Exogenic Origin Research Articles

Exogenic origin for the volatiles sampled by the Lunar CRater Observation and Sensing Satellite impact

Returning humans to the Moon presents an unprecedented opportunity to determine the origin of volatiles stored in the permanently shaded regions (PSRs), which trace the history of lunar volcanic activity, solar wind surface chemistry, and volatile delivery to the Earth and Moon through impacts of comets, asteroids, and micrometeoroids. So far, the source of the volatiles sampled by the Lunar Crater Observation and Sensing Satellite (LCROSS) plume has remained undetermined. We show here that the source could not be volcanic outgassing and the composition is best explained by cometary impacts. Ruling out a volcanic source means that volatiles in the top 1-3 meters of the Cabeus PSR regolith may be younger than the latest volcanic outgassing event (~1 billion years ago; Gya).

Origin and Dynamics of Termite Mound Soils in Southern India

Aims: In Southern India, termite above-ground nests can have the shape of cathedral (CAT) or lenticular (LENT) mounds. Although CATare built by the fungus-growing species Odontotermes obesus, the origin and evolution of LENT remain unknown. Therefore, the aim of to study was to estimate the origin and dynamics of LENT from their specific physical and chemical properties.
 Study Site: This study was carried out in the Bandipur Tiger reserve (dry deciduous forest), Karnataka, Southern India.
 Methodology: All the soil samples were collected in a Fluvisol in the Mule Hole experimental watershed.Only large size mounds between 1.5 - 1.8m high were considered in this study. Soil samples were collected from the outer wall of CATnest and from the soil surface layer (0-5 cm deep) and surrounding soil. Particle-size distribution and dispersion were obtained by process of sedimentation. All the statistical analysis such as principal component analysis (PCA) were calculated using R studio and R version 3.2.1.
 Results: Using elemental physical and chemical properties, this study showed a gradient of soil properties from the soil sampled between 50-100 cm depth to CAT, LENT and the surrounding topsoil (CTRL, Fluvisol), suggesting that: (i) CAT can be considered patches in the landscapes with specific physical and chemical properties in comparison with CTRL and LENT; (ii) LENT mounds can result from the progressive modification of CTRL (autogenic origin of LENT) and their degradation leads to a progressive recovery of CTRL properties or (iii) they originate from the colonization of abandoned CAT by other termite species (exogenic origin of LENT).
 Conclusion: This study confirms the complexity of CAT and LENT fates and the need for long-term datasets to determine the origin and evolution of termite mounds.

The morphology and age of the Iapetus equatorial ridge supports an exogenic origin

Both endogenic and exogenic formation mechanisms have been proposed for the equatorial ridge on Saturn's moon Iapetus. With photogeological mapping and crater statistics, we find that the morphology of the ridge is best explained by an exogenic origin, principally by the accretion onto the moon's surface of an orbiting ring of material.

Ganymede’s Surface Properties from Millimeter and Infrared Thermal Emission

Abstract We present thermal observations of Ganymede from the Atacama Large Millimeter Array (ALMA) in 2016–2019 at a spatial resolution of 300–900 km (0.″1–0.″2 angular resolution) and frequencies of 97.5, 233, and 343.5 GHz (wavelengths of 3, 1.3, and 0.87 mm); the observations collectively covered all Ganymede longitudes. We determine the global thermophysical properties using a thermal model that considers subsurface emission and depth- and temperature-dependent thermophysical and dielectric properties, in combination with a retrieval algorithm. The data are sensitive to emission from the upper ∼0.5 m of the surface, and we find a millimeter emissivity of 0.75–0.78 and (sub)surface porosities of 10%–40%, corresponding to effective thermal inertias of 400–800 J m−2 K−1 s−1/2. Combined with past infrared results, as well as modeling presented here of a previously unpublished night-time infrared observation from Galileo’s photopolarimeter–radiometer instrument, the multiwavelength constraints are consistent with a compaction profile whereby the porosity drops from ∼85% at the surface to at depth over a compaction length scale of tens of centimeters. We present maps of temperature residuals from the best-fit global models, which indicate localized variations in thermal surface properties at some (but not all) dark terrains and at impact craters, which appear 5–8 K colder than the model. Equatorial regions are warmer than predicted by the model, in particular near the centers of the leading and trailing hemispheres, while the midlatitudes (∼30°–60°) are generally colder than predicted; these trends are suggestive of an exogenic origin.

