Mineralogical Considerations Research Articles

Petrography and Geochemistry of Limestone Upper Cretaceous Kometan Formation (Azmir Anticline): A Preliminary Assessment for Cement Production Suitability in the Kurdistan Region Northeast Iraq

A succession of slightly siliceous limestone of the Kometan Formation is studied geochemically and strati graphically. The studied area is located on the SW limb of the Azmir anticline at the northeastern of Sulaimaniyah city. The studied section is situated at longitudes 45°38'310"E and latitudes 35°36'129''N inside the Folded Zone, Kurdistan Region, northeastern Iraq. The exposed section is sampled for lab studies, and inspected by eyes and hand lenses in the field. In this study, petrographic and geochemical analyses of 17 limestone samples were carried out. This study aims to investigate the major oxides of the limestone samples, using the X-Ray Fluorescence (XRF), for preliminary assessment for possible cement production. A petrographic study was also carried out, in order. Depending on the petrographic study, three major microfacies were recognized: lime mudstone microfacies, lime wackestone microfacies, and lime packstone microfacies, which subdivided into four submicrofacies are planktonic foraminifera lime mudstone submicrofacies, planktonic foraminifera lime wackestone submicrofacies, and planktonic foraminifera lime packstone submicrofacies and heterohelix lime packstone submicrofacies. The geochemical analysis shows that a range of variations in constituents: LOI (35.90% to 42,72%), SiO2 (3.77% to 14.66%), CaO (42.59% to 49.95%), Al2O3 (0.44% to 2.22%), Fe2O3 (0.02% to 0.78%) and MgO (1.50% to 2.26%); K2O and Na2O are present in traces. The high CaO (49.95%) indicates that calcite is the primary carbonate mineral. Due to mineralogical considerations, CaO with LOI shows a positive correlation, whereas CaO with SiO2 shows a negative correlation. The low MgO contents in calcitic limestone and calcitic limestone with chert nodules recommend a lack of dolomitization process. The silica modulus and lime saturation factor from geochemical data indicated that the siliceous limestone samples from the Kometan Formation and Azmir Anticline can be used in the cement-making process provided they are processed for silica removal treatment to reduce its percentage to less than 8%, as required level, where the CaO can be automatically enriched. Depending on field observation, petrography, and geochemistry analysis, we conclude that the source of the chert or silica minerals is diagenetic processes and depositional environment origin.

Thallium isotopic fractionation in soil: the key controls

We studied the key geochemical and mineralogical factors that could affect the fractionation of stable thallium (Tl) isotopes in soil. A set of grassland soil samples enriched in geogenic Tl in combination with selected Tl-containing mineral materials from the Czech Republic (Kluky) were investigated for this purpose. The results demonstrate significant incorporation of Tl in pedogenic (specific) Mn-oxide, which led to a large accumulation of the heavy 205Tl isotope (∼+14 ε205Tl units), presumably resulting from oxidative Tl sorption. Consequently, we concluded that the Mn-oxide-controlled Tl uptake is the primary cause of the observed 205Tl enrichment in the middle profile zone, at the A/B soil horizon interface, with up to +4 of ε205Tl. Furthermore, our results displayed a clear relationship between the Tl isotopic fractionation degree and the Mn-oxide soil concentration (R2 = 0.6), as derived from the oxalate-extractable data. A combination of soil and mineralogical considerations suggests that 205Tl enrichment in respective soil samples is also partly due to the Tl present in micaceous clay minerals, mainly illite, which is the predominant pedogenic Tl host phase. In line with our previous results, this Tl behavior can be inferred from systematic Mn-oxide degradation and the associated Tl (enriched in 205Tl) cycling in the studied soils and thus, presumably in the redoximorphic soils in general.

