Mineralogy Of Deposits Research Articles

The technology of tin smelting in the Rooiberg Valley, Limpopo Province, South Africa, ca. 1650–1850 CE

A substantial indigenous tin-smelting industry arose in the Rooiberg valley of northern South Africa in the second millennium CE. This study concentrates upon tin-smelting slags and refractory ceramics from two archaeological sites that date between ca. 1650 CE and ca. 1850 CE. These were studied by optical and electron microscopy, wavelength-dispersive x-ray fluorescence (WD-XRF), inductively-coupled plasma mass spectrometry (ICP-MS), and electron microprobe (EMPA). The slags are predominantly glassy; high SnO and relatively low SiO 2 contents indicate that tin is a major glass-forming element. Comparison of slag chemistries with the mineralogy of ore deposits and host rocks shows that alluvial cassiterite was used at one of the sites, while cassiterite from hard-rock mining was smelted at the other site. Since few preindustrial tin slags have been studied, we compare our findings to other published examples, mostly from southwest England.

Mineralogy and microstructure of ash deposits from the Zhuzhou coal-fired power plant in China

Ash deposition is one of the major problems encountered in coal-fired power plants. To understand its formation mechanism, six samples of the deposit were collected from different positions of boiler in the Zhuzhou coal-fired power plant in Hunan of China. The mineralogical, chemical compositions, and microstructure of ash samples were analyzed by X-ray diffraction spectrometry (XRD), X-ray fluorescence spectrometry (XRF), optical microscopy, and field scanning electron microscopy equipped with energy dispersive X-ray spectrometry (FSEM-EDX). The results show that the deposits were mainly composed of silica amorphous phases and their chemical compositions of different layers significantly varied. The identified minerals include mullite, cristobalite, hematite, quartz, hercynite, and anorthite. The silica-rich glass phases are derived from volatilization–recondensation of SiO and the interaction between aluminosilicates and other minerals. Several types of crystals were identified in the deposits, including iron-oxide crystals, Fe–Ca-bearing phase, Si-rich phase, and aluminosilicate phase. The deposition of crystals as well as the following melting is the main reason for the porosity structure of deposit. The interaction and eutectic of minerals in coal led to the serious deposition in the coal-fired power plant.

Physicochemical factors of formation of Au-As, Au-Sb, and Ag-Sb deposits

The physicochemical formation conditions of Au-As, Au-Sb, and Ag-Sb ores characterized by similar paragenetic mineral assemblages and sets of major ore elements but differing in their proportions have been studied. The composition of the solutions filling fluid inclusions in minerals of Au-Sb deposits, combined with mineralogical and geochemical data, indicates that these deposits were formed from a near-neutral to alkalescent chloride-sulfide (<5 wt % NaCl) solution. Au-As and Au-Sb deposits were formed from fluids of the same type, consisting of a predominately CO2-CH4 gas phase with N2 and a low-saline chloride-sulfide solution, where Au and Ag were predominantly transported as dihydrosulfide species and Sb as sulfide and hydroxy complexes. Superimposed minerals of the sulfide-sulfosalt stage that precipitated from chloride-rich solutions (up to 30 wt % NaCl equiv), which contained Ca and Fe chlorides in addition to NaCl, are identified at some Au-Sb deposits. These solutions are similar in composition to the ore-forming fluids of Ag-Sb deposits. Chloride complexes are dominant Au and Ag species in acid chloride-rich solutions of Ag-Sb deposits (up to 38 wt % NaCl equiv), while chloride and hydroxy complexes are characteristic of Sb. These solutions are distinguished by high concentrations of Ag, Sb, Cu, Fe, Mn, Bi, Pb, and Zn. The mineralogical and geochemical specialization of Ag-Sb ore is caused by chemical features of highly concentrated chloride solutions enriched in Ag, Sb, and Cu and by a relatively low Au content within the pH interval 3.5–4.0 (10−6 m). The factors controlling formation of Au-As deposits are a high capacity of a low-chloride sulfide solution with respect to metals and a high Au concentration therein (two orders higher than that of solutions of Ag-Sb deposits). The enrichment of the pyrite-arsenopyrite paragenetic assemblage in gold is a result of juxtaposed stability fields of native gold, arsenopyrite, and pyrite and their mass deposition with a decrease in temperature from 400 to 300°C. The main cause of the specific mineralogy and geochemistry of Au-Sb deposits is a high metal capacity of a near-neutral low-chloride sulfide fluid with respect to Sb, Au, and Ag, but a low Ag content. The mineralogical and fluid inclusion data combined with computer thermodynamic simulation allowed us to establish the factors of ore formation at P-T-X parameters close to natural conditions and made it possible to characterize the joint deposition of gold and silver in quantitative terms.

