The close association of lead-zinc deposits with dolomite and dolomitic limestone and the common occurrence of these deposits within dolomitic envelopes in limestone present an interesting and challenging problem to economic geologists. A review has been made of the manners in which dolomite and lead-zinc ore are found to be associated. Possible reasons for the association of dolomite and ore and processes by which lime stones in the vicinity of lead-zinc deposits may be altered to dolomite have been considered. Dolomites in general are believed to be very favorable host rocks for lead-zinc ore but whereas this favorability may facilitate the localization of ore in primary dolomites, it can hardly be regarded as the primary localizing factor in those deposits which occur within dolomitized zones in limestone. The alteration of limestone in the vicinity of lead-zinc deposits may be best attributed to magnesium-rich hydrothermal solutions, the magnesium of which is not genetically related to the parent magma. The mechanism proposed by Faust, whereby magnisium-rich solutions are derived from dolomites which have been thermally dissociated in the vicinity of an intruding magma, adequately fulfils the requirements of a dolomitizing agent. If we can assume that ore-bearing solutions have arisen from the same magma that brought about the dissociation of a pre-existing dolomite, then dolomite and ore may necessarily be closely associated by reason of dolomitizing and ore-bearing solutions having been localized by the same structural controls. A study of specimens from the Jackpot property, Ymir, B.C., a deposit occurring in dolomitized limestone, has revealed little information with respect to the process of dolomitization other than indicating that dolomitization preceded sulphide mineralization. Most of the sulphide mineralization at the Jackpot property occurs within calcitic zones in dolomite. It is believed that dolomite has been replaced by the sulphide minerals and has been later partially replaced by calcite in the zones of sulphide mineralization. If Faust’s proposal that magnesium-rich solutions may be derived from a thermally dissociated dolomite in the vicinity of an intruding magma is valid, one may conclude that at a late stage in the hydrothermal activity, when magnesium has been largely removed from the thermally dissociated dolomite, the solutions may become relatively rich in the less soluble calcium carbonate. These later calcium carbonate-rich solutions may be responsible for the replacement of dolomite by calcite in the mineralized zones. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate