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British Geological Survey
TECHNICAL REPORT WC/94/67R Overseas Geology Series
Preliminary appraisal of the environmental geochemistry of the Bau mining area, Sarawak, Malaysia. Neil Breward and Martin Williams
Minerals and Geochemical Surveys Division
with contributions from:
CJ Stanley and RJ. Bowel1
Natural History Museum, London, SW7
A Report prepared for the Overseas Development Administration under the ODA/BGS Technology Development and Research Programme, Project 92/6
ODA Classification Subsector: Geoscience Thcme: GZ-Identify and ameliorate minerals-related and
Project Titk: Environmental Impact of Gold and Complex Sulphide Mining Project Refemnce number: R5553
other geochemical toxic hazards.
Biblwgnaphk refennce: Breward, N & Williams, T M: 1994: Preliminary appraisal of the environmental geochemistry of the Bau mining area, Sarawak, Malaysia.
BGS Technial Report WC194/67R
Krywordr: Malaysia, geochemistry, environment, gold, mining, arsenic, antimony.
F m cover illurtretk: Tai Parit gold mine, Bau, Sarawak.
0 NERC 1994
Keyworth, Nottingham, British Geological Survey, 1994
CONTENTS
LIST OF FIGURES, TABLES AND PLATES
SUMMARY
INTRODUCTION
PHYSIOGRAPHY
GEOLOGICAL SETTING
METALLIFEROUS MINERALISATION
SAMPLING SITES
SAMPLING AND ANALYSIS
RESULTS
DISCUSSION AND CONCLUSIONS
ACKNOWLEDGEMENTS
REFERENCES
APPENDIX 1 - MINERALOGY
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1 6
LIST OF FIGURES
Sketch map of the Bau district, Sarawak, East Malaysia
Sketch map of the Sungai Johara and Bau Town area
Sketch map of the Jugan area Bau area pWEh data trend and correlation graphs Bau area sediment XRF data, AdSb and Heavy Metals
Bau area sediment XRF data: PWSb and MnO/Sb correlation graphs
Sungai Johara area waters: EMpH and As species graphs
Sun@ Johara area waters: SO4, HCO3 and Na, Ca graphs
Jugan stream waters: pWEh data trend and correlation graphs Jugan stream waters: Major ions and trace heavy metals
Jugan stream waters: Total As and Jugan stream waters: AI, Fe, SO4 and As correlations with pH
Jugan soils W-E transect: Arsenic and antimony data.
LIST OF TABLES
UMLl -le 2 m e 3 Bau stream sediments: XRF data and correlation matrix.
m l e 4 NonJugan stream waters data and correlation matrix.
mle 5 Jugan stream waters data and correlation matrix.
m l e 6 Jugan soils: XRF data and correlation matrix.
Minerals identified in the Bau area Practical detection limits for all elements determined in Bau waters
UST OF PLATES
Acicular stibnite in calcite, Kusa mine. Arsenic minerals from Kusa mine.
Tai Ton: Karst limestone landscape and flooded workings. Pik Yin Loon: Karst limestone outcrop and treatment plant.
Pik Yin Loon: Cyanidation processing plant. Tai Parit Mine: Open pit workings.
Jugan: exposed shale outcrop and view to the south-west.
Jugan: Highly-acid water draining from outcrop.
Jugan: Shale outcrop and outwash area, view to the east.
Jugan: Exposed shale outcrop and stream of highly acidic water near site 12.
Jugan: 'Flowstone' of iron oxides with algae and bacterial growths. Jugan: Village and fish pond above site 8.
SUMMARY
In April 1992, the UK Overseas Development Administration (Engineering Division)
approved funding for a three year study under the BGWODA Technology Development and
Research (TDR) programme to address specific environmental aspects of gold mining,
including studies of the release, dispersal and bioassimilation of potentially toxic trace elements (notably As and Hg) in a variety of climatic, geological and technological
development settings. The ultimate aim is to provide a clear scientific basis for the development of site remediation and pollution abatement strategies.
A field visit to East Malaysia was carried out in August-September 1993 by BGS staff to examine the geochemistty of a number of former gold mining sites in order to establish typical patterns of concentration and dispersion of As and other trace heavy metals.
The two principal areas chosen were the Mamut mine near Ranau, Sabah; and the Bau mining
area near Kuching, Sarawak. The work at Mamut is the subject of an earlier report
(Williams et al., 1994) and the Bau results are described here. A similar study was carried out previously in Peninsular Malaysia williams et al., 1994, Breward et al., 1994).
The most significant conclusion which can be drawn from the Bau area studies is that
the presence of high levels of As in waters is not dependent on the acidic conditions produced by sulphide mineral oxidation. The limestone-buffered stream waters of Bau are typically
neutral or slightly alkaline yet may still contain several hundred pgll As. Since the WHO
recommendations for a ‘safe’ As level in drinking waters is 10 pg/l and is being revised
downwards as new knowledge on the toxicity of As becomes available, these levels must be a cause for concern and may be hazardous to health if the stream waters are used as a potable
water supply without treatment to remove the As load.
Although the ‘natural’ level of As is high in the surface waters in the Bau area, there
should be some concern at the As concentration in the process water effluent from one of the
mines (Tai Parit). At more than 1800 pg/I total As this clearly carries some environmental risk as it flows through the town itself, and the relevant authorities should monitor this carefully and improve the wastewater treatment to ensure a reduction in As
content, a possible approach being suggested by the observations at Jugan.
