Stabilizing pyritic material

1989 ◽  
Vol 4 ◽  
pp. 244-248 ◽  
Author(s):  
Donald L. Wolberg
Keyword(s):  
Significant Contribution ◽  
Organic Materials ◽  
Sedimentary Rocks ◽  
Iron Sulfides ◽  
Decomposition Products ◽  
Iron Minerals ◽  
Pyrite Formation ◽  
Organic Sediments ◽  
Freshwater Environments

The minerals pyrite and marcasite (broadly termed pyritic minerals) are iron sulfides that are common if not ubiquitous in sedimentary rocks, especially in association with organic materials (Berner, 1970). In most marine sedimentary associations, pyrite and marcasite are associated with organic sediments rich in dissolved sulfate and iron minerals. Because of the rapid consumption of sulfate in freshwater environments, however, pyrite formation is more restricted in nonmarine sediments (Berner, 1983). The origin of the sulfur in nonmarine environments must lie within pre-existing rocks or volcanic detritus; a relatively small, but significant contribution may derive from plant and animal decomposition products.

Résultats préliminaires d'une étude sur la dispersion de l'or en milieu latéritique autour de l'indice aurifère de Misséni, au Mali

1990 ◽  
Vol 27 (12) ◽  
pp. 1686-1698 ◽  
Author(s):  
Frédéric Séa ◽  
Marc G. Tanguay ◽  
Pierre Trudel ◽  
Guy Perrault
Keyword(s):  
Sedimentary Rocks ◽  
Gold Deposits ◽  
Annual Rainfall ◽  
Iron Sulfides ◽  
Iron Enrichment ◽  
Lower Proterozoic ◽  
Short Rainy Season ◽  
The Mean ◽  
Oxide Minerals ◽  
Bottom To Top

A study of gold dispersion in laterite above a gold zone is based on 58 analyses of soil samples from two shafts and one trench located in the Misséni gold anomaly area, Mali. The bedrock in this area includes Birrimian volcano-sedimentary rocks (lower Proterozoic). At Misséni, primary gold is associated with disseminated copper and iron sulfides in a silicified shear zone within andesites. The area is dominated by a dry tropical climate, including two contrasting seasons (a short rainy season and a long dry season) and a mean annual rainfall of less than 1500 mm. Misséni area is characterized by low plateaus averaging 350 m in altitude and by a very thick weathered cover (> 35 m) of laterite topped by iron cuirasse. In general, the laterite profiles show, from bottom to top (i) saprolith ("pistache" laterite), variegated and mottled clays, (ii) iron hardpan, (iii) iron cuirasse, and (iv) eluvium. Mineralogical analyses reveal that the laterite is dominated by kaolinite, goethite, quartz, mica, and hematite. The mean chemical composition is 46% SiO2, 22% Al2O3, 20% Fe2O3, 1% TiO2, 1% K2O, 0.05% CaO2, and 0.03% Na2O. The laterite profile showed an iron enrichment and a silica depletion (upper part: 0–2 m) and a very weak variation in alumina. This iron enrichment is correlated with increasing goethite toward the surface, whereas silica decreases with lower mica content. The gold concentration increases in the iron hardpan immediately below the cuirasse. The upper saprolith provides low gold values but these increase with depth. Conversely, As and Co tend to increase towards the surface (0–2 m) in the hardpan, cuirasse, or eluvium. A deep core (> 35 m) assayed for gold reveals (i) anomalous gold in latérite (0.2–1.0 ppm) and (ii) higher gold values (5.5–8.8 ppm) occurring between 11.45 and 17.75 m depth) associated with oxide minerals in certain saprolith levels, reflecting probably an ancient groundwater table. These preliminary results would call for further studies to explain the concentration of oxide minerals and gold in some soprolith levels inasmuch as they may lead to potential gold deposits in laterite soils. [Journal Translation]

MAGNETIC ZONATION OF SEDIMENTARY ROCKS AND THE SPATIAL DISTRIBUTION OF AUTHIGENIC IRON MINERALS IN HYDROCARBON HALOS

1986 ◽  
Vol 28 (6) ◽  
pp. 734-739 ◽  
Author(s):  
V. N. Yeremin ◽  
E. A. Molostovskiy ◽  
Ye. V. Pervushova ◽  
A. F. Chernyayeva
Keyword(s):  
Spatial Distribution ◽  
Sedimentary Rocks ◽  
Iron Minerals

scholarly journals A quantification of the effect of diagenesis on the paleoredox record in mid-Proterozoic sedimentary rocks

Geology ◽  
2021 ◽  
Author(s):  
Alec M. Hutchings ◽  
Alexandra V. Turchyn
Keyword(s):  
Iron Sulfide ◽  
Sedimentary Rocks ◽  
Total Iron ◽  
Total Iron Content ◽  
Geological Time ◽  
Iron Minerals ◽  
Reactive Iron ◽  
Time Period ◽  
Geological Past ◽  
Iron Sulfide Minerals

