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USGS1984

Ferromanganese micronodules from the surficial sediments of Georges Bank

Ferromanganese micronodules have been found on Georges Bank, off the U.S. northeast coast, distributed throughout the surficial sediments within an area about 125 km long and at least 12 km wide. These coarse, sand-sized concretions have precipitated from metal-rich interstitial waters and contain many of the textural and structural features common to other neritic nodules. Most of the nodules have accreted around detrital grains, and X-ray powder diffraction analyses indicate the presence of geothite and vernadite (  -MnO 2 ) in the ferromanganese layers. Chemical analyses of the micronodules, when compared with similar data on deep-sea manganese nodules, reveal lower Mn/Fe ratios, significantly higher concentrations of V and As, comparable values of Mo, and an order of magnitude less of Co, Ni, Ce and most other metals.

Georges Bank↗

USGS2002

Ordonezite from the Theodoso Soto Mine, Sapioris, Durango, Mexico: New data and structure refinement

A new occurrence of the rare mineral species ordonezite has been found at the Theodoso Soto tin mine, near Sapioris, Durango, Mexico. The average composition of the samples is (Zn 0.98 Fe 0.02 ) Σ1.00 Sb 2.00 O 6 ; the core of the crystals is slightly richer in Fe than the rim. The mineral is uniaxial (+), with all n greater than 2.30 (n calc is 2.38 at 589 nm); D obs 6.66 g/cm 3 , D calc 6.67 g/cm 3 . It is isostructural with ferrotapiolite, with a 4.668(2), c 9.269(6) A (from powder-diffraction data), space group P4 2 /mnm, and is twinned on {103}. Its crystal structure, refined to R=4.1, wR=4.3% using 163 observed reflections, is fully cation-ordered.

Durango↗

USGS2006

Spectral reflectance properties (0.4-2.5 um) of secondary Fe-oxide, Fe-hydroxide, and Fe-sulfate-hydrate minerals associated with sulfide-bearing mine waste

Fifteen Fe-oxide, Fe-hydroxide, and Fe-sulphate-hydrate mineral species commonly associated with sulphide bearing mine wastes were characterized by using X-ray powder diffraction and scanning electron microscope methods. Diffuse reflectance spectra of the samples show diagnostic absorption features related to electronic processes involving ferric and/or ferrous iron, and to vibrational processes involving water and hydroxyl ions. Such spectral features enable field and remote sensing based studies of the mineral distributions. Because secondary minerals are sensitive indicators of pH, Eh, relative humidity, and other environmental conditions, spectral mapping of these minerals promises to have important applications to mine waste remediation studies. This report releases digital (ascii) spectra (spectral_data_files.zip) of the fifteen mineral samples to facilitate usage of the data with spectral libraries and spectral analysis software. The spectral data are provided in a two-column format listing wavelength (in micrometers) and reflectance, respectively.

Open-File Report↗

USGS1958

Origin of manganese deposits of Busuanga Island, Philippines

The manganese deposits of Busuanga Island, Palawan, are tabular and broadly lenticular bodies which lie conformably within a thick sequence of deformed abort beds. The purpose of this study is to determine the probable mode of origin of the deposits. Similar deposits in other parts of the world have been described by others as products of several different genetic processes. Field and laboratory methods of research were employed in the course of the investigation. Detailed geologic mapping was done on the surface and underground, and many samples of rocks and ores were obtained. Later, intensive study of samples from four typical deposits and from the rooks in the surrounding areas was undertaken, using a variety of laboratory techniques. Microscopic study of thin sections and polished surfaces was supplemented by X-ray and chemical work. More than one hundred X-ray diffraction powder photographs were made to identify minerals, and qualitative chemical studies were made of a number of aamples by use of the X-ray spectrograph. In addition, quantitative chemical analyses were made of certain samples. Finally, published accounts of the occurrence and geological behavior of manganese and silica were consulted to aid in interpretation of the data at hand. Oherty layers in the manganese deposits are lithologically similar to the chart wallrooks and country rook beds. Radiolarian fossils are common in the chart and are also found in some ore specimens. Manganese content of the wallrocks and the country rock beds, however, in essentially nil. The manganese deposits contain mostly psilomelane-type oxides in their near-surface parts, and in the deepest mines this ore grades downward into siliceous protore. In three of the deposits studied, the protore consists mainly of braanite and quartz; in the fourth deposit, hausmannite and the silicate alleghatvite make up the milk of the protore. Some of the protoro is massive, but cherty stones are commonly well layered parallel to the wall rock structure. Grain size is very small, but, like the silica in the chert beds, becomes relatively coarse where the rocks are much deformed. No evidence of large-scale replacement or cross-cutting veins is found in the protores. It is concluded that the original manganiferous deposits were largely non-clastic or oolloidal marine sediments laid down in a reducing environment. The protorea were developed from these beds by processes of diagenesis and low-grade regional metamorphism. The protores were in turn altered to black oxide ore by near-surface agencies during the present erosion cycle. Particular interest is attached to the occurrence of alleghanyite and traces of pyroxmangite and hubnerite(?) in the protorea.

