American Mineralogist, Volume 67, pages 97-113, 1982 Alteration of spodumene,montebrasite and lithiophilite in pegmatites of the White PicachoDistrict, Arizona Davrp Lor.rooxrnNo DoNer-uM. Bunr Department of Geology Arizona State University Tempe, Arizona 85281 Abstract The crystallization sequence and metasomatic alteration of spodumene (LiAlSizOe), montebrasite(LiAIPO4(OH,F)), and lithiophilite (Li(Mn,Fe)PO+)are describedfor nine zoned lithium pegmatitesin the White Picacho district, Arizona. The observedcrystalliza- tion trends suggesta progressiveincrease in the activities of lithium species(spodumene follows microcline as the principal alkali aluminosilicate), as well as an increase in the activities of the acidic volatiles phosphorus and fluorine (montebrasite succeedsspodu- mene as the stableprimary lithium phase).Much of the lithiophilite occurs with columbite, apatite, beryl, zircon, and tourmaline in cleavelanditecomplexes that formed in part at the expenseof quartz-spodumenepegmatite. Fracture-controlledpseudomorphic alteration of the primary lithium minerals is widespread and apparently is the result of subsolidus reactionswith residualpegmatitic fluids. Spodumenehas been replacedby eucryptite, albite, and micas. Alteration products of montebrasite include low-fluorine secondary montebrasite,crandallite (tentative), hydroxylapatite, muscovite, brazilianite, augelite (tentative),scorzalite, kulanite, wyllieite, and carbonate-apatite.Secondary phases identi- fied in altered lithiophilite include hureaulite, triploidite, eosphorite, robertsite, fillowite, wyllieite, dickinsonite,fairfieldite, Mn-chlorapatite, and rhodochrosite.Initial subsolidus metasomatismof the lithium minerals took place in an alkaline environment, as evidenced by albitization of spodumeneand calcium metasomatismof the phosphates.The formation of secondarymicas in spodumene,montebrasite, tourmaline, and much feldsparreflects a changefrom alkaline to relatively acidic postmagmaticfluids, as (K+H)-metasomatism producedgreisen-like or sericiticalteration. The abundanceof mineralscontaining Li, Be, Mn, Nb, Ta, and Bi indicate that these pegmatitesoriginated from a highly differentiated granitic source.These pegmatites were not fluorine-rich,as evidencedby the low fluorine contents of primary and secondarymontebrasite, by the formation of OH- and Cl-apatites, and by the absenceof topaz and the rarity of lepidolite, triplite, and fluorite. Introduction also Precambrian(Laughlin, 1969),although a pre- The White Picachopegmatite district lies nearthe cise age has not been established. southeastend of the Arizona pegmatite belt (Jahns, Only nine lithium pegmatiteshave been identified 1952; see Fig. 1). The district, which is located in the district. Most of these were mapped and mostly on the Red Picacho7.5' topographicquad- described by R. H. Jahns (1952), and his work rangle map (U.S. Geological Survey, 1964),con- provideda foundationfor subsequentstudies by us tains severalhundred pegmatites. These pegmatites (Burt, London, and Smith, 19771'London,Bandy, intrudelow- to medium-gradePrecambrian schists, and Kealy, 1978;London and Burt, 1978;London, gneisses,and amphibolitesthat Jahns(1952) tenta- 1979).At present, most of Jahns' maps are still tively correlated with the Yavapai Series in the usable,inasmuch as only minor mining and devel- Jerome and Prescott areas (Jagger and Palache, opment have been carried out in the district over 1905;Anderson et al., l97l). The pegmatitesare the past thirty years. Additional maps of the region and of the pegmatites are available in London and rPresentaddress: Geophysical Laboratory, 2801Upton Street, Burt (1978)and in London (197il. N.W., Washington,D.C. 20008. In the White Picacho pegmatites,as at many m03-004)vE2l0r 02-0097$02.00 97 98 LONDON AND BURT: SPODUMENE, MONTEBRASITE AND LITHIOPHILITE Moore, 1971,1972; 1973, 1974), the significanceof these replacements as indicators of pegmatite chemistry and evolution remains poorly under- ti::::i i- stood.In the White Picacholithium pegmatites,the t:::i: t i:i paragenetic tl sequenceof these secondaryminerals can be determined for each of the parent lithium minerals.Each paragenesisis interpretedas indicat- ing systematic changesin the geochemistry of the postmagmatic fluids. The central purpose of this paper is to characterize these pseudomorphic re- placementsand to evaluate their geochemical sig- nificance.Seventy-eight representative electron mi- croprobe analyses and refined X-ray powder dif- fraction data for most of these phasesare listed in AppendicesI and2, respectively.ISome theoretical rTo receivecopies of theseAppendices, order Document AM- 82-187(analyses, Appendix l) and AM-82-188 (X-ray data, Appendix 2) from the BusinessOffice, Mineralogical Society