Zoisite-(Pb), a New Orthorhombic Epidote-Related Mineral from the Jakobsberg Mine, Värmland, Sweden, and Its Relationships with Hancockite

The new mineral zoisite-(Pb), ideally CaPbAl3(SiO4)(Si2O7)O(OH), was discovered in a sample from the Jakobsberg manganese-iron oxide deposit, Värmland, Sweden. Zoisite-(Pb) is found as pale pink subhedral prisms elongated on [010], up to 0.3 mm in size, associated with calcite, celsian, diopside, grossular, hancockite, hyalophane, native lead, phlogopite, and vesuvianite. Associated feldspars show one of the highest PbO contents (~7–8 wt%) found in nature. Electron-microprobe analysis of zoisite-(Pb) point to the empirical formula (Ca1.09Pb0.86Mn2+0.01Na0.01)∑1.97(Al2.88Fe3+0.10Mn3+0.04)∑3.02Si3.00O12(OH)1.00. The eight strongest diffraction lines [dobs, Iobs, (hkl)] are 8.63 s (101), 8.11 mw (200), 4.895 m (011), 4.210 m (211), 3.660 s (112, 311), 3.097 mw (312), 2.900 s (013), and 2.725 m (511). Zoisite-(Pb) is isostructural with zoisite and its crystal structure was refined up to R1 = 0.0213 for 2013 reflections with Fo > 4σ(Fo). Pb shows a stereochemically active lone pair leading to a lopsided distribution of its coordinating oxygens. A full chemical and Raman characterization of zoisite-(Pb) and of the Pb-bearing epidote hancockite is reported, together with an improved crystal structural model of hancockite, refined up to R1 = 0.0254 for 2041 reflections with Fo > 4σ(Fo). The effects of the incorporation of Pb in the crystal structure of zoisite-(Pb), hancockite, and related synthetic and natural phases are described and discussed.

Lawsonite eclogites and metasomatites of the Utarbaev Association of the Maksyutov complex

Research subject. This article presents mineralogical, petrological and geochemical studies of lawsonite eclogites and metasomatites of the Utarbayev Аssociation of the Maksyutov complex. The Utarbayev Association forms an independent unit in the Maksyutovsky complex accretion structure. This Association features a variety of lawsonite-bearing metasomatites that form zonal halos in the frame of block-like diopside-grossular bodies included in the antigorite-serpentinite melange. The Utarbayev Association differs from typical lawsonite-blue shale complexes of collisional oro genes by the absence of mineral parageneses of lawsonite-bearing rocks of blue amphibolites.Methods. A microprobe analysis of the mineral composition was performed using a Cameca SX-100 microanalyzer. The content of petrogenic, rare and rare-earth elements was determined by X-ray spectroscopy (CPM-18) and mass spectroscopy (ICP-MS, ELAN-90). Results. An indicator mine ral paragenesis (Grt + Omp + Lws + Di) ± (Coe-Qz + Ttn) that characterizes lawsonite eclogite was found. Omphacite (Jd38–44) and unchanged lawsonite (Н2O-OH – 11.8%, Ca/Al = 0.48–0.51 и Fe/Al = 0.01 0.02%) are represented as inclusions in grossular-almandine garnet (Alm39–46Grs41–51), coesite – as microinclusions in omphacite. Thermobarometry (Grt-Omp, Grt-Omp-Ph) showed the following formation conditions of lawsonite paragenesis: T = 495–622°C under P = 2.2–2.4 GPa. The age of crystallization of lawsonite eclogite was found to be Lower Paleozoic (471–444 Ma).Conclusions. The lawsonite eclogite of the Utarbayev Association is similar to the complexes of «cold» eclogites, which are formed under the conditions of a very low geothermal gradient and are rarely preserved when removed into the upper crust. The latest review published in the «Journal of Metamorphic Geology» (2014) mentions 19 sites, where lawsonite eclogites were discovered on the earth’s surface. Тhe HP-UHP lawsonitebearing Utarbayev Rock Association complements this list.

