinc values with respect to lead

occur near the top and northernmost parts of the section shown in Figure

15. Relative zinc enrichment, however, parallels an overall decrease in

combinated lead-zinc grade. The horizon is characterized by an almost

complete lack of soft sediment deformation except in diamond drill sections

18/19 and 55/56 (Figure 16) where intense small scale folding and faulting

are commonly seen, especially near the top of the unit. Thickness of

Horizon D varies from 6.5 m to 23.5 m, reaching a maximum towards the

north end of the section studied. - 105 -

Lateral limits of Horizon E as shown in Figure 15 are, for the most part, arbitrary. Distinctive lithologies of this horizon, seen in core from only one diamond drill hole, consist of contorted and disrupted laminae of black cherty argillite, witherite and/or baritocalcite, barite and sulphide minerals. Assay values are erratic, ranging up to 12% Zn,

2% Pb and 0.15 oz/ton Ag while averaging about 8% Zn, 1.2% Pb and trace amounts of silver (Figure 16). Silver values display no obvious correlation with lead assays. Sulphide mineral laminations, which range in thickness

from 0.2 mm to 1.2 mm, are predominately composed of dark brown sphalerite with lesser pyrite, galena and very minor amounts of chalcopyrite. Idio- morphic pyrite grains are scattered throughout the sphalerite while galena

intergrowths are interstitial to sphalerite grains. Framboidal pyrite

occurrences are limited to black siliceous argillite laminae. Elongate

chalcopyrite blebs are present only at sphalerite grain boundaries. Quartz

lined fractures, which commonly cross-cut contorted lamination, are filled

with coarsely crystalline brown sphalerite and minor interstitial galena.

Large, elongate cavities lined with euhedral barite crystals may have

resulted from partial dissolution of adjacent and enclosing barium carbonate

laminae. Contortion of laminae, small scale folding and micro-faulting

are best developed at the base of Horizon E (Figure 16), diminishing in

frequency of occurrence and degree of development toward the top of the

unit. Horizon E, seen.in only one diamond drill hole, has a thickness of

15.3 m.

Horizon F is laterally equivalent to Horizon E, concordantly over•

lying Horizon D mineralization and occupying an elongate body with a

saucer-shaped cross-section (Figure 15). Interlaminated barite, sulphide - 106 -

minerals, black siliceous argillite and minor grey chert are indistinguishable

in outward appearance and grade from mineralization of Horizon D. Metal

values are surprisingly consistent throughout the unit, averaging 6% Zn,

1.5% Pb and trace amounts of Ag (Figure 16). Galena and sphalerite do not often occur together. Wispy, discontinuous lamellar concentrations of

galena occur with iUi.omorphi.c pyrite crystals in siliceous argillite.

Sphalerite occurs in three modes: as Targe and irregular clots in barite

laminae, as disseminations and small blebs in siliceous argillite,and as

coarsely crystalline fracture fillings with quartz and barite. Mineralized

fractures may be related to early dehydration of cherty argillite since

they are irregularly spaced, do not cut adjacent barite laminae and are

often partially filled with sags or injections of overlying laminae

(Plate Z). Cherty argillite laminations also: contain small, euhedraul

pyrite cubes and large framboids which range up to 0.12 mm in diameter.

Assay values within the horizon are erratic and no systematic mineral .

zonation appears to be present, either laterally or vertically (Figure 16).

Horizon F attains a maximum thickness of 9.5 m.

Much of the West Zone is capped by a thin layer of finely and evenly

interlaminated dark brown sphalerite and siliceous black argillite very

similar in outward appearance to stratiform mineralization of Horizon B.

Sphalerite laminae average less than 1 mm in thickness while argillite

laminae vary from 0.4 mm to 6 mm thick. Sphalerite, galena and framboidal

pyrite are disseminated throughout argillite laminae. Horizon G is zinc

rich. Metal values do not display much variation throughout the horizon,

averaging 0.8% Pb, 7% Zn and trace amounts of silver. No systematic metal

zonation is present other than a general vertical increase in zinc content Plate Z: Photograph of Horizon F mineralization (Tom West Zone) showing quartz filled dehydration cracks in cherty argillite beds. - 108 -

with respect to lead. Horizon G reaches a maximum thickness of 5.0 m near the north end of the West Zone section studied.

A zone of intensely silicified and pyritized silty black shale which

ranges in thickness from about one metre to about two metres forms the

immediate footwall to stratiform ore of the West Zone (Figure 15). Pyrite

framboids ranging up to 0.01 mm in diameter form 2 mm to 5 mm thick,

discontinuous laminae (Plate AA). Massive concentrations of framboids are

partially recrystal1ized to nearly idiomorphic pyrite which retains ghostly

outlines of framboidal textures when etched. Large euhedral pyrite grains

are frequently rimmed by tangentially arrayed, fibrous chalcedonic quartz.

Silica enrichment of the host shales, qualitatively determined by relative-

rock hardness, roughly parallels the overall concentration of pyrite;

silica, too fine grained to determine petrographically, probably occurs as

c.ryptocrystal 1 ine quartz cement. The base of the pyrite and silica enrich•

ment zone is sharply defined. Content of both pyrite and silica within

this interval increases gradually towards the contact with stratiform

mineralization of Horizon B. Scattered quartz-siderite veinlets are weakly

mineralized with sphalerite and galena.

A similar but less siliceous and less pyritic zone appears in the

immediate hanging wall shales of the West Zone (Figure 15). No lead-zinc

mineralization, either as disseminations or in veins, was seen in these

rocks. Upper contact of hanging wall silicified shales with more typical

shale of Unit 3b is gradational. Contacts between stratiform mineralization

and both footwall and hanging wall are abrupt.

A relatively large area of brecciated rock,:,approximately funnel-

shaped in cross-section, underlies massive sulphide mineralization of - 109 -

Plate AA: Photomicrograph (reflected light) of framboidal pyrite from the immediate footwall (Unit 3a, Canol Formation) of the Tom West Zone. - no -

Horizon A.(Figure 15). Breccia fragments are silicifed, pyritized and sideritized. Pyrite, galena, sphalerite, chalcopyrite, chalcocite and a variety of sulfosalt minerals;.including bouronite, boulangerite, tetrahedrite, proustite and pyargarite occur with quartz and siderite as breccia matrix, veins and disseminations in breccia fragments. Base metal values range as high as 2% Cu (estimated), 17% Zn and 6% Pb (Figure 16).

Silver, present in amounts as high as 11 oz/ton, displays no obvious correlation with lead. Several generations. Of mineralization are recognized. Footwall clasts in the south part of the funnel-shaped breccia

body are extensively sheared as are disseminated galena and sphalerite within the clasts. Sheared clasts are, in turn, brecciated and cemented

by mineralized quartz-siderite mosaics which are not deformed. Both

breccia matrix and clasts are cut by later, undeformed mineralized quartz-

siderite veins.

Sulphide and sulfosalt minerals occur in a variety of textures.

Sphalerite, the most common ore mineral, usually contains inclusions of

chalcopyrite-chalcocite, bournonite and tetrahedrite. Massive sphalerite

occurs in quartz-siderite veins, as fracture fillings and in the breccia

matrix. Sphalerite also occurs as disseminations in breccia clasts near

their.margins and adjacent to quartz-siderite veins. Large idiomorphic

pyrite grains occur in breccia clasts as well as matrix. Matrix pyrite

is commonly intergrown with concentrations of bournonite (Plate BB).

Matrix pyrite may also contain minute inclusions of galena and sphalerite.

Chalcopyrite, chalcocite, sphalerite, tetrahedrite and boulangerite form

complex intergrowths in euhedral bournonite crystals contained in the

quartz-siderite breccia matrix. Galena and chalcopyrite are usuallyiinter-

grown with sphalerite in breccia matrix, in quartz-siderite veins, as - Ill -

Plate BB: Photomicrograph (reflected light) of pyrite-bournonite inter- growth from epigenetic breccia mineralization underlying the south end of the Tom West Zone (py = pyrite, bn = bournonite, si = sphalerite, cp = chalcopyrite, qz = quartz). - 112 -

fracture fillings and as disseminations along clast boundaries. Sulphide veins are often mineralogically zoned across their widths although zonation does not appear to be consistent from vein to vein. Chalcopyrite of all types commonly contains minute inclusions of chalcocite. Small blebs of proustite, pyrargarite and tetrahedrite (var. freibergite?) are observed in vein galena. Calcispheres in brecciated silty shales are nearly always replaced by metallic minerals where seen, commonly pyrite but occasionally tetrahedrite, sphalerite and chalcopyrite (Plate CC). Framboidal tetra• hedrite and chalcopyrite in the clasts might be.replacements of pre• existing pyrite framboids. Tetrahedrite is occasionally seen as rims around pyrite framboids. Trace amounts of chalcopyrite, tetrahedrite, tennantite, boulangerite, pyargarite and proustite occur as micron-sized, discrete mineral grains in quartz-siderite breccia matrix and veins.

