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Geothermal Resources Council, TRANSACTIONS, Vol. 12, October 1988

SECONDARY MINERALOGY OF CORE FROM GEOTHERMAL DRILL HOLE CTGH-1, HIGH CASCADE RANGE, OREGON

Keith E. Bargar

U.S. Geological Survey, Menlo Park, CA

ABSTRACT physical and chemical conditions responsible for Geothermal drill hole CTGH-1 , located near secondary mineralization of the drill core. The Breitenbush Hot Springs in the Cascade Mountains drill core samples were studied using binocular of northwest Oregon, was drilled to a depth of microscope, X-ray powder diffraction (XRD), and 1463 m. The maximum reported temperature at the scanning electron microscope (SEMI methods. bottom of the drill hole was 96.4OC. The drill core consists Predominantly of basalt to basaltic . Detailed stratigraphic and petrographic andesite lava flows, tuffs, and volcanic descriptions of Tertiary to Quaternary rocks breccia. Red to orange iron-oxide stained tuffs recovered from the drill hole are provided by are at least partly altered to smectite. Conrey and Sherrod (1988). Except for one Vesicles , fractures, and open spaces between section of andesite and dacite lavas, drill core breccia fragments are partly to completely filled from the CTGH-1 drill hole consists predominantly by secondary minerals: hematite, goethite, of basaltic andesite to basalt lava flows, tuff, smectite, celadonite, zeolite minerals (analcime, and breccia (Conrey and Sherrod, 1988). The more chabazite, clinoptilolite,' erionite, heulandite, silicic rocks contain some vapor-phase tridymite mordenite, phillipsite, scolecite, thomsonite, and ilmenite (in one sample) in addition to and wellsite), silica minerals (chalcedony , primary minerals: quartz, plagioclase, f -c ris toba 1i te , c.-c ris t obali t e , and quartz) , magnetite, and pyroxene. Primary minerals of the native copper, calcite, apatite, and adularia. mafic rocks are mostly plagioclase, pyroxene, All of the above minerals are compatible with the magnetite, olivine, and hornblende (identified in present low-temperature conditions. one sample only) ; c-cristohalite from devitrification occurs in several samples.

INTRODUCTION Textures of the lava flows vary from massive to vesicular; fracturing ranges from moderate to Geothermal drill hole CTGH-1 is located about very intense. Most fractures and vesicles 14 km northeast of Breitenbush Hot Springs and 6 contain at least traces of mineralization and the km northwest of Olallie Butte, at an elevation of majority of open spaces are partly to completely 1170 m, near the Western Cascades-High Cascades filled by secondary minerals. boundary in northwest Oregon. Drilling of the 1463-111-deepcore hole by Thermal Power Company SECONDARY MINERALIZATION and Chevron Geothermal on a cost sharing basis with the U.S. Department of Energy began on June Drill cuttings above 161- depth in the drill 7, 1986 and was completed September 7, 1986 hole were not sampled for this investigation. (UURI, 1987). The hole was rotary drilled to From 163- to 622-111depth the secondary mineralogy 161-m depth and then cored to the hole bottom consists of smectite, hematite, and rarely, with essentially 100 percent core recovery. The z eo1 i t es ( chabaz it e , we1 1s it e , and heulandite) maximum reported temperature at the bottom of the (fig. 1). Between depths of 622 m and 885 m, hole was 96.4OC (Blackwell and Steele, 1987) and smectite and chabazite are the predominant the temperature gradient below '500111 depth was alteration minerals although significant amounts about 83OC/km (Priest and others, 1987). of analcime and other zeolite minerals (c linopt i lolite , heulandite, phi 11ips i t e, Drill core from the CTGH-1 drill hole is scolecite, and thomsonite) are present with minor stored in the University of Utah Research hematite, calcite, and apatite. Below 885111 Institute (UURI) core library in Salt Lake City, depth, smectite remains the dominant secondary Utah. A total of 307 core samples between the mineral and is found along with celadonite, depths of 163 m and 1463 m, consisting of zeolite minerals (clinoptilolite, erionite, fracture fillings, vug fillings, or heulandite, and mordenite), and silica.minerals representative samples of stratigraphic ( r-cristobalite, c-cristobalite, chalcedony, intervals, was obtained to identify the and quartz); less-abundant hematite and rare alteration minerals in the drill core and to gain goethite, native copper, and adularia were also a preliminary understanding of the identified.

