Australian Geothermal Energy Conference 2011

Synchysite from the Soultz high-heat producing monzogranite, Soultz-sous-Forêts, France: Implications for titanite destabilisation and differential REE and Th mobility in hydrothermal systems

Alexander W. Middleton*1,3, I. Tonguc Uysal1, H.-J. Förster2 and Suzanne D. Golding3 1 Queensland Geothermal Energy Centre of Excellence, The University of Queensland, Brisbane, QLD. 4072 2 GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany 3 School of Earth Sciences, The University of Queensland, Brisbane, QLD. 4072

In order to better understand the relatively European investigations into enhanced unstudied high heat producing granites (HHPG) of geothermal systems (EGS) and was found to the Australian continent, this project has focused have highly fertile values of radiogenic elements, on the European analogue: Soultz-sous-Forêts K (~4%), Th (24-35ppm) and U (6-13ppm (France). HHPGs are characterised by their (Hooijkaas et al., 2006). The enrichment in radiogenic element (U, Th and K) content, which radiogenic as well as REE (rare earth elements) is higher than average continental crust values. may be related to assimilation-fractional crystallisation as postulated by Stussi et al. In a similar manner to ore deposit exploration (2002). Zircon U/Pb work by Alexandrov et al. where intrusive bodies are partially characterised (2001) dates the monzogranite at 331 ± 9 Ma by their alteration assemblages, this hot-dry rock indicating a possible early Namurian geothermal research will also attempt to emplacement (Gradstein and Ogg, 1997). The characterise the alteration of HHP felsic igneous monzogranite is porphyritic, consisting of 1-8cm rocks. Hydrothermal alteration (metasomatism) is K-feldspar megacrysts within a phaneritic matrix classed as the chemical, textural and of quartz, plagioclase, biotite, hornblende with mineralogical changes ensuing from mineral-fluid accessory apatite, allanite, titanite, zircon and interaction in a hydrothermal system. As the magnetite (Genter and Traineau, 1991). Further pervasiveness of metasomatism can be whole-rock geochemistry by Stussi et al. (2002) dependent on the degree of natural fracturing showed that distinctive geochemical enclaves within the granitic body, the understanding of existed within the monzogranite. These ranged alteration mineralogy and its position within the from monzogabbrodiorite- quartz-monzodiorite- granitic body could prove integral when locating quartz-monzonite and quartz syenite and are sites for ensured forced circulation during geothermal energy exploitation. Moreover, as believed to be mantle-derived. metasomatic phases indicate palaeo- hydrothermal temperature and chemistry it may thus illuminate potential impacts arising from injecting saline solutions whilst utilising the EGS. This paper may therefore illuminate such impacts, including mobilisation of rare earth elements and * thorium entrained within conduits of high fluid-flow as well as has implications to the greater *Soultz-sous-Forêts understanding of Th mobility in hydrothermal solutions, a conventionally considered “immobile” element. This will be done by analysing the various heat-producing metasomatic accessory phases, with focus on synchysite, found in the Soultz-sous-Forêts monzogranite, a subject which has received no previous attention. Keywords: Rare earth elements, Soultz-sous- Fig 1: Possible tectonic suture configuration of Hercynian orogeny from Matte (2001). Forêts, titanite Introduction Titanite Geological Setting As one of the Soultz monzogranite principle REE The Soultz monzogranite (Stussi et al., 2002) is (and Y) and Th-bearing phases in the Soultz situated in the western district of the Rhine monzogranite, titanite is known to have a highly Graben (40km NW of Strasbourg), proximal to the variable composition which can depend on the Vosges fault and is overlain by Mesozoic to composition of the host rock. Where basic rocks Cenozoic sedimentary cover. The monzogranite show a classic CaTi[SiO4] (O,OH,F) composition, was drilled with borehole EPS1 as part of highly evolved (Pollard et al., 1987) granitic rocks

