Service: Seismic data filtering and interpretation

Seismic data analysis service post image

SEISMIC imaging appears on the upsurge in mining and mineral exploration settings. Because the petroleum exploration industry spent decades honing the technique, explorers in hard-rock environments should be able to hit the ground running. We provide a look at a site amenable to the seismic method in a Western Australian case study.

The seismic method has come a long way. At around the 1920s, petroleum explorers took seismic surveying under their wing and shepherded it though some significant developmental stages.

Those stages included the need to:

  • obtain reliable models about the velocity of seismic waves through various lithologies,
  • grapple with signal-to-noise and other data acquisition issues, such as 'sideswipe', 'multiples' and 'scatter',
  • move away from recording data on paper,
  • convert ('migrate') raw time-based data into accurate depth-related depictions,
  • develop sophisticated data-processing tools to cope with phenomena such as lithological anisotropy,
  • gain more continuous data coverage by developing the 3D seismic method,
  • deal with the 3D method's requirements for substantial computing grunt, and
  • adopt digital modes of data interpretation.

Ingenuity will be needed from minerals explorers and miners to ensure that seismic surveys done in complex crystalline environments yield results that are scientifically rigorous and meaningful. But the task at hand is not insurmountable — it's more akin to renovating a sturdy home than building something entirely from the ground up.

What follows is a backgrounder on seismic data, for readers who are relatively new to this type of survey. Veterans of the seismic method can go to the 'Seismic on the upswing' section, if desired.

Seismic waves

Seismic surveying involves deducing subsurface structure by seeing how it interacts with acoustic (seismic) energy sent into it. This is an inversion exercise, because it's by looking at the seismic data that we arrive at the relationships among the causative geological bodies and structures.

Seismic energy sent into the earth propagates largely as a pressure wave. In a pressure wave, the material the wave is passing through moves back and forth in the same direction as the wave's trajectory.

A good pressure-wave analogy is a metallic toy 'slinky' coil that is stretched out straight and taut on the ground and anchored at its far end. If the coil is grabbed and shunted forward and backward at its free end using a piston-like motion, then alternating compressions and expansions propagate along through the coil's loops and travel toward the anchored end.

If you do the same experiment with different coils, each being made out of different types and thicknesses of metal, and different coil diameters, you'll find that compressions and expansions would travel with a speed and amplitude that differs among the coils. This is because each coil has different inherent elastic properties.

Similarly, different rock types possess different elastic properties. The reasons why include variations in mineral assemblage and fabric, density, degree of clast consolidation and cementation, sedimentary layer thickness, depth of occurrence, porosity, stress, and fracture density.

So just as a pressure wave traveling through a metal coil is controlled by the elastic properties of the coil itself, seismic energy moving through the subsurface is controlled by the elastic properties of the rocks and other materials it encounters down there.

Reflected seismic waves

When a survey crew sends seismic waves into the earth, if those waves encounter a change in the subsurface's elastic properties, the waves can be reflected (bounced back towards the surface), or refracted (continue on to deeper zones, but now traveling at a changed angle of trajectory). The proportion of the down-going wave's amplitude that is reflected back up is called the reflection coefficient at that location.

A good thought experiment that helps with picturing the sort of effects occurring at an elastic-property change is to imagine linking together a series of metal coils of different stiffnesses and sending a pressure wave along them.

A change in the subsurface's elastic properties can be abrubt or gradual. A relatively abrubt change is often called an interface, because it is where two rock volumes with appreciably different elastic properties abut each other.

Changes can include:

  • a lithological contact, such as a transition from a shale to a volcanic rock,
  • a transition from fluid-filled porosities to mineral cement-filled porosities in a single sandstone,
  • an increase in a given lithology's density with depth, or
  • a change from thickly-bedded to thinly-bedded sedimentary units.

It means when looking at seismic data, it's important to keep in mind that a change in the subsurface's elastic properties doesn't necessarily imply that a changeover in rock type has occurred. You might still be in the same lithological package or unit, but something else about the rocks has changed, something that produces a change in their elastic behavior.

The converse may be true too, sometimes: a changeover in rock type may not necessarily announce itself in the seismic data if rocks elastically behave similarly.

Capturing and presenting seismic data

Surveyors send out seismic waves from a site on the earth's surface by setting off an explosive charge or by employing a truck-mounted shake source.

Reflected seismic waves that make it back to the surface after bouncing at an interface are sensed by the seismic crew's network of motion detectors. (This is a very broad-brush description of the scenario, but it's good enough for the purposes of this discussion.)

The crew then moves to the next station site located a little farther on, generates another burst of seismicity, and detects the subsequent reflections. Data for the remaining stations are collected the same way.

