A diamond exploration project area comprising nine mineral exploration licences located in the central Mount Lofty Ranges was taken up by new public company Flinders Diamonds (FDL) to search for possible commercial accumulations of diamonds, thought to be present in the region either as detrital sedimentary deposits or preferably as primary source kimberlite intrusions. Historical records describing the nineteenth century placer gold rush mining activities which took place near Echunga mentioned the discovery between 1859 and 1909 of around 100 small detrital macrodiamonds by the early miners, but no modern diamond exploration methods had been used over the intervening century to follow up these fortuitous finds, until the late 1970s when two Gem Exploration subsidiary companies commenced sediment bulk sampling and airborne geophysical surveying of EL 493 (see Env 3563). Initial work performed by the subject project operator FDL, after its successful Australian Stock Exchange listing made on 20/2/2002, consisted of the compilation of a summary of regional diamond exploration literature, studies of local geomorphology, heavy mineral sampling of Tertiary gravels, and assessment of aeromagnetic anomalies to recognise potential signatures of kimberlitic bodies. Heavy mineral sample results from previous exploration were tabulated as the basis for FDL's ongoing work. Additional heavy mineral gravel samples were taken to infill areas which had not previously been adequately sampled, to follow-up previous positive kimberlite indicator mineral (KIM) results, and to obtain dispersion train orientation samples near known kimberlite and diamond occurrences. A geomorphological assessment performed by consultant Richard Russell, which included mapping of transported regolith and trenching of palaeo-gravels, defined a Tertiary palaeo-catchment located west of the Meadows Fault scarp between Kuitpo and Mount Pleasant, from which the Echunga diamonds would most likely have come and which therefore formed the exploration focus area. However, it was soon realised that the task of establishing the existence of a coherent train of KIMs within the surviving remnants of Tertiary fluvial deposits would prove to be exceedingly difficult. Nevertheless, it was regarded as highly significant that a single grain of pyrope found by FDL in Echunga Creek trap sample AG04, collected 4 km downstream from the Echunga diamond occurrence at Chapel Hill, is the first indicator mineral coming from this catchment which has been able to be precisely identified both morphologically and geochemically as originating from a kimberlite source, possibly the same one as had shed the macrodiamonds. The lack of signs of abrasive wear on the surface of this euhedral pyrope grain suggested a proximal source, i.e. within a few tens of kms. Conversely, several other very weathered grains of garnet, possibly pyrope, were also recovered from the Tertiary conglomerate bed purported to host the macrodiamonds. Orientation heavy mineral sampling of Long Gully Creek downstream of the Echunga diamond occurrence recovered 150 subrounded grains of chromite, but yielded no picroilmenite or diamonds. The chromite mineral chemistry was determined by electron microprobe analysis to be consistent with a dolerite source rock. A sample submitted for palynological analysis to Liliana Stoian of PIRSA, which was collected from the unconformity at the base of the Tertiary units at Chapel Hill which are thought to host the recorded Echunga macrodiamonds, gave an age of Late Miocene-Early Pliocene (about 4-5 million years old). The environment was estuarine, open eucalypt woodlands were widespread and mallee vegetation was dominant. A type section for the Late Miocene-Early Pliocene sediments of the Echunga area was established by Ms Stoian within Meadows Bore 1, drilled just south of Meadows, at the instigation of FDL (see RB 2004/21). As the historic Echunga macrodiamonds were found in sediments of the same age, a better understanding of this sequence may help to find an indicator mineral train which is traceable to source. For the project licences as a whole, aeromagnetic features likely to be caused by kimberlite or lamproite, and the status of their follow-up by previous explorers, were compiled as a database and used as a guide for a re-interpretation of reprocessed and ERMapper computer imaged regional aeromagnetic data undertaken by consultant geophysicist Graham Bubner early in 2004. He produced a list of 232 magnetic anomalies which could represent potential kimberlites, and FDL began a field programme of loam heavy mineral sampling and ground magnetic profiling of these anomalies. A 60 ha