Hydropotes of young and mature leaves in Nuphar lutea and Nymphaea alba (Nymphaeaceae): Formation, functions and phylogeny

Hydropotes are specialized trichomes in aquatic plants, especially in species of the Nympaeaceae and Cabombaceae; yet their function remains controversial. In this paper, we present data on the hydropotes formed on the abaxial surface of young etiolated leaves tightly packed in the rosette at the rhizome flattened apex in Nuphar lutea (L.) Sm. and Nymphaea alba L. (Nymphaeaceae). The edges of the leaf blade are twisted in 3–5 scrolls. In N. lutea, long glandular hydropotes secreting mucilage are formed on the leaf abaxial surface and inside scrolls. In N. alba, non-glandular three-celled hydropotes are present but each leaf inside the rosette is enclosed by a thin film without mucilage. Only three-celled hydropotes are formed on the abaxial epidermis of green floating leaves of both species. Based on the similarity in initiation and first development of glandular hydropotes and hydropotes, we propose to distinguish two types of hydropotes: type I consisting of an apical cell that continues to divide and type II – an apical cell terminating division. This is well demonstrated by the presence of both types of hydropotes in N. lutea. We assume the function of type I is the secretion of mucilage to protect and facilitate growth of young etiolated leaves inside the rosette and that of type II the accumulation and removal of substances of endogenic and exogenic origin, perhaps residuals of metabolism and/or toxins, in green submerged growing and floating mature leaves. Phylogenetic implications of these morphological structures in Nymphaeales are discussed.

Highly porous nature of a primitive asteroid revealed by thermal imaging.

Carbonaceous (C-type) asteroids1 are relics of the early Solar System that have preserved primitive materials since their formation approximately 4.6 billion years ago. They are probably analogues of carbonaceous chondrites2,3 and are essential for understanding planetary formation processes. However, their physical properties remain poorly known because carbonaceous chondrite meteoroids tend not to survive entry to Earth's atmosphere. Here we report on global one-rotation thermographic images of the C-type asteroid 162173 Ryugu, taken by the thermal infrared imager (TIR)4 onboard the spacecraft Hayabusa25, indicating that the asteroid's boulders and their surroundings have similar temperatures, with a derived thermal inertia of about 300Jm-2s-0.5K-1 (300tiu). Contrary to predictions that the surface consists of regolith and dense boulders, this low thermal inertia suggests that the boulders are more porous than typical carbonaceous chondrites6 and that their surroundings are covered with porous fragments more than 10 centimetres in diameter. Close-up thermal images confirm the presence of such porous fragments and the flat diurnal temperature profiles suggest a strong surface roughness effect7,8. We also observed in the close-up thermal imagesboulders that are colder during the day, with thermal inertia exceeding 600tiu, corresponding to dense boulders similar to typical carbonaceous chondrites6. These results constrain the formation history of Ryugu: the asteroid must be a rubble pile formed from impact fragments of a parent body with microporosity9 of approximately 30 to 50 per cent that experienced a low degree of consolidation. The dense boulders might have originated from the consolidated innermost region or they may have an exogenic origin. This high-porosity asteroid may link cosmic fluffy dust to dense celestial bodies10.

