Hasil untuk "Mineralogy"

J. W. Anthony

S. Stanley, L. Hardie

The primary mineralogy of oolites and early marine carbonate cements led Sandberg [Nature 305 (1983), 19–22] to divide the Phanerozoic Eon into three intervals of `aragonite seas' and two intervals of `calcite seas'. Hardie [Geology 24 (1996), 279–283] has shown that these oscillations, together with synchronous oscillations in the mineralogy of marine potash evaporites, can be explained by secular shifts in the Mg/Ca ratio of seawater driven by changes in spreading rates along mid-ocean ridges. The Hardie model also predicts that high-Mg calcite should precipitate along with aragonite, as it does in today's aragonite sea. We have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms (ones that have produced massive skeletons, large reefs, or voluminous bodies of sediment) that correspond to Sandberg's aragonite seas and calcite seas and that are predicted by the Hardie model. Particular groups of corals, sponges, and algae appear to have been dominant reef builders only when favored by an appropriate Mg/Ca ratio in seawater. In early and middle Paleozoic calcite seas (Calcite I), reefs were dominated by calcitic tabulate, heliolitid, and rugose corals and calcitic stromatoporoids. In contrast, during the period of late Paleozoic–early Mesozoic aragonite seas (Aragonite II), aragonitic groups of sponges, scleractinian corals, and phylloid algae, as well as high-Mg calcitic red algae, were principal reef builders. During Late Cretaceous time, at the acme of Calcite II, massive rudists displaced aragonitic hermatypic corals. In today's aragonite sea (Aragonite III) scleractinian corals are again dominant reef builders, along with high-Mg calcitic coralline algae. Major sediment-producing algae exhibit temporal patterns similar to those of reef builders. Calcitic receptaculitids flourished during Calcite I, whereas aragonitic dasycladaceans did not become dominant rock formers until Aragonite II. During Calcite II, calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the Late Cretaceous, after the Mg/Ca ratio of seawater had reached a very low value and calcium concentration, a very high value. As the Mg/Ca ratio of seawater rose and calcium concentration fell during the Cenozoic Era, individual coccoliths, on average, became less massive and encrusted cells less thickly. By Pliocene time, during Aragonite III, the prominent genus Discoaster secreted only narrow-rayed coccoliths that covered less than 25% of the cell surface. Also during Aragonite III, the aragonitic green alga Halimeda emerged as the dominant skeletal sediment producer in reef tracts. The influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification. Such groups include algae, sponges, corals, and bryozoans. Morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs. This linkage, in addition to the basic chemical demands of hypercalcification, has given the Mg/Ca ratio of seawater strong control over the success of individual reef-building taxa. More generally, this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history. We conclude that throughout Phanerozoic time a chain of causation has extended from mid-ocean ridge processes, via seawater chemistry, to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits.

Katy Jane Chamberlain, Matthew Pankhurst, David Neave et al.

The 2021 Tajogaite eruption was the longest and most voluminous in recorded history on La Palma, Canary Islands. Extensive geophysical and geochemical data were collected before and during the eruption; however petrological monitoring saw little usage, largely restricted to rapid stereo microscope observations or off-island analyses. Here, we analyse lava and tephra sampled at near-daily frequency to investigate magmatic processes driving petrological, geochemical, and geophysical variations. Published whole-rock major and trace element data are combined with new QEMSCAN textural and mineral abundance data, major element analyses of macrocryst phases, and clinopyroxene trace element data, supported by mineral growth pressure–temperature modelling. Olivine Fe-Mg diffusion timescales from early tephra are compared with timescales of climactic unrest. Results indicate that more-evolved, mineralogically diverse magmas were tapped during the first week. Magma mixing only becomes apparent when more primitive magmas erupted after the first ~10 days, exemplified by reverse-zoned olivines. Clinopyroxene barometry suggests most material is fed from the upper mantle throughout. Timescales overlap and extend climactic unrest records, suggesting that destabilisation began before geophysical detection. From Stage 2 (~5–10 days) to eruption cessation (~85 days), crystal cargo chemistry is surprisingly uniform, with previously observed whole-rock and tephra glass changes not obviously reflected in the mineral record. We highlight the importance of combining both whole-rock and mineral scale observations to understand how eruptions progress, and ultimately end.

سید سعید قنادپور, مرتضی حصیری, سمیه طالبی اسفندارانی et al.

