ALBERT

Description: The stable isotope ratios of various elements (e.g., H, C, O, S) have numerous uses to improve the understanding of the genesis and formation of hydrothermal and magmatic ore deposits, as well as having various applications to mineral exploration. However, stable isotope data has not been routinely collected during mineral exploration for various reasons related to cost per sample, the speed at which analytical data can be collected, and uncertainty regarding the benefits of stable isotope measurements to mineral exploration. Recent advances in analytical technologies which utilize infrared absorption spectroscopy (e.g., off-axis integrated cavity output spectroscopy [OA-ICOS]) mean that stable isotope data can now be collected in far greater quantities than has been previously possible. This advance in analytical technology, which allows for significantly more rapid and less expensive stable isotope analyses, has significant implications for the way in which stable isotope data can be collected and utilized during mineral exploration. Potential applications of stable isotope ratios to mineral exploration include delineating property- to district-scale stable isotope alteration halos and identifying "blind deposits" at depth, as well as vectoring toward new deposits within endowed districts. Stable carbon and oxygen isotope data collected using OA-ICOS from carbonate rocks surrounding the Screamer Carlin-type gold deposit in Nevada demonstrate that stable isotope alteration can be detected at distances of up to (and potentially more than) 3 km laterally around mineralization.

Description: The geochemistry of pyroclasts sampled from four volcanoes along the Kermadec arc in the SW Pacific is used to investigate the genesis of silicic magmas in a young (〈2 Myr), archetypical intra-oceanic arc setting. Raoul, Macauley and Raoul SW volcanoes in the northern Kermadec arc, and Healy volcano in the southern Kermadec arc have all recently erupted dacitic to rhyolitic crystal-poor pumice. In addition to whole-rock analyses, we present a detailed study of mineral and glass chemistries to highlight the complex structure of the Kermadec magmatic systems. Major and trace element bulk-rock compositions mostly fall into relatively narrow compositional ranges, forming discrete groups by eruption for Raoul, and varying with relative crystal contents for Healy. In contrast, pumices from Macauley cover a wide range of compositions, between 66 and 72·5 wt % SiO 2 . At all four volcanoes the trace element patterns of pumice are subparallel to both those of previously erupted basalts and/or whole mafic blebs found both as discrete pyroclasts and as inclusions within pumices. Pb and Sr isotopic compositions have limited ranges within single volcanoes, but vary considerably along the arc, being more radiogenic in the southern volcanoes. Distinctive crystal populations and zonation patterns in pumices, mafic blebs and plutonic xenoliths indicate that many crystals did not grow in the evolved magmas, but are instead mixed from other sources including gabbros and hydrothermally altered tonalites. Such open-system mixing is ubiquitous at the four volcanoes. Oxygen isotope compositions of both phenocrysts (silicic origin) and xenocrysts or antecrysts (mafic origin) are typical for mantle-derived melts. Whole-rock, glass and mineral chemistries are consistent with evolved magmas being generated at each volcano through ~70–80% crystal fractionation of a basaltic parent. Our results are not consistent with silicic magma generation via crustal anatexis, as previously suggested for these Kermadec arc volcanoes. Although crystallization is the dominant process driving melt evolution in the Kermadec volcanoes, we show that the magmatic systems are open to contributions from both newly arriving melts and wholly crystalline plutonic bodies. Such processes occur in variable proportions between magma batches, and are largely reflected in small-scale chemical variations between eruption units.

Description: In this article we show how to model a range of notions in the context of delegation and revocation applied to security scenarios. We demonstrate how a range of delegation–revocation models and policies may be represented in pictorial form and formally represented in terms of reactive Kripke models and a first-order policy specification language. We translate first-order representations of our reactive Kripke models into an equivalent Answer Set Programming form that enables users to apply flexibly well-defined definitions of predicates to represent their requirements in terms of delegation–revocation policy specification.

Description: Bilateral animals are featured by an extremely compact mitochondrial (mt) genome with 37 genes on a single circular chromosome. The human body louse, Pediculus humanus , however, has its mt genes on 20 minichromosomes. We sequenced the mt genomes of two other human lice: the head louse, P. capitis , and the pubic louse, Pthirus pubis . Comparison among the three human lice revealed the presence of fragmented mt genomes in their most recent common ancestor, which lived ~7 Ma. The head louse has exactly the same set of mt minichromosomes as the body louse, indicating that the number of minichromosomes, and the gene content and gene arrangement in each minichromosome have remained unchanged since the body louse evolved from the head louse ~107,000 years ago. The pubic louse has the same pattern of one protein-coding or rRNA gene per minichromosome (except one minichromosome with two protein-coding genes, atp6 and atp8 ) as the head louse and the body louse. This pattern is apparently ancestral to all human lice and has been stable for at least 7 Myr. Most tRNA genes of the pubic louse, however, are on different minichromosomes when compared with their counterparts in the head louse and the body louse. It is evident that rearrangement of four tRNA genes (for leucine, arginine and glycine) was due to gene-identity switch by point mutation at the third anticodon position or by homologous recombination, whereas rearrangement of other tRNA genes was by gene translocation between minichromosomes, likely caused by minichromosome split via gene degeneration and deletion.

