Stage 1 (Antas North)
Antas North forms part of the Rio Verde Exploration area, consisting of a single Mining License. The site is some 25 km directly southeast of the city of Parauapebas and is located approximately 10km along an easterly gravel road from the sealed road connecting Parauapebas with the town of Canaa.
Parauapebas is a well-developed city with a population of over 154,000 (IBGE in 2010) that services the agricultural needs of the region and also provides services to the large Vale iron ore and copper mines nearby. Possessing fabrication and engineering facilities, as well as hosting the regional offices of the large mining equipment suppliers, the city is set up to support mining projects in the area.
The project is some 35km from the Carajás airport that has direct flights from and Belo Horizonte, Belem and Brasilia (via Maraba).
The Antas North deposit is on hilly ground to the north of the Itaboca Creek running from the top and along the western flank of a significant hill, with available water and a major power line nearby.
Access Road with Antas Deposit in Background
The area is used exclusively for cattle farming and has no environmental constraints.
The climate in the region is tropical and humid with two distinct seasons. The dry season extends from June to September and the rainy season from October to May. Annual rainfall is approximately 1,600mm.
Table 1: Antas North – JORC Reported Ore Reserves. August 2014.
Reported using a ROM cut-off grade of 0.9% Cu.
In July 2007 Avanco compiled a portfolio of exploration projects, one of which is the Rio Verde Copper Project. This project was included in the Company’s portfolio of assets included in the Prospectus for the admission to the official list of Australian Securities Exchange in December 2007.
Drilling commenced at Rio Verde in January of 2008 during which a significant copper oxide deposit was discovered at Antas South.
In 2011 drilling turned to focus on sulphide mineralisation, resulting the discovery of Antas North sulphide deposit. Between 2011 and April 2014, 89 exploration holes were drilled at for a total of approximately 14,800m, culminating with the JORC Reported Resource shown below.
Table 2: Antas North – Total JORC Reported Mineral Resource. April 2014.
Reported above a Cut-off Grade of 0.9% Cu.
Table 3: Antas North – Sulphide JORC Reported Mineral Resource. April 2014.
An impression of the Antas North underground
The Carajás Mineral Province (CMP) is located in the southern part of the Amazon Craton, which is one of the largest cratonic areas in the world. This province is divided into two tectonic blocks, the southern Rio Maria greenstone terrain, and the northern Itacaúnas Shear Belt. The oldest units in the province occur in the southern block and encompass the 2.98– 2.90 Ga Andorinha Supergroup greenstone belt sequences and the Arco Verde Tonalite (2.97– 2.90 Ga). These sequences were intruded by 2.96 Ga trondjemites, 2.87 Ga latetectonic I-type calc–alkaline Rio Maria-type granodiorite, 2.81 Ga granites, and 2.54–2.52 Ga leucogranites.
Within the northern block of the CMP, the Archean basement comprises granulites of the Pium Complex (∼3.0 Ga) and tonalitic to trondhjemitic gneiss and migmatites of the Xingu Complex (∼2.8 Ga). The basement rocks are overlain by metavolcanic–sedimentary units of the Rio Novo Group and the 2.76 Ga Itacaiúnas Supergroup (Igarapé Salobo, Igarapé Pojuca, Grão Pará, and Igarapé Bahia Groups, which form the Archean Carajás Basin). The Igarapé Salobo Group consists of paragneiss, amphibolite, quartzite, meta-arkose, and iron formation, whereas the Igarapé Pojuca Group contains basic metavolcanic rocks, pelitic schists, amphibolites, and iron formations metamorphosed to greenschist to amphibolite facies. The Grão Pará Group comprises lower greenschist facies metamorphic units including metabasalts, felsic metavolcanic rocks, and iron formations. Greenschist facies metavolcanic, metapyroclastic, and metasedimentary rocks, including iron formations, define the Igarapé Bahia Group.
