Jake C Spiteri

Sergey A Denisov

Gediminas Jonusauskas
email: gediminas.jonusauskas@ubordeaux.fr

Sylwia Klejna

Konrad Szacilowski
email: szacilow@agh.edu.pl

Nathan D Mcclenaghan
email: nathan.mcclenaghan@ubordeaux.fr

David C Magri
email: david.magri@um.edu.mt

Konrad Szaciłowski

Molecular engineering of logic gate types by module rearrangement in 'Pourbaix Sensors': the effect of excited-state electric fields

Keywords: IR, HRMS, DFT frontier molecular orbital diagrams, UV visible absorption, fluo rescence decay curves and spectra. See

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

As an extension of the molecular engineering aspects of molecular-logic based computation, it is imperative to explore design flexibility. [1][2][3] The first two molecular logic gates demonstrated by de Silva combined two selective receptors, two alkyl spacers and an anthracene fluorophore. 4,5 These examples provided the well-established 'fluorophore-spacer 1 -receptor 1spacer 2 -receptor 2 ' 4 and 'receptor 1 -spacer 1 -fluorophorespacer 2 -receptor 2 ' 5 formats. Both examples functioned as twoinput AND logic gates. The latter design provided a greater fluorescence switching ratio as the distance for electron trans-fer between receptor 2 and the fluorophore was reduced. Subsequently, de Silva later demonstrated a different pair of analogous switches that functioned as AND logic gates given the same chemical inputs. [START_REF] Callan | The fluorescence of a single-input H + -driven PASS 1 logic gate is high irrespective of the H + level. Conversely, single-input H + -driven PASS 0 shows no fluorescence[END_REF] However, due to structure-specific effects the logic gates could be modulated to give rise to other logic behaviour from elementary one-input H + -driven PASS 0 and H + -driven YES to Ca 2+ -enabled, H + -driven off-on-off ternary logic.

Recently, there has been much interest in optical molecular devices responsive to acid-base and redox chemistry. [START_REF] Magri | [END_REF] For example, Tian and Qu have demonstrated dual responsive 4-aminonaphthalimide-based molecular shuttles incorporating photoinduced electron transfer (PET) and internal charge transfer (ICT) mechanisms. 8 In another example, Mukhopadhyay has reported a series of tetrastable naphthalenediimides as colorimetric combinatorial logic gates from radical-anion and anion-induced ICT states. 9 Herein we now report the pH and redox dependent steadystate and time-resolved fluorescence and transient absorption spectroscopy of two pairs of 4-aminonaphthalimide regioisomers. 10 The regioisomer pairs 1 and 2 were designed to function as 'Pourbaix sensors '. 11 Four supramolecular models 1a-b and 2a-b were synthesised with the same modular format according to an 'electron-donor-spacer 1 -fluorophore-spacer 2 -receptor' arrangement (Fig. 1). Due to the asymmetric nature of the 4-aminonaphthalimide fluorophore, the regioisomer pairs 1 and 2 were synthesised by alteration of the imide and 4-amino substituents. Ferrocene was chosen as the oxidant-sensitive electron donor module and dimethylamine or morpholine as the proton receptor module. The receptor plays a dual role of being both an acceptor for protons and an electron donor for quenching the emissive excited state when unprotonated. [START_REF] Magri | [END_REF] In the case of 1a and 1b, ferrocene is connected by a methylene spacer at the imide position and the dialkylamino moieties are connected to the 4-aminonaphthalimide position by an ethylene spacer. For 2a and 2b the ferrocene and dialkylamino modules are connected inversely (Fig. 1).

Based on molecular engineering first principles, 3 1a-b and 2a-b were predicted to function the same as all module parameters are constant with the exception of the PET/ICT trajectories. During the course of the study we discovered that 1a-b and 2a-b exhibit remarkably different logic behaviour. This observation is an unprecedented example of functional discrimination by module rearrangement. [START_REF] Callan | The fluorescence of a single-input H + -driven PASS 1 logic gate is high irrespective of the H + level. Conversely, single-input H + -driven PASS 0 shows no fluorescence[END_REF] While many parameters controlling PET and ICT in supramolecular systems are generally well understood, our understanding of the influence of regiochemistry and electric field effects still remains underdeveloped. 10 This study provides new insight into the influence of field effects on PET/ICT phenomena and constitutes a new paradigm for controlling molecular logic gate functions.

Results and discussion

Logic gates 1a and 1b were synthesised from ferrocenylmethylamine 12 and 4-bromo-1,8-naphthalic anhydride in 2-methoxyethanol to yield N-ferrocenyl-4-bromo-1,8-naphthalimide in 64% yield, which was reacted with N,N-dimethylethylenediamine or 4-(2-aminoethyl)morpholine to give 1a or 1b in 70% and 13% yield after purification. Molecules 2a and 2b were synthesised by refluxing 4-bromo-1,8-naphthalic anhydride with N,N-dimethylethylenediamine or 4-(2-aminoethyl) morpholine, respectively, in 1,4-dioxane to give the intermediates in 70% and 46% yield, followed by aromatic nucleophilic substitution with ferrocenylmethylamine. Purification by column chromatography gave 2a and 2b in 34% and 22% yield, respectively. Synthetic details and analytical spectroscopic data including 1 H & 13 C NMR, IR and HRMS are provided in the Experimental and ESI (Fig. S1-S16 †).

The thermodynamics for the photo-initiated charge transfer processes, to a first approximation, are expected to be identical for the regioisomers 1 and 2. The driving forces for PET are -0.63 eV and 0.07 eV from the ferrocene and tertiary amine to the excited fluorophore, respectively. [START_REF] Weller | The driving forces for charge transfer are calculated as ΔG PET = eF(E OX -E[END_REF] With polyaromatic molecular logic gates, such as those based on anthracene with substitutents at the 9 and 10 positions, these simple calculations based on the Weller equation are a good guide for predicting the feasibility of electron transfer reactions and molecular logic gate performance. 5,[START_REF] Callan | The fluorescence of a single-input H + -driven PASS 1 logic gate is high irrespective of the H + level. Conversely, single-input H + -driven PASS 0 shows no fluorescence[END_REF] However, the 4-aminonaphthalimide fluorophore is a push-pull π-electron system with a 4-amino group as donor and the naphthalimide (specifically the carbonyl end) as acceptor. 10 Consequently, a considerable large dipole moment (11 D) exists in the singlet excited state with a positive charge at the 4-amino end, and a negative charge build-up at the imide carbonyl end. Gao and Marcus' theoretical study predicted the imide nitrogen atom is a node in the frontier orbitals (vide infra). [START_REF] Gao | [END_REF] Evidence for ICT character can be observed from the UVvisible absorption spectra. In 1 : 1 (v/v) MeOH/H 2 O and 10 -9 M H + 1a and 1b exhibit a broad absorption band at 445 nm (Fig. S17 and S18 †). Titration with up to 10 -4 M H + causes a 14 nm hypsochromic shift due to protonation of the tertiary amine, which is attributed to a less stable Frank-Condon excited state. Superposition of the absorption spectra as a function of pH reveals an isosbestic point at 435 nm. In contrast, titration of 2a and 2b as a function of H + results in practically no observable change in the absorption spectra (Fig. S17 and S18 †). Table 1 provides a summary of the photophysical data. The Boolean logic characteristics of regioisomers 1 and 2 in 1 : 1 (v/v) MeOH/H 2 O are shown in Fig. 2. In the absence of threshold levels of H + or Fe 3+ or both inputs, no fluorescence is observed for 1a and 1b (Fig. 1, top, vials A, B and C). As expected, addition of 10 -4 M H + and 50 μM Fe 3+ resulted in a bright green fluorescence visible to the naked eye (Fig. 1, vial D) in agreement with two-input AND logic. The emission spectrum exhibits a band centred at 530 nm. This band is a consequence of both the ICT state, resulting in a Stokes shift of 95 nm, and the prevention of PET, which allows for the fluorescent enhancement (Table 1, Fig. S17 and18 †). The fluorescence switching ratios between the 'off' and 'on' states are 16-fold and 10-fold for 1a and 1b. The fluorescence quantum yields (Φ Flu ) in the 'on' state are 0.041 and 0.032 for 1a and 1b, respectively.

The emission spectra of 2a and 2b exhibit a larger Stokes shift of 115 nm and a band centred at 550 nm. No fluorescence is observed with the naked eye in the absence of threshold levels of H + or Fe 3+ or both inputs as anticipated. Rather unexpectedly, no fluorescence was observed in the presence of 10 -4 M H + and 50 μM Fe 3+ (Fig. 1, bottom, vials A, B, C andD). The combined outputs fit the definition of two-input PASS 0 logic (Table 2).

The reason for this divergent logic behaviour is intimately linked to the driving force for charge transfer, as mentioned earlier, which is sluggish from the tertiary amine to the 4-aminonaphthalimide fluorophore. Nonetheless, charge transfer from the dialkylamino receptor to the 4-aminonaphthalimide fluorophore readily occurs in 1a and 1b assisted by the positive electric field at the 4-amino end. In the case of 2a and 2b, charge transfer from the dialkylamino receptor is hindered by the negative electric field at the imide end. [START_REF] Gao | [END_REF] Hence, the negative electric field at the imide end is a kinetic barrier for PET.

However, we should note that unidirectional 10 and bidirectional 15 PET/ICT phenomena have been demonstrated with 4-aminonaphthalimide systems.

