La Ronge ‘Horseshoe’ Project: Geological Context of the Bassett
Lake Mafic Intrusion and the Surrounding Volcanoplutonic
Complex (Parts of NTS 73P/10 and /11), La Ronge Domain
Ralf O. Maxeiner1
Maxeiner, R.O. (2014): La Ronge ‘Horseshoe’ project: geological context of the Bassett Lake mafic intrusion and the
surrounding volcanoplutonic complex (parts of NTS 73P/10 and /11), La Ronge Domain; in Summary of Investigations 2014,
Volume 2, Saskatchewan Geological Survey, Sask. Ministry of the Economy, Misc. Rep. 2014-4.2, Paper A-11, 12p.
This report is accompanied by the map separate entitled:
Maxeiner, R.O. (2014): Bedrock geology of the Bassett Lake area (parts of NTS 73P10 and 11); 1:20 000-scale prelim. map with
Summary of Investigations 2014, Volume 2, Saskatchewan Geological Survey, Sask. Ministry of the Economy, Misc. Rep.
2014-4.2-(1.4).
Abstract
2
The bedrock geology of a 40 km area centred on Bassett Lake—located at the southern end of the La Ronge
Domain, within the Trans-Hudson Orogen of Saskatchewan—was mapped at 1:20 000 scale as part of the La
Ronge ‘Horseshoe’ project. This multi-year project is aimed at improving knowledge of the existing geological
framework of the southwestern Reindeer Zone in north-central Saskatchewan.
The Bassett Lake intrusion consists of a series of inwardly younging bodies of magnetiferous leucogabbro, gabbro,
gabbronorite, and anorthosite. Rhythmic cumulate layering is locally very well preserved and is on the scale of
centimetres to metres in thickness. Other interesting textural features within the mafic intrusion include irregular
pegmatitic zones, crossbedded rhythmic layering, and metre-scale mafic volcanic xenoliths contained within a
distinctly layered unit toward the central portion of the pluton. The Bassett Lake intrusion has cut a succession of
felsic to mafic volcanic rocks, which represent the main volcanic sequence of the La Ronge Domain (historically
referred to as ‘Central Metavolcanic Belt’). The mafic intrusion itself is cut by leucotonalite in its western side and
by diorite and tonalite to quartz diorite in its eastern margin.
Two mineral showings are known in the area. The Triangle Lake copper-nickel showing is in the central part of the
intrusion and consists of disseminated magnetite, pyrrhotite and chalcopyrite contained within a well-layered
sequence of gabbro, anorthosite, gabbronorite, and minor troctolite. Ten grab samples of mafic to ultramafic rocks
were collected and evaluated for platinum group elements: results were at or near the detection limits of 1 ppb. The
Vidgy Lake gold showing is in the northern margin of a diorite-tonalite-quartz diorite intrusion, where it cuts felsic
to intermediate volcanic rocks and the Bassett Lake intrusion.
Keywords: La Ronge Domain, Paleoproterozoic, Reindeer Zone, Bassett Lake intrusion, bedrock mapping, mafic
intrusion, cumulate layering, platinum group elements, gold.
1. Introduction and Previous Work
Ten days in the middle of August 2014 were spent at Bassett Lake, as part of the final year of mapping on the La
Ronge ‘Horseshoe’ project (see Maxeiner et al., 2013 and references therein for more details on the ‘Horseshoe’
project). The focus of this work was the mafic intrusive rocks in the vicinity of Bassett Lake, termed here the
Bassett Lake intrusion (Padgham, 1960; Harper, 1983; Hulbert, 1986; Graham et al., 1986, 1987; Thomas, 1993).
The mafic nature of these rocks makes them prospective for copper-nickel and platinum group element (PGE)
mineralization. The Bassett Lake area is host to the Triangle Lake magnetite-pyrrhotite-chalcopyrite showing and
the Vidgy Lake gold showing. Most of the mineralization at the Triangle Lake showing, located in the central part
of the Bassett Lake intrusion, is described as consisting of titaniferous magnetite. A limited number of samples have
been analyzed for PGEs (Graham et al., 1987). Descriptions in previous reports and assessment files of anorthosite,
norite, and extensive gabbro, with local pegmatitic and brecciated textures, suggests a more complex intrusive
structure than is depicted on current maps.
The aim of the 2014 field investigation was to 1) map the Bassett Lake intrusion in detail, facilitated by a 2006
forest fire that created good exposure over large parts of the pluton; 2) re-evaluate the contact relationships between
1
Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, 200 - 2101 Scarth Street, Regina, SK S4P 2H9.