lagoon known as the Hoffnungsthal, which is situated about 2 km south-east of Lyndoch, was investigated as a potential kimberlite intrusion occupying a topographic depression surrounded on three sides by prominent hills of Neoproterozoic bedrock. Samples of soil were taken from the bottom of a deep dam at this locality, but their analysed indicator mineral and soil geochemical properties did not support the kimberlite proposition. FDL's orientation sampling done in a small creek 3.5 km downstream of the known 'Angaston 1' occurrence of kimberlite, that had been discovered by Rio Tinto Exploration in 1994, and which lies 7.5 km east-southeast of the town, showed that the indicator mineral dispersion train is complicated by the presence of both 'kimberlitic' and 'non-kimberlitic' types of chromite, pyrope and chrome spinel, which suggested that multiple discrete intrusion sources exist within the catchment. Two intrusive phases of the Angaston 1 kimberlite, that were directly sampled by FDL, contained 10,000 and 67,000 indicator mineral grains per 20 kg of fresh rock, whilst over twice these numbers of indicator grains were found in overlying soil samples. During 2003 and early 2004, many creek gravel and rock samples were collected from FDL's Kapunda, Mount Pleasant and Echunga licences and submitted for indicator mineral and multi-element geochemical analyses. Gravel sample indicator mineral and multi-element anomalies detected in the North Para River were traced upstream, past the deep Tertiary-Recent basin of the Barossa Valley and into the Barossa Ranges. Sampling of streams near Lyndoch gave large numbers of indicators, implying that sources should exist in the upper catchment areas of Jacobs and Tanunda Creeks. Comparable but much more widespread indicator mineral anomalies containing numerous grains of chromite, picroilmenite and pyrope, with some of these species having kimberlitic geochemistry, were found in another six creeks within a region extending from Williamstown to Stockwell and Springton, which gave strong probability that a field of kimberlite intrusions occurs in the Barossa Ranges. Subsequently, on-ground inspections made there of FDL's selected aeromagnetic anomalies resulted in the discovery of a new kimberlite outcrop on the 'Bunyara' property, 6 km north-east of Angaston, which contains pyrope garnet with a geochemistry suggesting that this intrusion may have good diamond potential. A further four shallowly buried kimberlite bodies were interpreted from aerial photographs to lie on the same linear structural feature. A second new kimberlite, also containing pyrope garnet, was found in a talc quarry (Ian Ross) located south-east from Lyndoch, also in the Barossa Ranges. A ground magnetic survey conducted over the confirmed Bunyara kimberlite occurrences did not detect any magnetic anomalies. Magnetic susceptibility measurements made on the outcropping kimberlite were very low, with an average value of only 50 x 10-5 SIU. Magnetic susceptibility measurements made on the fresh Ian Ross kimberlite exposure in the talc quarry returned this same low average value. By contrast, magnetic susceptibility measurements made along ground magnetic survey lines crossing the two Angaston 1 kimberlite magnetic features showed very distinct high readings of up to 620 x 10-5 SIU. The low indicator mineral concentrations found in rock samples of the Bunyara and Ian Ross kimberlites (100 grains and 8 grains per 20 kg, respectively), when compared with the high concentrations in the Angaston Kimberlite (142,000 grains per 20 kg), implied to FDL that larger samples and higher sample density should be considered during surface KIM exploration. It was recommended that, going forward, all magnetic anomalies and indicator mineral occurrences should be followed up, any ultramafic rocks encountered should be sampled for their micro-diamond content, and any diamondiferous bodies should be bulk sampled. To help define the new-found kimberlite field, many members of which might have quite a subtle magnetic and/or geochemical expression, FDL contracted Fugro Airborne during June-July 2004 to fly an ultra high resolution, gradient-enhanced aeromagnetic/radiometric survey covering 781 square km of the Barossa Ranges, along 100 m spaced north-south lines with a 60 m mean terrain clearance. Two smaller areas, at Hutton Vale and Echunga (20 sq km and 70 sq km respectively), were covered at 50 m line spacing. The total distance flown was 11,359 line km. After the new very high quality aeromagnetic data was processed and interpreted, the number of potential kimberlite targets was reduced to 50 from the initial selection of 176, by deleting those