Minas Gerais, Brazil
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The Turmalina Mine Complex is located in the municipality of Conceição do Pará in the state of Minas Gerais, ~120 km
NW of Belo Horizonte and 10 km south of the town of Pitangui. The complex comprises Orebody A, B and C, the latter of which is also known as Satinoco (#Location: 19° 44' 21"S, 44° 53' 0"W).
The Turmalina deposits occur within the southern São Francisco Craton and are located in the Brumal-Pilar region in the western part of the Quadrilatero Ferrifero, which is underlain by Archaean and Proterozoic rocks. The Archaean includes a granitic basement and the Nova Lima and Quebra-Ossos groups of the Rio das Velhas Supergroup. The Pitangui greenstone belt, which hosts the Turmalina deposits, forms a NW-trending synclinorium, that has been recognised to represent a distinct rock succession, separate from, but equivalent to the well-known Rio das Velhas greenstone belt of the eastern Quadrilatero Ferrifero (Brando Soares et al., 2020).
The most primitive crust known from the São Francisco craton include 3.6 Ga gneisses (Oliveira et al., 2020), which were cratonised during several trondhjemite-tonalite-granodiorite (TTG) magmatic events, mainly between 3.2 and 2.7 Ga (Lana et al., 2013). These rocks in part form the granite gneiss basement which comprises leucocratic and homogeneous gneisses and migmatites, that constitute a complex with an initial tonalitic composition intruded by younger Archaean granitic rocks. The upper contact of the sequence is discordant and tectonically controlled by reverse faulting. Regionally, the overlying Rio das Velhas Supergroup is predominantly composed of mafic, meta-volcaniclastic and meta-epiclastic schists of the Nova Lima Group, and metamorphosed aultramafic and mafic rocks of the Quebra-Ossos Group which includes serpentinites, talc schists and metabasalts.
The Pitangui Group dominates the regional geology in the western part of the Quadrilatero Ferrifero, and based on lithostratigraphic correlations, it is regarded as an equivalent to the Nova Lima Group in the Rio das Velhas greenstone belt to the SE (Romano, 2007; Brando Soares et al., 2017; Fabricio-Silva et al., 2019). Regionally, the Nova Lima Group, which has been studied in more detail, is composed of volcanogenic-sedimentary rocks, the most prominent of which are 'Algoma-type' iron formations. It has been sub-divided into three units (after references cited in Hill and Tomaselli, 2020):
• A basal unit composed of mafic to intermediate metavolcanic rocks interlayered with meta-pelites, banded iron-formations, and rare felsic meta-volcaniclastic rocks;
• An intermediate unit composed of mafic to felsic volcanic and volcaniclastic rocks interleaved with graphitic phyllite and banded iron-formation horizons;
• An upper unit composed of meta-pelites interleaved with felsic meta-volcanic and meta-volcaniclastic rocks, quartzites and meta-conglomerates.
The rocks in the southern São Francisco craton have been subjected to three orogenic events:
• the 2750 to 2670 Ma Rio das Velhas orogeny (Carneiro, 1992; Baltazar and Zucchetti, 2007);
• Palaeoproterozoic deformation at ~2100 Ma with mostly SE-directed strain markers (Alkmim and Marshak, 1998; Teixeira et al., 2015); and
• the Neoproterozoic Brasiliano Pan-African orogeny from 650 to 500 Ma, evident only in the eastern portion of the São Francisco craton (Chemale et al., 1994; Alkmim and Marshak, 1998).
In the Pitangui area, Archaean and Proterozoic rocks predominate. The Archaean granitic basement is overlain by the Neoarchaean Pitangui Group, a sequence of ultramafic to intermediate volcanic flows and pyroclastics with associated sediments that includes a sequence of sheared, banded, sulphide-facies and silicate-facies iron formations and cherts that in the deposit area broadly strikes at 135° and dips moderately to steeply to the NE. The Turmalina deposit is hosted by chlorite-amphibole schists and silicified biotite schist within this sequence. The overlying Proterozoic succession include the Palaeoproterozoic Minas Supergroup which includes basal quartzites and conglomerates as well as phyllites, some of which higher in the sequence are hematitic; and the Neoproterozoic Bambuí Group which is composed of calcareous sediments.
