Isotopic, Chemical, and Textural Evidence for Pervasive Calcite Dissolution and Precipitation Accompanying Hydrothermal Fluid Flow in Low-Temperature, Carbonate-Hosted, Gold Systems
Bibliographic record
Abstract
<p>Oxygen isotope ratios measured from microdrilled calcite in limestone wall rocks at the Banshee Carlin-type Au deposit show marked depletion proximal to Au mineralization, indicating isotopic exchange between wall-rock calcite and hydrothermal fluids. Isotopic alteration is spatially coincident with mineralization and puts minimum constraints on hydrothermal fluid infiltration outside of visible indicators (i.e., carbonate dissolution and silicification). Additionally, <sup>18</sup>O depletion is nearly homogeneous at hand-specimen scale indicating near-complete alteration of limestone protolith. The primary mechanism of isotopic exchange is coupled dissolution- precipitation leading to pseudomorphic replacement of calcite during hydrothermal fluid infiltration. Surface reactions between calcite and the hydrothermal fluids are evidenced by textural and chemical variations between altered and unaltered calcite in wall-rock limestone and limestone breccia. Cathodoluminescence (CL) reveals distinct changes in the luminescence of altered calcite relative to unaltered equivalent calcite, and laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) data from altered and unaltered calcite show that observed CL responses are due to changes in calcite mineral chemistry. Altered samples exhibit bright CL responses in calcite with increases in Mn and Fe. In addition to wall-rock calcite alteration, calcite veins without clear paragenetic relationships can be related to hydrothermal alteration owing to <sup>18</sup>O depletion, CL response, and positive Eu* anomalies. Together, isotopic alteration of wall-rock calcite and evidence of hydrothermal calcite veins define the distal expression of low-temperature hydrothermal alteration in calcite-bearing rocks at the Banshee deposit.</p>
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".