TI{E AMERICAN MINERALOGIST, VOL 4J, NOVEMBER.DECEMBER, 1958 PHOSPHAI'EIIINERALS OF THE BORBORET{APEG}IATITES: II BOQUEIRAO Josnlu \Iunnocn, Uniaersityof CatiJorniaal. Los Angeles. ABSTRACT The "alto" Boqueirlo is a tl,pical zoned pegmatite of the heterogeneoustype, which carries some unusual minerals besides those of the normal ber1,1-tantaliteassemblage. Among them are minor arnounts of uraninitc, altered in part to uranophane and other secondary compoundsl native bismuth. Lithiophilite and manl' secondary phosphates appear as usual in the general inner portion of the pegmatite near the cluartz core. Among these phosphates appear a pink variscite (carrying minor ber)'jlium); metastrengite as sometimes showy blue coatings of minute crystals; huriaulite and minor tavorite as coat- ings on fractures of lithiophilitel stewartite, massive or in rare crystals; mitridatite (a hydrous calcium iron phosphate), in deep red blades, or very fine grained massesyerlowish to greenish in color. A new mineral, chavesite is described. rt is a hydrous calcium man- ganese phosphate, occurring as thin platy crystals coating lithiophilite, and associated rvithhur6auliteandtavorite. Triclinic, ooS 49bol3.O7,coS79;a97"lgl;,,p 109.3,,t99"44,. The powder pattern resemblesthat of monetite, ivith which it may be isostructural. The stronger powder lines have the follou'ing spacings and intensities: :.35 A-lo, 3.0% A-2, 2.945i\-3,2.74 A-2. IxrnoouctroN This is the secondin a projectedseries of reportson the phosphatesand associatedminerals from the complex, lithium-bearing beryl-tantalite pegmatitesof NortheasternBrazil. Their generalposition is shown on the key map (Fig. 1). The first report wason the ,,alto',patrimonio, \,Iurdoch (1955) and the present one describesthe occurrenceat the ,,alto,' Boqueirao. The general geologicsetting, describedin some detail by Johnston (1945)and others,is the same for both deposits:complex peg- matites intruded into a pre-Cambriancomplex and exposedby erosion of the rock cover to form the Borborema,'planal16,'-a more or lesswell developedpeneplane of possibly Cretaceousage, standing now at an elevation of 500 to 550 metersabove sealevel. rn the Statesof paraiba and Rio Grandedo Norte, later erosionhas loweredthe earliersurface so that the pegmatitesstand up in relief on it, hencethe name ,,alto,,given to their outcrops.Even in Cear6,where there has been no suchdifierential erosion,the name is still applied. The pre-Cambrian rocks are largeiy gneissesand mica schists(the Serid6schist), which showsno pronounced regional trend, striking sometimes northwesterly, sometimes north- easterly. Boquernao The "alto" Boqueirlo lies at the northern summit of a ridge reaching an eievation of about 300 meters above the surrounding territory, some 1148 PI]OSPHAT'EMINEIIAI,S, BORBORE]TAPEGMA'TITE 1149 three kilometers southeastof the town of Pareihas,in the State of Rio Grande do Norte (seeindex map, Fig.2) . The following descriptionis taken largelyfrom Johnston (1945).Exposed cont/acts are nearly every- wherepractically vertical. The outcrop is some 240by 25 meters,pinch- ing out to the west, and cut off sharply by the steepslope of the ridge to the east. Johnston'szone If (coarsetextured quartz-feidspar)with con- siderablebiack tourmaline. composedabout half the outcrop. His zone 4ll4rv rtc ) (--.-- P E R N AIMEUCO Frc. 1. General map of area. III (very large crystals),has huge microclines,partially kaolinized The qtarfz core is multiple, and the various patches are made up largely of milky quartz, with occasional vugs carrying euhedral quartz crystais up to 200 kilograms in weight. The occasionalphosphates occur, as is normal, in the third zone, and often close to the core. The following minerals are reported: arrojadite, vivianite, spodumene, lepidolite, rhodonite (?), pitchblendeand its alteration products, metallic bismuth with bismutite, and some chalcocite.These are in addition to the usual quartz-feldsparmixture, with beryl, tantalite, muscovite,etc. Of theseno arrojadite, rhodonite or chalcocite were observed by the writer. The "arrojadite" is presumablyrepresented by lithiophilite and its alteration products (sicklerite etc.); the "vivianite" is apparently metastrengite, and the rhodonite (?) is probably a pink variscitewhich was observedin some of the alteration Droducts.Several other minerals were observed 1150 J. MURDOCH by the writer, and are includedin the descriptivelist. The seriesof altera- tion products of lithiophilite form an interesting group, essentiallythe sameas that describedfrom Patrimonio. SpooulroNo is not abundant, and is commonly altered to a fine grainedmica (probably muscovite),associated with fine grainedbotryoi- dal growths of cookeite. LBproorrtn is sparingly present as rather fine