Fluorine in the environment in an endemic fluorosis area in Southwest, China

Soils in large areas of China are enriched in fluorine (F). The present study analyzed F concentrations in cultivated soil, water, chemical fertilizer, and human hair, and metal concentrations in soils from an endemic fluorosis area in Southwest, China. In order to reveal the effects of industry on F concentration in the environment, 3 towns mainly with agriculture production and another 3 towns with developed phosphorus chemical industry in a same city were selected for sample collection. The total F concentrations of the 277 surface agricultural soil samples were 378.79–1576.13 μg g−1, and F concentrations of nearly 95% of the soil samples were higher than the Chinese average topsoil F concentration (480 μg g−1). Only a small fraction (0.75%) of total F was water soluble. The average total F, water soluble F, Ca, Cr, Fe, K, Mn, Rb, and Sr concentrations in soil samples from towns with intensive industry were higher than those from towns mainly with agriculture. Significant correlations were found between soil pH with total F (p < 0.01) and with water soluble F concentration (p < 0.1). Low F concentrations (<0.5 mg L−1) were found in irrigation water, well water and tap water in a town where the industry is dense. The phosphorus fertilizer and compound fertilizer had hundreds of times of contribution to soil F increment than the nitrogen fertilizer and potassium fertilizer. Nearly half percent of F in the human hair samples was of exogenic origin. Based on soil ingestion pathway, the health risk for adults exposure to F in soils was acceptable, however, F may pose possible health risks to children in high F concentration areas.

Simulations of magnetic fields produced by asteroid impact: Possible implications for planetary paleomagnetism

The origin and evolution of the Moon's magnetic field, specifically whether it has an endogenic or exogenic origin, has been a major question in lunar science. The lunar field today is a patchwork of magnetic anomalies carried as remnant magnetization in the rocks of the lunar crust. Recent publications suggest some magnetic anomalies may be associated with magnetized impact melt sheets of some large lunar basins cooling in the presence of an early lunar core dynamo or associated with portions of the impactor that formed the South Pole-Aitken Basin. By performing CTH simulations of asteroid impacts incorporating magnetic field generation and thermoremanence magnetization models, this paper helps explain the origin of lunar magnetic anomalies by showing: 1) transient magnetic fields produced by impact events will increase to substantial magnitude at the scale of large lunar basins and 2) magnetization of lunar rocks can occur during crater formation at nearly all scales. If occurring in pristine feldspathic lunar highlands rocks with relatively low thermoremanence susceptibility, the magnetic anomalies resulting from (1) and (2) produce magnetic fields observable in orbital magnetic field data only for large and relatively rare impact craters - large lunar basins greater than ~200 km diameter. If occurring in thick units with higher thermoremanence susceptibility, craters as small as 50–100 km may produce orbital anomalies. Craters at nearly all scales may leave behind remnant magnetic fields observable at the surface or in samples. This paper concludes magnetic fields produced by impacts may be an important contributor to the present state of the Moon's magnetic field.

Sedimentary records of paleoseismic events in the Late Pleistocene sediments of the Southern Yangtze River deltaic plain, East China, and their implications for differential subsidence of the Taihu block

Drilling cores from the Hangjiahu Coastal plain in the southwestern corner of the Southern Yangtze River deltaic plain, East China, contain a variety of soft-sediment deformation structures in the Late Pleistocene lacustrine and tidal sediments. They include load-flame structures, ball-and-pillow structures, diapir structures, liquefied sand veins, liquefied breccias, syn-sedimentary fault, seismo-cracks and brittle breccias. Sedimentary facies assessment of host deposits and development features rule out an exogenic origin of the soft-sediment deformation structures, such as gravity-flow, storm activity, wave action or flood. These soft-sediment deformation structures in the study area are interpreted as seismites, their spatial distribution suggest that the earthquakes were sourced from the intersection of the Majin-Wuzhen Fault and the Huzhou-Jiashan Fault. Seismites recognized in cores indicate three episodes of short and sudden seismicity (magnitude > 5), which are interpreted as a response to syn-depositional tectonic activity and differential subsidence of the Taihu block during the Late Pleistocene period. Systematic study of spatial and temporal distribution of these seismites improves the understanding of the tectonic context and evolutionary history of sedimentary basement.

