Regional geological setting

At Honeymoon Well the greenstone belt is 6-7 km wide and composed of a regional west-younging sequence of a lower basalt/gabbro unit, including a laterally persistent basaltic komatiite flow, felsic to intermediate volcanic and volcaniclastic rocks, a heterogeneous komatiite sequence and a western felsic/basalt sequence (Liu et al., 1995). Local eastyounging is due to minor folds associated with fault zones. The ultramafic sequence, which within the Honeymoon Well complex is 1.5 to 3.0 km wide, consists of a diverse suite of metamorphosed komatiite lithologies including spinifex-textured rocks, olivine orthocumulate, mesocumulate and adcumulate (oOC, oMC, oAC). Minor augite and augite-plagioclase cumulates define fractionated cyclic units within the presumed upper parts of the ultramafic sequence. All the ultramafic lithologies are interpreted to have formed in a volcanic setting (see Hill et al., 1990, 1995).

In the area around Wiluna and within the Honeymoon Well ultramafic complex the komatiite stratigraphy has been duplicated by faulting. Duplication is interpreted to have taken place during D1 thrust faulting. Folding and deformation during D 2 resulted in the formation of talccarbonate-rich NNW trending strike slip faults and shear zones that further duplicated parts of the sequence. The stratigraphic stacking accounts, in part, for the anomalous thickness of the ultramafic rocks atHoneymoon Well compared to the remainder of the belt. Much of the ultramafic sequence, particularly at Honeymoon Well and probably to the immediate south, appears to be allochthonous. Strike-slip faulting has removed a 5 km long section of the ultramafic sequence immediately north of the Honeymoon Well ultramafic complex. Some of the D2 faults and shears are probably reactivated D1 thrust surfaces. The main metamorphic alteration in the area is associated with D2 strike slip fault development (Eisenlohr, 1992). This structural and metamorphic evolution is similar to that proposed for the southern part of the Norseman-Wiluna greenstone belt (Swager, 1997). Metabasalt assemblages at Honeymoon Well indicate lower-most greenschist facies metamorphic grade (Donaldson and Bromley, 1981). Komatiites are altered to serpentine-dominant and local talc-carbonate assemblages.