Download - Roundup 2010 Poster

Natural ResourcesCanada

Ressources naturellesCanada

Geological Survey of Canada

Commission géologique du Canada

46721 m1 mm = 200 m

m a

sl

1 c

m =

200 m

x10 vertical exaggeration

X X’

500

700

900

1100

1300

Nechako Valley

Stewart Valley

extensive Chilcotin Group

?

093K/01 093J/04

093G/13093F/16

X

X’

bedrock (m asl)

400 1300850

drift thickness (m) = 7n 50

< 5 5 - 10 10 - 20

20 - 50 > 50

bedrock intersection point

“push down” point

10km0

1:500,000

Vanderhoof

Tachick Lake

Stewart Valley

Cluculz Lake

Nechako Valley

CO

AST

MTN

S

INTERIOR

PLATEAUS

CARIBOO

MTNS

ROCKY

MTNS

Distribution and Thickness of basalts and drift on the Interior PlateauDistribution et épaisseur des basaltes et des sédiments glaciaires de la région du plateau intérieur

1. Geological Survey of Canada, 625 Robson Street, Vancouver, British Columbia. V6B 5J3 Canada;2. EOS-UBC, 6339 Stores Road, Vancouver, British Columbia. V6T 1Z4 Canada3.

email: [email protected]

Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario. K1A O8E Canada

Graham D.M. Andrews , Jackie Dohaney , Kelly Russell , Alain Plouffe , Robert G. Anderson1 2 2 3 1

093B/15 093B/16

093G/01093G/02

Quesnel

X

X’

24341 m1 mm = 200 m

900

700

500

300

m a

sl

1 c

m =

200 m


X X’

Fraser Valley

perchedremnantsof Chilcotin Group

bedrock (m asl)

400 1300850

drift thickness (m) =n 2150

< 10 10 - 20 20 - 50

50 - 100 > 100



10km0

1:500,000

Fra

ser

Valle

y

Fra

ser V

alle

y

CO

AST

MTN

S

INTERIOR

PLATEAUS

CARIBOO

MTNS

ROCKY

MTNS

X

X’

1500

1300

1100

900

61360 m1 mm = 300 m

m a

sl

1 c

m =

300 m


X X’

Green Lake

Chilcotin Group veneer

092P/14092P/15

092P/11

092P/06

092P/07

092P/10

bedrock (m asl)

400 1300850

drift thickness (m) = 777n

< 5 5 - 10 10 - 20

20 - 50 > 50

10km0

1:500,000

100 Mile House

Lac la Hache

Forest Grove

Bridge Lake

70 Mile House

Lone Butte

Gre

enLake

Lac la Hache

Canim Lake

Rayfie

ldValle

y

CO

AST

MTN

S

INTERIOR

PLATEAUS

CARIBOO

MTNS

ROCKY

MTNS

“COVER”( ) Typical till veneer (<1 m) covering granitebedrock (092P). ( ) Forested till blanket (>1 m)covering “thin” (<20 m) Chilcotin Group basalt(092P). ( ) Gravel-rich esker (~10 m)deposited on an eroded bedrock surface. ( )“Thick” (>20 m) basalt lava pile filling apaleovalley at Chasm Provincial Park (092P).( ) Ancestral Chilcotin River filled by “thick”basalt and pillow-breccia succession nearAlexis Creek (093B).

AB

CD

E

A B

C

D

E

Quaternary deposits

basement -Mesozoic

sedimentary rocksbasement -Mesozoic

sedimentary rocks

subaerial lavassubaerial lavas

bedded hyaloclastitepillow breccia

Pliocene Chilcotin River valley floor

Quaternary deposits

Quaternary depositsPresent Chilcotin River valley floor

70 m

450 m

W E

Water Well Records ( = 10,486)n Bedrock Intersection Points ( = 3,189)n

V

PG

Q

100

WL

V

PG

Q

100

WL

092N 092O

092P

093C 093B 093A

093F 093G 093H

093K 093J 093I

0 50 km

V

PG

Q

100

WL

092N 092O

092P

093C 093B 093A

093F 093G 093H

093K 093J 093I

0 50 km

SkeenaDrainage

Basin

Colu

mbia

Dra

inage

Basi

n

0 km 100

Peace Drainage(Arctic)

‘Coastal’ Drainage

Basin

C - intraglacial >30 ka

alpine ice-cap

catchment boundary new canyon

river course

new river course

Dog Creek dam

abandoned channel

sea

impounded lake

decaying ice mass

continental divide

ice thickness (m)

SkeenaDrainage

Basin

0 km 100

Colu

mbia

Dra

inage

Basi

n

Fraser-PeaceDrainage Basin

(Arctic)

A - intraglacial c. 1.06 Ma

‘Coastal’ Drainage

Basin

0 km 100

B - deglaciation post-1.06 Ma

Prospectivity on the Interior Plateau has hitherto been hamperedby a lack of data to determine the areal distribution and verticalthickness of Chilcotin Group basalt lavas and Quaternary drift.Research at UBC supported by the GSC TGI-3 and MPB programsand Geoscience BC reveals that basalt cover is thinner and lessextensive than previously thought (<40%) across the InteriorPlateau. It is only thick (>20 m) in paleovalleys that can be readilyidentified in geological and geophysical surveys. Similarly,Quaternary drift, although areally extensive, is only thick inpaleovalleys. We have mapped cover thickness variations inseveral areas on the Interior Plateau (below) using a combinationof field observations, water well records, and archivedgeological, geochronological, geophysical, and MINFILE datasets; the results of which are presented here and will bepublished soon.

