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The Rhodesian approach to the vegetating of slimes dams

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					The Rhodesian approach to the vegetating
of slimes dams
                                       by J. R. C. HILL*, B.Sc.(Agric.) (Visitor) and W. F. NOTHARDt (Visitor)

                       SYNOPSIS
                          To prevent environmental pollution from mine dumps, it is necessary to stabilize them either mechanically or
                       biologically. In the long term biological stabilization is more attractive because of its permanent nature. Initially,
                       the basis of stabilization is in the correct siting and construction of the dump.
                          The main toxic factors influencing plant growth on Rhodesian mine dumps are arsenic, antimony, copper, nickel,
                       a high ratio of magnesium to calcium, excessive soluble salts, high pH, and Iow macronutrient content. Root-growth
                       studies in culture solution and pot experiments are used to supplement information on the suitability of plant
                       material obtained from replicated field trials on mine dumps.
                          In addition to the selection of plants for toxic tolerance, it is advisable to provide multiple-layer protection with
                       trees, shrubs, and grasses. Further, a range of different plant species gives greater biological stability.
                          Protection must be provided for young plants against wind erosion and the abrasive effects of windblown sand.
                       Planted wind breaks are preferred to mechanical forms; windrows of garden refuse make good wind breaks and at the
                       same time introduce organic material to the dump and provide a good environment for seedling establishment.
                          The use of artificial fertilizers and sewage effluent is recommended to hasten the development of a complete and
                       protective plant cover.


                       SAMEVATTING
                            Om omgewingsbesoedeling deur mynhope te voorkom moet hulle meganies of biologies gestabiliseer word.
                      Blologiese stabilisering is op die lang duur aantrekliker omdat dit van 'n permanente aard is. Die aanvanklike grond-
                      slag vir die stabilisering is die korrekte plasing en konstruksie van die hoop.
                         Die vernaamste giffaktore wat plantegroei op Rhodesiese mynhope beinvloed is arseen, anti moon, koper, nikkel,
                      'n hoe verhouding van magnesium tot kalsium, oormatige oplosbare soute, hoe pH en 'n lae makrovoedingstof-
                      inhoud. Wortelgroeistudies       in kultuuroplossings en poteksperimente word gebruik om die inligting oor die ge-
                      skiktheid van plantemateriaal deur replikaveldproewe op mynhope ingewin, aan te vu!.
                         Dit is raadsaam om benewens die keuse van plante wat teen gifstowwe bestand is, voorsiening te maak vir meer-
                      laagbeskerming met bome, struike en gras. Verder gee 'n reeks verskillende plantsoorte groter biologiese stabiliteit.
                         Die jong plante moet teen winderosie en die skuuruitwerking van waaisand beskerm word. Aangeplante wind-
                      skuttings is beter as meganiese vorms; rye tuinafval maak goeie windskuttings en voeg terselfdertyd organiese
                      materiaal by die hoop en verskaf 'n goeie omgewing vir die vestiging van saailinge.
                         Die gebruik van kunsmis en riooluitvloeisel word aanbeveel om die ontwikkeling van 'n volkome beskermende
                      plantbedekking te bespoedig.

         INTRODUCTION                          term, it is more permanent and less               mittee of the Natural          Resources
   In Rhodesia,     mine dumps have            costly to maintain.                               Board set up a Technical Committee
created    interest   more for their              The problem      can therefore   be            to investigate     thc stabilization     of
offence to aesthetic values than for           summarized as the establishment     of            mine dumps2. At their inaugural
any practical reason, but the situ-            any type of vegetation on the sterile             meeting, held on the 18th Septem-
ation is rapidly changing          as the      and, in varying degree, toxic medium              ber, 1961, this Committee agreed to
country     becomes more industrial-           provided by the waste materials of                undertake a country wide survey to
ized.    Industrial   progress     is as-      the mining industry that are dumped               (a) establish     the extent       of the
sociated with a greater demand for             on the land surface.                                    problem,
minerals, and technical progress will             The need to stabilize mine dumps               (b) draw up a list of problem dumps,
make the mining of lower-grade ores            has been recognized for some time;                      and
economically      more attractive.      In     the Rhodesian Chamber of Mines, in                (c) gain information         about     the
consequence, more and bigger mines             collaboration  with the Natural Re-                     growth of vegetation on dumps
will be the future trend, the mine-            sources Board, first drew attention                     where this had occurred.
dump problem        will escalate,    and      to the problem in their Mine Mana-                   The ensuing survey conducted by
with it the related practical prob-            gers' Circular entitled     'The Pro-             the Department of Conservation and
lems of environmental    pollution.            motion of Vegetative Covers on Mine               Extension,     and presented       to the
                                               Slimes Dams and Sands Dumps', in                  second meeting of the Technical
   This pollution will be in two main
                                               19611. Their stated intention was to              Committee in December, 1962, indi-
forms-chemical     and physical, each
                                               eliminate the unsightliness and dust              cated that the erosion occurring both
with its specific problems. To pre-
                                               nuisance of mine dumps and to pre-                on and away from mine dumps was
vent pollution from mine dumps, it
                                               vent the blockage of natural drain-               by no means wide spread or serious3.
is necessary to stabilize them either
                                               age channels by mine-dump erosion.                Further, the establishment        of vege-
mechanically       or     biologically.
                                               It was also suggested that certain                tation on mine dumps was generally
Naturally, the biological approach is
                                               slimes dams in Rhodesia would be                  greater than anticipated,     and a high
more attractive because, in the long
                                               difficult to vegetate because of the              percentage of the dumps investi-
*Post-graduate  Research Fellow, Depart-       presence of elements such as arsenic,             gated had a plant cover of more
 ment of Botany, University of Rhodesia.       antimony, copper, lead, and zinc in               than 40 per cent.
 Senior Pasture Specialist, Department of
 Conservation and Extension.                   gold ore residues. Later in the same                  The Chairman       of this second
tChief Surveyor, M.T.D. (Mangula) Ltd.         year, the Mineral Resources Com-                  meeting indicated that the survey