منطقه اکتشافی ظفرقند به عنوان یک کانسار مس پورفیری در شمال شرق اصفهان و جنوب شرق اردستان واقع شده است که ﺑﺨﺸﯽ از زون ﺳﺎﺧﺘﺎری اﯾﺮان- ﻣﺮﮐﺰی ﺑﻪ ﺷﻤﺎر ﻣﯽرود و به طور دﻗﯿﻖﺗﺮ در ﻧﻮار آﺗﺸﻔﺸﺎﻧﯽ ارومیه دﺧﺘﺮ ﻗﺮار دارد. در اکتشاف کانسارهای مس پورفیری، شناسایی و تعیین زون‌های دگرسانی اهمیت ویژه‌ای دارد. هدف از انجام مطالعه پیش رو، شناسایی و بارزسازی زون‌های دگرسانی منطقه اکتشافی ظفرقند، به کمک هندسه فرکتال در پردازش تصاویر ماهواره‌ای سنجنده استر است. بدین منظور با توجه به ماهیت رستری و رقومی بودن تصاویر ماهواره‌ای، مقادیر دیجیتال نامبر هر پیکسل از مجموعه ماتریس تصاویر، به عنوان یک نمونه در شبکه‌ای سیستماتیک در نظر گرفته شده است. در نهایت نیز الگوریتم مدل فرکتالی عیار- مساحت به عنوان یک روش کارآمد در تعیین نمونه‌های آنومال، بر روی مجموعه مقادیر دیجیتال نامبر پیکسل تصاویر ماهواره‌ای استر پیاده شده است. زون‌های دگرسانی شناسایی شده به کمک تکنیک یاد شده بر اساس گسترش آنها در منطقه، نمایانگر عملکرد بسیار موثر این روش است. به طوری که به ویژه در مورد دگرسانی‌های فیلیک و پروپیلیتیک، مطابقت بسیار بالایی بین نتایج حاصله از پردازش تصاویر ماهواره‌ای و گسترش دگرسانی‌ها در مطالعات صحرایی وجود دارد. عدم شناسایی دگرسانی‌های پتاسیک و آرژیلیک در نتایج حاصله نیز در ارتباط مستقیم با گسترش محدود آنها در منطقه مورد مطالعه است. در نهایت می‌توان اذعان داشت که به کارگیری مدل فرکتالی عیار- مساحت با توجه به ماهیت ساختاری بودن آن در تصمیم‌گیری، موفقیت‌آمیز بوده و در تعیین زون‌های دگرسانی موجود در منطقه ظفرقند بسیار موثر عمل کرده است.

Ye He, Bang-Tao Sun, Hai-Peng Wang et al.

ABSTRACT: The giant Upper Yangtze Pb-Zn metallogenic province, also known as the Sichuan-Yunnan-Guizhou (SYG) Pb-Zn province hosting >500 carbonate-hosted epigenetic Pb-Zn deposits that contain >20 Mt Pb + Zn base metal reserves. The giant Maoping Pb-Zn deposit is the second largest deposit in this province and owns >5 Mt Pb + Zn metal reserves with ore grades of 12 wt.%-30 wt.% Pb + Zn. Such large tonnages and high grades make it among the top 100 similar mineral deposits in the world. The ore bodies are predominantly located within the strata of the Upper Devonian (Zaige Formation) and Lower (Baizuo Formation)-Upper (Weining Formation) Carboniferous. The principal ore minerals consist of galena (Gn), sphalerite (Sp), and pyrite (Py), while the primary gangue minerals include dolomite (Dol), calcite (Cal), and quartz (Qtz). Three mineralization stages of carbonate minerals have been identified: (1) pre-sulfide stage 1, (2) syn-sulfide stage 2, and (3) post-sulfide stage 3. Trace elements and C-O-Sr isotopes of three stages’ carbonate minerals, together with S-Pb isotopes of sulfides, revealing that the metamorphic basement rocks played the role of the metal source during the early stage of Pb-Zn mineralization, whereas the metal contribution of the sedimentary wall rocks found to be more prominent during the late stage of Pb-Zn mineralization. In addition, the dissolution of marine carbonate rocks and CO2 degassing may have also played an important role in the formation of the Maoping deposit. Furthermore, syn-sulfide stage 2 calcite has a U-Pb age of 214 ± 20 Ma obtained by LA-ICPMS in-situ analyses, suggesting that the hydrothermal mineralization occurred during the Triassic. Our study proposes a new coupled metallogenic model of fluid-structure-lithology assemblage and provides new insights about the formation and evolution of the Maoping deposit with significant implication for understanding and exploration of similar Pb-Zn deposits worldwide.