283 Bargar

0 0

1000

500

2000 n I- n LL Y r Y I I + I- P n W w n n

3000

1000

4000

N 4-L Eo n 3 3 0 0 L I 8

Figure 1. Distribution of secondary minerals with depth in drill hole CTGH-1.

284 Bargar

t.iemat it e or as groundmass alteration (particularly in tuffaceous rocks). Characteristically, secondary Red-orange-brown iron-oxide stains are smectite from drill hole CTGH-1 has a basal scattered throughout the CTGH-1 drill core (fig . spacing of *14-15 A (although basal spacings 1) in abundances that range from a pervasive as low as -12A were noted in a few samples) brick-red coloring of an entire specimen to that expands to Q17A with glycolation, and microscopic orange-staining. In most cases the collapses to *lOA after overnight heating at iron oxide was identified as hematite by X-ray 450OC. Measurements of the 060 reflection for 12 diffraction. However, a few samples appear to selected clay samples from the core ranged from contain amorphous iron oxide. Much of the 1.50A (montmorillonite, commonly Ca- or Na-rich hematite occurs in volcanic breccia, highly smectite) to 1.52A (nontronite, an Fe-rich vesicular basalt, or tuffaceous deposits where it smectite) and 1.53A (saponite, Mg-rich probably formed by oxidation of primary magnetite smectite) (Starkey and others, 1984) with during cooling of the volcanic rocks. A few, apparent random distribution of dioctahedral thin, red hematite stains on fracture surfaces or (montmorillonite and , nontronite) and vesicle walls in the lower part of the drill hole trioctahedral (saponite) smectite species appear to be closely associated with later (Brindley and Brown, 1980). Semiquantitative secondary mineral fillings. Similarly, soft chemical analyses of smectite were obtained using orange-red goethite coats a fracture surface at an X-ray energy dispersive spectrometer (EDS) on 1456- depth. The only other secondary the scanni.ng electron microscope (SEMI. Samples iron-oxide mineral identified in the drill core from 564 m, 764 m, and 861 m contain (in addition is ilmenite which occurs as black, metallic, to Si and Al) FeXaag; the two shallower hexagonal crystals that' are closely associated samples also contain minor amounts of K, and Ti. with vapor-phase tridymite at 440- depth. Using EDS, low concentrations of Na are difficult to detect, but Na is possibly present in clay Smec t ite from 764-m depth. The 060 reflections for these clays are too indistinct for accurate measurement Core samples from depths of 163-480 m contain on routine X-ray diffractograms. Because Fe is light-brown to orange (locally white or pink) the predominant cation; however , these three clay that commonly coats the exterior core clays are most likely dioctahedral nontronite, surfaces and partly to completely fills open although trioctahedral saponite with high Fe spaces in the drill core. Much of this clay is content has been reported (Weaver and Pollard, probably residual drilling mud. X-ray 1973). . diffraction analyses of clays from this part of the drill core mostly show low, broad X-ray peaks Celadonite that suggest poorly crystalline or even amorphous material. Several analysed samples probably The micaceous mineral celadonite occurs contain a mixed-layer illite-smectite consisting intermittently below 1130-111depth, normally as a predominantly of illite as evidenced by a soft, blue-green clay-like material deposited as *10A peak that shows very slight expansion horizontal layers (later than green smectite) in after being placed in an atmosphere of ethylene cavities and fractures. In a few vesicles, the glycol at 60°C for 1 hour. In geothermal areas, blue-green clayey layers are sandwiched between mixed-layer illite-smectite typically forms at horizontal beds of medium- and dark-green temperatures well above the Q0"C that were smectite. At 1133- depth, celadonite that measured in the upper part of the CTGH-1 drill produces a low, broad %10A X-ray peak formed hole (Aumento and Liguori , 1986). Mixed-layer earlier than a heulandite-group mineral (probably illite-smectite was not found below 403m depth c linopt i lo1 i t e and &cr is t oba li t e. Later in the drill core, and whenever the mineral was emerald-green micaceous celadonite, characterized identified in open-space fillings by XRD analysis by a high, sharp 10A X-ray peak, is sprinkled it was presumed to be drilling mud residue. Most on top of the B-cristobalite. An EDS analysis of the X-ray diffraction analyses of clays from of soft blue-green celadonite from 1133- depth this interval also contained a Y5A peak that shows, in addition to Si and Al, high expanded to *17A after exposure to ethylene concentrations of Fe and K, and very minor glycol, which is typical for smectite. Smectite amounts of Mg, Ti, Cas and possibly Na. was determined to be a component of several samples of drilling mud. where it occurs alone or Zeolite Minerals in association with the mixed-layer illite-smectite. In fig. 1, a few smectite In the interval from 163 to 622 m, the only samples between depths of 163 and 480 m are secondary minerals other than hematite and classified as secondary based on the mode of smectite are rare occurrences of chabazite, occurrence. It is possible that additional heulandite, and wellsite. The first two of these secondary smectite exists in samples from this zeolite minerals will be discussed later. zone, but any such occurrences are masked by Wellsite, an intermediate zeolite mineral in the drilling mud contamination. phillipsite-harmotome group was identified only in vesicles of basalt from 564-111 depth. It forms Below 480- depth, smectite (various colors randomly oriented, elongate, prismatic crystals , but predominantly green) occurs in virtually clusters of radiating crystals, or closely spaced every sampled interval as fracture coatings, elongate crystals that are deposited as lining vesicle walls, between breccia fragments, overlapping radiating hemispherical crystal BtU”g€tX

