Ashes to Ashes - Searching for Evidence of Ancient Volcanoes
Helen Thompson
York House School
Floor Location : J 002 V

The purpose of my project was to attempt to discover ash in the sedimentary rocks in the Nanaimo group setting by testing the samples to identify the ash qualities. The main evidence needed in order for it to be an ash is zircons. In addition, the zircons must be perfectly shaped like a crystal. Zircons are trace minerals composed of zirconium, silicon and oxygen. Zircons can also give us a very accurate age of the rock. My hypothesis is that volcanic ashes will be in the rocks on Salt Spring island and that zircons will be in that ash. rnrnI did three valuable steps in order to complete my task. First I had determine the geology, e.g the placement of the rock and observations on the color and texture of the sample. To achieve this, I went to Salt Spring island and collected the sample using a hammer and a sample bag. My next step was to send in the sample to Vancouver Petrographics to receive thin sections. Under a microscope I examined the section to look for ash characteristics. Next, I had to grind the rock down to 200 micron particle size. Putting this new formed sample through methylene iodide in a funnel, the heavier minerals drifted from the rest of the sample to the bottom of the funnel. Releasing it quickly, I collected the heavier minerals and put them under a heat lamp to dry. Following this, I used a small hand magnet to pull out any metal that may have come off the grinding machine. I then took the sample to a microscope and examined the minerals closely. Once I managed to concentrate all the zircons to one side of the plastic plate, I took the zircons out and put them on a metal stub to look at under the SEM (scanning electron microscope). Under the SEM the zircons were much more apparent in their shape and size.rnrnAs a result, I observed that the rock layer from where the sample was collected was a thin beige line that streaked across the plain mudstone, quite like an ash is expected to. Also, I examined the thin sections and found many ash qualities including extremely fine grained angular material and possible accretionary lapilli. Finally, after examining the separated zircons and taking a couple pictures through the SEM, it became obvious that the zircons had perfect pencil shapes. I conclude that the rock is definitely an ash.rnrnAfter further studies into the background of the Nanaimo group and Salt Spring island it became apparent that this is the first ash ever to be discovered in the sedimentary rocks in the Nanaimo group setting. The zircons within this rock could be used to provide an accurate age of the sediments. rnrn