SHOT ROCK (Au) Nova Scotia
In 2018 Northern Shield confirmed the discovery of a low sulphidation epithermal system at the Shot Rock, in Nova Scotia. This is the first time that this style of gold mineralization has been identified in Nova Scotia. The gold mineralization (up to 3.3 g/t Au) is found within quartz veining exhibiting textures consistent with those from known epithermal systems. Textures observed include crustiform banding, colloform banding and bladed calcite locally pseuomorphed by quartz, comb texture and other void fillings.
Low sulphidation deposits are highly prized for their potential to host “bonanza” grades of gold and silver.
The Shot Rock Property is currently composed of 24 mining licenses units staked under the terms of the Mineral Resources Act of Nova Scotia, which represents a total area of around 300 square km. It is located along the Trans-Canada Highway between New Glasgow and Antigonish in Nova Scotia.A railway and power
In 2017, Northern Shield, through wholly-owned subsidiary, Seabourne Resources, signed an option agreement with prospector, Patrick Bellefontaine that gives the Company the right to acquire up to an 80% interest in the Shot Rock Gold Property. Under the terms of the Option Agreement, Seabourne Resources can earn a 50% interest in the Property by incurring $500,000 in expenditures on the Property within two years. The Option Agreement also contains cash payments totalling $50,000 and share issuances totalling 650,000 Company shares to the prospector over three installments during the initial two-year period.
Over an additional two-year period, Seabourne Resources can increase its interest to 80% by incurring an additional $1.5M in expenditures, while making an additional $50,000 in cash payments and issuing an additional 500,000 Company shares to the prospector.
The prospector will retain a 1% NSR of which half (0.5%) can be bought back by Northern Shield for $1M.
Exploration commenced at Shot Rock in June 2018. The initial phases focused on stream sediment sampling while at the same time getting a better understanding of the geology of the area. The stream sediment sampling results:
- confirmed the presence of anomalous gold in the streams in the Barney’s River South area, where historic sampling in the 19070s had identified highly anomalous gold in heavy mineral concentrate samples;
- identified highly anomalous gold in what is now termed the Highway Zone where the two highest gold assays (1,015 and 1,045 ppb Au) from the stream sediment sampling program are located;
- identified several other areas anomalous in gold and/or pathfinder elements often associated with epithermal systems.
Prospecting in the Highway Zone to follow-up on the gold-anomalous stream sediment samples identified a number of angular float samples of quartz vein material exhibiting classic low sulphidation epithermal textures including colloform and crustiform banding, bladed carbonate, comb textured quartz with jasper infilling and brecciated colloform chalcedonic quartz with japer fragments and selvages. Many of the rock samples of quartz vein material from the area returned anomalous gold assays (>25 ppb) with a high of 3.3 g/t Au. Further prospecting led to the discovery large 0.5 meter wide, colloform banded quartz veins in outcrop and zones of stockwork-style epithermal quartz veins. Samples from the stockwork outcrop assayed up to 0.95 g/t Au.
The gold mineralization is found within quartz veins exhibiting textures consistent with those from known epithermal systems. Textures observed include crustiform and/or colloform banding, bladed calcite locally pseuomorphed by quartz, comb texture and other void fillings. The outer margins of the veins are often jasper and barite-rich. Although studies on these textures are on-going, the mineralogy would suggest a relatively high erosional level of the vein system.
Epithermal veins are known to exhibit strong vertical zonation in gold grades and associated elements. Particularly, gold may only show very weak enrichment (few tens of ppb) high in the system above the boiling zone, but can increase significant downwards within and below the boiling cap. If the current erosional level of the vein system is indeed proven to be relatively high at the Highway Zone, then the gold grades observed to date are suggestive of a much richer system at depth.
To date, outcrop and boulders of epithermal quartz veining, along with alteration, pathfinder elements and preliminary geophysical interpretation suggest a strike-length of the system of over 4 kilometers and open at both ends. The overall system trends E-W but large veins are also seen in NNW trending dilatant structures and stockwork zones are seen to trend ENE in the eastern portion.
Compilation Map of the Highway Zone showing the footprint of the low sulphidation epithermal gold system based on sampling, geology and preliminary geophysical interpretation.
The Shot Rock Property is located in the Antigonish Highlands, along the southern margin of Avalonia, a fault-bounded terrane between the Meguma Terrane to the South and the Ganderia Terrane to the North throughout the northern Appalachian orogen. The following descriptions are mostly based on White (2012) are references therein.
The oldest rocks found within the Property are part of the Late Neoproterozoic Georgeville Group, including units from the Keppoch and James River formations. The Keppoch formation is composed mainly of rhyolitic to dacitic tuffs and flows while the James River formation in this area is mostly represented by laminated cherty siltstones and sandstones. The late Neoproterozoic Bears Brook formation overlies the Georgeville Group formations in what appears to be a somewhat conformable contact, at least within the area of the Property.
The rest of the Property is underlain by rocks from the Silurian Arisaig Group composed of shales, mudstone, siltstone and sandstone sequences (some fossiliferous) and red carbonate units and limestone. There are no known volcanic rocks nor sills and dikes associated with the Arisaig Group.
