Mineralogy Of Deposits Research Articles

PROFESSOR YA. V. SAMOILOV: CONTRIBUTION TO THE DEVELOPMENT OF PALEOBIOCHEMISTRY, THE DOCTRINE OF BIOLITHS AND AGRONOMIC ORES. TO THE 150TH ANNIVERSARY OF THE BIRTH

Yakov Vladimirovich Samoilov (1870-1925) - a large and original mineralogist, geologist, paleobiogeochemist of the early 20th century, one of the first students of V.I. Vernadsky at Moscow University, a talented teacher, professor at Moscow University, Moscow Agricultural Institute, Novoaleksandriysky Institute of Agriculture and Forestry. As a mineralogist he worked in the Urals, in Central Russia, in the Donetsk basin. Head of a large-scale program for the study of phosphorites in European Russia, founder and first director of the Scientific Institute for Fertilizers, an active participant in several international geological congresses. Developed the doctrine of biolites and agronomic ores. He made an original contribution to the substantiation of paleobiochemistry, sedimentology and lithology. I'M IN. Samoilov was one of the first scientists to pay attention to the study of the mineralogy of sedimentary deposits. Organizer and head of a large-scale program for studying phosphorite deposits in European Russia with the aim of using phosphorus fertilizers in agriculture. Organizer of the Public Committee and the Scientific Institute for Fertilizers (now the Ya.V. Samoilov Scientific Institute for Fertilizers and Insectofungisides), an active participant in the organization of research in mineralogy and geochemistry at the Institute of Applied Mineralogy and the Floating Marine Scientific Institute, chairman of a number of commissions at the Supreme Council of the National Economy of the USSR, a consultant State Planning Committee of the USSR. All his life he was in close communication with V.I. Vernadsky.

Mineralogy and Geochemistry of talc deposits in the Khogyani district of the Nangarhar province, Afghanistan

Mineralogy and Geochemistry of talc deposits in the Khogyani district of the Nangarhar province, Afghanistan

Effect of oil shale semi-coke on deposit mineralogy and morphology in the flue path of a CFB burning Zhundong lignite

The effect of oil shale semi-coke (SC) on the mineralogy and morphology of the ash deposited on probes situated in the flue path of a circulating fluidized bed (CFB) which burns Zhundong lignite (ZD) was investigated. 10 wt% or 20 wt% SC was added to ZD, which were then combusted in the CFB furnace at 950°C. Two probes with vertical and horizontal orientations were installed in the flue duct to simulate ash deposition. Both windward and leeward ash deposits on probes (P1W, P1L, P2W and P2L) were analyzed by using a scanning electron microscopy with energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), an inductively coupled plasma optical emission spectrometry ICP-OES, and a particle size analyzer. When ZD was burned alone, the P1W deposit was comprised of agglomerates (< 30 µm) enriched in CaSO4 and Na2SiO3, incurring significant sintering. The P1L and P2W deposits, however, were of both discrete and agglomerated particles in similar mineral phases but with coarser sizes. The P2L deposit was mainly fine ash particles where Na2SiO3 and Na2SO4 were absent. As SC was added, the agglomerates in both P1W and P1L decreased. Moreover, SiO2 and Ca/Na aluminosilicates dominated the mineral phases whereas Na2SiO3 and Na2SO4 disappeared, showing a decrease in deposit stickiness. Likewise, the P2W deposit was found less spread on the probe, decreasing its deposition propensity. Na-bearing minerals turned into (Na, K)(Si3Al)O8 and (Ca, Na)(Si, Al)4O8 in the P2W deposit. Moreover, Na in the deposits decreased from 32 mg/g to less than 15 mg/g as SC presented. The addition of SC would therefore help alleviate the propensity of ash deposition in the flue path in the CFB combustion of ZD.

