Temagami Greenstone Belt
Temagami Greenstone Belt | |
---|---|
Stratigraphic range: Neoarchean | |
Type | Geological formation |
Unit of | Abitibi Subprovince |
Sub-units | Arsenic Lake Formation, Link Lake Formation, Turtle Lake Formation |
Location | |
Coordinates | 47°04′43.85″N 79°48′43.23″W / 47.0788472°N 79.8120083°W |
Region | Ontario |
Country | Canada |
Extent | 32 by 25 km (20 by 16 mi) |
Type section | |
Named for | Temagami |
Location of the Temagami Greenstone Belt in Ontario |
The Temagami Greenstone Belt (TGB) is a small 2.7 billion year old
Part of the Canadian Shield, the TGB contains some of the oldest known rocks on Earth. The belt is made up of a number of geologic features such as
.Geology
Geologists assume that greenstone belts were formed by many geological processes, such as
The variety of volcanic deposits and intrusions in the TGB indicates that magmatic activity played a significant part in its formation.
Along with nearby granitic intrusions, the TGB is bounded by layers of rock comprising the Huronian Supergroup. Strathy Township is dominated by metamorphosed volcanic rocks of the northeastern portion of the belt. It is approximately 24 km (15 mi) north of the Grenville Front Tectonic Zone. The volcanic rocks possibly total as much as 6,000 m (20,000 ft) thick. However, portions of the sequence might have been repeatedly sheared by one or several local fault zones. Every large volcanic event is capped by metamorphosed sedimentary rocks and/or iron formations. The metamorphosed sedimentary units range in thickness from 60 m (200 ft) to 300 m (980 ft) and consist of laminated slate and greywacke with or without volcanogenic tuffs. The iron formations are composed of alternate layers of magnetite, white quartzite, jasper, grey cherty quartz, and/or tremolite-chlorite tuff. They are intruded by sills composed of medium-grained, white-weathering, quartz diorite that range in thickness from 100 m (330 ft) to 210 m (690 ft). These rocks are similar to the coarse thicker parts of lava flows, but are interpreted to be partly intrusive, likely conduits that produced mafic volcanism.[5]
Intrusions
A layered intrusion composed of diorite,
The Kanichee layered intrusive complex, also known as the Kanichee Intrusion and Ajax Intrusion, is the most voluminous mafic-
An intrusion of light-coloured diorite lies at the northern end of the
At least three large
Intrusive dikes composed of quartz and feldspar-quartz porphyry are widespread in Strathy Township. All dike types were placed in the Earth's crust during the formation of the TGB. At least some of these dikes may have been
Felsic volcanic vents
Volcanic vents composed of felsic rocks are thought to have been located at the iron-bearing Sherman Mine, the former Temagami
Just north of the Milne Townsite lies a minor felsic volcanic vent exposed along the Milne-Sherman Road. A
Several north-trending felsic dikes, composed mainly of feldspar and quartz-feldspar, are located north of the former Temagami garbage dump. These dikes are not known to extend across the Link Lake Deformation Zone, suggesting that they might represent the feeders of a minor volcanic vent, manifest now by felsic lava flows. Because certain lithologies can be correlated through the Link Lake Deformation Zone, it is unlikely that the lack of felsic dikes south of the former town dump area is an expression of displacement along the deformation zone.[9]
Volcanic complexes
The TGB consists of two large volcanic sequences that were formed during several phases of volcanic activity. These two sequences, known as the Older and Younger volcanic complexes, consist of volcanic rocks ranging in composition from felsic to mafic. The Older Volcanic Complex is composed mainly of felsic lava flows and pyroclastic deposits with smaller amounts of mafic volcanic rocks.
