Applications of Mass-Balance Calculations to Weathered Sulfide Mine

Chapter 31

Applications of Mass-Balance Calculations to Weathered Sulfide Mine Tailings Downloaded by UNIV OF NEW SOUTH WALES on September 18, 2017 | http://pubs.acs.org Publication Date: December 20, 1993 | doi: 10.1021/bk-1994-0550.ch031

Edward C. Appleyard and David W. Blowes Department of Earth Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada

The oxidation of sulfide minerals in mine tailings impoundments releases SO , Fe(II) and other metals to tailings pore-waters. The subsequent precipitation of secondary oxide and hydroxide minerals can decrease dissolved metals through accompanying precipitation, coprecipitation or adsorption reactions. Quantitative assessments of the fluxes of metals in tailings systems resulting from weathering require determinations of the changes in total solid phase metal which are independent of apparent changes caused by mass, and concomitant volume and density changes resulting from sulfide oxidation and hydroxide reprecipitation. Mass changes during weathering were calculated for samples collected through the weathered zones in the high-sulfide Heath Steele Zn-Pb-Cu tailings impoundment, New Brunswick, and the low-sulfide Delnite Au tailings impoundment, Ontario. The results of these calculations show that the degree of metal mobility varies according to the duration of weathering, the sulfide content and the buffering capacity of the tailings. Results of the mass-balance calculations complement the results of pore-water chemical analyses. 4

Sulfide-oxidation reactions and subsequent acid-neutralization reactions occurring in inactive mill tailings result in the depletion of sulfide minerals, carbonate minerals and some aluminosilicate minerals with the concomitant accumulation of metal-hydroxide and sulfate minerals. To assess the potential effects of a tailings impoundment on water quality it is necessary to distinguish the amounts of all the constituents that remain within the tailings from those that have been displaced out of the tailings impoundment. Recently, numerical models that combine geochemical reactions with solute-transport mechanisms have been used to describe the movement of dissolved constituents in tailings impoundments and in adjacent aquifers (1,2). To apply these models accurately it is necessary to constrain model simulations as closely as possible using field observations of dissolved and solid masses of chemical components. 0097-6156/94/0550-0516$06.00/0 © 1994 American Chemical Society Alpers and Blowes; Environmental Geochemistry of Sulfide Oxidation ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

Downloaded by UNIV OF NEW SOUTH WALES on September 18, 2017 | http://pubs.acs.org Publication Date: December 20, 1993 | doi: 10.1021/bk-1994-0550.ch031

31.

APPLEYARD & BLOWES

Weathered Sulfide Mine Tailings

517

Oxidation of sulfide minerals and precipitation of hydroxide and sulfate minerals typically result in changes in the density of tailings as well as in the volume occupied by the solid materials. Thus, changes in mass occur during weathering that may produce erroneous indications of elemental mobilities if raw chemical analyses are relied upon, i.e. it is usually incorrect to compare 100 g of the altered material with 100 g of the starting material. Chemical data corrected for weathering-related changes in mass provide a way of determining elemental mobilities independent of apparent variations due to mass-change effects. This paper describes the application of mass-balance corrections to mine tailings from two mineralogically dissimilar impoundments, the high-sulfide Heath Steele ZnPb-Cu tailings impoundment, New Brunswick, and the low-sulfide Delnite Au tailings impoundment, Ontario (Figure 1). To apply this approach successfully a group of ele ments must be identified with effectively immobile characteristics under the conditions of weathering. Immobile elements provide a reference for evaluating changes in mass resulting from chemical weathering and permit the quantification of elemental fluxes independent from calculations based on pore-water analyses. In addition, these studies reveal the influences of different mineralogical compositions of tailings on the mobilities of elements. In our experience, this is the first application of a mass-balance technique to mine tailings. Mass-Balance Calculations Quantitative estimates of elemental fluxes (gains and losses) which occur during alter ation of any solid geological materials (e.g. soil, rock, ore etc.), can only be determined if the ratio of the after-alteration mass to the starting mass is known. This ratio, F , is generally unknown and must be determined to proceed. A method of determining the value of F M for each sample of altered material is provided through the application of Gresens' General Alteration equation (3). There is a family of equations, one for each element, which express the relationships between the before-alteration and the after-alteration compositions of any solid material and the resultant mass-change. The general form of these equations can be represented as follows: M

