Lecture: Sri Lankan gem Deposits-occurrence and geology

Lecturer: Sanjeewa P.K. Malaviarachchi（Academician/Professor,University of Peradeniya，Sri Lanka)

Time: 15:00-16:30,12^thDec..

Venue: C205, Mingbianlou Building

Dr. Sanjeewa Maalviarachi，Academician of the Sri Lankan Academy of Sciences, completed his PhD from the Institute of Planetary Materials at Misasa, Okayama University, Japan, majoring in mantle petrology, geochemistry and radiogenic isotope geology. He held MSc from Shimane University, Japan, in metamorphic petrology and BSc (Honours) from University of Peradeniya in Sri Lanka. His research interests are igneous and metamorphic petrology, hard rock geochemistry, and isotope geology. He is a professor at the Department of Geology, University of Peradeniya. Currently, he serves as a Visiting Scholar at the Institute of Geology and Geophysics, Chinese Academy of Sciences, Bejing, China.

Sri Lanka is well known for its wide variety of gem minerals for over 2500 years. Gem discoveries in India, Madagascar, Tanzania, Mozambique etc share common geological origin with respect to the high-grade metamorphism at continental collision zone in the Gondwana, highlighting occurrences of good quality corundum, spinel, topaz, zircon, aquamarine, amethyst, gem varieties of quartz, tourmaline, chrysoberyl, zircon, beryl, garnet, sphene, topaz etc. Geologists have found similar gem minerals in eastern Antarctica, confirming the presence of a Pan-African mineral belt (originated at about 550 million years ago) from east Africa through India-Sri Lanka to Antarctica. The similarity of the geological features of these gem-bearing lithologies has been attracted internationally by both geologists and gemmologists.

Nearly all the gem formations are located in the central high-grade metamorphic terrain of the Highland Complex geological unit in Sri Lanka. The gem deposits are classified as sedimentary, metamorphic, and magmatic; the sedimentary types being the most abundant. Nearly all the gem deposits of Sri Lanka are derived from the granulite facies metamorphic rocks of the Highland Complex, clearly indicating that there were high-temperature petrological conditions (>600 °C) suitable for the formation of gemstones. Overall, the source rocks of the gem minerals are skarns, marbles, pegmatites, garnetiferous and charnockitic gneisses.

Natural Gas Geology Key Laboratory of Sichuan Province

School of Geoscience and Technolgoy

Institute of Science and Technology Development, SWPU