Another possible reason for the lack of fluorescence switching with 2a and 2b could be the formation of a weak intramolecular hydrogen bond on protonation. 10 Hydrogen bonding between the ammonium cation and one of the carbonyl oxygen atom may occur in the excited state via a six-membered transition state providing a non-radiative deactivation pathway. Similar phenomena have been observed with naphthalimide systems on complexation of metal ions such as Na + and Cu + . 16,17 Therefore, in order to gain further insight into the influence of the electric field effect on the excited state of 1 and 2 DFT calculations were performed. Energy level diagrams are shown in Fig. 3

(v/v) MeOH/H 2 O abcde Input 1 f (H + ) Input 2 g (Fe 3+ )
1a AND 1b AND 2a PASS 0 2b PASS 0 0 0 0 (0.0004) 0 (0.0003) 0 (0.0010) 0 (0.0010) 1 0 0 (0.0025) 0 (0.0031) 0 (0.0006) 0 (0.0009) 0 1 0 (0.0014) 0 (0.0011) 0 (0.0020) 0 (0.0006) 1 1 1 (0.041) 1 (0.032) 0 (0.0014) 0 (0.0006) (LUMO) reside exclusively on the 4-aminonaphthalimide in both the neutral and amine-protonated states. The methylene and ethylene spacers generally serve their purpose to effectively separate the fluorophore from the receptor and the electron donor. On oxidation, the HOMO orbital of 1a involves the 4-aminonaphthalimide and amine moieties. For 1b the HOMO is localised exclusively on the 4-aminonaphthalimide. In all cases, the LUMO resides on the ferrocenium moiety. The distinct change in the location of the HOMO and LUMO clearly illustrates ICT character. The incorporation of a methylene bridge in 2a and 2b results in a significant reduction in the HOMO delocalization.

Non-radiative deactivation of the 4-aminonaphthalimide fluorophore excited state is expected to be naturally feasible for the neutral, protonated and ferrocene-oxidised forms (i.e. 1a, 1aH + , 1a •+ ). Photoinduced electron transfer can occur from the ferrocene moiety (neutral and amine-protonated forms) and the amine moiety (neutral and oxidised forms). With 2aH 2•+ and 2bH 2•+ fluorescence quenching is also possible via non-radiative decay from the lowest 4-aminonaphthalimidelocalised LUMOs to the 4-aminonaphthalimide HOMO via a series of ferrocenium-localised states (green arrow in Fig. 3, Fig. S19 †). For 1aH 2+ and 1bH 2+ the ferrocenium-centred orbitals are localised at much higher energies and do not contribute to quenching of the luminescent state, in agreement with the experimental steady-state results.

We surmise that the reason no fluorescent enhancement is observed with regioisomers 2 is a consequence of an electric field effect. The ICT excited state dipole with its negative terminal at the imide end contributes to accelerate an electron transfer from the fluorophore to the ferrocenium unit across a positive electric field at the 4-amino terminus. Consequently, fluorescence is not observed under oxidising (and protonated) conditions in the case of 2a and 2b. With 1a and 1b electron transfer from the fluorophore to the ferrocenium unit is retarded by an attractive positive force situated at the 4-amino end and inhibited by a negative electric field at the imide nitrogen atom. Hence, regioisomers 1 experience a synergistic effect from the excited state electric field while regioisomers 2 experience an antagonistic effect.

The fluorescence lifetimes (τ f ) of 1a, 1b and 2b were measured by time-resolved fluorescence spectroscopy in 1 : 1 (v/v) methanol/water under the four input conditions (Fig. S24-26 †). The short-lived components of 1a and 1b correspond to the quenched PET/ICT lifetimes (<1.1 ns). 18 Upon protonation and oxidation the decay curves of 1a and 1b display single components (>99%) with fluorescence lifetimes of 8.3 ns and 8.1 ns, respectively. Hence, fluorescence becomes the predominant photophysical process.

The regioisomer 2b, in stark contrast to 1b, has bi-exponential components at all conditions including in the presence of high H + and Fe 3+ . Time-resolved experiments confirm that fluorescence is not restored in the presence of both inputs in agreement with the steady-state fluorescence measurements. Once again, the long-lived and short-lived decay components correspond to back electron transfer and residual PET/ICT in the quenched state, respectively. Back electron transfer occurs on the nanosecond timescale of 4-6 ns, whereas the residual PET/ICT is <1 ns. The ICT character of the lowest energy transitions within the 4-aminonaphthalimide chromophore is much more pronounced in the case of 2a and 2b than in the case of 1a and 1b, which show mostly π-π* character (Fig. S20-S23 †). The spatial distribution of HOMOs and LUMOs in 1a and 1b overlap almost ideally, whereas in 2a and 2b the contours of HOMOs and LUMOs differ significantly.

Femtosecond transient absorption studies provide further insight into the regioisomer pair 1b and 2b. 11e,19 After excitation, 1b undergoes a large charge density shift (<1 ps) within the 4-aminonaphthalimide fluorophore (Fig. 4). Ground state bleaching occurs at 450 nm (blue), stimulated emission at 550 nm (blue), and positive absorption at 460-500 nm and 650-700 nm due to redistribution of electron density (red) as a result of the ICT character. 10 The transient signal recovery rate proceeds on the order of ∼10 ps. (Note: The negative perturbation at the zero delay is due to Kerr lensing produced by an intense femtosecond pump pulse with a weakly absorbing sample). In contrast, 2b exhibits ground state bleaching at 380-440 nm (red) and stimulated emission between 500-620 nm (blue) (Fig. 5). The time delay is considerably longer on the nanosecond timescale. This observation is consistent with the absence of fluorescence switching.

Conclusions

Two pairs of 4-aminonaphthalimide-based regioisomers 1 and 2 were synthesised with the intended purpose of simultaneous detection of pH and redox potential. Regioisomers 1 successfully operate as two-input AND logic gates for H + and Fe 3+ , in agreement with the definition of 'Pourbaix sensors'. [START_REF] Magri | [END_REF]11 In the absence of one or both inputs, the PET and/or ICT processes within 1a and 1b are efficient and shut off the fluorescence, while upon simultaneous protonation and oxidation, PET and ICT are non-competitive, resulting in a green fluorescence output. Regioisomers 2 are functionally dormant and behave as two-input PASS 0 logic gates. In other words, 2a and 2b do not behave as Pourbaix sensors because the negative charge at the imide and the positive charge at the 4-amino synergistically contribute to accelerate the transfer of an electron from the excited stated fluorophore to the ferrocenium unit under oxidising (and acidic) conditions.

The findings from this study open up a new approach for regulating the logic functions of fluorophores endowed with an ICT excited state and delineate the limitations of the 'electron-donor-spacer 1 -fluorophore-spacer 2 -receptor' format.

A future research direction is to rationally design a series of 4-aminonaphthalimide prototypes with varying intermediate driving forces for PET (-0.60 eV < ΔG PET < 0.0 eV) with less strong electron donors compared to ferrocene at the 4-amino, and most notably at the imide positions, in order to evaluate the PET kinetics. 20 Application of Marcus' electron transfer theory would allow for determination of the activation barrier and electronic coupling factor. 21 Hence, a better understanding of this regulatory directional electron transfer phenomenon will undoubtedly contribute to the future development of various smart functional materials for application in the domains of photocatalysts, 22 artificial photosynthetic reaction centres, 23 multi-component molecular devices, 8 cellular imaging probes, 24 lab-on-a-molecule systems 25 and molecular steganography. 26

Experimental

A list of chemicals and instrumentation are provided in the ESI. † Compounds 1a and 1b were synthesised from N-ferrocenyl-4-bromo-1,8-naphthalimide. 11d Compounds 2a and 2b were synthesised from 4-bromo-1,8-naphthalic anhydride with the appropriate amine followed by substitution with ferrocenemethylamine. Full synthetic details and spectra are provided in the ESI. † N-Ferrocenylmethyl-4-(2-dimethylaminoethyl amine)-1,8naphthalimide (1a) N-Ferrocenyl-4-bromo-1,8-naphthalimide (0.219 g, 0.462 mmol) and N,N-dimethylethylenediamine (5.0 mL, 46 mmol) were refluxed at 100 °C for 5 hours. The product was purified by column chromatography with silica gel and eluted with 4 : 1 (v/v) chloroform/methanol. Recrystallisation from 1 : 1 (v/v) acetone/water gave an orange solid in 70% yield. R f = 0.73 (2 : 1 (v/v) CH 2 Cl 2 /MeOH); m.p. = 164-166 °C; 1 H NMR (CDCl 3 , ppm): δ 8.55 (dd, 1H, J = 7.3, 0.9 Hz, Ar-H), 8.43 (d, 1H, J = 8.4 Hz, Ar-H), 8.10 (dd, 1H, J = 8.2, 0.9 Hz, Ar-H), 7.58 (dd, 1H, J = 7.8, 0.9 Hz, Ar-H), 6.63 (d, 1H, J = 8.5 Hz, Ar-H), 6.25 (m, 1H, -NH), 5.11 (s, 2H, -CH 2 spacer), 4.52 (t, 2H, J = 1.8 Hz, Cp), 4.20 (s, 5H, Cp), 4.06 (t, 2H, J = 1.8 Hz, Cp), 3.36 (m, 2H, -NHCH 2 CH 2 N), 2.72 (t, 2H, J = 5.8 Hz, -NHCH 2 CH 2 N), 2.33 (s, 6H, -N(CH 3 ) 2 ); [START_REF] Weller | The driving forces for charge transfer are calculated as ΔG PET = eF(E OX -E[END_REF] C NMR (CDCl 3 , ppm): δ 164. 5, 163.9, 149.6, 134.6, 131.1, 129.8, 126.4, 124.5, 123.1, 120.4, 110.1, 104.3, 83.8, 70.5, 68.6, 67.9, 56.9, 45.0, 40.1, 38.9; IR (KBr, cm -1 ): 3393, 3092, 2955, 2866, 2828, 2783, 1684, 1636, 1582, 1541, 1385, 1369, 1339, 1300, 1246, 1188, 1126, 1105, 773 N-Ferrocenyl-4-bromo-1,8-naphthalimide (0.759 g, 1.60 mmol) and 4-(2-aminoethyl)morpholino (0.50 mL, 11 mmol) were dissolved in 1,4-dioxane and refluxed for 4 hours at 95 °C. The product was purified by column chromatography with silica gel eluted with CH 2 Cl 2 and 50 : 1 (v/v) CH 2 Cl 2 /MeOH. Recrystallisation from 1 : 1 (v/v) acetone/water gave an orange solid in 13% yield. R f = 0.53 (20 : 1 (v/v) CH 2 Cl 2 /MeOH); m.p. = 218-224 °C (dec.); 1 H NMR (CDCl 3 , ppm): δ 8.56 (dd, 1H, J = 7.3, 0.9 Hz, Ar-H), 8.43 (d, 1H, J = 8.4 Hz, Ar-H), 8.04 (dd, 1H, J = 8.5, 0.9 Hz, Ar-H), 7.60 (dd, 1H, J = 7.9, 0.9 Hz, Ar-H), 6.63 (d, 1H, J = 8.5 Hz, Ar-H), 6.21 (m, 1H, -NH), 5.11 (s, 2H, -CH 2 spacer), 4.52 (t, 2H, J = 1.8 Hz, Cp), 4.20 (s, 5H, Cp), 4.06 (t, 2H, J = 1.8 Hz, Cp), 3.78 (t, 4H, J = 4.5 Hz, -N(CH 2 CH 2 ) 2 O), 3.41 (m, 2H, -NHCH 2 CH 2 N), 2.82 (t, 2H, J = 5.9 Hz, -NHCH 2 CH 2 N), 2.57 (m, 4H, -N(CH 2 CH 2 ) 2 O); [START_REF] Weller | The driving forces for charge transfer are calculated as ΔG PET = eF(E OX -E[END_REF] C NMR (CDCl 3 , ppm): δ 164. 4, 163.8, 149.3, 134.4, 131.1, 129.6, 125.9, 124.7, 123.2, 120.3, 110.3, 104.4, 83.7, 70.5, 68.6, 67.9, 67.1, 56.0, 53.1, 38.9 (two peaks); IR (KBr, cm -1 ): 3416, 3362, 3084, 2963, 2818, 1684, 1647, 1582, 1533, 1368, 1344, 1333, 1300, 1246, 1188, 1134, 1117, 1103, 775; HRMS (ES-ToF): calculated C 29 H 30 N 3 O 3 Fe [M + H] + 524.1637, found 524.1639.