167 Australian Geothermal Energy Conference 2011 are likely to bear titanite with a more chemically Potsdam, Germany. ZAF oxide corrections were exotic composition. For example, the Skye employed with specific operating conditions to Granite contain titanites with REE2O3 (rare earth minimise degradation of the sample. Operating element) values of up to 46.1 per cent (Exley, conditions were: acc. Volatage 15kV, beam 1980). This may result from a Ca2+ + Ti4+ = REE3+ diameter 10μm and beam current 5 nA. + (Al, Fe)3+ (Exley, 1980; Vuorinen and Hålenius, 2005) substitution allowing for a balance in Results valency. This lithological dictation on composition is due to the relative enrichment in incompatible elements available in the late stages of melt evolution. In hydrothermal environments titanite may destabilise in the presence of Ca-poor, Qtz moderate pCO2 fluids forming: calcite + quartz + rutile ± REY-bearing phases including allanite, Cal bastnaesite, monazite and xenotime (Hunt and Syn Kerrick, 1977; Bancroft et al., 1987; Pan et al., 1993). The assemblage was also postulated to contain fine grains of synchysite (Ca(REE)(CO3)2F) however this was never Ant confirmed (Pan et al., 1993). This paper therefore not only holds implications to lower temperature destabilised titanite assemblages but also records the first, to date, analysable example of synchysite from titanite destabilisation in the Fig 2: PPA replacing titanite. Cal = calcite, Qtz = literature. quartz, Ant = anatase, and Syn = synchysite.

Hydrothermal Alteration Titanite is readily identifiable in the Soultz pluton Three predominant alteration styles have been and whether or not it appears as unaltered, highly identified in the Soultz pluton: minor “pervasive” birefringent rhombic crystals or as polyminerallic, propylitic, vein-related and weathering-related pseudomorph assemblages (PPA) is dependent argillisation to haematisation (Genter, 1991). on the proximity to fracturing. With increasing Although the primary K-feldpsar and quartz fracturing and hence fluid/rock ratio samples show appear unaltered, the primary ferromagnesian an increasing degree of alteration. Under minerals (biotite and hornblende) have undergone transmitted-light microscopy altered titanites are almost complete chloritisation forming present as either “dusted-opaque” rhombs or as assemblages of: chlorite + siderite + opaque euhedral-subhedral alteration pseudomorphs. The (haematite-magnetite) and chlorite + epidote mineralogy of the “dusted” grains are difficult to (Genter and Traineau, 1991). Plagioclases show identify under transmitted or reflected light due to a similar extent of selective alteration, forming the nature of formation. The subhedral needles of illite. Zones proximal to fracture pseudomorphs, on the other hand, were less networks appear pervasively altered with varying difficult allowing accurate identification of the degrees illitisation and carbonatisation. For this subhedral anatase with supporting quartz- study we will focus on this varying pervasive carbonate matrix. EDS and microRAMAN analysis alteration and its chemical influence on the identified the assemblage: anatase + calcite monzogranite. +quartz + synchysite ± bastnaesite. Analytical Work Synchysite either formed highly birefringent, tabular sub- to euhedral crystals or anhedral- Samples K102, K108, K177 and K206 were subhedral acicular laths with nano-scale provided by the Soultz-sous-Forêts Hot-Dry Rock intergrowths of anatase. The acicular laths appear project and represent granite of increasing depth to concentrate within the titanite void, whereas the and varying alteration intensity. Samples were cut tabular phases either rim or are proximal to the and made into polished thin-sections. mineral void. The formation of euhedral laths can EDS (enhanced dispersive spectroscopy) and be traced to the pooling of hydrothermal fluids BSE (back scattered electron) images were following vein-directed fluid movement. Analysing acquired using the JEOL XL30 SEM at the CMM, synchysite grains proved difficult as samples were Hawken Lab, University of Queensland, Brisbane. either too small or were decomposed under the Operating parameters were kept at 20kV and spot electron beam too readily. Those most size 5. Low vacuum analysis was performed on appropriate for analysis occurred as sub- to JEOL 6460 SEM in the same facility. euhedral tabular 15-50 by 30-40 micron grains. Although commonly present in PPA from K177, it Electron-microprobe analyses of samples were is rare and almost exclusive to one PPA from performed in the wave-dispersive mode of the K108, where monazite is the predominant REE- JEOL JX-8500F at the GeoForschungsZentrum,

168 Australian Geothermal Energy Conference 2011 bearing phase. Monazite, xenotime and thorite After chondrite normalisation REE and Y patterns are the principle REE and Th-bearing phases indicate a relative enrichment of LREE to HREE in found in samples K108 and K206 representing a titanite, allanite, synchysite and monazite. For La- different fluid chemistry. Although not analysable, Sm titanite, synchysite and monazite share similar due to its grain size, synchysite was also patterns, whereas allanite patterns are steeper. identified as a common phase in Mn-rich zones of Patterns of synchysite and monazite appear to carbonate veinlets of K108. diverge at Sm with significant divergence at Y.

