[INDONESIA-L] Mark Cloos' Geotimes

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Date: Mon, 16 Jun 1997 12:47:47 +0000
From: FM Webhelp <fmwebhelp@comm.net>
To: apakabar@clark.net
Subject: Mark Cloos Article in Geotimes on the Grasberg mine

Geotimes - January 1997

This article is the first of three features on the Grasberg mine which
will run this year in Geotimes. In the future issue, Dr. Cloos will
explore the environmental and social issues associated with development
of the mine. A third article will examine a model program for
industry-academic research collaboration that uses Grasberg as a "real
world" laboratory.

The Discovery and Development of Grasberg

Over the past 30 years, only two 1-billion-tonne-plus copper orebodies
have been discovered -- La Escondida in Chile in 1981 and Grasberg in
Indonesia in 1988. La Escondida tells a fairly well-known geologic
story. A low-grade porphyry copper system weathered in a desert
environment to form an ore-grade body by surficial (supergene)
enrichment processes.

Grasberg -- a porphyry-type copper-gold orebody in the remote province
of Irian Jaya (west New Guinea) -- is a far less known, but more
remarkable discovery. This extraordinary high-temperature (hypogene)
deposit, found at an elevation of 14,000 feet near the glaciated peaks
of the Central Range of New Guinea, is only a few kilometers from the
large skarn orebodies of the Ertsberg District -- a significant ore
system in its own right, but one now dwarfed by the more than
1.7-billion-tonne reserves of the Grasberg. These reserves average 1.1
weight percent copper and 1.2 grams-per-tonne gold.

The Grasberg Igneous Complex is a two-kilometer-wide plug of intrusive
and volcanic rock that contains, in retrospect, remarkably little
surface evidence of copper mineralization. Grasberg was discovered
during a five-hole drilling program directed by Freeport Indonesia
geologist Dave Potter from January to June 1988. This drilling was
inspired by surface samples collected by Potter and geologist Tom
Collinson -- samples that revealed anomalous gold concentrations.

The first exploration hole was inclined at 15 meters and completed to
321 meters. It contained three zones of ore-grade rock totaling 144
meters and averaging 1.63 weight percent copper and 1.69
parts-per-million gold. The abundance of chalcopyrite was a great
surprise. The second, third, and fourth holes also contained long
intercepts of copper-gold ore.

The fifth hole was vertical and completed to 611 meters depth. From 90
meter to the bottom, 521 meters of core were recovered averaging 1.72
weight percent copper and 1.95 parts-per-million gold. This may be the
most extraordinary core ever recovered in the history if hard-rock
minerals exploration. To date, drilling extends 1,500 meters below the
initial surface, and the bottom of the Grasberg orebody has not yet been

Because considerable infrastructure already existed for mining the
nearby skarn orebodies, Freeport Indonesia was able to extract its first
Grasberg ore in December 1989, less than two years after the orebody was
discovered. The Gras berg mine now supplies more than 5 per cent of the
world's new copper.

The open pit operation at Grasberg will remain active for several more
decades. The underground history of the district will also be long;
mining will probably continue for at least a century. Proven reserves
alone have a value of more than $70 billion at current metal prices.

The story of the discovery and development of the Grasberg mine is one
of the great natural resource sagas of our time. It is a story, however,
that begins at Ertsberg.

Evidence of copper mineralization in the mountains of western New Guinea
was found during a 1936 Dutch expedition led by A. J. Colijn. Colijn's
goal was to climb the 16,024 foot tall Carstenz Top (now known as Puncak
Jaya). He was accompanied by Jean Jacques Dozy, a geologist for the
Royal Dutch Shell Company, and Lieutenant Franz Wissel, a pilot in the
Dutch Navy.