N,N-Dimethylethylenediamine-4-N-ferrocenyl methyl-1,8naphthalimide (2a) N,N-Dimethylethylenediamine-4-bromo-1,8-naphthalimide (0.440 g, 1.27 mmol) and ferrocenylmethylamine (0.301 g, 1.40 mmol) were dissolved in 10 mL of DMF and refluxed at 75 °C for 72 hours. The product was purified by column chromatography with silica gel eluted with gradient diethyl ether/methanol eluent (see ESI †). Removal of the solvent by rotary evaporator gave a reddish orange solid in 34% yield. R f = 0.51 (3 : 1 (v/v) (CH 3 CH 2 ) 2 O/MeOH); m.p. = 165-170 °C (dec.); 1 H NMR (CDCl 3 , ppm): δ 8.60 (dd, 1H, J = 7.4, 0.9 Hz, Ar-H), 8.50 (d, 1H, J = 8.4 Hz, Ar-H), 8.07 (dd, 1H, J = 8.5, 0.9 Hz, Ar-H), 7.64 (t, 1H, J = 7.9, 0.9 Hz, Ar-H), 6.80 (d, 1H, J = 8.4 Hz, Ar-H), 5.46 (t, 1H, J = 4.5 Hz, -NH), 4.35 (t, 2H, J = 1.8 Hz, Cp), 4.33 (t, 2H, J = 7.2 Hz, -NCH 2 CH 2 N(CH 3 ) 2 ), 4.25-4.28 (m, 7H, Cp), 4.23 (d, 2H, J = 4.5 Hz, -HCH 2 Cp), 2.66 (t, 2H, J = 7.2 Hz, -NCH 2 CH 2 N(CH 3 ) 2 ), 2.37 (s, 6H, -NCH 2 CH 2 N(CH 3 ) 2 ); [START_REF] Weller | The driving forces for charge transfer are calculated as ΔG PET = eF(E OX -E[END_REF] C NMR (CDCl 3 , ppm): δ 164. 7, 164.2, 148.8, 134.6, 131.2, 130.9, 125.7, 124.9, 123.2, 120.1, 110.6, 104.5, 84.2, 68.7, 68.6, 68.4, 57.1, 45.7, 43.1, 37.9;IR (KBr, cm -1 ): 3441, 3084, 2944, 2860, 2820, 2773, 1734, 1684, 1653, 1648, 1636, 1577, 1541, 1506, 1456, 1362, 1339, 1242, 1124, 775; HRMS (ES-ToF): calculated C 27 H 28 N 3 O 2 Fe [M + H] + 482.1531, found 482.1530.

4-(2-Aminoethyl)morpholine-4-N-ferrocenyl methyl-1,8naphthalimide (2b) 4-(2-Aminoethyl)morpholine-4-bromo-1,8-naphthalimide (0.375 g, 0.960 mmol) and ferrocenylmethylamine (0.315 g, 1.47 mmol) were dissolved in 10 mL DMF and refluxed at 90 °C for 5 hours. The product was purified by column chromatography with silica gel with a gradient diethyl ether/methanol eluent (see ESI †). Removal of the solvent by rotary evaporator gave a reddish orange solid in 22% yield. R f = 0.40 ((CH 3 CH 2 ) 2 O); m.p. = 94-98 °C; 1 H NMR (CDCl 3 , ppm): δ 8.57 (dd, 1H, J = 7.3, 1.1 Hz, Ar-H), 8.47 (d, 1H, J = 8.2 Hz, Ar-H), 8.44 (dd, 1H, J = 8.5, 1.1 Hz, Ar-H), 7.66 (dd, 1H, J = 7.9, 1.1 Hz, Ar-H), 7.12 (d, 1H, J = 8.2 Hz, Ar-H), 5.70 (m, 1H, -NH), 4.33 (t, 2H, J = 7.1 Hz, -NCH 2 CH 2 N(CH 2 CH 2 ) 2 O), 4.20 (d, 2H, J = 5.6 Hz, -NHCH 2 4.19 (t, 2H, J = 1.8 Hz, Cp), 4.17 (s, 5H, Cp), 4.15 (t, 2H, J = 1.8 Hz, Cp), 3.69 (t, 4H, J = 4.6 Hz, -NCH 2 CH 2 N(CH 2 CH 2 ) 2 O), 2.70 (t, 2H, J = 7.1 Hz, -NCH 2 CH 2 N(CH 2 CH 2 ) 2 O), 2.59 (m, 4H, -NCH 2 CH 2 N(CH 2 CH 2 ) 2 O); [START_REF] Weller | The driving forces for charge transfer are calculated as ΔG PET = eF(E OX -E[END_REF] C NMR (CDCl 3 , ppm): δ 164. 6, 164.1, 160.1, 132.7, 131.2, 131.0, 125.3, 124.9, 123.1, 115.0, 113.4, 84.1, 68.6, 68.3, 68.2, 67.1, 56.2, 53.8, 44.8, 37.5; IR (KBr, cm -1 ): 3320, 3080, 2953, 1684, 1657, 1655, 1589, 1456, 1423, 1390, 1381, 1346, 1242, 1142, 1113, 1009, 864, 779; HRMS (ES-ToF): calculated C 29 H 30 N 3 O 3 Fe [M + H] + 524.1637, found 524.1633.

Computational

The ground and excited states electronic structure was computed with the TURBOMOLE suite of quantum chemical programs. 27 Hybrid DFT was employed within the B3-LYP exchange-correlation functional 28 and atom-centred triple-zeta valence basis functions, augmented by double polarization functions, TZVPP2. 29 Unrestricted Hartree-Fock method was used for open shell systems. Unconstrained optimization of the molecular geometry was carried out until the total energy was converged to 10 -8 Ha in the self-consistent electronic loop. The minimum nature of the stationary point was confirmed by the vibrational analysis.

Fig. 1

 1 Fig.1The colour coded design concept of the two types of logic gates consisting of the same modular components arranged in two different ways and the molecular structures of series 1 and 2.

  Fig.2Fluorescence spectra of 6 μM 1a, 8 μM 1b, 8 μM 2a and 8 μM 2b in 1 : 1 (v/v) methanol/water excited at 435 nm. Conditions for the vials irradiated with a 365 nm lamp and emission spectra are: (A) 10 -9 M H + , (B) 10 -4 M H + , (C) 10 -9 M H + , 50 μM Fe 3+ and (D) 10 -4 M H + , 50 μM Fe 3+ . The y axis scale on the plots of 2a and 2b are magnified. See Table2for relative fluorescence quantum yields.

Fig. 3

 3 Fig. 3 Energy diagrams for neutral, protonated, oxidised, and proto nated and oxidised forms of compounds 1b and 2b. Energy levels associated with ferrocene/ferrocenium, amine and 4 aminonaphthali mide are shown in black, blue and red, respectively. The green arrow highlights transitions from ferrocenium localised states.

Fig. 4 Fig. 5

 45 Fig. 4 Transient absorption map of 1b in acetonitrile in the presence of 10 -4 H + and 50 μM Fe 3+ .

Table 1

 1

	Photophysical data for 1 and 2 in 1 : 1 (v/v) MeOH/H 2 O a,b
		1a	1b	2a	2b
	λ Abs (pH 9) /nm (log ε) c λ Abs (pH 4) /nm (log ε) c λ Isos /nm e /nm λ Flu Δλ f /nm	445(4.23) 432(4.20) 435 530 95	445(4.00) 430(4.01) 435 530 95	451(4.05) 452(4.06) d 550 115	443(3.89) 447(3.91) d 550 115
	FE g	16	10	<1	<1
	pβ H + h,i pβ Fe 3+ h pβ H + h, j τ f k /ns	7.4 4.6 8.1 8.3	5.6 4.6 5.8 8.1	8.2 7.6 l	6.0 5.7 m

a ∼5 10 μM. b pH adjusted with aqueous NaOH and CH 3 SO 3 H solu tions. c Molar absorptivity ε in L mol -1 cm -1 . d No isosbestic point observed. e Excited at λ Isos at 10 -4 M H + and 50 μM Fe 3+ . f Δλ λ Flu λ Abs at 10 -4 M H + and 50 μM Fe 3+ . g Fluorescence enhancement (FE) (I max (50 μM Fe 3+ at 10 -4 M H + )/(I max (10 -4 M H + ))). h Determined by log [(I max I)/(I I min )] log[H + ] + log β H +. i In the absence of Fe 3+ . j In the presence of 50 μM Fe 3+ . k τ measured at 10 -4 M H + with 50 μM Fe 3+ . l Not measured. m Experimentally measured. Bi exponential.