X

X’

092O/16

1000

800

600

28889 m1 mm = 200 m

m a

sl

1 c

m =

200 m


X X’Williams Lake

Creek

Chilcotin Group veneer

Williams Lake

150 Mile House

Miocene

McLeese Lake

Springhouse

Fra

se

r V

alle

y

bedrock (m asl)

400 1300850


< 5 5 - 10 10 - 20

20 - 50 > 50



10km0

1:500,000

092P/13

093A/04093B/01

093A/05

093B/08

CO

AST

MTN

S

INTERIOR

PLATEAUS

CARIBOO

MTNS

ROCKY

MTNS

WATER WELL MODELINGY

Y’

X’

X

bedrock (m asl)

400 1300850


< 10 10 - 20 20 - 50

50 - 100 > 100



10km0

1:500,000

Nechako Valley

Fra

ser

Valle

y

Fra

ser

Valle

y

Chi

lako

Val

ley

Prince George

Beaverley

Ferndale

093G/09

093G/10093G/11

093G/16093G/15

093G/14

093J/01093J/02093J/03

X’X

m a

sl

1 c

m =

200 m

400

600

800

1000

1200

48131 m1 mm = 200 m

Fraser ValleyChilako Valley


CO

AST

MTN

S

INTERIOR

PLATEAUS

CARIBOO

MTNS

ROCKY

MTNS

49167 m1 mm = 200 m

m a

sl

1 c

m =

200 m

Y Y’

800

600

Fraser Valley

Fraser Valley


buried paleochannel

buriedpaleochannel

buriedpaleochannel ?

buriedpaleochannel ?

Please see accompanying student posters by Jackie Dohaney (new map of Chilcotin basalt distribution) and Rebecca-Ellen Farrell (new map of Chasm Provincial Park)

1

2

3

45

1 - Quesnel area

3 - 100 Mile House area

2 - Williams Lakearea

4 - PrinceGeorge area

5 - Vanderhoof area

Water well logs recorded by the Province of BritishColumbia provide valuable subsurface data, in particularfor identifying the cover - bedrock surface. Wells areunevenly distributed across the Interior, concentratedaround cities and along major highways ( .

The base of the drift and the base of the Chilcotinbasalts have been identified in over 7,000 and 3,000wells respectively. These points can be interpolated toform bedrock elevation maps ( and )depicting the drift thickness (points). These maps areimproved by integration of outcrop and surficial geologymap data-sets. Cross-sections can be drawn to depictthe present-day and buried bedrock surfaces.

The take-home messages are:1. - the use of this data-set to constrain the depth to

bedrock (data and maps available soon!)2. - the discontinuous and thin nature of the Chilcotin

basalts, and thick drift only in major valleys.3. - the presence of abandoned valleys and major

erosion along the Fraser River after eruption ofbasalts and before the last glaciation (

).

above)

below right

see nextpanel - Reversal of the Fraser River

0 km 100

D - present-daypresent course

parallel ancient drainage

anti-parallel ancient drainage REVERSAL OF THE FRASER RIVERAnewly identified volcanic dam, formed at 1.06 Ma, indicates northward

flow of the Fraser River and the absence of the Fraser Canyon at that time.This requires reversal of the Fraser River’s flow and carving of the canyonin the last 1 million years. Erosion of the Fraser Canyon caused the baselevel of the drainage basin to drop, carving deep canyons in sometributaries, and abandoning others. We attribute the reversal to ice-damming during the end of a c. 1 Ma glaciation.

The implications of this for exploration are as follows:1. - Reversal means that the Fraser River and some tributaries

have changed their course in the last 1 Ma. Fluvialsediments and detrital minerals deposited before 1 Ma were transportedaway from source (e.g., mineral deposit) Tributariesin the west appear unchanged, but those in the east may be completelyreversed.

2. - Reversal probably occurred multiple times after initial reversal at c. 1Ma, therefore, detrital minerals may have been carried

3. - Contemporary and later glacial deposits recycled this alluvialsediment and redistributed it - therefore tills in the reversed valleys andadjacent areas, especially older tills, may have very complex detritalsource histories.

4. - This event abandoned channels of the old drainage on the InteriorPlateau, many subsequently buried. These are potential .

apparently upstream!

upstreamdownstream.

and

placer deposits

(e.g., theThompson River) the