At Jugan, the outwash sediment fan shows clear potential as a semi-natural filter and reactor bed, and is worthy of further investigation. Laboratory and site experiments could be devised to confirm that similar ferric oxide-rich gravel beds can be used to reduce As loading in streams by sorption reactions, and subsequently this could lead to the development
of a relatively low-cost and effective amelioration system for the treatment of arsenic-rich
effluents.
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i N TRODUCTION
In April 1992, the UK Overseas Development Administration (Engineering Division) approved funding for a three year study under the BGWODA Technology Development and Research (TDR) programme to address specific environmental aspects of gold and complex
sulphide mining, including studies of the release, dispersal and bioassimilation of potentially toxic trace elements (notably As and Hg) in a variety of climatic, geological and
technological settings (Project 92/6, R5553). The ultimate aim is to provide a clear
scientific basis for the development of site remediation and pollution abatement strategies. Detailed models of the geochemistry and dispersal of elements such as As (widely used as a
gdd 'pathfinder' element on account of its common association with Au) may also prove of
value for the interpretation of high-resolution exploration data.
Mining activities account for approximately 10% of Malaysia's total GDP (1 991
figures) and are of major importance for employment and infrastructure development. Continued investment in the minerals sector is officially encouraged, alongside increasing
recognition of the need for effective site monitoring and post-extractive remediation
strategies to minimise the adverse impacts of mining on the environment, the non-mining
economy and, ultimately, human health.
Problems of aciddrainage and the attendant mobilisation of potentially toxic metals due to the mining and oxidation of auriferous- and complex heavy-metal sulphides are well documented (e.g. Alpers and Nordstrom, 1991; Plumlee et al., 1993; see UNEP 1991 for
summary). Additional contaminants, including mercury (Hg) and cyanide compounds, may
be released during the processing of primary and alluvial gold. Such problems are often
accentuated in humid tropical environments, where rates of chemical weathering (and
possibly biochemical processes such as Hg methylation) are particularly high.
A field visit to East Malaysia was carried out in August-September 1993 by BGS
staff to examine the geochemistry of a number of former gold mining sites in order to
establish typical patterns of concentration and dispersion of As and other trace heavy metals.
The two principal areas chosen were the Mamut mine near Ranau, Sabah; and the Bau mining
area near Kuching, Sarawak. The work at Mamut is the subject of an earlier report (Williams et al., 1994b) and the results from sampling in the Bau area are described here.
A similar study was carried out in previously in Peninsular Malaysia (Williams et al., 1994a, Breward et al., 1994).
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PHYSIOGRAPHY
The town of Bau lies approximately 30 km south west of Kuching, Sarawak‘s capital
city. The area lies within the flood plain of the major Sarawak river and its tributaries, and
its topography is that of an alluvial plain surmounted by steep-sided wooded karstic limestone hills and lesser features of moderate relief where the bedrock is not deeply covered by alluvium. The area has a humid tropical, high-rainfall climate and a
correspondingly lush vegetation, comprising mainly primary and secondary forest, and rubberloil palm plantations.
GEOLOGICAL SETTING
Sarawak is built up of rocks of the West Borneo Basement and the Northwest Borneo
‘geosyncline’. The West Borneo Basement is the exposed part of the Sunda Shield which
forms the framework of the Borneo Island and consists of Palaeozoic and Mesozoic sedimentary rocks with pre-Tertiary plutonic rocks. The ‘geosyncline’ is composed of mostly Cretaceous and Tertiary sedimentary rocks intruded by Tertiary plutons. A good
summary of the geology of Sarawak is given by Gunn (1994).
The Bau area (see Fig.1) is underlain chiefly by Basement rocks which are
stratigraphically classified into four units termed:
1. The Serian Volcanics, consisting of Late Triassic andesitic to basaltic volcanic rocks.
2. The Bau Limestone of Late Jurassic to Cretaceous age, mainly limestone with some sandstone. This forms the characteristic karst features and also
occupies some lower relief ground.
3. The Pedawan Formation - Cretaceous shale, mudstone and sandstone.
4. The Jagoi Granodiorite of at least Early Jurassic or Late Triassic age.
In the north-western and south-eastern parts of the area, the Pedawan Formation is
overlain by a Late Cretaceous to Tertiary sedimentary pile termed the Kayan Sandstone
which was deposited in localised sedimentary basins. Tertiary (mid-Miocene) acid intrusive
rocks, accompanied by a volcanic tuffaceous facies, are emplaced along a discordant lineament with NNE trend stretching from G. Api near the Indonesian border to G. Sirenggok just north of Bau town. The Mesozoic rocks have undergone extensive and strong tectonic
movements since the end of Late Cretaceous times resulting in the development of a ENE-
WSW trending major anticline and other foMs and fault structures. After the deposition of
the Kayan Sandstone, the area again underwent a tectonic episode accompanied by the
emplacement of the Tertiary igneous rocks and by mineralisation, which is mostly related to the igneous intrusions and the reaction between these and the Bau limestone.
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METALLIFEROUS MINERALISATION
Since the beginning of the 19th century, many small gold, antimony and mercury
deposits have been mined in the Bau area. According to government records, approximately
39 tonnes of gold, 91,000 tonnes of high-grade antimony ore and 750 tonnes of mercury
have been produced to date in Sarawak, mostly from the Bau mining district.
