by Vladimir ZNAMENSKY. Cand. Sc. (Geol. & Mineral.), RAS Institute of Ore Geology, Petrography, Mineralogy and Geochemistry

This cluster of small vulcanoes-dome- and cone-shaped, and more than one kilometer high-is located on the northern tip of Iturup, one of the biggest in the Kuril Islands chain in the Pacific. The cluster occupies a large caldera-a picturesque and austere volcanic crater emitting jets of steam mixed with gas from a maze of cracks and fissures-fumaroles. The most prominent in the group is the Kudryavy volcano which has caught the attention of geologists by its unusually broad "menu" in eruption products, including considerable quantities of rhenium-the most rare stable element in the Mendeleyev Table.

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IN GUINNESS BOOK OF RECORDS

As different from its southern neighbor Kunashir, the Iturup Island is more stern and difficult of access. It takes about an hour to make one's way uphill through some hundred meters of thicket of bamboo, cedar, alder and birch rubbery. And one also needs some mountain climbing skills, having to negotiate, almost right from the water edge, rocks and cliffs some tens and hundreds of meters high. The picture looks especially forbidding at capes, protruding into the foaming breakers. And even the names of these islands are quite impressive and kind of speak for themselves: Besheny (Crazy), Neukrotimy (Indomitable), Neschastye (Bad Luck), Neproidyosh (Impassable), or Goryushko (Lamentable). But, believe it or not, all of these exotic sites and places have been investigated and mapped by geologists and topographers-even with heavy bag of supplies and equipment on their backs. Their zeal and dedication have only been matched by colleagues-volcanologists.

The strain and stress of the perilous climb, however, are richly rewarded with a truly fantastic sight-a panorama of the island which opens up from top of the volcano. But even there and then you cannot relax and must be on your guard for fear of slipping into some pool of mud or, still worse, into a pit of molten sulphur or into a jet of some poisonous gas. In bad weather, with mist and poor visibility, one can easily lose one's way or plunge down from a cliff and, if you are wearing wet clothes after some recent shower and have no time to change, chances are that you will catch a bad cold. Colleagues on my own team were "impressed" with the rain on top of Mount Kudryavy which never stops for days and which hits you and your gear not vertically as one would expect, but at a horizontal angle because of strong wind. Fog, mixing with volcanic gases, turns into acid which melts your overalls into colorless rags in a matter of days; and we also know from personal experience that this acid rain can erode some even the hardest of rocks. Working at fumarole you step on ground which is so hot that even special fire-proof overalls you put on can catch fire-and I also know this from my own experience.

The crater, or caldera wherein Kudryavy is located has been given the name of Medvezhya (of bears) because of geologists' frequent encounters with these beasts. By its rim, it has in places a diameter of more than 12 km and its walls are eroded on the side of the gulf.

My period of studies of volcanoes, products of their eruptions and the subsequent behavior extends over 40 years. But even so, I find Kudryavy the most interesting case of them all. It was there that considerable amounts of rhenium in the form of its disulfide (ReS (2))- called rheni-it-were found for the first time in the world. And, secondly, a team of specialists from our institute, of which I was a member, traced and studied in greater or lesser details more than 70 other minerals, including rare metals like indium, cadmium and bismuth. All were found in the crusts of what we call fumarole fields. And, finally, we recovered there some of the world's highest known temperatures of permanently emitted fumarole steam-gas jets-of up to 920C because of which Kudryavy was inscribed into the Guinness Book of Records.

BIOGRAPHY OF MEDVEZHYA

About one million years ago the part of the Medvezhiy Peninsula on Iturup, where the caldera is located now, was a large and high volcanic plateau covered with a basalt layer more than 500 m thick. There in the bowels of the earth, in what we call magmatic foci, or chambers, at depths of 10 to 20 km took place the process of differentiation, or splitting of magma into fractions with the lighter one, saturated with gases, floating on top.

When the pressure in magmatic chambers became higher than the weight of overlaying rocks-due to high temperature and accumulation of gases-there occurred an explosion, or several explosions as is usually the case in such circumstances, with an outburst of a colossal mass of foamy acidic lava (what we call pumice, or volcanic froth). The voids formed in this way were filled with fragments of the upper crust which were "cemented" by the residue of the degassed melt. According to its level of silicon oxide (SiO(2)) the latter is called sour, or acid as different, for example, from basalts and their alkaline melts. The acidous melt popped up in part on the surface in the form of cupolas and other volcanic shapes which are so many now in the Medvezhya caldera. Over the decades they have been exposed to erosion which is rather strong there because of lots of natural precipitation. What we call the reconstructed volume of such acidic cupolas reaches 5 km(3).

