Mineral chemistry and oxygen isotope studies on Sn (±W) mineralization from Pedra Branca Granite Massif, Central Brazil

Abstract Central Brazil hosts Paleo-Mesoproterozoic A-type granitic suites related to the Goiás Tin Province (GTP) that contain Sn (±W, Nb-Ta, REE) mineralization associated with greisen, veins, and small pegmatite bodies. The Pedra Branca granite massif (1.77–1.74 Ga) is the main representative of GTP, marked by important cassiterite (±wolframite) contents. The cassiterite contains SnO2= 96–100 wt. %, with the sum FeOtotal, TiO2, WO3, Ta2O5, Nb2O5, In2O3, and UO2 content below 4 wt.%, while wolframite contains WO3= 71.5–74.5 wt.%, FeOtotal= 14.3–17.4 wt.% and MnO = 6.3–9.9 wt.%, as well as Sn, Ca, Ti, Ta, Nb, Pb, In, and U as trace elements. The δ18O data on the quartz-cassiterite pair (quartz = 9.4–10.4‰, cassiterite = 2.6–2.9 ‰) from greisen reveal a magmatic-hydrothermal signature with calculated crystallization temperatures between 410 and 485°C. However, during the Neoproterozoic Brasiliano/Pan-African Orogeny (800–500 Ma), all lithologies and ore sites were subjected to flattening, fragmentation, and mylonitic deformation. Fluid inclusion data revealed the presence of low-salinity aqueous solutions with homogenization temperatures between 215 and 100°C related to Neoproterozoic deformation. Finally, during the Phanerozoic, prolonged erosive produced Sn (±W)-rich alluvium around the Pedra Branca granitic massif.


