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JaminCristallPDAC_VTEMCollinsBayU
- 1. Geological Sources of VTEM Responses along the Collins Bay Fault, Athabasca Basin Jamin Cristall and Dan Brisbin Cameco Corporation Giant Uranium Deposits Short Course PDAC 2006
- 2. Objectives • To explain how different geological scenarios along a prospective structure affect VTEM responses • To demonstrate the use of state-of-the-art forward modeling and inversion technologies in understanding VTEM responses • To describe how improved integration of geology and geophysics leads to more effective exploration in mature uranium plays Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006
- 3. Outline • Uranium Exploration Strategies • Introduction to Study Areas • Principles of VTEM Surveying • Review of Fault Zone Terminology • Examples of Integration • UEX Hidden Bay Study Area • Cameco Eagle Point Study Area • Discussion Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006
- 4. Athabasca Uranium Exploration Strategies • Before 1975 • Locate radioactive boulder train, drill apex area • Present - Future • Integration of geology and geophysics (geophysics maps subsurface geology) Modeling / Inversion Subsurface earth modelData acquisition Anomaly picking • 1975 - Present • Locate conductor, drill conductor axis along strike (focus on geophysical anomalies)
- 5. Study Area – Collins Bay Fault
- 6. 00 25 50 75 100 125 150 175 200 225 250 MillionPoundsU3O8 KeyLake CigarLake Total AZone BZone DZone HistoricalEP 02NEXT 163Zone Collins Bay Fault Deposits Eagle Point A World Class Uranium-Bearing Structure RabbitLake
- 7. Collins Bay Fault Deposits: Structural Setting ~60 Mlbs 69.8 Mlbs
- 8. Think Outside the Box !!! Collins Bay Fault Deposits: Structural Setting ~60 Mlbs ~70 Mlbs
- 9. Principle of VTEM: EM Induction Tx Rx Jp/t = Hp/t Primary Magnetic Field!
- 10. Principle of VTEM: EM Induction Tx Rx Induced Currents! -Hp/t = E E = Js Secondary Magnetic Field! Js/t = Hs/t
- 11. 110100100010000100000 Feldspar Porphyry Arkosic Gneiss Felsic Gneiss Pegmatite Granitic Gneiss Graphitic Metapelite Calcpelite Metapelite Sandstone Alteration Lake Seds Lake Water Overburden Athabasca Region Resistivities Resistivity (m) = 1/Conductivity (S/m)
- 12. Amplitude time decay at one position VTEM Survey Data Presentation Colored amplitude map for one channel Data amplitude profiles for multiple channels
- 13. Amplitude time decay at one position f(t)=Aoe-t/ = 1.496 ms VTEM Survey Data Presentation Colored amplitude map for one channel Colored decay constant () map t Data amplitude profiles for multiple channels
- 14. VTEM Response to a Thin Graphitic Fault Depth Easting VTEMAmplitude Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006
- 15. Depth Easting VTEMAmplitude Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006 VTEM Response to a Thin Graphitic Fault
- 16. Depth Easting VTEMAmplitude Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006 VTEM Response to a Thin Graphitic Fault
- 17. Depth Easting VTEMAmplitude Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006 VTEM Response to a Thin Graphitic Fault
- 18. Depth Easting VTEMAmplitude Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006 VTEM Response to a Thin Graphitic Fault
- 19. Depth Easting VTEMAmplitude Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006 VTEM Response to a Thin Graphitic Fault
- 20. Fault Zone Terminology (e.g. Rabbit Lake Fault) Core Zone Bedded ss 2m Basement meta-arkoses Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006 Damage zone in basement meta-arkoses
- 21. Collins Bay Fault Overview Map N Plan View Collins Bay Fault Rabbit Lake Fault Eagle Point Mine Rabbit Lake Pit Hidden Bay Study Area Eagle Point Study Area
- 22. UEX Hidden Bay Study Area N Plan View
- 23. Geological Section - VTEM Line 13730 Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006
- 24. Geophysical Results - VTEM Line 13730
- 25. Geophysical Results - VTEM Line 13730
- 26. N Plan View UEX Hidden Bay Study Area
- 27. Geological Section - VTEM Line 13660 Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006
- 28. Geophysical Results - VTEM Line 13660
- 29. Geophysical Results - VTEM Line 13660
- 30. ArjunAir 2.5D Finite Element Model Ch. 1-8 Ch. 1-8 non-graphitic gneiss sandstone 700m 500 m sandstone non-graphitic gneiss graphitic damage zone graphitic core zone non-graphitic damage zone UC
- 31. N Plan View UEX Hidden Bay Study Area
- 32. Geological Section - VTEM Line 13570 Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006
- 33. Geophysical Results - VTEM Line 13570
- 34. Geophysical Results - VTEM Line 13570