Saskatchewan Geological Survey
1
Summary of Investigations 2014, Volume 2
the intrusion and felsic to mafic volcanic rocks of the La Ronge Domain located to the north and south; 3)
investigate the contact relationships of the Bassett Lake intrusion with dioritic and tonalitic intrusions to the west
and east of the pluton; 4) collect samples for whole-rock geochemical analysis of the volcanic and plutonic rocks in
the area; 5) collect samples to test for anomalous PGE concentration in the Bassett Lake intrusion; and finally, 6)
visit the area of the Vidgy Lake gold showing.
2. Exploration and Bedrock Mapping History
The Triangle Lake copper-nickel showing occurs in the centre of the Bassett Lake intrusion, approximately 60 km
north-northeast of the town of La Ronge, at the southern end of the La Ronge Domain within the southwestern
Reindeer Zone (Figure 1). It can best be reached by float-equipped aircraft from Missinipe, which is located 13 km
to the east. The Triangle Lake showing is found on the northwest side of a lake bearing the same name (Figure 2), 1
km to the southeast of Bassett Lake. While traversing in this area we were wondering if the lake had been awarded
its name because of its obvious shape, or if it possibly had a double meaning, alluding to the Bermuda Triangle, as
the use of a compass in this area was impossible due to the magnetite-rich rocks.
For a detailed description of the exploration history of the area, with assay results and drill core intercepts, the
reader is referred to the descriptions in SMDI2 #0819 and #2294. However, some pertinent aspects of the
exploration history and findings in the Bassett Lake area are presented in the following paragraphs.
Although the area was staked in 1954, drilling on the Bassett Lake intrusion did not occur until 10 years later, when
the claims were held by A. Studer. Only minor amounts of disseminated sulphides and magnetite were encountered.
Airborne and ground electromagnetic and magnetic surveys were carried out in the late 1960s to early 1970s and
were accompanied by prospecting, geological mapping, and some further diamond drilling in 1970 (7 holes totalling
651 m). Magnetite was discovered in the drill core, along with disseminated to massive pyrite + pyrrhotite and
minor chalcopyrite. In 1976, two additional diamond-drill holes (totalling 168 m) were completed, and as part of
that work low-grade titaniferous magnetite mineralization was confirmed through assays (Harper, 1983).
The area was first systematically mapped by Padgham (1960) at 1 inch to the mile (1: 63,360 scale), who described
the intrusion as a complex consisting of hornblende gabbro and hornblende diorite. As part of a study on the context
of iron ores in Saskatchewan, Harper (1983) recognized a layered complex consisting of gabbro, olivine gabbro,
magnetite-rich gabbro, peridotite, and pyroxenite, as well as minor norite and anorthosite layers. Cumulate layering,
consisting of layers 1 to 4 cm thick of pyroxene + plagioclase with minor olivine were described, along with
abundant intercumulus magnetite.
Graham et al. (1986, 1987), in a paper documenting his thesis work, described the intrusion as consisting mainly of
gabbro and norite along with minor anorthosite. It was further described as having intruded volcanic rocks and
being itself intruded by diorite and granodiorite on its eastern and western margins, respectively. Deuteric alteration
is reported to have affected a number of the mineral phases and rock types making up the pluton (Harper, 1983;
Graham et al., 1986); plagioclase, pyroxene and olivine being the most altered phases. Thomas (1993) largely
confirmed all of the observations by previous workers and summarized their mineralogical findings. Hulbert (1986)
and Graham et al. (1986, 1987) assayed a handful of samples collected in the main sulphide occurrence of the
Bassett Lake intrusion for PGEs, but did not obtain any anomalous results; the highest concentrations of Pd and Pt
did not exceed 23 and 47 ppb, respectively.
3. Description of Main Units3
An area measuring approximately 5 km by 5 km (Figure 2) was mapped for this study. All of the outcrops
encountered lie within the southern confines of the La Ronge Domain. At the time of writing, neither geochemical
analyses nor thin sections were available, therefore the following rock descriptions are based solely on the field
investigations and on observations made by previous workers.
The geological map of the Bassett Lake area has been subdivided into several broad elements: 1) a belt of mafic to
felsic volcanic rocks, intruded by 2) gabbroic rocks of the Bassett Lake intrusion, which is itself intruded by 3)
dioritic to tonalitic rocks on its east side and 4) leucotonalite along its western boundary.
2
SMDI – Saskatchewan Mineral Deposit Index file number.
