Sulfur isotope compositions in the weathering profile of magmatic Ni-Cu deposits in SW Australia
Notice bibliographique
Résumé
The Nova-Bollinger Ni-Cu sulfide ore deposit is hosted in layered mafic and ultramafic intrusive rocks of the Mesoproterozoic Albany-Fraser zone, located about 160 km east-northeast of Norseman, Western Australia. Nova and Bollinger are two adjacent but spatially distinct orebodies with a combined pre-mining resource estimate of 13.1 million tonnes (Mt) with about 2 % Ni, 0.8 % Cu, and 0.1 % Co (IGO Ltd., unpublished data, 2018) 1. Significant challenges are posed in exploring for magmatic Ni-Cu deposits that are buried under post-mineral cover. For example, electromagnetic and gravity surveys identify numerous targets but are unable to distinguish economic mineralization. Previously, it was suggested that the regular pattern of S isotope compositions (δ34SCDT) of surficial sulfate in lakes and groundwaters in southern Australia provides an ideal baseline against which to search for anomalous δ34SCDT values associated with base-metal or gold mineralization 2. In the absence of lakes and readily accessible groundwaters in prospective areas, soils and rocks make a convenient sampling medium. Here, we investigated the exploration potential of δ34SCDT of the trace sulfur content of unconsolidated surface sediments, saprolite, and bedrock samples above Nova and two nearby sub-economic prospects, Griffin and Chimera. The δ34SCDT values likely reflect a two end-member system, with values ranging from -5.8 at depth to 21.4 ‰ near the surface, showing little dependence on lithology. Values in samples closer to the surface are similar to modern seawater sulfate that has a globally homogenous δ34SCDT value of 21.0 ± 0.2 ‰ 3, whereas at depth, values approach typical mantle S isotopic compositions of 0 ± 2 ‰ 4. In support of this, rocks at Nova have a δ34SCDT of around 0 ‰ and regional metagabbro are between -2 and 4 ‰ 5. On a regional scale, in both Western Australia (Yilgarn Block) and South Australia, the δ34SCDT values of surficial gypsum have a regular pattern over distances of up to 1000 km, with the highest values (~ 21 ‰) near coastlines decreasing to δ34SCDT values of ~ 14 ‰ further inland 2. This is suggested to be predominantly the result of the delivery of salts to the Australian landscape as aerosols, with volatile biogenic S compounds of mostly marine origin (δ34SCDT of ~ 1 ‰) that proportionately increase in importance further inland resulting in decreasing δ34SCDT values 2. Located approximately 200 km inland, δ34SCDT results in samples within 10 metres of the surface at Nova, Griffin, and Chimera are in agreement with this and range from 12.6 to 20.4 ‰. Given that near-surface δ34SCDT values above Nova, Griffin, and Chimera appear to be mostly related to seawater-derived sulfate with minimal magmatic influence, δ34SCDT shows little potential as a field sampling technique to vector for deposits buried under post-mineral cover. However, at depth, δ34SCDT shows a clear relationship between the mixing of seawater sulfate and magmatic S weathering into the environment, indicating that analysis of S isotopes of otherwise apparently barren cores has utility in mineral exploration.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».