- 35. Collins Bay Fault Overview Map N Plan View Collins Bay Fault Rabbit Lake Fault Eagle Point Mine Rabbit Lake Pit Hidden Bay Study Area Eagle Point Study Area
- 36. Cameco Eagle Point Study Area N Plan View 02NEXT
- 37. Geological Section - VTEM Line 8790 Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006 Graphitic Fault Contact
- 38. Geophysical Results - VTEM Line 8790
- 39. Geophysical Results - VTEM Line 8790 Graphitic Fault Contact
- 40. 1.1 S 1951 m 488 m 5326 m LeroiAir 3D Plate Model - VTEM Line 8790 Amplitude(pV/Am^4) Observed Data Predicted Data Depth(m) 100 m RMS Error = 16%
- 41. Discussion • Forward modeling and inversion technologies are useful for bridging the gap between geology and geophysics • Character and distribution of graphite is dominant source of VTEM response • No known geophysical technique can detect basement-hosted mineralization directly • VTEM provides the basis for understanding fault architecture, deposits are fault controlled • Improved prediction of geology from geophysics (integration) will lead to more effective exploration for basement-hosted mineralization Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006
- 42. Acknowledgements • Cameco Corporation • UEX Corporation • Colin Farquharson (MUN) and Doug Oldenburg (UBC-GIF) • Art Raiche (CSIRO) • Geotech Ltd. / Condor Consulting • Roger Lemaitre, Charles Roy, Vlad Sopuck • Dave Thomas, Brian Powell • Amanda Dahl, Kylene Baxter • Clayton Durbin • Rabbit Lake and Hidden Bay teams Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006
- 43. Questions? Geological Sources of VTEM Responses along the Collins Bay Fault, PDAC 2006
- 44. Extra Slides
- 45. VTEM Survey Description Figures courtesy of Geotech Ltd. Jamin Cristall and Dan Brisbin, Geological Sources of VTEM Responses
- 46. AEM System Apertures ~ Resistivity Ω-m
- 47. Inversion of LeroiAir Synthetic Data 0.441 0.151 0.0519 0.0178 0.00612 Ch. 1 – 15 (pV/Am4) 1D Inversion for 3D Plates 49 S 6114 Ohmm 70 Ohmm Ch. 10 - 25 Observed Data Predicted Data LeroiAir EM1DTM
- 48. Geophysical Terminology • Resistivity, Conductivity • Inherent physical property of the rock • Resistivity = 1/Conductivity Resistivity = Conductivity • Conductance • Conductance = Conductivity Thickness • Channel (time gate) • One of a series of times at which secondary magnetic field measured after primary field switched off • Amplitude • “Strength” of the secondary magnetic field • Strongly influenced by dip, depth, and conductance • Time (decay) constant • Derived from decay curve (decrease in secondary field amplitude from early to late time channels) • Strongly influenced by conductance, not so influenced by dip or depth
- 49. Amplitudes versus Decay Constants
- 50. Amplitudes versus Decay Constants
- 51. Amplitudes versus Decay Constants
Editor's Notes
- VTEM is a recently developed helicopter-borne time-domain electromagnetic system…
- … as shown in this picture
- -U Exploration strategies Past, Present, and Future
- Before 1975 The main strategy was to locate a radioactive boulder train with airborne scintillometers, follow it up with hand-held scintillometers on the ground, and drill the head area. (In addition to a gravity anomaly) This was the strategy that led to discovery of the basin’s first high-grade uranium deposit Rabbit Lake deposit in 1968 1975 = Key Lake Discovery Discovery of the Key Lake deposits in 1975 was very influential to subsequent exploration because this is where the classic unconformity uranium model was developed and the relation between uranium mineralization and basement graphitic faults was first recognized. This realization sparked off a period of exploration that focused upon the search for basement graphitic conductors using electromagnetic methods. The basic strategy was to locate a graphitic conductor and drill the conductor axis along strike at a defined drill hole spacing. This strategy served Cameco and others very well as it led to the discovery of the the two biggest high-grade uranium deposits in the world: Cigar Lake and McArthur River. Present – Future Discovery of the Millenium deposit in 2000 and 02NEXT zone in 2003 reaffirmed to explorationists that high-grade mineralization does not have to occur immediately at the intersection between the unconformity and graphitic conductor economic mineralization can occur within the basement and several hundred meters off the conductor axis as well. This realization has inspired explorationists to take a more integrated, model-driven approach; and geophysics is becoming more of a tool for general mapping of subsurface geology, rather than hunting for anomalies.
