Aeromagnetic signature of porphyry copper systems in northern Chile and its geologic implications

compilation of a large aeromagnetic high-resolution dataset acquired for ba se metals exploration in northern Chile between lat 19 degrees 45' S and 27 degrees 15' S revealed a pattern of transorogenic regional magnetic anomal ies. These anomalies occur as generally east-west stripes of negative resid ual magnetic intensity of more than -100 nanotesla (nT). They have an east- west extension of some tens of kilometers and a north-south width of some 5 to 10 km. Some of thc ln can be observed continuously from the coast to th e volcanic belt. Their residual intensity is typically more than -100 nT Th ey also show a loose north-south spacing. It is observed that all known por phyry copper deposits of the investigated segment are spatially related to these transverse magnetic anomalies. We propose that tile transverse magnet ic anomalies are the magnetic response to the loci of emplacement of intrus ive bodies of batholithic size along paths of the advancing magmatic front of tile active continental margin. Tile occurrence of several important por phyry copper deposits grouped in clusters within a district is explained as being related to a common parental intrusive complex, which is geophysical ly signaled by a corresponding transverse magnetic anomaly. A possible impl ication of the observed relationship between porphyry copper deposits and t ransverse magnetic anomalies is the quasideterministic restriction of porph yry copper deposits to certain orogen transverse loci (necessary condition) and the corresponding consequences for future exploration strategies.