quaternary geology of the buchans area, newfoundland: implications for mineral exploration

15
Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration1 R.A. Klassen and Julian B. Murton Abstract: Mineral exploration for volcanogenic massive sulphide deposits in the Buchans area of central Newfoundland is hindered by thick and widespread Quaternary overburden comprising glacial, glaciolacustrine, glaciofluvial, and resedimented deposits. Mapping of striations and indicator erratics suggests that the area was affected by four ice-flow events: I, southward; II, northeastward and westward to southwestward; 111, southward; and IV, northeastward and southwestward. Vertical and areal distributions of lead, copper, and zinc indicate that till and glaciolacustrine sediments overlying sulphide deposits can be enriched in mineralized debris. Near mines at Buchans surficial debris-flow deposits contain much material derived from the Topsails igneous terrane and are generally impoverished in mineralized debris. Southwest of Buchans, however, they can be enriched. Mineral exploration in the Buchans area must take into account that (i) sulphide-rich debris in till does not reflect only the youngest ice-flow event; (ii) glaciolacustrine sedimentation and resedimentation can result in burial of older sediments containing mineralized debris, in the redistribution of that debris, and in the geochemical masking of subcropping ore deposits; (iii) dispersal of sulphide debris during resedimentation is not necessarily related to ice-flow directions indicated by striations; (iv) a geochemical dispersal train originating at Buchans reflects both southwestward glacial transport and later redistribution of mineralized debris within debris-flow and glaciolacustrine deposits; and (v) marked geochemical variations with depth can occur with small variations in sampling depth, reflecting change in provenance and depositional process. The depositional and ice-flow model developed for the Buchans area likely has wider application in central Newfoundland. R6sum6 : La prospection de gites de sulfures massifs d'origine volcanogenique dans la rCgion de Buchans, partie central de Terre-Neuve, est compliquCe par la prCsence d'une couverture de matkriaux meubles incluant des dkp6ts d'origine glaciaire, glaciolacustre, glaciofluviale et de reskdimentation. La cartographie des stries glaciaires et des blocs erratiques indicateurs suggbe que la rkgion a subi quatre Cvknements d'Ccoulements glaciaires : I, vers le sud; 11, vers le nord-est et ouest h sud-ouest; 111, vers le sud; et IV, vers le nord-est et sud-ouest. Les dissCminations verticale et surfacique du plomb, cuivre et zinc indiquent que le till et les skdiments glaciolacustres qui recouvrent les indices de sulfures peuvent avoir CtC enrichis de fragments min6ralists. Prts des mines h Buchans, les dCp6ts de surface composCs de dkbritites glaciaires renferment une forte proportion de matkriel dtrivC du terrane ignC de Topsails, et gCnkralement les fragments minCralisCs y sont peu friquents. Cependant, au sud-ouest de Buchans ils peuvent &re plus abondants. La prospection miniere dans la region de Buchans doit tenir compte que (i) les fragments riches en sulfures dans le till ne reflttent pas uniquement le dernier Cvknement d'Ccoulement glaciaire; (ii) la skdimentation glaciolacustre et la reddimentation peuvent avoir eu pour consiquences un enfouissement de skdiments plus anciens contenant des fragments minCralisks, une redistribution des fragments et un masquage gkochimique des indices minkralists recouverts par les matkriaux meubles; (iii) la dispersion des fragments minCralis6s en sulfures durant le processus de reskdimentation n'est pas nkcessairement relike aux directions des kcoulements glaciaires rkklkes par les stries; (iv) la tralnke secondaire de dispersion gkochimique partant de Buchans tCmoigne h la fois du transport glaciaire vers le sud-ouest et de la redistribution subsiquente des fragments minCralisCs observks dans les dkp6ts glaciolacustres et les dCbritites glaciaires; et (v) d'importantes variations gkochimiques avec la profondeur peuvent apparaitre suite & de petites variations dans la profondeur de l'khantillonnage, indiquant un changement de provenance des matkriaux et du processus de dCp6t. Le modtle d'Ccoulement glaciaire et de dCp6t ddCeloppC pour la rkgion de Buchans peut &re appliquC ailleurs dans toute la partie centrale de Terre-Neuve. [Traduit par la rCdaction] Received December 1, 1994. Accepted May 3, 1995. R.A. Kla~sen.~ Geological Survey of Canada, 601 Booth Street, Ottawa, ON KIA OE8, Canada. J.B. Murton. Department of Earth Sciences, University of Wales, Cardiff, P.O. Box 914, Cardiff CF1 3YE, Wales, United Kingdom. ' Geological Survey of Canada Contribution 43894. Corresponding author (e-mail: [email protected] .ca) . Introduction The Buchans area of central Newfoundland is well known for volcanogenic massive sulphide (VMS) deposits (Fig. 1) (Kirkham 1987). Mined until recently near Buchans, they were among the richest and most productive in Canada, yielding average grades of 14.5 % zinc, 7.6 % lead, and 1.3 % copper. Although the deposits were originally discovered by tracing mineralized boulders in glacial drift (Neary 1981), Can. I. Earth Sci. 33: 363-377 (1996). Printed in Canada / Imprim6 au Canada Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITY OF PITTSBURGH on 11/12/14 For personal use only.

Upload: julian-b

Post on 16-Mar-2017

216 views

Category:

Documents


1 download

TRANSCRIPT

Page 1: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration1

R.A. Klassen and Julian B. Murton

Abstract: Mineral exploration for volcanogenic massive sulphide deposits in the Buchans area of central Newfoundland is hindered by thick and widespread Quaternary overburden comprising glacial, glaciolacustrine, glaciofluvial, and resedimented deposits. Mapping of striations and indicator erratics suggests that the area was affected by four ice-flow events: I , southward; II, northeastward and westward to southwestward; 111, southward; and IV, northeastward and southwestward. Vertical and areal distributions of lead, copper, and zinc indicate that till and glaciolacustrine sediments overlying sulphide deposits can be enriched in mineralized debris. Near mines at Buchans surficial debris-flow deposits contain much material derived from the Topsails igneous terrane and are generally impoverished in mineralized debris. Southwest of Buchans, however, they can be enriched. Mineral exploration in the Buchans area must take into account that (i) sulphide-rich debris in till does not reflect only the youngest ice-flow event; (ii) glaciolacustrine sedimentation and resedimentation can result in burial of older sediments containing mineralized debris, in the redistribution of that debris, and in the geochemical masking of subcropping ore deposits; (iii) dispersal of sulphide debris during resedimentation is not necessarily related to ice-flow directions indicated by striations; (iv) a geochemical dispersal train originating at Buchans reflects both southwestward glacial transport and later redistribution of mineralized debris within debris-flow and glaciolacustrine deposits; and (v) marked geochemical variations with depth can occur with small variations in sampling depth, reflecting change in provenance and depositional process. The depositional and ice-flow model developed for the Buchans area likely has wider application in central Newfoundland.

R6sum6 : La prospection de gites de sulfures massifs d'origine volcanogenique dans la rCgion de Buchans, partie central de Terre-Neuve, est compliquCe par la prCsence d'une couverture de matkriaux meubles incluant des dkp6ts d'origine glaciaire, glaciolacustre, glaciofluviale et de reskdimentation. La cartographie des stries glaciaires et des blocs erratiques indicateurs suggbe que la rkgion a subi quatre Cvknements d'Ccoulements glaciaires : I, vers le sud; 11, vers le nord-est et ouest h sud-ouest; 111, vers le sud; et IV, vers le nord-est et sud-ouest. Les dissCminations verticale et surfacique du plomb, cuivre et zinc indiquent que le till et les skdiments glaciolacustres qui recouvrent les indices de sulfures peuvent avoir CtC enrichis de fragments min6ralists. Prts des mines h Buchans, les dCp6ts de surface composCs de dkbritites glaciaires renferment une forte proportion de matkriel dtrivC du terrane ignC de Topsails, et gCnkralement les fragments minCralisCs y sont peu friquents. Cependant, au sud-ouest de Buchans ils peuvent &re plus abondants. La prospection miniere dans la region de Buchans doit tenir compte que (i) les fragments riches en sulfures dans le till ne reflttent pas uniquement le dernier Cvknement d'Ccoulement glaciaire; (ii) la skdimentation glaciolacustre et la reddimentation peuvent avoir eu pour consiquences un enfouissement de skdiments plus anciens contenant des fragments minCralisks, une redistribution des fragments et un masquage gkochimique des indices minkralists recouverts par les matkriaux meubles; (iii) la dispersion des fragments minCralis6s en sulfures durant le processus de reskdimentation n'est pas nkcessairement relike aux directions des kcoulements glaciaires rkklkes par les stries; (iv) la tralnke secondaire de dispersion gkochimique partant de Buchans tCmoigne h la fois du transport glaciaire vers le sud-ouest et de la redistribution subsiquente des fragments minCralisCs observks dans les dkp6ts glaciolacustres et les dCbritites glaciaires; et (v) d'importantes variations gkochimiques avec la profondeur peuvent apparaitre suite & de petites variations dans la profondeur de l'khantillonnage, indiquant un changement de provenance des matkriaux et du processus de dCp6t. Le modtle d'Ccoulement glaciaire et de dCp6t ddCeloppC pour la rkgion de Buchans peut &re appliquC ailleurs dans toute la partie centrale de Terre-Neuve. [Traduit par la rCdaction]

Received December 1, 1994. Accepted May 3, 1995.

