The character of the Erkelenz intrusive as derived from geophysical data

Abstract

In the framework of the first National Research Program for Geothermal Energy in The Netherlands, geophysical measurements were performed in an area in the Dutch province of Limburg and the adjacent part of Germany, covering the Erkelenz intrusive. Surface magnetic data confirm the magnetic anomaly known from the German magnetic maps. That anomaly had been interpreted by Bosum (1965) to be caused by a huge intrusive of basic composition (the Erkenlenz intrusive). The gravity data, those at the surface as well as those measured in the Sophia Jacoba colliery, do not show a big anomaly. This agrees better with an intrusive of acid than one of basic composition and it means that relatively high temperatures can still be expected due to radio-active heat production. The existence of high temperatures in the past could be proven by analysis of rock samples from the colliery. For recent high temperatures there are a few indications.