Hydrothermal Mobility of Ti, Zr and REE: Examples from the Bergell and Adamello Contact Aureoles (Italy)

Sonderdrucke aus der Albert-Ludwigs-Universität Freiburg

RETO GIERÉ

Originalbeitrag erschienen in: Terra nova 2 (1990), S. 60 - 67 OMEal, RESEARCH Hydrothermal mobility of Ti, Zr and REE: examples from the Bergell and Adamello contact aureoles (Italy)

Reto Giere Institut fur Mineralogie and Petrographie, ETH-Zentrurn, CH-8092 Zurich, Switzerland

ABSTRACT Contact metamorphic marbles, affected by metasomatic fluids at the BERGELL contact to the Bergell and Adamello Intrusives, contain various In the Bergell contact aureole (on the accessory minerals (zirconolite, allanite, titanite, rutile, geikielite, border between Switzerland and Italy) hoegbomite), which provide new evidence for the hydrothermal mobility of these elements has been in- ferred in a metasomatically altered mobility of Ti and Zr. In both examples, Ti and Zr migrated along with spinel—calcite—marble occurring at the U, Th, Y and REE in a metasomatic fluid rich in potassium. The eastern margin of the Tertiary calc- composition of the main minerals (fluorine-rich phlogopite, pargasite alkaline intrusives. Geological setting and titanian clinohumite) and the abundance of fluor-apatite and detailed mineralogy of the skarn demonstrate that fluorine and phosphorus were important were given by Giere (1986). The components of the fluid. The textural relationships indicate that the mineralogy is briefly summarized here. formation of the accessory phases is linked to the crystallization of the The contact metamorphic spinel—cal- hydrous minerals. cite—marble has been transformed by a metasomatic fluid into a coarse-grained skarn that consists mainly of fluorine- Terra Nova, 2, 60-67 bearing phologopite, anorthite and par- tially altered spinel, with interstitial relics of calcite. Textural relationships INTRODUCTION Groot, 1983; Nystrom, 1984; Robins, indicate that the spinel has been altered The rare earth elements (REE) and other 1984; Giere, 1986; Cathelineau, 1987; in three consecutive steps to (1) hoeg- trace elements such as titanium, zir- Vocke et al., 1987). The occurrence of U- bomite (a complex Fe—Mg—Al—Ti-oxide) conium and yttrium have long been REE daughter crystals in fluid inclu- or corundum+ magnetite, (2) margarite, considered to be immobile during sions infers that the REE are present in and (3) chlorite. These relationships are metamorphism or alteration. In geo- high concentrations in certain hydro- illustrated in Fig. 1, where a spinel crys- chemical studies their abundance has thermal fluids (Kwak and Abeysinghe, tal is pseudomorphically replaced by commonly been used as a critical diag- 1987). Similarly, titanite, anatase and corundum+ magnetite, which was then nostic tool to evaluate empirically the rutile in fissures from the granitic mas- overgrown by chlorite. Furthermore, petrogenesis (by chondrite-normalized sifs of the Swiss alps (e.g. Mercolli et al., the skarn contains large amounts of REE-patterns) and the tectonic setting 1984) indicate that titanium can be an fluor-apatite as well as the accessory (by the Ti—Zr—Y-discrimination diag- important constituent of metamorphic REE-bearing minerals zirconolite (ideally rams of Pearce and Cann (1973) of basic fluids. Large amounts of Ti, Zr and REE CaZrTi207), allanite and titanite, of volcanic rocks. have also been found in highly al- which zirconolite is the most abundant. There is increasing evidence, how- kaline (pH = 12), fluorine-, silica- and The Bergell zirconolites exhibit three ever, that these elements, particularly sodium-rich groundwaters from the deep discrete growth zones, each possessing the REE, may be transported by meta- zones of the Lovozero alkaline massif a distinctive chemical composition. morphic fluids under a wide variety of (Kraynov et al., 1969). Besides having markedly different geological conditions (e.g. Rudashev- This paper is a review of the current yttrium and major element (Ca, Zr, Ti) skiy, 1969; Rekharskiy and Rekhar- knowledge on the mobility of Ti, Zr and contents, the three zones are clearly dis- skaya, 1969; Sinyakov and Nepeina, REE. It provides a description and com- tinguishable on the basis of their charac- 1969; Pavelescu and Pavelescu, 1972; parison of two localities (Bergell and teristic REE patterns (for details see Zhuravleva et al., 1976; Staatz et al., Adamello contact aureoles, Italy), Williams and Giere 1988). 1977; Graf, 1977; Hellman and Hender- where contact-metamorphic marbles Because of its ability to accommodate son, 1977; Van Wambeke, 1977; Konev, have been affected by metasomatic a large variety of elements, which range 1978; Martin et al., 1978; Hellman et al., fluids enriched in the high-valence both in ionic radius and charge (30 or 1979; Ludden and Thompson, 1979; cations of the above-mentioned ele- more elements with concentrations in Alderton et al., 1980; Dostal et al., 1980; ments. This type of metasomatism is re- excess of 0.1 wt%; see Wark et al., 1974), Hynes, 1980; Taylor et al., 1981; Taylor stricted in both places to a rather narrow zirconolite provides important qualita- and Fryer, 1980, 1983; Baker and De zone along the intrusive contact. tive information on the availability of

