geological interpretation of a high resolution reflection seismic survey at the buchans mine,...
TRANSCRIPT
Geological interpretation of a high resolution reflection seismic survey at the Buchans mine, Newfoundland1
J. G. THURLOW 72 Central Street, Corner Brook, NJd., Canada A2H 2M8
C. P. SPENCER AND D. E. BOERNER Geological Survey of Canada, I Observatory Crescent, Ottawa, Ont., Canada KIA 0Y3
L. E . REED BP Resources Canada Ltd., 55 University Avenue, Toronto, Ont., Canada M5J 2H7
AND
J. A. WRIGHT Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NJd., Canada AIB 3x5
Received January 20, 1992 Revision accepted May 6, 1992
Sixteen kilometres of high resolution Vibroseis reflection seismic data have been acquired in the vicinity of the former Buchans mine. Direct identification of the cause of several reflectors is possible because the geology is tightly constrained by underground workings and drill holes both of which locally exceed 1 km depth. Many of the mine-scale thrust faults are imaged as reflectors but conformable and intrusive contacts generally responded poorly. A significant shallow-dipping thrust, the Powerline Fault, is recognized below the orebodies and traced throughout the Buchans area, primarily as a result of the seismic survey. It truncates ore stratigraphy and forms the floor thrust of a large duplex-stack, which hosts all the orebodies. Its presence has negative implications for exploration in the immediate mine area. Several lines of evidence suggest that this fault has a significant component of out-of-sequence movement. A strong reflector 4.5 km below Buchans is correlated with the surface expression of the Victoria River Delta Fault, an important regional structure, newly recognized southeast of Red Indian Lake. This shallow, north-dipping sole thrust forms the structural base of the Buchans Group and brings it above a younger fossiliferous Llanvirn volcanic sequence. This fault is not itself the Red Indian Line but is one of a series of faults that collectively effect substantial geological contrasts in central Newfoundland. The seismic survey was a cost-efficient means of gaining knowledge of Buchans structure, which might otherwise have been acquired at much higher cost and over a longer period of time.
Un lev6 de sismique rCflexion Vibroseis, i haute rCsolution, a CtC complCtC sur 16 km dans les environs de I'ancienne mine Buchans. L'identification directe de I'origine de nombreux rtflecteurs est possible, car la gCologie est connue en detail grlce aux travaux souterrains et aux trous de forage qui, l'un et I'autre, renseignent sur une profondeur excMant 1 km. Plusieurs des failles de chevauchement i I'Cchelle de la mine sont exprimCes par les rkflecteurs, mais les contacts concordants et intru- sifs sont en gCnCral moins tvidents. La faille de Powerline, un chevauchement important i pendage peu profond, a CtC recon- nue sous les corps minCralisCs et sa trace a CtC suivie au travers la region de Buchans, surtout grlce aux donnCes sismiques. Elle tronque la stratigraphie de la zone minCralisCe et elle forme la base du chevauchement d'un grand duplex-empilement qui est I'h6te de tous les corps minCralisCs. Sa prCsence crCe des difficult& pour l'exploration de la rCgion immkdiate ?I la mine. Plusieurs indices suggkrent que cette faille inclut une composante d'un dCplacement hors-sCquence significatif. Un fort rCflecteur 2 4,5 km sous le site de Buchans est mis en corrClation avec la faille de Victoria River Delta visible en surface, une structure rCgionale majeure, nouvellement reconnue au sud-est du lac Red Indian. Cette surface de dCcollement, peu profonde, inclinke vers le nord, reprCsente la base structurale du Groupe de Buchans qui fut transport6 au-dessus d'un sCquence plus jeune, fossilifkre et volcanique datCe du Llanvirnien. Cette faille ne reprCsente pas en rCalitC la ligne Red Indian, mais elle est une parmi une sCrie de failles qui, collectivement, crCent les principaux contrastes gCologiques observks dans la partie centrale de Terre-Neuve. Le lev6 de sismique a CtC un moyen Cconomiquement rentable pour acquCrir des renseignements sur la structure de Buchans, qui autrement auraient CtC obtenus i un coQt beaucoup plus Clevt et auraient nCcessitC une plus longue pCriode de temps.
[Traduit par la rtdaction] Can. J . Earth Sci. 29, 2022-2037 (1992)
Introduction We present geological interpretations from the first major
Vibroseis reflection survey at a mine site in North America. The opportunity to conduct a high resolution seismic experi- ment in the Buchans mine area was presented by its proximity to the Lithoprobe Meelpaeg Transect across the island of New- foundland in 1989 (Fig. 1). A controlled source audio fre- quency magnetotelluric (CSAMT) survey was run along the
'Geological Survey of Canada Contribution 12792; Lithoprobe Contribution 306.
Printed in Canada 1 Imprimt au Canada
same profile as the seismic program; the results of this survey are also described briefly here.
Mineral exploration at Buchans has traditionally had a strong geological component with aspects of structure and stratigraphy playing important roles. With ongoing explora- tion, the probability of new, near-surface ore discoveries has diminished. However, the potential at depth is considered to be substantial, since it has been demonstrated through under- 1
ground exploration and mining that the productive ore stratig- raphy is structurally repeated many times by thrust faults.
The decision to participate in the Lithoprobe program was based on the expectation that physical responses resulting from
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
THURLOW ET AL. 2023
FIG. 1. Location of Buchans with respect to Lithoprobe Meelpaeg Transect (heavy line) and the tectonic - stratigraphic subdivisions of central Newfoundland (after Williams er al. 1988).
known features (e.g., stratigraphic units, faults) could be recog- nized and used to extend knowledge of the geological succes- sion into areas of unknown geology. The possibility of direct identification of orebodies, such as that described by Fais et al. (1991), was considered to be a possible, but unlikely out- come. Given the importance of thrust faults in controlling the distribution of ore it was hoped that the new knowledge of deep structure would lead to new exploration concepts and tar- gets. The detailed traverses were also part of the regional Meelpaeg Transect making it possible to integrate easily data and interpretations from local and regional scales. This aspect was of particular interest because of the proximity of Buchans to the Red Indian Line (Williams et al. 1988).
