ABSTRACT. The object of our investigation was to study a mechanism of water formation in the Surdulica geothermal system (recharge area, age and homogeneity of the waters). We collected 56 samples to determine the chemical, stable isotope, 4C and tritium content of the waters. We found large stable isotope variations in precipitation collected at different altitudes, whereas the geothermal waters are largely homogeneous and seasonally independent. Data on springs and rivers, the local meteoric water line and recharge; area were obtained. Three groups of groundwater were identified by age -modern from natural springs, old from mines and very old from the Vranjska Banja. Because the initial 14C activity of infiltrated waters from the recharge area is unknown, the age of thermal waters can only be inferred, from HCO3, i4C and 3H content, to be 10,000 to 28,000 years old. INTRODUCTION Surdulica is one of the largest geothermal systems in southeast Yugoslavia. The system produces water (ca 100LIs cold water) and geothermal energy (near 70L/s, 80°-126°(;) . A drainage system of ca 200L1s cold water is being planned by building underground galleries and increasing exploitation of the thermal springs from 50-100%.

It is frequently important in agroeconomics, on examing form example in plant breeding the problem might be to decide whether a plant or plant progeny belons to a high-yealding or low-yealding grop up. Sometimes decisions can be made on the basic of a single varialble, but more often of the 2 group differ in several variables, each of which gives some indication as to group in which the individual should be placed. This is a clasical problem of discrimination, where the general problem is to find a disrimination function.