clusters to produce a botryoidal coating. At and K, which indicates that the mineral is not a 564- depth, the wellsite crystals are partly pur e ana lcime en d-membe r of the coated by later smectite; however, the majority analcime-wairakite solid solution series and of the light- to dark-green smectite layers were probably should be considered a calcian analcime earlier deposits that formed horizontal layers in (Gottardi and Galli, 1985). the bottoms of vesicles. Two semiquantitative EDS analyses of wellsite show significant Ba, and Fracture fillings in drill core between 764- K, and a little Ca in addition to Si and Al. to 785711 depth contain radiating clusters of X-ray powder diffraction patterns of the wellsite colorless, acicular crystals that were seen in are similar to phillipsite and harmotome, but the SEM to be deposited later than thomsonite, approximately equal proportions of Ba and K chabazite, and analcime at 767- depth. detected by EDS analysis suggest that the mineral Semiquantitative EDS analyses indicate that the is wellsite rather than Ba-poor phi11 ipsite or crystals are rich in Ca, Al, and Si and the K-poor harmotome (Cerny and others, 1977). mineral is identified as scolecite rather than structurally similar Na-rich natrolite or Na+Ca In the interval from 622- to 885-m depth, mesolite (Gottardi and Galli, 1985). zeolites occur with orange to green smectite and local iron-oxide staining (mostly hematite but An abrupt change in secondary mineralogy amorphous iron oxide may be present). These occurs at 885- depth in the CTGH-1 drill hole. minerals fill vesicles, fractures, and open Except for one occurrence of chabazite at 892-m spaces between volcanic breccia fragments, and depth, the zeolite minerals discussed above are are dispersed in altered tuffaceous rocks. absent and the interval below 8853 depth is Phillipsite, an early-formed zeolite mineral in characterized by the heulandite-group zeolites this drill core, was identified by XRD in only heulandite and clinoptiloli t e. Ahundan t three samples (at 821 m, 812 m, and 821 m). At mordenite and minor erionite are also present in 821- depth, colorless phillipsite crystals this part of the drill core. Early-formed formed in basalt vesicles, whereas at 812-m depth reddish hematite staining is sporadically the phillipsite pervasively lines open spaces in distributed through the interval. Later-formed volcanic breccia, forming clusters of closely smectite is the dominant open-space filling. spaced elongate crystals that appear partly Below 1130- depth fracture- and vesicle-filling dissolved in scanning electron micrographs. deposits of blue-green clayey minerals, Semiquantitative EDS analyses indicate that both identified as celadonite in several X-ray samples have approximately the same chemical diffraction analyses, formed either later than composition: Si, Al, and KXa. green smectite or are sandwiched between horizontal green smectite layers. At 812- depth, phillipsite is associated with later clusters of colorless tabular or Three samples between the depths of 886 m and lamellar crystals that were identified as 888 m contain acicular to columnar appearing thomsonite in XRD analysis. At 764- depth, crystals, identified as erionite by XRD, that thomsonite crystals were deposited as irregularly were deposited later than green smectite. In the oriented tabular clusters; whereas, at a depth of SEM, these columns consist of bundles of fibrous 767 m, the tapered, tabular, thomsonite crystals crystals and, occassionally, appear to have form somewhat fan-shaped crystal clusters. EDS hexagonal cross sections. The erionite crystal analyses for three samples of thomsonite from clusters formed earlier than associated blocky widely separated intervals have Ca, Si, and A1 as heulandite crystals at 8873 depth. An EDS their major constituents. Fractures and vesicles analysis of erionite indicates Ca, K, Al, and Si. in highly altered basaltic drill core at 663111 depth contain a soft, colorless, botryoidal Heulandite and clinoptilolite, two coating that consists of hemispherical-shaped heulandite-group zeolite minerals, are both clusters of closely spaced thomsonite crystals. present in the lower part of the CTGH-1 drill core.. The two minerals have virtually the same At 663- depth, the thomsonite crystals are structure and are indistinguishable in X-ray overlain by later-deposited colorless crystals diffraction analyses. Mump t on (1960) identified as chabazite by XRD. Pseudocubic discriminated between clinoptilolite and rhombohedral chabazite (frequently twinned), heulandite on the basis of overnight heating at deposited in association with earlier smectite in 45OOC. If the 020 reflection at q.OA is many open spaces, is the predominant zeolite unchanged after heating, the mineral is mineral in this interval (fig. 1). EDS analysis identified as clinoptilolite, whereas heulandite of chabazite from 634-m depth shows the presence is characterized by destruction of this of Ca, Al, Si, and very minor K. reflection. However, Gottardi and Galli (1985) favor nomenclature based on the chemical Scattered open-space deposits of colorless, composition, as suggested by Mason and Sand trapezohedra1 crystals identified as analcime in (1960). In this classification, heulandite XRD are closely associated with chabazite contains more Ca+Sr+Ba than Na+K, and Na+K is although the depositional sequence is predominant in clinoptilolite. undetermined; SEM observations show that analcime formed later than thomsonite, and phillipsite. Samples containing a hculandit e-group Semiquantitative EDS analyses of the analcime mineral, collected from 14 depth intervals, were show significant Ca, in addition to Si, Al, Na, heated overnight at 450OC. At depths shallower