Mineralisation in the area can be generally divided into four types depending on the
i). Au-Sb vein type. ii). iii). iv). Mercury vein type.
main ore minerals:
Pb-Zn vein-shaped replacement type, often Au-bearing.
Cu-MO disseminated porphyry copper type.
A comprehensive review of gold mineralisation in the Bau area is given by Hon
(1990) and summarised in Gunn (1994). The Au-Sb and Pb-Zn mineralisation occurs in
limestone and marble of the Bau Limestone surrounding Tertiary acid stocks, especially near NNE-SSW major faults, in which calcite is the predominant gangue mineral along with
quartz. Stibnite is especially common in some of the veins, for example at Kusa, where fine
specimens occur in association with As minerals (realgar, orpiment) and occasionally native arsenic. The mineralising fluids appear to have risen through fractures in the
limestones and precipitated as replacement bodies on contact with shale lenses. Where the
limestone overlies the intrusions, contact metamorphism has produced skarn assemblages
containing abundant wollastonite.
At other sites, such as at Jugan, the mineralisation is more disseminated in siltstone and mudstone, with a predominantly pyrite/arsenopyrite host for the gold. Cu-MO
porphyry copper type mineralisation is confined to one of the Tertiary quartz-porphyry
stocks (G. Ropih). Mercury deposits are found to the south of the gold and antimony mining
area, where shales and mudstones of the Pedawan formation and Tertiary intrusive rocks
occur, and are genetically unrelated to the Au-Sb mineralisation.
At present, more than 50 small-scale mine sites and workings are known in the study area.
Most of these are now worked out or abandoned, while a few continue working, or have recently been reopened, for gold.
SAMPLING SITES
A number of former, current and potential mine sites were sampled to give a broad indication of the geochemistry of the area and the variety of potential problems. These were
Kusa, Tai Ton, Lucky Hill, Pik Yin Loon, Tai Parit and Jugan; and these are discussed in turn. For locations see Fig. 1 and several of the colour plates.
. . 1. b a . ( B U
This was a small mine, now comprising a series of flooded pits and some spoil
heaps on a flat part of the Bau Limestone outcrop. The spoil heaps show good specimens of
stibnite (Plate I ) , along with arsenic minerals and native arsenic (Plate 2), in a mainly
calcite matrix with subordinate quartz. Since the processing plant at Kusa was suported by
the output of several small mines including Tai Ton, some of the material on the waste dumps
may not be of local origin. Water samples were taken from one of the flooded pits and a stream draining the pit system. The pools appeared fairly stable and biologically productive
with obvious algal growth and a fish population.
2. Tai To&
The Tai Ton deposit consists of a thick vein with subordinate lenticular bodies, in which large white and black calcite crystals are accompanied in places by quartz veinlets, fine-grained quartz with minor amounts of stibnite and arsenic minerals, and
gossanised clay. The gold content is more closely associated with the quartz-stibnite
assemblage than with the large calcite crystals. A large cave adit worked a lenticular vein
mass within a steep outcrop face of the Bau limestone, with flooded pit workings nearby.
Water samples were taken from the stream leaving the partially-flooded adit and the nearby pool, which also appeared to be biologically productive. (Plate 3)
3. w This was predominantly an antimony mine, and had produced more than 5000
tons of high-grade antimony ore by the time it ceased operation in 1982. The area is
underlain by limestone and marble of the Bau Limestone group intruded by quartz porphyry dykes, and the ore occurs in the limestone as fracture-filling and replacement-type bodies consisting of quartz-calcite veins with abundant stibnite, associated with pyrite,
arsenopyrite, calc-silicates and minor amounts of gold. Two adits running into a limestone cliff, and several flooded pits, are visible at site. Water drains from one of the adits, and
from the pond, into the small Sungai Johara river which was sampled for lkm along its
length to determine any downstream impact of the mine.
- 5 -
4. Pik Yin Loon. A small mine working a gold-bearing low-sulphide calcite vein in a series of
pits and a limestone cliff outcrop (Plate 4). A water sample was taken from the pool in a partially-flooded section of the vein excavation. The mine uses an on-site cyanidation plant
to extract gold from the hand-picked ore, which consists of a series of connected tanks loaded
with a mixture of limestone and ore, and which can be seen in Plate 5.
5. Tai Parit
A recently reopened mine on the southern edge of Bau town, the flooded open-
pit workings of the former Bukit Young sett having been drained (Plate 6). The gold occurs
in a low-sulphide quartz-cakite ore body at the faulted junction of the Bau limestone and shales of the Pedawan Formation. Water is pumped from the open-pit workings through a leat into the Sungai Johara, and through a deep roadside drain in Bau town into a north-
flowing stream. Water samples were taken from both drains and from the unaffected stream.
6. Juaan. Jugan is a prospective mine site to the north-east of Bau, consisting of a
small hill of outcropping Pedawan Formation shale and siltstone, intruded by a highly- altered rhyolite dyke, and containing abundant disseminated pyrite and arsenopyrite. A
small-scale mine operated here for a short period in the early 20th century. The outcrop has largely been cleared of vegetation and soil (by pressure hosing?) producing an outwash
fan of derived sediment on the east side, and extensive exposure of the bedrock (Plates 7, 9).
The exposed sulphide ore weathers rapidly under the tropical climate and several of the
small drainage streams are notable for very low pH values (Plates 8,lO). Re-precipitation of iron oxides often leads to the formation of flowstones on some outcrops, and some algae and
bacteria use the high Fe3+ content of the waters as an energy source and form colonies on
these sites (Plate 11).