60 1'EM2L RESEARCH

trace elements, particularly of REE, during its crystallization. In a metasomatic environment the zirconolite composition thus reflects the composition of the fluid. The chondrite-normalized REE plots of the Bergell zirconolites (Fig. 2) indicate a progressive, but stepwise evolution of the fluid from light to heavy REE enrichment during crystallization from the inner (El) to the outer (E2) zones. This three-stage crystallization seems to reflect the three-stage alteration of spinel. However, these two processes can only be linked to one another through one textural relationship observed in thin section; the crystallization of zirconolite zone El preceeds the third alteration stage, during which both the metasomatic phlogopite and

10 f the spinel have been chloritized (see Fig. 1. Photomicrograph of Bergell skarn, showing a spinel-pseudomorph consisting of Giere 1986). This means that at least one corundum (high relief)+ vermicular magnetite (opaque). The pseudomorph contains tiny zirconolite zone formed contemporan- relics of spinel (Sp, dark coloured) and is overgrown by chlorite (Chl) and margarite (Mar, eously with phlogopite. It further leads lower left side of pseudomorph). Relics of hoegbomite (Hoeg) and margarite as well as to the suggestion that the metasomatic zirconolite grains (Zirc) and fluor-apatite (Ap) are visible in chlorite. Cc = calcite. The fluid transported potassium together largest diameter of pseudomorph is 0.7 mm. with Ti, Zr, U, Th, W, Nb, Y and the 5 REE (see Williams and Giere 1988). The 10 abundance of idiomorphic fluor-apatite and fluorine-bearing phlogopite, as well as their close association with the accessory minerals that incorporate these elements, point to F - and PO43- as likely ligands for complexing the above- mentioned elements in the fluid phase.

ADAMELLO Similar metasomatism is also found at -0 4 the contact between the Tertiary c 10 Adamello batholith (northern Italy) and 0 the dolomitic country rocks. Along the contact, the hornblende- a) and biotite-bearing tonalite of the E southernmost Adamello pluton is altered to an assemblage of diopside and plagioclase, with minor titanite and calcite. The adjacent contact-metamorphic pure dolomite marbles are crosscut by dikes of altered tonalite and aplitic granite as well as by a complex system of different vein types. The mineral 3 assemblages of one vein type indicate 10 La Ce Pr Nd Sm Gd Dy Er Yb that a fluid containing Ti, Zr, REE Fig. 2. Chondrite-normalized REE plots (electron microprobe data) for the three zones of the and actinides was present during its metasomatic Bergell zirconolites. Zone El represents the core, zones E2 and E3 form rims formation. around El and E2 respectively. The distinct REE patterns reflect a progressive, but stepwise This vein type is characterized by four evolution of the fluid from light to heavy REE enrichment during the three-stage alteration of mineralogically distinct zones, separ- the skarn. Shaded areas show range of values within each zone. Chondrite values after Wakita ated from each other by sharp bound- et al. (1971). Diagram from Williams and Giere (1988). aries. From the vein centre to the rim,

