PROJECTS – bungalow & minbrie
The Bungalow and Minbrie BIF prospects are located on the eastern coastal plain of NE Eyre Peninsula 9km NNW and 16km N of Cowell respectively. They are both located immediately E of the Cleve Uplands under unconsolidated Cainozoic sediments along the western margin of the Cowell Basin. Both prospects are on a broad (>800m wide) 18km-long NE-trending very intense aeromagnetic anomaly; a fault just W of Minbrie separates the anomaly into two segments distinguished as Bungalow and Minbrie (Fig. 12).
Historical Drilling
The more intense part of the Bungalow anomaly is at the SW end and this area was the subject of geophysical surveys and drilling by SADM in the late 1950’s (Seedsman, 1958 and 1959; McMutrie, 1959 and 1961). Drilling results have never been formally reported but are contained in old SADM dockets (DM 7262/58 and 1262/58).
SADM ground magnetics at Bungalow define two subparallel anomalies that merge and bifurcate along their length. Gravity data show similar patterns but separate anomalies are not as discrete.
BD2 drillhole intersected a variety of silicate and oxide facies BIF horizons intruded by biotite granite sills and interbanded with quartz-anthophyllite-cordierite schist, quartz-biotite schist and minor amphibolite. Banded quartz-cummingtonite-magnetite iron formation is the dominant BIF lithology but grades from quartz-magnetite and magnetite-talc BIF to anthophyllite schist with disrupted layers of magnetite (Whitehead, 1978). A significant feature in drillcore from BD2 is the presence of isoclinal folds with axes locally subparallel to the core but refolded by later crenulations and buckle folds.
Magnetite in BD2 is fine to medium grained. Intergrown with quartz it is commonly 0.02-0.15mm but ranges up to 0.5mm. With amphibole and no quartz, magnetite is commonly 0.5-2mm in grainsize. Monomineralic bands can be slightly coarser again.
The composition and texture of the magnetite and BIF are very similar to BIFs in the Middleback Range, which is only 40km NNE of Bungalow. Trace pyrite coating magnetite has been recorded (Whitehead, 1978).
Assays from BD2 are included in PIRSA Open File Env. 6284 based on work by Shell Metals Ltd in 1985. The best intersections were: 15m @ 29.4% Fe (148.4-163.4m) and 8.9m @ 39.6% Fe (168.2-177.1m). In BD2, the iron formation is interspersed with granite sills that dilute the potential orebody.
Resampling by SAIOG on drillcore from Bungalow BD-9 outlined 13.05m @ 30.6% Fe (149.96-163.01m), 8.9m @ 43.1% Fe (168.55-177.45m) and 7.01m @ 28.33% Fe (175.87-182.88m). Centrex assays for BD-10 outlined 27.13m @ 31.5% Fe (49.07-76.2m) and 23.7m @ 32.1% Fe (81.69-105.46m) but BD-10 only clipped the top (weathered) edge of the BIF.
SAIOG Drilling
Exploration by SAIOG included 701 line kilometres of low-level (20m agl) high-resolution (40m line spacing) aeromagnetics and 6 diamond drillholes for a total of 1735m of drilling.
The detailed aeromagnetic survey resolved the complex Bungalow anomaly into a number of narrow elongate high amplitude magnetic anomalies. As noted above, these anomalies are clearly related to a number of individual magnetite BIF units that are interpreted to be limbs of major NE-SW oriented folds. These typically bifurcate with many disruptions as a result of later folding, faulting, shearing or granite intrusion.
Modelling of the southern part of the western anomaly zone (Cowan, 2005a) suggests a tabular body at a depth of 70m and dipping 70ºNW. The body width is 130m and apparent susceptibility 0.076 cgs units. Modelling of the northern Bungalow BIF, which has not been drilled, suggests a tabular body at a depth of 61 m but dipping 64ºSE.
Drilling was carried out along two section lines spaced 2400m apart to obtain better geological control of the complex magnetic pattern. Drilling intersected individual BIF bands with an average true thickness of 36m. Generally, target BIF bands are steeply dipping.
Drillhole BUDD006 was drilled on the northern section line and intersected an overturned sequence of marble, BIF and biotite sillimanite schist. The schist, interpreted to be higher in the stratigraphy, was intersected towards the base of the hole in the axial zone of an interpreted synform.
Three separate BIF bodies were intersected in the southern section 2000NE but they appear to be the one unit repeated by regional scale folding (Fig. 13). The sequence in BUDD001/1a has been disrupted by granite intrusion but represents the same overturned limb as in BUDD006. The lower BIF intercept in BUDD005 has been interpreted to represent the opposing limb of the synform. BUDD003 and BUDD004 started within a broad chloritic schist or shear zone that appears to account for a major zone of disruption in the magnetics. The BIF intersected in BUDD004 is interpreted as an antiformal hinge zone. BIF units are variably but significantly diluted by granite and to a lesser extent by amphibolite dykes and sills.
