REDISCOVERING SOUTHEAST MISSOURI MISSISSIPPI VALLEY-TYPE Pb-Zn DEPOSITS: THE Co-Ni ENRICHED HIGDON DEPOSIT, MADISON AND PERRY COUNTIES
Bibliographic record
Abstract
The Higdon deposit is located on the east flank of the St. Francois Mountains, approximately 11.5 km NE of Fredericktown, MO in the Mine LaMotte-Fredericktown district of the world renown Southeast Missouri (SEMO) region of Mississippi Valley-type (MVT) deposits. It was discovered in the 1950s and an attempt to mine the deposit was made in the 1960s. In the 2000s the importance of the Higdon deposit increased after extensive exploration by The Doe Run Mining Co. revealed a larger deposit, greater Ni-Co content than initially estimated and the presence of a low grade Unconformity-type Uranium deposit, similar to those of the Athabasca Basin in Canada. The overall paragenetic sequence, stratigraphy and stratigraphic controls of the Higdon deposit resembles those present in other SEMO MVT deposits located at the east flank of the St. Francois Mountains. The stratigraphy includes the Cambrian formations: Eminence, Potosi, Derby-Doe Run, Davis, Bonneterre and Lamotte which unconformably overlies Precambrian granitic intrusions. A common feature is the presence of collapse breccias especially at the base of the Bonneterre Formation and a relatively thin Lamotte Formation. Fine-grained, disseminated sulfides of Fe, Pb, Zn, Co and Ni are hosted in the lower one third of the Bonneterre Formation and upper two thirds of the Lamotte Formation, in a series of grainstone beds, open spaces in collapse breccias, near pinch outs of the Lamotte Formation against basement highs. Disseminations and nodules of pitchblende (uraninite) occur through the entire Lamotte Formation. The Higdon deposit differs in several important ways from the deposits of the Viburnum Trend on the west flank of the St. Francois Mountains. These differences include a distinctly lower stratigraphic interval of collapse breccias and mineralization, greater abundance of Co-Ni minerals, presence of pitchblende, and a significant fault control of mineralization. Several regionally extensive high angle faults aligned parallel to the NW-striking Simms Mountain and Mine LaMotte fault systems bound the deposit, especially the high Ni-Co-U portion. Petrographic and microprobe studies at Higdon revealed a mineral paragenetic sequence of uraninite (pitchblende, within a carbon matrix), pyrite, marcasite, chalcopyrite, bravoite, siegenite, gerdorsffite, sphalerite and galena. These minerals were deposited in four different stages: (1) a U dominated stage that precipitated the pitchblende during Early Ordovician to Permian time; (2) a Fe sulfide dominated sulfide characterized by pyrite, marcasite and bravoite; (3) a Cu-Co-Ni stage dominated by chalcopyrite and siegenite, and (4) a Zn-Pb stage characterized by the precipitation of sphalerite and galena. Precambrian uraniferous granitic intrusions in the vicinity of the Higdon deposit supplied the U for the pitchblende mineralization. At Higdon the U mineralization represents an overlapping deposit in an otherwise MVT system. This required leaching by fluids migrating through the basement along high angle faults and U precipitation in a reducing environment as the fluids encountered the Lamotte Formation. The Ni and Co were possibly leached from mafic and ultramafic intrusions along the Reelfoot Rift or from the Precambrian basement and transported to the Higdon area by fluids migrating along the regional NW-trending faults. Mixing with connate Pb-Zn brines moving laterally through the Lamotte Sandstone and other permeable units may have triggered the sulfide precipitation. Finally, the Higdon deposit is anomalous in the tonnage and grade of its Ni-Co resource (0.17 % Ni, 0.14 % Co) with significant values contained in siegenite (30.9 % Ni, 23.9 % Co), bravoite (0.04 % Ni, 6.3 % Co), gerdorsffite (26.1 % Ni, 8.0 % Co) and marcasite-pyrite (0.3 % Ni, 0.2 % Co).
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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 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".