of T nO America,2000 Florida Avenue,N.W., Washington,D.C. 20fi)9. Pleaseremit $1.00in advance for each microfiche. ARIZONA SCALEOi MILES 0 20 40 60 t0 t00 Table l. Alteration products of spodumene,montebrasite, and lithiophilite in pegmatitesof the White Picacho district. Ideallzed fornula* Fig. 1. Map showingthe location of the White Picachodistrict in the Arizona pegmatitebelt (stippled area) as defined by Jahns sDodmene Lijl1S1206 (r95D. alblte I{aA1Si308 eucryPtlte r,tals104 K(Ll,A1) (S1'A1)4o10 (F'On) 3 2 xAr3sl30ro(oH) other localities, the lithium minerals have been 2 metasomatically altered to a large number of rare and mineralogically phases(Table rcntebraslte L1A1P04(0H'r) complex 1). This Iow-F nontebraaite LrA1P04 (oH'F) cleavage-controlledpseudomorphic replacement of crandallile csA13(PO4)(?o30H) (oH)6 the primary lithium mineralsis pervasiveat most of hydroxylepatlte ca, (PoO), (olt,F) nuscovlte KAl35130rO(OH) the pegmatitesand apparentlyis the result of sub- 2 brazillanlte N€al3(Po4) (oH) 2 4 solidusreactions with residual aqueouspegmatitic augellte A1, (Po/ ) (orl) r fluids. The sporadic distribution of alteration within scotzalite (rl2+,ile)er,ipo,) 2+, "<ou), kulenlte r. 1re r.1',ig ) rir r'tro" i {oH) individualpegmatites and even within singleunde- " " (va,ca,iln)(r'ln, ie2+; 1r"2]r"lig1er 1roo1, formed crystals suggeststhat the replacement was carboMEe-apatite ca, (P00,c0r), (oll,F) not producedby regionalmetamorphism or by local hydrothermal alteration related to brittle deforma- llthtophillte Lt (Mn,Fe)P04 hureaulite L!n5(PO4)2 (PO3oH)2 ' 4H2o tion. trlploidite Mn2PO4(Otl) (On) This mainly descriptive paper focuses on the eoaphorite MnA1P06 r'llr0 mineralogyof replacementassemblages observed in robe!tsite c.runf+troointonl u. lrro Narba(}ln, Fe), (POO) primary fIllowlte U spodumene,montebrasite, and lithiophilite Karca(h,Ie) A1(oH),(Po/ dlcklnsonlte r / '.!-t ) 1, from the White Picachopegmatites. Although meta- vyllteite (Na,ca,ltn) (l,tn,Fe- (Fe-, Fe-,1{e)A1 (Po4) ) 3 falrfleldlte ca2(ltn,Fe2+) (?04) somatic replacement features such as those that 2'H2o h-chlorapatlte (ca,ler) (c1,oH,I) occur in the White Picacho pegmatiteshave re- 5(?o4) 3 Ehodochtosi!e "t"o3.. ceived considerableattention from mineralogists slcklerlte Li(lrn- ,Fe- )PO4 (e.9., Brush and Dana, 1878,1879a, 1879b, 1880; LONDON AND BURT: SPODUMENE, MONTEBRASITE AND LITHIOPHILITE 99 modelsdeveloped in two other papers(London and Table 2. Occurrences of spodumene, montebrasite, and Burt, 1981a,1981b) are based in part on observa- lithiophilite at individual pegmatites in the White Picacho district. * tions from the White Picachopegmatites. Abundances denoted by: Geologyof the lithium pegmatites X = abundant O = comon Of the nine known lithium pegmatites in the R = rare A = not reported district, the Homestead, Independence,Midnight or observed Owl, North Morning Star, and White Ridge were Pegmatite6 Spodumene I'lontebrasite Lithiophilite chosenfor detailedstudy, as thesefive pegmatites Homeslead 0 RX appearto encompassall variationsin generalgeolo- IndepeDdence 00 gy and in the occurrenceand alterationof primary Lone Giant OR lithium minerals (see Jahns, 1952, and London, Lower Junbo AA Midnlght ow1 x XO 1979,for index maps and detailed geologic maps I'lorning Star 0 AR and desqriptionsof the pegmatites). The lithium North Morning Star x XA pegmatitesdisplay highly irregularoutcrop patterns Picacho View 0 OA &trite Ridge x OR and usually occur as clustersof small steeplydip- ping pods or lenses rather than single, isolated *See Jahns (1952) and Londan (1979) for inder ncps md geo- bodies. Spodumene (LiAlSi206), montebrasite LogLe naps and deseiptims of indiuiduaL pegnatite.s. (LiAIPO4(OH,F)),and lithiophilite (Li(Mn,Fe)pOa) are the primary lithium minerals in these pegma- tites. Micas generally are not abundant, and true lepidolitesoccur only as replacementsof primary occurs in the quartz cores and apparently was the lithium minerals.Green lithium tourmaline (verde- last primary lithium mineral to crystallize. Lithio- lite) occurs at one locality but dobs not figure philite also occurs with columbite, manganoantour- prominentlyin the paragenesisof the lithium miner- maline, zireon, and manganoanapatite in massesof als. relatively coarse-grainedalbite (cleavelandite)or All of the lithium pegmatitesare sharplyzoned by cleavelandite * mica. Although lithiophilite nod- grain size and by composition. With few excep- ules are abundantin these complexesat the White tions, the lithium mineralsare concentratedin the Ridge, Homestead,and Midnight Owl pegmatites, inner zonesand coresof essentiallygranitic pegma- the primary phosphateis usually highly altered. tite. The distributionof zoneswithin eachpegmatite In the White Picachopegmatites,