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679

The Canadian Mineralogist Vol. 37, pp.679-690 (1999)

UVAROVITEIN PODIFORMCHROMITITE: THEMOA- OPHIOLITIC MASSIF.

JOAQUINPROENZA

Departamento d.eGeologia, Instituto Superior Minero Metalilrgico de Moa, Las Coloradas s/n, 83320 Moa, Cuba and Departament de Cristal.lografia, Mineralogia i Dipdsits , Universitat de Barcelona, C/ Marti i Franquis s/n, E-08028 Barcelona, Catalonia, Spain

JESUS SOLE AND JOAN CARLES MELGAREJO$

Departament de Cristal.lograJia, Mineralogia i Dipdsits Minerals, Universitat de Barcelona, C/ Marti i Franquis s/n, E-08028 Barcelona, Catalonia, Spain

Assrnlcr

The pods of the Moa-Baracoa massif, in the easternophiolitic belt of Cuba, contain pre-existing gabbro sills. This association is affected by two processesof hydrothermal alteration. The and the hosting and harzburgites are affected first by regional serpentinization; a second alteration, representedby chloritization accompanied with formation of ferrian , is mainly located in the pods and their immediate vicinity. The altered chromitite pods and enclosedgabbro sills iue cross cut by millimeter-wide veins. The vein filling consists of a sequenceof clinochlore, , chromian clinochlore, rutile, titanite and calcite. Uvarovite also occurs in the vicinity of veins Uvarovite is concentrically zoned, covering compositions in the uvarovite- solid solution seriesbetween Uva17and Uvae:; the component is very low. These composi- tions suggesta complete miscibility along the grossular-uvarovite join at relatively low temperature.On the basis of the sequenceand mineral chemistry (major and trace elements), the uvarovite crystals, as well as the vein assemblage,formed by a low-temperature leaching, Ca probably from the gabbro sills, and Cr and Al from the chromite dunng the formation of ferrian chromite Cr and A1 would have been mobile only at the scale of a pod during this process.

Keywords: uvarovite, zoning, hydrothermal, chromitite, ophiolite, Moa-Baracoa massif, Cuba

SorratraeJns

Les lentilles de chromitite du massif de Moa-Baracoa, dans la partie orientale de la ceinture ophiolitique de Cuba, contient des filon-couches de gabbro. Cette association a subi les effets de deux stades d'alt6ration hydrothermale. Les lentilles de chromitite et la et la harzburgite encaissantesont d'abord subi l'influence d'une serpentinisationr6gionale. Une deuxidme altdration a caus6une chloritisation et la formation de chromite ferrique, surtout dans les lentilles et leurs environs. Les lentilles de chromitite alt6r6es et les f,rlon-couchesde gabbro sont recoup6s par des veines millim6triques tapiss6es de clinochlore, uvarovite, clinochlore chromifbre, rutile, titanite et calcite. L'uvarovite se trouve aussi tout prbs des veines. Les cristaux d'uvarovite montrent une zonation concentrique, et les compositions s'6talent entre uvarovite Uva63 et grossulaire Uva17.La teneur en andradite est trbs faible. Ces compositions font penser qu'il y a une miscibilitd compldte entre grossulaire et uvarovite d temp6raturerelativement faible. A la lumibre de la s6quenceparag6ndtique et de la composition desmin6raux (6l6mentsmajeurs et traces),les cristaux d'uvarovite, ainsi que I'assemblagedes veines, se sont form6s par lessivaged faible temp6rature,le venant probablement des filon-couches de gabbro, et le Cr et Al contribu6s par la chromite lors de la formation de la chromite ferrique Le chrome et I'aluminium n'auraient 6t6 mobiles qu'd l'6che11ed'une lentille pendant ce processus.

(Traduit par la R6daction)

Mots-clds'.uvarovite, zonation, altdration hydrothermale, chromitite, ophiolite, massif de Moa-Baracoa, Cuba.

