RED LAKE GOLD ORE
The rock shown below leaves me speechless, in terms of
its gold content and beauty. This is a sample of extremely high grade
gold ore from the richest gold mine on Earth - northwestern Ontario's Red
Lake Mine.
The rocks and mineralization features in this area are
fairly complex. The host rock here is a metamorphosed tholeiitic basalt
dating to ~2.85 billion years (early Neoarchean). This basalt has been
subjected to biotite-carbonate alteration and auriferous silicification.
In addition to gold, the sample has a fair amount of biotite, some carbonate
(it fizzes in acid), and many small, black rods of tourmaline. It also
has patches of glassy gray quartz.
Geologic Provenance: extremely high-grade gold ore, possibly from the HWA
Vein (Hanging Wall A Vein), upper High Grade Zone (HGZ; a.k.a. Goldcorp
High Grade Zone), Balmer Assemblage, Red Lake Greenstone Belt, Uchi
Subprovince, Superior Province.
Age:
~2.85 billion year host rock (altered basalt) with hydrothermal metamorphism
and gold mineralization at 2.712-2.723 billion years (during collision-related
emplacement of several nearby igneous intrusions - Uchian Phase of the Kenoran
Orogeny) & at 2.63-2.66 or 2.699 billion years (during a regional
thermal event or another igneous intrusive event).
Comment:
the sample shown below is very similar to those shown in figures 18 and 19 of
Dubé et al. (2001, The Goldcorp High Grade Zone, Red Lake Mine, Ontario: a
photographic atlas of the main geological features. Geological Survey of
Canada Open File 3890), which illustrate extreme high grade gold ores from
Red Lake Mine's level 34.
Locality:
unrecorded locality in the Red Lake Mine, northeastern side of Balmertown, just
south of Balmer Lake, Campbell-Red Lake Gold District, northwestern Ontario,
south-central Canada.
Red Lake Gold Ore (6.6 cm across at its widest) - highly concentrated
network of gold-filled veinlets (gold veinlet stockwork) in biotite-carbonate
altered, partially silicified metabasalt. Black = altered basalt;
whitish-gray = quartz; gold = native Au. The crusts of gold are Au-filled
fractures broken along the plane of the veinlets. Other Au-filled
veinlets can be seen in cross-section view (see lower left side in above photo
& left side in photo below).
Red Lake Gold Ore (field of view 2.4 cm across) - highly concentrated
network of gold-filled veinlets (gold veinlet stockwork) in biotite-carbonate
altered, partially silicified metabasalt. Rocks from the Goldcorp High
Grade Zone average about 80 to 81 ounces of gold per ton of rock.
Some info. generously provided by geologists Chris
Osiowy & Paul Barc (Red Lake Gold Mines).