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Understanding the association between precious metals and trace elements in ore minerals is integral to ore deposit research and exploration. In situ characterization of ore minerals is now at the forefront of this field. The power of in situ element mapping and characterization is the ability to combine geochemistry with mineralogical and broader geological context. Synchrotron radiation (SR) X-ray techniques such as X-ray Fluorescence (XRF) and X-ray Absorption Near Edge Spectroscopy (XANES) are incredibly powerful tools for studying ore systems with applications in exploration, geometallurgy, and remediation. We provide examples of these applications to gold-bearing samples from across the world-class Timmins gold camp in Canada. Analysis of thin sections, billet offcuts, as well as cut rock slabs highlights the versatility of SR-XRF and XANES analysis at multiple stages of deposit investigation and for multiple sample types. SR-XRF mapping of large areas at 20 μm resolution is very effective for quickly identifying and characterizing gold and trace element associations with gold, even in low grade and nuggety samples. Large area mapping is integral to quickly providing key geochemical information within the sample context as well as for improving efficiency and mitigating bias in grain selection for higher resolution analyses. High-resolution SR-XRF mapping and XANES analysis of individual mineral grains are compared to conventional EPMA mapping and reveals micrometer scale associations with trace metals, Au, and As. The characterization of trace element associations with different fluid events and gold mineralization styles is integral to understanding mineralizing systems and developing exploration vectors. Point XRF and XANES identified and characterized the presence and nature of refractory gold in pyrite as well as grain scale variability in As speciation. An early understanding of the distribution and redox state of gold, trace metals, and deleterious elements at the exploration stage has implications for mitigating future geometallurgy and remediation issues. The examples presented highlight the potential for the application of synchrotron studies early in the mine cycle for characterizing gold mineralization in orogenic systems.

The Dome mine is host to over 16 Moz of orogenic gold deposited during a period of up to 25 Ma through multi-stage enrichment. The earliest economic stage of veining is an extensive set of ankerite veins which were historically considered barren except where overprinted by subsequent veining events. Gold in these veins is intimately associated with pyrite mineralization, and three stages of pyrite growth have been identified (Py1,2,3). The trace element content of each stage of pyrite growth determined by dynamic-secondary ion mass spectrometry and synchrotron radiation x-ray fluorescence reveals that there were three auriferous fluid events, each with a unique gold and trace element fingerprint which can be related to deposits wide mineralization events. Early ankerite vein forming fluids were auriferous, lower temperature (200–250 °C) and deposited Py1 enriched in gold, metals and metalloids (As, Cu, Ni, Zn). Py2 growth is related to deposit wide quartz-tourmaline and quartz-fuchsite veining based on trace element geochemistry, Au:Ag, and associated mineral assemblages. This deposited Ni enriched pyrite, tellurides, galena, and gold with anomalously high Au:Ag ratios. There is also evidence for remobilization of early gold and trace elements from Py1 pyrite during the Py2 forming event. The final stage of gold endowment in the ankerite veins is related to a deposit (and camp) wide quartz veining event. Py3 growth is trace element (As, Ni, Cu) and Au poor with respect to Py1 and Py2, however, this veining event contributed the bulk of the ankerite vein gold endowment. The remobilization of gold and trace elements from sieve textured Py1 in addition to overprinting Py2 and Py3 and their associated gold endowments helps explain the difficulty in applying bulk rock trace element vectors to gold at the Dome mine. The work also provides conclusive evidence for the auriferous nature of early ankerite veining at the Dome mine, and reveals that the system was fertile for a period of over 7 to 25 Ma, a key component for the formation of a world-class deposit.

