Sulfate Mineral Paragenesis in Pennsylvanian Rocks and the Occurrence of Slavikite in Nebraska

Home , Aluminite, Alunogen, Copiapite, Epsomite, Halotrichite, Rozenite

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Spring 2007

Sulfate Mineral Paragenesis in Pennsylvanian Rocks and The Occurrence of Slavikite in Nebraska

R. Matthew Joeckel University of Nebraska - Lincoln, [email protected]

K. D. Wally University of Nebraska - Lincoln

S.A. Fischbein Nebraska Department of Environmental Quality

P.R. Hanson University of Nebraska - Lincoln, [email protected]

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Joeckel, R. Matthew; Wally, K. D.; Fischbein, S.A.; and Hanson, P.R., "Sulfate Mineral Paragenesis in Pennsylvanian Rocks and The Occurrence of Slavikite in Nebraska" (2007). Great Plains Research: A Journal of Natural and Social Sciences. 877. https://digitalcommons.unl.edu/greatplainsresearch/877

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SULFATE MINERAL PARAGENESIS IN PENNSYLVANIAN ROCKS AND THE OCCURRENCE OF SLAVIKITE IN NEBRASKA

R.M. Joeckel and K.D. Wally

Conservation and Survey Division School ofNatural Resources University ofNebraska-Lincoln Lincoln, NE 68583-0996 [email protected]

S.A. Fischbein

Nebraska Department ofEnvironmental Quality 1200 "N" Street, Suite 400 Po. Box 98922 Lincoln, NE 68509

and

P.R. Hanson

Conservation and Survey Division School ofNatural Resources University ofNebraska-Lincoln Lincoln, NE 68583-0996

ABSTRACT-The acid weathering of pyrite-bearing Pennsylvanian clastic sedimentary rocks in southeastern Nebraska locally produces the secondary sulfate minerals alunogen, copiapite, epsomite, felsobanyaite/basalu minite, gypsum, halotrichite, jarosite, rozenite, and slavikite. Of these mineral occurrences, four are first-time discoveries in the state or the surrounding region. Slavikite (NaMg2Fes(S04h(OH)6· 33H20), which has been reported only once before in North America and from a handful of sites in Europe and South America, was found in abundance at an outcrop at Brownville, NE. The pH values in 1:1 solutions of deionized water of the studied minerals, excluding epsomite, range from 1.94 to 4.82. Therefore, segregations of secondary minerals in themselves are significant microenvironmental reservoirs of acid that can be mobilized during precipitation events. Because of its role in liberating and concentrating ions such as AP+, Fe2+, Fe3+, Mg2+, and sOi-, acid rock weathering should be considered in local to regional assessments of surface-water and groundwater chem istry. Observations also suggest that rock weathering by the growth of sulfate salts is a potential factor in local hillslope development, one that has not previously been considered in the study area.

Key Words: hydrated sulfate minerals, Nebraska, pyrite oxidation, slavikite

INTRODUCTION

The oxidation and acid weathering of naturally occur et al. 2001; Schippers 2004; Knoeller et al. 2004). Near-sur ring metal sulfides, especially pyrite (FeS2), play important face acid weathering of sulfide minerals, whether natural roles in geochemical cycling, soil development, and the or anthropogenic (iron-ore and coal mines, tailings piles, evolution of surface-water and groundwater chemistry etc.), assumes several different manifestations and pro (e.g., Van Breemen 1973, 1982; Jambor et al. 2000; Keith duces a large variety of sulfate salts in the forms of surface efflorescences, crusts, and massive alteration zones (e.g., Manuscript received for review, September 2006; accepted for publication, December 2006. Bandy 1938; Michel and Van Everdingen 1987; Jakobsen

