Quaternary Investigations in the Patterson Island Area ... · rocks including pyroxenite, gabbro, leucogabbro, anorthosite, and diorite. It also includes the alkaline syenite to monzonite

Saskatchewan Geological Survey 1 Summary of Investigations 2003, Volume 2

Quaternary Investigations in the Patterson Island Area (part of NTS 64E-10 and -15), Reindeer Lake, Eastern Peter Lake Domain

J.E. Campbell

Campbell, J.E. (2003): Quaternary investigations in the Patterson Island area (part of NTS 64E-10 and -15), Reindeer Lake, Eastern Peter Lake Domain; in Summary of Investigations 2003, Volume 2, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2003-4.2, CD-ROM, Paper A-7, 16p.

Abstract Quaternary geological investigations were initiated in the Patterson Island area, Reindeer Lake (part of 64E-10 and -15), as part of the multidisciplinary, multi-year Peter Lake Domain Project. The Quaternary component of the project involves surficial mapping at 1:50 000 scale, recording ice-flow indicators, and regional till sampling surveys.

Multiple ice-flow directions were documented. The dominant ice-flow direction was to the south-southwest (205° to 210°); becoming more southwesterly (215° to 220°) towards the southern boundary of the map area. Two older regional ice flows were recorded: a more southerly (~190°) direction and a west-southwesterly (228° to 240°) one. Rare, faint striae sets trending 154°/332º (two sets) and 295°/115º (one set) were also recorded.

Drift cover in the Patterson Lake area is variable. In the northern two thirds, the terrain is dominated by bedrock (approximately 40 to 50 percent) mantled with a thin (less than 2 m), discontinuous drift cover. Thus, the present day landscape is controlled by the bedrock topography with little geomorphic expression of the glacial deposits. Southward, the drift thickens and is more extensive, with bedrock exposure less than 10 percent. Here, the landscape is more subdued and reflects both glacial geomorphic features and bedrock topography.

The dominant surficial sediments in the Patterson Island area are till and organic deposits. Sand and gravel deposits are associated with esker systems, minor meltwater drainage channels, stagnant ice hummocky moraines, and glaciolacustrine littoral deposits. Minor glaciolacustrine silts and sands are not sufficiently extensive to differentiate at this map scale. Till occurs primarily as ground moraine veneer (less than 2 m thick) and plain (greater than 2 m thick), hummocky moraine and stagnant ice moraine. Ridged moraine and streamlined forms such as drumlins and crag and tails are less common. Till composition varies with the type of deposit, thickness and source rocks from which it is derived. At least three facies were identified: a silty-sand to sandy till, sandy till and a gravely sand diamicton.

Sporadic lacustrine deposits and raised strandlines, such as sand and cobble beaches, terraces and wave-cut notches indicate that Glacial Reindeer Lake and glacial Lake Agassiz extended further north and west than originally thought. Much of the area below ~350 m asl is characterised by exposed outcrop, boulder lags and winnowed till.

A large part of the northern half of the area is not very suitable for drift prospecting, as bedrock, ice marginal and wave-reworked deposits dominate the terrain. Drift prospecting techniques are more applicable in the south where the drift cover is more extensive. Interpretation of pending till compositional data will help determine the effectiveness of till sampling in this region.

Keywords: surficial geology, Quaternary geology, glacial geology, till geochemistry, drift prospecting, Reindeer Lake, Peter Lake Domain, northern Saskatchewan.

1. Introduction Although the economic potential of the Peter Lake Domain in northeastern Saskatchewan (Figure 1) has long been recognized, mineral exploration in this region has been limited, partly due to poor bedrock exposure and the lack of a clear understanding of the regional geological history and setting. In 2002, the Saskatchewan Geological Survey (SGS) launched a multidisciplinary, three-year mapping project to upgrade the geological framework for the Peter Lake Domain and its boundary zones and to evaluate the economic potential of the region (Maxeiner and Hunter, 2002). The main focus is on the mafic intrusive complexes in the southern part of the domain which are perceived to have substantial potential for platinum group elements (PGE) (Hulbert, 1989).