Busuanga Island↗

USGS1989

Pb-Bi-Ag-Cu-(Hg) chemistry of galena and some associated sulfosalts. A review and some new data from Colorado California and Pennsylvania

Galena, associated with Pb-Bi-Ag sulfosalts and simple sulfides, contains varied amounts of Ag and Bi in the Dandy vein system, Idarado mine, Ouray, Colorado; the Jackass mine, Darwin District, California; and the Leadville district, Colorado. Silver- and bismuth-bearing galena associated with minor amounts of pyrite, chalcopyrite and sphalerite occur at the Pequea mine, Lancaster County, Pennsylvania. Ag and Bi contents in the Dandy suite of galena range from about 1.4 to 3.4 and 2.5 to 6.5 wt.% respectively, and are comparable or lower in galena from the other localities. Exsolved matildite is present in galena from the Dandy, Jackass and Leadville localities. The presence in significant amounts of both Ag and Bi in a Pb-rich sulfide system is necessary for formation of PbSss (galena solid-solution). If Ag (especially) and Bi (to a lesser extent) are absent, the galena formed will be essentially pure PbS. Some minor Sb may substitute for Bi. Compositional data for all of the galena samples are in agreement with a previously proposed linear relationship between a and Ag-Bi(Sb) content. Matildite and seven additional Pb-Bi-Ag-Cu sulfosalts have been identified from the Dandy vein system, based on electron-microprobe analyses and some X-ray powder-diffraction data.

Canadian Mineralogist↗

USGS1994

Hogtuvaite, a new beryllian member of the aenigmatite group from Norway, with new X-ray data on aenigmatite

Hogtuvaite is a new beryllian member of the aenigmatite group that was discovered in Nordland County, Norway. It is a metamorphic mineral, hosted by Proterozoic granitic gneisses and mafic pegmatites of metamorphic origin. Compositional variations within and between gneiss-hosted samples of hogtuvaite are minimal; however, pegmatite-hosted samples of hogtuvaite are significantly different, containing less Al and Sn, and more Ti and Mn, than those from the gneisses. The mineralogical, optical and crystallographic properties of hogtuvaite are described. A new and uniquely indexed set of X-ray powder diffraction data for aenigmatite is presented. -from Authors

Canadian Mineralogist↗

USGS2004

Petrography and character of the bedrock surface beneath western Cape Cod, Massachusetts

Cores collected during recent drilling in western Cape Cod, Massachusetts provide insight into the topography and petrology of the underlying bedrock. 62 drill sites spread over a ???140 km2 study area produced cores of granitoids (31), orthogneisses (20), basalts/diabases (4), amphibolites (3), felsic mylonites (2), and dolomitic rock (2). Granitoid cores range in composition from granite to tonalite to quartz diorite, but are dominated by single-mica granites. Alteration is common in nearly all cores examined in this study, and is evidenced by the secondary growth of chlorite and epidote. The granitoids resemble rocks of the Dedham and Fall River terranes (Wones and Goldsmith 1991). Gneisses from the study area generally contain the mineral assemblage hornblende+plagioclase+quartz+biotite+epidote??chlorite?? sphene??K-feldspar??sericite+oxides. Based on mineral assemblages, we estimate peak metamorphic grade to be of lower amphibolite facies. X-ray powder diffraction of unmetamorphosed dolomitic cores shows presence of layered silicates (clays), plagioclase, and possible magnesite. Contours of the bedrock surface show locally irregular topography suggesting erosion by glacial scour. The distribution of lithologies suggests a possible continuation of the New Bedford gneissic terrane that outcrops 25 km to the west. Dolomitic rocks may represent a lithified fault gouge material at the eastern edge of the gneissic zone. Basalts/diabases are interpreted to be post-metamorphic dikes of Late Paleozoic age, or possibly associated with Mesozoic rifting.