Roméite-Group Minerals Review: New Crystal Chemical and Raman Data of Fluorcalcioroméite and Hydroxycalcioroméite

The roméite-group is part of the pyrochlore-supergroup and comprises cubic oxides of A2B2X6Y formula in which Sb5+ predominates in the B-site. The A and Y main occupants determine different minerals in the group and are important for the discovery of new mineral species. Two different roméite-group mineral samples were analysed by electron microprobe analysis (EMPA), Raman spectroscopy and single-crystal X-ray diffraction (XRD). The first sample is from Prabornaz Mine (locality of the original roméite), Saint Marcel, Valle d’Aosta, Italy, whereas the other one occurs in Kalugeri Hill, Babuna Valley, Jakupica Mountains, Nezilovo, Veles, Macedonia. Sample 1 was identified as fluorcalcioroméite, and sample 2 as hydroxycalcioroméite. Both samples belong to the cubic crystal system, space group Fd3¯m, Z = 8, where a = 10.2881(13) Å, V = 1088.9(4) Å3 for sample 1, and a = 10.2970(13) Å, V = 1091.8(4) Å3 for sample 2. The crystal structure refinements converged to (1) R1 = 0.016, wR2 = 0.042; and (2) R1 = 0.023, wR2 = 0.049. Bond-valence calculations validated the crystal structure refinements determining the correct valences at each crystallographic site. Discrepancies observed in the Sb5+ bond-valence calculations were solved with the use of the proper bond valence parameters. The resulting structural formulas are (Ca1.29Na0.55□0.11Pb0.05)Σ=2.00(Sb1.71Ti0.29)Σ=2.00[O5.73(OH)0.27]Σ=6.00[F0.77O0.21(OH)0.02]Σ=1.00 for sample 1, and (Ca1.30Ce0.51□0.19)Σ=2.00(Sb1.08Ti0.92)Σ=2.00O6.00[(OH)0.61O0.21F0.18]Σ=1.00 for sample 2. The Raman spectra of the samples exhibited the characteristic bands of roméite-group minerals, the most evident corresponding to the Sb-O stretching at around 510 cm−1.

New data on gersdorffite and associated minerals from the Peloritani Mountains (Sicily, Italy)

Gersdorffite, ideally NiAsS, and associated minerals from Contrada Zillì (Peloritani Mountains, Sicily, Italy) have been characterized through electron microprobe analysis and X-ray diffraction. Primary minerals, hosted in quartz veins, are represented by gersdorffite, tetrahedrite-(Fe), and chalcopyrite with minor pyrite and galena. Rare aikinite inclusions were observed in tetrahedrite-(Fe) and chalcopyrite. Gersdorffite occurs as euhedral to subhedral crystals, up to 1 mm in size, with (Sb,Bi)-enriched cores and (Fe,As)-enriched rims. Its chemical composition is (Ni0.79−0.95Fe0.18−0.04Co0.04−0.01)(As0.90−1.03Sb0.10−0.00Bi0.02−0.00)S0.98−0.92. It crystallizes in the space group P213, with unit-cell parameters a=5.6968(7) Å, V=184.88(7) Å3, and Z=4, and its crystal structure was refined down to R1= 0.035. Associated tetrahedrite-(Fe) has chemical formula (Cu5.79Ag0.07)Σ5.86(Cu3.96Fe1.59Zn0.45)Σ6.00(Sb3.95As0.17Bi0.03)Σ4.15S13.06, with unit-cell parameters a= 10.3815(10) Å, V=1118.9(3) Å3, and space group I-43m. Its crystal structure was refined to R1=0.027. Textural and crystallographic data suggest a polyphasic crystallization of gersdorffite under low-temperature conditions.

A Study of Some Aspects of the Volcanic History of the Lake Taupo Area, North Island, New Zealand