The earliest auriferous veining event in the development of the over 16 Moz gold endowment at the Dome mine was an extensive set of ankerite veins (over 5400 m strike length). The depositional context of the Dome mine ankerite veins has been historically contentious and their role in the mineralization history of the deposit not well understood. We present a deposit wide geochemical study of the ankerite veins and their host rocks, with observations from new underground mapping. Ankerite veining across the mine is almost exclusively restricted to the Vipond Formation, which is Fe rich and tholeiitic in nature. Metamorphic fluids and ankerite vein formation generally focused along flow boundaries in the volcanic sequence, however, carbonatization is ubiquitous. The flows of the Vipond Formation maintain their protolith geochemical signatures as REE, Zr, Al2O3, TiO2, and Y are largely immobile during mineralization and alteration, which mobilized Na2O, K2O, and locally Fe2O3. The ankerite vein structures are reactivated and overprinted by quartz and quartz-tourmaline veining, and gold grade is variable, ranging from

Rocks that make up the Mesoarchean (~3Ga) Buhwa greenstone belt (BGB) of the Zimbabwe craton divide into three associations: shelf, basinal, and transitional. Chert and iron formation exist within the three associations, allowing the unique opportunity to compare textural and geochemical attributes of iron- and silica-rich rocks from distinct positions within a single basin. We analyzed major-, trace-, and rare-earth-elements, and silicon and oxygen isotopes of chert and iron formation from the shelf, basinal, and transitional associations within the BGB. Samples possess elemental signatures consistent with formation from mixed seawater and hydrothermal fluids (LaSN/LaSN* > 1; PrSN/YbSN

Silica-rich Precambrian rocks often preserve geochemical information and microfossil remnants from the early biosphere and could play a critical role in the formation of early crust. Because these rocks are important geochemical and paleontological archives, we need to better constrain their geochemical and isotopic attributes and generate a refined picture of the evolving Archean silica cycle. Here, we investigate a series of sub- to greenschist facies Si-rich Archean rocks from the ~ 2.7 Ga Abitibi greenstone belt, Canada, that represent chemical sedimentary rocks and rocks formed via silica-addition through the process of silicification. We report data for major and trace element geochemistry, multi-crystal silicon and oxygen isotopes of quartz using isotope ratio mass spectrometry, and texture-specific silicon isotope values measured using secondary ion mass spectrometry on Neoarchean chemical sedimentary rocks, their silicified equivalents, and associated silicified volcanic rocks. We find that in such a well-preserved terrane we can utilize petrographic textures and geochemical attributes to establish rock origin, distinguishing siliceous rocks that form via chemical sedimentation from those that form via silicification. Chemical sedimentary rocks display a wide range of 30Si-depleted silicon isotopes values that vary with stratigraphy similar to other Archean iron formation. Silicified volcanic rocks possess 30Si-enriched values, similar to Archean silicified basalts. We conclude that because silicon isotope values of iron formation shift toward 30Si-enriched values up stratigraphy, basinal changes in the composition of the silicon isotope reservoir may be preserved. Silicon isotope values of silicified volcanic rocks by contrast, likely represent precipitation from an isotopically heavy silicon reservoir, influenced by downward percolating seawater and upward moving convecting fluids interacting with host volcanic rock (basalt or andesite). Overall, we confirm that Neoarchean silicified rocks are 30Si-enriched like their Paleoarchean counterparts.

Here we provide the first high-resolution geochemical evidence for microbial metabolism to be preserved in impact-generated materials. This study is unique as not only do we merge complimentary analytical techniques such as high-resolution spectromicroscopy to assess the biogenicity of tubules in impact glasses, but we compare these results to those from co-occurring abiotic quench crystallites as an intrinsic negative control. Scanning transmission X-ray microscopy (STXM) near edge X-ray absorption fine structure spectroscopy (NEXAFS) at the Fe L 3 - and C K-edges revealed iron speciation patterns and organic C associated with tubular features in the impact glass. The high spatial resolution of STXM combined with NEXAFS allowed organic carbon to be localized to the tubule features. The fine energy resolution of NEXAFS allowed for unique populations of organic carbon to be spectrally differentiated between the tubule features and the matrix. The distinct and systematic variation in iron redox states observed is consistent with microbially mediated dissimilatory iron reduction. The Ries tubules comprise the first trace fossil preserved in a substrate unique to the impact process, thus illustrating the potential for microbial metabolism to be preserved in impact materials.