General geology The Lower Ordovician Buchans Group forms part of the
Dunnage Zone of central Newfoundland (Fig. I), a structur- ally assembled collage of rocks that record the opening and subsequent closure of the Iapetus Ocean (Williams 1979). Four volcano-sedimentary formations were defined by Thurlow and Swanson (1987), each consisting of varying proportions of proximal felsic and mafic volcanic and volcaniclastic rocks that display complex, but well-understood facies interactions characteristic of an active volcanic -tectonic environment. The Buchans orebodies were economically important, poly- metallic, volcanogenic, sulphide deposits that occurred within felsic pyroclastic rocks and breccias of the Buchans River For- mation. Spectacularly high grade, resedimented breccia ores of debris flow origin are particularly well developed and preserved (Thurlow and Swanson 198 1 ; Binney 1987).
Conodonts recovered from the Buchans Group indicate a Whiterockian (Llanvirn-Llandeilo) age (Nowlan and Thurlow 1984), which is consistent with a U-Pb (zircon) age of
473': Ma (Dunning et al. 1987) on rhyolite from the Buchans River Formation.
Buchans Group structure The recognition of the first thrust faults at Buchans in 1974
marked the beginning of a revolution in understanding of Buchans Group structure. The Buchans Group structurally overlies the Skidder Basalt and Ordovician volcanic and volcaniclastic rocks of the Harbour Round Formation and Victoria Lake Group southeast of Red Indian Lake (Fig. 2) and is overthrust from the north by deformed plutonic rocks of the Hungry Mountain Complex (Thurlow 1981). The Buchans Group stratigraphic succession has been extensively telescoped by thrust faults and displays duplex and antiformal stack fault geometries nested at various scales (Calon and Green 1987; McClay 1987; Thurlow and Swanson 1987; ter- minology after Boyer and Elliott 1982). The orebodies were contained within two adjacent thrust slices, the Lucky Strike panel and Oriental panel, separated by the Buchans River - Ski Hill fault system (Thurlow and Swanson 1981, 1987). Within the Lucky Strike panel, the orebodies are contained within an antiformal stack (termed the Buchans Anticline by Swanson and Brown 1962) over which the Airport Thrust is passively folded causing an outlying klippen of the Middle Branch Panel (Fig. 3). On a smaller scale, both Lucky Strike and Oriental orebodies themselves comprise antiformal stack structures, which disrupt and repeat ore stratigraphy and thereby thicken the mineable deposit (Calon and Green 1987). The nature and distribution of faults below the Lucky Strike panel were very poorly known prior to the seismic survey, due to both the lack of outcrop and the fact that drilling was gener- ally terminated upon reaching the Old Buchans Fault at the floor of the panel.
The analysis of branch-lines (lines defined by the inter- section of splaying thrust surfaces) was introduced by Hossack (1983) and has application to the understanding of thrust fault interactions at Buchans. Branch-lines of significant thrust faults generally show east -west trends (Fig. 4), parallel to fold hinges of hanging-wall anticlines and to cutoff lines defined by the intersection of stratigraphic contacts with thrust fault sur- faces. These lines are perpendicular to mineral stretching lineations, suggesting south-southeastward directed thrusting (Thurlow 198 1 ; Calon and Green 1987). The relative positions of branch-lines and the seismic survey traverse lines are an issue affecting interpretation of the seismic data.
Seismic survey procedures Seismic data at Buchans were collected along three lines, the
location of which was determined by the presence of roads with adequate capacity to carry the 15 000 kg vibrator trucks. Fortunately, the road network allowed for orthogonal tra- verses parallel and perpendicular to geological strike (Fig. 3) and only these two traverses will be discussed. Details of the methods employed, survey parameters, and data processing procedures are given by Boerner et al. (1990) and Spencer et al. (1993).
Seismic interpretation philosophy
The distribution of reflectors in this survey and that of thrust faults, whose distribution is tightly constrained, is remarkably similar. In the absence of direct velocity measurements, the philosophy adopted is that reflectors on the time sections cor-
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
2024 CAN. J. EARTH SCI. VOL. 29, 1992
FIG. 2. Regional geology of the Buchans area showing major faults and geological units. Buchans Group is shaded. Windows through, and klippe floored by, the Airport Thrust are removed for simplicity. HMC, Hungry Mountain Complex; LVM, Lloyds Valley mylonite; TIS, Topsails Igneous Suite.
respond to major faults, which are well mapped in three dimensions from observations underground and in drill core. This approach is justified in that the velocities implied by fix- ing the reflector depths with geological information are fully consistent with the stacking velocities derived from the mul- tichannel data.
The thrust fault zones have been observed in outcrop and drill core. They are typically 0.5-5 m wide and consist of poorly consolidated, porous, sandy to clayey gouge and frac- tured rock overprinting earlier ductile deformation fabrics. The movement zones are surrounded by areas of brittle frac- ture and weak foliation, generally 5-20 m wide. The faults separate panels of undeformed to weakly deformed volcanics containing joints, shear fractures, and Riedel shears (McClay 1987). The various formations of the Buchans Group are simi- lar in their physical properties. Conformable stratigraphic contacts present little seismic impedance contrast and cor- respondingly weak to undetectable reflections.
The interpretation of reflections emanating from relatively thin fault zones is seismically similar to that of a pioneering study in crystalline rocks at Lokken by Gjoystdal et al. 1983. They report reflections from a 5m thick layer of low velocity ' 'soapstone" within crystalline rock.
Seismic survey results: Line 14 The locations of the two seismic traverses are shown on a
geological base in Fig. 3. The seismic section of Line 14
shows the most continuous and strongest reflectors in the Buchans survey (Fig. 5). The line runs west-east, parallel to geological strike (Fig.3) and over the site of the mined-out Rothermere orebody (Fig. 10). The section also runs perpen- dicular to the direction of tectonic transport, with thrust panels having moved directly toward the viewer (north to south), thereby accounting for the apparent unusual interactions of thrust faults in the interpreted geological section (Fig. 6), which only represents the upper portion of the data shown in Fig. 5. In general, reflectors can be resolved at depths greater than 150 m from surface.
Three thrust panels are of importance on the geological sec- tion (Fig. 6), which was constructed from detailed drill core logging. The panel bounded by the Ski Hill - Buchans River faults in the floor and the Airport Thrust in the roof hosts the Oriental orebodies (off section). The panel below, floored by the Old Buchans Fault, hosts the Lucky Strike and Rothermere orebodies, below which is the panel bounded by the Powerline Fault in the floor and the Old Buchans - Buchans River Fault in the roof, which hosts the Clementine Prospect. The Ski Hill and Old Buchans faults merge into one fault at three points on this section, indicating that their branch-line is essentially sub- horizontal and in the plane of the section.