R.A. Kla~sen.~ Geological Survey of Canada, 601 Booth Street, Ottawa, ON KIA OE8, Canada. J.B. Murton. Department of Earth Sciences, University of Wales, Cardiff, P.O. Box 914, Cardiff CF1 3YE, Wales, United Kingdom.

' Geological Survey of Canada Contribution 43894. Corresponding author (e-mail: [email protected] .ca) .

Introduction

The Buchans area of central Newfoundland is well known for volcanogenic massive sulphide (VMS) deposits (Fig. 1) (Kirkham 1987). Mined until recently near Buchans, they were among the richest and most productive in Canada, yielding average grades of 14.5 % zinc, 7.6 % lead, and 1.3 % copper. Although the deposits were originally discovered by tracing mineralized boulders in glacial drift (Neary 1981),

Can. I. Earth Sci. 33: 363-377 (1996). Printed in Canada / Imprim6 au Canada

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 2: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

364

Fig. 1. Location map of Buchans. Inset map of Newfoundland.

Can. J . Earth Sci. Vol. 33, 1996

Buchans Stratigraphic sections 1 Buchans Lake 2 Backhoe Pit 3 Sandfill Quarry

d 7"OO' W 56'30' W

subsequent exploration has been hindered by the thickness and stratigraphic complexity of the drift. Glacigenic sedi- ments in the Buchans area locally exceed 50 m in thickness (e.g., Sparkes 1985) and form the most complete svati- graphic sequence known in central Newfoundland. Within this sequence, compositional variations record changes in provenance resulting from varied directions of sediment transport and processes of deposition. Thus, in order to trace VMS debris to its source(s), there is need for a Quaternary framework for mineral exploration that defines the directions of transport, the depositional processes, and the areal and stratigraphic distribution of VMS debris.

The objectives of this paper are (i) to identify and inter- pret the relationships between drift composition, stratigra- phy, transport directions, and depositional processes; and (ii) to discuss their implications for mineral exploration, both near Buchans and in the wider context of glaciated terrain in the Maritimes. The study area lies within NTS map area 12 Al15, although most detailed work was carried out within 10 krn of Buchans.

Bedrock geology The Buchans VMS deposits occur within the Buchans River Formation, which comprises felsic tuff, rhyolite breccia, pyritic siltstone, wacke, breccia, and conglomerate, and belongs to the late Arenig - early Llanvirn Buchans Group (Kean et al. 198 1 ; lhurlow and Swanson 1987). Some of the VMS deposits subcrop beneath glacial drift, for example at the Oriental and Lucky Strike mines (Fig. 1). Ore-bearing rocks of the Buchans Group contain more barium, lead, and zinc than equivalent rocks unrelated to mineralization (Thurlow et al. 1975).

The country rocks near Buchans belong to the Buchans Group and consist largely of a bimodal suite of basalt and rhyolite (Fig. 2) (Kirkham 1987; Thurlow 1981; Thurlow and Swanson 1987). The ophiolitic Skidder Basalt occurs west and southwest of the Buchans Group, and volcanic and sedimentary rocks of Victoria Lake Group occur south of Red Indian Lake (Kirkham 1987). To the north and northeast of the Buchans Group lies the Topsails igneous terrane (Early Silurian), which includes peralkaline and granitic rock of the Topsails igneous suite, volcanic and sedimentary rocks of the Springdale Group, and intrusive and metamorphic rocks of the Hungry Mountain Complex (Kean 1977; Whalen and

Fig. 2. Bedrock geology map of the Buchans area. Geology simplified after Geological Survey Branch (1988, 1992).

Red Inditw L.

57"OO' W 5630' W

Devono-Carboniferous

Red sandstone, siltstone, conglomerate

Silurian and Younger

Intrusive rock (Topsails igneous suite)

Sedimentary and volcanic rock (Springdale Group)

Ordovician and Younger

Oph~olitic rock (Skidder Basalt)

) Intrusive and metamorphic rock (Hungry Mountain Complex)

Volcanic and sedimentary rock

(Buchans Group)

(Victoria Lake Group)

Thrust Fault (Hungry Mountain)

Currie 1987, 1988). Silurian and Carboniferous sedimentary and volcanic rocks occur in Red Indian Lake basin (Thurlow 1981).

Physiography Central Newfoundland is characterized by broad hills with

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 3: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

Klassen and Murton

Fig. 3. Topography, striations, and glacial landforms of the Buchans area.

----- . Limits of zinc anomalies in drift Stratigraphic sections (after James and Perkins 1981) 1 Buchans Lake

?/, Meltwater channel (sidehill, proglacial; 2 Backhoe Pit direction of flow indicated) 3 Sandfill Quarry

Glacially streamlined landform

Striation

relief of tens to more than a hundred metres and regional ele- vations of 150-500 m asl. Topographic trends in the volcanic temane of the Buchans Group are generally elongate northeast - southwest, parallel to the principal structural trends in bedrock. The highest elevations are over the Topsails Plateau (Fig. 3), an upland of rounded hills and scattered monad- nocks and underlain by the Topsails igneous terrane (Fig. 2). Red Indian Lake occupies part of a northeast-trending fault zone (Kirkham 1987), and Buchans townsite lies within a northwest-trending saddle containing Hinds and Buchans lakes.

Quaternary geology The glacial history of central Newfoundland has been sum- marized by Grant (1974), Grant and Tucker (1976), and Vanderveer and Sparkes (1982). Streamlined landforms define a prominent record of ice flow toward the northeast and southwest, and isolated striations indicate other flow direc- tions (Prest et al. 1969). South of Red Indian Lake, striations and granitic erratics indicate predominantly northeastward ice flow (Murray 1955; Grant and Tucker 1976). In the Buchans area, northwest-southeast trends are evident on radar images (Graham and Grant 1991), and striations record ice flow toward the southwest, southeast, and northeast (Sparkes 1985; Grant and Tucker 1976; Klassen and Hender- son 1992; Klassen 1994a).

Stratigraphic sequences with two compositionally distinct tills occur at OrientaI mine, and in h m w pits south of Red Indian Lake (Mihychuk 1985; Sparkes 1985, 1987). At the former (Fig. I$, the sequence has been interpreted to include ( i ) an older lodgement till containing Buchans Group vol- canic rock and dtposited by northeastward-flowing ice, and (ii) a younger (?meltout) till containing granitic debris deposited by southwestward-flowing ice (Sparkes 1985).

From drift prospxting studies near Buchans, James and Perkins (1981) inferred three ice-flow directions, from oldest to youngest, " . . . a dominant ice movement from the north- east, a prominent movement from the northwest, and an

Fig. 4. Ice-flow events inferred from the trend and relative age of striations. Events are named from oldest to youngest (I -1V) (after Klassen 1994~).

Plateau

48"4S N 57"OO' W

youngest IV

111

11" [= 1 " [=

oldest

obscure movement from the west-southwest. " On the basis of zinc concentrations in "till," they identified a glacial dis- persal train extending more than 8 km southwest of Buchans and containing mineralized erratics of Buchans-type ore (Fig. 3). They also noted that similar erratics occur 10- 20 km east and northeast of Buchans.

Four ice-flow events have been inferred in the Buchans area (Fig. 4) (Klassen and Henderson 1992; Klassen 1994a). They include, from oldest to youngest, early southward flow from the Topsails Plateau (Ia, Ib); a regional northeastward flow possibly followed by a local southwestward flow (Ha, Ib); northward and southward flow, likely confined to the topographic saddle (111); and southwestward and northeast- ward flow within Red Indian Lake basin (IV). Ice divides near Buchans are inferred during events II -1V. Changes in ice-flow direction that cannot be ascribed to a separate ice- flow event are identified by lowercase letters. The model of Klassen (1994~) is more comprehensive than that of James and Perkins (1981) because it establishes the regional context and relative ages of the ice-flow events.

Grant (1974) postulated that ice margins receded during deglaciation toward an ice divide, across central Newfound- land, which later split into separate, shrinking ice caps. Glacial landforms in Buchans saddle indicate that the ice margins receded both eastward toward a cap on the Topsails Plateau and southward from Hinds Lake toward Red Indian Lake basin, where final ice disintegration took place (Grant 1974). A lake, informally named glacial lake Shanadithit, extended to about 59 m above the present level of Red Indian Lake, dammed by the last remnants of ice within Exploits River valley (Mihychuk 1985; Vanderveer and Sparkes 1982).

