DETAILED GEOLOGICAL MAPPING AND INTERPRETATION OP THE
GRAND FORKS-EHOLT AREA, BOUNDARY DISTRICT
BRITISH COLUMBIA
by
ARNE REINSBAKKEN B.Sc, University of British Columbia, 1968
A THESIS SUBMITTED IN PARTIAL FULFILMENT OP THE REQUIREMENTS FOR- THE DEGREE OP MASTER OF SCIENCE
in the Department or Geology
We accept this thesis as conforming to the required standard
THE UNIVERSITY OP BRITISH COLUMBIA December, 1970 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study.
I further agree tha permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.
Depa rtment
The University of British Columbia Vancouver 8, Canada A northward view up Granby River Valley from Thimble Mountain. The ridge in the foreground and across the Valley is underlain by the Middle Triassic Sharpstone Conglomerate and Brooklyn Limestone sequence. iii
ABSTRACT
The Grand. Forks-Eholt map area is underlain predominantly by a sequence
of moderately deformed and slightly metamorphosed sedimentary and volcanic
rocks, previously termed the "Anarchist Group" and ranging in age from
Permian/or Earlier to Middle Jurassic. These rocks are divisible into two
distinct sequences: (a) cherts (Knob Hill), quartzites, phyllites, and
greenstones of Permian/or Earlier age. The term Anarchist Group is now
restricted to this lower sequence which resembles the Cache Creek Assemblage
(Penn.-Lower Triassic) widespread throughout southcentral B.C.; (b) Sharp-
stone Conglomerate/Brooklyn Limestone sequence (Middle-Upper Triassic),
and overlying Pragmental Andesites (Middle Jurassic) which correlates with
the Takla-Hazelton Assemblage (Middle Triassic - Middle Jurassic) in north
central B.C. This upper sequence rests unconformably on -the lower and the
Sharpstone Conglomerate forms the basal conglomerate separating the two
sequences.
The Grand Forks Group (pre-Cambrian/or Early Paleozoic), consisting
of paragneisses, minor marble and amphibolites crops out east of the Granby
River Fault. The fault forms approximately the eastern boundary of the
map area.
Latest Jurassic Nelson granodiorites; Latest Cretaceous quartz-diorite,
quartz-monzonite porphyries, leuco-gabbros and diorites; and Eocene Coryell
syenites and related alkalic rocks intrude the sediments and volcanics pre•
dominantly in the northern part of the map area. The Nelson granodiorites
occur as large batholith-like masses and the younger intrusions form small
irregular plugs, dykes and sills. iv
A NNE to N trending nearly recumbent synclinal structure is outlined within the Sharpstone Conglomerate/Brooklyn Limestone/Fragmental Andesite
sequence. It is transected by prominent NW trending shear/fault zones and has been broken by these into blocks that are downdropped and shifted to
the southwest from north to south in the map area. The eastern part of the
map area is transected by the NNE trending Granby River Fault which forms
the northern projection of the Eastern Boundary Fault of the Republic
Graben - a major structural element to the south in Washington State.
Prominent NW and NE Late Cretaceous to Tertiary fractures are ubiquitous
and often filled by sheared serpentinites and Tertiary pulaskite and
diorite dykes.
The Middle Jurassic and older sediments and volcanics have been regionally metamorphosed to the Greenschist Facies. The Grand Forks Group
to the east has undergone metamorphism to the Almandine-Amphibolite
Facies. Large hornfelsed metasedimentary aureoles surround the larger
Nelson granodiorite masses. The Brooklyn Limestone has been thermally altered to marble and locally to chalcopyrite-magnetite bearing calc-
silicate skarns, which are often of economic value. Thin contact thermal aureoles surround the Latest Cretaceous quartz-diorite and quartz- monzonite porphyry plugs and dykes, indicating high level intrusion. V
TABLE OF CONTENTS Page
SECTION I; INTRODUCTION
a. Nature and Scope of Project 1
b. Field Approach and Laboratory Studies 2
c. Location and Accessibility 3
d. Previous Work 6
e. General Geology 7
SECTION II; STRATIGRAPHY
A. SEDIMENTARY SUCCESSION 10
a. Grand Forks Group 10
b. Anarchist Group 13
c. Sharpstone Conglomerate Sequence 19
d. Brooklyn Limestone Formation 30
e. Fragmental Andesites 38
f. Tertiary Layered Rock 44
- Kettle River Formation 44
- Marron Volcanic Formation 47
B. SERPENTINITES 51
C. INTRUSIVE ROCKS 54
a. Nelson Intrusions 54
b. Valhalla Intrusions 56
c. Diorites and Gabbros 57
d. Tertiary Intrusions
- Quartz-diorite and quartz-monzonite porphyry intrusions; includes "Scatter Creek Formation" rocks 63 vi
Page
- Coryell Syenite and Pulaskite Dykes 66
SECTION III; STRUCTURES 71
a. Republic Graben 71
b. Northwest and Northeast Fault Patterns 73
c. Dyke s 74
d. Folds 75
e. Tertiary Block Faulting and Tilting 80
SECTION IV: METAMORPHISM 84
a. Regional Metamorphism 84
b. Contact Thermal Metamorphism 87
SECTION V: SUMMARY AND CONCLUSION 91
a. Summary 91
b. Conclusions 97
c. Suggestions for Further Work 101
SECTION VI; REFERENCES 103
APPENDIX I; ECONOMIC GEOLOGY 106
- Mining History 106
- Mineralization 107
APPENDIX II: FOSSIL LOCATION AND DESCRIPTION 111 LIST OF TABLES
Table " Page
1 Table of Formations 11
LIST OF FIGURES
Figure Page
1 Location map of the Grand Forks-Eholt map area, Boundary District, British Columbia. 5
2 General geological setting of the Boundary District and adjacent Curlew quadrangle in northern Washington. 8
3 Idealized diagram of the possible source and formation of Triassic marine basins and the related deposition of the Sharpstone Conglomerate sequence and the Brooklyn Limestone. 28
4 NW-SE diagrammatic cross-section (looking NE) from the Rathmullen Creek - C.P.R. track intersection to where Lime Creek flows into the Granby Valley. 81
5i E-W diagrammatic cross-section through Baker Ridge. 82
6. SW-NE diagrammatic cross-section through Hardy and Goat Mountains. 83
7. Observed stratigraphic range of metamorphic minerals and other features of the Early Paleozoic, Permian, and Triassic-Jurassic rocks (after Parker and Calkins (1964), with modifications). 85
8. Possible outside correlations of various rock units and formations outcropping throughout the Grand Forks area. 96
9. Sketch and Measurements of Megaphyllites. 113
10. Mature to Juvenile Suture Patterns of Megaphyllites 114 viii
LIST OF PLATES Plate Page
Frontispiece A northward view up Granby River Valley from Thimble Mountain. The ridge in the foreground and across the valley is under• lain by the Middle Triassic Sharpstone Conglomerate and Brooklyn Limestone sequence. ii
1. Photograph Typical bedded sharpstone conglomerate with distinct alignment of angular chert pebbles. Note large weathered pits still containing limestone cobble remnants, and an increase in maroon colour towards the top of the picture. 22
2. Photograph Sharpstone conglomerate. Showing predominance of light green to grey angular chert pebbles. Several dark red jasper pebbles can be seen. 22
3. Photograph Typical "Puddingstone" or limestone cobble conglomerate from exposure along C.P.R. tracks north of Neff Creek. The white elongate rounded cobbles are aligned roughly parallel to bedding. 26.
4. Photograph A thin lens of sharpstone conglomerate interbedded with a maroon-coloured fine• grained wacke of the uppermost "Puddingstone" sequence, found west of Baker Ridge. 26.
5. Photograph "Aeolian limestone" or Seraphim's "Peanut Brittle" limestone forming the basal section of the Brooklyn limestone NW of Baker Ridge. Note alignment of the frosted chert ovoids. 34
6. Photograph Brooklyn Limestone, thinly bedded, well banded,unit from area immediately west of Grand Forks. Thin more resistant beds are tuffaceous and impure limestone. 34. ix
Page 7. Photograph Typical fragmental andesite from Goat Mountain. Note several large rounded porphyritic frag• ments and the light green-yellow epidote and chlorite alteration. 41
8. Photograph Spectacular andesite agglomerate outcropping along the southern Provincial Highway in the July Creek Valley. Camera case - extreme left for scale. 41
9. Photograph Intensely sheared, steeply dipping serpentinite body found within a NW trending fault zone northeast of Hardy Mountain. 53
10. Photograph Coarse-grained slightly foliated leuco- gabbro or mela-diorite from east of Hardy Mountain. Composed of plagioclase and hornblende. 53
11. Photograph Coarse-grained quartz-monzonite porphyry ("Scatter Creek Formation"?) from easterly trending dyke at Eagle Mountain. 68
12. Photograph Coryell syenite "clot porphyry" variety from east of Wilgress Lake. 68
13. Photograph A NE view of the limestone cliff directly opposite the Granby River from the Hummingbird showing. Shows synclinal fold minor structure within the well banded limestone unit and several flat dipping Tertiary dykes. 77 X
MAP
I. GEOLOGY Grand Forks-Eholt Area (l"=2000') in pocket at back xi
ACKNOWLEDGEMENTS
The author wishes to thank Texas Gulf Sulphur Company for the opportunity of working on the project and for allowing full use of all data and maps on which this thesis is based. The author was ably assisted in the field by C.N. Forster, K.A. Komenac, R.Taylor and P.T. Edwards at various times throughout the summer. Special thanks goes to J.M. Newell, who supervised the field mapping and with whom the author has spent many hours discussing various aspects of the project. His guidance and enthusiasm were much appreciated.
The author would like to thank Mr. J. Paxton, mine geologist at
Granby's Phoenix Copper Division, for his discussions and the loan of several maps' on the pit geology. Dr. E.T. Tozer of the Geological Survey of Canada at Ottawa discussed the ages of several fossils found in the
Grand Forks-Phoenix vicinity.
The author would also like to thank his supervisor, Dr.A.J. Sinclair, and other faculty members of the geology department for their discussions and advice given during the preparation of this thesis.
Financial assistance during the winter session was obtained from the
National Research Council and a teaching assistantship from the University of British Columbia. Texas Gulf Sulphur Company paid for all thin sections and final drafting of the accompanying geological map. 1.
DETAILED GEOLOGICAL MAPPING AND INTERPRETATION OP THE
GRAND FORKS-EHOLT AREA, BOUNDARY DISTRICT,
BRITISH COLUMBIA
Nature and Scope of the Project
During the 1969 field season, May to September, the author was employed by Texas Gulf Sulphur Company to do detailed geological mapping in an area adjacent to the Phoenix mine, near Grand Forks, in southern
British Columbia.
Objective of the programme was to outline the stratigraphy in the area, paying particular attention to the Triassic Sharpstone Conglomerate and overlying Brooklyn Limestone, the "ore sequence" (Newell, 1969).
Previous reconnaissance geology, summer 1968, by J.M. Newell showed that the "ore sequence" formed a good reference throughout the map area.
Special emphasis was placed on outlining possible ore localizing struc• tures such as folds and faults. The different intrusive rocks and related metamorphism, and faulting and fracturing were noted with their possible relations to mineral deposits.
The programme was oriented towards the discovery of deposits similar to the Phoenix mine, about mile west of the map area. Early prospectors in the area appear to have left no stones unturned, hence, it was felt that if any new mineralization were to be discovered it would be by projecting the favourable rock types and structures under areas of glacial drift or Tertiary sedimentary and volcanic cover. 2.
Field Approach and Laboratory Studies
The author spent four months in the Grand Forks area. Detailed
mapping was accomplished using T mile aerial photographs with transparent
acetate overlays. Outcrop patterns, air photo linears and the geology were
plotted directly onto the overlays in the field and this data was later
transferred onto tracing paper over a 1 inch to 1000 feet preliminary
topographic map. Interpretations of faults, contacts and possible struc•
tures v/ere made directly on the air photo overlays.
Two long traverses following road cuts along the eastern and western
boundaries of the map area and along numerous interconnecting logging
roads, forestry access roads and abandoned railway grades, provided good
exposures and an initial overall geological picture. This formed a skel•
eton from which later interconnecting traverses and helicopter traverses
were planned to cover the more open mountain sides and ridges.
Much emphasis in the geological mapping was placed on Newell's
"ore sequence", because these relatively unmetamorphosed sedimentary units
contained abundant minor structures, fossils, and housed all the major
copper skarn deposits in the Boundary district. Very little emphasis was
given to distinguishing various layered. Tertiary rocks for they seem un•
related to copper mineralization in the area. However, the possible
thickness of this Tertiary cover was of major importance in this project...
Some 80 thin sections were studied to check the validity of field names and compositions in order to postulate possible depositional envir•
onments for the finegrained rocks of dubious origin. From such studies 3. it was hoped that some criteria would emerge that would prove useful in distinguishing the fine-grained hypabyssal basic intrusive rocks from fine-grained intermediate volcanic flows. A similar problem was outlined by Monger (1968) in his studies of the Tertiary Marron extrusives and
Coryell intrusives in the area in which he interpreted some of the Coryell intrusives as feeder dykes to the middle and upper parts of the Marron
Formation.
The degree of metamorphism was also checked, especially the andesites and greenstones that are unstable in their present environment, hence very susceptible to metamorphic change.
Much of the detailed mapping was restricted to areas between and away from the mines and working of the Summit and Phoenix camps, where much of the previous work has been confined. In such areas, the author spent only a short time checking and correlating other workers' data.
Location and Accessibility
The map area covers approximately 56 square miles immediately west and northwest of the city of Grand Forks at the southeastern extremity of the Boundary District of British Columbia (Figures 1 and 2; pp. 5 and 8, respect.). It is elongate in a north-northeasterly direction, is about 5 miles wide at its widest point and about 11 miles long. On the east it is bounded by the drift covered Granby River Valley; on the west by July
Creek, on the south by the International Boundary and on the north by the
Canadian Pacific Railway tracks and Brown Creek running east from Eholt 4.
(see Geological map in back folder).
Access to the western and eastern edges of the map area is provided by the Southern Provincial Highway and the Granby River road respectively.
The present Canadian Pacific Railway tracks also provide good rock expo•
sures along the eastern and northern boundaries of the map area. Several abandoned railway grades run through the map area to the old mine workings and are passible by most motorized vehicles. Numerous old and presently used logging roads and wagon trails can be used by 4-wheel drive vehicles and provide easy access to most points of the map area. Near the southern part of the map area a powerline and a natural gas pipeline access road was also used.
The Boundary District occupies the southern extremity of the British
Columbia Interior Plateau and the western flank of the Monashee mountains forms the eastern margin. The country is typified by generally rounded hills and deeply incised glacial valleys. Much of the area lies between the 3000 foot and 4500 foot elevation and the maximum relief is in the order of 2500 feet, the lowest elevation of 1700 feet being in the Kettle
River Valley at Grand Porks. The highest point is Thimble mountain at the north end of the map area which reaches a height of 4300 feet. To the north the mountains become much more rugged, generally rising as pyramidal peaks to heights of about 7000 feet.
Most of the south facing slopes are open and grassy, with the dry slopes overlooking Grand Porks typical of the open "Cariboo type" cover.
The northern and western slopes are well wooded,with spruce,lodgepole pine, firs and alders predominating. The gently sloped drift-covered valley Figure I Location Map.
Grand Forks - Eholt map area within dotted area
west of Grand Forks. 6. bottoms are in places swamp-like with dense cedar growths, making traverses next to impossible. The mountain tops and ridges are generally open and grassy providing numerous helicopter landing spots.
Previous Work
Early geological mapping (Brock, 1901, 1902; Daly 1912; McNaughton,
1945)> was confined mainly to old workings and adjacent areas. Many of their ideas are now out of date in the light of some recent detailed mapping. Recent work by Seraphim (l956), sets forth some criteria for separating the various rock types that were previously believed products of silica metasomatism. H.T. Carsxrell (1957), a few years later extended
Seraphim's division of rock units to the Summit Camp, but mainly confined his detailed work to the old showings.
More recently, field studies in the Grand Forks-Greenwood area by the
Geological Survey of Canada include: a 1 inch=4 mi. map of the Kettle
River area (East Half) by Little (1957) in xvhich no attempts were made to separate the Permian and younger sedimentary and volcanic rock units; a complete study in the Greenwood map area of the Tertiary sedimentary, volcanic and igneous rocks by Monger (1968); and a field report of regional mapping carried out by Little and Thorpe (l965), in which they appear to have applied Seraphim's breakdown of the Permian and younger rock units on a regional scale.
The most recent article about the Grand Forks map area is a compila• tion from various geological reports and maps by J.M. Newell (1969).
Newell*s report reiterates Seraphim's criteria for separating various 7. rock units and emphasizes Seraphim's belief in a sedimentary origin for the controversial Sharpstone Conglomerates. It was from Newell's report that the author obtained many of his early ideas, some of which have become incorporated into this thesis.
Detailed mapping, in northern Washington State, for the United States
Geological Survey was done by Parker and Calkins (1964), however the only subdivisions made in the Permo-Jurassic sedimentary and volcanic rock sequence was the Triassic (?) carbonates versus the other rock types.
Correlation from the Grand Forks map area into northern Washington is further hampered by the difference in nomenclature, different map units and different map scales.
General Geology
The Grand Forks map area is underlain predominantly by a sequence of moderately deformed and slightly metamorphosed sedimentary and volcanic rocks ranging in age from Permian and/or earlier to Jurassic, that prev• iously had been termed the "Anarchist Group". These rocks were intruded by several Cretaceous and younger granodiorite, diorite, quartz-monzonite and alkalic intrusive bodies. Block faulting and shearing along northwest and northeast trending faults is common. An intermittent covering of
Tertiary continental sedimentary and volcanic rock marks much of the
Tertiary history (Figure 2, page 8).
The map area is bounded on the east by the Granby River Fault, which extends for some 50 miles south into Northern Washington and across which lies the intensely metamorphosed gneissic terrain of the Monashee Range
(Figure 2). 8.
J Early Tertiary intrusive rocks
Early Tertiary sedimentary • and volcanic rocks
j3 Ultrabasic intrusives
Nelson and Valhalla equivalent acid intrusives
Miles Pemian to Mid. Jurassic un• • divided sed. and vol. rocks 0 10 20 "I Shuswap type metamorphic ' ' terrain
' Major faults
Grand Forks-Eholt map area
Figure 2. General geological setting of the Boundary District BC, and adjacent Curlew quadrangle in northern Washington, (after Monger,1967-, G.S.C. map 932Aj Parfcer and Calkins; 1964.) 9.
