John L. MacLeod

The Gays river lead zinc deposit is located in central Nova Scotia within a lower Carboniferous carbonate complex. The primary constituents of the carbonate sediments include fecal pellets, micritized grains, grapestone, and skeletal sand in a microsparry dolomite matrix. Fossils observed include brachiopods, gastropods, bryozoa, tabulate coral, and ostracods.

Pre-burial diagenetic processes produced fragmentation of skeletal material, growth of blue~green algae, micritization, and algal foram encrustations. Early cementation of grains, geopetal structures, pustular mat development, and early lithification of algal_bound sediments, and dessication fracturing, are the effects of very early-burial diagenesis.

Early-burial diagenesis produced internal sedimentation in lithified layers, dissolution of aragonite, compaction phenomena in less indurated sediments, and diagenetic iron sulphides. Processes up to this point in the diagenetic history affected different portions of the studied section at different time intervals. Dolomitization then occurred, fairly early in the diagenetic history, but acted on the carbonate complex after the total thickness (minimum thickness present today) had been deposited. Dolomitization and evaporite deposition may have been related in time and space

The economic sulphide mineralization consists of idiomorphic to xenomorphic crystals of sphalerite, galena, and minor chalcopyrite. Barite andfluorite are associated gangue minerals. The sulphides act as cements in the diagenetic environment. Pore spaces utilized by the mineralization consisted of interparticle, sheltered, fenestral, intraskeletal, fracture, and moldic porosity. Petrographic relationships support a close association of mineralization with evaporite deposition.

Post mineralization diagenetic features consist of; diagenesis in the phreatic environment, vadose sedimentation secondarily concentrating sulphides, secondary fracturing, stylolitization which also acted to concentrate the sulphides, the generation of allochonthonous pore filling calcite, dedolomitization, and the important concentration of massive sulphides through dissolution of soluble calcitized dolomite( dedolomite).

The carbonate complex records subtidal to supratidal conditions of a developing fringing tidal flat - bank, with localized indurated wave resistant structures. At least one transgression and regression is recorded in the sediments.

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