report on a combined helicopter borne · web: email: [email protected] vtem™ plus geophysical...

Geotech Ltd. 245 Industrial Parkway North Aurora, ON Canada L4G 4C4

Tel: +1 905 841 5004 Web: www.geotech.ca Email: [email protected]

VTEM™ Plus

GEOPHYSICAL INTERPRETATION REPORT ON A HELICOPTER-BORNE

VERSATILE TIME DOMAIN ELECTROMAGNETIC (VTEM™ plus) AND

HORIZONTAL MAGNETIC GRADIOMETER GEOPHYSICAL SURVEY

PROJECT: GOWGANDA WEST PROJECT

LOCATION: GOWGANDA, ONTARIO

FOR: IMETAL RESOURCES INC.

SURVEY FLOWN: DECEMBER 2018

PROJECT: GL180370

http://www.geotech.ca/

mailto:[email protected]

Project GL180370 iMetal Resources Inc. VTEM™ Geophysical Interpretation Report

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TABLE OF CONTENTS EXECUTIVE SUMMARY ...................................................................................................... III 1. INTRODUCTION ............................................................................................................. 1

1.1 interpretation objective .......................................................................................................... 1 1.2 survey locations ..................................................................................................................... 1

2. GEOLOGY AND GOLD MINERALIZATION .......................................................................... 2 2.1 Geology ................................................................................................................................ 2 2.2 Gold Mineralization ................................................................................................................ 5 2.3 Typical geophysical signatures of potential polymetallic vein gold mineralization ........................ 6

3. INTERPRETATION OF MAGNETIC DATA ........................................................................... 8 3.1 magnetic data interpretation .................................................................................................. 8 3.2 mvi inversion ......................................................................................................................... 8

4. AIRBORNE INDUCTIVELY INDUCED POLARIZATION (AIIP) ...............................................11 4.1 aiip mapping ....................................................................................................................... 11 4.2 determination of frequency factor c ...................................................................................... 12 4.3 aiip depth of investigation .................................................................................................... 15 4.4 aiip mapping results ............................................................................................................. 19

5. SELECTION OF POTENTIAL EXPLORATIONTARGETS ........................................................24 6. CONCLUSIONS AND RECOMMENDATIONS .......................................................................28 REFERENCES ....................................................................................................................30 APPENDIX A: AIIP MAPPING ............................................................................................... 1 APPENDIX B: INTERPRETATION OF COLE-COLE PARAMETERS .............................................. 1 APPENDIX C: FINAL DELIVERABLES .................................................................................... 1

LIST OF FIGURES Figure 1: The location of the VTEM survey in the Gowganda area, Ontario, over Google Earth Image. ..... 1 Figure 2: Regional geology of the Gowganda West project and surrounding areas (from Hamilton, 1997,

OGS open file report 5962); the approximate location of the VTEM block is marked by a red polygon.

................................................................................................................................................... 2 Figure 3: Stratigraphy of Shining Tree area with geochronology locations and ages and studied deposits

(after Ayer et al. 2013). The approximate location of the VTEM block is marked by a white polygon. 3 Figure 4: Local geology (from OGS, ca. 1971-78) and Juby Au developed prospect and known Au

occurrences (from MNDM) and precious and base metal exploration zones (Z-1 to Z-4, from iMetal

Resources website) and drilling zone (iMetal 2019) within Z-1. ........................................................ 4 Figure 5: Local pre-cambrian geology of the central and western parts of VTEM block (Leonard & Tyrrell

Townships), from Johns, G.W., 2003, Precambrian Geology, Shining Tree Area; OGS, Preliminary

Map P.3521, Scale 1:50,000. ......................................................................................................... 5 Figure 6: Simplified exploration model for polymetallic vein gold mineralization in the Cobalt Embayment

(modified after Potter & Taylor, 2010). The original portion of the image showing uranium bearing polymetallic veins is covered up with transparent shade. ................................................................ 6

Figure 7: Frist vertical derivative of the RTP data, with the inferred and known faults and dykes overlay. . 8 Figure 8: The MVI 500 m magnetization amplitude depthslice and the inferred basement district-scale

fault zones. .................................................................................................................................. 9 Figure 9: The MVI 250 m magnetization amplitude depthslice and the inferred district-scale fault zones. 10 Figure 10: Forward modelled VTEM decays for different chargeability m values; the observed VTEM decay

(black) was from Mount Milligan, British Columbia, fits well with the modeled decay (red) with m=0.66. .................................................................................................................................... 12

Figure 11: The locations of VTEM decays for Cole-Cole frequency factor c determinations over EM

induction time-constant TauSF data............................................................................................. 13


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Figure 12: Cole-Cole parameters of four AIIP forward models from Eastmain block and corresponding

decays; purely inductive m=0 (green), observed data (black) and forward modeled data (red). ...... 14 Figure 13: The relationship between the distribution of grain sizes and the frequency factor c is illustrated

in the Cole-Cole spectra of c=0.7. ............................................................................................... 15 Figure 14: The setup of the 3D prismatic model for AIIP depth of investigation. ................................... 16 Figure 15: AIIP apparent chargeabilities for prisms located 50m, 75m and 100m below ground; the same

color scheme is used. ................................................................................................................. 17 Figure 16: AIIP apparent resistivities for prisms located 50m, 75m and 100m below ground; the same

color scheme is used. ................................................................................................................. 18 Figure 17: The Digital Elevation Model (DEM) data. ............................................................................... 19 Figure 18: AIIP apparent resistivity data. ............................................................................................ 20 Figure 19: AIIP apparent chargeability data. ....................................................................................... 21 Figure 20: Cole-Cole time-constant data. ............................................................................................ 22 Figure 21: The tau-scaled chargeability (TSC) data. ............................................................................ 23 Figure 22: Selected potential exploration targets for possible polymetallic vein gold mineralization over

the TSC data. ............................................................................................................................. 24 Figure 23: Selected potential exploration targets for possible polymetallic vein gold mineralization over

the 3D MVI magnetization amplitude 500 m depthslice. ................................................................ 25 Figure 24: Selected potential Au targets from Dave Gamble (A1-A12, B1-B4) over the EM induction time-

constant and the potential Au target zones (GWG_01 to GWG_07) identified by Geotech. .............. 26

LIST OF TABLES NO TABLE OF FIGURES ENTRIES FOUND.

APPENDICES A. AIIP Mapping .........................................................................................................................

B. Interpretation of AIIP Cole-Cole Parameters ............................................................................. C. Final Deliverables....................................................................................................................


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EXECUTIVE SUMMARY Geophysical interpretation report on VTEMTM survey of Gowganda West project, Gowganda, Ontario

During December 12th to December 18th, 2018 Geotech Ltd. carried out a helicopter-borne geophysical survey over the Gowganda West project situated near Gowganda, Ontario. Principal geophysical sensors included a versatile time domain electromagnetic (VTEM™plus) system and a horizontal magnetic gradiometer with two caesium sensors. Ancillary equipment included a GPS navigation system and a radar altimeter. A total of 589 line-kilometres of geophysical data were acquired during the survey.

Geotech Ltd carried out airborne inductively induced polarization (AIIP) chargeability mapping, MVI 3D inversions, and geophysical interpretation of the VTEM data and the advanced products. The objective of geophysical interpretation of the VTEM magnetic and EM data of Gowganda West project is to identify exploration targets (or prospects) for possible polymetallic vein gold mineralization. The objective is achieved by interpreting the magnetic and EM data, MVI 3D inversions and selected advanced AIIP product, e.g., tau-scaled chargeability (aiip_chargeability*Cole-Cole_time-constant). The selected AIIP product could help the search for possible alteration zones at shallow depths (< 100 m). The alteration zones could be associated with polymetallic vein gold mineralization. Seven (7) potential exploration targets for possible polymetallic vein gold mineralization in the Gowganda West project VTEM survey area. Final deliverable products are:

AIIP databases and grids; MVI databases, depthslices, 3D sections, 2D maps, and consolidated sections in PDFs; Geophysical interpretation maps; Polygons for potential exploration targets; Geophysical interpretation report.


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1. INTRODUCTION

1.1 INTERPRETATION OBJECTIVE The objective of the geophysical interpretation of the VTEM data is to identify potential exploration prospects for possible polymetallic vein gold mineralization in the surveyed area.

1.2 SURVEY LOCATIONS The centre of the VTEM block is located approximately 15 kilometers southwest of Gowganda, Ontario (Figure 1).

Figure 1: The location of the VTEM survey in the Gowganda area, Ontario, over Google Earth Image.

The survey area was flown in an east to west (N 90° E azimuth) direction with traverse line spacings of 100 metres.


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2. GEOLOGY AND GOLD MINERALIZATION This chapter describes the regional and local geology of the Gowganda West project area and provides discussions on possible polymetallic vein gold mineralization in the area.

2.1 GEOLOGY Regional Geology The VTEM block is located geographically mostly in the Leonard and Leith Townships, and the northern part of the block extends into the Tyrrell and Milner Townships. The eastern half and the northwestern parts of the survey area are underlain mainly by the Gowganda Formation of the Huronian-Cobalt Supergroup of metasedimentary rocks, Figure 2. The remaining area is underlain mainly by mafic to intermediate metavolcanic rocks and Nipissing diabase sills. A cluster of gold geochemical anomalies are located just western of the VTEM block (Hamilton, 1997).