anomalies arising from cultural installations such as sheds, power poles and water tanks, and by concentrating on the anomalies that lie within KIM-positive catchments. The 50 valid anomalies were soil sampled and assayed for Nb, Ni, Cr and Ce or Zr by XRF. In addition, soil sample grids were placed over KIM-positive catchments which had no magnetic anomalism. Trenches were dug at thirteen soil sample sites which were anomalous in Nb, Ni and Cr when compared with the Angaston 1 kimberlite. By this means two small satellite kimberlite diatremes were found near the 300 m x 50 m Angaston 1 kimberlite diatreme. A high diamond potential was suggested by some types of the many indicator minerals present in these bodies (i.e. knorringitic garnet, and highly distorted chromite with very good geochemistry); however, they contained no micro-diamonds. Of interest petrologically is the presence of eclogite nodules to 30 cm in diameter within the kimberlite exposed by trench AHT34, dug to the south-west of the main Angaston 1 kimberlite. In September 2004, a freelance prospector, Trevor Scholz, and a geologist, Bruce Menzel, collected 11 samples of undesignated soil, rock or gravel (AR021-031), which were sent by FDL for indicator mineral analysis. One of these samples (AR022), taken from a creek east of Williamstown with a very small catchment, contained kimberlitic chrome diopside, chromite and enstatite, the geochemistry of each mineral species plotting in the diamond stability field. The remaining samples were KIM-negative. To follow-up five circular topographic features at Bunyara evident on aerial photographs, which it was thought could represent buried pipe-like kimberlite intrusions located near the previously discovered outcropping kimberlite, FDL drilled 4 RAB percussion vertical holes for a total penetration of 151 m during November 2004. All of the holes failed to encounter kimberlite. Geochemical analyses of over 300 chromite grains originating from the whole project area were assessed by consultant Wayne Taylor of Pterodia Pty Ltd, mostly using discriminate analysis techniques which he has developed. His report concluded that chromite-bearing areas around the Angaston kimberlite (near sites of drillhole and alluvial samples) and north of Lyndoch (alluvial samples) offer the best potential for finding diamondiferous kimberlite sources. Taylor also assessed the diamond potential via the thermo-barometry mineral genetic information residing in available chrome-diopside geochemical data, which had mainly been obtained from indicator grain samples collected from near the Angaston 1 kimberlite. The results, summarised on a graph of pressure versus temperature, showed two populations for grains from both the Angaston kimberlite and from the catchment immediately to the south (AG103). A 'cold' geothermal gradient indicates a source of garnet lherzolite in the diamond stability field, whereas a 'hotter' geotherm indicates a source of garnet lherzolite in the graphite stability fields. Taylor (pers. com.) believes that this unusual situation implies significant structural complexity in the mantle (cf. Eggler, et al, 1988). FDL now intends to bulk sample the Angaston kimberlite cluster for microdiamond content, in view of Taylor's findings. KIM grains recovered from Jacobs Creek and Tanunda Creek (AG35 and AG44) were initially identified under the microscope as picroilmenite. However, a later electron microprobe analysis revealed their low total oxide values and high titanium contents, suggesting that the grains may belong to the titanate mineral series lindsleyite-mathiesite (LIMA). Because these rare LIMA minerals are known to be present in south African kimberlites at the Jagersfontein and De Beers diamond mines, they were regarded by FDL as important KIMs worth pursuing within the Adelaide Hills. Recently, a more detailed microprobe analysis has revealed that the grains are probably davidite containing high La, Ce, Y, V, Cr and U. They may derive from a similar rock to that in which davidite was found in the Mesoproterozoic Houghton Inlier. There the davidite occurs as blebs with sphene and apatite, in albitized bands up one metre wide in actinolite-diopside gneiss (Whittle, 1959, and Hayton, 1960). However, only Neoproterozoic and Cambrian rocks are known to occur in the relevant southern Barossa Ranges catchments, and so a kimberlite or carbonatite source is possible. A black mineral from a pegmatite sampled in the Moolooloo Road area was assayed by FDL and found to be titanomagnetite with high values of Cr (1150 ppm) and Nb (390 ppm). However, this pegmatite is not thought to be the source of the Barossa Ranges LIMA/davidite grains.