Satellite and airborne images, including Landsat, ASTER, and Hyperspectral data, are widely used in remote sensing and Geographic Information Systems (GIS) to understand natural earth related processes, climate change, and anthropogenic activity. The nature of this type of data is usually multi or hyperspectral with individual spectral bands stored in raster file structures of large size and global coverage. The elevated number of bands (on the order of 200 to 250 bands) requires data processing algorithms capable of extracting information content, removing redundancy. Conventional statistical methods have been devised to reduce dimensionality however they lack specific processing to handle data diversity. Hence, in this paper we propose a new data analytic technique to classify these complex multidimensional data cubes. Here, we use a well-known database consisting of multi-spectral values of pixels from satellite images, where the classification is associated with the central pixel in each neighborhood. The goal of our proposed approach is to predict this classification based on the given multi-spectral values. To solve this classification problem, we propose an improved decision tree (DT) algorithm based on a fuzzy approach. More particularly, we introduce a new hybrid classification algorithm that utilizes the conventional decision tree algorithm enhanced with the fuzzy approach. We propose an improved data classification algorithm that utilizes the best of a decision tree and multi-criteria classification. To investigate and evaluate the performance of our proposed method against other DT classifiers, a comparative and analytical study is conducted on well-known Landsat data., The International Conference on Ambient Systems, Networks and Technologies, ANT-2015, the International Conference on Sustainable Energy Information Technology, SEIT-2015, 2 June 2015 through 5 June 2015

The East Scotia Ridge is an active back-arc spreading centre located to the west of the South Sandwich island arc in the Southern Ocean. Initial exploration of the ridge by deep-tow surveys provided the first evidence for hydrothermal activity in a back-arc setting outside of the western Pacific, and we returned in 2010 with a remotely operated vehicle to precisely locate and sample hydrothermal sites along ridge segments E2 and E9. Here we report the chemical and isotopic composition of high- and low-temperature vent fluids, and the mineralogy of associated high-temperature chimney material, for two sites at E2 (Dog’s Head and Sepia), and four sites at E9 (Black & White, Ivory Tower, Pagoda and Launch Pad). The chemistry of the fluids is highly variable between the ridge segments. Fluid temperatures were ?350 °C at all vent sites except Black & White, which was significantly hotter (383 °C). End-member chloride concentrations in E2 fluids (532 - 536 mM) were close to background seawater (540 mM), whereas Cl in E9 fluids was much lower (98 - 220 mM) indicating that these fluids are affected by phase separation. Concentrations of the alkali elements (Na, Li, K and Cs) and the alkaline earth elements (Ca, Sr and Ba) co-vary with Cl, due to charge balance constraints. Similarly, concentrations of Mn and Zn are highest in the high Cl fluids but, by contrast, Fe/Cl ratios are higher in E9 fluids (3.8 – 8.1 × 10?3) than they are in E2 fluids (1.5 - 2.4 × 10?3) and fluids with lowest Cl have highest Cu. Although both ridge segments are magmatically inflated, there is no compelling evidence for input of magmatic gases to the vent fluids. Fluid ?D values range from 0.2 to 1.5 ‰, pH values (3.02 - 3.42) are not especially low, and F concentrations (34.6 - 54.4 ?M) are lower than bottom seawater (62.8 ?M). The uppermost sections of conjugate chimney material from E2, and from Ivory Tower and Pagoda at E9, typically exhibit inner zones of massive chalcopyrite enclosed within an outer zone of disseminated sulphide, principally sphalerite and pyrite, in an anhydrite matrix. By contrast, the innermost part of the chimneys that currently vent fluids with lowest Cl (Black & White and Launch Pad), is dominated by anhydrite. By defining and assessing the controls on the chemical composition of these vent fluids, and associated mineralisation, this study provides new information for evaluating the significance of hydrothermal processes at back-arc basins for ocean chemistry and the formation of seafloor mineral deposits.