Granitic and alkalic rocks of the Nelson, Valhalla and Coryell intrusive complexes pervade the area immediately north of the map area. Permian
Anarchist cherts and greenstones predominate the area west of Phoenix.
Tertiary sedimentary and volcanic rocks underlie most of the area west of
Greenwood, and also appear to become more abundant within the Republic
Graben, a major NNE trending structure in Curlew County N.Washington (Pig.2).
It appears probable that the so called "Anarchist Group" in this area includes both Permian and Triassic-Jurassic rocks, which, as suggested by Newell (1969), may possibly correlate with Cache Creek and Nicola-Takla
Groups elsewhere in British Columbia. The regional geology of the area suggests that an unconformity exists between the Permian and Triassic units, marked by the basal Sharpstone Conglomerate. The lithologies of the older units suggest a deep-quiet, offshore, marine,possibly island arc environment; lithologies of the younger units, on the other hand, indicate rapid deposition in shallow water, suggesting "a shore line environment at the edge of the Nicola Sea" (Newell, 1969). This indicates that the area was not completely submergent during Triassic time, in agreement with
Campbell (1966, pp.63-64). 10.
SECTION II; STRATIGRAPHY
A. STRATIGRAPHIC SUCCESSION
Grand Forks or Monashee Group
Host of the author's field work in the Grand Forks area was restric• ted to the western side of the Granby River Valley and consequently very little information was compiled on the Grand Forks Group. These rocks are of general interest because they form the abrupt eastern boundary against which the rocks underlying the Grand Forks-Eholt area abut. Most of the information herein is derived from the reports of Parker and Calkins
(1964) and Little (1957).
The Grand Forks Group contains the oldest rocks in the Boundary area.
Brock (l902) described them as crystalline mica and hornblende schists with a few bands of crystalline limestone. Later mapping by Little (1957), has outlined an intensely metamorphosed terrain comprised of granite gneiss, marble, hornblende schists and foliated granite sills. Parker and
Calkins (1964), to the south of Grand Forks in northern Washington, mapped in some detail, a sequence of intensely regionally metamorphosed sediments and igneous rocks having a thickness of about 17,000 feet, which they called the Tenas Mary Creek Formation. These Tenas Mary Creek rocks are typified by a gradual decreasing degree of metamorphism with decreasing stratigraphic depth: orthoclase-quartz-oligoclase gneiss characterizes the lowermost strata; through marble, quartzites, hornblende schists, quartz-plagioclase gneiss to schists and phyllites in the upper parts.
However, Parker and Calkins' Tenas Mary Creek Formation encompasses both TABLE I; TABLE OF FORMATIONS
ERA PERIOD OR EPOCH FORMATION AND THICKNESS LITHOLOGY IN FEET Recent Stream alluvium, talus, soil.
Cenozoic Pleistocene Glacial drift
Oligocene Coryell intrusives Biotite and potash-feldspar syenite porphyry, pulaskite, and related alkalic rocks.
("Scatter Creek" Quartz-monzonite, quartz-diorite Formation?) porphyries; minor diorites.
Intrusive Contact?
Eocene-Oligocene? Marron Formation Intermediate volcanic flows. 300 feet Sodic trachytes, andesites, phonolites; generally porphyritic.
Middle Eocene Kettle River Formation Arkose, and volkanic sandstone, 1200 feet acid tuffs, local conglomerate and shale.
Fault bounded and intrusive contacts
Late Cretaceous or Diorites and gabbros Diorites and leuco-gabbro, Early Tertiary found as dykes and irregular intrusive bodies associated with the NW prominant fault zones. May include coarse• grained andesites and border phases of Nelson granodiorites.
Fault contacts, contemperaneous
Late Cretaceous Serpentinites and Serpentinized ultrabasics, or Early Tertiary Pyroxenites pyroxenites; locally altered to carbonate, talc, and mariposite rock. Restricted to NW shear zones.
contact not seen (sheared?)
Mesozoic Upper Jurassic Valhalla intrusives Coarse-grained granite generally non-porphyritic
Nelson intrusives Granodiorite to quartz-diorite generally non-porphyritic
Intrusive contact
Middle.Jurassic Fragmental Andesites Andesites; flow breccias, massive maximum 2000' flows, agglomerates and minor (variable) pillows, and greenstones.
Unconformity; conformable in part
Upper Triassic . Brooklyn limestone Mostly massive, bedded, argillaceous maximum 2000' limestone, with banded tuffaceous limestone, minor breccias, limy chert pebble sandstone, local marble and skarn.
Gradational and sharp
Middle? to Upper Sharpstone conglom• Angular chert pebble conglomerate, Triassic erate sequence as beds and lenses, interbedded with 2000' maximum argillites, mudstones, siltstones, and water-laid tuffs. Includes the maroon coloured limestone cobble conglomerate or "Puddingstone" and "Rawhide Shale". Unconformity-
Paleozoic Permian and/or Anarchist group, Intensely sheared and fractured penn. thickness unknown. cherts, quartzites, phyllites, cherty argillites and black massive argillites; greenstones, locally quartz-mica schist; undivided argillaceous and siliceous hornfelsed meta- sediments.
Faulted contact
Early Paleozoic Grand Forks and Layered paragneisses, minor marble, or Pre-Cambrian Monashee Group, amphibolites, quartzites, etc. thickness unknown. 12. the Grand Forks Group and the schists and phyllites of the upper portion of the Anarchist Group that in the Boundary District appears to overly the
Grand Forks Group. Parker and Calkins stated that the lower part of the
Tenas Mary Creek Group most likely correlates with rocks of similar lithology and gross structure in the vicinity of Grand Forks. Considering the Tenas Mary Creek Formation to be one continuous stratigraphic sequence, then one finds in the Grand Forks area the lowermost paragneisses (Grand
Forks Group) and the uppermost schists and phyllites (Anarchist Group) of this stratigraphic column in faulted contact with each other.
The Grand Forks Group contains gently dipping east-west gross struc• tures as do the Tenas Mary Creek rocks to the south. Contact relations with younger rocks in the map area are obscure for the Granby River
Fault forms the western boundary of the Grand Forks Group. The high-grade metamorphic rocks are believed either, the uplifted, deeply weathered basement on which the younger, less metamorphosed Anarchist rocks were deposited, or, as Parker and Calkins suggest, they may represent the lower more intensely metamorphosed portion of a continuous stratigraphic sequence stretching up into the upper reaches of the Anarchist Group.
Brock (1902) noted that the Grand Forks rocks resembled the highly metamorphosed rocks of the Shuswap complex; and Parker and Calkins (1964) also stated that the Grand Forks rocks appear continuous with high-grade schists and gneisses in the Orient region of northern Washington State, postulated as being pre-Cambrian in age and similar to the Shuswap terrain of southern British Columbia. The age of the Shuswap metamorphic complex and time of metamorphism is not well documented at present but 13.
Reesor (l970,p.73) in discussing the structural evolution and regional
setting in part of the Shuswap metamorphic complex, of which the Christina
Lake segment is part, felt that:
"rock involved in the gneiss complex are considered to be the stratigraphic equivalents of the Windermere (latest pre-Cambrian) and Paleozoic successions of the Purcell-Selkirk mountains. Deformation and metamorphism of these strata is post Mississippian (Milford Group) and possibly post Triassic (Slocan Group)".
Hence it appears that the Grand Forks Group can be as old as latest pre-
Cambrian age.
Anarchist Group
Previous mapping of the so-called "Anarchist Group" within the
Boundary District included a variety of sedimentary and volcanic rocks ranging in age from pre-Permian to Jurassic. Recently, Little (l965),
redefined the Anarchist Group as Permian and/or pre-Permian, highly
deformed and intensely fractured meta-cherts, argillites, phyllites,
schists and greenstones.
Anarchist rocks crop out only sparsely within the Grand Forks-Eholt map area:
1. immediately west of Grand Forks, north of the International
Boundary;
2. south of Fisherman Creek along the Canadian Pacific Railway
tracks - east of Baker Ridge; and
3. immediately east of the Shickshock and Sailor Boy showings at
the northeast corner of the map area. 14.
Anarchist rocks within the map area are divisible into two mappable units; a lower siliceous unit and an upper argillaceous unit. The lower siliceous unit consists of intensely fractured white to grey micro- crystalline chert and quartzite with minor quartz-sericite (?) schist.
Cherts are characterized by a slight foliation or micaceous (white mica) parting that parallels the original bedding (Parker and Calkins,1964), and a complete recrystallization of the chert and clear quartz filling the numerous criss-crossing fractures, giving the rock a cross-hatched pattern in outcrops. This foliated chert predominates in the southern area west of
Grand Forks where the foliation trends south-southeast, dipping moderately to the northeast. A similar chert unit also underlies the northern area east of the Shickshock and Sailor Boy showings. In this area, a thin dis• continuous band of grey chert pebble conglomerate is found interbedded with the white foliated chert unit. The pebbles, typically pale grey to black, are composed predominantly of grey chert and dark argillaceous chert set in a microcrystalline cherty matrix. The fragments are well sorted and sub-rounded.
Quartz-muscovite schists also crop out in the northern area immediately adjacent to the fault zone separating the siliceous unit from limestones to the west. Muscovite partings parallel the fault plane, dipping moderately to the west, and probably were formed during mechanical shearing associated with movements along the fault zone. Quartz-muscovite or sericite schists have been found closely associated with this lower siliceous unit throughout the Grand Forks area.
Several outcrops and bands of grey microcrystalline chert and chert 15.
pebble conglomerate are present in Anarchist rocks that crop out immed•
iately south of Fisherman Creek. These rocks, however, occur within a
major northwest trending fault zone that appears to have brought the
siliceous rocks from depth, and relationships between the individual blocks
and outcrops are obscure.
Little (1965), divided the Anarchist Group into six units. The
author's siliceous unit correlates with Little's map unit 2, which consists
of "bedded chert"* commonly with argillaceous partings, chlorite schists
and mica schists.
Overlying the siliceous unit with apparent conformity, although with
obscure contact relationships, is a relatively thin sequence of dark
argillaceous rocks ranging from black to grey well bedded argillites and black cherty argillites, with minor grey cherts, cherty siltstones and an angular chert pebble conglomerate. This argillaceous sequence correlates with Little's map unit 3. An extensive sequence of this black well bedded argillite, cherty argillite with minor interbedded dark shale, grey
chert and chert pebble conglomerate is found underlying the area adjacent
to the Canadian Pacific Railway tracks immediately south of Fisherman
Creek. These extremely fine-grained argillites occur as small elongated, fault bounded blocks, caught up in an extensive north-west trending shear s
zone, that obscur^ internal structure and relations between the outcrops, making correlations highly speculative. Several of these well bedded argillites are sheared. Present thicknesses of these argillaceous units are generally under 100 to 150 feet. Minor syngenetic pyrite and pyrrhotite (?) has been found conformable to bedding planes within the 16. dense black argillite, suggesting deposition in a deep restricted basin under quiet,reducing conditions.
The angular chert pebble conglomerate found interbedded with the black massive cherty argillites and well bedded argillites has been mapped as part of the Sharpstone Conglomerate sequence by the author, but may well be a conglomerate unit occurring within the Anarchist Group, as it contains numerous grey to black sub-rounded chert fragments, set in a cherty matrix. The fragments appear much more rounded, sorted, and homo• genous in composition than those typical of the Sharpstone Conglomerate cropping out to the south. The Sharpstone Conglomerate also has a greenish coloured chloritized matrix and is not composed of microcrystalline chert.
A much more detailed study is needed to separate these two conglomerate units.
Immediately west of Grand Forks a thin sequence of dark phyllite apparently lies with gradational contact, above the foliated chert unit.
Foliations and crenulations within the phyllite have the same north-north• west trend as in the underlying cherts. This phyllite is composed of sericite, chlorite and biotite parallel to claysize dark laminae, imparting a silky lustre. These micas, surrounding rounded to elongate broken quartz grains and laminae, suggest rotation and mechanical movement.
A thin, dark, well-bedded argillite unit is found underlying the
Sharpstone Conglomerate sequence east of the siliceous unit at the north• eastern corner of the map area. The bedding within the argillite appears conformable to the overlying Sharpstone Conglomerates and as the argillites appear relatively undeformed and unsheared, rather atypical of the 17.
Anarchist cherts to the west, this argillite unit may well be a strati• graphic equivalent of the Rawhide shales found by Seraphim, underlying the Sharpstone Conglomerate at Phoenix.
Little (1965) mapped a massive limestone unit with minor chert inter- beds, below the Knob Hill massive cherts and greenstones, south of
Phoenix. A similar unit of thin well-bedded argillaceous limestone crops out along the Canadian Pacific Railway tracks approximately 3,500 feet to
4,000 feet southeast of Goat Mountain. This 50-foot-thick limestone band occurs between two thin grey cherty siltstones and appears to underlie a thick? massive amygdaloidal basalt or greenstone which may be equivalent to the Knob Hill greenstone in the Phoenix area to the west. The basalt unit appears to be overlain to the west by the Triassic Brooklyn Limestone and lower Jurassic Fragmental Andesites, but contact relations are obscured by the numerous cross-cutting faults and a more detailed study is needed to separate the various limestone units and greenstones in this area.
Contacts between the Anarchist rocks and the older rocks are not seen in the map area, but appears to be faulted - the Granby River Fault separates the Anarchist rocks from the Grand Forks and Monashee gneissic terrain to the east. Parker and Calkins (1964) believe that the schists and phyllites in northern Washington, equated to the Anarchist Group in the Boundary District, form the uppermost strata of a continuous strati• graphic sequence from the Early Paleozoic Tenas Mary Creek Formation or
Grand Forks Group equivalent, up to the Permian schists and phyllites.
Contacts between the Anarchist rocks and the younger Triassic and Jurassic 18. rocks in the Grand Forks area are either drift-covered or faults, but most writers agree that the Triassic and younger layered rocks lie unconformably on top of the Anarchist rocks, the Sharpstone Conglomerate representing a basal conglomerate.
The Anarchist Group is believed to be Permian and/or earlier. Little
(1965) mentions possible Paleozoic fossils from several localities within the dark well-bedded argillites, his unit No. 3. Waters and Krauskopf
(l94l) postulate a Permian and possibly Pennsylvanian age for protoclastic border rocks surrounding the Colville Batholith near Orville, Washington, that have been correlated with the Anarchist rocks.
Deformation within Anarchist rocks is intense but internal struc• tures and degree of folding are obscured by the intense mechanical move• ment associated with the fracturing and shearing, and because of the general lack of good marker beds. Poor outcrop exposures and the great distances between these exposures within the Grand Forks-Eholt map area makes correlations difficult.
The Anarchist Group appears to by typical of the widespread Cache
Creek Assemblage as described by Campbell (1966). This assemblage is characterized by massive cherts, ribbon cherts, greenstones, black phyllites, schists, amphibolites and argillites, that were deposited in a quiet deep water, marine environment. The Cache Creek Assemblage is also characterized by intense fracturing and primari ly a lack of distinctive units or marker horizons and has an age range from Mississippian to Early
Triassic, similar to the Anarchist Group.(see Figure 8, p. 96).
Little (1957) also mentions the similarities of the Anarchist rocks 19. to the Mount Roberts Formation underlying the Rossland Formation some
30 miles east of the Grand Forks area.
Sharpstone Conglomerate Sequence
The Phoenix Sharpstone Conglomerate has been the subject of much controversy over the years. Early writers (Brock, LeRoy) classified the rock as a "jasperoid" and postulated derivation from limestone by a process of silicification. The calcareous matrix was believed to represent un• altered rock, the "fragments", the products of hydrothermal processes related to ore formation.
McNaughton (1945) preserved the jasperoid terminology and it remained in the literature until the term "sharpstone conglomerate" was first proposed by Seraphim (l956), wherin he presents reasons for assigning a sedimentary origin to this lithologic unit. Seraphim (1956, p.688), suggests a slight recrystallization of the quartz or chert accom• panying the subsequent metamorphism. Seraphim also lists several convinc• ing reasons for a sedimentary origin for the Sharpstone Conglomerate, summarized below:
1. The sharpstone conglomerate has a heterogeneity of colour,
structure, and composition of fragments that can not be
attributed to a metamorphic origin.
2. The rock is bedded; shale, impure limestone and siltstone
beds a few inches thick and hundred foot thick fragmental beds
have conformable contacts. The fragments are rudely aligned
parallel to the bedding. 20.
3. Several outcrops containing interbedded fragmental rock and silt-
stone or shaly siltstone show scour and fill structures. The
author also noted graded beds and cross bedding.
4. In fragmental beds that are stratigraphically close to the beds
of limestone, shale or siltstone, the chert fragments are smaller,
more rounded and better sorted in size than the chert fragments
in most fragmental beds elsewhere, usually occurring strati•
graphically below the former. This suggests longer transport or
some reworking or sorting.
5. The large rounded limestone remnants, mentioned by LeRoy, so
numerous in the jasperoid near the contact with the limestone,
are actually pebbles and boulders deposited with the chert
fragments. These limestone remnants are suggestive of rapid
transport.
The Sharpstone sequence encompasses a great variety of clastic rocks ranging from angular chert pebble conglomerate or "sharpstone conglomerate", to bedded and massive fine-grained argillites, mudstones and siltstones with minor interbeds of greywacke or fine-grained sharpstone conglomerate equivalents and minor water laid tuffs. Thin calcareous bands have also been noted within the upper argillite sequences.
This relatively thick sequence of coarse-to-fine-grained clastic debris rests unconformably on the Permian and earlier Knob Hill cherts and greenstone as mapped by Seraphim (1956) at Phoenix, and probably forms a basal conglomerate representing the unconformity separating the deep 21. water siliceous Anarchist rocks from the overlying shallow water clastic
"Sharpstone Conglomerate" sequence and Brooklyn Limestones (Figure 3, p.28
The sharpstone conglomerate is composed essentially of angular pebble
of white to grey microcrystalline chert, minor dark to light green lithic
volcanic and dark shaly fragments and rare jasper fragments set in a
finer-grained matrix of similar composition with minor micaceous, carbona•
ceous and some tuffaceous matter (Plate 1 and 2, p. 22). Angular
fragments average from T"-%" in diameter but locally can be larger and
commonly much smaller. The fine-grained matrix is extremely variable but
appears to be about 5-6 orders of magnitude smaller.
