THE AMERICAN MINERALOGIST, VOL. 48, JANUARY_FEBRUARY, 1963

MINERALOGICAL NOTES PHENAKITEFROM THE MOUNT WHEELERAREA, SNAKE RANGE,WHITE PINE COUNTY,NEVADA1

Donarn E. LBB aNo Rrcuann C. Eno, U. S. GeologicalSurvey, Menlo Park, Calif .

INrnooucrroN The mode of occurrenceof the nonpegmatiteberyllium depositsat the Mount Wheelermine, White Pine County, Nevada, has been described by Stager (1960). Whitebread and Lee (1961) report the discovery of similar mineralization more than a mile north of the Mount Wheeler mine (sample 54-MW-60, below) and outline the geology of the mine area. Briefly, the known mineralization in this area replaces the Wheelerlimestone member, of local usage,of the Cambrian PiocheShale. The mineralization is invariably associatedwith veins in this lime- stone,but the exact relationshipsbetween the two are not clear. In order to investigate the physical and chemical properties of the phenakite (BerSiOa)present in this area, pure fractions of this were recovered from three separate field samples.The locations of these samples(Table 1) can be relatedto the geologyof the areaby referenceto Whitebread and Lee (1961) and Drewes (1958). Sample 2-MW-60 was collectedabout 3,920 feet back in the Pole Canyon adit of the Mount Wheeler mine. The phenakite in this sample was not observed in thin section,but separationwork shows that it is present in an irregularly shapedberyl veinlet that cuts a sandy layer below(?)the Wheelerlime- stone member. This veinlet is 1-3 inches wide. Along with beryl and phenakite, the present are quattz, carbonate, fine-grained mus- covite (predominantly 2M , but with minor amounts ol lM) , scheeliteand pyrite. Samples54-MW-60 and 122-MW-60 were collectedat the surface.In each of these samplesthe phenakite is part of a limestonereplacement deposit in an area cut by qtartz veins and veinlets. Along with phenakite the minerals present are fluorite, carbonate, fi4e-grained muscovite (mostly 2M, but also smaller amounts oI IM), and minor amounts of scheelite,pyrite, qlrartz and beryl. The phenakite is most closely associ- ated with fine-grainedmuscovite, carbonate and fluorite, and it is present as euhedralto anhedralcrystalsl the euhedralcrystals are prismatic and attain a length exceeding2 mm in somecases. The pure -150 meshphen- akite analyzedhas a snow-white color. was not identified in any of the three samplesdescribed.

1 Publication authorized by the I)irector, U. S. Geological Survey.

189 190 MINERALOGICAL NOTES

Tlsr-n 1. LocerroNs ol PrrrNarrre-Bn,mrr.rcSmrprrs

Elevation Sample N. Lat. W. Long. (feet)

2-MW-60 39"53',52', 114"19',12u 7,900 54-MW160 38054t49il 114"20'2' 8,760 122-MW-60 38054',06', 714"20',15', 7,gffi

Prrvsrcar AND CrrEMrcALPRopERTTDs oF PupNexrrB A pure phenakitefraction was recoveredfrom eachof thesethree sam- ples by centrifuging-150 mesh material in heavy liquids checkedwith a Christian Becker specific gravity balance. Thus the specific gravity fig- ures listed (Table 2) apply to individual grains in the given fraction, as well as representinga bulk value for the fraction as a whole. Refractive indices (Table 2) were determined in sodium light by the immersion method. For comparison,Table 2 alsoincludes data for a phenakitefrom Minas Gerais, Brazrl; there is very little difierence among the figures Iistedfor thesefour phenakites. Quantitative spectrographicanalyses are listed in Table 3 along with spectrographicdata for the phenakite from Minas Gerais,Brazil. The fiqureslisted for Ge and B are perhapsthe most noteworthy feature of Table 3. Theseelements are presentin eachof the Mount Wheelerphen- akites and possiblyin the Brazilian phenakite too in amounts that well exceedtheir crustal abundances.In this connectionit is interesting to note that the beryi presentwith phenakitein sample2-MW-60 contains neither B nor Ge in detectableamounts (1.a.,less than 20 ppm for each element). Apparently it is not uncommonfor phenakiteto carry minor amounts

