Geological Model

During the Miocene Period (between 24 to 20 million years ago), several volcanic centres in the Macusani District in Puno, southeastern Peru, were active. The animation below illustrates the how the acidic lavas formed into uranium-rich rocks.

Local Geology

In the Macusani region, late Tertiary tuffs, ignimbrites and associated sediments are preserved in a NW-SE trending graben. Much of the Early Tertiary and Mesozoic cover were eroded prior to deposition of the pyroclastics so they were deposited in part directly on the Palaeozoic rocks including Late Palaeozoic intrusives (Hercynian granites) and extrusives (Mitu volcanics).

The geological plan of the area indicates that the concession is underlain by rocks of the Neogene Period, Quenamari Formation (dated between 22.5Ma to 1.8Ma). The youngest rocks (Pliocene Epoch) are known as the Yapamayo Member and these outcrop over the Colibri Project. The older Sapanuta and Cacacuniza Members (Miocene Epoch) underly the Yapamayo Member.

The known uranium occurrences in the Macusani area identified by the International Uranium Resources Evaluation Project (IUREP) are associated with Pliocene Quenamari Formation tuffs, ignimbrites and interbedded sediments in a NW_SE trending graben. Uranium in the form of pitchblende, uranophane, gummite and meta-autunite occurs predominantly in a fluvio-lacustrine sediment between two pyro-clastic units. The thickness of the sedimentary unit varies from less than 1m to over 5m.

Other uranium minerals are indicated by IUREP (1984) to be hosted in acidic volcanic rocks of rhyolite composition that cover large areas of the Macusani Plateau in horizontal formations from surface to a depth of about 100m but these appear to be lenticular or confined to fracture zones.

Project Geology

The deposits are hosted by acidic tuffs with pyroclasts of size 60mm to sub-macroscopic. The main minerals constituting the tuff are quartz, orthoclase and plagioclase in a groundmass of amorphous glass. A crude bedding was evident some outcrops based on strata containing larger and smaller pyroclasts as well as differential weathering. In both cases a flat dipping tuff is interpreted.