3
Descriptions of plutonic rocks follows the IUGS classification of igneous rocks (Streckeisen, 1976). A ‘metamorphic colour index’, based on the
percentage of mafic minerals in a metamorphosed rock, was used in the field to distinguish between mafic (>35), intermediate (35 to 15) and
felsic (<15) variants of volcanic and plutonic rocks. As all of the rocks in the Bassett Lake area have been metamorphosed, the prefix ‘meta’ is
omitted in the discussion of rock types.
Saskatchewan Geological Survey
2
Summary of Investigations 2014, Volume 2
Figure 1 – Regional geological map of the western Reindeer Zone (modified from Macdonald and Slimmon, 1999), showing
location of 2010-2014 La Ronge ‘Horseshoe’ mapping projects and outline of Figure 2. Index map abbreviations: FFD –
Flin Flon Domain, GD – Glennie Domain, KD – Kisseynew Domain, LRD – La Ronge Domain, MD – Mudjatik Domain,
PLD – Peter Lake Domain, RD – Rottenstone Domain, WB – Wathaman Batholith, WD – Wollaston Domain.
Saskatchewan Geological Survey
3
Summary of Investigations 2014, Volume 2
Figure 2 – Simplified bedrock geology map of the Bassett Lake intrusion and area. See accompanying map separate
(Maxeiner, 2014) for more details.
Saskatchewan Geological Survey
4
Summary of Investigations 2014, Volume 2
a) La Ronge Domain Volcanic Rocks
Only a few outcrops of La Ronge Domain volcanic rocks were investigated. These rocks predominantly underlie the
portion of the study area not affected by the 2006 forest fire and where glacial drift is widespread – along the west
and north margins of the Bassett Lake intrusion (Figure 2) – therefore outcrops of these rocks are sparse. The most
prominent type of supracrustal rocks encountered are plagioclase-phyric intermediate volcanic rocks (unit Iv). These
rocks weather a light greenish grey, are very fine grained, with equant, randomly oriented plagioclase phenocrysts up
to 1 mm in size (Figure 3A). A number of outcrops of mafic volcanic rocks (unit Mv) were also encountered. These
rocks are also feldspar-phyric, but weather a dark greenish grey to black, and are interlayered with the intermediate
volcanic rocks on a scale of tens to hundreds of metres.
One unit of felsic volcanic rock occurs in an interpreted F2 antiform on the north side of the Bassett Lake intrusion
(Figure 2). On the west and southwest sides of the intrusion, two small units of felsic volcanic rocks are intruded by
leucotonalite. The felsic volcanic rocks are generally fine grained and light grey, with millimetre-size plagioclase
phenocrysts. They contain little potassium feldspar and are locally interlayered with intermediate volcanic rocks
(Figure 3B). Minor layers of tuff breccia containing lapilli- to bomb-size felsic volcanic clasts were identified
(Figure 3C) in the felsic component.
Dykes of felsic to mafic composition were identified in a number of outcrops (Figures 3D, 3E). They are quite
difficult to differentiate from the volcanic equivalents, as the presence of primary volcanic features is rare. The
proportion of dykes to volcanic rocks is therefore difficult to ascertain. One unit of mixed intermediate to felsic
volcanic rock (Ivx) and dykes on the southeast side of Beaudry Lake exemplifies this statement well. It is a
complexly interlayered succession of intermediate and felsic volcanic rocks that is cut by abundant felsic,
intermediate and mafic dykes. It is strongly foliated and locally sheared, particularly along its southeast margin
where it borders leucotonalite.
The intermediate volcanic rocks are commonly intruded by either dioritic, gabbroic and/or tonalitic intrusive rocks
(Figure 3F), locally giving rise to intrusion breccias. This is also the case at the Vidgy Lake gold showing, where
silicified intermediate volcanic rocks have been intruded by dioritic rocks.
b) The Bassett Lake Intrusion
The central part of the map area is underlain by the Bassett Lake intrusion, a layered gabbroic pluton consisting of
several concentric units that locally exhibit very well-developed cumulate layering and that are interpreted to young
towards the centre of the intrusion. The predominant rock type identified in the field is gabbro, with minor
anorthosite, gabbronorite, melagabbro and leucogabbro, all showing a number of textural variations. All rocks of the
pluton are massive to moderately foliated (?S2). The units are described below from the outer margin towards the
interior of the intrusion, in order of their presumed relative age. Unit codes correlate to those in Figure 2. Magnetite
is prominent within every unit and is locally accompanied by minor amounts of other sulphide minerals.
