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Hydrothermal zeolites (laumontite, yugawaralite, analcime, heulandite, clinoptilolite), prehnite and pumpellyite have been recognised in a succession of volcanic, autoclastic, pyroclastic, resedimented volcaniclastic and mixed siliciclastic–volcaniclastic deposits. In cone-building lithofacies association attaining 310 m, the alteration minerals commonly change within a single normally graded depositional unit or alternate in the section on a dm- to m-scale, according to the host-rock lithofacies. Fine-grained deposits rich in juvenile glassy pyroclasts are altered to heulandite and clinoptilolite or analcime, and laumontite widely occurs in coarse-grained host-rocks (lapilli tuff, hyaloclastite breccia, volcaniclastic breccia, hyaloclastites) and fracture systems. In near-vent lithofacies association attaining 420 m, prehnite–laumontite, laumontite–analcime, and laumontite–heulandite–clinoptilolite zones developed as a result of superimposed thermal regime generated by the emplacement of an over 200 m thick sill. The recognised dependence of alteration on porosity, permeability and fracturing of the host-rock is closely related to hydrological conditions in the stratovolcano-hosted hydrothermal system with convective–advective flow regime. After separation of steam and gases from convecting hydrothermal fluids, denser liquids outflowed intermittently, preferentially through steeply inclined (20–30°) high-permeability layers in the stratovolcano edifice. In low-permeability layers the flow was slow and thermal conditions were mainly attained by conduction. Zeolites developed only in coarse- and fine-grained vitroclastic tuffs, presumably by the dissolution of volcanic glass. The interstratified siliciclastic siltstones, tuffites and resedimented deposits with low content of glassy particles are devoid of zeolites and indicate compositional constraint on zeolitisation. Lava flows, cooling in a submarine environment and undergoing disintegration and mingling with the enclosing water-saturated sediment were individual, ephemeral and spatially localised high-temperature hydrothermal systems favourable for the formation of pumpellyite, prehnite and laumontite.

Some secondary minerals such as prehnite, pumpellyite, babingtonite and laumontite occur in druses, veins, and nodular aggregates in the hydrothermally altered Miocene dolerite sills distributing in the north coast of Shimane Peninsula, Japan. This study gives a special focus on the occurrence of prehnite from Mitsu area. Prehnite shows two modes of occurrences: a druse and vein mineral (prehnite I) which is associated with Fe-rich pumpellyite and laumontite, and a replacement of the primary plagioclase (prehnite II). Main minerals in rock specimens containing prehnite I are plagioclase and K-feldspar, but they are not observed in those containing prehnite II. Total Fe_2O_3 contents of prehnite I and II attain up to 8.14 and 8.61 wt.%, respectively. The Fe content of prehnite I varies in a range between 0.33 and 0.44 Fe^ atoms per formula unit (apfu; per O_(OH)_2), whereas the Fe content of prehnite II from 0.01 to 0.46 Fe^ apfu. Their different compositional ranges can be due to the formation process: prehnite I formed directly from hydrothermal fluids and / or vapor in the druses and fissures; prehnite II occurring as pseudomorph of plagioclase was crystallized through alteration process of plagioclase by hydrothermal fluids / vapor. In general, iron in prehnite is ferric in prehnite. However, in some prehnite I grains deficient in Ca, Fe^ is assumed to replace a part of Ca.

Honeaite, ideal formula Au3TlTe2, is a new mineral from the late Archaean Karonie gold deposit, Eastern Goldfields province, Western Australia. Honeaite is found with native gold, tellurobismuthite, petzite, hessite, calaverite, melonite, mattagamite, frohbergite, altaite, pyrrhotite and molybdenite. These minerals are concentrated in microvughs and microfractures mainly within areas of prehnite alteration of amphibolite. The mineralisation appears to have been deposited under greenschist-facies conditions at lower temperatures than most gold deposits in the Eastern Goldfields. Single-crystal X-ray studies identified the structure of honeaite as orthorhombic, space group Pbcm , with a = 8.9671 (4) A, b = 8.8758(4) A, c = 7.8419(5) A, giving V = 624.14(6) A3 with Z = 4. The strongest reflections of the calculated powder X-ray diffraction pattern are [ d in A (Irel)( hkl) ]: 2.938(100)(022), 2.905 (39,8)(322, 411), 2.989 (31)(300), 2.833 (23)(310), 1.853 (17)(332). Electron-microprobe analysis (EDS mode) gave (wt%) Au 56.33, Tl 19.68, Te 24.30, total 100.31, leading to an empirical formula (based on 2 Te apfu ) of Au3.00Tl 1.01Te 2.00. Honeaite is black with a metallic lustre and no observed cleavage. The calculated density is 11.18 g/cm3. In reflected plane-polarized light it is slightly bluish grey. Between crossed polars it is weakly anisotropic with dark brown to dark blue rotation tints. Reflectance values in air and in oil are given. Honeaite is named after the late Russell M. Honea (1929–2002).

In the Bogazkale region (Corum, Central Anatolia), pieces of Neotethyan oceanic lithosphere are found in an ophiolitic melange. Within the melange, there are occurrences of isolated diabase dykes that intrude serpentinized and carbonatized ultramafics. The diabases are phaneritic, holocrystalline and equigranular, and consist of plagioclase and hornblende as the main primary mineral phases. They have all undergone low-grade alteration, to varying extents, as reflected by the presence of secondary minerals, including chlorite, epidote, prehnite and actinolite. Immobile trace element systematics suggest that all diabases are of subalkaline basalt composition and display negative Nb anomalies in the N-MORB-normalized plots. They also display flat to slightly LREE-depleted patterns in chondrite-normalized diagrams. The relative Th (and La) enrichment coupled with N-MORB-like HFSE composition of the diabases suggests their derivation from a depleted mantle source metasomatized by slab-derived fluids/melts. Overall trace element characteristics are consistent with an oceanic back-arc origin. 40Ar-39Ar radiometric dating on the hornblende grains extracted from the two diabase dykes yield ages of 176.30 ± 0.52 Ma and 178.82 ± 0.80 Ma (Toarcian, Early Jurassic). This suggests the existence of an intra-oceanic subduction zone within the Izmir-Ankara-Erzincan (IAE) Ocean during the Early Jurassic, which can also be traced along the western (Vardar Zone) and the eastern (Sevan/Akera ophiolites) extensions of the Northern Neotethys. This result requires the presence of a Northern Neotethyan oceanic crust of pre-Early Jurassic age, which in turn may suggest that oceanization of the IAE Ocean have occurred during the Late Triassic or earlier.

High-pressure Raman and infrared spectra of a natural sample of prehnite, with a chemical composition of Ca2(Al0.74,Fe0.26)2Si3O10(OH)2, are presented. Analyses of the spectra indicate that prehnite undergoes a reversible structural change between 6 and 8 GPa that is most likely associated with a subtle alteration in the orientation and/or deformation of the polyhedra comprising the framework of the structure. At pressures in excess of ~11 GPa, the high-pressure spectra indicate that prehnite undergoes a reversible phase transition involving the collapse of the framework structure. Published version

The Serido Mobile Belt hosts numerous mineralized skarns in the Borborema Province, northeastern Brazil. The Bonfim W-Mo-Au-Bi-Te skarn occurs within a Neoproterozoic metasedimentary sequence (Serido Group), within marble and schist lenses, or at the contacts between both. An ASD-FieldSpec™ 3 High-Resolution spectrometer was used to characterize the mineralogy of a representative drill core interval (181 m) from the Bonfim deposit, in order to generate the spectral characterization to define the gold mineralization. Skarns are characterized by the presence of diopside, actinolite-tremolite, clinozoisite-zoisite, muscovite and prehnite. Prehnite and epidote constitute the main components of the calc-silicate assemblage associated with late-stage gold mineralization. The diagnostic absorption feature of prehnite at 1478 nm (OH) can be used to identify its presence, and the prehnite index proposed in this case study (a reflectance ratio of 1465 nm/1478 nm) allows highlighting the prehnite enriched sections along the core. Geochemical data show a positive correlation between gold and the presence of a prehnite absorption at 1478 nm. The results suggest that the prehnite spectral signature can be used as a reliable and efficient (rapid) indicator for gold skarns, perhaps under geologically similar circumstances to those at Bonfim.

