Sudbury Basin: gabbroic rocks, economic significance

THESE TERMS GOVERN YOUR USE OF THIS DOCUMENT
Your use of this Ontario Geological Survey document (the “Content”) is governed by the
terms set out on this page (“Terms of Use”). By downloading this Content, you (the
“User”) have accepted, and have agreed to be bound by, the Terms of Use.
Content: This Content is offered by the Province of Ontario’s Ministry of Northern Development and
Mines (MNDM) as a public service, on an “as-is” basis. Recommendations and statements of opinion
expressed in the Content are those of the author or authors and are not to be construed as statement of
government policy. You are solely responsible for your use of the Content. You should not rely on the
Content for legal advice nor as authoritative in your particular circumstances. Users should verify the
accuracy and applicability of any Content before acting on it. MNDM does not guarantee, or make any
warranty express or implied, that the Content is current, accurate, complete or reliable. MNDM is not
responsible for any damage however caused, which results, directly or indirectly, from your use of the
Content. MNDM assumes no legal liability or responsibility for the Content whatsoever.
Links to Other Web Sites: This Content may contain links, to Web sites that are not operated by MNDM.
Linked Web sites may not be available in French. MNDM neither endorses nor assumes any
responsibility for the safety, accuracy or availability of linked Web sites or the information contained on
them. The linked Web sites, their operation and content are the responsibility of the person or entity for
which they were created or maintained (the “Owner”). Both your use of a linked Web site, and your right
to use or reproduce information or materials from a linked Web site, are subject to the terms of use
governing that particular Web site. Any comments or inquiries regarding a linked Web site must be
directed to its Owner.
Copyright: Canadian and international intellectual property laws protect the Content. Unless otherwise
indicated, copyright is held by the Queen’s Printer for Ontario.
It is recommended that reference to the Content be made in the following form: <Author’s last name>,
<Initials> <year of publication>. <Content title>; Ontario Geological Survey, <Content publication series
and number>, <total number of pages>p.
Use and Reproduction of Content: The Content may be used and reproduced only in accordance with
applicable intellectual property laws. Non-commercial use of unsubstantial excerpts of the Content is
permitted provided that appropriate credit is given and Crown copyright is acknowledged. Any substantial
reproduction of the Content or any commercial use of all or part of the Content is prohibited without the
prior written permission of MNDM. Substantial reproduction includes the reproduction of any illustration or
figure, such as, but not limited to graphs, charts and maps. Commercial use includes commercial
distribution of the Content, the reproduction of multiple copies of the Content for any purpose whether or
not commercial, use of the Content in commercial publications, and the creation of value-added products
using the Content.
Contact:
FOR FURTHER
INFORMATION ON
PLEASE CONTACT:
The Reproduction of
Content
MNDM Publication
Services
The Purchase of
MNDM Publications
MNDM Publication
Sales
Crown Copyright
Queen’s Printer
BY TELEPHONE:
Local: (705) 670-5691
Toll Free: 1-888-415-9845, ext.
5691 (inside Canada,
United States)
Local: (705) 670-5691
Toll Free: 1-888-415-9845, ext.
5691 (inside Canada,
United States)
Local: (416) 326-2678
Toll Free: 1-800-668-9938
(inside Canada,
United States)
BY E-MAIL:
[email protected]
[email protected]
[email protected]
LES CONDITIONS CI-DESSOUS RÉGISSENT L'UTILISATION DU PRÉSENT DOCUMENT.
Votre utilisation de ce document de la Commission géologique de l'Ontario (le « contenu »)
est régie par les conditions décrites sur cette page (« conditions d'utilisation »). En
téléchargeant ce contenu, vous (l'« utilisateur ») signifiez que vous avez accepté d'être lié
par les présentes conditions d'utilisation.
Contenu : Ce contenu est offert en l'état comme service public par le ministère du Développement du Nord
et des Mines (MDNM) de la province de l'Ontario. Les recommandations et les opinions exprimées dans le
contenu sont celles de l'auteur ou des auteurs et ne doivent pas être interprétées comme des énoncés
officiels de politique gouvernementale. Vous êtes entièrement responsable de l'utilisation que vous en faites.
