Gold mineralization in Lower Cambrian McNaughton Formation, Athabasca Pass, Canadian Rocky Mountains: structural, mineralogical, and temporal relationships

Abstract

Gold-bearing quartz veins were recently discovered in archimetamorphic quartzite–rudite and quartzite–pelite sequences of the Lower Cambrian McNaughton Formation in the main ranges of the central Canadian Rocky Mountains. There are two distinct vein types: an early syntectonic, syn- to postmetamorphic, auriferous, bedding-parallel type, generated during repeated northeast-directed compressive tectonism; and a late, postpenetrative deformational discordant type, which contains only minor gold (<500 ppb Au). Gold emplacement and discordant veining were confined to the onset of late compression leading to development of the Chatter Creek Fault.The spatial distribution and dimensions of the veins attest to mechanically founded lithologic anisotropy. Bedding-parallel veins are confined to less competent, volumetrically minor pelitic rock types. Discordant veins are confined to competent quartzitic units.Bedding-parallel vein filling took place in two paragenetic stages: a protracted, pre-gold stage (quartz ± minor white mica and pyrite) depositing over 90% of vein material; and a late gold-bearing–post-gold stage (quartz–pyrite–gold–galena ± white mica and Fe carbonate). Gold usually occurs in association with brecciated pelites and penecontemporaneous sulfides. Discordant veins (quartz ± minor pyrite) record a single stage of vein filling broadly coeval with gold deposition. Minor hydrothermal alteration (pyrite ± white mica ± carbonate) of adjacent wall rocks accompanied gold emplacement and is mineralogically congruent with the regional archimetamorphic and bedding-parallel vein assemblages.In terms of their setting and morphology, the Athabasca Pass gold lodes are viewed as a siliciclastic-hosted analogue of the turbidite-hosted class of gold deposits. Principle geochemical differences from published process models for turbidite-hosted gold deposits are a function of the mineralogical maturity of the siliciclastic host strata in the Athabasca Pass.

A fluid inclusion study of quartzite-hosted lode gold mineralization at Athabasca Pass, Central Rocky Mountains, Canada

“…However, it is noteworthy that P-T constraints proposed above are in agreement with the broader constraints imposed by the regional pumpellyite to lowermost greenschist facies conditions (ca. 200 ø to 350øC and 1 to 4 kb; Turner, 1981;Kisch, 1987) under which the Athabasca Pass lodes are con- sidered to have been emplaced (Shaw and Morton, 1990). …”

“…Discordant veining was approximately coeval with gold emplacement; however, these quartz veins contain only occasional pyrite. It was postulated that pelite fragments contained within bedding-parallel vein structures played an important chemical role in gold deposition through the triggering of desulfidation reactions, accounting for the presence of gold uniquely within bedding-parallel veins (Shaw and Morton, 1990).…”

“…Information on lode gold deposits within this domain is lacking, the apparent first comprehensive documentation of gold lodes in this region being that of Shaw and Morton (1990). In that paper the structural, mineralogical, and paragenetic relationships of gold-quartz veins contained within the McNaughton Formation of the Athabasca Pass were established, and the hypothesis was forwarded that the Athabasca Pass lodes represented a quartzitehosted variety of the turbiditc-hosted class (Keppie et al, 1986;Hutchinson, 1987) of gold deposits.…”