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Julimar Intrusive Complex - Gonneville, Hartog, Baudin, Jansz |
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Western Australia, WA, Australia |
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Pd Pt Ni Cu Co Au PGE PGM
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The nickel-copper-PGE-gold mineralised Julimar intrusive complex is located ~70 km NE of Perth and 25 km west of Toodyay in Western Australia. The complex contains the Gonneville deposit and the Hartog, Baudin and Jansz prospects with similar geophysical and geochemical signatures progressively to the NE.
The Julimar Complex is located within an inferred 1200 x 100 km Ni-Cu-PGE province that follows the western margin of the Yilgarn Craton, from the Narryer Terrane in the north to the southwestern tip of the Southwest Terrane in the south. The Archaean Julimar Complex has a >26 km strike length and up to 3 km width. It has an open 's' shape, varying from a near north-south strike at the northern and southern ends, with the central section curving to near NE-SW. It is a mafic-ultramafic layered intrusive complex, the structure of which has has been delineated with high-resolution regional aeromagnetics in an area of poor exposure. The bulk of the complex lies within State Forrest with restricted access. Following the recognition and outlining of the Julimar Complex, an initial reverse circulation drilling program was commenced in the early 2020 concentrating on the southern end of the complex on private farmland where access was immediately available. This program led to the discovery of near surface high-grade PGE-Ni-Cu-Co-Au sulphide mineralisation at what was named the Gonneville prospect. This mineralisation was subsequently tested and a resource delineated within what is known as a the Gonneville Intrusion on the southern tip of the Julimar Complex.
The Gonneville Intrusion strikes NNE and covers an area of ~1.9 x 0.9 km and is interpreted to be a layered mafic-ultramafic 'sill' with a maximum thickness of ~650 m, with a moderate ~45°WNW dip and gentle northerly plunge. PGE-Ni-Cu-Co±Au sulphide mineralisation is widespread throughout the intrusion and has been intersected to depths of ~850 m below surface. It is predominantly composed of serpentinised olivine peridotite/harzburgite (serpentine-magnetite- amphibole-chromite), with lesser intervals of pyroxenite (amphibole-chlorite), gabbro and leucogabbro (clinozoisite-amphibole). The main intrusion is cut by a later granite body that is broadly parallel to the dip and strike of the mafic-ultramafic package. The entire intrusive package is crosscut by a series of sub vertical, NE to NW striking, dolerite dykes. Both the granite and dolerite dykes contain no Ni-Cu-PGE mineralisation. The Gonneville intrusion is surrounded by a package of meta-sedimentary rocks (Chalice Mining ASX Release, November, 2021).
Images in the Chalice Mining ASX Release of 9 November, 2021 show the Gonneville Intrusive Complex to be composed of a west dipping sequence of tabular intrusions, or 'domains', as follows and illustrated on the image below. From oldest to youngest and generally from SE to NW, these are: Domain 1 - serpentinite/harzburgite → Domain 2 - gabbro → Domain 3 - pyroxenite → Domain 4 - high-Cr ultramafic → Domain 5 - serpentinite/harzburgite → Domain 6 - high-Cr ultramafic → Domain 7 - low-Ni pyroxenite → Domain 8 - anorthosite-gabbronorite. A sequence of metasedimentary gneisses sandwich the intrusion to the east and west. To the west, the contact with the meta-sedimentary sequence is discordant with the intrusive 'stratigraphy', progressively cutting across and terminating Domains 8 to 5. To the east it similarly cuts across Domains 6 to 3, while internally Domains 1, 2, 4 and 5 obliquely abut Domain 3. To the south the complex is cut by the later intruded granite, while a complex of anastomosing dolerite dykes are the youngest intrusion, cutting across all other lithologies. These dykes have strikes varying from SW-NE, parallel to the domain boundaries, to north-south and near NW-SE, with widths of from a few metres, to as much as 60 m. The tabular Gonneville domains have thicknesses that range from 50 to 250 m. At a depth of 80 m, the width of the succession of domains from the domain 8 to 7 contact, to the contact between Domain 3 and metasediments, is ~900 m.
While the textures of the intrusive rock-types that comprise the complex are moderately well preserved, allowing the use of igneous terminology, all have been replaced by mineral assemblages consistent with upper greenschist to lower amphibolite facies metamorphism. A number of litho-chronological domains have been recognised within the complex that are interpreted to represent discrete magma influxes and associated fractionation units. These litho-chronological domains are broadly parallel in strike and dip to the overall Gonneville Intrusion (Chalice Mining ASX Release, November, 2021). No ages have been determined for the Gonneville intrusion (as of Nov. 2021), although it lies within the Jimperding Metamorphic Belt which has metamorphic ages dated at ~3.2 to 2.8 Ga (Cassidy et al., 2006).
Primary Ni-Cu-PGE sulphide mineralisation within the Gonneville is mostly found within the ultramafic harzburgite and pyroxenite domains, but also within the minor gabbroic domains within the intrusion. This mineralisation occurs as sub-parallel, >20% sulphide zones that are typically 5 to 40 m thick, that are found within broader ~100 to 150 m zones of weakly disseminated sulphides. The higher-grade mineralised sulphide zones are orientation such as to suggests an association with the litho-chronological domains within the intrusion (Chalice Mining ASX Release, November, 2021). At least 13 high, ribbon like high grade, anastomosing (>1 g/t Pd) zones have been delineated (at November, 2021). These appear to be only shallowly to flat plunging, with lengths of from a few hundred to 1500 m and widths an breadths of a few up to 100 m (Chalice Mining presentation, October, 2021).
