The Boya West Hill prospect is primarily a tungsten-molybdenum porphyry-skarn deposit, situated in the Boya 7 claim, on the northwest corner of a triangular hill, 11.5 kilometres north-northeast of the confluence of the Turnagain and Kechika rivers (Assessment Report 7252, Figure 4N).
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).
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 West Hill showing; another occurrence, the Boya Main Face (094M 021), deals with the Main Face showing 3.5 kilometres to the southeast. A smaller showing, on ‘Paint Can Hill’, occurs approximately halfway between them and is described briefly here, at the end.
The West Hill area, which including the nearby Night Hawk Hill measures approximately 600 square metres, consists of massive limestone underlain by interbedded shales, siltstones and quartz sandstone, and minor carbonate (Assessment Report 7252). These rocks have been variably metamorphosed due to the intrusion of dykes, sills and small stocks of medium-grained quartz-biotite-feldspar porphyry, and quartz porphyry. The aphanitic groundmass in these rocks contains abundant potassium feldspar, were unaltered. Most porphyries are composed of quartz monzonite or granodiorite, whereas more leucocratic varieties are aplitic and only weakly porphyritic (Assessment Report 7252). The age of the intrusions is unknown but they may be Mesozoic (Assessment Report 7252).
The stratified rocks are quite strongly deformed, shown by numerous minor folds with subvertical axial planes and foliation (Assessment Report 7252). The foliation, and bedding and compositional banding in the limestone, all generally strike north-northwest and dip very steeply.
A thermal aureole is developed around the porphyritic intrusions in the West Hill area, extending southeastwards towards the Boya Main Face area. It is marked by hornfelsing, hydrothermal alteration and mineralization. The shales and siltstones have been converted to purplish-brown biotite hornfels and the main limestone contains marble and bands of coarse-grained pyrrhotite-diopside-quartz skarn. Locally, these skarn zones cut across bedding in the limestone, indicating a metasomatic origin (Assessment Report 7252). Between the limestone and the hornfels is a narrow zone of 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).
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, both in the porphyries and in fractured and altered metasediments. The quartz or quartz-carbonate veins are typically 2 centimetres thick but may be much thicker. The density of veining ranges from sparse to 'swarms' of quartz veins, constituting up to 50 per cent of the rock volume. Most veins strike east-northeast and dip steeply.
Probably the main mineralization in the West Hill-Night Hawk Hill areas occurs in diopside-quartz skarn in marble or porcellanite, where lenses up to 3 metres wide of massive to semi-massive pyrrhotite contain traces of extremely fine grained scheelite and chalcopyrite (Assessment Report 7252). Values of tungsten and copper are low, however, averaging (5 assays) approximately 0.09 per cent tungsten trioxide and 0.13 per cent copper (Assessment Report 7252). Two other outcrops of diopside-quartz skarn occur on the southwest side of West Hill, near a small intensely quartz-veined porphyry body. These skarns contain disseminated pyrrhotite and significant molybdenite, with lesser chalcopyrite and scheelite (Assessment Report 7252).
Diamond drilling was done to test the extent and grade of the tungsten-molybdenum mineralization and porphyry alteration (Assessment Reports 7431, 8008, 8024, 9299). The drilling intersected variably altered, fractured and quartz-veined porphyries; hornfelsed metasediments and skarn. Pyrrhotite and pyrite is locally strong but scheelite and molybdenite are erratic and generally only weak to moderate. In addition, minor or trace amounts of arsenopyrite, sphalerite, galena and bismuthinite were found in the drillcore. Assays ranged up to only 0.64 per cent molybdenum disulfide and 0.38 per cent tungsten trioxide (Assessment Reports 7431), and most are much lower. A 6-metre-long interval in hole B-7-79 intersected strong zinc and lead mineralization (Assessment Report 8024).
Paint Can Hill, 1.5 kilometres southeast of the West Hill, 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. 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).