INTRODUCTION
Central Brazil hosts Paleo-Mesoproterozoic granitic suites, located mainly in the central-north and northeast regions of the State of Goiás (Fig. 1A), which have Sn (±W, Nb-Ta, REE) mineralization and make up the so-called Goiás Tin Province (GTP) (Marini and Botelho 1986).In general, these granite suites have petrographic and geochemical signatures similar to A-type magmatism, with a high content in alkalis, Sn, W, F, Rb, Th, Y, Nb, Ga, and REE, and often contain records of late to post-magmatic transformations, such as microclinitization, albitization, and greisenization (Botelho and Marini 1984, Marini and Botelho 1986, Botelho 1992, Botelho et al. 1993, Lenharo et al. 2002).
The Pedra Branca granite massif is the main mineralized magmatic system of the GTP (Fig. 1B).It was discovered in 1973 during a regional mineral prospecting stage carried out by the Rio Doce Geology and Mining Company, but the local was subsequently invaded by small prospectors, known as "garimpeiros" in Brazil ( Jacobi 2003).The Sn (±W) concentrations occur in paleo-alluvium, greisenized granitic cupula named Bacia zone (endo-to exogreisen) and along with a greisenized NE-SW fracture/fault zone named Faixa Placha (exogreisen).Previous geological surveys carried out by mining companies estimate about 15,000 t/Sn in only 1.5 km in length from the Faixa Placha ore site (internal technical report), which have about 5 km in length.In this deposit, cassiterite occurs associated with wolframite, scheelite, arsenopyrite, chalcopyrite, sphalerite, pyrite, galena, chalcocite, stannite, and covellite (Padilha and Laguna 1981, Botelho and Marini 1984, Botelho and Rossi 1988, Botelho and Moura 1998).Despite the mineral diversity found in this deposit, investigations into the chemical composition, the stable isotopes, and the contents of the fluid inclusions in the ore minerals are still limited or nonexistent (e.g., Botelho and Marini 1985, Botelho and Moura 1998, Sparrenberger and Tassinari 1999).
In this study, we analyze the chemical composition and oxygen isotopes (δ 18 O) of cassiterite, wolframite, and quartz found in the Faixa Placha ore site.Identifying the ion substitution mechanisms responsible for zonation and mineral intergrowth features, as well as the temperature and nature of the fluids will aid in the understanding of the metallogenic processes responsible for Sn (±W) mineralization at the Pedra Branca granitic massif.
investigations were carried out at the Universidade de Brasília.The ore samples studied (cassiterite, wolframite, and quartz) were collected at the mining front explored by the EDEM mining company.During the SEM/EDS and EPMA analyses, the samples studied were in polished rock thin sections covered by a carbon film.
For SEM/EDS microanalysis technique, an FEI QUANTA 450 model was used, which has a high-performance EDAX Octane EDS/SDD spectrometer system, Chroma C2L cathodoluminescence imaging system for use in scanning electron microscopes (SEMs), and an EDAX DigiView electron backscatter diffraction (EBSD) camera.The imaging was acquired at a focal distance of 10 mm for 10-20 s, with a probe between 0.1 and 0.2 nm, beam current of 400-500 pA°, and an accelerating voltage of 20 kV.For the EPMA microanalysis technique, a JEOL JXA-8230 microanalyzer with five coupled wavelength dispersive spectrometers was used.The analytical conditions consisted of accelerating voltage of 20 kV, beam current of 40 nA, beam diameter of 1-2 μm, and counting times of 15 and 10 s for peak and background positions, respectively.Data reduction was performed with the ZAF program applying the specific standards of cassiterite and wolframite.
The fluid inclusion study was carried using double-polished sections (~1-mm thick) from ore samples.The conventional petrography was performed at room temperature (±25°C) with the aid of an Olympus petrographic microscope (model BX51) applying the criteria of Roedder (1984), Shepherd et al. (1985), and Van den Kerkhof and Hein (2001).Microthermometric data were acquired using a cooling stage and LTS420 heating from LINKAM, with a temperature range between -200 and 420°C, coupled with a petrographic microscope with long-distance objectives with magnification from 10× to 50×.The calibration was performed with H 2 O-NaCl synthetic biphasic fluid inclusions, applying speed rates from 5 to 15°C/min, with an estimated accuracy of ±0.2°C for the freezing (+25 to -100°C) and ±2°C for heating (up to 350°C).The oxygen isotope (δ 18 O) study was carried out at the Isotope Geoscience Units of the Scottish Universities Environmental Research Centre Laboratories in Glasgow, Scotland.The oxygen isotope analyses were applied on cassiterite and quartz with a size between 0.5 and 1 cm.The nearly pure crystals samples (> 90%) were handpicked from selected specimens from the greisen.Approximately 1 mg of oxygen-bearing samples reacted with chlorine trifluoride (ClF 3 ) using laser heating fluorination techniques (Fallick et al. 1993, Macaulay et al. 2000).A mass spectrometer (VG SIRA 10 model) was used for the analyses, whose precision of determination from laboratory replicate analysis is 0.2‰ for δ 18 O relative to Vienna Standard Mean Ocean Water.