Soil organic matter relationships with the geotechnical-hydrological parameters, mineralogy and vegetation cover of hillslope deposits in Tuscany (Italy)

Soil organic matter (SOM) represents a main fraction of superficial soil characterized by a mechanical-hydrological behaviour different from that of the inorganic fractions. In this study, a method to measure the SOM content was applied to 27 selected sites in Tuscany (central Italy) characterized by the presence of soil types common in the region: cambisols and regosols. The method included the contribution from root fragments, which is a fraction often neglected or underestimated in measurements, in the overall estimate of the SOM content. The retrieved SOM contents were analysed considering the vegetation cover at the sites and the selected attributes of geological interest, such as geotechnical parameters and the mineralogical composition of the soils. The SOM normalized to the bulk samples ranges between 1.8 and 8.9% by weight, with the highest values of the SOM content being associated with vegetation cover classes of forest and woodlands without shrubs. The SOM values showed close relationships with the abundance of the finer fractions (silt and clay) of the soil samples, and considering the relations with geotechnical properties, moderate correlations were found with the plasticity index, unit weight and effective friction angle, overall demonstrating the importance of considering SOM when the geotechnical and hydrological properties of soils are evaluated.

Mineralogy, geochemistry and genesis of bentonite deposits in Lam Narai volcanic belts, Lop Buri province, central Thailand

Alteration in the subaqueous basaltic rock of the Lam Narai volcanic belts, Lop Buri province, central Thailand has resulted in the formation of bentonite deposits. The bentonite deposits have been geological, mineralogical and geochemical studied to determine their genesis. The characteristics of the bentonites were examined by using X-ray Diffractometer and Scanning Electron Microscope with Energy Dispersive Spectroscopy. The mineralization zone of bentonite shown X-ray diffraction patterns of montmorillonite as the major constituent with minor hematite and calcite. Morphology of the minerals and groundmass in the bentonite deposits display the “cornflake,” “oak leaf,” or “cellular” textures that are typical and representative of montmorillonite in smectite group and composed of Si, Al, O, Ca, Mg and Fe in their chemical compositions. Geochemistry of the bentonite and their parental volcanic associations were analyses by using X-ray Fluorescence Spectrometry for major and trace elements. The representative samples were selected for the analysis of the rare-earth elements by using Inductively Coupled Plasma-Mass Spectrometry. The AI–CCPI alteration box plot revealed that the bentonite is mainly altered by hydrothermal alteration associated with basaltic layer in the Lam Narai volcanic belt. The basaltic layers in this area are composed of pillow lavas, inter-pillow and basic glassy inter-pillow (hyaloclastite) that indicated the subaqueous environment. The smectite formed by hydrothermal alteration from altered basic glassy inter-pillow (hyaloclastite) in the basaltic layers. Hydrothermal fluids in this area are possibly derived from the major fault along Pa Sak River or the youngest intrusive rocks in the Lam Narai volcanic terrain.

Deposition of metals and metalloids in the fumarolic fields of Guallatiri and Lastarria volcanoes, northern Chile

A detailed study on the mineralogy and chemistry of fumarolic deposits with a focus on metals and metalloids is presented. Two active volcanoes in northern Chile, Guallatiri and Lastarria, are characterised by vigorous and persistent fumarolic activity and the formation of zoned fumarolic deposits. Twelve minerals were identified in the studied deposits by X-ray diffraction: anhydrite, barite, gypsum, rhomboclase, orpiment, pyrite, galena, cristobalite, quartz, magnetite, sassolite, and native sulphur. Chemical analyses revealed the presence of 30 chemical elements, including metals and metalloids such as As, Hg, Pb, Sb, Te, and Tl. Backscattered-electron imaging revealed four types of rock textures in the fumarolic deposits: i) massive and poorly vesiculated, ii) highly vesiculated, iii) clastic-like, and iv) flow-like. Micro-chemical analyses showed the presence of cinnabar nataliyamalikite and unidentified mineral assemblages of AsS, TeS, PbS, HgS, TlI, and Tl-I-Pb compositions. Based on colour, outlet gas temperature, mineralogy, and chemistry, four distinct zones of fumarolic deposits are identified. (1) Grey zone: sulphide and silicate dominant with minor native elements, high concentrations of Pb and As, and a clastic-like texture (gas outlet temperature > 265 °C). (2) Red zone: sulphide and silicate dominant with minor oxides and native elements, small As, Pb, Tl, I, and Te minerals, and predominance of a flow-like texture (200–280 °C). (3) Yellow-orange zone: dominated by native sulphur and minor borates and sulphur with small As-, Sb-, Hg-, and I-containing minerals, massive and vesiculated texture (80–200 °C). (4) Yellow-white zone: formed by native sulphur, minor borates and As-rich zones, usually displaying a vesiculated texture (<100 °C).