286 Bargar than 892 m, only one sample showed no change in consists of spherical clusters of blocky peak position or intensity after heating and the crystals. However, the two minerals are best mineral is probably clinoptilolite. In the distinguished by X-ray diffraction. remaining samples above 892 m-depth, the 020 8-cristobalite has a broad major peak between reflection was destroyed, so the mineral should 4.07A and 4.11d and a single minor peak near be heulandite according to Mumpton's (1960) 2.50A; a-cristobalite has a sharp major peak classification. None of the heated samples, between 4.04A and 4.07A and several other below 8923 depth, showed a change in the 020 minor peaks. In fig. 1, a-cristohalite and reflection after heating, so presumably 8-cristobalite were combined because the clinoptilolite is the only heulandite-group presence of the two minerals was only spot zeolite present. checked by X-ray diffraction and no attempt was made to determine their precise distribution. In the distribution diagram of fig. 1, the heulandite-group minerals were combined because Tiny, colorless, euhedral quartz crystals semiquantitative EDS analyses of CTGH-1 samples occur in vesicles from seven drill core samples. do not tota1 ly support the Many other open-space-filling white, colorless, heulandite-clinoptilolite distinction suggested yellow, or green massive silica deposits give an by Mumpton (1960). .Calcium undoubtedly is more X-ray diffraction pattern indicative of quartz abundant than Na+K, in heulandite. from 887-10 but when viewed in immersion liquids are observed depth, as would be suggested by the heating to have a fibrous structure and are chalcedony. test. 'Below 8924 depth heating tests showed Chalcedony, a cryptocrystalline variety of quartz only the presence of clinoptilolite; however, can be distinguished from quartz in thin-section Na+K is clearly dominant over Ca only at a depth or in immersion media. No attempt was made, of 983 m. In four other samples below this however, to distinguish between the massive depth, Ca appears to be dominant over Na+K quartz and chalcedony deposits for fig. 1. A although the difficulty in detecting Na by EDS further complication arises from a few X-ray analyses makes the distinction between diffraction analyses of botryoidal silica that clinoptilolite and heulandite unreliable when showed the presence of chalcedony in addition to significant Ca is present. a- or bcristobalite.

