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THE KOLAR GOLD MINES, INDIA: PRESENT STATUS AND PROSPECTS FOR
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THE KOLAR GOLD MINES, INDIA: PRESENT STATUS AND
PROSPECTS FOR PHYTOMINING
Rachna Chandra*, V. Sathya*, B Anjan Kumar Prusty#,$, P. A. Azeez$ and S. Mahimairaja*
* Department of Environmental Sciences, Tamil Nadu Agricultural University (TNAU),
#Environmental Impact Assessment Division, Gujarat Institute of Desert Ecology (GUIDE), P.O.
Box-83, Mundra Road, Opp. Changleshwar Temple, Bhuj-370001, Kachchh, India
$Environmental Impact Assessment Division, Sálim Ali Centre for Ornithology and Natural
History (SACON), Anaikatty (P.O.), Coimbatore-641 108, India
Mineral exploration and processing is a major industrial sector in India and contributor to its
Gross Domestic Product (GDP). The present study briefs the history of Kolar Gold Mines
(KGM), options for further mineral exploration and opportunities to implement new scientific
tools for sustainable mining and environmental management. With a recorded history of 200
years of mining activities, KGM at Kolar Gold Fields (KGF), were once considered world's
second deepest gold mine. The KGM have so far produced 800 tonne of gold per 51 million
tonne of gold bearing rock. During 1972, Bharat Gold Mines Limited (BGML) took over KGM.
The KGM yielded 47g of gold per tonne of ore during 1881-1890. However, during 1990’s the
returns were 03g/t due to the depletion of the high grade ore reserve and increase in production
costs, which lead to its closure few years later. Mine wastes in the form of rock fragments and
mill tailings have been stacked in huge piles and heaps in KGF, occupying about 15-20% of the
lease area. In 1994, BGML floated 02 global tenders a) exploration and exploitation of gold in
leasehold area, and b) extraction of gold from mine tailings. Notwithstanding earlier attempts of
joint explorations, there have been recent initiatives for the revival of these mines. BGML has 33
million tonne of tailings with 0.72g/t gold spread all over the mining township of KGF. We have
recently initiated a study exploring the potential of gold phytomining from tailings at KGF.
Chelate assisted phytoextraction, effect of co-metal ions on phytoextraction and metal
accumulation with respect to soil particle size are being explored for optimizing gold extraction.
The work also attempts at leachate studies with respect to gold and chelates. Thus, the present
study aims at sustainable mineral exploration and integrating environmental management.
Key words: gold phytomining, KGF, mineral exploration, phytoextraction, sustainable mining
In India, gold is presently produced from three mines viz. Hutti, Uti, Hirabuddni in Karnataka
and as by-product from base-metal sulphide deposits of Khetri (Rajasthan), Mosabani,
Singhbhum (Jharkhand), in public sector and Kundrekocha in private sector. India’s total gold
production in the year 2006-2007 was 12.82 tonne, (0.5% of world production), of which, 2.36
tonne was from primary source, 0.127 tonne from base-metal mines as by-product, and the
remaining was recovered from secondary source (http://www.portal.gsi.gov.in, accessed on 12th
February 2014) by smelting of imported copper concentrates (IBM year book 2007, and mineral
commodity summaries-2006). According to Geological Survey of India (GSI), gold evolves as a
siderophile element from the iron-nickel core at crustal spreading centers. During partial melting
2014 - SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT/SHECHTMAN INTERNATIONAL SYMPOSIUM
Volume 1: MINING
Edited by Florian Kongoli, FLOGEN, 2014
of the mantle, gold along with metals derived from sulphides rises with basaltic fluids into the
crust along mid-oceanic ridges and at subduction zones. It is then associated with complex
processes (convection, subduction, partial melting, hydrothermal processing, weathering, erosion
and deposition) before returning to the mantle for recycling again at subduction centers. The
deep-seated ore bearing solutions containing gold are of both magmatic and metamorphic origin.
Gold occurs in a variety of litho assemblages, and multiple geological environments such as
greenstone belts, mantle derived intrusions, diaperic juvenile plutons and granulites. In the
Indian subcontinent, prominent granite greenstone belts of Peninsular Shield are located in
Dharwar, Bastar, Singhbhum and Rajasthan cratons. The Dharwar craton (the eastern and
western block), hosts the maximum number of gold occurrences. The Eastern block provides an
important and favourable lithologic, structural and stratigraphic milieu for gold mineralization
and hosts major deposits like Kolar and Hutti. In the northwestern Indian Shield, gold occurs in
association with copper in the Archaean greenstone-like sequence (at Dhani Basri, in Mangalwar
Complex) and Proterozoic meta volcano sediments (at Bhukia and Dugocha, in Aravalli
Supergroup). Puga geothermal system, a hot spring type epithermal gold deposit, occurs in
Ladakh region of Jammu and Kashmir (Figure 1).