Taxitic Leucogabbro, Gabbro (Unit BLt)
A unit of taxitic leucogabbro and gabbro forms the marginal zone of the pluton on its western side. Taxitic texture is
characterized by widely varying grain size (Figure 4A) from medium grained to pegmatitic on a scale of decimetres,
which results in a heterogeneous rock. The mafic mineral content varies from 15% to 40%, with leucocratic
compositions dominating. Igneous layering is only locally preserved in this unit, but one spectacular example of
crossbedded layering was encountered (Figure 4B).
Gabbro, Melagabbro (Unit BGa)
Gabbro and melagabbro is exposed over a width of about 100 to 200 m. The gabbro and minor melagabbro are
generally coarse-grained, locally grading into pegmatitic zones (Figure 4C). Cumulate layering is locally preserved
and generally defined by decimetre-scale layers of melagabbro within the gabbro. A more extensive layer of
melagabbro (unit BGm) was mapped within the southwestern part of unit BGa and locally grades into ultramafic
compositions.
Pegmatitic Oikocrystic Leucogabbro (Unit BLo)
The coarse-grained to pegmatitic oikocrystic leucogabbro is characteristically quite homogeneous and lacks smallscale cumulus layers. The rock is identified by its leucocratic nature and bluish grey–weathering, calcium-rich
plagioclase crystals that are partly enclosed by clusters of larger poikilitic mafic minerals (pyroxene) that can be up
to 5 cm in diameter (Figure 4D).
Saskatchewan Geological Survey
5
Summary of Investigations 2014, Volume 2
Figure 3 – Outcrop photographs of volcanic rocks and crosscutting dykes of the La Ronge Domain in the Bassett Lake area.
A) Porphyritic intermediate volcanic rock: station RM14-19-015, UTM 4 504201 m E, 6161463 m N. B) Well-layered outcrop
of felsic to intermediate volcanic rocks: station RM14-23-003, UTM 500577 m E, 6162832 m N. C) A felsic volcanic tuff
breccia layer: station RM14-23-002, UTM 500953 m E, 6162385 m N. D) Folded felsic dyke (arrow) cutting sequence of
intermediate to felsic volcanic rocks, crosscut by a late intermediate dyke (sides marked by dashed line): same station as ‘B’.
E) Complex outcrop of felsic volcanic flows (Fvf) and interlayered tuff breccia (Fvt), cut by younger dykes of mafic (Md) and
intermediate (Dip) compositions; note that mafic dyke is terminated by a fault on the right (arrow) and by the intermediate
porphyritic dyke on the left: same station as ‘C’. F) Xenolith of intermediate volcanic in leucotonalite; note well-developed
foliation in volcanic rock (long dashes) is at an angle to a weaker foliation (short dashes) preserved by the leucotonalite:
station RM14-24-015, UTM 500158 m E, 6159608 m N.
4
All UTM coordinates in this paper are in NAD83, Zone 13.
Saskatchewan Geological Survey
6
Summary of Investigations 2014, Volume 2
Figure 4 – Outcrop photographs of the Bassett Lake intrusion. A) Gabbro with taxitic texture characterized by widely varying
grain size; local pegmatitic and breccia zones, which are common to this unit, are not visible in this outcrop: station RM1421-003, UTM 500582 m E, 6160018 m N. B) Well-developed crossbedded cumulate layering: station RM14-17-020, UTM
500840 m E, 6158664 m N. C) Pegmatitic zones in unit of gabbro, melagabbro: station RM14-19-016, UTM 503997 m E,
6161227 m N. D) Characteristic weathering of oikocrystic leucogabbro, with centimetre-scale glomeroporphyritic pyroxene
crystals in a plagioclase-rich matrix: station RM14-18-004, UTM 500998 m E, 6159463 m N. E) Younger anorthositic
material cutting gabbroic rocks of unit BGh, resulting in an intrusion breccia: station RM14-21-014, UTM 501472 m E,
6160945 m N. F) Rhythmic cumulate layers of anorthosite (centimetres thick) and gabbro (decimetres thick): station RM1418-017, UTM 501717 m E, 6158739 m N. G) Metre-scale layering in outcrop of oikocrystic leucogabbro (Lg), gabbronorite
(Gn), and melagabbro (Mg); dashed lines enhance contacts: station RM14-18-004, UTM 500998 m E, 6159463 m N. H)
Large mafic volcanic xenolith (?roof pendant) in background (Mv), partially invaded by the enclosing gabbro in foreground:
station RM14-18-012, UTM 501252 m E, 6158866 m N.
