This issue of the AAPG Bulletin is dedicated to structurally controlled hydrothermal alteration of carbonate rocks and reservoirs. This type of alteration covers the spectrum of carbonate-hosted sulfide ore deposits to hydrothermal dolomite to leached limestones, and in many cases has a major impact on reservoir type, geometry, quality, and distribution. Hydrothermal dolomite (HTD) reservoirs have a long history of exploration and development in North America, extending from the earliest discoveries in the Ordovician Lima- Indiana and other trends of the northeastern United States (Hurley and Budros, 1990; Wickstrom et al., 1992), and continuing today
with the Trenton–Black River play and other hosts in the Michigan and northern Appalachian basins of the northeastern United States
and eastern Canada.