The Lytton map area, with 101 known mineral occurrences, lies within the
Intermontane Belt comprising the Quesnellia, Bridge River, Methow, Shuksan and Cache Creek
terranes as well as undifferentiated Post Terrane Accretion Overlap Assemblages. Much
of the map sheet is underlain by plutonic rocks, mainly Jurassic/Triassic Guichon Creek
Batholith dioritic rocks in the northeast, Mount Lytton Complex diorites and amphibolites
of the same age in the centre, Late Cretaceous Scuzzy Pluton granodiorites in the
southwest and Eocene Nicola Batholith granodiorites north of the Scuzzy Pluton. Stratified
rocks include Upper Triassic Nicola Group volcanics, metasediments of the Lower/Middle
Jurassic Ladner and Jurassic/Cretaceous Relay Mountain groups, Lower/Middle Cretaceous
Jackass Mountain Group sediments and Middle/Upper Cretaceous Spences Bridge Group
volcanics.Volcanics and sediments of the Eocene Princeton and Kamloops
groups occur as outliers within the Mount Lytton Complex as well as small Miocene
intrusions of intermediate composition. Quaternary sediments occur as thick drifts along
the main rivers and some of the larger creeks.
Metamorphic assemblages consist of Carboniferous to Jurassic Cache Creek Complex
melanges, Permian to Lower Cretaceous Bridge River Complex metamorphic and ultramafic
rocks and Upper Triassic Nicola Group volcanics.
The Guichon Creek Batholith is by far the most extensively explored and
documented region and hosts large Cu-Mo porphyry deposits. The Highland
Valley Mine (092ISW012) has measured reserves of 776 million tonnes grading 0.41
per cent copper (1989). Ore milled in 1989 totalled 32 million tonnes. In 1980, Lornex
(092ISW045) reserves measured 412 million tonnes. The O.K.
(092ISW010), a past producer, contains approximately one million tonnes of ore grading
2.33 per cent copper and 11.6 grams per tonne silver in six zones. The Victor
(092ISW005 - past producer) has possible reserves of 100 000 tonnes grading 1.5 per cent
copper. In 1985, the Highmont
West (092ISW036) contained measured reserves of 21 million tonnes at 0.25 per cent
copper and 0.047 per cent molybdenum. These deposits occur within the core (Bethsaida
phase) of the Guichon Creek Batholith. Numerous showings and prospects have been
discovered and worked using mainly geophysical techniques. Other small copper showings
within the batholith are hydrothermal vein and shear-hosted deposits. The Mount Lytton
Complex also contains copper mineralization. Lead and zinc are conspicuous by their
absence.
Precious metal showings occur mostly in Bridge River-Relay Mountain groups, the Serpentine/Summit
showing (092ISW055), east of Pyramid Mountain, being the best known historically.
Industrial minerals are common in the Bridge River and Nicola groups as well as in Fraser
River gravels (agate, jade, garnet). The H
showing (092ISW063), southeast of Pyramid Mountain, contains low grade talc (62 per cent)
in Bridge River serpentinites; the Rawhide
showing (092ISW051), east of Antimony Mountain, assayed 94.48 per cent talc. The Bob
skarn showing (092ISW058) occurs in limestone lenses within the Mount Lytton Complex.
BC Geological Survey Publications for
NTS 092I
