VHMS mineralisation at Erayinia in the Eastern Goldfields Superterrane: Geology and geochemistry of the metamorphosed King Zn deposit

Abstract

Despite having been a target for volcanic-hosted massive sulfide (VHMS) deposits since the 1960s, few resources have been defined in the Archean Yilgarn Craton of Western Australia. Exploration challenges associated with regolith and deep cover exacerbate the already difficult task of exploring for small, deformed deposits in stratigraphically complex, metamorphosed volcanic terranes. We present results of drillcore logging, petrography, whole rock geochemistry and pXRF data from the King Zn deposit, to help refine mineralogical and geochemical halos associated with VHMS mineralization in amphibolite facies greenstone sequences of the Yilgarn Craton. The King Zn deposit (2.15 Mt at 3.47% Zn) occurs as a 2-5m thick stratiform lens dominated by iron sulfides, in an overturned, metamorphosed volcanic rock-dominated sequence located ~140km east of Kalgoorlie. The local stratigraphy is characterized by garnet amphibolite and strongly banded intermediate to felsic schists, with rare horizons of graphitic schist. Massive sulfide mineralization is characterized by stratiform pyrite-pyrrhotitesphalerite at the contact between quartz-muscovite schists ('the footwall dacite') and banded quartz-biotite/amphibole±garnet schists of the stratigraphic hanging-wall. A zone of pyrite-(sphalerite) and pyrrhotite-pyrite-(chalcopyrite) veining extends throughout the stratigraphic footwall. Footwall garnet-amphibolites are of sub-alkaline basaltic affinity, with a central zone dominated by chlorite±magnetite interpreted to represent the Cu-bearing feeder zone. SiO2, CaO, Fe2O3T, MgO and Cu concentrations are highly variable, reflecting quartz-epidote±chlorite±magnetite±sulfide alteration. Hydrothermal alteration in stratigraphically overlying intermediate to felsic rocks is characterized by a mineral assemblage of quartz-muscovite±chlorite±albite±carbonate. Cordierite and anthophyllite are locally significant and indicative of zones of Mg-metasomatism prior to metamorphism. Increases of SiO2, Fe2O3T, pathfinder elements (e.g. As, Sb, Tl), and depletions of Na2O, CaO, Sr, and MgO occur in footwall quartz-muscovite schists approaching massive sulfide mineralization. Within all strata (including the immediate hanging-wall), the following pathfinder

Petrogenesis and geochemical halos of the amphibolite facies, Lower Proterozoic, Kerry Road volcanogenic massive sulfide deposit, Loch Maree Group, Gairloch, NW Scotland

“…Geochemically, these zones are associated with an increase in aluminous minerals relative to the host rock due to intense hydrothermal leaching of alkalis under acidic high fluid/rock conditions (e.g., Galley et al, 2007;Dusel-Bacon, 2010). During metamorphism, the primary alteration mineral assemblage changes to aluminous minerals (garnet, chloritoid, staurolite, kyanite/andalusite/sillimanite and cordierite), orthorhombic Mg-Fe-Mn amphiboles and gahnite (zincian spinel) (e.g., Nesbitt and Kelly, 1980;Corriveau and Spry, 2014;Hollis et al, 2019). The final metamorphic assemblage depends on the peak metamorphic grade and the original composition of the host rock and alteration zone.…”

“…The final metamorphic assemblage depends on the peak metamorphic grade and the original composition of the host rock and alteration zone. To date, most studies on metamorphosed VMS deposits focused on mineralization hosted in metasedimentary and felsic volcanic/volcaniclastic rocks (e.g., Nesbitt and Kelly, 1980;Barrett et al, 2005;Duuring et al, 2016;Mathieu et al, 2016;Hollis et al, 2019). It is expected that VMS deposits hosted in metamafic rocks would contain a different mineral assemblage due to their higher abundance of Mg, Fe and Ca.…”

Lithogeochemical and Hyperspectral Halos to Ag-Zn-Au Mineralization at Nimbus in the Eastern Goldfields Superterrane, Western Australia

“…Figure 2. Regional Nd isotope variations of the Yilgarn Craton [17]. The positions of significant VMS occurrences and prospective greenstone belts associated with the Cue and Kurnalpi paleorift zones are indicated by red stars.…”

Geology, alteration and lithogeochemistry of the Paleoproterozoic Korpela VMS occurrence in Eastern Finland

“…All the Paleoproterozoic VMS deposits in Finland and elsewhere have been affected by deformation and regional metamorphism, resulting in recrystallisation of the original alteration minerals to variable metamorphic assemblages (e.g. Roberts et al 2004;Latvalahti 1979;Mäki et al 2015;Barrett et al 2005;Caté 2016;Kampmann et al 2017;Hollis et al 2018). This often leads to complex classification of metamorphic mineral assemblages and difficulties in discriminating between lithological units.…”

“…Many of the more recent lithogeochemical studies applied to metamorphosed hydrothermal ore systems have either been undertaken in relation to an active mine or brownfield exploration targets where large amounts of data is available (e.g. Schlatter et al 2003;Barrett et al 2005;Imaña et al 2005;Mercier-Langevin et al 2007;Schlatter 2007;Mäki et al 2015;Mills et al 2016;Caté 2016;Chmielowski et al 2016;Kampmann et al 2017;Hollis et al 2018). Although here the target is in a greenfield area, the same methods are applied, with the following objectives: (1) describe the main geological, mineralogical and geochemical features of the target and hosting volcanic succession.…”