Summary:
The Pilar property hosts four deposits: Pilar, Três Buracos, Maria Lázara, and Caiamar.
The Pilar property covers the Guarinos and Pilar Greenstone Belts and a portion of the Moquém gneissic complex. Gold mineralization at the Pilar and Guarinos Greenstone Belts is typical of orogenic gold deposition.
The Guarinos Greenstone Belt is represented by a succession of basic rocks, mostly basalt and amphibolite, and by meta-sedimentary layers, related to inter-flow sedimentary events. Chlorite-quartz-garnet-schist is also present. The main structure is the Carroça Shear Zone, a reverse-dextral major shear zone, parallel to the main regional foliation with several kilometres of strike length. The shear has a mylonitic fabric and an associated 400 m wide hydrothermal alteration zone. Gold mineralization at the Caiamar and Maria Lázara mines is related to this structure.
The Pilar Greenstone Belt is composed of a thick sequence of ultramafic and mafic flows, sedimentary rocks, and felsic volcanic rocks. The Pilar and Três Buracos deposits are in this belt along the main trend near the Moquém Complex contact. Mafic-ultramafic rocks are represented by basalt and komatiitic flows. The sedimentary sequence contains graphite schist, greywacke, and argillite, while the felsic volcanic rocks are acid tuffs and felsic flows. Gold mineralization is mainly concentrated in the graphite schist but also occurs within the greywacke layers.
Pilar deposit
Gold mineralization at the Pilar mine occurs in three levels, with each level containing a high grade core surrounded by a lower grade halo. Diamond drilling has outlined an area of gold mineralization with a strike length of 3.3 km, a width of 2.6 km, and a thickness between 10 m and 30 m.
Mineralization at the Pilar mine is located in three main zones:
• HG1 (Basal zone): the most continuous and important style of mineralization in the deposit. The Bazal zone is controlled by carbonaceous schists and intercalated chlorite schists. It is hosted on the basal contact of the chlorite schist with the graphite schist.
• HG2 (Upper zone): an important zone with similar volume to HG1 but with lower grades. The zone is essentially controlled by quartz veins inside the chlorite schists. It is located in the hangingwall portion of the main thrust fault.
• HG3 (Lower zone): the smallest and most discontinuous zone at the Pilar deposit, with location and average grades similar to HG2.
The Upper zone is continuous along the Pilar-Três Buracos trend (the Upper zone forms the lower part of the Três Buracos mineralization), with a width of up to 60 m. This zone is characterized by the presence of thin quartz veins and associated sulphides, mostly pyrite.
The Basal zone is characterized by strong silicification and sulphidation. Arsenopyrite, the main sulphide, commonly constitutes up to 5% of the rock. The Basal zone averages 10 m wide and is continuous along the main trend. The highest grades are closely associated with high sulphide (arsenopyrite) and quartz content and are associated with structurally controlled mineralized shoots distributed along the trend.
Strong silicification and sulphidation are the main forms of hydrothermal alteration. Host rocks and most carbonaceous metasedimentary rocks are well silicified and contain shear-related quartz veins. Arsenopyrite is the main sulphide related to the gold mineralization, while pyrite, and minor chalcopyrite, and pyrrhotite are also present. Gold is present both as free grains in clusters related to quartz veining, and in association with arsenopyrite and other sulphides.
Maria Lázara deposit
Mineralization at Maria Lázara is hosted by silicified biotite-chlorite-sericite schists and with quartz veins concordant with the main foliation. These schists show an average thickness of 2.0 m in diamond drill holes and mine openings. The mineral assembly contains sericite, chlorite, biotite, tourmaline, albite, quartz, and sulphides, mainly arsenopyrite with minor pyrite, pyrrhotite, sphalerite, galena, and chalcopyrite. The schists exhibit a porphyroblastic texture, containing porphyroblasts of garnet and occasionally magnetite. Native gold occurs associated with arsenopyrite and quartz or quartz-albite veins.
Diamond drilling has outlined an area of gold mineralization with a strike length of 3.6 km, a width of 720 m, and an average thickness of 10 m.
Caiamar deposit
Gold mineralization at the Caiamar mine occurs in four parallel zones and on a set of small shoot-like structures related to a transpressional shear zone. The most significant gold mineralization at the Caiamar mine occurs in zones A1 and A2 associated with intense hydrothermal alteration.
They are described as follows:
• Zone A0: small zones of discontinuous mineralization not related to hydrothermal alteration, hosted by quartz-biotite-graphite schist.
• Zone A1: the most important and continuous zone in the deposit. The zone is hosted in a hydrothermally altered meta-greywacke and the mineralization is associated with quartz-albite-arsenopyrite veinlets. Contains small, scattered higher-grade zones associated with porphyritic intrusions.
• Zone A2: similar setting and slightly less tonnage than zone A1. It is separated from A1 by an amphibolitic metasediment. Contains small, scattered higher-grade zones associated with porphyritic intrusions.
• Zone A3: small, scattered patches of mineralization in a similar environment to A1 and A2.
Diamond drilling has outlined zones of steeply plunging gold mineralization within an area with a strike length of approximately 1.4 km, a vertical extent measuring 600 m, and thicknesses ranging from one metre to 20 m.
Três Buracos deposit
Gold mineralization at the Três Buracos deposit occurs in three levels. All three levels have been investigated by an extensive chip sampling campaign and followed by detailed geological interpretation:
• The uppermost level comprises chlorite schist with thin quartz veins and hydrothermal alteration. It is approximately 30 m thick and shows encouraging results for gold grades along strike. Chip sampling at this level shows low, but consistent, gold grades of about 1.4 g/t Au to 2.6 g/t Au.
• The intermediate level comprises intensely silicified and sulphidized rocks, with up to 20% arsenopyrite as the main sulphide. Sericite and fuchsite are common and concentrated in a 1.0 m thick layer. Gold grades are high, mainly in highly sulphidized, sericite-fuchsite-rich layers, ranging from 13 g/t Au to 85 g/t Au. The main mineralized horizon is at the contact zone between the upper level and the underlying graphite schist. The intermediate level is at least 3 m thick, and is characterized by strong hydrothermal alteration.
• The basal level of graphite schist is close to the contact with quartz sericite schist, is mineralized, and was mined during the 18th century.
Diamond drilling has outlined gold mineralized lenses at Três Buracos over a strike length of approximately 1.7 km, a width of 1.0 m, and a thickness of between 25 m and 60 m.