Decay Process of Serpentinite: The Case of the San Giovanni Baptistery (Florence, Italy) Pavement

Serpentinite is a low-grade metamorphic rock derived from the transformation of ultramafic rocks. Mainly because of its aesthetic characteristics it has been widely used as a building and ornamental stone. “Verde di Prato” is the most common local name used in Tuscany to refer to this type of rock, historically quarried in this area and used for many centuries in a large number of monuments of this region. In this paper, we report the results of a study carried out on the serpentinite from the pavement of the Florence baptistery, to properly characterize it from a physical point of view, describe the rock conservation state, and understand the phenomena responsible for its decay. The studied rock displays numerous forms of decay including fractures, loss of material, erosion, discolouration and efflorescence. X-ray diffractometer analyses of the efflorescence revealed the presence of numerous salts whose formation can be imputed to multiple, possibly concomitant, causes such as the high relative humidity and the variation of inside temperature, the presence of concrete and/or cementitious mortars in the subsoil, atmospheric pollution and the burial ground existing close the baptistery.

Practical and Thermodynamic Constraints on Electromicrobially-Accelerated CO2 Mineralization

By the end of the century tens of gigatonnes of CO2 will need to be removed from the atmosphere every year to maintain global temperatures. Natural weathering of ultramafic rocks and subsequent mineralization reactions can convert atmospheric CO2 into ultra-stable carbonates. But, while natural weathering will eventually draw down all excess CO2, this process will need hundreds of thousands of years to do it. The CO2 mineralization process could be accelerated by weathering ultramafic rocks with biodegradable lixiviants like organic acids. But, in this article we show that if these lixiviants are produced from cellulosic biomass, the demand created by CO2 mineralization could monopolize the world's supply of biomass even if CO2 mineralization performance is high. In this article we demonstrate that electromicrobial production technologies that (EMP) combine renewable electricity and microbial metabolism could produce lixiviants for as little as $200 to $400 per tonne at solar electricity prices achievable within the decade. Furthermore, this allows the lixiviants needed to sequester a tonne of CO2 to produced for less than $100, even with modest CO2 mineralization performance.

Investigation of the Anisotropic Structure of Travertine in Terms of Geological and Physico-Mechanical Properties: Sarıhıdır (Avanos-Nevşehir) Travertine Quarry

Travertine is a sedimentary rock with generally layered structure, mainly comprising carbonate. They are used for different purposes in interior and exterior spaces by cutting parallel or perpendicular to the bedding according to use. Travertine may contain several facies linked to variations in conditions during formation. With these features, travertine is one of the rocks with anisotropy most commonly observed. In this study, the anisotropic structure due to facies and layering in travertine was investigated considering geological and engineering properties. The Sarıhıdır travertine quarry face was divided into four different zones with different features. Chemical, mineralogic, physical, index and mechanical properties of the samples taken from these zones were determined. During determination of engineering parameters, samples were prepared parallel and perpendicular to bedding. The source of the travertine is a mixture of limestone, dolomite, evaporite and ultramafic rocks and they have epigean character, though they were affected by the hypogean environment. It appeared there were textural differences between the zones, rather than differences in chemical and mineralogic composition. When travertine was cut parallel to layering, all zones were suitable for decoration and facing. Only T-4 zone samples cut parallel were useable for flooring and load-bearing elements. In terms of compression and abrasion resistance, T-4 zone was better than the other zones. The cut direction of the travertine samples is an important factor for physical and mechanical behavior. Samples cut parallel to layering were observed to provide better results. According to the results, it is recommended to use products from the same travertine zone side-by-side in structures and to consider the cutting direction for long life of the building and to prevent economic losses.

Gold and silver accessory minerals in ultramafites of the Kyzyr-Burlyuksky ultramafic massif (Western Sayan)

The study focuses on gold and silver accessory minerals (native silver, cuprous gold, luanheite (Ag3Hg), unspecified mineral phase (Cu,Ag,Hg), first diagnosed in dunites and apodunite serpentinites of the Kyzyr-Burlyuksky ultramafic massif, which is part of the Kurtushibin ophiolite belt of Western Sayan. The revealed ore minerals are mainly observed in the form of single hypidiomorphic, irregular microscopic precipitates (0.5– 3.0 μm) mainly inside magnetite, much less often in grains of avaruite. Typomorphic and chemical features of ore minerals, their natural setting in rock-forming silicate matrix are characterized. Formation and concentration of these accessory minerals is associated with superimposed low-temperature transformation (hydration) processes affecting original ultramafic rocks. At the same time, the presence of luanheite and an unnamed phase (Cu,Ag,Hg), along with the previously identified potarite (PdHg), is probably evidence of low-temperature conditions of mineral formation during the manifestation of epigenetic processes of serpentinization (lowgrade metamorphism) due to solutions enriched in mercury. The source of such solutions could be gabbro intrusions that penetrated later into the main ultramafic body.