Mineralogy and Geochemistry of Gold Ore Low Sulfidation -Epithermal at Lamuntet, Brang Rea, West Sumbawa District, West Nusa Tenggara Province

There are two Artisanal Small scale Gold Mining (ASGM) location in Lamuntet, Brang Rea Subdistrict, West Nusa Tenggara Regency, namely Nglampar and Song location. Nglampar and Song location are included in the low sulfidation epithermal gold deposit system. The research purposes to analyze mineralogy and geochemistry of gold vein deposits and determine system of low sulfidation gold ore in Nglampar, Lamuntet Village. The methods used to determine the mineralogy of gold vein deposits are petrography, mineragraphy and X-ray diffractometer (XRD) analysis, while geochemical analysis using Scanning Electron Microscope (SEM) with Energy Dispersive X-Ray Spectroscopy (EDS), Fire Assay (FA) and Atomic Absorption Spectrophotometry (AAS). The results showed that the minerals contained were quartz (Qz), sericite (Ser), Chalcedon (Chc), chlorite (Chl), pyrite (Py), sphalerite (Sph), galena (Gn) , gold (Au), chalcopyrite (Cp), argentite (Ag), arsenopyrite (Apy), Azurit (Az), Malakit (Mal) and bornite (Bn). Abundant mineral availability such as sphalerite, galena, chalcopyrite and arsenopyrite are characterized by high levels of Zn, Pb, Cu and As the metal in vein deposits. This can be seen on the chemical content of ore in gold vein deposits ie Au 0.1 ppm -27.8 ppm, Ag 3 ppm-185 ppm, Pb 101 ppm - 35,800 ppm, Zn 73 ppm-60,200 ppm, Cu 26 ppm - 1,740 ppm, and As 150 ppm - 6,530 ppm. Based on the results of SEM-EDS analysis shows that the type of gold mineral is the electrum because of the content of Ag&gt; 20%. Based on those characteristics of the mineralogy and geochemistry in this study showed that low sulfidation gold ore in this area is categorized as polymetallic gold-silver system.

Mineralogy of Chub Lake-Type Hematite Deposits in St. Lawrence County, NY

Numerous localities of specular hematite have been found in the Grenville Province in St. Lawrence County, New York. Here, we focus on six of them: the Dodge mine, the Chub Lake prospect, the Toothaker Creek prospect, the Bowman prospect, the Whitton prospect, and the Toothaker Pond prospect. We used literature research, interviews, and personal observations to establish the history of each site as a source of mineral specimens. We examined extensive holdings of specimens from each site in the New York State Museum. We used sight identification, chemical tests, x-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy as necessary to identify all the mineral species present. We had determinations made of the stable oxygen isotope content of quartz, hematite, and calcite from the Chub Lake prospect, reported as 18O relative to Vienna Standard Mean Ocean Water (VSMOW). We conclude that these occurrences formed from groundwaters at a temperature of about 170 °C in areas of low topography on the surface of the Precambrian basement rocks. Two hypotheses for this process are presented and evaluated. Well-crystallized specimens of bladed specular hematite and Cumberland-habit quartz are the most common minerals found. Noteworthy accessory crystallized minerals include barite, calcite, and goethite. All six deposits are relatively free of sulfides, so that secondary goethite formed from weathering of iron-rich carbonates at some sites. It is likely that more such deposits will be discovered in this region in the future.