Mineralogy and composition of Kuroko deposits from northeastern Honshu and their possible modern analogues from the Izu-Ogasawara (Bonin) Arc south of Japan: Implications for mode of formation

The Kuroko deposits of NE Honshu are a key type deposit for the study of volcanogenic massive sulfide deposits. However, these deposits have not been studied in detail since the early 1980's and knowledge of their mode of formation is now dated. In this study, we present the analysis of 12 samples of the Kuroko deposits, 12 samples of submarine hydrothermal minerals from the Sunrise deposit and 6 samples from Suiyo Seamount, both of which are located on the Izu-Ogasawara (Bonin) Arc, for 27 elements. For the Kuroko deposit, Cd>Sb>Ag>Pb>Hg>As>Zn>Cu are highly enriched, Au>Te>Bi>Ba>Mo are moderately enriched, In>Tl are somewhat enriched and Fe is not significantly enriched relative to the average continental crust. Within each of these deposits, a similar pattern of element associations is apparent: Zn–Pb with As, Sb, Cd, Ag, Hg, Tl and Au; Fe–Cu–Ba with As, Sb, Ag, Tl, Mo, Te and Au; Si–Ba with Ag and Au; CaSO 4. The enrichment of the chalcophilic elements in these deposits is consistent with hydrothermal leaching of these elements from the host rocks which are dominantly rhyolite–dacite in the case of the Kuroko deposits, rhyolite in the case of the Sunrise deposit and dacite–rhyolite in the case of the Suiyo Seamount deposit. However, this pattern of element enrichment is also similar to that observed in fumarolic gas condensates from andesitic volcanoes. This suggests that there may be a significant magmatic contribution to the composition of the hydrothermal fluids responsible for the formation of the Kuroko deposits, although it is not yet possible to quantify the relative contributions of these two sources of elements. The compositional data show that Sunrise and Suiyo Seamount deposits are much closer compositionally to the Kuroko deposits from NE Honshu than are the submarine hydrothermal deposits from the JADE site in the Okinawa Trough which contain, on average, significantly higher concentrations of Pb, Zn, Sb, As and Ag than each of these deposits. In spite of the greater similarity in tectonic setting of the Hokuroku Basin in which the Kuroko deposits formed to the Okinawa Trough (intracontinental rifted back-arc basin) compared to Myojin Knoll and Suiyo Seamount (active arc volcanoes), it appears that submarine hydrothermal deposits from Myojin Knoll and Suiyo Seamount are closer analogues of the Kuroko deposit than are those from the Okinawa Trough. The present data are consistent with the magmatic hydrothermal model for the formation of Kuroko-type deposits as formulated by Urabe and Marumo [Urabe, T., Marumo, K., 1991. A new model for Kuroko-type deposits of Japan. Episodes 14, 246–251].

