Interrogating the composition and genesis of argillite-hosted pyrite nodules at the LaRonde Penna gold-rich volcanogenic massive sulphide deposit, Abitibi, Quebec: insights into metallogenic implications
Bibliographic record
Abstract
This study investigates pyrite nodules hosted in argillite horizons within (Zn-Ag-Au-Cu±Pb) massive sulphide ore of the 20N Zn zone at the LaRonde Penna Au-rich volcanogenic massive sulphide deposit, Abitibi greenstone belt, Quebec. Two pyrite nodules are examined in detail: LA-001 and LA-002. These nodules are spherical and oblate spheroidal in shape and display similar textures, including a core (zone 1) composed of fine, equigranular grains with variable amounts of silicate-carbonate inclusions; a rim (zones 2a to c) that varies from inclusion-poor to -rich and consists of equigranular to radially oriented, acicular pyrite grains; and a thin layer of idiomorphic pyrite overgrowth that surrounds the nodules (zone 3). Sulphide inclusions in nodule LA-001 consist predominantly of sphalerite, whereas sulphide inclusions in nodule LA-002 include an assemblage of sphalerite, Zn-bearing stannite (Cu2(Fe,Zn)SnS4), and galena, all of which occur also in the surrounding massive sulphide ore. In nodule LA-002, sphalerite is intimately associated with stannite, and together they are preferentially concentrated along both the concentric zones of the inclusion-rich section of the rim (zone 2b) and within the radially bladed rim (zone 2c), parallel to blade elongation. Whereas textures are similar in the two nodules, compositional maps generated by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) reveal important distinctions in element distribution patterns for inclusion-partitioned elements (Cu, Zn, Sn, Pb, Bi), which reflect the mineralogy and bulk abundances for lattice-bound elements (Ni, As, Au). Gold is mainly concentrated in the fine-grained cores, but in different amounts in LA-001 (average of 0.38 ppm Au; n = 6918) and LA-002 (average of 1.04 ppm Au; n = 10,539). Nickel and As values in LA-001 are respectively 10 and 3 times greater than in LA-002. In both nodules, Ni is enriched in the rim relative to the core. The pyrite nodules have in situ delta-34S values (secondary ion mass spectrometry analyses) that range from -0.8 to +5.0 per mille (average +2.1 per mille, n = 50), with the core showing slightly lighter values than the rim. Based on these results, the nodules (zones 1 and 2) are interpreted to have formed by diagenetic processes and the presence of stannite, sphalerite, and galena (enrichment in Zn, Sn, Cu, and Pb) is likely the expression of a previously hydrothermally enriched sediment rather than a direct hydrothermal contribution during crystal growth. While more work is needed, the composition of pyrite nodules could potentially be used as vectors toward syngenetic mineralization.
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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 | 0.000 |
| 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) | 0.001 | 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".