Summary:
The Cuiú Cuiú Gold Project lies within the Tapajós Mineral Province of the Amazon Craton, characterized by extensive Paleoproterozoic magmatism and deformation linked to the Trans-Amazonian Orogen.
Mineralization
Several main types of primary gold mineralization are evident in the fresh basement rocks within the project area: pervasive replacement-style mineralization, sheeted and stockwork vein mineralization, and quartz vein or quartz flooding mineralization. All styles of gold mineralization are present in the larger gold deposits on the property, with higher grades typically associated with quartz-vein or quartz flooding mineralization. All of these styles occur within extensive hydrothermally altered envelopes with lower gold tenor. The sulphide content is generally a good indicator of gold grade.
Three deposit types also occur within the weathered rocks:
1. The up-dip projections of the fresh basement mineralized zones are weathered to saprolite at depths of up to 100 m from the surface. This basement saprolite exhibits a significantly lower density and completely different mineralogy compared to the unweathered primary mineralization, but it largely maintains the general orientation (strike, dip and widths) of the underlying primary mineralization.
2. Soil and colluvium have developed at the top of the saprolite, forming extensive, broad, sub-horizontal transported mineralized zones known as “blankets.” These blankets are angularly unconformable and overlie Type 1 deposits.
3. Over millions of years, the Blanket mineralization has been carried downslope into drainages by surface erosion, with both gold and colluvial materials eventually reaching larger streams and rivers to form placer deposits. Cabral Gold is not currently assessing Type 3 placer mineralization, but Types 1 and 2 could represent significant future economic resources for the company.
The Cuiú Cuiú property hosts approximately 50 gold target areas at various stages of exploration. Of those, six are relatively advanced, including the:
1) Central deposit,
2) MG deposit,
3) CN deposit,
4) JB deposit,
5) Machichie target area, and
6) PDM target area.
The two largest primary fresh rock gold deposits outlined to date are Central and MG. These constitute the bulk of the current Cuiú Cuiú basement resources. The CN and JB deposits are considerably smaller. Although PDM and Machichie have much larger footprints than CN and JB, they have not been drilled sufficiently to determine resources.
Central Gold Deposit
The Central deposit is composed of three distinct gold-bearing units: 1) unweathered basement mineralized rocks that are highly altered and brecciated, 2) in situ weathered and saprolitized basement rocks, and 3) unconformable subhorizontal Blanket mineralization.
The primary basement deposit at Central consists of a laterally extensive, northwest-trending, steeply dipping series of subparallel mineralized zones that extend below the depth of the deepest drill holes completed to date. The primary gold mineralization within 80 m of the surface has been extensively weathered into saprolite. The intensity of weathering and saprolitization decreases with depth, while density correspondingly increases. The basement extending up to 20 m directly beneath the saprolite profile, is commonly weakly weathered, with intrusive rocks appearing bleached and containing rusty fractures. Locally, more deeply penetrative saprolite weathering is concentrated along these fractures.
The primary Central deposit lies within a broad, northwest-trending, highly altered deformation zone that transects, and has deformed and altered multiple primary rock types, including coarse- to medium-grained granite, granodiorite, quartz monzonite, and tonalite along with narrower intermediate, mafic and felsic dykes.
Moreira Gomes (MG) Gold Deposit
The MG gold deposit consists of three components: 1) an extensive primary basement gold deposit, 2) weathered in situ mineralized saprolite, and 3) an extensive sequence of unconformable Blanket mineralization.
The MG area is primarily underlain by the slightly older Cuiú Cuiú Complex (2.02 Ga) intrusive suite. The majority of igneous rocks hosting MG gold mineralization are diorites, and they vary from fine to coarse-grained and are predominately porphyritic, with abundant megacrysts of plagioclase.
Gold mineralization at MG occurs within several subparallel, east-trending, steep north-dipping deformation zones that have been subjected to intense hydrothermal alteration. This combined alteration envelope has been drilled over a strike length of 2,100 m, with the altered zone locally reaching widths of up to 200 m wide, although it typically measures less than 100 m in width.
Central North (CN) Deposit
The Central North (CN) deposit is located 250 m north of the main Central deposit. There is limited drilling between Central and CN, suggesting that the two may be connected by alteration.
The CN is now interpreted to extend 650 m along a northwest strike, comprising two mineralized zones that span over a 65-m width, and dipping steeply to the northeast. It has been drilled to maximum vertical depth of 240 m. The Blanket area outlined by Cabral Gold’s drilling is relatively small and low grade, covering an area of 10.5 Ha and elongated from northwest to southeast.
Jerimum de Baixo (JB) Deposit
The JB deposit is interpreted to comprise three steeply dipping, northwest-striking, subparallel higher-grade zones, surrounded by a lower-grade shell. It is approximately 650 m long, 150 m wide at its widest point, and has been tested to a depth of 180 m.
Mineralization occurs within a weakly to moderately brecciated and altered granite, primarily characterized as stockwork to sheeted vein type. The highest-grade individual intercept (0.5 m grading 17.3 g/t Au from 223.2 m in CC-100) occurs in a more strongly brecciated, weakly sheared, and silicified grey rock with quartz veining.
PDM Target
The current PDM resource is restricted to weathered rocks, which include in situ basement saprolite and the unconformably overlying Blanket.
Primary Fresh Rock Proterozoic Basement Gold Mineralization
All fresh basement gold zones discovered at Cuiú Cuiú to date are associated with either extensive deformation zones or smaller-scale faults and fracture systems. The larger gold zones are mainly associated with extensive deformation and hydrothermal alteration.
Narrow mafic dykes are common within these gold zones. These dykes exhibit varying degrees of deformation, ranging from massive and undeformed to highly deformed chlorite schist. This variation may reflect a prolonged period of intrusion occurring before, during and after the deformation and gold mineralization events. These dykes are typically subvertical and steeply dipping, though some sub-horizontal mafic dykes have also been observed. Additionally, various felsic, pegmatite, and aplite dykes have been intersected in drill holes, with the exception of crowded diorite porphyries, which tend to be narrow and less abundant.
Deposit Types
The Cuiú Cuiú Gold Project features orogenic gold deposits, most likely linked to the Trans-Amazonian Orogen, a Paleoproterozoic regional event caused by the collision of the Guiana Shield and the West-African Craton. The gold mineralization is classified as mesozonal or hypozonal, indicative of formation at depths greater than six kilometers under greenschist facies conditions. Unlike Intrusive-Related Gold Systems (IRGS), Cuiú Cuiú’s gold deposits are associated with syn-deformation processes, evident in features like dilation structures, shear veins, and banded quartz breccias. The region’s mineralization model highlights structural discontinuities as pathways for hydrothermal fluids, depositing gold in zones of high strain during episodic seismic pumping.