McGILL UNIVERSITY LIBRARY

THE GEOLOGY OF THE VICINITY

OF BRALORNE MINES BRITISH COLUMBIA

DEPOSITED BY THE FACULTY OF

GRADUATE STUDIES AND RESEARCH

M£GILL UNIVERSITY

LIBRARY

THE GEOLOGY OF THE VICINITY OF BRALORNE M:I:NES

BRITISH COLUMBIA

(A Thesis submitted in Partial Fulfilment

of the requirements for -the degree of

Master of Science)

Courtney Ernest Cleveland, B.Sc.

Department of Geological Sciences

McGill University

May, 1938.

ACKNOWLEDGEMENTS

The writer wishes to express his indebtedness

to Dr. F. F. Osborne of the Department of Geological

Sciences of McGill University for his helpf~l criticism

and suggestions in connection with this thesis; also to

Mr. R. Bosustow and Dr. Howard James of Bralorne and

Pioneer Mines respectively, who furnished the necessary ore

samples required for microscopic work.

ABSTRACT

This thesis deals With the general geology in

the vicinity of Bralorne Mines, British Columbia. Late

Palaezoic and Mesozoic sedimentary and volcanic rocks

have been intruded by igneous masses genetically related to

the Coast Range Batholith which has given rise to metall­

iferous deposits.

The ore deposits of Bralorne Mines and Pioneer

Mines are described particularly with regard to structural

features. Irhe vein bearing :rlssures of these deposits are,­

believed to be the result of compressive stresses originating •

southwest of the area. The ore shoots are believed due to

various causes, among which the faulted and branched nature

of the vein fissures are considered of prime importance.

The presence of soda-rich rocks in the vicinity

of the ore deposits is stressed, with the belief that such

rocks have been developed by changing conditions in the

differentiation of a normal magma stem. These conditions

have given rise to the albite-rich diorite, the albite

granite, related dykes, and subsequently the ore deposits

~themselves.

TABLE OF CONTE1TTS

Introduction:

Location and Size of Area • • • • • • • • • • • • • • • • • • • • • • •

Object of Thesis • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Previous Work

Topography:

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

General • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Local

Geology:

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

. (

General • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Local • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Fergusson Series • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Subdivisions of Cadwallader Series • • • • • • • • • • •

Noel Formation • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Pioneer Formation

Hurley Formation

Bralorne Intrusives

Bralorne Diorite

••••••••••• • e •••••••••••••

• • • • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • • • •

Bralorne ~bite Granite • • • • • • • • • • • • • • • • • • •

President Intrusives • • • • • • • • • • • • • • • • • • • • • • • • •

Minor Intrusives • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Ben-dor Intrusives • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Kersantit.e Dykes •••••••••••••••••••••••••••••

Pleistocene Deposits •••••••••••••••••••••.•••

Recent Deposits ••••••••••••••••••••••••••••••

Page 1

1

2

3

3

6

8

11

15

15

18

23

27

28

30

34

37

40

45

46

46

II

TABLE OF CONTENTS (Cont'd)

Structural Geology:

General Statement • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . '/

Local • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Veins and Faults of Pioneer and Bralorne Mines ••

Veins ••••••••••••••••••••••••••••••.•••••••••

Faults • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Origin of the Vein Bearing Fissures •.•••••••••••

Mode of Vein-Fissure Filling ••••••••••••••••••••

Mineralogy of the Veins •••••••••••••••••••••••.•

Paragenesis of the Vein Minerals •.•••••••••••••••

The Ore ••••••••••••••••••••••••••.•••••••••••••••

Ore Shoots:

General Description • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Theoretical Considerations • • • • • • • •• ••••••••••••

Page 48

49

53

53

57

60

61

64

69

70

172

74

Genetic Considerations of the Ore Deposits ••••••••• 82

Bibliography and Reference •••.••••••••••••••••••••• 86

ILLUSTRATIONS

I. Key Map of Thesis Area' - Showing Relation to

Surrounding ·Geological Formations.

II. Generalized Geological Plan - Bralorne and Pioneer

Mines.

INTRODUCTION

Location and Size of Area

The Cadwallader Creek mining area, which lies

in the Bridge River district of British Columbia, is on

the east flank of the Coast Range, 100 miles north of

Vancouver. The area is drained by Cadwallader Creek and

the Bridge River, which flows into the Fraser River at

Lillooett.

Investigations presented in this thesis, deal

principally with that part of the Cadwallader Creek mining

area, including, and immediately adjacent to, the property

of Bralorne and Pioneer Mines. The mineralized zone on

which these properties are located trends in a general

northwest-southeast direction, through the centre of this

part of the Cadwallader Creek area. The zone is 3 miles

long and one-half mile wide.

Object of Thesis

The object of this thesis is to emphasize the

geographical relationships, and in as far as possible, the

geological relationships between the ore deposits of the

Bralorne and Pioneer Mines and their surrounding country

rocks. The structural features of these deposits and their

poss'ible bearing on the oCQ,urrence of oreshoots wi thin the

-2-

mines are also emphasized.

Previous Work

The geology of the district, and some features

of the mines in the early stages of their development,

have been described by various members of the Geological

Survey of Canada, by several officials of both the above

mining companies, and most recently by C. E. Cairnes of

the Geological Survey of Canada.

Considerable general geological intormation

concerning the underground workings at Bralorne ~nes

has been gathered during the past tew years by the author.

Unfortunately, detailed geological maps drawn by him are

not available for inclusion in the thesis and certain

descriptions are thus somewhat incomplete.

-3-

TOPOGRAPHY

General

The Coast Mountains, which are commonly known

as the "Coast Range", fringe the Pacific Coast ot British

Columbia and extend from the Fraser River near the Inter­

national Boundary northward to Alaska, a distance of 900

miles. The range is 100 miles wide at the south, but less

than 50 miles wide at the north.

The Bridge River map area, of which the thesis

area is a part, includes approximately 600 square miles

of mountainous country, on the eastern flank of the Coast

Range mountains.

Local

The area under discussion is bounded on the south

side by the Cadwallader mountains and on the north side by

the Bendor mountains. The mountains are of the erosional

type, ,and show more than on'e cycle of development. There

are broad characteristic upland stretches, which are sur­

mounted by rugged snow-capped peaks and ridges. The summi ts

are from 8000 feet to 9600 feet above sea level, whereas

the bottoms of the main valleys are from 1900 feet to 3000

feet elevation. Timberline is at about 6500 feet.

-4-

The effects of glaciation are well marked.

Hanging valleys, glacial cirques, "V" shaped valleys,

with steps in the valley floors, truncated spurs and

morainal drift are common in the region.

Above Pioneer Mine, the valleys of Cadwallader

Creek and its tributaries are typically V-shaped. The

tributary streams, which occupy hanging valleys, enter the

ma1n stremn through canyons. Below Pioneer Mine, the main

valley walls recede and give way to a relat1vely level,

glaciated, bench-like area, with an average elevation of

about 3500 teet. In post-glacial times the principal streams

have cut through this bench to form rock canyons, some of

which are several hundred to a thousand feet deep. The

dra1nage of the minor streams on the surface of the bench

is still unorganized, and for the most part, these streams

are in glacial drift. (4) P.3.

Cadwallader Creek, which drains the present area,

is an important tributary of the Bridge River which flows

eastward into the Fraser River. The drainage of the Bridge

River area, as a whole, is still in a youthful stage.

The topography in many places conforms closely

to bedrock struoture, the trend line of the mountains and

valleys following fairly closely the formational strikes.

-5-

The Bridge River map area has been considered by McCann

to be a broad anticlinal arch striking northwest and

plunging gently to the west. (24) P.2l. This structural

feature is well emphasized by the arcuate course described

by the Bridge River, as it flows around the nose of the

anticline.

In the northern part of the district, there is

a marked difference between the topography that is carved

on soft Cretaceous rocks and that developed in the other

more resistant rocks. In the northern" part the ridges

are broad and smoothly rounded. In the soathern part of

the district, with which this thesis is concerned, the

ridges are unrounded, and their slopes in places very

steep. This is due to the fact that large parts of this

area are underlain by igneous rocks and hard cherty sed­

imentary rooks, whioh have a considerable resistance to

erosion.

-6-

GEOLOGY

Introduct~ry.Statament

Carrying out this study at McGill University

afforded the author an opportunity to compare the gold

deposits of the region with those of Eastern Canada.

The general geology of the Bridge River district as des­

cribed here, is mildly similar to that of the gold belt

of the east; a series of volcanic rocks have been altered

to a grade comparable to that of the Keewatin. Siliceous

sedimentary rocks analagous to those ot the Timiskaming

are present and the serpentine and albitite rocks show a

mild similarity to those of northern ~uebec.

The similarity in the two districts suggests

something of the genesiS of such gold deposits and are

probably the result of the operation of the facies principle

so strongly advocated by Eskola.

General

A general geological description of the Bridge

River map area will perhaps form a background by which a

better understanding of the problems discussed in this

thesis area may be gained.

McCann (24 - P.23) describes the oldest rocks 1n

the Bridge· River distriot as Pennsylvanian-Permian age.

~hey consist of metamorphosed· sedimentary formations with

interbedded volcanic roc'ks. The chief member of the sedi­

mentary formations is a banded c·hert grading to cherty

quartzite and argillite.

~he volcanic rocks are dense, black, altered

basal ts , wi th occasional pronounced pillow structure'.

Three formations of Triass.ic age (4 - P.9) lie

conformably above this older series. The upper and lower

~or.mations are sedimentar,y rocks With minor amounts of igneous ,

material, whereas the middle formation is amygdaloidal and

finely orystalline andesites and andesitic breccias. 'rhese

formations of.Permian and Triassic age are invaded by stocks . ~

( ot augite dlori te and peridoti te in part altered to serpent,ine

-anddy~es of quartz albitite and albitite. Cairnes has de­

ct~r.m1ned these intrusions as Jurassic.

Batholiths of granite, granodiorite, and diorite,

and'dykes of-felsite and lamprophyre were intruded in Post ~'., i: ~'. -~~ .

Lower Cretaceous time.

In many .places 'the bottoms of the valley walls are­

coveredbyunconsolidat~d deposits of till, gravel, sand, -silt , -

and clay, of glacIal and post-glaCial age. The most recent

-8-

deposit is a thin bed of volcanic ash which mantles large

areas of the distriot. McCann describes (24 - P.20) this

ash as overlying recent river gravels in many parts of the

district.

~he Bridge River area contains the most important

mineral deposits of the Lillooet mining division, and in

recent years the auriferous quartz veins of the Cadwallader

Creek area have supported the leading gold-producing mines

of British Columbia.

Both metallic and non-metallic deposits occur

in the area (4 - P.45). The metalliferous deposits contain •

placer gold, lode gold, silver, copper, chromite, platinum

and nickel. The non-metallic deposits contain asbestos,

talc, magnesite, limestone and pumice. Cairnes has indicated

the relationships between these deposits and the various

intrusive rocks of the area (4 - P.45) •

. Local

The following table indicates the geological form­

ations within the present area. The age relationships and

grouping of formations in this table.are, based on the results

of field work by Cairnes, (4 - P.S) whose work in the district

has led to the most comprehensive classification to date of ..

the'formations.

Era

Cenozoic

Cenozoic and?