Peakaboo is a platform for the analysis of full spectrum synchrotron X-ray fluorescence (XRF) map data. It offers robust, automated fitting of XRF spectral peaks, increasing the sensitivity to trace chemical elements. Large arrays of spectral data can also be processed into element maps to define spatial relationships. The modifications to Peakaboo introduced since 2017 are particularly designed to help new users to become rapidly competent in the handling of complex XRF spectra. Some of the most important innovations of the software are described below. Finally, we share examples of its application in Earth and Environmental Sciences.

Surficial deposits of the OH-bearing iron sulfate mineral jarosite have been observed in several places on Mars, such as Meridiani Planum and Mawrth Vallis. The specific depositional conditions and mechanisms are not known, but by comparing martian sites to analogous locations on Earth, the conditions of formation and, thus, the martian depositional paleoenvironments may be postulated. Located in a cold semi-arid desert ∼100 km east of Norman Wells, Northwest Territories, Canada, the Golden Deposit (GD) is visible from the air as a brilliant golden-yellow patch of unvegetated soil, approximately 140 m × 50 m. The GD is underlain by permafrost and consists of yellow sediment, which is precipitating from seeps of acidic, iron-bearing groundwater. On the surface, the GD appears as a patchwork of raised polygons, with acidic waters flowing from seeps in troughs between polygonal islands. Although UV–Vis–NIR spectral analysis detects only jarosite, mineralogy, as determined by X-ray diffraction and inductively coupled plasma emission spectrometry, is predominantly natrojarosite and jarosite, with hydronium jarosite, goethite, quartz, clays, and small amounts of hematite. Water pH varies significantly over short distances depending on proximity to acid seeps, from 2.3 directly above seeps, to 5.7 several m downstream from seeps within the deposit, and up to 6.5 in ponds proximal to the deposit. Visual observations of microbial filament communities and phospholipid fatty acid analyses confirm that the GD is capable of supporting life for at least part of the year. Jarosite-bearing sediments extend beneath vegetation up to 70 m out from the deposit and are mixed with plant debris and minerals presumably weathered from bedrock and glacial till. This site is of particular interest because mineralogy (natrojarosite, jarosite, hematite, and goethite) and environmental conditions (permafrost and arid conditions) at the time of deposition are conceivably analogous to jarosite deposits on Mars. Most terrestrial analogues for Mars jarosites have been identified in temperate environments, where evaporation rates are very high and jarosites form along with other sulfates due to rapid evaporation (e.g. Rio Tinto, Spain; Western Australian acidic saline lake deposits). The GD is a rare example of an analogue site where jarosite precipitates under dominant freezing processes similar to those which could have prevailed on early Mars. Thus, the GD offers a new perspective on jarosite deposition by the upwelling of acidic waters through permafrost at Meridiani Planum and Mawrth Vallis, Mars. The GD also demonstrates that martian deposits may show considerably more chemical and mineral variability than indicated by the current remote sensing data sets.