Description: New zircon U–Th model-age and trace element datasets are presented from Taupo volcano (New Zealand), which are used to investigate the timescales and broad-scale magmatic processes involving zircon crystallization after the caldera-forming 25·4 ka Oruanui supereruption. Detailed 14 C-based chronologies and controls on vent locations allow the timing and location of post-caldera eruptions to be spatially and temporally constrained to an extent not possible for any other supervolcano. After ~5 kyr of post-Oruanui quiescence, Taupo erupted three dacitic units, followed by another ~5 kyr break, and then a sequence of rhyolitic units in three subgroups (SG1–SG3) from 12 ka onwards. Despite overlapping vent sites and crustal source domains between the Oruanui and post-Oruanui eruptions, U–Th zircon model ages in Taupo SG1 rhyolites (erupted from 12 to 10 ka) indicate only minor inheritance of crystals from the Oruanui magma source. Post-Oruanui model-age spectra are instead typically centred close to eruption ages with subordinate older pre-300 ka equiline grains in some units. U–Pb dating of these older grains shows that both 300–450 ka plutonic-derived and pre-100 Ma greywacke basement-derived zircons are present. The former largely coincide in age with zircons from the 350 ka Whakamaru eruption products, and are dominant over greywacke in young units that were vented within the outline of the Whakamaru caldera. Despite multiple ages and vent sites, trace element compositions are broadly similar in zircons, regardless of their ages. However, a small subset of zircons analysed from SG1 rhyolite (Units B and C) have notably high concentrations of U, Th, P, Y + (REE) 3+ and Nb but with only minor variations in Hf and Ti. SG2 zircons typically have higher Sc contents, reflecting large-scale changes in melt chemistry and crystallizing mineral phases with time. The age spectra indicate that most Oruanui zircons were removed by thermally induced dissolution immediately following the supereruption. U–Th ages from single post-Oruanui eruptions show consistent inheritance of post-Oruanui grains with model ages that centre between the temporally separated but geographically overlapping eruption groups, generating model-age modes. Within the statistical limitations of the isotopic measurements, we interpret these repeated modes to be significant, resulting from incorporation of crystal populations from cyclic post-Oruanui periods of magmatic cooling and crystallization, acting within a crustal protolith chemically independent of that which was dominant in the Oruanui system. These periods of cooling and crystallization alternate with times of rejuvenation and eruption, sometimes demonstrably accompanying syn-eruptive regional rifting and mafic magma injection. Not only were the processes that developed the supersized Oruanui magma body rapid, but this huge magma system was effectively reset and rebuilt on a comparably short timescale.

Description: Past glacial-interglacial climate transitions were accompanied by millennial-scale pulses in atmospheric CO 2 that are widely thought to have resulted from the release of CO 2 via the Southern Ocean. However, direct proxy evidence for a Southern Ocean role in regulating past ocean-atmosphere CO 2 exchange is scarce. Here we use combined radiocarbon and neodymium isotope measurements from the last deglaciation to confirm greatly enhanced overturning and/or air-sea exchange rates relative to today, in particular during the Bølling-Allerød warm interval. We show that this deglacial pulse in ocean ventilation was not driven by the North Atlantic overturning alone, and must have involved an increase in the ventilation of southern-sourced deep waters. Our results thus confirm the removal of a physical and/or dynamical barrier to effective air-sea (CO 2 ) exchange in the Southern Ocean during deglaciation, and highlight the Antarctic region as a key locus for global climate/carbon-cycle feedbacks.

Description: Blood-sucking lice of humans have extensively fragmented mitochondrial (mt) genomes. Human head louse and body louse have their 37 mt genes on 20 minichromosomes. In human pubic louse, the 34 mt genes known are on 14 minichromosomes. To understand the process of mt genome fragmentation in the blood-sucking lice of mammals, we sequenced the mt genomes of the domestic pig louse, Haematopinus suis , and the wild pig louse, H. apri , which diverged from human lice approximately 65 Ma. The 37 mt genes of the pig lice are on nine circular minichromosomes; each minichromosome is 3–4 kb in size. The pig lice have four genes per minichromosome on average, in contrast to two genes per minichromosome in the human lice. One minichromosome of the pig lice has eight genes and is the most gene-rich minichromosome found in the sucking lice. Our results indicate substantial variation in the rate and extent of mt genome fragmentation among different lineages of the sucking lice.