Either a two-dimensional dataset (depicting a vertical slice of the subsurface extending down from a survey line), or a three-dimensional dataset (depicting a cube of the subsurface extending down from a survey area) can be built up in this way.

The raw seismic dataset acquired by sensors records the two-way time interval taken for the seismic wave to travel from its source at the surface to a seismic interface and back to the surface again.

A seismic dataset is displayed as though stations' data were collected simultaneously, and as though the set of seismic sources and the set of sensors had coinciding locations (that is, the offset distance between each source and sensor pair is set to zero). In this scenario, the reflected wave takes the same path but in the opposite direction to the path taken by the incident wave. It's done this way to avoid the complications that would arise if the offset distance were not zero. Pressure waves incident at less than right angles to a reflection interface produce not one but two reflected waves: a reflected shear wave is created in addition to the reflected pressure wave. This creates a data interpretation headache.

Data processing, done to facilitate data interpretation, involves, among other things, converting ('migrating') the time-based seismic section or seismic cube. Migration produces an equivalent display of seismic reflection response with respect to depth.

Note, however, that the migration step is one of those garbage-in garbage-out procedures. If you think back to basic physics, you may recall the interrelationship among distance, velocity and time. Distance (in this case depth) travelled is a product of one's velocity and one's travel time.

It means an important prerequisite for accurately migrating from time-based to depth-based seismic data is making sure the seismic velocity model — the model describing what lithologies and general conditions are thought to be present at various depths — represents reality as fully as possible.

Seismic on the upswing

Use of seismic survey data seems to be garnering increasing attention in mineral exploration circles. [1]

The Society of Exploration Geophysicists dedicated a special section of the September-October 2012 issue of its Geophysics journal to the topic of 'Seismic methods in mineral exploration and mine planning', with the explanation:

"To date, tens of 2D and 3D surface seismic surveys have been acquired in Canada, Europe, Australia and South Africa to help in targeting mineral deposits at depth or for designing deep mines. Based on these activities, it appears that seismic methods are becoming established within the mining sector. ... The recent increase in the use of seismic methods in both industry and academia foreshadows developments and applications in the crystalline environment that are certain to be forthcoming." [2]

Some of the benefits of using seismic data include:

  • Seismic data is high resolution, is good for assisting structural analyses, and offers new perspectives on a piece of ground (the latter being a help toward more fully understanding and appraising an area's prospectivity). [3] [4]
  • Done right, dollars spent on acquiring appropriate seismic data can yield a good return on investment. [5] [6]
  • Seismic data may help reduce drilling costs, by giving explorers a way to identify the locations truly warranting drilling follow-up. [7]
  • Seismic surveys can permit imaging to greater depths than other geophysical methods, such as resistivity and induced polarization techniques. [8]
  • Seismic results can help to support or repudiate earlier conclusions made through geophysical, geochemical, and other geoscientific methods. Conversely, seismic results can be used as inputs when carrying out subsequent geophysical methods (e.g., during gravity inversion). [9]

The industry seems to be gathering solid momentum in grasping how best to execute seismic surveys in the onshore mineral exploration and mine-planning arenas. [10] [11] [12] [13]

Groups using seismic techniques lately at the mine scale include:

