Retained areas report Bynoe joint venture.

Abstract

During the 1988-1989 programme exploration involved both backhoe trenching of pegmatite and excavator trenching of alluvial concentrations of tin/tantalum mineralisation. During the 1988 field season sections of Annie River, Arltunga East, Arltunga West, Johnstones and Leviathan Creek drainages were tested. This work was either a follow-up to initial trenching to obtain a reserve estimate or preliminary trenching to test the potential of individual drainages.. It was carried out with the PC 400 Komatsu Excavator in EL 4183. The drainages are described in the 1984 Annual Report as long, broad, shallow, mature systems varying up to several kilometres in length and 200m to 300m in width. At their deepest they rarely contain more than 4m of alluvium although the southern sections of Booths drainage sometimes exceeds 6m. In profile the drainages are virtually the same and consist of a surficial black soil horizon 100 mm to 200 mm thick, underlain by a mottled ferruginous clay whioh grades into a sandy clay to clayey gravel wash containing significant cassiterite and tantalite concentrations. Within the alluvial sediments at least three sedimentary cycles are recognised, the earliest produced the basal clayey sand or clayey gravel wash which is up to 2.5 in thick and usually contains subangular quartz and siltstone clasts of up to 200 mm in length. This basal, or C horizon, contains the major portion of tin tantalum reserves. Directly overlying the horizon, and usually combined within it or separated by thin bands of clayey sand is a second minor gravel horizon (8 horizon) which is up to 1 m thick. The B horizon contains minor concentrations of cassiterite and tantalite and may be absent due to reworking or unrecognised if it is represented by the A horizon, a thin, rarely observed band of small 5 - 10 m pebbles which usually occurs about 0.5 m below the organic clay layer - The A horizon is generally no more than 0.5 m thick and is essentially unmineralised. In places all horizons have been subjected to recent working and resultant in-filling with black organic clays. The underlying bedrock is usually weathered to clay directly beneath the C horizon, weathering becomes less intense towards the margins of the drainage channel which are usually marked by an abrupt increase in bedrock elevation. Costeaning has been selected as the method of appraisal of alluvial reserves.. The Komatsu PC 400 excavator was used to costean the width of the alluvial channels on line 100 m apart, it is usual for the trench to begin within a section of wash and proceed outwards until the limits of the channel are reached. After a short period of familiarization competent field crews are able to recognise the channel margins' and the alluvial horizons of interest. Vertical channel samples are collected from the B and C horizons (if present) at 5 m intervals, the depth and thickness of individual horizons are noted and the samples processed according to standard practice. The work carried out in 1988 involved 250m of excavator trenching in Arltunga East, Arltunga West and Johnstones Drainages, and subsequently involved 364.5 m of auger drilling of alluvials in the Annie River and Leviathan Creek. Johnstones Drainage is located in P0 16 and EL 4183. The work detailed in this section was carried out in the northern part of the drainage (Johnstones North) past its confluence with Hang Gong drainage. In this area the drainage has developed a rejuventated profile with a well defined channel. During 1988 two trench-lines were planned one along 9800E and the other along 9700E. However, the line along 9700E was found to have been scoured to bedrock, so trenching results were obtained for line 9800E only. A total of 75m of excavator trenching was completed% producing 12 samples for processing. Two of the samples had grades of interest with only one of these exceeding 0.500 kg/tonne tin equivalent. Further work is warranted to locate potential economic concentrations further downstream. The most encouraging results this season have come from excavator trenching of Johnstones Alluvial, and subsequently excavator trenching of the two Arltunga drainages downstream in EL 5118. Results from these trenches show a continuation of enhanced tin/tantalum grades downstream from the significant deposits already identified upstream in MLN 16. These results have led to the application for an Exploration Retention Licence over part of the remaining two blocks of EL 4183, to enable further evaluation of this alluvial potential.