Extensional magmatism in a continental collision zone,Tafresh area, western central Iran: structural, geochemical and mineralogical considerations

The Tafresh area, located on the middle part of Urumieh-Dokhtar magmatic arc, is a suitable area for considering the effects of tectonic structures on development of the volcanic facies in the magmatic provinces. The main structure in the area is a dextral fault (so called Rahjerd Fault) that has produced the local extensional basins and also the parallel dyke swarms (or feeder dykes) on its both sides. So, the pyroclastic deposits, basaltic-andesitic lava flows, parallel dyke swarms were appeared by explosive subaqueous and then effusive subaerial eruptions and eventually a dioritic stock intruded in the volcanic pile. Petrologically, the magmatic rocks are belonged to the calcalkaline suite that had been changed and evolved in the magma chambers of local extensional basins in a collisional tectonic setting. The mineral chemistry and geochemical modeling as well as the coexistence of different mineral paragenesis of plagioclases (An47-72 and An17-37), pyroxenes (diopside and pigeonite) and amphiboles (magnesiohastingsite and magnesiohornblende) reveal that the AFC process is a dominant process in the magma chamber. Also, according to geothermobarometric calculations, the investigated volcanic rocks of the area could be grouped into two types: one type with higher P-T (>6Kbar and about 900 °C) including Eocene pigeonite-magnesiohastingsite bearing andesites (PHA) and Miocene andesites and other with lower P-T (1-4 Kbar and 600- 800 °C) including the Eocene diopside-magnesiohornblende bearing andesites (DHA) and the dioritic stock.

Mineralogical and thermal characterization of soft rock from Campinas, Brazil

In this study, the main purpose was the mineralogical and thermal characterization of clayey siltites sampled in a quarry located near Viracopos Airport, Campinas city, Sao Paulo State, Brazil. The sedimentary rocks are fissile and expansive and are therefore easily disaggregated. These characteristics make the rock of difficult geomechanical characterization, because it undergoes defragmentation very easily. Mineralogical considerations about the composition of this rock were carried out by petrography analysis, scanning electronic microscopy (SEM), X-ray diffraction pattern and energy-dispersive spectroscopy. Thermal characterization of powdered rock was carried out by thermogravimetry (TG/DTG) under synthetic air and nitrogen purge gases. The dehydration kinetics of this rock was studied by a non-isothermal method. The mineralogical results show that this rock had quartz, feldspar and kaolinite as the major components and pyrite and chlorite as the minor constituents. The presence of organic matter was verified as fragments present in the rock and seen by SEM. The amount of organic matter was also determined by the gravimetric method, and the results showed a loss of 3.27%. The differential thermal analysis results under nitrogen purge gas exhibit the transition phase of quartz at 575 °C. The kinetic evaluation was made with two dehydration stages obtained from DTG curves, which show that the dehydration stage occurs with two behavior patterns.

Seismic reservoir characterization of Utica-Point Pleasant shale with efforts at fracability evaluation — Part 2: A case study

The Utica Formation in eastern Ohio possesses all the prerequisites for being a successful unconventional play. Attempts at seismic reservoir characterization of the Utica Formation have been discussed in part 1, in which, after providing the geologic background of the area of study, the preconditioning of prestack seismic data, well-log correlation, and building of robust low-frequency models for prestack simultaneous impedance inversion were explained. All these efforts were aimed at identification of sweet spots in the Utica Formation in terms of organic richness as well as brittleness. We elaborate on some aspects of that exercise, such as the challenges we faced in the determination of the total organic carbon (TOC) volume and computation of brittleness indices based on mineralogical and geomechanical considerations. The prediction of TOC in the Utica play using a methodology, in which limited seismic as well as well-log data are available, is demonstrated first. Thereafter, knowing the nonexistence of the universally accepted indicator of brittleness, mechanical along with mineralogical attempts to extract the brittleness information for the Utica play are discussed. Although an attempt is made to determine brittleness from mechanical rock-physics parameters (Young’s modulus and Poisson’s ratio) derived from seismic data, the available X-ray diffraction data and regional petrophysical modeling make it possible to determine the brittleness index based on mineralogical data and thereafter be derived from seismic data.

