canada - government of newfoundland and labrador

L'Initiative G oscientifique Ciblée 3é

Targeted Geoscience Initiative 3G

Buchans

CTGBuchans

* 1A. Zagorevski , G.W.H van Hees , N. Rogers1

*corresponding author email: [email protected] Survey of Canada, 601 Booth St., Ottawa, Ontario, Canada; Department of Earth Sciences, University of Ottawa, 140 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5

Provisional nomenclature of the volcanic rocks in the Buchans area, central Newfoundland

CanadaRessources naturellesCanada

Natural ResourcesCanada

A.

B.

SKI HILL Fm.

Erosion

BUCHANS RIVER Fm.

C.

Inversion

Internal imbrication

“Footwall Arkose”

D.Local overtuningSANDY LAKE FORMATION

SKI HILL FORMATION

H-3329 H-2854H-2853H-2849

100

200

300

De

pth

(m

)W E

?

?

H-3329 H-2803 H-2802 H-2801 H3342H3343 H3341

G

G

G

G

N S

O*G

G

GG

G

G

GG

G G

OO O

OG

G

O

Granitoid clasts

Pb-Zn-Ba ore

Felsic volcanic

Sedimentary and epiclastic rocks

Mafic volcanic

Diabase

Jasperite

H-2849 H-2850 H-1817 H-1826 BR2K0104 H-1570 H-1545 H-1437 H-1287 H-1326 H-1306 H-1247 H-1241 H-1357 H-1252 H-3180 H-3181 H-3177/8/9

N S

H-08-3369A H-08-3365H-08-3372H-08-3376H-08-3396H-08-3388 H-08-3395 H-08-3393H3341H-08-3378

100

200

H3344

300

400

De

pth

(m

)

W E

SKI HILL FORMATION

SANDY LAKE FORMATION

“Footwall Arkose”

SKI HILL FORMATION

BUCHANS RIVER FORMATION

100

200

300

De

pth

(m

)

SKI HILL FORMATION

SKI HILL FORMATION

BUCHANS RIVER FORMATION

BUCHANS RIVER Fm.

BUCHANS RIVER Fm.


?

?

Humber Zone

Gander Zone

Avalon Zone

Go

nd

wan

an

Marg

inL

au

ren

tian

Marg

in

Dunnage Zone

Dunnage Zone

Notre Dame Subzone

Carboniferous Basins

Ophiolitic Rocks

Avalonian rocks in theHermitage Flexure

Exploits Subzone

Notre DameBay

Gulf of St. Lawrence

N

RIL

RIL

RIL

HMT

HMT

Gullbridge

Notre Dame Arc

Exploits Subzone

Annieopsquotchaccretionary tract

Gander Zone

57°49°

57°

49°

050 100km

Buchans

DiscussionThe presence of multiple tectono-stratigraphic units in the Buchans area provides an exciting opportunity

for exploration in multiple adjacent VMS-prospective terranes that include the Mary March Brook formation, Buchans Group and Red Indian Lake Group. Each unit is distinguished by its own stratigraphy and geochemistry; hence, the exploration strategy has to be catered to individual terranes. The terranes form a thrust stack (cf. Thurlow et al., 1992) with Mary March Brook formation occupying the highest structural level and Red Indian Lake Group at the lowest structural level. The stacking and internal imbrication of the units indicates that mineral potential is open at depth. The stratigraphies of the Mary March Brook formation and Red Indian Lake Group have been previously discussed (Zagorevski and Rogers, 2008, 2009 and Zagorevski et al., 2006 respectively). The following discussion concentrates on the Buchans Group.

Relogging and examination of historical diamond drill hole logs has revealed significant thickness variation in the Buchans River Formation. The Buchans River Formation rhyolite flows and epiclastic-sedimentary rocks thicken dramatically south of Ski Hill. This variation is attributed to existence and preservation of a syn-volcanic extensional fault system that controlled the primary distribution of the volcano-sedimentary units. Such faults have been suggested but not identified by several previous researchers (e.g., Kirkham and Thurlow, 1987). Subsequent tectonism resulted in structural inversion and reactivation of the fault fault system as a steep reverse fault, accompanied by structural imbrication of the Buchans River Formation (cf. Calon and Greene, 1987).