Mineralogy, geochemistry, and fluid action process of uranium deposits in the Zhiluo Formation, Ordos Basin, China

Some controversies still exist regarding the genesis of sandstone-type uranium deposits in the northeastern Ordos Basin. Herein, based on boreholes and well logging data, we selected sandstone samples representing different epigenetic alteration environments as the research object and comprehensively utilized polarizing microscopy, scanning electron microscopy, electron probe analysis, elemental analysis, and other test methods to research sandstone genesis. The main altered minerals in the sandstone of this area include limonite, pyrite, achavalite, carbonate, sulfate, clay, and uranium minerals. The complex characteristics of alteration minerals indicate multi-stage fluid mixed mineralization in this area. According to the relationship between the major elements in different types of sand bodies, the components were classified into three groups. The first is the reduction media group, including CaO, MnO, total oxygen carbon (TOC), S, U, and burning loss. The second is the detrital particle group, including SiO2, K2O, and Na2O, and the third contains the clay and volcano component group, including Fe2O3, P2O5, TiO2, FeO, MgO, and Al2O3. Among these, the content of reduction media is positively correlated with uranium enrichment, whereas detrital particles and clay components reflect the influence of alteration on the sand body composition, which indirectly affects the uranium adsorption and precipitation. Through the normalization of rare earth element (REE) chondrites, we find that the distribution patterns of REEs in rocks with different geochemical environments show a fractionation of light and heavy rare earth elements (HREEs), a right-leaning enrichment of light rare earth elements (LREEs), and relatively flat HREE. Further, via the Post Archean Australian Shale (PAAS) normalization, we observe that the mudstone of the Zhiluo Formation exhibits a relatively flat curve, whereas the sandstones have strongly positive Eu anomalies. The difference in REE values for different types of sand bodies indicates that, although all types of rocks have a similar sedimentary environment, their original sediments underwent fluid alterations such as oxidation and reduction. Based on the uranium mineralization evolution history in the study area, the water-rock reaction process and mineral-alteration sequence were determined on the basis of alteration types and elemental concentrations. Our findings provide new insight into the petrological significance, mineralogy, and geochemical composition of uranium deposits in the Ordos Basin.

Sr isotope and major ion compositional evidence for formation of Qarhan Salt Lake, western China

Qarhan Salt Lake (QSL) is the largest potash brine deposit in the continental Qaidam Basin (QB) of western China. The origins of the Qarhan brines, whether from migration of Qaidam mega-paleolakes, paleoriver capture, or mixing of modern river water and Ca-Cl spring water, are controversial. Details about the origin (hydrothermal, diagenetic or both) of the Ca-Cl inflow waters entering QSL in the QB are unclear. Here we show from the strontium (Sr) isotope ratios of river waters, intercrystalline brines, spring waters, halite, gypsum, and Corbicula shells from Qarhan playa, that 87Sr/86Sr increases from Bieletan (western QSL) to Huobuxun (eastern QSL). This trend verifies that river water-spring water mixing has been operating at QSL for the past 50,000 years. Contributions of Ca-Cl inflow waters to the QB have profoundly influenced the brine evolution and mineralogy of salt deposits. Mixing between low Sr2+ concentration, low 87Sr/86Sr value of river waters and high Sr2+ concentration, high 87Sr/86Sr value of Ca-Cl spring inflow waters has produced various intercrystalline brines and salt deposits at QSL. Ca-Cl inflow waters and brines are enriched in Sr2+ and Ca2+ and depleted in Mg2+ and SO42−. These characteristics suggest brine-sedimentary rock (silicate) interactions at burial diagenetic or hydrothermal conditions. Ca-Cl inflow waters and brines have a similar Sr isotopic range as oilfield brines and celestite deposits in the QB, which also suggests a diagenetic-hydrothermal origin. Ca-Cl brines discharge as springs or seeps along fault zones in the QB. They are interpreted to reach the surface of the northern margin of Qarhan playa by topographically driven circulation.

