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Ministry of Energy Mines and Responsible for Core Review

Bedrock and Surficial Geology of the Tsacha Lake Map Area
(NTS 93F/2)

BCMEMPR Open File 1995-16

by L.J. Diakow, I.C.L. Webster, J.A. Whittles, T.A. Richards, T.R. Giles and V.M. Levson

Scale 1:50 000


View Open File 1995-16 (11.7 MB)


Open File 1995-16 presents the bedrock and surficial geology, and the mineral occurrences of the Tsacha Lake area (93F/2) in central British Columbia. The map, at 1:50 000 scale, shows the geology, a legend, references, and assay data.

The oldest stratified rocks in the area are of Lower to Middle Jurassic age. They consist of the Nechako Range assemblage, quartz-bearing crystal tuff, sandstone and siltstone; the Fawnie Range subaerial rhyolitic volcanic sequence; and the Kuyakuz Mountain assemblage, which consists of rhyolitic tuffs and volcaniclastic sediments. Overlying Middle Jurassic rocks comprise the Naglico formation, which consists mainly of andesitic and basaltic flows with pyroxene phenocrysts, feldspathic sandstone and siltstone, and subordinate, andesitic tuff and dacite porphyry flows.


Unconformably overlying Lower Cretaceous conglomerate with chert clasts has interlayers of sandstone and siltstone. Eocene Ootsa Lake Group strata include rhyolite flows, andesite flows, rhyolite ash-flow tuff, and andesitic volcaniclastic rocks. Overlying Miocene and Pliocene Chilcotin Group olivine basalt flows have prominent columnar joints.

Intrusive rocks are Middle (?) Jurassic to Eocene and younger (?). The oldest comprise coarse gabbro, augite porphyry and diorite plutons. Late Jurassic to Early Cretaceous rocks are of the Capoose batholith, which is mainly quartz monzonite. Late Cretaceous porphyritic diorite has pyroxene phenocrysts. Eocene plutons are granites. Eocene and possibly younger dikes and sills are rhyolite porphyry, felsite, and biotite-feldspar porphyry.

Strata are offset along northeast and north to northwest-trending faults. One northerly trending fault is interpreted to be contractional in nature.

The oldest surficial sediments are of Late Pleistocene age. They consist of resedimented glacial debris, morainal diamicton, mainly basal tills, glaciofluvial pebble to boulder gravel and sand, and glaciolacustrine sand, silt and clay. Holocene sediments comprise organic deposits, colluvium, and fluvial sand, pebble gravel and silt.

The Nechako Plateau is underlain by rocks that have potential for porphyry copper, molybdenum or copper-molybdenum deposits, and epithermal precious metal and structurally hosted, porphyry-related precious and base metal-bearing occurrences. There is also potential for skarn mineralization and stratabound base with or without precious metal mineralization. Poor exposure has hampered exploration but known mineral occurrences are encouraging.


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