Conadian Minerologist Vol. 25, pp.22l-226 (1987)
FORMATIONOF A JAROSITEDEPOSIT ON CRETACEOUSSHALES IN THE FORT NORMAN AREA. NORTHWESTTERRITORIES*
FREDERICKA. MICIIEL Ottawa-Carleton Centlefor GeoscienceStudi?r., Deportnent of Geologlt, Caileton (Iniversity, Ottowo, Ontaio KIS 586
ROBERT O. veN EYERDINGEN Arctic Institute of North America, The Universityof Calgary,Calgory, Alberto T2N IN4
ABSTRACT pyritiferous shales.A large number ofinvestigations into the formation of jarosite by the oxidation of A 5800+ m3 deposit composedprimarily of jarosite, 54 pyrite have beensummarized by van Breemen(1973). km northeast of Fort Norman, N.W.T., is being precipi- He found that natrojarosite, the sodium member, tated as a yellow ochrefrom an acidic (pH 2.9), iron-bearing forms only after depletion of all available potassi- groundwater seep.Subsequent weathering of the surficial um and, therefore, is rarer than the jarosite end- jarosite crust resulfsin alteration of the to goethiteand gyp- member. sum. The groundwater chemistry is attained tlrough dis- (1981) solution of dolomite followed by Ca+Mg forNa+K cation Yorath & Cook have reported on the for- exchange,sulfide oxidation and gypsrr- precipitation dur- mation of jarosite due to the combustion of ing subsequentmigration tlrough a Cretaceousshale unit. bituminous pyrite-bearingshale in the Smoking Hills Formation eastof the MackenzieDelta. Ross& Ivar- Keywords: jarcsite, groundwater, pyrite oxidation, cation son (1981) suggestedthat natrojarosiie is generally exchange, Great Bear Lake, N.W.T. more abundant than jarosite in the asidic sulfate soils ofwestern and northern Canada. The occurrenceof SoMraarns natrojarosite in polar regions has also beenreported by Vennum (1980) and by Foscolos & Kodama Un gisement de plus de 58@ m3, compos6 surtout de (1981). In most instances,the jarosite group of jarosite, e$t en train de se former par prdcipitation sous mins1afuoccurs as yellow mottles or stains within forme d'ocre jaune i partir d'une exsudation d'eau acidi- acidic sulfate soils, and is due to in situ wathet'rng que (pH 2.9) fenif€re, 54 km au nord-est de Fort Norman, of exposed sulfides. This paper describesa major Territoires du Nord-Ouest. Un lessivagede la crotte en sur- accumulation of jarosite, referred to informally as face transforme la jarosite en goethite + g;ypse.Le chi- the Golden Deposit, precipitatedfrom a groundwater misme de I'eau 6volue par dissolution de la dolomite, sui- seep in the Northwest Territories. vie d'un 6changecationique de Ca+Mg pour Na+K, orydation des sulfure,set prdcipitatiotr du gypse au cours de sa migration i tavers d'une unit6 de shale Cr€tac6. DEscRrPTroNoF THE SrrE
(Iraduit par la R6daction) The Golden Deposit, located 54 km northeast of Fort Norman, N.W.T. (latitude65"11'58', N, lon- Mots
tions of rozenite FeSOr.4HrOl gypsum. silica and one other mineral. On the basisof X-ray diffraction and X-ray fluorescencedata, {his other mineral is tentatively reported as varisclte AIPO4.2H2O (J. Wong and A.G. Heinrich, pe{s. comm.).