Saskatchewan Geological Survey
7
Summary of Investigations 2014, Volume 2
Heterogeneous Taxitic Gabbro (Unit BGh)
Heterogeneous taxitic gabbro is similar in character to unit BLt, although it is generally more mafic and commonly
overprinted by irregular networks of anorthositic veins. With the presence of the younger anorthositic material
(Figure 4E), the rock takes on a heterogeneous brecciated appearance in addition to having highly variable grain
size.
Layered Oxide Gabbro, Anorthosite, Gabbronorite, Troctolite (Unit BGl)
One of the most prominent units of the Bassett Lake intrusion is also the most variable, and is the unit that hosts the
Triangle Lake copper-nickel showing. This unit of layered oxide gabbro, anorthosite, gabbronorite, and troctolite is
characterized by rhythmic cumulate layers of the aforementioned compositions. Layering is on the scale of
centimetres to metres (Figures 4F and 4G, respectively) and in many cases is very well defined, with rhythmic layers
similar to those observed in some of the famous layered intrusions such as the Stillwater (McCallum, 1996) or
Skaergaard (Irvine et al., 1998) intrusions. Concentrations of magnetite are high, locally attaining 20% or more in
hand sample (see also Harper, 1983). Metre-scale xenoliths of foliated mafic volcanic rock were also noted in the
unit in two separate places (Figure 4H), possibly representing roof pendants. As is the case in many of the gabbroic
rocks within the Bassett Lake intrusion, local pegmatitic zones were noted, particularly in close proximity to the
Triangle Lake showing.
Brecciated Gabbro (Unit BGx)
The final major unit of the Bassett Lake intrusion is a brecciated gabbro, which is a coarse-grained rock with a
colour index of about 50. It contains locally abundant, fine-grained, intermediate xenoliths, possibly of volcanic
origin. The gabbro is itself intruded by up to 30% dioritic material (unit Di), likely related to a younger dioritetonalite intrusion that cuts the Bassett Lake intrusion along its western margin (Figure 2).
Amygdaloidal Gabbronorite (Unit BGq)
A minor unit of the intrusion, amygdaloidal gabbronorite, is represented by a peculiar outcrop that is entirely
surrounded by a younger dioritic intrusion. The gabbronorite is a coarse-grained mafic rock with large (1 to 2 cm
diameter) crystals of clinopyroxene and orthopyroxene. Ovoid patches, 10 by 30 cm in size, of amygdaloidal rock of
the same composition are distributed irregularly across the outcrop. Amygdules appear to be filled by quartz,
carbonate, and chlorite. The origin and significance of this rock are unclear. Possibly it is part of the layered oxide
gabbro series (unit BGl) with the amygdaloidal mafic rock representing xenoliths of mafic volcanic rocks within a
gabbronorite. Alternatively, it could be related to fluid alteration processes related to the intruding diorite.
c) Younger Intrusions
One of the most widespread units in the map area is leucotonalite (unit Lt). This unit is a medium- to coarse-grained
rock that weathers white to light pink and is generally moderately foliated. The leucotonalite contains up to 5%
biotite, with minor amounts of hornblende and magnetite. It cuts the western margin of the Bassett Lake intrusion
and is, in a number of locations, intruded by dioritic rocks (unit Di), porphyritic diorite dykes (unit Dip), and mafic
dykes (unit Md).
Based on mapping by Thomas (1993) and on this summer’s observations, the eastern portion of the Bassett Lake
intrusion is sharply crosscut by a younger dioritic to tonalitic pluton. The intrusive nature of the diorite is evident by
a relatively wide zone of intrusion breccias where dioritic material invades the gabbroic components of the Bassett
Lake intrusion. The diorite (unit Di) is typically medium to coarse grained, and mottled white and black on the
weathered surface as a result of the presence of about 25% hornblende. It also contains minor amounts of magnetite.
The rock is homogeneous and generally massive to weakly foliated (?S2). With a decrease in mafic mineral content,
accompanied by an increase in quartz, the diorite grades into a tonalite-quartz diorite (unit T; Figure 2) towards the
central part of this younger intermediate intrusion.
Several dykes of porphyritic diorite-microdiorite (unit Dip) intrude the leucotonalite and intermediate to mafic
volcanic rocks. These dykes vary in width from a few decimetres to several decametres. They are possibly related to
the larger dioritic intrusion that postdates and lies to the east of the Bassett Lake intrusion.
