Although vast regions within the TREK study area had been covered by previous geochemical surveys of sediment, water, till and biological materials, several key tracts of prospective ground still had limited or no geochemical coverage. The thick vegetation cover, few lakes and limited road networks in these areas had hindered the types of traditional geochemical survey techniques that could be applied.
Indigenous groups, communities, the mineral exploration sector and land managers need access to reliable earth science information to make informed decisions in the TREK area where resource potential is high.
Extending geochemical coverage for the TREK project area required innovative approaches to meet the challenge of accessing locations to collect appropriate sample material. Ongoing research supports the effectiveness of biogeochemistry, and combined with advances in analytical methods, has established these types of surveys as valid exploration options for generating geochemical information. In addition, helicopter supported tree-top programs can be an economic method to quickly acquire samples over large inaccessible areas.
Coniferous trees such as spruce are useful as a biogeochemical sample medium since they can tolerate and maintain significant concentrations of trace elements . Extracted from underlying materials such as soil, overburden, groundwater and bedrock, elements are absorbed and transported throughout the tree including twigs and needles where elements can be locally concentrated. Analytical data derived from the analysis of tree-top samples that that have been systematically collected and prepared can be used to identify point-source anomalies and geochemical trends.
This 1,000 km2 biogeochemical survey area is located 40 km north of Anahim Lake within the Fraser Plateau and extends north from the Itcha and Ilgachuz mountain ranges to the West Road (Blackwater) River Basin. The area is characterized by gentle north-facing slopes that are blanketed with glacial drift and dissected by streams that flow into the flat-floored valley.
The survey area is underlain by Hazelton Group and Ootsa Lake Group rocks, and Chilcotin Group volcanic rocks. There are several developed mineral prospects in the region that contain Au, Ag, Zn, Pb and Cu mineralization, including the Blackwater Gold Project (NTS 093F/02; MINFILE 093F 037; BC Geological Survey, 2015) located 15 km north of the survey area, and the 3T’s polymetallic Ag–Pb–Zn±Au deposit (NTS 093F/03; MINFILE 093F 068) located along the northern survey boundary.
How was data collected?
The survey was conducted during a six-day period in June 2015. A total of 421 side-branch samples, comprising twigs, needles and cones, were systematically collected near the tops of 399 healthy spruce trees spaced 1,500 m apart. Samples of approximately 500 g of material were sent to a commercial analytical laboratory for drying and separation into twigs and needles. The twigs were analyzed for 53 elements by inductively coupled plasma-mass spectrometry (ICP-MS). A 50 g split of dry needles were analyzed for 53 elements plus rare-earth elements by ICP-MS.
What was found?
Geoscience BC Report 2016-05 includes a Summary Report outlining the survey details, sample collection methods and analytical methods. Field observations and analytical results are presented in Appendix A and summary statistics of individual elements are presented in Appendix B. Appendix C contains a suite of maps, including a sample location map, bedrock and surficial geology map, airborne geophysical maps, as well as proportional symbol and gridded image maps for a selection of metals in twigs and ashed needles. The raw datasets are included, together with a README file with additional details. A complete list of elements and analytical detection limits for both macerated twigs and ashed needles is provided in Tables 1 and 2.
Samples from this project were further analyzed as part of Geoscience BC Project 2018-031.