ASEG Extended Abstracts - ASEG2006 - 18th Geophysical Conference, 2006

Effective surface geochemical techniques to help map buried ore deposits are one means of limiting the high cost of unsuccessful holes drilled to test new targets or to define extensions to known orebodies. With this in mind, a version of the CHIM electro-geochemical prospecting technique developed at Guilin University, China was demonstrated at the Challenger Gold Mine in South Australia to test its suitability under Australian conditions.

Two survey lines were completed over the projected extension of ore shoots at the mine. The results were inconclusive. Elevated levels but inconsistent results for Au and As were detected at the surface over shoots projected to depths of between 200 and 400 m. Some modification to the equipment is required to make the system more robust. Ongoing collaboration is planned that will look at improvements to the technique for use in Australian arid conditions.

The Geotech Ltd. VTEM heli-time domain EM system entered into commercial service in late 2002 after a de-velopment program that started in early 2001. Since then, the system has performed commercial surveys in North and South America, Australia, Africa, Europe and Asia.

The VTEM system has been used to explore for a wide variety of deposit styles in a diverse range of settings. The results of four surveys are presented that demon-strate the performance of the VTEM compared with other airborne and ground EM geophysical outcomes.

Noble gas isotopes of He, Ar, Kr and Xe and the halogens Cl, Br, I present within fluid inclusions of hydrothermal quartz or sulphide, provide new insights on the origin of mineralising fluids. He and Ar isotopie ratios enable contributions of meteoric, crustal or mantle volatiles to be quantified. Together with Kr and Xe they can also provide evidence for phase separation or the presence of modern air. The halogens Cl, Br and I provide otherwise unavailable information on the acquisition of salinity.

Contrasting styles of Cu-rich ore deposit in the Mt Isa terrane have been selected for study. The noble gas and halogen data indicate the composition of Proterozoic crustal fluids of diverse origin and from a deeper level of the crust than has hitherto been sampled. Magmatic and metamorphic fluid end-members provide insights into the composition of the Proterozoic mantle and deep crustal devolatilisation processes. Mineralisation resulted from mixing of surface- derived crustal fluids and deeply derived magmatic fluids in the east, and metamorphic devolatilisation fluids in the west.

The ANSIR Major National Research Facility significantly enhanced national capacity for recording distant seismic events using recorders distributed across the continent. Both the broad-band and short-period recorders have been deployed in innovative experimental designs that have made major contributions to the understanding of 3-D structure beneath the Australian Region. The Facility continues its national role with investment in equipment suitable for both seismic and electromagnetic sounding.

Passive seismic recording offers a cost-effective way of obtaining structural information across substantial areas of the continent. The results are valuable in their own right, but can also provide important constraints on seismological structure that are valuable in planning more expensive deep crustal reflection profiles.

After a number of years of development and implementation Inco has a vigorous mines geophysics program in place at our sulphide nickel operations in Canada. This involves geophysical support in exploration, delineation and production. The work in these areas is mutually reinforcing with a common set of physical properties being exploited at a wide variety of scales. The exploration work continues to generate new ore zones in an established but prolific camp and the production related work has resulted in ongoing savings and more efficient mining operations.

We review a number of the main applications including blasthole surveying, televiewers, crosshole seismic tomography, pulsed neutron borehole probes, and BHEM. These programs and a number of other initiatives have been technically successful and are invarious stages of implementation. Overall our mines geophysics work has been a very successful with significant new in-mine discoveries and savings in production. We believe that this is still an underdeveloped area with many more opportunities for geophysical imaging of ore at multiple scales