The stratigraphic succession in the Pitangui district is as follows, from the base (after Hill and Tomaselli, 2020):
Basement - foliated, leucocratic granite and gneisses, locally characterised by migmatite sections with porphyroblasts of quartz and K feldspars. Granitic intrusions with fine to medium textures, and dolerite dykes are common.
Pitangui Group - divided into the following stratigraphic sequence (after Hill and Tomaselli, 2020):
• Metamorphosed ultramafic and mafic volcanic unit, composed of interlayered igneous ultramafic and mafic flows represented by serpentinites, chlorite-actinolite schists and amphibolites with layers of talc schists, oxide-facies BIFs and carbonaceous phyllites;
• Metamorphosed mafic and sedimentary unit (Middle Unit): composed of interlayered metamafic rocks, with chlorite-actinolite schists and dacitic intrusions at the top;
• Meta-sedimentary unit: cummingtonite BIFs and meta-chert rich horizons interlayered with carbonaceous and chlorite schists. Locally, layers of meta-arkoses are evident;
• Meta-mafic unit - alternating layers of amphibolite and chlorite-actinolites;
• Pyroclastic and meta-pelites - volcanic meta-conglomerates at the base, grading to, or alternating with, foliated meta-lapilli tuffs and meta-tuffs at the top of the sequence, where the meta-tuffs become dominant;
• Meta-sedimentary unit (Upper Unit) - numerous narrow interleaved layers of quartz-sericite schists, quartz-chlorite schists, quartz-sericite-chlorite schists and carbonate-rich schists.
The Pitangui Group is alternatively subdivided by Marinho et al., (2018) as the:
• Rio Pará Formation, a succession of komatiite to tholeiitic metabasalt, interbedded with metapelites and metatuffs;
• Rio São João Formation, composed of rhythmites interbedded with quartzite, metabasalt and banded iron formation (BIF); and
• Onça do Pitangui Formation, consisting of phyllite, black shale, arkose, and intercalations of metaconglomerate, metachert and BIF.
• Antimes Formation, which overlies the Pitangui Group and is mainly composed of fine- to coarse-grained quartzites.
Minas Supergroup - which comprises a clastic and chemical sedimentary succession composed of thin to coarse quartzites with layers of a basal conglomerate. The quartzites are overlain by grey carbonatic phyllites and white sericitic phyllites in which hematite increases towards the stratigraphic top of the sequence (Hill and Tomaselli, 2020).
Intrusive Rocks - The Pitangui greenstone belt is surrounded by the Divinópolis and Belo Horizonte Complexes that represent a trondhjemite-tonalite-granodiorite (TTG) terrane in the continental crust of the São Francisco craton (Machado et al., 1996; Noce et al., 2007; Brando Soares et al., 2020). The TTGs range from ~2750 to 2695 Ga (Romano et al., 2013; Marinho et al., 2018; de Melo-Silva et al., 2020). The TTG-greenstone terranes were intruded by late to post-tectonic granitic magmas (Renger et al., 1994; Alkmim and Marshak, 1998; Noce et al., 2007; Romano, 2007), that include younger, high K calc-alkaline granites, which include the 2694.7±9 Ma (U-Pb zircon age; de Melo-Silva et al., 2020) Casquilho pluton.
The geology and geochemistry of the mafic magmatism in the Pitangui greenstone belt reveal an E- to N-MORB signature with a back-arc affinity (Verma et al., 2017; Brando Soares et al., 2020; de Melo-Silva et al., 2020).
Mineralisation at the Turmalina occurs of a number of tabular bodies that are spatially related to either BIF bands or to a package of weakly silicified biotite schists. Individual tabular bodies are grouped together, based on their spatial configuration and gold content, into Orebodies A, B, and C. Gold can occur within the BIF itself, but can equally occur in the other host lithologies. Each of these orebodies can be summarised as follows:
Orebody A which has historically been the main producer in the mine. It is mostly composed of a folded, steeply NE dipping tabular deposit with a steep, predominantly SE linear plunge. A number of additional tabular mineralized zones occur in close proximity and are generally sub-parallel to this main folded zone. The bulk of the better grade gold is hosted by weakly silicified biotite schist host rocks. Mineralization has been outlined over a strike length of ~250 to 300 m with an average thickness of 6 m and to a depths of ~1100 to 1150 m below surface. The southeastern portion of the orebody is composed of two parallel narrow veins. The northwestern portion of the orebody is much the same as the southeastern, although the two parallel zones nearly or completely merge and therefore the economic zone is much wider overall with a combined thickness of up to 10 to 12 m (Hill and Tomaselli, 2020).