Geology and Mineralogy of Rare Earth Elements Deposits and Occurrences in Finland

Rare earth elements (REE) have critical importance in the manufacturing of many electronic products in the high-tech and green-tech industries. Currently, mining and processing of REE is strongly concentrated in China. A substantial growth in global exploration for REE deposits has taken place in the recent years and has resulted in considerable advances in defining new resources. This study provides an overview of the mineralogical and petrological peculiarities of the most important REE prospects and metallogeny of REE in Finland. There is a particularly good potential for future discoveries of carbonatite hosted REE deposits in the Paleozoic Sokli carbonatite complex, as well as in the Paleoproterozoic Korsnäs and Kortejärvi Laivajoki areas. This review also provides information about the highest known REE concentration in the alkaline intrusions of Finland in the Tana Belt and other alkaline rock hosted occurrences (e.g., Otanmäki and Katajakangas). Significant REE enrichments in hydrothermal alteration zones are also known in the Kuusamo Belt (Uuniniemi and Honkilehto), and occurrences of REE-rich mineralisation are also present in granite pegmatite bodies and greisens in central and southern Finland (Kovela monazite granite and the Rapakivi Granite batholith at Vyborg, respectively). REE minerals in all of the localities listed above were identified and analyzed by scanning electron microscopy (SEM) and electron microprobes (EMPs). In localities of northern and central Finland, both primary rock forming and epigenetic-hydrothermal REE minerals were found, namely phosphates (monazite-Ce, xenotime-Y), fluorcarbonates (bastnäsite-Ce, synchysite), and hydrated carbonates (ancylite-Ce), hydrated aluminium silicates (allanite-Ce, Fe-allanite, cerite, chevkinite), oxides (fergusonite, euxenite) and U-Pb rich minerals. The chondrite normalized REE concentrations, the La/Nd ratios and the REE vs. major element contents in several types of REE bearing minerals from prospects in Finland can be used to identify and define variable REE fractionation processes (carbonatites), as well as to discriminate deposits of different origins.

Composite origin of magnetite deposits hosted in Oman peridotites: Evidence for iron mobility during serpentinization

We describe mineralogy of magnetite deposits concentrated within a nonconformity surface between Aniba serpentinites and overlying limestones in the Southern Oman ophiolite and discuss their origin to understand iron mobility during serpentinization, with special reference to factors controlling the magnetite-orebody sizes. The Aniba magnetite deposits occur in several forms such as fibrous crystals, oval or rounded grains, strings and cluster shapes, in fine-grained iron-rich chlorite and calcite matrices. The chromian spinel (Cr# = 0.38–0.56) within the magnetite deposits is similar in texture, mode of occurrence and chemical composition to that in the underlying serpentinized harzburgites (chromian spinel Cr# = 0.37–0.50), and plots in the space of abyssal peridotites. The mineral chemistry of chromian spinel, olivine and clinopyroxene (Cpx) suggested that the Aniba harzburgites are refractory residue after high-degree (15–25%) partial melting and are similar to abyssal harzburgites from a normal ridge segment. This is confirmed by a Cpx trace-element character with high depletion in light rare earth elements (LREE), Ta and Zr relative to heavy REE. The iron of our magnetite deposits was possibly derived from two sources: one is an essentially internal source of iron from the breakdown of Fe-rich serpentines after olivine during low-T serpentinization (<400 °C) and the external source of iron from hydrous fluids. The essential origin of our magnetite deposits is hydrothermal one due to the mobility and leaching of iron from serpentinites and the in-situ selective precipitation of iron within the nonconformity surface. This process was feasible because the nonconformity zone was a weathering surface, a channel for both hydrothermal-fluid flow providing high fluid/rock ratios that enhance iron mobilization in serpentinites and leach iron, besides chromian spinel grains, from the host ultramafic rocks. Chromian spinel grains (up to 10 vol%) in the magnetite deposits were of a residual detrital origin from the underlying serpentinized peridotites on weathering, and acted as a nucleus for magnetite precipitation. The morphology and colloform shape of some magnetite grains reflect their supergene origin. Factors controlling the size of the magnetite deposits include the compositions of the underlying serpentinized harzburgites as a main source of iron, high fluid/rock ratios and high iron mobility within fluid conduits such as a nonconformity surface, abundance of chromian spinel grains as a nucleus for magnetite concentration, low silica activity, pressure of water and oxygen fugacity.

