Ontario Mineral Inventory

Ontario Geological Survey
Permanent Link to this Record: MDI52O08NE00010

Record: MDI52O08NE00010

General

Commodities

Primary Commodities: Gold

Location

Township or Area: Dona Lake Area

Latitude: 51° 24' 49.17"    Longitude: -90° 5' 25.62"

UTM Zone: 15    Easting: 702322   Northing: 5699843.99    UTM Datum: NAD83

Resident Geologist District: Thunder Bay North

NTS Grid: 52O08NE

Point Location Description: Mill/Shaft area

Location Method: Field Visit with GPS

Exploration History

1980-1985: Geophysical and geological surveys and diamond drilling by Dome Exploration. 1985-1987: Advanced exploration including sinking of a 176 m exploration shaft by Dome Mines and Campbell Red Lake Mines. 1987-1993: Mining by Placer Dome. 1993-1994: Mining by Ross Finlay.

Assessment Work on File

Geology

Province: Superior

Subprovince: Uchi

Terrane: North Caribou

Domain: Uchi

Belt: Pickle Lake

Geological Age: Mesoarchean  

Geology Comments

Feb 07, 2007 (Mark Puumala) - The Dona Lake Mine is located in the southeastern portion of the Pickle Lake Greenstone Belt and is hosted in supracrustal rocks of the >2860 Ma Pickle Crow Assemblage (Young 2003). The supracrustal rock sequence that hosts the deposit trends approximately north-south, and is dominated by tholeiitic (usually pillowed) basalt and amphibolite that contains one major semi-continuous and several discontinuous iron formation units, as well as local horizons of tuff, felsic metavolcanics and clastic metasediments (Cohoon 1986). Young (2003) identified numerous gabbro lenses and sills throughout the Dona Lake area that may represent the same units referred to as amphibolite by Cohoon (1986). Cohoon (1986) indicates that the metamorphic grade of the supracrustal rocks is amphibolite facies based on the presence of garnet, biotite, blue-green hornblende and a general lack of chlorite. The supracrustal rocks have been intruded to the west by the felsic 2741 Ma Ochig Lake Pluton. Numerous felsic dikes, many of which have compositions similar to the Ochig Lake Pluton also intrude the supracrustal rock sequence (Cohoon 1986). Immediately to the east of the mine, Young (2003) has identified a separate, younger supracrustal rock assemblage that has been assigned to the approximately 2744 Ma Confederation Assemblage. The rocks at the base of this east-facing assemblage are dominated by pillowed mafic volcanic flows that are geochemically distinct from those found in the Pickle Crow Assemblage (Young 2003). The Confederation Assemblage also contains significant units of intermediate to felsic metavolcanic rocks that include tuff, lapilli tuff and agglomerate. Cohoon (1986) indicates that stratigraphy (and foliation) in the Dona Lake Mine area generally strikes north-south. However, to the north and south of the mine, these fabrics follow the boundaries of the Ochig Lake Pluton, striking northwest-southeast to the north and southwest-northeast further south. Cohoon (1986) indicates that stratigraphy (and foliation) consistently dip to the east (i.e., away from the intrusion) at approximately 60 degrees. Cohoon (1986) also indicates that stratigraphy faces to the east. Cohoon indicates that the mafic metavolcanic rocks are typically most strongly-deformed (i.e., schistose and foliated) near the contacts with iron formation. The iron formation units have also been isoclinally folded, with axial planes parallel to stratigraphy (i.e., north-south strike and steep dip to east). The fold axes plunge steeply to the east. Low amplitude cross-folds with wavelengths of 200 m and amplitudes of 20 m have also been noted in the iron formation by Cohoon (1986). The Dona Lake gold deposit occurs at the axis of one of these cross-folds. A stratigraphy-parallel shear zone has also been noted in the footwall of the deposit by Cohoon (1986). This structure post-dates the peak of regional metamorphism, as it is mineralized with chlorite.