Table 2

 2 Truth tables for 1 and 2 and the fluorescence quantum yields (Φ Flu ) in parentheses in 1 : 1

  pH adjusted with aqueous NaOH and CH 3 SO 3 H solu tions. c 1a 1b excited at λ isos and 2a 2b at 435 nm. d Digital threshold limit set at Φ Flu > 0.021 for 1a and Φ Flu > 0.016 for 1b. e Estimated Φ Flu errors for input (1,1) from an average of three experiments: 1a (±0.005), 1b (±0.005), 2a (±0.003) and 2b (±0.002). Relative Φ Flu measured with reference to anthracene in ethanol (Φ Flu 0.27). f High input level 10 -4 M H + . Low input level is 10 -9 M H + . g High input level 50 μM Fe 3+ . Low input level no Fe 3+ added.

a ∼5 10 μM.

b

Acknowledgements

We thank the University of Malta for financial support. Prof. Robert M. Borg is acknowledged for NMR assistance and Maria Szaciłowska for assistance processing the DFT data. We extend our appreciation to the reviewers for their helpful comments. DFT calculations were performed at the Academic Computer Centre CYFRONET AGH within the computational grant "GRAPHENE" with funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 664786. The Embassy of France to Malta, the CNRS and the MCST (Malta Council for Science and Technology) are thanked for financial aid.

Conflicts of interest

There are no conflicts of interest to declare.


Keywords: magmatic-hydrothermal activity, Panasqueira, tourmaline, growth bands, flow direction, flow velocity

Deciphering the behavior of fluid flow at the magmatic-hydrothermal transition is crucial to understand physical processes leading to the formation of intrusion-related ore deposits and hence to predict the localization of mineralized bodies. However, the hydrodynamics (direction and velocity) of the hydrothermal fluid flow related to this transitional stage remains poorly constrained. Here we present a coupled textural and chemical study performed on tourmaline growth bands to constrain fluid flow during the initiation of the hydrothermal system of the W-Sn-(Cu) Panasqueira deposit. This exceptional deposit consists of a dense network of flat wolframite and cassiterite-bearing quartz veins intensely developed above a well-known hidden greisen cupola. The W-Sn mineralization is preceded by a tourmalinization stage occurring as metasomatic halos around veins and as selvages developed along the vein-wall-rocks contacts.

Results emphasize the key role of the greisen cupola on fluid focusing and the role of fluid overpressure during the vein opening. Velocity values highlight an efficient transport of metals in veins largely dominated by advective process (10 -4 to 10 -3 m.s -1 ), whereas fluid flow in the altered wall-rocks is slow and pervasive (10 -6 to 10 -5 m.s -1 ), suggesting that the element transport through the metasedimentary host rock was low and limited to the alteration haloes. LA-ICP-MS analyses of tourmaline growth bands reveal that fluids coming from the cupola are enriched in Na, K, Li, Sr and Sn, thus emphasizing the contribution of magmatic fluids during the vein formation and the metasomatic alteration of the wall-rocks. More generally, this study demonstrates that the apical portions of granite bodies play as emanative centers of mineralized fluids, and highlights the usefulness of mineral growth band analysis in the search for intrusion-related mineralization.

Introduction

The formation of hydrothermal ore deposits and the development of alteration halos in rocks involve the transfer of a large amount of fluids through permeable rocks during several episodic pulses integrated over a long period of time [START_REF] Barnes | Geochemistry of Hydrothermal Ore Deposits[END_REF][START_REF] Robb | Introduction to Ore-forming Processes[END_REF]. To form a high-grade deposit, the flow of metal bearing fluids must be focused in a restricted space and coupled with an efficient precipitation and trapping mechanism. Hence, understanding hydrothermal fluxes constitutes a major issue of metallogeny and requires resolving some fundamental questions related to: (i) the driving force of fluid flow and (ii) the direction and the velocity of fluid flow.

The search for answers to these issues involves a combination of approaches including recognition of permeable pathways [START_REF] Sibson | Implications of fault-valve behaviour for rupture nucleation and recurrence[END_REF][START_REF] Cox | Coupling between Deformation, Fluid Pressures, and Fluid Flow in Ore-Producing Hydrothermal Systems at Depth in the Crust[END_REF], mineralogical and geochemical analysis [START_REF] Cartwright | Determining the direction of contact metamorphic fluid flow: an assessment of mineralogical and stable isotope criteria[END_REF][START_REF] Ferry | The direction of fluid flow during contact metamorphism of siliceous carbonate rocks: new data for the Monzoni and Predazzo aureoles, northern Italy, and a global review[END_REF] and fluid hydrodynamics (Ingebristen and Appold, 2012).

Among hydrothermal ore deposits, those triggered and driven by magmatic felsic intrusions represent a main primary source of economically important metals, including copper (Cu), tungsten (W), tin (Sn), molybdenum (Mo) and gold (Au) [START_REF] Hedenquist | The role of magma in the formation of hydrothermal ore deposits[END_REF][START_REF] Černý | Granite-Related Ore Deposits[END_REF]. There is general agreement that these magmatic-related deposits are partly formed by releasing and expulsion of metal-bearing fluids during the emplacement and the cooling of magmatic intrusions [START_REF] Hedenquist | The role of magma in the formation of hydrothermal ore deposits[END_REF][START_REF] Černý | Granite-Related Ore Deposits[END_REF]. Another important process for metal transport in magmatic-hydrothermal systems is the development of large convective cells around plutons driven by the thermal contrast between intrusive bodies and the host rocks. This convective fluid flow is able to mobilize a large amount of fluids from the surrounding host rock and has a marked effect on the fluid flow patterns [START_REF] Norton | Thermal aspects of ore deposition[END_REF][START_REF] Eldursi | Numerical investigation of transient hydrothermal processes around intrusions: Heat-transfer and fluid-circulation controlled mineralization patterns[END_REF]. More specifically, it has been commonly observed that mineralized systems are usually centred on small plutons, apices or feeder zones [START_REF] Dines | The metalliferous mining region of South-West England. 2 volumes[END_REF]Dilles and Proffett, 1995;[START_REF] Gloaguen | Tracing the Magmatic/Hydrothermal Transition in Regional Low-Strain Zones: The Role of Magma Dynamics in Strain Localization at Pluton Roof, Implications for Intrusion-Related Gold Deposits[END_REF] suggesting a strong control of the pluton roof geometry on mineralizing fluid flow. Indeed, some numerical models have demonstrated that fluid flow is optimal above the apical part of intrusions and predict the formation of ore deposits in these areas [START_REF] Sams | Models of convective fluid flow and mineralization in Southwest England[END_REF][START_REF] Eldursi | Numerical investigation of transient hydrothermal processes around intrusions: Heat-transfer and fluid-circulation controlled mineralization patterns[END_REF][START_REF] Weis | The dynamic interplay between saline fluid flow and rock permeability in magmatic-hydrothermal systems[END_REF]. Despite these elegant numerical results, this expected fluid flow pattern (flow direction and velocity) needs to be verified by field investigations. Moreover, it is widely recognized that magmatic-hydrothermal systems integrate a complex history encompassing episodic stages of fluid flow related to polyphase intrusion emplacement, which have important effects on the geometry of hydrothermal systems. In this scheme, the magmatic-hydrothermal transition is a key event that marks the initiation of the hydrothermal system and defines the future behavior of fluid flow. Indeed, it is usually during this transitional stage that permeable structures open and drain mineralized fluids. However, fluid flow related to this specific hydrothermal stage is difficult to access and thus remains poorly constrained due to the lack of recognized methods to implement in the field.

The textural analysis of mineral growth bands has provided significant information about the direction and velocity of fluid flow involved in the formation of hydrothermal ore deposits [START_REF] Kessler | Direction of flow mineralizing solutions at Pine Point[END_REF]) and during metasomatic processes [START_REF] Sizaret | Estimating the local paleo-fluid flow velocity: new textural method and application to metasomatism[END_REF]Majhoubi et al., 2016). This direct approach constitutes a powerful tool to constrain fluid flow related to a specific hydrothermal event such as the magmatic-hydrothermal transition. In the present study, we perform a textural analysis of tourmaline growth bands to decipher fluid flow at the initiation of the magmatic-hydrothermal stage of Panasqueira (Portugal). This textural analysis is combined with trace elements analysis of tourmaline growth bands to constrain the chemical characteristics of fluids from which the tourmalines have crystallized. Panasqueira is an historic world-class W vein deposit characterized by a well-preserved magmatic-hydrothermal plumbing system. This deposit is one of the best-documented and characterized in the world and represents a reference site to study magmatic-hydrothermal processes leading to the formation of a Sn-W ore deposit [START_REF] Thadeu | Geologia do couto mineiro da Panasqueira[END_REF][START_REF] Kelly | Geologic, fluid inclusion and stable isotope studies of the tintungsten deposits of Panasqueira, Portugal[END_REF]Poyla, 1989;Poyla et al., 2000;[START_REF] Foxford | Extensional failure and hydraulic valving at Minas da Panasqueira, Portugal: Evidence from vein spatial distributions, displacements and geometries[END_REF][START_REF] Lecumberri-Sanchez | Fluid-rock interaction is decisive for the formation of tungsten deposits[END_REF][START_REF] Codeço | Chemical and boron isotopic composition of hydrothermal tourmaline from the Panasqueira W-Sn-Cu deposit[END_REF]. From the results of estimated fluid directions and velocities, we discuss the key parameters controlling the behavior of fluid flow at different scales, such as: (i) the role of granitic cupolas on the localization of mineralized areas by fluid flow focusing, (ii) the role of fluid overpressure conditions on vein opening and propagation of alteration halos in wall-rocks, and (iii) the required duration of fluid flow during the W-Sn mineralization stage.

