Prior to 1984, the Vezza property area received little attention with respect to exploration from metallic deposits. Gold mineralization had been reported from drilling east of the Allard River in 1940 and 1958. Exploration work from the late 1950s to the early ’80s was directed mainly at testing electro-magnetic (em) conductors for base metal massive sulphides.
As a result of discoveries in the Casa Berardi area, some 100 km to the west, exploration activity spilled over into the Joutel and Matagami areas in the early ’80s. During 1984, Kennco Explorations (Canada) acquired 149 claims covering a 14.5- km strike length of favorable stratigraphy. Reconnaissance ground geophysical surveys were carried out, and one hole was drilled testing an em conductor.
In early 1986, 51 claims adjoining the Kennco ground were acquired by Dundee-Palliser and North American. In September, 1986, these and the Kennco claims were combined under the Kennco option and the Dundee- Palliser/North American/Kennco joint-venture agreements. The present Vezza property consists of 221 claims, including other claims staked later.
Systematic exploration work since September, 1986, includes: airborne and ground geophysical surveys; reverse-circulation, overburden drilling (95 holes); and diamond drilling of 161 holes, including wedges, totaling 41,227 m. The first hole drilled by the Dundee-Palliser/North American joint venture, in December, 1986, intersected 0.135 oz per ton (4.5 g per tonne) over 1.9 m in the vicinity of a 1958 hole which averaged 0.11 oz per ton (3.8 g per tonne) over 2.44 m. Several holes were drilled in 1958 by Berthianume Development to follow up a gold showing, located in 1940 by St. Francis Mining, in the Allard River about 1.3 km west of the present Vezza deposit.
The Vezza gold deposit does not appear to have a distinct geophysical response, although various geophysical surveys are useful in interpretation of the geology. Results of reverse circulation drilling indicate that anomalous gold is present in basal till in an area 200×500 m, immediately to the south and west of the deposit. Geological Setting
Regionally, the Vezza property is situated in the northern part of the Archean Abitibi Greenstone Belt, which consists of mafic to felsic volcanic rocks, clastic sedimentary rocks interlayered with banded iron formation, granitic rocks and mafic intrusives (see Fig. 1). Iron formations occur intermittently within a turbidite sequence for a strike length of at least 180 km, from north of the Joutel area east and southeast to 30 km north of Lebel-Sur-Quevillon.
The property is underlain by mafic volcanic rocks and the turbidite sequence containing chert-magnetite iron formations. The property covers about 15 km of strike length of the turbidite sequence as well as a lineament, marked by EM and magnetic anomalies, associated with the iron formations. Locally, this lineament is referred to as the Taibi Fault (Fig. 1). Several gold occurrences in the area, including Vezza, occur along this li neament.
Bedrock in this part of the Abitibi Belt is covered with thick deposits of Pleistocene till and post-glacial sand, gravel and lacustrine clay, and outcrops are rare. Overburden depths on the property vary from 10 m to 80 m. Terrain is generally flat.
Because of the extensive overburden cover, geology must be interpreted from geophysical surveys, air photos, topographic maps and drill hole data. The entire property has been covered by both airborne and ground electromagnetic/magnetometer surveys. Much of the property has been covered by induced polarization surveys. The most detailed geophysical coverage, as well as most of the drilling, is concentrated in the eastern part of the property, in the area of the Vezza deposit.
The geology of the deposit area consists of an east-west striking sequence of sedimentary and volcanic rocks. The units dip steeply south but face north, based on numerous graded beds. From the drilling, the main units are, from south to north:
* Intermediate to felsic volcanic flaws and tuffs (more than 400 m);
* Sandstones with conglomerate units (150 to 200 m);
* Mudstones, siltstones and iron formations (150 to 300 m);
* Interbedded sandstone and mudstone (50 to 75 m) including the Main Alteration zone; and
* Mafic metavolcanic rocks ( more than 200 m).
Dark, graphitic, highly sheared and fissile mudstone (0.3 to 2 m thick) with thin layers of grey-green mudstone and cherty material marks the sedimentary contact with the volcanic rocks.
The metasedimentary rocks consist of sandstone sequences interlayered with mudstone successions that include several banded iron formation sections. The sandstone successions, with bedding units up to 30 m thick, contain various proportions of fine- to coarse-grained, light- colored feldspathic and quartzose units interbedded with dark, lithic greywacke, minor fine-grained pebble conglomerate beds and felsic volcaniclastic units, with minor zones of silty mudstone. By contrast, the mudstone successions consist mainly of light to dark grey and greenish beds with minor sandstone zones. In places, thin units of banded cherty magnetic iron formation are present within greenish chloritic mudstone sections.
The metavolcanic rocks are fine- grained mafic flow rocks, consisting primarily of chlorite, amphibole and plagioclase with abundant quartz- carbonate veinlets. Porphyritic gabbro units occur extensively in the metavolcanic unit. Prominent, highly siliceous quartz-feldspar porphyry dykes are also present in the mafic sequence and are subparallel to the volcanic-sedimentary rock contact.
