Abstract: There is convincing mineralogical evidence such as metasomatic pseudomorph and replacement remnants to support that dual replacements have taken place in the Early Paleozoic carbonate rocks form southern part of the Huabei basin. Two kinds of replacements that have proceeded in opposite directions in two different periods were found to occur even in the same grain. The dual opposite metasomatism between the ferromagnetic magnetite and the paramagnetic pyrite would produce noise on the palaeomagnetic data to distort the palaeomagnetic results of a given region,if passed unnoticed.