THE ROLE OF JAROSITE AND COPIAPITE IN THE CHEMICAL EVOLUTION OF ACID DRAINAGE WATERS, RICHMOND MINE, IRON MOUNTAIN, CALIFORNIA
by
Clare Robinson
A thesis submitted to the Department of Geologicai Sciences and Geological Engineering in confonnity with the requirements for the degree of Master of Science
Queen's University Kingston, Ontario, Canada January, 2000
Copyright O Clare Robinson, 2000 National Library Bibliothèque nationale 1*1 of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395, me Wellington Otbw ON KIA ON4 Ottawa ON KIA ON4 Canada Canada
The author has granted a non- L'auteur a accordé une licence non exclusive licence allowuig the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, luan, distribute or sen reproduire, prêter, distriiuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/nlm, de reproduction sur papier ou sur format électronique.
The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fkom it Ni la thése ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. The Richmond Mine at Iron Mountain, California is host to the most extrerne acid mine drainage ever reported. Prior to treatment, pH values of mine water as low as -3.6 with dissolved solid concentrations near 1000 g/L have been recorded- A si,bnificant contrïbuting factor to the water quaiity at this site is the cyclic precipitation and dissolution of secondary sulphate rninerals. The exact influence of many of these rninerals is not completely understood. Copiapite [F~"F~~~'(S~&(OH)~.~OH~O]and jarosite P~~~(SO~)~(OH)~]minerais, with CO-existing waters, have been collected and studied to obtain a beuer understanding of mineral-water interaction within the Richmond Mine-
EIectron microprobe, scanning electron rnicroscopy and x-ray diffraction techniques identified two phases in the copiapite samples: (1) a predominant magnesiocopiapite phase of serni-rectangular, platy crystals (10-50 pm) and (2) a rninor aluminum-rich femcopiapite phase existing as srnaller platy crystals (55 pm) of spheroidal aggregates.
Pore-water extracted frorn the copiapite has world-record femc iron concentrations of 147 g/L, a pH of -1.0 t 0.5, and a measured density of 1.5 g/mL. The predominance of fenic iron - and alurninum in this fluid suggest that at the tirne of analysis it was supersaturated with respect to the Al-rich ferricopiapite, as opposed to the dominant Mg-rich phase. Insufficient data are available to evaluate the activity coefficients for al1 the eIements in acid mine waters, particularly femc iron. Interaction parameters and temperature dependence for al1 the constituents. including copiapite, must be defined in order to completely describe the system thermodynamically-
The composition of jarosite stalactites and mud determined by electron microprobe and X-ray diffraction is primarily between the K-H30end-members within a K-Na-H30 solid solution. An amorphous sika minera1 occurring with the stalactites was identified, supporting saturation predictions by other authors doing geochemical modeling of the Richmond Mine effluent (Nordstrom and Alpers, 1990). An iron-nch red mineral occumng with the jarosite stalactites was tentatively identified as goethite, following single crystal x-ray analysis.
Geochemical modeling with the speciation program WATEQ4F indicates that the drip waters collected from the stalactites are in equili brium with jarosites that have compositions primarily between the potassium and hydronium end-members of the jarosite solid solution, supporting mineral chemistry findings. Saturation of goethite and an amorphous silica phase were predicted in geochemical modeling of the stalactite drip water. Speciation calculations with jarosite mud pore-water were not reliable due to an apparent anion surplus reported by WATEQ4F. Sensitivity analyses with both data sets revealed pH to be a very significant variable in determining sulphate speciation and jarosite composition.
Copiapite is a relatively solubIe sulphate and has very acidic pore-water. Dissolution of significant quantities of this mineral during wet seasons likely contributes to a short-tem influx of iron and sulphate in the Richmond Mine effluent. Given the relative low solubility of jarosite, it will attenuate certain elements more effectively than more soluble sulphates (Le. copiapite). TABLE OF CONTENTS
Abstract
Table of Contents
List of Figures
List of Tables
Acknowledgements
Chapter One: Introduction 1.1 General Statement 1.2 Acid Mine Drainage and Secondary Minerals - Definitions 1.2.1 Acid Mine Drainage (AMD) 1.2.2 Secondary Minerals 1.3 iron Mountain, California 1.4 Purpose and Scope 1.5 Methods
Chapter Two: Literature Review 3.1 Introduction 2.2 Iron Mountain 32.1 Regional Geology 3-22 Paleoenvironment 2.2.3 Mining History and Previous Work in the West Shasta Cu-Zn District 2.2.4 The Lron Mountain Deposits 2-25 Environmental ProbIems 2.1 .S. 1 Historical information 2.1.5.3 Development of extrerne acid mine water at iron Mountain - previous work 2.3 Secondary Sulphate Minerals 2.3.1 Iron Sulphate Paragenesis 3-32 Minera1 Solubility and Ternporary Storage of Inorganic Elements 2.3.2.1 Implications for remediation and treatment 2.3.3 Secondary Iron Sulphates in This Study 2.3.3.1 Copiapite 2.3.3.2 Jarosite
Chapter Three: Sample Collection 3.1 Introduction 3.2 Inside the Richmond Mine 3.3 Mineral Collection 3.4 Water Collection 3.4.1 Measuring and Reporting Negative pH 3.4.2 Field Measurements and Sarnpling Procedures 3.4.3 Average Water Chemisrry of Drifts A, B. C, and D 3.4.4 Copiapite Pore Water 3.4.5 Jarosite Stalactite Drip Water 3.4.6 Jarosite Pore Water Chapter Four: Copiapite 4.1 Introduction 4.3 SampIe Description and Petrographic Summary 4.3 Scanning Electron Microscopy 4.3.1 Results 4.4 Major Elements - Electron Microprobe Analysis 4.4- 1 Results 4.5 Trace Elements - Proton Microprobe Analysis 43.1 Results 4.6 Crystal Structure 4.6.1 Results 4.7 Solubility 4.8 Discussion
Chapter Five: Jarosite 5.1 Introduction 52 Sample Description and Petrographic Sumrriary 5-21Stalactites 5.2.2 Mud (centrifuge residual) 5-23 Crust 5.3 Scanning Electron Microscopy 5-4 Major Elements - Electron Microprobe AnaIysis 5.4.1 Jarosite Results 5.4.1.1 Evaluating ZAF 5.4.2 Unknown Red Mineral 5.5 Trace Elements - Proton Microprobe Analysis 5.6 Crystal Structure 5.7 Solubility 5.7.1 Geochemical Modeling 5.7.1. 1 Speciation of jarosite stalactite drip water 5.7.1.2 pH sensitivity analysis 5.7.1.3 Speciation of jarosite mud pore-water 5.8 Discussion
Chapter Six: Conclusions and Recommendations 6.1 Conclusions 6.1.1 Copiapite 6.1.2 Jarosite 6.2 Recornmendations
References
Appendix A Appendix B Appendix C Appendix D LIST OF FIGURES
Figure 1.1: Location of Iron Mountain in Nonhern California. 6 Figure 2.1: Geologic map of major formations in the West Shasta District. 12 Figure 2.2: Cross-section of Iron Mountain showing Homet and Richmond deposits. 18 Figure 2.3: Eh-pH diagram. 38 Figure 2.4: Copiapite structure. 36 Figure 2.5: Jarosite structure- 41 Figure 3-1: Map of drifts. 48 Figure 3.2: Colourful secondq minerals in the Richmond Mine. 50 Figure 3.3: D-drift copiapite. 53 Figure 3.4: Wall of jarosite in D-drift. 54 Figure 3.5: Bacceria coated stalactites. 55 Figure 3.6: Standard solutions in effluent sueam. 58 Figure 3.7: Water sampling (Dr. HE.Jarnieson). 61 Figure 3.8: Filtering samples (Mike Hunerlach - USGS) 61 Figure 3.9: Dripping jarosite stalactites. 63 Figure 3.10: Beakers of drift water. 64 Figure 4.1: Copiapite polished thin section. 68 Figure 4.7,: SEM of two phases of copiapite. 70 Figure 3.3: SEM and EDS of Mg-rich copiapite. 71 Figure 4.3: SEM and EDS of AI-rich copiapite. 72 Figure 4.5: SEM showing copiapite phase relationships. 73 Figure 4.6: Relative Mg and Al content of copiapite. 79 Figure 4.7: Diffraction pattern for copiapite. 87 Figure 4.8: Relative peak percentages. 90 Figure 5.1: Jarosite stalactite thin sections. 102 Figure 5.2: Photomicrographs of jarosite. 103 Figure 5.3: Pyrite in jarosite stalactite. 104 Figure 5.4: Jarosite mud thin section. 106 Figure 5.5a: Jarosite crust with red mineral. 107 Figure 53: Photomicrographs showing textures of the red mineral. 108 Figure 5.6: SEM of jarosite stalactite with EDS showing Si peak. 110 Figure 5.7: SEM of jarosite mud. 11 1 Figure 5.8: Jarosite stalactites plotted on temary diagram. 118 Figure 5.9a: Diffraction patterns of mixed jarosire phases. 128 Figure 5.9b: Close-up of figure 5.9a emphasizing mixed jarosite phases. 129 Figure 5.10: Jarosite staIactite drip water plotted on Eh-pH diagram. 144 LIST OF TABLES
Table 1.1: Secondary minerals discussed in this study. Table 1.2: Canadian mine water maximum values with extrerne mine water. Table 2.1: Brief historical summary of activities at the Iron Mountain site. Table 2.2: A summary of environmentai literature on Iron Mountain. Table 2.3: End-mernber formulae for jarosite. TabIe 2.4: Crystallographic properties of jarosite minerais. Table 3.5: Summary of thermodynarnic data for jarosites. Table 2.6: Free energy and solubility products of jarosite solid solution rnembers. Table 3.1: Catalogue of minera1 and water sarnples. Table 3.2: Water samples from drifts A, B and C. Table 3.3: Chemistry and colour of Dzlrift drip water. TabIe 4.1: List of primary analytical standards used in sdphate EMPA. Table 4.2: MarysvaIe aiunite standard analyses and expected composition. Table 4.3: Calculated wt % elements from known copiapite species- Table 4.4: Copiapite EMPA in wt % element. Table 4.5: Copiapite EMPA in wt % oxide and minerai fonnulae. Table 4.6: Significant trace elements in copiapite. Table 4.7: Unit ce11 parameters for copiapite. Table 4.8: Copiapite pore-water chemistry. Table 4.9: Drift water chemistry. Table 5.1: Features in jarosite hand sarnples. Table 5.2: Calculated wt % elements for cornmon jarosites. Table 5.3: EMPA of jarosite stalactites in wt % element. Table 5.4: EMPA of jarosite stalactite in wt % oxide with minerai formulae. Table 5.5: EMPA of jarosite rnud in wt 95 eIement. Table 5.6: EMPA of jarosite rnud in wt % oxide wi th minerai formulae. Table 5.7: Cornparing the ZAF and #pz correction program. Table 5.8: Wt % element data for comrnon iron oxides. Table 5.9: Significant trace elements in jarosite stalactites. Table 5.10: Significant trace elements in jarosite rnud samples. TabIe 5.1 1: Gandolfi results on red mineral. Table 5.12: StaIactite drip water chemistry. Table 5.13: Thennodynamic data used in WATEQ4F. Table 5.14: Speciation of jarosite stalactite drip water. Table 5.15: Sensitivity analysis of pH range. Table 5.16: Sensitivity analysis of pH effects on jarosite pore water- ACKNO WLEDGEMENTS
First and forernost 1 thank my advisor, Dr. Heather Jarnieson for her guidance, enthusiasm and support - frnancially, intellectually and ernotionally- Your confidence in my abilities has done more for me than you realize. Thank you for the challenge!
1 owe tremendous thanks to Dr. Ron Peterson- Your time, patience and interest will be remembered. Thank you to Dr. Dugald Cannichael, Dr. Peter Roeder, and Dr, Stephen Brown for many meaningful discussions.
Gratitude is extended Dr. Charlie Aipers and Mike Hunerlach of the US Geological Survey for arranging the freldwork - an unforgettable experience. Water analyses were provided by the USGS analytical laboratory in Boulder, Colorado. Dr. Jirn Ball and Btaine McCleskey provided a great deal of assistance interpreting the water chernistry results and running WATEQ3F. Thanks to Gilles Laflamme at CANMET for taking on the copiapite chailenge! The polished thins sections were great.
Thanks to the operators of the micro-PIXE at the University of Guelph, Drs. Campbell and Nejedly for their tirne and assistance. Bob Whitehead at RMC graciously provided time in the X-ray lab for many hours of analyses.
The Queens Geology Department - staff and students - bas been incredibly supportive! Thanks to everyone for providing me with assistance, inspiration and an excuse to take a break now and then! Especially Tom UIlrich - a graphics wizard, Joey Meldrum, Dr. Liz Turner, Amelia Rainbow, Jerry Grant, Sara Ryan, Ian Russell and Dr. Doug Archibald. You have al1 helped to make this my home away from home.
Special thanks to Sonya Billiard, Erin Carruthers and Doug Angus for making me laugh and putting up with me these past crazy weeks of final thesis crunch-time!
1 would also like to thank my friends and farnily "back east" for their love and encouragement that 1 feel with me wherever I go and in whatever I do. Where would 1 be without you?
Finally, 1thank Dr. Peter Giles and Dr. Marcos Zentilli. Peter for showing me to how to look ar: rocks in a new and interesting way. Marcos for helping me find rny niche. And both of them for never doubting me. CHAPTER ONE: INTRODUCTION
1.1 General Statement
Rapid oxidation of sulphide minerals in mine-waste environments results in the formation of
metal-nch sulphuric acid solutions that pose a potential threat to surrounding ecosystems. Every
year, rnining companies and taxpayers in North Arnenca spend millions of dollars on mitigating
acid drainage problems. Worldwide, it is arguably the largest environmental problern facing the
mining industry. The Iron Mountain Superfund site in northern California is host to the worst
acid mine drainage (AMD) ever reported (Nordstrom and Alpers, 1999b; Jamieson et al., 1999)-
Prior to treatment, mine waters at this site have pH values as Iow as -3.6 and total dissolved solid
concentrations approaching 1000 g/L (Nordstrom and Alpes, 1995), figures that surpass
acceptable guidelines by orders of magnitude (CCME,1998). This lowquality discharge is
predicted to continue for more than 2000 years at current weathering rates, in the absence of effective remediation efforts (Nordstrom and Alpers. 1995).
The repeated precipitation and dissolution of secondary sulphate minerals has been identified as a significant contrïbuting factor to the AMD problern at Iron Mountain (Nordstrom and Alpers,
1990; Nordsuorn and Alpers, 1999b; Jarnieson et al.. f 999). These soIuble rnineraIs store metals and acidity in dry seasons and release them during wet seasons. This cycle results in drarnatic seasonal variations in water quality. senously affecting surrounding ecosystems (Alpers et al.
L994). Secondary sulphate formation and its influence on water quality are not well undentood.
Ongoing research by govemrnent agencies. university facilities, and private companies is leading to a more thorough awareness of the mechanisms involved.
The Richmond Mine at Iron Mountain is an ideaf site at which to study secondary sulphates.
Secondary minerals are abundant and cornparatively coarsely crystalline. In addition, the site provides a rare opportunity to sample certain minerals with coexisting water. Jarosite
[KF~~"'(SO~)~(OH)~]and copiapite [F~~~F~~'(so~)~(oH)~.~oH~o]rninerals were collected in July 1998 with coexisting waters in an attempt to understand better how the precipitation and dissolution of these minerals affect water quality. This thesis examines the role these two sulphates play in the chernical evolution of acid drainage waters at Iron Mountain.
1.2 Acid Mine Drainage and Secondary Minerais - Definitions
1.2.1 Acid Mine Drainage (AMD)
The production of AMD is controlled by five key components: sulphides, oxygen, water, neutralizing substances, and the presence of iron- and sulphur-oxidizing bacteria (Nordstrom and
Alpers. 1990). Oxidation can proceed inorganically, but the rate is greatly accelerated by acidophilic bactena such as Thiobacillrts ferrooxidans and Leptospirillrrnz ferrooxidans (Schrenk et al,, 1998; Edwards et al., 1998). The complete chernical reaction involved in acid generation from pyrite is a multi-staged process that can be characterized by the following four reactions
(Sturnrn and Morgan, 198 1):
The oxidation of suIphide to sulphate releases dissolved ferrous iron and acidity into the water
(equation 1.1). The dissolved ferrous iron is then oxidized to femc iron (equation 1.2). Femc iron hydrolyses to form insoluble ferric hydroxide, releasing more acidity into the water (equation
1.3). Ferric iron can also be reduced by pyrite (equation 1.4), a process in which sulphide is oxidized and hydrogen ions are released with additional ferrous iron which may re-enter the reaction cycle via equation 1.2. Typically, AMD has a pH of c 4 and high concentrations of sulphate (soi'). ferrous (Fe'?
and femc (~e~+)iron. and significant amounts of other elements such as copper. rnagnesium, zinc,
cadmium, rnercury, lead and arsenic (Forstner and Wittman, 1983; Stumand Morgan, 1981:
Ritchie, 1994). The actual chernical composition of AMD is dependent in part on the rnineralogy
of the deposit from which it is generated.
It is important to note that sulphide oxidation occurs naturally in the absence of mining. The
rates of reaction and the scale of environmental impact, however, are often different. Acid rock
drainage production is cornrnonly more intense in mined areas because: (1) mine workings and
tailings piles promote air circulation; (2) rocks crushed during aggregate production and ore
beneficiation greatly increase the surface area of exposed sulphides; and (3) minera1 processing
can create tailings piles with diverse compositions. Natural weathenng of unmined mineral
deposits typically takes place over longer intervals, providing the surrounding ecosystem with
enough time to cope with the influx of contaminants. In many cases this allows for new, more
stable and insoluble phases to form (Nordstrom and Alpers, 1999a).
1.2.2 Secondary Minerals
Jambor (1994) distinguishes secondary minerals from other types of rninenls in tailings
impoundments. Minerals that constitute the ore and gangue assemblages are considered primary.
Secondary minerals are defined as those that crystallize by chemical reactions within the acid
mine drainage environment. Tertiary phases forrn during subsequent oxidation or evaporation of
pore-water following removal from the impoundrnent. Minerals that forrn during storage, after
the samples have dried, are considered quatemary. It is important to recognize that according to this classification scherne, the formation and dissolution of secondary minerals is controlled by existing conditions at the acid mine drainage site.
Secondary minerals are common in mine-waste environments. They typically form during weathering of deposits when solubility products are exceeded in the weathering solutions, so that States of mineral saturation or supersaturation are achieved. These minerals can precipitate from weathering solutions or fom on the surface of other rninerds in response to a number of processes including oxidation, dilution, mixing, evaporation and neutralization. The most common secondary minera1 compositions are hydrous iron oxide and hydrated iron sulphate-
Other types include additional sulphates and oxides, carbonates, secondary sulphides, arsenates. phosphates, and hdides (Alpers et al., 1994, Nordstrom and Aipers. 1999a)- Secondary rninerals discussed herein are shown in Table 1.1.
Precipitation and dissolution cycles of soluble sulphate minerals may be responsible for seasonal variations in the concentrations of elements and acidity measured in mine waters at many sites (Alpers et al., 1994a; Alpers et al., 19946; Bayless and Olyphant, 1993; Blowes and
Jambor, 1990; Kwong et al., 1997; Lin and Herbert Jr., 1997; Lin, 1997). This cyclicity has both positive and negative effects in the mine-waste environment. Precipitation of relatively insoluble sulphate minerais may help to remove metals from the water, but dissolution of more sohbte sulphates owing to seasonal influx of rain water and snowmeIt, and rising groundwater levels, can result in increased concentrations of dissolved metals (Cravotta, 1994; Nordstrom and Alpers,
1999). These secondary minerals represent a volumetrically minor constituent within the rnine- site, but their impact can be very significant. It is necessary to understand the composition and stability of secondary rninerals in the mine-waste environment to ensure accurate prediction of effiuent quality and implementation of appropriate treatment strategies.
1.3 Iron Mountain, California
Iron Mountain is located in Shasta County. nonhem California, approximately fifieen kitometres northwest of the town of Redding (figure 1.1) dong the southeastern border of the
Klarnath Mountains, Gold, silver, copper, zinc, iron and pyrite were mined at various times over an interval of one hundred years- Mining began in the early 1860's and ceased with the termination of open-pit mining in 1962. This massive sulphide deposit was once the targest Table 1.1: Secondary minerais discussed in this study.
MINERAL IDEAL FORMULA TYPE RELATNE (Fïeischer and Mandarino, 1995) SoLmHI.41Ty Melamente ~e"~0,.7Hfl ~e"sulphace soluble Rozenite ~e"sulphate soluble Szomolnokite ~e"sulphate soluble Halotrichite Fe' sulphaze soluble Copiapite ~e"-~e"sulphate soluble Magnesiocopiapite ~e'-Fe" sulphate soluble Voltaite Feff-~e'*sulphate soluble Romerite Fe"-~e" sulphate soluble Coquimbite ~e~ sulphate soluble Paracoquimbite ~e"sulphate soluble Ferricopiapite FeU'sulphate soluble Rhomboclase Fem sulphate soluble Chalcanthite Cu sulphate soluble Gypsum Ca sulphate soluble Jarosite ~e'' hydroxysulphate Iess soluble Hydronium jarosite ~e"hydroxysulphate Iess soluble Natrojarosite Fe"' hydroxysulp hate less soluble Schwertmannite Fe"' hydroxysulphate less soluble Hematite Fe oxide less soluble Goethite Fe hydroxide Iess soluble Femhydri te Fe hydroxide less soluble MckDam
&m Sacramento
Figure 1.1: Location of Iron Mountain and the West Shasta District in northem California (fiom Alpers et al., 1992b). producer of copper in the state of California. It now produces some of the most acidic waters reported in the world (Nordstrom and Alpers, 1995).
The Iron Mountain site possesses dl of the components required to promote sulphide oxidation and acid generation. These include: (1) ore with a high sulphide content (95-98% pyrite); (2) low acid-bufiering capacity of the rhyolitic host rock; (3) availability of oxygen and water in the mine workings; (4) the presence of iron- and sulphur-oxidizing bacteria; and (5) elevated temperatures (3847°C) caused by exothermic pyrite oxidation. The heat effect is strong enough to induce evaporation of subsurface mine waters, which efficiently concentrates the acidity in the water and is one of the factors Ieading to the formation of acid iron sulphate minerais (Nordstrorn and Alpers, 1990).
These five factors, combined with a regional climate that is arid in the surnmer and wet in the winter, make iron Mountain a prolific acid mine drainage machine. Table 1-2 compares examples of extreme mine-water compositions rneasured from several sources. The Canadian mine water quality Iimits are inciuded to help put the values in context. It should be noted that the samples from the locations at Iron Mountain were collected pnor to effluent treatment. The waters from these locations are considered record-breaking in many respects, with the Iowest pH and highest iron and sulphate content compared to other extrerne examples frorn around the world. Sample 98CR03 from this study has the highest published value of totai and ferrous iron.
Previous authors have ctaimed the Richmond Mine effluent to possess the "most extreme conditions of natural acidity developed from pyrite oxidation yet reported" (Nordstrom and
Alpers, 1990).
1.4 Purpose and Scope
The careful study of water-rock interactions in the mine-waste environment is important because results may control the accurate prediction of effluent quality and the design of appropriate treatrnent strategies. This work examines jarosite and copiapite with their CO-existing Tablc 1.2: A cornparison of Canadiaii minc writer iiiaximum iillo~ableliniits (NRCuii) witli extitnie mine wiiier coinpositions prior io trcnttiient. Bxaniplcs include tliosc measiired at lron Mountain (IM) for this study in July of 1998 and the most acidic cxiirnples n~easurcdnt 1M in 1991 (Nordsirom et al,, 1991). pH values are in standard units, concentrations are iii niilligrams per litre, Mine wall drips iire fiom jiirosite ~iüliictit~~and siilphate poiwwatcr is froin copiupilc, both from the D-Drift of the Richmond Mine. Specific aniilytical mcthods iind resulis for these waters nrc disciissed in Cliaptcr 4 (copiapite) and Chapter 5 (jarosite). Locations of the other exticme waters: Golevil et al. (1970) and Golcvii (1977) - foriiier Soviet Uniaii, Blowcs ct al, (199 1) - Wiiitc Alnulet, Quct~cc, Brneuning (1977) - Biirma, Lindgrcn (1928) - Nevada and Butte, Montana, iih - not uvnilable.
-t- Canadian Richniaiid Mine wall Su1pli;ilc pore lron Moiintain niax liniits I'arial, IM drips, IM watcr, IM 1991 -- - -- (NHCan) . (98CA 101-FU) -.- (9RCA.- IOSA-IW)- (98CHOJ-FU)---- PH 6.0 0.7 3.0 -1.0 -0.7 -2.5 -2.6 -3.6 -- Fe (T) dii 86 200.00 1 1 1 000.00 10 1 000.00 I G 300.00
Fc (II) iilu 79 7(H).(tO 34 500,OO 34 900.00 9 800.00
Fe (II 1) n/a 6 500.00 76 500.00 66 100,QO 6 500.00 cTJ so4 n/a 360 O~.W760 Oü0.00 650 000.00 nia Al nla nia di\ nlri nia
Cu 0.3 2 300.00 4 800.00 3 200.00 niil
Zn OS 7 700.00 23 500.00 20 000.00 da
As 0.5 150.00 340,00 220,00 nia
Cd nla 48.00 2 10.00 170.00 4 1.00 Lindgrcn (1928)
I Pb 0.2 n/n nia n/n da n/n I The federal Metnl Min g Liquid Effluent Regulations were publishcd iinder section Fislieries regulations prescribe outhorized limits for total arsenic, copper. lend, nickel, zinc, suspended maiier and the radionciivity of radium 226 in. and the pH of, effluents discharged to fish bcaring waters from al1 base metal, iron ore and uranium mines coining into productioii nfier 25 Fcbruary 1977 (Natural Rcsourccs Canada - NRCan, 1999). waters to obtain a better understanding of how they contribute to the chemistry of the Richmond
Mine effiuent. Jarosite and copiapite were chosen priniarily because they are common sulphates in iron-sulphide-rich deposits. and because the sarnples taken from the Richmond Mine could be collected with enough co-existing water for analysis. An additional objective is to uncover more information about the structure and composition of copiapite, an extremely soluble sulphate rnineral known to be present at rnany mine-waste sites, but which has rarely been studied in detail in this context.
This work describes the rnineral chemistry and crystal structure of jarosite stalactites, jarosite mud, and moist copiapite samples coliected in the Richmond Mine. The rnineral compositions are compared to the chemistry of stalactite dnp-water, and jarosite and copiapite pore-waters, respectively. Pore-waters were obtained from spinning the jarosite mud and moist copiapite in a centrifuge, The influence these two types of suIphates have on the effluent chemistry is evaluated.
1.5 Methods
Jarosite and copiapite mineral and water sampIes were collected in July 1998 from the
Richmond Mine at Iron Mountain. Prelirninary water andyses perforrned in the field include pH, redox, electrical conductivity and temperature. In the lab, powders were made from mineral sarnples and identification was confirmed using X-ray powder diffraction. Polished sections were made from the mineral samples and examined petrographically. Grain size and crystal morphoiogy were determined using scanning electron rnicroscopy (SEM). Major element analysis was collected with an electron microprobe and trace elements were analyzed at the
University of Guelph with micro-PiXE (Particle induced X-ray Emission). Minerai formuIae were calculated using an APL cornputer program (Carmichael, 1999). Detailed powder diffraction was done on copiapite at RMC (Royal MiIitary College of Canada) to obtain results with better resolution to accurately characterize the phases present in the sample. This was required in order to attempt Rietveld analysis for cell-refmement calculations. Single crystal
analysis was perfomed ar Queen's University to identifL an unknown phase found in the jarosite
samples.
Waters were anaiyzed at the United States Geological Survey (USGS) laboratory in Boulder,
Colorado for dissolved cations and anions, and speciated for Fe and As. The geochemical modeling program WATEQ4F (Ball. f 987, 1999) was used to compute aqueous speciation, ion activities. and minera1 saturation indices. CHAPTER TWO: LITERATURE; REVIEW
2.1 Inîroduction
The literature review for this thesis focussed on the background geology, rnining history. and current environmental problem at lion Mountain as well as the available publications on secondary sulphate rninerals, especially copiapite and jarosite. This chapter presents an overview of this material.
2.2 lron Mountain
The existing literature on Iron Mountain more or less falls into two categories: (1) mining history and geology of the deposit and (2)environmental problems that now plague the district.
The economic importance of massive sulphide deposits has prompted a great deal of research and exploration within the West Shasta district, which hosts the deposits of Iron Mountain. In addition, the success of the mines at Iron Mountain and subsequent environmental problems have resulted in a comprehensive collection of papers devoted specifically to this site.
2.2.1 Regional Geology
The West Shasta district of northern California is located at the north end of the Sacramento valley. in the foothiIls of the Klarnath Mountains (figure 1.1). The rocks in the region are
Paleozoic in age. They range from Middle Devonian to Mississippian and are described in detail by KinkeI et al. (1956) and Reed (1984). Figure 2.1 is a geologic rnap depicting the major formations that comprise the district.
The oldest formation exposed is the Copely greenstone of Middle Devonian age. The unit is estimated to be at least 1130 rneters thick, however the base is not visible in this region. It is composed of light to dark green, fine grained lava and tuff predominantly keratophyric (sodium
and alurninum-nch) in composition. It includes many porphyritic and amygdaloidal flows in
which the phenocrysts and amygdules are composed of quartz, calcite, chlorite, epidote,
clinozoisite, albite and zeolites. The upper third part of the formation contains abundmt spilitic
pillow lavas associated with lapilli and hyaloclastite breccias (Kinkel et al, 1956; Reed, 1984).
The Middle Devonian BalaWala rhyolite conforrnably overlies the Copely greenstone. The
entire formation is approximately 1050 meters thick in the central part of the district, but thins at
the edges. It is composed of sodium-nch rhyolitic ffows and pyroclastic material. The lithologies
within this unit have been subdivided as nonporphyritic rhyoIite and porphyriuc rhyolite
containing phenocrysts of quartz and aibite. The porphyritic rhyolite is fur-ersubdivided
according to phenocryst size: medium-phenocrysts of 1 to 4 millimeters in diarneter and coarse-
phenocrysts of more than 4 millimeters in diameter. Kinkel et al. (1956) describe the Balakiala in
terms of lower, middle, and upper stratigraphie units. Nonporphyritic rhyolite dominates the
lower unit. Al1 of the known massive sulphide deposits occur within the middle unit, which is
characterized by medium-sized phenocrysts. Coarse phenocrysts are dominant in the upper unit.
The rhyolite in al1 units is quartz and albite-rich, with minor chlorite, sericite, epidote and pyrite.
The Balaklala rhyolite is considered to have an unusually high sodium content, with an average weight percent of 5.08. This is 0.6 to 1.0 percent higher than typical rhyolite (KinkeI et al, 1956;
Reed, 1984).
The copper-zinc ore deposits found within the BalaWala rhyolite are bodies of massive pyrite that contain chalocopyrite, sphalerite and minor quantities of bornite, arsenopyrite, gold and silver. The ore is approximately 95 percent pyrite and averages roughly 1 percent chakopyrite and 2 percent sphaiente. Trace amounts of gangue minerals present in the ore include quartz, calcite, muscovite, and chlorite. The economic deposits predominate on or near the axes of broad folds and are further localized by the intersection of bedding-plane foIiation and fracture cleavage. Some faults formed pnor to rnineralization and acted as pathways for ore-bearing solutions- The bodies of massive sulphide ore, before post-mineral faulting, ranged in size from the Iargest at Iron Mountain which is 1.4 kilometers long, up to a few hundred meters wide, and
30 to 40 rneters thick, to srnaII bodies under 10 meters in maximum dimensions. Many of the
orebodies in the district have rnaintained their original lenticular form, but several are offset by
faults into separate blocks of ore (Kinkel et al., 1956).
Post-ore formations present in the rnap area include two sedimentary units: the Kennett and
the Bragdon formations; and two igneous intrusions: the Mule Mountain stock and the Shasta
Bally batholith. The Kennett Formation of Middle Devonian age overlies the BalakLala rhyolite-
The maximum thickness of the formation is estimated at approximately 120 meters. An exact
thickness has not been detennined due to repetition of beds caused by foIding and faulting. The
Kennect is composed of black siliceous shale, gey shale, rhyolitic tuff, and limestone. The
Bragdon formation of Mississippian age conforrnably overlies the Kennett formation in rnuch of
the map area. It is predominantIy shale, but also contains beds of conglornerate and sandstone.
The Mule Mountain stock intrudes the Copely greenstone and the BalaklaLa rhyolite. It is a
sodium-rich, silicious granite. primarily cornposed of albite and quartz with rninor amounts of
epidote. It is considered to be syntectonic with the Middle Devonian Balaklala rhyolite. The
Shasta Bally batholith is a post-tectonic intrusive of Iate Jurassic or Early Cretaceous age. It is a
biotitequartz diorite and it intrudes the Copely greenstone, the Bragdon formation, and the Mule
Mountain stock (Kinkel et al. 1956; Reed, 1984).