g

Δχ„ = x χ;) - χζ (D where Δχ = change in mass of the element 77, m /m = mass-change ratio for the whole sample ( F M ) , Χη = concentration of element 77 in the altered sample, and χ = concentration of element 77 in the precursor (unaltered) material. Because the value of m /m is initially unknown, an alternative form of the equation substituting the product of density p, and volume v, for mass m, is more commonly used: a

p

η

ρ

a

p

Δ

*" = (5 * £* *) -


3

3

Description of the Study Areas The Heath Steele tailings are located in northeastern New Brunswick (Figure 1), 50 km from the town of Newcastle. The tailings are contained in two impoundments, an older impoundment, covering ca. 10 ha, which operated from 1957 to 1965, and a new impoundment covering ca. 200 ha, which operated from 1965 to 1982 and from 1989 to the present. Core samples were collected from two locations on the old impoundment (holes OW3 and OW8) to a depth of ca. 5 m, and to a depth of ca. 3 m at one location on the new impoundment (hole NW10). The tailings contain approximately 85 wt% sulfide minerals and 3 wt% carbonate minerals. Boorman and Watson (4) conducted a detailed study of the tailings and dis cerned the geochemical zones within the old tailings impoundment to be, from the surface downwards, an Oxidation Zone, a Hardpan Layer, and a Reduction Zone overlying un weathered tailings. Our sampling, conducted in 1986-1987, confirmed the presence of the same three alteration zones in the old impoundment. The Delnite Au tailings are located 5 km from Timmins, Ontario (Figure 1). The tailings were deposited continuously from 1937 to 1964, and are contained in a single elevated tailings impoundment, ca. 25 ha in area. Core samples were collected from site D5 on the Delnite tailings. The water table at this location was at a depth of 2.7 m when the samples were collected. No hardpan layer was detected in the section. The tailings contain ca. 5 wt% sulfide minerals, primarily pyrite and pyrrhotite, with lesser amounts of arsenopyrite. The tailings also contain about 20 wt% of carbonate minerals, primarily dolomite and siderite. A revegetation program, initiated in 1971, established a self-sustaining cover of grass and small trees on the tailings surface. Methods Mass-balance calculations in this study were conducted using the SOMA computing package (5). The procedures utilized are outlined in greater detail by Taylor and Appleyard (6) and Appleyard (7). Samples for the whole-rock analyses were collected in 7.6 cm (3 in.) thin-walled aluminum tubing. Core samples were cut into 10 cm intervals and lightly ground.

Alpers and Blowes; Environmental Geochemistry of Sulfide Oxidation ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

31. APPLEYARD & BLOWES

521


Particle density measurements of all samples were made prior to analysis using a Beckman Model 930 Air Comparison Pycnometer. Total carbonate was determined using the technique of Barker and Chatten (8) and total sulfur concentrations were de termined using a LECO induction furnace. Sample splits were analyzed by Activation Laboratories Ltd., Ancaster, Ontario. The major elements, Si, Ti, Al, Fe t /, Mn, Mg, Ca, Na, K, and Ρ and the trace elements Ba, Sr and Y were analyzed by inductively cou pled argon plasma atomic emission spectrometry (ICP-AES) following a Li-metaborate fusion. Copper, Pb, Zn, Ni and V were measured by ICP-AES following a HN0 -HC1HCIO4-HF digestion. Silver, As, Au, Mo, Sb and Se were determined by ICP-AES following digestion with solvent extraction (9). Rubidium, Zr, and Nb were analyzed by X-rayfluorescenceanalysis on a pressed powder pellet. Cobalt, Cr, Cs, Hf, Se, Ta, Th, U, and the rare earth elements La, Ce, Nd, Sm, Eu, Tb, Yb and La were determined by instrumental neutron activation analysis and Β was measured using the prompt gamma modification. to

a


3

Results Application of Mass-Balance Studies to Heath Steele Tailings. General. Immobile elements identified within the weathered zones of the Heath Steele tailings impoundments include Ti, Sc and Zr at sites OW3, OW8 and NW10. In addition, V and Hf were immobile at sites OW3 and NW10. Rare-earth element data for site OW8 indicate that La, Yb and Lu were generally immobile. Compositional variability within unweathered sections presents a problem in estab lishing the compositions of the precursors of the weathered samples. The procedure adopted was to use the mean composition of tailings immediately underlying the weath ered sections. For site OW3, the precursor composition was taken as the mean of five samples collected over the depth range 90 to 180 cm. For site OW8, two samples over the depth range 90 to 120 cm and for site NW10, four samples over the depth range 60 to 100 cm served as the precursor compositions. Uncertainties in establishing precursor compositions for weathered samples form the greatest limitations on the credibility of calculated mass-changes. Mass-change ratios (F = m /m ) calculated for weathered samples range from 0.765 (23.5% mass loss) to 1.23 (23% mass gain). The Oxidation Zone in the old tailings is marked by prominent mass loss, signifying net leaching, while the Hardpan Layer and the top of the Reduction Zone are marked by mass gains presumably associated with precipitation, coprecipitation and adsorption. The best-developed profiles are found at sites OW3 and OW8 in the old tailings impoundment. Patterns in the new impoundment (hole NW10) are marked by a nearsurface zone of mass loss corresponding to leaching, but a subjacent hardpan layer was not detected either megascopically or geochemically. a