International audience; Amazonian-aged Lyot crater is the best-preserved and deepest peak-ring impact crater (diameter, D = 220 km) in the northern lowlands of Mars. Morphological features including scouring channels emanating from its ejecta and small channels within the crater have been examined previously to understand hydrological activity associated with the crater. In this study, we analyze images acquired by the Compact Reconnaissance Imaging Spectrometer for Mars on board the Mars Reconnaissance Orbiter to investigate the mineralogical record in Lyot and its surroundings, which are presently enriched in ground ice, to understand the associated aqueous processes, their relative timing, and a possible role for ground ice in hydrous mineral formation. We find diverse hydrous minerals, including Fe/Mg phyllosilicates, chlorite, illite/muscovite, and prehnite in Lyot crater walls, central peak, and ejecta, as well as in two craters to the west of Lyot. The exposure and distribution of the hydrous minerals suggest that they are related to the impact process, either exposed by the excavation of hydrothermally altered rocks or formed through syn-depositional hydrothermal alteration immediately after impacts. The Lyot impact induced channel formation to the north, but no mineralogical evidence of aqueous alteration associated with the channels is observed. The sinuous channels within Lyot, diverted by bedrock units with hydrous mineral detections, did not cause mineralization but likely represent the last stage of water activity in Lyot crater. The separate episodes of water activity indicate flow of liquid water on Mars' surface during the Amazonian but limited to no aqueous alteration to generate hydrous minerals. Plain Language Summary Though liquid water is not stable on the surface of Mars presently, water may have had a more active role on Mars in the recent geologic epoch. In particular, meteor impacts may melt ground ice, creating local environments with liquid water activity. Lyot crater is the deepest, well-preserved impact crater in the northern plains of Mars, with a diameter of 220 km, formed in the most recent geologic epoch. In this work, we study the mineralogy and morphology related to water activities within and adjacent to Lyot crater. One of the mineral types (prehnite) found in Lyot form at relatively high temperature (>200°C) in hydrothermal environments. From the distribution of water-bearing minerals, we found that they probably represent an earlier episode of water activity before or during the impact. While liquid water has carved small channels inside the crater long after the impact, they probably did not exist on the surface long enough to alter the composition of the bedrock materials. Liquid water may be present but probably quite short-lived in the most recent epoch on Mars.

The Orange Mountain Basalt of New Jersey is a Mesozoic formation consisting of three units: a single lower inflated sheet lobe about 70 m thick (OMB1), a middle pillow basalt about 10 to 20 m thick (OMB2), and an upper compound pahoehoe flow about 20 to 40 m thick (OMB3). The Orange Mountain Basalt is part of the Central Atlantic Magmatic Province. Quarry and road-cut exposures of OMB1 near Paterson, New Jersey, display some unusual layering that is the focus of this study. OMB1 exposures displays the typical upper crust, core, and basal crust layers of sheet lobes but throughout the Patterson area also display distinct light gray layers of microvesicular basalt mineralized with albite directly over the basal crust and under the upper crust. The lower microvesicular layer is associated with mega-vesicular diapirs. We propose that the upper and lower microvesicular layers were composed of viscous crust that was suddenly quenched before it could devolatilize immediately before the solidification of the core. During initial cooling, the bottom of the basal layer was mineralized with high concentrations of calcite and albite during a high-temperature hydrothermal event. Subsequent albitization, as well as zeolite, prehnite, and calcite precipitation events, occurred during burial and circulation of basin brine heated by recurring Palisades magmatism below the Orange Mountain Basalt. Some of the events experienced by the Orange Mountain Basalt are unusual and place constraints on the fluid dynamics of thick flood basalt flows in general. The late penetration of vesicular diapirs through the entire thickness of the flow interior constrains its viscosity and solidification history.

Seawater-basalt interaction taking place at mid-ocean ridges was studied using numerical modeling to determine the compositional evolution of hydrothermal fluids and associated alteration mineralogy forming within newly emplaced crustal material. Geochemical modeling was carried out in a closed seawater-basalt system at discrete temperature intervals between 2 and 400°C at 500 bars, varying fluid/rock ratios, and secondary mineral assemblages representative of basalt alteration in natural systems. In addition to temperature, the fluid/rock ratio has a fundamental control on the resulting system chemistry. At rock-buffered conditions (low fluid/rock ratios), the mineral-solution equilibrium was characterized by high cation to proton activity ratios foraCa2+/(aH+)2andaNa+/aH+and very low dissolved Mg concentrations due to the precipitation of smectites and chlorite. A complex secondary mineral alteration assemblage dominated by Ca- and Na-bearing minerals including zeolites, calcite, epidote, prehnite, clinozoisite, and albite was predicted to form. The resulting fluid composition was alkaline and reduced relative to ambient seawater, with Eh values ranging between −0.2 and −0.6 V. In contrast, seawater-buffered conditions (high fluid/rock ratios) resulted in lower cation to proton activity ratios foraCa2+/(aH+)2andaNa+/aH+and higher dissolved Mg concentrations comparable to the value of this element in ambient seawater. A more simple mineral assemblage was predicted to form at these conditions with the predominance of Al-Si- and Mg-bearing minerals including kaolinite, quartz, and talc in addition to large amounts of anhydrite. The resulting fluid composition was mildly acidic and oxidized relative to seawater with Eh values ranging between −0.2 and 0 V. These modeling results were compared to a compilation of submarine hydrothermal vent fluid compositions from mid-ocean ridge settings and analogous basalt-dominated environments. The agreement obtained between the simulations and the compiled fluid data indicates that mid-ocean ridge hydrothermal processes can be closely reproduced by mineral-solution equilibria for a broad range of temperatures and fluid/rock ratios.

Compositions of basaltic and ultramafic rocks analyzed by Mars rovers and occurring as Martian meteorites allow predictions of metamorphic mineral assemblages that would form under various thermophysical conditions. Key minerals identified by remote sensing roughly constrain temperatures and pressures in the Martian crust. We use a traditional metamorphic approach (phase diagrams) to assess low-grade/hydrothermal equilibrium assemblages. Basaltic rocks should produce chlorite + actinolite + albite + silica, accompanied by laumontite, pumpellyite, prehnite, or serpentine/talc. Only prehnite-bearing assemblages have been spectrally identified on Mars, although laumontite and pumpellyite have spectra similar to other uncharacterized zeolites and phyllosilicates. Ultramafic rocks are predicted to produce serpentine, talc, and magnesite, all of which have been detected spectrally on Mars. Mineral assemblages in both basaltic and ultramafic rocks constrain fluid compositions to be H2O-rich and CO2-poor. We confirm the hypothesis that low-grade/hydrothermal metamorphism affected the Noachian crust on Mars, which has been excavated in large craters. We estimate the geothermal gradient (>20 °C km−1) required to produce the observed assemblages. This gradient is higher than that estimated from radiogenic heat-producing elements in the crust, suggesting extra heating by regional hydrothermal activity.

Graphite-3R was found at an outcrop in Kanayamadani, central Japan that had green-black jadeitite, altered jadeitite, and fracture zones in serpentine melange. The graphite from the three zones was characterized using polarizing microscopy, XRD, Raman spectroscopy, SEM, HRTEM, and stable carbon-isotope mass spectrometry. Graphite in the black jadeitite zone is possibly crystallized simultaneously with prehnite in the stability field of prehnite ( P

This paper, based on CIE1976 Uniform-Chromaticity scale, devotes to distinguish prehnite and other similar stones (Jadeite, Olivine, and Emerald) by discriminant analysis, and explore the possibility to identify them by color. The Color i5 device is adopted to get information about L, a, b, C, h of four kinds of stones. And here takes L, a, b as variables, classify 4 kinds of samples into 8 classifications through K-means cluster analysis by SPSS16.0. Here also use Fisher discriminant analysis to test the reasonability of classification. Through discriminant analysis, most stones of four kinds can be distinguished by color.

