Secondary Quartzites Research Articles

U-Pb AGE OF ZIRCONS FROM PALEOPROTEROZOIC SECONDARY QUARTZITES OF THE BOLSHOI TYUTERS ISLAND AND FROM SANDY MATRIX OF EARLY RIPHEAN CONGLOMERATES OF THE GOGLAND ISLAND (GULF OF FINLAND): FEATURES OF THE PRE-RIPHEAN HIATUS IN SEDIMENTATION IN THE NORTHEAST OF THE EAST EUROPEAN PLATFORM

The paper presents the results of U-Pb isotope dating of zircons extracted from rocks of the southern part of the Baltic Shield (Early Riphean conglomerates and Paleoproterozoic secondary quartzites) and makes a comparison of these results with the ages of crystalline complexes of the East European Platform (EEP). The paper presents the study results on composition of quartzites from the Bol. Tyuters and Gogland islands. There has been discussion about tectonic and paleogeographical features in the period prior to the beginning of Riphean sedimentation in the northeastern part of the EEP. It is concluded that the conglomerates are composed of erosional products of mainly Paleoproterozoic and less frequently Archean crystalline complexes. At the same time, the rocks at the base of the generalized section of Riphean deposits (Gogland group), did not contain any zircons with ages referring to 200 million years prior to the inferred time (1640–1660 Ma) of the beginning of the conglomerate sequence formation. The rocks that compose the Gogland group and their underlying Paleoproterozoic basement rocks have significant differences. We associate these differences with the existence of pre-Riphean sheet-like deposits, comprising rocks of essentially quartz composition, in the southern Baltic Shield, in the upper levels of the peneplenized Paleoproterozoic basement structure. The deposits relics are only found on the Bol. Tyuters Island; in all other places, these deposits were completely eroded or underwent significant structural and material transformations. The absence of detrital zircon grains with ages ranging from 1.87 to 1.65 Ga in the clastic rocks of the Riphean basal horizons implies no noticeable Pre-Riphean and Early Riphean orogenic movements in the northeastern part of the EEP. Tectono-magmatic reactivation in this region occurred only in the middle of the Early Riphean.

Epithermal Deposits of Kamchatka, Russia

The results of studying the epithermal deposits of Kamchatka, one of the most promising gold-mining provinces of the Russian Federation, are generalized. The deposits are divided into acid–sulfate (Ac-Sul) and adularia–sericite (Ad-Ser) types (Heald et al., 1987). The disadvantages of the scheme, which is the most popular in the English-language literature and is based on the sulfidation state of mineral parageneses in ores (LS, IS, and HS types), are shown. The classification that we proposed includes differences in mineral associations in circum–ore metasomatites, which are determined by the acidity–alkalinity and an oxidation state of mineral-forming fluids, and are clearly diagnosed at the first stages of studying the deposits. Kamchatka epithermal deposits of the Ad-Ser-type are associated with andesite volcanism of the volcanic belts. Gold ore associations are concentrated in quartz, carbonate–quartz, and adularia–quartz veins, as well as in sericitized metasomatites, which are replaced by argillizites and propylites towards the periphery. The Ad-Ser-type is characterized by combination with polysulfide (Pb, Zn) (Amethyst, Kumroch, Vilyuchinskoe deposits), sulfosalt (Ag, Sb, As, Bi, Sn) (Ozernovskoe, Baranyevskoe), and selenide (Ag, Se) (Amethyst, Asachinskoe, Rodnikovoe) assemblages. Low-fineness native gold (220–310‰) is typical of the early polysulfide assemblage. With an increase in the fugacity of Te and Se, the gold fineness increases to 510–740‰, and with the progressive activity of Sb, As and Bi and the formation of sulfosalt associations, it reaches 998‰. The homogenization temperatures of primary fluid inclusions in quartz from gold-bearing associations of the Ad-Ser-type are 260–250°C; the minerals crystallize from solutions containing no more than 3 wt % NaCl eq. Maletoyvayam, the only Ac-Sul-type deposit in Kamchatka, is localized in quartz, secondary quartzites, and alunite–sericite–kaolinite–quartz metasomatites. Gold-bearing parageneses indicate the leading role of selenium in mineral formation, contain high-fineness native gold, sulfoselenotellurides, tellurides, and selenides of Au, which crystallize from acidic fluids with salinity of 1–5 wt % NaCl eq. at temperatures of 290–175°C.

