HORIZONTAL LOOP EMAG LINE CUTTING MAG RPT · undergrowth, which was an impediment to the horizontal...
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Transcript of HORIZONTAL LOOP EMAG LINE CUTTING MAG RPT · undergrowth, which was an impediment to the horizontal...
GRAND u RESOURCES CORPORATION
CLEAR LAKE PROPERTY FA ULKENHAM LAKE AREA
REDLAKE MINING DIVISION ONTARIO
REPORT ON MAGNETIC AND HORIZONTAL LOOP E.M. SURVEYS
- by - 2 .
Colin Bowdidge, Pb.D., P.Geo.
October 2004
0 2 8
PROVINCIAL RECOR ,NG OFFICE - SUDBU Y
RECEIV_C
JUL 1 ~ 2005 c A.r.t q: \$ S~ ! ~ 9 19 l.ll~ ! ~ : ~ ? ~
- I -
TABLE OF CONTENTS
INTRODUCTION ............................................................. 1
PROPERTY, LOCATION AND ACCESS .......................................... 1
HISTORY AND PREVIOUS WORK .............................................. 2
GEOLOOY .................................................................. 2
2004 PROGRAM ..........•................................................... 3
Line Cutting ............................................................ 3
Horizontal Loop EM Survey ............................................... 3
Magnetic Survey ........................................................ 4
SURVEY RESULTS ........................................................... 4
CONCLUSIONS AND RECOMMENDATIONS .................................... 5
REFERENCES ............................................................... 7
FIGURES
Figure 1: Location Map
Figure 2: Regional Geology
Figure 3: Claim Map with Grid and Anomalies
Figure 4: Geology with Grid and Anomalies
PLATES (in rear pocket)
Plate 1: Horizontal Loop Survey Data Postings, 1 :2,500
Plate 2: Horizontal Loop Survey Profiles, 1 :2,500
Plate 3: Magnetic Survey Data Postings, 1:2,500
Plate 4: Magnetic Survey, Total Field Contours, 1 :2,500
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INTRODUCTION
This report presents the results of magnetic and horizontal loop electromagnetic surveys carried out
during 2004 on the Clear Lake property of Grandcru Resources Corporation. The work was
commenced during the spring of2004 but had to be abandoned because of poor snow, ice and slush
conditions. It was completed during September 2004.
PROPERTY, LOCATION AND ACCESS
The property consists of five claims comprising 43 claim units, as detailed in the following table:
CLAIM SUMMARY:
Claim No. No. Units r;:ording date Expiry date Work Req. Reserve
1185210 8 2003.08.26 2005.08.26 3200 0
1185211 15 2003.08.26 2005.08.26 6000 0
1185212 12 2003.08.26 2005.08.26 4800 0
1185232 2 2003.08.26 2005.08.26 800 0
1185233 6 2003.08.26 2005.08.26 2400 0
Source: MNDM Mining Claims Information (MCI)
The claims are held by Perry English, and are under option to Grandcru Resources Corporation.
They are situated in the Faulkenham Lake area, 15 kilometres south-southwest of the town of Red
Lake and 7 kilometres southeast of the small community ofStarratt-Olsen, which is at the end ofthe
paved road running southwest from Red Lake to Madsen.
Access to the property during the summer months is by float-equipped light aircrafit from Red Lake.
In winter, a snowmobile trail can be used, that leads from the end of the road at Starratt-Olsen leads
to a cabin on Bug Lake (now locally referred to as either Clear Lake or Crystal Lake), just northwest
of the property.
Figure I shows the location of the property.
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CLEAR LAKE PROPERTY FAULKeNHAM lAI(E AREA
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mSTORY AND PREVIOUS WORK
In 1976, Selco Mining Corporation carried out horizontal loop (EM-I 7) and magnetic surveys over
an area that corresponds approximately to the western half of the 2004 grid (Thorsen, 1976). The
survey defined conductor A (as shown on the naps in this report) and shows conductor B as a weak
feature.
In 1985, Golden Terrace Resources Corp. carried out an airborne EM and magnetic survey, using
the Aerodat system, over the Dixie Lake area, including the present property (Podolsky, 1985).