Figure 1 - Location of the Patterson Island map area (part of NTS 64E-10 and -15), Reindeer Lake, eastern Peter Lake Domain, Saskatchewan (after Maxeiner and Hunter, 2002).


In conjunction with the bedrock mapping (Maxeiner and Leatherdale, this volume), Quaternary geological investigations were initiated this past summer in the Patterson Island area, Reindeer Lake (part of NTS 64E-10 and -15; Figures 1 and 2). The primary focus was on the region underlain by the dioritic to gabbroic rocks (unit Ptm, Figure 1) of the Archean Swan River Complex (Corrigan, 2001). The Quaternary component of this project involved mapping at 1:50 000 scale, recording ice-flow indicators, and regional till sampling surveys. The specific objectives of this project are to:

1) provide a Quaternary geological framework for drift prospecting, 2) determine the signatures of precious and base metals in the till, 3) determine whether till composition reflects the local bedrock and propose a glacial dispersal model for the

region, 4) provide till geochemical and surficial materials databases to serve as a baseline for mineral exploration and

environmental assessment, and 5) provide ground-truthing for the proposed NATGAM airborne gamma ray survey of the Peter Lake Domain. This paper summarizes the work done to date and presents the highlights from this summer’s field investigations.

Figure 2 - Detailed location map of the study area showing geographic names, mineral occurrences and the location of 2003 field and till samples sites. Unofficial lake names are in quotations.


a) Previous Work The surficial deposits of the entire Peter Lake Domain were mapped at 1:250 000 scale in the late 1970s as part of a Quaternary reconnaissance mapping program of the Precambrian Shield of Saskatchewan by the Saskatchewan Research Council (Schreiner, 1984a, 1984b, and 1984c). Limited overburden drilling was conducted along Highway 905 as part that program to gain stratigraphic information.

Campbell (1992) conducted a regional orientation study aimed at determining the applicability of drift prospecting for mineral exploration in the Peter Lake Domain. Selected SRC archived till samples collected during the reconnaissance mapping program were analyzed for major and trace elements plus gold. Ten additional bulk till samples were collected, primarily along Highway 905, for more detailed studies of till composition. On a regional scale, the composition of the till reflects the local bedrock geology, either underlying or immediately up ice of the sample site (Campbell, 1992; Campbell et al., 1999). The geochemistry of the silt-clay fraction (<0.063 mm) revealed elemental associations characteristic of the metasedimentary, granitic, and mafic source rocks.

Swanson (1996) collected samples from eskers in the Peter Lake Domain as part of a reconnaissance kimberlite indicator minerals (KIM) sampling program in northern Saskatchewan. The data from these samples are included in the Kimberlite Indicator Minerals Digital Database housed on the Saskatchewan Industry and Resources website (www.ir.gov.sk.ca).

b) Current Work Current surficial geology mapping is based on interpretation of 1:25 000 scale aerial photographs and Landsat 7 imagery with follow-up ground checking. Ground-truthing focussed on characterization of the various surficial deposits, measurement of ice-flow indicators, collection of till samples and examination of the surficial sediments and geomorphologic features. Unfortunately, no exposures were found to provide stratigraphic information. Field verification was restricted to areas accessible by boat and foot traverse. Limited fixed-wing air support allowed some access to the western part of the map area.

Till samples were collected at 110 of the 204 field sites (Figure 2). They were spaced at 1 to 2 km where accessibility was good. Bulk till samples (~10 kg) were taken, where possible, from the C-horizon in pits hand-dug to an average depth of 1 m. These samples will be submitted for both kimberlite and base metals indicator minerals, as well as gold (Au) and platinum grain counts. A 1 kg sample was also collected from each pit for major and trace elements plus Au and textural analyses. Samples overlying or down ice from mafic/ultramafic intrusive rocks were also submitted for platinum (Pt) and Palladium (Pd) analyses. The pebbles from the 6 to 20 mm fraction will be used for lithology counts. The lithological, mineralogical, geochemical, and textural data will be used to define the composition of the till deposits which, in turn, will aid in defining the provenances(s) of the till(s) and the development of a glacial dispersal model for the area. Two 25 kg samples were collected from eskers for kimberlite indicator mineral analyses.

