Palaeoproterozoic Willyama Supergroup metasediments, intrusive igneous rocks and volcanic rocks, plus Mesoproterozoic granitoids and associated mafic dykes, which occupy the south-western corner of the Broken Hill basement domain in an area centred about 70 km WSW of Broken Hill, have been explored for possible economic Olympic Dam and Cloncurry style epithermal/hydrothermal copper-gold deposits and for Broken Hill type stratiform/stratabound lead-zinc-silver deposits, as well as for magmatic nickel mineralisation. Based on its successful earlier application by Minotaur in the company's northern Gawler Craton leases, initial ground reconnaissance via regional and infill calcrete sampling was applied at Mutooroo, along with new structural interpretations made from regional geophysical data, aiming to identify trace metal anomalies that are related to dilatant zones in potential lode horizons. A number of strong anomalies were detected, such as at Record prospect where a peak gold-in-calcrete value of 45 ppb Au was returned. Further encouragement was provided by the results of re-assaying of previous explorer's stored drillhole samples for gold, since this target commodity had received only limited attention in the past. Hole PTF4 drilled by Seltrust in 1978 when re-assayed returned 16 m @ 0.2 g/t Au and 54 m @ 0.3% Cu. During licence Year 2 (1998) continuing infill calcrete sampling at 50 m sample spacing confirmed the Record and Fallout prospects as coherent, robust Au-Cu anomalies that were recommended for drilling during Year 3. The common features of the basement so far observed by Minotaur at 31 anomalous locations suggested that there is extensive Fe-metasomatism with related, post-Olarian Orogeny retrogressive shear zone structural controls on copper-gold mineralisation in the region. Another exploration strategy pursued by Minotaur on its Mutooroo and Thackaringa tenements was to conduct auger drilling in covered portions of the ground, aimed at detecting garnets, a mineral class regarded as key to identifying buried prospective Broken Hill Group lithologies from amongst a great diversity of highly metamorphosed bedrock types that have varying levels of alteration, and now lack any remaining clear signs of igneous or sedimentary protoliths. The thus partially revealed garnet-bearing horizons were then geophysically signature-typed by Minotaur through interpretation of detailed aeromagnetic data. After Billiton signed a joint venture agreement with Minotaur in August 1999, a review of the Broken Hill Group prospectivity, which included field checking of Wolfgang Leyh's previously compiled 1:10,000 scale detailed geological maps for the region, identified four preferred drilling targets on EL 2264 spanning a lode horizon strike extent in excess of 12 km. These prospects were then geologically mapped by Minotaur at 1:500 scale, and also rock chip sampled, and the outcropping lode horizons were shown to have high lead (6.3% Pb) and silver (31 g/t Ag) contents, with accompanying zinc carried by both sulphide and spinel (gahnite) mineral phases. Mineralogical examinations of the rocks determined that the surface lode exposures contain original sulphide mineralisation, rather than products of regional high grade metamorphism. The reprocessing and interpretation of historic airborne EM survey data located a number of conductors lying at 150 to 300 m depth which are near the sporadically outcropping surface lodes, and this evidence also suppported the JV's choices of proposed drilling targets. During Year 4 of tenure the Mutooroo JV's exploration activities were focussed primarily on drilling the four targets with Broken Hill style Pb-Zn-Ag mineralisation potential identified from detailed outcrop mapping. This Phase I RC/diamond drilling, carried out during March 2000, identified Pb-Zn-Ag sulphide occurrences at each of the target prospects, and confirmed the interpreted regional stratigraphic trends within the delineated Broken Hill Group north-east trending “corridor of interest”. A best intercept of 1 m @ 7.28% Zn, 1.91% Pb and 16g/t Ag from 229 m depth was obtained in diamond drillhole DRD-01 at the Dingo Ridge prospect, within an 18 m wide zone of 1.2% Zn+Pb. A broad zone of zinc sulphide mineralisation (16 m @ 1% Zn from 79 m depth) was also intersected at the Two Mile Ridge prospect, in drillhole TMRC-02. This first pass RC percussion and diamond drilling of the four lode horizons at Mutooroo, together with structural studies, downhole geophysical surveying and follow-up airborne EM surveying, has indicated a link to a larger, structurally modified sulphidic system. Importantly, the drilling verified that gahnite occurrences at surface indicate a zinc sulphide source at depth, as opposed to them representing highly metamorphosed zinc-impregnated clays. A precursor regional aircore drilling programme undertaken by the JV during January-February 2000 (147 vertical holes drilled along 16 traverses for a total penetration of 3279 m) identified garnet-tourmaline alteration haloes within the “corridor of interest” that typically are associated with Broken Hill type lode development, yet did not encounter any mineralised lodes. Discriminate function analysis, a geochemical data interpretation technique utilising element ratios, was trialled by Minotaur on auger soil sample assay results from two prospects as a way of delineating lode rock occurrences: it was moderately successful at identifying such horizons at the prospect scale. However, the JV partners have since concluded that in general the aircore bedrock drilling/sampling method would be an inadequate exploration tool for delineating lode rocks within covered portions of the Mutooroo and Thackaringa tenements, because of the highly erratic and narrow widths that the lode horizons display at prospect scale. Broad zones of variably mineralised, poorly outcropping lode rock were latterly delineated at the Homestead Ridge and Burta Tank prospects, returning significant rock chip geochemical values that included 3.23% Pb and 4.11% Zn, and 1.38% Pb and 10.9% Zn respectively. Interpretation of the 552 line km of Mutooroo tenement airborne Tempest EM survey data acquired in July 2000 for Minotaur by Fugro Airborne Surveys, was facilitated by the integration of all available drillhole information, geology and structure. A further four targets were selected for follow-up drill testing.