The Boya Main Face prospect is primarily a tungsten-molybdenum porphyry-skarn deposit, situated in the southeast corner of the Boya 1 claim, on the east flank of a triangular hill, 11 kilometres northeast of the confluence of the Turnagain and Kechika rivers (Assessment Report 7252, Figure 4S).
The Boya claims are located over a patchily mineralized area of several square kilometres, exposed on the hill, which rises above generally subdued terrain of the Rabbit Plateau. The area is just northeast of the Northern Rocky Mountain Trench, and the hill is underlain by Cambrian and Ordovician rocks, and possibly some Upper Proterozoic rocks, belonging to Ancestral North America (Geological Survey of Canada Maps 46-1962, 1712A, 1713A).
The geology is complicated in detail. Essentially, it consists of siliciclastic, carbonate and volcanic rocks, which have been intruded, metamorphosed and skarnified by possibly Mesozoic quartz-rich porphyritic intrusions. As well as tungsten skarns, mineralization consists of quartz-vein stockworks carrying molybdenite and scheelite.
There are several showings in the area. Two MINFILE occurrences have been assigned to cover the most important of them. This occurrence deals with the Main Face showing; the Boya West Hill (MINFILE 094M 016) occurrence, deals with the West Hill showing 3.5 kilometres to the northwest. A smaller showing, on ‘Paint Can Hill’, occurs approximately halfway between them and is described briefly here, at the end.
The Main Face area measures roughly 600 by 300 metres, and consists of a sequence, at least 490 metres thick, of quartzite, calcareous shale, siliceous shale, siltstone, sandstone and massive limestone and marble (Assessment Report 7252). Included in the upper portion is a 40-metre-thick volcanic subunit, comprising amygdaloidal andesitic flows, volcanic breccia and thinly bedded tuffaceous rocks. Bedding generally strikes 010 degrees and dips between 20 and 60 degrees west. Folding is not as evident as elsewhere on the property. These stratified rocks are intruded by dykes, sills and small stocks of medium-grained quartz-biotite-feldspar porphyry. The aphanitic groundmass in these rocks contains abundant potassium feldspar, where unaltered. Most porphyries are composed of quartz monzonite or granodiorite, whereas more leucocratic varieties are aplitic and only weakly porphyritic (Assessment Report 7252).
A thermal aureole is present in the stratified rocks around the intrusions, which is marked by contact metamorphism, hornfelsing and recrystallization, hydrothermal alteration and mineralization. One of the most common products is a finely banded quartz-diopside calc-silicate rock known in the area as ‘porcellanite’, probably derived from limy shale or siltstone (Assessment Report 7252; Fieldwork 1979). Several outcrops of this rock contain layers of pyrrhotite-chalcopyrite-scheelite mineralization, a select grab sample of which assayed 0.11 per cent copper and 0.15 per cent tungsten trioxide (Assessment Report 7915, page 11). This mineralization also occurs in a volcanic layer elsewhere (Assessment Report 7252, Figure 6). Locally, coarse-grained garnetiferous skarn in limestone or marble units carries disseminated or semi-massive pyrrhotite and lesser chalcopyrite, molybdenite and scheelite. Molybdenite occurs locally in the porphyry.
Hydrothermal alteration is widespread, in the form of progressive chloritic and carbonate-sericite alteration. It is strongest in the intrusions but also affects the metasediments, particularly where they are fractured.
Quartz stockworks and veins are common at the Main Face, both in the porphyry intrusions and the altered metasediments, and they host probably the most significant mineralization, namely molybdenite. This occurs notably in two places, mainly in the porphyry but extending into the surrounding porcellanite and other metasediments. Molybdenite occurs as continuous thin streaks in 'ribbon veins' or as fine selvages in veinlets. The strongest molybdenite is generally accompanied by a smaller amount of scheelite. Coarse rosettes of molybdenite do not occur. The quartz or quartz-carbonate veins are typically 2 centimetres thick, but may be much thicker, and strike west-northwest and dip vertically. In some places there are 'swarms' of quartz veins, constituting up to 50 per cent of the rock volume. More 'delicate' quartz stockworks host fine-grained scheelite and molybdenite. Sampling of this material suggests that the tungsten content is erratic and probably does not exceed 0.1 per cent tungsten trioxide over appreciable widths.
Diamond drilling was done to test the extent and grade of this mineralization and porphyry alteration (Assessment Reports 8008, 8024, 9299, 9532). Samples of drillcore yielded low assay values, no more than 0.2 per cent molybdenum disulfide and 0.55 per cent tungsten trioxide (Assessment Report 8008); most are considerably less.
Other quartz veins at the Main Face may contain abundant pyrite, minor molybdenite, scheelite and chalcopyrite, and traces of galena, sphalerite, bismuthinite, chalcopyrite and arsenopyrite (Assessment Report 7252, Fieldwork 1979).
Paint Can Hill, 2 kilometres northwest of the Main Face, is a small area of massive limestone and marble, with bands of coarse-grained garnetiferous skarn (Assessment Report 7252, Figure 4N). There is at least one quartz-feldspar porphyry dyke exposed. The marble contains a zone of 10 metres by 30 centimetres with semi-massive mineralization consisting of arsenopyrite, pyrite, sphalerite, chalcopyrite and traces of scheelite. Diamond drilling indicated only very weak mineralization in this area (Assessment Report 9532).
In 1996, Tizard Explorations Inc. completed aerial magnetic and very low frequency-electromagnetic surveys, and a follow-up soil sampling program. Sampling yielded only scattered chemical anomalies, and Tizard Explorations did not recommend further work in their report (Assessment Report 25281).
In 2010, Strategic Metals Inc. evaluated the property predominantly for its gold potential, working on a model of comparison to their Rau property in Yukon. During a brief property visit, 15 rock grab samples and 41 soil samples were collected. Rock sample G006210 yielded 0.720 grams per tonne gold and 0.1540 per cent zinc. Additional work was recommended to better assess the character and extent of mineralization (Assessment Report 31559).
In 2011, Archer, Cathro & Associates conducted a four-day prospecting and geochemical sampling program on behalf of Precipitate Gold; a total of 409 soil samples and 11 silt samples were collected from newly staked parts of the property. The program yielded moderately anomalous values for gold (up to 88 parts per billion), very elevated values for silver (up to 2.39 parts per million) and zinc (up to 2160 parts per million) and slightly elevated values for copper (up to 80.6 parts per million; Assessment Report 32846). In addition, a biogeochemical survey was conducted across the property’s Main Skarn area, targeting white spruce tree twig tops. 14 samples were collected and results corroborated several important metallogenic relationships observed in other sample sets (Assessment Reports 32846, 33974).
