The Hollinger Open Pit is a part of Porcupine Gold Mines, is situated in the gold-mining City of Timmins, in northern Ontario, Canada. The Porcupine Camp, located above a sequence of Archean basaltic volcanic rocks, led to the establishment of Timmins.

The Hollinger-McIntyre is a giant deposit, located in the Porcupine Mining Camp of northeastern Ontario.

The Hollinger-McIntyre deposit is hosted by mafic volcanic rocks of the central and upper Tisdale assemblages that are intruded by porphyritic intrusions. Mafic volcanic rocks in the deposit have generally been divided into three units: the Northern, Central and Vipond Formations.

The Hollinger Mine historically was developed on gold bearing veins which are structurally controlled by lithologic contacts and deformation zones associated with altered Central and Vipond Formation volcanics. These units strike N55E and 70 SE, and are folded into an anticline. The Northern formation occurs in the core of Central Tisdale Anticline. The Central Formation hosts most of the major veins systems in the Hollinger and McIntyre mines. It is comprised of a heterogeneous sequence and the basal units in the Central Formation are the most important ore hosts in the deposit. The Vipond Formation is the youngest volcanic package in the deposit area.

The lavas have been intruded by a group of porphyry stocks, the largest of which is the Pearl Lake Porphyry. The porphyries are generally conformable to the folds within enclosed rocks and plunge at 45 to 50 degrees E. The porphyry deposits occur in areas of bedrock depressions beneath the lakes, suggesting that they are softer and more prone to erosion than the mafic volcanic rock units that they intrude into.

The core of the Hollinger-McIntyre deposits is an elliptical area of high strain developed along the south limb of the Central Tisdale anticline which surrounds the Pearl Lake porphyry and is approximately 450 to 600 m wide by more than 3 km in length. The elliptical fold of Central Tisdale anticline contains a series of subsidiary folds including the Northern anticline, Hollinger syncline and the Hollinger anticline. The elliptical nature of this structure in plan is due to the non-cylindrical, doubly plunging properties that closes the structure to both the east and west.

There is sufficient grade at specific gold price-points to mine a 150m deep pit, with the rock being processed at the nearby Dome Mine mill. The voids (sub-vertical stopes, shafts, and connecting drifts/drives) are sometimes spaced nearly 20-50m apart extending several hundred metres deep in a 2km square area beneath the City. The pit design was constrained by a regional highway (and the City’s water tower) along the northern wall, with homes and businesses on all other sides of the Property.

The Hollinger is being mined using three 6m and two 9m cuts making up 18m high benches in mostly FAIR to GOOD ground. All blasting is done with blast-mats to reduce fly-rock and noise. Because the mine is in-town, damage needs to be minimised. Earlier, blast trials were conducted to determine the depth of blast-damage induced by varying sizes of confined blasts. These trials indicated that a three-row trim shot onto a pre-sheared final wall would not induce excessive damage. To reduce the damage further, the pre-shear drill-hole spacing is adjusted for ground conditions within the immediate vicinity of voids.

This strategy sufficiently decreases the back-wall damage to less than 4m. The multi-use of probe holes to presupport the rock mass before blasting is part of the production cycle. Grouting cables into the final slopes, above and alongside voids, before blasting reduces the amount of final wall crown and wall rehabilitation required. This pattern has 8m cable-bolts on 4m spacing, drilled at -45° and -05° from the pre-shear line. On the North Wall, the dominant fabric (72/155°) is the main control on the bench face angle. This highly foliated rock mass tends to delaminate when blasted. To reduce the bench-crest attrition from delamination, pre-support is applied using 6m cables on a 6m spacing, drilled at -45° into the crest from the pre-shear line.

For each of the larger multi-bench voids encountered, individualised support designs are being implemented.

Ore from Hollinger is processed at the existing Dome mill.

Gold is recovered using a combination of gravity concentration and cyanidation techniques. The circuit consists of primary, secondary and tertiary crushing, rod/ball mill grinding, gravity concentration, cyanide leaching, carbon-in-pulp gold recovery, stripping, electro winning and refining.

Gravity gold is recovered by the use of five Knelson CD-30 Concentrators fed from the cyclone underflow. A Consep CS6000 Acacia Reactor is used to intensively leach the Knelson concentrate. The Acacia loaded solution has a dedicated electrowinning circuit. Gravity recovery accounts for up to 45% of the recovered gold, depending on ore type.

The cyclone overflows reports to a 155' thickener where the slurry density is increased to 55-60% solids. The thickener underflow feeds six leach tanks in series, which provide about 32 hours residence time.

Lime is added to the mill discharge pump boxes, thick ........