Earth Sciences Report 1987-02

Earth Sciences Report 1987-02

ESR 1987-02

Geology and Resource Potential of Phosphates in Alberta

Author(s) MacDonald, D.E. Date 1987-01-01

In this study is an outline of the resource potentials of phosphate rock in Alberta and portions of southeastern British Columbia, primarily of the phosphorus content and secondarily of the associated uranium, vanadium, fluorine and rare earth elements.

Phosphate is found in for major geological units in the Cordillera of Alberta and southeastern British Columbia: the Devonian-Mississippian Exshaw Formation, the permo-Pennsylvanian Rocky Mountain Supergroup, the Jurassic Fernie Formation and the Triassic Spray River Group. Within these four major units, 33 stratigraphic zones contain varying amounts of phosphatic material. Only two zones seem to have any real future potential-the base of the Ranger Canyon Formation and the base of the Fernie Formation.

The Exshaw Formation has its best phosphate potential in the Crowsnest Pass region of Alberta. Grades of phosphate are up to 25 percent P2O5. However, none of the seams are thicker than 50 cm, and mining would be very difficult because the deposits are not easily accessible and are under thick overburden. The maximum in situ resources of the Exshaw Formation are estimated to be less than 10 million t of lowgrade phosphate rock.

The Rocky Mountain Supergroup has its best phosphate potential in the Johnston Canyon Formation (16-99 million t) and at the base of the Ranger Canyon Formation (39-235 million t). These resources are mostly low grade.

Within the Fernie Formation, there are 29 to 175 million t of medium-grade phosphate in the Fernie Basin area of British Columbia. There are an additional 260 million t of low-grade phosphate in Alberta. Uranium contents have a mean value of 34 ppm in the Alberta phosphorites and show a weakly positive linear relationship with phosphurus. The correlation is stronger within certain P2O5 ranges (particularly 18-32 percent P2O5).

Vanadium content in phosphatic rocks was found to have very little relationship to phosphurus content, with only a slight tendency to be negatively correlated. Vanadium contents in phosphorites vary from 26 to 225 ppm, and reach up to 0.4 percent in non-phosphatic shales.

Fluorine content averages 4.09 percent in phosphorites. Rare earth and trace elements show anomalous concentrations above normally enriched phosphorites, especially in the elements La, Ce, Nd, Sm, Eu, Tb, Dy, Ho, Tm, Yb, Lu, As, Cd, Mo, Ni, Se, V, Zn and Zr.

The mineralogy of the phosphorites is transitional between pure francolite and pure fluorapatite. A variety of petrographic lithotypes are present and include pellets-nucleated, elliptical and structureless; intraclasts and pebbles; nodules; and fossil material.

All phosphate occurrences were, at the time of deposition, in a low paleolatitude (<40�n) within="" the="" trade="" wind="" belt="" and="" had="" shorelines="" paralleling="" the="" dominant="" winds.="" such="" conditions,="" together="" with="" the="" presence="" of="" a="" landmass="" or="" submarine="" rise="" area="" in="" the="" northern="" montana/idaho="" area="" (montania?),="" may="" have="" contributed="" significantly="" to="" promoting="" oceanic="" upwelling="" and="" phosphate="" precipitation.="" it="" is="" believed="" that="" the="" fernie="" formation="" pelletal="" phosphates="" formed="" somewhere="" between="" the="" shelf="" margin="" to="" basin="" position,="" within="" a="" sequence="" of="" black="" shales,="" cherts="" and="" mudstones.="" the="" exshaw="" formation,="" rocky="" mountain="" supergroup="" and="" spray="" river="" group="" phosphorites="" apparently="" formed="" in="" shallower="" water="" shelf="">

Most of the phosphorites studied are related to worldwide sea level rises throughout the Paleozoic and early Mesozoic, marked by major transgressive events. The remaining occurrences are found at unconformities.

Macdonald, D.E. (1987): Geology and resource potential of phosphates in Alberta; Alberta Research Council, ARC/AGS Earth Sciences Report 1987-02, 80 p.