On May 5, 2025, Northern Star Resources confirmed that its acquisition of De Grey Mining Ltd (De Grey) by way of a court-approved Scheme of Arrangement was completed.
On 6 May 2025, De Grey was delisted from the ASX and became a wholly owned subsidiary of Northern Star.
De Grey owns 100% of the Hemi Gold Project.
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Summary:
The Hemi discovery comprises a series of gold deposits, Aquila, Brolga, Crow, Diucon, Eagle and Falcon, hosted within predominately diorite to quartz diorite intrusions and sills that have been emplaced within the Mallina Basin.
Gold mineralisation is associated with localised to massive zones of fractured to brecciated albite, chlorite and carbonate (calcite) altered intrusion with disseminated sulphides and stringers containing pyrite and arsenopyrite with minor occurrences of pyrrhotite, overprinted in places by quartz-sulphide veins that occasionally host visible gold. Sulphide abundance in the mineralised intrusions typically ranges from 2.5% to 10% and there are strong correlations between gold, arsenic, and sulphur.
The rock sequence at Hemi has undergone a complex deformation history commencing in extension during basin development and basin inversion during a compression event that resulted in folding and brittle-ductile shear zone development. This has important constraints on the three-dimensional lithostratigraphy and mineralisation at the Project.
There are two main deposit alteration and mineralisation styles, informally named as the Brolga-type and the Diucon-type. The Brolga-type all occur south of the Diucon Thrust whereas the Diucon-type straddle the Diucon Thrust. The Aquila, Brolga, Crow and Falcon deposits are interpreted as Brolgatype and Diucon and Eagle are interpreted as Diucon-type.
At the Brolga-type, strong albite-chlorite-sulphide alteration occurs within the intrusions and this alteration is intimately associated with a stockwork of chlorite-sulphide veins. Rarer sericite and later chlorite alteration and veins are also observed.
At the Diucon-type a similar assemblage of alteration minerals is present with the exception of an initial development of sericite and albite alteration and smoky quartz veining. Later brittle-ductile shear zones exploit the alteration and veining, where later chlorite-carbonate-talc alteration and sulphide-gold mineralisation is observed.
Sulphide abundance in the mineralised intrusions typically ranges from 2.5 % to 10 %, whilst marginal alteration zones peripheral to the gold mineralised zones comprise sulphide contents that typically range from 0.5 % to 1 %. The ore mineralogy is consistent in type but not content across the different deposits and consists of arsenopyrite, pyrite, trace galena, sphalerite, chalcopyrite, and native gold. In general, the gold mineralisation is semi-refractory in nature.
Native gold is typically constrained to the Diucon and Eagle deposits. Likewise, higher contents of galena, sphalerite and chalcopyrite are observed at the Diucon and Eagle deposits. Away from the gold mineralised zones the arsenopyrite content drops off rapidly to <0.5 % and pyrite is the main sulphide mineral. Arsenopyrite is generally absent within the country rock away from mineralisation.
The alteration in the country rock / waste rock units away from the intrusions is typified by regional metamorphic chlorite (possibly with calcite) alteration.
An extensive regolith profile is present at Hemi and includes aeolian and colluvial cover, a calcrete silcrete (duricrust), a transported (alluvial) cover sequence, a basal pebble and gravel palaeochannel sequence at the base of the transported (alluvial) cover sequence, upper saprolite, lower saprolite, saprock, strongly joint weathered fresh rock, weakly joint weathered fresh rock and fresh rock.
Dimensions
The Hemi Mineral Resource area extends over a north-south strike length of 2,000 m, and an eastwest extent of 3,600 m. It has been drilled and interpreted to a maximum vertical interval of 885 m from surface at 65 mRL to -820 mRL.