『Abstract
　Orebody thickness, grade, cutoff grade and tonnage are the most important parameters in assessing the economic values of ore deposits. Despite abundant research about the relationships among tonnage, grade and cutoff grade, the tonnage-thickness relationship is still undefined in the case of the orebody parameters following fractal distributions. Referring to the deduction from the number-size fractal model to the number-median size model, the median concentration-area (MC-A) model is derived from the concentration-area (C-A) model. Utilizing the C-A model to analyze the plane distribution of orebody thickness (grade・thickness), the orebody area delimited by a given thickness has a fractal relationship with the median thickness (grade・thickness) for that area according to the MC-A model. Ore tonnage, then expressed by the product of the area, median thickness and ore density, has a power-law relationship with the median thickness, as is named tonnage-thickness model. Correspondingly, contained metal tonnage in the ore tonnage shows a fractal relationship with the median grade・thickness, i.e., a metal tonnage-grade・thickness model. The tonnage-thickness model and metal tonnage-grade・thickness model are helpful in understanding orebody spatial distribution, which is demonstrated by a case study from bauxite orebody in Western Guangxi, China.

Keywords: Tonnage; Thickness; Fractal; Reserve』

1. Introduction
2. Methodology
　2.1. Basic equations
　2.2. Model derivation, utilization and comparison
3. Case study
4. Conclusions
Acknowledgments
References