4. Structural Geology and Metamorphism
Plutonic rocks in the area are generally massive to weakly foliated. There are many instances where cumulate
layering, which constitutes an S0 fabric, is well preserved within the Bassett Lake intrusion. In most cases, this
Saskatchewan Geological Survey
8
Summary of Investigations 2014, Volume 2
igneous layering is developed parallel to the contact of the intrusion with the country rock and is overprinted by a
weak tectonic foliation (S1), which is slightly oblique to S0. On the north margin of the Bassett Lake intrusion, and
within the younger tonalite-quartz diorite-diorite intrusion to the east, a moderately west-dipping foliation is either an
S2 or an S3 fabric. Pre-existing tectonic fabrics in supracrustal xenoliths contained within the leucotonalite (Figure
3F) and in the Bassett Lake intrusion (Figure 4H) likely are a representation of the earliest S1 fabric.
Volcanic rocks in the Bassett Lake area are generally weakly to moderately foliated, and locally sheared. This
foliation constitutes an S1 fabric, and more likely a composite S1/S2 foliation. It is generally developed parallel to
primary volcanic layering. Northeast of the Bassett Lake intrusion, the felsic to mafic volcanic strata and S1 foliation
are interpreted to have been affected by a tight to isoclinal map-scale fold, likely an F2 structure (Figure 2). On the
scale of the map (Figure 2), the Bassett Lake intrusion appears to truncate this interpreted F2 structure.
Sedimentary rocks are absent from the area and estimates of metamorphic grade are therefore somewhat hampered.
Hornblende is variably developed within the tonalite and the intermediate to mafic volcanic rocks, and is in stable
paragenesis with plagioclase. No obvious in situ partial melt was recognized in the tonalite or felsic volcanic rocks.
Based on these sparse observations, the metamorphic grade at Bassett Lake is likely at middle amphibolite facies,
consistent with earlier assessments by Thomas (1993).
5. Economic Geology Notes
a) The Triangle Lake Copper-Nickel Showing
As mentioned in ‘Introduction’, the Triangle Lake showing has been investigated sporadically since the 1950s,
mostly for its copper-nickel and iron ore potential (e.g., Harper, 1983; Thomas, 1993). The Triangle Lake showing is
one of the best known examples of titaniferous magnetite in Saskatchewan. Harper (1983) gave a conservative, nonNI43-101–compliant estimate of 27 million tonnes of ore grading <20% Fe with about 2% Ti. The showing is
described as being on the northwest side of Triangle Lake, where an 8 m by 4 m trench is reported to expose a
layered gabbro–peridotite–anorthosite sequence. This trench was not encountered during the brief visit to the area
during this study. However, an outcrop on the south side of the lake that exhibited a very well-layered sequence of
rusty weathering oxide gabbro-melagabbro was mapped. This outcrop is contained within the same unit that hosts the
Triangle Lake showing (Figure 2). Similar magnetite-rich rocks were also encountered on the west and east sides of
the lake. Magnetite is accompanied by minor disseminated pyrrhotite and chalcopyrite. Texturally, the gabbro on the
southeast and north sides of Triangle Lake is characterized by well-defined cumulate layering (Figure 4F) and local
pegmatitic features.
Ten samples of gabbroic rocks, focusing in particular on the coarse-grained and pegmatitic varieties, and
representing most of the units in the Bassett Lake intrusion (Figure 2), were collected during this study and submitted
to Activation Laboratories in Ancaster, Ontario for analysis for Pt, Pd and Au; the results are reported in Table 1.
Results with respect to potential PGE mineralization in the Bassett Lake intrusion are discouraging.
Table 1 – Results of platinum group element and gold analyses for selected samples of mafic rocks from the Bassett Lake
intrusion. (Sample locations are shown in Figure 2.)
Sample Number
Range of Detection
RM14-17-013-01
RM14-17-021-01
RM14-18-013-01
RM14-18-015-01
RM14-18-015-02
RM14-19-007-01
RM14-21-004-01
RM14-21-007-01
RM14-21-010-01
RM14-21-027-01
Rock Type
(Code on Figure 2)
Easting
Northing
Gabbro (BLt)
Microgabbro (BGa)
Gabbro (BGI)
Gabbro (BGI)
Gabbro (BGI)
Gabbro (BGq)
Gabbro (BGa)
Gabbro (BLt)
Gabbro (BGh)
Gabbro (BGa)
501435
500816
501390
501720
501720
504451
500725
500554
500968
501130
6158199
6158802
6158690
6158472
6158472
6160271
6159962
6159444
6160125
6161477
Au
(ppb)
2-30000
3
3
<2
31
3
3
2
<2
3
5
Pt
(ppb)
1-30000
<1
<1
<1
5
<1
1
<1
<1
<1
<1
Pd
(ppb)
1-30000
<1
<1
<1
5
1
2
<1
<1
<1
<1
Analyses were carried out by Activation Laboratories Ltd., Ancaster, Ontario, using analytical package ‘1C - Exploration’. The
analytical method for this package is preparation of the sample by mixing it with fire assay fluxes and Ag, running the mixture
through the fire assay process, and finally analyzing it with an inductively coupled plasma mass spectrometer.