<p>Rhyolitic pyroclastic eruptives from the Taupo area, New Zealand have been mapped as nine tephra formations of Holocene (0-10 kyr B.P.), and six of late Pleistocene age (20-c.50 kyr B.P.). Only the 10 younger tephras are dated by radiocarbon. All formations contain PLINIAN type airfall units but three, KAWAKAWA, WAIMIHIA and TAUPO also contain a major pyroclastic flow deposit (IGNIMBRIIE) unit. Dome extrusion can only be demonstrated for KARAPITI eruptive episode, but is inferred for the other Holocene episodes. TAUPO IGNIMBRITE is the product of the most recent eruption and is a particularly well preserved and extensive, unwelded pyroclastic flow deposit, up to 50m thick. Its variety of appearance is described in terms of three lithofacies; valley facies, fines depleted facies and veneer facies, each being formed by particular mechanisms within a pyroclastic flow. Abundant charred logs, lying prone within Taupo Ignimbrite, are radial about the source and attest to a radially outward moving mass dominated by laminar flow. Lake Taupo today covers most of the volcanic source area, preventing close examination and the identification of individual source vents. A vent for each Holocene tephra is inferred from isopachs, grainsize and lake bathymetry, but the vents so inferred show no spatial distribution with time. Nevertheless they are evenly spaced along a northeast trending line and lie on intersections with a northwest trending set of lineations, indicating deep, crustal, structural control on volcanism. Cumulative volume of airfall and ignimbrite material erupted in the Taupo area in the last 50 kyr has amounted to about 175 km3 of magma. Eruptions have proceeded in a step-wise manner, indicating the period to the next eruption is about 8 kyr. By the same approach, the next eruption from the Okataina area, 50 km to the north of Taupo is expected in less than 400 years. Whole rock and mineral chemistry clearly distinguishes between the Holocene and the late Pleistocene tephras, but within each group variations are subtle and no trends with time are apparent. None of the formations exhibit evidence for a chemically zoned magma body, but some data, especially pyroxene phenocryst chemistry, suggests magma inhomogeneities of mafic elements. The Holocene tephra were probably all erupted from the same magma chamber in which crystallisation was the dominant process but convection, crystal element diffusion and chamber replenishment were all probably operative. Results obtained by electron microprobe analysis of glass shards are critically dependent on the beam diameter and current used. By standardising these at 10 microns and 8 nanoamps respectively, comparable major element analyses on glass shards from numerous tephras ranging in age from 20 kyr to 600 kyr were obtained. The stratigraphic relationships between sets of samples (located mainly distal from source) and the close chemical similarity of some samples enabled a comprehensive tephrostratigraphy to be established. In particular, MT. CURL TEPHRA has a glass chemistry quite different from other stratigraphically separate tephras, establishing correlation of Mt. Curl Tephra to Whakamaru Ignimbrite. Likewise, other ignimbrite formations can be correlated to widespread airfall tephras, so establishing an absolute ignimbrite stratigraphy. Microprobe analysis of glass shards provides a method for indirectly determining the amount of hydration. For dated samples from a known weathering environment, the parameters controlling hydration can be quantified. For glass of uniform chemistry, shard size and porosity, ground temperature and groundwater movements are the most important parameters. No shards in the 63-250 micron size range have been found with more than 9% water, suggesting once this maximum is reached, glass rapidly alters to secondary products. Detailed knowledge of the volcanic history of the Taupo area, particularly since 50 kyrs B.P. allows the volcanic hazards of the region to be assessed. Fifteen major eruptions in 50 kyr gives a frequency of 1 in 3300 years, but the timing of individual events is not evenly spread throughout that time. Monitoring for volcanic Precursory events (not being undertaken at present) is essential to gauge the present and short-term future volcanic activity of the Taupo Volcanic Zone.</p>

A Study of Some Aspects of the Volcanic History of the Lake Taupo Area, North Island, New Zealand

<p>Rhyolitic pyroclastic eruptives from the Taupo area, New Zealand have been mapped as nine tephra formations of Holocene (0-10 kyr B.P.), and six of late Pleistocene age (20-c.50 kyr B.P.). Only the 10 younger tephras are dated by radiocarbon. All formations contain PLINIAN type airfall units but three, KAWAKAWA, WAIMIHIA and TAUPO also contain a major pyroclastic flow deposit (IGNIMBRIIE) unit. Dome extrusion can only be demonstrated for KARAPITI eruptive episode, but is inferred for the other Holocene episodes. TAUPO IGNIMBRITE is the product of the most recent eruption and is a particularly well preserved and extensive, unwelded pyroclastic flow deposit, up to 50m thick. Its variety of appearance is described in terms of three lithofacies; valley facies, fines depleted facies and veneer facies, each being formed by particular mechanisms within a pyroclastic flow. Abundant charred logs, lying prone within Taupo Ignimbrite, are radial about the source and attest to a radially outward moving mass dominated by laminar flow. Lake Taupo today covers most of the volcanic source area, preventing close examination and the identification of individual source vents. A vent for each Holocene tephra is inferred from isopachs, grainsize and lake bathymetry, but the vents so inferred show no spatial distribution with time. Nevertheless they are evenly spaced along a northeast trending line and lie on intersections with a northwest trending set of lineations, indicating deep, crustal, structural control on volcanism. Cumulative volume of airfall and ignimbrite material erupted in the Taupo area in the last 50 kyr has amounted to about 175 km3 of magma. Eruptions have proceeded in a step-wise manner, indicating the period to the next eruption is about 8 kyr. By the same approach, the next eruption from the Okataina area, 50 km to the north of Taupo is expected in less than 400 years. Whole rock and mineral chemistry clearly distinguishes between the Holocene and the late Pleistocene tephras, but within each group variations are subtle and no trends with time are apparent. None of the formations exhibit evidence for a chemically zoned magma body, but some data, especially pyroxene phenocryst chemistry, suggests magma inhomogeneities of mafic elements. The Holocene tephra were probably all erupted from the same magma chamber in which crystallisation was the dominant process but convection, crystal element diffusion and chamber replenishment were all probably operative. Results obtained by electron microprobe analysis of glass shards are critically dependent on the beam diameter and current used. By standardising these at 10 microns and 8 nanoamps respectively, comparable major element analyses on glass shards from numerous tephras ranging in age from 20 kyr to 600 kyr were obtained. The stratigraphic relationships between sets of samples (located mainly distal from source) and the close chemical similarity of some samples enabled a comprehensive tephrostratigraphy to be established. In particular, MT. CURL TEPHRA has a glass chemistry quite different from other stratigraphically separate tephras, establishing correlation of Mt. Curl Tephra to Whakamaru Ignimbrite. Likewise, other ignimbrite formations can be correlated to widespread airfall tephras, so establishing an absolute ignimbrite stratigraphy. Microprobe analysis of glass shards provides a method for indirectly determining the amount of hydration. For dated samples from a known weathering environment, the parameters controlling hydration can be quantified. For glass of uniform chemistry, shard size and porosity, ground temperature and groundwater movements are the most important parameters. No shards in the 63-250 micron size range have been found with more than 9% water, suggesting once this maximum is reached, glass rapidly alters to secondary products. Detailed knowledge of the volcanic history of the Taupo area, particularly since 50 kyrs B.P. allows the volcanic hazards of the region to be assessed. Fifteen major eruptions in 50 kyr gives a frequency of 1 in 3300 years, but the timing of individual events is not evenly spread throughout that time. Monitoring for volcanic Precursory events (not being undertaken at present) is essential to gauge the present and short-term future volcanic activity of the Taupo Volcanic Zone.</p>

