Search CRC LEME :

powered by FreeFind

Publication Policy

Open File Report Series

OFRS Index


Regolith Maps

Annual Reports

Articles & Papers


Minerals Briefs

"Focus on Salt"

Other LEME Reports

Order Form

Open File Report 130

Alluvial landscapes of the Northern Kennedy Gap Area, Mt Isa District, Queensland

M. R. Jones

Quaternary landscape evolution has been investigated in an area located mid-way between Mt Isa and Camooweal, on the Kennedy Gap 1:100 000 sheet. Here, Proterozoic bedrock forms prominent ridges having a general north-south orientation and rising up to 180 m above the surrounding plains. Drainage is provided by streams, whose upper catchments are confined by bedrock ridges. The area extends only marginally onto the plains that continue from the base of the Mt Isa Inlier to the south and west. Despite the arid environment, the principal agents of landscape evolution are the rivers and creeks which carry away the products of weathering in the high country and distribute these sediments across the lowlands. The study area lies across the divide separating northward drainage to the sea and southward drainage to central Australia.

There are six major streams present, each with distinctive drainage patterns associated with different levels of erosional activity. The most active of the streams is the northward-flowing Judenan Creek, which has a highly channelled catchment. The stream is continuing a long-term trend for expansion to the west and south along erosion scarps in bedrock. Weathered Eastern Creek Volcanics in the Judenan Creek catchment are susceptible to erosion, and the numerous channels ensure that the weathered mantle is readily removed. The sediments produced are derived from a wide area of bedrock, and are predominantly "new" sediments. In contrast, the adjoining Cattle Creek catchment to the west contains a mixture of older alluvial deposits now being reworked, and only minor "new" sediments derived from low lying bedrock outcrops.

Other catchments in the area include the bedrock-confined and aligned Gidya Creek, which drains to the north, and Buckley River, which flows westwards across the strike of the bedrock. In the south, Johnson and Wilfred Creeks are conduits for westward moving sediments produced in their upper catchments. Johnson and Cattle Creeks join Buckley River, and contribute to the drainage towards central Australia.

The sediments are derived from the area within 2-5 km of the drainage divides between the upper catchments. For the most part, the surficial sediments are thin and young. There is no evidence of widespread thick sequences of transported deposits overlying an incised and back filled bedrock surface. Rather, the alluvial deposits are mainly confined to narrow corridors along the valley floors. The alluvial deposits form a blanket which protects the shallow underlying bedrock from significant erosion.

The alluvial deposits are only a proportion of the total sediment throughput during the evolution of the landscape to its present form. The blanketing unconsolidated sediments are in transit to distant depositional areas. It is unlikely that these deposits would remain in place long enough for geochemical haloes to develop from underlying mineral deposits. Overall, the processes of erosion, transport and deposition are diffusive for indicator minerals. However, there is the potential for stream bed concentrations of heavy minerals which could be related to up-catchment sources.

The differences between the catchments are related to the confining geology that determines the lateral limits of catchment development, and the underlying geology that determines the erodability of the catchment substrate. Judenan Creek is the main catchment where erosional processes are most active. In part, this can be related to Judenan Creek having a steeper slope to its base level (Gulf of Carpentaria) in comparison with the other streams draining to the west and south towards Lake Eyre. The Judenan Creek catchment may also contain more erodable bedrock than in neighbouring streams. The erodability could be related to deep weathering and or fracturing of the bedrock allowing surface or near-surface chemical concentrations indicating underlying mineral deposits. The Judenan Creek catchment contains known occurrences of copper and uranium mineralisation. This catchment may need further evaluation of its potential to contain economic mineral deposits.

The Eastern Creek Volcanics also underlie parts of the Gidya Creek catchment, which may warrant investigation for anomalies in the regolith. Stream sediment geochemistry could assist exploration in the Judenan and Gidya Creek catchments.

Iron-rich pisoliths and nodules have proved to be useful sampling media for geochemical exploration in Western Australia. In the Kennedy Gap area, iron pisoliths and nodules are abundant. Haematitic and goethitic pisoliths and nodules occur in-situ in weathering profiles, and also in transported deposits where secondary goethitic cementation has occurred. Geochemical analyses of goethitic cutans and haematitic centres of iron pisoliths are expected to give different results. Careful interpretation of the environment of deposition is required before selecting samples for analysis. This is essential if geochemical anomalies are to be successfully related to source areas.


Cooperative Research Centres Australia

About Us | News & Events | Research
Publications | Education | Staff Only | Links

Contact Us | Disclaimer | Sitemap
© CRC LEME 2004

CRC LEME is established and supported under the Australian Government's Cooperative Research Centres Program. The CRC Program is an Australian Government initiative which brings together research groups with common interests.

CRC LEME Core Parties