The Upper Burdekin Basalt extents web service delivers province extents, detailed geology, spring locations and inferred regional groundwater contours for the formations of the Nulla and McBride Basalts. This work has been carried out as part of Geoscience Australia's Exploring for the Future program.

The Upper Burdekin Basalt extents web service delivers province extents, detailed geology, spring locations and inferred regional groundwater contours for the formations of the Nulla and McBride Basalts. This work has been carried out as part of Geoscience Australia's Exploring for the Future program.

The Upper Burdekin Chloride Mass Balance Recharge web service depicts the recharge rates have been estimated at borehole locations in the Nulla and McBride basalt provinces. Using rainfall rates, rainfall chemistry and groundwater chemistry, the recharge rates have been estimated through the Chloride Mass Balance approach.

The Upper Burdekin Chloride Mass Balance Recharge web service depicts the recharge rates have been estimated at borehole locations in the Nulla and McBride basalt provinces. Using rainfall rates, rainfall chemistry and groundwater chemistry, the recharge rates have been estimated through the Chloride Mass Balance approach.

This report provides an initial summary of the hydrogeochemistry of the McBride Basalt Province (MBP) and Nulla Basalt Province (NBP) of the Upper Burdekin Region of North Queensland, completed as part of Exploring for the Future (EFTF)—an eight year, $225 million Australian Government funded geoscience data and information acquisition program focused on better understanding the potential mineral, energy and groundwater resources across Australia. Groundwater hydrogeochemistry studies can improve system understanding by reflecting host formation compositions and groundwater processes. These studies also provide regional baseline groundwater datasets that can inform environmental monitoring, resource use and decision making. During 2017 and 2018 Geoscience Australia collected 38 groundwater samples and 80 surface water samples (including quality control samples) to evaluate groundwater system processes including potential flow paths, recharge and groundwater-surface water-interactions. These surveys were conducted across three months of fieldwork, sampling water for a comprehensive suite of hydrogeochemical parameters. The present report includes surface water and groundwater data and information on: 1) sampling sites; 2) field physicochemical parameters (EC, pH, Eh, DO and T); 3) field measurements of total alkalinity (HCO3-); 4) laboratory results of major anion and cation results; 5) laboratory results for isotopes of water (δ18O and δD), DIC (δ13C), and dissolved strontium (87Sr/86Sr); and 6) hydrogeochemical maps representing the spatial distribution of these parameters. Pending analyses include: CFCs, SF6 and radiogenic isotopes δ14C and δ36Cl. Analysis that were largely below detection limit include: trace element concentrations, dissolved sulfide (S2-), ferrous iron (Fe2+), and dissolved sulfate (affecting sampling of δ34S and δ18O). This study demonstrates that hydrogeochemistry surveys, with full suites of chemical parameters including isotopes, can reveal fundamental groundwater system processes such as groundwater flow paths, groundwater recharge and groundwater-surface water interactions. The chemical ‘fingerprints’ identified here indicate groundwater flow paths are largely restricted to within the MBP and NBP aquifers, which have little interaction with adjacent and underlying non-basaltic rocks. The results also indicate groundwater is largely recharged from rainfall in higher elevations of the basalt provinces, with variable rainfall inputs to groundwater from lower elevation and rivers along flow paths. Groundwater-surface water interactions show several chemical signatures linking groundwater to springs, tributary rivers and the Burdekin River. Results from the Upper Burdekin Hydrogeochemistry Survey for the MBP and NBP have been plotted and mapped with initial interpretations presented below. Further detailed interpretation of this hydrogeochemistry data will be the focus of future publications. This data release is part in a series of staged outputs from the EFTF program. Relevant data, information and images are available through the Geoscience Australia website.

This report presents key results of groundwater barometric response function development and interpretation from the Upper Burdekin Groundwater Project in North Queensland, conducted as part of Exploring for the Future (EFTF)—an eight year, $225 million Australian Government funded geoscience data and information acquisition program focused on better understanding the potential mineral, energy and groundwater resources across Australia. The Upper Burdekin Groundwater Project is a collaborative study between Geoscience Australia and the Queensland Government. It focuses on basalt groundwater resources in two geographically separate areas: the Nulla Basalt Province (NBP) in the south and the McBride Basalt Province (MBP) in the north. The NBP and MBP basalt aquifers are heterogeneous, fractured, vesicular systems. This report assesses how water levels in monitoring bores in the NBP and MBP respond to barometric pressure changes to evaluate the degree of formation confinement. The main process used to evaluate water level response to barometric pressure in this study is based on barometric efficiency (BE). The BE of a formation is calculated by dividing the change in monitoring bore water level by the causative barometric pressure change. Both parameters are expressed in the same units, so BE will typically be some fraction between zero and one. BE is not necessarily constant over time; the way BE changes following a theoretical step change in barometric pressure can be described using a barometric response function (BRF). BRFs were calculated in the time domain and plotted as BE against time lag for interpretation. The BRF shape was used to assess the degree of formation confinement. Although there is some uncertainty due to monitoring bore construction issues (including long effective screens) and potentially air or gas trapped in the saturated zone, all BRFs in the current project are interpreted to indicate unconfined conditions. This finding is supported by the identification of recharge at many monitoring bores through hydrograph analysis in other EFTF project components. We conclude that formations are likely to be unconfined at many project monitoring bores assessed in this study.