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY                                                        DECEMBER 1973 197
                                                                                                     and likely to cause environmental
                                                                                                     pollution. To prevent pollution from
                                                                                                     mine dumps, it is necessary to 'find
                                                                                                     an economic and permanent method
                                                                                                     of stabilizing mine wastes. .. both
                                                                                                     to prevent pollution and to improve
                                                                                                     the visual appearance of mine work-
                                                                                                     ings'6.
                                                                                                            THE  STABILIZATION             OF
                                                                                                                  MINE DUMPS
                                                                                                        Effective stabilization and control
                                                                                                     of the mine-dump         problem can be
                                                                                                     achieved      by two methods           or a
                                                                                                     combination      of the two, namely
                                                                                                     mechanical      and biological stabili-
                                                                                                     zation.
                                                                                                        Mechanical control is more effect-
                                                                                                     ive than biological control in the
                                                                                                     initial instance,      but it could be
                                                                                                     more costly to implement and cer-
                                                                                                     tainly requires       maintenance        and
                                                                                                     therefore does not solve the problem
                                                                                                     permanently.      Biological control re-
                                                                                                     quires detailed       research    initially,
Plate    I-Physical      effect of mine dumps: the inundation    of valuable    township   land      but, once the information has been
                      by mine-dump    erosion originating in the foreground.
                                                                                                     obtained, the solution is permanent
had shown so many similarities to                  dumps is common to all forms of                   and, in the long run, is considerably
the position in South Africa that it               mining throughout    the world-a                  less costly than mechanical             con-
was reasonable to work almost com-                 number of workers are investigating               trol14.
pletely on South African experience.               the problem with the same objective                  Smith and Bradshaw6 discuss two
However, a limited series of trials                in view but with different philo-                 alternative    methods of dealing with
was planned and initiated in Feb-                  sophies6-12.                                      toxic mine wastes-removal            or re-
ruary     1963. These trials lacked                   For a successful conclusion to the             clamation. Removal of the material
direction, and, as no results or con-              problem, it is necessary to classify              for use as grit for roads or as a
clusions were obtained,       the trials           the problem      into its component               base for construction is considered a
can be classed as a failure.                       parts as represented     below. How-              possibility in parts of Britain, where
   This earlier failure to understand              ever, environmental   reaction is com-            the amount of material is limited
the problem is now producing          its          plex, and factors contributing       to           relative to the population         density.
results, and recent records of the                 cause, effect, and control of the                 In the more distant parts of the
Natural Resources Board4 indicate                  problem are completely interrelated.              British countryside        and in large-
that a mine dump on the Camper-
down Mine, near Selukwe,            con-                         Cause                             Effect                          Control
                                                                 Slimes dams                      Physical                       Biological
sidered stable twenty years ago, was
seriously eroding in 1962 and required                    Concentrate    dams       J-~
                                                                                                                  1    J-~

urgent and essential action to pre-                                                               Chemical                       Mechanical.   .
                                                                        Dumps   }          {                      J          {
vent serious siltation of the Um-
tebekwe River. Because the Um-                        Rhodesian mine dumps are often                 scale operations      elsewhere in the
tebekwe     River supplies water to                more or less devoid of vegetation.                world, these rather limited uses are
250 ha of existing irrigation farming              This is due to several factors, the               unlikely to make much impression
and has a further potential of over                most important     of which are prob.             on the vast volume            of mining
1000 ha, a silt trap was constructed               ably the presence of toxic com-                   wastes.
on the Camperdown Spruit at a cost                 ponents {Table 1)13, the deficiency of               'Reclamation      by covering with
of R.$1O 810. The alternative to this              macronutrients,   poor physical struct-           vegetation     thus seems the only
would have been mechanical works                   ure of the rooting environment,     and           possible alternative, although stabili-
on the dump itself, estimated          to          the absence of humic/organic        ma-           zation by resin compounds and other
cost R.$1O0 000.                                   terial and its associated soil micro.             physical means may be a temporary
   There are a number          of other            flora. Other factors of importance                solution'6.
mine dumps in Rhodesia that can be                 are dump construction, past erosion,
predicted    to result in similar en-              slope, surface stability     of dump                                 BIOLOGICAL
vironmental     pollution in the near              material, wind, and climatel4.                                     ST ABILIZA TION
future 5.                                             Because mine dumps are devoid                      Biological stabilization is the most
   The inherent       problem   of mine            of cover, they are prone to erosion                permanent     solution and will ulti-