The genesis of acid alteration in the Luohe IOA-type deposit, Eastern China and its constraints on mineralization

Luohe is the largest IOA-type deposit in the Middle and Lower reaches of the Yangtze Metallogenic belt. The iron ore body is hosted in thick volcanic rocks, and widespread acidic alteration (secondary quartzite) developed at shallow depths, providing an excellent opportunity to study the genesis of acidic alteration rocks and the genetic links with the IOA mineralization. In this study, detailed mineralogy, in situ sulfur isotopes, and trace element analyses were performed on pyrite from a shallow drill hole in the Luohe deposit. The results indicate that the formation time of acidic alteration is between magnetite (stage II) and anhydrite-pyrite (stage IV), with pyrite sulfur isotopes ranging from −14 to 4‰, which is significantly different from those in stage IV (7-9‰). The anomaly negative sulfur isotope suggests the existence of SO2 disproportionation reaction, and the δ34S of pyrite increases with depth decrease, ultimately falling within the mantle sulfur range. This indicates that the sulfur origin of acidic alteration pyrite is a single magma sulfur source, which is significantly different from the deep iron mineralization system (magmatic + evaporite). The trace elements Co, Ni, As, Ti, Cu, Sb, Tl in pyrite indicate that the acidic alteration fluid has the characteristics of low temperature, low pH, and is rich in F and Cl. Combined with the sulfur isotope results, it is believed that pyrite in the acidic alteration rock of the Luohe was formed by the mixing of gaseous SO2 and shallow groundwater, which is a part of the Luohe magmatic-hydrothermal mineralization system and an important indication for regional exploration of similar deposits.

Forecasting of Gold-Silver Mineralization within the Pepenveem Ore Zone of the Chukchi Peninsula Based on Space Surveys of Resource, Canopus and ASTER

When deciphering the materials of space sensing of the eastern part of the Chukchi Peninsula on a scale of 1 : 50 000, structural elements of tectonic-volcanogenic genesis were revealed, represented by linear, arc, annular, zonal-concentric structural elements of various ranks. Ring structures with a diameter of up to 2 km and their dissecting disjunctiva mainly of the north-eastern and submeridional strike control the localization of gold mineralization of the Pepenveem ore-placer zone. On the basis of computer processing of the ASTER infrared satellite image in the Pepenveem zone, the areas of development of hydrothermally altered rocks (berezites, secondary quartzites, sericite-hydrosluidic-quartz metasomatites) genetically associated with mineralization were identified. The use of high-resolution satellite imagery in conjunction with geophysical data made it possible, on a scale of 1 : 10 000, to identify gold-prospective areas associated with volcanic dome structures, which are characterized by an increased density of lineaments and are associated with the formation of subvolcanic rhyolites.

The Current State of Research on Secondary Quartzites of the Northern Segment of the Jungar-Balkhash Folded System and Their Au Mineralization (Central Kazakhstan)

In this paper, we outline a study conducted on altered rocks in Central Kazakhstan, in particular, focusing on secondary quartzites. The study reveals a connection between copper-porphyry deposits in Central Kazakhstan and secondary quartzites. Recent research has unveiled gold mineralization in various secondary quartzite massifs, which has spurred further investigations in the region. Over the past three decades, extensive studies have been conducted that have demonstrated similarities among the gold deposits in this area and epithermal gold-silver deposits in volcanic-plutonic arcs around the world. By identifying patterns in the distribution of gold mineralization and developing regional exploration criteria, researchers have comprehensively assessed 48 secondary quartzite massifs and have prioritized promising areas for further exploration. Valuable findings have emerged from detailed examinations of the Akgirek and Birlestik massifs, which have involved drilling exploration wells up to a depth of 250 m. These investigations have shed light on the depth distribution of metasomatites and their association with gold mineralization. Consequently, these findings strengthen our belief in the significant potential for gold mineralization in the secondary quartzites of the Jungar-Balkhash folded system.