Description: Many Carlin-type gold deposits in northern Nevada are found adjacent to steeply dipping faults that channeled hydrothermal fluids upward into mineralized regions. However, some Carlin deposits comprise gently dipping tabular ore zones lacking any obvious large, steeply dipping, feeder structure beneath them. The goal of this paper is to test whether fluid flow into such ore zones also involved largely vertical upwelling, or whether lateral fluid flow, particularly along low-angle fault structures, may have played a significant role in their formation. In this study we use carbon and oxygen isotopes in conjunction with trace element geochemistry to investigate pathways taken by hydrothermal ore-forming fluids into the tabular subhorizontal ore zones of the Pipeline deposit, a giant carbonate rock-hosted Carlin-type deposit in Nevada. We sampled deep drill holes within, below, and to the side of the main ore zone to assess the extent of lateral versus vertical fluid flow up to 600 m below mineralization. The main ore zone at the Pipeline deposit is dominated by carbonate host rocks having 18 O and 13 C values that are depleted in the heavier 18 O and 13 C isotopes compared to global background values for rocks of the same age. Depletion results from the progressive buffering of the rock by an infiltrating auriferous hydrothermal fluid. There is significant heterogeneity in the spatial pattern and relative degree of 18 O and 13 C depletion through the ore zone, most likely reflecting multiple flow paths with different total integrated fluid fluxes, path lengths, rates of fluid cooling, and possibly fluid mixing. A lack of a pervasive reduction in 18 O and 13 C values, and low concentrations of trace elements in the rocks immediately beneath the main ore zone indicate that the deposit was not a product of large-scale vertical upwelling of auriferous hydrothermal fluid directly into the mineralized region. Rather, flow was focused along preexisting low-angle thrusts, particularly the Abyss fault, with fluids flowing laterally underneath and then up into the area of the main ore zone. Enhanced permeability along these low-angle structures most likely derived from fault reactivation and the generation of fracture networks in damage zones peripheral to a relatively impermeable fault core. Such reactivation would have required suprahydrostatic fluid pressures, relatively shallow crustal depths, and a lack of more optimally oriented, high angle faults (〉50°) that would otherwise have preferentially failed and focused fluid flow steeply upward.

Description: The duration of hydrothermal activity required to form ore deposits is poorly constrained. We demonstrate that thermochronology data, coupled with thermal modeling, can be used to constrain the duration of hydrothermal fluid flow. Apatite fission-track (AFT) thermochronology data define a conductive halo around an Eocene hydrothermal system that formed the Betze-Post gold deposit on the northern Carlin trend in Nevada. The premineralization Goldstrike stock acted as an essentially impermeable side to the auriferous Carlin hydrothermal system. The hydrothermal fluid conductively heated the intrusion over the time that it flowed past it. To derive first-order estimates for the maximum duration of this flow we numerically modeled one-dimensional conductive heat flow into the intrusion and used the results to forward model ensuing AFT annealing. Modeled levels of annealing were compared to AFT dates and track length data measured across the intrusion. Our results indicate that the episode of main ore-stage hydrothermal fluid flow (mean temperature of 200°C) that formed the ~1,150 metric ton (t) Betze-Post gold deposit had a maximum duration of 〈15 to 45 ka. The average gold flux over this period was ~80 to 30 kg yr –1 , comparable to that measured in the deep reservoirs of several modern geothermal fields. Conservative estimates of gold concentration in the main ore-stage fluids imply that fluid upflow rates and total advective heat flow were also comparable to modern geothermal systems. This suggests that the most important factors for generating the large gold deposits of the northern Carlin trend were a large and/or continuous source of gold, and a very efficient means of removing it from the fluid, rather than the hydrologic system itself. The short duration of main ore-stage fluid flow is unlikely to represent a steady-state convective system. Instead, it most likely reflects a transient period of flow following slip and permeability generation along the steeply dipping Post-Genesis fault system that hosts many of the deposits along the northern Carlin trend. A sudden increase in the permeability of a fault may have led to a transitory period of peak fluid temperature as the fault initially tapped meteoric fluid that had resided at depth and had thermally equilibrated with the host rocks. With continued convection the flow drew cooler, less rock-buffered meteoric water down from higher in the system.