Microstructure investigations of Kamchatka geyserites

ISSN 0145-8752, Moscow University Geology Bulletin, 2008, Vol. 63, No. 5, pp. 311–319. © Allerton Press, Inc., 2008.Original Russian Text © V.S. Urusov, L.V. Shvanskaya, A.Yu. Bychkov, A.V. Mokhov, E.A. Labutova, 2008, published in Vestnik Moskovskogo Universiteta. Geologiya, 2008, No. 5,pp. 19–26.

311

INTRODUCTION

Silica is one of the principal components of theEarth’s crust. Its solubility grows with increasing tem-perature and therefore thermal water becomes gener-ally oversaturated with silica due to its cooling near theground surface. Silicic acids have an ability to formoversaturated solutions that are stable for long periods,and therefore amorphous and non-crystalline phasesprecipitate from them. The influence of solution com-positions upon the stability of metastable true and col-loid silica solutions has been insufficiently examined sofar. Silica oversaturation of thermal water relative toquartz has been recorded in almost all the thermal sys-tems of the world, and different geyserites (siliceoussinter) precipitate from these solutions under the influ-ence of a number of factors. These consist largely ofamorphous opal; tridymite, crystobalite, and quartzoccur mainly in recrystallized sediments, as well astraces of pyrite, gypsum, and clay minerals.

The great variability of structures is typical of gey-serites depending on their formation location, condi-tions, and chemical composition of the medium: fromtypical chalk-like loose or consolidated formations toexotic ones (tabular, acicular, dome- and column-shaped) to those having a pinecone shape [Göttlicher,1998; Campbell, 2002]. Professionals call morpholo-gies having a layered texture and enclosing variablesilicified microfossil remains (bacteria, blue-greenalgae, and diatoms) microstromatolites [Campbell,2002; Jones, 1997; Konhouser, 2001; Jones, 1997].

The discovery of morphologic similarity betweensiliceous sediments in the Yellowstone National Parkand Precambrian stromatolites, i.e., organic–sedimen-tary formations originating as a result of carbonate sed-imentation due to the vital activities of microorganismhas attracted particular attention to the origin and struc-ture of siliceous sediments in thermal sources [Walter,1972; Walter, 1976]. However, their origin was associ-ated with abiogenous processes for a long time. Only

after several decades of investigations, researchersusing electron microscopy proved that most hot springsediments, including geyserites, enclose microfossils[Cady, 1996; Jones, 1997]. It is noteworthy that theidentification of microfossils is hampered by their dif-ferent preservation degree and by their different preser-vation upon silica replacement.

In addition, experimental data [Jones, 2004] fromthe examination of microbe silicification in a basin inthe Waimangu Iodine Geothermal Region in NewZealand showed that along with silicified and partlysilicified microbes siliceous rocks also contain pseud-ofilaments that consist of aggregates of spherical opalparticles condensed on mucus filaments, i.e.,the bio-genic or abiogenous origin of opal can scarcely bedetermined in a number of cases. Some authors havedemonstrated in their publications that films of micro-organisms facilitate silica precipitation from oversatu-rated solutions and formation of specific opal structures[Guidry, 2003; Inagaki, 2003]. Such compatibilitybetween inorganic material (opal) and organic matter isvery heavily investigated at present. [Samoilovich, 2005].

Thus, according to published data, opal sedimentsfrom thermal sources are rather variable, and their for-mation may be related to both biogenic and abiogenousprocesses and to their combinations [Jones, 2003b;Guidry, 2003].

In our country, sediments from thermal sources inKamchatka were first described in publications[Naboko, 1954; Ustinov, 1955], and they did not attractany specific interest for a long time due to their limiteddistribution on the geological scale. Somewhat later,when the relation of gold deposits to geyserites wasdemonstrated [Karpov, 1988], these sediments againattracted researchers’ attention. Some later publicationreported the results of examining microorganismsinhabiting thermal regions, as well as their silicifiedremains [Bonch-Osmolovskaya, 1999; Zhegallo, 2007].Thus far not a single publication on petrographical or

Microstructure Investigations of Kamchatka Geyserites

V. S. Urusov, L. V. Shvanskaya, A. Yu. Bychkov, A. V. Mokhov, and E. A. Labutova

Received June 29, 2007

Abstract

—This paper discusses the results of examining solid geyserite specimens from two present-day Kam-chatkan hydrothermal systems: from geysers of the Academy of Sciences and from the Eastern Thermal Fieldin the caldera of the Uzon Volcano. These studies were performed using methods of IR spectroscopy, XR spec-tral analysis, and electron microscopy. Three types of geysers were discriminated: underwater, subaerial, andthose that originated under the ground surface. All geyserite varieties consist of amorphous opal, and differ-ences between them are caused by the shape, dimensions, and distribution character of silica aggregates. Mostexamined geyserites enclose silicified microfossil remnants.