Tltel,r 2. SpncrlrcGnevrrv eNn Optrcer, Pnopnnrrns or ANeryznoPnntlrrtrs

Specific Optic Sample gravity Sign

2-MW-60 2.964+.0071 1.670+ 002 1.654+.002.016 uniaxial (*) 54-MW-60 2 -964+.0071 1.669 + .002 1.653+002 .016 uniaxial (f) 122-l'{W-60 2.966+.0072 1.669+ 002 1.653+.002.016 uniaxial (f) Minas Gerais, Brazil 2 960gm/cm33 1.6693 1.6533 ,016 uniaxiai (f)3

1 Centrifuged at 2.970 and,at 2.957. 2 Centrifuged at 2.973 and 2.960. 3 Density at 25"C. as calculated from the NBS lattice constants. Data for density, refractive indices and optic sign from Swanson et a1,.,1959. See Table 3 for spectrogaphic data. MINERALOGICAL NOTES 19l

Tesr-r 3. Sprctnocnepntc ANer,vsrs on PsnNerrrB

2-MW-601 54-MW-60r 122-MW-601 Minas Gerais, Brazil2

Cu <.0002 <.0002 <.0002 .001- .01 Ge .010 .015 .013 .001- .01 - Sn <.001 < 001 <.001 .01 .10 Pb <.002 <.002 <.002 .001- .01 - Zn <.04 <.04 <.04 .01 .10 Mn <.0002 .015 .0003 .001- .01 - Ni <.0004 <.0004 <.0004 .01 .10 - Fe .15 .16 .10 .01 .10 Cr <.0002 <.0002 < .0002 .001-.01 -1 AI .25 .23 .02 .10 .0 - Ti < .001 <.001 <.001 .01 .10 Zr <.002 <.002 < o02 .001- .01 Be MM M - Mg .o32 050 .0052 .01 .10 - Ca .0030 .0019 .0041 .01 .10 Sr .0004 .0004 .0004 .001- .01 Ba .0050 .011 .0004 B .020 .060 .030 .001- .01 - Na .01 .10

1 Robert Mays, analyst. Looked for but not found: Ag, Au, Ru, Rh, Pd, Os, Ir, Pt, Mo' Tb' W, Re, As, Sb, Bi, Se, Te, Cd, Tl, In, Co, V, Ga, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Hf, Th, Nb, Ta, U and P. For limits of sensitivity, see Bastron et aI.,1960. detec- The above results have an overall accuracy of * 15 per cent except near limits of tion where only one digit is reported. 2 Swanson,et ol.,1959.

amountsof B, a finding that is supportedby the presentresults' Wickman (1943)reports 20 ppm Ge in phenakitefrom Kragerd, Nor- way, and this, taken *itf, tft. resultslisted in Table 3, indicatesthat it may not be uncommon for phenakite to carry minor amounts of Ge' In view of the fact that fluorite accompaniesthe Mount Wheeler beryllium mineralization, and each of the phenakites describedhere contains 100- 150 ppm Ge, it may be pertinent to note that the silicates and Iepidolite that are high in germanium (Papish, 1929) arc formed in fluorine-rich environments. A complete analysis is presented for the phenakite from sample 122- 192 MINERALOGICAL NOTES

Teelr 4. CHrurcnl eNn Sprcrnocpernrc Alr,lr, srs ol pnrNaxnr (BezSiOa) 122-MW-60 lnou Wurrn prvr CouNrv, Nuv,q.l,tr

wt 70 Elements

SiOz .)+-.)" 6.oosl A1203 .04 .oosl FezOa .14 .012[ Mgo .009 6.024 CaO .006 GeOz .019 BzOa .097 BeO 45.08 tl.952

Total 99.89

1 Sioz and Beo determinations by R. E. stevens and A. c. Bettiga. Ali other oxides calculated from Table 3. Specific gravity and optical properties of this phenakite given in Table 2. 2 Average of 2 determinations.