1.0E+06 1.0E+06 Similarly, synchysite shows relatively lower La/Dy of 38.5 to monazite, 77.4, as well as higher 1.0E+05 1.0E+05 average Y2O3 values of 1.2 wt% and 0.24 wt%, respectively. As predominant REE in synchysite, 1.0E+04 1.0E+04 La2O3 and Ce2O3 are on av. 10.9 wt% and 22.3 wt% respectively. The remaining REE2O3 wt% is 1.0E+03 1.0E+03 on av. 14.9 wt%.

Sample/Chondrite 1.0E+02 1.0E+02 Analysed grains had CaO values of 16-17 wt% and average F values of 5.4 wt%. The average 1.0E+01 1.0E+01 0.4 wt% TiO2, has been attributed to nano-scale inclusions of anatase inclusions. 1.0E+00 1.0E+00 La Ce Pr Nd Sm Gd Tb Dy Y Ho Er Tm Yb Discussion Fig 3 showing REE and Y plot for monazite (black), synchysite (red), allanite (green) and titanite (blue). Titanite Destabilisation from CO2-F-rich fluid Synchysite was confirmed as a REE REE and Th Source fluorocarbonate by identifying C, O and F peaks in low vacuum SEM EDS. Trace element The peraluminosity, as defined by its aluminium concentrations of synchysite were determined saturation index (Zen, 1986), and hence the CaO using EPMA as seen in Table 1 and Figure 3. content (Cuney and Friedrich, 1987) of granite can dictate the primary accessory phases to Table 1. Trace element concentration (wt%) of synchysite uptake incompatible elements such as REEs and in sample K177 HFSE (Watt and Harley, 1993; Wolf and London, 1994). As shown by Wolf and London (1994) Sample K177G K177G K177G K177G whilst the peraluminosity tends towards an ASI P2O5 0.02 0.02 0.00 0.02 index of >1, the solubility of apatite will increase

SiO2 0.82 0.40 0.34 0.34 therefore promoting both P2O5 in the melt and the

TiO2 0.45 0.39 0.81 0.51 likelihood of phosphates being the primary carrier of REE and HFSE. However, the Soultz ASI ZrO2 0.00 0.00 0.00 0.00 ThO 0.69 1.18 0.81 1.23 indicates a metaluminous (<1) and CaO-rich melt 2 (~2%) (Stussi et al., 2002) within the stability field UO 0.08 0.00 0.04 0.00 2 of Ca-bearing silicates (Cuney and Friedrich, Al2O3 0.27 0.59 0.23 0.25 1987) such as titanite and allanite. As these Y2O3 2.42 3.02 0.94 1.73 phases require a stability limit of 1.5% CaO, they, La2O3 9.70 7.19 8.46 8.00 along with thorite (Bea, 1996) and minimally Ce2O3 21.56 21.09 22.26 22.88 apatite ,will act as the predominant incompatible

Pr2O3 2.33 2.86 3.00 2.62 element-bearing minerals. With the above in

Nd2O3 8.79 10.30 10.59 10.21 mind, the most likely parent-source of REE for the pseudomorph assemblages will be titanite as Sm2O3 1.29 1.44 1.58 1.57 shown from the synchysite and bastnaesite grains Gd2O3 1.08 1.39 0.89 1.24 within or rimming the parent-mineral void. This is Tb O 0.11 0.15 0.06 0.14 2 3 further substantiated by EPMA mapping in the Dy2O3 0.44 0.60 0.23 0.46 present study indicating the presence of REE Ho2O3 - - - - within the crystal structure as well as an almost Er2O3 0.19 0.33 0.00 0.09 identical REE pattern between titanite and Tm2O3 - - - - synchysite. Discrepancies of REE pattern Yb2O3 0.06 0.07 0.00 0.00 symmetry do however; lie in the La and to a

Lu2O3 - - - - lesser extent Ce contents with % values of CaO 17.08 16.66 16.67 16.68 synchysite being enriched with respect titanite, FeO 0.00 0.35 0.08 0.23 relative to ΣREE (Fig 4). Elevated values of lanthanum and cerium are due to sourcing from a F 5.44 5.70 5.77 5.86 relatively enriched source of LREE with respect to F=O2 2.29 2.40 2.43 2.47 titanite, such as allanite or LREE-rich Sum 70.53 71.34 70.33 71.62 uranopolycrase. Enrichment of LREE in allanite (Fig 3) can be traced to the timing of crystallisation within the chamber (Gromet and

