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Tucano - Urucum, Tapereba, TAP AB, Duckhead |
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Amapa, Brazil |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Tucano Mine gold mine is located in Amapá State, Brazil, ~125 km northwest of the state capital, Macapá. The mine comprises three open pits, Urucum, Taperebá or TAP AB and Duckhead, distributed over a 7 km strike length. (#Location - treatment plant: 0° 48' 54"N, 51° 52' 5"W).
The mineralised shear at Tucano was discovered in 1994 by Anglo American Plc, who undertook extensive exploration between 1995 and 2002, and through its subsidiary AngloGold, completed a feasibility study of the oxide Mineral Resources in October 2002. AngloGold sold the property to EBX Gold Limited in 2003, who conducted a feasibility Study of the sulphide mineralisation. In 2004, the deposit was acquired by Wheaton River Minerals Ltd. which was taken over by Goldcorp Inc. in 2005. Mine construction began in July 2004, with the first gold poured in late 2005. The Tucano Gold Mine was operated by a subsidiary, Mineracao Pedra Branca do Amapari, as a heap leach operation until January 2, 2009, when it was placed on care and maintenance due to the inability to treat transition material in the deeper parts of the pits. Goldcorp sold the mine to Peak Gold Ltd. in April 2007, which company was later merged with Metallica Resources Inc. and New Gold Inc. in June 2008. The renewed operation did not attain predicted gold production due to the clayey nature of the saprolite mineralisation. Following metallurgical studies a milling and CIL treatment circuit was installed to predominantly treat sulphide, and remnant oxide, material. Up to the closure of the mine in 2009, 8.8 Mt of ore @ 1.12 g/t retrieved Au had been mined for 9.83 t of contained gold. In 2010, Beadell Resources Ltd., through its local subsidiary Mina Tucano Ltda, acquired the Tucano Gold Mine and commenced construction of a CIL plant to augment the existing process infrastructure. Mining and stockpiling of ore commenced in 2011 and the CIL plant was commissioned in November 2012. Beadell upgraded the plant from 2018 to 2019 including a ball mill, pre-leach thickener, leach tank and oxygen plant. In 2018, Great Panther Mining acquired Beadell Resources and production continued. Since 2009 a further 34.367 tonnes of gold have been produced to the end of 2020.
The Tucano Mine is located within the Guyana Craton, the northern the three main components of the South American Precambrian Shield, the other two being the Amazon (or Guapore) immediately south of the Amazon Basin, and the São Francisco Craton futher to the south again. The Guyana Craton is mostly composed of a granite gneiss complex, including some highly metamorphosed supracrustal belts, of which greenstone belts represent a small proportion. The Tucano gold deposits lie within the Guyana Craton, also described as the Maroni - Itacaiunas Mobile Belt that runs through Par&aacure; and Amap&aacure; States of northern Brazil, through the Guyanas and into Venezuela. This belt takes in gold deposits from Amapa, though French Guiana (e.g., Dorlin), Suriname (e.g., Merian), Guyana (e.g., the Aurora Project deposits and Omai) and Venezuela (e.g., Las Cristinas and Choco 10). In central-south Amapá, this mobile belt is characterised by a typical ‘greenstone’ suite, the Vila Nova Greenstone Sequence, that is composed of clastic metasedimentary rocks interspersed with meta-basalts and meta- andesites, containing subordinate layers of iron and manganese formations, calc-silicate schists and marbles.
