HYDROTHERMAL DOLOSTONES IN LOWER SILURIAN CARBONATES OF THE

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

SIMPLIFIED GEOLOGICAL MAP OF GASPÉ AND LOCATION OF STUDIED SECTIONS. e. R c n e wr a L St- Lac Matapedia Syncline Isabelle Creek e St-Lawrence Gulf on Z r e b m Hu Chaleurs Bay i h c i m e ira ran M er T Bourque et al. (2000) Dev. Gaspé Ss Gr. Upper Gaspé Ls + Fortin Grs. Sil. - Dev. Chaleurs Gr. Ord. -Sil. Matapédia Gr.

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

PALEOGEOGRAPHIC MODEL OF THE SAYABEC CARBONATE RAMP Synsedimentary collapse Cambrian-Ordovician Taconian unconformity

FIELD OCCURRENCE OF MASSIVE DOLOSTONES Lac Matapédia Syncline Massive dolostone breccia

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

Seawater STABLE ISOTOPES Matrix dolomite -18 -14 -12 4 2 -6 -4 -2 -2 HTD Meteoric calcite -4 -6

Salinity wt % Na. Cl FLUID INCLUSIONS 30 HTD 20 Other calcite cements 10 0 Meteoric calcite 50 100 150 200 Homogenization Temperatures (Lavoie and Chi, 2001)

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

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