Structural logging of drill core has confirmed the presence of earlier intrafolial isoclinal folds (F2 folds) and later more open F3 folds. The latter have axes that plunge moderately towards both the NE and SW (ie doubly plunging to define keel-shaped synforms as in the Middleback Range). There are a number of possible fold closures evident in the magnetics. These represent zones with potential for thicker mineralisation at shallow depth.
Basement rocks are overlain by poorly sorted alluvium / colluvium of the Cowell Basin. Cover depth increases from 20m on section 2000N to 75m on section 4400N (BUDD002).
Basement rocks have been affected by lateritic weathering extending 20-40m below the younger cover. Depth to fresh magnetite is 30-90m below ground level.
Best magnetite grades occur in micro- to mesobanded magnetite-rich BIF. Typically, magnetite occurs in monomineralic bands alternating with bands rich in quartz, iron-rich silicates and carbonate. Generally magnetite is quite fine grained with a significant fraction finer than 75µm.
Fig. 13 :: Bungalow :: Geological section across the northern deposit, section 2000N
Table 23: XRF assays on DTS magnetic concentrates aggregated for intercepts with >20% DTS
| Drillhole | From (m) | To (m) | Intercept (m) | DTS Magnetic Con (%) | Al2O3 (%) | Fe (%) | MnO (%) | P2O5 (%) | SiO2 (%) |
| BUDD002 | 152.37 | 168.8 | 15.88 | 40.01 | 0.06 | 66.31 | 0.05 | -0.01 | 7.04 |
| BUDD002 | 172.6 | 188.5 | 15.35 | 40.69 | 0.07 | 66.95 | 0.05 | -0.01 | 6.10 |
| BUDD002 | 192.18 | 193 | 0.82 | 37.51 | 0.1 | 68.31 | 0.03 | -0.01 | 5.05 |
| BUDD002 | 199.45 | 208.24 | 8.79 | 42.66 | 0.06 | 68.08 | 0.03 | -0.01 | 4.88 |
| BUDD002 | 213.16 | 214.2 | 1.04 | 38.61 | 0.09 | 66.22 | 0.03 | -0.01 | 6.81 |
| Weighted Average Section 4400N | 40.73 | 0.07 | 66.95 | 0.05 | -0.01 | 6.20 | |||
| BUDD001 | 81 | 93.9 | 12.9 | 30.18 | 0.02 | 66.49 | 0.03 | -0.01 | 6.39 |
| BUDD001A | 104.35 | 106 | 1.65 | 23.44 | 0.14 | 62.52 | 0.05 | -0.01 | 11.3 |
| BUDD001A | 107.3 | 113.1 | 5.8 | 41.65 | 0.02 | 65.59 | 0.04 | -0.01 | 8.17 |
| BUDD001A | 118.82 | 120.95 | 2.13 | 20.32 | 0.07 | 67.47 | 0.04 | -0.01 | 5.89 |
| BUDD001A | 122.5 | 170.03 | 45.56 | 38.46 | 0.03 | 67.72 | 0.05 | -0.01 | 5.32 |
| BUDD004 | 189 | 190.2 | 1.2 | 37.28 | 0.14 | 69.77 | 0.03 | -0.01 | 2.68 |
| BUDD004 | 193.75 | 221.2 | 27.45 | 41.30 | 0.01 | 68.62 | 0.06 | -0.01 | 4.35 |
| BUDD004 | 228.95 | 249.79 | 20.51 | 41.46 | 0.01 | 68.74 | 0.07 | -0.01 | 4.17 |
| BUDD004 | 252.27 | 254.84 | 2.57 | 41.6 | 0.01 | 69.29 | 0.04 | -0.01 | 3.58 |
| BUDD005 | 168.61 | 191 | 22.39 | 31.15 | 0.02 | 68.27 | 0.05 | -0.01 | 3.24 |
| BUDD006 | 307 | 313 | 6 | 35.1 | 0.01 | 70.47 | 0.03 | 0.01 | 3.45 |
| BUDD006 | 315 | 320 | 5 | 20.77 | 0.02 | 66.22 | 0.03 | 0.03 | 1.89 |
| BUDD006 | 333.48 | 365.55 | 31.71 | 40.27 | 0.02 | 67.31 | 0.05 | 0.02 | 6.95 |
| BUDD006 | 370.35 | 378.6 | 8.25 | 40.1 | 0.02 | 67.26 | 0.03 | 0.01 | 6.66 |
| BUDD006 | 383.38 | 384.28 | 0.9 | 47.4 | 0.03 | 65.03 | 0.39 | 0.01 | 9.04 |
| Weighted Average Section 2000N | 37.44 | 0.02 | 67.81 | 0.05 | -0.01 | 5.19 | |||
| Global Weighted Average, Bungalow | 38.02 | 0.03 | 67.66 | 0.05 | -0.01 | 5.37 | |||
The average intercept grade for all SAIOG drillholes at Bungalow at a cut off grade of 20% DTS was 38.02% DTS @ 67.66% Fe and 5.37% SiO2 (Table 23). This represents the best DTS grade achieved in any BIF investigated by SAIOG on Eyre Peninsula. High silica and lower Fe content of concentrate reflects the finer grained nature of magnetite compared with some other prospects and suggests that a finer grind would be required to obtain optimal grades.
