1. HYDROTHERMAL DOLOSTONES IN LOWER SILURIAN CARBONATES OF THE GASPÉ BELT: RELATIVE TIMING AND HYDROCARBON CHARGE DENIS LAVOIE Natural Resources Canada and CLAUDE MORIN Hydro-Quebec Oil and Gas exploration

2. St-Lawrence R. St-Lawrence Gulf Chaleurs Bay Miramichi Terrane Humber Zone Chaleurs Gr. Gaspé Ss Gr. Upper Gaspé Ls + Fortin Grs. Sil.- Dev. Dev. Matapédia Gr.Ord.-Sil. Bourque et al. (2000) SIMPLIFIED GEOLOGICAL MAP OF GASPÉ AND LOCATION OF STUDIED SECTIONS Isabelle Creek Lac Matapedia Syncline

3. Pridolian Ludlovian Wenlock. Llandov. Lochkov. Pragian Ashgill. SILURIAN DEV. 400 420 440 Ma SALINIC DISTURBANCE Regressive phase 1 Regressive phase 1 Regressive phase 2 Regressive phase 2 Transgression 2 Transgression 1 Upper Gaspé Lst West Point Sayabec Source rocks Reservoirs Stratigraphy of the Gaspé Belt Production

4. Cambrian-Ordovician Taconianunconformity PALEOGEOGRAPHIC MODEL OF THE SAYABEC CARBONATE RAMP Synsedimentary collapse

5. FIELD OCCURRENCE OF MASSIVE DOLOSTONES Lac Matapédia Syncline Massive dolostone breccia

6. PETROGRAPHY OF SAYABEC DOLOSTONES Paragenesis Early dolomite replacement Fracturing – hydrothermal fluids Leaching – secondary Po Saddle dolomite HYDROCARBON MIGRATION Burial calcite Sub-aerial exposure Meteoric calcite

7. -2 -4 -6 2 4 -2-4-6 -12-14-18 HTD Meteoric calcite Matrix dolomite Sea- water STABLE ISOTOPES

8. FLUID INCLUSIONS Homogenization Temperatures Salinity wt % NaCl 50100150200 (Lavoie and Chi, 2001) 0 10 20 30 Meteoric calcite HTD Other calcite cements

9. HTD Model and Hydrocarbon charge 300 m 25 m 1 cm St-Léon SAYABEC Val-Brillant UM HTD Hydrocarbon chargeMeteoric calcite cement VUG

10. CONCLUSIONS The Lower Silurian Sayavbec Formation is the oldest shallow marine carbonates in the Gaspé Belt Massive dolostones and breccias are currently known at two localities in northern Gaspé Field occurrence, petrography, stable isotope geochemistry and fluid inclusions point to fault-controlled pulses of Mg +2, saline and high temperature fluids for dolomitization Hydrothermal dolomitization of the Sayabec limestone facies is currently an under-evaluated play in the Gaspé belt