GEOLOGICAL SETTING
A large part of central Brazil lies within an important regional geotectonic unit named Tocantins Province (Almeida et al. 1981), which brings together different tectonostratigraphic domains and subdomains that were amalgamated through thrust, nappe, and strike-slip mega-faults, under a complex tectonic architecture, occurred during the Neoproterozoic convergences and collisions between paleocontinents related to Brasiliano/Pan-African Orogeny (Uhlein et al. 2012, Brito Neves et al. 2014, Fuck et al. 2014, 2017, Pimentel 2016, Valeriano 2017).
The Pedra Branca granite massif is inserted in the Rio Paranã subprovince (Fig. 1B).It represents the type area for the homonymous intrusive suite (CPRM 2007) and is considered one of the granitic bodies with the greatest economic potential of the GTP.It stands out in remote sensing products through its semicircular shape with about 90 km² of outcropping area and 1,000 m altitude over a pediplanized region around of 500 m.It was emplaced during the late Paleoproterozoic (Statherian period), intrusive in the basement Archean-Paleoproterozóic units: paragneisses, shales, and peraluminous granites from Ticunzal Formation and Auruminas Suite (> 2.15 Ga), respectively, as well as quartz-diorite to granodiorite Nova Roma (2.14 Ga).The Pedra Branca granitic plutonism occurred relatively close to voluminous Paleoproterozoic bimodal volcanism related to the early stages of the Araí intracontinental rift evolution (Arraias Formation, positioned at the basal portion of the Araí Group).However, during the Neoproterozoic Brasiliano/Pan-African Orogeny (800-500 Ma), a reasonable lithostratigraphic inversion occurred, accompanied by different deformation stages (foliation, shear zone, faults, and fractures) under low-grade metamorphic, which affected all lithologies (Pimentel et al. 1991, Botelho 1992, Alvarenga et al. 2007, CPRM 2007, Tanizaki et al. 2015, Martins-Ferreira 2019, Silva et al. 2021).
Additionally, the pb2 term also associates metric porphyritic dykes, as well as wide and irregular greisen aureole surrounding the pb2d petrographic type.
The Sn (±W) mineralization is linked to the most evolved magmatic pulse from pb2 term, represented by Li-mica leucogranite or pb2d petrographic type, associated to greisen bodies, distributed in the main greisen sector named "Bacia zone" and along with the "Faixa Placha" (Fig. 2).The Bacia zone hosts several irregular endogreisen bodies, as well as quartzveins and some pegmatites small bodies.This place presents a concave geomorphology, formed from partial erosion of the granitic cupola (Fig. 3A), which favored the concentration and distribution of Sn (±W) mineralization to the drainage network located below the Pedra Branca massif, thus contributing to the discovery of this mineral deposit (e.g., Jacobi 2003).On the contrary, the Faixa Placha is a NE-SW linear and subvertical structure formed by greisenized tensile fractures/faults sets or exogreisen (Figs. 2 and 3B), probably generated or reopened during the intrusion of the pb2 magmatic phase.However, during Brasiliano/Pan-African Orogeny, this structure was then reactivated under a ductile-brittle regime and with sinistral cinematic (shear fault regime), favoring flattening, fragmentation, and partial mylonitic deformation on the lithologies.Lenticular greisen bodies, quartz veins-veinlets, greisen-filled tensile fractures/fissures, some breccia, and tension gashes also are observed in that ore site (Figs.3C and 3D).

PETROGRAPHIC AND MINERAL CHEMISTRY DATA
These data were obtained from ore samples encapsulated in greisenized tensile fractures/faults sets (exogreisen) of the Faixa Placha site, whose results are presented below.

Cassiterite
The euhedral to subhedral cassiterite crystals are zoned, slightly to moderately fractured containing microinclusions of ilmenite, rutile, tantalite, and magnetite.Pleochroism is weak in lighter varieties and medium to strong in darker varieties.In general, its typical zoning is marked by alternating bands of pale yellow, orange, light brown, to dark brown (Figs.4A and 4B).However, in the Faixa Placha ore site, some greisen bodies, as well as tensile and shear fractures/fissures, have cassiterite crystals broken and sometimes stretched as a result of the deformation related to the Brasiliano/Pan-African Orogeny (Figs. 4C and 4D).
The cassiterite has SnO 2 contents between 96.2 and 99.7 wt.%, while the sum of the other elements analyzed has content below 4 wt.%(Table 1).FeO total , TiO 2 , and WO 3 are the main impurities, while Ta 2 O 5 , Nb 2 O 5 , In 2 O 3 , and UO 2 appear as trace elements.The colors of lesser intensity, ranging from dark yellow, orange, to light brown, have higher contents in SnO 2 and lower in FeO total , TiO 2 , Ta 2 O 5 , Nb 2 O 5 , WO 3 , In 2 O 3 , and UO 2 .On the contrary, the zones whose colors vary from dark red to dark brown have a lowered SnO 2 content accompanied by a relative increase FeO total , TiO 2 , and WO 3 .These geochemical characteristics corroborate with what is already known in the literature regarding the chemical composition of zoned cassiterites from other deposits in the world (Giuliani 1987, Neiva 1996, Murciego et al. 1997, Costi et al. 2000, Souza and Botelho 2009, Nascimento and Souza 2017).

