High Concentrations Of Pyrite Research Articles

Ferns and lycophytes in coal mining waste and tailing landfills.

Mineral coal extraction in Santa Catarina State (Brazil) Carboniferous Basin has degraded the local ecosystem, restricting the use of its areas. One of the biggest environmental impacts in the mining areas is the uncontrolled disposal of waste and sterile mining with high concentrations of pyrite, which in the presence of air and water is oxidized promoting the formation of acid mine drainage (AMD). These contaminants can be leached into water resources, restrict the use of water and soil, and cause threats to fauna and flora. This study aimed to characterize these areas as to the content of Cd, Pb, Ni and Zn metals in the tailings and waste resulting from coal mining and to survey the species of ferns and lycophytes present. Wastes and tailing samples and specimens of ferns and lycophytes were collected in 23 landfills in six municipalities in the region and in four underlying areas used as controls. Chemical and physical analyses (pH in water and pH in KCl, Ca, Mg, P, K, Na, Mn, Fe, Al, clay and OM contents) were carried out and the total contents of heavy metals Cd, Pb, Ni and Zn were determined. Sampling of ferns and lycophytes was carried out by walking. The levels of heavy metals, Cd, Ni and Zn, were below the prevention concentrations established by CONAMA Resolution 420/2009. Pb levels were above prevention values in four landfills. Sixteen species of ferns and one lycophyte were found, with hemicryptophytes the most frequent and helophytes the most adapted to the environment. Of the species found, Pteridium esculentum (G. Forst.) Cockayne, Pityrogramma calomelanos (L.) Link and Telmatoblechnum serrulatum (Rich.) Perrie, DJ Ohlsen & Brownsey demonstrated resistance to degraded and contaminated environments with Pb, which may constitute an alternative for project monitoring and environmental recovery.

Biogeochemical and mineralogical effects of Fe-P-S dynamics in sediments of continental shelf sea: Impact of salinity, oxygen conditions, and catchment area characteristics

In this study, we investigate how salinity, oxygen concentration and catchment area characteristics impact the dynamics of Fe-P-S cycling in the continental shelf sea sediments. Samples were collected from three sites representing different environmental conditions: Gdańsk Deep (southern Baltic Sea), Gotland Deep (central Baltic Sea) and Bothnian Sea (northern Baltic Sea). Sediments were analysed for their mineral composition and speciation of iron and phosphorus. The main groups of Prokaryota involved in Fe-P-S cycling in sediments were indicated. Concentrations of sulphate, hydrogen sulphide, alkalinity, chloride, calcium, phosphate and iron were measured in pore waters. We demonstrated that in the eutrophicated southern region with moderate salinity and oxygen deficit in bottom water, sediments had high potential for retaining Fe and releasing P as indicated by high concentrations of pyrite and labile forms of phosphorus, respectively. Strong salinity stratification and intermittent pelagic redoxcline in the central Baltic Sea resulted in a clearly higher rate of pyrite deposition. Sediment was enriched with Mn due to the formation of Ca-Mn carbonates driven by intensive Mn redox cycling and sulphate reduction. Because of high availability of Mn oxides connected with episodic inflows of oxic seawater from the North Sea, sulphate was present in the entire profile of the studied sediments in the Gotland Deep. Sediments in the well-oxygenated, virtually fresh and rich in land-derived iron northern Baltic Sea retained significant amounts of P in authigenic minerals. Organic matter mineralisation in the surface sediment of this area was dominated by iron reduction. The variability of environmental conditions and consequent availability of electron acceptors were the cause of regional differences in the composition of Prokaryota communities – the number of sulphate reducers in the Gdańsk and Gotland Deeps was greater than in the Bothnian Sea, where there were more Fe reducers and bacteria that oxidise Fe and S.