Massachussets↗

USGS1989

Mineralogic and textural relations in deeply buried rocks of the Simpson Group (Middle Ordovician)--implications in diagenesis and petroleum geology

The mineral composition and petrography of sandstones, shales, carbonates, and intermediate lithologies were determined on 112 core samples of the Middle Ordovician Simpson Group in the Sunray DX Parker No. 1 Mazur well, Grady County, Oklahoma. Core was recovered from present depths of about 15,900-17,200 ft and included all or parts of the Bromide, Tulip Creek, McLish, Oil Creek, and Joins Formations. The bulk-rock mineral composition of Simpson Group rocks is diverse. The mean weighted composition of 50 sandstone samples is 66% quartz, 14% clay, and 18% carbonate, as determined by X-ray powder diffraction (XRD). Some sandstones from the Oil Creek and Tulip Creek Formations contain as much as 96% quartz. These quartz-rich sandstones were cemented early by silica. Feldspar averages 2%; some sandstones from the McLish Formation contain as much as 15% feldspar. Potassium feldspar is commonly more abundant than plagioclase; potassium feldspar overgrowths are found in some of the sandstones. Most of the shales are clay-rich and quartz-poor, averaging about 85% clay minerals, 7% quartz, and 3% feldspar, by weight, as determined by XRD. Carbonate, fluorapatite, and pyrite are present in variable amounts. Such high clay/quartz ratios are not characteristic of shales and suggest that silica has been expelled by diagenetic processes during burial. The main clay mineral in the Simpson Group at these depths is illite, although iron-rich chlorite is locally concentrated in sandstones. Illite typically makes up >90 wt. % of the clay minerals in sandstones and >95 wt. % of those in shale and carbonate. Total clay content, determined from XRD, correlates closely with total gamma-ray intensity from geophysical logs, because illite is the primary potassium-bearing phase in these deeply buried rocks. Therefore, the gamma-ray log is a good indicator of "shaliness" in potential Simpson reservoirs at similar depths. Much of the carbonate was introduced into the sandstones during burial as calcite, dolomite, or ankerite cement. Early iron-free calcite is commonly replaced by iron-bearing calcite, dolomite, or ankerite. Sandstones and carbonate rocks also contain rhombic dolomite. Many of the dolomite rhombs contain overgrowths of ferroan dolomite or ankerite, as evidenced by staining. Ankerite cementation is later and less selective than earlier dolomite and commonly replaces earlier carbonate or silica cements. Dolomite commonly replaces detrital clay and calcite. Spatial and textural relations suggest that the conversion of smectite to illite contributed, in part, to the formation of dolomite and ankerite cements. Scanning electron miscroscopy reveals that much of the diagenetic illite occurs as tabular fibers in pores or as pseudomorphic intergrowths after smectite. Most chlorite in sandstones is authigenic and occurs as a pore-lining cement or as a pseudomorphic replacement after kaolinite. Secondary porosity, formed mainly from the dissolution of intergranular carbonate cements, is best developed in sandstones from the Oil Creek and Tulip Creek Formations.