Geological and metallogenic framework

Regional geology

The W-Sn-(Cu) Panasqueira ore deposit is located in the Central Iberian Zone (CIZ), which constitutes the axial zone of the Iberian Variscan belt (Fig. 1a) [START_REF] Julivert | Mapa Tectonico de la Peninsula Iberica y Baleares E[END_REF]. The CIZ is composed of the Schist-Greywacke-Complex (SGC) intruded by a large volume of granitoid intrusions resulting from an extensive magmatic event during the latest stages of the Variscan orogeny [START_REF] Dias | U-Pb zircon and monazite geochronology of syn-to post-tectonic Hercynian granitoids from the central Iberian Zone (northern Portugal)[END_REF]. The SGC consists of a thick (8-11 km) sequence of late Neoproterozoic schists and greywackes affected by a regional greenschist metamorphism (Martínez-Catalán et al., 2007). Deformation of the SGC consists of tight and upright folds with NW-SE sub-vertical axial planes produced by a NE-SW shortening related to the earliest compressive stage of the Variscan orogeny (Dias and[START_REF] Dias | The Ibero Armorican Arc: a collision effect against an irregular continent?[END_REF]Martínez-Catalán et al., 2007). This folding is associated with a regional sub-vertical penetrative axial planar cleavage (S1) (Fig. 1a and1b). The CIZ host numerous Sn-W ore deposits and occurrences related to granitic intrusions and formed by magmatic-hydrothermal processes [START_REF] Derré | Caractéristiques de la distribution des gisements à étain-tungstène dans l'ouest de l'Europe[END_REF].

The W-Sn-(Cu) Panasqueira ore deposit

The Panasqueira ore deposit is located in the Beira Baixa province in the southern flank of the Serra da Estrela massif constituted by late to post tectonic granitic intrusions. In this region the late Neoproterozoic folded and metamorphosed SGC is locally named Beira Schist. At Panasqueira, spotted schists mark the presence of a thermal metamorphic aureole related to an underlying S-type granite [START_REF] Thadeu | Geologia do couto mineiro da Panasqueira[END_REF][START_REF] Clark | Preliminary study of the temperatures and confining pressures of granite emplacement and mineralization[END_REF]. The intrusive body is limited by the Cebola fault to the north and the Rio Zêzere fault to the south (Fig. 1b) [START_REF] Clark | Preliminary study of the temperatures and confining pressures of granite emplacement and mineralization[END_REF]. As exposed by underground mining works and drill cores, the upper part of this granite includes a quartz-muscovite greisen cupola formed by interaction between granitic rocks and acidic F-B and Li-rich fluids [START_REF] Shcherba | Greisens[END_REF][START_REF] Bishop | Petrology. Encyclopedia of Earth Science[END_REF] (Fig. 1b and2a).

The W-Sn mineralization is hosted by a dense network of low dipping veins crosscutting the vertical foliation of the Beira Schist and the greisen cupola (Fig. 2a). The veins system is centered above the greisen cupola and extends over an area of 6 km² for a depth extension of about 200-300 meters (Fig. 1b) [START_REF] Kelly | Geologic, fluid inclusion and stable isotope studies of the tintungsten deposits of Panasqueira, Portugal[END_REF]Poyla et al., 2000). This unusual shallow dipping orientation of mineralized veins is compatible with the regional stress field that involved NE-SW shortening with a vertical σ3 leading to the formation of tight and upright folds accompanied by the development of the regional NW-SE sub-vertical foliation [START_REF] Dias | The Ibero Armorican Arc: a collision effect against an irregular continent?[END_REF]Martínez-Catalán et al., 2007). Based on textural and structural analysis of the vein swarms, [START_REF] Foxford | Extensional failure and hydraulic valving at Minas da Panasqueira, Portugal: Evidence from vein spatial distributions, displacements and geometries[END_REF] proposed a crack-and-seal model involving episodic vein dilation and filling induced by injections of fluids at supralithostatic pressure conditions in a compressive crustal regime.

Although this mechanism is quite appealing, these conditions of fluid overpressure in veins remain unproven. The structural control of the vein formation has probably induced permeability anisotropy with a strong horizontal component which could affect the pattern of fluid flow at the mineralization time. A late NNW-SSE and ENE-WSW sub-vertical fault system crosscuts the veins and the granite intrusion (Fig. 1b) [START_REF] Thadeu | Geologia do couto mineiro da Panasqueira[END_REF][START_REF] Kelly | Geologic, fluid inclusion and stable isotope studies of the tintungsten deposits of Panasqueira, Portugal[END_REF], Foxford et al., 2000).

As evidence in the field, these faults postdate mineralization event and have not controlled fluid flow during the W-(Sn) mineralization [START_REF] Thadeu | Geologia do couto mineiro da Panasqueira[END_REF].

The complex paragenetic sequence of veins was described in detail by [START_REF] Kelly | Geologic, fluid inclusion and stable isotope studies of the tintungsten deposits of Panasqueira, Portugal[END_REF] and improved by Poyla et al., (2000). At least five mineralization stages occurred in the veins from oldest to youngest: the Quartz-Tourmaline (QTS) stage, the Main Oxide Silicate Stage (MOSS), the Main Sulfide Stage (MSS), the Pyrrhotite Alteration Stage (PAS) and the Late Carbonate Stage (LCS). The MOSS (Fig. 2b) and the MSS (Fig. 2c) are the most economically relevant ore stages. The MOSS carries the W-Sn mineralization and consists in muscovite and quartz accompanied by wolframite and cassiterite. The two earliest mineralization stages (QTS and the MOSS) constitute a continuous sequence which is then superimposed and/or cross-cut by the late sulfide stage (MSS). The MSS, which carries the Cu mineralization, is mainly composed of arsenopyrite, chalcopyrite, sphalerite pyrite and pyrrhotite [START_REF] Thadeu | Geologia do couto mineiro da Panasqueira[END_REF][START_REF] Kelly | Geologic, fluid inclusion and stable isotope studies of the tintungsten deposits of Panasqueira, Portugal[END_REF], Poyla et al. 2000). Based on fluid inclusions analyses, [START_REF] Kelly | Geologic, fluid inclusion and stable isotope studies of the tintungsten deposits of Panasqueira, Portugal[END_REF] and [START_REF] Bussink | Geochemistry of the Panasqueira Tungsten-Tin Deposit[END_REF] have reported that fluids related to the MOSS and the QTS have been trapped at temperatures between 300 and 350°C. Although the tourmaline stage (QTS) is volumetrically of minor importance (mm to cm of thickness), it marks the initiation of the Panasqueira hydrothermal system (Poyla et al., 2000).

Tourmaline occurrence

At Panasqueira, tourmaline is common, especially in metasedimentary host rock surrounding mineralized veins (Fig. 3a). Tourmaline is present within alteration halos, which are developed along schist-vein contacts within the lower and the upper wall-rocks. These halos result from metasomatic reactions induced by fluid-rock interactions during hydrothermal fluid flow in the veins. Locally, it is possible to observe alternation of quartz-rich and tourmaline-muscovite rich layers inherited from lithological heterogeneities of the Beira Schist. These tourmalines are fine and their trigonal axes are randomly oriented in the vertical cleavage planes of the schist.

Tourmaline is also present in veins along schist-vein contacts (Fig. 3b and3c). They occur as fine acicular crystals (1-3 mm) with <c> axes vertical and perpendicular to the vein edge and consequently to the inferred plane of fluid flow (Fig. 3c). These tourmalines grains are commonly associated with apatite, rutile and muscovite (Fig. 3d), while their relation with the ore minerals (wolframite and cassiterite) is difficult to observe. However, in some veins tourmaline appears to shortly predate wolframite and can be texturally associated with cassiterite (Fig. 3e). Consequently, tourmaline represents a good candidate to track W-Sn mineralized fluid flow related to the QTS and the MOSS in the Panasqueira veins system.

For both types of tourmaline, the sections normal to the <c> axis are characterized by growth band zonation with a core and well-defined rims (Fig. 3d and Fig. 3f). These bands emphasize an anisotropic growth and highlight a symmetry breakdown due to a directional fluid flow (Fig. 4a and 4b).

Sampling and methodology

Owing to its remarkable mechanical and chemical stability, tourmaline is able to record significant information about its host environment [START_REF] Henry | Metamorphic tourmaline and its petrologic applications[END_REF]Van Hinsberg et al. 2011a). In particular, tourmaline provides a powerful tool to constrain hydrodynamics (direction and velocity of fluid flow) of geological processes involving fluid flow [START_REF] Sizaret | Estimating the local paleo-fluid flow velocity: new textural method and application to metasomatism[END_REF]Mahjoubi et al., 2015). Moreover, tourmaline incorporates a diversity of traces elements and constitutes a geochemical monitor of fluid compositions [START_REF] Marks | Trace element systematics of tourmaline in pegmatitic and hydrothermal systems from the Variscan Schwarzwald (Germany) : the importance of major element composition, sector zoning, and fluid or melt composition[END_REF][START_REF] Van Hinsberg | Determining subduction-zone fluid composition using a tourmaline mineral probe[END_REF]. In this study, tourmaline growth bands were used to track both flow and chemical composition of hydrothermal fluids involved during the earliest stages of the vein formation at Panasqueira.

Oriented vein samples with tourmaline were collected in the mine and at the surface, at different places around the cupola, both horizontally and vertically to have a full spatial distribution, and to establish a paleo-fluid flow map around the granitic intrusion (Fig. 1b).

Unfortunately, no samples were available in northwestern part of the studied area.

The vertical migration of the alteration front (tourmalinization) within the metasedimentary host rocks appears to be driven by the sub-vertical foliation planes (S1). To study the vertical fluid flow related to the alteration of the wall-rocks, samples of alteration halos have been collected

above and below veins perpendicularly to the vertical foliation planes (NE-SW section). The orthogonal NW-SE sections are parallel to the foliation planes and hence do not permit to perform fluid flow reconstruction in the wall rock due to the preferential crystallization of tourmaline in parallel within the foliation planes.

