Geology
The Musgrave Block is a Proterozoic metamorphic-igneous province containing several large layered mafic and mafic-ultramafic intrusions belonging to the ~1080 Ma Giles Complex. The Blackstone Range intrusion and Michael Hills Project both lie within the axis of a strong positive gravity anomaly that extends for the entire, east-west length of the Musgrave Block. The source of this anomaly can be interpreted to reflect thick accumulations of gabbroic rocks not exposed at surface.
Blackstone Range Project
The Blackstone Range Project comprises of two tenements (E69/2108, E69/2109) which overlies a significant mafic – ultramafic intrusion known as the Saturn Complex. The magnetic feature (Figure 2) shows 15 discernable magnetic rings and is interpreted to be a core – shaped feeder to the Giles Intrusion Complex.
Figure 2. The Blackstone Saturn Magnetic Anomaly
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This type of layered intrusion is comparable to mineralised feeders at Jinchuan in China and the Great Dyke of South Africa, both hosting world class Nickel (Ni), Copper (Cu) and Platinum Group Elements (PGE) mineralisation.
Halleys Cu-Ni-PGE
The Halleys target was first drilled with RAB and shallow RC in 2007. A mineralized zone in excess of 100m thick was defined which yielded a peak intercept of 74m of 0.33% Cu and 0.24g/t PGE+Au including 20m @ 0.56% Cu, 0.14% Ni and 0.32g/t PGE+Au (from 16m).
A second round of drilling was conducted in April 2008 at the Halleys prospect to determine the limits of the Halleys pipe-like body and to clearly define the geometry of the mineralized system in preparation for deeper drilling.
This drilling better defined the geometry of the Halleys Ni-Cu-PGE body. Disseminated sulphides with significant copper-PGE grades (>0.1%Cu and 200ppb PGE) occur in an ovoid shaped pipe 300m x 230m in size. The pipe is coincident with an elongate magnetic high defined by ground magnetics. A large EM anomaly occurs from the pipe to the northwest, and the EM anomaly is thought to be related to deeper regolith cover (conductive overburden). However, it is possible that the EM anomaly reflects a shallow NW plunging pipe, similar to Babel Nebo. Drilling has indicated a minimum dip of 40º to the NE for the body, however a steeper dip is implied in several areas and the actual dip might be highly variable if a plunging pipe is present. The body is zoned, with a central core of Cu-PGE and an outer zone richer in Ni with Cu and PGE.
RAB drilling intercepts from the second drill phase (1m split samples) include:
• 9m @ 0.67% Cu, 0.1% Ni and 0.76 g/t PGE (BSB0512) along the eastern margin from an overall intercept of 43m @ 0.31% Cu, 0.06% Ni and 0.30 g/t PGE + Au;
• 16m @ 0.50% Cu, 0.11% Ni and 0.53 g/t g/t PGE + Au; and
• Along the western margin 11m @ 0.56% Cu, 0.25% Ni and 0.16 g/t PGE from an overall intercept of 35m @ 0.29% Cu, 0.12% Ni and 0.16g/t PGE + Au (BSB0536).
Deeper exploratory drilling is planned to follow up the thick intercepts of mineralisation, in order to test the down-dip and down-plunge position at Halleys prospect.
Michael Hills Project
This project (E69/2106, E69/2107) covers the Michael Hills Gabbro and the southern section of the Hinckley Range Gabbro.
The Michael Hills Gabbro is a sub-horizontal intrusion consisting of predominant gabbro layers with lesser pyroxenite and anorthosite. It is estimated to be 8000 metres thick, and has been divided into four units:
• a lower 1500 metre thick zone of gabbro and anorthosite;
• two overlying zones each over 2000 metres) of well layered gabbro; and
• a basal marginal zone of mixed and assimilated gabbro and felsic country rock.
The Hinckley Range Gabbro, which dips steeply to the north is dominated by gabbro, and abundant layers of troctolite, anorthosite and gabbronorite. The mafic granulite and granitic gneiss/ felsic granulite underlies the intrusion. The mafic granulite may represent the higher metamorphic grade marginal facies of the gabbroic intrusion within a thrust sheet.
The magnetics indicate high anomalies at the base of the Michael Hills Gabbro and the thrust fault in the metamorphic basement north and north west of the Michael Hills Gabbro. The position of these anomalies may indicate prospectivity for Voisey Bay style mineralisation. The coincident nickel and magnetic anomaly along the basal section of the gabbro in the south west section of the Michael Hills is encouraging.
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