Many of the rocks of the West Shasta district have undergone alteration and metarnorphism.
Reed (1984) distinguishes hydrothermal alteration associated with mineralization, regional hydrothermal metarnorp hisrn, and late regional greensc hist metamorphism. Metamorphic minerals are more comrnon in the greenstone and the lower and rniddle rhyolite units. This can be attributed to regional seawater hydrothermaI metarnorphism that occurred during mineralization. Hydrothermal alteration is present beneath the ore deposits where metarnorphism was the most intense. Farther away from the mineralized zone it produces keratophyres and spilites. These effects are weakly present in the upper unit of the rhyolite. There is no evidence of greenschlst metamorphism in the conforrnably overlying Iirnestones and shales of the Kennett and Bragdon formations. The clays are preserved in shales; chlorite, biotite, epidote, graphite, chlontoid, and gamet are absent; slatey cleavage is absent; limestone is extremely fine grained and unrecrystallized. It is suggested that as the volcanic pile cooled, regional scale hydrothermal circulation deched, and by Kennett time it appears to have ceased (Reed, 1984).
22.2 Paleoenvironment
Several authors have resolved that submarine voIcanogenic processes, forrning at the same time as the country rock, created the or2 deposits of the West Shasta mining district. Most have proposed an island arc setting as the depositional environment. This shared opinion is based on field mapping, petrogaphy, geochemistry and isotope studies (Kinkie et al., 1956; Barker et al.,
1979; Casey and Taylor, 1982; Reed, 1984; and Lindberg, 1985). The folIowing description of the geologic setting and origin of West Shasta massive sulphide ore deposits is the mode1 proposed by Lindberg (1985):
The Copely Greenstone is a product of early Devonian island-arc volcanism, These subrnarine lava eruptions gradually evolved into Iower unit Balaldala Rhyolite assemblages dong a north-northeast-trending spreading axis. This volcanic ridge may have breached sea level midway through the rhyolitic cycle. Major graben systems developed in the vicinity during a period of subsequent crustal extension. Widespread aIteration effects of heated seawater and sea floor hot spring activity resulted in massive sulphide deposition in sea-floor depressions, such as the Eureka graben. Large-scale metal leaching of the altered volcanic footwall rocks rnay account for the metal values contained within the massive sulphide ore deposits. Once the period of rnineralization was complete. no further volcanogenic ores of any significance were produced in the district. Post-ore rhyolitic volcanism resumed and appears to have continued from the same magma source as before. Lavas predominate earlier pends of rhyolite eruptions however post-ore varieties are dominated by rhyolite crystal tuffs with quartz phenocrysts greater than 4 rnilIimeters in diameter. Following the penod of volcanism, sedirnents of Devonian and later age
began to accurnuIate around the edges of the supposed volcanic islands. Codatolls later fo~ed
around the outer flanks.
. 2.2.3 Mining History and Prevwus Work in the West Shasta Cu-Zn District
The volcanogenic massive sulphide deposits that constitute the Shasta mining district contain
two main areas of ore enrichment known as the East and West Shasta copper-zinc districts. Iron
Mountain and eight other base-metal mines are hosted within the West Shasta district, which
trends northeastward and is approxirnately 13 kilometers long and 3.5 kilometers wide. The ore
consists of large bodies of massive pyrite that contain copper and zinc sulphides and minor
amounts of gold and silver. From the late 1800s to the early 1960s, the ore bodies were prirnarily
mined for copper and zinc. By 1946. 1 1.5 miIIion tonnes of ore were mined with an average
grade of 4-38 percent copper, 3.8 1 percent zinc, 110.74 g/t silver, and 1.47 g/t gold. in addition,
4.2 million tonnes of massive pyrite were mined at the Iron Mountain site for sulphur (Kinkel et
al., 1956). During the early part of this century. this district contrïbuted approximately 54 percent
of the copper produced in California. Most of the mines were forced to close by the mid-1920s.
due to adverse prices and environmental problems, with the exception of Iron Mountain where
the deposits were worked continuously from 1895 until 1962. Neariy al1 the deposits in the district still contain unmined massive sulphide. In fact. as much as 28 million tonnes may still
remain in the ground (AIbers. 1985).
The earIiest geologic studies of the West Shasta district were by Diller (1906) and Graton
(1909). Diller focussed on the regional geology and he named and described most of the formations in the area. Graton was interested specifically in the ore deposits and his studies were directed toward the understanding of their genesis. Dunng the lare 1940s the geology of the district was studied in detail and mapped at a 1:230M) scale by the U.S. Geological Survey, and a cornprehensive report was published as Professional Paper 285 (Kinkel et al., 1956). This report and the maps have served as the basic source of geologic information for subsequent studies. It
was Kinkel et al- (1956) who recognized that nearly al1 the massive sulphide deposits in the
district are strata bound within the middle unit of the Balaklala Rhyolite- Reed (1984) published
a comprehensive paper from his Ph.D- thesis descnbing the geology, waI1-rock alteration and
massive sulphide rnineralization in the West Shasta district. In December of 1985, a speciaI issue
of Econontic Geulogy was devoted to the massive sulphide deposits of the West Shasta district It
was based on a cooperative study that was conducted in order to charactenze and distinguish the
deposits in this district from other volcanogenic massive sulphide deposits around the worId
(Albers. 1985; Albers and Bain, 1985; Lapierre et al., 1985; Howe, 1985; Kistler et al., 1985; Doe
et al., 1985; Taylor and South, 1985; Bence and Taylor, 1985; South and Taylor, 1985; Botinelly
et al., 1985; Sanzolone and Domenico, 1985; Horton et al-, 1985; Raines et al., 1985; and
Lindberg, 1985).
2.2.4 The Iron Mountain Deposits
The Lron Mountain site is Iocated in the south end of the West Shasta copper-zinc district,
roughly 15 kilometers northwest of the city of Redding (figure 2.1). There are a collection of
eight mines at Iron Mountain including Old Mine, No. 8 Mine, Confidence Complex, Brick Flat
Open Pit, Mattie Mine, Richmond and Richmond Extension Mine, and Homet Mine. Most of
these mines were established to exploit two main sulphide bodies, the Homet and Richmond
deposits (figure 2.2). At the tirne of ore genesis, these deposits were probably a single massive
sulphide body at least 800 meters long, and greater than 60 meters wide and 60 meters high. This
pod-shaped ore-body was later offset by two normal faults. The pyrite-rich Brick Flat deposit
(not shown in figure 2.2) was likewise origindly connected to the Richmond deposit and offset
by normal faulting. iron Mountain is capped by a large gossan that consists of oxidized iron minerals (primariIy goethite and hematite) and residual silica. Portions of it outcrop in the area of
Boulder Creek, near the Lawson portal (Kinkel et al., 1956; Nordstrom and Alpers, 1995). NOTE: Horne? Mine workings not shown O 1C03 FEET
Figure 2.2: Cross section through Iron Mountain, showing the Iocation of the Hornet and Richmond deposits (from Alpers et al., 1992b). Following the discovery of the gossan in the late 1860s- the property was acquired as an iron
mine. Mining did not begin until silver was found in the gossan in 1879 where it was mined until
1894. At that time, the property was sold to British interests who formed the Mountain Mining
Company Ltd- in 1895. Ln the sme year, large massive sulphide deposits were discovered
beneath the gossan, and smelters were built in the nearby town of Keswick to process the ore.
Mining at the site continued under the Mountain Copper Company, Ltd. of London until 1967
when the Stauffer Chernical Company purchased it. Lron Mountain Mines, Inc. took over the
property from Stauffer at the end of 1976 (Nordstrom and Alpers, 1995).
Copper mining slowed dramatica1Iy in 1919 due to a decrease in its market value. Only very
Iirnited and intermittent copper rnining took place until World War II, when the US Government
subsidized the production of copper and zinc- The iron Mountain deposits were worked
continuously dunng this time, prirnarily for copper and sulphur. In addition, more than 2.9
million tonnes of gossan were rnined for gold and silver between 1929 and 1942. Most of the gossan was mined and processed by cyanide extraction. Mining for copper and zinc continued during and shonly after World War II, and massive pyrite was excavated for sulphur until 1962.
The Hornet deposit was rnined for its copper content by underground methods from 1907 to 1926.
The Richmond deposit was discovered around 19 15 but was not rnined for copper and zinc on a large scale until the 1940s. The Brick Flat deposit was mined principally for its pyrite content by open pit methods from 1950 to 1963. In total, approximately 5.7 million tonnes of sulphide ore have been mined by underground rnethods from Iron Mountain. From 1955 to 1962, 10.5 million tonnes of waste-rock were removed from the top of Iron Mountain, and 660 thousand tonnes of pyrite were open pit mined for suiphuric acid production. In addition, copper cementation was used to extract copper from effluent mine waters. From 1962 to present, cementation has been the only active process for metal recovery. It has also served as a remediation measure to decrease the discharge of copper to the Sacrpmento River (Albers et al., 1985; Nordstrom and
Al pers, 1995). 2.2.5 Envuonmental Problems
2.2.5.1 Historical information
The recorded history of environmental problems at Iron Mountain can be traced back to the
earliest days of rnining at the site. The first ore processing for copper was open-air heap roasting
near the mouth of Spring Creek and in 1895 srnelters were built at the site. These processes
resulted in toxic ernissions that created air pollution, destroyed vegetation. contaminated soils,
increased soi1 erosion, and increased turbidity and sedimentation rates in the Sacramento River.
Adverse eIements likely to have been released into the air include arsenic and lesser arnounts of
lead, cadmium, and zinc. The smelters were forced to shut down by 1907 due to lawsuits filed by private parties and the U.S. Forest Reserve (Nordstrom and Alpers, 1995). This was not the end of the environmental problems at the site. Pnor to the late 1980s. when major remediation efforts began, approximately 2750 tonnes of pyrite weathered every year frorn the Richmond Mine alone. Runoff from the site carried roughly 300 tonnes per year of dissolved Cd, Cu, and Zn to the Sacramento River. Massive fish kills in the river have been connected to periods of high runoff from the site since 1939. The quality of water is also important to human residents in the area. The town of Redding (with approxirnately 100,000 residena) draws its drinking water from the river, downstream of the Iron Mountain site. Table 2.1 provides a brief historical summary of rnining and related environmental activities at the site. It is interesting to note that environmental problems associated with Iron Mountain began long before they were first recorded. Prior to mining, an estimated 11 million tonnes of gossan existed at this location, evidence that at least
16.5 million tonnes of massive sulphide weathered naturally (Nordstrom and Alpers, 1999b).
2.2.5.2 Development of exireme acid mine water a? Iron Mountain - previous work
Sulphide oxidation has the potential to acidify surface and groundwater resources. The pH values of waters that infiltrate disseminated sulphide deposits, base-rnetal tailings, and piles of sulphidic waste-rock, typically range from 1.5 to 3.0 (Stumm and Morgan, 1981). However, Table 2.1: Brief historicd summary of minine and related environmental activities at the Iron Mountain site (from Nordstrom and Mpers. 1999)-
YEAR ACTIVITY Discovery of massive gossan outcropping SiIver discovered in gossan and mining begins Mountain Copper Company acquires property and underground rnining begins US Forest Reserve sues Company for vegetation damage from smelting activities Smelting ends and ore is transporteci to Martinez. CA. for processing Califomia Fish and Garne Commission files cornpiaint regarding tailings dam State initiates water quality and fish toxicity studies Shasta Dam, upstream from Iron Mountain outflows, is cornpleted Keswick Dam, downsuearn from Iron Mountain outflows, is cornpleted Open-pit mining of pyrite at Brick flat for sulphuric acid production Spring Creek Debris Dam is cornpleted, regulating outfIow of acid mine waters to the Sacramento River Stauffer Chemical Company acquires property Approximateiy 47,000 trout killed in one week, due to a sudden surge of acid mine water inio the Sacramento River Thesis study by Nordstrom prompts a cleanup and abatement order to be issued to the Stauffer Chemical Company Iron Mountain Mine Inc. acquires property in December State of Califomia fines Company for unacceptable release of metals Six orders issued to reduce metal discharges in violation of state Iaw (1977-1989) Iron Mountain listed on National Priorities List (NPL)for Environmental Protection Agency @PA) Superfund, ranking as the third-largest polluter in the State of California Four Records of Decision by EPA have instituted several remedial activities that include partial capping, surface-wrtter diversions, tailings removal, and Iime neutralization of the most acidic, metal-rich flows. reducing copper and zinc loads by 80-90% extremely high aqueous concentrations of sulphate, iron, a.nd other inorganic elements can
deveIop within these environments, accompanied by pH values of less than 1.0. The Iron
Mountain site is an important example that provides researchers the rare opportunity to study
geochemical mechanisms that lead to the attainment of such extremely low pH.
Nordstrom's Ph.D. thesis (1977) reveals key components of the acid mine drainage systern nt
lron Mountain and Iays the ground work for further investigations of the hydrogeochemical and
microbiological mechanisms that promote extrerne acid generation at the site (Nordstrom. 1982;
Nordstrom and Dagenhart. 1978; Nordstrom et al., 1979). These studies initiated public and
govemrnent attention to water quality issues and potential remediation strategies. The site was
officially listed on the Environmental Protection Agency's (EPA) National Pnorities List for
Superfund in 1983 and the first remedial investigation and feasibility studies began. Nordstrom
and Alpers (1990) provide the first comprehensive geochernical evaluation identifying subsurface
chernical and hydrogeological controls on acid water generation at the site. It is a report prepared
for the EPA to explain the production of contaminants and describe the potential
hydrogeochemical consequences of hydraulic seals as a remediation technique. The study was
based on a three-day sarnpling trip into the Richmond Mine and it was the first recorded
observation of the underground workings for 35-40 years. The investigators found acidic seeps
with pH values as Iow as - 3.6 and total dissolved solids concentrations of more than 900 g/L with several moles/L of sulphuric acid- Soluble iron sulphate minerais were found in great abundance inside the mine and were attributed to excessive evaporation. Subsurface air temperatures were recorded as high as 50°C. Following mass balance and themodynamic rnass transfer computations, mine plugging was not recommended- The back-filled water is predicted to have approximateIy the same water quality as the presentday portal effluent whether it is allowed to fi11 through natural infiltration or whether clean water is injected into the subsurface.
Pyrite oxidation and acid generation would continue because large quantities of femc iron (Fe13 would dissotve from the efflorescent sulphate rninerals and attack the pyrite (reaction 1.4). This form of remediation would result in the storage of approximately 600 000 m3 of acidic. metal-rich water above the water table. creating a possibility for leaching and the spread of contamination into groundwater (Nordstrom and Aipers, 1990; 1999b).
Nordstrom and Alpers (1990) refer to five hydrogeochernical characteristics present at Zron
Mountain that combine to create optimal conditions for the production of extrerne acid mine drainage: (1) high pyrite concentration, (2) easy access of oxygen, (3) elevated temperatures enhancing evaporation, (4) site-specific hydrologic factors, and (5) Low neutralizing capacity of the host-rocks.
First, the ore-bodies are extensive and consist of pyrite that is nearly 100 percent pure- The largest, the Richmond ore body, is a welldefined massive suIphide roughly 60 metres wide, 45 metres high and 800 metres long. The original Richmond and Richmond Extension ore bodies are estimated to have been about 10.4 million tonnes, or 2.2 million cubic metres, averaging around 1 percent Cu and 3 percent Zn. The amount of gangue minerals present in the massive sulphide ore is very low, consequently the concentration of the sulphide at Iron Mountain is essentially at a maximum.
Second, the massive sulphides are extrernely vulnerable to oxidation for both natural and anthropogenic reasons. The sulphide bodies occur within the unsaturated zone, and furthemore are full of exploration drill holes, tunnels, shafts and stopes. Air flows effectively through these passageways and is probabiy aided by thermal convection due to the high heat output from the pyrite oxidation. Seasonal rain and snowmelt percolate throughout the deposits providing dissolved oxygen to the pyrite surfaces.
Third, the intense heat within the mines causes subsurface waters to evaporate, contributing further to the acidity. Concentration by evaporation could lead to extrernely Iow subsurface pH values that are difficult to achieve by continuous pyrite oxidation alone. Evaporation coupled with an oxidizing environment creates optimal conditions for the formation of certain iron suiphate minerais. Some of these minerals, found in abundance in the Richmond Mine, are known to occur only under conditions of very low pH. The precipitation and dissolution of iron
sulphate rninerds exercise a strong controi over the acidity and dissolved solid concentration of acid mine waters (Nordstrom and Alpers, 1999b). This is discussed further in the next section of this chapter.
Fourth, the open pit is located above the Richmond Mine. A fresh supply of surface and ground water is efficiently drawn inward to the centre of the deposit and then drained through the portal tunnel. This hydrogeologic configuration perpetuates the production of acid mine waters, which are primarily directed out of the main portal.
Fifth, the swrounding rhyolitic bedrock does little to help neutraiize the acidity of the effluent. The rock consists of submarine extrusives that have previously been affected by hydrothermal alteration. Carbonate minerals are rare, therefore there is little opportunity for any significant aikalinity to develop. Alkalinity that does develop is defeated by the extrerne acidity of the environment.
Several research projects and remediation investigations have followed Nordstrom and
Alpers (1990). Table 2-2 provides a sumrnary of the existing literature. Ongoing research at the site will likely provide even more valuable information concerning the geochernical, hydrogeoIogicaI, therrnodynamic, and biological controls on the evolution of acid mine waters.
This research will undoubtedly lead to improved remediation and treatment strategies.
2.3 Secondary Sulphate Minerais
In the context of AMD, secondary rninerals are distinguished as those that crystdlize by chernical reactions initiated by weathering processes within the mine waste environment (Jambor,
1994; Nordstrom and Alpers, 1999a). They usually form when solubility products are exceeded in the weathering solutions, so that States of mineral saturation or supersaturation are achieved.
These minerals can precipitate from weathering solutions or occur on the surface of other minerals in response to a number of processes including: (1) oxidation and hydrolysis, (2) Table 2.2: A summary of some of the environmental literature existing on bon Mountain since 1990. Refer to reference list for cornplete citation.
DATE AUTHORS TITLE Reports / publications: 1992 C.N. Alpers, D.K. Nordstrom, Compilation and interpretation of water- and J-M. Buchard quaIity and discharge data for acidic mine waters at Iron Mountain. Shasta County, Caiifomia, 1940-91 US- Environmental Protection Public comment feasibility study, Boulder Agency Creek operable unit, Iron Mountain mine, Redding, California C.N. Alpers, D.K. Nordstrom Seasonal variations of ZdCu ratios in acid and J.M. Thompson mine water fiom Iron Mountain, California in Environmental Geochemistry of Sulphide Oxidation Ivf .O. Schrenk, K J-Edwards, Dism-bution of ThiobaciIlus ferrooxidans and R.M. Goodman, R.J. Leptospirillum femooxidans; implications for Hammers, J- Robert and J.F. generations of acid mine drainage Banfield K.J. Edwards, M.O. Schrenk, Microbial oxidation of pyrite; experiments R.J- Hamrners, and J.F. using rnicroorganisms from an extreme acidic Banfield environment D.K-Nordstrom and C-N. Geochemistry of acid mine waters, in The Alpers Environmental Geochemistry of Mineral Deposits, Part A. Processes, Techniques. and Health Issues. D.K. Nordsuom and C.N. Negative pH, efflorescent mineralogy, and Aipers consequences for environmental restoration at the Iron Mountain Superfund site, California Abstracts / conference proceedings: 199 1 C.N, Alpers and D.K. Geochemical evolution of extremely acid mine Nordstrom waters at Iron Mountain. California - are there any lower lirnits to pH? D.K. Nordstrom, C.N. AIpers, Measurement of nepative pH and extremely and J.W- Bal1 high metal concentrations in acid mine water from Iron Mountain, California C.N. Alpers, C. Meinz, D-K. Storage of metaIs and acidity by iron-sulphate Nordstrom, R.C Erd, and J.M. minerals associated with extremely acid mine Thompson waters from Iron Mountain, California D.K. Nordstrorn and C.N. Remedial investigations, decisions, and Alpers geochemical consequences at Iron Mountain Mine, California E.I. Robbins, T.M. Rogers, Subsurface geochemistry and ecology of the D.K Nordstrom. and C.N. food chain at pH 0-4 in Iron Mountain, Al pers California D.C. Keith and D.D. Runnells Chemistry, rnineraIogy, and effects of efflorescent sulphate salts in acid mine drainage areas H.E. Jarnieson, C.N. Alpers, Substitution of zinc and other metais in iron- D.K. Nordsuom, and R.C. sulphate minerais at Iron Mountain, CaIifornia reaction of acid solutions with ore minerais, gangue rninerals, and country rock (3) rnixing of acid mine waters with more dilute waters, and (4) evaporation of acid mine waters (Nordstrom and Alpers, 1999a).
Secondary rninerals can be divided into five categories: (1) metal oxides, hydroxides and hydroxysulphates, (2) soIuble sulphates (efflorescent saits), (3) less-soIuble sulphates. (4) carbonates, and (5) secondary sulphides (Jambor, 1994; Nordstrom and Alpers, 1999a). The most common are hydrous iron oxides and hydrated iron sulpbates, reflecting the relatively high concentrations of dissolved iron and sulphate present in mine waters (Jarnieson et al.. 1999). As this thesis examines iron suiphate minerals copiapite (soluble) and jarosite (less-soluble hydroxysulphate), the following discussion will focus on these types of secondary rninerals.
2.3.1 Zron Sulphate Parugenesis
The nine soluble iron sulphates listed in Table 1.1 are recorded in approximate sequence downward from eariy formed to later forrned. This paragenesis is proposed according to the oxidation state of the various iron species. The sequence has been confmed in the Iaboratory where if acid mine water from iron Mountain is allowed to evaporate under ambient conditions, meianterite appears first and rhornboclase and voltaite are the Iast to form (Nordstrom and Alpers,
1999a). Similar relationships have been observed in the field. however in the author's experience it is rare to find a sample that possesses more than two or three of the minerals in their expected sequence. This is a reflection of the volatility that exists within the natural geochemical environment.
In support of these theories, it is reasonable that dissolved iron will stay in the ferrous state as long as acid mine water remains in contact with pyrite, due to its strong reducing capacity.
RapidIy flowing mine water will sustain a high proportion of ferrous iron because the oxidation rate often cannot keep up with the Flow rate of the water. It is expected then that only iron sulphate rninerals containing exclusively ferrous iron. such as melanterite, rozenite and szomolnokite. should be found closest to pyrite minera1 surfaces and rapidly flowing mine waters.
Altematively, femc-bearing salts Iike coquimbite, femcopiapite and rhomboclase. usually form
under more stapant conditions. They are considered by some to be hydrogeologic "dead-ends".
where most of the ferrous iron has had time to oxidize to ferric iron (Merwin and Posnjak, 1937;
Nordstrom and Alpers, 1999b)-
As acid mine water evoIves chernically. different sulphate minerals will form based on
acidity, water composition, and the amount of oxygen and time available. Generally in more
oxidized environments, dissolved femc iron wiII eventually reach saturation with respect to Iess
soluble minerals such as jarosite, ferrihydrite, goethite, and hernatite (Table 1.1) (Posnjak and
Menvin, 1922)- Al1 of these rninerals are cornmon in the acid mi~edrainage environment,
existing under different Eh-pH conditions (figure 2.3). These less soluble secondary minerals
tend to form spatially further away from the more soluble salts (Merwin and Posnjak, 1937;
Nordstrom. 1982; Bigham, 1994).
Observations made in the Richmond Mine during the field work for this study support and
challenge the theones outlined above. In general. mineral sequences do tend to follow the expected path. Pyrite minerals are predominately coated in ferrous secondary sulphates
(melanterite, rozenite, halotrichite) with some ferrous-femc (copiapite, voltaite) and femc minerals (coquimbite) disserninated on the outer surfaces. However, considerable amounts of magnesicopiapite with minor ferricopiapite were sarnpled (98CR03,98CR04) forming directly on the surface of loose pyrite lying on the floor at the end of two of the drifts. Copiapite minerais were found on exposed pyrite surfaces in the gossan at Iron Mountain as well(98CR23ad).
Kwong et al., (1997) have made similar observations in the Keno Hill mining district in the
Yukon Temtory. In addition, jarosite was discovered fonning directiy on the pyrite ore surface, on a drift wall within the mine (98CR 14abc, 98CR15ab, 98CWOab). Reasons these minerds appear to exist out of their normal geochemical sequence are related to the diverse environmental Figure 2.3: Stability relations for some less soluble secondary minerals in the Fe-S-K-O-H system at 25°C (Nordstrom and Alpers, 1999a, modified from Alpers et al.. 1989). This diagram shows that pyrite is stable under a large range of strongly reducing conditions. K-jarosite forms at approximately pH 2 in more oxidized environments and goethite is stable under mildly acidic to basic conditions over a range of redox. Hematite (not plotted on this diagram) has a redox similar to goethite, but it is not as stable in the more reducing environments. Femhydnte (not pIotted) is stable abovepe = -2.5 and between pH 5.2 and 10.6. Schwemannite is stable in oxidized environments benveen a pH of 3.0 and 4.0 (Bigham, 1994). Variable pe-pH conditions in the acid mine drainage environment promotes the conditions of extreme acidiy, and the dissolution of these less soIubIe rninerals. Nore: the relationship between Eh and pe at 25C: Eh = 0.059 Fe- conditions existing throughout the Richmond Mine. These ideas are discussed further later in this thesis-
2.3.2 Mineral Solubiliiy and Temporury Storage of Inorganic EZements
Nordstrom and Alpers (1990, 1999b) cite efllorescent mineral formation and dissolution as two of the key processes that contribute to the evolution of the extremely acid effluent that is characteristic of lion Mountain. Understanding how and why secondary minerals fonn and dissolve has important consequences for the proper design of effluent treatrnent facilities and mine-site reclamation plans.
Elements that are potentially hazardous to ecosystems such as Zn, Cu, Cd, Al, Pb and As become sequestered in secondary minerals through the processes of coprecipitation and adsorption. Coprecipitation is substitution within the rnineral structure while adsorption is adhesion of the element to the rnineral surface. These mechanisms are effective in removing dissolved elements from the liquid phase and converting them into solid components of iron sulphate minerals. Unfortunately, most iron sulphates are extremely soluble and therefore they serve only as temporary storage sites. As secondary rninerals dissolve, trace elernents are released back into solution (Jamieson et al., 1999; Blowes and Jambor, 1990).
The elements present in prirnary ore associated with a mine, as well as additional elements that may be present in weathering solutions, dictate the composition of secondary minerals. The temperature, pH, and oxidation state of weathering solutions control precipitation and dissoIution reactions, contributing to the overall solubility of the minerals. A major process responsible for regulating the concentration of an element in solution is equilibrium with a solid phase of which the element is a major cornponent (Drever, 1997).
The saturation index (SI) describes the approach to equilibrium through the relationship IAP SI = log- K~P
where: (a) the IAP is the ion activity product, deterniined from observed concentrations of
solution following the appropriate activity and speciation calculations, and (b) the Ksp is the
theoretical solubility product adjusted to the observed water temperature. A saturation index of
less than zero indicates water undersaturated with respect to a mineral phase. When the
saturation index is greater than zero supersaturation is achieved. If the saturation index equals
zero equilibriurn conditions exist. EquiIibrium conditions with respect to a certain mineral phase
suggest that precipitation or dissolution of that phase controls the dissolved concentrations of the
cornponents contained in the phase (Drever, 1997; Alpers et al., L994a; Bayless and Olyphant,
1993).
Precipitation and dissolution reactions can have both positive and negative effects in the rnine
waste environment. For example, precipitation of relatively insoluble minerals such as anglesite
(PbSOs) can limit the dissolved concentrations of lead in tailings pore-water, while
simultaneously increasing the lead concentration in tailings soIids. (Alpers et al., 1994a; Blowes
and Jambor, 1990). Rapid dissolution of soluble salts occurs during wet periods and cm result in
significant increases in certain element concentrations (Bayless and Olyphant, 1993; Kwong et
al., 1997; Lin and Herbert Jr., 1997; Lin, 1997). The sudden pulse of metals released into aquatic
environments dunng these high-flow flushing events is extrenely detrimental to ecosystems
(Forstner and Wittman, 1983).
Cyclic precipitation and dissoIution of Zn-Cu bearing rnelanterite solid solutions, dunng the annual wetting and drying cycles, explain annual cycles in the Zn/Cu ratios that are observed in the rnine effluent frorn the Richmond and Lawson portals. High discharges during the wet season result in low (Zn/Cu),,, ratios, and little chance of melanterite precipitation. The higher values of the (ZdCu),, ratios during the dry season for both portais are similar to the values of the
residual waters after melanterite precipitation (Alpers et al., 1994b).
In addition to the geochemical rules goveming mineral solubility, it is important to recognize
the crystallographic controls- In crystals of most rninerals and inorganic compounds the binding
is considered ionic. Therefore their structures essentially folIow the pnnciples governing the
structures of ionic crystals as deterrnined by Linus Pauling (1929). Pauling's rules describe
features which. if present in an ionic structure, tend to minirnize its overall potential energy
(BIoss, 197 1). Several theoretka1 rnodels, based on Pauling's rules have been proposed to exphin
the physical and chernical properties of transition metal compounds inchding: electrostatic,
crystal field, valence bond, molecular orbital and ligand field theories- The interpretation of the
behavior of transition metal ions in simple and complex chernical systems provides a method for
understanding the properties and behavior of these and other ions in complex geologic media
(Burns, 1970).
2.3-2.1 lrnplications for rernediation and treutnzent
Subaqueous disposal of sulphidic mine wastes is a technique used at many sites to prevent
acid mine drainage. It is common practice to flood existing tailings impoundments or place
reactive waste rock in mined-out, flooded open pits. It is very important that waste rock and
tailings be discharged under water imrnediately after milling, and they must rernain perrnanently
submerged to avoid oxidation (Pedersen et al., 1999; Cravotta. 1994). If oxidized waste rock is
placed in a flooded pit without neutralization, the oxidation products may dissolve in the pore
water. Potentially, this may cause subsequent release of contaminants to the overlying water or
groundwater, perpetuating the need for further treatrnent. In a coIumn leaching experiment
conducted by Li and St-Arnaud (1997), oxidized waste rock from Noranda Mining and
Exploration hc., Heeth Steele Division in Newcastle, New Brunswick, was rnixed with alkaline
material and flooded. This helped to immobilize some metaIs such as Fe(II), AI, Cu and Pb. However, it did not prevent the release of other elements such as Zn, As, Cd and Mo. It would appear that the most appropriate measures to be taken with oxidized waste rock disposai in flooded pits are derermined by site-specific conditions. The conditions include both the local hydrology and the specific eIernents most prone to rnobilization, according to the equilibrium solubilities of the neutralization products.
Water chernists can use aqueous speciation-saturation calcuIations to help predict the rninerals Iikely to dissolve or to precipitate fiom water of a known composition. This is particularly useful in the study of the mine waste environrnent, when designing waste and water treatment strategies. These concepts are being used to treat the waste at the Iron Mountain site.
A highdensity sludge is created when H2S is added to tailings, fixing metals as secondary sulphides. The sIudge can then be disposed of in an open pit (U.S. EPA, 1992)-
Understanding the nature of precipitation and dissolution reactions and how they Vary with rnineral species aIIows the water chemist to predict the overall potential toxicity of the mine waste environment, in both the short and long term. Appropriate treatment strategies can be designed based on these predictions. Alpers and Nordstrom (1999) provides a comprehensive overview of geochemical modeling and the types of computer programs available-
2.3.3 Secondary Iron Sulphates in This Study
The role of secondary iron sulphates in the evolution of acid mine waters is a relatively new science, and only recentIy has their influence on the overdl geochernistry of the mine waste site been appreciated. Most of the existing Iiterature on iron suIphates describes rnineral structure and chemistry and cornes frorn faboratory studies. Little has been written about the natural paragenesis of secondary rninerals mainly because depositional sequences are ofien difficult to discern. The existence of many secondary sulphates represents only a bnef snap-shot of the geochemical record. Physical conditions, as well as the chemicd composition of meteonc solutions passing downward through a deposit, change rapidly over time and distance traveled. Consequently, many of the more soluble minerals dissolve and the less soluble are often covered
by a new mineral phase.
2.3.3.1 Copiapite - XR~'~(SO&(OH)~-~0~0
The copiapite group of minerals is one of the more common iron sulphate groups (Berry,
1947; Nordstrom 1983). Generally it is found in the oxidation zone of sulphidic iron-ore deposits. It forms as canary-yellow to orange tabular (010) crystals in loose aggregations and cmsts on the surface of ore minerais and tailings piles, and in paragenetic sequences with other sulphate minerais (Merwin and Ponsjak, 1937; Bandy, 1938; Bayless and Olyphant, 1993:
Jarnbor, 1994; Alpers et al., 1994). In addition, it rnay occur as efflorescent salts near acidic drainage streams (Nordstrom and Alpers, 1999b) and in association with coal seams
(McCaughey, 19 17; Zodrow, 1980; Cravotta, 1994).
