The nature of heavy metal contamination in organic lake sediments near the Buchans massive sulphide base metal mines, Central Newfoundland
Bibliographic record
Abstract
The Buchans mine closed in 1984 after 57 years of operation. Several orebodies, including Luck Strike, Oriental, Old Buchans, Rothermere and MacLean, produced 16,196,876 tonnes of ore with an average grade of 14.51% Zn, 7.56% Pb, 1.33% Cu, 126 grams/tonne Ag and 1.37 grams/tonne Au. Copper (chalcopyrite), lead (galena) and Zinc (sphalerite) concentrates were shipped from the port of Botwood The baritic, polymetallic orebodies were Canada’s highest grade volcanogenic massive sulphide deposits. -- To determine the impact that mining activities in and around the Buchans community had on the watersheds of the area, six lake sediment cores were collected. Four of these were taken in Red Indian Lake and two were taken in Buchans Lake, also named Sandy Lake. All cores were extracted with a K.B. Gravity lake Sediment Corer and due to the water depth in Red Indian Lake, a Deep Water operating Kit had to be used as an attachment. -- To determine the availability of the heavy metals to the environment that might be caused by subtle changes of pH or Eh, this study utilized a four step sequential extraction procedure. The four discrete operationally defined fractions that were measured were as follows: (I) Exhangeable/Carbonate, (II) Fe/Mn Oxide, (III) Organic/Sulphide, and (IV) Silicate. -- Each core was sectioned into two centimeter intervals and total concentrations were measured on 29 elements, including Cu, Pb and Zn, on all dry sediment intervals by inductively coupled plasma-optical emission spectroscopy (ICP-OES) using HCl/HF/HClO₄ digestion. Furthermore, select base metals (Cu, Pb and Zn) were analysed on the ‘wet’ and ‘dry’ samples extracted from lake sediment core RIL2B using the four step sequential extraction procedure to determine the degree to which the various metals reported to the different phase fractions. -- The total element analysis on all cores showed significant enhancement in base metals in the upper sediment intervals, particularly in Red Indian Lake, where the concentrations of copper, lead and zinc were reported as high as 4270 ppm, 2993 ppm and 12,576 ppm (dry weight) respectively. The results for all duplicate samples showed excellent correlation demonstrating a high degree of reproducibility. The agreement between the results obtained from the standard reference materials (LKSD 1-4) and the ‘certified’ published results also demonstrated a high degree of reliability. -- The sequential extraction analyses on the ‘wet’ and ‘dry’ sediment intervals from lake sediment core RIL2B showed that a significant amount of copper, lead and zinc reported to the Exchangeable/Carbonate phase with the highest values measured as 715 ppm, 2070 ppm and 2675 ppm respectively. It was also demonstrated that sediment drying appears to have a significant redistribution effect on the amount of metal reporting to the different phases. Drying of the sediment appears to increase the amount of Cu and slightly decreases the amount of Pb and Zn reporting to the Exchangeable/Carbonate phase. The reproducibility and reliability of the sequential extraction procedure was demonstrated from the analyses of the standard reference ore MP-1A. -- In conclusion, the upper lake sediments in Red Indian Lake and Buchans Lake are heavily contaminated with base metals, with the most pronounced effects occurring in Red Indian Lake. Furthermore, as demonstrated from the high concentrations of Cu, Pb and Zn that report to the first phase of the four step sequential extraction procedure, a significant amount of the metals in the lake sediments of Red Indian Lake are potentially available for release to the environment with moderate increases in acidity. The sediments have incorporated a considerable burden of pollutants and a significant portion of the lake sediments from Red Indian Lake could be considered as hazardous waste. However, since the mine closure, the lake sediments appear to be showing reduced levels of pollutants, proper site remediation is essential for lake sediment recovery.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".