In 2003 and 2004, PIRSA, pmd*CRC and Geoscience Australia, in conjunction with ANSIR, acquired ~200 line km of deep seismic reflection data along an east-west transect across the Curnamona Province in South Australia. At the eastern end of the seismic transect, the crust is divided into several horizontal “bands” of differing reflectivity. In the middle part of the seismic transect, there is a distinctive bland zone within the middle to lower crust. Its significance is unknown but in terms of its origin, it could result from reduced acoustic impedance contrasts due to partial melting, metasomatism, or be a zone of high fluid flow that has homogeneously altered a large part of the crust. It is interesting to note that similar bland zones have been noted on seismic sections in the Olympic Dam and Kalgoorlie regions, hi the western part of the seismic section, a westward-thickening wedge of Neoproterozoic-Cambrian sediments up to 9 km thick overlies basement, and passes west into the even thicker, and more highly deformed, cover of the same age in the Flinders Ranges. This deformation is inferred to be Delamerian in age. Much of the crust beneath this succession is highly reflective, but it is not as obviously partitioned into subhorizontal layers as the eastern end of the line. A shallowly east-dipping surface is potentially the boundary between two different types of crust, one underlying Willyama Supergroup, and the other at depth beneath the Flinders Ranges.

As an aid to better understanding fluid flow processes and potential source rocks for the Zambian Copper Belt, preliminary numerical fluid flow modelling has been undertaken, coupled to salinity and heat transfer. The computer code used for the modelling is from Yang and Large (2001), and has been previously used to successfully model fluid flow-salinity-heat transfer in the McArthur Basin related to Stratiform Zn-Pb-Ag ore genesis (Large, et al., 2002).

A 43.5km x 17km theoretical geological section was constructed, based on our current understanding of the structure, stratigraphy and basin architecture in the ZCB. The geological model section incorporates elements of basement, footwall succession, Ore Shale, hangingwall lower Roan siltstones and carbonates, upper Roan siltstones, carbonates and a layer of salt, Mwashia and overlying Kundelungu shales. Porosity and permeability parameters have been assigned based on our understanding of the sedimentary facies, alteration zones, petrographic evidence and local to regional structures. The most permeable elements assigned in the model are; the Mindola Clastics in the immediate footwall to the Ore Shale; crosscutting breccias in the hangingwall (below salt layer) and fault zones. The least permeable elements assigned are the Ore Shale, hangingwall carbonates and siltstones, the Mwashia shales and the basement.

A one km thick salt layer in the Upper Roan has been assigned a salinity of 30 wt% (the maximum allowable by the computer code). Other sedimentary units have been given lesser initial salinities depending on the interpreted sedimentary environment (evaporitic, marine or lacustrine). A normal geothermal gradient through the basin of 30°C per km has been assumed.

The model has been designed to test fluid flow and temperature gradients associated with the downward flow and convective circulation of saline fluid, from the hanging wall evaporitic salt layer into the Lower Roan stratigraphy and basement. A number of scenarios have been tested by varying the permeability of certain basin elements and fault structures. The results indicate that the most likely scenario to account for the stratiform Cu deposits involves penetration of high salinity brines from the Upper Roan salt layer down into the basement along a series on normal master faults, with brine circulation and leaching of Cu from the basement terrain. The oxidised metalliferous fluids more upwards along second order faults and are channelled into the Mindola Clastics below the organic-bearing shale cap rocks where potassic alteration and Cu-mineralisation occurs.

Evidence for shallow gas has been derived from geophysical and field data during a marine survey in the Arafura Sea (SS05/2005). Sub-bottom profile evidence includes enhanced reflections, acoustic blanking, phase reversal and low frequency events. These geophysical attributes have been studied within staged post processing. This has allowed the identification of areas within various parts of the section at depths between 1 to ~70m below sea floor. This evidence has been correlated with side-scan sonar and multi-beam with pockmark fields and mud domes identified over areas of interpreted sub-surface gas.

Australia has by far largest identified uranium resources of any country. This uranium endowment appears to be related directly or indirectly to the emplacement of uranium enriched felsic igneous rocks in the late Archaean, the Palaeo- to Mesoproterozoic and the mid Phanerozoic. International trends in nuclear power generation point to high and increasing demand for Australia’s uranium for the foreseeable future.