Alkaline leaching pretreatment and cyanidation of arsenical gold ore from the Carlin-type Zarshuran deposit

ABSTRACTCarlin-type refractory gold deposits are complex bodies which only occur in certain regions such as the western United States, southwest China, and northwest Iran. It is important to investigate the most suitable treatment option for each deposit from the point of the mineralogical composition. The present study investigates the effect of atmospheric NaOH alkaline pretreatment on the cyanidation gold recovery of the arsenical Carlin-type gold ore from the Zarshuran deposit, Iran (4.2 g t−1 Au feed grade). The results are explained based on the mineralogical considerations and with the aid of thermodynamic and kinetic investigations of the leaching behaviour of the main gold-bearing phases including orpiment, pyrite, and sphalerite. It was found that the high arsenic content of Zarshuran (3.7%) has some implications on the pretreatment and cyanidation processes. Solution potential and pH decreased significantly by the oxidation of arsenic sulphides which resulted in the decreasing oxidation extent of the other sulphides, specifically sphalerite. It was also found that pretreatment only in highly alkaline media (pH > 13) can be effective in gold recovery. Gold and silver extractions during subsequent cyanidation were improved from 69.4 to 80.7% for gold and 44.4 to 88.9% for silver, where the extraction yields of arsenic, iron, and zinc were 93.7, 75.9, and 26.9%, respectively.

Orogenic-type copper-gold-arsenic-(bismuth) mineralization at Flatschach (Eastern Alps), Austria

Structurally controlled Cu-Au mineralization in the historic Flatschach mining district (Styria, Austria) occurs in a NE–SW to NNE–WSW oriented vein system as multiple steep-dipping calcite-(dolomite)-quartz veins in amphibolite facies metamorphic rocks (banded gneisses/amphibolites, orthogneisses, metagranitoids) of the poly-metamorphosed Austroalpine Silvretta-Seckau nappe. Vein formation postdated ductile deformation events and Eoalpine (Late Cretaceous) peak metamorphism but predated Early to Middle Miocene sediment deposition in the Fohnsdorf pull-apart basin; coal-bearing sediments cover the metamorphic basement plus the mineralized veins at the northern edge of the basin. Three gold-bearing ore stages consist of a stage 1 primary hydrothermal (mesothermal?) ore assemblage dominated by chalcopyrite, pyrite and arsenopyrite. Associated minor minerals include alloclasite, enargite, bornite, sphalerite, galena, bismuth and matildite. Gold in this stage is spatially associated with chalcopyrite occurring as inclusions, along re-healed micro-fractures or along grain boundaries of chalcopyrite with pyrite or arsenopyrite. Sericite-carbonate alteration is developed around the veins. Stage 2 ore minerals formed by the replacement of stage 1 sulfides and include digenite, anilite, “blue-remaining covellite” (spionkopite, yarrowite), bismuth, and the rare copper arsenides domeykite and koutekite. Gold in stage 2 is angular to rounded in shape and occurs primarily in the carbonate (calcite, Fe-dolomite) gangue and less commonly together with digenite, domeykite/koutekite and bismuth. Stage 3 is a strongly oxidized assemblage that includes hematite, cuprite, and various secondary Cu- and Fe-hydroxides and -carbonates. It formed during supergene weathering. Stage 1 and 2 gold consists mostly of electrum (gold fineness 640–860; mean = 725; n = 46), and rare near pure gold (fineness 930–940; n = 6). Gold in stage 3 is Ag-rich electrum (fineness 350–490, n = 12), and has a high Hg content (up to 11 mass %). The Cu-Au deposits in the Flatschach area show similarities with meso- to epizonal orogenic lode gold deposits regarding the geological setting, the structural control of mineralization, the type of alteration, the early (stage 1) sulfide assemblage and composition of gold. Unique about the Flatschach district is the lower-temperature overprint of copper arsenides (domeykite and koutekite) and copper sulfides (djurleite, yarrowite/spionkopite) on earlier formed sulfide mineralization. Based on mineralogical considerations temperature of stage 2 mineralization was between about 70 °C and 160 °C. Gold was locally mobilized during this low-temperature hydrothermal overprint as well as during stage 3 supergene oxidation and cementation processes.