Breccia clasts generally are sheared and deformed along a 2 m to 10 m wide zone whiclv.defines the southernmost limit of the funnel-shaped breccia body, however, some clasts are only slightly rotated and weakly deformed.

Normal faulting of poorly lithified sediments may have initially controlled the development of brecciation and epigenetic mineralization. All breccia clasts are intensively silicified, pyritized, and weakly sideritized.

Rims of most clasts are altered and partially replaced by very fine inter- growths of siderite and quartz (Plate DD). Matrix of the breccia is predominantly coarsely crystalline quartz with lesser plumose siderite, sulphide minerals, barite and barium carbonate.

Diamond drill core of the epigenetic breccia mineralization was not assayed rigorously enough to evaluate metal zonation within the body, however greatest variety of ore minerals and highest grades of Cu, Pb, Zn, and Ag appear to occur near the top of the zone. - 113 -

Plate CC: Photomicrograph (reflected light) of calcispheres replaced by pyrite (py) and tetrahedrite (tt) from the breccia body which underlies the south end of the Tom West Zone stratiform mineral• ization.

Plate DD: Photomicrograph (plane light) of siderite (high relief) replacing the rim of a chert clast in Unit 2 massive conglomerate from the breccia body which underlies the south end of the Tom West Zone. - 114 -

A similar style of epigenetic mineralization occurss in stratiform mineralization of Horizons B and E in diamond drill section 54/55 (Figure

15).where brecciation and partial dissolution of syngenetic mineralization has left open boxwork cavities after pyrite, sphalerite and galena. Barite masses are commonly etched. Pyrite, sphalerite, galena, chalcppyrite.and minor amounts of tetrahedrite occur in quartz veins, as disseminations and cavity fillings. Footwall sha.Lessof Unit 3a are locally brecciated and mineralized with minor amountsoof,. pyrite, galena, sphalerite, chal• copyrite and tetrahedrite in quartz veins and disseminations.

GENESIS OF STRATIFORM BARITE AND BARITE-LEAD-ZINC DEPOSITS OF MACMILLAN PASS AREA

Review of Current Theories on Genesis of "Sedimentary- Exhalative" Deposits with Reference to the Tom West Zone

The Tom and Jason deposits exhibit many similarities with the McArthur

(Australia), Meggen (West Germany), Rammelsberg (West Germany) and

Sullivan (British Columbia) stratiform base metal deposnts. Examination and comparison of the similarities between them serves to outline a model for their genesis. Characteristics of these deposits are summarized in

Table III.

The syngenetic nature of this type of stratiform mineralization is almost universally accepted. Recent studies of these deposits have independently suggested an "exhalative" source for mineralizing fluids in each case. Conduits for mineralizing brines are theorized to have been located along deep-seated faults or fracture zones associated with the initiation of locally active tectonism expressed as rifting or differential subsidence of enclosing sedimentary strata. Table III: Characteristics of some stratiform barite and base metal deposits

DEPOSIT AGE SIZE PUBLISHED HOST POSSIBLE FOOTWALL RELATIVE INFERRED REFERENCES (tons x 106) OVERALL ROCKS TECTONIC CONTROLS ALTERATION STRENGTH BRINE TYPE GRADE ON ORE GENESIS PIPE OF MINERAL (Sato, 1972 RECOGNIZED? ZONATION and 1977)

McArthur, Middle 200 102 Zn dolomltlc differential no unzoned Type I Lambert, 1976 Austral 1a Proterozoic « Pb shale, subsidence 0.2X Cu shale adjacent to 1.5 oz/ton Ag normal fault

Heggen, Middle 66 10X Zn shale, differential no low Type I Krebs, 1976 West Devonian 1.3* Pb turbidites, subsidence Germany 0.21 Cu pelagic adjacent to limestone normal fault 16.5 961 BaSOa Sullivan, Middle 170 6.21 Pb turbidites, Intersection yes moderate Type I la Kanasew1ch,1968 British Proterozoic 6.IX Zn shale of fracture Ethler et al, 1976 Columbia 1.66 oz/ton Ag zones and Thompson and" normal fault Panteleyev, 1976 Ransom, 1977 Campbell, et a]_, 1978

Tom, Upper 9* 8.61 Pb* shale, differential yes moderate Type I la Carne, 1976 Yukon Devonian 8.4X Zn* turbidites subsidence Dawson, 1976 Territory 2.8 oz/ton Ag* adjacent to The present work 25* BaSOa* "hinge zone" Ramnelsberg, Middle 33 191 Zn shale, differential yes high Type lib Hannak, 1968 West Devonian 9X Pb tuffaceous subsidence Krebs, 1976 Germany IX Cu shale, adjacent to 3.0 oz/ton Ag turbidites "hinge zone" 22X BaSOa

Gataga Lakes Upper turbidites, not known none unzoned Type III R.J. Cathro, oral barite belt, Devonian shale recognized (barren) communication, 1978 British Columbia

•Initial development figures - 116 -

Recent publications by Hodgson and Lydon (1977) and Lydon (1978) outline models for submarine exhalative systems associated with block faulting by comparison with active continental geothermal systems.

Hydrothermal activity of this type is generated when and where an impermeable cap rock overlies a permeable aquifer and when discharge channels develop following faulting or fracturing of the cap. A heat source for the driving process could involve the tapping of heated groundwater or connate water by deep-seated faults or by the intrusion of magma bodies at depth along these fault zones. The generation of a hydrothermal fluid in a geothermal system then requires:

(a) a heat source;

(b) an aquifer unit which acts as a resevoir for the heated

solution; and,

(c) an overlying cap rock which contains the hydrothermal fluids,

preventing the dissipation of heat by mass transfer thus

allowing the maintenance of elevated temperatures within the

aquifer over an extended period of time.

Fluids in submarine geothermal systems possibly originate as recirculated seawater with the addition of hot connate or deep-seated groundwaters and/or magmatic fluids depending on the tectonic, igneous and sedimentary history of the area.

Initial composition of discharge fluids in exhalative systems is determined by fluid-mineral equilibria in the aquifer. Aquifer rocks should then be altered and depleted in elements enriched in stratiform ores formed by the hydrothermal system. Aquifer pyrite, in the case of moderate to high temperature systems, would be oxidized. The oxidation - 117 -

of ferrous iron to ferric iron contributes to the inorganic reduction of seawater or connate fluid sulphate. Turbidites and associated clastic rocks of Unit 1 in the Macmillan Pass area satisfy the requirements for a paleoaquifer system. Coarse fractions of the trubidites have relatively high initial porosity and permeability which is augmented by alteration of matrix material and complete destruction of diagenetic pyrite grains.

Clay mineral alteration in fine grained fractions of the turbidites is limited to areas adjacent to coarse grained laminae (Plate A) suggesting that alteration was accomplished by fluid movement through coarse clastic horizons in Unit 1.

The accumulation of heat energy in a geothermal system is favoured when and where an impermeable, insulating cap rock is present between the aquifer and the zone of submarine discharge. In the absence of a naturally occurring impermeable cap, many active hydrothermal systems contain "self- sealed" caps. Self-sealed caps form when near-surface boiling of hydro- thermal fluids causes rapid precipitation of their constituents, forming an effective barrier to further fluid movement. Unit 2 massive chert pebble conglomerate which overlies Unit 1 acquifer turbidites has an extremely low porosity and permeability due to the almost complete destruction and replacement of matrix and matrix porosity by pervasive cryptocrystalline quartz cementation. Relatively minor amounts of sphalerite and siderite accompany secondary silicification of the conglomerate. Regionally, this rock unit does not display well developed cementation. Indeed, the selective, locally occurring si 1icification of the conglomerate is difficult to explain without invoking some sort of secondary hydrothermal process.

If fluid boiling is a requirement for self sealing, then a massive - 118 -

sulphide ore horizon lying above a self-sealed cap should have an

associated, cross-cutting zone of alteration and stringer mineralization

related to discharge of boiling hydrothermal fluids at sites where the

cap is breached. The funnel-shaped breccia body which underlies massive

sulphide mineralization of the Tom West Zone probably served as the fluid

discharge conduit for most of the West Zone ore deposition. Epigenetic

mineralization and a coexisting zone of quartz-carbonate alteration within

this body might have resulted from the precipitation of constituents of a

geothermal brine during depressurization. Angular clasts of footwall

rock which are incorporated into overlying stratiform mineralization may

have resulted from steam-blast eruptions caused by periodic clogging of

the discharge vent by mineral precipitation. General size grading of

footwall clasts from coarse, cobble-sized fragments in massive sulphide mineralization of Horizon A to silt and sand sized detritus in the northern part of the West Zone reflects distance from the discharge vent.

