Composition Of Rock-forming Minerals Research Articles

Carbonatization of Serpentinites of the Mid-Atlantic Ridge: 1. Geochemical Trends and Mineral Assemblages

Abyssal peridotite outcrops compose vast areas of the ocean floor in the Abyssal peridotite outcrops compose vast areas of the ocean floor in the Atlantic, Indian, and Arctic Oceans, where they are an indispensable part of the structure of the oceanic crust section formed in low-velocity oceanic spreading centers. The final stage in the evolution of abyssal peridotites in the oceanic crust is their carbonatization, which they undergo on the surface of the ocean floor or near it. The main goal of this study was reconstruction of the geochemical trends accompanying the carbonatization of abyssal peridotites using the example of MAR ultramafic rocks and to identify the main factors that determine their geochemical and mineralogical differences. It is shown that variations in the composition of rock-forming minerals and their characteristic assemblages indicate that the initial stages of carbonatization of abyssal peridotites occur in intra-crustal conditions simultaneously with the serpentinization of these rocks. The final stage in the crustal evolution of abyssal peridotites is their exposure to the surface of the ocean floor, to which they are transported along the detachment faults. Here, abyssal peridotites in close association with gabbro form oceanic core complexes, and the degree of their carbonatization sharply increases with the duration of their exposure on the surface of the ocean floor. The presented data made it possible to qualitatively reconstruct the sequence of events that determined the mineralogical and geochemical features of carbonatized abyssal peridotites of the MAR.

Рентгеноспектральный анализ активированного трепела Краснослободского месторождения Тамбовской области

The features of the change in the composition of rock-forming minerals during thermal activation of tripoli were established. At temperatures above 500°С, decomposition of clay minerals occurs with the formation of a high-temperature modification of aluminum oxide. In the temperature range of 200-500°С, the ordering of the amorphous opal-cristobalite structure increases due to phase changes in cristobalite, a further increase in temperature leads to its transformation into tridymite.

Влияние вещественного и гранулометрического состава гидрогенных руд на интенсивность осаждения кольматантов при подземном скважинном выщелачивании

During the development of hydrogenous uranium deposits using the in-situ well leaching method, there is a gradual loss of productivity of technological wells. This phenomenon is caused by coltmation processes in the productive formation. The most negative impact on the loss of well productivity has mechanical and chemical types of colmatation. Mechanical kolmatation is related to the accumulation of thin clay particles in the near-filter zone of injection wells, which plug up the near-filter space. Chemical kolmatation is the deposition of chemical compounds formed during destruction of rock-forming minerals of the productive formation in the near-wellbore zone by sulfuric acid. Earlier studies of these phenomena showed a direct relationship between the intensity of colmatants’ formation and the material composition of rock-forming minerals composing the host rocks of hydrogenous deposits and their granulometric composition. Each deposit is characterized by a specific set of mining-geological and granulometric parameters, so the colmatation processes for each deposit are individual. This article is devoted to establishing the correlation between the intensity of colmatation processes in the deposits of the Khiagda ore field and their characteristics. The object of the study - technological installations for in-situ borehole leaching. The research objectives are to establish the intensity of colmatation phenomena in the near-filter zone of technological wells and to develop regimes of repair and restoration work with reference to mining and geological and hydrogeological conditions of deposits of Khiagda ore field. The research methodology are presented by collection of information, its chemical and statistical processing and establishment of connection between the material and granulometric composition of ores in order to predict colmatation phenomena. The following research methods: chemical and granulometric analysis of processes occurring during underground borehole leaching of hydrogenous uranium ores, mathematical and statistical analysis of the results, simulation of processes of sedimentation and liquidation of colmatants from the filter zone of technological wells have been used.

Chemistry of rock-forming silicate and sulfide minerals in the granitoids and volcanic rocks of the Zefreh porphyry Cu–Mo deposit, central Iran: Implications for crystallization, alteration, and mineralization potential