As a mineral, copiapite was first described and analyzed by Rose (1833) and later narned by
Haidinger (1845). Bandy (1938) is credited with sorne of the earlier thoughts concerning the conditions of formation of the mineral. as one of the earliest to form from the oxidation of pyrite ores. Many kinds of basic hydrated iron sulphates with different chernical compositions are grouped under the name copiapite. In 1947. Berry chemically analyzed 42 copiapite samples, from different countries, and determined the general formula:
where X may be one or more of the elernents Na. K. Ca. Cu, ~e. Mn. Mg, Zn, AI, ~e~+;R is rnainly ~e~~but sometimes AI'+; and the value of n is usually 20. The names ferricopiapite, ferrocopiapite, magnesiocopiapite. aluminocopaipite, cuprocopiapite and zincocopiapite are proposed for species where X is rnainly ~e".~e'+. Mg, Al, Cu, and Zn respectively (Fanfani et al., 1973). The term "copiapite" is commonly used in the Iiterature to describe ferrocopiapite, and wiII be used the sarne herein. Table 2.3 Iists the members of the copiapite goup with their
corresponding minerai formulae and unit ce11 parameters.
Copiapite minerals are triclinic and have a complex structure of multiple chains built ty
meral-containing polyhedra and S04groups (figure 2.4). There are three notable features in the
atomic arrangement of the copiapite group of minerais: (1) chains formed by S04 tetrahedra and
Fe(OH)(H20)203octahedra, (2) isolated octahedra at the centre of the cell, and (3) water
molecules not Iinked directly to cations that contribute to a complex arrangement of hydrogen
bonds (Fanfani et al., 1973). Features 2 and 3 are common to other iron sulphates. Isolated
octahedra and free water molecules have been found in romerite (Fanfani et al., 1970)
coquimbite, and paracoquimbite (Robinson and Fang, 1971). Although the water limit of the copiapite structure is 20 molecules per ceII, the presence of "free" water molecules accommodates partial dehydration. without significant damage to the frrimework of the minera1
(Susse, 1972; Fanfani et al., 1973).
Detailed structural analysis can account for the wide range of isornorphous replacement in the
X site and the large variability in wnter content of minerals in the copiapite group. Since the space group of copiapite is P X rnust occupy the central position in the cell, assuming a fully ordered atornic arrangement. If the O/X ratio equal to one is the most likely one for copiapites
(Berry, 1947), where O represents tl (one oxygen equivalent) and X = Z (cationic charge x occupancy of the cation). then the X position is completely filled when it is represented by a divalent cation. When a trivalent cation is present in the X site. the occupancy is only 2/3 full. forming copiapites with cation vacancies. The O/X ratios diffenng from a value of one can be explained from a structural point of view. assuming that a change of OHt, H20can occur in the structure without affecting the atomic arrangement (Fanfani et al., 1973).
On the basis of the pnnciple of electrostatic valence, cations of lower charge (ca2+,CU**,
~e", M~"or zn'3 preferentiail y occupy the X site compared to cations of a higher charge (AI" CL.+ C) % t=l n ad pT,+ uC) Figure 2.4: Magnesiocopiapite structure wg~e';(S0,)6(OH)2.20H20] consists of layers of Mg(H20), octahedra aIternating with iayers containing Fe' octahedra and sulphate on (010). Layer sequence is ABA ABA (etc.), where A is Fe-sulphate and B is Mg(H,O),. Only hydrogen bonds join Iayers (Gaines et al., 1997). or ~e)3(Bay liss and Atencio, 1985). Substitution occurs because the coordination polyhedron
has a weak bond with the rest of the structural chah This weak connection also allows for the
AI-Fe substitution that occurs preferentidly in X(&o)6isolated octahedra in ferricopiapite
(Fanfani et al., 1973) and in coquimbite (Fang and Robinson, 1970).
The diverse chernical composition and arrangement of water molecules within the structure of various copiapite minerals account for the differences observed in the principal refractive indices and atornic coordinates (Posnjak and Merwin, 1932; Merwin and Posnjak, 1937; Bandy.
1938; Berry, 1947; Fanfani et aI., 1973; Zodrow, 1980, Bayliss and Atencio, 1985). The basic topology is the same for the different types of copiapite, however the atomic coordinates have significant differences in the positions of al1 the atoms. The main change occurs in the orientation of the X octahedron and the location of water molecules between the chains. Average bond lengths will Vary depending on which ekment has substituted into the structure (Bayliss and
Atencio, 1985). For example, when Ai occupies the X site, the average AI -O bond length is
1.93 A (Fanfani et al., 1973). If Mg is found in the X position. the average Mg - O bond length is
2.07 A (Süsse, 1972). These average bond lengths will increase to allow substitution of elernents wi th larger atornic radii (ca2: ~e". ~n'? and they will shrink for the occupancy of those with relatively smaller atornic radii (CU". M~". ~e",AI'? (Bayliss and Atencio, 1985). These displacements affect the system of hydrogen bonding, which differs noticeably between the femc
(Fe3+) and magnesiocopiapite (M.& species. The relationship between chernid data and atomic arrangement is poorly constrained because of the mixture of the many different cations found in naturd materials. They require more data and further studies to resolve whether or not the femcopiapite and rnagnesiocopiapite structures are typical of certain compositions or whether they present two polymorphic forms (Süsse, 1972; Fanfani et al., 1973).
The role of copiapite minerals in the acid mine drainage environment is a subject in need of funher study. The presence of this mineral group at mine sites has been noted by several authors
(Nordstrom and Alpers, 1999b; Lin, 1997; Cravotta, 1994; Jambor, 1994; Bayless and Olyphant, 1993. Zodrow, 1980). It is a known indicator of extreme acidity, but its specific geochernical significance is poorly defined. Formation of copiapite minerals effectively rernoves certain elements from the drainage, however infiltration of meteoric water will cause rapid dissoiution and subsequent release of the elements. As copiapite is a relatively soluble mineral, it is only capable of temporary storage of adverse elements.
Merwin and Posnjak (1937) speculate on a relative solubility of copiapite minerals between
30 - 40°C based on controIled laboratory studies of the Fe-03- SOS- HzO system at 25°C and 50 -
200°C (Posnjak and Merwin, 1922). However specific equilibrium constants and saturation indices have not yet been defined. This is due to the complex aqueous system from which copiapite minerak forrn. The high acidity and high concentration of dissolved solids within the waters associated with these minerais compIicate calculations used to define solubility reactions,
An objective of this study is to provide information about copiapite minerak and associated water, which may help define thermodynamic parameters, so that these minerals may be considered in modeling acid drainage waters.
2.3.3.2 Jarosite - A B~'I(so,),(o ~)6
Jarosite is a member of the alunite-jarosite group. This class consists of a large number of isostructural rhombohedral minerais in the R 3%~space group with the general formula:
where the A site is predominantly fiIled by monovalent K, Na, and H30,and to a Iesser extent
NI& and Ag. Divalent ion substitutions include pb2'and ca2+. CU'+ and ~n'+ may be incorporated into the structure in mutual substitution with pb2+(Jambor and Dutrizac, 1983).
Synthetic end-members include Rb, TI, Cs, ~~ysr2+ and ~a'+. The B site is filled by trivalent
Fe (jarosite) or Al (alunite). Additional replacement within the jarosite structure is possible when al1 or some of the SO~'is replaced by PO?-,ASO:-, s~o:-, cd4'-,~i0f or CO>'- (Scott,
L987)- End-member formulae comesponding to more cornrnon s~bstitutionsin the A position for jarosite are given in Table 2.4, with unit ce11 parameters- Potassium-rich jarosite is the most
widespread type, consequently the term 'f'arosite" usuaily applies to this group-member.
Jarosite minerals are the most prevalent naturally occumng iron-sulphates (Bigham, 1994).
They usually occur as yellow-gold crusts and coatings in the oxidized zone of sulphide deposits.
They are cornmon efflorescent rninerds in acidic, high-sulphate aqueous environments, especially near acid mine drainage streams (Nordstrom, 1982; Chaprnan et al., 1983, Alpers et al., 1994a;
Baron and Palmer, 1996). Precipitation ofjarosite is of interest to metallurgists because of its ability to scavenge unwanted elements from hydrometallurgical ore processing solutions
(Dutrizac, 1983; Norton et al., 199 1). Unlike other minerais associated with minedrainage ochres, jarosites are usually well-crystallized and easily identified €rom characteristic XRD patterns (Bigham, 1994)-
The atomic arrangement of jarosite group minerals is trigonal and consists of altemating sulphate chains and layers of iron hydroxide (figure 2.5). Large variations of the ionic radii of the ion in the A position are allowed by the structure, ranging from r = 0.95 A for Na to r = 1.33 A for
K. This range is considerably greater than that found in most isomorphous mineral groups
(Gaines et ai., 1997). As a result, ce11 dimensions for these rnineraIs Vary significantly with changes in composition (Dutrizac and Kaiman. 1976).
Most natural jarosites are considered to be a soiid solution of jarosite, natrojarosite, and hydronium jarosite (Kubisz, 1964; Brophy and Sheridan, 1965; Scott, 1987). Non-ideal substitution in the aIkaIi site is expected, given the difference in size between the K and Na ions and the molar volumes of jarosite (159.26 cm3) and natrojarosite (155.98 cm3) (Dutrizac and
Kaiman, 1976). The molar volume for hydronium jarosite (158.48 cm3; Duuizac and Kairnan,
1976) is much closer to that of jarosite, suggesting that K-H30 substitution is likely more ideal than either the Na-K or the Na-H30 substitution (Alpers et al., 1989). Table 2.4: The jarosite group minerals (Gaines et al., 1997). Note: a and c are crystrilIographic axes; D refers to D spacing. Hydronium jarosite values are from Dumzac and Kaiman (1976).
MiNERAL FORMULA a c D Jarosite ~~e~'3(sod2(orr>, 7.304 17.268 3.25 Natrojarosite ~e3+3(s0.t>2(orr), 7.327 16.634 3.29 *Hydronium jarosite (H3~)~e3+3(~~r)z(~~)s7.35 16.99 3.0 1 Ammoniojarosite (NK,)F~~+~(so&(oH), 7.327 17.5 3.1 13 Argentojarosite A@~~~(so&(oH)~ 7.347 16.580 3 -66 Plumbojarosite P~[F~'+~(SOI)~(OH)~I= 7.305 33.675 3.71 Beaverite pbcu(Fe3+,Ai)2(S04)2(OH)6 7.356 34.30 4.3 1 Dorallchari te ~lo.s&.2~e~+3(~0d1(0~)ci 7.330 L7.663 3 -85 Figure 2.5: Jarosite structure [KFe3(S04)2(OH)6] consists of altemating layers of potassium sulphate and layers of iron hydroxide. Hydroxide atorns form onIy four of the six corners of the Fe(Ai) - O octahedra. The other two are sulphate oxygens. Layers are also tied together with K-OH bonds (Gaines et ai., 1997). Hydronium ion substitution in the alkali position causes variable degrees of alkali element
deficiency and a general excess of water in synthetic jarosites. As much as 15 - 25 mole percent
hydronium replacement is cornmon (Duuizac, 1983). Al1 jarosites contain hydronium, the
concentration of which is detennined by Kt activity and the pH of the system (Baron and Palmer,
1996; Dutrizac and Kaiman, 1976; B igham. 1994). Hydroniumjarosite is the only minera1
recopized by the International MineraIogical Association in which hydronium is an essential
component in the structure (Alpers et al., 1989).
A consistent iron deficiency is prevalent in synthetic (Dutrizac and Kaiman, 1976, Wartig et al., 1984; Ripmeester et al., 1986; Baron and Palmer, 1996) and naturally occurring jarosites
(Alpers, et al-, 1989). Values of the Fe:S04 molar ratio have been reported that are significantly
Iess than the ideal (32) (Hartig et al., 1984,2.20:2 to 2.572; Ripmeester et al., 1986,2.33:2;
Alpen et al.. 1989, 2.85:2 to 2.962; and Baron and Palmer, 1996,2792). A deficiency of ~e~+ causes a charge deficit that is Iikely balanced by partial substitution of H20 for OH (Hartig et al.,
1984; Kubisz, 1972).
Evaluating the solubility of jarosite minerals and the saturation state of natural waters with respect to jarosites allows for a more cornprehensive understanding of the role these rninerals play in the evolution of mine waters. In order to use the composition of jarosite rninerals and coexisting waters to accurately evaluate the solubility of jarosite solid solutions, it must be deterrnined that the jarosite mineral phases are homogeneous and that equilibrium with the coexisting water is attained (Alpers et al.. 1989). Solubility determinations for a wide range of naturd and synthetic jarosite solid solutions are necessary to quantify the binary and ternary mixing parameters in the K-H30-Na system (Alpers et al., 1989; Baron and Palmer, 1996).
There is a large degree of uncertainty about the thermodynarnic properties of jarosite minerds. A significant discrepancy exists in reported solubility products for K-jarosite dissolution reactions (log Ksp = -7.12 to -14.8) and free energy dues (AG >29s = -33 17.9 to -
3 192 I25kJ mol-') (Table 2.5). Baron and Palmer (1996) discuss these discrepancies in detail Table 3.5: Summary of solubilities and values reported for jarosites (fiom Baron and Palmer, 1996). Baron and Palmer (1996) provides an excellent summary of the previous studies from which this data was taken.
Reported Reporteil Comments log K, at 25 OC AGous8 (kJ mol-') Allison et al. - 14.8 - - (1990) Alpers et al. - 11.14 - 3300.2 t 2.6 for (&.83N~.07H30'o.io)-jarosite precipitated (1989) from acid mine drainage water in the lab at ambient temperature ---- Baron and - 11.0 20.3 - 3309.8 k 1.7 dissolution experiment with Paimer (1996) ~~Z.~~(SO~)~(OEI)S~~CHZO)O.~~ Bladh (1982) - 7.12 - - Brown (1970) - - 3276 + 84 tiom precipitation experiment - -3I92f25 fiom dissolution expenment
- ,3302 + 84 recalculated by Zotov et al. (1973) who noted - - 3300 + 5 an arithmetic error in Brown's caiculations and used thermodynamic data from Naumov et al. (1971)
- 3299 recalculated fiom the dissolution experiment by Van Breeman (1973) using therrnodynamic data from Robie and Waldbaurn (1968) Chapman et al. - 9.21 - based on Kashkay et al. (1975) and (1983) themodynamic data from Naumov et al. (197 1) Hladky and - 9.08 based on Kashkay et al. (1975) SIansky (1981) Kashkay et al. - 3299.7 t 3 precipitation expenment ( 1975) - 15.8 - 3184 (at 100 OC) (at 100 OC) Scoffregen - - 3416.3 i 1-7 at 200 OC, 100 bar (1993) (200 OC, 100 bar) Vlek et al. - 14.56 - 33 10.4 dissolution experiment (1974) Zotov et al. - 3305.8 + 1 based on jarosite precipitated from a natural ( 1973) water sample
- 3317.9 estimated from a natural (Na,K)- jarosite precipitated at 45 OC and Iist four reasons for the variation: (1) inconsistent therrnodynarnic data for calculation of free
energies and aqueous ion activities, (2) substitution of other ions in the jarosite structure,
especially hydronium (3) the use of different experimental approaches to determine mineral and
water compositions, and (4) analytical uncertainty.
A key source of variation in the values for the free energy of formation of jarosite is
the use of different values for the free energies for the ions in the calculations used by the
different researchers. The values for the free energy offormation and the solubility product of
jarosite solid solution end-members that are currently considered the most reliable are reported in
Table 3.6. Values reported by Kashkay et al, (1975) and Chapman et al. (1983) for Na- and H30-
jarsoite are considered the most reliable because they are based on actual solubility
measurements and a consistent thermodynamic database. A Ksp value for K-jarosite was also
reported by these authors, but it has since been disputed. Alpers et al. (1989) and Baron and
Palmer (1996) discovered that the free energies of formation of K-H30-Na jarosite solid solutions
are more consistent with the free energy for pure jarosite reported by Vlek et al. (1974) and Zotov
et al. (1973). indicating a lower and a Iower Ksp for K-jarosite than what Kashkay et al.
(1975) and Chapman et al. (1983) had reponed. Baron and Palmer (1996) propose that the higher
Ksp obtained by the previous researchers may represent the solubility product of a thin surface
layer of hydroniumenriched jarosite that could have forrned in their precipitation experiments.
The significantly lower solubi li ty product obtained by Baron and Palmer (1996) indicates that jarosite is more stable and may occur at pH values higher than previously thought. It is difficult to define ce11 panmeters and therrnodynamic data for jarosites due to the presence of this multicomponent solid solution series. A combination of X-ray and chernical data is needed to accurately define a mineral phase.
Weil defined solubility parameters can be used in aqueous speciation prograrns such as
WATEQ4F (Bal1 et al., 1987, 1999) to accurately mode1 solid solution precipitation and Table 2.6: The values for the free energy of formation and the solubiiity product of jarosite solid solution end-members that are currentiy considered the most reliable. K-jarosite values are fiom Baron and Palmer (1996). Na- and H30-jarosite values are based on AGorts8reported by Kashkay et al. (1975) and Iog Ksp caiculated from this tiee energy by Chapman et al. (1983).
End-member minerd Formuta AGOf.298 log Ksp jarosite rne3(~~4)2(~~)6 -3309.8 -1 1-00 nauojarosite NaFe3(SO&(OW6 -3256.8 -5.28 hydronium jarosite H3oFe3(s04)2(0~6 -3232.1 -5.39
dissolution. The more thermodynamic parameters included in the database, the more precise the prediction of the composition and abundance of jarosite precipitation in various settings. including acidic mine environments and oxidized gossan zones of sulphide ore deposits (Alpers et al., 1989). A goal of this project is that the analyses of the jarosite rninerals and coexisting waters collected at Iron Mountain will provide more information on the specific geochemical influences on jarosite composition. This information may help determine more of the thermodynamic parameters needed to better define the system. CHAPTER THREE: SAMPLE COLLECTION
3.1 Introduction
Fieldwork for this study was carried out at Iron Mountain in July of 1998. Minerai and water sarnples were collected inside the Richmond Mine during a three day sampling mp to the site. In total, twenty-two minera1 samples were gathered and fifieen water sarnples (Appendix A). Of the minerals, two of the copiapite and two of the jarosite samples were coliected with coexisting water, in the form of pore-water andor stdactite drip-water. These parricular samples became the focus of this study, in order to help define better the mineralogical influence copiapite and jarosite rninerals have on the evolution of the acid rnine waters in the Richmond Mine (table 3.1).
Other secondary minerals. not analyzed for this project. were collected to concibute to ongoing studies of suiphate mineralogy. AnatyticaI results for the relevant mineral and water samples are reported and discussed in Châpter 4 (copiapite) and Chapter 5 (jarosite).
3.2 Inside the Richmond Mine
Restoration of the underground workings in the Richmond Mine were completed between
1988-1990 at a cost of more than $1 (US) miIlion, allowing entry to stopes which had ken abandoned since the early 1950's (Alpers and Nordstrom. 1991). Access to the rnine is through a we1l-lit and ventiIated portal tunnel approximately 400 meters long and 2 to 3 meters in diameter.
It terrninates at a five-way intersection beyond which lighting and ventilation do not exist. A series of four drifts (A, B, C, and D) branch off frorn the five-way intersection (figure 3.1).
Unstable wall rock and poor air quality prevent exploration further than approximately 20 m into drifts A. B and D. No minera1 samples were collected from the C-Drift for this project. due to extrerneiy poor air quality. Streams of effluent 38 to 48 OC flow from drifts A, B and C and the average air temperature in the rnine is 28 to 38 OC. These warm ternperatures promote mine water evaporation, and with the extreme acidity of the waters and vapours, they combine to create Table 3-1: Catalogue of minerai and water samples collected in the Richmond Mine in July 1998. examined in this study. 98CR03W and WW are copiapite pore-water sarnples exvacted fiom the minerd samples (03 and 03) three week after the trip to Iron Mountain, in the USGS Iab in Sacramento.
MINERALS: SAMPLE # MAIN MINERAL DESCRIPTION 98CR03 copiapite (moist) dark yellow. peanut-butter-like muck, left in Sacramento to centrifuge 98CR04 copiapite (moist) same as 98CR03 98CR14abc jarosite (stalactites) duIl yeiiow stalactites, 1-10 cm long, 0-5-1 cm in diameter, hard texture, collected with drip water (98CA105 series) 98CR15ab jarosite (rnud) mustard coloured mud, centrifuged on site (supernatant: 98CA106) 98CR19ab jarosi te yellow crust beneath dripping jarosite stalactites - (%CR 14) 9SCNOab jarosite (crust) brown-red crust, in area of bacterid slime and yelIow jarosite 98CR23ad copiapite (gossan) a: copiapite with pyrite d: copiapite
WATER: SAMPLE LOCATION DESCRIPTION 98CA102 C-drift at weir composite sarnple of effiuent leaving C-drift Adrift at weir composite sample of effluent teaving A-drift Bdnft at weir composite sample of effiuent leaving B-drift 0-drift, S wall jarosite stalactite drip water (contributes to D-drift effluent) Ddrift, S wall jarosite stalactite drip water (contributes to D-drift effluent) D-cirift, S wall jarosite stalactite drip water (contributes to D-cirifi effluent) Ddrift, S walI jarosite sraIactite drip water (contributes to D-drift effluent) D-drift, S wall jarosite stalactite drip water (contributes to D-drift effluent) Darift, S waii jarosite stalactite dnp water (contributes to Ddrifi effluent) D-drift, S wall yellow rnuck - pore water (contributes to D-drift effluent) D-drift, end copiapite pore water (contributes to D-drift effiuent) D-drift, end copiapite pore water (contributes to D-drift effluent) Location
a E-Manway to upper level
Figure 3.1: Plan view of Richmond Mine workings showing a series of four drifts (A, B, C, and D) branching off fiom the five way intersection (fiom Alpers et al., 1992b). Note: access Iimits were mapped dunng the 1990 field trip (Nordstrom and Alpers, 1990) and were slightly different during the 1998 trip, as descnbed in the text. challenging working conditions- Airquality was monitored constantly with a portable device, to
ensure safety.
33 Mineral Collection
Efflorescences, stalactites and stalagmites composed of soluble sulphate minerals coat the
pyrite-walls and the timber and concrete supports of the mine passages, creating a colourful array
of blue, green, yellow, orange, pink and white (figure 3.2). They are abundant, diverse and
coarse-grained. Table 3.1 iists only the mineral samptes that were exarnined in the course of this
study. Appendix A provides a comprehensive Iist of al1 the samples collected. Initial minera1
identification done in the field was confinned with powder X-ray difiaction. Even though the
primary objective of this field study was to collect minerals with coexisting water, several other
sulphates were sampled in case the original project proved impossible and other studies had to be
considered. Water collected in conjunction with the minera1 samples is discussed in section 3.4.
As most secondary sulphates are sensitive to oxidation and extremely soluble, special care
was taken to ensure preservation (Waller. 1992)- Samples were coIIected and carefully wrapped
in plastic (dry-cleaning film. bubble wrap) and Styrofoam. For further protection they were placed in jars or freezer bags. Some were immersed in mineral oil and placed in jars on site, but
most were placed in dry packages. A week following the collection, the "dry" minerals were split and half of each sarnple was placed in oil.
Al1 of the samples collected with coexisting water came from the D-Drift of the Richmond
Mine. The conditions in this drift were dry relative to the other three drifts. The only water present, in addition to mineral pore-water. was dnpping from cracks and stalactites in the walls and ceiling. The other drifts had substantial streams of effluent running dong the floor.
Two 5 Iitre jars were filled with damp copiapite found at the end of the D-Drift on loose piles of pyrite that had fallen to the floor during a cave-in (98CR03 and 98CR04) (figure 3.3). The
Figure 3.2 (continued): More colourful secondary minerals observed in the Richmond Mine. Top: Blue melanterite and yeilow copiapite forming on pyrite wails of the five way intersection. Bottom: Close-up of melanterite and copiapite on the pyrite. White halotrichite and black voltaite crystals are also visibte (photos: AIpers). Figure 3.3: Damp copiapite found forrning at the end of the D-drift (98CRû3 and 04) (photo: Alpers). cave-in occurred approximately 20 meters from the five-way intersection, Access to the rest of the tunnel is terminated beyond this point.
Approximately 10 metres in from the five-way intersection, a 1.0 to 1.5 metre high and 3 to 4 metre Ionp section of the West wall of pyrite was coated in a yeIIow jarosite mud (figure 3.4). in addition, water was observed dripping from a senes of du11 yellow jarosite staiactites- This water was collected (98CA105 series) and the stalactites were sampled (98CR14abc). Many stalactites appeared to be coated in a bacterial slime (figure 3.5).
Jarosite stalactite sarnpIes are relatively hard, opaque and a du11 yellow coiour- They range in Iength from 1 to 20 cm and in diameter from c 1 to 3 cm. Initidly, it was difficult to tell if water was rushing over or flowing through them. On close inspection, many have a small hollow tunnel through the centre of a series of what appear to be growth rings, indicating that water was flowing through (98CA105A. 8,D-G). These sarnples were broken off the wall by hand and placed in three centrifuge tubes to protect them from further breakage.
Jarosite mud sample 98CR15ab was collected from the muddy part of the wall, located 2 to 3 metres to the left (east) of the stalactites (figure 3.4). It is yellow and has a smooth mustard consistency. Initially, it appeared that most of this portion of the wall was composed of yellow mud, however the majority of materia1 was a hard yellow crust. Consequently, it was onIy possible onIy to fil1 two centrifuge tubes by carefully scooping the mud from the wall by hand.
The tubes were spun on site in a srnaII portable centrifuge and yielded water sample 98CA106.
The only other obvious secondary rnineral phase present in this section of the wall was a red mud (98CR16abc) and crust (98CR20ab) which was found coating the jarosite mud and stalactites, respectively. Not enough sample was available for detailed analysis of the red rnud.
Sample 98CR20ab was removed from the muddy section of the wall that was coated in bactenal slime. The sample is predominantly a jarosite crust. but it contains a crusty version of the deep rust-red coloured rnineral. Figure 3.4: Wall of jarosite forming on pyrite surface in the D-drift of the Richmond mine. The portion of the wall on the left side of the photograph is composed of muddy jclrosite and pyrite. The minerals found to the right of this muddy section are crystaliine jarosite stalactites and crusts. Much of this side of the waiI is covered in a thin layer of red-mineral and bacterial slime (photo: Alpers). Figure 3.5: Bacterial slime coating much of the jarosite stalactites and cmts in the D-drift of the Richmond Mine (photo: Alpers).
55 3.4 Water Coiiection
3.4.1 Measun'ng und Reporting Negative pH
pH values are based on the dissociation constant for water at 25°C which is
H20t, H' + OH-, K,, = arrsorr = 10‘'~ (3-1) where K represents the equilibrium constant for water and a is the activity or active concentration
(see equation 4.3). The product a~,ao~is fixed for al1 water solutions. H' is present even in suongly basic solutions and OH-in strongfy acidic ones ensuring that the product of a~+a~~is always equal to IO-'". Accordingly, the acidity or alkalinity of a solution is specified by giving the activity of either or OH. It is conventiond to characterize solutions in terms of their acidity or a~,. For example a IN (normal - equivalents of acid per litre of solution) extremely acidic solution has I am, a neutral solution has loJ a~,and a strong base has 10"' a~,The pH of a solution is the negative logarithm of the hydrogen ion activity. A negative pH value is therefore a measurement of high hydrogen ion activity (Krauskopf and Bird, 1995).
The reporting of negative pH values is somewhat controversial. The conventiond definition of pH discussed above limits the range of definable and measurabIe pH values to that of O to 14.
The measurement of pH outside this range is diE~cuIt.A new definition of pH rnust be fonnulated that is consistent with the conventional definition, different buffers must be used, and electrode performance and interferences must be detennined (Nordstrom and Alpers, 1999b).
The most accepted mode1 for defining pH below 1.0 is the Pitzer ion-interaction approach
(Pitzer, 1973)- Acid mine waters are solutions of sulphuric acid, so the Pitzer mode1 applied to sulphuric acid essentially serves as a definition for pH. Standardized suIphurïc acid solutions would then act as buffer solutions for calibration. The performance of the standard glas membrane electrodes under these extreme conditions then needs to be assessed (Nordstrom and
Alpers, 1999b). For a more involved discussion on how negative pH waters are attained, and the problerns
associated with measuring and reporting these extrerne acidities see Alpers and Nordstrom ( 199 1)
and Nordstrorn and Alpers (1999b) and the references therein.
3.4.2 Field Memurement and Sampling Procedures
Two pH metres (98A and 98B) and four electrodes (Triode 1 and 2, Ross 3 and 4) were used for fieId measurements. Both the Ross and Triode are combination pH electrodes, which means they both include a reference cell. The reference cell measures a voltage relative to the standard hydrogen eIectrode (Bates, 1964). In addition, the Triodes measure temperature whereas the Ross electrodes only measure pH (voltage). The electrodes were soaked in standard T-2, a sulfuric acid solution of pH +1.0 for 23 hours to condition thern. An Orion probe 9678 BN was used for redox readings.
Before entenng the Richmond Mine pH meters and electrodes were calibrated using sulphurk acid standard solutions to 28 OCt 12°C- The redox probe was also calibrated. These calibration measurements are found in Appendix A. Four pH electrodes were calibrated initially.
The readings from the 98-1 Triode and the 98-4 Ross electrodes correlated the best with one another and were used to measure the mine waters- However, part way through the sampling the
98-4 Ross electrode failed and was rephced by the 98-3.
Prior to taking any water measurernents in the mine, it was necessary to re-calibrate the instruments and standards at the temperature of the mine waters. The 98-1 redox probe, the 98-1
Triode and the 98-4 Ross eIectrodes were re-calibrated in the C-Drift mine waters as this location was expected have the most representative effluent temperatures (46OC f 1.6"C). The standard solutions used in the calibration were placed in the effluent, which acted as a water bath, adjusting them to the higher temperature conditions in the mine (figure 3.6). These recalibration measurements are provided in Appendix A. Figure 3.6: Standard solutions were placed in the streams of mine effluent to adjust hem to the higher temperature conditions within the mine (photo: Alpers). To accommodate accurate interpretation of extrerne acidity, the pH values of four known
sulphuric acid standards of pH 1,2,3, and 4 were used to make regression curves for each
temperature of standardization. The curves are then applied to interpolate pH values from the mV
readings for each of ten sulphuric acids standards of extrerne hydrogen content and the water
samples that were collected (Appendix A).
3.4.3 Average Water Chernistry of Dnps A, B, C, and D
Following the re-calibration of the instruments, temperature, pH, redox and specific
conductance were measured in water samples collected from Drifis A, B, C and D (tabIe 3.2). The
purpose of these measurernencs is to characterize the average water chernistry of each of the four
drifts that conuibute to the Richmond Portal effluent-
Water samples 98CA102, 103 and 104 (from Drifts C, A and B respectively) were coliected
in 500 rnL containers from the water running over the weir at the entrance to each drift (figure
3.7). Temperature, pH, redox and conductiviry measurements were taken and the water was
discarded. Conductivity was always measured in a srnall(10 mL) beaker, filIed to the same point
for unhowns and standards. In situ measurements were taken in these three locations from pools
found behind the weirs. Water was collected for further laboratory analysis in 500 mL disposable
capsule filters and filtered through 0.30 micron filters with a hand-pump (figure 3.8). The fdtered
sample was then transferred to several. smalier bottles. The bonles were completely filled
to prevent oxidation and placed in an incubator to prorect the sampIes from severe fluctuation in
temperature.
The volume of water flowing from the D-Drift was comparatively much less than that
leaving the other three drifts at this tirne of year. The tunnel was damp. with water dripping from
overhead and from stalactites that were actively forming on the south waii. There was not enough water to form a Stream dong the floor of the drift to collect a representative sample. Table 3.2: Wnter samples chnracicristic of drifts A, B, and C. calc - c;ilculnted.
SAMPLE LOCATION pl4 (mV) pl4 (mV) pl1 TEMP REDOX SPECl BI C BLOW RAT& ROSS 98-4 TRIODE 98-1 (calc) (OC) (nw CONDUCTANCE (pS/cni) * 98CA 102 C-Dri fi 388 378.2 1.O 45.4 390 3.8 x lu3ni3 1 (ben ker) secoiid 98CA 102 C-Drift 39 1 382S 1 ,O 48.1 89 O00 33x lu3nl" (in sitii) secoiid 98CA 103 A-Drift 370 413 1.1 39.0 373 6.3 x 1 o4II? / (beaker) secoiid 98CA 103 A-Dri fi 37 1.3 409 1,1 39,4 375 71 00 62 X lu4IIIV (in situ) sccorid 98CA104 . R-Drift 381.1 383.6 < 1.0 36.8 374 3,2 x 10"in" (beaker) second E 98CA 104 383 1.0 37.9 374 1 10 000 3.2 x / V B-Dri ft 385 < 10.~n1~ (iii sitiij secoiid *Specific conductance values are an average of 2-3 nieasurenicnts froni a snisll(10 niL) berikcr, Note: Beaker teniperature rcading is lowcr duc to the ''cooler" air tenipcraturc Lbchilling''the gtnss. Figure 3.7 (idl):Water sampls 98CAIO2.103 and 104 (from Drifts C A and B respcctivmcly) were collected as shown in 500 mL containers hmthe water running ovcr the weir at the entrance to each drif~Temperature, pH. redox and conductivily rneasurements were îaken and the water was discardcd. hi situ mmcasurements were [ahin thcse Uvee locations fmm pwis found behind the wein.