Based on stable isotope and fluid inclusion studies, submarine exhalative metal deposits are theorized to form from variations on three different types of geothermal brines (Sato, 1972; Sato, 1977). Low temperature (up to about 150°C) brines with relatively high salinites (Type I) may have evolved from formational or connate waters. Moderate temperature fluids

(about 200°C) with moderate salinities (Types Ha and lib) are derived from either magmatic waters or mixtures of evolved connate fluids and circulating seawater. Higher temperature fluids (greater than 200°C) with relatively low salinities (Type III) most likely originate from circulating seawater in areas of high heat flow and -fluid 'permeability'such as oceanic rift zones.

In general terms, cationic composition of geothermal fluids is - 119 -

primarily determined by solution-mineral equilibria in the resevoir

(Lydon, 1977). Solution-mineral equilibria are, in turn, regulated by temperature and salinity of fluids in the aquifer providing that metals are carried in chloride complexes.

Assuming that bulk metal ratios of stratiform ores represent bulk metal ratios of mineralizing fluids, stratiform ores rich\in zinciand

lead with low copper content would be expected to form from low to moderate temperature, relatively saline hydrothermal fluids because of the generally low stability of copper chloride complexes with respectc:to those of lead and zinc. Furthermore, the relatively unstable nature of lead chloride complexes with respect to zinc chloride complexes in these fluids should

favour high zinc to lead ratios. Higher temperatures and lower brine salinities will favour an increase in relative amounts of lead and copper carried in solution with respect to zinc (Lydon, 1977).

Behavior of exhalative ore-forming fluids in seawater has been

predicted by Sato (1972 and 1977) according to their varying physio- chemical characteristics. Sato's calculations are based on the assumption

that physical properties of geothermal brines can be approximated by those of the NaCl^O system and that modification of their behavior in seawater by contributions of heat conduction, reaction heat and heat of dilution

are negligible in comparison with behavior predicted by heat capacity.

Behavior in seawater of three types of brines which are theorized to form

exhalative deposits are shown in Figure 17.

Type I brines are low temperature brines of relatively high salinity which will theoretically produce deposits with high zinc to lead ratios

and little to no copper. These fluids, upon their exhalation, will always

be heavier than seawater during their cooling history and should be - 120 -

Type I

Figure 17. Theoretical behavior of four types of exhalative fluids in seawater. The dashed line represents the hypothetical interface between anoxic and oxygenated seawater. Shaded areas are pooled exhalative brines (modified after Sato, 1972). - 121 -

initially deficient in reduced sulphur species because of their poor leaching capability and negligible capacity to inorganically reduce sulphate of connate waters or circulating seawater. Consequently, distribution of stratiform mineralization formed by these brines will be controlled directly by supply of biogenically reduced sulphur at the site of deposition. Margins of the deposit with enclosing sediments will be diffuse and sulphide mineral laminae should be finely alternated with sediments as stagnant brines precipate slowly when organically reduced sulphur becomes available. Homogenization of the pooled brines will produce very little metal zonation within the deposits. Since very little mixing with seawater occurs during the cooling history of the brines, barite (if present at all) will be largely separated from sulphide minerals at the margins of the anoxic depositional basin where sufficient seawater sulphate is available. Alteration zones or stringer mineralization in footwalll sediments will be poorly developed or not present. Furthermore, discharge vents may be spatially removed from stratiform mineralization if they occur upslope from the eventual depositional basins. Examples of stratiform base metal deposits that probably formed from Type I brines include the

Red Sea deposits, McArthur and Meggen.

Type II brines are moderate to high temperature fluids of moderate salinity that will theoretically produce deposits with high zinc.:.arid lead content and low copper content. Because of their relatively high temperatures, the brines have increased leaching capacity in the aquifer and may carry higher quantities..of inorganically reduced sulphur than Type I brines.

Brines of Type I la are heavier than seawater. Upon exhalation, minor mixing with seawater takes place (Figure 17)..and, if some reduced sulphur - 122 -

is carried in solution, a massive sulphide body may precipiate near the vent while much of the brine will flow downslope and pool in topograhic depressions as in the case of Type I. Relatively slow precipitation of pooled brines should produce.,a deposit which contains a higher degree of intercalated sedimentary laminae than associated massive sulphide bodies.

Barite, if present, would be concentrated at margins of the brine traps where oxygenated waters are present although, since some mixing with sea• water occurs at exhalation, nucleated barite crystals may be carried downslope with the brines and persist metastably in the brine pools.

Alteration pipes of stockwork stringer mineralization should underTy massive;:sulphide deposits. Both the Tom deposit and Sullivan Mine exhibit many of the characteristics of deposits that theoretically form the sub-i. marine exhalation of Type I la brines.

Type lib brines are slightly hotter than Type Ila.and, perhaps, less

saline. Upon exhalation into seawater, the density of these fluids will be less than, but will eventually exceed, that of seawater as convection•

like mixing above the vent causes cooling (Figure 17). Consequently, distribution of stratiform mineralization formed from Type lib brines will not be controlled by basin topography to the same extent as those

formed from Type I or Type I la brines. Rapid precipitation of fluid

constituents will occur as disequilibrium is reached at exhalation forming

high grade, and commonly cupiferous, sinter-like deposits of massive

sulphide mineralization about the vent. Degree of metal zonation away

from the discharge site, both vertically and laterally, will vary with

temperatures of exhaled brines. Boundaries of deposits formed by Type lib

brines will be sharp and enclosing sediments will usually not contain - 123 -

anomalous amounts of metal. Since some mixing with oxygenatedoseawateri^r occurs immediately after exhalation, barite, when present, will be intimately associated with layered sulphides. Alteration pipes or zones of stringer mineralization along brine conduits in footwall sediments should be well developed. Rammelsberg, which is strongly zoned and contains a well mineralized alteration pipe, may have formed from Type lib brines.

Type III brines are high temperature, dilute solutions which are always lighter than seawater during their cooling history. Accordingly, the fluids will rise until they reach surface water.;or until they are infinitely diluted by seawater (Figure 17). Because reduced sulphur is not readily available in surface water, constituents of Type III brines will probably precipitate as oxides although some sinter deposits of sulphide mineralization may form about the vent. Initial chemical studies on bedded barite of the Muskwa Ranges, northeast British Columbia, using barium-strontium ratios as a guide to relative temperatures of deposition, indicate that barren barite deposits which occur attthe same stratigraphic interval as Upper Devonian stratiform barite-lead-zinc mineralization at

Driftpile Creek (N.T.S. 94 K/4) formed at higher temperatures than the barite which accompanies mineralization (R.J. Cathroi oral communication,

1977). The barren barite deposits, which attain thicknesses of as much as 30 m and strike lengths of more than one kilometre, are contained within a horizon of extremely siliceous and pyritic black shale which carries anomalous but subeconomic quantities of lead, zinc and silver. These barren barite deposits and similar deposits in the Selwyn Mountains may have resulted from exhalation of Type III geothermal brines. Rapid cooling - 124 -

and dispersionoof this type of fluid in seawater prevents the effective concentration of base metals while barite, which precipitates immediately on contact of the brine with seawater sulphate, will be deposited as a

"snowfall" of barite crystals in close proximity to the vent producing blanket-like deposits of relatively pure barite. This mechanism may help to explain why most stratiform barite deposits of Yukon Territory and northeast British Columbia are not intimately associated with significant quanti;ti;es:;of base metals.

Barite is an important volumetric component of many massive sulphide deposits. The distribution of barite within deposits can be satisfactorily explained by physio-chemical models of ore deposition from exhalative brines but controls on the initial presence of barium in these fluids is not well understood. The model proposed here for the genesis of sedimentary- exhalative base metal deposits does not satisfactorily explain the presence of absence of barite. The Tom deposit is located at the same stratigraphic

interval as literally hundreds of sulphide-deficient bedded barite deposits

in southeast Yukon and northeast British Columbia. Since bedded barite occurs at the same stratigraphic interval and is morphologically similar to barite of the Tom deposit, these barite and barite-lead-zinc deposits probably share a similar genetic history.

Theories on the genesis and distribution of these stratiform barite and barite-lead-zinc deposits must, of course, be refined with isotopic

and temperature data. The geothermal theory proposed for the genesis of

hydrothermal solutions by Hodgson and Lydon (1977) and Lydon (1978) in

combination with Sato's (1972 and 1977) exhalative brine models can be

used effectively, however, to broadly predict the characteristics of a - 125 -

particular sedimentary-exhalative deposit once preliminary data about its morphology, metal content and relationships to host rocks are known.

