Annual report, EL 803 Crawford Range Area 1, year ending 27 December 1973

Abstract

The tin bearing pegmatites near the Ivy Mine in EL 803 have been investigated by the writer only on a casual basis. The pegmatites intrude the Archaean Arunta basement. They are limited in extent and exhibit a boudinage structure, that is they commonly swell and pinch. The widest section is approximately 15 thick. The tin mineralization, in the form of cassiterite, is not evenly distributed through the host rock but tends to stick to the margins and more gneissenous zones. A grab sample from one of the richest sections exposed in a pothole was assayed for tin and tantalum. Values obtained were 0.76% Sn and 0.0056 Ta. Both grade and tonnage do not indicate a mining proposition on a company basis. Even individuals or small parties would be hard put to make a living from it in this remote and dry region. Tungsten in the form of scheelite is found in the calc-silicates within the Archaean Arunta Complex on the Ivy grid area in EL 803. As they have not been examined by the writer no comment will be made. However, it is suspected that the scheelite distribution is extremely erratic within the structural complex calc-silicates which like the surrounding country rocks have undergone multiple stage folding. These areas were investigated during the tenure of AP 2651 and were commented on in reports submitted to the Department. No copper nickel mineralization is known to occur on EL 803 although good oxide copper is present just to the south at the Home of Bullion Mine, to the north within the metabasic sills in Prospect U, EL 804 and in the Mt Strzelecki area, EL 372 within a dolerite sequence. Airborne magnetic data flown during late 1972 has been quite useful in regional geological mapping and interpretation. The magnetic character of the Archaean Arunta Complex is very pronounced and intense. This is probably due to magnetite rich bands in particular those associated with gneissic rock types. The Arunta Complex outlined in the report by Layton and Associates in the eastern portion of the survey correlates with the regional mapping in that area. Although no mention is made of Archaean rock types cropping out in the northwestern portion, as mapped northwest of the Osborne Range, the magnetic character is similar to that in the eastern section.

The Hatches Creek Group sediments exhibit two distinct magnetic patterns. The report mentions that the sedimentary section of the Hatches Creek Group has no magnetic expression, however, there are many linear magnetic zones associated with this group. These linear zones were mapped by the B.M.R. as being Archaen in age.

The report suggests that this is unlikely, since the anomalous areas are contiguous with the Hatches Creek Group. Geological mapping has indicated that the Hatches Creek Group can be divided into two units, lower and upper, and each unit has its own magnetic expression. The lower unit, consisting of a pelitic sequence, corresponds to the linear zones referred to. The number of magnetic highs within the linear magnetic trends are directly related to dacite laccoliths and sills and dolerite stocks. This is particularly well illustrated in Prospect A area, where there is a zone of magnetic intensity which to the southeast trends along the base of the North Osborne Range. This magnetic intensity corresponds to a large dacite exposure which trends parallel to the North Osborne Range for some distance and has been verified under cover by regional airtrac geochem and geological drilling in the vicinity. The mapped granites and inferred granite areas correlate closely to the large granitic intrusions suggested by the magnetic data. There is one exception; the magnetic high near Ikyes Bore was attributed to originate from a dolerite intrusion as mapped by BMR. However, the dolerjte is nonexistent. The intrusives in the area are the foliated granodiorite and the Barrow Creek granite, both of which have no magnetic expression. The writer believes that this high is associated with the remnant Mt. Stewart beds of limonitic sandstone found in the area. On May 2nd, airborne Input - EM reconnaissance was flown as a test case over the mineralized metabasic sill in Prospect D. Although there was no response over the mineralized zone, one low order anomaly was out- lined centered approximately 2300W, 170 5. In view of the geologically favourable Warramunga Formation, which does not crop out and the possibility of massive suiphides being present therein, it was decided to conduct an airborne EM - Input survey over an area between the Crawford - Osborne Range and over a narrow strip north of the Osborne Range. The comprehensive airborne survey was conducted on 16/7/73 by Geoterrex. Eleven low order anomalies were outlined, two of which, no. 8 and no. 10, fall within EL 803. To date they have not been tested by airtrac drilling. Anomaly 8 may be due to remnant outcrops of ferruginous Mt. Stuart beds but this theory has not been tested to date as the exact location is not known at the time of writing. Anomaly 10 was very close to the southern boundary of EL 803 and is due west of anomaly 8. It is located at the NW end of a brecciated quartz - quartzite ridge within a thickly vegetated area containing large, mature eucalypts. This anomaly appears to lie along a quartz filled fault zone. No geochemistry was done on this E.L. with exception of a grab sample taken at the Ivy Mine which assayed 0.76% Sn and 0.0056 Ta. A limited airtrac program was undertaken over a moderate magnetic high outlined by last years airborne magnetometer and scintillometer survey near the old army campsite on Taylor Creek. A grid was bulldozedover the area which is thought to be underlain by the Lower Hatches Creek Unit or possibly Warramunga Formation. This program had to be terminated prematurely in view of difficult drilling and wofl requirements on other areas held by the Company. A number of holes were started but had to be abandoned. One hole reached 100 vertical depth and was still within overburden. No diamond drilling was done on this EL although comprehensive program was undertaken on EL 804. The expenditure on this area during this year, including field camp expenses, consultants time and related over-heads in addition to the work program is calculated to exceed $17,000.00. The work committment for this Exploration Licence was $10,000.00.