HYDROTHERMAL DOLOSTONES IN LOWER SILURIAN CARBONATES OF THE GASPÉ BELT: RELATIVE TIMING

AND HYDROCARBON CHARGE

DENIS LAVOIENatural Resources Canada

andCLAUDE MORIN

Hydro-Quebec Oil and Gas exploration

St-Lawrence R.St-Lawrence

Gulf

Chaleurs Bay

Mira

mich

i

Terra

ne

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 GASPÉAND LOCATION OF STUDIED SECTIONS

Isabelle Creek

Lac Matapedia Syncline

PridolianPridolian

LudlovianLudlovian

Wenlock.Wenlock.

Llandov.Llandov.

Lochkov.Lochkov.

PragianPragian

Ashgill.Ashgill.

SIL

UR

IAN

SIL

UR

IAN

DE

V.

DE

V.

400400

420420

440440

MaMa

SA

LIN

ICS

ALI

NIC

DIS

TU

RB

AN

CE

DIS

TU

RB

AN

CE

Regressivephase 1Regressivephase 1

Regressivephase 2Regressivephase 2

Transgression 2Transgression 2

TransgressionTransgression 1 1

Upper Gaspé LstUpper Gaspé Lst

West PointWest Point

SayabecSayabec

Source rocksSource rocks ReservoirsReservoirs

Stratigraphy of the Gaspé Belt

ProductionProduction

Cambrian-OrdovicianCambrian-OrdovicianTaconianTaconianunconformityunconformity

PALEOGEOGRAPHIC MODEL OF THE SAYABEC CARBONATE RAMP

Synsedimentary collapseSynsedimentary collapse

FIELD OCCURRENCEOF MASSIVEDOLOSTONES

Lac Matapédia SynclineLac Matapédia Syncline

Massive dolostone brecciaMassive dolostone breccia

PETROGRAPHY OF SAYABEC DOLOSTONES

Paragenesis

Early dolomite replacementFracturing – hydrothermal fluidsLeaching – secondary PoSaddle dolomiteHYDROCARBON MIGRATIONBurial calciteSub-aerial exposureMeteoric calcite

-2

-4

-6

2

4

-2-4-6-12-14-18

HTD

Meteoriccalcite

Matrixdolomite

Sea-water

STABLE ISOTOPES

FLUID INCLUSIONS

Homogenization Temperatures

Sal

init

y w

t %

NaC

l

50 100 150 200

(Lavoie and Chi, 2001)

0

10

20

30

Meteoric calcite

HTD

Other calcite cements

HTD Model and Hydrocarbon charge

300 m

25 m 1 cm

St-Léon

SA

YA

BE

C

Val-Brillant

UMHTD

Hydrocarbon charge Meteoric calcite cement

VUGVUG

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 Hydrothermal dolomitization of the Sayabec limestone facies is currently an under-evaluated limestone facies is currently an under-evaluated

play in the Gaspé beltplay in the Gaspé belt