Geophysical Signature of the DeGrussa Copper Gold Volcanogenic Massive Sulphide Deposit, Western Australia

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1 Geophysical Signature of the DeGrussa Copper Gold Volcanogenic Massive Sulphide Deposit, Western Australia by Kelvin Blundell 1 Bill Peters 1 Margaret Hawke 2 Summary The DeGrussa copper gold Volcanogenic Massive Suphide (VMS) deposit is located 150kms north of Meekatharra, Western Australia. The deposit is a very recent (2009) discovery with a present indicated and inferred resource of 7.13 million tonnes grading 5.2% copper, 1.9 grams per tonne gold and 15gpt silver for 372,000t copper, 439,000oz gold and 3.4 million ounces of silver, using a cut off grade of 1% copper. The initial discovery at DeGrussa was from a drilling program to test, at depth, a zone of gold mineralisation discovered from geochemical programs. This gold mineralisation also carried elevated copper, arsenic, bismuth, silver, antimony, tellurium and selenium. Close to the completion of the RC drilling program a deep vertical hole intersected massive copper rich sulphides from 98m (near the base of oxidation) to 235m depth. Down hole electromagnetic (DHTEM) surveying showed the DeGrussa conductor to be relatively small; however, follow up fixed loop and moving loop surface electromagnetic surveys identified the presence of a significantly larger underlying conductor referred to as Conductor 1. Spectacular high grade copper gold intersections through Conductor 1 have elevated DeGrussa to one of the most significant copper discoveries in Australia in recent years. DHTEM surveying has been used to complement the diamond drilling program in defining the extent and geometry of the deposit, as well as to explore for possible extensions to the known mineralisation. This method was also instrumental in the discovery of a third body of copper gold massive sulphides at depth, referred to as Conductor 4. Physical property tests were carried out of representative samples of mineralisation and country/host rocks, and the results confirm that TEM surveying is the best tool for detecting further massive sulphide mineralisation in the area. Good contrasts in chargeability, resistivity, and density confirm that induced polarisation and gravity surveying would be valuable tools to complement the TEM surveys. Detailed airborne EM and magnetic radiometric surveys have been flown, and the airborne, surface and down hole electromagnetic signatures of the mineralisation at DeGrussa are being used to search for similar deposits along strike. 1 Southern Geoscience Consultants 2 Sandfire Resources NL

2 Introduction The DeGrussa copper gold Volcanogenic Massive Suphide (VMS) deposit is one of the most significant copper discoveries in Australia in recent years. At present it has an indicated and inferred resource of 7.13 million tonnes grading 5.2% copper, 1.9 grams per tonne gold and 15gpt silver for 372,000t copper, 439,000oz gold and 3.4 million ounces of silver, using a cut off grade of 1% copper. It has also propelled Sandfire Resources from a little known company trading at 4.7 cents on the Australian Stock Exchange at the beginning of 2009, to a household name with a share price of over AU$4.00 by October of the same year an 8000% return for those who bought in at the right time. DeGrussa is located 150kms north of Meekatharra, Western Australia (Figure 1). The deposit is within the Narracoota Formation of the Palaeoproterozoic Bryah Basin, which is thought to be an oceanic, back arc rift basin. The Narracoota Formation is a sequence of metamorphosed, extrusive mafic volcanic rocks and mafic intrusions. Felsic volcanic and volcanoclastic rocks have also been recorded within the formation, but have not yet been identified in the vicinity of the DeGrussa Prospect. Most of the project area is deeply weathered, with very little outcrop, and there is essentially no outcropping geology over the prospective volcanic sequence between the Robinson Range and DeGrussa. Figure 1. Location of the Doolgunna Project and DeGrussa Copper Gold Deposit Exploration History The gold potential of the area around DeGrussa was first highlighted by a regional soil and shallow vacuum drilling program carried out between 2004 and A single line of shallow RAB drillholes was drilled in December 2007 after the vacuum drilling program had returned a 96 ppb Au bedrock sample. This drilling defined a sequence of saprolitic clay and sheared volcaniclastic sediments about 200m to the

