Etsuo Uchida

Deterioration of stone materials in the Angkor monuments, Cambodia

The Angkor monuments in Cambodia are built mainly of sandstone and laterite. This paper mainly describes the deterioration of sandstone blocks. The sandstone in the monuments can be classified into three types based on the colour, texture, chemical composition and constituent mineral; grey to yellowish brown sandstone, red sandstone and greenish greywacke. The deterioration is distinct in grey to yellowish brown sandstone because of its low compressive strength, high porosity, well developed bedding, and constituent minerals susceptible to alteration such as feldspar and biotite. The main causes of deterioration identified are chemical weathering, efflorescence related to bat guano, and biodeterioration by the growth of trees, algae and lichens. An water supply is also indispensable for deterioration.

The Construction Process of the Angkor Monuments Elucidated by the Magnetic Susceptibility of Sandstone

The Angkor monuments in Cambodia are mainly constructed of grey to yellowish-brown sandstones. No differences in the constituent minerals and in the chemical composition of the sandstones have been confirmed among the monuments. However, we have found their magnetic susceptibility a useful parameter by which to distinguish them. The principal monuments of Angkor Wat, Ta Prohm, Preah Khan, Banteay Kdei and Bayon, constructed from the Angkor Wat period to the Bayon period (from the beginning of the 12th century to the beginning of the 13th century AD), were investigated in detail using a portable magnetic susceptibility meter. We succeeded in dividing the periods of construction into stages. This elucidated the enlargement process of the monuments and correlated their construction stages.

Application of arsenopyrite geothermometry and sphalerite geobarometry to the Taebaek Pb-Zn(-Ag) deposit at Yeonhwa I mine, Republic of Korea

The Taebaek Pb-Zn(-Ag) deposit of the Yeonhwa I mine, Republic of Korea, occurs in a broadly folded and reverse-faulted terrain of Paleozoic sedimentary rocks: the Taebaeksan basin. The orebodies consist of several thin tabular orebodies of hydrothermal replacement type where they are hosted by carbonate rocks. The Pb-Zn(-Ag) mineralization can be divided into four distinct stages based upon the mode of occurrence of ore minerals, ore textural relationships and their composition. Based on temperatures inferred from arsenopyrite compositions by means of electron microprobe and fluid inclusions, the estimated temperatures for the stages I, II, III and IV reach 330 to 350 °C, 270 to 340 °C, 230 to 250 °C, and <220 °C, respectively. The sulphur activity (atm) of ore formation at the Taebaek deposit was estimated for each stage as 10−11 to 10−11.5, 10−9.5 to 10−13, 10−13.5 to 10−15, and <10−15, respectively. Even though application of sphalerite geobarometry is problematic because of the absence of good mineral assemblages, sphalerite coexisting with pyrite but not with pyrrhotite was used to estimate the minimum mineralization pressure (about 1 kbar).

Blackening of the Surfaces of Mesopotamian Clay Tablets Due to Manganese Precipitation

Blackening was observed on the surfaces of Mesopotamian clay tablets from Umma, Dilbat, Larsa, Ur, Babylon, Uruk, Sippar, and Nippur produced between the Third Dynasty of Ur and the Early Achaemenid Dynasty. Portable X-ray fluorescence analysis revealed that manganese was concentrated on the blackened surfaces. Rod-shaped materials with a length of 100 - 200 nm and a width of 30 nm were observed using a field emission scanning electron microscope. Distinct peaks were not necessarily obtained by micro-X-ray diffractometer analysis, but several samples of the black material showed peaks identifiable as buserite. These results may suggest that blackening on the surfaces of the clay tablets can be ascribed to the activity of manganese-oxidizing microbe. However, the size of the rod-shaped materials is too small compared to common bacteria.

AMS RADIOCARBON DATING OF WOOD SAMPLES FROM THE ANGKOR MONUMENTS, CAMBODIA

In the Angkor monuments of Cambodia, pieces of wood remain (as head frames of doorways, crossbeams, ceiling boards, etc.) in the following 8 monuments: Bakong, Lolei, Baksei Chamkrong, North Khleang, Angkor Wat, Banteay Kdei, Bayon, and Gates of Angkor Thom. Accelerator mass spectrometry (AMS) radiocarbon dating carried out on 15 wood samples collected from the above 8 monuments revealed that most of the wood samples are original, except for the head frame of a doorway in Baksei Chamkrong, the ceiling boards in the northwest tower, and a crossbeam with pivot hole in the southwest tower of the Inner Gallery of Angkor Wat. The 14C age for the head frame of a doorway in the inner wall under the central tower of North Khleang supports the hypothesis that the inner walls are additions from a later period.