Probable Genetic History of the Tom West Zone

Based on the assumption that the upper surface of stratiform minerali• zation will be horizontal following itsscomplete'ideposition, stages leading to the deposition of the Tom West Zone section shown in Figure 15 were determined by successively removing individual sedimentary and mineralized horizons and restoring the "new" surface to horizontal (Figure 18). Three locally occurring tectonic events which are expressed as differential subsidence correlate with mineralizing events. Succession and morphology of ore types, their relationship to epigenetic mineralization and metal distribution suggest the following sequence of events leading to the formation of the Tom West Zone:

Stage 1: Deposition of Unit 1 turbidites and associated clastic rocks was followed immediately by deposition of the coarse grained, unsorted debris flow deposit of Unit 2 on a flat or gently sloping seafloor after uplift and erosion of Road River Formation (?) cherts to the west and northwest.

Local deposition of Unit 3a slide and slump debris deposits followed movement on deep seated faults within the Macmillan Pass area. Heated

connate waters moving upward along these faults mixed with circulating

seawater to some degree (Figure 18).

Stage 2: Rapid, differential subsidence continued in the Macmillan Pass

area('(Figure 18). Geothermal fluids rose along active fault and fracture

zones until they reached the porous and permeable strata of Units 1 and 2. - 126 -

Movement of hot brines through Unit 1 and underlying shales released metals through alteration of silicate minerals and oxidation of pyrite. Fluid boiling in the near surface Unit 2 conglomerate precipitated silica which cemented the unit and formed a self-sealed cap over the geothermal system.

Renewed localized differential subsidence .in now cemented Unit 2 formed the funnel-shaped breccia body as a result of faulting and/or explosive release of geothermal brines ascending along a fracture system. Type lib brines discharging through thecbfeccia body resulted in alteration and mineralization of the breccia as well as the eventual precipitation of massive sulphide mineralization near the vent (Horizon A) and inter- laminated sulphides and silicified sediments away from the vent (Horizon B).

Bedded siderite found atthe base of the massive sulphide body is probably indicative of a relatively high initial dissolved CO^ component.to the brines,.'released by depressurization.! Copper-bearing minerals such as chalcopyrite, chalcocite, tetrahedrite and other sulfosalts precipitated in the fluid conduits and in stratiform mineralization near the vent because of the relatively low stabilities of copper-chloride complexes.

Both vertical and lateral zonation of galena and sphalerite within

Horizons A and B may reflect the relative stabilities of lead and zinc chloride complexes in moderate to high temperature brines. Some of the sulphide sulphur of Horizon A may have originated with the exhalative;; fluids while interlaminated sediments and stratiform mineralization on

Horizon B probably precipitated slowly as biogenically reduced seawater sulphate became available.

Stage 3: Continued subsidence formed a small sub-basin immediately north of the vent area (Figure 18). Exhalative fluids, because of their slightly - 127 -

cooler nature, now behaved as Type I la brines and were pooled in the depression precipitating slowly to form ore Horizons C and D. Some mixing with seawater may have occurred immediately over the vent where interlaminated sulphides and argillite of Horizon C approach massive sulphide quantities. As mixing occurred about the discharge area, barium combined with seawater sulphate to form very fine barite crystals which were carried downslope in suspension with the heavy Type I la brines.

Interstitial sphalerite and galena in barite of Horizon B probably precipitated in situ in the barite mud created by settling of barite crystals from the brines. Cyclic alteration of sulphide mineral, barite and siliceous argillite laminae of Horizon D probably resulted from

individual exhalative episodes. Barren siliceous argillite laminae reflect

periods of normal pelagic sedimentation when the rate of exhalative

discharge was minimal. Episodic discharge from submarine geothermal

systems may be related to "seismic pumping" (Lydon, 1978) in which pore

solutions of resevoir rocks are expulsed from the focus of shallow earth•

quakes by collapse of the dilatant zone. Generation of earthquakes was

likely related to local differential subsidence which continued through

deposiUon'Oif Horizons C and D (Figure 18). Discharge rate of geothermal

brines gradually waned as pressure within the system decreased and fluid

conduits became clogged by mineral precipitation. The 2 cm to 4 cm

thickness of barren, pyritic chert which caps Horizons C and D probably

represents the last significant contribution from this discharge site in

a situation analgous to volcanogenic-exhalative systems (e.g. ferruginous

chert horizons which overlie Kuroko massive sulphide deposits). - 128 -

Stage 4: Differential subsidence continued locally in an area north of the now dormant vent (Figure 18). Highest degree of soft-sediment deformation in drill core from Horizons A, B and D occurs on the flanks of the subsiding basin, reflecting the post-depositional instability of the poorly consolidated chemical and pelagic sediments. Fluids under high pressure in the sealed .geothermal system broke through to the sea• floor along a zone of weakness coincident with the axis of greatest subsidence. These hot and acidic solutions leached and altered the brecciated footwall rocks and chemical sediments of Horizons B and D.

Fluids were probably similar to the Type I la brines which formed the earlier Horizon C and D mineralization/ The significant amount of barium carbonate minerals in Horizon E reflects a relatively high dissolved CO^ content in the brines. Time equivalent barite-lead-zinc mineralization of Horizon F precipitated from pooled brines inr.a manner similar to under•

lying mineralization of Horizon D.

Stage 5: Subsidence continued along the earlier formed ttrough (Figure 18).

Exhalative fluids now behaved in a manner akin to Type I brines as

temperature of the geothermal system decreased. Lack of well developed metal zonation, abundant interlaminated sediments and the absence of

barite in Horizon G suggests that sulphide mineral formation proceeded

slowly in a shallow topographic depression. Locus of discharge for these

fluids is not indicated within the section studied but it is not incon•

ceivable that it may have been located off the plane of the section.

Currently available information about the Tom deposit does not provide

insight into the total size and metal distribution of down dip extensions

of the West Zone mineralization discussed in the preceeding pages. - 129 -

Exhalative sites or geothermal vents were probably located at.the.c intersections of fracture zones-or along fault zones where interstratal permeability is highest. In addition to ore horizons established for the adit-level cross-section, additional drilling down-dip might reveal significantly different deposit morphology and metal content as distances

from exhalative centres varies.

The scenario presented in the preceeding pages will, of necessity,

remain speculative until data are obtained on the salinity and temperature

of ore-forming fluids and on the source of sulphur in the ores. Studies

of the type described can, however, be instrumental in determining

continuity or possible extensions of sedimentary-exhalative deposits which are in the advanced exploration stage..

SUMMARY AND CONCLUSIONS

The study area, located near Macmillan Pass at the Yukon-Northwest

Territories border, has been of economic interest since the discovery of

stratiform barite-lead-zinc-mineralization on the Tom claims by Hudson Bay

Exploration and Development Co. Ltd. prospectors in 1951. Renewed interest

in the area results from the recent discovery of similar mineralization on

the Jason claims, six km west of the Tom showings.

Intensive exploration of the Tom mineral deposits by Hudson Bay

Exploration and Development Co. Ltd., utilizing surface diamond drilling,

geochemical and geophysical surveys, underground exploration and under•

ground diamond drilling, has delineated approximately nine million tons

of ore grade .material averaging 8.6% lead, 8.4% zinc and 2.8 oz/ton silver - 130 -

using an 8% lead and zinc cut-off grade. Recent work on the nearby Jason showings has outlined mineral deposits of similar size and grade.

The Macmillan Pass area Ties along the northern edge of Selwyn Basin, a northwest trending epicontental trough of lower to middle Paleozoic age.

Selwyn Basin is bounded partially on its seaward side by shallow water carbonate rocks of the Pelly-Cassiar Platform and on the east and north• east by carbonate rocks of Mackenzie Arch. Selwyn Basin sedimentation was characterized by non-interupted shale and chert accumulation from early Cambrian to Middle Devonian times. A flood of late Devonian and

Lower Mississippian coarse clastic rocks derived from uplifted source terranes within the basin host numerous stratiform barite and barite-lead- zinc deposits including those of the study area. These rocks, informally

referred to as the "Black Clastic Group" have been tentatively divided

into a lower, dominantly pelitic member(Canol Formation) and an upper clastic member (Imperial Formation).

Canol Formation has been subdivided into four distinct lithological

packages called, for the purposes of this report, Units 1, 2, 3a and 3b.

Unit 1 attains a thickness of at least 45 m. Lithologies dominantly

consist of finely interbedded silty shales and sandy siltstones, thick

bedded silty sandstones, medium to thickcbedded sandy siltstones and

irregular pebble conglomerate bodies deposited, respectively, as contourites,

turbidites, grain flows and debris flows. A general upwards coarsening

of coarse clastic components is noted. Oxidation of constituent pyrite

in coarse grained laminae and bleaching of organic matter in adjacent

pelitic laminae is indicative of localized hydrothermal alteration of

Unit 1 rocks. - 131 -

Unit 2 consists of a 70 to 240 m thick, massive chert pebble conglomerate debris flow deposit overlain by a 6rm section of chert granule turbidites. Paleocurrent directions for both sequences indicate source terranes to the north or northwest. Pervasive secondary

ic. sil^ification and minor sideritization of clay-sized matrix material has effectively destroyed any porosity and permeability that might have once existed in the conglomerate.