Fates of hydrous materials during planetesimal collisions

Hydrous minerals are found on the surfaces of asteroids, but their origin is not clear. If their origin is endogenic, the hydrous minerals that were formed in the inner part of a planetesimal (or parent body) should come out on to the surface without dehydration. If their origin is exogenic, the source of hydrous minerals accreting onto asteroids is needed. Collisions in the asteroid belt would be related to both origins because collisions excavate the surface and eject the materials. However, the fate of hydrous minerals in large planetesimals during the collisional process has not been well investigated. Here, we explore planetesimal collisions by using the iSALE-2D code, and investigate the effect of an impact for the target planetesimal containing hydrous minerals. Our numerical results for the fiducial case (5 km/s of the impact velocity) show that hydrous minerals are slightly heated during the collisions. This moderate heating indicates that they can avoid the dehydration reaction and keep their original composition. Some hydrous minerals have larger velocity than the escape velocity of the collision system. This means that hydrous minerals can escape from the planetesimal and support the theory of exogenic origin for the hydrous minerals on asteroids. Meanwhile, the velocity of other hydrous minerals is smaller than the escape velocity of the system. This also indicates the possibility of an endogenic origin for the hydrous minerals on asteroids. Our results suggest that hydrous minerals on asteroids can be provided by planetesimal collisions.

Insights into Europa's ocean composition derived from its surface expression

The global ocean believed to exist beneath Europa's thick ice shell is often cited as one of the most likely places in the solar system to find evidence of extraterrestrial habitable environments or even extant life. However, given the technical challenges and the costs associated with outer solar system exploration, direct analysis of the ocean appears unlikely in the foreseeable future. Therefore, constraints on the chemical composition of the ocean will need to be inferred, for example, from analysis of the surface ice, either via remote sensing or landed surface missions. In this paper, we combine our recent body of work studying the chemistry of frozen putative Europa ocean brines with new experiments to develop predictions of the sequence by which the hydrated minerals form when a four-ionic component ocean (Na+, Cl−, Mg2+, and SO42−) freezes as a function of relative ionic concentrations and pH. This in turn provides a means to begin linking observed surface chemistry and the chemical environment of the subsurface ocean as well as insight into endogenic versus exogenic origin of detected species.

Modeling an exogenic origin for the equatorial ridge on Iapetus

Iapetus has a ridge along the equator that extends continuously for more than 110° in longitude. Parts of the ridge rise as much as 20 km above the surrounding terrains. Most models for the formation of this enigmatic ridge are endogenic, generally requiring the formation of a fast-spinning Iapetus with an oblate shape due to the rotation speed. Many of these require specific scenarios and have constraining parameters in order to generate a ridge comparable to what is seen today. An exogenic formation mechanism has also been proposed, that the ridge represents the remains of an early ring system around Iapetus that collapsed onto the surface. Thus far, none of the models have conclusively identified the origin of the ridge. In this study, an exogenic origin for the ridge is assumed, which is derived from a collapsing disk of debris around Iapetus, without invoking any specific model for the generation of the debris disk. Here, we evaluate whether it is possible to generate a ridge of the size and shape as observed by simulating the impact of the collapsing debris using the CTH hydrocode. Pi-scaling calculations suggest that extremely oblique impact angles (1°–10°) are needed to add to ridge topography. These extreme impact angles severely reduce the cratering efficiency compared to a vertical impact, adding material rather than eroding it during crater formation. Furthermore, material is likely to be excavated at low angles, enhancing downrange accumulation. Multiple impacts from debris pieces will heighten this effect. Because infalling debris is predicted to impact at extremely low angles, both of these effects might have contributed to ridge formation on Iapetus. The extreme grazing angles of the impacts modeled here decouple much of the projectile energy from the target, and impact heating of the surface is not significant. These models suggest that a collapsing disk of debris should have been able to build topography to create a ridge around Iapetus.