Figure 2: Regional geology of the Gowganda West project and surrounding areas (from Hamilton, 1997,

OGS open file report 5962); the approximate location of the VTEM block is marked by a red polygon.

The central and eastern parts of the VTEM block are located in the Cobalt Embayment (Figure 2 insert, from Easton 2000), an irregular domain of Paleoproterozoic (2.45 – 2.22 Ga) siliciclastic


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sedimentary rocks (Huronian Supergroup) that unconformably overlies Archean basement rocks of the Abitibi greenstone belt (Potter & Taylor, 2010). The Nipissing diabase sills and dykes intruded the Huronian Supergroup ca. 2.22 Ga. The Cobalt Embayment is best known for Ag-Co veins of the Cobalt mining camp, but it also hosts numerous polymetallic (Cu, Ni, Co, Au, Ag) calcite-quartz vein systems (Potter & Taylor, 2010). In a more recent study by Ayer et al. 2013, new geochronology data from the unconformity (conglomerate and sandstone) in the western parts of the VTEM block suggest they are part of the Archean Porcupine Assemblage (2690 – 2680 Ma), as shown in Figure 3.

Figure 3: Stratigraphy of Shining Tree area with geochronology locations and ages and studied deposits

(after Ayer et al. 2013). The approximate location of the VTEM block is marked by a white polygon.

The Cook (MacMurchy Township), Hydro Creek, Big Dome and Juby (Tyrrell Township) deposits (See Figure 3) all appear to be structurally controlled along the southeast trending Tyrrell fault in the eastern part of the Shining Tree area. In these deposits, gold is associated with thin, relatively late, high-grade quartz-carbonate-sulphide veins with broader alteration zones consisting of carbonatization, sericitization and chloritization with disseminated pyrite and lower gold values (Ayer et al., 2013). Proterozoic Cu mineralization, found in the northern margin of the Cobalt Embayment, occurs in quartz veins or breccias within Upper Huronian stratigraphic units and Nipissing diabase dykes with relatively thin alteration zones consists of chlorite, sericite, biotite, alkali feldspar, epidote, hematite


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and carbonate. The Proterozoic mineralized zones are dominantly east-striking and are proximal to northerly trending regional faults which transect the Embayment, a similar structural setting to mineralization for many of the Cobalt Embayment deposits (Ayer et al., 2013). Local Geology The local geology (ca. 1970s from OGS) of the Gowganda West project area is shown in Figure 4. The eastern parts of the VTEM block (Milner & Leith Townships) are underlain by Nipissing diabase sills and the Gowganda Formation of Huronian-Cobalt Supergroup consisting of argillite, siltstone, arkose, quartz arenite and greywacke.

Figure 4: Local geology (from OGS, ca. 1971-78) and Juby Au developed prospect and known Au

occurrences (from MNDM) and precious and base metal exploration zones (Z-1 to Z-4, from iMetal Resources website) and drilling zone (iMetal 2019) within Z-1.

The geology of the central and western parts of the VTEM block in Leonard & Tyrrell Townships is shown in Figure 5. The area is underlain mainly by Archean mafic to intermediate metavolcanics, metasediments of the Porcupine Assemblage (2690 – 2680 Ma), now known as the Indian Lake group of conglomerate, arenite sandstone and greywacke (Dave Gamble, pers. comm. with Jean Legault, April 12, 2019), and the Proterozoic Nipissing diabase sills.


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Figure 5: Local pre-Cambrian geology of the central and western parts of VTEM block (Leonard & Tyrrell

Townships), from Johns, G.W., 2003, Precambrian Geology, Shining Tree Area; OGS, Preliminary Map P.3521, Scale 1:50,000.

2.2 GOLD MINERALIZATION The Juby gold prospect (developed with reserves of indicated resources of 1.09 Moz Au and inferred resources of 2.9 Moz Au, Campbell et al., 2018 NI 43-101 technical report), is located just north of the VTEM block (red star), probably located in the Abitibi greenstone belt. Two Au occurrences are located less than 1 km southwest of Juby. The gold exploration zone (Z-1 and Z1-S) is located about 1.5 kilometers south of Juby. Drilling of Z1-S had intersected gold mineralization (iMetal Resources website). Z-2 (Cu, Au) is located in the central part of the VTEM block. The Juby gold prospect belongs to Archean mesothermal or lode gold deposit hosted in quartz veins with associated carbonatized wall rocks (Campbell et al. 2014). The quartz veins have strike and dip extents of up to several hundreds of meters. The deposits occur in low- to medium-grade metamorphic terranes in deformed Archean greenstone belts, near major faults and the gold mineralization sited on splays off the major faults. Simplified Exploration Model of Polymetallic Vein Gold Mineralization The Archean basement (Abitibi greenstone belt) in the Cobalt Embayment is overlain by the Huronian-Cobalt Supergroup (Gowganda Formation) and Nipissing diabase sills, also as the case for central and eastern parts of the VTEM block. The Juby-type gold mineralization in the basement of the VTEM block, if existed, could be overlain by the Porcupine metasediments, the Gowganda


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Formation and Nipissing sills. The gold mineralization could be brought up near the surface along both the regional unconformity and reactivated faults that offset the unconformity, as illustrated by the exploration model for polymetallic vein gold mineralization in Figure 6 (modified after Potter & Taylor, 2010). The polymetallic veins are interpreted as shallow components of large-scale hydrothermal systems where the mineralizing fluid flow was focussed, Potter & Taylor, 2010. The key for exploring potential polymetallic vein gold mineralization in the Gowganda West project is to identify structures that exhibit hydrothermal alteration which could be associated possibly with gold mineralization (iMetal Resources research report, March 2019; Rocks to Riches).

Figure 6: Simplified exploration model for polymetallic vein gold mineralization in the Cobalt Embayment

(modified after Potter & Taylor, 2010). The original portion of the image showing uranium bearing

polymetallic veins is covered up with transparent shade.

2.3 TYPICAL GEOPHYSICAL SIGNATURES OF POTENTIAL POLYMETALLIC VEIN GOLD MINERALIZATION

The direct detection of Archean mesothermal (lode) disseminated gold mineralization in greenstone belts by geophysical methods is highly challenging and unfortunately rarely successful in exploration; detection is further complicated by the presence of minerals that have a geophysical response but are not of economic interest, for example, disseminated barren sulphides (Mir, Perrouty, Astic, Bérubé & Smith, 2019). If the Archean greenstone belts are covered by Proterozoic sediments, then the task of exploring for polymetallic vein gold mineralization is even more difficult geophysically. The airborne magnetic and time-domain electromagnetic (TDEM) signatures of potential


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polymetallic vein gold mineralization can be even more challenging. Whereas, in some cases, airborne EM has been successful at defining EM conductors from semi-massive sulphide indirectly associated with known Au deposits, such as Borden Gold (Orta et al., 2019, in press), Casa Berardi and Detour Lake (Devriese and Witherly, 2018). However, in general, disseminated sulphides associated with gold mineralization, i.e., disseminated chalcopyrite and pyrite, are typically barely detectable by TDEM systems as strong or moderate or even poor conductors. In the case of disseminated sulphide Au deposits, it has been proposed (Kwan et al., 2019 in press; Kaminski et al., 2017) that Airborne Inductively Induced Polarization (AIIP) mapping could potentially be used to map the weak and chargeable conductive zones associated with hydrothermally altered clays located at very shallow depths (< 100 m in resistive terrains). The airborne magnetic data reflect in general the magnetite content in the ground and are routinely used to map magnetite depletion due to hydrothermal alteration that relates to possible gold mineralization, and more commonly to also map lithology, geological structures such as faults or contacts. Typical and detectable geophysical (airborne magnetic and time-domain electromagnetic TDEM) expressions of polymetallic vein gold mineralization are summarized below; Airborne Magnetic/TDEM Signatures Causes

Magnetic highs metavolcanics;

Magnetic lows Sediments, metasediments, faults, magnetite depletion;

Increased conductivity (AIIP) Hydrothermal clays;

Chargeability (AIIP) Hydrothermal clays;

The main objective of this interpretation project is to identify exploration targets for possible polymetallic vein gold mineralization in the Gowganda West project. The objective could be achieved by identifying second order faults splayed off district-scale fault/shear zones that may be accompanied by alteration zones in close proximity. The possible alteration zones may have strong AIIP signatures.


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3. INTERPRETATION OF MAGNETIC DATA Because the polymetallic vein gold mineralization is structurally controlled, it is important to map the basement faults from the magnetic data.

3.1 MAGNETIC DATA INTERPRETATION The first vertical derivative data of the reduced to the magnetic pole (RTP) of Gowganda West project are shown in Figure 7. The inferred and known faults, as well as the dykes, are also displayed.

Figure 7: Frist vertical derivative of the RTP data, with the inferred and known faults and dykes overlay.