Three prominent reflection zones visible on seismic section 14 are labelled A, B, and C in Fig. 5. The quality of response from all three reflectors is degraded in the central part of the section by a zone of noisy data that correlates with two close-
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
THURLOW ET AL
LATE DIABASE
SANDY LAKE FORMATION SKI HILL FORMATION [3 0 BUCHANS RIVER FORMATION . . . . . . . LUNDBERG HILL FORMATION
FIG. 3. Simplified Buchans area geological map showing location of seismic traverses (solid lines). Numbers along traverses are shotpoints, which are also shown in Figs. 5 and 14. APT, Airport Thrust; BRF, Buchans River Fault; EPF, Epidote Fault; HMT, Hungry Mountain Thrust; OBF, Old Buchans Fault; PLF, Powerline Fault.
spaced sharp bends in the road traverse. The lack of continuity of reflectors through this "noise zone" is viewed as a data acquisition -processing problem and has little to do with geo- logical complications. Improvements of the signal -noise ratio in this region have shown continuity of reflectors into, and nearly through, the noise zone.
Rejector A (Old Buchans Fault) Comparison of the seismic and geological sections shows
spatial coincidence between Reflector A and the Old Buchans Fault, a thrust traced by diamond drilling throughout a 7 by 2 km area around the mine (Fig. 7). The fault zone varies in attitude from vertical to horizontal and varies in width from centimetres to 20 m. It is laterally heterogeneous, consisting of variable amounts of unconsolidated, porous fault breccia and clayey fault gouge within a somewhat broader zone of fractured rock. The fault is locally intruded by syn- to post- tectonic diabase sills, which widely intrude Buchans Group thrusts and are themselves commonly fractured and broken. These brittle fault features overprint a zone of earlier ductile shear, which is manifest by thin zones of foliated wall rocks that contrast markedly with adjacent weakly foliated to
unfoliated Buchans Group lithologies. Reflector A is easily recognized at the west end of Line 14,
but it is less easily traced beyond the noise zone to the east. If the reflector originates from the Old Buchans - Buchans River Fault system, the reason for lack of continuity should be explicable, since these faults are continuous across the sur- veyed area and juxtapose differing lithologies (Figs. 3, 6). Although systematic logging of the physical characteristics of the fault along its length has not been conducted, no readily obvious change in the character of the fault has been recog- nized. As well, there is little apparent correspondence between strength of reflections and contrast in lithologies across the fault. Figure 7 shows structural contours along this fault sys- tem with the seismic traverses superimposed. It can be seen that the best-imaged section of the fault is in areas of shallow dip. Throughout much of the region where it is poorly imaged, the fault dips at nearly 45". The fault is imaged at the extreme east end of the line (Reflector D), where dips are again rela- tively flat. The seismic line and the branch-line between the Old Buchans and Epidote faults are almost coincident along the section of enhanced seismic response (Fig. 7). Certain branch-lines at Buchans are characterized by thicker zones of
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
-
2026 CAN. J. EARTH SCI. VOL. 29, 1992
SANDY LAKE
-48'50'
- KILOMETRES 56'50' w 'N
I -.- FIG. 4. Map showing branch-lines and surface position of branch-points (terminology after Hossack 1983) of thrust faults in the Buchans
mine area. Subsurface branch-lines are solid, above-surface interpolated branch-lines are broken. Antiformal stacks evolve at the points where single branch-lines diverge into three lines. Cutoff lines (not shown) of formational contacts against the thrusts generally display the same east-west pattern. The surface trace of the Airport Thrust is shown for reference. APF, Airport Thrust; BRF, Buchans River Fault; EPF, Epidote Fault; HAG, H. A. Guess Fault; OBF, Old Buchans Fault; PLF, Powerline Fault; SHF, Ski Hill Fault.
LINE 14 E 1010 2010 3010 4010 5010 6010 7010 8010 SP
0.0 , I I I I 1
LINE 15a FIG. 5. Line 14 seismic section. Reflectors designated by bold letters are discussed in the text. Reflector A is the Old Buchans Fault, Reflector
B is the Powerline Fault, and Reflector C is the Victoria River Delta Fault.
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
THURLOW ET AL. 2027
fracturing, gouge development, and porosity but because they are linear zones, they should not give rise to reflectors as would planar features with similar impedance contrast.
Reflector B (Powerline Fault) Reflector B is a west-dipping feature at 0.45-0.65 s
(1 125 - 1625 m vertical depth) at the west end of Line 14, structurally below the Old Buchans Fault. Direct identification of the cause of this reflector is not possible because the region where this package of events is most prominent is not inter- sected by any mine workings or drill holes. However, by enhancing the data in the noise zone, the structure can be traced eastward into a significant fault zone mapped under- ground in MacLean mine and in nearby diamond drill holes 2785 and 2788 (Fig. 6). Simple updip projection of this fault places it among a series of deformed outcrops beneath a powerline, 1600 m south of the Lucky Strike orebody. Cleaved and foliated siltstone-wacke beds in these outcroDs are deformed into an inclined fold system with detachments detween the folded panels (Fig. 8). Quartz-wacke beds are locally boudinaged and dis- membered into isolated wacke inclusions within a siltstone matrix (Fig. 9), a texture characteristic of ''broken formation mtlange" (Cowan 1985). Moderately plunging, north-northeast trending hinges of Z-shaped folds suggest a hanging-wall-up (reverse) component of movement. These outcrops define a deformed belt in excess of 1 km in length and at least 60 m wide. The considerable strike length of deformed sediments strongly suggests the presence of a significant detachment zone (T. Calon, personal communication, 1990). The zone is here- after termed the Powerline Fault. The east-northeast strike and gentle northwestward dip of the zone is consistent with the interpretation that the Powerline Fault is the same zone as that which was intersected in holes 2785 and 2788. Reflector B there- fore is interpreted to be exposed at the surface as the Power- line Fault.
The Powerline Fault is visible on airborne magnetic surveys as a prominent, straight magnetic lineament andcan be traced southwestward to a single outcrop that defined the Wileys River Fault (Fig. 10). The magnetic correlation is evidently due to diabase sills that are observed within the deformation zone both in outcrop and in drill core. Eastward, the Power- line Fault can be correlated with important shear zones in holes 269, 459, and 3319 (Fig. 10) before it reaches the branch-point with the Airport Thrust. Deformed sediments in these holes adjacent to the shear zone resemble those in out- crop from the type area, implying that detachment followed this clastic sedimentary horizon within the Sandy Lake For- mation.
