The Porcupine–Destor Fault
Significant gold potential

Marc Legault and Jean Goutier
Géologie Québec

Since the first discovery of gold by John Beattie on an island in Duparquet Lake in 1910, the Porcupine–Destor Fault has continued to attract gold seekers. Although the area was the site of gold mining from 1933 to 1956 (Beattie, Donchester, Central Duparquet, and Duquesne mines) and from 1983 to 1990 (Duquesne and Yvan Vezina–Davangus mines [eastern sector]), little gold was extracted on the Québec side (~ 55 t Au – production + resources) compared to the Ontario side (~ 2300 t Au – production + resources).

In 2002, Géologie Québec undertook a metallogenic study along the Porcupine–Destor Fault in order to complete the regional mapping work begun in the early 1990s. The objective of this project is to develop new tools for gold exploration through a regional metallogenic study and 3D modelling. The purpose of the metallogenic study is to characterize the various gold occurrences in order to define the chronology, mineralization controls and regional alteration patterns. This study should explain the enormous variation in gold concentrations on either side of the border.

Regional geology

The Porcupine–Destor Fault region has been divided into three sectors: eastern, western and central. Only the western and central sectors have been examined to date. The western sector generally exhibits simple geology (basalt, gabbro) with a few felsic and ultramafic intrusions. Ultramafic volcanic rocks of the Kinojévis Group and wackes of the Kewagama Group are commonly found pinched inside the Porcupine–Destor Fault. The central sector features a shallower structural level, thereby preserving calc-alkalic (2,689 Ma) to alkalic (2,682 Ma) porphyry intrusions and a significant unconformable accumulation of Timiskaming-type conglomerate (Duparquet Formation).

Economic geology

Over 70 gold showings (> 1g/t Au) are present in the area studied along the Porcupine–Destor Fault. The gold mineralizations in the western and central sectors have different characteristics. In the western sector, there is a close spatial relationship between the location of the gold-bearing zones, the carbonate alteration and the Porcupine–Destor Fault. The mineralizations exhibit several characteristics that are typical of orogenic deposits, including a ratio of Au/Ag>>1, carbonate–quartz veins, a high iron-carbonate alteration, and structural control. Just one deposit has been defined to date in the western sector (Structure 71 (Cambior) - 195,000 t at 5.2 g/t Au). The central sector (Duparquet Basin) is distinguished by the fact that several ore-bearing zones are located far from the Porcupine–Destor Fault, being associated with subsidiary structures or porphyry intrusions. The carbonate alteration is associated with the Porcupine–Destor Fault as well as with the subsidiary structures. Several old mines and deposits are known in the central sector, including the Beattie (resources > 2.6 Mt at 3.8 g/t Au) and Duquesne (resources of 0.22 Mt at 7.8 g/t Au) mines. The ore in the Duparquet Basin is generally associated with fine-grained disseminated pyrite with few quartz–carbonate veins, as well as sericite alteration. It appears to be somewhat rheologically and/or chemically controlled and exhibits metal contents typical of epithermal deposits (Au/Ag<1, up to 50 ppm Hg, 0.34% Sb, 0.61% Zn, 0.19% Pb). However, orogenic-type mineralization has been noted in the central sector. This mineralization is generally found peripheral to the Duparquet Basin and is associated with an iron-carbonate alteration. Hence, two types of alteration (carbonates±sericite and sericite) in association with the gold mineralization are present in the central sector. This suggests the superposition of at least two separate mineralization episodes for this sector or a variation in the hydrothermal-fluid composition due to the various depths of the mineralization emplacement.

Exploration

The recent exploration work conducted by Cambior and the Globex/Kinross partnership reaffirms the gold potential along the Porcupine–Destor Fault. The presence of the Holloway and Holt–McDermott mines approximately 17 km west of the Ontario border has strongly influenced the approach of exploration in the western sector. At these two deposits, high albitization is spatially associated with the best gold values, and it is located in the centre of sericitization and carbonatization halos. However, such an alteration is rarely observed in the western sector. At the Holloway deposit, albitization and economic gold values begin at a depth of approximately 300 m. At shallower depths, only sericitization and carbonatization are present, suggesting that the highly sericitized structures must be explored at greater depths. Structure 71 exhibits high carbonate and sericite alteration but has not been explored at depths of more than 180 m. In addition, the Holt–McDermott deposit is associated with an ENE subsidiary structure south of the Porcupine–Destor Fault. Certain structures having a similar orientation are also present on the Québec side but have been only slightly explored.

In the central sector, the epithermal-type mineralization in the interior of the Duparquet Basin is possibly associated with a mineralization event prior to the Porcupine–Destor Fault and related to the development of this basin. The orogenic-type mineralization peripheral to the basin possibly represents the deep extension of the epithermal mineralization discovered during late vertical movements along the faults bordering the Duparquet Basin. It is also possible that this orogenic mineralization is associated with the Porcupine–Destor Fault and that it is not associated with the epithermal mineralization. In the central sector, exploration work is concentrated near the Porcupine–Destor Fault and some of the subsidiary structures, such as the Duquesne Fault. Little exploration work has been done on the subsidiary faults bordering the northeastern part of the basin, such as the Ottman and Lépine faults, despite their significant alteration zones (carbonate and sericite maps). In addition, except in a few sectors (Beattie, Shaft, Patino), little exploration work has been done at depths greater than 500 m.

Deep gold potential

The environment of the eastern part of the Porcupine–Destor Fault differs from that of the western part (Timmins sector) by exhibiting a lower metamorphic facies and hence a shallower structure. The lack of gold on the Québec side is therefore possibly associated with its epizonal position, as illustrated by the presence of epithermal mineralization. Therefore, the potential of the Porcupine–Destor Fault is at depth, a dimension that has been, to date, underexplored.