GnouNnwersn 'gr cs of the groundw was collected from YU(ON A sample RtTOST-C one of the discharge points the middle of the TERRITORY deposit, for major-ion and a partial heavy-metal analysis(Iable 2). Field indicate that the groundwater is and acidic OH 2.9). All three major cations *, Mg2*, Na+) are Fro. l. Locationof the GoldenDeposit, near Great Bear present in significant with mag- River,N.W.T. nesiumd9min6!, whereas is the only abun- dant major anion present 4). Potassium is presentin low concentrations The lack ofbicar- Middle Devonian and Ordovician age ate exposed bonate ions is due to the low . A typical recharge within the Keele Arch, approximately 12 km west of water for this area has also plotted in Figure the deposit. 4 for comparison.Major betweenthe two plots indicate that discharging at the Golden Deposit has been iallv altered dur- M[rrsRAlocv oF THE Dnposrr ing subsurfaceflow. The low concentrationof indicatesthat 5amples of the yellow clay were collected from halite is not the source of the concentration of points of active dischargeof groundwater and from sodium. We believe, that the sodium is the drier crust of the deposit. In addition, crystals derivedfrom shaleduring exchangewith cal- encrusted on vegetation surrounding the exposed cium and magnesium. During the cation-exchange deposit were sampled. The mineralogy of samples process,calcium and in solution would for all three materialsis given in Table l. be adsorbedonto the surfaces,whereas Analysis by X-ray diffraction revealedthat tlte yel- sodium (and potassium)would releasedinto solu- low ochre collested at points of groundwater dis- tion from the shale.The datawere analyzed charge contains primarilf jarosite (6690) with using the PHREEQE program of Park- a:7.303Q), c = 17.09(1)A, and a small amount hurst e/ a/. (1980). From analysis, the high of goethite (990). Clay minerals carried in suspen- Mg2+lguz+ ratio of 3.87 is to calcium sion comprise the remaining 250/0.The crust, which depletion due to gypsum ration and precipi- coversmost of the deposit (darker portions in Fig. tation. 3), hasbeen altered to goethite, with only minor jaro- Negative PS values and values closeto zero site remaining. In addition, somegtrpsum has formed (Table 3) indicate that the sulfate and the during breakdown of the jarosite. The formation of precipitated sulfates in the are derived from goethite and gypsum is believed to be due to leach- the oxidation of sulfidesratier marine sulfates, which have 6eS values +15.1and +32.6 ing by rain and snowmelt, such that: o/oo o/oo, and 6180values between 12.0and + 17.l in this area (van Everdingen al.1982). Oxidation I(Fe3(SO)2.(OH)6+ 4H2O + 2C8+ - of sulfides is also suggested high concentrations gro relative to most 3FeOOH+2 [CaSOa.2H2O]+K++3H+ (1) of trace metals in the groundwaters studied by (1977)n the cen- tral Mackenzie Yalley Clable The exceptionally During midsumrner, some of the vegetationgrow- high value for iron that pyrite is the subsurface rng alonE the perimeter of the exposeddeposit was {ominant sulfide during flow' found encrustedin "salts",r r owingvvtuE toev evapotranspi"wr4!,v!rluel, (1981) on the widespread ration of the saline eroundwater. Analysis of these Yorath & Cook pyrite-bparing shalesof Creta- "salts" by X-ray diffraction, at .the Institute of existenceof Sedimentary and Petroleum Geology in Calgary, ceousage in the region. The of sucha unit indicated that they are composedprimarily of bloe- along the flow systerrlwould the requirements dite NazMg(SO42o4HrO, with smaller concentra- for cation exchangeand a sourceof sulfide. FORMATION OF A JAROSITE DEPOSIT 223
q Golden N Deposit @ <)
fl kt 4\ ,03^ o S\' \ \ O
nt st. @ ce q@ @
Kilometres Spring .-> Sinkholes 'o Contour Interval 500 Feet Ftc.2. Topography and location of springs and karst features (modified from van Everdingen l98l; elevation contours in feet).
FoRMATIoNoF TTIEDEPoSIT tated from groundwater discharetng at the site. It constitutes the largest concentrated occurrenceof a The Golden Deposit representstle accumulation jarosite-group mineral reported to date in Canada. ofjarosite (and products of its weathering) precipi Allen & Day (1935)have also describedthe deposi- 224 THE CANADIAN MINERALOGIfIT
Frc.3. a. Aerial photoeraphof the GoldenDeposit and adjacentarea. Deposit is 126mebes b[ 46.5metres. b. Close up of an activedisiharge-point of groundwaterwitlin the GoldenDeposit.
