Exploration field activities operated by the parent company of the new licensee commenced during March-May 2003, when Argonaut Resources (Argonaut) undertook a rotary mud/diamond drilling programme to test targets located at Netherleigh Park,...
Exploration field activities operated by the parent company of the new licensee commenced during March-May 2003, when Argonaut Resources (Argonaut) undertook a rotary mud/diamond drilling programme to test targets located at Netherleigh Park, Alford East and Alford South-east. Hole ALDDH01 at the Netherleigh Park prospect was located 160 m north-northeast of MIM's earlier drillhole MPBD03, which had intersected 14 m @ 1.5% Cu. ALDDH01 was drilled on a declination of 60 degrees to the east, down to a total depth of 251.8 m. It intersected chalcocite, bornite and chalcopyrite plus minor galena and sphalerite, yielding an average copper grade of 76 m @ 0.95% Cu from within a carbonaceous siltstone unit. Petrological examination of the assayed drill core from the drilled interval 146-208 m found that high silver values detected therein, e.g. 10 m @ 180 g/t Ag, grading up to 402 g/t Ag, are probably due to silver ions present in solid solution within a hypogene chalcocite phase. At the two other targets drilled, no significant mineralisation was encountered by drillholes ALDDH02 and ALDDH03 (completed at TD 251.1 m and TD 206.5 m respectively). During May 2003, Argonaut drilled a second rotary mud/diamond drillhole at Netherleigh Park. This hole, ALDDH04, which was taken to TD 332.1 m, attempted to scissor ALDDH01 by following a trajectory that was declined to the west: however, difficulties in drilling the precollar through hardpan calcrete caused the hole's azimuth to deviate towards the south, and hence it missed cutting through the plane of hole ALDDH01 by approximately 25 m. A ground magnetic survey was undertaken during June 2003 for Argonaut by Euro Exploration over the Netherleigh Park prospect, in order to better define concealed folding and faulting of the metasedimentary host strata, for assisting with the design and siting of future drillholes. This survey delineated the host unit to the ALDDH01 mineralisation as being a north-south orientated, de-magnetised horizon that has an 1800 m strike length and is up to 400 m wide. Argonaut's review of the work completed by past explorers had highlighted the main Alford Shear Zone, on which the Moonta and Wallaroo mining fields are situated, as a conduit for mineralising fluids, but so far no structural or chemical trap to focus the mineralisation had been identified. A number of geophysical anomalies on late faults cross-cutting the magmatic centres had been identified, and were considered highly prospective for IOCG style deposits. A large portion of the past exploration work had been directed at the magnetic highs, with only limited success. However, the outcomes of recent work completed by new entrant explorers in the Copper Triangle region suggested that demagnetised zones with associated gravity highs, that lie along the main structural corridors, are the most prospective geophysical anomalies. Argonaut realised that a number of targets which fit these criteria are present within EL 3037, but to date these had been poorly tested or not tested at all. [Likewise, immediately to the south of Argonaut's Alford Project, along the Alford Shear Zone, Red Metals (the Australian exploration arm of American copper company Phelps Dodge) had identified 12 geophysical and geochemical targets, with drill testing due to commence in late 2003.] During January-February 2004, Argonaut completed a two-hole (339 m) rotary mud/diamond drilling programme aimed at further defining the strike extent of the Netherleigh Park prospect. The work yielded encouraging results, including a mineralised intercept of 28 m @ 0.47% Cu and 12.7 g/t Ag from hole ALDDH006, which meant that significant copper mineralisation had now been found to occur over 200 m of strike, and remained open both along strike and down dip. The mineralisation occupies dilational veins running parallel to the foliation in breccia and shear zones in country rock consisting of Early to Middle Proterozoic mudstone/schist, siltstone/quartzite and hornfels, and consists predominantly of variable amounts of bornite, chalcopyrite, chalcocite, pyrite and hematite, plus traces of gold, silver and base metals. Several important features were determined by the two diamond holes drilled. The first was that transported cover only extends downwards for 20 m. The second was that strongly anomalous assays were returned from depths as shallow as 40 m. Because the subcropping host rock is a conductive graphitic siltstone, Argonaut envisaged that a suitable geophysical method such as IP could be used to trace the strike of this unit and would also aid in targeting future drill holes. Alternatively, aircore drilling would give immediate results. As far as geochemistry work was concerned, Argonaut also believed that the implementation of calcrete sampling to the south of Netherleigh Park would also serve as a useful orientation study in how best to explore the subject tenement. A review and gap analysis of the geophysical coverage in the Alford area, commissioned early in 2004 by new licence operator Hillgrove Resources from Southern Geoscience Consultants, was thorough, but did not propose using untried techniques or reliance on existing ones other than detailed gravity acquisition, which the consultant hoped could provide a better option for detecting IOCG mineralising systems with dimensions similar to Prominent Hill (5 km x 2 