Orebody B includes two lower grade, tabular-shaped lenses that are generally parallel to Orebody A, ~50 to 75 m in the structural hanging wall. A third lens is located possibly along an axial plane. The mineralisation in these lenses has been defined over a strike length of ~350 to 400 m and to depths of 650 to 700 m below surface (Hill and Tomaselli, 2020).
Orebody C or Satinoco is located to the SW in the structural footwall of Orebody A. It is hosted by meta-basalt and meta-komatiite with interbedded meta-tuff, BIF and black shales of the lowermost units of the Pitangui Group, the Rio Pará Formation. The shear zone-related ore lenses that make up the orebody consist of three 2 to 4 m thick auriferous corridors extending over a strike length of ~ 1400 m and to a depth of 1000 m below the surface. The lenses trend NW-SE with a dip of ~60°NE and constitute subbodies referred to as Satinoco-NW (C-NW), Satinoco-Central (C-Central) and Satinoco-SE (C-SE) (Hill and Tomaselli, 2020; Fabricio-Silva et al., 2021).
The host rocks are cut by a series of granitic apophyses which have the same high K granitic geochemical signature as the main Casquilho granite batholith exposed near the deposit at surface (Brando Soares et al., 2020). This granite is leucocratic, coarse-grained and composed of 40 to 55 vol.% quartz; ~25 vol.% Ca-rich, partially saussuritised plagioclase; 15 to 20 vol.% microcline; and 10 to 15 vol.%, partially chloritised biotite. Some of these generally discordant apophyses converge with and become parallel to the orebodies and shear zones where they are partially deformed, forming pinch-and-swell structures (Fabricio-Silva et al., 2021).
High-grade and sulphide-rich (i.e., 10 vol.%) ore is associated with quartz veins. Sulphides occur within, or are disseminated as centimetre-thick bands parallel to the quartz veins or as matrix of hydraulic breccias. Arsenopyrite is a visual indicator of high-grade gold, although gold is also frequently associated with pyrrhotite and pyrite, mainly occurring as >0.1 µm visible inclusions, and as 'invisible gold' within arsenopyrite and löllingite (Fabricio-Silva et al., 2021).
The host rocks of the Satinoco area have experienced at least three deformation events. D1 developed during a stage of compression and is represented by isoclinal regional folds and associated S1 WNW-ESE-striking axial-planar foliation (with an average plunge of 62° and azimuth of 12°) that obliterated the primary compositional banding. D2 produced NW-SE striking and NE dipping ductile shear zones that host mineralisation, quartz veins and resulted in the generation of an LS2 stretching lineation with a mean plunge at 25° and azimuth of 85°, and an S2 crenulation cleavage that strikes between NNW and NNE, dipping at 65 to 75°W. D3 is reflected by metre-sized open folds with an axial plane dipping around 60°NE and axis plunging 65° and azimuth of 325°. It also produced several reverse faults, most commonly found in the Satinoco-SE orebody. These reverse faults cut the open folds, strike mainly NW-SE and dip 50 to 60°NE (Fabricio-Silva et al., 2021).
The distribution of metamorphic mineral assemblages is spatially related to the D2 shear zones and the granite stock. Shear zones are approximately orthogonal to the granite-host rock contact with the highest metamorphic grades occurring in the same areas. Hydrothermal mineral assemblages proximal to orebodies indicates recrystallisation under amphibolite-facies conditions, although peak metamorphic minerals have subsequently undergone retrograde metamorphism. In the proximal zone, the metamorphic mineral assemblage in meta-basalt is quartz-garnet-cummingtonite-actinolite ±biotite; whereas the meta-tuff is characterised by quartz-garnet-cummingtonite-ilmenite ±staurolite. Staurolite and larger (>25 mm) garnet crystals are most common in close proximity to the granite contact in the western part of the deposit. Slightly further removed, at ~7 m from ore, the metamorphic mineral assemblage reflects a markedly lower grade, with a typical assemblage of quartz-chlorite ±garnet, reflecting upper greenschist-facies conditions. At even more distal locations, the regional metamorphic mineral assemblage is quartz-chlorite-calcite ±muscovite, reflecting a lower greenschist facies (Romano, 2007). The low-grade regional metamorphism affected both the higher grade contact metamorphic aureole in the vicinity of the granite, where chlorite ±calcite ± developed as retrograde phases, and biotite became chloritised and quartz partly recrystallised in the granite itself.