p

M

Heath Steele: Old Tailings. The effects of sulfide alteration are most evident in the older tailings impoundment (Figures 2,4), most clearly at location OW8. At this location (Figure 2, Table II), the mass-change ratio, F ^ , shows an abrupt increase at the hardpan layer, with decreases in mass immediately above and below. The similar distribution


522

ENVIRONMENTAL GEOCHEMISTRY OF SULFIDE OXIDATION Mass Change Ratio

g / 0

>

0

100 c m

g /

3

100,,150,,2Q0,.2?0

0.

0

1

100 cr

f •

-HO / Ι Ο

0.3

1 M M

0.6

>

0.9


1.2

4000

9 / m

1.2 g / m

5

40000

3

8000 0.0

80000

:

0.3 • I l l 0.6

**> \

1.2 \ 3

0.0 ; 0.3 ·

Ζη

0.3

to

g / 100 c m 0.5 1.0 1.5 2.0

o.o

:

g / 100 c m 10 2.0 30

w. 0.3 Φ 0.6 ; 0.9 ; 1.2

Ψ é..

100 c m

l.O 1.0 2,0 3,0

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0.3

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w

3

4

3

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g / m .

ITT

0.6

•

0.9

g / 100 c m 0.0 1.0 2.0

Η.ρ.

Γ^=β

o.

^0.000

g / 100 c m 1 2 j 4 .5

g / m

3

0.0

9

«40 o.o'

0.3

frp^

o.3

0.6

i

0.6

1.2

3

400

-r

0.9

0.9

:

*

Al

1.2

Cr

Figure 2. Geochemical profiles for mass change ratios (FM) and selected element concentrations for site OW8 from the Heath Steele "old" tailings impoundment. Unweathered samples are indicated in solid circles and dashed line. Weathered samples located near the tailings surface are marked by open circles and solid line. The compositions of the weathered samples include calculated mass changes and are given as "net compositions" (see text). H.P. = Hardpan Layer. The water table was at a depth of 2.5 m at the time of sampling. Alpers and Blowes; Environmental Geochemistry of Sulfide Oxidation ACS Symposium Series; American Chemical Society: Washington, DC, 1993.



523

Table II. Average Compositions of Weathered and Unweathered Tailings from Heath Steele Hole OW8 * Zone Depth Ν S.G. F

M


Si Ti Al EFe Mn Mg Ca Na Κ Ρ

Upper Oxidation 0-20 cm 2 4.43 1.07

Lower Oxidation 20-40cm 2 4.42 0.893

Hard Pan 32 cm 1 4.40' 1.23

Reduction 40-60 cm 2 4.28 0.938

Unweathered 60-120 cm 5 4.32 1.00

18.3 0.21 2.48 188 0.09 0.49 1.08 0.16 0.29 0.20 0.00 188

17.5 0.19 2.87 146 0.12 1.15 0.82 0.11 0.50 0.18 0.00 142

8.22 0.19 1.35 208 0.12 0.63 0.37 0.08 0.22 0.77 0.00

21.2 0.20 4.04 159 0.42 2.05 1.24 0.14 0.40 0.15 0.00 157

19.1 0.21 3.26 170 0.75 2.46 1.23 0.12 0.53 0.17 1.79 160

5.23 112. 138 2590 41.8 20100 51900 18200 162 20.8 62.6 20.5 85.6 31.3 115 542 0.418 1570 34.3 58.9 24.5 8.53 9.29 1.29 1.94 0.332 3.38 2.42 6.64 8.97

4.94 96.6 98.7 2790 37.6 16900 57300 17100 150 21.6 89.5 28.0 97.4 15.4 96.7 518 0.432 1610 33.6 54.8 15.8 9.10 12.6 0.852 1.62 0.173 3.10 2.47 5.67 3.60