Primary sedimentary structures, particularly graded bedding, in many places indicate that the succession is overturned and faces north. The older metasedimentary rock section thus forms the structural hangingwall on the south side of the volcanic-sedimentary rock contact.
Rocks on the Vezza property are considered to have undergone at least two deformation phases, low-grade regional metamorphism and at least two phases of hydrothermal alteration. Structural deformation includes regional folding and subsequent faulting. Prominent crosscutting fault trends are northeast and northwest. Alteration and Gold Mineralization
Significant gold mineralization occurs within altered and deformed sedimentary rocks in the eastern part of the property. The altered rocks form a 20-to-40-m-wide Main Alteration (MALT) zone, which straddles the volcanic-sedimentary rock contact. The MALT zone extends up to 25 m into the sedimentary sequence on the south side of the contact as well as up to 25 m into the mafic volcanic unit on the north side of the contact. Alteration of the volcanic rocks consists of chloritization and carbonate (calcite) alteration. Gold values are uniformly low in the altered volcanic rocks.
On a few drill sections, narrow dykes of silicified, sericitized quartz-feldspar porphyry are present near the volcanic-sedimentary contact. These contain only very low gold
values.
The MALT zone in the sedimentary rocks is marked by increased disruption, sericitization, quartz flooding and veinlets, fracturing carbonitization (dolomite and ankerite), albitization and pyritization. Fracturing is predominantly strain-slip and fracture cleavage. The fracture planes are commonly coated by highly fissile sericite. Quartz veining and flooding are pervasive, in varying intensity. and are associated with 1% to 2% sulphide mineralization. The sulphide is mainly pyrite with minor pyrrhotite locally. Traces of arsenopyrite and, to a lesser extent, very minor sphalerite and chalcopyrite occur in some intersections. Pyrite is present as fine-grained clots and stringers along fine fractures and as later, coarser-grained, euhedral crystals. Gold mineralization tends to be associated only with the former pyrite habit and postdates albitization.
The MALT zone has been tested by drilling over a strike length of 2.5 km. The best gold values occur over a strike length of 600 m and to a depth of at least 500 m below surface (see Fig. 2). The deposit strikes east-west and dips 70 degrees to the south.
The bulk of the Vezza gold mineralization is within a relatively continuous, planar zone (3 to 11 m thick) of highly altered and deformed argillaceous sedimentary rocks within the broader MALT zone. This highly altered zone, called the Main zone, generally is within 1 m of the volcanic- sedimentary contact. Within it, the gold bearing intervals are characterized by:
* intense quartz flooding up to 40% of rock volume;
* fracturing, including random, very fine “filigree” brecciation and veinlets;
* fine-grained, disseminated pyrite;
* iron carbonate alteration, giving a bleached appearance; and
* pervasive silicification.
As well as the Main zone, other, less continuous, gold zones and scattered gold intersections are present within altered sedimentary rocks. Most of these are associated with veined, pyritized, silicified and weakly sericitized chert-magnetite iron formations. The most prominent such zone is about 30 to 50 m south of the sedimentary volcanic rock contact, and, in plan, is at a low angle to the MALT zone. Minor gold also occurs rarely in altered volcanic rocks, at intervals immediately north of and parallel to the main gold zone. The intervals are commonly less than 2.5 m thick and occur within bleached rock with associated quartz veining and flooding, calcite veinlets, pyrite clots, fuchsite, albitization and ankerite. Geometry and Reserves
The distribution of the MALT zone gold intersections is shown in longitudinal section in Fig. 2. Grade- thickness contours indicate that several higher-grade pods are present. There are suggestions of both a southwesterly and a southeasterly plunge to the mineralization.
Probable and possible reserves have been estimated using longitudinal sections contoured with grade-thickness and thickness. For the Main zone, on an undiluted, in situ basis, probable reserves are 1.5 million tons of 0.166 oz gold per ton (2 million tonnes of 5.7 g per tonne), and possible reserves are 596,000 tons of 0.148 oz per ton (542,000 tonnes of 5.1 g). These reserves are estimated using a cutoff grade of 0.10 oz per ton (3.43 g per tonne) and a 2-m minimum width. In addition, estimated possible reserves of the upper, subparallel mineralized lenses are 200,000 tons at an average grade of 0.137 oz per ton (181,800 tonnes at grading 4.7 g per tonne). Hrayr Agnerian and William Roscoe are consulting geologists with Roscoe Postle Associates of Toronto. Peter Mills and James Gaunt are independent consulting geologists associated with the firm.
The authors wish to thank Stanley Hawkins, president of North American Rare Metals, and Richard Brissenden, president of Dundee-Palliser Resources, for permission to publish this paper. They also acknowledge the contribution of Robert Metcalfe at an early stage of exploration.
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