Changes in the composition and size of the angular pebble fragments are variable throughout the map area. The lithologic variations of the conglomerate fragments have not been studied to any great extent but a few general trends were noted. The thick Sharpstone Conglomerate sequence cropping out west of Baker Ridge and towards Phoenix contains a great abun dance of grey to white angular chert pebbles with minor dark green lithic volcanic and shaly fragments, and several brick red jasper pebbles,
(Plate l), probably reflecting a source from the more siliceous rocks of
Knob Hill cherts that underDie the Sharpstone sequence to the west and
south of Phoenix. Sharpstone conglomerates exposed northeast of Thimble
Mountain along the Canadian Pacific Railway tracks at the northeast corner of the map area, however, contain numerous dark greenish lithic volcanic fragments with minor light coloured lithic fragments and minor white chert or quartz fragments, probably reflecting a source from the Anarchist greenstones to the west. No jasper fragments were found. The Sharpstone 21. water siliceous Anarchist rocks from the overlying shallow water clastic
"Sharpstone Conglomerate" sequence and Brooklyn Limestones (Figure 3, p.28).
The sharpstone conglomerate is composed essentially of angular pebbles of white to grey microcrystalline chert, minor dark to light green lithic volcanic and dark shaly fragments and rare jasper fragments set in a finer-grained matrix of similar composition with minor micaceous, carbona• ceous and some tuffaceous matter (Plate 1 and 2, p. 22). Angular fragments average from T"-1T" in diameter but locally can be larger and commonly much smaller. The fine-grained matrix is extremely variable but appears to be about 5-6 orders of magnitude smaller.
Changes in the composition and size of the angular pebble fragments are variable throughout the map area. The lithologic variations of the conglomerate fragments have not been studied to any great extent but a few general trends were noted. The thick Sharpstone Conglomerate sequence cropping out west of Baker Ridge and towards Phoenix contains a great abun• dance of grey to white angular chert pebbles with minor dark green lithic volcanic and shaly fragments, and several brick red jasper pebbles,
(Plate l), probably reflecting a source from the more siliceous rocks of
Knob Hill cherts that underlie the Sharpstone sequence to the west and south of Phoenix. Sharpstone conglomerates exposed northeast of Thimble
Mountain along the Canadian Pacific Railway tracks at the northeast corner of the map area, however, contain numerous dark greenish lithic volcanic fragments with minor light coloured lithic fragments and minor white chert or quartz fragments, probably reflecting a source from the Anarchist greenstones to the west. No jasper fragments were found. The Sharpstone Plate 1: Typical bedded sharpstone conglomerate with distinct alignment of angular chert pebbles. Note large weathered pits still containing limestone cobble remnants, and an increase in maroon colour towards the top of the picture.
Plate 2: Sharpstone conglomerate showing pre• dominance of light green to grey angular chert pebbles. Several dark red jasper pebbles can be seen. 23.
Conglomerate occurring west of Grand Forks also contains predominantly- dark brown-black lithic volcanic pebbles, with very few, if any, light chert fragments. Within both the southernmost and northernmost localities just mentioned, the conglomerate pebbles and especially the finer-grained matrix have been noticably silicified and contain minor amounts of disseminated pyrite.
Sharpstone Conglomerates in the vicinity of Hardy Mountain appear very similar in composition to the conglomerate found west of Baker Ridge and along the Canadian Pacific Railway tracks east of Baker Ridge, but a decrease in pebble size is noted with an accompanying slight rounding of the pebbles southeast from the Phoenix cut-off road to Eagle Mountain.
The Sharpstone Conglomerate occurs generally as thick masses and lenses in the northeastern and western parts of the map area and displays sharp vertical stratigraphic boundaries and rapid lateral facies changes.
Sharpstone conglomerate typically occupies the bottom of the Sharpstone sequence but also occurs as thinner lenses higher in the sequence inter- bedded with the finer-grained greywackes and mudstone-siltstones. The conglomerate appears to thin and pinch out southeast of Eagle Mountain, where thin bedded argillites and mudstone predominate.
West of Baker Ridge, north of Thimble Mountain and at Eagle Mountain, the basal sharpstone conglomerates show a marked upward decrease in the proportion of coarse clastic fragments. The sharpstone conglomerate, therefore, grades upwards into the finer-grained argillites, mudstones, siltstones with minor intercalated greywacke bands, frequently showing scoured bottom contacts. Higher in the sequence the fine-grained 24.
argillites are typically well-bedded and continuous, reflecting a
relatively quiet environment of deposition.
Greywackes are typically a finer-grained equivalent of the sharpstone
conglomerate, the fragments appear more rounded and smaller, probably re•
flecting a reworking of a previous conglomerate source or a less rapid
deposition and more distant source.
The argillites, mudstones and the finer-grained matrix of the
sharpstone conglomerate are composed predominantly of microscopic clastic
quartz, feldspar and lithic fragments mixed with abundant clay-size
particles aligned roughly parallel to the bedding. The finer-grained
matrix contains abundant alteration shreds of chlorite and minor sericite,
carbonate and possibly pyrophyllite? The overall great abundance of
chlorite, up to 25-30% of the matrix in places, imparts a prominant
greenish colouration to the rocks that is so characteristic in the Grand
Porks area.
Near the top of the Sharp: tone sequence, an increase in carbonate
material is noted and in several places, such as immediately southeast of
Eagle Mountain, several distinct 20-30 foot thick bands of white recrys-
tallized limestone have been found interbedded with the argillites.
Similar thin carbonate bands have been found within the maroon coloured
mudstone-siltstone along the highway immediately west of Baker Ridge.
A maroon coloured angular chert pebble conglomerate and mudstone,
siltstone, carbonaceous rock sequence, lithologically identical to the
Sharpstone Conglomerate sequence, occupies the upper stratigraphic posi•
tion within the Sharpstone sequence south of the Phoenix road junction 25. and along the Canadian Pacific Railway tracks immediately north of Neff
Creek. Called "Puddingstone" by the oldtimers, this rock derives its name from the large white rounded limestone cobbles set in the maroon coloured angular chert pebble conglomerate matrix that appears to occupy a certain stratigraphic horizon near the top of the conglomerates underlying the argillites (Plate 3 and 4, p. 26). These limestone cobbles help to out• line the bedding.
Several outcrops show the clear transition from a green colour to this typical maroon or dark red-brown colour up strata, (Plate l). The maroon colour results from finely disseminated hematite or oxidized iron and suggests formation under oxidizing conditions. This maroon colour is also typical of the overlying limestones which thin and pinch out immediately west of Baker Ridge and appears to represent an ancient oxidized erosion surface roughly underlying Baker Ridge. Similar maroon coloured argillites have also been noted within the Phoenix open pit and might represent a similar erosion surface. On the other hand, it could represent oxidation conditions produced from hydrothermal alteration associated with ore formation at Phoenix.
Large rounded, white limestone cobbles, generally less than 1 foot across, so characteristic of the "puddingstone", are also found in several localities occupying a similar stratigraphic level within the sharpstone conglomerate(Plate 1, p.22): along the abandoned railroad grade some 5>000 feet northwest of Hardy Mountain; weathered limestone pits are found paralleling the bedding of the Sharpstone Conglomerates underlying Eagle
Mountain; skarnified limestone boulders also occur within the sharpstone Plate 3: Typical "Puddingstone" or limestone cobble conglomerate from exposure along Canadian Pacific Railway tracks north of Neff Creek. The white rounded limestone cobbles are aligned roughly parallel to bedding.
Plate 4: A thin lens of sharpstone conglomerate interbedded with a maroon-coloured fine• grained wacke of the uppermost "Puddingstone" sequence, found west of Baker Ridge. 27. conglomerates immediately west of Grand Forks. These limestone cobbles appear to decrease in size and increase in roundness towards the south• east from the Fhoenix road junction to Eagle Mountain, suggesting a similar source, from the west or northwest and an increasing distance of transport to the southeast.
Most writers believe the sharpstone conglomerates are derived from the cherty sediments of the Knob Hill series (Anarchist Group), with local variations in the amounts of lithic, volcanic, sandstone, minor shale and jasperoid fragments depending on the lithology of the source e.rea.
The thickly bedded sequence of angular conglomerate probably repre• sents rapid accummulation of talus deposits on a steep fault scarp formed at the edge of the shallow Triassic sea (Figure 3» p.28). These ancient fault scarps appear to have been northerly trending structures with the downdropped block tilting westerly. With, a rapid inpouring of coarse clastic debris from the west, a large talus or deltaic pile of sharpstone conglomerate formed against the western edge of this scarp. Farther from the source, within the basin (to southeast), the conglomerate lenses thin rapidly and fine-grained greywackes, mudstones, siltstones and well-bedded argillites interfinger and intercalate with the conglomerates. The finer sediments become more prominent farther out into the basin, representing a more quiescent environment of deposition. Some fine-grained water laid tuffs have been found associated with the argillites and probably repre• sents ash from nearby volcanic activity.
As the basin filled and the source area became eroded, the sediments deposited became finer and finer-grained, marked by siltstone, mudstone, Figure '3 Idealized diagram of the formation of a Triassic marine
basin and the related depositional sequence of
Sharpstone conglomerate and Brooklyn limestone. 29. argillite sequences, overlying the conglomerates. Near the top of these finer sediments, carbonaceous bands increase in abundance, being typically light tan coloured and microcrystalline with carbonaceous matter- sugges•
tive of shallow water deposition under saline conditions.
The Sharpstone Conglomerate appears to be thickest at or near Phoenix, approximately T mile west of the edge of the map sheet, where Seraphim
(l956) quotes a total thickness of 2000 feet. A large Sharpstone
Conglomerate body found immediately west of the southern Provincial High• way west of Baker Ridge dips moderately to gently to the east and here reaches approximately 2000-2500 feet in thickness, with some 500 feet of finer mudstone and siltstone overlying the conglomerate. A similar
Sharpstone Conglomerate band occurring west of the Canadian Pacific
Railxray tracks at the northern edge of the map area is also approximately
1200-1500 feet thick, with another 200-300 feet of fine siltstone over• lying the conglomerate. Throughout the remainder of the area the Sharpstone
sequence is not found completely intact mostly because of block faulted contacts.
The Sharpstone Conglomerate, as already mentioned, pinches out to the
SE of Eagle Mountain and in the vicinity of Goat Mountain and to the south is probably represented by several thin lenses of green to brown mudstones or argillites interbedded with the thicker well bedded argillaceous
Brooklyn Limestone. These argillite bands seldom reach thicknesses greater than 10-20 feet. One block of argillaceous limestone found at the western contact of the gabbro body northeast of Hardy Mountain and possibly brought up from depth along the steep fault zone shows a 40-50 foot 30. argillite bed between two bands of bedded argillite limestone.
Little (1965) mentions that a fossil of Middle to Upper Triassic
Age was found by Thorpe within the Rawhide Formation, which according to
Seraphim (1956) occurs at Phoenix as a thin unit of local lateral extent at the base of the Sharpstone Conglomerate. This puts a maximum age of
Middle to Upper Triassic for formation of the sharpstone basin of deposi• tion, and the author feels that the shape and thickness of the Sharpstone
Conglomerate sequence found in the Grand Forks area, suggests a very short time interval of formation, probably well within several million years.
Sharpstone Conglomerate lenses and bands associated with overlying limestones, similar to that exposed in the Grand Forks-Eholt map area have been found in several isolated, discontinuous areas throughout the southern Boundary District (Newell, 1969): south of Bridesville, some 38 miles west of Grand Forks; the Midway window and at the Deadwood Camp, west of Greenwood, B.C. are several such examples. Dr. W.H. White
(personal communication, 1970), also mentioned similar conglomerates within the Franklin Camp, some 40 miles north of Grand Forks along the
Granby River.
Brooklyn Limestone
The Brooklyn Limestone conformably overlies the Sharpstone
Conglomerate sequence in the map area. The contact is gradational, con• sisting of a gradual increase in carbonate and a decrease in argillaceous matter upward in the sequence, until finally calcium carbonate prevails.
This probably represents a complete inundation of the shallow Nicola Sea. 51.
The Brooklyn Limestone Formation in the Grand Forks-Eholt area is
divisible into three distinct lithologic units.
The lowest unit lying conformably and gradationally above the well-
bedded argillites and siltstones of the Sharpstone sequence consists of a
white to tan rounded chert pebbly to sandy limestone. These chert ovoids
form Seraphim's (l956, pp. 689) "Peanut Brittle Limestone" and which are
typically well rounded, frosted, white to pale grey chert fragments, l/8
to l/4 inch in diameter set in a white to tan limestone matrix and, as
Seraphim noted, is strongly suggestive that the chert ovoids are windblown
pebbles: hence the term"Aeolian limestone" (Plate 5, p. 34). Generally
the chert sand grains are evenly disseminated throughout the limestone
but in places have been found concentrated along bedding planes and some•
times as streaks along planes of high shear. The sand grain content
generally is about 10-15$ of the limestone, but a 60$ content has been
found in the limestone just north of the Phoenix road turn-off.
Sand grain concentrations along bedding planes and cross-bedding are
suggestive of strong current action, near shore, deltaic depositional
environment. The frosted ovoid chert grains were probably wind lofted(?)
from a near shore dune or beach deposit.
Thickness of this sandy limestone member is quite variable but
appears to be maximum near Phoenix and immediately to the east, where it is
about 100 feet thick. This member appears as a lens that thins rapidly to
the southeast, being about 20 feet thick just north of Hardy Mountain.
A 5 foot band within dark argillaceous limestone, immediately north of
Hardy Creek, probably represents re-working of these chert sand grains. 32.
The "aeolian limestone" appears to grade upwards into a tan to white dense microcrystalline limestone generally devoid of any primary struc• tures. Microscopic argillaceous matter forms about 5-10$ of this unit.
Total thickness of this unit is unknown, but does not appear to be greater than several hundred feet thick.
Limestone breccias occur within this stratigraphic unit in several localities throughout the northern part of the map area and probably reflect slumping or cataclastic breccias associated with contemporaneous faulting within the basin of deposition. These breccia fragments are angular to sub-rounded elongate slabs, and range in size from several inches to several feet across, but generally less than one foot. The breccia fragments are closely packed and cemented together by a fine• grained carbonate matrix carrying much clay and sand-size fragments of similar composition to the larger fragments. Thicknesses of these breccias are not known but they appear to be 50 to 100 feet thick and quite restricted in lateral extent. A good exposure of a typical breccia can be found along the southern Provincial Highway about one mile south of the
Oro Denoro workings.
The second mappable limestone unit is a distinct continuous sequence of well banded limestone that conformably overlies the sandy and micro- crystalline units. These bands are pale buff-brown to greenish-brown and form thin continuous layers that range in thickness from less than l/8 inch to 6 inches, but average about one inch or less. The frequency of these bands also varies considerably. The bands are composed, generally, of a microcrystalline argillaceous to tuffaceous matter, very rarely 33.
cherty, vrith a minor carbonate matrix and form characteristic resistant
ridges in outcrop in contrast to the less resistant pale buff coloured
microcrystalline limestone that houses these bands (see Plate 6, p.34).
Total thickness of this banded limestone unit is variable through•
out the map area and appears best developed and thickest near the southern
part of the map area, west of Grand Porks, between the intrusive bodies,
where it appears to be about 100 feet thick.
This thin-bedded limestone unit could very well be a transitional or
offshore facies of the nearshore fine-grained microcrystalline limestone
because in the southern part of the map area the banded limestone sits on
top of a cross-bedded sandy limestone unit.
A thick sequence of massive to well bedded grey to black argillaceous
limestone, stratigraphically overlying the well banded limestone, forms
the third and uppermost limestone unit. Contact relations with the under•
lying limestones have not been observed but are presumably gradational and
could be abrupt (?).
A typical argillaceous limestone, dark grey to black on a fresh
surface, weathers light grey and is composed of fine-grained to micro•
scopic, thin,black to dark brown argillaceous laminae that parallel bedding planes and is set in a microcrystalline calcareous matrix. Several large,
1 mm diameter, rounded to elongate re-crystallized crinoid stems and other bioclastic fragments are found roughly paralleling the bedding. The amount of argillaceous matter in these carbonates is variable. South of
Hardy Creek and along the highway in the lower reaches of July Creek, the Plate 5' "Aeolian limestone" or Seraphim's "Peanut Brittle" limestone forming the basal section of the Brooklyn Limestone NW of Baker Ridge. Note alignment of the frosted chert ovoids.
Plate _6_: Brooklyn Limestone, thinly bedded, well banded unit from area immediately west of Grand Forks. Thin more resistant beds are tuffaceous and impure limestone. 35.
limestones are typically black, thin bedded, shaly and fissile, with a well developed slaty cleavage. Intrafolial folds have been noted (Ross,
1970). The more massive argillaceous limestones are frequently strongly fractured and irregularly veined by white to pale calcite. Graded bedding and numerous minor folds (Plate 13, p. 77 ) are well developed within the bedded argillaceous limestones and the banded limestones below, and almost all of the Triassic fossil evidence to date has come from these litho• logic and stratigraphic units. Fossil locations and descriptions are given in Appendix II.
Total thicknesses of the Brooklyn Limestone vary considerably through• out the map area from a maximum of about 2000 feet (Seraphim, 1956) near the northwest corner of the map area to a minimum total stratigraphic thickness of 100-150 feet immediately south of Goat Mountain (SE corner of the map area). Here the Brooklyn Limestone is comprised almost wholly of massive to well bedded argillaceous to shaly limestone, with a 5-8 foot bed of chert pebble to sandy limestone present near its eastern or lower boundary. It appears to lie on a very thin veneer (25 feet thick) of fine-grained argillite or water laid tuffaceous argillite which probably represents the scant presence of the Sharpstone sequence.
This decrease in thickness and increase in the dark argillaceous matter within the Brooklyn Limestone sequence towards the southeast of the map boundary suggests a quiet, deep water deposition farther out into the basin of deposition. On the other hand, some of the thinning of the
Brooklyn Limestone is attributed to pre-Fragmental Andesite erosion sur• faces such as that depicted by the less than 50 foot limestone band 36. immediately east of Eagle. Mountain, and especially to the west and beneath Baker Ridge where the limestone completely pinches out to the southeast and the andesites directly overlie the "Puddingstone".
In the northern part of the map area in the vicinity of the R.Bell,
Bluebell, Mt.Rose and Swallow showings, where the Brooklyn Limestone crops out in the vicinity of intrusive masses, the massive limestones occur as coarse to fine-grained, white recrystallized limestone or marble. The limestones are generally fractured and quite granular due to re-crystalli• zation, hence, primary structures are obscured. In the immediate vicinity of several large granodiorite or quartz-diorite masses, the Brooklyn massive argillaceous limestones occur as fine-grained hornfelsed marble.
Complex calc-silicate skarns intimately associated with copper mineraliza• tion throughout the Summit Camp are found localized adjacent to several granodiorite - or quartz-monzonite masses. A detailed description of
Skarn and related copper mineralization is given in Appendix I.
