A large part of the Harris Greenstone Domain basement tectonostratigraphic block, extending from 10 km to 130 km west of Kingoonya, is being explored for possible buried economic gold, nickel and other base metal mineralisation which may be...
A large part of the Harris Greenstone Domain basement tectonostratigraphic block, extending from 10 km to 130 km west of Kingoonya, is being explored for possible buried economic gold, nickel and other base metal mineralisation which may be associated with demagnetised shear structures and with igneous intrusions of Archaean to Mesoproterozoic age. The licensee took up the subject ground when it noticed that significant EM anomalies located therein, which were hinted at by open file data from a SA Government-operated TEMPEST AEM survey flown in April 2001, had not been followed up by either government or industry explorers. Reprocessing and interpretation of this AEM data revealed 20 conductors which could possibly represent buried metallic mineralisation still awaiting discovery. During the first two years of tenure, however, Endeavour Discoveries chose to follow a conventional gold search strategy by undertaking a surface geochemical sampling programme across the entirety of the subject licences that addressed areas previously untested or showing historic anomalous gold-in-calcrete sampling results. 205 calcrete samples, 143 MMI samples and 583 plant biogeochemistry samples were collected. This field and laboratory work was part of a collaborative PhD research project that was established between Endeavour Discoveries and the Adelaide University. The principal aim of this gold vectoring project was to test plant biogeochemistry over varying regolith terrains (aeolian sand dunes, alluvial/colluvial cover and residual saprolite) and to compare the results to spatially corresponding calcrete geochemical data. To complement this study, vegetation and calcrete data were also collected over known mineralisation at the historic Glenloth Goldfields (permission granted from ML owners). The results of the surficial sediment and vegetation geochemical sampling proved inconsistent and of low tenor, and the licensee concluded that the methods are unreliable in this particular region of the craton for detecting buried primary mineralisation. In the third year of tenure, Endeavour Discoveries set out on a different search path, to prove that there was sulphide saturation in the Archaean komatiites which could thus host nickel sulphide mineralisation. To start afresh, during the period April to June 2012 the company compiled all available open file drilling data for its granted ELs, and then generated drill targets using a range of available geophysical, geological, surface geochemical data and the compiled drilling database. A diverse range of targets were generated along with regional interpretations on known and potential new komatiitic units. Next, during September-October 2013, a campaign of mainly RAB and aircore drilling plus limited RC drilling was conducted on the subject licences to test a variety of inferred ultramafic intrusion drill targets as well as secondary gold and base metal targets generated within the Archaean and younger bedrock. 77 inclined or vertical holes were completed for a total penetration of 2920 m. The drilling was belatedly successful, as bedrock gold mineralisation was discovered when drilling near Hopeful Hill, at the HH_16 gold-in-calcrete anomaly, in TARC075, the last hole of the entire campaign. This intercept of 19 m @ 0.51 g/t Au was returned from 8 m downhole, and remained open at depth and in most directions. To follow up the gold discovery at what became called the Double Dutch prospect, grid-based soil sampling was later undertaken there on 25 m centres along N-S lines 50 m apart. 210 x minus 100 microns samples were assayed. Values were relatively subdued, with those of at least half of the analysed elements being at or close to detection limits. Analysis of results using a correlation matrix shows no significant association with gold. Contouring of gold values using a lower value of 5 ppb Au defined two main areas of anomalism having an overall E-W trend. The eastern anomaly with a peak of 130 ppb Au coincides with the maximum downhole gold intercept recorded in TARC-075, and extends to the ENE for a further 90 m. The western anomaly with a peak of 98 ppb Au trends E-W for 200 m and is open to the west, where further soil sampling is planned. The drilling performed near Lake Harris was also successful in outlining a thick package of ultramafic and lesser mafic rocks having locally anomalous Ni-Cu and Ni-PGEs. Best results here included 27 m @ 0.40% Ni from 12 m downhole in TARC065 (including a maximum 1-metre sample interval assay value of 0.69% Ni), and 23 m @ 0.17% Ni from 17 m downhole in TARC062, with elevated Au-Pt-Pd of 67+20+25 ppb over 1- metre sample intervals. The best Ni-Cu result was 3 m @ 0.21% Ni + 256 ppm Cu, also encountered in TARC062 from 17 m downhole. The elevated copper content of >200 ppm Cu, besides the elevated nickel of >1000 ppm Ni, and the locally elevated Au-Pt-Pd, are regarded as positive signs that potentially economic occurrences of nickel sulphide mineralisation may exist in the Lake Harris Komatiite. The maximum nickel value of 0.69% Ni is by far the highest reported to date for this metal in the Lake Harris Komatiite. Two ground magnetic surveys were performed during Year 3. In late September 2013, due to the lack of drilling success achieved to that time, 20 traverses for ~32 line km were read by Endeavour geophysicists across selected magnetic features to refine drill targeting of ultramafic rocks. On 9/12/2013, 28.2 line km of ground magnetic data were collected by contractor AMG Surveys over the Double Dutch prospect, along N-S lines spaced 50 m apart which covered an area of 1.4 square