Structural contours on the Powerline Fault based upon the drill core and seismic information (Fig. 10) indicate that the fault is extraordinarily planar compared with other folded thrust faults at Buchans. The Powerline Fault is herein intemreted to be the floor thrust to the large duplex structure that has the Air- port Thrust in the roof and which contains all the known Buchans-type mineralization. The leading branch-line of floor and roof thrust faults is evidently east - west trending, undulat- ing and gently eastward plunging (Fig. lo), parallel to other branch-lines of significant faults at Buchans (Fig. 4). The con- sistent east -west attitude of branch-lines strongly suggest thrust movement from the north. The combined Powerline - Airport fault system (termed Airport Fault east of the branch-point) can be traced eastward from the branch-point another 25 km, where it joins other regional structures.
Several lines of evidence suggest that the Powerline Fault, though part of the Buchans thrust stack, has a significant out-
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
2028 CAN. J . EARTH SCI. VOL. 29, 1992
SUBSURFACE LEADING BRANCH-LINE,
SURFACE TRACE SUBSURFACE LEADING
FAULT - 0 I D 0 10c-3 -
METRES
FIG. 7. Plan showing structural contours on the Old Buchans - Buchans River Fault surface. Small dots are drill penetrations of the fault. Contours are in metres relative to sea level; ground surface is 200-300 m asl. Also shown are the seismic traverse lines and the branch-line between Old Buchans and Epidote faults. The noise zone along traverse Line 14 is marked by a broken line. The best reflectivity from the fault zone occurs where the traverse line is straight and where it coincides with the branch-line and with relatively shallow dips of the fault surface.
of-sequence component of movement. The flat, planar charac- ter of the fault, as suggested by both the magnetic and seismic data, suggests that it has not been passively folded over foot- wall ramps or distorted by antiformal stacks generated in its footwall, as is characteristic of all other Buchans area thrusts. It also cuts thick sections of stratigraphy at nearly 90" and apparently places younger formations on older ones; neither is characteristic of in-sequence thrusts. The Powerline Fault lies structurally below the H. A. Guess Fault, a thrust with demon- strated out-of-sequence movement based upon structural repe- tition of a distinctive noncohesive cataclasite lithology containing high grade sulphide clasts. Linear faults at surface south of, and parallel to, the Powerline Fault are not folded (Fig. lo), suggesting that they might also be out of sequence. This southeastward change from the in-sequence thrust stack to thrusts with out-of-sequence movement may represent a tran- sition of structural styles approaching the Siluro-Carboniferous Red Indian Lake basin and Victoria Lake Group to the southeast. The unusual character of the Powerline Fault is also highlighted by the CSAMT data (Boerner et al. 1993), which shows a sig- nificant resistivity contrast across the fault. Out-of-sequence motion on major floor and roof thrusts is apparently a common phenomenon (Butler 1987), although in this case, there is no evidence for such motion on the Airport Thrust.
Small outliers of Carboniferous molasse, which occur along the Powerline-Airport fault system east of Buchans, imply that Carboniferous extensional detachments in the Red Indian Lake basin were propagated along existing Buchans Group thrusts.
Reflector C (Victoria River Delta Fault) The lowermost reflector seen on the seismic sections
(Reflector C , Fig. 5 ) , at about 1.8 s (approximately 4.5 km
depth) gave the strongest return of seismic energy of any fea- ture in the survey. This reflector is also clearly imaged on the regional Meelpaeg Transect where it rises closer to the surface toward the southeast, indicating a shallow northwesterly com- ponent to the dip. The surface trace of this reflector cannot be located exactly because of its relatively shallow dip, the com- paratively poor resolution of the regional survey at very shal- low depths, and the fact that this section of the Meelpaeg Transect runs nearly parallel to the geological strike (Fig. 2). However, simple updip projection places this reflector at a point on the surface coincident with a fault of regional sig- nificance, which is exposed in a series of outcrops at low water in the delta of Victoria River (Fig. 1 I). Termed the Victoria River Delta Fault, this feature separates Buchans Group "arkosic conglomerate" from an underlying sequence of basaltic flows and sorted pyroclastic rocks with minor lime- stone lenses and marks the structural base of the Buchans Group. The limestones have yielded conodonts of Llanvirn- Llandeilo age (Stouge 1980) and intrusive rhyolite, presumed to be temporally related to the basalts, has been dated at 462!!, Ma (Dunning et al. 1987), in agreement with the fossil age. khese rocks have traditionally been assigned to the Victoria Lake Group (Kean and Jayasinghe 1980), but recent unpublished mapping suggests that they are more likely to be stratigraphically related to the Harbour Round Basalt and an overlying sedimentary unit, informally known as the Healy Bav siltstone. which structurallv overlie the Victoria Lake Group. These units structurally overlie and are in fault contact with underlying mineralized units at the Victoria Mine. Since the Victoria River Delta Fault brings older Buchans Group rocks on top of younger volcanics, thrust motion is implied.
The fault zone is a composite feature consisting of zones of both ductile and brittle deformation. Mylonitized basalt and
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
FIG. 8. Detached panels of folded and boudinaged wacke (light colour) and siltstone in the Powerline Fault zone.
FIG. 9. Broken formation mClange from Powerline Fault showing folded and dismembered, lighter coloured, wacke inclusions in cleaved siltstone matrix.
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
CAN. J. EARTH SCI. VOL. 29, 1992
KENS BROOK VOLCANICS
TOPSAILS GRANITE
FIG. 10. Structural contours on the Powerline Fault. 8 , diamond drill holes; X, outcrops. Seismic traverses, from which surface and depth control data are derived, are shown. Three branch-points between the Airport Thrust and Powerline Fault are labelled BP and define an east-west trending branch-line. Hanging-wall cutoff lines of the Ski Hill - Buchans River (SH-BR) and Buchans River - Sandy Lake (BR-SL) Formation contacts on the Powerline Fault are also shown. Faults at surface south of the Powerline Fault may be imaged as reflectors in Line 14.
recrystallized, sheared limestone at the base of the zone pass upward into a melanocratic, strongly cleaved, scaly, chloritic broken formation melange composed of dismembered wacke beds in a shaley -silty matrix (Fig. 12). The strong cleavage anastomoses around blocks and phacoids and dips northward at 45 -65". The zone has an aggregate surface width of 75 m and true width of approximately 50 m. Shear bands in the melange suggest a hanging-wall-up (thrust) sense of motion.