DOI:

10.3103/S0145875208050037

312

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mineralogical examination of Kamchatka geyseriteshas been published.

SPECIMEN DESCRIPTION

The examined geyserites were collected from sedi-ments of two present-day hydrothermal systems inKamchatka: (1) from sources of the Academy of Sci-ences (Akademii nauk) and (2) from the Eastern Ther-mal Field in the caldera of the Uzon Volcano. Thedescription and catalog of specimens are presented inthe table.

Sediments of the first group were collected fromsediments at sources of the Academy of Sciences on theshore of the Lake Karymsky. Thermal sources arelocated there on a high shore of the lake on a terraceconsisting of ancient geyserite. The specimens werecollected around geyser vents, from pulsing sources,and at water discharges from the sources. They presentchalk-like sinters that are layered, soft, and white orgray in color. Several specimens of ancient geyseritewere collected from deeper portions of the geyseritedome. These geyserites are considerably more compactcompared to the previous specimens; they display con-

spicuous lamination with wave-like folds, and arecream or white colored.

The Eastern Thermal Field in the caldera of theUzon Volcano is located on a flat site consisting of allu-vial gravelly–sandy sediments. As opposed to sourcesof the Academy of Sciences, the iron, arsenic, and anti-mony sulfides precipitated from thermal sources in thecaldera of the Uzon Volcano. Geyserite samples werecollected from sediments accumulated around thesources. These geyserites make crusts, druses, and filmsof different colors (white, yellow, pink, and dark gray)cementing gravel particles. The geyserite color usuallydepends on sulfide and elemental sulfur admixture in it.Geyserite samples of another group were collectedfrom gravel at a depth of 40–50 cm and present flow-stones that are dark gray to almost black in color andshowing conchoidal fracturing.

During sampling, several genetic types of geyseriteswere recognized, which distinctly differed from eachother in their morphology and in their position in thezones of thermal solutions discharge:

(1) Subaerial geyserites that originated in the atmo-sphere around geysers, thermal springs, and on steamyplatforms. Capillary rise and active evaporation

Catalog of geyserite specimens

Item Sample number Sampling site Specimen description

Solid geyserite samples from sources of the Academy of Sciences near Lake Karymsky

1 KMT-16/3/05 1st thermal stream, streambed Light colored, crumbling, non-laminated**

2 KMT-16/2/05 1st thermal stream, spring Pinkish white, compact**

3 KMT-15/05g “Stove” spring Gray, contaminated, with clay admixtures**

4 KMT-15/01/05 “Stove” spring White-gray, compact**

5 KMT-12/05 Old Geyser Brown crust on rock*

6 KMT-09/05 New Geyser Gray-white, layered, compact**

7 KMT-08/4/05 New Geyser Crust on rock*

Specimens of ancient geyserites (underwater type) from an outcrop on the shore of Lake Karymsky

8 KMT-1pg/05 Three meters above water edge White interlayer 4 cm thick

9 KMT-2pg/05 1.5 meters upsection Gray-white, layered

10 KMT-3pg/05 1.5 meters upsection Gray-white, compact, layered

11 KMT-4pg/05 1 meter upsection Gray-white, layered

12 KMT-5pg/05 1.7 meters upsection Light colored, brittle, of indistinct lamination, porous

13 KMT-6pg/05 1 meter upsection Gray-white, layered, alternation of compact and more porous layers

Eastern Thermal Field in the Uzon Caldera (subaerial)

14 I-28d Site II Crusts around boiling-water thermal vents

15 I-31d Site I Gray-colored crusts (pyritized)

16 I-32d Site I Crusts of yellow and gray color

Uzon Caldera (a section in the Eastern Thermal Field)

17 20/5 Site II, from a depth of 40–50 cm Flowstones and nodules on gravel

Notes: * Subaerial-type geyserite.** Underwater-type geyserite.


