In this paper, we propose a conceptual indexing documents approach based on an enriched ontology. We used a minimal generic basis of association rules (ARs) between terms, in order to automatically enrich an existing domain ontology. The final result is a proxemic conceptual network which contains additional implicit knowledge. Therefore, to evaluate our ontology enrichment approach, we propose a document indexing approach in IR based on this proxemic network. The experiments carried out on the OHSUMED document collection of the TREC 9 filtring track and MeSH ontology, showed that our conceptual indexing approach could considerably enhance information retrieval effectiveness.