Abstract The Potterdoal volcanogenic massive sulfide deposit is hosted by a tholeiitic-komatiitic succession located in northern Munro Township, Ontario. An integrated surface and drill core study of this property was undertaken to document the three-dimensional structure and stratigraphy of the deposit. The Pot-terdoal deposit is hosted by volcanic rock of an iron tholeiite affinity emplaced within an ocean-floor rifting environment. The chemistry of the tholeiites shows similarities to that of large deposits like Kidd Creek but lacks the felsic component of bimodal volcanism. The deposit consists of a stockwork zone overlain by an extensive massive sulfide lens which lies along a scarp structure defined in the paleosurface. Stockwork mineralization is narrowly confined to conduits within a fault breccia in the footwall ore flow gabbro and widens into an overlying tectonic breccia. Sul-fide paragenesis appears to be controlled by the thermal solubilities of the sulfide minerals and consists of pyrite, sphalerite, pyrrhotite, and chalcopyrite in both stockworks and the massive sulfide lens. The lens occurs at the top of the tectonic breccia near the paleoseawater interface; it was formed by direct replacement of the tectonic breccia. The lens locally exhibits ore-grade base metal values (i.e., combined Cu and Zn content > 3%) and shows an upward and outward gradation from chalcopyrite- to sphalerite-dominated ore. These features suggest that exhalation of the hydrothermal system was focused into local vent sites. Mass change associated with the hydrothermal alteration envelopes surrounding ore flow fault breccia conduits involves loss of Si, Ca, Na, and Sr, and gain of Fe, Mg, K, Cu, and Zn. These changes are attributed to fluid-rock reactions which are consistent with hydrothermal alteration associated with other vol-canogenic massive sulfide deposits. The genetic model suggested for the Potterdoal deposit involves a hydrothermal system driven by heat from the intrusion of the Munro-Warden sill at a high stratigraphic level. The relatively small size of the deposit is probably due to the rapid cooling of the sill, which shortened the lifespan of the hydrothermal system. The primary source of metals was apparently the upper portion of the Munro-Warden sill, as indicated by the high degree of pervasive hydrothermal alteration of this part of the gabbro.

Specimens spanning 10 m across the Cretaceous/Tertiary (K/T) boundary in Core 32 at DSDP Site 527, Walvis Ridge, were analyzed for trace elements and for evidence of shock deformation. Results from INAA/RNAA chemistry of the 45 samples suggest that multiple events are recorded at this site, including at least two enrichments of chalcophile elements possibly related to basaltic volcanism. A major event, coincident with the paleontological K/T boundary, is marked by a strong Ir anomaly and high frequency of shock deformation in quartz and feldspar. A strong secondary peak in elemental enrichment and mosaicism occurs at 1.87 m below the K/T boundary, suggesting appreciable volcanic activity about 10 5 years prior to the K/T event. Carbon and oxygen isotopes from the site also suggest that changes in climate began before the shock event at the boundary. Correlations between biostratigraphy, isotopes, and the data from this study suggest that the decline in marine productivity over an extended period of time may be the result of complex coupling of basaltic volcanism to climate change.