Analysis of Karst Tufa from Guangxi, China

The paper presents an analysis of characteristic karst tufa from Guangxi, China, which has not been studied before. A comparison with tufa from Dinaric Karst of Croatia is discussed in view of the C-type climate. The major mineral is calcite. Minor minerals are quartz and dolomite, depending on location. The content of calcium carbonate varies from 65% to 92%, and that of magnesium carbonate from 0.03% to 1.77%. Among other elements, the most abundant are Fe, from 0.02% to 1.50%, and Ti, from 0.15% to 0.27%. Many other trace elements (V, Cr, Mn, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Hg and Pb) are also present. Specific activity of radionuclides 40K, 232Th, 137Cs, 226Ra and 238U varies from sample to sample. Concentration of U in tufa is close to that reported for sedimentary carbonate. Low concentration of 137Cs indicates that this part of the world was not exposed to nuclear explosions. The concentration of 226Ra is the highest in Mashan County. The ratio 238U/226Ra (0.21-0.71) in tufa from Mashan Co

Analysis of Karst Tufa from Guangxi, China

The paper presents an analysis of characteristic karst tufa from Guangxi, China, which hasnot been studied before. A comparison with tufa from Dinaric Karst of Croatia is discussed in view of theC-type climate. The major mineral is calcite. Minor minerals are quartz and dolomite, depending onlocation. The content of calcium carbonate varies from 65% to 92%, and that of magnesium carbonatefrom 0.03% to 1.77%. Among other elements, the most abundant are Fe, from 0.02% to 1.50%, and Ti,from 0.15% to 0.27%. Many other trace elements (V, Cr, Mn, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Hgand Pb) are also present. Specific activity of radionuclides 40K, 232Th, 137Cs, 226Ra and 238U varies fromsample to sample. Concentration of U in tufa is close to that reported for sedimentary carbonate. Lowconcentration of 137Cs indicates that this part of the world was not exposed to nuclear explosions. Theconcentration of 226Ra is the highest in Mashan County. The ratio 238U/226Ra (0.21-0.71) in tufa fromMashan County is significantly lower than the theoretical value of 1. In 5 of the 11 studied samples,stable isotopes δ13C and δ18O were analyzed. They were dated by means of the 14C method. One tufasample originated in the Pleistocene and the others in the Holocene. Because all of the tufa samplescontain traces of Na and K, and K ＜ Na, the tufa from Guangxi belong to the CO2-outgassing "N" typeaccording to the classification of Liu and He (1994).