Before the expedition, Wissel and Colijn flew reconnaissance to map out
the best route. Colijn and Dozy began the overland expedition while
Wissel parachuted supplies to several strategic points before making the
overland trek to join his fellow adventures for the final push to the

The expedition, assisted by 38 porters, took 57 days to traverse the
foreland swamps and jungle, climb the steep southern flank of New
Guineaís Central Range, and reach the equatorial glaciers that blanket
the flanks of the Carstenz Massif. Near the base of the glaciated
mountain, Dozy discovered a large malachite-stained outcrop which he
named Ertsberg (Dutch for "ore mountain"). The discovery was really an
accident, for the copper-stained outcrop just happened to jut upward
from the flat meadow at the exact location where the expedition emerged
after making a tortuous climb up the steep headwall of the glaciated

Dozy only collected a few ore-grade samples because he had already
collected 80 specimens on the way to the top. In 1939, he published a
short report that documented his field observations and included a
description of the Ertsberg ore samples by C. Schouten. Schouten
acknowledged that "the copper-content appears to be high," but closed by
stating that "even if the ore should prove to occur in large quantities,
an economical exploitation will hardly be possible owing to the remote
position of the locality."

Dozy also reconnoitered and mapped a distinctive grass-covered mountain
under-lain by igneous rock approximately four kilometers northwest of
the Ertsberg. He named a distinctive-shaped peak Dom (the Dutch word
for cathedral) and a distinctive vegetation anomaly Grasberg (Dutch for
ìgrass mountainî).

In 1959, the East Borneo Company, a Dutch mining concern interested in
potential nickel deposits in western New Guinea, made a search for
papers on the geology of the region. The search turned up Dozy's
forgotten report. Soon afterwards, geologist Forbes Wilson, manager of
minerals exploration for Freeport Sulphur, visited the Dutch company's
headquarters in The Netherlands and learned of the Ertsberg.

Wilson immediately recognized that the copper rich outcrop might be the
surface exposure of an even larger copper deposit underground. He
visited Dozy at The Hague to learn firsthand about the Ertsberg.

In 1960, Wilson and geologist Delos Flint mounted a $120,000 expedition
to see if the outcrop Dozy described was big enough to be an orebody.
After an arduous 17 day trek, they reached the Ertsberg and discovered
that it was even larger than they had expected. Most of the talus
samples they examined contained chalcopyrite and bornite. The 300
kilograms of ore samples they collected averaged nearly 3.5 weight
percent copper.

In early 1967, Freeport Indonesia, a subsidiary of Freeport Sulfur,
became the first foreign mining company to enter into contractual
arrangements with the government of Indonesia after the country enacted
a new Foreign Investment Law. This contract gave Freeport exclusive
mining rights for a 100 square kilometer area centered on the Ertsberg.

By December of that year, Freeport had started helicopter supported
drilling to investigate the subsurface extent of the orebody and the
feasibility of mine development. Drilling soon showed that the tooth
shaped orebody extended 350 meters below the surrounding meadow.
Geologists estimated that the orebody totaled 33 million tonnes
averaging 2.5 weight percent copper. The Ertsberg was the largest above
ground copper deposit ever discovered.

Construction of an open pit mine began in May 1970, and the first trial
shipment of ore occurred in December 1972. On July 1, 1973, the Ertsberg
mine was declared fully operational.

Officials at Bechtel, the primary building contractor on the project,
called mine development in the Ertsberg District "the most difficult
engineering project they had ever undertaken." The many challenges
surmounted included building a 101 kilometer long access road (a project
that required boring kilometer long tunnels through two mountains) and
constructing the world's longest single span tramways. Aerial tramways
were needed to move people, supplies, and ore because a 2,000 foot
glacially sculpted cliff separates the Ertsberg mine (at 12,000 feet
elevation) from the mill (at 10,000 feet). Getting copper concentrate
from that mill to the shipping port (which Freeport built in the
coastal mangrove swamp) required installation of a 109-kilometer long
slurry pipeline - then the world's longest.

Mine startup cost about $200 million. Ore production during most of the
1970s was steady at approximately 7,500 tonnes per day. But while the
development of the Ertsberg District was an engineering marvel, the
mine's financial performance was less than spectacular. Depressed copper
prices and high operating costs kept the operation marginal during the

During survey work in 1968, Delos Flint noticed two areas of malachite
staining approximately one kilometer due east of the Ertsberg. In 1973,
Frank Nelson began a systematic program of geologic mapping in the area
of copper staining.

In 1975, exploration drilling at one site revealed another copper skarn
orebody, which was named Ertsberg East (Gunung Bijih Timur in
Indonesian). Development of an underground block cave mine began in
1977, and mining started in 1980. Subsequent drilling in 1985 revealed
that the Ertsberg East extends downward, forming the Intermediate Ore
Zone (IOZ) and the Deep Ore Zone (DOZ).