Present fossil evidence suggests that the Brooklyn Limestone ranges in age from Middle to Late Triassic. Little and Thorpe (l965) state a
Middle Triassic age for their Brooklyn Limestone equivalent on the basis that it contains Dapjiella and that the Rawhide Formation, conformably below, contains Middle to Upper Triassic fossils. Upper Triassic (Norian) corals have been found by Little (l965) in a massive limestone associated with the author's "Puddingstone" conglomerate which lies conformably below the Brooklyn Limestone.
In Lower July Creek, grey shales interbedded with argillaceous lime• stones are, according to Newell (1969), identical to the Upper Triassic 37.
pelecypod HaJ^obia •» bearing beds found some 5 miles to the south near
Lanville, Washington. The author also found shell fragments that appear
to be r^gnella or HaJ^bia within the Brooklyn Limestone along the south•
ern Provincial Highway, north of the Phoenix road turn-off.
A rather tiny, primitive, ceratitic ammonoid, tentatively correlated with P^raEP^ajnjp^exas or Megaphyllites (Figures 9 and 10, pp. 113 , 114 ) by the author, was found in a thin shaly limestone unit some 2500 feet
south of Goat Mountain. A detailed description of this ammonoid is given
in Appendix II. Tozer (l970, personal communication) gives an age range
of late Middle Triassic (Anisian) to middle Upper Triassic (Norian) for
Megaphyllites, which suggests that this thin limestone unit is at least a time equivalent of the Brooklyn Limestone Formation.
Possible outside correlations may be calcareous sediments of the
Triassic Slocan Group to the northeast, and the Old Tom, Shoemaker
Formations of the Oliver/Keremeos area in the southern Okanagan District
(Ross, 1970).
The possibility exists that more than one limestone sequence makes up the Brooklyn Limestone as mapped by the author. Several thin limestone beds have been mapped at Eagle Mountain intercalated with the upper part of the Sharpstone sequence. Several thin limy beds are also found within the upper part of the Puddingstone argillites near the Phoenix turn-off.
Seraphim (l956) describes several lenses of limestone breccia or angular conglomerate intercalated with his upper Sharpstone sequence at Phoenix.
However, these units appear to be very similar to the angular limestone cobble conglomerate or Puddingstone sequence mapped by the author to the east. 38.
Fragmental Andesites
The term "Fragmental Andesite" has here been coined to include a host of clastic and massive Jurassic andesite, agglomerates, flow breccias and porphyritic andesite flows with minor tuffs and pillows. The andesites incorporate a good portion of the trachytic andesites and the pyroclastic fractions of Carswell's (l957) "Eholt Formation".
For the most part these fragmental andesites unconformably over] ie the Brooklyn Limestones and Sharpstone sequence and appear to have been deposited on an uplifted erosion surface of the Triassic sediments.
However, slightly altered andesite pillows overlying the limestones in one locality suggest in part, conformity or continuous deposition of the andesite with the Triassic sediments.
Massive andesites are prevalent throughout the map area but more prominent in the vicinity of Goat and Hardy Mountains. Here the andesites are massive, coarse to medium-grained, porphyritic, slightly trachytic, dark to moderate avocado green rocks with prominant straight blocky joint surfaces forming angular outcrops. Laths of plagioclase phenocrysts are typically buff to tan, generally 2 mm in length, set in a dark green fine-grained matrix. These laths make up about 30$ of the rock and the remaining fine-grained matrix is composed of about 10$ hornblende.
Plagioclase phenocrysts are clouded with fine-grained sericita, epidote and minor carbonate, imparting a creamy speckled appearance in hand specimen. The centres of the phenocrysts are almost completely altered - making composition determinations impossible. Chlorite, epidote, 39. and minor carbonate occurs ubiquitously throughout the fine-grained matrix, imparting the typical pistachio to dark green colour characteristic of the andesites throughout the Grand Pork-Eholt area. Total alteration; chlorite, epidote, sericite, carbonate, and minor pyrite in places reaches as much as 30$ of the whole rock. Hornblende crystals, found in places making up to 20$ of the rock, can occur as subhedral grains sometimes as large as the plagioclase laths.
A maroon porphyritic andesite forming a flow top underlying the
Tertiary Kettle River sediments at Baker Ridge carries up to 50$ plagio- clase laths, 15$ finely disseminated opaques (hematite or oxidized iron) and 20$ hornblende. About 1-2$ minor quartz and potash-feldspar have been noted. The remainder of the rock is composed of the all pervasive chlorite, epidote, sericite, and carbonate, alteration products.
Some of the massive andesites such as in the vicinity of Hardy
Mountain are very coarse-grained (plagioclase, hornblende) and can be mistaken for the coarse-grained diorites found in several places within the map area.
Pyroclastic or flow breccias occur, ubiquitously throughout the map area and form by far the greater percentage of the andesites. They occur as thick piles (?) that grade into the more massive andesites and no distinct boundaries have been found. Even the more massive andesites under close scrutiny generally contain some minute fragments or ashy particles. These breccias are typified by sub-angular to sub-rounded volcanic fragments of variable size, composition, and colour set in a massive, dense to slightly porphyritic fine-grained matrix (Plate 7> p.4l).
The fragments range in colour from pale grey through dark and light greens 40.
to brown-green, and themselves are porphyritic to massive, generally
very similar to the host. The size of the fragments is variable from large
rounded boulders (Plate 8, p. 4l) to microscopic, but for the most part
average about T to 1 inch in diameter and generally compose less than 10$
of the rock. Up to 70-80$ breccia fragments have been observed in several
localities throughout the map area. The matrix surrounding the fragments
is typical of the more massive dense andesites with a slight addition of
glass and tuff fragments. Invariably, patches of pale green epidote
alteration can be observed surrounding some of these fragments, and
probably represent deuteric or autometamorphism (Plate 7, p.4l).
Agglomerates have been found in several localities within the map
area. That cropping out along the highway in the southern reaches of
July Creek is the most spectacular (Plate 8, p. 4l). Here, large rounded
to oval-shaped dark green andesite cobbles up to 1 foot in length occur
tightly packed and surrounded by a much finer pyroclastic and tuffaceous matrix. A slight foliation of the elongate cobbles hints of flow
directions (Plate 8). The thicknesses of these clastic piles are not known but appear greater than 30 feet and probably about 50 feet.
What appear to be pillows of slightly altered andesite are found at
the basal part of the Fragmental Andesite sequence overlying the skarni-
fied Brooklyn Limestone along the Canadian Pacific Railway tracks north of
Fisherman Creek. The pillows, relatively small, slightly elongate and about 10-14 inches in length are flattened parallel to the limestone
contact - dipping steeply to the west. These pillows are continuous for a thickness of 15 to 20 feet then appear to grade into a dense fragmental 41.
Plate 7: Typical fragmental andesite from Goat Mc ntain. Note several large rounded porphyritic fragments and the light green-yellow epidote and chlorite alteration.
•I
Plate 8: Spectacular andesite agglomerate outcropping along the southern Provincial Highway in the July Creek Valley. Camera case - extreme left for scale. 42. andesite. Below the base of the andesite pillows numerous 1-2 foot thick tuffaceous beds are found interbedded with the limestone. The pillows are indicative of subaqueous volcanic activities and probably represent an inpouring of andesitic lava into a carbonate basin as the pillows appear quite conformable with the underlying skarnified limestone.
Fragmental Andesites are characteristic in appearance and can quite easily be distinguished from the older Anarchist greenstones and basalts.
The andesites are generally lighter shades of green, fragmental, blocky and quite massive in outcrop, as opposed to the intensely sheared and metamorphosed Anarchist greenstones. Stratigraphic position is also an indication. However, in intensely sheared and faulted areas such as sur• rounding the serpentine bodies, the andesites appear as greenstones that could well be mistaken for Anarchist rocks. Such an example is the green• stone immediately south of the serpentine body that crosses the highway south of the Phoenix turn-off.
Problems arise near the northern edge of the map area where porphy• ritic diorite or quartz-diorite intrusive rocks become prevalent. Some of these greenish coloured fine-grained feldspar-porphyry intrusions or hypabyssal intrusive rocks have a slight trachytic texture and can easily be mistaken for andesite flow rocks such as those on the western slope of
Baker Ridge. The outlier of volcanic rock overlying the Brooklyn Lime• stone south of Oro Denoro may be a case in point. A similar situation occurs immediately north-northeast of the Bluebell showing, where the fine• grained, trachytic textured rock appears identical to the trachytic ande• sites underlying Baker Ridge. A detailed petrographic study is needed to 43.
solve this problem.
The total thickness of the Fragmental Andesites is not known and
appears to be quite variable. Tertiary continental sediments and volcanics
unconformably overlie the top of the andesites, suggesting an erosional
contact between the two. Since the Tertiary cover is missing in most
places, much of the andesites may also be eroded. Baker Ridge is one of
the few places that shovsboth the top and bottom contacts and here the
Fragmental Andesites are only about 500-1000 feet thick. Throughout the
map area the andesites appear to be less than 2000-2500 feet thick. The
general lack of stratigraphic markers and later fracturing and settling
greatly hinder any thickness measurements within the andesites.
The more massive andesites probably represent the centres of flows
that have had time to crystallize before solidification, and the fragmental
andesites or breccias probably represent flow tops or pyroclastic
ejections. In several places some of the fragments are reddish-brown
possibly due to oxidation of the iron content upon exposure to atmosphere.
Tuffaceous matter in the matrix also indicates that exhalation processes
wee involved. Some of the andesite flows must have poured into shallow car• bonate depositional basins as suggested by a thin sequence of pillows
forming the basal part of the Fragmental Andesites found overlying the
limestones in one locality. Thin tuffaceous beds within the underlying
limestone suggest that volcanic exhalations had been present for some
time before the outpouring of lava.
Little and Thorpe (1965) state that these andesites megascopically
resemble the Rossland Formation of Lower to Middle Jurassic age, found 44.
some 35 miles to the east of Grand Forks-Eholt area. Campbell (1966)
includes the Nicola volcanic and Rossland Formations in his widespread
Takla-Hazelton Assemblage (Late Triassic to Middle Jurassic), and since
the Fragmental Andesites of the Grand Forks area resemble the Rossland
volcanics, the Fragmental Andesites may well reflect the late spread of
the Nicola volcanic activity to the southeast during Middle Jurassic
time. The (Middle Triassic) Sharpstone Conglomerate - Brooklyn Limestone
sequence and overlying (Middle Jurassic) Fragmental Andesites appear to
correlate with the widespread (Middle Triassic-Middle Jurassic) Takla-
Hazelton Assemblage as described by Campbell (l966, pp.63-64). (See
Figure 8, p. 96 )
Tertiary Layered Rocks
Kettle River Formation
Since much of the field work was spent outside the Tertiary cover
most of the data herein is taken from Monger (1968) and Parker and
Calkins (1964). For a detailed description of the various Tertiary rock
units and their relationships the reader is referred to Monger (1968).
For occurrences of Tertiary stratified rocks and intrusive activities in county N-Washington State, the reader is referred to Parker and Calkins
(1964).
The Kettle River continental sediments crop out in three localities within the map area, namely: Baker Ridge*, • Thimble Mountain, immediately
north of Fisherman Creek} and an isolated locality immediately north of
Wilgress Lake. These sediments overlie the Mid. Jurassic Fragmental 45.
Andesites unconformably and as yet have not been found overlying rocks older than this. At Baker Ridge, the Kettle River sediments and younger
Marron volcanics occur in a gently warped syncline draped over an east• ward tilting block of older Andesites. As Monger states, the Kettle
River sediments are everywhere overlain by the younger Marron volcanics, except where erosion has proceeded below the stratigraphic level of the volcanic rocks. The basal contact of the Kettle River sediments at Baker
Ridge is a depressed area and distinguishable on aerial photographs.
Individual flow contacts within the overlying Marron volcanics also have a pronounced topographic expression.
The Kettle River sediments, according to Monger (1968), are composed dominantly of feldspathic volcanic sandstones, lithic volcanic sand• stones and finer-grained equivalents of these. Minor tuffs of inter• mediate composition (dacite) and locally shales and conglomerates also occur. Monger's basal conglomerate is not present at Baker Ridge where the preponderance of the Kettle River sediments are feldspathic volcanic sand• stones.
The feldspathic volcanic sandstones, forming the lower part of the
Kettle River Formation are composed of sand-size grains,1-2 mm in diameter, of feldspar (in part plagioclase in order of An^ 45^' anc* su*>ordinate quartz. In outcrop, the sandstone or arkose appears white to pale grey and has much the appearance of a granite, the clastic crystal fragments being angular and fresh. The rock is typically structureless and thick bedded with a few feet of tuffs and conglomerates present at all strati- graphic levels. The tuffs are pale grey, dense and generally thin bedded. 46.
Conglomerates found at Baker Ridge form a 20 foot thick section, the composition of the boulders is variable ranging from granitic to volcanic.
The upper grey to brown weathering lithic volcanic sandstone unit noted by Monger (1968) appears to be missing in the Grand Forks-Eholt map area.
Monger cites four sources for the derivation of the clastic Kettle
River sediments:
1. acid volcanic rocks supplying volcanic feldspars and quartz;
2. intermediate volcanic rocks;
3. basement rock - granitic detritus;
4. intraformational shales supplying shale chips; and the possibility of conglomerates formed from contemporaneous faulting has been suggested.
The local relief at the time of formation must have been considerable judging from the size of conglomerate boulders,and the rate of accumula• tion must have been rapid judging from the relative angularity of the clastic fragments and the thickness of the individual beds. The thin shale sequences probably represent local intraformational shallow(?) depositional basins. Contemporaneous faulting probably aided to the continual uplifting of the source areas.
Monger believes the original thickness of the Kettle River sediments to be about 2000 feet in the southern part of the Boundary District, but only about 1,200 feet is present at Baker Ridge, and much less throughout the remainder of the map area. LeRoy (1912) estimates a thickness of only
260 feet at Phoenix, to the west.
Both plant fossils and radiometric ages indicate that the Kettle 47.
River Formation is of Kiddie Eocene age and Monger (l968) cites various
lines of evidence for this.
Clastic rocks of Early Tertiary age, lying unconformably on top of
pre-Tertiary rocks, crop out in relatively small isolated areas across much of south-central British Columbia, and northern Washington. Equiv• alent rocks have been described as far north as the Franklin Camp, some
30 miles north of the city of Grand Forks (Drysdale, 1915). In northern
Washington, Parker and Calkins (1964), have demonstrated the presence of
Eocene(?) pyroclastic and sedimentary rocks called the O'Brien Creek For• mation as far as 50 miles south of the Grand Forks map area and consider
them roughly equivalent to the Kettle River Formation. Church (l967s p.
25) in discussing possible correlations to the Early Tertiary Spring- brook Formation from the White Lake area in the Southern Okanagan District, mentioned:
Kettle River Formation - (Midway area)
Curry Creek Formation - (Beaverdell area)
Coldwater Formation - (Kamloops area)
Allenby Formation - (Princeton area)
O'Brien Creek Formation - (Republic area, N. Washington State).
Marron Volcanic Formation
The author uses the terminology applied by Monger (l968) and the
Marron Formation incorporates the Midway Volcanic Group (Daly, 1912), and
the Phoenix Volcanic Group (Little, 1957). Again the reader is referred
to Monger (1968) for a more detailed account on the Marron Formation in 48.
the Boundary District. No attempt was made in the field to subdivide the
Tertiary volcanic rocks of the area. This has been done in some detail by
Parker and Calkins (1964) in northern Washington and recently in the
Greenwood map area to the east, by Monger (l968).
Within the Greenwood map area, the Marron Formation is a well strati• fied sequence of extrusive rocks of porphyritic andesite to trachyte composition, with minor intercalated beds of pyroclastic material. Basalt is present locally.
Near Grand Forks, the Marron Formation occurs at several localities as an east-dipping succession of flow rocks lying conformably on top of the early Tertiary Kettle River sediments; as at Baker Ridge. At Thimble
Mountain, Marron volcanics directly overlie the folded Triassic sediments with marked disconformity and is believed in faulted contact. Several other outcrops of Tertiary volcanic rocks are found in the vicinity of
Wilgress Lake that have been mapped as Marron Formation.
Division 4A which forms the lower division of Monger's Marron Forma• tion, is composed predominantly of sodic trachytes approaching phonolite in composition. All are porphyritic and phenocrysts of feldspar are in• variably anorthoclase and/or orthoclase. Monger recognizes 5 main litho- logic varieties in division 4A. They are in order of decreasing age:
1. basal lavas, local flow breccias and agglomerates;
2. pyroxene-feldspar porphyry and pyroxene-feldspar rhomb porphyry;
3. dark analcite bearing rhomb porphyry;
4. fine-grained feldspar porphyry.
The pyroxene-feldspar porphyry is the most common lithologic type 49.
in Monger's division 4A and forms much of the lower part of the Marron
Formation. Similar rocks occur at Baker Ridge directly overlying the
Kettle River sediments. Here the lower contact is not visible and
/occupies a depression that may well signifiy a basal flow breccia or
agglomerate.
The pyroxene phenocrysts are stubby, euhedral, dark green, and
generally about 5 mm long. In thin section they are colourless to very
pale green and have abnormally high birefringence for common augite.
Some pyroxenes enclose small apatite euhedra or opaque mineral grains,
and some mantle feldspars. The potash-feldspar phenocrysts are generally
smaller than the pyroxenes and are generally zoned with a core and mantle
of different composition. The cores are partly altered to carbonate and/
or sericitic white micas and numerous minute opaque inclusions, whereas
the mantles are fairly clean. Twinning is not common. Biotite has been
noted as small euhedra.
Amygdaloidal volcanic rocks, found locally by Monger, has also been
noted at Baker Ridge and the vesicles are here filled with a white to
pinkish zeolite(?).
The original thickness of the Marron volcanics in the Grand Forks
area is unknown since the upper surface is erosional, however a maximum
thickness of about 6000 feet has been mapped by Monger (l968) just west
of Greenwood, British Columbia. The Marron volcanics at Baker Ridge have
an apparent thickness of about 4000-5000 feet.
Evidence for the base of the Marron Formation being synonymous
(diachronous) with the top of the Kettle River Formation has been cited 50. by Monger (1968). He also states that the middle part of the Marron
Formation is of Middle Eocene age based on plant fossils collected by
W.H. Little and a radiometric age of 49+2 M. years from Mathews (l963) and 48+2 M. years on a syenite porphyry sill intrusive into Kettle River sediments. Monger believes that the syenite porphyry intrusive is equiv• alent to the trachy - andesites of his Middle Division (4B).