Mesozoic

Mesozoic

-9-

Table of Formations

Period Formation

Modern

Lithology

Recent; stream deposits; volcanic ash. soil ,

Pleistocene: fluvioglacial, glacial, and stream deposits

Kersantite and basaltic dykes

Post Lowet~ ______________ ~ __________________________ _

Cretaceous

Jurassio?

Bendor In­trusives

President Intrusives

Bralorne In­trusives

may in part be younger than

the President Intrusives

Hornblende-biotite-quartz diorite;granitej grano­diorite; diorite

Quartz albit1te, albitite, and related, less sodic dykes; greenstone dykes

Peridotite; dunite; pyroxenite

Serpentine (mainly)

Albite granite

Gabbro, augite diorite and quartz diorite (ma1nly sodie plagio­clase)

Era Period

Triassic

Mesozoic and (or)

Jurassic

r

Palaeozoic . . Permian?

-10-

Formation

Hurley Formation

Pioneer Formation

Noel Formation

Fergusson Series

Lithology

Banded argillaceous and tuffaceous sediments. C~erty halleflinta and trachytlc flows; inter­calated greenstones

Green, massive amygdular to finely crystalline andesites; andesite tuffs and breccias; associated intrusive dioritic phases

Banded argillaceous and tuffaceous sediments; thinly banded chert and argillite associated with greenstone. Con-glomerate tuff and breccia

,';

Thinly interbedded chert and dark grey to black graphitic argillite. Massive ohert

-11-

Fersuspon Series

Distribution

The Fergusson series, or Bridge River series, of

Drysdale (14 - P.79), which is the oldest formation in the

area, occurs in the northeast and southwest portions of

the area. It has a general northwest strike.

Petrology

The series consists of well-banded and highly­

contorted quartzites with shale. The bands of quartzite

are half to one and one half inches thick and are separated

by thinner bands of shale, Which, in some places, have been

altered to mica schist. Well-bedded argillaceous material

is also present. Cry~talline limestone lenses of a dark

grey to bluish grey or white color occur in the northeastern

part of the area, but have not been encountered near the

Pioneer and Bralorne Mines.

Associated volcanic rocks are interbedded With

the sedimentary rocks and consist of amygdaloidal andesites

-, ,

together with minor gmounts of breccia and tuff.

Thickness

It has been found extremely difficult to estimate v

-12- .

the thickness of the Fergusson series due to the fact that

both the igneous and sedimentary rocks have been highly

metamorphosed, folded and sheared. McCann expresses the

belief that near the eastern boundary ot the Bridge River

map area, the series is about 1000 teet thick, whereas

Cairnes, in the area surrounding the Pioneer and Bralorne

Mlnes, believes the thickness is several thousand feet.

(4 - P.g).

Structural Relations

The strike of the formations is approximately

N.45°W., and near the Bralorne Mine the beds exposed are

on the steep-dipping limbs of an appressed syncline. The

series is overlain conformably by the sedimentary rocks

of the Noel formation. (4 - P.14).

According to McCann, (24 - P.25) the sedimentary

rocks of the Fergusson series were deposited as a succession

-ot thin sandstone beds, one or more inches thick, with thin

interbeds ot mud. Intense dynamic metmnorphism caused the

disappearance ot primary structures.

Cairnes suggests an interesting origin tor the

banded ohert and argillite rooks in the vioinity of the

Bralorne and Pioneer Mines. He surmises that· the chert

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of these,banded rocks was chemically precipitated from

solutions, emanating from submarine siliceous springs and

associated volcanic rocks. This precipitation was accom­

panied by the normal deposition of material obtained by

erosion. The banding he ascribes to rythmic action in

precipitation.

Davis (IO- P.353) discusses four possible sources

of the silica in the Radiolarian cherts of the Franciscan

group which in many ways resemble the cherts of' the Fergusson

series. The last two sources which he ·discusses, depend on

the supply of' silica from igneous emanations, and from sub­

marine siliceous springs.

Cairnes favors such a source because of support

fUrnished by "the int~ate association of' greenstone" with

the cherty sediments of the Fergusson ser1es, and also because

of the common ellipsoidal character of the lavas and their

assooiation with limestones, indicative of accumulation

under the sea. Some of the chert bands have a distinct

nodular character which McCann attr~.buted to regional meta-.l'i - f. )~-

morphism. Regarding these he says 22 - P.25): "Some of'

these thin beds of chert have been broken into f'ragments

which have b.een elongated and flattened, and appear as

disconnected and overlapping lenses several inches in

-14-

1ength----". Cairnes attributes this condition to localization

in the supply of silicate solutions and to irregularity in

precipitation. (4 - P. 11).

The chert bands of the Fergusson series have

distinct but minute veins which he believed to be due to

the development of secondary quar~z, derived from the silica

of the cherts and deposited in fractures. (4- P.ll).

McCann has termed this "crowfoot quartzite". (24 - P.23).

Age and Correlation

McCann found no fossils in the Bridge River series

of Drysdale (22 - P.25), but Cairnes has reported indeterminate

microscopic fossils in a thin section of a banded chert specimen

in his Fergusson series (Bridge River series). (4 - P. 13).

Dawson (11 - P.84) ref"ers to a formation in the

Cache Creek district of British Columbia which is character­

istically composed of a grey, cherty quartzite, interbedded

with black argillaceous schists. This formation is part of

a series which he called the Cache Creek series, which contains

the Pennsylvanian fossil, Fusilina. structural conditions

are analagous with those of the Fergusson series, and

investigators previous to Cairnes, correlated this latter

series with the Cache Creek series of rocks. The fossil,

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Fus1l1na, has been known to occur in Permian time also,

and Cairnes assumes the Fergusson series to be Permian.

(4 - P.13).

Subdivisions of Cadwallader Series

The Cadwallader serie.s has been described by

McCann as consisting or basaltic and andesitic greenstone,

with some conglomerate, sandstones and shales. (24 - P.2S).

This series or rocks in the vicinity of, and within, Pioneer

and Bralorne Mines, consists of three distinct units, named

by Cairnes (4 - P.15) the Noel, Pioneer, and Hurley formations.

Noel Formation:

Distribution

The Noel formation Which lies on the southwest

side of the belt of Bralorne intrusives, 1s exposed for a

considerable distance in the long adit of the King Mine.

This formation strikes approximately parallel to the Ferg­

usson series of sedimentarY'rocks and extends eastward

parallel to the southwest edge of the large stock in the

area.

Petrology

The formation consists for the most part of ~ .

-16-

black we~l-banded argillite. Cairnes describes these bands

as alternately fine grained and dark grey, coarser grained,

and light grey. Included in this succession of sediments

are beds of pebbles and angular fragments, of chert and

volcanic rock, which Cairnes considers as detrital material

from the underlying Fergusson series. (4 - P.5l). Above

the highway, north of Bralorne, Cairnes describes conglomeratic

sediments consisting of "well ----- rounded pebbles and

cobbles, as much as several inches in diameter; disseminated

or, in places, closely packed in a matrix identical with the

sedimentary rock on either side". He believes that, although

the stratigraphic position of this conglomerate is uncertain,

it appears to be intraformational, rather than basal. This

conglomerate includes a few cherty pebbles which resemble

that of the Fergusson series. In McCannts Cadwallader series,

he describes conglomerate with pebbles, made up principally

of quartzite, and minor amounts of limestone and serpentine

pebbles. (24 - P.28). It is not quite clear from McCannts

description of types associated with the conglomerate, . .

whether he is describing the same conglomerate which Cairnes

believes to be intraformational, or whether he is describing

a local conglomerate.

A specimen of argillite, taken from the adit of

King'Mine, w~s examined undJr the microsoope. In the hand

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specimen, the argillite is somewhat banded and dark grey

to black. In the thin seotion the mass is fine grained

and oonsists of sub-angular to angular fragments ot quartz

and small amounts of feldspar in a fine-textured base of

altered material oonsisting principally of chlorite with

occasional grains of epidote. Scattered particles of pyrite

and a few grains of apatite are present. Fracturing is

prominent; the fractures are filled with carbonate, some

sericite, and small amounts of secondary quartz. Due to

the angularity of the original fragments (mostly quartz)

present, the rock may be more correctly termed a tuffaceous

argillite.

Thiokness

According to Cairnes the formation is of variable

thiokness, from 1200 feet to 2500 feet, but due to its com­

plex structure and lack of key beds, he doubts these figures.

Struotural Relations

As previously stated, the Noel formation has a

general northwest trend and almost vertical dips. Cairnes

believes this formation to conformably overlie the older

Fergusson series. In several places he found suggestions

of an angular unconformity, but suspected that this conflict­

ing ~vidence might be the ~esult of faulting. (4 - P.l5).

-18-

Age and Correlation

No fossils have been found in the Noel formation,

but it represents a part of those formations mapped by

McCann as Cadwallader Series, in which north of the present

area he found fossils of Upper Triassic age. This formation

is therefore considered as Upper Triassic in age.

Pioneer Formation:

Distribution

The Pioneer formation has been so named beoause

of its excellent exposures at the Pioneer Mine. This form-

ation, although widely exposed in the above mentioned loc­

ality, is greatly restricted in the western part of the

area, where at the King Mine it is present as a narrow

band ocourring on the northeast side of the large stock

of Bralorne intrusives.

PetroJ.ogy

The Pioneer greenstones are fine-grained andesitic

rocks, with variations to more basaltic material, as well as

to defini tely more acidic material, probably daci ttc. Mo st

of the rocks are fine grained and structureless. Some flow

breccia is present as well as considerable quantities of

amygdaloidal material. Andesitic rocks displaying pillow

-19-

structures have been noted at one place in the King Mine,

and more frequently in the Pioneer Mine. Some of the

more massive phases of the greenstone are fine-grained,

even granular rocks, resembling fine grained diorite, and

in such cases, it is impossible to distinguish such phases

from the fine grain margins of the diorite which will be '. , .

referred to later.

Specimens of Pioneer greenstone were examined under

the microscope, several of them having been collected from

the ~Ody of greenstone exposed ·in the King Mine.workings,

and the remaining ones from the large greenstone body in

the Pioneer Mine.

Representative specimens examined are of aphanitic

grain, dark to light greyish green, in color, and present

either an amygdaloidal or massive structure.

In thin section they are holocrystalline, inequi­

granular with porphyritic texture. The phenocrysts and ground­

mas's appear, for the most p'art, to be composed of feldspar,

averaging from An25 to An36 , whereas the feldspar of the ground­

mass is probably more albitic. In one specimen the mass displays

a somewhat trachytic texture due to the parallel arrangement

of microlite feldspar laths. Phenocrysts in this specimen

were composed of feldspar and hornblende, some of which were

-20-

twinned. It has been suggested that in one or two of the

specimens the amygdules may be due to metasomatism and

since these speoimens were taken from slightly altered

wall rocks of the King vein, this may aotually be the case.

In the amygdaloldal varieties the amygdules consist

of chlorite or quartz. Where the amygdules consist of chlorite,

sericite is often present in small gmounts as part of the

vesicular filling. In other cases, small flakes ot biotite

have developed Within the chlorite, and probably this latter

mdne~al, along with sericite and the iron frequently present

in the form of pyrite, has given rise to biotite as one of

the first stages of metamorphism. (16 - P.106).

Where quartz amygdules are present, they are

frequently bordered by carbonate with an outer ring of

chlorite, and in many places, the amygdules have been re­

placed by large well-developed crystals of epidote.

examined.