The redefinition of the Sandy Lake Formation mainly results from the re-interpretation of historical diamond drill hole logs. The Sandy Lake Formation pillow basalts lie either above sheared Buchans River Formation or above a diabase. Considering that Silurian diabase dykes commonly intrude along Ordovician thrusts, the occurrence of sheared rocks and diabase along the contact between the Buchans River and Sandy Lake formations is interpreted to represent a thrust. Since the type locality of the Sandy Lake Formation occupies the highest structural level in the Buchans Group, it must represent either a structural repetition of the Ski Hill Formation or the stratigraphic base of the Ski Hill Formation.

IntroductionThe Buchans - Robert’s Arm belt comprises an imbricated peri-Laurentian continental arc

sequence that hosts the world-class Buchans VMS ore bodies. The Buchans mining camp produced 16.2 million tonnes of ore at an average grade of 14.5% Zn, 7.6% Pb, 1.3% Cu, 126 g/t Ag and 1.37 g/t Au. The ore was predominantly mined from five main orebodies thought to represent a single stratigraphic horizon within the Buchans Group (Thurlow and Swanson, 1987). Re-evaluation of the Buchans - Robert’s Arm belt tectonostratigrapy suggests it is a composite terrane comprising several tectonically juxtaposed, unrelated units with a complex structural history.

In this contribution, the stratigraphy proposed by Thurlow and Swanson (1987) is provisionally revised. The definition of the Ski Hill Formation is expanded to include some Lundberg Hill Formation rocks. The definition of Buchans River Formation is also expanded and now includes some Sandy Lake Formation rocks. The definition of the Sandy Lake Formation is revised to be consistent with its type locality. Lundberg Hill Formation is abandoned as a stratigraphic term. Several new litho-stratigraphic units are proposed. These include Harry’s River ophiolite complex, Mary March Brook formation and Ken’s Brook formation. Other units are included in the previously defined Red Indian Lake Group (Zagorevski et al., 2006; Rogers et al., 2005).

Revised Nomenclature

SPRINGDALE GROUPKen's Brook formation – Commonly red-weathering subareal flow-banded to massive rhyolite and

commendite associated with coeval mafic sills and tuffaceous sediments (c. 426 Ma).

HARRY'S RIVER ophiolite complexTholeiitic BAB-like pillow basalt, sheeted diabase, massive diabase and gabbro. Highly strained and

metamorphosed to amphibolite facies below the Hungry Mountain Thrust (ca. 473-468 Ma on the basis of correlation with the Lloyds River Ophiolite Complex).

(The following units do not have any stratigraphic linkages with the type localities of the Buchans Group nor Robert’s Arm Group. They appear to be correlative to some tracts in the Gullbridge area: see O’Brien, 2009 and 2008)

Mary March Brook formation – Bimodal tholeiitic sequence comprising massive to flow-banded, aphyric to quartz and feldspar-phyric, locally columnar jointed rhyolite and associated pyroclastic rocks interlayered with pillowed to brecciated mafic volcanic rocks. Type locality occurs to the east of and along the shores of Mary March Brook (ca. 462 Ma and older: Zagorevski and Rogers, 2008, 2009).

Woodman's Brook member – colourful volcanic and sedimentary derived breccia that includes jasper, chert, siliceous black siltstone, basalt, rhyolite and dacite blocks in a locally soft-sediment deformed gritty sedimentary matrix. Associated with blue-grey dacite tuff and domes that locally form peperitic contacts with sediment and rare limestone. The Woodman’s Brook Member is well exposed along the Middle Branch Brook; however, the name is derived from Woodman's Brook breccias from exploration diamond drill cores in the Woodman's Brook area.

Seal Pond member – quartz-megacrystic rhyolite. Type locality occurs to the east of Seal Pond (c. 462 Ma). May have been previously mapped as the “prominent quartz rhyolite”.

BUCHANS GROUPBuchans River Formation – Predominantly massive to flow banded (ca. 465 Ma Clementine

rhyolite) and locally columnar jointed (ca. 465 Ma Oriental rhyolite) calc-alkaline rhyodacite to rhyolite and related pyroclastic rocks. Also includes blue-grey calc-alkaline dacite and related tuffaceous rocks (ca. 463 Ma MacLean dacite), granitoid-bearing conglomerate, volcanogenic conglomerate, sandstone, and turbiditic wacke. These rocks are locally associated with Ba-Pb-Zn-Cu bearing exhalative VMS (transported orebodies) and stockwork Cu-rich mineralization (e.g., Lucky Strike). Type locality occurs along the Buchans River near the “Discovery” outcrop. The revised formation includes some c. 463 Ma rocks previously assigned to the Sandy Lake Formation as those are either indistinguishable from Buchans River Formation or do not form mappable units. Basalt structurally underlying the “footwall arkose” remains unnamed (Tilley’s Pond?).

