The influence of dikes on auriferous shear zone development within granitoid intrusions: the Bourlamaque pluton, Val-d'Or district, Abitibi greenstone belt

Abstract

Shear-zone-related gold–quartz veins in granitoid intrusions are commonly intimately associated with mafic dikes, which may have a profound influence on the localization, orientation, and kinematics of auriferous shear zones. The Bourlamaque pluton of the Val-d'Or district contains several economic auriferous shear zones, most of which follow and overprint diorite dikes. Mineralization in all deposits consists of quartz–tourmaline–pyrite veins in reverse- oblique orientation with a significant range of strike, dip, and slip direction. The geometry and kinematics of shear zone and vein array within the pluton is more complex than the simple conjugate pattern predicted for a deforming homogeneous intrusion. The stress tensor determined from the auriferous shear zones within the pluton indicates the same northerly-directed compression recorded by similar shear zones outside the pluton. This indicates that the complex shear zone and vein pattern within the pluton reflects the influence of diorite dikes, which acted as weak layers that were activated during subsequent deformation, showing the importance of layer anisotropy in auriferous shear zone development.The plunges of orebodies bear simple geometric relationships to the slip direction along a host shear zone: these are generally perpendicular to, or in some cases parallel to, the slip direction. Knowledge of the slip directions along activated dikes would therefore allow prediction of the possible plunge(s) of orebodies at early stages of exploration programs. Slip direction along an activated layer is controlled by the orientation of the layer with respect to the stress field and by the relative magnitudes of the three principal stresses. Using techniques developed for analysis of fault slip data, both parameters can be determined, provided there is a sufficient database, and slip direction can be predicted for activated layers of any orientations.

Modelling Seismically Induced Mesothermal Goldfields along the Deep-Rooted Cadillac-Larder Lake Fault, Abitibi, Canada

“…Several deposits in the Val-d'Or and Bourlamaque districts (including Sigma-Lamaque), correlating with predicted damage zones, have previously been interpreted as formed during reverse movement on E-W faults associated with N-S shortening [94][95][96]. However, faults recorded in these deposits mostly display oblique reverse movements that are compatible with NW-SE shortening [97,98], meaning that part of the mineralization in these districts can be related to the late dextral strike-slip deformational event. Moreover, damage zones in Val-d'Or and Bourlamaque districts are triggered by the Rivière-Héva and Lapause Faults, both of which are southeast-striking and steeply dipping.…”

Drill-Hole Design for Dilational Ore Shoot Targets in Fault-Fill Veins

“…Other examples in epithermal systems include (1) the strike slip-hosted Caylloma Ag-Au-base metal quartz vein system in southern Perú, a low-to intermediate-sulfidation deposit hosted in Tertiary volcanic rocks ( Fig. 8.10a) and the reverse-oblique slip Dumont deposit (Belkabir et al, 1993, cited in Robert et al, 1994 fig. 4B; Echavarría et al, 2003).…”

Geochemical and mineralogical diagnosis on gold ores: A case study from the Cadillac–Larder Lake Fault Zone, Abitibi, Canada

“…The Bourlamaque quartz diorite pluton hosts a number of gold deposits (Jébrak et al, 1991), and has an ovoid shape with a long axis parallel to the dominant regional E-W-trending structure in this area (Jébrak et al, 1991). This pluton is thought to have formed during the same volcanic and magmatic event that formed the Val-d'Or Formation (Belkabir et al, 1993;Kerrich and King, 1993;Faure, 2009). Two types of gold deposit have been identified within the Val-d'Or sediment, namely (1) disseminated gold with sulfides, hosted by massive, fractured, or brecciated wall rocks, and (2) vein-type deposits (Robert, 1990(Robert, , 1994Jébrak et al, 1991;Couture et al, 1994).…”