The other malachite stained area discovered by Flint had been drilled in
1976, revealing the Dom orebody. Delineation drilling and workings for
an underground mine were completed, but this orebody has yet to go into

In 1982, production of ore from underground mining at Ertsberg exceeded
that from the open pit operation. Two multi-million dollar expansion
programs during the 1980s eventually allowed ore production at Ertsberg
to increase to 20,000 tonnes per dayósome 13,500 tonnes more than in the
previous decade.

In the early 1980s, the future demand for copper appeared questionable.
The invention of fiber optic cable for communications and the short
lived substitution of aluminum for household electrical wiring suggested
to many that the era of strong copper demand was ending. A financial
evaluation of Freeport Indonesia (commissioned by its new parent
company, Freeport McMoRan, Inc.) concluded that the Ertsberg District
was worth no more than $200 million. But there was little interest in
the isolated copper mine, and the mining rights were not sold.

In 1984, petroleum geologist James Robert Moffett became chief executive
officer and chairman of the board for McMoRan. In 1986, Moffett
instructed Freeport Indonesia geologists to begin an evaluation of the
potential for new ore deposits in the Ertsberg District.

Many geologists had seen Grasberg in the 1970s and early 1980s, but all
had dismissed the likelihood of significant high grade copper
mineralization. There was little evidence of skarning along the margins
and no surface indicators of leached cap rock had been found to suggest
the presence of a supergene enriched copper oxide orebody at depth. In
fact, there was so little surface evidence of economic mineralization
that I believe that the Grasberg orebody would have remained
undiscovered to this day if not for the persistence of the field
geologists led by Dave Potter and the exploration perspective of CEO
Moffett. Petroleum geologists like Moffett know that subsurface geology
can only be truly evaluated by drilling.

The five hole exploration program quickly revealed evidence that copper
mineralization in the core of the Grasberg probably exceeded the total
of all of the Ertsberg skarns combined. Grasberg ore also contained
significant amounts of gold (the Ertsberg skarns have only relatively
minor byproduct gold). By 1995, hundreds of kilometers of core from
Grasberg had shown that the deposit contains the largest proven reserves
of gold of any mine in the world and the third-largest proven reserves
of copper.

Development of the Grasberg mine was put on a fast track when it became
apparent that ore reserves there measured in the hundreds of millions of
tonnes. Engineers George Mealy and Tommy Williams directed this
remarkable undertaking, keeping the project on time and within budget.

Phase I was underway by 1989 - an effort that included expanding mill
capacity to 32,000 tonnes per day. In 1990, Phase II was in progress.
Engineers started with the goal of expanding ore flow and mill capacity
to 57,000 tonnes per day But that goal grew progressively; current
capacity is 115,000 tonnes per day. The total cost of the Grasberg
expansions ó which included massive increases in capacity for mining,
crushing and milling, conveyor belt transport of ore, additional ore
passes, sulfide flotation cells to make concentrate, slurry pipelines,
power plants, housing, and shipping - exceeded $750 million.

Mine operators soon learned that the mining shovels and trucks that
could be hauled to the top of the mountain via the tramway were too
small for an operation of this scale. Over a two-year period, McMoRan
built a remarkable road with 18 hairpin turns (called the Heavy
Equipment Access Trail or HEAT road) to provide a drivable trail to the
mine. In a Herculean effort, teams of bulldozers have towed and pushed
sleds loaded with more than $200 million of dismantled heavy equipment
up the HEAT road to the Grasberg mine.

Presently the mining operation uses four giant electric shovels with 42
cubic meter buckets, two with 34 cubic meter buckets, and numerous
smaller shovels and loaders. The fleet of haul trucks is among the
largest in the world - it includes 45 218-ton capacity trucks, 21 130
ton capacity vehicles, and 13 trucks that can haul up to 80 tons.
Sixteen large bulldozers, eight blast hole drill rigs, and two crushers
have also been dismantled, placed on sleds, and dragged up the HEAT

While Grasberg development was underway, Freeport Indonesia exploration
geologists under the direction of Steve Van Nort, Tom Collinson, Dave
Mayes, and Chuck Brannon were making more discoveries in the district.
In 1991, exploration drilling revealed the Big Gossan copper gold skarn
orebody about one kilometer west of the Ertsberg. In 1993, exploration
drilling southwest of the Grasberg detected the Lembah Tembaga copper
porphyry deposit. In 1994, geologists discovered that copper skarns are
present next to the Grasberg Intrusive Complex, about one kilometer
below the surface. This deposit was named Kucing Liar, and its deep
subsurface reserves appear substantial.

