Geology

Geological Setting

A large portion of the Project area is under a thick lateritic and saprolitic weathered horizon up to 50 m metres in vertical depth. Little outcrop is present on the property limiting the amount of local bedrock mapping to artisanal pits (where deep enough). Based on the drilling results and mapping done in artisanal pits, the felsic and mafic volcanic units of the Lower Nyanzian stratigraphy constitute the lithologies of the license area Quartz veins cross cut the lithologies and generally contain gold only within shear zones that have developed on lithological contacts. Mineralisation is pronounced when veins are associated with sulphide minerals (i.e. FeS2).

Mineralisation

Gold at Imwelo occurs in three main forms:

1.    Auriferous quartz veins – Significant intersections announced by Mincor as well those from Barrick’s RAB and RC programs are associated with quartz veins.
2.    Alluvial gold – Near-surface, artisanal workings are found in the north-western area of the tenement.
3.    Fine disseminated gold within laterite – Commonly associated with strongly fractured and weathered quartz, suspended in the laterite matrix. This is the main material which villagers are recovering gold currently.

The LVG recent drilling campaign confirms the presence of gold within quartz veins, but further notes that not all veins are auriferous and the presence of shearing is regarded as a prerequisite. Gold is also not associated with vein only and the country rock (i.e. hanging and footwall) also hosts mineralization (also to a lesser grade) at least 0.5 m into country rock from the quartz vein.

Mineralisation Type and Model

Mesothermal, gold (Au) deposits (also labelled Orogenic gold) are a distinctive class of mineral deposit that has been the source for much of world gold production. The ores are widely recognized in both Phanerozoic mobile belts and older cratonic blocks (i.e. the Lake Victoria Goldfields, located within the Tanzania Craton). Mesothermal gold deposits have formed over more than 3 billion years of Earth’s history, episodically during the Middle Archaean to younger Precambrian, and continuously throughout the Phanerozoic.

Mesothermal gold deposits are characteristically associated with deformed and metamorphosed midcrustal blocks, particularly in spatial association with major crustal structures i.e. shear zone or thrusts. A consistent spatial and temporal association with granitoids of a variety of compositions indicates that melts and fluids were both inherent products of thermal events during orogenesis. Including placer accumulations, which are commonly intimately associated with this mineral deposit type, recognized production and resources from economic Phanerozoic orogenic-gold deposits are estimated at just over one billion ounces of gold. Consistent geological characteristics include (Goldfarb et. al., 2001):

1.    Deformed and variably metamorphosed host rocks
2.    Spatial association with granite
3.    Normally, a spatial association with large-scale compressional to transpressional structures
4.    Orogenic gold mineralisation normally consist of abundant quartz-carbonate veins

The granite-greenstone sequences of the Tanzanian craton show many features that are typical of other Archaean cratons around the world, including the existence of numerous granitoids within and around substantial masses of greenstones (metavolcanic unit), a predominance of greenschist facies regional metamorphism, regional scale crustal deformation and the existence of numerous gold deposits (Taylor, 2009).

Model for gold deposits at the LVGF

The Lake Victoria Goldfields (LVGF) have recorded bedrock gold mining as early as 1898 which continued intermittently into the 1970s in the Mara, Musoma, Serengeti, Iramba Plateau and Geita areas. These operations were primarily on mesothermal lode-type deposits within the greenstone belts, most of the veins being associated with faults and shear zones (Taylor, 2009).

Significant greenstone hosted gold in quartz vein mineralisation is typically distributed along specific regional structures and at the boundaries between contrasted lithologic and / or age domains. Shear zones and faults are developed along lithologic contacts between units of contrasting competencies and along thin incompetent lithologic units. Along these contacts and along incompetent rocks, deposits will preferentially develop at bends, and structural intersections.

Induced Polarisation (IP) Geophysics overlain on Magnetics Geophysics