Ontario Mineral Inventory

Ontario Geological Survey
Permanent Link to this Record: MDI000000001316

Record: MDI000000001316

General

Commodities

Primary Commodities: Gold

Location

Township or Area: McComber

Latitude: 49° 37' 43.15"    Longitude: -87° 47' 16.74"

UTM Zone: 16    Easting: 443094   Northing: 5497642    UTM Datum: NAD83

Resident Geologist District: Thunder Bay North

NTS Grid: 42E12NW

Point Location Description: From location in OFR6233

Location Method: Field Visit with GPS

Exploration History

2007: Buck Lake Ventures carried out prospecting and sampling. 2008: Buck Lake was renamed to Ultra Uranium Corp. 2010: Ultra Uranium carried out prospecting and sampling.

Assessment Work on File

Geology

Province: Superior

Subprovince: Wabigoon

Belt: Beardmore-Geraldton

Geological Age: Archean  

Geology Comments

Nov 15, 2011 (Robert Cundari) - The Gwyn Lake property lies entirely within the thickest portion of the western part of the “Southern Metavolcanic Sub-belt”, which marks the southern boundary of the eastern Wabigoon Subprovince (Devaney and Williams 1989). As part of the main Beardmore–Geraldton belt, the Southern Metavolcanic Sub-belt is host to one former producing mine, the Northern Empire (Roxmark Mines Limited), which is situated approximately 10 km southwest and along strike of the Gwyn Lake claim group. From 1934 to 1941, the mine produced 149 493 ounces of gold at a grade of 0.35 ounce gold per ton (Mason and White 1986). The Southern Metavolcanic Sub-belt, which averages 2 to 3 km wide across Summers, McComber and Vincent townships, typically consists of a series of massive to pillowed mafic metavolcanic flows, lesser intermediate tuffs and interflow iron formations. The mafic metavolcanic and flanking sequences within the main belt trend east-northeast. Foliations within the mafic flow units are usually steeply north dipping. The entire sub-belt is interpreted to be an overturned anticlinal structure (Carter 1987). These mafic units are overlain by clastic metasedimentary rocks to the north and separated from locally migmatized metasedimentary sequences of the Quetico Subprovince to the south by the Blackwater River fault zone. The mafic metavolcanic rocks of the Southern Metavolcanic Sub-belt are intruded by semi-conformable feldspar to quartz-feldspar porphyry sills and diorite to gabbro dikes and sills. As documented by Carter (1987) and observed in the field, these dikes are commonly boudinaged and ellipsoidal bodies which range in width from 0.5 to 2 m. Some are sulphide mineralized and anomalous in gold, and as mentioned previously, may be important to local gold metallogeny. Younger, northeast-trending diabase dikes occur throughout the property and a regionally extensive, Mesoproterozoic diabase sheet or sill occurs along the western boundary of McComber Township. Four showings, uncovered by recent stripping in the central portion of the Gwyn Lake property, were visited by staff of the Thunder Bay North Resident Geologist office in late spring of 2008 (Figure 10). Three of these occurrences (Clay Road occurrence: UTM Zone 16, 441584E 5498491N; Blacksmith zone: 441787E 5497878N; and the Gwyn Southwest showing: 443094E 5497642N) are characterized by carbonatized, intensely sheared, mafic metavolcanic rocks hosting chert or chert-magnetite banded iron formation. At the Blacksmith zone and the Gwyn Southwest showing (Figure 11), the iron formation can be traced along strike (075° to 080°) for 200 to 250 m. It dips steeply to the north at 85° and varies in width from 0.5 to 3 m. In places, the iron formation is highly deformed and brecciated, resulting in chaotic disruption of the chert bands. Gossanous, sulphidized iron formation is dominated by pyrite and arsenopyrite (with lesser amounts of chalcopyrite and pyrrhotite) and often crosscut by quartz and quartzcarbonate veins. Conformable, boudinaged quartz veining was also noted. Veins are generally discontinuous and vary from 7 to 40 cm wide. Sulphide content in the iron formation may ranges from 40 to 100%, but overall averages 5 to 10%. Units of semi-conformable quartz feldspar porphyry, in places mineralized with 1% to 3% disseminated pyrite, are exposed at the No. 4 East Extension (441721E 5498234N) and Blacksmith zone.

