The sulfosalt minerals are of great importance for a better understanding of ore forming conditions and mineralization distribution, especially in the case of hydrothermal deposits. So far, few Raman studies were conducted on this type of minerals. In the present work, were studied several samples from Baia Sprie ore deposit, Romania—a worldwide classic example for hydrothermal mineralizations. Bismuthinite, lillianite-gustavite, heyrovskyite, cosalite, tetrahedrite-tennantite, bournonite and semseyite have been analyzed using electron microprobe and Raman spectrometry. The Raman spectra of bismuth sulfosalts, Ag-rich tetrahedrite and semseyite are discussed for the first time. The Bi sulfosalts show typical ν1 symmetric stretching modes of the MS6 octahedra at 286–279 cm−1, ν2 stretching at 216–207 cm−1 and ν5 bending modes at 140–112 cm−1. The transition from tetrahedrite to tennantite is very clearly observed in the Raman spectra. Several changes are marked through the solid solution, as the Sb—As isomorphic substitution takes place. Therefore, as the composition changes from As-member (tennantite) to the Sb-member (tetrahedrite), a shifting trend is observed in the Raman spectra, especially for the fundamental modes. The spectra of bournonite are dominated by two very strong lines at 325 and 296 cm−1. The Raman band at 331 cm−1 in semseyite is assigned to ν1 symmetric stretching modes of the octahedra. The ν2 stretching is observed at 212 cm−1, while the bending mode ν5 appears at 148–143 cm−1.
The Baia Sprie epithermal system, a well-known deposit for its impressive mineralogical associations, shows the proper conditions for acid mine drainage and can be considered a general example for affected mining areas around the globe. Efflorescent samples from the abandoned open pit Minei Hill have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and near-infrared (NIR) spectrometry. The identified phases represent mostly iron sulfates with different hydration degrees (szomolnokite, rozenite, melanterite, coquimbite, ferricopiapite), Zn and Al sulfates (gunningite, alunogen, halotrichite). The samples were heated at different temperatures in order to establish the phase transformations among the studied sulfates. The dehydration temperatures and intermediate phases upon decomposition were successfully identified for each of mineral phases. Gunningite was the single sulfate that showed no transformations during the heating experiment. All the other sulfates started to dehydrate within the 30-90°C temperature range. The acid mine drainage is the main cause for sulfates formation, triggered by pyrite oxidation as the major source for the abundant iron sulfates. Based on the dehydration temperatures, the climatological interpretation indicated that melanterite formation and long-term presence is related to continental and temperate climates. Coquimbite and rozenite are attributed also to the dry arid/semi-arid areas, in addition to the above mentioned ones. The more stable sulfates, alunogen, halotrichite, szomolnokite, ferricopiapite and gunningite, can form and persists in all climate regimes, from dry continental to even tropical humid.
Electron microprobe analyses are reported on newly-identified occurrences of Pb–Sb/As sulfosalts from the Coranda-Hondol ore deposit, Certej area, South Apuseni Mountains, Romania. The Coranda-Hondol deposit is an intermediate-sulfidation Au–Ag epithermal system hosted in propylitic altered andesitic rocks covered by Cretaceous and Neogene sediments. The main base-metal sulfides are sphalerite, pyrite and galena. Subordinate amounts of chalcopyrite, arsenopyrite, pyrrhotite, marcasite, tetrahedrite–tennantite, bournonite–seligmannite ± geocronite–jordanite, stibnite and Au–(Ag)–tellurides complete the paragenetic sequence. Gangue minerals are quartz, calcite and barite. Hydrothermal alteration is expressed as pyritisation, silicification, potassic alteration, carbonitisation and phyllic (or sericitic) alteration.
Minerals of the bournonite–seligmannite and geocronite–jordanite series are described for the first time in samples from different levels of the Coranda-Hondol open pit. Both series show chemical variations in terms of Sb/(As + Sb) ratio, and display a general spatial trend within the deposit in which the Sb content of both series tends to increase towards upper levels. Textural relationships between the two sulfosalt series and their chemical variations suggest that the presence of Sb in hydrothermal fluids favors precipitation of bournonites, whereas As favors precipitation of jordanites. Compositions of minerals from the bournonite–seligmannite and geocronite–jordanite series extend from Bnn35 to Bnn98, and from Gcn14 to Gcn76, respectively. Back-scattered electron imaging reveals grain-scale compositional heterogeneity in bournonite–seligmannite, seen as concentric and layered oscillatory zoning patterns. These zoning patterns were observed only in the upper parts of the deposit, and suggest an increasing As content in late fluids.
