Brockman Geology

The Brockman rare metals deposit is hosted by a fine-grained volcaniclastic unit informally termed the Niobium Tuff. This volcaniclastic unit is the lowermost unit of a sequence of lavas, subvolcanic rocks, and volcaniclastic units of the Brockman Volcanics.

There is ample outcrop within the Brockman area, and the Niobium Tuff can be traced over a strike length of 3.5km. It occurs here on the western flank and northern closure of a major south-west plunging synclinal structure. The Niobium Tuff varies in width to 35m, and has a vertical or steep easterly dip.

Only minor faulting is evident, and drilling has established continuity of the unit to a vertical depth of 250m. Weathering is limited, with oxidation observed only down to depths of 20-30m.

Two cross sections provided as Figure 3 and Figure 4 show the interpreted shape of the mineralised zone towards the southern and northern end of the drilled portion of the deposit, respectively. The major fold structure shown in Figure 3 was intersected in a number of holes providing intersections exceeding 100 metres down hole.

Figure 3: Brockman Cross Section 9400mN

Figure 4: Brockman Cross Section 10200mN

Drilling in 2015 tested the Southern Extension to the Main Zone and two regional targets.

Mineralogical studies have defined the ore mineral assemblage as zircon and its unusual hydrous counterpart gel-zircon, along with columbite and yttrium-bearing rare earth niobates.

All the ore minerals are fine grained, with few grains larger than 10 microns. Columbite occurs only in grains of 1-2 micron diameter.

Hastings has had two samples analysed by the Australian Nuclear Science Technology Organisation (ANSTO), an Australian government agency.

The first sample of near surface mineralisation predominantly composed quartz (38%) and muscovite (36%). The elements of interest were typically contained in the niobate phases columbite (Nb, Ta) and titanian samarskite (Y, Ce, Nd, La, Dy, Er, Ta, Nb) and in gel-zircon (Y, U, Th).

The second sample from deeper, primary mineralisation comprised predominantly quartz (45%), muscovite (25%) and albite (11%). The elements of interest were typically observed in the niobate phases columbite (Nb, Ta) and titanian samarskite (Y, Ce, Nd, La, Dy, Er, Ta, Nb), and in gel-zircon (Y, U, Th) and cerianite (Ce, Nd, La, Y, Th).

This post is also available in: Chinese (Simplified)