TIIE AMERICAN MINERALOGIST, VOL. 56, SEPTEMBER-OCTOBER' 1971 NEW OCCURRBNCE OF YUGAWARALITE FROM THE CHENA HOT SPRINGS AREA, ALASKA1 G. DoNarl EnEnluN, R. C. Enn, Fr-onBNcBWnnnn, aNp L. B. Bn.n'rrv, U. S. GeologicalSuroey, Menlo Park, California 94025. ABSTRACT Yugawaralite (CaAlzSieOro'4IIzO)' a relatively rare calcium zeolite, was found in a new locality near chena Hot springs, east-central Alaska in a geologic setting that difiers from quartz- that described for occurrences in Japan and Iceland. It occurs as well-formed' encrusted crystals up to 8 mm long, elongate along the a axis and tabular parallel to [ 0101. reported by previous workers. Chemical analysis shows SiOz61.47, AI2OB17.38, FerOr<0.04, TiOr<0.01, MgO(0'01, CaO 8.51, SrO 0.21, NazO 0.06, KrO 0.09, HrO+ 9.33, t{zo- 2.79, total 99.90 wt' /6' In which is 0.3737 apparent deficiency of cations lruror/(nro+no):1.09] disappears if H+, ions per formula in excess of that required by an ideal SH:o in the unit cell, is present as oxonium ion. Thermogravimetric analysis gives good agreement with TGA curves from the tlpe Iocality. Ion-exchange values determined show a low-exchange capacity as compared with most zeolites. Infrared absorption spectra obtained are distinctive but have similarities to tlose of the heulandite grouP. INrnooucrroN Yugawaralite, a relatively rare calcium zerolite, was first describedby Sakurai and Hayashi (1952) fiom "Fudo-no-taki" Fall, near Yugawara Hot Spring, Kanagawa Prefecture, Japan. It has since been reported from Heinabergsjiikull, southeasternIceland (Barrer and Marshall' 1965; Walker, in pressl See Kerr and Williams, 1969, p. 1190); the Onikobe geothermal area of northeast Japan (Seki and Okumura, 1968); Shimoda' Shizuoka Prefecture, central Japan (Sameshima,1969); and the Tanzawa a Mountaihs area of central Japan (Seki el el., 1969). We here report on new occurrenceof yugawaralite in a geologicsettiDg different from those eprlier described.To facilitate comparigon,this first complete description since that of Sakurai and Hayashi (1952) includes corrected and refined I Publicationauthorized by the Director,U' S. GeologicalSurvey' 1699 1700 EBERLEIN, ERD, WEBER, AND BEATTY crystallographic data obtained by restudying samples from the type locality. Unlessotherwise specified, all statementsregarding yugawaralite refer to material from the vicinity of Chena Hot Springs,Alaska. FrBr,n OccuRRENcEAND GEoLocrc SETTTNG The new occurrence of yugawaralite is in the yukon-Tanana upland on the north bank of the chena River, approximately 40 miles east of Fairbanks,Alaska (NW1/4NWlf 4, sec.20,T. I N., R. I E., Fairbanks meridian). The upland is underlain by complexly folded and faulted schist, gneiss,quartzite, phyllite, slate, and metachert of precambrian or early Paleozoic age which have been intruded by granitic rocks of Mesozoic and Tertiary age. Yugawaralite, associatedwith quartz, laumontite, stelrerite (Erd, et al., 1967),and stilbite, occursmainly in a siliceousxenolith about 150 feet long and 60 f eet wide near the edgeof a small porphyritic quartz monzo- nite piuton 1-| miles long and f mile wide (Fig. 1). The quirtz monzonite plutc-n may be an apophysis of a much larger intrusive that is exposed acrossthe chena valley to the southeast.The host rock of the yugawaral- ite is brecciated, sugary-textured metachert, or very fitr. g.uio.d quart- zite that is veined with quartz, chalcedony, and. minor opal. At ioint EXPLANATION tsC )z Alluvium oi Cnve| sand,and silt ) Ir N! v^s NU< Porphyriticquartz monzonite 9iE ) =E F|iTnrfim III/JJJJJIII Gray-black multicolored phyllite and;slate Stippling idicates honlels . e Quartzite, metachen, and argillite 3 Stippl i ng indi c ateshonle t, f/7- d= zH Calcareousphyllite <x : -:---\ gi Con tac t I Dashed where nferred e 5 t0 MTLES l**l Quartzite, quartz muscovite,and biotite schist Frc. 1. Index and geologic sketch maps of yugarvaralite localitl', Chena River area. Alaska i VUGAWARALIT E FROM A LASKA t70l Frc. 2. Yugawaralite (y) and stibite (s) encased in quartz (q) scalenohedrons intersections, quartz-encrusted yugawaralite erystals up to 8 mm long coat joint surfacesand v\rg-like enlargements.Locally, fractures are com- pletely filled with yugawaralite, quartz,'stellerite, stilbite, and laumon- tite. A film of hydrous irbn oxide coats quartz and'the surface of many yugawaralite crystals. Crystals of stellerite and stilbite are closely associ- ated with the yugawaralite (Fig..2). A soft white powdery coating of Iaumontite commonly occurs on crystals of yugawaralite, stellerite, stilbite, and quartz in the vugs. The quartz monzonite contains 25-30 percent plagioclase (Anas15), 35-40 percent quartz, 25-30 percent potassium feldspar, and about 5 percent biotite; accessoryminerals are zircon, allanite, greenish-brown tourmaline, and cerite. Potassium feldspar occurs as xenomorphic phenocrysts, up to 1-] cm in diameter, that enclosethe other minerals. The pluton has many. features in common with other intrusives in the Yukon-Tanana Upland that have yielded tate Cretaceous to early Tertiary isotopic dates. 