A multidisciplinary study of silica sinter deposits with applications to silica identification and detection of fossil life on Mars

Surface features observed on Mars and evidence from martian meteorites both suggest that hydrothermal systems have operated in the crust of the planet. Hydrothermal systems are a potential habitat for living organisms and identifying these on Mars is, therefore, important in the search for life beyond the Earth. One of the surface expressions of hydrothermal systems on Earth are silica sinters, deposited during the cooling of hydrothermal solutions. In this paper we present analyses of the mineralogy, textures, chemistry and organic chemistry of silica sinters from two very different geothermal provinces, Waiotapu, New Zealand and Haukadalur, Iceland, in order to determine common features by which silica sinters can be identified. Infrared reflectance spectroscopy was utilised in combination with textural studies to evaluate the mineralogy of sinter deposits in terms of the abundances of different polymorphs of SiO 2. Concentrations of organic molecules, principally lipids, within regions of the sinters in which there is textural evidence for micro-organisms were identified in the infrared spectral data and their presence was confirmed using gas chromatography mass spectroscopy. The results of this study indicate that reflectance spectra in the wavelength region from 2.5 to 14 μm, when calibrated against natural terrestrial analogues, can be used to identify silica sinters, as well as the possible presence of recent microbial communities on Mars.

Geochemistry and mineralogy of travertine deposits of the SW flank of Mt. Etna (Italy): Relationships with past volcanic and degassing activity

Travertine deposits outcropping in the lower SW flank of Mt. Etna were studied for their mapping, as well as for their chemical, mineralogical and isotopic compositions. These deposits are dated to about 24 to 5 ka in the Adrano area, located at the western limit of the study area. In this area travertines show high Mg contents and are composed mostly of dolomite, thus apparently ruling out any primary deposition in favour of a diagenetic origin. Travertines outcropping near Paternò, in the east part of the study area, should be younger than 18 ka. Those located to the SSW of Paternò (Paternò–Diga) show high Sr contents and aragonite as dominant mineralogical phase, thus suggesting primary deposition. Those located to the W of Paternò (Paternò Simeto–Stazione) are instead poor both in Mg and in Sr and show calcite as dominant phase. Carbon isotope composition of travertines indicates a magmatic origin of CO 2 that formed them. Based on the estimated volume of travertines, between 10 and 20 Gg/a of CO 2 were involved in their formation. The time-span of travertine formation coincided with the eruptive cycles of Ellittico and the first part of Mongibello, which were probably characterised by a greater amount of CO 2 transported through groundwater circulation. Widespread travertine deposition probably ceased after the opening of the Valle del Bove depression that modified the volcanologic and hydrologic conditions in the summit crater area.

Clay mineralogy and chemistry of halloysite and alunite deposits in the Turplu area, Balikesir, Turkey

AbstractA field-mapping and crystal-chemical study of two alunite- and halloysite-rich deposits in the Turplu area, situated northwest of Balıkesir on the Biga Peninsula of northwest Turkey reveals a mineralogically diverse and a potentially economic clay deposit. The mineral assemblage along fault zones is dominated by halloysite and sometimes alunite. The alunite is nearly end-member in composition (a = 6.995 Å, c = 17.195 Å) often occurring with a minor Ca phosphate phase. Of the two deposits studied, the more northerly mine contains more alunite relative to halloysite. Geochemical alteration indices suggest that the northern mine has experienced a slightly greater degree of hydrothermal modification. Halloysite is found in both hydrated and dehydrated states and assumes a tubular morphology. Observations by transmission and scanning electron microscopy are consistent with a model of halloysite dehydration, where the shapes transform from an open-hole tubular morphology to a closed-hole unfurled morphology.Mineral paragenesis includes the effects of initial deposition of volcanic tuffs and andesite on top of karstic terrain. The contact between altered volcanics and underlying limestones is irregular and appears to have provided a mechanism to flush both hydrothermal and meteoric waters through the volcanics. Periods of hydrothermal alteration (hypogene) contemporaneous with extensional and strike-slip faulting have resulted in alunite and halloysite deposits. Hydrothermal alteration is concentrated near the fault zones. Because of subsequent weathering (supergene) away from the fault zones, much of the andesitic volcanic rocks have been altered to a more smectite-rich and kaolinite-bearing assemblage. The deposits continue to be both plastically deformed in the alunite/halloysite regions and to undergo brittle deformation in the saprolitized volcanics. Tectonic deformation has mixed the contacts, such that limestone blocks are entrained into parts of the alteration zones. Gibbsite and gypsum are common weathering products associated with limestone block inclusions. Genetic models for the origins of alunite-halloysite deposits in NW Turkey should consider as possible influencing factors the underlying lithologies, the extent of hydrothermal alteration, and recent weathering by meteoric fluids. In the case of the Turplu deposits, karstic limestones, hydrothermal circulation of sulfate-rich waters, and a post-alteration history of meteoric weathering were all important factors in their formation.