Trace elements (Te, Se and Fe) are preferentially incorporated into Sb-rich members of Bnn–Slg series. This is consistent with the association of gold–silver–tellurides and bournonites identified at the Coranda-Hondol deposit. Variable conditions within the Coranda-Hondol hydrothermal system suggest that precipitation of Au ± Ag–tellurides occurred via two possible mechanisms: (i) Te vapor condensation into precious metal brines during boiling and (ii) by fluid throttling with periodic release of volatiles.
The Baia Sprie epithermal ore deposit is one of the best-known deposits in Romania and Europe. It consists mainly of a vein system with two major veins: (1) Principal Vein and (2) Southern Vein, along fractures that delimitate an andesitic block and a subvolcanic intrusion. The Principal Vein is one of the longest hydrothermal veins in Europe, with more than 5 km in length, a thickness that varies between 0.5 and 22 m and it extends vertically on more than 800 m. Samples belonging to different levels of Principal Vein have been analyzed using electron microprobe. A new occurrence of bismuth minerals was identified within the deeper part of the deposit: bismuthinite, lillianite–gustavite, disordered intergrowths of lillianite homologues, heyrovskyite and cosalite. The presence of Bi-sulfosalts suggests temperature of ~ 350 °C, while the As content in arsenopyrite indicates formation temperatures between 320 and 360 °C. The oscillatory zoning bands of pyrite and tetrahedrite–tennantite members indicate an increased Sb and As concentration in hydrothermal solutions. The zoning textures suggest a high S and low As concentration in the early fluids followed by multiple pulses of As-rich solutions in the late fluids. The high content of As in pyrite and the presence of bismuth minerals at Baia Sprie deposit can represent indicators for significant Au concentrations within the lower level of the mineralization. From the type locality Baia Sprie new analytical data for semseyite were presented and for the first time a new occurrence of geocronite–jordanite series was identified in the intermediate and upper part of the deposit.
The Coranda-Hondol ore deposit (Certej, Romania) is a sulfide ore deposit that was mined primarily for gold, silver, lead, and zinc. Secondary minerals were formed through a precipitation process from sulfate solutions with a high concentration of dissolved metals (especially Fe). These sulfate solutions resulted from acid mine drainage. Fourteen waste samples were analyzed through Raman spectrometry, X-ray diffraction, and scanning electron microscopy. Fe3+-, Fe2+-, Cu-, Zn-, Ca-, Mg-, and MnAl-hydrated sulfates were identified. All are unstable when exposed to the laser beam of the Raman spectrometer. Coquimbite, copiapite, ferricopiapite, hydroniumjarosite, and gunningite turn into anhydrous forms or oxides, depending on the laser power. Gypsum turns into bassanite, while apjohnite loses all water molecules at 53.6 mW laser power on the surface of the sample. Rhomboclase, melanterite, rozenite, antlerite, and brochantite break down without forming new minerals. Fe2+-sulfates do not change into hematite under laser irradiation. Epsomite and hexahydrite are stable at 53.6 mW laser power.
Au-Ag- and Ag-tellurides are widely abundant in the vast majority of the “Golden Quadrilateral” (Metaliferi Mts., Romania) ore deposits. Optical microscope observations, electron microprobe and μ-Raman analyses have been successfully carried out to identify Au-Ag-Te minerals from Coranda-Hondol open pit (part of Certej deposit, South Apuseni Mountains, in Romania). The identified tellurides are hessite (Ag2Te), petzite (Ag3AuTe2) and stützite (Ag5-xTe3, where x = 0.24-0.36) and they usually occur as patches (reaching 90-100 μm in length) in galena, bournonite-seligmannite or at the contact between the last three minerals. In general, all the microanalytical data are stoichiometric with a slightly compositional variation in the case of hessite. The μ-Raman spectrum of stützite shows a characteristic Raman fingerprint with a very strong band at 147 cm-1. The broadness of the Raman band (147 cm-1) indicates a non-homogeneous distribution and, in conjunction with the strong heterogeneity observed under microscope, it suggests that the tellurides have formed contemporaneously and they can possibly be attributed to a later silver-rich telluride-bearing substage.
