A Fluid-Inclusion Study and Genetic Model of Wolframite-Bearing Quartz Veins, Garganta De Los Montes, Spanish Central System

A fluid-inclusion study and genetic model of wolframite-bearing quartz veins, Garganta de los Montes, Spanish Central System

E. OUILEZ, J. SIERRA AND E. VINDEL Departamento de Cristalografia y Mineralogia, Facultad de C.C. Geologicas, Universidad Compiutense, 28040 Madrid, Spain

Abstract Wolframite-bearing quartz veins from Garganta de los Montes, Madrid province, are hosted by banded gneisses that have undergone intense migmatization processes. The ore deposit is closely related to the La Cabrera granitic batholith. The veins strike 075 ~ and dip 75~ The mineral association includes wolframite, quartz and minor amounts of scheelite and sulphides (sphalerite, chalcopyrite, pyrrhotite, stannite and marcasite). The fluid phases associated with quartz from the vein margin (early barren quartz) and from the vein centre (late wolframite-bearing quartz) have been studied using microthermometry, scanning electron microscopy and crushing test analyses. Four hydrothermal stages have been distinguished. The earliest fluids, only recognized in the barren quartz, contain brine, daughter phase (halite) and trapped minerals. The second hydrothermal stage is characterized by complex carbonic-aqueous inclusions of low salinity (3 to 7 wt.% eq. NaC1) and low density (0.4 to 0.7 g.cm-3). They mainly homogenize into liquid between 300 and 420 ~ The third stage is represented by low to moderate salinity inclusions (<9 wt. % eq. NaCI) of moderate density (0.8 to 0.96 g.cm-3), homogenizing between 120 ~ and 330~ The latest fluids correspond to aqueous solutions of higher salinities (H20-NaCI , with Ca 2+ and Mg 2+) and densities (>1 g.cm-3), with TH ranging between 50 and 130~ The role of the complex-carbonic aqueous fluids in the transport and precipitation of tungsten is highlighted. KEYWO RO S: fluid inclusions, wolframite, quartz, Spanish Central System.

Geological setting terized by neosomes forming light and dark layers in the paleosome, generally parallel to the plane T n E wotframite-bearing quartz veins of Garganta de los Montes are located in the central part of of schistosity. Ptygmatic structures exhibit highly the Spanish Central System, on the northern mar- disharmonic, tortuous folds. The migmatites gin of the La Cabrera granitic batholith. This zone showing schlieren structures are formed by lami- is characterized by the presence of pre-Ordovician nar flow and finally in nebulitic structures paleo- lithologies affected by medium- to high-grade some and neosome can no longer be identified regional metamorphism (Fig. 1). separately. Migmatites with granitic facies can be The tungsten deposit is hosted by banded recognized in the deepest zones ('diatexites'). gneisses belonging to the B1 member of the Bui- The pluton of La Cabrera constitutes the only trago Formation (Fernfindez Casals, 1974) of peli- granitic outcrop of the area. It corresponds to an tic provenance, in which layers of quartz, feldspar evolved granitic intrusion of calc-alkaline trend, and cordierite alternate with biotite-sillimanite composed of granites and granodiorites at the layers. margins (310 +_ 14Ma, 280 + 5 Ma; Vialette etal., The high metamorphic grade to which these 1981). Numerous aplitic and pegmatitic bands can rocks were subjected has led to the progressive be recognized in the granite and in the surround- formation of migmatitic structures. According to ing metamorphic rocks. The last ones introduced descriptive field work, stromatic, ptygmatic, tourmaline and muscovite, corresponding to schlieren and nebulitic structures are dis- later, more differentiated bodies. tinguished. The stromatic structures are charac- Compared to analyses of 'average' granites, Mineralogical Magazine, June 1990, Vol. 54, pp. 267-278 (~ Copyright the Mineralogical Society 268 E. QUILEZ ETAL. / / /

AUGENGNEISSES ~ LLANDEILO

~ +'1"+++4-+§ " ++'t- ~+ § + "b "t'+.