61 taV 0RRhL RESEARCH

the following assemblages occur (see Titanium is a major element in the rutile (see Fig. 3). Fig. 3): three central assemblages: this is dem- Two generations of zirconolite can be (1) titanian clinohumite + Vanadium- onstrated by (a) the occurrence of tita- distinguished on the basis of their com- rich spinel+ calcite + sulphides, nian clinohumite as a main constituent position and crystal shape: in the tita- (2) phlogopite + calcite + titanite + sul- in one zone, (b) the abundance of nian clinohumite zone, zirconolite is phides, titanite in the pargasite and phlogo- present as idiomorphic (Fig. 4), U- and (3) pargasite+ calcite+ titanite+ sul- pite zones, and (c) the presence of Th-rich crystals with low REE contents phides, various accessory Ti-minerals—zircono- [UO2 = 11.7 wt%, Th02 = 6.9 wt%, (4) forsterite + calcite. lite, geikielite (Mg-analogue of ilmenite), (REE203 + Y203) = 2.3 wt% ], whereas, in the phlogopite zone it occurs as xenomorphic (Fig. 5) grains characterized by lower U and Th contents and generally higher, but variable REE con- TiCl+Sp+Cc+Sult. centrations [UO2 = 2.2 wt%, Th02 = (Zirc, Ap, Geik) 3.5 wt%, (REE203 + Y203) = 2.1-17.5 wt%; R. Giere and C.T. Williams, in preparation]. Sulphides, mainly pyrrhotite and chalcopyrite, as well as idiomorphic fluor-apatite (Fig. 6), are found in all the Ti-rich vein zones. The main minerals in • • • • these zones are hydrous silicates (tita- •

• nian clinohumite, pargasite, phlogo- • • • • • • • pite) with high proportions of their • • • • . • • • OH- groups substituted by F - (R. Giere, in preparation). No apatite has so far been found in the forsterite + calcite zone which does not contain any of the accessory phases rich in Ti, Zr, Y and REE. Whole-rock Nd isotopic data for the three central zones show only little variation (ENd = –2.1 to –2.5 at t = 40 Ma, Phlog+Cc+Tit+Sulf i.e. time of intrusion); they are iden- (Zirc, Ap, Rut) tical or close to the data for the unaltered hornblende—biotite—tonalite (ENd = –2.5), but significantly different from those for the altered tonalite at the immediate contact with the dolomite marble (E Nd = –4.4, Giere et al., 1988). The preliminary Nd data indicate that

• • . . . • . • • : . . . • . the vein-forming fluid was isotopically • • • different from the fluid involved in the • • • • Parg+Cc+Tit+Sulf above-mentioned alteration of the tona-

• • lite. The data also point to a Nd-isotope • (Ap, Phlog) • • • • • • • equilibrium between the fluid and the • • • unaltered tonalite, which suggests that • • the veins have been generated during the emplacement of the tonalite (Giere et al., 1988). A syn-intrusive formation • ..... of the veins is also implied by the field ..... relationships...... The differences in composition of zir- • • • 5 cm conolite in the phlogopite and the titanian clinohumite zones most probably Fig. 3. Mineralogical map of a Ti- and Zr-rich vein in contact metamorphic dolomite marble reflect a change in trace element content (Do) from the Adamello contact aureole. Fo = forsterite, TiC1 = titanian clinohumite, of the metasomatic fluid. Xenomorph- Phlog = phlogopite, Parg = pargasite, Sp = spinel, Cc = calcite, Tit = titanite, ism and compositional variability of zir- Sulf = sulphides, Rut = rutile, Ap = apatite, Zirc = zirconolite, Geik = geikielite. conolite within the phlogopite zone Black areas represent large aggregates of sulphides (pyrrhotite, chalcopyrite) might be due to partial dissolution and