Methods

Drift samples collected from soil pits and stratigraphic sections were analyzed for geochemical and lithological properties to

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 4: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

366 Can. J. Earth Sci. Vol. 33, 1996

Fig. 5. Graphic logs showing sediments overlying VMS deposits at Oriental mine (A, B) and Lucky Strike mine (C), and sediments at Buchans Lake (D-G), away from known deposits. Logs (A) and (B) are - 100 m apart, logs (D) and (E) 10 m apart, logs (E) and (F) 50 m apart, and logs (F) and (G) 30 m apart. Localities are shown in Fig. 3. *, fabric analysis. Legend on facing page.

(A) Oriental (B) Orlental (C) Lucky Strike .3~% *05;

"nit depth (mi @+& &'& "nit depth (m) @& 4:' "nit depth @l &"& *̂ @I.@

bedrock or boulder surface

Unit

I.. . - . ' * I

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 5: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

Klassen and Murton

Fig. 5 (concluded). Legend.

Sedimentary features - planar to undulatory,

parallel to subpamllel, continuous Strata

inclined, undulatory, 7 contin. to discontin. strata

- planar to undulatory, -- discontinuous strata

irregular (deformed) -%- discontinuous strata

t graded strata

climbing ripple cross-stratification

,A isolated ripple forms

,, muddy lens

sand lens

sand partings

anastomosing fine sand laminae (in silty sand)

Q@ ~rregular sand inclusions - highly irregular sediment fl bodies and streaks

diamicton pods - mud clast

/ fault

OF faceted clast

Bed contacts - - - - - - - gradational

sharp planar - sharp undulating

sharp irregular

DS = decollement surface ES = erosion surface

silty m 6 y gravel

Sediments

Wbbly diamicton - ti rhythmites

I ( sand

determine drift provenance and distances and directions of glacial dispersal. Copper, lead, and zinc were analyzed to trace the dispersal of VMS debris; and chromium, to trace the proportions of Topsails-derived material, which is depleted in this element. The clay-sized ( < 0.002 mm) frac- tion was analyzed using inductively caupled plasma - atomic emission spectrometry (ICP -AES), following hot nitric and hydrochloric acid (LRForte) leach; results are given by Klassen (1994b).

The fine sand fraction (0.063-0.250 mm) was retained for heavy mineral (specific gmvity > 3.3) separation, and the pebble fraction (4.0-5.6 mm) for rock identification. Heavy minerals are reported as percentages of grains counted (1 001, and pebbles as weight percentages; pebble sample weights were typically 20-40 g, representing 50-150 clasts. Two rock types are identified as glacial indicators: (i) unmeta- morphased, pink, medium-grained granite from the Topsaih igneous terrane; and ( i i ) volcanic rock, with a vesicular to amygdular texture, from the Buchans Group.

Grain-size analysis of the < 2.0 mm fraction of sand-rich sediments was by dry sieving at 0.5 4 intervals to 4.5 4. Fabrics were measured from the trend and dip of elongate clasts (2 - 10 cm long) within diamicton; they are character- ized according to their principal, normalized eigenvdues IS1), which represent the degree of maximum clustering about an eigenvector, mean lineation vector, and the strength of clustering (K) (Woodcock 1977).

Sedimentology and stratigraphy

Oriental mine sections

Section A description Two sections, A and B (Figs. 5A, 5B), are located on the southwest and northeast sides of the Oriental mine open pit, - 100 m apart. In section A, five units me distinguished. Unit 1, overlying pyrite-rich bedrock, is a grey compact diamicton (3 m thick). The diamicton is massive and variably matrix to clast supported, the latter being most common in the basal 1 m. The matrix is dominated by poorly sorted coarse sand (84.0-99.0% sand; 1.0-16.0% silt and clay; n = 8) and is locally fissile. Clasts are mainly angular to subrounded pebbles to cobbles. Clast fabric in the lowermost 1.5 m of diamicton shows a weak preferred orientation (S1 = 0.51, K = 0.4, n = 51) and a mean lineation vector of 85", whereas the fabric in the uppermost 0.5 m is strong (S1 = 0.7, K = 1.8, n = 50) and has a mean lineation vec- tor of 224". Single inclusions of sandy diarnicton and clayey silt were observed within the compact diarnicton, as well as several sand lenses about 1 cm thick.

Two metres above bedrock the diamicton contains an irregular body of silt and clay (10-25 cm thick). The body contains indistinct laminae typically 1-5 mrn thick, (sub)- horizontal, discontinuous, and either pinching out or trun- cated by (sub)horizontal sand lenses. The latter are 1 -5 mm thick, 5-50 cm long, and either slightly curved or gently

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 6: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

Can. J . Earth Sci. Vol. 33, 1996

Fig. 6. Silty sandy diamicton containing (A) granitic boulders (arrow) derived from the Topsails igneous terrane, Oriental mine (Geological Survey of Canada (GSC) photograph 1994-618F); (B) sand inclusions (contact with glaciolacustrine sediment shown by broken line; sand inclusions shown by dotted lines and indicated by arrows) (GSC photograph 1994-618A); and (C) thin graded strata with erosive bases, Lucky Strike mine (contacts indicated by broken lines and arrows) (GSC photograph 1994-61 8C).

undulating. The sand lenses and silt and clay laminae curve around and run (sub)parallel to lenses of compact diarnicton (5 10 cm thick and at least 20 cm long) with sharp upper and lower contacts (cf, Hart and Boulton 1991, Fig. 4c). All of the lenses and laminae are (sub)pardel to the bedrock sur- face. Amorphous patches of sandy diamicton are present. Upper and lower contacts of the silt and clay body are irregu- lar and sharp to gradational.

Unit 2 is a 0.6 m thick bed of grey sandy diamicton (91 .O% sand; 9.0% silt and clay in < 2.0 mrn fraction). The loose nature of the diamicton readily distinguishes it from unit 1, and the darker grey colour and composition from unit 3 (see below). The diamicton is matrix supported and mas- sive to poorly stratified, and contains indusions of compact diamicton and red silty sand likely derived from Carboni- ferous bedrock. Elongate clasts show a moderate preferred orientation (SI = 0.63, K = 0.63, n = 50) and a mean line- ation vector of 240".

Unit 3 (1-38 cm thick) comprises pink-grey poorly laminated silt and clay similar to that within the compact diamicton of unit 1 but forming a more distinctive strati- graphic horizon. Unit 3 contains lenses of fine to medium sand, some with granules and pebbles. The lenses are 0.1 - 3.0 cm thick, 2-40 cm long, and commonly bifurcate; they vary laterally in thjckness and truncate the silt and clay Iami- naiat low angles. Unjt 3 has a sharp gently undulating lower contact and a sharp irregular (erosive) upper contact.

Unit 4 is a silty sandy diamicton (3-4 rn thick). It is read- ily distinguished from the diamictons of units 1 and 2 by its pink colour, indicating sand-sized feldspar derived from Topsails igneous terrane. The most distinctive feature of the diamicton-is its textural heterogeneity, reflecting abundant sandy inclusions and a variable distribution of clasts and matrix. The inclusions have an irregular, commonly "smudged" appearance, and consist of fine to coarse sand, in places pebbly. The matrix of the diamicton ( ~ 2 . 0 mm) is poorly sorted silty sand (76-88 1 sand; 12-24% silt and clay; n = 9), commonly with a bimodal or polymadal grain- size distribution and containing numerous vesicles ( 5 3 rnrn diameter). Clasts are subangular to rounded granules to boulders (1 0.8 m long); the boulders, including white intru- sive rock derived from Topsails igneous terrane, are concen- trated in the upper 2 m of the unit (Fig. 6A). Clasts may be faceted, striated. and (or) bullet shaped, and many have silty or sandy caps or rims; clast fabric is weak (S, = 0.45, K = 1 .O, n = 50), with a mean Lineation vector of 217". The diamicton is generally matrix supported. loosely compacted, and massive to poorly stratified, the strata comprising sub- horizontal sand lenses ( 5 5 cm thick; 20.8 m long) tex- turally similar to the sandy inclusions. Lacally present is an anastornosing network of sand partings, 1-2 mm thick. some of which join sand lenses. A single intraclast of silty clay was observed similar to that within unit 3.

Unit 5 is a brown sandy gravel (0.2-0.3 m thick). It is massive and clast supported, the clasts generally rounded to subangular pebbles and cobbles, and the sand medium to coarse grained.

Section A interpretation Unit 1 is interpreted as lodgement till possibly overlain by subglacially deformed sediment (deformation till sensu Hicock

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 7: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

Klassen and Murton

and Dreimanis 1992). Lodgement of the basal part of unit 1 is suggested by its compact, massive, and locally clast- supported nature, and by the occurrence of diamicton directly above bedrock (e.g., Shaw 1985). That the clast fabric in the basal metre is weaker than those commonly ascribed to lodgement (e.g., Dowdeswell and Sharp 1986) may reflect clast -clast interactions and (or) local deflection of glacier ice by the undulating bedrock surface.

