Abstract: Downhole trace and major element chemostratigraphic patterns relating to igneous fractionation processes in the Golden Mile Dolerite, Western Australia
Bibliographic record
Abstract
The largest gold mine in Australia is the Fimiston Superpit, located in the Golden Mile Camp, Kalgoorlie, Western Australia. This mesothermal gold mine is jointly owned by Barrick Gold Corp. and Newmont Mining Corp. through Kalgoorlie Consolidated Gold Mines. The main host to mineralization is the differentiated Golden Mile dolerite: a sill up to 940 m thick. Previous research has subdivided the Golden Mile dolerite into ten units based on mineralogy, primary igneous texture and iron/titanium oxide mode and morphology. The area is structurally complex and boasts several deformational events. Zones of intense hydrothermal alteration with concurrent obliteration of primary igneous textures are common. These factors have made chemostratigraphic studies of the intrusion important for determining stratigraphic position within the sill during deep exploration drilling. Distinct downhole geochemical patterns in both major and trace elements using molar element ratios have constrained a set of igneous differentiation processes responsible for the mineral mode and textural diversity of the sill. (Al/2+Na/2)/Zr and (Ca/2+Fe/2+Mg/2-Al/4+Na/4)/Zr molar ratios that specifi cally track the addition or loss of plagioclase and pyroxene, exhibit patterns that allow recognition of pyroxene cumulates in the lower units of the sill, despite the textural ambiguity created by subsequent hydrothermal alteration. A major lithological discontinuity associated with the introduction of magnetite to the liquidus assemblage occurred at the base of Unit 6. Differences in shapes of the Ti/Zr and V/Zr downhole patterns give insight into the chemical controls that infl uenced the distribution of these elements in the magma chamber. V has a higher magnetite-melt partition coeffi cient than Ti. The steeply-decaying V/Zr downhole pattern refl ects the rapid depletion of V from the magma chamber as it strongly partitioned into the fractionating magnetite. The ‘box’-shaped downhole depletion pattern observed for Ti/Zr is a result of the coupled substitution of Ti with ferrous iron in the magnetite-ulvospinel phase. Additionally, the downhole plots of base metals (Cu/Zr, Zn/Zr and Ni/Zr) exhibit enrichments that coincide with magnetite saturation. However, detectable concentrations of these elements are not observed in magnetite. They reside in anomalous concentrations of disseminated sulphide minerals (chalcopyrite and pyrite) in the magnetite-bearing portion of the sill. The presence of these co-occurring sulphide minerals with magnetite likely resulted from liquid immiscibility of a sulphide melt triggered by the saturation of magnetite in the magma chamber. In summary, chemostratigraphic patterns observed in ratios tracking the material transfers of major elements and igneous minerals, and ratios responding to trace element partitioning of V, Ti, Cu, Ni and Zn into magnetite and an immiscible sulphide liquid, reveal new information about the igneous evolution of the Golden Mile dolerite. These patterns facilitate confi dent recognition of stratigraphic level in deep exploration drill cores, despite subsequent hydrothermal alteration effect.
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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 | 0.000 |
| 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) | 0.002 | 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".