Lithology

Lithology Comments

Oct 16, 2019 (Therese Pettigrew) - Gold mineralization at the Gwyn Lake is hosted by the east-northeast- west-southwest trending iron formations and associated shear zones and veins that are regionally related to the late shearing along the boundary between the Wabigoon and Quetico sub-provinces. The gold mineralization is closely tied to the geophysical anomalies and conductors. The mineralization developed during, or shortly after the Precambrian trans-pressional, brittle-ductile, shearing deformation of an Archean greenstone belt, which in the prospect comprises metavolcanics, metasediments and porphyry rocks, locally intercalated with BIFs. A shear - fault system set up during the regional deformation and subsequent extensional processes resulted in the deposition of quartz veins with sulphide ± gold mineralization (Assessment report 20000005755).

Mineralization

Mineralization Comments

Oct 16, 2019 (Therese Pettigrew) - The mineralization continues intermittently on strike with the geophysical anomalies throughout the Gwyn Lake Gold Prospect and remains open to the east and west. Mineralized BIFs, shears and veins are hosted by meta-volcanic and meta-sedimentary rocks. Sulphide replacement of magnetite occurs within banded iron formations, which are interbedded in the meta-volcanic greenstone. The replacement of magnetite with pyrite in the BIF followed development of a late, regional cleavage along the Wabigoon-Quetico subprovince boundary and accompanied veining and gold deposition in shear zones. The sheared and altered BIFs contain quartz-carbonate veins and stringers running parallel or sub-parallel to the general structure. Veins and veinlets are common throughout the prospect, but their thickness and texture varies significantly from a few millimeters or centimeters to as much as 1.5 meters. The veins commonly have pinch-and-swell structure, and locally form discontinuous lenses. Quartz is essentially white in colour, but may be locally stained by iron oxides and iron oxy-hydroxides that lend it brown to ochre colouration. The vein quartz is commonly crystalline, whereas the quartz in the banded iron formations has saccharoidal texture. Where accompanied by significant sulphides, the vein quartz can be vuggy. Typically, mineralized areas have been identified where there is evidence of strong oxidation with limonite and gossanous features. The BIFs at Gwyn Lake belong mainly to arsenical-silicate facies. Principal sulphides are arsenopyrite, pyrite and pyrrhotite, while chalcopyrite occurs subordinately. The sulphides occur as fine- to very fine-grained disseminations and/or as lenses of massive sulphide up to 20 centimeters across, which may contain much coarser, euhedral arsenopyrite and/or pyrite crystals. The Gwyn Lake West Extension, Gwyn SW, and Gwyn Lake East Extension showings are all on trend with one another and measure about 635 m from end to end. The Gwyn Lake West Extension (Zone 16 442800 m E, 5497600 m N) assayed up to 12.331 ppm Au. Gwyn Lake East Extension (Zone 16 443359 m E, 5497657 m N) assayed up to 13.304 ppm Au (Assessment report 20000005755). Initial grab samples collected in 2008 of sulphide seams in the iron formation returned up to 30.97 g/t Au and 76.35 g/t Au from the Gwyn Southwest showing. Grab samples were collected by Thunder Bay North Resident Geologist Program staff. The highest assay was obtained from the main sulphidized zone within the iron formation at the Gwyn Southwest occurrence (0.95 ounce gold per ton) (Smyk et al., 2009).

Assay Samples

Mineral Record Details

References

Mono - Report of Activities 2008, Resident Geologist Program, Thunder Bay North Regional Resident Geologist Report: Thunder Bay North District

Publication Number: OFR6233 Scale:     Date: 2009

Author: Smyk M.C., White G.D., Hinz P., Komar C.L.

Publisher Name: Ontario Geological Survey

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For detailed information regarding this mineral record please contact the Thunder Bay North Resident Geologist District Office