The Voronet Monastery is one of the greatest cultural treasures of Romania, dating from the 15th century. In the present study, the green and blue pigments of its exterior frescoes (16th century) were analyzed through fibre-coupled Raman spectroscopy. A wide range of typical pigments, including malachite, basic Cu sulphates, azurite, lazurite, smalt, gypsum, anhydrite and calcite were found, together with other “rare pigments,” such as conichalcite and dolerophanite. The green pigment is either a mixture of malachite and conichalcite or Cu sulphates while the blue pigment contains either lazurite, or a mixture of azurite and a minor quantity of smalt, gypsum and anhydrite. The identification of these pigments is very important for the restoration work, the monastery being a UNESCO World Heritage Site.
Natural sphalerite samples collected from the Baia Sprie ore deposit (Romania) were analyzed through Raman spectroscopy, SEM-EDX and XRD. The most intense Raman lines at 300, 331 and 350 cm−1 were used to improve iron determination method from sphalerites by Raman spectroscopy. It is well known that the iron content of synthetic sphalerite can be quantified by measuring the height of Raman lines (h1, h3). By using the new h2/h3 and (h1 + h2)/h3 ratios and two additional linear equations, this method is improved and becomes suitable to natural sphalerites. The results are in good agreement with the SEM-EDX data.
A multi-technique characterization and a provenance study of the black pigment used in Cucuteni pottery painting (Neolithic age, Romania) were carried out. 127 Cucuteni shards were analyzed by Raman spectrometry. The main components of this pigment are pyrolusite and/or jacobsite. Hematite and quartz are frequent minor components and Ti oxides were seldom found. The manganiferous corpuscles discovered at Neamţ county (eastern part of Romania) were the raw material of the Cucuteni black pigment. The Mn corpuscles were studied using XRD, Raman, FT-IR and Atomic Absorption Spectrometry. The main components are birnessite, goethite and frequently, quartz. Raw material was subjected to a temperature of 750 °C for 6 h and,once cooled, analyzed through Raman and FT-IR spectrometry. Pyrolusite, hematite and quartz were found in the heated powder sample.
Two stone axes of Late Bronze Age from Moldova region (Romania) have been studied by Raman spectroscopy. The first axe (A1) belongs to the archaeological site Vînători (Neamț county). From a petrographic viewpoint, the sample is an andesite with pyroxenes and amphiboles, having a porphyric texture. The Raman study reveals the presence of plagioclase feldspar, pyroxene, hornblende, hematite and prehnite. The second artefact (A2) belongs to Topolița archaeological site (Grumăzești, Neamț county). Petrographically, the sample is a meladiorite with hornblende. Besides plagioclase and amphibole, Raman spectroscopy also identified titanite, quartz, epidote and hematite. On the surface it has a thin and transparent layer of black carbon. The Raman spectral lines of black carbon corespond to those of the highly disordered graphite due to the broaden D and G peaks and also due to the inclusion of D2 band (~1630 cm-1) in the broad G band (~1600 cm-1).The black carbon uniform layer of the axe A2 was achieved by firing in a reducing atmosphere.
Raman and infrared spectroscopy has been used to analyze three samples from the Hondol open pit, in order to identify and characterize these samples using vibrational features. The minerals found are secondary hydrated sulfate minerals associated with both the alteration of sulfide-bearing mine wastes and primary minerals. The minerals found by vibrational spectroscopy are: ferricopiapite Fe3+0.66Fe3+4(SO4)6(OH)2 • 20(H2O); coquimbite Fe3+2(SO4)3 • 9(H2O); and epsomite Mg(SO4) • 7(H2O). The spectral features observed in these minerals allowed four distinct hydrous sulfates to be discriminated without conventional methods, such as XRD or chemical analyzes. The study shows the potential of Raman and infrared spectroscopy to identify hydrous sulfates very fast, ondestructively, non-invasively, with a very small volume samples. Both Raman and infrared spectra show the fundamental vibrational modes of SO4 groups. Also, the spectral variations of the internal modes of sulfate tetrahedra were used to discriminate between minerals from the same group, where divalent or trivalent cations from the octahedral sites or H2O in different proportions were the only differences.
