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File Created: 24-Jul-85 by BC Geological Survey (BCGS)
Last Edit:  10-Sep-12 by Larry Jones(LDJ)

Summary Help Help

NMI 082L12 Gyp1
Name FALKLAND, SALMON RIVER Mining Division Kamloops
BCGS Map 082L053
Status Producer NTS Map 082L12E
Latitude 50º 30' 40" N UTM 11 (NAD 83)
Longitude 119º 33' 09" W Northing 5598573
Easting 319028
Commodities Gypsum, Anhydrite Deposit Types G03 : Volcanogenic anhydrite/gypsum
Tectonic Belt Intermontane Terrane Quesnel
Capsule Geology

The Falkland gypsum deposits are located in a series of lenses along the northeast side of the Bolean Creek valley, north of Falkland.

Gypsum occurs along two parallel shear zones that are slightly discordant with a northwest striking and northeast dipping sequence of interbedded volcanic and argillaceous rocks of the Upper Triassic and? Lower Jurassic Nicola Group. The dip of the hostrocks varies from 45 degrees to vertical. The shear zones strike 308 degrees with steep and vertical dips to the northeast.

Volcanic rocks consist of a series of flows that are dark grey to grey to black, medium grained, slightly schistose and composed primarily of amphibole. Beneath the flows are thin bedded, fine grained, limy argillites. Argillite close to the gypsum has been altered, generally in the form of colour changes; the colour changes from black to reddish brown. Within the alteration zone, pyrite and quartz stringers and veinlets are common. Underlying this unit are thin bedded, light green to greyish brown, brown-weathering argillites. The oldest rocks consist of bedded tuffs and a lower sequence of interbedded black argillite and tuff.

Gypsum, which is conformable with the enclosing rock, occurs in a series of irregular, discontinuous lenses along strike for 2.4 kilometres. The irregular nature of these lenses, both in plan and vertical section, is partly attributed to displacement along the shear zones. It varies in colour from pure white through various shades of grey, grey and white banded, brown and white banded to reddish brown. Locally, the siliceous and argillaceous content reaches considerable proportions especially in certain banded and brecciated material. Variations are sharp but generally unpredictable. Also present within the gypsum, are inclusions of dark red-brown to orange-brown, severely fractured argillaceous rocks that range in size from masses measuring 10 by 15 metres, down to dust size. These inclusions consist of a fine grained aggregate of quartz and albite, pyrite cubes, tiny tourmaline prisms and calcite in masses and small rhombs. At depths ranging between 20 and 35 metres gypsum grades abruptly into anhydrite. Mineable gypsum was generally confined to depths less than 25 metres.

In thin section, the gypsum consists of subhedral crystals, fibrous masses and aggregates of gypsum with various impurities. Also observed is anhydrite being replaced by gypsum. The gypsum remaining appears to be of high purity.

McCammon (Minister of Mines Annual Report 1952) believed that the gypsum formed by the hydrothermal replacement of argillites and tuffs along a shear zone. He based his interpretation on the fact that the gypsum is related to the shear zones. In thin section, he observed that gypsum was the last mineral to form and that it replaced all other minerals. The mineral assemblage observed was at least partially a hydrothermal suite. Cummings (1940) interpreted the gypsum to have formed by the replacement of limestone by sulphate solutions. This replacement was believed to have been related to volcanic activity. He was able to observe calcite crystals being replaced by gypsum. Anhydrite then formed as a result of the metamorphism of gypsum and then subsequently was re-hydrated to form gypsum in the uppermost parts of the deposit. Baird (1964) concluded that the gypsum-anhydrite bodies were deposited pre-Nicola as part of a sedimentary sequence and were later squeezed into their present position by plastic flow.

The gypsum deposits were first staked in 1894 with production beginning in 1926. Production was continuous through to 1956 during which time 1.25 million tonnes were produced. During the period 1976-1980, gypsum and anhydrite was mined intermittently from 7 quarries and trucked to the Canada Lafarge Cement plant, 18 kilometres east of Kamloops. There is still minor intermittent quarrying being done at these quarries, although these deposits are virtually mined out of gypsum. Anhydrite is still present in the deeper part of the quarries.

Bibliography
EMPR AR 1913-K205,K206; 1915-K219; 1919-N179,N180; 1922-N153; 1923-
A169; 1924-B157; 1925-A189; 1926-A189; 1927-C199; 1928-C213; 1929-
C229; 1930-A197; 1932-A285,A286; 1934-G40,G41,D29; 1935-D16, G32;
1936-D58; 1939-A112; 1940-A98; 1941-A92,A93; 1942-A90,A91; 1943-
A85,A86; 1944-A81,A82; 1945-A131; 1946-A204,A205; 1947-A214; 1948-
A188; 1949-A255; 1950-A220; 1951-A219; *1952-251-257; 1953-A190;
1954-A179; 1955-93; 1956-A152
EMPR ENG INSP 1989
EMPR MAP 65 (1989)
EMPR MINING 1975-1980 Vol.I, p. 44; 1981-1985, p. 60,61; 1986-1987,
pp. 85,86; 1988, p. 84
EMPR OF *1991-15; 1992-1; 1992-9; 1994-1; 1995-1; 1998-8-L, pp. 1-49
EMPR PF (General File - Dawson, G.M. (1898): Geology map of Shuswap
Sheet; see 082LNW077 (Squilax) - Western Homes and Living,
October 1961, pp. 21,22; Cummings, J.M. (1940): Preliminary
Geological Report on Falkland Gypsum Deposits)
GSC ANN RPT 1888-89; 1895-37; 1931-96,97
GSC MAP 1059A
GSC MEM 296
GSC OF 481; 637 (Occurrence 226)
GSC P 48-4; 74-1A, pp. 25-30; 86-1A, pp. 81-88; 89-1E, pp. 51-60;
90-1E
CJES Vol.1, No.1, pp. 1-9 (Baird, 1964); Vol.21 (Oct.1984),
pp. 1171-1193

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