Tracing this fault downdip to the north at an average of 45" places it at about the position of the reflector on the regional Lithoprobe line, which can be traced westward directly into Reflector C on Line 14. The foliation and porosity of the fri- able melange lithology contrast markedly with the relatively massive rocks above and below. These differing physical prop- erties suggest a probable seismic impedance contrast.
Other seismic features on Line 14 Reflector E (Figs. 5, 6) occurs at the shallowest limit of
resolution on Line 14 at the position of the mined-out Rother- mere orebody. Virtually all the ore was removed during min- ing and stopes were filled with sand, which are now water saturated because of flooding of the mine. Therefore, seismic responses are not from ore but from a sand and water-filled cavity up to 20 m thick. A small, unnamed thrust in the hang- ing wall of the orebody is locally intruded by a thick (150 m) diabase sill. The Old Buchans Fault, below the orebody, comes to within 60 m of the ore on this section and even closer
in the southwest. The coincidence of these natural and man- made planar features appears to be imaged by reflectors.
The interpreted eastern extension of the Powerline Fault is labelled as Reflector G . An important mine-scale thrust, the H. A. Guess Fault, appears to be imaged as Reflector H.
A number of reflectors can be discerned between Reflectors B and C. At least one important lineament, which is defined by coincident magnetic, very low frequency - electromag- netic, and topographic features occurs at the surface structur- ally below the Powerline Fault. This feature, termed the Tilleys Pond Fault, disrupts geological units and is evidently a fault of some magnitude, though it has not yet been exposed in outcrop or drill core. This and other structurally lower lineaments (Fig. 10) are probably being imaged as reflectors I and J.
Reflector P, at the west end of the line, mimics the easterly dip of stratigraphy, thrusts, and diabase sills, as indicated by drilling in this area. These easterly dipping reflectors appear to be truncated by the Powerline Fault. The Buchans River Formation, which hosts the Clementine Prospect, is one of the truncated units, indicating that this stratigraphic unit has a limited downdip extent in this fault panel. The cutoff lines of the base and top of Buchans River Formation above the Powerline Fault (Fig. 10) run nearly perpendicular to the general east - west trend of branch-lines, suggesting that this cutoff occurs along an oblique ramp. A similar oblique hanging-wall ramp truncates the Buchans River Formation
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
THURLOW ET AL.
FIG. 11. Geological map of the Victoria River Delta area. F, location of conodont fossils; Zr, location of U-Pb radiometric date on zircon. Dots indicate areas of outcrop. Unit 1: unseparated mafic flows, pyroclastics, diabase, minor fossiliferous limestone, and siliceous intrusives similar to rocks of units 4 and 5. Unit 2: Victoria River Delta Fault Zone. Unit 2a: mtlange with blocks of competent sediment in scaly cleaved chloritic matrix. Unit 2b: Mylonitic mafic volcanics, locally with strongly deformed limestone lenses. Unit 3: Buchans Group, granite cobble conglomerate, litharenite ("arkose"). Unit 4: late- to post-tectonic feldsparphyric siliceous intrusive rocks. Unit 5: late- to post-tectonic amphibole - phyric intrusive rocks.
north of the Oriental orebody (BP Resources Canada Ltd., M, whereas the floor of Stack K is not clearly imaged. The unpublished data). These observations obviously have impor- more flatly dipping culminations of these stacks are better tant implications for mineral exploration. imaged than the flanks. Neither of these structures had been
The Airport Thrust, the major roof thrust above the mineral- inferred prior to the seismic survey. Other, less obvious, but ized thrust stack, is present at the east end of the section line equally likely, antiformal stacks can be envisioned on this pro- near the shallow limit of detection (Reflector Q). file. The Airport Thrust (Reflector 0) can be traced to the
Seismic survey results: Line 15a Line 15a runs north-south, normal both to Line 14 and to
geological strike (Fig. 3). Consequently, the seismic and geo- logical sections (Figs. 13, 14) present geometries and inter- actions of structures that are more typical of sections through thrust belts. Generally, this section lacks the presence and con- tinuity of important reflectors as seen on Line 14.
The Powerline (Reflector B) and Victoria River Delta faults (Reflector C) are both seen as north-dipping structures and tie directly to their counterparts on Line 14 at the line of inter- section of the two traverses (Fig. 13). Reflector H is 100- 150 m below the Old Buchans - Buchans River fault system and probably represents an eastern extension of the H. A. Guess Fault. The Buchans River Fault (Reflector A) is only very weakly imaged despite lithologic contrasts across the fault.
Two domal reflective structures (areas K and L) display the geometry of antiformal stacks. Stack L is floored by Reflector
-,
north, where it appears to be passively folded over both stacks.
Prominent on this section are a number of south-dipping structures (e.g., Reflectors M, N, 0 ) . South-dipping thrusts are not uncommon in the Buchans Group, occurring almost exclusively on the foreland flanks of antiformal stacks. Their south dip is due to passive folding during growth of the under- lying stack (Boyer and Elliott 1982). Reflectors N and 0 have the appearance of faults within a larger antiformal stack that is floored by the Victoria River Delta Fault. If this is the case, it is unusual that Reflector F, and higher structures, show no propensity to be folded over this stack. This may indicate that Reflector F is out of sequence, providing further support for the suggestion that the nearby Reflector B (Powerline Fault) has an out of sequence component. There are alternative explanations for the south-dipping thrusts. They may be north- directed back thrusts, although only one minor occurrence of this type of structure has been documented at Buchans. Reflec- tor N might represent the contact between Buchans Group and
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
CAN. J , EARTH SCI. VOL. 29, 1992
FIG. 12. Phacoids of wacke in cleaved, scaly matrix from mClange zone of the Victoria River Delta Fault.
underlying Skidder Basalt. Unpublished data (C. P. Spencer) therefore may represent a higher conductivity in the hanging from Line 15c indicates that the cutoff line defined by Reflec- wall relative to the footwall. tor N and the Victoria River Delta Fault (Reflector C) plunges The Buchans Group is devoid of strong electrical conduc- northeast and projects back to surface at the cutoff point of tors, and most weak conductive features have been shown to Skidder Basalt on the Victoria River Delta Fault (Fig. 2). be faults or hematitic zones. Overpressured calcium chloride
brines were intersected in deer, drilling below the mine (E. A. - - - - Interpretation of CSAMT data Swanson, personal communication, 1976) at a position
interpretation of the CSAMT data collected along the approximately coincident with the Powerline Fault. Whereas
west end of Line 14 is depicted in Fig. 15 (Boerner et al. these brines were not detected by the CSAMT survey, their
1992). The data indicate a marked change in resistivity across presence at the level of the Powerline Fault may be indicative
a gently west-dipping planar zone throughout the mine area at of a decrease in effective porosity below the fault zone. Such
a depth that is approximately coincident with Reflector (the an interpretation is consistent with the electrical structure
Powerline Fault). The inference is that the Powerline Fault inferred from the electromagnetic studies.
forms a significant boundary between a relatively more con- ductive slab above and a more resistive "basement" below. The Old Buchans Fault is also represented in Fig. 16, but the CSAMT data do not resolve a property contrast across the fault.
