Peter Rose

Evaporitic rocks exposed in the workings of the Canadian Salt Company Mine at Pugwash, Nova Scotia consist of massive, nodular and stylolitic anhydrite and clear white, reddish brown to black halite with minor occurrences of carnallite and sylvite. The anhydrite and halite occur both as thick beds and as thinly bedded intervals transitional to each other. The beds exposed in the mine are intensely deformed and are generally steeply dipping (i.e. 60-70 degrees).

The division of anhydrite into well defined units has been the subject of some debate. Based on macroscopic observations anhydrite has been divided by different authors into two, three and even ten distinct units. At the present time the most likely division of the anhydrites appears to be a threefold one.

Representative core samples have been collected from four diamond drill holes from the 192 m (630 ft.) and 250 m (830 ft.) levels of the mine. The drill holes were carefully chosen in an attempt to represent type sections through three macroscopically different anhydrite bodies. This study proves the validity of the current division of anhydrites into three units using techniques such as petrographic microscopy and geochemistry. Based on mineralogies and textures observed in thin sections and on differences in chemical composition, three anhydrite units are recognized. Each of the three anhydrite units has been subjected to a complex sequences of diagenetic processes. Mineral replacements such as calcite psueudomorphs after anhydrite and diagenetic products such as borate nodules and elemental sulfur make the present appearance of the three units very different. The shaft anhydrite was probably deposited in shallow water and may have been subjected to periodic subaerial exposure. The borate anhydrite was probably deposited under more saline conditions than the shaft anhydrite.

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Pages: 145
Supervisors: Paul E. Schenk