3 south of the anomalous vacuum drill hole sample, and returned a 10m gold intersection with an average grade of 5.67g/t. A second round of RAB drilling in April May 2008 was focused around the identified shear zone and returned higher and more consistent Au grades. A third round of RAB drilling in July 2008 returned more exciting Au grades over a strike length of more than 100m. Multi element analysis geochemistry was carried out on selected mineralised and un mineralised samples in early 2009 and, with the exception of Ni, all of the analysed elements were elevated against background levels (Tables 1 and 2), which indicated the potential for a polymetallic deposit in the area. av. Au Table 1: Weighted mean values for samples where Au values are >1ppm Ag As Bi Cu Pb Sb Se Te W Zn Table 2: Weighted mean values for samples where Au values are between 0.1 and 0.99 ppm av. Au Ag As Bi Cu Pb Sb Se Te W Zn A sub audio magnetic (SAM) and ground magnetic survey was carried out over the area in early 2009, neither of which showed any indication of a world class VMS deposit. A follow up RC drilling program was carried out in May 2009 over the anomalous Au zone delineated by the previous RAB drilling program. Toward the end of the drilling program, hole DGRC 083 intersected a significant gold intersection 4.2 g/t) from a depth of 40m. A second, deeper hole (DGRC 101) was drilled nearby to a depth of 144 m and intersected significant massive Cu Au sulphide mineralisation below the zone of oxidisation (DeGrussa massive sulphide mineralisation). A further five RC holes were drilled, all of which intersected significant intervals of high Au grades, and a second hole that intersected the DeGrussa massive sulphide zone. At this stage, very little was known about the geometry or size of the discovery. Initial Time Domain Surface and Down hole Electromagnetic Surveying Conventional down hole time domain electromagnetic (DHTEM) surveys were conducted on selected RC holes to help define the geometry and extents of the intersected DeGrussa massive sulphide mineralisation. Modelling of the DHTEM data showed that zones of native copper within the oxide zone are extremely conductive (>17000S), but very localised. In comparison, models for the DeGrussa massive sulphide mineralisation only had a conductance of S, which is considered relatively low for massive sulphide mineralisation. A lack of consistency in models generated for the DeGrussa massive sulphide mineralisation from DHTEM data from different holes and transmitter loop positions suggested a complex geometry; however, in general the modelling suggested a strike and depth limited conductor,

4 steeply dipping and plunging to the west. DHTEM data from some of the northernmost holes indicated that there may be another, deeper off hole conductor to the north. A large fixed loop TEM survey was conducted over the intersected mineralisation and surrounds. The early time data from this survey shows a strike extensive east west conductive zone to the north of the DeGrussa mineralised zone, but peak amplitudes of the FLTEM data rapidly migrate southward into a WSW ENE trending local anomaly (Figure 2). A single reconnaissance line of in loop moving loop TEM data was acquired with a lower frequency over the peak late time FLTEM anomaly to better define the anomaly shape and aid in the modelling. Models from both the MLTEM and FLTEM data confirmed the presence of a large conductive source referred to as Conductor 1 centred about 200 m northwest of the DeGrussa mineralisation. The models suggested a moderately south dipping conductor at a depth of about 230 m and strike length of 300m. The conductance of these surface models was about 450S. The DeGrussa massive sulphide mineralisation was subsequently referred to as "Conductor 2" Figure 2. Late time channel amplitude image from the fixed loop survey showing locations of preliminary models for the DeGrussa (Conductor 2) and Conductor 1 massive sulphide mineralisation A follow up round of vertical RC drilling targeting Conductor 1 intersected significant grades of massive Cu Au sulphide mineralisation in two of the four holes drilled, but much shallower than expected from the modelling of the surface TEM data. Models derived from follow up DHTEM surveying were consistent with the massive sulphide intersections and indicated that western part of the conductor is steeply dipping to the south and shallowly west plunging. The difference between the surface TEM and DHTEM models is attributed to the effect of the conductive regolith, which was still significant at 20 msec in the FLTEM data. The DHTEM models also showed the lode to be more conductive ( S) than that modelled from the surface TEM data.

5 Airborne TEM (VTEM) Surveying Given the conductivity of the regolith in the area, forward modelling was carried out to determine whether the combined response of the DeGrussa conductor and Conductor 1 would be detectable by an airborne TEM system. The modelling confirmed that the conductive system would be clearly evident above expected noise levels for the VTEM system, although the responses of the individual conductors would probably not be resolved (Figure 3). Furthermore, the forward modelling showed that with a line spacing of 150m, a mineralised zone of similar size, depth and conductance of Conductor 1 should be evident in at least two lines of data. Line mE Line mE Figure 3.. Late time forward model response of the combined preliminary Conductor 1 and Conductor 2 models for a 25Hz VTEM airborne system. The red line is the expected noise level of this system A regional VTEM survey was flown in September 2009 over and along strike from the intersected mineralisation at DeGrussa. The resulting data show that the prospective volcanic sequence is generally resistive, but is flanked to the north and south by very conductive and strike extensive sedimentary units. The northern such unit appears to have preferentially influenced weathering, as it is overlain by a broad conductive zone of regolith. There are also a broad, roughly north south trending zone of conductive channel fill that crosses the area, as well as numerous narrower drainage related conductive zones. Furthermore, the late time VTEM profiles show extensive areas affected by ground polarisation, which manifest as slowly decaying negative EM amplitudes. The massive sulphide mineralisation at DeGrussa lies on the southern flank of the broad conductive zone of regolith described above; however, there was a clear latetime response in two VTEM profiles, which appear as small but discrete, lowamplitude late time peaks (Tau = 6.3 msec) within an enveloping broad mid time anomaly (Tau = 1.4 msec) (Figure 4). The mineralised zones at DeGrussa are evident in both late time B field channel amplitude imagery and time constant imagery (Figure 5).