- -The study area for this presentation on the Eastern side of the Athabasca Basin near the sandstone margin -This is the most explorationally mature part of the Basin where several major uranium deposits have been found, as shown by the red dots on this map -We will look at geological and geophysical sections across the Collins Bay Fault, which runs through UEX’s Hidden Bay property and is the primary structure associated with the majority of mineralization on Cameco’s Rabbit Lake Mining Lease
- -The Collin’s Bay Fault is a world class uranium-bearing structure -The Eagle Point deposit, associated with the fault, is, in fact, the fourth largest high-grade uranium deposit in the Basin; bigger than Rabbit Lake -Cumulatively, the deposits along the Collin’s Bay fault have produced or are in resource in excess of 135 million pounds -This compares very favorably with the more famous Key Lake and Cigar Lake deposits, especially considering favorable impact that shallow sandstone and readily available infrastructure have on project economics
- -The vast majority of historical holes along the Collins Bay Fault were short and vertical, targeting the conductor sub-crop (within this little box) in order to test for unconformity-type mineralization -This strategy was quite successful as it identified roughly 60 million pounds along the Collins Bay Fault in the B, D, and A Zones
- -However, the greatest proportion of reserves along the Collin’s Bay Fault are hosted by off-conductor subsidiary structures, such as the Eagle Point Fault, where the majority of mineralization occurs in veins oriented at a high angle to the conductor -Obviously, shallow, vertical holes targeted at the conductor axis would fail to find the majority of mineralization -As says our brilliant and talented exploration manager, to find most of the mineralization, we have to “Think Outside the Box!!”
- -Now that I’ve drawn all the geologists in with my core box title slide and the doors have been chained shut, I will describe the principle of VTEM surveying: EM induction. -I am going to show some of Maxwell’s equations on this slide, but these will be explained in an intuitive way by the animation… feel free to ignore them if you prefer. -The important parts of the VTEM system are the Transmitter (about 26 m diameter) and the Receiver located at its center. -The Tx and Rx are separated from the helicopter by a 45 m long boom in order to avoid electrical interference -At each station (click), VTEM emits a time-varying current pulse through its transmitter (click). -By Ampere’s Law this creates a time-varying Primary Magnetic Field which penetrates into the Earth (click)
- -By Faraday’s Law, the time-varying magnetic field Induces an electric field, which drives currents flow (click click). -These induced currents propagate downward and outward with time and flow preferentially in the most CONDUCTIVE materials (click). -As the current loops decay by ohmic (or heat) losses, by Ampere’s Law again, they create a secondary magnetic, which is measured at the receiver (click).. -By analyzing the secondary magnetic field, and understanding the process of EM induction, we can gain information about the conductivity structure of the subsurface Earth
- -As I mentioned in the previous slide, the currents induced by VTEM, or any EM system, flow preferentially in the most CONDUCTIVE materials -CONDUCTIVITY, or equivalently RESISTIVITY is an inherent physical property of any material, like density -RESISTIVITY and CONDUCTIVITY are the reciprocal of one another, so a rock with high conductivity has low resistivity and vice versa -Shown in this slide are a range of resistivities for a variety of materials commonly encountered in the Athabasca Region -The graph shows that Graphitic Metapelites tend to be by far the most conductive. -Their Upper Bound Conductivity, corresponding to faulted, highly graphitic metapelites with structurally enhanced graphite along fractures, could certainly reach 1 S/m, which is about 2 orders of magnitude more conductive than any of the other materials -Since Graphitic Metapelites are the most conductive, this implies that VTEM will be more sensitive to Graphitic Metapelites than to any of the other materials -A current subject of research and debate is whether VTEM can detect and discriminate illitic clay alteration zones which are located in the proximity of but are of much lower conductivity than faulted graphitic metapelites -This remains a challenging task for time domain systems, such as VTEM, which are optimized for the detection and discrimination of targets of high conductivity*thickness .
