Ongoing resource definition drilling completed by Aberfoyle at its Angas prospect during Year 4 of EL 1706 identified sub-economic mineralisation in the form of a narrow tabular, steeply dipping body containing approximately 2 Mt of base metal...
Ongoing resource definition drilling completed by Aberfoyle at its Angas prospect during Year 4 of EL 1706 identified sub-economic mineralisation in the form of a narrow tabular, steeply dipping body containing approximately 2 Mt of base metal sulphides grading on average ~15% combined Pb+Zn. The downdip limit to this body remains open below 600 m depth as at March 1995. Initial investigation of a geophysically indicated second zone of mineralisation located east of the above described main zone produced only one notable drillhole intercept, of 4.8 m @ 11% Pb+Zn. This lode has a strike extent of 200 m, and although as yet undrilled at depth, there is no supporting evidence seen from current dowhhole EM surveys of any downdip extensions to it. The latest drilling programme entailed completing, during March-June 1993, a further 4 inclined diamond holes for a total penetration of 2004.2 m (including 178.7 m of RC precollars), and a single percussion hole for 168 m. DHEM surveys were run in only three of the holes, due to collapse of the other two post-drilling. In addition, a three-loop surface EM survey was carried out over the eastern part of the prospect area, and 4 lines of ground magnetic profiles were also read there, at 5 m station intervals, for 32 line km. The best new drilling result was obtained in DDH AN21, which successfully showed that the lode strata in the centre of the Angas deposit extend downdip for at least 200 m below the previous best intercept of 2 m @ 10% Pb+Zn made in hole DDH AN16. However, in DDH AN21 the main lode mineralisation was also found to pinch out over a 9 m wide interval below 596 m depth; firstly it became a 2 m wide band of pyrrhotite, and then the drillhole passed into a major altered (?shear) zone that continued down to 792 m depth. Overall at Angas, the accumulated drilling results by late 1993 had outlined a narrow, steeply dipping orebody of high grade base metal sulphide mineralisation that is roughly triangular in plan outline, having a maximum strike length of 400 m and a downdip extent exceeding 370 m. Lode widths vary from 1.7 m to 7.7 m. In March 1994 the pre-resource potential of the deposit was estimated by Aberfoyle as 2.1 Mt @ 4.9% Pb, 10.7% Zn, 60 ppm Ag and 1.0 ppm Au. Early in 1994, regional exploration of the licence via surface prospecting and rock chip sampling discovered a promising bedrock gold anomaly 4 km to the north of the Angas prospect, which may originate from the same mineralised stratigraphic horizon. This anomaly, called the Strathburn prospect, which extends for about 1.5 km as sampled float and rare outcrop, was given priority for further definition via geological mapping, ground magnetic surveying, soil geochemical sampling and RAB drilling. Surface gossanous ironstones and quartz veins assayed up to 60 ppm Au, and garnetiferous schists with dissseminated iron oxides returned up to 0.2 ppm Au. The gold anomaly coincides with the southern part of a prominent airborne magnetic ridge type anomaly situated between the historic abandoned Strathalbyn and Wheal Ellen Pb-Zn-Ag mines, which Aberfoyle had recognised in 1991 and had considered as probably being sourced by magnetite and pyrrhotite. Later in the year, ground magnetics were read at Strathburn along 100 m spaced lines, to better define the aeromagnetic anomaly; it was shown to be strongest in the north, where banded iron formation rocks occur as float. Aberfoyle thought that the southern part of the magnetic ridge might be a tight fold closure, but the area is soil covered, and this interpretation could not be checked. Soil profiles over the magnetic anomaly were also sampled at 25 m intervals along the 100 m spaced grid lines (177 samples collected for assaying). Elevated zinc and copper values were found to lie in separate zones further out on the flanks of the magnetic anomaly, mainly on its western side. During May 1994, 176 shallow RAB holes totalling 368 m were drilled into weathered bedrock (mostly garnetiferous metasediments) underlying the Strathburn prospect grid. Surprisingly, no significantly gold or base metal - enriched rocks were encountered. To explain this, it was suggested that the real (checked) gold anomalies that were detected in float material may have in part originated from the spread of mullock from now obliterated past small surface workings, or alternatively, the gold may be stratabound and restricted to rich, steeply plunging shoots which possibly could lie between the existing RAB traverses. Elsewhere on the tenement, during Licence Year 5, regional base metal exploration was carried out via prospecting and rock chip geochemical sampling of mapped sulphide-gahnite-garnet rock unit occurrences and of magnetic anomalies that Aberfoyle had modelled from its reprocessed 10-year old CRA Exploration airborne magnetic survey data. The acquisition during mid-1994 of a joint Aberfoyle Resources / Mines and Energy SA - funded aeromagnetic survey over the southern Fleurieu Peninsula (SAEI Area B12) allowed the licensee to make a re-assessment of the base metal potential in areas south of Angas, with magnetic segments of the Tapanappa Formation being particularly targeted. The southern closure of the Strathalbyn Anticline and the complementary Macclesfield Syncline to the west were examined, and known minor base metal occurrences at the Glenalbyn mine and at CRAE's Rushmore prospect were closely inspected, but were deemed unimportant and downgraded because their geological characteristics do not match the exhalative style of the Angas mineralisation.
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