In recent years evidence for spring deposits on Mars has been mounting. It seems increasingly likely that groundwater upwelling and surfacing as springs may be responsible for some mineral deposits on Mars’ surface. In order to more easily detect and better understand potential spring deposits on Mars, it is pertinent that we gain a better understanding of the distribution of minerals at cold spring systems on Earth. Here, we report on the detailed mineralogy and distribution of precipitates in crusts and sediments of three non-volcanic perennial saline cold spring systems associated with gypsum/anhydrite diapirs on Axel Heiberg Island, Canada: Wolf spring (WS; also known as Lost Hammer), Colour Peak springs (CP), and Gypsum Hill springs (GH). At these sites permafrost, frigid winter temperatures, and arid atmospheric conditions approximate conditions of present-day, as well as past, Mars. Mineralogy of the three springs is dominated by halite (NaCl), calcite (CaCO 3 ), gypsum (CaSO 4 ·2H 2 O), thenardite (Na 2 SO 4 ), mirabilite (Na 2 SO 4 ·10H 2 O), and elemental sulfur (S°). Minerals at WS are more sodium-rich than at the other two sites, and water salinity is much higher, suggesting water flows through halite in the subsurface. Mirabilite is likely deposit at WS during winter months and dehydrates to thenardite during summer months. Elemental sulfur is typically associated with gypsum, and may be related to microbial metabolism. Spring sediments are home to thriving microbial communities in winter and summer months, and presumably year round. If spring systems did exist on the surface of Mars, they may represent environments capable of supporting microbial life. It is not known to what extent mineral crusts in cold saline spring systems on Earth preserve evidence of microbial life, or if they ever did on Mars. Therefore, studying terrestrial saline spring mineral deposits such as those on Axel Heiberg Island may help us to better understand cold spring precipitation on Mars and guide us in the search for minerals that may have been precipitated in spring systems and that may contain evidence of life. Additionally, spectral data from Europa indicates the presence of mirabilite. While the depositional environment on Europa differs from Axel Heiberg Island, the springs may still be a good mineralogical analogue, given the precipitation of mirabilite by the upwelling of cold, salty subsurface water, in a cold, semi-arid desert environment.

It has long been suggested that hydrothermal systems might have provided habitats for the origin and evolution of early life on Earth, and possibly other planets such as Mars. In this contribution we show that most impact events that result in the formation of complex impact craters (i.e., >2–4 and >5–10 km diameter on Earth and Mars, respectively) are potentially capable of generating a hydrothermal system. Consideration of the impact cratering record on Earth suggests that the presence of an impact crater lake is critical for determining the longevity and size of the hydrothermal system. We show that there are six main locations within and around impact craters on Earth where impact-generated hydrothermal deposits can form: (1) crater-fill impact melt rocks and melt-bearing breccias; (2) interior of central uplifts; (3) outer margin of central uplifts; (4) impact ejecta deposits; (5) crater rim region; and (6) post-impact crater lake sediments. We suggest that these six locations are applicable to Mars as well. Evidence for impact-generated hydrothermal alteration ranges from discrete vugs and veins to pervasive alteration depending on the setting and nature of the system. A variety of hydrothermal minerals have been documented in terrestrial impact structures and these can be grouped into three broad categories: (1) hydrothermally-altered target-rock assemblages; (2) primary hydrothermal minerals precipitated from solutions; and (3) secondary assemblages formed by the alteration of primary hydrothermal minerals. Target lithology and the origin of the hydrothermal fluids strongly influences the hydrothermal mineral assemblages formed in these post-impact hydrothermal systems. There is a growing body of evidence for impact-generated hydrothermal activity on Mars; although further detailed studies using high-resolution imagery and multispectral information are required. Such studies have only been done in detail for a handful of martian craters. The best example so far is from Toro Crater (Marzo, G.A., Davila, A.F., Tornabene, L.L., Dohm, J.M., Fairen, A.G., Gross, C., Kneissl, T., Bishop, J.L., Roush, T.L., Mckay, C.P. [2010]. Icarus 208, 667–683). We also present new evidence for impact-generated hydrothermal deposits within an unnamed ∼32-km diameter crater ∼350 km away from Toro and within the larger Holden Crater. Synthesizing observations of impact craters on Earth and Mars, we suggest that if there was life on Mars early in its history, then hydrothermal deposits associated with impact craters may provide the best, and most numerous, opportunities for finding preserved evidence for life on Mars. Moreover, hydrothermally altered and precipitated rocks can provide nutrients and habitats for life long after hydrothermal activity has ceased.

