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Ojolali is located in the southern foothills of the Barisan Range, a chain of Quaternary volcanoes that form the backbone of Sumatra. Gold mineralisation is widespread along the range with several mines operational during Dutch colonial times. In modern times, gold has been mined at Lebong Tandai and Lebong Donok in the adjacent Benkulu Province. Two gold projects are at an advanced stage of evaluation at the Purnama deposit in the Martabe district of N Sumatra (Oxiana Ltd) and at Way Linggo in Lampung where a feasibility study has been completed. The regional geology (Figure 7) is dominated by sediments, andesitic and basaltic lava flows and breccias associated with Quaternary volcanic centres. These overlie the mineralized Tertiary-age volcanics, comprising thick intercalated volcaniclastics, and calcareous and tuffaceous claystones, sandstones and conglomerates. .These mineralized Tertiary volcanics are exposed in windows in the Quaternary in an eroded caldera or volcanic centre. The structure of the area is controlled by extensional tectonics related to the Sumatra Fault Zone with dominant east-west, north-south and northwest orientations. Hydrothermal alteration and epithermal vein systems are closely associated with these structural trends and the circular caldera centre. Local Geology Seventeen named prospect areas defined on the basis of local pitting, mapped veining, alteration and vein float have been interpreted by Finders within the Ojolali Tenement. Significant extensions to these areas, as well as new targets, have also been indicated by resistivity and chargeability anomalies from extensive closely spaced gradient array Induced Polarization surveys completed by Finders. At surface, quartz veins and vein swarms, with individual veins ranging from millimetres up to approximately 1m true width, occur in wide zones that show a range of textures typically associated with epithermal mineralisation. Veins are hosted by andesite and siltstones. Visible gold is common, especially in the areas of local pitting. Jambi, Tambang and Batu Kuning have been the main focus of previous exploration work. It is noteworthy that the average depth of historical drilling is shallow and averages 105 metres. Plans, which incorporate the results of field investigations to date, indicate that the surface expression of precious metals epithermal mineralisation is widespread in the project area (Figure 8). H&S noted that Finders’ recent detailed geological mapping had identified new coherent zones of mineralisation and alteration in areas that had not been previously recognised. There does not appear to have been any similar previous detailed geological mapping and synthesis of information at Ojolali. H&S observed close correlation of resistivity and chargeability anomalies from Finders Induced Polarisation geophysics survey (IP) with outcropping and mapped vein systems. The IP gradient survey has been completed on 50-100m line spacing in the main prospect areas and selected areas are now being followed up with more detailed offset IP dipole surveys to provide three dimensional targeting information.
Project Summary Map showing named prospect areas Results from the previous geochemical based soil surveys undertaken by Antares appears to have been based on sieved samples and an aqua regia digestion. It is likely, in the opinion of H&S, that mineralisation hosted in coarser grained weathering-resistant quartz-hosted grains may have been excluded by sieving, leading to subdued gold anomalism in the soils. By drawing analogies with the discovery history in other similarly endowed epithermal mining districts, H&S regards the prospectivity of the Ojolali project to be high. Ojolali can be compared with the Mt Muro district in Indonesia, (characterized by numerous vein swarms, undrilled by Aurora but a source for new ore reserves for Straits), and the Pajingo deposits in Queensland (where initial shallow drilling failed to establish the full potential of the gold deposits at depth). Terry Leach, an acknowledged world expert on epithermal gold-silver deposits, compared the Tambang-Chandra vein system to shallow epithermal deposits such as Cikotok-Cirotan (west Java), Misima (PNG) and Karangahake (NZ).
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