Symbiogenesis as a model for reconstructing the early stages of genome evolution

Symbiogenic evolution, which involves transformations of bacteria into the cellular organelles, is represented as a model for reconstructing the early stages of genome evolution, including the origin of DNA genomes from RNA genomes and the emergence of template processes on the basis of self-replicating molecular complexes in the ancestral metabolic systems. The antiquity of RNA genomes is supported by an increased evolutionary stability of ribosomal protein synthesis (translation) with respect to the DNA-dependent template processes (replication, transcription, recombination, and reparation). This stability is demonstrated by analysis of the deeply reduced genomes of symbiotic bacteria and cellular organelles as well as the "minimal" genomes which are common to phylogenetically diverse organisms. Higher evolutionary conservation of template biosynthetic processes with respect to step processes determining the metabolism and development in cells does not support the hypothesis about emergence ofgenomes within the ancestral cellular metabolic systems which are thought to be of abiogenic origin, instead suggesting dualistic origin of life on Earth. We suppose that the genome-free organelles of some eukaryotes (mitosomes, many hydrogenosomes, and some plastids) represent the products of reversion of symbiotic bacteria into ancestral forms which implemented their basic cellular functions using the informational macromolecules of exogenic origin. In the framework of this hypothesis the eukaryotic cells functioning based on the massive transfer of gene products (RNAs, proteins) from cytosol to organelles may represent the analogs of ancestral biocenoses that possessed integral hereditary systems (metagenomes).

Exogenic olivine on Vesta from Dawn Framing Camera color data

In this paper we present the results of a global survey of olivine-rich lithologies on (4) Vesta. We investigated Dawn Framing Camera (FC) High Altitude Mapping Orbit (HAMO) color cubes (∼60m/pixel resolution) by using a method described in Thangjam et al. (Thangjam, G., Nathues, A., Mengel, K., Hoffmann, M., Schäfer, M., Reddy, V., Cloutis, E.A., Christensen, U., Sierks, H., Le Corre, L., Vincent, J.-B, Russell, C.T. [2014b]. Meteorit. Planet. Sci. arXiv:1408.4687 [astro-ph.EP]). In total we identified 15 impact craters exhibiting olivine-rich (>40wt.% ol) outcrops on their inner walls, some showing olivine-rich material also in their ejecta and floors. Olivine-rich sites are concentrated in the Bellicia, Arruntia and Pomponia region on Vesta’s northern hemisphere. From our multi-color and stratigraphic analysis, we conclude that most, if not all, of the olivine-rich material identified is of exogenic origin, i.e. remnants of A- or/and S-type projectiles. The olivine-rich lithologies in the north are possibly ejecta of the ∼90km diameter Albana crater. We cannot draw a final conclusion on their relative stratigraphic succession, but it seems that the dark material (Nathues, A., Hoffmann, M., Cloutis, E.A., Schäfer, M., Reddy, V., Christensen, U., Sierks, H., Thangjam, G.S., Le Corre, L., Mengel, K., Vincent, J.-B., Russell, C.T., Prettyman, T., Schmedemann, N., Kneissl, T., Raymond, C., Gutierrez-Marques, P., Hall, I. Büttner, I. [2014b]. Icarus (239, 222--237)) and the olivine-rich lithologies are of a similar age. The origin of some potential olivine-rich sites in the Rheasilvia basin and at crater Portia are ambiguous, i.e. these are either of endogenic or exogenic origin. However, the small number and size of these sites led us to conclude that olivine-rich mantle material, containing more than 40wt.% of olivine, is basically absent on the present surface of Vesta. In combination with recent impact models of Veneneia and Rheasilvia (Clenet, H., Jutzi, M., Barrat, J.-A., Gillet, Ph. [2014]. Lunar Planet Sci. 45, #1349; Jutzi, M., Asphaug, E., Gillet, P., Barrat, J.-A., Benz, W. [2013]. Nature 494, 207–210), which predict an excavation depth of up to 80km, we are confident that the crust–mantle depth is significantly deeper than predicted by most evolution models (30km; Mittlefehldt, D.W. [2014]. Asteroid 4 Vesta: A Fully Differentiated Dwarf Planet. NASA Technical Reports Server (20140004857.pdf)) or, alternatively, the olivine-content of the (upper) mantle is lower than our detection limit, which would lead to the conclusion that Vesta’s parent material was already depleted in olivine compared to CI meteorites.