Recent observations of carbonate minerals in ancient Martian rocks have been interpreted as evidence for the former presence of circumneutral solutions optimal for carbonate precipitation. Sampling from surface and subsurface regions of the low-pH system of Río Tinto has shown, unexpectedly, that carbonates can form under diverse macroscopic physicochemical conditions ranging from very low to neutral pH (1.5-7.0). A multi-technique approach demonstrates that carbonate minerals are closely associated with microbial activity. Carbonates occur in the form of micron-size carbonate precipitates under bacterial biofilms, mineralization of subsurface colonies, and possible biogenic microstructures including globules, platelets and dumbbell morphologies. We propose that carbonate precipitation in the low-pH environment of Río Tinto is a process enabled by microbially-mediated neutralization driven by the reduction of ferric iron coupled to the oxidation of biomolecules in microbially-maintained circumneutral oases, where the local pH (at the scale of cells or cell colonies) can be much different than in the macroscopic environment. Acidic conditions were likely predominant in vast regions of Mars over the last four billion years of planetary evolution. Ancient Martian microbial life inhabiting low-pH environments could have precipitated carbonates similar to those observed at Río Tinto. Preservation of carbonates at Río Tinto over geologically significant timescales suggests that similarly-formed carbonate minerals could also be preserved on Mars. Such carbonates could soon be observed by the Mars Science Laboratory, and by future missions to the red planet.

A breccia facies of mafic composition in the subaqueous Misema shield volcano building phase and Misema caldera of the Blake River caldera complex, Abitibi Greenstone belt, Canada preserves putative microbial ichnofossils in formerly glassy breccia fragments. These Neoarchean ichnofossils are comparable in morphology, distribution, and mineral association to similar textures found in other Archean cratons as well as Phanerozoic ophiolite successions and are interpreted to represent an early Earth subaqueous biosphere. However, a detailed volcanological facies analysis of the rocks that host these purported microbial ichnofossils is lacking from previous studies. The present field locality (Hurd property) is a 62 m-thick volcanic succession that displays two main lithological facies: (i) a massive to lobate facies and (ii) breccia facies. The 5–25 m-thick massive to lobate facies contains massive basalts that grade into lobate flows toward the top. The 1–15 m-thick breccia facies displays delicate volcanic textures that are preserved due to extensive silica precipitation, a low temperature hydrothermal process, and the subgreenschist metamorphic grade. Geochemically, the mafic flows are tholeiitic basalts with TiO2 contents of 1–2% but high SiO2, up to 71%, related to hydrothermal silica precipitation. Microbial ichnofossils are found in the glassy fragments of the breccia facies. The breccia facies that displays evidence of associated hydrothermal activity, as in modern seafloor and summit caldera smoker settings, provided a favourable environment for ancient biological interactions between glassy rocks and microorganisms during formation of the Abitibi Greenstone belt.

Recent studies have demonstrated that terrestrial subaqueous basalts and hyaloclastites are suitable microbial habitats. During subaqueous basaltic volcanism, glass is produced by the quenching of basaltic magma upon contact with water. On Earth, microbes rapidly begin colonizing the glassy surfaces along fractures and cracks that have been exposed to water. Microbial colonization of basaltic glass leads to the alteration and modification of the rocks and produces characteristic granular and/or tubular bioalteration textures. Infilling of the alteration textures by minerals such as phyllosilicates, zeolites and titanite may enable their preservation through geologic time. Basaltic rocks are a major component of the Martian crust and are widespread on other solar system bodies. A variety of lines of evidence strongly suggests the long-term existence of abundant liquid water on ancient Mars. Recent orbiter, lander and rover missions have found evidence for the presence of transient liquid water on Mars, perhaps persisting to the present day. Many other solar system bodies, notably Europa, Enceladus and other icy satellites, may contain (or have once hosted) subaqueous basaltic glasses. The record of terrestrial glass bioalteration has been interpreted to extend as far back as ∼3.5 billion years ago and is widespread in oceanic crust and its metamorphic equivalents. The terrestrial record of glass bioalteration strongly suggests that glassy or formerly glassy basaltic rocks on extraterrestrial bodies that have interacted with liquid water are high-value targets for astrobiological exploration.