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Table 1.Electron microprobe analysis results on cassiterite crystals.The composition of oxides in percent by weight (wt.%) and of element in atoms per formula unit (apfu) calculates on the basis of two oxygens.The symbol (-) represents values below the detection limit.
In general, the darker zones have more Ti than the lighter zone, indicating the effective substitute Sn 4+ ↔ Ti 4+ associated with higher content of inclusions or exsolutions of titanium oxide minerals (rutile and ilmenite).According to Neiva (1996), the mechanism of incorporation of Fe, Mn, W, Nb, and Ta in the Ti-darker zones can be explained by equations 2(Nb, Ta) 5+ + (Fe, Mn) 2+ ↔ 3Ti 4+ and (Mn, W) 6+ + Fe 2+ ↔ 2Ti 4+ .The regular decrease in Ti as Fe+Mn+Nb+Ta increases also indicates that the mechanism (Nb, Ta) 5+ + Fe 3+ ↔ 2Ti 4+ might have operated.The increase of W+Mn+Fe in Ti-rich darker zones can indicate the formation of a specie of metastable molecular wolframite in these sites, marked by substitution of Sn 2 O 4 by (Fe,Mn)WO 4 (according to Möller et al. 1988, Neiva 2008).
The irregular anomalous contents (100-700 ppm) of In and U in the cassiterite structure are also associated with Fe-Ti darker zones, indicating the important mechanism of substitution of Sn by Fe+Ti on the coupled incorporation of other chemical impurities, as suggested by the equations 2(Sn, Ti) 4+ ↔ (Nb, Ta) 5+ + (Fe, In) 3+ or 2(Sn, Ti) 4+ ↔ U 4+ + 2Fe 2+ .

Wolframite
Wolframite crystals are relatively rarer and occur disseminated in greisen and veins, normally associated with cassiterite crystals (Fig. 4B).It displays opaque euhedral to subhedral crystals and tabular in shape, but can also occur in small massive aggregates (Fig. 6A), often with a wide range of a size (500-8,000 μm).Wolframite crystals commonly host niobium-tantalate and ilmenite as microinclusions or exsolutions (Figs.6B and 6C).
The Nb and Ta incorporation (niobium-tantalate species) like a kind of solid solution in the wolframite structure may result from coupled substitutions, expressed by the equation Fe 2+ + W 6+ ↔ Fe 3+ + (Nb, Ta) 5+ , which can favor zoning on (Fe, Mn)(W, Nb, Ta)O 4 mineral specie (Polya 1988, Tindle and Webb 1989, Neiva 2008).This mechanism of substitution also favors the decrease of W 6+ versus (Nb + Ta) 5+ increases, with the electrostatic charge deficiency resulting in the iron oxidation Fe 2+ ↔ Fe 3+ (Neiva 2008).According to Harlaux et al. (2018), the isovalent substitution Fe 2+ ↔ Mn 2+ in octahedral coordination has a nonlinear trend and leads to a minor excess in Fe 3+ into the structure of wolframite.
This mechanism can be observed by negative correlation of Fe versus Mn (Fig. 7C), corresponding to the isovalent substitution of Fe 2+ ↔ Mn 2+ , or by a regular decrease in W followed by an increase of Nb+Ta at the wolframite structure from the Faixa Placha ore site (Fig. 7D).The decrease in W 6+ is also flowed by irregular increases of Sn 4+ , In 3+ , and U 4+ , which may also be linked to accidental microinclusions and exsolutions, or as a result of 2Fe 2+ + W 6+ ↔ 2(Fe, In) 3+ + (Sn, U) 4+ coupled substitutions.

OXYGEN ISOTOPE DATA (δ 18 O)
Oxygen isotopic data have been widely applied to mineral pairs focusing on the source and geothermometry of magmatic-hydrothermal systems (e.g., Kelly and Rey 1979, Zhang et al. 1994, Taylor Jr. 1997, Crowe et al. 2001, Faure and Mensing 2004, Mering et al. 2018).We obtained δ 18 O data on the quartz-cassiterite pair under association paragenetic encapsulated in mica-quartz greisen bodies from the Faixa Placha ore site, whose results are presented below.
Table 2. Electron microprobe analysis results on wolframite crystals.Compositions of oxides in percent by weight (wt.%) and of elements in atoms by unit formula (apfu), calculates on the basis of four oxygens.The symbol (-) represents values below the detection limit.Quartz (δ 18 O = 9.4-10.4‰)and cassiterite (δ 18 O = 2.6-2.9‰)have subtle variations in their respective isotopic compositions, indicating isotopic equilibrium with a common magmatic-hydrothermal system (Table 3).Otherwise, significant differences in δ 18 O values between quartz-cassiterite reveal the mineral isotopic fractionation signatures during the rise of the hydrothermal system (Alderton 1989, Burnham 1997, Taylor Jr. 1997).In general, cassiterite from Sn-W magmatic-hydrothermal deposits typically record low δ 18 O values (δ 18 O < 10‰), due to its greater sensitivity to isotopic fractionation, which have been attributed to the temperature drop during a mixing phase between meteoric fluids (isotopically light) and magmatic fluids (Kelly and Rye 1979, Jackson and Helgeson 1985, Sun and Eadington 1987, Taylor and Wall 1993, Heinrich et al. 1996).In contrast, quartz often records higher δ 18 O values (δ 18 O ~ 10 ‰) due to its low sensitivity to isotopic changes in the hydrothermal system (Clayton et al. 1972, Taylor Jr. 1997, Sharp et al. 2016).

Wolframite
We used δ 18 O data from the quartz-cassiterite pair in the geothermometric study of the Pedra Branca magmatic-hydrothermal system.The geothermometric calculations were made based on the fractionation curve given by 1,000 lnα = 1.259 × 10 6 /T 2 + 8.15 × 10 3 /T -4.72 and 1,000 lnα = 2.941 × 10 6 /T 2 -11.45 × 10 3 /T + 4.72 (Li et al. 2022), as well as 1,000 lnα = 3.38 × 10 6 /T 2 -3.40 (Clayton et al. 1972), applied to the quartz-cassiterite-water system.Considering that cassiterite and quartz are in paragenetic association, we then obtained the geothermometric range calculated from 410 to 485°C, applying a correlation between the different quartz δ 18 O values (9.4-10.4‰)for each cassiterite δ 18 O value (2.6-2.9‰) in order to obtain an isotopic range, which we interpret as the temperature range for ore crystallization during the evolution of the Pedra Branca magmatic-hydrothermal system.This isotopic temperature range has also been recorded in other Sn-W deposits around the world linked to the Sn-specialized granitic magmas evolution (e.g., Linnen and Williams-Jones 1995, Bettencourt et al. 2005, Macey and Harris 2006, Li et al. 2021).