Earlier studies have shown surficial materials to be effective in identifying areas of concealed PGE mineralization (Coker et al., 1991). To test for the occurrence of Pt, Pd, and Au in the till, and assess the applicability of drift prospecting for PGEs in the Swan River Complex, seven bulk till samples were collected from the vicinity of the Antoine showing.

The orientations and relative ages of nearly 300 erosional ice-flow indicators were measured at 253 sites. Indicators measured included striations, microstriations, grooves, crescentric gouges and fractures, chattermarks, roche moutonées, whale backs, and other streamline bedforms. Measurements were collected primarily from outcrops along lake shorelines and from flat-lying surfaces to avoid the effects of local topography. Sense of ice flow was derived from the roche moutonées, crescentric gouges, and stoss and lee topography. When possible, the relative ages for multiple sets of diverging ice-flow indicators were determined. The criteria used were: a) a set located in a lee-position relative to another is older, b) a set found only on the top of an outcrop is considered the youngest movement, c) a set preserved only in the depressions is interpreted as older, and d) deeper grooves and/or striae cross-cut by a finer set are usually older.

2. Regional Setting The Patterson Island area straddles the boundary between the largely Archean Peter Lake Domain of the Hearne Province and the Paleoproterozoic Wathaman Batholith of the Reindeer Zone. The northwestern part of the map area is underlain by the syenogranites, megacrystic monzogranites and dioritic orthogneisses of the Peter Lake Complex (Ray and Wanless, 1980). These rocks are massive to mylonitic and have been metamorphosed under upper amphibolite facies conditions. The central part is primarily underlain by mafic and alkaline intrusives of the Swan River Complex (Stauffer et al., 1981; Corrigan, 2001) and a subordinate package of older mafic rocks


(Corrigan, 2001). The Swan River Complex is composed of massive to layered mafic, ultramafic and intermediate rocks including pyroxenite, gabbro, leucogabbro, anorthosite, and diorite. It also includes the alkaline syenite to monzonite intrusives such as the Patterson Island Pluton (MacDougall, 1988). These rocks have been metamorphosed to upper amphibolite facies. The eastern part of the area is underlain by megacrystic granitoid rocks of the Wathaman Batholith (Stauffer et al., 1981; Corrigan, 2001). Maxeiner and Leatherdale (this volume) provide a more comprehensive summary of the regional bedrock geology for the Peter Lake Domain and its boundary zones.

The Patterson Island area lies within the Churchill River Upland eco-region and the Hudson Bay drainage basin. The landscape is characterised by bedrock outcrop, glacial deposits, wetlands, and lakes. Local relief can be as great as 50 m but rarely exceeds 25 m. The natural vegetation is largely black spruce and jack pine interspersed with white birch. The wetlands are commonly underlain by permafrost and support black spruce and tamarack. The lakes are predominantly southwest-trending, parallel to the regional bedrock structure and direction of glacial ice movement.

During the late Wisconsinan glaciation, the Keewatin Lobe of the Laurentide Ice Sheet advanced south-southwestward over the region from a dispersal centre in Nunavut (Prest et al., 1968; Prest, 1984). As the ice retreated from the Reindeer Lake area approximately 8500 to 8200 yrs BP (Schreiner, 1984a) portions of the region were inundated by proglacial Reindeer Lake and later, glacial Lake Agassiz. Reindeer Lake is a modern remnant of Lake Agassiz which apparently abandoned the area by 8000 yrs BP (Schreiner, 1984a). Models for deglaciation and the northern extent of the proglacial lakes in Saskatchewan are presented by Schreiner (1983), Teller et al. (1983), Dyke and Prest (1987), Dyke and Dredge (1989), Dyke et al. (2002), and Dyke et al. (2003).

