Mineral exploration of the Nechako plateau, Central British Columbia, using lake sediment geochemistry
Notice bibliographique
Résumé
A lake sediment geochemical survey was undertaken over the Nechako plateau, central British Columbia, to test applicability of lake sediment sampling to regional exploration. Organic-rich samples were collected near the centres of approximately 500 lakes on a helicopter-assisted survey covering some 16,000 km². It was found that lakes overlying each of five major lithologies contain distinctive suites of trace metals, and that regional variations of Cu, Mo, Pb, Zn, Ni, Cr, Sr, Ba, Ag, Co, V, and Ga are related to differences in underlying geology, whereas anomalous levels of Cu, Mo, Pb, and Zn reflect mineralized bedrock or rock types favourable to the occurrence of sulphide concentrations. Possible mechanisms of anomaly generation were examined by detailed studies of the Capoose Lake Cu-Mo-Pb-Zn anomaly, and the Fish and Portnoy Lake Cu-Mo anomalies, both previously defined by the regional survey. Capoose Lake, a large cligotrophic lake, occupies a 'U'-shaped valley, and is characterized by Fe- and Mn-rich and organic-poor sediment. In contrast. Fish and Portnoy Lakes are small dystrophic and eutrophic ponds, respectively, completely surrounded by bogs. They contain organic-rich and Fe- and Mn-poor sediment. These studies show that anomalous accumulation of Cu, Zn, and Mo in soils, streams, and lakes reflects weathering of sulphide occurrences. Cu, Zn, Mo, Fe, and Mn concentrations associated with chemical phases comprising overburden materials were partitioned using partial extraction experiments. Cu, Zn, and Mo anomalies in soils reflecting mineral occurrences are commonly hydromorphic, although anomalies formed by mechanical processes are prominent near bedrock exposures. Cu and Zn are more firmly bound in soils and stream sediments than lake sediments, with the proportion of these elements associated with (and presumably scavenged by) amorphous Fe oxides increasing from soils to stream sediments to lake sediments. Mo is held by both amorphous and crystalline Fe oxides. An increase in the scavenging ability of amorphous Fe oxides from soils to streams sediments also is observed in the Fish and Portnoy Lakes area. However the bulk of the Cu, Zn, and Mo in the latter two lakes is apparently bound to organic matter. Metal levels within lake sediments are highly variable, and within each lake the maximum range of concentrations commonly exceeds an order of magnitude. Zones of greatest Cu, Zn, and Bo enrichment are within 10 to 150 m from shore, downslope from mineral occurrences. Metal accumulation favours zones slightly above the base of the nearshore slope, where the volume of emerging groundwater presumably is greatest. Anomalies are also generated by inputs of metal-rich fines carried by streams. Consequently for maximum anomaly contrast, samples should be collected from zones where dissolved metals or metal-rich silt and clay are flowing into a lake. Coarse clastic sediment should be avoided.
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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 | 0,002 |
| Études des sciences et des technologies | 0,002 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,001 |
| 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 ».