Workshop 2001 NEW ZEALAND GEOTHERMALAREAS B.W. L.G. D.J. 'Institute of Geological and Nuclear Sciences, Wairakei Research Centre, Taupo, New Zealand ofEarth Sciences, of Leeds,

SUMMARY - Several experiments are underway to investigate the role of in the formation of unique textures in sinter deposits at New Zealand areas,. results are presented fiom three areas: Rotokawa, and Waiotapu. In the Drain at Wairakei, thermophilic bacteria are growing at at a rapid pace and are progressively sheathed or replaced by amorphous silica, building large 3-D structures. Siliceous microstromatolites at Rotokawa, located in the hot springs (60 - grow at a much slower rate a level just above the water Growth is initiated on pumice stones wood At Champagne Pool, Waiotapu, siliceous microstromatolitesgrow on native sulphur accumulated around the pool edge or on protruding parts of the pool bottom. Their of growth(0.02-0.03 and size is greater than at Rotokawa. Orange precipitates in the pool, previously as flocculated rich and sulphur, appear to be entirely biomediated. It is not known whether the bacteria are actively metabolising sulphur or antimony or whether is passive. These effects strongly increase areas for potential metal - mineral - interactions and thus effect metal distributionsin sinter deposits.

1. INTRODUCTION This contribution presents some early results ftom three of the seven geothermal New Zealand geothermal areas are well known for areas where experimentsare underway. their spectacular features. The overall distribution of hot springs, geysers, mud pots, 2. METHOD sinter flats and ground in each of these areas is a of structural, topographic and Seven geothermal systems were chosen for this hydrological parameters. However, micro- study. These included Rotokawa, organisms have a role in determining Waiotapu, Orakei Korako, morphology and mineral textures, as well as, the and Tokaanu. In each of these areas, glass spatial distribution of chemical components. microscope slides have been placed to allow organisms are remarkable for their bacterial growth and consequent to thrive in the solute-rich, high temperature mineralization to form. Water samples were waters of environments and all collected and analyzed for major components at geothermal are expected to contain viable the Laboratory, IGNS. Table 1 lists the . temperature, and of slides in each area. The presence of bacteria in hot springs such as those in Yellowstone and Iceland has been Table 1. and Temperature of documented (Walter et al., 1972; Konhauser and Ferris, 1996) and contributions on the in also sinter deposits of New Zealand are available 8.5 49-66 Jones et al., The of viable bacteria in silica deposits in Iceland led to the Drain 8.2 83 -86 conclusion that bacteria have evolved 8.5 50 65 stream polysaccharide sheaths which prevent silicification of the bacteria wall and cytoplasm yet promote 3 silica precipitation outside the cell thus creating Main upflow 3.8 82 biomediated sinter growth(Phoenix et al., V-Notch 3 49 Pool 5.5 71-75 The present study was initiated to investigate the geochemical aspects of using Artificial 7.6 55 - New Zealand areas as natural 7.2 83 laboratories. It is not our aim to 7.4 76 91 but to understand the chemical nature of the interactions between dissolved species and Old 7.5 55 65 microbes. The initial objective is to conduct field experiments to determine the types of mineralization and the rate of growth of this

27 3. RESULTS

Main Drain. Two slides were in the drop to stream (Fig. This drain from the western The chemistry of water is throughout a -8.5, 570 Under rate at the site is I however. this rate can is but can the station goes on or is a heavy In the of the about that the left drain a strong with a of 62°C at the surface tu a of about Figure 2. the at the two of the Field of 1.5 Water bottom to top of

Figure 3. electron

28 I

Microbiologists at Hort Research successfully cultured these bacteria at 60°C. Bacterial were pink in colour. This is attributed to the presence of a xanthene pigment that may help to protect the bacteria light. The species of bacteria has not as yet been but they are thought to be subsisting on dissolved as their source.

The plan was to collect one glass slide on a monthly to determine rates. However, the rate of silica growth is 3vm - incredibly rapid and after one month the entire I plastic tray was encased in amorphous silica. A drain Figure 4. Silicified coccoidal bacteria W59 second set of slides was placed in the and side drain. these were collected over about eight days. The weight of silica deposited on the slides was The plastic tray and slides placed in the stream in determined and an approximate growth rate of 10 March 2001 were rapidly encased in silica. After g was estimated. two months a layer approximately 1 cm in thickness covered the slides making their W59 Side Drain. This small drain was chosen recovery The silica deposits were similar because of its high temperature and close to those the main however, they proximity to an operating bore (-20 m away). lacked the oriented nature of the fibres and The flashed water is slightly more dilute contain distinct green layers. These layers are 8.21, 1450 ppm 390 ppm to that of the drain attributed to the growth of at times The W59 is with a when the water temperature was lower. How hard layer of silica that is dark gray in colour. A these are preserved when temperature rises is single plastic tray containing 6 slides was placed drain uncertain. In general, SEM studies show textures in the and these were collected on a similar to those found in the main drain with one monthly basis. interesting exception. Some samples show a distinct bimodal size of size SEM examination of a specimen of amorphous suggesting the presence of two species of silica showed an irregular agglomeration of bacteria (Fig. 4). At times when rough grains. No other minerals were water temperature was lower, a found and the explanation for the gray cyanobacteria such as grow is uncertain. Interestingly, imparting a green coloration to the silica. Deeper searching revealed the presence of portions of the silica fibre meshwork showed an formed particles composed of amorphous silica increase in amorphous silica spheres. This (Fig. 4). These are interpreted to be the silicified indicates that the induced silica is remnants of bacteria. is an example of the promoting abiogenic silicification of the void extreme resilience of some primitiveforms of life. spaces. Presumably, given time, the These bacteria are able to in void space would be entirely with borewater at -85°C that contains very amorphous silica. nutrients.