17 18 Great Plains Research Vol. 17 No.1, 2007

1989; Shamshuddin et ai. 1995; Jambor et aI., 2000). The MATERIALS AND METHODS specific occurrences of these various mineral species de pend on climatic or microclimatic conditions, time, pH, Mineral efflorescences and crusts from weathering rock intensity of oxidation, and other factors (Jambor et al. surfaces were collected in April, July, and September from 2000; Keith et ai. 2001; Jerz and Rimstidt 2003; Buckby et four sites (Fig. 1, Table 1) and were stored in sealed plastic 2 ai. 2003). Almost all of these minerals contain Fe +, Fe3+, bags at room temperature. Subsamples were processed and or a combination thereof, or AI. Some also incorporate analyzed by x-ray diffraction (XRD) within a month after K, Na, or Mg. As a general rule, salts produced by acid collection and within two hours after removal from storage weathering are hydrated and highly soluble in water; most bags. Prior to XRD analysis, these subsamples were hand of them persist in large volumes only where climatic or picked under a binocular microscope to remove host-rock microclimatic conditions limit or prohibit dissolution by debris and were powdered using a ceramic mortar; manual rainfall or percolating meteoric waters (e.g., Bandy 1938; grinding was limited to less than 1 minute to minimize Jakobsen 1989; Jambor et ai. 2000). its peak-broadening effect on x-ray diffractograms. To Until very recently (Joeckel et al. 2005), acid rock obtain randomly oriented powder mounts, each of the weathering in Nebraska had not been described. More hand-picked, ground subsamples was screened to minus over, the phenomenon has been described only sparingly 63 /-lm, and the oversize fraction was rejected. A Rigaku from surrounding states in the American Midwest (e.g., Mini-Flex™ X-ray diffractometer using CuKa radiation Tien 1968; Cody and Biggs 1973; Blevins 1989; Davis and Webb 2002), although it should be a common phe nomenon under existing geologic conditions. Our recent observations, detailed herein, as well as those of Joeckel 96° 30' et al. (2005), indicate that acid-weathering processes occur or have occurred at different temporal and spatial scales in many places in southeastern Nebraska and, by inference, in the surrounding region as well. At the largest scale of observation, there are regional oxidation fronts resulting from past and present meteoric weathering at the upper contacts of widespread, pyrite-bearing Creta I I ceous sediments such as the Dakota Formation, Carlile D o 30 km Shale, and Pierre Shale (see Condra and Reed 1959 for Lincoln OTOe regional stratigraphy). Likewise, the widespread and con spicuous oxidation of Pliocene-Pleistocene (~2.5 Ma-600 40° 30'-I----I-----,~ ___ - ...L- ka) glacial tills in the eastern quarter of the state doubt less involves the weathering of finely disseminated pyrite derived from eroded sedimentary rocks to the north. At much smaller scales, there are extant microenvironments of acid weathering in quarries, natural outcrops, and road cuts in both Pennsylvanian and Cretaceous strata, some of which change on short-term timescales, depending on rainfall and atmospheric humidity (e.g., Joeckel et al. 2005). These microenvironments constitute a new realm of investigation in the study of regional mineralogy and mineral paragenesis. The purposes ofthis paper are to describe some unique NEBRASKA environments of pyrite oxidation, acid rock weathering, and new mineral formation in Nebraska, to document the occurrence of multiple mineral species never before de scribed in the state or region (including slavikite, a rarely documented hydrated Mg-Fe hydroxide sulfate), and to Figure 1. Study sites in southeastern Nebraska (see Table 1 for comment on the larger significance of these phenomena. locations).

TABLE 1 LOCATION OF STUDY SITES IN NEBRASKA

Study site Legal description Latitude/longitude Stratigraphic unit

NE'i4 NE'i4 NW'i4 SE'i4 40° 10' 34.0"N Indian Cave Sandstone Section 18, T. 5 N., R. 16 E. 96° 35' 5.8"W

