Data release - as updated : Sherlock. Annual reports to licence expiry/full surrender, for the period 25/6/2012 to 24/6/2017.
Created: 12 Nov 2024 Revised: 12 Nov 2024

An area centred ~50 km south-east of Tailem Bend has been explored for possible economic buried primary stratiform and epithermal deposits of base metals that may have formed within Cambrian bedrock, close to where the current licensees and...

An area centred ~50 km south-east of Tailem Bend has been explored for possible economic buried primary stratiform and epithermal deposits of base metals that may have formed within Cambrian bedrock, close to where the current licensees and previous explorers have located narrow zones of low to high grade Zn-Pb-Cu mineralisation that are akin to the Angas deposit style of orebody, i.e. hosted within the Tapanappa Formation adjacent to its basal contact with the Talisker Calc-siltstone. During licence Year 6, under tenure of renewed EL 5134, the licence operator logged the geology of the drill core recovered from hole 12_SHR_004, which had been completed at the end of Year 5. This core contains a typical (for the area) sequence of metasediments that are interbedded with abundant mafic to ?intermediate intrusive igneous rocks (possibly including some volcanic strata); however, the target calc-silicate sequence was not intersected. Trace amounts of pyrite and pyrrhotite are present, but no significant chalcopyrite, galena or sphalerite was noted. In other work, data obtained from past drilling undertaken by Rockwell/Kelpie and previous explorers (notably Pasminco) were re-assessed and modelled. As a result, the licensees concluded that their earlier diamond drillhole 08SHR001 had been terminated short of reaching the target zone. Re-entering and extending this hole was not now possible because it has been fully cement backfilled and rehabilitated. Consequently, plans were made to drill a fifth exploratory hole, collared approximately mid-way between holes 08SHR001 and 12_SHR_003, and inclined 60° west, with an intended total depth of 750 m. Upon completion of drilling, a downhole EM survey would be conducted. During licence Year 7, the re-appraisal single inclined diamond drillhole, 14_SHR_005, was completed to a total downhole depth of 637.13 m (111 m rotary mud precollared). Its drill core was seen to contain several zones of sphalerite mineralisation within carbonate rich metasediments, plus a zone of pyrrhotite-chalcopyrite mineralisation within altered mafic and metasedimentary host rocks. The latter comprise laminated to banded to massive quartz-biotite schists, originally sandstone and shale, with subordinate limestone (now marble), and show variable silica, chlorite, garnet and calc-silicate alteration. The frequently intruding mafic dykes contain trace to common (and rarely abundant) pyrrhotite, mostly as thin, fine, discontinuous, foliation parallel laminar aggregates. Sphalerite and galena were found to occur in several zones, mostly within marble/calc-silicate rocks. They are present as disseminated aggregates or fine veins. Representative drill core assay values are: from 422.85-424.74 m, 1.89 m @ 0.28% Zn, 0.17% Pb, 2.9 g/t Ag from 550.21-551.00 m, 0.79 m @ 1.8% Zn from 557.36-559.05 m, 1.69 m @ 0.36% Zn Also from drill core sample assaying, a significant copper-mineralised intercept was found to occur from 539.27-543.09 m downhole, of 3.82 m @ 1.12% Cu + 2.5 g/t Ag, including 1.6 m @ 2.33% Cu + 5.4 g/t Ag. This mineralisation ranges in habit from disseminated to semi-massive, and appears to be of late emplacement, probably shear-related. Structural data measured from the core indicated that the copper-bearing zone dips steeply (~70°) towards the east-southeast (075°M). Encountering such a type of copper sulphide mineralisation in this hole was regarded by the licensees as demonstrating the potential for discordant, shear-hosted chalcopyrite/pyrrhotite deposits to occur in the Sherlock area, perhaps with features analogous in some respects to those of the Kanmantoo deposit. The find thus represented a new base metal conceptual target worthy of intensified exploration effort. While doing the core logging of hole 14_SHR_005, it was noted that the mineralised intervals in it are dense and commonly contain abundant pyrrhotite. These features presented the licensees with opportunities for refining their drillhole targeting, and so specific gravity and magnetic susceptibility measurements were made of selected core intervals, including the copper mineralised zone at 539-543 m, which was found to have a high magnetic susceptibility. In consequence of this result, a trial ground magnetic survey was conducted by the licensees over a small area surrounding hole 14_SHR_005. Fourteen 1.8 km long east/west lines at 50 m spacing were profiled at 0.1-0.2 m station intervals using a Geometrics G859 magnetometer. In addition, because of the conductive sulphides present within the copper-bearing zone in that hole, a trial mise-a-la-masse survey was conducted adjacent to the hole along five x 500 m long east-west lines spaced 100 m apart, with readings taken at 50 m intervals. The main current input electrode was placed 543 m downhole, with minor azimuth position adjustments then made to establish the greatest current flow back to surface. Preliminary results indicated that a distinct conductor anomaly is present, with a pronounced north-south trend. Subsequent analysis of the primary voltage values showed that their peak is displaced to the west of the projected electrode position, which suggested a possible continuation of the sulphide zone above the drill intercept, with a steep westerly dip. Early in Licence Year 8, during August 2014, the licensees contracted Zonge Engineering to conduct a downhole EM survey in 14_SHR_005 to further investigate the copper bearing zone at 539-543 m. DHEM data were recorded using four transmitter loops (E,W,S and N). Quantitative modeling of the DHEM results was undertaken by Southern Geoscience Consulting, who interpreted that the drillhole had intersected the bottom edge of a narrow, sub-vertical conductive zone. A fifth rotary mud precollared inclined diamond hole, 15_SHR_006, was drilled by the licensees in March 2015 at a location west of hole 08SHR001, for a total penetration of 372.27 m. It reached pre-Cainozoic basement metasediments at 96.3 m downhole. This hole also encountered several zones of sphalerite mineralisation within carbonate rich metasediments, as well as pyrrhotite/chalcopyrite mineralisation within altered mafic and metasedimentary rocks. Peak mineralised intercepts revealed by drill core sample assaying were: from 322-325.5 m, 3.5 m @ 0.66% Zn from 325.5-327.4 m, 1.9 m @ 0.49 % Cu from 334.5-335.65 m, 1.15 m @ 0.63 % Cu. Specific gravity measurements were made of selected intervals of the drill core. From them and from the SG measurements made previously on hole 14_SHR_005 it was evident that the pyrrhotite/chalcopyrite mineralised zones are substantially denser (densities of 3.7-4.16 gm/cc) than unmineralised host rocks (densities usually ranging from 2.8-3.0 gm/cc). Therefore the licensees inferred that in future exploration at Sherlock utilising a combination of gravity and magnetic surveys should be capable of identifying any significant buried copper targets. During licence Year 9, the above idea was tested by conducting ground gravity and magnetic surveys over a prominent magnetic anomaly (possible mineralised shear zone) situated fairly close to the Sherlock prospect.The gravity data were acquired on 12/11/2015, along three east-west traverses spaced 200 m apart, whereon 117 stations were read at 20 m intervals. Complementary ground magnetic data were acquired shortly afterwards at sub-metre precision along the same three traverses, which confirmed the presence of a strong magnetic anomaly. However, this survey work demonstrated that no gravity anomaly existed, thereby downgrading the magnetic feature as a copper-prone target. No drilling was undertaken, and the exploration focus shifted towards assessing other, regional targets. During the tenth and final year of tenure, exploration was confined to conducting a review of past exploration drilling results. Plans had been made to carry out further gravity surveys over the projected northern extensions of the Zn-Pb mineralised zones intersected in holes 12_SHR_003, 14_SHR_005 and 15_SHR_006, with any significant gravity anomalies so identified to be tested by diamond drilling. However, attempts to secure a joint venture partner to assist in funding such work were unsuccessful under the prevailing economic climate, and although an application for a replacement Exploration Licence was lodged with DSD/DPC within the stipulated advance timeframe, the partners decided shortly afterwards to withdraw it.