Fluid flow reconstruction by growth band measurements

In hydrothermal systems, the crystal shape is controlled by its intrinsic symmetry and the effects of external forces, such as fluid flow, that induce anisotropic growth [START_REF] Curie | [END_REF]). The method used for reconstruction of local fluxes is based on the notion that crystal faces exposed to the chemical flux (i.e. the upstream faces) grow faster than downstream faces [START_REF] Kessler | Direction of flow mineralizing solutions at Pine Point[END_REF][START_REF] Sizaret | Crystallization in flow part II: modelling crystal growth kinetics controlled by boundary layer thickness[END_REF]and 2009). The relationship between flow velocity and the relative growth rate of upstream and downstream faces can be modelled and quantified [START_REF] Sizaret | Crystallization in flow part II: modelling crystal growth kinetics controlled by boundary layer thickness[END_REF]2009). From this postulate, it is possible to deduce local fluid flow directions and velocities in the hydrothermal system. Oriented thin sections were cut parallel to the expected stream-line, i.e.

parallel to veins, within the vein, and vertically and perpendicular to foliation planes in altered host rocks. Tourmaline crystals were examined on polished thin sections using optical transmitted light and scanning electron microscope. Then, on tourmaline basal section (i.e., perpendicular to the trigonal axis) the growth band thickness of equivalent crystal faces (d1, d2 and d3) and their respective directions (α1, α2 and α3) have been measured (Fig. 4c). The three normalized thicknesses dmax, dint (intermediate) and dmin were determined. Assuming that the thickest band (dmax) received the largest chemical flux, the orientation of dmax gives the direction of the paleofluid flow recorded by the crystal (Fig. 4c).

The relationship between fluid velocity and growth ratios (dmax/dmin) was established by solving the coupled Navier-Stokes and chemical transport equations with the Comsol Multiphysics finite element code [START_REF] Sizaret | Estimating the local paleo-fluid flow velocity: new textural method and application to metasomatism[END_REF]. In this modeling the edge size of tourmaline is 50 µm and the fluid (water) viscosity is chosen at realistic mineralizing conditions, taken here at 350°C (7.3.10 -5 Pa.s source NIST WebBook, 2017). Varying flow velocity provides a relationship between chemical flux ratio (upstream/downstream) and fluid velocity (Fig. 4d). The growth band thicknesses measured on minerals can be considered as chemical fluxes integrated over a given period of time. Consequently, the fluid velocity can be determined by inverse method by reporting the measured dmax/dmin ratio on the flux ratio (Upstream/downstream) vs velocity curve (Fig. 4d) [START_REF] Sizaret | Crystallization in flow part II: modelling crystal growth kinetics controlled by boundary layer thickness[END_REF]2009).

To obtain representative measurements, basal sections of tourmaline were chosen from the following criteria: absence of contact with another crystal of tourmaline, absence of recrystallization and corrosion and easily identifiable equivalent faces.

For each site, flow directions and velocities deduced from each tourmaline section were implemented and treated with the free meteorological software WRPLOT View TM (Lake Environmental, 2016) in order to establish "wind roses" of local paleo-fluid flow. These rose diagrams are then reported on the map.

Tourmaline growth band chemistry 4.2.1 Major and minor element analysis

The major and minor element compositions of tourmaline were determined on polished thin sections using a Cameca SX-Five electron probe micro-analyzers (EPMA) at the Institut des Sciences de la Terre d'Orléans (ISTO). Analyses were performed using an accelerating voltage of 15 kV, a beam current of 6 nA with a diameter of 2 μm. The elements analyzed were Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, F and Cl. For calculation of the structural formulae and site allocation in tourmaline, analyses were normalized to 15 cations (T + Z + Y-sites) and B2O3 and H2O contents were calculated by stoichiometry, considering B = 3 apfu and OH + F + Cl = 4 apfu. Analytical conditions and calibration are detailed in electronic supplementary materials (ESM1).

Trace element analysis

Trace element concentrations in tourmaline were determined by laser ablation inductively coupled plasma-mass-spectrometry (LA-ICP-MS). These analyses were performed at BRGM (French Geological Survey) using a ThermoScientific X series II quadrupole ICP-MS coupled with a Cetac Excite 193 nm laser ablation system. Ablations were performed with a repetition rate of 8Hz and laser energy of 3.5 J/cm² with a beam size of 40 μm. Analyses comprise 20 seconds of gas blank measurement following by 60 seconds of ablation. Elements analyzed were 7 Li, 23 Na, Mg, 27 Al, 29 Si, 47 Ti, 51 V, 55 Mn, 66 Zn, 88 Sr and 118 Sn. Data reduction was performed with the software Glitter 4.0 using the NIST SRM-612 glass standard for external standardization and 29 Si as the internal standard. Concentrations in Mg and Al obtained by LA-ICP-MS data reduction were compared with EPMA analyses to check the accuracy of the results. Analyses of certified standard NIST-612 SRM give a good accuracy with a relative standard deviation (RSD) below 10%. Detection limits for most elements range between 0.2 and 5 ppm. Higher detection limits were achieved for Zn, Ti and Na (respectively 5.5 ppm, 15.4 ppm and 37.4 ppm).

Results

Large scale fluid flow

Fluid flow directions and velocities are summarized in Table 1 (complete measurements in electronic supplementary materials ESM2) and illustrated in Figure 5. For veins-hosted tourmaline, an average ratio of dmax/dmin was determined for each of the 8 sample sites. These average ratios range from 2.0 to 2.9 implying a fluid velocity varying from 10 -4 to 10 -3 m.s -1 in veins (Table 1 and Fig. 4d). Figure 5c shows the histogram representation of all velocity values, which are characterized by an asymmetric distribution centered on 10 -4 -5.10 -4 m.s -1 . This wide variable distribution is probably due to the sinuous nature of the fluid flow path. Indeed, a narrowing of the pathway can be responsible of the local high velocity value recorded by some tourmalines. For each sample of veins, the flow directions are dispersed with a significant mean direction (Fig. 5a). In the "rose" diagrams, these directions generally host the highest velocity values (10 -4 to 10 -3 m.s -1 ). Conversely, lowest fluid velocity values are not aligned with these mean directions of fluid flow (Fig. 5a). Considering all the sites, the mean orientations of flow depict a large-scale streamline structure with radial directions coming from a center located on the greisen cupola (Fig. 5a and5b). The vertical fault system crosscutting the veins does not influence flow direction in the veins (Fig. 5b). The pitch of flow direction vectors on the vein plane is not aligned to the dip direction of veins (Table 1). Consequently, flow directions are not influenced by veins orientation.

Fluid flow in host rock

In altered schist, tourmaline growth bands show a fluid flow escaping sub-vertically from veins toward the host rock, with an averaged angle of 55° above and 60° below the vein (Fig. 6).

This symmetrical behavior may be related to the horizontal component of fluid flow within the vein, as suggested by measurements on the P21 sample. Mean velocities obtained in altered wallrocks are 1 to 2 orders of magnitude lower than fluid velocity obtained in the veins (Fig. 4d and Fig. 6). In addition, it would appear that velocities are higher above (10 -5 -5.10 -5 m.s -1 ) than below veins (5.10 -6 to 10 -5 m.s -1 ) (Fig. 6).

Coordinates

Tourmaline growth band compositions

Chemical compositions of tourmalines are summarized in Table 2 (complete analyses in electronic supplementary materials ESM3 and ESM4). General features and classification of Panasqueira tourmalines have already been described by [START_REF] Codeço | Chemical and boron isotopic composition of hydrothermal tourmaline from the Panasqueira W-Sn-Cu deposit[END_REF]. Here, we focus on compositional differences in minor and trace elements between core and growth band used for fluid flow reconstruction. It appears that this growth band zoning is systematically associated with chemical variations in major, minor and trace elements (Table 2). In the veins, cores and rims of tourmaline exhibit compositions that suggest equilibration with Li-depleted granitic rocks (Fig. 7a). However, rims are richer in Fe and poorer in Mg and Al than cores. In altered wall-rocks, cores are characterized by a wide range of compositions suggesting equilibration with metasedimentary host rocks and Li-depleted granitic rocks; whereas rims exhibit a more restricted composition identical to rims of veins-tourmalines and that suggest equilibration with Li-depleted granitic rocks (Fig. 7a). This range of core compositions (in altered wall-rocks) reflects the contribution of hydrothermal fluids and the metasedimentary host rocks during the core crystallization of tourmaline.

It is generally accepted that magmatic fluids contain significant amounts of Na, K and Cl. As a result, the trace eleement concentrations in cores and rims of tourmaline contents of core and rims of tourmaline are plotted as a function of the Na concentration to show the possible evolution of the magmatic contribution during tourmaline crystallization. Cores of tourmalines from veins and from altered wall-rocks are characterized by the same compositional ranges. This observation is also valid for rims (Table 2 and Fig. 7b). Consequently, crystallization of tourmalines in the veins is probably contemporaneous with the development of tourmalines in the altered wall-rocks. In addition, results show strong compositional differences between core and rims of tourmalines (Fig. 7b). Indeed, the core to rim enrichment in Na is positively correlated with core to rim enrichments in K, Ti, Li, Mn, Sn, and Sr (Fig. 7b). Average concentrations in rims display high contents of Li, K, Mn, Ti and Zn (several hundreds to thousands of ppm) and moderate concentrations of Sn and Sr (several tens of ppm). Conversely, cores are characterized by lower trace element abundances (< 100 ppm for most elements). 20 These compositional differences between cores and rims, which are similar in the veins and in the wall-rocks, suggest that tourmalines were formed during two distinct stages. The first stage is related to core crystallization (both in veins and in wall-rocks) whereas the second stage is related to the rim overgrowths.

The absence of experimental partitioning coefficients between tourmaline and hydrothermal fluids do not permit to quantify the chemical signature of the hydrothermal fluid from which tourmaline has crystallized. Nevertheless, according to Van Hinsberg et al., (2011a;2017), the compositional changes between cores and growth bands provide a robust tool to track external changes in the trace-element budget of fluids from which tourmalines have crystallized. The present study suggests that rims have crystallized from a fluid richer in Na-K-Sn-Li-F-Zn than the fluid from which cores crystallized.