Oklahoma↗

USGS1974

Mineralogical studies of the nitrate deposits of Chile IV. Brüggenite, Ca(IO3)2-H2O, a new saline mineral

Br ü ggenite, Ca(I0 3 )2 - H2 0, is found in veins of high-purity soda niter in rhyolite tuff at Pampa Pique III, Oficina Lautaro, Chile, as long columnar anhedral crystals, as prismatic crystals, and as irregular anhedral crystals or encrusting masses. The mineral is colorless to bright yellow, and transparent to translucent, has vitreous luster and a hardness of about 3 1 / 2 , is brittle, and has conchoidal fracture. It is biaxial and has variable optic angle and refractive indices, which were determined by the spindle-stage method. Refractive indices are as follows: n α =1.772-1.779, n β =1.795-1.802, and n γ =1.817-1.824 (all ± 0.003); optic angle shows a range of 2 V Z = 86°-96°; Z = b and X ∧ c = -47°; dispersion (Z) is r < v , moderate. Brüggenite is monoclinic, space group P 2 1 / c , with a=8.509±0.001 A, b = 10.027±0.002 A, c = 7.512±0.001 A, β = 95°16.00'±0.55', volume 638.2 A 3 , Z = 4, G (calc) = 4.244, G (meas) =4.24±0.01. The X-ray diffraction powder pattern of brüggenite has the following strong lines ( hkl , d hkl 1 ): 031, 3.051 A (100); 220, 3.238 A (90); 200, 4.235 A (80); 002, 3.739 A (60); 012, 3.503 A (60); 231, 2.522 A (60). The composition was confirmed by chemical analyses.

Antofagasta Province↗

USGS2013

Powder X-ray diffraction of florencite-(Nd)

Florencite-(Nd) [(Nd,Ce)Al 3 (PO 4 ) 2 (OH) 6 ], was first described by Milton and Bastron (1971) from fracture surfaces in weathered cherts of the Franciscan Complex, south of Sausalito in Marin County, California. Florencite-(Nd) occurred there as a moderate-brown pulverulent earthy material; individual crystals were not discernible under microscopic examination. A semi-quantitative spectrographic analysis showed the presence of Nd (3 wt. %) and Ce (0.5 wt. %). No powder data for florencite-(Nd) exists in the current powder diffraction file.

California↗

USGS2014

Powder X-ray diffraction laboratory, Reston, Virginia

The powder x-ray diffraction (XRD) laboratory is managed jointly by the Eastern Mineral and Environmental Resources and Eastern Energy Resources Science Centers. Laboratory scientists collaborate on a wide variety of research problems involving other U.S. Geological Survey (USGS) science centers and government agencies, universities, and industry. Capabilities include identification and quantification of crystalline and amorphous phases, and crystallographic and atomic structure analysis for a wide variety of sample media. Customized laboratory procedures and analyses commonly are used to characterize non-routine samples including, but not limited to, organic and inorganic components in petroleum source rocks, ore and mine waste, clay minerals, and glassy phases. Procedures can be adapted to meet a variety of research objectives.

Virginia↗

USGS2021

Unmixing multiple metamorphic muscovite age populations with powder X-ray diffraction and 40Ar/39Ar analysis

A combination of modal estimates from powder X-ray diffraction (XRD) experiments and argon isotopic data shows that muscovite 40 Ar/ 39 Ar total gas age correlates with muscovite composition near the retrograde Bald Mountain shear zone (BMSZ) in Claremont, New Hampshire, and that the shear zone was active at ∼245 Ma. Petrologic study demonstrates that chemical disequilibrium is preserved in muscovite grains in these samples. The recognition of this preservation is critical to the interpretation of the 40 Ar/ 39 Ar step-heating experiments, which never produce age plateaus and yield spectra with steps that range in age by ∼20 Ma. Petrographic, compositional, and crystallographic data all indicate that the age spectra reflect dissolution of metastable Na-rich muscovite and precipitation of stable Na-poor muscovite associated with deformation in the BMSZ.Comparison of whole rock and muscovite concentrate XRD patterns from individual samples demonstrates that the mineral separation process can fractionate these muscovite populations. Therefore, four muscovite concentrates of varying magnetic susceptibility were prepared from a single hand sample, analyzed by XRD, and dated. These four splits define a mixing line that resolves end-member ages of 244.5 ± 4.2 Ma and 302.5 ± 12.5 Ma (1σ). Although the ages are imprecise, the petrologically supported conclusion that these schists preserve two discrete ages is distinct from an interpretation that the spectra reflect cooling through closure at ∼270 Ma, as might be concluded in the absence of petrologic characterization. The XRD results also demonstrate that, even well above anchizone conditions, petrologic information relevant to 40 Ar/ 39 Ar dating is observable in subtle variations in the crystallography of muscovite grains.

