Abstract The Mount Keith and Yakabindie deposits are type examples of large-tonnage, low-grade type 2 nickel sulfide systems. Discovered in 1969, the MKD5 deposit at Mount Keith has been in production since 1994 and is Australia’s largest Ni producer. The Yakabindie deposits (Six Mile Well and Goliath North), discovered over the 1970 to 1971 period, are being evaluated at the time of writing. Both groups of deposits occur within the Archean Agnew-Wiluna greenstone belt and are hosted in giant olivine cumulate ultramafic bodies interpreted to be subsea-floor intrusions in a felsic and/or intermediate volcanic sequence. The bulk of the nickel mineralization is in the form of intercumulus sulfide blebs and is interpreted to have formed by cotectic, olivine sulfide crystallization. The Goliath North deposit shows a Ni grade distribution, which may reflect an element of entrained sulfide (type 1) as well as cotectic mineralization. Following regional metamorphism, all these deposits have been extensively overprinted by retrograde metamorphic fluids, resulting in alteration assemblages dominated by serpentines, magnesite, talc, and hydrotalcite group minerals. D2 structures formed the main fluid conduits during this event resulting in extensive talc-magnesite alteration around these structures.Due to the fact that sulfides are essentially only an accessory component of the ore, modifications to silicate mineralogy during hydrothermal alteration have consequently modified sulfide phase relationships as well.This has resulted in a crude zonation of ore mineral assemblages in the MKD5 deposit and extensive zones of high tenor sulfides such as millerite, godlevskite, and heazlewoodite. The MKD5 deposit is mined using conventional, staged-cutback, open-cut methods and processed to sulfide concentrate using froth flotation. ore blocks for direct processing are selected to avoid deleterious components such as talc, arsenic, and excessive fibers, which negatively affect Ni recoveries and concentrate quality. Using conventional flotation Ni recoveries are typically around 70 percent and are limited by the fact that significant Ni in ore occurs in ultrafine sulfide particles and in silicate form which is not readily recovered. Concentrate Ni grade is generally high (18–30%) due to hydrothermal modification of sulfides, however, low Fe/MgO ratios of the bulk of the concentrates generated means the concentrate is not directly smeltable without blending with concentrates from other sources.Introduction