  • The Deep Exploration Technologies Cooperative Research Center: At the Hillside copper-gold deposit, situated on South Australia's Yorke Peninsula, high-resolution 2D reflection profiles and a 3D seismic mini-cube produced "very good indications of sub-vertical mineralized bodies" as part of a proof-of-concept investigation looking at "cost-effective, integrated high-resolution surface seismic methods to map regolith and deeper structures in a complex hard-rock environment." [14]
  • The Center for High Definition Geophysics at Curtin University: In Western Australia's Kambalda region, targets for massive sulfide deposits were generated via high-quality 3D seismic images, and several targets were verified. [15] In a detailed account published in late 2012, researchers said it was advanced volumetric seismic interpretation, supported by seismic forward modeling, that permitted them to generate and rank targets. "Three of [the highly-ranked] targets subsequently have been drilled and new zones of mineralization were intercepted," they said, concluding: "The probability of hitting such small bodies by underground fan drilling is small. Hence, the role of high-resolution seismic for targeting ore bodies underneath Lake Lefroy may be crucial for further development of Beta Hunt and expansion of nickel mining in the Kambalda region." [16]
  • First Quantum Minerals: A nine-square-kilometer 3D seismic survey at the Kevitsa ultramafic nickel-copper-platinum group deposit in northern Finland flushed out several new drilling targets that warranted follow-up. The findings were made in addition to characterizing major fault zones for pit-planning purposes. The investigators said that "... this is only the beginning of the story, as the [seismic data] cube will be tested again and again against new information as it is gathered when [mine] excavation proceeds and new drill holes are drilled". [17] Because steep open-pit walls were needed to mine the deposit, pit-crossing faults and shear zones needed to be well understood. "An extensive number of drillholes suggest that the geology of the ore and its host rock is simple, with only a few shear zones intersecting the planned open pit," researchers said in a recent paper. "[T]he seismic data, on the other hand, suggest numerous faults." [7] Seismic data also suggested "... a possible shared origin of the Kevitsa intrusion and the nearby Satovaara intrusion," another group of authors said. [18]
  • The Geological Survey of Finland: A five-kilometer-deep 3D interpreted geology model, which incorporated seismic data, helped in mapping basement rocks in a flat, swampy copper-zinc district in western Finland. The area's basement rocks contained an important lithological marker-horizon that was relevant to ore formation. [19]
  • The Outokumpu Deep Drilling Project: The project's partners found that high-resolution seismic data correlated well with drilling data at the Outokumpu area in eastern Finland. The area features Precambrian copper-zinc-cobalt-nickel-silver-gold sulfide deposits hosted in altered ultramafics derived from ophiolites. The project's seismic study authors found that "... seismic reflection surveys could be used for directly detecting potential host rocks of the massive sulphide deposits in the Outokumpu area." [20] And in a 2012 paper, Outokumpu researchers confirmed the notion, saying: "Because the ophiolitic rocks are also systematically the host rocks of the sulfide ores of the Outokumpu type, the reflection seismic data provide a direct roadmap to potentially interesting exploration environments." [21]
  • Mining companies and researchers working in the Kristineberg mine area in northern Sweden: Mining company Boliden supported work by Uppsala University and Lulea University of Technology researchers, who were able to image steeply-dipping structures using high-resolution seismic data. They said, "... the new data also suggest that the Kristineberg mineralization and associated structures dip to the south down to at least a depth of about two kilometers." [22] In 2012, re-processing of a seismic dataset acquired in the area in 2003 allowed the (desired) high-frequency seismic signal to be retained better. "The re-processed seismic section allows correlation of most of the shallow reflections with the surface geology," the researchers involved in that study said. [23] As well, Kristineberg researchers found that the combination of two intersecting 2D seismic profiles, when processed in 3D, gave the true orientation of a seismic reflection of interest that was located west of the mine. "This contact also is an important target for future mineral exploration in the study area and the determination of its geometry is highly relevant for designing appropriate exploration strategies," they said. [24]
  • Various others: Seismic work has been undertaken at other locations around the globe as well. For instance, investigators have employed seismic methods at the Flin Flon mining camp in Canada [25], at the Clare joint venture in Ireland [26], at the St. Ives gold mine area in Western Australia [27], and (in arguably the most well-known and long-lived hive of seismic work in the industry to date) at South Africa's Witwatersrand Basin and Bushveld Igneous Complex. [28]

Meantime, the use of seismic techniques at the regional scale have been fruitful as well, and have included:

  • Characterization of large-scale relationships and structures in Queensland [29]
  • Evidence suggesting extensive deep-seated metasomatism took place in Canada's Slave Craton, which may have set the scene for metallogenesis at shallower locales [30]
  • A re-thinking of assumptions about relationships among 'tectonic blocks' in the Fennoscandian region [31]
  • Visualization of the depth-extent of granites in the Tanami region of Australia; and definition of the eastward extent of the gold-hosting Tanami Group; and deduction of whether the crust is continental or oceanic in origin. [32]

Case study: Bullabulling seismic

A high-resolution 2D surface seismic survey was carried out at Bullabulling, which is hosted in Archean greenstone-granite southwest of Coolgardie in Western Australia.

Bullabulling is situated in the Kalgoorlie Terrane of the Yilgarn Craton's Eastern Goldfields. [33]

Bullabulling is a structurally-controlled gold project 100%-held by Bullabulling Gold Limited. The Deeps Exploration program there has been aiming to uncover deeper high-grade mineralization to complement efforts underway towards first gold production in 2015. [34]

Three approximately parallel seismic lines were acquired at Bullabulling in early 2012. [35]

Fathom Geophysics performed filtering on depth-migrated Bullabulling seismic data (supplied by HiSeis Pty Ltd) and delivered a manual interpretation of each of the three Bullabulling seismic lines in April 2012. As part of the data analysis, airborne magnetic data were also used to help establish preliminary correlations among interpreted contacts and faults/shears appearing each of the three seismic profiles. (Correlation results are not shown in this case study for reasons of brevity.)