Precious metal and telluride mineralogy of large volcanic-hosted massive sulfide deposits in the Urals

The study focuses on the mode of occurrence of Au, Ag and Te in ores of the Gaisk, Safyanovsk, Uzelginsk and other volcanic-hosted massive sulfide (VHMS) deposits in the Russian Urals. Minerals containing these elements routinely form fine inclusions within common sulfides (pyrite, chalcopyrite and sphalerite). Gold is mostly concentrated as ‘invisible’ gold within pyrite and chalcopyrite at concentrations of 1–20 ppm. Silver mainly occurs substituted in tennantite (0.1–6 wt.% Ag). In the early stages of mineralization, gold is concentrated into solid solution within the sulfides and does not form discrete minerals. Mineral parageneses identified in the VHMS deposits that contain discrete gold- and gold-bearing minerals, including native gold, other native elements, various tellurides and tennantite, were formed only in the latest stages of mineralization. Secondary hydrothermal stages and local metamorphism of sulfide ores resulted in redistribution of base and precious metals, refining of the common sulfides, the appearance of submicroscopic and microscopic inclusions of Au–Ag alloys (fineness 0.440–0.975) and segregation of trace elements into new, discrete minerals. The latter include Au and Ag compounds combined with Te, Se, Bi and S. Numerous tellurides (altaite, hessite, stutzite, petzite, krennerite etc.) are found in the massive sulfide ores of the Urals and appear to be major carriers of gold and PGE in VHMS ores.

Erratum: Terrane and basement discrimination in northern Britain using sulphur isotopes and mineralogy of ore deposits

Erratum: Terrane and basement discrimination in northern Britain using sulphur isotopes and mineralogy of ore deposits

Terrane and basement discrimination in northern Britain using sulphur isotopes and mineralogy of ore deposits

Abstract This study of four well characterized and adjacent terranes in Northern Britain outlines the sulphur isotope variations, assesses the overall importance of crustal and mantle sulphur, and presents a model that can be applied to terrane distinction throughout the North Atlantic Caledonides. The characteristics of metal components within the mineralization provide additional information that can be related to the nature of underlying basement and events from the onset of sedimentation to the cessation of mineralization within stratigraphically linked packages of rock. The δ 34 S data show that the dominant crustal units in each terrane, whether upper crustal sediments or cratonic basement, provide the main alternative sulphur source to the mantle and act also as the main contaminant of subcrustal melts. The δ 34 S values of granitoid-related mineralization are either within the subcrustal melt-range of −3‰ to +3‰ or deviate toward the values of major crustal units in the terrane, i.e. toward 34 S depletion in the Southern Uplands and toward 34 S enrichment in the Lakesman and Grampian terranes. More complex mineralization in the Northern Highland terrane is linked to the presence of thick North Atlantic craton beneath upper crustal metasediments. Across the region the vein systems beyond the influence of magmatic components represent homogenized sulphur, metals and fluids from local upper crustal units. The sulphur isotope data and style of mineralization for the British terranes are compared with terranes of similar age along strike in Eastern Canada revealing notable correlations.

