Constraining the dark matter annihilation cross-section with Cherenkov telescope observations of dwarf galaxies

The presence of dark matter in the halo of our Galaxy could be revealed through indirect detection of its annihilation products. Dark matter annihilation is one possible interpretation of the recently measured excesses in positron and electron fluxes, provided that boost factors of the order of 10³ or more are taken into account. Such boost factors are actually achievable through the velocity-dependent Sommerfeld enhancement of the annihilation cross-section. Here, we study the expected γ-ray flux from two local dwarf galaxies for which Cherenkov telescope measurements are available, namely Draco and Sagittarius. We use recent stellar kinematical measurements to model the dark matter haloes of the dwarfs and the results of numerical simulations to model the presence of an associated population of subhaloes. We incorporate the Sommerfeld enhancement of the annihilation cross-section. We compare our predictions with the observations of Draco and Sagittarius performed by MAGIC and HESS, respectively, and derive exclusion limits on the effective annihilation cross-section. We also study the sensitivities of Fermi and of the future Cherenkov telescope array to cross-section enhancements. We find that the boost factor due to the Sommerfeld enhancement is already constrained by the MAGIC and HESS data, with enhancements greater than ∼10⁴ being excluded.     

Monte Ollasteddu, a new gold discovery in the Variscan basement of Sardinia (Italy): first isotopic (40Ar−39Ar, Pb) and fluid inclusion data

The Monte Ollasteddu deposit represents a major gold discovery in the Variscan basement of southeastern Sardinia. Gold occurs in late-Variscan extensional brittle structures hosted by meta-volcanic, and subordinately meta-sedimentary, rocks. The vein mineralogy is dominated by quartz; arsenopyrite is the main sulphide. Reconnaissance ⁴⁰Ar–³⁹Ar dating gives ages around ∼260 Ma on K-feldspar from mineralized veins, whereas metamorphic white mica from the host rock gives ages clustering at ∼307 Ma. The best age estimate for biotite from a nearby leucogranite body is 286.3±2.2 Ma. The Pb isotope signature of ore and gangue minerals is entirely consistent with literature data for Variscan deposits of Sardinia, and for European Variscan gold deposits. Fluid inclusion data point to the presence of both CO₂-bearing and CO₂-free fluids, with homogenization temperatures ranging from 220 to 415°C, with low-to-moderate salinities (0.4–6.2 wt% NaCl equivalent). Monte Ollasteddu shows several features similar to European Variscan gold deposits; however, the age of mineralization might post-date granitoid intrusion by as much as 30 Ma, being instead coeval with very late calc-alkaline basaltic dykes, marking the transition to a post-orogenic, pre-Tethyan geodynamic setting. Electronic Supplementary Material Supplementary material is available for this article at     

Source of metals in metamorphic ore-forming processes in the Apuane Alps (NW Tuscany,Italy): Constraints by Pb-isotope data

Summary A total of 19 samples of sulfides, barite and country rocks from three important deposits of the Apuane Alps district (Bottino, Pollone and Monte Arsiccio) were analyzed for Pb-isotopic compositions. Ore lead shows a fairly homogeneous isotopic signature (206/204: 18.2-18.4; 207/204 15.7; 208/204: 38.5-38.6), defining a high , high W province suggestive of an evolution in a crustal environment since at least the Middle Proterozoic. Pb-Pb model age of the ores is in the order of 350 Ma, in gross agreement with the Lower-Middle Paleozoic age assigned to most country rocks. The present-day Pb-isotope ratios of presumed exhalative tourmalinites associated with the Bottino deposit and of other country rocks from mineralized areas are also similar. Moreover, most of these rocks show relatively high total Pb contents (> 70 ppm). HCl-soluble lead in these samples also has a roughly similar isotopic signature. In contrast, rock samples collected at greater distances from mineralized bodies have lower Pb concentrations (< 10 ppm) and more radiogenic 206/204 and 208/204 ratios (18.6 to 18.9 and 38.9 to 39.3 respectively). HCl-soluble lead in these samples has distinctly lower 208/204, and to a lesser extent 206/204 ratios (38.6 to 38.9 and 18.5 to 18.9 respectively). In agreement with previously established genetic models, these results may be interpreted in terms of a major episode of lead extraction in the Paleozoic, possibly in association with exhalative tourmalinites, followed by remobilization and reconcentration in vein mineralization during the Apenninic orogeny. The isotopic signature of country rocks in mineralized areas may be ascribed to a Pb-isotope halo effect induced by metamorphism. When compared with Pb-isotope data from deposits of the southern Tuscany mining district, the ore lead in Apuane Alps exhibits similar isotopic patterns, but with lower 208/204 and 206/204 ratios. This fact suggests for the two districts source(s) with similar evolutions of their U/Pb and Th/Pb ratios, but distinctly different times of Pb extraction.

