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Geology of Sri Lanka
According to the geological history, 90 % of Sri Lanka
consists of Precambrian metamorphic rocks (Figure
11). Metamorphic rocks are one of the three main
types of rocks in the rock cycle, which have been
originated from the rocks subjected to high pressure and
temperature. These have been considered as the oldest
rocks in the world aged in between 270 to 3900 million
years. The other 10% is consists mainly of Miocene
Limestone. This 10% is restricted to the northwestern
Sri Lanka from Puttlum to Jaffna. Miocene limestone in
this area is aged 7-26 Myrs and therefore it is
considered as young strata based on the geological age.
Other than this, we find few shale beds around Thabbowa,
Andigama area which have been deposited under the
Jurassic age.
Based
on the rock type, their origin and the metamorphic
condition, Sri Lanka’s metamorphic terrain is divided
into 3 main geological units and one subordinate; The
Highland Complex (HC), the Vijayan Complex (VC), the
Wanni Complex (WC) and the Kadugannawa Complex (KC). The
central highlands, extending towards northeast up to the
east coast and the southwest up to the south west coast
are taken into HC. The rocks in HC had been originated
under very high temperature (700-8000C) and
high pressure (5-10Kb). VC occupies the eastern section
of HC and WC inhabits the western portion of HC up to
the Miocene limestone section. The geological boundary
between HC and VC has been considered as a mini plate
boundary (Munasinghe and Dissanayake, 1982) especially
due to the mineralization occurs along this, such as
Serpentinite at Ussangoda and Udawalawa, magnetite at
Wellawaya, Quartzite at Wellawaya, copper-magnetite
deposit at Seruwawila, several hot springs and several
gem crystal formations along the boundary. However,
there is no definite margin showing the plate boundary
but it rather shows a widespread mineralized belt. KC
lies at the middle of HC.
Economic geology of Sri Lanka
Gems of Sri Lanka
Mining and the environment
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