Damaged goods: regional deformation history and structural controls on the Hammond reef gold deposit, Atikokan, Ontario
Bibliographic record
Abstract
Hammond Reef is a low-grade (< 1 g/t or 1 ppm Au), disseminated gold deposit located in an anastomosing deformation corridor along the western margin of the 3.0 Ga Marmion tonalite gneiss, adjacent to the Marmion Shear Zone. The Marmion Shear Zone separates the Marmion gneiss and Finlayson Lake greenstone belt of the Mesoarchean Wabigoon subprovince. Most known Archean gold deposits are hosted in greenstone belt terranes. This places Hammond Reef in an under-explored environment with respect to gold exploration targets and warrants a detailed understanding of the deposit to elucidate the deformation history of the two adjoined terranes and the events that led to the gold enrichment at Hammond Reef.The deformation, intrusion and alteration events of the Finlayson Lake greenstone belt and Marmion gneiss cover over 200 million years, from the onset of deformation at 2.92 Ga to the youngest reactivation and fluid flow at around 2.70 Ga. The clockwise pressure--temperature pathway of the greenstone belt during deformation records deep subduction along a cool geothermal gradient ~ 20◦C/km), followed by underplating and exhumation. The Finlayson Lake greenstone belt docked with Marmion gneiss during exhumation. The emplacement of the Diversion Stock along the Marmion Shear Zone effectively locked the shear zone and sutured the Marmion gneiss and Finlayson Lake greenstone belt.The anastomosing deformation corridor in the Marmion gneiss is defined by local foliation that strikes parallel to the Marmion Shear Zone. Cross-cutting structural, alteration and intrusive relationships indicate that the anastomosing foliation developed after cessation of shear along the Marmion Shear Zone, during the exhumation of the sutured Marmion and Finlayson terrane. Flattening of sericite after altered feldspar was aligned parallel to the shear zone, which suggests that the anastomosing foliation developed in response to a shortening axis perpendicular to the shear zone. The deformation is kinematically correlated to the ~ 2.7 Ga Neoarchean tectonism and accretion of the Wabigoon subprovince to the Wawa subprovince. Therefore, alteration and mineralization along the Marmion Shear Zone and damage aureole occurred during the regional accretion of the Superior Province, even though the Hammond Reef gold deposit is located in a Mesoarchean terrane that experienced peak metamorphism and deformation up to 200 million years earlier. Throughout the Superior Province, gold deposits are spatially associated with east-west-trending sutures of the ~ 2.7 Ga Neoarchean tectonism. Hammond Reef is located along the northeast-trending Marmion Shear Zone to the north of the Quetico Fault, which is one of these east-west structures. The Wabigoon subprovince was located in a supra-subduction zone setting associated with the northward-directed subduction of the Wawa subprovince. This setting allowed for subduction-related fluids to migrate up through the subvertical Marmion Shear Zone and damage aureole, which led to the alteration and gold mineralization at Hammond Reef along a dormant structure. Future exploration for gold deposits of similar style should include (steep) crustal-scale structures, suitable for reactivation and fluid migration above ancient subduction zones.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".