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The Estmere salt deposit is defined by a single deep well (Noranda 227-1) drilled in 1981 as part of a regional exploration program for salt and potash. This well was cored from a depth of 345 m to TD at 860 m. The first salt layer was intersected at approximately 396 m in strata near the top of the middle Windsor Group. The well bottomed in the main salt of the lower Windsor Group. No potash salts were encountered.
Using cores and mechanical logs, the stratigraphic position of the salt cored in the Estmere 227-1 well can be determined with a high level of confidence. Comparison with the central Cape Breton Island composite section is straightforward, but some question remains regarding the first downhole appearance of bedded halite. In deposits at Malagawatch, bedded rock salt extends upwards into the Upper Windsor Group, and in the Strait of Canso area, salt is well documented even above the highest beds of the Windsor Group. At Estmere, salt is not documented above the uppermost beds of the Middle Windsor Group, and its absence could be due to facies change or to salt dissolution. The close similarity in facies and unit thickness in the lower parts of the Middle Windsor Group favours salt dissolution as the explanation. This implies that active ground water dissolution of halite extends to considerable depth at the Estmere deposit.
The correlation suggested below indicates that the level of the "A" Potash was not reached in the Estmere well.
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Mechanical logs are a valuable tool for correlation within the Windsor Group. In many of the Cape Breton Island salt deposits, both cores and mechanical logs are available, providing the best of all possible worlds for stratigraphic study.
Selected examples of the log character of marker intervals within the Windsor Group are illustrated, showing the correlation of Noranda 227-1 with other wells.
Click colour coded circles to view geophysical expressions of Windsor Group marker horizons in detail. |
The 227-1 well cored an apparently undisturbed succession of middle and lower Windsor Group strata. Mechanical logs, compared with the Malagawatch succession data located south and west of the Estmere deposit, show that the lower beds of the upper Windsor Group were also encountered in the upper part of the well. The succession can be correlated with the composite Windsor group succession with considerable confidence from a level slightly above the B3 limestone (upper Windsor Group) to the total depth within the lower Windsor Group salt beds. Unlike other wells drilled in the central part of Cape Breton Island, the Estmere 227-1 well shows no evidence for fold or fault repetition within the Windsor Group.
The uppermost succession in the well, known only from mechanical logs and cuttings descriptions, provided by the Noranda well description, remain problematic. Recorded descriptions indicate that mudrocks extend from surface to approximately 143 m. This thickness of uninterrupted mudrock is unknown within gently to moderately dipping Windsor Group beds, but is not atypical in general terms in the overlying Mabou Group. Without any available data concerning tectonic tilt of beds in the highest part of the well, it is not possible to identify the stratigraphic position of these mudrocks. Only if they were steeply dipping could they be reasonably assigned to the Windsor Group. In southwestern Cape Breton Island, many wells have penetrated Mabou Group strata faulted against underlying Windsor Group strata. This might also be the case in the Estmere salt deposit.
All salt deposits in southwestern and central Cape Breton Island show varying degrees of structural complexity. The apparent simplicity of structure in the Estmere deposit may be real. However, considering the scale of fold structures well documented at Malagawatch, where fold limbs reach more than 600 m in thickness, structural simplicity at the Estmere deposit could be quite misleading for any future development, and would require independent substantiation. Potash potential has not been established, although the well may not have penetrated to sufficient depth in the lower Windsor Group to test for the "A" Potash. The "B" Potash in the middle Windsor Group was not recorded in cores through the target interval, and it is presumed to be absent in this deposit. Nevertheless, several thick and relatively pure salt intervals are prospective both for salt as a resource, and as horizons with potential for cavern development.
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