Геохимические особенности Ag-Au рудопроявления Кыплатап (центральная Чукотка)

The article considers the geochemical features of unconventional mineralization in secondary quartzite’s of the Kyplatap ore occurrence, located on the southeastern flank of the volcanic dome structure (VDS) of the same name, complicating the Palyavaam-Pykarvaam volcanotectonic depression (VTD) in the Chaun zone of the Central Chukotka sector of the Okhotsk-Chukotka volcanic Belt (OChVB). The Kyplatap VDS was formed due to the intrusion into the Late Cretaceous Alkaquun volcanites of a large laccolith-like subvolcanic body composed of rhyolite-trachyriolite-trachydacites. Based on the geochemical studies of the Kyplatap ore occurrence, the authors compiled a representative database of geochemical data, including the results of analyses of express-RFA, PKSA and XSA with coordinates and composition of ores and rocks. Correlation analysis of the database showed a positive relationship between Au and Ag, as well as Sb for ore mineralization, and a negative correlation of these elements with the association of the rock group of elements (Ti, Y, Zr, Nb and Yb) that were removed during ore formation. The authors also distinguished the second rock group of elements (K, Ga, Sn, Ba, V, W, Pb, Sc, La and B), characterized by medium and weak correlation of the first group of elements. They calculated the coefficients of enrichment and deficiency of ore-forming elements for the samples taken within the ore zones of the Kyplatap ore occurrence. The extreme enrichment group includes elements Au, Ag, Sb, Bi, As, the average contents of which are 100 times or more, and the minimum concentrations are at least 2-10 times higher than the average contents in the upper crust. The normal enrichment group includes elements S, Sn, Cu, Zn, Mn, Mo and Pb, the average contents of which are 2-10 times, and the maximum concentrations are 5-100 times higher than the average concentrations of the upper crust. The obtained values of the enrichment coefficients indicate a sufficiently intensive metensomatoses and ore formation within the Kyplatap ore occurrence.

Петрография вторичных кварцитов месторождения Алкамерген (Павлодарская область)

This paper presents the results of studying the features of formation and mineral composition of secondary quartzites of the Alkamergen deposit (Pavlodar region) through mineralogical and petrographic studies of samples on an automated diffractometer. The hydrothermal-altered rocks of the deposit, which are represented by medium-temperature secondary quartzites of the alunite facies, have been studied. The results of the research made it possible to establish the genetic features of the formation of the Alkamergen deposit. In terms of rock composition and ore mineralization, this object is a typical representative of acid-sulfate type deposits.

Hydrothermal and Metasomatic Kaolin Resource Estimation in the Quang Ninh area, Northeastern Vietnam

In northeastern Vietnam, hydrothermal‐metasomatic kaolinite-pyrophyllite from the secondary quartzite origin has been found in many places, including Pin Ho, Ban Ngai, Khe Khoai, Pec Sec Leng, Tan Mai ore occurrences, etc. They are exploited together with pyrophyllite, alunite, and high‐alumina quartzite as a byproduct. There were 810 chemical and mineral samples in the Quang Ninh area collected to investigate hydrothermal‐metasomatic kaolin resources. The ore minerals consist of kaolin-group minerals (kaolinite, dickite), pyrophyllite, quartz with minor sericite, alunite, diaspora, etc. They were identified by X-ray diffraction, and microscope and scanning electron microscope coupled with energy-dispersive X-ray spectroscopy analyses. Chemical analyses of major oxides were carried out on clays and parent rock samples by X-ray fluorescence spectrometry. The similarity-analogy in ore geology and mineral resource estimation based on statistical methods are employed to estimate hydrothermal‐metasomatic kaolin resources from the Quang Ninh area in northeastern Vietnam. The mineral resource estimation based on statistical methods shows 2.21 million tons of kaolin obtained by the content of aluminum oxide over 28% of the Pec Sec Leng mine, accounting for 14.3% in total. The similarity-analogy in ore geology indicates 158.16 million tons of kaolinite-pyrophyllite ores, of which, 22.0 million tons are kaolin. These methods display that the Quang Ninh area contains mainly pyrophyllite rather than kaolin resources. Our study suggests that the Quang Ninh area can be considered as a potential pyrophyllite resource in northeastern Vietnam for future exploration. Furthermore, the one resource estimation based on similarity-analogy in ore geology method shows an overview of the prospect on kaolinite-pyrophyllite resources in the Quang Ninh area, northeastern Vietnam.