Numerous conductors were identified; they are shown on figures 3 and 4.
The map of Thurston and Paktunc (1985) shows a diamond drill hole in the approximate area of
conductor A (see fig. 4). No record of this drill hole was found in the Red Lake assessment files.
A 1946 report by the Red Lake Resident Geologist (Thomson, 1946) describes a visit to the Bug
Lake area with a prospector named Cecil Alcock. Mr. Alcock had reported located a gold-stibnite
occurrence in the 1930s. A number of old pits were found "near the northeast end of a small lake
and nearby swamp", but the showing itself was not relocated at the time.
GEOLOGY
The property lies in the Uchi subprovince of the Canadian Shield. It covers part of a narrow (1 km
or less) greenstone belt that is one of the branches from the west end of the Confedl::ration Lake be It.
Figure 2 shows the regional geological setting of the property.
The area was mapped on a reconnaissance basis by Thurston & Paktunc (1985). Figure 4 shows the
geology taken from their map. In the centre of the property the southern half ofthe belt consists of
mafic volcanics, and the northern half consists of clastic metasediments. At the west end of the
property a wedge of mafic volcanics appears on the north side of the belt, and at the east end of the
property the metasediments appear to change laterally into felsic metavolcanics.
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Fig. 2: R g ional Geology and Tectonic Units of tho Red Lak -
Birch Lake Area, Ont;ulo
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Thomson (1946) reports a number of sulphide occurrences in granitoid or gneissic rocks, in old pits
"near the northeast end of a small lake" east or southeast of Bug Lake. These w(!re found when
looking for the Alcock gold-stibnite showing. He also reports that "at the west end ofthe V-shaped
lake fprobably the lake that the 2004 baseline runs along] plentiful angular boulders up to 4 feet by
3 feet by 2 feet of hard white siliceous altered rock with pyrite occur".
2004 PROGRAM
Line Cutting
A 3000 metre long base line was laid out with azimuth 083 degrees (relative to VTM north). Cross
lines were turned off at 50 metre intervals. The entire grid was cut in winter; those lines at the
eastern end of the grid that were surveyed in September were cleaned out because of heavy
undergrowth, which was an impediment to the horizontal loop survey. The line cutting contractor
was Top Notch Exploration (now Ackewance Exploration and Services) of Red Lake .
Horizontal Loop EM Survey . I~ 8 '~ )
The electromagnetic survey was carried out using an Apex Parametrics Maxmin II horizontal loop
system. Cable length was 100 metres and the frequencies used were 444 Hz and 1777 Hz. Readings
were taken at 25 metre intervals. Coplanarity ofthe coils was achieved using the standard method
of measuring the slope between each station and the next with an inclinometer and calculating an
average slope for the four station intervals making up the length of the cable for each reading
position. The transmitter and receiver coils were tilted by the amount ofthis slope.
Receiver operator was Dusan Dmitrovic, and transmitter operators were Ted Cox (in spring) and Joe
Brandstrom (in September). Data processing was performed by the writer using Geosoft® software.
The results of the survey are presented on Plate 1 (data postings) and Plate 2 (profiles with
interpreted conductors). Apparent conductances at 1777 Hz were calculated using standard models
for thin sheet conductors, and are shown on Plate 2.
Magnetic Survey
The west part of the grid (from line 0 to line] 700W) was carried out in the spring using an EDA
Omni Plus system. The east part of the grid, from line 0 to line 1300E, was surveyed in September,
using a Scintrex ENVI magnetometer. Both instruments store readings for the duration of a day's
surveying, and the data can be dumped each day into a computer. Base stations were used during
both phases of the survey for correction of diurnal variations. In September, line 0, which had been
surveyed in the spring, was resurveyed to verity that the new instrument gave readings consistent
with those of the earlier survey. No adjustments were required.
The magnetometer operator was Dusan Dmitrovic. Magnetic data are presented on Plate 3 (total
field data posting) and Plate 4 (total field contours with HLEM conductors superimposed).