3.2 MVI INVERSION In conventional 3D magnetic inversions, the direction of the earth’s magnetic field is assumed to be in the same direction as the anomalous magnetic field (MacLeod and Ellis, 2013). Conventional 3D magnetic inversions typically consider the induced magnetization only. In many cases the direction of the anomalous field is a different from the earth’s inducing field due to remanent magnetization and potentially other factors. Magnetic Vector Inversion (MVI) is commonly used to resolve the issue of magnetic remanence. In the MVI process the total field magnetic data is inverted for a three-component subsurface magnetization vectors as oppose to a to a conventional scalar susceptibility value (Lelièvre and


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Oldenburg, 2009). Along with the three dimensional vector information the MVI results also include a scalar MVI susceptibility. Using the total magnetic intensity data of regular survey lines (no ties) from the VTEM survey, 3D MVI inversion (Ellis et al., 2012) is carried out. The size of the mesh in the horizontal direction (X and Y) is 50 m and in vertical direction (Z) is 25 m. The MVI deliverables include databases, voxels, depth slices, 3D section grids, 2D section maps, and PDF files showing all the sections on a line by line basis for the traverse lines. The MVI 500 m magnetization amplitude (susceptibility) depthslice data are shown in Figure 8. Several district-scale fault zones trending mainly in the NW-SE direction (same direction as the Tyrrell Fault to the north) are inferred from the depthslice. The polymetallic vein gold exploration zones Z1, Z1-S and Z-2 are located just off the major faults.

Figure 8: The MVI 500 m magnetization amplitude depthslice and the inferred basement district-scale fault

zones.

The MVI 250 m magnetization amplitude depthslice data are also shown in Figure 9.


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Figure 9: The MVI 250 m magnetization amplitude depthslice and the inferred district-scale fault zones.


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4. AIRBORNE INDUCTIVELY INDUCED POLARIZATION (AIIP)

4.1 AIIP MAPPING The objective of AIIP mapping of the VTEM data is to derive Cole-Cole parameters for a fixed frequency factor c. Airborne VTEM data from the Gowganda West project reflect mainly two physical phenomena in the earth:

1. Electromagnetic (EM) induction, related to sub-surface conductivity and governed by Faraday’s Law of induction;

2. Induced polarization (IP) effect, related to the relaxation of polarized charges in the ground (Pelton et al., 1978, Weidelt, 1982, Kratzer and Macnae, 2012 and Kwan et al., 2018 and 2015)

For mineral exploration, near-surface sources of AIIP are clays through membrane polarization (electrical energy stored at boundary layer) and most metallic sulphides (fine-grained < 0.2 mm; see Appendix B for more details), some oxides (i.e. magnetite) and graphite through electrode polarization (electrical charges accumulated through electrochemical diffusion at ionic-electronic conduction interfaces). The absence of negative transients does not preclude the presence of AIIP (Kratzer and Macnae, 2012). The case is clearly illustrated in Figure 10, showing forward modeled VTEM decays over a chargeable half-space of different chargeabilities, using the Cole-Cole relaxation model (explained in Appendix B). As chargeability value increases from m=0 (purely inductive), the rate of VTEM decay increases (pulling down) also in mid-times and eventually crosses into the negative when m≈0.8 V/V. But for vast majority of m values less than 0.8 V/V, there are no negatives in the VTEM decays. The amount of deviation from the ideal inductive response of a half space with resistivity 0 is a

measure of the strength of AIIP.


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Figure 10: Forward modelled VTEM decays for different chargeability m values; the observed VTEM decay

(black) was from Mount Milligan, British Columbia, fits well with the modeled decay (red) with m=0.66.

The Cole-Cole parameters, e.g., AIIP apparent resistivity, apparent chargeability and Cole-Cole time-constant, for a given frequency factor c can be extracted from VTEM data using the AIIP mapping algorithm described fully in Appendix A. AIIP processing is applied to VTEM data desampled to 10 m interval. VTEM data with ground clearances greater than 100 m are excluded from AIIP mapping.

4.2 DETERMINATION OF FREQUENCY FACTOR C Geotech’s AIIP chargeability mapping algorithm described in Appendix A requires fixed frequency factor c, while the Cole-Cole resistivity, chargeability and time constant are allowed to vary. The determination of frequency factor c for selected VTEM data is carried out by interactive forward modelling software, also based on Airbeo from CSIRO/AMIRA. The locations of selected VTEM decays from the VTEM data for c calculations, over EM induction time-constant TAU, are shown in


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Figure 11. Eight (8) frequency factor c values are determined from the selected VTEM decays in relatively resistive areas. All c values equal to 0.7.

Figure 11: The locations of VTEM decays for Cole-Cole frequency factor c determinations over EM

induction time-constant TauSF data.

Full Cole-Cole forward modelling results for four selected VTEM decays are shown in Figure 12.


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Figure 12: Cole-Cole parameters of four AIIP forward models from Eastmain block and corresponding decays; purely inductive m=0 (green), observed data (black) and forward modeled data (red).

Typical Cole-Cole spectra for c=0.7 is shown in Figure 13. The width of the phase curve depends on c. For large c, the grain sizes of the polarizable material are distributed in a narrow range (or more uniformly distributed). The peak of the phase curve is related to the Cole-Cole time-constant , or the average grain size of the polarizable materials.


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Figure 13: The relationship between the distribution of grain sizes and the frequency factor c is illustrated in the Cole-Cole spectra of c=0.7.

4.3 AIIP DEPTH OF INVESTIGATION

Using a buried chargeable prism in a uniform, non-polarizable ground, the depth of investigation of AIIP is studied. A 200 m by 200 m by 20 m prism of resistivity 𝜌1 = 10 ∙ 𝑚, 𝑚 = 0.6 v/v, = 0.0003𝑠 𝑎𝑛𝑑 𝑐 = 0.7 is placed at various depths below ground in a resistive half space of resistivity 𝜌0 = 500 ∙ 𝑚, Figure 14. The size of the prism is within the footprint of the VTEM system. The software MarcoAir (CSIRO/AMIRA, Xiong and Tripp 1995) is used to generate the synthetic VTEM data in the AIIP depth of investigation. MarcoAir computes the airborne electromagnetic responses for prisms in layered earth. The Cole-Cole relaxation model is incorporated in MarcoAir.


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Figure 14: The setup of the 3D prismatic model for AIIP depth of investigation.

The AIIP apparent chargeability maps for the prisms buried at 50m, 75m and 100m depths are shown in Figure 15. For the case of 50 m deep prism, the maximum value of the recovered AIIP apparent chargeability is 0.63 V/V. The maximum recovered AIIP apparent chargeability for the 75m deep prism is 0.49 V/V. At 100m depth, maximum recovered AIIP apparent chargeability is 0.36 V/V, and the prism can still be detected and mapped by the VTEM system.


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Figure 15: AIIP apparent chargeabilities for prisms located 50m, 75m and 100m below ground; the same color scheme is used.

The AIIP apparent resistivity maps for the prisms buried at 50m, 75m and 100m depths are shown in Figure 16.


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Figure 16: AIIP apparent resistivities for prisms located 50m, 75m and 100m below ground; the same color scheme is used.

The Archean metavolcanics and the Proterozoic Gowganda Formation and Nipissing sills in the Gowganda West project area are fairly resistive in general, >500 ∙ 𝑚. Therefore, the AIIP depth of investigation should be greater than 75 m, but still less than 100 m.


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4.4 AIIP MAPPING RESULTS The DEM data of Gowganda West are shown in Figure 17. The relatively higher grounds are located in the eastern part of the VTEM block. Two drainage systems in the central part of the block are trending NS. The drainages in the western part are trending mainly NW-SE, e.g., the Soot and Spider Lakes.

Figure 17: The Digital Elevation Model (DEM) data.


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The AIIP apparent resistivity data are shown in Figure 18. As expected the AIIP apparent resistivity results correlate very well with the VTEM data and related RDI resistivity imaging results (see GL180370 logistics report). The relatively strong AIIP conductive zones are located in the central parts of the VTEM block, in low-lying areas or drainages, and in the western parts in Soot and Spider Lakes.

Figure 18: AIIP apparent resistivity data.


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The AIIP apparent chargeability data are shown in Figure 19. The strongest chargeability responses are located in low-lying areas or drainages SE of Z-1 & Z1-S, north of Z-3, east of Z-2 and in Soot and Spiker Lakes. It is interesting to note that there is no strong chargeability response in the low-lying areas north of Z-4.

Figure 19: AIIP apparent chargeability data.


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The Cole-Cole time-constant data are shown in Figure 20. The Cole-Cole Tau data reflect the size of polarizable grains, albeit all fine grained. However, the relatively coarser grained polarizable materials (possibly hydrothermal clays) are located SE of Z-1 (Z1-S), east of Z-2, north of Z-3 and in the southern end of Spider Lake.

Figure 20: Cole-Cole time-constant data.


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The tau-scaled chargeability (apparent_chargeability*Cole-Cole_time-constant) data (TSC; Kwan et al. 2018) will highlight the areas with strong chargeable responses and relatively coarser grain sizes. Detailed descriptions of TSC are provided in Appendix B. The TSC data are shown in Figure 21. The TSC highs are located SE of Z-1 (Z1-S), east of Z-2, north of Z-3, and in the Soot Lake and the southern end of Spider Lake.

Figure 21: The tau-scaled chargeability (TSC) data.


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5. SELECTION OF POTENTIAL EXPLORATIONTARGETS The selection of potential exploration targets for polymetallic vein gold mineralization in Gowganda West project is based on the structural and geophysical characteristics within the surrounding areas as discussed in Section 2.3. The selected potential polymetallic vein gold mineralization prospective zones are:

in close proximity to regional-scale shear/fault zones in the Archean basement belong the Huronian Gowganda Formation sediments;

close to strong AIIP chargeability and Cole-Cole time-constant responses, e.g., tau-scaled chargeability (TSC) highs;

having higher-order known or inferred faults splayed off the district-scale shear/fault zones; Seven (7) potential exploration prospects for possible polymetallic vein gold mineralization are selected for the Gowganda West project and are shown in Figure 22, over the tau-scaled chargeability (TSC) data. The UTM coordinates of the targets are provided in Appendix C – Final Deliverables. The results show that the targets are associated with a mix of TSC highs, moderate highs and even lows and contact type signatures that could be associated with extensive hydrothermal alteration zones. The extensive TSC highs in the waterbodies could be associated with hydrothermal and polarizable materials, e.g. clays, which could be transported from higher elevation grounds.