Volcanogenic Deposits of Non-ferrous Metals in the Lesser Caucasus and Eastern Pontides

The paper presents brief characteristics of geological environments of ore deposit occurrences in Turkey, Georgia and Armenia. They can be attributed to Kuroko-type deposits, being distinguished by the character of ore accumulation. To the west, in Turkey, there are epigenetic and hydrothermal-sedimentary copper-zinc deposits that were formed in deep restricted basinal settings. An example of the latter is the Chayeli deposit.To the east, in the Caucasus, we have predominantly only epigenetic deposits. Besides, in the Bolnisi mining district (Georgia) there is the Madneuli deposit which represents an example of polyformational deposit. Here, within the restricted territory, have been concentrated:barite, barite-polymetallic, gold-bearing secondary quartzite, large-scale stockworks of copper ores. Judged by the 87Sr/86Sr ratios, some volcanites which are spatially associated with ores, might have been products of the “differentiation” of undepleted mantle, or other magmas that were generated in the lower part of the earth crust.In the Alaverdi ore district in Armenia, there are Jurassic volcanodepressions that host copper, copper-zinc and barite-sulfide ores. All the deposits of the Alaverdi district, porphyry copper including, contain economic reserves of ores.On the basis of available literature material and our own data, there has been created a mental-logical geological-genetic model of volcanogenic deposits.

New perspective Reza gold deposit (Gedabek ore district, Lesser Caucasus, Azerbaijan)


 
 
 The article describes Reza gold deposit of Ugur exploration area located in Geda- bek Ore District of the Lesser Caucasus in NW of Azerbaijan. It is established that main mineralization in the Reza gold deposit consists of hematite-barite-quartz-kaoline veins- veinlets and breccia, pyrite stock-stockverk and quartz-sulfide veins. On the main orebody surface center secondary quartzites with vein-veinlets barite-hematite mineralization have occured over which remain accumulations of hydrous ferric oxides cementing breccias of quartz and secondary quartzites. “Reddish mass” is also observed in erosion parts, being an oxidation product of stock and stockverk limonite-hematite ores. Representing typical gossans, these accumulations by the data of trenches for thickness about 5-10 m contain gold 0.3-3.5 ppm and silver 1.0-45.0 ppm. There are three zones of gold mineralization within the Reza gold deposit: oxide mineralization; transition zone mineralization; sulfide mineralization. The oxide gold mineraliza- tion consists of clay-gravel weathering crust of kaolinite type. The gold-bearing mineralization has been oxidized to a depth of ap- proximately 50-100 meters. Typically, the gold mineralization is coarser and a minor increase in gold grade occurs within the oxides compared to the original rocks. The nugget effect increase in the gold grade of the oxides does not exceed approximately 10%. Deposit alteration signature has characteristics which suggest the current outcrop level may be near the top of a mineralized, gold-bearing high sulfidation epithermal (HSE) system. The gold mineralization at the deposit is interpreted as forming in shallow high sulfidation epith- ermal systems. The mineralization has been noted in well-confined hydrothermal breccia and associated with pyrite stock-stockwork. The majority of the deposit material and current estimates are formed within the barite-hematite-quartz-kaoline mineralization in the secondary quartzite rocks. The main brecciation and stockwork are hosted within secondary quartzite, sometime massive silicified andesite porphyritic rocks.
 
