--> Abstract: Pre-Mineralization Dolomitization of Host-Rocks to Pb-Zn, Gays River Deposit, Nova Scotia, by M. M. Savard; #91012 (1992).

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ABSTRACT: Pre-Mineralization Dolomitization of Host-Rocks to Pb-Zn, Gays River Deposit, Nova Scotia

SAVARD, M. M., Centre Geoscientifique de Quebec, Ste-Foy, Quebec, Canada

The Gays River Formation (Visean) that hosts the Gays River Pb-Zn deposit mostly consists of dolomitized algal mud mounds. The formation unconformably overlies clastic rocks of the underlying Meguma Group and is in turn covered by younger evaporites of the Carrolls Corner Formation. Two types of dolomite constitute the bulk of the dolomitized mounds: early anhedral replacive microdolomite and coarser pore-filling rhombohedrons. Paragenetically, the replacive dolomitization occurs after marine cementation, and before microbrecciation, microfracturing, dolomite cementation, mineralization, calcite cementation, and stylolitization.

The Oxygen 18 values of the replacive dolomite range between -9 and -5o/oo (PDB), which is markedly lower than that for the estimated marine dolomite for the Visean age (approximately 0 to +4o/oo relative to PDB), and even partly lower than the theoretical signal of mixed-water dolomites (-4 to -6o/oo). Their 87Sr-86Sr ratios (0.7079 to 0.7080) are slightly more radiogenic than the Visean marine signal (0.7075-0.7079). Moreover, their 0.5 to 2.5 mole % of Fe and 0.3 to 0.7 mole % of Mn are much higher than the average contents of modern surficial dolomites. The succeeding pore-filling dolomites are even more enriched in Fe and Mn: 1.4 to 4.1 and 0.4 to 2.7 mole %, respectively. Furthermore, preliminary fluid inclusion results indicate that dolomite precipitated from brines at temperat res varying between 60 and 105 degrees C. Integration of the above results does not support a simple dolomitization in hypersaline or mixed water systems as advocated in other studies, but instead suggests dolomitization by hot brines.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)