km x 5 mGal). Accordingly, a gravity survey was undertaken by Haines Surveys for Hillgrove over two campaigns in October 2004 and January 2005, to infill gaps in the historical data. 302 and 612 gravity readings respectively were read along 28 lines spaced ~2-3 km apart, at a 200 m station interval. Numerous previously unresolved anomalies were generated from the survey. Unfortunately, the largest anomaly (Anomaly C) mapped lies under the township of Port Broughton. Four gravity highs were selected for drill testing, along with one gravity low. Hillgrove performed a short scout drilling programme during March 2005 in the Alford East area, where a total of 13 holes for a total of 871 m (2 aircore, 11 rotary mud) were drilled to test gravity anomalies at the southern end of the Netherleigh Park prospect. The drilling confirmed the presence of a broad envelope of low grade copper mineralisation that was still open along strike, and 3 holes returned encouraging narrow (4-8 m wide) intercepts of around 1-2% Cu. The visible mineralisation that was seen in cuttings from 5 holes occurs primarily within an unweathered graphitic shale unit as disseminated or discrete bands of sulphides, or less commonly as blebby sulphide layers. Mineralisation within weathered material is less common, and is associated with haematite alteration. Malachite was the observed oxide ore. Next, a staged 99 hole aircore drilling programme (7920 m) was planned by Hillgrove for the Netherleigh Park and Target 3 geochemical anomalies, besides the five new gravity targets, with most of the holes to be sited 40 m apart and drilled to a planned depth of 80 m, giving 100% coverage. The Netherleigh Park holes were intended to further delineate southern extensions of the known mineralisation, in particular focussing on a large cross-cutting structure, which might be one of the key controls to mineralisation in the area. Two fences of holes were also designed to test for any potential northern extensions to the mineralized zone. Drilling at Target 3 was aimed at following up the numerous RAB bedrock geochemical anomalies in this area, particularly around MPBD5, which had intersected 26 m @ 0.7% Cu. The above drilling programme, for which partial funding was obtained under Theme 2 of PIRSA's PACE Initiative (as approved project DPY2-44), commenced in February 2006 and was conducted by Bullion Drilling using a high capacity aircore rig. This rig was completely suited to the task of efficiently penetrating the transported cover with relatively few blockages and no equipment left in the ground, and quickly completed 55 vertical aircore holes for a total of 3300 m. Aircore drilling done south of Port Broughton on the three gravity anomalies selected as IOCG targets failed to detect any significant mineralisation, but confirmed the presence of haematite alteration along with specular haematite at Anomalies A and B, and haematite/magnetite alteration at Anomaly E. The dominant lithology was black shale. Aircore drilling done at Colin Skidmore's Target 3 was designed to follow up historical RAB drilling results and to confirm whether a large occurrence of low grade mineralisation was present here, as at Netherleigh Park. A number of short traverses were drilled at peak copper anomalism from the RAB drilling. While the aircore holes verified that anomalism was indeed present, only one hole encountered significant mineralisation. Hillgrove concluded that there is a strong chance that if more drilling was done around the southern 2 traverses at Target 3, it would yield similar very low grade mineralisation to that present at Netherleigh Park. The main lithologies encountered in the holes at Target 3 were siltstone, felsic intrusive rocks and black shale. Two traverses of aircore holes were drilled north of Netherleigh Park to test the probable northern strike extension to this prospect, and to investigate a historical RAB anomaly located about 700 m to the north. The first drill traverse ended in anomalism, thus indicating that the mineralised zone was still open beyond hole ALAC034. The more northern traverse encountered mineralisation in the bottom of one hole, ALAC030, but the other five holes were relatively barren. The overall indication was that mineralisation still remains open to the north. At the opposite end of Netherleigh Park, six aircore traverses were drilled in an attempt to define mineralisation to the south of previous diamond drilling, in an area where a possible cross-cutting structure may exist. The drilling was successful in defining a broad very low grade envelope of copper mineralisation to the south, the disposition of which seemed to verify the presence of a structure. Determining a dip direction for the mineralisation was difficult due to its low grade supergene nature, and the drillhole spacing and depth penetration. For this reason two sets of cross sections were constructed, one parallel to bedding, the other parallel to the interpreted structure. These didn’t provide any clear answers, although it appeared from past drilling that holes drilled to the east had exaggerated intersections. Treating Netherleigh Park as being the principal worthwhile target that had been addressed by the 2006 PACE drilling programme, it was concluded by Hillgrove that the work carried out there had defined a broad very low grade copper-mineralised envelope approximately 200 m x 600 m in extent, with mineralisation still open to the north and to the south- east of ALAC022. The average grade within this envelope is 2000 ppm Cu. There is a richer but still low grade core within which averages