3. Ice-Flow Record Multiple ice-flow directions were documented in the area. The striae record and streamlined landforms indicate regional ice flow during the Late Wisconsin was to the south-southwest (Figure 3) sub-parallel to the regional bedrock structural grain, which suggests bedrock topographic influence on ice flow. Ice flow shifted slightly from 205° to 210° in the north and central part of the map area to 215° to 220° in the south. Two older regional ice flows directions have been recognized. Preserved striations and roche moutonées indicate a more southwesterly flow of 230° to 240° which predates the regional 210° ice flow. A more southerly direction (~190°) has been documented in the northern half of the study area (Figure 4) but was not observed south of Wiley Bay (Figure 3). This earlier southerly direction was also reported in the northeast quadrant of the Phelps Lake map area (Campbell, 2002a, 2002b). The relative ages of these two older regional directions have not been determined.

These flow directions most likely represent shifts in ice-flow direction in response to changing glacial conditions related to the advance and retreat of the Keewatin ice lobe during the Late Wisconsin glaciation. The main ice direction to the south-southwest reflects ice flow during deglaciation. Local variations in the striae record reflect topographic deflection of ice flow.

Rare, faint striae sets trending 154°/334° (two sets) and 295°/115° (one set) were also recorded. Schreiner (1984a, 1984b) and Campbell (1992) also reported a similar 151° striae direction in the western part of the Peter Lake Domain. Johnston (1978) also reported a north to northwest ice-flow direction recorded by several sets of striae in the southern part of Reindeer Lake. He felt that these striae were older than the south-southwest main flow but formed during the last glaciation, likely during the initial ice advance.

4. Surficial Geology Drift cover in the Patterson Lake area is variable. In the northern two thirds of the map area, the terrain is dominated by bedrock outcrops (approximately 40 to 50%) mantled with a thin (less than 2 m thick), discontinuous drift cover (Figure 5A). Thus, the present day landscape is controlled by the bedrock topography with little geomorphic expression of the glacial deposits. Southward, the drift thickens and is more extensive with less than 10% bedrock exposure. The landscape here is more subdued and reflects both geomorphic features related to glacial processes and bedrock topography (Figure 5B).

The depth to bedrock in areas of thick drift is unknown due to the lack of exposed sections and limited drill hole information; however, Schreiner (1984a) and Scott (1970) reported thicknesses of greater than 20 m in the western Peter Lake Domain. Therefore, it is likely that glacial deposits associated with streamlined till plains, ice marginal deposits, and esker complexes could exceed 20 m in thickness.

The dominant surficial sediments in the Patterson Island area are till and organic deposits. Sand and gravel deposits are associated with several esker systems, minor meltwater drainage channels, stagnant ice hummocky moraine, and


Figure 3 - Regional ice-flow directions compiled from detailed mapping of erosional ice-flow indicators and landform analysis.

glaciolacustrine littoral deposits. Glacial lake silts and sands form minor surficial deposits generally too small to differentiate at this map scale.

a) Till Deposits and Associated Landforms Till occurs primarily as ground moraine veneer (less than 2 m) and plain (greater than 2 m), hummocky moraine, and stagnant ice moraine. Ridged moraine and streamlined forms such as drumlins and crag and tails are less common. The composition of the till varies with the type of deposit, thickness, and source rocks.

Only one till unit composed of several till deposits or facies has been identified in the Patterson Island area. The surface tills were deposited by the last major Late Wisconsinan glacial advance. Where glacial deposits are thick, multiple till units may be present. Based on stratigraphic drilling, Schreiner (1984a, 1984b) indicated that at least two till units were present in the western Peter Lake Domain with a lower till preserved in deep topographic lows. This is likely the case in the Patterson Island area. At least three till facies were identified: 1) a silty-sand to sandy till, 2) sandy till, and 3) a gravely sand diamicton. Till veneers consist primarily of locally derived material whereas the thicker till deposits, such as till plains, crag and tails and stagnant ice deposits, have a higher component of exotic or allogenic detritus.