Geophysical Study of Gold Mineralized Zones in the Carolina Terrane of South Carolina

Abstract Large pyrite-dominated gold deposits are hosted in hydrothermally altered metamorphic rocks in the Carolina slate belt of South Carolina and are partly covered by Coastal Plain sedimentary rocks. In this study, we investigate the utility of geophysical data including aeromagnetic, electromagnetic (EM), and land gravity surveys as exploration tools. Observed geophysical anomalies are correlated with rock properties such as resistivity, susceptibility, and density. Mineral concentrations were measured for 40 samples from 16 new drill holes, as well as densities and pyrite concentrations for 49,183 samples from 448 drill holes in the Haile ore zone. Regional positive gravity anomalies are observed over the Haile, Ridgeway, and Barite Hill mine areas, and residual high-pass filtered positive gravity anomalies are observed over all mine areas. New measurements for drill cores in the Haile mine area directly confirm high rock densities and high pyrite concentrations in the ore zone. In the Haile and Brewer mine areas, high-conductivity EM anomalies are observed over the ore zones as well as over nearby metasedimentary rocks. The high concentration of pyrite in the metasedimentary units and in the ore zones may explain the high conductivities observed. All gold deposits in the Carolina slate belt are hosted in similar geologic settings near the contact between the Persimmon Fork metamorphosed volcaniclastic rocks and Richtex metamorphosed sedimentary rocks. Density and conductivity contrasts between the Persimmon Fork and Richtex Formation rocks may permit mapping of the contact zone between the two units. The magnetic anomalies do not correlate with the mineralized zones but rather with granite and gabbro plutons and diabase dikes. A prominent east-northeast linear magnetic anomaly correlates with the Modoc shear zone that separates low-grade metamorphic rocks of the Carolina terrane from higher-grade metamorphic rocks of the Kiokee belt. We use the Modoc linear magnetic anomaly to predict the southeastern boundary of the Carolina slate belt where it is covered by Coastal Plain sedimentary rocks.

Gravity, aeromagnetic and electromagnetic study of the gold and pyrite mineralized zones in the Haile Mine area, Kershaw, South Carolina

New high resolution gravity, electromagnetic (EM) and magnetic data are tested for the detection of disseminated sulfides in the area of the Haile Gold Mine, South Carolina. Geophysical interpretations were constrained with densities and mineral concentrations measured for 49,183 samples from 448 drill holes. Positive residual gravity anomalies from spectral analysis correlate with the mineralized ore zone. Similar correlations between positive anomalies and the ore zones are observed in the first vertical derivative of Bouguer anomaly and tilt derivatives of the residual gravity. Euler deconvolution of the gravity field also shows numerous shallow sources in the ore zone. Drill core measurements show that metasediments (Richtex unit), (2.76 g/cm3) and gold bearing samples (2.73 g/cm3) are slightly denser than metavolcanics (Persimmon Fork Formation), (2.69 g/cm3). Correlation coefficients for sample density and mineral percentages are pyrite (0.18) and sericite (0.15), indicating that pyrite is the main mineral increasing sample density. 2D forward gravity models constrained by dense drilling match the predicted depth range of density anomalies from Euler deconvolution. Drilling results confirm a spatial correlation between high densities, high pyrite concentrations, and the mineralized zones. High conductivity anomalies are observed over the Haile ore zone as well as over the metasediments. Core drilling and 2D inversion show that high conductivity anomalies coincide with zones of high pyrite concentrations. The magnetic field is dominated by anomalies produced by granite plutons 3 km north and 5 km west of Haile and northwest-trending Jurassic diabase dikes. East-northeast trending linear anomalies have been sampled and dated as Alleghanian lamprophyre dikes providing the first magnetic map of these intrusions in the southeastern United States.

Low-Light Anoxygenic Photosynthesis and Fe-S-Biogeochemistry in a Microbial Mat.

We report extremely low-light-adapted anoxygenic photosynthesis in a thick microbial mat in Magical Blue Hole, Abaco Island, The Bahamas. Sulfur cycling was reduced by iron oxides and organic carbon limitation. The mat grows below the halocline/oxycline at 30 m depth on the walls of the flooded sinkhole. In situ irradiance at the mat surface on a sunny December day was between 0.021 and 0.084 μmol photons m-2 s-1, and UV light (<400 nm) was the most abundant part of the spectrum followed by green wavelengths (475–530 nm). We measured a light-dependent carbon uptake rate of 14.5 nmol C cm-2 d-1. A 16S rRNA clone library of the green surface mat layer was dominated (74%) by a cluster (>97% sequence identity) of clones affiliated with Prosthecochloris, a genus within the green sulfur bacteria (GSB), which are obligate anoxygenic phototrophs. Typical photopigments of brown-colored GSB, bacteriochlorophyll e and (β-)isorenieratene, were abundant in mat samples and their absorption properties are well-adapted to harvest light in the available green and possibly even UV-A spectra. Sulfide from the water column (3–6 μmol L-1) was the main source of sulfide to the mat as sulfate reduction rates in the mats were very low (undetectable-99.2 nmol cm-3 d-1). The anoxic water column was oligotrophic and low in dissolved organic carbon (175–228 μmol L-1). High concentrations of pyrite (FeS2; 1–47 μmol cm-3) together with low microbial process rates (sulfate reduction, CO2 fixation) indicate that the mats function as net sulfide sinks mainly by abiotic processes. We suggest that abundant Fe(III) (4.3–22.2 μmol cm-3) is the major source of oxidizing power in the mat, and that abiotic Fe-S-reactions play the main role in pyrite formation. Limitation of sulfate reduction by low organic carbon availability along with the presence of abundant sulfide-scavenging iron oxides considerably slowed down sulfur cycling in these mats.