tion of jarosite from springsin YellowstoneNational stituents in the groundwater, is important to exa- Park, Montana (Brophy & Sheridan 196t. Sincethe mine tle flow sYste,mand evolution of the Golden Depositjarosite is a product of dissolvedcon- chemistry of the FORMATION OF A JAROSITE DEPOSIT 22s
lgSB 1. UINERAIGI(nI @!'PCSTECN CF SE GCIDBI DEPGTT. N.W.T. meqlL Yellry ocbre at Crystals
MlperaL Dlscharqe PoIntg cruat on Plant n2
Jarosite
Go€thlle
GyI,Bu sillcatee r 8
Bledi.te Golden
Rozetrite 10 Deposit varLscite 2 I4
Iz@tioE tn t. x-ralFdtftuisr MIys c&airEd d tbe Instltut€ ot sedtl@tarj' aDd Pstsl@ G@fogy' Galoglel.$r€Y of Calada' rr6ry (J. tlfq ed LG. Eetndch, M11&). I Csly Eij@l€ artl stlie: '? Inferredr @ emclea b' @u1ts of Fa!-fll@ I *__.r,
\ / IABLE 2. @E!,lICAI, CIPCGTETON @' G8O'INDIGER DIIY'@A@ AD 1HA GTf'!T{ DEF6I3, IICRIHI{E T EFRIIIRIE \v/ Teup ('c)r 3.7 MN 6.5 ( o.05)2 pB r 2.9 0.03 ( 0.00sF \/ Eh (nv) r +683 Pb o.r2 ( o.oo5)2 \/ Conduc t lv I tY z\ o.17 ( 0.05)2 \/ r (o.ooo5)2 1ug/m) 89oo o.oo05 Recharge-w;r# \. / ca 341 uCo3 0.0 I ug S00 s04 5300 10 \ I Na 5oo 24 \/ K 7.0 0.r5 \/ 22O ( t.5)2 sio2 \/ \-.. I C.@ositlsE qEted l! !gA. Ar€\@ lEfo@d at tlE w8ts \J OElity Eerch, InLard t{ats Dit€ffite, Bf,ritwtt CarEda, G.Lqara. I rioltl tlwrqgfs. 2 I'igrc ln patsltl@ lq[€dt EllE lor aFfpamcefy 908 of, @re tlB 100 aD\zed 84)1€ of qnD&Ets fim ttE €tcEl ltaclsEiE vauey (dala f@ laldEl Cl SO+ HCO3 Ign\. Ca Mg Na+K
Frc.4. Semilog plot showing major-ion data for water from tie Golden Deposit and atypical rechaxge flow systemis believed samples The recharge area for the water in the area (data from Michel 197). to be situated approximately 12 km west of the deposit, along a 300-metre-high ridge that trends northwest from Mount St. Charles and the St. rSLE 3. ISOAOPTC DATA FOR SULFATE FROM TSE COLDEN DEPOSTA Bear River (Fig. 2). Charles Rapids on Great 34s l8o Recharge, into sinkholes developed in dolomitic Materlal t {
rocks of the Bear Rock and Franklin Mountain For- Groundf,ate! -22.A t 0.2o/@ +0.5 t 0.2ol@ gives the ground- mations exposedalong the ridge, Y€ll@ ochte at -22.3 water an initial composition enrished in Ca2+, atischargo lDlnls +2.4 Mc3* and HCO3-. During subsequentflow ttrrough Crust -24.9 +4.d pyritiferous Cretaceous shales, cation exchange crysta!.€ on plsnts -I9.1 -0.8 results in a loss of calcium and magnesium, and an Data f,roD Sbakur (1982r' eacepl f,or thode gn crust (fr@ addition of sodium and potassium to the ground- Stable lgoteEe Laborelory' Phtslcs Dopt. of the tolversLty of, pyrite in the shales Calqary. 6Jag and 6160 quotqd Plth rdatEct to CDT and SliOU, water. Biochemical oxidation of resp€c!lveIy. leads to high concentrations of iron, sulfate and hydrogen ion in the groundwater. The high concen- tration of sulfate in turn leadsto precipitation ofgyp" (Stumm & Morgan 190). Van Everdingen el a/. sum and a preferential loss of calcium over mag- (1985)have determinedthat over 5090of the orygen nesium. in the sulfate of the Golden Deposit is derived from The oxidation of pyrite can be described by the water molecules,and that Thiobacillusferrooxidaru reaction: likely plays a role in the oxidation process.With the dwelopment of acidic conditions (increasiug[H+]), 4FeSr+ lOHrO + l5Olaq) - bicarbonateions are consumedto form carbonic acid 4FeOOH + 8SOr + l6H+ Q) H2CO3. 226 THE CANADIAN MINERALOCIST
