The geophysical response of the Goldrush-Fourmile orebody and implications for camp-scale Carlin-type deposit exploration, Cortez District, Nevada
Bibliographic record
Abstract
Abstract Since discovery of the Goldrush and Fourmile deposits, numerous geophysical surveys have been acquired over the footprint of mineralization and surrounding areas to focus exploration. The Goldrush-Fourmile system extends more than 7 km in strike length and averages approximately 300 m wide. Most of the orebody lies more than 300 m below ground surface and continues to depths of more than 900 m. Direct detection of the ore system using geophysical tools is impeded by several factors. The system is relatively flat lying and sits in the hinge of a doubly plunging anticline. This gives the shallowest zones a very small lateral footprint. The ore consists of thin strata-bound zones of silica-sulfide mineralization with a tight alteration selvage. Structural controls along faults are limited, with only small displacements. Strong petrophysical contrasts exist between unaltered rock units. Finally, the terrain is rugged. Resistivity inversions of airborne electromagnetic data show that mineralization sits within a complex zone of resistivity responses. Close to intrusions, the host stratigraphy is resistive. Away from intrusions, the same stratigraphic units show highly variable but commonly very low resistivities. This suggests the possibility of redistribution of carbon around intrusions during premineralization metasomatism. Within the orebody, sulfide content increases conductivity within individual formations related to the distribution of fine-grained sooty pyrite. The geometry of the Red Hill Anticline is imaged as a positive density contrast in the observed gravity and geologically constrained gravity inversions. The positive density contrast represents the gross geophysical signature of denser carbonates within the Paleozoic stratigraphy. Magnetic surveys are crucial for mapping the distribution of igneous rocks and potentially hornfelsed sedimentary rocks. The challenges associated with exploring for deeply buried Carlin mineralization notwithstanding, the application of innovative geophysical tools tuned to assess specific geologic questions, combined with best-practice geologic and geochemical modeling, is helping drive exploration for additional Carlin-type mineralization across the Cortez District.
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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".