Flin Flon - Snow Lake Region Deposits and Mining

Copper-Zinc-Gold-Silver resources of the Flin Flon, Snow Lake region (West-Central Manitoba)

Introduction

Manitoba has significant mining operations centred on the communities of Bissett, Thompson, Flin Flon-Snow Lake, Leaf Rapids and Lynn Lake. However, world-class volcanogenic massive sulphide (VMS) deposits of copper, zinc, gold, and silver have been mined in the Flin Flon and Snow Lake areas for over 100 years. Through the years, with the help of advanced geological/geophysical technologies many new mineral deposits have been found.

In nature, metallic ore bodies typically occur as sulphides and/or oxides interspersed within rock. Sulfides are compounds of a metal ion bonded with sulphur, such as galena (PbS); sphalerite ((Zn,Fe)S); and pyrite (FeS2). Alternatively, oxides are a metal ion combined with oxygen, such as cuprite (Cu2O); and hematite (Fe2O3). Few elements occur in nature uncombined, such as native gold or copper. When concentrations of these minerals in rock are high enough that they can be extracted at a profit, the rock is called ore. Ore bodies at or near surface can be mined by open-pit methods.

In Manitoba, copper-zinc production is primarily related to ancient subaqueous volcanic activity and are referred to as volcanogenic massive sulphide (VMS) deposits, such as first discovered at Flin Flon in 1914. The open pit Mandy mine near Flin Flon was in operation by 1918 and the ore was transported by barge from Sturgeon Landing (shown in Photos 1 & 2 below) to The Pas from whence it was shipped by rail to a smelter at Trail, BC.

Photo No. 1 - Mandy Mine Schist Lake Open Cut No.1, Photo Courtesy of Bill Brisbin collection.

Photo No. 2 - Mandy Mine Ore dump and barge loading at Sturgeon Landing, Photo Courtesy of Bill Brisbin collection.

In 1922, a copper-zinc deposit was discovered north of Flin Flon at Cold Lake, now known as the community of Sherridon. By 1951, the ore at Cold Lake was depleted, and the owner (Sherritt Gordon Mines Limited) moved all the infrastructure 190 km north to Lynn Lake. Copper and zinc deposits were found at Fox Lake southwest of Lynn Lake and at Ruttan, east of Leaf Rapids in 1960. The Fox Mine operated from 1970 to 1985 producing 12-million tonnes, whereas the Ruttan Mine began production in 1973 and closed in 2002 after producing 55-million tonnes. (1)

Where an ore body occurs at depth and cannot be reached by an open pit, it is mined by underground methods. A vertical shaft is sunk, and sub-horizontal tunnels are driven from the shaft at planned intervals to break and haul the ore efficiently to surface. There, it is transported to a processing facility to be crushed and concentrated. One such mine is the Hudbay Minerals Inc. 777 (also know as Triple 7) deposit beneath the town of Flin Flon. The deposit is a large copper-zinc-gold-silver ore body that was discovered in 1993; it reached full production in 2004 and is slated to operate until 2022.

In the 1950’s copper-zinc-gold-silver mineralization was discovered in the Snow Lake area and the ore has been mined using open pit and underground methods. Today, Lalor is the only operating mine in this portion of the district.

The most important tools to detect conductive rocks at depth are airborne geophysical survey systems tracked by computer and geographic positioning systems (GPS). Helicopters equipped with a time-domain electromagnetic (TEM) system along with a magnetometer can fly low and slow to provide information about the location and orientation of subsurface features such as dykes, folds and fault structures. This map combined with conductor anomalies mapped by airborne electromagnetic (EM) survey results provide leads for more detailed ground exploration. The interpreted surface targets of interest are ultimately tested by drilling. The number of drill holes often correlates with the number and quality of new discoveries.

Geology and mineral exploration in the Flin Flon belt

To date, more than 156-million tonnes of sulphide ore has been mined from 29 VMS deposits. The deposits have a well-documented association with the 1.92-1.78-billion-year-old arc volcanic rocks. So, understanding their geology and geochemistry provides a powerful predictive tool for exploration. Exceptionally high gold contents of many of the deposits make them especially attractive exploration targets.

The recent discovery of high-grade zinc-copper-gold mineralization below a depth of 1000 m in the Pine Bay area (west of Snow Lake) further demonstrates the exceptional exploration potential in the region. Significant ore bodies in the Flin Flon domain and the details about past producers, current producers and advanced projects are shown in Figure 1 and Table 1, respectively. The exposed portion of the Flin Flon domain is approximately 250 km from east to west, 75 km from north to south and extends up to 150 km south beneath a thin, geophysically transparent layer of Paleozoic sedimentary rocks. The sub-Paleozoic portion of the favourable domain is at least twice the size of the exposed portion and is thought to have similar mineral potential. Exploration in this portion of the Flin Flon domain has led to several high-grade VMS discoveries, including the past producing Reed Lake and Tower deposits.

Figure 1 - Geological map of the Flin Flon domain (Manitoba Geological Survey, 2017)

Table 1 - Ore Inventory of different VMS deposits in Manitoba(Manitoba Geological Survey, 2017)

   Abbreviations used in Table 1: 
   g Ag/t, grams silver per tonne; g Au/t, grams gold per tonne; Mt, million tonnes; P, producer; PP, past-producer; AP, advanced project 

  The current important producers in Table 1 are:
  * Triple 7 (777) and
  * Lalor (Hudbay Minerals Inc.) 

