The Honeymoon Uranium Project comprises the Honeymoon Deposit,
Goulds Dam Deposit and Yarramba Prospect in the Southern Lake Frome
region, South Australia. Both the Yarramba Prospect and Honeymoon
Deposit (which includes Honeymoon and East Kalkaroo orebodies) are
located in the Yarramba Palaeovalley. The Goulds Dam Deposit is about
75 km north west of Honeymoon, in the Billeroo Palaeovalley.
Exploration for sediment-hosted uranium began in the area in the late
1960s, culminating in the discovery of Honeymoon and Goulds Dam in
the early 1970s. In 1982, a 25 L/s demonstration plant was built at
Honeymoon to confirm suitability for in situ leaching. The project was put on hold in 1983 due to changes in government policy. Southern Cross Resources Australia Pty Ltd acquired the project in mid 1997.
Roll-front deposits form from a migrating geochemical cell, an
advancing reduction-oxidation interface between oxygenated
uranium-bearing groundwater and its reduced aquifer host. The source of metal is uranium-anomalous granites, which were eroded from
surrounding ranges. The weathered granites and resultant sediments are stripped of uranium by oxidised groundwaters, to form solutions carrying uranyl carbonate complexes. The solutions percolate down-slope through permeable sand zones until contacting a reduced environment where uranium precipitates. Uranium mineralisation occurs interstitially between and as thin coatings on sand grains, usually in the form of uraninite or coffinite.
The palaeovalleys (previously termed palaeochannels) are incised into
underlying Cambrian/Precambrian basement rocks and filled with
semi-consolidated, largely un-cemented, Tertiary sediments of the Eyre Formation. The late Palaeocene to middle Eocene Eyre Formation is the basal unit of the Tertiary succession in the Callabonna Sub-basin of the Lake Eyre Basin. Further to the north, the Lake Eyre Basin overlies the Jurassic-Cretaceous Eromanga Basin, which comprises much of the Great Australian Basin. Eyre Formation sediments are in turn overlain by the late Tertiary Namba Formation and terrestrial Quaternary units.
At Honeymoon, the Eyre Formation includes immature, pyritic,
carbonaceous sands and gravels interbedded with lignite and
kaolinite-illite-montmorillonite clays. It was deposited by braided
streams during epeirogenic uplift of the Olary Ranges, accompanied by
subsidence of the Lake Eyre Basin. The Eyre Formation comprises a
consistent stratigraphy of interbedded sand and clay units that are
continuous over the Honeymoon Deposit but with local variation
indicating some hydrological connection between aquifers.
In the Honeymoon orebody, uranium occurs within coarse-grained,
pyritic sands where the basal sand pinches out between overlying
carbonaceous clay and the southern palaeovalley slope. Its characteristics are typical of the well-developed, planar limb of a roll-front uranium deposit. Zonal changes related to the reduction-oxidation interfaces across the deposit are readily observable. The orebody extends for nearly 1000 m along the valley margin, is 400 m wide at its maximum and averages about 6 m in thickness.
The East Kalkaroo orebody also lies near the southern margin of the
Yarramba Palaeovalley. It extends discontinuously for approximately 3.5 km and averages 200 m width, with significant uranium present in the Middle as well as the Basal Member.
The Billeroo Palaeovalley extends northward for 40 km sub-parallel to
the western side of the Benagerie Ridge, is up to 5 km wide and has
gently dipping banks. Eyre Formation within the palaeovalley is
concealed beneath 90 m of Quaternary and Namba cover, is
approximately 40 m thick, and is sub-divided into three upward-fining
units, which are remarkably similar to the Yarramba Palaeovalley
sequence.