The Abminga Diamond Project, undertaken by Caldera Resources NL, was granted exploration project status, including permission for EL joint reporting, in July 1996. This event followed up to two years of work by other operators on a number of scattered Exploration Licences, and the execution of joint venture agreements between Caldera and the holders of several of these tenements. The Project has comprised twenty-two licences held over sixteen discrete areas, and the early exploration work was reported on in thirteen separate Envelopes prior to being jointly reported. During the progress of Project investigations a number of licence full surrenders and acreage partial relinquishments were effected, with data being progressively released to Open File. First-pass exploration entailed the interpretation of available TEISA programme (PIRSA/MER) 400 m line-spaced aeromagnetic data, eventually identifying more than 100 potentially significant dipolar magnetic anomalies. Subsequently infill aeromagnetic surveys were carried out during 1994, initially using fixed-wing aircraft at 100 m flight line spacing and 80 m sensor height, and later using helicopters to achieve 40 m flight line spacing and 20 m sensor height. Several magnetically anomalous areas were also investigated by conducting gravity surveys. Most of the magnetic anomalies were inspected in the field, and loam, stream sediment and rock samples were collected. The samples were examined, both in Australia and overseas, for heavy mineral assemblage determinations, for microprobe analysis of possible indicator minerals, and for preparing petrological descriptions. This work disclosed the presence of rare kimberlitic indicator minerals, including baddeleyite, plus one macrodiamond, while the petrological interpretations of mafic mineral - rich float samples encountered in the field indicated possible volcanic tuffs, and fission track analyses of the isotopic mineral chemistry of detrital zircon grains gave several results (uranium-depleted, 15-30 ppm U content) indicative of a deep mantle source. In 1995 MIM Exploration entered into joint venture with Caldera on ELs 1879 and 1890. They carried out approx. 3000 line km of detailed aeromagnetic infill (helicopter-borne) and ground magnetic surveys to define drilling targets, then completed test drilling on 12 anomalies (21 aircore holes totalling 1954.5 m plus 28.9 m of diamond core in three tails). MIM concluded that the magnetic anomalies were caused by diagenetic accumulations of magnetic iron-rich minerals within the topmost 40 m of Cainozoic cover sediments, and that the geological sequence was typical Mesozoic Bulldog Shale. They noted no diamond indicator minerals or rocks of probable volcanic origin, and withdrew from the joint venture. During 1997 Caldera continued exploring alone on ELs 1915 and 1936, flying further detailed helicopter-borne aeromagnetic surveys to refine target anomalies, most of which were sampled and tested for heavy minerals and diamond indicators. Cuttings and core from the MIM drillholes were also re-sampled and tested for diamond indicators by Caldera, and a very small microdiamond was recovered from drillhole samples obtained at Magnetic Anomaly 150. Two drilling programmes were completed, the first on five anomalies (9 holes comprising 860.9 m of aircore/percussion pre-collar, and 396.8 m of BQ diamond core), and the second on another six anomalies having kimberlitic chromite indicators at surface (23 vertical RC holes, total penetration 6106 m), to obtain downhole bulk samples for heavy mineral analysis. Laboratory testing of the ~60 tonnes of bulk samples reported large numbers of indicator minerals, particularly chrome-rich pyrope garnets and spinels, while petrologic examinations reported the likely widespread existence of volcanogenic sediments and pyroclastic beds of possible diatreme origin, including lapilli tuff, lithic tuff and crystal tuff that are interbedded with very fine-grained crater lake sediments. The tuffaceous rocks appear to be strongly altered through weathering, the effects of which are seen extending down to 200 m below the ground surface. Beneath this crater facies sequence lie interpreted microbreccias and disaggregated kimberlite extending to the furthest drilled depth of about 300 m, which are assumed to represent the upper levels of the diatreme facies of eruptive pipes. The kimberlite samples comprise fresh carbonate metasometic vein material and up to 90% chlorite pseudomorphs after olivine (forsterite). In 1998 aspiring project farminee Astro Mining NL undertook a six-month due diligence study, which comprised a review of all available data, the re-processing of all aeromagnetic data, the conduct of detailed ground magnetic surveys, followed by the drilling in June 1998 of three fully NQ cored vertical diamond holes (total penetration 501.2 m), to test three magnetic targets not previously investigated by Caldera, and heavy mineral laboratory processing of more than two tonnes of drill cuttings, core and surface samples. No microdiamonds or diamond indicator minerals were recovered, and the drill cores were logged as indicating a normal Mesozoic stratigraphy for the area. Astro therefore did not enter into joint venture. Exploration by Caldera continued with the collection of surface and shallow auger loam samples, which were processed for heavy mineral extraction. Indicator minerals were inspected by scanning electron microscope and by microprobe. During May 2002 a detailed aeromagnetic survey was flown at 150 m to 50 m line spacing over 161 square kms of ELs 2561 and 2566, and further source body modelling of 12 selected magnetic anomalies was also undertaken, with 6 new targets being identified for follow-up ground-based sampling. Difficulties with Native Title negotiations necessary for obtaining land access, and the failure to positively identify unaltered or intact kimberlites, finally led to cessation of the project when a Years 5 to 6 renewal of the ultimate licence, EL 2994, was made on 17th March 2004. However, a separate exploration programme for base metals continues in the follow-on EL 3186, issued over a reduced area.