The reason for a conductivity change across the Powerline Fault is not readily apparent in the geology. The electrical boundary is too shallow to be the contact between the Skidder Basalt and the Buchans Group, and lithologies exposed on sur- face and in drill core are essentially similar above and below the fault. Thrusts above the Powerline Fault are intensely imbricated and passively folded, causing widespread brittle fracturing of the volcanic formations. The character of faults below the Powerline Fault is poorly known, but the seismic data seem to suggest more widespread planar faults. This change in structural style suggests less bulk fracturing and
Thickness of the Buchans Group
Line 15a traverses north - south across the widest outcrop of the Buchans Group. However, the Buchans Group can be seen in Fig. 14 to have an aggregate structural thickness of less than 5 km from the Victoria River Delta Fault at the base to the Hungry Mountain Thrust in the roof. The total stratigraphic thickness of the Buchans Group, which was estimated to be 3 -6 km (Thurlow and Swanson 1987), is now interpreted, on the basis of this new information, to be less than 3 km.
Implications for the nature of the Red Indian Line The detailed observations documented above can be set in
the context of the regional geological and geophysical interpretation of central Newfoundland. The Red Indian Line
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
THURLOW ET AL.
S LINE 15a
LINE 14
FIG. 13. Line 15a, seismic section. Reflectors designated by bold letters are discussed in the text.
is a structural boundary, defined by Williams et al. (1988), that divides the Dunnage Zone of central Newfoundland into two fundamentally different volcano-sedimentary terranes termed the Notre Dame and Exploits subzones. Williams et al. (1988) positioned the Red Indian Line exactly at the location of the Victoria River Delta Fault. The new seismic and geo- logical observations, which indicate that this fault is a shallow north-dipping thrust at the base of the Buchans Group, are not in agreement with the interpretation of the line as a steeply dip- ping rectilinear fault. O'Brien (1991) described Red Indian Line in Notre Dame Bay as a 2-3 km wide mClange and mylonite belt, lithologically similar to the Victoria River Delta Fault but evidently much wider.
Red Indian Line was defined by Williams et al. (1988) on the basis of contrasts in stratigraphy, structure, fauna, and Pb isotopic signatures, among other criteria, across the line. Each of these aspects is discussed briefly in the ensuing paragraphs to determine whether the characteristics of the Victoria River Delta Fault meet the criteria for the Red Indian Line.
Stratigraphy-Red Indian Line separates the Notre Dame Subzone, characterized by a sub-Silurian unconformity, from the Exploits Subzone, characterized by conformable Ordo- vician-Silurian stratigraphy (Williams et al. 1988). Red sandstone and conglomerate of presumed Silurian age crop out along the south shore of Red Indian Lake (Williams 1970) and overlie, with faulted contact, complexly folded, largely over-
turned beds of Healy Bay siltstone. The exposed, faulted con- tact between the weakly cleaved, red sandstones and underlying Healy Bay siltstone marks the position of Red Indian Line (Williams et al. 1989), but it also occupies a struc- tural position similar to that of the Victoria River Delta Fault. Boulders of conglomerate in glacial till, which resemble poorly exposed inland outcrops of Silurian conglomerate, con- tain strongly cleaved siltstone clasts, which resemble Healy Bay siltstone but do not resemble Buchans Group lithologies. Both the mapping and these clasts imply a sub-Silurian uncon- formity on the Healy Bay siltstone, suggesting that it forms part of the Notre Dame Subzone. This implies that the Victoria River Delta Fault does not display the stratigraphic contrast ascribed to Red Indian Line and that the line therefore must be farther to the east.
Structure-Feldsparphyric intrusive rocks intrude the mklange of Victoria River Delta Fault and truncate the cleavage, sug- gesting syn- or post-tectonic emplacement. These intrusives lithologically resemble the rhyolite body only 200 m distant, which was dated by Dunning et al. (1987). If these rocks record the same event, then the age of thrusting is bracketed very closely between the time of Llanvirn -Llandeilo deposi- tion of the limestones and 462'; Ma. This age of tectonism predates the widespread deposition of Caradocian shales, which are characteristic of much of the Exploits Subzone. The volcanic and volcaniclastic sequence exposed immediately
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
2034 CAN. J. EARTH SCI. VOL. 29, 1992
4-SANDY LAKE FORMATION
3-BUCHANS RIVER FORMATION
2-SKI HlLL FORMATION
I-LUNDBERG HlLL FORMATION
METRES ( V - H )
FIG. 14. Line 15a, geological section. Bold letters refer to the position of reflectors in Fig. 14 and are discussed in the text.
0
RESISTIVITY ( a . m) h
E - a 6900
I 1000
4400
W a 2800
n 1700
1
24 22 20 18 16 14 12 10 8 6
STATION LOCATIONS
LClr
0 METRES
400
FIG. 15. Interpreted resistivity -depth section of CSAMT data from Line 14. The Old Buchans and Powerline faults correspond to reflectors A and B respectively (Figs. 5 and 6).
below the Victoria River Delta Fault displays a single very weak cleavage, parallel to that in the overlying Buchans Group and is therefore interpreted to have undergone the same Ordo- vician structural history as the Buchans Group. Since Williams et al. (1988) indicate that large parts of the Exploits Subzone are unaffected by Taconic orogeny, this further suggests that these rocks below the fault are part of the Notre Dame Zone.
Fauna-The faunal contrasts across the Victoria River Delta Fault may not be diagnostic of a change in faunal provincial- ity, since faunas of exactly the same age are not present for comparison (G. Nowlan, personal communication, 1991).