New Hampshire↗

USGS1975

Quantitative determination of dawsonite in Green River Shale by powder-sample X-ray diffraction; effect of grinding

In an effort to evaluate the method of quantitative analysis by X-ray diffraction as a means of determining dawsonite abundances in Green River" oil shale, we performed a series of grinding experiments. Weighed mixtures of dawsonite + quartz and dawsonite + quartz + shale were ground for preset lengths of time, and the following X-ray diffraction peaks were measured for intensity: dawsonite (110) at 15.6 2 θ and (211) (002) at 32.1° 2 θ , and quartz (100) at 20.9° 2 θ and (101) at 26.6° 2 θ . Heights and areas were measured. Intensity ratios were plotted as functions of grinding time with a calculated probable error. Intensity ratios generally decrease as grinding time increases. The intensity of the 15.6° peak, D 15.6° , is most affected, and the most drastic reduction occurs during the first 20 min of grinding. The D 32.1° peak is least sensitive to grinding but is subject to interference by other minerals in the shale. We conclude that the X-ray diffraction method is not well adapted to the routine quantitative determination of dawsonite in oil shale of the Green River Formation.

Journal of Research of the U.S. Geological Survey↗

USGS2018

Delindeite titanosilicates and lourenswalsite, two new from the Magnet Cove region, Arkansas

Delindeite and lourenswalsite are two new barium titanosilicate minerals found as microscopic crystals in miarolitic cavities in nepheline syenite in the Diamond Jo quarry, Hot Spring County, Arkansas. Delindeite is found as aggregates of flake-like crystallites in compact spherules, light pinkish grey in colour, with a resinous, pearly lustre. The flakes are biaxial positive with average n ∼ 1.813; the measured density is 3.3 g/cm 3 . Electron diffraction revealed a monoclinic unit cell in space group C 2 l m or subgroup, with a = 21.617(13), b = 6.816(5), c = 5.383(3) Å, β = 94.03(5)° (refined from X-ray powder data). The strongest X-ray lines are ( hkl , d obs , I rel ): (200, 10.80, 100); (311, 3.54, 24); (6̄01, 3.083, 28); (601, 2.888, 31); (2̄21, 2.806, 20); (910, 2.262,18). The crystals are submicroscopically twinned on (100) and also produce additional continuous diffraction streaks parallel to a *, which double the b and c axes. The formula derived from electron and ion probe analyses (H 2 O by difference), as constrained by density and molar volume data, is approximately (Na,K) 2.7 (Ba,Ca) 4 (Ti,Fe,Al) 6 Si 8 O 26 (OH) 14 , with Na > K, Ba ≫ Ca, Ti ≫ Fe,Al; Z = 1. Lourenswalsite occurs as very thin hexagonal plates in rosettes, silver grey to light brownish grey in colour. The crystals are biaxial negative with very low 2 V angle. Indices of refraction are n α = 1.815, n β ≈ n γ = 1.840; the measured density is 3.17 g/cm = 1.840; the measured density is 3.17 g/cm 3 . X-ray and electron diffraction show a sharp pseudohexagonal lattice with a = 5.244 Å, but extremely diffuse diffraction streaks normal to the hk 0 plane. In these streaks a period of 20.5 Å can be discerned. A hexagonal unit cell with a = 5.244(2) Å, c = 20.49(3) Å can be refined from the powder diffraction data but does not account for some lines, probably because of extreme layer disorder as shown by precession single-crystal patterns. The strong X-ray powder lines are (002, 10.22, 20); (-, 3.93, 20); (111, 2.608, 100); (300, 1.5145, 80); (220, 1.3111, 25). The formula given by microprobe analyses, constrained by density and molar volume data, is approximately (K,Ba) 2 (Ti,Mg,Ca,Fe) 4 (Si,Al,Fe) 6 O 14 (OH) 12 with K > Ba, Ti ≫ (Mg,Ca,Fe), Si > Al > Fe; Z = 1. These minerals are formed under oxidizing weathering conditions, and iron is assumed to be in the Fe 3+ state.