Arsenic in framboidal pyrite from recent sediments of a shallow water lagoon of the Baltic Sea

AbstractArsenic is a redox‐sensitive element of environmental relevance and often enriched in iron sulphides. Because sediments from the Achterwasser lagoon, a part of the estuarine system of the river Oder, south‐west Baltic Sea, show unexpectedly high pyrite concentrations of up to 7·5 wt% they were used to investigate the influence of authigenic pyrite on the mobility and burial of As in the coastal environment. Micro‐X‐ray‐fluorescence measurements of 106 micrometre‐sized pyrite framboids from the anoxic sediments show highly variable As concentrations ranging from 6 to 1142 μg g−1. Even within a 1 cm thick layer, the As concentration of different framboids varies greatly and no clear depth trend is visible throughout the 50 cm long sediment core. Pyrite can account for 9 to 55% (average 22%) of the total As budget of the sediments and the degree of trace metalloid pyritization for As ranges from 26 to 61%, indicating that authigenic pyrite formation is an important process in the geochemical cycling of As in coastal sediments. High‐resolution micro‐X‐ray fluorescence mapping of single pyrite grains shows that As is distributed inhomogeneously within larger framboids, suggesting changing pore water composition during pyrite growth. X‐ray absorption near edge structure spectra indicate that As is usually present as As(‐I) substituting S in the pyrite lattice. However, in samples close to the sediment/water interface a considerable part of As is in higher valence states (+III/+V). This can be explained by frequent re‐suspension of the surficial sediments to the oxic water column due to wave action and subsequent re‐deposition, leading to the adsorption of As oxyanions onto pyrite. Although reduced As(‐I) becomes more important in the deeper samples, reflecting decreasing redox potential and a longer time since deposition, the occurrence of oxidized As species (AsIII/AsV) in pyrite in the anoxic part of the sediment suggests formation under dysoxic conditions.

Characteristics of authigenic pyrites in shallow core sediments in the Shenhu area of the northern South China Sea: Implications for a possible mud volcano environment

Distinct pyrites have been recovered from a shallow sediment core from Site 4B in the Shenhu area of the northern South China Sea. Based on the lithology, texture and structure of sediments, the stable sulfur isotope of pyrite and the total organic carbon (TOC) concentration of the sediments, a distinctive sediment interface is identified at a depth of about 1 m below the seafloor in the core sediments. The pyrites only accumulate in the lower part of the core as rods and foraminifera-infillings, and mainly within three intervals marked by high pyrite concentrations. The amount of pyrite in the sediments shows no remarkable correlation with TOC in the Site 4B core sediments. The stable sulfur isotopes of the pyrite have extremely negative values ranging from −41.69‰ to −49.16‰. They are considered to be the mutual product of sulfate bacterial reduction and sulfur bacterial disproportionation. Our research proposes that Site 4B might be located in or near a possible mud volcano sedimentary environment; a large amount of methane could migrate from deep to shallow sediments in an active mud volcano and thereby play a key role in the intensity of sulfate bacterial reduction and the amount of pyrite formed at Site 4B. Further, the variation in flux of deep methane fluid by intermittent mud volcanic eruptions might result in the deposition of authigenic pyrite intervals.