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MICROSTRUCTURE INVESTIGATIONS OF KAMCHATKA GEYSERITES 313

resulted in fast precipitation of geyserite in the form ofbumpy and acicular formations at the solution–airboundary. Recurrent reflux is particularly typical ofgeysers and pulsed springs where conic structures orig-inate around the central bath and a train forms in thearea of water discharge. Subaerial geyserites grow at ahigh rate, varying from a few millimeters to severaldozens of millimeters a year. Subaerial geyserites alsoinclude siliceous crusts on steamy platforms due to cap-illary water rise. Water evaporation from the surface isthe principal factor for precipitating geyserites of this type.

(2) Underwater geyserites originate on the floors ofthermal waterways. They are characterized by lami-nated texture and smooth surfaces complicated by rip-ple marks and current marks. The geyserite density var-ies depending on the current velocity: crusts that aremore compact originate as a rule at a higher velocity,while loose, powder accumulations and even gel forma-tions originate in still water. A low growth rate, gener-ally up to 1 mm/year at the most, is typical of compactunderwater geyserites, which is determined by geyser-ites overgrowing different substrates. Aging of oversat-urated solutions accompanied by precipitation of silicacolloids is the principal factor in depositing underwatergeyserites.

(3) Geyserites of the third type accumulate at mix-ing waters of different compositions, either in a watermedium or in permeable sediment. They form edificesaround the sites of thermal water discharge in cold-water ponds, as well as swells and walls in zones ofwater mixing and bedded bodies in sediments. Geyser-ites of this type have been less examined because theyare poorly accessible for examination and sampling.

Geyserites of all three types are present in the exam-ined collection.

STUDY TECHNIQUES

XR diffractometer examination of all specimenswas performed using a DRON-UM1 diffractometer(SoK emanation,

λ

= 1.7889; Fe filter with continuousscanning). IR absorption spectra were measured inpowder preparations on a KBr substrate within fre-quency ranges of 3800–3000 and 1800–400 cm

–1

usinga Specord-75IR infrared spectrophotometer and FurieFCM 1201 spectrometer.

Electron microscopic examination of all specimenswas performed using a JSM-5610LV scanning electronmicroscope equipped with a JED 2300 energy dispers-ing spectrometer at low vacuum and without prelimi-nary sputtering, and examination under scanning elec-tron microscope was performed using a Cam Skan 4electron microscope combined with an Sbs 50M NPO(Production Association) UNI-Expert microanalyzer(single-board). Nickel was sputtered on the specimen.

STUDY RESULTS

Investigation of mineral forms of silica precipita-tions, determination of their structural and morphologicspecific features, and finding their relations with theprecipitation conditions were the principal goals of thepresent study.

From XR diffraction data, all examined specimensbelong to the group of amorphous opals (opal-A) sinceall XR patterns showed a broad washed increase, i.e., ahalo in the ~4 Å region. No additional peaks corre-sponding to crystallized phases (cristobalite, tridymite,and quartz) were detected either in contemporary or inancient geyserites.

The principal absorption bands in all IR spectra ofthe examined specimens are broad washed bands atabout 1100, 800, and 470 cm

–1

(Fig. 1a). The presenceof broad absorption bands is also typical at 3400, 3200,and 1640 cm

–1

(Fig. 1b), which is caused by OH-valence (asymmetric and symmetric) and deforma-tional oscillations of water molecules. In addition,weak washed bands were detected at 3750 cm

–1

, whichcan be attributed to valence oscillations of OH-isolatedsilanol Si–OH groups [Kronenberg, 1994]. A weakband at 3650 cm

–1

is typical of OH-valence oscillationsof silanol groups connected by hydrogen bonds withother silanol groups or water molecules. The presenceof an arm related to OH deformational oscillations wasrecorded in all spectra in the 960 cm

–1

region. Suchabsorption bands are present in accumulations of bio-genic opal that precipitated from marine water [Plyus-nina, 2004].

In Plyusnina’s opinion [Plyusnina, 1973], changesin the angle of the most flexible Si–O–Si bridge bondsare the most probable during changes of thermody-namic conditions in metastable silica modifications. Ina series of ancient geyserite specimens, a growth of theintensity of ~800 cm

–1

band responsible for valence–symmetrical Si–O–Si oscillations was recorded downthe section (Fig. 2). In addition, the absorption bandwidened in the 1100 cm

–1

region and the intensity of theband ~560 cm

–1

(tridymite trace) decreased, which mayindicate rearrangement of the Si–O–Si bond angleaccording to the tridymite crystobalite type, i.e., thatthe Si–O–Si bridge tends to rectilinear configuration.

Two morphologic forms of silica were distinctlyrecognized in the examined specimens under an elec-tron microscope: (1) spherical particles and (2) com-pact glass-like mass. The spherical particles are glob-ules of silicic acids that precipitated from solution. Thegreatest differences in the geyserite structure revealthemselves in the mutual arrangement and dimensionsof these globules.

The microstructure of contemporary geyserites(specimens KMT-09/05 and KMT-15/01/05) shows adistinct evidence of biogenic origin. Figure 3a shows anaggregate of filiform

Cyanoprocaryota

asynchronouslyformed and to different degrees fossilized.

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The inner and outer surfaces of silicified trichs arecovered with an aggregate of silica microglobules mea-suring ~900 nm (Fig. 3b). Two (and more rarely three)silicification layers can be recognized in sections ofbacterial filaments with inner diameters of 1.9–3.74and, more rarely, 7.5

µ

m (Fig. 3c). The inner layersshow massive texture, whereas the outer ones are glob-ular. Figure 3d shows a wide (0.7–1.4

µ

m ring spacebetween the outer silicification zone and the walls ofthe bacterial filaments. This is possibly a result of algalorganic matter destruction in the process of its modifi-cations (Zhegallo, 2007].

Areas of sieve-like structure, on which short fila-ments and aggregates of globular microscopic accumu-lations, are rarer (Fig. 3e). The globule dimensions are1.28–1.44

µ

m on the average; they are ~9

µ

m long andlocally they are flattened along their axes. Similar bio-genic microstructures were described in the literature;for instance, in sediments of the Yellowstone NationalPark (USA) [Inagaki, 2003].

Specimens of ancient geyserites also showed bio-genic microstructures: filiform aggregates from 5 to80

µ

m long consisting of opal-A spherical particlesmeasuring ~1

µ

m. Both highly porous and compactcondensed areas are typical of them. Shells consistingof microorganisms in compact layers of these geyser-ites are covered, as a rule, by globules of amorphousopal, whereas the spaces between them are filled with aglass-like silica mass (Fig. 4).

Investigations of subaerial geyserites specimensunder an electron microscope revealed a greater varietyof microstructures and microorganism remains. Tabular(Fig. 5) and conical forms (Fig. 6a) are typical of them,and finely laminated structure is the main specific fea-ture of the latter. This structure presents an alternationof two different layers: (a) a compact layer with a con-choidal fracture (without apparent indications of bio-logical components) and (b) a more porous layer enriched,as a rule, in remains of silicified microorganisms.

Figure 6 shows a general outer view (a) and a cross-section (b) of cone-shaped druses in Sp. KMT-12/05.The fracturing (in the section) of each cone shows a

40080012001600cm

–1

1630

1200

1110

950 80

5 560

475

1630

1210

1100

955 80

0

555

475

1630

1210

1110

960

800

550

475

1635

1200

1120

960 80

5

650

560

475

1200

1105

960 80

0 560

475

1630

1200

1110

960 80

0

475

KMT-16/2/05

KMT-15/01/05

KMT-09/05

KMT-1pg/05

I-32g

20/5

30003800 3400cm

–1

34003630

3400

34003200

3635

KMT-1pg/05

I-32g

20/5

34003200

3650

37503630

34003200

37503630

3400 3200

KMT-09/05

KMT-15/01/05

KMT-16/2/05

1635

Fig. 1.

IR spectra of geyserites from Kamchatka thermal springs: (a) 400–1800 cm

–1

region; (b) 3000–3800 cm

–1

region.

40080012001600

1630

1630

1210

1200

1110

1110

950

960

800

795 55

055

047

547

5

KMT-6pg/05

KMT-1pg/05

cm

–1

Fig. 2.

IR spectra of ancient geyserites from Kamchatkathermal springs (400–1800 cm

–1

region).


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concentric structure. The more compact, glass-like lay-ers with conchoidal fractures alternate with ones thatare more porous. The minimal dimensions of silicaglobules in the latter are ~300 nm. The compact layerprobably originated under conditions of a less oversat-urated solution. No evidence of biogenic origin is visu-ally discernible. Qualitative microspectral chemicalanalysis recorded a considerable Al proportion, whichmay indicate the presence of argillaceous (terrigenous)material and a low sedimentation rate of silica.

