Gold Mining and Estuarine Evolution: A Study of the Accelerated Sedimentation of Parapara Inlet, Golden Bay, New Zealand

<p>Estuaries are depositional environments formed within drowned river embayments which receive sediment from both marine and terrestrial sources. In many cases a beach-barrier sequence forms subaerially at the mouth of the flooded embayment and the area behind it is termed a barrier estuary. Such estuary types are found around the New Zealand coast especially in areas of relative tectonic stability and their sediments are often used to reconstruct Holocene sea level. Infill of these estuaries is initially dominated by marine flood tide delta sediments, with later infill occurring through fluvial processes. The final stages of infill within these estuaries is poorly understood. Parapara Inlet in Golden Bay, New Zealand, is a Holocene barrier estuary influenced by hydraulic sluice mining within its river catchment. A study of Parapara Inlet was undertaken to discover how human disturbance within a river catchment can affect the evolution of a barrier estuary, by comparing previous models of barrier estuary evolution to the stratigraphy record within Parapara Inlet. 18 vibracores were sampled from Parapara Inlet in November 2009. Radiocarbon dating (AMS) within these cores provided a maximum age of 7090-6910 Cal BP. Deposition within the estuary has occurred in three stages; the first in Pre-Holocene marsh or lake environments; the second after inundation 6500-7500 years Cal BP, as fluvial sediments dominate the centre of the estuary; and thirdly in a series of quartz dominated gravels and sands within 1m of the surface. These units vary from the traditional models of evolution as the topography of the estuary has influenced the extent of deposition within the central mud basin. Mining sediment forced Parapara Inlet into a late stage of evolution, however the amount of sediment provided through sluice mining was not large enough to force the estuary into a supratidal stage.</p>

Gold Mining and Estuarine Evolution: A Study of the Accelerated Sedimentation of Parapara Inlet, Golden Bay, New Zealand

<p>Estuaries are depositional environments formed within drowned river embayments which receive sediment from both marine and terrestrial sources. In many cases a beach-barrier sequence forms subaerially at the mouth of the flooded embayment and the area behind it is termed a barrier estuary. Such estuary types are found around the New Zealand coast especially in areas of relative tectonic stability and their sediments are often used to reconstruct Holocene sea level. Infill of these estuaries is initially dominated by marine flood tide delta sediments, with later infill occurring through fluvial processes. The final stages of infill within these estuaries is poorly understood. Parapara Inlet in Golden Bay, New Zealand, is a Holocene barrier estuary influenced by hydraulic sluice mining within its river catchment. A study of Parapara Inlet was undertaken to discover how human disturbance within a river catchment can affect the evolution of a barrier estuary, by comparing previous models of barrier estuary evolution to the stratigraphy record within Parapara Inlet. 18 vibracores were sampled from Parapara Inlet in November 2009. Radiocarbon dating (AMS) within these cores provided a maximum age of 7090-6910 Cal BP. Deposition within the estuary has occurred in three stages; the first in Pre-Holocene marsh or lake environments; the second after inundation 6500-7500 years Cal BP, as fluvial sediments dominate the centre of the estuary; and thirdly in a series of quartz dominated gravels and sands within 1m of the surface. These units vary from the traditional models of evolution as the topography of the estuary has influenced the extent of deposition within the central mud basin. Mining sediment forced Parapara Inlet into a late stage of evolution, however the amount of sediment provided through sluice mining was not large enough to force the estuary into a supratidal stage.</p>

Effect of Using Different Chemical Dispersing Agents in Grain Size Analyses of Fluvial Sediments via Laser Diffraction Spectrometry

Laser diffraction spectrometry allows for efficiently obtaining high-resolution grain size data. However, pretreatment and dispersion of aggregates in sediment samples are essential pre-requisites for acquiring accurate results using this method. This study evaluates the effectiveness of five dispersing agents in deflocculating the investigated fluvial sediments and the resulting grain size distribution obtained by laser diffraction spectrometry. We also examine the ability of the different dispersing agents to deflocculate sediment samples treated by thermal combustion. Distilled water presented a low efficiency in deflocculating the samples and yielded a near-zero clay content for samples with an expected clay content. The other chemical dispersants were effective in dispersing aggregates and yielding clay, albeit with different efficiencies. Calgon had the highest dispersing ability, followed closely by sodium tripolyphosphate. The performance of chemical treatment with sodium oxalate approaches that of sodium tripolyphosphate. However, it leads to the formation of precipitates in the samples, obscuring the actual grain size data. Sodium pyrophosphate derived the least amount of deflocculation among the four chemical dispersants. Furthermore, all the chemical dispersants were found to be ineffective in dispersing aggregates in samples treated by thermal combustion.