Magdalena Balonis, B. Lothenbach, G. Saoût et al.

Minaev Vasilii, Ustinov Stepan, Petrov Vladislav et al.

The results of a comprehensive analysis of fault tectonics of the Kola Peninsula, carried out on a regional scale, are considered. Based on a digital relief model, generalized for various scale levels, lineaments were identified manually and automatically. The results obtained in combination with literature data made it possible to carry out tectonophysical reconstructions using the Hancock model. Based on the results of these reconstructions, the proposed areas of tectonic structures were identified that had the greatest hydraulic activity at the time of the introduction of mafic-ultrabasic massifs and dike complexes of pegmatite belts, which are associated with ore deposits of scarce types of strategic minerals of the Kola Peninsula (copper, nickel, chromium, rare metals, etc.) The areas were identified, promising for the discovery of new ore objects.

Q. Tian, Q. Tian, Q. Tian et al.

<p>The global marine biogeochemical cycle of aluminium (Al) is believed to be driven by marine diatoms, due to the uptake of dissolved Al (DAl) by living diatoms from surface seawater. The occurrence of Al in diatom biogenic silica (BSi) can inhibit the dissolution of BSi, thus benefiting the effects of the ballast role of diatoms in the biological pump and forming a coupled Si–Al biogeochemical cycle. However, the occurrence characteristic of Al in marine diatoms is still unclear. In particular, whether or not Al is incorporated into the structure of BSi of living diatoms is unrevealed, resulting in difficulties in understanding the biogeochemical behaviours of Al. In this study, <i>Thalassiosira weissflogii</i>, a widely distributed marine diatom in marginal seas, was selected as the model to evaluate the occurrence of structural Al in BSi based on culturing experiments with the addition of DAl. The structural Al in BSi was detected by combining focused ion beam (FIB) scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS) mapping analysis. Visible, direct evidence of structural Al in living BSi was obtained, and the distribution and content of this Al were revealed by the EDS-mapping analysis. The effects of structural Al on BSi dissolution–inhibition are discussed based on the content of this Al. The fundamental results indicate the significant contribution of marine diatoms to the biogeochemical migration of marine Al.</p>

George Mustoe, Chiraporn Aranyanark, Nareerat Boonchai et al.

Thailand contains two notable fossil forest regions. Pleistocene fluvial sediments in the Tak region in the northern highlands contain silicified trunks of large trees. Deposits in the Khorat Plateau in northeast Thailand contain a multitude of wood fossils that span a probable age range of Miocene to Pleistocene. At Ban Tak fossil logs are primarily mineralized with crystalline quartz. Incomplete mineralization is characteristic of the Tak wood, with intercellular spaces commonly remaining open. The resulting permeability allows penetration of moisture, and allows introduction of microbes and the accumulation of clays, iron oxides, soluble salts and other materials that may cause discoloration and deterioration. Hydration swelling of these components results in stress. Excavation of the huge logs means that they occupy topographically low positions prone to flooding during the monsoon season. These factors make the fossils vulnerable to weathering. A variety of methods have been employed in attempts to reduce the damage, including the construction of various styles of shelters to protect the fossil logs from direct precipitation. At Khorat, compositions of individual specimens range from pure quartz and pure opal to mixtures of the two polymorphs. Many specimens are preserved indoors in the Khorat Fossil Museum in Mueang Nakhon Ratchasima District, both as indoor exhibits and as outdoor displays in a garden plaza. The environmental complexities at the Tak and Khorat fossil wood localities challenge conservators, but their creative attempts provide useful lessons for future preservation efforts. Our report describes the geologic setting and our research mineralogy of specimens at both localities, and discusses conservation strategies.

A.V. Kasatkin, A.M. Kuznetsov, N.A. Arzamastsev3

Primary and supergene Pb, Bi, Te, Cu, Mo, Ag, Au and Hg minerals are found in samples from the dumps of the Buranovskoe tungsten deposit (Chelyabinsk oblast). The paper presents the most complete list of mineral species of the deposit based on available literature and our data. Fourteen tellurides and sulfotellurides are identified. They occur as individual grains and intergrowths with each other or simple sulfides and form numerous inclusions in fahlores in quartz-scheelite veins. Among the oxidation products of fahlores, galena and tetradymite, we found rare supergene minerals – telluroperite and perite, which form a limited solid solution series, as well as choloalite and a Ag and Hg sulfide-iodide corresponding to hanauerite by its chemical composition. The findings of telluroperite and hitachiite are the first at the territory of the Russian Federation and perite and choloalite are found for the first time in the Urals.

