North Royal Pit, Norseman, Dundas Shire, Western Australia, Australiai

Regional Level Types
North Royal Pit	Mine (Flooded)
Norseman	Town
Dundas Shire	Shire
Western Australia	State
Australia	Country

The North Royal Gold Mine is 10 kilometres north north-east of Norseman, between the Eyre Highway and Lake Cowan salt-pan. It has been mined at various times by Norseman Gold Mines, the last as an extension to the open pit between 2010 and when the company closed down in 2014. The site contains a very large open pit.

The deposit is hosted by the Woolyeenyer Formation. Rock types in order of emplacement are north north-east striking west dipping basaltic flows; composite north striking east dipping gabbroic dykes; north north-east striking west dipping Ajax Suite felsic porphyries; Dinky Buoys porphyry suite; and east striking norite dykes of the Jimberlana Dyke Suite. This last rock is 3 kilometres south of the deposit, and is a giant dyke system 200 kilometres long by 1 kilometre wide.

The dominant structure at the deposit is the north north-west striking, east dipping, Princess Royal Fault Zone. This is a reverse dextral ductile shear zone up to 100 metres wide. The majority of the ore is hosted in north-east striking subhorizontal to south-east dipping laminated quartz veins, between north striking east dipping shear zones, and partly within them. These structures are truncated by the Princess Royal Fault Zone.

The quartz veins are up to 10 metres wide, averaging 1 to 3 metres wide, the quartz containing abundant wall rock inclusions. The stringers in the wall rock, away from the main veins, have been folded and boudinaged, with less deformed stringers cross-cutting their more deformed counterparts. Massive to brecciated quartz veins are found within narrow ductile shear zones.

The rocks have been highly disrupted by faults, leading to pervasive fluid movement and the deposition of gold. In high Mg tholeiite the least altered mineral assemblage is actinoltic hornblende to actinolite and chlorite, with subordinate ilmenite, and minor quartz, and plagioclase. In tholeiitic gabbros the least altered mineral assemblage is actinolite to hornblende, and plagioclase, with minor quartz, epidote, ilmenite, apatite, titanite, leucoxene, and biotite. Amphibole-plagioclase-ilmenite-apatite metamorphic assemblage has retrogressed to quartz-albite-epidote-chlorite-calcite. The altered assemblage in the shear zones has locally retrogressed to calcite-sericite-chlorite-albite along vein margins, and along brittle fractures that cross-cut other assemblages. Gypsum has precipitated from groundwater along the brittle fractures.

In lode gold deposits hosted by tholeiites, the least altered amphibole assemblage has been progressively altered to an outer zone of chlorite and then an inner zone of chlorite-biotite, progressively increasing to this closer to the quartz veins. In high Mg tholeiite, the least altered amphibole-chlorite-quartz-plagioclase, has been altered to chlorite-carbonate-quartz-biotite, increasing again closest to the quartz veins. Sporadically intergrown quartz-sulphides-scheelite-schorl is found within the assemblage.

Pyrrhotite is the dominant sulphide in the outer and inner zones. Pyrite and arsenopyrite is locally abundant adjacent to the veins. Where sulphides are abundant, ilmenite has been progressively altered to leucoxene, titanite and Fe sulphides, however in sulphide poor areas, ilmenite is stable.

The earliest stage quartz veins show fine grained chlorite, subordinate biotite, and locally abundant tourmaline fibres, intimately intergrown with quartz, euhedral arsenopyrite or pyrite crystals, and granular aggregates of carbonate, chlorite, and scheelite adjacent to the veins , wall rock inclusions, isolated patches of quartz, and early fractures in quartz. Rimming and infilling these fractures is galena, sphalerite, tellurides altaite, hessite, petzite, and native gold. The gold is found as free grains in quartz, and sporadically is a dispersion halo within a few metres of the quartz veins.

Other Regions, Features and Areas containing this locality

References