b'Michael Astens best of Exploration GeophysicsFeatureMichael Astens best of Exploration Geophysicsthe geophysical interpretations (guided by the adjacent Que River deposit) were indicative of vertical mineralisation. Jovans work on Hellyer became a core part of a subsequent PhD thesis. Students interested in the evolution of the understanding of the geometry of the orebody and its EM responses will find more details in reports on subsequent borehole EM surveys (Eadie 1987; Silic and Eadie 1989).The Hellyer case history has especial significance in the history of EM geophysics because it ranks as perhaps the first Australian orebody discovery by EM methods followed by drilling. Earlier EM case histories of the copper-rich Elura orebody near Cobar (NSW) exist but the ore deposit was found primarily by magnetic and gravity methods (Davis 1980), although it later Michael Astenbecame a proving ground for a wide range of electrical and EM ASEG President 2009 - 2010methods. EG published a special issue in 1980 bringing together michael.asten@monash.edu about 35 papers on geophysical and geological studies on Eluraa great step in understanding various geophysical technologies, but not crediting EM geophysics with the Our ASEG President of the time, Ted Tyne, kicked off this series indiscovery.February 2020 (Tyne 2020), noting that our journal ExplorationEM studies on nickel sulphide orebodies at Forrestania (WA) Geophysics (EG) is now 50 years old50 years that cover threealso exist prior to the Hellyer paper, but like the Elura history, literal generations of geophysicists, and all the new paradigmsForrestania was discovered by other methodsthe recognition, of instrumentation and interpretation devised over that span ofgeochemistry and drilling of near-surface gossans (Porter and time. Ted asked me to contribute my perspective on the best ofMcKay 1981). Characterisation of the EM response followed geophysics in the EG pantheon; the timing makes for a pleasantdiscovery (Staples 1984).task amidst the murky greys of the COVID-19 second wave/second lockdown in my home city (Melbourne). Multiple discoveries of orebodies by their EM response were I am giving my vote to The application of geophysics to thereported in EG in the decades following the Hellyer body; the discovery of the Hellyer ore deposit, Tasmania by Tom Eadie,Eloise copper-rich body (Brescianini et al., 1992) and the Ernest-Jovan Silic and Doug Jack (Eadie et al., 1985). Henry copper-gold orebody (Webb and Rowston 1995) are two examples of orebodies below blind cover in the Mt Isa block, I confess to some subjectivity; having spent about half of myQueensland, but the Hellyer case history remains a beacon of professional life (both academic and in industry) workingearly EM achievement in the pages of EG.with electromagnetic (EM) methods in mineral exploration, I continue to be fascinated at how time-domain EM in expertSo what happened to the two geophysicists who analysed hands was successful in detecting this major orebody in thethe EM data over Hellyer, and stuck the proverbial pins in rough and tough terrane of western Tasmania. The immediatethat geologically blind cover some four decades ago? Tom attraction was the existence of the near-by and near-surfaceEadie rose through the exploration ranks to be Executive small Que River lead-zinc mine. However, the mineralGeneral Manager Exploration of Pasminco, and now holds a assemblage of pyrite, zinc (sphalerite) and lead (galena) ores isnumber of board positions in mining companies. Jovan Silic only moderately conductive when compared with copper orhas remained a specialist geophysicist consulting globally to nickel targets in the Mt Isa block (Qld) or the Yilgarn (WA). And,a wide range of mineral exploration groups, while taking time the top of economic mineralisation for the main Hellyer orebodyin the northern summers to cruise the Mediterranean Sea. is at a depth of 150 to 400 m below barren host rocks and blackJovans take-home message from the Hellyer story, and one shales, that made for a low amplitude subtle anomaly whichwhich was also applied to other major discoveries (Silic and many geophysicists of that time may have found unconvincing. Seed 2001), is Never ignore the subtleties of the data until you have fully explained them. Today with too much reliance Jovan expands on some of the exploration challenges of theon automatic interpretation techniques it is quite likely that time (Silic, Eadie, and Jack 1985) and they offer instructivesome would walk away from the Hellyer response without fully lessons for any who think geophysics is a routine process. Theunderstanding why.original Que River deposit was a vertical structure and EM interpretation followed similar thinking. However, due to theThe last word from Tom Eadie; post-retirement he operates only moderately conductive nature of the Hellyer mineralisationthe Black Cat truffle farm south of Creswick in the Victorian and its particular geometry, the EM response was principally agoldfields. He comments that the patterns of the truffles current channelling not inductive responsea class now welloutline geological structures - perhaps a tool for finding the understood (but not then!) to be very insensitive to dip. Tomgold! Should we expect a research proposal early next April for recalls some tense sessions with company geologists when thethe use of truffle dogs supplementing geoscientists in future early drilling suggested flat-lying mineralisation at a time whengold exploration?AUGUST 2020 PREVIEW 48'