The Jugan area is treated in greater detail than the other sites, as it provides a more
self-contained study area. Rock samples, soil traverse samples and stream sediments were collected in addition to a full suite of water samples from the local drainage system.
SAMPLING AND ANALYSIS
Selected Lpck and mineral W l e s from the Bau area were collected and submitted to
the British Museum, Department of Mineralogy, for mineralogical characterisation. Preliminary results of optical and electron microscope (with the Link analytical system) analyses of the samples, supported by additional X-ray diffraction (XRD) examinations,
indicate the presence of a broader spectrum of minor accessory minerals than was
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previously documented, including a variety of As, Sb and secondary phases, and are summarised in Table 1 and Appendix 1.
se- were taken at selected sites in the Bau area, following the standard
BGS procedures (Plant 1971, Plant and Moore 1979) and the sub-150 pm material was
subsequently analysed by X-Ray Fluorescence.
les, comprising unsieved ‘8’ horizon material at depths varying from 5 cm
to 35 cm depending on the soil profile development, were taken along an east-west traverse at Jugan. These samples were later sieved to < 2mm, ground and analysed by XRF.
surface w W H and Eh was determined in the field using temperature-compensated
(Pt) electrodes and a Radiometer Instruments pWmV meter. Calibration of the electrodes was undertaken prior to each site measurement using a series of commercial buffer solutions (PH 4, 7 and 9) and Zobell Eh standard.
m l e 1. Minerals identified in samples from the Bau area. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - ~ ~ ~ ~ - - ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - ~ - ~ ~ ~ - - ~ ~ ~ - ~ ~ ~ ~ - ~ o ~ ~ ~ ~ ~
Mineral Notes Calcite - Widespread. These two are the main gangue Quartz =2 minerals. Wollastonite CaSiO3 A calc-silicate mineral, typical of skarns.
Orpi men t h 2 s 3 Realgar k 4 S 4
Stibnite Sb2S3 Best seen at Kusa and Lucky Hill Pyrite F e Arsenopyrite FeAss Most common at Jugan, along with pyrite Arsenolite 4 0 3 Native arsenic As Good examples at Kusa Native antimony sb Best seen at Kusa Pitticite Fe2AsOqS040H- n w P ha r m acol i t e caHAsO4.2Hfl Sarabauite ~ ~ 1 0 0 1 O s 6 Sti bicon i te Sb3+Sb$+Os( OH) Scorodite FeA&t.W@ Limonite ‘F8o.W’ Used in senso lab -secondary hydrous Fe oxide. Mi te AI-Silicate Clay mineral. Usually as an alteration product.
Lucky Hill - The type area for this mineral.
~ ~ 0 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 0 ~ ~ ~ ~ 0 ~ ~ 0 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 0 0 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
The suite of water samples collected at each site for geochemical analysis routinely included :- a) 30 ml unfiltered HN03-acidified water
b) 30 ml filtered (0.45 pm Millipore) unacidified water (for ‘anions’ determination) c) 30 ml filtered (0.45 pm) HN03-acidified water (for the bulk of the ICP analysis)
d) 30 ml filtered (0.45 pm Millipore) HCI-acidified water (for the As”VAsv analysis)
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Additional samples, collected only at selected localities, included: e) 30 ml filtered (0.20 pm Millipore) HNOg-acidified water
9 30 ml (0.45 pm) filtered water with 5 ml dipiridyl reagent.
Filtered waters were obtained by drawing 30 ml of water into a sterile plastic syringe and passing it through a sealed filtration cartridge (loaded with a filter of appropriate pore-size) into a Sterilin storage tube. Acidification of samples was carried out
within 4 hr of collection through the addition of 0.3 ml of concentrated ARISTAR grade acid (HNO3 and HCI). The addition of 1% volhol. acid reduced the pH of samples to c. 1.0, thus
precluding adsorption of dissolved metals to the interior tube walls and minimising post- sampling microbial activity.
Determinations for K, SOS, Na, Mg, Fe, Mn, P, Cu, Zn, Pb, CO, Ni and Cr were made
by direct ICP-AES methods, while As analyses were made by hydride-generation ICP-AES. Data for NO3, and CI were obtained by ion chromatography. Analyses of HCO3- were made by
HCI titration. The dipiridyl reagent was used in a colorimetric method for the determination
of reduced (Fe*+) iron in solution (Moss and Meon, 1952.)
Practical detection limits for all elements are given in Table 2.
Table 2: Practical detectbn limits for all elements determined in Bau waters (pdml).
m m m m m m m m m m m m 1 m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m - m m m m m m m m ~
Na 0.020 Mg 0.030 HCO3- 20.0 K 0.100 AI 0.030 c I- 2.00 Q 0.020 P 0.030 NO$ 1.00
Mn 0.005 cb 0.010 As 0.0002 Zn 0.005 Ni 0.010 Pb 0.030 QI 0.007
Fe 0.010 Cr 0.010 SO$' 0.100
m m m m m m m m m m m m m m m m ~ m m m m m m - m m ~ m m m m m m m m m m m m m m m m m ~ m m m m m m m m m m m
Biological samples, mostly of algae, were collected on a subsequent visit by Natural History Museum staff, and these results will be included in the project's final Completion Report.
