Summary:
The key geological feature of the Project area is the Mesozoic Poços de Caldas Alkaline Complex (PCAC) which was intruded into the metamorphosed Paleoproterozoic rocks of the Brazilian shield.
The main rock types found are intrusive and volcanic alkaline rocks of the nepheline syenite system, comprising phonolites and foidolites (syenites). High rainfalls and the unique potassium enriched chemistry of the intrusives that lack any primary quartz has led to the formation of a deep regolith profile. Within the regolith profile, clays and partially weathered rock (transition) have been identified up to 200m below the current land surface.
The geological interpretation of Meteoric’s exploration drilling subdivides the regolith into three main zones:
- A soil layer 0 – 2m thick;
- A clay zone 5 – 70m thick comprising illite, montmorillonite, halloysite and gibbsite as the main clay species; and
- A transition zone defined by the appearance of visible weathered rock fragments which gradually increase with proximity to fresh rock in a zone that can vary between 5 – 120m thick.
Primary uranium and REE deposits have been known within the area since the 1950s and are characterised by late stage sulphidic breccias containing uranium oxides and bastnaesite with accessory monazite and xenotime as the major REE ore minerals. However, away from the higher-grade U-REE deposits, the dominant REE mineral in the source rock (syenite) beneath the clay zone is bastnaesite, a major source of REE worldwide. Bastnaesite is the primary REE mineral at well-known deposits such as Mountain Pass (USA) and Bayan Obo (Asia). Bastnaesite is a REE carbonate-fluoride mineral (REE)CO3F which has very low levels of uranium and thorium in its mineralogical structure. Concentration of REE within ion adsorption deposits has been proposed to be a dominantly supergene process, where easily degradable REE-minerals break down and release REE that are then adsorbed onto clay mineral surfaces.
The target REE mineralisation for Meteoric occurs below the soil layer within the clay zone. This is where REE grades and leaching recoveries are highest due to the ionic adsorption nature of the bonds between the REE and the clay minerals. The target ionic clay REE mineralisation (defined by >40% recovery of REE using a standard AMSUL wash at pH 4) is confined to the soil, clay, and weakly weathered transition layers. A total of 65% to 90% of these highly weathered zones are composed of minerals in a clay fraction (granulometry <2µm). Mineralisation ranges from 2ppm to 56,000ppm REE. Mineralisation is present throughout the vertical profile, but it is not distributed homogenously.
The Alkaline Complex of Poços de Caldas represents in Brazil one of the most important geological terrains which hosts deposits of bauxite, clay, uranium, zirconium, rare earths and leucite. The different types of mineralization are products of a history of post-magmatic alteration and weathering, in the last stages of its evolution (Schorscher & Shea, 1992; Ulbrich et al., 2005).
The dominant REE mineral in the source rock (syenite) beneath the clay zone is Bastnaesite, a major source of REE worldwide. Bastnaesite is a REE carbonate-fluoride mineral (REE)CO3F and has very low levels of U and Th in its structure. Due to the chemistry of the underling intrusives and the intense weathering of the region, a thick profile comprising soil, clay and saprolite (regolith) has formed, and these are the hosts to the ionic clay REE mineralization.
The deposits are recognized as Ionic Adsorption Clays, where the Rare Earth Elements ions are trapped by the surface or between the layers of the clays and these REE are easily leached with a moderate acid substance.
Depth of Mineralised Clays at key Caldeira Project deposits:
- Capão do Mel
• Mineralised Clay Depth (m): 4 – 50;
• Average Depth (m): 23.4.
- Figueira
• Mineralised Clay Depth (m): 4 – 62.5;
• Average Depth (m): 28.2.
- Soberbo
• Mineralised Clay Depth (m): 1.5 – 77.4;
• Average Depth (m): 16.9.
- Barra do Pacu
• Mineralised Clay Depth (m): 8 – 50;
• Average Depth (m): 29.2.
Dimensions
The Mineral Resources have the following dimensions:
• Soberbo - 2,600m x 3,800m in NE-SW direction;
• Capao do Mel - 2,600m x 3,800m in NE-SW direction;
• Figueira - 2,600m x 1,200m in N-S direction;
• Barra do Pacu - 1,900m x 4,000m in N-S direction.
The top of the rare earth element mineralization is generally the topographic surface.