An Alternative Experimental Method to Discriminate Magnetic Phases Using IRM Acquisition Curves and Magnetic Demagnetisation by Alternating Field

CHAPARRO, M.A.E.; SINITO, A.M.

REVISTA BRASILEIRA DE GEOFíSICA

Sociedade Brasileira de Geofísica (SBGf)

Lugar: Rio de Janeiro (Brasil); Año: 2004 vol. 22 p. 17 - 32

0102-261X

Separation of different magnetic phases in natural samples composed by a mix of several magnetic minerals become necessary in rock magnetism in order to identify and describe the main magnetic carriers. However, this task may be difficult to carry out successfully. The goal of the proposed method in this paper is to determine and discriminate experimentally magnetic (soft and hard) phases in synthetic and natural samples. The present method uses two different magnetic techniques, isothermal remanent magnetisation acquisition and magnetic demagnetisation alternately. After the entire process of induced remanent magnetisation and demagnetisation is performed, three residual isothermal remanent magnetisation curves are obtained. This discrimination is achieved by using as filters (sorter) different peak values for alternating demagnetising fields. Well-known pure and mixed synthetic iron oxides (magnetite and hematite) were firstly studied to investigate and corroborate the reliability of our experimental method, obtaining successful results. Subsequently, natural samples containing soft and hard minerals (magnetite, hematite, goethite, etc.) from stream-sediments, soils and a mine were also studied. Comparisons with other purely numerical methods were carried out, yielding a good agreement among them. Our method is more time-consuming than others, but separation of individual magnetic curves is achieved by an experimental procedure, which is more realistic. It is also possible to apply this method to backfield isothermal remanent magnetisation measurements obtaining valuable information of HCR and S-ratio for each phase.