MAGNETIC SIGNATURE OF MAGNETITE-ENRICHED ROCKS HOSTING PLATINUM-GROUPELEMENT MINERALIZATION WITHIN THE ARCHEAN BOSTON CREEK FLOW, ONTARIO

Ground-based magnetometer surveys detect high-positive magnetic anomal ies (up to 72000 nT) which coincide with the location of subeconomic, magnetite-associated platinum-group element (PGE) mineralization withi n the Boston Creek Flow iron-rich basalt, Archean Abitibi Greenstone B elt, Ontario. The magnetic anomalies confirm the presence of magnetite -enriched zones (up to 20 modal%), and reveal that they are ovoid in s hape, up to 10 m in size, and along strike from each other in the cent ral gabbro-diorite layer. Geological and geochemical surveys and miner alogical studies indicate that these zones host smaller zones of disse minated chalcopyrite+pyrite, some of which, in turn, host platinum-gro up minerals (PGM) and are enriched in PGE and related metals (whole-ro ck Sigma PGE + Au = up to 1000 ppb, Ag = 1300 ppb, Cu = 0.3%, V = 0.1% , Ni = 0.05%, Ti = 2.5%, and Fe = 25%). The coincidence of the high-po sitive magnetic anomalies with the location of PGE mineralization, poi nts to ground-based magnetometer surveys as a valuable exploration too l for magnetite-associated PGE ore deposits. The distribution of the r esidual magnetic field anomalies indicate that such surveys are especi ally useful in: (1) identifying rock types and mapping their distribut ion in areas of limited outcrop exposure; (2) locating magnetite-enric hed gabbroic rock bodies, even in close proximity to serpentinized oli vine cumulate rocks; and (3) delineating the detailed geometry of magn etite-enriched rocks that may carry significant amounts of PGE and PGM s. Exploration strategies should be designed to use ground-based geoph ysical surveys, in conjunction with geological and geochemical surveys , to locate and delineate the geometry of magnetite-enriched zones wit hin thick, differentiated mafic-ultramafic volcanic flows and plutonic bodies.