Adanac molybdenum deposit, Surprise Lake, Atlin Mining Division, British Columbia, Canadai

Regional Level Types
Adanac molybdenum deposit	Deposit
Surprise Lake	Lake
Atlin Mining Division	Division
British Columbia	Province
Canada	Country

The Adanac molybdenum deposit is located near the headwaters of Ruby Creek, which drains into Surprise Lake, about 23 kilometres north-east of Atlin, British Columbia.

There is a lengthy description of the deposit and its history, on the British Columbia “Minfile” site, current to 2020, to which interested readers are referred. Brief excerpts are quoted below:
“The Adanac/Ruby Creek deposit is a disrupted, ring-shaped occurrence formed late in the development of a localized plutonic complex. It is associated with granitic to quartz monzonitic rocks of the Late Cretaceous Surprise Lake Plutonic Suite, east of Atlin.”
“The Adanac/Ruby Creek deposit consists of a stockwork of veins of molybdenite and quartz-molybdenite found in all the principal rock types. However, it is best developed in the early stage plutonic rocks (mafic quartz monzonite porphyry and coarse grained quartz monzonite and its variants) that overlie and surround the buried sparse quartz monzonite porphyry stock under the Ruby Creek valley. The veins are most commonly without other metallic phases, although pyrite is found locally and chalcopyrite has been observed. The veins locally contain traces of scheelite, orthoclase, fluorite, biotite, sericite and carbonate.”
“The mineralization commonly consists of sulphide veins, as coatings on quartz-free fractures and as coarse and fine rosettes and blebs in both smokey and lesser clear quartz. It also occurs as streaks and smears in deformed rock and may, locally, be enriched in fault zones. In the "higher-grade" zone explored by Kerr Addison, much of the mineralization is in horizontal to subhorizontal veins and fractures from 1 to 5 millimetres wide that are interspersed with veins that are considerably wider, up to 20 millimetres wide. The near-horizontal vein set is commonly cut by narrow 1 to 3 millimetre quartz veins that are oriented at a high angle to the (vertical) core axis. Both vein sets are mineralized and blebs of molybdenite commonly occur at the intersection of crosscutting veinlets.”
“The near-horizontal vein set is locally extremely well mineralized. Veins exposed through underground development in the 1970s show that coarse rosettes of molybdenite up to 30 millimetres in diameter formed in the plane of the vein, and that the spacing between the rosettes is variable, causing a pronounced "nugget effect" in drilling.”
“In December of 2007, Adanac Moly Corp. announced updated measured and indicated combined resources of 212,907,000 tonnes grading 0.063 per cent molybdenum . . . .”
The deposit has been described in detail by White, et al. (1976) and by Pinsent and Christopher (1995).
Comments by Giles Peatfield on some of the minerals reported from the locality:
Allanite: White, et al. (1976) noted that “In addition, allanite-rimmed epidote is most abundant in the medium-grained granite within the molybdenite zone.” There is no information regarding which of the many recognized varieties of allanite is represented.
Amphibole group: Sutherland Brown (1970) reported “hornblende” in the granodiorite of the Fourth of July Creek Pluton to the north of the deposit.
Apatite: Reported as an accessory mineral in alaskite by Sutherland Brown (1970).
Chalcopyrite: Reported by Christopher and Pinsent (1982) as a rare constituent of some quartz veins.
Chlorite group: White, et al. (1976) described “Weak propylitic alteration in the Ruby Creek deposit is defined by chlorite after biotite, . . . .”, but gave no specific data for the mineral. This lack of detail is common in the older literature. Sutherland Brown (1970) described the chlorite as “penninite”.
Epidote: See comment above for allanite.
Galena: Reported by Sutherland Brown (1970) from peripheral veins north of the deposit.
Ilmenite: Reported by Sutherland Brown (1970) in amphibolite gneiss (Cache Creek Group rocks) north of the deposit.
Plagioclase: Reported by several workers. Sutherland Brown (1970) described “andesine” in the amphibolite gneiss, intermediate plagioclase (An50-An34) in the granodiorite of the Fourth of July Creek Pluton to the north of the deposit, and oligoclase in the host-rock alaskite.
Powellite: Sutherland Brown (1970) reported “Clear yellow powellite . . . .”, but it is not clear whether he was referring to the colour of the mineral grains or the colour of fluorescence. Later workers, e.g. Pinsent (1981); Christopher and Pinsent (1982); and Pinsent and Christopher (1995) all reported scheelite, but none gave information regarding fluorescence. I would regard powellite as tentative and scheelite as more likely for the deposit.
Thorite: Reported by Pinsent (1981), and by Pinsent and Christopher (1995) who commented that “Electron microprobe data from the Geological Survey of Canada show that the element [U] is in the mineral thorite (S. B. Ballantyne and A. L. Littlejohn; pers. comm.).”
Titanite: Sutherland Brown (1970) reported “sphene” as a conspicuous accessory in the crowded porphyry phase of the alaskite pluton.
Wolframite group: Christopher and Pinsent (1982) reported “wolframite” in a quartz vein in drill core, but gave no compositional data. It is probable (but not definite) that the mineral is ferberite.
Zircon: Sutherland Brown (1970) reported zircon as an accessory in the Fourth of July Creek granodiorite.

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Link to British Columbia Minfile:	104N 052

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References