Assessing the importance of an ancient iron production site beneits to the historian in his research about authorities' wealth and strategies, including military needs. When preserved archives are lacking, archaeology is a mandatory framework, and only site artefacts allow for production assessment. Applied geophysical methods, as tools for slag heap characterization, help to understand site ... [Show full abstract] spatial organization. However, magnetic and electromagnetic methods do not preserve means, and do not lead to conservative estimators. Conversely, Induced Polarization (IP), which is by the way widely used in mining research since the middle of the 20th century, ofers a speciic and linear response. We use it on the "Grand Bois" (Saint-Vincentsur-l'Isle, Dordogne, France) where it allows characterizing the shape of the slag heaps, and inally leads to a suitable iron ancient production.