We were unable to the rate of growth of silica on the glass slides they were in the hot water and began to disintegrate after a couple of months. It is clear that the rate of growthis very slow.

Stream, located on the south side of the Wairakei Borefield, has recently been cleaned out by for their tourist park scheme. The base of the stream is unconsolidated soil with a of leaves and branches. Small weirs, of stones and branches, cross the stream along its length to slow water flow. Borewater 8.3, 1900 ppm 580 ppm Figure 5. Silica casts of filamentous bacteria diverted the Waraikei borefield passes Stream. At least two different species through the stream. A thick layer of silica has of bacteria are interpreted to be present based on deposited on stones and plant material. the bimodal width distribution.

29 3.2 entirely submersed in water. When collected these slides were covered with a thin layer of fine The North at Rotokawa are two ebullient mud which had presumably settled out of the hot with temperatures greater than 85°C turbid water. This mud consists of fine sulphur, located on the northwest side of the sinter clays, and amorphous silica. examination Outflow from the springs 2.7 3.2, 400 - showed no however, 1200 ppm 600 - ppm flows as a TEM studies did show a few with These results show that although ranging from 60 to 85°C. The bacterial activity is present to some degree in the waters are turbid due to high concentration of hot waters, the activity of just suspended material composed of above the water is greater. native sulphur, clays, and amorphous silica. This material is carried in the outflow and has built up The V-notch is located at the most a thick layer of fine mud in the outflow area. of the sinter where the thermal populate this area as waters flow into Lake Rotokawa. Water by Jones et al. These temperature is much lower than at other sites start on pumice and wood that (49°C) although water chemistry is similar originally protruded out of the water. As the mud 3.0, ppm 600 ppm Glass slides thickens the grow upwards collected the last several months show slow and creating structures. growth of a lime green layer but no Also present in the subsurface mud are yellow obvious silicification. At present, no SEM and layers containing amorphous sulphide work been done on these samples. mineralization. 3.3 Waiotapu In order to study how these structures grow and the trace metals incorporated into them, a series Pool a large explosion of glass slides were into the mud at crater (-60 m diameter) in the Waiotapu thermal regular distances the in May area. Water is 75°C but can collected at monthly show that be as low as in shallow areas around the no growth has occurred in the this a edge of the The contains chloride-rich yellowish layer 1 - 2 in thickness composed waters at near neutral 5.5, 1926 ppm of native sulphur is present and above this is a 430 ppm On the west and southwest dark gray layer of hard silica (Fig. 6a). There is margins of the pool, the sinter edge is up to 40 wave action to keep the entire slide above the water's while at the wet and the growth of the silica layer is northeast marginthe water is dammed by a raised interpreted to form as a result of capillary action terrace of silica. The pool empties to the through the sulphur layer and up the slide. northeast forming the well-known Irregular protuberances on the sides of the slides Terrace. The geometry of the sinter suggests that may represent the beginnings of spicules but, at the ground surface is slowly tilting downwards present, there has been growth to towards the northeast. It is growth rates are slow. Another g is that A complex series of silicification the microorganisms that form the spicules features are present around the margins of the not to on the sides ofthe glass slides but pool (Jones et al., 1997). Figure 6b shows the east prefer more horizontal The of the margin of the The bottom is with slides are approximately 2 cm above the water an orange precipitate, identified as amorphous surface where temperatures to 45°C or antimony sulphide by (1986). lower, thermophile growth. adjacent to the water is a rim of native sulphur that overhangs the The Main at Rotokawa is located in the This is followed by a series of conical southeast section of the sinter flat. It is a large, up to 3 in height. Towards dark pool approximately 20 metres in length and the top of the sinter, these are 10 metres width. to with a suggesting that 90°C and is of acid sulphate cyanobacteria are present. The 3.8, 1540 ppm 420 ppm 336 also form islands in the where the ppm The side of the is undulating bottom has come close to the composed of complex biomediated sinter surface to allow native sulphur to accumulate (Jones et al., that at are creatinga "raft"that is slightly above the not active. Only adjacent to the These then allow the growth of the water are active found microstromatolites (Fig. and SEM 'on of a small spine Glass slides were place in the water adjacent to shows that their bases are of the edge of the in March 2001. These were

