High-Grade Magmatic Platinum Group Element-Cu(-Ni) Sulfide Mineralization Associated with the Rathbun Offset Dike of the Sudbury Igneous Complex (Ontario, Canada)
Bibliographic record
Abstract
Abstract Quartz dioritic impact melt dikes around the 1.85 Ga Sudbury Igneous Complex, locally referred to as offset dikes, are well endowed with respect to Ni-Cu-platinum group elements (PGE). However, only those dikes proximal (<6 km) to the main mass of the Sudbury Complex are mineralized at an economic grade and, in places, host world-class deposits. We report on a new discovery of such heavily mineralized offset dike at Rathbun Lake, about 15 km east of the currently known extent of the Sudbury Igneous Complex. There, a segment of amphibole quartz diorite is exposed at the contact between Huronian metasedimentary rocks and gabbro of the 2.22 Ga Nipissing Suite, xenoliths of which are abundant throughout the diorite and record textural evidence of partial melting. The mafic inclusion-bearing quartz diorite is the host of the Rathbun Lake showing, a small but high-grade PGE-Cu(-Ni) sulfide occurrence of hitherto controversial origin. A detailed petrographic and mineralogical characterization of this occurrence revealed a two-stage mineralization history. Disseminated to semimassive (net-textured) chalcopyrite ± loop-textured pentlandite ± magnetite containing Pd-bismuthotellurides and, more rarely, sperrylite and native gold—all of which are closely associated with base metal sulfides—are interpreted as magmatic. The semimassive sulfide averages ~40 g/t Pd + Pt + Au at a Cu/(Cu + Ni) of >0.9 and a Pd/Ir of >100,000. Mineralogy, ore textures, and mantle-normalized PGE + Au patterns match a specific type of Cu-rich mineralization in the Sudbury Igneous Complex known as footwall mineralization. By analogy with these footwall deposits, the occurrence is interpreted as having formed by downward percolation of a highly fractionated sulfide melt toward the bottom of a now largely eroded offset dike. The magmatic paragenesis was hydrothermally overprinted at lower greenschist-facies conditions to pyrite-chalcopyrite-violarite ± covellite ± millerite. This involved also local remobilization into pyrite-chalcopyrite veinlets and the liberation of precious metal minerals from their sulfide hosts. In contrast to base metal sulfides, most precious metal minerals were resistant to hydrothermal alteration, although corrosion of some grains is noted as well as their truncation by chlorite and epidote. Micron-scale X-ray mapping revealed a progressive replacement of magmatic Pd-Bi-Te minerals, where in contact with hydrous silicates, by Sb- and Hg-bearing Pd minerals such as temagamite, Pd3HgTe3. The timing and nature of this hydrothermal overprint remains uncertain, but a connection to later regional metamorphism and faulting seems most plausible. Our finding of magmatic PGE-base metal sulfide at Rathbun Lake suggests a new subtype of distal offset dike-hosted mineralization in an area so far not known for offset dikes. It opens up new opportunities in the search for unconventional ore deposits around the Sudbury impact structure and improves our understanding on the distribution of impact melt-derived dikes around complex craters.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.014 | 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 teacher head, 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".