The main objective of this research is to analyze -from a diachronic perspective- the productivity of the processes of noun formation in Mapudungun, based on the hypothesis that the processes observed in periods of less contact with Spanish will exhibit greater linguistic genuineness than those found in periods where contact is more intense. For this purpose, we analyzed the formation process of 2,779 nouns, classified into three groups according to their primary source of record: early period, composed of 274 units documented in Valdivia (1606); intermediate period, comprising 855 units documented in Febrés ( 1882); and recent period, which includes 1,650 units documented in Augusta (1916). The analysis reveals that certain processes remain highly productive across the periods (compounding and derivation), others lose productivity (syntactic conversion, semantic changes and borrowing), and others remain unproductive over time (onomatopoeia, reduplication, syntagmatic compounding, clipping and regressive derivation). Furthermore, it is observed that noun formation evolved along time from a situation characterized by a high degree of productivity of several formation processes to another situation in which productivity concentrated on a shorter number of procedures, implying a genuinity loss in our opinion. These results could serve as a basis for the policy planning of a lexicon that aims to encourage the establishment of new units and to strengthen the linguistic identity of the speakers of this language.