New work undertaken on EL 4187 during the 2009-2010 licence year has included: • Ongoing documentation and interpretation of MGD 55 & 56 • Drilling of MGD57 to 1243 m at Emmie Bluff prospect • Down hole EM and IP logging of...
New work undertaken on EL 4187 during the 2009-2010 licence year has included: • Ongoing documentation and interpretation of MGD 55 & 56 • Drilling of MGD57 to 1243 m at Emmie Bluff prospect • Down hole EM and IP logging of MGD57 • Petrophysical measurements on core from MGD57. The new diamond drillhole was designed to test a target, identified from earlier surface EM surveying, which lies on the Con Ryan prospect, north-east of MGD55. It reached the pre-Pandurra Formation basement at 960.7 m, considerably deeper than expected. The basement consists of haematite- altered granitoid and dolerite overlying (at 1158 m) a sequence of strongly haematitic sediments interpreted to be part of the Wandearah Formation. Minor copper mineralisation averaging almost 0.3 % Cu occurs within this latter sediment unit, with increased anomalous copper and gold values being associated with the main zones of iron enrichment (maximum 2.93 m @ 1.62% Cu and 0.3 ppm Au from 1159.8 m). Upon completion of MGD57 (following various attempts at performing downhole IP and TEM wireline logging which were complicated by a combination of hole blockages and logging cable entanglements), and following a review of available surface and downhole geophysical data, it was concluded that the conductivity high on which the hole was sited may be attributable to ponded saline ground water within the Pandurra Formation arenites, and not to a basement-related feature as had been thought previously (Hanneson, 2010). To test this interpretation, 12 samples of NQ drill core from the Pandurra Formation sequence intersected in the hole were sent for porosity and resistivity determinations. The petrophysical properties found were regarded as explaining the EM survey electrical responses that had been observed. The DHEM logging attempts did yield some data suggestive of basement anomalism, but there was no indication of a strong off-hole conductor. The downhole IP survey efforts were thought to have eventually produced reasonable quality data that support the anomalies picked from the surface EM conductivity-depth images which formed the basis for siting the hole. New work undertaken during the 2010-2011 licence year included the acquisition of an infill gravity survey, the measurement of magnetic susceptibilities of rocks which had been cored at the Con Ryan prospect in April 1990 by Carpentaria Exploration in historic drillhole SAE-7, the conduct of additional MT surveys to test for deep, significant conductive bodies within broad zones of gravity and magnetic anomalism at the Emmie Bluff prospect, and the completion of further exploratory drilling there. 280 new regional infill gravity stations were read during April 2011 over 250 m x 500 m and 500 m x 500 m regular grids at the Con Ryan and Windabout prospects. The new gravity data was incorporated into 3D inversion models along with the results of the October 2010 helimag/rad survey. To assess whether hole SAE7 had actually encountered MIM's Con Ryan “intense magnetic source”, magnetic susceptibility readings were taken on the stored drill core over the entire basement interval 898 to 1221.7 m. These readings are consistently high, averaging in excess of 0.2 SI (to a maximum of up to 1 SI, which equates to around 30% magnetite), and match the original geological log descriptions which noted sections of intense alteration (amphibole-magnetite) and brecciation throughout the basement rhyolite porphyry and underlying metasiltstones. In consequence of now proving this hole's realisation of its geophysical target, the current JV partners have decided to do no further work at the Con Ryan prospect. Six MT traverses spaced 1 km apart were made late in 2010 at Emmie Bluff, with reading taken at 500 m station intervals to yield 2D inversion resistivity sections for interpretation. On all lines, the upper 600-1000 m is characterised by mostly layered variations in an overall low resistivity package. Most of the extremely low resistivities (1-2 ohm-m) appear to correlate with the Whyalla Sandstone and Tapley Hill Formation. The transition to basement looks the same on all sections, with the unconformity position quite evident at approximately 100 ohm-m. The basement shows resistivities of 100–1000 ohm-m that generally increase with depth. It was concluded that the presence of a thick, electrically conductive cover sequence at this prospect has lowered the chances of detection of subtle conductivity features within the underlying basement. Two fully cored deep vertical diamond drillholes were completed at the Emmie Bluff prospect by Noranda Pacific between July and October 2011, for a combined penetration of 2121.1 m. Their aim was to separately test the northern and southern flanks of the residual gravity feature, seeking to find better grades of mineralisation. Hole MGD68 reached basement deeper than expected, at 877.6 m, after passing through a typical Stuart Shelf Adelaidean cover sequence (although here the Whyalla Sandstone and Tapley Hill Formation are absent). However, the middle section of the underlying Pandurra Formation contains an 80 m thick zone of extremely broken and void-riddled rock. Consequently, drilling conditions from this point onward were very poor, with coring pumped water return being lost completely for the rest of the hole, to TD 1043.6 m. Basement comprises a thin zone of weakly haematised and bleached sediments and volcanic rocks of the GRV. This is underlain by a two mica+feldspar granite/granitic gneiss, probably of the Donington Suite, which shows pervasive weak haematite-sericite-chlorite alteration. No significant mineralisation was encountered (maximum copper assay value 243 ppm Cu). Sulphides are present only in trace amounts, and the strong/intense alteration that maybe expected to be associated with IOCG systems is absent. The alteration seen in this hole gave the JV partners the impression of it being distal from the focus of the IOCG mineralising system. The features of a deeper pre-Pandurra palaeosurface and the presence of GRV rocks (instead of Wandearah Formation metasediments) indicated that there is probably a fault with significant displacement causing these structural and stratigraphic differences with respect to holes SAE3 and MGD55, which are located 1.2 km to the NW. This disruption thus puts a control of the maximum southern extent of the Emmie Bluff alteration horizon. Hole MGD69 also reached basement deeper than expected, at 900 m, which shows that the central part of the residual gravity anomaly at Emmie Bluff (previously drilled by SAE3 and MGD55) is a considerable paleo-topographic high and/or upfaulted block. This hole's TD was 1076.1 m, within Wandearah Formation arkosic metasediments. The uppermost basement rock underlying the Mesoproterozoic unconformity palaeosurface is strongly fractured and quite weak for approximately 10 m. This zone is underlain by a 48.6 m thick horizon of intense, pervasive iron oxide alteration (that is also weakly mineralised), with red, black and steely grey haematite±magnetite flooding probable sediments. Original rock textures are generally destroyed or severely disrupted, although it is evident that some of the protolith was laminated. There are also patches of material with ovoid clusters of quartz and feldspar, that look rather like amygdales, in a fine matrix. The mineralised depth interval 946-958 m (12 m @ 0.39% Cu, including 2 m @ 0.97% Cu), which comprises black to steely grey haematite±magnetite and chlorite with disseminated to blebby and vein chalcopyrite-pyrite (and also sparse bornite), occurs in the lower 10 metres of the iron-oxide altered horizon, where the alteration appears to be most intense. Some minor gold mineralisation is also present within the iron-oxide altered horizon (12 m @ 0.24 g/t Au from 908 m), perhaps as an enrichment related to palaeo-topography. During the 2011-2012 reporting period, the JV partners undertook a magnetotelluric survey over the Elizabeth North prospect, which had been identified as a weak gravity anomaly on an interpreted structural trend, besides performing drill site rehabilitation at five sites. MT data was acquired from 72 stations along four prospect transects to try to detect any lower resistivity associated with a complex structural zone, alteration system or mineralisation. Results obtained from the survey were subdued, the main discernible feature being a rise in the basement unconformity (seen as a rapid transition from low to high resistivity) from west to east. The MT data suggested that the gravity feature is also a resistivity high. No further work was recommended at this prospect.