6 Response of broad conductive zone to the north (Tau ~1.4 msec) Low-amplitude, late-time response of Conductor 1 (Tau ~6.3 msec) Figure 4.Late time VTEM response of Conductor 1 B-Field Channel 35 Image Time-constant Image DeGrussa Anomaly DeGrussa Anomaly Figure 5. Anomalies in the B field Channel 35 amplitude and Time Constant images over the massive sulphide mineralisation at DeGrussa (combined Conductor 1 and Conductor 2) Several VTEM targets have been identified along strike from DeGrussa, and are the focus of ongoing follow up MLTEM and drilling progams. Airborne Magnetic Surveying Prior to acquisition of the VTEM data, the best available airborne magnetic data over most of the project area was 400 m line spaced government data flown at 60m elevation (Figure 6a). The magnetic data acquired in conjunction with the 150m linespaced VTEM data significantly improved the resolution (Figure 6b), despite the higher elevation of the sensor, which was at about 70m above ground. There is no characteristic magnetic response over the DeGrussa deposit in either of these datasets.

7 A high resolution airborne magnetic radiometric survey was flown in December 2009 with the aim of better defining structures and lithology in the area of DeGrussa in order to identify similar structural/lithological settings along strike. This survey was flown with a 50 m line spacing and a nominal flying height of 30m. The data resolution was significantly improved (Figure 6c). However, the survey delineated extensive areas of shallow drainage containing surficial magnetic material that significantly affect the data and tend to mask the more subtle magnetic structures and lithological contacts. a) b) 4 km c) Figure 6. Comparison between airborne magnetic datasets over DeGrussa flown with a) 400m, b) 150m and c) 50m line spacing. Location of DeGrussa is shown by the red circle

8 DHTEM Surveying of Diamond Holes and Discovery of Conductor 4 In July 2009, the first diamond drill hole at DeGrussa intersected both the DeGrussa (Conductor 2) and Conductor 1 massive sulphides, with some spectacular thicknesses and grades (Figure 7). Since then, there has been an intensive diamond drilling program in place to define the resource. In the early stages of the drilling program peripheral holes were routinely surveyed with DHTEM (Figure 8), with transmitter loops designed to explore for possible extensions to the known mineralisation, as well as to help constrain the extents of Conductor 1. DGDD001 DeGrussa (Conductor 2) Conductor 1 Figure7. Interpreted geological cross section through DGDD001 Early DHTEM models based only on these peripheral holes suggested that Conductor 1 formed an inclined V shape, with the two limbs of the V diverging to the east, and the point terminating suddenly at its southwest extent. Subsequent drilling has confirmed that these early models were good approximations of the general shape of the conductive system, with thick massive sulphide zones to the northeast and southeast separated by a zone of relatively thin mineralisation.

9 Conductor 1 Conductor 2 DHTEM surveyed Diamond Holes Conductor 4 DHTEM surveyed RC Holes Figure8. Perspective view of all diamond drill hole intersections and DHTEM models to date showing the holes surveyed with DHTEM There was no indication in the DHTEM surveys of the peripheral holes of any offset extensions to Conductor 1 to the west or south (down dip), where the mineralisation appears to have been truncated by mafic intrusions. A weak below hole anomaly in the northern most drill hole (DGRC 020) was followed up by extending the hole, but unfortunately only black shales were encountered at about 520m down hole depth. Two deep holes on the eastern periphery intersected only stringer zones, but DHTEM surveying of these holes showed that a weak in hole anomaly (Tau = 0.66 msec) corresponding to the stringer zone in DGRC 016 migrated into a strong offhole anomaly (Tau = 19 msec) to the east (Figure 9). The modelled off hole anomaly suggested the source was about 140m x 70m in size with a conductance of over 3000S. A hole targeting this model intersected 17.7 m of high grade massive sulphides from 629m down hole depth (Conductor 4), and significantly added to the total resource estimate for the deposit. A further four holes were drilled into the conductor, DHTEM surveying and modelling of which has consistently shown that it is a mineralised zone about m 2, again shallowly plunging to the west, but much shallower dipping that Conductor 1 and Conductor 2.