In drill hole CTGH-1, heulandite-group Other Minerals zeolites, deposited in vesicles, fractures, and between breccia fragments , formed later than The only other secondary minerals in this hematite, smec t i t e, c eladonit e, and erionit e, but drill core are calcite, apatite, adularia, and earlier than a-cristobalite, kristobalite native copper. Native copper was identified (by or mordenite. SEM observations indicate that EDS in SEM studies) in two samples from near minor smectite appears to be deposited later than 1015- depth as an open-space deposit that formed . some heulandite-group crystals. The crystal earlier than botryoidal &cristobalite and morphology of the heulandite-group minerals in white smectite. The other minerals, whose mode drill core CTGH-1 ranges from a tabular of occurrence is unknown, were identified only in tombstone-like habit at 13413 depth to a more X-ray diffraction analyses from depths of 663 m blocky morphology in samples from shallower and 675 m (calcite), 665 m (apatite), and 1293 m depths. (adularia).

White cotton-like mats of interwoven long SUMMARY AND DISCUSSION thin fibrous crystals or small tufts of fibrous mordenite crystals appear to be the latest The rocks penetrated in the CTGH-1 drill hole mineral deposited in many open spaces below consist predominantly of basalt to basaltic 1099m depth in drill core from the CTGH-1 hole. andesite. Early vapor-phase tridymite and An EDS analysis of mordenite from 12603 depth possibly ilmenite are present in a dacitic showed only Ca, Al, and Si. section from 2603 to 339-10 depth. Minor scattered ecristobalite, formed by Silica Minerals devitrification, is present in a few pieces of drill core. Some mafic minerals and what was Silica minerals ( B-c ris toba 1it e, probably the glassy groundmass of several drill a-cristobalite, chalcedony, and quartz) from core samples are altered to iron oxide (mostly the CTGH-1 drill hole occur as deposits in open hematite but also amorphous iron oxide) and spaces that formed later than most other minerals smectite. Vesicles, fractures, and open spaces except for mordenite and minor smectite. Between between breccia fragments are partly * to depths of 956 and 1372 m, silica forms colorless, completely filled by secondary minerals that frosted, or bluish botryoidal deposits identified include iron oxide minerals (hematite and as 8-cristobalite in several X-ray diffraction goethite), smectite, celadonite, zeolite minerals analyses. Deposits of 8-cristobalite alternate (analcime, chabazite, clinoptilolite, erionite, with similar appearing bot ryoida 1 heulandite, mordenite, phillipsite, scolecite, a-cristobalite between 1061-m and 1372- t homsoni t e, and weilsite), silica mineral; depth. Below 1372- depth, ecristobalite is ( 8-c r ist oba 1i t e, a-cristobalite, chalcedony, the predominant silica phase. In the SEM, and quartz), native copper, apatite, calcite, and 8-cristobalite has a smooth, non-crystalline adularia. appearance, whereas a-cristobalite usually Bargar Iron oxide (primarily hematite) which temperatures. Apparently the silica minerals are probably formed by oxidation of magnetite during compatible with temperatures of formation below the cooling of lava flows, is the earliest-formed 100°C and have been reported at similar significant secondary mineral in the CTGH-1 drill temperatures in core from several holes drilled core. Locally, iron- and magnesium-rich green in the Columbia River Basalt Group (CRBG) in the smectite (nontronite and saponite) was deposited Pasco Basin of south-central Washington (Benson later than reddish iron oxide in fractures or and Teague, 1982). In fact, nearly all of the vesicles. More than one generation of smectite secondary mineral phases identified in drill hole was deposited in the drill hole and some vesicles CTGH-1 and their distribution within the drill were observed to contain multiple horizontal core are remarkably similar to secondary mineral layers consisting of different shades of green assemblages reported in the Pasco Basin drill smectite. Smectite color is quite variable in holes by Benson and Teague (1982). The CRBG the CTGH-1 drill core and