From then on volcanism took a different course. Formed inside the caldera is the presently existing and nearly flat massif of acidic rock of more than 1 km(3), named Ameba because of its shape. After that there popped up-one after the other and in the direction from east to west along a line associated with a deep fault-several volcanic cones about one kilometer high which differ from one another by their lava composition, called-Medvezhiy, Sredniy, Kudryavy and Menshoi Brat (junior brother).

The relatively recent and historically recorded eruptions occurred on Medvezhiy Peninsula in 1879 and 1883 and the very latest in October 1999. Left after them were basalt slag cones and lava streams, or sheets, on Kudryavy and Menshoi Brat. These are characterized by increased levels of magnesium and other chemical parameters which made them different from the ordinary basalts of the volcanic island arcs-Kurillo-Kamchatsky, Aleutian, Japanese and many others,

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marking the border areas between the ocean and the continent. It may well be that the sharp change in the composition of eruption products within that historical period somehow provided for the peculiar metal content of the Kudryavy gas jets and its fumarole mineralization.

Little is known, however, about the plutonic structure of the Medvezhiy caldera. But, according to geophysicists, the underlying earth crust thickness there is greater by 40 km and its bottom "basalt layer" is anomalously expanded by up to 25 km. They also traced large displacements of rock strata along the steeply dropping fault planes. Experts believe that there are several magmatic foci of different depths down there and also a small, almost near the surface (0.5-1 km), magmatic chamber right under Kudryavy.

"INFERNAL" LANDSCAPES

Located on top of Kudryavy, stretching from east to west, are several blast craters of different age, hundreds of meters in diameter, to which the steam-gas jets gravitate. In one of them a magmatic dome was pushed up from down below after an eruption of lava and volcanic bombs. Located there are the fumaroles with the highest temperature of 250 to 920C. On the western part of the crest the temperature is even below 200C. There, as a result of a reaction between hydrogen sulflde, bubbling up from down below, with atmospheric oxygen colorful bright-yellow sulfur is produced whose quantities here are estimated by geologists at nearly 10,000 tons.

Everywhere in the centers of gas escapes this native sulfur melts down and its vapors crystallize into bright-yellow crusts, druses and veins. The flame of burning sulfur is

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of bluish color and on the rare clear nights these tongues of fire are quite a sight, framing as they do the red-hot or orange-red fumarole fields, and the picture is truly infernal.

In the composition of their main ingredient the volcanic gases of Kudryavy are quite ordinary. There prevails water steam, followed by carbon dioxide, sulfur dioxide and hydrogen sulfide. According to measurements conducted by Yuri Taran, Dr. Sc. (Chem.) of the RAS Institute of Volcanology (Petropavlovsk-Kamchatsky) dry fumarole gas at a temperature of 770C contains 63.8 percent of CO(2), 13.4 percent-SO(2), 9.0-H(2), 6.7- H(2)S, 6.5-HC1, 0.4-HF and 0.2 percent CO.

The microcomponent composition of fumarole gases and vapors from this volcano, artificially condensed in special coolers, is rather interesting. Its condensates contain increased levels of potassium, iodine, titanium, cadmium, lead and tin (as different from condensates from many other volcanoes). According to measurements conducted by Sergei Tkachenko, Cand. Sc. (Mineral.) of the RAS Institute of Experimental Mineralogy, one ton of Kudryavy condensate can contain up to 120 kg of heavy metals with lead predominating among them.

The volume of steam-gas emission, or discharge, of the volcano approaches 19 mln tons a year. In comparison, the mass of magmatic fluid discharged during the catastrophic eruption of the Bolshoi Tolbachinsky volcano on Kamchatka in 1975-1976 amounted to 190 mln tons over one and a half years. So it turns out that the Kudryavy fluid erupted at the fumarole activity stage (measured over a long period of time) can appreciably exceed

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by its mass the level usually discharged on the eruptive (explosive) phase. While the eruptions of some volcanoes usually take place once in tens and even hundreds of years (Tolbachik - 1941 and 1975), the steam and gas release of Kudryavy continues without a break.

It is important to bear in mind that considerable volumes of volcanic underground gases are accumulated in ground and surface water. The flow of mineralized water to the piedmont of Kudryavy and Menshoi Brat is estimated at about 150 liters per second. And although its mineral content is low (about 0.5 g/1), vast amounts of dissolved salts-more than 6 tons per day-are carried out over long periods of time. And gradually, at the outlet of the main mineral water source, there formed a lake with a temperature of about 36C in which an original microfauna was formed. There are vertical ribbons and braids of thermophillic algae some of which are more than a meter high.