The Vila Nova Group comprises, from the base:
Meta-volcanic Unit
- Metamafic and ortho-amphibolites - Plagioclase amphibolites, biotite-amphibole schists, plagioclase-cummingtonite-hornblende schists;
Chemical Sedimentary Unit - the William Formation
Calc-magnesian Domain
- Marble and carbonate schists - Calcic marble, serpentine marble with tremolite, forsterite, fayalite, hastingsite, chlorite and magnetite; actinolite-tremolite-carbonate schists;
- Schists with diopside porphyroblasts - Actinolite-tremolite-diopsides, hornblende-diopsides, amphibole-diopsides, with epidote, biotite and garnets;
Ferruginous Domain
- Iron formation oxide-silicate facies - (Hornblende)-diopside-grünerite-quartz with magnetite; (diopside)-hornblende-garnet, quartz-magnetite-grunerite schist;
- Iron formation oxide facies - (Grunerite)-quartz-magnetite / hematite, sometimes with garnets and diopside;
- Iron formation, silicate facies - Garnet-hornblende-grunerite-diopside; magnetite-grünerite-hornblende schists;
Clasto-chemical Sedimentary Unit
Transitional Unit
- Quartz-amphibole schists and amphibole schists with lenses of silicate facies iron formation and calc-silicates;
Clasto-pelitic Sedimentary Unit
Pelitic Domain
- Quartz-mica schists - Quartz-biotite-muscovite schist with garnets, interspaced with lenses of calc-silicates, iron formation and muscovite;
Quartz Domain
- Muscovite quartzites - Muscovite–quartz schist, muscovite quartzite, locally with fuchsite and / or sillimanite.
The sequence has been extensively intruded by younger dykes of dolerite and gabbro, as well as acid pegmatites.
These units have been subjected to several orogenic deformational events under low to medium metamorphic conditions, reaching upper greenschist to mid amphibolite facies, under intermediate pressure. The greenstone complex was affected by a widespread process of deformation and metamorphism, resulting in a regional S1-2 foliation oriented 290 to 275°. This foliation is overprinted by a later deformation event that generated regional scale F3 folds with NW-SE axes.
The western quarter of the Tucano deposit area is composed basement gneiss, while the remainder comprises ortho-amphibolite and meta-sedimentary rocks of the Palaeoproterozoic, 1.75 to 1.9 Ga Vila Nova Group. The latter essentially includes gneisses, granites, amphibolites, banded iron formations (BIF), massive iron formations, schists and quartzites. These are intruded by granitic pegmatites, dolerite dykes and gabbro bodies. The metasedimentary units are similar to those of the Serra do Navio Formation which hosted manganese deposits previously mined by Indústria e Comércio de Minerios S/A (ICOMI).
The metasedimentary rocks hosting the Tucano gold mineralisation lie along the western limb of a north-south striking syncline. In the north, the strike is north-south, with dips of ~65°W, while to the south, the dip steepens to vertical, to slightly overturned to the NE, with the strike trending NNW.
Gold mineralisation is associated with iron and carbonate-rich units of the William Formation, a chemical-sedimentary unit, with gold predominantly closely related to the BIF facies, although carbonate and calc-silicate rocks also host economic mineralisation. Sub-economic gold may be hosted by any of the lithological units shown in the stratigraphic succession, with the exception of the late intrusions.
Laterite and lateritic colluvium are common throughout the area, and tend to be thicker over topographic highs, with thick laterites developed in the proximity of BIF. The colluvium is characterised by deeply weathered rock, in which all traces of original structure have been obliterated, and which commonly include angular fragments that imply only limited transport. This colluvium hosts secondary gold mineralisation.
Gold deposition appears to have been controlled by gold-bearing hydrothermal fluids or by remobilisation of pre-existing mineralisation. Mineralization is both conformable and discordant to meta-sedimentary contacts within the William Formation.
Mineralisation occurs as a string of separate deposits associated with a north-south trending zone of shearing producing continuous, steeply to shallowly plunging high grade gold-bearing lodes. These deposits are distributed over a 14 km strike length, coincident with a north-south line of ridges. This zone of shearing is located near the contact between the dominantly clastic/chemical sedimentary suite and the meta-volcanic amphibolite package. The geometry and plunge of the lodes are interpreted to be controlled by the intersections of gently plunging F2 fold hinges and more steeply dipping faults, whilst the texture and intense hydrothermal alteration assemblage within the mineralised zone of shearing indicate a high-temperature hydrothermal system. The hydrothermal alteration assemblage includes silicification and sulphidation, accompanied by auriferous pyrrhotite, and pyrite. The interaction of favourable lithologies, structure, heat and mineralised solutions has produced gold bearing, non-refractory sulphides concentrated near or on major lithological contacts. Alteration is most intense in the proximity of reactive meta-sediments such as BIF, followed by amphibolite, carbonate, schist and to a lesser extent, calc-silicate rocks.
The separate deposits are, from north to south: TAP A, B, C and Urucum. TAP D is a separate structure in the west, whilst Duckhead deposit is located 4 km to the southeast of the TAP AB deposit.