The Tertiary volcanic rocks described by Monger (l968), from the
Boundary District have been correlated with volcanic rocks of mid.-Eocene age widely dispersed across southern British Columbia, and according to
Church (1967), are comparable to the type section for the Marron Formation at the White Lake area in the southern Okanagan District. Church also states that the ages of the "Midway Group" (a Tertiary volcanic section found several miles west of the Grand Forks map area, that resembles the
Marron Formation) correlates with volcanic rocks of the Kamloops and
Princeton Groups, based on Potassium-Argon ages from Mathews (1964).
Early Tertiary (Eocene?) volcanic rocks extending over a wide area in northern Washington and termed "Sanpoil Volcanics" by Parker and
Calkins (1964) have been equated by Monger to his Upper Division (4C) of the Marron Formation. 51.
B. SERPENTINITES
Serpentinized ultramafic bodies in the Grand Forks-Eholt area occur typically along northwest trending, steeply dipping shear/fault zones
(Plate 9, p. 53). They form elongate, rounded, intensely sheared bodies that parallel the steeply dipping fault zones and in some of the larger bodies where the outer edges of the ultramafic body is intensely sheared, a characteristic dark to pale green polished surface or fish scale serpentine is well developed. The central core of the larger bodies are generally massive, less sheared and composed of a dark green to black dense matrix with several partially serpentinized relics of original pyroxene crystals (bastites?) present. The dense matrix in most cases is a micro• scopic felted serpentine mass.
Serpentine bodies cropping out in the vicinity of limestones contain mariposite, magnesite, talc, dolomite and other carbonate alteration products (Parker and Calkins, 1964). Some of these minerals were found by the author associated with a serpentinite southeast of Hardy Mountain.
A large serpentinized pyroxenite body crops out along the Provincial
Highway near the headwaters of July Creek, south of the Phoenix road turn-off. This large northwest trending body is composed almost wholly of large 4 inch long blades of dark green pyroxene intergrowths that have been fractured and partially serpentinized; minor chlorite has been noted along crystal faces. The outer edges of this body is also intensely sheared and serpentinized.
Serpentinite and pyroxenite bodies in the Grand Porks map area weather a characteristic dun to dark brown to sometimes black-green colour 52. and are devoid of vegetation except for moss, grasses, and lichens, providing easily mappable shear zone and fault trend. All of these serpentinites and pyroxenites are strongly magnetic and should show up on aero-magnetic maps of the area.
Several large northwest trending serpentinized ultramafic bodies have been mapped by Parker and Calkins (1964), west of Danville,
Washington, south of Grand Porks, that carry carbonate and quartz veins with galena mineralization. The serpentinite mass about 5000 feet west of Hardy Mountain, contains several vertical easterly-trending small quartz and carbonate veins with very minor galena mineralization.
According to Parker and Calkins (1964) these serpentinites are interpreted as having originated from an ultramafic intrusive, suggested by the presence of relict outlines of original crystals, fractures filled with serpentine, and the presence of chromitiferous magnetite(?) and pods of chromite. Little (1957) states that the serpentinized ultra- basic bodies intrude rocks of Late Paleozoic to Jurassic age and in turn are themselves cut by granodiorites and related rocks of the Nelson intrusion. No direct evidence for the age of these serpentinites was found by the author, but Parker and Calkins (l964, p.36) cite several convincing reasons from other areas that suggest a Late Triassic age for their initial intrusions. They state that"commonly however, the exposed serpentines ... are in sheared contact with Upper Triassic rocks and these bodies are considered to be "diapiric" intrusions or
"water melon seed" type cold intrusive ultramafic bodies that have been squeezed up along deep fault zones subsequent to the initial intrusions. ^ "*•»» '* '
Plate 9: Intensely sheared, steeply dipping serpentinite body found within a N¥ trending fault zone northeast of Hardy Mountain. 54.
The serpentinites in the Grand Forks-Eholt area exhibit such sheared contacts with rocks as young as the Eocene Kettle River sediments and appear typical of diapiric intrusions. This suggests that the steeply dipping fault zones containing these serpentine bodies have been inter• mittently active up to Middle Tertiary time.
C. INTRUSIVE ROCKS
Nelson Intrusions
Intrusive granitic rocks, defined by Little (l957) as Nelson
Intrusions, occur as several large bodies within the northern part of the map area and consist predominantly of coarse-grained equigranular to sub-porphyritic quartz-diorite or granodiorite. One such large body occurs as a tongue of coarse-grained granodiorite in the vicinity of the
Oro Denoro and Emma working that appears to extend westward towards the great expanse of similar granodiorite rocks north of Greenwood. Several smaller isolated plugs of Nelson granodiorite have been found in the southern and middle parts of the Grand Porks area, a marked contrast to the vast expanse of Nelson intrusive rocks that Little (1957) has mapped to the north, and probably indicates the dwindling effects of Nelson activities southward into the Grand Porks area. One such small granodiorite plug is found about 3000' northwest of Eagle Mountain.
The most abundant rock type within the map area is a leucocratic coarse-grained, slightly sub-porphyritic, hypidiomorphic-granular granodiorite. Microscopically the rock consists of: 55.
44$ tabular, zoned plagioclase, composition averaging
about An.rt 40
20$ small anhedral orthoclase grains
15$ large rounded quartz grains
10$ prismatic black hornblende
5$ biotite altered to chlorite and epidote and about 1% combined magnetite and pyrite. The hornblendes are elongate prismatic, can reach 1 cm in length, and in some cases impart a slight porphyritic texture to the granodiorite. Feldspars are in most cases strongly altered to sericite, white mica and minor carbonate and epidote, probably representing deuteric alteration. Minor chalcopyrite was found along small joints cutting the granodiorite intrusive north of Brown Creek.
A dark, fine to medium-grained diorite border phase of the grano• diorite is found in several localities along the granodiorite contact west of the Oro Denoro workings. Previous workers have considered this rock unit a more massive coarse-grained part of the Fragmental Andesite units, but the author believes that such a close association to the granodiorite contact and a separation from other areas underlain by inter• mediate and basic volcanic rocks, indicates some genetic relationship and probably represents a contaminated border phase. The diroite is mapped as a distinct unit.
Nelson granodiorites are found cutting all rocks Middle Jurassic and older in the Grand Forks area. Immediately north of Grand Forks, a grano• diorite body cuts through the Grand Forks gneisses. The large granodiorite body mentioned west of the Oro Denoro workings intrudes Brooklyn Limestone, 56.
Sharpstone Conglomerate sequence and Anarchist meta-cherts, meta-argillites and greenstones. The small granodiorite plug northwest of Eagle Mountain cuts the Lower to Middle Jurassic Fragmental Andesites, and hence the
Kelson granodiorite appears to be post Middle Jurassic in age. Parker and
Calkins (1964) assign a Late Jurassic to Middle Cretaceous age to similar
Nelson-type intrusives in northern Washington State. Recent radiometric studies by Sinclair et al (1968), have determined the emplacement of the northern part of the Nelson Batholith at about 160 M. years (at the base of Upper Jurassic).
The granodiorites found in the Grand Forks-Eholt area appear identical to the Greenwood stock to the west, mapped as a Nelson intrusion by Little (1957, 1965). W. Livingstone (1970, personal communication) mentioned that the so-called Nelson granodiorites from the Grand Forks area appear to be identical to rocks mapped by Little as the West Kettle
Batholith in the vicinity of Beaverdell, some 30 miles west of Grand Forks.
Valhalla Intrusions
Valhalla Intrusions are also medium to coarse-grained plutonic rocks, but are generally more acid than the Nelson intrusives. Granites and quartz-monzonites predominate and leucocratic varieties are abundant.
Valhalla intrusives can be distinguished from Nelson by the presence of smoky quartz, rarity of hornblende and an allotriomorphic granular texture, generally porphyritic (Little, 1957).
Valhalla rocks are found in only two localities within the map area.
An extremely small outcrop of very coarse-grained granite crops out about 57.
mile south of Oro Denoro along an abandoned railroad grade. Here the
coarse-grained granite has sheared contacts with the surrounding Brooklyn
Limestone. A large intrusive body found occupying the Granby Valley
immediately east of Fisherman Creek, about 3-4 miles north of Grand Forks,
is believed related to the Valhalla intrusions because of its very coarse•
grained allotriomorphic texture, roughly granitic composition (although
closer to a syenite) and the pink colouration of the orthoclase. However,
this intrusive could well be a syenite similar to the coarse-grained
Tertiary intrusives found by Parker and Calkins (l964) in Curlew county northern Washington.
Little (1957) states that the Valhalla is gradational with and
cross-cuts the Nelson Intrusives. Therefore it has here been assigned
a Late Jurassic age for emplacement, similar to the age of the northern
part of the Nelson Batholith (Sinclair et al., 1968).
Because of the scarcity and minute size of the exposures of Valhalla
intrusives in the Grand Forks area, they have been mapped with the Nelson
intrusives by the author, knowing that in a more detailed petrological
study these two rock types could be separated.
Diorites and Gabbros
This map unit includes various fine to coarse-grained dark basic rocks of variable ages and of obscure relations to other igneous rock
types in the area. They have been mapped together as a lithologic unit and contain basic rocks of variable compositions and probably reflect
several intrusive activities. They occur as numerous sirall diorite dykes 58. and plugs scattered throughout the map area - generally more prominant in the south; as a large northwest elongate, somewhat sheared, leucogabbro body closely associated with a serpentinite filled northwest fault zone centered about the middle of the map area, south of Baker Ridge; and as a dark medium-grained massive diorite forming the border phase(?) of the
Nelson granodiorite near the Oro Denoro workings.
As previously mentioned in discussing the Nelson intrusions, a medium to fine-grained dark green diorite crops out south of the Ore
Denoro workings and is believed to be a border phase of the Nelson granodiorite. Similar dark, fine to coarse-grained, sheared rocks have been noted at various locations along both the southern and northern contacts of the large granodiorite body. Previous workers had mapped such dark rocks as a coarser phase of the Jurassic basic and intermediate volcanic suite found in the area, but these diorites do not appear to carry the typical propylitic alteration, characteristic of the volcanic suite, and also they appear restricted to the granodiorite contacts and display intrusive contacts in places. The freshness in hand specimen, on the other hand, may suggest association with some Tertiary basic dykes found to the east.
A large,east-west,elongate,coarse-grained diorite body displaying chilled margins and intrusive contacts outcrops within the large tract of limestone west of Grand Porks. Near the centre of this body the rock is intensely fractured in a north-west direction. Several small north• east trending dykes were found within fault zones immediately south of this diorite body. Conformable contacts with the bedded limestone at the 59.
eastern contact may suggest that these coarse-grained diorites are in
fact coarser-grained massive volcanic flows associated with the Mid.
Jurassic intermediate volcanics that overlie the Brooklyn Limestone in
the area.
Approximately 1000 feet north of Hardy Mountain, a small plug of
medium to coarse-grained diorite containing well formed euhedral plagio• clase crystals has been mapped,and appears very similar to the coarse•
grained massive andesites extending for some 1000 feet to the southeast.
This diorite plug may in fact be genetically related to the andesites and
may represent a feeder dyke to the andesite volcanic pile overlying the
Triassic Brooklyn Limestone. Because of the large quantity of propylitic
alteration associated with the andesites, it is very difficult to
compare textures and compositions with the diorites which also contain
some alteration products.
A large 30-40 foot wide, relatively unfractured northwest trending
dark diorite dyke occupies a large fault zone west of Eagle and Hardy
Mountains. The dyke-filled fault zone appears to be the southern
extension of a major fault mapped by Little (l965, p.60) that
11 has been traced from near Phoenix, where it marks the northern boundary of the Snowshoe orebody, southeastward ... ".
This fault, according to Little, is pre-Tertiary and is "partly occupied by dykes of Tertiary diorite". In the vicinity of Eagle Mountain, this diorite is coarse-grained, slightly porphyritic with large well developed e-
quidimensionalpotash-feldspar phenocrysts set in a fine-grained matrix of anhedral plagioclase, potash-feldspar, and biotite intergrowths. The 60. term diorite, used for this Tertiary dyke, emphasizes the dark colour of the rock, but the diorite may well approach monzonite and syenite in composition. This Monz/no-or Syeno-diorite probably represents a more contaminated southern variety of the Tertiary Coryell syenites found to the north.
A large northwest elongate, fine to coarse-grained gabbroic intrusive body occupies the central part of the map sheet, between Hardy
Mountain and Baker Ridge. This "gabbroic" body becomes coarser grained towards its centre, the grain size of the medium-grained border phase being about 1 mm and the coarse plagioclases within the central part of the body have been measured up to 2 cm. across the elongate direction.
A composition of about 50$ white to pale grey plagioclase and 50$ dark green to black hornblende imparts a characteristic mottled or salt and pepper appearance to this gabbro in hand specimen (see Plate 10, p.53). The rock is roughly equigranular,slightly foliated in places and the plagioclases are rounded to embayed in outline with the hornblendes generally forming irregular interstitial intergrowths. The plagioclases, typically unzoned, are in most places slightly aligned and bent or broken, strongly indicative of some movement subsequent to crystallization. The plagioclases are also clouded with white-mica and calcite alteration products making composition determinations virtually impossible. Hornblendes have been found locally almost completely altered to chlorite and epidote, forming a complete fibrous felted mass.
The intense alteration of both the plagioclases and hornblendes, plus the broken and bent nature of these plagioclases, the slight foliation, 61.
and the numerous quartz and carbonate filled fractures found roughly
paralleling the northwest sheared contact directions, strongly suggest
movements within the gabbroic body contemporaneous with and subsequent
to the cooling history of the gabbro, and probably reflect intermittent
movements along the steeply dipping shear/fault zone within which this
gabbro lies (see Figure 6, p. 83). Near the middle and at its western
edge, the gabbro was found with intrusive contact into a sheared serpen-
tinite. Farther to the north a serpentine body was found within a
sheared zone cutting northwesterly across the gabbro. These facts
strongly suggest that the gabbro was emplaced contemporaneously with the development of the large northwest trending shear zone, and that subse•
quent movements along this fault zone have sheared some of the gabbroic body. The gabbro is believed to be Latest Cretaceous or Early Tertiary in age.
The gabbroic mass is bounded on both the west and east sides by northwest trending fault zones containing serpentinite bodies. Both argillites and limestones in contact with the southern part of this gabbroic body, east of Hardy Mountain, have been hornfelsed somewhat.
The limestone appears to be silicified in several places.
Using Williams,Turner,and G±lbert>s(1954, p.106) classification, this gabbro has the characteristics of both a diorite and a gabbro: its colour index is approximately 50 - within the limits of diorite; it contains hornblende as its principal mafic constituent - as a diorite; but a rough composition determination of the plagioclases gives An^ 54 ~ wit*1111 the range of gabbro. Williams, Turner,and Gilbert (1954), state that 62. such borderline rocks could be termed either ."meladiorites" or
"leucogabbros". The author prefers "leucogabbro" to emphasize the peculiar bimineralic composition, the large grain size, and the light coloured mottled appearance in outcrop, so very distinctive from diorites in the map area.
Ages of these dark basic rocks are quite variable, but it appears from their close association to the northwest and northeast steeply dipping fault zones and Tertiary fracture system, that most of these basic rocks are probably Late Cretaceous or Early Tertiary in age.
Movements have occured along some of these fracture zones subsequent to solidification of the intrusive rocks.
The diorites occurring as plugs within the Fragmental Andesites and representing feeder dykes are probably of Middle Jurassic age. The dark diorite border phase of the Nelson granodiorite is probably lowest Upper
Jurassic in age.
Tertiary Intrusions
Tertiary igneous rocks within the map area are quite widespread and variable in composition, age and structural habitat. They can be divided into two distinct mappable units:
1. Feldspar porphyry quartz-monzonite: predominantly in the
southern part of the map area and occurring typically as
easterly trending dykes and larger masses, that are equivalent
to Parker and Calkin's "Scatter Creek Formation". Also included 63.
in this unit is Carswell's (1957) "Emma Intrusions", or
quartz-diorite and related quartz-monzonite feldspar porphyries,
found predominantly in the northern part of the map area. A
small alaskite dyke has also been included in this unit.
2. The second and apparently younger rock unit is a complex-
sequence of syenites known as the "Coryell Intrusives" (Monger,
1968), and includes syenite porphyries, feldspar, biotite, clot
porphyries, feldspar rhomb porphyries and pulaskites occurring
as dykes and sills.
Scatter Creek Formation
The "Scatter Creek" feldspar porphyry quartz-monzonites found in the Grand Forks area are variable in texture and composition. The quartz- monzonite is fine-grained and strongly porphyritic with abundant white prismatic plagioclase crystals, black biotite crystals, with minor hornblende and chloritized augite grains, and rounded clear quartz grains. These porphyritic crystals are set in a moderate grey dense groundmass (Plate 11, p. 68). This groundmass is composed of varying proportions of microcrystalline chlorite, biotite, feldspar and quartz.
The plagioclase phenocrysts, commonly euhedral and zoned, reach lengths of 3 mm. The felted or micro-granitic groundmass is generally less than
5 mm. Plagioclase, both phenocryst and groundmass, is andesine in composition and constitutes about 30-60$ of the rock. Orthoclase is confined to the groundmass and commonly forms graphic intergrowths with quartz (Parker and Calkins, 1964). Most of the quartz is also restricted to the groundmass and generally forms less.than 5-10$ of the rock. 64.
Irregular biotites also occur as a common accessory and augite and
hornblende has been noted within the groundmass. Minor accessory minerals
include apatite, sphene, magnetite, pyrite and zircon. The plagioclase
is incipie.ntly altered to sericite, and chlorite and carbonate has been
found as deuteric alteration products from augite and hornblende.
The Scatter Creek cuartz-monzonite porphyries are abundant within
the Republic Graben (Parker and Calkins, 1964). However, similar
intrusive rocks are found cropping out in only a few localities in the
southern part of the Grand Forks map area and occur as small easterly
trending dykes and irregular masses. Due west of Grand Forks, a large
irregular elongate mass cuts across the Triassic Sharpstone Conglomerate/
Brooklyn Limestone contact. Intrusive contacts are sharp and contact
thermal metamorphism is weak. The surrounding rocks are hornfelsed for
approximately 20-30 feet. Similar easterly trending vertical dykes are
found south of Hardy and Eagle Mountains that appear to continue for
some two miles to the east.
Direct relationships between the quart-monzonite feldspar porphyry
"Scatter Creek Formation" and the Coryell syenites have not been found in the Grand Forks area. However, Parker and Calkins (1964) believe the "Scatter Creek Formation" to be Eocene to Oligocene in age, since it has been found cutting Kettle River and Marron volcanic equivalents in northern Washington. This suggests a contemporaneous age with the
Coryell intrusives in the southern Boundary District.