Gabriel Partl, Marcus Rauter, Lukas Fliri et al.

3-(1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-Perfluorooctyl)-1-vinylimidazolium chloride [2126844–17–3], a strong fluorosurfactant with remarkably high solubility in water, was expediently converted into the respective doubly NHC-complexed silver salt with nitrate as counter ion in quantitative yield. Due to its vinyl substituents, [bis(3-(1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-perfluorooctyl)-1-vinylimidazol-2-ylidene)silver(I)] nitrate, <b>Ag(FNHC)₂NO₃</b>, represents a polymerizable <i>N</i>-heterocyclic carbene transfer reagent, thus potentially offering simple and robust access to coordination polymers with crosslinking metal bridges. The compound was characterized by infrared and NMR spectroscopy, mass spectrometry as well as elemental analysis, and supplemented by X-ray single-crystal structure determination. It crystallizes in the monoclinic crystal system in the space group <i>P</i>2₁/c. With 173.3°, the geometry of the Ag-carbene bridge deviates slightly from linearity. The disordered perfluoroalkyl side chains exhibit a helical conformation.

Hatem M. El-Desoky, Ali Shebl, Ahmed M. Abdel-Rahman et al.

Through various scales of observation, ranging from remote sensing data, field investigations, hand specimens, microscopic petrographic examinations, XRD, to SEM, indicators of various mineralization types are highlighted in Ras El-kharit-wadi Khashir (Eastern Desert, Egypt). Systematic remote sensing exploration of the mineralized zones is performed through integrating Sentinel 2 and ASTER datasets. False-color combinations, informative band ratios, relative absorption band depth, and CEM techniques were applied to discriminate rock units and various types of hydrothermal alterations. Moreover, ALOS PALSAR DEM was utilized to decipher the structural lineaments. Intensive field investigations confirmed hydrothermally altered zones that were picked out through remote sensing analysis and revealed that the study area is affected by cataclastic metamorphism to some extent. Magmatic and metamorphic rock types are represented by propylitic, phyllic, argillic, and silicification zones. Sericitization, chloritization, epidotization, kaolinitization, carbonatization, and silicification are recorded utilizing petrographic and remote sensing investigations. Moreover, the current study reveals that the detected alteration is the main reason for the apparent wide range of petrographic characteristics of each rock type and bearing several opaque minerals, such as pyrite, magnetite, titanomagnetite, chalcopyrite, arsenopyrite, covellite, galena, goethite, and hematite. Most of these opaques were identified using ore microscopy, XRD, and SEM. The distribution of hydrothermal alterations, representative samples bearing mineralization, structurally dissected zones are integrated to build a mineral potentiality map of the study area. The resultant MPM was confirmed via field survey and emphasized the usefulness of the current integrated approach besides highlighting about 125 km2 as potential mineralized zones.

N. Stoll, J. Eichler, M. Hörhold et al.

<p>Impurities deposited in polar ice enable the reconstruction of the atmospheric aerosol concentration of the past. At the same time they impact the physical properties of the ice itself such as its deformation behaviour. Impurities are thought to enhance ice deformation, but observations are ambiguous due to a shortage of comprehensive microstructural analyses. For the first time, we systematically analyse micro-inclusions in polar fast flowing ice, i.e. from the East Greenland Ice Core Project ice core drilled through the Northeast Greenland Ice Stream. In direct relation to the inclusions we derive the crystal preferred orientation, fabric, grain size, and microstructural features at 10 depths, covering the Holocene and Late Glacial. We use optical microscopy to create microstructure maps to analyse the in situ locations of inclusions in the polycrystalline, solid ice samples. Micro-inclusions are more variable in spatial distribution than previously observed and show various distributional patterns ranging from centimetre-thick layers to clusters and solitary particles, independent of depth. In half of all samples, micro-inclusions are more often located at or close to the grain boundaries by a slight margin (in the areas occupied by grain boundaries). Throughout all samples we find strong indications of dynamic recrystallisation, such as grain islands, bulging grains, and different types of sub-grain boundaries. We discuss the spatial variability in micro-inclusions, the link between spatial variability and mineralogy, and possible effects on the microstructure and deformation behaviour of the ice. Our results emphasise the need for holistic approaches in future studies, combining microstructure and impurity analysis.</p>

F. Kaminsky

Don H Butler, Zachary C Dunseth, Yotam Tepper et al.