Le contenu ne constitue pas une source fiable de conseils juridiques et ne peut en aucun cas faire autorité
dans votre situation particulière. Les utilisateurs sont tenus de vérifier l'exactitude et l'applicabilité de tout
contenu avant de l'utiliser. Le MDNM n'offre aucune garantie expresse ou implicite relativement à la mise à
jour, à l'exactitude, à l'intégralité ou à la fiabilité du contenu. Le MDNM ne peut être tenu responsable de tout
dommage, quelle qu'en soit la cause, résultant directement ou indirectement de l'utilisation du contenu. Le
MDNM n'assume aucune responsabilité légale de quelque nature que ce soit en ce qui a trait au contenu.
Liens vers d'autres sites Web : Ce contenu peut comporter des liens vers des sites Web qui ne sont pas
exploités par le MDNM. Certains de ces sites pourraient ne pas être offerts en français. Le MDNM se
dégage de toute responsabilité quant à la sûreté, à l'exactitude ou à la disponibilité des sites Web ainsi reliés
ou à l'information qu'ils contiennent. La responsabilité des sites Web ainsi reliés, de leur exploitation et de
leur contenu incombe à la personne ou à l'entité pour lesquelles ils ont été créés ou sont entretenus (le
« propriétaire »). Votre utilisation de ces sites Web ainsi que votre droit d'utiliser ou de reproduire leur
contenu sont assujettis aux conditions d'utilisation propres à chacun de ces sites. Tout commentaire ou toute
question concernant l'un de ces sites doivent être adressés au propriétaire du site.
Droits d'auteur : Le contenu est protégé par les lois canadiennes et internationales sur la propriété
intellectuelle. Sauf indication contraire, les droits d'auteurs appartiennent à l'Imprimeur de la Reine pour
l'Ontario.
Nous recommandons de faire paraître ainsi toute référence au contenu : nom de famille de l'auteur, initiales,
année de publication, titre du document, Commission géologique de l'Ontario, série et numéro de
publication, nombre de pages.
Utilisation et reproduction du contenu : Le contenu ne peut être utilisé et reproduit qu'en conformité avec
les lois sur la propriété intellectuelle applicables. L'utilisation de courts extraits du contenu à des fins non
commerciales est autorisé, à condition de faire une mention de source appropriée reconnaissant les droits
d'auteurs de la Couronne. Toute reproduction importante du contenu ou toute utilisation, en tout ou en partie,
du contenu à des fins commerciales est interdite sans l'autorisation écrite préalable du MDNM. Une
reproduction jugée importante comprend la reproduction de toute illustration ou figure comme les
graphiques, les diagrammes, les cartes, etc. L'utilisation commerciale comprend la distribution du contenu à
des fins commerciales, la reproduction de copies multiples du contenu à des fins commerciales ou non,
l'utilisation du contenu dans des publications commerciales et la création de produits à valeur ajoutée à l'aide
du contenu.
Renseignements :
POUR PLUS DE
RENSEIGNEMENTS SUR
VEUILLEZ VOUS
ADRESSER À :
la reproduction du
contenu
Services de
publication du MDNM
l'achat des
publications du MDNM
Vente de publications
du MDNM
les droits d'auteurs de
la Couronne
Imprimeur de la
Reine
PAR TÉLÉPHONE :
Local : (705) 670-5691
Numéro sans frais : 1 888 415-9845,
poste 5691 (au Canada et aux
États-Unis)
Local : (705) 670-5691
Numéro sans frais : 1 888 415-9845,
poste 5691 (au Canada et aux
États-Unis)
Local : 416 326-2678
Numéro sans frais : 1 800 668-9938
(au Canada et aux
États-Unis)
PAR COURRIEL :
[email protected]
[email protected]
[email protected]
Ontario
Ministry of
Northern Development
and Mines
ONTARIO GEOLOGICAL SURVEY
Open File Report 5732
Gabbroic Rocks of the Sudbury Basin
and their possible Economic Significance
by
Burkhard Dressler
1990
Parts of this publication may be quoted if credit is
It is recommended that reference to this
given.
publication be made in the following form:
Dressler, B. 1990. Gabbroic rocks of the Sudbury Basin and
their possible economic significance/ Ontario Geological Survey,
Open File Report 5732, 13p.