Diverse amounts of quartz are present in specimens

One specimen in which it is abundant has much

chlorite in the groundmass, along with scattered grains of

leucoxene.

Carbonate is present in varying amounts, and where

scarce, the lime and alumina which was present in the feld-.

spars has probably reacted With the silica of the amygdules

-21-

to form epidote, instead of carbonate.

The abundant chlorite has probably been derived

from ferromagnes1an minerals formerly present •

One specimen contained euhedral crystals of pyrite,

in many places surrounded by quart~ in pressure shadows, the

result of stress in the rock. Another specimen has biot1te

in flakes, scattered throughout the mass, indicating early

stages of metamorph1sm. The b-ioti te has probably developed

from chlorite and ser1citic material originally present in

the ~ock. (16 - P.lll).

From thin sections examined, and the composition

of the fel~spars, and varying amounts of quartz determined,

the rocks appear to vary in composition, from andesite to

somewhat more acidic varieties of dacitic or rhyolitic com­

position.

Thickness

The normal thickness of the greenstones is 1200 to

1500 feet, but in the eastern section of th~ area the apparent

thickness is about 3000 teet. To the west the series has

but a fraction of its normal ~dth and evidence suggests that

the increase in the width of the greenstones to 3000 feet in

-22-

the east is the result of repetition of the series by

faulting.

Structural Relations

Cairnes found great difficulty in interpreting

the contact relations of the Pioneer greenstones with the

Noel formation. He considers two possibilities:

1. The two formations are essentially the same age.

2. The greenstone formation is younger.

He does_not believe that the evidence for con~

temporaneity of the two formations is convincing, because

of "the lack of intermingled volcanic and and sedimentary

materials within the larger area of Pioneer greenstone."

That the greenstone is younger seems to be more

probable, and in the light of field relationships found, he

has reason to believe that probably the "greenstone formed

from local vents, and that in places it cut through the under­

ly-ing formations and elsewhere spread over them."

It is interesting to note that the combined thickness

of the d~orite and the greenstones is essentially constant, ~

even although the diorite wedges out to a point at the east

end, and, on the other hand accounts for the greater part of

the combined width toward the centre and west. This condition

-23-

is strongly suggestive of a very close relationship between

the two formations.

Age and Correlation

The P.ioneer greenstones belong to the same group

of volcanic rocks which MoCann inoluded in the Cadwallader

series (24 - P.28), and which he found to be Upper Triassic

in age.

The Pioneer greenstone is younger than the Noel

sedimentary rocks which may be Late Triassic. (4 - P.lS).

Cairnes believes the age to be late Triassic or Jurassic.

Hurley Formation:

Distribution

The Hurley formation is exposed in the King Mine

as a discontinuous body ot sedimentary and associated volcanic

rocks, lying on the· northeast flank of the ~arge stock of

diorite, and separated from it by the Pioneer greenstones.

To 'the east, in the locality·of the Pioneer Mine, the Hurley

tonnation is again exposed flanking the east side of the

Pioneer greenstone. As a whole, the formation. represents

a somewhat discontinuous belt~ sedimentary and associated

igneous rocks.

-24-

Petrology

The formation consists essentially of sedimentary

rocks, but here and there includes volcanic rocks as in the

King Mine, where cherts, cherty halleflinta, and dense

rhyolitic or dacitic lavas have been described by Cairnes.

(4 - P.19).

He describes these rocks as follows: "The chert

occurs in irregular, lens-like masses, not over a few feet

long and apparently grading into banded cherty halleflinta. ~

The chert is dark grey to black, very dense and flinty, and

lacks the numerous, minute, intersecting quartz veinlets

that characterize the banded cherts of the Fergusson series.

The associated cherty halleflinta forms bodies up to 400

feet thick. It is dense, light grey to dark, in part mottled

and mostly finely banded."

Many of the sedimentary rocks are banded, light

and dark grey, argillaceous and tuffaceous in character and

in many cases indistinguishable in appearance from the

banded strata of the Noel formation.

A few thin sections of the Hurley formation rocks,

both of igneous and sedimentary origin, were examined under

the microscope. The igneous material examined was pyroclastic.

-25-

Kegascopically the fragmental rocks are dark. to

grey-green in color, aphanitic, and of brecciated structure,

the angular fragments in one specimen averaging about 1/4

inch in size.

In thin section one spec~en displays the brecciated

struoture, whereas the original grain and texture of the

rock is completely obliterated by alteration. The minerals

present, for the most part, consist of quartz and sericite,

constituting a fine grain mass through which is scattered

both~large and small gra~~s of pyrite. The specimen is too

altered to form conclusions as to its original composition,

although the abundance of quartz suggests a volcanic breccia,

of an acidic composition. Another specimen displays consider­

able quartz and chlorite. The chlorite has probably resulted

from original ferromagnesian minerals which have now completely

disappeared. The original rock may have been an acidic flow

of rhyolitic or dacitic composition.

Another specimen is aphanitiC, light grey, and

extremely hard. In thin section the mass is fine textured,

and consists of small fr~ents of feldspar and quartz, with

an altered base of secondary quartz and sparse epidote.

Megascopically the rock looks like a chert, but

trom microscopic study it may be correctly termed a halleflinta. ~

-26-

The argillites in the hand specimen are fine grained,

brownish with distinct blocky fracture.

In thin section one specimen consists of sub-angular

to angular, fragments of quartz and some feldspar, in a fine

textured base of biotite and interstitial chlorite. Fine

grains of pyrite With lesser mnounts of magnetite occur

scattered through the mass. The angularity of the fragments

makes the name "tuffaceous argillite" most suitable for this

specimen. Alteration has entirely concealed the character

of t~e original cement present.

Thickness

Cairnes believes that the maximum thickness of the

formation may not be more than 1500 feet.

structural Relationships

The Hurley formation conformably overlies the

Pioneer greenstone, and is invaded by the Bralorne intrusives.

~h1s formation is the youngest, consolidated sedimentary rocks

of the area, and seems to have suffered about the same amount of 1

deformation as the older formations of the area. (4 - P.20).

Age and Correlation

I

The Hurley sedimentary formation has been referred

-27-

by Cairn~s provisionally to the Jurassic. The formation

closely resembles the Eldorado series of McCann which is

Upper Jurassic (?) and Lower Cretaceous. (24 - P.2l).

Bralorne Intrusives

General Statement

A group of igneous rocks, which have acted as the

principal host to the auriferous quartz veins of the area,

have been collectively termed by Cairnes as, ftBralorne In­

trusives", because of their typical development on the

property of Bralorne Mines. These intrusives have been

referred to by previous writers as augite diorite of the

Bridge River district. Bateman (1 - P.2l) has mentioned

the fact that these igneous bodies are probably connected

with the Coast Range granitic batholith, and were intruded

contemporaneously with the earlier granites, which are con­

sidered as Jurassic in age. (1 - P.194).

Distribution

• In the present area three intrusive masses are

known, two of which are relatively small, and ~ie north of

the workings of the King ~ne. The third, and largest body,

occupies the central part of the area and is about 11,000

feet long by 1500 feet wid~. The Bralorne intrusives include

-28"

two principle types, Bralorne diorite, and Bralorne albite

granite. (4 - P.2l). Much of the intrusive rock in Pioneer

ground is albite granite, constituting the whole east end

of the "diorite" and extending westerly along the north side

of it. A fairly extensive body of the same rock occurs north

of the Bralorne Empire shaft, and small tongue-like bodies

occur in the west end of the large diorite stock. -The two

isolated masses at the west end of the main intrusive are

this type of rock. For convenience of description the

pet·rology of the Bralorne dlori te and albi te gran1 te will ....

be dealt with separately.

Bralorne Diorite:

Petrology

The average diorite is a medium gra1ned grey rock

in which feldspar and hornblende or augite appear in hand

specimen to be the only essential constituents. The most

characteristic feature of this type of rock is the minute

veining by tiny stringers of quartz and feldspar, which criss­

cross the rock in a closed network. Variations in texture

and composition within individual masses of the diorite are

common, and coarse-grained gabbroic facies may grade within

a relatively short distance into the normal medium-grained

diorite and the diorite into quartz-bearing diorite, and to t .

-29-

a fine-grained marginal facies identical in appearance with

certain members of the Pioneer greenstones. All the thin

sections examined contained plagioclase feldspar averaging

about An9 in composition, and such rocks represented must /

be referred to as syenites. The specimens collected were

few in number and not representative of the igneous mass.

Chemical analysis have been given by Cairnes (4 - P.23) and

indicates the rocks of the intrusive body to be diorite.

T~erefore the name diorite will be retained in the thesis

with the understanding that rocks of syenitic composition ~

are present.

A typical specimen examined in this section is

holocrystalline, medium grained, equigranular, and of granitic

texture. The essential minerals consist of plagioclase

feldspar and hornblende. The feldspar is Ang , and the

crystals are subhedral. The hornblende is pale green,

subhedral, with in places lamellar twinning and alteration

to chlorite. Accessory minerals consist of small amounts of

quartz, aegerine-augite, and pyrite. The aegerine-augite

is present in subhedral forms, While occasional grains of

pyrite fill interstices between fragments of hornblende.

Alteration products consist of sericite and chlorite. Accord­

ing to the predominance of hornblende and sodic plagioclase

present, together with the small amount of Quartz, the rock

-30-

oan be classed as a hornblende syenite.

Bralorne Albite Granite:

Petrolosy

Several specimens of quartz diorite, or albite

granite, were examined in thin section. Megascopically

these rocks are typically light colored, moderately coarse

grained, with minor amounts or highly-altered ferromagnesian

mdnerals present, and abundant quartz with feldspar.

In thin section a typical speCimen is holocrystalline,

ooarse to medium grained, and of equigranular granitic texture.

Essential minerals are quartz and feldspar, of composition

averaging An6• One specimen from near the Crown shaft, Empire

Ulne, contained considerable gmounts of common hornblende,

1rregularly bounded) wi th occasional lamellar twinning. The

feldspar crystals are subhedral and contain minute flakes of

sericite and carbonate. The small quantity of ferromagnesian

minerals visible in the hand specimen seem in thin section

to be aggregates of alteration products. Pyrite, with a few

grains of apatite, are present as accessory minerals.

Alteration products consist of large masses of chlorite,

carbonate, sericite, zoisite, and epidote. The chlorite,

epidote and zoisite, probably represent in part at least,

-31-

the alteration of now absent ferromagnesian minerals.

The rock types represented by such thin sections

above, might be termed sodic granite, or more suitably

albit1c granite. These typical specimens represent albite

granite occurring in the west end of the area, in the

isolated intrusive bodies, north of the principal Bralorne

diorite stock.

The albite granite of Pioneer Mine presents the same

characteristics in the hand specimen with even lesser amounts

of dark mdneral present.

In thin section one specimen showed the usual

abundance of quartz. The plagioclase feldspar tends to

be in subhedral crystals with sharp, clear albite twinning

and of c anposl tion Ang. Many of the feldspars are coated

with fine aggregates of sericite and some carbonate. Ferro­

magnesian minerals are present in small quantities. Accessory

minerals are small amounts of pyrite and leucoxene, and the

alteration products are large masses of chlorite, and lesser

amounts of sericite and carbonate.