2 SYZ NW'i4 SW'i4 40° 24' 2.5"N White Cloud Sandstone Section 34, T. 3 N., R. 12 E. 95° 39' l6.3"W (Scranton Formation)

3 NE'i4 SE'i4 SE'i4 SW'i4 40° 40' 8.5"N Willard Formation Section 10, T. 8 N., R. 14 E. 95° 49' 51.5"W

4 SW'i4 NE'i4 NW'i4 NE'i4 40° 2' 35.0"N Nodaway Coal in Severy Shale Section 23, T. 1 N., R. 12 E. 96° 2' 9.7"W

Notes: Refer to Condra and Reed (1959) and Fischbein (2005) for stratigraphy. T = township and R = range at 30 kV and 15 rnA was employed for XRD analysis. comparison with site 1. All the study sites are outcrops of Scans were made from 2° to 90° 28 at a step time of 1° Upper Pennsylvanian sandstones, tidal rhythmites (thinly 28/minute. Mineral identification was facilitated by the interlaminated sandstone and shale deposited in estuaries search-match function in JADETM release 7.1.2 software or similar settings under tidal influence), shales, or coal from Materials Data, Inc. (Livermore, CA), which -uses the (Table 1). At two of the sites, as at the sites described by Powder Diffraction Files or PDFs (International Centre for Joeckel et al. (2005), efflorescences of different colors Diffraction Data 2001) as references. Repeated onscreen and mineralogical compositions are spatially segregated. qualitative comparisons of diffractograms and match lines This kind of segregation is not unusual in acid-weathering were employed in addition to peak-matching software. settings (e.g., Bayless and Olyphant 1993) and reflects the The pH values of 1: 1 suspensions of powdered crusts existence of localized physical and chemical controls on in deionized water were measured with a Thermo Orion mineral precipitation. 550ATM pH meter and a combination pH electrode. Colors Site 1 is an outcrop of sandstone-shale rhythmites at of mineral crusts and sediments were estimated using the steep base of a wooded bluff along the Missouri River, Munsell Soil Color Charts (Munsell Color 1998). Infra under a slight overhang. It is the only one of the four study red spectroscopy was carried out with a Thermo Avatar sites where fresh, macroscopic pyrite can be observed 380™ Fourier transform infrared spectrometer; data were on the outcrop face. Sandstones at the site are locally ce I acquired with 16 scans/sample at a resolution of 4 cm- . mented by carbonate. Because the outcrop is east-facing, Samples were made into pellets with CsI (instead of KBr) it is partly protected from westerly winds and, to some to allow any peaks between 225 and 4,000 cm-I to be seen. degree, from frontal weather systems associated with the Scanning electron microscopy (SEM) was carried out with most heavy rainfall in eastern Nebraska. The compara a Hitachi S-3000NTM electron microscope. An Oxford tive persistence of surface salts at the site differs from 7021™ EDX (energy-dispersion x-ray) analyzer was used that at fully exposed acid-weathering sites (e.g., Joeckel to determine elemental spectra for selected samples. et al. 2005), at which surface salts are regularly dissolved by rainfall events and reprecipitate during intervals of RESULTS dry weather. At site 1, surface efflorescences and crusts form in horizontally elongate, partly intergrown patches Site Cha racteristics as much as 150 mm in width, on sandstone-shale rhyth mites. Whitish and yellowish efflorescences originally Site 1 (Fig. 1; Table 1), at Brownville, NE, is the primary form directly on the exposed surfaces of elongate, bed study site because surficial accumulations of secondary ding-parallel pyrite nodules 20-100 mm in length. Pus minerals are best developed and most prominent there, and tulose ("popcorn-like") white (2.5Y 8/1) to pale yellow because minerals never described before from Nebraska (2.5Y 8/2) crusts have formed atop shalier rhythmite were found there at an early stage in our investigation. Sites intervals. These crusts are markedly "puffed" above the 2,3, and 4 (Fig. 1; Table 1) were investigated primarily for level of the outcrop face. Soft, powdery, white efflores-

Figure 2. (A) Northern port of exposure at site 1 (20 cm scale), showing (1 white crusts of halotrichite, (2) yellow copiapite or slavi kite-dominated crusts, and (3 pile of sloughed rock debris weathered by salts, which seasonally contains halotrichite and epsomite efflorescences. (8) Weathering pyrite nodule at site 1 Such mineral efflorescences around pyrite nodules may be halotrichite or rozenite, depending on the season. (C) Yellow copiapite crusts at site 1