- -This slide shows various ways of looking at VTEM data -Here we have a profile plot showing the amplitude of the secondary magnetic field measured at each Easting position. A line is drawn for each of the 26 points in time at which the secondary field is measured. The earliest time channel is the highest amplitude line and the latest time channel is the lowest amplitude line. These profiles show the characteristic M-shaped VTEM anomaly over a vertical conductor -(click) We can also take one time channel and grid it in plan view to map how the amplitude changes over an area. -(click) If we take one position (such as at this green line), and plot how the amplitudes decay over time at this one position, we can fit an exponential to the late time data to derive the decay-constant. -(click) Then, we can take all the decay constants from all the positions over an area and grid them to make a decay constant map. The advantage of looking at the gridded time constants rather than the gridded amplitudes is that the time constants are almost only affected by conductor strength, or Conductance, whereas the amplitudes are very affected by the dip and depth of the conductor as well. -This particular survey was flown at a 200 m line spacing. The interpreted conductor axis is shown in yellow with little lines to indicate the direction of dip. -An exciting thing about having this density of high quality data, which would have been prohibitively expensive to acquire on the ground, is that we can see a lot of variations in the conductor along strike, such as changes in the strength of the conductor, flexures, and bifurcations. -This is exciting because it provides the basis for a structural geology map.
- -This slide shows various ways of looking at VTEM data -Here we have a profile plot showing the amplitude of the secondary magnetic field measured at each Easting position. A line is drawn for each of the 26 points in time at which the secondary field is measured. The earliest time channel is the highest amplitude line and the latest time channel is the lowest amplitude line. These profiles show the characteristic M-shaped VTEM anomaly over a vertical conductor -(click) We can also take one time channel and grid it in plan view to map how the amplitude changes over an area. -(click) If we take one position (such as at this yellow line), and plot how the amplitudes decay over time, we can fit an exponential to the late time data to derive the decay-constant. -(click) Then, we can take all the decay constants from all the positions over an area and grid them to make a decay constant map. The advantage of looking at the gridded decay constants rather than the gridded amplitudes is that the decay constants are almost only affected by conductor strength, or conductivity*thickness, whereas the amplitudes are very affected by the dip and depth of the conductor as well. So you can think of the decay constant map as essentially a map of conductor strength (conductance). -This particular survey was flown at a 200 m line spacing. The interpreted conductor axis is shown in yellow with little lines to indicate the direction of dip. -An exciting thing about having this density of high quality data, which would have been prohibitively expensive to acquire on the ground, is that we can see a lot of variations in the conductor along strike, such as changes in the strength of the conductor, flexures, and bifurcations. -This is exciting because it provides the basis for a structural geology map.
- -An important thing to know about looking at gridded VTEM maps is that the fault-conductor is not at the position of the red bulls-eye on the map, but rather off to the side. -The following animation will explain why this is. -When the transmitter is far from the conductor, no primary field lines pass through the conductor so the secondary field amplitudes are small
- -As the transmitter gets closer to the fault, primary field lines begin to pass though it so the measured secondary field amplitudes increase
- -The amplitudes are highest when the transmitter is at a distance from the fault such that the maximum number of field lines pass through it at right angles
- -When the transmitter is directly overtop of the conductor, it is null coupled. No field lines pass through the conductor and the secondary magnetic field amplitudes are small.
- -A second maxima occurs on the up-dip side of the conductor, but it is smaller than the maxima on the down-dip side because the primary field lines are passing through the conductor at a more obtuse angle… the transmitter and conductor are not as well coupled
- -Finally, the amplitudes are small when the transmitter is far from the conductor again -We can see that VTEM is very instructive of conductor dip as the larger lobe occurs on the down-dip side -The morals of this story is that the conductor subcrop is not the big red bulls-eye shown on colored amplitude maps, that would correspond to the big lobe shown here. -Inspection of the data profiles is necessary to pick the conductor axis accurately.