The Sinyukhinskoe deposit (>100 t Au with average 9.2 g/t Au) is situated in the Altaid orogenic system and is part of the regional system of Devonian-Carboniferous Cu-Au to Au-Cu porphyry, skarn and other deposits. Productive plutonic suites were emplaced in a Devonian subduction-related continental magmatic arc setting, with its further evolution toward a late- and post-collisional environment in the late Devonian-Carboniferous. The deposit is related to a magnetite-series, I-type multiphase pluton, with the evolution of the intrusive phases from early gabbroic through diorite-granodiorite to the late granitic phases. The igneous rocks belong to medium-K calc-alkaline series or are transitional from medium- to high-K calc-alkaline varieties. Prior to granitic phases, this evolution was interrupted by the intrusion of intramineral high-K mafic dikes exhibiting a shoshonitic affinity. The deposit is characterized by the development of abundant andradite-rich garnet and wollastonite in prograde and retrograde skarns, locally together with magnetite and bornite. The subsequent propylitic (epidote-chlorite-amphibole-albite-calcite-quartz, locally with clinozoisite and prehnite) alteration assemblages bear more intense Cu mineralization (chalcopyrite, bornite, locally tennantite) and high fineness (~940–910‰) native gold. Later phyllic (quartz-sericite to quartz-sericite-chlorite) alteration assemblages comprise the most intense intermediate-fineness (910–880‰) native gold and Cu (bornite, chalcocite) mineralization that is followed by low-fineness (820–760‰) native gold and telluride minerals. The retrograde skarn was formed from a high-salinity (22–23 wt% NaCl-eq.), hot (450 ± 50 °C), high-pressure (2.5 ± 0.5 kbar) homogenous magmatic-hydrothermal fluid, under its possible direct separation from crystallizing magma. After intrusion of intramineral mafic dikes, propylitic alteration assemblages were formed from a moderate salinity (15–18 wt% NaCl-eq.) homogenous aqueous fluid at the temperatures of 380–400 °C. This fluid could be supplied by crystallizing magma, with its further mixing with heated meteoric waters. Fluid inclusions in phyllic alteration minerals indicate a new influx of homogenous, high-salinity (18 wt% NaCl, 22 wt% KCl, 10 wt% CaCl2), high-pressure (1.3 ± 0.1 kbar), aqueous-chloride fluid at lower (~280 °C) temperatures. Elevated Bi, Hg, Te contents, as well as δ34S values close to meteorite standard (0 ± 1.5‰) suggest at least partial fluid sourcing from a mantle-derived magma at the phyllic alteration stage.

The gemstones, covering the spectrum from jeweler's to showcase quality, have been presented in a tripartite subdivision, by country, geology and geomorphology realized in 99 digital maps with more than 2600 mineralized sites. The various maps were designed based on the “Chessboard classification scheme of mineral deposits” proposed by Dill (2010a, 2010b) to reveal the interrelations between gemstone deposits and mineral deposits of other commodities and direct our thoughts to potential new target areas for exploration. A number of 33 categories were used for these digital maps: chromium, nickel, titanium, iron, manganese, copper, tin–tungsten, beryllium, lithium, zinc, calcium, boron, fluorine, strontium, phosphorus, zirconium, silica, feldspar, feldspathoids, zeolite, amphibole (tiger's eye), olivine, pyroxenoid, garnet, epidote, sillimanite–andalusite, corundum–spinel − diaspore, diamond, vermiculite–pagodite, prehnite, sepiolite, jet, and amber. Besides the political base map (gems by country) the mineral deposit is drawn on a geological map, illustrating the main lithologies, stratigraphic units and tectonic structure to unravel the evolution of primary gemstone deposits in time and space. The geomorphological map is to show the control of climate and subaerial and submarine hydrography on the deposition of secondary gemstone deposits. The digital maps are designed so as to be plotted as a paper version of different scale and to upgrade them for an interactive use and link them to gemological databases.

A new mineral, kasatkinite, Ba2Ca8B5Si8O32(OH)3 · 6H2O, has been found at the Bazhenovskoe chrysotile asbestos deposit, the Central Urals, Russia in the cavities in rhodingite as a member of two assemblages: (l) on prehnite, with pectolite, calcite, and clinochlore; and (2) on grossular, with diopside and pectolite. Kasatkinite occurs as spherulites or bunches up to 3 mm in size, occasionally combined into crusts. Its individuals are acicular to hair-like, typically split, with a polygonal cross section, up to 0.5 mm (rarely, to 6 mm) in length and to 20 μm in thickness. They consist of numerous misoriented needle-shaped subindividuals up to several dozen μm long and no more than 1 μm thick. Kasatkinite individuals are transparent and colorless; its aggregates are snow white. The luster is vitreous or silky. No cleavage was observed; the fracture is uneven or splintery for aggregates. Individuals are flexible and elastic. The Mohs' hardness is 4-4.5. D meas = 2.95(5), D calc = 2.89 g/cm3. Kasatkinite is optically biaxial (+), α = 1.600(5), β = 1.603(2), γ = 1.626(2), 2V meas = 30(20)°, 2V calc = 40°. The IR spectrum is given. The 11B MAS NMR spectrum shows the presence of BO4 in the absence of BO3 groups. The chemical composition of kasatkinite (wt %; electron microprobe, H2O by gas chromatography) is as follows: 0.23 Na2O, 0.57 K2O, 28.94 CaO, 16.79 BaO, 11.57 B2O3, 0.28 Al2O3, 31.63 SiO2, 0.05 F, 9.05 H2O, -0.02 -O=F2; the total is 99.09. The empirical formula (calculated on the basis of O + F = 41 apfu, taking into account the TGA data) is: Na0.11K0.18Ba1.66Ca7.84B5.05Al0.08Si8.00O31.80(OH)3.06F0.04 · 6.10H2O. Kasatkinite is monoclinic, space group P21/c, P2/c, or Pc; the unit-cell dimensions are a = 5.745(3), b = 7.238(2), c = 20.79 (1) A, β = 90.82(5)°, V = 864(1) A3, Z = 1. The strongest reflections (d A-I[hkl]) in the X-ray powder diffractions pattern are: 5.89-24[012], 3.48-2.1[006], 3.36-24[114]; 3.009-100[121, 121, 106], 2.925-65[106, 122, 122], 2.633-33[211, 124], 2.116-29[133, 133, 028]. Kasatkinite is named in honor of A.V. Kasatkin (b. 1970), a Russian amateur mineralogist and mineral collector who has found this mineral. Type specimen is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. © 2013 Pleiades Publishing, Ltd.

[1] Widespread occurrences of phyllosilicates, predominantly nontronite and Mg saponite, in the Noachian-aged crust of Mars place constraints on water availability and surface conditions. However, the Noachian atmosphere likely lacked oxidants capable of forming nontronite from the basaltic crust and its origins are thus uncertain. In this study, scenarios for the formation of iron-bearing phyllosilicates from the weathering and hydrothermal alteration of Martian basalt were investigated using geochemical modeling to establish plausible pathways of nontronite generation and the effect of redox conditions on associated secondary phases. Hydrothermal alteration produced FeII and Mg saponite, serpentine, and zeolites at 100°C and chlorite, prehnite, and talc at 250°C, consistent with phases observed in crater deposits on Mars. Anoxic weathering produced primarily FeII and Mg saponite. High water-rock ratios produced Al-clays and amorphous silica and high pCO2 conditions inhibited smectite formation because of carbonate precipitation. Oxic weathering produced primarily nontronite and Mg saponite. Later oxidation of anoxic weathering products also formed nontronite-Mg saponite assemblages; oxidation products of hydrothermal assemblages included nontronite, Mg saponite, and either Al smectites or residual zeolites or prehnite. These calculations demonstrate that there are multiple plausible routes to form Fe/Mg smectites on early Mars and that an oxidizing atmosphere need not have existed in the Noachian. Decoupling iron oxidation from initial clay formation raises the possibilities that Mars transitioned to conditions favoring widespread iron oxidation after phyllosilicate formation ceased and that residual, unoxidized ferrous iron phyllosilicates still exist today in the Martian subsurface.

To better understand geodynamic processes related to the assembly of various belts of volcanic^sedimentary rocks in the Avalonian Mira terrane of SE Cape Breton Island (protolith ages 680^560 Ma) we investigated metamorphic processes in 20 white-mica-bearing mafic and felsic metavolcanic rocks. The felsic metavolcanic rocks are foliated and partly sheared with blastoporphyritic relict fabric and contain the assemblage phengite^epidote^chlorite^ albite^K-feldspar^quartz^titanite stilpnomelane calcite ilmenite. In contrast, many mafic metavolcanic rocks are relatively undeformed and display relict porphyritic and amygdaloidal textures. They contain the assemblages epidote^chlorite^albite^quartz^titanite phengite pumpellyite prehnite calcite K-feldspar and actinolite^epidote^chlorite^albite^quartz^titanite phengite calcite K-feldspar. Heterogeneous metamorphic overprinting is indicated by local relicts of magmatic clinopyroxene, magnetite and plagioclase. Metamorphic minerals formed by local precipitation in clusters and are due to continuous nucleation of very low-grade phases during pulses of variably pervasive fluids, which were released during intense dehydration at 250^3008C. Nucleaction rate dominated over growth rate at these conditions. Potassic white mica in both mafic and felsic rocks is mostly phengite with a wide compositional range (3·11^3·41 Si a.p.f.u.). Maximum Si contents are typically between 3·30 and 3·41a.p.f.u. P^T pseudosections were calculated for the range 200^4008C and 1^7 kbar. The peak metamorphic assemblages occupy P^T fields consistent with the position of isopleths for corresponding maximum Si contents in white mica. Peak P^Tconditions in the Mira terrane samples lie within a narrow range of 3·5 0·4 kbar and 280 308C in samples representing all of the assembled volcanic^sedimentary belts. The derived peak metamorphic conditions suggest syn-collisional burial to 11^14 km depth and a low metamorphic geotherm of 20^258C km. Under these conditions subsequent strike-slip deformation is attributed to the final assembly of magmatic arc slices to form the crust of the Mira terrane.

