Mbetilonga
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The Mbetilonga Tenement is situated over a large feature interpreted as a nested volcanic collapse structure (Mbetilonga Caldera), the northern boundary of which lies 8km south of Honiara . The area was gridded and intensively sampled in the 1970's by Utah, which discovered widespread, often high tenor, copper mineralisation in soils over an area of several square kilometres. Minor drilling by Utah defined zones of lower grade copper mineralisation on low order targets. Up to 13.7 % copper was obtained in rock chip float samples, with many results over 1 % copper. The Mbetilonga Caldera is defined by radiometrics, aeromagnetics and topography. Epithermal gold mineralisation and associated characteristics dominate the margins of the caldera while the topographically low sections are characterised by copper-rich supergene mineralisation. The area of the system is sufficient to have the potential to host a world class copper and/or gold mineral system.
- Area of copper mineralised caldera - 56km2
- Area of Utah soil grids - 5.9km2
- Area >0.1 % copper in soils at Hambusimaloso - 2.1km2
Work conducted by ARM between 1996 and 1998 confirmed the earlier Utah results. Virtually the entire volcanic structure contains copper mineralisation, although the copper grade appears to increase to the west of the structure, with only about 10 per cent. of the prospective structure sampled by Utah. The rocks are intensively weathered and leached, consisting of white clay with limonite bands and often depleted of copper, although in places high grade chalcocite, covellite and bornite occurs at the surface.
At Hambusimaloso, on the western side of the Mbetilonga Caldera, pitting and trenching over a total of 1,700m at eleven locations across the core of the 2.1km2 copper anomaly encountered chalcocite-covellite stockwork material grading, in one of the trenches, 155m at 1.31 % copper (no cut-off), including 70m at 2.2 % copper. There is evidence of active faulting and displacement of blocks with high grade copper occurring at various topographic levels in a number of locations, both above and below leached material.
The high grade copper occurrences at Hambusimaloso are therefore tentatively interpreted as a result of local tilting that has brought the chalcocite enrichment layer to the surface.
The prospect has a number of important similarities with the Nena copper deposit at Frieda River in PNG. The abundance of chalcocite, covellite and bornite, all minerals with high copper contents in enrichment zones in a volcanic agglomerate host at Hambusimaloso and the relative paucity of these minerals in the overlying leached zones is the most important similarity with Nena. Along with the presence of gypsum in the leached cap this indicates that, as at Frieda River, the porphyry postulated to lie beneath the enriched supergene zone would have been exposed to water which leached the copper in the top of the porphyry downwards into the supergene zone. Based on the comparison with Nena, the Directors believe that at Hambusimaloso, a mineralised copper porphyry underlies the mineralised volcanic agglomerate. At Nena, the enriched ore zone overlying part of the porphyry attains 50Mt at a grade of 2 % copper.
Elsewhere in the Mbetilonga Caldera, strong copper and clay/pyrite mineralisation has been sampled in the creeks at Vurukuvekuve, Vuanimaho, Olsen's, Vuralosa, Lotu, Vuralanggoma and Vatuchichi. As early as 1957, BSIP geologists recognised alluvial gold in the Mbetilonga River, downstream from the Olsen's prospect, which covers a broad area 1,500m x 600m of clay pyrite alteration in andesite volcanics and agglomerates. To the north of the Olsen's prospect lies the Vuralanggoma prospect in the centre of an area of extensive copper mineralisation in float with alluvial gold in the Mbetilonga River. At Vatuchichi north of Hambusimaloso and Vurakuvekuve east of Hambusimaloso, the volcanics are similarly altered and alluvial gold is frequent in the creeks. The Hahala porphyry lies 500m to the north-east of the Hambusimaloso prospect and the Directors believe this represents a gold mineralised intrusion; having returned up to 0.5g/t in outcrop in this area.
High grade gold in epithermal quartz veins is recorded from the Vatuchichi prospect and this zone is postulated to represent an epithermal location, distal to an underlying porphyry.
Detailed mapping and sampling has confirmed the presence of very high order copper gold mineralisation and 5 drillholes were put into the target areas during the first six months of the Solomon Gold exploration program. Very complex geology and a barren cover sequence has masked the host mineralisation which has not yet been intersected in the drilling. The presence of extensive areas of copper mineralisation in soils over 0.1% copper and rock chip results up to 13% and aeromagnetic and radiometric signatures characteristic of large porphyry systems highlights the unconcluded prospectivity of this area.
Solomon Gold intends to review the results of the work carried out to date in an effort to redefine drilling targets at Mbetilonga.
