1964 Report on Drilling Programme, Angel Group of Leases

Abstract

A programme of diamond and percussion (waggon) drilling was undertaken during the period May-September 1964 on the Angel Group of Leases, Tennant Creek Goldfield, Northern Territory, Australia. The purpose of the programme was: To determine whether any gold ore was present in the zone of oxidation and enrichment beneath surface geochemical anomalies at the Crusader and Black Angel workings; To determine whether other surface geochemical anomalies beyond the immediate confines of the workings persisted in depth. If the anomalies persisted in depth, gold and/or copper ore could possibly be present. To achieve these two aims 48 percussion (waggon) drill holes totalling 4770 feet and 5 diamond drill holes totalling 1309 feet were drilled. The holes were sampled over their entire length. All samples in which no gold was visible were examined by semi-quantitative spectrographic analyses. Anomalous results were assayed for gold. Five diamond drill holes and twelve waggon drill holes were sited to test the Crusader and Black Angel copper, bismuth and cobalt geochemical anomalies. Two of the diamond drill holes (DDA 1 and 2) were sited to test the zone of oxidation and enrichment in the Crusader area. The remaining three drill holes (DDA 3, 4 and 5) tested the zone of oxidation and enrichment beneath the Black Angel anomaly. The twelve waggon drill holes were drilled prior to siting diamond drill holes DDA 4, 5. In the Crusader area the drill holes (DDA 1 and 2) intersected the ore zones but did not completely test the zone of enrichment because the effects of oxidation extend to greater depths than in the Black Angel and White Devil areas. Anomalous concentrations of copper, cobalt, nickel and bismuth were found in the leached ore zone but no gold was found. The depth of oxidation in the Crusader area being greater than 260 feet below the surface is comparable to elsewhere in the Goldfield where depths of oxidation range down to 700 feet and average about 350 feet. The diamond drill holes in the Black Angel area did not encounter any gold or copper in the zone of oxidation and enrichment. Anomalous amounts of copper in the holes did confirm the downward continuation of the mineralised zone. The twelve waggon drill holes drilled in the vicinity of No. 6 workings indicated that mining might reveal pockets of secondary gold ore. The work done has shown that concentrations of copper minerals being outside the 4000 gamma magnetic contour are peripheral to the magnetic anomalies and consequently negative results of testing the central part of the magnetic anomalies alone is not conclusive evidence that copper ore is absent. However, the Black Angel geochemical anomaly was tested by Peko Mines N. L. drill hole BA4 about 260 feet vertically below the surface outcrop but not in the zone of oxidation and enrichment. No copper or gold was found in BA4 nor in DDA4, 200 feet to the east. On this basis the Black Angel zone has a lower exploration priority than the Crusader geochemical anomaly. Nevertheless the persistence in depth of the sheared, hematised and brecciated zone of mineralised sediment and its peripheral position with respect to the magnetic anomaly tend to suggest that the zone should be tested at a depth of about 800 feet below the surface. The location of the geochemical anomalies beyond the 4000 gamma magnetic contour at the Black Angel suggest that in the White Devil Area extension of the geochemical survey, particularly northwards, might reveal other anomalous areas. The geochemical anomalies beyond the area of the Black Angel and Crusader workings were tested by 36 waggon drill holes. The results show that the copper anomalies continue downwards. Investigation of the primary zone in some places could possibly be worthwhile, more particularly in the area of anomaly 3b. The work done has confirmed that no assessment can be made of the value of the Angel Group with respect to secondary gold ore. The Black Angel mine still ranks as one of the fifteen mines on the Tennant Creek goldfield that has produced more than 3000 ozs of gold. Additional pockets of gold ore are quite possible. However, it would be extremely expensive to systematically drill closely spaced holes for any likely pockets of gold ore. If the leases or portions thereof could be let on tribute then such pockets might be found less cheaply than by carrying out a costly pattern drilling campaign in an attempt to locate them. Notwithstanding the above remarks the proving of the continuity of the gold ore zone encountered by Peko Mines NL in diamond drill hole BA3 should be undertaken. Hole BA2 drilled by the same company 100 feet to the east did not encounter the zone probably because of its displacement along a fault. During the drilling programme an appraisal was made of a 48 square mile Authority to Prospect held by Aurous Development Limited. The area straddles a magnetic ridge which passes through the Explorer 5 prospect and Ivanhoe Mines held by Peko Mines NL. The geological characteristics of the Authority to Prospect and the Angel Group of Leases indicate that they represent some of the worthwhile exploration targets in the Tennant Creek Goldfield. However, exploration expenditures can rise sharply and it is deemed advisable to determine the limit of exploration expenditures on the Angel Group. A statistical analysis of the probability of success should be determined by a full evaluation of the facts available concerning the exploration expenditures and occurrences of the economically productive orebodies on the Tennant Creek Goldfield before proceeding with surface exploration in the Authority to Prospect and with diamond drilling on the Angel Group. Recommendations - The diamond drilling programme did not reveal any ore in the zone of oxidation and enrichment. Extreme leaching might be one of the causes responsible for the lack of ore or the weakly mineralised zones may represent the near surface expression of ore at depth and not the central or lower leached and enriched section of a mineralised zone. In view of the fact that both the percussion and diamond drilling have indicated the downward continuity of sheared and brecciated zones mineralised at the surface, the following recommendations are submitted in order of priority: The leases should be let on tribute to prospectors and miners with the expectation that pockets of secondary gold ore will be found because an extensive programme of exploration and development by Aurous Development Ltd. would be too costly to fully explore the ore zone in detail. Areas recommended for such operations are: a) The Crusader workings, b) To the south of the 54 feet and 100 feet levels of No. 6 shaft, c) At the western end of the White Devil ironstone body; Determine the economic limit of exploration expenditures in the area by carrying out a statistical analysis for the probability of success in finding an orebody in the Tennant Creek Goldfield. If the economic limit of exploration expenditure after having been determined allows a capital outlay in addition to the money already expended then: Test the Crusader geochemical anomalies between 800 to 1000 feet below ground level by diamond drilling one hole; Test the auriferous zone encountered by Peko Mines N.L. in diamond drill hole BA 3 by drilling at least two holes; Test the zone of mineralisation beneath the Black Angel workings between 800 and 1000 feet below ground level by diamond drilling one hole; Test geochemical Anomaly 3(b) centred about 700W, 400S at a depth of 800 feet below ground level; Test Anomaly 1 centred at 1200 W, 700N by drilling one hole to a vertical depth 500 feet below the surface; Extend the geochemical survey of the White Devil area northwards and eastwards; and Carry out ground geophysical and geochemical surveys in the Authority to Prospect.