many colors (white, alteration minerals are attributed to formation pink, brown, orange, or red) other than green at temperatures less than 100°C and are were observed. Differences in X-ray basal characterized as diagenetic. spacing and position of 060 reflections suggest that some of the later smectite deposits may The secondary mineral assemblage of the contain Ca, Na, or K as exchangeable cations CTGH-1 drill core is similar also to hydrothermal rather than Fe and Mg. alteration mineralogy of late Tertiary volcanic rocks in the Breitenbush-Austin Hot Springs area Blue-green clay identified as celadonite was (Keith, 1988). Even though the depth of burial deposited later than green smectite in many open at the bottom of the CTGH-1 drill hole is nearly spaces, and is sandwiched between horizontal 1.5 km, the bottom-hole temperature of 96.4"C green smectite layers in a few vesicles. (Blackwell and Steele, 19871, the current high Celadonite, containing abundant Fe and K, also heat flow of the area (Blackwell and Baker, 1988) occurs as an emerald-green micaceous deposit that and the nearby hot springs suggest that the formed later than .smectite, blue-green clayey alteration mineralogy of the CTGH-1 drill core celadonite, clinoptilolite, and B-cristobalite should be characterized as lort emperature at 1133- depth. hydrothermal alteration rather than diagenetic.

Several zeolite minerals were deposited later ACKNOWLEDGMENTS than the above Fe, Mg, and K minerals. The first zeolite minerals to be deposited appear to be The author thanks P.M. Wright of UURI for K-rich wellsite and phillipsite. Wellsite occurs making the drill core available for this study. in the upper zeolite zone along with the Ca-rich R.O. Oscarson assisted in the scanning electron minerals heulandite and chabazite (exact order of work. R.C. Erd and L.C. Calk provided helpful deposition is uncertain). In the middle zeolite reviews and constructive criticisms of the zone, calcian analcime and Ca-rich thomsonite, manuscript. chabazite, and scolecite were deposited later than phillipsite. The lower zeolite zone REFERENCES contains Ca- and K-rich erionite along with later-formed clinoptilolite, heulandite, and Aumento, F., and Liguori, P.E., 1986, Conceptual Ca-rich mordenite. Silica minerals apparently reservoir models through geoscientific were deposited later than the zeolites (except investigations: Geothermics, v. 15, p. for mordenite). B-c r is tobal it e and 7 99- 806. a-cristobalite alternate in open-space fillings of the lower zeolite zone. Chalcedony and quartz Benson, L.V., and Teague, L.S., 1982, Diagenesis crystals appear to be deposited €ater than either of basalts from the Pasco Basin, cristobalite mineral in several vesicles and Washington-I. Distribution and composition of fractures of this lower zone. The order of secondary mineral phases : Journal of deposition for apatite, calcite, and adularia is Sedimentary Petrology, v. 52, p. 595-613. unknown because they were detected as only minor components in X-ray diffraction analyses. Native Blackwell, D.D., and Steele, J.L., 1987, copper was deposited in a few open spaces and Geothermal data from deep holes in the Oregon formed earlier than Scristobalite and white Cascade Range: Geothermal Resources Council smec t ite . Transactions, V. 11, p. 317-322. The paragenetic sequence of secondary Blackwell, D.D., and Baker, S., 1988, Thermal minerals from this drill core suggests that analysis of the Brei t enbush geo th erma 1 rock/water interaction, initially through system: in Sherrod, D.R., ed., Geology and alteration of basaltic glass and mafic minerals, geothermal- resources of the provided sufficient Fe and Mg to form the earlier Breitenbush-Austin Hot Springs area, deposited secondary minerals. During later Clackamas and Marion Counties, Oregon: mineralization, K, Na, Ca, and Si were more Oregon Department of Geology and Mineral prevalent in the fluids, and the minerals that Industries Open-File Report 0-88-5, in press. formed were mostly zeolites, and silica minerals. Smectite and most of the zeolite minerals (Kristmannsdottir and Tomasson, 1977) are compatible with the present low