around 5000 ppm Cu and is approximately 20-30 m wide. The style of mineralisation observed at Netherleigh Park is generally stratabound within a graphitic shale which has provided the appropriate chemical trap for mineralised fluids. Hillgrove was of the opinion that the grades encountered so far would require an extremely large body to be present for the prospect to be economic. Its drilling had indicated that no appreciable metal depletion occurs below the transported cover, and therefore the historical RAB assay results would serve as an adequate assessment of the Alford Shear. Thus, given that a base grade of 2000 ppm Cu would be required over a significant area to rival Netherleigh Park, it appears that other than at Target 3, which has now been tested, the rest of the Alford Shear corridor appears relatively barren. During 2006-2007, EL 3037 exploratory work undertaken by Hillgrove concentrated on re-assessing previous work and on evaluating the suitability of calcrete sampling as a first pass exploration tool for the Alford Shear. During February 2007, orientation calcrete sampling was conducted at the Target 1 prospect, where there is partial RAB drilling coverage. The analyte suite for the calcrete samples comprised copper, lead, zinc, gold, silver, cobalt, molybdenum and uranium. The assay results highlighted a number of element associations including copper-gold-cobalt, copper-molybdenum-uranium, and lead-zinc. These three associations when combined outline a north-west trending corridor of zoned mineralisation. It is intended to incorporate Target 1 into the next round of aircore drilling to further test the calcrete anomalies. Because of the element associations identified by the calcrete sampling trial, a batch of 1163 pulps from Hillgrove’s previous drilling was selected for re-assaying. The samples in the batch were chosen from the broad mineralised zones detected at Netherleigh Park and Target 3 prospects, and were submitted for assaying of uranium, cobalt and molybdenum. The results for molybdenum and cobalt were definitely encouraging, since several broad low grade anomalies were revealed. With the current cobalt and molybdenum metal market prices being approximately ten times that of copper, these additional metals would serve as valuable credits to any mining of the copper mineralisation. The results for uranium were generally very low, with only a couple of narrow (1-3 m thick) zones detected. This is in line with what has been returned from previous drillhole sampling. During April 2007, Hillgrove drilled another two inclined diamond drillholes at Netherleigh Park prospect, for 473 m. The drilling proved difficult, as seems to be the case in this region. Holes consisted of a rotary mud precollar followed by HQ, then NQ and NQ3 core. ALDDH007 was abandoned at 172 m depth due to swelling clays, and did not reach the target depth of 300 m. ALDDH008 was successfully drilled to 301 m; this was attributed to the hole having been drilled further with HQ diameter rods. This allowed it to be cased off through the thickest zones of clay alteration, which were swelling after the introduction of water. The aim of the drilling was to test the Netherleigh Park mineral occurrence at depth and to determine the true nature of mineralisation beneath the supergene ‘blanket’. While hole ALDDH007 didn’t reach its target depth of 300 m, it went deep enough to test the main zone of mineralisation. The hole was collared in black shale, and drilled down into strong red rock alteration (either haematite or K-feldspar) accompanied by weak pyrite mineralisation. Several major breccia zones and numerous mafic dykes were cut. The hole was drilled as NQ3 in an attempt to gain some structural information, although this proved impossible due to the highly fractured nature of the ground. Judging by the downhole sample assay results, this hole is apparently improving with depth in terms of grade, which seemed to indicate that the mineralisation is subvertical. If this is the case, then it would explain the exaggerated width of mineralisation encountered in ALAC022, which was further enhanced by supergene enrichment. Better results from ALDDH007 included 1.8 m @ 1% Cu from 154 m, and 9 m @ 117.6 g/t Co also from 154 m. The second hole ALDDH008 was drilled as HQ3 in an attempt to get longer coring runs and better recoveries. While drilling was still problematic due to the clay zones, this hole did manage to get to 200 m where the ground conditions improved remarkably. The core barrel size was then switched to NQ2 and coring was successfully continued to 301 m. The hole encountered strong red rock alteration and brecciated sediments with epigenetic hydrothermal mineralisation characterised by minor pyrite and lesser chalcopyrite. A broad zone of about 50 m of very low grade copper mineralisation (~ 2000ppm Cu) has been enriched within a 75-100 m thick section of the regolith profile near surface, to give a broad ‘mushroom - like’ supergene halo. The primary mineralisation in ALDDH008 appeared to be dipping to the east. Better results included 9.8 m @ 0.58% Cu from 65 m, and 13 m @ 556.6 g/t Mo from 199 m. It is now planned to shift the focus of exploration away from Netherleigh Park and onto the Target 1 and 3 prospects, where aircore drilling traverses will be carried out. Surface calcrete geochemical coverage will be extended to cover the whole of the Alford Shear Zone wiithin EL 3037. More attention will be given to the large Anomaly C gravity high situated mainly beneath Port Broughton township, with a view to determining its IOCG mineralisation potential.