Pb isotopes-Pb isotopes from Buchans (above the Power-
line Fault), Mary March (below the Powerline Fault), and the Victoria mine (below the Victoria River Delta Fault) display a progression toward more radiogenic compositions eastward across the structural grain of this portion of central Newfound- land (data from Cumming and Krstic 1987; Swinden and Thorpe 1984). The data from the Victoria Mine clearly sug- gest that this deposit has more in common with deposits in the Exploits subzone (Swinden et al. 1988), thereby suggesting that the Red Indian Line does indeed pass between the Victoria mine and the Buchans Group.
The arguments above suggest that the Victoria River Delta Fault does not display many of the characteristics of the Red
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
THURLOW ET AL. 2035
FIG. 16. Schematic geological cross section through the Buchans area to illustrate the general relationships between thmst faults. No vertical exaggeration.
Indian Line. We suggest that the concept of a single fault that marks a profound structural boundary may not be entirely appropriate in the Red Indian Lake area. Near the Exploits Dam, Red Indian Line evidently bifurcates into a series of splays (Fig. 2), one of which is the shallow-dipping Victoria River Delta Fault. Other splays traverse southwestward, dis- secting the Victoria Lake Group into a series of terranes with differing isotopic ages (Evans et al. 1990). It is not known whether one of these splays is dominant or whether the con- trasts described by Williams et al. (1988) occur progressively across the several fault structures.
At the southwest end of Red Indian Lake, mylonitic rocks in the Lloyds Valley bring deformed plutonic rocks on top of the Ordovician volcanic terrane, in much the same manner as the Hungry Mountain Thrust north of Buchans. The Lloyds Valley mylonite can be traced north of Red Indian Lake (Fig. 2) to the point where it disappears below Carboniferous strata (D. Barbour, personal communication, 1989) and prob- ably correlates with the Hungry Mountain Thrust. These correlations suggest that the structure in Lloyds Valley is also not, in itself, Red Indian Line. The points cited above suggest that the Red Indian Line is not a steep rectilinear fault in the Red Indian Lake area. The collective changes in the various criteria that define the line probably occur across a series of structures that bound and transect the Harbour Round Forma- tion and Victoria Lake Group.
A geologic cross section, which integrates the seismic and geological data in the Red Indian Lake area, is shown in Fig. 16.
Exploration significance
Recognition of the Powerline Fault as a significant thrust with out of sequence movement has important implications for deep mineral exploration at Buchans. The Fault truncates the productive Buchans River Formation downdip from the Clementine Prospect (Fig.6) and thereby places well-defined limits on the depth extent of the favourable stratigraphy. Deep stratigraphic drilling in search of mineralization in this horizon above the Powerline Fault, as had been contemplated before the seismic survey, is now suggested to be less attractive. Spe-
cifically, drilling east of the Buchans River - Sandy Lake cutoff line (Fig. 10) will not intersect Buchans River Forma- tion above the Powerline Fault.
The Powerline Fault evidently occurs within a few tens of metres below the deepest drilling at MacLean and MacLean Extension orebodies. The potential for new orebodies structur- ally below mine-scale thrusts in the immediate mine area is therefore also limited, in a practical sense, by the Powerline Fault.
All known Buchans-style mineralization is contained within the thrust duplex bounded between the Airport and Powerline faults. The relatively shallow dip of the Powerline Fault places a limit on the depth to the base of the favourable structure. This observation tightly constrains the volume of crust with high potential for Buchans-type ore. Since this fault seems to have significant out-of-sequence movement, classical balanc- ing of cross sections across the fault is not possible without first resolving and correcting for this movement. Therefore, accurate predictions as to where the productive Buchans River Formation lies at depth below the fault are not currently possible.
The amount of movement on the Powerline Fault is uncer- tain, but considering the seismic, magnetic, and geological signature, it is probably considerably more than the 1000 m displacement that is typical of larger thrust faults in the mine area. The mineralized areas of Buchans River Formation above the fault probably existed geographically several kilo- metres distant from stratigraphic equivalents below the fault.
The results of the seismic survey have had significant impact on exploration geological thought at Buchans and from this standpoint the application to this "hard rock" mining environ- ment was an unqualified success.
Conclusions
The high resolution, reflection seismic survey carried out over the structurally and stratigraphically complex volcanic sequences at the Buchans mine was successful from several standpoints. Direct identification of the cause of many reflec- tors is possible because of the abundant diamond drill hole and underground geological mapping data to depths that exceed
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
2036 CAN. J . EARTH SCI. VOL. 29, 1992
1 km. The strongest reflections emanate from relatively shal- lowly dipping brittle-ductile thrust fault surfaces, whereas the responses from intrusive and stratigraphic contacts are generally poor. The distribution of the Old Buchans Fault, a mine-scale thrust fault that records approximately 1 km of fault movement, is confirmed by the seismic survey and extended downdip beyond the limits of drill information. Another fault, the Powerline Fault, is newly recognized as the floor thrust to the large duplex structure, which hosts all of the known orebodies. The correlation of the widely space drill hole and outcrop observations of this fault zone was not made prior to the seismic survey and its significance was not appreciated. This fault is believed to have a significant out-of- sequence component of motion because it is not folded and because it brings younger formations on top of older ones. The anomalous character of this fault is highlighted by CSAMT data, which show a substantial resistivity contrast across it. The seismic profiles show that the ore-bearing Buchans River Formation is cut off at depth by the Powerline Fault, thereby limiting exploration possibilities in certain areas.
Below the depths of drill holes and mine workings, a strongly reflective zone is correlated with surface at the site of the Victoria River Delta Fault, on the southeast side of Red Indian Lake. This moderately northwest-dipping thrust brings older Buchans Group on top of younger volcanics, which are tentatively correlated with the Harbour Round Formation. Intrusive relationships within this fault suggest an age of thrusting that immediately postdates deposition of the vol- canic~. The Victoria River Delta Fault is located at the site of the Red Indian Line, but significant contrasts in stratigraphy, structure, and fauna across it cannot be demonstrated. It is proposed that the geological contrasts, which occur across a single Red Indian Line elsewhere in Newfoundland, occur progressively across a series of faults that dissect the Victoria Lake Group and Harbour Round Formation.
Acknowledgments This project was funded jointly by Lithoprobe, the Geologi-
cal Survey of Canada, Memorial University of Newfoundland, the Natural Sciences and Engineering Research Council of Canada, and BP Resources Canada Limited, with whose per- mission we publish. Tenacious outcrop stripping and mapping by Larry Hicks was instrumental in locating outcrops of the Powerline Fault. Discussions with Tom Calon were, as always, most helpful. An early version of the manuscript was improved by comments from Scott Swinden, Alan Green, and by former colleagues at BP Mining.