This project is a component of the Northern Ontario Geological
Survey (NOGS) Program.
Queen's Printer for Ontario 1990.
Ontario Geological Survey
OPEN FILE REPORT
Open File Reports are made available to the public tubject to the following
conditions:
This report is unedited. Discrepancies may occur for which the Ontario Geological
Survey does not assume liability. Recommendations and statements of opinions expressed
are those of the author or authors and are not to be construed as statements of govern
ment policy.
This Open File Report is available for viewing at the following locations:
(1) Mines Library
Ministry of Northern Development and Mines
8th floor, 77 Grenville Street
Toronto, Ontario
(2) The office of the Regional or Resident Geologist in whose district the area
covered by this report is located.
Copies of this report may be obtained at the user's expense from a commercial
printing house. For the address and instructions to order, contact the appropriate
Regional or Resident Geologist's offices) or the Mines Library. Microfiche copies
(42x reduction) of this report are available for 12.00 each plus provincial sales tax at the
Mines Library or the Public Information Centre, Ministry of Natural Resources, W-1640,
99 Wellesley Street West, Toronto.
Handwritten notes and sketches may be made from this report. Check with the
Mines Library or Regional/Resident Geologist's office whether there is a copy of this
report that may be borrowed. A copy of this report is available for Inter-Library Loan.
This report is available for viewing at the following Regional or Resident Geologists'
Algonquin - Box 190, Dorset, Ontario, POA 1EO
Cobalt - Box 230, Presley St., Cobalt, Ontario, POJ ICO
London - Box 5463, 659 Exeter Rd., London, Ontario, N6A 4L6
Timmins - 60 Wilson Ave., Timmins, Ontario, P4N 2S7
Sudbury - 200 Brady St., 6th Floor, Sudbury, Ontario, P3A 5W2
The right to reproduce this report is reserved by the Ontario Ministry of Northern
Development and Mines. Permission for other reproductions must be obtained in writing
from the Director, Ontario Geological Survey.
V.G. Milne, Director
Ontario Geological Survey
iii
Table of Contents
Abstract ....................................... . ..... . . vii
Introduction ...................... . . . . . . . . . . . . . . . . . . . . . . . l
Gabbroic Rocks within the Sudbury Basin ................ . . 3
Magnetic Anomaly Related to the Gabbroic Rocks
within the Sudbury Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Conclusion and Recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figures
Figure 1: Geology of the Sudbury Structure . . . . . . . . . . . . . . 10
Figure 2: Schematic cross-section of the Sudbury
Structure before deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 3: Sublayer of North Range . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 4: Aeromagnetic contour map and separation
of total field magnetic intensity/ Sudbury Area . . . . . . . . . 13
v
Abstract
The Sudbury nickel-copper deposits occur at the base of the
Sudbury Igneous Complex, within the quartzdioritic Sublayer,
the Footwall Breccia or the footwall rocks, and within the
Offset dikes in the footwall. Several phases of Sublayer
exist, of which only the oldest phase appears to be
mineralized.
Gabboic rocks occur at several locations within the Sudbury
Basin where they intrude all formations of the Whitewater
Group. These gabbros are unmineralized, but at one location
they macroscopically and microscopically resemble rocks of
the Sublayer. A magnetic anomaly in the Basin has been
interpreted to represent a gabbro intrusion. Could this
anomaly represent a Sublayer intrusion?