---

Die Herkunft von Metallen bei metamorphen erzlagerstättenbildenden Prozessen in den Apuanischen Alpen (NW Toskana, Italien): Eigebnisse von Pb-Isotopendaten

Zusammenfassung In den Apuanischen Alpen (NW Toskana) treten prämetamorphe, schichtförmige Fe-Ba Erzlagerstätten in grünschieferfaziell metamorphen Serien sedimentären und vulkanosedimentären Ursprungs auf (e.g. Pollone und Monte Arsiccio), die von syn- bis spätkinematisch gebildeten, diskordanten Vererzungen begleitet werden. Ein Gangsystem mit Quarz, Karbonat und Pb-Zn-Ag (Bottino) wird von einem stratiformen Turmalinithorizont mit erhöhten Metallgehalten begleitet.Um die Frage eines metamorphogenen Ursprungs der gangförmigen Vererzungen im Gefolge der Appenninischen Metamorphose (Oligozän-Miozän) und die vermutete Herkunft der Metalle aus den schichtförmigen Lagerstätten und Metallanreicherungen zu überprüfen, wurden Pb-Isotopenuntersuchungen an Sulfiden, Bariten, Turmaliniten und Nebengesteinen durchgeführt. Das Erzblei aus stratiformen wie auch gangförmigen Lagerstätten zeigt nur geringe Variationen der Pb-isotopenverhältnisse und ist innerhalb eines Vorkommens homogen (206/204: 18.2-18.4; 207/204: 15.68; 208/204: 38.538.6). Seine relativ hohen - and W-Werte weisen auf eine Bleientwicklung in kontinentalem Krustenmilieu, spätestens seit dem mittleren Proterozoikum hin. Die 207/206 Modellalter von ca. 350 Ma stimmen größenordnungmäßig mit dem vermuteten paläozoischen Alter des Nebengesteins überein, sind aber für die gangförmigen tertiären Vorkommen zu hoch. Baryt-, Turmalinit- und Gesamtgesteinsproben aus der Nähe der Lagerstätten zeigen alle ähnliche Pb-Isotopenverhältnisse wie die Sulfide. Die Gesteine weisen hohe Pb-Gehalte von > 70 ppm auf. In größerer Entfernung zu den Lagerstätten sind die Pb-Gehalte mit < 10 ppm deutlich niedriger und die Pb-Isotopenverhältnisse sind radiogener (206/204: 18.8-18.9; 208/204: 38.9-39.3). Ihr HCl-1ösliches Blei ist hingegen weniger radiogen.Die Resultate stützen die neueren Ansichten, daß es im Paläozoikum zur Bildung von exbalativen Turmaliniten verbunden mit einer Metallanreicherung und von stratiformen Fe-Ba-Lagerstätten kam. Während der appenninischen Metamorphose wurden die Metalle remobilisiert, und es kam zur Bildung von gangförmigen Vorkommen und Lagerstätten. Die hohen Pb-Gehalte der Nebengesteine und die Isotopensignatur des HC1-löslichen Bleis deuten auf eine metamorphogene Halo-Bildung. Die Bleiisotopen von jungtertiären Erzen aus der südlichen Toskana sind im Vergleich mit dem apuanischen Erzblei radiogener. Sie weisen aber dieselben hohen - und W-Werte auf. Das heißt, das Blei stammt aus Gesteinen, die eine qualitativ wie auch quantitativ ähnliche Entwicklung bezüglich der U/Pb und Th/Pb Verhältnisse durchlaufen haben wie jene, die das Blei der apuanischen Lagerstätten geliefert haben.

---

---

This paper was presented at the IGCP 291 Project Symposium Metamorphic Fluids and Mineral Deposits, ETH Zürich, March 21–23, 1991.     

A sulfur isotope study on pyrite deposits of Southern Tuscany,Italy

The S-isotope composition (δ³⁴S_CDT) of 213 samples of sulfides, sulfates and native sulfur from the pyrite mineralizations of southern Tuscany and associated country rocks were determined. The sulfur isotopic composition of pyrite is quite homogeneous and similar for all studied ore bodies, with an average δ³⁴S value near +9,5‰. Pyrite disseminated within the Filladi di Boccheggiano formation, and thought to be authigenic, shows a much larger range of δ³⁴S values (-13.1 to +14.5‰). The isotopic compositions of other sulfides associated with pyrite in the deposits show that isotopic equilibrium among sulfides was approached on a regional scale, but seldom fully attained. Isotopic data suggest that sedimentary marine sulfate was the ultimate source of sulfur in ores. Sulfates (mostly anhydrite) from the sulfate-carbonate lenses associated with both the Filladi di Boccheggiano and the Calcare Cavernoso formations also have similar and homogeneous compositions (average δ³⁴S=+15–16‰). Coexisting sulfates and sulfides are not in isotopic equilibrium. In the light of the isotopic data, among the many proposed genetic models for the largest stratabound pyrite bodies the two following alternatives appear the most likely: 1) in agreement with recently suggested hypotheses, the ore bodies are older than the emplacement of the Mio-Pliocenic granitoids in the area, and are probably hydrothermal-sedimentary in origin, coeval with associated country rocks; 2) the ore bodies were formed as a consequence of bacterial reduction of anhydrite in low-temperature convection systems related to the early stages of the Mio-Pliocenic thermal anomaly. In both cases, the emplacement of the Mio-Pliocenic granitoids caused metamorphism and remobilization of the pre-existing ores, producing smaller discordant mineralized bodies.     