- -Before we move on to the geological cross-sections, I will review a bit of the Fault Zone Terminology that will come up -Here is a picture of the Rabbit Lake Fault nicely exposed in the Rabbit Lake pit and (click) here is a diagram from a text book for reference -The Rabbit Lake fault is completely analogous to the Collins Bay Fault because they are both regional, post-sandstone, dextral, oblique reverse faults, that host major uranium deposits -The main plane of shearing is the Core Zone indicated here (click) -We can see that this is a reverse fault because basement gneisses in the hanging wall are juxtaposed against Athabasca sandstone preserved in the footwall -Another important feature, which we will refer to in the subsequent slides, is the zone of damage in the basement gneisses -The damage zone shows how faults are not a single plane, but have some width associated with them
- -This is an overview map showing the Collins Bay Fault at a district scale -The colors here are representative of VTEM channel 3 amplitude -For reference, the Rabbit Lake pit, that we just looked at, is here and the Eagle Point Mine is here -We can see that VTEM maps out the Collins Bay Fault very nicely, running all the way along here and up and around the Collins Bay Dome -Using small, patchwork, ground EM surveys, as budgets permitted, it took over 10 years to map out this stretch of the Collins Bay Fault -We mapped it out with VTEM in 1 year -This balanced, district-scale picture has given us a much better understanding of the variations along the Collins Bay Fault and the relation between the Collins Bay Fault and the Rabbit Lake Fault -The first portion of the Collins Bay Fault that we’re going to zoom-in on is the Hidden Bay Study Area here
- -Here is a larger-scale view of a portion of the Collin’s Bay Fault on UEX’s Hidden Bay Property showing the interpreted conductor trace -The colors are representative of the VTEM channel 3 amplitude -This survey was actually flown at a 200 m line spacing (the grid is based on the 200 m spaced data) but I’m only showing the lines across which we did geological cross-sections -We can see that there are a number of interesting variations in the conductor at this scale -For instance, there is a flexure in the conductor and variations in amplitude from here to here to here -The question is: what do these variations mean geologically? -To answer that question, first we’ll look at the VTEM data and geological cross-sections across these lines, starting here
- -The two drill holes in this section show that there is an oblique reverse fault that juxtaposes the yellow sandstone preserved in the footwall against the gneisses in the hanging wall -There is a lot of conductive graphite in the second drill hole with structurally enhanced graphite along the fault
- -So what does the VTEM have to say? -The first panel shows the various time channel profiles -The amplitudes are fairly high and the anomaly shape is indicative of a discrete conductor dipping to the south-east with a conductor subcrop about here
- -The second panel shows a stitched series of 1D inversions computed with UBC-Geophysical Inversion Facility code EM1DTM. -The way this code works is, at each station, the code fits the decay curve to a 1D layered-earth model -In this figure, we’ve stitched all the 1D conductivity models together to produce a pseudo-2D section. -The advantage of doing this sort of 1D modeling is that it is very automated. You can just throw a little extra uranium in the reactor and let your computers crunch through an entire data set. -The disadvantage is that the 1D code is not really designed for strong lateral conductivity contrasts, such as steeply dipping graphitic faults, as we commonly encounter in the Athabasca Region. -The inversions show a dipping, highly conductive feature in the basement. -Comparing this to the geology, we can see that it corresponds very well to the dipping, grey graphitic units -it’s at about the right depth, dips in the right direction, and even the angle of dip is not too bad (note that the dip angle in the geological section is not very well constrained by the 1 drill hole and could be a bit shallower). -Since the two graphitic units are quite close together, the inversion is averaging them together into one thick conductive unit -So, in this case, although it’s not really designed for steeply dipping structures, the 1D inversion code is doing quite a good job of recovering a conductivity distribution from the geophysical data which is consistent with the observed geology
- -Next we’ll look at this section at a kink in the conductor and across a dimmer portion
- -In this section, we see that the reverse fault is still present, with a wide damage zone, but there are no graphitic lithologies encountered in any of the holes
- -The early time profiles are indicative of a weak discrete conductor, but the position of the down-dip peak migrates significantly towards the southeast from early to late-time
- -Now looking at the inversion section and comparing it to the geology -The inversion shows moderate conductivities near the holes, possibly indicative of the damage zone and faulting -but the conductivities seem to significantly improve down-dip
- -As I said before the 1D inversion code is not really designed for 2D structures like steeply dipping faults -so to investigate this VTEM line further, I constructed a 2.5D finite element model using the CSIRO ArjunAir code. -This type of model consists of many small cells that extend infinitely in the along strike direction -The reason it’s called a 2.5D model is because the model is 2D, like the section shown here, but the fields are calculated in the full 3D-spatial domain -The advantage of this type of model is that it is well suited for long strike-length features, like regional faults, but the disadvantage is that it takes a lot of work to try to get the model to match the observed data. -Zooming into the shallower part of the model near the fault subcrop, the model shows the sandstone in the footwall juxtaposed against the non-graphitic semipelites in the hanging wall, the unconformity is here, and here we have the non-graphitic damage zone, as seen in the geological section -The model reaffirms the EM1DTM inversions as it shows that the real conductive material, the graphitic fault zone, is east of and deeper than the fault sub-crop -for the modeled data to match the observed data, as it does reasonably well here, the conductor must improve at down-dip -Geologically this could mean that here the graphite peters out before it reaches the unconformity
- -Next we’ll look at the brightest portion of the conductor along this stretch
- -Here we see a wide, well developed fault and damage zone involving graphitic host rocks near the surface -The fault is a fair bit more complex than in this section than the previous sections and is composed of of several fault strands.