Mineralogy, geochemistry, and palynology of modern and late Tertiary mangrove deposits in the Barreiras Formation of Mosqueiro Island, northeastern Pará state, eastern Amazonia

A coastal environment has been interpreted from 110 cm thick mudstone deposits found at the base of a 10 m immature laterite profile, which forms the modern coastal cliff on Mosqueiro Island in northeastern Pará state, northern Brazil. The late Tertiary sediment deposits of the Barreiras Formation are studied by multi-element geochemistry and pollen analyses. The mineralogical and geochemical results show that the gray, organic-rich deposits are composed of kaolinite, quartz, and illite/muscovite, as well as pyrite and anatase. They are rich in SiO 2, Al 2O 3, and some FeO. The composition is homogenous, indicating that the detritus source area is formed of lateritic soils derived from acid rock composition. Their chemical composition, including trace elements, is somewhat comparable to continental shale, and the values are below the upper continental Earth crust composition. The pollen analytical data document that the mudstone deposits were formed by an ancient mangrove ecosystem. Mineralogical, geochemical, and pollen analytical data obtained from late Tertiary mangrove deposits are compared with modern mangrove deposits from the Bragança Peninsula of the northeastern coast of Pará state. Although the pollen composition of the deposits is very similar to the modern one, the geochemical and mineralogical composition is different. Smectite was only found in the modern deposit; illite/mica occurs in the ancient deposit, along with Mg, K, and Na. The pollen signature and detrital minerals (kaolinite, quartz and anatase) found in both mangrove deposits show that during the Miocene, a humid tropical climate condition prevailed, similar to modern conditions.

GEOCHEMISTRY AND MINERALOGY OF NEOPROTEROZOIC BANDED IRON-FORMATIONS AND SOME SELECTED, SILICEOUS MANGANESE FORMATIONS FROM THE URUCUM DISTRICT, MATO GROSSO DO SUL, BRAZIL

This study characterizes the precursor mineralogy and geochemistry of the Neoproterozoic iron ore deposits as well as some associated Na-containing manganese assemblages of the Urucum district, Mato Grosso do Sul, Brazil. It is based on ten mineralogically well characterized samples (six of banded iron-formation (BIF), three of manganese formations, and a sample of a veinlet that crosscuts the manganese assemblage), which were carefully selected so as avoid as much as possible supergene enrichment and secondary alteration (weathering), both of which are pervasive in the Urucum district. The six BIF samples are representative of the extensive Urucum BIF sequence from which the rich iron ores were developed by supergene enrichment and are considered to be precursors to the iron ore. The manganese-rich samples are part of unusual siliceous manganese horizons that contain complex silicate assemblages with braunite, cryptomelane, some pyrolusite, and authigenic aegirine. The Urucum BIF sequence is distinctive because it consists almost entirely of hematite and chert (jasper) with almost all of the iron present as only Fe2O3. This is in sharp contrast to the iron chemistry of much older (Archean and Early Proterozoic) BIF, in which a very large proportion of the iron occurs as ferrous iron in magnetite, carbonates, and silicates. As such, the Urucum BIF are essentially identical to those of the Neoproterozoic Rapitan sequence (755–730 Ma) of the Yukon and Northwest Territories of Canada. The Urucum sequence contains abundant dropstones, whereas the Rapitan sequence is set among diamictites but also contains dropstones. The δ 13C values of carbonates at Urucum are low, ranging from –5.2 to –7.0 per mil, which reflects their deposition in a glaciomarine setting. The REE concentrations of the BIF, as well as three Mn formation samples, are very similar and are almost completely lacking positive Eu anomalies (relative to NASC). This is in sharp contrast to the pronounced positive Eu anomalies of Archean and Early Proterozoic iron-formations. The general trend of the REE profiles (in NASC plots), with some enrichment of the heavy REE, is qualitatively very similar to that of modern seawater. The source of the Fe, Mn, and Si is concluded to be from typical ocean water with some deep-sea hydrothermal component. The reappearance of the Neoproterozoic Urucum sequence with BIF and interlayered manganese formations, together with the Rapitan sequence of similar Neoproterozoic age, after an absence of such sedimentary sequences in the geologic record for about 1.1 billion years, is considered to reflect ocean stagnation (with anoxic conditions), which may have been caused by a near-global ice cover, referred to as snowball Earth.