Release of toxic elements from rocks and mine wastes at the Furtei gold mine (Sardinia, Italy)

The Furtei gold mine in Sardinia (Italy) exploits a volcanic-hosted high-sulphidation epithermal deposit. Large amounts of materials derived from exploitation are present in open pits, waste rock dumps and cyanidation tailings impoundment. Mineralized rocks in outcrops and waste dumps contain significant amounts of sulphides (mainly pyrite and enargite). These materials have a high potential for acid drainage generation and release of toxic elements (notably Cu and As, but also Al, Ni, Co and Cd) as pointed out by laboratory leaching tests and in agreement with chemical composition of waters draining the mining area, that show pH as low as 2, up to 180 mg/L Cu, up to 5 mg/L As, and up to 788 mg/L Al. On the other hand, leaching solutions and waters interacting with mineral assemblages of the propylitic alteration zone (mainly composed of chlorite, quartz, and calcite, with relic magmatic plagioclase) show higher pH, and lower metal loads. Leachates from cyanidation tailings show variable pH (between 6.2 and 9.7, depending on sulphide content in tailings); cyanide concentration varies between 110 µg/L and about 3 mg/L, whereas contents of toxic elements in leachates are, with the exception of Hg, within the limits of Italian regulations for non-dangerous industrial wastes. Reclamation plans provide for confinement of tailings within specific repositories. This measure should effectively reduce the environmental impact of these materials. Reclamation plans should also include an adequate management of other high-sulphide wastes.     

Space-borne global astrometric surveys: the hunt for extrasolar planets

The proposed global astrometry mission GAIA , recently recommended within the context of ESA's Horizon 2000 Plus long-term scientific programme, appears capable of surveying the solar neighbourhood within ∼200 pc for the astrometric signatures of planets around stars down to the magnitude limit of V =17 mag, which includes late M dwarfs at 100 pc.
Realistic end-to-end simulations of the GAIA global astrometric measurements have yielded the first quantitative estimates of the sensitivity to planetary perturbations and of the ability to measure their orbital parameters. Single Jupiter-mass planets around normal solar-type stars appear detectable out to 150 pc ( V ≤12 mag) with probabilities ≥50 per cent for orbital periods between ∼2.5 and ∼8 yr, and their orbital parameters are measurable with better than 30 per cent accuracy to about 100 pc. Jupiter-like objects (same mass and period as our giant planet) are found with similar probabilities out to 100 pc.
These first experiments indicate that the GAIA results would constitute an important addition to those that will come from the other ongoing and planned planet-search programmes. These data combined would provide a formidable testing ground on which to confront theories of planetary formation and evolution.     

Some Aspects of Relativistic Astrometry from Within the Solar System

In this article we outline the structure of a general relativistic astrometric model which has been developed to deduce the position and proper motion of stars from 1 µarcsecond optical observations made by an astrometric satellite orbiting around the Sun. The basic assumption of our model is that the Solar System is the only source of gravity, hence we show how we modeled the satellite observations in a many-body perturbative approach limiting ourselves to the order of accuracy of (v/c)². The microarcsecond observing scenario outlined is that for the GAIA astrometric mission.     

The nature of the fluids associated with the Monte Rosa gold district, NW Alps, Italy

Recent O-isotope and fluid inclusion studies have provided evidence on the nature of the fluids associated with the late-Alpine quartz-gold deposits of the Monte Rosa district. The most abundant inclusions in quartz from these deposits contain a low salinity aqueous fluid (about 2% to 10% wt. NaCl eq.), and a CO₂ phase (usually less than 20% mol), in places with minor methane. CO₂ densities and total homogenization temperatures vary widely throughout the district, reflecting diverse conditions of trapping (P = 1 to 3 kb, T = 300° to 450°C). At Miniera dei Cani, unmixing between CO₂-rich and H₂O-rich fluids possibly occurred. A second type of inclusion contains an aqueous brine without recognizable CO₂, and is especially abundant at Val Toppa. O-isotope studies suggest that fluids were largely equilibrated in a metamorphic environment. It is concluded that the gold-related fluids in the district were mainly of a metamorphic nature; at Val Toppa, both isotopic and fluid inclusion data point to contributions of unexchanged meteoric waters. Mechanisms of gold transport and precipitation are less contrained. A possible model involves transport of gold as bisulfide complexes, and precipitation due to one or more of the following processes: decrease of sulfur activity due to precipitation of sulfides, wall-rock reaction, cooling/dilution, and/or fluid unmixing.