© 2007 Center for Greot Ploins Studies, University of Nebrosko Lincoln Sulfate Mineral Paragenesis in Pennsylvanian Rocks • R.M. Jaeckel et 01. 21 cences also form episodically, mostly on and immediately TABLE 2 around pyrite nodules and carbonate-cemented sandstone MINERAL SPECIES DISCUSSED IN DETAIL lenses, especially where the efflorescences are protected IN THIS PAPER by small overhangs on the outcrop face. Subsequent analyses demonstrate that these efflorescences, although Mineral Formula similar in color and appearance, consist of different min Alunogen* Al2(S04)3 . 17H2O erals at different times of the year. Distinct, pale yellow (2.5Y 8/4) to yellow (2.5Y 7/6 and 8/6) crusts form in Copiapite* (Fe,Mg)Fe4(S04)6(OH)z· 20H2O close proximity to the whitish crusts and efflorescences, Epsomitet MgS04 ·7H2O but in many cases they form at separate stratigraphic intervals. Gypsum* CaS04· 2H20 The weathering of bedrock by surficial salt growth is Halotrichite* FeA}z(S04)4· 22H2O strongly evident at the site (Fig. 2), where spalled sheets of weathered material collect in a pile at the foot of the out Jarosite* KFe3(S04)2 (OH)6 crop. The weathering of soft bedrock by the salt precipita RozeniteT FeS04· 4H20 tion appears to be a self-reinforcing phenomenon in that the spalling of surficially weathered rock creates inden Slavikitet NaMg2FeS(S04)7(OH)6· 33H2O tations that provide yet further protection for the subse quent growth of new sulfate-mineral crusts. In the driest * Previously described from Nebraska by Pabian (1993) or by Joeckel et al. (2005). weather periods during our study, the outcrop at site 1 was First described occurrence from Nebraska. nearly dry, even though salts were present. Therefore, any discharge of porewater through the outcrop face at site 1 must be minimal, very diffuse, and episodic at best, slavikite (Tables 2 and 3) occur in crusts, efflorescences, rather than persistent. Atmospheric moisture appears to and small nodules on and in weathering sedimentary rocks exert a larger influence on weathering at the site, making at the study sites. Fels6banyaite and basaluminite were it differ from the acid-rock-weathering site in Nebraska long considered to be polymorphs, but it now appears that described previously by Joeckel et al. (2005). the latter is merely a microcrystalline variety of the former Site 2 (Fig. 1; Table 1) is an outcrop with a slight over (Farkas and Pertlik 1997). The name "felsobanyaite" has hang, concealed by thick woods at the base of a south-fac priority (Jambor et al. 1998), although databases of various ing hill. Site 3, an east-facing bluff on the Missouri River kinds (e.g., International Centre for Diffraction Data 2001) (Fig. 1; Table 1), is much more exposed to the elements still list the two minerals as distinct and separate entities. than site 1. Rare surface salts, either pale yellow (2.5Y Whitish cauliflower-like crusts from site 1 actually 8/2) to bright white or yellow (2.5Y 7/8 and 8/6), occur have a discernable horizontal microzonation consisting of as moist efflorescences whose slightly pasty consistency a silky-appearing underlayer of long (2-7 mm), hairlike, is the result of their content of free water. These efflo radiating crystals, and an outer crust of shorter, bundled, rescences appear on tidal rhythmites under very small subhorizontally oriented crystals tipped with subhedral overhangs produced by thin, resistant beds. Site 4 (Fig. 1; masses of unknown alternation products (Fig. 3A-C). The Table 1) is a south-facing, unprotected, weathered natural underlayer of fine crystals in the crust has the distinctive exposure along a stream bank, where soft nodules of pale morphology of halotrichite-group minerals (Fig. 3A-C), yellow (2.5Y 8/4), earthy mineral material have formed and the corresponding diffractogram (Fig. 4A) verifies within coal and an underlying shale. Strata at this site, that identification. The XRD patterns of halotrichite and although by no means intensely weathered, are nonethe pickeringite, another halotrichite-group mineral (Table less the most obviously weathered, in terms of oxidation 2), are difficult to distinguish, however, and the two min features and rock character, of all four sites. erals form a solid solution series with respect to Mg2+ (pickeringite) and Fe2+ (halotrichite). Intermediate com Mineralogy positions are indeed possible (Jambor et al. 2000), and EDX spectra (Fig. 3D) of samples from site 1 indicate that Several minerals can be identified in the samples the halotrichite identified by XRD is in fact "magnesian" through XRD (Table 2). Felsobanyaite/basaluminite, copia or is comparatively rich in Mg (cf. Brant and Foster 1959), pite, epsomite, gypsum, halotrichite, jarosite, rozenite, and but the Mg2+ content is too low for pickeringite. The outer

TABLE 3 CHARACTERISTICS OF SAMPLED EFFLORESCENCES AND CRUSTS

Site Sample Color* Mineralogy Date collected pHt

ICSS white 2.5Y 8/1 Halotrichite April 2006 3.07 ICSS yellow 2.5Y 7/6 Slavikite, copiapite April 2006 3.60 ICSS 706-yellowl 2.5Y 8/4 Copiapite July 2006 1.82 ICSS 706-whitel 2.5Y811 Rozenite, pyrite July 2006 2.27 ICSS 706-white2 2.5Y 811 Halotrichite, pyrite July 2006 1.90 ICSS 706-white4 2.5Y 811 Halotrichite July 2006 2.65 ICSS 706-yellow2 2.5Y 7/6 Copiapite July 2006 1.95 ICSS 706-yellow3 5Y 8/6 Copiapite July 2006 1.94 ICSS 906-yellowl 2.5Y 7/6 Slavikite, alunogen September 2006 2.55 ICSS 906-whitel ~2.5Y 811 Epsomite September 2006 7.13 2 TRE-l lOYR 8/1 Halotrichite July 2006 3.02 3 NCB-l 2.5Y 8/6 Copiapite August 2006 2.12 3 NCB-2 2.5Y 712 Copiapite August 2006 1.99 3 NCB-3 2.5Y 8/2 Halotrichite August 2006 2.69 3 NCB-4 ~2.5Y 811 Halotrichite August 2006 2.20 4 FF-l 2.5Y 8/4 Jarosite August 2006 4.82