s E-mail address: [email protected] es 680 THE CANADIAN MINERALOGIST

INrnooucrroN westem part of the Mayari-Baracoa belt, is mainly com- posed of serpentinizedultrabasic rocks (harzburgite and The uvarovite end-member of the group, interlayeredharzburgite and dunite), with microgabbros Ca:Crz(SiO+):, has not yet been found in nature. Natu- and a diabase dike complex overlying the unit (Iturralde- ral uvarovitic garnet typically contains significant Vinent 1996). Chromitite pods occur within the dunite; amounts of both grossular and andradite components. the chromite is relatively Cr-rich, with Crl(Cr + Al) = Such compositions have been recorded in diverse geo- 0.75 (metallurgical grade). logical settings: chromitites associatedwith basic and The Moa-Baracoa massif is also mainly composed ultrabasic rocks (Chakraborty 1968, Jan et al. 1984, of serpentinized ultrabasic rocks; harzburgite grades Graham et al. 1996, Proenza & Melgarejo 1996, upward to harzburgite and dunite. In the uppermostpart Melcher et al. 1997), rodingites (Mogessie & of the mantle section, sills and dikes of gabbro are com- Rammlmair 1994), skarns (von Knorring et al. 1986, mon; this suite is covered by a crustal section compris- Pan & Fleet 1989), and kimberlites (Meyer & Boyd ing, from bottom to top, banded gabbro, isotropic 1972, Sobolev et al. 1973). The range of envfuonments gabbro, gabbro with diabase dikes and, finally, basalt in which it is found suggestsa broad field of stability and chert. The chromitite pods, commonly with dunitic (Kalamarides& Berg 1988). envelopes,occur in the uppermost part of the mantle- Our aim in this paper is to provide new chemical and crust transition zone (MTZ). Many chromitites enclose structural data on this important garnet, and to describe and replace the older gabbro sills parallel to the elonga- its mineral association and petrological significance rn tion of the pods (Fig. 2). This feature is typical of most the Mayari-Baracoa ophiolitic belt, Cuba. chromite depositsof the Moa-Baracoa district (Proenza et al. 1997a, 1999), as well as of other districts in cen- Gror-ocrcal SBrrrNc tral Cuba (Flint et al. 1948\ and at Coto in the Zambales ophiolite in Philippines (Leblanc & Violette 1983). The northem part of the island of Cuba is character- These chromitites are made up of Al-rich chromite or ized by a 1000-km-long Upper Jurassic- Lower Creta- chromian hercynite, with Cri(Cr+Al) = 0.45 (refractory ceous ophiolitic belt (Iturralde-Vinent 1996). The grade). easternpart, the Mayari-Baracoa ophiolitic belt (Fig. 1), Uvarovitic garnet related to chromitites has been is 170 km long, l0 to 20 km wide, and comprises two found only in the Moa-Baracoa massif (Grild 1947, allochthonous massifs: Mayari-Cristal and Moa- Kenarev 1966, Lewis et al. 1994,Proenza&. Melgarejo Baracoa. Both massifs contain abundant podiform de- 1996). Consequently, the Moa-Baracoa chromite ores posits of chromitite (Thayer 1942, Guild 1947, will be described with greater detail. However, therr Murashko & Lavandero 1989, Proenzaet al.1997a, absencein Mayari-Cristal massif has genetic implica- 7999, Proenza 1998). The Mayari-Cristal massif, the tions as discussedlater.

MAYARI.CRISTAL "\

Frc. 1. Geological sketch of the northwestern Caribbean ophiolites (modified from Wadge et al. 7984). UVAROVITE IN PODIFORM CHROMITITE, CUBA 681 nTYt" v .Effx*;l>*" " " i:ti::;::t:ir;l:rdur

i:ril:;lW!:;::iii;i!iiil

vvuuv har*urgite

F\c 2 Schematicsketchofthechromitebodies,showingthegabbrosillsandthetwosets of veins

Tnr, CHnoN4treOnns n Moe-Beneco,q Uvarovite appearsalso in an alteration zone, up to sev- ANDTHE Uvanovrre OccunnpNcBs eral centimeters in width, that replaces the hosting chromitite along these fractures. In this case, the A first stagein the formation of the chromitite pods chromite grains are partly corroded and replaced by involved the magmatic processesthat produced the de- uvarovite, and the replacement of chromite progresses posit. Primary mineralization is formed by chromite plus along the grain boundaries and the pull-apart fractures. interstitial and, as small inclusions in chromite, minor amounts of clinopyroxene, amphibole and pla- gioclase. This association replaced the enclosed pre- chromitite gabbro sills, as well asthe hosting dunite and harzburgite (Proenzae t al. 1997a, 1999, Proenza 199 8). W The texture of the chromitite is massive, grading in some deposits to disseminated,and displays pull-apart fractures. This type of is very common in T podiform deposits of chromite, and it is visible in hand samplesas well as on the scale of the deposit (i.e., [W]1 Leblanc & Nicolas 1992). FI=.rr.'.,::Tl Subsolidus hydrothermal processesproduced sec- l:i':jill:l.r:l:iiil ondary minerals that widely replaced the above mineral : association.Two main stagesof alteration can be dis- t*--,J F;";--i tinguished. The first stage was regional, and affected the"chroriitite pods ani the hosirocks (dunite and harzburgite), replacing the olivine grains by an qssem- FTlr+rTi blage of serpentine plus . The second stage took place largely in the chromitite pods and their vi- cinity, and comprises chromite alteration into ferrian E tt-::-:1-1 chromite ("ferritchromit"), coupled with replacementof serpentine by Cr-poor clinochlore (clinochlore-I, i;,;":'l Proenza et al. 1997b). This type of alteration is poorly developed in harzburgite or dunite occurring far from W the pods, and is restricted to a millimeter scale in the vicinity of the small grains of accessory chromian spinel. Frc. 3. Schematic cross-section of the garnet-bearing veins. The chromitite bodies of the Moa-Baracoa massif Symbols: 1) chromite, 2) fertran chromite, 3) clinochlore- are cross-cut by two sets of mineralized joints (Fig. 3). I, 4) uvarovite, 5) clinochlore-Il (chromian clinochlore)' Uvarovitic garnet appearsonly within the first set. 6) titanite, T) rutile, 8) calcite, and 9) clinochlore-Ill.