The partly to pervasively metasomatized doleritic and gabbroic dykes or small to medium sized bodies found in East Othris, within Mid to Late Jurassic serpentinized peridotites of ophiolitic units and ophiolitic melange formations are classified as rodingites and can be divided into two types. Type 1 rodingites are mainly characterized by the frequent occurrence of prehnite, while Type 2 rodingites include mostly garnets and vesuvianite. Isocon analysis showed that rodingitization essentially occurred with mass and volume preservation. Desilification, depletion of alkalies, as well as Ca enrichment was more intense for the Type 2 rodingites. Al, Fe and Mg remained rather immobile, while Ti, Y, Zr and REE were variably depleted. Rodingitization took place in an intraoceanic subduction system. It occurred in three successive stages during the exhumation of the mafic–ultramafic mantle wedge rocks in a fore-arc setting within a serpentinitic subduction channel, which developed close to the slab. The incorporation of the mafic rocks to the subduction channel probably resulted after entraining a directed mantle flow towards the slab. The first stage of rodingitization formed mainly grossular, hydrogrossular, Ti- and Cr-bearing hydrogarnets and calcite under relatively acidic and mildly oxidizing physicochemical conditions, with increased CO2/H2O ratio. During the second and more extensive rodingitization stage, alkaline and reducing conditions prevailed and CO2/H2O ratio was decreased. The modeling of the mineral reactions of this stage, using the software winTWQ v. 2.34 in the CFMASH system, reveals that in Type 1 rocks prehnite replaced most of the initial garnet, while Type 2 rocks continued to be rodingitized, mostly forming grossular and/or hydrogrossular and chlorite. Hydrogrossular, instead of grossular, was crystallized from hydrous fluids under high silica activity. Type 2 rodingites underwent further rodingitization during the third stage, due to infiltration of Ca-rich hydrothermal fluids of oceanic and/or subducted slab origin, at lower temperatures and depths. This stage is characterized by the appearance of hydroandradite and vesuvianite, under alkaline and oxidizing conditions, due to very low CO2/H2O ratio and relatively high fO2. All three rodingitization stages are estimated to have occurred under relatively moderate temperature and pressure (~ 300 to 400 °C; ~ 3–6 kbar respectively). Locally, Type 2 rodingites show derodingitization of variable extent, forming high-variance assemblages mostly consisting of chlorite ± pumpellyite. Some chlorite marginal zones in rodingite dykes may also have been developed by Mg-rich diffusional fluid flow, during this derodingitization process.

[1] Phyllosilicates have been identified in some of the most highly cratered Noachian terrains on Mars. To study the effects of such impacts on the properties of phyllosilicates, we experimentally shocked six phyllosilicate minerals relevant to the Martian surface: montmorillonite, nontronite, kaolinite, prehnite, chlorite, and serpentine. The shock-treated samples were analyzed with X-ray diffraction (XRD), near- and mid-infrared (NIR and MIR) spectroscopy, Raman spectroscopy, cathodoluminescence (CL), and the shock pressures and temperatures in some were modeled using Autodyn modeling software. XRD data show that the structure of each mineral, except prehnite, underwent partial structural deformation or amorphization. We also found that while the NIR spectra of shocked samples were very similar to that of the original sample, the MIR spectra changed significantly. This may explain some of the discrepancies between CRISM/OMEGA data (NIR) and TES/THEMIS (MIR) observations of phyllosilicates on Mars. Quartz was identified as a secondary phase in the XRD of shocked chlorite.

Merelaniite is a new mineral from the tanzanite gem mines near Merelani, Lelatema Mountains, Simanjiro District, Manyara Region, Tanzania. It occurs sporadically as metallic dark gray cylindrical whiskers that are typically tens of micrometers in diameter and up to a millimeter long, although a few whiskers up to 12 mm long have been observed. The most commonly associated minerals include zoisite (variety tanzanite), prehnite, stilbite, chabazite, tremolite, diopside, quartz, calcite, graphite, alabandite, and wurtzite. In reflected polarized light, polished sections of merelaniite are gray to white in color, show strong bireflectance and strong anisotropism with pale blue and orange-brown rotation tints. Electron microprobe analysis (n = 13), based on 15 anions per formula unit, gives the formula Mo4.33Pb4.00As0.10V0.86Sb0.43Bi0.33Mn0.05 W0.05Cu0.03(S14.70Se0.30)Σ15, ideally Mo4Pb4VSbS15. An arsenic-rich variety has also been documented. X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy show that merelaniite is a member of the cylindrite group, with alternating centered pseudo-tetragonal (Q) and pseudo-hexagonal (H) layers with respective PbS and MoS2 structure types. The Q and H layers are both triclinic with space group C1 or C 1 ¯ . The unit cell parameters for the Q layer are: a = 5.929(8) A; b = 5.961(5) A; c = 12.03(1) A; α = 91.33(9); β = 90.88(5); γ = 91.79(4); V = 425(2) A3; and Z = 4. For the H layer, a = 5.547(9) A; b = 3.156(4) A; c = 11.91(1) A; α = 89.52(9); β = 92.13(5); γ = 90.18(4); V = 208(2) A3; and Z = 2. Among naturally occurring minerals of the cylindrite homologous series, merelaniite represents the first Mo-essential member and the first case of triangular-prismatic coordination in the H layers. The strongest X-ray powder diffraction lines [d in A (I/I0)] are 6.14 (30); 5.94 (60); 2.968 (25); 2.965 (100); 2.272 (40); 1.829 (30). The new mineral has been approved by the IMA CNMNC (2016-042) and is named after the locality of its discovery in honor of the local miners.

The main aim of this research is to find the most appropriate weathering indices among geomechanical, chemical and petrographical indices to characterize Malayer granitic rocks. In the study area, physical weathering and hydrothermal alteration are predominant degradation phenomena. Therefore, it is necessary to distinguish between the effect of these two phenomena and chemical weathering on mineralogy as well as on geomechanical rock properties. The most important evidences of hydrothermal alteration are the selective sericitization of plagioclase and the occurrence of prehnite. Also, statistical analyses, including simple and multiple linear regressions, were applied to identify those indices that are most influenced on the progression of weathering. Based on the simple regression analysis, petrographical and chemical indices do not show any good trend by increasing weathering degrees (R 2 0.72). Finally, a new quantitative weathering index (Kr4) has been developed regarding quick absorption index, P-wave velocity (Vp), point load index (Is) and total porosity (n). All the mentioned parameters can be quickly and inexpensively determined by portable laboratory instruments. This new index (Kr4) has strongly correlated with weathering degrees (R 2 = 0.96). Based on some results, it seems that Kr4 could be more suitable and credible to numerically evaluate the physical weathering accompanied by hydrothermal alteration processes of the studied rocks.