169 Australian Geothermal Energy Conference 2011

Silver, 1983). As titanite crystallised first, it This formula however uses an idealised produced relative depletion in HREE and allowed composition for titanite which is uncommon in a now LREE-enriched melt to crystallise allanite. most igneous bodies especially those of evolved The topic of primary magmatic enrichment is felsic granites such as the Soultz monzogranite however beyond the scope of this project and will (Stussi et al., 2002; Xie et al., 2010) where not be discussed further. Apatite may take up titanites contain recognisable concentrations of REE and HFSE in metaluminous granites (Watt incompatible elements. Taking into account the and Harley, 1993); petrographic analyses of K177 mineralogy seen at Soultz as well as notably in the current study found shielded quartz-bound similar geochemical occurrences found by Pan et euhedral apatite with no to minimal evidence of al. (1993), a more likely equation will result: dissolution. Those apatite grains with minor dissolution-reprecipitation structures generally contain monazite or synchysite within voids Titanite + CO2 + F Anatase+ Calcite indicating minimal if any release of REE into the + Quartz + Synchysite ± Bastnaesite surrounding rock (cf. Harlov et al, 2005). Those released into solution are unlikely to have been mobilised significant distances due to the (Ca, REE, Ti, Th)SiO5 TiO2 + CaCO3 + presence of Ca2+ (Salvi and William-Jones, 1996), SiO2 + CaCe(CO3)2F ± REE(CO3)F (2) a common cationic ligand destabiliser of REE and HFSE that have complexed with bi-ligands such - 3- as F HCO (Wood, 1990b). The only other REY and Th mobility potential source of REE and Th is thorite; this is however, rather unlikely as thorite grains appear REE and Y (hereafter REY) are variably mobilised minimally, if at all, affected by the degree of by hydrothermal fluids depending on a number alteration found in the CO2-F-dominated K177. geochemical parameters such as pH, composition and Redox conditions (Wood, 1990b, a; Bau, The origin and role of volatiles 1991; Uysal et al., 2011). The composition of the hydrothermal fluid, for example, will preferentially With the appearance of contemporaneous mobilise HREE and Y over LREE when synchysite and ankerite, one must assume the dominated by hard ligands like F-, but will mobilise availability of CO2 in the metasomatic system HREE in solutions dominated by soft, bicarbonate (Förster, 2001). Moreover, fluid inclusion (FI) ligands (Bau and Dulski, 1995). Conversely, studies by (Dubois et al., 1996)on carbonate- Wood (1990b) found in fluids rich in chlorine quartz veins from EPS1-2052.1 m (10m above above “geologically unimportant” temperatures this study’s sample site) found CO2-rich solutions (25 °C), LREE will have higher Cl-ligand stability within isolated and euhedral quartz FI clusters, constants. The LREE will therefore be entrained 2+ with homogenisation temperature-pressure pairs in solution as REECl or REECl30 with the latter of ~350°C -~2.2kbar and 295°C -0.6kbar (± being prevalent at temperatures above 300 °C. 0.06kbar) respectively. This may be sourced from This theory could also be invoked for the either pressure and crystallisation related- introduction of La and Ce into synchysite degassing from deeper mafic enclaves contemporaneously with titanite destabilisation. (Lowenstern, 2001; Stussi et al., 2002) or from the As seen from Fig. 4a, there is a substantial influx of meteoric water that has interacted with increase in the percentage of La in the REE from carbonate/organic-rich sedimentary units (Fouillac “parental” titanite to synchysite or monazite, and Genter, 1992). indicating the destabilising fluid was enriched in Upon ingress of a CO -rich solution, chloritisation the very LREE. This enrichment may originate 2 from high concentrations of Cl- in solution during of biotite would have liberated portions of Fe and Mg cations, now available for ankerite formation. allanite destabilisation. Upon precipitation of Similarly, CO is integral to the formation of this resultant metasomatic phases, residual La and Ce 2 in solution may have complexed with available Cl- assemblage as it may not only account for the 2+ destabilisation of the primary parent phase, as REECl or REECl30 (Wood, 1990b) and been titanite (Corlett and McIlreath, 1974; Hunt and transported to the site of titanite dissolution. Consequent breakdown of chloride complexes Kerrick, 1977; William-Jones, 1981) after would then have freed-up La and Ce to be chloritisation, but also the transport of REE in - aqueous phase (Wood, 1990b). incorporated in synchysite permitting free Cl to remain in the fluid phase (Förster, 2001). An Works by Hunt and Kerrick (1977) found that at alternative theory of enrichment arises from REE 0.5 XCO2, <500 °C and 2 kbar, titanite will transport by sorption over complexation. destabilise by the following equation: Assuming a mildly acidic pH (Bau and Möller, 1991; Sanematsu et al., 2011), hydrothermal Titanite + CO Rutile + Calcite + Quartz 2 fluids may be depleted in HREE as their sorption CaTiSiO5 TiO2 + CaCO3+ SiO2 (1) strength is higher than that of their lighter counterparts in the presence of certain sheet

