Ontario Geological Survey
Permanent Link to this Record:
MDI42E04SE00003
| Record Name(s) | Thorsteinson Amethyst Occurrence - 1973, D. Thorsteinson - 1973, Nagunagisic - 1973 |
|---|---|
| Related Record Type | Simple |
| Related Record(s) | |
| Record Status | Occurrence |
| Date Created | 1982-Oct-29 |
| Date Last Modified | 2022-Feb-28 |
| Created By | |
| Revised By |
Primary Commodities: Amethyst
Secondary Commodities: Mineral Specimen
Township or Area: Gravel River Area
Latitude: 49° 1' 1.43" Longitude: -87° 43' 24.49"
UTM Zone: 16 Easting: 447101.924 Northing: 5429604.691 UTM Datum: NAD83
Resident Geologist District: Thunder Bay South
NTS Grid: 42E04SE
Point Location Description: Stripped area, pits.
Location Method: Conversion from MDI
Access Description: The occurrences area located on the northwest shore of Nagunagisic Lake, 40 km due east of Nipigon. Naunagisic Lake is approximately 12 km north of the mouth of the Gravel River. Access may be gained by aircraft--either fixed wing or helicopter--or by overland travel from the Gravel River, 4 km to the east. A bush road leads to the north along the Gravel River approximately 2 km to the east of the showing. The road, however, is commonly washed out.
1973: An amethyst vein was discovered by D. Thorsteinson and N. Cox in June of 1973. The occurrence was stripped and pitted. Further prospecting led to the discovery of the Burning Rock Pb, Zn, Cu occurrence. 1974: A. Castagne staked several adjoining claims in the area. 1990: The Burning Rock property was staked and prospected by R. Reukl and B. Michon. 1992: Prospecting and diamond drilling were carried out on the Burning Rock occurrence. 1995: The Thorsteinson amethyst occurrence (TB 350313) has been leased and is held by N. Cox, the estate of D. Thorsteinson and S. Lukinuk.
Province: Superior
Geological Age: Archean
Dec 07, 2005 (B Nelson) - The area is underlain by a granite-migmatite complex of Archean age. Carter (1971) described pink granitic rocks alternating with metamorphosed dark grey greywacke and pale yellow or white sandstone. The underlying rocks consist of biotite gneisses which have been intruded by a potassic feldspar-rich, hornblende granite. A strong foliation trends 60 degrees. Four separate locations of amethyst were visited by the Resident Geologist. Location 1 or the Camp Location is located on the lakeshore just southwest of a small bay. Amethyst veins and a granite breccia was obserbed striking 45 to 60 degrees. Location 2 is approximately 60 m south of Location 1. An amethyst vein strikes approximately 100 degrees. This vein may be the extension of the main occurrence at Location 3 and 4. Location 3 is approximately 75 m west of the shoreline and consists of a 10 m hill which includes a 3 m to 12 m wide breccia zone. Numerous vugs, amethyst veins and granite breccia was observed, with clasts up to 10 cm observed in the breccia. Location 4 is located approximately 170 m west of Location 3. Here a 15 m cliff face displays a zone up to 2 m wide, which includes amethyst veins from 10 to 30 cm in width. The vein strikes 115 degrees and is hosted by breccia. Vos (1976) further described the showing as: At the time of visiting the author found veins with amethyst in two additional locations on claim TB350313, both along the lakeshore. One outcrop shows a vertical vein with a 0.3 m wide vug in a granitic host rock. The strike of the vein is east-west, and may be an extension of the main vein. A second occurrence along the lakeshore occurs approximately 300 m northeast of the first, along the base of a large outcrop of granitic rock jutting out into the lake. Here, in a 1.5 m wide vertical breccia zone striking N80 degrees E, several quartz veins contain vugs up to 15 cm wide.
| Rock Type | Rank | Composition | Texture | Relationship | Granite | 1 | Granite-Migmatite | Brecciated | Host |
|---|---|---|---|---|
| Sandstone | 2 | Greywacke | Near | |
| Sandstone | 3 | Near | ||
| Gneiss-Unsubdivided | 4 | Biotite | Near | |
| Vein | 5 | Amethyst | Host |
Dec 07, 2005 (B Nelson) - Carter (1971) described pink granitic rocks alternating with metamorphosed dark grey greywacke and pale yellow or white sandstone. The underlying rocks consist of biotite gneisses which have been intruded by a potassic feldspar-rich, hornblende granite.
| Rank | Mineral Name | Class | Economic Mineral Type | Alteration Mineral Type | Alteration Ranking | Alteration Intensity | Alteration Style |
|---|---|---|---|---|---|---|---|
| 1 | Amethyst | Economic | Ore | ||||
| Quartz | Alteration | Silicification | 1 |
Dec 07, 2005 (B Nelson) - Location 2: Several vugs up to 30 cm were observed, along with amethyst crystals up to 2 cm. Location 3: Amethyst crystals up to 5 cm were observed. In one vug, a 3 m pole was pushed down with no bottom being reached. The color of the amethyst varies from black to smoky to hematite red to deep purple. Location 4: Deep purple crystals up to 4 cm were observed and the dark purple color was 'impressive'. Excellent specimens of amethyst have been collected from the Thorsteinson Amethyst occurrence. The amethyst vein system appears to be at least 300 m in strike length and up to 12 m wide in one location. Thorsteinson (1974) stated the vein reached 50 feet in width and the zone was followed for a mile in each direction.
Date: Feb 26, 1997
Geologist: B Nelson
Notes: Resident Geologist personnel visited the occurrence May 21, 1990.
Book - Amethyst deposits of Ontario
Publication Number: GB05 Scale: Date: 1998
Author: Vos M.A.
Publisher Name: Ontario Division of Mines
Location:
Map - Nipigon-Schreiber, geological compilation series, Thunder Bay District
Publication Number: M2232 Scale: 1:253,440 Date: 1973
Author: Carter M.W., McIlwaine W.H., Wisbey P.A.
Publisher Name: Ontario Division of Mines
Location:
Mono - Mineral Occurrences in the Nipigon-Marathon Area, Volumes 1 and 2.
Publication Number: OFR5951 Scale: Date: 1996
Author: Schnieders B.R., Smyk M.C., Speed A.A., McKay D.B.
Publisher Name: Ontario Geological Survey
Location:
We are continuously updating our assessment file / technical report information. If you notice errors in the data, please contact us.
Please review our Terms of Use agreement for this data product.
For detailed information regarding this mineral record please contact the Thunder Bay South Resident Geologist District Office