r + +++++ + + + +

o ~ io 15 20 2eKm. I. a I I

Fro. 1. Geological map of the Spanish Central System, showing study area (Capote et al., 1977). those of La Cabrera show increased SiO 2 and K20 The mineral assemblage was first described by contents and lower FeO, MgO, CaO and TiO 2. Canepa (1968) and later revised by Vindel (1980). Minor element analyses reveal an enrichment in The dominant constituent of the veins is massive Pb, Rb and Th, with a deficiency of Ba, Ca and quartz. Wolframite is concentrated as irregular Zr (Bellido, 1979). They also contain normative pods in the vein centre, suggesting that pre- corundum and, therefore, show characteristics of wolframite quartz occurs in the vein margins. 'specialized granites', spatially and genetically Accessory scheelite is the product of alteration related to Sn-W ore deposits (Tischendorf, 1977). of wolframite. Minor amounts of sulphides (sphalerite, chalcopyrite, pyrrhotite, stannite and marcasite) have been found in this study, occur- Tungsten-bearing quartz veins ring in cavities and fractures in wolframite and The ore deposit consists of four main veins quartz. Covellite, chalcocite and goethite replace striking 075 ~and dipping 75 ~ southward. The veins primary minerals (Fig. 2). vary in width from I to 2 m, and show en echellon As a result of the hydrothermal process, altera- structure in the horizontal direction. Ore was tion affected the wallrocks adjacent to the wolfra- extracted between 1948 and 1955. mite-bearing quartz veins. It is difficult to WOLFRAMITE-BEARING QUARTZ VEINS 269

PRIMARY MINERALS SECONDARY MIN 1

Q - W PERIOD SULPHIDE PERIOD

Wolframite A

Quartz

Scheelite

Sl~halerite

Cholcopyrite T-l- T t PyrrhOtlte -f I Stonnitl

Morcoslte L{ Covellite Chalcosite

Goethite A

FtactutQ Dho$11 19. R eDlacement processes --~- Exsolution processet FIG. 2. Mineral paragenesis in the main mineralized stages of the Garganta de los Mantes tungsten deposit. establish the actual spatial distribution of this Subtype IIA: Three-phase inclusions at room alteration because granite emplacement induced temperature. a wide thermal contact-metamorphic aureole. In Subtype IIB: Two-phase inclusions at room tem- spite of this, quartz-sericitization and chloritiza- perature. tion are recognized as the most important types Type llh Low to moderate-salinity aqueous in- of hydrothermal alteration. clusions (H20-NaC1). Type IV: Mixed-salt aqueous inclusions (HzO-NaC1 and other chlorides). Fluid-inclusion study: types of fluid inclusions Type I inclusions are present only in the quartz In order to define the nature and physicochemi- from the vein margin and they are usually iso- cal evolution of the mineralizing solutions, fluid lated. They contain brine, a gas bubble (10-30% inclusions in massive microcrystalline quartz have of the total inclusion) and one or several solids. been studied using microthermometry, crushing Type II. Two subtypes have been distinguished test analyses and SEM, with EDS analysis of solid here. Subtype IIA inclusions are three-phase phases. inclusions at roem temperature, containing liquid The quartz samples were collected wherever CO2, CO2 vapour and aqueous phase. They have possible from both the vein margin (V/M) and subrounded shapes and usually occur isolated in from the vein centre (V/C), i.e. early barren the quartz from the vein centre, whereas they are quartz and later wolframite-bearing quartz re- scattered along healed fractures at the margin. spectively. Inclusion sizes range from 5 to 25 ~m. These inclusions are the most abundant in the On the basis of their microthermometrically- quartz of the Garganta de los Mantes deposit. calculated chemical composition and the phase Subtype IIB are two-phase at room tempera- ratios observed at room temperature, four main ture. Vapour occupies between 30 and 70% of types of fluid inclusions have been recognized: the total volume. These fluid inclusions are isolated and extremely abundant at the vein centre, Type I: Inclusions containing brine, daughter while they occur only rarely in healed fracture phases, and trapped minerals. planes at the margins. Type H: Complex carbonic-aqueous inclusions. Type III inclusions are two phase, aqueous and 270 E. QUILEZ ETAL.

i 7

I"3 13d r,"