170 Australian Geothermal Energy Conference 2011 silicates allowing preferential mobilisation (Coppin attributing PPA the distance of transport of REY et al., 2002) in aqueous phase. Since CO2 is and Th via ligand complex was, on the most part, present in the system, the acidity can be inferred minimal. The apparent immobility is however from the formation of carbonic acid (Barclay and expected as calcium’s strong affinity for CO32- Worden, 2000) and may therefore allow sorption and F- will buffer the concentration of ligands to dominate as the REY transportation available for complexation causing mineral mechanism, hence enriching the newly forming precipitation (Salvi and William-Jones, 1990, synchysite in La and Ce. 1996). HREE (including Y; HREY) and Th on the other hand, show an increased mobility as seen

by the relative depletion of Y and Th in synchysite 40 40 (Fig 4b and c). The loss of HREY and Th may be attributed to not only the preferential incorporation of LREE (Wang et al., 1994; Förster, 2000, 2001) 30 30 into its crystal structure but also the comparatively higher stability constants for HREY (Wood, 20 20 1990b). Furthermore, the particularly large

La% of LREE of La% depletion in yttrium may indicate that in the presence of bi-ligand complexes such as 10 10 fluorocarbonates, it will act as a “heavy pseudolanthanide” (Bau and Dulski, 1995) and 0 0 hence be highly mobile. The unusual depletion of 0.000 10.000 20.000 30.000 40.000 50.000 60.000 Σ REE Th in synchysite and therefore increased mobility 14 14 of Th is potentially due to the lack of

12 12 accommodation space in synchysite resulting from La and Ce abundance but also the 10 10 3- availability of residual F-CO2 to mobilise the Th

8 8 from the site of precipitation. This finding is of great importance, as it not only implies the

Y % Y % of REE 6 6 mobility of Th in fluorocarbonate ligand-rich

4 4 solutions but also, if fluorocarbonate phases are destabilised during forced circulation-based fluid- 2 2 rock interaction, there may be regional

0 0 mobilisation of Th within the system. 0.000 10.000 20.000 30.000 40.000 50.000 60.000 70.000 ΣREE + Y

5 5 Implications and Conclusions Following emplacement at approx. 331 ± 9 Ma 4 4 (Alexandrov et al., 2001) the Soultz monzogranite (Stussi et al., 2002) underwent a succession of 3 3 hydrothermal alterations. Ignoring the preceding ubiquitous propylitic alteration (Ledésert et al., 2 2

Th % Th % of REY + Th 2010), vein-fracture-related alteration significantly modified the original mineralogy with varying 1 1 degrees of intensity. Co-genetically with carbonate and illite precipitation, multiple 0 0 accessory phases have undergone 0 10203040506070 ΣREY + Th destabilisation. Titanite, allanite and previously Fig. 4 (a) La % of REE against ΣREE, (b) % of REE + Y against Σ unfound uranopolycrase have been altered to, REE + Y and (c) Th % of REY + Th against ΣREY + Th. Green and among other minerals various incompatible Purple = titanite, synchysite = red and blue = monazite. element-bearing phases. This may therefore Following destabilisation of titanite, REY and Th provide initial insight into potential metasomatic may have been held in aqueous phase via phases by which characterise HHPGs. These speciation with soft ligands (Bau, 1991; Bau and products are not only dependent on the fluid/rock ratio and the availability of fixing anions, in this Möller, 1991) such as (bi)carbonate or 3- fluorocarbonate complexes (Wood, 1990b, a; instant CO2-F and PO4 , but also the degree of Förster, 2000) as insinuated by the presence of REY, Th and U enrichment. In K177 where synchysite and bastnaesite. These species are alteration was limited as low to moderate degrees likely to prevail over the more stable single ligand of selective alteration, CO2-F prevailed due to the F- complex (Wood, 1990b) as the abundance of metastability of apatite. free fluorine would trigger the precipitation of fluorine-bearing phases such as fluorite (Förster, 2001). As most synchysite grains form part of the pseudomorph or are either proximal to the