Hydrothermal alteration is generally distributed parallel to the S1 foliation and is associated with the mineralised envelope, forming zoned halos with gradational contacts with the host rocks surrounding the orebodies. Hydrothermal alteration minerals include mainly quartz, carbonate, chlorite, arsenopyrite, löllingite, pyrrhotite, galena, pyrite and sericite, as well as grunerite, biotite, tourmaline and epidote. Less common hydrothermal minerals are gold, chalcopyrite, sphalerite, ullmannite, monazite, rutile, magnetite and hematite (Fabricio-Silva et al., 2021).
Silicification is the dominant alteration, leading to the formation of milky and smoky quartz veins and granoblastic quartz that is moderately sheared and recrystallised. Quartz is generally completely recrystallised in shear zones, while carbonate alteration remains as centimetre-thick calcite veins with associated pyrrhotite and pyrite, in places as breccias, or as interstitial ankerite and calcite associated with thin bands of sericite and recrystallised quartz. Sulphide alteration occurs as at least three assemblages that developed as disseminated grains in bands, breccias, or along the margin of quartz veins. Up to 40 vol.% chloritisation is pervasively associated with sericitisation, whilst tourmaline is concentrated in layers that are generally parallel to the S1 foliation proximal to orebodies, where euhedral fine-grained crystals are associated with sericite. In places, tourmaline crystals contain inclusions of quartz, cummingtonite and sulphides, mainly pyrrhotite, subordinately arsenopyrite. In the mafic host rocks, incipient hydrothermal alteration occurs as grunerite, biotite, epidote, magnetite, hematite and monazite (Fabricio-Silva et al., 2021).
At least three generations of veins have been identified, composed of quartz, carbonate and sulphides, with a minor amount of feldspar, tourmaline, grunerite, biotite and actinolite (Fabricio-Silva et al., 2021).
• V1 veins represent the principal vein system which is parallel to S1, and developed pre- to syn-kinematically to the ductile D2 event. These veins are composed of milky to smoky quartz and contain 5 to 10 vol.% gold-bearing sulphides with grades of 3 to 7 g/t Au. They are oriented NW-SE and have laminated and brecciated textures which also contain 'inclusion bands' up to 5 cm wide oriented subparallel to the vein walls. These 'inclusion bands' contain amphibolite- and sulphide-rich rock fragments. The milky quartz comprises 40 to 70% of the total quartz and is dominant where the veins have greater thicknesses, whereas the smoky quartz occurs mainly in boudin boundaries or in the 'necks' of pinch-and-swell structures (Fabricio-Silva et al., 2021).
Hydrothermal alteration halos associated with the V1 veining have been divided into five zones: i). the main lode zone, represented by V1 veins surrounding by sulphide-enriched zones that contain the highest Au grade; ii). proximal quartz-chlorite-carbonate-sericite-grunerite-biotite-garnet-sulphide ±epidote ±tourmaline; iii). proximal to intermediate quartz-chlorite-carbonate-sericite ±sulphide ±biotite ±garnet ±grunerite ±epidote zone; iv). distal to intermediate quartz-chlorite-carbonate ±sericite zone; and v). distal quartz-carbonate-chlorite ±sericite zone (Fabricio-Silva et al., 2021).
• V2 veins are 10 to 25 cm wide and are extensional shear-related. The predominantly comprise 80 to 90 vol.% milky quartz, <5 vol.% carbonate, and ~5 vol.% sulphide. They fill reverse faults and cross-cut most granite apophyses. They also cut the main shear zone and V1 veins. V2 veins occur at low angles to the shear zone corridors or are oriented along the S2 foliation. These extensional veins contain coarse-grained ~1 to 2 cm euhedral to subhedral quartz, in places forming growth fibres oriented both perpendicular and oblique to vein margins. Some are weakly mineralised, ranging from 0.1 to 0.5 g/t Au. V2 veins also frequently occur as 1 to 2 mm thick veinlets that cut S1 and V1 veins, and usually contain fine-grained, euhedral to subhedral milky quartz, up to 20 vol.% carbonate grains, mainly ankerite and gold-bearing sulphides (Fabricio-Silva et al., 2021).