SURVEY RESULTS
The magnetic survey shows a distinct group of more or less linear, discontinuous anomalies that
coincide, on a gross scale with the conductive trend that crosses the grid. The strongest of these
anomalies has a peak amplitude of2500 nT. This trend, as can be seen on figure 4, lies close to the
volcanic-sedimentary contact as mapped by Thurston & Paktunc (1985). To the south of this
trend/contact, in the volcanic terrain, the magnetic pattern is quite flat, with a few isolated magnetic
highs with amplitudes up to 1000 nT.
In the area underlain by metasediments north ofthe conductive/magnetic trend, the magnetic pattern
is much more active. There are numerous erratically distributed magnetic highs, a few of which are
linear and are presumed to be caused by fonnational units. The number and intensity of these
anomalies increase progressively from east to west.
In the northwest comer ofthe grid, presumed to be underlain by granodiorite, the magnetic pattern
is again quite flat.
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The horizontal loop survey shows four separate conductors, which line up to fonn a more or less
continuous trend along the volcanic-sedimentary contact. There is a possible structural disruption
in the vicinity of line 700W, where the magnetic-conductive trend may be offse:t by 100 to 150
metres.
Conductor A is 950 metres long, and is mostly narrow, with a section up to 60 metres wide between
lines 1200W and 1500W. Apparent conductance is between 2 and 27 siemens. There is an irregular
magnetic response, with alternating highs and lows, suggestive of concentrations of pyrrhotite.
Conductor B is 200 metres long and up to 25 metres wide, with apparent conductance of up to 23
siemens. The magnetic response again features highs and lows.
Conductor Cis 150 metres long and is up to 15 metres wide, with much lower conductance, up to
6 siemens. It has no magnetic association.
Conductor D has been traced for 1400 metres, and extends beyond the east end of the grid. It is very
weak, and conductance calculations derived from in-phase/quadrature ratios would suggest a
moderately good conductor at considerable depth, which would probably be misleading. It is
probably narrow, but the amplitudes are so low that widths cannot be reliable measured. It loosely
follows a number of magnetic anomalies, but it tends to flank them.
CONCLUSIONS AND RECOMMENDATIONS
The highlight of the geophysical surveys is the recognition of a more or less continuous magnetic
and conductive trend aligned along the contact between a (lower?) mafic volcanic unit and an
(upper?) unit of clastic metasediments. In the greenstone belts ofthe Uchi subprovince which have
a simple stratigraphy, this contact is a favourable locus for gold mineralization.
It is recommended that the grid be mapped and prospected, with particular attention paid to the
conductors and magnetic anomalies along the volcanic-sedimentary contact. An attempt should be
- 6-
made to relocate the old trenches described by Thomson (1946). The pyritic boulders at the west end
of the V-shaped lake should be easy to locate. Soil geochemistry (either conventional or MMI,
depending on the terrain) would also be a valuable exploration tool.
Further attempts might be made to locate reports used by Thurston & Paktunc (1985) to place a drill
hole on their map. It is likely that this hole was drilled by Selco, and it is further likely that, if a drill
log, or at least a hole number can be found, the core is stored in the MNDM core library at Red Lake.
They have numerous Selco drill holes for which they do not have any written record. It is probable
that Thurston & Paktunc (1985) were given access to Selco's records including data that may not
have been filed for assessment work.
Respectfully submitted,
CoHn R. Bowdidge, Ph.D., P.Geo.
31 October 2004
- 7 -
REFERENCES
PODOLSKY, G., 1985. Report on Combined Helicopter-borne Magnetic, E1ectromagnetic and VLF Survey, Dixie Lake Area, Ontario for Golden Terrace Resources by Aerodat Ltd. MNDM Assessment File 52K 13NW0053
THOMSON, R., 1946. Report on a Visit to the Alcock Property. Unpublished n!port in MNDM Red Lake Resident Geologist Files.
THORSEN, K., 1976. Selco Mining Corporation, Block 150-6, Dixie Lake Area, Geophysical Report. MNDM Assessment File 52K 13NW8937
THURSTON, P.e. & PAKTUNC, D., 1985. Western Uchi Subprovince (Troutlake River Area), Madsen Sheet, District of Kenora (Patricia Portion): Ont. Geol. Surv. Map P.2857.
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