Kaolinisation of granite in an urban environment

Under natural acid and wet conditions, one of the main weathering processes affecting granitic rocks is the kaolinisation of Na, Ca and K-feldspar minerals by H₂O + CO₂ attack. We here report the occurrence of authigenic kaolinite on the surface of an eighteenth century granitic monument covered with sulphate-rich weathering patinas. We suggest that, in humid mesothermic climates, anthropogenically derived gaseous SO₂ from air pollution is responsible for accelerated kaolinisation of feldspars in an urban environment; SO₂ from air pollution thus plays a dual role in the weathering of silicate rocks being responsible for the well known sulphation of Ca-bearing materials leading to the formation of sulphate salts such as gypsum as well as the weathering of feldspar minerals to kaolinite. The kaolinisation reaction weakens the granite microfabric leading to enhanced decay of the building stone.     

Trend analysis and first time observations of sulphur dioxide and nitrogen dioxide in South Africa using TROPOMI/Sentinel-5 P data

The 17 Sustainable Development Goals (SDGs) aim to end extreme poverty and create a healthy, sustainable world by the year 2030. Goal 7 is of interest to this study as it targets access to clean and affordable energy. However, in this study we show that the energy created in South Africa is not necessary clean. South Africa has numerous coal-fired power station located in the Mpumalanga (MP), Gauteng (GP) and Limpopo (LP) provinces. These power station produce tons of toxic pollutants including sulphur dioxide (SO₂), nitrogen dioxide (NO₂) and sulphates (SO₄). These pollutants are known to have a negative impact on human health, climate and the environment. In this study we use the sequential Mann-Kendall test to investigate the 39 year (1980–2019) trends of SO₂, NO₂ and SO₄ from these source areas. We also report for the first time on the observations of SO₂ and NO₂ from the Sentinel-5 P sensor over South Africa. Increasing trends of SO₂ were observed in the MP, LP and GP regions. The increase was mostly due to the emissions from coal-fired power stations. Moreover, the increase of SO₂ over the years could be due to the increasing demand in electricity, aging power stations and the low quality of coal used. Sentinel-5 P observations of SO₂ and NO₂ over South Africa were observed in the MP, GP and LP regions as a result of coal-fired power stations. Dispersion of SO₂ and NO₂ over South Africa were observed in the winter months, while confined SO₂ and NO₂ in the source region were observed in the summer months.     

The peat bog at Zinnwald-Georgenfeld revisited after 25 years: Geochemical investigation of water,Sphagnum moss and peat cores

From 1992 to 1994, trace metal concentrations of bog water, Sphagnum mosses and peat cores of the bog “Georgenfelder Hochmoor” at Zinnwald-Georgenfeld in the Eastern Ore Mountains (Germany) were investigated. A sampling campaign in September 2019 allows the comparison of the older measurements with today's trace metal concentrations. No changes were found in the bog waters, while the trace metal concentrations of the Sphagnum mosses have decreased significantly. Due to the low growth rate of the peat and despite certain heterogeneity between the peat cores, the investigated elemental data for the peat sampled in the 1990s and in 2019 are in the same concentration range. The maximum concentrations are measured in the upper samples of all peat cores for the analysed elements (except sulphur). Compared to upper crustal data, a different behaviour of the elements is observed: Cr, Sc, Ti, and V, rare earth elements show crustal ratios, while Al and Si are also influenced by crust-air fractionation. Cd, Cu, Ni, Pb, and Zn are additionally enriched by anthropogenic atmospheric inputs from industry and transport. These results confirm the assumption that peat cores record past atmospheric deposition.     

Chromite compositions in nickel sulphide mineralized intrusions of the Kabanga-Musongati-Kapalagulu Alignment,East Africa: Petrologic and exploration significance

Chromite is a ubiquitous accessory mineral in the olivine-pyroxene cumulate bodies that host massive and disseminated nickel sulphide mineralization in intrusions of the Kabanga-Musongati-Kapalagulu Alignment in East Africa. Its composition is related to the conditions of emplacement and petrologic evolution of its host magma in a spectrum of intrusions ranging from classical lopolithic layered intrusions to groups of smaller, discrete sill-like chonoliths.The Kapalagulu lopolithic intrusion, emplaced into polymetamorphosed Archæan-Palæoproterozoic crust, contains abundant chromite with relatively oxidized compositions, whereas chromites from the highly-mineralized Kabanga chonolith intrusions, emplaced into graphitic and sulphidic schists, are strongly reduced in terms of their Fe³⁺/Fe^total ratio. Ni in chromite correlates with Ni in olivine: Ni in both is depleted in the more strongly sulphide-mineralized intrusions. The Musongati intrusion, also emplaced through graphitic schists, but much larger and less-well mineralized in sulphides than Kabanga, has chromites intermediate in character. The compositions of the chromites can be used to determine the petrologic history of the intrusions, and may prove to be a useful exploration tool in such mineralized belts.     