The formation of deposits and their evolutionary characteristics during pressurized gasification of Zhundong coal char

The characteristics of deposits formed on stainlesssteel substrate (boiler tube) during pressurized gasification of Zhundong coal char with excessively high Na content were investigated in this work. The occurrences of alkali and alkaline earth metallic species in raw coal and its derived chars were determined by a sequential extraction method. The morphology, mineralogy and chemical compositions of deposits and bottom ash produced during the gasification of Zhundong coal char at 800, 1000 and 1200 °C were analyzed by X-ray diffraction and scanning electron microscopy combining energy dispersive X-ray spectrometer. Results show that water-soluble and ammonium acetate solution soluble sodium and potassium in raw coal tended to be converted to hydrochloric acid solution soluble form during Zhundong coal pyrolysis. Rising pyrolysis temperature increased the content of water-soluble calcium by enhancing the decomposition of CaCO3 and organically bonded calcium. During the gasification of Zhundong coal char, the released inorganic species, especially Na, Ca, Cl and S, could condense and/or agglomerate as sticky fine particles, resulting in fouling and slagging on the probes. Specifically, after Zhundong char gasification at 800 °C, alkali and alkaline earth metallic species-bearing minerals loosely clung on the probes as silicate or aluminosilicate. During char gasification at 1000 °C, a Na-S-O and/or Na-S deposit layer with a thickness of ca. 2 μm was formed on the probe No. 1 at 514 °C, while abundant Ca-Mg-Si-O and few Na2SO4 crystals were accumulated on the probe No. 2 at 771 °C. During Zhundong char gasification at 1200 °C, the minerals deposited at low temperature region (599 °C) were mainly composed of agglomerated and sintered alkali and alkaline earth metallic species-bearing compounds (mainly NaCl, KCl and Ca-Mg-Si-O). However, only few isolated particles were observed on the probe with temperature higher than 924 °C. Residual alkali and alkaline earth metallic species in bottom ash could form low-melting eutectics, such as NaAlSiO4 and Ca2Al2SiO7.

Mode of Occurrence and Mineralogy of Northern Khetri Copper Deposits, Jhunjhunu District, Rajasthan

Copper deposits in Khetri copper belt are hosted in the proterozoic sequence of rocks belonging to Ajabgarh group of Delhi supergroup situated in foot hill zone of Aravalli mountain range North-West, India. Khetri copper belt is about 100 km long NE-SW trending metallogenic province, starting from Singhana in the north to Sangarava in the south. The study area is the northern Khetri copper belt 190 km SW of Delhi, the capital city of India. In the present work an attempt has been made to determine the mode of occurrence and nature of mineralization with special emphasis on mineragraphic study of copper ores. The ore bodies are found in the form of multiple lodes regionally but locally in the forms of veins, stringers, dissemination, sporadic, cavity filling and replacement. Enriched mineralized zones are localized along the contact of Alwar and Ajabgarh group. Copper, the main entity in the belt occurs dominantly as sulphides, oxides, carbonates and sulphosalts mineral hosted in pelitic and psammitic rocks. Pyrrhotite, pyrite, magnetite and sphalerite are the other ore mineral associated with the copper ore in a considerable amount. From the textural, structural and multigenerational minerals, mineral assemblage studies, it is assumed that deposit has undergone metamorphism and multi-stage mineralization. Replacement has a profound influence on mineralization in the northern Khetri copper deposits.