A majority of Unit 3a consists of finely interbedded silty sandstones and shales deposited by turbidity currents. Lesser amounts of coarse

intraformational conglomerate and pebbly mudstone are included in some sections. Unit 3a generally exhibits an overall upwards decrease in grain size to an evenly fine grained black shale at the top of observed

sections. Although the above generalities serve to describe the overall

character of Unit 3a in the study area, each exposure contains its own

irregularities and peculiarities. Incorporation of constituents of

underlying Unit 2 into pebbly mudstones, deposition of chaotic intra•

formational conglomerates and locally variable directions of transport

for Unit 3a clastic rocks suggest a coincident period of basin instability,

perhaps reflecting local tectonic activity. Deposition of fine grained

pelitic rocks capping the Unit 3a section is interpreted as a return to

normal depositional regimes.

Distinctive silvery grey weathering, pyritic black shales and lesser

coarse clastic rocks and thin bedded limestones of Unit 3b underlie most

of Macmillan Pass area. Thickness of the unit varies from less than 30 m

to at-Jeast 1430 m near the central part of the study area. Tentative

correlation of fetid limestone marker horizons between diamond drill holes - 132 -

and scattered outcroppings suggests that rapid differential subsidence of the central Macmillan Pass area accompanied deposition of Unit 3a.

Subsidence appears to have been "hinged" along a north-south trending zone paralleling the east edge of the study area. Southerly, westerly and northerly limits of this down-dropped basin are not defined by the present study.

Imperial Formation is divided into a lower and an upper member,

Units 4a and 4b respectively. Unit 4a, which unconformably overlies

Unit 3b, consists of cycl ic alternations of reddish brown and grey coloured clastic sedimentary rocks. Total thickness varies from areas where it is

not present to accumulations over 100 m thick. Evidence of diagenetic evaporite mineral formation, in conjunction with other diagnostic features

such as mud cracks and flat pebble conglbmeraterare indicative of shallow water to peritidal environments of deposition.

Unit 4b consists of a monotonous assemblage of resistant, cliff-

forming, silty mudstones and muddy siltstones which generally coarsen

upward. Well developed, small-scale, climbing cross-ripple lamination

of most lithologies indicates a southerly direction of transport.

Gradational contact with underlying shallow water sedimentary rocks of

Unit 4a suggests a uniform and gradual progradation of sea level to the

north.

Four independent tectonic events have shaped the Middle Paleozoic

to Upper Mesozoic structural evolution of the Macmillan Pass area.

Upper Devonian sedimentation patterns record a period of contemporaneous

tectonic instability, resulting in rapid differential subsidence "hinged"

along an approximately north-south trending zone of flexure near the - 133 -

eastern margin of the study area. During lower Mississippian time, easterly directed congressional forces resulted in faulting and folding of the eastern basin margin along the earlier formed "hinge" zone. Mild folding of the Devono-Mississippian unconformity at that location suggests that this deformation may have been reactivated at a later time.

The Macmillan Pass area is located along the southern margin of a 20 km wide, structurally anomalous belt that extends at least 100 .km west and about 30 km to the east. Within this belt, Paleozoic and older rocks are generally deformed into isoclinal, easterly trending folds while northerly to northwesterly trending open folds are characteristic of the regional

structural style. Although both types of deformation are undoubtedly

Mesozoic in age, anomalous structural trends in the Macmillan Pass area may reflect earlier formed zones of structural weakness.

Mild doming of intruded sedimentary rocks about a Cretaceous granitic

body, which lies immediately south of the Macmillan Pass region, is

reflected by minor, concentrically arrayed, open folds in the south part

of the study area.

Stratiform barite-lead-zinc mineralization on the Tom claims occurs

in two separate bodies, the discovery or West Zone and the East Zone.

The East Zone is 160 m long, 3 m to 20 mhthick and dips steeply west.

The West Zone, a much larger body about 1200 m in length and 3 m to 60 m

thick, dips 50° to 70° west. East Zone mineralization has been explored

in its entirety by surface and underground diamond drilling to a depth

of 350 m. Only the higher grade south half of the West Zone has been

explored in detail, where ore grade material has been outlined to a depth

of 260 m. The two deposits together total nine million tons of ore - 134 -

grade material averaging 8.6% Pb, 8.4% Zn and 2.8 oz/ton Ag. Ten million tons of sub-ore grade material which averages 4.6% Zn, 0.9% Pb and trace amounts of silver have been outlined in the north half of the West Zone.

Both of the deposits occur at the same stratigraphic interval, marking the sedimentary transition between locally derived slide and slump debris deposits of Unit 3a,: with fine grained pel itic rocks of Unit 3b.

South half of the Tom West Zone was selected for detailed study. In order to best utilize textural,-.assay and mineralogical data, information derived from detailed logging of diamond drill core was used to reconstruct a cross-section through the south half of the West Zone as it would have appeared at the culmination of ore deposition. Seven distinct types of

stratiform mineralization are recognized (Horizons A to G). Horizon A

appears at the base of the south end of the West Zone. Its massive, poorly

laminated galena, sphalerite, pyrite, siderite, minor quartz and barite

form the highest grade of mineralization yet discovered in the Macmillan

Pass area. Accessory sulphide and sulfosalt minerals include chalcopyrite,

boulangerite, bournonite and tetrahedrite. Thickness of the horizon

ranges from 2.5 m to 3.5 m.

Horizon B, which underlies most of the West Zone, consists of evenly

laminated black cherty argillite, dark grey chert and lesser barite with

interlaminated and disseminated sphalerite, galena and pyrite. Thickness

of the horizon is relatively constant, averaging 2.4 m. Strata of Horizon

B are likely facies or time equivalents of Horizon A massive sulphide

mineralization.

Horizon C is contained within a small body, lense shaped in cross-

section, which concordantly overlies Horizon A at the south end of the - 135 -

West Zone. Inter!aminated sphalerite, galena, pyrite, cherty argillite and barite are similar in appearance to mineralization of Horizon B, although Horizon C contains significantly more barite and mineral lamination is much more contorted. Horizon C varies from 2.2 m to 6.4 m thick.

Horizon C, which contains the bulk of the West Zone tonnage, appears to grade laterally northward from Horizon C. Finely laminated barite gangue contains interlaminated and disseminated sphalerite and galena.

Horizon D varies from 6.5 m to 23.5 m thick, reaching a maximum thickness towards the worth end of the section studied.

Distinctive lithologies of Horizon E, seen in core from one diamond drill hole, consist of contorted and disrupted laminae of cherty black argillite, witherite and/or baritocalxite and barite with interlaminated and disseminated galena, sphalerite, pyrite and minor chalcopyrite. The

horizon has a thickness of 15.3 m in this location.

Horizon F is laterally equivalent to Horizon E, concordantly over•

lying Horizon D mineralization and occupying an elongate body with a

saucer-shaped cross-section. Interlaminated barite, black siliceous

argillite, minor chert and disseminated galena, sphalerite and pyrite

are indistinguishable in appearance from mineralization of Horizon D.

Horizon F reaches a maximum thickness of 9.5 m.

Much of the West Zone is capped by a thin layer of finely and evenly

laminated siliceous black argillite and sphalerite called Horizon G.

Siliceous argillite laminae contain disseminated sphalerite, galena and

framboidal pyrite. Horizon G reaches a maximum thickness of 5.0 m near

the north end of the section studied. - 136 -

Stratiform mineralization from the Tom West Zone displays systematic, overall metal and mineral zonation. Based on these parameters, West Zone mineralization can be divided into three separate, stacked ore bodies each with relatively consistent internal zoning patterns. Contacts between these packages are marked by abrupt changes in metal ratios;,

The lowermost and, presumably, oldest of the three discrete mineralized bodies consists of Horizons A through D. Here metal grades generally decrease systematically up section and to the.north, from highest values of 31% Pb, 14% Zn and 11 oz/ton Ag occurring near the base of Horizon A

to il.% Pb, 5% Zn and trace amounts of silver near the top of the northern

limit of Horizon D. An overall decrease in lead to zinc ratios accompanies

the decrease in combined lead and zinc grade, while lead to silver ratios

increase in a like manner. Discrete silver and copper bearing minerals

are only found in the highest grade portions of Horizons A and C. A

general increase in barite content of the ore accompanies the overall

decrease in metal grades. Mineralization of this package is capped by a

2 cm to 4 cm thickness of grey pyritic chert.

