The purpose of this study was to develop a quick and valid X-ray method to determine the alteration models for acidic and intermediate type of altered rocks. Four alteration minerals--alunite, kaolinite, montmorillonite, and sericite--and total quartz in certain altered porphyritic rocks were determined and evaluated by using the APD (Automatic Powder Diffractometer) system with external standard methods.

The findings indicate that the APD system can successfully be used in the quantitative analysis of these five mineral phases. The best results are obtained from samples with low iron minerals and of a grain size not coarser than 325 mesh.