stratigraphic framework of the larder lake area, insights ... · sedimentary, unconformity...

A new Canadian research initiative funded

by Canada First Research Excellence Fund.

Structural and stratigraphic framework of the Larder Lake area,

insights from new mapping,

geochronology, and geophysics

Kate Rubingh,

Research Associate,

Mineral Exploration Research Centre,

Harquail School of Earth Sciences,

Laurentian University

Transect Scale Research

Sudbury

Timmins

Val d’Or

Thunder Bay

Red Lake

Manitoba

Ontario

Quebec

0 200 600km

Gold Deposits

2017-2021

• Project Overview• Transect Scale Research

• Regional Geological Setting

• Ben Nevis – Larder Lake Transect

• Stratigraphy and Structural Geology

• Main research problems to be addressed

• Research / Thesis areas• Preliminary results from targeted

geological mapping, geochronology, seismic and MT data

Outline

Transect Scale Research

Sudbury

Timmins

Val d’Or

Thunder Bay

Red Lake

Manitoba

Ontario

Quebec

0 200 600km

Gold Deposits

2017-2021

Timmins

Kirkland Lake

Val d’Or

Abitibi Transects

Regional Geological Setting

Ben Nevis Larder Lake transect Outline

Ben Nevis – Larder Lake transectStratigraphy

• 45km transect

• Ben Nevis Volcanic Complex

• Larder Lake Cadillac Break

• Timiskaming assemblage

• Larder Lake Group

• Porcupine Type Sediments -Hearst assemblage

• Lincoln Nipissing Shear Zone

Blake River Group (2704 – 2695 Ma)

Ben Nevis Volcanic Complex hosted in the Blake River Group

The Ben Nevis Volcanic Complex consists of basaltic-andesite to rhyolite lavas and volcaniclastic rocks.



• 45km transect







Timiskaming assemblage

(2679 – 2669 Ma)

• Marine facies to alluvial-fluvial facies

• Marker unit defines the Larder Lake Cadillac Break at the contact with the Larder Lake Group

Coarse clastic sedimentary basin units



• 45km transect







Larder Lake Group – ultramafic rocks (2710 – 2704 Ma)

• Larder Lake Group equivalent to the Tisdale assemblage

• Contact interpreted as fault bounded slivers of the crust structurally juxtaposed against the Timiskaming sedimentary rocks.



• 45km transect







Greywackes and siltstones to mudstonesLocal arenites and interbedded conglomerates (similar to the Timiskaming type sediments)

Hearst assemblage

U-Pb thermal ionization mass spectrometry (TIMS) from granitoid boulders within the basal conglomerate provided a maximum age of deposition for the Hearst assemblage to be at least <2709.5+/-1.1 Ma (M.A. Hamilton, 2018).



• 45km transect







Timiskaming aged intrusions

Intrusive rocks along the LNSZ are spatially associated with gold mineralization.

Photo from Sean Brace

Sequence of Deformational EventsD1 Isoclinal folding and

imbrication of Timiskaming and olderTisdale volcanic rocks

D2 Regional east-west F2

folding and formation of a regional S2 foliation, east-plunging to steeply-plunging L2 stretching lineation along the Larder Lake Cadillac Deformation Zone

D3 Dextral reactivation of

the Larder Lake Cadillac deformation zone and formation of a regionalS4 foliation axial planarto dextral F4 folds Modified from Poulsen 2017

Ben Nevis Larder Lake transect Research area and students

Ben Nevis – Larder Lake transectResearch areas

Rebecca MacDonald MSc Student (Starting May 2019)

Research project in the Ben Nevis Volcanic complex.

• Project to address the lack of metal endowment in the Blake River Group, compared to Noranda camp, host to significant VMS deposits.

Nadia St. Jean MSc Student

Research focused along the LLCDZ

• Project to understand the primary relationship of the contact between the Timiskaming and the Larder Lake group.

Sean Brace, MSc Student

Research focused on a series of weakly mineralized intrusions along the Lincoln Nipissing Shear Zone (LNSZ)

• Thesis to characterize these composite stocks

Kate Rubingh, Research Associate

• Research focused along the LNSZ and the Hearst assemblage

Nadia St. Jean MSc student

Research project

Detailed mapping and characterization of the Timiskaming - Larder Lake Group contact at several locations along the Larder Lake Cadillac deformation

zone.

Cross section through the C-LL

break

Structural juxtaposition between the Blake River and Larder Lake groups.

