Origin of Au-Rich Carbonate-Hosted Replacement Deposits of the Kassandra Mining District, Northern Greece: Evidence for Late Oligocene, Structurally Controlled, and Zoned Hydrothermal Systems
Bibliographic record
Abstract
Abstract The Au-rich polymetallic massive sulfide orebodies of the Kassandra mining district belong to the intrusion-related carbonate-hosted replacement deposit class. Marble lenses contained within the Stratoni fault zone host the Madem Lakkos and Mavres Petres deposits at the eastern end of the fault system, where paragenetically early skarn and massive sulfide are spatially associated with late Oligocene aplitic and porphyritic dikes. Skarn transitions into predominant massive and banded replacement sulfide bodies, which are overprinted by a younger assemblage of boulangerite-bearing, quartz-rich sulfide and late quartz-rhodochrosite vein breccias. The latter style of mineralization is most abundant at the Piavitsa prospect at the western end of the exposed fault system. The sulfide orebodies at the Olympias deposit are hosted by marble in association with the Kassandra fault, where textural and mineralogical similarities to the sulfide bodies within the Stratoni fault zone suggest a genetic relationship. Estimated trapping temperatures and pressures based on fluid inclusion data indicate that carbonate replacement mineralization took place at depths less than about 5.9 km. Carbon and oxygen isotope patterns in carbonate from the Stratoni fault zone support isotopic exchange principally through fluid–wall-rock interaction, whereas decarbonation and fluid-rock exchange reactions were important at the Olympias deposit. Carbonate minerals associated with skarn and replacement sulfide throughout the district have isotopic compositions that are consistent with formation from a hydrothermal fluid of magmatic origin. Lower homogenization temperatures and salinities in the younger quartz-rich sulfide assemblage and quartz-rhodochrosite vein breccias, together with low δ18O values of gangue carbonate, suggest dilution of a primary magmatic fluid with meteoric water late in the evolution of the hydrothermal system in both the Olympias area and the Stratoni fault zone. The replacement sulfide orebodies in the district likely inherited their uniform Pb isotope composition from a late Oligocene igneous source and the isotopically heterogeneous metamorphic basement units. Metal distribution patterns at the scale of the Stratoni fault zone show diminishing Cu concentration with decreasing Pb/Zn and Ag/Au ratios from Madem Lakkos to Mavres Petres and the Piavitsa prospect in the west. The sulfide orebodies at the Olympias deposit exhibit elevated Cu values in the east with increasing Pb/Zn and Ag/Au ratios down-plunge to the south-southwest. Metal concentration and ratios support zoning related to temperature and solubility changes with increasing distance from a probable magmatic source. Structural and igneous relationships, together with fluid inclusion microthermometric and carbon-oxygen isotope data and metal distribution patterns, are supportive of a zoned hydrothermal system that exceeded 12 km along the Stratoni fault zone, sourced by an igneous intrusion to the southeast of the Madem Lakkos deposit. The Olympias replacement sulfide orebodies, associated with the Kassandra fault, resulted from a local hydrothermal system that was likely derived from a concealed igneous intrusion to the east of the deposit.
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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) | 0.001 | 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".