A major lithogeochemical study of the basin sediments surrounding the stratiform copper deposits of the Zambian Copper Belt has revealed extensive stratabound zones of both potassio and sodic alteration. The syn-ore potassio alteration is represented by enrichment of biotite and K-feldspar in the enclosing sediments, with whole rock K20 values varying from 3.5 to 10 wt%. The sodic alteration (albite-calcite), post-dates the copper mineralisation, and occurs in the Upper Roan siltstone-carbonate sequence overlying the potassio alteration zone. Na20 values vary from 1.5 to 6.3 wt%, corresponding to a maximum of 60 wt% albite in the altered rock.

A comprehensive study of carbon and oxygen isotopes of various carbonate types throughout the sediments of the Zambian Copper Belt has shown a systematic relationship to alteration and copper mineralisation that has significant application in mineral exploration. Mineralised and potassically altered zones show strong coupled depletion in both carbon and oxygen isotopes, with δ¹³C = -6 to –26 per mil and δ ¹⁸O = 6 to 20 per mil. The strongly negative δ ¹³C values of carbonate in the ore shale and potassio footwall elastics indicates the significant role of oxidation of organic carbon in the mineralising process. The fact that the relatively clean altered and mineralised footwall elastics also show this negative carbon isotope shift suggests that organic reaction products migrated out of the shale into the permeable footwall elastics prior to mixing with the ore fluid, leading to redox reactions causing coupled oxidation of organic matter and reduction of sulfate to H2S resulting in copper sulfide precipitation.

Laboratory spectral measurements of soil samples collected from a range of environments in the Perth region demonstrated the ability to identify characteristic features of acid sulphate soils. Airborne hyperspectral imagery will be utilised to evaluate the ability to map acid sulphate soils on the Swan Coastal Plain. The expected results of the image processing will include surface mineralogy maps which will be used to identify areas of acid sulphate soils.

Over the past 14 years, CSIRO Industrial Physics has developed High Temperature Superconducting (HTS) SQUID (Superconducting Quantum Interference Device) sensor systems for TEM prospecting. Initially this work was done in collaboration with BHP P/L, now BHP Billiton, and some early successes were achieved. Collaboration with BHP ceased in 1998 after completion of a series of airborne trials. Interest in the rf SQUID sensor was revived in 2000, when it was successfully used to delineate targets at Falconbridge Ltd.’s Raglan, Quebec, mine site. As a result, CSIRO entered into a contract to build a ruggedised version of the SQUID sensor system for Falconbridge’s use under a rental agreement. Since September 2001, a number of CSIRO SQUID systems have been built and deployed over three continents. A local Australian firm, Outer-Rim Developments, has been licensed by CSIRO to manufacture the rf SQUID systems now called LANDTEM™. Technology transfer from CSIRO to Outer-Rim Developments was facilitated by Outer-Rim having a sub-contractor work within CSIRO for a number of months.

In this paper, the results from some of the seminal SQUID surveys are presented and discussed. Finally a direct comparison between the noise performance of CSIRO’s HTS SQUID sensors and a Bartington flux-gate sensor is presented.

The Sudbury Igneous Complex (SIC) is widely believed to be the result of melt generation due to meteorite impact, and so models of Ni-Cu-PGE sulphide ore formation must be reconciled with this hypothesis. Moreover, the formation of the Ni and Cu sulphide ores is a product of sulphide saturation and segregation of immiscible sulphide melts, and like the ores at Noril’sk, those at Sudbury leave a fingerprint of the process in the comagmatic silicate rocks which are bereft of much of their Ni, Cu and PGE. At Sudbury, the thickest part of metal-depleted norite is located proximal to the largest known deposits, viz. the Creighton, Copper Cliff and Frood-Stobie Deposits. It is believed that the formation of the initial immiscible sulphide took place shortly after melt sheet formation, but well before any significant amount of silicate crystallization; sulphide saturation and segregation from the crustal melt sheet likely occurred under superheated conditions. The geological data provide important constraints on the sequence of events that formed the different orebodies in contact, footwall and offset dyke environments.