The biogenic layer in Sp. I-32d consists of well-pre-served silicified remains of microorganisms of variousshapes. Their shells show rows of square and round(Fig. 7a) openings approximately 6

µ

m across in diam-eter. In addition, fragments of shells, evidently of dia-toms and pennate algae are present. A vitreous mass ofamorphous opal covers their valves. Essentially bio-genic porous layers alternate with more compact and

massive layers (Fig. 7b). It is noteworthy that a ring offinely dispersed pyrite up to 6

µ

m wide is present.Framboidal pyrite aggregates can be replacement prod-ucts of microorganisms under anaerobic conditions athigh temperature [Inagaki, 2003].

The bulk of the rock in Sp. I-28d consists of tinyshells (Fig. 8a) that are flattened spheres ~2.5–3

µ

macross in diameter with grooves where the wall thick-ness is ca. 400 nm; most spheres are partly broken.These are, obviously, remains of coccolith bacteria.Similar silicified forms of microorganisms wererecorded in rocks at the Champagne Pool hot spring(Waiotapu, New Zealand) [Jones et al., 2001].

Diatom algae remains are particularly distinctly vis-ible in Fig. 8b (Sp. I-28d) where they show a shell valverather well preserved in the rock. The visible silicaaggregates in the examined specimen are of subaerial

10

µ

m

30

µ

m 10

µ

m

3

µ

m

3

µ

m

(a) (b)

(c) (d)

(e)

Fig. 3.

Biogenic microstructure in present-day geyserites of underwater origin (Sp. KMT-15/01/05): (a) silicified thread-like micro-organisms; (b) inner parts of bacterial filaments are lined with opal globules; (c) section across a bacterial filament; three silicifiedlayers are visible; (d) section across thread-like microorganism; annular space is visible between the outer silicified zone and thewall of a bacterial filament; (e) sieve-like microstructure.

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URUSOV et al.

origin and measure <500 nm (Fig. 9), so that theobtained magnification does not permit determiningtheir shape. Figure 10c shows cyanobacteria with arather distinctly seen cellular structure.

Geyserites from a succession of gravelly sedimentsare opal-like flowstones (Fig. 10a) with both almostideally spherical shapes and flattened types; they showa globular structure and consist of colloid SiO

2

particlesof various dimensions. The particle dimensions varybetween 0.7 and 10

µ

m. Larger globules have a hierar-

chic structure (Fig. 10b), i.e., they consist of severalparticles of smaller diameters. Chip surfaces of theseforms are absolutely flat and do not display any indica-tions of their inner structure.

DISCUSSION

The wide variety of observed morphologic forms ofsilica accumulations from hot springs in Kamchatkaand all over the World is related to the different condi-tions of stage-by-stage process (nucleation, polymer-ization, coagulation, and precipitation) of silica acidtransformations during aging of oversaturated solu-tions. Variations in the temperature, acidity of themedium, presence of admixtures (both chemical andmechanical), changes in the flow velocity, presence ofmicroorganisms, and so on result in the formation ofdifferent opal-A forms at the nanno- and micro-levelsand render each sediment unique. Three varieties ofopal-A were recognized in one publication [Jones andRenaut, 2003a]: (1) Spherical particles (globules) pre-cipitated from strongly oversaturated solutions due topolymerization; (2) Opal replacing organic matter; and(3) Opal filling pore space like cement. This classifica-tion permits the description of any geyserite micro-structure and assigning its formation process.

All geyserites examined by the present authors con-sist of amorphous opal and differ from one another indimensions and arrangement of silica particles, as wellas in the presence of silicified microorganism remains.

We visually recorded the presence of microorgan-ism remains both in compact and porous layers in allspecimens of underwater-type geyserites. Silica glob-ules are concentrated both on inner and outer surfacesof microorganism shells. This permits the hypothesisthat they originated owing to the trapping of colloidalsilica particles on algae and bacteria surfaces and thesubsequent filling of the space between them with com-pact opal acting as cement. Differences in the degree offilling pore spaces between silicified microorganismslead to the observed laminated structure of the sedi-ment. Obviously, filling of the pore space with opal

20

µ

m

Fig. 4.

Microstructure of ancient geyserite specimens fromoutcrops on the shore of Lake Karymsky: silicified thread-like microorganisms from a compact layer.

50

µ

m

Fig. 5.

Tabular texture of subaerial-type geyserite(Sp. KMT-08/4/05).

500

µ

m(a) (b) 50

µ

m

Fig. 6.

Conical texture of subaerial-type geyserite (Sp. KMT-12/05): (a) general view; (b) cone structure in cross-section; alternationof compact and porous layers is visible.