2 +

4+

c s2

Sc V Cr Co Ni Cu Zn As Se Rb Sr Y Zr Mo

3.75 79.0 75.5 2140 33.4 6900 10200 12700 221 54.8 89.6 18.9 85.1 14.2 161 756 0.471 2680 41.1 60.0 26.0 8.02 6.37 1.02 1.53 0.259 4.00 3.37 6.34 1.18

Ag Sb Cs Ba La Ce Nd Sm Eu Tb Yb Lu Hf Au Th U

4.84 109. 153. 1850 199. 29400 31200 23300 162 18.8 54.7 18.4 90.4 28.2 88.6 564 0.377 1450 31.9 56.7 26.9 8.86 6.97 1.30 1.88 0.299 3.69 2.01 8.81 6.62

— 5.19 166. 275. 2800 25.9 33700 57100 51900 223 25.9 25.9 31.1 88.2 5.19 130 934 0.052 1070 32.7 51.9 7.78 3.68 8.77 0.259 0.208 0.026 4.67 2.99 13.0 1.30

* Values for weathered samples (first four columns) are "net compositions", i.e. corrected for mass changes during weathering (see text); values for unweathered samples are raw analytical results. Mean values are arithmetic means for major constituents (Si to S) and logarithmic means for trace components (Sc to U). EFe is Fe i expressed as Fe . Units are g/l 00 cm of the precursor for major constituents and g/m of the precursor for trace constituents. Column 5 is the assumed precursor composition. 2+

2+

3

iota

3



524

ENVIRONMENTAL GEOCHEMISTRY OF SULFIDE OXIDATION

of Fttotai probably accounts for most of the F M change. Pore-waters contain >60 g/l dissolved Fe in the shallow tailings water and >100 g/l dissolved SO*" (Figure 3; 10). Pyrrhotite is depleted near the tailings surface (H). The sulfophile elements, Zn, Cu and As are also depleted near the tailings surface as a result of sulfide-oxidation reactions. Shallow pore-waters contain dissolved concentrations >6 g/l Zn, > 100 mg/l Cu, (Figure 3) and >0.4 g/l As, indicating that oxidation of sphalerite, chalcopyrite, tetrahedritetennantite and arsenopyrite has released some of the solid-phase concentrations of these elements to the tailings pore-water. (See Figure 4.) Copper and As in the hardpan layer are enriched in the solid phases compared to unweathered tailings below the hardpan layer (Figure 2, Table II). This secondary solidphase enrichment is accompanied by decreases in the dissolved concentrations of Cu and As. High concentrations of covellite (CuS) and an As-bearing secondary oxidation product occur at this depth (Π). Zinc is depleted at the tailings surface but is enriched in the hardpan layer where it is incorporated into melanterite, which occurs as a cementing mineral. The behavior of Cr is similar to that of Cu and As. Chromium may have been derived from the milling reagents or from the oxidation of magnetite. Geochemical speciation calculations conducted using the computer code MINTEQA2 suggest that Cr may accumulate near the depth of the hardpan layer as Cr(OH) . Acid-neutralizing, carbonate-dissolution reactions have consumed the carbonate con tent of the upper 50 cm of the old tailings at location OW8. The pore-water pH in this zone increases from 4.5 near the depth of the hardpan (Figure 3). These pH-buffering reactions are probably the cause of the depletion of solid-phase Ca and Mg near the tailings surface. The concentration of Ca is further de pleted near the hardpan layer, possibly through aluminosilicate dissolution, and enriched 15-20 cm below the hardpan layer as the result of gypsum precipitation. Aluminosilicate dissolution is suggested by the depletion of Al relative to Si at the tailings surface. High concentrations of dissolved Al (up to 1,030 mg/l) and Si (up to 722 mg/l H Si0 ) are present in the oxidation zone above the hardpan layer. MINTEQA2 calculations indicate that these water samples show supersaturation with respect to amorphous silica. Similar degrees of supersaturation have been observed at other oxidized mine-tailings impoundments where aluminosilicate dissolution has been inferred (13-15). These dissolved Al and Si concentrations decrease abruptly at the depth of the hardpan layer. Slight solid-phase enrichment of Al occurs immediately below the hardpan layer, possibly because of the formation of aluminum hydroxide or aluminum hydroxy-sulfate minerals. Mineralogical study has confirmed the presence of aluminum sulfate, but not aluminum hydroxide precipitates. 3

4

4

Heath Steele: New Tailings. The composition of the new tailings is variable, as indicated by the elemental profiles for the unweathered samples in NW10 (solid dots in Figure 5). Thesefluctuationsare indicative of irregularities in the composition of the ore feed to the mill and/or in the efficiency of the beneficiation processes. In spite of this variability, the mass-change-corrected whole-rock data reveal some distinct trends after calculation of net composition values for weathered samples. The mass-change ratio indicates that a loss of mass has occurred near the tailings surface. This change is the result of losses of Festal, S, Cu, Zn, C, Ca, Mg, Al, Si and K. The losses of S, and the metals Fe, Cu and Zn, probably result from sulfide-oxidation


31.