Mineralization of Horizons E and F displays no systematic mineral

or metal zonation although overall grades are slightly higher in Horizon

E than in the adjacent Horizon F (averaging 1.5% Pb, 8% Zn and trace amounts

of silver; and 1.5% Pb, 6% Zn and trace amounts of silver, respectively).

Combined lead and zinc grades are, in addition, slightly higher than those

for underlying mineralization of Horizons C and D while lead to zinc

ratios are generally lower, decreasing upsection.

The youngest mineralization, Horizon G, does not display much lateral

or vertical variation in metal values, averaging 0.8% Pb, 7% Zn and trace - 137 -

amounts of silver. Transition with underlying Horizons E and F is marked

by an abrupt increase in lead to zinc ratios of the mineralization.

A mineralized breccia zone, approximately funnel-shaped in cross-

section, underlies massive sulphide mineralization of Horizon A at the

south end of the Tom West Zone section studied. Footwall breccia fragments

composed of rock units 2 and 3a are silicified, pyritized and sideritized.

Pyrite, galena, sphalerite, chalcopyrite, chalcocite and a variety of

sulfosalt minerals including bournonite, boulangerite, tetrahedrite,

proustite and pyargarite occur with quartz and siderite as breccia matrix,

veins and disseminations in breccia fragments. Metal values range as

high as 2% Cu, 6% Pb, 17% Zn and 11 oz/ton Ag. Cross-cutting relationships

define several generations of epigenetic mineralization.

In a manner akin to the McArthur (Australia), Meggen (West Germany),

Rammelsberg (West Germany) and Sullivan (British Columbia) deposits, the

Tom West Zone was derived through exhalation of heated, metal-bearing,

saline fluids onto the sea-floor. Based on reconstructed .profiles, with

accompanying assay and mineralogical data, three successive mineralizing

episodes are postulated for the Tom West Zone. Each episode was preceeded

by an interval of locally occurring tectonic activity. Succession and

morphology of ore horizons, their relationship to epigenetic mineralization

and metal distribution suggest the following sequence of events:

Stage 1: Deposition of Unit 1 and Unit 2 turbidites, debris flows and

associated clastic rocks followed uplift and erosion of Road River

Formation cherts to the west and southwest of the Macmillan Pass area.

Localized deposition of clastic rocks of Unit 3a followed movement on

deep-seated faults within the study area. Circulating sea water, mixing - 138 -

with heated connate brines, ascended along the cross-strata! permeability provided by these faults.

Stage 2: Boiling of geothermal brines in the near-surface Unit 2 conglomerate precipitated silica which eventually cemented the rock, providing a temporary barrier to the further ascent of fluids. Circulation of hot fluids through underlying sedimentary strata released metal and sulphur through alteration of silicate minerals and oxidation of pyrite. The confining barrier of the self-sealed cap rock was eventually breached

through faulting and/or the explosive release of pressurized resevoir

fluids. Discharge of hot and moderately saline brines resulted in epi• genetic mineralization and alteration in the breccia, as well as the eventual deposition of sinter-like massive sulphide mineralization near

the vent (Horizon A) and interlaminated sulphide minerals and silicified

sediments away from the vent (Horizon B). Much of the reduced sulphur

species of Horizon A may have originated with the exhalative fluids while

the high degree of sediment intercalation with Horizon B mineralization

suggests that slow formation of sulphide minerals from pooled metalliferous

brines was regulated by the availability of biogenically reduced seawater

sulphate.

Stage 3: Continued subsidence formed a small sub-basin immediately north

of the vent area. Mineralization of Horizons C and D formed from exhalative

fluids pooled in this depression. Discharging brines were now cooler as

fluid pressure in the geothermal resevoir gradually decreased. Some

mixing with oxygenated seawater probably occurred immediately over the

discharge area. Barium in the exhalative fluids combined with seawater

sulphate, nucleating barite crystals which were carried downslope in . - 139 -

suspension with the cooling brines. Interstitial sphalerite and galena of Horizon D precipitated in situ in a barite mud created by gravitational settling of the barite crystals. Decrease in the lead to zinc ratios of stratiform mineralization with distance from the vent may reflect the relative stabilities of the respective ionic species in the presence of some reduced sulphur carried with the disequi1ibrated geothermal fluids.

The observed increase of zinc with respect to lead mineralization with increasing distance upsection in Horizons A-B and C-D;..may be a result of evolving fluid-mineral equilibria in the aquifer as a result of depressurization and consequent cooling of the system. Discharge of geothermal brines gradually lessened and eventually ceased as pressure within the system decreased and fluid conduits became clogged by mineral precipitates.

Stage 4: Differential subsidence continued locally in an area north of the now dormant vent. Fluid pressure in the sealed geothermal system i increased until it was sufficient to break through overlying sediments and stratified, mineralized muds along a zone of weakness coinciding with the axis of greatest subsidence. Exhalative fluids, probably similar in character to those which formed the earlier Horizon C and D mineralization, pooled in the depression. Slow precipitation of constituents formed stratiform mineralization of Horizons E and F.

Stage 5: Subsidence continued along the earlier formed trough. Relatively cool, saline fluids frorrk.the nearly exhausted geothermal system were relatively enriched in zinc with respect to lead. Lack of well developed mineral zonation, abundant sediment intercalation and the absence of barite in Horizon G suggests that the sulphide mineral formation proceeded slowly, regulated)by.the availability of biogenically reduced sulphur. - 140 -

REFERENCES

Abbate, E., Bortolotti, V. and Passini, P. 1970: Development of the northern Appenines geosyncline -; 01istostromes and olistoliths; Sed. Geol., Vol. 4, pp. 521-557.

Allen, J.R.L. 1973: A classification of climbing-ripple cross-lamination; Jour. Geol. Soc. London, Vol. 129, pp. 537-541.

Archer, Cathro and Associates Limited 1972: Northern Cordillera Mineral Inventory (Revised 1978): •T Private report available to subscribers.

Baadsgaard, M., Folinsbee, R.E. and Lipton, J. 1961: Potassium-argon age of biotites from Cordilleran granites^,, central British Columbia; Geol. Soc. Amer., Bull., Vol. 72, pp. 689-702.

Bassett, H.G. 1961: Devonian stratigraphy, central Mackenzie River region, Northwest Territories, Canada; j_n Raasch, G.O. (ed.)

Geology of the Arctic;:Vol. 1, Alta. Soc. Petrol. Geol. and Univ. Toronto press, pp. 481-495.

Baxter, J.W. I960;: Calcisphaera from the Salem (Mississippian) Limestone in southwestern Illinois; Jour. Paleon., Vol. 34, pp. 1153-1157.

Berner, R.A. 1969: The synthesis of framboidal pyrite; Econ. Geol., Vol. 64, pp. 383-384.

1970: Sedimentary pyrite formation; Am. Jour. Sci., Vol. 268, pp. 1-23.

1971: Principles of Chemical Sedimentology, McGraw-Hill, New York, 256,.p..

Blatt, H. 1959: Effect of size and genetic quartz type on sphericity and f form of beach sediments, northern New Jersey; Jour. Sed. Pet., Vol. 29, pp. 197-207.

Blatt,i.H,, Middleton, G. and Murray, R. 1972: Origin of Sedimentary Rocks; Prentice-Hall Inc., New Jersey, 634 p.. - 141 -

Blusson, S.L. 1971: Sekwi Mountain map-area (105P), Yukon Territory and District of Mackenzie; Geol. Surv. Can., Paper 71-22.

1974: Geology of sheets 105 N, 105 0, 106 A, 106 B and 106 C, Yukon and Northwest Territories; Geol. Surv. Can., Open File 205.

1976: Selwyn Basin, Yukon and District of Mackenzie; ij^ Report of Activities, Geol. Surv. Can., Paper 76-1 A, pp. 131-132.

Bostock, H.S. 1948: Physiography of the Canadian Cordillera, with special reference to the area north of the fifty-fifth parallel; Geol. Surv. Can., Mem. 247.

Bouma, A.H. 1962: Sed.imentology of some flysch deposits; Elsevier Publ. Co., Amsterdam, !T68 pp.

1973: Fossil contourites in Niesen flysch, Switzerland; Jour. Sed. Petrol., Vol. 42, pp. 917-921.

Calvert, S.E. 1974: Deposition and diagenesis of silica in marine sediments; Spec. Pub. Int. Assoc. Sed., Vol. 1, pp. 273-299.

Campbell; F.A., Ethier, V.G., Krouse, H.R. and Both, R.A. 1978: Isotopic composition of the Sullivan orebody, British Columbia; Econ. Geol., Vol. 73, pp. 246-268.

Campbell, R.B. and Dodds, C.J. 1978: Operation Saint Elias, Yukon Territory; i_n Current Research, Geol. Surv. Can., Paper 78-1 A, pp. 35-41.