Detection of serpentine in exogenic carbonaceous chondrite material on Vesta from Dawn FC data

The Dawn mission’s Framing Camera (FC) observed Asteroid (4) Vesta in 2011 and 2012 using seven color filters and one clear filter from different orbits. In the present paper we analyze recalibrated HAMO color cubes (spatial resolution ∼60m/pixel) with a focus on dark material (DM). We present a definition of highly concentrated DM based on spectral parameters, subsequently map the DM across the Vestan surface, geologically classify DM, study its spectral properties on global and local scales, and finally, compare the FC in-flight color data with laboratory spectra.We have discovered an absorption band centered at 0.72μm in localities of DM that show the lowest albedo values by using FC data as well as spectral information from Dawn’s imaging spectrometer VIR. Such localities are contained within impact-exposed outcrops on inner crater walls and ejecta material. Comparisons between spectral FC in-flight data, and laboratory spectra of meteorites and mineral mixtures in the wavelength range 0.4–1.0μm, revealed that the absorption band can be attributed to the mineral serpentine, which is typically present in CM chondrites. Dark material in its purest form is rare on Vesta’s surface and is distributed globally in a non-uniform manner. Our findings confirm the hypothesis of an exogenic origin of the DM by the infall of carbonaceous chondritic material, likely of CM type. It further confirms the hypothesis that most of the DM was deposited by the Veneneia impact.

Mercury concentration in some calcareous soils of western Iran with a focus on pedological evolution and weathering process

The aim of this study was to evaluate total mercury concentration and its lithogenic and exogenic fractions in some calcareous soils of western Iran, where water contamination and bioaccumulation of mercury have been reported in the bottomland’s reservoir. In particular, we investigated soil physico-chemical properties and weathering conditions related to lithogenic and exogenic fractions of mercury for two groups of calcareous soils with a known comparative pedological evolution and weathering condition that was evident in the presence or absence of underlying layers of accumulated clay. Our results showed that the total mercury content of the studied soils ranged from 45.40 to 830.36 with a mean of 486.81 μg kg−1. Furthermore, calculation of mercury fractions revealed that lithogenic and exogenic fractions vary slightly according to the three reference elements (Fe, U and Nb) used in the calculations for the two groups of studied soils. The results also illustrated that most of the mercury content is of exogenic origin; therefore, total mercury variations are closely related to the content of exogenic mercury, while the lithogenic fraction exhibited no relationship with total mercury concentration. Moreover, application of the weathering indexes of Parker and the CaO/ZrO2 molar ratio supported the dependence of lithogenic mercury accumulation on weathering intensity in the studied calcareous soils. However, the significance of this relationship is stronger for more weathered calcareous soils; in such cases, fine-particle fractions are more developed, which encourages carrier phases such as organic materials and iron oxyhydroxides to become involved in more efficient fixation of mercury. Nevertheless, the formation of underlying layers of accumulated clay, i.e. argillic horizons, may restrain fixation of exogenic mercury by limiting its atmospheric input.

Powdery mildew on spinach (Spinacia oleracea L.)