RESULTS
A. General observations.
As &sewed in previous studies in Malaysia, the surface waters in the Bau area (see
Tables 4 and 5) show a distinct inverse relationship between pH and Eh, with high Eh/low pH values being typically indicative of acid mine drainage (AMD) due to sulphide oxidation
and low EMhigh pH values being more characteristic of waters in the low-sulphide
limestone-dominated areas. The wide range of Eh and pH values makes the comparative and
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correlation graphs in Fig. 4 especially distinctive, with the Jugan AMD sites clearly distinguishable from the rest of the Bau area samples.
The Bau stream sediments data (Table 3), though a rather limited dataset, clearly show high levels of As at some sites (Fig. 5), but more significantly show that the area is clearly an antimony enrichment province (as can be deduced from the locally-recorded minerals) with even the lowest value (29 pglg) about two orders of magnitude above the
typical crustal abundance value (0.2-0.3 pglg). Even allowing for the concentrating effects of stream sediment geochemical sorption processes, the Sb values in all the Bau sediments
are very high, as they are also in the Jugan soils (see below). Unfortunately, Sb in water
data are not available, so the mobility of the Sb cannot be determined. However, the tendency
of Sb to form strong and stable complexes with secondary iron oxides and other substrates in
soils and sediments, and the low solubility and instability of Sb species in water, suggests
that the Sb is predominantly immobile.
Although the correlation matrix for the Bau sediments could be misleading due to the small number of samples and the rather too obviously bimodal dataset, it is clear that the Sb is only weakly correlated with As and Fe2O3, and is much more strongly linked to the Pb and
MnO values, although this correlation depends too greatly on values from one site (822) to
be reliable. (Fig. 6).
B. Sltes other than Jugan.
1. )(us8 (water samples, sites 615 and B16). Near-neutral pH, low Eh water
samples taken from the flooded open-pit workings at Kusa show low sulphate, calcium
bicarbonate dominated waters with very high total dissolved As levels (1129 and 941 pg/l
respectively, of which 28 and 22 pg/l are in the more toxic AsI'l form). Due to the limited number of samples it is not possible to determine the lateral extent and the persistence of
these very high As levels, but clearly such waters must be a potentially serious health risk
if they are used for domestic or agricultural purposes.
2. Tal Ton (water samples, sites B24 and 825). These samples proved to be very
similar to the waters from Kusa, showing low Eh values, near-neutral pH and high dissolved As levels (751 and 439 pgA, with 14 and 9.7 pgA in the Ad1' form).
3. plk Yln 1 oon (Water sample, site 626).
The water sampled here is very similar to that at Tai Ton and Kusa, i.e.. low Eh,
near-neutral pH and high dissolved As levels, in this case 548 pgA total As, with 11.2 pgA in the more toxic As111 form. This is clearly characteristic of the low-sulphide, limestone-
- 9 -
hosted As/Sb/Au mineralisation type common in the Bau area and also shows the
independence of high dissolved As levels from pH.
4. U k v Hill and Tal P a l t - The S. Johara river catchment.
(Water and sediment samples, sites 817-823, 827-828: see map, Fig. 2).
The location of these two mines immediately to the south of Bau town and their effect
on the S. Johara river and its tributaries makes for an interesting study area. The S. Johara drains an area mostly of limestone with igneous intrusions, and receives water from the
Lucky Hill mine (and probably others further upstream) by natural drainage, and from Tai
Parit as pumped drainage and spent process water.
Sample 817 was taken from water collecting in pools within the mine adit, and shows
low pH - high Eh values markedly different from those prevailing in the wider area (Fig. 7). However, As and SO4 values are both low at this site suggesting that sulphide oxidation is
not the prime acid-generating process here (Fig. 8). Sample 618, taken from the settling
pool at Lucky Hill, shows higher As levels but not remarkably high in the Bau context (144
pg/I). Site 619, on the S. Johara upstream of its confluence with streams draining from
Lucky Hill, actually shows total As levels (713 pgA) well above those at 818. This suggests
that either the As levels in the S. Johara are high due to the effects of mines further
upstream, or that they are reflecting the high natural As level in the area and that the mines have only a limited impact. The total As in solution remains steadily high downstream from
site B19 to site 822, supporting the ‘high natural background’ explanation.
The sample from site 823, situated on an artificial leat carrying pumped drainage
water from the Tai Parit open pit mine into the S. Johara, shows low total As (75 pg/l) but a relatively high proportion of this (10.4 pg/l) is in the As111 form. This water also has elevated levels of Ca, SO4 and HCO3, but apart from its high turbidity is scarcely an
‘effluent’, as its As and heavy metals load ( except for manganese) is below that of the river into which it discharges.
To the east, spent process water from the Tai Parit mine flows northwards through a deep drain and joins a tributary of the S. Johara on the outskirts of Bau town. This drain was
sampled at site B28, and the tributary upstream of the confluence with the drain was sampled at site 827. This sample (827) is on a relatively pure stream (for this area) with only 85.9 pg/l total As, and background levels of SOS, HCO3, Na and Ca, but rather higher Fe
than usual. However, it makes a good contrd sample with which to compare the mine waters
at site 628. This effluent is notable for its very high As content (1844 pg/l, of which 25.5 pgA is in the Asll’ form. Sodium, Ca, Mg, SO4 and HCO3 levels are also high, although of the
trace heavy metals only Cu (20 pgA) is above the analytical detection limit. The fate of the
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high As levels in the stream downstream of the confluence is not known, reaction and sorption with the stream sediments probably limiting the dispersion and reducing the levels
rather quickly, but it is to be hoped that this stream is not used as a local water supply, and
its As content should be monitored by the relevant authorities.