288 Bargar

Brindley, G.W., and Brown, G., 1980, Crystal Kristmannsdottir, HI, and Tomasson, J., 1978, structures of clay min.erals and their X-ray Zeolite zones in geothermal areasin Iceland: i den t i f kation : Mineralogical Society -in Sand, L.B., and Mumpton, F.A., (eds.) Monograph No. 5, Mineralogical Society, Natural Zeolites: Occurrence, Properties, London, 4958 Use, Petgamon Press, Oxford, p. 277-284.

Cerny, P., Rinaldi, R., and Surdam, R.C., 1977, Mason, B., and Sand, L.B., 1960, Clinoptilolite Wellsite and its status in the from Patagonia, the relationship between phillipsite-harmotome group: Neues Jahrbuch clinoptilolite and heulandite: American fur Mineralogie Abhandlungen, v. 128, p. Mineralogist, V. 45, p. 341-350. 312-330. Mumpton, F. A., 1960, Clinoptilolite redefined: Conrey, R.M., and Sherrod, D.R., 1988, American Mineralogist, vI 45, p. 351-369. Stratigraphy and geochemistry of drill holes in the Breitenbush-Austin Hot Springs area, Priest, G.R., Woller, N.M., Blackwell, D.D., and Cascade Range, Oregon: in Sherrod, D.R., Gannett, M.W., 1987, Geothermal exploration ed, , Geology and geothermarresources of the in Oregon, 1986: Oregon Geology, v. 49, p* Breitenbush-Austin Hot Springs area, 67-73. Clackamas and Marion Counties, Oregon: Oregon Department of Geology and Mineral Starkey, H.C., Blackmon, P.D., and Hauff, P,L., Industries Open-File Report 0-88-5, in press. 1984, The routine mineralogical analysis of clay-bearing samples: U.S. Geological Survey Gottardi, G., and Galli, E., 1985, Natural Bulletin 1563, 32 p. Zeolites: Minerals and Rocks, V. 18, Springer-Verlag, Germany, 409p. UURI, 1987, Cascades geothermal program U.S. Department of Energy: Cascades Newsletter no. Keith, T.E.C., 1988, Hydrothermal alteration 3, 3P* patterns in the Breitenbush- sti in hot springs area of the Cascade Range, Oregon: Weaver, C.E., and Pollard, L.D., 1973, The -in Sherrod, D.R., ed., Geology and geothermal chemistry of clay minerals: Developments in resources of the Breitenbush-Austin . Hot Sedimentology V. 15, Elsevier Scientific Springs area, Clackamas and Marion Counties Publishing Company, The Netherlands, 213p. Oregon: Oregon Department of Geology and Mineral Industries Open-File Report 0-88-5, in press.

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