The Thermal Emission Imaging System (THEMIS) for the Mars 2001 Odyssey Mission

The Thermal Emission Imaging System (THEMIS) on 2001 Mars Odyssey will investigate the surface mineralogy and physical properties of Mars using multi-spectral thermal-infrared images in nine wavelengths centered from 6.8 to 14.9 μm, and visible/near-infrared images in five bands centered from 0.42 to 0.86 μm. THEMIS will map the entire planet in both day and night multi-spectral infrared images at 100-m per pixel resolution, 60% of the planet in one-band visible images at 18-m per pixel, and several percent of the planet in 5-band visible color. Most geologic materials, including carbonates, silicates, sulfates, phosphates, and hydroxides have strong fundamental vibrational absorption bands in the thermal-infrared spectral region that provide diagnostic information on mineral composition. The ability to identify a wide range of minerals allows key aqueous minerals, such as carbonates and hydrothermal silica, to be placed into their proper geologic context. The specific objectives of this investigation are to: (1) determine the mineralogy and petrology of localized deposits associated with hydrothermal or sub-aqueous environments, and to identify future landing sites likely to represent these environments; (2) search for thermal anomalies associated with active sub-surface hydrothermal systems; (3) study small-scale geologic processes and landing site characteristics using morphologic and thermophysical properties; and (4) investigate polar cap processes at all seasons. THEMIS follows the Mars Global Surveyor Thermal Emission Spectrometer (TES) and Mars Orbiter Camera (MOC) experiments, providing substantially higher spatial resolution IR multi-spectral images to complement TES hyperspectral (143-band) global mapping, and regional visible imaging at scales intermediate between the Viking and MOC cameras.

Microbial biosignatures in evaporite deposits: Evidence from Death Valley, California

We report on a microstratigraphic layering of mineral types that correlates with layering of the microbial community. Environmental Scanning Electron Microscopy–Energy Dispersive X-ray Spectroscopy analysis showed that in the upper layers of the community, dominated by cyanobacteria, gypsum (CaSO 4·2H 2O) and bassanite (CaSO 4·H 2O) give way to rosickyite, a rare form of sulfur ( γ-sulfur; monoclinic symmetry), which is not thermodynamically predicted to be stable at Earth surface temperatures, reverting to the more common α-sulfur form (orthorhombic symmetry) and yet exists and is stably maintained within the endoevaporitic microbial community implying a biogenic role in its formation. This mineral may be formed by a cycle of microbial dissolution of gypsum to sulfide and re-oxidation of the sulfide to elemental sulfur (rosickyite) within a stable oxygen–sulfide gradient maintained by the organisms and appears specifically in association with the cyanobacterial layer. Cells in the lower region of the pigmented phototroph-dominated layers (i.e., purple and green bacteria) have associated strontianite (SrCO 3) and calcite in the form of fine-grained minerals deposited on the cell surfaces and within the extracellular polymers surrounding them. Knowledge of how microbial communities can affect the mineralogy of evaporite deposits on Earth can help us to identify potential markers of the past or present existence of life on extraterrestrial bodies bearing evidence of ancient seas or lakes.

Genesis, Mineralogy and Geochemistry of Kaolin Deposits of the Jari River, Amapá State, Brazil