 

The Patterson Lake corridor of Saskatchewan, Canada: defining crystalline rocks in a deep-seated structure that hosts a giant, high-grade Proterozoic unconformity uranium system

The Patterson Lake corridor in the Athabasca Basin region of Saskatchewan, Canada, hosts a large-scale uranium system with two major deposits already delineated. The corridor developed in crystalline rocks of the SW Rae Province, which host all of the known uranium endowment. Orthogneisses along with voluminous pegmatites are the hosts of the uranium mineralization. These rocks, however, underwent significant open-system metasomatic–hydrothermal modification. Principal amongst these alterations is early and pervasive quartz flooding that resulted in the development of widespread secondary quartzites and associated rock types. These secondary quartzites and their altered host rocks suffered ductile deformation, typically focused at silicification fronts. Late carbonatite dykes exploited the associated shear zones. Semi-brittle deformation zones nucleated near the previously developed ductile high-strain zones. Graphite and associated iron-sulfides precipitated in a semi-brittle structural regime. These graphitized zones provided the necessary structural architecture to focus the uranium system, which exploited the conduit hundreds of millions of years later at c. 1.425 Ga. Host rocks of the Patterson Lake corridor prove that metasedimentary rocks are not a requirement for the development of giant Proterozoic unconformity uranium deposits. Crustal-scale fault zones with access to the mantle (i.e. carbonatites) should be considered a key parameter in the exploration model for Proterozoic unconformity uranium deposits. Given the similarity of the mineral assemblages in the crystalline basement rocks of the main exploration corridor in the eastern Athabasca Basin region, it is likely that a similar, cryptic geological boundary focused the giant uranium system in that region. Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

PROSPECTS OF NEWLY DISCOVERED UGUR AREA IN THE NORTHWEST OF THE GEDABEY ORE DISTRICT (LESSER CAUCASUS, AZERBAIJAN)

The article describes Ugur exploration area located in Gedabey Ore District of the Lesser Caucasus in NW of Azerbaijan. Results of trenches and channels sampling on the surface, RC bore holes and summary of significant drill intercepts (>0.29 ppm Au) of Ugur Exploration area are presented. It has been established that The deposit is enlarged by highly gold-silver result of surface outcrop rock chip samples over an area of 2.5 kms North-South by 2 kms East-West, with the Reza gold deposit located in the central part. Out of metallic minerals crystalline hematite was observed. On surface intensive barite and barite-hematite vein and veinlets, also gossan zones were observed. The main mineralization zones have been sampled in three trenches at a distance up to 270 m by trenches #1, #2 and #3 and received positive results for gold and silver. Also there have taken approximately 550 samples from outcrop #1 and #2. On the main orebody at surface centre there occured secondary quartzites with vein-veinlets barite-hematite mineralization over which there remain accumulations of hydrous ferric oxides cementing breccias of quartz and quartzites. And in erosion parts "reddish mass" being oxidation product of stock and stockverk hematite ores were observed. Representing typical gossans, these accumulations by the data of trenches for thickness about 5-10 m contain gold 0.3-2.0 ppm and silver 1.0-15.0 ppm. Ten diamond drill holes, named UGDD 01-10 were drilled in the center part of the deposit. The drill holes were sampled mainly in 1 meter lengths from the top of the hole to the bottom. The core samples were marked and placed into standard boxes. Significant intervals of weighted averages greater than 0.29 ppm over down hole intervals of 1 metres or greater (>0.29 ppm Au and >0.9 m) are summarized in table 3 below. In conclusion, the outcropping alteration at the deposit is typical of the upper steam-heated levels of high-sulfidation epithermal (HSE) deposits, which in most mineralized systems of this type, may cap higher-grade gold mineralization which is hosted by underlying vuggy and oxide zones.

Formation Environments of Metasomatites and Ores of the Epithermal Gold–silver Deposits

