Modelling of hydrothermal fluid compositions in the crust and upper mantle

Carbon-oxygen-hydrogen (COH) fluids are integral to the formation of many hydrothermal ore deposits (including orogenic gold, graphite), and diamond. Typically, a crustal/upper mantle COH fluid comprises H2O, CO2, CH4, H2, CO, C2H6, and O2. Crustal and upper mantle fluid compositions are constrained by pressure, temperature and redox state, and can be calculated if: (1) A reliable equation of state for fluid mixtures is available for the relevant pressure-temperature conditions is available for the calculation of fugacity coefficients; (2) Reliable thermodynamic variables including enthalpy, entropy and isobaric heat capacity can be obtained. Here, we used the equation of state by Zhang and Duan (2009) in conjunction with the NIST reference dataset to develop a user-friendly Excel spread sheet that allows the calculation of fluid compositions for a pressure-temperature range of > 0.5 kbar and 300-1500°C, respectively. Data manipulation and modelling was achieved with a combination of VBA, Python and SQL scripting and allowed us to validate the model calculations in the Excel spread sheet. Here, we used the equation of state by Zhang and Duan (2009) in conjunction with the NIST reference dataset to develop a user-friendly Excel spread sheet that allows the calculation of fluid compositions for a pressure-temperature range of > 0.5 kbar and 300-1500°C, respectively. Data manipulation and modelling was achieved with a combination of VBA, Python and SQL scripting and allowed us to validate the model calculations in the Excel spread sheet

Large-scale carbon transfer between crust and mantle during supercontinent amalgamation and disruption

Early Cambrian (Pan-African orogeny, ca. 600 Ma) amalgamation of the Gondwana supercontinent through linear hot orogenic belts occurred in Africa and Southern India. These orogenic belts are characterized by ultrahigh temperature (UHT, ca. 1000°C) metamorphic events, which have played a fundamental role in the development and stabilisation of the continents. Granulite and UHT-metamorphism are linked to major episodes of supercontinent amalgamation at least since the late Archean, traces of which having been found in virtually all known supercontinents so far. Depending on the geodynamic setting (continent collision or basin-inversion after lithospheric thinning), the duration of these UHT-episodes is variable, from less than 15 Ma in the recent granulites from Hokkaido (Japan) or Seram (Indonesia) to more than 100 Ma in the long-lived and slowly-cooled Napier complex (Antarctica). But whatever their age or geodynamic settings, minerals of all UHT-granulites worldwide contain a great quantity of primary fluid inclusions, containing dense or superdense (> 1.1 g/cm3) mantle-derived CO2. It shows that, during UHT events, large quantities of mantle-derived CO2 were injected into the continental lower crust. The occurrence of these syn-metamorphic CO2 fluids is so systematic in UHT granulites, that it can be assumed that they played a critical role in the genesis of the extremely high temperatures reached during this metamorphism. In addition to CO2 another fluid is present, namely high-salinity aqueous brines, the source of which can be the sedimentary protolith, the mantle, or both. Both fluids were immiscible at peak metamorphic conditions, but they became miscible and mutually reactive at decreasing pressure and temperature. The amalgamation of the Gondwana supercontinent lasted for more than 400 Ma, starting about 1000 Ma ago in the Trivandrum bloc, India and ending in Eocambrian times (ca. 600 Ma) during the Pan-African orogeny, which affected Africa, Madagascar, Sri-Lanka and Southern India. At this time, the large fluid influx in the lower crust caused instability, leading to breakup and disruption of the supercontinent immediately after its final amalgamation. Elimination of the UHT-granulite fluids occurred rapidly during post-metamorphic uplift, with important consequences for both at local and regional scales. Local scale (10 to 100’s m.) effects are due to the intergranular migration of brines, resulting in the formation of granulite mineral assemblages at the periphery of the main granulite complex (incipient charnockites, granulite “islands”). Less mobile CO2 fluids can only migrate through crustal-scale (10 to 100 km) shear zones, probably caused by major earthquakes. CO2 fluids can either be reduced, resulting in graphite veins, or oxidized, resulting in the quartz-carbonate shear zones found in the vicinity of many granulite terranes