Intense pyrite formation under low-sulfate conditions in the Achterwasser lagoon, SW Baltic Sea

In comparison to similar low-sulfate coastal environments with anoxic-sulfidic sediments, the Achterwasser lagoon, which is part of the Oder estuary in the SW Baltic Sea, reveals unexpectedly high pyrite concentrations of up to 7.5 wt%. Pyrite occurs mainly as framboidal grains variable in size with diameters between 1 and 20 μm. Pyritization is not uniform down to the investigated sediment depth of 50 cm. The consumption of reactive-Fe is most efficient in the upper 20 cm of the sediment column, leading to degrees of pyritization (DOP) as high as 80 to 95%. Sediment accumulation in the Achterwasser takes place in high productivity waters. The content of organic carbon reaches values of up to 10 wt%, indicating that pyrite formation is not limited by the availability of organic matter. Although dissolved sulfate concentration is relatively low (<2 mmol/L) in the Achterwasser, the presence of H 2S in the pore water suggests that sulfate is unlikely to limit pyrite authigenesis. The lack of free Fe(II) in the pore waters combined with the possibility of a very efficient transformation of Fe-monosulfides to pyrite near the sediment/water interface suggests that pyrite formation is rather controlled by (i) the availability of reactive-Fe, which limits the FeS formation, and by (ii) the availability of an oxidant, which limits the transformation of FeS into pyrite. The ultimate source for reactive-Fe is the river Oder, which provides a high portion of reactive-Fe (∼65% of the total-Fe) in the form of suspended particulate matter. The surficial sediments of the Achterwasser are reduced, but are subject to oxidation from the overlying water by resuspension. Oxidation of the sediments produces sulfur species with oxidation states intermediate between sulfide and sulfate (e.g., thiosulfate and polysulfides), which transform FeS to FeS 2 at a significant rate. This process of FeS-recycling is suggested to be responsible for the formation of pyrite in high concentrations near the sediment surface, with DOP values between 80 and 95% even under low sulfate conditions. A postdepositional sulfidization takes place in the deeper part of the sediment column, at ∼22 cm depth, where the downward diffusion of H 2S is balanced by the upward migration of Fe(II). The vertical fluctuation of the diffusion front intensifies the pyritization of sediments. We suggest that the processes described may occur preferentially in shallow water lagoons with average net-sedimentation rates close to zero. Such environments are prone to surficial sediment resuspension, initiating oxidation of Fe-sulfides near the sediment/water interface. Subsequent FeS 2 formation as well as postdepositional sulfidization leads to a major pyrite spike at depth within the sediment profile.

Petrology, mineralogy and geochemistry of the Permian and Triassic coals in the Leping area, Jiangxi Province, southeast China

Permian and Triassic coals from a series of mines in Jiangxi Province, China, exhibit a number of unusual geochemical, mineralogical, and petrographic characteristics. The high volatile bituminous Permian coals have high concentrations of the suberinite-like maceral “barkinite.” The origin, and even the distinct character, of “barkinite” are in dispute and, consequently, it has not been recognized as a distinct maceral by the International Committee for Coal and Organic Petrology (ICCP). The Permian bituminous coals have relatively high concentrations of pyrite and marcasite. Otherwise, detrital minerals dominate their geochemistry. The Triassic coals, all from one mine complex, have higher rank (a Permian coal is also mined). Most samples straddle the low volatile bituminous/semi-anthracite boundary. The one semi-anthracite-rank Permian coal shows signs of incipient coking. A Triassic coal in the same fault block is coked by an igneous intrusions found in the mine. The coals have, in general, been dolomitized. Aside from the geochemical imprint of the dolomitization, trace element associations suggesting a contribution from a detrital mineral assemblage dominate the coals.

Sulfur diagenesis and partitioning in Holocene Peru shelf and upper slope sediments

