Abstract

New structural and geochronological data and interpretations from the Timmins-Porcupine gold camp, Abitibi subprovince, more precisely define the stratigraphy and the generation, timing, and effects of deformation. Tisdale (basalts) and Porcupine (volcaniclastic and turbiditic sedimentary rocks) assemblage rocks exhibit three major foliations (S2, S3, S4, plus a late constrictional fabric), of which S3 and S4 are also present in younger Timiskaming assemblage sedimentary rocks. Pre-Timiskaming folding has long been recognized in Tisdale assemblage rocks, but no foliation had previously been attributed to such an event.

D1 regional uplift and extension produced a low-angle unconformity between the Tisdale and Porcupine assemblages, with partial excision of upper Tisdale stratigraphy and perhaps of the Blake River assemblage. D2 involved imbrication of a set of south-over-north thrust sheets rooted in the Porcupine-Destor deformation zone. D3 en echelon folds along the northern flank of the Porcupine-Destor deformation zone are a result of left-lateral strike-slip along this zone. The Timiskaming basin, lying along the curvilinear trace of the Porcupine-Destor deformation zone, formed as a D3 transtensional half graben, and the Dome fault formed its faulted margin. S4 foliation formed during subsequent right-lateral strike-slip movement and folding of S3 foliation. Intense D5 constrictional strain deformed earlier lineations, as the previously dilatational jog that hosts Timiskaming assemblage rocks acted as a compressional jog during right-lateral movement along the Porcupine-Destor deformation zone. These D2 to D5 phases represent an overall thrusting–strike-slip transpressional regime.

There were several phases of gold mineralization in the Timmins-Porcupine gold camp. Clasts of ankerite veins occur in Timiskaming assemblage conglomerate at the Dome mine, and D3 foliation and folds crosscut early ankerite veining and alteration and some quartz veining. Thus, low-grade mineralization and possibly the quartz-fuchsite veins predate Timiskaming sedimentation. However, the bulk of gold postdates Timiskaming sedimentation. Quartz-carbonate-tourmaline-gold veins (Hollinger-McIntyre, Hoyle Pond, Dome, Aunor–Delnite mines) formed within Timiskaming assemblage and Tisdale assemblage rocks. These gold deposits developed largely as oblique slip and extensional vein arrays formed during north-south shortening and local strike-slip faulting. Younger deposits (Pamour) are associated with D4 dip-slip faulting and were weakly deformed during late D4. Thus, the largest known Archean lode gold camp formed throughout protracted orogenesis consisting of a broadly transpressional regime with unusually well developed early thrusting.

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