Saskatchewan Geological Survey
9
Summary of Investigations 2014, Volume 2
b) Vidgy Lake Gold Showing
The predominant rock type in the area of the Vidgy Lake gold showing is an intermediate volcanic rock that has been
silicified and cut by abundant mineralized quartz veins. The intermediate volcanic rock is also cut by dioritic
intrusions, in places creating spectacular intrusion breccias. None of the outcrops mapped showed any evidence of
ductile shearing. Locally the volcanic rocks have preserved layering; in these instances it appears this unit formed as
flows, possibly with some interbedded tuffaceous sections. The crosscutting diorite is generally massive to weakly
foliated and is locally cut by minor veins and zones of silicification.
We visited the area of the showing during this study and found an exposed ridge of outcrop north of a small unnamed
lake (Figure 2). As discussed in ‘Introduction’, visible gold has been reported at this location. According to available
files in the Saskatchewan Mineral Assessment Database, the recorded exploration history ended in 1994, but stacked
core boxes encountered in the field indicate that there has been some drilling on the property subsequent to the 2006
forest fire. Several mineralized sections were noted in the top core boxes, characterized by dilational quartz and
sulphide veins. The main sulphide minerals noted are pyrrhotite, pyrite, and chalcopyrite.
The best reported assay results (non-NI43-101–compliant) from drilling conducted in 1989 by Cogema included a 70
cm intersection grading 2030 ppb Au within a quartz-veined diorite, and a 1.5 m intersection grading 1160 ppb Au
within a sulphidic volcanic rock. Results from two grab samples of volcanic rock collected in the area during the
present visit are reported in Table 2.
Table 2 – Results of gold and other selected trace element analyses for two samples from the area of the Vidgy Lake gold
showing. (Sample locations are shown in Figure 2.)
Sample No.
(Easting, Northing)
Rock Type
Element
RM14-19-010-01
(504287, 6160630)
RM14-19-013-01
(504249, 6161096)
Felsic Volcanic
Intermediate
Volcanic
Unit of
Measure
Detection
Limit
Analytical
Method
Au
ppb
2
25
<2
Ag
ppm
0.3
0.5
<0.3
Cu
ppm
1
91
40
TD-ICP
Mo
ppm
1
4
5
TD-ICP
INAA
MULT INAA / TD-ICP
Pb
ppm
3
10
<3
TD-ICP
Ni
ppm
1
22
53
MULT INAA / TD-ICP
Zn
ppm
1
58
61
MULT INAA / TD-ICP
S
%
0.01
1.11
0.71
TD-ICP
As
ppm
0.5
290
10.6
INAA
Ca
%
0.01
3.91
5.17
TD-ICP
Br
ppm
0.5
<0.5
<0.5
INAA
Co
ppm
1
12
23
INAA
Cr
ppm
2
46
111
INAA
Cs
ppm
1
<1
<1
INAA
Eu
ppm
0.2
2.1
0.7
INAA
Fe
%
0.01
3.49
3.63
INAA
Hf
ppm
1
6
<1
INAA
Hg
ppm
1
<1
<1
INAA
Ir
ppb
5
<5
<5
INAA
K
%
0.01
0.67
0.27
TD-ICP
Li
ppm
1
11
7
TD-ICP
Mg
%
0.01
0.62
2.11
TD-ICP
Mn
ppm
1
315
658
TD-ICP
Na
%
0.01
3.82
2.79
INAA
P
%
0.001
0.051
0.076
TD-ICP
Saskatchewan Geological Survey
10
Summary of Investigations 2014, Volume 2
Table 2 (cont’d)
Sample No.