* Munsell Color (1998). t Values for pH represent 1:1 solutions in deionized water. crust atop the fine-crustal underlayer appears similar to shown in SEM photographs by Hammarstrom et al. the bundled halotrichite crystals illustrated by Coskren (2003). EDX spectra confirm the presence of Mg in these and Lauf (2000) and also produces a diffractogram char crystallites (Fig. 7A). acteristic of halotrichite. The terminal subhedral masses Copiapite was the dominant mineral co-occurring on these crystal bundles, however, may consist of the with slavikite in April (Fig 5A) and July, whereas alu minerals bilinite or romerite, hydrated iron sulfates that nogen was more common in September (Fig. 5B). This sometimes occur with halotrichite in pyrite-weathering pattern may reflect the concentration of A13+ in evaporat environments. Halotrichite, bilinite, and romerite have ing porewaters in the late summer. Copiapite also grows overlapping XRD peaks (see International Centre for Dif directly on pyrite at site 1 (Fig. 6C). fraction Data 2001), and differentiating among them in a Felsobanyaite/basaluminite (Fig. 8A) occurs at site 1 mixed sample by XRD is impossible. as a 2-mm-thick seam of white, earthy material above a Rozenite appeared in white efflorescences associated 3-mm-thick seam of coarsely crystalline gypsum under with weathering pyrite nodules exposed in the outcrop a deep overhang of fine, micaceous, pyritic sandstone. face in samples taken during July from site 1 (Fig. 4B). The overhang provides the best protection from the ele The diffractogram of rozenite is sufficiently different ments of any microenvironment at the site. Epsomite (Fig. from other possible co-occurring hydrated sulfate salts 8B) was found in September at site 1 as a dry, powdery that its identification is straightforward. Also at site 1, yel efflorescence at spots protected from rainfall by slight low slavikite-copiapite-alunogen crusts consistently form overhangs on the outcrop face. The mineral occurred on the outcrop face, and yellow copiapite forms directly alone around small lenses of calcite-cemented, pyrite on or around weathering pyrite. Slavikite (Table 2) can be bearing sandstone and with halotrichite in the loose pile differentiated from copiapite through XRD analysis (Fig. of sloughed rock at the base of the outcrop. Immediately 5). Slavikite yields, among others, intense X-ray reflec south of the study site, epsomite was also found within tions corresponding to approximate dvalues of 11.7, 10.1, loose, fluffy soil at the base of an outcrop that has been 5.8,4.2,2.9, and 2.7 A. Copiapite and magnesiocopiapite, covered by a large corrugated-steel shelter to minimize in comparison, yield intense reflections corresponding to mass wasting along the banks of the Missouri River. approximately 18-18.5 A (Fig. 5A). Slavikite occurs as At site 2, sparse, thin, white (lOYR 8/1) surface crusts fine (4-20 /lm) crystallites (Fig. 6A, B) similar to those consist ofhalotrichite, although macroscopic halotrichite

outer crust c JI' ("A" at left)

5mm

D fibrous crystals Q) LL ("8" at left) o

(j)

EDX spectrum of fibrous crystals

o 2 4 6 8 10 12 14 16 18 20 keV

Figure 3. (A) SEM image of outer, crusted surface of whitish crust collected at site 1 in April 2006. Bundled, needle-like crystals are halotrichite, which appears to be altering into subhedral terminal masses (arrow), possibly bilinite or romerite. (8) SEM image of underlayer of fibrous halotrichite crystals in the crust depicted in (A). (C) Light microscope image of intact halotrichite crust. (D) EDX spectrum of fibrous crystals, like those in (B), showing Mg content of halotrichite.

crystals are not visible, as they are at site 1. Crusts at site values range from 1.90 to 4.82, but almost all the values 2 form directly on the outcrop face, but only in sheltered register at less than pH 2.70. As expected, jarosite produced indentations. Halotrichite (whitish), again without macro the highest pH of all samples except those of epsomite (cf. scopic crystals, and copiapite (yellowish) appear: in moist Van Breemen 1973, 1982). Samples dominated by copia efflorescences at site 3 (Fig. 9), the latter mineral growing pite, or consisting of copiapite alone, produced the lowest directly on pyrite in some cases. Pale yellow (2.5Y 8/4) pH values. nodules in coal and underlying shale at site 4 are jarosite (Fig.6D). DISCUSSION

Acidity Felsobanyaite/basaluminite, epsomite, rozenite, and slavikite have never before been described from Nebraska. Excluding epsomite from site 1, which produces a Slavikite, moreover, has been described from only one oth nearly neutral pH, ground samples of the mineral efflores er locality in North America (Flohr et al. 1995; Lauf 1997; cences, crusts, and nodules all produce acidic pH values in Coskren and Lauf 2000; Hammarstrom et al. 2003). Cody 1: 1 deionized-water solutions (Table 3). These acidic pH and Biggs (1973) found rozenite on Pennsylvanian sand-

