Summary:
The Boda-Kaiser Project is a large gold-copper porphyry system.
Boda
The Boda Deposit is located within a northwest trending structural corridor on the northwestern margin of a significant magnetic complex with dimensions of approximately 2km x 0.7km. The mineralisation is hosted within a package of submarine basaltic to andesitic lavas. The volcanic sequence is intruded by monzogabbroic and monzodiorite volcanic feeder dykes and later monzodiorite-monzonite units and related magmatic-hydrothermal breccias. The deposit is crosscut by numerous post-mineralisation dykes and sills of varying composition.
Intrusive- to magmatic-hydrothermal breccias appear to be the focus for the calc-potassic alteration and gold-copper mineralisation at Boda. The mineralisation is related to a series of northwest-trending monzodiorite intrusions that manifest as a series of vertically extensive intrusive breccias forming a stock central to Boda and Boda 2-3. These intrusive breccias transition to hydrothermal breccias to which the highest gold-copper grades are related. The majority of brecciation is in the form of a ‘crackle breccia’ that can either have a hydrothermal matrix usually comprising of calcite ± actinolite ± pyrite ± magnetite ± chalcopyrite or an igneous matrix dominantly of monzodiorite.
The magmatic-hydrothermal brecciation event was likely to have occurred syn- and postemplacement of monzodiorites and pre-emplacement of the weakly altered and mineralised monzonites. The intrusive breccia is a likely ‘causative’ to the main Boda mineralisation and is observed as monzodioritic in composition.
The Boda volcanic package has undergone intense and extensive calc-potassic to potassic alteration often replacing both phenocrysts and the groundmass. This alteration is apparent over a strike length of approximately 3.5km from Kaiser, southeast to Boda, then rotating and continuing south to Boda 2-3, with more significant mineralising centres occurring at each of the deposits.
Veining within the calc-potassic zone is dominated by calcite-quartz vein assemblages that are typically sulphide poor. Fine grained calcite occurs both as veinlets, usually along brittle fractures and as a widespread disseminated phase within the calc-potassic altered rocks.
Copper mineralisation is observed throughout the prospect primarily as chalcopyrite with subordinate bornite and chalcocite, and rare covellite. Within the magmatic hydrothermal breccias, chalcopyrite and to a lesser extent bornite occur predominantly as a cement mineral between the calc-potassic altered clasts. Outside of the breccias, copper mineralisation is observed within calcite ± quartz ± epidote dominant veins and as disseminations and patches, often intergrown with epidote.
Gold is observed within the mineralised breccias often without magnification, associated with chalcopyrite and bornite in the hydrothermal cement.
Calc-potassic alteration grades into propylitic alteration away from the breccia complex and has a typical assemblage of actinolite-hematite-epidote-pyrite (± trace chalcopyrite) proximal to the calc-potassic alteration zone. Moving further away from the mineralised centre, the typical assemblage becomes more chlorite-calcite-albite-pyrite dominant.
Boda is overprinted in the northeast by phyllic alteration comprising sericite-quartz-calcite ± albite with up to 10% pyrite by volume. The pyrite occurs as disseminated spots, aggregates, and short veinlets. The phyllic alteration is copper-poor, however gold grades over hundreds of metres can average from 0.2g/t – 0.6g/t Au with occasional thin intervals of >10g/t Au.
Three significant west dipping reverse faults (Solar, Moonlight and Reids) bound and dislocate the mineralisation at Boda and Boda 2-3. The Solar Fault bounds the western margin of mineralisation at Boda and Boda 2-3. Moonlight Fault dislocates the calc-potassic Au-Cu mineralisation at Boda and Boda 2-3. The Reids Fault is the easternmost fault and bounds the shallow level Au-pyrite mineralisation from calc-potassic Au-Cu mineralisation to the west at Boda 2-3. All three thrusts have an inferred movement of over 400 metres along the moderately west dipping structures.
Weathering and oxidation of the mineralised bedrock extends on average approximately 15 metres from surface.
Kaiser
The Kaiser Deposit is located within a northwest trending structural corridor on a significant magnetic high with dimensions of approximately 800m x 700m, named the Kaiser Intrusive Complex (KIC). The mineralisation is hosted within a package of submarine basaltic to andesitic lavas. The volcanic sequence is intruded by monzodiorite-monzonite units and related magmatic-hydrothermal breccias. The deposit is crosscut by several post-mineralisation dykes and sills of varying composition.
Intrusive to magmatic-hydrothermal breccias are the focus for the calc-potassic alteration and gold-copper mineralisation at Kaiser. The mineralisation is related to a series of northwesttrending monzodiorite-monzonite intrusions that manifest as a series of vertically extensive intrusive breccias forming a stock central to the KIC. These intrusive magmatic breccias transition to hydrothermal breccias to which the highest gold-copper grades are related.
The majority of brecciation is in the form of a ‘crackle breccia’ that can either have a hydrothermal matrix usually comprising calcite ± actinolite ± pyrite ± magnetite ± chalcopyrite or an igneous matrix. The intrusive breccias are a likely ‘causative’ to the main mineralisation event at Kaiser.
The volcanic package at Kaiser has undergone intense and extensive calc-potassic to potassic alteration, often replacing both phenocrysts and the groundmass. The calc-potassic alteration comprises fine-grained biotite-actinolite-epidote-magnetite with lesser internal zones of potassic alteration comprising only hydrothermal biotite. Veining within the calc-potassic zone is dominated by calcite-quartz vein assemblages that are typically sulphide-poor.
Copper mineralisation is observed throughout the deposit primarily as chalcopyrite with lesser bornite and subordinate chalcocite and covellite. Within the intrusive hydrothermal breccias, chalcopyrite and to a lesser extent bornite occur predominantly as a cement mineral between the calc-potassic altered clasts. Outside of the breccias, copper mineralisation is observed within calcite ± quartz ± epidote dominant veins and as disseminations and patches, often intergrown with epidote.
Gold is observed within the sulphide cemented breccias often without magnification, associated with pyrite, chalcopyrite and/or bornite in the hydrothermal cement.
Calc-potassic alteration grades into propylitic alteration away from the breccia complex and has a typical assemblage of actinolite-hematite-epidote-pyrite (± chalcopyrite). More distal from the mineralised centre, the assemblage typically becomes more chlorite-calcite-albite-pyrite dominant.
Kaiser includes a zone of potassic alteration comprising wholly of biotite alteration with quartzcalcite veining, with up to 10% pyrite by volume along its northeast flank. The pyrite occurs as disseminated spots, aggregates, and as breccia cement. The alteration is generally copper-poor, however gold grades over several tens of metres can average from 0.2g/t – 0.4g/t Au, with occasional thin intervals of >10g/t Au associated with pyrite cemented breccias.
Two significant reverse faults bound and dislocate the central zone of calc-potassic mineralisation at Kaiser. The Kaiser Fault dips east and thrusts the deeper Kaiser Main zone over the Kaiser West zone of mineralisation. The Solar Fault dips west and thrusts the Kaiser Main zone over the Kaiser East zone.
The Kaiser Fault zone is associated with minor supergene copper forming as native copper. The native copper zones can extend hundreds of metres down the Kaiser Fault.