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At low northern latitude, a simple induced total-field magnetic anomaly is generally asymmetric and bipolar, not a symmetric central positive peak. A compact body more magnetic than its surroundings, magnetized parallel to a northward, downward ambient field, gives its principal positive lobe on the southern side and a negative lobe toward the north. At exactly zero magnetic inclination its central anomaly reverses relative to the pole; latitude and survey orientation must therefore be included.^[ref]

For an original explicit sketch, put a dipole at depth $d$ and let $x$ increase northward. In a north–south vertical section with inducing inclination $I$, an induced magnetization parallel to the ambient field givesA geocentric-dipole approximation at latitude $20^{\circ }$ gives $I\simeq \arctan (2\tan 20^{\circ })=36.1^{\circ }$, only an illustrative field direction, not a measured local value.

For the actual crater, breccia, water and sediment may replace more magnetic basalt, giving negative magnetization contrast. In that case reverse the simple positive-body sketch: a dominant southern low and a northern high are possible even with purely induced contrasts. The magnetic sign cannot be inferred from density or from the word “crater” alone.

Assume the greenstone belt is more magnetically susceptible than the host rocks and granite, its magnetization is mainly induced magnetization, and the body is roughly east–west elongated so that the south–north line crosses it. At southern magnetic latitudes the main field has negative magnetic inclination in a north-and-down coordinate convention. The total-field magnetic anomaly is then generally asymmetric: the principal negative lobe is on the southern side and the positive lobe is displaced northward for the simple induced source illustrated here. The exact lobe sizes and peak positions depend on body geometry and the actual magnetic inclination.^[ref]

An explicit sketching model is an induced magnetic dipole at depth $d$. With northward coordinate $x$, $\mathbf{r}=(x,-d)$ and unit field direction $\hat{\mathbf{F}}=(\cos I,\sin I)$, its normalized total-field magnetic anomaly isThe plot uses $I=-36^{\circ }$ only as an illustrative dipole-field inclination for a latitude near $20^{\circ }$ south, not a measured modern field at the site. A wide greenstone belt would broaden the response and can produce prominent edge anomalies. Remanent magnetization or a magnetic granite could change the sketch substantially; gravity alone cannot identify the magnetic source.