Kolar Gold Mines (KGM), India, with a recorded history of 200 years, since Tipu Sultan era,
were among the deepest gold mines in the world. The Champion Reef Mine at Kolar Gold Fields
(KGF) was 3.2 km deep i.e. the deepest point below the sea level ever reached by humans. The
KGM were systematically exploited by John Taylor & Sons during 1880. Subsequently, the
mines were taken over by Government of Karnataka in 1950. In 1972, the mines were taken over
by the Government of India when Bharat Gold Mines Limited (BGML) was formed. KGM have
produced more than 800 tonne of gold per 51 million tonne of ore before its closure in 2001.
During 1881-80, the gold production in KGF was about 47g/t of ore (Subbaraman 2006).
However, during 1991-1999, KGM returned only 03.0g/t (Table 1). All these factors had a
growing impact on KGM functioning, thus leading to the closure of KGM due to losses incurred.
At present, BGML has nearly 33 million tonne of tailing sand with the gold content of 0.72g/t.
These tailings are source of 24 tonne of gold (Mohan 2005). Ever since the production of gold
started systematically and in large scale, the mine wastes have been stacked in huge piles at
different locations of the leasehold area. Due to huge mineral exploration, the volume of this
waste increased steadily thus, currently occupying 15-20% of the total leasehold area.
BGML is a pioneer enterprise in mining with more than 118 years of experience in deep level
hard rock mining. BGML has/had two metallurgical plants i.e. at KGF in Karnataka and at
Yeppamana mine in Andhra Pradesh. The declining ore quality demanded to upgrade the
technologies in metallurgical process to recover gold both from refractory and free-milling ores.
Thus, BGML proposed carbon-in-pulp technology initially at Yeppaman mine followed up by
KGF. Later, BGML introduced heap-leaching technique first time in India, for extracting gold
from mill tailings accumulated on the leasehold area over the years. Both these techniques are
considered as improved technologies. Eventually, 02 global tenders were floated in this
connection. Notwithstanding earlier attempts of joint explorations, there have been recent
initiatives for the revival of KGM.
Figure 1. Distribution map of gold occurrences in India. (Source: http://www.portal.gsi.gov.in)
Table 1. The quantum of gold production at KGF during each decade
Ore milled (tonne)
Average grade (g/t)
Courtesy: BGML, Kolar Gold Fields
The 12,500-acre stretch of the KGF is occupied with around 33 million tonne of mill tailings
which contain residual gold left over from the earlier extraction (Plate 1, Plate 2). Commercial
mining requires huge investment and high quality ore in abundance. However, continuous
mining with conventional technologies in KGM has led to exhaustion of high quality grade ore
bodies. Thus, sub-grade or low-grade ore occupies much larger areas in KGM, which is not
economically feasible following conventional ore extraction techniques. Conventional practices
for the remediation of metal contaminated soils involve the removal of contaminated soil to a
landfill, or to cap-and-contain the contaminated areas (Pulford and Watson 2003).
Phytoextraction is a sustainable, eco-friendly and economically viable technique for extracting
precious group of metals from low-grade ore and mill tailings (Anderson et al. 1999a).
Hyperaccumulators efficiently extract metals from the metalliferous soils and translocate them to
above ground biomass. After maturity, the plant is harvested, dried, and reduced to ashes with or
without energy recovery, which is further treated by roasting, sintering, or smelting methods,
which allow the metals in an ash or ore to be recovered (Robinson et al. 1997). Phytomining is
the in-situ removal of metals from mill tailings in an economical manner (Chaney et al. 1998,
Anderson et al. 1999b). Thus, phytomining has lead the researchers to explore the potential of
plant species towards phytoextraction of metals from soil or mill tailings. The cost-efffectiveness
of phytoextraction of heavy metals has attracted many researchers across the globe, especially
during 1970s. According to Robinson et al. (1997), low-grade ore deposits are scattered
throughout the world and support wide range of plant species. Plants show various responses to
the presence of high metal concentrations in the soils. The plant species on these native
metalliferous soils have constitutive and adaptive mechanisms for accumulating or tolerating
high metal concentration (Khan et al. 2000). While most plants are sensitive to high metal
concentration, some plants have developed resistance or tolerance, and/or accumulate them in
roots and above ground biomass (Robinson et al. 1997). Metals and other inorganic contaminants
are among the most common forms of contamination found at wastesites, and their remediation
in soils is among the most technically difficult ones. Nevertheless, these techniques involve risks
during the excavation, handling, transport, exploring sites for disposal, long-term monitoring and
their maintenance, and other associated risks (Vidali 2001). These techniques are known to be
suitable for smaller areas, where rapid and complete elimination of contamination is essential
(Martin and Bardos 1996).
