Ground gravity surveys were conducted in 2001 and 2004 to enable...

Ground gravity surveys were conducted in 2001 and 2004 to enable better modelling of the subsurface geology and to identify drill targets more precisely. The Herakleion Prospect was drilled in late 2003 and 2004. The gravity surveys and drilling are discussed below.

Anomalous stream geochemistry (elevated copper and zinc) in an area of complex magnetics and a coincident gravity anomaly have been identified at the Herakleion Prospect. The target at Herakleion is an "Olympic Dam" type deposit. The critical characteristics of the Olympic Dam Ore body include a gravity anomaly, caused by the dense iron rich rocks which are associated with the economic mineralization, occurring in a region of complex magnetics thought to be caused by deeply buried volcanic rocks.

Additional favourable features observed at Herakleion include:

a zone of structural complexity defined in 200 m line spaced and regional magnetic survey data
a WNW structural trend, identified in magnetic data, aligning with Early-Mid Proterozoic granite to the ESE, interpreted by SADME (South Australian Department of Mines and Energy)
( - the Olympic Dam ore body lies within Mid Proterozoic granite in a WNW trending structural corridor)
0.12 % Cu and anomalous REE (rare earth elements) in rock chip samples from the area of the gravity high
haematite/magnetite (iron rich) veining observed in outcrop to the south of the gravity high
Coominaree Copper mine, located a couple of kilometres to the south, where mineralization is hosted in quartz-goethite-malachite veins which have associated uranium anomalism (up to 240 ppm U) and gold (up to 2 g/t Au)
Gravity Surveys (2001, 2004)
Ground gravity survey, 2001:

conducted by then-joint-venture-partner Phelps Dodge;
followed selected traverse lines only - e.g. tracks & fence lines - over the Herakleion & Santorini Prospects;
defined and enhanced the gravity anomalies far better than the regional gravity data had (click here to view an image);
was used to target the first two Herakleion drill-holes (HD-01, HD-02 - see discussion below).
Ground gravity survey, 2004:

conducted by the Edward Creek Base Metals Joint Venture (ECBMJV);
is significantly more detailed - a 200m x 200m station grid over 7km x 10km covering the Herakleion Prospect;
facilitated far superior interpretation which has discounted the highest amplitude part of the anomaly (to the northwest, interpreted to be a shallow thin rock unit) and identified four main initial target areas within the overall gravity anomaly (which remains a large 3.5km x 8.5km target) (click here to view an image);
used to target the third Herakleion drill-hole (HD-03 - see discussion below), and the planned 2005 drilling.
Three-dimensional computer modelling has been applied to the available gravity and magnetic data to generate modelled 3D geological bodies which best fit the data.
To view a 3D perspective view of the 2001 gravity survey data, plus magnetics - click here ;
To view a 3D depth slice (at 200 m depth) of the 2004 gravity survey data, in Target Areas 1 & 3, showing proposed drill-hole locations - click here.

This modelling indicates:

the gravity and magnetic anomalies are due to separate bodies - they do not coincide;
the bodies of high density rocks (causing gravity highs) - are relatively shallow;
the bodies of high density rocks are large, with dimensions up to several kilometres;
the shapes of the modelled high density bodies suggest that they are intrusive rocks.
These factors all support RLC's conceptual model that the Herakleion gravity anomaly may be due to Olympic Dam type mineralization. The Olympic Dam orebody is hosted by dense rocks formed in a massive intrusive vent system.

It should be noted that the complexity of the detailed gravity data confirms the complex geology mapped at surface in this area. The "top of basement" - where it is hoped drilling will identify a source for the gravity anomalism - is likely to be at various depths in different areas, due to faulting. And the density of the source rocks for the gravity anomalism will vary also (as it does at Olympic Dam), meaning that the strongest gravity anomaly areas may not represent the shallowest source rocks. The true range of densities and depths will be more complex than any modelling can predict.
It may require a number of drillholes, in various locations, to identify the gravity anomaly source.

Drilling (2003, 2004)

The Edward Creek Base Metals Joint Venture (ECBMJV) drilled two holes at the Herakleion Prospect in November-December 2003 and one in October-November 2004. All were vertical diamond drill holes. Drillhole HD-01 (2003) was drilled in the highest amplitude part of the gravity anomaly, to the northwest, and was terminated at 69.8 metres in monzonite (similar to granite). The monzonite is extensive at surface here but is not dense enough to explain the gravity anomaly. The later detailed gravity survey indicated that the high amplitude gravity in this area is probably due to a thin shallow rock unit, making this a lower priority area than elsewhere.

Drillholes HD-02 and HD-03 were drilled into the second of the prioritised target areas identified from the detailed 2004 gravity survey (area 2 on the gravity image - click here). Drillhole HD-02 (2003, before the more detailed gravity) extended to 399.25 metres in a mix of late Proterozoic (Adelaidean) rocks and Ordovician diapiric breccia. The hole did not encounter any rocks dense enough to explain the gravity anomaly and did not strike the "basement" rocks (early-mid Proterozoic) underlying the Adelaidean sequence. (Any Olympic Dam -aged mineralization would be in the "basement" rather than the Adelaidean. Refer to the "Geology" section above for more detail on the project geology, including maps.) Within the diapiric breccia in HD-02, however, was an 80 metre interval of strongly deformed and altered and/or metamorphosed rocks. This sequence may represent a large "raft" of basement caught up in the breccia, or (more probably) may represent an intense deformation (and alteration) zone passing through monzonite and associated rocks caught up in the breccia. This 80 metre sequence produced assays elevated in Cu, U, LREE, F, Ba and Co, which are elements associated with Olympic Dam -style mineralization. If this sequence represents a deformation zone extending to depth, this slight anomalism may be derived from Olympic Dam -style mineralization at depth.

Drillhole HD-03 was drilled in late 2004 to 612.4 metres depth, about 300 metres east of HD-02 (at the peak of the gravity in this target area). The hole is interpreted to pass from diapiric breccia (including monzonite intervals) into less disturbed Adelaidean rocks. Veined and altered zones became increasingly common in the lower 100 to 150 metres of this hole, with trace-minor associated iron oxide (?) mineralization also increasing with depth. The drillhole could not be extended further (at this time) due to drill-rig limitations. The original modelled target depth for the top of the gravity source was 450-475 metres. The hole does not appear to have encountered rocks dense enough to explain the gravity anomaly. Revised modelling suggests a possible source depth below 750 metres. The increasing veining and alteration towards the end of HD-03 may indicate that major faulting - possibly the basement contact - is nearby.

Assaying from HD-03 showed no significant Olympic Dam -style mineralization. Maximum copper assays were 358 ppm and 411 ppm. Significant mineralization is not anticipated in the Adelaidean rocks (such as in HD-03), as they post-date any possible Olymic Dam -aged mineralization in the older underlying basement.

Work planned during 2006:


Herakleion Autumn Drill Program:
Target Area 1 - new hole (HD-04) to 850 metres:
site preparation is complete
drill rig is estimated to be on site by mid April
After completion of HD-04 (at TA1) the Joint Venture partners will determine to
continue drilling atTarget Area 2 - extend HD-03 from 612.4 metres to 1,000 metres
or
await results from HD-04 before determining subsequent drilling

Drilling was previously also planned at Target Area 3. However, a heritage survey conducted in February 2006 identified areas of importance to Aboriginal people in the vicinity of TA3. As a consequence no drilling or other work will be conducted in this target area. The people who participated in the survey have advised that further discussion amongst their people may enable some works at TA3 to be conducted in the future.

Are we going to have better results this time?