Nowadays, geometallurgical modeling, as a rapidly growing discipline in mining engineering, has significant role in mine designing/planning especially for porphyry copper projects. In porphyry copper deposits, the copper ore often is composed of two main parts including oxide and sulfide ores. The oxide rock type consists a fraction of total copper which would be recovered by heap leaching. Flotation plant is used when the fraction of sulfide ore is high enough. The mineralogical inequality constraint linking both grade variables (total copper and oxide copper) is a difficulty which often complicates the joint modeling and simulation of variables. To simplify such complicated joint simulation, the stepwise conditional transformation technique is presented which transforms multiple variables to the univariate and multivariate Gaussian with no cross correlation. This makes it easy to simulate multiple variables with arbitrarily complex relationships. This study addresses the application of stepwise conditional transformation and sequential Gaussian simulation for reproduction of the total and oxide copper in different rock types of the Sungun porphyry copper deposit honoring the relationship between Cu-oxide and Cu-total of the initial data. Validation results show that the simulation model has a good agreement with the sample data and geological facts of deposit.