Cl ~ tJU

+~ (:30 gul~ (DO 40 0 "~ ~q D ~ ,~ ~ /x A ZZ

~ o ~ t- t

o o) o I § O ~ ,-~ LD tu(j rU O

OO i ~ o ZZ +

o co o] i:z:~

H (_1 ,~ ,~ ,-3 0 i I~ 03 H Z p~ O] 0 ~ 03 O] + + e,l I,Ll --1 m ~,o~ - e4 o ~; 0 O U IN 04 I I ~ &~ Z '~ O i.{-, tq ~ + i + g~ (j x3 o o ~ 5 % ~ ~, 5o 03 .,2 ~, .l~ ~ i"q uq H :t-~ o~ g% '~ "'o pi [-, u] ~ U ;z; cq I -t- / +

dd O O ~ u3 [.J 1::3 ~ ~ 123 + + g

+ OZ A 03

-8 ~ o + '5

Z +i 0 :i (3 i.-4 n." o m I~ L9 h

.~ III O ..9 O~ 0 ~ .~ ~f.z4 rYZ ~ ZZ ,Y,Y

Ill

u >. h~ ~ ~0 t.3 D 03 ~O 0 WOLFRAMITE-BEARING QUARTZ VEINS 271

TYPE~A

A VIC

" =b Zl ~ =3 =4 Z5 ~ ~ ~ Zg 3O ~l 3a TPt~2 _ a, , .~" " -,~ " -~3 A, " -. -~T -ss

T~ co 2

N v/c

20 7--1VlCv,~ .

. ,. ~ , ,~, ,~ ..;F, o 9 ~o t z ~ eL <'z]o - zso =7o ' =~Do 3~o ~3o 3~o 370 39o" ,rio 4~0 v.

FIG. 3. Microthermometric data of type IIA inclusions. V/C: vein centre V/M: vein margin. A, melting temperature of CO 2 (TmCO2); B, melting temperature of clathrate (Tmclath); C, partial homogenization of CO 2 (THCO2); D, total homogenization (TH) (All in ~ irregularly shaped, with vapour bubbles amount- the dissolution of the solids. The inclusions de- ing to between 10 and 50% of the total volume. crepitated between 280 and 450 ~ At 450 ~ the They always occur along secondary healed frac- solids are almost dissolved; consequently this tem- ture planes in the centre, as well as in the vein perature would be near to the total homogeniza- margin. tion. This observation indicates that these Type IV inclusions are mixed-salt, aqueous, inclusions probably correspond to the highest- two phase inclusions at room temperature and the temperature fluids of the deposit. volume of the gas bubble comprises 5-10% of Sometimes the crystals contained in these in- the total inclusion. They are scarce in the studied clusions remained unchanged during heating. samples and always located in healed fractures. Type H. Subtype IIA: the occurrence of CO 2 is indicated by the nucleation of solid CO~ between -95 and -100~ during cooling and by the formation of a solid phase considered to Microthermometric data be clathrate during the subsequent heating. Microthermometric investigations have been The microthermometric data, melting tempera- performed with a Chaixmeca heating-freezing tures of CO 2, melting temperatures of clathrate, stage of the type described by Poty et al. (1976), partial homogenization of CO2 and total homo- using doubly-polished sections of 0.3ram thick- genization of the inclusions are displayed in Fig. 3. ness. Table 1 summarizes the microthermometric The carbonic phase is not pure carbon dioxide features. as these inclusions exhibit melting temperatures Type I inclusions. The disappearance of the of solid CO 2 between -56.6 ~ (CO 2 triple point) vapour phase occurs in the range 160 to 340~ and -69 ~ and occasional clathrate melting tem- However, total homogenization was never peratures above +10~ (Hollister and Burruss, achieved due to decrepitation occurring before 1976; Swanenberg, 1979). 272 E. QUILEZ ETAL.

TYPE- II - B N TYPE~r Frequency A

~J V/C

,, A [ I V/M ~v,c 14 r--Iv,, ~z _1

z 4 5 I II 12 5 S 7 8 9 ~0 wt ~'/eer NO CI l"m~t"

Frequency

B ~] V/C -~V/M

V/C I I v-'

. . . , ...... : : : : : :

FiG. 5. Type Ill fluid inclusions. A, salinity expressed in wt.% eq. NaCI; B, homogenization temperatures Z40 Z60 ZeO 300 320 34O T H (TH) (All in ~

