Page 149 - Introduction to Mineral Exploration

132 J. MILSOM

(a) I = 90°
H = 60,000 nT

(b)

To equator To pole

(c)

I = 0°
(d) H = 35,000 nT

I = 0°
H = 35,000 nT
MI = 90°

X

FIG. 7.4 Variations in shape of
magnetic anomalies with latitude
I = 60°
(e) and orientation. (a–c) The variation
H = 55,000 nT
with magnetic inclination of the
anomaly produced by the body X
when magnetized by induction
only. (d) The anomaly at the
equator if, in addition to the
Y
Y Y induced magnetization, there is a
permanent magnetization in the
vertical direction. This situation is
I = 60° common with vertical intrusions
(f)
H = 55,000 nT (dikes and volcanic pipes) in low
latitudes. (e,f) The variation in the
anomaly produced in mid-latitudes
by an inductively magnetized sheet
with varying dip. All profiles are
Y oriented north–south and all bodies
Y
Y are assumed to be “2D,” i.e. to
have infinite strike length at right
angles to the profile.