A number of volcanic rocks comprise the Link Lake Formation, such as feldspar-phyric, calc-alkaline basalt and andesite lava flows and less abundant quartz and quartz-feldspar-phyric felsic lava flows. Feldspar-phyric basalt lava flows are normally pillowed. Pyroclastic deposits, quartz-phyric and feldspar-felsic rocks are also present. The largest of the less common felsic lava flows is located between Link Lake and Turtle Lake. It is 2.5 km (1.6 mi) long and less than 200 m (660 ft) thick. The thickest portion of this lava flow or dome is located at the western end of Link Lake, where it is likely associated with a volcanic vent. The bulk of felsic rock in the Link Lake Formation occurs as subaqueous pyroclastic flow deposits. Subaerial pyroclastics are normally quartz-phyric and range up to 30 cm (12 in) in crosssection. Dark green subaerial pyroclastics composed of chlorite and sericite are uncommon and have sustained preferential compression in response to shear throughout the Link Lake Deformation Zone. These dark compressed pyroclastics have been interpreted to be pumice. Some of the subsequence pyroclastic deposits contain fragments of pyrite and quartz, suggesting that discharged sulfide hydrothermal activity took place throughout the volcanic source area.[9]
Resedimented felsic, epiclastic and turbiditic sediments compose the Turtle Lake Formation. The base of this formation consists of a heterolithic, volcaniclastic,
A series of dark green, massive and pillowed iron-rich tholeiitic basalt lava flows compose an unnamed upper volcanic formation of the Younger Volcanic Complex. It is situated in the core of the Tetapaga Syncline. Not much is known about this volcanic formation because only a small portion of it remains exposed in western Strathy Township.[9]
Deformation zones
Many north-trending shear zones intersect iron-rich tholeiitic basalts of the Arsenic Lake Formation. These zones range in width from less than 1 m (3.3 ft) up to 5 m (16 ft), and might maintain a larger area of weakness that was tectonically active over the past billion years. Evidence for early
Extending from Net Lake to Vermilion Lake lies a northeast–southwest trending high strain zone known as the Net Lake-Vermilion Lake Deformation Zone. Because geologic mapping has not been done comprehensively throughout this zone, its exact width is unknown. The expression of this deformation zone is clearly identifiable by the intense change in volcanic rocks of the TGB. Volcanic units comprising the northwestern portion of the shear zone have shifted to the northeast while the volcanic rocks comprising its southeastern portion have shifted to the southwest. Along the northeastern arm of Lake Temagami in Strathcona Township lies the Northeast Arm Deformation Zone. This northeast-trending shear zone has not been studied in detail, but casual studies of many islands along the northeastern arm of Lake Temagami have shown that there is severe foliation and minor ferroan carbonate across an area about 1 km (0.62 mi) wide. The Link Lake Deformation Zone, also known as the Link Lake Shear Zone, is an area of deformation 0.5 km (0.31 mi) wide and over 3 km (1.9 mi) long in Strathy Township. It extends through Link Lake to east of Highway 11, but it is uncertain whether it extends west of Link Lake because no expression of it has been found in the Sherman Mine area. Therefore, the Link Lake Shear Zone might be a northern extension of the Northeast Arm Deformation Zone further south. Strain intensity of the Link Lake Shear Zone is diverse. Generally, the greatest strain intensity is throughout pyroclastic rocks.[9] Extending from the western boundary of central Chambers Township through Tasse Lake to the east is the Tasse Lake Deformation Zone. This deformation zone is roughly 3 km (1.9 mi) long and at least 0.5 km (0.31 mi) wide. It is uncertain if this deformation zone extends east of Tasse Lake.[11]
Rock alteration
Many forms of rock alteration can be seen in the TGB. Its overall structure has attained
Outcrops of silicified mafic pillow lava are found along and west of the Ontario Northland Railway, east of the Big Dan Shear Zone and adjacent to Outlet Bay and Boot Bay of Net Lake. This form of alteration occurs in deformation zones and is the product of low temperature seawater alteration. Volcanic rock replaced by carbonate is commonly found in the Northeast Arm Deformation Zone, the Link Lake Shear Zone and in the Net Lake-Vermilion Lake Deformation Zone. Within the high strain zones, carbonate is also manifest as 1 m (3.3 ft) wide veins that have been traced along strike for more than 100 m (330 ft).[9]
Basalt has been replaced by calcite in a restricted area just north of the Temagami's former garbage dump. Although developed adjacent to the Link Lake Shear Zone, rocks within and just outside the calcite alteration zone do not normally contain significant foliation. Thus, if the calcite alteration zone was located within the Link Lake Shear Zone, it did not form inside the zone of the highest strain.[9]
Mineralization