684 THE CANADIAN MINERALOGIST parameterswere detemined using the Rietveld method TABLE I REPRESENTATI\IERESULTS OF implemented in the FULLPROF program (Rodriguez- ELECTRON-MICROPROBE ANALYSES OF UVAROVITIC GARNET, MOA_BARACOA MASSIF. CIIBA Carvajal 1990). The pattern was refined in spacegroup Ia3d (Deer et al. 1992), but it is imporlant to note that Samplel234 5678 other cubic space groups also are possible for garnet SiO, (wt,%) 38 67 38 60 38 85 37 81 3'749 3'773 37 64 38.03 compositionsof this type (l.e.,Pinet & Schmidt 1993). Tio2 044 083 047 095 314 157 193 208 Al2o3 15_90 1534 1346 1008 6 79 12 07 9,26 8 62 MrNBner-Cuelrrsrny vzo: 0 13 0 26 0 18 023 0.72 0r9 038 03'l Cr2O3 7 28 8 87 10 39 150l 16 87 I 1 78 15.8s t6 22 Major elements Fe2O3 069 020 042 03E 0'15 037 034 0.30 CaO 3621 3605 3591 3566 34.60 3s s7 35 06 3491 Total 99.32 100.149969 10011 10036 A representativeset of microprobe results is given 99.28 10047 10052 in Table 1. Their compositions cover a large interual of Slructml foroula basedon 8 cations uvarovite-grossular solid solution, with a very low an- dradite component (Fig. 9). Garnet present as intersti- Si (aptu) 3 0l 299 3 04 3 00 3.02 2 99 2.99 3.03 Ti 003 005 003 006 19 tial grains from the alteration zone of chromitite has the 0 0.09 0.12 0 13 Ar 1.46 | 40 124 0.94 064 113 087 same 081 composition as gamet from the veins. The Fe con- v 001 002 001 001 005 001 002 002 tent is low, and charge-balanceconsiderations suggest Cr 045 054 064 0.94 107 074 100 102 that all the iron is trivalent; nevertheless,it is difficult Fe 004 001 002 002 005 002 0,02 002 to assign the correct charge to such small amounts of Ca 3O2 299 301 303 298 302 298 2.98 Fe. The Ti was assignedto occupy octahedralpositions. Uva 2292 2'7ss3346 49.01s933 388s 5220 5457 ',7105 The amounts of V, Mn and Mg are very low or below Grs 7459 6464 490'7 3559 5935 454.1 4321 the detection limit, and these garnet compositions can Adr 207 059 130 t.t1 252 tt5 108 0,97 therefore be representedessentially as solid solutions Go 0.42 0.81 0.60 0.76 2.55 0.65 1.26 ]rzs l,2,3, 4 md,5 ftactxe-filliug uvarovite of the binary series grossular-uvarovite, with 17 to 63 6, 7 md 8 disseminateduv4ovite gnins close to the veins in cbromitite mo1.70uvarovite. End-membenmolecules calculated afur Rickwood(1968) Uva

Grs Adr

FIG.9. Plot of compositions of chromian garnet from the Moa-Baracoa Massif, Cuba, in terms of mol Ea, compued to literature data. 1) Reaume Township (Duke & Bonardi I982),2)Labrador (Kalamarides & Berg 1988), 3) White River (Pan & Fleet 1999),4) various localities in Canada(Dunn 1978), 5) Luikonlahti (von Knorring et al. 1986),6) Outukumpu (von Knorring et al. 1986),7) Jijal Complex, Pakistan (Jan et al 7984). UVAROVITE IN PODIFORM CHROMITITE, CUBA 685

