Exploration Geophysics - Volume 34, Issue 1-2, 2003

The Wallaby deposit in Western Australia, which consists of several stacked gold lodes, is now recognised as being hosted by an actinolite-magnetite alteration pipe. Identification of the pipe geometry resulted from a combined interpretation of the aeromagnetic anomaly and drill core magnetic susceptibility measurements.

Gold was discovered in 1997 in the northern part of the deposit, called Just in Case. By September 1999 the complete Just in Case - Wallaby zone had been drilled to 500 m depth, outlining gold mineralization within magnetic basaltic conglomerate. The challenge then was to develop targets to 1000 m.

Magnetic susceptibility measurements made on all core proved invaluable. A susceptibility block model was studied in conjunction with models derived from the surface magnetic anomaly. Although the gold zones tended to be flat-lying, susceptibilities displayed an annular pattern in plan, and a southerly dip in a central north-south section. The magnetic zone was interpreted as being a plunging pipe, with a plunge of 50° toward 190° determined from modelling the aeromagnetic anomaly. Complementary to recognition of the pipe was evidence that gold was effectively restricted to the magnetic zone.

The pipe model provided a well-defined target, and drilling to 1000 m confirmed the structure as well as discovering four more gold lodes.

The St Ives terrain is covered by a thick regolith that is saturated with hyper-saline groundwater. The regolith forms a major barrier for electrical and EM surveys designed to detect gold-bearing structures in bedrock.

The down-hole magnetometric resistivity (DHMMR) method was trialled at St Ives and detected only small responses from known structures. DHMMR does not detect strong anomalies because the structures are often less than 10 m thick, and have small cross-sectional areas for channelling current. The resistive bedrock does not support large current densities for channelling into targets.

Down-hole electromagnetic (DHEM) surveys were trialled at St Ives and detected a strong well-defined anomaly at the Junction gold mine. The anomaly was modelled as a plate in layered earth, and the plate corresponded to a major gold-bearing shear. Petrophysical tests suggest that the shear is conductive because of brine-saturated porosity.

DHEM surveys did not detect strong anomalies from a gold-bearing shear at the Argo gold mine, despite the shear having low resistivity relative to host rock in downhole resistivity logging. The absence of DHEM response may be because the shear is not conductive enough to support an anomalous current system, or because the conductivity is not connected on a large scale.

Since the mid nineties Cameco Australia Pty Ltd (Cameco) has been involved in exploration for unconformity-related uranium deposits in Arnhem Land, Australia. During this time the exploration model has evolved from the initial Athabasca Basin (Canadian) unconformity model. Physical property measurements and orientation programs have led to the current integrated exploration strategy that incorporates the disciplines of geology, geochemistry, and geophysics.

Airborne radiometric surveys continue to be the primary tool for identifying near-surface uranium anomalies. However, other geophysical techniques are utilised to aid in mapping basement lithologies, alteration, and the depth of sandstone cover, which are all keys to Cameco’s exploration objectives. With these aims in mind, hyperspectral, magnetic, and electromagnetic airborne geophysical techniques have been extensively utilised as efficient methods for quickly evaluating large areas, where rugged topography prevents effective use of ground techniques. Examples from Cameco’s King River project, located in northwest Arnhem Land, show that integration of airborne electromagnetics, and hyperspectral surveys, is a significant factor in improving the exploration process.

The Internet, Intranets, and general globalization of networking technology have produced a dramatic increase in the type and volume of spatial data that are available to geoscientists. The development of protocols and underlying technologies for computers to access and share spatial data, both privately within organisations, and globally on the Internet, is key to our ability to use this information efficiently.

In this paper, we describe the Data Access Protocol (DAP), which is a suite of client tools and proprietary server applications that enables geoscientists to find and evaluate data, and to automate windowing, reprojecting, and reformatting the data to suit a specific requirement. DAP technology addresses a variety of network situations including:

1. Simple web browser-based discovery and retrieval of data of interest in a specified format and coordinate system.

2. Support for the Open GIS Consortium Web Map Server (WMS) interface to allow any WMS-compatible application to retrieve "images" of the data for use as layers in a GIS application.

3. Direct support for DAP-enabled thick clients, such as Oasis montaj^TM, to optimally retrieve data directly for their own use, and to transfer data to a hosting DAP environment.

When communicating with DAP-enabled client applications, DAP addresses the movement of data (lossless compression, encryption and streaming) both to and from a data server over a network. The core DAP protocol effectively abstracts data formats to allow client applications to work in whatever environment is required. DAP servers can also connect to data in whatever native format is in use by a hosting organisation, which makes DAP suitable for use in many data storage environments. DAP also includes a number of spatially optimised data stores that can be used to deliver extremely high performance for data extraction and retrieval.