62 M OEM RESEARCH

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63 (aV: OMMff, RESEARCH

fluid was enriched in the trace elements of interest: important information, however, can be provided by isotope data. In the Adamello example, the Nd data suggest that the vein-forming fluid was in Nd-isotope equilibrium with the unaltered tonalite. Furthermore, the carbon and oxygen isotope data for the pure dolomite marble, the vein calcite (from all mineral zones) and the tonalite 50.00P WDSWDS 15.0100 50.00P WDSWDS 15.0 (see Fig. 7) point to a fluid that has been derived from the tonalite and diluted by wall rock (dolomite) components. These results indicate a magmatic (ton- alitic) origin of the vein-forming fluid, and suggest that the trace elements were fractionated into the fluid during its separation from the melt, and not during the alteration of the tonalite which was caused by a fluid from a different source.

Fig. 6. Characteristic X-ray distribution pictures of Ca, P, Mg and Si, showing an Transport idiomorphic fluor-apatite crystal enclosed in titanian clinohumite from the central zone, The nature and activity of dissolved Adamello veins (see Fig. 3). Electron microprobe analytical conditions were 15 kV and 20 nA anionic or molecular species in the fluid measured on a Faraday cage (Cameca SX-50). play an important role not only during the mobilization of these metals, but also during their transport. Although leaching by the fluid at a later stage of haviour of these elements in fluids, and few data are available, it has been vein formation (i.e. during the genera- most of them deal with the REE only. demonstrated both empirically (in field tion of the titanian clinohumite zone). Consequently, little is known about the studies, references cited) and experi- The high F-contents of titanian processes responsible for (1) their mentally (Kosterin, 1959; Balashov and clinohumite, pargasite and phlogopite, mobilization by the fluid in the source Krigman, 1975; Flynn and Burnham, as well as the abundance of fluor- area, (2) their transport in the fluid, and 1978; Bilal and Becker, 1979; Bilal et al., apatite, indicate that fluorine and (3) their deposition as metasomatic 1979; Bilal and Koss, 1980a,b; Nguyen, phosphorus were important compo- minerals in veins or skarns. 1985), that the anions F - , Cl- , 0H-, nents of the metasomatic fluid during CO32-, SO42- and PO43- can be effective the formation of the three Ti-, Zr- and ligands for complexing REE and U. Mobilization REE-rich mineral zones. The origin and Mobility of Ti and Zr seems to be significance of sulphur in the veins is Mobilization of these trace elements can favoured by relatively high activities of not yet understood on the basis of the be caused either by separation of a fluid CO2 (Hynes, 1980), B - (Alderton et al., currently available data. phase from the melt in magmatic envi- 1980; Konev, 1978) or F- and PO43 ronments or by alteration processes (Kraynov et al., 1969; Giere, 1986) in (e.g. dissolution, leaching) involving metasomatic fluids; they also migrate in DISCUSSION magmatic, metamorphic or meteoric surface waters at ambient temperatures The examples from the Bergell and the fluids. This is indicated by experimental and pressures, mainly because of com- Adamello contact aureoles provide new investigations on the partitioning of plex formation with humic and fulvic evidence for migration of elements that REE between vapour and melt and be- acids (e.g. Samchuk and Sushchik, commonly are regarded as immobile. In tween vapour and crystals; the experi- 1986). Furthermore, the mineralogy of both cases, these elements mainly comments demonstrate that the extent of many Ti- and Zr-rich skarns or veins prise Ti, Zr, U, Th, REE and Y, all of REE partitioning into the fluid is suggests that these metals migrated in which are characterized by a high- strongly dependent on pressure and those cases along with potassium and/or valent ionic state. temperature as well as on melt, crystal sodium (e.g. Moleva and Myasnikov, Many studies show that these ele- and fluid composition (Cullers et al., 1952; Semenov et al., 1963; Mineyev, ments, particularly the REE, are mobile 1973; Balashov and Krigman, 1975; 1963; Zhuravleva et al., 1976; Konev, under a wide variety of physical and Flynn and Burnham, 1978; Mysen, 1979; 1978), possibly as mixed-metal polynuc- chemical conditions (references cited Wendlandt and Harrison, 1979). lear complexes with K± or Na + (see also earlier). Unfortunately, there are very It is difficult to determine the charac- Bandurkin 1961). However, veins that few experimental studies on the be- teristics of the environment where the contain titanian hydroxyl-clinohumite,