Numerous aspects of the daily mining operations impress a visitor to the
district. All of the development has occurred in a place where a day
without rain is the exception. Average rainfall in the mining district
is about three meters per year. The 101 kilometer long access road is
the lifeline of the operation, and everything needed to support the
17,000-person workforce must pass along it. Some 240 supply trucks
constantly move up and down the road. People make the trek via 70 buses
and 860 light trucks. Because of the steepness of the roads, every
vehicle in the mining district is permanently locked in low gear four
wheel drive.

Each year, more than 100 ships leave the port carrying copper ore
concentrate. Cargo ships offload 1,500 ocean going cargo containers each
month. At any one time, more than 8,000 of these 20 foot-long containers
are on the move in the district.

The nearest supply center in Indonesia or Australia is many hundreds of
kilometers away. Hundreds of thousands of items - everything from
pencils and nails to computers and a massive inventory of replacement
parts - must be monitored and ordered on schedule. The logistics
involved are mind boggling.

Until recently, nearly all the copper ore concentrate shipped out of the
district was sent to Japan for smelting and refining into copper wire.
Almost every American probably owns some household or work item that
contains copper from the mines of the Ertsberg District.

With the expanded production from the Grasberg, the district now
supplies copper for hundreds of millions of people worldwide. It will
remain a major source of copper for many decadesómaybe even beyond the
end of the next century.

Without doubt, the discovery of the Grasberg orebody is one of the most
important mineral discoveries of this century. Grasberg has been called
"Asia's greatest mine." The superlative is more than warranted.

Mark Cloos
Department of Geological Sciences, University of Texas at Austin,
Austin, Texas

Dr. Cloos teaches structural geology and tectonics at the University of
Texas at Austin, where he is professor and chairman of the Department of
Geological Sciences. He has visited the Ertsberg District 11 times since
1989 and has supervised eight studies by students of the region's
geology, including four Ph.D. dissertations. Freeport McMoRan, Inc. has
supported this work.

Additional Reading

"Asia's Greatest Mine." Asian Journal of Mining, p. 35 84, May June

The Conquest of Copper Mountain by Forbes Wilson. Atheneum (New York),

Grasberg by George A. Mealy. Freeport-McMoRan, Inc. (New Orleans), 1996.

The author has provided the following key words for this article:
copper, gold, porphyry, Grasberg, Ertsberg. To find additional
information about these topics, you may search the GeoRef database.
Contact your reference librarian or the American Geological Institute.


Date: Mon, 16 Jun 1997 12:48:04 +0000
From: FM Webhelp <fmwebhelp@comm.net>
To: apakabar@clark.net
Subject: Second - Mark Cloos Article in Geotimes on the Grasberg mine

Geotimes - May 1997

This article is the second in a series on the Grasberg mine that will be
published this year in Geotimes. Dr. Cloos' first article "Anatomy of a
Mine: The Discovery and Development of Grasberg" appeared in the January
1997 issue. A third article will examine a model program for
industry-academic research collaboration that uses Grasberg as a "real
world" laboratory.

Environmental Management At Grasberg

Long term river management became an important environmental concern for
Freeport Indonesia as it planned for the increases in ore production and
tailings disposal that would come with opening the Grasberg mine.


The discovery of large deposits of high grade ore that can be
economically extracted now almost always occurs in remote parts of the
world - regions where the landscape is largely pristine and the local
population is isolated. No deposit fits this description better than
the Grasberg copper gold orebody of Irian Jaya, Indonesia, which was
discovered and is now noticed by P.T. Freeport Indonesia, a subsidiary
of Freeport-McMoRan, Inc. Mining this massive mountain deposit has
proven both an engineering and environmental challenge.

Copper mining in the Ertsberg District began, of course on a much
smaller scale (see "Anatomy of a Mine: The Discover and Development of
Grasberg," Geotimes, January 1997, p. 16-20). The impact of mining
operations on the environment was also relatively small, and in the mid
1980s the district had an expected life span of only 10 to 15 years.