Comparative studies on hydrothermal alteration of submarine peperitic basalt occurrences related to the Triassic early rifting of the Neotethys were carried out in various parts of the Dinarides and Hellenides. The study areas included the displaced fragments of the Dinarides in the Darnó Unit, NE Hungary, the Kalnik Mts in Croatia and the Vares-Šmreka area in Bosnia and Herzegovina. In the Hellenides, similar environments were studied in the Stragopetra Mts., Greece. Jurassic pillow basalts formed in a back-arc-basin of the Neotethys were also studied (in the Szarvaskő Unit, NE Hungary, which also represents a displaced unit of Dinaridic origin). Within the submarine basaltic lava flows, six volcanic facies were distinguished. The hydrothermal alteration was characterized according to those facies. The first process was the albitization of the rock-forming plagioclase at ~300°C temperature in all localities. During the higher temperature stage of the subsequent cooling, chloritization in the ground mass is typical for all types of basalts, however chlorite and rarely quartz formed in the fractures and amygdales of the Triassic basalts, while chlorite, quartz and prehnite precipitated in the fractures of the Jurassic rocks. At lower temperatures of this cooling-related process, calcite is a common mineral filling up the larger amygdales, jig-saw type fractures and other open spaces, but some epidote, pumpellyite, prehnite and laumontite also occur in the Triassic basalts. The late stage alteration (happened at the lowest temperature) is characterized by argillitization at every locality. The observed hydrothermal alteration patterns also show slight differences according to the volcanic facies as a function of the distal/proximal setting in relation to the eruptive centers and the presence/absence of water-saturated and unconsolidated carbonate or siliciclastic sediments at the time of the emplacement of lava flows. The study revealed that the most important factors influencing mineralogy and zoning of hydrothermal alteration in these short living local hydrothermal systems are the rapid cooling of the hydrothermal fluid, the dominance of the not much evolved seawater as the source of hydrothermal fluid and the local, i.e. effective water/rock ratio, determined by the degree of fracturing in the rock. The mineralogical-textural peculiarities of the highly localized hydrothermal fluid/rock interaction in the studied submarine sea-mount type volcanoes are clearly different from the products of the large-scaled hydrothermal processes occurring at mid-oceanic ridges. Recognition of these differences is important in the evaluation of ore potential of Neotethyan realm or other areas with occurrences of submarine basaltic units

Groundwaters from areas of granitic bedrock in Daejeon, Eonyang and Yeongcheon in South Korea mainly belong to Ca–HCO 3 and Na–HCO 3 groundwater types according to their chemical composition, with fewer examples of the Ca–(Cl + SO 4 ) and Na–(Cl + SO 4 ) types. To explain the hydrogeochemical evolution of these groundwaters during deep circulation in granitic rocks, we performed reaction path modeling. The results show that the hydrochemical type of groundwater progressively evolves from an initial Ca–Cl type (rainwater) to a final Na–HCO 3 type (of deep groundwater), through an intermediate Ca–HCO 3 type. The reaction path model agrees well with the clay mineralogy of the granites. As the reaction between rainwater and granitic rock progresses, the activity of hydrogen ion decreases (i.e., pH increases) and the concentrations of cations are controlled by the dissolution of major rock-forming minerals, followed by the precipitation and dissolution of secondary minerals, according to the pH. The continuous reaction with granite causes the formation of secondary minerals in the following sequence: gibbsite plus hematite, Mn-oxide, kaolinite, chalcedony, chlorite, muscovite (a proxy for illite here), calcite, laumontite, prehnite, and finally analcime. Silica minerals are predominant in abundance among the minerals formed through the granite–water reactions. The results of this study can provide geochemical information for the preliminary site characterization for high-level nuclear waste disposal at depth in granitic rocks in South Korea and elsewhere.

The island-arc volcanics situated in the eastern part of the Cǎpi{dotless}îlnaş-Techereu nappe (South Apuseni Mountains, Romania) were studied to evaluate the temperature, fluid properties, and mineral chemistry during low-temperature metamorphism. Detailed observations of metamorphic mineral assemblages were conducted using powder X-ray diffraction and electron microprobe. The metamorphism involved albitization of plagioclase feldspar and the formation of mafic phyllosilicates, zeolites, and other hydrous Ca-Al-silicate minerals. Mafic phyllosilicates consisted of transitional dioctahedral-trioctahedral smectites, mixed-layer chlorite-smectite (C/S, 6-96% chlorite), and discrete chlorite. The zeolites were analcime, stilbite ± stellerite, heulandite, laumontite, epistilbite, and mordenite. Also present, as secondary minerals filling amygdales and veins, are prehnite, pumpellyite, and secondary amphibole. Two mineral assemblages were identified which provide important information about metamorphic conditions (temperature, reaction progress, and fluid properties): (1) heulandite + analcime + quartz; and (2) laumontite + albite + quartz + prehnite ± pumpellyite amphibole. The types of and relations between minerals in the first assemblage suggest the occurrence of low-temperature hydrothermal metamorphism in the zeolite facies at ~125°C, whereas the second assemblage was metamorphosed at 200°C. The composition and variability of the mineral assemblages in the study area suggest that, due to slow reaction rates, the low-temperature transformations and mineral assemblages were influenced not only by temperature but also by local rock composition, fluid-rock ratio, and fluid chemistry.

Hydrothermal alteration of Proterozoic granitic rocks in the Äspö underground laboratory, southestern Sweden, resulted in the formation of chlorite with large variations in textural and chemical characteristics, which reflect differences in formation temperatures, fluid composition, and reaction mechanisms. The mineral assemblage associated with chlorite, including Ca-Al silicates (prehnite, pumpellyite, epidote, and titanite), Fe-oxides, calcite, albite and K-feldspar, suggests that chloritization occurred at temperatures of between 200–350°C during various hydrothermal events primarily linked to magmatism and rock deformation. Petrographic and electron microprobe analyses revealed that chlorite replaced biotite, amphibole and magnetite, and hydrothermal chlorite phases filled fractures and vugs in the granitic rocks. While fracture-filling chlorite reduces fracture permeability, chloritization reactions in the host granite resulted in the formation of new localized microporosity that should thus be taken into consideration when evaluating the safety of the granitic basement rocks as a repository for nuclear waste. It is also important to take into account that similar alteration reactions may occur at the site of stored nuclear waste where temperatures in excess of 100°C might be encountered.

The South Filson Creek mineralization occurs above the basal units of the South Kawishiwi intrusion and represents an uncommon geologic setting of Cu-Ni-platinum-group element (PGE) mineralization within the Duluth Complex. Unlike other mineralization of economic interest in the basal heterogeneous troctolite units along the lower contact, it is located at an approximate stratigraphic height of 1,000 m above the contact with the footwall granitoids in the usually unmineralized homogeneous troctolite unit. Magmatic sulfide mineralization forms disseminated fine-grained patches and pockets in an area of approximately ½ km2 of homogeneous troctolitic rocks in the northeastern part of the South Kawishiwi intrusion. Pyrrhotite, chalcopyrite, pentlandite, and cubanite are the main sulfide minerals with subordinate amounts of other copper-bearing phases (bornite, covellite, talnakhite). Cu/Pd ratios for unaltered mineralization indicate that sulfides were formed from multiple injections of magma that segregated sulfides with different R factors or having different initial compositions. Variation in the halogen contents of apatite from pegmatoids within troctolitic rocks revealed that a fluid has segregated from the crystallizing melt into which fluid Cl and rare earth elements partitioned. Amphibole, chlorite, sericite, prehnite, pumpellyite, and carbonate are associated with alteration along brittle structures and isolated patches in the area. The hydrothermal fluid-rock interaction has affected the composition of primary magmatic sulfide mineralization and is also responsible for mineralization in the anorthositic hanging wall of the South Kawishiwi intrusion. Hydrothermal alteration resulted in a slight Pd depletion in magmatic sulfide mineralization, which might indicate remobilization of precious metals to an unknown location. The hanging-wall mineralization is characterized by relative Cu enrichment in comparison to the magmatic sulfide mineralization with no PGE enrichment. Partial remobilization of platinum group elements (PGE) has also occurred as a result of a separate alteration event, on the evidence that platinum group minerals (PGM) are also associated with serpentinization of olivine and Ca enrichment of plagioclase along grain boundaries with sulfides. This alteration was probably effective on a very local scale.

The geochemistry and mineralization of H 2 S in the geothermal system hosted by basaltic rock formation at Hellisheidi, SW Iceland, was studied. Injection of mixtures of H 2 S with geothermal waste water and condensed steam into the > 230 °C geothermal aquifer is planned, where H 2 S will hopefully be removed in the form of sulphides. The natural H 2 S concentrations in the aquifer average 130 ppm. They are considered to be controlled by close approach to equilibrium with pyrite, pyrrhotite, prehnite and epidote. Injection of H 2 S will increase significantly the reservoir H 2 S equilibrium concentrations, resulting in mineralization of pyrite and possibly other sulphides as well as affecting the formation of prehnite and epidote. Based on reaction path modelling, the main factors affecting the H 2 S mineralization capacity are related to the mobility and oxidation state of iron. At temperatures above 250 °C the pyrite mineralization is greatly reduced upon epidote formation leading to the much greater basalt dissolution needed to sequestrate the H 2 S. Based on these findings, the optimum conditions for H 2 S injection are aquifers with temperatures below ~ 250 °C where epidote formation is insignificant. Moreover, the results suggest that sequestration of H 2 S into the geothermal system is feasible. The total flux of H 2 S from the Hellisheidi power plant is 12,950 tonnes yr − 1 . Injection into 250 °C aquifers would result in dissolution of ~ 1000 tonnes yr − 1 of basalt for mineralization of H 2 S as pyrite, corresponding to ~ 320 m 3 yr − 1 .