Abstract Cu–Mo mineralization and associated hydrothermal alteration zones in the Zefreh porphyry Cu–Mo deposit are a result of the emplacement of the early Miocene granodioritic-to-granitic porphyritic intrusions into the Eocene volcanic rocks (dacites, pyroclastic rocks, and andesitic lavas) during active subduction along the Urumieh–Dokhtar Magmatic Belt (UDMB) of Iran. The compositions of rock-forming minerals, such as plagioclase, amphibole, and biotite, in the granitoids of the Zefreh magmatic suite are used to determine temperature and oxygen fugacity in the magma during crystallization and emplacement. Plagioclase is locally unaltered and ranges widely in composition with reverse, normal, and oscillatory zoning, but there is no evidence of excess aluminum. Primary calcic amphiboles in the granodiorite porphyry are mainly magnesio-hornblende with high Mg#’s. The crystallization temperature of the granodiorite is in the range of 765–867 °C (average 821 ± 28 °C for amphibole–plagioclase geothermometer) and 706–861 °C (average 808 ± 35 °C for amphibole alone). Whereas, the zircon saturation temperature for the Zefreh granodiorite is lower and ranges from 724° to 733 °C (average 729 ± 4 °C). Biotites in the least-altered granodiorite and in the potassic alteration are Mg-rich and Ti-poor, and mainly fall within the fields of phlogopite and re-equilibrated primary biotite, because of their low TiO2 contents (2.7–4.5 wt%, average 3.5 wt%). Copper and molybdenum in the Zefreh porphyry deposit appear to have been transported by Cl-rich hydrothermal fluids as chloride complexes, based on the calculated halogen fugacity ratios of the fluid in equilibrium with hydrothermal biotite that range from 5.0 to 5.4 for log (ƒH2O)/(ƒHF), 4.3 to 4.8 for log (ƒH2O)/(ƒHCl), and –2.0 to –1.4 for log (ƒHF)/(ƒHCl). The calculated fugacity ratios indicate that the biotites equilibrated with hydrothermal fluids that varied in composition, including oxygen, sulfur, and halogen fugacities. The intercept values for biotites from the Zefreh porphyry Cu–Mo deposit [IV(F) = 1.9 to 2.2 and IV(Cl) = –4.8 to –4.3] correspond to those from other well-known porphyry Cu–(Mo–Au) deposits worldwide [IV(F) = 1.5 to 2.8 and IV(Cl) = –5.0 to –3.5]. On the other hand, hydrothermal chlorite and epidote in the propylitically altered granodiorite of the Zefreh deposit are more Fe-rich and Mn-poor than those in some mineralized porphyry systems. The calculated temperatures of chlorite formation by the geothermometer of Cathelineau (1988) are all similar (300–330 °C), suggesting the potassically altered granodiorite was also affected by later, cooler hydrothermal fluids associated with the distal propylitic alteration zone. Disseminated chalcopyrite in the matrix of the potassically and propylitically altered granodiorite hosts as much as 1.3 wt% Zn and 0.1 wt% As. Based on whole-rock and mineral compositions, we conclude that the Zefreh magmatic system is similar in many regards to subduction-related ore systems, but it is unlikely to host a major porphyry Cu–Mo deposit.

The Bystrinskii gabbro massif: the first data concerning composition, age and formation affiliation

Research subject. The research covered the geological position, material composition and rock age of a comparatively small (about 32 km2) Bystrinskii gabbro massif. This massif underlies a tectonic plate package consisting of serpentinized dunits and harzburgites of the ophiolite association in the Eastern boundary of the Middle Urals. Methods. The content of petrogenic elements was measured by the Х-ray fluorescence method using an Х-ray multichannel spectrometer CPM-35. The analysis of rare-earth element contents was conducted using a NexION 300S mass-spectrometer. The composition of rock-forming minerals was studied using an Х-ray microanalyzer CamecaSX100. The age of the massif was determined by the 147Sm-143Nd method of isotope dating. Amphibole geobaometers were used to determine the depth of the rock formation. Results. According to the petro- and geochemical features and composition of the rock-forming minerals, the 147Sm-143Nd isotope age of the rocks was found to be 587 Ma. It was shown that gabbroids in the massif are represented by two petrographic varieties. The predominant type of the rocks is gabbrodolerites, which are similar to the isotropic gabbros of undisturbed ophiolite sections in terms of mineral composition, structure, geochemical features and the depth of formation (not more than 2–3 km). The mapping results showed the massif under study to be the largest among those described thus far. The medium grained gabbroids, which are present in lesser quantities, differ sharply from gabbrodolerites in terms of lower contents of Fe, Ti, both rockforming (K, Na) and rare (Li, Rb, Cs) alkalis, Ba, V, Y, Nb, Zr, Hf and elements of rare-earth group, as well as by significantly higher quantities of Ca, Mg and Cr. The depth of their formation is 10–12 km, which corresponds to the upper mantle. Conclusions. The obtained information demonstrates that fragments of two levels of the ophiolite section are tectonically aligned in the Bystrinskii massif: relatively shallow isotropic gabbros of the upper part of the ophiolite section and deep gabbros of the mantle part of the ophiolite section.