With the discovery of copper and gold ore reserves in excess of 1
billion tonnes in the Grasberg, the life span of the Ertsberg District
suddenly stretched far into the next century. Ore production increased
from a 1988 peak of 20,000 tonnes per day to the present level of
120,000 tonnes per day. The corresponding impact on the environment
increased as well.

Before the l960s, many people dismissed such concerns. But the modern
mining industry considers mitigating the environmental impact of mining
a necessary cost - and responsibility - of doing business.

In 1991, Freeport Indonesia began a special long term monitoring program
to assess potential environmental changes and ensure that engineering
work minimizes the impact of the mining operation. The company's team
of environmental scientists and engineers is backed up by a steady
stream of consultants, who visit the site to investigate specific

The program tracks the meteorological, hydrological, and biological
impact of mining and tailings disposal along the Ajkwa River. Control
sites nearby are studied for comparison. Water samples are routinely
collected from 60 strategically located monitoring sites; mine runoff,
mill tailings, and groundwater are examined as well as water from the
river and its estuary. Biological sampling includes routine testing of
tissues from plants and bottom
dwelling catfish and shrimp. All public drinking water supplies and
sewage treatment plant discharges are also continually monitored.

The water and tissue samples collected are analyzed at the company's
$2.5 million, state of the art environmental laboratory - a laboratory
that would be the envy of nearly all academic geoscience departments. A
professional staff of analytical and environmental chemists and
technicians rigorously screen hundreds of water and tissue samples each
month for aluminum, arsenic, calcium, cadmium, chromium, copper, iron,
lead, magnesium, manganese, mercury, nickel, potassium, selenium,
sodium, and zinc at the parts per million or parts per billion level.
Other water parameters monitored include temperature, pH, conductivity,
salinity, dissolved oxygen, alkalinity, total suspended solids,
hardness, and sulfate and chloride content. Selected samples are split
for blind duplicate analysis at other laboratories.

Any large mining operation will inevitably change the landscape to some
degree, mine operators, however, can plan for and manage that change.
Environmental monitoring is only part of this process at Grasberg.

The Ertsberg orebody, the original deposit for which the district is
named, is now mined out and the resulting open pit contains a lake which
provides water for the mill. The open pit of the much larger Grasberg
mine will also eventually become a lake. The upper benches will be
hydromulched, and the rest of the affected area will be contoured and
revegetated. Some of the disturbed areas near both pits as well as some
of the areas where mill tailings have been
deposited have already been revegetated using local plants.

Piles of overburden - waste rock moved to mine the Grasberg - create a
long term environmental concern in the highlands. The infiltration of
rainwater into this porous rock and the bacterially assisted oxidation
of the small amounts of sulfide minerals it contains could result in
drainage of acidic, metalladen water from the piles.

Fortunately, less than half the waste rock from the Grasberg has a
measurable capacity to produce acidic waters. Also, die Grasberg
complex is located within a vast terrain of limestone, some of which
must be excavated during the later stages of open pit mining. Where
appropriate, limestone will be blended with waste rock to neutralize the
acid generating potential. The Grasberg mine plan also calls for
burying the waste rock piles with a layer of clay and up to 20 meters of
inert rock to seal out oxygen and thus minimize the production of

Based on long term plans, the mines in the Ertsberg District will
eventually modify about 15 square kilometers of the 100-square kilometer
area that Freeport Indonesia has contractual rights to develop. Most of
the rugged area will only be visited by exploration geologists via foot
or helicopter.

The areas occupied by the town of Tembagapura (built to house mine
workers), the airport and related facilities in Timika, and the port for
shipping the concentrate are all quite modes. The access road is a
thread like lifeline to the mines.

The overall environmental impact of maintaining the workforce is about
as small as possible. The region is served by a modern, state of the art
sanitary landfill near Timika, perhaps the best engineered in all of
Indonesia. Recycling is required and involves significant amounts of

Tailings disposal is a key environmental challenge. The discharge of
mill tailings into the Aghawagong River (a mountain tributary of the
Ajkwa River) for transport to the lowlands has been a focus of concern.

