Clay-Mineral Authigenesis in the Late Permian Coal Measures, Bowen Basin, Queensland, Australia

Abstract

Abstract--Mineralogical studies were performed on authigenic clay minerals of mudrocks, sandstones, and bentonites from 38 boreholes in the Late Permian coal measures of the Bowen Basin. Clay-mineral separations of samples from the northern Bowen Basin consist mainly of (Reichweite, R) R = 1 and R --> 3 interstratified illite-smectite (I-S), chlorite, and kaolinite. In the southern Bowen Basin, samples from higher stratigraphic sections are characterized by randomly ordered (R = 0) I-S mixed layers, and kaolinite and chlorite in smaller amounts. Samples from the lower sections consist of (R -> 3) I-S, chlorite, chloriterich chlorite-smectite (C-S), and laumontite.Examination of the mineralogy and distribution of authigenic clay minerals from the Late Permian coal measures in the northern part of the Bowen Basin indicated that the presence of clay minerals is not systematically related to depth and clay occurrences do not occur regularly. These mineralogical variations of clay in volcaniclastic sediments are incompatible with thermal control. Variations in the rate of fluid flow and potassium supply owing to permeability exert major influences on clay-mineral paragenesis and the reaction of illitization. In more permeable zones (possibly faults or fracture zones), highly illitic clays with lath-shaped morphologies may have precipitated directly from potassium-rich fluids migrating from deeper parts of the basin. In addition, abundant chlorite precipitated contemporaneously with illitic clays, which may have resulted from sufficient magnesium and iron occurring in the fluids as a result of dissolution of intermediate or mafic-rock fragments. At the same time, clay paragenesis with less illitic I-S, kaolinite, and minor chlorite occurs outside the channelized zones of high fluid flow, where a diffusive-flow regime may have predominated with lower ratios of the activities of K § and H + (i.e., etK+/ aH~) in the solutions.In the southern Bowen Basin, depth-related changes in the distribution of clay minerals are evident and may be indicative of thermal control on clay-mineral reactions. Zeolites are present locally in the Late Permian volcaniclastic rocks in the southern Bowen Basin, but not in the north. This is attributed to a low ratio of aco2/C~H2o (where c~ = activity) and/or more saline and alkaline solutions.

Carbon dioxide-rich coals of the Oaky Creek area, central Bowen Basin: a natural analogue for carbon sequestration in coal systems

“…TAJE_60-01_O.indd Page 134 11/03/13 9:04 PM user-f-401 TAJE_60-01_O.indd Page 134 11/03/13 9:04 PM user-f-401 ~/ Desktop/11.03.2013/TAJE_60-01/Desktop/11.03.2013 irregularly over short intervals. Similar vertical variability and zonation of clay minerals were observed for illitic clays in sandstones from the Bowen Basin (Uysal et al 2000b, d). In our previous studies, we explained the irregularity in illite compositions as being the result of hydrothermal activity leading to changes in the porefluid composition controlled largely by variable fluid/ rock ratios (Uysal et al 2000b, c).…”

“…Illite-smectite occurs as regularly ordered (R1-type, 60-85% illite) and long-range ordered (R3-type, 490% illite) mixed-layered minerals in the Oaky Creek TAJE_60-01_O.indd Page 133 11/03/13 9:04 PM user-f-401 TAJE_60-01_O.indd Page 133 11/03/13 9:04 PM user-f-401 ~/ Desktop/11.03.2013/TAJE_60-01/Desktop/11.03.2013 samples, with more advanced mineralogical reactions evident in the CO 2 -rich well than in the CO 2 -poor well. The formation of illitic clay minerals is controlled mainly by temperature, although there are also other factors affecting illite formation, such as chemical composition of fluids and water-rock ratios related to permeability (Uysal et al 2000b). Therefore, the occurrence of mixed-layered I-S provides an opportunity to gain some information on temperature and the chemistry of fluids as well as the fluid flow mechanism (Uysal et al 2000b-d).…”

CO2 degassing and trapping during hydrothermal cycles related to Gondwana rifting in eastern Australia

“…The formation of such illitic clay minerals is controlled mainly by temperature, although there are also some other factors affecting the illite formation, such as chemical composition of fluids and water-rock ratios related to permeability (e.g., Uysal et al, 2000c). By analogy with literature data (Pollastro, 1993 and references therein), the occurrence of different types of illite-smectite in the study area indicate a temperature range of formation from roughly 80°C (smectite-rich) to 170°C (illite-rich).…”

Thermal models and clay diagenesis in the Tertiary-Cretaceous sediments of the Alava block (Basque-Cantabrian basin, Spain)

“…One drawback to using these reactions as geothermometers is the need for both reactant phases and products to be in chemical equilibrium, a circumstance not common in diagenesis (Essene & Peacor, 1995, 1997. Most of the phases involved in such processes are metastable and, in addition to temperature, kinetic factors such as time, composition of initial phases and solutions, and permeability are key (Scotchman, 1987;Freed & Peacor, 1989;Huang et al, 1993, Uysal et al, 2000aAbid et al, 2004). Nevertheless, clay minerals evolve during diagenesis towards lower free-energy states; therefore, they are indicative of the reaction progress (Essene & Peacor, 1995).…”