Albite ± Actinolite-Altered Porphyry Dykes in Archean Gold Deposits of the Boulder Lefroy-Golden Mile Fault System, Yilgarn Craton, Western Australia: Petrography, Chronology, and Comparison to Canadian Albitites

The Boulder Lefroy-Golden Mile fault system in the Archean Yigarn Craton is the most productive gold-mineralized structure in Australia (>2300 t Au). The New Celebration deposit (51 t Au) is part of a group of hematite- and anhydrite-bearing mesothermal deposits and Fe-Cu-Au skarns associated with monzodiorite-tonalite intrusions in the strike-slip fault system. Ore-grade biotite-carbonate and late sericite-carbonate-alkali feldspar replacement is bound to the contacts of a felsic (low Cr, Ni, V) quartz-plagioclase porphyry dyke dated at 2676 ± 7 Ma. The sodic-potassic alteration of the felsic boudinaged dyke contrasts with the albite-actinolite alteration in the adjacent mafic (high Cr, Ni, V) plagioclase porphyry dated at 2662 ± 4 Ma, although both share the same sulfide-oxide assemblage: pyrite ± chalcopyrite, magnetite ± hematite. The younger porphyry locally crosscuts foliation and is bordered by post-kinematic actinolite-pyrite selvages overprinting talc-chlorite-phlogopite-dolomite schist. It contains auriferous pyrite (70 ppb Au; 610 ppb Ag) where sampled for zircon U-Pb chronology at +224 m elevation. Above the sample site, the dyke was mined as gold ore (1–6 g/t Au) at +300–350 m. Temperature estimates based on actinolite-albite pairs (300–350 °C) agree with the fluid inclusion trapping temperature of main-stage auriferous veins (330 ± 20 °C). These relationships are interpreted to indicate syn-mineralization emplacement. Gold-related albite-altered porphyry dykes (albitites) also occur in the world-class Hollinger-McIntyre (986 t Au) and Kerr Addison-Chesterville deposits (336 t Au), Abitibi greenstone belt, Canada.

Bulk Viscous Damping of Density Oscillations in Neutron Star Mergers

In this paper, we discuss the damping of density oscillations in dense nuclear matter in the temperature range relevant to neutron star mergers. This damping is due to bulk viscosity arising from the weak interaction “Urca” processes of neutron decay and electron capture. The nuclear matter is modelled in the relativistic density functional approach. The bulk viscosity reaches a resonant maximum close to the neutrino trapping temperature, then drops rapidly as temperature rises into the range where neutrinos are trapped in neutron stars. We investigate the bulk viscous dissipation timescales in a post-merger object and identify regimes where these timescales are as short as the characteristic timescale ∼10 ms, and, therefore, might affect the evolution of the post-merger object. Our analysis indicates that bulk viscous damping would be important at not too high temperatures of the order of a few MeV and densities up to a few times saturation density.

Two methods for temperature measurement in super-hot geothermal systems based on synthetic fluid inclusions

<p>Super-hot geothermal systems are promising targets for near future geothermal exploration either for direct fluid exploitation or as potential reservoirs of Enhanced Geothermal Systems. Although reservoir conditions assessment is crucial for the evaluation of the geothermal resources, temperature measurement is still a major challenge in super-hot systems since their extreme conditions (i.e. very-high temperature, possible presence of aggressive fluids) preclude the use of conventional logging methods. During two EU projects (i.e. IMAGE (FP7) and the DESCRAMBLE (H2020)) two methods based on fluid inclusions synthesis were developed for in-situ measurements of very high-temperature (i.e. ≥400°C). Synthetic fluid inclusions are produced by trapping fluid within pre-fractured minerals, free of natural fluid inclusions, placed in a gold capsule together with an aqueous solution. Laboratory tests showed that fluid inclusions in quartz form in a relatively short time (down to 48 hours) if an alkaline-saline solution (0.4 M of NaOH + 10 to 20 wt.% NaCl) is used. In the first method synthetic fluid inclusions in quartz chips are produced within gold capsules placed inside a micro-reactor containing a volume of de-ionised water in such amount that the density of water in the micro-reactor has the critical value. Under these conditions, the trapping temperature of synthetic inclusions can be computed by the intersections between inclusion isochores, determined through microthermometry, and the critical isochore of water. Thus, if the micro-reactor is kept for at least 48 hours at the depth of measurement in a geothermal well, the trapping temperature of fluid inclusions formed in capsules would correspond to the well temperature at that depth. The second method consists in the production of fluid inclusions in gold capsules in direct contact with the environment of the geothermal well. Under the conditions of the super-hot systems characterized by relatively low pressure (such as the deepest part of the Larderello-Travale geothermal system in Italy), pressure-temperature conditions would cause fluid immiscibility in the gold capsule (i.e. the saline-alkaline fluid splits in a high-salinity liquid and a low-salinity vapor). In this case, the trapping temperature of both high-salinity and low-salinity inclusions is equal to their homogenization temperature. Laboratory tests demonstrated that the trapping temperatures of fluid inclusions produced by both methods can provide a good estimate of the experimental temperatures. Two field tests following the first method were performed in geothermal wells of Krafla (Iceland) and Larderello-Travale (Italy) characterized by measured temperature at the test depth of 336°C and 249°C, respectively. These tests showed that synthetic fluid inclusions trapping temperatures closely approach the temperature measured using conventional methods. Finally, a field test was also attempted in the Venelle 2 (Larderello-Travale) geothermal well characterized by super-hot conditions. Trapping temperatures of fluid inclusions formed at 2900 below ground level (b.g.l.) by both methods resulted compatible with independent measurement by an electronic device which gave 444°C at 2810 m b.g.l..</p><p>The research leading to these results has received funding from the EC Seventh Framework Programme under grant agreement No. 608553 (Project IMAGE) and from the Horizon 2020 Programme under grant agreement 640573 (Project DESCRAMBLE).</p>