Mineralogy, technological properties, and industrial application of kaolin deposits at Nivasht and Kabudkamar areas, northwest of Saveh, Central Province

Mineralogy, technological properties, and industrial application of kaolin deposits at Nivasht and Kabudkamar areas, northwest of Saveh, Central Province

Recovery of Copper Metal through Reprocessing of Residues from a Hydrometallurgical Plant

The Chemical of Africa (CHEMAF) is a hydrometallurgical plant operated in Katanga since 2001. It produces copper metal using a process comprising the sulphuric acid leaching of copper-cobalt oxide ores under reducing conditions (Na 2 S 2 O 5 or SO 2 ) followed by the leach liquor purification by solvent extraction (SX) and electrowinning of copper. The leach liquor is recovered during the thickening of pulps from the leaching section and the scavenging of residues by washing in the counter-current decanters (CCD). The process residues were anciently dumped near the plant. With the increase in the run of mine (ROM) ores sulphide minerals content related to changes in the Kalukuluku deposit mineralogy and considering that the storage of residues may result in toxic pollutants release to the environment, their reprocessing is gaining the ground as the best option. The present research aims at recovering copper metal from residues (2.01% Cu and 0.32% Co) through their reprocessing based on the sulphuric acid leaching prior to the recovery of copper metal through cementation with iron shavings. The results from the experiments have showed that the leaching of copper (≈ 90%) and cobalt (86%) was successful when conducted during 90 minutes at 75°C using 150 g of residues subjected to stirring (500 rpm) in 1 L of H 2 SO 4 (30 g/L) in the presence of Na 2 S 2 O 5 (330 mV). Consequently, one recovers satisfactorily copper metal (2.5 g of solids assaying 93% Cu recovered at 86%) when 1 g of iron shavings was stirred (400 rpm) during 60 minutes at constant speed and at the room temperature in 250 mL of the metalliferous solution (10.84 g/L Cu and 1.73 g/L Co) prepared by the leaching of residues.

Geology, mineralogy, geochemistry and δ34S of sedimentary rock-hosted Au deposits in Song Hien structure, NE Vietnam

The Song Hien rift basin is considered to be one of the most important regions of gold mineralisation in North East Vietnam. A number of gold deposits in the Song Hien rift basin are hosted in Triassic and Devonian sedimentary formations of the basin. The largest among them are the Bo Va, Tham Riem and Khung Khoang deposits. The Bo Va deposit is hosted in carbonaceous sedimentary rocks of Triassic age, whereas the Tham Riem and Khung Khoang deposits are hosted in carbonaceous sedimentary rocks of Devonian ages. Based on the mineral composition of the ores, the deposits can be divided into to two types: (i) pyrite dominated and (ii) pyrite-arsenopyrite dominated. The Khung Khoang is of the first type and the Bo Va and Tham Riem deposits belong to the second type. The isotopic composition of pyrite and arsenopyrite in the Tham Riem deposit however, is close to that for the ores of the Bo Va deposit. The δ34S value for pyrite ranging from −3.7‰ to −7.4‰ and for arsenopyrite ranging from −3.2‰ to 7.4‰. The δ34S of pyrite in the ore from the Khung Khoang deposit however, has a much heavier isotopic composition of +18.9 to +20.2‰. A narrow range of the variation of sulfur isotopic composition of pyrite and arsenopyrite, the presence of visible gold as inclusions, the presence of chalcopyrite, sphalerite and other inclusions in arsenopyrite and pyrite, the large size of the grains of major ore minerals allow us to assume that the primary gold ores of the Bo Va and Tham Riem deposits underwent metamorphic transformations. The absence of arsenic, antimony, mercury and other characteristic elements in the ores of the Khung Khoang deposit, and substantially heavier isotopic composition of sulfur similar to the sulfur isotopic composition of marine sulfates in the Devonian, allow us to assume another source of the ore components, not connected with the Triassic sedimentary rocks of the Song Hien rift.