gar- TABLE 2 REPRESENTATI\,IE RBSIILTS OF Infrared-absorption and Raman analysis of the FT FCTRON-MICROPROBE ANALYSES OF CLINOCHLORE' net was performed on two samplesto check for the pres- CHROMIAN CLINOCHLORE, TITANITE AND RUTIIJ, ence of structurally bound OH. The results were not MOA_BARACOA MASSIF, CIJBA conclusive with IR, but the Raman spectra shows two bands that may correspond to a very small amount of Smplel2345678 SiOr(vt,%) 31.'16 32.14 27.92 26.81 31.40 30.95 H2O. On the other hand, the chemical compositions Tio2 001 0.02 0,00 000 39133852 9977 9942 obtained by electron microprobe agree with those ex- - Ta2O5 000 002 pected of anhydrous garnet, because the tetrahedrally Nb205 007 000 coordinated position is nearly always completely filled Al2Or 1832 l'1 96 2020 2050 082 063 011 0.16 with Si. Cr2O1 006 007 578 705 034 138 008 003 The zoning is oscillatory, as is easily detected by Mgo 3594 35 88 31 13 3020 0.00 0.01 0.00 0.03 variations in hues of green. These variations in color CaO 0-01 003 000 000 2E55 28,16 0 03 0 00 reflect variations in the Al:Cr ratio, i.e., the proportion MrO 000 002 000 0.00 0.00 0.00 0 00 0 07 181 000 000 of uvarovite and grossular components (Fig. 10). Thts FeO 059 080 178 Fe2O3 000 006 kind of zoning is common in chromian gamet (Ian et aI. Nio 009 001 022 0 19 1984). The Cr-rich zones are also the richest in Ti and Nazo 002 000 001 003 V. A comparable Cr-Ti correlation has also been ob- Kzo 0.01 0 00 0.03 0 02 served in the chromian andradite from Reaume Town- Eo 128'7 128a 1255 1242 9902 10025 99.6s 9962 99't9 ship, Ontario (Duke & Bonardi 1982). Total 9968 s98r 99,64 the three Somedifferences in Cr content exist among si (aptu) s92 599 534 5 18 102 1.01 _ _ generationsof chlorite. The early-formed chlorite does NAt' 208 201 266 282 not contain Cr (Table 2). It can be classified as 'Al 195 193 189 185 0.03 0.02 0 00 0.00 clinochlore, after Hey (1954). The secondgeneration of ri 000 000 000 000 095 0.95 100 100 chlorite, which overgrows uvarovite, has Cr contents ra 000 000 0.00 0.00 between 2.5 and 7.5 wt%oCr2O3, and is classified as T oo, oot ott 108 001 004 000 000 (Table chromian chlinoclore 2). The third generation is il" 9.99 996 887 869 000 000 000 000 again Cr-free. In all three generations,Fe content is very c" 000 001 000 000 099 099 000 000 low, and nickel values are lower than 0.2 wtToNiO, with Mn 000 000 000 000 000 000 0.00 000 an averageas low as 0.057o.Rutile crystals are of end- Fe2- 009 012 028 o-29 0,00 0 00 0 00 member composition (Table 2). Titanite contains 39Vo Fer* 0.00 001 0.00 003 003 TiOz and 107o AlzOz, with variable amounts of Cr, up Ni 00r 000 0.01 001 - ro l.4vo Cr2oj. )" 000 000 0.01 0.00 - - - I *d ,=ltt""Ll-" (*tit*"l",iltted on the basis of 28 O) 28 O) 3 md 4: chromim clinochlore (cations calculated on the basis of 5 md 6: titmite (cations calrulated on the bdis of 3 cat') 7 md 8; rutile (cations caleulat€d on the basis of2 O)

t6 t4 12 s 10 E o 8 X

2 0 | 2 3 4 5 6 1 8 9 10111213141516171819 AnalYsedPoints Rim Core -

Frc. 10. a) Back-scattered-electron(BSE) image of oscillatory zoning in uvarovite. The line indicates the profile of the crystal analyzed.b) Profile of electron-microprobe data along the line 1-19. 686 THE CANADIAN MINERALOGIST

Trace elements assumea linear relationship between cell parameterand composition in the solid solution uvarovite-grossular, One sample of garnet was analyzed for 31 trace ele- and neglect the small andradite component, the cell pa- ments by ICP-MS. As far as we know, quantitative data rameter obtained is equivalent to an average composi- ofthis type have not been published before. As shown tion of Uvaa7Grs53. in Table 3, the Moa-Baracoa uvarovite has no detect- able amounts of Pb and Ce, a few ppm of Li, Co, Cu, DrscussroNAND CoNcLUSroNs Ga, Rb, Sr, M, Sn, Cs, Ba, Hf, Ta, Th and U, and,20O ppm of Ni. The V contents (1000 ppm) is similar to the The garnet-bearingveins are confined to the interior concentration obtained by electron microprobe. Lan- of the chromitite bodies. These veins can be interpreted thanide contents are relalively low. not farfrom being to be the responseto deformation of a rigid body (the chondritic{Fig.lt). chromitites) enclosed by more ductile rocks (the Compared with the semiquantitative data of Wan & ).Their formation took place well after the Yeh (1984), the levels of Ni, Cu, Nb, Sn, Ba and pb are serpentinizationprocess, as is suggestedby Bamba of a similar order of magnitude, but levels of Co, Sr and (1984) for some alpine podiform deposits of chromite La are lower in the uvarovite from Moa. The lanthanum in Turkey. content reported by Wan & Yeh (1984) is probably too The textures of the idiomorphic crystals, as well as high becauseit implies a concentration of lanthanides their position in the veins, indicate that they formed from ten thousandtimes the chondritic values, which is ques- a hydrothermal fluid in an open space,along fractures. tionable in such garnet. The mineral associationpoints to a formation by a low- temperature hydrothermal process. The existence of a DerpnvnnrroN oF THECBlr- Penaueren pure Fe-poor clinochlore that cocrystallized with uvaro- vite in the veins suggeststhe possibility to estimate the We obtaineda cell parametera of I1.922 A using temperatures of formation of this assemblage using all reflections. This value is a weighed average of the chlorite geothermometry. The first generation of different values of the cell parameter in this slightly clinochlore yields a low temperature,about l8G-190'C, zoned gamet. It can be compared to values given by using the geothermometer of Hillier & Velde (1991), Deer et al. (1992) for the end-member samets. If we and230-240C using the geothermometer of Kranidiotis