Sustainable resource management is of central importance among agrarian societies in marginal drylands. In the Negev Desert, Israel, research on agropastoral resource management during Late Antiquity emphasizes intramural settlement contexts and landscape features. The importance of hinterland trash deposits as diachronic archives of resource use and disposal has been overlooked until recently. Without these data, assessments of community-scale responses to societal, economic, and environmental disruption and reconfiguration remain incomplete. In this study, micro-geoarchaeological investigations were conducted on trash mound features at the Byzantine-Early Islamic sites of Shivta, Elusa, and Nesanna to track spatiotemporal trends in the use and disposal of critical agropastoral resources. Refuse derived sediment deposits were characterized using stratigraphy, micro-remains (i.e., livestock dung spherulites, wood ash pseudomorphs, and plant phytoliths), and mineralogy by Fourier transform infrared spectroscopy. Our investigations detected a turning point in the management of herbivore livestock dung, a vital resource in the Negev. We propose that the scarcity of raw dung proxies in the studied deposits relates to the use of this resource as fuel and agricultural fertilizer. Refuse deposits contained dung ash, indicating the widespread use of dung as a sustainable fuel. Sharply contrasting this, raw dung was dumped and incinerated outside the village of Nessana. We discuss how this local shift in dung management corresponds with a growing emphasis on sedentised herding spurred by newly pressed taxation and declining market-oriented agriculture. Our work is among the first to deal with the role of waste management and its significance to economic strategies and urban development during the late Roman Imperial Period and Late Antiquity. The findings contribute to highlighting top-down societal and economic pressures, rather than environmental degradation, as key factors involved in the ruralisation of the Negev agricultural heartland toward the close of Late Antiquity.

E. Journet, Y. Balkanski, S. Harrison

Abstract. The mineralogy of airborne dust affects the impact of dust particles on direct and indirect radiative forcing, on atmospheric chemistry and on biogeochemical cycling. It is determined partly by the mineralogy of the dust-source regions and partly by size-dependent fractionation during erosion and transport. Here we present a data set that characterizes the clay and silt-sized fractions of global soil units in terms of the abundance of 12 minerals that are important for dust–climate interactions: quartz, feldspars, illite, smectite, kaolinite, chlorite, vermiculite, mica, calcite, gypsum, hematite and goethite. The basic mineralogical information is derived from the literature, and is then expanded following explicit rules, in order to characterize as many soil units as possible. We present three alternative realizations of the mineralogical maps, taking the uncertainties in the mineralogical data into account. We examine the implications of the new database for calculations of the single scattering albedo of airborne dust and thus for dust radiative forcing.

P. Barré, O. Fernández‐Ugalde, I. Virto et al.

A. Aikin

M. J. Wilson, L. Wilson

Abstract The instability of shales in drilled formations leads to serious operational problems with major economic consequences for petroleum exploration and production. It is generally agreed that the nature of the clay minerals in shale formations is a primary causative factor leading to their instability, although the exact mechanism involved is more debateable. Currently, the principal cause of shale instability is considered to be volume expansion following the osmotic swelling of Nasmectite. However, illitic and kaolinitic shales may also be unstable, so that interlayer expansion cannot therefore be considered as a universal causative mechanism of shale instability. This review considers alternative scenarios of shale instability where the major clay minerals are smectite, illite, mixed-layer illite-smectite (I/S) and kaolinite respectively. The influence of interacting factors that relate to shale clay mineralogy such as texture, structure and fabric are discussed, as are the pore size distribution and the nature of water in clays and shales and how these change with increasing depth of burial. It is found from the literature that the thickness of the diffuse double layer (DDL) of the aqueous solutions associated with the charged external surfaces of clay minerals is probably of the same order or even thicker than the sizes of a significant proportion of the pores found in shales. In these circumstances, overlap of the DDLs associated with exposed outer surfaces of clay minerals on opposing sides of micropores (<2 nm in diameter) and mesopores (2–50 nm in diameter) in a lithostatically compressed shale would bring about electrostatic repulsion and lead to increased pore/ hydration pressure in smectitic, illitic and even kaolinitic shales. This pressure would be inhibited by the use of more concentrated K-based fluids which effectively shrink the thickness of the DDL towards the clay mineral surfaces in the pore walls. The use of soluble polymers would also encapsulate these clay mineral surfaces and so inhibit their hydration. In this scenario, the locus of action with respect to shale instability and its inhibition is moved from the interlamellar space of the smectitic clays to the charged external surfaces of the various clay minerals bounding the walls of the shale pores.

J. Chermak, M. Schreiber