Deposits of the Udokan-Chineysky ore-magmatic system of Eastern Siberia

The aggregate of ore deposits localized in the Udokan-Chineysky ore district is unique and is the result of multi–stage, polygenetic formation. The deposits of copper and other metals formed at various depths occur within a limited area. The oxide and sulfide ore are spatially associated in the sedimentary rocks pertaining to the Paleoproterozoic Udokan Supergroup and the intrusive mafic–ultramafic rocks of the Chineysky Complex. The granite rocks of the Kodar Complex and gabbro rocks of the Chineysky Complex also date back to Paleoproterozoic. The same age has been established for metasomatic Nb–Ta–Zr–REE–Y and U mineralization in the albitized terrigenous rocks of the Udokan Supergroup (Katugin deposit and Chitkanda prospect) and U–Pd prospects hosted in terrigenous rocks. The U–REE mineralization superposed on the titanomagnetite deposits in the Chineysky pluton has not analogues in the world’s practice. The occurrences of uranium mineralization have been noted in form of pitchblende and U–Th rims around chalcopyrite grains at the Unkur copper deposit hosted in sedimentary rocks. The enrichment in U and Pb has been documented in crosscutting quartz veinlets with bornite mineralization at the Udokan deposit.

Multi-stage serpentinization of ultramafic rocks in the Manlay Ophiolite, southern Mongolia

Serpentinization of ultramafic rocks in ophiolites is key to understanding the global cycle of elements and changes in the physical properties of lithospheric mantle. Mongolia, a central part of the Central Asian Orogenic Belt (CAOB), contains numerous ophiolite complexes, but the metamorphism of ultramafic rocks in these ophiolites has been little studied. Here we present the results of our study of the serpentinization of an ultramafic body in the Manlay Ophiolite, southern Mongolia. The ultramafic rocks were completely serpentinized, and no relics of olivine or orthopyroxene were found. The composition of Cr-spinels [Mg# = Mg/(Mg + Fe2+) = 0.54 and Cr# = Cr/(Cr + Al) = 0.56] and the bulk rock chemistry (Mg/Si = 1.21–1.24 and Al/Si < 0.018) of the serpentinites indicate their origin from a fore-arc setting. Lizardite occurs in the cores and rims of mesh texture (Mg# = 0.97) and chrysotile is found in various occurrences, including in bastite (Mg# = 0.95), mesh cores (Mg# = 0.92), mesh rims (Mg# = 0.96), and later-stage large veins (Mg# = 0.94). The presence of lizardite and chrysotile and the absence of antigorite suggests low-temperature serpentinization (<300 °C). The lack of brucite in the serpentinites implies infiltration of the ultramafic rocks of the Manlay Ophiolite by Si-rich fluids. Based on microtextures and mineral chemistry, the serpentinization of the ultramafic rocks in the Manlay Ophiolite took place in three stages: (1) replacement of olivine by lizardite, (2) chrysotile formation (bastite) after orthopyroxene and as a replacement of relics of olivine, and (3) the development of veins of chrysotile that cut across all previous textures. The complex texture of the serpentinites in the Manlay Ophiolite indicates multiple stages of fluid infiltration into the ultramafic parts of these ophiolites in southern Mongolia and the CAOB.

Geochemical heterogeneity of polychronous relict zircons from restitogenic ultramafic rocks of the Shaman massif (Eastern Transbaikal region)

Research subject. The distribution patterns of rare earth elements (REE), as well as Y and Th, in the grains of polychromous zircons from the restitogenic ultramafic rocks of the Shaman massif (Eastern Transbaikalia). This massif is a steeply inclined protrusion that is part of the eastern branch of the Baikal-Muya ophiolite belt.Materials and methods. 31 zircon grains 100–150 μm in size were isolated from a composite sample of harzburgites and dunites with a total weight of 4 kg for their subsequent U-Pb isotope dating. These analyzes were performed by the LA-ICP-MS method by scanning along straight profiles on the plane of sections of representative zircon grains.Results. All zircon grains from the general collection are characterized by a rounded shape, a rough surface, microfracturing, a weak cathodoluminescent glow to a complete absence, and an irregular oscillatory zoning. In some grains, microinclusions of epigenetic minerals, such as quartz, mica, etc. were found. It was previously determined that, within the entire collection of zircon grains, the values of their age, as well as U and Th contents, vary across rather wide intervals (3049–502 Ma), the reasons for which are the subject of discussions. The LA-ICP-MS scanning over the profiles of representative zircon grains from the general collection showed that REE, Th, and Y are distributed highly unevenly, occasionally showing signs of zoning. It is assumed that the zircons found in the ultramafic rocks of this massif are a relict phase and appeared as a result of the transformation of very ancient (more than 3 billion years old) juvenile crystals of this mineral, which had been originally located in the upper mantle protolith.Conclusions. Transformations of juvenile zircons and their transformation into a relict phase occurred in the process of partial melting of the protolith, during which they underwent thermal action (annealing), chemical resorption, as well as disturbances in their U-Pb systems, which caused uneven “rejuvenation” of their isotopic age. It is also assumed that the revealed geochemical heterogeneity of relict zircons was mainly due to the later redistribution of trace elements with the simultaneous formation of microinclusions of epigenetic minerals in the process of infiltration along microcracks into ultramafic rocks, precipitated by acidic melts.