Figure 22: Selected potential exploration targets for possible polymetallic vein gold mineralization over the

TSC data.


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Figure 23 presents the seven (7) potential exploration prospects for possible polymetallic vein gold mineralization over the 500 m MVI magnetization amplitude depthslice. It reveals that the targets are mainly associated with weak magnetic susceptibility (magnetite depletion) and located in close proximity to the inferred district-scale faults the trending in the same NW-SE direction as the Tyrrell Fault to the north. These inferred district-scale faults could act as conduits for transporting Au-carrying mineralizing fluids.

Figure 23: Selected potential exploration targets for possible polymetallic vein gold mineralization over the

3D MVI magnetization amplitude 500 m depthslice.


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A number of potential gold targets have been picked by iMetal, based on favourable VTEM conductivity high and magnetic low associations and the picks were provided to Geotech (Dave Gamble, pers. comm. with JM Legault, April 12, 2019) and are shown in Figure 24. Most of iMetal’s picks are located in clusters around the Geotech targets, i.e., B2 and A6 around GWG_07; B1 and A3 around GWG_06; A1, A2, A7 and A8 around GWG_01; A11, B3 and B4 around GWG_02. Target A9 from iMetal coincides with the southern part of GWG_04. Geotech’s picks have the benefits of AIIP/MVI products, in addition to the magnetic and EM induction time-constant data. There are no picks from iMetal in the eastern parts of the VTEM block in the Leith and Milner Townships for now, whereas Geotech picks a low priority target GWG_05 in the area.

Figure 24: Selected potential Au targets (A1-A12, B1-B4) from iMetal Resources (D. Gamble, pers. comm.,

April, 2019) over the EM induction time-constant and the potential Au target zones (GWG_01 to GWG_07) identified by Geotech.


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Descriptions of the high priority targets GWG_01 and GWG_02 Potential exploration targets GWG_01 and GWG_02 are located short distances off an inferred district-scale fault trending in approximately NW-SE direction, possibly in the extension of the South Corridor Au Trend (iMetal Resources website). The northern end of GWG_01 covers the Z-1 and Z1-S Au zones. There are strong AIIP responses north of the GWG_01 and south of GWG_02 in the low-lying areas or drainages. GWG_03 Potential polymetallic vein gold exploration target GWG_03 is located south of an inferred regional-scale fault. The northern part of the target zone covers the Z-2 Cu-Au zone (iMetal). There are strong AIIP responses north of the target zone, in drainages. GWG_04 Potential target GWG_04 is located north of an inferred district-scale fault. The Z-3C Cu-Au zone (iMetal) is located to the south (outside VTEM survey block). There are strong AIIP responses north of GWG_04. GWG_05 Potential target GWG_05 is located just north of an inferred district-scale fault (same one for GWG_03). GWG_06 Potential polymetallic vein gold mineralization target GWG_06 is located just north of an inferred regional-scale fault, east of Soot Lake. There are strong AIIP responses in the Soot Lake, possibly associated with hydrothermal clays. GWG_07 Potential target GWG_07 is located just east of the Spider Lake, where there are some strong AIIP responses possibly associated with hydrothermal clays. There are high Au geochemical anomalies west of the Spider Lake (see Figure 2).


28

6. CONCLUSIONS AND RECOMMENDATIONS

A helicopter-borne versatile time domain electromagnetic (VTEM™plus), horizontal magnetic gradiometer geophysical survey has been completed, in December 2018, over the Gowganda West project situated near Gowganda, Ontario. The AIIP mapping of the VTEMTM electromagnetic (EM) data and MVI 3D inversion of the magnetic data have been carried out on behalf of iMetal Resources Inc. (iMetal). The objective of interpretation of VTEMTM magnetic, EM, MVI depthslices and selected AIIP tau-scaled chargeability data is to identify potential exploration targets or prospects for possible polymetallic vein gold mineralization in the Gowganda West project area. Since the polymetallic vein gold mineralization is structurally controlled, the identification of district-scale fault zones is of the paramount importance, and this is achieved by interpreting the MVI depthslices at 500 m level. Additionally, potential polymetallic vein gold mineralization may be associated with hydrothermal alteration. One of the hydrothermal alteration products is the fine-grained clays, which can be detected at shallow depths less than 100 m by AIIP. The potential exploration targets for possible polymetallic vein gold mineralization should have weak to moderately AIIP signatures (tau-scaled chargeability) and should be located in close proximity to regional-scale shear or fault zones. Seven (7) potential exploration targets, GWG_01 to GWG_07, for possible polymetallic vein gold mineralization in the Gowganda West VTEM survey area have been identified. We recommend that the follow-up should begin with the evaluation of the selected potential exploration target zones using all available geoscientific data available to iMetal, including geochemistry soil sampling, trenching and drilling results. If there are existing airborne or ground geophysical data, especially ground IP, they should be evaluated carefully as well. Ground IP follow-up is nevertheless recommended prior to drill testing. If the selected potential exploration targets have to be ranked, then the ranking of the targets is given below;

Potential Targets Rank GWG_01, GWG_02, GWG_03, GWG_04 First priority GWG_06, GWG_07 Second priority GWG_05 Third priority

The final AIIP and interpretation deliverables include:

AIIP databases and grids; MVI products; Interpretation maps; Polygons for selected targets; Interpretation report.


29

Respectfully submitted,

____________________________________________ ___________________________________________ Karl Kwan, M.Sc. P.Geo. (Limited1) Jean M. Legault, M.Sc.A, P.Eng, P.Geo. Senior Geophysicist/Interpreter Chief Geophysicist ____________________________________________ Kanita Khaled, P.Geo. Project Manager Geotech Ltd. April 26, 2019

1 The designation of P.Geo (Limited) by Association of Professional Geoscientists of Ontario permits the principal interpreter to practice in the field of exploration geophysics only.


30

ACKNOWLEDGEMENTS The AIIP chargeability mapping algorithm, developed by Geotech, is based on Airbeo (CSIRO/AMIRA), which is part of a suite of software of project P223F released to the public in 2010 by CSIRO/AMIRA.

REFERENCES

Ayer, J.A., Barrett, T.J., Creaser, R.A., Hamilton, M.A., Lafrance, B. and Stott, G.M., 2013, Section 1: Shining Tree and Gowganda Archean gold study and northern Cobalt Embayment Proterozoic vein study; report in Results from the Shining Tree, Chester Township and Matachewan Gold Project in the Northern Cobalt Embayment Polymetallic Vein Project, Ontario Geological Survey, Miscellaneous Release – Data 294. Campbell, Joe, Sexton, Alan and Studd, Duncan, 2014: NI 43-101 technical report on the updated mineral resource estimate for the Juby gold project, Tyrrell Township, Shining Tree area, Ontario, for Temex Resources Corp. Cole, K. and Cole R., 1941: Dispersion and absorption in dielectrics, Part I. Alternating current characteristics: Journal of Chemical Physics, 9, 341-351. Devriese, Sarah G.R. and Witherly, Ken, 2018: Lessons from the past: exploring for Abitibi greenstone-hosted gold deposits using geophysics, Extended Abstract, SEG Anaheim 2018 International Exposition and 88th Annual Meeting. Easton, R. Michael, 2000: Metamorphism of the Canadian Shield, Ontario, Canada; Part II: Proterozoic metamorphic history, The Canadian Mineralogist, 38, 319-344. Ellis, Robert G., de Wet Barry and MacLeod, Ian N., 2012, Inversion of Magnetic Data from Remanent and Induced Sources, ASEG-PESA, 22nd International Geophysical Conference and Exhibition, Brisbane, Australia. Hamilton, S.M., 1997: A high density lake sediment an water geochemical survey of 32 geographic townships in the Montreal River headwaters area, centred on Gowganda, Ontario; Ontario Geological Survey, Open File Report 5962, 156p. Kaminski, Vladislav and Viezzoli, Andrea, 2017: Modeling induced polarization effects in helicopter time-domain electromagnetic data: Field case studies, Geophysics, 82, 2, B49-61. Kratzer, T. and Macnae, J.C., 2012: Induced polarization in airborne EM, Geophysics, 77, E317-327. Kwan, Karl, Legault, Jean M and Khaled, Kanita, 2019: Understanding Archean greenstone-hosted gold mineralization in Ontario Canada through helicopter TDEM data, Expanded Abstract, AEGC 2019: From Data to Discovery, Perth, Australia (in press). Kwan, Karl, Legault, Jean M., Johnson, Ian, Prikhodko, Alexander and Plastow, Geoffrey, 2018: Interpretation of Cole-Cole parameters derived from helicopter TDEM data – Case studies, Extended Abstract, SEG Anaheim 2018 International Exposition and 88th Annual Meeting.