With the continued success of the Mars Exploration Rovers and the return of humans to the Moon within the next decade, a considerable amount of research is being done on the technologies required to provide surface mobility and the tools required to provide scientific capability. Here, we explore the utility of lidar and the mobile Scene Modeler (mSM) – which is based on a stereo camera system – as scientific tools. Both of these technologies have been, or are being considered for, technological applications such as autonomous satellite rendezvous and rover navigation. We carried out a series of field tests at the 23 km diameter, 39 Ma, Haughton impact structure located on Devon Island in the Canadian Arctic. Several sites of geological interest were investigated, including polygonal terrain, gullies and channels, slump/collapse features, impact melt breccia hills, and a site of impact-associated hydrothermal mineralization. These field tests show that lidar and mSM provide a superior visual record of the terrain, from the regional (km) to outcrop (m to cm) scale and in 3-D, as compared to standard digital photography. Thus, a key strength of these technologies is in situ reconnaissance and documentation. Lidar scans also provide a wealth of geometric and structural information about a site, accomplishing the equivalent of weeks to months of manual surveying and with much greater accuracy than traditional tools, making this extremely useful for planetary exploration missions. An unexpected result of these field tests is the potential for lidar and mSM to provide qualitative, and potentially quantitative, composition information about a site. Given the high probability of lidar and mSM being used on future lunar missions, we suggest that it would be beneficial to further investigate the potential for these technologies to be used as science tools.

Alteration textures in volcanic glass from the seafloor fall into two classes, one suggestive of abiotic/diffusive hydration and chemical exchange, and another likely to be caused by microbial, cavity-forming, congruent dissolution. Glass bioalteration is common in submarine lavas throughout the world's ocean, dominant in the upper 300 m of the oceanic crust, and found in all well-preserved ophiolites and greenstone belts dating back to 3.5 Ga. It may yield a significant fraction of the global biomass and geochemical fluxes and is relevant to the development of the earliest life on Earth. We present a critical review concerning these glass bioalteration textures and present new data on their microchemical environment. We explore arguments for their biogenicity and further develop the prevalent model for their formation by relating corrosion morphology to the mechanism of microbial dissolution. Biological alteration produces conspicuous micron-scale granular and tubular textures. Granular glass alteration is well explained by colonizing microbes that selectively dissolve the glass in their contact area, forming a sponge-like interconnected network of micron-sized cavities along glass surfaces. Tubular alteration meanwhile, is more likely to be caused by filamentous cell extensions in a process similar to fungal tunneling of soil feldspars and marine carbonates. While we see clear functional similarities to fungal dissolution behavior, we do not know whether fungal or prokaryotic organisms are involved. However, this functional constraint may eventually help to identify potential microbes responsible for these features, potentially including eukaryotic or prokaryotic organisms. Yet, we caution that these organisms may be difficult to identify and to study, because they are likely to be sparsely distributed, slow growing, and difficult to cultivate.

Bioalteration of basaltic glass in pillow lava rims and glassy volcanic breccias (hyaloclastites) produces several distinctive traces including conspicuous petrographic textures. These biologically generated textures include granular and tubular morphologies that form during glass dissolution by microbes and subsequent precipitation of amorphous material. Such bioalteration textures have been described from upper, in situ oceanic crust spanning the youngest to the oldest oceanic basins (0–170 Ma). The granular type consists of individual and/or coalescing spherical bodies with diameters typically around 0.4 μm. These are by far the most abundant, having been traced up to ∼550 m depths in the oceanic crust. The tubular type is defined by distinct, straight to irregular tubes with diameters most commonly around 1–2 μm and lengths exceeding 100 μm. The tubes are most abundant between ∼50 m and 250 m into the volcanic basement. We advance a model for the production of these bioalteration textures and propose criteria for testing the biogenicity and antiquity of ancient examples. Similar bioalteration textures have also been found in hyaloclastites and well-preserved pillow lava margins of Phanerozoic to Proterozoic ophiolites and Archean greenstone belts. The latter include pillow lavas and hyaloclastites from the Mesoarchean Barberton Greenstone Belt of South Africa and the East Pilbara Terrane of the Pilbara Craton, Western Australia, where conspicuous titanite-mineralized tubes, have been found. Petrographic relationships and age data confirm that these structures developed in the Archean. Thus, these biologically generated textures may provide an important tool for mapping the deep oceanic biosphere and for tracing some of the earliest biological processes on Earth and perhaps other planetary surfaces.