From Poulsen 2017

Blake River (2704–2696 Ma)

Timiskaming (2679–2669 Ma)

Larder Lake grp. (Picheequivalent)

(ca. 2710-2704 Ma)

unconformityunconformity

Cadillac-Larder Lake Break

Timiskaming (2679–2669 Ma)

Level of exposure


• Cheminis Mine site

• Kerr Addison Mine site

• Road cut sections along the LLCDZ

Modified from Thomson 1941, 1943

Research Locations

2 km

Cheminis Mine SIte


• Cheminis Mine site

• Review of north and south contacts

Research Locations

Map from Nadia St-Jean MSc thesis

Timiskaming turbidites

Timiskaming turbidites

Larder Lake Group ultramafic and mafic volcanic rocks


Northern contact between Larder Lake group and Timiskaming assemblage

Research Locations –Cheminis Mine Site

• Transition zone between Timiskaming and Larder Lake group

• Carbonatized, rounded to subrounded fragments in Timiskaming sedimentary matrix.

• Photomicrograph of fragmental unit at the Timiskaming –Larder Lake Group contact.

• Rounded mafic to ultra mafic fragments, composed primarily of chlorite-carbonate-quartz-albite in a quartz and sericite-rich siltstone matrix

Photos from Nadia St-Jean MSc thesis


• Drillhole across northern contact between Larder Lake Group ultramafic flow (fuchsite altered) and Timiskaming sediments.

• Fragmental unit at contact and graded beds youngingdownhole (to the north, away from ultramafic flow).




• South contact - very fine-grained Timiskaming greywacke is in sharp contact with intercalated mafic to ultramafic volcanic flows to the north.

• The greywacke youngs to the south, away from the Larder Lake Group volcanic rocks.




• Contact between Larder Lake group and Timiskaming assemblage was initially sedimentary, unconformity

• Subsequently modified by several deformation events (D3)

• Mineralization syn-D2, associated with K-alteration in green carbonate and albite alteration in mafic volcanic rocks

Results

Level of exposure

Blake River (2704–2696 Ma)

unconformity

Cadillac-Larder Lake Break – is the

structural juxtaposition between the Blake River and Larder Lake grps.

Nature of the north contact interpreted as an unconformity due to:-• Gradational contact between the two assemblages • Lack of a major shear zone or structure at the contact • Consistent younging directions away from the volcanic rocks are strong

evidence for an unconformable contact. Juxtaposition of the Timiskaming and Larder Lake Group prior to D2

Justified by F2 folded contact relationships between the two groups

Sean Brace MSc student

Research project

To examine the relationship between a number of gold prospects, an inferred fault zone and a chain of mafic to felsic intrusive rocks.


Research project

Wisconsin- SkeadStock

Brace et al., 2018


Research project

• Tonalite hosted by altered basalt, with rafts of basalt incorporated into the tonalite.

• Alteration assemblage = chlorite + sericite + ankerite

• U-Pb zircon age 2672.5Ma +/- 0.9 Ma (Hamilton, M.,2018).

Wisconsin- Skead Stock (La Fonde showing)

Photos from Sean Brace


Research project

MacGregor stock

Brace et al., 2018


Research project

• Composed of two compositional suites, a hornblende-rich diorite to- leucodiorite and a biotite-rich diorite.

• Close timing relationship indicated by irregular, diapir-like contacts.

• Current interpretation is that mafic magmas were injected multiple times into partially-differentiated, but not fully consolidated magmas

• Further work will establish whether all units are petrogenetically related.


MacGregor Stock


Research project

Webster stock

Brace et al., 2018


Research project

• Quartz feldspar porphyry hosted in altered pillowed basalt and gabbro and cut by gabbroic and lamprophyric phases

• Alteration assemblage = iron carbonate+ chlorite+ sericite+ silica and minor hematite alteration

Webster Stock


Gold Mineralization – Vein Hosted

Lafonde MacGregor Webster

Vein hosted in Tonalite Vein hosted in leucodiorite Vein hosted in QFP

Intense albitization Intense albitization Carbonate altered

Sericite, ankerite, chlorite Sericite, ankerite, chlorite, (hematite) Sericite, ankerite, chlorite, silica (hematite)

Disseminated pyrite within veins and host rock



Field observations document a high degree of modification indicating that all rocks experienced extensive fluid-rock interaction and varying degrees of metasomatism.

Ben Nevis Larder Lake transect Results and Future work

Sean Brace MSc studentResults and further work

Petrography and geochemistry of the intrusive rocks from the 3 stocks.

To assess their origin in the context of other magmatic centres in this part of the Abitibi Greenstone Belt.

Pegmatoidal leucodiorite sample from MacGregor submitted for U-Pb zircon dating.

This will complement the age for the felsic centre already dated from the Wisconsin-Skead stock.

Research focused in the Townships of Skead and Hearst, where significant clastic sedimentation south of the LLCDZ is restricted to the area north of the LNSZ.