km. Interpretation of the gridded magnetic data revealed a series of irregular generally E-W trending magnetic highs, one of which coincides with the newly identified gold mineralisation which has associated biotite – magnetite alteration. The Hiltaba granite displays a neutral/flat magnetic response, while the variety of felsic gneisses display variable magnetic intensity. During October 2013, a detailed resistivity survey was carried out by ZZ Resistivity Imaging over the gold mineralised historic Lake Labyrinth and Company Well prospects. It was designed to test the effectiveness of the resistivity technique for mapping bedrock shear-hosted gold, as had been mined underground in the old workings. The trial survey was undertaken at a 10 m line spacing to try to resolve the quartz shear zones, but proved to be quite ineffective in mapping the mineralised system. Anomalies seen on the resistivity profiles were thought to be indicative of probable weathering depth variations. Late in November 2013, a detailed, 20 m station spacing dipole-dipole survey IP survey was carried out by Search Exploration Services over the Lake Labyrinth and Company Well prospects, and a gradient array IP survey was also read over Company Well. The reason given for undertaking this second trial ground electrical geophysical survey was to check whether disseminated sulphides, mainly pyrite, that may be associated with the known gold mineralisation, could give rise to a noticeable chargeability anomaly. Disappointingly, the IP survey proved to be quite ineffective in detecting chargeability anomalism that correlates with known mineralisation, although both the dipole-dipole and gradient survey results do correlate with structural interpretations made from interpreting the magnetic data. Geological field mapping was conducted over 2 days in December 2013. The area mapped is centred on the gold mineralised drillholes and covers a more extensive area than the current soil sampling. There is locally extensive sub crop and float and lesser outcrop in the area covered, as well as unconsolidated alluvium in recent drainages. A georectified Google Earth image was used as a base and GPS points of 107 mapped localities were logged. Data was digitised into MapInfo and a geological interpretation was produced. During the 2014 project reporting year, the following work was done: - RC drilling at the Double Dutch prospect (Tarcoola Project), at the Lake Harris nickel prospect (Tarcoola Project) and at several gold prospects (on Theseus Project ELs 5256 and 5280). A total of 136 angled holes were completed for 9025 m; - acquisition of detailed helimagnetic/radiometric/DTM survey data over the Double Dutch to Hopeful Hill area, the Lake Harris Komatiite ultramafic bedrock, and part of the Theseus project ground. A total of 4720 line km were flown during early September 2014 on 20 m and 50 m line spacings, using a 30 m mean sensor height above the ground surface; - soil geochemical sampling at Double Dutch, extending westwards to Hopeful Hill, and also in the historic Lake Labyrinth mine area within the Theseus Project ground; - 1:5000 scale field geological mapping at the Ariadne gold prospect, performed by Peter Hill early in November 2014; and - acquisition of a ~37 line km, 200 m line spaced, 100 m station interval moving loop ground EM survey during September-October 2014 at the Lake Harris prospect. The most encouraging results were obtained by the drilling of 19 holes at Double Dutch, where significant but patchy gold mineralisation was encountered along six traverses over a 100 m strike length and remains open at depth (a best 1-metre sample interval downhole assay result of 6.8 ppm Au was returned from below 119 m in hole TARC162, at the lower end of an 80 m long section averaging 1.02 ppm Au). Endeavour considers that this epigenetic occurrence may represent a new style of prograde metamorphic altered gold mineralisation which it could recognise in the Gawler Craton. Most other documented gold mineralisation in the Gawler Craton such as at Tunkillia, Tarcoola, Barns, Earea Dam and Lake Labyrinth is associated with retrograde, lower temperature, sericite-chlorite assemblages. But the biotite-magnetite association seen in the ?Tunkillia Suite granite gneiss host at Double Dutch may reflect a higher temperature style possibly related to the Hiltaba granite intrusive event, because of the aplitic Hiltaba Suite dykes and Gawler Range Volcanics dykes which intrude the host sequence. The 68 holes drilled along five traverses at the Lake Harris nickel occurrence made several new intercepts of anomalous nickel (>1000 ppm Ni) and copper (>50 ppm Cu), but the associated gold content was generally subdued. The latest drilling did not identify any obvious anomalous Ni-Cu trends linking drill traverses, while the ground MLEM survey did not detect any conductors that might indicate possible sulphide accumulations. It was decided not to do further work to appraise this occurrence, as its prospectivity had been downgraded. Drilling of the newly defined Minos and Ariadne gold prospects in the Lake Labyrinth mine area, which are located in and adjacent to a major shear zone, produced a number of promising intercepts over 400 m and 450 m strike extents respectively. Of particular significance here was the recognition of a number of broad zones of weak to moderate sericite-chlorite alteration with commonly associated, trace to 2%, disseminated fine grained pyrite mineralisation. These zones were able to be recognised high up in the weathering profile. Basement lithologies are dominated by weakly foliated, medium to coarse grained K-feldspar rich granite gneiss, which is strongly deformed at Ariadne, under 2 to 10 of variably cemented (calcrete+silcrete) transported cover. Depth to fresh rock ranges from 50-80 m under saprolite + saprock domains.