© 2007 Center for Great Plains Studies, University of Nebraska-Lincoln @ a :E :!"! N N ...., :::r(O .j::>. o CD _. r::: o '-l :::I CD Cti n a (3 ~ :::I N • ~ (0 CD- ~ ~ ~.~ (3 CD ~ ~ 3 (') ...., ~ C/') ...., a o.-+ 0.... m I\.) » "o ~g~ ~. ~~ g ~ C ~~. 0 ~ c.. =Clicg o ~. CD (') a .::: 6.784 roz (011) C :. £. 3 ::l :::I CD 0 <' 0....(') ...... 5.427 roz (110) ~ O' Cli :E ~~======------4.767 roz (101) 4.440 roz (120) I\.) ~. ~o....:::r o ...-.. _0 ;:::::t.0 3.952 roz (002) ~ :::r:::lCD ~'--:::r Z -.:::::!::.. a -3.359 roz (f30) 3.401 roz (040) g- :::;';""c G')., a~ (1) 0 (') N ...... 0 ...... ::r rl' (000 0 o o I,\) "1J ...., O'l ... (1) 0- C a a 0(1) :J 3 .-+ "'0 (fl ,C/') ~. "C N ..... ::!. en c.. , _. I (fl < ...... 0 ;::;:;::;:..l::: ,.. ..a. (1) a· ~ o 3: cO; __CDCDc; ::r CDI .,0 CD_ .;;;;;;::=-1 .153 pyr (332) C/') N "C ... _. N (') o 0 -~::r::r ::r -::-:~ o , ""-J a a o Z ...., ~ !=> C/') 0 ""C(Oa ...., ~ (') a N :S. 3 0 0 ~~ ""-J Sulfate Mineral Paragenesis in Pennsylvanian Rocks • R.M. Jaeckel et 01. 25

N 0-_0 i.O CON -0 (f)- e. i.O (0 a. co 0 A ","0 u; OU ~ ~ .~ N co co u; If) a> 0 co u; ,...0 ~ M ICSS-2-yellow ~ ..... slavikite (sla) co u; copiapite (COp) a>~ alunogen (alu) ~ Iii ~ & April 2006

a. o U co co ~ u; co N u; I ~ I I 0- I

50 60 70 80 9028

ICSS-906-yellow1 slavikite (sla) B alunogen (alu) September 2006

..... N ~ N I

2 10 30 40 50 60 70 80 9028 Figure 5. (A) X-ray diffractogram of yellowish slavikite-dominated crust collected in April 2006 at site 1. (8) X-ray diffractogram of yellowish slavikite-dominated crust collected in September at site 1 (see Figs. 6A, B; 7).

Figure 6. (A) SEM of (1) slavikite and (2) probable copiapite crystallites in yellowish crust collected in April 2006 from site 1. (8) SEM image of slavikite crystallites collected in September 2006. (C) Copiapite crystallites (between arrows) growing on oxidizing pyrite at site 1. (0) Jarosite crystallites from a small nodule in shale below coal at site 4 (see Fig. 9C). stones in north-central Iowa, more than 300 km northeast of paragenesis at Iron Mountain, CA (Nordstrom and of the study area, and Kopsick (1978) produced rozenite by Alpers 1999), although its presence clearly does not repre 2 3 laboratory dehydration of melanterite in Kansas coal spoil, sent the complete oxidation of Fe -t- to Fe +, a process that but she did not note its occurrence in the field. Tien (1968) typifies late-stage sulfate paragenesis as a whole (Jambor found basaluminite in southeastern Kansas. et al. 2000; Jerz and Rimstidt 2003). In some settings, Halotrichite and jarosite were previously reported halotrichite appears only in dry weather (Jerz and Rim from Nebraska by Pabian (1993). Joeckel et at. (2005) de stidt 2003) or it persists only in microenvironments that scribed alunogen- and copiapite-bearing crusts resulting have some degree of protection from the elements, such from the weathering of pyrite in the Cretaceous Dakota as the outcrop at site 1. The halotrichite at site 1 has some Formation in Jefferson County, NE. degree of substitution of Mg2+ for Fe2+, which in this case Halotrichite is a common alteration product in pyritif is highly compatible with the co-occurrence of slavikite erous rocks worldwide, and after jarosite, it may indeed and epsomite, both of which contain Mg. Both pickerin be the most widespread mineral in acid-weathering en gite, the Mg end member of the solid-solution series with vironments in Nebraska. Halotrichite can form directly halotrichite, and Mg-rich halotrichite have previously following the precipitation ofrozenite (cf. Jerz et al. 2001) been described from weathering pyrite-bearing Penn or as a result of the increase in AI:Fe ratios in host-rock sylvanian sedimentary rocks in the midwestern United porewater as outcrop-surface evaporation occurs (Jerz States (Brant and Foster 1959; Kerns 1967), and given the and Rimstidt 2003). Halotrichite occurs in the late stage potentially widespread existence of Mg2+-bearing calcite

Figure 7. (A) EDX spectrum of slavikite crystallites from site 1, showing the presence of Mg. (8) Infrared spectrum of slavikite-alu nogen crust (slavikite dominant) collected in September 2006 from site 1. The presence of lattice water is indicated by absorption bands marked "W"; strong absorption at 1109 cm-1 corresponds to S042- ion.