The results were used as an input by Kenex Limited to inform its 3D geological modeling of Bullabulling. [36]

As part of the case study presented here, we show you some of the end results of seismic data filtering, using one of the three Bullabulling seismic lines, Line 1, to illustrate the general relationships among the more-common filters.

Note that the vertical exaggeration of Line 1 images is very nearly 1:1, which helps avoid distortion of structural phenomena such as dip angle and curvature paths. [37] The length of strike covered by the Line 1 seismic section is about 6.9 kilometers.

Major structures

Structures were interpreted to exist where seismic reflections were truncated, changed their dip rapidly, appeared offset, or showed rapid amplitude (strength) changes.

In this case study, we reproduce only relatively major interpreted structures, for the sake of clarity when viewing images.

The interpreted structures can be clearly seen even in the original seismic data, which contains the strongest noise signature because it has not been filtered out in any way (see Figure 1).

Vertical structures are shown as magenta lines, while obliquely dipping structures appear as green lines.

Seismic data analysis service figure 1a

Seismic data analysis service figure 1bFIGURE 1: AT TOP: The Line 1 seismic profile at Bullabulling, Western Australia (original depth-migrated seismic data). The seismic data is shown as a variable density display that uses a blue-white-red color scale to depict detected waveforms [blues = negative amplitudes (troughs); whites = near-zero amplitude; reds = positive amplitudes (peaks)]. AT BOTTOM: Some of the major structures manually interpreted for the Line 1 seismic profile at Bullabulling, Western Australia. Structures are superimposed on the line's original depth-migrated seismic data. Vertical structures are shown in magenta; obliquely dipping structures are shown in green.

Lithological relationships

When it came to the manual interpretation of lithology in the seismic data, we:

  1. took the deepest strong reflector as the signpost for the greenstone-to-granite contact,
  2. used the instantaneous amplitude to help define lithological packages likely to host ultramafics (i.e., strongest reflectors have the largest instantaneous amplitude),
  3. positioned possible ultramafic horizons in the interpretation where troughs occur, to be consistent with the known cases (ultramafics were known to be 15 meters thick at most; and two known ultramafic horizons coincided with seismic troughs, which are colored blue throughout the case-study images here), and
  4. called everything else 'greenschist', namely a mix of volcanics and volcaniclastics.

Note that images showing the interpreted lithology relationships do not appear in this write-up. This is because in the period since the interpretation work was completed, concepts were revised in light of new exploration evidence. In other words, the interpretation was not current at the time of writing. (In a future write-up we may be able to show you a seismic-based lithology interpretation we've done that we know to be current.)

Other seismic information

Data processing Fathom Geophysics completed for the Bullabulling seismic lines included:

  • trace mix filtering
  • instantaneous amplitude filtering
  • automatic gain control filtering
  • semblance filtering
  • instantaneous frequency filtering

The trace mix, shown in Figure 2, is a moving average.

Seismic data analysis service figure 2a

Seismic data analysis service figure 2bFIGURE 2: AT TOP: The Line 1 seismic profile at Bullabulling, Western Australia (trace mix filter results, which has removed high-frequency noise from the original seismic data). The seismic data is shown as a variable density display that uses a blue-white-red color scale to depict detected waveforms [blues = negative amplitudes (troughs); whites = near-zero amplitude; reds = positive amplitudes (peaks)]. AT BOTTOM: Some of the major structures manually interpreted for the Line 1 seismic profile at Bullabulling, Western Australia. Structures are superimposed on the line's trace mix filter results.

The instantaneous amplitude, shown in Figure 3, is the strength of the reflected seismic signal, regardless of whether it is positive or negative in polarity.

Seismic data analysis service figure 3a

Seismic data analysis service figure 3bFIGURE 3: AT TOP: The Line 1 seismic profile at Bullabulling, Western Australia (instantaneous amplitude filter results, which map out the signal strength of the original seismic data). AT BOTTOM: Some of the major structures manually interpreted for the Line 1 seismic profile at Bullabulling, Western Australia. Structures are superimposed on the line's instantaneous amplitude filter results.

The automatic gain control evens out the amplitudes of the reflected signal, boosting weaker-signal zones and subduing booming zones. The semblance is a statistical measure of the continuity (or similarity) of seismic data. The instantaneous frequency is the average frequency of the seismic data at a given location.

In this case study, we have presented only the original seismic data, the trace mix filtering results, and the instantaneous amplitude results, for the sake of relative brevity. (Automatic gain control, semblance filtering and instantaneous frequency filtering contained similar sorts of information.)

Figure 4 and Figure 5 provide a qualitative reconciliation, in plan view and in section view, respectively, of how magnetic data textures and discontinuities tie in spatially with seismic data textures and discontinuities.