It must be noted with regard to both the Bralorne

diorite and albite granite, that there is an absence of

potash feldspar, and nowhere in any of the slides examined . could this type of mineral be found. The chemical analysis

-32-

of these rocks (4 - P.22) confirms this absence, and the

small amount of potash is probably in solid solution in the

sodie plagioclase-

In most of the thin sections examined, epidote,

(and some zolsite) are abundant secondary constituents of

the Bralorne intrusives. Cairnes found little evidence

of saussuritization 9r albitization of what might have been

originally more anorthic feldspars, and came to the con­

clusion, consequent upon examination of many slides, that

the amphibole of the altered diorite is the alteration

of an original pyroxene mineral, and that this substitution

of a less lime-rich mmphibole for the pyroxene, accounted

for the excess lime (and alumina) required in the formation

of the epidote minerals and free carbonate.

Structural Relationships

Offshoots of the albite granite in places cut

across the normal diorite, but more commonly the contact

relationships are gradational. Rock which 1s principally v-

diorite containing very little quartz, frequently but a

tew yards away, will change to diorite containing irregular

patches of albite granite. Within another rew yards, such

types will grade into a rock composed Wholly of siliceous

albi·te grani te. This fact has lead Cairnes to believe that

-33-

the Bral~rne diorite and albite granite are related in _origin, ,

~

and that some, or all of the albite granite, may be younger

than the diorite. (4 - P.27).

In many places the relationsh~ps of the augite

diorite to surrounding rocks is not very definite. In

Bralorne ground, no clean-cut contacts are found between

the greenstones and the diorite, but there is a gradual

change from one rock type to another over a zone which may

be many tens of feet in width, which makes it difficult

to distinguish fine grained marginal facies of the diorite

from massive phases of the greenstone. On the other hand,

in the Pioneer Mine, the contact between albite granite and

the greenstones is remarkably sharp. With respect to the

diorite greenstone relationships, Cairnes (4 - P.24) has

noticed many places where, "diorite can be seen sharply

crosscutting the Pioneer greenstones, yet at none of these

places are the volcani.c rocks metamorphosed, nor do the

diorite bodies present chilled edges to the greenstones."

Thus, such features seem to point to a close

relationship in origin and association between the diorite

and greenstone formations. Cairnes, with the above evidence

in mind, came to the conclusion, which hardly seems justified,

that "the Pioneer greenstones and the Bralorne diorite and

associated intrusives originated from the same, deeply buried

-34-

magma body and were intruded and erupted during a long

period of igneous act1vlt,r-----." This period he has

divided into three, the first being one of much volcanic

activity and which witnessed the introduction of the

Pioneer greenstones; the second, one of relative quiescence

during which the Hurley sedimentary rocks were layed down;

the third, a period which witnessed igneous activity of an

intrusive nature. He believes the diorite to have been

introduced, particularly, in the first and last periods,

with perhaps intermediate connecting intrusions. (4 - P.24).

President Intrusives

Distribution

The President intrusives in the vicinity of the

Bralorne and Pioneer Mines, occur as a narrow but persistent ,

band of serpentine along the southerly side of the principal

diorite stock. Where intersected by Ddne workings, this band

has an average width of some 200 feet. Simdlar rocks occur

in adjacent parts of the area, and throughout the Bridge River

district, and were previously called, "serpentine rocks of

the Shulaps volcanics", by McCann and others. (24 - P.26).

Petrology

Surface outcrops of the President intrusives

present a rock very dense and ~ark in color, while underground

-35-

exposures, in Bralorne and Pioneer Mines, present masses

intensely sheared and greasy to the touch.

Only one specimen of serpentine was examined

microscopically. In the hand specimen the rock is massive,

bluish black in color, and on unbroken surfaces presents

greasy slickensided surfaces.

In thin section the rock consists of a mass of

roughly bladed antigorite serpentine, some of which shows

that peculiar network structure indicative of alteration

from olivine. Carbonate and small amounts of talc are

present, as well as iron oxide, (magnetite and (or) limonite).

The carbonate occurs for the most part as distinct veinlets

and is the result of paulopost alteration.

Structural Relationships

Alteration is so intense along the contacts, as

exposed in the present area, that it is not possible to

determine the exact relationship of the serpentine to ad-

joining rocks.

Correlation and Age

McCann has described serpentine rocks of a similar

nature occurring in other parts of the Bridge River area, ,

(24 - P.27) and he concluded- that they were extruded over v

-36-

the erosion surface of the Bridge River series, (present

Fergusson series) before Upper Triassic rocks were laid

down. Thus he regarded them as post-Pennsylvani an-Permian ,

and pre-Upper Triassic in age. On the other hand, he found

structural features that might suggest the serpentine rocks

to have been sills intruded along the unconformable contact

of the Bridge River series with later fonnations, in which

case the rocks might be regarded as younger than the Cad­

wallader series, that is, post-Triassic in age.

Cockfield and Walker (6 - P.SO) express the view

that the serpentine rocks may represent intrusive phases of

diverse rocks of various ages in the district, as well as

intrusive phases of the Shulaps volcanics. They also venture

the opinion that the serpentine may represent altered basic

marginal phases of the Bralorne diorite.

Cairnes has examined contacts of serpentine with

Bralorne diorite"'and found that in the diorite no change of

grain occurred near the co~tact. From other supporting

evidence Cairnes· came to the conclusion that the Bralorne

and President intrusives were introduced separately, but

may be related, (4 - P.30) and that "later siliceous phases

of the Bralorne intrusives may be younger than the President

intrusives and their serpentinized equivalents."

-37-

Minor Intrusives

"' Distribution

Many dykes and minor intrusive bodies occur within

the Bralorne diorite and albite granite, and are closely

associated with the vein deposits of the present area. These

dyke rocks may be divided into three types, as follows:

1. Dyke-like masses of albite granite

2. Albi ti te and quartz albi ti te dykes L--.

3. Greenish fine grain dykes

Rocks of type I are numerous in both Pioneer

and Bralorne Mines. The albitite and quartz albitite rocks

belonging to type 2, in the Bralorne Mine, frequently occur

along with the quartz veins forming a prominent, sheeted,

hanging wall or footwall to the veins. Dyke rocks belonging

to type 3 occur in a somewhat similar manner, and appear

more numerous in the Empire Mine, where the largest body

known forms the hanging wall of the Blackbird vein for

considerable distances.

Petrology

The rocks of group I are typically porphyritic

and light grey colored. According to Cairnes, in thin section

they consist of phenocrysts of albite and quartz in a fine

-38-

grained groundmass of the same minerals. Secondary minerals

are present in the groundmass, as oarbonate and sericite in

varying amounts. Pyrite is usually present, frequently

giving to the hand specimens a stained brownish buff color.

None of these rocks were examined in thin section by the

present writer.

The second type have much the same mineral com­

position as the first. A specimen was examined microscop-,"

ically. In the hand specimen the rocks vary in texture from

finely crystalline to porphyritic. Their color is burf to

almost white and they carry enough iron sulphides, in most

oases, to cause staining of the weathered surfaces.

In thin section the specimen examined displays

a somewhat allotriomorphic texture, with anhedral crystals

of Quartz and very Ddnor amounts of feldspar (plagioclase).

Alteration products consist of abundant carbonate and lesser

amounts of seriCite. Pyrite and leucoxene are present as

small scattered grains. The alteration producing abundant

carbonate is probably due to hydrothermal conditions, such

rocks having been composed originally of quartz and very

sodie plagioclase feldspar, according to Cairnes. The specimen

is an altered albitite, the original feldspars being almost

entirely oblitereated by alteration.

-39-

The third type consist of massive fine grained

rocks of variable greenish color, which in some cases,

grade to a grey white, and makes them indistinguishable

from the above two types. On the other hand, they may

grade, as well, into a darker green color which makes them

difficult to separate from nearby bodies of Pioneer green­

stone. ~he diverse shades of color have been ascribed to

degrees of alteration present in the rocks, the more intense

alteration producing the lighter colored verities.

A specimen examined was aphanitic and greenish­

grey in color, with a characteristic blocky fracture and

hardness.

In thin section the rock is porphyritic, with sub­

hedral to anhedral crystals of feldspar as phenocrysts,

in a matrix of quartz and feldspar with a somewhat sutured

texture, which on closer examination, proved to be distinctly

igneous. The feldspar phenocrysts which are plagioclase,

have been partially altered to sericite and carbonate. Large

amounts of pyrite and small amounts of Umenite, with

associated particles of leucoxene are present, as well as

minor amounts of chlorite. Alteration has been produced

by solutions prob~bly associated with vein formation. The

original rock probably had a composition similar to the

albitite dykes of type 2 mentioned above.

-40-I

Structural Relationships

As stated pre~lously, the dykes of type 1 occur

as dyke-like masses of the larger bodies of albite granite,

or as less regular small intrusions of the same rock (4 - P.34).

The dykes described as belonging to type 2, and type 3, are

frequently followed long distances by vein-bearing fissures.

They are often sheeted parallel With the vein structures and

vary in width from a few feet to 100 feet. The dyke rocks

of type 3 are inclined to be more clearly jointed and blocky

than those of type 2.

Age Relations and Genetic Significance

The mdneral composition of the above types of dyke

rock 1s essent1ally the same for all three types. Cairnes

believes them to be genetically related, and to bear a close

genetic relationship to the albite granite (4 - P.34). These

dykes intersect the Bralorne diorite and albite granite and

are, therefore, younger than these rocks.

Bendor Intrusives

General Statement

The Bendor intrusives lie one to two miles north­

east of the present area. These rocks are of general interest,

owing to the fact that mention has been made at various times

-41-

ot their possible relationship to the albite granite of

the Bralorne intrusives, and to the fact that they constitute

a mass of batholithic dimensions close to the area under

discussion, and present interesting petrographic and struc­

tural features.

Distribution

The Bendor intrusives form the general mass of

the Bendor mountains. They are batholithic in size and

shape, the long axis of the general mass being somewhat

arcuate and striking from due east, in its eastern extremity,

to northwest in its western extremity. The length of this

batholithic body is about 16 miles and the width about 5

miles.

Petrology

McCann states that the rocks show a general uniformity

in composition and texture, and a marked absence of metamorphism.

The sgme opinion is expressed by Do~age (12 - P.422) who

says, "Throughout the batholith, difference in composition

is very slight, and over large areas the rocks are monotonously

uniform in composition."

The rocks are relatively fresh and massive, and

consist principally of quartz-diorite and granodiorite. They

-42-

differ significantly from any facies of the Bralorne intrusives,

in that they contain potash feldspar, which Is apparently

absent, even in the most siliceous types of the Bralorne

albi te grani tes.

Only one specimen was examined microscopically.

The mass displays a coarse grain, and contains about eq~al

amounts of light and dark minerals, large platy crystals of

biotite being particularly conspicuous.

In thin section the rock is holocrystalline, ooarse

grained, and equlgranular granitic in texture. Essential

constituents consist of abundant quartz, fresh ~ubhedral

forms of plagiQclase feldspar, of composition An35 , biotite,

and common hornblende displaying lmmellar twinning. Apatite

is present as the accessory mineral. ~'he thin section appeared

lacking in potash feldspar and is remarkably fresh and free

from alteration. Erom the composition of the feldspar, amount

of quartz present, and lack of potash feldspar, the rock may

suItably be called a quartz-diorite or biotite-quartz-diorite.

