Petromagnetic characteristics and ore minerals of crystalline rocks in theAldan-Stanovoi ring structure

Petromagnetic characteristics (magnetic susceptibility, saturation magnetiz ation, magnetic anisotropy, etc.) were studied on 283 samples from the peri pheral part of the Central Aldan dome. The samples are represented by vario us enderbites, metabasites, variously amphibolized schists, amphibolites, a nd igneous rocks (pyroxene syenites, sviatonossites, granites, and granodio rites). Ores are represented by isolated, rather large grains (a few tens t o a few hundreds of micrometers) of ilmenite and magnetite and, more often, by their intergrowths. Magnetic characteristics of the rocks are mainly co ntrolled by magnetite produced during subsolidus transformations of primary magmatic oxide phases represented by titanomagnetite and hemoilmenite. The decomposition structures of solid solutions of these phases are well devel oped. The magnetic susceptibility distribution is shown to be bimodal, with its modes lying within intervals of (0.035-0.1) x 10(-3) and (10-20)x 10(- 3) SI units. The magnetite concentrations estimated from magnetic data are less than 0.1 to 13 vol %. The magnetization of the samples virtually does not depend on the extent and type of secondary alterations of the rocks and on their fabric state.