64 OMIEJL RESEARCH

perovskite and hydroxyl-apatite from ever speciation) in the metasomatic high-valence cations), resulting in their the Malenco serpentinites, northern fluid during formation of the skarn precipitation. Italy (Trommsdorff and Evans, 1980) (Bergell) and the mineral zones rich in However, in the Bergell and demonstrate that the transport of Ti, Zr, U, Th, Y and REE (Adamello). Adamello examples, the textural re- titanium is not restricted to fluids rich in Furthermore, the occurrence of abun- lationships observed in thin section in- potassium or fluorine. dant sulphides (Adamello only) and cal- dicate a different cause for precipitation A more direct inference on fluid com- cite indicates the presence of sulphur of the trace elements: a decrease in positions can be drawn either from the and CO2 as well. A more quantitative ligand activity of the fluid due to crystal- analysis of ground waters and waters approach to determining the fluid com- lization of hydrous minerals. The latter from active hydrothermal systems (e.g. position is currently underway by ap- (Bergell: phlogopite, apatite; Adamello: Kraynov et al. , 1969) or from analysis of plying experimentally determined phlogopite, pargasite, titanian clinohu- fluid inclusions in vein or skarn miner- fluid/mineral exchange equilibria to mite, apatite) are generally idiomorphic als; Kwak and Abbeysinghe (1987), for some Adamello vein minerals. (see Fig. 6) and closely associated with example, demonstrated in their fluid in- the accessory phases that incorporate clusion study that a high-temperature the high-valence cations. Similar tex- Deposition (550-670°C), saline (30-70 wt% total tural relationships have also been re- dissolved salts, mainly CaC12) and The deposition of these trace elements ported from other localities (Moleva and oxydizing ore solution was able to as metasomatic minerals is closely Myashnikov, 1952; Semenov et al., 1963; transport large quantities of REE and U. linked to changes in temperature and Zhuravleva et al., 1976; Konev, 1978), Unfortunately, no fluid inclusions fluid composition. Both an increase in and support the hypothesis of trace ele- suitable for analysis have been found in salinity of the fluid, due to its reaction ment deposition caused by a lowering the Bergell or the Adamello rocks. How- with the wall rock (e.g. Kwak and of ligand activity due to crystallization ever, the composition of the main min- Abeysinghe 1987), or a temperature de- of hydrous minerals (including apatite). erals (including fluor-apatite) implies crease in space or time could cause A better understanding of these pro- relatively high activites of fluorine, supersaturation with respect to less sol- cesses is not only required for a petro- phosphorus and potassium (in what- uble compounds (e.g. complexes with genetic interpretation of veins and skarns rich in these metals, but also for the exploration of their economically 3 important ore deposits. Mobilization of radioactive elements, in particular, is dolomite one of the main concerns in evaluating 2 - possible disposal options for high-level nuclear waste. Currently, the most • veins promising form for immobilization of 0 1- radioactive waste is a synthetic titanate tonalite ceramic (SYNROC-C), in which zirconolite is the principal host for Zr and 0 tetravalent actinides as well as one of a the most resistant phases with res- a pect to hydrothermal leaching (e.g. a- -1 Ringwood and Kelly, 1986). Detailed petrographic studies and determination of the composition of metasomatic -2 fluids that coexisted with naturally occurring zirconolite may provide further information on the leaching behaviour -3 - of zirconolite in ceramic waste forms.

