PINE POINT LEAD-ZINC DEPOSITS, NWT, CANADA INTRODUCTION AND PALEOCOLOGY OF PRESQUILE REEF

The zinc-lead deposits at Pine Point, N.W.T., comprise known ore reserves of 42.5 million tons averaging 7% Zn and 2.6% Pb in a 20 by 4 mile belt of barrier carbonate of Middle Devonian age, now exposed or at shallow depths amenable to open pit mining. Fore reef, reef and back reef facies in the Middle Devonian Pine Point, Presqu'ile and Sulphur Point Formations are recognizable in an elongate platform bounded on the north by the Mackenzie Shale basin and on the south by the Elk Point evaporites. During the development of this carbonate buildup the barrier platform was subject to periodic exposure, followed by renewed reef growth; ultimately late Middle Devonian and Upper Devonian transgressions of the sea caused the barrier buildup to be succeeded by carbonates of a more open marine character. The ore bodies that form an integral part of the upper Pine Point and the Presqu'ile formations are elongate lens shaped bodies ranging from a few hundred thousand to 10 million tons in size. Margins are sharp, most of the ore was deposited in open cavities and vugs. Colloform and crystalline sphalerite and galena are the only ore minerals; abundant marcasite, pyrite, calcite and dolomite comprise the gangue. Evaporites, deposited in a supratidal (Sabkha) environment, appear to have played a major role in the development of porosity that governed later dolomitization and ore emplacement. © 1969 Society of Economic Geologists, Inc.