Mineralogy and geological significance of hydrothermal deposits from the Okinawa Trough

Abstract The study of hydrothermal deposits in the Okinawa Trough can help us to uncover the hydrothermal mineralization characteristics in the back-arc basin during the early expanding stage. Mineralogy and geological significance of hydrothermal deposits from both the middle and southern trough are studied in this paper. First of all, using optical microscope to confirm the mineral compositions, characteristics of crystal shape, paragenetic relationship and minerals crystallization order. Then the minerals chemical composition were analyzed in virtue of electron microprobe. On these basis, the paragenetic sequence and the mineralization characteristics of the hydrothermal deposits were discussed. The results show that the hydrothermal deposit from the mid-Okinawa Trough belongs to Zn-Cu-rich type, consisting dominantly of sulfide minerals such as sphalerite, chalcopyrite, pyrite, etc. The minerals crystallization order is first generation pyrite(PyI)-sphalerite-chalcopyrite-galena-second generation pyrite(PyII)-amorphous silica. While the deposit from the southern Okinawa Trough is Ba-Zn-Pb-rich type mainly composing of barite, sphalerite, galena, etc. The minerals crystallization order is barite-pyrite-sphalerite-tetrahedrite-galena-chalcopyrite-amorphous silica. Hydrothermal fluid temperature in the mid-Okinawa Trough undergoes a process from high to low, which is high up to 350 °C in the early stage, but decreasing gradually with the evolution of hydrothermal fluid. On the contrary, the hydrothermal activity in the southern Okinawa Trough is low temperature dominated, but the mineralization environment is unstable and the fluid temperature changes drastically during the period of hydrothermal activity.

Geology, mineralogy and geochemistry of Pleistocene-Holocene deposits in the Çiftlik Basin (Niğde) (Central Turkey)

Geology, mineralogy and geochemistry of Pleistocene-Holocene deposits in the Çiftlik Basin (Niğde) (Central Turkey)

Hydrothermal alteration of surficial rocks at Solfatara (Campi Flegrei): Petrophysical properties and implications for phreatic eruption processes

Solfatara crater is located within the Campi Flegrei caldera to the west of Naples (Italy). It is one of the largest fumarolic manifestations known, and the rocks hosting the hydrothermal system are affected by intense hydrothermal alteration. Alteration can result in changes of degassing behavior, and in the formation of a cap rock thereby increasing the probability of phreatic eruptions. Here, we investigate the effects of alunitic (solfataric) alteration on the mineralogy, the physical properties (porosity, density, permeability) and the mechanical properties (strength) of the rocks involved, as well as its influence on fragmentation and ejection behavior. Our results show that the pristine mineralogy of deposits from the vicinity of the Solfatara cryptodome and from Pisciarelli is almost completely replaced by amorphous silica and alunite. The differences in the degree of alteration among the samples series are reflected in the investigated properties and behavior as well as in the analysis of the experimentally generated particles. Alunitic alteration increases porosity and permeability, whereas it reduces density, elastic wave velocity and strength leading to higher fragmentation and ejection speeds for the sample series examined in this study. Our results also show that alteration results in the generation of a high fraction of fines (particle sizes <10μm) during fragmentation, mainly composed of alunite crystals. Due to their potential for inducing chronic disease, dispersion of such material should represent a serious health hazard on a local scale and the evaluation of precautions should be considered.