Fine to medium-grained quartz-monzonite and quartz-diorite porphyries 65.
that are similar to and include Carswell's (1957) "Emma Intrusions" form
numerous small irregular masses cutting the Triassic and Jurassic sediment•
ary and volcanic rocks, in the northern part of the map area.
Their texture is generally porphyritic, with light-coloured, strongly
altered euhedral plagioclase crystals occurring as phenocrysts. These
phenocrysts are so strongly altered to fine-grained white mica and
carbonate that the original character of the crystals is obscure, and
also imparts a pale cream to light greenish colouration that characterizes
this unit in hand specimen. The plagioclase phenocrysts are slightly
elongate, generally average 2-3 mm in length and comprise up to 20$ of
the rock in some of the finer-grained varieties. The groundmass consists
of varying amounts of plagioclase, quartz, biotite, hornblende(?),
chlorite and accessory magnetite forming a dark fine-grained denee matrix.
The mafics are somewhat chloritized.
Carswell (1957) states that the plagioclase is andesine in composi•
tion and he suggests a genetic association with basic rocks. This quartz-
diorite porphyry unit has been found adjacent to every major copper magnetite skarn prospect in the Summitt Camp, except for Oro Denoro.
Age relations of these quartz-diorite and quartz-monzonite feldspar porphyries are obscure. However, in several places these intrusives have been found cutting the Middle Jurassic Fragmental Andesites and in turn themselves intruded by the younger Coryell syenites and pulaskite dykes and are therefore post-Middle Jurassic to pre-Eocene in age. Since these feldspar porphyry intrusives contain abundant propylitic alteration products, it is believed these intrusives were emplaced prior to the 66. termination of the regional metamorphic effect, possibly Cretaceous and even Early Tertiary age. However, autometamorphism could also have produced this low grade of alteration.
The quartz-monzonite and quartz-diorite feldspar porphyry masses occur close to or along major structural breaks and appear in areas of maximum displacements and deformation.
In several localities the intense pale alteration of the plagioclases, the overall moderate green colouration of the matrix and a slight foliation of the plagioclase phenocrysts impart a strong resemblance of these quartz- diorite porphyries to the altered, trachytic Fragmental Andesites (e.g. immediately east of the Bluebell Showing). This striking resemblance may well emphasize Carswell's (1957) belief that these quartz-diorite porphy• ries have a genetic relation to basic rocks.
Coryell Syenites and Pulaskite Dykes
Abundant Coryell intrusive units in the Grand Forks area consist of a complex sequence of fine to medium-grained syenites and include, in part, the intrusive equivalents to Monger's (1968) Marron volcanics and hypabyssal dykes, sheets, and flows of pulaskite, phonolite and syenite porphyries. Monger (1968, p.27-32) relates these Coryell syenites to the
Middle and Upper Division of the Marron Volcanic Formation.
A syenite porphyry forms the most abundant intrusive unit of the
Coryell Complex within the Grand Forks area and is characteristically brownish-pink in colour with approximately 10$ of the rock as feldspar phenocrysts and the remaining 90$ of the rock composed of a finely 67.
crystalline groundmass. This rock has a "clot porphyry texture" (Monger,
1968), with clots, or small white plagioclase laths generally arranged
radially about a biotite nucleus (see Plate 12, p. 68). The size of
plagioclase phenocrysts is quite variable, and in some cases the biotites
are also of phenocryst size. The groundmass is finely crystalline and
composed of a randomly oriented mesh of plagioclase feldspar laths, with
interstitial opaque minerals, quartz and chlorite; clinopyroxene and
biotite crystals also occur in the groundmass. The plagioclase in the
coarser-grained varieties are generally clouded with fine micaceous and
carbonate alteration and the clinopyroxenes are somewhat altered to
chlorite. The dark biotites on the other hand are generally clean and
unaltered. A variety of this clot porphyry has been found containing
large clear to pink, zoned, elongate plagioclase laths set in a pale
brown extremely fine-grained matrix containing small specks of dark
biotite.
Monger, (1968, p.30) states that:
"pulaskites or alkalic syenites are merely a variety of the above syenite, characterized by its aphanitic fawn to buff matrix and appears to occur only in the smallest intrusive bodies".
This also applies in the Grand Porks area where the pulaskites occur in dykes and sills that are the southernmost extensions of the Coryell
syenites. Numerous northwest trending dykes are found in the northern part of the map area.
Microscopically, the pulaskite is composed of small laths and pheno• crysts of perthite and cryptoperthite; phenocrysts of albite; nepheline 68.
CENTIMETERS 2
Plate 11: Coarse-grained quartz-monzonite porphyry (Scat ter Creek Formation?) from easterly trending dyke at Eagle Mountain.
Plate 12: Coryell syenite "clot porphyry" variety from east of Wilgress Lake. 69.
as inclusions in early minerals; biotite, hornblende, riebeckite, aegirine-augite, magnetite; rare interstitial quartz and very rare
pigeonite (Monger, 1968). The feldspars are clouded and strongly altered
to micaceous minerals and the mafic minerals also appear slightly altered.
The fawn colouration appears to be from microscopic disseminations of
iron oxide. Sutherland-Brown (1967), mentions that he found no feld-
spathoids associated with the pulaskites from the Oro Denoro area and would consider these rocks as andesite dykes.
East of Wilgress Lake, within the large expanse of alkalic intrusive
rocks, the "clot porphyry" becomes characteristically grey on a fresh
surface and the groundmass appears extremely fine-grained and dense.
Here also, another variety of the syenite porphyry is found, which as
Monger (1968) notes, has a high "phenocryst to groundmass ratio" and thus appears medium-grained equigranular rather than porphyritic. This intru•
sive is speckled in appearance, composed almost wholly of coarse plagioclase phenocrysts with biotite phenocrysts restricted to the inter•
stitial groundmass.
Plagioclases are zoned and have a composition range from An^-Ang^.
Biotites are fresh but the pyroxenes in groundmass have been almost completely altered to uralite (Monger, 1968). Anhedral grains of quartz have been found in trace amounts throughout the groundmass.
Monger (l968) states:
"there are other intrusive rocks in the map area whose Tertiary age is demonstrated by cross- cutting relationships but cannot be related to any particular lava type" (Marron Formation). 70.
These syenites commonly occur as feldspar porphyry syenite dykes such as
that found immediately northwest of the Hummingbird showing. Here,
potash-feldspars form extremely large (up to 1 inch long) pink, euhedral
crystals set in a pale brown fine-grained matrix. Epidote and chlorite
forms a characteristic yellow-green alteration rim around the large
feldspar phenocrysts.
Radiometric dates for Coryell intrusives in the immediate map area
are not available, but ages of 56 to 60 million years have been obtained
from the type Coryell batholith to the east (Monger, 1968). Ages
obtained from Tertiary lavas in southcentral British Columbia are
45-53 million years, and Monger states that
"at least part of this particular intrusion appears to have been emplaced earlier than rocks related to the Marron Formation".
Therefore, it appears that the main Coryell intrusive activity within
the map area conforms to that of the Coryell batholith and is probably
Eocene in age. Monger concludes that:
"there is no proven relationship between the Coryell intrusions and Marron Formation at present and they appear merely to have been formed at roughly the same time in the same general area and show the same general range of compositions". 71.
SECTION III: STRUCTURES
The Grand Forks map area contains several major structural elements: the Granby River Fault, an extension of the eastern boundary fault of the
Republic Graben in northern Washington State; other related northwest and northeast trending fracture patterns; the overturned western limb of a north-northeasterly gently plunging, nearly recumbent syncline outlined within the Triassic-Jurassic sediments and volcanics; several major northwest trending steeply dipping fault/shear zones that appear to divide the synclinal fold structure into separate entities that are shifted progressively to the south-southwest from north to south; and eastern tilting and gently warping of the Early Tertiary sedimentary and volcanic units.
Republic Graben
The north to northeast trending Republic Graben, which is the principal structural element in Curlew County N-l/ash., and has been traced for some 30 miles to the south, and has an apparent maximum stratigraphic separation of some 17,000 feet, appears to lose its identity as it crosses the International Boundary into the Grand Forks area (Parker and
Calkins, 1964). The Granby River Fault, trending north-northeast immediately west of Grand Forks, appears to be the northern extension of the Drummer Mountain Fault or the eastern boundary fault of the
Republic Graben. Like the Drummer Mountain Fault, the Granby River Fault appears to be a steep, westerly-dipping normal fault that separates the 72.
down-dropped Permo-Triassic and younger rocks to the west, from the up• lifted highly metamorphosed Grand Forks Group on the east.
The northern extension of the Granby River Fault is obscure, but
several geological maps of British Columbia show it extending some 25-30 miles north of Grand Forks. Vertical movement on the fault near Grand
Forks is unknown, but Parker and Calkins (1964), state that "the vertical component decreases northerly" so that near Grand Forks and to the north,
it is probably very much less than the 179000 feet maximum.
The extension to the Bacon Creek Fault or the western boundary fault of the Republic Graben has not been found north of the International
Boundary. However, a 30 foot thick north-northeasterly trending vertical to steep southeasterly dipping mylonite zone, was found within fragmental andesites along the old abandoned railroad grade about one half mile west of Eagle Mountain. This mylonite zone may be the northernmost extension of the Bacon Creek Fault that is said to die out as it crosses the
International Boundary into Canada (Parker and Calkins, 1964). However, this sheared zone does not appear to extend for any great distance to the northeast.
Parker and Calkins (1964), state that the
"boundary faults and the general shape of the graben were established before and during deposition of the O'Brien Creek Formation".
The latter is the Kettle River Formation equivalent in northern Washington, hence dates the faulting as Late Cretaceous or Early Tertiary. They also mentioned that movements along the boundary faults were intermittent, and persisted until well after deposition of the Marron volcanic equivalents, or well after Oligocene time. 73.
Northwest and Northeast Fault Patterns
Most other faults in the graben trend north to northeast parallel
to the boundary faults. Other numerous northwest trending cross faults with associated serpentinites, and quartz filled fractures have been noted, especially in the Republic gold-quartz mining district some 30 miles south of the Grand Forks map area (Parker and Calkins, 1964), and near Goosemus Creek immediately south of the International Boundary.
Within the Grand Forks area, similar northeast and northwest trending conjugate fracture patterns have been mapped and are very well demon• strated within the massive more competent fragmental andesites southwest of Goat Mountain. These two fracture systems appear to persist through• out the map area, with local variations, and the northwest direction appears to dominate the Grand Forks area. The most striking feature about these northwest trending fault zones is their association with elongate sheared, serpentinized ultrabasio and pyroxenite bodies. North• west fault zones commonly have a steep southwest dip, as demonstrated by the shearing in the serpentinites and the foliations within the sur• rounding country rocks, and are believed to be steep thrust planes.
Absolute directions and distances of movement along these zones are difficult to ascertain.
The accompanying geological map demonstrates, from north to south, many northtfest trending steeply dipping fault zones, that cross the map at what appear to be regular intervals, suggesting probably some unique control to their even distribution and directions.
Northwest and northeast fracture patterns and northwest fault zones 74.
are believed to be related to the same stress system that ••
formed the Republic Graben and its related fault and fracture sets to
the south. With the loss of the western boundary fault, on crossing the
International Boundary, the northwest direction appears to have taken up
much of the displacements and movements in the Grand Forks district.
All the major faults appear to have been active during the Tertiary
period, but much of this relatively recent movement may have taken place
on structures that originated when the Triassic and Jurassic rocks were being deposited. Many of the ultrabasic bodies scattered throughout the area have been intruded along these older breaks, and probably slivers of these serpentinized ultrabasics were sheared and brought up along
these deep fault zones in late Tertiary time.
Similar Tertiary northwest and northeast conjugate fracture patterns are prominant in many places in the southern Boundary and Okanagan
Districts (Church, 1967; pp.96-99) and (Ross and Christie, 1969). This pattern is shown in Figure 2, p.
Dykes
Throughout the northern portion of the map area is found a promin nt northwest to north and minor northeast trend of numerous pulaskite and alkalic Coryell intrusive dykes. Several of these dykes have a moderate southwest dip and are believed related to the formation of the northwest shear zones and northwest-northeast fracture systems. In several places an apparent horizontal displacement of several thousand feet can be seen, such as the limestone found on either side of the northwesterly trending 75.
pulaskite dyke southwest of the B.C. mine and immediately north of the
R. iell mine. This dyke appears to dip moderately to the northeast.
Near Hardy and Eagle Mountains, several vertical easterly trending
quartz-monzonite porphyry dykes are found. These intrusives are probably related to the "Scatter Creek Formation" in northern Washington, and here appear to be early Tertiary, definitely pre-Coryell or Eocene in age.
These easterly trending dykes probably reflect a relaxation and change in stress fields forming the Republic Graben.
Folds
An overturned western limb of a large, open, nearly recumbent
synclinal structure that opens to the east and whose fold axis plunges gently to the north-northeast and axial plane clips gently to moderately to the northwest, is demonstrated within the Triassic sediments and
Jurassic volcanics underlying Hummingbird Ridge, northeast of Thimble
Mountain (Figure 4, p. 81, shows a diagramatic cross-section). Several inverted graded beds and the complete reversal in the normal strati• graphic sequence here suggest the overturning. The general pattern of this open synclinal structure is well demonstrated in the cliff directly north-northeast across the Granby Valley from the Hummingbird prospect
(Plate 13, p. 77).
Southward from Hummingbird Ridge, the synclinal structure has been transected by a series of northwesterly trending, steeply dipping fault zones and appears to have been shifted progressively towards the west, as counterparts of this overturned western limb are found at the 76.
Shickshock and Sailor Boy showings, at the B.C. mine and at the Emma and
Oro Denoro mines. If these are indeed fragments of the same limb, then several miles of apparent horizontal displacement are represented here.
South of Oro Denoro, the stratigraphic sequence is found right side up and dipping moderately to gently northeast to easterly, and appears to represent the unfolding or opening of the overturned to vertical limb,at Oro Denoro,into the western limb of a north or northwesterly plunging open trough or basin structure underlying Baker Ridge and to the west (see Figure 5, p. 82).
Several major northwest trending structural breaks appear to have stepped down the northeasterly dipping Triassic sedimentary sequence at almost regular intervals to the south and southwest of Baker Ridge as similar sedimentary sequences occur at Hardy and Eagle Mountains and immediately west of Grand Forks.Occurrences of similar rock units immediately south of the International Boundary in northern Washington probably represents a further downdropping to the southwest.
A closure in this northwesterly plunging basin or syncline is demonstrated within the Brooklyn Limestone south of Hardy Creek, north• west of Grand Forks, where the beds swing from-a northwest trend/ northeast moderate dip to a northeast and northerly almost vertical dip.
The northwesterly plunge of the synclinal structure is also demonstrated by several minor synclinal and anticlinal closures within the Brooklyn
Limestones some 2500 feet south of Goat Mountain and approximately
2000 feet west of Hardy Mountain. Trends of minor fold axes within the
Triassic sediments also attest to this northerly plunge.
i 77.
Plate 13: A NE view of the limestone cliff across the Granby Valley, directly opposite the Hummingbird Showing. Shows synclinal minor fold structure within the well banded limestone unit and several flat dipping Tertiary dykes. 78.
A gradual swing in the plunge directions of these minor fold axes, from
a gently plunging north-northeasterly direction in the northeast corner
of the map area to a moderate to gentle northwesterly plunge south of
Goat Mountain suggest a warp in the axial plane and fold axis of the north to northeasterly trending gross structures. However, trends of minor fold axes could be greatly affected by the numerous shear and
fault zones that cross-cut the gross structural trend, and direct
relationships between the individual faulted blocks are unknown.
The age of this synclinal structure is pre- Late Jurassic since it
is cut by the Nelson granodiorites at Oro Denoro. It is probably post-
Early to Middle Jurassic as it involves the Middle Jurassic Fragmental
Andesites. Furthermore, since these andesites in part lie unconformably
on limestone erosion surfaces, the deformation may well have started
slightly before or during the deposition of the Fragmental Andesites.
Intense faulting and intrusive activities obscure the structures of
the area west of Grand Forks, but in general the minor folds within the
limestones appear to plunge gently southeast, almost a direct reversal
to the gentle northwesterly direction found to the north.
Structures within the Anarchist cherts and phyllites below the
Triassic sediments at the southern part of the map area are obscure due
to the intensely fractured nature of the rock and general lack of good
exposures. However, one minor fold was found whose axis plunges
moderately to the southeast, which appears to conform roughly to the
southeast-northwest trending structures mapped by Parker and Calkins(l964)
in similar rock units some 6 miles to the southwest in northern Washington. 79.
The structural grain of the highly metamorphosed Grand Forks rocks lying to the east of the map area, is almost at right angles to that within the Triassic and younger rocks. The Grand Forks paragneisses contain east-west major structural trends that are clearly visible from aerial photographs and Parker and Calkins (1964) state that similar rocks of the Tenas Mary Creek Formation have gently dipping east-west struc• tures .
It appears from the mapping by Parker and Calkins that structural trends shift from a general east-west direction within the Pre-Cambrian or Early Paleozoic Grand Forks equivalent rocks, to a northwest-southeast trend in the Permian-Pennsylvanian Anarchist equivalent rocks.
As previously mentioned, the Mid.Triassic - Mid. Jurassic sediments and volcanics in the Grand Forks-Eholt map area contain northwest to northeast trending structures. This suggests that there is a change in the structural grain with depth or with age of the host rocks, probably reflecting several different periods of deformation or a different structural style with depth of burial. Hence the deeply buried, highly metamorphosed Grand Forks gneisses house predominantly east-west struc• tures and the Triassic to Jurassic rocks contain NW to NE trending structures.
V. Preto (personal communication, 1970) mentioned that the NNE trending recumbent fold found at the northeast corner of the map area appears typical of the phase 3 structures found in the high grade meta- morphics of the Grand Forks Group north of Grand Forks. 80.
Tertiary Block Faulting and Tilting
Eastward tilting and gentle warping have been recorded by Monger
(1968) within the large Tertiary covered blocks throughout the southern
Boundary District. This is demonstrated by the Tertiary covering at
Baker Ridge where the Kettle River sediments and overlying Marron volcanics dip about 45° to the east and appear to form the western limb of a broad gentle syncline (Figure 5? p.82). The hinge zone and eastern limb of this
Tertiary basin has been faulted and eroded off to the east of Baker
Ridge. This Tertiary faulting, tilting, and warping is probably contempo• raneous (but late) with the development and settling of the Republic
Graben,northwest and northeast fracture system in the area.
Eastward tilting and warping presents a problem when correlating structures between individual fault bounded blocks since in most places the Tertiary cover is absent, having been eroded away, and. therefore gives no control to the amounts and directions of tilting. NW
Figure 4 NW-SE diagramatlc cross-section (looking NE) from the Rathmullen creek — C.PR. track intersection to where Lime creek flows into the Granby valley.
