Nano-scale phase separation encountered in metallic glasses is investigated for amorphous Fe80B20 and Fe83B17 alloys in an interaction field calculated via electronic theory of alloys in pseudopotential approximation combined with MC equilibration and reverse MC simulation. The phenomenon is identified regarding three topological aspects: (1) pure Fe-clusters as large as similar to 0.9 nm and pure Fe-contours similar to 0.72 nm thick are found to exist; (2) Fe-rich highly deformed-bcc regions are observed; (3) B-centered prismatic units are found to form distinct regions of high and low coordination. Polytetrahedral order prevails for B-prisms. All topological aspects are compiled into a two-dimensional projection model for predicting contributions to short- and medium-range order and corresponding spacing relations. The outcome geometrically involves proportions approximating the golden ratio. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.