The TGB contains massive banded iron formations and several precious metal and base metal deposits. The banded iron formations range from 1 m (3.3 ft) to 2 m (6.6 ft) to more than 150 m (490 ft) thick.[5] Remnants of volcanic vents are an important locator for mineral potential in the Temagami belt because they are adjacent to rocks that contain certain types of mineralization. At the Link Lake Formation, good evidence for copper-zinc massive sulfide deposits has been discovered in associated volcanic rocks. Some gold mineralization may also be associated with volcanic vents. Studies of greenstone terranes in the Superior craton have shown that large gold deposits are associated with regional deformation zones. Therefore, the Northeast Arm Deformation Zone, the Link Lake Shear Zone and the Net Lake-Vermilion Lake Deformation Zone are obvious high potential areas. A number of scattered pyrite deposits can be found throughout the Northeast Arm Deformation Zone. The high frequency of gold mineralization in and near the Net Lake-Vermilion Lake Deformation Zone suggests that this deformation zone may very well also contain gold deposits;[9] at least 11 have been discovered within a 4 km (2.5 mi) length of the deformation zone. The gold deposits are found in many rock types, indicating a stronger gold-bearing system with the potential of larger gold deposits.[15] A number of gold-pyrite deposits exist in felsic volcanic rocks overlying the Older Volcanic Complex, near and on the northwestern part of the Net Lake-Vermilion Lake Deformation Zone. These deposits were likely formed during the creation of the Net Lake-Vermilion Lake Deformation Zone. At the Younger Volcanic Complex, gold exists in quartz veins containing base metal sulfides. It is also known to exist in pyrite associated with deformed magnetite-rich iron formations, sericitized and carbonatized felsic volcanic rock, quartz-pyrrhotite-chalcopyrite-pentlandite-pyrite zones within deformation zones and in north-trending, chloritized shear zones containing arsenopyrite, pyrrhotite, pyrite and chalcopyrite.[9]
A variety of iron, copper, arsenic and zinc ores such as arsenopyrite, pyrrhotite, pyrite and chalcopyrite with sphalerite, are present as small veins and in quartz veins throughout north-trending shear zones that cut the iron-rich tholeiitic basalts of the Arsenic Lake Formation. Dikes composed of quartz-feldspar porphyry run parallel to or lie within the shear zones and are cut by the mineralization. Chalcopyrite occupies later fractures which intersect massive arsenopyrite. Sparse quartz veins normally exist in or adjacent to the arsenopyrite-rich zones. Several northeast-trending deformation zones intersect pyroxenite of a mafic sill in northwest Strathy Township. Within these high-strain zones quartz veins normally contain chalcopyrite, pyrite, pyrrhotite with exsolved pentlandite and traces of sphalerite and galena. Chalcopyrite, pyrrhotite and pentlandite are deposited throughout shear zones which lack quartz veining. These zones are not known to contain large amounts of gold, although investigations are incomplete. It is also unknown if platinum group metals (which include platinum, palladium, rhodium, iridium, osmium and ruthenium) exist in these zones because no searches for platinum group elements have been undertaken.[9]
Gold and copper values occupy a northeast-trending iron formation within the Net Lake-Vermilion Lake Deformation Zone. This mineralization is only known to exist southeast of Cooke Lake and immediately south of Net Lake. A unit of chert, magnetite and pyrrhotite outcrops along the southwest shore of Net Lake at Temagami North. Pyrrhotite, the most common sulfide mineral, occurs as small veins and disseminations. Small amounts of pyrite, sphalerite and exsolved pentlandite and chalcopyrite are present with the pyrrhotite. The main exposure lies immediately south of the Kanichee Mine Road, which branches off Highway 11. Minor gold and copper values constitute this zone. This sulfide-bearing unit is located within felsic volcanic rocks of the Older Volcanic Complex and is capped by large, dark green, iron-rich tholeiitic basalts of the Arsenic Lake Formation. It has been interpreted that the sulfide zone represents a volcanogenic massive sulfide ore deposit based on the structure of the sulfide zone and the associated rock types.[9] These ore deposits are created by volcanic-associated hydrothermal events in submarine environments.[17] However, there is evidence that the sulfide mineralization does not have a volcanogenic origin. An unusual feature of this sulfide deposit is the large degree of magnetite at the actual showing. Studies have shown that the chert-magnetite iron formations in the West and North Pits of Sherman Mine extend under and along a series of small lakes from Vermilion Lake to Net Lake. These iron formations are located at roughly the same stratigraphic position as the magnetite-bearing iron formation on the southwestern shore of Net Lake. A northwest-trending cross fault is accompanied by drag folding of a chert-magnetite iron formation unit southeast of Cooke Lake. Also exposed in this area is a dark yellow 40 cm (16 in) wide quartz vein composed of pyrite that cross cuts the iron formation at the northeastern end. This west-northwest trending quartz vein is about 60 m (200 ft) long.[9]
Layered chert-magnetite and lesser chert-pyrite-pyrrhotite iron formations are located at the base of the Arsenic Lake Formation. Former drilling near Vermilion Lake and spatial relationships observed on the surface, suggest that the sulfide-rich iron formation lies up to 10 m (33 ft) stratigraphically under the oxide facies iron formation. Iron production from the West and North Pits of Sherman Mine came from this chert-magnetite iron formation unit while chert-magnetite iron formations at the South and East Pits compose the Turtle Lake Formation. The South and East Pit iron formations reach thicknesses of 30 m (98 ft) and overlie a thinly bedded turbidite package on the southern limb of the Tetapaga Syncline.[9]