198     DECEMBER 1973                                 .JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY
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JOURNAL   OF THE SOUTH      AFRICAN                              INSTITUTE                  OF MINING AND METALLURGY                                                                                                                             DECEMBER   1973   199
                                                                                                               heavy metals, pH, and salt concen.
                                                                                                               trations, both in the dump and in
                                                                                                               the water.
                                                                                                                  Plant life on a mine dump is
                                                                                                               closely related to the chemical con-
                                                                                                               ditions of the environment,              and,
                                                                                                               until pioneer plants become estab-
                                                                                                               lished, the nutritive         value of the
                                                                                                               dump material is dependent on its
                                                                                                               mineral composition.          Under these
                                                                                                               circumstances,      it is particularly    im-
                                                                                                               portant     to have the constituent
                                                                                                               materials analysed. See Table I.
                                                                                                                  Certain plants can be found grow-
                                                                                                               ing in situations that would normally
                                                                                                               be considered toxic to plant growth.
                                                                                                               In the initial instance, the plants
                                                                                                               must have become established in an
                                                                                                               inhospitable environment and modi-
                                                                                                               fied it, and subsequently          improved
                                                                                                               the situation      to the point where
                                                                                                               other plants have been able to
                                                                                                               invade the area. The pioneer plants
                                                                                                               must have exhibited an ability to
Plate   II-Biological          stabilization:    the effect     of planted     grass   in stabilizing   the    withstand the situation. These toler.
sides of a mine dump. The upper terrace                      is planted      with Cynodon doctylon, the       ances are genetically controlled and
                   lower terrace           is unprotected     and is eroding     rapidly.
                                                                                                               are specific to a situation, but the
mately prove to be the least ex-                            biological stabilization        of modern         physiological mechanism involved is
pensive method of stabilizing mine                          mine dumps.                                       not clear15. Turner16 concludes that
dumps. Although            ideal, biological                    Biological    stabilization     can be        copper and zinc tolerance in popu-
stabilization     is the more exacting                      approached      through the ecological            lations of Agrostis tenuis is due to
method, having numerous associated                          process of plant successiolf, using               complexing of the metal ions in the
problems that must be investigated                          pioneer plants that have very low                 walls ofthe root cells, thereby render-
and understood         before stabilization                 nutrient requirements         and are cap-        ing them immobile and innocuous.
can be effective.                                           able of existing        under extremely           Accordingly, plants adapted to one
   The sooner biological control starts                     harsh soil conditions. Through their              toxic situation will not necessarily be
after dumping commences, the easier                         root action and the deposition             of     successful in establishing themselves
it is to stabilize the dump. While                          organic material,        these particular         in other situations, and plants of the
dumping is in progress, labour and                          plants gradually improve the dump                 same species growing under normal
capital resources are available for                         environment       to a level at which             environmental         conditions     will not
planting, fertilization,        and mainte-                 more sensitive plants are able to                 necessarily     exhibit the same toler-
nance until the vegetation            is suffi-             establish themselves.        On the other         ances to specific toxic materials as
ciently established to persist. There                       hand, the dump condition may be                   those growing in that toxic situ-
is also the possibility of the use of                       improved by incorporating            organic      ation17.
sewage effluent and water for plant                         waste with the mine-dump material                    In commenting on the ability of
establishment,      and, more important,                    before attempting       to establish vege-        plants to withstand         higher than
responsibility       for stabilization        is            tation. Where the establishment            of     normal concentrations       of toxic ma-
definite.     Once mines have been                          vegetation     on mine dumps is con-              terial,   with specific reference        to
abandoned,      the problem of stabili-                     templated,     a combination       of these       copper, Wild18 states that there
zation is considerably          increased as                two general approaches           is usually       appear to be various methods by
the situation        deteriorates,     further              adoptedll.                                        which this is accomplished.          Some
responsibility     is difficult to allocate,                   Considerable work has been done                plant species are tolerant of a toxic
and there is little or no supervision                       on the biological stabilization            of     situation through resistance to the
on site.                                                    mine dumps. Unfortunately,              time      uptake of toxic materials; these are
   In general, the extraction              pro-             and effort have been wasted by                    commonly       ruderal    or adventive
cesses used in modern-day              mining               workers who have not always fully                 species, which are often well-known
reduce the majority           of toxic sub-                 understood the subject.                           weeds. Their resistance          to toxic
stances to levels that do not seriously                                                                       materials    is part of their general
                                                             TOLERANCE             TO TOXICITY
affect plant growth; because other                                                                            tolerance of a very wide range of
factors are involved, however, this                            The term toxicity is used in its               habitats, which is one of the main
reduction does not necessarily mean                         broad sense to include all toxic                  factors    making      them     successful
that     no problems remain in the                          situations. It includes   chemicals,              weeds.