FUMAROLE CRUST MINERALS

Hot and often red-hot ores in various parts of fumarole fields are somewhat different in their composition. They usually form crusts of grey color which are several tens of centimeters thick. Traced in them with different degree of confidence are more than 70 minerals (the figure is not final). Bearing in mind the very common phenomenon of isomorphism-replacement of some atoms in minerals with the atoms of other chemical elements with the preservation of the form (morphology) of crystal, and also the incomplete nature of studies required, the number of the mineral phases could be increased considerably. In the

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crusts of fumarole fields several groups of minerals are represented: native elements (sulfur, silicon-titanium minerals, graphite), sul-fides of lead, bismuth, molybdenum, zink, cadmium, copper, indium, rhenium, arsenic, etc.; selenides, chlorides, sulfates, molibdates, tungstenites, oxides of the above and other metals and also silicates and alumosilicates of calcium, potassium, sodium and less frequently-magnesium. And let me stress that pure rhenium disulflde was found and studied for the first time. The most common among sulfides are what are called lead-bismuth sulfosalts of varying composition.

In the crusts of the fumarole fields, through which volcanic gas is filtering all the time, three zones are identified: the lower sulfide one, the intermediary mixed one and the upper oxide-sulfide one, often with chlorides of sodium and potassium. And there are also observed numerous crossings and repetitions of such zones with veins of minerals from one penetrating into the other. The best studied are the zonal structures of molybdenum minerals which can be generally reduced to their interchange from bottom to top in the following succession: powellite (Ca[MoO(4)])- molybdenite (MoS(2))-tugarinovite (MoO(2))-molybdite (MoO(3))-ilse-mannite (Mo(3)O(8) x n H(2)O + soluble Mo-phase). The aforesaid distribution shows that the primary source of this all is molybdenum anhydrate, the appearance of hydrogen sulfide is observed closer to the surface (due to hydrolysis of SO(2)), found still higher is sulfur oxidation and, in connection with a growing oxygen potential, the valence of molybdenum grows which is accompanied by a transition of this

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metal in the topmost zone into a dissolved state.

Many of the minerals form peculiar patterns such as incrustations and "films" on the walls of gas channels and cavities. Also often observed are very fine and winding veins, or ribbons, of rhenium disulfate. There also occur hollow sulfide crystals, sometimes filled by even finer aggregates-crystals of cadmium wurtzite (ZnCd)S, and of the aforesaid tugarinovite, etc. One can see the rounded forms of crystals and aggregates, their twisting facets and ribs. Finally, some multifarious morphology is observed with one and the same composition, etc. All this attests to a dynamic mode of crystal growth and dissolution conditioned, among other factors, by rapid filtration of the primary fluid and just as rapid change of crystallization medium under the effect of atmospheric precipitation.

WHO DISCOVERED RHENIITE?

Rhenium sulfides in my samples from the fumarole crusts of Kudryavy were first identified under the microscope in 1991 by our Institute researcher Irina Laputina. They turned out to contain rather much molybdenum with the content of rhenium varying from 0 to 49 percent which made it possible to raise the question of the existence of some new and hitherto unknown mineral.

In the autumn of 1992 a team including researchers from the RAS Institute of Experimental Mineralogy Mikhail Korzhinsky and Sergei Tkachenko and later Anton Yakushev and myself collected at the edge of one of the fumarole fields some samples with their cavities lined with some glittering mineral which looked like

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the aforesaid molybdenite. As was later established, this was pure rhenium disulflde. The discovery came as a real shock because prior to that no such reliably identified mineral was known to experts. Under my guidance detailed studies were conducted of the find in keeping with the requirements for formal applications on the discovery of new minerals and a check-list was prepared. After that our work was submitted for expert assessment to the Moscow Branch of the Mineralogical Society and documents were also sent to the All- Russia Society on new minerals and later still-to the International Commission on New Minerals and Names of Minerals (ICNMNM).

The expert team, apart from the already mentioned specialists, also included members of analytical labs and the organizer of studies at Kudryavy Kirill Shmulovich, Dr. Sc. (Geol. & Mineral.) and the leader of the expedition Genrich Shteinberg, Dr. Sc. (Geol. & Mineral.) of the Institute of Marine Geology and Geophysics of the Far Eastern Branch, RAS.

It so happened, however, that samples with the new mineral somehow turned up abroad- with British researchers. Shortly after the first application (1993) the International Commission received another one, and again on the discovery of rhenium disulflde from the Kudryavy volcano. It was submitted by M. Korzhinsky, S. Tkachenko and K. Shmulovich together with two British scientists. Having no precedent of this kind, the Commission must be taking time on the new mineral and more than 6 years have already passed since we submitted our application.

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MINING OR TOURISM?

