摘要
Plutonic and volcanic rocks were analyzed by INAA （Instrumental Neutron Activation Analysis） ana XRF （X-ray flurescence） in their major components for its classification. The samples proceed from the sites/regions corresponding to the Precambrian to Paleozoic/Postpaleozoic magmatism in the eastern and western Paraguay. The analysed elements were Si, A1, Na and K and thus the SiO2, AI/O3, Na2O and K2O content determined. The activation were performed in an annular 25Ci Am-Be neutron source with total flux of 5×10^7n.s^-1. The reactions used were （1） ^28Si （n, p） ^27A1, （2） ^27A1 （n, p） ^27Mg; （3） ^23Na （n, γ） ^24Na, the fourth element of interest, potassium, was analysed by XRF. The procedure overall uncertainties were checked as per the analysis of three compositae samples of SiO2： ＋ A12O3 ＋ NaHCO3 ＋ K2CO3 prepared as standards in convenient proportions. The determination of these parameters according to the last recommendations of the IUGS （International Union of Geosciences）, permits the classification of the rocks in the categories acid, intermediate, basic and ultrabasie, as well as the identification of the rock family and in certain cases, the norm and their magmatic provenance.
