b'FeatureDiscovery and geophysics of the Khamsin depositDiscovery and geophysics of the Khamsin iron oxide - copper - golddeposit, Gawler Craton, South Australia James E. HannesonAndrew Thompson Adelaide Mining Geophysics Pty Ltd BHP Adelaide, Australia Adelaide, Australia E Jim.hanneson@bigpond.com E A.Thompson@bhp.comLisa VellaMitchell Newman Fortescue Metals Group LtdBHP Perth, Australia Adelaide, Australia E lvella@fmgk.com.au E Mitch.Newman@bhp.com IntroductionEarly workThe Khamsin iron oxide - copper - gold (IOCG) depositThe Khamsin prospect, formerly known as Salt Creek, occurs some 95 km SE of Olympic Dam and 10 km NW ofexhibits a double peaked gravity high of about 1 to 2 mGal, the Carrapateena Deposit (see Figure 1). Initial estimatesapproximately coincident with a 60nT residual magnetic (ASX, 2014) indicate that it comprises 202 Mt of 0.6% copper,ovoid. In 1977, hole PSC4 was drilled by Australian Selection 0.1g/tAu and 1.7 g/t Ag. The objective of this article is toTrust Pty Ltd located on the weak magnetic anomaly, as part present observations that led to its discovery and to discussof a larger percussion stratigraphic drilling campaign, and the results of transient electromagnetic (TEM) surveying datahole SASC2 is a diamond drilling extension of this hole into carried out later. basement. Basement at 517 m was found to comprise altered biotitic granite with sericite, chlorite and hematite alteration, and anomalous copper was noted in the basal conglomerate Geologyabove the unconformity. Gravity data was collected as part of The deposit occurs at the basal unconformity under 460 to 680the Bowen Anomaly survey in 1983, using a variety of station m of mostly sedimentary cover. Disseminated mineralisationspacings. Early models of the Khamsin gravity anomaly used occurs within the Khamsin Breccia Complex, which is atwo separate bodies to simulate the two peaks. polymictic granite-hematite-carbonate breccia surroundedIn 2005 Teck Australia Pty Ltd joint ventured into the by altered granite and some dykes within the c. 1856 MaCarrapateena project with RMG Services Pty Ltd (the discoverer Donington Suite granitoid, towards the eastern margin of theof Carrapateena) and shortly after holes KH001 and KH002 were Gawler Craton of South Australia. designed to test a density model that used two dense model bodies to simulate the double gravity peak. KH002 indicated minor copper grades at the 457 m deep unconformity. After a change in drilling technique and then access, OZ Minerals drilled DD12KMS003 in 2012 intersecting 600 m of hematite, siderite and chlorite altered breccias associated with the eastern gravity peak. Further drilling discovered the best grades and hematite breccias are associated with the western gravity peak. Gravity and magnetics In 2007, following the acquisition of the tenement by TeckCominco in 2006, one of us (LV) recommended the collection of detailed gravity (200 x 200 m) data. The new data led to the recognition of the NS linear gravity low, interpreted as a low density palaeochannel in the cover and passing over the deposit, as an alternate cause for the double peaked gravity anomaly. When the palaeochannel was included in the density model it was found that the response of a single contiguous dense ovoid could replicate the data and still simulate the double gravity peak. The detailed data yielded the images shown in Figure 2 (topography), Figure 3.1 (Bouguer gravity) and in Figure 3.2 (residual gravity, created by smoothing the Bouguer gravity to estimate regional trends and forming the difference). Figures4.1 and 4.2 show the aeromagnetic data and a residual magnetic Figure 1. Location Map.42 PREVIEWFEBRUARY 2024'