as a cement phase in sedimentary rocks, the occurrence of Fe2+ sulfate salt under hotter, lower-relative-humidity con Mg-rich halotrichite and pickeringite is likely to be much ditions (Ehlers and Stiles 1965; Chou et al. 2002; Hammar more common than the published literature suggests. strom et al. 2003). The appearance of rozenite is concluded Rozenite is typically considered to be an early-parage to be a seasonal phenomenon at site 1. netic species (cf. Jambor et al. 2000; Jerz et al. 200l; Jerz Slavikite, persistently identified at site 1, is of par and Rimstidt 2003). Its presence directly atop pyrite nod ticular interest because it has been described from a ules represents the initiation of a new cycle of weathering comparatively small number of sites in Europe (e.g., during midsummer at site 1. However, because ambient Meixner 1939; Van Tassel 1947; Makovicky and Stresko humidity controls the occurrence of rozenite at surface 1967; Parafiniuk 1991), one in South America (Gordon temperatures (Baltatzis et al. 1986; Young and Nancarrow 1941), and from one site, Alum Cave Bluff in Tennessee, 1988), rozenite is also likely to be the most stable hydrated in North America (Flohr et al. 1995; Lauf 1997; Coskren

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Figure 8. (A) X-ray diffractogram of white, earthy material (felsobanyaite/basaluminite) associated with the gypsum seam on the underside of a deep overhang at site 1. Felsobanyaite and basaluminite are listed as separate minerals in various databases (e.g., International Centre for Diffraction Data 2001), but recent work suggests that they are one mineral. XRD peaks of felsobanyaite and basaluminite largely overlap (International Centre for Diffraction Data 2001), but distinct peaks assigned to felsobanyaite in powder diffraction files (PDF) are indicated; most peaks assigned to "basaluminite" also correspond to felsobanyaite. (8) X-ray diffractogram of white, powdery efflorescence around calcite cemented sandstone lenses, collected in September 2006 at site 1 (see Figs. 6A, B; 7).

© 2007 Center for Great Plains Studies, University of Nebraska-Lincoln I\.) V'l cQ'cQ'" " C C ::::;:; O'l"" 0 OCD » rT 9.605 hal (012) CD '7'~ -'" 7.978 hal (022) ~ 0 ~ 0 I\.) ::::l '< 6.074 hal (023) CD..., 0.. 5.285 hal (042 & 033) 0 0 4.785 hal (024) - ~ I\.) ...... ,/4.295 hal (140) '"'0 0 -'" 0 ...,0 ~ 0 3.961 hal (025~ 0 0 co ~5.953 jar (101) .768 hal (133 & 062) 3.494 hal (124 & 006) <0 ..., CD 0 5.731 jar (003) 3.337 hal (134) ::::l CD 3 - 5.107 jar (012) en CJ> v.> -/2.983 hal (017 & 164) I\.) 2.881 hal (074) (ii' ...... 0 0 0 :::r 2.671 hal (182) I» ::::l » '"'0 0- CD :r 2.396 hal (224) ::::l 0 3.117 jar (021) !3:z ::::l 0 ~ -(')(') en ...,...... v.> 0 :::r:::rOJ '< n' 0 2.972 jar (202) I» _. <" :r ~2.866 jar (006) ..:::CirJ:.. 0 ;:j: 2.009 hal (314) ::::l CD 2.550 jar (024) 0 0 1.860 hal (336) ::::l ::J 0'1 0.. ~ 2.294 jar (107) 0 ;;0 0 0 I\.) (') ~ 7' en (') 18.510 cop (010) ""' N ;;: en 1.539~ar ~226) ~ 0 0 1.513jar(0 10 CD 0 ...... "-oJ ~ 9.273 cop (020) Q n :] :-- D 0 ? ~ Cll ~ -....I 1.346 jar (413) 6.189 cop (110) ~ 0 0 Gl '< 5.326 cop (111) iti 0.. -.I» I\.) ~ ~ 0 ~4.035 cop (131)_ 0 a "0 (') til ,.....;--3.592 cop (210 & 012) 3.52 cop (141) ~. 8' ex> ;::t: co 0 CD ~ ..., ~ 3.459 cop (141) c.. 0 v.> 3.084 cop (141) ~~. 3 -"_."1». 0 c ~ ..::!.-"" ::J (0 (') <' c·..., 0 0 Cll 0 V> CJ> I\.) _ "2. Z ~. ;:j: CD ~ ;:.: ~ CD 0'1 , .j::>. 0 ::J (') u;-- I\.) 0 CD N s- CD

