Plotting Grade-Tonnage Curves with Fractal Methods and Comparing Them by Geostatistical Methods; a Case Study: Koh-e-Zar Gold Deposit in Torbat-e-Heydaryeh

The variation in tonnage and average grade vs. cut-off grade، called grade-tonnage curves، is one of the most important factors in investment، risk assessment and uncertainty for exploitation of a deposit. These curves are plotted with the use of exploration data and through classic and geo-statistical methods. In this paper، new fractal methods have been used to plot these curves. In fractal methods، without replacing or omitting outliers، one can fit a power-law function to data. Then، using this relation، one could calculate volume (using thickness variable)، average grade (using grade variable) and metal content (using grade-thickness variable) and then with these parameters، grade-tonnage curves are plotted. In this case study one of the mineralization zones of Koh-e-Zar gold deposit is used and through using number-size and concentration-area fractal models tonnage-grade curves have been plotted. Finally، the results are compared with traditional geo-statistical methods that indicate the minimum difference between geo-statistics and fractal methods in resource estimation is zero and the maximum difference is 22. 2%. These differences for average grade estimation are 0. 3% 14. 4% respectively. The descriptive statistics proves no significant difference between the results. The most important advantages of applying fractal method include the use of initial data، the possibility of estimation with irregular and low-density data، and easier calculations.