Arkansas↗

USGS2005

Arsenate adsorption mechanisms at the allophane: Water interface

We investigated arsenate (As(V)) reactivity and surface speciation on amorphous aluminosilicate mineral (synthetic allophane) surfaces using batch adsorption experiments, powder X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS). The adsorption isotherm experiments indicated that As(V) uptake increased with increasing [As(V)] o from 50 to 1000 μM (i.e., Langmuir type adsorption isotherm) and that the total As adsorption slightly decreased with increasing NaCl concentrations from 0.01 to 0.1 M. Arsenate adsorption was initially (0−10 h) rapid followed by a slow continuum uptake, and the adsorption processes reached the steady state after 720 h. X-ray absorption spectroscopic analyses suggest that As(V) predominantly forms bidentate binuclear surface species on aluminum octahedral structures, and these species are stable up to 11 months. Solubility calculations and powder XRD analyses indicate no evidence of crystalline Al−As(V) precipitates in the experimental systems. Overall, macroscopic and spectroscopic evidence suggest that the As(V) adsorption mechanisms at the allophane−water interface are attributable to ligand exchange reactions between As(V) and surface-coordinated water molecules and hydroxyl and silicate ions. The research findings imply that dissolved tetrahedral oxyanions (e.g., H 2 PO 4 2 - and H 2 AsO 4 2 - ) are readily retained on amorphous aluminosilicate minerals in aquifer and soils at near neutral pH. The inner-sphere adsorption mechanisms might be important in controlling dissolved arsenate and phosphate in amorphous aluminosilicate-rich low-temperature geochemical environments.

Environmental Science & Technology↗

USGS2012

Mineralogical, chemical, and crystallographic properties of supergene jarosite-group minerals from the Xitieshan Pb-Zn sulfide deposit, northern Tibetan Plateau, China

Supergene jarosite-group minerals are widespread in weathering profiles overlying Pb-Zn sulfide ores at Xitieshan, northern Tibetan Plateau, China. They consist predominantly of K-deficient natrojarosite, with lesser amounts of K-rich natrojarosite and plumbojarosite. Electron microprobe (EMP) analyses, scanning electron microcopy (SEM) investigation, and X-ray mapping reveal that the jarosite-group minerals are characterized by spectacular oscillatory zoning composed of alternating growth bands of K-deficient and K-bearing natrojarosite (K 2 O >1 wt.%). Plumbojarosite, whenever present, occurs as an overgrowth in the outermost bands, and its composition can be best represented by K 0.29 Na 0.19 Pb 0.31 Fe 2.66 Al 0.22 (SO 4 ) 1.65 (PO 4 ) 0.31 (AsO 4 ) 0.04 (OH) 7.37 . The substitution of monovalent for divalent cations at the A site of plumbojarosite is charge balanced by the substitution of five-valent for six-valent anions in XO, 4/sub> at the X site. Thermogravimetric analysis (TGA) of representative samples reveal mass losses of 11.46 wt.% at 446.6 °C and 21.42 wt.% at 683.4 °C due to dehydroxylation and desulfidation, respectively. TGA data also indicate that the natrojarosite structure collapses at 446.6 °C, resulting in the formation of NaFe(SO 4 ) 2 and minor hematite. The decomposition products of NaFe(SO 4 ) are hematite and Na, 2 SO 4 . Powder X-ray diffraction (XRD) analyses show that the jarosite-group minerals have mean unit-cell parameters of a =7.315 ä and c =016.598 ä. XRD and EMP data support the view that substitutions of Na for K in the A site and full Fe occupancy in the B site can considerably decrease the unit-cell parameter c , but only slightly increase a . The results from this study suggest that the observed oscillatory zoning of jarosite-group minerals at Xitieshan resulted mainly from substitutions of K for Na at the A site and P for S at the X site.