APPLEYARD & BLOWES


pH Units

mV

mg/liter


P. . 2$0 . .5QQ . . 7$0

mg/lïter JO

1000

0

ο J .

0 0

-

mg/liter 100000

100

525

. IQQOQ

.1QQPQ0

mg/liter 10000

0.0

0.01

1.0

1000

2.0

4.0

6.0

8.0

J

Cu

8.0

mg/liter 1

1.0

mg/liter 100

150

mg/liter 20

40

300

450

mg/liter 600

500

mg/liter 60

0.0

0.1

10 100

100.0

1500

mg/liter 10000

100

1000

2.0 i

4.0 -·

2.0 \

S.·

3.0

3.0

4.0

4.0

Ca

5.0

g / 1 0 0 cm 0,0 0.5 1.0 1,5 2.0 2.5 0.0

0.0 s

g / 100 cm 10 20 30 40 50

2.0

Mg

5.0

3

0

i"

3

O.i0

0.0

g / 1 0 0 cm 0.5 1.0 1.5 2.0 2.5

&—λ

H.p.

5.0

g / 100 cm 0.0 0.1 0.2 0.3 0.4 0.0

1.0

1.0

1.0

"5 2.0

2.0

2.0

(0

k.

Al

Φ

-C

3.0 "a. Φ a 4.0 5.0

N

3.0

4

\

··

3.0

..-·*

4.0 Si

5.0

4.0

K

5.0 ^

Na

Figure 4. Geochemical profiles of mass change ratios ÇF ) and selected element concentrations for site OW3 from the Heath Steele "old" tailings impoundment. V = water-table at time of sampling. · and dashed line = unweathered samples; ο and solid line = weathered samples. H.P = Hardpan Layer. M


31.

APPLEYARD & BLOWES

g /

Mass Change Ratio

1

0.0

1

1

ι

J

527


ο. ?ο

100 c m

?5Q.. ?,9f?

0

?y

LI

g /

3

100 c m

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1.0

1.0

1.0 4

2.0

2.0

2.0

3.0

3.0 :

3.0

3

• 1W • 2Q0

O.

Φ


4.0 g / m 0

1JÎ000

FM

4.0 -

60000

o

TFe g / m

3

4.0

J

3

g0000

100000 V

0.0

1.0

1.0 :

2.0 \

2.0 •

2.0

3.0

3.0

40

g / m 100

3

1.0^

"©

φ 3.0

Cu

4.0

g / 100 c m 1.0 2.0 3.0

4.0

Zn

J

3

0,0 0.0 1.0

4 Cr

4.0

g / 100 c m 2.0 4.0 6.0

•r

1.0 •

g / 100 c m 1.0 2.0 3.0 4.0 3

3

0.0 0.0

0.0 0.0 1.0

>

2.0

2.0 \

2.0

3.0

3.0 \

3.0

4.0

4.0 '

a

Φ

a

g / 100 c m 10 20 30 40 50 3

0.0

Ca

:

0

4.0

g / 100 c m P.O 2.0 4.0 6.0 8.0 .

g / 100 c m 1.0 2.0 3.0 3

3

o.o

Mg

J

o.o

0.0

"Λ

CL Φ O

1.0

1.0 \

1.04

2.0

2.0 \

2.0

3.0

3.0

4.0

d

Si

ΐ

4.0 '·

•c:

3.0 Al

4.0 = •

κ

Figure 5. Geochemical profiles of mass change ratios (FM) and selected element concentrations for site NW10 from the Heath Steele "new" tailings impoundment. V = water-table at time of sampling. · and dashed line = unweathered samples; ο and solid line = weathered samples.


