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Type: Thesis
Title: Regional Carbonate Geochemistry and Biogeochemistry for Cu Exploration on the Yorke Peninsula, South Australia
Author: Wolff, Keryn Dianne
Issue Date: 2018
School/Discipline: School of Physical Sciences : Geology
Abstract: This thesis describes the geochemistry from carbonate rocks and biogeochemistry from mallee across the Yorke Peninsula to better characterise and define mineral systems that may occur in IOCG prospective basement rocks masked by various overlying cover sequences. Presented here is geochemical data from three cliff escarpments (vertical geochemical profiles) which preserve cover sequences overlying basement rocks. Ca/Sr ratios were found to be a defining discriminator between marine and pedogenic carbonate rocks within the profiles; pedogenic carbonates have Ca/Sr ratios less than 650 and marine carbonates have Ca/Sr ratios greater than 1260. This simple discriminant can also be used to identify samples appropriate for carbonate sampling in mineral exploration, particularly in drill cuttings, as well as retrospective filtering of multi-element geochemical exploration data sets. A regional sampling program was undertaken in the context of the regolith landform setting from a newly constructed map of Yorke Peninsula. The majority of carbonate material occurring at the surface across the Yorke Peninsula has Ca/Sr <650, with lesser occurrences of carbonate preserving Ca/Sr ratios between 650 and 1260 and one preserving marine Ca/Sr >1260. The majority of surface carbonates have Ca/Sr consistent with a mixture of rainfall sources and marine carbonate sources. With the dominant contributor of Ca and Sr from rainwater. Surface carbonates with Ca/Sr ratios >650 have a greater proportion of Ca and Sr sourced from marine carbonates, incorporated either from wind-blown dust or from in-situ marine carbonates. The systematically lower Ca/Sr of rainwater, compared to marine carbonates, translates into systematically lower Ca/Sr in pedogenic compared to marine carbonates. This is an effective discriminator of carbonates formed by pedogenic processes and weathered marine carbonates. The dominantly pedogenic nature of the carbonate rocks sampled across the Yorke Peninsula means that they are appropriate for use in mineral exploration geochemistry for underlying iron oxide-copper-gold deposits. The range of the Cu values in the carbonate rocks is 1.4–36ppm. Elevated Cu concentrations (1.4–36ppm) occur more commonly within carbonate rocks within 3km of known Cu occurrences. . Eucalyptus foliage was collected at a suitable time of year to maximise root absorption and minimise contamination from farming practices. The range of Cu concentrations within Eucalyptus with mallee-form was 1.6–10ppm. Mallee within 3km of known mineralisation has a concentration of 2–10ppm Cu. There was little statistical difference between the four mallee species sampled so that it is reasonable to use all data as a collective dataset. As mallee occur across a large portion of southern Australia, this method of sampling could prove to be a useful tool for frontiers in exploration where tenure occurs typically over large areas, with widespread cover and restricted access due to environmental and cultural sensitivities.
Advisor: Giles, David
Tiddy, Caroline
Hill, Steve
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2019
Keywords: Copper
Yorke Peninsula
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