1702 EBDRLEIN, ERD, WEBER, AND BEATTY At least three episodesof fracturing-and late mineral deposition are indicated: (1) Early minor fracturing of the host rock and introd.uction of white vein quartz that probably was derived from the enclosingsiliceous host rocks. (2) Brecciation and recementation by chalcedony and white quartz, probably at the time of intrusion by quartz monzonite. (3) Late fracturing and introduction of quartz, yugawaralite, stellerite and./ot stilbite, laumontite, chalcedony and "minor opal in the order given. The associationof yugawaralite with laumontite and quartz in an area of thermal-spring activity near Yugawara Hot Spring, Japan (Sakurai and Hayashi, I9S2); the occurrence of yugawaralite with laumontite, analcime, and quartz in a drill-hole core at an active geothermal areaat northeast Japan (seki and okumura, 1968); and the fact that the Alas!.a occurrenceis only 14 miles from chena Hot springs suggestthe possibil- ity of a similar geothermal origin. There is, however, no evidenceof past or present thermal spring activity at the yugawaralite locality. Further- more, th.e.chena Hot Springs are dilute thermal waters of probable meteoric fuiqin that contain considerablesilica and sulfate ions, Lut little calcium afld magnesium. very little mineral deposition is now taking place at Chena Hot Springs. GBocgBurcer, IuplrcarroNs The geochemistry of zeolites and their natural associationshave been reviewgd and brought into better perspective by coombs et at,. (19s9), Senderov (1965), and seki et at. (1969); and significant contriburions ro the understanding of high-silica calcium zeolite assemblageshave been perature range 200o-300oc.Deposition probably occurred from relatively alkaline aqueous solutions in which the activity of silica was equal to or exceeded that of quartz. Cnvsrnr,rocRApEy X-ray dota. The fuh\,0k1, h\t, hhI, and,hll reciprocal nets were photo- graphed using Zr-filtered Mo radiation. systematic absencesindicate the Y UGAWARA LIT' E FROM A LASKA 1703 space group to be either Pa or P2fa.1 Yugawaralite from Alaska and Japan is piezoelectric at various frequency intervals between 1.3 and 3.6 MHz. Furthermore, pyroelectricity and etch-pit symmetry (de- scribed below) confirm the absenceof centrosymmetry. These data agree with the findings of Barrer and Marshall (1965, p. 485), Kerr and Wil- Iiams (1967, p. 222), and Leimer and Slaughter (1969, p. 94), all of whom, by statistical study of intensities, found yugawaralite to be non- centrosymmetric. Our data for the unit cells of yugawaralite from Alaska and from the type locality at Yugawara Hot Spring, Kanagawa Prefec- ture, Japan, are shown in Table 1. Our X-ray powder data for yugawaralite from Chena, Alaska (Table 2) agree closely with such data for yugawaralite from Heinabergsjcikull, Iceland (Barrer and Marshall, 1965,Table 3) and from the Onikobe and Tanzawa Mountains areas, Japan (Seki and Okumura, 1968, Table 2). Our data for yugawaralite from the type locality (Table 2) agreewell with those given for yugawaralite from this locality by Neumann et al. (1957, Pl. VII, no. 49) and by Seki (written communicatipn, 1965), but they are in poor agreement with the original X-ray powder data of Sakurai and Hayashi (1952). The later data of Sakurai (1953) and Harada et al. (1969a)for material from the type locality are in good accord with ours. Morphology. Crystals of yugawaralite are tabular to lath-like, flattened parallel to the most prominent form {010} , and elongateon o. Somelarger crystals occur in elongate tabular aggregatesof as ma.ny as eight indi- viduals oriented parallel to {0 10} . The central crystals of such aggregates tend to be thickest and longest with progressively thinner and shorter crystals developed outward alongb. The crystals are euhedral; no twin- ning was observed.No doubly terminated crystals were found. The forms noted and the interfacial angles measures on 18 crystals are shown in Table 3. A typical crystal is sketched as Figure 3. Morphological departures from centrosymmetry are slight; this is con- sistent with the presenceof a pseudocenterfor the yugawaralite frame- work reported by Kerr and Williams (1967, p. 223; 1969, p. 1188). Nonetheless, the absence of a center of symmetry is expressed by perceptible differencesin the interfacial angles oI l\hll and {0ft7} domes r We have followed the recommendation of the Commission on Crystallographic Data, International Union of Crystallography (Kennard, Speakman, and Donnay, 1967) in tawng cla in designating the space group. Transformation from tle setting of previous workers (space group Pc) may be accomplished by use of the matrix 01T/0T0/100. The setting of sakurai and Hayashi (1952) may be transformed to our setting by using the matrix00T/0T0/$ 00. 1704 EBERLEIN, ERD, WEBER, AND BEATTY TABLE ].. UNIT-CELL DATA FOR YUGAI,IAMI,ITE Chena Hot Springs, Alaskaa Yugawara Hor Spring, JapanD Crystal systen Monoclinic Monocllnic Space group gd 10. 04310.0021 10. 05oio. oo2!, 13. 997iO. OO3i. 14.00810.OO3L c 6.725!O.OO2L 6.7 2g!O,OOzf', B 111'L1 | 11 | 111'11 | 11' Cell voluoe 881.