Deformation within the silt and clay body is inferred from the shear-like form of the diamicton lenses, and the laminae and lenses that curve around them. The texture and remnants of what appears to have been parallel stratification resemble glaciolacustrine rhythrnites described below. Shearing is thought to have disrupted the laminae, incorporated lenses of compact diamicton, and deflected the laminae and sand lenses around them. Similar structures have been described from subglacially deformed sediment by Boulton (1987) and Hart et al. (1990). Although the direction of the glacier movement responsible for the deformation is not known, the relatively strong clast fabric of the overlying compact dia- micton is consistent with northeastward movement, inde- pendently inferred from striations (event II). The fabric is in the range of fabrics reported by Dowdeswell and Sharp (1986, Fig. 2) from deformed lodgement tills.

The origin of unit 2 is not clear. The sandy diamicton may represent a basal melt-out till. Its fabric, however, is weaker than those commonly associated with such tills (e.g., Shaw 1982; Dowdeswell and Sharp 1986, Fig. 2), and its strati- graphic position and composition could alternatively reflect derivation from unit 1, possibly by debris flow.

Unit 3 is interpreted as deformed glaciolacustrine sedi- ments. The style of deformation resembles that within the silt and clay body in unit 1, although lenses of diamicton are absent from unit 3. Deformation was probably subglacial and related to deformation of unit 1. A glaciolacustrine origin for the sediment in unit 3 is strongly suggested by its texture, colour, and poorly preserved lamination. Similar but unde- formed glaciolacustrine sediment is preserved on the oppo- site side of Oriental mine (unit 2 of section B).

The origin of units 4 and 5 is discussed below, in the light of other sections.

Section B description Section B is overlain by several metres of slumped silty sandy diamicton similar to, and in the same stratigraphic position as, the diarnicton in unit 4 of section A. Three units are distinguished. Unit 1 is a 30 cm thick bed of pebbly sand. The sand is medium to fine grained and contains mainly rounded to subrounded pebbles and some intraclasts of clayey silt. The unit is massive to faintly stratified, the strata being wavy, horizontal, and a few millimetres thick. Unit 1 overlies either the surface of the VMS deposit or a large boulder just above it.

Unit 2 is 2 rn thick and dominated by rhythrnites and dianicton. Each rhythmite (0.3-7.5 cm thick) fines upward from fme sand or sandy silt to clayey silt or silty clay. The thicker, sandier rhythmites contain occasional pebbles but their bedding is not deformed. Strata are horizontal. planar to gently undulating, and parallel with sharp lower contacts. Above and below the rhythmites occur two beds of diamic- ton. Both are massive and matrix supported, and contain

rounded to subrounded pebbles or cobbles. The lower bed (0.3 m thick) has a matrix of grey muddy sand, the upper (1.0 m thick), a matrix of mottled grey, white, and pink silt and clay similar in colour and texture to the underlying rhythmites. The latter are folded and contain a dkcollement surface.

Unit 3 is at least 1.8 m thick and comprises mainly fine sand. The basal 1 m is massive and contains a few rounded to subrounded granules to pebbles and an intraclast (I 10 cm thick; 20 cm long) of grey compact diamicton. The lower contact of the sand is sharp and slightly irregular, the upper gradational. The uppermost 0.8 m of unit 3 consists of indistinctly rippled sand with several lenses or layers of pebbly sand. The latter are up to 10 cm thick and typically a few to several decimetres long, with sharp undulating to irregular upper and lower contacts. The upper 0.8 m of unit 3 contains numerous high-angle faults.

Section B interpretation The origin of unit 1 is not clear. The intraclasts of clayey silt texturally similar to rhythmites in unit 2 suggest erosion of preexisting glaciolacustrine sediment (see interpretation of unit 2). If the clayey silt was deposited and eroded in the same glacial lake as the overlying rhythrnites, then the pebbly sand may represent subaqueous outwash. But no clearly diagnostic features of the latter (Rust and Romanelli 1975; Rust 1977) were observed.

Unit 2 was likely deposited proximally within an ice- contact lake. The upper bed of diamicton may represent a slump or debris-flow deposit formed by partial remolding of rhythmites similar to those beneath it. Folding and dCcolle- ment in the underlying rhythmites are consistent with slump- ing. Slumping may have been triggered by rapid deposition of gravel on silt and clay (cf. Eyles 1990), the gravel being derived from the same source as the pebbles in the overlying unit 3 (see also discussion of unit 1 in Fig. 5G). The lower bed of diamicton is interpreted as a debris-flow deposit because of its stratigraphic position and massive, matrix- supported nature. Its texture suggests that it formed by com- plete mixing of sediments similar to pebbly sand of unit 1 and rhythmites of unit 2.

The rhythmites were probably deposited by underflows. The repeated graded beds suggest episodes of waning- current deposition, and the thick sandy rhythrnites suggest proximity to a sediment source. The absence of sedimentary structures apart from graded bedding may indicate rapid deceleration of the underflows (Sturm and Matter 1978; cf. Banerjee 1977). The association of these rhythmites with diamictons of inferred slump or debris-flow origin is consis- tent with a surge-current origin for the rhythmites (Smith and Ashley 1985), the surging underflows likely evolving either from debris flows (e.g., Hampton 1972) or slumps (e.g., Gilbert 1975). The inferred association of processes is most simply explained by deposition in an ice-contact lake (cf. Liverman 1991, p. 245; see below).

The massive sand in unit 3 is tentatively interpreted as a sediment gravity flow deposit. This is suggested by the presence of an intraclast and the massive nature of the sand (cf. Jones and Rust 1983; Turner and Munro 1987). The tex- ture of the sand and the size and shape of the clasts are consistent with resedimentation of sediment similar to the

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 8: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

Can. J. Earth Sci. Vol. 33, 1996 I

stratified sand above it. Interpretation of the latter is dis- cussed below.

Lucky Strike mine

Lucky Strike mine description The section at Lucky Strike mine extends to the subcropping VMS deposit. Three units are distinguished. Unit 1, resting upon weathered bedrock, comprises a layer ( 50 .5 m thick) of pebbles to boulders set in a sandy matrix. The layer is clast to matrix supported, the clasts subrounded to subangular. The layer is overlain by finely laminated grey silt.

Unit 2 is a 6 m thick sequence of pebbly silty sand and contains a distinctive bed of cobbly diamicton (Fig. 5C). The sand in the lower 3.5 m is grey, compact, poorly sorted, and coarsens upward from silty sand to coarse sand. The <2.0 mm fraction commonly has a bimodal or polymodal grain-size distribution. Dispersed rounded to subrounded pebbles are common, except in the basal 1 m, and clasts that appeared to be intraformational were observed at a depth of 4.0-4.5 m. The sand is massive to faintly stratified, the strata occurring as isolated and (or) folded laminae ( 5 a few mm thick) of sand and silt. Irregular streaks and wisps of silt occur near the base.

A cobbly diamicton is present 1 m below the top of unit 2. The diamicton is 0.4-0.5 m thick, clast to matrix supported, massive, and inversely graded. Clasts are sub- angular to rounded and include large cobbles; silt caps are well developed on the tops of clasts. The matrix comprises granule-rich silty sand. The lower contact is sharp and irregular (erosive), the upper gradational.

The upper 0.8 m of unit 2 comprises a 60 cm thick bed of muddy sand beneath a 20 cm thick bed of massive sand. The former is mottled pink and grey and consists of a textur- ally heterogeneous mixture of fine sand and pebbly silty sand occurring as irregular patches and streaks. The bed contains dispersed rounded to subrounded pebbles and small cobbles and wavy horizontal sand lenses ( I 1 cm thick and 5 20 cm long). The lower contact is sharp and undulating. The massive sand is pinkish grey and fine grained, and contains irregular patches of silty sand. The contact between the two beds is sharp, irregular, and disturbed by flame structures.

Unit 3 is a silty sandy diamicton similar to that in unit 4 of section A at Oriental mine (Fig. 5A). The clast fabric is of moderate strength (S1 = 0.62, K = 1.48, n = 50) and has a mean lineation vector of 187". Unit 3 includes a few undulatory, (sub)horizontal strata (0.5 -4.0 cm thick) with erosive bases (Fig. 6C). Each stratum grades upward from pebbly sand to silty sand.