The Urucum, Taperebá (or TAP) AB and TAP C lie within a north-south striking section of the deposit, within multiply deformed volcano-sedimentary sequence that is bounded to the west by the Amapari Granite. Deformation has produced steeply dipping north-south shear zones in which gold is associated with alteration and sulphide mineralisation that has affected various lithologies. Mineralization is distributed over a strike length of at least 7 km and has been interpreted to extend to a depth of >700 m below the surface. A suite of late post-gold pegmatites has been emplaced throughout the sequence in various orientations and is largely barren of gold.
TAP AB is composed of three mineralised zones with dimensions, as known in 2020, as follows:
• TAP AB1 - 580 m strike length, 450 m down plunge to 300 m depth, with average thickness of 9.0 m;
• TAP AB2 - 600 m strike length, 440 m down plunge to 350 m depth, with average thickness of 5.5 m;
• TAP AB3 - 420 m strike length, 480 m down plunge to 460 m depth, with average thickness of 5.5 m.
TAP C, which has not been mined nor has resources in the mine plan, is to the north of TAP AB, separating it from Urucum, and is composed of four mineralised zones with dimensions as follows:
• TAP C1 - 800 m strike length, 150 m down plunge to 150 m depth, with average thickness of 6.0 m;
• TAP 3C - 450 m strike length, 150 m down plunge to 300 m depth, with average thickness of 7.0 m;
• TAP C3N - 350 m strike length, 150 m down plunge to 90 m depth, with average thickness of 5.5 m;
• Gap (170 m west of line) - 170 m strike length, 100 m down plunge to 130 m depth, with average thickness of 11.0 m.
At Urucum, which is ~2.5 km north of TAP AB, gold mineralisation is predominantly stratabound, following specific sheared lithological units within the BIF, and is characterised by strong disseminated and shear fabric pyrrhotite. There is a strong visual association between gold and pyrrhotite in fresh rock making it easy to discern from non-mineralised BIF and other rocks. However, not all pyrrhotite rich zones have high gold values, and high gold values can be found in strongly altered but sulphide poor zones.
Urucum is composed of two mineralised zones with dimensions as follows:
• Urucum North - 1000 m strike length, 780 m down plunge to 500 m depth, with average thickness of 4.0 m;
• Urucum South - 1300 m strike length, 750 m down plunge to 360 m depth, with average thickness of 10.0 m.
Urucum East is located east of the northern tip of the Urucum Mine, on the northern fold hinge of the Tucano Gold Mine stratigraphy. It comprises a single, east-west striking and shallowly (30°) north dipping sulphide lode that has dimensions as follows:
• - 230 m strike length, 180 m down plunge to 75 m depth, with average thickness of 7.0 m;
Mineralisation is hosted in a wedge of carbonate and altered BIF located within a swarm of parallel, east-west striking and north dipping (-30°) pegmatite dykes/sills which have intruded the host schist unit. The deposit is overlain by a blanket of poorly mineralised colluvium that is up to 10 m thick, below which the deposit has been weathered to a depth of ~50 m below the surface.
Duckhead is located ~4 km south east of the TAP AB deposit. Mineralisation is controlled by the interpreted intersection of steep east-west striking shear zones with the lithological BIF contact to form steeply west plunging high grade shoots. The texture and mineralogy found along the shear zone suggest high-temperature hydrothermal alteration, particularly silicification and sulphidation, accompanied the development of auriferous pyrite. Mineralised zones include the following:
• Main Lode - 80 m strike length, 220 m down plunge to 210 m depth, with average thickness of 12.0 m;
• HW Lode - 90 m strike length, 180 m down plunge to 165 m depth, with average thickness of 15.0 m,
Most of the deposits have been subjected to deep weathering, such that hypogene sulphide mineralisation within fresh rock is only observed in drill core and does not outcrop at the Tucano Gold Mine. Never-the-less, gold mineralisation persists upward from the fresh bedrock, through the saprolite zone that was generated by in situ weathering, and into the overlying colluvium that forms blanket that spreads laterally over the hill slopes. The saprolite and colluvial mineralisation are collectively referred to as 'oxide mineralisation'.