200     DECEMBER        1913                                   &JOURNALOF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY
    Other species are more specific in        favourable      environment      for plant    to a toxic situation, or to low macro-
their tolerance      to toxic concen-         establishment.       Mulching will also       nutrient     levels, the addition    of
trations,   in that     their tolerance       stabilize surface conditions, thereby         further plant nutrients in the form
follows from their ability to take            preventing severe erosion by wind or          of fertilizer is still desirable.
up the toxic material         to varying      rain. Excessive erosion is often re-
maximum levels without detrimental            sponsible     for the destruction        of             EXPERIMENTAL
effect. These species can also occur          many shallow-rooted        seedlings; it is               PROCEDURE
out of the toxic situation, but often         also responsible for the dispersal of         Plant Material for Planting on Mine
become more frequent under toxic              planted seed. When vegetative mulch           Dumps
conditions, possibly because of their         is used, it is necessary to stabilize              The ability of plants to develop a
ability to survive conditions        that     the mulch with weights or with                tolerance      to toxic substances      has
eliminate other plants and thereby            brushwood.                                     been established6, 15-17, 21, 22. There-
reduce competition.                              The use of garden refuse as a              fore, provided the toxic component
    Other methods of biological stabili-      mulching material has a number of             is established in each toxic situation,
zation have been used. These have             advantages in its favour. Firstly, it          somewhere a plant will be found
frequently   involved the blanketing          usually contains a wide range of              that either exhibits a tolerance to
of mine waste with a layer of non-            successful ruderal or adventive weeds         this toxic situation,          or can be
toxic material such as soil, sewage           and, secondly, if collected near the          selected for tolerance in a breeding
sludge, or domestic         refuse, into      mine dump, the weeds concerned                programme. This forms the basis of
which seed is sown. A modification of         will have developed some tolerance            the Rhodesian approach to the bio-
this method is partial turfing in the         to toxic substances in the dump.              logical stabilization      of mine dumps.
hope that vegetation        will colonize        Alternatively,     mulching materials      Any artificial aids in ameliorating the
from the turf lines6 or soil pocket-          such as plastic sheeting, bitumastic           dump environment           are avoided if
ingl9. These methods         are usually      compounds, and paper pulp can be              they are aimed at enabling plant
successful in the beginning, but the          used 2°, but the cost and the practic-         survival.     However,      once suitable
vegetation    slowly dies back as the         ability     of application        of these     plants have been selected, the use of
non-toxic    material    becomes     con-     materials     must be taken into ac-          organic and inorganic ameliorants
taminated     with toxic components           count.                                        is encouraged,       but the decision is
from the dump. Further, the plants                                                          left to the mining authority.
tend to root only in the non-toxic                 HUMAN    AND ANIMAL
                                                                                                 The approach        presupposes    the
material, thus forming a skin more                    INTERFERENCE
                                                                                            need for a careful analysis of each
or less unattached        to the mine             An important factor in determin-          toxic situation. Notwithstanding        the
dump6. Once erosion starts in this            ing the successful establishment      of      extreme variability         of toxic com-
layer, there is nothing to prevent it         vegetation on mine dumps is whether           ponents in Rhodesian mine dl1mps
cutting deep into the dump. In any            or not plantings have been inter-              (Table I), the following are con-
event, transport costs and the quan-          fered with, injured, and ultimately           sidered to comprise the main toxic
tity of non-toxic material required           destroyed    by animals or humans,            factors influencing plant growthl3:
make these methods prohibitively              particularly children.                           (i) Presence of toxic metals and
expensIve.                                       Fencing is of value in preventing                 soluble salts
                                              newly planted vegetation from being                  (a) Arsenic and antimony
    SURFACE        PROTECTION                 disturbed     during   the period     of             (b) Copper
   The bare, unprotected        surface of    establishment. It also excludes anim-                (c) Nickel
mine dumps is exposed to extreme              al and human movement,         thereby               (d) High ratio of magnesium to
temperature     variations    and to the      allowing stabilization of surface con-                     calcium
abrasive action of wind-borne sand            ditions without the introduction      of             (e) High soluble-salt content.
particles. These two factors affect           paths or tracks that will lead to               (ii) High pH values.
the soil environment       as well as the     erosion.                                      (iii) Absence of or very low macro-
plants themselves, and have a sig-                                                                 nutrient content.
nificant influence on any vegetation            THE     USE OF ARTIFICIAL                        Once the main toxic components
programme.                                               FERTILIZERS
                                                                                            in mine wastes had been defined,
   Wind erosion must be countered                Ideally, it should be possible to          selection of suitable plant material
with adequate       windbreaks,      either   select plants that will establish them-       was based on
planted    or mechanical.        Although     selves on dump material          without      (1) the ability of plants to establish
brushwood      or wickerwork         wind-    artificial assistance;   this should be             and colonize existing mine dumps
breaks can be used, tree wind-                the long-term objective in any pro-                 known to contain the defined
breaks are to be preferred because            gramme of biological stabilization.                 toxic components, and
their roots and leaves contribute             In practice, it is usually necessary to       (2) aggressive       plants    growing    in
organic material to the dump.                 assist plants in their initial estab-               natural situations known to have
   Where practical, mulching can be           lishment in order to speed up the                   similar toxic components to Rho-
used in conjunction          with wind-       process and also to encourage initial               desian mine dumps.
breaks to control surface tempera-            root development. Even where plants               A considerable        range of plant
ture and also to create a more                have been selected for their tolerance        material has been collected from a

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY                                                         1973 201
                                                                                                                 DECEMBER
                                                                                                           (i) a tree phase to serve as a wind
                                                                                                               break and for biological stabili-
                                                                                                               zation at depth through greater
                                                                                                               rooting ability,
                                                                                                          (ii) a shrub phase to streamline
                                                                                                               wind movement         over the tree
                                                                                                               windbreak, and to provide pro-
                                                                                                               tection at an intermediate level,
                                                                                                               and
                                                                                                         (iii) a stoloniferous-type      grass phase
                                                                                                               for complete surface protection.
                                                                                                             Replicated field trials of selected
                                                                                                         tree, shrub, and grass species have
                                                                                                         been undertaken           on four mine
                                                                                                         dumps containing         the main toxic
                                                                                                         factors encountered         in Rhodesian
                                                                                                         mine dumps. Treatments             are indi-
                                                                                                         cated in Table 11.
                                                                                                             In spite of the poor rainfall of the
                                                                                                         past summer,         dump trials have
                                                                                                         made considerable growth, and cer-
                                                                                                         tain species of tree, shrub, and
                                                                                                         grass are showing great promise. It is
                                                                                                         interesting to report that the growth
Plate Ill-Tolerance   to toxicity: Acacia karroo adapted to growth in mine-dump                          response of a single plant species
material  that has eliminated    or excluded all other plant growth. Note the un-                        varies on the different dumps. This
usual development   of the lower branches, probably through lack of competition
                                  from other plants.                                                     fact verifies the philosophy of the
                                                                                                         Rhodesian approach in that different
number of mine dumps and natural               selected plants to single toxic sub-                      plants differ in their response to
salt pans in Rhodesia.           A large       stances is still in progress       and,                   toxic components, and that tolerant
number of tree and shrub species               when complete, will assist in the                         plants can be found for most toxic
were obtained     from the semi-arid           final selection     of suitable   plant                   situations.
areas of Western         Australia   and       material.                                                    A full analysis of these dump
Israel; other species came from the               Pot trials are being conducted on                      trials has commenced and will in-
Republic of South Africa (see Ap-              mine-dump      material from selected                     clude determinations         of the mech-
pendix). The more promising plant              mines, under semi-controlled         en-                  anism whereby certain plants are
species have been bulked up and                vironmental     conditions. The object                    able to make successful growth in
are available for distribution.                of these trials is to determine the                       toxic situations.
Laboratory Studies                             rooting ability of different      plant
                                               species in dump material, and the                                            GENERAL
   Plants    growing     successfully     in   effect of fertilizer in increasing the
toxic situations produce normal root                                                                        For practical purposes, it would
                                               rooting ability.
growth, whereas non-adapted          plants                                                              appear that the line to be followed is
fail to produce roots or they are              Field Trials on Selected Mine Dumps                       already    clear, but an adequate
malformed.     Therefore, root studies            If undesirable    dump erosion is                      period of further work is necessary
of plants introduced        into a toxic       to be prevented,     the ideal type of                    to confirm and guarantee these pre-
situation are likely to give a good            vegetation   to be established   seems                    liminary recommendations.
indication    of the plants'      possible     to be the following:                                         In the interim period and based on
success in the biological stabilization                                                      TABLE II
of mine dumps containing that toxic                     REPLICATED     FIELD    TRIALS   ON MINE         DUMPS:       FERTILIZER   TREATMENTS
situation.                                     1. TREES AND        SHRUBS
   Root-study    techniques developed          TREATMENT    A       No fertilizer
                                                            B       Compound 'D' fertilizer (8.15.10) 50 g per tree (8,82 kg/ha)
by Wilkins21, 22, Jowett23, and Brad-                       C       Single superphosphate   (20 % P.O5) 0,5 kg per tree (882 kg/ha)
shaw16 have been modified to suit                              D     Compound      'D'   fertilizer      +   single    superphosphate    as above
                                                                     Annual nitrogen top dressing (50 g ammonium nitrate 34,5% N per
this research programme. The tech-                                   tree) - applied to treatments 'B' and 'D' in December.
nique involves the measurement            of                         Planting distances: 2,4 X 2,4 m (1764 trees/ha)
root growth of single plants in a
growth solution for 48 hours, com-             2. GRASSES
pared with a similar period of growth          TREATMENT       A     No fertilizer
                                                               B     Compound 'D' fertilizer -               100 g/m' (1000 kgfha)
in the same growth solution con-                               C     Grass mulch
taining a known concentration             of                   D     Compound     'D' fertilizer + mulch as above
toxic substance.                                                     Annual nitrogen top dressing (37,5 g/m' ammonium                   nitrate   34,5   % N)
                                                                     (375 kg/ha)-applied              to treatments       'B' and 'D' in December.
   This study of the reaction             of