Figure 4 - Preserved 184° to 194° striae on protected outcrop surfaces provide evidence of a southerly ice flow predating the main south-southwesterly ice flow. The relative age of the 154° striae set cannot be determined. A) Three sets of striae at Porter Bay (UTM 637063mE, 6394870mN, NAD83). B) Early 191° striae and main 213° striae, west of Wiley Bay (UTM 637907mE, 6386806mN, NAD83).

Figure 5 - The northern part of the area is characterised by outcrop ridges with thin, sparse glacial drift cover and interspersed peatlands. A) Aerial view of the terrain north of the Antoine Showing. B) Ground view of this region. C) In contrast, the landscape in the south is more subtle due to the thicker and more extensive drift cover (UTM 631300mE, 6390100mN, NAD83); D) Ground view of thick ground moraine typical of the south (UTM 631340mE, 6382500mN, NAD83).


Silty-sand to Sandy Till

The most common till is moderately compact, commonly texturally mottled, greyish brown to grey with a non-calcareous silty-sand to sandy matrix, and contains 10 to 25% clasts (Figure 6A). Boulders are typically concentrated in the upper 30 to 40 cm, but pebbles and cobbles dominate the clast fraction below. Textural mottling is a descriptive term for discontinuous, irregularly-shaped (deformed?), thin sand lenses (<1 cm thick, 5 to 20 cm long), which appear either interbedded or contained within a compact silty-sand matrix. Clasts are typically clay capped, with thin linings of sand underneath. These sedimentary features are common in northern Saskatchewan tills, and suggest that much of this till was deposited, at least in part, by subglacial meltout processes (Campbell, 2001a, 2002a; Shaw, 1979).

The texture of the till is dependant on the dominant rock type from which it was derived. Tills with a grey silty-sand matrix and higher clay content tend to be enriched in mafic intrusive, metavolcanic and/or metasedimentary detritus. Tills derived from felsic intrusive rocks and orthogneisses are more brown and sandier.

A matrix-rich (5% clasts), soft, very silty fine sand to sandy-silt diamicton was encountered at several sites below a gravely diamicton in the Wiley Bay area.

The silty-sand to sandy till is primarily associated with flat to low-relief till plains and veneers (Figure 6B) and, to a lesser extent, drumlinoid landforms. The surface till of the crag and tail landforms is variable, and exhibits a greater degree of meltwater sorting. This till is associated with the main south-southwest ice-flow direction.

Sandy Till

A brown to greyish brown bouldery, sandy till with a sandy to very sandy matrix was noted between Dobson and Pearce lakes and south of “Cloud” Lake (Figure 2). Less extensive deposits of this unit were observed elsewhere. The composition of this till is highly variable both vertical and laterally. Commonly, these deposits consist of a moderately loose, massive to crudely stratified, slightly silty, pebbly and bouldery diamicton with a very sandy matrix containing 40 to 60% clasts (Figures 6C and 6D). Clasts generally have a thin clay cap. The ratio of locally and distally derived rock types in the clast fraction is highly variable among sites.

The sandy till is associated with ice marginal deposits such as crevasse fills, moraine ridges (Figure 6E) and hummocky, stagnant ice moraine. The terrain is typically hummocky, ranging from gently undulating to high-relief (>10 m) knob and kettle topography (Figure 6D). The surface of the moraine is commonly strewn with boulders of variable size and lithology. This sandy till is differentiated from the previously described sandy till by its lower silt-clay content, lack of textural mottling, looser compaction and its landform association.

Where the sandy till occurs as a veneer (< 1m) overlying the silty-sand till, there is little morphological evidence of the stagnant ice sediments. The ground surface characteristics are those of the underlying ground moraine.