CONCLUSIONS 10 20 30 The following conclusions can be drawn from the comparison of the Bergell 8180 skarn and the Adamello veins. (SMOW) [0/00] (1) In both examples Ti and Zr migrated Fig. 7 . 8"C vs. 8 180 diagram for the Adamello samples. The dolomite field represents the in the metasomatic fluid along with U, range of values for the pure, dolomite marble wall rock unaffected by metasomatism. The 8I3C Th, Y and REE. and 8 180 values for calcite from all four vein zones (see Fig. 3) show only little variation and (2) Potassium was an important con- are markedly lower than all data for dolomite. The tonalite field represents the whole rock 8180 stituent of the metasomatic fluid trans- data only (no values for 8 13C for tonalite because of its very low carbon contents). porting the high-valence cations (in the

65 OEM1, RESEARCH

Adamello at least during two stages of bearing model system at various ionic P. (1979) The mobility of rare earth ele- vein formation). strengths, J. Inorg. Nucl. Chem., 41, ments: Evidence and implications from (3) The Nd isotopic data (Adamello) 1607-1608. selected terrains affected by burial suggest a magmatic origin of the REE Bilal B.A., Herrmann F. and Fleischer W. metamorphism, Contrib. Miner. Petrol., and, in combination with oxygen and (1979) Potentiometric study of fluoro 72, 81-85. carbon isotope data, of the fluid itself. complexes of rare earth elements in Hynes A. (1980) Carbonatization and (4) The composition of the main miner- fluorite bearing model systems, J. Inorg. mobility of Ti, Y, and Zr in Ascot Forma- als (including apatite) suggest F - and Nucl. Chem., 41, 347-350. tion metabasalts, SE Quebec, Contrib. PO43- to be the most likely ligands for Bilal B.A. and Koss V. (1980a) Studies on Miner. Petrol., 75, 79-87. complexing of the high-valencece the distribution of fluoro complexes of Konev A.A. (1978) Les mineraux de titane cations. rare earth elements in fluorite bearing et de zirconium dans les skarns du mas- (5) Deposition of the trace elements is model systems, J. Inorg. Nucl. Chem., 42, sif alcalin de Tagerane (Baikal, Siberie), probably induced by the lowering of 629-630. Bull. Mineral., 101, 387-389. ligand activity in the fluid, resulting Bilal B.A. and Koss V. (1980b) Study on Kosterin A.V. (1959) The possible modes from crystallization of the hydrous the distribution of sulfatocomplexes of of transport for the rare earths by hydro- minerals. rare earth elements in fluorite bearing thermal solutions, Geochem. Int., 4, (6) Ti, Zr and REE are mobile under cer- model system, J. Inorg. Nucl. Chem., 42, 381-387. tain geological conditions, and there- 1064-1065. Kraynov S.R., Merkov A.N., Petrova fore, extreme caution is needed in the Cathelineau M. (1987) U-Th-REE mobility N.G., Baturinskaya I.V. and Zharikova interpretation of altered rocks on the during albitization and quartz dissolu- V.M. (1969) Highly alkaline (pH 12) basis of their trace element contents and tion in granitoids: evidence from south- fluosilicate waters in the deeper zones proportions only. east French Massif Central, Bull. of the Lovozero massif, Geochem. Int., Mineral., 110, 249-259. 