Proterozoic Lode Gold and (Iron)-Copper-Gold Deposits
Bibliographic record
Abstract
Abstract More than 150 Moz of gold has been added in production and resources from Proterozoic deposits in the last ten years, and many Proterozoic basins are now considered high priority exploration targets. The bulk of Proterozoic gold is produced from lode gold and Cu-Au (U-REE-Ba-F) deposits which are found in northern Australia, South Dakota, West Africa, Canada, South Africa, Scandinavia, and Central America. Proterozoic lode gold deposits are restricted to late collisional stages in the development of Proterozoic orogenic belts. They appear to have a systematic sequence of events in common and occur in linear belts associated with regional ductile structures at, or near, the greenschist facies brittle-ductile transition. Gold occurs in a large variety of rock types and has a close spatial association with regional-scale domes, anticlines, strike-slip shear zones, duplex thrusts, and in some deposits, geochemically distinct granites. Deposit styles can be subdivided into several types, directly related to the host structure and to contrasts in host-rock competency and mineralogy. These deposits have fluids and geochemical associations that overlap those of Archean lode gold deposits. Proterozoic Cu-Au-(Fe) deposits formed in a broader range of crustal and tectonic environments and display a great variety of structural and host-rock controls and styles. It is evident in all districts where the timing relationships are known that these deposits have spatial and temporal relationships to granites. These deposits display a range of fault and shear zone controls and are commonly associated with regions of geometric complexity, structural intersections, or regionally anomalous structural orientations. There is considerable evidence of variable fluid chemistry in Cu-Au-(Fe) deposits. Districts are commonly characterized by regional metasomatism and alteration at both regional and deposit scale which is commonly intense. Fe oxide-Cu-Au environments tend to produce similar alteration assemblages in all aluminous rock types. The influence of magmas as sources of fluid and ore components appears to have been greater in at least some Cu-Au-(Fe) systems and the associated granitoids are typically oxidized and include both mafic and felsic varieties. Sodic alteration styles are commonly prevalent regionally; the larger ore systems in particular are hosted specifically within substantial bodies of rock that are depleted in Na and enriched in K-Fe-(H).
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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 | 0.000 | 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".