ABSTRACT

The stable isotopic compositions of hydration water in carnallites (KMgCi3*6H20) from the Esterhazy Member of the Prairie Evaporite indicate that this mineral in its present form was not deposited during the evaporation of ancient seawater, but has been recrystallized and subjected to diagenetic processes involving fluids that have their origins in formations above the evaporite. Most of the carnallite now present as intercalations in the ore and as carnallite pods is the result of relatively recent fluid events at low temperature (25-40°C). The stable isotopic compositions of hydration waters in carnallites collected from potash mines at Rocanville and Esterhazy, Saskatchewan, indicate that there have been at least three different fluid events responsible for the formation of carnallite, whereas samples from a drill-hole core near Lanigan indicate carnallite formed from a number of distinct fluid events. Much of the carnallite in this evaporite deposit may be the result of subsurface, post-depositional processes involving the reaction of sylvite (KC1) with Mg-rich basinal brines. These Mg-rich brines may be related to de-watering of primary carnallite during early burial of the potash deposit and may have reacted with limestones in this basin to produce dolomites, therefore affecting the porosity of these potential reservoir rocks.