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File Created: 24-Jul-1985 by BC Geological Survey (BCGS)
Last Edit:  20-Feb-2003 by Ron McMillan (RHM)

Summary Help Help

BCGS Map 092P074
Status Showing NTS Map 092P11W
Latitude 051º 42' 15'' UTM 10 (NAD 83)
Longitude 121º 21' 06'' Northing 5729422
Easting 613900
Commodities Hydromagnesite Deposit Types F09 : Playa and Alkaline Lake Evaporites
Tectonic Belt Intermontane Terrane Overlap Assemblage
Capsule Geology

The Watson Lake hydromagnesite deposits are located about 500 metres southwest of Watson Lake and about 1.5 metres above the lake level. Watson Lake is a small lake covering about 1.2 hectares about 1.5 kilometres west of 105 Mile House on Highway 97.

Physiographically, it is in the Cariboo Plateau, a semi-arid plateau area averaging 1130 metres elevation which is host to several playa lakes. The area is underlain by alkaline plateau basalt flows of the Miocene to Pleistocene Chilcotin Group, mantled by a thin cover of glacial till and glaciofluvial sediments. Annual precipitation averages between 300 and 400 millimetres (EMPR Paper 1991-1).

Several deposits of hydromagnesite, some associated with impure hydromagnesite are located in a swampy depression to the southwest of Watson Lake.

The larger area, to the west, is about 200 by 60 metres along a northeast trend. It has a variable depth, to an underlying dark grey mud, up to about 2.16 metres. The hydromagnesite has a white surficial layer which varies between 50 and 100 centimetres in thickness with an average of about 58 centimetres. Underlying the upper layer is a cream to brown hydromagnesite in the order of 1.5 metres thick but with a higher calcium content. Sample No. 1 (Reinecke, 1920) is of 66 centimetres of white hydromagnesite and part of the layer of cream colored hydromagnesite.

The second significant area is about 180 metres southeast of the first. The white surface layer of hydromagnesite is about one metre thick with fairly pure material to depths of 0.9 to 1.5 metres. Sample No. 2 is of white hydromagnesite collected from 0 to 92 centimetres from surface.

Sample No. 3 (Cummings, 1940) is a composite sample of white hydromagnesite collected from seven drill holes representing all deposits in the Watson Lake occurrence. Sample No. 4 (Reinecke, 1920) was collected from a small isolated patch of hydromagnesite located about 1.5 kilometres northeast of the main occurrence. It is estimated that, in total, the Watson Lake deposits cover approximately two hectares and contain slightly more than 20,000 tonnes of hydromagnesite.


MgO CaO CO2 SiO2 Al2O3 Fe2O3 H2O H2O

(+105) (-105)

1 41.06 1.62 38.04 6.36 0.20 0.12 11.25 1.32

2 43.17 1.14 43.64 4.62 0.16 0.16 5.26 1.42

3 39.40 2.10 50.5 5.70 - 1.30 - -

4 36.70 1.54 31.08 8.62 0.33 0.57 14.86 2.21


EMPR BULL *4, pp. 108-110
GSC MEM 118, pp. 29,31,46-48; 363
EMPR AR 1918-K243; 1921-194; 1922-N155
EMPR OF 1987-13