31

Kwan, K., Prikhodko, A., Legault, Jean M., Plastow, G., Xie, J. and Fisk, K., 2015: Airborne Inductive Induced Polarization Chargeability Mapping of VTEM data, ASEG-PESA 24th International Geophysical Conference and Exhibition, Perth, Australia. Lelièvre, P. G., and D. W. Oldenburg, 2009: A 3D total magnetization inversion applicable when significant, complicated remanence is present: Geophysics, 74, L21-L30, doi: 10.1190/1.3103249. Luo Y. and Zhang G. 1998: Theory and application of Spectral Induced Polarization, Geophysical Monograph Series. MacLeod, Ian N. and Ellis, Robert G., 2013, Magnetic Vector Inversion, a simple approach to the challenge of varying direction of rock magnetization, ASEG-PESA 23rd International Geophysical Conference and Exhibition, Melbourne, Australia. McNeill, JD, 1980: Applications of Transient Electromagnetic Techniques, Technical Note TN-7, Geonics Limited.

Mir, Reza, Perrouty, Stéphane, Thibaut Astic, Thibaut, Bérubé, Charles L. and Smith, Richard S., 2019: Structural complexity inferred from anisotropic resistivity: example from airborne EM and compilation of historical Resistivity/IP data from the gold-rich Canadian Malartic district, Québec, Canada, Geophysics (in press), 1-52, https://doi.org/10.1190/geo2018-0444.1. Nabighian, M. N., 1984: Toward a three-dimensional automatic interpretation of potential field data via generalized Hilbert transforms—Fundamental relations: Geophysics, 49, 780–786. Nelder, J.A., and Mead, R, 1965: A Simplex Method for Function Minimization, Computer Journal, 7 (4), 308-313. Orta, Marta, Legault, J.M., Kwan, K and Espinosa, Sergio, 2019: The Borden Gold deposit, northern Ontario: Contributions of VTEM helicopter time-domain EM and magnetics leading to discovery, Expanded Abstract, AEGC 2019: From Data to Discovery, Perth, Australia (in press). Pelton, W.H., Ward, S.H., Hallof, P.G., Sill, W.R., and Nelson, P.H., 1978, Mineral discrimination and removal of inductive coupling with multi-frequency IP: Geophysics, 43, 588–609. Porter, Eric G. and Taylor, Richard P., 2010: Genesis of polymetallic vein mineralization in the Paleoproterozoic Cobalt Embayment, Northern Ontario: Implications for metallogenesis and regional exploration, Conference Paper, GeoCanada 2010, Working with the Earth; Raiche, A., 1998: Modelling the time-domain response of AEM systems: Exploration Geophysics, 29, 103–106. Weidelt, P., 1982: Response characteristics of coincident loop transient electromagnetic systems, Geophysics, 47, 9, 1325-1330. Wong, J., 1979. An electrochemical model of the induced polarization phenomenon in disseminated sulfide ores: Geophysics, 44, 1245-1265.


32

Xiong, Zonghou and Tripp, Alan C., 1995: A block iterative algorithm for 3-D electromagnetic modeling using integral equations with symmetrized substructures, Geophysics, 60, 1, 291-295.


1

APPENDIX A: AIIP MAPPING

INTRODUCTION

In recent years, it has been widely accepted that the data

acquired by helicopter TDEM systems reflect mainly two

physical phenomena in the earth:

1. Electromagnetic (EM) induction, related to the ground

conductivity and governed by Faraday’s Law;

2. Induced polarization (IP) effect related to the

relaxation of polarized charges in the ground (Weidelt

1982 and Kratzer and Macnae 2012);

It has been shown by Smith and West (1989) that the in-

loop EM system is optimally configured to excite a unique

AIIP response, including negative transients in mid to late

times over resistive grounds, from bodies of modest

chargeability.

Negative transients observed in airborne time domain EM

data (e.g. Smith and Klein, 1996 and Boyko et al. 2001) are

attributed to airborne inductive induced polarization (AIIP)

effects. However, the absence of negative transients does

not preclude the presence of AIIP, because of the IP effect

takes finite time to build up or the IP effect may be

obscured by the conductive ground (Kratzer and Macnae,

2012).

In mineral exploration, near-surface sources of AIIP are

clays through membrane polarization (electrical energy

stored at boundary layer) and most metallic sulphides and

graphite through electrode polarization (electrical charges

accumulated through electrochemical diffusion at ionic-

electronic conduction interfaces). Some kimberlites in Lac

de Gras kimberlite field are known to have AIIP signatures

(Boyko et al., 2001).

The widely used theory to explain the IP effect is the

empirical Cole-Cole relaxation model (Cole and Cole,

1941) for frequency dependent resistivity 𝜌(),

() = 0 [1 − 𝑚 (1 −1

1+(𝑖)𝑐)],

(1)

where 0 is the low frequency asymptotic Cole-Cole

resistivity, m is the Cole-Cole chargeability, is the Cole-

Cole time constant, = 2𝑓, and c is the frequency factor.

The extraction of AIIP chargeability m using the Cole-Cole

formulation from VTEM data had been demonstrated by

Kratzer and Macnae, 2012 and Kwan et al., 2015.

An improved version of AIIP chargeability mapping tool

based on CSIRO/AMIRA Airbeo has been developed for

VTEM system and tested on VTEM data from Mt Milligan,

British Columbia, Canada, and Tullah, Tasmania.

IMPROVED AIIP MAPPING

ALGORITHM Search for m and using Airbeo forward modeling

The extraction of the four Cole-Cole parameters (0, m,

and c) from airborne VTEM data can be a difficult task.

The AIIP mapping algorithm originally developed by

Kwan et al., 2015 suffers lack of precision for the derived

apparent chargeability m and resistivity 0, and is

computationally very slow. Geotech has recently developed

an improved version of AIIP mapping algorithm, based on

Airbeo from CSIRO/AMIRA1 (Raiche 1998) to extract the

(0, m and ) parameters while keeping the frequency

factor c fixed. The new method applies the Nelder-Mead

Simplex minimization (Nelder and Mead, 1965) in the two-

dimensional (m,) plane. At each required test point (mi, i),

the optimal background resistivity 0is found by one-

dimensional Golden Section minimization (Press et al.,

2002). The algorithm uses only Airbeo’s forward modeling

kernel, which can generate synthetic VTEM data with high

precision. The Nelder-Mead AIIP mapping algorithm

generates much more precise (0, m, ) parameters.

The Nelder-Mead Simplex Minimization method can be

explained in the five (5) moves, reflection, expansion,

outside and inside contraction, and shrink, as illustrated in

Figure 1.

Figure 1: Nelder-Mead Simplex moves (modified from

Wright 2012).

The new improved AIIP mapping algorithm based on the

Nelder-Mead simplex minimization consists of following

steps.

Let e(0 , m, ) be the RMS error function defined as

𝑒(0, m, ) =

1

𝑁−1 (∑ ( f(0

, m, , 𝑡𝑖) − 𝑣(𝑡𝑖))2𝑁−1𝑖=0 )1/2 , (2)

where f(

0, m, , 𝑡𝑖) is the forward modelled data and 𝑣(𝑡𝑖)

measured VTEM data at off-time 𝑡𝑖.

1 Commonwealth Scientific and Industrial Research Organization and

Amira International;


2

Step 1 (Sorting)

Sort the vertices such that e(P1) < e(P2) < e(P3). Point P1 is

the best point, P2 is the next-to-worst point and P3 is the

worst point;

Step 2 (Reflection)

Reflect the worst point P3, through the centroid of (P1 and

P2) to obtain the reflected point Pr, and evaluate e(Pr).

If (e(P1) < e(Pr) < e(P2)), then replace the worst point P3

with the reflected point Pr, and go to Step 5.

Step 3 (Expansion)

If (e(Pr) < e(P1)), then extend the reflected point Pr, further

pass the average of P1 and P2, to point Pe, and evaluate

e(Pe)

(a) If e(Pe) < e(Pr), then replace P3 with Pe, and go to Step

5

(b) Otherwise, replace the worst point P3 with the reflected

point Pr, and go to Step 5

Step 4 (Contraction or Shrink)

If the inequalities of Step 2 and 3 are not satisfied, then it is

certain that the reflected point Pr is worse than the next-to-

worst point P2, (e(Pr) > e(P2)) and, a smaller value of e

might be found between P3 and Pr. So try to contract the

worst point P3, to a point Pc between P3 and Pr and

evaluate e(Pc);

The best distance along the line from P3 to Pr can be

difficult to determine. Typical values of Pc are one-quarter

and three-quarter of the way from P3 to Pr. These are call

inside and outside contraction points Pin and Pout;

(a) If MIN(e(Pin), e(Pout)) < e(P2), then replace P3 with

the contraction point Pin or Pout, and to Step 5.

(b) Otherwise shrink the simplex into the best point, P1,

and go to Step 5.

Step 5 (Convergence Check)

Stop if the standard deviation of RMS errors of the current

simplex is less than user-specified tolerance RMSTOL, i.e.

√1

𝑛∑ (𝑒𝑖 − 𝑒𝑎𝑣𝑔)2𝑛−1

𝑖=0 ≤ 𝑅𝑀𝑆𝑇𝑂𝐿, (3)

where 𝑒𝑎𝑣𝑔 is the average of RMS misfits of the current

simplex.

Perhaps the most important feature in the Nelder-Mead

simplex method is Step (4b), the shrink. It allows the shape

of the simplex to “adapt itself to the local landscape”,

Nelder and Mead, 1965. In essence, all the moves in the

Nelder-Mead (NM) Simplex method are designed to move

away from the worst point.