Symptoms resembling powdery mildew appeared on spinach crops during April and May in 2007. Infected plants have suppressed growth, smaller and degenerated young leaves. The affected leaves become yellowish and wilt in a short time. High temperatures and draught conditions cause drying out of the affected plants. The symptoms are similar to physiological degeneration but are found on single plants or on small groups of plants. When plants are carefully examined, fine, exogenic mycelium is found on the leave blades. The mycelium can be clearly seen close to the main veins where it becomes denser and forms mycelium patches. On the leaf and flower stalks and plant stems the mycelium is white and fine at the beginning, and later becomes grayish. Under microscope analysis ectophytic mycelia of exogenic origin and short chains of spores are observed. On short conidiophores, chains with two types of conidia are formed: macro conidia that are one-celled, colorless, thin-walled, elliptical to cylindrical, sized 24.5-28.4 x 17.5 ?m; and micro conidia - ovoid to elliptical, sized 10.4-14.1 x 7.7 ?m. Teleomorphs are found in groups or as a single structure mainly close to the leaf veins. They are roundish and have appendages with uncinate-circinate to helicoids apex, sized - 87.5- 150 ?m. Cleistothecia have 4-5 to 8 asci (68.0 x 38.0 ?m), with 4 to 8 elliptical ascospores, sized 15.5-22.0 ? 11.0-17.5 ?m. The causal agent of powdery mildew on spinach found in Bulgaria has been identified as Uncinula spp. (Sawadaea spp.), Euoidium type anamorph, subspecies spinaciae.

Nature of ore-forming fluids of the Dal’negorsk deposit: Isotopic and geochemical parameters of the altered host rocks

Oxygen isotopic composition was studied in the altered host rocks of the Dal’negorsk borosilicate deposit in order to establish a boron source and the origin of ore-forming fluids responsible for deposition of economic borosilicate ore. The relationships between oxygen isotopic composition and geochemistry of the altered igneous rocks occupying various structural and temporal positions in the ore zone were studied, including premineral high-potassium minor intrusions located in the zones of datolite mineralization; alkali basalt, gabbro, and breccia from the sedimentary framework of the deposit; and postmineral basaltic andesite, basalt, and dolerite dikes. It was suggested that interaction of aqueous fluid with host rocks brought about not only variation in oxygen isotopic composition but also shifts in geochemistry of these rocks, especially as concerns the chemical elements contained in ore-forming fluid. The disturbance of oxygen isotopic system is typical of all studied rocks: δ18O values sharply decrease indicating interaction with aqueous fluid at elevated temperatures. The lowest δ18O (from −2.9 to +0.1‰) is characteristic of the premineral high-potassium and ultrapotassium minor intrusions from skarn-datolite zone. Igneous rocks from the sedimentary framework of the deposit have δ18O of +2 to −0.9‰ The δ18O of postmineral basaltic andesite, basalt, and dolerite dikes varies from 0 to +7‰ with increasing distance from the ore zone. The oxygen isotopic composition of aqueous fluid evidences its exogenic origin. The geochemical and isotopic characteristics of ore-forming fluid show that it could have been deep-seated subsurface water similar to the contemporary water of the Alpine fold zone, which contain up to 700–1000 mg/l B and is distinguished by high K, Li, Rb, Cs contents and high K/Na ratio. Similar geochemistry is characteristic of the fluid inclusions in quartz from ore zones. It cannot be ruled out that continental evaporites were a source of boron as well. The relationships between δ18O, K-Ar age, and geochemical parameters of premineral and postmineral altered intrusive bodies allow us to suggest that the subsurface B-bearing water discharged through narrow channels controlled by premineral basaltic bodies. The discharge was probably initiated by emplacement of basalt and dolerite dikes.

TEM and Raman characterisation of diamond micro- and nanostructures in carbon spherules from upper soils

Carbonaceous spherules of millimeter size diameter and found in the upper soils throughout Europe are investigated by TEM, including SAED, HRTEM and EELS, and Raman spectroscopy. The spherules consist primarily of carbon and have an open cell-like internal structure. Most of the carbon appears in an amorphous state, but different morphologies of nano- and microdiamond particles have also been discovered including flake shapes. The latter observation, together with the original findings of some of these spherules in crater-like structures in the landscape and including severely deformed rocks with some spherules being embedded in the fused crust of excavated rocks, points towards unique conditions of origin for these spherules and particles, possibly of exogenic origin.