Lucky Strike mine interpretation The sandy pebble-boulder unit 1 may represent a fluvial or glaciofluvial lag. Unit 2 comprises glaciolacustrine and resedimented deposits. A glaciolacustrine origin is suggested by remnants of silty and sandy rhythmites at a location requiring ice damming for a lake to have formerly existed. Resedimentation of glaciolacushine sediment is inferred from the massive to faintly stratified nature of unit 2, folded laminae, intraformational clasts, and, in massive subunits, bimodal or polymodal grain-size distributions. Resedimenta- tion probably occurred by debris flows and (or) slumping,

and resulted in textural inversion of the silt, sand, and gravel (cf, Eyles 1990, Fig. 10). Clasts were likely derived from till and (or) outwash. Subaqueous resedimentation is suggested by interbedding of massive subunits with rhythmite rem- nants. The cobbly diamicton is interpreted as a debris-flow deposit because of its massive nature, very poorly sorted matrix, and crude inverse grading (e.g., Nemec and Steel 1984).

Resedimentation is also inferred to account for the muddy sand and massive sand in the upper 0.8 m of unit 2. The tex- tural heterogeneity of these sediments suggests incomplete mixing of texturally distinct sediments during sediment gravity flow (cf. Dec 1992; see interpretation of silty sandy diamicton as Buchans Lake).

Unit 3 is discussed below.

Other sections in the Buchans area Stratigraphic sections were also examined along - 130 m of the southern shore of Buchans Lake (Fig. 5: logs D -G), within the Sandfill Quarry, and in a backhoe pit 1 km south- west of Lucky Strike mine (Fig. 1). Sedimentological units are discussed selectively to infer depositional processes and to facilitate stratigraphic correlation.

Inferred glaciolacustrine sdrnents are shown in units 1 -3 of log D, units 1 and 2 of log F, and unit 1 of log G. in a similar stratigraphic position to those in units 2 and 3 at sm- tion B, Oriental mine (Fig. 5B). Normally graded rhythmites in unit 2 of log D and unit 1 of log F resemble those described in unit 2 at section B, Oriental mine (Fig. 5B), and are also attributed to deposition from waning surge currents. Some currents transported small pebbles into the lake, form- ing rhythmites with pebbly bases (e.g., beside the ES in log D) and thin erosively based beds of pebbly sand in a unit containing type A and B climbing-ripple cross-lamination (Ashley et al. 1952; unit t , log G, 2.5 rn depth). The latter sandy unit resembles the upper 0.8 m of unit 3, section B. Oriental mine, but the ripples are not deformed. Deformed ripples similar to those at Oriental mine do occur in sand in the upper 3.0 m of unit 2, log F, which is at the same strati- graphic depth as unit 1, log G. Thus, it is probable that all of unit 3, section B, Oriental mine, was originally deposited as rippled sand within the same lake as more clearly recorded in the Buchans Lake sections. The lake probably extended over the Lucky Strike mine, for the thick sequence of glacio- lacustrine sediment there (Fig. 5C, unit 2) also occurs beneath the silty sandy diamicton (unit 3).

Thick (>40 m) sand and gravel deposits underlie silty sandy diamicton in Sandfill Quarry - 1 km east of Oriental mine (Klassen and Henderson 1992). The sediments coarsen upwards from silty sand, through medium- to coarse-grained sand and pebbly sand, to gravel. Sedimentary structures were poorly exposed due to slope stabilization but included cross-bedding, planar parallel lamination, and small channel fills. In part, the sediments are of glaciofluvial origin.

Silty sandy diamicton at Oriental and Lucky Strike mines (Fig. 5A, unit 4; Fig. 5C, unit 3) is present in three sections at Buchans Lake (Fig. 5D, unit 4; Fig. 5E, unit 1; Fig. 5F, unit 3) and forms a widespread surficial unit in the Buchans area (sandy diamicton of Klassen and Henderson 1992, p. 15). The diamicton varies considerably in terms of (i) matrix or clast support, (ii) sand or silt content, and

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 9: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

Klassen and Murton

(iii) stratification. Unit 2 of log G is massive, whereas units 4, 1, and 3 of logs D, E, and F, respectively, show crude stratification. Strata (0.5 cm to - 1.5 m thick) are defined by erosion surfaces, sand laminae, and variations in clast size and abundance (Fig. 5F). Crude inverse grading is l d y present. Inclusions of silt, sand, and pebbly sand occur as lenses or amorphom patches (commonly -5-30 cm long axis), typically with diffuse margins (cf. Narcussen 1973, Fig. 7; Dec 1992). Many indusions are well sorted, similar to underlying glaciolacustrine sediments (Fig. 6B). Two clast fabrics measured in unit 3, log F, are weak (S, = 0.50, K = 1.27, n = 50) (S, = 0.57, K = 0.6, n = 50) with mean lineation vectors of 008 " and 026". Upper and lower contacts may be erosional or gradational. The diamicton is readily distinguished from the compact diamicton in sec- tion A, Oriental mine (unit 1) by its textural heterogeneity, stratification, rounded clasts, and poorly consolidated nature.

Silty sandy diamicton is attributed to debris-flow resedi- mentation of glacigenic, glaciofluvial, and glaciolacustrine sediments. This is suggested by (i) the textural hetero- geneity; (ii) abundance and textural similarity of sandy matrix with adjacent sediments; ( i i i ) commonly bimodal or polymodal grain-size distribution of the matrix; (iv) inclu- sions of sand and rhythmites; (v) disorganized to weak clast fabrics; (vi) rounded (previously abraded) clasts, some of which are striated; (vii) abundance of boulder erratics having a Topsails igneous terrane provenance; and (viii) commonly massive nature (cf. Lawson 1979; Nemec and Steel 1984; Eyles et al. 1988; Mills 1991; Dec 1992). The textural heterogeneity reflects incomplete mixing of mud, sand, and gravel derived from adjacent till and glaciolacustrine (Figs. 5D, 5F, 5G) and glaciofluvial sediments.

Many of the debris flows were partially cohesive, result- ing in disorganized to weak clast fabrics, common absence of grading, and inclusions of sand (cf. Lawson 1981, 1982; (type Il flows); EyIes 1990; Dec 1992). Cohesion was likely due to the incorporation of mud from rhythmites, which imparted sufficient matrix strength for suspension of boul- ders. In contrast, some small, water-rich and turbulent debris flows are suggested by thin-graded beds with erosive bases (Figs. 5C, unit 3; Fig. 5F, unit 3; Fig. 6C; cf. Nemec and Steel 1984).

Related to the diarnicton is silty sandy gravel in unit 2, log G, at Buchans M e . The gravel is interpreted as an end member of the surficial resedimented deposits because it is IocaUy matrix supported and contains the texturally hetero- geneous matrix and sandy inclusions characteristic of the silty sandy diamicton. However, interpretation of gravels elsewhere at Buchans Lake (Fig. 5E, unit 2) and at Oriental mine (Fig. 5A, unit 5) is problematic. Although the rounded clasts are probably of glaciofluvial origin, it is not clear whether the units themselves have been redeposited.

Drift composition The areal distribution of red granitic pebbles in surficial deposits reflects glacial erosion and southward transport from the Topsails Plateau during event KU, and subsequent debris-flow resedimentation (Fig. 7A). The 5 wt. % isopleth outlines a tongue of granite-rich debris extending >5 km south and southeast from the plateau to Buchans and is largely confined to the Buchans saddIe (Fig. 3). The 0 wt. %

Fig. 7. Indicator pebbles within drift in the Buchans area: (A) red granitic rock (Topsails igneous group); (B) arnygdular volcanic rock (Buchans Group).

0

Topsails Plafeau

Saddle

Till sample location

-01. isopleth: (wt.% pebbles. 4-5.6 mm)

Bedrock Source

isopleth indicates glacial transport of > 10 km to Red Indian Lake; larger granitic erratics were transported south of the lake and across much of the Lake Ambrose map area (NTS 12 AI10; Klassen 1994~). Volcanic pebbles derived from the Buchans Group are most abundant (2- > 10 wt. 96) in drift near Buchans (Fig. 7B).

Drift geochemistry shows two significant features. First, drift overlying and derived from Topsails igneous terrane contains lower concentrations of copper, zinc, and chromium than drift derived from rocks of the Buchans Group (Fig. 8). Second, drift southwest of Buchans is enriched in lead and zinc compared with till derived from Buchans Group bedrock elsewhere (Fig. 8). The zone of enrichment extends up to 10 km from the Buchans VMS deposits, coinciding with the geochemical dispersal train originating at Buchans and rec- ognized by James and Perkins (1981).

At Oriental mine mineralized clasts (pyrite rich) derived from the underlying VMS deposit occur within lodgement

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 10: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

372 Can. J . Earth Sci. Vol. 33, 1996

Fig. 8. Geochemistry of the clay-sized (<0.002 mm) fraction of glacial drift. (A) Lead. (B) Copper. (C) Zinc. (D) Chromium.