Origin of salts in stone monument degradation using sulphur and oxygen isotopes: First results of the Bourges cathedral (France)

The crystallisation of soluble sulphate salts is one of the most important factors of stone monument degradation. The origin of these salts is variable: marine, air pollution, building or restoration material. The lack of certainty about these sources represents a problem for restoration campaigns. The use of sulphur and oxygen isotopic tracers allows to discriminate the origins of materials and some stone deterioration patterns like black crusts (e.g. [Šrámek J., 1988. Sulfur Isotopes in the revealing corrosion mechanism of stones. 6th International Congress on Deterioration and Conservation of Stone,. Proceedings, ed. J. Ciabach. Nicholas Copernicus University, Torun, Poland, 341–345.]). First results obtained on the Bourges cathedral (France) show that the sulphur and oxygen isotopic composition of sulphates from external (atmospheric pollution) and internal (mortars, plasters and sulphates coming from stone sulphide oxidation) origins constitute well differentiated poles. The isotopic composition of sulphates implied in different stone deterioration patterns is well explained by a combination of these poles. The present study will be extended to other French monuments located in different lithological and hydroclimatic settings where contributions of sea salts and ancient chemical treatments are suspected.     

Metamorphic ore remobilization in the Hällefors district, Bergslagen, Sweden: constraints from mineralogical and small-scale sulphur isotope studies

The marble- and metavolcanic-hosted Pb–Zn–(Ag–Sb–As) deposits of the Hällefors district, located in the Palaeoproterozoic Bergslagen ore province, south central Sweden, comprise both stratabound sulphides and discordant, Ag-rich sulphide–sulphosalt veins. The complex sulphide–sulphosalt assemblages of the Alfrida-Jan Olof mines at Hällefors were investigated by a combination of ore microscopy, electron-microprobe analysis, and in situ laser sulphur isotope analysis. The massive ore is characterized by positive and homogeneous ³⁴S (+1.4 to +2.7 V-CDT), whereas vein-hosted sulphides and sulphosalts exhibit similar, but generally less positive to slightly negative ³⁴S (–0.6 to +2.0). Comparison of the observed ore mineral assemblages with calculated phase equilibria in the system Fe–As–S–O–H and isotopic fractionation as a function of temperature, oxygen fugacity and pH indicates that the vein-type mineralization was formed from relatively reduced and rather alkaline hydrothermal fluids. At these reduced conditions, fractionation of ³⁴S via changes of fO₂ is insignificant, and thus the isotopic signatures of the vein minerals directly reflect the composition of the sulphur source. We therefore conclude that the vein-type ore essentially inherited the sulphur isotope signature from the pre-existing massive sulphides via metamorphic remobilization at approximately 300–400°C and 2–3 kbar. Scales of remobilization observable are on the order of about 5 mm to 30 cm. Overall, the sulphide–sulphosalt assemblages from the Alfrida-Jan Olof mines exhibit ³⁴S values which are comparable to a majority of metasupracrustal-hosted deposits in the Bergslagen province, thereby suggesting a common origin from ca. 1.90–1.88 Ga volcanic-hydrothermal processes.Editorial handling: S. Nicolescu     

Isotopic ratio and concentration of sulfur in the undersaturated alkaline magmas of Vulture Volcano (Italy)

Both the ³⁴ value and the total S content of products from Vulture Volcano, Italy are mainly controlled by the separation of S gases, predominantly SO₂, from high f _O2magmas containing S predominantly as SO _2- ⁴ . The addition of evaporites to such magmas appears to be a relatively uncommon and limited phenomenon. The total S content of the most primitive product of Vulture Volcano (5600 mg/kg) is very high. The high ³⁴S value of 4 indicates an origin through the partial melting of a mantle containing high S, enriched in ³⁴S of unknown origin.     

