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In recent years, there has been a growing awareness that a better understanding of physical property information is required in mineral exploration. As a consequence, there has been a strong push to collect more data and to use these data more intelligently. There are a multiplicity of reasons behind this impetus: geophysicists want more information about physical property data to enable better surveys to be planned and better interpretations to come from the data acquired and geologists want physical properties to provide addition information about the geology that might allow them to see variations in rocks that are not easy to see using traditional or more expensive methods (hand specimen examination, thin sections, lithogeochemistry, assays, etc.). If a hole is drilled on a geophysical target, then a physical property measurement of the core or the rocks surrounding the core can confirm if the target was intercepted and provides data that can be used to model the target response.<br/><br/>In recent years, there has been a growing awareness that a better understanding of physical property information is required in mineral exploration. As a consequence, there has been a strong push to collect more data and to use these data more intelligently. There are a multiplicity of reasons behind this impetus: geophysicists want more information about physical property data to enable better surveys to be planned and better interpretations to come from the data acquired and geologists want physical properties to provide addition information about the geology that might allow them to see variations in rocks that are not easy to see using traditional or more expensive methods (hand specimen examination, thin sections, lithogeochemistry, assays, etc.). If a hole is drilled on a geophysical target, then a physical property measurement of the core or the rocks surrounding the core can confirm if the target was intercepted and provides data that can be used to model the target response.<br/><br/>Some of the impetus is also coming from computer tools that can use the physical property information. For example, the mine planning and GIS tools that are now being used more commonly are able to display physical property data, so people would like to make better use of this capability. The ultimate result should be a better understanding of the significance of physical property data so the information displayed can be interpreted. There is also a more widespread understanding that it is possible to obtain better results from the computer programs that invert geophysical data because the physical property information provides constraints. These inversion programs are now being used more frequently for gravity and magnetic data and this creates a demand for better density, magnetic susceptibility and remnant magnetization data. Physical property information is available in tables published in textbooks and the like, but certain rocks and minerals frequently have properties which span a broad range of values. Having a more precise value in a local area will be a significant advantage. Normally this local value is obtained by measuring the physical properties of samples from the local area. These local samples can be the outcrop, removed from the outcrop, or the core extracted from boreholes. The measurements can be made with sensors on the outcrop or in the boreholes. Alternately, the samples can be removed from the site and measured in a remote laboratory.<br/><br/>With this enhanced impetus, a workshop was held at SEG's 2010 Annual Meeting. The talks discussed the current state-of-the-art in the measurement and use of physical property data.<br/><br/>The first talk, by Desmond Rainsford and Tom Muir of the Ontario Geological Survey (OGS), was about the physical property databases that the OGS has been acquiring over the last few years: a density data base comprising measurements made from rock samples collected in the field and a magnetic susceptibility database built up of multiple measurements made on outcrop. The magnetic susceptibility meters can lose calibration, so meter serial numbers are recorded as part of the measurement protocol, and instruments compared against in-house standards before and after field seasons. These measurements are taken by the field geologists along with a UTM location. The primary purpose of the measurements is to help in geological mapping, an important part of which involves using the aeromagnetic data. In addition to this, it has been observed that in some cases susceptibility measurements can help in the field to distinguish between two rock types that otherwise look similar. An important but occasionally problematic part of the databases is the rock names selected by the geologists. The choice made is sometimes subjective and will depend on the personal biases and experience of the geologist. In the case of the OGS databases, this issue has been addressed by standardizing the number of rock types to a smaller less ambiguous set. Furthermore, the rock type is selected by the mapping geologist who is familiar with the area.<br/><br/>Vince Gerrie from DGI Geosciences then spoke about the advantages and disadvantages of physical properties measurements in boreholes. One of the key advantages is (near) continuous, high-resolution in-situ measurements. The importance of calibration and QA/QC were emphasized. Gerrie feels that the data are being underutilized and proposed that one way of extracting value from the data is to undertake a cluster analysis. These points were illustrated with a case history from the Lalor Lake deposit in Snow Lake.<br/><br/>Don Emerson had prepared some material on physical properties measurements made in the laboratory. He was not able to attend the workshop, so his material was presented by Richard Smith. Emerson also feels that more physical properties measurements can be made and that more use can be made of the data. He argues that sophisticated measurements are not necessary, but that a basic suite of density, susceptibility, galvanic and inductive resistivity, and acoustic P-wave velocity can provide sufficient information to assist in the mineral exploration process. However, it is not sufficient to take the measurements; time is required to analyze the data. In order to extract information, he showed how crossplots of one physical property against another (which is essentially a form of cluster analysis) are useful for distinguishing between rocks. Emerson also emphasized that physical properties are strongly dependent on the mineralogy and the texture of the sample. Another important point he made relates to the question of scale: physical property measurements of a rock type in hand sample, in a borehole, on an outcrop and with a geophysical measurement are all sampling the formation over a different scale length. A similar measurement value should not be expected because the mineralogy and texture can also appear different at different scale. Another issue raised by Emerson was that resistivity (or conductivity) measurements can be strongly dependent on the amount and type of water present in the sample. Ideally, the condition of the sample when measured should be as close as possible to the condition of the rock when it is in the ground. He also emphasized that a single measurement should not be considered definitive as many samples are anisotropic, so the measured property is dependent on the orientation of the sample.