Interpretation of Magnetic & Gravity Data.

Abstract

The Jervois mine is located some 270 km north-east of Alice Springs. The area is on the northern boundary of the Arunta Block and contains the main outcrop of the Jervois sequence which consists of mica and chlorite chists, with or without andalusite and/or cordierite, impure limey rods, quartz magnetite-garnet-chlorite rock, quartz-tourmal rock, amphibolite and meta gabbro. At least three phases of folding are recognized; the second of which is thought to have formed the J structure; so- called because of its shape. Forming the bulk of the Jervois sequence, the low but prominent hills and ridges of the J structure lying on the plain below the Jervois Range escarpment, contain patchy mineralisation of several types: copper and tungsten in calc-silicate rock, lead-zinc-silver and copper in calc-silicate rock and copper in quartz-magnetite-garnetchlorite rock. The association of the latter type of mineralisation with a magnetite-rich rock makes it a good target for a magnetic survey. A gravity survey should also be able to detect this rock type as it has a higher density than the surrounding schist. A magnetic and gravity survey of the area was undertaken in June 1982. The magnetic survey on the covered western limb of the J structure has enabled several horizons to be traced to the north. An isoclinal fold and a few small faults are postulated. The gravity survey showed a large fault contact at the base of the escarpment to the west. Younger Precambrian and Phanerozoic rocks of the escarpment are usually only referred to as 'being unconformable with the Jervois sequence. The results of these surveys help with the understanding of the structural geology of the area and also provide some indication of potentially mineralised zones.