A well-developed fracture-filling network is filled by dominantly Ca-Al-silicate minerals that can be found in the polymetamorphic rock body of the Baksa Gneiss Complex (SW Hungary). Detailed investigation of this vein network revealed a characteristic diopside fi epidote fi sphalerite fi albite ± kfeldspar fi chlorite1 ± prehnite ± adularia fi chlorite2 fi chlorite3 fi pyrite fi calcite1 fi calcite2 fi calcite3 fracture-filling mineral succession. Thermobarometric calculations (two feldspar: 230‐336� C; chlorites: approximately 130‐300� C) indicate low-temperature vein formation conditions. The relative succession of chlorites in the mineral sequence combined with the calculated formation temperatures reveals a cooling trend during precipitation of the different chlorite phases (Tchlorite1: 260 ± 32� C fi Tchlorite2: 222 ± 20� C fi Tchlorite3: 154 ± 13� C). This cooling trend can be supported by the microthermometry data of primary fluid inclusions in diopside (Th: 276‐362� C) and epidote (Th: 181‐359� C) phases. The identical chemical character (0.2‐1.5 eq. wt% NaCl) of these inclusions mean that vein mineralization occurred in a same fluid environment. The high trace element content (e.g. As, Cu, Zn, Mn) and Co ⁄Ni ratio approximately 1‐5 of pyrite grains support the postmagmatic hydrothermal origin of the veins. The vein microstructure and identical fluid composition indicate that vein mineralization occurred in an interconnected fracture system where crystals grew in fluid filled cracks. Vein system formed at approximately

Late Alpine fissures and fractures in amphibolite-facies basement gneisses at Arvigo (Val Calanca, Swiss Alps) show distinct cm-sized reaction selvages parallel to the fracture walls that composed of subgreenschist facies assemblages produced by the interaction of water present in the fracture porosity with the old high-grade gneiss assemblages. The process of selvage or reaction-vein formation occurred in the brittle deformation regime and at temperatures characteristic of, first the prehnite-pumpellyite facies and then later of the zeolite facies. The vein formation occurred during uplift and cooling at very late stages of the Alpine orogeny. The reaction veins are composed of a selvage of altered gneiss on both sides of the central fracture and a central zone with fissure minerals that have been growing in the open fracture pore space. The central zone of the Arvigo veins contains an early assemblage with epidote, prehnite and chlorite and a late succession sequence of various species of zeolite. The veins of the Arvigo quarry are convincing evidence that fracture fluids in gneiss and granite have the potential to precipitate Ca–zeolite. This is an important find because many fluids recovered from deep continental drill holes and from geothermal energy exploration are found to be oversaturated in respect to a number of Ca–zeolite species. Vein formation during late uplift and cooling of the Alps occurred at continuously decreasing T and at hydrostatic pressure: (1) coexisting prehnite/epidote records temperatures of 330–380°C, (2) chlorite formation at temperature of 333 ± 32°C and (3) formation of zeolites

Calc-silicates have proved to be important rock types to place constraints on the fluid behaviour in high grade metamorphic rocks. Here we describe amphibolite facies calc-silicate rocks of Wadi Solaf, Egypt which is one of the highest grade basement complexes of Egypt and was exhumed in close connection with the Najd fault system – one of the largest pre-Mesozoic fault systems on the Earth. Calc-silicates formed around 7–8 kbar in temperature range of 600–720 °C and can be classified into three groups (CS 1 , CS 2 and CS 3 ). CS 1 and CS 2 are characterized by the presence of garnet porphyroblasts which contain concentrically arranged wollastonite inclusions. CS 3 has a similar paragenesis but is characterized by the presence of clinozoisite/epidote and the absence of wollastonite as well as a pervasive late overgrowth of prehnite. Garnet in CS 1 lies along a grossular–andradite solid solution, while the garnet composition of CS 2 and CS 3 is hydrogrossular and hydroandradite. There is a positive correlation between Al 2 O 3 and Na 2 O as well as between Al 2 O 3 and Fe 2 O 3 from CS 2 through CS 1 to CS 3 possibly indicating a successive increase in fluid flow between the different calc-silicate types. During the peak metamorphism, the X CO 2 is 0.02–0.08 and 0.2–0.44 for the CS 1 and CS 3 , respectively. The mineral assemblage of CS 1 and CS 2 buffered the composition of the fluids along the reaction: q + cc = wo + CO 2 . During post-peak metamorphism the rocks were intruded by syn-tectonic granites. CS 2 records the contact metamorphic conditions. The rocks reached a peak contact metamorphism conditions at temperature 790–828 °C and X CO 2 = 0.22–0.41. Finally, the rocks reached a temperature range 296–311 °C during the cooling path.

Several hydrated silicate deposits on Mars are observed within craters and are interpreted as excavated Noachian material. Toro crater (71.8°E, 17.0°N), located on the northern edge of the Syrtis Major Volcanic Plains, shows spectral and morphologic evidence of impact-induced hydrothermal activity. Spectroscopic observations were used to identify extensive hydrated silicate deposits, including prehnite, chlorites, smectites, and opaline material, a suite of phases that frequently results from hydrothermal alteration in terrestrial craters and also expected on Mars from geochemical modeling of hydrothermal environments. When combined with altimetry and high-resolution imaging data, these deposits appear associated predominantly with the central uplift and with portions of the northern part of the crater floor. Detailed geologic mapping of these deposits reveals geomorphic features that are consistent with hydrothermal activity that followed the impact event, including vent-like and conical mound structures, and a complex network of tectonic structures caused by fluid interactions such as fractures and joints. The crater age has been calculated from the cumulative crater size–frequency distributions and is found to be Early Hesperian. The evidence presented here provides support for impact-induced hydrothermal activity in Toro crater, that extends phyllosilicate formation processes beyond the Noachian era.

The Tianshan rodingite was formed from eclogite tectonically included in ultramafic rocks of the Changawuzi ophiolite in the southwestern Tianshan, China. Rodingites derived from eclogite contain a mineral assemblage of prehnite, clinozoisite, hydrogrossular, diopside, vesuvianite, chlorite and minor zircon. Pervasive rodingitization took place during exhumation of the subducted slab under conditions of 250–350 °C and 2–10 kbar. Cathodoluminescence imaging and geochronological characteristics allow the identification of two types of zircons in the rodingite. Type I zircon consists of sector-zoned grains, commonly with distinct rims and cores. A well-defined weighted mean 206 Pb/ 238 U age of 422 ± 10 Ma for the rims records an early metamorphic event that affected the Changawuzi ophiolite during the Silurian, and represents the emplacement of the ophiolite complexes along the South Tianshan Paleo-ocean coast. The type I zircon cores reflect variable degrees of alteration during subsequent serpentinization and rodingitization at ∼ 290 Ma. The U–Pb ages of the cores vary from 416 Ma to 301 Ma, implying patchy and incomplete alteration. The type I zircon shows rather uniform, flat rare earth element (REE) patterns, but with a marked increase in total REE in the cores. Type II zircon has a weighted mean 206 Pb/ 238 U age at 291 ± 15 Ma, within error of the youngest ages obtained from the cores, and is therefore considered to define the time of pervasive rodingitization. This age is consistent with known regional geological events recorded from the magmatic arc along the southern margin of the Tarim–Yili suture zone and with low P –high T metamorphism to the north, attributed to dehydration of the subducted oceanic slab when the combined Tarim–North China block collided with the Yili–Central Tianshan micro-plate.

Hydrated Minerals on Martian Northern Plains The presence of hydrated minerals on the surface of Mars implies that the crust of the planet was once altered by the action of liquid water. This conclusion is well established for the ancient southern highlands of Mars, but the situation in the northern lowlands, which are thought to have been resurfaced by lava flows during the Hesperian period about 3 billion years ago, is not so clear. Carter et al. (p. 1682 ) report the detection of hydrated minerals in nine northern plain craters, which are thought to have exposed the ancient, pre-Hesperian crust. The results suggest that the degree of alteration of the ancient martian crust is more extensive than previously assumed.