Red lnclinn L. /

56

----. Lithological isopleth (5 wt.%) (red granite pebbles, 4-5.6 mm)

Bedrock source

Geochemical isopleth (ppm) - 40 - (<0.002 mrn)

Sample location

till, preferentially within its lowermost metre (Fig. 9). Red granite pebbles occur in low concentrations ( < 5 wt.%) throughout the lodgement till, subglacially deformed sedi- ment, and meltout till - debris-flow deposit, and they syste- matically increase upward from < 5 to > 20 wt. % in the overlying debris-flow deposit. Volcanic pebbles occur in low concentrations (1 2 wt. %) throughout the section. Pyrite, copper, lead, and zinc are enriched in the basal metre of lodgement till and in the melt-out till - debris-flow deposit; concentrations decrease upward within the overlying debris- flow deposit, particularly in its lower 1.5 m.

In the surficial debris-flow deposit at Lucky Strike mine, red granitic pebbles decrease upward from I0 to 2 wt. % , and pyrite increases upward from 1 to 10% (Fig. 10). Pyrite is enriched in fine sand around basal cobbles (24 %), and within the glaciolacustrine and resedimented deposits overlying it (1 1 %, 26%). Lead and copper are enriched in the basal 0.5 m of the section and in the subaqueous debris flow (cobbly diamicton) of the glaciolacustrine sequence. Zinc is present in high but variable concentrations throughout. The

basal enrichment of lead and copper reflects the proximity of the underlying VMS deposit and the occurrence of VMS clasts within the sediments. The lowest concentrations of lead, copper, and zinc are in the subaerial debris-flow deposit making up the uppermost unit. Within it copper decreases upward, whereas lead and zinc show little vertical variation, although both are enriched in the uppermost 0.1 m. Within this deposit, chromium increases systemati- cally upward, displaying a broad inverse correlation with red granitic pebbles.

At the backhoe pit, red granitic pebbles were not found within glaciolacustrine sediment at the base of the section and make up 2 -5 wt. % of pebbles in the overlying debris-flow deposit (Fig. 11). By contrast, volcanic pebbles are most abundant in glaciolacustrine sediment (9 wt. %), and least abundant in the debris-flow deposit ( < 2 wt. %). Pyrite occurs in low amounts ( < 2 %) throughout the section, except near the base of the debris-flow deposit (10%). Copper, lead, and zinc concentrations decrease upward through this deposit. Concentrations in the glaciolacustrine sediment are

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 11: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

Klassen and Murton

Fig. 9. Vertical profiles of stratigraphy and drift composition, Oriental mine. Legend for stratigraphic log as in Fig. 5.

depth (rn) Interpretation

n .

Glacioff uvial

percent

0 10 20 30

A Copper r Lead

similar to those in the overlying diarnicton; concentrations of copper and lead are slightly less, and of zinc, slightly greater. Chromium is - 32 ppm in the glaciolacustrine sedi- ment, and decreases upward within the overlying debris-flow deposit from 50 to < 10 ppm.

Discussion Depositional and stratigraphic framework We synthesize our observations in terms of a depositional and stratigraphic framework representing at least two glacial events and an intervening ice-free period. Ice-flow events named here are linked to the interpretation of striations in central Newfoundland given by Klassen and Henderson (1992) and Klassen (19941). In the absence of evidence such as buried organic material, all events are presumed to be of Wisconsinan age. However, differential staining of striated surfaces south of Red Indian Lake could indicate ice-free intervals between glacial events, and thus event I could be of pre-Wisconsinan age (e.g . , Grant 1989; Klassen 1994~).

The oldest glacial deposits are represented by lodgement till at the base of the Oriental mine section. Glacial dispersal of VMS debris within it is indicated by mineralized clasts, pyrite, and high concentrations of lead, copper, and zinc. The upward decrease in VMS debris may reflect changes in ice-flow direction, net distance of glacial transport, bedrock source exposed to glacial erosion, mixing with non-VMS debris, or some combination of these factors. The marked

at Zinc 1 . Red granitic rock Q Chromium 0 Volcanic rock

Pyrite

enrichment of pyrite, lead, copper and zinc within the over- lying melt-out till - debris-flow deposit records a second influx of VMS debris, perhaps from a second, local source. The lodgement till is attributed to ice flowing northeastward during event 11, because mean lineation vectors of clast fabrics are more or less parallel with striations ascribed to that event, and volcanic pebbles in the till were probably derived from the southwest.

After deposition of the VMS-bearing till the Buchans area was inundated by an ice-contact lake. The lake is strati- graphically recorded by rhythrmtes at Oriental pit and else- where (Fig. 5) and is presumed to be associated with event II deglaciation. The lake was dammed by ice in Red Indian Lake basin, consistent with the deglacial model pro- posed by Grant (1975). Lake outflow was northward via Buchans saddle into Grand Lake, and the lake likely occupied the Buchans saddle and the valley extending southwest of Buchans. The maximum lake level was - 300 -3 10 m asl, based on the elevation and distribution of glaciolacustrine deposits and sill elevations at Hinds Lake (Fig. 3); maximum water depths at Buchans (-250 m asl) would have been -50-60 m. The glacial lake inundating Buchans was an important site for redistributing VMS debris. This is indi- cated by high concentrations of pyrite, lead, copper, and zinc in glaciolacustrine and resedimented deposits at Lucky Strike mine (Fig. 10) and in the backhoe pit (Fig. 11). VMS debris was likely carried into the lake by debris flows reworking glacigenic sediment. The marked enrichment of VMS debris

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 12: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

374 Can. J. Earth Sci. Vol. 33, 1996

Fig. 10. Vertical profiles of stratigraphy and drift composition, Lucky Strike mine. Legend for stratigraphic log as in Fig. 5.

Debris flow

-

(subaqueous g~." . Od~".'.: debris flow) ]Tei!+ -,

4 ---

%

Glaciofluvial z ES

A bedrock (VMS deposit) A Copper

r Lead

within the cobbly diamicton at Lucky Strike mine (Fig. 10) is most simply attributed to redeposition of VMS-enriched till by a subaqueous debris flow. However, redistribution of VMS debris did not take place throughout the lake, for glaciolacustrine sediments sampled at Buchans lake contain relatively low concentrations of such debris (see Bell and Murton 1995) (Fig. 6). The origin of the coarsening-upward sequence of inferred glaciofluvial sediments at Sandfill Quarry is not fully understood. It may reflect progradation of a glaciofluvial system resulting from a fall in lake level caused by retreat of glacier ice in Red Indian Lake basin and exposure of lower outlets. It is consistent with shorelines reported at lower elevations (e.g., 216 m asl; Mihychuk 1985) on hillsides adjacent to Red Indian Lake.

Ice-free conditions are inferred in Buchans saddle between events 11 and 111. This is because the silty sandy diamicton (see below) overlies and incorporates glaciolacustrine sedi- ment. Local readvance of ice into the lake during event 111 accounts for the erosion and deformation of the glaciolacus- trine sediments at Oriental pit, the tongue of granite-rich debris derived from the Topsails igneous terrane that extends southward from Buchans saddle (Fig. 7), and the restriction of Event 111 striations to the Buchans area (cf. Klassen 1994a) (Fig. 5A).

x Zinc 0 Chromium

percent

8 J Red granitic rock

0 Volcanic rock Pyrite

The last major depositional event to occur in the Buchans area involved resedimentation by debris flows and formed the widespread surficial unit of silty sandy diamicton (Figs. 5, 9 - 11). The debris flows probably resulted from slope insta- bility associated with final lake drainage and exposure of unconsolidated sediments. Resedimentation of this material and mixing with glaciolacustrine and glaciofluvial sediments likely occurred near the ice margin, when the newly deglaciated topographic saddle formed a natural sediment sink for unstable glacigenic debris. A subaerial origin for many of the flows is inferred from the absence of interbedded subaqueous deposits and the abundance of air-filled vesicles (bubble cavities; cf. Bull 1964; Lawson 1982).

The debris-flow sediments incorporate variable amounts of Buchans Group and Topsails material, the differences in their geochemical signatures being accentuated by the inclu- sion of VMS debris. They are compositionally distinct from older till exposed in the Oriental mine section, containing more red granitic pebbles and lower trace element concentra- tions. VMS debris occurs preferentially in the basal metre of the debris-flow deposits at Oriental mine (Fig. 9) and, by contrast, within the uppermost 0.1 m at Lucky Strike mine (Fig. 10). The vertical lithological trends defined by red gra- nitic pebbles are opposite, increasing upward at Oriental and

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 13: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

Klassen and Murton

Fig. 11. Vertical profiles of stratigraphy and geochemical dispersal train defined by James Legend for stratigraphic log as in Fig. 5.

drift composition, Backhoe pit. The pit is located near the margin of the and Perkins (1981) to the southwest of Buchans. Locality is shown in Fig. 3.

PPm percent 10 100 1000 0 5 10

decreasing at Lucky Strike. The compositional variations reflect local changes in debris source, the distribution of sub- cropping VMS sources, and possibly local topographic diversion of debris flows; Lucky Strike mine is 40 m higher than Oriental mine.

