VTEM airborne EM system clearly detects Abra polymetallic base metal deposit; an ongoing comparison to other airborne and ground EM systems

Transcription

1 A Practical One-Day Workshop on Airborne Electromagnetics, November 2012 VTEM airborne EM system clearly detects Abra polymetallic base metal deposit; an ongoing comparison to other airborne and ground EM systems J. Meyers, J. Wood, D. Stannard and N. Cantwell: Resource Potentials Pty Ltd Keith Fisk: Geotech Airborne Pty Ltd M. Wang and L. Hardy: Abra Mining Pty Ltd

2 Abra is a SEDEX (Sedimentary Exhalative) deposit Discovered in 1981 by drilling a blind coincident magnetic and gravity anomaly to over 250m depth

3 Upper Stratabound zone main source of magnetic anomaly with MAGNETITE alteration and some PYRRHOTITE, underlain by HEMATITE alteration Entire mineralised zone contains some BARITE alteration, iron oxide minerals with minor Pb and Cu sulphides which contribute to gravity anomaly Deep base metal deposit still in the ground and is free of cultural interference Excellent geophysical testing ground

4 Lies within the Former Bangemall Basin Abra Now the Edmund and Collier Basins

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6 West Creek Fm ABRA Gap Well Fm

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8 REPRODUCED FROM VOGHT AND STUMPFL, 1987

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10 Abra Orebody Wireframe Aeromagnetics Gravity

11 Abra Orebody Wireframe AEM - VTEM Ground EM - SIROTEM

12 r o 1kHz (sat) ohm m Fig R sat vs P A 1.E+06 1.E+05 Archie Equations, theoretical, clean formations, sat. saltywater r w = 1 ohm m r o = F r w, F = P A -2 ILLUSTRATIVE, NOT DEFINITIVE 1.E+04 1.E+03 1.E+02 1.E+01 6 barite gal + qtz banded mtt 4 +py/gal 4 jaspilites 8 conductive solids (sulphides, mtt) 1.E carbonate + gal, py 1.E NOTE THE NOTE THE LOW ANISOTROPY POROSITIES max 10 min 11 barite +gal +/- py 1.E SYSTEMS EXPLORATION (NSW) PTY LIMITED apparent porosity, P A, %

13 GEOTEM Geoterrex / Fugro XTEM - GPX VTEM Plus - Geotech

14 System VTEM Plus Geotem Deep XTEM Abra Survey Date Configuration In Loop Towed Bird In Loop Frequency (Hz) Terrain Clearance (m) Tx Dipole Moment (Am2) Waveform Trapezoidal Half Sinusoid Square Wave 25% Duty Cycle Number Off Time Channels Latest Channel Time Centers (ms) Components Z & X db/dt & B Field Z & X db/dt (3 comp B Field now vailable) Z db/dt

15 Moment (Am2) Moment (Am2) Moment (Am2) Moment (Am2) 800,000 Airborne EM Waveforms 800,000 VTEM Plus 600, , , ,000 VTEM GEOTEM XTEM 400, ,000 Waveform Reciever Sampling Time (ms) GEOTEM Deep Time (ms) XTEM 800, , , , ,000 Waveform 400,000 Waveform 200,000 Reciever Sampling 200,000 Reciever Sampling Time (ms) Time (ms)

16 VTEM Plus Ch 35 B Field GEOTEM Deep Ch 15 db/dt XTEM Ch 20 db/dt

17 VTEM Plus 2012 (Geotech) GEOTEM Deep 1996 (Geoterrex / Fugro) N XTEM 2011 (GPX) S ABRA N S

18 B z / t (mv/a) B z / t (mv/a) B z / t (mv/a) Early delay time Asymmetric response Late delay time Dip = 90 Dip = 45 Dip = 0 o Abra Dipping approx 30 S

19 Preliminary data Good mid late time response S N S N ABRA Z Component B Field ABRA X Component db/dt

20 Weak mid - late time response S N S N ABRA Z Component db/dt ABRA X Component db/dt

21 No detectable response X S ABRA Z Component db/dt N

22 SmarTEM (200m In Loop) SIROTEM (200m Coincident Loop) N FLEM (Single Large Loop) S ABRA N S

23 S ABRA N S ABRA N S ABRA N 2006 MLEM 1982 MLEM 2006 FLEM Good Mid to late time EM response, but still decays away at late times Only moderately conductive overall

24 S ABRA Z Component N S N ABRA S N ABRA X Component Preliminary data to date, received last night Y Component

25 Preliminary results to date Z Component db/dt Conductivity Depth Image Good correlation to known mineralisation S ABRA N

26 S N Westerly view of CDI and known mineralisation VTEM CDI Voxel Abra 3% Pb grade shell Good correlation to depth VTEM likely seeing the upper mineralised zone

27 S N NE view of DHEM and known mineralisation Locally some high conductivities Abra 3% P grade shell Abra 3% Pb grade shell Complex conductivity regime Possibly due to brecciated sulphide zones, giving a poor overall EM conductor

28 Westerly view of IP Section and known mineralisation Inverted IP Chargeability model Abra 3% Pb grade shell S N

29 Scope for more AEM (VTEM) exploration in the area based on fantastic results at Abra

30 SOUTH 0m 400 CHANNELS, 5m SHOTS+RECEIVERS, DEPTH MIGRATED NORTH 500m 1000m

31 Abra is a good deep geophysical test range -Clean and still in situ Clearly detected by the VTEM plus system Locally has high conductive zones but overall is only moderately conductive FUTURE WORK TEST OTHER AEM SYSTEMS: HeliTEM Fugro SpectrEM Anglo VTEMmax and VTEM 35m Geotech Airborne ZTEM Geotech Airborne More EM MT, AMT 3D Seismic

32 A Practical One-Day Workshop on Airborne Electromagnetics, November 2012 VTEM airborne EM system clearly detects Abra polymetallic base metal deposit; an ongoing comparison to other airborne and ground EM systems J. Meyers, J. Wood, D. Stannard and N. Cantwell: Resource Potentials Pty Ltd Thanks to: Keith Fisk: Geotech Airborne Pty Ltd M. Wang and L. Hardy: Abra Mining Pty Ltd