Preore metasomatites of epithermal gold–silver deposits are formed by various types of hydrothermal solutions—from highly acidic and oxidized (argillization, alunitization, secondary quartzites) and moderately acid (sericitization) to rather reduced and alkaline (adularia). The possible processes creating highly acid mineralizing fluids at shallow depths are: (a) the condensation of the acid gas phase of heterogenized fluids (including also the condensation of gaseous HCl, HF and H2SO4 whose water solutions possess properties of maximum boiling azeotropic mixtures); (b) the oxidation of containing SO2 and H2S magmatogene gases by meteoric waters rich in oxygen; and also c) possible disproportionation of sulfur from SO2 to H2S and H2SO4. The epithermal gold–silver deposits of high sulfidation type form at the upper parts of heterophase fluid systems. The major gold–silver and sulfide mineralization (except small amounts of earlier generations of pyrite, enargite, and luzonite) precipitates not synchronously with the acid metasomatites, but essentially later, when the water table of liquid and less acid fluids raise into the realm of ore deposition. At zones of flat subducting ocean crust, the deposits of copper–porphyry type are quite often found beneath the epithermal Au–Ag deposits. However, the former cannot be considered the bottom of the gold–silver ore-forming systems, because they sometimes form much earlier and in closed systems; therefore, they have their own bottom part of the ore-forming system (a zone of K-feldspathization with related molybdenum ore) and the top part (a zone of sericitization with related copper mineralization). In addition, in steep subduction zones typical of the Central West Pacific region, including Khabarovsk and Primorsky krais and Japan, epithermal Au–Ag deposits have no spatial or temporal relations to copper–porphyry deposits due to the nearly complete absence of the latter. There are the alkaline metasomatites that form in the lower, bottom parts of epithermal heterophase fluid systems, creating the major bonanza gold–silver and sulfide mineralization of the adularia (low sulfidation) type in the Russian Far East, western America, and Japan. The term high sulfidation widely used now was created by the artificial combination of the terms high sulfate and high oxidation and is very ambiguous, because it really does not imply sulfidization processes. This type of mineralization would be better named acid sulfate.

Argillizite “Hats” of Kompleksnoe Ore Occurrence in Kayenmyvaam Volcanic Uplift (Central Chukotka)

The article is devoted to the results of mineralogical and geochemical studies of argillizites at Compleksnoe Au–Ag ore occurrence, localized on the southern flank of the Kajenmyvaam volcanic uplift in the inner zone of the Late Cretaceous marginal–continental Okhotsk-Chukchi volcanic belt (OChVB). At the ore occurrence, a series of isometric (oval) in plan view argillizite “hats” with diameters of 200 to 900 m are described. They are composed of red and light gray clay formations and accompanied by complex (Au–Ag–Mo–Cu–Pb–Zn–Bi–Sn) anomalies. In the recent relief, argillizite “hats” are characterized by gently sloping domes and crown subvolcanic bodies of granitoids and explosive breccias. A series of argillizite “hats” is surrounded by elongated lenticular bodies of secondary quartzites, which form the outer boundary of a large annular volcanostructure. The argillizites are composed of the following minerals: illite-smectite (mixed-layered formation), kaolinite, muscovite, jarosite, quartz, and rutile. The average content of Au and Ag in bulk samples are 0.06 and 0.075 g/t, respectively. Au is found in invisible form. According to the geological and geochemical data, argillizite “hats” record a near-surface (up to 300 m), slightly eroded, level of a large porphyry-epithermal mineral-forming system.

Types of metasomatic rocks: temperature conditions, buildups, features of composition, minerageny