Subsequentcombination of liberated iron and sul- Bnopsv, G.P. & Ssrnrpan, $4.F. (1965): Sulfate fate ions with potassium released during cation studies.tV. The jarosite- natfojarosite- hydronium exchangeleads to the production of jarosite. The jarosite solid solution serjes'nAmer. Mineral, 50, overall reaction can be expressedas: 1595-1607. Foscor,os,A.E. & Kopaue,H. ( l): Mineralogy and 6FeS2+ 2CaMg(COs)z+ 4(Na,K).Clay + chemistry of arctic desert r on Ellef Ringnes 20H2O+2002- 2KFer(SO)2.(OH)6+ 2(Ca,Mg). Island,Arctic Canada.Soi/ Soc.Amer. J. 45, Clay + 4H2CO3+ CaSOa+ 7SO42-+ 20H+ + 987-993. Mg2+1J112+ (3) Mrcns, F.A. (1977): Studiesof Springs jarosite in the Central Mockenzie Vr North West Ter- In addition to the formation of describedin ritories, Canada. M.Sc. Univ. Waterloo, equation (3), small quantities of goethite are precipi- Waterloo, Ontario. tated, and the total concentration of dissolvedsulids in the groundwater increasesas tle reaction proceeds Pemnunsr, D.L., D.C. & Pluuurn, -A to the right. L.N. (1980):PHREEQE programfor geochemical (l - The formation jarosite has resulted in only low calculations. Geol.Sum. Water- of (NTIS potassium present Resources Invest. 80-96 Tech. Rep, concentrationsof being in the dis- PB81-167801). charging groundwater. This has led to the unusually high Na',/K+ ratio of 120.7. Even with the high Ross, G.J. & IvensoN, K.C. (l l): The occurrenceof concentration of sodium in the groundwater, no basicferric sulphatesin Canadiansoils. Caz. sodium was detected in the precipitate (analysis by J. Soil Sci.61,99-107. microprobe). This supports the conclusionof van Snarun,M.A. (1982):FaS and Variationsin Ter- Breemen(1973), who noted that natrojarosite would restrial Sulfates.Ph.D. Univ. Calgary, Cal- form only after depletion of all available potassium. gary, Alberta. Regardless of the actual iron sulfate mineral formed, it is important to recognizethat the Golden Sruuu, W. & MonceN,J.J. Aquatic Chemis' Sons, York. Deposit is the result of a concentrated discharge of rry. J. Wiley and mineralized groundwater that has encountered a veN BnBeNtsNl,N. (1973):Soil processesin acid sulfide-bearing horizon during subsurfaceflow. The sulphate soils. .Iz Acid Sul Soils (H. Dost, ed.). recognition and understandingof systemsof ground- Inst. for Land and Improvement water flow and their related deposits,especially those (Wageningen,Netherlands), Publ.It,1, 66-130. that contain substantial concentrations of iron and (1981): hydrology other heavy metals, could become as important in vaN EvenonceN,R.O. , karst in permafrost terrain gos- and hydrochemistryof the exploration ofunexposed sulfide deposir as nearGreat Bear Lake, Northl Territoiq. Inland sans are where the sulfides are exposedto surficial WatersDbectorate, Canada, Sci. Ser. weathering. 114(NHRI Pap. 11). (1982): ACtrn.IOWLEDCEMBNTS Ssarun, M.A. & H.R. 6:aS and dlsO abundances Upper Cambrian Lower Devonian ing units, Dstrict Wong and A.G. Heinrich of the and We thank J. of Mackenzie, N.W. pdate. Can. J. Eqrth ISPG, GeologicalSurvey of Canada,for the X-ray- Sci. 19, 1246-1254, diffraction analyses,G.Y. Chao of Carleton Univer- sity for independently confirming the jarosite spe- & Mrcurl, F. (1985):Orygen and geochemistry cies, and P. Jones of Carleton University for the sulphur isotope f acidiceroundwater dischargein British Columbi Yukon and District microprobe analysis.Isotope analyseswere provided Mackenzie, J. Earth Sci, X2, Department of of by the Stable Isotope Laboratory, 1689-1695. Physics, The University of Calgary. We also thank G.J. Rossof Aericulture Canada, the two reviewers and R.F. Martin for their valuable suggestionsfor improving the manuscript. Funding for this research was provided by Environment Canada and by the (M&6). senior author's NSERC operating $arfi Yonern,C.J. & Coor, D.G. l): Cretaceousand Tertiary stratigraphyand , northern District Geol, Sum, RrrsREllcrs Interior Plains, of Con.,Mem,39E. Ar,lrN, E.T. & Dev, A.L. (1935):Hot springsof the YellowsloneNational Park. CarnegieInst. Wash., ReceivedApril 3, 1986, manuscript accepted Publ.466, July il, 1986.