Structural Relations

Collectively, the Bendor intrusives or Bendor

batholith as McCann termed these rocks, appear in strong

contrast to the metamorphosed condition, and to the presence

-43-

of mineralized veins in the Bralorne intrusives. (24 - P.37).

The jointing is extremely regular (24 - P.37), the

master joint planes striking in a northeast direction, trans­

verse to the elongation of the intrusive, and dipping to the

southeast at an average angle of 40 0 • In many cases they

are closely space~ and lend a coarsely stratified appearance

to the rocks.

A second jOinting system, less pronounced, displays

similar strike, and dips at right angles to the major system,

the two systems forming a conjugate system of jOinting.

The batholithic mass makes steep dipping contacts

with the enclosing formations, which have similar strikes, and

dip away from the intrusive bodies. (4 - P.39). McCann,

from field evidence, came to the conclusion that the batholith

reached the surface by magmatic stoping, and pushing aside

and squeezing the intruded rocks. (24 - P.38).

The borders of the batholith show signs of slight

differentiation (1 - P.37). There is a noticeable concentration

of ferromagnesian minerals giving the rock a dark color, the

outcrops of which weather readily, the pyrite formed through

contact metamorphism, giving to them a risty color •

. Many small inclusions, or "schlieren", of dominant

-44-

ferromagnesian composition occur in the Bralorne q~artz

diorite. McCann states (24 - P.37) that they probably

represent p~ts of an earlier and more basic differentiation

of the original magma, and are not related, in origin, to

the partial ass~ilation of included country rook fr~ents.

Age and Correlation

The Bendor batholithic rocks invade the Fergusson

series, Noel and Hurley formations, and the President

intrusives, (4 - P.39) and sinoe the Hurley for.m~tion is

considered as Jurassic in age, the Bendor batholith must be

younger than Jurassic.

McCann (24 - P.3S) found that the Bendor batholith

intruded the Eldorado serie.s of Lower Cretaceous age, but

found difficulty in definitely assigning any age to the body

beyond this. Furthermore, he correlated it with the Okanagan

composite batholith, described by Daly as, "a part of a com­

posite batholith stretching from the eastern contact of the

Osoyoos batholith, to the western contact of the Remmel

batholith." (8 - P.432).

However, north of the Bridge River district, Dolmage

found an extension of the Bendor batholith invading fossil­

iferous formations, ranging in age fro~ Upper Jurassic to •

late Lower, or early Upper Cretaceous (12 - P.8S). Thus the

-45-

Bendor intrusives are definitely post-Lower Cretaceous.

Kersantite Dykes.

Distribution

Several narrow lmaprophyre dykes occur exposed

in the underground workings of Pioneer and Bralorne Mines

and represent the youngest igneous activity in the area.

The dykes strike at right angles, or approxbnately so, to

the quartz vein fissures, and intersect them. They have

not been fpund in surface outcrops.

Petrology

A typical example of these lamprophyre rocks was

taken from the Empire Mine and may be described as follows:

The rock is holocrystalline, fine grained, and has

a porphyritic texture with phenocrysts of biotite, and is of

a general dark grey oolor.

In thin section the phenoorysts of biotite are

frequently euhedral, and occasionally contain intercalated

orystals of apatite. The groundmass, which i~ microcrystalline,

consists of minute crystals of plagioclase feldspar, carbonate,

and scattered grains of magnetite. Small amounts of chlorite

and epidote are also present. From the presence of biotite

-46-

and plagioclase feldspar, the rock may be called a kersantite.

Pleistocene Deposits

The Pleistocene deposits consist '01' unconsolidated

glacial and stream gravels. Unassorted glacial drift mantles

much of the valley slopes, and consists of erratic materials,

and deposits of boulder clay, that occasionally attain depths

over 200 feet. Such depths have been found over the Blackbird

vein of the Empire .ine, where attempts were made to raise

through to the surface from underground workings.

The main valley bottoms contain thick deposits

of roughly sorted sands and gravels. They consist, for the

most part, of glacial, or post-glacial stream deposits. (4 - P.40).

Recent Deposits

Recent deposits consist of stream and glacial deposits,

slide debris, and volcanic ash. (4 - P.40). The post-glacial

streams collected th.is material by active cutting, during

which time they created deep rock canyons in their lower courses,

distributed the eroded material along the main valleys, and

formed alluvial fans and deltas at their mouths. (4 - P.40).

In places, the recent stream gravels carry placer

gold, which was probably derived from the Pleistocene glacial ,

-47-

and stream deposits. (4 - P.40).

The volcanic ash or pumioe has been described by

McCann as yellowish grey to creamy white, and as gritty to

the touch. This ash covers the area to the north of Bralorne

more plentifully, and occurs as a thin mantle which thins

out considerably to the east. Bateman (1 - P.193) /has

suggested that the souree of the material is in the west,

towards the headwaters of the Bridge River, and that prevailing

westerly winds have carried it westward.

Analysis of a sample collected by Drysdale, (l4 - P.53)

proved the composition of this volcanic ash, or pumice, to

be equivalentto that of a dacite. (4 - P.73).

-48-

STRUCTURAL GEOLOGY

General Statement

The structure of the Bridge River area has been

described by Drysdale (14 - P.SO) as a broad anticlinal

fold, trending northwest and pitching in the same direction

at a low angle. The eastern limb of this broad anticline

extends to the border of the Interior Plateau and is entirely

outside the area in question. The western limb of the

anticline dips towards the Coast Range batholith and, in

the immediate vicinity Of the Bralorne-Pioneer ore deposits,

consists of a number of closely compressed folds intruded

by bodies of augite diorite, and related rocks, as well as

by the younger rocks of the Bendor intrusives.

The formations composing the major anticlinal

structure trend northwest in the southern part of the Bridge .

River area, and in the vicinity of Bralorne and Pioneer Mines,

but farther north,parallel the arcuate course of the Bendor

batholith and approach a true north strike in the northern

·part of the area.

The diorite and serpentine intrusives occupy a

comparatively narrow zane on the western limb of the anticline.

In the vicinity of Bralorne Mines, this zone corresponds with

-49-

the strike of the major synclinal axis in the area, and the

intrusives are elongated roughly parallel to this axis.

(4 - P.44). North of the Br1dge River the synclinal structures

are broken by anticlinal folds and crossoutting by the intrusives

is much more pronounced, and elongation less noticeable.

The Bralorne intrusives, which contain the ore­

bearing veins, were probably intruded immediately after the

enclosing formations were strongly compressed, (24 - P.2l)

and immediately after the uplift of the anticlinal arch.

Intrusion of the Bendor batholith followed, by stQping into

the Fergusson series, Noel and Hurley formations, engulfing

large masses of these rocks and shoving aside the enclosing

fonnations, making them schistose along the contact. As

a result of this intrusion the neighboring sedimentary and

intercalated volcanic rocks stand at high angles, and in

oertain looalities are overturned. (24 - P.43). McCann has

attributed the movement along the vein fissures in the

Bralorne intrusives and the sheeting and ribboning in the

veins to stresses accompanying this later intrusion.

Local

The Bralorne intrusives have penetra~ed a z~ne of

weakness, on the western flank of the Bridge River anticline.

In the vicinity of the Bralorne and Pioneer deposits, this

-50-

zone is marked by a tightly-folded syncline, (4 - P.79),

the axis of whioh is the loci of the igneous intrusions.

A normal stratigraphic sequence of the sedimentary formations

1s seen on the southwest limb of the syncline, but on the

northeast side of the syncline, b~yond the workings of the

King Mine, there is evidence of a fault (4 - P.79) which

has brought the Fergusson series in contact with the Hurley

formation.

The elongated stock of Bralorne intrusives, in

which the Bralorne and Pioneer ore deposits occur, displays

exceedingly steep contacts on its northeast and northwest

sides. The northeast contact, where the King vein passes

into adjoining greenstones, is vertical, and the southwest

contact With serpentine is also steep and at Pioneer has

an average dip of 70° to the south. To the northwest the

contact of the stock passes at a high angle beneath the

Noel and Hurley sedimentary rocks.

The most southerly of the two igneous bodies lying

to the north of the large stock, as far as can be determined

from mdne openings, has more gentle-dipping contacts' with

the enclosing sedimentary for.mations. The average dip is

about 60°. The more northerly body appears to possess ~

steeper dips, although lack of mine openings in this mass

--51-

•

leaves d?ubt as to the actual contact relationships with

enclosing formations.

Cockfield (6 - P.48) noticed that the stock-like ,

bodies present in the area seamed to present an "en echelon"

arrangement, and that the apparent offsetting was character­

istic of post-mineral faulting in the area, and might be the

result of such structural conditions. Gradational contacts

and inclusions of the surrounding sedimentary rocks in the

diorite bodies, proved to h~ that the "echelon" arrangement

of the igneous bodies is not the result of faulti~g, but

rather, represents the apexes of a single stock that has

been partially unroofed.

Contact relationships between Bralorne intrusives

and enclosing formatIons are, in many cases, obscured, either

by intense shearing, where associated with sedimentary or

serpentine rocks, or by gradational conditions, where

associated with certain greenstone formations.

Two fault systems traverse the area and intersect

all formations of pre-Bendor age. (4 - P.43). Faults of

the first system consist of two fracture sets which strike • approximately northwest cutting s~ightly across the formational

trend and dipping at various angles both to the north and

to the south. These faults are of economic importance and

-52-•

contain the principal gold quartz veins of the area.

In the immediate region of Bralorne Mines,

faults of the second system intersect and offset these

ot the first. They strike north, with one set dipping

to the west, and the other, a more rare set, dipping to

the east.

Towards the eastern limit ot the Pioneer Mine

a fault has been encountered in underground workings, which

has been held responsible for the thickening of the Pioneer

formation in that region. The same structure has been

encountered in the Pacific Eastern Gold Mine workings

farther east, (4 - P.44) and Cairnes believes this same

structure to be related to the No.3 fault ot the King Mine.

On the No. 8 level north of the King Mine, in Taylor

(Bridge River) workings, a broad shear zone occurs which

Cairnes believes to strike southeast and pass to the north

ot the Pioneer workings. (4 - P.44).

The above mentioned two principal fault zones are

believed to be continuous for long distances down Cadwallader

Creek valley, (4 - P.43) and the major post-o~e faults ot

Bralorne Mines are probably related to these zones.

~nor faults related to the principal fault

-53-

systems are abundant. They strike at all angles and

particularly in the upper workings of the King Mine have

complicated mining of the veins.

Veins and Faults of Bralorne and Pioneer M[nes

A somewhat detailed description of the principal

veins and faUlts occurring in Pioneer and Bralorne Mines

will serve to give a clearer pioture of structural conditions

as so far defined· by mining operations in the area. This

description, previously set forth (5 - Pp.18-24), is the

result of information gained during that period when the

major fault system of the King Mine ore deposits was dis­

closed. Much information is still to be gained conc~rning

the nature and extent of the Empire fault zone lying farther

to the east.

Veins:

The principal veins in the western section of the

area occur in the King Mi~e and are known as the North,

Shaft and King veins, and the "C" vein. In the central

.part of the area lie the Blackbird, 59, Empire and Coronation ..,

veins and in the eastern section, the Pioneer vein with , related Footwall and H.anging wall veIns.