<br/><br/>Mark Shore then made a presentation on how physical properties measurements have been used in some of the mineral exploration projects he has worked on. He feels that physical properties measurements can be made with relatively inexpensive test equipment that can be set up on an exploration site. These measurements will not be as precise as laboratory-based analyses, but Shore believes that the data can be used to extract additional understanding from the geophysical and geological work already undertaken. He also stated that some reasonably good data is better than no “perfect” data. He spoke briefly about his experience putting together equipment for measuring the density, magnetic susceptibility, galvanic and inductive resistivity, and time-domain IP effects of samples.<br/><br/>There were then a number of presentations on the use of physical property measurements in exploration programs. Heather Schijns spoke about some work she and some colleagues from the University of Alberta and Finland undertook to assist base metal exploration in Finland. In this case, she argued that the understanding of reflection seismic and vertical seismic profiling results is enhanced by measurements of the seismic velocity taken in the laboratory. Seismic anisotropy was blamed for a deep stratigraphic drill hole missing a target reflector in the Outokumpu area. In this particular case, collection of accurate measurements of S- and P-wave anisotropy proved to be challenging.<br/><br/>The final presentation, by Emmanuel Bongajum and colleagues from the University of Toronto, argued that physical properties can be used to help determine the grade distribution of an ore deposit in three dimensions. In the case of the Nash Creek deposit, it has been noted that there is correlation between density and grade. By using the physical property measurements, building a geostatistical model and using cokriging methods, it is possible to develop a statistically consistent grade estimate. He argues that this technique is better for determining the ore body outline than linearly interpolating between the locations that are above the cutoff grade. The Nash Creek deposit called for more sophisticated data processing because mineralization is contained in a number of different host lithologies with varying physical properties.<br/><br/>The presentations were followed by a discussion period. There is a general feeling that not enough people are taking physical property measurements. If more measurements were being made, then more use might be made of that data. Greater use might lead to a better understanding, positive outcomes, and then more use: a positive reinforcement cycle. The reason why physical properties measurements are not being made is because there are few facilities able to make these measurements. And, even if it is possible to find someone to take the measurements, it is generally expensive. A solution to this might be if there is a commercial laboratory that can provide a service measuring the physical properties of rocks. It was felt that a lab that specialized in physical properties measurements might bring the price down due to economies of scale and encourage more people to send in samples for measurement. Some geophysical contractors had looked at measuring physical properties, but have found that there is not enough business or revenue so the service was provided largely as a favor to clients as part of a larger job. If a physical properties laboratory is to operate commercially, some innovation or paradigm shift in business models is required.<br/><br/>Another issue is that selecting representative samples for sending to a lab is not straightforward—if one or two samples from an outcrop or drill hole are being sent to a lab, then they must be representative of the rock. It is also important to pack and ship the samples in such a way that they will not get destroyed (if fragile) or dried out (if wet); this can be onerous. In addition, geologists do not like their core samples to leave the job site. Borehole logging can overcome some of these issues, as the measurements are made in situ. However, this is not always possible depending on the condition of the hole, the remoteness of the location, and the additional cost of having a logging crew on site and available. When the physical properties measurements are being acquired, the drill crew must be paid a standby rate, which adds to the cost. Finally, there is the potential for a probe to be lost in a drill hole. If the probe lost is an active gamma or neutron source (used for density or chemical composition measurements), then this can potentially incur extremely high costs (replacement or retrieval costs, loss of minable ore, regulatory body intervention).<br/><br/>The issue of scale of measurement raised by Don Emerson was emphasized by Jim Macnae, who said that laboratory or borehole measurements of conductivity rarely relate to the estimates of conductivity from a large-scale electromagnetic experiment. This is because the conductivity is dependent on the large-scale structures in the rock and has frequency-dependent responses that scale as a power of the linear dimensions of the samples.<br/><br/>Representatives from a number of companies with intense drilling programs spoke briefly about their experiences with setting up a small physical properties measurement facilities on an exploration site. These facilities are able to provide a suite of basic measurements (magnetic susceptibility, density, galvanic resistivity) and to build an extensive data set at a relatively small incremental cost.<br/><br/>There were a number of concrete outcomes from the discussion period. One was that it was felt that, in addition to the case studies at the workshop, more people should be encouraged to talk about case histories when physical properties measurements have added value to exploration programs. Hopefully these successes will lead to more people acquiring and using physical properties data, thus reinforcing the positive cycle. Another way of encouraging people to take physical properties measurement is to give a simple description of how to set up a basic on-site facility to take physical properties measurements. On-site measurements can be done quickly and cost-effectively and the samples never have to leave the site. It was felt that this process would be good for the industry as it would encourage other physical properties measurements (in boreholes and in the laboratory).