The Itacaiúnas Supergroup hosts all the Carajás IOCG deposits and is thought to have been deposited in a marine rift environment. The metamorphism and deformation of this supergroup has been attributed to the development of the 2.7 Ga Itacaiúnas sinistral strike-slip ductile shear zone and to the Cinzento and Carajás sinistral ductile–brittle to brittle transcurrent fault systems (2,581– 2,519 Ma). The Itacaiúnas Supergroup is overlain by an extensive succession of Archean (2,681±5 Ma) marine to fluvial sandstones and siltstones, known as the Rio Fresco Group or the Águas Claras Formation.
Syntectonic alkaline granites (2.76–2.74 Ga Estrela Granite Complex, Plaquê Suite, Planalto and Serra do Rabo) intrude the Itacaiúnas metavolcano–sedimentary sequence. Other Archean intrusions include the Luanga (2,763±6 Ma), Vermelho, Onça, Puma, and Jacaré– Jacarezinho mafic–ultramafic layered complexes, as well as 2.76–2.65 Ga gabbro dikes and sills.
A suite of post-tectonic Middle Proterozoic granites intruded the Carajás sequences at around 1.8 Ga (U-Pb) ago. Best known major bodies are: Central, Cigano, and Musa Granites.
To the southwest of the CMP there is a suite of Middle Proterozoic tin bearing granite intrusives (1.8 Ga) called Velho Guilherme Suite, in which the best known bodies are: Velho Guilherme, Antonio Vicente, Benedita, Ubim/Sul, and Mocambo.
The CMP contains a number of different ore deposit types and represents one of the best-endowed mineral districts in the world. Small, shear zone- related, lode-type gold and Au–Cu–Bi–Mo deposits occur in the southern portion of the CMP. The northern portion of the CMP contains the world class Carajás iron deposits (e.g., Serra Norte, Serra Sul) in rocks of the 2.76 Ga Itacaiúnas Supergroup, which have estimated reserves of 18 billion tonnes @ 63% Fe, as well as iron oxide-poor Cu–Mo–Au deposits (e.g., Serra Verde) in metavolcanic rocks of the Rio Novo Group close to the contact with the 2.76 Ga Estrela Granite. The CMP also has chrome–PGE deposits (e.g., Luanga) and lateritic nickel deposits (e.g., Vermelho, Onça-Puma) associated with mafic–ultramafic complexes. The ∼2.68 Ga Águas Claras Formation in the central and northern CMP contains the Azul and Sereno manganese deposits (Coelho and Rodrigues 1986) and intrusion-related Cu–Au–(Mo–W–Bi–Sn) and W deposits associated with the 1.88 Ga anorogenic granite intrusions. The Águas Claras Formation also hosts the Serra Pelada/Serra Leste Au–Pd–Pt deposit, which became famous due to a spectacular gold rush in the early 1980s.
The CMP also contains the world’s largest known concentration of large-tonnage IOCG deposits (e.g., Sossego, Salobo, Igarapé Bahia-Alemão, Cristalino, Gameleira, and Alvo 118). The Carajás IOCG deposits display a number of similarities including: (1) variable host rock lithologies, in most cases including metavolcano–sedimentary units of the ∼2.76 Ga Itacaiúnas Supergroup; (2) association with shear zones; (3) proximity to intrusions of different compositions (granite, diorite, gabbro, rhyolitic, or dacitic porphyry dikes); (4) intense hydrothermal alteration including sodic, sodic–calcic or potassic assemblages, together with chloritization, tourmalinization, and silicification; (5) magnetite formation followed by sulphide precipitation; and (6) a wide range of fluid inclusion homogenization temperatures (100–570°C) and salinities (0 to 69 wt% NaCl eq.) in ore-related minerals.
Major differences among Carajás IOCG deposits include distinct hydrothermal alteration assemblages (e.g., high temperature silicates, such as fayalite and almandine, present only at Salobo) and ore minerals (e.g., chalcopyrite– chalcocite–bornite at Salobo; chalcopyrite ± chalcocite– digenite–covellite at Igarapé Bahia; and chalcopyrite– pyrite in Sossego Mine and the Pedra Branca, Cristalino, and Alvo 118 deposits).
