Geophysics and drilling collaboration, final report for drilling program, Lake Woods Project

Abstract

The Lake Woods project is located 700 km south of Darwin and 200 km north of Tennant Creek. The licences are centred on the Ashburton Range, which runs north-south along the eastern margin of Lake Woods, a large seasonal lake. The Stuart Highway passes through the centre of the area. The project is comprised of five exploration licences, EL 23687, EL 24520, EL 25631, EL 27317 and EL 27318; the latter two were granted in November 2009. Previous exploration within the district has been directed towards the potential for diamonds and base metals but has been limited due to poorly developed drainage and widespread alluvial and aeolian cover. Crossland began exploration in 2004 following recommendation by Paradigm Geoscience, which utilised their confidential concepts of target identification. The aim of their technology is to identify targets for mineral exploration with the same signatures as major mineral deposits. The selection technique does not permit identification of target commodities, and these must be determined by consideration of regional metallogenic factors and field reconnaissance. Geologically the project is located within the Ashburton Province (1400-1700 Ma), which consists of a sequence of unmetamorphosed and weakly deformed, predominantly shallow marine sediments. The oldest rocks that outcrop in the area are Middle Proterozoic evaporitic sandstones and conglomerates of the Renner Group, which form the ridges of the Ashburton Range. A regionally extensive intrusion of what has been previously termed a 'dolerite' (NTGS 2001) has recently become the focus of Crossland's exploration efforts. Diamonds were the target commodity initially. With the increased knowledge gained over several years of exploration, the geological setting of the target area suggested that other deposit types were possible here such as base metals and manganese, or potassic evaporates in the Proterozoic sediments, or copper-nickel in intrusive complexes. An aircore drilling program conducted in 2008 produced samples of the intrusive rock, which were tentatively identified as syenite. Subsequent petrographic work concluded that the 'syenite' might represent a phase of a differentiated intrusion, the presence of which has potential economic implications. In 2009 Crossland applied for, and was granted funding by the Northern Territory Government, to carry out a diamond drilling program to obtain core for geochemical analysis, petrographic and mineragraphic studies and age dating. Four holes were drilled for a total of 461.6 metres (includes one abandoned hole for 48.3 metres). Seventeen (17) samples were collected for geochemistry and 7.5 kg of core was made available for age dating. The overall result of the drilling has clarified the situation as to what rock type we are dealing with and has provided a platform to suggest a possible origin for the unusual classes of micro diamonds identified by previous workers. However, it has not provided any definitive evidence of an association with rock types that may host potentially economic mineral deposits although ideas and assumptions have been put forward to suggest that this type of rock has possible genetic affiliations with layered intrusive complexes and carbonatites. There is also the question posed regarding the part played by the intruded sediments in influencing a compositional change in the intrusion. There were no indications of significant anomalous base or precious metals, or PGE. From the current data set the best estimate for the crystallisation age of the scarce baddeleyite grains recovered from the sample is 1295 +- 14 Ma.