A new compound model is developed to calculate volumetric strains of unsaturated and saturated structured soils. In this model, structured soils are regarded as the composite of undisturbed and disturbed parts, both of which are uniformly distributed. The proportion of the two parts can be calculated through the combination of a pore size distribution curve, a suggested geometric structural model, the structural instability criterion and constitutive models for remoulded soils. The overall volumetric strain increment includes three components: the elastic increment of the undisturbed part, the plastic increment of the disturbed part determined by the application of the generalized suction theory, and the structure collapse contribution which is particularly relevant to the change of void ratio from undisturbed soils to disturbed soils. The relationship between the angle-stiffness of the structural instability criterion and the degree of saturation is determined by the structural strengths revealed by compression tests of natural structured soils. The validity of this model was established by comparing calculated results with published experimental data of collapsible loess.

Geotech’s airborne Audio Frequency Magnetics (AFMAG) system was successfully flown in a helicopter towed bird configuration over selected test sites in Sudbury, Canada.

Airborne trials were conducted over Vermillion Lake, the Trillabelle deposit, north range of the Sudbury Basin, and over the Reid-Mahaffy test site. The results over Reid-Mahaffy show that exploration sized targets can be detected while the conductors seen in the Sudbury trials show that larger, and regional conductors are detected as well.

Research and development is underway to implement the system onto Geotech’s Grand Caravan, although the noise characteristics of a fixed-wing aircraft are challenging.

In practice, acquisition and processing solutions to poor seismic illumination begin with an effort to compensate for gross holes in the density of target illumination using conventional Narrow-Azimuth streamer acquisition. As the complexity of the problem increases the case for Multi-Azimuth acquisition builds. Wide-Azimuth acquisition is required in the most challenging scenarios. Correspondingly, the processing and imaging technologies deployed must also improve in sophistication. Recent and ongoing global R&D efforts, complementing several large innovative projects, demonstrate that each of the target illumination concepts and challenges discussed here can be evaluated and contrasted in clear and unambiguous terms.

Direct utilization of geothermal energy consists of various forms for heating and cooling instead of converting the energy for electric power generation. The geothermal resources that can be utilized are in the lower temperature range that are more wide-spread than the higher temperature resources used for electricity generation. The major areas of direct utilization are: heating of swimming pools and for balneology, space heating and cooling including district heating; agriculture applications (greenhouse heating and crop drying); aquaculture applications; industrial processing; and geothermal heat pumps. Direct utilization projects are reported in 72 countries with an installed capacity of 28,268 MWt and annual energy use of 273,372 TJ (75,943 GWh) reported in 2005. The equivalent annual savings in fuel oil amounts to 170 million barrels (25.4 million tonnes) and 24 million tonnes in carbon emissions to the atmosphere. Recent trends are to combined geothermal heat and power projects in order to maximize the use of the resource and improve the economics of the project. With the recent increases in fossil fuel prices, it is estimated that direct utilizations will more than double in the next 10 years.

Deep seismic reflection data acquired in the eastern Gawler Craton show the crustal architecture and Palaeoproterozoic crustal-scale thrusts controlling the locus of fluid-flow leading to Fe oxide Cu-Au mineralisation. They define a northwest-trending exploration fairway.

The thrusts are temporally related to the 1.6 Ga Olarian Orogeny of the adjacent Curnamona Province, hut a causal link is yet to be established.

The crust below the Adelaide Rift System, at the northern end of the north-south seismic line, may be allochthonous; docking with the proto-Gawler Craton, as a separate terrane prior to final amalgamation of the craton, or it could be part of the Curnamona Province.