A laser ablation–multiple collector–inductively coupled plasma mass spectrometry (LA–MC–ICP-MS) analytical protocol is used to date accessory minerals (zircon, monazite, and titanite) at high spatial resolution (5–40 μm) using standard petrographic thin sections. The MC–ICP-MS instrument is equipped with a modified collector array containing a combination of Faraday buckets and multiple ion counters, which produces accurate and precise geochronological data using small sample volumes (pit depth ≤2 μm at 5 μm and ≤15 μm at 40 μm spot sizes). Standardization and normalization factors for the 206Pb/238U and 207Pb/235U values are calculated based on well-characterized external mineral standards previously dated by high precision ID-TIMS analysis. During an analytical session, the 2σ relative standard deviation (i.e., external reproducibility) for the 206Pb/238U and 207Pb/235U values is ≤3%. The measured 207Pb/206Pb value is simultaneously corrected for instrumental mass bias by the aspiration of a Tl solution resulting in a 2σ relative standard deviation of between ∼0.3 and 1%. The accuracy of the analytical protocol was verified on petrographic thin sections of several samples previously dated by ID-TIMS. The capacity of this new, ‘small volume’ in situ dating technique to provide contextual, relatively rapid and accurate age information is a substantial improvement in reconnaissance-style studies of geological areas with scarce geochronological age information.

Exceptionally well-preserved pillow lavas and inter-pillow hyaloclastites from the Barberton Greenstone Belt in South Africa contain textural, geochemical, and isotopic biomarkers indicative of microbially mediated alteration of basaltic glass in the Archean. The textures are micrometer-scale tubular structures interpreted to have originally formed during microbial etching of glass along fractures. Textures of similar size, morphology, and distribution have been attributed to microbial activity and are commonly observed in the glassy margins of pillow lavas from in situ oceanic crust and young ophiolites. The tubes from the Barberton Greenstone Belt were preserved by precipitation of fine-grained titanite during greenschist facies metamorphism associated with seafloor hydrothermal alteration. The presence of organic carbon along the margins of the tubes and low d 13 C values of bulk-rock carbonate in formerly glassy samples support a biogenic origin for the tubes. Overprinting relationships of secondary minerals observed in thin section indicate the tubular structures are pre-metamorphic. Overlapping metamorphic and igneous crystallization ages thus imply the microbes colonized these rocks 3.4–3.5 Ga. Although, the search for traces of early life on Earth has recently intensified, research has largely been confined to sedimentary rocks. Subaqueous volcanic rocks represent a new geological setting in the search for early life that may preserve a largely unexplored Archean biomass. D 2005 Elsevier B.V. All rights reserved.

Evidence of microbially-mediated alteration of basaltic glass is preserved in originally glassy basalts (rims of pillow lavas, hyaloclastite breccias, and chilled margins of dykes) from the well-preserved 1.95Ga Jormua ophiolite complex (JOC) of Northeastern Finland. Although textural evidence of microbial alteration is commonly observed in relic glass from recent oceanic crust and some ophiolites, these textures have been destroyed during greenschist to lower amphibolite facies regional metamorphism and deformation of the JOC. However, another robust biosignature is found in the generally depleted d 13 C values of disseminated carbonate extracted from originally glassy basalts, relative to crystalline samples. The same distribution of d 13 C values is well documented in samples from recent oceanic crust as well as ophiolites of Phanerozoic age. This characteristic contrastinthe d 13 Cvaluesofdisseminatedcarbonateisinterpretedtoresultfrommicrobe-inducedfractionationduringoxidation of organic matter. X-ray mapping of initial alteration zones has identified residual carbon associated with highly-concentrated S that is unrelated to carbonate. We attribute these biosignatures to microbially-mediated alteration of originally glassy material prior to ophiolite emplacement. © 2004 Elsevier B.V. All rights reserved.