Figure 3.8 (right): Drift water was collected for funher Iaboratory analysis in 500 mL disposable capsule filtcrs and xreened Uuough 0.20 micron Blten with a hand-pump show here. 3.4.4 Copiapite Pore Water
Pore-water was obtained from copiapite mineral sarnples 98CR03 and 04 by cenuifuging thern in Sacramento three weeks after collection. They were spun down at 10,000 rpm for 20 minutes. Approxirnately 200 mL of opaque brown pore-water with a pH of -1.0 +/- 0.5 was obtained from each sample. Analytical results are discussed in Chapter 4.
3.3.5 Jarosite Stalactite Drip Water
Seven beakers of various sizes were placed beneath stalactites (98CR14abc) that were actively dripping yellow-coIoured water, and left over night (figure 3.9). Sixteen hours later, four of the seven beakers were completely filled with dnp water, two were partially filled and one was ernpty- Pnor to measuring the redox and pH of the drip sarnples, the instruments were re- calibrated (Appendix A). A puddle in the D-Drift was used as a water bath for the standard solutions.
Table 3.3 provides pH, specific conductance, redox and temperature rneasurements for the drip water (98CA105). Using a pipette. only the necessary arnount of water needed to obtain a reading was colleczd from each the container. The water was released from the pipette into clean fIasks. Efectrodes were placed in the fiasks to obtain the readings and then the water in the fiasks was discarded. The pipette and eIectrodes were rinsed with deionized water between measurements. The remaining water in the drip containers was transferred into bottles.
Analytical results are discussed in Chapter 5.
The waters varied in cotour between dark and very light orange. The Iighter coloured waters correspond to waters with Iower redox measurements and darker waters with those of higher redox values (figure 3.10, table 3.3). This is a reflection of the amount of dissolved femc iron present in the sample (Chapter 5). In addition, it was observed that the stalactites forming the dnps with the lighter orange coloured water had siime coating the tips. The darker water seemed to be originating from "slime-free" stalactites. Figure 3.9: Beakers of stalactite drip water (lefi) and close up of dripping jarosite stalactite (right) (photo: Alpers). Table 3.3: Chemistry and colour of D-Drift drip waters (98CA105 series) and pore water (98CAI06). da - not available.
SMLE CoLOuR pH(mV) pn(mV) PH TEMP REDOX SPECIFIC ROSS 984 TRIODE 98-1 (real) (OC) CONDUCTANCE (mV) (,&cm) 93CA105B Orange tint 298 301 2.05 28.9 457 7 300 98CA105G Orange tint 283 282 2.35 28.6 443 5 300 98CA105F Light orange 287 284 2.30 29.1 547 5 O00 98CA105E Dark orange 290 285 2.25 29.4 570 5 300 98CA105D Dark orange 29 1 286 2.20 29.3 604 5 300 98CA105A Dark orange 299 294 2-05 29.5 514 7 000 98CAiO6 n/a 340 322 4.5 20.0 521 31 O00
Figure 3.10: Beakers of samples described in table 3.3. From let to right beginning with the Iargest beaker in the back - 105A, LOSD, 105E, 105F, and behind F is 105G. The two srnaller beakers in the front, from left to ripht, are 105B and 105C (which is empty) (photo: Alpers). 3-4-6 Jarosite Pore Water
Two 50 mL centrifuge tubes, each containing approxirnately 40 mL of yeilow, mustard-Iike jarosite (98CR15a&b) were spun down on site in a small portable centrifuge for 20 minutes. The
supematant was filtered through 0.45 Fm filter paper. Sarnple 98CA106 refers to both the filtered
water and the residual that would not pass through the filter. Measurements of pH. temperature, redox and conductivity were obtained from placing the probes into the residual material. This residual was then retumed to the centrifuge tubes. These measurements are reported in table 3.3.
Analytical results are discussed in Chapter 5. CHAPTER FOUR: COPIAPITE
4.1 Introduction
The purpose of this chapter is to describe the crystai rnorphology, structure and chemistry of
the copiapite rnineral samples selected for this study and characterize the coexisting pore-water.
The hand samples were examined with a binocular microscope. A petrographic microscope was
used to study polished thin sections under transmitted and reflected light. Scanning electron
rnicroscopy heIped distinguish crystal textures, grain size and morphology. EIectron microprobe
analysis detennined the major elements present in the samples and trace elements were detected
with a proton rnicroprobe. Average mineral compositions were calculated using an APL
cornputer program, developed by Dr. D.M. Carmichael (Queen's University). Powder X-ray
diffraction techniques helped define crystal structure.
Copiapite pore-water was charactenzed by the following rnethods: Inductively CoupIed
Plasma - Optical Emission Spectrometry (ICP-OES) for al1 cations except Na, K, and Li which
were analyzed by Flame Atomic Absorption Spectrometry (FAAS); anions were determined with
Ion Chromatography (IC); FerroZine (Stookey, 1970) was used for Fe(T-total) and Fe(II); and
As(IIi) was detennined by Flarne Ion Absorption Spectrometry (FIAS). For convenience, detailed descriptions of equipment and techniques used to study both copiapite and jarosite are surnrnarized in this chapter.
4.2 Sample Description and Petrographic Summary
Copiapite samples 98CR03 and 98CR04 collected in the D-drift of the Richmond Mine have a moist, globular appearance. This material was placed in a centrifuge to extract the pore-water for analysis. The remaining material was stored in four 500 m.containers at 29 OC, in a
Precision Scientific Low Temperature BOD Incubator (Mode1 8 IS), which has a temperature range of -10 to i50 OC + 0.02 OC. The rnineral samples are yeilow-orange in colour (MunseII colour 5Y 5-6/6) and have a thick, dense, tacky consistency. A thin film of opaque brown fluid is present on the surface of the solid matenal- A few small grains of pyrite (c2 mm), introduced during sarnple collection, are disseminated throughout (t10%).
Three polished thin sections of copiapite (98CR04) were prepared by Gilles Laflarnme at
CANMET in Ottawa. The sarnple was placed in a desiccator and Iefi for two days to dry at roorn temperature. Fragments were mounted in a polyethylene mould, 30 mm in diameter, in pre-rnixed epoxy (5: 1 mixture of CIBA-GEIGY epoxy resin 502 and hardener HY 956) and left overnight to harden. The cold-setting epoxy-resin was favored in this case over polyester and acrylic, mainly because epoxy resin has strong adhesive properties, a low viscosity, low shrinkage, and fairly high polishing hardness* Most importantly, this epoxy does not require high heat or pressure for preparation, which was essential, as copiapite is so sensitive. Sample pIugs were then rernoved from the molding assemblies, and the grinding was done using a 15 prn diamond impregnated disc, with a peuoleurn ether lubricant. The polishing was done on Durener polishing machines using lead laps, in two successive stages; first with diarnond particles of 1-3 pm and second with particles of O-Fm. A mixture of minera1 oil and kerosene was used as a lubricant. Contact with water was avoided (Laflamme, 1999; Stanley and Laflamme, 1998).
Since the polishing was done using lead laps, contamination of the sample is possible. In this study lead in copiapite is below the minimum detection Iimit (Appendix C). For future work, an alternate method of polishing is recomrnended if samples are to be analyzed for Iead, especially when working with sensitive, potentially unstable rninerals such as sulphides and oxides. Many laboratones are rnoving toward paper or cloth laps. hpregnating the specimen with a cyanoacrylate adhesive is another option that may protect the sampie from lead contamination during polishing (Stanley and Laflamme, 1998).
In polished thin section, copiapite is opaque in transrnitted light and colourless in reflected light. Grains are euhedral-rectangular in shape and are 150prn in lengtfi. They display an internai reflectance at higher rnagnification (20-40x) (figure 4.1). Figure 4.1: Polished thin section of copiapite sample 98CR04PS-1in reflected light at 20x (top) and 40x (bottom) magnification. Stacked and flat euhedral grains I50 pm in length are cIearly visible in the top photo-micrograph, scale bar 50 pm . Internal reflectance displayed by the mineral under higher magnification is prominent in the bottom photo-micrograph, scale bar 50 Pm. 43 Scanning Electron Microscopy (SEM)
SEM was used in conjunction with qualitative energy dispersive spectrometry (EDS) to
obcain a better understanding of minera1 morphology and detect any additional phases present
within the samples- The JEOL JSM-840 scanning electron microscope at Queen's University and
the PhiIips XL30 CP at the Royal Military College of Canada (RMC) were used. SEM proved to
be an extremely valuable tool. providing visible evidence of additionai phases to support elecuon
microprobe and X-ray diffraction data.
A portion of copiapite sample 98CR04 was removed from the incubator and left to dry at
room temperature for 24 hours- The sample was exarnined under the binocular microscope before and after drying. The most notable changes were in colour and consistency. The clumps
turned a much Iighter yellow colour (5Y 718). and becarne less stichy. A dusting of srnall white minerals (< 1 mm) appeared as sparsely disseminated patches on some copiapite surfaces. The major copiapite phase remained dominant- The sample was then mounted on a carbon disk and coated with carbon for the analyses at Queen's University and gold for that at RMC to prevent charge build-up.
4.3. I Results
Two distinct morphologies are visible in the SEM images (figure 4.2). The sample is predorninantly composed of larger semi-rectanguli platy crystals (10-50 pm), with a minor phase of smaller platy crystals (I5 prn) existing as spheroidal aggregates (5 15 prn in diameter)-
Qualitative EDS analysis indicates there are chemical differences in the phases. Spectrum for the larger platy crystals display a fairly distinct magnesium peak that is not present in the spectrum for the spheroidal aggregates (figure 4.3). The spectrum for this second phase suggest duminum is present in the sarnple (figure 4.4). The predorninance and position of the larger platy crystals implies that they were the primary copiapite phase to exist, and the minor spheroidal aggregates of crystals formed as a secondary phase (figure 4.5). Figure 4.2: Scanning electron micrographs of copiapite sample 98CR04 showing two distinct morphologies. The sample is predominantly composed of larger-semirectangular,platy crystals (10-50 pm), with a minor phase of smailer plaq crystals (< 5 pm) existing as spheroidal aggregates. Figure 4.3: Scanning electron micrograph of copiapite sample 98CR04 with the EDS of the predomulant semi-rectangular, platy, Mg-nch crystals. Figure 4.4: Scanning electron micrograph of copiapite sample 98CR04 with the EDS of the minor phase of spheroidal aggregates of smaller, platy, Al-nch crystals. Figure 4.5: Scanning electron micrograph of the two copiapite phases found in sample 98CR04. 'ha relationships evident in this and previous photos suggest that the large serni-rectaxgular magnesiocopiapite crystals were the primary phase present in the sample, and that the alurninum-r :h spheroidal aggregates formed later. 3.4 Major Elements - EIectron Microprobe Analysis
The ARL-SEMQ Electron Microprobe at Queen's University was used to perfonn major
elernent analyses on the minerals and confm their identification. It is equipped with an energy
dispersive specuometer (EDS) for accurate quantitative analysis. Standard analytical conditions
included an accelerating voltage of 15 kV, a take-off angle of 52S0,an ernission current of 100
mA and a beam current of approximately 40 nA.
Prirnary analytical standards were chosen based on expected concentrations of certain
elements in the copiapite and jarosite sarnples (table 4.1). An alunite standard served as a
secondary analytical iron sulphate standard (table 4.2) (Stoffregen and Alpers, 1987). Alunite
was chosen as a standard as it differs only slightly from jarosite in composition (AI'+ instead of
~e~'in the A site) and there was no iron sulphate standard available. Prior to every session,
calibration of the microprobe was performed by collecting three 50 second analyses with a
rastered bearn of O. 1 on a11 of the standards (Rainbow, 1999)- The rastered beam and relatively
short analysis time were chosen to minirnize bearn damage on the fragile sulphate standards and
samples. The secondary alunite standard was continually checked throughout the probe session,
typically every 10-15 analyses, to ensure consistent resuIts. Table 4.2 shows typical
reproducibility in the alunite standard analyses. Ail standards were rechecked at the end of the
session. The accuracy of analyzed iron is confirrned in the analysis of a pyrite grain in jarosite
sarnple 98CRlSTS-A.
Analytical spectra were processed by fitting the reference spectra using the least squares
program to obtain uncorrected k-ratios. The k-ratios were then corrected for atomic nurnber (Z), absorption (A) and fluorescence (F) by the "ZAF" program (Doyle and Chambers, 1981). A thorough discussion of the 2A.F method can be found in GoIdstein et al. (1992). The reasoning behind the decision to use the ZAF method in this study is found in Chapter 5.
Mineral fonnulae were calcdated using an APL cornputer program (Carmichael, 1999). -
This program works by converting probe data from weight % element to weight % oxide and Table 4.1: List of primary analytical standards used in the EMPA of sulphate minerals in this study. The standards were chosen based on expected concenvations of certain elements in copiapite and jarosite.
ELEMXNT LIST PRIhIARY STANDARDS SOURCE Fe S-332 - chalcopyrite sulphide L. Cabri, Western Mines S PRN-92B - barite sulphate A. Rainbow, Queen's University Pierina Gold Mine. Peru K S-96 - orthoclase silicate Ingamels and Suhr, Penn State Na S-205 - kaersutite amphibole Smithsonian USNM 143965 and silicate T. Frisch, GSC Al S-204 - glass silicate US National Bureau of Standards Mg S-204 - glass silicate US National Bureau of Standards Ca S-204 - glass silicate US National Bureau of Standards Si S-204 - glass silicate US National Bureau of Standards
Table 4.2: Expected composition of Marysvale rilunite standard (Stoffregen and Alpers, 1987) and typical EMP results from this study. Aiso included is the expected composition of stoichiometric pyrite and the results from a pyrite pain analyzed during the probe session. Ali values are expressed in wt % element. Oxygen values are calculated by difierence. n/a - not analyzed.
ELEMENT MARYS VALE 1 -3 3 4 5 6 ALUNITE (ideal) (grain) Si 0.00 0.06 0.00 0.00 0.13 0.00 0.00 0.00 0.09
H nia da n/a nia da nia nia da nia totais 100.00 100.06 99.96 99.93 100.00 100.00 100.03 computing the minera1 formula according to charge balance for each analyses. ft does this with the stipulation that a11 sulphur cations occupy 6 sites, therefore the program fills 6 of the 50 cation sites in copiapite with exactly 6.0 S. The rest of the cations are renormalized to satisfy the charge constraint. Sulphur was chosen as it is present in concentrations closest to the stoichiometric value,
4.4.1 Results
Copiapite grains were analyzed for 50 seconds, under a rastered beam of 0.1. Wt % elements were calculated for known copiapite species most similar to the data set in order to evaluate the results (table 4.3)- Raw probe analyses in wt % element are reported in table 4.4. Magnesium concentrations in sample 98CR04 range from 0.34 to 2.06 wt % element and aluminum 0.2 to
1.49 wt % element. The concentration of these two elernents is related in that the Mg-rich grains have lower Al and the Al-rich grains have lower Mg (figure 4.6). Six out of fourteen analyses have Mg concentrations chat correspond to the magnesiocopiapite composition. Four others have aluminum values near the wt % element content of Al-rich ferricopiapite or Al-rich aluminocopiapite. The four remaining are of intermediate composition. Iron analyses are higher
(1-2 wt 9% element) than those for magnesiocopiapite, and Al-rich ferri and aIu~nocopiapite.
Sulphur in the analyses is consistently higher than the calculated values by approximately 2 wt 6 element. Excess sulphur is reported by other authors however it is unclear whether the excess is real or a result of analytical or mathematical error (Zodrow, 1980; Bayliss and Atencio, 1985).
Analyses recalculated by APL (Carmichael, 1999) as wt % oxide and structural formulae are listed in table 4.5. A cation deficiency is more prominent in the Al-rich grains. This is likely due to the vacancy in the A site predicted by Fanfani et al. (1973) in copiapites with a trivalent cation present in the X site, as rnentioned in section 3.3.3.1. The high totals are most Iikely a result of minor bearn damage to the specimen (Goldstein et al.. 1992). Copiapite minerals are especially hydrous and may suffer structural water Ioss due to the heat from the beam current. This rnay
Table 4.4: Electron microprobe anaiyses of copiapite wiiected in the Richmon Mine. These are the raw probe data in wt 5% element.
Analyses (wc % element):
1 Si 0.11 Na 0.11
M_r 2.01 K 0.00 Fe 20.26 AI 0.28 S 17.34 Crt O. 10 O 59.78 H da tau 100.00
Oxygen is calculated by differencc. nia - not analysed. Magnesium and Aluminum in Copiapite
EMP analysis #
Figure 4.6: Magnesium and alurninum concentrations in 14 electron microprobe analyses of copiapite sarnple 98CR04PS-1 Table 4.5: Electron microprobe analyses in wt 5% oxide and structural formulae for copiapite from the Richmond Mine.
Analyses (wt C/o oxide): 1 Si02 0.24 A1203 0.53 Fe203 24.76 Fe0 3.83 Mg0 3.33 Ca0 O- 14 Na20 O. 15 Km 0.00 S03 43 20 H30 33.92 --- 110.10
Structural formulae: 1 Si 0.04 Au) O. 12 Fe3+ 3 -45 Fe?+ OS9 MC 0.92 Ca 0.03 N3 0.05 K 0.00 (-1 0.00 (+) 0.30 S 6.00 O 24.00 OH 3.00
(-) overall cation deficit in the formula (+) overall cation surplus in the formula Table 1.5 (continued): Eiectron microprobe analyses in wt % oxide and structural forrnulae for copiapite from the Richmond Mine. halyses (w 92 oxide): 8 Si02 0.43 A1203 3-57 Fe303 28 -45 Fe0 0-00 Mg0 0-66 Ca0 0.00 Na20 0.00 KO O-17 S03 44.20 WO 34.72
Stnictural formul ae: 8 Si 0.08 AM) 0.55 Fe3+ 3.88 Fe?+ 0-00 Mg O. 18 Ca 0.00 Na 0.00 K 0.04 !-1 0.28 (+) 0.00 S 6.00 O 23.00 OH 2.00 H20 20-00
(-) overall cation deficit in the fom-iula (+) overdi cation surplus in the IormuIrt occur without sigificant damage to the framework of the minerai (Fanfani, et al., 1973)- The
high totals may also be a reflection of variable water content in copiapite, indicating fewer than
20 water molecules in the structure. This possibiiity has been suggested by Zodrow (1980), who calculated between 16 and 20 water molecules in the structure,
The formulae for the copiapite analyzed for this study reflect a composition range from the mos t Mg-nc h:
(~g(~~è'+~.12))(~e~+~3~86}~1~.07))(~0~)6.08(o~~20 to the most Ai-rich:
1~~(~e3+~x~~l~~)(~04)s.08(~~2-2~~2~-
These analyses support the SEM work in that they indicate that the copiapite sampled in the D-
Drift of the Richmond Mine consists of two distinct phases: a predominant magnesium-rich phase and a secondary durninum-rich phase.
4.5 Trace Elements - Proton Microprobe Analysis (Micro-Pm)
As the purpose of this thesis is to examine copiapite and jarosite and how they influence mine drainage chernistry, it is necessary to examine mineral compositions on both a major and trace elernent scale. For this study trace elements were detected using micro Particle bduced X- ray Emission (micro-PIXE) analysis at the Scanning Proton Microprobe Laboratory at the
University of Guelph, under the direction of Dr- J.L. Campbell and Dr. 2. Nejedly.
As micro-PIXE is not weIl recognized and applied in quantitative studies of ore rnineralogy, an elementary introduction to the instrument and technique is included in Appendix C. The reader is referred to Cabri and Campbell (1998) and the references therein for a more detailed discussion of operating principles. Czamanske et al. (1993) provides more specific information on applying micro-PIXE in geoiogical investigations. 4.5.1 Results
Polished thin sections (98CR04PS-1 and 2) were coated in carbon and placed inside the chamber, one at a time, for analyses. The proton beam was rnagnetically focused to a spot on the surface of the specimen. The spot was first located under 60x mapification. and further manipulated using a computer keyboard under a 300x microscope equipped with a television canera. To start, a beam current of 10 nA and lOpm was applied tu the sample, however as the sample is predominantly composed of semi-rectangular platy crystals LO-50 pm thick, the grains quickly detenorated under this intensity. A reduced beam current of 1.4 nA was applied to avoid penetration into underlying material. The reduced current lengthened the analysis time to approximately 700 seconds as the stopping time corresponds to charge accumulation. Usually at
400-500 seconds a sizable hole appeared in the grain (- 10 pm). The analysis was terminated when the charge reached 1 pC. As copiapite and jarosite are both iron bearing rninerals usually a filter would be chosen that would reduce the contribution of iron X-rays (2I 26). In this case iron X-rays were included to qualitatively compare PIXE results to those of EMPA.
For this session, an Al-mylar filter (150 microns thick) in combination with a Mylar filter
(125 microns thick) were used to stop the backscattered protons and reduce the intensity and number of X-ray photons with Iower energy and longer wavelength.. These filters attenuate iron
X-rays by almost 3 orders of magnitude. therefore the iron concentration data may carry a high error. The quantitative use of any data below the atornic number for copper (2= 29) is not recomrnended.
These analytical conditions were considered acceptable as analyticai consistency was achieved from grain to grain and the iron analyses by PIXE corresponded with iron composition obtained using EMPA. Each analysis was evaluated independently by ensuring an acceptable fit error and limit of detection (LOD). The concentration reported must be 3x above the LOD in order for it to be considered real. In addition. it is important to examine the spectra for each analysis to see if any of the observed peak are residuals. The raw data for this study and furrher
discussion of detection limits, fit error and confidence leveIs is included in Appendix C.
Significant trace element data for copiapite sarnples 98CR04PS-1 and 2 are reported in table
4.6. The average compositions are as follows: Zn (- 1420 ppm), Cu (- 270 ppm), and As (- 64
pprn). Zn and Cu are lmown to substitute in the X site (equation 2.2). Presumably AS" replaces
~e)+or AI^' in the R site. Some analyses show appreciable amounts of other elements. Co in
particular. The amount of cobalt is questionable as it rnay be inffuenced by the iron (Cabri and
Campbell, 1998). Other elements anaiyzed are not present in concentrations 3x that of their
LOD. Iron concentrations average at approximately 203 ppt (parts per thousand), roughly 1 ppt
less than that measured by EMPA. This is considered a fair correlation.
4.6 Crystal Structure
X-ray diffraction techniques helped confirrn the initial identification of many minerals collected for this study and were valuable tools in deterrnining specific species of copiapite, jarosite and related rninerals. X-ray laboratones at Queen's University (under the direction of
AIan Grant) and RMC (under the direction of Bob Whitehead) were used during the course of the study. Al1 X-ray work was supervised by Dr. Ron Peterson.
Mineral identification was deterrnined with powder diffraction analysis. Samples were air dried (when necessary), ground with monar and pestle, and mounted with VaseIine on a glass slide. A Siemens powder diffractomerer with nickel fîltered Cu Ka-radiation (A= 1.5318 A) was used at Queen's University. Samples were scanned from 6" - 60" 29, with a O.1° step and a 6 second preset time. The patterns produced were then matched by computer with ICDD (Joint
Cornmittee on Powder Diffraction Standards, 1997) mineral diffraction files to characterize the specimen (table 3.1). Table 4.6: Si,onificant trace eIements in copiapite sample 98CRWPS-L and 2. obtained by micro-Pm.
Zn Cu CONC ERROR LOD CONC ERROR LOD (PPM) (56 FET) (PPM) (PPM) (96 F.TT) (PPM) Techniques used to determine ce11 parameters and characterize the phases present in the
copiapite samples required precise sample preparation and data collection to avoid probtems
associated with preferred orientation and multiple phases. Copiapite sarnple 98CR04 was
removed from its sealed container in the incubator and carefully side-packed into a flat, square,
alurninurn holder (2.5 x 3.5 cm x 1 mm). The holder was mounted in a Scintag XI powder
diffractometer at RMC. The matenal is quite dense and sticky, making it difficult to manipulate-
Great care was taken to avoid massaging the sample whiIe packing, as this aligned the platy
crystals of the copiapite, creating a strong preferred orientation. Drying the sample to create a
powder was not an option as new phases formed soon after it was rernoved from the contziner.
Coquirnbite [F~~+(SO.&.~H~O]peaks began to complicate the copiapite pattern when drying was
attempted. The sample was scanned with nickel filtered Cu Ka-radiation (A = 1.5418 A) from 5'
- 100" 28, with a 0.02' step and a 10 second preset time. The analysis took 866 minutes. Minor
phase changes that 1ikeIy occurred due to oxidation and evaporation during the sample
preparation and analysis tirne were unavoidable. The rnost relevant low angle refraction data was
measured within the first two hours of the analysis-
4.6.1 Results
The diffraction pattern reveals two phases of copiapite (figure 4.7). Unit ce11 parameters for
the primary phase were deterrnined according to the peak positions and intensities of the pattern
using the cornputer programs Win-Fit and Celsiz. The ce11 volume was calculated using the
following equation:
When compared to the known ce11 dimensions of copiapite group rninerals, the primary phase present in the diffraction pattern correlates with other magnesiocopiapite niinerals (table 4.7). 4 secondary
O i i//j I 11 't ii i 11 11 L11 11 11 11 -2 O00 -
4 000 8 9 10 11 12 13 14 15 2-THETA
Figure 4.7: Part of the difitaction pattern for copiapite sample 98CR04 showing the characteristic peaks for two phases: (1) prîmary - magnesiocopiapite with strong peaks at approximately 9.5 and 14.3 degrees 2-theta, and (2) secondary - ferricopiapite with weaker peaks at 9.8 and 14.7. The observed data is denoted with black crosses (+) and the solid red line fohgthe peak expresses the Rie~eldfit. The stretched blue crosses below each peak indicate the quaiity of the fit. The closer together the two crosses are the better the fit The lower blue line represents the observed counts minus the calcdated counts, obtained fkom the Rietveld refkement for the main magnesiocopiapite phase. Rietveld dysisis explained in section 4.6, Table 4.7: Unit ce11 parameters for the two phases of copiapite found in 98CRW with other minerals in the copiapite group summarized fiom X-ray diffraction data in the iiterature by Bayliss and Atencio (1985). The ce11 dimensions and volume of the primary phase fa11 wirhin the range of magnesiocopiapite and those of the secondary phase match with femcopiapite. See BayIiss and Atencio (1985) and the references therein for more information on the different types of copiapite Iisted here.
MINERAL a b c a B Y CELL VOLUME rnagnesiocopiapite 7.351 102-17 98.79 985.7926 98CRM (primry) magnesiocopiapite magnesiocopiapi te rnagnesiocopiapite copiapite zincocopiapite duminocopiapite Ferricopiapite cdciocopiapite femcopiapite . ferricopiapite ferricopiapite ferricopiapite femcopiapite 98CROJ (secondary) ferricopiapite cuprocopiapite CeIl parameters for the Iess prorninent secondary phase were estirnated given the Iow intensity of
the diffraction peaks, other than the {OKO) reflections. The (020) peak position for the b-axis is estirnated at 8.97O 20 (17.94 A), therefore the second phase matches well with the ferricopiapites
Iisted in Table 4.7. This is an acceptable cornparison because the b-axis shows the rnost variability among the copiapite group rninerals. The other parameters were borrowed from the prirnary phase to obtain an estirnated ce11 volume.
Peaks in figure 4.8 were cut out and weighed on a balance to estimate the percentage of each phase- According to this method approximately 97% of the copiapite in sarnple 98CR04 is magnesiocopiapite and the rernaining 3% is femcopiapite. This result correlates well with the
SEM work, but is not supported by the EMPA. In the probe analyses, only slightly more grains were Mg-rich than Al-rich, suggesting that the two phases occur in relatively equal proportions.
However, the visual evidence and qualitative EDS supplied by the SEM is more compeIling than the probe results. The distribution of AI-rich vs. Mg-rich grains throughout the sample is not hornogeneous, consequently the spots analyzed by microprobe were areas that had ciusters of the
Al-rich spheroidal aggregares. Overall, the ratio of phases in the sample is probably closer to that found by weighing the peaks.
An attempt was made to do site refinements on copiapite sample 98CR04 using Rietveld analysis. This method uses least squares to refine atomic coordinates for an observed pattern of a mineral and provides details on the individual sites within the mineral structure. A refinement makes it is possible to distinguish structura1 changes due to atornic substitution, and determine the capability of a particular minera1 to contain certain elements in its structure. The program refines the atornic structure using positions and intensities of the lines in the observed pattern (figure
4.7). In this study, problems of preferred orientation and multipIe phases complicated the difiaction pattern, making it impossible to successfuily complete a Rietveld analysis. Only the diffraction patterns obtained from this detaiIed work are used here. For a discussion on how to magnesiocopiapite
ferricopiapite
Figure 4.8: The relative percentage of the two phases present in the sample 98CR04 was determineci fiom these peaks in the difhction pattern. The peaks were cut out and weighed on a balance. Approxhate percentages : magnesiocopiapite = 97%; femcopiapite = 3%. use the Rietveld me thod to describe crystal-chernical variations within a mineral structure see
Peterson et al. (1998).
4.7 Solubility
Supernatant from copiapite samples 98CR03 and 04 were analyzed in the USGS laboratory
in Boulder, Colorado for dissolved cations and anions, as well as Fe and As speciation (table 4.8)-
These sarnples were collected from the sarne minera1 pile and therefore serve as field
dupiicates. Al1 three samples were filtered (0.45 pm pore diarneter membrane) to rernove
particulates. Two samples were acidified with HN03 for cation andysis and HCI for Fe and As
speciation. Acidification is usually done to preserve the integrity of the sample by preventing the
precipitation of solid phases. The acidified version of a sample may therefore generally have a
slightiy higher concentration of dissolved cations than the unacidified version. Due to the already
high acidity of these samples, acidification had little effect. The difference in the FA and FU samples is srnaIl and consistent. The error of the analysis in this case is Iarger than the dilution, therefore no correction was performed on the acidified data (McCleskey, 1999). Only the FU data was interpreted for this project.
The degree of saturation of these pore-waters is particularly irnpressive when compared to zcid mine waters rneasured elsewhere at Iron Mountain and other extreme examples from locations around the world (table 1.2). This copiapite pore-water has possibly the highest dissolved femc iron concentration ever reported.
When cornpIete water analyses for the major ions are available, usually a speciation computation can be done to determine the state of saturation with respect to any particular rninerals for which thermodynamic data are available. Currentiy there are no thermodynarnic data for copiapite rninerals. However, the mineral pore-water in samples 98CR03 and 04 is presumabIy in CO-existenceor near equilibrium to the mineral phase therefore it should be Table 4.8: Cations. anions. and densities of copiapite pore-water sarnples 98CR03 and 04. Methods: cations - Na, K. and Li by Flame Atornic Absorption Spectrometry (FAAS); ail others by Inductively CoupIed Plasma - Optical Ernission Spectrometry (ICP-OES); anions - Ion Chromatopphy (IC);Fe(T-tord) and Fe(n) - FerroZine; As0by Rame Ion Absorption Spectrometry (FLAS). Abbreviations: FA - filtered acidified with HCI (Fe. As) and HN03(cations); FLJ - filtered unacidified (anions); n/a - not anal-vzed. UNITS 98-CR-O3 98-CR-03 98-CR-04 FA FU FA Temperature OC
density e/mL 1.5218 1.5218 possible to calculate a solubility constant for one of the two copiapite phases present in the sample.
The solubility of copiapite minerals at 2S°C can be described as:
where Keq is the unknown equilibriurn constant and a is the activity (effective concentration).
The activity of aqtieous solutions is defmed by: a =pz where ni is molality (concentration or mols of solute per kilogram of water) and y is the activity coefficient, The relation between the activity or effective concentration and the molality or actual analytical concentration of a substance (i.e. those reported in table 4.8) is expressed by rneans of the factor of the activity coefficient. In general, activity coefficients of ionic species are near unity in dilute solutions and rise above unity in concenuated ones. Departures from ideality in ionic fluids are due to interactions between the vanous ions in solution. The total concentration of ions in aqueous solution has to be corrected for the effect of electrostatic shielding and for the presence of aqueous complexes. In the presence of charged solutions, additional electrostatic shielding occurs and the reactivity of the ion is reduced. The activity of the ion approaches its molal concentration as the concentration of al1 solutes approaches zero (Drever, 1997).
The effect of a high concentration of solutes is expressed as the ionic strength of the solution.