Seismic data analysis service figure 4FIGURE 4: Plan view of the location of the 6.9 kilometer-long Line 1 seismic profile (white line) at Bullabulling, Western Australia, relative to airborne reduced-to-the-pole magnetic data in the area. Note the pronounced north-south-trending shearing, faulting and lithological fabrics evident in the magnetic data.

Seismic data analysis service figure 5FIGURE 5: 'Perspective' section view of the Line 1 seismic profile (trace mix image) at Bullabulling, Western Australia, relative to airborne reduced-to-the-pole magnetic data in the area.

Acknowledgements

Fathom Geophysics gratefully acknowledges Greg Partington of Kenex Limited for permission to discuss the Bullabulling case study and to present some imaged results of data processing and manual interpretation on the area.

References

[1] See discussion in: I.T. Kukkonen, P. Heikkinen, S. Heinonen, J. Laitinen and HIRE Working Group (2011) "Reflection seismics in exploration for mineral deposits: Initial results from the HIRE project", In: K. Nenonen and P.A. Nurmi (eds) "Geoscience for Society", 125th Anniversary Volume, Geological Survey of Finland, Special Paper 49, 49-58. In this paper, the authors said: "The rapidly improving technological capabilities have gradually changed the situation in favour of applying seismic reflection surveys for mineral exploration...", and they cited various papers supporting this statement.

[2] Society of Exploration Geophysicists (2012) "Call for papers: Seismic methods in mineral exploration and mine planning", seg.org.

[3] For instance, Kukkonen and others (2011) said: "[M]any factors support the use of the [seismic] method in mineral exploration. One of them is the unprecedentedly high spatial resolution, which surpasses that of any other geophysical surface method. Assuming that sufficient impedance contrasts exist, reflectors with a vertical thickness as thin as 10m and with horizontal dimensions greater than about 350m can be directly detected in the uppermost 1-2km. The resolution does not essentially decrease with depth in the depth range where exploration is concerned (to 1-2km depth)." They also said: "[R]eflection seismics can be a very efficient tool in the structural analysis of environments where deposits are already known. In such areas, seismic data also provide a powerful means for 3D modelling with modern visualization software. In exploration, the application of new methods, or methods that have not previously been applied in an area, usually provides new perspectives on the subsurface, which often results in novel ideas and discoveries. Mineral exploration requires and benefits from new methods and technologies."

[4] D.W. Eaton, E. Adam, B. Milkereit, M. Salisbury, B. Roberts, D. White and J. Wright (2010) "Enhancing base-metal exploration with seismic imaging", Canadian Journal of Earth Sciences, 47, 741-760. The authors said: "In almost every case [studied], [multichannel] seismic surveys in mining camps revealed coherent mappable reflections from lithologic contacts and (or) fault zones that have provided an effective framework for interpreting the geological environment of ore deposits."

[5] C.C. Pretorius (2009) "Exploration and mining geophysics and remote sensing in 2009: Where have we come from and where are we going to?", 11th SAGA Biennial Technical Meeting and Exhibition, 16-18 September 2009, 330-340. In this paper, the author said: "New structural insights, and some surprises, such as this [previously unrecognized major graben, which had escaped detection despite decades of surface drilling on the property], with major mine-planning implications, have been detected on the majority of the 17 hard-rock 3D seismic survey projects [that] I have managed over the last 16 years. The total value-add is difficult to quantify, but probably amounts to several billion dollars. Today, at least one phase of 3D seismic imaging would be considered mandatory on Anglo-managed mine developments in the Witwatersrand Basin and Bushveld Complex. In some cases, follow-up high-resolution infill 3D seismics has been conducted around new shaft sites." Note that Pretorius also said that if he believed the use of seismic surveying was not appropriate in a particular instance, then he would not hesitate to recommend alternatives. He added: "... I spend a lot of my time convincing keen, potential clients in our business units not to use this relatively costly technique if I believe that there is a significant risk of poor results."

[6] See, for example, Kukkonen and others (2011), who said: "[T]he rapid development of digital signal acquisition and processing in the last 30 years has significantly improved the situation, and at present high-fold, high resolution surveys can be readily carried out and the results processed at a reasonable cost and time."

[7] A. Malehmir, C. Juhlin, C. Wijns, M. Urosevic, P. Valasti and E. Koivisto (September-October 2012) "3D reflection seismic imaging for open-pit mine planning and deep exploration in the Kevitsa Ni-Cu-PGE deposit, northern Finland", Geophysics, 77, 5, WC95-WC108.