Ardennite-bearing mineral association related to sulfide-free ores with chalcophile metals at Nežilovo, Pelagonian Massif, North Macedonia

Among numerous minerals determined at Nežilovo, Pelagonian Massif, North Macedonia, ardennite-(As) has been discovered in two different associations and studied by means of optical microscopy, electron microprobe analysis (EMPA), and single-crystal and powder X-ray diffraction methods. The refractive indices of ardennite-(As) from Nežilovo are α=1.537(2), β=1.579(1) and γ=1.741(1), where γ corresponds to the c direction. The optical axial angle is 2Vx=49(1)∘. EMPA of the investigated samples yields the following empirical formulae: [Mn3.272+Ca0.73]Σ4.00[Al4.18Mg1.24Fe0.29Mn0.193+Zn0.10]Σ6.00(Si4.73Al0.27)Σ5.00(As0.96Si0.03V0.01)Σ1.00O22 [OH5.36(H2O)0.64]Σ6.00 for ardennite-(As) and (K0.95Na0.04Ba0.02)Σ1.01(Al1.44Fe0.303+Mg0.20Mn0.03Ti0.02 Zn0.01)Σ2.00(Si3.21Al0.79O10) (OH1.97O0.03)Σ2.00 for the associated red mica. The unit cell parameters of ardennite-(As) determined by X-ray powder diffraction are a=8.757(2) Å, b=5.836(2) Å, c=18.578(2) Å and V=941.97 Å3. The unit cell parameters of ardennite-(As) were also determined by single-crystal X-ray diffraction and are a=8.760(1) Å, b=5.838(1) Å, c=18.582(2) Å and V=950.30 Å3. Regularities of isomorphism in ardennite-related minerals are discussed. The presence of ardennite-(As) in association with 2M1 and 3T phengite polytypes provides evidence for three separate stages of formation. Conditions at which ardennite-(As) crystallized have been estimated based on compositional features of associated micas.

Aqua Traiana, a Roman Infrastructure Embedded in the Present: The Mineralogical Perspective

Construction materials from the internal ducts of Aqua Traiana, a still operative Roman aqueduct built in 109 AD to supply water to Rome, were characterized by optical microscopy (OM), scanning electron microscopy (SEM-EDS), X-ray powder diffraction (XRPD) and electron microprobe analysis (EMPA). Petrographic analysis and XRPD revealed that mortar aggregates are compatible with Vitruvius’ harena fossicia and allowed the distinction of the original mortars from those of the 17th-century papal restoration. The first showed an amorphous binder while the latter have a typical lime binder. By SEM-EDS and EMPA, the microstructure of mortar aggregates was analyzed and the composition of specific minerals quantified. Microanalysis testifies the Romans’ great expertise in the selection of pozzolanic building materials, giving evidence of the possible use of local tuffs from the Sabatini Volcanic District. It also confirms the exploitation of red pozzolan from the Roman Magmatic Province, specifically from the Alban Hills district. OM also proves a high compatibility with local supplies for bricks and cocciopesto. Of these, the first were fired at moderately low temperature, while the latter show an amorphous binder as in the original Trajan mortars. All building materials thus stand for similar technological choices and a coeval production.