10.00

t 2

U o

1.00 ""

(t)

a Uvarovite €- Sillofgabbro 0.10 LaCe PrNd SmEuGdTbDyHoErTmYbLu

FIG 1 1. Plot of the REE data normalized to chondrite for both uvarovite and sabbro sill UVAROVITE IN PODIFORM CHROMITITE, CUBA 687

TABLE3 TRACE.ELEMENTCONCENTRATIONSIN I'VAROVITE most feasible explanation for the oscillatory zoning of FROM TI{E MOA.BARACOA MASSIF. CUBA the Moa-Baracoa garnet. A portion of the compositional field of uvarovitic Li 51 Sn 03 Lr 0 451 plotted in Figure 9. It is sig- V 1060 CB 0 ll Ce nd garnet published to date is Co 2.6 Ba 06 Pr 0 171 to note that the suite from the Moa-Baracoa 'l nificant Ni 238 lrf 127 Nd oll massif contains compositions not yet reported in the lif Cu 15 Ta 002 Sm 0 360 Ga 40 Pb nd Eu daru erature on natural examples of the solid solution uvaro- Rb 03 Th 009 Gd 0 46E vite-grossular, despite the fact that these compositions Sr 10 U 04 Ib 0 093 Nb 01 Dy o 677 have already been synthesized (Huckenholz & Knittel Ho o 172 r9'ts). Er o 6't3 TE 0 t23 Kalamarides & Berg (1988) discussedin detail the Yb 0 999 gaps in this series. On the basis of their own data, ex- Lu 0 200 perimental work by Huckenholz ( I 975) and Huckenhoiz & Knittel (1975), and data supplied by Duke & Bonardi Analysisby ICP-MS tr d : oot detwled, All valuesre in ppm (1982) and Jan et al. (1984), they concluded that ugrandite garnet shows complete solid-solution at high temperatures (800-1550'C) and variable pressures (1 bar to 10 kbar). They concluded, also, that a compo- & Maclean (1987). The estimatedtemperatures for the sitional gap exists between uvarovite and grossular at second generation of clinochlore (which is associated low temperatures.The paragenesisand hydrothermal with uvarovite) are 280-300'C using the first geother- mode of occulrence at Moa-Baracoa indicate that the mometer. The second yield higher temperatures,about garnet crystals formed at relatively low temperature and 340-3'10"C.Therefore, the significant increasein the Cr low pressure. Our data suggest a complete miscibility content of the clinochlore of the second generation re- along the grossular-uvarovite join (i.e., very low level sults in unrealistically higher temperaturesthan those of the andradite component) at low temperatures.The of the first generation.The temperaturesobtained using potential of a miscibility gap at greater andradite com- both geothermometersin the Cr-free clinochlore of the ^GangulyDonent cannot be discarded from the data presented. first generation,however, are in the range of those ob- (1976) presenteda model of the solid solution tained by Christidis et al. (1998) for chlorite formation in the system grossular- uvarovite - andradite.Its cal- in the Vourinos ophiolitic complex in Greece. culated spinodal at 400'C does not intersect the uvaro- The complex zoning surfaces of the Moa-Baracoa vite-grossular join. Becausethe Moa-Baracoa suite was garnet do not seemto be linked to dissolution processes, very likely formed below this temperature,our data do but rather to growth. Moreover, their formation at a very not conflict with this diagram. low temperatureprevents solid-state diffusion as an ef- These veins formed from a Ca- and Al-bearing hy- fective mechanism to explain this zoning (Shore & drothermal fluid. The Al may have been extracted dur- Fowler 1996). As stated by Jamtveit et al. (1995), in ing the replacement of chromite by ferrian chromite ugrandite-type garnet in skarns, the compositions and (Proenzaet al.199'7b, Proenza 1998), according to the morphological properties of a hydrothermal mineral are reaction: controlled by: a) bulk composition of fluid, b) local transport processesnear the fluid-solid interface, and aluminian chromite + ferroan antigorite - ferrian c) surfacekinetics. Changesin the chemistry of the min- chromite + chromian clinochlore eralizing solution are unlikely in this case,because the veins are strictly related to the inner parts of the chromite The activity of Ca in this fluid led to the develop- bodies. This fact suggeststhat the fluid phase precipr- ment of uvarovite, and the development of titanite tated in an essentially closed system. The composition instead of rutile. The source of Ca-rich fluids in of the fluid, therefore, must have been strongly con- ophiolites is controversial. Mittwede & Schandl (1992) trolled by the composition of both chromitites and the suggestedliberation of Ca linked to the phenomenonof gabbro sills included in the chromitite pods. Conse- serpentinization.In our case,the Ca-rich fluids entered quently, it is difficult to explain oscillatory zoning by into the system much later than the serpentinization re- changesin the bulk composition of the fluid. action, during low-temperature hydrothermal alteration In the opinion of Jamtveit et al. (1995) and Ivanova that replaced serpentineby chlorite. Since the ultrabasic et al. (1998), covariation among major elements and rocks hosting the chromitite pods display a very limited similarities among crystals suggestthat zoning in gar- extent of chloritization, the composition of chlorite- and net is confrolled mainly by extemal forces (flow rates uvarovite-producingfluids seemsto be controlled by the or chemical changes),with only minor participation of composition of the assemblageof chromitites plus the surface kinetics. Although the gamet in our suite dis- enclosedgabbro sills. The enclosedgabbros could have plays the same type of correlations, we believe that a been an alternative source for Ca. These gabbros were self-organizationprocess (e.g., Putnis et al. 1992) is the hydrothermally altered, and crystals were 688

