Porphyry Targets
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Porphyry targets are deposits of igneous intrusive rock, formed when volcanic magma cooled and solidified within the earth hundreds of years ago, which can contain a common zoned distribution of precious and base metals mineralisation. The key porphyry targets for Dart are:
Dart has achieved substantial progress toward understanding the porphyry style of mineralisation in their tenements through the development of the Polygonal Vortex Model which assists Dart in identifying porphyry targets and key areas of mineralisation for future exploration. Regional water geochemistry sampling has continued to build up data for Model, which the Company uses to focus exploration for intrusive related gold mineralisation (in particular reduced intrusive related gold (RIRG) polymetallic mineralisation). A generic cross section through such a system is shown in Figure 5a and illustrates the way in which ground water analysis is able to help locate buried mineralisation. Deep faults and fracture systems associated with the intrusions allow ground water to reach the surface via springs and creeks, carrying with it trace amounts of indicative metals. Tracking this water flow has been proven well overseas to be a very useful tool in determining the occurrence of mineralisation. Gold, silver and base metals mineralised systems are evident in the southern sector of the Dart tenement at the Mammoth-Donovan Hill system, and in what the Company refers to as the Northern Sector Porphyries. Gold and base metals mineralisation is associated with the Cravensville Volcanic Arc as RIRG style, with similarities to Fort Knox and other major gold and base metal deposits in the Tintina belt of North America. The significant molybdenum discovery at Unicorn combined with a similar anomaly at Morgan, emphasises the potential of Dart’s so far underexplored porphyry targets within the Cravensville Volcanic province. MORGANA program or non-intrusive geochemistry sampling was carried out at Dart’s porphyry targets, during which a ring of molybdenum mineralisation was identified at the Morgan prospect. The anomalism, which measures between 50-300m in width, has been defined in a 2km x 1.3km ring, with sporadically high peaks of molybdenum at 6700ppm Mo, Tin at 3.14% Sn and up to 698ppm Bismuth (which has the lowest toxicity of the heavy metals and is often used as a substitute for lead). The cylindrical nature of the Morgan anomaly indicates that depth targets, with potentially high levels of mineralisation, will occur. Dart is continuing to receive and analyse assays from the in-fill program at Morgan, and plans to conduct a short drilling program at the site once interpretation of these is complete. NORTH MAMMOTHNorth Mammoth was the first of the porphyry targets in the Dart EL to undergo detailed exploration. Geochemistry samples from North Mammoth, identified and confirmed the presence of a prospective gold, silver and base metals mineralised system which warrants further exploration. Dart was awarded a Rediscover Victoria Drilling (RVD) grant for $59,194 from the Victorian Government for exploration drilling of North Mammoth in February, 2008. The RVD grants are a government initiative to re-invigorate the mining industr, in particular greenfields exploration, within Victoria. Dart will match the grant dollar for drilling dollar. Drilling at North Mammoth commenced in late July 2008. The short 2-3 week program will see six diamond drill holes drilled at North Mammoth, for a total of approximately 1200m up to 275m deep. Early drilling at North Mammoth has identified the presence of a fault, beneath which sulphides occur in highly silicified and sericitised sediments and fine grained pyritic porphyry. Dart’s interpretation of the systems encourages further exploration of the porphyries within the Dart tenement with the objective of a major gold or base metals discovery. The Polygonal Vortex Model has been the first step in understanding this structurally complex system. |
Figure 5aClick to enlarge |
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last updated August 2008 |
