50 Ont ari O Mining and expl O ra ti O n direct O r y and res O urce guide 20 20 E xplor a tion in the Abitibi cla y b elt or other r egions wher e conduc t iv e r egolith is dominant eg saline al luvial co v er sediment co v er in deser t valle ys under r ange fr ont pediments etc can gr ea tly lim it the ef f ec tiv e ness of tr aditional elec tr omagnetic EM or elec trical IP Res geoph ysical e xplor a tion It is essential when planning an e xplo r a tiv e geoph ysical surv e y to tak e into account the potential masking ef f ec t s tha t conduc tiv e co v er can cr ea te Galvanic SAM minimizes induc tiv e r esponse fr om conduc tiv e co v er b y utilizing long galvanic d ipoles t o driv e curr ent deep into t he underlying b edr ock geology ther eb y cr ea ting linear elec trical curr ent fo w along str uc tur es b elo w the conduc tiv e co v er The Galv anic SAM metho d measur es the m agnet ic feld induced b y a timevarying elec t rical curr ent applied to the Ear th The applied curr ent is cr ea t ed with a highpo w er tr ansmitter system pr o ducing a lo wfr e quency squar e w a v e signal tha t is intr o duced into the gr ound t hr ou gh distant elec tr o des placed along strik e of the str uc tur e or lithology under in v estiga tion The tr ansmitter curr ent is pr ef er entially channelled along geol ogical f ea tur es tha t ar e r ela tiv ely less r esistiv e t han their surr ou ndings The elec tr omagnetic signal fr om curr ent distribution within the gr ound is measur ed simultaneously with the Ear th s spa tially varying magnetic feld using a Cs Vapour total feld magnetometer tha t samples a t a v ery high sample r a te b y r y an Olson 1 b r ent r obertson 2 deriv ed fr om w orks b y Malc olm c a ttach 3 1 G apDisc o v ery HeliS AM 2 Disc o v ery Int l Geoph y sics 3 G ap Geoph y sics A us tr alia Exploring under conductive clay cover g alv anic h eli s a M case s tudies fr om a us tr alia and c anada using the magnet ometric c onductivity t echnique C ase study fr om W est ern A ustr alia Magnet ometric c onduc tivit y o v er salt lak e Sho wing c onduc t ors mask ed fr om tr aditional induc tiv e EM c our tesy of g a P g eo P h y sics