About Epithermal Gold
The following description is mostly based on a thorough compilation paper by Simmons et al. (2005), in which references to a large number of relevant papers can be found.
Epithermal systems have been and continue to be a very important source of gold and even more important source of silver. The typical orebody found in an epithermal system varies in shape, size and grade, and can easily be hidden underneath a blanket of barren alteration or even unaltered volcanic rocks. Deposit-size to district-size range from <10 km2 to 200 km2.
Drilling is crucial in exploring for epithermal deposits because surface features may not be representative of what is at depth.
Efficient exploration must include the integration of the following at every scale, from deposit to regional:
- Geological data – vein mineralogy and texture, patterns of hydrothermal alteration
- Geochemical data – patterns of dispersion
- Geophysical data – three dimensional signatures
Deposits form in the lower temperature, shallow portion (< 1.5 km depth and < 300° C) of a high temperature hydrothermal system.
This type of hydrothermal system most commonly develops in association with magmatic sequences of andesite, dacite and rhyolite of calc-alkaline and alkaline affinity, which are related to volcanic arc at convergent margins, intra-arc, back-arc and postcollisional rift settings. Au-rich deposits (low Ag/Au ratio) are also found in tholeiitic bimodal (basalt-and rhyolite) systems.
The mineralization develops in zones of high permeability within the volcanic rocks genetically related to the hydrothermal system and in the older basement rocks below them. Steep dipping veins are generally host to the highest-grade ore. Lower-grade but potentially high tonnage ore can also be found in breccias, coarse clastic rocks and intensely leached rocks.
Epithermal deposits are historically classified based on either:
- Alteration and gangue mineral assemblages
- Metal content
- Sulphide content
- Sulphide mineral assemblages
The first is generally preferred because potentially high degree of oxidization of the ore can make the other three methods difficult.
Two main types or mineral assemblages reflecting pH of hydrothermal solutions are recognized:
1. Mineralization associated with quartz ± calcite ± adularia ± illite
- Au-Ag, Ag-Au or Ag-Pb-Zn
- Au and Ag in electrum, acanthite, silver sulfosalts, silver selenides and Au-Ag tellurides
- Sphalerite, galena and chalcopyrite generally minor but occasionally dominant
- Quartz is main gangue, other minerals are chalcedony, adularia, illite, pyrite, calcite and/or rhodochrosite (in Ag-base metal rich deposits)
- Banded, cruciform-colloform textures, lattice textures of platy calcite and their quartz pseudomorphs
- Hydrothermal alteration is zoned from bottom to top:
- Deep regional propylitic
- Increasing amounts of clay, carbonate and zeolite minerals
- Proximal enveloping orebody is quartz, adularia, illite and pyrite
- Mineralization can be concealed under a regional alteration blanket of clay-carbonate-pyrite or kaolinite-alunite-opal ± pyrite
2. Mineralization associated with quartz ± alunite ± pyrophyllite ± dickite ± kaolinite
- Au ± Ag ± Cu ores
- Au and Ag as native gold and electrum
- Variable amounts of pyrite, Cu-bearing sulphides (mainly enargite, a high sulfidation indicator) and sulfosalts, sphalerite and telluride minerals
- Main gangue is massive and vuggy quartz and alunite, other minerals are kandite minerals (dickite and/or kaolinite) and/or pyrophyllite
- Hydrothermal alteration forms concentric envelops, from inside out:
- Ore-hosting vuggy and massive quartz
- Alteration zone of quartz and alunite, dickite ± kaolinite or pyrophyllite and illite or smectite
- Regional propylitic alteration
- Zone of illite or pyrophyllite alteration may occur in the roots below deposit
Hibbard, J P, van Staal, C R, Rankin, D W, Williams, H. 2006: Lithotectonic map of the Appalachian Orogen, Canada-United States of America. Geological Survey of Canada, "A" Series Map 2096A, 2 sheets, https://doi.org/10.4095/221912
Simmons, S.F., White, N.C. and John, D.A., 2005. Geological characteristics of epithermal precious and base metal deposits. Economic Geology 100th Anniversary Volume, pp. 485-522.
White, C. E. 2012: Preliminary geology of the Antigonish Highlands, northern mainland Nova Scotia; in Mineral Resources Branch, Report of Activities 2011, ed. D. R. MacDonald and E. W. MacDonald; Nova Scotia Department of Natural Resources, Report ME 2012-001, p. 75-91. https://novascotia.ca/natr/meb/data/pubs/12re01/12re01_14White.pdf
General geology of the Shot Rock area (modified from White, 2018) with gold anomalous stream sediment samples collected by Northern Shield in 2018 shown in yellow dots and historic heavy mineral concentrates (HMC) shown by yellow stars.
Recently collected samples exhibiting variably banded epithermal quartz veins from Shot Rock.
Banded and brecciated quartz vein with possible ginguro band and fragments of acid altered wall-rock.
Quartz vein hosting bornite, chalcopyrite and other sulphides.
Acid alteration of wall-rock of bornite bearing quartz vein.
Recently discovered colloform banded quartz vein in excess of 1 meter thick.