Geology and Mineral Occurrences of the Downie Creek Area,
Northern Selkirk Mountains
(NTS 82M/8 and part of 1)

BCMEMPR Open File 1996-02

by J.M. Logan and M. Colpron and B.J. Johnson

Revision and Cartography in 2008 by J.M. Logan and C.Y.M. Lin

Scale 1:50 000

View Open File Color Map, Updated 2008 (PDF, 8.8 MB)

View Open File Black and White Map (PDF, 1.1 MB)

Open File 1996-02 presents the geology and mineral occurrences of the Downie Creek area (82M/8, part of 1) in the northern Selkirk Mountains of southeastern British Columbia. The Open File map portrays geology at 1:50 000 scale and includes a legend, cross sections, and tables of isotopic age data and mineral occurrences. The work complements information in Open Files 1995-02 and 1995-03.  In 2008, Open File 1996-02 was updated with geology, geochemistry and addition of color.

The geology and structure are complex. Proterozoic (?) to Paleozoic (?) rocks include undivided metasediments that feature sillimanite, kyanite and amphibole-bearing calcareous schist, and also Monashee complex amphibolite-bearing pegmatitic gneiss and minor calc silicate gneiss. Neoproterozoic Horsethief Creek Group rocks consist of three units. The lower is phyllite interlayered with micaceous quartzite and dolostone; the intermediate unit is phyllite with local dolostone interbeds; and the upper unit is phyllitic dolostone interlayered with phyllite and some quartzite. Eocambrian Hamill Group comprises three units. The lowest consists of micaceous quartzite interlayered with phyllite. Above are massive and cross-bedded quartzite with micaceous quartzite and phyllite layers, then mafic massive to amygdaloidal metavolcanic flow and associated epiclastic rocks. The Lower Cambrian Mohican Formation has a unit characterized by phyllite, calcareous phyllite and calcareous grit with dolostone intercalations, and a unit dominated by siliceous phyllite with dolostone and micaceous quartzite interlayers. The Lower Cambrian Badshot Formation is dolomitic marble. The Cambrian (?) to Devonian (?) Lardeau Group consists of the Index Formation, a Micaceous Quartzite and Grit assemblage, and the Jowett Formation. The Index Formation is divided into five units. From lowest to highest, the units consist of white orthoquartzites breccia; graphitic to calcareous phyllite; marble, dolomitic marble and phyllitic carbonate; mafic metavolcanic flows including massive flows and pillow breccia, and diorite sills; and a unit with mostly phyllite and quartz grit. The Micaceous Quartzite and Grit assemblage consists of a unit dominated by micaceous quartzite with interbedded phyllite, grit and schist, and a unit with interbedded grit and phyllite with minor marble interbeds. The Jowett Formation is made up largely of actinolite schist and phyllite but includes marble layers.

Intrusive rocks in the area that are of uncertain age include metadiorite and metagabbro bodies and ultramafic intrusions. The Early Mississippian Downie Creek and Clachnacudainn gneisses are foliated granite and quartz monzonite. The Middle Jurassic Pass Creek pluton is megacrystic quartz monzonite. Biotite-hornblende diorite may be Cretaceous and possibly mid-Cretaceous stocks are locally megacrystic biotite granites. The Late Cretaceous (?) Downie stock consists of muscovite-biotite leucogranite that is locally garnet bearing.

Rocks in the area have been multiply deformed into a series of thrust slides that dip easterly and host upright to overturned to west verging isoclinal folds. The map sheet is bounded on the west by the Columbia River fault, which dips moderately toward the east and shows normal movement. Rocks west of this fault comprise the Monashee complex.

Mineral occurrences include: copper-zinc-silver-gold-bearing Besshi-type volcanogenic massive sulphide deposits, like the formerly producing Goldstream mine; stratabound carbonate replacement deposits with lead, zinc, silver and gold values; zinc-copper-silver and tungsten-gold skarns; base metal veins with or without tungsten and gold; placer gold; and industrial mineral potential, particularly for garnet.