It differs fiom total concentration in that it considers the greater electrostatic effectiveness of polyvaIent ions. Activity coefficients of the dissolved constituents are normatly calculated fiom the ionic strength according to methods such as the extended Debye-Huckel equation, the Davies
equation, or a Brgnsted-Guggenheim equation. These models allow activity coefficients to be
calculated on the basis of the effect ionic interactions should have on free energy. These methods
are not applicable to solutions with ionic strengths greater than 0.1 rnolal (Alpers and Nordstrom,
1999). The copiapite pore-water is a highly concentrated solution. In this case, Pitzer equations
(1987) are used to define minera1 equilibria- Pitzer allows for activity coeffkients to be fit to
experimental data for ionic strengths up to 10 molal and higher. This model is considered to be
the most successful in predicting the solubilities of highly soluble salts and modeling very
concentrated waters (Drever, 1997). The mode1 assumes al1 ions interact to some degree and
these interactions are incorporated into terms that are added to an electrostatic Debye-Hückel
term (Alpers and Nordstrom, 1999).
There are drawbacks with the application of the Pitzer model to acid drainage waters.
Insufficient data are available to model the activity coefficients for al1 the trace elements found in
acid mine waters, particularly femc iron. Interaction parameters and temperature dependence for
al1 constituents must be defined in order to completely describe the system (Alpers and
Nordstrom, 1999). Ongoing research on the ~r"-~e-H2SOd-H20 system will contribute to the therrnodynarnic database, allowing for more sulphate minerals to be considered in geochernical models of acid drainage waters. At this time only the actual analytical concentrations of the species in the copiapite pore-water solution will be reported.
4.8 Discussion
In studying the copiapite and its pore-water it is possible to observe, on a small scale, the evolution of mine water due to changes in the geochemical environment and to see the different elements that are incorporated into the minera1 structure as a result of those changes. These observations can be applied to the overall picture in three ways. It is possible to determine (1) how and why secondary minerais sequester elements, (2)how geochernicai waters evoive, and (3)
how individual minerals can influence the overall effiuent quality.
The data collected from SEM, XRD and EMPA identify two phases of copiapite in sample
98CR04: (1) rnagnesiocopiapite and (2)aiuminum-rich ferricopiapite- Micro-PIXE analyses
indicate that Zn, Cu and As are the most common trace elernents substituted into the structure of
the copiapite from the Richmond Mine- The predominance of these particular trace elements is
due to the relative high concentration of the sarne elements in the pore-water.
Textural relationships prominent in scanning electron photomicrographs illustrate that the
magnesiocopiapite phase is predominant in the sample and that it was likely the prirnary phase. It
probably forrned within the Richmond Mine with the Al-rich ferricopiapite forrning from
subsequent oxidation and evaporation of minera1 pore-water. It is difficult to Say with certainty
whether this second phase formed due to an altenng geochemical environment within the mine or due to changes incurred following removal frorn the mine.
The existing pore-water is mainly composed of sulphate, ferric iron, ferrous iron, alurninum and magnesium, with lesser amounts of zinc and copper. The prevalence of femc iron and alurninum in the pore-water suggests the fluid may be supersaturated with respect to alurninum- rich ferricopiapite. The predominance of magnesiocopiapite in the sample implies that previously magnesiocopiapite was the supersaturated phase. Perhaps dunng sample collection andlor through processes of sample preparation and analysis, the geochernical environment evolved and becarne more oxidized, stabiIizing a copiapite more rich in ferric iron relative to ferrous iron.
This, in turn, allowed for substitution of trivalent Al creating spheroidal aggregates of aluminum- nch femcopiapite.
The streams of effluent emptying from the A, B and C drifts of the Richmond Mine are characterized by extremely high ferrous iron, sulphate, zinc and aluminum concentrations (table
4.9). The geochernical characteristics of this water compared to that of the copiapite pore-water imply a very different geochemical environment. Table 4.9: Cations, anions and densities of the effluent streams running from three of the four drifts in the Richmond Mine. Methods and abbreviations are the same as those used to describe copiapite pore-water in table 4.8.
C Drift A Drift B Drift 98CA102 98CA102FU 98CA103 98CA103FU 98CA101 98CAl 04FU Temperatur 48.1 48.1 39.4 39.4 37.9 37.9 1 .O 1 .O 1.1 1.1 < 1.0 < 1.0 redox 390 390 375 375 374 374 specific 89 000 89 000 71 000 71 000 Il O000 11 O000 conductance FdT) Magnesium and alurninum-rich copiapites are forrning in the end of the D-Drift of the
Richmond Mine due to a number of factors. The thermodynarnics of the system are determined by the characteristics of the water and air in the imrnediate geochemical environment- Iron
(predominantly ferric), sulphate, aiuminum and rnagnesium are sign;f~cantlyconcentrated in mine waters of a particular pH, Eh, temperature and conductivity. The end of the D-Drift is relatively dry and stagnant with an air temperature in excess of 30°C. These factors combine to make a complex geochemicai environment conducive to the formation of magnesiocopiapite and Al-nch femcopiapite.
Given its high solubility, there is litde doubt that the dissolution of large quantities of copiapite during a wet season wouId cause a short-term increase in iron and sulphate concentrations in the effluent. The relatively high solubility of copiapite rnay explain why piles of it were found forming in the more dry areas of the mine, such as in the D-drift. During dry seasons, these copiapite rninerals may temporarily sequester sorne elements such as Mg, Al, Fe, and S04, but not all. It is important ro take into account the limitations of the crystal structure in addition to the overall geochemical environment when considenng which elements will be precipitated or dissolved. For example, given the high concentration of zinc that is present in the effluent and copiapite pore-water, it is reasonable to expect to find some zincocopiapite. Zinc is incorporated in large quantities in other iron sulphates at Iron Mountain such as mehterite, szomoInokite, and voitaite (Jarnieson et ai., 1999). Perhaps it is because zinc has an aversion to the copiapite octahedral sites that none appears to have fonned (Burns, 1970).
Examining the composition of thz pore-water coexisting with these rninerals provides insight into the relative solubility of the mineral phase. The precise solubility of the minera1 phase can only be suggested, due to the lack of thermodynarnic data for copiapite group minerals. The pore-water analyses can be used to perforrn speciation calculations with respect to the copiapite rninerals when the interaction parameters for the ~e'+-~e-H2S04-H20 system have been more clearly defined. Speciation calculations can then be used to indicate the degree of saturation with respect to various copiapite rninerals and predict which reactions are possible thermodynamically,
Sirnilar work with other sulphate minerals associated with copiapite will clear up any ambiguity surrounding the paragenesis of these minerais. Resdts wiI1 promote a bener understanding of more concentrated mine water systerns and will improve treatment and remediation strategies. 5.1 Introduction
This chapter describes the crystal morphology, structure and chemisuy of the jarosite mineral samples seiected for this study. The composition of drip-water collected from jarosite stalactites and mud pore-water is reported. Saturation indices of minerals associated with the drip-water are assessed using the aqueous speciation program WATEQ4F (BalI, 1987, 1999).
A petrographic microscope was used to study thin sections under transmitted and reflected light. Scanning elecuon microscopy distinguished crystal textures, grain size and rnorphology of phases present in the sarnples. Powder X-ray diffraction was used to confirrn rnineral identification. A minor, poorIy crystalline phase occumng with jarosite was examined using single crystal techniques, with a Gandolfi camera. Major elements were determined with an electron microprobe and a proton probe detected trace elements. The average rnineral compositions and structural forrnulae were cakulated using an APL cornputer program
(Cannichael, 1999).
Jarosite stalactite drip water and mud pore water was characterized by the following methods:
Inductively CoupIed Plasma - Optical Emission Spectrometry (ICP-OES) for al1 cations except
Na, K,and Li which were analyzed by FIame Atornic Absorption Spectrornetry (FAAS); anions were determined with Ion Chrornatography (IC); FerroZine (Stookey, 1970) was used for Fe(T- total) and Fe(II); and As(III) was detennined by Rame Ion Absorption Spectrometry (FIAS).
Refer to Chapter 4 for detailed descriptions of equipment and techniques used to study both copiapite and jarosite. 5.2 Sample Description and Petrographic Summary
Stalactites (98CR14), mud (98CR15) and cmst (98CR20) predominantly composed of
jarosite were exarnined in hand specimen and polished thin section, Table 5.1 lists prominent
features observed in each.
5.2.1 Stalacrites
Under the binocular microscope the stalactites are a dull orange-yellow colour (Munsell:
2.5Y 6-7/7-8)- Some srnall grains (c2 mm) of pyrite, gypsurn and quartz are loosely adhered to
the rough outer surface of the sample. FIaky orange and dark red (5Y 98)inner rings are visible
in cross-section. Most samples have an obvious hollow centre to accommodate the passage of drip water.
Three polished thin sections of stalactites were studied in detail:
(1) 98CR14TS-A - Iength cross-section (figure 5. laj,
(2) 98CRl4TS-B - length cross-section (figure S-lb), and
(3) 98CR14TS-D - end cross-section (figure 5. lc).
Jarosite appears similar in al1 three stalactite sections and other thin sections of jarosite samples.
In uansmitted Iight the grains are rounded, yeliow-orange blebs (figure 5.2). The blebs Vary in size but are dl under 40 Fm- OccasionaIIy, under high rnagnification, they display colorful birefringent fibers that radiate outwards- In the stalactite thin sections, distinctive layering of blebs is apparent. varying in colour and grain size (5. lc). Changing conditions in the mine
(temperature, pH, oxygen level. and presence of water and bacteria) which rnay alter jarosite composition dunng the stalactite formation rnay explain the variance in colour and texture in the layers.
Minor pyrite grains are found as incIusions in the stalactites (c 1%) (figure 5.3). The grains are small (c50 pm), anhedral, and very degraded. The surrounding environment in the mine is Table 5.1: Notable features observed in hand sampIe and thin sections of jarosite minerai samples from the Richmond Mine.
SAMPLE # TYPE HAND SAMPLE THIN SECTION 98CR13 stalactites 1. du11 rutcolour 1. yellow-orange-brown thin sections: small grains of pyrite, spheroidal pins(< 40 p m) in 98CR14TS-A gypsum, and quartz on transmitted light (end cross-section) surface (c2 mm) 98CR14TS-B 2. obvious rings (14D) (length cross-section) 2. inner rings 98CR13TS-D 3. patches of red mineral (length cross-section) 3. semi-hollow centre alteration ( 14A)
4. solid mineral consistency 98CR15 mud 1- Iike smooth mustard in 1. clumps of powder thin section: (centrifuge colour and consistency 98CRls'TS-A residual) 2. dark-orante-yellow to (dried mud) 2. contains srna11 grains of opaque in transmitted light pyrite and gypsurn (c05 mm) 98CR20 crus t 1- red-brown mineral occurs 1. small, anguku partides (I thin section: with jarosite 0.5 mm) 98CR2OTS 2. solid minerd consistency 2. associated with edges of jarosite mineralization Figure 5.1: Photographs of three jarosite stalactite thin sections: (a) 98CR14TS-A: length cross-section, (b) 98CR14TS-B: length cross-section, and (c) 98CR14TS-D: end cross-section. Important features are indicated in each figure. Vertical sde:2 cm (a and b), 1 cm (c). Figure 5.2: Photomicrographs of typical jarosite in transrnitted light. Note the variable grain size as both photos are taken at 40x. The crystals appear as rounded, yellow-orange blebs. Scale bars equal44prn. Figure 5.3: Photomicrographs showing minor pyrite inclusions in the jarosite staiactites in transmitted (top) and reflected light (bottom). The grains are srnail (c 50 pm), anhedral, and very degraded. Scale bars equal 176 Pm. predorninantly loose pyrite. Consequently, it is possible these grains were introduced to the
sarnple during coIlection or they may have traveled through the stalactite in the drip water.
Some stalactites have patches of poorly crystailine red-brown (10R 3/4) materid on outer and
inner surfaces (figure 5.la)- It is rnostly opaque in transrnitted light, but in places small red-
brown grains are visible. It is impossible to identiQ by optical methods, but the environment in
which the staiactites are forrning would indicate that it is probably amorphous iron oxide or femc
hydroxide.
5.2.2 Mzfd (centrifuge residual)
The jarosite rnud was spun in a centrifuge for 20 minutes to separate the pore-water fiom the
minera1 sarnple. It has the consistency and colour of smooth mustard (2SY 7/6)and contains
small grains of pyrite and gypsum (< 0.5 mm). The sample was air-drïed for 24 hours and thin
section 98CRlSTS-A was made from the powder (figure 5.4). Most of the section appears dark
orange-yellow to opaque in transmitted lighr. Anhedral pyrite grains are visible in reflected light
(< 1%).
5.2.3 Crust
SampIe 98CEU0 was selected for further analysis because it contains a substantial amount of the minor, poorly crystalline red mineral obsrrved in the jarosite stalactite samples. It was necessary to define this phase in order to do accurate speciation computations. The mineral is deep brown-reà in colour (10R 3W4-6) and it is closely associated with jarosite in the muddy section of the D-Drift wall. It appean much the same in this sarnple as in the stalactite samples, except it is more abundant and more easily isolated. In thin section it is red to opaque in colour and it may occur as small angular particles nmming jarosite (50.5 mm) or as interesting textures within the jarosite mass (figure 5.5a and b). Figure 5.4: Photograph of thin section 98CR15TS-A, the jarosite mud sample. Note how the mineral powder has dried in clumps. Vertical scale: 2.5 cm, Figure 55a: Photograph (top) and photomicrograph (bottom) of thi.section 98CR20TS. This is a sample of trust removed fkom the wali of the D-Drift. It is predomimmtly composed ofjarosite, but has a signincant amount of the poorly crystalline red-brown mineral. In these photos the red-brown mineral is associated with the edges of the jarosite and it occurs in platy, angular clumps. The scale bar in the top photo is 4 mm and in the bottom it is 88 pm. Figure 5.5b: Photomicrographs of textures of the red-brown minera1 closely associated with jarosite. It rnay occur as a rim around the edge or as alteration within the jarosite. Scale bar equals 88 pm in the top photo and 44 1m in the bottom photo. 5.3 Scanning Electron Microscopy
Pieces of the stalactites (98CR14a) were mounted on disks and coated with carbon for
analyses at Queen's University and gold, for that at RMC. The SEM images show rhombohedral
crystals, no Iarger than 10 prn in diameter. Many grains are partially encrusted with finer grained
Iight coloured nodules identified as sitica with qualitative EDS (figure 5.6). Jarosite mud
(98CR15b) was also mounted on a disk and carbon coated. These images show perfect
rhombohedra, Iess than 8 pm in diarneter (figure 5-7)-No other phases were identified-
5.4 Major EIements - Electron Microprobe Analysis
The ARL-SEMQ Electron Microprobe at Queen's University was used to perform major
elernent analyses on the stalactites, mud and crust to determine the composition of jarosite in each. Probe resuIts aIso aided in the identification of unknown phases present in the samples.
Standard analytical conditions. operating procedures and details on the standards chosen for this study are provided in section 4.4 of Chapter 4. The same methods were applied to both copiapite and jarosite, as they.are both reIatively fragile iron sulphates.
5.41 Jarosite Results
Thin sections of jarosite stalactites (98CR14) and mud (98CR15)were analyzed for 50 seconds under a rastered beam of O. 1, Wt % element values frorn ideal jarosite formulae with similar compositions to the unknowns were calcdated in order to evaluate the results (table 5.2).
Representative analyses of the stalactites in wt % elexnent are given in table 5.3. The same analyses in wt % oxide and the corresponding structural formulae are Iisted in table 5.4- Al1 mud probe analyses in wt % element are in table 5.5 and the matching wt 96 oxide data and formulae are in table 5.6. A complete list of al1 the probe data and minera1 formuIae calculations for the jarosite stalactites are included in Appendix B. Low totals in the wt 8 oxide data are rnainly Figure 5.6: Scanning electron micrograph of jarosite stalactite sample 98CR14a. The jarosite crystals are rhombohedral and coated in a £ke grained material identified as silica with EDS. Figure 5.7: Scanning electron micrograph of jarosite mud sample 98CR1 Sb. The crystals are rhombohedral in shape. No other significant phases are obvious. Table 5-2: Calcuiated wt % elements for the most cornmon jarosite species (Fleischer and Mandarino, 1995).
potassium jarosite hydronium jarosite natrojarosite Na 0.00 0.00 4-74
total 100.00 100.00 100-00 Table 5.3: Representative eiectron microprobe analyses of jarosite stalactites (%CR 14) collected in the Richmond Mine. These are the raw probe data in wt % element The complete dataset ic in Appendix a
Analyses (WC % element):
Oxysen is calculated by clifference. da- not analysed. TnbIe 5.4: Representative eiectron microprobe analyses of jarosite stalactites (98CR13)colIected in the Richmond Mine.
Analyses (wt % oxide): 1 A1203 0.3 8 Fe203 43.87 Fe0 0.00 Mg0 0.00 Ca0 0.23 Na20 0.00 =O 8-00 S03 31.19 H30 10.53
Structural fodae: 1 N6) 0.04 Fe3 + 3.87 Fez+ 0.00 Mg 0.00 Ca 0.03 Na 0.00 K 0.59 H30 0.11 (-1 0.03 s 2-04 O 8.00
(-) this row displays the overalt cation deticit in the formula. Complete data set is in Appendix B. Table 5.5: Elecuon microprobe analyses of jarosite mud (98CR15) coiiected in thc Richmond Mine. These are the raw probe data in wt 8 element
Analyses (wt % element): 36 Si 0.45 Na 0.59 M,o 0.00 K 3.04 Fr: 30.36 Al o. 17 S 12.80 Ca 0.00 O 53.60 H n/a n/a da da nia totals 99.99 100.00 99.99 99.98 99.99
Oxygen is caiculated by difference. da- not anaiysed. Table 5.6: Electron microprobe analyses ofjarosite mud (98CRI5) coliected in the Richmond Mine.
halyses (wt % oxide): 36 Si02 0.96 A1203 0.33, Fe303 43 -40 Fe0 0.00 Mg0 0.00 Ca0 0.00 Na20 0.80 E(20 2.46 S03 3 1.96 EO 11.63
Structurai formdae: 3 6 Si 0.08 AW) 0.03 Fe3t 2.78 Fez+ 0.00 Mg 0.00 Ca 0.00 Na O. 13 K 0.37 H30 0.60 (-1 0.07 S 2.04 O 8.00 OH 6 -00 6.00 6.00 6.00
(-) this row displays the overall cation dettçit in the formula attributed to the srnaIl grain size of the jarosite (< 5 pm). It is possible that for many of the
malyses the elecuon beam was not completely centered on the grain- A smaller point beam was
not used because it was found that it caused sarnple darnage (Rainbow, 1999). The presence of
trace elements and excess water in the structure, as weil as probtems of non-stoichiometry
discussed further below rnay also contribute to the low totals.
AI1 samples have significant concentrations of potassium (2.04 - 6.97 wt % element), but faIl
short of the calculated potassium concentration in the potassium-jarosite end member of 7.8 1 wt
% element. Sodium is not present in significant arnounts (c1 wt 96 e1ernent)- A continuous
solid-solution series exists between K-Na-H30 jarosites, as a result of element substitution under
Iow temperature and pressure conditions (Brophy and Sheridan, 1965), therefore the low K
content in the Richmond Mine jarosites is probably due to hydronium substitution- It is not
possible to analyze hydrogen with the electron microprobe but the continuous solid-solution
aIlows for the hydronium content of the jarosite to be calculated according to charge balance-
Calculated mineral fonnulae for both the stalactite and the mud are plotted in figure 5.8.
The iron content in the stalactites ranges from 29.1 to 32.79 wt 96 element and 24.9 to 33.59
wt 9% element in the mud. The majonty of analyses lie below the caiculated values for jarosite
(33.43, natrojarosite (34.57) and hydronium jarosite (34.85). Iron deficiency in synthetic jarosites is not uncommon. as discussed in Chapter 2 with respect to Fe:S ratios (Hartig et al.,
1984, 2.202 to 2.572; Ripmeester et al., 1986, as low as 2.33:2; Alpers et al., 1989,2.85:2 to
2.96:2; Baron and Palmer, 2.792, 1996). The Fe:S ratios of the jarosites in this study are
between 2.492 to 2.8 12.
Sulphur concentrations faIl between 12.62 to 13.8 L wt 9% element in the stalactites and 10.86
to 13.19 wt % element in the mud. Most exist within the range of the three calculated values: K- jarosite (12.80), Na-jarosite (13.23) and hydronium (13.34). Oxygen calculated by difference
ranges from 48.69 to 58.29 wt %, slightly below expected amounts of oxygen in the three most comrnon forrns of jarosite (table 5.2). The higher values discemed from the analyzed samples Figure 5.8: Compositioo ofjarosite stalactites (98CR14)and rnud (98CRL 5) in K-Na-H,Otemary. Stalactite data is denoted with open symbols and mud are closed. Both forms ofjarosite found in the Richmond Mine plot within the same mge. rnay be a result of other elements present in trace amounts that were not analyzed by the probe
(section 5.5).
The EMP did detect some silicon in the jarosite stalactites (< 0.53 wt 96). It was not included
in the stoichiometric calcuIations because evidence from SEM indicates that the siiicon occurs as a separate phase.
5.4.I.I Evaludng ZAF
The wt % element results were generated using the ZAF correction scheme, which accounts for three major matrix affects: atomic number (Z), absorption (A), and fluorescence (F). The
#pz) correction method was applied to the jarosite stalactite data set to determine if low iron values obtained with ZAF were true or a function of the program. A cornparison of the resuhs for five representative analyses is shown in table 5.7. Iron results increase by 1.0 wt % element with
#pz) bringing the average closer to the expected iron content for jarosite. Silicon, sodium, rnagnesium, aiuminum, and calcium values remain the same, occasionally increasing with @pz) by 0.01 wt % elernent. Potassium increases 0.1 wt % element on average. Sulphur increases 0.2 wt 9% element.
In addition, comparisons of the two correction rnethods were made using the alunite standard analyses (table 5.7). Potassium increases approximately 0.3 - 0.6 wt % element, closer to ideal amount. Aluminurn increases by approximately 0.6 wt % element. Al values using ZAF are below the ideal arnount and with $(pz) they are above the ideal by 0.1 - 0.3 wt 96 element.
Sulphur values with ZAF are higher than they should be by roughIy 0.4 wt % elernent and with
@(pz)they increase by an additional 0.5 wt % element. The other elernents (Si, Na, Fe, and Ca) are unaffected by @pz) corrections.
The validity of the ZAF method was originally qucstioned due to the high sulphur result observed in the copiapite analyses and the iron deficiency seen in the jarosites. The #pz) method Table 5-7: Thse LWO mblts compare the ZAF rind PR2 correction pm~pms.The top shows five diffmtjdte dactift: analyses 11.1. 10. 1 1. and 16 j and the bottom shows represenfative ;Mîrysvale aiunite standard analyses.
wt 8 clcmcntr
Z4F PRZ ZAF PRZ ZAF PRZ ZAF PRZ ZAF PRZ
oxygcn calcuhtcd by diffcrcncc idcal - Stoffregcn and iUpcrs, 1987 da- not analyscd was applied to the jarosite analyses as a test, in an attempt to improve the results. Jamieson
(2000) found that for probe andysis of voltaite and szornolnokite, NE) corrections increased the
wt % element values of both Fe and S by 1 to 2 %- As low iron in jarosites has been documented
in the litenture as a cornrnon problem. the results obtained by ZAF in this study no longer appear
questionable. The observed increase in S content. upon applying Npz) corrections to the jarosite
and alunite standard data, indicate chat this would not solve the problem of the higher than ideal S
reported in the copiapite. In light of these discoveries, the validity of the ZAF method as an
acceptable correction program for the sulphates analyzed in this study is confirmed.
5.42 Unknown red minera1
Microprobe analysis of the red rnineral associated with the jarosite was attempted in order to
gain an understanding of the major etement composition of the material and allow for a proper
identification. The gains were analyzed for 200 seconds, under a point beam. A hematite (new -
Island of Alba) and magnetite (S-33 1) standard were probed as secondary anaiytical standards dong with the Marysvale alunite. Preliminary qualitative probe work on this mineral indicated
that it was an iron oxide or oxy-hydroxide. It was speculated, given the environment in which it
fonned, that it was possibly ferrihydrite, goethite, or hematite.
In transmitted Iight, the beam was focused on a deep red area on the section occurring within the jarosite. Backscattered eiectron irnaging (2000~)was used to distinguish the jarosite from the red rnineral. Brightness corresponds to the atomic number of elements present in the sample. An iron oxide (ferrihydrite, hematite. goethite) should be bnght compared to an iron sulphate
(jarosite) as it has more iron. Many of the brighter grains (iron-rich) are relatively well crystallized with several grains displaying distinct grain boundaries, but others have an anhedral rnorphology with non-distinct grain boundaries. In addition, the surface of many of the grains does not appear completely "smooth". Varying intensities of bnghtness across the grain surface indicate possible heterogeneities in the structure of the mineral created by fluctuations in element
content observed in the analyses. Table 5.8 compares 7 representative analysis with wt %
element values of comrnon iron oxides. The other 19 analyses are found in Appendix B.
There is significant sulphur present in 6 of the 26 analyses- These six are probably jarosite
grains. Al1 S present in significant amounts are above what is characteristic of schwertmannite
(4.15 wt % element). Iron varies from 44.98 - 69.03 in the analyses without sulphur, This falls
into the rather generous range of the calculated wt % element for femhydrite, but also goethite. It
is just under the expected Fe wt % elernent for hernatite. It is interesting to note that Fe content
varies between two analyses within the same grain ( 9-10.21-22 and 25-26 in Appendix B).
Significant (> 1 %) Ca is present in sewen analyses (between 1.06-2.71). There is significant Si present in 18/36 analyses (> 1%). Silicon is known to occur in ferrihydrite, as much as 9 wt % element (ChiIds, 1992). There is some interna1 reflectance visible in reflected Iight, which suggests that goethite may be present.
In sumary, a positive identification of the red-mineral is impossible with microprobe data alone.
5.5 Trace Elements - Proton Microprobe Analysis
Trace elements were derected in jarosire samples using micro carticle bduced X-ray
-Ernission (micro-Pm) analyses at the University of Guelph. Thin sections were carbon-coated prior to analyses. The analyticril procedure used for the copiapite analyses was ako ernployed for the jarosites (section 4.5.4). This was t.ested and found acceptable as malytical consistency was achieved from grain to grain. For the jarosite stalactite analyses, the iron determined by PIXE corresponded reasonably well with iron determined by EMPA (- 10 ppt lower with PIXE). The iron in the rnud did not correlate as well with the EMPA (- 100 ppt lower with Pm). It was refit using the probe iron concentration near 296.6 ppt (29.655 wt % element). It is likely that low iron in the jarosite mud analyses by PIXE is related to the greater depth of analysis of the Table 5.8: Caiculated wt 8 element values of common iron oxides and representative electron microprobe analyses of the poorly crystalline red-minerd comrnody occuing with jarosite in the Richmond Mine (98CRL4 and 98CKO). T&B - Towe and Bradley; F&M - FIeischer and Mandarino).
dement fdydnie fenihydrïte fdydrite fenihydnte goelhite hmtitr schenmuinite (Dana. 1997) (Russell, 1979) (Dana. I997j ITm. 1967) FSciM. 1995) IFBLM, 1995'1 E&M. 19951 Si 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Na 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Mt 0.00 0-00 0.00 0.00 0.00 0.00 0.00 K 0.00 0.00 0-00 0-00 0.00 0.00 0.00 Fe 58.14 59.37 62-85 74.39 67.85 69.94 57.8 1 Al 0.00 0.00 0.00 0.00 0.00 0.00 0-00 S 0.00 0.00 0-00 0-00 0.00 0.00 4.15 Ca 0.00 0.00 0.00 0.00 0.00 0.00 0.00 O 39.97 38.73 36.0 1 21.3 1 36.0 1 30.06 37.36 H 1.89 1.80 1.13 4.30 1.13 0.00 0-78 tolals 100.00 100.00 99.99 100~00 99-99 100.00 100.00 red minera1 anaiyses (wt 56 elemenr): 1 2 3 4 5 6 7
Si 0.06 1.51 O. 1 1 0.83 2.30 2.69 252
Na 0.60 0.30 0.29 O. 1 1 0.12 0.00 0.00
Mg 0.03 0.03 ().O( 0.02 0.13 0.30 0.12 K 1.5 1 1.9G 2-46 0.03 0.04 0.06 0-05 Fe 37.32 38.67 3(i.67 44-98 63.25 56.32 62.21
AI O. 10 0.17 0.1 1 0.20 0.52 0.33 0.28 S 13.85 6-95 13.58 0.50 0.33 0.63 0.20 Ca 0.03 0.36 o. 13 0.35 0.65 0.57 1.O6 O 46.50 50.23 -16.74 52.97 32.66 39.28 33.56
H da da da nta nia da da totals 99.99 1UO-UY 1oo.o(i 99.99 99.99 100.00 99.99
Oxygen is caldated by difference. da- not anaïysrd. proton probe compared to that of the electron probe. Each andysis for both the stalactites and the
mud was evaluated independently by ensuring an acceptable fit error and Iirnit of detection
(LOD). The concentration reponed must be 3x above the LOD in order for it to be considered
significant (Appendix C).
Significant trace element data for jarosite staiactite (98CRll) and mud (98CRlS) samples are
reported in tables 5.9 and 5.10. Significant differences appear in each. The stalactites are rich in
Zn (- 97 ppm), As (- 169 ppm), and Pb (- 1719 pprn), with significant Rb, Sr, and Sb, but in
Iower concentrations (Appendix C). In the jarosite mud, concentrations of Zn are not significant
and the average composition of Pb (- 5961 ppm) and As (- 435) is much geater than in the
stalacrites. These differences are discussed further in section 5.8- Bi, Se and Sn are also
considered significant as they are preser.t in concentrations 3x that of thek LOD.
Trace element data obtained from the red rnineral occurring with the jarosite stalactites
(98CR14)and cmst (98CR20)can only be considered qualitative- It was diff~cuitto obtain
consistency from grain to grain during the session and due to the range of values obtained by the
EMP for this rnineral. it was impossible to evaluate the PiXE results using the electron probe
data. Consequently, the results are only qualitative and indicare that Zn (37 - 266 ppm) and As
(35 - 8462 ppm) occur in significant amounts (Appendix C).
5.6 CrystaI Structure
Powder X-ray diffraction techniques were used to confirrn rnineral identification of the jarosite samptes. The jarosite rnud (98CR15) was air dned and the stalactite samples (98CR14) were crushed to a powder. Sarnples were then gound with mortar and pestle and mounted with
Vaseline on a glass slide. The Seimens powder diffractometer at Queen's University was used with nickel filtered Cu Ku-radiation (A = 1.5418 A). Samples were scanned from 6O - 60° 28, with a 0.1 step and a 6 second preset time. The patterns were then matched by cornputer with Table 5.9: Significant trace elements in jarosite stalactite samples 98CR14TS-D and 98CR14TS-A obtained by micro-PIXE. Rb, Sr, and Sb are also significant, but not in very high concentrations (Appendix
Zo Pb CONC ERROR LOD CONC ERROR LOD (PPM) (%FIT) (PPMj (FPM) (8FIT) (PPM) Table 5.10: Si,onificant trace elements in jarosite mud sample 98CR15TS-A obtained by micro-PIXE. Zn is not significant in the rnud, but is included in this table to ernphasize the differences between the rnud and stalactite analyses. Refer to Appendix C for the complete list of results.
Zn* As Pb AhtALYSIS CONC ERROR LOD CONC ERROR LOD CONC ERROR LOD (PPM) (55 (PPM) (PPM) (%FIT) (PPM) (PPM) (8 FIT) (PPM) 1990209.039 38 14 8 427 4 19 6059 1 22 1990209.Wo 27 21 9 349 5 21 5498 1 26 19902û9.041 25 23 9 502 4 19 7298 1 27 1990209.042 26 27 11 354 4 21 5202 1 2 8 1990709.043 40 15 9 448 4 21 5860 1 24 1990209.0~ 35 18 10 431 5 25 5850 I 32 Bi Se Sn AISALYSIS CONC ERROR LOD CONC ERROR LOD CONC ERROR LOD (PPM) (8 (PPLM) (PPM) (6FIT) (PPM) (PPM) (5% FlT) (PPM) 19902û9.039 342 6 30 218 3 6 208 12 25 I ICDD (Joint Comrnittee on Powder Diffraction Standards, 1997) minerd diffraction files to characterize the specimen (figure 5.9a and b).
Detailed structural analysis was not perfonned on these samples. The range in chernical composition of the jarosites in this study indicate that there would be a sirnilar range in the crystallographic properties, the rnajority lying somewhere between the K-H30 solid-solution end- mernbers (table 2.4)- Close inspection of the two patterns reveal that the peaks match the d- spacings of both the K-jarosite (22-0827) and the hydronian jarosite (&.siH300.Jfle3(sû4)2(oH>6
- 36-0427) suggesting the sarnple is heterogeneous, consisting of a mixture of K-H30 solid- soIution jarosites. More detailed analyses would possibly indicate specific differences in the crystallographic parameters, reflecting the observed K-H30 solid-solution substitution. However, if the jarosite is not pure, but instead a mutti-component solid solution phase as in these samples,
X-ray diffraction alone is an unreliable means of identification. It must be carefully compIimented with crystal chernical data in order to properly define the phase.
