PROJECTS – stony hill
Stony Hill is located 22km W of Iron Baron and, along with its associated aeromagnetic anomaly, has a strike length ca. 6km and estimated width of 90-180m. A shallow (<40m) deposit of oxidised BIF grading ca. 30% Fe has been identified at Stony Hill (Davies, 2000). In outcrop, jaspilites are comprised of medium-grained quartz-hematite (and magnetite) BIF with minor amphibole (cummingtonite). Grainsize is coarser (0.03-3mm) than BIF in the Middleback Range.
Ground magnetic profiles over Stony Hill are ca. 8,000 gammas in amplitude and suggest that the magnetite body is about 100m wide. However, interpretation of structural data suggests that the BIF is somewhat thinner ca. 60m wide albeit tightly folded in a series of N-plunging drag folds (vanWees in BHP, 1971). An increase in the amount of magnetite/hematite was noted in the hinge zones of minor folds. The BIFs dip steeply ca. 70ºE.
Drilling by BHP Ltd to 60m depth intersected mainly hematite- and limonite-rich BIF with assays up to 36% Fe, low alumina (<0.3%) and low P (<0.05%). Magnetite content ranged up to 20%. Beneficiation tests (BHP, 1971) indicated that the jaspilites are especially suitable for beneficiation with recovery of most iron oxide after grinding to 150µm. Minus 100µm magnetic concentrates averaged 47.9-49.5% DTS @ 64.8-69.1% Fe.
Fig. 14 :: Western Middleback region :: Location of drillholes and BIF outcrops/prospects inrelation to aeromagnetic imagery (Click to see image)
On regional aeromagnetics, Stony Hill and Stony Hill South are on the western limb of a probable synform (Fig. 14). The hinge zone 2.7km N of Stony Hill is a prominent aeromagnetic anomaly and would be a favourable location for enrichment and thickening of any potential orebody. Stony Hill South is also a good magnetic anomaly and possibly close to the hinge zone.
In late 2005, UTS Geophysics flew a low-level, high-resolution aeromagnetic survey over part of the Stony Hill EL for Centrex. The data were processed by Cowan Geodata Services (Cowan, 2005e) to generate a series of images and maps that provide a clear picture and dramatically improve resolution of BIF trends, folds, mafic dykes, faults and structures considered to be highly prospective for hematite and magnetite mineralisation. The central BIF zone consists of several parallel trends with variations in anomaly amplitude along strike. The main high amplitude BIF anomaly has a strike length of approximately 6 km with a separate high amplitude zone in the south. Depths to the tops of magnetic units range from 0-300+m but are predominantly <150m.
Based on location, structure and previous work (Davies, 2000; BHP, 1971), the Stony Hill area is promising. Depth of weathering and hematite-limonite enrichment extend down to at least 60m so previous drilling was not deep enough to evaluate the magnetite potential of the prospect.
