An experimental investigation of the potential role of liquid hydrocarbons as ore fluids for sediment-hosted ore deposits
Bibliographic record
Abstract
Crude oils and the solidified remains of hydrocarbon fluids are commonly found in sediment hosted ore deposits. Little is known, however, of the role that petroleum may play in the formation of these deposits. Here we use an experimental approach to determine whether crude oil may act as an ore fluid for these deposits by dissolving the ore metals from the underlying sediments and transporting them to the site of ore deposition. To this end, the steady-state concentrations of Ni, Zn and Pd in crude oil at 150, 200 and 250ºC were determined. The experimental approach involved reacting wires of native metal with a series of crude oils for variable periods of time until metal concentrations were seen to plateau. Metal concentrations were determined by digesting the reacted oils and analyzing the resulting solutions using Inductively-Coupled Plasma Mass Spectrometry (ICPMS). The surface of the reacted metal wires was then analyzed using X-ray Photoelectron Spectroscopy (XPS) to identify the ligands in crude oil that bind to these metals. The results of these experiments indicate that Pd, Ni and Zn are all highly soluble in crude oil from an ore deposit perspective, reaching concentrations of up to 1700 ppm Zn, 240 ppm Ni and 127 ppb Pd. From the results of the XPS experiments it is evident that Zn solubility is highest as carboxylate complexes in very acidic oils. During catagenesis, these oils may be expelled from their source rocks and injected into carbonate reservoir rocks, where they become altered through reactions with aqueous sulfate to form large volumes of hydrogen sulfide gas. This reaction is referred to as Thermochemical Sulfate Reduction (TSR) and occurs commonly in petroleum carbonate reservoirs and the carbonate-hosted ore zones of Mississippi Valley Type (MVT) deposits, a class of sediment hosted Zn-Pb deposits forming at temperatures between 100 and 140ºC. An experiment was devised to emulate the geochemical environment present in the ore zones of MVT deposits by reacting Zn-rich crude oil, with hydrogen sulfide gas and a calcite-buffered brine. Sphalerite (ZnS), the principal Zn ore mineral in MVT deposits, was observed to crystallize from the oil at the oil-brine interface, demonstrating that MVT deposits can be created from petroleum. The composition of the crystals was confirmed using X-ray Diffraction (XRD). The results of the XPS analyses of the reacted Pd and Ni wires show that these metals are most readily dissolved in crude oil as thiol complexes. Coincidentally, anomalous concentrations of thiols are commonly found in crude oils that have undergone TSR. Moreover, the results of this research indicate that Ni, Fe (and potentially Pd) play a role in catalyzing the reduction of sulfur compounds in crude oil to form thiols. Thus, it is likely that the dissolution of Ni, Fe and Pd in crude oil is not only enhanced by TSR but may also promote the reaction. Furthermore, sediment-hosted deposits containing large concentrations of these metals (e.g., the Kupferschiefer Deposit in Poland and the Talvivaara deposit in Finland) display signs of having interacted with crude oil, and the reduced sulfur in the ore minerals in these deposits appears to have been derived from TSR. It is therefore proposed that during arc-tectonic events, crude oils are generated and travel along faults in sedimentary basins, leaching metals along the way. Reactions between these crude oils and sulfate-bearing sequences are catalyzed by transition metals dissolved in the hydrocarbon liquid. As the reaction proceeds, crude oil is gradually consumed and sulfide ore minerals are precipitated to form a deposit
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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 | 0.000 | 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) | 0.001 | 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".