Hydrothermal Au mineralisation caused by fluid decompression and cooling in dilatational cavities

It has been demonstrated that numerous hydrothermal mineralised (Au) quartz veins are related to seismic faulting (Wilkinson and Johnston, 1996; Weatherly and Henley, 2013). Dilatational cavities created during seismic faulting will result in (1) rapid fluid flow from the host rock into the cavities and (2) instantaneous fluid decompression under near-adiabatic and near-isenthalpic conditions (Fig. 1). Adiabatic-isenthalpic decompression of the fluid can either result in fluid heating or cooling (Fig. 1). Calculations demonstrate that for an initial lithostatic fluid pressures of 3-4 kbar and an initial fluid temperature ranging between 400 and 500°C, a CO2-bearing aqueous fluid has the ability to cool more than 100°C during decompression. The decrease in temperature will reduce the metal solubility largely due to its effect on the sulphur and oxygen fugacity

Fluid-rock interaction during high-grade metamorphism: instructive examples from the Southern Marginal Zone of the Limpopo Complex, South Africa

The Southern Marginal Zone of the Limpopo Complex documents strong evidence that CO2-rich (XCO2=0.7–0.9, XH2O= 0.1–0.3) and brine fluids of greatly reduced water activity interacted with cooling metapelitic granulite during the thrust-controlled emplacement at 2.69–2.62 Ga onto the granite-greenstone terrain of the northern Kaapvaal Craton. Interaction of cooling metapelitic granulite with CO2-rich fluids at T 900°C, P > 7.5 kbar. Interaction of hot melt with metapelitic granulite continued until final emplacement in the middle crust (P = 6 kbar, T = 630°C). Brine fluids also initiated shear zone-hosted metasomatism of quartzo-feldspathic gneisses at T between 600 and 900°C and amphibolite-facies lode-gold mineralization. Available data implicate devolatilization of underthrusted greenstone material as the dominant deep crustal source for infiltrating CO2-rich and brine fluids

Short-wavelength infrared spectroscopy as a tool for characterising hydrothermal alteration at the Geita Hill gold deposit, Tanzania

Geita Hill is a world-class gold deposit located in north-western Tanzania and hosted within an ironstone-dominated sedimentary package, intruded by diorite dykes and sills. The host rocks were metamorphosed to greenschist facies and show a complex deformation history comprising early ductile, and late brittle-ductile events. The regional metamorphic assemblage at the deposit is characterised by Bt + Chl + Act + Kfs ± Phg ± Mt ± Po ± Py. The gold-related alteration overprints the regional metamorphism, and manifests as a series of silicification and sulfidation fronts, and/or microfracture and vein networks. Gold is closely associated with secondary pyrite, and occurs as free-Au and gold tellurides. The mineralized vein/microfracture networks contain Bt and Kfs as primary accessory minerals. The mineralising alteration is overprinted by barren, multiphase quartz-carbonate and carbonate-chlorite veins, characterised by the assemblage Ca + Sd + Chl ± Qtz ± Py ± Ba. The close association between gold and biotite in the mineralized vein/microfracture networks and the scarcity of retrograde chlorite makes the Geita Hill deposit ideal to test the change of the biotite short-wave infrared (SWIR) spectral response with the proximity to the gold alteration. SWIR spectra were collected from three well-characterised drill holes that intercepted the gold mineralization and the results were compared to the gold grades. The SWIR data shows that there is a good correlation between the biotite spectral response and the gold grades. The position of the 2250 nm biotite absorption feature is changing systematically as a function of the ore proximity indicating that SWIR can be used to trace gold mineralization and has the potential to be a powerful exploration tool if used in conjunction with well characterised mineral paragenesis

Pengembangan Agrowisata Di Pulau Nusakambangan(agritoarism Dewlopment of Nusakambangan Isi.and)

