Investigations of base metals and gold biogeochemical anomalies in the Mabel Lake area, southern British Columbia (NTS 82L09 and 10)
Authors: Dunn C E , Thompson R I 
Published: January 2011

In 2007, GSC Open File 5538 was released that detailed the spatial distribution of elements within top twigs from Douglas-fir collected over an area of 700 km2. The survey was aimed at determining if this regional exploration geochemical approach would assist in
identifying base-metal targets. The widespread regional distribution of thin prospective homotaxial calcareous stratigraphie units that host five known Zn/Pb deposits in and around NTS 82L lends credence to the concept that similar mineralization may lie beneath the extensive area that is covered by
a veneer of glacial deposits and dense forest. Exploration in this environment, illustrated on the frontispiece, is challenging because of the rugged terrain, poor access, forests and till cover. Geophysical signatures provide some guidance, but the ore-bearing lithologies do not generate a
distinctive geophysical signature. An additional exploration tool is needed. During a four day period in late March, 2006, a helicopter-supported survey was conducted within 700 km2 of an area centred upon Mabel Lake, B.C., to collect 562 samples of foliage and twigs from the tops of Douglas-fir
trees. Sampling was at 1 km intervals on an offset grid, with closer spacing over the Kingfisher deposits and an area of interest with similar stratigraphie units that borders Tsuius Creek. Total helicopter time, including daily mobilization and refuelling, was 35 hours involving 656 kilometres of
air travel. The final dataset comprised, including controls, data for 53 elements in 628 milled twig samples for a total of over 33,000 analytical determinations, and a number of anomalous enrichments of metals were identified. The present report examines the robustness of the dry twig signals by
taking the needles archived from these twigs and reducing them to ash prior to analysis for the same suite of elements, and conducting field studies and more detailed sampling over areas of interest. Data and results from these follow-up studies include: Douglas-fir Needles (archived from the
tree-top collection): 446 samples of needles were reduced to ash and analyzed; element distribution patterns generally substantiate those obtained from the twigs, and enhance signatures for some elements (notably Ag), thereby attesting to the robustness of the technique. Kingfisher Area - Needle
Ash: A subset of 56 Douglas-fir needle ash samples from the Kingfisher area was assessed in more detail. Boron, Cd and Zn proved to be the best indicator elements of mineralization. Halogens in Needle Ash: 88 Douglas-fir needle ash samples that were not part of the above, were selected from sites
in three areas (Kingfisher, Tsuius Creek and over a Au anomaly west of Mabel Lake) and were analyzed for the halogen elements (Cl, Br, F and I). Although signatures were not definitive, the distribution patterns indicate that halogens might be used to further substantiate zones of base metal
mineralization Gold in Tree-top Anomaly: 40 Douglas-fir outer bark samples were collected around a 'Au in tree-top' anomaly, but yielded only very subtle enrichments centred upon the original site of Au enrichment in dry twigs. Thallium in Tree-top Anomaly: 90 outer bark samples of western hemlock
were collected around a Tl anomaly, south of Tsuius Creek. The zone of Tl enrichment extends for 600 x 600 m, and linear patterns of Hg, Pb, Sb and Fe suggest structural control. This area looks promising for Sedex base metal mineralization. From this study, it appears that, when used in conjunction
with other geological data and concepts, biogeochemical signatures are robust and methods may assist in the exploration for base metal deposits in this environment by identifying spatially-related multi-element zones of subtle enrichments. The technique is rapid and cost effective, and particularly
appropriate for use in rugged areas such as the area of this survey where access is difficult and other surface sampling media may be inconsistent or difficult to obtain.