Binney, W. P. 1987. A sedimentological investigation of MacLean channel transported sulphide ores. In Buchans geology, New- foundland. Edited by R. V. Kirkham. Geological Survey of Canada, Paper 86-24, pp. 107 - 148.
Boerner, D., Spencer, C. P., Wright, J. A, , and Reed, L. E. 1990. Developing new methods at an old mine: high resolution seismic and electromagnetic mapping at Buchans Mine. Engineering and Mining Journal, 191: 25 -29.
Boerner, D. E., Wright, J. A, , Thurlow, J. G., and Reed, L. E. 1993. Tensor CSAMT studies at the Buchans Mine in central New- foundland. Geophysics, 58: 12 - 19.
Boyer, S. E., and Elliott, D. 1982. Thrust systems. American Association of Petroleum Geologists Bulletin, 66: 1196- 1230.
Butler, R. W. H., 1987. Thrust sequences. Journal of the Geological Society (London), 144: 6 19 - 634.
Calon, T. J., and Green, F. K. 1987. Preliminary results of a detailed structural analysis of the Buchans Mine area. In Buchans geology, Newfoundland. Edited by R. V . Kirkham. Geological Survey of Canada, Paper 86-24, pp. 273-288.
Cowan, D. S. 1985. Structural styles in Mesozoic and Cenozoic mClanges in the western Cordillera of North America. Geological Society of America Bulletin, 96: 45 1-462.
Cumming, G. L., and Krstic, D. 1987. Detailed lead isotope study of Buchans and related ores. In Buchans geology, Newfoundland. Edited by R. V. Kirkham. Geological Survey of Canada, Paper 86-24, pp. 227-234.
Dunning, G. R., Kean, B. F., Thurlow, J. G., and Swinden, H. S. 1987. Geochronology of the Buchans, Roberts Arm and Victoria Lake groups and Mansfield Cove Complex, Newfoundland. Cana- dian Journal of Earth Sciences, 24: 1175- 1184.
Evans, D. T. W., Kean, B. F., and Dunning, G. R. 1990. Geological studies, Victoria Lake Group, central Newfoundland. In Current research. Newfoundland Department of Mines and Energy, Geo- logical Survey Branch, Report 90- 1, pp. 13 1 - 144.
Fais, S., Porceddu, E., and Tocco, R. 1991. High resolution seismic reflection survey of a massive sulphide orebody in Sardinia, Italy- an experiment. Ore Geology Reviews, 6 : 1-8.
Gjoystdal, H., Sandvin, A. O., Bakken, A., and Dahle, A. 1983. Seismic reflection experiments and 3-D ray modelling in the crys- talline rock of Lokken mining area, Norway. Society of Explora- tion Geophysicists, Annual Meeting, Extended Technical Program Abstracts 1983.
Hossack, J. 1983. A cross-section through the Scandinavian Caledonides constructed with the aid of branch-line maps. Journal of Structural Geology, 5: 103 - 11 1.
McClay, K. R. 1987. Aspects of the structural geology of the Buchans area. In Buchans geology, Newfoundland. Edited by R. V . Kirkham. Geological Survey of Canada, Paper 86-24, pp. 47-57.
Nowlan, G. S., and Thurlow, J. G. 1984. Middle Ordovician conodonts from the Buchans Group, central Newfoundland, and their significance for regional stratigraphy of the central volcanic belt. Canadian Journal of Earth Sciences, 21: 284-296.
O'Brien, B. H. 1991. Geological development of the Exploits and Notre Dame Subzones in the New Bay area, Notre Dame Bay, Newfoundland. In Current research. Newfoundland Department of Mines and Energy, Geological Survey Branch, ~ e ~ o i 91-1, pp. 155 - 166.
Spencer, C., Thurlow, G., Wright, J. A., White, D., Carroll, P., Milkereit, B., and Reed, L. 1993. A vibroseis reflection seismic survey at the Buchans mine in central Newfoundland. Geophysics, 58: 154-166.
Swanson, E. A, , and Brown, R. L. 1962. Geology of the Buchans orebodies. Canadian Mining and Metallurgical Bulletin, 55: 618- 626.
Swinden, H. S., and Thorpe, R. I. 1984. Variations in style of vol- canism and massive sulphide depositions in Early to Middle Ordo- vician island arc sequences of the Newfoundland Central Mobile Belt. Economic Geology, 79: 1596- 1619.
Swinden, H. W., LeHuray, A. P., and Slack, J. F. 1988. Lead iso- topes in volcanogenic sulphides of the northern Appalachians: application to the correlation of Paleozoic terranes (abstract) Geo- logical Association of Canada, Program with Abstracts, 13: A121.
Thurlow, J. G. 1981. The Buchans Group: its stratigraphic and struc- tural setting. 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. 79-90.
Thurlow, J. G., and Swanson, E. A. 1981. Geology and ore deposits of the Buchans area, central Newfoundland. In The Buchan ore- bodies: Fifty years of geology and mining. Edited by E. A. Swan- son, D. F. Strong, and J. G. Thurlow. Geological Association of Canada, Special Paper 22, pp. 79-90.
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.
THURLOW ET AL, 2037
Thurlow, J. G., and Swanson, E. A. 1987. Stratigraphy and structure In Current research, part B. Geological Survey of Canada, Paper of the Buchans Group. In Buchans geology, Newfoundland. Edited 88-lB, pp. 91 -98. by R. V. Kirkham. Geological Survey of Canada, Paper 86-24, Williams, H., Piasecki, M. A. J. , and Coleman-Sadd, S. P. 1989. pp. 35-46. Tectonic relationships along the proposed central Newfoundland
Williams, H. 1970. Red Indian Lake (east half) Newfoundland. Geo- LITHOPROBE transect and regional correlations. In Current logical Survey of Canada, Map 1106a, scale 1 : 250 000. research, part B. Geological Survey of Canada, Paper 89-lB,
Williams, H. 1979. Appalachian orogen in Canada. Canadian Journal pp. 55-66. of Earth Sciences, 16: 792-807.
Williams, H., Coleman-Sadd, S. P., and Swinden, H. S. 1988. Tectonic-stratigraphic subdivisions of central Newfoundland.
Can
. J. E
arth
Sci
. Dow
nloa
ded
from
ww
w.n
rcre
sear
chpr
ess.
com
by
SAV
AN
NA
HR
IVN
AT
LA
BB
F on
11/
14/1
4Fo
r pe
rson
al u
se o
nly.