MORPHOLOGICAL AND CHEMICAL STUDY OF PLACER GOLD FROM THE SAN LUIS RANGE, ARGENTINA
Bibliographic record
Abstract
The composition of placer gold from the San Luis Range, Argentina, is poorly documented, although these deposits have been known since the 18th century. A detailed study of gold grains collected from different streams in the La Carolina gold district was carried out. We performed 502 analyses on 191 grains. The core composition of the gold grains is heterogeneous, with an average chemical composition of 58 to 74 wt. % Au, 25 to 40 % Ag, up to 0.5 % Hg, and less than 0.4 % Cu. The rim of each grain is generally richer in gold than the core, and the contact between rim and core is very sharp but of irregular shape and complex texture. There are populations with different chemical composition, but the compositional differences among rounded grains and those having a more delicate morphology are not invariably either significant or consistent. All sources are restricted to deposits associated with Tertiary volcanic rocks in the area, and the variable and wide range of fineness points to low-sulfidation epithermal-type deposits as the most likely source. The sharpness of the core–rim contact may result from either electrochemical processes active in the stream or stream sediments, or Au and Ag dissolution processes followed by Au precipitation in surface or near-surface environments. The presence of overgrowths of gold on gold grains suggests that there was secondary precipitation of gold after the host grain was formed. Gold grains do grow in low-temperature geochemical settings, and we believe that their composition becomes more gold-rich as the grains move downstream or are buried in the sediments. Anthropogenic Hg was detected in some of the streams, and even where there are several sources for it, we believe that all of it is coming from the
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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 | 0.002 | 0.001 |
| 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".