The Kidd Creek volcanic hosted massive sulphide (VHMS) deposit lies within the Archaean Superior Craton in the Timmins-Porcupine district, and is located 25 km north of Timmins, Ontario, Canada.
The ore deposit is hosted by the Kidd Volcanic Complex which is part of the 2.710 to 2.717 Ga Kidd-Munro assemblage, that in turn lies within the western Abitibi-Wawa Sub-province of the Superior Province. The Kidd-Munro assemblage is a east-west striking steeply dipping and folded package of intercalated ultramafic, mafic and lesser felsic metavolcanic rocks and intrusions which extends from 30 km west of Kidd Creek, eastward for 165 km to the Quebec border. In Quebec it is interpreted to be continuous with the similar age and composition Stoughton-Roquemaure and lower Malartic groups to the north and east. The Kidd-Munro assemblage contains other lesser VHMS deposits, including the Chance deposit (2.25 km west of Kidd Creek), the Potter and Potterdoal mines (100 km east of Kidd Creek), and several small deposits and occurrences in the Stoughton-Roquemaure and lower Malartic groups in Quebec.
At Kidd Creek, the Kidd Volcanic Complex is a coherent, although structurally complicated lithostratigraphic package containing a strongly bimodal suite of komatiitic and high silica rhyolite flows overlain by tholeiitic basalts. It is structurally underlain by younger Porcupine Group wackes, across a contact that takes the form of a steeply dipping folded thrust or unconformity. In the mine area, the sequence if overturned, strikes north-south, face west and dip at 70 to 80° east, to define an asymmetric, S-shaped, steeply north plunging F1 fold.
The known stratigraphic sequence of the Kidd Volcanic Complex in the mine area commences with up to 500 m of carbonate altered komatiitic flows and intrusions which appear to have formed a broad, low-relief lava plain upon which the Kidd Creek rhyolitic dome and ridge complex was constructed. The Footwall rhyolite dome complex (variously dated at 2717.0 ±2.6 Ma, 2716.1 ±0.6 Ma and 2716.0 ±0.5 Ma) comprises domes, cryptodomes and associated volcaniclastic rocks. The rhyolites are interpreted to have been extruded from two fissures to produce an up to 350 m high monogenetic dome and ridge complex that extended below, and along the entire 3 km length of the known orebodies. The Footwall rhyolite and massive sulphides are conformably overlain by the 120 m thick, 2711.5 ±1.2 Ma, QP rhyolite. The Footwall and QP rhyolite ridges and the massive sulphide deposits all appear to have restricted but linear, ridge-like morphologies which have been accentuated during subsequent deformation. These observations are interpreted to indicate primary and pronounced structural control of both volcanism and emplacement of hydrothermal mineralisation (Gibson et al., 2003). Zircon U-Pb dating indicates that the eruption of the Footwall and QP rhyolites spanned a period of up to 2.8 Ma.
Volcaniclastic rocks sandwiched between the Footwall and QP rhyolites, also referred to as epiclastic deposits appear to be primary, syn-eruptive, locally-transported deposits derived from autobrecciation and collapse of underlying Footwall rhyolite domes and pre-existing massive sulphide accumulations and contain blocks and lapilli-sized fragments of massive pyrite and sphalerite in proximity to the massive sulphide lenses.
The QP Rhyolite is conformably overlain by a thick succession of tholeiitic basaltic and andesitic flows, while gabbro sills that have dilated the rhyolite stratigraphy in the mine area are taken to represent hypabyssal intrusive equivalent of these overlying basaltic flows.
The Kidd ore system comprises the three geochemically distinct and physically separated North, Central and South sulphide orebodies, each of which is characterised by i). pyritic tops and lateral fringes, ii). Zn-rich interiors (sphalerite-pyrite), iii). massive to semi-massive, Cu-rich bases (chalcopyrite-pyrrhotite-pyrite-sphalerite), and, iv). underlying chalcopyrite-pyrrhotite-pyrite stringer mineralisation. In addition, the South orebody also had a bornite zone within the Cu-rich massive and stringer ore.
Significant sections of all three orebodies were developed by replacement of the adjoining footwall volcaniclastic units, as indicated by: a). post-depositional replacement of rhyolitic fragments and matrix by pyrite and sphalerite; b). preservation of relicts of massive pyrite and sphalerite within the chalcopyrite-pyrrhotite ore; and c). discordant contacts between massive sulphides and bedding.
In general, each of the orebodies is composed of stringer and massive banded and brecciated pyrite, sphalerite and galena associated with carbonaceous rocks. The composite shape of the massive and breccia, and the stringer ore respectively, for the three orebodies may be broadly represented as two parallel, adjoining, elongate flattened cylindrical masses, with gaps and offsets. The massive sulphide lens is generally 100 to a maximum of 400 m wide and around 30 m thick, with a down plunge extent of more than 3000 m.
A broad halo of sericitisation envelopes the massive sulphide orebodies, characterised by K2O enrichment and Na2O depletion. This alteration is preferentially developed within the footwall but which also extends into the overlying QP Rhyolite. Fe-chloritisation is restricted to the margins of footwall chalcopyrite stringer zones. Both the sericitisation and chloritisation overprint a broad and widespread silicification.
Published production and reserve figures include:
Production 1963 to 2003 - 124.22 Mt grading 6.18 % Zn, 2.31% Cu, 0. 22% Pb and 87 g/t Ag,
Reserve in 2003 - 23.66 Mt @ similar grades.
In 2003 the deposit had been intersected from within 8 m of the surface to a depth of 3109 m vertically below ground level, where an intersection within the orebody cut 442.5 m @ 1.16% Cu, 7.76% Zn, 0.73% Pb and 84 g Ag, and finished in sulphides.
At December 2006, the reserves and resources quoted by Kidd Creek Division of Xstrata Ltd were:
Proved ore reserves - 19.6 Mt @ 2.00% Cu, 5.29% Zn, 0.17% Pb, 53 g/t Ag,
Probable ore reserves - 1.4 Mt @ 1.61% Cu, 5.97% Zn, 0.11% Pb, 33 g/t Ag,
Measured mineral resources - 21.3 Mt @ 2.24% Cu, 5.73% Zn, 0.19% Pb, 57 g/t Ag,
Indicated mineral resources - 1.8 Mt @ 1.80% Cu, 6.28% Zn, 0.13% Pb, 38 g/t Ag,
Inferred mineral resources - 0.4 Mt @ 1.7% Cu, 3.2% Zn, 0.2% Pb, 34 g/t Ag,
Production in 2006 was 2.5 Mt @ 2.05% Cu, 5.24% Pb, 66 g/t Ag.
(Source: Porter Geoconsultancy, http://www.portergeo.com.au/, 2008)
