Evaluation of methods to characterise the geochemistry of limestone and its fracturing in connection to heating

University essay from Lunds universitet/Geologiska institutionen

Abstract: Abstract: In 2011 Vinnova funded a joint project between Nordkalk AB, Kalkproduktion Storugns AB (KPAB) and the department of Geology at the University of Lund. The goal of the project is to increase the general knowledge of limestone and in extension, facilitate for the industry. This thesis is a part of the project and consists of two separate parts which look into the geochemistry and thermal properties of limestones. Part one focuses on a 29 m drill core from the Storugns quarry on Gotland consisting of calcarenite, calcilutite, marl/marlstone, stromatoporoid, fragment and reef limestone. The drill core was scanned with a high resolution XRF (ITRAX) and the geochemistry between the different types of limestones was compared. Focus ended up on silica (SiO2) and calcium oxide (CaO) as they were the most common elements in the core and a statistical comparison using a student’s t-test was conducted. To get comparable data to other studies from the area, a handheld XRF was used on polished and cut parts of the core which represent the different types of limestone (except the marl/marlstone). Samples from each rock type (again except the marl/marlstone) were dissolved in acetic acid and the residual material was analysed in a SEM, more specifically using EDS. The results show that beside calcite and dolomite, the rock mostly contain pyrite and quartz. The ITRAX scan confirms that geochemistry varies between the rock types, especially when looking at the CaO and SiO2. Therefore, the ITRAX scan was deemed a reliable method to distinguish different types of limestone whereas the handheld XRF was not. Part two of the thesis focuses on the thermal properties of limestone and more specifically if x-ray computed tomography (CT) is a viable method for distinguishing dolomite from calcite and if it can be used to study heat related fractures. Four samples were collected from the Storugns quarry on Gotland and after drilling six cores per sample, the sample containing the most magnesium was determined by using an acid test, handheld XRF and SEM (EDS). Five cores from this sample were scanned with a CT. After scanning, the cores were heated to 400, 500, 600, 650 and 700 ˚C respectively and then scanned in the CT again. Using a program called Fiji ImageJ, five levels were chosen in the images from the unburnt samples and the corresponding levels were located in the burnt cores’ images. The images were then compared and all fractures were marked and measured. The results show that CT is a good method for studying fractures however additional studies would be needed to modify the method in order to use it to distinguish dolomite from calcite.

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