Carne, R.C. 1976: Stratabound barite and lead-zinc-barite deposits in eastern Selwyn Basin, Yukon Territory; Open File Report EGS 1976-16, Dept. Indian and Northern Affairs, 41 pp.

Craig, D.C. and Laporte, P. 1970: Mineral Industry Report, Yukon Territory and southwesternr:: sector, District of Mackenzie, 1969 and 1970, Vol.'il, Dept. of Indianr.Affairs and Northern Development.

Crowel1, J.C. 1957: Origin of pebbly mudstones, Geol. Soc. Amer., Bull. Vol. 68, pp. 993-1010. 142 -

Crowell, J.C., Hope, R.A., Kahle, J.E., Ovenshine, A.T., and Sams, R.H. 1966: Deep-water sedimentary structures, Pliocene Pico Formation, Santa Paula Creek, Ventura Basin, California; Calif. Div. Mines Geol., Spec. Rpt. 89, 40 p.

Davies, D.K. and Williamson, E.A. 1976: Shallow-marine origin for Ordovician rocks of the Quachita Mountains, Arkansas; Geol., Vol. 4, pp. 340-344.

Dawson, K.M. 1977: Regional metallogeny of the northern Cordilla; i_n_ Report of Activities, Geol. Surv. Can., Paper 77-1 A, pp. 1-4.

Dawson, K.M. and Dick. L.A. 1978: Regional metallogeny of the northern Cordillera: Tungsten and base metal-bearing skarns in southeastern Yukon and southwestern District of Mackenzie; jn_ Current Research, Geol. Surv. Can., Paper 78-1A, pp. 287-292.

Dimroth, E. 1975: Paleo-environment of iron-rich sedimentary rocks, Geol. Rundschau, Vol. 64, pp. 751-767.

Douglas, R.J.W., Gabrielse, H., Wheeler, J.O., Stott, D.F., and Belyea, H.R. 1970: Geology of western Canada, j_n Geology and Economic Minerals of Canada, Geol. Surv. Can., Econ. Geol. Rept. No. 1, pp. 365-448.

Embly, R.W. 1976: New evidence for occurrence of debris flow deposits in the deep sea; Geology, Vol. 4,., pp. 371-374

Ethier, V.G., Campbell, F.A., Both, R.A. and Krouse, H.R. 1976: Geological setting of the Sullivan orebody and estimates of temperatures and pressures of metamorphism; Econ/ Geol., Vol. 71, pp. 1570-1588.

Farrand, M. 1970: Framboidal sulphides precipitated synthetically; Mineral. Deposita, Vol. 4, pp. 237-246.

Findlay, D.C. 1969: The mineral/industry of Yukon Territory and southwestern District of Mackenzie, 1968; Geol. Surv. Can., Paper 69-55.

Fisher, R.V. 1971: Features of coarse-grained, high concentration fluids and their deposits; Jour. Sed. Petrol., Vol. 41, pp. ..916-927.

Folk, R.L. and Pittman, S.'J. 1971: Length-slow chalcedony: a new testament for vanished evaporites; Jour. Sed. Petrol., Vol. 41, pp. 1045-1058. - 143 -

Freberg, R.A. 1976: Tom Property, Macmillan Pass, Yukon Territory (abst.); Can. Inst. Min. Metal., Bull., Vol. 69, p. 667.

Fritz, W.H. 1976: Ten stratigraphic sections from the Lower Cambrian Sekwi Formation, Mackenzie Mountains, northwestern Canada; Geol. Surv. Can., Paper 76-22.

Gabrielse, H. 1967: Tectonic evolution of the northern Canadian Corillera; Can. Jour. Earth Sci., Vol. 4, pp. 271-298.

1976: Environments of Canadian cordi'llera depositional basins; in Circum-Pacific Energy and Mineral Resources, Amer. Assoc. Petrol. Geo!., Mem. 25, pp. 492-502.

1978: Operation Dease; i_n Current Research, Geol. Surv. Can., Paper 78-1 A, pp. 1-4.

Gabrielse, H. , Blusson, S.L., and Roddick, J.A. 1973: Geology of Flat River, Glacier Lake and Wrigley Lake map areas, District of Mackenzie and Yukon Territory, Geol. Surv. Can., Mem. 366.

Gabrielse, H. and Dodds, C.J. 1977: The structural significance of the northern Rocky Mountain Trench and related lineaments in north-central British. Columbia; Geol. Assoc. Can., Ann. Mtg., Program with Abstracts, Vol.2, p.19.

Gabrielse, H. , Dodds, C.J. and Mansy, J.L. 1977: Operation Findlay, British Columbia; i_n Report of Activities, Geol. Surv. Can., Paper 77-1 A, pp. 243-246.

Gabrielse, H. , and Wheeler, J.O. 1961: Tectonic framework of southern Yukon and northwestern British Columbia; Geol. Surv. Can., Paper 60-24.

Godwin, C., Harakal, J., Carne, R., and Mortensen, J. 1979: (in press), Geocnronometric analysis of Tertiary sill, Macmillan Pass, Yukon Territory.

Goldstein, A. , Jr., and Hendricks, T.A. 1953: Siliceous sediments of Ouachita facies in Oklahoma; Geol Soc. Amer., Bull., Vol. 64, pp. 421-442.

Gordey, S.P. 1977: Stratigraphy, structure and tectonic evolution of the southern Pelly Mountains in the Indigo Lake area, Yukon Territory; unpub. PhD thesis, Queen's University, 200 p. - 144 -

Gordey, S.P. 1978: Stratigraphy and structure of the Summit Lake area, Yukon and Northwest Territories; jn_ Current Research; Geol. Surv. Can., Paper 78-1 A, pp. 43-48

Green, L.H. 1965: The mineral industry of Yukon Territory and southwestern District of Mackenzie, 1964; Geol. Surv. Can., Paper 65-19.

Green, L.H., Roddick, J.A. and Blusson, S.L. 1967: Geology of Nahanni Map Sheet (105 I) Yukon and Northwest Territories; Geol. Surv. Can., Prelim. Map 8-1967.

Hannak, W. 1968: Die Rammelsberger Erzlager; Vere. Freunde Miner. Geo!., Son. Augschuss Jahr. , No. 17, pp. 62-74.

Hesse, R. and Butt. A. 1976: Paleobathymetry of Cretaceous turbidite basins of the east Alps relative to the calcite compensation level; Jour. Geol Vol. 84, pp. 505-534.

Hodgson, C.J. and Lydon, J.W. 1977: Geological setting of some volcanogenic massive sulphide deposits and active hydrothermal systems:: some implications for exploration; Can. Inst. Min. Metall., Bull. Vol. 70, pp. 95-106.

Hsu , K.J. 1974: Melanges and their distinction from olistostromes; in Soc. Econ. Paleont. Mineral., Spec. Vol. 19, pp. 321-333.

Huang, W.T. 1962: Petrology; McGraw-Hill, 480 p.

Hume, G.S. and Link, T.A. 1945: Geological investigations in the Mackenzie River area, Northwest Territories and Yukon; Geol. Surv. Can., Paper 45

Javor, B.J. and Mountjoy, E.W. 1976: Late Proterozoic microbiota of the Miette Group, southern British Columbia; Geology, Vol. 4, pp. 111-119.

Kal1iokski, J. 1974: Pyrite framobid: animal, vegetable or mineral? Geology, Vol. 2, pp. 26-27.

Kanasewich, E.R. 1968: Precambrian rift: genesis of stratabound ore deposits; Science, Vol. 161, pp. 1002-1005. - 145 -

Kindle, E.D. 1945: Geological reconnaissance along the Canol Road from Teslin River to Macmillan Pass, Yukon; Geol. Surv. Can., Paper 45-21.

Kinsman, D.J.J. 1969: Modes of formation, sedimentary association, and diagnostic features of shallow water and supratidal evaporites; Amer. Assoc. Petrol. Geol., Bull. Vol. 53, pp. 824-829.

Krauskopf, K.B.

1967: Introduction to Geochemistry, McGraw-Hill, 721 p.

Krebs, W. 1976: Geology of European stratabound 1 ead-zinc-rcopper deposits; Can. Soc. Petrol. Geol., Seminar Proc, Calgary, 1976. Krumbein, W.C. 1934: Size frequency distributions of sediments; Jour. Sed. Petrol., Vol. 4, pp. 65-77.

Krumbein, W.C. and Sloss, L.L. 1963: Stratigraphy and Sedimentation; W.H. Freeman and Co., San Francisco, 660 p.

Lambert, I.B. 1976: The McArthur zinc-lead-silver deposit: features, metallogenesis and comparisons with some other stratiform ores; i£ Wolf, K.H. (ed.), Handbook of Stratabound and Stratiform Ore Deposits, Elsevier, Chap. 12, pp. 555-583.