Single-crystal electron paramagnetic resonance (EPR) spectra of gamma-ray-irradiated prehnite (Jeffrey mine, Quebec, Canada) measured at 298 and 160 K reveal an aluminum-associated oxygen hole center (Al—O − ). Spin Hamiltonian parameters g and A ( 27 Al) fitted from the 298 K spectra suggest that this Al—O − center represents hole trapping on an apical hydroxyl oxygen atom (after removal of the proton) coordinated to an octahedral Al 3+ ion ( i.e. , an [ • OAlO 4 (OH)] center from the [(OH)AlO 4 (OH)] precursor, where • denotes the unpaired spin). Pulsed electron nuclear double resonance (ENDOR) spectra measured at 25 K allow the identification and quantitative analysis of two sets of 27 Al hyperfine structures and five proton hyperfine structures, which are all consistent with the proposed structural model. Isothermal and isochronal annealing experiments show that this center is bleached out completely at 375 °C, but can be readily restored by gamma-ray irradiation, and exhibits second-order decay kinetics. These results from the Al—O − center in prehnite provide support for and new insights into Clozel et al . (1995)’s VI Al—O − — VI Al model for B-centers in kaolinite.

The Reykjanes geothermal system is a seawater-recharged hydrothermal system that appears to be analogous to seafloor hydrothermal systems in terms of host rock type and low water/rock alteration. The similarities make the Reykjanes system a useful proxy for seafloor vents. At some time during the Pleistocene, the system was dominated by meteoric water recharge, and fluid composition at Reykjanes has evolved through time as a result of changing proportions of meteoric water influx as well as differing pressure and temperature conditions. The purpose of this study is to characterize secondary mineralization, degree of metasomatic alteration, and bulk composition of cuttings from well RN-17 from the Reykjanes geothermal system. The basaltic host rock includes hyaloclastite, breccia, tuff, extrusive basalt, diabase, as well as a marine sedimentary sequence. The progressive hydrothermal alteration sequence observed with increasing depth results from reaction of geothermal fluids with the basaltic host rock. An assemblage of greenschist facies alteration minerals, including actinolite, prehnite, epidote and garnet, occurs at depths as shallow as 350 m; these minerals are commonly found in Icelandic geothermal systems at temperatures above 250 °C (Bird and Spieler, 2004). This requires hydrostatic pressures that exceed the present-day depth to boiling point curve, and therefore must record alteration at higher fluid pressures, perhaps as a result of Pleistocene glaciation. Major, minor, and trace element profiles of the cuttings indicate transitional MORB to OIB composition with limited metasomatic shifts in easily mobilized elements. Changes in MgO, K 2 O and loss on ignition indicate that metasomatism is strongly correlated with protolith properties. The textures of alteration minerals reveal alteration style to be strongly dependent on protolith as well. Hyaloclastites are intensely altered with calc-silicate alteration assemblages comprising calcic hydrothermal plagioclase, grandite garnet, prehnite, epidote, hydrothermal clinopyroxene, and titanite. In contrast, crystalline basalts and intrusive rocks display a range in alteration intensity from essentially unaltered to pervasive and nearly complete albitization of igneous feldspar and uralitization of clinopyroxene. Hydrothermal anorthite (An92–An98) occurs in veins in the most altered basalt cuttings and is significantly more calcic than igneous feldspar (An48–An79). Amphibole compositions change from actinolite to hornblende at depth. Hydrothermal clinopyroxene, which occurs in veins, has greater variation in Fe content and is systematically more calcic than igneous pyroxene and also lacks uralitic textures. Solid solutions of prehnite, epidote, and garnet indicate evolving equilibria with respect to aluminum and ferric iron.

In this paper, we show how studies of fracture mineral paragenesis, their orientation and Ar-40/Ar-39 geochronology can be applied in order to recognise the brittle tectonothermal evolution in an area. Samples were selected from nearly 18 km of drill cores from the upper I km of the Fennoscandian Shield obtained during the site investigation for a repository of spent nuclear fuel in Forsmark, central Sweden. Four major events of fracturing and/or reactivation of fractures associated with fracture mineralisation have been distinguished. The first event was characterised by precipitation of epidote, quartz and chlorite, along preferably sub-horizontal and gently-dipping fractures or steep, WNW-ESE to NW-SE fractures. Precipitation occurred between 1.8 and 1.1 Ga, possibly during the late stage of the Svecokarelian orogeny close to 1.8-1.7 Ga. The second event is associated with precipitation of hematite-stained adularia and albite, prehnite, laumontite, calcite and chlorite, preferably along steep, ENE-WSW to NNE-SSW and NNW-SSE fractures. Precipitation occurred around 1107 +/- 7 to 1034 +/- 3 Ma, probably due to effects from the Sveconorwegian orogeny. This event was followed by a period with dissolution of fracture minerals and subsequent precipitation of mainly calcite, quartz, pyrite and asphaltite during the Palaeozoic. The formation fluid emanated from an overlying organic-rich sedimentary cover. Precipitation occurred during reactivation of Proterozoic fractures, but formation of new fractures is also inferred, possibly due to far-field effects of the Caledonian orogeny, or elevated hydrostatic pressure due to its foreland basin. The latest event is dominated by clay minerals, chlorite and calcite along hydraulically conductive fractures. These minerals are prominent along sub-horizontal and gently-dipping fractures, but also occur in sets of steeply-dipping fractures. It is inferred that the hydraulically conductive fractures are Proterozoic structures in which mineral precipitation has occurred during a long period. However, some of the near-surface, sub-horizontal fractures may be Quaternary in age. (C) 2009 Elsevier B.V. All rights reserved. (Less)

The Los Santos scheelite skarn deposit, located in the province of Salamanca, northwest Spain, occurs in meter-thick strata-bound but irregular lenses of ≤1 km in length and contains a current total resource of 3.09 million metric tons (Mt) with an average grade of 0.54 percent WO3. It was produced by the metasomatic alteration of Upper Vendian-Lower Cambrian metasedimentary rocks and granitic rocks located in the western part of the Avila batholith plutonic complex. Magmatic activity in the Los Santos zone comprises two intrusions, including biotite monzogranite (281–280 ± 6 Ma, granite I) and porphyritic biotite granodiorite-monzogranite (270-269 ± 6 Ma, granite II). The mineralized skarn distributed close to the intrusions occurred in two main stages: (I) prograde skarn, and (II) retrograde alteration of the stage I skarn. The prograde exoskarn is made up of a thick, almost monomineral mass of hedenbergite (Hd82–87), accompanied by grossular (Grs53–73) and scheelite rich in Mo (Sch I). Early mineralization is associated with granite I; thus, it is possible to recognize an endoskarn of calcic plagioclase and clinopyroxene developed over aplitic granite. The stage I skarn formed from H2O-rich fluids (XCO2

The Reykjanes Peninsula in southwest Iceland is the landward extension of the Mid-Atlantic Ridge spreading center. At present seawater penetrates the coastal Reykjanes geothermal system at depth, mixes with magmatic volatiles and reacts with the basaltic host rock to form secondary geothermal minerals in progressively higher-grade mineral alteration zones with depth where highest recorded temperatures are ~320°C. Within the epidote-chlorite and portions of the epidote-actinolite zones of alteration, epidote-prehnite-calcite-quartz-fluid constitutes a quadravariant assemblage that, under conditions of specified temperature, pressure, and activity of H2O allows prediction of geothermal fluid PCO2 as a function of the composition of the solid solution minerals epidote or prehnite. This assemblage is most common at temperatures >250°C and 600m between the reference temperatures of 275°C and 310°C range from ~1 to ~6.5 bars, when only epidote, prehnite and quartz are observed. When all members of the assemblage are present, including calcite, the calculated range in PCO2 is from ~0.5 to 6 bars. If calcite is absent from the assemblage, the computation of PCO2 using equilibria for reaction 1 provides the maximum value of PCO2 at which calcite will not be present. Actual PCO2 values of geothermal fluids from the Reykjanes system were derived from analytical data on liquid and vapor samples collected at the surface using both the WATCH and SOLVEQ speciation programs. The geothermal fluids at reference temperature between 275°C and 310°C have PCO2 concentrations ranging from 1.3 bars to 4.0 bars. The calculated PCO2 values based on epidote compositions are in close agreement with present-day measured CO2 in the Reykjanes geothermal system fluids. 74% of the calculated PCO2 values based on epidote compositions where the complete epidote-prehnite-calcite-quartz assemblage is observed fall within the range of measured present-day fluids, while 62% of the calculated PCO2 values fall within the range when calcite is not present in the assemblage. Therefore, our method for calculating fluid PCO2 is proven quite reliable when all four index minerals are present. Additionally, if only epidote, prehnite and quartz are observed, our method still serves as a moderately accurate predictive proxy for fluid PCO2 composition in the Reykjanes geothermal system. Ultimately, the correlation between measured and predicted fluid compositions, provides insight into future abilities to characterize spatial and temporal concentrations of CO2 in active and fossil hydrothermal and low-grade metamorphic environments in mafic lithologies based on compositional variations and paragenesis of hydrothermal minerals. In addition, this study will aid in understanding the nature of reactions that involve natural sequestration of CO2 derived from magmatic degassing, and injection of industrial CO2-rich fluids within hydrothermal environments in basaltic rocks.

