Brockman Geology

Hastings’ interest in the Brockman Project area lies in a number of rare earths- and rare metals-bearing extrusive and intrusive volcanics.

The current JORC resources are hosted by a unit termed the Niobium Tuff, a fine-grained silica-sericite, fluorite-bearing, tuffaceous rhyolitic volcaniclastic unit. This volcaniclastic unit is the lowermost unit of a sequence of trachyte-to-rhyolite lavas, trachyandesite subvolcanic rocks, and volcaniclastic units of the Brockman Volcanics located within the Halls Creek Group, a thick early Proterozoic volcano-sedimentary sequence.

The host volcanics were erupted from a small shield volcanic complex probably in an intraplate rift-related basin in a shallow marine setting. The Niobium Tuff is interpreted to have been an extremely liquid fractionated differentiate of the magma chamber forming a volatile enriched “cap”. The lithophile-element enriched facies are characterised geochemically by elevated rare earth elements zirconium, niobium and tantalum. The fluorite content gives the Niobium Tuff its distinctive purple tint.

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The Niobium Tuff can be traced over a strike length of 3.5km. It occurs on the western flank and northern closure of a major south-west plunging synclinal structure. The unit varies in width to 35m. It has a vertical or steep easterly dip but is locally overturned to dip to the west, as shown in the cross sections below. Weathering is limited, with oxidation observed down to depths of 20-30 metres below natural surface.

Minerals hosting rare metals at Brockman include bertrandite, bastnaesite, calcian-bastnaesite, parisite and synchisite. Potassium mica is the host for gallium which is found within the lattice structure. The potential ore minerals are found dispersed throughout the quartz, potassium mica and albite host.

Hastings drilled the Southern Extension to the current resources in 2014 with results indicating slightly higher grades than to the north. Two other targets, Levon and Haig, were also drilled in 2014 returning grades of similar tenor, but lower HREO, to the current resources.