Geochemical stream and soil sampling in AP 2372, Huckitta, NT

Abstract

Field procedure and results - Before embarking on the main survey, a number of soil and drainage samples were collected from the Turkey Creek Prospect and its surroundings by way of an orientation survey. Results of this survey are shown on Plan No?s, NT 669 and NT 670. These results are fairly self evident, and while it is recognised that the prospect is a low grade one of substantial size, the following comments are offered; 1. Background values for Pb and Zn (based also on results from APs 2372 and 2392) are 5-10 ppm, and 10-20 ppm, respectively. 2. Although galena is the dominant mineral both at surface and at depth, Zn values generally reach higher levels than Pb values, even in residual soil samples. 3. Pb tends to fall off more rapidly than Zn away from the mineralised zone, reflecting the former?s relative low mobility. The poorly defined drainage in parts of APs . 2372 and 2392 necessitated grid sampling over relatively large areas, particularly in AP 2392. A 0.8km (0.5 mile) grid spacing was arbitrarily chosen, while in areas of defined drainage a sample density of 1 sample per 1.5km2 was aimed for and achieved for the most part. Although some portions of the sandy plains, particularly in the south of AP 2392, are composed of eolian sand, and analytical values from these areas will be next to meaningless, significant portions are composed of residual soil and material which has undergone only limited alluvial transport, and it was felt at the time that a geochemical survey over these low relief areas was justified, although, on reviewing results, the degree of effectiveness of geochemical sampling over these areas is difficult to assess. It is possible that the proportion of transported to residual material is considerably greater than had previously been assumed. The method of gridding was crude, employing compass and Landrover speedometer, aided by photo identification wherever possible. Consequently, location errors of up to 400m (1/4mile) at the end of the long traverses across featureless country have been recorded. However, these are random errors and are not considered to be serious since overall coverage of the area will have been maintained. The Ooratippra Creek Floodout and the sand plains in the east and south of AP 2372 were omitted from the survey. Total area of the two APs is 1825km2 of which outcrop accounts for approximately 60-70%. The total number of collected samples is 1,565, 1,025 in AP 2392 and 510 in AP 2372. All samples were dry sieved to -80 mesh and forwarded to the Zinc Corporation for analysis; the following elements were sought: Cu, Pb, Zn, Ag, Ni, Mo, U. Inspection of the metal values plans shows that no major anomalies were encountered. Two weakly anomalous zones have been outlined in AP 2392 and two smaller ones in AP 2372 and their approximate positions are shown on the plans. The two zones on AP 2392, particularly the northern one, are associated with or close to mapped faults, however, since the source and nature of the mineralisation were not seen, further speculation on structural control seems futile at this stage. Maximum Pb values obtained in these two zones reach up to 20 times average background. Somewhat more interesting results were obtained from an occurrence of heavily ferruginised, leached limestone and sandstone in the northeast of AP 2392 at approximately 136 deg 211?E and 21 deg 56?S. The country rock in this instance is a light grey to buff coloured siliceous limestone or dolomite with interbedded quartz sandstone. The attitude of the beds is more or less horizontal, and ferruginisation has proceeded along cracks and fissures, often leaving unferruginised cores; the resulting rock resembles a breccia or conglomerate. The ferruginous material is mainly hematite/goethite, and manganiferous encrustations are common. Samples from this material gave the following assay results (samples 83 and 84 by AAS Zinc Corporation, sample 85 by emission spec AMDEL). Sample No 83: Pb 3l9Oppm, Zn 670, Cu 71, Ni 59. Sample No 84: Pb l57Oppm, Zn 400, Cu 54, Ni 37, Ag l Sample No 85: Pb 400ppm, Zn 300, Cu 60, Ni 100, Ag 1, Co 50, Cr 150, V 2, W Not detected, Mn 5000ppm, Nb not detected, Sn 2ppm. It will be noted that this occurrence lies within one of the anomalous zones referred to earlier and as such may be worthy of more detailed examination. Except for Pb, the metal values of these samples are similar to those obtained from laterite deposits at the Wilkawillina/Parachilna contact at Mt. McKinlay Creek, South Australia (Kostlin, 1969).