FIG. 4. Type IIB fluid inclusions. A, melting temperature of clathrate (Tmclath); B, homogenization temperatures (TH) (All in ~ mation of liquid CO 2 are not observed in these inclusions. The occurrence of small amounts of carbon dioxide and other volatiles is indicated by the formation, at moderately low temperatures, These inclusions homogenize at temperatures of a solid phase considered to be clathrate due ranging between 300 ~ and 420 ~ although most to its melting temperature of between 6~ and 10 ~ of the values are concentrated between 350 ~ and (Fig. 4A). 370~ Homogenization occurs mainly into the The fact that liquid CO 2 has never been liquid phase. observed indicates that the amount of CO 2 and The aqueous phase is a dilute brine with salini- volatiles in the fluid phase is small. Homogeniza- ties between 3 and 7 wt. % eq. NaC1. The salinities tion temperatures are between 280 ~ and 350~ were determined by clathrate melting and by the (Fig. 4B). depression of freezing point due to the effect of Type Ili inclusions. This type of inclusion is dissolved CO2 in the aqueous phase (Collins, less abundant than Type II. The temperature of 1979). the first observable melting of ice takes place The density of the inclusions ranges from 0.4 around -20~ These results suggest that the to 0.75 g.cm -3. The calculation is based on the aqueous solution contains mainly Na + cations in knowledge of the composition and density of the solution. The final melting temperature of ice aqueous and carbonic phases at a temperature of values range between -0.8 ~to -5.7 ~ indicating <31~ a salinity lower than 9 wt.% eq. NaCI, with most Subtype liB: Nucleation of solid CO 2 and for- between 7 and 8 wt.% eq. NaCI (Fig. 5A). WOLFRAMITE-BEARING QUARTZ VEINS 273

TYPE-IV Electron microscope data r~.enay VlC Qualitative analysis of the solid phases con- A tained in the Type I inclusions was undertaken 2 by electron microscopy with coupled energy- dispersive detectors. The determinations were performed combining the morphology of the 1 solids with qualitative chemical analysis. Solid phases found in the cavities are halite cubes (as a daughter mineral) and lamellar muscovite (probably a trapped mineral). r ~'~ ~6 I'e ' ~o' :' i, I ~s' /e' ~' 3'2 ' 3', ' ~'e ' 4k wt % e~,Nacl Crushing tests The crushing-test analyses were carried out using a Chaixmeca crushing stage. The exper- iments were carried out on 8 samples: 5 on wolframite-bearing quartz from the vein centre (V/C) B ~ V/C and vein margin (V/ME, V/MW, V2/MW, V3/ E~ Vl M ME), 1 on wolframite (V/C), 1 on the barren quartz vein and 1 on the pegmatite. Between 5 and 10 crushing tests were performed on every sample. The liberated gas intensity was evaluated using the crushing test of Leroy (1979). Histograms of crushing-test analyses (Fig. 7) exhibit the following characteristics: (1) The liberated gas intensity from the quartz ~ 5 ~ 16o .b la'o i o r. of the vein centre (V/C) was strong (Fig. 7a), F]6.6. Type IV fluid inclusions. A, approximate salinity whereas that from the quartz of the vein margin expressed in wt.% eq. NaCI; B, homogenization tem- (V/ME, V/MW, V2/MW, V3/ME) was inter- peratures (TH) (~ mediate (Fig. 7b, c, d and e). (2) Wolframite shows very strong liberated gas intensity (Fig. 73'). (3) The barren quartz vein and pegmatite also Homogenization temperatures are widely scat- show strong liberated gas intensity (Fig. 7g and tered between 120~ and 330 ~ (Fig. 5B). All in- h). clusions homogenize into the liquid phase. The data above indicate that fluids trapped Densities for these inclusions (0.8 to throughout the vein complex contain consider- 0.96 g.cm -3) were calculated using the homogen- able quantities of gaseous carbonic compounds. ization temperatures and salinities of Ahmad and These results agree with the microthermometric Rose, 1980. analyses, thus indicating that the liberated gas Type IV inclusions. On cooling, these inclusions intensity decreases from the centre towards the exhibit special characteristics: the ice begins to vein margin. The presence of those gases in melt between -40 ~ and -60 ~ and the final melt- wolframite suggests some relation between this ing temperature of ice ranges from -22.3 ~ to mineral and the CO2-aqueous fluids. The im- -11.7~ portant amount of gas liberated by the pegamtite In accordance with the eutectic temperatures indicates the relevance of carbonic vapours in the and the final temperatures of ice-melting, it is last stage of the granite evolution. likely that the trapped solution contains significant amounts of CaC12 or MgC12 (Crawford, Hydrothermal evolution of the Garganta de los 1981). The approximate value of the salinity in Montes deposit terms of the final melting temperature of ice is over 15 wt. % eq. NaC1 (Fig. 6A). Estimation of the fluids' thermobarometric con- During heating, these inclusions homogenize ditions was made on the basis of the microther- into the liquid phase between 50~ and 130~ mometric data and experimental data calculated (Fig. 6B).. The calculated density is greater than for the systems HeO (Fisher, 1976), HeO-NaCI 1 g.cm (Ahmad and Rose, 1980). (Potter and Brown, 1977) and H20-CO2-NaC1 274 E. QUILEZ ET AL.

