Lennard Shelf, Australia
Project Description
The Lennard Shelf is an ancient Devonian-aged limestone reef that hosts a world-class Mississippi Valley Type (MVT) zinc-lead province with reported resources in June 2003 of 22Mt @ 6.9% Zn and 2.8% Pb (9.7% Zn+Pb). Production between 1994 and 2003 has amounted to 13.3Mt @ 7.6% Zn and 3.1% Pb (10.7% Zn+Pb). Clusters of MVT deposits have been found on the Lennard Shelf, including Cadjebut, Pillara, Goongewa, Fossil Downs, Pinnacles and Kapok. Other deposits have been found further to the northwest at Narlarla and Wagon Pass.
The deposits were originally found by BHP and Billiton in the late 1970’s and early 1980’s. Development by BHP went ahead in about 1988, and the mines were then sold to Western Metals who operated them for a few more years before going into administration because of foreign exchange and hedging difficulties (not operational problems).
Rox has signed a 12 month option with Avalon Minerals to form a joint venture on Avalon’s tenements. During the option period Rox must spend $500,000 on exploration. After the option period Rox can withdraw, however if Rox elects to form the joint venture then it can earn a 60% interest by expending a further $1.5 million over three additional years.
The joint venture tenements cover a 2,600km2 area in the central and southeast Lennard Shelf where the largest deposits (Cadjebut and Pillara) are located. Pillara is currently being mined by a Teck-Xstrata joint-venture and quoted ore reserves are 3.0Mt @ 7.3% Zn and 1.8% Pb.
Previous exploration has been concentrated along the southwest margin of the ancient reef complex where most base metal deposits and occurrences are located. The exploration model for the Lennard Shelf has been developed over more than 20 years by a variety of exploration companies and research organisations (including CSIRO, The University of Western Australia and BHP). Rox believes this extensive database will not only enable rapid exploration progress on the joint venture tenements, but the exploration concepts and techniques will be equally applicable to its Pha Luang project in Laos as well.
Zinc-Lead deposits are found throughout the complete carbonate sequence (from lowermost Pilbara Limestone to uppermost Nullara Limestone and the common theme is structural control. Therefore, even though most exploration has taken place along the reef front outcrop, deposits are possible anywhere within the carbonate sequence as long as the necessary structural elements are present.
A secondary exploration target is within adjacent calcareous sediments (e.g. Fairfield Formation, Piker Hills Formation), where structural elements may be present and the sediments contained enough carbonate to reduce mineralising fluids.
Exploration techniques to be used include geochemical analysis by Niton XRF of residual soils and stream sediments, geophysical surveys to highlight unseen structures and possible mineralisation, and most critically, geological understanding and interpretation. From these results, drill targets can be more accurately determined and prioritised.
Avalon has three project blocks of tenements termed Oscar Range, Lawford and Barramundi.
