The K Deeps magnetite mineralisation at Koolyanobbing, Western Australia

摘要

K Deposit (Dowd's Hill), at Koolyanobbing, Western Australia, hosts enriched magnetite mineralisation below the presently mined goethite-hematite ore zone. Two highly magnetic bodies which are elongated NW-SE and dip to the NE, appear to reflect the geophysical signature of this deeper mineralisation. Magnetic modelling indicates significant remanent magnetisation with Koenigsberger ratios (Q ratios) around 1-5, directed shallow down. The NW anomaly is overlain by a ridge of uneconomic BIF and the present waste dump, whereas the SE body was partly exposed during ongoing mining of overlying hematite-goethite ore. Sections of the magnetite mineralisation (about 45-69 wt-%Fe) in this SE anomaly were intersected previously by diamond drill holes and further evaluated by reverse circulation (RC) drilling. Review of the historic drill cores identified potential magnetite enrichment, with grades and mineralogy that might be amenable to beneficiation. The following magnetite mineralisation assemblages are recognised from cores, RC drill cuttings and pit mapping of the SE magnetic body: higher-grade magnetite-hematite±goethite and magnetite + pyrite, and lower-grade, recrystallised magnetite-quartz (BIF), magnetite-carbonate, magnetite-talc, and minor magnetite-bearing mafic schist. Disseminated specular hematite is locally present in the assemblages. Talc-schist and massive pyrite occur along the footwall contact. Magnetic susceptibility measured from core and drill chips within the magnetite-enriched zones reveals an apparent susceptibility values range of 0-2 to 1-3 SI. Results from Satmagan and Davis Tube Recovery analysis show that the magnetite content in these mineralised zones correlates well with existing geophysical data and magnetic susceptibility measurements.