Study cases of thermal conductivity prediction from P-wave velocity and porosity

Laboratory measurements of porosity, P-wave velocity and thermal conductivity from samples from two geothermal reservoirs in France and Australia are compared to the predictions from different models involving mineralogical considerations, and effective medium theory models yields <10% error in dry and saturated conditions in the Australian aquifer, and <30% deviation under saturated conditions in the French reservoir. Thermal conductivity derived from models involving detailed mineralogy is in good agreement with laboratory-measured data. Possible explanations for minor discrepancies using SEM/XRD include the effects of secondary minerals (i.e. ±undetected carbonates and fine particles) and the hydration of clays.

Physicochemical and mineralogical considerations of Ediki sandstone-hosted kaolin occurrence, South West Cameroon

Field mapping, colour, particle size distribution, pH and x-ray diffraction studies were undertaken to elucidate the genesis of Ediki kaolin. The kaolin occurs within the Mungo formation of upper cretaceous age, ascribed to the Douala sedimentary basin. The kaolin profile consists of upward coarsening sandstone – siltstone – sandstone sequence with a gradient of 35 to 40°. Texturally, the kaolin is mainly silt loam with a constitution of sand (18.1 to 24 wt.%), silt (68 to 73.3 wt.%) and clay (7 to 13.5 wt.%). The pH of the sample is acidic with values ranging from 4.8 to 5. Kaolinite and quartz are the dominant mineralogical phases whereas, muscovite + microcline and illite + goethite occur as minor and trace phases respectively. High porosity and permeability of the sandstones favoured migration of fluids which enhanced the formation of secondary diagenetic minerals. The presence of detrital feldspars and mica grains in the sandstones, were favourable parent phases for kaolinite formation. Kaolinization was further enhanced by the hot humid tropical climate, acidic pH, fairly gentle relief (40°), low K and Na concentrations (inferred from the mineralogy), as well as the low energy depositional environment. Key words: Diagenesis, kaolinization, secondary kaolins, supergene enrichment, tropical climate.

Static tests response on 5 Canadian hard rock mine tailings with low net acid-generating potentials

It is crucial for mining operators to predict the acid-generating potential of their mine wastes as early as possible in a mine development project, because of the high remediation costs of acid-generating tailings and the risks of environmental issues associated with an incorrect classification of the wastes. However, many tailings having low net acid-generating potentials fall into the uncertainty zone of the static test. Different chemical and mineralogical static test results are compared in this paper for 5 Canadian hard rock mine tailings having low net acid-generating potential, in order to help determine which method is more appropriate for such tailings. Static test methods showed significant result variations (NNP or NP/AP) for each tailings tested, demonstrating the need to develop tools to identify the most appropriate technique for a given mine waste. Thus, static test selection guidelines were developed based on mineralogical considerations for each test. A modification to the Lawrence and Scheske method based on the Paktunc CNP method is proposed in order to improve its accuracy, which enables to account for the presence of oxidizable cations (such as iron and manganese) within the minerals.

Mineralogy, petrology, and chemistry studies to evaluate oxide copper ores for heap leaching in Sarcheshmeh copper mine, Kerman, Iran

In recent years, as a result of biological, environmental, and economic considerations, available copper in copper oxide ores that could not be recovered by pyrometallurgical methods was accumulated in so-called oxide dumps. Suitable material is treated with dilute sulfuric acid in a heap-leaching process, whereupon the copper content of the rock slowly dissolves in the acidic solution. The performed investigations show that one needs to consider the action of the acid on the copper oxide-containing rocks at the microscopic level. In this paper, we describe research carried out on oxide samples from the western dump of the Sarcheshmeh copper mine. Each sample was split into two parts and a portion of each was exposed to heap-leaching conditions in a column. Subsequently, polished sections, thin sections, and powdered samples were subjected to chemical analysis as well as petrographic and mineralogical considerations. Changes in the weight percentages of non-metal and metal minerals before and after acid treatment were measured. Microscopic studies have indicated that chemical analyses do not provide a complete picture of the effects of acid on the rock. Thus, microscopic studies on sections are shown to be a necessary requirement, neglection of which can have negative economic and environmental effects.