Implications for mineral exploration Drift prospecting for VMS deposits in the Buchans area is encumbered by dispersal of VMS debris at different times, in different directions, and by different processes. Glacial erosion of VMS sources probably last occurred during event 11, based on striations at Lucky Strike and stratigraphic sections where subcropping mineralization is capped by either event 11 till (Fig. 9) or glaciolacustrine sediments (Fig. 10). Glacial dispersal of VMS debris during this northeastward - south- westward ice-flow event is reflected both by the VMS signa- ture in lodgement till and melt-out till - debris-flow sediment at Oriental mine associated with event 11, and by the trends of the geochemical dispersal train mapped by James and Perkins (1981) (Fig. 8). Thus, one strategy for exploration would be to sample till associated with event II; in the Buchans area this would require overburden drilling. As shown at Lucky Strike mine, however, sediment in contact with bedrock is not necessarily till.

The geochemical dispersal train extending southwest of Buchans (cf. James and Perkins 1981) lies outside the tongue of Topsails-rich debris that extends across Buchans (Fig. 7A). Small ribbon-shaped units of zinc enrichment within the train are consistent with deposition as till from southwestward- flowing ice (event 11). However, based on the sections near the edge of the train (Figs. 10, 11) and soil pits dug within it, much of the train likely comprises debris-flow deposits that overlie and incorporate glaciolacustrine sediments. As such, the sediments within the train are stratigraphically younger than those deposited during event I1 (e.g., Figs. 9 - 11) and the train probably reflects reworking of VMS-enriched debris. Reworking is attributed to subaqueous debris flows within a glacial lake, and later by mainly sub- aerial debris flows following glaciation of the Topsails Plateau and Buchans area (event 111). The southwest trend of

x Zinc Red granitic rock

0 Chromium 0 Volcanic rock

Pyrite

the train may reflect both glacial dispersal during event I1 and local topographic control of reworking, for, as noted by James and Perkins (1981), the train is largely confined to the floor of a broad valley.

Based on the above model, a comparable glacial dispersal train may extend northeast of Buchans as the result of event I1 glacial dispersal. Within 5 km of Buchans it would be masked by the thick ( >40 m) glaciolacustrine and glacio- fluvial deposits exposed at the Sandfdl quarry, which are extensive below the 305 m as1 level of the former glacial lake (Fig. 3). Although the mineralized erratics of Buchans-type ore in drift 20 krn northeast of the Buchans area (James and Perkins 1981) may relate to this train, there is no geochemi- cal evidence for northeastward ice flow (Klassen 1994~).

The main Quaternary features of importance to mineral exploration near Buchans include complex ice-flow history, glacial lake deposition, and debris-flow resedimentation. These features are likely characteristic of other interior basins in Newfoundland, and the Maritimes generally. According to Grant (1989), most glacial deposits in the Mari- times are the product of radial ice flow, reflecting the former existence of numerous local ice caps (Grant 1989, Fig. 5.1 la). Thus, ice-flow directions were typically complex, with topo- graphic effects increasingly important during the late stages of deglaciation (e.g . , Vandemeer and Sparkes 1982). As ice margins retreated to coastal areas, leaving remnant ice caps on highlands, large lake basins in interior Newfoundland became ice free and were occupied by glacial lakes (Batter- son et al. 1993). Within those lakes, the extent and thickness of glacial lake sediments are variable, in part reflecting sedi- ment input and topographic controls. Those sediments can be capped by debris-flow sediments that resemble till and have a provenance reflecting local, late-glacial glacial events. This style of deglaciation and deposition is consistent with the results of the present study, and with the recognition of glacial lake Shanadithit in Red Indian Lake basin (Mihychuk 1985).

A prerequisite for drift prospecting in the Maritimes is the identification of resedimented overburden, which can be of subaqueous and subaerial origins, and the existence and

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 14: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

Can. J. Earth Sci. Vol. 33, 1996

extent of former glacial lakes. The incorporation of mineral- ized debris in resedimented material is highly variable and its distribution can be topographically controlled. In some areas, it may preserve geochemical anomalies that reflect original glacial dispersal from mineralization, as illustrated in the geochemical dispersal train extending southwest of Buchans (Fig. 8). But in other areas it may bury and mask geochemical anomalies, as shown from the section at Orien- tal and Lucky Strike mines (Fig. 9). Since resedimented deposits can resemble till, careful sedimentological exarnina- tion is necessary to distinguish them.

Acknowledgments

J.B.M.'s work was funded by Natural Sciences and Engineering Research Council of Canada strategic grant "Mineral exploration using Pb isotopes in glaciated ter- rains" (to Dr. K. Bell) and undertaken while a research associate in the Department of Earth Sciences at Carleton University. We thank S. Bayne, C. O'Hara, A. Ivanoff, C. Johns, B.P. Lowe, and J. Rutherford for field and (or) laboratory assistance; J.W. Card for technical assistance; ASARCO for permission to collect samples at Buchans; G.N. Neary for information concerning the abandoned mine sites; Dr. T. Dec for information about resedimented deposits; and Dr. K. Bell for permission to publish material collected for the Pb-isotope study. The manuscript was reviewed by Drs. P. Henderson, I. Nichol, and D. Liverman and it has been improved by their constructive comments.

References Ashley, G.M., Southard, J.B., and Boothroyd, J.C. 1982. Deposi-

tion of climbing-ripple beds: a flume simulation. Sedimen- tology, 29: 67 -79.

Banerjee, 1. 1977. Experimental study on the effect of deceleration on the vertical sequence of sedimentary structures in silty sedi- ments. Journal of Sedimentary Petrology, 47: 771 - 783.

Batterson, M.J., Liverman, D.G.E., and Kirby, G. 1993. Glacial lake development and marine inundation, Deer Lake area, New- foundland, Canada: topographically controlled deglaciation of an interior basin. Journal of Quaternary Science, 8: 327-337.

Bell, K., and Murton, J.B. 1995. A new indicator of glacial disper- sal: Pb isotopes. Quaternary Science Reviews, 14: 275 -287.

Boulton, G.S. 1987. A theory of drumlin formation by subglacial sediment deformation. In Drumlin Symposium. Edited by J. Menzies and J. Rose. A.A. Balkema, Rotterdam, pp. 25 - 80.

Bull, W.B. 1964. Alluvial fans and near-surface subsidence in western Fresno County, California. United States Geological Survey, Professional Paper 437A.

Dec, T. 1992. Textural characteristics and interpretation of second- cycle, debris-flow-dominated alluvial fans (Devonian of north- em Scotland). Sedimentary Geology, 77: 269-296.

Dowdeswell, J.A., and Sharp, M.J. 1986. Characterization of pebble fabrics in modem terrestrial glacigenic sediments. Sedimentology , 33: 699 - 7 10.

Eyles, N. 1990. Marine debris flows: late Precambrian "tillites" of the Avalonian - Cadomian orogenic belt. Palaeogeography , Palaeoclimatology and Palaeoecology , 79: 73 - 98.

Eyles, N., Eyles, C.H., and McCabe, A.M. 1988. Late Pleistocene subaerial debris-flow facies of the Bow Valley, near Banff, Canadian Rocky Mountains. Sedimentology, 35: 465-480.

Geological Survey Branch. 1988. Mineralized occurrence map, Sandy Lake, Nfld. Department of Mines and Energy, New- foundland, Map 83-60, scale 1 : 250 000.

Geological Survey Branch. 1992. Mineralized occurrence map, Red Indian Lake, Nfld. Department of Mines and Energy, Newfoundland, Map 91-172, scale 1 : 250 000.

Gilbert, R. 1975. Sedimentation in Lillooet Lake, British Colum- bia. Canadian Journal of Earth Sciences, 12: 1697 - 171 1.

Graham, D.F., and Grant, D.R. 1991. A test of airborne, side- looking synthetic-aperture radar in central Newfoundland for geological reconnaissance. Canadian Journal of Earth Sciences, 28: 257-265.

Grant, D.R. 1974. Prospecting Newfoundland and the theory of multiple shrinking ice caps. In Report of activities, part B. Geological Survey of Canada, Paper 74-lB, pp. 215 -216.

Grant, D.R. 1975. Surficial geology of Red Indian Lake map-area, Newfoundland: a preliminary interpretation. In Report of activities, part B. Geological Survey of Canada, Paper 75-1, pp. 111-112.

Grant, D.R. 1989. Quaternary geology of the Atlantic Appalachian region of Canada. In Quaternary Geology of Canada and Green- land. Edited by R.J. Fulton. Geological Survey of Canada, Geology of Canada, No. 1, Chapt. 5 , pp. 393-440 (Also Geological Society of America, The Geology of North America, Vol. K- 1 .)

Grant, D.R., and Tucker, C.M. 1976. Preliminary results of terrain mapping and base metal analysis of till in the Red Indian Lake and Gander Lake map areas of central Newfoundland. In Report of activities, part A. Geological Survey of Canada, Paper 76- lA , pp. 283-285.