A Gandolfi camera was used for single crystal analysis in an attempt to obtain a diffraction pattern indicative of the red, poorly crystalline phase that occurred with the jarosite (98CR14 and
98CR20). A small amoun t of sample was scraped from thin section 98CR14TS-A and mounted in the canera for a 24 hour scan, exposed to Co radiation. The resulting pattern is complicated by two phases existing in the sample. It appears that goethite is present as it is the only minera1 to match the 80 intensity line (table 5.1 1). The most intense hematches with that of both potassium and hydronium jarosite- Neither schwertrnannite, fenihydrite nor hematite provide
Iikely matches. Repeated attempts to better isolate the red mineral were unsuccessful.
5.7 Solubility
Six drip water samples (98CA105 series) collected from the jarosite stalactites and pore- water (98CAlG6) from the jarosite mud were analyzed in the USGS iaboratory in Boulder,
Colorado for dissolved cations and anions, as well as Fe and As speciation (table 5.12). AI1 water 22,827 JAROSITE. SYN
jarosite stalactite (98CR14)
jarosite mud (98~~15)
50.00 2-Theta Angle (deg) File Name: c:\ ...\robinson\fig5.9a c:\ ...\98crl5al .xpl
Table 5-11: Rcsuis of sin& ayxtaf ~ljiysisof the unkno~ndmincr;ll vsing i hdolGrarnm~. The obsavcd pattern of the unknwn u compdto hepanaas tiutmbst likcly muh ir- Zhc pancm is cornpliutcd howeva. by two phases eüsring in the sunpk KI app- hi gathite is pmsuir ns it is the oniy minmiaal ro mrch the EO miensiry liar The nrosr intense üne (100) in ihc unknown rnntchcs wi1A ihat of both polusium and hydtunium j~ositcNcik schwcrtrrunnitc. fcrrhydnte nor hcnutite (mt inrludcd) provide Iikcly matdia.
ICPDS llle niimba: L9-07ï3 36U7 47-1775 IhTS GOETfiiTE ITHEï LmkU0-JST ZTIlEïA INTS SCKWERT 3THEI'A DIFF DlFF DlFF 20 17351 0249 1J LS.Lil 60 20.283 -O.OS3 37 21.212 -1.01-
16 162V- -0.192 3 29.374 1.636 46 30598 0.412 70 33364 100 33.822 -0.082 J 3.730
IhTS - intcnsity SCHWERT - schwertmannite 7 Eo~ J U 13 d 'os (IIIBV CLBV d3!-~~ 3 U LIW)'U> wu> II SOLO> qf iiniw JS 10'0 !.L ffro !-1 Y l 'O '3 Ç0'0 !N O 1'O P3 C l'O A EI'O 1';) X'O 11.3 ut-O Y 61'C WJ 05'5'1 EN tUi'0L IrL IWLS %IV OVILi 1v IMM1 ? )!s a.') llVll=:l (11Pi1 (1111.1 W=:I Ifil 1 IJ a~niuxltii;?~ samples were filtered (0.45 pm pore diameter membrane) to remove particulates. Splits were
made of al1 drïp sarnples and 250 mL of each pair was diluted with 2.0 mL, HN03 for cation
analysis and 125 rnL of each with 2.0 mL HCl for Fe and As speciation. Because there was very
Iittle jarosite pore-water, 5.5 mL of the filtered sarnple was diluted with 2.5 rnL of HCI and
brought up to 100 rnL with deionized water for Fe speciation and cation analysis. For S04
analysis, 2.5 mL of the sarnple was liIuted to 100 mL with deionized water. Norrnalty samples are acidified to prevent precipiration of solid phases. In this case, because the samples already have very low pH (< 2.5), the acidification is considered a dilution.
Al1 cations were andyzed using hductively Coupled PIasma - Optical Emission
Spectrometry (ICP-OES)except Na, K, and Li which were done by Flarne Atornïc Absorption
Spectrometry (FAAS)- Anions were deterrnined using Ion Chrornatography (IC). The FerroZine method (Stookey, 1970) was used to detect Fe(T-total) and Fe(I1) and As(III) was analyzed by
FIame Ion Absorption Spectrometry (FIAS), except in the pore-water sarnple where As was measured with ICP due to lack of sample voiume. Sulphuric acid standards were titrated using an
Orion 940/960 autotitrator- Density was deterrnined using a pycnometer (20°C).
5.7.1 Geochemical Modeling
Geochernical modeling propms are used to interpret water analyses of major ions in order to compute the degree of saturation of an aqueous solution with respect to vanous rninerals.
Aqueous speciation refers to the distribution of dissolved constituents arnong various aqueous complexes and individual free ions. Speciation calculations can be used to identify constraints on water-rock interactions but rnostly they reveal which reactions are therrnodynamically possible.
These reactions do not always occur due to kinetic barriers that inhibit many minera1 precipitation or dissolution reactions. Speciation and mineral saturation are calculated by a sequence of steps containing both thermodynamic quantities and numencal approximations. The overall calculation seeks a minimum in the Gibbs free energy of the system (Alpers and Nordstrom.
1999).
Speciation calculations for this study were made using the cornputer program WATEQ4F
(Bal1 et al., 1987 - revised 1999). The thermodynamic data for jarosites and related ions used by
WATEQ4F in these calculations is in table 5.13. Appendix D provides an exarnple of a
WATEQ4F output. The results for al1 jarosite waters are sumrnarized in the following tables and
discussion.
5.7.1. I Speciation of jarosite stahctiîe drip water
Table 5.14 highlights the results from the speciation computations on the jarosite stalactite
drip water. It is a fundamental principIe of solution chemistry that aqueous solutions are
electrically neutral. The total concentration of cations must equal the total concentration of
anions (Drever, 1997). The program calculates charge balance from the input data pnor to and
folIowing the speciation calculations and may report an apparent imbalance. This provides a
measure of the quality of the analytical data and the integrity of the speciation calculations. The
charge balance calculated directly from the input data assumes al1 species are present in the
sample solution in a simple fom (eg. al1 Ca as ca? . The validity of this assumption is
evaluated by the degree of the apparent charge irnbalance. An improved charge balance
following speciation indicates many of the aqueous species are present as complexes instead of
independent ions (eg. ~a"as CaSOJO.CaHS04', &OH+).
WATEQ4F reports an apparent anion surplus for al1 drip waters pnor to speciation
computations. This apparent charge imbalance is improved in samples 105A. B, D, and G
following speciation. This is probably because the major source of anions in the input data is sulphate (~04"). WATEQ4F calculates a new sulphate concentration less than the original amount input in the program by speciating the suIphate to complexes of a lesser charge and to uncharged species (eg. HSOi, HzSOAO). This effectively decreases the overall apparent charge Table 5.13: Thermodynarnic data for relevant minerals and aqueous species used in the WATEQ4F computer program for speciation calcuIations of jarosite stalactite drip water and pore-water (afier Alpers et al., 1989).
FORMULA MINERAL STATE AGau9s log Ksp SOURCE (id mol") KFe3(SOdr(OH)6 jarosite c - 3309.8 3- 1-7 - 11.0 t 0-3 1 NaFe3(so4)2(oH)6 natrojarosite c - 3256.8 - 5.2s 2.3 H30Fe3(S04)2(OH)6 hydroniurn jarosite c - 3232.1 - 5.39 2.3 K.77Na.o3(H30).20 jarosite solid- c - 32935 -C 2.1 - 9.83 4 Fe3(So-t)dOrr)6 solution FeO(0H) goethite c - 490.4 5 Fe-0, hematite c - 742.4 5
Fe(OH)3 ferrihydrite PC - 712.3 3 FeS2 pyrite c - 162.8 5 ~e" aq - 92.26 5 ~e~' FeSO FeS04' FeHS04+ F~HSO," H2S HS - HS04- s04'- Kt Na' OH' H20 I - 237-18 8 c - crystalline; pc - poorly crystaIline; aq - aqueous; 1 - Iiquid
Sources for data: Baron and Palmer, 1996 Kashkay et al., 1975 Chapman et al., 1983 AIpers et al., 1989 Naurnov et al.. 1971 Bal1 et ai.. 1980 Bal1 et al., 1987 HeIgeson et al.. 198 1 Tdile 5-14: Sumcnav of imp~a~feam in output of WATEQ~Fspecîrition caldations far thejmsite sfaiacti~e drip watrr &ta (98CA105 sezies). Aii the phases htare ~portedas supersatur;itd by \VPL?E@F are themodyn-dy stable. bnt only those that arein boId are brinclicany stable- A rhemodynamicdy mbIe phase i5 abIrwith respect to the activities of parriculru phases and wili plecipimte in rhe absence of hetic bmierç.
nftcr -3.13 -S. 16 -1-45 -15.75 -2 1-72 0.19 Eli (v) - memred 0.75 1 0.694 0341 0.570 O-7% 0.680 cniculuted from Fe 0.75 1 0,652 0.566 0.526 0305 0.693 cdculuted from As 0.473 0.47 1 0.460 0.357 0.454 0.450 pe - from memircd Eh 11.505 11541 14.013 14.491 13 .O72 1 1.357 cdçulatcd from Fe 12.50 1 1 1 -343 14.43 1 13.754 13-416 1 1560 cdcuiatcd from As 7.550 7.531 7.665 7.606 7572 7.510 total ionic strength 0.254 0.199 0.236 0.230 0.206 O. 167 effcctive ionic strcnath 0.057 0.052 0.070 0.070 0.065 0.067 supersaturatcd pliases annite mnik annite annite curnik nnnik chaicedony ciidccdony chniccdony chniccdony rhalccdonq- chdcedony
hemrititc hrmatitr hçmtite hemtite hematik hematite jnrosïte K jarositc K jnrositc K jarositc K jarosite K jurosite R jarosite H,O jrirositc (ss) jarositc H,O jnrosite HSO jorositc H30 jarositc HJO
jarositc (ss) rwgrietitt: jarosite (ss) jarosite (ss) jnrosite hh jnrositc (ss) rurignrti te quaQ mpctite mngnetitc: jnrosite (ss) mngetite quartz silica gci 9- quaaz mapetite CI- silirv gel SiO= (a) silicn gel silia gel quartz silica gel SiO, (u) SiOz (a) silica gel SiOz (n) sio, (a) jarosite (ss) some fonn of amorphous Si02
beforc - colculsted befori: specistiori from rwv &[ri dtcr - cdculoted derspecîation (a) - amorphous imbalance. In samples 105E and F the apparent charge imbalance is worse afier speciation. This
may indicate that rnost of the species present in these two samples occur as highly charged ions.
The measured Eh is reported in the WATEQ3F output as well as the Eh that is calculated by
the program using ~e''/~e" and AS~*IAS'+ratios. The Eh calculated according to the iron redox
pair is closer to the rneasured value than chat calculated by the arsenic, therefore it may be
interpreted that this particular couple defines the Eh of the system as dernonstrated in other acid
mine water research (Nordsrrom and Munoz, 1986).
The list of supersaturated phases are those that are thermodynamically stable with respect to
the activities of the particuIar phases. Those that are expected to be kineticaily stable are in bold
text. Only one jarosite phase can be kinetically stable with a specific analysis. Potassium-jarosite
and the jarosite solid solution (ss) defined by Alpers et al. (1989) are supersaturated in al1 six drip
water samples. The me phase in equilibrium with these waters is constrained within the K-H30-
Na solid solution. The specific composition of the CO-existingmineral phase is required in order
to calculate free energy values and solubility products for particular phases within the solid-
soIution. It is interesting to note that jarosite (ss), two fonns of amorphous silica and goethite are predicted to precipitate from these waters by WATEQ4F because sirnilar phases are observed in the stalactite samples coexisting with these waters*
Akhough previously undiscovered as a solid phase, silica was predicted with mass balance calculations preformed by Nordstrom and AIpers (1990) on the Richmond Mine effluent. The silica concentrations in the mine waters were found to be consistentiy near amorphous silica saturation levels. Researchers could only speculate that arnorphous silica saturation at temperatures approaching 50 OC was the most likely control of aqueous silica concentrations within the Richmond Mine effluent. EMPA and speciation calculations for this research substantiate these previous speculations. 5.7.1.2 pH sensitivity analys&
Field pH measurements of these waters were done using two different electrodes, Triode and
Ross, as discussed in Chapter 3. Millivolt readings fiom each electrode were converted to pH by setting up regression curves for values measured from standards (pH 1, 2, 3, and 4) at three different temperatures of cali bration (28, 29 and 45°C) (Appendix A). Two pH values were detennined for each stalactite drip water sample using each of the two electrodes and the 29°C curve. These two values were averaged to obtain a pH for each sample for WATEQ4F calculations. A sensitivity analysis was conducted to determine the variability in the speciation results over the greatest range of pH values that were averaged (table 5.15).
Data from jarosite drip sample 98CAlOSB was run through WATEQ4F with pH values of 1.9
(Triode 98-1), 2.05 (average). and 2.2 (Ross 98-3). Changes of this magnitude in pH has significant effects on some parameters and leaves others unchanged. In examining the charge balance, the apparent anion surplus becomes greater as the pH is increased- This is mostly due to the sulphate speciation. The totai sulphate input into the program is divided arnonp a number of species, the two most prominent being sulphate (~0~")and hydrogen sulphate (HsoI1-).The change in the ratio of these two species is reflected in the changes observed in the charge balance.
As pH is increased. more SOJ" is present relative to HSOJ'-. creating an apparent anion surplus.
This is because the log K for the reaction HSO~"=H? + ~0~'-is -1.988 at 25 OC meaning that both ~0,'-and HSO~'-occur together with equal activities at a pH of 1.988 (Drever, 1997). The ratio of these two species is therefore especially sensitive to slight changes in pH, especially in this range.
Subtle changes in pH also affect the thermodynarnic stability of the jarosite minera1 phases.
Hydronium jarosite is undersatunted at the lower pH's and becornes supersaturated at pH 2.2, indicating that this type of jarosite is more stable at a higher pH compared to the potassium end- member. It is possible to predict how the relative solubilities of the four types of jaro,cites will Ta bIe 5.15: Sensitivity analysis examining the possible range of pH values for 10% All the phases that are reported as supersaturated by WATEQ4F are thermodynamically stable, but only those that are in bold are kineticaiIy stable. A themodynamically stable phase is stable with respect to the acuvities of particular phases and will precipitate in the absence of kinetic barriers.
Triode 98-1 average Ross 98-3 pH 1.9 pH 2.05 pH 2.2 conductivity (uS/cm) 7300 7300 7300 temperature (OC) densi ty (g/mL) ~e'+/F'e- 0.966 0.966 0.966 charge baiance - input -12.86 -17-11 -20.22 calculated 6.54 -8.16 -20.19 Eh (v) - measured 0.694 0.694 0.694 caiculated from Fe 0.684 0.682 0.68 1 pe - from measured Eh 1 1.541 11.541 1 1.541 calculateci €rom Fe 1 1.376 11.344 11.317 total ionic strength 0.20 1 0.199 O. 198 effective ionic strength 0.083 0.083 0.082 % SO,'~ 35.3 1 39.14 43.53 % HSO," 23.99 28.89 14.54 s upersaturated phases annite annite annite chalcedony chalcedony chaicedony cristobalite cristobalite cnstobalite
hematite hematite hematite jarosite K jarosite K jarosite K jarosite (ss) jarosite (ss) jarosite H30 magnetite mapetite jarosite (ss) quartz quartz magnetite silica gel silica gel quartz SiO- (a) SiOz (a) silica gel SiOt (a) jarosite saturation index jarosite K jarosite H30 jarosite Na -2.828 - 2 -968 - 1.108 jarosite Css) 0.686 1.51 1 2.336 input - calculated before speciation from raw data output - calculated after speciation (a) - arnorphous % SO," and % HSOL' refer to the percentage of the total dissolveci sulphur that exists as these two species following speciation calculations by the program. react to changes in pH by examining their saturation indices. It appears that K-jarosite is stabIe at
the Iowest pH range for jarosite rnineralization. As pH increases, the solid soIution (K-H30)
defrned by Alpers et al. (1989) is the next to precipitate. If the pH continued to increase,
eventually H30-jarosite would form and finally Na-jarosite. The type of jarosite is therefore
strongly dependent on pH.
Not al1 parameters were effected by changes of this magnitude in pH. The caIculated Eh
values do not change significantly indicating iron speciation is not affected by fluctuations in pH
in this range.
5.7.1.3 Speciation of jarosite rnud pore- water
The previous sensitivity analysis illustrates the significance of pH in the jarosite system. The results are important to consider when evaiuating the jarosite pore-water data (98CA106). It was dificult to deterrnine an accurate pH for the pore-water because the temperature of the sample was measured at only 20°C. The electrodes had not been calibrated to temperatures below 2g°C, therefore the regression curves couId not be used directly to deterrnine an accurate pH from the rniIIivolt readings. Instead a pH range was estimated using the 38°C curve which represents a maximum (Appendix A). The data for the pore-water was run through WATEQ4F from pH 1.0 -
1.5 to determine the likely pH for jarosite (ss) stability and to understand better how sensitive the precipitation and composition of jarosite is to changes in pH (table 5.16).
The charge balance shows an apparent anion surplus that increases with pH. Once again the change in the ratio of ~0~":~~~~''s~eciated by WATEQ4F is reflected in the changes obsewed in the charge balance. As pH is increased more SO~"is present relative to HSO~'',creating an apparent anion surplus. At pH 1.4 WATEQ4F issues a charge balance warning dedaring that the charge balance is > 30 and is unacceptable. K-jarosite and the jarosite (ss) are listed as supersaturated at pH 1.4 and 1.5, but under poor apparent charge balance. A pH near 1.3 is the Table 5.16: Srnsitivity anaiysis exegthe effects of pH on jaronte porewaterdata (98CAi06).The exact pH of this watcr at 20°C was not calcdated because the electrodrs were calirateci at hi&ertemper;inues. thdore no dibntion curve could be conslnrcted for this water. & SW2and 5% IBO41 derto the mentrige of the tod sulphte rbat rxists as these two sperirs foiiowk specirition ulculations by the prnzam
temperature (OC) 20 20 20 20 20 20 densïîy (glmL) 0.999 1 0.999 1 0.9991 0.999 1 0.999 1 0.99 9 1 ~e'-/i~e& 0.14253 O. 14253 O. 14253 0.14253 0-14253 0.13253 charge balance -
after 23.57 9 A1 4.70 -15.19 -30.8L -4230 Eh (v) - rneasured 0.755 0.758 0.755 0.755 0,755 0.755 culculotcd from Fe 0.7 16 0-715 0.713 0.7 1 1 0.71 0 0.705 pe - From merisurcd Eh 13.03 1 13.03 1 13.03 1 13.03 1 13.931 13.031 cdmlnted from Fe 12.3 13 12.185 12.356 12-27 22.199 12.173 toird ionic strength 1-439 1-429 1.431 1.415 1.409 1.405 effective ionic strength 0.449 0.43 1 0.416 0.041 0.395 0.394 S SO,-= 15.40 17-32 19.53 21.70 23-59 26-04 8 HSO;' 39-50 36.40 32-55 29.32 25-52 33.45 jorosite snturation index
jarosi te ?;a -6.366 -5.755 -5-157 4570 -3.990 -3.416 iarositr (ss) -1.553 -1.263 -0.6S7 -0.192 0.335 0-957 input - cdcuiatd before qxxïation hmruw da& most likely for this sarnple, as K-jarosite and the solid solution are near saturation at this point and the apparent anion surplus is less than the two higher pHs.
The higher than usual apparent anion surplus calculated for the pore-water data prior to speciation challenges the quality of the data. The smailer sarnple volume may have complicated the analyses.
The exueme sensitivity of jarosite composition to changes in pH is reinforced in examining the data in table 5-16. It is irnperative that the pH be reaily wel1 defined in order to perforrn accurate speciation calculations.
5.8 Discussion
Studying the jarosite and coexisting water collected in the Richmond Mine presents the opportunity to Iearn more about the geochemical complexities of these minerals and the influence of jarosite solubility on acid mine waters. Results frorn this work can be used to cornplement previous laboratory studies on jarosite solubility (Alpers et al., 1989) and provide insight on what actually occurs in the field. Geochemical modeling with WATEQ4F allows for a more detailed assessrnent of the effects of pH on jarosite composition.
The composition of jarosites in this study plot within the K-Na-H30 solid solution series prirnariiy between the K-H30 end-members. These findings correspond to the composition of jarosite precipitated from Richmond Mine eftluent by previous authors conducting solubility expenrnents (Alpers et al., 1989). An amorphous silica phase occurring with the stalactites was detected in the EMPA and confirmed wi th SEM. Other authors studying the Richmond Mine effluent had predicted the saturation of amorphous silica, but a solid phase had not been previously identified (Nordstrom and Alpers. 1990). An iron-rich red mineral occumng with the jarosite stalactites is believed to be goethite. following the X-ray anaiysis of a very srnall fragment, using a Gandolfi camera. Saturation of goethite and an amorphous silica phase were predicted in geochernical modehg of the stalactite drip water. Micro-PIXE analyses indicate that Zn, As and Pb are the most common trace elements substituted into the structure of the jarosite stalactites. As, Pb, Bi, Se and Sn occur in significant concentrations in the jarosite mud, however Zn is below detection- The predominance of a particular trace elernent in a minera1 may be partially attributed to the relative high concentration of the same element in the pore-water. Ln this case, however, Zn is present in the mud pore-water in concentrations 150 rnz& greater than that measured in the stalactite drip water. One would therefore expect to find significant Zn in the jarosite mud. This apparent inconsistency may be attributed to different pH conditions, The pH of the jarosite rnud pore-water is estirnated to be <
1.5. Perhaps a pH > 2, as rneasured in the stalactite drip water, is needed for Zn-bearïng jarosite to precipitate.
The composition of the jarosite stalactite dnp water rnainly consists of sulphate, femc iron, calcium. silica, and ferrous iron with lesser amounts of aluminum, magnesium and zinc. The jarosite mud pore-water is far more concentrated, with most of the same elernents present in concentrations an order of magnitude higher than in the drip water- Both fluids are seerningly saturated with respect to jarosite. therefore the differences in water composition may be attributed to the more diIuted nature of the drip water.
The results of speciation calculations of the jarosite stalactite drip waters list the potassium jarosite (Baron and Palmer. 1996) and the jarosite solid solution (Alpers et al., 1989) found in the
WATEQ4F database as supersaturated phases. The composition of jarosite in equilibrium with the stalactite drip waters falls within the jarosite solid solution system, likely within the same composition range as the jarosite stalactite and rnud minerais. Similar assumptions are not possible for the jarosite pore-water due to the questionable integrity of the data, as indicated by the apparent anion surplus and the inability to calculate a precise pH.
In addition to phase equilibria information, modeling also provides valuable insight with respect to the specific thermodynarnic conaols on jarosite solubility in acid mine waters. It was discovered that in this particular system the Fe2+/Fe3+ redox couple controls the Eh. Sensitivity analyses demonstrate that pH is probably the most significant variable in determining sulphate
speciation and jarosite composition. The charge balance of the solution used to asses the quality
of the analytical data and the integrity of the speciation calculations is dictated by the sulphate
speciation and is therefore dependant on an accurate pH measurement.
WATEQ4F results indicate that K-jarosite is stable at the lower pH range for jarosite
saturation- As pH increases the jarosite solid solution (Alpers et al.. 1989), H30and Na jarosites
will become supersaturated. The precipitation of these phases as acidity decreases suggests that
the known pH range of K solubility can be extended to include less acidic conditions, if these
other mernbers of the solid solution are present (figure 5.10). This pH sensitivity is extremely
important to consider when working with these systerns. Field measurements must be incredibly
accurate to ensure the results of the geochemical rnodeling are reliable.
As is the case with the copiapite and its coexisting pore-water. the geochemicaI environment
responsibie for creating the wall of jarosite in the D-drift of the Richmond Mine is very different from the conditions required to produce the effluent streams (table 4.8). The effluent leaving the
Richmond Mine is characteristic of a very geochemicalIy reduced environment. Jarosite is a comrnon mineral in oxidized environments. and although its range of geochernical stability
(figure 5.10) indicates it can occur at low pHs (< 2.5). it is unusual to find it underground. Its presence in the Richmond Mine adds to the complexity of what is already considered to be a highly dynarnic and compIicated environment.
To find jarosite forrning directly on pyrite surfaces contradicts the opinion that this ought to be too reducing an environment (Merwin and Posnjak, 1937; Nordstrom and Alpers, 1999b). An explanation for its occurrence may be that in this particular location ferrous iron is very eficiently oxidizing to ferric iron for a variety of reasons. First, the jarosite is Iocated approximately 10 metres from the ventilated area at the 5 way junction. It is possible that because of the shape of the tunnels, air currents within the mine continually supply fresh oxygen to this particular spot. Second. this drift is much drier compared to the other three drifts. As Figure 5.10: Measured pH andpe ofjarosite stalactite drip waters (98CA105 series - see table 5.14) plotted within the Fe-S-K-O-H system at 25 C (Nordstrom and Alpers, 1999%modified fiom Alpers et al., 1989).-Thesewater -sarnples-plo~jus~to-the rightofthe stabilitfr-mgefoi.-K+osi.tMBQ4F - calculations show K-jaroslte is more stable than hydroniq- and Na-jarosite at lower pH copditions. This diagram shows that if hydronium andfor Na are present in the samples, as tbey have found to be in this study, the jarosite stability field can be extended to include Iess acidic conditions. In addition, this drip water plots near the boundary between the jarosite and goethite fields, providing additional support for the tentative identification of goethite in the jarosite stalactite samples. discussed in Chapter 2.3.1 rapidly flowing mine water will sustain a high proportion of ferrous
iron because the oxidation rate cannot keep up with the flow rate of the water. Third, there is a
high concentration of bacterial slime in this location, unlike anywhere else in the mine. The
presence of iron- and sulphur-oxidizing bacteria such as Thiobacillus ferrooxidmrs and
Leprospirilliwn ferrooxidam are know to greatly accelerate the oxidation of sulphide minerals
(Schrenk et al., 1998; Edwards et al., 1998). In addition, it is interesting to note that the Scott
Fault occurs in this vicinity and may have influence on the geochernical environment. As a result, appropriate conditions for the formation of secondary rninerals with more intermediate
ferrous-ferric iron compositions do not exist.
Jarosite is a relatively insoluble secondary minera1 in cornparison to most of the other secondary minera1 phases that are present within the Richmond Mine. Accordingly, it is expected to attenuate elements more effectively. Due to the extreme acidity typical of the Richmond Mine however, it cannot be considered a long-term storage mineral for adverse elements.
It is important to study jarosite minerals with coexisting water in order to determine thennodynamic parameters which forrn solid soiutions in acidic mine environments. The determination of the mixing properties in jarosites is essential for accurate assessrnent of the saturation index of jarosite in acid mine water (Alpers et al., 1989). A thorough understanding of these systems will Iead to the development of modeis that clearIy predict the composition and abundance of jarosite precipitation in various settings. In turn this will resuIt in more accurate prediction of acid generation and effluent quality. CHAPTER SIX: CONCLUSIONS AND RIECOMMENDATIONS
6.1 Conclusions
Previous authors have noted the unique hydrogeochemicd conditions particular to the
Richmond Mine at Iron Mounrain (-Alpers and Nordstrom, 1999b; Jamieson et al-, 1999). The
extreme acidity and abundance of rare secondary sulphate minerals is fairly well documented.
These features combine to provide an excellent opportunity to study rnineral-water interactions in
an exceptional acid mine drainage environment
6.1.1 Copiapiîe
The copiapite samples studied from the Richmond Mine consisc: of two phases: (1)
rnagnesiocopiapite and (2) alurninum-rich ferricopiapite. Magnesiocopiapite is the predominant
phase, with spheroidal aggregates of finer grained aluminocopiapite forming from subsequent
oxidation. Zn, Cu and As are the significant trace elements found in the structure. The predominance of these particular elements is due to the relative high concentration of the same elements in the pore-water,
Copiapite pore-water has a high concentration of sulphate, ferric iron. ferrous iron, aluminum and magnesium. It has the highest femc iron concentration yet reported (147 a),a pH of -1.0 +
0.5. and a density of 1.5 p/mL. The predominance of ferric iron and aluminum implies that the fluid at the time of analysis is supersaturated with respect to Al-nch femcopiapite, as opposed to the dominant Mg-rich phase. The pore-water has likely evolved to a more oxidized state.
The presence of copiapite in the Ddrift is due to a number of specific geochemical factors including pH, Eh, temperature and conductivity. Given its relatively high solubility, it will contribute significantly to the concentration of iron and sulphur in the effluent at times of high discharge. Therrnodynamic parameters for copiapite minerals and highly concentrated femc iron-rich solutions (Le- saturation indices, solubility products and activity coefficients) need to be
deterrnined in order to predict the exact influence.
6.1.2 Jarosire
The Richmond Mïne jarosite stalactites and mud accompanied by coexisting water samples
provide the opportunity to study the geochernical cornpkxities of these rninerals and the influence
of jarosite solubility on acid mine waters. Geochernical modeling with the speciation program
WATEQ4F allows for a more in-depth look at the effects of pH on jarosite composition.
The composition of the jarosites in this study plot pnrnarily between the K-H30 end-
members within a K-Na-H30 solid solution. An arnorphous silica phase occurring with the
stalactites was identified, supporting saturation predictions by other authors doing geochernical
modeling of the Richmond Mine effluent (Nordstrom and Alpers, 1990). An iron-rich red
minera1 occumng with the jarosite stalactites was tentatively identified as goethite, following
detailed X-ray analysis. Saturation of goethite and an amorphous silica phase were predicted in
geochemical modeling of the stalactite drip water.
Zn, As and Pb are the most cornmon trace elements substituted into the structure of the
jarosite stalactites. As, Pb, Bi, Se and Sn occur in significant concentrations in the jarosite mud.
Zn was not detected in the rnud despite its relatively high concentration in the mud pore-water (>
150 mg/L than Zn in the stalactite drip water). The pH of the jarosite mud pore-water is
estimated to be c 1.5. A pH > 2. as measured in the stalactite drip water, may be required for Zn-
bearing jarosite to precipitate.
Speciation calculations indicate that the jarosites in equilibrium with the stalactite drip waters
have interrnediate compositions between the jarosites found in the WATEQ4F database.
Qualitatively, this appears to correlate welI with the EMPA and X-ray data for the stalactites,
providing a range of apparent equilibrium for the jarosite stalactites and the drip water. Sirnilar assumptions are not possible for the jarosite mud pore-water as a precise pH could not be determined. In addition, an apparent anion surplus calcdated by WATEQ4F pnor to speciation
signais possible inaccuracies in the analyzed constituents. A small sample volume in this case
may be responsible for the inac&acies.
WATEQ4F calculations demonstrated that in this particuk system the Fe24Fe3-t- redox
couple controls the Eh.
Two separate sensitivity analyses indicate pH is likely the rnost significant variable in
detennining sulphate speciation and jarosite composition- WATEQ4F resuhs also indicate that
K-jarosite is more stable than hydronium- or Na-jarosite at the lower pH range for jarosite saturation. Moreover, the known pH range of K-jarosite solubility can probably be extended to include less acidic conditions if other members of the solid solution are present (figure 5.10).
Jarosite is known to be stable in oxidized environments and it is usually found spatially farther away from active areas of pyrite oxidation (Merwin and Posnjak, 1937; Nordstrom and
Alpers, 1999b)- In the Richmond Mine jarosite was found forming directly on the surface of pyrite in the Richmond Mine. in what should be an environment that is too reducing for it to be stabIe, One explanation for this may be that in this particular focation ferrous iron is very quickly oxidizing to ferric iron due ro several possible reasons:
(1) the jarosite is found only 10 metres from a weIl-ventilated area at the 5 way junction;
(2) the D-drift is relatively dry compared to the other three drifts. Ferrous iron is
therefore not stabilized by fast moving effluent suearns;
(3) a high concentration of iron- and sulphur-oxidizing bacteria are present in this
location. These organisms greatly accelerate the oxidation of sulphide minerals (Schrenk
et al., 1998; Edwards et ai., 1998); and
(4) the presence of a fault in this particular area of the mine may be influencing the
geochemical environment.
Jarosite is a relatively insolubIe secondary mineral and is therefore expected to attenuate metals more effectively than more soluble minerals like copiapite. However, the jarosite found in the D-drift of the Richmond Mine cannot be considered an effective storage mineral of adverse
elements due to the extremely low acidity of the effluent characteristic of this site.
6.2 Recommendations
Analyzing the minerai chernistry of copiapite and jarosite by EMPA provided results
comparable to those obtained by other authors using alternative methods. Ambiguity exists with
respect to the amount of water occurring within the mineral structure and as free water molecules,
especially in the copiapite analyses. Analyzing the water contenr of these samples with a
different technique may provide a more definitive explmation of wt 96 total results above and
below 100 %.
The sensitivity analyses discussed in Chapter 5 highlight the importance of taking careful
fieId measurernents of acid mine waters, especially for the purpose of geochemical modeling. pH
is probably the most significant variable in deterrnining sutphate speciation. The charge balance of the solution, used to assess the quaIity of the analytical data and the integrity of the speciation calculations, is dorninated by the sulphate speciation and is therefore dependant on an accurate pH rneasurement.