Han and Neumann 2006 showed that the NM simplex

method deteriorates when the number of parameters to be

minimized (n) increases. For n=1 or 2, NM convergence is

acceptable. As n≥3, NM convergence slows dramatically

as N increases. Due to this reason, Geotech applies the NM

method only in the 2D (m,) plane, to ensure convergence

as well as that all the NM moves can be checked visually.

AIIP MAPPING RESULTS

Mt. Milligan, British Columbia, Canada

Mt. Milligan Cu-Au deposit is located within Early Mesozoic Quesnel Terrane that hosts a number of Cu-Au porphyry deposits, Oldenburg et al, 1997. The Mt. Milligan intrusive complex consists dominantly of monzonitic rocks, including the MBX and Southern Star (SS) zones, all which host mineralization at Mt. Milligan (Figure 2). Mineralization in both zones consists of pyrite, chalcopyrite and magnetite with bornite localized along intrusive-volcanic contacts (Terrane Minerals Corp. NI 43-101, 2007). Copper-gold mineralization is primarily associated with potassic alteration with both copper grade and alteration intensity decreasing outwards from the monzonite stocks. Pyrite content increases dramatically outward from the stocks where it occurs in association with propylitic alteration, which forms a halo around the potassic-altered rocks.

Helicopter-borne VTEM surveys, including a small survey over Mt. Milligan, were carried out from July 29th to November 1st, 2007, on behalf of GeoscienceBC as part of the QUEST project in central British Columbia. The data were released to the public by GeoscienceBC and can be downloaded from http://www.geosciencebc.com.

Figure 2: Mt. Milligan geology.

VTEM Z-component data, from 0.091 to 10.126

milliseconds in off-times, were processed to recover the

http://www.geosciencebc.com/


3

AIP apparent chargeability. Very weak negative transients

above noise level are observed in the VTEM data from a

location south of DWBX. The inverted Cole-Cole

chargeabilities are shown in Figure 3. Weak chargeabilities

can be seen along the east and west flanks of the MBX

stock, especially over DWBX, and in a small area

southwest of SS stock. For comparison, the chargeability

slice at 40m depth, created by UBC 3D airborne IP

inversion of the same VTEM data from Kang et al., 2014,

is also shown.

Figure 3: Mt. Milligan AIIP apparent chargeability.

The AIIP apparent resistivity of Mt. Milligan area is shown

in Figure 4. A relatively low resistivity halo can be seen

surrounding the SS stock.

Figure 4: Mt. Milligan AIIP apparent resistivity.

Tullah, Tasmania

The most important metallogenic event in Tasmania

occurred in Middle Cambrian as the post collisional

proximal submarine volcanism and the deposition of the

Mount Read Volcanics (MRV) and associated world-class

deposits (Seymour et al., 2007).

The study area is located near Tullah, northwest Tasmania.

The western half of the study area is covered by Late

Cambrian quartz sandstone, Ordovician limestone and

Quaternary alluvium and marine sediments (Figure ). The

eastern half is dominated by the Middle Cambrian

volcanics (Corbett, 2002).

The Mount Lyell, located south of the study area, hosts 311

Mt 0.97% Cu and 0.31 g/t Au disseminated chalcopyrite-

pyrite ore bodies in alteration assemblages of mainly

quartz-sericite or quartz-chlorite-sericite.

Figure 5: Regional geology of study area, Tullah,

Tasmania.

From December 2012 to February 2013, Geotech carried

out a helicopter-borne geophysical survey over the study

area. Numerous negative transients were observed in the

VTEM voltage data (Figure ). The Z-component data, from

0.216 to 7.56 milliseconds in off-times, were processed for

AIIP apparent chargeability.


4

Figure 6: Sum of negative transients and two VTEM

profiles, Tullah, Tasmania.

The amplitudes of VTEM data over resistive grounds are

relatively now. If the number of decay data in the off-time

windows is below a user specified noise threshold, then the

decay will be skipped. The calculated AIIP apparent

chargeability and resistivity of the study area are shown in

Figure . The chargeability map follows the sum of negative

transients closely. The sources of the AIIP could be clays

or sulphides, or a combination of both.

Figure 7: AIIP apparent chargeability and resistivity,

Tullah, Tasmania.

DISCUSSION

For real VTEM data contaminated with noise and geology

different from uniform half-space, two constraints, a

restricted range of inverted apparent resistivity and the use

of proper frequency factor, are required in order to for AIIP

mapping tool to generate geologically meaningful outputs.

The range of acceptable inverted AIIP apparent resistivity

can be estimated by other means and one of them is the

Resistivity Depth Imaging (RDI) technique based on the

transformation scheme described by Meju (1998).

Extensive discussions on frequency factor are provided in

Pelton et al. (1978). A reasonable average of frequency

factors can be obtained using AIIP forward modeling of

VTEM decays of selected locations within a survey area. If

the frequency factors are widely distributed, then AIIP

mapping should be run using several frequency factors.

CONCLUSION

An improved version of AIIP mapping tool based on

Airbeo (CSIRO/AMIRA) has been created for the in-loop

VTEM system, which is optimally configured to excite a

unique AIIP response, including negative transients in mid

to late times over resistive grounds from bodies of modest

chargeability. Test results on field VTEM data prove that

the new AIIP mapping tool can work, if the inverted

resistivity range is restricted and the proper frequency

factor is used. The derived AIIP apparent chargeability map

provides additional information for the interpretation of

VTEM data.

ACKNOWLEDGMENTS

We would like to thank Yunnan Tin Australia Pty Ltd. for

permission to use the VTEM data from an area near Tullah,

Tasmania for this study. This work is not possible without

the source codes from CSIRO/AMIRA project P223F.

REFERENCES

Boyko, W., Paterson, N.R. and Kwan, K., 2001, AeroTEM

characteristic and field results: The Leading Edge, 20,

1130-1138.

Cole, K. and Cole R., 1941, Dispersion and absorption in

dielectrics, Part I. Alternating current characteristics:

Journal of Chemical Physics, 9, 341-351.

Corbett, K.D., 2002: Updating the geology of the Mount

Read Volcanics belt Western Tasmanian Regional Minerals

Program Mount Read Volcanics Compilation: Tasmanian

Geological Survey Record 2002/19, Mineral Resources

Tasmania, Department of Infrastructure, Energy and

Resources, Tasmania.

Han, Lixing and Neumann, Michael, 2006, Effect of

dimensionality on the Nelder-Mead simplex method,

Optimization Methods and Software, 21, 1-16.

Kang, S., Oldenburg D.W., Marchant, D., Yang, D. and

Haber, E., 2014, On recovering IP information from

airborne EM data: presented at Geotech airborne

geophysics workshop, AME BC Mineral Exploration

Roundup 2014 Conference.

Kratzer, Terence and Macnae, James C., 2012: Induced

polarization in airborne EM: Geophysics, 77, E317-327.

Kwan, K., Prikhodko, A., Legault, Jean M., Plastow, G.,

Xie, J. and Fisk, K., 2015: Airborne Inductive Induced

Polarization Chargeability Mapping of VTEM data, ASEG-

PESA 24th International Geophysical Conference and

Exhibition, Perth, Australia.

Meju, Maxwell A., 1998: A simple method of transient

electromagnetic data analysis: Geophysics, 63, 405-410.

Nelder, J.A., and Mead, R, 1965: A Simplex Method for

Function Minimization, Computer Journal, 7(4), 308-313.

Oldenburg, Douglas W., Li, Yaoguo and Ellis, Robert G.,

1997: Inversion of geophysical data over a copper gold

porphyry deposit: a case history for Mt. Milligan:

Geophysics, 62, 1419-1431.

Pelton, W.H., Ward, S.H., Hallof, P.G., Sill, W.R., and


5

Nelson, P.H., 1978, Mineral discrimination and removal of

inductive coupling with multi-frequency IP: Geophysics,

43, 588–609.

Press, W.H., Teukolsky, S.A., Vetterline, W.T. and

Flannery, B.P., 2002: Numerical Recipes in C, The Art of

Scientific Computing, 2nd Edition, Cambridge University

Press.

Raiche, A., 1998: Modelling the time-domain response of

AEM systems: Exploration Geophysics, 29, 103–106.

Seymour, D.B., Green, G.R. and Calver, C.R., 2007: The Geology and Mineral Deposits of Tasmania: A summary: Geological Survey Bulletin, 72.

Smith, R. S. and J. Klein, 1996, A special circumstance of

airborne induced polarization measurements: Geophysics,

61, 66–73.

Smith, R. S. and West, G.F., 1989, Field examples of

negative coincident-loop transient electromagnetic

responses modeled with polarizable half-planes:

Geophysics, 54, 1491-1498.

Welhener, H., Labrenz, D., and Huang, J., 2007, Mt.

Milligan Project Resource Report, Omenica Mining

District: technical report (NI43-101) prepared for Terrane

Metals Corp., by Independent Mining Consultants, Inc.,

113 p.

Witherly, K., Irvine, R., and Morrison, E.B., 2004, The

Geotech VTEM time domain electromagnetic system:

SEG, Expanded Abstracts, 1217-1221.

Wright, Margaret, 2012: Nelder, Mead, and the other

simplex method, Documenta Mathematica, Extra Volume

ISMP, 271-276.