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(cement) can occur both due to solution filtrationthrough the primarily sedimentary porous rock [Jonesand Renaut, 2003a] and under conditions that changethe silica concentration in the primary solution [Iiler,1979] as a result, for example, of changing the state ofa thermal spring. The dimensions of recorded silicaglobules in underwater geyserites is ~1

µ

m; in this case,no ordered structures originate.

Opal from subaerial geyserites consists of silica par-ticles with dimensions half of those of globules fromunderwater geyserites or even smaller. This could berelated to their origin: fast evaporation of thermal waterdoes not facilitate the maturation of silica acid colloids.A layered structure is also typical of subaerial geyser-

10

µ

m(a) (b) 50

µ

m

Fig. 7.

Microscopic texture of subaerial-type geyserite from the Uzon Caldera (Sp. I-32): (a) silicified remains of microorganisms;(b) alternation of highly porous (essentially biogenic) and vitreous layers; arrow indicates a ring of finely dispersed pyrite.

10

µ

m(a) (b)

(c)

3

µ

m

10

µ

m

Fig. 8.

Diversity of silicified microorganisms in subaerial-type geyserite (Sp. I-28d): (a) remains of coccoid bacteria; (b) shell valveof a diatom alga; (c) cyanobacteria.

3

µ

m

Fig. 9.

Silica aggregates from subaerial-type geyserite(Sp. I-28d).

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URUSOV et al.

ites, viz., alternation of compact vitreous and porouslayers. The porous layer in the examined specimens iseither rich in silicified microorganism remains or com-pletely devoid of them. It is noteworthy that the layerthickness is persistent, both down the section and in dif-ferent thermal systems. This textural specific feature istypical both of geysers and of pulsed thermal springsand, consequently, is not associated with periodic erup-tions and refluxes. Some authors [Hindman, 1996 andLowe, 2003] relate the layered texture to seasonal tem-perature oscillations, flow velocities, water levels, andto seasonal variations in biological activity [Konhauseret al., 2001].

For example, the intensive growth of microorgan-isms during spring–summer periods allows them tomaintain a high rate of silicification, which facilitatessilica deposition on their shells. Slow growth of livingorganisms during dark autumn–winter periods resultsin predominantly abiogenous sediment accumulation,and the colony resumes its vital activity with the onsetof favorable conditions.

Accumulation of the compact vitreous layer isrelated to low oversaturation of the solution with silica,and, as a result, no polymerization of monomeric silicaacid occurs (opal globules do not form), and the silicaaccumulates directly as a compact vitreous mass [Iiler,1979]. Silica precipitation can be initiated, in this case,by clay mineral particles, and was supported by anincrease in Al concentration in the vitreous layer in oneof the examined specimens, according to the data fromqualitative spectral XR microanalysis.

Subaerial geyserites from the Eastern Thermal Fieldin the Uzon Volcano Caldera differ from those in theAcademy of Sciences springs by the presence of vari-able microorganism remains: coccolith bacteria, cyano-bacteria, and diatoms, which were related, possibly, todifferent sedimentation conditions. The surfaces of theKarymsky subaerial geyserite accumulation are charac-terized by the alternation of periods of abundant waterwith long periods of complete dewatering. The fastevaporation of a water film prevents the growth anddevelopment of biological films, which results in abio-genic silica sedimentation. The accumulation surface inthe Uzon Volcano caldera is almost permanently wet

due to capillary rise and this creates favorable condi-tions for the vital activity of microorganisms. Fastwater evaporation can lead to sedimentation of smallersilica globules than those on microorganism shells dur-ing underwater colloid aging. Silica precipitates asglass-like mass in the case of complete water film evap-oration and (or) because of slow vital activity (death) ofmicroorganisms.

Opals from the Eastern Thermal Field do not showa clear influence of microorganisms upon silica precip-itation. Opal globules of various diameters (from 700 nmto 10

µ

m) were seen on surfaces of nodular, flowstonegeyserite formations. Chip surfaces of these formationsare absolutely smooth and glass-like. Natural acid etch-ing pits recorded in similar rocks from the Taupo Vol-canic Zone (New Zealand) [Jones and Renaut, 2003a]show a concentric structure and, consequently, are aresult of consecutive layer growth from the nucleus tothe periphery. Filling of spaces between globules withopal-A leads with time to formation of a homogeneousopal mass with no visible evidence of globular struc-ture. Growth in global dimensions can probably occurdue to conglutination of smaller globules, i.e., accord-ing to the mechanism of hierarchic aggregation [Kama-shev, 2006].