N 6- o) s. b)

5- V IC (Quartz) ~,- V/M. (Quartz)

4- 4-

~o 3- =-E e~ 2- 2- h. I&. IL. I- I-

! I , Ig ! I I 1 I I Z 3 4 t 2 3 4 5 N S- S- c) d) 4, V21Mw (Q.art=) V/M w (Quonz) 4-

:, 3

= 2 I., L U. ! 1"

, I , I I Ig I I Ig t Z 3 4 5 t 2 3 4 5 N N 5" 5" e) %/ME(a-. v/c f) 4- 4- (W.ifromitu)

I= 3"

cr Z k. i. U. t

; I f I I Ig , , , [ I Ig I 2 3 4 5 2 3 4 N N S- Barren ~oMz wm 5 Pegmutit. g)

3 c 3 ~

i :m 2- cr

U. I

, : , .~ : Ig .' , ,. l0 'i Iu I, 2 3 4 5 ! 2 3 4 5 FIG. 7. Results of crushing-test analyses. N, number of analyses; Ig, intensity of liberated gas using the crushing test of Leroy (1979); V/C, vein centre; V/ME, vein east margin; V/MW; vein west margin; V2/MW, associated vein west margin; V3/ME, associated vein east margin. WOLFRAMITE-BEARING QUARTZ VEINS 275

/ P Ibors)

15OO.

1" I~

Fro. 8. P-T diagram exhibiting significant isochores of Type II (Nos. 20, 23, 45), Type III (Nos. 24, 55, 83) and Type IV (Nos. 16 and 19) inclusions. Isocompositional curves: 1, (H20); 2, (7mo1.% CO 2, 4wt.% NaCI); 3, (10 mol. % CO2, 5 wt. % NaCI); and 4, (21 tool. % CO2, 5 wt. % NaCI).

(Gherig, 1980). Since there are no data for the temperatures (120-330~ and pressures above system H20-NaC1-CO2-CH 4 some selected iso- 100 bars. chores of representative inclusions were con- (4) The final stage: the hydrothermal evolution structed using a modified Redlich-Kwong ended with cooler fluids, corresponding to equation with the Nicolls and Crawford (1985) aqueous solutions of higher salinities (HzO-NaC1 computer program. The isochores of representa- with Ca 2+ and/or Mg 2+) at minimum trapping tive H20-NaCI inclusions were calculated using temperatures below 130~ and pressures above the Potter and Brown (1977) tables. The isochores 50 bars. were then projected into the isocompositional Therefore, the hydrothermal evolution of the curves on P-T diagrams (Fig. 8). Garganta de los Montes tungsten deposit results Based on the results obtained in this study four from several stages of fluid generation, with de- hydrothermal stages have been defined: creasing temperatures and pressures. An homogenization temperature-density diagram (Fig. 9) (1) The first hydrothermal stage probably corre- indicates that with descending temperature the sponds to an early high temperature fluid, is repre- solutions increase in density and contain decreas- sented by trapping of Type I inclusion containing ing amounts of CO2 and volatile compounds. The brine and halite as daughter minerals. dilution of the complex CO2-aqueous fluid is (2) The second hydrothermal stage is character- represented by the trapping of subtype IIB inclu- ized by complex carbonic-aqueous solutions sions. (Type II inclusions) circulating at minimum temperatures in the range of 300~ to 420 ~ and pressures above 500 bars. Discussion and conclusions (3) The third hydrothermal stage corresponds to the circulation and trapping of low to moderate The fluid inclusion study at the Garganta de salinity aqueous solutions, represented by Type los Montes ore deposit provides a better under- III inclusions, homogenizing at low to moderate standing of the circulation of hydrothermal solu- 276 E. QUILEZ ETAL.

,0% (r169 ~~ 35% t.! 30%

0.9"

0.8' zs%

0.7.

