Summary:
The mineral deposits at Dome Mountain are structure-controlled orogenic (mesothermal) quartz-carbonate-sulphide veins with associated gold and silver mineralization. Controlling structures are east-west and northwest southeast trending brittle fault zones that dip moderately to steeply south and southwest. The host rocks are Lower to Middle Jurassic subaerial volcanic flows, pyroclastic, and related volcanoclastic rocks.
The most significant gold mineralization on the Dome Mountain Project is contained within five zones of the past-producing Boulder Vein System (listed in order of importance):
- Boulder Main Vein: This zone has a strike ranging from 090° to 100° and dips ranging from 45° to 70° south. The vein has been defined over a strike length of 440 metres from section 652,800 UTME to 653,240 UTME and a down-dip extent of more than 300 metres starting at the surface. The mineralized zone within the vein has a shallow easterly plunge with an average horizontal width of 2.4 metres, ranging from less than a meter to 21.2 metres. The majority of the 43,900 tonnes of past production came from this zone.
- Argillite Vein: The Argillite Vein is a splay off the Boulder Main Vein. It strikes at 120° and dips to the southwest at angles ranging from 35° to 50° and it appears to flatten along strike to the southeast. The zone is somewhat discontinuous over the defined strike length of 240 metres and a maximum down-dip extent of 90 metres. The mineralized zone in the vein has an average horizontal thickness of 3.2 metres, ranging from less than a meter to 8.0 metres.
- Boulder Footwall Vein: This zone is sub-parallel to the Boulder Main Vein and is located at the east end of the Boulder Vein System. It has been defined by drilling over a strike length of 550 metres from 653,300 UTME to 653,850 UTME and over a down-dip extent of approximately 200 metres. The zone has an average horizontal width of 1.9 metres, ranging from less than a meter to 15.4 metres. The zone is open down-plunge to the east and down-dip. Minor past-production came from this zone.
- Boulder West Hangingwall Vein: This vein is also sub-parallel to the Boulder Main Vein. It is a somewhat discontinuous vein with an overall strike length of 100 metres located between 652,960 UTME and 653,060 UTME and a defined down-dip extent of approximately 100 metres. It has an average horizontal width of about 2.4 metres, ranging from 1.8 to 3.8 metres.
- Boulder East Hangingwall Vein: This is a thin and somewhat discontinuous vein that occurs over a strike length of about 320 metres at the east end of and sub-parallel to the Boulder Main Vein.
Veins are characterized by quartz with lesser carbonate and sulphide mineralization. Massive quartz-carbonate veins lacking sulphides are typically barren with respect to gold and silver.
Quartz occurs as both as white, massive variety or as clear and associated with higher gold grades. Carbonate minerals (ankerite and calcite) occur as cream to beige crystals. Small scale folds in the veins attest to continued movement after their formation.
Sulphide minerals in the Boulder Vein constitute approximately 10% of the vein mineralogy. In decreasing order of abundance, the sulphide minerals are pyrite (6%), sphalerite (2.5%), chalcopyrite (1%), and galena-tetrahedrite-arsenopyrite (<1%). Pyrite occurs are fine euhedral cubic crystals disseminated throughout the wall rock alteration and quartz veins. Coarse masses of pyrite also occur as well as some individual pyrite crystals up to one centimetre wide. Often the pyrite crystals show evidence of crushing with the interstices filled with other sulphides. Aggregates of fine-grained reddish-brown sphalerite occur as irregular masses associated with pyrite, galena, chalcopyrite and arsenopyrite. Chalcopyrite is commonly intergrown with pyrite. Fine-grained tetrahedrite, galena and arsenopyrite occur as disseminations, as thin fracture coatings, or as fine irregular masses with the other sulphides (Hanson, 2013).
Even though gold grades as high as several grams per metric tonne are present, visible gold is rare. Microscopic examination indicates that the gold usually occurs as minute grains along the pyrite crystal margins and in microfractures within the pyrite crystals. Metallurgical testwork indicates an average grain size of 25 microns. Gold may be present as electrum since gold analyses indicate contents of 18% to 23% silver.
Silver values up to 500 grams per tonne have been reported from core assays although no silver minerals have been identified. It appears that the silver values reflect the abundance of galena and tetrahedrite as indicated by an analysis of tetrahedrite that contained 2% to 4% silver (Hanson, 2013).
In addition to the past producing Boulder Vein System, gold mineralization at the Dome Mountain Project is present at twelve separate locations: Free Gold, Forks, 9800, Ptarmigan, Elk, Eagle, Gem, Raven, Hawk, Chance, Hoopes, Jane, Cabin, and Pioneer. The Free Gold and Forks zones are classified as past producers by the B.C. Government Minefile database while the others are listed as either prospects or showings. The Cabin Vein is considered to be the westward extension of the Boulder Vein.
The veins occur in a roughly northwest-southeast 12-kilometer trend from southeast of Dome Mountain to Mt. McKendrick. This trend may reflect the presence of a deep-seated structure. A modest amount of diamond drilling has been conducted on the various veins but to date no minerals resources have been defined.