[8] For instance, in their paper, Eaton and others (2010) said: "A significant gap remains, however, betweeen the maximum depths from which [base-metal] ores can be profitably mined (greater than 2 kilometers in many cases) and the effective penetration depths of traditional geophysical methods used in mineral exploration, such as controlled-source electromagnetics, induced polarization, and resistivity survey methods (less than 0.5 kilometer in most cases)."

[9] See, for example: S. Tavakoli, T.E. Bauer, S.-A. Elming, H. Thunehed and P. Weihed (2012) "Regional-scale geometry of the central Skellefte district, northern Sweden—results from 2.5D potential field modeling along three previously acquired seismic profiles", Journal of Applied Geophysics, 85, 43-58. In their paper, the authors said: "The magnetic and gravity models of the three profiles were created using previous interpretations of seismic reflection data as fundamental constraints. ... The use of the results from the seismic interpretation reduces ambiguity in the models. At the same time, it provides an assessment of the link between seismic features and potential field signatures to test a possible consistency between the interpretations of the two data sets. Previous studies indicate integration of seismic reflection and potential field data in the interpretation to be successful."

[10] See, for example, Eaton and others (2010), who said that in light of their Canadian seismic work in the Abitibi region, the Sudbury district, the Buchans mine and the Thompson nickel belt, along with multidiscipline follow-up work done at Sudbury, Manitouwadge, Matagami, Louvicourt and Bathurst: "Taken together, these investigations have contributed a great deal to our understanding of cost-effective approaches to seismic survey design, processing, modelling, and interpretation of unconventional seismic data (in the sense that the vast majority of seismic data is acquired within sedimentary basins), and the physical basis of seismic reflections in hard-rock terranes."

[11] See also, for example, Kukkonen and others (2011), who cited a variety of sources when they said: "The rapidly improving technological capabilities have gradually changed the situation in favour of applying seismic reflection surveys for mineral exploration and waste disposal site studies."

[12] An example in the realm of mine planning, for example, is: C.C. Pretorius, M.A. Gibson and Q. Snyman (2010) "Development of high-resolution 3D vertical seismic profiles", 4th International Platinum Conference, Southern African Institute of Mining and Metallurgy, 47-56. In their paper, the authors said: "[S]ome areas such as shaft infrastructure can benefit from the ability to [seismically] detect smaller structures prior to shaft sinking. ... Anglo Platinum has developed the method of high-resolution 3D vertical seismic profiles (VSPs) for structural sterilization of shaft sites prior to shaft sinking. VSPs utilize a surface source and subsurface receivers deployed down a borehole. This means that seismic energy goes through the near surface only once, and therefore suffers less frequency loss than when both source and receivers are on [the] surface."

[13] See also: M. Salisbury and D. Snyder (2007) "Application of seismic methods to mineral exploration", In: W.D. Goodfellow (ed.) Mineral deposits of Canada: A synthesis of major deposit types, district metallogeny, the evolution of geological provinces and exploration methods, Geological Association of Canada, Mineral Deposits Division, Special Publication No. 5, 971-982. In their paper, the authors said: "Since 2D surveys are best suited to structural reconnaissance, 3D surveys to discovery and delineation, and vertical seismic profile surveys to delineation, and the costs are significantly different, it is important to match the method to the intent of the survey and the type of deposit sought."

[14] S. Yavuz, K. Tertyshinikov, E. Strobach and M. Urosevic (2012) "The use of seismic methods for imaging complex mineral bodies in hard rock environments", 18th European Meeting of Environmental and Engineering Geophysics, European Association of Geoscientists and Engineers, Extended Abstract.

[15] P.K. Williams, M. Urosevic, A. Kepic and M. Whitford (2012) "Recent experience with use of high definition seismic reflection for nickel sulphide exploration in Western Australia", European Association of Geoscientists and Engineers, Extended Abstract.

[16] M. Urosevic, G. Bhat and M.H. Grochau (September-October 2012) "Targeting nickel sulfide deposits from 3D seismic reflection data at Kambalda, Australia", Geophysics, 77, 5, WC123-WC132.

[17] P. Valasti, A. Malehmir and C. Wijns (2012) "3D seismic surveying in Kevitsa open pit mine", ASEG 22nd International Geophysical Conference and Exhibition, 26-29 February 2012, Brisbane, Australia. The authors said: "Processing results suggest that the 3D seismic survey has been successful in imaging both gently dipping and steeply dipping reflections as shallow as about 150m, many of which correlate with fault systems and lithological contacts observed at the surface." See also: (a) E. Koivisto, A. Malehmir, P. Heikkinen, S. Heinonen and I. Kukkonen (2012) "2D reflection seismic investigations in the Kevitsa Ni-Cu-PGE deposit, northern Finland", Geophysical Research Abstracts, Volume 14, EGU2012-4303-2. The authors said: "The known Kevitsa deposit was found to have a specific seismic signature, and the seismic images were used to establish [the] previously unknown shape and extent of the ore-bearing Kevitsa intrusive complex, thus providing a framework for effective future exploration in the area." (b) Kukkonen and others (2011), who discuss Kevitsa, and whose full bibilographic details are listed above.