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Reactant Product References Titanite Synchysite ± Bastnaesite Alexandrov, P., Royer, J.-J., and Deloule, E., Allanite Synchysite + Bastnaesite +Thorite 2001, 331 ± 9 Ma emplacement age of the Soultz Uranopolycrase Rutherfordine monzogranite (Rhine Graben basement) by U/Pb ion-probe zircon dating of samples from 5km Due to its lower degree of LREE enrichment, depth: Comptes Rendus de l'Acedémie des titanite showed a smaller diversity in the Sciences, v. 332, p. 747-754. destabilisation products. The conclusive identification of synchysite however, represents its Bancroft, G.M., Metson, J.B., Kresovic, R.A., and first documented citing from titanite destabilisation Nesbitt, H.W., 1987, Leaching studies of natural in the literature. Moreover, as anatase acted as and synthetic titanties using secondary ion mass the principle TiO2, our results expand on previous spectrometry: Geochimica and Cosmochimica works (Hunt and Kerrick, 1977; William-Jones, Acta, v. 51, p. 911-918. 1981; Pan et al., 1993; Troitzsch and Ellis, 2002) Barclay, S.A., and Worden, R.H., 2000, and, in a qualitative manner, expand on the Geochemical modelling of diagenetic reactions in stability field in which titanite may destabilise a sub-arkosic sandstone: Clay Minerals, v. 35, p. under moderate pCO2. 57-67. Where alteration was pervasive and texturally Bau, M., 1991, Rare-earth element mobility during destructive from high f/r (K206), we assume a low hydrothermal and metamorphic fluid-rock pH, from abundant CO2, led to the increased interaction and the significance of the oxidation solubility of apatite. This would have allowed 2- state of europium: Chemical Geology, v. 93, p. HPO4 (Harouiya et al., 2007) in solution 219-230. therefore contributing to the prevalent phosphate- silicate over fluorocarbonate metasomatic phases. Bau, M., and Dulski, P., 1995, Comparative study K108 represents a mixture of end-member of yttrium and rare-earth element behaviours in products as seen by the presence of REY and Th- fluorine-rich hydrothermal fluids: Contributions to bearing fluorocarbonates and phosphates. With Mineralogy and Petrology, v. 119, p. 213-223. the exception of one quartz-shielded titanite grain, Bau, M., and Möller, P., 1991, REE systematics all synchysite grains are found in Mn-rich zones of as source of information on minerogenesis, in complex ankerite-illite veinlets. This coupled with Pagel, M., and Leroy, J.L., eds., Source, semi-quantitative mass balance studies (Fig 4b), Transport and Deposition of Metals: Rotterdam, and the known presence of Th in synchysite can 3- A. A. Balkema. infer the mobility of Th in solution where F-CO2 acts as the principle ligand complex. We stipulate Bea, F., 1996, Residence of REE, Y, Th and U in that, based on the enhanced mobility of HREE Granites and Crustal Protoliths; Implications for and Y in F-bearing solutions (Bau and Dulski, the Chemistry of Crustal Melts: Journal of 1995) as seen in Fig 4b, thorium may also be Petrology, v. 37, p. 521-552. mobilised in solutions where F acts a significant Coppin, F., Berger, G., Bauer, A., Castet, S., and component, such as in low pH hydrothermal Loubet, M., 2002, Sorption of lanthanides on solutions rich in fluorocarbonate or bicarbonate smectite and kaolinite: Chemical Geology, v. 182, ligands. This, in combination with previous works p. 57-68. indicating fluorine and CO2 loss during forced re- injection (Pauwels, 1997), may therefore indicate Corlett, M.I., and McIlreath, I.A., 1974, An potential thorium mobilisation during exploitation authigenic Quartz-Calcite-Rutile Assemblage in of geothermal energy. This is under the premise Ordovician Limestones: Canadian Mineralogist, v. that forced re-injection occurs through fracture 12, p. 411-416. networks accommodating carbonates ± Cuney, M., and Friedrich, M., 1987, synchysite. Physicochemical and crystal-chemical controls on Moreover, as EPMA results prove titanite to be a accessory mienral paragenesis in granitoids: substantial sink of Ca (20 wt%), this work implications for uranium metallogenesis: Bulletin illuminates an alternative source for numerous de Minéralogie, v. 110, p. 235-247. permeability-reducing (self-sealing) calcite veins Dubois, M., Ayt Ougougdal, M., Meere, P., Royer, (Pauwels, 1997; Ledésert et al., 1999). As such, J.-J., Boiron, M.-C., and Cathelineau, M., 1996, understanding the degree of titanite and whole Temperature of palaeo- to modern self-sealing rock alteration is of great importance as it may not within a continental rift basin: The fluid inclusion only influence permeability but also the chemical data (Soultz-sous-Forêts, Rhine graben, France): stimulation required for efficient hydraulic European Journal of Mineralogy, v. 8, p. 1065- connection (Ledésert et al., 2009). 1080. Exley, R.A., 1980, Microprobe studies of REE-rich accessory minerals: implications for Skye granite