Kate Rubingh, Research Associate

• Research objective is to understand the structural and stratigraphic framework of this area.

• To provide further insight into the depositional environment of the basin at the time of sedimentation.

• This may have implications for the development of the LNSZ and the LLCDZ.

Geochronology of the Hearst

assemblage

Basal unconformity developed between (a) the Larder Lake grp. (ca. 2710-2704 Ma) and (b) the Hearst ass. (ca. 2700 Ma)

Similar structural / stratigraphic relationships as the Cadillac –Larder Lake break

Geochronology of the Hearst

assemblage

• The detrital zircon geochronology is consistent with Ayer et al. (2003), however presence of the single zircon at 2681 Ma, implies the age of the Hearst assemblage sedimentation is not definitive.

• Samples collected during the 2018 field season will further constrain the depositional age of these sediments.

The detrital age determined a maximum depositional age of 2697+/- 9 Ma (Rasmus Haugaard, 2018). (Based on the weighted mean of the youngest 5 zircons, and includes a single zircon at 2681 Ma).

Lincoln Nipissing Shear Zone

• Lincoln Nipissing shear zone separates the Skead volcanics from the Larder Lake group. and the Hearst clastic sediments

• Intruded by small-volume stocks and associated gold mineralization

Lincoln Nipissing Shear Zone

Field observations

Characteristics of the shear zone

• Fe carbonate alteration

• Strong down dip foliation and associated lineation

Differences

Lincoln Nipissing Shear Zone vs the Larder Lake Cadillac Deformation Zone

• Similar structural juxtaposition of different assemblages

• Similar lithologies – Ultramafic – mafic volcanic rocks and clastic sedimentary rocks.

• Similar alteration:-

• Strong iron carbonate alteration, quartz and quartz – carbonate veins

• Fuchsite and sericite

• Strong foliation and down dip lineation

• Numerous gold prospects

• Similar intrusive complexes but neither show significant intrusive bodies on the seismic section

• Both show as truncations on the seismic section

Similarities

• The main break has widespread alkalic volcanic rocks intercalated with Timiskaming sedimentary rocks.

• A wide damage zone is observed in the footwall of the main break

• Large gold deposits (11Moz Kerr Addison) associated with the main LLCDZ.

• The main break can be traced up to 30 km on the seismic section

Larder Lake Transect - Seismic

• On the basis of truncated reflectors

• Can trace C-LL break to >15 km

• Can trace Lincoln-Nipissing shear zone to approximately 6 km

Larder Lake MT – AMT section, 3D inversion

N facing Skead Volc

LN Shear

Blake River volcanic rocks

CLL Break

Graham Hill, Personal Com..

Higher conductive material at approx. 30 km depth

Larder Lake MT – AMT section, 3D inversion

Graham Hill, Personal Com..

N facing Skead Volc

LN Shear

Blake River volcanic rocks

CLL Break

C-LL break has conductivity contrast traced to +30km

LN shear very minor conductivity contrast to < 3km

Contrast typically considered alteration effect

Larder Lake Transect – Seismic and MT combined

• Volcanic domains higher resistivity

• HW of C-LL break low resistivity (result of alteration and sedimentary rocks)

• Lincoln-Nipissing limited depth extend

• C-LL extends to + 30km, into lower crust / mantle ?

Blake River Volc

3 km

9 km

15 km

21 km

Further work

Larder Lake Area Preliminary Results and Future work

• Both Cadillac-Larder Lake and Lincoln Nipissing fault systems are the result of reactivation of an unconformity developed between mafic and ultramafic volcanic rocks and clastic alluvial-fluvial sedimentary rocks

• Both have similar small-volume alkaline intrusive stocks that are Timiskaming in age

• Both have gold associated with syn-D2 deformation

• C-LL system hosts world class gold deposits and numerous smaller deposits with similar geometries and structural / stratigraphic controls

• LN shear zone has a series of showings

• Difference between the two is mapped by reflection seismic and MT which correspond well to large-sale crustal features

Preliminary Results

• The preliminary work conducted in 2018 will be expanded in 2019 to further examine the nature of the LNSZ and investigate the structural and stratigraphic setting of the Hearst assemblage.

• Samples were collected from greywackes of the Hearst assemblage for a detrital geochronology study.

• Additional samples for U-PbGeochronology were collected.

• Aeromagnetic, Magnetotelluric and Seismic data completed in 2017 and 2018 will compliment the transect targeted mapping performed by the research group.

A new Canadian research initiative funded

by Canada First Research Excellence Fund.

Thank you.

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stratigraphic framework of the larder lake area, insights ... · sedimentary, unconformity...

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