The Red October deposit owned by Saracen Mineral Holdings Ltd, and is located approximately 80 km south of Laverton, Western Australia. The deposit sits within Lake Carey and is hosted within an ultramafic-mafic sequence of rocks. There is a minor shale rich unit apparent on a NE trending contact within the sequence and this is host to the currently known mineralised zones. The main NE mineralised shear zone is located on the north-western limb of a tight isoclinal fold, which appears to buttress a felsic intrusion to both the west and north-west. The main mineralised zones are located within this northeast trending shear zones and in particular around intersections with subsidiary structures. The overall geometry of the main fault zone and its geometrical relationships with the smaller subsidiary structures suggests that these structures are fault-related tensile vein/fracture arrays. These structures would most likely have formed during a left-lateral sinistral movement on the main fault, most likely during the D4b regional event. However, there has most likely been a localised rotation of the stress field from NE to more NNE to be at an optimal orientation for sinistral movement on the main structure.
Rock relationships were also observed during the mine visit and it appears that both brittle and ductile (elastic-plastic) deformation is evidenced throughout the mine and core samples. Shearing along faults planes has enabled reactivation and dilational structures to focus both stress and strain and result in the formation of brittle and brecciated domains. The paragenetic sequence observed from both core and underground relationships appears to be related to the reactivation of the earlier structures formed during the sinistral movement on the main fault. This dextral reactivation on earlier structures is probably responsible for the main mineralising phase of the deposit. The approach taken by GMEX in this project to assist the Saracen Red October exploration team with continued exploration and targeting within the mine sequence was to help them understand the geomechanical response of the mine area during deformation. During simulations of the proposed deformation events this would ultimately help to indicate areas of volumetric changes (dilation), shear stress/strain and fluid focusing which would help to identify potential targets for mineralisation. Geomechanical modelling displayed maximum shear strain rates and volumetric strain increments localising particularly well around inflections on all surfaces, and also at depth. These areas are probably a good indication of pre-conditioning of the architecture for later mineralising fluids. The modelling results correlated very well with the known mineralisation and several potential targets. Some of these targets have been successfully drilled resulting in the discovery of two high-grade shoots (see Saracen ASX Media statement 16/01/2104 and Quarterly Report Dec 2014). Further follow-up drilling on remaining targets has been planned (recent drilling results have indicated intersections such as 3.7m @120.8g/t and 12m @32g/t).
Having a better understanding of the geological processes through simulation of the deformation events, using geomechanical modelling technologies, has led to more informed decision making and exploration success at the Red October Gold Mine.