Vll
GABBROIC ROCKS OF THE SUBDURY BASIN
by
Burkhard Dressler
Geologist, Precambrian Geology Section, Ontario Geological Survey
Manuscript approved for publication and published with the
permission of V.G. Milne, Director, Ontario Geological Survey,
April 30, 1990.
IX
Introduction
The nickel-copper deposits associated with the Sudbury
Structure represent the largest concentration of nickel on
Earth. These deposits occur at the base of the Sudbury
Igneous Complex, within the inclusion-bearing,
quartzdioritic Sublayer (Souch et al. 1969, Naldrett et al.
1984); within the heterolithic Footwall Breccia (Dressler
1984 a); and within the footwall rocks. Some of the largest
nickel-copper deposits occur within the quartzdioritic
"Offst Dikes" in the footwall around the Sudbury Igneous
Complex (Figure 1).
Current hypotheses (Naldrett 1984) associate the formation
of the nickel-copper sulphide ore with magmatic sulphide
precipitation in a mafic magma. The precipitation of the
sulphides is believed to have been triggered by the
assimilation of silica-rich, strongly brecciated and
possibly shock-melted country rocks by the mafic magma.
The sulphide masses have accumulated at depth at the base of
sill-like protrusions (Figure 2) of the main Sudbury Igneous
Complex (Naldrett 1984). Later magmatic Sublayer pulses
transported the ores to their present locations.
Three or more phases of Sublayer exist (Naldrett et al.
1984). All are characterized by inclusions in a gabbroicquartzdioritic groundmass (Figure 3). They occur at the base
of the Sudbury Igneous Complex and also make up the Offset
dikes. Two phases have been recognized that are younger than
the norite of the Igneous Complex, contain inclusions
derived from the footwall of the Sudbury Structure , and are
very little mineralized or unmineralized. The oldest
Sublayer phase is commonly strongly mineralized and contains
a variety of mafic and ultramafic inclusions which possibly
were derived from lower, unexposed portions of the Sudbury
Igneous Complex (Naldrett et al. 1984; Naldrett 1984). The
relative age of this oldest phase with respect to the norite
of the Igneous Complex is not known but is probably also
younger than the norite. It is important to note that the
unmineralized phases of Sublayer are commonly spatially
associated with the mineralized phase.
The Sudbury Igneous Complex has intrusive contacts with the
footwall rocks at its base and with the heterolithic
breccias and melt rocks of the Onaping Formation of the
Whitewater Group at its top. Therefore the Sudbury Igneous
Complex is younger than both the Onaping Formation and the
footwall rocks. The relative age of the two upper formations
of the Whitewater Group (namely the Onwatin Formation
(mudstones) and the Chelmsford Formation (wackes)) with
respect to the Sudbury Igneous Complex is not known.
Gabbroic Rocks within the Sudbury Basin
Gabbroic rocks occur at several localities within the
Sudbury Basin (Burrows and Rickaby 1930, Dressler 1984 b)
They intrude all three formations of the Whitewater Group.
In most places, they have been subjected to strong carbonate
alteration. At one location, near Vermilion Lake (location
A, Figure 1), part of an outcrop exhibits a relatively
fresh, inclusion-bearing rock that resembles the younger,
sulphide-poor phases of the Sublayer. The matrix, as the one
of the Sublayer, is quartzdioritic and hosts inclusions. The
present study deals with this observation and its
significance.
Burrows and Rickaby (1930) described the gabbroic rocks
intruding the Whitewater Group as being strongly altered to
chlorite and carbonate. The present author visited most
known occurrences of these rocks and petrographically
studied one well exposed occurrence of an altered gabbro. It
is located in northeastern Fairbank Township just north of
the Vermilion Lake Road (easting 474900, northing 5154075;
location A on Figure 1).
The main mass of the outcrop is a medium-grained,
porphyroblastic/ dark greenish-grey rock. It is completely
altered, consisting of porphyroblasts of very pale brownish
amphibole set in a fine- to medium-grained mass of light
greenish actinolite with a little epidote and carbonate. Two
to three cm thick, pink, medium-grained, hornblende-bearing
aplite veins cut the altered gabbro. The aplite consists of
brown hornblende set in a dense mass of saussuritized
plagioclase, minor actinolite, apatite, and very minor
carbonate and quartz.