MW-60 (Table 4). An tc-ray difrractometer pattern of this phenakite (122-MW-60) was preparedusing tungstenas an internal standard. The sample was scannedat +" 20 trom l7-742o 2g using Fe/Mn radiation, trFeKa1: 1.93597A. fn" maximum variation for d-spacingsin the region 76-142"20 f.romthose given by Swansonet al. (1959)for phenakite from Minas Gerais, BraziI, is*0.0004" A. this appearsto be random error only as there is no consistentvariation suggestinglarger or smaller unit cell dimensionsthan thosegiven for the Brazilian phenakite.See Table 3 for a spectrographic analysis of this Brazilian phenakite and rable 2 for its specificgravity and optical properties.

CoxcrusroN Pending further field and laboratory study of the beryllium mineraliza- tion in the Mount wheeler area it is not possibleto assessthe significance of the relatively large boron and germanium contents of the phenakites describedhere. The beryllium borate, hambergite (Bez(OH)BOa),is not isostructuralwith phenakite.Hambergite is a rare mineral that appears to be confined to granitic and syenitic (see for example, Warner et al., 1959), and the writers have not yet identified this mineral in the Mount Wheelerarea. Apropos of the boron content of these phenakites,there is a further shred of intriguing information. Several miles north of the known beryl- lium mineralizationhere, in the generalarea of 114o18,W.and 39o04,N., the intrusive rock is well jointed, and one set of joints strikes E-W and MINERALOGICAL NOTES 193

of dips about 75.S.The surfacesof this joint set are coatedto a thickness (The field 1 io 2 mm with black tourmaline that is extremely fine grained. identificationof this material was "manganeseoxide")' While this type of tourmaline occurrencehas not been observed in the larger intrusive

the possibility of a direct relationship between the beryllium mineraliza- tion and the intrusive rocks that are exposedin the Mount Wheeler area (Lee and Bastron, t962), and in this connection the tourmaline men- tioned aboveis under studY.

AcrNowrnlGMENT Donald H. whitebread of the u. s. GeologicalSurvey provided helpful adviceon the geologyof the Mount Wheelerarea'

REFERENCES

Soc.Am.69,221-240. und mag- H,lnorn, Hnnuan (1959) Beitrag zur Geochemie des Bors' I Bor in Mineralen S, 67-122' matischen Gesteinen. Ahad. Wiss. Gdttingen,Nackr.' Moth.-Phys. Klasse area' White Pine Lrn, D. E. .q,NoH' -BASTRON(1962) Allanite irom the Mount Wheeler County, Nevada. Am Mineral,. 47, 1327-1331' II' The occurrence of germanium PAprsE, J,tcot (1929) New occutrences of germanium' in silicate minerals. Dcon. Geo|.24,470480. mine' White Pine Sreonn, H. K. (1960) A new beryllium deposit at the Mount Wheeler Geol' Surt;ey ProJ' County, Nevada, in Short pape.s in tle geological sciences' U' S' PaPer, 40O-8, 870-B71. lrvl P' C' P'tms (1959) SwlNsoN, H. E., N. T. Grllnrcu, M. T. Coor, R. S:rrNcrunro StandardX-raydifiractionpatterns.Nat'IBur'Stand'ariJsCirc'539'8'11-13' Wheeler mine area' Wrtrennner, D. H. er"'l D. E. LBt (1961) Geology of the Mount sciences: White Pine County, Nevada, in Short papers in the geologic and hydrologic L/. S. GeoL Suney ProJ. Paper 424-C, Cl20-122' rocks and of differ- Wrcruex, F. E. (1943) Some aspects of the geochemistry of igneous entiation t'y crystailization' Geol F iiren Fiirh. 65, 37 l-396'