1

APPENDIX B: INTERPRETATION OF COLE-COLE PARAMETERS

Introduction

The interpretation of Cole-Cole parameters may be

enhanced by considering the AIIP normalized chargeability

𝑚/0 and the AIIP tau-scaled chargeability (TSC) 𝑚 ∙ .

The former is analogous to the metal factor (MF). It

responds well to clay and is here given the label AIIP Clay

Factor. The TSC is better suited for tracking relatively

more chargeable materials with relatively longer Cole-Cole

time-constants. The implications of AIIP normalized and

tau-scaled chargeabilities for mineral exploration are

demonstrated with cases from the Tli Kwi Cho kimberlite

complex in Lac de Gras, NWT, Canada and the Cerro

Quema high sulphidation epithermal gold deposits in

Panama.

Pelton et al., 1978 were the first to demonstrate the

suitability of the Cole-Cole impedance model to explain the

results from IP/resistivity surveys and the amplitude and

phase responses of various IP targets. Johnson (1984)

applied the Cole-Cole model to time domain IP. Under the

Cole-Cole model, the dispersive resistivity 𝜌() is defined

as,

() = 0 [1 − 𝑚 (1 −1

1 + (𝑖)𝑐)] (1)

where 0 is the low frequency asymptotic resistivity, m

(0≤ 𝑚 ≤ 1.0) is the Cole-Cole chargeability in (V/V), is

the Cole-Cole time-constant in seconds and = 2𝑓, and c

(0≤ 𝑐 ≤ 1.0 ) is the frequency factor. The Cole-Cole time-

constant is not the time-constant used to characterize a

purely exponential decay, commonly used to model VTEM

decays with no AIIP contribution. The four Cole-Cole

parameters (0, m, and c) are characteristic of the intrinsic

polarizability of the ground. In general, the Cole-Cole

chargeability m and time-constant depend on the quantity

and size of polarizable material (Pelton et al., 1978). The

frequency factor reflects the size distribution of the

polarizable elements (Luo and Zhang, 1998).

AIIP tau-scaled chargeability 𝒎 ∙ and normalized

chargeability 𝒎/𝟎

The Cole-Cole chargeability m is related to the quantity or

volume percent/volume of chargeable material in the

ground, and Cole-Cole time-constant is related to grain

size; see Figure 1a taken from Pelton et al., 1978. The

current range of AIIP tau sensitivity for VTEM systems

operating with a base frequency of 25/30 Hz is 10−5 to

10−3 seconds. In the exploration for potentially economic

sulphide mineralization, AIIP anomalies with relatively

high sulphide content and fine-grained (in AIIP) are

preferred as potential targets, as the region of interest

highlighted by a red dashed ellipse.

Figure 1: (a) Metallic sulphide content and grain size contours over

the chargeability vs Cole-Cole time-constant (from Pelton et al.,

1978), and (b) the 𝑚 ∙ 3D surface plot showing high values

occur only if both 𝑚 and are high.

One way to select high chargeability 𝑚 and high Cole-Cole

time-constant anomalies is to use the product 𝑚 ∙ . As

illustrated in Figure 1b, the surface 𝑚 ∙ is high if and

only if both m and are high. The product 𝑚 ∙ can be

considered as a good indicator of chargeable materials in

the ground with relatively longer Cole-Cole time-constant

or grain sizes in the order of 0.2 mm.

The ratio 𝑚/0 was named by Lesmes and Frye, 2001, the

normalized chargeability (MN), which was proposed first

by Keller, 1959, and called the “specific capacity”. The

normalized chargeability was further developed and

interpreted by Slater and Lesmes, 2002. The normalized

chargeability quantifies the magnitude of surface

polarization and is proportional to quadrature conductivity.

For non-metallic minerals, the quadrature conductivity is

closely related to surface lithology and chemistry.

Normalized chargeability varies linearly with clay content

(Slater and Lesmes, 2002). Therefore, we called the

normalized chargeability the AIIP Clay Factor (CF).

In frequency-domain galvanic IP the Metal Factor (MF) is

defined as 𝑀𝐹 = 2 × 105𝐹𝐸/𝑑𝑐 (Marshall and Madden,

1959), where 𝐹𝐸 = (𝑑𝑐 − 𝑎𝑐)/𝑎𝑐 , and 𝑑𝑐 and 𝑎𝑐 are

apparent resistivities measured at DC and very high

frequency (Slater and Lesmes, 2002). The frequency effect

𝐹𝐸 and the chargeability 𝑚 are closely related (Slater and

Lesmes, 2002, equations 11 and 12). Consequently, AIIP

CF is analogous to MF in spectral IP for clays.

Tli Kwi Cho DO-27/DO18 kimberlites, Lac de Gras,

NWT, CAN

The DO-27 and DO-18 are two well-known kimberlites in

the Tli Kwi Cho (TKC) kimberlite complex, located about

360 kilometers NE of Yellowknife, Northwest Territories,

Canada, in the Lac de Gras kimberlite cluster of the

Archean Slave Craton, Jansen & Witherly, 2004 (Figure

2a). The kimberlites are located in the permafrost zone. The


2

outline of the DO-27 and DO-18 is shown in Figure 2b.

The magnetic signatures from the TKC kimberlites are

easily identifiable (Figure 2c). DO-27 is coincident with a

shallow-lake, while DO-18 is exposed (Figure 2d).

Figure 2: (a) The location of TKC complex in the Archean Slave Craton; (b) the outline of TKC complex and DO-27/DO-18

kimberlites, and two geological sections over DO-27 (from Jansen

& Doyle, 2000); (c) and (d) The total magnetic intensity and digital elevation data acquired from the helicopter VTEM survey.

The improved AIIP mapping is applied to the helicopter

VTEM data over the two pipes. The Z-component dB/dt

voltage data in off-time windows from 0.12 milliseconds to

6.9 milliseconds are used. Cole-Cole parameters (0, m, )

are derived using a fixed frequency factor c of 0.7.

The AIIP CF data in (mV/V*S/m) and TSC data in

(V/V*Milliseconds) are shown side by side in Figure 3.

They look quite similar (Figure 3c). The distribution

pattern of both seems to be spatially associated with the

TKC kimberlite complex, and they almost match perfectly

with DO-27, strongly suggesting that the AIIP effects over

the TKC kimberlites are related to clay. However, the

electrical properties of DO-18 and DO-27 are different, as

the former is quite resistive and the latter relatively

conductive (Figure 3b). Kang et al. 2017 suggest that the

AIIP source may be a frozen ice/clay mixture (highly

resistive) at DO-18 and conductive clay for DO-27 and

both show strong chargeable responses (Figure 3a). We

agree. In the study of Drybones Bay kimberlite, NWT,

Kaminsky & Viezzoli, 2017 concluded also that the clay in

the lake sediments is the main source of AIIP effects.

It is worth noting that the CF and TSC data being quite

similar over the TKC complex. For non-metallic minerals

at low frequencies (𝑓 ≤ 1000 𝑘𝐻𝑧), the imaginary part of

the low-frequency complex conductivity can be considered

a function of the surface conductivity, and the imaginary

component is primarily indicative of the surface

polarization, Slater & Lesmes, 2002. The Cole-Cole time-

constant is proportional to the surface area of clay grains,

i.e., ≈ 𝑘𝑟2, where k is a constant and r is the radius of the

chargeable grain (Revil, Florsch & Mao, 2015), or

TSC=𝑚 ≈ 𝑚𝑘𝑟2. CF and TSC are related to the surface

conductivity/polarization and specific surface area of clay,

and hence their similarities.

Figure 3: Cole-Cole (a) apparent chargeability, (b) apparent resistivity, (c) time-constant, (d) The normalized chargeability or

Clay Factor (CF), and (e) the TSC over the TKC complex;

Cerro Quema high sulphidation epithermal gold

deposits, Panama

A helicopter-borne VTEM, magnetic and gamma-ray

spectrometric survey was carried out in March 2012 over

the Cerro Quema high sulphidation epithermal gold

deposits located in the Azuero Peninsula, Panama, Figure

4a. The survey was flown on behalf of Pershimco

Resources Inc.

The study area consist of mainly sedimentary,

volcaniclastic and extrusive volcanic rocks of the Rio

Quema Formation, deposited in a forearc basin, overlying

the Azuero Igneous Basement, Corral et al. 2011, Figure

4d. The Cerro Quema gold deposits (La Pava, Quemita and

Quema) are hosted in the Upper Unit of the Rio Quema

Formation, an east to west trending belt of porphyritic,

pyroclastic flows, and lavas of dacite and andesite

composition. The Rio Joaquin Fault is located to the south

of the deposits. The deposits are located in elevated

grounds, Figure 4b.

Figure 4: (a) Survey area; (b) The Digital Elevation Model (DEM) data; (c) Alterations section over the La Pava deposit (after Valliant et al., 2011); (d) General geology of the study


3

area (after Corral et al., 2011).

Three alteration types are identified by detailed geologic

mapping and drill core logging: silica-pyrite, clay-pyrite

and propylitic alteration (Valliant et al., 2011), Figure 4c.

Figure 5: Cole-Cole (a) apparent chargeability, (b) apparent

resistivity, (c) time-constant and (d) RTP data from Cerro Quema.