The mill at Grasberg uses froth flotation to concentrate and remove
sulfide minerals from the ore mined. Some environmental groups charge
that the wastes generated - crushed rock powder from which the sulfide
minerals have been extracted - are toxic. But these tailings are simply
powdered rock unmodified by any chemical processing. Freeport
Indonesia's environmental scientists and consultants all report that the
tailings are not toxic by any government-established criteria.

Froth flotation at the mill recovers an exceptional 85 to 90 percent of
the copper sulfide minerals in the ore. Since the flotation process
separates sulfide from non sulfide minerals, most iron sulfides are also

Freeport Indonesia has long received a premium price for its ore because
it is so free of noxious elements such as arsenic, mercury, and lead.
Ertsberg District ore concentrate is known as one of the cleanest in the

University of Texas faculty and students have extensively studied the
igneous rocks and ore of the Ertsberg District. We now understand the
probable reason why the ores are so clean

Most noxious elements are volatile in magmatic fluids. Else deposits in
the Ertsberg District formed at such high temperatures (from 400 to 700
C or greater) that noxious elements were almost entirely carried away in
solution from the high temperature core of the orebody where bornite and
chalcopyrite were precipitated. Noxious elements were either vented at
the surface or were precipitated after cooling nearer the surface in the
naturally denuded parts of the ore forming system.

The tailings are eventually deposited along the Ajkwa River, where they
are rapidly colonized with a local swamp grass. Work at two large test
plots has shown that the tailings support the growth of many types of
grass, corn, pineapples, rice, and coffee trees. To date, every plant
tested for viability on the deposits has lived, if not thrived.

Tailings disposal at Grasberg begins with their discharge into the
headwaters of the Aghawagong River at 2,900 meters elevation near the
mill and ends with their deposition at less than 100-meters elevation in
the lowlands. The river flows so fast that the tailings rapidly move
downhill, 40 kilometers past the base of the mountain to near the
lowland town of Timika.

River systems along the southern slope of the Central Range in Irian
Jaya have enormous natural sediment loads because the relief is
extremely steep, the rock is readily eroded, and landslides are common.
Resistant rock formations weather into boulders and cobbles. Several
rock formations weather entirely into sand and finer sized particles.

Most impressively, sediment transport is not episodic nor limited by
water supply. River flow is remarkably uniform because it rains almost
every day. Yearly rainfall totals in the region range from three to l 1
meters and are among the highest in the world.

The Aghawagong River merges with the Otomona River, which then merges
with the Ajkwa River. Along the way, numerous tributaries add water and
rock material, which mixes vote the tailings. The daily sediment load
in the Ajkwa River under normal flow conditions is 15,000 to 20,000 tons
per day. (Periodic floods, however, mean that the rate of sediment
transport on the scale of a decade or longer is actually much higher.)

Before the discovery of the Grasberg orebody, the daily addition of
tailings to the river system roughly doubled the natural sediment supply
and had only a relatively modest effect. Now, however, some 120,000
tons of tailings enter the river each day. the increased sediment load
has, of course, greatly sped up the evolution of the depositional system
in the lowlands.

The turbidity of the river is elevated, but the water meets the
published water quality criteria of the World Health Organization and
the U.S. Environmental Protection Agency. Biological studies comparing
the Ajkwa with other nearby rivers show little difference in the
diversity and abundance of plants and animals.

In the lowlands, the rivers widen, slow, and deposit their load in
distributary systems. As the river gradient lessens and flow slows,
first the cobbles stop moving, then pebbles, then sand, and finally
silt. Clay largely remains in suspension and is carried to the ocean
where it is deposited after it flocculates when the freshwater mixes
with seawater.

Deposition in the lowlands (even without tailings) forms a dynamic
system of sediment choked braided channels with many shallow channels
separated by small islands, which are created and destroyed. Large
islands become heavily vegetated, and their destruction adds organic
matter to the system. Over geologic time, rivers have merged and
diverged millions of times as their
deposits transformed the shallow ocean separating New Guinea from
Australia into the swampy lowlands of today.

During major floods, water spills out of the channel and slows,
spreading as a sheet of water into the surrounding jungle. This
"sheetflow" drops its sediment load, forming a distinct type of deposit
called sheetwash. Small plants are buried or toppled. Tall trees are
left standing, but their bases are buried by as much as a meter of
sediment. After the flood is over, a new water table is established and
large trees that require air to reach their upper roots will slowly die.

