by Mathew Wilson, President & CEO at Sterling Metals Inc.
Canadian high-grade silver districts bear a rich history. In the early 1900s, the discovery of the Cobalt Camp in Ontario initially provided over 10% of the world’s silver and has contributed over 450 Moz since its discovery. In Yukon, Canada, Keno Hill is still one of the world’s richest silver districts producing 200 Moz of silver from just 5.3 MT since its discovery in 1913. Now, over 100 years later, and without a globally significant silver discovery since, there is smoke emerging from the eastern corner of Canada in the form of an early stage, high grade, district-scale potential silver project.
The Sail Pond project in Northwest Newfoundland was discovered in 2016 and while it is without a drill hole, the preliminary data demonstrates the potential for a district-scale discovery due to a large geophysical and geochemical footprint. Preliminary work has identified a 9 km-long (5.6 mi) combined strike of two zones via a large soil grid, geological mapping and trenching, and several geophysical programs. Grab samples from trenching have yielded world-class grades up to 4500 g/t Ag and 15% copper while grab samples from an outcrop of similar veining, nearly 12 km (7.5 mi) away, have yielded grades up to 300 g/t Ag. The asset is held in a small junior exploration company listed on the TSX Venture exchange with an experienced team familiar with recent large discoveries in Canada and in Newfoundland. The project will be drilled for the first time this spring and perhaps the eastern side of Canada can join the west and the central in providing a globally significant high-grade silver district to the world.
In December 2016 local school principal Tony Kearney discovered rock samples from an outcrop yielding up to 464 g/t silver, 2.48% Cu, and 4.53% Zn and 2.48% Pb. After staking 30 claims, he sold the project to Altius Resources, a leader in Newfoundland exploration, which then went on to stake an additional 600 claims to amass a land package of over 15 000 hectares (37 065 acres).
Over the next two years, Altius defined two primary zones of combined 2 km (1.24 mi) and 7 km (4.35 mi) in strike via soil sampling, trenching and via grab samples that yielded grades over 2000 g/t Ag and 8% Cu. In 2018, after refining the land package to 13 500 hectares (32 124 acres), the project was optioned by the now dominant Newfoundland gold explorer Newfound Gold that spent the next two years commissioning an IP survey, gravity and magnetics. In February 2020, with the emergence of Newfound Gold’s terrific Queensway gold project, Newfound Gold returned the early-stage Sail Pond project to Altius minerals. In October 2020, Sterling Metals entered into an agreement to earn 100% for USD 1.5 million in spending over 3 years and issued 19.9% of its stock to Altius.
Since then, Sterling has undertaken an additional Geochemistry and Geophysics program to fill in a few holes of the last three years. These programs have yielded grades up to 4500 g/t Ag, 15% Copper and 15% Pb+Zn from grab samples within trenches and grab samples of over 300 g/t Ag from an outcrop over 12 km (7.46 mi) away from this high-grade sample.
Both the North and South Zones are distinguished by thick, massive sequences of pervasively altered (i.e. silica ± calcite ± sericite) dolostone (or dolomitized limestone) of the St. George Group (possibly Catoche and/or Aguathuna formations) which seems to be the primary rheological (± chemical) trap rock for fluids in this region. Commonly, these dolostones are folded and bounded by shear zones or thrust faults, and often deform brittlely. Conjugate quartz veins are the predominant host for the Ag-Cu-Pb-Zn-Sb (± Au) mineralization and are found almost entirely within sequences or blocks of massive dolostone. Quartz veins can constitute upwards of 30-40 volume percent of the exposed rock, with individual quartz veins generally less than 10 cm (4.94 in) in thickness but can reach up to 2 m (6.56 ft) in some locations. Mineralization has been observed in both sets of quartz veins. Similar styles of mineralization are present throughout the property, albeit hosted in narrower units of dolostone with widths of 0.5-5 m (1.64–16.4 ft) and there has been little work conducted thus far to evaluate these areas.
Sulphide mineralization within the two zones is comprised mostly of chalcocite, tetrahedrite, tennantite, sphalerite, boulangerite, galena and locally trace to minor amounts of pyrite, bornite, covellite, mimetite, sulfosalts, fluorite and apatite. Silver is almost exclusively associated with the tetrahedrite. Mineralization is generally within, or spatially associated with quartz veins; as open-space infilling (clots), disseminations and as vein-parallel massive bands or veinlets. Mineralization also occurs within the matrix of dolostone breccias, possibly as a solution breccia matrix replacement similar to Mississippi-Valley-type sulfide mineralization.
Vein-hosted silver-lead-zinc deposits hosted within metasedimentary sequences have several key criteria. These include:
- Vein networks consisting of structurally controlled quartz +/- carbonate vein swarms hosting variable amounts of sphalerite and galena with various Sb-Ag-(As)- bearing sulfosalts (e.g., tetrahedritetennantite, pyrargerite, argentite);
- They are typically hosted in greenschist facies metamorphic sequences dominated by shales, sandstones, and/or carbonates and calc-silicate rocks;
- Alteration associated with mineralization is not laterally extensive and is often proximal to the veins (within meters), consisting predominantly of clay (phyllic) alteration (e.g., sericite-chlorite) owing to the typical low-temperature nature of the ore-forming fluids;
- Mineralization is often proximal to regional-scale structures, but not necessarily hosted directly within the main structures (i.e., on subsidiary faults). The faults can be thrusts, transtensional or extensional faults. In some cases, they can be hosted within the cleavages of folds (e.g., Coeur d’Alene; Leach et al., 1988 );
- The metals for the mineralization are interpreted to have been sourced from basement rocks; sulfur is interpreted to be at the site of deposition and derived from local country rocks; and the fluids are interpreted to be a combination of metamorphic-hydrothermal fluids, meteoric fluids, and potentially basinal brines that range from dilute to saline;
- Mineralization forms as a result of mixing of fluids and/or fluid boiling within structurally favorable domains and/or reactive host rocks (i.e., orogenic vein systems) in conjunction with interaction with a proximal sulfur-rich country rock;
- Exploration targeting can be undertaken using a combination of geological and structural mapping; geophysical methods and induced polarization due to the low sulfide content and lack of connectivity of sulfide lenses of the mineralization; and surficial geochemical methods.
While it is still early, the quartz-(carbonate)-like nature of mineralization, and the Ag-Sb-rich nature of the primary Zn-Pb mineralization could suggest this is similar to the structurally hosted Zn-Pb-Ag-(Sb) veins found in metasedimentary belts around the world such as Coeur d’Alene in Idaho or Keno Hill in Yukon.
The company is funded for a strong initial >5 000 m (16 404 ft) drill program this spring targeting both known areas of mineralization identified from surface work as well as strong and robust geophysical and geochemical anomalies which point to mineralization at depth. The kilometric size and scope of the system, as identified through systematic soil sampling and geophysical tools, potentially point to a very large body of mineralization. Comparable silver districts, including the Keno Hill district of the Yukon – 23 300 hectares (53 576 acres) – are comparable in size to Sterling’s 13 500 hectares (32 124 acres) land package. Led by a team and advisory board that have been part of some of the top discoveries in Canada over the last 10 years and a host of preliminary work and target generation done to date, investors can now look forward to an exciting inaugural drill campaign. While early, it is clear that there is a robust high-grade silver target in northwest Newfoundland.
For more information visit: www.sterlingmetals.ca