b'Minerals geophysics Minerals geophysicsTerry Harvey Associate Editorfor Minerals geophysicsterry.v.harvey@glencore.com.auBits and bobsIn this piece, Id like to touch on two somewhat peripheral propositions for mineral geophysics: that the range ofFigure 1.Piezoelectric measurements at a gold-bearing quartz deposit at Ustnerinskoe (Yakutia, Russia). The observed signals are the t 0-wave generated at the interface of thawed and permafrost ground and the t petrophysical properties of minerals1-wave generated by ore-quartz zones (Neishtadt etal., 2006).potentially usable for mineral exploration has not been exhausted, and, that the application of existing geophysicalunder development is the biasedproperties and comprehensive reference survey techniques extends well beyondheterodyne technique which seeks tolists for further study. And, to whet your mineral exploration usage. discriminate between the non-linearappetite, Ive included an illustration electrical response of disseminated semi- (Figure 1) from the paper by Neishtadt For the first proposition, geophysicists areconductor metallic sulphides and theetal. (2006).familiar with the mineral petrophysicallinear electrical response of disseminated properties normally utilised in mineralgraphite, clays, etc. If youre interested,For the second proposition, utilisation exploration: density, magneticas a starting point, two papers (Oertelof geophysical field techniques susceptibility, electrical conductivity/ etal. (2018) and White etal. (2018))beyond the field of mineral exploration resistivity, IP effect, natural radioactivity,discussing this technique were presentedincludes the more obvious extensions and sonic velocity. Expanding theat the 2018 AEGC Sydney Conference.into environmental, archaeological, category to include petrophysicalIve previously alluded to this work (seeengineering, water and energy properties of rocks would addressMineral Geophysics in Preview 193), and Iresource exploration disciplines, and the way minerals are distributed, andwont elaborate further. even treasure hunting with portable would include additional petrophysicalmetal detectors. Less obvious, for properties such as porosity, permeability,Piezoelectricity is the electric charge thatexample, is the adaption of geophysical etc. which are arguably more pertinentaccumulates in certain solid materials intechniques for the detection, mapping to the application of geophysics toresponse to applied mechanical stress.and assessment of buried pipes and other fields such as environmentalQuartz, a frequent accompaniment tocables. This latter field is surprisingly engineering and the exploration forepithermal gold mineralisation, candiverse, both in the range of geophysical water and energy resources. But theexhibit strong piezoelectric effects, andtechniques used and in the way they petrophysical properties Im interested inthe potential application of piezoelectricare used. A preliminary search on the are the somewhat more esoteric mineraland seismoelectrokinetic phenomenanet shows that magnetics, galvanic properties. Examples could include semi- to mineral exploration geophysics haveresistivity, electromagnetics, ground conductor properties such as asymmetricsparked (sorry about that!) interest atpenetrating radar and seismics may electrical conductivity, and dielectricvarious times in the past. In fact, thebe employed. The ingenuity in the properties such as the piezoelectric andrather dim memories I have of reading aapplication of some of these techniques seismoelectrokinetic phenomena. paper on the application of piezoelectricis impressive. In electromagnetics, for effect in mineral exploration early in myexample, a wide range of frequencies Semi-conductor properties are ofcareer, prompted the inclusion of thismay be utilised, and the technique particular interest in mineral explorationtopic in my piece for this issue of Preview.can be used in the passive mode geophysics because metallic sulphides,My initial search on the net found two(receiver only), active mode (transmitter including ore minerals such aspapers (listed in the references) whichand receiver), and activation mode chalcopyrite and galena, exhibit these.trace developments in this field over a(transmitting a signal along the target One geophysical survey applicationwide time range; both include tables ofpipe or cable itself).DECEMBER 2022 PREVIEW 38'