Lithology

Mineralization

Mineralization Comments

Feb 07, 2007 (Mark Puumala) - The Dona Lake Mine went into production in 1989 and ceased operations in 1994. During this time period it is estimated that a total of 939,237 tonnes of ore was milled to produce approximately 6988 kg (246,500 oz) of Au. This estimate is based on grade and tonnage estimates obtained from the Northern Miner (May 30, 1994 article), Janes et al. (1994) and Jen and McCutcheon (1995). The first source summarizes production under the ownership of Placer Dome from 1989 to 1993, while the second and third sources summarize production under the ownership of Ross Finlay from 1993-1994. At the time of mine closure, it is estimated that reserves of approximately 40,000 tonnes grading 5.95 g/t Au remained at depth (Chronicle-Journal article June 24, 1994). The geology in the vicinity of the Dona Lake deposit is described by Cohoon (1986) as consisting of tholeiitic basalt separated by several major units of iron formation and intruded by felsic dikes and albite porphyry. Stratigraphy generally strikes north-south and dips 60 degrees to the east. Gold mineralization occurs entirely within two iron formation units (possibly a faulted repetition of the same unit) near the axis of a low-amplitude cross-fold having an east-west striking axial plane. The ore body had a strike length of approximately 200 m, with 80% of the reserves located in a 100 m section at the core of the fold where the ore body attained a maximum thickness of approximately 25 m (Cohoon 1986). Dona Lake Gold Mine Ltd. (1993) later indicated that the ore body thickness ranged from 3 to 19 m. The deposit was mined to a total depth of approximately 455 m, while additional reserves delineated to a depth of 505 m are believed to have been left in place following mine closure (Northern Miner article, May 30, 1994). The overall geometry of the ore body is that of a flattened pod that plunges east down the axis of the cross-fold (Cohoon 1986). A north-south-striking sinistral fault is reported to cross-cut (at low angle) and offset a portion of the ore body (Cohoon 1986). The non-mineralized iron formation is comprised of finely-bedded magnetite, chert and hornblende with local grunerite, garnet, calcite and sulphides (Cohoon 1986). The gold mineralized iron formation contains 5 to 15% pyrrhotite and <3% pyrite. The pyrrhotite, which apparently replaces magnetite, is fine-grained and wispy and cross-cuts the original bedding, which in some cases is completely destroyed. Mineralization is also noted by Cohoon (1986) to occur in a portion of the iron formation that is finely fractured and brecciated. This brittle deformation is likely attributable to the same deformation event responsible for the development of the cross-fold. The mineralization also includes visible gold and trace chalcopyrite and sphalerite. Cohoon (1986) also indicates that gold values typically are much lower in sections of iron formation where the pyrite concentration exceeds 3-4%. This relationship applies even if the pyrrhotite content remains high. Quartz veining is virtually absent from the ore, although the variable quartz content of the iron formation indicates the possibility of silicification. There is no evidence of significant silicification of the adjacent mafic metavolcanic rocks (Cohoon 1986).

Mineral Record Details

Site Visit Information

Date: Jul 17, 2007

Geologist: Mark Puumala

Notes: During a site visit conducted on July 17, 2007, evidence of a significant northwest-southeast-striking structure was observed in the vicinity of the mine portal. In this area, the primary tectonic fabrics of the mafic metavolcanic rocks and iron formation (S1) are cross-cut by a later (S2) schistosity that is axial planar to small-scale folds of the S1 fabric. The approximate orientation of the S2 fabric ranges from 130 to 145, with near-vertical dip. The fold hinges generally plunge toward the southeast at approximately 45 degrees. The S2 fabric at this location is likely to be related to the major northwest-striking shear zone mapped in this area by Stott et al. (1989b).

References

Book - Gold in an Iron Formation, the Dona Lake Deposit

Publication Number: Vol 1, No. 8 Date: 1996

Author: Cohoon, G.A. 1986.

Publisher Name: Northern Miner Magazine, p. 16-20.

Location: Thunder Bay RGP

Book - Northern Miner 84-04-26, New Gold, p. 1,2

Publication Number: NMINER Date: 1996

Author:

Publisher Name: Northern Miner

Location:

Book - Northern Miner 84-05-03, Map, p. 6

Publication Number: NMINER Date: 1996

Author:

Publisher Name: Northern Miner

Location:

Book - Northern Miner 85-06-06, Dome, p. 3

Publication Number: NMINER Date: 1996

Author:

Publisher Name: Northern Miner

Location:

Compend - Report of activities, 1984, Regional and Resident Geologists

Publication Number: MP122 Page: 45,49  Date: 1985

Author: Kustra C.R.

Publisher Name: Ontario Geological Survey

Location:

Article - Sioux Lookout Resident Geologist's District - 1990

Publication Number: MP152.004 Date: 1997

Author: Janes D.A., Seim G.Wm., Storey C.C.

Publisher Name: Ontario Geological Survey

Location:

File - Resident Geologist personal communication, 84-11-02

Publication Number: Date: 1984

Author:

Publisher Name:

Location:

Thesis - New Structural, Geochronological, and Geochemical Constraints on the Tectonic Assembly of the Archean Pickle Lake Greenstone Belt, Uchi Subprovince, Western Superior Province

Publication Number: Date:

Author: Young, M.D. 2003.

Publisher Name: unpublished thesis, Queen¿s University, Kingston, Ontario, 182p.

Location:

Mono - Report of Activities 1993, Resident Geologists

Publication Number: OFR5892 Date: 1994

Author: Baker C.L., Dressler B.O., Mason J.K., Newsome J.W.

Publisher Name: Ontario Geological Survey

Location:

Book - Principal Canadian Nonferrous and Precious Metal Mine Production in 1994; Canadian Minerals Yearbook, 1995, p. 68.1 - 68.7.

Publication Number: Date:

Author: Jen, L. and McCutcheon, B. 1995.

Publisher Name: Canadian Minerals Yearbook, 1995, p. 68.1 - 68.7.

Location:

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