All the principal veins dip to the north at diverse

-54-

angles except in certain rare sections. A reversal of ,.

dip has been noted in the King Mine in a non-productive

portion of the Lorna block between 6 and 8 levels, and

in the Pioneer vein between 13 and 14 levels. The "C"

vein, in the King Mine, a fault fissure-vein is the only

commercially important north-south striking vein discovered

in the area to date. ,It occupies a part of No. 2 fault

and dips to the west.

Spli tting in the vein fissures is common'. Where

splits occur they torm either hanging wall or footwall

branches and appear strongest where the main quartz fissures

are widest. In many places the widest ore bodies have flat

looal rolls in their footwalls.

In vertical section several ,of the veins pos~ess

strong hanging wall branches which diverge from the parent

vein down the dip. Such branching stru~tures m'ay unite'

again at depth to form single'vein fissures since many of

them followed horizontallt coalesce.

The Pioneer vein contains a number of branch veins

whioh are of economic importance. The two most important

are the Hanging wall vein and the Footwall vein. The latter

strikes about 30· south of the main vein fissure and dips

-55-

about 70 0 to the north. The deposits of this fissure show

more fracturing and shearing than is found in the main vein

fissure. This condition is probably due to a localized and

intense post-mineral faul ting. The Hanging wall vein lies

north of the main vein-fissure and dips northerly at about

65°.

The Pioneer vein and Footwall vein have no well­

defined intersection, and the same is true of the North

vein and the Shaft ve in of the King Mine. This may be as­

cribed, in part, to the action of strike faulting, which

may have interrupted and obscured the junction of the fissures.

As a general rule t~ose veins which lie in the

sedimentary rocks are narrower, whereas those in the diorite

tend to be wider and stronger. A marked change can be noted

in the King vein where it enters the greenstones, the fissura

becoming noteably narrower. On the other hand, the Pioneer

vein, which for the greater part of its length lies in green­

stones, in which its width is not markedly different from

that of the part in the adjoining diorite, displays a strong

contrast. The greenstones as exposed in the Bralorne wo~kings

are somewhat schistose whereas those in the Pioneer area

appear more competent and yie~ded by clear-cut fracturing.

The vein fissures,.- in several cases are deflected

-56-

from th~ir normal strike on approaching serpentine. This \

might be attributed to structural movements or adjustments

which have taken place along the diorIte-serpentine contact,

sin~e this contact shows strongly sheared rocks.

In many places the veins show no indication of

reaching the surface as well-defined fissures. The King

vein has over its entire length but few zones which can be

maned to the surface. In the upper horizons of the mine

it becomes weakened by splitting and pinching with resultant

haphazard and scanty distribution of t.he ore. Somewhat

similar conditions obtain in the Pioneer vein.

With respect to this condition, Joralemon (19 -

Pp.483-485) believes that the present surface of the Bralorne

intrusives is a~ost at the original tops of the veins. He

believes that the great number of inclusions in the diorite

is sufficient proof that the present surface is "at the top

or near the top of an extensive diorite batholith that stoped

its way into the overlying sedimentary rocks."

The following evidence affords proof that the

vein fissures are fractures along which considerable movement

has taken place, and furthermore, that the fissures were

active during and long after the period of mineralization:

57-

1. The hanging wall rocks of the main Pioneer and

Footwall veins in the vicinity of the greenstone­

albite granite contact have been thrust up and

over the footwall rocks, with a resultant horizontal

displacement and vertical displacement of about

150 feet.

2. Late intense movement has taken place along the

strike of the "0" vein fissure, in the west end

of the area. The original fissure has been filled

with quartz and subsequent movements along its

strike have displaced the east-west trending King

vein a horizontal distance of 220 feet and 150

feet vertically.

3. A lRmprophyre dyke of Tertiary age, striking at

right angles to the vein has been faulted along

the vein fissure for a distance of 19 feet. This

is evidence of post-Tertiary movement, and a

further indication of faulting at a late date.

4. The presence of striations and grooving is common

in the quartz and in the walls of the vein fissures.

Faults:

In the King Mine, the east-west fissures have

been offset by three faults Which strike roughly north and

south with displaoements of th~ west side to the north. The

-58-

master fault ot this section of the area appears to be

No. 3 fault which is the most westerly and dips steeply

to the west. Nos. 1 and 2 faults, lying to the east.

are branohes of it. No. 2 fault dips west, at 45° to

70 0, and No. 1 steeply to the east. On the 8th level,

the King vein fissure is oftset 220 feet by No. 2 tault

and 240 feet by No. 1 fault, in both cases to the north.

The wedge-shaped block ot ground between the No. 1 and

No. 2 faults is termed the "A" blook. It is bordered

on the east by the Lorne block. West o't the "A" block

is the "D" block, lying between the No. 2 and the No. 3

faults.

The Empire fault, which is the remaining major

tault to be described, occurs in the Empire Mine. It has

an average strike of N.20oW. and an average dip of 53°W.

It appears in all likelihood that the 53 vein is the faulted

segment of the Empire vein; the 63 vein the faulted segment

of the Blackbird vein, and a seotion of vein lying west of

the Empire fault and 250 feet on the hanging wall side of

the Blackbird vein, a faulted segment of the 59 vein. The

aotual displaoement on the Empire fault has not been

determined, but from the above this would define three

distinot veins, eaoh of whioh has been int.erseoted by the

Empire fault and displaced f mean horizontal distance of

-59-

300 feet. The vertical displacement is in the order of

200 feet.

The Empire fault consists of a main footwall

break from which secondary branches have diverged from

the hanging wall side in an upward direction. These

branches, in some cases, cause considerable difficulty

in development and exploration work, in that they make

the width of fault zone to be crossed by exploratory work­

ings extremely variable and difficult to determine.

On all major faults, as has been noted, there

has been both a horizontal and a vertical component of

movement, and these have acted in the same relative direction

for all the faults. Each of the faults is considered as

a thrust from the southwest at an upward angle, with a

resultant hinge motion in each fault block. (20 - P. ).

This motion which has brought two different and differently

dipping horizons of the same vein to the same elevation,

has produced displacements which vary to a marked degree

from level to level. On No. 1 fault in the King Mine, the

measured horizontal displacement of the King vein on the

7th level is·220 feet, whereas on the lOth level it is 300

feet--80 fe~t or 36% greater. Similar conditions exist

on No. 2 fault.

-60-

Origin of the Vein-Bearing Fissures

McCann has expressed the view, that the two

intersecting sets of fractures forming the veins and faults

of the area, might be expected to result from powerful

torsional forces accompanying crustal movements. Experiment­

ally, however, Lindgren has pOinted out that fissures produced

by torsional stresses are nearly always curved and warped

surfaces, and not approximate planes. (23 - P.169). For

this reason it does not seem probable that the vein-bearing

fissures have been caused by torsional stresses. McCann

also suggests (24 - P.53) that stresses induced by regional

uplift might have been instrumental in producing the fissures,

since uplifts of this nature were active in certain parts

of the Western Cordilleras, about late Jurassic time.

The intrusion of the Bendor batholith may have

created stresses which resulted in the later movement along

the fissures, producing the characteristic ribbon structure

in the veins. (24 - P.53).

According to Cairnes, (4 - P.5l), the forces

producing the fissures have been of a compressive nature

and acted normal to the axis of deformation, horizontally

or upwards. (4 - P.5l). Movement occurred along the

fraeture~ relieving the accumulating stresses of compression,

-61-

and in such a direction, that for the east-west fissures

the north wall moved upwards and to the west, and for the

north-south fissures the west wall moved upward and to the

north.

Striae in the walls of the fissures dip at various

angles, indicating that the verticai and horizontal components

of movement varied considerably in different sections of the

fissures, depending on the relative strength of the two

components involved. Since in several places the north

striking faults offset the east-west vein fissures, Cairnes

has concluded that the principal stresses causing compression

acted, in the later stages, mainly from the southwest.

MOde ot Vein Fissure Filling

A large unsupported inclusion of wall rock was

seen by the writer in the Empire vein. This inclusion was

5 teet long by 3 feet wide, and by subsequent mining operations •

was found to lie entirely unsupported in a section of vein

12 teet wide, composed entirely ot quartz. The inclusion

displayed the same degree of alteration as the adjacent

hanging wall, and lay oriented With its long axiS, roughly

parallel to, and at a distance of some 4 feet fram it.

Smaller tra~ents of a somewhat similar nature

have been seen in various other localities throughout the

-ES2-

Bralorne Mine, but especially in drift faces where it is

not certain but that the fragments were supported in one

dimension.

If the vein filling had resulted from a process

of replacement, angular fragments Ddght have been produced,

according to Bateman (2 - P.25), the replacement proceeding

outward from intersecting fractures. This would explain

the angularity of small fragments often seen in drift faces, • but does not entirely explain the roundness of the large

fragments mentioned above, although a~guments have been

put forth stressing the fact, that, angular inclusions, as

well as rounded ones, may be produced by replacement. (28 - P.ESOl).

If replacement processes were not active, the vein

matter may have been injected into fissures which opened more

or less contemporaneously with the advance of the vein-forming

material. The subsequent vein structure, according to Berg,

(3 - P.93), would then depend on whether the opening of the

fissure was faster, or slower, than the filling.

That the vein fissures in question were active

during depositlon of the quartz, or before its consolidation,

is a fact tram evidence seen in the quartz filling of a

part of the King vein fissure, where banded quartz is con-

torted and free from fracture.

-63-

The vein fissures, as indicated previously, are known

to have been active during and subsequent to fissure fill­

ing, so that disturbances could be caused during the vein

filling process by which fragments might break from the

unsupported hanging wall of large open spaces temporarily

created in the fissures. Berg (3 - P.89) believes, in this

case, that such fragments could then rest on the product

of crystallization ,already deposited on the footwall. Such

fragments would subsequently appear entirely unsupported.

Nothing definite can be said concerning· the mode

of tissure filling in this area, but it must be born in

mind, that if filling of open spaces took place, that these

open spaces were constantly changing in size and shape, since

they were part of fissures along Which movement was active

for a longer per10d than that of deposition of the quartz

filling.

-64-

MINERALOGY OF THE VEINS

General Charaoteristics of the Veins

The gold quartz veins occur as fillings of well­

defined fault fissures and are characterized by frequent

pinches and swells along their entire lengths. Banding,

or ribbon structure, along with pronounced sheeting in the

veins is the result of subsequent movements along the planes

of the veins. McCann suggests (24 - P.54) that the ribbons

are probably the result of movement along regular lines of

original sulphide deposition in the quartz.

Gangue Minerals

Quartz

Much of the quartz occurring in the veins is

milky white with a glassy lustre. Very glassy quartz

often indicates poor ore. Fluid inclusions are not un­

common and in some places are arranged in geometriC lines

(4 - P.53). From examination of a number of speclmeas of

quartz under the microscope, Cairnes came to the conclusion

that the inclusions were more abundant, an'd active bubbles

more conspicuous, in specimens of the higher grade gold

quartz.

-65-

Chalcedony

Small amounts of chalcedony have been seen by

the present writer in the Blackbird vein of the Empire Mine. : ~~"

It occurs as irregular masses in the quartz.

Calcite

Where calcite occurs in conspicuous amounts it

is usually oonfined to a band along either wall of the vein,

and is frequently the only constituent in the outer ends ot

branch veins.

