· Open File 2012-04: Dease Lake – Little Tuya River Geology (NTS 104J/08 & 07E)
· Property File update: Digital Archive of Regional Geochemistry Survey (RGS) Maps
BCGS Open File 2012-04 / Geoscience BC Map 2012-08-01: Dease Lake – Little Tuya River Geology (NTS 104J/08 & 07E)
J.M. Logan, D.P. Moynihan, L.J. Diakow and B.I. van Straaten
Geoscience BC's QUEST-Northwest Project is a multidisciplinary, integrated project designed to help focus mineral exploration in a highly prospective area of northwestern BC. The project's main activities include: two airborne magnetic surveys flown at line spacing of 250 metres, bedrock geological mapping and a geochemical program. The digital bedrock data set presents the field mapping results of the QUEST-Northwest Dease Lake Geoscience project - a partnership between Geoscience BC and the BC Geological Survey. The project completed regional scale bedrock geological mapping over a 1275 km2 area extending south west from the community of Dease Lake to the Tuya River that coincides with the northwest corner of the QUEST-Northwest Block 1 airborne magnetic survey area (released through Geoscience BC in January).
The Dease Lake map sheet 104J/08 and the east half of Little Tuya River map sheet 104J/07 are underlain mainly by Paleozoic to Late Triassic sedimentary, volcanic and plutonic arc rocks of the Stikine Terrane, which locally host large Cu-Au porphyry deposits like Red Chris, Schaft Creek and Galore Creek. In the northeast part of the map these rocks are thrust imbricated with similar aged volcanic and sedimentary oceanic rocks of the Cache Creek Terrane along the north-dipping King Salmon Fault. Early to Middle Jurassic sedimentary rocks of the Takwahoni and Inklin formations of the Whitehorse Trough overlie the Stikine and Cache Creek terrane rocks respectively. Middle Jurassic granodiorite and an equi-dimensional Paleocene granite with associated molybdenum mineralization intrudes the Early Jurassic Takwahoni sedimentary rocks. Unconformably capping some of the highest peaks in the area are columnar basalts of the Miocene to Pliocene Tuya Formation. Preserved beneath these young basalts in the southwest corner of the map are lower Tertiary coal-bearing sediments of the Tanzilla Canyon Formation.
The map provides revised geology, geochemical analyses of alteration and mineralization and new isotopic dates for volcanic and plutonic rocks in the area which when integrated with regional exploration target models and the new airborne magnetic and geochemical data collected by Geoscience BC are expected to benefit the exploration community.
Hardcopy maps showing sample locations for the Regional Geochemical Surveys (RGS) in BC have been scanned and digitally archived. In total, 875 maps are indexed and archived as “RGS Maps” Collection in the Property File, accessible to the public at This work is the result of a joint effort by the BC Geological Survey and Geoscience BC.
The RGS program in BC started in the 1970s and over the last 40 years has involved the Geological Survey of Canada, the BC Geological Survey, Geoscience BC and contractors. The original hardcopy maps used to locate the sample sites range in map scales from 1:250,000 to 1:50,000, and were stored Ottawa, Victoria and other locations. While effort was made to archive the original hardcopy maps, other sources were retrieved and digitized if the original maps were not available. These secondary sources include the hardcopy maps used in the field, as well as Mylar and consolidated maps with transcribed sample locations.
The digital archive of the RGS maps not only helps to preserve this important source of data, but also makes these maps accessible to the public. These maps can be used to validate exact sample locations, within the context of streams and other geographic features shown on the original topographic maps used during sample collection. This is especially important at locations where streams have changed course over time, or where the streams shown on the original topographic map at a smaller scale do not match up with the streams shown on a more recent topographic map at a large scale. Errors in the sample locations may also occur when transcribing and transferring into the database.
Most provincial geoscience data can be easily accessed over the internet in map format at: and through various thematic pages at
BC Geological Survey Publications are available online at
Questions or to update your contact info please contact the BC Geological Survey:
Email: Tel: 250-952-0372 Fax: 250-952-0381
BC Geological Survey
British Columbia Ministry of Energy and Mines
Mines and Mineral Resources Division
Release Notification 2012-05
April 3, 2012