A SURVIVOR AND THEN SOME: Macassa is the lone mine in Kirkland

On May 23, 1990, the three millionth ounce of gold from the Macassa mine was poured. Macassa, owned and operated by LAC Minerals Ltd., is located on the outskirts of the town of Kirkland Lake, in Teck Township, Ont., and contains proven and probable reserves of 1,672,000 tons of ore grading 0.53 oz. of gold per ton. Since the start of mining in 1913, production from the Kirkland Lake district as a whole has amounted to 23 million oz. of gold and 4.3 million oz. of silver, making it one of the largest gold camps in Canadian history. The past producing mines span a distance of three “golden” miles from east to west and include Tobrun, Sylvanite, Wright Hargreaves, Lake Shore, Teck Hughes, Kirkland Lake Gold, and the operating Macassa mine. The Macassa property was successfully developed in 1933 when arrangements were made to drive westward from the adjoining Kirkland Lake Gold Mines property on their 2,475-ft. level (755 m) to intersect the down-plunge extension of ore along the Kirkland Lake Main Break and in subsidiary veins in the hangingwall. The Macassa No. 1 shaft was sunk to connect with the workings at this level, 3,100 ft. vertical (945 m). As the orebody was followed westward down-plunge, a second shaft and two vertical winzes were sunk and, in 1983, the No. 3 shaft was sunk to a vertical depth of 7,275 ft. (2,217.4 m) or 6,198 ft. (1,890 m) below sea level, the deep- est single-lift shaft in the Western Hemisphere. The active workings begin at the 4,250-ft.level (1,295 m) and extend down to the 7,050-ft. level (2,150 m) over a strike length of 4,500 ft. (1,370 m). Macassa Gold Mines was reorganized into Willroy Mines during the 1960s. From 1970 to 1976, the property mining rights were optioned to Upper Canada Mines. It withdrew in 1976 when the price of gold dropped to below $170 per oz. In 1983, Willroy Mines was incorporated into LAC Minerals. Gold deposits at Kirkland Lake occur within a faulted sequence of Timiskaming-age alkaline volcanic and sedimentary rocks, which are discordant to the adjacent and slightly older Keewatin volcanic and sedimentary rocks of the south-central Abitibi Greenstone Belt. The Macassa property is underlain by north-east striking, moderately south-dipping and south-facing alkaline volcanic and sedimentary rocks intruded by augite syenite, felsic syenite, and porphyritic syenite. The sedimentary rocks consist of pebble conglomerate, greywacke, and finer-grained interbedded wackes. The volcanic rocks, which are interlayered with the sedimentary rocks, consist of well-preserved pyroclastic flows, and lithic and ash tuff. Augite syenite is the oldest and most widespread of the intrusive rocks and it is intruded by felsic syenite. Both the augite and the felsic syenite are intruded by the porphyritic syenite. The intrusive bodies are elongated parallel to the stratigraphy along strike but are steeply dipping to the south and, hence, cross-cut stratigraphy down-dip. All of the rock types are cross-cut by late-stage diabase dykes. Ore occurs in three general types. The first type consists of branching, sub-parallel, steeply dipping faults, which include the “Main Break” (also referred to as the Kirkland Lake Fault) and the “04 Break.” The Main Break is a 1- to 20-ft.-wide (0.3-7m), northeast striking, steeply dipping, post-ore thrust, or reverse, fault traversing the length of the property and has a north and a south branch at depth. It is marked by a zone of mylonitized and sometimes brecciated wallrock, chlorite schist, and mud or gouge. The 04 Break is sub-parallel to the Main Break and on surface is equivalent to the Main Break. It has been explored from the 4,250-ft. level (1,295 m) to 800 feet (245 m) below the 7,050 ft. (2,150 m). For the past 35 years the 04 Break has been the main source of ore in the mine. Gold occurs adjacent to and within these faults, sometimes as coarse visible gold that coats slip planes and fractures. The second way that the ore occurs is in a series of stacked shallow-to moderately-dipping, gold-bearing veins and faults that occur at depth between the steeper faults. Some of these veins have been traced for more than 1,200 ft. (365 m) along strike and 500 ft. (150 m) vertically. The third way that ore occurs is as pyritic, generally fault-bounded “breccia ore” at the west end of the mine. It consists of brecciated white quartz cemented by grey cherty quartz, both of which are auriferous. Although ore occurs throughout all rock types, with the exception of diabase, the main host is the augite syenite. Gold occurs as fine-grained to coarse-grained native gold, as inclusions in the telluride minerals calaverite and petzite, and as minute inclusions in pyrite. Wallrock alteration includes hematization in close proximity to the Breaks and more widespread carbonitization. Silicification, sericitization, and, in some cases, fine sulphide mineralization is generally concentrated in areas near ore. The Macassa mill treats up to 500 tons per day from the mine and about 750 tons of tailings per day from the old Lake Shore property.