Sand and Gravel Diamicton

A sand and gravel diamicton is the dominant surface material in the east, particularly on Patterson Island, in the vicinity of the Ant and Antoine showings and along the shore of Reindeer Lake. The diamicton occurs as a discontinuous, but extensive veneer, overlying either bedrock or the silty-sand till. It consists of a loose, poorly to moderately sorted gravely, medium to coarse sand which locally contains small amounts of silt and clay. These sediments are highly oxidized and commonly iron cemented (Figure 6F). The diamicton is massive to crudely stratified, with clast content ranging from 40% in a matrix-supported framework to 80% in the clast-supported framework. The clasts range from pebbles to boulders. Clast-supported diamictons consist of sub-angular to sub-rounded pebbles to cobbles with a clean granule matrix. The coarse texture, degree of sorting and irregular bedding of these deposits indicates meltwater sorting. Where diamicton overlies the silty-sand till the contact is typically sharp, but not erosional; locally the contact is gradational.

The sand and gravel diamicton has no geomorphic expression and its similarity to bouldery till made it difficult to distinguish on the aerial photographs and on the ground. Furthermore in a sample hole it is difficult to distinguish between this type of deposit and ice contact sands and gravels or washed tills. The diamicton is interpreted as an ice marginal ablation till deposited by the retreating ice during the final phase of deglaciation.

Eroded and Washed (Reworked) Tills

Boulder lags commonly form armored surfaces (Figure 7A), particularly below 350 m above sea level (asl). A coarse-grained, poorly sorted diamicton is commonly associated with the boulder (Figure 7B) lags. These deposits


Figure 6 - Till Deposits. A) Silty-sand till to sandy with textural mottling. B) Ground view of silty-sand ground moraine, boulders are obscured by the moss (UTM 638363mE, 6387375mN, NAD83). C) Sandy ablation till. D) Ground view of hummocky terrain of the sandy till (UTM 633196mE, 6397971mN, NAD83). E) Moraine ridges (arrow) south of Dobson Lake. F) Iron-cemented sand and gravel diamicton (UTM 643362mE, 6395952mN, NAD83).


Figure 7 - A) Boulder armored surfaces produced by reworking of till by wave action are common below 350 m asl (UTM 639482mE, 6393697mN, NAD83). B) Close-up of boulder lag and reworked till overlying silty-sand till.

are generally less than 50 cm thick and grade into the underlying till. They are interpreted to have been produced by winnowing of the fines from the till by wave action when the region was occupied by a proglacial lake.

The landscape between Pearce Lake and Porter Bay (Figure 2), is characterized by flat-topped streamlined landforms with extensive boulder pavements and terraced scarps formed from eroded till uplands dissected by channels (Figures 8A and 8B). These features are similar to those in the northern Phelps Lake mapsheet (Campbell, 2001a, 2001b, 2002a, 2002b; NTS 64M), which were interpreted as products of subglacial meltwater erosion. Glaciolacustrine silts found in the channel bottoms indicate the low-lying areas were subsequently inundated by glacial lake waters.

Localized boulder pavements, boulder fields, and small deposits of modified till also occur within valleys which drained meltwater away from the ice. These channels were active both beneath (subglacial) and/or in front of the ice (proglacial).

b) Glaciofluvial Sediments (Stratified Drift) and Associated Landforms Stratified sand and gravel, and minor silts constitute approximately 20% of the surficial sediments. These sediments are primarily ice-contact deposits associated with esker complexes, stagnant ice moraine and ice margin features, and small outwash plains and terraces associated with meltwater channels (Figure 9).

Figure 8 - A) Flat-topped, boulder armored, streamlined landforms with steep, eroded sides are thought to be remnants of a till plain carved by subglacial meltwater (UTM 6355591mE, 6398646mN, NAD83). B) Ground view of boulder armored eroded slope and top.


Figure 9 - Ice contact glaciofluvial deposits in the Patterson Lake area. A) Low-relief ridges and plain (UTM 635600mE, 6377550mN, NAD83) composed of B) moderately sorted stratified sand and gravel. C) Large kettled (K) esker system north of Dobson Lake. The esker ridge is indicated by the arrow. D) Stratified sand and gravel deposit (UTM 636989mE, 6390667mN, NAD83).