AIIP mapping of Cerro Quema helicopter TDEM data was

carried out using c=0.7. The AIIP apparent chargeability

data are shown in Figure 5a. The strong chargeable

responses are located around La Pava and along the

interpreted contact north of the deposits. The AIIP apparent

resistivity data are shown in Figure 5b. Two conductive

trends can be seen, the contact trend and the Quemita-

Quema trend. The Cole-Cole time-constant data are shown

in Figure 5c, with higher values located around La Pava,

the contact and the Rio Joaquin Fault. The RTP data are

displayed in Figure 5d, showing clear association of the

magnetic data with the inferred contact and the Rio Joaquin

Fault.

The AIIP CF data are shown in Figure 6a, side by side with

the TSC data in Figure 6b. The CF data maps the clay

alterations. In Cerro Quema, we see clear separation

between the CF and the TSC. Most of the CF highs are

located in the low lying areas north of the interpreted

contact, south of the Rio Joaquin Fault, and the southern

base of the mountain hosting the Quemita and Quema

deposits. Most of the TSC highs are located along the

interpreted contacts north of the Cerro Quema deposits,

along the Rio Joaquin Fault and in the halos surrounding

the La Pava and south of the Quemita. In this case study,

the TSC data better reflects the disseminated and fine-

grained pyrite alteration halos. The semi-circular halos

could potentially be used an exploration vectors for high

sulphidation epithermal gold mineralization.

Figure 6: A clear divergence is seen between (a) the CF data and (b) the TSC data from Cerro Quema.

Discussions

Figure 7: AIIP zone of interest for low concentrations of

disseminated metallic sulphides in a resistive host;

chargeability vs. time constant plot from Pelton et al., 1978.

Many Canadian Archean lode gold deposits in glaciated

terrains are chargeability and resistivity highs. Therefore

the 𝑚0 and 0 maps could potentially be used for

targeting these kinds of mineralization.

Many Archean lode gold deposits and most disseminated

sulphide ores are considered ‘fine-grained’ in ground IP, in

contrast to coarse grained stringer to massive sulphides.

They show high resistivities and short time constants.

For potential Archean lode gold mineralization with low

sulphide concentration, low chargeability and variable

Cole-Cole time-constant, as illustrated in Figure 7, the

∙ 𝑙𝑜𝑔(0) and 0 maps could be potential targeting tools

as well.

The AIIP resistivity and resistivity-associated maps should

be interpreted in conjunction with magnetic maps, since

many explorationists look for lode gold in areas of

magnetite depletion, due to hydrothermal alteration.

Conclusions


4

We have found that the interpretation of the derived Cole-

Cole parameters can be enhanced by the use of AIIP

normalized chargeability (𝑚/0) and AIIP tau-scaled

chargeability (TSC) 𝑚 ∙ . The former can be treated as an

indicator of very fine-grained polarizable materials, such as

clay, and is named the AIIP Clay Factor (CF). The AIIP

TSC is considered to be a good indicator of relatively more

chargeable fine-grained materials with relatively longer

Cole-Cole time-constants or grain sizes in the range of 0.2

mm.

AIIP mapping results from TKC kimberlite complexes in

NWT Canada and Cerro Quema high sulphidation

epithermal gold deposits in Panama indicated the AIIP CF

and TSC can be used to separate clay-dominated and fine-

grained disseminated metallic sulphide-dominated

polarizable materials in the ground.

REFERENCES

Cole, K. and Cole R., 1941, Dispersion and absorption in

dielectrics, Part I. Alternating current characteristics:

Journal of Chemical Physics, 9, 341-351.

Corral, I., Griera, A., Gómez-Gras, D., Corbella, M.,

Canals, À., Pineda-Falconett, M. and Cardellach, E., 2011,

Geology of the Cerro Quema Au-Cu deposit, Geologica

Acta, 9, 3-4, 481-498.

Jansen, J., and K. Witherly, 2004, The Tli Kwi Cho

kimberlite complex, Northwest Territories, Canada: A

geophysical case study: 74th Annual International Meeting,

SEG, Expanded Abstracts, 1147–1150.

Jansen, J. C., and B. J. Doyle, 2000: The Tli Kwi Cho

Kimberlite Complex, Northwest Territories: A Geophysical

Post Mortum.

Johnson, I.M., 1984: Spectral induced polarization

parameters as determined through time-domain

measurements, Geophysics, 49, 11, 1993-2003.

Kaminski, V. and Viezzoli, A., 2017, Modeling induced

polarization effects in helicopter time-domain

electromagnetic data: Field case studies, Geophysics, 82

(2), B49-B61.

Kang, S., Fournier, D. and Oldenburg, D. W., 2017,

Inversion of airborne geophysics over the DO-27/DO-18

kimberlites – Part 3: Induced Polarization, Interpretation, 5

(3), T345-T358.

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measurements on igneous, sedimentary and metamorphic

rocks, in Wait, J. R., Ed., Overvoltage research and

geophysical applications: Pergamon Press; 92–111.

Kratzer, T. and Macnae, J. C., 2012, Induced polarization

in airborne EM, Geophysics, 77, E317-327.

Kwan, K., Prikhodko, A., Legault, J.M., Plastow, G., Xie,

J. and Fisk, K., 2015, Airborne inductive induced

polarization chargeability mapping of VTEM data,

Expanded Abstract, ASEG-PESA 2015.

Lesmes, D.P. and Frye, K., 2001, Influence of pore fluid

chemistry on the complex conductivity and induced

polarization responses of Berea sandstone, Journal of

Geophysical Research, 106, B3, 4079-4090.

Luo, Y. and Zhang, G., 1998: Theory and application of

Spectral Induced Polarization, Geophysical Monograph

Series.

Marshall, D.J. and Madden, T.R., 1959: Induced

polarization, a study of its causes, Geophysics, 24, 4, 790-

816.

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inductive coupling with multi-frequency IP: Geophysics,

43, 588–609.

Revil, A., Florsch, N. and Mao, D., 2015: Induced

polarization response of porous media with metallic

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semiconductors, Geophysics, 80, 5, E525-D538.

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Valliant, W.W., Collins, S.E. and Krutzelmann, H., 2011,

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Wilson Roscoe Postle Associates Inc.

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Modeling induced polarization effects in helicopter time

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Geophysics, 82 (2), E31-E50.

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APPENDIX C: FINAL DELIVERABLES

C1: Databases Primary voltage correction is applied to SFz channel, correcting the amplitudes of the early off-time channels, up to 290 s after transmitter turn-off. The amplitude drop in the early off-time channels is caused by the residual or parasitic voltage effect of the primary current in the transmitter loop. The correction applied to early off-time channels and the results are saved in the SFzc channel, which is used to AIIP mapping. gowganda_west_prvoltcorrected.gdb; Primary voltage corrected database channel descriptions: Channel Descriptions Unit x UTM Easting (NAD83, UTM Z17N) meter y UTM Northing (NAD83, UTM Z17N N) meter z GPS elevation (NAD83, UTM Z17N) meter sfz Original dB/dt Z component array pV/Am4 sfzc Corrected dB/dt Z component array; (used for AIIP) pV/Am4 gowganda_west_aiip_final.gdb; AIIP Database channel descriptions; Channel Descriptions Unit x UTM Easting (NAD83, UTM Z17N) meter y UTM Northing (NAD83, UTM Z17N) meter radarb EM TX-RX height above ground meter sfzo Observed dB/dt Z component array (Ch 10 to 45), 36 chs pV/Am4 sfzc Calculated dB/dt Z component array (Ch 10 to 45), 36 chs pV/Am4 chg_final Final AIIP apparent chargeability V/V res_final Final AIIP apparent resistivity Ohm-m

tau_final Final Cole-Cole time-constant msec

C2: Grids gowganda_west_chg_final.grd: AIIP apparent chargeability (V/V); gowganda_west_res_final.grd: AIIP apparent resistivity (Ohm-m); gowganda_west_tau_final.grd: Cole-Cole time-constant (msec); gowganda_west_tauscaled_chg.grd: AIIP tau-scaled chargeability (V/V*msec); C3: Interpretation Maps


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mag_inferred_faults.map.map: known and inferred faults; mag_inferred_district-scale-faults.map: inferred district-scale faults; interp_targets.map: Selected potential exploration targets for possible polymetallic vein gold mineralization; C4: Target Polygons \target_polygons folder: containing the polygons of the selected potential polymetallic vein gold exploration targets; The UTM coordinates (NAD83, UTM Z17N) of the target polygons in Gowganda West project are listed below.

Potential Polymetallic Vein Gold Exploration Targets

(X,Y) in NAD83 UTM Z17N Coordinate System

GWG_01 Index X Y Index X Y

1 502373 5270254 4 504612 5268709 2 502750 5270407 5 504247 5268403 3 503705 5269405 6 502950 5269464


1 504801 5268368 3 505555 5267460 2 505720 5267743 4 504647 5268108


1 505803 5269428 4 506203 5268792 2 507158 5268627 5 505685 5269110 3 507017 5268332


1 503492 5267460 4 505036 5266588 2 503669 5267755 5 504730 5266611 3 505190 5266741 6 503999 5267154


1 508808 5268332 3 509940 5267283 2 510070 5267543 4 508702 5268085


1 500675 5269240 3 501948 5268214 2 500887 5269405 4 501736 5268049


1 499308 5267436 3 500133 5266824 2 499473 5267590 4 499956 5266694


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C5: Geophysical Interpretation Report GL180370_iMetal_Interp_Report_Apr26-2019.docx (and future revised versions);

report on a combined helicopter borne · web: email: [email protected] vtem™ plus geophysical...

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