Study of Heat and Mass Transfer in Electroosmotic Flow of Third Order Fluid through Peristaltic Microchannels

An analysis is carried out to evaluate the effects of heat and mass transfer in an electro-osmotic flow of third order fluid via peristaltic pumping. Solutions are derived for small wave number and Peclet number. The emerging non-linear mathematical model is solved analytically and compared numerically by the built-in scheme of working software. The table is inserted for shear stress distribution and a graph for comparison of solution techniques and accuracy of obtained results. The effects of various parameters of interest on pumping, trapping, temperature, heat transfer coefficient, and concentration distribution have been studied graphically. Electro-osmotic exchange of energy and mass has a role in reservoir engineering, chemical industry, and in micro-fabrication technologies.

FLUID INCLUSION STUDIES OF THE EPITHERMAL QUARTZ VEINS FROM SUALAN PROSPECT, WEST JAVA, INDONESIA

Sualan prospect is located at Talegong Sub-district of Garut Regency, West Java, Indonesia. The area constitutes calc-alkaline volcanic and volcaniclastic rocks of Tertiary age. The rocks have experienced regional propylitic and argillic alteration. Fluid inclusions from quartz veins were studied in order to constrain the nature, characteristics and evolution of fluids. Microthermometric measurements on fluid inclusion were carried out by freezing and heating experiment. Temperatures of homogenization (Th) and final melting of ice (Tm) were measured for primary, liquid-dominated, two-phase inclusions. The values of Th range from 160°C to 210°C and salinities range from 0.35 to 4.96 wt.% NaCl equiv. Formation temperature of the quartz veins are estimated at 180°C and 190°C and paleo-depth of formation are at 80m and 140m, respectively. Microthermometric data indicates that fluid mixing and dilution were important processes during the evolution of hydrothermal system. Based on fluid inclusion types, microthermometric data, trapping temperature, paleo-depth, texture of quartz and hydrothermal alteration types, quartz veins from prospect were developed under epithermal environment. Keywords: Quartz vein, fluid inclusions, microthermometry, salinities, formation temperature, paleo-depth, epithermal, Sualan prospect.

CO2 fluid inclusions in ultramafic xenoliths from the Iblean Plateau, Sicily, Italy

The Iblean Plateau (Southeastern Sicily, Italy) consists of a thick Meso-Cenozoic carbonate sequence with interbedded volcanic horizons (alkaline and tholeiitic basalts). The alkaline basalts contain ultramafic (peridotites and pyroxenites) and mafic xenoliths. The peridotites are spinel-bearing lherzolites and lherzolitic harzburgites, with porphyroblastic to protogranular texture. Pyroxenites consist of Cr-diopside-bearing and Al-augite-bearing websterites. The mineral chemistry of the nodules indicates temperatures between 700 and 1050°C.Fluid inclusions containing CO2 and (sometimes) various proportions of silicate glass have been studied in olivine, orthopyroxene and clinopyroxene. The secondary inclusions occur as trails of CO2-rich inclusions, often cross-cutting deformation lamellae. The few primary inclusions, generally empty, show clear evidence of decrepitation. Of the 390 inclusions examined, 97% homogenized to the liquid phase (Th → L = −43.9 to +30.9°C); 3% homogenized to the vapour phase (Th → V = + 20.5 to +30.3°C, yelding CO2 densities in the range 0.20–1.13 g/cm3. Assuming a trapping temperature of 1100°C, the corresponding trapping pressure for a pure CO2 system lies in the range 0.6–11.0 kbar, i.e. a depth of ∼2.2 to 42 km.The majority of CO2 trapping events in the xenoliths occurred from 2.2 to 11.0 kbar, with no major trapping events at pressures less than 2.3 kbar, indicating the absence of a shallow magma reservoir below the Iblean Plateau.

Diagenetic palaeotemperatures from aqueous fluid inclusions: re-equilibration of inclusions in carbonate cements by burial heating

Diagenetic palaeotemperatures determined from aqueous fluid inclusions can be affected by re-equilibration during burial heating. Calculations based on the observed behaviour of inclusions in fluorite under external confining pressure allows prediction of the temperatures and depths of burial necessary to initiate re-equilibration of aqueous inclusions in the common size range 40 to 4 µm. Heating of 20° to 60°C over the initial trapping temperature may cause errors of 10° to 20°C in the homogenization temperature. This suggests re-equilibration may cause aqueous inclusions in carbonates to yield a poor record of their low-temperature history, but a useful record of the maximum temperature experienced by the host rock. Previous work suggests inclusions containing petroleum fluids will be less susceptible to re-equilibration.