202   DECEMBER 1973                               JOURNAL OF THE SOUTH AFRIC' AN INSTITUTE OF MINING AND METALLURGY
 the experimental results obtained to              Siting of Slimes Dams                               Commencement of Stabilization Pro-
 date, highly successful practical pro-               The construction       and siting of             gramme
 grammes of stabilization have been                slimes dams have a significant effect                  The sooner stabilization        follows
 completed. Present knowledge and                  on the ease of stabilization.    A dam              the commencement           of dumping,
 experience indicate that a successful             situated on steep and sloping land                  the more successful it is likely to be.
 dump-stabilization programme has                  has additional      hazards caused by               In the long-term, biological stabili-
 sequentialized components. These                  natural    drainage    from above the               zation is more attractive than mech-
 are well illustrated in the programme             site. There is also the problem of                  anical stabilization,    because of its
 being followed on slimes dams at                  flood-water disposal from the dam                   permanent      nature.    There     is an
 Mangula Mine, and therefore slimes                itself, as well as from the increased               additional    advantage     in biological
 dams on this mine are discussed in                down-slope side. At Mangula these                   stabilization in that the dam can be
 more detail.                                      hazards are reduced by dumping on                   made productive.        Dickinson 7 re-
                                                   a slope of 2 per cent average. How-                 ports increasing evidence of various
                                                   ever, there is a further problem in                 forms of wild life establishing them-
 PROGRAMME            AT MANGULA
                                                   that the area allocated for slimes                  selves     on biologically      stabilized
                   MINE                            dams is partially swamped. This has                 slimes dams. At Mangula it has
     Mangula, the local African name               dictated an additional base-drainage                been necessary      to protect experi-
  for red metal, is situated         190 km        system to supplement the toe drain-                 mental plots from over-utilization       by
  north-west of Salisbury, at an alti-             age.                                                antelope and hares.
  tude of 1200 m. The area experiences             Angle of Slope                                         AdamsI9 has found that Euca-
  hot summers and mild, frost-free                    Where the slope is less than 45 °,               lyptus paniculata planted on slimes
  winters, with an average rainfall of             physical problems    of stabilization               dams at the Mazoe Mine have a
  900 mm falling between November                  seldom occur. The steeper the side,                 more rapid growth rate than trees
  and March. There are strong, des-                the more difficult it is to stabilize               planted adjacent to the dam, and
  iccating   north-easterly       winds      in    the dam. Slimes-dam walls on the                    are providing a valuable Rource of
  September and October.                           Mangula Mine have a slope of ap-                    mine timber. Elsewhere slimes dams
     The ore deposit lies within rocks             proximately 20 °.                                   have been used for recreational
  of the Deweras System, which is                 Access                                               purposes9,11.
  composed      of      arkoses,      arkosic        Irrespective of the type of stabili-
  schists, and chlorite-sericite      schists,                                                        Plant Selection
                                                  zation programme,       access to the
 with occasional conglomerates            and     top of the dam must be provided for                    It is essential that the selection of
 grits. The sulphide          minerals     are    vehicles. This greatly facilitates the              plant material      is based on toxic
  bornite and chalcocite, which occur             transport of implements, plant ma-                  tolerance, and there are a number of
 in a finely         disseminated        form     terial, fertilizer, and mulching ma-                other important      considerations.
 throughout    the rocks. Chalcopyrite            terials.
 occurs marginally.        The oxidation                                                              M uUiple-layer Protection. It is pre-
 zone, with malachite,          chrysocolla,      Analysis                                            ferable to select trees, shrubs, and
 pseudo-malachite,        and     occasional         A detailed chemical analysis of                  grasses to provide elevated protection
 cornetite is mined in opencasts down             the slimes dam is necessary to show                 and stabilization at depth.
 to a depth of about 45 m.                        the toxic components,     as well as                   Diversity of Species. A range of
     The mine produces HO 000 tonnes              the degree to which plant nutrients                 different plant species gives greater
 of sulphide ore a month from under-              are deficient. Table III is supple-                 biological    stability.    The use of
 ground by a method of sublevel                   mentary to analysis No. 23 in Table                 legumes and non-leguminous        nitro-
 stoping.   Before hoisting,        the ore       I.                                                  gen-fixing     plants    should be en-
 passes through       primary      crushers,
 which reduce the rock size to ap-                                                           TABLE       III
                                                                          SUPPLEMENTARY      ANALYSIS:         SLIMES   DAM NO.   3
proximately      minus 200 mm. The                                                        MANGULA MINE
surface grinding circuit consists of
two identical Aerofall mills, 6700 mm                     Total             Mineral nitrogen                      Available P           Exchangeable K
                                                        nitrogen          Ammonia + nitrate       N              resin extract           mg equivalents
in diameter by 1570 mm, plus two                                                 p.p.m.                               P.O5                 per 100 g
                                                             ~I.
2440 mm by 4570 mm long trunnion                                    -----------                                      p.p.m.
overflow ball mills, which reduce the                                  Initial      After incubation
ore to 65 per cent minus 200 mesh                 ---
                                                          0,000           3                   9                         6                    0,18
(the required      size for copper ex-
traction by flotation).
    Slimes are pumped on to a 20 ha
slimes dam via a 30 m diameter                          SiO.                         62,90%                    Specific conductivity:      110 micromho
thickener, through a 200 mm steel
pipe for a distance of 300 m. At                        FeO                           9,3%                      pH 9,5 reducing to 8,0 over a period
the slimes dam, a peripheral system                                                                                of years
                                                        AI.O3                        11,1 %
of discharge is employed. The slimes                    S                             0,12%
are 54 per cent solids by weight.