(Easting, Northing)
Rock Type
Element
Unit of
Measure
RM14-19-010-01
(504287, 6160630)
RM14-19-013-01
(504249, 6161096)
Felsic Volcanic
Intermediate
Volcanic
Detection
Limit
Analytical
Method
Rb
ppm
15
<15
<15
Sb
ppm
0.1
0.3
0.2
INAA
INAA
Sc
ppm
0.1
4
16.3
INAA
Ti
%
0.01
0.18
0.29
TD-ICP
Th
ppm
0.2
6.1
1.2
INAA
U
ppm
0.5
2
<0.5
INAA
V
ppm
2
46
143
TD-ICP
W
ppm
1
<1
<1
INAA
Y
ppm
1
5
10
TD-ICP
La
ppm
0.5
58.4
9.8
INAA
Ce
ppm
3
117
16
INAA
Nd
ppm
5
23
<5
INAA
Sm
ppm
0.1
5.2
2.9
INAA
Yb
ppm
0.2
<0.2
0.9
INAA
Lu
ppm
0.05
<0.05
<0.05
INAA
g
-
35.7
35.6
INAA
Mass
Analyses carried out by Activation Laboratories Ltd., Ancaster, Ontario, using analytical package ‘1H’. This package analyzes
for some elements using instrumental neutron activation analysis (INAA) and for others using total digestion of the sample
followed by inductively coupled plasma mass spectrometry (TD-ICP). The analytical method used for each element is shown in
the table. ‘MULT INAA’ indicates an element that was analyzed by multiple methods.
6. Acknowledgements
Sean Lobb and A. Ross LeMessurier, geological field assistants, are thanked for their diligent work ethic and the
cheerful attitude they displayed all summer. Murray Rogers reviewed an earlier manuscript, which helped improve it.
Ken Ashton’s comments as part of the final edit of the manuscript also helped improve it. Osprey Wings are thanked
for getting us safely in and out of Bassett Lake, which is a pretty small lake, also affectionately known as ‘Dancing
Moose Lake’ because of its peculiar shape.
7. References
Graham, I., Watters, B.R., and Hulbert, L. (1986): The Bassett Lake mafic intrusion: preliminary report; in Summary
of Investigations 1986, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 86-4, p150-153.
Graham, I., Watters, B.R., and Hulbert, L. (1987): Geology and geochemistry of the Bassett Lake Complex: progress
report; in Summary of Investigations 1987, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep.
87-4, p140-147.
Harper, C.T. (1983): Iron Ores of Northern Saskatchewan; Sask. Energy Mines, Rep. 220, 103p.
Hulbert, L. (1986): An investigation of mafic and ultramafic intrusions in northern Saskatchewan: preliminary
findings; in Summary of Investigations 1986, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep.
86-4, p143-144.
Irvine, T.N., Andersen, J.C.Ø., and Brooks, C.K. (1998): Included blocks (and blocks within blocks) in the
Skaergaard Intrusion: geological relations and the origins of rhythmic modally graded layers; Geol. Soc. Amer.
Bull., v110, p1398-1447.
Saskatchewan Geological Survey
11
Summary of Investigations 2014, Volume 2
Macdonald, R. and Slimmon, W.L. (compilers) (1999): Geological map of Saskatchewan; Sask. Industry and
Resources, 1:1 000 000 scale.
Maxeiner, R.O. (2014): Bedrock geology of the Bassett Lake area (parts of NTS 73P10 and 11); 1:20 000-scale
prelim. map with Summary of Investigations 2014, Volume 2, Saskatchewan Geological Survey, Sask. Ministry
of the Economy, Misc. Rep. 2014-4.2-(1.4).
Maxeiner, R.O., Matthews, M., and Morelli, R. (2013): La Ronge ‘Horseshoe’ Project: bedrock geology of the
Nistowiak-Mountain-Otter lakes area, Glennie and Kisseynew domains (parts of NTS 73P/07, /08, /09, and /10);
in Summary of Investigations 2013, Volume 2, Saskatchewan Geological Survey, Sask. Ministry of the
Economy, Misc.Rep. 2013-4.2, Paper A-7, 22p.
McCallum, I.S. (1996): The Stillwater Complex; in Cawthorn, R.G. (ed.), Layered Intrusions, Developments in
Petrology, v15, p441-483, Elsevier, Amsterdam.
Padgham, W.A. (1960): The Geology of the Otter Lake Area (West Half), Saskatchewan; Sask. Dep. Miner. Resour.,
Rep. 41, 34p.
Streckeisen, A. (1976): To each plutonic rock its proper name; Earth Sci. Rev., v12, p1-33.
Thomas, D.J. (1993): Geology of the Star Lake–Otter Lake Portion of the Central Metavolcanic Belt, La Ronge
Domain; Sask. Energy Mines, Rep. 236, 132p.
Saskatchewan Geological Survey
12
Summary of Investigations 2014, Volume 2