• V3 veins are barren, represented by extensional veins that are 1 to 15 cm thick and comprise coarse-grained, euhedral, milky quartz and calcite. These veins are sulphide-poor but contain some pyrite-chalcopyrite, with no gold content and are randomly oriented (Fabricio-Silva et al., 2021).
Fabricio-Silva et al. (2021) conclude from a study of the Satinoco orebody that it was formed as follows:
• Stage I gold mineralisation took place between 2720 and 2684 Ga prior, during, and after the emplacement of granitic magma. WNW-striking shear zones appear to be a critical controlling factor on the ore deposit location and ore shoot geometry during the early pregranite stage between 2720 and 2695 Ma related to hydrothermal fluid infiltration, associated alteration and mineralisation stage I.
• Stage II was an Fe-rich, late- to postmagmatic mineralising event with respect to the 2720 to 2695 Ma Casquilho granite, taking place between ~2695 and >2684 Ma, and involving metasomatism by late-magmatic Fe-rich fluids;
• Granitic magma intrusion may have driven host rock dehydration and generated a mixture of metamorphic and magmatic fluids with a high fluid/rock ratio, essential to mineralisation;
• Stage III occurred during later post-granite uplift and/or exhumation and accompanying decrease in temperature, which led to the recrystallisation and remobilisation of sulphides and gold.
Reserves and Resources
Mineral Resources and Ore Reserves as at 31 December 2019 (Jaguar Mining Inc. Reserve and Resources Report, 2020) were:
Orebody A - Measured + Indicated Resources - 1.493 Mt @ 6.24 g/t Au;
- Inferred Resources - 0.364 Mt @ 4.65 g/t Au;
Orebody B - Measured + Indicated Resources - 1.545 Mt @ 3.66 g/t Au;
- Inferred Resources - 0.018 Mt @ 6.46 g/t Au;
Orebody C - Measured + Indicated Resources - 2.189 Mt @ 4.27 g/t Au;
- Inferred Resources - 1.436 Mt @ 4.1 g/t Au;
TOTAL - Measured + Indicated Resources - 4.227 Mt @ 4.89 g/t Au, for 20.65 t of contained gold;
- Inferred Resources - 1.818 Mt @ 4.3 g/t Au, for 7.7 t of contained gold;
TOTAL gold in Resources - 28.347 t of contained gold.
Ore Reserves - included in resources
Orebody A - Proved + Probable Reserves - 0.806 Mt @ 5.34 g/t Au;
Orebody C - Proved + Probable Reserves - 1.591 Mt @ 3.79 g/t Au;
TOTAL Proved + Probable Reserves - 2.397 Mt @ 4.31 g/t Au, for 10.33 t of contained gold.
This summary is drawn from Fabricio-Silva et al. (2021) referenced below, and Hill and Tomaselli, 2020 - Technical report on the Turmalina Mine Complex, Minas Gerais State, Brasil; an NI 43-101 Technical Report prepared by Deswik Brasil with and for Jaguar Mining Inc. 182p.
The most recent source geological information used to prepare this summary was dated: 2021.
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.
Fabricio-Silva, W., Frimmel, H.E., Shutesky, M.E., Rosiere, C.A. and Massucatto, A.J., 2021 - Temperature-Controlled Ore Evolution in Orogenic Gold Systems Related to Synchronous Granitic Magmatism: An Example from the Iron Quadrangle Province, Brazil: in Econ. Geol. v.116, pp. 937-962.|
Maurer, V.C., de Melo, G.H.C., Lana, C.deC., Marinho, M.deS., Batista, S.P.V., da Silveira, L.M., Queiroga, G., Castro, M.P. and Silva, M., 2021 - Trace elements in pyrite and pyrrhotite in the Pitangui Orogenic Au deposit, Pitangui greenstone belt, Sao Francisco Craton: Implications for the ore-forming fluids and metal sources: in J. of South American Earth Sciences v.111, 22p. doi.org/10.1016/j.jsames.2021.103459.|
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