FLUID INCLUSION DATA
Fluid inclusion studies also have been widely applied in the physicochemical characterization (composition, temperature, and pressure) of the magmatic-hydrothermal system (e.g., Chang et al. 2018, Daele et al. 2018, Audétat 2019).In this study, we present fluid inclusion data obtained on deformed quartz and cassiterite crystals from mica-quartz greisen bodies of the Faixa Placha ore site (Figs.8A and 8B).The results are presented and discussed below.
The quartz and cassiterite crystals often occur broken and stretched in this ore site, but quartz still exhibits different stages of recrystallization, features that are not clearly observed in cassiterite.They host, at 25°C room temperature, monophasic and biphasic aqueous fluid inclusions, characterized as pseudo-secondary and secondary types (Figs.8C-8F).The pseudo-secondary type occurs isolated or in small groups on trails, displays irregular, elongated, and subrounded shapes, with 5-60 μm in size.The secondary type form trails along healed microfractures, with elongated and rounded shapes, but with a size below 5 μm, thus making it impossible to obtain microthermometric data in the equipment used.
The biphasic (H 2 O liq + H 2 O gas ) pseudo-secondary type has a gas phase volume (Vg/V total ) estimated between 5 and 10%, while the monophasic pseudo-secondary type can have a liquid or gas phase, filling the entire cavity (Figs.8C-8F).The microthermometry results are summarized in Table 4.
These microthermometric data reveal an aqueous fluid system with lowered salinity and density, trapped under low to moderate temperature (108-270°C), contrary to oxygen isotope data that revealed temperatures above 400°C.The fluid inclusions studied here represent rebalanced solutions trapped during or just after nucleation and mineral growth.
The coexistence of liquid-and vapor-rich fluid inclusions in the same fluid inclusions assemblage (Figs.8C-8F) may indicate the presence of some fluid immiscibility process, such as boiling (e.g., Ramboz et al. 1982, Bodnar et al. 1985, Loucks 2000, Bodnar 2003).However, this process type was not clear to us in this study.Furthermore, the pseudo-secondary fluid inclusions show different salinity and Tht values, clearly noted in the salinity versus Tht diagram (Fig. 9E), indicating different intervals of fluid trapping between quartz and cassiterite.This characteristic suggests different degrees/ratios of mixing fluids (e.g., hydrothermal/magmatic vs. meteoric), favoring the fluid rebalancing.The flattening and mineral recrystallization features mostly seen in quartz also suggest that important fluid volume may have been trapped during the Faixa Placha reactivation phases, related to Brasiliano/Pan-African Orogeny.
The Sn (±W) greisen bodies found in the Bacia zone and Faixa Placha of the Pedra Branca granite massif are linked to highly fractionated Li-mica leucogranite magmatic phase (1.74 Ga) or pb2d petrographic type (Botelho 1992).In this metallogenetic framework, the forceful to passive magma emplacement favored fractures and faults generation at the cupula granitic zone, followed by a hydrothermal recirculation convective process that led to greisenization at the contact zone and dilated sites (fractures and faults), thus forming endo-to exogreisen related to the Bacia zone and Faixa Placha (Fig. 10), respectively.In these greisen bodies, the higher content of cassiterite in relation to wolframite (Sn >> W), as well as high content of ilmenite, magnetite, and hematite, indicates the predominance of the oxidizing environment during the greisenization phase.However, some oscillations in the hydrothermal oxidation state may have favored the precipitation of wolframite and S-minerals under a reduced condition.
