Ore reserve evaluation of sodium sulfate deposit in the central part of Mighan-Arak ‎using geometric and geostatistical methods

In present research geometric method using Surfer software and geostatistical estimation ‎method have been used to evaluate sodium sulfate reserve in the central part of Mighan-‎Arak sedimentary basin. Using geometric method, average assay of the deposit and net ore ‎reserve were calculated 25.1 percent and 3223581.7 tons respectively. In order to employ ‎geostatistical method, first assay and thickness data of test pits, was statistically analyzed. ‎The results of this stage showed a log-normal distribution for assay data and a normal ‎distribution for thickness data. According to the results of variography and analysis of ‎spatial structure, ordinary block log kriging was employed for assay data as well as inverse ‎squared distance method for thickness data. By this method the size of estimated blocks ‎was selected 60*58 m, average assay of sodium sulfate was obtained 24.98 percent with ‎average standard deviation of 1.09 percent, average thickness of blocks was gained about ‎‎2.57m with average standard deviation of 0.23 m while the upper and lower limit of the ‎mineral deposit are 5275221.4 and 6286683.8 tons respectively in the reliability surface ‎of 95 percent. Based on the results of this research, the difference of calculated reserve by ‎geometric method through Surfer software and kriging is 2557370.9 tons that means 44.2 ‎percent. However the results of kriging estimation are highly accurate and more reliable ‎due to be unbiased having minimum estimation error. ‎