converted to prehnite and epidote; clinopyroxene crys- ish Instituto de Cooperaci6n Iberoamericana with an ICI tals are replaced by fibrous tremolite. grant for J.P. (Ph.D. thesis). As pointed out above, the uvarovitic garnet as well as the chromitite pods occur in direct association with RBrennNcBs gabbro sills in the Moa-Baracoa massif (Proenza 1998, Proenza et al. 1999). Likewise, the lanthanide pattems BeMsa, T. (1984): A model illustrating the formative process (Fig. 11) of gabbros and gamet reflect a similarity in of the podiform chromite depositsin some alpine orogenic their light rare-earth element contents, with a similar terains. Syngenesis and epigenesis in the formation of mineral deposits (A. Wauschkuhyn, Kluth positive Eu anomaly. The positive Eu anomaly in the C. & R.A. Zirnmer- mann, eds.).Springer-Verlag, Berlin, Germany (507-518). fresh gabbros is due to Eu2+enrichment in plagioclase owing to the high partition (Dplacioclaseniquid) coefficient Cne.rneronrv, K.L (1968): Mineralogical note on the of this element (Hamois et al. 1990i).As during the early chrome-chlorite (KZimmererite) and chrome-garnet stagesof vein infilling, it is uvarovite that is by far the (uvarovite) from the chromite depositsof Kalrangi, Orissa, dominant calcium-bearing phase, Eu can also be ac- lndia. Am Mineral. 53, 962-965. commodated in the garnet structure, replacing calcium. On the other hand, the heavy rare-earth enrichment in Cunrsrmrs, G 8., EcoNolrou-Erropoulos, M., MARcopoulos, the garnet is an expressionofthe general preferenceof T & LAsKou, M. (1998): An unusual assemblageof high- Ti oxides and ferroan these elements for the garnet structure (i.e., Hanson clinochlore along zones of brittle deformation in the Vourinos (Rodiani) ophiolite complex, 1980). The garnet thus seemsto have inherited its lan- Greece. Can. Mineral 36, 1327-1338. thanide pattern from the gabbro sills during the leach- ing processthat affected both the chromitite bodies and DEER,W.A., Howm, R.A. & ZussrvraN,J. (1992): Rock-Form- the cross-cutting sills of gabbro. ing Minerals. lA. Orthosilicates (second ed.). Longrnan, We conclude, therefore, that the Moa-Baracoa London. U.K. uvarovite was formed by the leaching of Ca from the gabbro sills, and Cr and Al from chromite. The process DUKE,J.M & BoNm.or, M. (1982): Cbromian andradite from is associatedwith low-temperature formation of chlo- Reaume Township, Ontario. Can. Mineral. 20,49-53. rite and ferrian chromite in the chromitite pods. Exten- DUNN,P.J. (1978): On the composition of some Canadiangreen sive crystallization of chlorite and uvarovite is reStricted Earnels.Can. Mineral 16,205-206. to the chromitite pods. This fact can be attributed to a low mobility of Cr and Al during low-temperature hy- FI-tNr, D.E., DEALBEAR, J.F. & Gun-r, P.W. (1948): Geology drothermal processesoperating on ophiolites. These re- and chomite depositsof the Camagiiey district, Camagiiey sults agree with the low mobility of Cr described in Province, Cuba. U.S. Geol. Suw., Bull. 954-8,39-63. many environments (1.e.,S6nchez-Vizcaino et al. 1995, and referencestherein), and explain the conlmon occur- GrNcuI-y, J. (1976): The energeticsof natural gamet solid so- rence of uvarovite in Moa-Baracoa massif. In contrast, lution. II- Mixing of the calcium silicate end-members. Mineral. uvarovite is absentin Mayari-Cristal massif. Although Contrib Petrol. 55, 81-90. this massif underwent the same processes of Gnlrterra,I.T., FuNrlnv, B.J. & MensHlr-L, B (1996): Chem- serpentinization and chloritization as at Moa-Baracoa, istry and mineralogy of podiform chromitite deposits, gabbro sills or other Ca-rich rocks do not occur. Hence, southernNSW, : a guide to their origin and evolu- in the Mayari-Cristal massif, the supply of Ca to the ion. Mineral. Petrol. 57, 129-150. hydrothermal fluids was lower and, consequently, uvarovite did not form. GuIlr, P.W. (1947): Petrology and structure of the Moa chromite district, , Cuba. Trans. Am. Acrc{owr-socBN4sNrs Geophys. Union 28, 218-246.