- -The profiles show a wide, high amplitude anomaly with asymmetry indicating a dip towards the southeast
- -Looking at the inversions, we see that there is a wide zone of shallow conductivity that dips to the east and becomes broken up at depth. -Comparing this to the geology, we can see that the complexity of the fault in the shallow area intersected by the drill holes is reflected down dip by the complicated, broken-up conductivity in the inversion section. -This is significant because, if you’re looking for hangingwall mineralization, a complicated hanging wall plumbing system is definitely a positive thing -It’s my opinion that, based on the three sections we’ve seen on this portion of the UEX property, this would have highest priority for drilling deep-angled holes through the hanging wall to test for basement hosted mineralization
- -Back to the overview map, next we’re going to look at the Eagle Point Study Area (here)
- -Here’s the VTEM anomaly and the holes that we’re going to look at in the final section. -This section goes across some actual mineralization: Cameco’s 02NEXT deposit discovered in 2003. -The VTEM was flown subsequently to discovery of the 02 NEXT deposit, which was found by a combination of ground geophysics and infill drilling, as described in Roger’s talk
- -In this section we have a graphitic fault zone at the contact with the granitic Collin’s Bay Dome, as I’m going to highlight here -Variably graphitic metapelites in the hanging wall are shown in grey -Everything else in the hanging wall is non-conductive gneisses and intrusions. -Mineralization is shown in red. This upper zone is the one currently being developed by the Eagle Point Mine.
- -Here we have the VTEM line across the deposit -The VTEM was flown subsequently to the discovery of the 02NEXT deposit, which was discovered by a combination of ground geophysics and infill drilling, as described by Roger in yesterday’s talk -The profiles are fairly consistent with a discrete conductor dipping towards the southeast
- -Accordingly, the inversion shows a conductive feature dipping towards the east -Comparing the inversion to the geology, the dipping conductive feature corresponds very well to the graphitic fault contact along the Collins Bay Dome. -The fact that the feature in the inversion is really not all that conductive, as compared to the first section shown on the UEX property in particular, is consistent with the fact that the graphite observed in these holes was really not all that impressive
- -Another geophysical model for the 02NEXT geological section is shown here -This is an integral equation model that consists of a 3D thin-plate embedded in a three-layered earth with layers representing Wollaston Lake, lake bottom sediments, and the Basement rocks -Comparing this model to the geological section (click) we can see that the plate corresponds very well to the graphitic fault contact with the Collins Bay Dome. -The predicted position and dip of the conductor are very accurate, which would make this sort of model very good for planning deep, off-conductor, angled holes -This model has an RMS error of 16% between observed and predicted data, meaning that it is is able to explain 84% of the data. -Close inspection of the observed and predicted data curves shows that the late-time channels are better fit by the model than the early time channels -Could this be because the model does not account for the weakly conductive alteration associated with the deposit, which decays away quickly? -Although EM inversion technology isn’t there yet, we are hopeful that, in the future, 3D finite-element inversion codes will be able to account for and image these subtle alteration features in the presence of a discrete conductor.
- -To conclude the presentation, we have seen that… -We have also seen that… -Since deposits are structurally controlled, this leads to better prioritization of where to drill fences of deep, angled holes across a regional fault structure. -Considering this, we believe that…
- -Now that I’ve drawn all the geologists in with my core box title slide and the doors are locked, I will describe the principle behind VTEM surveying. -The main parts of the VTEM system are the Transmitter (about 26 m diameter) and the Receiver located at its center. -The transmitter emits a trapezoidal current pulse and data are measured in a series of time windows after termination of the pulse. -People have been performing ground EM surveys in the Basin since the 70s. The advantage with VTEM is that by mounting the transmitter and receiver on a helicopter large areas can be covered at reasonable costs and in a consistent manner so that inferences can be made about changes in the nature of a conductor along strike; such as variations in dip, quality of graphite, or structural kinks in the conductor.