As detailed above, in un-weathered bedrock, sulphide mineralisation follows the shear plane foliation, often crosscutting BIF and other host meta-sedimentary rocks, forming plunging mineralised shoots, but also occurs as stratabound lenses that dip either east or west along the limbs of the folded BIF units. Distal to the shears and faulted zones, host rocks are sulphide and gold poor. The most abundant sulphides are pyrrhotite and pyrite, although trace amounts, i.e., <1%, chalcopyrite, arsenopyrite, sphalerite and galena also occur. At Urucum, this mineralisation is accompanied by intense silicification, and pyrrhotite is the dominant sulphide. At TAP AB, the gold is associated with masses of 5 to 10% pyrite, with only trace pyrrhotite. These pyrite accumulations are several metres thick and may be elongated with NNW or north-south oriented strikes. Sulphide mineralisation extends to depth with a 10 to 40° plunge on an azimuth of 350°, with dips that vary from near vertical to 30°W in the western carbonate lode at the south of the TAP AB deposit. In all of these deposits, gold is free, and not tied into the crystal lattice of the sulphide minerals, and mineralization is not confined to any one lithology.
Intense tropical weathering produced an in situ saprolite zone, which extends to ~30 m depth in the Urucum pit and to >300 m below the surface at TAP AB. The saprolite is mainly composed of iron oxides and hydroxides, clay and silica. Gold zones within saprolite mimic the strike, dip and plunge of the pre-weathering sulphide mineralisation, with semi-oxidised sulphide relicts becoming more frequent with depth. Weathering has rendered much of the saprolite material amenable to free digging, although some has required blasting prior to excavation. The mineralisation in these more competent intervals range from entirely oxidised to silicified with partially or even fresh sulphides.
Mineralisation is also preserved within colluvium overlying the saprolitised host sequence and is spatially related to the bedrock mineralisation from which it is interpreted to have been derived. The colluvial mineralisation occurs along north-south ridges that are as much as 185 m higher than the parallel William Creek. The crest and slopes of these ridges are covered by alluvial and colluvial sediments which are difficult to differentiate in the field. The character of the mineralised colluvium is heterogeneous, reflecting the varies sub-surface lithologies, occasionally including semi-decomposed, angular fragments of those lithologies. The distribution of gold grades reflect those of the underlying ore shoots, although mineralisation in colluvium tend to be wider and somewhat more irregular than in underlying saprolite due to mechanical down slope transport and development of some secondary mineralisation due to variations in surface soil chemistry.
The deep weathering and intense iron oxide development in the upper soil profile often produces a laterite profile. The top of the colluvium is usually a layer that is rarely >1 m thick composed of silty, clayey and sandy material, with little or no limonite fragments. This is immediately underlain by a variable, up to 10 m thick, layer of lateritic fragments rich in iron oxide dispersed in a ferruginous clay-sand matrix which becomes rich in manganese at the base. Occasional semi-decomposed, angular fragments of the underlying lithologies are found within the colluvium.
Mineral Resources
Remaining Mineral Resources at December, 2020:
Open-pit Oxide Mineralisation
Urucum - Measured + Indicated Resource - 0.155 Mt @ 0.8 g/t Au at a 0.3 g/t Au cutoff;
Urucum East - Measured + Indicated Resource - 0.164 Mt @ 2.02 g/t Au at a 0.3 g/t Au cutoff;
- Inferred Resource - 0.007 Mt @ 1.65 g/t Au at a 0.3 g/t Au cutoff;
TAP AB - Measured + Indicated Resource - 4.19 Mt @ 1.62 g/t Au at a 0.3 g/t Au cutoff;
- Inferred Resource - 0.306 Mt @ 2.73 g/t Au at a 0.3 g/t Au cutoff;
Duckhead - Measured + Indicated Resource - 0.064 Mt @ 4.35 g/t Au at a 0.4 g/t Au cutoff;
- Inferred Resource - 0.006 Mt @ 1.71 g/t Au at a 0.4 g/t Au cutoff;
TOTAL Open-pit Oxide - Measured + Indicated Resource - 4.574 Mt @ 1.64 g/t Au;
TOTAL Open-pit Oxide - Inferred Resource - 0.319 Mt @ 2.69 g/t Au.