JOURNAL     OF THE SOUTH       AFRICAN     INSTITUTE          OF MINING AND METALLURGY                                            DECEMBER 1973 203
                                                                                                                                                  couraged to improve the low nutrient
                                                                                                                                                  status of the dam.
                                                                                                                                                     Plant Propagation.     The use of
                                                                                                                                                  plants easily established   from seed
                                                                                                                                                  is preferable for practical reasons.
                                                                                                                                                  The majority of the more successful
                                                                                                                                                  stoloniferous  grass species are un-
                                                                                                                                                  fortunately poor seed producers and
                                                                                                                                                  must be planted vegetatively.     This
                                                                                                                                                  did not exclude their use, and semi-
                                                                                                                                                  mechanized methods have been de-
                                                                                                                                                  veloped to overcome this problem.
                                                                                                                                                     Low Nutrient Requirement.       The
                                                                                                                                                  plant must be able to survive in the
                                                                                                                                                  low-nutrient  situation experienced.
                                                                                                                                                  Surface Stability
                                                                                                                                                     Wind erosion was a serious prob-
                                                                                                                                                  lem on the Mangula slimes dam. It is
                                                                                                                                                  calculated that 85 tonnes per day
                                                                                                                                                  was removed in the form of dust
                                                                                                                                                  during the five-year period prior to
                                                                                                                                                  stabilization. This wind erosion must
                                                                                                                                                  be countered       with adequate     wind
Plate IV-A            well-prepared access road to the top of a mine dump. The 200 slope                                                          breaks, either planted or mechanical.
                           of the dam walls at Mangula Mine is illustrated.                                                                       Windrows of garden refuse were used
                                                                                                                                                  to provide an excellent mulch for
                                                               TABLE              IV
                                                                                                                                                  the establishment       of seedlings and
                     COST OF PLANT           ESTABLISHMENT                      ON MINE     DUMPS       IN RHODESIA
                                                                                                                                                  surface protection.      Garden refuse is
                                                                                                                                                  also a valuable         source of plant
                                                                                                               Trees       Grass
                                                                                                                                                  nutrients     and often contains large
Preparation         of hole and planting                  ($1,00 per 60 trees              per day)       .    $29,40      $24,70                 quantities     of viable plant material
                                                                                                                                                  that establishes in the windrow and
Fertilizer:        882 kg Single       Superphosphate.                             . . . .                      44,10
                   8,82 kg 'S' mixt (6:18:6)                                                                     0,48                             colonizes outwards onto dump ma-
                   8,82 kg ammonium                 nitrate.          """"'"   . . . . . . . . . .               0,54                             terial. Planted lines of Napier fodder
                   1O00kg'D'(9:15:9)                                                                                        55,40                 (Pennisetum purpureum)         and sugar
                                                            """""'"
Cost of plant material:                                                                                                                           cane (Saccharum officinale) were also
   1764 trees $10 per 1000                                                                                      17,64                             used.
  Grass 6 bags at $1,00                        """"""""                                                                             6,00
                                        """""""'"                                                                                                 Fertilizer Ameliorants
TOTAL          COST      per hectare                  . . . . .                           . . . . . .          $92,16      $86,10
                                                                                                                                                     The use of artificial fertilizer is
                                                                                                                                                  recommended to hasten the develop-

                                                                                                        TABLE     V
                                                                      COMPARISON           OF   COSTS    OF   MINE-DUMP   STABILIZATION



         Country                                               Method             of stabilization                                    Effectiveness       Maintenance         Cost per
                                                                                                                                I
                                                                                                                                                                               hectare
                                                                                                                                    ---                                             ---
U.S.A.                                     Physical:           Straw harrowing                                                             Fair             Moderate        U.S. $99-185
                                                               Soil covering  (10 cm)                                                      Excellent        Minimal            617-1482
                                                               Slag covering   (22 cm)                                                     Good             Moderate         2350-2600

                                           Chemical:             Bituminous      base                                                      Good             Moderate           741-1852
                                                                 Lignosulphonate                                                           Good             Moderate           617-1482

