Orangedale Salt Deposit Stratigraphy and Structure
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The Orangedale salt deposit is defined by three wells in the Orangedale area, 10 km northwest of Malagawatch, in central Cape Breton Island. |
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The host strata are part of the regionally extensive Viséan Windsor Group. A composite Windsor Group succession, shown to the left, can be constructed using data from the Malagawatch and McIntyre Lake deposits. The record provided by Orangedale deposit cores is shown by the heavy black line. Important marker beds intersected include the "A" and "B" potash horizons and the regionally diagnostic "Triplet Marker" horizon. Mechanical log interpretation permits identification of the Herbert River limestone member at the base of the Upper Windsor Group, and the B3 limestone above the Herbert The record at River. |
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Stratigraphic summary for the three wells which define the Orangedale salt deposit. Arrows indicate the position of fold axes and downhole direction. Overturned sections have been returned to normal stratigraphic orientation to show correlation across fold axes and between wells .
Click the Noranda-225-5A and 225-4 Triplet Marker horizon to view geophysical expressions in detail.
Well Noranda-225-3 drilled into a moderate to steeply dipping succession of interbedded siltstone, gypsum and minor limestone. At 75 m, the well intersected the Herbert River Limestone, the base of which marks the defined base of the Upper Windsor Group. At 260 m, the well penetrated the first salt layer. This salt interval contains thin interbeds of anhydrite with minor limestone as the well passes into the lower part of the Middle Windsor Group. At 355 m, anhydrite with interbedded dolostone becomes the dominant lithology. At 430 m, the thicker dolostone units disappear, indicating the change-over to Lower Windsor Group rocks and the second major zone of salt. The "A" potash was encountered at 575 m and intersected again at approximately 650 m in overturned Lower Windsor strata. The well did not encounter the Middle Windsor Group "B" potash, which was possibly removed by salt dissolution. Total depth of the well is 754 m.
Noranda-225-4 drilled into 171 m of leached caprock consisting of lower Middle Windsor Group gypsiferous siltstone and carbonate before intersecting the first salt with interbedded siltstone of the upper parts of the Lower Windsor Group at 160 m. At 268 m the drill penetrated overturned Lower Windsor salt and proceeded downhole but up-section into Middle Windsor dolomite and anhydritic dolomite before intersecting 240 m of overturned Middle Windsor salt. Noranda 225-4 did not encounter the "A" or "B" potash zones. Overall, the well records an overturned asymmetrical fold containing Middle and Lower Windsor Group rocks.
Well Noranda-225-5A contains 1078 m of Middle Windsor Group strata. The hole first drilled into overturned leached caprock of gypsum, and siltstone. It penetrated five fold axes repeating the distinctive "Triplet Marker" horizon six times, and the Middle Windsor "B" potash zone three times. The thickest intersected salt zone was encountered between 450 m and 450 m in a folded section of strata.
Fold repetition within the Middle Windsor Group is a striking feature of the Orangedale deposit. The scale of folding is best illustrated by drillhole 225-3, which collared in an upright limb and proceeded down-section for approximately 600 m before intersecting a major fold axis.
Click the Noranda-225-4 drillhole to view the geophysical expression of the "Triplet Marker" horizon.
In general terms, the structural setting for the Orangedale deposit is a series of west-verging tight to isoclinal folds.
The Orangedale salt deposit displays a complex post-depositional tectonic history in which Windsor Group rocks are folded and overturned to form northeast-southwest to north-south inclined horizontal folds. The plunge of the folds is not well constrained, but is thought to be moderate.The area has relatively good economic potential for salt resources. However, the potash may be of lesser economic potential due to the structural complexity of the deposit.
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