Plate 1. Waste tailings at Kolar Gold Fields, India
Plate 2. Attempt by Bharat Gold Mines Limited to stabilize mine tailings
INTERNATIONAL STUDIES ON PHYTOMINING / PHYTOEXTRACTION OF GOLD
Gold has been suggested as a potential metal for phytomining (Sheoran et al. 2009). Tailing of
gold mines may contain low concentrations of residual gold. Gold occurs in non-bioavailable
form, which implies that under normal conditions gold can’t be accumulated by plants. This
residual gold could be extracted through induced hyperaccumulation. The amount of gold that
can be taken up by a plant is mainly dependent upon the gold concentration in the soil.
Application of chelates for the uptake of metal is widely explored by scientific fraternity. In the
case of gold, potential of various chelating agents such as sodium cyanide, ammonium
thiocyanate, ammonium thiosulphate, sodium thiocyanate, sodium thiosulphate, potassium
iodide, potassium bromide, etc. have been studied. During induced gold hyperaccumulation, the
geochemistry of the substrate determines the choice of the solubilizing agent. Anderson et al.
(1998) induced Indian mustard (Brassica juncea) with ammonium thiocyanate at different rates
in pots containing artiﬁcial gold rich material. Hyperaccumulation of Au was achieved in a
thiocyanate treatment level of 160mg/kg and yield up to 57mg/kg Au. A similar experiment with
B. juncea grown in a medium containing 05mg/kg of Au and treated with ammonium
thiocyanate conﬁrmed the findings (Anderson et al. 1999b). Anderson et al. (1999b) suggested
the application of ammonium thiocyanate as a chelating agent in the case of low pH sulphide
tailings. In an induced hyperaccumulation operation of gold, the geochemistry of the substrate
(pH, Eh, and chemical form of gold) will govern the choice of the solubilizing agent necessary to
affect the uptake of the precious metal. However, for high pH unoxidised sulphide tailings,
ammonium thiosulphate should be used. Anderson et al. (2003) stated that approximately 02mg
of gold per kg of soil is needed essential to accumulate 100mg of gold in 01kg of plant dry mass.
Msuya et al. (2000) analyzed gold accumulation in carrot, red-beet, onion and two cultivars of
radish, grown in an artiﬁcial gold substrate. The study reported that addition of soil amendments
increased the gold yield (kg/ha) by almost 02 times. Lamb et al. (2001) used potassium iodide,
potassium bromide, sodium thiocyanate, etc. to study induced accumulation of gold in plant
species. Gardea-Torresdey et al. (2005) reported Chilopsis linearis as a potential plant for gold
phytomining. Wilson-Corral et al. (2011) examined the feasibility of gold uptake by sunﬂower
(Helianthus annus) and magic tower (Kalanchoe serrata) in combination with the chelates
NaCN, NH4SCN, (NH4)2S2O3, and thiourea from the Magistral mine in Sinaloa state, Mexico.
Thus, on the basis of concentration of gold accumulated in H. annus, they concluded Magistral
tailings to be a potentially economically viable option for phytomining.
HYPERACCUMULATORS, CHELATES, UPTAKE
The essential approach for improving phytoextraction and sustainable mining is to explore and
exploit the biological processes involved in metal acquisition, transport and shoot accumulation.
Phytomining / phytoextraction offers the possibility of exploiting metals from low-grade ores,
overburdens, mill tailings, or mineralized soils (Sheoran et al. 2009). For the success and
economic viability of phytoextraction operation, a well deﬁned planning is necessary. The most
important step is the identiﬁcation of auriferous soil region. Usage of synthetic chelates to the
soil is most common methods for soil bound metal mobilization. While chelators help promoting
the process of phytoextraction / phytomining, they also have the tendency to leach out. Thus,
synthetic chelators viz. sodium cyanide may further pollute the environment. Anderson et al.
(1998) raised issue of disadvantages associated with the usage of synthetic chelates in
phytomining of gold. Nevertheless, there is an advantage in using natural root exudates for this
purpose. Several studies on phytosiderophores, which are iron chelating compounds released
during iron deficiency, exist. According to one study conducted in 1993, mugineic,
deoxymugeneic and avenic acids from barley, corn and oats, respectively, are probably the best-
studied plant phytosiderophores.
In the mining activities, once the minerals are processed and target metal is recovered from the
ore the remaining rock becomes another form of mining waste called tailings. It is estimated that
globally total volume of mine tailings generation is about 18 billion m3/year, which is expected
to double in the next 20-30 years (Aswathanarayana 2003). These tailings contain other metals
except target metals which are not recovered in the mineral processing plants due to their low
concentration. Tailings with less than 01mg/kg gold are unlikely to have sufficient gold to justify
economic phytoextraction. Gold phytomining is also reported to be economically and
environmentally friendly technology in comparison to heap leaching.