Thermodynarnic parameters must be determined for more sulphate species and activity coefficients for highly concentrated soIutions in order to properly assess the saturation indices of rninerals that occur in the acid mine drainage environment and predict how they effect eKluent quality, Contributions of this nature will refine the accuracy of geochemical modeling prograrns
1i ke WATEQ4F.
The ultimate goal in studying these rnineral-water interactions in the acid mine drainage environment is to promote a more thorough understanding of these kinds of hydrogeochemical systems. New developments in this field can be appIied to existing methods used to predict acid generation potential at prospective mine sites and can be incorporated in the design of more effective, and hopefully less costly, treatrnent strategies. REFERENCES
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Alpers. C.N. and Nordstrorn. D.K. 1999. Geochemical modeling of water-rock interactions in mining environments. 111: The Environmental Geochernistry of Mineral Deposits. Part A, Processes, Techniques, and Health Issues. Reviews in Economic Geology 6A,(eds.) G.S. Plumlee and M.J. Logsdon, pp. 289-323.
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This appendix contains a complete Iist of the mineral and water samples collected in the Richmond Mine in July, 1998. Brief descriptions of secondary minerals are provided.
Recorded calibration measurements are listed for the pH and redox meters during the field work.
The calibration curves and relevant data for four pH standards that were used to determine pH from mV readings for the jarosite waters and the drift waters are included. Details about the application of this method as well as a clarification regarding filter choice is provided. 1. COMPLETE LISTS OF MINERAL AND WATER SAMPLES COLLECTED FROM THE RICHMOND MINE
Catalogue of rnineral samples collected in the Richmond Mine and in the gossan at Iron Mountain in July, 1998. Note: * denotes the samples chosen for debiied analyses in this study. Al1 rnineral identification confirmed with XRI). f 11 SAMPLE # MAIN MINERAL LOCATION 98CR01 copiapite B-Drift: -20 rn from 5 way intersection 98CR02 copiapite. rhyolite B-Drift: -20 m from 5 way intersection 98CR03* copiapite (mud) D-Drift: -20 m from 5 way intersection
9SCR04* copiapite (mud) D-Drift: -20 m from 5 way intersection * 98CR05 copiapite D-Drift: -18 m from 5 way intersection 98CR06 copiapite D-Drift: -18 rn from 5 way intersection 98CR07 rhyolite B-Drift: -20 m frorn 5 way intersection 98CR08 pynte wdI 3-4 rn lefi of entrance to B-Drift 9SCRO9 pynte wdl 3-4 rn Ieft of entrance to B-Drift 98CR10 pynte .wall 3-4 m left of entrance to B-Drift 98CRl l pyrite wall 3-4 m Ieft of entrance to B-Drift 98CR13 pynte A-Drift: -20 m from 5 way intersection 98CR13 pyrite A-Drift: -20 m from 5 way intersection 98CR14abc* jarosite (stalactites) D-Drift: -10 m from 5 way intersection 98CR15ab* jarosite (mud) D-Drift: -10 rn fiom 5 way intersection 98CRl6abc iarosite D-Drift: -10 rn from 5 wav intersection 98cm7abcdef pyrite rift: -10 m from 5 way intersection 98CRl8abc ~vrite D-Drift: -10 rn from 5 wav intersection 98CR19ab jarosite D-Drift: -10 m from 5 way intersection 98CR20ab* jarosite (crust) D-Drift: -10 m from 5 way intersection 98CRXab pynte D-Drift: -10 m from 5 way intersection 98CRî3ad* copiapite surface - gossan
Catalogue of water samples collected in the Richmond Mine in July, 1998. IISAMPLE ILOCATION (DESCRIPTION II 1198C~101 IDdrift. S waIl lcom~ositesarn~le of effluent leaving D-drift II 98CA102 Cdrift at weir composite sample of effluent leaving Cdrift - 98CA103 Adrift at weir com~ositesarniile of effluent leaving A-drift 1 98CA104 B-drift at weir composite sample of effluent leaving B-drift - 98CAlOSA Ddrift, S wall jarosite stalactite drip water (contributes to D-drift effluent)
98CAL05B Ddrift. S wali iarosite stalactite dri~water (contributes to D-drift effluent) 4 98CA105D Ddrift, S walI iarosite stalactite drip water (contributes to D-drift effluent)
L98CAlOSE Ddrift. S wall b.iarosite stalactite dri~water (contributes to D-drift effluent) 98CA105F Ddrift, S wall jarosite stalactite drip water (contributes to D-drift effluent) 98CA105G Ddrift, S wall jarosite stalactite drip water (contributes to D-drifi effluent) 98CA106 Ddrïfi, S wall jarosite mud - pore water (contributes to D-drift effluent) 98CA107 Ddrift, S wall pyrite pore water (contributes to Ddrift effluent) 9SCA107A Ddrift, S walI pyrite pore water (contributes to Ddrift effluent) 98CR03W D-drift, end copiapite pore water (contributes to Ddrift effluent) 98CR04W Ddrifi, end copiapite pore water (contributes to Ddnft effluent) 2. SIGNIFICANT SECONDARY MlNJDZALS NOTED LN THE RICHMOND MINE
Catalogue of samples collected in the Richmond Mine and in the gossan at Iron Mountain in Juiy 1998. A description of the significant sulphates and other secondary rninerafs included in the sample is provided- Note: * denotes samples chosen for detaiied analyses in this study. AU mineral identification confirrned with XRD. - SAMPLE # MAIN MINERAL DESCRIPTION 98CR0 1 copiapite dark yellow, very rnucky, colloidd-like, with small coquimbite and voltaite-grains 98CR03 copiapite, rhyolite dark yellow copiapite, with coquimbite and bleached rhyolite, not as mucky 98CR01 98CR03* copiapite (muck) dark yellow, peanut-butter-Iike muck, left in Sacramento to centrifuge 98CR04* copiapite (muck) same as 98CR03 98CR05 copiapite globular yellow copiapite, not as wet as 98CR03 and 04 98CR06 copiapite from same pile as 98CR05, similar texture, but more orange than yellow, halohichite also present 98CR07 rhyolite massive rhyolite sarnple, noticeable copiapite, coquimbite, voltaite, halotrichite 98CRO8 pyrite massive pyrite sample with numerous phases: copiapite, coquimbite, halotrichite, chalcanthite, voltaite 98CRO9 pyrite same as 98CR08 98CR10 pyrite same as 98CR08 98CR1 L pyrite same as 98CR08 98CR12 pyrite massive pyrite with copiapite, chalcanthite, voltaite - sample hot to touch during coIIection! 98CR13 pyrite massive pyrite with voltaite, copiapite. halotrichite 98CR14abc* jarosite (stalactites) du11 yellow stalactites, 1-10 cm Iong, 0.5-1 cm in l 1 diameter. hard texture. collected with drip water (98CA105 series)
98CR15ab* jarosite (rnuck) mustard coloured muck, centrifuged- on site (supernatant: 98CA 106) 98CRL6abc jarosite red muck associated with 98CR15 and pyrite. red not directly touching pyrite (layered sequeGe: pyrite - I 1 -. yellow jarosite muck - red jarosite muck) 98CR17abcdef pyrite pyrite muck, centrifuged on site (blue supernatant: 98CA 107 and 107A) 98CR18abc pyrite massive pyrite ore 98CR19ab jarosite yel low cmst beneath dnpping jarosite stalactites (98CR14) 98CWOab* jarosite (cntst) brown-red crust, in area of bacterial slime and yeI1ow
98CR2lab pyrite massive pyrite ore taken from mucky part of wall; 98CR23ad* copiapite a: copiapite with pyrite 3. INSTRUMENT CALIBRATION
Two pH metres (98A and 98B)and four electrodes (Triode 1 and 2, Ross 3 and 4) were used for field measurements. Both the Ross and Tnode are combination pH elecuodes, which means they both include a reference ceII. The reference ce11 measures a voltage reIative to the standard hydrogen electrode (Bates, 1964). In addition, the Triodes measure temperature whereas the Ross electrodes only measure pH (voltage). The electrodes were soaked in standard T-2,a sulfuric acid solution of pH +1.0 for 23 hours to condition them.
Before measuring the sarnples. the pH meters and electrodes were calibrated using sulphuric acid standard soIutions to 28 OC k 12°C. These calibration measurements are presented here- Acid mine waters are solutions of sulphunc acid, so the Pitzer mode1 (1973) applied to sulphunc acid serves as an acceptable definition for pH. Standardized sulphuric acid solutions would then act as buffer solutions for calibration-
Four pH electrodes were caiibrated initiaiiy. The readings from the 98-1 Triode and the 98-4 Ross electrodes correlated the best with one another and were used to measure the mine waters. Part way through the sarnpling the 98-4 Ross electrode failed and was replaced by the 98-3.
The instruments were re-calibrated to mine water ternperatures, by measurinp the standards after placing them in a water bath of mine effluent. These recalibration measurements are provided in this appendix as well.
Water sampies were filtered with 0.45 pm paper, which is the conventional choice. The constituents that pass through are assumed to be dissolved, but it is possible that srnaIler iron colloids may slip through. However, at low pH values such as those measured for these samples, it is unlikely that colloids are present. INITIAL CALBRATION:
pH - Triode electrode calibration at entrance to Richmond Mine. SOLUTION 1 TRIODE 1 TRIODE 1 TEMP 1 TIME 11
pH - Ross eIectrode calibration at entrance to Richmond Mine.
1 SOLUTION 1 ROSS 1 ROSS 1 TEMP 1 TIME 1 98-3 (mV) 98-1 (mV) (OC) pH 4 181 184 11:58 1 pH3 250 245 11:58 pH 2 30 1 304 11:58 pH 1 360 364 12:03 Ul 368.5 372.3 28 13:03 U2 387 39 1 12: 10 U3 404.1 407.3 28 12: 14 U4 423 425 -7 1216 U5 435.6 439.3 12: 19 U6 442.4 445.7 1222 U7 450.3 454.6 1238 U8 459.4 363.3 12:3 1 U9 467 470.8 1234 U10 483.6 487 28 1237 *Note: cIcctrodc Ross 98-3 low in frliing solutiun: onc inch lcft in the tube. Should be threc inches.
REDOX calibration at entrance to Richmond Mine.
ELECTRODE mV 4R 255 32.5
7R 80- - 32.0-- - 1 Actual Reading * 1 58.3 1
+ Value denved by subtracting the 7R rcading from the 4R readi and dividhg the result by three- C-DRIFT RE-CALIBRATION:
SOLUTION TRIODE ROSS TEMP 98-1 (mV) 98-4 (mV) (OC) pH 4 184 192.6 44.3 pH 3 257 26 1 44.5 pH 2 311 3 18.4 45.8 - DH 1 374 381 46.9
Ü9F 482 492 46.6 U10 500 509 46.7 *Note: These pH mV readings are higher than the previous calibration ouiside the portal. The average difference is 23.3 mV.
REDOX - Re-calibration (C-Drift).
ELECTRODE rnV Temperature (OC) 4R 316.3 47.0 7R 1 42.5 47.0 1 ActuaI Reading * 1 57.9 I II * Value derived by subtracting the 7R reading frorn the 4R reading and dividing the result by three. Note: The re-calibration value is 0.3 mV less than the ptimary reading taken outside the portal. D-DRIFT RE-CALIBRATION:
pH - Re-calibration @-Drift)- /( SOLUTION 1 TRIODE 1 *ROSS 1 ROSS 1 TEMP 1 98-1(mV) 98-4(mV) 98-3 (mV) (OC) pH 4 178 77 185 29.1 pH 3 246 149 252 29.2 pH 2 301 183 305.5 29.1 pH 1 348 230 363.3 29.2 Ul 354.6 225 29.3 U3 370 234 29.3 U3 381 241 29.3 U4 398 237 29.6 * Ross 98-4 readings are low. Switching to Ross 98-3. REDOX - Re-calibration (D-Drift).
ELECTRODE rnV (reading 1) mV (reading 2) Temperature (OC) 4R 230 243 28.5 7R 56 65 28.5 Actual Reading * 58 593
-- * Value derived by subtracting the 7R reading Frorn the 4R reading and dividing the result by three. 4. CALIBRATION CUFtVES USED TO DETERMINE pH FROM mV
To accommodate accurate interpretation of high acidity, the pH values of four known sulphuric acid standards of pH 1,2,3, and 4 were used to make regression curves for each temperature of standardization, The curves are then applied to interpolate pH values from the mV readings for the drift waters and the jarosite waters.
Essentially the same method cm be applied to determine the pH of the ten sulphuric acids standards of extreme hydrogen content and the copiapite pore-water sarnples. However, these waters require more detailed calculations using the Pitzer ion-interaction approach (Pitzer, 1973) as discussed in Chapter 3. This method is the rnost accepted mode1 for defining pH below 1.0. The pH values of the unknown standards calculated using this method range from 0.979 to - 3.66.
The copiapite pore-water solutions are very concentrated and more acidic than the other waters measured. The high ~e~+content of these waters complicates the calculations, as Pitzer coefficients for highly concenuated femc iron solutions are yet to be determined. 4. CALIBRATION CURVES USED TO DETERMINE pH FROM mV
Table 1: pH - Triode eIectrode cdibntion (38 deg C) SOLUTION TRIODE TRIODE TEMP TIME
98-1 (mV) 98-1 (mV) (OC) PH 1 354 360 28 1 1 :27 pH 2 293 3075 27 11:ll PH 3 235 253 11:11 pH4 175 187 28 3 11111
Table 2: pH - Ross electrode calibnrion (28 deg C) SOLUTiON ROSS ROSS TEMP TlME 98-3 (mV) 98-4 (mV) (Oc) PH 1 360 364 12:03 pH 2 30 1 304 1158 PH 3 250 245 1158 pH 4 18L 18-5 1 I:58
Table 3: pH - Re-calibration (C-Drift) (45 deg C) SOLUTION TRIODE ROSS TEMP
98-1 (mV) 983(mVj (Oc) PH 1 373 38 1 46.9 pH 2 31 1 3 18.5 15.8 PH 3 257 26 1 13.5 PH4 181 192.6 -U-3
Table 3: pH - re-cdibrxion (D-Drifc) (29 deg C) SOLUTION TRIODE *ROSS ROSS TEMP 98- 1 (mV) 984 (mV) 98-3 (mV) (OC) PH 1 348 220 363.3 29 -2 pH 2 30 1 183 305.5 29.1 pH 3 246 149 252 29 -2 pH 4 178 77 185 29.1 0 ! 1 l O 1 2 3 4 5 1 r PH i r -29 deg C l I 1 I + -28 deg C l -Linear (-29 deg C) y = -58.U~+ 423.55 ,i y = -58.8~+ 420 i I -Linear (-28 deg C) !
Ross 984
-28 deg C
i -45 deg C - y = -59.9~+ 424 -Linear (-28 deg C) y = -46.3~+ 273 Linear(-29 deg C) y = -62.26~+ 443.9 -Linear (-45 deg C) Triode 98-1
m -45 deg C -29 deg C -28deg C Linear(-45 deg C) Linear(-29 deg C) Linear(-28 deg C)
! I , Triode 98-2 I
! y = -57.25~+ 420.25 i - 28 deg Linear (- 28 deg) ! - APPENDIX B: ELECTRON MICROPROBE DATA
This appendix contains a raw eleciron microprobe data for jarosite stalactites and the red rnineraI. A11 dara are expressed in WCC/o element, Oxygen is calculated by difference. da- not andysed. 98CRl4TS-D: jarosite stalactite wt %eIement 1 2 3 4 5 6 7 8 9 - -- - .. . - . O. 13 0.00 0.3 1 0.34 0.77 0.00 0.00 0.58 0.52 0.53 0.00 0.00 O. 12 0.00 0.00 6.85 5.34 2.80 2.78 2-95 30.66 30.03 30.95 30.20 30.99 0.14 0.2 1 0.10 0.26 0-14 13.29 13.81 13.42 13 .O9 12.8 1 0.10 0.15 0.07 0.00 O. 14 48.69 50.57 5 1.74 52.85 5 1-70 nia nia nia nia nia 99.86 I00*10 100.08 100.05 100.0 1
0.38 0.4 1 0.09 0.07 0.00 0.00 O. 13 0.00 0.00 0.00 0.00 0.07 6.77 6.54 6.08 6.97 30.33 30.52 29.96 30.20 0.09 0.1 1 0.17 0.28 12-62 12-70 13.21 13.17 0.1 1 0.00 0.15 0.1 1 49.70 49.72 50.23 49.04 nia nia nia nia 99.99 100.0 1 100.02 99.90 98CR11TS-A: jarosi te stalactite
H nia nia nia nia nia da nia totals 100.05 100.06 99.97 100.02 99.94 100.08 99-97
98CRl1TS-B: jarosite stalactite
H da n/a nh n/a da da nia n/a totals 99.97 100.01 99.99 99.99 100.02 100.05 99.95 99.93 L'KKYOWN RED MINERAL: wt CT, clcmcnt
10 11 11 13 14 15 16 17 18 Si 1-47 5.48 1.43 0.07 0.04 O. 13 1-44 1.40 4.24 Ka 0.00 0.00 O. 13 0.11 0.29 0.24 0.00 O. 19 0.1 1 Mg O. 13 0.32 0.09 03 1 0.00 0.27 0.13 0.08 027 K 0.00 O. 13 0.06 0.04 0.6 1 0.40 0.05 OSU 0.07 Fe 64.72 55.U 64.19 29.09 37.44 32.71 65.15 58.93 57.64 XI 0.21 0.56 0.32 0.75 0.15 0.87 0.23 020 0.44 S 0.21 O. 17 0.5 1 13-22 14.27 13.83 0.22 038 0.24
Cn 0.83 771 039 O. 13 0.00 . 0.03 0.90 0.68 3 13 O 3351 35.60 3385 51.26 47.2 1 51-51 3 1.88 38-10 3.86 H da da da da nia da da da da totals 100.08 99-99 99-99 ~win to0.00 100.00 100.00 100.00 99.97 wt % clcmcnt APPENDIX C: MICRO-PIXE
This appendix provides additional information about the micro-PIXE instrument and techniques used during the analyses. It also includes al1 the data collected on copiapite samples 98CR04PS-1 and 2 and jarosite samples 98CRl4TS-A ,D, 98CR15TS-A, and 98CR20TS. Instrumentation and Analytical Technique Micro-PE uses an accelerator to produce X-rays from MeV-energy proton beams and energy-dispersion X-ray Si(Li) detectors to record the spectra. It is used to obtain multi-element quantitative analysis of trace and major elements of selected individual rninerals or fine-scale elernent zonation of minerals in polished or thin sections. Generaily the elements analyzed range in atornic number from Fe to U (2 1 26) at levels of detection of a few parts per million (ppm), with spatial resolution of 10-20 Pm- It is considered a non-destructive technique, however the proton beam penetrates much deeper than an electron beam, producing X-rays from well below the surface of the minera1 (Cabri and Campbell, 1998). Microanalysis by PIXE is similar to electron-probe microanalysis (E,PMA). Minerals are analyzed as charged particles peneuate a selected grain causing ionization, the production of two types of radiation (characteristic X-rays and brernsstrahlung), and the attenuation of X-rays. However, two important differences exist between the techniques. First, the calcuIation of X-ray yields is much more straightforward for PIXE. The MeV-energy protons travel through solid material with Little deviation, and lose energy in a way that is well understood and quantified. In contrast, keV-energy electrons do not travel in the same manner and correction programs such as ZAF and $(pz) are used to approximate rnatrix effects. A second difference is that the smaller scattering of the protons gives sub-micrometer spatiaI resolution which is particularly useful in irnaging applications. Third, the characteristic X-ray intensities excited per unit of bemcharge are sirnilar. however the bremsstrahlung emitted by protons is much lower than that ernitted by electrons. In PKE analysis, a more continuous background is produced by the protons in the sample due to bremsstrahlung frorn the secondary electrons. This results in the signal-to-noise ratio king better in PIXE than in the case of EMPA and lower detection levels are obtained for quantitative analysis (Cabri and Campbel 1. 1998).
Th2 accelerator used to produce ri proton beam needed for mineral analyses is a large instrument that operates at 3 MeV. It is shielded from the target area in order to contain noise and harmful y-radiation. The proton beam travels horizontally through a 5-10 cm diameter tube and is focused by systerns of tenses, which are usually quadrupole rnagnets. In Guelph, the beam is incident on the target at 45" and has a 45" take-off angle from the target surface. The X-ray detector and viewing microscope are connected to a TV camera and positioned around the target- The specimen stage is easily moved using a compter keyboard. Large-area (80 mm') Si (Li) detectors are mounted as close to the target as possible (- 25 mm) to maximize X-ray collection efficiency (Czarnanske et al., 1993). Filters or foils, usually of MyIar and AI, 100-700 Pm thick, are placed between the target and the detector to attenuate the highly intense bremsstrahiung continuum and the X-rays of the Iight major elements (22 22). This enhances the much less intense X-rays of trace elements which are only slightly attenuated because of their higher energy. The filters aIso work to reduce the contribution fiom major elements in minerais, such as Fe in copiapite and jarosite. One disadvantage in using a filter is that it can hinder in the anaiysis of some elements whose spectral lines are near ons of the major elements (e.g., Co in a major iron-bearing mineral) (Czamanske et al-, 1993; Cabri and Campbell, 1998).
Standardiza tion It is difficult to find or synthesize standards with homogeneously distributed trace elements, therefore PlXE analysis relies on a technique that elirninates the need for andytical standards. The following includes a discussion of the principles used in the methoci followed by the operators at Guelph. These ideas are descnbed in more detail in Cabri and Campbell (1998). The theoretical intensity of any characteristic X-ray Iine of a trace element (2 122)that is distributed hornogeneously throughout a matrix of known composition can be computed using the following equation:
where Y(Z)is the measured trace element X-ray intensity (extracted fiom the X-ray spectrurn by least squares fitting), YI(Z) is the computed intensity in X-ray counts per steradian per microcoulomb of charge (pC) per ppm (gt) of concentration, R is the solid angle of the detector, Q is the rneasured charge (nA), f is any normaIization factor used in calibration of the charge measurement. el- is the intrinsic detector eficiency (calculoted from its dimensions), - is the transmission through an attenuating filter, and Ccis the desired concentration. The accumulated proton charge on a specimen rnay be measured directly, with an accuracy of about 1 %, if the specimen is electrically insulated from the surrounding structure and is connected direcùy to an elecuonic charge integrator- It is necessary to carbon-coat insulating specimens to prevent charge buiId-up and enhanced continuous background. At Guelph the technique is to combine f and Q into a single instrument constant (H) which can be determined using a minimal number of standards. The measurement of quantity H rnay be obtained using known trace elements and major elements in synthetic sulphide standards or the known contents of a steel standard fiom the National Institute of Standards. The advantage of this rnethod is that it overcomes errors arising from absorption corrections (especially in highly absorbing matrices), however the difficulty of obtaining tnily homogenous standards still rernains. Another approach to determine H consists in using a major or minor element in the sarnple itself if its concentration is known fiom previous EMPA (Cabri and Campbell, 1998; Czamanske et al., 1993).
Interpretation The interpretation of micro-PIXE analyses can be complicated by a number of factors. The frrst factor to consider is whether the detected trace elements are uuly present, or are they due to interference or X-rays derived from sub-surface inclusions or very fine-grained exsolution products. hterference X-ray peaks are fairly weI1 characterized in X-ray spectroscopy. They rnay be caused by either the overlapping of the KP peak of one element and the Ka peak of another element with a lower abundance, or to peak pileup fiom combinations of major element Ka and @ peaks. Other problerns anse in areas near the majorelement peaks where attenuation and secondary fluorescence effects may influence the analysis. In addition, micro-PIXE analyses are more subject to contamination from sub-surface inclusions than EMPA because the deeper penetration of protons produces characteristic X-rays from deeper regions of a matrix. Because of this retatively deep penetration, which depends mainly on the density of the mineral, it is not practical to anaIyze with confidence mineral grains smaller than about 50 prn in diameter. Anomalous or unexpected trace elements rnust be investigated further, either by reexarnining under high magnification the particular area of analysis. or by multiple analyses in the same grain to see whether the particular trace element is present consistently. Another important aspect to consider when interpreting micro-PKE data is that the minimum detection level or limit of detection (LOD)varies for each elernent in each analysis. In an interference-free principal peak of an element. a concentration would generate an intensity equal to a three-standarddeviation excursion in the intensity of the background continuum. This is summed over a region spanning the full-width at half-maximum of a hypothetical peak to determine the LOD. The LOD is a function of the operating conditions, the element of interest, the presence of interfering elements. and the design of the instrument (Cabri and Campbell, 1998). Appcndix C: Copiapile ampk 98CROJPS-1 and 2 &PME aoaianîlycs
TYP Swmn Thne ch=w ~p FWWI chiA= C~E bfn~ FCK CO li~ CO ~6 Conc 19990209.011 706 1.0 1.4 151.6 05 O O 198476 2162 12 Conc 19990109.0lT 815 1.0 12 149.0 0.6 O O 189278 2419 O Conc 1599039.013 861 1.O 1.2 150.0 05 619 O 192515 382 24 Conc 19990209.0 14 946 1.0 1.1 1495 O5 O O 193795 2478 66 COOC ~999012.015 932 1.0 1.1 147.0 O5 301 O 196086 2581 O Conc 19990209.016 1008 1.O 1.0 149.0 05 O O 211450 2646 103 Conc 19990209.017 1014 1 .O 1.0 149.7 O5 IW3 O 230073 2404 -'> Conc 19990209.0IS 883 1.0 1.1 1503 O. 6 O O 203193 230.8 O Conc 19990209.0 19 975 1.0 1.0 1481 05 O O 165268 1896 90 Conc 19990209.020 1765 1.0 0.6 1483 0.7 255 O 205992 2744 35 Conc I9990209.û21 49 l 1.0 LO 1489 05 265 O 203600 247l O Conc 19990209.022 556 1.0 1.8 150.2 05 603 O Z133 LS26 O Conc 19990209.m 548 1.0 1.8 149.0 0.7 O O ZW77 353 O Conc 19990109.ir4 550 1.0 1.8 149.1 0.6 O O 194698 2758 68
Err 19990209.01l 706 1.0 1.J 151.6 O5 O O 7 28 387
Err 19990109.0 12 8 15 1.0 1.2 149.0 0.6 O O -7 24 O Err 19990209.013 86 1 1.0 12 150.0 05 l& O 2 25 189 Err 19990209.014 946 1.0 LI l495 0.5 O O Z 24 70
EIr 19990209.OIS 932 1.O 1.1 147.0 05 398 O -I 13 O
Err 19990209.016 1008 1.0 1.0 149.0 OS O a -1 IS 48 Err 19990209.0 17 1014 1.O 1.0 149.7 05 134 O 2 28 2228 Err 19990209.018 883 1.0 1.1 150.3 O. 6 O O 2 27 O Err 19990209.019 975 1.0 1.0 1482 05 O O 2 27 47
Err 19990209.070 1765 1.0 0.6 1483 0-7 4g8 O 2 -77 134 Err 19990209.02 1 49 1 1.0 10 148.9 O5 465 O 7 25 O
Err 19990209.E 556 1.0 1.8 150.1 05 215 O -7 24 O
Err 1990209.023 548 1.0 1.8 149.0 0.7 O O 7 25 O
Err 19990209.024 550 1.0 1.8 149.1 0.6 O O 2 YI 66 LOD 19990209.0 1 1 706 1.0 1.4 151.6 0.5 5419 603 223 821 Ti LOD l9990209.012 815 1.0 12 149.0 0.6 F-il 585 157 TI1 78 LOD 19990209.013 66 1 1.O 1.2 150.0 0.5 3334 639 120 786 74 LOD 19990209.01~ 946 1.O 1.1 1495 O5 5139 682 24 1 792 67 LOD 19990209.015 931 1.0 1.1 141.0 05 321 694 721 ns n LOD 19990209.016 l00B 1.O 1.0 149.0 05 5589 706 297 873 74 LOD 19990209.0 17 1014 1.O 1.0 149.7 05 3570 755 3 80 907 87 LOD 19990209.018 883 1.O 1.1 150.3 0.6 5689 719 236 827 85 LOD 19990Z09.019 975 1.O 1.0 148.2 0.5 4893 548 169 683 60 LOD 19990209.020 1765 1.0 0.6 148.3 0.7 3454 663 20 1 8 18 76 LOD 19990209.0Zl 49 1 1.0 LO 118.9 05 3360 697 207 814 & LOD I99W709.CCE 556 1.0 1.8 1502 0.5 3632 722 90 88 1 84 LOD 19990209.023 548 1.0 1.S 149.0 0.7 5478 682 170 824 80 LOD 19990209.024 550 1.0 1.8 149.1 0.6 5476 625 253 788 7 1
DER 19990209.011 706 1.O 1.4 151.6 0.5 h' h' Y 9 N
Dm 19990209.012 815 1.O 1.2 149.0 0.6 S N Y 7 N
Dm! 19990209.013 86 1 1.O 1.2 150.0 05 N N Y 7 N
DEI? 19990209.0L4 946 1.0 1.1 1495 0.5 N N Y 7 7
DET? 19990209.015 93 2 1.0 1.1 147.0 05 N N Y 7 N
DEI? Im09.016 1008 1.0 1.0 149.0 OS N N Y 1 7
DET? 19990209.023 548 1.0 1.8 149.0 0.7 N N Y 7 N
DR? 19990209.014 550 1 .O 1.8 149.1 0.6 N h' Y 7 9 ~ppcndiiCr Copiapite nmple 98CRO-SPS-I aad 2 micro-PiXE dyws(contuuird).