铂族元素矿床的主要类型、成矿作用及研究展望

铂族元素(PGE)矿床的研究在过去几十年取得了重要的进展.它可以赋存于不同的岩石类型、形成于不同的时代.内生PGE矿床与不同的岩浆类型及热液活动有关.由于铂族元素特殊的化学性质,比较稳定且难熔于普通的酸、碱等,故铂族元素成矿具有特殊性.PGE矿床可划分为岩浆型、热液型、火山块状硫化物型(VMS)和外生型四大类型.岩浆型又可分为铜镍硫化物型、铬铁矿型和磁铁矿型,热液型主要有斑岩型和夕卡岩型,外生型包括黑色页岩型和砂铂矿型.本文讨论了各岩浆演化过程中:(i)硅酸盐和氧化物的分异,(ii)富Fe矿物(橄榄石、辉石、磁铁矿、铬铁矿)的分异,(iii)岩浆的混染,(iv)不同成分、硫不饱和的岩浆的混合等,都可以导致岩浆中硫达到饱和,一旦形成不混熔硫化物熔体,硫化物富集,将形成有经济价值的PGE矿床.同时,成矿还受温度、Ni和Cu含量、体系中其它组分和硫逸度的控制.岩浆后期的热液蚀变会改变PGE的含量和品位,但典型的铂矿床一般没有遭受热液蚀变作用的显著影响.本文指出了铂族元素矿床研究存在的主要问题.如PGE矿床的物质来源、PGE演化过程中的分配规律、铂族元素矿物(PGM)的赋存状态,并对以后的发展前景做了展望,指出西藏(蛇绿岩套铬铁矿亚类和俯冲增生弧斑岩型Cu-Au矿)和新疆(碰撞后二叠纪岩浆Cu-Nj硫化物型和黑色页岩型)是我国寻找PGE矿床的最有利地区.     

滇中铅锌矿床地球化学与成因研究

滇中地层铅锌丰度高,成矿元素对于地层有继承性和一致性;硫同位素分散,富重硫;铅同位素稳定,多为单阶段演化正常铅,模式年龄与地层时代大体一致,矿质来自地层,矿床为层控型。同生沉积形成矿源层,后期改造(叠加)形成矿体。为中低温度的地下水热液成矿。     

Influence of structural setting on sulphur isotopes in Archean orogenic gold deposits,Eastern Goldfields Province,Yilgarn, Western Australia

The published mean δ³⁴S values of ore-related pyrites from orogenic gold deposits of the Eastern Goldfields Province, Yilgarn Craton lie between −4‰ and +4‰. As for orogenic gold deposits worldwide, most deposits have positive means and a restricted range of δ³⁴S values, but some have negative means and wider ranges of δ³⁴S values. Wall-rock carbonation and back-mixing of similar-source fluids with different fluid pathways can explain some of the more negative δ³⁴S signatures. However, structural setting appears to be the most important factor controlling ore-fluid oxidation state and hence the distribution of δ³⁴S values in gold-related pyrites. Shear-hosted deposits appear to have experienced fluid-dominated processes such as phase separation, whereas stockwork, vein-hosted or disseminated deposits formed under conditions of greater rock buffering. At Victory-Defiance, in particular, negative δ³⁴S values are more common in gently dipping dilational structures, compared to more compressional steeply dipping structures. It appears most likely that fluid-pressure fluctuations during fault-valve cycles establish different fluid-flow regimes in structures with different orientations. Rapid fluid-pressure fluctuations in dilational structures during seismic activity can cause partitioning of reduced gas phases from the ore fluid during extreme phase separation and hence are an effective method of ore-fluid oxidation, leading to large, local fluctuations in oxidation state. It is thus not necessary to invoke mixing with oxidised magmatic fluids to explain δ³⁴S signatures indicative of oxidation. In any case, available, robust geochronology in the Eastern Goldfields Province does not support the direct involvement of oxidised magmatic fluids from adjacent granitic intrusions in orogenic gold genesis. Thus, negative mean δ³⁴S values and large variations in δ³⁴S values of ore-related pyrites in world-class orogenic gold deposits are interpreted to result from multiple mechanisms of gold precipitation from a single, ubiquitous ore fluid in varying structural settings, rather than from the involvement of oxidised ore fluids from a different source. Such signatures are indicative, but not diagnostic, of anomalously large orogenic gold systems. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.