Ski Hill Formation – Predominantly calc-alkaline mafic breccia (Ski Hill) with minor sedimentary and felsic pyroclastic rocks underlain by mafic tuff, chert, jasperite, turbiditic sedimentary rocks (previously Lundberg Hill Formation) and minor limestone. Type locality is “Ski” Hill immediately north of the Lucky Strike Glory Hole.

Sandy Lake Formation –Calc-alkaline pillow basalt, massive basalt, basaltic breccia and mafic tuff, quartz-phyric rhyolite (“prominent quartz dacite/rhyolite”) with subordinate jasperite, felsic tuff and minor sedimentary rocks including limestone. Contained in a thrust sheet structurally overlying Buchans River Formation and Ski Hill Formation. Type locality occurs along the western shore of Sandy Lake and in DDH along the southeastern shore of Sandy Lake.

Wiley's Brook complex – Defined by the quartz-phyric pink-weathering biotite and locally hornblende-bearing granodiorite (c. 467 Ma). Appears to be associated with felsic volcanic and pyroclastic rocks. Type locality is on Wiley’s Brook.

RED INDIAN LAKE GROUP (follows Zagorevski et al., 2006 and Rogers et al., 2005)

Healy Bay Formation – Felsic tuffs and rhyolite hosting Connel Option prospectHarbour Round Formation – Calc-alkaline mafic volcanic rocks hosting Mary March prospect Skidder Formation – Tholeiitic mafic volcanic rocks hosting Skidder prospect

ABANDONED STRATIGRAPHIC TERMINOLOGY

Lundberg Hill Formation – There is no geographic feature called Lundberg Hill.Feeder granodiorite – Renamed to Wiley's Brook granodiorite to conform to the type locality and to remove any genetic implications from the nomenclature.Footwall arkose (informal) – Re-assigned from the Sandy Lake Formation to the Buchans River Formation and to the Healy Bay Formation where it occurs below the Powerline Thrust.Prominent quartz rhyolite/dacite (informal) – this a distinctive but non-unique rhyolite that occurs in several distinct structural panels including tholeiitic Mary March Brook formation and calc-alkaline Buchans River and Healy Bay formations.

BUCHANS GROUP

Buchans River Formation

Buchans Group

Ski Hill Formation

Sandy Lake Formation

Mary March Brook formation

Red Indian Lake Group

Healy Bay formation

Harbour Round formation

Skidder formation

Harry’s River ophiolite complex

Springdale Group

Ken’s Brook formation

Basalt (Tilley’s Pond ?)

Felsic volcanic rocks

Polylithic breccia-conglomerate


Basalt

Interlayered felsic and mafic tuff, chert, jasper, and siltstone

Basalt

Calc-alkaline basalt

Polylithic breccia-conglomerate

Tholeiitic basalt

Felsic volcanic rocksFelsic volcanic rocks

Tholeiitic felsic volcanic rocks

Woodman’s Brook member

Basalt or bimodal volcanics

Tholeiitic basalt, diabase an gabbro


465

467

463 462

465

463

465

466

467i

467i

462 c. 462 Ma U/Pb zircon igneous crystallization age

c. 467 Ma U/Pb zircon youngest igneous provenance age

6 km

N

PQ “Prominent quartz”

.1

1

10

100

Th Nb La Ce Nd Sm Zr Hf Eu Ti Gd Dy Y Er Yb Lu

Rock/N-MORB Sun and McDonough, 1989 (redux)

.1

1

10

100



.1

1

10

100



.1

1

10


BR basaltMcLean daciteOriental rhyoliteSL rhyoliteSki Hill basaltSL basalt


WB granodiorite

.1

1

10

100



PQ

PQ

PQ

PQ

PQ

PQ

PQ

PQ

PQ

PQ

H2762H1896 H2841H1960 H1939 H2851 H3330H2105

PQ

PQ

PQ

?

W E


Wiley’s BrookComplex

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