© 2007 Center for Great Plains Studies, University of Nebraska-Lincoln Sulfate Mineral Paragenesis in Pennsylvanian Rocks • R.M. Joeckel et 01. 31 in an area where it has not been previously recognized, Chou, I.M., R.R. Seal II, and B.S. Hemingway. 2002. should be considered in local to regional assessments Determination of melanterite-rozenite and chal of surface-water and groundwater chemistry in south canthite-bonattite equilibria by humidity mea eastern Nebraska because of the long-term role of such surements at 0.1 MPa. American Mineralogist weathering in liberating and concentrating ions such as 87:lO8-14. AP', Fe2+, Fe3+, Mg2+, and S042-, all of which can have Cody, R.D., and D.L. Biggs. 1973. Halotrichite, szomol a significant impact on water quality. The release of A13+ nokite, and rozenite from Dolliver State Park, Iowa. into surface waters by the dissolution of surface salts Canadian Mineralogist 11 :958-70. produced during weathering has a potentially detrimental Condra, G.E., and E.e. Reed. 1959. The Geological Sec effect on aquatic organisms. The precipitation of sulfate tion of Nebraska. Nebraska Geological Survey salts can also cause engineering problems, particularly Bulletin 14A. Conservation and Survey Division, in road construction, and the potential of such effects in University of Nebraska-Lincoln, Lincoln, NE. southeastern Nebraska should be reconsidered in the light Coskren, T.D., and R.l Lauf. 2000. The minerals of Alum of the results presented herein. Cave Bluff, Great Smoky Mountains, Tennessee. Mineralogical Record 31:163-75. ACKNOWLEDGMENTS Davis, A.D., and e.l Webb. 2002. Hydrologic issues at the Gilt Edge Superfund Site in the Black Hills of We thank Dr. Han Chen (Microscopy Core Facil South Dakota. Transactions of Society for Mining, ity, University of Nebraska-Lincoln) and Barbara Ang Metallurgy, and Exploration 312:113-15. Clement (Department of Biology, Doane College) for Ehlers, G.E., and V.D. Stiles. 1965. Melanterite-rozenite assistance with electron microscopy and two anonymous equilibrium. American Mineralogist 50: 1457-61. reviewers for their helpful comments toward improving Farkas, L., and F. Pertlik. 1997. Crystal structure de the original manuscript. terminations of felsobanyaite and basaluminite, AI4(S04)(OH)1Q. Acta Mineralogica-Petrographica REFERENCES Szeged 38:5-15. Fischbein, S.A. 2005. Lithofacies, architecture and se Baltatzis, E., M.G. Stamatakis, and K.G. Kyriakopoulos. quence stratigraphic interpretation of the Upper 1986. Rozenite and melanterite in lignitic layers Pennsylvanian Indian Cave Sandstone, Northern from the Voras mountain, western Macedonia, Midcontinent Shelf, U.S.A. (southeastern Nebras Greece. Mineralogical Magazine 50:737-39. ka). Ph.D. diss., University of Nebraska-Lincoln, Bandy, M.e. 1938. Mineralogy of three sulphate deposits Lincoln, NE. of northern Chile. American Mineralogist 23:669- Flohr, M.lK., R.G. Dillenburg, and G.S. Plumlee. 1995. 760. Characterization of secondary minerals formed as a Bayless, E.R., and G.A. Olyphant. 1993. Acid-generat result of weathering of Anakeesta Formation, Alum ing salts and their relationship to the chemistry Cave, Great Smoky Mountains National Park, Ten of groundwater and storm runoff at an abandoned nessee. Open-File Report 95-477. U.S. Geological mine site in southwestern Indiana, U.S.A. Journal Survey, Reston, VA. of Contaminant Hydrology 12:313-28. Frondel, e.l 1968. Meta-aluminite, a new mineral from Blevins, D.W. 1989. Sources of coal-mine drainage and Temple Mountain, Utah. American Mineralogist their effects on surface-water chemistry in the 53:717-21 Claybank Creek basin and vicinity, north-central Gadsen, lA. 1975. Infrared Spectra of Minerals and Missouri, 1983-84. Water-Supply Paper 2305. U.S. Related Inorganic Compounds. Butterworth Group, Geological Survey, Reston, Virginia. London, UK. Brant, R.A., and W.R. Foster. 1959. Magnesian halo Gordon, S.G., 1941, Slavikite, butlerite, and parabutlerite trichite from Vinton County, Ohio. Ohio Journal of from Argentina. Notulae Naturae ofthe Academy of Science 59:187-92. Natural Sciences ofPhiladelphia 89:1-8. Buckby, T., S. Black, M.L. Coleman, and M.E. Hod Gricius, A., 1971. Basaluminite in Iowa. Earth Science son. 2003. Fe-sulphate-rich evaporative mineral 24:30l-3. precipitates from the Rio Tinto, Southwest Spain. Hammarstrom, lM., R.R. Seal II, A.L. Meier, and le. Mineralogical Magazine 67:263-78. Jackson. 2003. Weathering of sulfidic shale and

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