The relevance of the work is due to the importance of metasomatic rocks associated many ore and non-metallic mineral resources. Purpose of the work: study of temperature conditions of formation, the characteristics of the chemical and mineral composition, the mineralogy of metasomatites. Results. The extended classification of the main types of metasomatic rocks (alkaline, basic, acidic) formed in the early alkaline and acid stages of the hydrothermal process is given. Temperature conditions of formation, features of chemical and mineral composition and metasomatite mineralogeny are considered. Alkaline metasomatites are subdivided into potassium (pyroxene phenites, microclinites, biotite-orthoclase metasomatites, gumbaites) and sodium (nepheline-pyroxene phenites, albites, sodic alterations). Deposits of tungsten, molybdenum, gold and uranium are associated with potassium metasomatites (gumbaites), and deposits of beryllium, lithium, tantalum, and niobium are associated with sodium metasomatites (albite). The main metasomatic rocks (basificates) include calcium and iron-magnesian metasomatites (calcareous and magnesian skarns, diopside-lapis lazuli metasomatites, rhodingites, kamaforites, carbonatites, apocarbonate calcites, dolomite-ankerite, magnesite and sideroplesite metasomatites). The formation of deposits of iron, boron, and phlogopite is associated with skarn; deposits of rare-earth elements, tantalum, niobium, and apatite are associated with carbonatites. Acid metasomatites are subdivided into aluminous and siliceous. Aluminous metasomatites include propylites, chloritolites, microcline-sericite and tourmaline-sericite metasomatites, secondary quartzites, argillizated rocks. Alumina deposits (kaolins, bentonites) are associated with secondary quartzites. Siliceous metasomatites include the largest number of species: uralite metasomatites, greisens, listvenites and berezites, chlorite-sericite-quartz and sericite-quartz metasomatites, charoitites, serpentinites, nephrites, anthophyllite metasomatites, carbonate-talc metasomatites and talcites, magnetite quartzites, jaspers, jasperoids. There is a group of metasomatites among them consisting of quartz in association with hydrous alumosilicates (muscovite, topaz, and chlorite). The other group includes low-alumina metasomatites, the mineral composition of which is dominated by hydrous calcium and magnesian silicates (charoite, serpentine, antophyllite, tremolite, talc). The third group is represented by metasomatites of quartz composition (magnetite quartzites, jaspers, jasperoids). The formation of deposits of iron, tin, tungsten, molybdenum, gold, polymetals, nonmetallic raw materials (asbestos, talc, charoite, nephrite, jasper) is associated with siliceous metasomatites. Conclusions. According to the formation temperature, high-temperature (above 500o С), medium-temperature (500–300о С) and low-temperature (below 300o С) metasomatic rocks are distinguished. The average compositions of alkaline metasomatites are characterized by high concentrations of potassium or sodium oxides, the predominance of feldspars (orthoclase, microcline, albite) in association with pyroxenes, carbonates. The main metasomatites are distinguished by high contents of calcium, magnesium and iron oxides at low silica concentrations prevailing in the mineral composition of silicates (pyroxenes and garnets) or carbonates (calcite, dolomite, magnesite, breunnerite). The composition of acid metasomatites is characterized by high concentrations of alumina or silica, the predominance of hydrous aluminosilicates, silicates and quartz.

Unusual (ice?) formations in the area of the Vneshniye ostrova of Finnish bay

When carrying out complex expeditions of the Russian Geographical Society within the archipelago of the Vneshniye Ostrova (Outer Islands) of the Gulf of Finland, fundamentally new geological objects were found, that were not previously known, some of them were identified as secondary quartzites, others whose nature is debatable are discussed in this article. On the island of Moshchnyj greeted boulders with a destroyed upper hemisphere. The nature of the destruction resembles the structures known as the Cone of Destruction or Shatter Cone, which in some cases are the only indicators of a meteorite nature for some ring structures. Three options for the formation of destroyed boulders are discussed: external meteorite impact similar to the structures of the Shatter Cone type, as a result of an endogenous explosion followed by coffered collapse of fragments of deep rocks and the main version is the fall of large boulders from a vertical glacier cliff and their impact on the underlying boulder, which under the influence of impact cracks. A similar situation is possible within the regional part of the cover glacier, which was located in the area of the future Island of Moshchnyj and known as the Neva end moraine with age of the 12000 years.

Geochemistry of sillimanite-magnetite-kaolinite of metasomatic rocks of the island of Great Tyuters (gulf of Finland, Russia)

Among the secondary quartzites of the island of the Great Tyuters there are extended linear zones with a capacity of up to 3 meters, clearly visible in detailed satellite images. They are composed of sillimanite-magnetite-kaolinite metasomatites discovered for the first time. The formation of metasomatites is associated with fragmentation of quartzites and the subsequent introduction of fluids of a substance saturated with various components. Metasomatites are enriched with Al2O3 (16–23 wt.%), in contrast to 2–5 wt. per cent of this oxide is present in their substrate – quartzite. In metasomatic rocks dominated by iron oxide, quartzite – ferrous. The rocks do not contain any alkaline and alkaline-earth elements. They are enriched with Zr (146–199 g/t) and a number of other elements, including impurities and rare earth, among which prevail Ce (34 g/t) and La (17 g/t). REE of both breeds is characterized by a small and close degree of fractionation ((La/Yb)n=6.55 and 6.17). Metasomatites on a set of minerals do not differ from quartzites, but differ in their quantitative ratios and composition. Of particular interest is the magnetite of metasomatites. It contains many quartz inclusions with kaolinite edges. Quartz inclusions, in turn, contain inclusions of titanium magnetite crystals. In the formation of metasomatites, there were several stages of the metasomatic process with a changing composition of fluids and different acidity-alkalinity of the mineral formation medium. The development of metasomatites in linear zones, the disintegration of their substrate, the high content of kaolinite – all this gives them a similarity with weathering cows. However, the same set of minerals in metasomatite and its substrate, the complete absence of sulfides and sulfur, the presence of magnetite with double mineral inclusions – such features distinguish these rocks from the classical weathering crust.