Penelitian dalam rangka menyusun rencana induk pengembangan pariwisata telah Dilakukan di Pulau Nusakambangan. Salah satu program yang diusulkan dalam Rencana Induk PengembanganPariwisata Pulau Nusakambangan 2001-2005 adalah pengembangan agrowisata. Lokasi yang diperuntukkan menjadi kawasan agrowisata terletak di sekitar bekas Lapas ( Lembaga Pemasyarakatan) Karanganyar dengan luas area sekitar 100ha. Tulisani ni bertujuan untuk menginformasikan kelayakan investasi dalam pengembangan agrowisata di Karang anyar yang merupakan bagian dari pengembangan pariwisata Pulau Nusakambangan. Hasil analisis dengan menggunakan kriteria investasi terhadap Salak pondoh yang diambil sebagai contoh komoditas yang hendak dikembangkan diperoleh hasil : (1) NPV dengan discount factor ( dt) 30% sebesar 5.906.591,8 dan dengan df 26% sebesar 9.450.546,9 (;2 ) IRR : 36,6%; ( 3) Net B / C : 4,45;( 4) ROI = 345,3%; dan (5) BEP untuk produk 21.895,6 k g dan untuk hargaR p 1.112,219/kg. Berdasarkan hasil analisis tersebut disimpulkan salak pondoh termasuk komoditas yang layak investiasi untuk pengembangan agrowisata.D isarankan, k omoditas lain yang direkomendasikan untuk pengembangan agrowisata yang diminati oleh calon investor hendaknya dilakukan analisis seperti metode di atas untuk menilai kelayakani ivestasinya

Spallation reactions. A successful interplay between modeling and applications

The spallation reactions are a type of nuclear reaction which occur in space by interaction of the cosmic rays with interstellar bodies. The first spallation reactions induced with an accelerator took place in 1947 at the Berkeley cyclotron (University of California) with 200 MeV deuterons and 400 MeV alpha beams. They highlighted the multiple emission of neutrons and charged particles and the production of a large number of residual nuclei far different from the target nuclei. The same year R. Serber describes the reaction in two steps: a first and fast one with high-energy particle emission leading to an excited remnant nucleus, and a second one, much slower, the de-excitation of the remnant. In 2010 IAEA organized a worskhop to present the results of the most widely used spallation codes within a benchmark of spallation models. If one of the goals was to understand the deficiencies, if any, in each code, one remarkable outcome points out the overall high-quality level of some models and so the great improvements achieved since Serber. Particle transport codes can then rely on such spallation models to treat the reactions between a light particle and an atomic nucleus with energies spanning from few tens of MeV up to some GeV. An overview of the spallation reactions modeling is presented in order to point out the incomparable contribution of models based on basic physics to numerous applications where such reactions occur. Validations or benchmarks, which are necessary steps in the improvement process, are also addressed, as well as the potential future domains of development. Spallation reactions modeling is a representative case of continuous studies aiming at understanding a reaction mechanism and which end up in a powerful tool.Comment: 59 pages, 54 figures, Revie

Fusion and Binary-Decay Mechanisms in the 35^{35}Cl+24^{24}Mg System at E/A ≈\approx 8 MeV/Nucleon

Compound-nucleus fusion and binary-reaction mechanisms have been investigated for the $^{35}$Cl+$^{24}$Mg system at an incident beam energy of E$_{Lab}$= 282 MeV. Charge distributions, inclusive energy spectra, and angular distributions have been obtained for the evaporation residues and the binary fragments. Angle-integrated cross sections have been determined for evaporation residues from both the complete and incomplete fusion mechanisms. Energy spectra for binary fragment channels near to the entrance-channel mass partition are characterized by an inelastic contribution that is in addition to a fully energy damped component. The fully damped component which is observed in all the binary mass channels can be associated with decay times that are comparable to, or longer than the rotation period. The observed mass-dependent cross sections for the fully damped component are well reproduced by the fission transition-state model, suggesting a fusion followed by fission origin. The present data cannot, however, rule out the possibility that a long-lived orbiting mechanism accounts for part or all of this yield.Comment: 41 pages standard REVTeX file, 14 Figures available upon request -