84.
SECTION IV: METAMORPHISM
Regional Metamorphism
The Permian, uppermost Anarchist cherts and phyllites, the Triassic
sediments and the Jurassic Fragmental Andesites that underlie the Grand
Forks map area have all undergone low-grade regional metamorphism and
contain metamorphic minerals typical of the Lower Greenschist Facies.
The gneissic terrain east of the Granby River Fault, on the other hand,
contains high-grade metamorphic minerals similar to the Tenas Mary Creek
Formation to the south, which Parker and Calkins (1964) have classified as Almandine-Amphibolite Facies (after Turner and Verhoogen I960, p.554).
Parker and Calkins suggest that from the lowermost gneisses of the
Tenas Mary Creek Formation up through the overlying Permian schists, phyllites and greenstones, is represented a continuous change in meta• morphic grade from Almandine-Amphibolite Facies at the bottom, to
Greenschist Facies at the top. This probably suggests an increase in metamorphic intensity with stratigraphic depth or burial (Figure 7,p.85).
Within the Grand Forks area, this encompasses rocks from the gneisses of
the Grand Forks Group to the Knob Hill cherts and greenstones at the top of the Anarchist Group. Such a metamorphic gradation is suggestive of a Barrovian type Facies Series (after Winkler, 1967 pp.88-89).
A series of amphibolites mapped by Little (1965) below the uppermost massive cherts and greenstones and limestone of the Anarchist Group contain minerals very typical of the transition between the uppermost
Greenschist Facies and lowermost Almandine Amphibolite facies. 85.
Mid. Jurassic CO andesites UJ Triassic o a> clastic < \ a sediments o a> o I— Tz. o Permian CO greenstones X o and cherts CO \ -z. UJ phyllites UJ V cc o o 2500feet o •5 o schists
i 2500 feet \ ! f
quartz, plagioclase CO UJ o gneiss ' o s I 700 - 5300 LU feet _J o go hornblende X schist a. quartzite < •I 500- 3000feet. UJ 1 marble Q
< granite I gneiss I 1 3500 feet I 1
Figure 7 Observed stratigraphic range of metamorphic minerals and
other features of the Early Paleozic- Permian and
Triassic - Jurassic rocks. Checks represent features
observed by the author.
(after Parker and Calkins, 1964; with modifications.) 86.
Parker and Calkins (1964) state that:
"The transition from the Greenschist Pacies to the Almandine-Amphibolite Pacies apparently takes place in the stratigraphic interval between the middle of the schist unit and several hundred feet above the base of the phyllite, a zone that contains minerals characteristic of both facies".
This corresponds to somewhere near the top of the Anarchist Group
in the Grand Forks area.
The highly metamorphosed Grand Forks gneisses have not been
studied by the author, and according to Parker and Calkins (1964), minerals found within the Tenas Mary Creek rocks (Grand Forks Group
equivalent) typical of the Almandine-Amphibolite facies are: biotite, muscovite, pink garnet, dark green hornblende and actinolite, orthoclase, plagioclase (oligoclase and minor albite), sillimanite, and cordierite.
Metamorphic minerals characteristic of the Permian Anarchist cherts, mica-schists and phyllites in the Grand Forks area include muscovite,
sericite?, biotite and chlorite. Some recrystallization of quartz occurs in the siliceous units. These foliated rocks are highly deformed and sheared, very suggestive of dynamic thermal metamorphism. The low thermal grade probably fits near the Upper Greenschist Facies as suggested by Parker and Calkins (1964).
The fine-grained matrix of the Sharpstone Conglomerate, wacke, argillite and mudstone sequence contains abundant shreds of chlorite, sericite, minor epidote and possibly pyrophyllite, typical of the low- grade Greenschist Metamorphic Facies. The Puddingstone sequence, a maroon coloured equivalent of the Sharpstone, appears to have very little chlorite alteration but contains much microscopic disseminated 87. hematite and iron oxide.
The overlying Brooklyn Limestone shows relatively little evidence of this widespread low-grade metamorphic effect except for slight re• crystallization and sparry calcite filling numerous fractures is ubiquitous.
Jurassic Fragmental Andesites found throughout the Grand Forks map area provide the best evidence of this low-grade metamorphism, having in places up to 25-30$ alteration minerals, mainly: chlorite, epidote and carbonate with minor albite, sericite and opaques (pyrite?).
Contact Thermal Metamorphism
Towards the northern part of the map area, near the large body of
Nelson granodiorite and in the vicinity of the smaller intrusive plugs throughout the map area, the Permian to Jurassic folded sedimentary and volcanic rocks have undergone extensive thermal alteration and charac• teristic thermal aureois are found extending for some distance away from these intrusives.
South of the Oro Denoro workings, and adjacent to the Nelson granodiorite the Brooklyn Limestone is recrystallized to a fine-grained marble,and to the south, farther from the contact, becomes coarser- grained. The thermal effect appears to have extended some 2000 feet to the south. The more impure massive and banded limestones alter to a coarse-grained garnet (andradite?), epidote, pyroxene, calcite skarn that often carries magnetite, pyrite, chalcopyrite and hematite minerali• zation, occasionally forming economic grade. Oro Denoro, Emma, B.C., 88. and R. Bell mines of the Summit Camp are examples (see Appendix I, p.106, for a detailed description of the mineralization in the area). Farther from the intrusive contact the well-bedded limestone units occur as distinct bands of dense microcrystalline garnet, pyroxene and epidote hornfels with minor mineralization, all interbedded with coarsely crystalline marbles.
The Sharpstone Conglomerate sequence adjacent to the larger intru• sive bodies also displays this thermal effect and in places appears as a dense siliceous hornfels with associated disseminated pyrite (i.e. west of Grand Forks). North of the Emma workings, a conglomerate appears white and bleached with the grey chert pebbles remaining unaffect.
Some distance from the intrusive contact, the fine-grained matrix of the Sharpstone sequence is almost totally altered to a fine fibrous mass of dark green hornblende. Northwest of the Hummingbird showing, in the immediate vicinity of the railroad tunnel, the Sharpstone Conglomerate is silicified and carries disseminated pyrite. Here also the fine• grained matrix is almost completely altered to dark green hornblende and chlorite.
Dense siliceous and biotite-muscovite hornfelsed metasediments are typical of the Anarchist cherts and cherty argillites found adjacent to the Nelson granodiorite contact some 4000 feet west of Oro Denoro. The interbedded Anarchist greenstones have been almost totally altered to coarse-grained amphibolites. In several places, both north and south of the granodiorite body, these metasediments have a schistose to gneissic texture which roughly parallels the intrusive contact, probably 89. suggesting some flowage associated with forceful intrusion of the
Nelson granodiorite.
Lack of chilled margins at the intrusive contacts, large surrounding thermal aureoles and the coarse-grain size and mineralogy of the associated skarn deposits, suggest a deep seated slow cooling or
Mesozonal environment for the Nelson granodiorite emplacement.
Coarsely crystalline fibrous radiating actinolite crystals have been found replacing limestone cobbles within an altered sedimentary sequence south and adjacent to a quartz-diorite porphyry found along the Canadian Pacific Railway track north of Fisherman Creek.
Wollastonite, as coarsely bladed radiating crystals confined to the lower coarser-grained section of graded beds, was found in a slightly hornfelsed bedded argillaceous limestone unit at the Hummingbird workings. The occurrence of wollastonite and of pyrrhotite and sphalerite mineralization within the mine workings suggests a high temperature of formation. Winkler (l967, pp.35-36) states that wollastonite found in thermal aureoles is indicative of high level intrusions with high temperature (600°-700°C) and associated low pressure conditions. Several small quartz-diorite porphyry intrusives are found to the west and a similar mass probably underlies the
Hummingbird showing.
These Late Cretaceous-Early Tertiary quartz-monzonite and quartz- diorite porphyries are therefore probably high temperature high level intrusions that formed rather narrow thermal aureoles and must have 90. cooled very rapidly; very different from the conditions surrounding the
Upper Jurassic Nelson granodiorites.
Thermal aureoles surrounding the Tertiary Coryell syenites and hypabyssal dykes and sheets appear to be very small, and the thermal effect surrounding these rather anhydrous intrusives must have been weak.
They also appear to be high level intrusions that have cooled rapidly as they contain chilled border phase and have very little thermal effect on the surrounding rocks.
The age of overall regional metamorphism is probably post-Middle
Jurassic (Fragmental Andesites) to Upper Jurassic (Nelson granodiorite).
The Triassic sediments and Middle Jurassic andesites appear to have been folded prior to or during the onset of any extensive period of meta• morphism, and is probably related to the intense folding, deep burial, and elevated temperature and pressures that occurred at this time.
Parker and Calkins (1964, p. 79) state that:
"Although the granodiorite did not cause the metamorphism at its present position, an intrusive magma that formed the granodiorite could very well have been generated at depth by processes related to regional metamorphism. Broadly speaking, the granodiorite is considered to be a late phase in the overall period of metamorphism".
Chlorite was noted along some of the Tertiary fracture and jointing planes indicating that some local low-grade metamorphism occurred during Middle Tertiary time (?). 91.
SECTION V: SUMMARY AND CONCLUSIONS
Summary
Prior to the deposition and accumulation of the Permian Anarchist cherts, argillites, greenstones and minor limestone lenses, much of the geological history of the Grand Porks area is unknown. Paragneisses, marbles,amph±bolites and schists of the Grand Porks Group found east of I the map area hold the oldest history within the Boundary District. These rocks were originally marine sediments, probably representing part of a eugeosynclinal belt along the then western continental border during
Early Paleozoic or Late pre-Cambrian time, that have subsequently under• gone deformation and intense metamorphism. A continual marine depositio- nal sequence probably exists from Early Paleozoic (Grand Porks Group) to
Permian or Early Triassic (Anarchist) time with several periods of up• lift, erosion and resubmergence (Parker and Calkins, 1964). Emplacement of felsic and mafic sills, dykes and irregular intrusive bodies accom• panied these movements.
During Permian time the region was depressed below sea level and large quantities of mafic volcanic tuffs and flows, black shales, cherts, ribbon cherts and lenticular limestones accumulated therein under deep water quiet sedimentation, probably in an island arc type environment.
This sequence is similar to the Cache Creek Assemblage found more wide• spread through south and central British Columbia.
Before the Middle Triassic, Anarchist rocks must have undergone intense deformation since they appear much more internally deformed p.r-c. 92.
sheared than the overlying unconformable sediments and volcanics. During
Middle Triassic time, the Anarchist rocks were uplifted(?), folded and
eroded. Breaks (faults) developed throughout the Boundary District,
forming several northerly trending deep marine basins at the edge of the
Triassic (Nicola?) Sea. Into these basins poured rapid accumulations of
coarse angular chert and lithic volcanic fragments from the highlands to
the north and northwest, forming numerous fanglomerates and deltaic
deposits at the edge of the Triassic sea (Figure 3, p. 28). Farther from
the source, within the basin to the southeast, these conglomeratic
lenses pinch out and interfinger with finer thin-bedded wackes,
argillites, siltstones and mudstones deposited under quieter deep water
conditions. Infilling of the basin coupled with erosion of the source-
land is reflected in the increasingly finer-grained sediments grading
outwards and stratigraphically upwards within the basin.
Eventually, with an increase in carbonate content, the basin became restricted and shallow water microcrystalline limestone deposi•
tion prevailed,marking the start of the Brooklyn Limestone sequence.
Windblown chert ovoids within the basal limestones suggest a near shore and onshore arid environment. Tuffaceous bands within the limestone indicates nearby volcanic activity (Nicola volcanic activity to the NW?).
Local cataclastic limestone breccias attest to contemporaneous faulting and slumping within the carbonate basin. Interbedded black shales and argillaceous limestone units thin to the east and southeast farther within the basin of deposition. Carbonate deposition probably continued until Early Jurassic to Mid-Jurassic time with very little contribution 93. of clastic material since relief appears to have been very low in the surrounding positive areas.
During Middle Jurassic time, much of the area was uplifted with accompanying erosion of some of the carbonates. Contemporaneous with this uplift began a time of widespread volcanism. Explosive andesite pyroclastic debris, massive flows and agglomerates overlie the limestone unconformably in most places. Andesite flows poured into the remaining shallow carbonate basins and quickly flooded the surrounding area. The extent, thickness and duration of the andesite volcanism is unknown.
The beginning of Middle Jurassic volcanism probably reflects the early onset of structural deformation, burial, and accompanying in• creased geothermal gradient that produced: the northwest to northeast trending gross structures within the Triassic and Jurassic rocks; related low-grade Greenschist Facies regional metamorphism within the
Permian to Mid-Jurassic rocks; and high-grade regional metamorphism within the deeper buried older Grand Forks rocks. The final result of this increased deformation, burial, and metamorphism was the emplacement of the Nelson granodiorites and related Valhalla granites during Early
Late -Jurassic time.
These Upper Jurassic acid intrusions were emplaced under Mesozonal conditions, forming large thermal aureoles in surrounding country rocks and, in several localities, coarse-grained copper bearing skarns within the Brooklyn Limestone adjacent to intrusive contacts. After emplacement, the intrusives and surrounding rocks cooled slowly with subsequent decrease in the geothermal gradient, leaving the contact thermal 94. aureoles and regional metamorphic grade now found in the Jurassic and older rocks. Extensive erosion stripped away late Jurassic or Cretaceous sediments that may have accumulated and exposed the deformed low grade metamorphic and Nelson intrusive rocks. The region was uplifted during
Late Cretaceous or Early Tertiary time and appears to have remained above sea level up to the present.
During this Late Cretaceous or Early Tertiary time, block faulting, the initial development of the Republic Graben and related northeast and northwest fracture systems were established in northern Washington and the Grand Porks area. Contemporaneous with the intermittent settling and movements along the northwest steeply dipping fault zones, was the emplacement of diapiric serpentinized ultramafics and pyroxenites, large coarse-grained diorite and leucogabbro bodies, and diorite dykes. In the northern part of the map area, small irregular quartz-diorite and quartz-monzonite porphyry high level intrusions are confined to areas close to these northwest structural breaks, and appear to have been intruded about this time.
Deposition of the (Eocene-Oligocene?) continental Kettle River sediments followed the initial development of the Republic Graben.
These fast accumulating coarse clastic sediments have a varied origin from local volcanic activity presumably associated with the faulting, to detritus eroded from the nearby uplifted blocks (Monger, 1967).
Local relief during their deposition must have been considerable, indicated by the thick beds and large cobble conglomerate units that suggest contemporaneous faulting. The Kettle River sediment equivalents 95.
to the south of the Grand Forks area appear confined to the sunken block of the Republic Graben and similar local but smaller continental basins may have existed to the north in the Boundary District. Sub•
sidence and faulting may not have been as great in the Boundary District and this accounts for the relatively few local occurrences of Kettle
River sediments found. Parker and Calkins (1964) believe that these arkosic sediments continued to accumulate as long as movements and re• adjustments cont ued along the main boundary faults and the numerous
subordinate north-^northeast trending faults.
After much of the subsidence and adjustment within the individual blocks had ceased, lavas and pyroclastic accumulations of the Marron
Formation were deposited conformably on top of the Kettle River sediments and older rocks of the tilted blocks. During and following the extrusion of the Marron Volcanics, Coryell alkalic intrusions invaded the country rocks as hypabyssal plugs, sheets and dykes, in many places filling the prominent northwest and northeast Tertiary fractures. These alkalic rocks cut the Kettle River sediments and older rocks and are believed in part, feeder dykes to the middle and upper parts of the Marron extrusives. The upper part of the Marron Formation has been subsequently eroded and is missing in the Grand Forks area. The easterly trending
"Scatter Creek" quartz-monzonite porphyry dykes, found at the south of the map area, were intruded about this time.
Later volcanic activity within the Grand Forks area, suggested by the pyroclastic and glassy basaltic rocks of the Miocene Klondike Moun• tain Formation in northern Washington is missing and believed eroded Correlation with assemblages Formations in the Possible correlations in S.E. of widespread extent Age British Columbia and N.Washington. in British Columbia Grand Forks-Eholt Area Marron Formation . * Sanpoil Volcanics
dw y Daly, Oligocene includes: ^ ° ^°-' /I.M1.l of northern Washington Phoenix Vol. Group (Little) OBrian Creek Formation Kettle River Formation Eocene of northern Washington
Fragmental Andesites Mid.-, c Rossland Formation (Campbell) in part Eholt Volcanics(Carswell) Jurassic Takla Hazelton (Nicola?) Upper Assemblage J Brooklyn Limestone Formation Triassic Slocan Group (L — M. Triassic) ( U. Triassic — j M. Jurassic) / Middle Sharpstone Conglomerate Sequence Triassic
Cache Creek Anarchist Group -^fc — - Perm. Mount Roberts Group (Little) Assemblage includes Knob Hill cherts and greenstones ( Miss. — L.Triassic) Penn. V Tenas Mary Creek Formation / of northern Washingfon ^ Shuswap Terrain Grand Forks and Monashee Groups Early Paleozoic
pre- Cambrian / ?
Figure 8 Table showing possible correlations of the various layered rock units and formations outside the Grand Forks- Eholt area. 97. away. Late Tertiary diastrophism is evident from the many northwest and northeast faults found cutting the Tertiary rocks. Regional tilting of some 30°to 45° to the east accompanied gentle folding or warping of the
Tertiary sediments and volcanics. Extensive erosion followed, stripping almost all of the Tertiary layered rocks from the area.
In the Pleistocene, glacial erosion and deposition modified the topography and drainage. The receding ice left the upland areas mantled with glacial till and laid down glacial outwash deposits in the present valleys such as Granby and Kettle River valleys. Present river action has modified the valley bottoms.
Conclusions
From the mapping and interpretations involved in this thesis, several conclusions can be drawn:
1. The previously mapped Anarchist Group underlying the Grand
Forks-Eholt erea appears to have included rocks as young as
Middle Jurassic, and can be divided into two rather distinct
assemblages: the more widespread Takla-Hazelton Assemblage
sitting unconformably on top of the Cache Creek Assemblage
(Figure 8 , p. 96 ).
a. The lowermost Permian and/or Earlier Anarchist Group
proper, composed of cherts, phyllites, mica schists,green•
stones and minor limestone lenses is typical of the more
widespread (Miss, to Lower Triassic) Cache Creek Assemblage
(Campbell, 1966), characteristic of a deep water marine 98.
offshore environment. b. The Anarchist is unconformably overlain by a (Middle to
Upper Triassic) Sharpstone Conglomerate - Brooklyn Limestone
- (Middle Jurassic) Fragmental Andesite sequence that is
typical of the more widespread (Upper Triassic - Middle
Jurassic) Takla-Hazelton Assemblage (Campbell, 1966).