[18] E. Koivisto, A. Malehmir, P. Heikkinen, S. Heinonen and I. Kukkonen (September-October 2012) "2D reflection seismic investigations at the Kevitsa Ni-Cu-PGE deposit, northern Finland", Geophysics, 77, 5, WC149-WC162.

[19] E. Laine, J. Luukas, A. Ruotsalainen, I. Suppala, J. Kousa and R. Lahtinen (2011) "3D modeling of the bedrock surrounding the Lampinsaari and Kuuhkamo Zn-Cu deposits in the Vihanti area, Finland", Volume 13, EGU2011-11434-1.

[20] S. Heinonen, I.T. Kukkonen, P.J. Keikkinen and D.R. Schmitt (2011) "High resolution reflection seismics integrated with deep drill hole data in Outokumpu, Finland", In: I.T. Kukkonen (ed.) Outokumpu Deep Drilling Project 2003-2010, Geological Survey of Finland Special Paper 51, 105-118.

[21] I.T. Kukkonen, S. Heinonen, P. Heikkinen and P. Sorjonen-Ward (September-October 2012) "Delineating ophiolite-derived host rocks of massive sulfide Cu-Co-Zn deposits with 2D high-resolution seismic reflection data in Outokumpu, Finland", Geophysics, 77, 5, WC213-WC222.

[22] M. Dehghannejad, C. Juhlin, A. Malehmir, P. Skytta and P. Weihed (2010) "Reflection seismic imaging of the upper crust in the Kristineberg mining area, northern Sweden", Journal of Applied Geophysics, 71, 125-136.

[23] S.A. Ehsan, A. Malehmir and M. Dehghannejad (2012) "Re-processing and interpretation of 2D seismic data from the Kristineberg mining area, northern Sweden", Journal of Applied Geophysics, 80, 43-55. The authors said: "The comparison between the previous processing and the re-processing results clearly demonstrates significant improvements in the number of reflections and their continuity and strength."

[24] M. Dehghannejad, A. Malehmire, C. Juhlin and P. Skytta (September-October 2012) "3D constraints and finite-difference modeling of massive sulfide deposits: The Kristineberg seismic lines revisited, northern Sweden", Geophysics, 77, 5, WC69-WC79.

[25] See, for example: (a) D.J. White, D. Secord and M. Malinowski (September-October 2012) "3D seismic imaging of volcanogenic massive sulfide deposits in the Flin Flon mining camp, Canada, Part 1: Seismic results", Geophysics, 77, 5, WC47-WC58. (b) M. Malinowski, E. Schetselaar and D.J. White (September-October 2012) "3D seismic imaging of volcanogenic massive sulfide deposits in the Flin Flon mining camp, Canada, Part 2: Forward modeling", Geophysics, 77, 5, WC81-WC93. (c) D.J. White and M. Malinowski (September-October 2012) "Interpretation of 2D seismic profiles in complex geological terrains: Examples from the Flin Flon mining camp, Canada", Geophysics, 77, 5, WC37-WC46. (d) D.J. White, C.J. Mwenifumbo, M. Salisbury, G. Bellefleur, D. Schmitt and B. Dietiker (2007) "Seismic exploration within the Flin Flon VMS mining camp, Manitoba, Canada", In: B. Milkereit (ed.) "Proceedings of Exploration 07: Fifth Decennial International Conference on Mineral Exploration", 1185-1189.

[26] See work planned in: Lundin Mining (2012) "Exploration 2012", company report, lundinmining.com (http://www.lundinmining.com/i/pdf/2012_exploration_program.pdf), accessed 19 Sep 2012.

[27] See, for example: (a) M. Urosevic, A. Kepic, E. Stolz and C. Julin (2007) "Seismic exploration of ore deposits in Western Australia", In: B. Milkereit (ed.) "Proceedings of Exploration 07: Fifth Decennial International Conference on Mineral Exploration", 525-534. (b) C.B. Harrison, M. Urosevic and E. Stolz (2007) "Processing and seismic inversion of the Intrepid seismic line at the St. Ives gold camp, Western Australia", In: B. Milkereit (ed.) "Proceedings of Exploration 07: Fifth Decennial International Conference on Mineral Exploration", 1087-1090. (c) E. Stolz, M. Urosevic and K. Connors (2005) "Reflection seismic surveys at St Ives gold mine, Western Australia", Australian Mining Technology Conference, 27-28 September 2005, 71-78.