Chlorite and Sericite

The chlorite is usually in small patches or in

short transverse gashes in the quartz. Pearly white sericite

is also found along small transverse fractures or occasionally

as little pockets in the vein.

Mariposite

This mineral is ~ound sparingly in a number of

the veins. It occurs underground in both the Lorne and

Pioneer Mines, and usually accompanies high grade ore.

Do1mage has concluded that the mdneral was introduced early

in the mineral sequence, probably with the first generation

of ,quartz. (12 - P.425). Mariposite occurs in the veins v

-66-

of the Grass Valley district in California. Lindgren has

desoribed it as a "bright green foliated mineral closely

allied to muscovite." (23 - P.115). The green color is

due to a small percentage of chromium and he sees no good

reason for separating it from fuchsite or chromiferous

muscovite.

Scheelite

This mineral is not rare in the veins and commonly

occurs as small isolated grains or aggregates. It is more

plentiful in the central and eastern part of the area than

in the extreme west end. An occurrence of this mineral

was found in the Empire vein, where for a distance of several

feet, the footwall of the vein consisted of a layer of scheelite

one to two inches thick. <>

Ore Minerals

Gold

Free milling gold is found associated in Bralorne

and Pioneer Mines with sphalerite, pyrite and arsenopyrite,

and to a lesser extent, with chalcopyrite and stibnite.

Towards the west end of the ore zone, defined by these mines,

the gold is inclined to be scattered throughout the vein

quartz as small, pin-po1nt to pin-head particles. At the

-6"-

east e~d of the zone, visible gold is more likely to. be

found along striated parting planes of the quartz.

Arsenopyrite

This mineral tends to occur in masses from a

tew pounds to several tens of pounds and is commonly

associated with high-grade gold content. Arsenopyrite

and mariposite occur together in many places.

Pyrite

Pyrite is the most abundant metallic mineral in

the vein as well as in the altered wall rocks. In the

veins it is commonly in massive form while in the wall rock

the crystals are often perfectly formed. A late generation

of pyrite has been described by JEmes occurring as th1n

plates in fracture planes of the quartz. (18 - P.344).

Sphalerite

Two varities ot sphalerite, both associated with

high-gold ore, are common. The brown sphalerite is the more

common. Light grey sphalerite has been found as isolated

crystals embedded in the quartz.

Chalcopyrite

This mineral is 0:0.- rather rare occurrence in the.

-se-

veins, and where present is closely associated with gold.

Some Of the best sections of ore in the Empire vein contain

chalcopyrite.

Tetrahedrite

Grey copper has a frequency of occurrence similar

to that of chalcopyrite, and in most cases the minerals

occur in the veins together.

Galena

Galena is a rare mineral in the veins. It occurs

infrequently in the King vein where it is associated with

much sphalerite and free gold.

Stibnite

This mineral is also of rare occurrence. It has

been observed in a small mineralized fault cutting the

Pioneer vein. The only known instance of its occurrence

as a vein mineral definitely associated with quartz is in

the 59 vein, at about the centre of the intrusive. It is

found here as bunches of radiating crystals in the quartz,

but not in any quantity.

Marcasite

Marcasite has been reported by Do1mage (12 - P.425)

-69-

trom the Pioneer vein. This mineral has not been discovered

in other veins of the present area.

Paragenesis of' the Vein Minerals

Due to the inadequate supply of~peoimans on

hand only a lim tad number of minerals occurring in the

veins were determined. The approximate age re~ation8hips

were worked out for these minerals and although not oomplete

represent those most commonly found in the ore.

The sequence of mineral deposition app~ars to be

as follows:

Q,uartz

Fracturing

Pyrite , Arsenopyrite

Fraetur1ng

'tuartz Carbonate? . Chal~opyr1te Sphaler1te Galena Tetrahedr1te Gold

Fracturing

Q,uartz Carbonate

-70- ..

Free gold frequently appears in the ore and

occurs as ve1nlets cutting fractures in the quartz, and in

some specimens in the arsenopyrite and pyrite. There

appears to be an assoc.iatton between tetrahedri te, sphalerit.,

chalcopyrite and gold, the latter mineral being invariably

present when the former mdnerals occur. In some places the

gold appears to replace these minerals, and in others, seems

to occur along their crystal boundaries.

Arsenopyrite occurred as a filling in well-defined

ribbons in one specime_n of Pioneer or·e. These p.articular

ribbons, therefore, represent early formed fractures in

the older quartz of the veins, sinc~ ar~enopyrtte was one

of the first mdnerals to be precipitated.

In one specimen the sequence chalcopyrite,

sphalerite, galena, appeared to be reversed. No doubt these

mdnerals were deposited a~ost contemporaneously.

The sequence of mineral deposition in the Pioneer

vein has been worked out in some detail by Smith and Do~age,

(12 - P.428) and they concluded that, "most, if not all, the

gold came in with the galena after the arsenopyrite, pyrite

·and pyrrhotite had been intensely fractured."

The-Ore

The bulk of the vora mined in Bralorne and Pioneer

-71-

Mines consists essentially of quartz with very minor amounts

of other non-metallic minerals, such as calcite, ankerite,

sericite, chlorite and scheellte. From 2~ to 5~ of the ore

by weight is sulphide, chiefly arsenopyr~te and pyrite,

with unimportant amounts of sphalerite,~galena, pyrrhotite,

chalcopyrite, marcasite, and under certain conditions,

stibnite. Gold tellurides have been reported but have not

been noted by recent writers. ~he only metals of economic

imp'ortance are gold and silver, the latter present in the

ratio of one ounce to from 5.5 to 7 ounces of gold.

-72-

ORE SHOOTS

General Description

To discover any particular reason tor the fact

that the gold occurs in definite ore shoots is difficult.

The gold tenor is equally high where the walls of the vein

are greenstone, albite-granite, augite-diorite, or any

combination of these rocks. The incompetent rocks, partic­

ularly the serpentine, have exerted a strong influence on

the distribution of ore merely because the veins died out

on entering them. Ore shoots at the extreme west end of

the veins, therefore, confor.m on their westerly margins

with the trace of the intersections of the vein and serpentine.

Thus the west end ore shoots of the King vein and of the

Pioneer- veins rake to the west in part, but there is a

definite tendency for an individual ore shoot to pull away

from the serpentine with depth and drop vertically down the

dip of the vein. A somewhat similar condition exists at

the east end of the veins in the centre and west sections

of the ore zone, where the greenstones are somewhat incom­

petent and do not carry good fissures. It'seams probable

that a westerly rake of the diorite greenstone contact is

partly responsible for a westerly rake of the ore shoots.

This same generalization does not hold, however, for veins

at the east end of the ore, zone, where, on the Pioneer main

-73-

vein, ~hree out of four of the principal ore shoots are "', ~f

in greenstone.

The most important ore shoot, to date, within

the Empire vein, rakes downward to the west and this may

be ascribed to the fact that the intersections of footwall

branches of the main fissure rake in this direction. In

the Blackbird vein, the trend of the ore shoot is likewise

conformable to the general direction of the line of inter­

se'otion of branch veins which, in this case, is downward

to the east •

• The centre and easterly ore shoots of the Pioneer

vein rake slightly to the east, and the lower centre ore shoot

which starts as a short section of ore on the 12th level,

spreads out both ways, chiefly to the west, as it descends.

Of the four principal ore shoots on the Pioneer

main vein, only one goes through to the surface, where its

length is reduced and its grade is lower than the maximum

found in the ore shoots below. The westerly ore shoot is

cut off by the serpentine, and the easterly shoot becomes

much shorter and lower in grade above No. 4 level, after

having attained a maximum of length and gold tenor near No.

5 level. The distribution of values in the King vein is

analagous to that in the Pioneer vein. Veins in the central

-74-

part of the ore zone have not been sufficiently developed

to add anything to the knowledge of the general distribution

of ore shoots.

Theoretical Considerations

Lindgren considers ore shoots as due to the

abundant preoipi tation of valuable m1ner.al~ from their

solutions, the causes of which are part physio-ohemical

and part mechanical. He lists the causes as follows:

1 22 - P. 19 5 ) •

1. Decrease of temperature and pressure

2. Chemical character of wall rocks

3. Mingling of solutions

4. Physical character of wall rocks

5. Structural conditions

In the case of the Pioneer-Bralorne veins,

there is no doubt that probably the go~d and other metals

were in solution in hot waters, which during their ascent

gradually encountered conditions favorable for precipitation.

From the chemical ohanges that have been involved in the

alteration of the augite diorite, namely the addition of

oarbon dioxide, potash and small amounts of combined sulphur

and water, and the loss of iron, silica, alumina, magnesium

-and soda, McCann (24 - P.55) came to the conclusion that

-75-

the mineralizing solutions must have been warm alkaline r

waters, containing much carbon dioxide along with salts

of sulphur and arsenic.

Decrease of temperature and pressure no doubt

played an important part in the precipitation of the metals

present, and the local temperature gradient probably had

a direct bearing upon, not only the persistency of ore in

depth, but on the uniformity of the ore, which in the

Pioneer vein extends to at least 3200 teet vertically below

the surface. In this regard, Cairnes (4 - P.Sl) suggests

that "special rather than normal temperature conditions

existed" and that a uniform low temperature gradient was

established. He believes that the steep sided form of the

Bralorne intrusives may have produced such temperature

conditions.

As previously stated, the chemdcal character of

the wall rocks seems to have no direct bearing on the

occurrence of the ore shoots. McCann suggested that the

loss of iron oxide as shown by analysis of fresh and

altered diorite has enriched the vein solutions 'and brought

about the preCipitation of the gold in the veins. In the

light of such a possibility, the iron content of the wall

rocks would be important.

-76-

Mingling of solutions in the vein fissures is

often brought about by junotions of intersecting veins.

Such junotions may afford favorable places for the prec­

ipitation of the gold and sulphides through the disturb­

ing of chemioal equilibrium.

A particular case bearing on the above is the

interseotion of the east-west King vein fissure in D block

with that of the north-south C vein fissure. Here the

vein matter joined to form a large ore body. Probably in

such a case as this the me~alliferous' solutions rising

in separate fissures and probably of different ohemioal

composition met where the fissures came together with a

resultant disturbance of chemical equilibrium causing an

inoreased precipitation of sulphides and gold.

Since the gold was found late in the sequence of

mineral deposition, contact of solutions with these early

sulphide minerals may have been partially responsible for

an increased precipitation of gold. Solutions oarrying

gold might have been guided by channelways which afforded

such oontaot relationships. Ferguson (15 - P.170) states

such possibilities in connection with the Alleghany district

of California and applies the reasoning to ore formation

in the wider parts of the veins.

-77-

.oLaughlin and Sales (25 - P.689) have stated

that the ca~ses of control by wall rock in ore deposition

are subtle and delicate. Physical properties of the rocks

are important. The hard rocks fracture more than the soft

and in the present area the diorite and granitic rocks as

well as the greenstone are of such hardness and brittleness

that clear-cut fissures have developed, whereas in the

sotter serpentine rocks they did not develope. These softer

serpentine rocks, however, acted as a guide to solutions

travelling through adjacent fissures in the diorite and are

partially responsible for the formation of ore shoots.

The structural conditions existing are ot greatest

importance in the development of ore shoots. Fractures, or

systems of fractures, serve a double purpose of a channel­

way for the ore and a place of deposition.