H.lNsoN, G.N. (1980): Rare earth elements in petrogenetic We thank the staff at the Mercedita mine, and spe- studies of igneous systems.Annu. Rev. Earth Planet. Sct. cially D. Rev6 and G. Rodriguez, for their aid in the 8,371-406 field work. All the analyses were performed at the "serveis Cientifico-Tdcnics" from ihe University of HnnNors, L., TRorrreR, J. & MonBNcy, M- (1990): Rare earth Barcelona (Spain). We thank Drs. X. Llovet and J. element geochemistry of Thetford Mines ophiolitic com- Garcia Veigas for their help with the electron-micro- plex, northern Appalachians, Canada. Contrib. Mineral. probe analyses,Dra. E. Pelfort, wirh the ICP-MS mea- Petrol 105,433-445. surements,Dr. R. Fontarnau,with the the BSE imaging, HBv, M.H. (1954): A new Dr. T. Jawhari-Colin, with the Raman analyses,and Dra. revision of the chlorite. Mineral. Mas.30,277-292. N. Ferrer, with the IR analyses.We also thank Drs. J.H. Berg, F. Gervilla, S. Gali, G. Franz and R.F. Martin for HtI-r-rrn,S. & Vrros, B. (1991): Octahedraloccupancy and the their valuable discussions and criticism of the manu- chemical composition of diagenetic (low-temperature) script. This work was partially supportedby the Span- chlorites. Clay Mineral. 26, 149-168. UVAROVITE IN PODIFORM CHROMITITE. CUBA 689

HucKENHoLz,H.G. (1975): Uvarovire stability in the CaSiO3- MIrrwEDE, S.K. & ScHANDL,E.S. (1992): Rodingites from the Cr2O3j oin up to 70 kbzr. N eue s Jahrb M ineral., M onat s h., southem Appalachian Piedmont, South Carolina, USA 337 -360. Eur. J. Mineral. 4, 7-16.

__ & KNrrrrL, D. (1975): Uvarovite: stability of MocEssrE,A. & RAMMLMAIR,D. (1994): Occurrence of zoned uvarovite-grossularite solid solution at low pressure. uvarovite-grossular gamet in a rodingite from the Vumba Contrib.Mineral Petrol. 49, 2ll-232. schist belt, Botswana, Africa: implications for the origin of rodingites. Mineral. Mag. 58, 37 5-386. IrunnlI-os-VnrBNT, M.A. (1996): Ofiolitas y arcos volcdnicos de Cuba. IGCP Project 364, Spec. Contib. l. MuRAsHKo,V.I. & LeveNopRo, R.M. (1989): Chromite in the hyperbasite belt of Cuba Int. Geol Rev. 31,90-99 IvANovA, T.I, SHrurrNnsnc, A.G., PuNrN,Yu O, FRANK- KaurNrrsreye, O.V. & SoreLov, P.B. (1998): On the PnN, YulNlrwc & FI-esr, M E (1989): Cr-rich calc-silicates complex zonality in grandite gamets and implications. Min- from the Hemlo area, Ontario Can. Mineral 27, 565-57'7 eral. Mag 62,857- 868 PINrr, M & ScHvnr, D.C (1993): La microsp6ctrometrie J.lurvrrr, B , RecNensoorrrn, K.V. & Wooo, B.J (1995): On Raman des gretats X3Y223O12.I La s6rie calcique the origin of zoned grossular-andradite in hydro- naturelle ouvarovite * grossulaire - andradite. Schweiz thermal systems.Eur. J. Mineral. 7 , 1399-1410 Mineral. Petrogr Mitt 73,21-40.

JeN, M.Q , WrNor-By,B F & WrsoN R N. (1984): Chromian PnonNza, J (1998): Mineralizaciones de cromita en la faja andradite and olivine-chromite relations in a chromitite ofiolitica Mayari-Baracoa (Cubn) Ejemplo del yacimiento layer from the Jijal complex, northwestern Pakistan. Cdn. Mercedita. Ph.D. thesis, Univ. of Barcelona, Barcelona, Mineral 22,341- 345 Soain

KaleNrlnrnes, R.I. & BERG,J.H. (1988): Coexisting Cr-rich Grnvrr-r-e,F. & MrlcenBro, J.C. (1997a): and Cr-poor gamet from a calc-silicate gneiss, Labrador. Compositional variations of podiform chromitites among Can. Mineral. 26, 335-342 different mining districts in the Mayari-Baracoa Ophiolitic Belt (eastem Ctba) In Mineral Deposits: Research and KnNenpv, V.V. (1966): Caracteristicasmineral6gicas del Exploration Where Do they Meet? (H Papunen,ed.) yacimiento Potosi, Cuba. Revista Tecnol6gica 4,3-6 Balkema, Dordrecht, The Netherlands G8'7-490).

