Hydrocarbons as ore fluids

Abstract

Conventional wisdom holds that aqueous solutions are the only non-magmatic fluids capable of concentrating metals in the Earth's crust. The role of hydrocarbons in metal concentration is relegated to providing geochemical barriers at which the metals are reduced and immobilised. Liquid hydrocarbons, however, are also known to be able to carry appreciable concentrations of metals, and travel considerable distances. Here we report the results of an experimental determination of bulk solubilities of Au, Zn, and U in a variety of crude oils at temperatures up to 300 °C and of the benchtop-scale transport experiments that simulate hydrocarbon-mediated re-deposition of Zn at 25-200 °C. It has been demonstrated that the metal concentrations obtained in solubility experiments are within the range of concentrations that are typically considered sufficient for aqueous fluids to form ore bodies. It has also been shown that Zn can be efficiently transported and re-deposited by hydrocarbons. These results provide direct evidence of the ability of natural crude oils to mobilise metals available in hydrocarbon-associated host rocks, and transport them in concentrations sufficient to contribute to ore-forming processes.

Tools for uranium characterization in carbonate samples: case studies of natural U–Pb geochronology reference materials

“…Recent work on modern calcite from a deep granite aquifer with a reducing fluid suggests a mechanism for U 4+ transport (Drake et al, 2018). Experimental work at elevated T has shown that U 6+ Cl 0 4 is soluble in acid solutions (Timofeev et al, 2018), and high T experiments of U in hydrocarbons indicate that economic concentrations can be produced via transport in hydrocarbons (Migdisov et al, 2017), but how would these processes result in incorporation in carbonates? There is likely more than one mechanism and this is a fruitful avenue for future research both of synthetic and natural carbonate samples.…”

“…Given that the major element composition of seawater has changed appreciably through time (Hardie, 1996;Lowenstein, 2001;Horita et al, 2002), that meteoric fluid compositions are controlled by water rock interaction (Chung and Swart, 1990;Banner and Hanson, 1990), and that deep brines have evolved since deposition in basins (Musgrove and Banner, 1993), we can imagine that there is no such thing as a typical fluid. A holistic approach to dating carbonates should involve an effort to see back to the fluid or fluids that have been responsible for its formation and how they might have changed through the diagenetic history.…”

Petroleum as source and carrier of metals in epigenetic sediment-hosted mineralization

“…In the present study, we do not focus on the metal-bearing basinal brines but on the other mixing end-member(s) for which petroleum and the associated aqueous phases are involved 4–10 . Besides the established role of such organic compounds in the production of reduced sulphur for mineralization, their possible contribution to the metal pool for sulphide mineralization has only been conceptualized and tested experimentally 11,12 . Indeed, several metals (e.g., Ni, V, Mo, Zn, Cu, and Pb) are present in liquid petroleum at concentrations up to several hundreds of parts per million, similar to those related to metal-chloride complexes in basinal brines 12–14 .…”

“…Besides the established role of such organic compounds in the production of reduced sulphur for mineralization, their possible contribution to the metal pool for sulphide mineralization has only been conceptualized and tested experimentally 11,12 . Indeed, several metals (e.g., Ni, V, Mo, Zn, Cu, and Pb) are present in liquid petroleum at concentrations up to several hundreds of parts per million, similar to those related to metal-chloride complexes in basinal brines 12–14 . Therefore, potentially, petroleum compounds involved in precipitation of sulphide minerals may have also supplied metals.…”

Solubility of gold in the reduced carbonic fluid

“…В последние годы получены первые экспериментальные данные по органометаллическим соединениям платины при относительно низких температурах 200-400°С и Р=1 кбар, образующимся при реакции с асфальтенами (Plyusnina et al, 2015) и при магматических условиях Т=950°С и Р=2 кбар во флюиде СО-СО 2 (Simakin et al, 2016). Экспериментально оценена растворимость золота в сырой нефти при Т до 200°С с максимальными значениями до 0.05 ррm (Migdisov et al, 2017). Конкретный тип соединений платины с компонентами асфальтена не установлен, а растворимость платины во флюиде состава СО-СО 2 обусловлена образованием карбонила.…”