Hampton, M.A. 1972. The role of subaqueous debris flow in gener- ating turbidity currents. Journal of Sedimentary Petrology, 42: 775 - 793.

Hart, J.K., and Boulton, G.S. 1991. The interrelation of glaciotec- tonic and glaciodepositional processes within the glacial envi- ronment. Quaternary Science Reviews, 10: 335 -350.

Hart, J.K., Hindmarsh, R.C.A., and Boulton, G.S. 1990. Styles of subglacial glaciotectonic deformation within the context of the Anglian Ice-sheet. Earth Surface Processes and Landforms, 15: 227-241.

Hicock, S.R., and Dreimanis, A. 1992. Deformation till in the Great Lakes region: implications for rapid flow along the south- central margin of the Laurentide Ice Sheet. Canadian Journal of Earth Sciences, 29: 1565 - 1579.

James, L.D., and Perkins, E.W. 1981. Glacial dispersion from sul- phide mineralization, Buchans area, Newfoundland. In The Buchans orebodies: fifty years of geology and mining. Edited by E.A. Swanson, D.F. Strong, and J.G. Thurlow. Geological Association of Canada, Special Paper 22, pp. 269-283.

Jones, B.G., and Rust, B.R. 1983. Massive sandstone facies in the Hawkesbury Sandstone, a Triassic fluvial deposit near Sydney, Australia. Journal of Sedimentary Petrology, 53: 1249-1259.

Kean, B.F. 1977. Geology of the Victoria Lake map area. New- foundland Department of Mines and Energy, Mineral Develop- ment Division, Report 7 7 4 .

Kean, B.F., Dean, P.L., and Strong, D.F. 1981. Regional geology of the Central Volcanic Belt of Newfoundland. In The Buchans orebodies: fifty years of geology and mining. Edited by E.A. Swanson, D.F. Strong, and J.G. Thurlow. Geological Associa- tion of Canada, Special Paper 22, pp. 65-78.

Kirkham, R.V. 1987. Tectonic setting of the Buchans Group. In Buchans geology, Newfoundland. Edited by R.V. Kirkham. Geological Survey of Canada, Paper 86-24, pp. 23 -34.

Klassen, R.A. 1994a. A preliminary interpretation of glacial history derived from glacial striations, central Newfoundland. In Current research, part D. Geological Survey of Canada, pp. 13-22.

Klassen, R.A. 1994b. Till geochemistry and ice flow data, central Newfoundland (NTS 12 A110, 15, 16; 12 Hl l ) . Geological Survey of Canada, Open File 2823.

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.

Page 15: Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration

Klassen and Murton

Klassen, R.A., and Henderson, P.J. 1992. Quatemaq geological studies, Buchans area of central Newfoundland. In Current research, part D. Geological Survey of Canada, Paper 92-ID, pp. 11-19.

Lawson, D.E. 1979. Sedimentological analysis of the western ter- minus region of the Matanuska Glacier, Alaska. Cold Regions Research and Engineering Laboratory, Report 79-9.

Lawson, D.E. 1981. Distinguishing characteristics of diarnictons at the margin of the Matanuska Glacier, Alaska. Annals of Glaciology, 2: 78 - 84.

Lawson, D.E. 1982. Mobilization, movement and deposition of active subaerial sediment flows, Matanuska Glacier, Alaska. Journal of Geology, 90: 279-300.

Livennan, D.G. 1991. Sedimentology and history of a Late Wis- consinan glacial lake, Grande Prairie, Alberta, Canada. Boreas, 20: 241-257.

Marcussen, 1. 1973. Studies of flow till in Denmark. Boreas, 2: 213-231.

Mihychuk, M. 1985. Drift prospecting in the Victoria and Tally Pond areas, central Newfoundland. In Current research. New- foundland Department of Mines and Energy, Geological Survey Branch, Report 85-1, pp. 99-104.

Mills, H.H. 1991. Three-dimensional clast orientation in glacial and mass-movement sediments: a compilation and preliminary analysis. United States Geological Survey, Open-file Report 90-128.

Murray, R.C. 1955. Directions of glacier ice motion in south- central Newfoundland. Journal of Geology, 63: 268-274.

Neary, G.N. 1981. Mining history of the Buchans area. In The Buchans orebodies: fifty years of geology and mining. Edited by E.A. Swanson, D.F. Strong, and J.G. Thurlow. Geological Association of Canada, Special Paper 22, pp. 1 - 64.

Nemec, W., and Steel, R.J. 1984. Alluvial and coastal conglomer- ates: their significant features and some comments on gravelly mass-flow deposits. In Sedimentology of gravels and con- glomerates. Edited by E.H. Koster and R.J. Steel. Canadian Society of Petroleum Geologists, Memoir 10, pp. 1-31,

Prest, V.K., Grant, D.R., and Rampton, V.N. 1969. Glacial map of Canada. Geological Survey of Canada, Map 1253A, scale 1 :500000.

Rust, B.R. 1977. Mass flow deposits in a Quaternary succession near Ottawa, Canada; diagnostic criteria for subaqueous out- wash. Canadian Journal of Earth Sciences, 14: 175 - 184.

Rust, B.R., and Romanelli, R. 1975. Late Quaternary subaqueous outwash deposits near Ottawa, Canada. In Glaciofluvial and glaciolacustrine sedimentation. Edited by A.V. Jopling and B.C. McDonald. Society of Economic Paleontologists and Mineralo- gists, Special Publication 23, pp. 177 - 192.

Shaw, J. 1982. Melt-out till in the Edmonton area, Alberta, Canada. Canadian Journal of Earth Sciences, 19: 1548-1569.

Shaw, J. 1985. Subglacial and ice marginal environments. In Glacial sedimentary environments. Edited by G.M. Ashley,

J. Shaw, and N.D. Smith. Society of Economic Paleontologists and Mineralogists, Short Course 16, pp. 7 -84.

Smith, N.E., and Ashley, G.M. 1985. Proglacial lacustrine environment. In Glacial sedimentary environments. Edited by G.M. Ashley, J. Shaw, and N.D. Smith. Society of Economic Paleontologists and Mineralogists, Short Course 16, pp. 135- 215.

Sparkes, B.G. 1985. Quaternary mapping, Central Volcanic Belt. In Current research. Newfoundland Department of Mines and Energy, Geological Survey Branch, Report 85-1, pp. 94-98.

Sparkes, B.G. 1987. Glacial geology and till geochemistry of the Buchans (12 Al15) map area, Newfoundland. Newfoundland Department of Mines and Energy, Mineral Development Divi- sion, Open File 12Al15 (396).

Sturm, M., and Matter, A. 1978. Turbidites and varves in Lake Brienz (Switzerland): deposition of clastic detritus by density currents. In Modem and ancient lake sediments. Edited by A. Matter and M.E. Tucker. International Association of Sedimentologists, Special Publication 2, pp. 147 - 168.

Thurlow, J.G. 1981. The Buchans Group; its stratigraphic and structural setting. In The Buchans orebodies: fifty years of geol- ogy and mining. Edited by E.A. Swanson, D.F. Strong, and J.G. Thurlow. Geological Association of Canada, Special Paper 22, pp. 79-90.

Thurlow, J.G., and Swanson, E.A. 1987. Stratigraphy and struc- ture of the Buchans Group. In Buchans geology, Newfoundland. Edited by R.V. Kirkham. Geological Survey of Canada, Paper 86-24, pp. 35-46.

Thurlow, J.G., Swanson, E.A., and Strong, D.F. 1975. Geology and lithogeochemistry of the Buchans polymetallic sulphide deposits, Newfoundland. Economic Geology, 70: 30- 144.

Turner, B.R., and Munro, M. 1987. Channel formation and migra- tion by mass-flow processes in the Lower Carboniferous fluvia- tile Fell Sandstone Group, northeast England. Sedimentology, 34: 1107 - 1122.

Vanderveer, D.G., and Sparkes, B.G. 1982. Regional Quaternary mapping - an aid to mineral exploration in west-central New- foundland. In Prospecting in areas of glaciated terrain. Edited by P.H. Davenport. Geology Division Publication, Canadian Insti- tute of Mining, Montrkal, pp. 284 -299.

Whalen, J.B., and Currie, K.L. 1987. The relationship of the Top- sails igneous terrane to the Buchans Group. In Buchans geology, Newfoundland. Edited by R.V. Kirkham. Geological Survey of Canada, Paper 86-24, pp. 69-73.

Whalen, J.B., and Currie, K.L. 1988. Geology, Topsails igneous terrane, Newfoundland. Geological Survey of Canada, Map 1680A, scale 1 : 200 000.

Woodcock, N.H. 1977. Specification of fabric shapes using an eigenvalue method. Geological Society of America Bulletin, 88: 1231 - 1236.

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

UN

IVE

RSI

TY

OF

PIT

TSB

UR

GH

on

11/1

2/14

For

pers

onal

use

onl

y.