The oxygen isotope (δ 18 O) data point to a crystallization temperature between 485 and 410°C, marked by an important isotopic fractionation process (quartz-cassiterite-water) during greisenization, which is linked to the lowering of temperature and the interaction between fluids from different sources (e.g., Taylor Jr. 1974, Taylor and Wall 1993, Zhang et al. 1994).The progressive changes in physical-chemical parameters (mainly temperature, pH,   Eh, and fO 2 ) on the hydrothermal system played an important role on the zoning and exsolution features identified in the cassiterite and wolframite, marked by different types of substitution controlling the entry of Fe, Ti, Mn, Nb, Ta, U, and In.The growth and zoning of cassiterite crystals had 2Sn 4+ + O 2+ ↔ Ti 4+ + Fe 3+ + OH -as the main replacement mechanism, followed by the entry of Nb, Ta, and In impurities, according to 2(Sn, Ti) 4+ ↔ (Nb, Ta) 5+ + (Fe, In) 3+ equation, under an oxidizing environment.However, some oscillations in the oxidizing environment (Fe 3+ ↔ Fe 2+ ), often linked to hydrothermal re-circulation convective, would have favored the entry of W, Mn, and U impurities, according to 2(Sn, Ti) 4+ ↔ (W, Mn) 6+ + Fe 2+ or 2(Sn, Ti) 4+ ↔ U 4+ + 2Fe 2+ equations.On the contrary, the wolframite growth had Fe 2+ + W 6+ ↔ Fe 3+ + (Nb, Ta) 5+ as the main replacement mechanism, which may have been accompanied by oscillations of the hydrothermal oxidation state (Fe 2+ ↔ Fe 3+ ) that favored to Nb + Ta increases, as well as the incorporation of some impurities (Sn 4+ , In 3+ , and U 4+ ).In this context, the high calculated Fe 2+ values (Table 2), associated with the presence of S-minerals and U 4+ , may indicate that the wolframite from the Faixa Placha ore site could also have been precipitated under reduced hydrothermal conditions (Hsu 1976, Heinrich 1990).According to Hsu (1976) and Ivanova (1988), Fe-rich wolframite is stable under oxidizing conditions at temperatures above 400°C.Therefore, it is possible that impurities identified in the wolframite are also linked to exsolution process during the lowering of the temperature.
Additionally, the U anomalous contents identified in cassiterite crystals from some granite-pegmatites of the Paranã subprovince (GTP) allowed obtaining U-Pb ages between 1.535 and 1.470 Ma (Sparrenberger and Tasinari 1999).The U content identified in cassiterite and wolframite from the Pedra Branca greisen could also be a good opportunity in the future to help in geochronological studies on the ore formation (e.g., Yuan et al. 2011, Li et al. 2016, Neymark et al. 2018, Li et al. 2022).
During Neoproterozoic, nonetheless, the transpressive tectonics linked to Brasiliano/Pan-African Orogeny (800-500 Ma) printed different deformational stages in overall lithologies.The greisenized bodies and tensile faults/fractures filled by ore related to Faixa Placha (exogreisen), as well as some greisen lenticular bodies linked to Bacia zone (endo-and exogreisen), were then subjected to directional mylonitic deformation.Faixa Placha structures sets, above all, were reactivated under a ductile-ruptile regime, with local generation of centimetric folds, breccia, and tension gash, as well as flattening and partial fragmentation of the mineral assemblage.The recrystallization features are more common in quartz, whose fluid inclusions study revealed the dominant presence of low salinity aqueous solutions (H 2 O-NaCl), probably channeled along the Faixa Placha during the Neoproterozoic shear at temperatures between 100 and 215°C.Aqueous solutions are also identified in broken cassiterite crystals, but with an increased salinity and total homogenization temperature range between 255 and 270°C, suggesting hydrothermal-magmatic systems involving recirculation of rebalanced aqueous solutions or immiscible aqueous fluid phase (e.g., Hulsbosch andMuchez 2020, Chen et al. 2021).However, fluid inclusions studies still need to advance on the ores of the Pedra Branca granite massif, in order to identify primary fluids with a thermal signature compatible with the oxygen isotope data presented here.
Finally, during Phanerozoic, the prolonged erosive process led to regional peneplanation, reaching the granitic cupolas and the surrounding wall rocks, carving relief in different intensities.The mineralized greisen zones present in the Bacia zone and Faixa Placha were then partially eroded, with their mineral components being channeled through the drainage system, and thus forming Sn (±W)-rich alluvium around the Pedra Branca granite massif.