Most other occurrences of gabbroic rocks in the Sudbury
Basin are very similar to the altered gabbro just described
and as such are different from any lithology of the Sudbury
Igneous Complex including the phases of Sublayer. Two rock
types, however, were observed within the Sudbury Basin that
are considerably different from the altered gabbros. One
forms the northern most portion of the outcrop at location A
of Figure 1; the other occurs south of Chelmsford where it
intrudes the Onaping Formation (location B, Figure 1).
The rock at location B is a fine- to medium-grained, grey
and greenish-grey rock forming a 1-2 m thick dike. It is
strongly altered containing saussuritized plagioclase,
chlorite, and actinolite and as such is similar to the
altered gabbros described above. It differs, however, from
these gabbros in containing optically determind talc. No
talc-bearing rock associated with the Sudbury Igneous
Complex including the Sublayer is known to exist. Brownishgreen hornblende of this rock is being replaced by
actinolite and a little apatite and secondary quartz are
present. No apparent similarity and relationship to any
phase of the Sudbury Igneous Complex exist.
The rock at the northern-most part of the outcrop at
location A of Figure l, however, in some aspects is very
similar to Sublayer and therefore of possible economic
significance. It is a slightly altered, fine- to mediumgrained, equigranular gabbroic rock that resembles the
felsic norite of the North Range Sudbury Igneous Complex. As
it contains inclusions of mafic igneous rocks, it is very
similar to the unmineralized phases of the Sublayer of the
Sudbury Igneous Complex. As seen in thin section, the matrix
of the rock consists of brown, probably primary hornblende,
small relicts of primary clinopyroxene, quartz, granophyre
and apatite. Plagioclase is saussuritized. Actinolite,
chlorite, epidote and leucoxene are alteration products. The
inclusions are altered, medium-grained gabbroic rocks, in
place exhibiting diffuse outlines suggesting incipient
assimilation. Similar observations have been made by the
author on inclusions in the Sublayer (Dressler 1984 c; Photo
4.11). - The rock described possibly is related to the
Sublayer of the Sudbury Igneous Complex.
Magnetic Anomaly Related to the Gabbroic Rocks within the Sudbury Basin
The total-field aeromagnetic map of the Sudbury area
(Figure 4a) clearly outlines the Sudbury Structure as a more
or less continuous, ring-shaped anomaly coinciding with the
Sudbury Igneous Complex (Gupta et al. 1984). A linear
anomaly of moderate strength lies just north of the South
Range of the Sudbury Igneous Complex (X-X, Figure 4b). No
apparent rock is causing this anomaly and the author
suggests that it is possibly related to the gabbroic rocks
described here.
Conclusions and Recommendations
The gabbroic rocks within the Sudbury Basin are possibly
related to the Sudbury Igneous Complex. Phases of them
resemble unmineralized Sublayer phases that are commonly
spatially associated with mineralized Sublayer at the base
of the Sudbury Igneous Complex. An aeromagnetic anomaly is
associated with these rocks. Its'signature possibly
indicates magnetic mineralization at depth.
The nickel-copper deposits of the Sudbury Structure occur at
the base of the Sudbury Igneous Complex and in the Offset
dikes. No such mineralization is known from the Sudbury
Basin. If it can be substantiated that the inclusion-bearing
rocks within the Basin described in this report are a phase
of Sublayer, then more extensive examination of the mineral
potential of the Sudbury Basin might be warranted.
References
Burrows, A.G. and Rickaby/ H.C. 1930. Sudbury Basin Area;
Ontario Department of Mines, Annual Report for 1929,
Volume 38, Part 3, 55p.
