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The Henderson Cu-Au deposit is contained within the metaanorthosite of the Dore Lake Complex, located at the eastern end of the Chibougamau-Matagami greenstone belt. Two ore zones, one enclosed within a shear zone (zone B) and the other in a subsidiary structure (zone D) offer an ideal situation to study the correlation between the mechanical development of a shear zone and its subsidiary structure and the evolution of mineralizing fluids. A geomechanical interpretation demonstrates thatat the onset of the development of the shear zone, subsidiary fracture patterns are developed in second order faults in the following sequence. At peak strength Riedel shears (R and R') are formed which propagate out into the walls of the shear zones producing the zone D structure. After peak strength, restraint (P) shears are developed in the thrust attitude within the shear zone. Principal displacement shears (D) developed toward residual strength in the direction of movement. The continuation of the shear displacement gives rise to schistosities within the main shear zone. While the main shear zone and the P and D shears within the main shear zone were in continual movement, the subsidiary zone D structure, once formed retained a simple fracture pattern and moved little in comparison to the main shear zone. The above model makes necessary an examination of the mechanics of dilation which created openings for fluid movements and ore concentrations. The general principle involves the mechanics of the overriding of irregular planes and surfaces and the work performed by the normal pressure a during the dilation or contraction of the system. Application of the shear fracture dilatancy model explains the dilation mechanisms in zones B and D. Although the effect of interstitial fluid pressure is incompletely known, increasing dilation should bring about a reduction of the pore fluid pressure which will change the effective normal stress and aid fluid movement.Mineralizing fluids introduced into this shear environment show a similar pattern of evolution, with a wider range of homogenization and halite disappearance temperatures in the more active zone B than within zone D. Systematic variations of Ca/Na and Ca/Mg ratios in the fluid between zones B and D indicate migration and accompanying chemical changes of the fluid from zones B to D, in keeping with the evolution of the main shear zone and its subsidiary structure. These correlations suggest strongly that fluid inclusion studies can be useful for documenting geomechanical processes.

The Linglong-Jiaojia district is one of the most important regions containing gold deposits in China. These gold deposits can be divided into: a) the pyrite-gold-quartz vein type (Linglong type), which is controlled by brittle-ductile to ductile deformation structures, and b) the alteration-zone type (Jiaojia type), characterized by small veinlets, or the disseminated type recognized in brittle shear zones. Lode gold deposits in the Jiaojia area occur in NE brittle fracture zones, formed in a dominantly simple shear deformation regime, mainly in thrust attitude with a minor sinistral strike slip component. In the Linglong area, the lode gold deposits are located at the intersection of three types of structures: NNE and NE brittle-ductile fault zones and the ENE ductile reverse shear zone in the south of the area. The structural characteristics of these brittle shear zones are consistent with a tectonic NNW-SSE principal stress field orientation. Similar stresses explain the ENE Qixia fold axes, the Potouqing and several other ENE reverse ductile shear zones elsewhere in the region, the Tancheng-Lujiang fault zone and its subsidiaries in the vicinity of the Linglong-Jiaojia district, as well as the southern ENE suture zone north of Qingdao. Therefore these structural systems occurred as part of different major tectonic events under NNW-SSE compression principal stress fields in the area.Gold deposits are hosted in smaller-scale structures within the brittle fault zones and brittle-ductile shear zones. Although ore bodies and, on a smaller scale, quartz ore veins often seem to be randomly oriented, it is possible to explain their distribution and orientation in terms of the simple shear deformation process under which they were developed. The progressive simple shear failure is characterized by various fracture modes (tension and shear) that intervene in sequence. The tension and shear fractures are influenced by the stress level (depth of burial beneath the paleosurface) in their structural behavior, show variable dilatancy (void openings) and extend on all scales. By making use of these characteristics, a progressive failure analysis can be applied to predicting the shape and extent of ore bodies as well as the styles of mineralization at any given location.

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