Different globule dimensions prevent the formationof an ordered opal structure under these conditions. Theformation of opal particles of different dimensions isrelated to their origin at a geochemical barrier with gra-dients of pH, temperature, and other parameters [Bych-kov, 1995]. Changes of physicochemical parameters in alimited region result in the fact that particles of variabledegrees of maturity participate in geyserite formation.

CONCLUSIONS

Investigations of siliceous deposits from two ther-mal fields in Kamchatka have permitted us to draw thefollowing principal conclusions. The bulk of all geyser-ite varieties consist of opal-A. The IR spectra of geyser-ites are identical to those of biogenic opal accumula-tions from oceanic water.

Opal in geyserites formed in underwater conditionsconsists of silica globules with average dimensions of

500

µ

m(a) 10

µ

m(b)

Fig. 10.

Opal-like flowstone texture of a geyserite specimen from gravelly sediments (Sp. 20/5): (a) general view; (b) SiO

2

globulesof opal-A (arrow shows a particle of hierarchic structure).


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~1

µ

m. Abundant silicified microorganism remains aretypical of them.

Geyserites formed under subaerial conditions have alayered structure and consist of alternating compactand porous zones. The porous zones contain silicifiedmicroorganism remains. The dimensions of recordedsilica particles are <500 nm.

Opal formed within a thermal field succession con-sists of globules whose dimensions vary within a widerange: from 700 nm to 10

µ

m. No ordered structureswere recorded.

ACKNOWLEDGMENTS

The authors are grateful to V.S. Kurazhkovskaya forperforming IR spectroscopic investigations and for herhelp in interpreting the obtained results and toG.A. Karpov for performing electron-microscopicstudies. This work was supported by the Russian Foun-dation for Basic Research (project no. 05-05-64721)and by the Program for Supporting the Leading Scien-tific School (grant NSh-8091.2005.5).

REFERENCES

Bonch-Osmolovskaya, E.A., Miroshnichenko, M.L., Slo-bodkin, A.I., et al., Biological Diversity of AnaerobicLithotrphic Prokariots in Terrestrial Kamchatkan Hydro-therms,

Mikrobiologiya,

1999, vol. 68, pp. 398–406.Bychkov, A.Yu.,

Geokhimicheskaya model’ sovremennogorudoobrazovaniya v kal’dere Uzon: Avtoref. kand. dis

(A Geochemical Model of Contemporary Ore Formation inthe Uzon Caldera: Cand. Sci. (Geol.–Miner.) ExtendedAbstract), Moscow, 1995.Cady, S.L. and Farmer, J.D., Fossilization Processes in Sili-ceous Thermal Springs: Trends in Preservation Along Ther-mal Gradients, in

Evolution of Hydrothermal Ecosystems onEarth (and Mars?). Ciba Foundation Symposium

, Chiches-ter, 1996, pp. 150–170.Campbell, K.A., Rodgers, K.A., Brotheridge, J.M.A., andBrowne, P.R.L., An Unusual Modern Silica–Carbonate Sin-ter from Pavlov Spring, Ngatamariki, New Zealand,

Sedi-mentology

, 2002, vol. 49, pp. 835–854.Göttlicher, J., Pentinghaus, H.J., and Himmel, B., On theMicrostructure of Geyserites and Hyalites, Natural HydrousForms of Silica,

J. of Sol-Gel Science and Technology

, 1998,vol. 13, pp. 85–88.Guidry, S.A. and Chafetz, H.S., Siliceous Shrubs in HotSprings from Yellowstone National Park, Wyoming, USA,

Canad. J. of Earth Sci, 2003, vol. 40, pp. 1571–1583.Hinman, N.W. and Lindstrom, R.F., Seasonal Changes in Sil-ica Deposition in Hot Spring Systems, Chem. Geol., 1996,vol. 132, pp. 237–246.Iiler, R.K., The Chemistry of Silica: Solubility, Polymeriza-tion, Colloid and Other Properties, Biochemistry, New York:Wiley, 1979.Inagaki, F., Motomura, Y., and Ogata, S., Microbial SilicaDeposition in Geothermal Hot Waters, Appl. Microbiol. Bio-technol, 2003, vol. 60, pp. 605–611.Jones, B. and Renaut, R., Hot Spring and Geyser Sinter: theIntegrated Product of Precipitation, Replacement, and Depo-sition, Canad. J. of Earth Sci, 2003a, vol. 40, pp. 1549–1569.Jones, B. and Renaut, R., Petrography and Genesis of Spicu-lar and Columnar Geyserites from the Whakarewarewa and