                                           Biological:           10 cm soil and vegetation                                                 Excellent        Minimal            741-1605
                                                                 Hydroseeding                                                              Excellent        Minimal            494-1111
                                                                 Chemical and vegetation                                                   Excellent        Minimal            247-617
                                                                                                                 - ----------
United        Kingdom                      Physical:           Slag (22 cm)                                                                Good             Moderate          £909-1818

                                           Biological:           Refuse           (5 cm) and vegetation                                    Excellent        Minimal              753

South     Africa                           Biological:           Leaching              and vegetation                                      Excellent        Minimal?          R400-700

Rhodesia                                   Biological:           Toxic-tolerant             vegetation                                     Excellent        Minimal     I   R$86-92 (309)
                                                                                                                                                                        I

204      DECEMBER 1973                                                              JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY
                                                                                    Human and Animal Disturbance
                                                                                        Some form of control of animal and
                                                                                    human movement must be planned
                                                                                    to prevent damage to young plants
                                                                                    in: i their vulnerable     establishment
                                                                                    period. This often necessitates         the
                                                                                    use of fencing; the destruction           of
                                                                                    wild-life as an alternative         is not
                                                                                    recommended        because in time wild-
                                                                                    life should be encouraged onto the
                                                                                    dump to assist in providing            bio-
                                                                                    logical stability.
                                                                                    Utilization
                                                                                       Ome plants have been established
                                                                                    on a slimes dam, some form of
                                                                                    utilization or harvesting should be
                                                                                    encouraged   to prevent them from
                                                                                    becoming moribund.
                                                                                    Costs
                                                                                       An analysis of the cost of estab-
                                                                                    lishing   vegetation  on Rhodesian
                                                                                    mine dumps is presented in Table
                                                                                    IV. It should be noted that the
                      Plate V-Experimental plots at Mangula                         amount     of compounded      fertilizer
                                                                                    applied to grasses under experi-
ment of a complete protective layer       are recommended during the summer
                                                                                    mental conditions was 1000 kg/ha
of plants. From the detailed chemical     period. Once full protection has been
                                                                                    in one application.  Under practical
analysis of the slimes dam it was         achieved, the application of further
                                                                                    conditions this has been reduced to
seen that there was adequate potas-       quantities  of fertilizer will be de-
                                                                                    400 kg/ha applied annually for two
sium, but nitrogen and phosphorus         termined by the use to which the
                                                                                    or three years.
were insufficient to support plant        dump is put.
                                                                                       For comparative   purposes, Table
growth.    As a result, an annual            Sewage effluent is a highly desir-
application of 70 g/m2 single super-      able source of plant nutrients,   and     V is included.
phosphate    (20 per cent P2O5) and       its use on the Mangula slimcs dam              ACKNOWLEDGEMENTS
monthly    top-dressings    of 20 g/m2    has provided a practical method of           The authors are grateful to Pro-
ammonium nitrate (34,5 per cent N)        sewage disposal.                          fessor H. Wild of the Department         of
                                                                                    Botany,    University      of Rhodesia,
                                                                                    for his helpful advice in the formu-
                                                                                    lation of experimental        procedures
                                                                                    and in the selection of plant ma-
                                                                                    terial; and to the Forestry Research
                                                                                    Centre, Salisbury, for assistance in
                                                                                    propagating seedling trees.
                                                                                       They would also like to thank the
                                                                                    RhC!desian Ministry       of Mines for
                                                                                    their financial    assistance      in the
                                                                                    provision    of research       fellowship
                                                                                    funds; and the Management           of the
                                                                                    Messina    (Transvaal)      Development
                                                                                    Company,     Limited,     for their en-
                                                                                    couragement and financial assistance
                                                                                    in the presentation of this paper.
                                                                                                 REFERENCES
                                                                                     1. THE CHAMBER OF MINES OF RHO-
                                                                                        DESIA. Promotion      of vegetative     covers
                                                                                        on mine      slimes     dams     and     sands
                                                                                        dumps.   Mine lYIanagers Circular No.
                                                                                        MM. 12/61, 1961.
                                                                                     2. NATURAL RESOURCES              BOARD. Re-
                                                                                        port on 1st Meeting        of Mine Dumps
                                                                                        Sub-Committee       of Natural     Resources
Plate Vi~Windrows      of garden refu3e. showing th2 variety of plant growth re-        Board,  Salisbury.     Cyclostyled     report.
sulting from viable plant material in the rubbish. Note the creeper (Ipomoea sp.)       1961.
                   colonizing dump material in the foreground.                       3. HACK, H. R. Mine dump survey. Re-

