Summary:
The Tiris Uranium Project lies in the north-eastern part of the Reguibat Craton, an Archaean (>2.5 Ga) and Lower Proterozoic (1.6-2.5 Ga) aged complex composed principally of granitoids, meta-sediments and metavolcanics. The resources lie within Proterozoic portions of the craton. This part of the craton generally consists of intrusive and high-grade metamorphic rocks of amphibolite facies grade. In addition to the Archaean and Paleoproterozoic basement rocks, two principal types of Cainozoic surficial sediments occur; Hamada (sand and outwash fan material) and Cailloutis (flat lying calcrete layers, typically one to three metres thick, in places partially silicified) which in this area stand out as small mesas up to a few metres above the surrounding land surface. Several small uranium occurrences were known in the Reguibat Craton from exploration during the 1950’s.
The project consists of two resource areas, referred to as the Western Tiris Resource and Eastern Tiris Resource, located approximately 230 km apart. Within each resource area, uranium occurs as near-surface (<6 m depth) deposits in several discrete minable zones, which occur in five clusters known as Hippolyte, Sadi, Marie, Lazare (all in the Eastern Tiris Resource Area) and Ferkik (Western Tiris Resource Area).
All the resource zones are generally at less than five metre depths and lie beneath flat land surfaces covered by surficial hamada and thin aeolian sand deposits. This shallow overburden largely covers the basement rocks, which only appear as scattered outcrops.
Mineralisation
The uranium resources generally lie either within weathered, partially decomposed red granite or in colluvial gravels developed on or near red granites. Small portions occur in other rock types such as meta-volcanics and meta-sediments. The resources are believed to have developed within shallow depressions or basins, either within weathered granitic rocks or where colluvial material has accumulated in desert sheet wash events. The pebbles within the gravels are generally unweathered fragments washed in from the nearby exfoliating granites and other crystalline rocks, mixed with sand, silt, calcrete, gypsum and yellow uranium vanadates. The gravels and weathered granite occur at surface or under a very thin (<30 cm) veneer of wind-blown sand and form laterally continuous, single, thin sheets overlying fresh rock, usually granite. The uranium mineralisation generally forms thin shallow horizontal tabular bodies ranging in thickness from 1 to 12m hosted in weathered granite and granitic sediments.
It is inferred that the deposits were formed by near-surface leaching of uranium from the uraniferous red granites by saline groundwaters during the wet Saharan “pluvial” periods. There have been several periods over the past 2.5 million years, the most recent ending only 5,900 years ago. Evaporation during the subsequent arid periods caused the precipitation of uranium vanadates, along with calcium, sodium and strontium carbonates, sulphates and chlorides.
The host material at Tiris is granitic gravel or weathered granite containing powdery calcium carbonate (calcrete) and sulphates. Although the Tiris mineralisation is associated with calcium carbonates, it differs from other well-known calcrete uranium deposits such as Langer Heinrich and Yeelirrie, in that they are river valleyfill deposits. The Tiris deposits have formed in shallow depressions in unconsolidated and uncemented gravels and in partially decomposed granites. In Namibia and Western Australia, the mineralisation is typically within calcareous clays or massive hard calcrete which forms below the water table, often at several levels related to the changing positions of the water table. In contrast, Aura's Tiris deposits are believed to be pedogenic calcrete occurrences that formed in the vadose zone by capillary action above the permanent water table.
Dimensions
The Mineral Resources (MR) occur in ten separate deposits in two areas (Tiris East and Tiris West) separated by ~200km.
Tiris East
The Tiris East area comprises 8 separate deposits within a rectangle around 35km north-south and 74km east-west. 1. The Sadi MR occurs in an irregular NNW trending area with a north-south length of 10.6km and an average east-west extent of ~3.0km. There are a few smaller patches of mineralisation outside the main zone. The MR starts at surface and extends to a maximum depth of 17m below surface, although the majority of mineralisation occurs within 8m of surface.
The Lazare North MR occurs over an area of 4.8km east-west and averages ~2.0km northsouth. It comprises two main areas with an additional small patch in the north-west. The MR starts at surface and extends to a maximum depth of 12m below surface, although the majority of mineralisation occurs within 7m of surface.
The Lazare South MR occurs over an area of 7.8km east-west and averages ~1.5km northsouth. It comprises two main areas with an additional smaller patch to the east. The MR starts at surface and extends to a maximum depth of 19m below surface, although the majority of mineralisation occurs within 6m of surface.
The Hippolyte North MR occurs as multiple lenses over an area of 6.1km east-west and 9.6km north-south, and was divided into 7 separate zones for grade estimation. The MR starts at surface and extends to a maximum depth of 11m below surface, although the majority of mineralisation occurs within 6m of surface.
The Hippolyte South MR occurs as multiple lenses over an area of 8.0km east-west and 9.2km north-south, and was divided into 5 separate zones for grade estimation. The MR starts at surface and extends to a maximum depth of 9m below surface, although the majority of mineralisation occurs within 6m of surface.
The Hippolyte East MR occurs as four separate lenses over an area of 3.8km eastwest and 4.3km north-south, and was divided into 3 separate zones for grade estimation. The MR starts at surface and extends to a maximum depth of 8m below surface, although the majority of mineralisation occurs within 5m of surface.
The Hippolyte West C MR occurs as a single irregular zone over an area of 3.6km northsouth and averages ~1.3km east-west. The MR starts at surface and extends to a maximum depth of 10 m below surface, although the majority of mineralization occurs within 7m of surface.
The Marie MR occurs as four separate zones over an area of ~12km east-west and ~7.5km north-south. Marie E extends 1.8 km N-S and 0.6km E-W; Marie F is 1.8km N-S and 0.75km E-W; Marie G is 1.5km N-S and 2.0km E-W; and Marie H is 4.0km N-S and 0.6km E-W.
The MR starts at surface and extends to a maximum depth of 9m below surface, although the majority of mineralisation occurs within 6m of surface.
Tiris West
The Tiris West area comprises 2 separate deposits within a rectangle around 3.4km north-south and 7.2km east-west.
The Oum Ferkik K MR occurs as a single irregular zone over an area with maximum dimensions of 2.6km north-south and 2.4km east-west. The MR starts at surface and extends to a maximum depth of 11m below surface, although the majority of mineralisation occurs within 6m of surface.
The Oum Ferkik L MR occurs as a single irregular zone over an area with maximum dimensions of 2.9km north-south and 1.9km east-west. The MR starts at surface and extends to a maximum depth of 11m below surface, although the majority of mineralisation occurs within 6m of surface.