Discussion

Role of the granitic cupola on focusing fluid flow

In hydrothermal systems, fluid velocity is proportional to pressure gradient and its average direction is parallel to this gradient. Here, our spatial distribution and orientations of flow velocities suggest a high-pressure zone centered on the greisen cupola with a lateral pressure gradient triggering fluid flow in veins. Hence, hydrothermal fluids have probably been injected into the vein system from the cupola, which, consequently, represents the emanative center from where mineralizing fluids rose and spread laterally in veins. Moreover, the ΣNa/ΣK ratio determined by Poyla et al., (1989) for the ore-forming fluids (W-Sn stage) suggests an extensive interaction of these fluids with the underlying granite at 350-400 °C and 1 kbar. The rim compositions of tourmaline confirm an equilibration of fluids with granitic rocks. Furthermore, the extensive greisenisation in the apical part of the granite provides evidence of this equilibration and corroborates our interpretation of a fluid flow focused by the cupola.

This fluid flow pattern can explain the spatial correlation commonly observed between localization of mineralized systems and emplacement of granitic cupolas [START_REF] Dines | The metalliferous mining region of South-West England. 2 volumes[END_REF]Dilles and Proffett, 1995). Indeed, it has been proposed that magmatic fluids are preferentially expelled from cupolas, and that can disturb the pattern of convective fluid flow around intrusions by relocating convective cells and discharge zones [START_REF] Norton | Thermal aspects of ore deposition[END_REF][START_REF] Eldursi | Numerical investigation of transient hydrothermal processes around intrusions: Heat-transfer and fluid-circulation controlled mineralization patterns[END_REF].

Hydrothermal fluxes determined in this study provide direct evidence of the control of apices on focusing of mineralizing fluids. This behavior of fluid flow can be explained by a preferential localization of thermo-mechanical instabilities around apices [START_REF] Guillou-Frottier | The development and fracturing of plutonic apices: implications for porphyry ore deposits[END_REF], which, when coupled with a preferential accumulation of fluids, leads to opening of permeable structures in which mineralizing fluids are then discharged.

Hence, the apical parts of plutonic intrusions represent convergence spots for hydrothermal fluids and thus are favorable zones for deposition of high grade mineralization. As a result, the approach applied in this study can be useful for mining exploration as pathfinder to discover hidden granitic cupolas and thus locate the emanative centers of mineralizing fluids.

Fluid escape in wall-rocks and role of fluid on vein opening

The vertical escape of fluids from veins toward metasedimentary host rock involves a vertical pressure gradient with overpressured fluid conditions in veins, causing pervasive fluid flow in the wall-rocks. This interpretation is consistent with the presence of alteration fronts observed around veins (Fig. 3a). Besides, [START_REF] Lecumberri-Sanchez | Fluid-rock interaction is decisive for the formation of tungsten deposits[END_REF] have demonstrated that schists proximal to the veins are systematically enriched in K, B, Sn and W. The rims of tourmalines present in altered wall-rocks are also enriched in certain of these elements (K and Sn). This is consistent with extensive fluid-rock interaction triggered by fluids coming from veins.

According to the rim compositions of vein-and schist-tourmalines, fluid flow in veins can be considered contemporaneous with pervasive fluid flow in altered wall-rocks. As shown above, fluid flow in wall-rocks is related to overpressured conditions in veins. Thus, our results suggest that veins opening and dilation have been induced by injection of fluids at supralithostatic conditions such as proposed by [START_REF] Foxford | Extensional failure and hydraulic valving at Minas da Panasqueira, Portugal: Evidence from vein spatial distributions, displacements and geometries[END_REF]. The low velocity values (not exceeding 5.10 -5 m.s -1 ) obtained in altered wall-rocks imply a low permeability in the host rocks. As a result, the element transport through the host rock was probably low and limited to the alteration haloes.

Based on the removal of iron (Fe) from the wall-rocks during fluid-rock interactions, [START_REF] Lecumberri-Sanchez | Fluid-rock interaction is decisive for the formation of tungsten deposits[END_REF] suggest that some elements such as Fe have migrated from the host rocks toward veins. At first sight, this chemical flux seems to be incompatible with the direction of fluid flow discussed above. However, iron migration through the host rocks was probably driven by diffusion following a strong chemical gradient between fluid in veins and metasedimentary host rocks, whereas fluid flow was driven by pressure gradient. These two processes have not involved the same driving force, and it is, therefore, possible to observe a chemical flux that is characterized by a vector that is opposed to the fluid flow direction.

Velocity analysis and estimation of fluid flow duration during the QTS-MOSS

In this study, the mean fluid flow velocity deduced from veins tourmalines (10 -4 m.s -1 ) is high and close to values obtained with the same method in the same type of deposit by [START_REF] Sizaret | Estimating the local paleo-fluid flow velocity: new textural method and application to metasomatism[END_REF] and [START_REF] Mahjoubi | Structural, mineralogical, and paleoflow velocity constraints on Hercynian tin mineralization: the Achmmach prospect of the Moroccan Central Massif[END_REF], and suggests an efficient metal transport in veins. Considering a porous media with an averaged porosity of 1%, the conversion of this mean velocity to a Darcy velocity (VDarcy = V*porosity) gives a value of 10 -6 m.s -1 . Darcy velocities obtained in contact metamorphic aureoles from mineral reactions and by numerical modeling range respectively from 10 -9 to 10 -11 m.s -1 [START_REF] Ferry | The direction of fluid flow during contact metamorphism of siliceous carbonate rocks: new data for the Monzoni and Predazzo aureoles, northern Italy, and a global review[END_REF], and from 10 -8 to 10 -11 m.s -1 [START_REF] Eldursi | Numerical investigation of transient hydrothermal processes around intrusions: Heat-transfer and fluid-circulation controlled mineralization patterns[END_REF]). It appears that velocities obtained in this study are 2 to 5 order of magnitude higher than those deduced from mineral reactions and numerical modeling. This difference may be due to the fact that velocities obtained from mineral growth bands are valid for a specific hydrothermal stage occurring over a short period of time, while those deduced from other methods are integrated over a larger scale and for the total duration of the hydrothermal system [START_REF] Ingebritsen | Geologic implications of a permeability-depth curve for continental crust[END_REF].

It is widely agreed that the overall time span of hydrothermal activity encompasses multiple fluid pulses, each of them occurring over only a short period of time. If geochronological methods allow dating hydrothermal activity, the uncertainties of these analytical methods do not always permit the estimation of the fluid flow duration for a specific stage. As in most cases, the Panasqueira deposit was formed during a long period of time lasting about 4.2 Myr [START_REF] Snee | Thermochronology of economic mineral deposits; dating the stages of mineralization at Panasqueira, Portugal, by high-precision 40Ar/39Ar age spectrum techniques on muscovite[END_REF] but subdivided into several pulses. Here we propose the use of the mean fluid velocity value obtained from veins-tourmaline to estimate the fluid flow duration required for the vein formation during the QTS and MOSS. To do this, we assume that the QTS and the MOSS were formed during the same continuous hydrothermal event with a constant fluid flow velocity. According to Poyla et al., (1989) the total volume of fluid that flowed through the vein system during the MOSS is about 1000 km 3 with 0.2 ppm of dissolved WO3. Considering a total volume of vein about 0.003 to 0.006 km 3 extending over an area of 6 km² [START_REF] Hebblethwaite | A report on the study of dilation patterns within the Panasqueira ore body: Barroca Grande[END_REF] characterized by an elliptical shape, we can calculate the surface of the vertical section of fluid flow. From this surface and the mean fluid flow velocity (10 -4 m.s -1 ) we obtain a fluid flow duration ranging from 35 000 to 70 000 years. This is consistent with the short time duration of mineralization emplacement estimated for a single magmatic-hydrothermal event (spanning only about 10 000 to 200 000 years) from numerical modeling [START_REF] Cathles | How long can a hydrothermal system be sustained by a single intrusive event?[END_REF][START_REF] Chelle-Michou | Tempo of magma degassing and the genesis of porphyry copper deposits[END_REF] and radiometric dating [START_REF] Parnell | Dating and Duration of Fluid Flow and Fluid-Rock Interaction[END_REF].

Hydrodynamic model of the Panasqueira deposit

Our results must be considered as 'snapshot' of the fluid flow at the incipient phase of the hydrothermal system of Panasqueira, corresponding to the magmatic-hydrothermal transition.

Considering chemical characteristics of tourmalines and our fluid flow reconstruction, a hydrodynamic model subdivided into two stages is proposed for the early hydrothermal event preceding the main stage of W-Sn mineralization (Fig. 8). The first stage is related to the core crystallization of tourmalines and involves an initial flow of boron-rich fluids. These fluids are partly buffered by the metasedimentary host rocks for Al, Mg and Fe during the crystallization of tourmaline in the wall-rocks (Fig. 7a). This first pulse does not seem to be associated with any W-Sn mineralization. This is consistent with the low contents in trace elements in cores of tourmaline. We have no information about directions of fluid flow related to this first pulse.

However, the chemical equilibration of cores of veins-tourmalines with Li-depleted granitic rocks suggests that the first stage can be related to a first expulsion of magmatic fluid during granite crystallization.