This is a raster representing the base surface of the McBride Basalt Province, inferred from sparse data available, dominated by private water bore records. This interpretation was conducted by a hydrogeologist from Geoscience Australia. Caveats • This is just one model, based on sparse data and considerable palaeotopographic interpretation • This model relies on the input datasets being accurate. However it is noted that substantial uncertainty exists both in the location of private bores and the use of drillers’ logs for identifying stratigraphic contacts. • The location of palaeothalwegs is imprecise, and often it is only indicative of the presence of a palaeovalley. • The purpose of this model is for visualisation purposes, so should not be considered a definitive depth prediction dataset.

This technical report details the methods and results the drilling programs of the Upper Burdekin Groundwater Project conducted as part of Exploring for the Future (EFTF)—an eight year, $225 million Australian Government funded geoscience data and information acquisition program focused on better understanding the potential mineral, energy and groundwater resources across Australia. This report was written by Queensland Government collaborators in the Department of Environment and Science, and is published here as supplied to Geoscience Australia at the conclusion of the project. The drilling program itself was conducted by the Department of Environment and Science as part of the Upper Burdekin Groundwater Project. A total of 17 holes were drilled in 2017-18 at 13 sites with a total combined depth of 943.2 metres. These comprise selected locations across both the Nulla Basalt Province and McBride Basalt Province. A network of 15 monitoring bores were constructed with two test holes backfilled and decommissioned.

This dataset includes point estimates of groundwater recharge in mm/year. Recharge rates have been estimated at monitoring bore locations in the basaltic aquifers of the Nulla and McBride basalt provinces. Recharge estimates have been calculated using the “chloride mass balance” method. The chloride mass balance process assumes that the chloride ion is a conservative tracer in precipitation, evapotranspiration, recharge and runoff; and that all the chloride is from rainfall, instead of for example halite saturation or dissolution processes. So the volumetric water balance and the flux of chloride balance must both be true. Assuming that runoff and evapotranspiration are negligible (so approximated by zero), the equation is simplified: Water balance P=ET+R+Q Water balance multiplied by chloride concentrations (chloridefluxbalance) P∙Cl_ppt=ET∙Cl_ET+R∙Cl_gw+Q∙Cl_riv | ΔCl_reac≈0 Assumptions to simplify equation P∙Cl_ppt=R∙Cl_gw | Q≈0 & ET≈0 Rearranging for recharge rate (unknown) R=P∙(Cl_ppt)/(Cl_gw ) | Q≈0 & ET≈0 Where P = precipitation rate; ET = evapotranspiration rate; R = recharge rate; Q = runoff to streams; Clppt = concentration of Cl in precipitation; ClET = concentration of chloride in evapotranspiration; Clgw = concentration of Cl in groundwater; Clriv = concentration of chloride in river runoff; ΔClreac = change in chloride concentrations from reactions.

This grid dataset is an estimation of the relative surface potential for recharge within the McBride Basalt Province. This process combined numerous factors together as to highlight the areas likely to have higher potential for recharge to occur. Soil permeability and surface geology are the primary inputs. Vegetation and slope were excluded from consideration, as these were considered to add too much complexity. Furthermore, this model does not include rainfall intensity – although this is known to vary spatially through average rainfall grids, this model is a depiction of the ground ability for recharge to occur should a significant rainfall event occur in each location. The relative surface potential recharge presented is estimated through a combination of soil and geological factors, weighting regions that are considered likely to have greater potential for recharge (e.g. younger basalts, vent-proximal facies, and highly permeable soils). Near-surface permeability of soil layers has been considered as a quantified input to the ability for water to infiltrate soil strata. It was hypothesised that locations proximal to volcanic vents would be preferential recharge sites, due to deeply penetrative columnar jointing. This suggestion is based on observations in South Iceland, where fully-penetrating columnar joint sets are more prevalent in proximal facies compared to distal facies in South Iceland (Bergh & Sigvaldson 1991). To incorporate this concept, preferential recharge sites are assumed to be within the polygons of vent-proximal facies as derived from detailed geological mapping datasets. Remaining geology has been categorised to provide higher potential recharge through younger lava flows. As such, a ranking between geological units has been used to provide the variation in potential recharge estimates. <b>References</b> Bergh, S. G., & Sigvaldason, G. E. (1991). Pleistocene mass-flow deposits of basaltic hyaloclastite on a shallow submarine shelf, South Iceland. Bulletin of Volcanology, 53(8), 597-611. doi:10.1007/bf00493688