Composition and genesis of magnetite from iron deposits of the Angara province (Russia)

In the Angara province a single rock series involving forsterites, ore fors terites, forsterite magenetitolites, forsterite magnetitolites, magnetitoli tes, and apatite-magnetite (nelosonite), and pyrite-magnetite ores was form ed. The relationship between rock and magnetite composition was caused by t he differentiation of the foscorite magma: the ore forsterites predominantl y contain Al-Mg-titanomagnetite, and Al-Mg-magnetite, the forsterite magnet itolites-Al-Mg-magnetite, and nelsonites-Si-, Ca-bearing Al-Mg-magnetite. T he presence of Si-, Ca-bearing Al-Mg-magnetites in nelsonites suggests thei r crystallization from the residual magmas. This conclusion is confirmed by the geological setting of the nelsonites (upper levels of the diatremes).