The mechanism of gold uptake by plants is a complex phenomenon and involves several steps
such as a) solubilization of metal from the soil matrix, b) uptake into the root, c) transport to the
shoots, and d) detoxiﬁcation and sequestration. Gold is known to be relatively immobile and
insoluble in soils and does not readily enter the aqueous phase. It has been reported that gold can
be solubilized from minerals and soils by cyanogenic plants (Girling and Peterson 1980) and by
microbial activity (Korobushkina et al. 1983). These plants produce free cyanide by hydrolysis
of cyanogenic glycosides within their tissues and leaf litter decomposition, which solubilizes the
gold in soil (Girling and Peterson 1978). Gold is dissolved by organic acids, which are produced
and excreted by bacteria during their metabolism. Savvaidis et al. (1998) isolated bacteria from
auriferous deposits that released high quantities of aspartic and glutamic acids. In addition, other
organic metabolites such as nucleic, pyruvic, lactic, oxalic, formic and acetic acid have also been
reported to be released into the environment and some of them can form stable complexes with
gold (Kuesel et al. 1999). Anderson et al. (1998b) also suggested the ability of some of the plants
to exude acid from root hairs, which may have an effect on soil pH adjacent to the roots, and
therefore affect gold uptake. Chemolithoautotrophic iron and sulphur-oxidizing bacteria in arid,
surﬁcial environments form bioﬁlms on metal sulphides and thus provide reaction spaces for
sulphide oxidation, sulphuric acid for a proton hydrolysis attack and keep Fe (III) in the
oxidized, reactive state. The high concentrations of Fe3+ and protons then attack the valence
bonds of the sulphides, which are degraded via the main intermediate thiosulphate. The oxidation
of sulphide minerals also leads to the release of associated metals in the environment (Friedrich
et al. 2005). In this process some iron and sulphur oxidizers in the presence of oxygen lead to
gold oxidation and complexation. Nakajima and Sakaguchi (1993) indicated that the uptake of
gold is via a complex mechanism and no ion exchange reactions are involved. In addition, pH
dependent and independent gold uptake has been observed, indicating the possibility of different
mechanisms of reduction and uptake in different plant species (Bali et al. 2010). Anderson et al.
(1999b) suggested evapo-transpiration, as a possible mechanism for transport of gold from root
to the shoot. A similar process of transpiration for root to shoot uptake was also reported by
Girling and Peterson (1980) in Hordeum vulgare. Once the metals are loaded into xylem vessel,
the ﬂow of xylem sap (the content of xylem vessels) will transport the metal to the leaves in
different cellular locations without destructing vital cellular processes.
PRESENT STUDY AND FUTURE PROSPECTS
One of the main bottlenecks for the application of phytotechnologies is the absence of economic
studies or cost evaluations. In conventional technologies, the stakeholders were aware of the cost
involved, time required, and associated benefits. However, real economics involved in
phytotechnology is yet to be progressed. While plant uptake is high due to the application of
chelates, it is largely not acceptable due to high leaching, plant uptake of the contaminant and
persistence of chelate in the environment. Nevertheless, success of phytomanagement relies in
less cost involvement rather than other remediation technologies, or a profitable business by
producing value added plant products.
Several studies, for more than past two decades, have been advocating the potential of various
phytotechnologies. Analyses of literature on phytoremediation since its introduction revealed
few lacunae in implementation of phytotechnologies. Even after several years of research there is
little result accomplished from these plant based remedial technologies. Phytoextraction, the
most promising technique, received increasing attention from researchers since its beginning.
While above few studies give good result for hyperaccumulators of gold, the economic
feasibility study of phytoremediation are scarce. The cost involved in production of gold is much
higher at KGF then its market price. Given the closure of KGF due to economic losses during
production of gold and sky touching rates of gold, assessing the phytomining potential to extract
gold by growing plants on mill tailing and on ore zones at KGF is essential. While, several
studies worldwide are under trials to develop an appropriate phytomining model for gold
extraction from mill tailings and low-grade ore, there is dearth of field trials in KGF to develop
economically feasible and sustainable extraction technology. Thus, we have planned to study the
gold accumulation pattern in different plant species with respect to different soil particle size
composition, impact of chelating agents on gold uptake, presence of co-metal ions and their
impact on metal uptake, and possibilities of using naturally occurring chelators. The study also
attempts at correlating the level of hyperaccumulation between ecotype and congeneric species.
Leachate studies are targeted during the entire pot culture experiments. The study would also
look at energy generated during biomass burning and its utilization in a more scientific manner.
Thus, our study attempts to develop an efficient phytoextraction technology for gold.
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