172 Australian Geothermal Energy Conference 2011 petrogenesis and REE mobility in hydrothermal Enhance Geothermal System: Journal of systems: Earth and Planetary Science Letters, v. Volcanology and Geothermal Research, v. 181. 48, p. 97-110. Lowenstern, J.B., 2001, Carbon dioxide in Förster, H.-J., 2000, Cerite-(Ce) and Thorian magmas and implications for hydorthermal Synchysite-(Ce) from the Niederbobritzsch systems: Mineralium Deposita, v. 36, p. 490-502. Granite, Erzegebirge, Germany: Implications for Pan, Y., Fleet, M., and MacRae, N., 1993, Late the Differential Mobility of the LREE and Th during alteration in titanite (CaTiSiO ): Redistribution and Alteration: Canadian Mineralogist, v. 38, p. 67-79. 5 remobilisation of rare earth elements and Förster, H.-J., 2001, Synchysite-(Y)-synchysite- implications for U/Pb and Th/Pb geochronology (Ce) solid solutions from Markersbach, and nuclear waste disposal: Geochimica and Erzgebirge, Germnay: REE and Th mobility during Cosmochimica Acta, v. 57, p. 355-367. high-T alteratio of highly fractionated aluminous Pauwels, H., 1997, Geochemical results of a A-type granites: Mineralogy and Petrology, v. 72, single-well hydraulic injection test in an p. 259-280. experimental hot dry rock geothermal reservoir, Fouillac, A.M., and Genter, A., 1992, An O, D, C Soultz-sous-Forêts, Alsace, France: Applied isotopic study of water/rock interactions in the Geochemistry, v. 12, p. 661-673. Soultz-sous-Forêts granite, in Bresee, J.C., ed., Pollard, P.J., Pichavant, M., and Charoy, B., Geothermal Energy in Europe: The Soultz hot dry 1987, Contrasting evolution of fluorine- and rock project, Volume 2: Montreux, Gordon and boron-rich tin systems: Mineralium Deposita, v. Breach Science Publishers, p. 105-118. 22, p. 315-321. Gradstein, F.M., and Ogg, J., 1997, A Salvi, S., and William-Jones, A.E., 1990, The role Phanerozoic timescale: Episodes, v. 19, p. 3-5. of hydrothermal processes in the granite-hosted Gromet, L.P., and Silver, L.T., 1983, Rare earth Zr, Y, REE deposit at Strange Lake, Quebec / element distributions amoung minerals in a Labrador: Evidence from fluid inclusions: granidiorite and their petrogenetic implications: Geochimica and Cosmochimica Acta, v. 54. Geochimica and Cosmochimica Acta, v. 47, p. Salvi, S., and William-Jones, A.E., 1996, The role 925-939. of hydrothermal processes in concentrating high- Harouiya, N., Chaïrat, C., Köhler, S.J., Gout, R., field strength elements in the Strange Lake and Oelkers, E.H., 2007, The dissolution kinetics peralkaline complex, northeastern Canada: and apparent solubility of natural apatite in closed Geochimica and Cosmochimica Acta, v. 11, p. reactors ar temperatures from 5 to 50°C and pH 1917-1932. from 1 to 6: Chemical Geology, v. 244, p. 554- Sanematsu, K., Kon, Y., Imai, A., Watanabe, K., 568. and Watanabe, Y., 2011, Geochemical and Hooijkaas, G.R., Genter, A., and Dezayes, C., mineralogical characteristics of ion-adsorption 2006, Deep-seated geology of the granite type REE mineralization in Phuket, Thailand: intrusion at the Soutlz EGS site based ondata Mineralium Deposita, p. 1-15. from 5km-deep boreholes: Geothermics, v. 35, p. Stussi, J.-M., Cheilletz, A., Royer, J.-J., 484-506. Chèvremont, P., and Féraud, G., 2002, The Hunt, J.A., and Kerrick, D.M., 1977, The stability hidden monzogranite of Soultz-sous-Forêts of sphene: experimental redetermination and (Rhine Graben, France). Mineralogy, petrology geologic implications: Geochimica and and genesis: Géologie de la France, p. 45-64. Cosmochimica Acta, v. 41, p. 279-288. Troitzsch, U., and Ellis, D.J., 2002, Ledésert, B., Berger, G., Meunier, A., Genter, A., Thermodynamic properties and stability of AlF- and Bouchet, A., 1999, Diagenetic-type reactions bearing titanite CaTiOSiO4-Ca-AlFSiO4: related to hydrothermal alteration in the Soultz- Contributions to Mineralogy and Petrology, v. 142, sous-Forêts Granite, France: European Journal of p. 543-563. Mineralogy, v. 11, p. 731-741. Uysal, I.T., Gasparon, M., Bolhar, R., Zhao, J.-X., Ledésert, B., Hebert, R., Genter, A., Bartier, D., Feng, Y.-X., and Jones, G., 2011, Trace element Clauer, N., and Grall, C., 2010, Fractures, composition of near-surface silica deposits - A hydrothermal alterations and permeability in the powerful tool for detecting hydrothermal mineral Soultz Enhanced Geothermal System: Comptes and energy resources: Chemical Geology, v. 280, Rendus Geoscience, v. 342, p. 607-615. p. 154-169. Ledésert, B., Hébert, R., Grall, C., Genter, A., Vuorinen, J.H., and Hålenius, U., 2005, Nb-, Zr- Dezayes, C., Bartier, D., and Gérard, A., 2009, and LREE-rich titanite from the Alnö alkaline Calcimetry as a useful tool for a better knowledge complex: Crystal chemistry and its importance as of flow pathways in the Soultz-sous-Forêts a petrogenetic indicator: Lithos, v. 83, p. 128-142.