The mechanism of self-reversal of thermoremanence in natural hemoilmenite crystals: new experimental data and model

New magnetic and mineralogical findings on self-reversing hemoilmenite (Fe 2− y Ti y O 3) grains from Pinatubo lavas (1991 eruption) provide important clues regarding the acquisition process of reverse thermoremanent magnetization (rTRM) in this solid solution series. Magnetic force microscopy indicates the presence of multidomain magnetic structures in coexisting strongly and weakly magnetic crystallographic regions having compositions of y≅0.54 and 0.53, respectively. Continuous thermal demagnetization of natural and laboratory TRM carried out on both whole rock samples and single hemoilmenite crystals shows that the magnitude of a normal TRM (nTRM) component, observed at temperatures above the Curie point of the self-reversing phase, is much too large to be carried by a phase that is entirely cation-disordered. Consistent with this observation are findings using transmission electron microscopy (TEM) which, in contrast to that what is commonly assumed, reveals the weakly magnetic regions to be magnetically heterogeneous. Specifically, these regions are found to contain tiny (20–40 nm) domains that are cation-ordered and evidently ferrimagnetic dispersed within the cation-disordered, presumably spin-canted antiferromagnetic matrix. Given these findings, we argue that the so-called nTRM-carrying x-phase is itself partially cation-ordered, and, thus, ferrimagnetic, as postulated first by Ishikawa and Syono (J. Phys. Soc., Jpn. 17 (1962) 714). We propose a “nanophase” self-reversal model for the ilmenite–hematite solid solution series in which the rTRM and nTRM components are carried by the cores and margins, respectively, of the tiny, partially cation-ordered nano-sized domains observed by TEM. Due to the partial cation order, both the core and the margin of each domain are expected to behave in a ferrimagnetic fashion at temperatures below their respective Curie points. However, given the kinetics of the ordering process, their cation distributions need be antiphase, which causes their magnetic moments to be oppositely aligned. Since it is most reasonable to consider each margin to be slightly more Fe-rich than the inside core, upon cooling, the margins acquire a magnetic remanence first (a nTRM). Then, upon further cooling, given that the intralayer and interlayer nearest-neighbor superexchange interactions are ferromagnetic and antiferromagnetic, respectively, the net magnetic moment of the core material need be oppositely aligned (producing a rTRM). The nano-sized regions would indeed behave in a superparamagnetic (SP) fashion if magnetically uncoupled to adjacent material; however, the spins in the margins (the x-phase) must be locked through superexchange to those of the surrounding disordered matrix, which we also claim to be locally enriched in iron. If so, then the magnetization of the x-phase can be both highly-coercive and thermally stable, as observed experimentally. Upon stepwise thermal demagnetization, the self-reversed remanence measured at room temperature is not destroyed until the unblocking temperature of the disordered Fe-enriched aureole (approximately 410°C) is reached. Mineralogical considerations and magnetic evidence from previous works suggest that this model is generally valid for self-reversed dacitic pumice, in particular the Mt. Haruna dacite and the 1985 Nevado del Ruiz dacitic andesite.

The relationship between manganese minerals and metallic elements in deep-sea manganese nodules

The relationship between manganese minerals and the concentration of Fe, Cu, Ni, Zn and Al in Mn-rich crystalline areas in deep-sea manganese nodules were investigated using microdiffraction and electron microprobe analysis. Thirty-three microsamples were obtained from eight polished sections of five Pacific Ocean manganese nodules. Birnessite and todorokite are the principal manganese minerals in the X-ray diffraction powder patterns on polished sections kept in a vacuum. Only birnessite was identified in sixteen microsamples. Only todorokite was identified in one microsample. Another sixteen microsamples were mixtures of birnessite and todorokite. Microsamples in which only birnessite was identified contain Cu, Ni and Zn in the same concentrations as the microsamples in which both birnessite and todorokite were identified. It appears that birnessite as well as todorokite can incorporate Cu, Ni and Zn. With the exception that no todorokite was observed in microsamples with very small amounts of Fe, Cu and Ni, there is no systematic correlation between the manganese mineralogy and the concentration of Fe, Cu, Ni and Zn in the microsamples. The microsamples examined in this study contain varying amounts of Al (0.01–2.57 wt%, 0.92 wt% on average). Todorokite appeared in the microsamples which contained more than 0.7 wt% Al. Mineralogical considerations suggest that at least part of the Al detected may be incorporated in todorokite.