528


reactions occurring in the shallow tailings. Of these elements, S, Cu and Zn show an enrichment 30-40 cm below the tailings surface. The depletions of C, Ca and Mg near the tailings surface probably result from the dissolution of calcite, dolomite and other carbonates through pH-buffering reactions. The apparent depletion of Al, Si and Κ from the tailings surface may represent aluminosilicate dissolution, but may also represent unknown changes in the precursor composition of the tailings (i.e. lower initial aluminosilicate content than that in the assumed precursor). Variations in pore-water composition with depth are illustrated in Figure 6. The brief period of sulfide oxidation in the new impoundment is reflected in the tailings porewater geochemistry. High concentrations of dissolved Fe and S 0 are limited to the shallow vadose zone. The maximum concentrations of Fe (10,200 mg/l) and S 0 (24,800 mg/l) are observed in the shallowest two samples (10 and 30 cm depth), near the depth of active sulfide oxidation. The pore-water pH in the shallow vadose zone is >5.5 indicating that H produced by sulfide oxidation has been consumed by reaction with carbonate minerals. The aqueous concentrations of Mg are high in the shallow vadose zone, also probably reflecting dissolution of dolomite. The concentrations of Ca and H S i 0 are relatively constant throughout the profile and geochemical calculations suggest that these concentrations are limited by the solubilities of gypsum and amorphous S1O2. High concentrations of Zn (200 mg/l) and Ni (2 mg/l) are restricted to the shallowest sampling points (not shown on Figure 6), also reflecting the brief duration of sulfide oxidation.


4

4

+

4

4

Results of Mass-Balance Studies for Delnite Tailings. Immobile elements identified in the Delnite weathered-zone tailings include Ti, Al, Se, V, Zr, Yb and Lu. Primary variances of some of these elements in the unweathered tailings are relatively high so the estimates of mass-change ratios andfluxesof individual elements are less precise than in the case of the Heath Steele tailings. The precursor composition used for the Delnite site was the mean composition of three unweathered samples collected from the depth range 90 to 140 cm. Mass-change ratios (Figure 7) range from 0.988 (1.2% mass loss) to 1.32 (32% mass gain) but because there is no mineralogical indication of the presence of a hardpan layer the latter value may represent an artificial increase due to a lower initial immobile-element content of the tailings at this depth relative to the average precursor values. Despite the uncertainty associated with this sample, a subtle leaching effect just below the tailings surface is suggested by decreases in the mobile elements S and As in a manner that parallels the behavior of these elements at Heath Steele. Similarly, loss of Ca, Mg and C in the upper 50 cm of the hole is probably associated with the dissolution of carbonate minerals. Such reactions are also indicated by high gas-phase C 0 concentrations, >10 vol% (12). 2

The Delnite Tailings Area: Results. The effects of sulfide oxidation on tailings geochemistry (Figure 7) are superimposed on probable compositional variations in the tailings as they were deposited. The mass-change ratio shows a distinct increase at 65 cm. As noted before, this increase may not be due to post-depositional mass transfer, because it is reflected by increases in the masses of Si, Al and Na which are suggestive of increased amounts of aluminosilicate minerals in the mill feed. Mineralogical study identified the first occurrence of talc at this approximate depth (16). The addition of talc to the tailings




pH Units

529

mg/liter

11 ι^ι 1111111 I^I 1111111 ι7ι I

0

J000

10000

1.0 2.0 3.0


4.0 5.0

5.0 6.0

pH

J

S0

6.0

0. 1

100000

10

4

mg/liter

mg/liter

mg/liter 1000

i

10000

0.0

300

O.o 1.0

400

500

600

4

2.0 3.0 4.0 5.0 6.0

mg/liter

mg/liter

mg/liter

10

1JJ0

0.0

0

1000

2000

10

o.o

1.0 \

1.0 :

2.0 (

2.0 \

3.0 \

3.0

4.0 \

4.0

5.0 \

5.0

6.0

1

Ca

J

Mg

100

i

6.0

H si0 4

4

Figure 6. Pore-water geochemical profiles for pH, Eh and selected elements for site NW10 from the Heath Steele "new" tailings impoundment. Sampling was carried out in June, 1986. ν water-table at time of sampling. =


530


Mass Change Ratio

g / 0

go,.p

3

100 c m 25,0 30..0

g / 0,

2.0

Q

100 cm

4,0

6,0

3

8,0

0.5 1.0 Ι 1.5

1

\

2.0


TFe g / 4000 0.0

m

3

g / 20000

200

m

/

2.5

g /

3

1000

m

400 0.0

3

ιορο

•—s

W

0.5

0.5

"o 1.0

1.0

L.

Applications of Mass-Balance Calculations to Weathered Sulfide Mine

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