The main structural trend at Rio Verde is WNW-ESE and is related to the regional Carajás fault (shear zone) to the south (NW-SE) and the Cinzento shear system (WNW-ESE) to the north, which are integral parts of the Itacaiúnas Belt. These WNW structures are probably the main conduits through which the granitic intrusives and the mineralised fluids ascended.
Regional Geological Setting
Local Geology and Mineralisation
The Antas orebody is located close to the southern border of the Estrela Granite Complex and is hosted predominantly by mafic metavolcanic rocks of the Parauapebas Formation (Gão Pará Group), which is cut by gabbro dikes.
Host rocks consist of felsic – mafic volcanics, with between a few per cent and 40 per cent deformed quartz, plus sulphide veins. Associated alteration shows a moderate to strong zonation from the surrounding unaltered country rock into the most strongly mineralised portions of the deposit. A broad outer halo consists of chlorite, biotite, weak silicification, and fine-grained magnetite and pyrrhotite. Where veins are particularly dense, the envelopes can coalesce, resulting in pervasive biotite + chlorite alteration.
Antas contains hydrothermal alteration zones similar to those recognised at other IOCG deposits in the Carajas. The orebodies display a generally consistent pattern of early regional sodic alteration (albite-scapolite) followed by potassic (biotite) and calcic alteration (actinolite– cummingtonite), the latter is associated with the formation of ilmenite–(apatite) replacement bodies, which are directly related to copper mineralisation. Carbonate alteration is a later phase. Sodic and sodic– calcic alteration types in most IOCG districts are typically developed below or peripheral to potassic alteration assemblages (Hitzman et al. 1992).
The complex stages of sodic, sodic–calcic, potassic, and hydrolytic alteration observed at Antas North are generally similar to those described by Monterio and Xavier (2008) from the Sossego – Sequeirinho IOCG system in Carajás. The temporal and vertical zonation observed in the Antas North system generally fits the “classical” system of alteration zoning predicted in IOCG systems, with ilmenite as the main oxide phase, rather than magnetite.
Detailed Geological map of Antas North – Ore body in red
The main orebody is oriented northeast and coincides well with the main soil anomaly (>1,000ppm copper) and VTEM anomaly. Zones of massive sulphide near the periphery of the ore zones help to generate the high-grade intercepts, typically seen n results reported historically.
Fine grained malachite with minor chalcopyrite in volcanic rock outcrop
The majority of mineralisation is concentrated within a steeply dipping body that contains fragments of massive sulphide and disseminated sulphide minerals, within a matrix of hydrothermal breccia. The ore body is cut by relatively narrow zones of gabbro dyke that form the focus for later structurally controlled, sub-vertical, breccia-hosted copper–gold mineralisation.
Massive Sulphide High Grade Zone;
Massive Sulphide High Grade Zone contains variable proportions of chalcopyrite and pyrrhotite as dominant minerals. Chalcopyrite is by far the most abundant sulphide, forming a massive aggregate. Sulphide veins are usually undeformed and planar.
Medium-High Grade Zone;
The Medium-High Grade Zone also contains variable proportions of chalcopyrite, pyrrhotite, as dominant minerals, and is by far the most abundant vein type within the mineralised zones. Sulphides frequently form the matrix of hydrothermal breccia’s, form stringers, and occur as fine disseminations in the transparent gangue.
Disseminated Low Grade Zone.
In the Disseminated Zone chalcopyrite occurs as fine-medium grained disseminations in the transparent gangue, usually surrounding transparent minerals. Sulphides also occur as fracture fill and as small blebs. Commonly this ore type occurs between narrow Medium-High grade and Massive Sulphide zones.
Massive sulphide high grade with silicification + amphibole alteration
Medium HG, breccia matrix with biotite + amphibolite alteration
Antas North Cross Section
Published August 2016
Drone Flyover of Site – February 2016
2nd Drone Flyover of Site – December 2015
Drone Flyover of Site – December 2015
Drone Flyover of Site – November 2015
Drone Flyover of Site – October 2015
Drone Flyover of Site – September 2015
Drone Flyover of Site – August 2015
Drone Flyover of Site – June 2015
Drone Flyover of Site – June 2015
Drone Flyover of Site – May 2015
Process Flowsheet and 3D Plant Flyover