Petrology of recrystallized ultramafic xenoliths from Merelava volcano, Vanuatu

Xenoliths in primitive olivine tholeiite lavas from Merelava Volcano, Vanuatu, include recrystallized wehrlites and harzburgites characterized by extremely fine grain size (0.02–2 mm) and equigranular textures. The harzburgites display mineral segregations, have highly variable ratios of ol: opx, minor clinopyroxene and accessory Cr-spinel, and are interpreted as the residues of high degrees of melting of upper mantle peridotite. Annealed Cr-spinel aggregates in harzburgite sample # 31564B enclose numerous small inclusions of sodic sanidine and minor plagioclase, attributed to infiltration of the harzburgite by a residual melt derived from an earlier period of island arc magmatism. The recrystallized wehrlites have high ol/cpx ratios and depleted REE patterns compatible with a cumulus origin. The refractory nature of the phases in both groups of recrystallized xenoliths compares closely with phases in ‘Alpine-type’ peridotites and primitive arc lavas, and is incompatible with compositions of abyssal peridotites. The recrystallized wehrlites give equilibration temperatures of 1070–1130° C and are interpreted as cumulates derived from an earlier period of Vanuatu Arc magmatism. The range of composition displayed by phases in the harzburgites is greater than phase variation in the wehrlites, and reflects a more complex thermal history. Textural, mineralogical, and geothermometric considerations indicate the harzburgites underwent cooling to 800°/900° C before being re-heated to 1000–1100° C by the current magmatic regime. A shallow crustal origin for these xenoliths is indicated by gravity data and tectonic considerations which strongly imply the presence of an ophiolite body beneath Merelava, representing the northward extension of the Pentecost Ophiolite. These interpretations are compatible with a published model for generation of the host basalts by partial melting at the crust/mantle boundary (ca. 17 km). Sr isotopic data show that the harzburgites are incompatible with residues of ocean-floor magmatism, or with residues of Merelava and Central Chain magmatism, but suggest an affinity with Vitiaz Arc magmatism of Eocene-lower Miocene age. Both groups of xenoliths were apparently entrained from wall rocks during ascent of the host magmas.

Comments on ‘Cements in radioactive waste disposal: some mineralogical considerations’

Comments on ‘Cements in radioactive waste disposal: some mineralogical considerations’

The Tugtutôq older giant dyke complex: mineralogy and geochemistry of an alkali gabbro-augite-syenite-foyaite association in the Gardar Province of South Greenland

AbstractThe Older Giant Dyke Complex is a differentiated alkaline intrusion of Proterozoic age (1154±16 Ma) and is the earliest of the late Gardar intrusions in the Tugtutôq-Ilímaussaq region. The dyke is approximately 20 km long by 0·5 km broad and comprises (i) marginal ‘border group’ rocks of alkali olivine gabbro, grading inwards to ferro-syenogabbro and (ii) an axial ‘central group’ of salic rocks ranging from augite syenite in the WSW to sodalite foyaite in the ENE.Chilled margins contain plagioclase (An53), olivine (Fo53), magnetite, ilmenite, and apatite as liquidus phases and later-crystallized augite (Di69Hd27Ac4) and biotite (Annite32). The coexisting Fe-Ti oxides indicate fO2 and T values just below the synthetic QFM buffer curve. In the border group, plagioclase cores zone into anorthoclase and soda-sanidine rims, olivines reach Fo16, pyroxenes Di32Hd59Ac9, and biotites Annite86. Interstitial pargasitic amphibole appears close to the innermost margins. In the central group, feldspars are all perthitic alkali feldspars and nepheline becomes a major, early crystallizing phase. Olivines range from Fo10-Fo4, in the augite-syenites where they coexist with ferro-salites Di50Hd47Ac3, but olivine is absent from foyaitic assemblages in which the pyroxenes range through aegirine-augite to pure aegirine. Interstitial amphiboles range from ferro-pargasite or hastingsite to katophorite and thence towards arfvedsonite, but are absent from the most differentiated rocks, whereas biotite occurs throughout the entire group in the range Annite71-Annite100.The parental magma, represented by the chilled margins, was a relatively anhydrous alkali olivine-basalt with an initial 87Sr/86Sr ratio of 0.70326. Its high Ti, P, Ba, and F contents are inferred to be features inherited from a primary magma, derived from the mantle as a small partial melt fraction which involved significant amounts of fluor-apatite and phlogopite. While all lithologies are considered as differentiates from this parental magma, there is both a well-defined field junction and a compositional hiatus between the border group and the central group rocks. Mineralogical considerations and REE patterns suggest that the later, more salic (?benmoreitic) magma from which the central group crystallized, related to the parental magma by ol-fsp-ap-FeTi oxide fractionation. Congelation in both border group and central group occurred by side-wall crystallization, but the salic magma became compositionally stratified, with upward concentration of alkalis and volatiles to produce a phonolitic upper facies which is preserved at the ENE end of the intrusion owing to subsequent axial tilting.