Laznicka, P. 1976: Barite nodules of possibly late diagenetic origin from Twitya River area, Mackenzie Mountains, Northwest Territories; Can. Jour. Earth Sci., Vol. 13, pp. 1446-1455.

Leech, G.B., Lowden, J.A., Stockwell, C.H. and Wanless, R.K. 1963: Age determinations and geological studies; Geol. Surv. Can. Paper 63-17.

Lobo, CF. and Osborne, R.H. 1976: Petrology of Late Precambrian-Cambrian quartzite sandstones in the Eastern Mojave Desert, southeastern California; Jour. Sed. Petrol., Vol. 46, pp. 829-846.

Lougheed, M.S. and Mancuso, J.J. 1973: Hematite framboids in the Negaunee Iron Formation, Michigan: evidence for their biogenic origin; Econ. Geol., Vol. 68, pp. 202-209.

Lowe, D.R. 1976: Grain flow and grain flow deposits; Jour. Sed. Petrol., Vol. 46, pp. 188-199. - 146 -

Lucia, F.J. 1969: Recognition of evaporite-carbonate shoreline sedimentation (abst.); Amer. Assoc. Petrol. Geo!., Bull., Vol. 53, pp. 729-730.

Lydon, J.W. 1977: The significance of metal ratios of hydrothermal ore deposits; unpub. PhD thesis, Queen's University, 598 pp.

1978: Some criteria for categorizing hydrothermal base metal deposits; j_n Current Research, Geol. Surv. Can. Paper 78-1A, pp. 299-302.

Machielse, S. 1972: Devonian algae and their contribution to the western Canadian sedimentary basin; Bull. Can. Petrol. Geo!., Vol. 20, pp. 187-237.

Massaad, M. 1974: Framboidal pyrite in concretions; Mineral. Deposita, Vol. 9, pp. 87-89.

Marszalek, D.S. 1975 Calcisphere ultrastructure and skeletal aragonite from the alga Acetabularia antillana; Jour. Sed. Petrol., Vol. 45, pp. 266-271.

McBride, E.F. 1966: Sedimentary petrology and history of the Haymond Formation (Pennsylvanian), Marathon Basin, Texas; Texas Bur. Econ. Geol.,.Rept. Inv. No. 57.

Middleton, G.V. and Hampton, M..A. 1973: Sediment gravity flows: mechanics of flow and deposition, in_ Turbidites and Deep Water Sedimentation, G.V. Middleton and A.H. Bouma, eds.; Soc. Econ. Paleon. and Mineral., short course, Anaheim, California.

Monger, J.W.H. 1975: Upper Paleozoic rocks of the Atlin Terrane, northwestern British Columbia and south-central Yukon; Geol. Surv. Can. Paper 74-47.

Ostroumov, E.A., Volkov, I.I. and Fomina, L.C. 1961: Distribution pattern of sulphur compounds in the bottom sediments of the Black Sea; Tr. Akad. Nauk. SSSR, Inst. Okeanol.,; Vol.. 7, pp. 70-90.

Petti John, F.J.

1975: Sedimentary Rocks, Third Edition; Harper and Row, 628 p.

Porsild, A.E. 1945: The alpine flora of the eastslope of Mackenzie Mountains, Northwest Territories; Nat. Mus. Can., Bull. No. 101. - 147 -

Ransom, P.W. 1977: Geology of the Sullivan Mine; i_n Field Trip Guidebook I, Lead-zinc deposits of southeastern British Columbia, Pt. 2; Geol. Assoc. Can., Ann. Mtg., Vancouver, 1977, pp. 7-21.

Rickard, D.T. 1970: The origin of framboids; Lithos, Vol. 3, pp. 269-293.

Roddick. J.A. and Green, L.H. 1961: Geology of Sheldon Lake Map Sheet (105 J), Yukon Territory; Geol. Surv. Can., Prelim. Map 12-1961.

Roddick, J.A. and Hutchinson, W.W. 1974: Setting of the Coast Plutonic Complex, British Columbia; Pac. Geol., Vol. 8, pp. 91-108.

Rodine,,J.D. and Johnson, A.M. 1976: The ability of debris, heavily freighted with coarse clastic materials, to flow on gentle slopes; Sedimentology, Vol. 23, pp. 213-234.

Rupp, A.W. 1966: Origin, structure and environmental significance of Recent and fossil calcispheres (abst.); Geol. Soc. Amer., Ann. Mtg., Program with Abstracts, p. 186.

Sangster, D.F. 1971: Geology of lead and zinc deposits in Canada; i_n, Report of Activities, Part B, Geol. Surv. Can., Paper 71-1B, p. 12.

Sato, T. 1972: Behaviors of ore-forming fluids in seawater; Min. Geol., Vol. 22, pp. 31-42.

1977: A genetic classification of submarine exhalative-sedimentary mineral deposits (abst.); Geol. Assoc. Can., Ann. Mtg., Program with Abstracts, Vol. 2, p.42.

Stanton, R.J., Jr. 1963: Upper Devonian calcispheres from Redwater and South Sturgeon Lake reefs, Alberta, Canada; Bull. Can. Petrol. Geo!., Vol. 11, pp. 410-418.

Stauffer, P.H. 1967: Grain flow deposits and their implications, Santa Ynez Mountains, California; Jour. Sed. Petrol., Vol. 37, pp. 487-508.

Sweeney, R.E. and Kaplan, I.R.- 1973: Pyrite framboid formation: laboratory synthesis and marine sediments; Econ. Geo!., Vol. 68, pp. 618-634. - 148 -

Tempelman-Kluit, D.J. 1976: The Yukon Crystalline Terrane: an enigma in the Canadian Cordillera; Geol. Soc. Amer., Bull., Vol. 87, pp. 1343-1357.

1977: Stratigraphic and structural relations between the Selwyn Basin, Pelly-Cassiar Platform, and Yukon Crystalline Terrane in the Pelly Mountains, Yukon; in_, Report of Activities, Geol. Surv. Can., Paper 77-1 A, pp. 223-227.

1978: Regional geology, Laberge map-area, Yukon; i_n Current Research, Geol. Surv. Can., Paper 78-1A, pp. 61-66.

Tempelman-Kluit, D.J., Blusson, S.L. 1977: Pelly-Cassiar Platform and Selwyn Basin: neither without the other (abst.); Geol. Assoc. Can., Ann. Mtg., Program with Abstracts, Vol. 2, p.52.

Tempelman-Kluit, D.J., Gordey, S.P., and Read, B.C. 1976: Stratigraphic and structural studies in the Pelly Mountains, Yukon Territory; in_ Report of Activities, Geol. Surv. Can., Paper 76-1 A, pp. 97-106.

Thompson, R.I. and Panteleyev, A. 1976: Stratabound mineral deposits of the Canadian Cordillera; in, Wolf, K.H. (ed.), Handbook of Stratabound and Stratiform Ore Deposits, Elsevier, Chap. 2, pp. 37-108.

Valdiya, K.S. 1970: Simla Slates: the Precambrian flysch of the Lesser Himalaya, its turbidites, sedimentary structures and paleocurrents; Geol. Assoc. Amerc., Bull., Vol. 81, pp. 451-468.

Vaughan, D. 1976: Sedimentary -geochemistry and mineralogy of the sulfides of lead, zinc, copper and iron and their occurrence in sedimentary ore deposits; jn_, Handbook of Strata-bound and Stratiform Ore Deposits, Elsevier, Chap. 10, pp. 317-336.

Walker, R.G. 1970: Review of the geometry and facies organization of turbidites and turbidite-bearing basins; i_n, Flysch Sedimentology in North America, J. Lajoie (ed.), Geol. Assoc. Can., Spec. Paper No. 7, pp. 219-252.

Walker, R.G. and Mutti, E. 1973: Turbidite facies and facies associations; i_n, Turbidities and Deep Water Sedimentation, G.V. Middleton and A.H. Bouma, eds.; Soc Econ. Paleont. Mineral., Pacific Section, Short Course, Anaheim, California. - 149 -

Wheeler, J.O., Aitken, J.D., Berry, M.J., Gabrielse, H., Hutchinson, W.W., Jacoby, W.R., Monger, J.W.H., Niblett, E.R., Norn's, D.K., Price, R.A. and Stacey, R.A. 1972: The Cordilleran structural province; j_n,Variations in Tectonic Styles in Canada, R.A. Price and R.J.W. Douglas, eds.; Geol. Assoc. Can., Spec. Paper No. 11, p. 1-82.

Williamson, W.C. 1880: On the organization of the fossil plants of the Coal Measures, Part X - Including an examination of the supposed Radiolarians of the Carboniferous rocks; Phil. Trans. Royal Soc. London, Vol. 171, pp. 493-539.