Iron speciation in ancient sedimentary rocks is widely used to reconstruct oceanic redox conditions over geological time, specifically to assess the extent of oxic, euxinic (anoxic containing sulfide), and ferruginous (anoxic containing iron) conditions. We explore how post-depositional sedimentary processes can skew particular geochemical signals in the rock record. One such process is when aqueous sulfide—including that produced in the sediment column—reacts with sedimentary iron, converting non-sulfide, highly reactive iron minerals to iron-sulfide minerals; this can lead to increased preservation of iron as pyrite and an overestimation of seafloor euxinia. We show that sedimentary rocks with higher (>5 wt%) total iron content are more buffered to this effect and thus are a more reliable indicator of true water-column euxinia. When considering this effect in the geological past, we estimate that true euxinia in the mid-Proterozoic may have been as much as fourfold less than previously thought—more in line with other recent paleoredox proxies not based on iron minerals. Marine iron and sulfate concentrations were more equivalent in Proterozoic–Neoproterozoic oceans, suggesting this time period was particularly susceptible to this post-depositional alteration, explaining the extent of euxinia suggested for this geological interval.

Influence of management on the composition of organic matter in a red-brown earth as shown by 13C nuclear magnetic resonance

Soil Research ◽  
1988 ◽  
Vol 26 (2) ◽  
pp. 289 ◽  
Author(s):  
JM Oades ◽  
AG Waters ◽  
AM Vassallo ◽  
MA Wilson ◽  
GP Jones
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Soil Structure ◽  
Organic Materials ◽  
Organic Carbon Content ◽  
Plant Debris ◽  
Soil Matrix ◽  
Decomposition Products ◽  
13C Nuclear Magnetic Resonance ◽  
Mixed Grass

Samples were obtained from the same red-brown earth: (a) in an undisturbed state, (b) after 60 years of an exploitive wheat-fallow rotation and (c) after 40 years under a fertilized mixed grass-legume pasture. Organic materials were concentrated in various fractions which enabled comparative chemical composition of the organic materials in the three soils by 13C CPMAS n.m.r. spectroscopy. Despite more than twofold differences in the organic carbon content of the soils, the chemistry of the organic matter in the soils was similar, particularly organic matter associated with clay fractions. Most of the differences detected were associated with plant debris in particles > 20 �m which contained most of the aromatic carbon. The results indicate a rapid disappearance of phenolic-carbon which originates in lignins. The composition of sodium hydroxide extracts reflects quite well the composition of the organic matter in the soil. It is concluded that in a particular soil type, changes in amounts and nature of added photosynthate do not change the composition of the organic matter which is controlled by the microbial biomass and interactions of the biomass and its decomposition products with the soil matrix. Implications of this conclusion for the turnover of organic carbon in soil and stability of soil structure are discussed.

Indice de sulfures sedimentaires de Taboca (municipe de Crato, etat du Ceara, Bresil)

1965 ◽  
Vol S7-VII (1) ◽  
pp. 177-186 ◽  
Author(s):  
Jacques Cassedanne
Keyword(s):  
Lower Cretaceous ◽  
Sedimentary Rocks ◽  
Iron Sulfides ◽  
Southwestern Part ◽  
Short Period ◽  
Bituminous Shale ◽  
Lead Zinc ◽  
Mineralized Zone

Abstract Sedimentary rocks in the southwestern part of Ceara state, Brazil, contain lead, zinc and iron sulfides. The mineralized zone is in unfaulted horizontal beds of lower Cretaceous age. The area of sedimentary sulfur corresponds to a shallow Precambrian basin which exhibits gaps in sedimentation, thinning, and rapid lateral facies variations. The mineralized bed is composed of bituminous shale with limestone pebbles and synsedimentary breccia. It corresponds to a short period of unstable sedimentation intercalated with a series of argillaceous sands, marls and shales.

Nature and Distribution of Pyrite in Iowa Coal

1976 ◽  
Vol 34 ◽  
pp. 620-621
Author(s):  
Raymond T. Greer
Keyword(s):  
Air Pollution ◽  
Significant Contribution ◽  
Size Range ◽  
Sulfur Removal ◽  
Optical Microscope ◽  
Energy Requirements ◽  
Local Correlation ◽  
Iron Sulfides ◽  
Environmental Considerations ◽  
Large Reserve

Iowa has a large reserve of high-sulfur coal. In view of the projected energy requirements for the state, in-state coal resources should provide a significant contribution. Environmental considerations and air pollution regulations emphasize the desirability of sulfur removal. Both microstructural and microchemical characteristics of Iowa coal relate to the choice and improvement of processing and purification procedures, as well as provide information which may aid in local correlation of deposits.Iron sulfides occur in the coal as nodules and narrow seams (up to 150 mm thick, thinning out over a distance of hundreds of millimeters) and in finely disseminated form. Individual pyrite euhedra occur predominantly in a size range of about one to 40 micrometers in diameter, with by far most of the crystallites being one to two micrometers in diameter (Fig. 1). This raises special characterization problems for routine conventional optical microscope studies. The pyrite also occurs as spherical assemblies of crystallites. These framboidal masses (after Framboise, the French for Raspberry) range from a few micrometers to several hundred micrometers in diameter, with most of them being approximately 10 and 20 micrometers in diameter (Fig. 2).

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