Study of Physicochemical Properties of Zeolite-Bearing Tuffs Modified with Magnetite

The paper presents data on the comparative assessment of the composition and properties of natural and magnetized zeolite-bearing tuffs (ZBT) from the Kholinsky, Transbaikalia, and Chuguevsky, southern Russian Far East, deposits in Russia. In addition, the composition and properties of magnetite synthesized by two methods and used for ferritization of ZBT were determined. The phase composition of the synthesized magnetically active material and the quantitative phase composition of natural and magnetized samples of the ZBT from the Kholinsky and Chuguevsky deposits were determined by X-ray powder diffraction. The composition of rock-forming minerals of the ZBT from the Kholinsky deposit was refined. The chemical composition of ZBT from the Kholinsky and Chuguevsky deposits and the initial and magnetized samples was analyzed by XRF. Magnetite content on the surface of the ferritized ZBT was demonstrated to be no higher than 5–7% and not to be able to affect the capacity of ZBT and the pH of the solution. Magnetization of the ZBT does not affect the structure and properties of the ZBT.

Обобщенный опыт изучения и диагностики конвергентных пород на примере карбонатизированных флюидоэксплозивных ультрамафитов дайкового комплекса Среднего Тимана

Fluid-explosive rocks of the dike complex are identified in the Middle Timan. The rocks have convergent properties due to a combination of explosive and metasomatic processes. The study of the petrographic features of the rocks revealed their explosive nature. Further study of the chemical composition of rock-forming minerals established the source of the mantle material and the paragenetic relationship with carbonatite magmatism. The fluid-explosive rocks of the dyke complex have a long-term multistage formation history. The fluids caused fenitization of the host strata and its disintegration. Solid-gas material of the mantle-crustal compound fills the cracks. At the last stage of formation of fluid-explosive rocks, the rare-metal, rare-earth, and sulfide mineralization took place.

Evolution of Mineral Composition during Eclogite Metamorphism in the Belomorian Mobile Belt: Data from Vichennaya Luda Island

The detailed mineralogical-geochemical study of eclogites and their retrograde products (amphibolites in a rim of eclogite boudin) from Vichennaya Luda Island (Keret Archipelago, White Sea) revealed systematic variations in major-, trace and rare-earth element composition of rock-forming minerals, which should be taken into account in geochronological and thermobarometric studies. Garnets from garnet–amphibole interlayers in the eclogites demonstrate a prograde zoning. In addition, garnet rims differ from their cores in a “hump-like” REE pattern owing to the elevated Sm, Eu, Gd and Dy contents and a negative slope of HREE pattern, as well as in an increase of Sm/Nd and a decrease of Lu/Hf ratio. It has been established that the eclogites contain clinopyroxene with depleted (to chondritic level) REE content, a positive Eu anomaly, and lowered Ti, V, Cr, Y, Zr, and Hf contents. Based on these geochemical features, the Cpx can be ascribed to relict that have preserved during peak eclogite metamorphism. Amphiboles in amphibolite rim of boudin differ sharply from amphiboles in eclogite in the lowered contents of LREE and some HREE. In addition to almost a two-fold decrease of Ti content in the eclogite–amphibolite sequence, amphiboles demonstrate a significant decrease of V, Sr, Y, Nb, and Hf contents. All biotites have sinusoidal REE pattern, which is typical of minerals formed through fluid-induced disequilibrium processes. Biotite from eclogites has higher Ti content and elevated contents of REE, Nb, V, Cr, Ba, and Hf as compared to biotites from the amphibolization rim. The eclogites and amphibolites developed after them are similar in major, trace, and rare-earth element composition.

The Nature and Age of Plagioclasites in the Ultrabasic Rai-Iz Massif (Polar Urals)

Corundum-containing and corundum-free plagioclasites localized in chromite-bearing ultramafites of the Rai-Iz Massif were explored for the composition and age. The composition of rock-forming minerals was studied, and the geochemical characteristics of the rocks were ascertained. The isotope age of plagioclasites determined by zircons using the U–Pb mode with a SHRIMP II device was equal to 398 ± 3 Ma. The age found conformed to the boundary on most of the Rai-Iz Massif took place against the background of a starting powerful collision, which caused the formation of the chromium mineralization of a high-chromic type, as well as the separation of a series of essentially plagioclase rocks of ruby mineralization at the discharge zones of the vein series.