AbstractKaolin samples from the Jari deposit (Amazon region) were studied using various techniques to characterize its structural and crystallochemical aspects, and to establish its origin and evolution. A profile 60 m thick was selected in a kaolin mine (Morro do Felipe) located at the banks of the Jari river. Despite the great thickness of the deposit and the variety of kaolin types, the mineralogical composition is rather homogeneous and is mainly kaolinite associated with gibbsite and small amounts of quartz, anatase, goethite and hematite. The field observations and the morphological analysis indicate the existence of sedimentary features throughout the whole profile except for the upper aluminous clayey layer (Belterra Clay). This is evidence that the Rio Jari kaolin deposit originated from sedimentary material, the Alter do Chão Formation. The presence of alternating clay and sandy layers is explained by sedimentation processes with great depositional energy variation. Thus, the accumulation of thick clay layers was related to a low-energy phase, and during the high-energy phases, the deposition process led to the accumulation of sandy materials, constituted essentially of quartz and showing strong textural and structural variation. Later on, periods of hydromorphy were responsible for iron removal and consequently for the bleaching of the sedimentary formation. The crystallinity data show an increase of the structural disorder toward the surface associated with an increase in the amount of structural Fe in the kaolinite. The Rio Jari kaolin deposits should be considered as having originated from kaolinitic clay sediments of the Alter do Chão formation (protore) that was submitted to intensive lateritic weathering processes.

Mineralogy of cave deposits on San Salvador Island, Bahamas

Speleothem samples from ten caves located in the northeastern and southwestern corners of San Salvador Island (Bahamas) were analyzed by means of X-ray diffraction, scanning electron microscopy, and the electron microprobe. In addition to the prominent calcite, aragonite, and gypsum, already known to occur in San Salvador caves, eleven other minerals were identified. The minerals are celestite, SrSO4; cesanite, Na3Ca2(SO4)3OH; ardealite, Ca2(HPO4)(SO4)·4H2O; brushite, CaHPO4·2H2O; hydroxylapatite, Ca5(PO4)3OH; fluorapatite, Ca5(PO4)3F; chlorapatite, Ca5(PO4)3Cl; collinsite, Ca2(Mg,Fe)(PO4)2·2H2O; witlockite, β-Ca3(PO4)2; niter, KNO3, and nitratine, NaNO3. Cesanite has not been previously reported from a cave. This is the second reported occurrence of collinsite. San Salvador Island, on the eastern edge of the Bahamian Platform, is the location of a large number of relatively small flank margin caves. In adition TO the more obvious speleothems — stalactites, stalagmites, and flowstone — the San Salvador caves contain a variety of crusts and soils of unknown mineralogy. This paper is an account of an investigation of samples collected from ten of these caves. Prior to the result reported here, only calcite, aragonite, and gypsum had been identified in the various speleothems from caves on San Salvador Island (Vogelet al. 1990; Schwabeet al. 1993).

Mineralogy and genesis of secondary uranium deposits, Um Ara area, south eastern desert, Egypt

Secondary U mineralisation is found in the oxidised zone pervading fractured albitised and alkali-feldspar granites emplaced at the northern boundary of Um Ara Pluton. It occurs as stains along crevices and fracture surfaces and as acicular crystals filling cavities. X-ray diffraction and SEM were used to identify secondary U minerals and the associated alteration products. Uranophane and β-uranophane are the most abundant U minerals, whereas Ca-montmorillonite and illite represent low temperature alteration products of the host granitic rocks. The genesis of secondary U minerals is mainly attributed to the action of oxic groundwater on previously corroded primary U minerals. These secondary U minerals were deposited near the surface from the circulating groundwater by evaporation.

Palaeoenvironmental and diagenetic control of the mineralogy of Upper Cretaceous–Lower Tertiary deposits of the Central Palaeo–Andean basin of Bolivia (Potosi area)