  The Advanced Projects are:
  * Tower (Rockcliff Metals Corp): 2.4 Mt resource
  * Talbot (Hudbay Minerals Inc., Rockcliff Metals Corp.): 4.2 Mt resource 
  * Rail (Rockcliff Metals Corp.): 0.8 Mt resource

The amount of drilling (number of drill holes and their depths) has a statistical correlation with the new discoveries shown in the graph of Figure 2 below. One can notice that most of the prolific deposits have been discovered and confirmed by large amount of drilling (in excess of 50,000 m often involving more than 50 drill holes).

Figure 2 - Discoveries verses amount of drilling in metres, (1950-2007 Hudbay, 2009)

Role of the Professional Geologist (P. Geo)

Kelly Gilmore, P. Geo- Geologist was part of Hudson Bay Exploration & Development Company Limited (a subsidiary of Hudbay) team of geologists that won the Bill Dennis award from the Prospectors and Developers Association of Canada (PDAC) in 2000 for its discovery of the 777, Konuto Lake and Photo Lake mines. The 777 mine, located in Flin Flon, has been Hudbay's flagship mine for many years. Hudbay minerals received the PDAC award a second time in 2009 for its discovery of the Lalor deposit in the Snow Lake area. Hudbay’s innovative adoption of electromagnetic geophysical surveys by Alan Vowels, P. Geo-Geophysicist for deeper exploration led to the discovery of the Lalor deposit. Located in the Chisel basin portion of the Flin Flon domain, the Lalor deposit is believed to be one of the largest VMS deposit found in the Flin Flon- Snow Lake region to date.

Despite nearly a century of systematic exploration, new high-grade VMS discoveries continue to be found in the Flin Flon-Snow Lake domain, including the world-class Lalor deposit of Hudbay Minerals Inc., which came into production in August 2012. The total resource at Lalor estimated at that time stands at over 27 -million tonnes grading 0.9% Cu, 5.1% Zn, 2.8 g/t Au and 28.2 g/t Ag, further demonstrating the exceptional potential of the region. Announcing the results, the company President Allen J. Palmiere said that data herein and contents of news releases have been verified by Kelly Gilmore, B.Sc., P. Geo, Chief Exploration Geologists, who is a “Qualified Person” within the meaning of NI43-101. This example is shown to provide an overview of the entire process from ore discovery to mining, crushing and final production of metals illustrated in Figures 3, 4 & 5. (2)

Figure 3 - Production Shaft with Head Frame and Surface Infrastructure at Lalor, 2015

An underground ramp was extended from the Chisel North mine to intersect the Lalor deposit at the 750 m level. More detailed underground drilling from this level during 2012, 2013-2014 & 2015 and subsequent drill core analysis confirmed zinc-rich ore at shallower depths with local gold-rich ore at intermediate depth and copper-gold rich ore at greater depth with localized high-grade intercepts as shown in Figure 4. The mined ore is taken to surface through a production shaft for ultimate transfer to the concentrator located at the Stall site.

Figure 4 - Lalor is showing classic VMS trend zinc to gold to copper-gold with depth

The finely crushed ore is mixed with water and appropriate chemicals to separate different individual mineral concentrates. While there are different technologies that are used to process the concentrate to ultimately yield individual metals, most utilize smelting. This is done in a process schematically shown in Figure 5 (Integrated Metallurgical Complex).

Figure 5 Integrated metallurgical complex

The Manitoba Geological Survey continues to support VMS exploration in the Flin Flon – Snow Lake domain with active projects in the Reed Lake area and in areas south of Reed Lake and south of Wekusko Lake in the sub-Phanerozoic extension.

Acknowledgements

Technical review by Christian Bohm and Kyle Reid has been very valuable. Overall review by Nash Soonawala and Christian Bohm. A large amount of historical information has been derived from published literature on the Flin Flon copper-zinc discovery and Hudbay Minerals Inc. corporate literature. The geology and mineralization information has been taken from web-based reports available from Manitoba Geological Survey. The Heritage Committee also provided input and review.

References

1. Manitoba Growth, Enterprise and Trade 2019: Copper-Zinc in Manitoba; Manitoba Growth, Enterprise and Trade, Manitoba Geological Survey, https://www.gov.mb.ca/iem/geo/commodity/files/comm_copperzinc.pdf accessed in May 2019
2. Annual reports & Investor presentation files of Hudbay Minerals Inc. (2009, 2012, 2019).
3. Copper in Canada, Mineral Policy Sector, Energy Mines and Resources Canada (1991) pdf

Compiled by

1. Ganpat S. Lodha, Ph.D, P.Geo, FGC, Honorary Life Member (Geoscientist)-EGM.

Review

1. Christian Bohm, P. Geo.
2. Kyle Reid, P. Geo.
3. Nash Soonawala, P. Geo. (retired)
4. Neil Richardson, P.Geo. Director of Exploration, HudBay Minerals 2022
5. Glen N. Cook, P. Eng.(SM), FEC

Editing

1. Jim Burns, PhD.

Posted by Glen N. Cook, P.Eng. (SM), FEC
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