Isolated ice contact ridges and hummocks too small to map are scattered throughout the area (Figures 9A and 9B). These deposits are characterised by poorly to moderately sorted, stratified clean gravel and sand (Figure 9B). The coarse fraction is predominantly sub-angular to rounded pebbles and cobbles. The landforms have a smooth, moulded appearance (Figure 9B). These deposits are commonly associated with stagnant ice moraine and meltout tills indicative of ice marginal depositional environments. A large ice-contact deposit composed of stratified sand and gravel occurs north of “Horseshoe” Lake.

The majority of the eskers are isolated, small ridges that overlie other deposits and follow the underlying topography. These eskers were deposited in englacial tunnels and let down by the melting ice. Eskers occur either on the floor or along the top of the side-wall of valleys formed at the base of the ice and indicate that these valleys were part of a subglacial meltwater drainage system during deglaciation. Associated deposits and features include exposed bedrock, boulder-armored eroded surfaces, terraces, eskers, and small outwash plains. The majority of these meltwater channels follow existing bedrock-controlled valleys. Once ice-free, many of the valleys appear to have continued to drain water away from the ice or were flooded by Glacial Reindeer Lake.


A kettled esker complex (Figure 9C) and large sand plain in the extreme northeast (north of Dobson Lake and northwest of Pearce Lake) are part of a large southwest-trending dendritic esker system that crosses the Peter Lake Domain. Southwest of “Cloud” Lake, a tributary to this trunk esker follows a fault-controlled valley which formed a subglacial channel draining meltwater southward from the Pearce Lake area. The eskers west and southwest of Bedford Island (P03- 0191) are part of a smaller regional esker system.

Minor, thin discontinuous veneers of well-sorted sands capping till and bedrock are scattered throughout the map area (Figure 9C). The sands are associated with nearby eskers, within and adjacent to meltwater channels or occur as discreet isolated patches on the till plains.

c) Glaciolacustrine Sediments and Associated Features Schreiner (1984a) reported that a proglacial lake with its maximum water level approximately 12 m above the present day lake (336 m asl) partly occupied the Reindeer Lake basin south of 57° latitude. The basin was later occupied by glacial Lake Agassiz during its lower phases approximately 8400 to 8200 yrs BP ( Schreiner, 1983, 1984a; Teller et al., 1983; and Leverington and Teller, 2003). Sporadic lacustrine deposits and raised strandlines, such as sand and cobble beaches, terraces, and wave-cut notches (Figure 10), indicate that Glacial Reindeer Lake and/or glacial Lake Agassiz extended further north and west than previously recognized.

The majority of the beaches are at approximately 350 ±5 m asl although wave-cut notches, boulder lags, and washed till were noted at several sites at elevations as high as ~362 ±5 m asl (Figure 10D). The 350 m elevation is consistent with Schreiner’s (1984a) estimation that high water level stood at approximately 348 m asl. The 350 m asl beaches are well developed (Figures 10A and 10B), indicating that the lake level stood at this elevation for some time. The strandlines above 355 m asl are poorly developed and less common, suggesting the lake level was at this

Figure 10 - Raised strandlines of Glacial Reindeer Lake and glacial Lake Agassiz. A) Terraced sand beach at ~350 m asl (UTM 637955mE, 6389138mN, NAD83). B) Aerial view of well-developed beaches at ~350 m asl west of the McLean Channel, Reindeer Lake (UTM 632750mE, 6375800mN, NAD83). C) Linear cobble lags and wave-cut notch at ~350 m asl (UTM 635707mE, 6377781mN, NAD83). D) Evidence of higher water levels, such as this poorly developed beach at ~362 ±5 m asl west of Patterson Island (UTM 636988mE 6391970mN, NAD83).


higher elevation for a only brief time, and likely before the 350 m asl lake stand. The higher strandlines are interpreted to be those of Glacial Reindeer Lake, while the lower ones represent the shoreline of glacial Lake Agassiz, that occupied the basin for a longer time. Figure 11 shows the extents of Glacial Reindeer Lake and glacial Lake Agassiz.

Much of the area below ~350 m asl is characterised by outcrop, boulder lags and winnowed till (Figure 11). Lacustrine silts and sands are restricted to low-lying areas such as around Pearce Lake and Thyme Hill River north of Porter Bay. Well-sorted sands that occur sporadically within valleys could be either fluvial or littoral deposits.

