Volcanic-associated massive sulfide (VMS) deposits range from lens shaped to sheet-like bodies of sulfide-mineral- rich rock spatially associated with volcanic rocks ranging in composition from basalt to rhyolite

OF RELEVANT GEOLOGIC, GEOENVIRONMENTAL, AND GEOPHYSICAL INFORMATION Deposit geology Volcanic-associated massive sulfide (VMS) deposits range from lens shaped to sheet-like bodies of sulfide-mineralrich rock spatially associated with volcanic rocks ranging in composition from basalt to rhyolite (fig. 1). VMS deposits can be divided into three general categories. Cyprus-type deposits (Model 24a; Singer, 1986a) tend to be small, medium-grade deposits rich in copper and zinc. They are generally lens or mound shaped accumulations of massive pyrite developed in ophiolite-related, extrusive basalt sequences. They are typically underlain by copper-rich "stringer-zones" composed of anastomosing quartz-sulfide mineral veins in extensively chloritized basalt. Kuroko deposits (Model 28a; Singer, 1986b) are typically developed in intermediate to felsic volcanic rock and are generally interpreted to have formed in extensional environments associated with arc volcanism. They are commonly high grade and can be very large. Relative to Cyprus-type deposits, they generally have much higher contents of zinc, lead, silver, and antimony, which reflects the composition of their felsic volcanic host rocks. They also have moundlike morphology and the abundance of coarse clastic sulfide minerals within many of these deposits attests to a moderately high energy, seafloor depositional setting. Kuroko-type deposits also tend to be underlain by copper-rich stringer zones and commonly have well developed geochemical zonation with progressive zinc, lead, and silver enrichment both vertically and laterally away from vent centers. Besshi-type deposits (Model 24b; Cox, 1986) are present in mixed volcanic-sedimentary environments. Deposits of this type are commonly hosted by turbidites that have been intruded by basaltic sills. These deposits are typically copper-rich and contain small abundances of lead and other lithophile elements. In contrast to other volcanic-hosted deposits, many Besshi-type deposits form thin, laterally extensive sheets of pyrrhotiteand (or) pyrite-rich massive sulfide rock; however, the characteristics of Besshi-type deposits vary considerably. Slack (1993) presents an expanded definition of Besshi-type deposits that includes deposits such as those in the Ducktown, Tenn., district and the large Windy Craggy deposit in British Columbia.