Open-pit Sulphide Mineralisation
Urucum - Measured + Indicated Resource - 2.973 Mt @ 1.52 g/t Au at a 0.4 g/t Au cutoff;
- Inferred Resource - 0.003 Mt @ 1.06 g/t Au at a 0.4 g/t Au cutoff;
Urucum East - Measured + Indicated Resource - 0.022 Mt @ 1.82 g/t Au at a 0.4 g/t Au cutoff;
- Inferred Resource - 0.001 Mt @ 0.94 g/t Au at a 0.4 g/t Au cutoff;
TAP AB - Measured + Indicated Resource - 3.415 Mt @ 1.50 g/t Au at a 0.4 g/t Au cutoff;
- Inferred Resource - 0.318 Mt @ 2.27 g/t Au at a 0.4 g/t Au cutoff;
Duckhead - Measured + Indicated Resource - 0.118 Mt @ 2.06 g/t Au at a 0.55 g/t Au cutoff;
- Inferred Resource - 0.005 Mt @ 4.14 g/t Au at a 0.55 g/t Au cutoff;
TOTAL Open-pit Sulphide - Measured + Indicated Resource - 6.528 Mt @ 1.52 g/t Au;
TOTAL Open-pit Oxide - Inferred Resource - 0.327 Mt @ 2.28 g/t Au.
Stockpiled Mineralisation
TOTAL Stockpiles - Measured Resource - 2.491 Mt @ 0.53 g/t Au;
TOTAL Open-pit + Stockpile - Measured + Indicated Resource - 13.593 Mt @ 1.38 g/t Au;
TOTAL Open-pit - Inferred Resource - 0.647 Mt @ 2.48 g/t Au.
Underground Oxide Mineralisation
Urucum East - Inferred Resource - 0.005 Mt @ 2.57 g/t Au at a 2.1 g/t Au cutoff;
Duckhead - Inferred Resource - 0.033 Mt @ 4.2 g/t Au at a 2.1 g/t Au cutoff;
TOTAL Underground Oxide - Inferred Resource - 0.038 Mt @ 4.00 g/t Au.
Underground Sulphide Mineralisation
Urucum North - Measured + Indicated Resource - 2.402 Mt @ 4.26 g/t Au at a 1.6 g/t Au cutoff;
- Inferred Resource - 3.262 Mt @ 2.94 g/t Au at a 1.6 g/t Au cutoff;
Urucum Central - Inferred Resource - 0.852 Mt @ 2.61 g/t Au at a 1.6 g/t Au cutoff;
Urucum East - Inferred Resource - 0.080 Mt @ 2.03 g/t Au at a 1.6 g/t Au cutoff;
TAP AB - Measured + Indicated Resource - 0.247 Mt @ 2.59 g/t Au at a 1.3 g/t Au cutoff;
- Inferred Resource - 0.899 Mt @ 2.72 g/t Au at a 1.3 g/t Au cutoff;
Duckhead - Inferred Resource - 0.230 Mt @ 2.05 g/t Au at a 1.60 g/t Au cutoff;
TOTAL Underground - Measured + Indicated Resource - 2.649 Mt @ 4.11 g/t Au;
TOTAL Underground - Inferred Resource - 5.350 Mt @ 2.80 g/t Au.
TOTAL Tucano - Measured + Indicated Resource - 16.242 Mt @ 1.83 g/t Au.
TOTAL Tucano - Inferred Resource - 5.997 Mt @ 2.77 g/t Au.
TOTAL Tucano - Measured + Indicated + Inferred Resource, December, 2020 - 22.239 Mt @ 2.083 g/t Au for 46.33 tonnes of contained gold.
Total past production to the end of 2020 - 44.217 tonnes of gold
The information in this description was extracted from: Pires, C.H.B., Cornejo, F.A., Hepworth, N., Winer, N., Pressacco, R. and Ciuculescu, T., 2021 - Technical report on the 2020 Mineral Reserves and Mineral Resources of the Tucano gold mine, Amapá State, Brazil; An NI 43-101 Technical Report prepared by Great Panther Mining Limited, 19 January, 2021, 377p.
The most recent source geological information used to prepare this decription was dated: 2020.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Tucano
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