Sediments of the Peru margin were sampled in two transects across the shelf and upper slope (75 to 1000 m) in October of 1992. This region is characterized by high surface-water productivity and consequent high organic carbon fluxes, low terrigenous inputs, as well as an intense oxygen-minimum zone (OMZ) impinging on the slope at depths between 75 and 550 m. Sediments analyzed in this study were collected from one ship-deployed box core and five submersible-deployed push cores. Organic carbon (TOC) concentrations in surface sediments range from 1 to 18% on a dry weight basis. Formation of pyrite begins at the sediment/water interface (SWI). Maximum concentrations of pyrite sulfur in the cores from this study range from 0.5 to 1.8 wt.%. Concentrations of pyrite are influenced by availability of reactive iron and an oxidant capable of converting AVS to pyrite. Highly reactive iron is stripped from terrigenous detritus in the core of the OMZ. Some of this iron may contribute to glauconite formation in sediments near the base of the OMZ, where it is concentrated into a glauconitic green sand as a result of reworking and winnowing. In a shallow-water site (109 m) at the upper edge of the OMZ, high concentrations of pyrite, total iron and iron/aluminum ratios indicate that easily reduced iron species are available for sulfidation at the SWI. Pyrite formation at this site is nearly complete in the upper 4 cm of the sediment. In contrast, pyrite concentrations are slightly lower at the surface of two of the deeper-water sites (at 309 m, in the center of the OMZ, and to a lesser extent at 671 m, at the bottom edge of the OMZ), and appear to be influenced, in part, by availability of reactive iron. Concentrations of acid-volatile sulfides (AVS) are low in all sediments (≤ 0.04 wt.%), but are slightly elevated in sediments from the center of the OMZ. The ratio of organic sulfur (S-org)to organic carbon (TOC)at the sediment surface of the cores examined here is remarkably constant (0.012 ± 0.002) and within the range observed in marine biota (0.01 to 0.02), suggesting that organic sulfur at the SWI is dominantly biogenic. Although S-org/TOC ratios increase downcore, there is no clear correlation between concentrations of organic sulfur and organic carbon below the SWI. There is also no clear relation between concentrations of organic sulfur and total iron. Organic sulfur concentrations vary from site to site (0.06 to 0.33 wt.%), but are relatively constant downcore at any given site. Maximum concentrations are in cores from the center of the OMZ.

Human and Natural Controls on the Accumulation, Acidification and Drainage of Pyritic Sediments: Pearl River Delta, China and Coastal New South Wales

There is increasing concern about environmental impacts of acidic drainage from acid sulphate soils on Holocene estuarine flood plains. Acidity derives from oxidation of iron pyrite in the sediments. Natural factors determine concentrations and distributions of pyrite accumulations, but human activities have reduced pyrite accumulation in the Pearl River Delta with land use practices increasing terrestrial sediment discharge. Large freshwater discharges and management techniques have enabled sustainable use of these soils. High concentrations of pyrite occur in many estuarine flood plains of Australia because of relatively greater marine inputs. Drainage of these soils enhances pyrite oxidation and estuarine acidification, which is associated with fish‐kills. For sustainable development, the problems of acid sulphate soil drainage must be recognised and overcome.

Sulfur isotope and porewater geochemistry of Florida escarpment seep sediments

Distributions of porewater constituents, SO 4 =, NH 4 +, Cl −, ∑CO 2, and H 2S, solid phase iron, and sulfur concentrations, and the sulfur isotopic composition of dissolved and solid phases were investigated in sediments from abyssal seeps at the base of the Florida escarpment. Despite the apparent similarity of seep sediment porewater chemistry to that of typical marine sediments undergoing early diagenesis, relationships between chemical distributions and isotopic measurements revealed that the distribution of pore fluid constituents was dominated by processes occurring within the platform rather than by in situ microbial processes. Ammonium and sulfate concentrations were linearly correlated with chloride concentrations, indicating that variations in porewater chemistry were controlled by the admixture of seawater and a sulfate depleted brine with a chlorinity of 27.5 ± 1.9%. and 2.2 ± 1.3 mM ammonium concentration. At sites dominated by seepage, dissolved sulfate isotopic composition remained near seawater values despite depletion in porewater concentrations. Porewater ∑CO 2 concentrations were found to be elevated relative to seawater, but not to the extent predicted from the observed sulfate depletion. Sediment solid phase sulfur was predominantly pyrite, at concentrations as high as 20% S by weight. In contrast to typical marine deposits, pyrite concentrations were not related to the quantity of sedimentary organic matter. Pyrite δ 34S values ranged from −29%. to + 21%. (CDT). However, only positive δ 34S values were observed at sites associated with high pyrite concentrations. Isotopically heavy pyrite was observed at sites with porewater sulfate of seawater-like isotopic composition. Isotopically light pyrite was associated with sites where porewater sulfate exhibited δ 34S values greater than those in seawater, indicating the activity of in situ microbial sulfate reduction. Thus, dual sulfide sources are suggested to explain the range in sediment pyrite isotopic composition: a δ 34S enriched (+10 to +20%.) source adverted from within the Florida platform, and a lighter 34S depleted component generated in situ from microbial reduction of seawater sulfate. The degree of pyritization of seep sediments was as high as 0.9 and was controlled by pyrite concentrations, which varied over a wider range than did the non-pyrite solid phase iron concentrations. The highest non-sulfide solid phase iron concentrations were observed in sediments that are believed to be at the “front” of the advancing seep fluids (i.e., hemipelagic sediments newly exposed to the seep fluids), indicating that dissolution of hemipelagic background sediment may be the source of at least half of the iron to the highly pyritized seep sediments. Porewater sulfide concentrations were variable, reaching a maximum of 5.7 mM, and were not correlated with the degree of pyritization of the sediments, suggesting that iron was not particularly limiting to pyrite formation.