11 fragments of wall painting from the Beroe fortress, Romania (4th –6th century) were analysed through Raman spectroscopy. The yellow-brown pigment on the fragments is jarosite and/or Na-jarosite. Other than at 445 cm-1, the Raman lines of all the spectra are identical. This Raman line is slightly shifted in different spectra, and this fact proves the presence of both jarosite and Na-jarosite.
Raman and infrared spectral studieswere performed on six natural minerals from the doublechain silicate group. We analyzed samples of grunerite, actinolite, tremolite, pargasite (+kaersutite) and riebeckite in order to determine the spectral differencesbetween them and to identify the vibrations that occur. Also, for one sample thought to be pargasitewe obtained the Raman spectrum of kaersutite, while anothersample was determined as a Ti-rich pargasite, since the difference between these two minerals consists in the presence of more than 0.50apfu VITi in kaersutite (titaniferous calcic amphibole). The Raman spectrum of kaersutite exhibits characteristic bands of the VITi-OH vibration around 580–590cm-1 and 750cm-1. These two bands are stronger than the symmetric stretching vibration of the Si-Ob-Si (ν1), which arises as the strongest band in all otheramphibole minerals ofthe present study, around 650–670cm-1. Both Raman and infrared spectra of all the analyzed samples reveal the presence of Fe2+, Mg2+ or other cations in the octahedral sites, displaying distinct bands in the ~300-450cm-1 spectral region, as well as in the OH stretching region (3600–3700cm-1).
The black pigment of 112 Cucuteni A and Cucuteni B pottery has been analyzed through Raman spectroscopy. The black pigment contains pyrolusite and jacobsite; quartz and anatase have only accidentally been observed. Black Carbon was also identified, but only in two samples. The spherical or oblate black corpuscles discovered at Feteşti-La Schit (Suceava county) were analyzed by means of X-ray diffractometry and Raman spectroscopy. They consist of Mn ± Fe oxihydroxides and quartz. No Mn carbonates or silicates have been identified. The mineralogical composition of the pigment applied to the pottery shards, as well as that of the raw pigment, together with the use of the same pigment over a long period of time (1100 years), suggest the exploitation of a large sedimentary mineral deposit, such as the Mn sedimentary ores from Nikopol (Ukraine).
Raman spectroscopy is a simple, powerful and fast method to identify and distinguish between different minerals from the amphibole group of the inosilicate class. We analyzed samples of grunerite, actinolite, nephrite, Cr – actinolite (smaragdite), uralite (var. of actinolite), tremolite, pargasite, glaucophane and riebeckite in order to determine their Raman spectra and their fingerprint. The structure of these amphiboles belongs to the space group C2/m. Also, through this work we intend to show types of linkages between Si and bridging O (Ob) or non-bridging O (Onb), and complex vibrations that occur in all amphibole spectra, corresponding to the symmetric stretching modes (νs) of the Si-Ob-Si bridges or O-Si-O linkages and to the asymmetric stretching modes (νas) of the Si-Ob-Si bridges and O-Si-O linkages. The most distinct Raman peak detected in this Raman study of amphiboles is around 660-675 cm-1, which is assigned to the ν1/νs (symmetric stretching vibrations) of the Si-Ob-Si bridges. Some spectra present two very weak peaks at ~2330 cm-1 and ~2437 cm-1, respectively, due to the substitution of K or Na with H3O+ (K, Na ↔ H3O+) and NH4+ (K, Na ↔ NH4+); these spectral bands were identified at potassium micas.
Some of the most common carbonates have been investigated by non-contact Raman spectroscopy. The synthetic alkali carbonates K2CO3 and Na2CO3 have also been studied. The Raman spectrum of aurichalcite is different from that of malachite. This spectrum has a characteristic intense band at 1069 cm-1 which is assigned to the ν1 symmetric stretching mode of the carbonate unit. The two low intensity Raman lines of 1485 and 1507 cm-1 may be ascribed to the ν3 asymmetric stretching modes. To the ν4 mode (doubly degenerate symmetric bending) are attributed the values of 706 cm-1 (ν4a) and 733 cm-1 (ν4b). A number of bands with different intensities are observed in the lowest spectral shift (285, 388, 430, 461 and 498 cm-1). These Raman lines are assigned to the CuO and ZnO stretching and bending vibrations. A single band of the OH-stretching modes is observed at 3344 cm-1.
Last update: June 10, 2015 at 6:05 pm