Cements in radioactive waste disposal: some mineralogical considerations

AbstractCementitious matrices are being assessed for immobilization of radioactive wastes. This paper discusses some mineralogical aspects of cement chemistry and the uses of siliceous minerals as selective sorbants to enhance immobilization potential.Studies of sorption and leaching of caesium from pulverized fuel ash (PFA), blast furnace slag, tobermorite, xonotlite, and clinoptilolite are reported. The role of incorporation of these additives in cement and the effect on the nature of the composite matrix on caesium behaviour has been investigated. Specific mechanisms of the interaction of additives with highly alkaline cement environment are described. While slags, PFA, and clinoptilolite undergo reaction at different rates, tobermorite and xonotlite appear to be stable in cement.

The World's Gold Supply Again Considered

QOME fifteen years ago, the writer had the pleasure of undertaking for the Harvard University Committee on Economic Research (predecessor organization of the Harvard Economic Society) a somewhat comprehensive and detailed study of the subject now under consideration; it appeared in this REVIEW for July I920.' The present purpose is simply to review subsequent developments, and to outline the major forces likely to affect future trends therein. For the present survey, it is not essential to dwell upon the detailed geological, mineralogical, and other considerations which have for so long influenced the history of gold production and of course still do so. A fairly detailed analysis of those considerations both in general, and for particular gold fields is already on record in the earlier study. Another reason why such physical factors can properly be given much less emphasis than before is that geological and mineralogical considerations are in a sense dominated, for the time being at least, by a single economic fact: the depreciation and devaluation of important currencies --among them, the United States dollar and the effect of that movement upon the profit margins of gold mining and refining. To deal comprehensively with these matters of currency depreciation and devaluation, the related matters of inflation of bank credit and price levels, and the curious Warren theory of the relationship between gold production and price levels, would lead us too far afield at this time; and they are therefore dealt with only in such incidental manner as is essential to the immediate question under review. Various analyses and critiques of these related economic matters have appeared elsewhere, particularly in the articles by Professor Bullock and Dr. Tucker, in previous issues of this REVIEW.2

The Elements of Geology

THIS is a further addition to the well written and well printed introductions to physical geography and geology which have been produced of late years for American schools. We do not quite agree with the author as to the novelty of the arrangement of his material, but it is certainly effective, and the questions attached to many of the illustrations are such as will draw out the reasoning powers of the pupil. Chemical and mineralogical considerations are kept in the background, and rocks are very broadly dealt with, as when syenite is defined (p. 274) as consisting of “feldspar and mica,” and diorite as being “still less siliceous, composed of hornblende and feldspar—the latter mineral being of different variety from the feldspar of granite and syenite.” The Elements of Geology. By Prof. W. H. Norton. Pp. x + 461. (Boston, New York, and London: Ginn and Co., n.d.) Price 6s. 6d.