CONCLUDING REMARKS
The set of information presented here leads us to the following conclusions about the Sn (±W) mineralization found in the Pedra Branca granitic massif (1.77-1.74Ga).
The Neoproterozoic shear linked to Brasiliano/Pan-African Orogeny (800-500 Ma) reactivated the Faixa Placha and printed different deformational features and stages on the exogreisen that led to flattening and partial fragmentation of the mineral assemblage.According to fluid inclusion data, this process favored the recirculation of low salinity rebalanced aqueous solutions (H 2 O-NaCl) at temperatures between 100 and 215°C channeled along the Faixa Placha.

ACKNOWLEDGMENTS
This research is the result of the Master's thesis presented by Santos I.K.M. (first author), which had financial support from the Brazilian National Council of Technological and Scientific Development (CNPq-Project n•443603/2014-6) and Coordination for the Improvement of Higher Education Personnel (CAPES) through scholarship.The authors are thankful to the EDEM -Development and Participations Mining Company -for fieldwork support.Thanks to Geosciences Institute and the Post-Graduate Program in Geology of the Universidade de Brasília (IGD-UnB) for the laboratorial infrastructure made available.Thanks also to the anonymous reviewers for the important contributions to the improvement of this manuscript.This research is linked to the study group named Granites and Associated Mineralizations (UnB-CNPq). 14/17

Figure 1 .
Figure 1.(A) Geological map of Central Brazil indicating the GTP location (adapted from Fuck et al. 2014).(B) Geological map of the GTP with highlighted study area (modified from Alvarenga et al. 2007). .

Figure 2 .
Figure 2. (A) Geological map of the Pedra Branca granite massif with emphasis on the A-B geological section, indicating the Bacia zone and the Faixa Placha ore sites.

Figure 3 .
Figure 3. General aspects of ore sites in the Pedra Branca granite massif: (A) Northwest panoramic view of the Bacia zone with a dashed line indicating the probable outline of the partially eroded granitic cupula; (B) partial view of the mining front in the Faixa Placha.Observe the NE-SW tensile fractures/faults sets, as well as the lenticular greisen bodies; (C) drill-cores set from Faixa Placha ore site showing the greisenization on the deformed coarse-grained pink porphyritic biotite granite (pb1b petrographic type); (D) greisen-filled tensile fractures/ fissures sets in the Faixa Placha ore site.

Figure 4 .
Figure 4. Photomicrographs of cassiterite (Cst) and wolframite (Wlf) crystals in greisen from Faixa Placha ore site (N// = parallel nicois).(A, B) Note the typical zoning and partially fracturing of cassiterite crystals as well as the tabular wolframite crystals associated in mica-quartz greisen.(C, D) Cassiterite crystals broken and stretched in mica greisen.

Figure 8 .
Figure 8. Morphological aspects and distribution of fluid inclusions in quartz and cassiterite crystals.(A) Macroscopic feature of mineralized mica-quartz greisen from the Faixa Placha ore site.Note the fields with fluid inclusions studied; (B) cassiterite with demarcated fragmentation.(C) Microscopic features of the biphasic and monophasic pseudo-secondary fluid inclusions in cassiterite; (D) detailed sketch of fluid inclusions in cassiterite; (E) microscopic features of the biphasic and monophasic pseudo-secondary fluid inclusions in quartz; and (F) detailed sketch of fluid inclusions in quartz.

Figure 9 .
Figure 9. Histograms and graphs showing the microthermometric data obtained for fluid inclusions in cassiterite and quartz.(A) Histogram with the ice melting temperature; (B) histogram with the calculated salinities for ice melt temperature; (C) histogram with the total homogenization temperature (Tht); (D) total homogenization temperature versus salinity diagram indicating density fields generated by the equation of state by Zhang and Frantz (1987), obtained by Wilkinson (2001) from Brown (1989); (E) total homogenization temperature versus salinity diagram indicating a possible mixing trend field for the aqueous fluid system studied here (Sharma and Srivastava 2014).

Figure 10 .
Figure 10.Proposed metallogenetic model for the mineralized greisen sites of the Pedra Branca granite massif.

Table 3 .
Oxygen isotope (δ 18 O) values obtained for cassiterite and quartz samples from mica-greisen of the Faixa Placha ore site with their calculated isotopic temperature ranges.

Table 4 .
Summary of microthermometric intervals obtained on fluid inclusions from quartz and cassiterite crystals.