Ontario Mineral Inventory

Ontario Geological Survey
Permanent Link to this Record: MDI000000002108

Record: MDI000000002108

General

Commodities

Primary Commodities: Kimberlite

Location

Township or Area: Caramat Lake Area

Latitude: 49° 37' 6.14"    Longitude: -86° 10' 1.68"

UTM Zone: 16    Easting: 560160   Northing: 5496534    UTM Datum: NAD83

Resident Geologist District: Thunder Bay North

NTS Grid: 42E09SE

Point Location Description: Bronco kimberlite in AFRI 2.57811

Location Method: Based on Assessment

Access Description: Highway 11 east of Longlac to Highway 625 provides road access to Caramat. There is an existing network of logging road throughout the area that come within several hundred meters of some of the locations, but all of the drillsites required helicopter access.

Exploration History

Early 1960s and mid 1980s: regional sediment sampling. 2012: De Beers Canada Inc. conducted till sampling. 2014: De Beers did detailed glacial mapping, ice flow reconstruction and focused till sampling. 2015-16: De Beers conducted a high resolution heliborne magnetic and DM survey, ground magnetic surveys, and drilled 16 DDH totaling 2250.3 m, 1 of which was on the Bronco kimberlite.

Assessment Work on File

Geology

Province: Superior

Subprovince: Quetico

Geological Age: Archean  

Geology Comments

Oct 31, 2017 (Therese Pettigrew) - The Pagwachuan kimberlite pipes are located within the Quetico Terrane of the Western Superior Province. The kimberlites are emplaced into a strain-flattened, fold-thrusted belt of deformed and metamorphosed basement rocks of Neoarchean age. The area around the central Quetico belt is conducive for kimberlite emplacement due to the presence of thick lithosphere, high strain tectonic corridors of the Trans-Superior Tectonic Zone and the presence of an array of upper crustal reactivation structures such as faults, shears and dykes possibly connected to a lower crustal plumbing pathway. Highly faulted internal architecture of NW-SE, NE-SW and E-W trenching intersection lineaments form complexly overprinted structural wedges which may disperse ascending melts and produce dyke-related bodies and smaller feeder pipes during emplacement events. Drilling results show that some of the kimberlite bodies are plunging suggesting emplacement may be guided by fold-thrust structures of the complexly deformed metasedimentary accretionary sequences. Other known occurrences located ~50 km south of the cluster consist of carbonatites, diamond-bearing kimberlite dykes and para-lamproites. Rubidium-strontium dating of the phlogopite from the Bronco kimberlite yields an average age of 252.9 +/- 2.4 Ma (Late Permian) (Delgaty et al., 2017).

Lithology

Lithology Comments

Oct 31, 2017 (Therese Pettigrew) - The kimberlites intersected in the 2015-16 drill program are classified as multi-phase, complex bodies consisting of several different facies types and morphologies: massive to bedded ash flow/pyroclastic kimberlite; interlayered hypabyssal and very coarse kimberlite; and interlayered very coarse kimberlite containing blocks of country rock. Where Archean rocks were encountered in the drill holes, these rocks were seen to be very convoluted, with fault planes, shear zones and contorted gneiss banding pointing to flexural slip along large crustal-scale structures during emplacement of the kimberlites. Localized rheological differences between the kimberlites and country rocks were also seen to have resulted in sheeted structures in some of the drillholes. Common characteristics among the intersected kimberlites include grain flow sequences, planar type ash bedding, serpentine alteration, phlogopite and high temperature, metasomatic carbonate alteration of the enclosing granite wallrocks (AFRI 2.57811). Overall, typical crater-facies volcaniclastic kimberlites suggesting phreatomagmatic explosions are identified in the Bronco pipe. The Bronco kimberlite is comprised of different volcaniclastic kimberlites emplaced by combined, primary pyroclastic and resedimentation processes. The Bronco kimberlites indicate mostly resedimentation, entraining exceptionally large and abundant crustal blocks and locally grain flows which concentrate abnormally high abundant ilmenite. The Pagwachuan kimberlites were discovered by drilling discrete magnetic highs with associated weak electromagnetic responses. Ground magnetic surveys were conducted over the kimberlites to confirm the 2D size of the kimberlite (Delgaty, 2017).

Mineralization

Mineralization Comments

Oct 31, 2017 (Therese Pettigrew) - Core samples for each of the Pagwachuan kimberlites were processed to quantify the abundance and composition of mantle derived indicators present (i.e. garnet, clinopyroxene, spinel and ilmenite). The general trend of recovered indicators for all kimberlites is of garnet (46%) > clinopyroxene (25%) > ilmenite (20%) > spinel (8%). The predominant size fraction of the recovered indicators is +0.5mm (47%) followed by +0.15mm (29%) and lastly +0.3mm (23%). However, variations in grain recoveries and proportions of indicators from the various size fractions do occur between kimberlites. The principal compositional features of the garnet populations recovered from the Pagwachuan kimberlites are a high proportion of megacrystics (53% G1) followed by lherzolitic (28% G9) and Ti-metasomatised (5% G11) compositions. The remaining garnet compositions consist of low proportions of eclogitic (4% G3), pyroxenitic (3% G4, G5), harzburgitic (2% G10), and wherlitic (2% G12) garnets. The presence of diamond-facies like compositions is rare (<0.5% of all garnets recovered) with most derived from the eclogitic, pyroxenitic and then harzburgitic compositions. Mantle barometry using the Cr/Ca-in-pyrope barometer of Grütter et al., (2006) shows a maximum P38 of 57 kbar indicating sampling of thick lithosphere, however, very few garnets fall above the 43 kbar “graphite diamond constraint” (GDC) which indicates sampling within the diamond stability field (Delgaty, 2017).

Mineral Record Details

References

Journal - Ontario’s Newest Kimberlite Cluster – the Pagwachuan Cluster

Publication Number: Abstract Date: 2017

Author: Delgaty, J., Fulop, A., Seller, M., Hartley, M., Zayonce, L., Januxzczak, N

Publisher Name: 11th International Kimberlite Conference

Location: http://www.11ikc.com

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