Preliminary results of electrical characteristics of mineralized and nonmineralized rocks from the Yellowknife area, Northwest Territories

Electrical resistivity characteristics of a suite of ten rock samples from the Giant and Con mines (Northwest Territories) have been investigated to provide information for development of exploration strategies and to aid interpretation of down-hole, ground, and airborne electromagnetic (EM) surveys. Samples include material from 1) gold-bearing quartz veins; from altered shear zones represented by 2) sericite schist immediately adjacent, and 3) chlorite schist further removed from these veins; and from 4) basalt that hosts the shears and veins. Preliminary results indicate that nonmineralized rocks display electrical resistivity (rr) values of 2000–24 000 W.m with weak electrical anisotropy (4:1–7:1). Some sections of the gold-bearing vein display low rr values (30–100 W.m), but without evidence of continuity. Mineralized sericite schist displays intermediate rr values (600–1000 W.m) and with continuity along foliation with relatively strong anisotropy (10:1), implying that it might form a good exploration target; however, inappropriate survey-line orientation could cause EM surveys to miss the target, due to the electrical anisotropy. 1 Contribution to the 1999-2003 Yellowknife, Canada-Northwest Territories Exploration Science and Technology (EXTECH III) Initiative 1 Resume : Les caracteristiques de resistivite electrique d’un ensemble de dix echantillons de roches provenant des mines Giant et Con (Territoires du Nord-Ouest) ont ete etudiees afin d’obtenir l’information necessaire a l’elaboration de strategies d’exploration et pour faciliter l’interpretation de leves electromagnetiques de sondage, au sol et aeriens. Les echantillons consistaient en materiaux tires 1) de filons de quartz aurifere; de zones de cisaillement alterees representees par 2) du sericitoschiste immediatement adjacent et 3) du chloritoschiste un peu plus loin de ces filons; et 4) de basalte encaissant les cisaillements et les filons. Les resultats preliminaires indiquent que les roches non mineralisees presentent des valeurs de la resistivite electrique (rr) de 2 000 a 24 000 W.m et une faible anisotropie electrique (de 4:1 a 7:1). Certains segments des filons auriferes presentent de faibles valeurs de rr (de 30 a 100 W.m), mais aucune indication de continuite. Le sericitoschiste mineralise presente des valeurs intermediaires de rr (de 600 a 1 000 W.m) et une continuite le long de la schistosite avec une anisotropie relativement forte (10:1), ce qui signifie qu’il pourrait constituer une bonne cible d’exploration. Cependant, des lignes de leves electromagnetiques mal orientees pourraient ne pas permettre la detection des cibles en raison de l’anisotropie electrique.