O,6-

,5% I00 200 300 400 TH (~

~TYPE "IT

~TY PE

FIG. 9. Homogenization temperature-density diagram of fluid inclusions in quartz from Garganta de los Montes, showing the hydrothermal evolution (0~10% lines indicate salinity). tions, most probably of magmatic origin. Early works (lvanova et al., 1976; Higgins, 1980) and brine high-temperature fluids have probably cir- for other W-Sn deposits (Ball et al., 1985; Shep- culated during a first phase of faulting. They were herd et al., 1985). The predominance of HCO; trapped as Type I inclusions in early barren quartz and CO 2 in these fluids suggests that carbonate that, after a second stage of fracturing, remained and bicarbonate complexes may be responsible at the vein margins. No brine inclusions have been for tungsten transport (Higgins, 1980). observed in the vein centre. Similar saline solution Regarding possible genetic links between two are described in the scheelite-bearing quartz vein fluids, no intermediate compositions have been from Poblet (Catalonian Coastal Range, Spain; observed between Type I and Type II. Accord- Ayora etal., 1987), as well as in the Sn-W deposit ingly, one may suppose that the two fluids belong of Aouam (Morocco; Cheilletz, 1984). to two distinct hydrothermal episodes. This con- Later, complex carbonic-aqueous solutions cir- clusion is in agreement with the early character culated from 300 ~ up to 420~ and pressures of of the brine inclusions and the later trapping of up to 0.5 kbar, and were associated with the wol- the Type II inclusions. framite-bearing quartz of the vein centre. Type Subsequently a new phase of fracturing allowed II inclusions are encountered isolated in the the flow of cooler, low to moderate salinity quartz of the vein centre and in healed fractures (1-9wt.% eq. NaC1) aqueous fluids, which may at the margins. These remarks suggest that com- be related to the sulphides accompanying wolfra- plex carbonic-aqueous fluids may play an import- mite. Temperatures of between 120~ and 330~ ant role in the transport of tungsten. This and pressures of 100 bar are minimum estimates conclusion has been proposed in experimental of temperature and pressure at the time of trap- WOLFRAMITE-BEARING QUARTZ VEINS 277 ping. Towards the end of the hydrothermal evolu- Fernfindez Casals, M. J. (1974) Significado geotect6nico tion, the salinity of the fluids increased greatly, de la formaci6n Gneises de la Morcuera. Studia Geo- as shown by type IV inclusions which homogenize logica, 7, 87-106. below 130 ~ Fisher, J. R. (1976) The volumetric properties of H20: a graphical portrayal. J. Research U.S. Geol. Survey, Taking into account that the wallrock adjacent 4, 189--93. to the wolframite-bearing veins has undergone Gherig, M. (1980) Phasenpleichgewischte und PVT intense hydrothermal alteration, the wolframite daten ternarer mischungen aus wasser kohlendioxid precipitation could have been favoured by fluid- und natriumchlorid bis 3KD und 550~ Ph.D. rock interaction. The reaction with the host rocks Thesis, Karlsruhe. caused progressive cooling of the solutions and Higgins, N. C. (1980) Fluid inclusion evidence for the increased the fluid pH by loss of H + used in the transport of tungsten by carbonate complexes in sericitization of feldspar and chloritization of bio- hydrothermal solutions. Can. J. Earth. Sci. 17, tires, thus destabilizing the tungsten-bearing com- 823-30. plexes. On the other hand, the carbonic vapour Hollister, L. S. and Burruss, R. C. (1976) Phase equilibria in fluid inclusions from the Khtada Lake meta- dilution by cooler aqueous fluids may be also a morphic complex. Geochim. Cosmochim. Acta, 40, mechanism that favoured the precipitation of the 163-75. tungsten. Ivanova, G. F., Khitarov, D. N., Levkina, N. I., Finally, a similar hydrothermal evolution has Milvsky, G. A. and Bannykh, L. P. (1976) Gas-liquid been proposed for other Spanish W-Sn ore inclusion data on the composition of Tungsten bearing deposits, e.g. La Parrilla, La Fregeneda, Golpe- hydrothermal solutions. Geochem. lnternat. 