The USGS has released an update of their 1986 report (Bulletin 1693) on the preliminary model of porphyry copper deposits.According to the announcement, "This update includes a greater variety of deposit attributes than were included in the 1986 model as well as more information about each attribute. It also includes an expanded discussion of geophysical and remote sensing attributes and tools useful in resource evaluations, a summary of current theoretical concepts of porphyry copper deposit genesis, and a summary of the environmental attributes of unmined and mined deposits."