Stream sediment samples were taken at sites 819 and 822, and data from these can be seen in Fig. 5. Trace heavy metal levels are unremarkable, Zn and Pb being the dominant
elements with 271 p u g Zn and 203 pg/g Pb at site B22. Arsenic values are high, as
expected, with over 1500 pglg at 822 probably associated by sorption with secondary iron
oxides. That the As content at site B22 is higher than that at 819 suggests some influence from Lucky Hill, but this is not conclusive. Of possibly greater significance is the value of
566 pg/g Sb from this site, and 243 p u g at site 819, implying some input from Lucky
Hill, and again emphasising that Bau is clearly an especially antimony-rich area. In the
absence of reliable Sb data from the waters, the distribution coefficient between sediments and waters cannot be calculated, but at the typical stream pH in the Bau area, the sorption
eq u i I i b ri u m position :
Dissolved Sb species + Sorbant in sediment e-----.--> Sediment Sb sorbtion complex
- must lie far to the right.
C. Jugan. (Stream waters, sediments and soils: See map, Fig. 3). Jugan, in marked contrast to the rest of the 8au area, is a shale-hosted auriferous
disseminated sulphide ore body with pyrite and arsenopyrite as its primary minerals.
Consequently its geochemistry is dominated by subaerial oxidation of these sulphides, giving
rise to acid mine drainage (AMD). The hydrogeochemistry data is shown in Table 5. The
graph of Eh and pH values for the 14 water samples and the relationship between them can
be seen in Fig. 9. The strong negative Eh-pH relationship and the values recorded are typical of AMD sites previously studied (e.g. at Mamut and Penjom, Williams et al., 1994a,
1994b). The lowest pH values were recorded at sites on the smallest streams draining directly from the shale outcrop, i.e. sites 6, 11 and 12, where exposed sulphides were
actively weathering. The design of the water sampling programme included upstream control
samples (sited, 8, 13) as well as streams affected by drainage from the Jugan site. The
influence of the Jugan AMD generator on its associated drainage is less dramatic on the
larger rivers such as the Siniawan (sites 1, 2, 3) than on the small tributary streams, since greater dilution factors are involved.
The highest levels of As and other cations and anions are also present in association with the low-pH sites, with total As levels up to 4000 pgA, SO4 up to 3500 pg/ml and Fe up to 675 pglml, with correspondingly high levels of trace metals (CO, Ni, Cu, Zn). (See
B B B B
B B
8 8 8
0
0
0 0 0 0
0 0 0 0 0 0 0 0
0 0 0
0
Figs. 10 and ll), The strong relationship with pH can be seen in Fig. 12 where the similarity of the AI, Fe, As and SO4 versus pH graphs, each with a sharp change in activity
at about pH 3.3, is well marked. This value (pH 3.3) corresponds closely to the precipitation equilibrium pH of Fe(OH)3 and, as would be expected, ferric hydroxide is
actively precipitating in parts of these small, acid streams giving a characteristic orange
ochre coating to the stream beds. (Plate 8).
Stream sediments were collected from sites 61, 83, 64 and 61 3; and selected data
are shown in Fig. 5. Arsenic values of 4500 pg/g and 5500 pg/g are present at sites 63 and 64, both strongly affected by the Jugan AMD, compared with 71 pg/g at site 613 and 89 pg/g at site 61, both unaffected control sites. The higher than expected value from the third control site 68 (495 pg/g) suggests that the shale outcrop, forming the slightly higher
ground beyond the village with its fish pod (Plate 12) above site 68, may also contain some
disseminated arsenopyrite mineralisation. Although Sb levels in the sediments at Jugan are high by 'normal' standards, they are lower than at the other Bau sites and there is no
significant increase in Sb levels attributable to input from the Jugan mineralisation. Arsenic and antimony are poorly correlated in waters, sediments and soils (see below), and
are showing clear independent geochemical behaviour in the Bau area as a whole.
Soil 6 horizon material samples were taken on a transect line running approximately west-east through the Jugan area, covering the outcrop, the outwash area, and the relatively
undisturbed ground at either end (see map, Fig. 3). XRF data for these soils is shown in Table 6, and the As and Sb results graphically in Fig. 13. High As levels are present in the
thin residual soils over the outcrop, reaching 13702 pg/g at site 8JS4, but similar and higher levels are present over the outwash area, reaching a maximum of 17198 pg/g at site
BJS13. As most of this outwash material consists of the former soil cover of the Jugan
outcrop, this is not surprising.
However, a significant amount of ferric hydroxide precipitate is also present within
these outwash sediments and the soils developed on them, and the sorption of As species from
solution by this material may be a further contributory factor to the total As load, and has the important and beneficial effect of limiting dissolved As movement through this area. In
effect, this outwash fan may be acting as a semi-natural filter bed, preventing the wider dispersion of As into the environment. Certainly there is a strong contrast in As levels between soils over the outwash area and those over the adjacent undisturbed ground to the east. To the west, As levels over the undisturbed ground are rather higher than those in the
east, which may be due to the topography: the fairly steep slope on which sites BJSl-BJS3
are located must receive some runoff water from the exposed Jugan outcrop, and this
probably increases the As content of these soils.
- 12 -
a 0
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Note that Sb, which has a mean value of around 60 pg/g in these soils, is remarkably
uniform throughout, and shows no relationship with the highly variable As levels.
