Plateau Energy Metals Inc. (Plateau) is the registered owner of 99.5% of the outstanding share capital of Macusani Yellowcake S.A.C. (Macusani), which owns 99.5% of the outstanding share capital of Macusani Uranium S.A.C. (Macusani Uranium), with the remaining 0.5% held by a Peruvian individual as recommended by the Ministry of Energy and Mines (MEM).
Following the acquisition of Plateau in May 2021, American Lithium Corp. has several uranium prospects on the Macusani Plateau with concessions being held by Plateau’s Peruvian operating company subsidiary Macusani Yellowcake S.A.C. (Macusani), formerly Global Gold and Minergia.
- subscription is required.
Summary:
In the area of interest, late Tertiary tuffs, ignimbrites and associated sediments are preserved in a northwest-southeast trending graben. Much of the Early Tertiary and Mesozoic cover was 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 known uranium occurrences in the Macusani region identified by IUREP are associated with these Pliocene and Miocene epoch Quenamari Formation tuffs, ignimbrites and interbedded sediments. Other uranium mineralisation was indicated by IUREP (1984) to be hosted in acidic volcanic rocks of rhyolite composition that cover large areas of the Macusani Plateau in horizontally bedded formations from surface to a depth of about 100 m but these appeared to be lenticular or confined to fracture zones (Young, 2013).
Uranium mineralisation is found in acidic volcanic pyroclastic rocks of rhyolite composition that cover large areas of the Macusani Plateau which are preserved in a NW-SE trending graben within the Andes. These pyroclastic rocks are dated between 10.0 and 6.7 Ma. Uranium mineralisation is found concentrated along steeply dipping fractures but constrained within horizontal or sub-horizontal zones and is disseminated into the surrounding host rock.
The style of mineralisation within fractured acidic pyroclastics is not a common form of uranium mineralisation. The main uranium mineral present is meta-autunite concentrated as disseminations and sometimes massively along fractures.
The host rocks and PEM are composed of an acidic tuff (Thatcher, 2011) (19) with pyroclasts of size 60 mm to sub-macroscopic. The main minerals constituting the tuff are quartz, orthoclase and plagioclase in a groundmass of amorphous glass. Crude bedding is evident in some outcrops, and is based on “strata” containing larger and smaller pyroclasts. Overall the uranium mineralisation is interpreted to be hosted in a flat dipping acidic tuff.
Uranium mineralisation is observed in these pyroclastic host rocks, and at a local scale is found concentrated along fractures and disseminated into the surrounding host rock. Zones in which the uranium mineralisation (either fracture and / or dissemination) is more concentrated, are identifiable by analysing uranium distribution profiles in drillhole core, and are occasionally observable in outcrop. These mineralised zones, referred to locally as “Manto’s”, typically have a horizontal or sub-horizontal orientation, and can vary from several metres to tens of metres in thickness.
The petrography of the samples analysed by Thatcher (2011) indicates that the acid volcanics (crystal lapilli tuffs) can have varying composition from rhyolite to dacite to latite which supports the likely presence of stratigraphic layering of the volcanic pile as noted in by Cheilletz et al (1992).
CORACHAPI COMPLEX
TMC undertook Mineral Resource estimates for the Corachapi deposit in 2010, and at that time, mineralisation was interpreted to be hosted in a single, sub-horizontal mineralised zone, which was oriented in a northeasterly direction.
COLIBRI COMPLEX
Mineralisation at the Colibri II & III and Tupurumani deposits is interpreted to be hosted in a subhorizontal, near surface zone, with a dip of approximately 2° - 3° to the northeast. The base of the near surface high-grade zone of mineralisation has a depth of approximately 35 m below surface at Tupuramani and 50 m below surface at Colibri II & III. Lower grade mineralisation is found below the base of the high-grade zone.
KIHITIAN COMPLEX
Within the Kihitian Complex, mineralisation is broadly contained within two distinct zones, referred to as Level A, an upper horizon and Level B, the lower horizon. A dip of 3° towards the southeast is interpreted. Most of the mineralisation for the Complex lies in Level B, while Level A has more sporadic and less continuous mineralisation. The Chilcuno Chico and Tantamaco deposits host both zones while at Quebrada Blanca the mineralisation occurs stratigraphically in Level B and the sparse nature of drilling on the Tuturumani deposits enabled the definition of only the Level A. The Tuturumani deposit has been minimally explored, thus Level B has not been fully tested by drilling. The contact between Level A and Level B zones has a characteristic grade spike which has been consistent but not continuous across the four deposits. The depth of mineralisation is related to the topography with maximum depths being 200 m and 260 m for Level A and Level B respectively.
ISIVILLA COMPLEX
Uranium mineralisation at the Calvario I, Puncopata, Calvario Real and Isivilla deposits is evident in two sub-parallel, near-horizontal zones, locally referred to as levels, separated vertically by 30 m of barren rhyolite.
At the Isivilla and Calvario Real deposits, two distinct zones referred to as Level A and Level B have been identified. The two levels have a highly diffuse contact with an irregular rhyolite parting. Both levels have been noted to outcrop. Although there are localised variations, generally the contact lies flat dipping up to a maximum of 4° to the northeast. The maximum depth of Level A is approximately 60 m and that of Level B approximately 130 m. During correlation, mineralisation in the Puncopata deposit was noted to be localised exclusively to Level B while in contrast, at the Calvario I deposit, mineralisation is localised exclusively to Level A horizon.
At the Calvario I and Puncopata deposits, the flat-lying interpretation of the mineralised levels is supported by radial radiometric anomalies which encircle the hilltop at the same elevation as the mineralised levels have been interpreted to outcrop. Although similar radiometric survey data is absent for the Calvario Real and Isivilla deposits, the extrapolation of the elevation of mineralisation coincides with the elevations as identified from the radiometric data available at the Calvario I and Puncopata deposits.
The uranium mineralisation occurrence is highly isolated although correlatable with the mineralisation in the Puncopata deposit to the north and Isivilla deposit to the south. Mineralisation occurs at variable depths from 30 m to 80 m.
CORANI COMPLEX
The Corani Complex is also interpreted to have two levels, Level A and Level B. These have an approximate dip / dip direction of 3°/157°. At the Calvario III and Nueva Corani deposits, mineralisation occurs within Level A, with less continuous mineralisation in Level B. At the Calvario II deposit, only Level B has been preserved, and Level A had been eroded.
SAYAÑA COMPLEX
The local dip / dip direction within the Sayaña Complex is 5°/117°. Two layers are identified in the geological logging information provided, comprising a polymictic rhyolite upper horizon and a monomictic rhyolite lower horizon (Henkle, 2014) (14). Analysis of the intersections revealed sporadic mineralisation in the Agaton and Sayaña West deposits while Sayaña Central has more continuous mineralisation with thicknesses of about 5 m to 10 m.