干旱区生态环境知识资源中心

The Precambrian meta-sedimentary fractured rock aquifers of the Hamersley Basin in northwest Australia are some of the oldest water-bearing formations on the planet and host enormous iron ore deposits. Groundwater is the only permanent source of water in the basin, therefore understanding the hydrological processes that effect water quality and quantity is a pre-requisite for sustainable water management. We used a combination of major dissolved ion concentrations, including Sr and Ca, in combination with delta H-2, delta O-18 and delta Sr-87 in flood water and groundwater as tracers to constrain the processes affecting groundwater chemistry. The delta Sr-87 composition of groundwater in three major aquifer types ranges from 11.8 parts per thousand to 40.6 parts per thousand and reflects the mineralogy of altered Precambrian dolomite (15.1 parts per thousand to 55.4 parts per thousand) rather than the host iron ore formations (22.5 parts per thousand to 46.5 parts per thousand >95% iron oxides) or highly radiogenic shale bands and clay minerals (200 parts per thousand to 2322.5 parts per thousand). Groundwater in the terminal Fortescue Marsh wetland of the basin has a rather constant delta Sr-87 signature of 36.6 +/- 1.4 parts per thousand irrespective of variations in TDS, delta O-18 and Sr concentration. This groundwater is considered to be mature in a geochemical sense, representing the final stage of water evolution on a basin scale. Mixing calculations utilising delta Sr-87 and Ca/Sr data demonstrate contributions of salts from three major sources: on average >92% from precipitation, similar to 7% from carbonate rocks and <1% from rocks with highly radiogenic signatures (shales and clays). These results demonstrate groundwater evolution from a recharge area to discharge area at the regional scale, but more importantly that water quality in the terminal wetland is primarily driven by rainfall chemistry in floodwaters rather than water-rock interactions in the catchment. (c) 2014 Elsevier B.V. All rights reserved.