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TIN MINI}IG AND SEDIMENTATIOI.I EFFECTS OT{ SI-IALLOW WATER BENTHIC COMMWITIES
Hansa Chaneang
Phuket Marine Biological Center
P.O.Box 60, Phuket, Thailand
ABSTRACT
Tin mining is a rna.ior economic activity in parts of South-East Asia. Bucket
or suction dredges are increasingly being used to mine tin deposits in shallow
coastal areas. Dredging depreciates coastline aesthetic values and lhus hurts
tourism. It also destroys irnporLant shallow water benthic communities such as
coral reefs, sea grass beds and mangroves, both by physical disturbance and
particularly by siltation. lnformation on lhe extent of damage to these resources
is sfill limited. Sludies of coastal resources in southern Thailand are being used to
plan measures to reduce the environrnental effects of mining activity, particularly
as they affect tourism and fisheries.
In South-East Asia, tin is me of the major mineral resources that are important Lo the
national economy. Explorabion for tin ore has been conducted extensively in lndonesiat
Malaysia and Thailand. tn 1980, Thailand produced 45,986 metric tons of tin, wort.h US$ 577
million, making it the second major Lin producing counlry of the world (Suwansing, f982).
Mgst of the tin ore is from the Lhree southern provinces of Ranong, Phang-nga and Phuket
along the Andaman coast.
Tin ore is mined as cassiterite (5nO.) which is often associated with granite and
pegmalitesr generally in alluvial deposils m fand and in coasLal waters. Ore deposits s-r land
are mainly mined hydraulically by what is locally known as the gravel punping npLhod.
Dredging is used to recover mineral deposits from shallow waters and swampy areas.
Tin mininq on land
Gravel punping mining involves liquefying unconsolidated deposits in an open pit wi[h a
high pressure water jet, after removing the top soil. The mixture is punrped to a slightly
sloping sluice box. Tin ore and other heavy materials settle m t}re bottom of the sluice box
and are prevented fnom flowing down by rows of baffles, while lighter materials are washed
away as mine tailings. Tailings are fed into hrnded areas and old mine pits where solids
seLtle out and water is recycled or discharged into natural water-ways. This nrethod of
mining creates several environnental problems both during qeraLion and after t}re mines are
abandmed.
One of the most obvious problems is surface water pollutionr although regulations exist
regarding the diseharge of water into natural water-ways. Tle limit on the amount of
*rspended solids in discharged water is high (6 q/l)p and often the regulations are not
enforced. During the rainy season, runoff from lailings areas and someLimes the failure of the
embankments of relention ponds result in liquid waste Btreams rich in zuspended materials.
This lesds to highly turtid waters and sediment deposition in the water-ways and coastal
waters, particularly in protected bays in areas of intensive mining.