The Collerina Project is located in the Cobar-Girilambone district in Central NSW. Collerina was subject to small-scale mining in the early 1900’s. The only modern exploration was conducted by CRA in the 1980’s; culminating in a three-hole drilling program. All three holes intersected copper mineralisation over varying widths, but were never followed-up. No significant exploration had been undertaken on the Prospect until Helix’s involvement.
The project area was earmarked early in a project generation process for the region and finally secured by Helix in early 2014.
The Cobar-Girilambone district in Central NSW is a region with excellent infrastructure, operating mines and preserved prospectivity for VMS style copper systems and related hydrothermal gold.
The Collerina Project is located in the eastern portion of the broad north-south trending Girilambone Anticlinorial Zone (“GAZ”). The dominant rock sequence in the GAZ are poly-deformed Ordovician meta-sediments (Girilambone Group) comprised of flysch sediments and mafic volcanics, volcaniclastics and volcanogenics forming a basin which extended from Condobolin in the south to north of Bourke in the North. The Girilambone Group represents sediments deposited in a back-arc basin formed to the west of the Macquarie Volcanic Arc overlain by the Cobar Basin to the west.
The Girilambone Group rocks comprise mainly quartz-mica and quartz-chlorite-mica schists and phyllites, having been strongly deformed and regionally metamorphosed generally to lower greenschist facies. The sequence is intruded by granitoids, intermediate, mafic and ultramafic intrusive rocks of a range of ages generally from Ordovician to Devonian.
Locally the Girilambone Group can be intensely folded on several axes relating to multiple syn-depositional to post-depositional deformation events. At the regional scale, lineaments oriented ~320°G and ~350°G and their intersections are seen to be important localising features to focus high grade base-metal mineralisation. Structures may be locally intruded by dykes of mafic to ultramafic composition, commonly serpentinised.
Most of the licence area is underlain by poorly outcropping Girilambone Group metasedimentary rocks. The Honeybugle ultramafic to mafic complex sub crops in the north-eastern corner of the licence area and extends to the southwest beneath alluvial cover. Narrow belts of serpentinised ultramafic sporadically intrude northwest-trending structures near the centre of the licence area, including the Collerina Structural Trend.
VMS systems in this district tend to form in clusters. Helix has exposure to regional upside through several copper (+gold) occurrences that are located along the +20km long regional structure that hosts the Collerina Prospect, none have been subject to modern exploration (refer Figure 2).
Work Completed by Helix:
In June 2014 Helix commenced field activities on Collerina. The following work has been completed to date (chronological order):
- Prospect scale mapping and sampling; rockchips along a +500m gossanous trend returned assays from surface material if up to 3% copper and 9.3g/t gold.
- Detailed hydraulic soil auger program; A 50m X 10m grid survey over the length of the sub-cropping gossan conducted in September 2014. The survey highlighted a robust +250ppm copper-in-soil anomaly (max 0.3% Cu) of approximately 500m x 150m, with coincident gold up to 0.4g/t Au in soils also noted.
- Moving Loop EM; A 5 line kilometre MLEM survey over the prospect area was conducted in late September 2014. The survey identified an EM conductor with a conductance of 55S modelled to a depth of 350m on a 55 degree dip. The plate was associated with the +500m of copper geochemistry at surface.
- Phase 1 drilling; 1,043m RC drilling program in 8 holes was undertaken in late 2014, the second hole drilled intersected 14m @ 4% Cu from 80m within 29m @ 2.2% Cu. Six of the nine holes drilled returned >1% copper results.
- Down Hole EM Survey; A DHEM survey was conducted in January 2015 in 4 holes surrounding and including the discovery intersection in CORC002. The DHEM modelling showed conflicting results in dip from 30 degrees to 60 degrees, although off-hole conductors modelled in a similar area east of the CORC002 result.
- Phase 2 drilling; 1,073m RC drilling program of 7 holes was completed with 5 of the 7 holes returning >1% Cu. Drill holes along strike from CORC002 return significant results including 7m @ 3.2% Cu withn 10m @ 2.6% Cu in CORC011 and 5m @ 3.2% Cu within 9m @ 1.9% Cu in CORC012.
- 2nd DHEM Survey; A second DHEM survey was conducted in the outlier holes to assess new targets beyond the drill pattern. The modelled plates continued to model in a similar location, however the conflicting dips remained.
- Geological Review; The company undertook a review of the data collected and concluded that it was likely the dip of mineralisation was steeper than 30 degrees and that there was likely to be two (or possibly three?) zones of mineralisation. A geological model was generated and all geophysics was re-assessed with this model in mind. A new interpretation which resulted from forward-modelling the DHEM into the MLEM data produced a priority target east of the drilling to date.
- Geology Model Test Drilling; Three set-depth 200m RC holes were then planned to test extensions and the EM plate position which was now modelled at a dip of 45 degrees. CORC017-19 were drilled, the first two holes intersected the interpreted hanging wall position, the third hole CORC019 intersected massive sulphides in the main zone returning 12m @ 5% Cu within 21m @ 3.2% Cu from 153m. This is the first primary sulphide intersection of the main zone.
- Regional Auger Soil Survey; Helix has commenced a step-out first-pass soil geochemistry survey on a 400m X 50m grid along the Collerina Structural trend. An initial 8km of the trend will be tested with further work continuing throughout the 2016 field season.
- Current work; At the time of writing Helix is undertaking an additional DHEM in the latest three holes drilled and is commencing a diamond drilling program. The diamond drilling program will assist in defining structural and lithological controls of the main zone mineralisation and target additional high grade mineralisation along strike and down dip.