Römischer Bergbau

Between the plots "Grunsenbruch" (group of trees with ponds on the right), "Bovenheck" (sports field Gressenich on the left) and the quarry, several sites of Roman settlement have been discovered, suggesting a center for Roman mining and smelting industry.

The two ponds in the "Grunsenbruch" represent the flooded pits of Roman mining. Notably many iron and heavy metal slags have been found in the debris scatterings. During
excavation work in the adjacent field "Schieverling", remnants of old tire shafts as well as Roman coins and other remains were found by miners from the Diepenlinchen mine in the 19th century.

The many finds of shards among the found slag remains, especially in the field "Mausbacher Hecken", were identified by the Landschaftsverband Rheinland (LVR) as being of Roman origin from the period of the 1st to the 4th century. The ancient extraction seems to have concentrated particularly on iron ore, lead, and probably also calamine, although no slag remains are produced during calamine smelting. Together with copper, the Romans already produced brass from this material, which was highly valued. For example, as a coin metal, sestertii were minted from it starting in the time of Emperor Augustus (63 BC to 14 AD). However, an area located on the Werther Heide seems to have been a calamine roasting site, as here a completely vegetation-free circular spot is found, which has a lush calamine flora in its border area.

The age of the site is not determined, but this form of calamine roasting has been practiced since antiquity until the early 19th century. The map shows the areas where scatterings of debris, bricks, and slags as well as shard finds have been made.

Roasting (Calcining) of Calamine: The roasting of calamine was essential for its further processing into brass. In this process, zinc carbonate is oxidized into zinc oxide and carbon dioxide (ZnCO₃ → ZnO + CO₂).

In its simplest form, a round area of about 40 meters in diameter is laid out with bundles of twigs, charcoal, or wood about one meter high, on which a dense layer of calamine chunks is then stacked. The resulting "kiln" is then burned.
As a result, "burnt calamine" is produced, which is ground and processed with copper into brass. Residual concentrations of zinc, lead, and cadmium remain at the roasting site.

(Text: Jens Mieckley)