Levels of the common trace heavy metals (CO, Ni, Cu, Cr, Pb and Zn) are unremarkable in the Jugan soils, the only point of note being the correlation between higher
levels of MnO and CO in the undisturbed soils at sites BJS9-BJS11.
DISCUSSION AND CONCLUSIONS
The most significant conclusion which can be drawn from the Bau area studies is that
the presence of high levels of As in waters is not dependent on the acidic conditions produced by sulphide mineral oxidation. The limestone-buffered stream waters of Bau are typically
neutral to slightly alkaline with pH values in the 6.5-7.5 range, yet may still contain several hundred pgA As. Since the WHO recommendations for a ‘safe’ As level in drinking
waters is 20 wg/l and is being revised downwards as new knowledge on the toxicity of As
becomes available, these levels should be a cause for concern and the stream waters may be a
serious health risk if they are drunk without treatment to remove the As load.
Although the ‘natural’ level of As is high in the surface waters (and probably the ground waters too) in the Bau area, there should also be some concern at the As
concentration in the process water effluent from Tai Parit. At more than 1800 pg/l total As
this clearly carries some environmental risk, and the relevant authorities should monitor this carefully and try to ensure a reduction in As content by encouraging the mine to
improve its waste water treatment.
It is unclear from the available data whether the high Sb levels in the soils and
stream sediments of the Bau area constitute any sort of an environmental or health risk.
Investigation of the Sb levels in water are recommended to complement the sediment and soil data, and so determine the extent of Sb mobility in the local environment.
At Jugan, the possible behaviour of the outwash sediment fan as a semi-natural filter
and reactor bed is worthy of further investigation. Clearly As accumulates within the bed,
but since As-rich waters can reach the streams without flowing through the outwash area, the high levels of As in the stream sediments at sites B3 and B4 cannot be used to show that As in solution is passing through the system without being sorbed. However, if it could be shown in a feasibility study (by laboratory and site experiments) that similar ferric oxide-
rich gravel beds can be used to reduce As loading in streams by sorption reactions, this could
lead to the development of a relatively low-cost and effective amelioration system for the
treatment of arsenic-rich effluents which would be most appropriate for those areas of the
- 13 -
developing world where resources for waste and pollution treatment are most limited, and
such a feasibility study is recommended for further work.
- 14 -
ACKNOWLEDGEMENTS
The authors wish to extend their gratitude to the Geological Survey of Malaysia,
particularly Mr Victor Hon and the GSM staff at the Kuching office, for the provision of data, vehicles, equipment, support personnel and local expertise throughout the August 1993 BGS
fieM visit. Thanks are also due to the owners and operators of the various mines in the Bau area for allowing access and providing much useful information. We are also grateful for the
assistance provided by Dr A.G. Gunn of BGS, then on secondment to GSM under a Technical Co-operation programme supported by the ODA.
REFERENCES
C N and N o r m D A: 1991:
Evolution of extremely acid mine-waters at Iron Mountain, California. Are there
any lower limits to pH? in : Proceedings of 2nd International Conference on the Abatement of Acidic Drainage. MEND, Ottawa, Canada, 2, 321-342.
d. N.. W m . T . M . 1 9 9 4
Environmental geochemistry of the Mengaur and Sungai Luit mining areas, near Kuantan, Pahang, Malaysia.
British Geological Survey Technical Report WC/94/26R
. .
m. A.Ll994
Overseas Development Administration: Gdd sub-programme; GSM-BGS.
Final Report: Summary, Conclusions and Recommendations.
Hon, v. 1990
Some exploration criteria for gold mineralisation in the Bau area, Sarawak. in: Proceedings of the GSM annual conference, Vd. 2.
-con. U 1 952:
Colorimetric determination of iron with 2,2 -bipyridyl. Ind. Eng. Chem. (Anal. Ed.) 14, 862-865.
ee. G S: Smith. K S: F i c w W H: R r w . P H J RI 1993: . .
Empirical studies of diverse mine drainages in Colorado.
Mined Land Reclamation Symposium, Billings, Montana, (Proceedings).
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a 0
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0
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e 0
1991 : Environmental Aspects of Selected Non-ferrous Metal Mining: A Technical
Guide.
Br-. N.. Gunn. A G and C-s. C; 1994a:
Environmental Geochemistry of the Penjorn Mine area, Kuala Lipis, Pahang,
Malaysia: Preliminary results with particular reference to Arsenic. British Geological Survey Technical Report WC/94/20R.
T. M: B r w d . N. and S-
Environmental Geochemistry of the Mamut Copper Mine, Sabah, East Malaysia: A
preliminary study.
British Geological Survey Technical Report WC/94/9R.
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Report on the mineralogy of specimens from the Bau district, Sarawak, carried out by C.J. Staniey and R.J. Bowell, Natural History Museum.
Specimens
1.
2.
3.
4.
5.
614, B2-R and B3-R from Kusa, Bau, collected by BGS J-1, J-2, and J-5 from Jugan, Bau, collected by BGS; also by R J Bowell
Specimens from Bidi mine, Bau, collected by R J Bowell
Specimens from Lucky Hill mine A, Bau, collected by R J Bowell
Specimens from Lucky Hill mine B, Bau, collected by R J Bowell
Descriptive mineralogy.