Conc 19990209.012 O 546 1293 8 2 186 15 4 O O Conc L9990209.013 O 252 1262 5 O *9 5 O 1 O Conc 19990209.0l4 16 286 1260 LI 5 47 3 3 O O Canc 19990209.015 O 414 1222 7 4 L IL 9 1 O O COLU 19990209.016 II 283 1552 17 -Y 64 4 O 1 O Conc 19990209.017 3 316 1726 16 a 60 .. O 4 O Conc 19990209.018 1 219 1865 10 4 59 2 O 3 O Conc 19990209.019 15 147 985 5 O 39 1 O O O Conc 19990209.020 O 126 IJa 4 4 JO 5 O 3 O Caac 19990209.07 1 3 32 1526 1 O 55 4 O O O Conc 19990209.022 O '31 IF2 8 O 43 3 3 1 O
Conc 19990209.03f 8 314 1441 9 1 57 7 O O O Conc 19990209.014 8 23 138 1 -1 O LI 6 3 O O Er 19990209.0 11 167 6 -Y 57 83 7 32 268 19 1 O ur ~9990209.011 O 4 -7 n 132 3 14 60 O 38 1 Err 19930209.013 O 5 -7 86 O 6 J3 O 307 O Gr 1999(r09.014 87 5 -Y 36 62 7 7- 73 O 568 Gr 19990209.0 15 O 4 -Y 55 7 1 4 23 147 O O Err 19990209.OI6 136 5 -I 26 152 5 54 O 182 O Gr 19990209.017 SU 5 -1 28 75 6 53 O 49 O Gr 19990209.018 117- 6 -Y 42 83 6 86 O 78 O
Err 19990209.m 69 5 -1 48 137 6 29 496 O O ~rr 19990209.02a 160 5 3 171 O 7 31 62 O O LOD 19990209.011 17 9 8 6 4 4 3 4 4 5 LOD L9990209.012 2g 9 8 6 4 3 3 3 5 3 LOD 19990209.013 28 8 3 6 7 4 3 5 3 5
LOD 19990209.014 17 4 5 5 4 4 4 3 6 3
LOD 19990209.0l5 28 7 8 S 4 3 J 3 5 5 LOD 19990209.016 18 9 5 5 4 4 4 6 3 5 LOD 19990W.O 17 20 1 I 8 6 4 6 4 6 3 5 LOD 19990209.018 18 9 a 6 4 4 3 5 3 6 LOD 1999039.019 13 . 6 6 5 6 3 3 4 5 5 LOD 19990209.020 19 9 8 6 4 4 3 5 3 5
LOD 19990209.021 19 8 -Y b 6 4 4 3 6 3 LOD 19990209.022 30 9 7 6 7 4 4 3 4 6 LOD L9990209.m 17 9 3 5 4 4 3 4 s 5 LOD 19990tû9.024 18 3 7 6 7 4 3 3 5 5
DET? 19990209.011 I Y Y Y 7 N N N
DEI? 19990209.012 N Y Y Y Y 1 N N
DIT! 19990209.0l3 N Y Y h' Y 1 N N N
DR? 1~0209.014 1 Y Y v 7 Y 1 1 N N
DET? 19990209.015 H Y Y 7 Y 1 N N N
DR? 19990209.016 1 Y Y P 7 Y 1 N N N
DEI-? Im09.017 N Y Y 3 1 Y 1 N 1 N
DEI? 19990209.018 N Y Y 9 1 Y 1 N 1 N
DEI-? 19990209.021 N Y Y N N Y e N H N
DEI? lm09.(r- N Y Y P N Y 1 7 N N
DET? 19990209.m -P Y Y 1 7 Y 1 N N H DEI? 199901û9.024 h' Y Y S N Y ? 1 h' N Appcndix C: Copiapite sample 98CRO-IPS-1 and 2 miao-PIXE (cootinncdL
TYPC SprrPum ZrlL h'hK MoP AKK CdK Inn SnK SbE WLB TiLI PbM Conc 19990209.01 1 O O O 1 O 4 12 O 5 6 8 Conc 19990209.012 4 2 -7 O 6 15 O 14 O 5 4 Conc 199901209.013 -7 O 3 O 6 12 O O 7 O 4
~IIC 1999mN.014 1 0 0 2 0 10 0 O O 0 5 Cooc 199907?.015 O I 1 4 O O 3 O O -5 6 Conc 19990209.016 O 1 O 10 O O 5 O O O Il Conc 19990L09.OL7 O 2 O 3 O O O O O O 70 Conc 19990209.018 O 6 O O O O O O O O 1 Conc 19990209.019 1 1 O O 3 O O O O 5 O
7 Corn L9990209.01-O i O 3 1 15 O 17 13 O -7 Conc 19990209.û21 3 O O O O 3 5 O O O 8
Conc 19990209.OÏ L 7 4 8 O 9 14 O O 1 6 Conc 19990209.023 O 3 O O O O 16 13 O O 7
Canc L999ûL09.024 1 3 7 O O 4 O O O 3 4 Err 19990209.01 1 O O O L 13 O 202 17 O 4% 81 62 Err 19990209.012 51 95 111 O 1 Or 49 O 92 O 90 119 Em 19990209.013 100 O 80 O IO4 65 O O 270 O 132 En- 19990109.014 47 O O 28 O 73 O O O O 96 En 19990209.015 O 239 246 119 O O 307 O O 289 83 Err 19990209.016 O 22 1 O 48 O O 186 O O O 51 I5r L9990209.017 O 96 O 178 O O O O O O 10 ETT 1999û209.018 0 31 0 O 0 0 0 0 O 0 223
En- 19990209.024 179 61 Il6 O O 182 O O O IU 137 LOD 19990209.01 1 5 5 6 7 10 11 12 10 89 13 25 LOD 19990209.011 3 3 .I 9 9 9 20 19 94 14 55 LOD t9990209.013 3 5 4 IO 9 6 15 2 1 83 15 26 LOD 19990209.0 14 3 5 6 S 13 8 17 17 91 16 26
LOD 1~109.015 6 4 4 7 Il 13 15 24 90 15 40 LOD 19990209.016 6 3 6 5 12 14 13 22 106 17 30 LOD 19990209.017 6 3 5 8 16 13 19 22 1 12 17 29 LOD 19990209.018 s 3 6 (0 13 12 16 22 120 17 29 LOD 19990209.019 3 3 5 1 I 8 13 18 18 80 II 26
LOD 19990209.010 3 6 4 8 7 15 14 20 101 13 15 LOD Im09.02l 3 6 6 9 II 12 15 19 103 16 29 LOD 19990209.m 3 3 4 6 II II 12 21 105 15 3 LOD 19990209.m 6 3 5 II II 16 Il 17 101 16 L9 LOD lm09.O21 3 3 3 1 O II 10 17 19 96 13 25
DIT! L9990209.011 K S Y t N S 7 N N v N
DET! 19990209.012 7 h' 7 3 h' 7 N 3 N
DET? lm09.013 7 h V 7 7 N N N N N
DEI? 19990209.018 N S V S N N N N N N
DEI-? I999û209.019 N S N V -, h' N h' N 3 N
DEI-? 19990209.020 -, K , V -7 N 9 7 N N N
DET! 19990209.021 7 N Y N N N h' N N N N
DET? 19990Zo9.OÏ 7 7 , N 7 7 N N N N
Dm 19990209.023 N N N s N 7 7 N N N
DR? 1~09.024 N 7 -1 N N N N N N N N Appendix C: Jarosite stahctite and mud micro-PIXE analyses.
Type Specrrum Time Charge Ip FlVHM ChiA2 CrK MnK FeK Conc Conc Conc Conc Conc Conc Conc Conc Conc Conc Conc Conc Conc Conc Co nc Conc Conc Conc Conc Conc
Conc 19990209.045 550 1.0 1.8 0.5 1- 9160 Err Err Err Err Err Err Err Err Err Err Err Err Err Err Err Err Err Err EK Err Err 19990209.045 550 1-0 1.8 153-1 0.5 O O 3 Appendix C: Jarosite sblactite and mud micro-PME anaiyses.
T-ype Spectrum Tie Charge ip FWHM Chin2 Cr K Mn K FeK- LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD LOD 550 1.0 1.8 153-1 O5 2184 260 . . DET? DET? DET? DET? DET? DET? DET? DET? DET? DET? DET? D ET? DET? DET? DET? Dm DET? DET? DET? DET? DET? Appendix Cs Jmsite stalactite and mud micro-PKE analyses-
COKA CoKB NiK CuK ZnK CaK GeK AsKS SeK RbK SrK Y K 3 879 O 11 O 93 37 O 131 12 37 43 2 Appendix C: Jarosite stalactite and mud micro-PKE anaiyses.
CoKA CoKB NiK CuK ZnK GaK CeK AsKS SeK RbK SrK Y K 1163 96 21 19 7 7 8 16 5 449
93 50 10 5 4 3 4 4 2 L 3 3 ? N ?NY Y N Y ? YYN ? N N N Y ? N Y ? YYN ? N N ? Y ? N Y ? Y Y ? ? ? N ? Y Y N Y ? YYN ? N NNY ? N Y ? YYN ? N ? NY ? N Y ? YYN ? N ? NY Y ? Y ? YYN ? N N NY ? N Y ? YYN ? ? ? ? Y ? N Y Y YYN ? N N ? Y ? N Y ? YYN ? N N ? Y N N Y Y ?YN ? N NNY ? N Y Y YYN ? N N ? Y ? N Y ? YYN ? N N ? Y ? N Y Y YYN
? N N Y ? ? ? Y Y YYN ? N N ? Y N N Y Y ? ? N ? N N ? ? N ? Y Y YYN ? N ? YY ? N Y Y ?NN Appendix C: Jarosite stalactite and mud micro-PME analyses.
ZrK NbK MoK ABK CdK InK SnK SbK WLB TlLA PbLB BiLA Appendix C: Jarosite stalactite and mud micro-PIXE analyses.
ZrK NbK MoK AgK CdK inK SnK SbK W LB TILA PbLB BiLA File : GUPIXMDL------,TXT May, 1989 by J.A. Maxwell, Physics Department, University of Guelph (extracted from the GUPIX manual)
The limits of detection values (LOD or MDL - minimum detection limits) are reported in two sections of the code, In the STATS section the LOD values are oucput in counts in che yak area sumrnary seccion ana in p.p.m. (for thick specimens) in the element concen~rationtable, In the LOD Table section Che MDL values zre oxt=ut only in concentrotions and thus require that H and Charge be defined for that case. - . .. . LOD values are calculatea 02 ~k-Lesis LI 2- S;EZ-GL, 2s-::âcions of the background areas over a 1 fwhm region centered about the elements principal peak centroi2. The LOD vzlzo rezcrted is for that zarricular element in the specified spectrum and is thus not normalized co any given charge. In councs, the LOD value is sirnply 3*Sigma, where Sigmz is sqrt (B) and B is the "background" crea over the 1 fwhm region. In p.p.m. the LOD value is given by
LOD (ppm) = (3 * Sigma)/(C H * Yt + e * T ), where
Sigma : the standard deoiation error, eg. sqrt (B) B : background area in one fwhm region, C: the charge in cc H : standardization value used in conversion of area to concentration, (contains solFc anqle etc.) Yt: theoretical ïkiz? ïarqet yiol5 of X,L or P! alpha x-rays/uC/ppm/ster in the 1 fwhm region centerec abouc =he element's principal peak, relative deteccor efficiency, transmission of x-rays ïhrouçh on- ~ksorberthat is present.
In the two cases mentionea above, (STATS & L3D Table) it is B che .. A- background value chaz is calcclated =? a crzzerent manner.
1) - LODS in STATS seczior,: . . In this section E Fs cciculacoc r~erz~r-rolyin the follo~Lng manner: first, the overell backqrour- in E -.I fwhm region is calculated by summing YDJ-TI - VFI~Lovor tne zefroz C: rnterest. Tho av=rags tl-.=s ac~cFz~2is used zc rscxc~:ît backgrom5 in cho 8ackground . - following manner - rz rz ariy chac?ol zhs czrsuted backgrouna exceeas the overage backqroü2d by F~ZEchat I si;~oth?- the backgrocnd co:tribution of ïhac chznnel Fs re~.~=skto rhs a-.-~regr-.-~IUP zna c ne" total . m. ~ackgrocnaare2 Fs cc, z~~a~oc.- ~.rs. :roc~5:r~, wnich coc=inues until the backqround arsa Fs n== :har.qcc, '-2s :ris a---=--2.-..~age of sxoozhinq out any aiscrepancies be~wer?frr an5 aazz rz~sqi-i-r~-9 a more acc:zaze ~icture ûf the real underlylns ssrkgrounc iz Z~LSrezion. the square-root of the "real" background to give Sigm~,i=.
Sigma = sqrt( B + O 1 + 0-01 * O, Then 3+Sigma is the LOG area (in counts) reported by STATS for eazh element specified in the fit and chat area is conrtrtec rc psa iz zhe concentration table,
2) - LODS in Table section: In this section the background B is calculated sirnply as the sum of counts of the raw speccrum in the 1 fwhm region. Ko accourt is tcssn of the fiz and thus LOD vclues for elernents thac are in cna speccruz will be artificially high while those for elemencs not in the spectrue should 8e reasonable. There are several points to remember:
2) kere LOD values ore in ppm and thus can only be calcclatea iE H>O;
b) LOD values are cornputed for al1 the trace elelients whose prixcipal peak's centroid would lie in the fit region for the Al & A2 values used, with the user having the option of specifying K x-ray =race elements, L x-ray crace elements, M x-ray trace elements ecc;
C) more reasonable escimates of LOD values for elercsnts Lhat a== present in the spectrum can be obtained by examinino LOD valxos for elements just before or after the one Ln quesrion, Remember, nowever, that LOD ;-zlues for elemenrs jus= etave oz k210w Zr. elemenc that is prosent ic the spectrun Zay t=v~larçor LOD -.-zluts chan chose from a ~lankspeccrurn Bue co =ne azesezce of overlspping peaks (K beta peaks, L beta or gamma peaks, escape peaks, czlls etc.). File: GUPIXCON .TXT May, 1990 by J,A.Maxwell, University of Guelph
CZSCZZL-----
EXCERPT from the original file GUPIXCON-TXT C*C*t+****CV
The decision column contains a 'Y', 'N' or '3' which is an automatic decision on the part of the program as to the presence of the element in this spectrum. A "Y" inaicaces that tne element is present in arnounts more than one sigma above the quantizacion lirnit. The quantization limit is IO sipa acd thus a 3 sigma error represents a 30% error at the quantiz~tionlimit. A "N" is an automatic rejection of the presence of that elernent at mimimum detection limit values. That is, it Fs nore thac one sis-= below the MDL level. This is not to Say that the element is noï present in the sample, it is simply to say that it IS NOT presenr a= zko level of the MDL value. A "?" represents al1 other cases, izhat is the reported value is somewhere between one sigma below the MDL value and one sigma above the quantization limit- It is up to the user in these cases to decide on the applicability of using the concentration values reported by the program. Ideally one would like to collect sufficient data to obtain values above the u-c.,,L,c,.lcr,'-..-*------1FrrL: 2: fcr 211 trztt =lc==r.ts ci5 ir-',orest Urrt t?Lr Is not alwayç possible due to the constraint of time. The user must decide if he or she is cornfortable at reporting numbers at or near the limit of decection or would prefer CO report with a 3 sigma error chus requiring scatistics ac or above =Be QL for errors cnder 30%.
Further Discussion of ~he"?" Decisioc: .--; - . . - -. - -.-- 1*31'- CS-:--sl:z - L-zs FL= i-zc rzrr zzLls fcr c r-szzzrr F-zr;os=. As there is no= a singls number wnere if the reportea concencracio~is belou thci vclce Fr is dezinitely COC 3r~Se:Z i~?th= sampie ~zdif Lt is above thêz nurrher ic is definitely prese-z ~s have chosen ~hefoiiowing linits: At tne 10%enc if the reportea c~ncsntrctionplus the error cerm is less than Che LOD value then wo sry ~heeleaent Fs NO- present at the linlt of dezection, ec. seo elorne-zs 24 (Cr), 32 (Ge), or 75 (Au) in the above table. Th5 user can Say rhzz =?.ose elomsn~sare noz wresenc or to be cechnizally corzecc ECZ ?resent ac the limit of de~eccion. LE the high end, we Say chat if zhe reporceb val~oFs larger than che quancization li~it(3.3*LOD) pLss errcr rhen the elornont is QeEi-FteLy prosocz ac Ir-:sis excerciin~ï?-s ;xan~ir~=icclixi:, eq. soe elenents 2@ (Mil, 39 (Y! or 40 (Zr) ic tks zbove tabl~. PLI zeporzed vô?uss becween these txr exirenos recci~zc?.~ "?" cssiqnatior aza Fc Fs us KG th^ end user cc cscice the a~~rû~rrzr~r~ess05 using ~hzz----*-a\=----
F-io fa ci lit^^^ rhs ena USE~nakrr; a 5ecisicx ç3our tkr resorted values ic LRI case wners e "?" has-. showz 2~ in the decision columc che folioxing informotion r.-.alVDe user^^. overlapping peak area. Note that this is a more pessimistic error than the sqrt (6 + O) + 0.01*0 chat is used over a I fwhm range to determine the LOD value. (See GUP1XERR.TXT for c more complete discussion of tnis error)
LOD(ppm) : the limit of detection is defined as three tirnes the error obtained for the background and overlap (but not the elements own area) in a 1 fwhm region centered about the principal peak of the element; that is, 3*( sqr~(B + O ) + 0-01 - O ) (See GUPIXMDL. TXT for the exacc recipe ,) Confidence levels: One sigma error bars give a confidence level of 68:, 2 sigma about 95% and 3 sigma about 99%, that is the user can be confident at these levels that the reported value Fs within the error bars of the true value,
With this in mind 1 would suggest that the user can quote the reported value with error of 1, 2 or 3 tlmes the reported error (8assd on ths confidence level he/she is cornfortable with). Depending on the confidence level chosen the error bars rnay indicate that the element mignt be present at levels well below the limit of detection or even not present at all. As an example, if an element had been roz~~zzor:as 13.9 pprn with an error of 5-2 ppm and an LOD of 8 -4 ppm, ~hiknumbez could be interpreted as:
13.9 +/- 5.2 ppm ~Fth68% confidence, (range above LOD thus present) 13.9 t/- 10.4 pprn with 95% confidence, (range extendinc below LODI or 13.9 +/- 15.6 pprn with 49% ccrtfidence tposslbly noc prêsEnï aï all)
This is wnere the user has ro make a decision.
€oz instance sone psopie woul~be confozzable zî reporting zumbozs such cs 6-2 +/- 3.3 pp~with an L3D nezr tkc reported value cr say E.0 =O 6.5 pprn, while ocners may hesizace to us2 such values.
These are tne sozt of jgdgement calls chat tne end user is required to make and rhis is why WE include rho "?" in tne decision colxrnr.
Pi zhe low enc of tk3 "?" scole theze is a great doal c5 ds-bc as to che presence or absence of che elsrnent whilz at the upper ~2dof che scalo ~hereis little C,3ubc as tc the prescnce of the eiern~?~3üt thtre is a zelazively larqe u.cer=aicty (>39I) ir. =no exacz qcz-ritezive valu=. APPENDIX D: WATEQ4F OUTPUT
This appendix contains a raw output fiom the geochemical speciation progarn WATEQ4F (Ball, 1987, 1999). This particular example is for stalactite dnp water sample 98CAf OSA. 1 98CAl05A-FU: jarosite stt drip water 1 5
6975. O, 91299 0.0000 0.0000 0.0000 0.0780 0,3080 0,0000 0.2180 TEMP - 29.5OOOOO PH - 2.O5OOOO EH(0) - O,751000 DOC - o.000000 DOX - o.000000 CORALK = O FLG - MG / L DENS - 1.OO5OOO PRNT - 3 PUNCH - 1 EHOPT(1) = O Use measured Eh to calculate Fe species distribution EHOPT(2) = O Use rneasured Eh to calculate Mn species other than +2 EHOPT(3) = O Use measured Eh to calculate Cu t1 species EHOPT(4) = O Use measured Eh to calculate As species distribution EHOPT(5) = O Use measured Eh to calculate Se species distribution EHOPT(6) = O Use measured Eh to calculate Ion Activity Products EHOPT(7) = O Use measured Eh to calculate atmospheric p02 EHOPT(8) = O Use measured Eh to calculate H2S from SO4 EHOPT(9) = O Use measured Eh to calculate U species distribution EMPOX - O 1 TDS - 0.000000 COND - 6975,000000 SIGMDO = o. 000000 SIGMEH = o. 000000 SIGMPH = o. 000000 Species Index No Input Concentration Ca Mg Na K Cl S04 HC03 Fe total H2S aq CO3 Si02 tot NH4 B tot PO4 A 1 F NO3 Fe Fe Li Sr Mn Cu Zn Cd As total ; As3 tot :
ITER Sl-AnalC03 AnalHüM 1 0.000000Et00 0.000000E~00 2 0.000000Et00 0.000000Et00 3 0.000000Et00 0.000000Et00 4 0.000000Et00 0.0000003+00 5 0.000000Et00 0.000000Et00 6 0.000000E+00 0.000000E+00 7 0.000000Et00 0.000000Et00 8 0.000000Et00 0.000000Et00 9 0.000000Et00 0.000000Et00 10 0.000000Et00 0.000000Et00 1 98CA105A-FU: jarosite stt drip water 6975. 0. 91299 0.0000 0.0000 0,0000 0.0780 0.3080 0.0000 0.2180 DOX = O. 0000 DOC = O. O INPUT TDS = O. O Anal Cond = 6975.0 Calc Cond = 10316.3 Activity H2S calc from SO4 and pe = 0.00Et00 Anal EPMCAT = 115.6049 Anal EPMAN = 129.9965 Percent difference in input cation/anion balance = -11,7195 Calc EPMCAT = 52.9771 Calc EPMAN = 55.2115 Percent difference in calc cation/anion balance = -4,1305 Total Ionic Strength (T.I.S.) from input data = 0.28376 Effective Ionic Strength (E.I,S.) from speciation = 0.08748 Sa to Input Sigma Fe3/Fe2 Sigma N03/NQ2 Sigma N03/NH4 Sigma S04/S= Sigma S/S= Sigma H202/02 Sigma H20/02 Sigma ------Eh------*-----
hs5/As3 Sigma As3/As Sigma Se6/Se4 Sigma Se4/Se Sigma Se/Se= Sigma U6/U4 Sigma Sigma ------Eh------0.473 0.000 0.009 0.000 9.900 0.000 9,900 0.000 9.900 0,000 9.900
C E3 7.880 0.000 0.122 0.000 100,000 0.000 100.000 0.000 100,000 0.000 100.000 Effective T pH TDS ppm Ionic Str p02 Atm ppm 02 Atm pC02 Atm ppm CO2 Atm log pC02 CO2 Tot Ncrb Alk aH20 29.50 2.050 8239.2 0.08748 4,303-24 1.39E-19 0.00E1-00 0.00Et00 0.000 0.00E+00 5.9931-
1 Species Anal ppm Calc ppm Anal Molal Calc Molal % of Total Activity Act Coef f -Log Act 50 Al 3 82.687 13.526 3,0903-03 5.055E-04 16.36 5.89SE-05 O. 1166 4.230 54 A1F 2 3.349 7.3453-05 2.38 2,8263-05 O. 3848 4.549 55 A1F2 1 0.055 8,596E-07 O. O3 6.77031-O7 O. 7896 6.169 56 A1F3 aq O O,O00033 3.9193-10 o. O0 3.9993-10 1,0203 9.398 57 A1F4 - 1 o. 000000 9.4503-15 0.00 7.443E-15 0.7876 18.128 203 AlHS04 2 o. 414 3.3663-06 o. 11 1.295E-06 O. 3848 5.888 2.280E-07 0.01 8.9733-08 O. 3848 7.057 52 A1 (OH)2 1 9.947 181 Al(OH)3 O 14,590 53 Al(OH)4 -1 18.236 58 AIS04 1 2.804 59 Al(S04)2 -1 3.394 261 As3 tot O 253 As03 - 3 34.028 252 HAs03 -2 22.730 251 H2As03 -1 12.761 250 H3As03aq O 5.655 254 H4As03 1 8,010 l-. \O 262 As5 tot: O P. 258 As04 - 3 19.322 257 HAs04 -2 9.824 256 H2As04 -1 5.124 255 H3As04ay O 4.913 O Ca 2 183.085 2.962 100 CaF 1 9,307 81 CaHS04 1 4.000 28 CaOH 1 13.692 31 Cas04 aq O 2.743 160 Cd 2 6.556 161 CdC1 1 8.163 162 CdC13 aq O o. 000001 7,2693-12 o.O0 7.4173-12 11.130 163 CdC13 -1 O. 000000 1.620E-15 0.00 1.2763-15 14.894 1 98CAlOSA-FU: jarosite stt drip water 1 5
1 Species Anal ppm Calc ppm Anal Malal Calc Molal % of Total Ac tivity Act Coeff -Log Act 164 CdF 1 o. 000000 2.074E-13 0.00 1,6333-13 0.7876 12.787 165 CdF2 aq O O,000000 1.8788-20 0.00 1,9163-20 1.0203 l9,718 173 CdN03 1 O. OOOOOS 2,7653-11 0.00 2.1783-11 O. 7876 10.662 167 CdOH 1 o.000000 4.568E-15 o.O0 3.5973-15 O. 7876 14.444 168 Cd(OH)2 O o.000000 1.527E-23 0.00 1,558E-23 1.0203 22.807 169 Cd(OH)3 -1 O. 000000 2,4873-34 0,oo 1.9593-34 O. 7876 33.708 170 Cd(OH)4 -2 o. 000000 5.0843-46 0.00 1.956E-46 O. 3848 45.709 k- \Ocn 171 Cd20H 3 O. 000000 3.972E-20 0.00 4.6313-21 O. Il66 20,334 172 CdOHClaq O o.000000 3.423E-16 0.00 3.4923-16 1.0203 15.457 174 CdS04 aq O O,133 6.4193-07 42.30 6.55OE-07 1.0203 6.184 277 Cd(S04)2 -2 O. 030 1.445E-07 9.52 5.561E-08 0.3848 7.255 4 Cl - 1 11.741 11.598 3.339E-04 3.299E-O4 98-79 2.5493-04 O. 7728 3.594 127 Cu 1 O. 000000 5.0393-16 0.00 3.9693-16 O. 7 876 15.401 128 CuC12 -1 o. 000000 1.025E-17 0.00 8.0723-18 O,7876 17.093 129 CuC13 -2 o. 000000 8.623E-21 0.00 3.3183-21 O. 3848 20.479 130 Cu 2 0.621 O. 380 9.8523-06 6.0373-06 61.27 2.323E-06 O. 3848 5.634 133 CuCl 1 O. 000247 2.5143-09 O,O3 1,9803-09 0,7876 8.703 134 CuC12 aq O 0.000000 2,7883-13 0.00 2,8443-13 1.0203 12.546 135 CuC13 -1 o. 000000 3.534E-19 0.00 2.783E-19 0.7876 18.555 136 CuCl4 -2 24.404 137 CuF 1 11.687 138 CuOH 1 11,585 139 Cu(OH)2 O 15.215 140 Cu(OH)3 -1 26.386 141 Cu(OH)4 -2 37.036 142 Cu2(OH)2 2 17.337 143 CuS04 aq O 5.410 61 F 7.331 125 HF aq 6.169 126 HF2 s 12.902 O\ 296 H2F2 aq 11.993 7 Fe 3,384 315 FeCl 6.838 308 . FeF 9.715 122 FeHS04 4.422 10 FeOH 10,691 79 Fe(OH)2 19.474 11 Fe(OH)3 27.906 33 FeSO4 aq O 3.198 8 Fe 3 1425.871 3.797 15 FeCl 2 S. 850 27 FeC12 1 O. 000223 1.77 6E-09 o. O0 8.854 32 FeC13 aq O 0.000000 3.4953-14 0.00 13.448 105 FeF 2 2.436 3.28331-05 0.12 4.899 106 FeF2 1 O. 002925 3.143E-08 0.00 7.606 107 FeF3 aq O o. 000000 1.8233-12 0.00 11.730 123 FeHS04 2 144,650 9.539E-04 3.47 3.435 9 FeOH 2 28.128 3,8933-04 1-42 3.824 76 Fe(OH)2 1 O. 744 8.3493-06 0.03 5.182 77 Fe(OH)3 O o. 000012 1.128E-10 O. O0 9.939 78 Fe(OH14 - 1 O. 000000 1,7853-17 0.00 16,852 179 Fe2(OH)2 4 3.314 2.2933-05 0.17 6.299 C D 180 Fe3 (OH)4 5 O. 042 1.7943-07 0.00 9.339 14 FeSO4 1 2935.485 1.9493-02 70.90 1.814 108 Fe(S04)2 - 1 848.590 3.4513-03 12.56 2.566 63 H 1 10.734 1.0743-02 0.00 2.050 3 K 1 0.712 O .672 1.837E-05 1.7343-05 94.40 4.873 1 98CA105A-FU: jarosi te stt drip water 1 5
1 Species Anal ppm Calc ppm Anal Molal Calc Molal % of Total Activi ty Act Coe f f -Log Act 45 KS04 -1 0.138 1.028E-06 5.59 8.0953-07 O,7876 6.092 80 Li 1 0.048 O. 046 6.9403-06 6.7073-06 96.64 5,2833-06 5.277 82 Lis04 -1 O. 024 2,3293-07 3.36 1.83431-O7 6,737 1 Mg 2 64.876 34.915 2,6913-03 1.4483-03 53,82 6.0643;-O4 3.217 19 M~F 1 O,O00111 2.573E-09 0.00 2.02731-09 8.693 18 MgOH 1 12.434 22 MgS04 aq O 2.897 109 Mn 2 4.731 110 Mn 3 17.455 111 MnCl 1 7.715 112 MnC12 aq O 11.668 113 MnC13 -1 15.822 116 MnF 1 11,222 118 Mn(N03)2 O 13.034 121 Mn04 - 2 55.117 120 Mn04 - 1 ;O 51.706 03 114 MnOH 1 13.115 115 Mn(OH)3 -1 33.383 117 MnS04 aq O 4.544 2 Na 1 17.413 3.237 297 NaF aq O 10.808 43 NaSO4 -1 4.624 84 NO3 - 1 2.776 4.449 26 OH - 1 11.805 34 Si02 tot O 138.308 23 H4Si04aq O 2.626 24 H3Si04 -1 10.341 25 H2Si04 -2 w 03 O ri 1 1 Cil Cil 43 m w m m O m rl
N O O O O O
P a O rl 1 I W w rD P w m N P 4 N
O O O m O r( O O O O O Ca/Mg = 2.8221Et00 Na/K = 2.4441Et01 Fe2/Fe3= 6,76903-02 Zn/Cd = 2.2000Et02 Na/Ca = 9.51093-02 Sr/Ca = 5.43483-06 Mn/Fe = 2.7320E-03 Cu/Fe = 4,07843-04 Zn/Fe = 2,44443-02 Cd/Fe 1.11113-04 1 98CA105A-FU: jarosite stt drip water
Phase Log IAP/KT Log IAP Sigma (A) ~,ogKT sigma (T) 195 a-Cryptomeln 178.472 39 Adularia -30.980 489 AlAs04, 2H2O -23.553 40 Albite -29.345 157 Allophane (a) -2.459 158 Allophane(P) -2.459 140 Al(OH)3 (a) 1.919 338 Alum k -13,308 50 Alunite 42 Analcime 17 Anhydrite 113 Annite 41 Anorthite 239 Antleribe 497 Arsenolite 488 As205 237 Atacamite 472 Basaluminite 48 Beidellite 292 Bianchi te 184 Birnessi te 186 Bixbyite 52 Boehmite 240 Brochantite 19 Brucite 490 Ca3As04)2,4w 312 Cd metal 320 Cd(OH)2 (a) 321 Cd(OH)2 (c) 323 Cd3 (OH)4SO4 w 324 Cd30H)2S04)2 C 325 Cd4 (OH)6SO4 317 CdC12, 1H20 316 CdCl2 318 CdC12,2,5H20 319 CdF2 322 CdOHCl 328 CdSi03 330 CdSO4, 1H20 329 CdS04 331 CdS04,2.7H20 143 Celestite 248 Chalcanthite 97 Chalcedony 49 Chlorite 14A 125 Chlorite 7A 20 Chrysotile 498 Claudetite 29 Clinoenstite 56 Clinoptilolt 99 Cristobalite 223 Cu metal 234 Cu(OH)2 238 Cu2(OH)3N03 -18.620 -9.569 228 Cu2S04 -30.902 -32.902 491 Cu3As04)2,6~ -20.427 -55.550 225 CUF -29.677 -22.732 1 98CA105A-FU: jarosite stt drip water 1 5
Phase Log IAP/KT Log IAP Sigma(A) LogKT Sigma (T) 232 CuF2 -19.530 -20.296 -0,765 233 CuF2, 2H20 -15.707 -20.297 -4.590 243 CuOCuSO4 -24.510 -13,368 11,142 249 CupricFerrit -2.289 3,169 5.458 226 Cuprite -25,221 -26.703 -1.482 229 CuprousFerit -2.038 -11.000 -8.961 247 CuS04 -10.546 -7.733 2.812 154 Diaspore -4.691 1,919 6.610 28 Diopside -22.770 -3.229 19.541 420 Dioptase -10.562 -4,160 6.402 340 Epsomite -3.212 -5.321 -2.109 55 Erionite -30.659 419 Fe3(OH)8 -14.805 5.4 17 181 FeOH)2.7C1.3 3.698 O. 658 112 Ferrihydrite -2.540 2.351 13 0 62 Fluorite -7.074 -17.623 lu 27 Forsterite -28.637 -0,860 313 Gamma Cd -44.959 -31.567 51 Gibbsite (c) -5.943 1.919 110 Goethite 3.509 2.352 293 Coslarite -4.102 -6.026 111 Greenalite -23.914 -3.104 18 Gypsum -0.479 -5.062 64 Halite -8.423 -6.831 47 Halloysite -13.474 -1.411 187 Hausmannite -32,718 27.215 108 Hematite 9.048 4.704 45 Illite -17.642 -57.313 205 Jarosite K 3.324 -8.167 337 Jarosite H O,646 -5.345 ,204 Jarosite Na -0,857 -6.531 133 Jarosite(ss) 2.345 -7.485 47 1 Jurbani te -1.050 -4.280 46 Kaolinite -8.461 -1.411 43 Kmica -16.994 -4.938 241 Langite -28.698 -12.340 128 Laumontite -19.402 -49.931 147 Leonhardi te -31.086 -99.861 199 Lithiophorit 98 Magadiite 109 Maghemite 107 Magnetite 189 Manganite 230 Melanothalit 339 Meianterite 66 Mirabilite 134 Mn2 (SO4)3 493 Mn3As04)2,8w 191 MnC12, 41.120 182 MnS04 326 Monteponite 115 Montmoril BF 116 Montmoril AB 63 Montmoril Ca 57 Mordenite 224 Nantokite 185 Nsutite 1 98CA105A-FU: jarosite stt drip water
Phase Log IAP 13 Sigma (A) Log KT Sigma (T) E: 54 Phillipsite -30.163 -19.874 44 Phlogopite -28.335 42.839 3.000 539 Portlandite 1.137 22.462 141 Prehnite -46.167 -11.582 180 Pyrocroite -0.632 15,200 183 Pyrolusite 28.478 40.670 53 Pyrophyllite -51.067 -48.314 101 Quartz -2.624 -3.915 200 Rancieite -87.772 492 Scorodite -23.121 153 Sepiolite {d) -6.111 36 Sepioli te (c) -6,111 100 Silica gel -2.624 395 Si02 (a) -2.624 399 SrF2 -23,212 37 Talc -7.852 242 Tenorite -1.535 65 Thenardite -8.574 198 Todorokite -109.749 31 Tremoli te -14.309 155 Wairakite -49.929 289 Willemite -2.271 282 Zincite (c) O. 177 290 Zincosite 265 Zn metal 275 Zn(0H)2 (el 272 Zn(OH)2 (c) 274 Zn(OH)2 (g) 273 Zn(OH)2 (b) 271 Zn(OH)2 (a) 278 zn2 (OH)2SO4 276 Zn2 (OH)3Cl 496 Zn3As0422.5~ 283 Zn30 (SO4)2 279 zn4 (OH)6SO4 277 ZnS(0H)ECl 267 ZnC12 270 ZnF2 280 ZnN03)2,6H20 281 Zn0 (a) 288 ZnSi03 291 ZnS04, 1H20