grained aggregates, NORTE 9lcurrocs Novos xlog6o do Andrc' et *1* .,,"; ii'o--..... €*'o ;li;' "***oxiqur xiqul opicui ..a Corngfbinhas doDinh.iF Jorclhos Frc. 2. Detailed map of area. occasionallyforming masseswith curved surfaces,and associatedwith platy albite. Small prismatic grains of apatite have been seen in this association. TeNtetrm, apart from the commercially large masses,is occa- sionally found in the quafiz-feldspar aggregateas small crystals of man- gano-tantalite.A few tabular crystals of columbite appear in a similar matrix. Brsuurn, as the native metal, has been found sparingly as grains or occasionaliyfair sizedrough crystalsinterstitial to quartz, and associated with coatingsand patchesof secondarybismutite. UnaNtNrrB. This has been reported as pitchblende, but one rough octahedralcrystal wascollected by the writer. This crystal is encrustedby a seriesof secondaryminerals in thin concentric layers, and showing roughly three distinct zones.The outermost of theseis uranophane,fhq PIIOSPHATEMINERAL,S, BORBOREMA PEGMATITE 1151 next an undetermineduranium mineral, or perhapsa mixture, in a num- ber of thin, slightly varied layers, and the innermost perhaps meta- torbernite, although the powder pattern doesnot match too closely.In addition, a dark red mineral appearsin thin veins in the uraninite, and is possiblysoddyite. An analysisof the uraninite is given in Table I. Other oxidized uranium minerals, mainly meta-torberniteand meta-autunite, were found in minor amount, usually as powdery or poorly crystallized coatineson columbite. Teeru 1. Cnrurcar- ANalvsns UrOs 91.40 FeuOs 1.00 FeO 1.97 Pbo 5.92 FeO 13.23 FezO:; ,10.38 CuO .04 Mso 1.11 AlrOr 1.20 Bi2o3 .015 CaO .t1 PiOr 39.18 FeO .026 MnO 29.80 MnzOs Al2o3 .30 PiOs 45.00 HtO- 17.42 Tio, .00.5 Li20 8.68 HzO-| .198 CaO .02 98.96 100.35 NazO .03 SiOz .Jl MnO tr. H:Oi l /O H:O- .54 100.37 1. Uraninile, anal;rsts,Johnson, Mathey & Co. Ltd (Zn, Ni, Co, P2O5,As, Sb, Sn not detected). 2. Lithiophilite, analyst L. C. Pech.3. Metastrengite, analyst E. L. Martin. VenrscrrB. One group of specimensshows a great variety of min- erals apparently derived from the complete alteration of lithiophilite crystals (as shown by the outlines of the aggregates).These occur in a matrix of mixed albite, amblygonite and quartz. One of theseminerals is variscite,in the form of a transparentcrystalline crust, coatingfracture surfacesand lining cavities. It was identified by optical properties, tr-ray powder pattern, and crystal form. It varies from colorlessthrough pale pink to raspberry red. Spectroscopictests show the presenceof a small amount of beryllium. This is in agreementwith the findingson the pink variscite of the Sapucaiapegmatite (l{rose, priv. commun.) N'Irrnroarrrn. This rare mineral occurs in these same specimens in clear, red bladed grains: also probably fine-grained,massive, yellowish brown; and alsoperhaps in compact,almosl earthy form, khaki colored. (This is somewhatdoubtful, but the powder pattern is at least in moder- ate agreementwith that of mitridatite.) tt52 J. MURDOCI! MoresrnoNGrrE occurs as crusts, finely crystalline, and ranging in color from nearly white through pink to pale blue in this seriesof speci- mens.It alsooccurs in considerableamount, deeppurplish blue,and often quite spectacular,as a late product of alteration of lithiophilite in other specimens.See Table I for analysis of this mineral. BBn,luNrrB. An orange colored mineral occurring as blade-like grains in the variscite specimens,may perhaps be assigned to this specieson the basisof a closelymatching powder pattern. Rocr<enrocBrrB. This mineral was found in small amount in dark green patches associatedwith alteration products of lithiophilite, and also in the variscite specimensas olive green, minute spherical clusters (probably partly altered). MaNceNrrn and CnyproMELANE.The end-productof weatheringbe- sides some limonitic powders,is manganeseoxide, which is sometimes crystalline, with powder pattern matching manganite, or in compact, steely masseswhich seemto be cryptomelane. Hun6.q.urrrB. This mineral is rather abundant as colorlessor red- dish brown crystallinecrusts on fracture surfacesand in open spaces,in lithiophilite. It not infrequently hassmall, rather well developedcrystals. TevonrrB. Associated with some of the hur6aulite, and approxi- mately contemporaneouswith it, tavorite occursin yellowishgreen films or clustersof minute radiating crystals.This occurrenceis identical with that at Patrimonio (lVlurdoch1955). SrBwenrrro. Stewartite is rare, occurring in the outer zone of alter- ation of the lithiophilite. Rather poorly developedsingle crystals enabled the writer to make determinations of cell-sizeand symmetry which agree ciosely with those of this mineral from the Palermo