Orakeikorako Geothermal Areas, North Island, New Zealand,Canad. J. of Earth Sci, 2003b, vol. 40, pp. 1585–1610.Jones, B., Konhauser, K.O., Renaut, R.W., and Wheeler, R.S.,Microbial Silicification in Iodine Pool, Waimangu Geother-mal Area, North Island, New Zealand: Implications for Rec-ognition and Identification of Ancient Silicified Microbes,J. of the Geol. Soc. London, 2004, vol. 161, pp. 983–993.Jones, B., Renaut, R.W., and Rosen, M.R., Biogenicity ofGold- and Silver-Bearing Siliceous Sinters Forming in Hot(75°C) Anaeribic Spring-Water of Champagne Pool, Waio-tapu, North Island, New Zealand, J. of the Geol. Soc. London,2001, vol. 158, pp. 895–911.Jones, B., Renaut, R.W., and Rosen, M.R., Biogenicity ofSilica Precipitation around Geysers and Hot-Spring Vents,North Island, New Zealand, J. of Sedimentary Res, 1997,vol. 67, pp. 88–104.Kamashev, D.V., Experimental Modeling of Processes ofSupra-Molecular Silica Structure Formation, ElektronnyiNauchno-Informatsionnyi Zhurnal “Vestnik Otdeleniya Nauk oZemle RAN”, 2004, no. 1.Karpov, G.A., Sovremennye gidrotermy i rtutno-sur’myano-mysh’yakovoe orudenenie (Contemporary Hydrotherms andMercury–Antimony–Arsenic Mineralization)), Moscow:Nauka, 1988.Konhauser, K.O., Phoenix, V.R., Bottrell, S.H., et al., Micro-bial–Silica Interactions in Icelandic Hot Spring Sinter: Pos-sible Analogues for Some Precambrian Siliceous Stromato-lites, Sedimentology, 2001, vol. 48, pp. 415–433.Kronenberg, A.K., Hydrogen Speciation and ChemicalWeakening of Quartz. Silica Physical Behavior, Geochemis-try, and Materials Applications, Rev. in Mineralogy, 1994,vol. 29, pp. 122–147.Lowe, D.R. and Braunstein, D., Microstructure of High-Temperature (>73°C) Siliceous Sinter Deposited around HotSprings and Geysers, Yellowstone National Park: the Role ofBiological and Abiological Processes in Sedimentation,Canad. J. of Earth. Sci, 2003, vol. 40, pp. 1611–1642.Naboko, S.I., Kamchatkan Geysers, Tr. Lab. Vulkanologii ANSSSR, 1954, no. 8, pp. 126–210.Plyusnina, I.I., Fiziko-khimicheskie osobennosti evolyutsiidispersnykh sistem v korakh vyvetrivaniya, v sedimento- ilitogeneze (Physicochemical Specific Features in the Evolu-tion of Disperse Systems in Weathering Crusts, in Sedimen-tation, and Lithogenesis), Arkhangelsk: Pomorskii univer-sitet, 2004.Plyusnina, I.I., Infrakrasnye spektry mineralov (Infra-RedSpectra of Minerals), Moscow, 1973.Samoilovich, M.I., Sergeeva, N.S., Belyanin, A.F., et al.,Three-Dimensional Matrices Based on Cubic Packing ofSiO2 nannospheres as a base for biologically compatiblematerials for cellular structures, in Vysokie tekhnologii vpromyshlennosti Rossii (High Technologies in RussianIndustry), Moscow: Tekhnomash, 2005, pp. 99–107.Ustinova, T.I., Kamchatskie geizery (Kamchatkan Geysers),Moscow: Gosgeografizdat, 1955.Walter, M.R., Geyserites of Yellowstone National Park: AnExample of Abiogenic Stromatolites, Stromatolites, Develop-ments in Sedimentology, Amsterdam, 1976, no. 20, pp. 87–112.Walter, M.R., A Hot Spring Analog for the DepositionalEnvironment of Precambrian Iron Formations of the Lake Supe-rior Region, Economic Geology, 1972, vol. 67, pp. 965–980.Zhegallo, E.A., Karpov, G.A., Lupikina, E.A., et al., Fossili-fied Algae–Bacterial Flora in Kamchatkan Geysers,Algologiya, 2007, vol. 17, no. 1, pp. 88–92.

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Microstructure investigations of Kamchatka geyserites