Dressler, B.O. 1984 a. The Effects of the Sudbury Event and
the Intrusion of the Sudbury Igneous Complex on the
Footwall Rocks of the Sudbury Structure; p.97-136, in
The Geology and Ore Deposits of the Sudbury
Structure, Pye, E.G., Naldrett, A,J., and Giblin,
P.E.; Ontario Geological Survey, Special Volume l,
603p.
Dressler, B.O. 1984 b. Sudbury; Ontario Geological Survey,
Geological Map 2491; Scale 1:50 000.
Dressler, B.O. 1984 c. General Geology of the Sudbury Area;
p.57-82, in The Geology and Ore Deposits of the Sud
bury Structure; Pye, E.G., Naldrett, A.J., and
Giblin, P.E. (editors); Ontario Geological Survey,
Special Volume l, 603p.
Gupta, V.K., Grant, F. S. and Card, K.D. 1984. Gravity and
Magnetic Characteristics of the Sudbury Structure;
p.381-410, in The Geology and Ore Deposits of the
Sudbury Structure; Pye, E.G., Naldrett, A.J., and
Giblin, P.E. (editors); Ontario Geological Survey,
Special Volume l, 603p.
Naldrett, A.J. 1984. Summary, Discussion, and Synthesis;
p. 533-569, in The Geology and Ore Deposits of the
Sudbury Structure; Pye, E.G., Naldrett, A.J., and
Giblin, P.E. (editors); Ontario Geological Survey,
Special Volume l, 603p.
Naldrett, A.J., Hewins, R.H., Dressler, B.O., and Rao, B.V.
1984. The Contact Sublayer of the Sudbury Igneous
Complex; p.253-274, in The Geology and ore Deposits
of the Sudbury Structure; Pye, E.G., Naldrett, A.J.,
and Giblin, P.E. (editors); Ontario Geological
Survey, Special Volume l, 603p.
Souch, B.E., Podolsky, T., and Geological Staff of Inco
Limited. 1969. The Sulfide Ores of Sudbury: Their
Relation to a Distinctive Inclusion-Bearing Facies
of the Nickel Irruptive; p.252-261, in Magmatic Ore
Deposits; Wilson, H.D.B. (editor), Economic Geology
Monograph 4.
Figure 1:
Geology of the Sudbury Structure.
A, Bf and x: Occurrences of gabbroic rocks within
the Sudbury Basin (compare with Dressler 1984b).
10
Early Mafic Norite
Contact Deposits
Contact Deposit
Ultramafic Cumulates
Ore Accumulation
AH Sublayer Magma
l -1 -1 -i Main Mass of SIC
'i 1 ! 1 ! (Sudbury Igneous Complex)
i-'i&id SIC Magma Pulse
in Main Conduit
Scale
5
10
Onaping Formation
Footwall Rocks
Figure 2:
NMain Conduit
Schematic cross-section of the Sudbury Structure
before deformation. Sublayer magma intrudes the
Sudbury Igneous Complex and the Whitewater Group
(after Naldrett 1984, with additions).
11
15
Figure 3:
Sublayer of North Range,
Levack Twonship. Coleman
Mine Road.
12
o
-P en
CD ^
G o
tn o
03 to
e u
•H
T3
rH
CD
•H
4-1
-H
O
H
42
42
03
rH tP
03
-P ^i
O 42
-P
4-J
O
13
CD '
03 —3 ^
G 03 co
O U c^
•H
rH
03 O 03
a -P
CD
-P
en T3 CD
(D
8(T45'
T3 > 03
G CD -P
03 -H O.
rH 3
— CD U
03 42
—
S
^ O
03 r-l ^
CD 03 4-1
to S ~
rt: o
G G
^ 03 -H
M
en
3 4-1 03
42 O ffl
T3
3 -P ^
W G M
CD 3
* -P 42
a x ^o
03 W 3
S
W
3 X 45
O l -P
4-1 l
G X G
O
-H
0-4^
—* -P
O ^2 -H
•H ~ S
-P
CD ^i Cn
G -P G
CJI-H -H
o3 en M
g G in
o CD 3
-P U
CD G U
< •H O
^
CD
13