JOURNAL   OF THE SOUTH    AFRICAN   INSTITUTE   OF MINING   AND METALLURGY                                  DECEMBER 1973 285
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206 DECEMBER 1973                                                                                  JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY
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JOURNAL   OF THE SOUTH   AFRICAN         INSTITUTE                         OF MINING                   AND METALLURGY                                                        DECEMBER   1973   207
                                                                                                                   industrial    waste land. C.A.B. Joint
                                                                                                                   Publication, No. 14. 1949.
                                                                                                             12.    LE Roy, J. C., and KELLER, H.
                                                                                                                   How to reclaim mined areas, tailing
                                                                                                                   ponds, and dumps into valuable land.
                                                                                                                    TVld Min., vo!. 25, no. I. 1972.
                                                                                                                   pp. 34-41.
                                                                                                             13.   WILD, H., and WILTSHIRE, G. H.
                                                                                                                   The problem of vegetating Rhodesian
                                                                                                                   mine dumps examined. Chamber of
                                                                                                                   Mines J., vo!. 13. 1971. pp. 26-30.
                                                                                                             14.   HILL, J. R. C. The mine dump prob-
                                                                                                                   lem in Rhodesia.        Rhod. Agric. J.,
                                                                                                                   vo!. 69, No. 4. 1972. pp. 65-7:1.
                                                                                                             15.   GREGORY, R. P. G., and BRADSHAW,
                                                                                                                   A. D. Heavy metal tolerance               in
                                                                                                                   populations of Agrostis tenuis Sibth.
                                                                                                                   and other grasse3. Dept. Agr. Bot.,
                                                                                                                   Univ. Co!. of North Wales, Bangor,
                                                                                                                   New Phytol., vo!. 64. 1965. pp. 131-
                                                                                                                   143.
                                                                                                             16.   TURNER, R. G. The subcellular dis-
                                                                                                                   tribution of zinc and copper within
                                                                                                                   the roots of metal-tolerant       clones of
                                                                                                                   Agrostis tenuis Sibth. New Phytol.,
                                                                                                                   vo!. 69. 1970. pp. 725-731.
                                                                                                             17.   BRADSHAW, A. D. Populations               of
                                                                                                                   Agrostis tenuis resistant to lead and
                                                                                                                   zinc poisoning.      Nature,    vo!. 169.
                                                                                                                   1952. p. 1098.
                                                                                                             18.   WILD, H. Geobotanical anomalies in
                                                                                                                   Rhodesia. I-The       vegetation of cop-
Plate VII-Biological     stabilization on the side of a slimes dam to prevent wind-                                per bearing soils. K irkia, vo!. 7,
blown sand from affecting adjacent agricultural    land: an excellent stand of planted                             No. I. 1968.
    grass (Cynodon dactylon and C. aethoPicus)with windbreaks at Mangu la Mine.                              19.   ADAMS, F. Notes on the establishment
                                                                                                                   of grass and trees on slimes dams.
      port to Mine Dumps             Sub-Committee               Mining Congo J., Oct. 1972. pp. 21-::6.           Cyclostyled report, 1971.
      of Natural       Resources       Board,       Salis-    8. McMAHoN, R. G. P. RevegetatLm of           20.    JAABACK, G., and MUZZELL, P. The
      bury. Cyclostyled        report.     1962.                 tailings dams. Bull. Aust. Mineral                establishment     of vegetation     in civil
 4.   NATURAL RESOURCES                 BOARD. Re-               Dev. Labs., No. 12. 1971. pp. 81-100.             engineering work. Proc. Grassld. Soc.
      clamation     works-Camperdown               Mine:      9. STREET, H. E., and GOODMAN,G. T.                  S. Afr., vo!. 6. 1971. pp. 181-184.
      Selukwe Intensive         Conservation        Area.        Revegetation techniques in the Lower       21.    WILKINS, D. A. A technique for the
      Final report.     Cyclostyled.        1970.                Swansea Valley. The Lower Swansea                 measurement       of lead tolerance       in
 5.   RHODESIA MINISTRY OF MINES. Un-                            Valley Project, ed. K. J. Hilton,                 plants. Nature, vo!. 180. 1957. pp. 37-
      published     reports.    Salisbury.                       London,     Longmans    Green.     1967.          38.
 6.   SMITH, R. A. H., and BRADSHAW,                             Chap. 5.
      A. D. Stabilization            of toxic       mine     10. CHENIK, D. The promotion           of a    22.    WILKINS, D. A. The measurement and
      wastes    by the use of tolerant              plant        vegetative   cover on mine slimes                 genetical analysis of lead tolerance in
      populations.          Trans.      Instn.      Min.         dumps and sands dumps. J. S. Afr.                 Festuca Ovina. Report Scottish PI.
      Metall.,    Sect. A, vo!. 81. 1972. pp.                    Inst. Min. Metall., vo!. 60. 1960.                Breed. Sta., 1960. pp. 85-98.
      A230-A237.                                                 pp. 525-555.                               23.    JOWETT, D. Population          studies on
 7.   DICK INS ON, S. Experiments              in propa-     11. WHYTE, R. 0., and SISAM, J. W. B.                 lead-tolerant     Agrostis tenuis. Et'o-
      gating    plant cover at tailing            basins.        The establishment    of vegetation    on          lution, vo!. 18. 1964. pp. 70.80.




Colloquium and general meeting
       CONSTRUCTION        OF                                Council has elected them to member-            From Student to M ember
          SLIMES     DAMS                                    ship of th~ Institute in the following           R. F. Hadfield, R. P. W. Henrard,
   A General Meeting and Collo-                              grades:                                          R. A. Lindsay, B. N. B. Lund
iquum on the above topic was held                            Fellow                                         From Student to Graduate
on November 14th and 15th, 1973,                                K. O. R. Gebhard                               J. R. W. Lindsay, 1. N. Sinclair.
at Kelvin House, Johannesburg.                               Graduates                                         I welcome      the newly elected
   Mr P. W. J. van Rensburg (Presi-                             A. M. Childs, R. H. A. Plaistowe,           members to the Institute and con-
dent) was in the chair.                                         L. Prinsloo, P. C. Pretorius, M. R.         gratulate   those    who have been
   The Colloquium was attended by                               Storey, J. W. Wilson                        transferred to a higher grade.
135 delegates and was opened by the                          Associate
President at 9.10 a.m.
                                                                                                                             GENERAL
                                                                P. A. G. Collett                               The President announced that the
           MEMBERSHIP                                        Student                                        Cocktail Party, which the Chamber
   The President:     I have      much                          T. M. Ferreira                              of Mines had kindly offered to hold
pleasure   in announcing     that the                        Transfers                                      for the delegates at the Colloquium,
names of the undermentioned      candi-                      From Graduate to Member                        would be held at the Chamber of
dates, having     been published      in                        R. D. Beck, 1. E. Francke, N.               Mines Sports Club at 5.30 p.m.
accordance    with    By-Law     5.2.2.,                        Kamp, C. G. Knobbs                             The meeting ended at 9.20 a.m.

208    DECEMBER         1973                                   JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

				
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