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About this record

Record No mesac27444
Topic Geoscientific Information
Type of Resource Document
Category Type
Document Type Mineral Company Report - Mineral Exploration
Contributor Zonge Engineering and Research Organisation (Australia) Pty Ltd;Daishsat Geodetic Surveyors
Sponsor Rockwell Resources Pty Ltd
Tenement EL 5134
Tenement Holder Rockwell Resources Pty Ltd;Kelpie Exploration Pty Ltd
Operator Rockwell Resources Pty Ltd;Kelpie Exploration Pty Ltd
Geological Province
Mine Name Sherlock prospect
Stratigraphy
Commodity
Notes
Geographic Locality: Murray Mallee;Sherlock;Peter Road;2015 Sherlock Gravity Survey;2015 Sherlock Ground Magnetic Survey
Doc No: Env 11877
Drillhole: 08SHR001;12_SHR_004;(295508);14_SHR_005;(295496);15_SHR_006;(295497)

Geographic Locality: Murray Mallee;Sherlock;Peter Road;2015 Sherlock Gravity Survey;2015 Sherlock Ground Magnetic Survey Doc No: Env 11877 Drillhole: 08SHR001;12_SHR_004;(295508);14_SHR_005;(295496);15_SHR_006;(295497)

Language English
Metadata Standard ISO 19115-3

Citations

Use constraints License
License Creative Commons Attribution 4.0
Persistent identifier https://pid.sarig.sa.gov.au/document/mesac27444
Citation Edgecombe, D.R.;Mann, S.;Wyschnja, B. Data release - as updated : Sherlock. Annual reports to licence expiry/full surrender, for the period 25/6/2012 to 24/6/2017. Mineral Company Report - Mineral Exploration
https://pid.sarig.sa.gov.au/document/mesac27444

Technical information

Status
Maintenance and Update Frequency
Geographic Reference GDA2020 (EPSG:7844)
Geo bounding box {"type":"Polygon","coordinates":[[[139.5,-35.5],[140,-35.5],[140,-35],[139.5,-35],[139.5,-35.5]]]}
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