Sheetwash events occur repeatedly in the lowlands both notch and south
of the Central Range. While an area subjected to sheetwash deposition
will appear devastated because of the death of large trees, this effect
is natural and temporary. Re-establishment of the ecosystem involves
progressive habitat changes over several decades.

Long term river management became an important environmental concern for
Freeport Indonesia as it planned for the increases in ore production and
tailings disposal that would come with opening the Grasberg mine. This
issue received even more attention after an "unusually violent 1990
storm toppled trees, which in turn caused a logjam that diverted much of
the flow of the Ajkwa River south of Timika This major flood resulted in
sheetwash deposition and the death of trees outside the previous river
channel. The addition of tailings to the river system undoubtedly
played some role in this event.

Freeport Indonesia's mining contract with the Indonesian government
requires the company to confine tailings to the Aghawagong Otomona Ajkwa
river corridor. Achieving such confinement is simple in the Aghawagong
Otomona segments and near the base of the mountain. It becomes more
difficult where the river gradient lessens and the Ajkwa River begins to
widen near Timika - the natural region of deposition of sand-sized

The company's solution was to build a pair of levees to contain the flow
and deposition of the Ajkwa River even during floods. The levees start
10 kilometers north of Timika, where they are three kilometers apart.
The controlled flood plain widens to nine kilometers at points 25
kilometers south of Timika.

An area of approximately 50 square kilometers has already been affected
by tailings deposition. This area will eventually cover some 135 square
kilometers. Vegetation of the tailings is a continuous process as the
river channels migrate laterally in the flood plain. Because the water
table in tile lowlands is almost at the surface, reducing conditions are
maintained and little acid is generated from the small amounts of
sulfide minerals in the tailings.

This engineering solution to the problem of tailings disposal offers
some long term benefits. When mining ends, there will be no stability
problems involving tailings piles. Sediment influx into the river will
immediately return to its pre mining character. And the accumulation of
sediment between the levees is forming an area of elevated, drainable
land far better suited for agriculture than the land now cultivated.

When the levees were built, Freeport Indonesia also constructed a
tailings free water course near Timika by channeling small tributaries
that drained into the Ajkwa to flow parallel to the west levee. Clean,
slow flowing water forms more than 500 hectares of lakes, which
residents use for swimming, fishing, and other forms of recreation.

A seemingly reasonable alternative to discharging tailings into the
river system would be to impound the wastes behind a dam near the mill
or in the foothills. Unfortunately, containment is an environmental time
bomb in places such as Irian Jaya, a seismically active area of high
relief and high rainfall. In Papua New Guinea, a major landslide
occurred at the tailings dam near the Ok Tedi mine in 1984 even before
full scale mine production had begun.

It has also been suggested that a slurry pipeline could be built to
carry tailings to a disposal site in the lowlands or even to the ocean.
Building a pipeline of sufficient capacity would be a monumental
engineering project that would also require construction of a parallel
maintenance road. An enormous amount of energy would be needed to pump
tailings uphill in parts of the mountains. A pipeline could easily be
damaged by earthquakes, floods, and
landslides. And in the end, you would still need an area for tailings
deposition that would affect tens of square kilometers in the lowlands.

Use of the river system to transport the tailings down the mountain
piecemeal is a safer, more effective method of tailings management than
impoundment dams or pipelines. But the real question is whether
Freeport Indonesia has acted to minimize the environmental impact of
tailings disposal.

>From my perspective, the answer to this question is "yes" - as it is to
other questions that have been raised about environmental management at
Grasberg. State of the art monitoring, careful planning, and the use of
engineering solutions are all part of the success story of Grasberg.

Mark Cloos
Department of Geological Sciences, University of Texas at Austin,
Austin, Texas

Dr. Cloos teaches structural geology and tectonics at the University of
Texas at Austin, where he is professor and chairman of the Department of
Geological Sciences. He has visited the Ertsberg District 11 times since
1989 and has supervised eight studies by students on the region's
geology, including four Ph.D. dissertations. Freeport McMoRan, Inc. has
supported this work.

Additional Reading

Grasberg by George Mealy. Freeport McMoRan, Inc. (New Orleans), 1996

The author has provided the following key words for this article:
porphyry copper, mining environment, Grasberg, Ertsberg. To find
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