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Wang, L., Ni, Y., Hughes, J.M., Bayliss, P., and available low-temperature data for inorganic REE Drexler, J.W., 1994, The atomic arrangement of speciation of natural waters: Chemical Geology, v. synchysite-(Ce), CeCaF(CO3)2 The Canadian 82, p. 159-186. Mineralogist, v. 32. Wood, S.A., 1990b, The aqueous geochemistry of Watt, G., and Harley, S., 1993, Accessory phase the rare-earth elements and yttrium: 2. Theoretical controls on the geochemistry of crustal melts and predictions of speciation in hydrothermal solutions restites produced during water-undersaturated to 350°C at saturation water vapour pressure: partial melting: Contributions to Mineralogy and Chemical Geology, v. 88, p. 99-125. Petrology, v. 114, p. 550-566. Xie, L., Wang, R.-C., Chen, J., and Zhu, J.-C., William-Jones, A.E., 1981, Thermal 2010, Mineralogical evidence for magmatic and Metamorphism of Siliceous Limestone in the hydrothermal process in the Qitianling oxidised Aureole of Mount Royal, Quebec: American tin-bearing granite (Hunan, south China): EMP Journal if Science, v. 281, p. 673-696. and (MC)-LA-ICPMS investigations of three types of titanite: Chemical Geology, v. 276, p. 53-68. Wolf, M., and London, D., 1994, Apatite dissolution into peraluminous haplogranitic melts: Zen, E.-A., 1986, Aluminium Enrichment in An experimental study of solubilities and Silicate Melts by Fractional Crystallisation: Some mechanisms: Geochimica and Cosmochimica Mineralogic and Petrogrpahic Constraints: Journal Acta, v. 58, p. 4127-4145. of Petrology, v. 27, p. 1095-1117. Wood, S.A., 1990a, The aqueous geochemistry of the rare-earth elements and yttrium, 1. Review of

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