Although the ratio between the primary sulphide phases changes between, and within, the sulphide-rich and sulphide-poor zones, sulphide mineralisation comprises a consistent assemblage of pyrrhotite-pentlandite-chalcopyrite±pyrite. The sulphide content correlates well with the metal grade, with higher sulphide concentrations corresponding to higher metal contents (Chalice Mining ASX Release, November, 2021). The style of sulphide mineralisation intersected consists of massive, matrix, stringer and disseminated sulphides, said to be typical of metamorphosed and structurally overprinted orthomagmatic Ni sulphide deposits (Chal ice Mining JORC Table 1, November, 2021).
The weathering profile in the area extends to a depth of ~30 to 40 m below the surface, with a well developed laterite and saprolite profile that contains elevated PGE grades from near surface to a depth of ~25 m. This is underlain by a narrow transition zone between the oxide and sulphide zones that is generally <15 m thick. Initial metallurgical testwork indicates that only palladium and gold are likely to be recovered in the oxide domain, whilst palladium, platinum, gold, nickel, copper and cobalt are recoverable to varying degrees from the transitional ore (Chalice Mining ASX Release, November, 2021).
The Hartog prospect is immediately to the NNE of Gonneville and has magnetic and AEM anomalies that extend over a 6.5 km strike length. It appears to be an offset continuation of Gonneville. It is reflected by a gravity-AEM anomaly with multiple late-time ground EM conductors, some of which are coincident with Ni-Cu-Pd anomalism in soil sampling that are comparable to those at Gonneville. Baudin is ~3.5 km NE of the northern tip of Hartog with a weaker magnetic signature, but has a large associated AEM anomaly and soil geochemical Ni, Cu and Pd anomalies comparable to those at Gonneville. Jansz is a further 6 km NE of Baudin and is characterised by magnetic and EM anomalies.
A maiden resource for the Gonneville deposit (Chalice Mining ASX Announcement, 9 November, 2021) comprises:
Indicated + Inferred Mineral Resource of - 330 Mt @ 0.94 g/t 3E (Pd+Pt+Au), 0.16% Ni, 0.10% Cu, 0.016% Co;
corresponding to grades of ~0.58% Ni equiv., or ~1.6 g/t Pd equiv.. The average 3E ratio is ~4:1:0.04 Pd:Pt:Au.
this resource includes 150 Mt Indicated and 180 Mt Inferred;
It is constrained within an open pit shell defined by a 0.4% Ni equiv. cut-off grade for sulphide mineralisation and 0.9 g/t Pd cut-off grade for oxides.
The pit constrained Resource includes a higher grade sulphide core at a 0.6% Ni equiv. cut-off from a depth of 30 m that comprises:
74 Mt @ 1.8 g/t 3E (Pd+Pt+Au), 0.22% Ni, 0.21% Cu, 0.021% Co (~1.0% Ni equiv., or ~2.8 g/t Pd equiv.);
containing 130 tonnes of 3E, 0.16 Mt Ni, 0.15 Mt Cu, 0.015 Mt Co (or 0.76 Mt Ni equiv., or ~205 t Pd equiv.).
The breakdown of these Indicated + Inferred Mineral Resources by ore type, is as follows:
Oxide - 8.8 Mt @ 1.8 g/t Pd, 0.06 g/t Au, at a 0.9 g/t Pd cutoff;
Transitional - 16 Mt @ 0.83 g/t Pd, 0.20 g/t Pt, 0.03 g/t Au, 0.18% Ni, 0.12% Cu, 0.024% Co (or ~0.70% Ni equiv., or ~1.9 g/t Pd equiv.)
at a 0.4% Ni equiv. cutoff;
Hypogene Sulphide - 310 Mt @ 0.72 g/t Pd, 0.17 g/t Pt, 0.03 g/t Au, 0.16% Ni, 0.10% Cu, 0.016% Co (or ~0.59% Ni equiv., or ~1.6 g/t Pd equiv.)
at a 0.4% Ni equiv. cutoff;
TOTAL - 330 Mt @ 0.75 g/t Pd, 0.16 g/t Pt, 0.03 g/t Au, 0.16% Ni, 0.10% Cu, 0.016% Co (or ~0.58% Ni equiv., or ~1.6 g/t Pd equiv.).
High grade mineralisation has been drilled below the pit constraint, but has not been included in the Maiden Resource.
NOTE: As of July 2022, the total resource had been increased to 350 Mt, and the high grade sulphide core to 82 Mt at similar grades (Chalice Mining Updated Gonneville Mineral Resource announcement, 8-July-2022).
Preliminary metallurgical testwork suggests high Pd-Pt-Ni-Cu-Co recoveries into two concentrates, namely Cu-PGE-Au and Ni-Co-PGE, using conventional flotation. Expected recoveries to the corresponding concentrates include 80 to 90% for Cu; 60 to 74% for Ni and Co; 75 to 85% for Pd to both; 65 to 75% for Pt to both and 35 to 75% for Au (Chalice Minerals Presentation, 14 October, 2021).
This summary is drawn from the Chalice Minerals website and presentations and ASX releases published therein, as cited above.
The most recent source geological information used to prepare this decription was dated: 2021.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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