Chemical composition of rock-forming minerals in granitoids associated with Au–Bi–Cu, Cu–Mo, and Au–Ag mineralization at the Freegold Mountain, Yukon, Canada: magmatic and hydrothermal fluid chemistry and petrogenetic implications

The chemical compositions of rock-forming minerals have been determined for both altered and least-altered igneous rocks spatially associated with numerous mineralized zones (Nucleus Au–Bi–Cu–As deposit, Revenue Au ± Cu and Stoddart Cu–Mo ± W mineral occurrences, and Laforma Au–Ag deposit) across the Freegold Mountain area, Yukon, Canada. Within the study area, K-feldspar has a narrow compositional range (89.4–91% Or), whereas plagioclase spans a wide range (4.4–70.07% An). In all of the investigated samples, T Ab = T An = T Or, suggesting that magmatic equilibrium between the coexisting plagioclase and K-feldspar was maintained. Igneous amphibole phenocrysts from hypabyssal dikes are typically calcic, whereas the Stoddart Cu–Mo ± W, Laforma Au–Ag, and Goldy Au mineralization are associated with Mg-enriched primary amphibole of edenite composition, and Au–Bi–Cu–As mineralization from Nucleus is related to Al-enriched primary amphibole of ferropargasite composition. Primary biotite phenocrysts across the Freegold Mountain area re-equilibrated with oxidized magma (f(O2) values between 10–13 and 10–11.5 bars, lying between the Ni/NiO and the magnetite/haematite buffers). However, biotite and amphibole phenocrysts from Stoddart, Goldy, Laforma, and the Highway zones crystallized from a more oxidized magma, as indicated by their elevated X Mg up to 0.65, relative to biotite and hornblende from Nucleus and Revenue characterized by a lower X Mg (typically < 0.50). This suggests that various sources and (or) rapid emplacement were involved in magma genesis, as further supported by the considerable variation of pressure (1.8–7.3 kb) of amphibole crystallization and of the total Al content in least-altered biotite (2.6–2.9 afu) within the Freegold Mountain area. Biotite and apatite equilibrated within the T range of 520–780°C, consistent with temperatures of equilibration between ilmenite and magnetite, and their compositions indicate that they formed from an oxidized I-type magma. Magma differentiated by fractional crystallization (indicated by the presence of normally zoned plagioclase with Ca-rich cores and Na-enriched outer rims) and multiple magma mixing (supported by the presence of reversed zoned plagioclase and coexistence of normally and reversely zoned plagioclase). Lower X Mg biotite associated with the mineralized (Cu–Mo ± W) potassic alteration incorporated more F and Cl relative to least-altered biotite with higher X Mg. In both Nucleus and Revenue Au–Cu mineralizations, secondary biotite composition varies with respect to the associated alteration mineral assemblages. Although secondary biotite in the skarn re-equilibrated with F-poor fluids, secondary biotite from the pervasive biotitization is related to F- and Cl-enriched fluids, and secondary biotite from the phyllitic zone is related to F-, Cl-, and Mg-depleted fluids, thus consistent with a change in mineralizing fluid composition during mineralization.

Petrochemistry of Kamen volcano: A comparison with neighboring volcanoes of the Klyuchevskoy group

The data on geology, petrography, mineralogy and petrochemistry for Kamen volcano in the Central Kamchatka Depression are presented. A study of the volcano’s rocks and comparison with rocks of neighboring active volcanoes of the Klyuchevskoy group allow the establishment of some relationships. The rocks and minerals of Kamen and Ploskie Sopky volcanoes show systematic differences in the chemistry of rocks and minerals such that they obviously could not be formed from the same primary melts. The rocks of dykes and Kamen stratovolcano on one hand and the rocks of the Klyuchevskoy Volcano on the other hand form differently directed trends on petrochemical diagrams and differ in their compositions of rock-forming minerals, such they also could not originate from the same primary melts. The lavas of the monogenetic cones of Kamen volcano and moderately magnesian basalts of Klyuchevskoy volcano are derivates of the same melts, i.e., the cones situated on the slopes of Kamen are cones of Klyuchevskoy. The rocks of Kamen and Bezymianny stratovolcanoes form a single narrow trend in all petrochemical diagrams in which the lavas of Bezymianny volcano show a silica-rich part, thus indicating a genetic relationship between these two volcanoes.

New data on the composition of ophiolites from the Kumroch-Valagin segment of the Achayvayam-Valagin paleoarc (Eastern Kamchatka)

This study presents new data on the geochemistry and mineral chemistry of ultramafic and mafic rocks in ophiolits from the base of the Kumroch segment of the Achayvayam-Valagin paleoarc. The new data enabled us to consider peridotites and the associated diabases and gabbros enclosed as separated blocks into a serpentinite melange as a single ophiolite complex formed in a supra-subduction setting and subsequently disintegrated as a result of nappe formation. The variations identified in the geochemistry and compositions of rock-forming minerals are shown to be characteristic of the other study ophiolite complexes of Eastern Kamchatka. This is suggested to reflect spatial-temporal heterogeneity of partial melting during evolution of the Achayvayam-Valagin island arc.