A white palladium
Paleogeology
The TGB, at 2.7 billion years old, dates back to the formation of the
After Rodinia broke apart, its southern half traveled south and crossed the
Human history
Naming
The name "Temagami" is
Mineral explorations
In May 1995 Pacific Mariner Exploration carried out a small drilling program on its properties in Strathy Township to estimate the likelihood of base metal deposits. A 215 m (705 ft) hole was drilled under Net Lake in Temagami North, but its collapse prevented the survey's completion. As a result, little is known about its geophysical features. Most of the property was influenced by Net Lake and included ten adjacent mining claims.[11]
At least five explorations took place in the Strathy Township property before 1995. In 1934 Strathy Basin and Erie Canadian Mines conducted prospected sections of the 1995 claim block. A 21.2 m (70 ft) wide rusted zone within a dike was announced as containing values of $7.50 combined gold, copper and
In 1952 Rib Lake Copper Mines explored areas adjacent to Whitney Lake and between Whitney Lake and Rib Lake, by creating trenches and carrying out diamond drilling. Nickel was discovered with widespread pyrrhotite in sheared mafic rocks. Gold mineralization was discovered with pyrite in slightly siliceous tuff. The highest assessment was 1.30 oz (37 g) of gold per ton and 0.99% of nickel over 1.8 m (5.9 ft), both from the same zone. Detailed work did not occur in the Rib Lake area of southern Gillies Limit Township and northern Best Township until 1968, when mapping took place, but it is unclear whether volcanic rocks in the Rib Lake area are part of the TGB, as they have not been mapped in any detail. With the existence of Early Archean age tholeiitic and/or calc-alkaline mafic to intermediate volcanic rocks, they may represent a minor continuation of the belt, which is located about 6 km (3.7 mi) to the southwest. Small intrusions and pyroclastics of mafic composition are also present in the area. In 1956 Silanco carried out geophysics south of Whitney Lake. In 1964 Nickel Rim Mines Ltd. had a greatest result of 1.30 oz (37 g) of gold per ton. The exploration and mining activity south of Gillies Limit Township observed nickel, copper and platinum group metals at Cuniptau Mine and gold, silver and copper at the Big Dan and Little Dan mines.[35]
Mining
Because of the high mineralization, several mines have opened in the belt. Sherman Mine, northwest of the town of Temagami, was a major producer of
The Kanichee Mine property, formerly known as Cuniptau Mine, was first discovered in the early 1900s just before World War I began. A 7.3 m (24 ft) mine shaft with 670 m (2,200 ft) of underground lateral workings was completed on two levels in 1934. At least 11 mine claims occupied the area at the time. The core of a widespread massive sulfide deposit composed of palladium, nickel, copper, gold, cobalt, platinum and silver was mined out from underground and by an open pit from 1934 to 1936. Since 1938, at least seven different ownerships have held the Kanichee Mine property. Subsequent mining from 1974 to 1975 increased the size of the open pit and removed the shaft pillar. The open pit and underground workings have remain flooded since the mine closed in the 1970s.[40]
Along the southeastern margin of the Net Lake-Vermilion Lake Deformation Zone lies the abandoned
About 1 km (0.62 mi) north of Beanland lies the abandoned Hermiston-McCauley Mine, situated on the northwestern side of the Net Lake-Vermilion Lake Deformation Zone. From 1935 to 1940, a 115.1 m (378 ft) three-compartment mine shaft was constructed. Three levels were created, two of which had 1,853.1 m (6,080 ft) of lateral work. Reserves have been variously estimated at 31,000 tons averaging 0.275 oz (7.8 g) of gold per ton, 45,700 tons averaging 0.30 oz (8.5 g) of gold per ton over 1 m (3.3 ft), or 9,000 tons averaging 0.5 oz (14 g) of gold per ton over 0.91 m (3.0 ft). A main and subsidiary quartz-rich zone occur in a ruptured intrusion composed of diorite, which intrudes felsic volcanic rocks in a northwesterly direction with the strike of the Net Lake-Vermilion Lake Deformation Zone. The main vein is at least 76.1 m (250 ft) long and up to 1.5 m (4.9 ft) wide. Pyrite with chalcopyrite and gold occupies the quartz-rich zones as blebs and small veins.[15]
Mining operations began at Leckie Mine, a now abandoned gold mine 3 km (1.9 mi) north of the Temagami, in the early 1900s with the construction of a 17 m (56 ft) mine shaft with 27.3 m (90 ft) of underground workings. In 1909 about 270 tons of ore was shipped out of the shaft. A 160.1 m (525 ft) mine shaft with five levels was constructed during a second period of exploration from 1930 to 1948. About 1,524 m (5,000 ft) of drifting and crosscutting was completed on all five levels.[42]
Production continued at the Big Dan Occurrences during the early 20th century. Two shallow mine shafts were created in 1906 and were used to ship ore out of the mine. At least 0.358 oz (10.1 g) of gold per ton was sent during this period. The mine was constructed in a 610 m (2,000 ft), north striking mineralized portion of the Big Dan Shear Zone.[15]
See also
- List of greenstone belts
- List of volcanoes in Canada
- Volcanology of Eastern Canada
References
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