Sharpstone Conglomerates form the basal section for the Middle
Triassic clastic sequence.
Both the Sharpstone Conglomerate - argillite and Brooklyn
Limestone units thin to the southeast and east from the Phoenix-
Oro Denoro areas, and the Triassic sediments become noticeably finer-grained in this same direction, suggesting deposition farther into the basin (from the source area). Triassic clastic sedimentation probably accumulated within northerly trending elongate basins, transportation was from west to east and the source area for the Sharpstone Conglomerate probably was the
Knob Hill cherts and greenstones to the west and northeast.
The Sharpstone Conglomerate and overlying Brooklyn Limestone sequence ("Ore sequence", Newell, 1969) forms a good marker unit throughout the Grand Forks-Eholt area, containing numerous primary and minor structures and some well preserved fossils.
New fossil evidence, Halobia and Megaphyllites, confirms the
Middle to Upper Triassic age for the beginning of deposition of the Sharpstone Conglomerate - Brooklyn Limestone sequences.
The old timers'1 "Puddingstone", previously mapped as a limestone 99.
cobble agglomerate, lies gradationally above the Sharpstone
Conglomerate sequence and is essentially a lithologic equiv•
alent except that the Puddingstone has a maroon coloured matrix
and contains finely disseminated hematite.
7. Andesite pillows overlying a Brooklyn Limestone unit suggests
that the unconformable Fragmental Andesites are in part
continuous with the end of carbonate deposition. There must have
been some shallow carbonate depositing basins still present at
the onset of andesite volcanism.
8. Pre-Permian to Middle Jurassic sedimentary and volcanic rocks
underlying the Grand Forks-Eholt area have undergone a
relatively low-grade of regional metamorphism typical of the
Greenschist Facies.
9. The overturned western limb of a large, open, nearly recumbent
syncline that opens to the east and whose fold axis plunges
gently fflE and axial plane dips gently to moderately to the NW,
is outlined within the Sharpstone Conglomerate/Brooklyn Lime-
stone/Fragmental Andesite Assemblage northeast of Thimble
Mountain. This overturned limb appears to be progressively shifted
westward from the Hummingbird area to the Oro Denoro-Emma
vicinity.by several N¥ trending shear/fault zones. South of
Oro Denoro, the overturned western limb unfolds forming the
gentle northeastward dipping western limb of a northwesterly
plunging trough or basin.
10. Variations in the plunge directions of minor fold axes and 100.
hinge zones within the Brooklyn Limestone from a NNE to a NW
direction from north to south within the map area, suggest a
marked warping of the major axial plane and fold sxis.
11. The Republic Graben, a prominent Late Cretaceous to Early Tertiary
ME trending structure in Curlew County, N.Washington, loses
its identity to the north in the Boundary District - the Granby
River Fault appears to be the northward extension of the
Drummer Mountain Fault, the eastern boundary fault in northern
Washington. A mylonite zone southwest of Eagle Mountain may be
a northern extension of the Bacon Creek Fault, the western
boundary fault.
12. A northwest and northeast conjugate fracture pattern predom•
inates in the Grand Forks area, similar to Tertiary fracture
patterns in other areas of the southern Boundary and Okanagan
districts.
13. Northwest trending steeply dipping fault/shear zones are pre•
dominant and cut the Grand Forks-Eholt area at seemingly regular
intervals. They all have right lateral horizontal apparent dis•
placement in the order of several thousand feet to several
miles.
14. Numerous diapiric, sheared, serpentinized ultramafic and pyro-
xenite bodies are confined to the northwest trending fault
zones within the map area. Diapiric serpentinites suggest a
source from depth and that these faults may at one time have
been thrust planes. 101.
15. Late Cretaceous to Early Tertiary diorite and gabbro intrusive
activity appears to be genetically related to and contemporaneous
with movements along some of the prominent northwest fault zones.
16. Quartz-diorite and quartz-monzonite porphyries (Carswell's
"Emma Intrusives") appear to be Late Cretaceous to Early
Tertiary in age, may be genetically related to basic rocks,
and appear confined to areas near the prominent northwest
structural breaks.
17. The quartz-diorite, quartz-monzonite porphyries are high level
intrusions indicative of high temperatures (600°-700°C) and
associated low pressure conditions.
Suggestions for Further Work
1. Detailed petrological and chronological studies of the various
intrusive rocks in the area.
2. Detailed petrographic study to separate the fine-grained
trachytic andesites from the Late Cretaceous-Early Tertiary
fine-grained quartz-monzonite and quartz-diorite porphyry
intrusives. Also to separate the coarse-grained diorite
intrusives from coarse-grained crystalline andesites.
3. A detailed study of minor structures, textures and fossil
evidences within the Triassic Sharpstone Conglomerate and
Brooklyn Limestone to elucidate: number of units involved,
facies changes, paleocurrents and lithology; to determine
directions of transport and source areas for the clastic 102.
debris, the chronological relationships between the various
layered units, and the depositional environments.
4. A detailed structural analysis of the Brooklyn Limestone and
and underlying Sharpstone sequence - numerous primary and
minor structures have been observed. One must work out the
structures within the individual fault bounded blocks, keeping
in mind the Tertiary block faulting, approximate 45° tilting
to east and gentle warping. Problem: Tertiary cover has been
eroded from most of the area.
5. The study of Wollastonite within the argillaceous limestone
hornfels and magnesium in calcite (marble) as temperature
indicators for emplacement of the contact thermal aureoles
surrounding the high level quartz-monzonite, quartz-diorite
porphyry intrusions in the Hummingbird vicinity. 103.
REFERENCES
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,1902. Preliminary Report on the Boundary Creek District, B.C.; Geol.Surv.Can. Summary Report 1902.
,1905. Geological Map of the Boundary Creek Mining District, B.C.; Geol.Surv.Can. Map 828.
Campbell, R.B., 1966. Tectonic of the South Central Cordillera of British Columbia; C.I.M.M. spec.vol. no. 8, pp.61-72.
Carswell, H.T.,1957. Geology and Ore Deposits of the Summit Camp, Boundary District, B.C.; (unpubl.M.Sc.thesis, U.B.C.)
Church, B.N.,1967. Geology of The White Lake Area. (unpubl.Ph.D. thesis, U.B.C.)
Daly, R.A., 1912. Geology of the North American Cordillera of the 49th parallel; Geol.Surv.Can. Memoir 38.
Drysdale, C.W.,1915. Geology of Franklin Camp, British Columbia; Geol.Surv.Can..memoir 56.
Kerr, P.F.,1959. Optical Mineralogy. McGraw-Hill Book Co. Inc.
Kulp, J.L., 1961. Geological Time Scale. Science, vol. 133, pp. 1105-1104.
LeRoy, D.E., 1912. Geology and Ore Deposits of Phoenix, Boundary District, British Columbia. Geol.Surv.Can.,memoir 21.
Little, H.W., 1957. Kettle River (East Half), Geol.Surv. Canada, Map 6-1957-
, 1957. Nelson Map Area (West Half), British Columbia. Geol.Surv.Can., memoir 308.
— and Thorpe, R.I., 1965. Greenwood (East Half): Geol.Surv. Can., paper 65-1.
Livingstone, W., 1970. Personal Communication.
Mathews, W.H., 1964. Thirteen Potassium-Argon Dates of Cenozoic Volcanic Rocks from British Columbia; Univ. Brit.Col., Dept. Geol., rept. no.2.
-, 1964. Potassium Argon Determinations of Cenozoic Volcanic Rocks from British Columbia. Geol.Soc.Am.,bull.v.75, pp.465-468. 104.
Monger, H.W.H., 1968. Early Tertiary Stratified Rocks, Greenwood Map Area, British Columbia. Geol.Surv.Can.,paper 67-42.
Moore, R.C., 1957. Treatise of Invertebrate Paleontology, part L. Geol.Soc.America, Univ.Kansas Press, pp.179-180.
, Lalicker, and Fischer, 1952. Invertebrate Fossils. . McGraw-Hill, pp.423-429.
McNaughton, D.A., 1945. Greenwood-Phoenix Area, British Columbia. Geol.Surv.Can.,paper 45-20.
Newell, J.M., 1969. Report on Preliminary Reconnaissance Boundary District, Greenwood Mining District, British Columbia. Texas Gulf Sulphur Company, unpublished report.
Parker, R.L. and Calkins, H.A., 1964. Curlew Quadrangle, Ferry County, Washington. U.S.Geol.Surv.,bull.1169.
Ross, J.V., 1970. Personal communication.
, and Christie, J. 1969. Geol.Soc.America, 65th Annual Meeting, Abstract, pt. 3, p.57.
Preto, V.A.G., 1970. Personal Communication.
Seraphim, R.H., 1956. Geology and Copper Deposits of the Boundary District, British Columbia. C.I.M.M. vol.LJX, pp.684-695.
Sinclair, Nguyen, Libby, 1968. Age of the Northern Part of the Nelson Batholith. Can.J.Earth Sci, vol.5, p. 955.
Sutherland-Brown, A., 1968. Lode Metals in British Columbia, 1968. Report of the Minister of Mines and Petroleum Resources, Victoria, pp.233-235.
Tozer, E.T., 1970. Personal communication. Geol.Surv.Can.,Ottawa, Ontario.
Travis, R.B., 1955. Classification of Rocks. Colorado Sch.Mines, Quart.,vol.50, no.1.
Turner and Verhoogen, I960. Igneous and Metamorphic Petrology, 2nd. ed. McGraw-Hill, p.544 pp.
Waters, A.C. and Krauskopf, K., 1941. Protoclastic Border of the Colville Batholith; Geol.Soc.America, bull., vol. 52, no. 9, pp.1355-1417.
White, W.H., 1970. Personal Communication. Williams, H., Turner, F.J., Gilbert, CM., 1954. Petrography; an introduction to the Study of Rocks in Thin Sections. W.H.Freeman and Co.
Winkler, H.G.F., 1967. Petrogenesis of Metamorphic Rocks; 2nd.ed., New York, Springer Verlag Inc., pp.88-115.
Yates, R.B., Becraft, G.E., Campbell, A.B., and Pearson, R,C.,1966. Tectonic Framework of North-Eastern Washington, Northern Montana. C.I.M.M. spec.vol.no.8, pp.47-60. 106.
APPENDIX I : ECONOMIC GEOLOGY
Mining History
Copper-bearing calc-silicate skarn deposits within the Grand Porks-
Greenwood area have been by far the most important metal producers in the Boundary District. First discoveries were made in 1891 and by the end of that year the three major mining camps: Deadwood camp, west of
Greenwood; Phoenix and Summit camps between Grand Forks and Greenwood had been discovered. Granby Mining Company's first copper smelter, in which 14 millions tons of ore were treated, was established at Grand
Forks in 1900. Two other smelters were located at Greenwood and Boundary
Falls, between 1900 and 1919. During the years of 1898 and 1904, the
Canadian Pacific Railway and Great Northern Railroad extended their lines to reach the town of Phoenix.
Summit City, now overrun by the present highway near the Oro
Denoro workings, was established in the late 1890's and became the centre of the Summit camp; which included the Oro Denoro, Emma, Jumbo,
Swallow, Pyrrhotite showings, Mount Rose, Bluebell, B.C., and R.Bell
Mine workings(see geological map in back folder). Total production from this camp between 1899 and 1939 amounts to approximately 507,346 tons of shipped/treated ore; producing 17,981,427 pounds of copper,
326,863 oz. of silver and 507,536 oz. of gold, the majority of this coming from the Oro Denoro, Emma and B.C. Mines (Carswell, 1957).
The average grade for the camp was about 1.1% copper, 0.03 oz./ton Au and 0.25 oz./ton Ag.
The districts' mining boom ended by 1920 and from then, until 107.
Granby Mining Company resumed operation at Phoenix in 1959, mining in
the district was sporadic and on a small scale. The present Granby
property at Phoenix encompasses the old Knob Hill - Ironsides, Brooklyn-
Stemwinder and Snowshoe workings together with several smaller properties.
Total production up to 1966 amounts to approximately 19 million tons
yielding 750,000 ounces of gold, 416 million ounces of silver and
384.6 million pounds of copper. Current production is at a rate of
2000 tons/day grading 0.65$ copper, 0.03 oz/ton Au and 0.15 oz/ton Ag.
(Newell, 1969). Attwood Copper Mines Limited conducted exploration work
throughout the Boundary district from 1951-53 and extended the areas of
known mineralization discovered by the old timers in the Phoenix camp.
Late in 1955, Noranda Exploration Company optioned 50 claims in the
Summit Camp and began detailed property examinations.
Recent history of the Boundary District presents a picture of
generally sporadic exploration, largely directed towards reactivating
old properties. Since the summer of 1967, many Vancouver-based companies have undertaken reconnaissance programmes in the area.
Mineralization
Copper skarn mineralization occurs typically within the argillace• ous Brooklyn Limestone close to the underlying Sharpstone Conglomerate and adjacent to or near intrusive bodies of Nelson granodiorite or
Tertiary quartz-monzonite or quartz-diorite porphyry. Metallic minerals are chalcopyrite, pyrite, specularite, and magnetite, the latter being 108.
strongly developed in the Summit Camp. Gangue is variable, but almost
always a calc-silicate in which chlorite, epidote, calcite, garnet,
quartz and various amphiboles or pyroxenes are developed to different
degrees; garnet, calcite and epidote predominating in the Summit camp.
At the Summit camp, sulphide minerals occur in irregular fractures usually filled with calcite, and as irregular coarse-grained streaks,
clots and relatively fine-grained disseminations. The orebodies,
particularly the high-grade sections, are irregular in shape, but con•
form to the gross stratigraphy.
High-grade ore was taken out of glory holes by the old timers.
The B.C. mine in the Summit camp, had the highest grade in the Boundary
District averaging about 9$ copper during early production and having an overall average grade of about 5.6$ copper up to 1901.
The richest mining camp of the Boundary District, Phoenix,
consists of much lower grade and larger mineralized areas than the
Summit camp. Here the predominent metallic minerals are pyrite and
chalcopyrite with minor specularite as opposed to magnetite and hematite
of the Summit camp. The preponderence of chlorite, epidote and calcite gangue in the skarn zone also differs from the andradite garnet and epidote found at the Summit camp.
Skarns of the Summit camp are products of contact metamorphism by the Kelson granodiorites, whereas Phoenix is believed to be a pyro- metasomatic skarn, since the nearest reported intrusive is several miles to the north.
Several small skarn-type prospects carrying minor magnetite, pyrite, 109.
and chalcopyrite have been found within the Brooklyn Limestone adjacent
to several small, irregular, quartz-diorite and quartz-monzonite
porphyry bodies in the northern part of the map area. These include
the Rathmullen, Sailor Boy, Shickshock showings and several small workings
northwest of Hardy Mountain and south of Eagle Mountain.
Veins and shear zone mineralization occur mostly within the Frag•
mental Andesite rocks and in some cases within the underlying Brooklyn
Limestone and Sharpstone Conglomerate sequence. This type of mineraliza•
tion, is ubiquitous and occurs as irregular veins and stringers of quartz
and calcite with pyrite as the common sulfide, but minor chalcopyrite
and in a few cases galena and sphalerite has been found. The diggings
west of Hardy and Eagle Mountains are typical examples that have not
gone past the prospect stage.
, Pyrite, pyrrhotite, sphalerite and minor galena? occur as concen•
trations along the apex of minor folds within a well-bedded, hornfelsed
argillaceous limestone unit at the Hummingbird showing. This mineraliza•
tion is typical of the high temperature contact thermal deposits sur•
rounding high level, high temperature intrusions. Galena, sphalerite,
pyrite and minor chalcopyrite? have also been found within granular,
hornfelsed, bleached limestone (marble?) adjacent to several easterly
trending quartz-monzonite porphyry dykes south of Eagle Mountain.
Several small pyrrhotite, pyrite and minor chalcopyrite massive
sulphide showings are found within intensely sheared areas underlain by
siliceous rocks of the Anarchist Group. The Packrat showing located about 1-jjr miles northeast of the B.C. mine is a typical example. Here 110. about 2000 tons of massive sulphides have been .stockpiled and it appears that very little if any has been shipped. 111.
APPENDIX II
FOSSIL LOCATION AND DESCRIPTIONS
1. Found in outcrop AR322 along the southern Provincial Highway
approximately 1 mile south of the Oro Denoro workings. Numerous
black to dark broken, flattened, often overlapping casts and
impressions of the pelecypod Halobia or related Daonella. Several
of the fragments up to 1" across, compressed parallel to bedding,
show the general outline of the pectinoid pelecypod and strongly
developed plicae.They occur within the pale grey to tan micro-
crystalline limestone unit of the Brooklyn Limestone. Suggests a
shallow water environment.
Halobia an early or medial Late Triassic age.
Daonella much larger range from Mid.-Late Triassic.
2. Found in outcrop AR251C. a large railroad cut along the Canadian
Pacific Railway tracks approximately mile south of Neff Creek.
Numerous, up to 1-2$ of the whole rock, broken crinoid stems, 2-3
mm in diameter and 3-4 times as long, have been found lying
parallel to the bedding plane with random orientations. The host
rock is a fine-grained dark grey argillaceous limestone. The crinoid
stems are composed of white, crystalline, sparry? calcite or
dolomite and appear to be totally recrystallized.
3. AR432A located approximately -jp-f mile south of Goat Mountain.
Consists of numerous minute partially recrystallized ammonoids set
in a fine-grained dark grey to black well bedded argillaceous lime•
stone. They are very small, generally from 1-5 mm, typically 112. subglobose, involute, low arched venter, smooth, exhibit ceratitic sutures with large number of elements, approximately six in mature specimens (see Figures 9 and 10, pp. 113 and 114). The ammonoid has been tentatively identified as possibly genus Megaphyllites or maybe
Parapopanoceras by E.T. Tozer (personal communication, 1970).
order Ammonoidea
suborder Ceratitina
superfamily Arcestaceae
family Megaphyllitidae
genus Megaphyllites
Range - Megaphyllites
Norian Mid-Upper Triassic
Anisian lowest Middle Triassic. Genus Megaphyllites (Mid. - Upper Triassic)
subglobose, involute, low arched ventre, smooth, ceratitic suture with large number of elements.
Figure 9 Sketch and measurements of Megaphyllites. Suture Patterns
Mature
f
The juvenile (early) whorls appear to have goniatitic sutures suggesting a very primitive ceratitic suture type.
Figure 10 Mature to juvenile suture patterns of Megaphyllites.