10 DGDD-016 Model Response Moderate in-hole conductor Strong off-hole conductor Figure 9. DHTEM profiles of DGDD 016 showing the migration from moderate in hole anomaly to strong off hole anomaly that led to the discovery of Conductor 4 The extent of the up dip eastern part of Conductor 1 is yet to be fully defined, and will constitute the next phase of DHTEM surveying at DeGrussa. Physical Property Tests on Drill Core Physical property tests were carried out on representative samples of mineralisation and host rocks in December 2009 to establish the effectiveness of other geophysical methods for exploring the region. At the time of these tests, there were no examples of disseminated or stringer sulphides samples included three styles of massive sulphide mineralisation, two samples of doleritic host/country rock, and two samples of volcanoclastic sedimentary host/country rock. As expected, there is a large contrast between the EM conductivity, resistivity, and chargeability readings of the massive sulphide mineralisation compared to the host rocks. Of the three mineralised samples, the mixed massive sulphide sample from Conductor 1 showed much higher EM conductivity probably due to the presence of pyrrhotite. It is interesting to note the relatively low conductivities of the massive chalcopyrite mineralisation when compared to the extremely high conductivities of massive nickel sulphides which are commonly the target of TEM surveys. Interestingly there was no significant contrast in the magnetic susceptibility of the mineralised and non mineralised samples, with the exception of the Conductor 1 sample, again attributed to its pyrrhotite content; however, this magnetic contrast would not be enough to recognise a similar mineralised zone along strike unless sufficiently large and shallow enough. The lack of contrast between the magnetic susceptibility of the dolerite and sedimentary rock samples shows that detailed magnetic surveying is not a particularly effective tool for lithological mapping in this area.

11 As would be expected, there is a good contrast in density between the mineralised and un mineralised samples, but again, the mineralised zone would need to be sufficiently large enough and shallow enough for it to be detected in detailed gravity data. Overall these tests confirm that TEM surveying is the best method for detecting other massive sulphide deposits along strike from DeGrussa, and IP/resistivity methods could be effective methods for detecting disseminated zones that were missed through the TEM surveys. Gravity surveying would be a useful survey method for detecting massive sulphide mineralisation beneath areas of conductive regolith, where the depth of investigation of the TEM method is severely limited if the mineralisation was large and relatively shallow. Given the lack of contrast in magnetic susceptibility in this area, gravity surveying would also be a useful tool to aid in structural and lithological mapping. Ongoing Exploration Airborne TEM surveying (VTEM) has now been completed over the remainder of Sandfire s tenements, with gravity surveying due to commence over the DeGrussa area in February March 2010, and ongoing follow up MLTEM surveys are in progress over selected VTEM anomalies. Trial IP surveys are to be surveyed over DeGrussa to see if the mineralisation has an associated IP response that may be used to help identify other sulphide systems along strike. Conclusions DeGrussa is a very significant high grade copper gold discovery that was initially discovered by a geochemical survey. The initial down hole TEM and surface TEM surveys discovered the larger and more significant Conductor 1 lode. The subsequent down hole TEM surveys helped significantly to delineate the mineralisation and discovered the Conductor 4 lode. TEM surveys are the most effective discovery geophysical exploration tool for this type of deposit; however, the conductive regolith and only moderate conductance of the mineralisation limit the depth penetration and delectability using surface and airborne TEM surveys. DHTEM surveys are very effective for delineation of the known mineralisation and detection of additional nearby mineralisation. Ultimately DHTEM surveys will probably be the most effective method for exploration at depth for new similar deposits. IP and gravity surveys should be capable of detecting this style of mineralisation at shallow depth, and IP surveys may detect undiscovered disseminated mineralisation. Magnetic data does not detect the mineralisation directly, and data from SAM surveying does not show the mineralisation.

12 Magnetic, gravity and to a small extent airborne EM surveys will be the main geophysical tools for lithological/structural mapping, although mapping from the detailed magnetic data is made difficult in certain areas due to the affect of surficial magnetic material. Acknowledgments The main authors would like to thank John Evans and Andy Hansen from Sandfire Resources NL for giving Southern Geoscience Consultants the opportunity to work on this project. We would also like to thank Margaret Hawke for contributing the geological and historical exploration information for this paper.