1. Kusa, Bau
B1-R
Consists mostly of massive coarsely crystalline vein-type calcite with prismatic development of stibnite (up to Scms x 0.2-0.3cms). Some of the calcite is strongly corroded, as also is some of the stibnite where it has been replaced by native arsenic. The latter has altered to arsenolite as a surface coating and is overgrown by realgar.
82-R
Mostly massive intergrown native arsenic and stibnite with calcite gangue. Realgar is common in vughs as also is a late development of quartz. Alteration of native arsenic to arsenolite as a surface coating was noted as was replacement of realgar by orpiment.
B3-R
Coarsely intergrown stibnite and native antimony. In most respects the mineralogy is similar to the other two specimens with arsenolite altering native arsenic and orpiment replacing realgar. In polished section, inclusions of quartz in stibnite and native arsenic, themselves contain finely divided inclusions and aggregates of arsenopyrite. Stibnite appears to be largely unaltered.
2. Jugan, Bau - Labelled as "weathered shale detritus with minor kaolinite veinlets and scorodite surface covering".
On a fresh surface the rock appears to be laminated and variably silicified with pyrite and abundant typically elongate prismatic grains of arsenopyrite (up to 2mm x 0.3mm) Weathered surfaces display a variety of amorphous ochres (probably mostly in the category of 'limonite') with in addition the amorphous hydrated iron sulphate-arsenate pitticite.
In thin section, subhedral pyrite and generally euhedral arsenopyrite occur in a quarWclay mineral matrix. This has been cut by later quartz veinlets. Some of the arsenopyrite shows evidence of alteration, particularly where close to open fractures or to shale bedding planes.
illwanz Labelled as "Fe-crusted siltstone ....." On a freshly fractured surface, the pale grey rock shows its highly bleached and altered nature. Pseudomorphs of pitticite (Fe2As04S040H .n H20) after arsenopyrite are particularly well
- 17 -
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developed. Pyrite appears to be less altered, but there is very little in the way of sulphide material left in this rock. Brown coatings on weathered surfaces appear to be iron oxyhydroxide minerals, again of 'limonite' affinity. In addition more massive pitticite occurs. The latter mineral was separated out and found to be X-ray amorphous; electron microprobe work showed the presence of variable Fe, As, and S contents. - Labelled as 'Weathered Fe-As-S-bearing shale"
Specimens from this sample are variably altered. However, some are relatively fresh and show prismatic development of arsenopyrite and euhedral pyrite in a dark grey shale host rock. Arsenopyrite is estimated to make up about 5% of the rock (by volume). Alteration again probably to amorphous iron oxyhydroxides has occurred along fractures and joint surfaces.
l L u I s Labelled as "weather ed........ Evidence of As secondaries in 'in situ' material".
An altered rock with abundant pyrite and quartz and minor arsenopyrite. Alteration of this rock has led to the formation of illite. No iron- or arsenic-bearing secondary minerals were identified by X-ray diffraction, and any arsenic removed by alteration of arsenopyrite is probably heid in p i ttici te.
Jugan specimens collected by R J Boweil.
These are similar to the representative specimens collected by the British Geological Survey, and have not yet been studied in detail.
3. Specimens from Bidi, Bau, collected by RJB
In most respects similar to the specimens described above from Kusa. Prismatic stibnite and botryoidal native arsenic are the most abundant ore minerals, with realgar in vughs. Replacement minerals are arsenolite (confirmed by XRD) altering native arsenic, and orpiment as an outer coating on realgar. Also found in open cavities, generally between native arsenic and calcite, is the mineral pharmacolite (CaHAs04.2H20 - confirmed by XRD). The clay mineral illite (XRD) occurs as a late development in cavities in mineralized material.
4. Specimens from Lucky Hill mine A, Bau, collected by RJB
Again, similar in many respects to Bidi and Kusa material. Specimens were collected both from in sifu in a drive at adit level and from the ore stockpile. The mineralogy consists almost entirely of native arsenic and stibnite in calcite with later realgar and orpiment. Stockpile material in particular is covered in secondary alteration products. It is evident from observation in polished section that the oxidation of native arsenic begins almost immediately; after a few days the surface is tarnished and then becomes totally dull due to the growth of octahedral crystals of arsenolib. Not surprisingly, arsenolite is by far the most abundant of the secondary minerals and appears to be relatively stable since no other secondary arsenic minerals were identified here with the exception of minor scorodite. In addition to sarabauite (confirmed by XRD) for which this is the type locality (formula: CaSbloO1Os6), stibnite also alters to stibiconite (Sb3+Sb$+Os(OH) (confirmed by XRD) in this assemblage.
5 Specimens from Lucky Hill mine B, Bau, collected by RJB
A skarn-type assemblage of stibnite and possibly Sb-sulphosalt species in a dominantly wollastonite-calcite skarn with minor epidote and reported garnet. No alteration minerals found here.
- 18 -
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Figure 2
Sketch map of the Sg. Johara - Bau Town area, showing sampling points, mines and drainage.
Figure 4
8
7 -
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5 - PH
4 -
3 -
2
8 Malaysia 93: Bau area (Sarawak) stream pH/Eh data
0 0.
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600
500
400
300
200
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Site (B)
0 Malaysia: Bau pH/Eh data correlation
0 e Eh (mV)
Figure 5
Bau area stream sediments (XRF data)
6000
300
200
E Q Q
100
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B1 83 84 B8 813 B19 822
Sample No.
Bau sediments xrf data: Heavy metals
I CO Ni cu
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