The discovery of rhenium mineralization on an area of less than 100 m(2) with the thickness of the ore-bearing layer being only 40 cm and the element content of about 0.1 percent (in the best samples) can in no way be described as a mineral deposit. This is especially so bearing in mind that technological tests of rhenium ore are very costly and can be more expensive than the total cost of the element contained therein. Its extraction in a pure form from the ore also costs quite a lot.

As for the idea of making use of high-temperature fluid, it is also of a doubtful value. As indicated by first assessments of the condensate content made at the aforesaid Academic institute, its rhenium content is of the order of one part per billion, which is clearly of no practical value. As a matter of fact, however, nothing is known about the results of such further tests, but according to information provided by Shteinberg no positive results have been obtained so far in the identification of forms of deposits or the content of rhenium in steam-gas jets.

The mining of the ore and the construction of appropriate facilities at the fumarole fields is hardly possible because of the high temperatures involved and the aggressive medium in which, as was said before, even native sulfur melts and ignites and also because the nature and the configuration of the fumarole fields are constantly changing, and so on. Rhenium extraction, even if it becomes technically feasible in principle, will require the building of a plant. And it will be necessary to condense the steam-gas jets or channel them through sedimentation filters so that rhenium could be extracted and purified, etc. What is more, the construction of the necessary props, steam traps and pipelines involves human interference into the very fragile nature around the vulcano and the chances of success in any such venture look very problematic.

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Another obstacle is volcanic activity. As was demonstrated by our expedition studies in the autumn of 1999, eruptions in the crater part of Kudryavy are very likely with the fumarole stage changing sharply into an eruptive one. Volcanic outbursts of more than 5 thousand cubic meters of rock took place there on October 7-10, 1999, accompanied by the formation of a deep enough well and a crater. After the eruption on October 22 magmatic melt was observed on the bottom of the well in the form of a lake of molten lava (pink- orange at night) with a turbulently active surface constantly disturbed by bubbles and splashes of escaping gas. The lake measured 2 to 3 m across and its south-eastern bank was hidden in a deep niche on the bottom of the well under the tallest vertical wall. Four days later, on October 26, the melt was seen no longer with only the red-hot bottom area in sight and the former numerous fumarole openings in the well walls scattered along the hot- heated vertical fracture in the wall of the former crater. So, it is dangerous for people to be on top of the volcano within the limits of the fumarole fields. This also applies to any technical facilities which could be blown away by volcanic explosions.

Summing it up, the unique high-temperature ores on top of Kudryavy and its steam-gas jets cannot be put to industrial uses. At the same time, however, they are the objects of great scientific interest above all for volcanologists, mineralogists and geochemists. Years of studies of high-temperature neo-genesis in the crater of the volcano and of the composition and properties of fluids and their condensates make it possible to have a new

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insight into the mechanisms of ore formation on the border of interaction of what could be described as piutonic and non-plutonic forces, that is magma and high-temperature gases with the atmosphere and natural precipitation. The main ore-forming factors- high temperature gradients and oxydation-reduction conditions within the limits of the constantly emerging and disintegrating fumarole crust of small thickness-of tens of centimeters only. The primary minerals, which crystallized earlier from magma and which comprise volcanic rock, lose completely their original character when reaching this border. They dissolve and some of their components are washed away by solutions while others precipitate but already in the form of new minerals. In their turn volcanic vapors emerging from the earth introduce and precipitate on this border their components above all sulfur and metals, some of which escape into the atmosphere.

The Kudryavy volcano is presently in its active stage which can be called stable only for some time. However, with the heavy atmospheric precipitation, typical for the Kuriles, and the resulting obstruction of the fumarole ducts by water there is the possibility of more or less powerful phreatic or phreatomagmatic eruptions (caused by heating of water at depth, its overheating and turning into steam with the subsequent release of energy during eruptions). Thus in Japan in October 1999 there was the catastrophic eruption of the Bandai volcano where a huge mass of water was heated at a relatively shallow depth. And that was despite the fact that the volcano had remained dormant for the past thousand of years. In the case of Kudryavy, the magmatic source is relatively shallow and the temperature even on the surface approaches 1,000C. In this strong heat some rocks begin to melt so that its eruption is rather not phreatic, but phreatomagmatic.

Contemporary basalts found recently in several places in Medvezhya caldera attest to the start of a new stage of Kudryavy's volcanic activity. In future there is a possibility of real eruptions of purely magmatic nature. In these circumstances human interference into natural process with the objective of mining some or other useful materials appears unjustified and even bordering on adventure.

But Kudryavy can well be used for the benefit of both science and adventure-or tourism. This spot of fantastic natural beauty will certainly attract visitors not only from this, but many other countries. All we need are sponsors and investors. (*)

* See also: A. Ivanov, "Southern Kuriles: Life Challenged by Odds", Science in Russia, No. 5, 1999-Ed.

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