13, jas, Laza, Teba, and San Finx (Mangas, 1987a, b, 17-26. 1988); however, Type I brine inclusions have not Leroy, J. (1979) Contribution 6 l'6talonnage de la pres- been recognized in them. sion interne des inclusions fluids lors de leur d6cr6pi- ration. Bull. Soc. Fr. Mineral. CristaUogr. 102, 584-93. References Mangas, J. (1987a) Estudio de las inclusiones fluidas en los yacimientos espaholes de estaho asociados a Ahmad, S. N. and Rose, A. W. (1980) Fluid inclusions granitos hercinicos. Ph.D. thesis, Univ. Salamanca. in porphyry and skarn ore at Santa Rita, New Mexico. --(1987b) Fluid inclusion study on different types of Econ. Geol. 75,229-50. tin deposits associated with the Hercynian granites Ayora, C., Guilhaumou, N., Touray, J. C. and Mel- of Western Spain. Chem. Geol. 61,193-208. garejo, J. C. (1987) Scheelite-bearing quartz veins --(1988) Hydrothermal fluid evolution of the Sn-W from Poblet (Catalonian Coastal Range). Charac- mineralization in the Parrilla ore deposit (Caceres, terization of fluid inclusions and genetic model. Bull. Spain). J. Geol. Soc. London, 145,147-55. Mineral. 110,603-11. Nicolls, J. and Crawford, M. L. (1985) Fortran pro- Ball, T. K., Fortey, N. J. and Shepherd, T. J. (1985) grams for calculation of fluids properties from micro- Mineralization at the Carrock Fell Mine, Cumbria, thermometric data on fluid inclusions. Computers and Northern England. Mineral Deposita, 20, 57-65. Bellido, F. (1979) Estudio petrol6gico y geoquimico del Geosciences, 11,619--45. plut6n granitico de La Cabrera (Madrid). Ph.D. the- Potter, R. W. and Brown, D. L. (1977) The volumetric sis, Univ. Complutense, Madrid. properties of aqueous sodium chloride solutions from Canepa, C. (1968) Contribuci6n a la metalogenia de la 0~ to 500 ~ and pressures up to 2000 bars based on Sierra de Guadarrama (Ho]as 484 y 509, Provincia a regression of available data in the literature. U.S. de Madrid). Ph.D. thesis, Univ. Complutense, Mad- Geol. Survey Bull. 1421-C. rid. Poty, B., Leroy, J. and Jachimowicz, L. (1976) Un nou- Capote, R., Casquet, C., Fernandez Casels, M. J., vel appareil put las mesure des t6mperatures sous Moreno, F., Navidad, M., Peinado, M. and Vegas, le microscope: l'installations de microthermom6trie R. (1977) The Precambrian in the central part of the Chaixmeca. Bull. Soc. Fr. Mineral. Cristallogr. 99, Iberian massif. Estudios Geol. 33, 343-55. 182-7. Cheilletz, A. (1984) Caract6ristiques g6ochimiques et Shepherd, T. J., Miller, M. F., Scrivener, R. C. and Thermobarom6triques des fluids associds ~ la sheelite Darbyshire, D. P. F. D. (1985) Hydrothermal fluid et au quartz des mineralisations de Tungst6ne du dje- evolution in relation to mineralization in southwest bel Aoun (Maroc. Central). Bull. Mineral. 107, England with special reference to the Dartmoor-Bod- 255-72. min area. In High heat producing (HHP) granites, Collins, P. L. F. (1979) Gas hydrates in CO2-bearing hydrothermal circulation and ore genesis. Inst. Mining fluid inclusions and the use of freezing data for estima- Metall., 345-64. tion of salinity. Econ. Geol. 74, 1435-44. Swanenberg, H. E. C. (1979) Phase equilibria in car- Crawford, M. L. (1981) Phase equilibria in aqueous bonic systems, and their application to freezing fluid inclusions. In Short course in fluid inclusions: studies of fluid inclusions. Contrib. Mineral. Petrol. applications to petrology. (L. S. Hollister and M. L. 68,303-6. Crawford, eds.), 75-100. Tischendorf, G. (1977) Geochemical and petrographic 278 E. QUILEZ ETAL. characteristic of silicic magmatic rocks associated with Vindel, E. (1980) Estudio mineral6gico y petrol6gico rare element mineralization. In Metallization asso- de las mineralizaciones de la Sierra del Guadarrama. ciated with Acid Magmatism. (M. Stemprok, L. Bur- Ph.D. thesis, Univ. Complutense, Madrid. nol and G. Tischendorf, eds.), 2, 41-96. Vialette, Y., BeUido, F., Fuster, J. M. and Ibarrola, E. (1981) Donn6s g6ochronologiques sur les granites de la Cabrera. Cuadernos de Geologla lb~rica, 7, [Manuscript received 5 April 1989; 327-35 revised 2 February 1990]