In several cases in the veins of the present area,

it appears as though the loci of deposition of the ore shoots

are due strictly to mechanical control. According to Hulin,

(17 - P.36) shoots often form at structural positions where

intra-mineralization fault movements produce reopenings of

the vein fissures, at a time immediately preceding, and dur­

ing metallization. There is no doubt but that the vein

fissures of the present area were active fissures before,

-78-

•

during, and after mdnera1ization, and that the above is

a pertinent fact with regard to location of the ore shoot.

Some of the following structural features may have

had an effect on the localization of at least some of the

ore shoots. (17 - P.36).

1. Variation in the Strike of the Vein

Variation in the strike of the vein fissure,

coupled with shear along the fissure, often will aid in

the deposition of ore.

The "C" vein in the King Mine offers an excellent

exmnp1e of this. Where the ore shoots occur the fissure

is S shaped and the ore occurred in those portions of the

S-where tensional openings exist. The irregular strike of

this fissure no doubt played an important part in controlling

the locus of these tensional openings. The Camp Bird vein •

haa been described by Spurr (29) as containing a series of

ore shoots which occupy positions of local variation in

strike of the vein fissure.

Spurr considers that the intensity of movement in

vein fissures has been sharply variable. (28 - P.6l5). The

original fissure is the result of slight movements which

later became most intense during the period of metallization, r

-79-

and developed slowly afterward through a very long period

of time.

2. Variations in Dip of the Vein

Variation in the dip of the vein fissure coupled

with a vertical component of shear may act in providing a

favorable site for ore deposition. A good deal depends on

whether the vertical component of faulting is normal or

reverse. Hulin (17 - P.39) states that if the faulting is

normal the steeper portions of the fissure are the more

favorable, whereas if the movements are of a reverse nature

the reopenings are more pronounced in the flatter portion

of the vein fissure. The veins of the present area, as prev-.

iously stated, are reverse faults and the above condition

seems to obtain in the "A" block of the King vein, where

between the 7th level and 8th level the vein fissure displays

a flat dip before continuing to the 9th level. Here the

ore was of exceptional width and excellent grade.

Vein Intersections

There seems to be no doubt that to a considerable

extent the ore shoots are related to vein intersections and

it has been long recognized that ore shoots commonly occur

at such locations. A vein intersection, as Hulin .(17 - P.43)

-80-

pOints out, is a position o~ weakness, since intra-mineraliz­

ation fault movements along either vein fissure tend to .

produce brecciation at this position. He considers vein

intersections, therefore, as ,"at least twice as favorable

a position for possible ore shoot formation as any other

random position on either vein."

In the Bralorne and Pioneer Mines the ore s.hoots

seem to extend for considerable distances along one or other

of the vein branches and terminate near the intersection.

~his applies specially to such veins' as the North vein, for

example, at its intersection with the Shaft vein, and .also

to the Pioneer vein at its intersection with the Footwall

vein. The explan~tion fer this may be found in the fact

that ,intra-mineralization movements were concentrated along . ,

only one vein fissure, and not the other. These movements

oaused brecciation whic.h may have been responsible for the

development of ore shoots. (17 - P.4l).

The relative position of branch fissures with

respect to rising metalliferous solutions is considered

by Cairnes as important. (4 - P.SO). Hanging wall fissures ,;:.11 .

WQuId not supply solutions of their own to the main fissure,

whereas footwall ~issures may add their own solutions to

tl).OS9 of the main fissure, and at their junctions may provide

-81-

increase in gold tenor. On the other hand, hanging wall

fissures might tend to carry away solutions from the main

fissure.

-82-

GENETIC CONSIDERATIONS OF THE ORE DEPOSITS

Any theory regarding the origin of the present

ore deposits must conform with the fact that all of the

productive veins so far discovered occur in or adjacent

to the various bodies of Bendor intrusives and that these

intrusives have undergone considerable differentiation,

one facies being represented by the albite granite so

plentiful in the Pioneer Mine and oertain parts of the

Bralorne Mine. (12 - P.429). Furthermore, the ore minerals

were deposited in two groups, most of the gold coming in

with the sulphides of the later group, such as sphalerite,

after the earlier minerals had been fractured and broken.

Cairnes (4 - P.49) attributes the highly variable

facies of the diorite, such as quartz diorite or albIte

granite, to the differentiation of the magma which produced

the diorite, and regards the mineral deposits as the last

products of differentiation. He recognizes the fact that

the important gold deposits found in the district, as a

whole, are closely associated with the more siliceous types

of diorite, suggesting a genetic relationship between the

gold quartz veins and these siliceous types.

Fluid inclusions in vacuoles, have been described

by.Knaebel (21 - P.389) in conneotion with the veins ot IJ

-83-

the Grass Valley district, and he noticed that they were

arranged in various ways, such as banding parallel to

vein walls, radially from pyrite, and in irregular bunches.

Cairnes (4 - P.53) found minute bubble cavities in the

quartz of the veins in the present area and found a com­

parison with that of the quartz in the albite granite,

sensing a genetic relationship, perhaps, between the two.

In regard to this he says (4 - P.54):"What the economic

significance may be is not known, but it seems probable

that it is more than a coincidence that the plutonic rock

most closely related to the auriferous vein quartz deposits

should possess a quartz of such like characteristics, and

distinct in this respect from the quartz of the other plutonic

intrusives."

Microscopic study or the mineralogy of the veins,

and careful observation of the actual occurrence of quartz

fillings in the vein fissures have lead to the belief that

no considerable time separated the various stages of m1neraliz~

ation, and that during the one prolonged period intra­

mineralization movements occurred and were followed by the

deposition of further vein matter. (4 - P.56).

The gold, therefore, is a late precipitant of a

single parent solution which g'ave rise to the various stages

-84-

of mineralization and originated in the m~a from which

the diorite was probably derived.

The present ore deposits probab.ly have an ancestral

relationship ~o the composite Coast Range Batholith, the

intrusion of each composite, Daly believes, being introduced

in the following order: gabbro or its chemical equivalent,

quartz diorite, granodiorite, quartz monzonite, and soda-rich

aplite. (9 - P.207).

Such a process has probably given rise to the

general Coast Range stem, which is intermediate between the

trondhjemitic type of the Quebec-Ontario gold belt (wet),

and the dry stem of the Morin series, Laurentian region,

Quebec, as defined by Osborne (26 - P.l27). ~his stem,

characteristic of the Coast Range magmas, may have looally

given rise to the albite-rich rocks of the present area.

According to Osborne (26 - P.l2S), this could be brought

about by the changing of conditions controlling differen­

tiation, in which local pockets enriched in soda are developed

from a normal stem. This process is known as "switching"

(,26 - P.12S) and gives rise to the trondhjemitic or soda-rich

type of rock, with high concentrations of water which aid in

the concentration of metals, and in the differentiation of

various siliceous rock facies.

-85-

Soda-rich rocks have been proved to be common in

the region of the Bralorne-Pioneer ore deposits, and as

pOinted out by Osborne, such rocks have been frequently

mentioned in association with gold deposits.

It therefore seems probable that the ore deposits

in the present area owe their origin to a fundamentally

basaltic magma from Which was differentiated an intermediate

type of rock stem. Perhaps by a subsequent process of

"switching", a local trondhjemitic type of magma, rich in

soda and high in water, gave rise to· the albite~rich diorite,

the albite granite, related dykes, and subsequently the ore

deposits themselves.

-'86-

BIBLIOGRAPHY AND REFERENCE

Bateman, A. M. 1. Lillooet Map Area. 2. Angular Inclusions

Vol. 19, No.6.

Berg, G.

Geol. Surv. Canada, Sum. Rept. 1912. and Replacement Deposits. Ec. Geol.

3. Vein Filling During the Opening of Fissures. Eo. Geol. Vol. 27, No.1.

Cairnes, C. E. 4. Geology and Mineral Deposits of Bridge River Mining

Camp, B. C. Geol. Surv. Canada, Mem. 213.

Cleveland, C. E. and Pioneer Staff 5. Bralorne and Pioneer Geology, C.I.M.M. Bull. Jan. 1938.

Cockfield, W. E. 6. Part of Cadwallader Creek Gold Mining Area, Bridge

River District, B. C. Geol. Surv. Canada, Sum. Rept. 1931, Pt. A.

Cockfield, W. E. and Walker, F. S. 7. Cadwallader Creek Gold Mining Area, Bridge River District,

B. C. Geol. Surv. Canada, Sum. Rept. 1932, Pt. AIl.

Daly, R. A. 8. North American Cordillera, 49th Parallel. Geol. Surv.

Canada, Mem. 38. 9. Igneous Rocks and the Depths of the Earth. McGraw Hill

Book Co.

Davis, E. F. 10. The Radiolarian Cherts of the Franciscan Group. Publ. of

Univ. of Calif,ornia, Dec. 23, 1918.

Dawson, G. M. 11. Palaeozoic of Bonaparte Valley, Geol. Surv. Canada, Am.

Rept. New Series, Vol. 7, Pt. B.

Dolmage, V. 12. Cariboo and Bridge River Gold Fields. C.I.M.M. Bull.

Aug. 1934. 13. Gun Creek Map Area. Geol. Surv. Canada, Sum. Rept.

1928, Pt. A.

Drysdale, C. W. 14. Bridge River Map Area, Lillooet Mining Division. Geol.

Surv. Canada, Sum. Rept. 1915.

-87-

Ferguson, H. C. 15. Lode Deposits of Allegnany District, Cal. Bull. U. S.

Geol. Surv. No. 580.

Harker, A. 16. Metamorphism. Metheun and Co. Ltd.

Hulin, C. D. 17. Structural Control of Ore Deposition. Ec. Geol.

Jan.-Feb. 1929.

James, H. T. 18. Features of Pioneer Geology. The Miner, Vol. 7, No.8,

Aug. 1934, Pp. 342-347.

Joralemon, Ira B. 19. Pioneer Gold. Eng. Min. Jour. Vol. 132, 1931. 20. Veins and Faults in Bralorne Mine. Trans. A.I.M.E.,

Vol. 115, 1935.

Knaebel, J. 21. The Veins and Crossings of the Grass Valley District,

Cal. E. Geol. Vol. 26, No.4.

Lindgren, W. 22. Ore Deposits. McGraw Hill Book Co. 23. The Gold Quartz Veins of Nevada City and Grass Valley

Districts, Cal. U. S. Geol. Surv., 17th Ann. Rept. Pt. II.

McCann, G. S. 24. Geology and Mineral Deposits of the Bridge River Map

Area, B. C. Geol. Surv. Canada. Mem. 130.

McLaughlin, D. H. and Sales, R. H. 25. Utilizati-on of Geology by Mining C·ompanies.

Ore Deposits of the Western states. Lindgren Vol. A. I .M.E. 1933.

Osborne, F. F. 26. Magma and Ore Deposits. Trans. Royal Soc. of Canada,

Vol. 31, 1937. -

Penrose, R. A. F. Jr. 27. Some Causes of Ore Shoots. Eo. Geol. March, 1910, Vol. 5.

Spurr, J. E. 28. The Relation of Ore Deposition to Faulting. Eo. Geol.

Vol. 11. No. 7 29. The Ore Magmas. McGraw Hill Book Co.

Talmage S. T. 30. T~e Significance 01' "Unsupported Inclusions". Ec. Geol.

Vol. 24, No.6.

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