30 -- la

Figure 6. (a) Three glass slides inserted in mud near one of the north springs, Rotokawa. Water temperature is 74°C and temperature at top of slide -45°C. Water depth is approximately 0.5 cm. No mineralization occurs in water. A thin sulphur layer occurs at water surface and dark gray silica mineralization grows above. Slide dimensions 25 x 75 (b) Northwest margin of Champagne Pool, Waiotapu showing orange precipitate in water, yellow native sulphur layer, conical microstromatolites and greenish cyanobacteria. Field of view 0.5 (c) Glass slide from Champagne Pool next to islands of microstromatolites. Note sulphur layer and cloudy silica mineralization on slide. (d) Glass slide wholly immersed in Champagne Pool. Slide is covered with orange precipitate but no sulphur or silica mineralization. Note sulphur layer around microstromatolites. (e) Glass slide partially immersed in Champagne Pool outlet. Microstromatolites on slide have grown over a five month period. Bottom of Champagne Pool. Orange precipitate is attached to bottom by fine filaments that move in the current. Field of view 20 cm. (g) SEM photograph of orange precipitate from Champagne Pool. Note the filamentous shape of the sulphur and antimony-rich precipitates. Spheres are amorphous silica beads. Scale bar is 1 (h) TEM photograph of Champagne Pool orange precipitate. Dark rimsare coatings of amorphous antimony sulphide and sulphur on filamentousbacteria. Scale bar is 500

31 crystalline masses of fine sulphur crystals. A and Al (0.6%). In addition, measurable porous mixture of organisms and amounts Ti, Fe, and Se were found. X-ray sulphur is built upon the sulphur rafts. The analysis gave strong peaks only for conical portion of the spine is composed of native sulphur. This is to be as the of silica and antimony sulphide impurities in the sulphur are bacterial-rich silicified layers. expected to be amorphous. It appears that thermophilic are thriving in the hot Glass slides were placed in three positions along waters of Pool. It is that this the edge of the pool in March These slides bacteria reduced sulphur to form were not to plastic trays and, as a result, large amounts of native sulphur. Concurrently, many of the slides fell into the pool due to wind antimony and are combining with or wave action. Slides that were entirely sulphide and native sulphur to form immersed in water showed no accumulation of and antimony which attach to yellow native sulphur but became with a the bacteria's cell walls along with the native layer of orange precipitate (Fig. 6d). This sulphur. However, it is that the precipitate did not appear to be attached to the is a passive to the slide and came when the slide was presence ofthe bacterid In either case, Slides that partially protruded the water the bacterial will have an reactive surface accumulated a layer of sulphur at area and thus scavenge other the water which they became trace metals Pool. cloudy due to the precipitation of amorphous silica (Fig. This probably forms by capillary 4.0 through the sulphur layer. An estimation of spiculegrowthrate of 0.03 was made Hedenquist, J.W. (1986). Waiotapu geothermal using a single slide which remained in place for field. In: Guide to the Active five months (Fig. This is a maximum rate (Geothermal) Systems and Precious Metal since it appears that the initial sulphur layer Zealand, Henley, RW., grows much more rapidly than the spicules J.W. and Roberts,P.J. Mon. themselves. Vol. 26, Bomtraeger, Berlin, 65.79. Except for a slides, most of the initial set from March fell into the pool. Also, most Jones, B., RW.and were located in drainage on the Stromatolites forming in acidic hot-spring water, side of the pool where the water is North Island, New Vol. 15, shallow but turbulent. A set of slides was placed in July 2001. These were secured in a plastic holder weighted with lead and placed in Jones, B., Renaut, RW. and the main pool. The tips slides protrude 2 of silica precipitation around - above the surface of the water. On our and visit in September 2001, the slides showed Sediment. Res., Vol. growth of excellent spicules about 1 mm in height (-0.02 mm at a regular spacing Jones, B., RW. and M.R along the top of the slide. We will continue to Vertical of biota in collect these samples on a bimonthly basis to associated with hot springs, measure growth rates and metal contents. North Island, New Zealand. Vol. 12, 220-236. (1986) noted the metal-rich composition of the orange precipitate in K. and Ferris, F.G. (1996). Champagne Pool. In order to examine the of iron and silica precipitation by microbial mats that bacteria were with this in hydrothermal Iceland: Implications for mineralization, samples of the orange precipitate iron formations. Geology, Vol. 24, were by SEM and Figure 6g 323-326. shows that it is composed of filamentous chains of an antimony-rich precipitate. Other Phoenix, D.G. and Konhauser, present were amorphous silica and kaolinite. The K.O. viability during unusual texture of the precipitate suggests a hydrothermal Chem. Geol., bacterial origin. This is by work 169,329-338. (Fig. 6h) where the entire sample to be a dark Walter, J. and RD. (1972). representing the antimony-rich precipitate. X-ray Siliceous algal and bacterial stromatolites in hot fluorescence analysis of a dried sample of the springs and geyser of Yellowstone orange material showed that it is of National Park.Science, Vol. sulphur Sb

32