Petrogeochemistry of rocks of the Ulitarechka Sequence, a new upper Archean lithostratigraphic unit in the central part of the Kola Peninsula

Fine-grained garnet amphibolites, amphibole plagioschists, biotite-amphibole, and amphibole-biotite, epidote-biotite and biotite plagiogneisses were identified during geological mapping in the Ulita River basin in the central part of the Kola Peninsula. These rocks bear evidence of volcanogenic origin and were combined into a single lithostratigraphic unit named the Ulitarechka Sequence. On the basis of the composition of rock-forming minerals, the metamorphism of amphibolites of the Ulitarechka Formation was determined as transitional between the amphibolite and granulite facies. In terms of petrography, chemistry, and mineralogy, the rocks of the Ulitarechka Formation are well correlated with the amphibolites of the upper Archean Voche-Lambina Sequence composing the base of the Lopian Tersk-Allarechensk greenstone belt. The REE distribution patterns of the Ulitarechka Sequence are similar to those of amphibolites of the Purnach and Kuksha formations of the lower part of the Paleoproterozoic Imandra-Varzuga rift structure, suggesting their derivation from a similar magmatic source. Since the boundary between the Kola and Belomorian blocks is marked by the Lopian rocks of the Tersk-Allarechensk belt, it can be shifted to the western contact of the recognized stratified rocks of the Ulitarechka Sequence.

New data on carbonatites of the Il’mensky-Vishnevogorsky alkaline complex, the southern Urals, Russia

Carbonatites that are hosted in metamorphosed ultramafic massifs in the roof of miaskite intrusions of the Il’mensky-Vishnevogorsky alkaline complex are considered. Carbonatites have been revealed in the Buldym, Khaldikha, Spirikha, and Kagan massifs. The geological setting, structure of carbonatite bodies, distribution of accessory rare-metal mineralization, typomorphism of rock-forming minerals, geochemistry, and Sr and Nd isotopic compositions are discussed. Dolomite-calcite carbonatites hosted in ultramafic rocks contain tetraferriphlogopite, richterite, accessory zircon, apatite, magnetite, ilmenite, pyrrhotite, pyrite, and pyrochlore. According to geothermometric data and the composition of rock-forming minerals, the dolomite-calcite carbonatites were formed under K-feldspar-calcite, albite-calcite, and amphibole-dolomite-calcite facies conditions at 575–300°C. The Buldym pyrochlore deposit is related to carbonatites of these facies. In addition, dolomite carbonatites with accessory Nb and REE mineralization (monazite, aeschynite, allanite, REE-pyrochlore, and columbite) are hosted in ultramafic massifs. The dolomite carbonatites were formed under chlorite-sericite-ankerite facies conditions at 300–200°C. The Spirikha REE deposit is related to dolomite carbonatite and alkaline metasomatic rocks. It has been established that carbonatites hosted in ultramafic rocks are characterized by high Sr, Ba, and LREE contents and variable Nb, Zr, Ti, V, and Th contents similar to the geochemical attributes of calcio-and magnesiocarbonatites. The low initial 87Sr/86Sr = 0.7044−0.7045 and eNd ranging from 0.65 to −3.3 testify to their derivation from a deep mantle source of EM1 type.

Composition of rock-forming minerals in the Kivakka layered massif, northern Karelia, and systematic variations in the chemistries of minerals in the rhythmic layering subzone

Data obtained on the compositions of rock-forming minerals from the Kivakka layered intrusion indicate that the #Fe of olivine increases up the vertical section of the intrusion, and the #Mg of the pyroxenes and the anorthite contents of the plagioclase simultaneously decrease, which reflects the fractionation of the parental melt. Emphasis is placed onto the compositional variability of minerals in the layered unit. A method is developed for the reliable calculation of the composition of pyroxenes before their exoslution (separately for ortho-and clinopyroxene). The composition of minerals in the zone of intercalating melano-, meso-, and leucocratic norites remains practically unchanged, which is generally consistent with the results of mathematical simulations: compositional variations of the bronzite (#Mg) and plagioclase (An content) during the crystallization of the bronzite-plagioclase cotectic were no greater than 5 mol %. The variations in the concentrations of trace elements in the cumulus and intercumulus clinopyroxene occurred to be the most informative. It was determined that the Cr concentration in the cumulus augite is statistically significantly lower than that in the intercumulus augite, which is at variance with fractionation laws and led us to suggest that the rocks with cumulus pyroxenes were formed by a melt with a higher degree of fractionation than those of the intercumulus melts of the adjacent layers.