The M15 magnetic anomaly (Dongwan anomaly) is a key prognostic area for copper and nickel deposits, to

which geologists both in China and abroad have paid close attention. As this anomaly lies in a fully covered area,

previous researchers considered it to be caused by an ultrabasic body. Using the gravity and magnetic method to

compare it with the magnetic anomaly related to the known Baijiazui ultrabasic body, the authors have reached the

following conclusions: The M15 anomaly is a noncognate gravity and magnetic anomaly characterized by

combinational magnetic high and gravity low and a rather large buried depth; the magnetic anomaly might result from

the ultrabasic rock below 1 200 m in depth, whereas the gravity low anomaly is probably caused by the Longshoushan

Proterozoic basement depression with a buried depth of 1 000 m or so. These findings are of active significance in

expanding copper and nickel resources.