KneNrororrs, P. & MAcLEAN, W.H. (1987): Systematics of & BorrNnn,J.L. (1999): Al- chlorite alteration at the Phelps Dodge massive sulphide rich and Cr-rich chromitites from the Mayari-Baracoa deposit,Matagami, Quebec. Econ. Geol 82, 1898-1911 ophiolrtic belt (eastern Cuba): consequenceof interaction between volatile-rich melt and in suprasub- LEBLANC,M &Nrcouls, A (1992): Ophioliticchromites Inr. duction mantle. Econ. Geol. 94, 547 -566 Geol. Rev.34,653- 686 & Mnlclnpro. J.C (1996): Granatesde la serie & VIoI-Brrs, J.F (1983): Distribution of aluminium- grosularia-uvarovita en cromititas podiformes del rich and -rich chromite pods in ophiolite yacimiento Mercedita (Cuba). Geogaceta 20, l5l7 -1519. pendotites. Econ. Geol. 78, 293-301. & Gpnvrr-rq, F (1997b): Proceso de Lrws, J F , MuNoz, J.N , PeNc, G., Cerrapos,M., Qurxrm, F alteraci6n a ferricromita en Cr-espinelas del yacimiento (1994): Mineralogy of silicate and chrome-spinel phasein Mercedita (Cintur6n ofiolitico Mayari-Baracoa, Cuba). the ophiolite rock and chromite deposits of the Moa- BoI Soc. Espaftola Mineral. 20A,29-30. Baracoa Nea. Restimenesdel Segundo Congreso Cubano de Geologia (),108 (abstr.) PurNrs, A., FERNANDEZ-DIAZ,L & PRrEro,M. (1992): Experr mentally produced oscillatory zoning in the (Ba,Sr)SO+ '7 L6pnz SANcuEz-VrzcniNo,V., FneNz, G & G6urz-PuGlqAInB, solid solution. Nature 358, 43-7 45. M.T. (1995): The behavior of chromium during metamor- phism ofcarbonate rocks from the Nevado-Fildbride Com- RrcKwooD, P.C. (1968): On recasting analysesof gamet into plex, Betic Cordilleras, Spain Can. Mineral 33, 85-104. end-membermolecrles. Co nt rib M iner al. P etro l. 18. l7 5- 198. MBr-csrn, F., Gnua, W., Sntou, G., THer-uaulrBn, TV. & SruMpFL,E F ( 1997): Petrogenesisof the Ophiolitic giant Roonrcunz-ClnvArAl, J (1990): FULLPROF: a program for chromite deposrts of Kempirsai, Kazakhstan: a study of Rietveld refinement and pattern matching analysis. Sarel- solid and fluid inclusions in chromite. J. Petrol. 38. l4l9- lite Meeting on Powder Diffraction of the XV Congress of 1458 the IUCr (Toulouse), I27

MByrn, H O A. & Bovo, F R (1972): Composition and origin SHoRE,M & Foupn, A D. (1996): Oscillatory zoning in min- of crystalline inclusions in natural diamonds. Geochim erals: a common phenomenon Can Mineral.34, l11l- Cosmochim.Acta 36, 1255-1273 t126. 690 THE CANADIAN MINERALOGIST

Sosor-Bv, N.V., LevnBNr'ev, Y.G., PorHil-sNro, N.P. & WAN, H.M. & YsH, C.L. (1984): Uvarovite and grossularfrom Usova, L.V. (1973): Chrome-rich garnets from the the Fengtien nephrite deposits, eastern . Mineral. kimberlites of Yakutia and their parageneses.Contrib. Min- Mag. 48,3I-37. eral. P etrol. 40, 39-52. Weocn, G., Dtepen, G. & LEwrs, J.F. (1984): Ophiolites of TsevBn, P.T. (1942): Chrome resourcesof Cuba. U.S. GeoI. the northern Caribbean: a reappraisal of their roles in the Surv.. Bull. 93-A. l-7 4. evolution of the Caribbean plate boundary. 1n Ophiolites and Oceanic Lithosphere (I.G. Gass, S.J. Lippard & A.W. voN KNoRRrNc,O., CoNor-rrs, E. & ToNG,Y.L. (1986): Some Shelton, eds.). Geol. Soc., Spec. PubI. 13,367-380. mineralogical and geochemical aspects of chromium-bear- ing skarn minerals from northern Karelia, . Bull. ReceivedAugust 20, 1997, revised manuscript accepted Feb- Geol. Soc. Finland 58, 27'7-292. ruarv 15.1999.