Magnetite Resources
Potential magnetite resources at Bungalow are quite considerable taking into account the relatively high average grade and extensive combined strike potential of magnetite BIF bands. SAIOG (Fielding & Parker, 2003) initially estimated potential for 267 Mt exploration target @ 38 % DTS (67.7% Fe and 5.4% SiO2) based on a single magnetite body 36.1m thick, 13.6km long and extending down to 200m below ground level. Interpreted fold closures reflected in drilling and magnetic data present potential situations where smaller tonnages of thicker mineralisation may occur in a shallower setting and hence significantly reduce the waste to ore ratio in an open pit. This is particularly so at the SW end of the deposit where cover is apparently much thinner.
Inferred resources based on drilling and interpretation of magnetic data for individual mineralised BIF lenses of the SW Bungalow deposit along section 2000N are outlined below in Table 24.
Table 24: Inferred magnetite BIF resources for Bungalow
| Section 2000N Western Deposit | Section 2000N Central Deposit | Section 2000N Eastern Deposit | |
| Average true thickness based on intercepts with >20% DTS magnetite | 28.2m (BUDD001 & 6) | 14.4m (BUDD005) | 33.3m (BUDD004) |
| Vertical extent of oxide zone below ground level | 73.15 | 69.86 | 62.79 |
| Assumed dip of BIF | 90'bc (fold envelope) | 80'bc NW | 75'bc NW |
| Drillhole declination | 60'bc SE | 60'bc SE | 60'bc SE |
| Dip extent of magnetite BIF (excluding oxide zone) to 200m below ground level | 126.85 | 132.15 | 139.33 |
| Strike length (based on aeromagnetic | 900m | 600m | 900m |
| interpretation) | |||
| Volume of magnetite BIF | 3.3 million m3 | 1.1 million m3 | 4.2 million m3 |
| Magnetite BIF density | 3.4 | 3.4 | 3.4 |
| Inferred magnetite BIF resource | 11.2 Mt @ 37.0% DTS (67.3% Fe) | 3.9 Mt @ 31.2% DTS (68.3% Fe) | 14.2 Mt @ 41.3% DTS (68.7% Fe) |
Inferred resources outlined above are restricted to the fault block shown in Figure 13. No other inferred resources have been calculated due to paucity of drilling information. However, since the main Bungalow aeromagnetic anomaly is 9km long, the exploration target for magnetite BIF is much larger than that identified in the above table (viz. >250 Mt).
Hematite Resources
Based on SADM and SAIOG drillholes, the thickness of sand, gravel, saprolite and laterite overlying the BIF at Bungalow along section 2000N is 25-30m thick and oxidation extends 45-80m below ground level. On this basis there is good potential for hematite-rich oxidised BIF with Fe >30% above the high-grade magnetite resources. However, drillhole data are too sparse or there are no assays to determine inferred hematite BIF resources over most of the prospect.
SADM BD-10, which is located just off the line of section 2000N, intersected 15.9m (10.2m true thickness) of oxidised BIF on the edge of the eastern BIF and this defines a small inferred low-grade hematite BIF resource ca. 0.7 Mt @ 29.9% Fe (based on 900m strike length and 25m dip extent of oxide BIF). Given that the high grade magnetite intercept for this BIF unit in BUDD004 is 33.3m true thickness, the potential exploration target for this hematite BIF unit within this fault block is about 2 Mt @ ca. 30% Fe. If this is representative of oxidised BIF overlying magnetite BIF along the length of the Bungalow anomaly, the potential hematite BIF exploration target is >20 Mt.
Minbrie
The Minbrie segment of the Bungalow-Minbrie aeromagnetic anomaly is about 7km long with the most intense part of the anomaly located near the SW end.
No recent exploration has been undertaken on Minbrie because casual examination of the aeromagnetics and ground magnetic profiles suggests that the magnetic bodies could be relatively deep. This is born out by the drilling, which has recorded cover thicknesses ca. 100-120m over the northern part of the Minbrie anomaly. Nevertheless, magnetic modelling inversion by Cowan (2005a) shows the southern Minbrie BIF at depths less than 100 m.
Drillhole MD1 intersected magnetite quartzite (with trace pyrite) from 126.8-138.2m (EOH) with an average iron content of 29.4% Fe.
