PROJECTS – iron mount & oolanta

The main Iron Mount magnetite prospect is located on a quite strong and reasonably large aeromagnetic anomaly along strike from Iron Mount Mine, where small parcels of hematite and limonite were mined in the early twentieth century and shipped to Port Pirie. Samples collected from an adit in the old mines averaged 39.3% Fe over 9m and another sample from the bottom of the main shaft assayed 42.1% Fe.

There are two jaspilite units in the Iron Mount Mine area but the southern is thicker (15-45m) and more extensive in strike length (>2km). Jaspilite is interbanded with gneiss, banded diopside quartzite, sericitic quartzite (Warrow Quartzite equivalent), amphibolite and marble. At the surface, the jaspilite is a medium grained, well-banded martite-quartz BIF with minor magnetite in addition to hematite and limonite. It is well exposed in an operating council quarry.

A ground magnetic and gravity survey was conducted over the Iron Mount Mine area in 1965 by SADM (Robinson and Hall, 1968) but the prospect was not drilled. A low-level airborne magnetics / radiometrics survey was flown over the area for SAIOG in 2002 at 20m agl and 40m line spacing (total 269 line km). The main Iron Mount deposit has one of the highest amplitude magnetic anomalies on southern Eyre Peninsula albeit of fairly short strike extent (ca. 250m). However, there are several similar anomalies along strike over a distance >1km.

Modelling of the low-level aeromagnetic data supports the field observation of two main magnetite BIF units steeply dipping ca. 70º NNW with a third major unit at depth on the southern edge of the anomaly. There are several long curvilinear magnetic bands south of the main Iron Mount magnetic anomaly but these bands have much lower magnetic susceptibilities, are thinner and are strongly attenuated within a major mylonite zone, the Kalinjala Mylonite Zone, clearly evident in the aeromagnetic images (Fig. 9).

Fig. 9 :: Iron Mount – Oolanta Prospects :: Location of drillholes and BIF outcrops in relation to aeromagnetic imagery (Click to see image)

CRAE Ltd drilled five percussion holes about 1.5km SW of Iron Mount in an area of low magnetic intensity. These holes intersected dolomitic marble with a few thin BIF interbands.

Drilling by SAIOG in 2002 (IRDD001) tested the central highest amplitude part of the aeromagnetic anomaly. Two BIF bands with relatively high magnetite grade (Table 17) were intersected in a carbonate, diopside-rich jaspilite / quartzite sequence interbanded with quartzo feldspathic gneiss. BIF units are strongly sheared and brecciated in places.

Table 17: DTS magnetic concentrate assays from Iron Mount

Drillhole	From (m)	To (m)	Intercept (m)	DTS magnetic con (%)	Fe (%)	SiO2 (%)
IRDD001	86.25	89.25	3	42.97	61.36	10.85
IRDD001	96	112.2	16.2	40.71	64.83	6.36
IRDD001	175.7	199.67	23.97	34.04	62.91	7.75
Weighted average			43.2	37.16	63.52	7.44

These results support the visual observation that while the magnetite content is high grade, grain size is finer than other deposits on southern Eyre Peninsula and gives rise to relatively poor DTS magnetic concentrate assays due to inclusion of minor silicates. Further grinding beyond 75µm would be necessary to establish the optimum grind for this deposit.

An estimate for the inferred magnetite resource at Iron Mount based on the IRDD001, outcrop mapping and combining the two main aeromagnetic anomalies is outlined in Table 18. Given the very broad quartzite interval between relatively thin and steeply dipping magnetite BIF zones in drillhole IRDD001, waste to ore ratios would be quite high.

Table 18: Inferred resource for Iron Mount

	Iron Mount
Average true thickness based on intercepts with >20% DTS magnetite	33.1m (IRDD001)
Vertical extent of oxide zone below ground level	60m (IRDD001)
Assumed dip of BIF	70ºNNW
Drillhole declination	60ºSSE
Dip extent of magnetite BIF (excluding oxide zone) to 200m below ground level	149m
Strike length (based on aeromagnetic interpretation and outcrop mapping)	400m
Volume of magnetite BIF	2.0 million m3
Magnetite BIF density	3.4
Inferred magnetite BIF resource	6.7 Mt @ 37.2% DTS (63.5% Fe)

Based on outcrop and BIF exposures in the council quarry, there could be a small hematite resource (<2Mt) at Iron Mount.

The Oolanta aeromagnetic anomaly just west of Iron Mount defines a keel-shaped NE-trending synform 5-6km in length. BIF and amphibolite crop out at the northern end of the synform and define a shallow S-plunging synform with magnetite best developed in the hinge zone (Robinson, 1965b). Two diamond drillholes OD1 and OD2 were completed by SADM in the 1960’s. Drillhole OD2 intersected a 40-45m interval of BIF, however whole rock assays at the time were a disappointingly low 5-15% Fe. Rock chip samples near OD1 drillhole assayed 29-39% Fe with the main horizon averaging 29.5% Fe over 14m. Near OD2 drillhole, two composite samples averaged 35.6% Fe and 46% Fe over, respectively, 8.5m and 10.5m.

A high resolution, low-level airborne magnetic survey was completed over Oolanta by SAIOG in 2002 but no drilling was undertaken. The magnetic data show thickening and repetition in the fold hinge with variation in apparent width along the western limb of the fold (Cowan, 2005a). The eastern faulted limb appears to consist of two BIF units. Given the results over magnetic anomalies with similar amplitude and characteristics at Koppio and elsewhere, there is potential for small satellite magnetite and/or hematite deposits at Oolanta.

The Rock Valley region along strike SW of Iron Mount also has potential for small satellite magnetite resources.