Depositional Facies and Diagenetic History of Trenton Limestone in Northern Indiana: ABSTRACT

Subsurface cores were studied petrographically to determine the facies and diagenetic history of the Trenton Limestone on a regional scale in northern Indiana. The Trenton Limestone is a yellowish olive-gray fossiliferous limestone, which is replaced by a light-gray dolostone in northern Indiana. Facies composing the Trenton are: (1) bryozoan-echinoderm packstone, (2) bryozoan-echinoderm grainstone, (3) bryozoan packstone to wackestone, (4) lime mudstone, and (5) dolostone. The bryozoan-echinoderm packstone is the major facies. As many as three muddying-upward (packstone to mudstone) sequences occur. Whether the muddying-upward sequences represent regional or local energy conditions is not known. Coarse-grained (1-4 mm) grainstones are typically 1 ft (30 cm) thick, have abrupt bases, and become muddy upward. They are considered storm deposits. Hardgrounds occur throughout the limestone facies, but they are most numerous toward the base. Thes facies indicate deposition below wave base, interrupted by periods of high energy during storms. Fossiliferous white and gray chert nodules are scattered throughout the unit. Also found in the limestone facies are prevalent stylolites and microstylolites, an indication of chemical compaction. The dolostone facies consists of coarsely crystalline (0.4 mm) idiotopic dolomite. Rhombs have cloudy centers and thin clear rims. Pyrite is associated with the dolomite. Porosity, found only in the dolostone, is discontinuous and characterized as intercrystalline, vuggy, and moldic. Porous zones are commonly oil stained or have been plugged by poikilotopic selenitic gypsum. Minor amounts of celestite are found as cavity fillings. The upper Trenton surface has high concentrations of pyrite and phosphate minerals and is interpreted to have been a submarine corrasion surface. End_of_Article - Last_Page 1919------------

RESISTIVITY, SELF‐POTENTIAL, AND INDUCED‐POLARIZATION SURVEYS OF A VAPOR‐DOMINATED GEOTHERMAL SYSTEM

The Mud Volcano area in Yellowstone National Park provides an example of a vapor‐dominated geothermal system. A test well drilled to a depth of about 347 ft penetrated the vapor‐dominated reservoir at a depth of less than 300 ft. Subsequently, 16 vertical electrical soundings (VES) of the Schlumberger type were made along a 3.7‐mile traverse to evaluate the electrical resistivity distribution within this geothermal field. Interpretation of the VES curves by computer modeling indicates that the vapor‐dominated layer has a resistivity of about 75–130 ohm‐m and that its lateral extent is about 1 mile. It is characteristically overlain by a low‐resistivity layer of about 2–6.5 ohm‐m, and it is laterally confined by a layer of about 30 ohm‐m. This 30‐ohm‐m layer, which probably represents hot water circulating in low‐porosity rocks, also underlies most of the survey at an average depth of about 1000 ft. Horizontal resistivity profiles, measured with two electrode spacings of an AMN array, qualitatively corroborate the sounding interpretation. The profiling data delineate the southeast boundary of the geothermal field as a distinct transition from low to high apparent resistivities. The northwest boundary is less distinctly defined because of the presence of thick lake deposits of low resistivities. A broad positive self‐potential anomaly is observed over the geothermal field, and it is interpretable in terms of the circulation of the thermal waters. Induced‐polarization anomalies were obtained at the northwest boundary and near the southeast boundary of the vapor‐dominated field. These anomalies probably are caused by relatively high concentrations of pyrite.