Note that the elevations presented here are estimations derived from GPS locations plotted on 1:50 000 scale topographic maps. Many of the strandlines are not visible on the 1:63,360 or 1:25 000 scale aerial photographs. Caution is advised when comparing these elevations with other quantitative paleo-lake elevation data.

Figure 11 - Map outlining the terrain inundated by Glacial Reindeer Lake (≤360 m asl) and/or glacial Lake Agassiz (≤350 m asl).


Figure12 - Effects of wave action. A) Boulder armored till below wave-cut notch. B) Unmodified till above the wave-cut notch (635751E 6398241N, NAD83, NAD83).

d) Organic Terrain Many of the streams and small lakes are bordered by wetlands. Peatlands commonly occupy low-lying areas between bedrock ridges and uplands. In the north, peatlands are relatively small and shallow. In areas of thicker drift, the peatlands are more extensive and are commonly thick enough to obscure the underlying topography. Discontinuous permafrost is present and is most commonly found within the peat deposits. Palsa, peat plateaus, and thermokarst features related to the presence of permafrost were observed in bogs and fens.

5. Implications for Drift Prospecting Although the till geochemical, textural, lithological, and mineral indicator data are unavailable at this time, some preliminary comments can be made concerning the application of drift prospecting in the Patterson Island area.

1) A large part of the northern half of the area is unsuitable for drift prospecting as bedrock, ice marginal sediments, and wave-reworked deposits dominate the terrain. Drift prospecting is more suited in the south where the drift cover is more extensive.

2) Although the area has been influenced primarily by ice flowing to the south-southwest, the ice-flow history (multiple directions and relative ages) must be taken into account when applying a dispersal model to geochemical or indicator mineral anomalies.

3) Soil profiles are well developed, with thick Ae and B horizons indicating heavy leaching and oxidation of the sediments. Till is oxidized to depths greater than 1 m at some areas. Iron-cemented B horizons, characteristic of Podzolic soils, were observed in the sandier, gravellier deposits. Due diligence is needed when sampling in order to obtain results representative of the metal concentrations in the till and minimize secondary accumulations associated with soil-forming processes.

4) Boulder lags and winnowed till are common below 350 m asl elevation. The boulders may hamper till sampling. The upper 40 cm of the till has commonly been affected by wave action, resulting in removal of the fines and natural concentration of heavy minerals. This concentration effect must be taken into account when interpreting grain count data. Till samples should be collected from the underlying, unmodified till.

5) Field observations suggest the silty-sand to sandy till is generally locally derived, however, thickness of the deposits is an important factor in controlling renewal distances (distance from source) of rock detritus and the degree of dilution by exotic debris.

6) Surficial conditions in the area surrounding the Ant and Antoine showings are not favourable for drift prospecting. The dominant surface materials are bedrock, ice contact sediments, and ablation tills interspersed with organic terrain. The drift is thin and typically highly oxidized. The high water table creates sampling problems.

6. Future Work Sample analyses and interpretation of the textural, geochemical, and lithological till data is in progress. The focus will be on characterizing the various till deposits, identifying their provenance(s), and developing a glacial dispersal


model for the region. Bulk tills will be processed for Au and Pt grain counts, and kimberlite and base metal indicator minerals. All analytical data is slated for release in 2004. Air-photo interpretation of the surficial geology for 2004 mapping program will also be carried out.

7. Acknowledgments The author wishes to thank Murray Lungal, Amanda Perrot, Lance Kostiw, and Rachel Sulz for their invaluable assistance in the field. Ice-flow indicator data collected by Ralf Maxeiner and Shawna Leatherdale improved the understanding of the ice flow history in the area. The manuscript benefited from critical review by Colin Card, Charlie Harper, and Gary Yeo.

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Quaternary Investigations in the Patterson Island Area ... · rocks including pyroxenite, gabbro, leucogabbro, anorthosite, and diorite. It also includes the alkaline syenite to monzonite

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