Effects of sulfide minerals on aromatic maturity parameters: Laboratory investigation using micro-scale sealed vessel pyrolysis

Abstract

a b s t r a c tSedimentary organic matter from the Here's Your Chance (HYC) Pb-Zn-Ag deposit (McArthur Basin, Northern Territory, Australia) displays increased thermal maturity compared to nearby non-mineralised sediments. Micro-scale sealed vessel pyrolysis (MSSVpy) of an immature, organic rich sediment from the host Barney Creek Formation (BCF) was used to simulate the thermal maturation of OM from the HYC deposit, and to assess the effect of sulfide minerals on organic maturation processes. MSSVpy at increasing temperatures (300, 330 and 360°C) resulted in increased methylphenanthrene maturity ratios which were within the range reported for bitumen extracted from HYC sediments. The methylphenanthrene index ratio from MSSVpy of the BCF sample was lower than in HYC, due to a reduced proportion of methylated phenanthrenes. Polycyclic aromatic hydrocarbons with four to six rings were produced in increasing abundance as pyrolysis temperature increased, although they did not approach the levels reported from HYC. Addition of lead sulfide, zinc sulfide and pyrite to the MSSVpy experiments resulted in a reduced response of the methylphenanthrene maturity parameters, possibly due to retardation of methyl-shift and transmethylation reactions.

Stability and hydrogenation of polycyclic aromatic hydrocarbons during hydropyrolysis (HyPy) – Relevance for high maturity organic matter

“…The controls on PAH methylation during HyPy treatment remain unclear, and if some structural systems are particularly prone to these reactions this may compromise the use of traditional parameters which compare the relative abundance of parent and methylated PAHs. For instance, similar methylation of phenanthrene during HyPy analysis would potentially distort thermal maturity indices based on phenanthrene and methyl-phenanthrene abundances (Radke et al, 1982;Dick et al, 2013;Holman et al, 2014;Le Métayer et al, 2014).…”

Microbial biosignatures in ancient deep‐sea hydrothermal sulfides

“…The δ 34 S signatures of −13‰ to +15‰ in early diagenetic sulfides suggest that microbial sulfur metabolism was involved in mineral formation (Eldridge et al, 1993). Organic matter in the HYC deposit has experienced significant hydrothermal alteration but still encodes information of ore genetic and geobiological significance (Chen et al, 2003; Greenwood et al, 2013; Holman, Greenwood, et al, 2014; Holman, Grice, et al, 2014; Logan et al, 2001; Williford et al, 2011). Preserved organic biosignatures include δ 13 C Org characteristics and biomarkers, among others indicating the presence of sulfate‐reducing and sulfide‐oxidizing bacteria in the environment (Holman, Grice, et al, 2014; Logan et al, 2001).…”

Release of Bound Biomarkers Using Microscale Sealed Vessel Catalytic Hydrogenation

“…Its main operational advantages are high precision and reproducibility, combined with milligram sample loading and batch processing capabilities, all conducted at low cost . While some offline studies have been undertaken, for example, concerning the carbon isotopic compositions of pyrolysates, it is online MSSV analysis that has been most frequently used, with a wide range of applications in kinetic modeling, isotopic investigations, and reservoir geochemistry studies. − Pyrolysis products occurring in high yield, such as n -alkanes, aromatic hydrocarbons, and thiophenes, have been the main focus of attention.…”