Finding deeply buried deposits using geochemistry

It has become increasingly common for geologists to drill through 100 m or more of cover in search for buried mineral deposits. Geochemistry is one tool applied to this search, using a variety of approaches, including selective leaching of soils to extract the mobile component of elements, and the measurement of inorganic and organic gases. This paper provides an overview of some of the work carried out by the project Deep-Penetrating Geochemistry, sponsored by the Canadian Mining Industry Research Organization (CAMIRO), and supported by 26 Canadian and international companies and by the Ontario Geological Survey and the Canadian Geological Survey. The objective was to provide the mining industry with information relating to processes that may form anomalies at surface over buried deposits and to provide comparative data on methods used to detect these anomalies. Phase I of the project considered the theoretical and experimental framework for the movement of material from deeply buried deposits to the surface; much of this information has come from research on the containment of buried nuclear waste. In arid or semi-arid terrain, with a thick vadose zone, advective transport, which is the mass transfer of groundwater or air along with their dissolved or gaseous constituents, is the only known viable means of moving elements to the surface; diffusion of ions in water or gases in air is orders of magnitude slower. Examples of advective transport are pumping of mineralized groundwater to the surface during seismic activity and the extraction of air plus gas by barometric pumping. Both mechanisms require fractured rock and the interpretation of the derived anomalies requires consideration of neotectonic structures. In wetter climates, where water lies close to the surface, a variety of mechanisms have been proposed for creating anomalies at the surface. Diffusion-based models again suffer from slow rates of migration. Electrochemical models show a cathodic zone at the top of a buried sulphide conductor. Cations are attracted to the cathode, rather than to the surface, yet metals that most commonly migrate as cations are found to form anomalies at the surface. Phase II of the CAMIRO study involved field studies at ten test sites. The test sites included buried porphyry deposits in northern Chile, a gold–copper deposit in the Carlin district of Nevada, and volcanogenic massive sulphide bodies covered by glacial sediments in the Abitibi greenstone belt of Ontario. In all cases anomalies were found in soils above buried mineralization. It is suggested that anomaly formation is an episodic and cyclic process, in which batches of metal in water-soluble form are introduced and the metal is then progressively incorporated with time into the secondary minerals of soil. Selective leaches have been developed to dissolve specific phases in the soil to detect these anomalies. We have compared the results for five selective leaches that are available from commercial laboratories: deionized water, ammonium acetate, hydroxylamine hydrochloride, Enzyme Leach and Mobile Metal Ion (MMI) plus one non-selective decomposition, aqua regia. In addition, the Institute of Geophysical and Geochemical Exploration laboratory in China has supplied data for four sequential selective leaches: water-extractable, adsorbed, organic-bound and iron- and manganese-bound. The weakest leaches dissolve mainly the most recently introduced metals that remain in water-soluble form. Other leaches dissolve specific secondary minerals, such as carbonates, or iron and manganese oxides, which contain the introduced metals. The usefulness of leaches that dissolve secondary minerals depends on the ratio of introduced (exogenic) metal that the minerals contain relative to that of endogenic origin derived from the primary minerals of soils. Our results indicate that this ratio is variable from site to site, so that there is no universal ‘best’ leach for dissolving secondary minerals in exploration surveys. For the test sites in Chile and Nevada, anomalies may have formed incrementally over a period of a million years or more, which permitted metals of exogenic origin to become incorporated into many secondary minerals. For these sites, some anomalies can be detected by aqua regia, although the anomaly/background contrast is less than for selective leaches. For the test sites in Ontario, only a few thousand years have elapsed since glacial sediments were deposited to conceal mineralization. Over this short period, metal of exogenic origin has been incorporated into only the most labile of secondary minerals and it is the leaches that dissolve these labile minerals that can successfully identify anomalies. At the two sites where the most detailed studies have been carried out, the Spence deposit in Chile and Cross Lake near Timmins, we have found that the optimum sampling depth in soils is critical to detecting anomalies.