Abstract A study, involving mainly X-ray diffraction, of the mineralogy of Upper Cretaceous and Lower Tertiary deposits (Aroifilla, Chaunaca, El Molino, Santa Lucia and Cayara Formations) of the Andean basin in the Bolivian Eastern Cordillera is presented. This work refines environmental reconstructions based on previous sedimentological studies in the Potosi Basin. The results including the clay mineralogy show that the sediments were deposited in a lacustrine system which suffered large variations of water level and groundwater influence. The siliciclastic sediments are characterized either by abundant feldspars or analcime, suggesting a perennial volcanoclastic influence. Tuff layers in the Santa Lucia Formation support this interpretation. The great diversity of clay minerals identified reflects both detrital influences and diagenetic overprinting. Although diagenetic changes are common in this sedimentary series, it is still possible to identify the nature of detrital supply. Illite and illite–smectite mixed-layer clays constitute the background clay sedimentation and reflect predominantly arid climate. This had already been deduced from sedimentogical and geochemical investigations. However, detrital kaolinite occurs in a 40 m-thick interval of the El Molino Formation which probably embraces the K/T boundary and reflects more humid conditions. Further work is necessary to locate more precisely this boundary in the absence of accurate biostratigraphical markers. Authigenic clays are also recognized: in the sandstones in the basal part of the Cayara Formation kaolinite developed authigenically; in the tuff layers of the Santa Lucia Formation well-crystallized authigenic smectite characterizes the clay fraction. In addition, chlorite replaces smectite in limestones beds of the El Molino Formation which were deposited in evaporitic environments.The clay assemblages including illite and chlorite at base of the stratigraphic column (Aroifilla, and Chaunaca Formations) probably results from the replacement of smectitic minerals either by chlorite or illite where depth of burial reached more than 2000 m.

Sulfate Minerals in Evaporite Deposits

Evaporite deposits preserve a wealth of information on Earth’s past surface conditions. The deposits are sensitive indicators of depositional environment and climate, recorded in a wide variety of mechanically and chemically produced sedimentary structures and fabrics. Unique to evaporite deposits is the record they carry of the hydrochemistry of surface waters, including seawater. Sulfate minerals are important components in understanding the hydrochemistry of ancient surface waters. Sedimentological aspects of evaporite deposits were compiled by Melvin (1991). In the compilation, sedimentology specific to Ca-bearing sulfates was described by Warren (1991); Lowenstein and Hardie (1985), Handford (1991), and Smoot and Lowenstein (1991) discussed the sedimentology of evaporites in general. These general principles can be applied specifically to the sulfate minerals in evaporite deposits. Sedimentological aspects of sulfate minerals in evaporite deposits are not discussed here. For this information, the reader is referred to the above references. Hardie et al. (1985) and Spencer and Lowenstein (1988) discussed the petrography of evaporites and the interpretation of fabrics of evaporite minerals. Examples of petrographic aspects of sulfate minerals in evaporites are presented here along with references specific to the sulfate minerals. For a more complete understanding of these aspects the reader is referred to the above references. The major focus of this chapter is on the chemical aspects of the common sulfate minerals that occur in evaporite deposits. The discussion begins with an explanation of the concept of chemical divides and the determination of evaporation paths, and the evolution of brines in accordance with mineral solubility and the composition of dilute inflow waters. Determination of the precipitation pathways of the more soluble salts is more complex. Examples of sulfate-mineral assemblages in evaporation systems, calculated via thermochemical modelling, are given for both marine and non-marine systems. The mineralogy of evaporite deposits is …

Mineralogy of Pb-P grains in the roots of Agrostis capillaris L. by ATEM and EXAFS

Abstract Analytical transmission electron microscopy (ATEM) and X-ray absorption spectroscopy (XAS) have been used to determine the mineralogy of Pb-P deposits in the roots of the heavy metal tolerant grass cultivar Agrostis capillaris L. cv. Parys Mountain. The deposits have a pyromorphite (Pb5(PO4)3Cl)-type structure and composition although some of the Cl may be substituted by OH. Energy-dispersive mapping under the scanning electron microscope demonstrated that the majority of these deposits are present in the outer cell wall of the epidermis (the outermost layer of root cells). The phosphate composition of these grains contrasts with the phytate (C6H18O24P612−) composition of Zn-P deposits observed in similar electron microscopy studies. The physiological role of heavy metal P deposits is unclear. Heavy metal P precipitates may form actively as a tolerance mechanism to heavy metals or passively, sequestering P in a metabolically inactive form.