1083 Grothite, representing an Aland Frich titanite variety that is described by the theoretical formula (Ca,REE)(Ti,Al,Fe)SiO4(O,OH,F) (1), is a relatively rare mineral, which was previously unknown in ores from noble metal deposits. Titanites with high concen� trations of Al (up to 14 wt %) and F (up to 2.5 wt %) are characteristic of eclogites, dolomites, and marbles of Austria (2, 3). Tinbearing minerals of the titanite- malayaite series (described by the theoretical formula CaSnO(SiO 4 )) are widespread in tin ore skarn deposits of the world, Russia included (4). Compositionally peculiar fluoraluminous titanite with respective Al2O3 and F contents ranging from 9.0 to 13.5 and from 3 to 5 wt %, which may be attributed to grothite, was estab� lished in metamorphosed carbonaceous-siliceous sediments of the cherty formation in the SikhoteAlin mountainous system (Primor'e region) (5). Grothite was first established in noblemetal objects during the mineralogical study of ores from the Berizitovoe gold-polymetallic deposit of the Verkhnii Amur region. The deposit is located in the northeast� ern flank of the Amur goldore province (6) in acti� vated structures of the southeastern North Asia Craton at its junction with surrounding structures of the Tuku� ringra-Dzhagda Terrane of the Mongol-Okhotsk orogenic belt (7). The ore body of this deposit is repre� sented by the nearmeridional zone of metasomatic rocks with sulfide mineralization localized in the mas� sif of Paleoproterozoic porphyric granodiorites. The zone consists of two steep funnelshaped bodies joined near the surface and pinching out downward (Fig. 1). In plan, the zone is characterized by a complex lentic� ular shape and dips at angles of 70°-75° in the south� western direction. It is 950 m long at the surface and from 10-15 to 110 m thick. Metasomatites of the deposit are represented by quartz-muscovite rocks with impregnated almand� ine-spessartine garnet and tourmaline. Accessory minerals with variable concentrations are orthoclase, chlorite, biotite, anorthite, zinc spinel (ferruginous gahnite), sphene, zircon, epidote, allanite (orthite), prehnite, fluorapatite, fluorite, and graphite. Polymetallic mineralization widespread in the metasomatic zone of the deposit occurs in the form of complex stringers and nests. The main ore minerals are sphalerite, galenite, pyrite, pyrrhotite, and magne� tite. Ores of the deposit are of the dominant zinc com� position with subordinate admixture of lead.

Thermodynamic reaction path models were applied to provide insights into the formation of rodingites at mafic/ultramafic boundaries. The models were set up to investigate the shifts in fluid–rock equilibria as fluids move from peridotite undergoing serpentinization into a gabbroic body. Phase relations were investigated in the direction of increasing extent of reaction of the serpentinization fluid with gabbro at 200 °C, 300 °C, and 400 °C. Phase assemblages typical of rodingite (grossular + diopside ± chlorite) are predicted to form at 200 °C and 300 °C, but only in areas where the fluid is essentially unaffected by reactions with gabbro, i.e., near the contact with ultramafic rock or adjacent to a fissure filled with serpentinization fluid. As the fluid becomes more affected by reactions with the gabbro, prehnite or epidote-ss replace garnet and tremolite replaces clinopyroxene. Once the fluid chemistry is completely reset by reactions with gabbro, the predicted assemblage is typical of greenschist facies: albitic plagioclase, actinolite, chlorite, and epidote-ss. These transitions predicted in the model are very similar to what is observed in natural rodingites from different settings. Our model results hence support the hypothesis that rodingites form during serpentinization and only in areas where fluids controlled by serpentinization reactions are present. Our calculations further indicate that the formation of mineral assemblages and spatial mineralogical variability within rodingites from the ocean floor is mainly driven by steep activity gradients in protons and aqueous silica in pore fluids. Mass transfer of Ca is likely by diffusion of the CaOH + species, which is predicted to show a very steep concentration gradient across a mafic–ultramafic boundary. Rodingites act as Ca traps because of the great stability of diopside and garnet at low SiO 2 activities. Our model calculations further predict the formation of diopsidite from gabbroic and clinopyroxenite precursor rocks at 200 °C and 300 °C, suggesting that very high temperatures on the order of 800 °C are not required in the formation of diopsidite veins.

Drilling through the Palaeoproterozoic bedrock at Forsmark, central Sweden, during the site investigation for a potential geological repository of highly radioactive nuclear waste has provided high quality drill-core material from the upper 1 km of the Fennoscandian Shield. Analyses of stable isotopes (δ13C, δ18O, δ34S, 87Sr/86Sr), rare earth elements and fluid inclusions in fracture filling calcite and pyrite from these drill cores have resulted in the discrimination of several episodes of fracture mineralisations. These events represent migration of fluids during a wide range of conditions, ranging from high-temperature hydrothermal to present-day groundwater circulation. Four major events have been distinguished: 1) Precipitation of epidote, chlorite and quartz under hydrothermal conditions (T > 150–200 °C) during the Proterozoic, sometime between 1.8 and 1.1 Ga. 2) Hydrothermal circulation at temperatures close to 200 °C with precipitation of adularia, albite, prehnite, laumontite, calcite and chlorite. Most of these minerals precipitated during a tectonothermal event between 1.1 and 1.0 Ga, possibly in response to far-field effects of the Sveconorwegian orogeny. 3) Precipitation of mainly quartz, calcite, pyrite and asphaltite occurred during the Palaeozoic, at temperatures between 60 and 190 °C (mainly at

Prehnite from the Jeffrey mine, in Asbestos, Quebec, has been investigated by optical microscopy, electron-microprobe analysis, single-crystal X-ray-diffraction (XRD) analysis, and electron paramagnetic resonance (EPR) spectroscopy. Electron-microprobe analyses yield an average iron content of 0.053(34) wt% Fe 2 O 3 ; single-crystal XRD intensity datasets confirm the space group P 2 cm . Single-crystal EPR spectra measured from 290 to 13 K reveal at least six paramagnetic defects: three Fe 3+ centers, a VO 2+ radical, a Mn 2+ center, and an Al-associated O − center. Spin-Hamiltonian parameters of the VO 2+ radical show that it resides at an octahedral site and most likely originated from a V 3+ O 4 (OH) 2 octahedron by removal of a proton and trapping of a hole to form a covalent V=O bond during natural radiation. Spin-Hamiltonian parameters, including the high-spin terms of type S 4 , BS 3 and BS 5 , for the dominant Fe 3+ center also show it to reside at an octahedral site. Two less abundant Fe 3+ centers have similar orientations in effective principal axes of g, indicative of occupancies at the octahedral site as well. Their differences in effective principal values of g may be attributed to different degrees of local distortion of the octahedral site. A previous interpretation of the powder EPR spectra for two Fe 3+ sites in prehnite has been shown to be incorrect. Spin-Hamiltonian parameters for Fe 3+ in prehnite have wide implications for interpretation of EPR spectra of Fe 3+ in layer silicates.

The equation of state and high-pressure behaviour of a natural sample of prehnite from Kuruman, South Africa, Ca2.07(Al0.98,Mn0.02)(AlSi3.09O10)(OH)2, have been investigated using single crystal X-ray diffraction up to 9.75(3) GPa. A second-order Birch–Murnaghan equation-of-state fit to the isothermal P - V data below 8.7 GPa yields values of K 0T = 109.29(18) GPa and K ′ = 4. A third-order Birch-Murnaghan equation fit to the P - V data results in K ′ values equal to four, within an estimated standard deviation. The compressibility of a, b , and c unit-cell parameters is non-linear and strongly anisotropic, with room-pressure moduli of K a 0 = 83.5(7) GPa, K b 0 = 113(1) GPa, and K c 0 = 146(3) GPa and K ′ a 0 =4.5(3), K ′ b 0 = 1.3(3), and K ′ c 0 = 8.8(8). Intensity data were collected over the entire pressure range. Bond lengths and angles, refined in the average space group Pncm , suggest that the structure compresses uniformly. Above 8.7 GPa there is an additional softening of the volume and the b -axis, but the average structure is maintained across the transition.