Geochemistry of Sillimanite–Magnetite–Kaolinite Metasomatic Rocks on Great Tyuters Island, Gulf of Finland, Russia

Secondary quartzites on Tyuters Island in the Gulf of Finland host long linear zones, up to 3 m thick, that are easily discernible in detailed satellite imagery. The zones consist of sillimanite–magnetite–kaolinite metasomatites, rocks that were first found in these zones. The metasomatites were produced at shattering of the quartzites and subsequent fluid introduction of material enriched in various components. The metasomatites are enriched in Al2O3 (16–23 wt %, as compared to 2–5 wt % in the quartzites). In contrast to the quartzites, iron in the metasomatic is contained mostly in the form of ferric oxide (whereas it occurs dominantly as ferrous oxide in the quartzites). The metasomatites contain practically no alkalis and alkali-earth elements and are enriched in Zn (146–199 ppm) and some other trace elements, including REE, first of all Ce (34 ppm) and La (17 ppm). Both the metasomatites and the quartzites show similar and insignificant REE fractionation: (La/Yb)n = 6.55 and 6.17. The metasomatites consist of the same minerals as the quartzites, but the proportions of these minerals and their composition in these rock types are different. It is worth mentioning magnetite of the metasomatites: it hosts abundant quartz inclusions with kaolinite rims. The quartz inclusions host, in turn, inclusions of magnetite crystallites. The metasomatites were produced in a number of stages of a metasomatic process, with changes in the fluid composition and its pH. The development of the metasomatites in the linear zones, the disintegration of their protolithic quartzites, and the high kaolinite contents in the rocks make these metasomatites similar, in a sense, to weathering crusts. However, the facts that the metasomatites and their protolithic quartzites consist of the same minerals, that the metasomatites contain absolutely no sulfides and sulfur but contain magnetite with complicated mineral inclusions make these rocks different from classic weathering crusts.

Alteration of volcanic rocks and changes in physical-mechanical properties on the South-Kambalny thermal field (South Kamchatka)

The aim of this research project was to consider hydrothermal alteration of volcanic rocks and accompanying changes in their physical and mechanical properties on the thermal field of South Kamchatka. Under the influence of thermal water and steam original andesites and basaltic andesites gradually transform to clay-rich soils and then to opalites and secondary quartzites. The changes in the mineral composition, microstructure, and physical-mechanical properties of rocks and soils in the thermal field were studied. Argillic hydrothermal alteration has gradually decomposed andesites to weak clay-rich soils which form a cover above the field. Elevated sites on the thermal field are composed of opalites and monoquartzites. Progressive hydrothermal alteration of andesites and changes in their properties promotes a broad range of geological phenomena including initiation of landslides, migration of thermal manifestations, changes in relief, and surface deformation.

Geological–Geophysical Model of the Nizhne-Koshelevskoe Vapor-Dominated Geothermal Deposit, the Largest in Kamchatka

Fundamentally new data on the structure of the Nizhne-Koshelevskoe vapor-dominated geothermal deposit (South Kamchatka) were obtained. An isometric area of intensely argillized rocks saturated with a vapor–gas mixture with the shape of an irregular cup occurring up to a depth of 250–300 m was distinguished in the central part of the deposit beneath the major zone of hydrotherm discharge. This area is controlled by a heat source through a subvertical channel of increased fracture–porous permeability for a vapor–gas fluid with a thickness of 300–350 m and a depth of >5 km. The elements of the paleohydrothermal system, such as relatively rock blocks composed of propylite and secondary quartzite with epithermal ore mineralization, were distinguished at the core of the deposit. The heat was transferred by the crustal flux of reduced hydrocarbon fluid.