Tibetan Plateau↗

USGS2005

Secondary sulfate minerals associated with acid drainage in the eastern US: Recycling of metals and acidity in surficial environments

Weathering of metal-sulfide minerals produces suites of variably soluble efflorescent sulfate salts at a number of localities in the eastern United States. The salts, which are present on mine wastes, tailings piles, and outcrops, include minerals that incorporate heavy metals in solid solution, primarily the highly soluble members of the melanterite, rozenite, epsomite, halotrichite, and copiapite groups. The minerals were identified by a combination of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron-microprobe. Base-metal salts are rare at these localities, and Cu, Zn, and Co are commonly sequestered as solid solutions within Fe- and Fe-Al sulfate minerals. Salt dissolution affects the surface-water chemistry at abandoned mines that exploited the massive sulfide deposits in the Vermont copper belt, the Mineral district of central Virginia, the Copper Basin (Ducktown) mining district of Tennessee, and where sulfide-bearing metamorphic rocks undisturbed by mining are exposed in Great Smoky Mountains National Park in North Carolina and Tennessee. Dissolution experiments on composite salt samples from three minesites and two outcrops of metamorphic rock showed that, in all cases, the pH of the leachates rapidly declined from 6.9 to <3.7, and specific conductance increased gradually over 24 h. Leachates analyzed after 24-h dissolution experiments indicated that all of the salts provided ready sources of dissolved Al (>30 mg L-1), Fe (>47 mg L-1), sulfate (>1000 mg L-1), and base metals (>1000 mg L-1 for minesites, and 2 mg L-1 for other sites). Geochemical modeling of surface waters, mine-waste leachates, and salt leachates using PHREEQC software predicted saturation in the observed ochre minerals, but significant concentration by evaporation would be needed to reach saturation in most of the sulfate salts. Periodic surface-water monitoring at Vermont minesites indicated peak annual metal loads during spring runoff. At the Virginia site, where no winter-long snowpack develops, metal loads were highest during summer months when salts were dissolved periodically by rainstorms following sustained evaporation during dry spells. Despite the relatively humid climate of the eastern United States, where precipitation typically exceeds evaporation, salts form intermittently in open areas, persist in protected areas when temperature and relative humidity are appropriate, and contribute to metal loadings and acidity in surface waters upon dissolution, thereby causing short-term perturbations in water quality.

Chemical Geology↗

USGS2010

A high-pyrite semianthracite of Late Permian age in the Songzao Coalfield, southwestern China: Mineralogical and geochemical relations with underlying mafic tuffs

The No. 12 Coal (Late Permian) in the Songzao Coalfield, Chongqing, southwestern China, is characteristically high in pyrite and some trace elements. It is uniquely deposited directly above mafic tuff beds. Samples of coal and tuffs have been studied for their mineralogy and geochemistry using inductively coupled plasma-mass spectrometry, X-ray fluorescence, plasma low-temperature ashing plus powder X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray analysis.The results show that the minerals of the No. 12 Coal are mainly composed of pyrite, clay minerals (kaolinite, chamosite, and illite), ankerite, calcite, and trace amounts of quartz and boehmite. Kaolinite and boehmite were mainly derived from sediment source region of mafic tuffs. Chamosite was formed by the reaction of kaolinite with Fe-Mg-rich fluids during early diagenesis. The high pyrite (Sp,d=8.83%) in the coal was related to marine transgression over peat deposits and abundant Fe derived from the underlying mafic tuff bed. Ankerite and calcite were precipitated from epigenetic fluids.Chemical compositions of incompatible elements indicate that the tuffs were derived from enriched mantle and the source magmas had an alkali-basalt character. Compared to other coals from the Songzao Coalfield and common Chinese coals, the No. 12 Coal has a lower SiO2/Al2O3 (1.13) but a higher Al2O3/Na2O (80.1) value and is significantly enriched in trace elements including Sc (13.5??g/g), V (121??g/g), Cr (33.6??g/g), Co (27.2??g/g), Ni (83.5??g/g), Cu (48.5??g/g), Ga (17.3??g/g), Y (68.3??g/g), Zr (444??g/g), Nb (23.8??g/g), and REE (392??g/g on average). Above mineralogical compositions, as well as similar ratios of selected elements (e.g., SiO2/Al2O3 and Al2O3/Na2O) and similar distribution patterns of incompatible elements (e.g., the mantle-normalized diagram for incompatible elements and chondrite-normalized diagram for rare earth elements) of coal and tuff, indicated that enriched trace elements above were largely derived from mafic tuffs, in addition to a minor amount from the Kandian Oldland. ?? 2010 Elsevier B.V.

International Journal of Coal Geology↗