Sault and District Prospectors Association
Eagle River Mine Fieldtrip
River Gold Mines Ltd., Mishisbishu Lake Area, Wawa
The Plan.....
At our last couple of meetings we had some discussion about where we should go on our annual fieldtrip. It came down to a choice between either Hemlo Gold Mines or River Gold Mines and after a show of hands it became pretty clear most were interested in River Gold. The question was really whether we'd be able to manage an underground tour of the Eagle River Mine. Everything rested on the number of participants, so it was decided we would focus on a surface tour and depending on the numbers we'd try to wrangle an underground trip. It had been suggested that two bottles of Scotch could do the trick, so after minor deliberation on who was to do what, Bud Clavet opted to buy the alcoholic refreshments, while Viv would acquire munchies and other food stuff.. Unlike the last couple of years, our rental van driver was not available, so we doubled-up and made our way up to Northern Lights Motel near Wawa in separate vehicles and then early the next morning, made our way into the Mishibishu Lake area.
Good Timing....
By good fortune the timing of the fieldtrip could not be better. Drifting on the 540 metre level had intersected the two high-grade zones discovered during development drilling in 2003. These new ore zones had values of up to 146 g/t over 4.7 metres and 107 g/t over 5.5 metres. These kinds of ore grades along with some tid bits of information about a new 'style' of high-grade gold mineralization occurring within a breccia, made us keenly interested in picking up a few samples and seeing for ourselves.
A little bit of history....
The Mishibishu Lake area was quite active during the late 1980's with much of the greenstone belt staked and actively explored for gold. As a result of the exploration effort, several gold deposits were discovered. The Magnacon deposit was brought into production in 1989 and a gold mill built to process the ore. Just to the west of Magnacon, the Mishi deposit was delineated and a small open pit was developed. Fifteen kilometres south of the Magnacon and Mishi deposits, the Eagle River deposit was discovered and developed. In the early 1990's the price of gold floundered and the mines and mill were shut down.
In 1994, River Gold Mines Limited was created to consolidate ownership and bring the Eagle River Mine into production. Most recently, River Gold has brought the Mishi deposit into production and has dewatered the Magnacon Mine with the intent of increasing additional ore reserves.
A little bit of geology....
On our arrival at the mine site we were met by George Mannard, Vice President, Exploration for River Gold Mines Ltd. We circled around the drafting table while George gave us a detailed overview of the mineralized zones, where we were going, and the kinds of assays that had been found within the areas under development.
We then headed off to the core shack where both George and Charlie gave an overview of the geology and the exploration being done on their large property holdings. The drill core on display was a section through the new 818 Zone
Notably, the mineralized shear zone hosting the Eagle River gold deposit extends well past the east and west ends of the diorite stock - into the greenstones. Some interesting gold prospects have been discovered, including a mineralized iron formation to the west and gold-bearing quartz veins to the east.
A little bit about Eagle River gold ore:
The Eagle River orebody consists of a series of near vertically dipping quartz veins and lenses hosted mostly in a sheared diorite host rock. The ore zones consist of thicker sections of veins and lenses which plunge steeply to the east. The veins have been traced over a strike length of 2.5 kilometres and to a depth of 650 metres.
Typically the vein-type ore consists of quartz veins separated by schistose sections of sheared diorite. Sulphide minerals generally occur along the quartz-schist contact and these appear to contain the higher grades of gold.
Most recently a new ore type was discovered, referred to as breccia-type ore, consisting of variable-size fragments of sheared and mineralized vein material contained within a quartz-calcite-Kfeldspar matrix. The mineralized breccia has only been found in the lower levels of the deposit and appears to occur as breccia veins in close association with the main vein-type ore.
Underground at the Eagle River:
One would have thought that we were about to enter the Sudbury Neutrino Observatory after donning our white coveralls and all the underground paraphernalia. After posing for a few pictures, we stepped into a couple of rather comfortable U/G personnel vehicles and headed down the ramp.
For some of the SDPA members it was their first time underground (Vivienne counted the number of turns the vehicles took and in which direction). As soon as we were out of the trucks everyone took to the U/G like ducks to water - and there was lots of it! At the 540 metre level the mine is about 350 metres below Lake Superior.
The 818 Zone:
The 818 Zone is dominated by breccia-type ore, containing fragments ranging from a few centimetres in size up to a metre. Fragments at various sizes have a 'splintered' appearance, having been broken along their length or shear fabric and then variably rotated. These zones of brecciation are also characterized by the presence of disseminated epidote alteration which is noted in drill core as the wall rocks and the mineralized breccia are intersected.
Other breccia veins were noted within the 818 Zone consisting of wall rock fragments contained in a predominantly calcite matrix with associated hematite-rich seams. This secondary breccia type forms large cavities and its relationship to the mineralized breccia-type ore is uncertain (Keweenawan age?).
The 650 Zone:
The 650 Zone is more typical of the classic vein-type ore that has provided the main stay for River Gold Mines for the last 8 years producing 517,000 ounces of gold from 1.8 million tonnes of ore at a recovered grade of 9.1 grams of gold per tonne. Proven and probable reserves at Eagle River currently stand at 1,268,000 tonnes at 10 grams per tonne.
High-grade intersections of 146 g/t over 4.7 metres and 50 g/t over 2.3 metres in the 650 Zone attest to the continued richness of the gold mineralization with depth and the longer term viability of this gold mine.
The Surface Tour
When it comes to access to the surface exposures of orebodies, you cannot find much better than a good access road directly over the surface expression of the 650 Zone. We simply drove up and stepped out of the vehicles - even the bugs were not that bad!
Here we had an opportunity to see how it all fits together. The folded and thickened quartz veins and lenses are contained within a shear zone which occurs at the contact between diorite and mafic volcanics. The 650 Zone is at the eastern edge of the diorite stock which hosts most of the vein system.
It is possible to walk from south to north through unsheared mafic volcanic rocks, to sheared mafic volcanic, folded quartz veins with sheared slivers of diorite and/or mafic volcanic, to sheared diorite and then unsheared diorite. A good lesson in geology!
The Eagles Nest
After such an 'exhaustive' day in the field, George Mannard invited us to share in some refreshments at the Eagles Nest. This is the location at the top of the hill where the original drill program was completed by Hemlo Gold Mines. Much of the drill core is still at the site. The small cottage has a spectacular view of Lake Superior with Miichipicoten Island in the distance.
Folks may not remember, but the nearest comparison to the Eagle River gold deposit both in size and style of mineralization in the Wawa area was the Renabie Mine. The Renabie produced over 1 million ounces during its lifetime which spanned over 25 years.
With the hard work and dedication evident in River Gold's mining and exploration team and the continuing resilience of the ore body, we can expect to see River Gold Mines Ltd. live long and prosper.
Source: https://sites.google.com/site/sdpaopa/activities/eagle-river-mine-fieldtrip
