Overview of Results from the Greenstone ... - Geology Ontario

from Halfmoon Lake, only 2 km to the northeast, and it is possible that this part of the KGC may intrude
an older succession (e.g., Kidd–Munro assemblage) with the KVC deposited on top of such a basement
complex. Elsewhere, rocks of the “granophyre zone” undoubtedly intrude the upper part of the KVC, for
instance in the Genex Mine area (see also Hocker, Thurston and Gibson 2005), where synvolcanic faults
have localized the emplacement of intrusive rocks.
PORCUPINE ASSEMBLAGE
Although the contact is not exposed, bedding orientation suggests there may be an angular unconformity
between the KVC and conglomerates exposed in central Godfrey Township, on the eastern margin of the
study area (see Figure 20). It is suggested that the conglomerates may form part of the Porcupine
assemblage (2696–2692 Ma: Ayer, Amelin et al. 2002).
KAM-KOTIA AND CANADIAN JAMIESON VOLCANOGENIC MASSIVE SULPHIDE
DEPOSITS
Detailed deposit-scale mapping indicates a similar stratigraphic position for VMS mineralization at these
two past-producing mines. At the Kam-Kotia Mine, two northeast-striking faults located immediately
south-southwest of the open pit show evidence for synvolcanic movement, including the presence of
dikes or apophyses of synvolcanic intrusions, abrupt changes in unit thicknesses, and offsets of a unit
with subsequent units not offset. Numerous faults on this trend intersect the VMS-hosting interval in
Robb and Jamieson townships. Field mapping and petrographic studies, suggest the presence of a
northeast-oriented discordant iron-rich chlorite-rich±sericite alteration pipe that is at least 200 m wide and
extends upward to the southwestern part of the Kam-Kotia open pit. At the Canadian Jamieson Mine, a
synvolcanic diabase sill or dike occurs in the immediate vicinity of the ore lenses, suggesting the presence
of an east-northeast-trending synvolcanic structure in this location. As at Kam-Kotia, rocks in the vicinity
of the Canadian Jamieson orebodies are strongly chlorite and sericite altered.
GENEX VOLCANOGENIC MASSIVE SULPHIDE DEPOSIT SUBPROJECT
A detailed subproject focussed on the Genex deposit (Hocker, Thurston and Gibson 2005a, 2005b) has
shown the metavolcanic rocks in the Genex Mine area are cut by numerous mafic and intermediate
synvolcanic intrusions. The synvolcanic timing of the mafic intrusions is indicated by the presence of
peperite, a pillowed base, irregular contacts, amoeboid dikes, and incorporation of felsic material. The
synvolcanic nature of the intermediate intrusions is evidenced by the presence of a mixed zone near the
upper contact, abundant spherulites and amygdules, and localization within synvolcanic faults.
Synvolcanic faulting occurred after emplacement of the mafic synvolcanic intrusions, and provided
conduits for the intermediate synvolcanic intrusions, as well as for the hydrothermal fluids responsible for
the base-metal mineralization and alteration at the Genex Mine.
The Genex mineralization is distributed in 3 zones: the first in pillow breccia and hyaloclastite, the
second at the contact between felsic tuff and intermediate intrusion, and the third within the intermediate
intrusion. The mineralization represents subseafloor replacement sulphides localized within zones of
higher permeability. All rocks have experienced hydrothermal alteration in the form of sericitization,
chloritization, epidotization, silicification, and iron-carbonatization. The small size of the synvolcanic
intrusions mitigates against them being the primary heat source associated with the hydrothermal system;
however, their occurrence indicates the presence of a localized high heat-flow thermal regime. Mapping
the distribution of these intrusions is important for defining synvolcanic structures, and potentially new
zones of base metal sulphide mineralization.
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