[28] See for example: (a) M.S.D. Manzi, M.A.S. Gibson, K.A.A. Hein, N. King and R.J. Durrheim (September-October 2012) "Application of 3D seismic techniques to evaluate ore resources in the West Wits Line goldfield and portions of the West Rand goldfield, South Africa", Geophysics, 77, 5, WC163-WC171. (b) M.S.D. Manzi, R.J. Durrheim, K.A.A. Hein and N. King (September-October 2012) "3D edge detection seismic attributes used to map potential conduits for water and methane in deep gold mines in the Witwatersrand basin, South Africa", Geophysics, 77, 5, WC133-WC147. (c) C.C. Pretorius (2004) "Use of geophysics for targeting: Some useful lessons from the Witwatersrand paradigm", SEG 2004, Predictive Mineral Discovery Under Cover, 134-138. (And citations within.)

[29] R.J. Korsch, D.L. Huston, R.A. Henderson, R.S. Blewett, I.W. Withnall, C.L. Fergusson, W.J. Collins, E. Saygin, N. Kositcin, A.J. Meixner, R. Chopping, P.A. Henson, D.C. Champion, L.J. Hutton, R. Wormald, J. Holzschuh and R.D. Costelloe (in press) "Crustal architecture and geodynamics of North Queensland, Australia: Insights from deep seismic reflection profiling", Tectonophysics. See also: B.R. Goleby, R.S. Blewett, R.J. Korsch, D.C. Champion, K.F. Cassidy, L.E.A. Jones, P.G. Groenewald and P. Henson (2004) "Deep seismic reflection profiling in the Archaean northeastern Yilgarn Craton, Western Australia: implications for crustal architecture and mineral potential", Tectonophysics, 388, 119-133.

[30] D.B. Snyder (in press) "Imaging Archean-age whole mineral systems", Precambrian Research.

[31] M. Mints, A. Suleimanov, N. Zamozhniaya and V. Stupak (2009) "A three-dimensional model of the Early Precambrian crust under the southeastern Fennoscandian Shield: Karelia craton and Belomorian tectonic province", Tectonophysics, 472, 323-339.

[32] B.G. Goleby, D.L. Huston, P. Lyons, L. Vandenberg, L. Bagas, B.M. Davies, L.E.A. Jones, M. Gebre-Mariam, W. Johnson, T. Smith and L. English (2009) "The Tanami deep seismic reflection experiment: An insight into gold mineralization and Paleoproterozoic collision in the North Australian Craton", Tectonophysics, 472, 169-182.

[33] For a description of the Bullabulling geological setting, see Auzex Resources Limited's 17 February 2012 merger-related announcement (available via Australian Securities Exchange), "Merger scheme booklet", pages 6-12.

[34] See Bullabulling Gold Limited's 18 June 2012 company presentation slides, "Developing a world class gold deposit in Western Australia's premier goldfield", www.bullabullinggold.com.

[35] See GGG Resources PLC's 6 March 2012 announcement (available at www.bullabullinggold.com), titled "Bullabulling gold project: New gold mineralisation identified at Gibraltar and Deeps Exploration update", which said: "The most interesting data received to date that has the potential to change the understanding of the geology, and consequently the potential of the Bullabulling Trend for high grade shoots, is the seismic data. This is one of the first times that this technique, which is routinely used in the oil industry, has been used in exploration for gold mineralisation in the Eastern Goldfields of Western Australia. The preliminary images confirm the controls on mineralisation in the near surface, but, more importantly, suggest the presence of feeder structures beneath the current low grade disseminated mineralisation that forms the current resource. The seismic data when combined with the detailed magnetic data and gravity data will provide new targets for exploration and even at this early stage have increased the potential for new discoveries to be made, especially to the east and directly underneath the current resource."

[36] See Bullabulling Gold Limited's 6 June 2012 stock-exchange announcement (available at www.bullabullinggold.com), titled "3D modelling confirms Bullabulling expansion potential", which said: "The modelling has shown that gold mineralisation at Bullabulling is associated with the largest fold in the region at the top and bottom contacts of the prospective ultramafic unit. ... This structural setting for gold mineralisation has not been described before and its identification has important implications for future exploration as, with the exception of the Bullabulling western limb, the limbs of the folds have not previously been targeted."

[37] See discussion, for example, in: S.A. Steward (August 2012) "Interpretation validation on vertically exaggerated reflection seismic sections", Journal of Structural Geology, 41, 38-46.