6/4, 635-640. Cullers R.L., Medaris L.G. and Haskin ACKNOWLEDGEMENTS Kwak T.A.P. and Abeysinghe P. B. (1987) L.A. (1973) Experimental studies of the Rare earth and uranium minerals pres- I would like to thank Dr Hugh J. Green- distribution of rare earths as trace ele- ent as daughter crystals in fluid inclu- wood (University of British Columbia, ments among silicate minerals and sions, Mary Kathleen U-REE skarn, Vancouver), Drs Volkmar Trommsdorff liquids and water, Geochim. Cosmochim. Queensland, Australia, Mineral. Mag., and Felix Oberli (both ETH Zurich), and Acta., 37, 1499-1512. 51, 665-670. Drs Terry Seward and Peter Blattner Dostal J., Strong D.F. and Jamieson R.A. Ludden J.N. and Thompson G. (1979) An (both DSIR, Lower Hutt, New Zealand) (1980) Trace element mobility in the evaluation of the behavior of the rare for their comments and critical reviews. mylonite zone within the ophiolite earth elements during the weathering of The financial support from the aureole, St. Anthony Complex, New- sea-floor basalt, Earth Planet. Sci. Lett., Schweizerischer Nationalfonds (Grant foundland, Earth Planet. Sci. Lett., 49, 43, 85-92. No. 2000-5.240) and from the Univer- 188-192. Martin R.F., Whitley J.E. and Woolley sity of British Columbia is gratefully Flynn R.T. and Burnham C.W. (1978) An A.R. (1978) An investigation of rare- acknowledged. experimental determination of rare earth mobility: Fenitized Quartzites, earth partition coefficients between a Borralan Complex, N. W. Scotland, Con- chloride containing vapor phase and trib. Miner. Petrol., 66, 69-73. REFERENCES silicate melts, Geochim. Cosmochim. Mercolli I., Schenker F. and Stalder H.A. Alderton D.H.M., Pearce J.A. and Potts Acta., 42, 685-701. (1984) Geochemie der Veranderung von P.J. (1980) Rare earth element mobility Giere R. (1986) Zirconolite, allanite and Granit durch hydrothermale LOsungen, during granite alteration: Evidence from hoegbomite in a marble skarn from the Schweiz. Mineral. Petrogr. Mitt., 64, south-west England, Earth Planet. Sci. Bergell contact aureole: implications for 67-82. Lett., 49, 149-165. mobility of Ti, Zr and REE, Contrib. Mineyev D.A. (1963) Geochemical dif- Baker J.H. and De Groot P.A. (1983) Miner. Petrol., 93, 459-470. ferentiation of the rare-earths, Geochem. Proterozoic seawater-felsic volcanics Giere R., Oberli F. and Meier M. (1988) Int., 12, 1129-1149. interaction. W. Bergslagen, Sweden. Mobility of Ti, Zr and REE: Mineralogi- Moleva V.A. and Myasnikov V.S. (1952) Evidence for high REE mobility and im- cal, geochemical and isotopic evidence On hoegbomite, and its variety zinc- plications for 1.8 Ga seawater composi- from the Adamello contact aureole hoegbomite. Dokl. Akad. Nauk. SSSR, tions, Contrib. Miner. Petrol., 82, 119-130. (Italy), Chem. Geol., 70(1/2), 161 83/5, 733-736 (in Russian). Balashov Y.U.A. and Krigman L.D. (1975) (abstract). Mysen B.O. (1979) Trace-element par- The effects of alkalinity and volatiles on Graf J.L. (1977) Rare earth elements as titioning between garnet peridotite rare-earth separation in magmatic sys- hydrothermal tracers during the forma- minerals and water-rich vapor: experi- tems, Geochem. Int., 12/6, 165-170. tion of massive sulfide deposits in vol- mental data from 5 to 30 kbar, Am. Bandurkin G.A. (1961) Behavior of the canic rocks, Econ. Geol. 72/4, 527-548. Miner., 64, 274-287. rare earths in fluorine-bearing media, Hellman P.L. and Henderson P. (1977) Nguyen T.C. (1985) Geochimie theorique Geochem. 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