The second stage is recorded by tourmaline growth bands and is related to the flow of the mineralized (Li-K-Na-Sn)-rich fluid in the veins system. During this second stage, the external convecting fluids and magmatic fluids released by granite crystallization are both focused by the cupola, which causes the greisenization in the apical part of the granite (Fig. 8). This focused fluid flow is injected into the vein system, whose the significant horizontal permeability anisotropy induces a horizontal fluid flow along the vein planes. The low permeability of the metasedimentary host rock promotes fluid pressure increase leading to the vein opening when fluid pressure reaches supralithostatic conditions (Fig. 8). The velocity contrast between veins (10 - permeability and suggests that fluid flow was mainly channeled in the vein system. This channelization of mineralizing fluids in veins could contribute to form a high grade deposit by an efficient metal transport in structural trap sites. The overpressured condition in veins enhances fluid-rock interaction and triggers a pervasive fluid migration in the wall-rocks (Fig. 8). According

to [START_REF] Lecumberri-Sanchez | Fluid-rock interaction is decisive for the formation of tungsten deposits[END_REF], the metasedimentary host rock is mainly affected by

Figure 1

 1 Figure 1 (a) Tectonic map of the Variscan Iberian massif showing the main tectonostratigraphic domains defined by Julivert et al., (1972). The location of the Panasqueira deposit is marked by a red star. CZ: Cantabrian Zone, WALZ: West Asturian-Leonese Zone, GTOMZ: Galicia Tràs-os-Montes Zone, CIZ: Central Iberian Zone, OMZ: Ossa-Morena Zone and SPZ: South Portuguese Zone (b) Geological map of the Panasqueira ore deposit including the height of the granite roof. The (A-A') geological cross section displaying the spatial relationship between mineralized veins and the greisen cupola (data source Beralt Tin & Wolfram S.A.).

Figure 2

 2 Figure 2 The mineralized system of the W-Sn-(Cu) Panasqueira deposit. (a) Contact between the greisen cupola and the tourmalinized metasedimentary host rock at the level 1 of the mine. Note the presence of mineralized veins which crosscut this contact. (b) Typical Quartz-Wolframite veins corresponding to the main oxide stage. (c) Quartz-Wolframite veins superimposed by the late sulfide stage carrying the Cu mineralization. Abbreviation from Whitney and Evans (2010) Ccp: Chalcopyrite, Ms: Muscovite, Qz: Quartz and Wf: Wolframite.

Figure 3

 3 Figure 3 Textural and petrographic characteristics of tourmalines present in the mineralized system of Panasqueira. (a) Quartz-tourmaline vein with tourmalinization of the metasedimentary wall-rocks. The white dashed line indicates the tourmalinization front in the metasedimentary host rock. c and d arrows give orientation of the thin sections c and d. Note the preferential migration of tourmalinization front in the vertical foliation planes S1 (b) Sample of mineralized veins showing the vertical growth of acicular tourmalines along the schist-vein contact. (c) and (d) photomicrographs of vein tourmaline showing sections parallel (c) and normal (d) to the trigonal axis of tourmaline. (e) Photomicrograph of mineralized vein showing tourmaline grains associated with cassiterite. (f) SEM photomicrograph of altered schist perpendicular to the foliations planes showing growth band zoning in tourmaline basal sections. Abbreviation from Whitney and Evans (2010) Ap: Apatite, Cst: Cassiterite, Ms: Muscovite and Qz: Quartz.

Figure 4

 4 Figure 4 Examples of basal sections of tourmaline from veins (a) and altered wall-rocks (b) displaying an asymmetric shape due to an anisotropic growth (c) Measurements of growth bands thickness and orientation on a basal section of tourmaline. (d) Curve deduced from numerical modeling showing relationship between fluid velocity and flux ratio (see text for details). The filled boxes indicate range of averages of fluid velocities derived from dmax/dmin ratio measured on tourmalines from altered wall-rocks (blue) and veins (red).

Figure 5

 5 Figure 5 Results of fluid flow at the ore deposit scale deduced from tourmaline growth bands in mineralized veins. (a) Large scale map of paleo-fluid flow around the hidden granite of Panasqueira. Local fluid flow direction and velocities are represented with "rose" diagrams, which give direction of tourmaline faces exposed to the fluid flow (dmax) and directional distr<ibution of fluid velocities. The orange arcs give the 95% interval of confidence, from where the fluid comes. The orange arrows on the map correspond to the mean directions of flow determined for each sample site. N corresponds to the number of measurements performed for each sample sites. (b) Results of fluid flow projected on the geological cross section (B-B') showing flow moving away from the cupola. (c) Histogram showing distribution of all fluid velocity values.

Figure 6

 6 Figure 6 Sketch showing vertical paleo-fluid flow deduced from tourmaline in altered wall-rocks. Fluid flow directions are represented with rose diagrams giving direction of faces exposed to fluid flow. The red arcs indicate the 95% interval of confidence, from where the fluid comes. Velocity values obtained above, below and within the vein are presented in histogram diagrams. N corresponds to the number of measurement performed for each sample.

Figure 7

 7 Figure 7 Geochemical characteristics of tourmalines used for fluid flow reconstruction in veins and in altered wall-rocks. (a) Al50Fe50-Al50Mg50 ternary diagram showing relation between tourmaline compositions and crystallization environment (from Henry and Guidotti, 1985). (1) Li-rich granitoids, pegmatites and aplites; (2) Li-depleted granitoids, pegmatites and aplites; (3) Fe 3+ -rich hydrothermaly altered granitoids; (4) Metapelites and metapsammites with Al-saturating phase; (5) Metapelites and metapsammites without Al-saturating phase; (6) Fe 3+ -rich metapelites and calc-silicate rocks with quartz and tourmaline; (7) Cr-Vrich metapelites and Ca-depleted meta-ultramafics rock; (8) Meta-carbonates and meta-pyroxenites. (b) Elements variation diagrams showing chemical core-rim evolution of tourmalines in minor (Na, K and Ti) and trace (Li, Mn, Sn and Sr) elements.

  tourmalinization and muscovitization reactions, which are crucial for the wolframite deposition by iron releasing into the fluid. Finally, the escape of fluids toward the wall-rocks observed in this study can constitute a crucial mechanism for the wolframite deposition by promoting fluid-rock interactions.

Figure 8

 8 Figure 8 Hydrodynamic model of fluid flow at the magmatic-hydrothermal transition of the W-Sn-(Cu) Panasqueira deposit (drafted on simplified cross section from Thadeu, 1951). With Pf: the fluid pressure condition, σ3: the vertical stress and T: the tensile strength.

Table 1 Results of directions and velocities of fluid flow deduced from tourmalines growth bands in veins and in altered wall-rocks (SD: Standard Deviation and N: 327 number of measurement).

 1

		(ETR S89/Portugal TM06)	Veins orientation		dmax/dmin			Fluid flow
	Veins:	X (m)	Y (m)	Z (m)	Strike	Dip	N	Mean	SD	Mean direction	Mean velocity (m.s -1 ) Pitch
	Pan70	31675.9	54649.3	620	N136	7°	30	2.06	0.66	N28	2.76E-04	77°
	Pan87	31410.9	54261.6	620	N300	5°	41	2.50	0.95	N64	6.65E-04	60°
	Pan21	31675.1	54253	560	N200	5°	31	2.06	1.06	N27	5.53E-04	10°
	Pan33	31217.9	53385.2	470	N130	15°	24	2.24	0.39	N40	3.33E-04	90°
	Pan78	33043.4	53490.3	618	N138	7°	31	2.29	1.13	N331	6.66E-04	26°
	Pan73	32933.2	53875.3	662	N127	10°	25	2.75	1.10	N321	9.46E-04	24°
	Pan95	33058.4	54287	741	N127	5°	18	2.92	1.27	N300	1.38E-03	8°
	Pan97	32833.3	55559.5	732	N160	10°	25	2.74	0.96	N201	9.47E-04	42°
	Altered wall-rocks :
	P20 Up	31675.1	54253	560	-	-	28	1.36	0.18	55	1.44E-05	-
	P20 Down	31675.1	54253	560	-	-	28	1.29	0.11	60	6.95E-06	-

Table 2 Summary of EPMA and LA-ICP-MS results for core and rim of tourmaline from veins and altered wall-rocks Tourmaline from veins Tourmaline from altered wall-rocks

 2

		Core		Rim		Core		Rim
	wt%	Ave (n= 20)	Stdev	Ave (n= 20)	Stdev	Ave (n = 20)	Stdev	Ave (n = 20)	Stdev
	SiO2	35.74	0.54	35.14	0.53	34.94	1.43	35.34	0.46
	TiO2	0.18	0.04	0.48	0.08	0.19	0.07	0.46	0.08
	Al2O3	33.79	0.56	31.10	0.82	34.40	1.07	30.18	0.47
	FeO	10.86	0.70	14.23	0.59	8.89	0.83	13.29	0.95
	MnO	0.05	0.05	0.11	0.08	0.04	0.06	0.08	0.06
	MgO	2.60	0.62	1.31	0.36	3.82	0.54	2.62	0.63
	CaO	0.04	0.05	0.08	0.04	0.09	0.05	0.03	0.05
	Na2O	1.39	0.10	2.07	0.20	1.69	0.14	2.26	0.13
	K2O	0.02	0.00	0.05	0.01	0.02	0.01	0.06	0.01
	F	0.00	0.01	0.00	0.00	0.00	0.00	0.00	0.00
	Cl	0.00	0.00	0.01	0.01	0.01	0.01	0.01	0.01
	Total	84.68		84.57		84.09		84.34
	ppm	Ave (n= 16)	Stdev	Ave (n= 17)	Stdev	Ave (n= 11)	Stdev	Ave (n= 14)	Stdev
	Li	28	9.6	175	82	43	24	211	33
	Na	8399	1049	17190	1739	6843	1887	14514	1463
	Ti	1146	211	2465	390	2096	660	3318	269
	V	84	29	98	27	61	63	55	16
	Mn	413	42	698	125	171	63	542	43
	Zn	545	80	908	181	302	105	853	78
	Sr	14	6.3	40	9.3	29	18	41	5.5
	Sn	9.6	2.9	18	6.1	9.1	6.0	14	3.8

to 10 -3 m.s -1 ) and altered wall-rocks (10 -6 to 10 -5 m.s -1 ) emphasize this strong contrast of

Acknowledgments

We are greatly thankful to Beralt Tin & Wolfram S.A. for the possibility to access to the Panasqueira underground mine. We thank Paolo Ferraz for help during the collection of samples in mine and for discussions about our results. We further would like to thank P. Lach for assistance in LA-ICP-MS analyses and proceeding of data. We are grateful to anonymous reviewers for their constructive remarks, which have greatly improved this manuscript. This research was financially supported by the French Geological Survey (BRGM), Region Centre, the Labex Voltaire (ANR-10-LABX-100-01) and has also taken part of the ERAMIN project "New Ores".