Geology of the banded iron formation-hosted Musselwhite gold deposit, Superior Province, Ontario, Canada / Géologie du gisement aurifère encaissé dans des formations de fer Musselwhite, Province du Supérieur, Ontario, Canada.
Bibliographic record
Abstract
La mine Musselwhite se situe pres du lac Opapimiskan dans le nord-ouest de l’Ontario, a 475 km au nord de la ville de Thunder Bay. En exploitation depuis 1997, plus de 4 Moz d’or y ont ete produites. Le gisement d’or de classe mondiale Musselwhite est encaisse dans les formations de fer rubanees (FFR) polydeformees au facies metamorphique des amphibolites de la ceinture de roches vertes mesoarcheenne (3.0-2.7 Ga) de North Caribou (CNC), dans le nord-ouest de la Province du Superieur. Ce type de gisement est relativement rare et peu d’etudes se sont penchees sur la genese et les controles regissant les mineralisations auriferes dans les FFR. Elles peuvent cependant former des gisements colossaux, comme l’illustre celui de Homestake de 40 Moz d’or, aux USA. Le present projet constitue une etude multidisciplinaire de la geologie et de la metallogenie du gisement d’or Musselwhite, caracterise a l’aide de donnees geologiques, structurales, petrographiques et geochimiques. La NCG est majoritairement composee de basalte et komatiite tholeiitiques dates entre 3,05 et 2,91 Ga, recouvert de greywackes syn-orogeniques (<2,85 Ga). De larges batholithes de type TTG dates entre ca. 2,85 et ca. 2,73 Ga entourent la CNC. Trois phases principales de deformation ont affecte les roches de la CNC qui sont metamorphisees au facies des amphibolites, date a ca. 2660 Ma. Les etroites enveloppes sub-verticales de minerai sont encaissees dans la FFR a grunerite-grenat affectee par des zones de forte deformation D2 associees a des plis fermes a isoclinaux. La mineralisation aurifere epigenetique s’est formee sous des conditions metamorphiques de la zone a grenat, via un remplacement a pyrrhotite et une silicification de la FFR par des fluides issus de la devolatilisation metamorphique des roches sous-jacentes. Elle est accompagnee d’une alteration distale potassique (biotite) et proximale calcique (hornblende) remplacant la grunerite dans la FFR. La teneur en or a une correlation positive avec celles de l’Ag, du Cu, Se et Te. La mineralisation aurifere a Musselwhite est synchrone a la deformation D₂ et au metamorphisme M₂, et s’est mise en place entre 2720 et 2660 Ma. Le gisement Musselwhite comporte des elements communs a d’autres gisements tels que Lupin (TNO, Canada), Homestake (USA), Nevoria (Australia), notamment le controle lithologique de la FFR silicatee sur l’or. Un tel horizon cle, un contexte structural complexe et de forts gradients de deformation sont des vecteurs d’explorations importants au sein de la CNC, du nord-ouest de la Province du Superieur, et dans d’autres terrains metamorphises precambriens. Abstract The Musselwhite mine is located near Opapimiskan Lake in northwestern Ontario, 475 km north of Thunder Bay. Over 4 Moz of gold have been produced since the start of operation in 1997. The world-class Musselwhite gold deposit is hosted by polydeformed, amphibolite-grade banded iron formations (BIF) in the Mesoarchean (3.0-2.7 Ga) North Caribou greenstone belt (NCG), in northwestern Superior Province. This deposit type is quite rare and few studies focused on their genesis and gold ore-forming processes. However, they can form large deposits, such as the Homestake mine (40 Moz of gold, USA). This project constitutes a multidisciplinary study of the geology and metallogeny of the Musselwhite gold deposit, using geological, structural, petrographic, and geochemical data. The NCG is mainly composed of tholeiitic basalts and komattites dated between 3.05 and 2.91 Ga, overlain by syn-orogenic greywackes (<2.85 Ga). Large TTG-type batholiths dated between 2.85 and 2.73 Ga surround the NCG. Three major phases of deformation affected rocks of the NCG, which were metamorphosed to amphibolite facies around 2660 Ma. Narrow sub-vertical ore zones are hosted by garnet-grunerite BIF in D2 high-strain zones associated with close to isoclinal folds. Epigenetic gold mineralization formed under garnet zone metamorphic conditions through pyrrhotite-replacement and silicification of the BIF by fluids stemming from metamorphic devolatilization of underlying rocks. It is accompanied by potassic (biotite) alteration and proximal calcic (hornblende) alteration of grunerite in the BIF. Gold grade is positively correlated with Ag, Cu, Se and Te. Gold mineralization at Musselwhite is synchronous to D₂ deformation and M₂ metamorphism, and was emplaced between 2720 and 2660 Ma. The Musselwhite deposit shows features common with other deposits such as Lupin (NWT, Canada), Homestake (USA), and Nevoria (Asutralia), notably the lithological control of silicate BIF on gold. Marker horizons, complex structural context, and strong deformation gradient are key exploration vectors in the NCG, the northwestern Superior Province, and other Precambrian terranes.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".